The Way and Life of General Carl A. Spaatz Essay -- essays research pa

The Way and Life of General Carl A. Spaatz      The name General Carl ‘Tooey’ Andrew Spaatz has gotten equivalent with the expression air force and tactician. Air power has tagged along route since Wilbur and Orville propelled the primary plane in 1902 in the city of Kitty Hawk. Acclaimed engineers have taken the Wright-Brothers structure and made incredible enhancements to them while gradually coordinating these new amazing methods for transportation, weaponry and correspondence helps into the military. Since the beginning of World War I there has been a discussion on the best way to most viably utilize these new planes in the Army’s assortment. Most people accepted that planes ought to be leveled out of the Army theater administrator, while not very many felt that these planes ought to be a different substance from the Army. One of these couple of individuals who accepted that the Air Force ought to be discrete is General Spaatz. General Spaatz had tirelessnes s, initiative traits and military information; all variables driving him turning into a considerable advocate of a different Air Force. Spaatz inheritance keeps on living on; his initiative aptitudes keep on affecting individuals today as General Spaatz is as yet ready to affect air power in the 21st century. It is no mishap that General Spaatz is an advocate of a different Air Force. Spaatz’s tirelessness, initiative properties and military information would lead him to be a defender of a different Air Force were all being formed, changed and imparted upon him during his initial plebe years at the United States Military Academy (USMA) starting in 1900. Thinking back on Spaatz’s vocation at the USMA, one would not foresee Spaatz to turn into the principal Chief of Staff of the recently free United States Air Force. Be that as it may, these four years spent at the USMA were exceptionally powerful, especially in Spaatz’s improvement as a pioneer and his capacity to continue on. While at the USMA Spaatz was a lot of an agitator and was continually disrupting the guidelines. In any case, Spaatz realized he was brilliant, he showed this by being positioned in the top portion of his group. Despite the fact that, as Spaatz entered his senior year, he believed he didn't have anything else to demonstrate and started to relax. In the end Spaatz wound up being positioned close to the base of his group. He went from the position of 39th to 98th of 107 inside a year. With the chance of getting kicked-out Spaatz utilized his perseve... ...orce is thankful for a man like General Spaatz and the occasions that happened in the course of his life. He may have been dependent upon incident, or even destiny, however whichever way Spaatz’s authority, diligence and military information is no mishap. Works Cited Davis, Richard G. "Carl A. Spaatz and the Development of the Royal Air Power U.S. Armed force Air Corps Relationship, 1939-1940." The Journal of Military History. Oct. 1990: EBSCOhost. 9 Nov. 2003 Davis, Richard G. "Gen Carl Spaatz and D Day." Airpower Journal. Winter 1997: Military & Government Collection. 10 Nov. 2003 Doughty, Robert An., and Ira D. Gruber. Fighting in the Western World. Vol. II. Boston, MA: Houghton Mifflin Company, 2001. 797. Glines, C.V.. "Air Power Strategist Carl A. Spaatz." Aviation History. Vol. 12, Issue 4. Blemish. 2002: Military & Government Collection. 8 Nov. 2003 McNeely, Gina. "Legacy of Flight." Aviation History. Blemish. 1998: Academic Search Premier. 8 Nov. 2003. Maj. Carl A. Spaatz. 7 June 2002. The Evolution of Aeronautical Improvement at the Aeronautical Systems Center . 8 Nov. 2003 . Mets, David R. Ace of Airpower. Novato, California: Presido, 1988. The Way and Life of General Carl A. Spaatz Essay - articles research dad The Way and Life of General Carl A. Spaatz      The name General Carl ‘Tooey’ Andrew Spaatz has gotten interchangeable with the expression air force and specialist. Air power has gone along path since Wilbur and Orville propelled the main plane in 1902 in the city of Kitty Hawk. Well known specialists have taken the Wright-Brothers structure and made extraordinary enhancements to them while gradually incorporating these new ground-breaking methods for transportation, weaponry and correspondence helps into the military. Since the beginning of World War I there has been a discussion on the best way to most successfully utilize these new planes in the Army’s assortment. Most people accepted that planes ought to be leveled out of the Army theater officer, while not many felt that these planes ought to be a different substance from the Army. One of these couple of individuals who accepted that the Air Force ought to be discrete is General Spaatz. General Spaatz had t irelessness, authority properties and military information; all elements driving him turning into a significant advocate of a different Air Force. Spaatz inheritance keeps on living on; his authority aptitudes keep on affecting individuals today as General Spaatz is as yet ready to affect air power in the 21st century. It is no mishap that General Spaatz is a defender of a different Air Force. Spaatz’s diligence, initiative properties and military information would lead him to be a defender of a different Air Force were all being formed, changed and imparted upon him during his initial plebe years at the United States Military Academy (USMA) starting in 1900. Thinking back on Spaatz’s profession at the USMA, one would not foresee Spaatz to turn into the primary Chief of Staff of the recently free United States Air Force. Be that as it may, these four years spent at the USMA were exceptionally compelling, especially in Spaatz’s improvement as a pioneer and his capacity to drive forward. While at the USMA Spaatz was a lot of a revolutionary and was continually disrupting the norms. By the by, Spaatz realized he was savvy, he exhibited this by being positioned in the top portion of his group. In spite of the fact that, as Spaatz entered his senior year, he believed he didn't have anything else to demonstrate and started to relax. In the long run Spaatz wound up being positioned close to the base of his group. He went from the position of 39th to 98th of 107 inside a year. With the chance of getting kicked-out Spaatz utilized his perseve... ...orce is thankful for a man like General Spaatz and the occasions that happened in the course of his life. He may have been dependent upon incident, or even destiny, however whichever way Spaatz’s initiative, diligence and military information is no mishap. Works Cited Davis, Richard G. "Carl A. Spaatz and the Development of the Royal Air Power U.S. Armed force Air Corps Relationship, 1939-1940." The Journal of Military History. Oct. 1990: EBSCOhost. 9 Nov. 2003 Davis, Richard G. "Gen Carl Spaatz and D Day." Airpower Journal. Winter 1997: Military & Government Collection. 10 Nov. 2003 Doughty, Robert An., and Ira D. Gruber. Fighting in the Western World. Vol. II. Boston, MA: Houghton Mifflin Company, 2001. 797. Glines, C.V.. "Air Power Strategist Carl A. Spaatz." Aviation History. Vol. 12, Issue 4. Blemish. 2002: Military & Government Collection. 8 Nov. 2003 McNeely, Gina. "Legacy of Flight." Aviation History. Blemish. 1998: Academic Search Premier. 8 Nov. 2003. Maj. Carl A. Spaatz. 7 June 2002. The Evolution of Aeronautical Advancement at the Aeronautical Systems Center . 8 Nov. 2003 . Mets, David R. Ace of Airpower. Novato, California: Presido, 1988.

I NDUSTRY R ESEARCH W ORKSHEET Essays - Free Essays

S ECTOR/I NDUSTRY R ESEARCH W ORKSHEET Essays - Free Essays S ECTOR/I NDUSTRY R ESEARCH W ORKSHEET Name: James Musasizi Period: 5 Group Name: Wolf Squad By gathering stocks into divisions and ventures, it is simpler for speculators to assess stocks inside a similar industry and evaluate the monetary quality or shortcoming of that industry. Go to a stock research site, for example, Google Finance or Yahoo! Money, and discover one stock in an industry under every part recorded beneath. Give the stock name, ticker image, current stock cost, and items/administrations of that organization. Segment Industry Name Organization Name Ticker Cost Item/Services Essential Materials Iron, Steel, factories and Foundries AK Steel Holding Corporation AKS 2.29 Creates level moved carbon, impeccable and electrical prepares and cylindrical items through its entirely possessed auxiliary Capital Goods Homestead and Construction Machinery Caterpillar INC. Feline 63.65 produces and sells development and mining hardware, diesel and gaseous petrol motors, mechanical gas turbines, and diesel-electric trains around the world Combinations Combinations Mitsubishi Corporation MBC 1,909,42 Behaviors framework ventures, related exchanging tasks, and different exercises in power age, water transportation, and other foundation fields. Customer, Cyclical TV Broadcasting Nexstar Broadcasting INC. NXST 44.82 The Company possessed, worked, customized or gave deals and different administrations to 87 TV slots and 26 advanced multicast diverts in 49 markets Customer, Non-repeating Business Fishing Omega Protein Corporation OME 16.54 The Company works through two portions: creature nourishment and human sustenance. The creature nourishment section comprises fundamentally of two auxiliaries: Omega Protein, Inc. (Omega Protein) and Omega Shipyard, Inc. Vitality Oil and Gas Drilling Atwood Oceanies, Inc ATW 14.35 A worldwide seaward boring contractual worker occupied with the boring and finishing of exploratory and formative oil and gas wells. Money related Land Services SouFun Holdings Ltd SFUN 5.82 Supports online networks and systems of clients looking for data on, and administrations for, the land and home-related segments in China. Medicinal services Forte and Advanced Pharmaceuticals Rockwell Medical Inc RMTI 7.86 A biopharmaceutical organization focusing on end-stage renal ailment and interminable kidney ailment with items and administrations for the treatment of iron insufficiency, optional hyperparathyroidism and hemodialysis. Mechanical Goods Concrete Cemex, S.A.B. de C.V. Supported CX 89.1 A structure materials organization, produces, advertises, circulates, and sells concrete, prepared blend solid, totals, and other development materials in Mexico, the United States, Northern Europe, the Mediterranean, South America, the Caribbean, and Asia. Administrations Markets Tesco PLC TSCO 174.95 It is occupied with the retail banking and protection benefits through Tesco Bank in the United Kingdom Bank. Innovation PC Hardware Apple INC. AAPL 110.17 Structures, makes and markets versatile correspondence and media gadgets, PCs, and convenient computerized music players, and an assortment of related programming. Broadcast communications Remote Telecommunication Services ATT INC. T 32.96 The Company gives broadcast communications administrations. Its administrations and items incorporate remote correspondences, information/broadband and Internet administrations, video administrations, nearby trade administrations, significant distance administrations, media communications hardware, oversaw systems administration and discount administrations. Transportation Dispatch Services Air T , INC AIRT 17.67 The ground hardware deals fragment comprises of its Global Ground Support, LLC (GGS) auxiliary, fabricates and gives portable deicers to traveler and freight carriers, air terminals, the military and mechanical clients. Utilities Petroleum gas Utilities Vitality Transfer Partners

