Midterm (R) Essay Example | Topics and Well Written Essays - 750 words

Midterm (R) - Essay Example The basic purpose of geographical value judgment is the implication of qualitative thinking to handle future geographical events. It is necessary for students to predict future events and have a clear view of what geographical events could occur in the future. Centripetal and centrifugal forces act in opposition to each other with centripetal force pulling creating a state of stability and centrifugal force destabilizing the state. The centripetal force binds the citizens together by creating this state of stability. The basic aim of nationalism is to promote and create cohesion in the state by creating allegiance and accepting the goals. Nationalism brings the people of a country and a nation together whereas getting true nation is rare in this world e.g. the national Canadian railway is a symbol of nationalism in the country. Also, we can say that institutions on small scale create a sense of unity in the nation by teachings of cohesion and commission. The promotion of social welfare and development of a nation’s culture is their responsibility. For a nation to be united, it should have one language. Different languages spoken by the people of one nation keep them from communicating with each other and create a sense of unrest in the community. This communication barrier may cause misunderstandings and raise conflicts which would lead to civil unrest and disruption of peace e.g. Quebec and Francophone are still fighting for their independence from Canada because of civil unrests due to different dialects and languages. Religion on the other hand is an important factor to create unity and allegiance in a nation. We can also say that different religions in a same country can lead to a state of competition and cause destabilization in the country. In the time of USSR, politicians worked in favor atheism to remove religion as a factor which might lead to disruption of peace and violence in the country

Welcome to India 2012 - Documentary (Episode 1 of 3) Essay

Welcome to India 2012 - Documentary (Episode 1 of 3) - Essay Example They wake up at 3am to dust the street to get gold that, in turns; they sell to Naukada- one of the gold merchants (YouTube). They get poor pay and gets frustrated. However, the have to sell to the same man as he own house in which they live in. Their struggle is highlighted as the prices for gold goes up. This means there is less available gold in dust, in the street. They opt to go for sludge. They acquire sludge in a most inhumane way, as it is full of ‘shit’. We are also shown Javeds employees working tirelessly to get pure gold (YouTube). The film also focuses on live of poor in Mumbai beach. The life is highlighted using Rajesh family. Rajesh is married to Sevita. They own a pub with no license from the council. Rajesh had been jailed due to this illegality. Sevita his wife also does part time jobs as a cleaner despite physical challenges (YouTube). The family also goes through challenges of constant eviction. They are forced to rebuild the house every time after the eviction. Rajesh is also forced to rely on moneylender to boost his stock and is faced with challenges of repaying. I disliked the way young people are forced to go through inhumane ways of making ends meet. In this film, I have learnt it is advantageous to learn how to interact and interview in order to get facts about people ways of

Si chuan earthquake Essay Example | Topics and Well Written Essays - 250 words

Si chuan earthquake - Essay Example ion System, reveals that most of the local governments in China lacked the Decision Support System for daily management; thus, even during emergency situation, they did not have this crucial tool. (Liu & Ren, 2009). This evidence supports my argument because it shows that there was no preparedness to handle emergency situations such as earthquake. Decision Support System is a crucial tool in handling management and emergency issues; hence, it should not lack in local government because earthquake is prone in rural areas (Liu et al, 2006). An article on the China Earthquake Geospatial Research Portal suggests that it was possible to predict the magnitude, and in addition, former researcher, Geng Qingguo of Institute of Geophysics claims that he handed a confidential written report about his prediction of the earthquake to the State Seismological Bureau (Pekevski & Mavrodiev, 2008). This article is essential in providing evidence because it reveals that the necessary agencies were warned of the impending earthquake disaster, but they failed to take necessary actions. Thus, they also failed to establish adequate preparedness to minimize loss of lives and property destruction. Finally, a two year UNICEF report dated May 2010 also indicates that much could have been done to create preparedness, for example, aligning emergency response initiatives or programs with upstream policy programs (UNICEF, 2010). This report reveals that there were no policies in place to deal with such emergencies, for instance, enhancing intervention in emergency situations require coordination of emergency programs with policy initiatives, which were lacking in this case. I will still need to get evidence on statistical data regarding the degree of loss of lives and connect it with poor preparedness. I will also need to get evidence on what the government authorities say about the predictions and their level of preparedness. These I will get from the Chinese government department’s

Nature And Nurture Influences On Child Essay Example for Free

