Research Final Exam Flashcard

Research Final Exam

buy custom Light Emitting Diodes essay

buy custom Light Emitting Diodes essay Introduction A light emitting diode is a semi conductor device that gives out infrared or visible light after it has been charged with an electric current. It has a wide range of uses for example in the brake lights and rear windows of vehicles, indicator lamps, full color posters, bill boards and also alphanumeric displays. They are also used as a source of light in fiber optic telecommunication; in television remote controls and autofocus cameras. This paper seeks to discuss in detail the functioning of light emitting diodes. History of Light Emitting Diodes In 1907, a British engineer and inventor H.J Round was the first to report the emission of light when he passed current through a semi conductor rectifying junction. Round used a used a contact that was in between a silicon carbide crystal and a metal wire. The John Allens group, at the Services Electronics Research Laboratory was the first to come up with first practical visible light emitting diode. The company set u a small production line in 1962. They used gallium phosphide that had controlled amounts of oxygen and zinc. Initially, this device was called crystal lamps, before it became known as light emitting diode. From 1962 into the late 1970s, the devices made of zinc and oxygen dominated the LED market (Physics and Anatomy) The General Electric Corporation was the first company to offer commercial Light Emitting Diodes. Their product gave out radiation in the red part of the spectrum. However, the company manufactured these products in low quantities as a result of the price of the product. A single light emitting diode went for 260 US Dollars. The LED was at that time offered through the Allied Radio Catalog which was widely distributed that dealt in amateur radio electronics. The mass production of LEDs came about in 1968, by the Monsanto Corporation. The company established a factory that produced low cost LEDs. Monsanto then formed a collaboration of some sort with Hewlett Packard Corporation; it was expected that Monsanto would provide the raw materials whereas Hewlett Packard would produce the LEDs. This relationship however did not last long because Hewlett Packard felt uneasy about the idea of depending on a single source for its raw materials. From the late 1960s to the mid 1970s, the greatest demand for LEDs came from calculators and then wrist watches; after the Hamilton Watch Corporation came up with the Pulsar digital watch. These two used numeric LED display. M. George Craford a manager and technical innovator at Monsanto, made huge contributions to the development of LEDs, with the most notable being the pioneering demonstration of a yellow LED (Shubert,F. pg 8-9). The Technology of LEDs In the light emitting diodes, the emission of light results when the positive hole and the negative electron, which are charge carriers, are injected into the semiconductor metallic contacts that are organic. These contacts are made on the opposite sides of the polymer films that are responsible for semi conducting. As soon as the hole and the electron come under the influence of the coulomb that they share, there is an attraction right inside the substance they recombine in thereby resulting in the emission of a photon. The emitted lights wavelength is dependent on the band gap of the semiconducting polymer. The holes and electrons are spin-1/2 particles, the resultant exciton can be a single exciton or a triplet exciton. Should the spin of the incoming charge carriers be random, then 75% triplet excitons and 25% singlet excitons will be formed. In a polymer material that has a relatively weak spin orbit coupling, the only excitons that can recombine in a radiative manner are single t excitons. This is because the ground state is a singlet state. LED is based on the principle of the injection luminescence principle. The LED is constructed of gallium arsenide phosphide, gallium arsenide, gallium phosphide. Silicon and germanium are not suitable since p-n junction prduce heat and hence no visible light. The LED consists of p-n junction diode in which diffusion of potential is generated in the depletion layer between the n-type and p- type materials. The LED junction is connected in the forward biased mode. Electron move across the junction from n- type to p- type material thereby make the hole and the electron to recombine. The diffusion potential inhibits electrons and holes from leaving the n- and p regions since they enter opposite regions (Physics of Light Emitting Diodes). Applying the external forward biased voltage, V, the barrier is reduced to e(. If Vthe barrier becomes zero enabling electrons to flow from n- side to p-side. The electron injected into the depletion layer recombines with holes thereby emitting a photon energy which is given by the formula hv. LED characteristics During forward