Pros and Cons of International Medical Schools

Pros and Cons of International Medical Schools Student Resources Print Deciding to Attend an International Medical School By Andrea Clement Santiago facebook twitter linkedin Andrea Clement Santiago is a medical staffing expert and communications executive. Shes a writer with a background in healthcare recruiting. Learn about our editorial policy Andrea Clement Santiago Updated on January 02, 2020 Cultura Science / Matt Lincoln / Riser / Getty Images More in Student Resources APA Style and Writing Study Guides and Tips Careers When its time to choose a medical school, the process and options can be overwhelming, from selecting the right program, applying, and interviewing to managing loans and passing board exams. It can be expensive, time-consuming, not to mention the competitive process, but there are ways to navigate the system. International medical schoolsâ€"such as Ross University in Barbados and other accredited schools in the Caribbean, as well as Mexico, Asia, and Australiaâ€"offer a way to pursue your passion for medicine without having to wait for spots in domestic schools to open. In fact, one quarter of physicians in the U.S. have graduated from international medical schools. Going to a medical school abroad may sound appealing, but there are pros and cons any candidate must consider.  Heres a look at the opportunities and potential obstacles. Pros of International Medical Schools Less restrictive requirements, lower tuition costs, and possible U.S. residency opportunities are all favorable aspects of applying to foreign medical schools, particularly in the Caribbean. Consider these factors when figuring out if medical school abroad is the right fit for you. Higher acceptance rates: Many medical schools in the Caribbean accept a much higher percentage of applicants than schools in the U.S. in part due to less restrictive entrance requirements.  For schools outside the Caribbean, acceptance rates vary.Broader entrance requirements: GPAs and MCAT scores are typically lower than average among international medical school applicants, making these programs a realistic option to consider for those with lower scores.Less expensive than domestic counterparts: Tuition for international schools is usually cheaper than medical schools in America, which can lessen the burden of student loans and financial stress that many medical students face.U.S. clinical rotation opportunities: In many of the Caribbean schools, the first two years of basic science is done on their campuses overseas, while clinical rotations are done in U.S. hospitals. Though your home school is still overseas, you have the advantage of the same clinical exposure and opportunities as the hospitals home medical students. Many past students cite this as an advantage in applying to U.S. residencies. Other overseas medical schools allow students U.S. clinical rotation opportunities, though usually on a more case-by-case basis. Cons of International Medical Schools While the early stages of going to medical school abroadâ€"like applications and tuition feesâ€"may be favorable, there are differences and potential challenges, particularly after youve graduated. Grading systems: While many U.S. medical schools use an Honors/Pass/Fail grading system, many medical schools overseas use a traditional Aâ€"F system. You might feel that such precise grading systems can add additional stress to an already competitive atmosphere and post-graduate job market and industry.New environment: This can be either a pro or a con, depending on your perspective. Keep in mind that politics, social norms, and weather usually differ, too.Match challenges with U.S. residency: Though many international medical graduates successfully match into residency programs across the U.S., they do so at significantly lower rates than their U.S. graduate counterparts: approximately 48% of international graduates compared to 94% of U.S. graduates. Many schools in the Caribbean, however, state that a significant percentage of their graduates find positions outside the match.Additional certifications: After graduating from an international medical school, youll be required to take an additional exam, the Educational Commission for Foreign Medical Graduates (ECFMG), that isnt required for domestic graduates. Additionally, each time you apply for a state license or any certification, the process may be slower, since the documentation must be obtained from overseas.Less favorable perception: Patients and employers typically have a less positive opinion of  international medical schools.  Some employers prefer to hire doctors who have graduated from a U.S.  medical school. A Word From Verywell Your choice of medical school can impact your future career prospects, so if youre considering applying to an international medical school, these pros and cons could help make your decision a little easier. Keep in mind that there are other avenues to practice medicine as well. For example, if youre interested in primary care and want to stay and practice in the U.S., you might consider applying to an osteopathic medical program. Whatever you decide, its important to research your options carefully so your path is fulfilling, tailored to your goals and capabilities, and falls within your budget.