Nature And Nurture Influences On Child Essay When it comes to child development there are two major influences. These influences are nature which are traits we inherit and nurture which are the traits we learn. Nature and nurture are different in several ways but they both play an important role in child development. Although they both influence development the topic of which has the greatest influence in frequently debated. This paper will describe the relationship between nature and nurture, explain the biological, environmental, societal, and cultural influences on child development in relation to nature and nurture, and discuss whether nature or nurture has the most influence on child development. Nature and nurture are different in several ways but share one similarity which is the fact that they both have an influence on child development. Both of them play an important role in how children develop as well as the type of people they will grow up to be. In the video â€Å"Nature vs. Nurture in Child Development† Shirael Pollack states that children are born with some traits and characteristics while they learn others (Pollack, S. n. d. ). Nature is one(s) genes. The traits and characteristics that they inherit such as skin tone, eye color, and hair color. Nurture is what they are taught or what they learn from the people around them such as manners; learning to say â€Å"please† and â€Å"thank you†. There are different influences on child development in relation to nature and nurture. These influences are biological, environmental, societal, and cultural. Nature is responsible for the biological influences. Biological influences are traits that are passed parents to their children. They include appearance, talents, and abilities, and also certain illnesses (Groark, C. , McCarthy, S. Kirk, A. , 2014). Nurture is responsible for environmental influences. These are things that are in a child(s) environment that they are exposed to or experience. Nurture can also be NATURE AND NURTURE 3 responsible for cultural and societal influences on child development which can be instilled subtly through natural interactions with others. The cultural and societal influences can be direct and indirect impacts of culture, race, and ethnicity as well as the powerful effects of economics, gender roles, marriage, divorce, single parenthood, and religion (Groark, C. , McCarthy, S. Kirk, A. , 2014). No matter what type of influence there is on child development it is either related to nature or nurture. Some people believe that nature and nurture are partners because of the fact that they both play a role in child development. However, theorists have different views about the two. Some theorists believe that nature is ultimately responsible for growth while other theorists believe that children become whatever their environment shapes them into (McDevitt, 2010). Regardless of what the different views of theorists are on the topic of nature versus nurture, the fact of the matter is that both of them play a role in how children develop and have some type of impact on what and how they will be when they grow up. Both nature and nurture play important roles in child development. Regardless of if one has more of an influence than the other, the fact is that they both impact how children develop. Truth of the matter is that they are different but share one important factor which is the fact that they help make children who they are. This paper described the relationship between nature and nurture, explained the biological, environmental, societal, and cultural influences on child development in relation to nature and nurture, and also discussed which of the two influences is more influential than the other. NATURE AND NURTURE 4 References Groark, C. , McCarthy, S. Kirk, A. (2014). Early child development: From theory to practice. Bridgepoint Education: San Diego, CA. McDevitt, T. M. (2010). Nature and nurture: Retrieved from http://www. education. com/reference/article/nature-nurture/ Pollack, S. (n. d. ). Nature vs. nurture in child development [Video file]. Retrieved from http://www. howcast. com/videos/513307-Nature-vs-Nurture-Child-Development.

Light Emitting Diode | Dissertation

Light Emitting Diode | Dissertation Introduction Alight-emitting diode(LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across thevisible, ultraviolet and infrared wavelengths, with very high brightness. When a light-emitting diodeis forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is calledelectroluminescenceand thecolorof the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1mm2), and integrated optical components may be used to shape its radiation pattern.LEDs present manyadvantagesover incandescent light sources includinglower energy consumption, longerlifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current andheat managementthan compactfluorescent lampsources of comparable output. Light-emitting diodes are used in applications as diverse as replacements foraviation lighting,automotive lighting(particularly brake lamps, turn signals and indicators) as well as intraffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology.InfraredLEDs are also used in theremote controlunits of many commercial products including televisions, DVD players, and other domestic appliances. History Discoveries and early devices Green electroluminescence from a point contact on a crystal ofSiCrecreatesH. J. Rounds original experiment from 1907. Electroluminescenceas a phenomenon was discovered in 1907 by the British experimenterH. J. RoundofMarconi Labs, using a crystal ofsilicon carbideand acats-whisker detector.RussianOleg Vladimirovich Losevreported on the creation of a first LED in 1927.His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades. Rubin Braunstein of theRadio Corporation of Americareported on infrared emission fromgallium arsenide(GaAs) and other semiconductor alloys in 1955.Braunstein observed infrared emission generated by simple diode structures usinggallium antimonide(GaSb), GaAs,indium phosphide(InP), andsilicon-germanium(SiGe) alloys at room temperature and at 77kelvin. In 1961, American experimenters Robert Biard and Gary Pittman working atTexas Instruments,found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED. The first practical visible-spectrum (red) LED was developed in 1962 byNick Holonyak Jr., while working atGeneral Electric Company.Holonyak is seen as the father of the light-emitting diode.M. George Craford,a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T.P. Pearsall created the first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths. Until 1968, visible and infrared LEDs were extremely costly, on the order of US $200 per unit, and so had little practical use.TheMonsanto Companywas the first organization to mass-produce visible LEDs, using gallium arsenide phosphide in 1968 to produce red LEDs suitable for indicators. Hewlett Packard(HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. The technology proved to have major uses for alphanumeric displays and was integrated into HPs early handheld calculators. In the 1970s commercially successful LED devices at fewer than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with theplanar processinvented by Dr. Jean Hoerni atFairchild Semiconductor.The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. These methods continue to be u sed by LED producers. History