The treatment of cancer - Free Essay Example

Sample details Pages: 25 Words: 7564 Downloads: 7 Date added: 2017/06/26 Category Statistics Essay Did you like this example? According to the statistics presented by the World Health Organization (WHO), with around 7.4 million deaths (around 13% of the total death) in 2004, cancer is the leading cause of death throughout the world (WHO, 2009). These levels are expected to rise further in future, with an estimated 12 million death in 2030 (WHO, 2009). There are more than 100 different types of cancer (Crosta, n.d.), among them the Lung cancer, stomach cancer, colorectal cancer, liver cancer and the breast cancer are the most common types. Don’t waste time! Our writers will create an original "The treatment of cancer" essay for you Create order Tobacco is the most important risk factor for cancer, with nearly 1.3 million deaths per year just due to lung cancer alone (WHO, 2009). Cancer At the primary level, human body consists of large number building blocks, called the cells. Under normal circumstances, new cells are formed by the body depending on the body requirement, in order to replace the dead cells. But sometimes, under abnormal conditions, there is an exponential (uncontrolled) increase in the formation and growth of new cells. The accumulation of these extra cells forms mass or lumps of tissues, called the tumor (National Cancer Institute, 2010). Most of the cancers, in general form tumors, but there are certain exceptions, like leukemia, that do not form tumors (in leukemia or blood cancer, the cancer cells hinder the normal blood functions due to abnormal cell disintegration in the blood stream (Crosta, n.d.)). The tumors can be of two types; benign tumor and malignant tumor. The benign tumors do not propagate to other sections of the body and have restrained growth (Crosta, n.d.), whereas the malignant tumor cells have the ability to invade into the sur rounding tissues. Also the malignant tumor cells can escape from their initial location and spread to other sections of the body through blood or lymph. Only the malignant tumors are cancerous in nature. Therefore, the cancer has three distinctive properties that distinguish malignant tumors from benign tumors: Uncontrolled growth Invasive nature Metastasis (ability to spread to other sections of the body) These disorders in cells are the result of the interaction between the genetic factors and external agents (which are called carcinogens) (WHO, 2009). The carcinogens can be categorized as (WHO, 2009): Biological carcinogens, like certain bacteria, viruses or parasites. Physical carcinogens, which includes the high energy radiations (ionizing radiations). Chemical carcinogens, these include substances like tobacco smoke, arsenic (water contaminant), aflatoxin (food contaminant), asbestos etc. Another factor essential in the development of cancer is the age. According to the studies conducted by the Cancer Research UK, the risk increase predominantly with increasing age, with nearly 74% of the cases of cancer diagnosed in people aged 60 and above (Cancer Research UK, 2009). Cancer Treatment Principle In case of normal cells there is specific pattern of growth, division and death (orderly destruction of cells is called apoptosis) (Crosta, n.d.). It is known that the cancer is the result of the uncontrolled growth of cells which do not die (Crosta, n.d.), that is, the apoptosis process fails in the cancer cells. The cancer cells thus do not die and rather continue to grow, resulting in the formation of tumors. As the problem in the cancer cells lies in the DNA, therefore a possible treatment of cancer is the destruction of the DNA in cancer cells, leading to a self initiated destruction of the cells. There are various methods used for the treatment of cancer depending upon the type of cancer. The most common types of treatment are (Fayed, 2009): Surgery Chemotherapy Radiation therapy or Radiotherapy Biologic or Targeted Therapy Radiotherapy Radiotherapy, also referred to as radiation therapy, is one of the most common types of treatments used for cancer. It is the utilization of higher energy radiations like x-rays, gamma rays in order to kill cancer cells, treatment of thyroid disorder and even some blood disorders, in a particular section (effected part) of the body (Nordqvist, 2009). The high energy ionizing radiations can be produced using a number of radioactive substrates like Cobalt (60Co), Radium (228Ra), Iodine (131I), Radon (221Rn), Cesium (137Cs), Phosphorus (32P), Gold (198Au), Iridium (192Ir), and Yttrium (90Y) (Howington, 2006). The cancer cells have the ability to multiply faster than other body cells. The high energy ionizing radiations are more destructive towards the faster growing cells, and thus they damage the cancer cell more than the other body cells (Mason, 2008). These high energy radiations like gamma rays and x-rays; especially damage the DNA inside these cancer cells (or tumor cells) thereby annihilating the ability of the cells to reproduce or grow. Apart from treatment of cancer, radiation therapy is also used to shrink a tumor before being surgically removed (Mason, 2008). Depending upon the method of irradiation, the process of radiation therapy is categorized into two forms (Mason, 2008): External Radiotherapy In this method (more common), the infected part of the body (tumor) is irradiated by high energy x-rays from outside the body. Internal Radiotherapy For this method, a radioactive substance are injected (or taken orally) into the body (close to the tumor) in the form of fluids. These substances, taken up by the cancer cells, radiate the tumor through internal beam radiation (or interstitial radiation) (Mason, 2008). Radiotherapy Planning A careful planning is essentially required for radiation therapy, as over exposure can be critically dangerous to healthy tissues in the body. The ionizing radiations have side effects, therefore once the full dose of radiations is decided; the patient is given these radiations in the form of small doses in a series of therapy sessions (Cancer Research UK, 2009). Each small dose of radiation is called a fraction. The gap between sessions provides the recovery time for the body, which may depend on the type of cancer and patients health condition. The area of the body that is radiated during the treatment is called the radiotherapy field and the section inside the body that experiences the maximum exposure dose is called the target volume (Cancer Research UK, 2009). The doctors decide the marginal area around the tumor that should be radiated to encapsulate any movement of the cancer cells. In order to accurately determine the position of tumor (or target volume), body scans are done. Computed Tomography (CT) scans are done as a planning procedure, this provides vital information regarding the location of the tumor as well as the kind of treatment required by the patient (Cancer Research UK, 2009). The radiotherapy treatment planning process can be divided into 6 major steps . Computer Tomography (CT) Scan The invention of Computer Tomography (CT) scanned is credited to Sir Godfrey Hounsfield in early 1970s, for which he along with Allen Cormack, was awarded the Nobel Prize in 1979 (Smith, n.d.). A CT scanner, also known as the Computed Axial Tomography (CAT) scanner uses X-rays to produce cross sectional images (or slices) of the body like a slice in a loaf of bread (FDA, 2010). The word tomography suggests the process of generating a two-dimensional image of a slice or section through a 3-dimensional object (a tomogram) (Nordqvist, 2009). These cross-sectional slides render an accurate picture of the size and location of the tumor along with the position of major organs in the body (Cancer Research UK, 2009). This would be essentially useful during the radiotherapy process, where these can be used to lower the dose of radiations on the organs. It is known that in case of radiation therapy treatment, the doses are given in fractions over a certain period of time (to prevent major side effects), which may vary from few weeks to months. Thus, before each fraction of radiation dose, computed tomography (CT) scan of the patients is done to determine the exact location of the tumor or cancer cells. So in case the full dose has been divided into 30 fractions, then the patient has to undergo 30 CT scans, each before a fractional therapy. The machine used for the radiation therapy planning is known as the simulator (Cancer Research UK, 2009). The simulator identifies the position of the tumor and marks the position of radiation on the body with the help of light rays. The radiographer uses ink markers on the body before the actual radiotherapy is begun. These linear ink marks are used by the radiographer for positioning the machine for radiotherapy (Cancer Research UK, 2009). Simulators take the pictures (CT scans) in the form of X-rays, which locates the accurate tumor position for the radiographer to carry out the treatment. During a CT scan, it is essential that the person remains completely still so that the measurements are accurate. In order to insure the correct position supports like neck rest, chest board or arm pole are used (Cancer Research UK, 2009). In case of children it is ensured by giving proper sedatives. Sometimes, under critical condition, extra measures are taken in order to prevent essential organs from being radiated during the therapy. These measures include injecting fluids or dyes which mark the position of vital human organs in the CT scan (Cancer Research UK, 2009). These markers may be given orally, through injections or rectally depending upon the requirement. Using this vital information from the CT scans, a treatment plan for radiation therapy is prepared. This plan indicates the position and direction of the radiations during the therapy, so as to minimize the exposure of healthy cells and organs. The scans generated by a CT scanner are in the form of 2 dimensional (2-D) slides, but by the used of digital geometry processing they can be used to generate a 3 dimensional (3-D) images of the body (Nordqvist, 2009). This can be achieved by integrating all the slides (along the same axis) together using a computer system. The CT scan can be understood as a technically advanced format of X-rays machines. The x-rays images are produced by the projection of a broad beam of x-rays on a film after passing through the body (Medindia, 2010). It provides a 2-dimentional projection of the body, where much of the information is lost. In case of CT scan, a thin beam of x-rays is absorbed by the detector after passing though the patients body (Medindia, 2010). Like the x-ray process, the CT scanning is a painless process for the patients but has been known to be accompanied with some side effects. These side effects may vary from the patient to patient depending upon the amount of radiation dose and health of the patient. The detailed discussion on the health effects of CT scanning has been discussed in the later sections of the project. Theory In order to understand the working of a computed tomography (CT) scanner it is essential to understand the properties of ionizing radiations (X-rays) used in the scanning process. The electromagnetic radiations are the arrangement of electric-field and magnetic-field vectors perpendicular to each other and also perpendicular to the propagation direction of the wave (Resnick et al., 2009). These Electromagnetic radiations have penetrating powers, which are directly dependent on the energy (or frequency) of these radiations. So that radiations with higher frequency have higher penetration powers. Therefore, on the basic the energy, the electromagnetic radiations are categorized as Non-ionizing radiations and Ionizing radiations. Non-Ionizing radiations refer to the electromagnetic radiations which have energy lower than that required for an atomic ionization (MIT, 2001). The non-ionizing radiations include radio waves, micro waves, visible light etc. These radiations have lower penetration powers. Alternatively the Ionizing radiations are the high frequency radiations which have enough energy to knockout an electron from an atom and thus causing ionization (MIT, 2001). The Gamma rays and X-rays are the common type of ionizing radiations. Even the alpha particles and beta particles emitted in a nuclear reaction are ionizing radiations (MIT, 2001). Due to the higher energy they have higher penetration power than the non-ionizing radiations. Principle of CT Scanning The most important section of a Computed Tomography (CT) scanning is the interaction of the ionizing X-ray radiations with the living tissues in the body. When the ionizing radiations (X-rays) interact with the living tissues in the body, they break up atoms and molecules from the living tissues and disrupt chemical reactions within the body (Zamanian Hardiman, 2005). The intensity of absorption of the x-ray radiations by the body varies depending upon the tissue coming in interaction. Different body tissues have different absorption power, where some are permeable to x-rays others are impermeable (Medindia, 2010). It is due to this difference in the absorption ability of different sections of the body, which results in the generation of a graded pattern in the scans. High density tissues like the bones appear white in the scan while the soft tissues (like brain and kidneys) appear dark. The cavities (like the lungs) are seen as black sections in the scan (Medindia, 2010). Therefore, this gradation in the pattern can be used as method to distinguish different body organs depending upon their absorption capacity. This forms the basic principle behind the working of an X-ray scanning. Radon (1917) was the first to develop the principles of computed tomography (CT) mathematically (Bushberg et al., 2002). According to Radon, with the help of infinite number of projections through an object, it could be possible to produce an image of an unknown object. In case of film imaging (as in conventional X-rays), a two-dimensional (2-D) projection of the body is generated on the film. Due to this, details in the dimension of the body along the direction parallel to the x-ray beam are lost. In order to overcome this drawback (only up to a certain level) projections can be taken along two directions; posteroanterior (PA) projection and lateral projection (Bushberg et al., 2002) (as shown in Figure 4). Increasing the number of scans improves the amount of information but in critical and complex cases where much more details are required. For these critical cases, CT scan is done. The CT scan provides the tomographical image, which is the picture of patients body in the sections or slabs. The thickness of these uniform slabs may vary from 1 millimeter to 10 millimeter (Bushberg et al., 2002), according to the program, depending upon the requirement. Each CT image consists of an array of large number of pixels forming a two dimensional (2-D) image, which corresponds to the same number of three dimensional thin rectangular slabs called the voxel. The voxels are the volume element whereas the pixels are the picture element (Bushberg et al., 2002). Every ray from the X-ray source passes (transmits) through the patient before the transmission measurement is done by the detector. Intensity of the un-attenuated x-ray radiation emitted by the source is Io whereas the intensity of the attenuated radiation after transmitting through the patient is given as It. The intensities Io and It are related by the equation (Bushberg et al., 2002): It=Ioe-ÃŽÂ ¼t Where;  µ is the total linear attenuation coefficient of the tissue (Smith, n.d.). t is the distance travelled by the radiation in the tissue i.e. the tissue thickness. The coefficient  µ is dependent on the atomic number and electron density of the tissues (Smith, n.d.). Higher the atomic number and electron density of the tissues, higher would be the attenuation coefficient (Smith, n.d.). This form the basic principle of CT scanning, that different tissues have different level of attenuation properties depending upon their atomic number and electron density. For every measurement, the overall attenuation coefficient is calculated using the above equation. During a complete 360o ­ scan, various transmission measurements for the intensity of X-ray photon are done. Using these intensity measurements specific attenuation values are allotted to every voxel (volume element). These attenuation numbers are directly proportional to the linear attenuation coefficient. The average of these attenuation values is called the CT number (Smith, n.d.). These values can be arranged on a linear scale, the units of which are called the Hounsfield units (HU). The scale for modern CT scanners varies from approximately -1,000 to 3,000 HU. The attenuation scale is based on binary system and therefore the exact values range from -1,024 to +3,071, with a total of 4,096 (or 212) attenuation numbers. Here, the lower represent the black section while the higher values represent the white section of the CT image. On this scale the attenuation value of water is zero HU and that of air is -1,000 HU (Smith, n.d.). Both of these values act as the reference points. Construction of a CT scanner CT scanner is a complex machine, but the basic structure is simple. A common CT scanner has been shown in Figure 2. Two most important parts of a CT scanner are the X-ray source and detector. The source and detector are placed in a circular structure, which has a shape similar to a doughnut. This doughnut shaped circular opening is called the gantry (RadiologyInfo, 2009), with an inner (opening) diameter varying from 60 cms to 70 cms. The X-ray source and detector are placed exactly (diagonally) opposite each other, so that the radiations emitted by the source pass through the body and the transmitted radiations are measured by the detector. The x-ray source and detector system in the gantry is motorized to rotate around the patient for measurements in different projection angles. The rational speed of the system is adjusted according to the detectors ability to measure and convert the x-ray beam into electronic signal. Cobalt (60Co) is generally used as the source of x-rays in the CT scanners. The detector used in CT scanner consists of an array of detectors in a slightly curved shape (like a banana). This curved shape is especially useful in fan-shaped beam projects. Two types of detectors are generally utilized in the CT scans; solid state or scintillation detector and Xenon gas detector (Reddinger, 1997). But the solid state detectors with scintillators like Cadmium Tungstate (CdWO4), yttrium, gadolinium ceramics etc are commonly used (Bushberg et al., 2002). The principle of the scintillation detector is that, when it is struck by a x-ray photon, it produces light. This light signal is then transformed to electrical signal with the help of photodiode. The Depending upon their structure, the detectors are categorized into two categories; single detector array and multiple detector array. Another essential part of a CT scanner is the motorized examination table. The table is controlled to move in and out of the gantry during the scanning process. As the position of the x-ray source and detector is fixed therefore the section being scanned is controlled by the movement of the examination table. For a better scan it is necessary that the patient remains completely still. To insure this table is equipped with neck rest, chest board and arm pole (Cancer Research UK, 2009). The detector measures the intensity of the radiation and converts them into electrical signals. These raw signals are analyzed and manipulated by the computer to convert them into images which can be understood by the radiologists and the technicians. Multiple computers are required in a CT scanner. The main computer that controls the operation of the entire system is called the host computer (Imaginis, n.d.). The computers and controls are located in a room adjoining the scanning room. This prevents the technicians and the radiographer from exposure to x-rays. Scanning Procedure in a CT scanner Initially the patient is positioned on the examination (or scanning) table in a flat upright posture (face towards the roof). In order to insure the correct and stationary position, straps and pillows may be used along the body. Once the patient is correctly positioned on the scanning table, the motorized table moves the patient into the circular opening of the CT scanner (FDA, 2010), which the x-ray radiations are projected on the patient from the scanning. For a particular position of the x-ray source and detector, the rays from the source pass through a region called the projection or view. There are two different types of projection geometries that are used in CT scanning; parallel beam geometry and fan beam geometry. In the parallel beam geometry, the rays projected on the patient are parallel to each other whereas in fan beam geometry, the rays diverge from the source in the shape of a fan (Bushberg et al., 2002) as shown in Figure 7. The fan beam projections are the most commonly in used x-ray projections in the CT scanners. The X-ray tube is attached with a collimator which controls the thickness of the fan beam. This thickness (of the fan beam projection) determines the width of the tissue slide in the scanning process. It is through the collimator that the slice thickness is varied between 1mm to 10mm (Smith, n.d.). The x-ray source and detector rotate around the patient (for imaging) in a circular motion such that they always remain exactly (diametrically) opposite to each other (as shown in Figure 7). During the rotation the source keeps emitting x-rays which are attenuated after passing through the patient. For a single projection (or slice), the x-ray source and detector make a complete 360o rotation around the patient. During the rotation the detector takes a large number of snapshots of the absorbed X-ray beam at different projection angles. A single image may involve approximately 800 rays and there can be up to 1,000 different projection angles (Bushberg et al., 2002). Therefore for a single projection (one slice), the detector does nearly 800,000 transmission measurements (Bushberg et al., 2002). The scanning of a single projection generally takes around 1 sec (for axial CT scanners) (FDA, 2010). Once all the transmission measurements (complete 360o) for a projection (or slice) are completed, the motorized table moves along the axis of the gantry so that the next slice of tissues forms the projection view. The process is continued till the complete required section of the body has been scanned. In the traditional CT scanners, the table moved on to the next projection (slice) only when the scanning of the previous was completed. Such conventional type of scanning is called the axial scanning. But in modern CT scanners, called the helical or spiral CT scanners, the rotation of the x-ray source and detector is accompanied with the uniform movement of the examination table, thus producing a helical projection. The helical CT scanning has been shown in Figure 9. These modern helical CT scanners are much faster than the traditional scanners due to continuous scanning process. They have been reported to take nearly half the time for scanning as compared to the traditional CT scanner s. In order to analyze and study the cardiac structure which is under constant motion, even helical CT is ineffective. For such applications a special CT scanner with an exposure time of 50ms and a maximum exposure rate of 17 images per second are used (Smith, n.d.). These scanners, called the cine CT, freeze the cardiac motion due to extremely low exposure time resulting in a sharp image (Smith, n.d.). These scanners use electron beam to generate x-rays, thus are also known as Electron Beam Computed Tomography (EBCT). In the CT scanning process large volume of data and operations are required to be processed, which is achieved with the help of multiple computers. The detector converts the intensity measurements of the attenuated x-rays in to electrical signals. The main computer, called the hub computer processes these signals and converts them into an image. These images can then be analyzed for radiotherapy planning. Result Computed Tomography (CT) has become an invaluable medical tool. It provides detailed 3-D images of various sections of the body like pelvis, soft tissues, lungs brain, blood vessels and bones (Nordqvist, 2009). Generally, CT scanning is the preferred method of diagnosing different types of cancers like liver, lungs and pancreatic cancers (Nordqvist, 2009). The tomographic images produced by the CT scan provide specific location and size of the tumor along with the details of affected tissues in the proximity of the tumor. This is especially advantageous in planning, guiding, and monitoring therapies like radiotherapy (FDA, 2010). CT scanning has various benefits over other traditional diagnostic techniques; some of the benefits are (RadiologyInfo, 2009): It is non-invasive, painless and extremely accurate. A major advantage is the ability to identify and distinguish bones, soft tissues and blood vessels in the same image. It also provides real time images which cannot be done in conventional X-rays. This technique is fast and simple; and is extensively used to locate internal injuries after accidents. It is less sensitive towards patient movement as compared to MRI. CT scanning can be used on patients with medical implants unlike the MRI. For an effective radiation therapy treatment, it is necessary that only the tumor is irradiated while minimum damage occurs to the surrounding health (normal) body tissues (Badcock, 1982). This is achieved with the help of CT imaging technique. In a study by Badcock (1982), 186 patients with various malignancies were studied and it was found that in nearly 39% of the treatment cases CT scanning was valuable in the assessment of the radiationdose calculation (Badcock, 1982). According to his study, CT scanner resulted in an alternation in target dose by more than 5%, (as compared to the traditional methods) in 27% of the patients (Badcock, 1982). The result has been shown in the table below. The mean alternation was 6.5% of the target dose and usually resulted in reduction of dose per fraction by factors upto 35% (Badcock, 1982). Even with these advantages, the adverse affect of the ionizing x-ray radiations cannot be neglected. Various experiments and researches have consolidated the fact that ionizing radiations like x-rays, gamma rays etc have adverse effect on living tissues. Zamanian Hardiman (2005) have explained that when high energy ionizing radiations interact with living tissues they strip-off atoms and molecules from them. This disrupts the chemical reaction within the body and failure in organ functioning (Zamanian Hardiman, 2005). The adverse effects of ionizing radiations were seen shortly after its discovery in 1890s, with a scientist involved in the study of radioactivity were reported with skin cancer in 1902. But is was not until 1944, that the role of radiations in causing leukemia in human was first documented, mainly in radiologists and physicists (Zamanian Hardiman, 2005). In recent years the use of x-rays has extensviely increased in medical field for diagonostic and treatment application. According to the U.S. Environmental Protection Agency, X-ray deveices are the largest source of man-made radiation exposure (US_EPA, 2007). According to NCRP Report No. 160 (2006), the average annual effective dose per individual in the US population, from all sources has increase from 1.7mSv in 1980s to 6.2mSv in 2006. This increase is mainly attributed to the striking growth of high dose medical imaging procedures that utilize x-rays and radionuclides (NCRP, 2008). Such man-made devices include X-ray machines, CT scans etc. CT scans, especially result in high dose x-ray exposure, with nealy 100 times the exposure dose as compared to standard x-ray equipments (Coach, 2008). Some of the major risks associated with CT scanning are: It is well documented that ionizing radiaitons like x-rays have the ability to cause cancer on exposure. Therefore, the CT dose in radiotherapy increase the probabilty of cancer in the future. Even though only 4% of the total x-ray examinations are CT scans, they account for more than 20% of the radiation dose to the population by medical x-rays (King Saud University, 2004). In general, the effective dose in a CT scan procedure ranges from 2 mSv to 10mSv, which is nearly equivalent to the amount of radiation that a person receive from the background exposures in three to five years (RadiologyInfo, 2009). A CT scan during preganacy make cause serious illness or even birth defects in the unborn baby (FDA, 2010). Children are more sensitive and vulnerable to x-ray exposures than the adults, therefore their CT scanning should be done only under extremely essential and necessary conditions. Women have higher risk of developing cancer in the lifetime, as compared to men under same levels of exposure (FDA, 2009). In some rare situation of high-dose prolonged radiation exposure, the x-rays can cause adverse effects like skin reddening (erythema), skin tissue injury, hair loss, cataracts etc (FDA, 2010). In a study, Sawyer et al (2009) estimated the effective dose resulting from a cone beam CT scanning for planning of radiation therapy using thermoluminescent dosemeters (TLDs) for organ dose and using International Commission on Radiological Protection (ICRP) 60 tissue weighing factor (Sawyer et al., 2009). The results obtained for effective dose from TLD measurements and ICRP 60 weighting factor, for breast, pelvis and head simulation have been shown in the table below. The scanning process results in the exposure of the normal tissues outside the treatment volume (Waddington McKenzie, 2004). It is thus important to analyze the effect that the irradiation caused by the CT scanning process has on the patients body. In a study, Waddington McKenzie (2004) analyzed the propability of developing cancer from the irradiations caused by the extended field portal imaging techniques, the results of which are given in the table below (Waddington McKenzie, 2004). In order to illustrate a real life situation, the calulations in the study were done for an average man with a height of 170 cms and weight of 70 kgs (Waddington McKenzie, 2004). Therefore, these values may change depending upon the height, weight and tumor size of the patient. Discussion Various studies have been done to statistically evaluate the effect of the ionizing radiations on the human health. These risks have severely amplified due to the rapid increase in the number of CT scans for diagnostic applications. CT scans form nearly 5% of all procedures used in diagnostic radiology in the developed countries (Wrixon et al., 2004). In U.S., nearly 70 million CT scans were done in 2007 as compared to just 3 million done in 1980 (Steenhuysen, 2009), this includes more than 4 million children in 2006 (Brenner Hall, 2007). Thus, according to the NCRP Report no. 160, the average radiation dose per person has increased from 3.6 mSv in early 1980s to 6.2 mSv in 2006 (NCRP, 2008). Steenhuysen (2009) has reported that the radiations from CT scans done in 2007 will cause 29,000 cancers and kill nearly 15,000 people in America (Steenhuysen, 2009). These stats explain the level of exposure caused by the CT scans. According to estimates by Amy Berrington de Gonzalez of the National Cancer Institute, one-third of the projected cancers will occur in people who were ages 35 to 54 when they got their CT, two-thirds will occur in women and 15 percent will arise from scans done in children or teens (Steenhuysen, 2009). They also estimate that there would be 2,000 surplus cases of breast cancer due to the CT scans done in 2007. The children are especially more vulnerable to cancer largely due to longer life expectancy (more exposure in the lifetime) and the rapid developing nature of the tissues and system. Even though CT scans add a lot of useful information in the diagnostic process but it is known that the CT scan of the chest exposes the patient to nearly 100 conventional chest X-rays (Preidt, 2009). Therefore, the radiation exposure from CT scans it much higher than that from the conventional x-rays. Normally, people are exposed to radiations from natural resources on Earth. On an average, a person in United States receives a radiation dose of around 3 mSv per year just due to natural resources like radioactive materials and cosmic radiations from outer space (Radiology Info, 2009). These radiations, referred to as the background radiations, may vary from one region to another within a country. In simpler terms, the radiation exposure from one chest x-ray is equivalent to the dose of radiations exposure experienced from natural environment (background radiations) in ten days (Radiology Info, 2009). The table below compares the effective radiation dose from various CT scans with the exposure from the background radiations. CT scanners along with portal imaging systems are an essential part of radiation therapy. Therefore in addition to exposures from the radiotherapy, patients are also irradiated by these imaging systems (Harrison et al., 2006), which might contribute significantly to the total dose of the patient. According to Harrison et al (2006), the concomitant irradiation from the imaging systems may range from 5% to 10% of the total organ dose and can reach up to 20% for bone surfaces (Harrison et al., 2006). Conformal radiotherapies are associated with an increased number of imaging operations for verification at different stages of the treatment (Harrison et al., 2007). Harrison et al (2007) have also analyzed the doses to critical organs (with higher cancer probability) for the realistic treatments of the larynx and breast including the doses from the concomitant CT and electronic portal imaging (Harrison et al., 2007). The results showed that the total dose to the critical organs due to imaging was in the range of 5% to 20% of the total dose but in case of bone marrow and bone surfaces this could reach up to 30%. Based on the data on CT scan use and risk estimates, from 1991 to 1996, it has been estimated that 0.4% of all cancers in U.S. may be attributed to the radiation from the CT scans (Brenner Hall, 2007). But with the rapid increase in the use of CT scans in recent year, the estimate may now be around 1.5% to 2.0% for the current data (Brenner Hall, 2007). Over the last decade there has been a rapid increase in the total number of CT scans, with over 70 million scans in 2007 in United States alone (Steenhuysen, 2009). According to the McKinsey Global Institute, an economic research group report (2007), from its invention in 1973, the CT scanners have grown largely in number, to nearly 24,000 machines in U.S. (Coach, 2008). This is almost equivalent to 81 CT scanners per million people in U.S. Only Japan has a higher CT scanner density with 91 scanners per million people (Coach, 2008). There has been a question regarding the necessity of the CT scans being order by the doctors. While in some cases the CT scans have proofed to be life saving, in some other cases it is not necessary. According to Rubin, a Stanford University radiologist, Its gotten into the culture of doctors (Coach, 2008). In a research conducted by Highmark Blue Cross Blue Shield of Pennsylvania in 2000 (when the number of scans were half of todays total), 162,000 scans were reviewed and at least 30% were found to be either inappropriate or un-useful in contributing any information (Coach, 2008). According to the Health Physics Society, there is no evidence of any benefits from the whole body CT scans and believes that such radiation exposures are unjustified (Richard J. Burk, 2007). Considering the vital information provided by the CT scanning along with the risks associated with it, it is necessary to keep the radiation dose to as small as possible, especially in case of children, who are more vulnerable to cancer that the adults. In this regard various recommendations have been proposed by the U.S. Food and Drug Association (FDA) to prevent unnecessary exposure during Computed Tomography scans (David W. Feigal, 2001). Optimized CT Settings. To prevent over-exposure it is necessary to change the CT scanning dose according to the patients body structure (weight and diameter) and the scanning region. Reduction in Tube current. The radiation dose is directly proportional to the current in the x-ray tube. So the exposure can be reduced by reducing the tube current. Developing and using chart with optimized tube current based on patient weight or diameter and anatomical region of interest (David W. Feigal, 2001). Such charts can standardize the scanning process, thus preventing over exposures. Increasing table increment (axial scanning) or pitch (helical scanning). The amount of radiation exposure can also be reduced by increasing the table increment and pitch. According to FDA, by increasing the pitch from 1:1 to 1.5:1, the radiation dose can be decreased by 33%, without the loss of diagnostic information (David W. Feigal, 2001). Reduction in the number of multiple scans with contrast materials. Often scanning is done before, during and after injection of contrasting material. Such exposures can be reduced by pre-contrast images (David W. Feigal, 2001). Elimination of unnecessary CT scanning. CT scan should be referred only when necessary. Radiation exposure can be eliminated or reduced if other imaging techniques are used. Regular monitoring and inspection of the CT scanner machines. Such checks should be done to meet the standards of radiation exposure limits. Other than this, even the manufacturers on CT scanners have worked on cutting down the radiation exposure and over the last 20 years they have been able to reduce the exposure by nearly 20 to 75% (Health Physics Society, 2009). The researchers have worked efficiently in finding methods to reduce the radiation dose due to the scanning process. Roxby et al (2009), in a research have documented that by introducing a copper filter (thickness, 0.15mm) in a Cone Beam Computed Tomography (CBCT), the dose on the phantom was reduced from 45 mGy to 30 mGy at the standard setting (Roxby et al., 2009). Even though the introduction of filter increase the noise but it does not affect the ability of identify soft tissues for the treatment verification purpose (Roxby et al., 2009). In 2008, American Association of Physicists in Medicine (AAPM) published a CT radiation dose management report. The report recommended methods for standardization of reporting doses along with educating users on the latest dose reduction technology (Health Physics Society, 2009). Conclusion The imaging technology has advanced ever since the invention of Computer Tomography (CT) scanning. CT scans (also called the CAT scans) have revolutionized the diagnostic process in the field of medicine. This has especially been useful in the study of tumors and cancers. CT scanning can determine the exact location and size of the tumor along with the extent of damage it has caused to the nearby tissues. Even in the treatment of cancer through radiation therapy (or radiotherapy), CT scan are extremely useful. But this revolution has come at a price of higher ionizing x-ray radiation exposure to the population. The adverse effects of CT scans (x-ray radiations) have come to light with the advancement in the understanding of the carcinogenic nature of low doses of radiations, especially for children (Brenner Hall, 2007). There are two important factors that contribute to the higher vulnerability of children, firstly, children have longer life expectancy (they have large number of years for exposure) and secondly, they have a developing system with cells multiplying rapidly. This contributes to higher risk of cancer. Another essential concern is the increasing number of CT scans in the recent years. In 2007 along, about 70 million CT scans procedures were conducted in United States (Steenhuysen, 2009). With just 3 million CT scans in 1980 (Steenhuysen, 2009), this number has multiplied many time over. According to reports, per person radiation dose due to medical x-rays has increased by about 500 percent since 1982 (FDA, 2009). From these results it is evident that there has been an increase in the number of unnecessary and unessential CT scans. The self requested CT scans by the patients has also been a key factor in the increasing number of CT scans in recent years. In order to control such high radiation exposures, United States Food and Drug Association have proposed some guidelines and recommendation for the patients and the radiologist. These guidelines would limit and reduce the amount of radiation exposure due to CT scans especially in case of children. A chest CT scan provides an exposure equivalent to more than 100 conventional x-rays (Coach, 2008). Therefore, CT scan should only be done when necessary. Even measures like decreasing the tube current, increasing the pitch (for helical scanning) etc. can largely reduce radiation exposure. The increasing radiation exposure among people is a cause of concern and should be controlled effectively. The radiologists and radiotherapists have to insure that CT scans are done only when necessary and when other low radiation alternatives are not applicable. As for people, they should work in collaboration with their physicians to insure that they are subjected to least amount of radiation exposure. Especially in case of children, additional attention must be given due to higher risk associated with radiation exposure. Bibliography Badcock, P.C., 1982. Has CT scanning a role to play in radiotherapy planning? Computer dose calculations. British Journal of Radiology, 55, pp.434-37. Brenner, D.J. Hall, E.J., 2007. Computed Tomography à ¢Ã¢â€š ¬Ã¢â‚¬  An Increasing Source of Radiation Exposure. The New England Journal of Medicine, pp.2277-84. Bushberg, J.T., Seibert, J.A., Leidholdt, J..E.M. Boone, J.M., 2002. The Essential Physics of Medical Imaging. 2nd ed. Philadelphia: Lippincott Williams Wilkins. Cancer Research UK, 2009. Cancer incidence by age UK statistics. 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[Online] Available at: https://www.medicalnewstoday.com/info/cancer-oncology/whatiscancer.php [Accessed 13 February 2010]. David W. Feigal, J., 2001. FDA Public Health Notification: Reducing Radiation Risk from Computed Tomography for Pediatric and Small Adult Patients. [Online] Available at: https://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/PublicHealthNotifications/ucm062185.htm [Accessed 20 February 2010]. Fayed, L., 2009. Methods of Treatment for Cancer. [Online] Available at: https://cancer.about.com/od/treatmentoptions/a/options.htm [Accessed 14 February 2010]. FDA, 2009. Reducing Radiation from Medical X-rays. [Online] Available at: https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095505.htm [Accessed 18 February 2010]. FDA, 2009. Reducing Radiation from Medical X-rays. Consumer updates. Silver Spring: U.S. Food and Drug Administration U.S. Department of Health and Human Services. FDA, 2010. Radiation-Emitting Products. [Online] Available at: https://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm115317.htm [Accessed 14 February 2010]. Harrison, R.M., Wilkinson, M., Rawlings, D.J. Moore, M., 2007. Doses to critical organs following radiotherapy and concomitant imaging of the larynx and breast. The British Journal of Radiology, (80), pp.989-95. Harrison, R.M. et al., 2006. Organ doses from prostate radiotherapy and associated concomitant exposures. The British Journal of Radiology, (79), pp.487-96. Health Physics Society, 2009. People Exposed to More Radiation from Medical Exams. [Online] Available at: https://hps.org/media/documents/NCRP_Report-People_Exposed_to_More_Radiation_from_Medical_Exams_9Mar.pdf [Accessed 20 February 2010]. Howington, J., 2006. Lung Cancer. [Online] Available at: https://www.netwellness.org/healthtopics/lungcancer/lcglossary.cfm [Accessed 13 February 2010]. Imaginis, n.d. How Does CT Work? 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The History of the Discovery of Radiation and Radioactivity. [Online] Available at: https://mightylib.mit.edu/Course%20Materials/22.01/Fall%202001/discovery%20of%20radiation.pdf [Accessed 10 December 2009]. National Cancer Institute, 2010. Cancer. [Online] Available at: https://www.nlm.nih.gov/medlineplus/cancer.html [Accessed 13 February 2010]. NCRP, 2008. IONISING RADIATION EXPOSURE OF THE POPULATION OF THE UNITED STATES: NCRP REPORT No. 160. NCRP Report No. 160. Bethesda: National Council on Radiation Protection and Measurements National Council on Radiation Protection and Measurements, Bethesda, MD, USA. Nordqvist, C., 2009. What Is a CT Scan? What Is a CAT Scan? [Online] Available at: https://www.medicalnewstoday.com/articles/153201.php [Accessed 15 February 2010]. Nordqvist, C., 2009. What is radiotherapy? [Online] Available at: https://www.medicalnewstoday.com/articles/158513.php [Accessed 13 February 2010]. Preidt, R., 2009. CT Scan Patients May Get Unnecessary Imaging. News Report. Health Day. Radiology Info, 2009. Safety. [Online] Available at: https://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray#6 [Accessed 19 February 2010]. RadiologyInfo, 2009. CT Boby. [Online] Available at: https://www.radiologyinfo.org/en/info.cfm?pg=bodyct [Accessed 15 February 2010]. Reddinger, W.L., 1997. CT Instrumentation Physics. [Online] Available at: https://www.e-radiography.net/mrict/Basic_CT.pdf [Accessed 17 February 2010]. Resnick, Halliday Waker, 2009. Fundamentals of Physics-Eighth Edition. John Wiley Sons. Richard J. Burk, J., 2007. Whole Body Computerized Tomography Screening shoould not be performed. Position Statement. Health Physics Society. Roxby, P. et al., 2009. Simple methods to reduce patient dose in a Varian cone beam CT system for delivery verification in pelvic radiotherapy. The British Journal of Radiology, (82), pp.855-59. Sawyer, L.J. et al., 2009. Estimation of organ and effective doses resulting from cone beam CT imaging for radiotherapy treatment planning. The British Journal of Radiology, July(82), pp.577-84. Smith, H.-J., n.d. Computed tomograpy. [Online] Available at: https://www.medcyclopaedia.com/library/radiology/chapter04/4_2.aspx [Accessed 17 February 2010]. Steenhuysen, J., 2009. Radiation from CT scans may raise cancer risks. News. Chicago: Medicine Plus Reuters Health Information. US_EPA, 2007. EPA-402-F-06-061 Ionizing Radiation: Fact Book. Fact Book. Environmental Protection Agency. Waddington, S.P. McKenzie, A.L., 2004. Assessment of effective dose from concomitant exposures required in verification of the target volume in radiotherapy. The British Journal of Radiology, (77), pp.557-61. WHO, 2009. Cancer: Fact Sheet. [Online] Available at: https://www.who.int/mediacentre/factsheets/fs297/en/ [Accessed 13 February 2010]. Wrixon, A.D., Barraclough, I. Clark, M.J., 2004. Radiation, people and the environment. Vienna: International Atomic Energy Agency. Zamanian, A. Hardiman, C., 2005. Electromagnetic Radiation and Human Health: A Review of Sources and Effects. High Frequency Electronics, (Summit Technical Media), pp.16-26. In the International System of Units, the sievert (Sv) or millisievert (mSv) describes equivalent or effective radiation dose. One sievert is equal to 100 rem. Rem is also the term used to describe equivalent or effective radiation dose (NCRP report). Also one sievert is equal to one Gray (Gy), which is the energy absorbed per unit mass. 1 Gy is 1 joule of radiation energy absorbed per unit kilogram (Brenner Hall, 2007)