Of LEDs and LED Technology Light Emitting Diode (LED) Light Emitting Diode (LED) is essentially a PN junction semiconductor diode that emits a monochromatic (single color) light when operated in a forward biased direction. The basic structure of an LED consists of the die or light emitting semiconductor material, a lead frame where the die is actually placed, and the encapsulation epoxy which surrounds and protects the die (Figure 1). The first commercially usable LEDs were developed in the 1960s by combining three primary elements: gallium, arsenic and phosphorus (GaAsP) to obtain a 655nm red light source. Although the luminous intensity was very low with brightness levels of approximately 1-10mcd @ 20mA, they still found use in a variety of applications, primarily as indicators. Following GaAsP, GaP, or gallium phosphide, red LEDs were developed. These devices were found to exhibit very high quantum efficiencies, however, they played only a minor role in the growth of new applications for LEDs. This was due to two reasons: First, the 700nm wavelength emission is in a spectral region where the sensitivity level of the human eye is very low (Figure 2) and therefore, it does not appear to be very bright even though the efficiency is high (the human eye is most responsive to yellow-green light). Second, this high efficiency is only achieved at low currents. As the current increases, the efficiency decreases. This pr oves to be a disadvantage to users such as outdoor message sign manufacturers who typically multiplex their LEDs at high currents to achieve brightness levels similar to that of DC continuous operation. As a result, GaP red LEDs are currently used in only a limited number of applications. As LED technology progressed through the 1970s, additional colors and wavelengths became available. The most common materials were GaP green and red, GaAsP orange or high efficiency red and GaAsP yellow, all of which are still used today (Table3). The trend towards more practical applications was also beginning to develop. LEDs were found in such products as calculators, digital watches and test equipment. Although the reliability of LEDs has always been superior to that of incandescent, neon etc., the failure rate of early devices was much higher than current technology now achieves. This was due in part to the actual component assembly that was primarily manual in nature. Individual operators performed such tasks as dispensing epoxy, placing the die into position, and mixing epoxy all by hand. This resulted in defects such as epoxy slop which caused VF (forward voltage) and VR (reverse voltage) leakage or even shorting of the PN junction. In addition, the growth methods and materia ls used were not as refined as they are today. High numbers of defects in the crystal, substrate and epitaxial layers resulted in reduced efficiency and shorter device lifetimes. Gallium Aluminum Arsenide It wasnt until the 1980s when a new material, GaAlAs (gallium aluminum arsenide) was developed, that a rapid growth in the use ofLEDsbegan to occur. GaAlAs technology provided superior performance over previously availableLEDs. The brightness was over 10 times greater than standardLEDsdue to increased efficiency and multi-layer, heterojunction type structures. The voltage required for operation was lower resulting in a total power savings. TheLEDscould also be easily pulsed or multiplexed. This allowed their use in variable message and outdoor signs.LEDswere also designed into such applications as bar code scanners, fiber optic data transmission systems, and medical equipment. Although this was a major breakthrough inLEDtechnology, there were still significant drawbacks to GaAlAs material. First, it was only available in a red 660nm wavelength. Second, the light output degradation of GaAlAs is greater than that of standard technology. It has long been a misconception withLEDsthat lig ht output will decrease by 50% after 100,000 hours of operation. In fact, some GaAlAsLEDsmay decrease by 50% after only 50,000 -70,000 hours of operation. This is especially true in high temperature and/or high humidity environments. Also during this time, yellow, green and orange saw only a minor improvement in brightness and efficiency which was primarily due to improvements in crystal growth and optics design. The basic structure of the material remained relatively unchanged. To overcome these difficult issues new technology was needed.LEDdesigners turned to laser diode technology for solutions. In parallel with the rapid developments inLEDtechnology, laser diode technology had also been making progress. In the late 1980s laser diodes with output in the visible spectrum began to be commercially produced for applications such as bar code readers, measurement and alignment systems and next generation storage systems.LEDdesigners looked to using similar techniques to produce high brightness and high reliabilityLEDs. This led to the development of InGaAlP (Indium Gallium Aluminum Phosphide) visibleLEDs. The use of InGaAlP as the luminescent material allowed flexibility in the design ofLEDoutput color simply by adjusting the size of the energy band gap. Thus, green, yellow, orange and redLEDsall could be produced using the same basic technology. Additionally, light output degradation of InGaAlP material is significantly improved even at elevated temperature an d humidity. Current Developments of LED Technology InGaAlPLEDstook a further leap in brightness with a new development by Toshiba, a leading manufacturer ofLEDs. Toshiba, using the MOCVD (Metal Oxide Chemical Vapor Deposition) growth process, was able to produce a device structure that reflected 90% or more of the generated light traveling from the active layer to the substrate back as useful light output (Figure 4). This allowed for an almost two-fold increase in theLEDluminance over conventional devices.LEDperformance was further improved by introducing a current blocking layer into theLEDstructure (Figure 5). This blocking layer essentially channels the current through the device to achieve better device efficiency. As a result of these developments, much of the growth forLEDsin the 1990s will be concentrated in three main areas: The first is in traffic control devices such as stop lights, pedestrian signals, barricade lights and road hazard signs. The second is in variable message signs such as the one located in Times Square New York which displays commodities, news and other information. The third concentration would be