The French Revolution And Its Effect On British Political...

What, if anything, was achieved by extra-parliamentary protest in the years 1790-1819? Radicalism was alive in Britain from the late eighteenth century, yet Parliament resolutely refused to reform itself until the late 1830s. It is therefore tempting to dismiss extra-parliamentary protest during this period as having failed to bring about any substantial reform in the face of Government repression. The French Revolution had a dramatic impact on British political life from the onset of its eruption in 1789. In November 1790, Edmund Burke published ‘Reflections on the Revolution in France’. Burke was not opposed to reform but he defended Britain’s existing constitution on the grounds that it had grown organically out of Britain’s unique history. In his book he maintained that government derived its authority from custom and tradition, not from the consent of the governed. 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The book The Age of Revolutions in Global Context, c. 1760-1840, put together and edited by David Armitage and Sanjay Subrahmanyam, is a book of essays collaboratedRead MoreThe American Of The British Empire Essay1672 Words   |  7 PagesIn the British Empire, existed thirteen colonies found between the 1600s and the 1700s on the Atlantic Coast of North America. These thirteen colonies later on combined together into a new nation currently known as the United State s of America. Immigrations from Britain and Germany had high growth rates and were all successful and thriving. These colonies had self-governments furthermore to similar political and legal systems. The self-government systems were based mainly on farmers who owned a pieceRead More Modern Political Thoery and Liberalism Essay1040 Words   |  5 PagesModern Political Thoery and Liberalism The subject given for this paper was to â€Å"assess the alienation from liberalism found in modern and contemporary political theory.† To be honest, I don’t see a correlation with alienating liberalism and modern political thought through the time line of political theory in the 18th and19th century and through the 20th century. So, for this paper, I will prove the opposite. I will show, in my opinion, how the rise of liberalism has kept alive modern and contemporaryRead MoreThe American Revolution-Eight Long Years852 Words   |  4 PagesThe American Revolution, also known as the American Revolutionary War and the War of Independence, lasted from 1775 to 1783. It stemmed from growing tensions between England’s 13 North American colonies and the colonial government representing England, as well as cost sharing imposed on English colonies by successive governments in London for debts attributed to former wars (Foner, 2012). The â€Å"cost sharing† encom passed a variety of measures including taxation on goods produced in the colonies,Read MoreThe Enlightenment Principles Of Rationalism And Universal Rights1684 Words   |  7 PagesJean-Jacques Rousseau were signposts of this era, inspiring populations locally and abroad. This revolution of ideas led to political and societal upheaval throughout the Western world. This essay will argue that the Enlightenment principles of rationalism and universal rights shaped modern Europe and North America through the rejection of absolutist government and the movement towards an equal society. The effect of these Enlightenment ideas is evident throughout the ‘Declaration of Independence’, writtenRead MoreThe American Revolution Was Truly Revolutionary Essay1382 Words   |  6 PagesMany revolutions have taken place throughout history, ranging from the unremarkable to the truly memorable, such as the French Revolution, the Bolshevik Revolution and the American Revolution. Through a n examination of the social, cultural, economic and political causes of the American Revolution, an exploration of key arguments both for and against the American Revolution, and an analysis of the social, cultural, economic and political changes brought about by the American Revolution it can be demonstrated

Adolescent Sex Free Essays

The prevalence of teenage pregnancy in the society and the alarming increase of such are often perceived to be caused by inadequate government and educational programs about sex. While most people continuously adhere to this idea, the role and responsibilities of parents in their child’s sexual quandaries, to some extent is set behind the veracity of the problem. Some parents even exhibit lack of authority over their children by allowing them to have sex at home. We will write a custom essay sample on Adolescent Sex or any similar topic only for you Order Now As a parent your basic instinct is to weigh the consequences when your child is already engaged in premarital sex or if his or her relationship is already progressing on that direction. On the affirmative side of the scale, today’s liberal society demonstrates that everyone is doing it and it is part of your child’s learning experience. The unconstructive scale on the other hand, carries out issues on morality, sexually transmitted diseases and pregnancy. Instead of allowing them to engage in premarital sex inside your home, provide your parental guidance by teaching them abstinence-only sex education which emphasizes morality and having sex within the boundaries of marriage (Religion and Ethics Newsweekly, Episode 823). This will establish a platform for your children to know that having sex at a very young age and outside the sanctity of marriage can result to heavy emotional and physical costs which are not only limited to diseases and pregnancy but is also a ground to bring into a halt their supposed bright future. Though, an open communication with your children regarding their sexual experiences is a great start to take a hold of them when they are already engaged in sexual activities, allowing them to do it in your home is improper and inappropriate decision to make as their parent and guardian. The foremost situation of your children living in your house and exclusively depending on you to fill their stomachs are substantial evidences that they still are not capable of taking care of themselves and their actions to include having premarital sex. References PBS, February 4, 2005 Religion Ethics Newsweekly, Episode 823 Retrieved on 2009-21-02 How to cite Adolescent Sex, Papers

The Sun and The Moon script Essay Example For Students

The Sun and The Moon script Essay Winnie-(Moon) Kson-(Sun) Noel-( Pluto) Zelly- (Earth)  W: Hi, Sun! Good morning, do u have a wonderful dream last night? Haha  K: Of course! And now it is a sunny day again! Can u see? Those human being are swimming and they feel so good in the earth.  W: Oh! Really? But dont u see when they are sleeping, how comfortable they are!  K: But I dont think so. Every time when they play, the Earth is so happy and the human being will so enjoy. Do u know why? It is because of my power! Haha  W: WHAT? Your power? Of course not! Havent u see when they are sleeping? They all have a good dream, and the Earth is sleeping comfortable. We will write a custom essay on The Sun and The Moon script specifically for you for only $16.38 $13.9/page Order now Z: You all are so troublesome,can u just give me a moment to take a rest?  W: Okay, Earth. Let me give u some sunshine, so that u will feel comfortable.  K: Get off! Sun. Let me give u a good night.  W: No! Sunshine.  K: NO! Night!  W: NO WAY! Sunshine.  K: NO! NO! NO!  Z: Can u all just shut up? Sometime it is a sunny day, and sometimes it is at night. U all make my world becomes crazy!!!  W: Sunshine  K: Night  Z: Pleasecan someone helps me?! Call them go away!!! N: What happen, Earth? Are you okay?  Z: Not reallyThe sun and the moon are arguing! And they almost make my world crazy!  N: Really? It seems terrible. Let me help you!  W: Sunshine  K: Night  N: Hey! Can u all just stop?  W: Cant u see we are having a competition to see who is the best, Pluto?  K: Yes! Pluto, u just leave us alone! N: Of course not! Cant u see the Earth are going to be crazy? And she is crying! K: Oh really? But we must know that who is the best!  N: Actually, u all are the best! The Earth need all of you!  W: Really? But we two cant stay together! How can the Earth need us?  N: OhErmm I know! The sun can stay in the morning, then you can give the sunshine to the Earth.  K: So, how about me?  N: You can stay at night, and the Sun takes a rest.  W+K: Thats good!  W: So.. u belong to the morning, Sun.  K: And u belong to the night time, Moon.  N: So every time, when it is morning, u can see the Sun; and when it is at night, u can see the Moon.  Z: And now I live happily forever!

Essay Sample on Forensic Science The Search for Justice

Essay Sample on Forensic Science The Search for Justice A Chicago native, Kathleen J. Reichs is an award winning international bestseller, winner of the 1997 Ellis award for best first novel. Her novel Deja Dead was only the first in a series of books. She went on to write four more novels: Death du Jour, Deadly Decisions , Fatal voyage and Grave Secrets. Kathy Reichs is a internationally recognized forensic anthropologist working on cases around the world, from examining the tomb of the unknown soldier, and working at ground zero, New York, to being an expert witness between Charlotte and Montreal were she currently divides her time. These experiences are what gave birth to her novels, each of her stories is based on her own personal experiences. Evil exists in every human being, the closest most get to this evil is by criminal activities. But, most people also have a natural need for justice when this evil called crime is committed. Justice is often acquired through the means of forensic science, or simply forensics, the application of science to law. Scientific procedures, methods, and technologies are used in investigating these crimes and proving the guilt of an accused suspect in a court of law. After the evidence is gathered from a crime scene, and photographs have been taken. A crime involving a body normally begins with the Medical Examiner ( also referred to as the ME) conducts an autopsy, the examination of the body after death. The ME studies the deceased to determine his or her identity, as well as the cause, method, mode and time of death. The ME determines the time of death by pathology. When a human dies he or she shuts down in stages, the bodies live temperature of 98,6 degrees, is maintained for one to two hours after death, then begins to cool, till it finally drops to it‘s surroundings temperature. But, this method is only used if the body has been discovered within 48 hours. For those cadavers found weeks after death a forensic entomologist enters the scene and uses his or her knowledge of insect life to determine the time and date of death. Insects are attracted to a decaying corpses odour. This may smell bad to humans, but for an insect it’s chow time, and a perfect place for laying eggs. Since insects go through different stages of life at different times, a forensic entomologist (FE) will take samples of the insects surrounding the body, and identify what species they are. Then the FE will cultivate the larvae to discover the time each stage takes. Once the species and stages of their life has been established, the entomologist can determine how many hours and days the body has gone unfound. Insects can also tell if the body has been moved after death by comparing the local insects found around the body and the insects inside the body. Identifying a corpse is sometimes very simple, people usually carry with them a wallet or some kind of identification, it’s a simple task to simply examen the contents of a wallet. But, in some infrequent circumstances a body is not carrying any identification and no one is able to identify him or her. Under these circumstances, the ME, and other forensic specialists are brought in to work with the evidence and make an identification. The easiest things to do are to describe the victims appearance and search the missing persons reports. The next step would be to take the body’s fingerprints and compare it with the federal fingerprint files. Since no two people have the exact same fingerprints and the pattern is unchanged through life if a match is found the deceased has an identity. Fingerprints can also link a suspect to his crime, fingerprints found at the scene of the crime are compared to a suspect’s fingerprints establishing absolute proof the suspected was there. If a body part or a bodies skeleton his found, enter the forensic anthropologists to identify the victim’s remains. A forensic anthropologist must suggest the age, sex, stature, ethnic group, and other unique characteristics of a descendent with anthropology, the study of human beings. In the novel Fatal Voyage, author Kathy Reichs has her heroine, forensic anthropologist Dr. Temperance Brennan, investigating plane crash victims. Body parts have been scattered and Dr. Brennan must determine which body parts go together to identify the body by comparing her description to the description of the passengers on the plane. In other cases without a passenger list investigators can take the description made by the forensic anthropologist and compare it to missing persons files. Forensic science depends on evidence to help solve a crime, and bring criminals to justice. Evidence is a reliable witness, it can be anything and everything in the physical universe that helps establish the facts. From a single hair, to a trail of blood, we humans are made of a cocktail of biological materials that can be left behind at the crime scene, which all can be used to identify the criminal with DNA analysis. Other evidence can suggest contact between the victim and the suspect. Like Sherlock Holmes depended on his trusty magnifying glass, the forensic scientists of today depend on their tools of the trade to uncover evidence. Without these technologies some evidence needed to solve the crime would be obsolete and others not even uncovered. An example would be the chemical luminol, used to highlight blood that has been washed away from the crime scene. . Many books, television programs and movies have based themselves on the idea of forensic science and detective work, from Sherlock Holmes to the popular television show CSI: Crime Scene Investigation. These stories show a glimpse of the work involved in forensics, but only a glimpse. On the television and in movies the hero or heroine often reveals the identity of the criminal with one piece of evidence, one clue, that solves the hole case. The real investigators are much harder working and cannot reveal the criminal that instantly. Very often the cases cannot be solved due to an insufficiency of evidence. The search for justice is a hard and long process, which involves many scientific methods procedures, and technologies. For some the search of justice is to strenuous, but for others who remind themselves that justice is needed in a society of laws, it’s a living. Kathy Reichs describes the reasons for doing what she does in her book Fatal Voyage when her heroine Dr. Brennan says, †I want to serve both the living and the dead. The dead have a right to be identified .To have their stories drawn to a close and to take their places in our memories. If they died at the hands of another, they also have a right to have those hands brought to account.† Forensic scientists require extensive knowledge, training, and skill. They also require a healthy appetite of curiosity, a quean eye of observation, the emotional stamina to work with human tragedies, and to be able to view the evil of man.

Free Money for Collegeâ€Paying for School With Grants

Free Money for College- Paying for School With Grants A grant is a sum of money that is gifted to someone for a specific purpose. For example, a grant might be awarded to a student so that the student can pay for tuition, books and other education-related costs. Grants are also known as awards or gift aid. Why You Need Grants Grants the best way to pay for college or business school. Unlike students loans, which can create a significant financial burden during and after school, grants do not need to be paid back. Getting Grants for School Students can receive grants from a variety of sources, including private organizations, educational institutions, professional associations, and federal and state governments.  Grants may be awarded based on a student’s financial need, ethnicity, religious affiliation, record of achievement, association or special interests. Education Grants From the Federal Government There are many different types of grants awarded by the federal government. Lets explore a few of the best grants for school. Federal Pell Grant- Federal Pell Grants are the most common grants awarded by the federal government. These grants are primarily designed for students who have not yet earned a bachelors degree. In other words, they are for undergraduate students. However, these grants might also be available to students in a  postbaccalaureate teacher certification program.  Federal Pell Grants are need-based; they are meant to help low-income students pay for school. Grant amounts vary by individual and are dependent on the cost of education and the students expected family contribution (EFC).Federal Supplemental Education Opportunity Grant- The federal government gives schools money through the FSEOG Program each year. These funds are then distributed by the school to financially-needy students. That means that FSEOG grants are campus-based aid. Not every school participates in this federal program, and the funds are usually available on a first-come, first-served based. Students who get FSEOG grants typically have a very low EFC and are usually Federal Pell Grant recipients. The amount of the award varies but usually falls somewhere between $100 and $4,000. Education Grants From the State Government Grants for school are also awarded at the state level. Each state has a different way of acquiring and distributing financial aid. Many states fund their programs with taxes and lottery earnings. State-based grants are usually designed to be spent at in-state schools, but again, rules vary by state. Some examples of state grant programs include the Pennsylvania State Grant Program, which is a need-based program that awards aid on a sliding scale based on annual income, and Cal Grants, a California-based program that awards aid to students who attend school at least half-time and falls under  income and asset ceilings. Education Grants From Other Sources Federal and state governments arent the only groups who award grants for school. Nearly all colleges and universities have some type of grant program for students who can demonstrate financial need. You should speak with your schools financial aid office to learn more about grant availability and application procedures.  You may also be able to receive merit-based grants from professional associations, corporations, and other groups who have formal and informal programs for students seeking education funds.   How to Apply for Grants The application procedure for grants varies depending on the organization. To apply for federal grants, you need to fill out the Free Application for Federal Student Aid (FAFSA) each year you plan to attend school. Some states also award grants based on information supplied in the FAFSA form. However, application rules for each state vary. Contact your states Department of Education to learn more about application procedures.

How do retailers make sure that they are reaching the older customer Thesis

How do retailers make sure that they are reaching the older customer How can they successfully keep the retail experience relev - Thesis Example Layout of products and websites (how are products presented) How easy is it to navigate? Screen Language used Promotional offers Delivery charges and methods Mailing, newsletter (sent according to previous purchase or not) Help and FAQ area Swot analysis and recommendations III. Conclusion Recommendations One of the major changes of the century is the global ageing population. As Richard Watson says in his book Future Files (2008), the ageing population is the biggest trend that will shape the next 50 years and that will radically modify the way people consume. According to the British Parliament website, 10 million people in the UK are over 65 years old.   The latest projections are for 5? million more elderly people in 20 years time and the number will have nearly doubled to around 19 million by 2050. We can explain the trend by the fact that people are now not only living longer thanks to great progress in the medicine but also the ageing of the large number of individuals born during the baby boom. Figure 1: Population by age in the UK in 1984, 2009 and 2034 Source: National Statistics Online, 2010 Hence, the 60 plus market represents a great market for retailers who shouldn’t ignore them since they not only have more time to shop than any other age category but they usually have a significant buying power across many product fields. However they have different needs, including the fact that, most of the time, they do not want to go shopping for hours in crowded and gigantic stores or others can’t because they don’t drive (mostly for seniors over 70 years old). As a consequence, the retailers have to find a way to reach these customers by bringing the products to them. Several ways can used to do so, for example Internet or catalogue shopping. They can also facilitate their shopping experience, for instance by offering to deliver the products that they choose in the shop directly at home for free. We will study in this report all of t hese channels focusing on the E-Retailing as a way to reach the older customer. Who are these seniors? As Barry Gunter explains in his book Understanding the older customer (1998), when it comes to communication, a major mistake that the retailers need to avoid is stigmatising the older customer with stereotypes regarding their physical and mental capacities as they could be misunderstood and depreciated. Age is a relative concept; we can’t really define seniors by their age but more by the age felt. For doctors, people become seniors at the age of 70 years old when specific diseases affecting their patients. For the state, the barrier is 60 years old at the time of retirement. But for our study, we will focus on people over 60 years old, the fact that they retire from their careers make them different consumers from younger age groups who buy differently and have much more free time on their hands. We will limit our study to 80 years old people who are part of the oldest gen eration who don’t really consume that much, due to their difficulty to move out of the house and the fact that they are in nursery houses. So how do senior citizens see themselves? At 65, there is a gap of almost 20 years between chronological age

Book Review about US History up to 1877 Essay Example | Topics and Well Written Essays - 750 words