in automotive applications. The visibleLEDhas come a long way since its introduction almost 30 years ago and has yet to show any signs of slowing down. A BlueLED, which has only recently become available in production quantities, will result in an entire generation of new applications. BlueLEDsbecause of their high photon energies (>2.5eV) and relatively low eye sensitivity have always been difficult to manufacture. In addition the technology necessary to fabricate theseLEDsis very different and far less advanced than standardLEDmaterials. The blueLEDsavailable today consist of GaN (gallium nitride) and SiC (silicon carbide) construction with brightness levels in excess of 1000mcd @ 20mA for GaN devices. Since blue is one of the primary colors, (the other two being red and green), full color solid stateLEDsigns, TVs etc. will soon become commercially available. Full colorLEDsigns have already been manufactured on a small prototype basis, however, due to the high price of blueLEDs, it is still not practical on a large scale. Other applications for blueLEDsinclude medical diagnostic equipment and photolithography. LED Colors It is also possible to produce other colors using the same basic GaN technology and growth processes. For example, a high brightness green (approximately 500nm)LEDhas been developed that is currently being evaluated for use as a replacement to the green bulb in traffic lights. Other colors including purple and white are also possible. With the recent introduction of blueLEDs, it is now possible to produce white by selectively combining the proper combination of red, green and blue light. This process however, requires sophisticated software and hardware design to implement. In addition, the brightness level is low and the overall light output of each RGB die being used degrades at a different rate resulting in an eventual color unbalance. Another approach being taken to achieve white light output, is to use a phosphor layer (Yttrium Aluminum Garnet) on the surface of a blueLED. In summary,LEDshave gone from infancy to adolescence and are experiencing some of the most rapid market growth of their lifetime. By using InGaAlP material with MOCVD as the growth process, combined with efficient delivery of generated light and efficient use of injected current, some of the brightest, most efficient and most reliableLEDsare now available. This technology together with other novelLEDstructures will ensure wide application ofLEDs. New developments in the blue spectrum and on white light output will also guarantee the continued increase in applications of these economical light sources. Practical use The first commercial LEDs were commonly used as replacements forincandescentandneonindicator lamps, and inseven-segment displays,first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches (see list ofsignal uses). These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors grew widely available and also appeared in appliances and equipment. As LED materials technology grew more advanced, light output rose, while maintaining efficiency and reliability at acceptable levels. The invention and development of the high power white light LED led to use for illumination, which is fast replacing incandescent and fluorescent lighting. (see list ofillumination applications). Most LEDs were made in the ve ry common 5mm T1Â ¾ and 3mm T1 packages, but with rising power output, it has grown increasingly necessary to shed excess heat to maintain reliability,so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-arthigh power LEDsbear little resemblance to early LEDs. Continuing development The first high-brightness blue LED was demonstrated byShuji NakamuraofNichia Corporationand was based onInGaNborrowing on critical developments inGaNnucleation on sapphire substrates and the demonstration of p-type doping of GaN which were developed byIsamu Akasakiand H. Amano inNagoya. In 1995,Alberto Barbieriat theCardiff UniversityLaboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a very impressive result by using a transparent contact made ofindium tin oxide(ITO) on (AlGaInP/GaAs) LED. The existence of blue LEDs and high efficiency LEDs quickly led to the development of the firstwhite LED, which employed aY3Al5O12:Ce, or YAG, phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white. Nakamura was awarded the 2006Millennium Technology Prizefor his invention. The development of LED technology has caused their efficiency and light output torise exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar toMoores law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. This trend is normally calledHaitzs Lawafter Dr. Roland Haitz. In February 2008, 300lumensof visible light per wattluminous efficacy(not per electrical watt) and warm-light emission was achieved by usingnanocrystals. In 2009, a process for growing gallium nitride (GaN) LEDs on silicon has been reported.Epitaxycosts could be reduced by up to 90% using six-inch silicon wafers instead of two-inch sapphire wafers. Illustration of Haitzs Law. Light output per LED as a function of production year, note the logarithmic scale on the vertical axis Technology Physics The LED consists of a chip of semiconducting materialdopedwith impurities to create ap-n junction. As in other diodes, current flows easily from the p-side, oranode, to the n-side, orcathode, but not in the reverse direction. Charge-carriers—electronsandholes—flow into the junction fromelectrodeswith different voltages. When an electron meets a hole, it falls into a lowerenergy level, and releasesenergyin the form of a photon. Thewavelengthof the light emitted, and thus its color depends on theband gapenergy of the materials forming thep-n junction. Insiliconor germaniumdiodes, the electrons and holes recombine by anon-radiative transitionwhich produces no optical emission, because these are indirect band gapmaterials. The materials used for the LED have adirect band gapwith energies corresponding to near-infrared, visible or near-ultraviolet light. LED development began with infrared and red devices made withgallium arsenide. Advances inmaterials sciencehave enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also usesapphiresubstrate. Most materials used for LED production have very highrefractive indices. This means that much light will be reflected back into the material at the material/air surface interface. Thus,light extraction in LEDsis an important aspect of LED production, subject to much research and development. The