Book Review about US History up to 1877 - Essay Example Whereas shorter and supplementary centered, "The Awakening" stays put an excellent review of a crucial era of historic political establishments such as setting up of American nationality and governance structures. An Overview of the then American society Dangerfield indicates the enlargement of both economic chauvinism and egalitarian nationalism and how these contradictory forces destabilized any hopes for an epoch of excellent feelings in the country’s politics. In case an individual is interested in understanding the significant political stage between the conclusions of the War of 1812 in addition to the Jacksonian time, this is an exceptional overview and, unsurpassed of all, is a simple read. The aim of this paper is to provide an evaluation of the history of the United States up to 1877. The evaluation of these crucial historical moments will be accomplished through the review of the book ‘The awakening of American nationalism, 1815-1828’ that was written b y Dangerfield, George (Livermore 595). Democracy and nationhood The book titled ‘The awakening of American nationalism, 1815-1828,’ perfectly covers the historic events that were crucial in the evolution of the United States during that particular period. ... The reader is treated to a simplistic evaluation of matters revolving the United States in the early 1800s, which then was a young nation nascent democratic structure. Livermore (596) believes a fortuitous and new retelling of the narrative of the surfacing of American nationalism is presented. By any approach the years subsequent to the tranquility of Ghent, an epoch inaugurated by what has been supposedly referred to as â€Å"the era of good feelings," must be measured an instance of outstanding growth and expansion in the United States. Above all, it may be well thought-out a point in time of the fruition and maturing of American nationalism. It is the extraordinary good quality of Dangerfield's sparkling synthesis of the stage that he manages to maintain the focus on this innermost theme-the challenge among the economic nationalism talked about by Henry Clay along with John Quincy Adams and the autonomous nationalism illustrated by the enthusiasts of Andrew Jackson. That he does so without disregarding America's position in global affairs and chiefly the mounting economic contention with Britain, nor devoid of diminishing the parts participated by the foremost actors on the countrywide stage, attests the impartial judgment as well as sense of amounts that are obvious throughout the book. In fact, it is the disagreement of the American trade and industrial nationalism in the midst of the Liberal Toryism of Lord Liverpool as well as William Huskisson that this manuscript delineates with outstanding brightness and depth. Dangerfield, a great craftsman, competently weaves numerous and different yarns into one wonderful tapestry. By digging deep into the roles of several individuals who were the key players in the history of America

Vocabulary Learning Through Computer Assisted Language English Language Essay

Vocabulary Learning Through Computer Assisted Language English Language Essay Abstract The importance of learning English as an international language requires the acquisition of vocabulary as the basic and necessary skill. By the improvement of technology, and computer in particular, many researches are done to show the influence of technology on vocabulary learning. This literary review is done to show the importance as well. Introduction Michael Levy defined Computer-assisted Language Learning (CALL) in his book as the search for and study of applications of the computer in language teaching and learning (p.1). It is recognizable in the academic literature for about the last thirty years. CALL has been made possible by invention and development of the computer. They developed from large mainframe computers to smaller, faster, and easier ones. For all those who whish to create new CALL materials, points of departure range dramatically from top-down approaches centered perhaps upon a theory of language or language learning, or a curriculum specification, while others might develop CALL materials from the bottom up, perhaps by using the computer to address a particular classroom problem. Other points of departure might include a learning strategy , a macroskill, computer conferencing, or an exploration of aspects of the technology itself. There are practical issues to considerfor example, the selection of the hardware a nd software development tools for the project, Hypercard, Authorware, Toolbook, CALIS, C, and Visual Basic, or a mark-up language to enable publishing on the World Wide Web such as Hypertext or Virtual Reality Mark-up Languages (HTML and VRML), are just a handful of many options now available. (Michael Levy, Oxford Linguistic Computer-Assisted Language Learning Context and Conceptualization, p.3) an interdisciplinary perspective on CALL shows it to be a relatively new field of study that has been subject to the influence of a number of other discipline. In addition to the fields of computing and language teaching and learning, real and potential influences in the development of CALL included aspects of psychology, artificial intelligence, computational linguistics, instructional design, and human-computer interaction. Many of these disciplines are relatively new in themselves, having developed significantly since World War II. They each have their own perspective and frame of reference, they often overlap and interrelate, and the extent to which any one discipline should influence the development of CALL has not been determined. At various times, CALL workers have called upon each of these fields to guide their own work in some way. (the same, p.7) Development of CALL Jing-hua suggested in his paper presented It is commonly known that the development of CALL mainly experiences three phases, namely, behavioristic CALL, communicative CALL, and integrative CALL. Each phrase is marked by distinct language teaching theories. For example, Behaviousristic CALL is based on the dominant behaviorist theories of learning and teaching of that time, which emphasizes the formation of speaking habit, thus, courseware mainly focuses on practice and drill of language patterns. After behaviorism lost its dominance, cognitive psychology began to gain popularity. Communicative CALL rejects the notion of habit-formation and focuses more on creative language use. So software at that time stressed the importance of communication and creative use of language instead of manipulation of language forms. Under the influence of constructivism, integrative CALL began to gain prominence. Constructivism focuses more on the connection between old knowledge and new knowledge and l earners are taken as active participators who can engage in creative thinking rather than follow ready made knowledge. The development of internet provides learners with enormous amount of authentic materials and also a platform where they can have a real conversation with peers, teachers or native speakers. The integration of the four skills becomes possible and learners individual needs are satisfied to some extent. Studies on computer assisted vocabulary learning have touched upon different aspects of vocabulary learning, among which a line of research is to examine the effects of electronic or online dictionary use or the effects of look-up behavior or the click behavior on word retention (p.60,61). What Does Vocabulary Mean? Vocabulary .. is an essential means of interchanging ideas and of acquiring new experiences Mans growth in ideas has always been accompanied by a corresponding expansion of his vocabulary. (Gray 1939, p.1). When a pupil reads and learns the meaning of familiar words by context, there is reason to believe that the knowledge will be genuine and important. (Thorndike 1934, p.11). The commonest way and perhaps the best way to promote growth of content in words is to allow the child to infer the meaning from context (Chambers 1904, p.50). Vocabulary Acquisition and L2/FL Reading Comprehension Reading is an active skill that involves the reader, the text, and the interaction between the two. Reading in a L2 or FL is a dynamic and interactive process, during which learners make use of a variety of skills and strategies, combined with background knowledge, L1-related knowledge and real-world knowledge to arrive at an understanding of written material (Aebersold and Field, 1997: ix). Constantinescu (2007) suggests that several researchers have argued that vocabulary plays a major part in reading proficiency Aside from knowing how to use the appropriate reading strategies, Grabe (1991, as cited in Butler-Pascoe and Wiburg, 2003: 124) argues that fluent L2/FL readers need to know about 2,000 to 7,000 words and sometimes even more if they want to reach native-like fluency. Similarly, Groot (2000: 62) argues that an adequate understanding of academic texts requires a vocabulary of at least 7,000 words. Generally, L2/FL readers need to recognize approximately 95 per cent of the words in a given text in order to comprehend its meaning and they need to know the different meanings of words according to context, as well as words grammatical properties. What are Language Learning Strategies? Seglar (2001) remarked, Language Learning Strategies could be any set of operations, steps, plans, routines used by the learner which affect this process (p,26). There are two ways for the second language vocabulary acquisition. S. Prell suggested in his articles wo ways for the second language vocabulary acquisition (p.2): The first method, the experimental method, is CAVOCA. The second method is a more familiar approach to the students, called the bilingual word list. Prell remarked, The first method is the bilingual word list presentation. The second is the Computer Assisted Vocabulary Acquisition (CAVOCA) program.The CAVOCA method attempts to replicate the way the first language is acquired, which is through an incremental process that gradually develops with repeated exposure and constant interaction between the various stages (Groot, 2000, p. 64). The program has four sections, which include storing the word in memory; using the word in several sentences to learn the spelling and meaning; giving examples for long-term memory; and a self-assessment. The second method is a more familiar approach to the students, called the bilingual word list. This method takes less time and produces favorable short-term results (Prell). Prell conducted some experiments and found that both of them wre valuable, yet through some experiments it was proved that they were different from each other: In the first two experiments, the bilingual word list yielded substantially higher results with the immediate tests given than the CAVOCA program. However, in testing the students two to three weeks later, the CAVOCA method produced better results for the retention of the vocabulary. In the third and fourth experiments, the bilingual word list did not show significant differences in the immediate tests from the first two experiments. However, the CAVOCA method showed higher rates of retention for the tests given two to three weeks after the initial test. Information Processing Iheanacho (1997) remarked in his research suggests that cognitive theorists assume that any complete theory of human cognition must include an analysis of the plans or strategies people use for thinking, remembering, understanding and producing language (p.18). Iheanacho (1997) remarked in his research The memory system explains the interrelationship among the three main storage structures of the brain: Sensory register, Short term memory (STM), and Longterm memory (LTM) (p.2). According to Schwartz and Reisberg (1991), the STM provides a small storage repository where the information is repeated over and over through a maintenance rehearsal process. When a piece of information is repeated and rehearsed, the probability of retaining that information can increase. But the STM is limited in how much information it can hold. The maintenance rehearsal helps to transfer the excess information which is not yet needed to another storage called Long-Term Memory (LTM). LTM provides a storage place of great size containing information that is not immediately active so that the information can be retrieved when needed. According to Miller (1989), LTM helps people to recall events, solve problems and recognize patterns. It is the repository in which we carry out all that we know (Schwartz Reisberg 1991). The interrelationship between STM and LTM explains how visual information can enhance retention and recall. According to Posner (1969), visual information can persist in STM after the stimulus is diminished. Additionally, visual information can be activated and retrieved from the LTM. The information processing model can account for the effectiveness of visuals in learning. Visual research Heinich, Molenda and Russell (1993) proposed that learning is facilitated when instruction follows a sequence from actual experience to iconic representation, and then to symbolic or abstract representation. Visuals make abstract information more concrete and are suited for analogical reasoning (Levie, 1987). Pictures and prose can be used to help both skilled and unskilled readers to enhance their reading skills ( Holmes, 1987). Holmes studied the ability of 116 fifth and sixth grade students to answer inferential questions. Three groups were established. The first group used pictures, the second group used prints, and the third group used a combination of prints and pictures. His purpose was to examine skilled and unskilled readers to see if there would be a significant difference in their ability to answer questions in each approach. He found that pictures enabled both skilled and unskilled readers to answer inferential questions. Holmes therefore suggested using pictures to initially improve inferential reading, and then gradually advancing to using print only. Imagery and vocabulary acquisition Furthermore, a study conducted by Paivio and his associates (1971) revealed that when learners are instructed to use images to commit a list of words to memory, recall is facilitated dramatically. In the study, subjects were required to learn pairs of words by rehearsing each pair, by making up a sentence for each pair of words, and by forming a mental image for each pair of words, with the image combining the words. They found that subjects who learned through imagery performed better on a recall test. Dual-coding theory Dual-coding theory contends that pictures and words activate independent visual codes (imagens) and verbal codes (logogens). The verbal system is language-like and specializes in linguistic activities associated with words and sentences, whereas, the visual system is thought of as a code for images and other picture-like representations (Rieber, 1994; Rieber, 1992). Rieber further explains that both verbal and visual subsystems have unique properties. Whereas logogens are stored in the verbal system as discrete elements, resembling words and sentences, imagens are stored as continuous units in the visual system. According to (Paivio, 1986; Rieber, 1992; Rieber, 1994), dual coding theory assumes that three levels of processing can occur within the verbal and visual systems. These are: representational connections, associative structure, and referential connections. Representational connections occur between incoming stimuli and either the verbal or visual system. Whereas verbal stimuli activate verbal memory codes, visual stimuli activate visual memory codes. Rieber (1994) explained that the important aspect of referential connections between the verbal and visual systems are not one to one, but can be one to many. For example, seeing a picture of a computer may invoke many verbal responses, such as an Applecomputer, an IBM computer or a Laptop computer. This concept can be applied when using pictures to learn vocabulary. Associative structures refer to activation or processing of information within any of the systems. The processing of information in the verbal system is assumed to be sequential or linear; whereas, processing of information in the visual system is believed to be parallel or synchronous. The separate coding systems, however, can aid each other so that something coded in both picture and verbal forms can be easily remembered (Rieber, 1994). The probability of recall is increased due to the availability of two mental representations instead of one. If one memory trace is lost, the other is still available (Rieber Kini, 1991). Multimedia CALL and vocabulary acquisition Studies (Reid, 1996; Davis Lyman-Hager, 1997; Zimmerman, 1997) showed the effectiveness of multimedia CALL on vocabulary learning in particular and language learning in general. Based upon this review, multimedia CALL programs that use motion pictures, still pictures, and text can help ESL students to improve their vocabulary skills. But it is not clear if a multimedia program with motion pictures or the one with still pictures will be more effective for intermediate level ESL students. More empirical studies to investigate the effectiveness of multimedia CALL with motion pictures and still pictures on vocabulary acquisition of ESL students can lead to the development of more effective methods for vocabulary acquisition. Motion graphics and still graphics Many studies (Rieber Kini 1991; Siribodhi, 1995; Rieber, 1990; Rieber, 1996) have shown that computer graphics are effective for gaining attention. Furthermore, Iheanacho (1997) suggested that computer graphics can encourage students to create mental images that in turn make it easier for them to learn certain types of information. The difference between motion graphics and still graphics is that motion creates the illusion of movement which helps to explain abstract concepts (Bricken, 1991; Rieber, 1994). In 1996, Rieber conducted a study to explore how users interact and learn during a computer-based simulation given graphical and textual forms of feedback. He found that subjects learned more when provided with animated graphical feedback than with textual feedback. Rieber hypothesized that interactive forms of multimedia, such as computer. simulations will promote different levels of processing depending on the type of representation used (e.g. text, graphics, motion and sound). In an earlier study, Rieber Kini (1991) contended that in contrast to static graphics, animated graphics can provide users with additional information through two important visual attributes: motion and trajectory. They also added that animation can provide information about whether the object is moving or whether the objects motion changes over time. Still or static pictures, on the other hand, lack motion and are more abstract than motion pictures. Still pictures suggest motion whereas motion pictures show life in action, can be used to study specific elements, and can bring us close to the point of visual contact (Dale, 1969). EXPERIMENTS ON COMPUTER-ASSISTED VOCABULARY ACQUISITION IN THE ESL CLASSROOM RESEARCH QUESTIONS Pelletreau (2006) conducted an experiment Of chief importance in this study was the degree to which students would take advantage of computer-assisted opportunities for incidental vocabulary learning while performing online reading tasks. The study necessarily addressed a more fundamental question: How would students learn new words in the course of completing computer-based reading tasks? Lastly, and most importantly for this study, how was the learning of non-target words related to the learning of target words? (p.16). In an earlier study (see Juffs et al., April, 2006), students frequently used the online dictionary to look up the meanings of target words. In fact, students accessed 71% of all the definitions available to them on average, and yet, such behavior did not correlate with mastery of words (r = .16, n.s.). The best predictor of word mastery (as defined by 2 correctly answered post-reading vocabulary questions) was number of texts read (r = .86, p à ¢Ã¢â‚¬ °Ã‚ ¤ .0001). In other words, students reading more texts mastered more words, though the time spent clicking on hints had almost no effect on word mastery (Juffs et al., April, 2006). If students were not benefiting from looking up target words, it may have been because they were not actually making use of target-word definitions. But what were they doing while reading? They were either unable or unwilling to learn target-word definitions. It became apparent that students were not gaining a substantial learning advantage by using the online dictionary. In other words, students were not achieving a desired learning outcome. They resisted their language-learning task and instead participated in a counter-task (Lantolf Thorne, 2006, p. 238) In this context, a decision was made to allow students to look up any word in the online dictionary. Perhaps students had been focusing their attention on non-target words, or maybe they had other preferred (and unknown) methods of using the program. It was clear that students were likely not using the REAP program the way they had been expected to, and it was also apparent that the instruments to gather data about students behavior in the LMC were lacking. As a result, REAP was modified to allow students to look up the meaning of any word, and the number of clicks of both target and non-target words was recorded. Because quantitative data alone would provide an incomplete picture of student vocabulary-learning behavior, qualitative data collection instruments were introduced. Students could be valuable sources of information about their own vocabulary-learning techniques. The acquisition of target vocabulary was thought to depend on student comprehension of non-target words. It was hypothesized that students would use information about non-target words to assist them in their target-vocabulary tasks. It may have been the case that knowledge of non-target words surrounding target words would aid students in making lexical and semantic connections that facilitated target-word acquisition. In line with such reasoning, a strong positive correlation between non-target and target-vocabulary acquisition was posited, at least up to a particular critical threshold. For those students who knew the meanings of very few of the words surrounding target words, it was reasoned, target-word acquisition would be minimal. In such a scenario, such students would have too many gaps in their word knowledge and too few resources to be able to acquire a considerable number of target words. In effect, students learning more non-target words were predicted to learn more target words, though only up to a point. Student accuracy on measures of target vocabulary knowledge should have correlated strongly with non-target vocabulary acquisition up to some critical point. After a certain threshold, the acquisition of additional non-target words might have led to a decrease in the number of target words acquired. Such a threshold may have depended in part on the general language proficiency of the student (measured in this case by the MTELP score). The finite nature of the students language-learning resources, including processing power, attention and memory, may also have been important. It was thought that students spending much of their time learning as many non-target words as they possibly could would likely perform as poorly with respect to target-word acquisition as those who paid little or no attention to non-target words. In such cases, it was plausible that temporal and cognitive constraints (Sweller, 1988; 1994) would lead to students acquiring relatively fewer target words. In effect, the distribution of target words acquired versus non-target words acquired should have been more or less nonlinear. That is, target-word learning should have reached some maximum value for a moderate value of non-target word learning. Additionally, the amount of non-target word acquisition occurring in the study should have been much less, on average, than that of target-word acquisition. While there may have been some exceptions, the explicit instructions to focus on target words coupled with the way the words appeared should have led to relatively greater student attention to target words. It should also be pointed out that students answered cloze questions testing their knowledge of target words (for which they received feedback) after each reading, while they answered no such questions and received no feedback pertaining to non-target words. Greater attention and in general, more cognitive resources devoted to target words should have translated to differential target and non-target vocabulary learning. In terms of predicting how many target and non-target words students learned, general language proficiency should have provided some indication of such information. Pelletreau (2006) concluded in this experimenr, Non-target word lookups did not correlate with target word acquisition. Students did not appear to learn target words faster or better by attending to non-target words. As a result, the relationship between the explicit and incidental learning students engaged in remains unclear. The relative effectiveness of each, as well as the optimal balance of explicit and incidental learning in such a context, is an open question. Benefits of CALL for Vocabulary Acquisition and Reading Comprehension According to Constantinescu (2007) Multimedia refers to computer-based systems that use various types of content, such as text, audio, video, graphics, animation, and interactivity. Constantinescu (2007) mentioned in his article Most research on vocabulary acquisition and CALL has focused on the effects of multimedia glosses, and the same is true for reading comprehension, since vocabulary and reading are closely and reciprocally related. This reciprocal relationship also accounts for the fact that many research studies on vocabulary development and CALL also examine reading comprehension, and vice versa. Multimedia Glosses and Vocabulary Development One of the first to examine the effects of multimedia glosses for vocabulary development were Lyman-Hager and Davis (1996), who integrated a computer program into the French foreign language curriculum and discussed vocabulary acquisition and students glossing choices for 262 intermediate level students studying French. Two conditions were used in this study: computerized reading and non-computerized reading using an excerpt of Oyonos Une Vie de Boy. Both groups had access to glosses: the computer group had access to multimedia annotations, whereas the control group could consult printed text with the same glosses. As to whether or not computer treatment offered significant benefits to FL students, the results of the written recall protocol indicated that the experimental group who used the computer program to read the text significantly outperformed the control group who used the glossed reading in the print form. Using Multimedia for Vocabulary-building Constantinescu (2007) mentioned in his article However, multimedia is not used only for glossing texts. Multimedia is a central component of good computer-assisted skill-building software. Thus, Chanier and Selva (1998) stressed the benefits of multimedia support for learning L2/FL vocabulary and presented ALEXIA, a lexical learning environment for French as a L2/FL, which includes a corpus of texts, a general and a personal dictionary, and a lexical activities unit. After reviewing various viewpoints about the effectiveness of multimedia for vocabulary learning, they propose useful criteria for evaluating the quality of a visual representation in a lexical environment. Groot (2000) presented another multimedia-enhanced computer-assisted word acquisition program, called CAVOCA, whose aim was to speed up the vocabulary acquisition process. CAVOCA is an interactive program that takes learners through different stages of vocabulary development: deduction, consolidation, and long-term re tention. Benefits of Multimedia-enhanced Dictionaries Other research that focused on vocabulary development with technology argued for the increased effectiveness of multimedia-enhanced electronic dictionaries designed specifically for English language learners, and which have several built-in aids that their book counterparts cannot provide (e.g. the Longman Interactive English Dictionary, the Oxford Picture Dictionary Interactive, etc.) (Butler-Pascoe and Wiburg, 2003: 126-12) Benefits of Multimedia for Reading Comprehension The positive effect that multimedia has on reading comprehension comes, according to Busch (2003: 278), from the great advantage that online readers have over traditional printed readers: the possibility to enhance computerized texts with glosses in multimedia format. The effects of multimedia glossing received increased attention as researchers considered the possibility that computer-aided reading could create more proficient readers by offering a choice of various types of glosses to develop better vocabularies, greater background knowledge surrounding the text, and more effective reading strategies (Lyman-Hager and Davis, 1996: 775). Constantinescu (2007) remarked some principles for instructors to increase the efficiency of the introduced strategies: First Principle: Instructors Should Pay More Attention to the Existence of Various Teaching Tools For vocabulary acquisition, instructors could make great use of technology by using multimedia glossed texts, electronic dictionaries, corpora and concordance software, as well as various vocabulary-building software. Second Principle: Instructors Should Introduce Multimedia-glossed Texts into Their Vocabulary/Reading Classes Multimedia glossing triggers better results when compared to print glosses. Moreover, full glossing seems to be the best facilitator of vocabulary acquisition and reading comprehension, as opposed to little or non-glossed texts. In addition, best results in retention are triggered by picture + text annotations, whereas pronunciation, video, and audio glosses seem to correlate negatively with reading comprehension. Third Principle: Instructors Should Be Acquainted with the Criteria for Software and Courseware Evaluation (e.g. goals, presentation, appropriateness, outcomes), As Well As Take Into Consideration Two Very Important Factors: Time and Effort Teachers must be aware that there are many different types of software or online materials available for ESL / EFL, however, not all of them are valuable for classroom instruction. Some materials focus on specific skills, while others focus on a wide range of skills and strategies. Moreover, instructors should also ensure that the materials used in class are motivating for students and are at an optimum, i+1 difficulty level, so that progress can be attained. Teachers should also pay attention to students level of familiarity with computers and keep in mind whether the chosen software will trigger the desired outcomes. Fourth Principle: Instructors Should Keep Up with Current Methodology and Make Best Use of Visuals and Multimedia Good CALL programs should make best use of visual elements and multimedia glossing, as well as generate students participation. The programs should be interactive, allowing the students to make choices. Also, they should consist of a wide range of different types of exercises in which students not only choose the right answers but also type in answers. Summary L2 comprehention depends mostly on acquiring vocabulary at least 7,000 words as was mentioned by Groot (2000: 62). Due to the importance of vocabulary acquisition some ways were discussed, and through some experiments by Prell it becomes clear taht the CAVOCA method produced better results for the retention of the vocabulary (p,3). So, in continuation, my research focused on the influence of different models of Call strategies on accelerating vocabulary learning and how the instructors should use them in the best way to increase their efficiencies. Conclusion Among different forms of computerized ways of vocabulary learning, some ways were mentioned. While being different from each other, it is proved that some of them are more efficient that others. All in all, CALL can be a useful instrument for both teachers and students in regard to the priority it has to the difficult traditional ways.