inner workings of an LED I-V diagram for adiode. An LED will begin to emit light when the on-voltageis exceeded. Typical on voltages are 2-3volts. Refractive Index Idealized example of light emission cones in a semiconductor, for a single point-source emission zone. The left illustration is for a fully translucent wafer, while the right illustration shows the half-cones formed when the bottom layer is fully opaque. The light is actually emitted equally in all directions from the point-source, so the areas between the cones shows the large amount of trapped light energy that is wasted as heat. The light emission cones of a real LED wafer are far more complex than a single point-source light emission. Typically the light emission zone is a 2D plane between the wafers. Across this 2D plane, there is effectively a separate set of emission cones for every atom. Drawing the billions of overlapping cones is impossible, so this is a simplified diagram showing the extents of all the emission cones combined. The larger side cones are clipped to show the interior features and reduce image complexity; they would extend to the opposite edges of the 2D emission plane. Bare uncoated semiconductors such assiliconexhibit a very highrefractive indexrelative to open air, which prevents passage of photons at sharp angles relative to the air-contacting surface of the semiconductor. This property affects both the light-emission efficiency of LEDs as well as the light-absorption efficiency ofphotovoltaic cells. The refractive index of silicon is 4.24, while air is 1.00002926. Generally a flat-surfaced uncoated LED semiconductor chip will only emit light perpendicular to the semiconductors surface, and a few degrees to the side, in a cone shape referred to as thelight cone,cone of light,or theescape cone.The maximumangle of incidenceis referred to as thecritical angle. When this angle is exceeded photons no longer penetrate the semiconductor, but are instead reflected both internally inside the semiconductor crystal, and externally off the surface of the crystal as if it were amirror. Internal reflectionscan escape through other crystalline faces, if the incidence angle is low enough and the crystal is sufficiently transparent to not re-absorb the photon emission. But for a simple square LED with 90-degree angled surfaces on all sides, the faces all act as equal angle mirrors. In this case the light cannot escape and is lost as waste heat in the crystal. A convoluted chip surface with angledfacetssimilar to a jewel orfresnel lenscan increase light output by allowing light to be emitted perpendicular to the chip surface while far to the sides of the photon emission point. The ideal shape of a semiconductor with maximum light output would be amicrospherewith the photon emission occurring at the exact center, with electrodes penetrating to the center to contact at the emission point. All light rays emanating from the center would be perpendicular to the entire surface of the sphere, resulting in no internal reflections. A hemispherical semiconductor would also work, with the flat back-surface serving as a mirror to back-scattered photons. Transition coatings Many LED semiconductor chips arepottedin clear or colored molded plastic shells. The plastic shell has three purposes: 1. Mounting the semiconductor chip in devices is easier to accomplish. 2. The tiny fragile electrical wiring is physically supported and protected from damage 3. The plastic acts as a refractive intermediary between the relatively high-index semiconductor and low-index open air. The third feature helps to boost the light emission from the semiconductor by acting as a diffusing lens, allowing light to be emitted at a much higher angle of incidence from the light cone, than the bare chip is able to emit alone. Efficiency and operational parameters Typical indicator LEDs are designed to operate with no more than 30-60mWof electrical power. Around 1999,Philips Lumiledsintroduced power LEDs capable of continuous use at oneW. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die. One of the key advantages of LED-based lighting is its high efficacy,[dubious-discuss]as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficacy of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with aluminous efficacyof 18-22 lumens per watt (lm/W). For comparison, a conventional 60-100 Wincandescent light bulbemits around 15 lm/W, and standardfluorescent lightsemit up to 100 lm/W. A recurring problem is that efficacy falls sharply with rising current. This effect is known asdroopand effectively limits the light output of a given LED, raising heating more than light output for higher current. In September 2003, a new type of blue LED was demonstrated by the companyCree Inc.to provide 24mW at 20milliamperes(mA). This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006, they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Also,Seoul Semiconductorplans for 135 lm/W by 2007 and 145 lm/W by 2008,which would be nearing an order of magnitude improvement over standard incandescents and better than even standard fluorescents.Nichia Corporationhas developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA. Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA. Note that these efficiencies are for the LED chip only, held at low temperature in a lab. Lighting works at higher temperature and with drive circuit losses, so efficiencies are much lower.United States Department of Energy(DOE) testing of commercial LED lamps designed to replace incandescent lamps orCFLsshowed that average efficacy was still about 46 lm/W in 2009 (tested performance ranged from 17lm/W to 79lm/W). Cree issued a press release on February 3, 2010 about a laboratory prototype LED achieving 208 lumens per watt at room temperature. The correlatedcolor temperaturewas reported to be 4579K. Lifetime and failure Main article:List of LED failure modes Solid state devices such as LEDs are subject to very limitedwear and tearif operated at low currents and at low temperatures. Many of the LEDs made in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25,000 to 100,000 hours but heat and current settings can extend or shorten this time significantly. The most common symptom of LED (anddiode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can occur as well. Early red LEDs were notable for their short lifetime. With the development of high-power LEDs the devices are subjected to higherjunction temperaturesand higher current densities than traditional devices. This causes stress on the material and may cause early light-output degradation. To quantitatively classify lifetime in a standardized manner it has been suggested to use the terms L75 and L50 which is the time it will take a given LED to reach 75% and 50% light output respectively. Like other lighting devices, LED performance is temperature dependent. Most manufacturers published ratings of LEDs are for an operating temperature of 25Â °C. LEDs used outdoors, such as traffic signals or in-pavement signal lights, and that are utilized in climates where the temperature within the luminaire gets very hot, could result in low signal intensities or even failure. LED light output actually rises at colder temperatures (leveling off depending on type at around −30C). Consequently, LED technology may be a good replacement in uses such as supermarket freezer lightingand will last longer than other technologies. Because LEDs emit less heat than incandescent bulbs, they are an energy-efficient technology for uses such as freezers. However, because they emit little heat, ice and snow may build up on the LED luminaire in colder climates.This lack of waste heat generation has been observed to cause sometimes significant problems with street traffic signals and airport runway lighting in snow-prone areas, although some research has been done to try to develop heat sink technologies to transfer heat to other areas of the luminaire. Ultraviolet and blue LEDs BlueLEDs. Blue LEDs are based on the wideband gapsemiconductors GaN (gallium nitride) andInGaN(indium gallium nitride). They can be added to existing red and green LEDs to produce the impression of white light, though white LEDs today rarely use this principle. The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride LED) atRCA Laboratories.These devices had too little light output to be of much practical use. In August of 1989, Cree Inc. introduced the first commercially available blue LED.In the late 1980s, key breakthroughs in GaNepitaxialgrowth andp-typedoping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated. By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaNquantum wellssandwiched between thicker layers of GaN, called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaNaluminium gallium nitrideof varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, instead of alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350-370nm. Green LEDs manufactured from the InGaN-GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems. With nitrides containing aluminium, most oftenAlGaNandAlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375-395nm are already cheap and often encountered, for example, asblack lightlamp replacements for inspection of anti-counterfeitingUV watermarks in some documents and paper currencies. Shorter wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 247nm.As the photosensitivity of microorganisms approximately matches the absorption spectrum ofDNA, with a peak at about 260nm, UV LED emitting at 250-270nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365nm) are already effective disinfection and sterilization devices. Deep-UV wavelengths were obtained in laboratories usingaluminium nitride(210nm),boron nitride(215nm)anddiamond(235nm). White light There are two primary ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit threeprimary colors—red, green, and blue—and then mix all the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works. Due tometamerism, it is possible to have quite different spectra that appear white. RGB systems Combined spectral curves for blue, yellow-green, and high brightness red solid-state semiconductor LEDs.FWHMspectral bandwidth is approximately 24-27 nm for all three colors. White lightcan be formed by mixing differently colored lights, the most common method is to usered, green and blue(RGB). Hence the

Essay --

Logan Liao Mr. Mervine A British Literature 21 November 2013 Neighborhood, Country, and Global Communities An impoverished man living on the outskirts of a neighborhood park walks through the forest and notices a block party. He thinks to himself, a â€Å"free† lunch. As the man strolls toward the party, he notices many people of all ages eating and talking. When he looks at the food on the table, his eyes’ yearn in hunger. He then comes across a sign reading â€Å"BLOCK PARTY, COMMUNITY ONLY.† Slowly his momentary happiness vanishes because he does not belong to this neighborhood community but part of the city. In the Merriam-Webster dictionary, the word community means a group of people who live in the same area (such as a city, town, or neighborhood). However, according to experts, â€Å"The word community itself changes coming to mean a group of like-minded people sharing common interests, when in the past it referred to a group of people of various skills and interests cooperating with one another in order to survive. Now we find and create communities based on geography, ethnicity, race, religion, class, and even language† (Shea, Scanlan, and Aufses). A community provides support and achieves a goal no matter what the cost. A community is a group of individuals striving to accomplish a common goal together. For example, communities of Buddhists look for enlightenment and inner peace within themselves and their bodies. The word â€Å"community† reminds one of a positive place to grow and develop. A community supports all people who want to learn more and to work together. For instance, community service lets people volunteer and become innovative in their community, in many ways, whether it is running a food drive or cleaning up the par... ... Communities are interacting populations with shared geography or common valued people as they connect mentally, physically or even spiritually. The world needs community because society lacks a family, lacks support. If communities cease to existence, the world would fall from total anarchy with everyone living for him or herself. The state of the earth would not exist if people could not understand they are all in a community. However if everyone knew of communities we would all live in a place with no strife, angry, or violence. There are many different types of communities from school, sports team, neighborhood, or even a family, but most of them seek one common goal or a passion that unites them. They work and endeavor to achieve it. Communities watch everyone’s back like a shepherd tending and watching his sheep. The world we live in is a community.

Regeneration’ and Kesey’s Essay

      However, McMurphy was only able to defeat the nurse from what he learned when she defeated him in his bid to change the television schedule. ‘Cheswick shows his hand higher and glares around. Scanlon shakes his head, and then raises his hand, keeping his elbow on the arm of the chair. And nobody else. McMurphy can’t say a word. ‘ In this defeat, McMurphy learns that he must convince the patients of an idea before being faced with the nurse; otherwise, the patients become frightened of her and lose their nerve. Once again, McMurphy attempted to change the TV schedule, but failed again due to technicalities such as the vote of the chronic patients, and the fact that the meeting had ended before McMurphy was able to get the majority vote so the motion was not carried. This incident formed a bond between the patients against the hospital staff, and they had gained an important ally in Dr Spivey, an unwary double agent. However, In Regeneration the patients of Craiglockhart do not treat staff as if they were afraid of them. The doctors and nurses of Craiglockhart are less authoritative and are lenient with the rules of conduct. ‘One of the VAD’s tugged at it. â€Å"There’s room for two in there,† she said, smiling, coaxing. â€Å"Have I to get in with you? â€Å"‘. The patients treat doctors with respect and are friendly towards other patients, however at times the patients appear to fear treatment. ‘†There’s no area of analgesia,† Rivers said to Sister Rogers. Prior snatched up the pad. â€Å"IF THAT MEANS IT HURT YES IT DID†Ã¢â‚¬Ëœ. On the other hand, in ‘One Flew Over The Cuckoo’s Nest’ the patients treat nurse Ratched with minimal respect and some of the patients are very unprofessional in what they say and do to her and the other student nurses. It can be said that Craiglockhart is more civilised as a hospital, and nurse Ratched’s ward can be compared to a high school classroom where the patients are conspiring as to how they can defeat the nurse, similar to the way students may act together to outwit a teacher. Nurse Ratched constantly undermines her patients in front of one another to make them feel inadequate; almost emasculating them. ‘Right at your balls. No, that nurse aint some kinda monster chicken, buddy, what she is, is a ball-cutter. ‘ On the other hand, Rivers sees his patients as his equals and treats them with high regard, even though Rivers himself is more intelligent and qualified than almost all of the patients that he treats. Patients in Ratched’s ward also resent the ward itself and its confines, and wish they could escape the dreariness of it all. The irony of this is that most of the patients who complain are not committed and are only in the hospital voluntarily, so they could walk out of the door at a moment’s notice; however, the patients are unable to do this due to nurse Ratched making them feel inadequate and therefore unfit for society. When McMurphy discovers that it is the Nurse who decides how long a patient spends on the ward, he is beside himself with anger, directed mainly at the other acute patients for egging him along against the nurse, when all the while they knew that it would only get him committed for a longer period. Conversely, we are given the impression that all the patients at Craiglockhart are committed, however they all have the freedom to roam most of the institution and the outdoor facilities such as the golf course ‘Prior watched the amber lights winking in his beer. He was sitting in the shadowy corner of a pub in some sleazy district of Edinburgh. ‘ The patients are allowed to leave the hospital premises and are trusted to be responsible enough to return. In ‘One Flew Over The Cuckoo’s Nest’, patients are not even allowed to leave the premises without an accompanied pass. This is needed in order for McMurphy to take a group of the patients and Dr Spivey, one of the resident doctors of the hospital, on a fishing trip later in the novel. The fishing trip was organised by McMurphy for a number of reasons that could only possibly be contrived by a person of sound mind. The first of these reasons is to deliver a blow to the nurse’s control over the patients and to show them that they are in fact free to do what they wish. His other incentives were money, which he acquired from the remainder of the funds from patients used hire the boat, and also the chance to spend some time alone with a woman who would be accompanying the men on the boat, something that we can presume McMurphy has not been able to do for a while now. During the fishing trip, we are able to see the effect of nurse Ratched’s enfeeblement of the patients when they enter the garage to buy fuel. The mechanics at the garage are taken aback by the sight of patients from a psychiatric institution, and the awkward exchanges between the doctor and the mechanics only make things worse. It is at this moment when McMurphy comes to the rescue of the patients and confronts the workers at the garage. ‘we’re every bloody one of us hot of the criminal-insane ward, on our way to San Quentin where they got better facilities to handle us. ‘ McMurphy lies and uses bravado to frighten the mechanics and empower the patients, who no longer feel as if they are the laughing stock of town and begin to order the workers around. This is an example of how mental illness is perceived in society at the time the book was set, and how the patients were able to overcome its stigma, if only for a short period. Their personal triumph was over once the patients had reached the fishing port and were confronted by sailors who took the opportunity to make suggestive jokes about the patients’ female companion, as they stood there helplessly, unable to defend her without the presence of McMurphy. In ‘Regeneration’, the reader encounters a similar stigma attached to mental illness. One particular case involves the character Prior, who is questioned about why he was not wearing his blue hospital badge. Prior retorts to Rivers’ question, stating that ‘I wasn’t wearing the badge because I was looking for a girl. Which – as you may or may not know – is not made easier by going around with a badge stuck on your chest saying I AM A LOONY. ‘ Prior assumes, perhaps from experience, that wearing his hospital badge would be a deterrent for women as nobody seems to jump at the opportunity to be involved with a mentally ill person. Another incident in involving the badge occurred with Sassoon when he went to the Conservative Club to meet Rivers. ‘looking at the young man in uniform evoked, and then – or perhaps he was being oversensitive? – with a slight ambivalence, a growing doubt, as they worked out what the blue badge on his tunic meant. ‘ Once again, the reader is presented with a situation in which people change their opinions when faced with an ‘outcast’ from society, someone who is irrational and is therefore supposed to be unacceptable to the general public. Near the end of ‘Regeneration’ Barker introduces another psychiatrist called Dr Lewis Yealland. He is similar to Rivers in that Yealland is also highly respected and acclaimed on his work; however, the underlying difference between the two characters is in the way they treat their patients. Where Rivers would tend towards having a conversation with the patient to solve the problem, Yealland prefers to cast a dominating presence to the patient, neglecting their views and suggestions. ‘†No†, Yealland said. â€Å"The time for more electrical treatment has not yet come; if it had I should give it to you. Suggestions are not wanted from you, they are not needed. â€Å"‘ Yealland does not allow patients to express themselves as he feels that any self-diagnosis by a patient is a threat to his judgement, and this is intolerable in his treatment. Yealland can be compared to nurse Ratched, in that both the characters require dominance in a situation and superiority over those under their jurisdiction. Another difference between Rivers and Yealland would be that Rivers, as mentioned before, endeavours to resolve the problem that the patient is suffering from, thus curing the patient of his illness, whereas Yealland merely addresses the symptom arising from the illness and treats the patient to rid them of this. He eradicates the symptom, while this is only the tip of the figurative iceberg, and neglects the patient’s psychological problem, which caused the symptom in the first place. In the novel, Yealland serves a larger purpose as a metaphor for the control that the government exerts over citizens, indifferent towards the voices of individuals, for example, the voice of Siegfried Sassoon, which was ignored and discredited by the government in the same way Yealland ignores and discredits his patients’ views. Yealland provides the reader with a clear, yet cleverly concealed allegorical view of the novel where the same concept is repeated for a greater effect on the reader’s opinion of both the presentation of mental illness and the way it is treated, and also the government’s approach to dealing with soldiers who cry out against the unjustness of war. Nearer the end of ‘One Flew Over The Cuckoos Nest’, McMurphy throws a party one night for his farewell as he plans to break out of the ward and make his escape that night. The party is not sanctioned by the nurse who has no idea of its taking place, so McMurphy knows that he must leave otherwise he will be punished severely for his actions. On the night of the party McMurphy organises for a girl to come onto the ward and make love to Billy Bibbit, making him lose his virginity. McMurphy’s plan of escape fails and the nurse returns in the morning to find the atrocities that have taken place on her ward. She confronts Billy Bibbit about his actions, and he seems confident, however once the nurse threatens to informs Billy’s mother of his wrong doing Billy breaks down and pleads with her not to do so. ‘†Nuh! Nuh! † His mouth was working. He shook his head, begging her. â€Å"You d-don’t n-n-need! â€Å"‘ Billy is so disturbed by the prospect of his mother finding out about his actions, that he takes his own life shortly after the nurse confirms that she will inform his mother. After this event, the ward changes dramatically. Patients who were not committed begin to leave; Sefelt, Frederickson, even Harding. McMurphy was taken away for a lobotomy, which succeeded in calming him down, but it did so to the point where he would not fit the description of a mentally ill patient, but more of a breathing corpse. The Chief cannot stand to look at this change in McMurphy so he resorts to suffocating him in order to put out his suffering once and for all. On doing so, the Chief escapes the ward by picking up the control panel in the tub room and throwing it through the window. This mirrors the event where McMurphy attempted to lift the control panel, the difference being that the Chief succeeded where McMurphy failed by learning from him. This event is a representation of the book as a whole, where one man’s titanic struggle and failure managed to stimulate another man’s will to live, and as one circle of life draws to a close, a new one begins. Emile Khan – 1 – Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Ken Kesey section.