biased state, the current increases rapidly and hence there need to protect the LED to prevent it from getting destroyed. The light output is linearly proportional to the current within its active region. LED can operate at low voltages and they dont consume a lot of energy since all the energy is converted into light energy. They should not be operated at more than 40mA or 2.2V. The range of wavelengths that can be visible is from 0.4 m to 0.7m. LED symbol The symbol for an LED is as shown below. Types of LED There are four major types of LED and these are pinned LED, surface mounted LED, power LED and chip on board LED. Pinned LED is made from metal lead frame. Light emitting die is placed on the lead frame and molded around the frame forming LED. They can be diffused pinned LED that give a wide angle of light or water clear that give more directional beam. They are easy to use and easy to assemble. The surface mounted LED has the smallest body into which the light emitting die is mounted. They are fitted into Printed circuit board. They are ideal at a premium space where they offer wide view angles of light. The other type of LED is Power LED which gives high light output. They are mounted on heat conductive material (heat sink) that draws away heat from LED die to avoid damaging the LED. The chip on board type of LED uses a die bonded directly to printed circuit board or substrate that eliminates the body of an LED. The bonded die is covered in a clear protective resin which is hard to the die from being damaged. Its advantage is that it is less costly and they are small (LED lighting and signs). New types of LED Semiconductor technology has resulted into Innovation of new devices. These new device types are surface-emitting (large area) LED (SLED), micro-cavity surface emitter, edge-emitting LED (ELED)and super-luminescent diode emitter (SLD).Surface-emitting LEDs (SLEDs) are the conventional LEDs which emit light from relatively large surfaces oriented orthogonally to the axis of the emission pattern. Micro-cavity surface emitters are SLEDs with an internal mirror and layer thicknesses closely fitted to act as a low-finesse Fabry-Perot cavity and they do not show optical gain. The cavity is added to reduce the optical line width as well as the emission half-angle because a layer thickness forming the cavity reduces emission efficiency at larger angles Edge-emitting LEDs have a device structure similar to that of the ridge wave guide laser but it does not have sufficient gain to lase. Typical dimensions of the emitting stripe are 3 3 100 m and it has active region hundreds of microns long. The energy density is concentrated in the long active region making it to achieve high radiances at the emitting facet thus; it becomes much easier to launch the light into an optical fiber. The emitting geometry for this device is different from the SLED. Super-luminescent edge emitters are similar to edge emitting LEDs, but they have wider central portion of the cavity than the emitting facet to allow more photons generated within the device reach the emitting facet than for a uniform cross-section, standard edge emitter, hence increases the emmitted radiance (ICNIRP). Considerations for use LED specifications applicable to safety Radiance (brightness) is conserved and it cannot be increased by optical lensing and manufacturers specification sheet for an LED which is expressed as either radiance or luminance is not given. The radiant intensity is always specified. When the apparent source size is known, then LED radiance can be calculated. The actual source size is applicable in cases where no lens is incorporated, magnified and that apparent source size must be used all hazard assessment. Exposure guidelines for eye safety Occupational and public health exposure limits and guidelines state that LEDs should be treated as incoherent optical sources where different hazards are assessed severally over a range of wavelengths. Incoherent-source limits are more applicable to certain types of LEDs than others. Conventional, surface-emitting LEDs are radiance limited and many eye injuries have not been documented for LEDs. Laboratory efforts to create ocular injury with high-power LEDs have been unsuccessful while laboratory studies using diode lasers produced retinal injury. Applications LED Displays Many businesses use LED lighting on their signs. Hey are also used in gas stations especially where the prices of gas are displayed, this gives the owner to change prices easily unlike in the old manual way. LED Flashlights Flashlights made of LED can be as little as key chains to high powered lanterns that are big in size. They are also used for traffic safety especially where roads are under construction where they are used to steer traffic away. LED Lights for the Home The use of LED lights is gaining popularity day after day especially for their use at home. It is increasingly being seen as a substitute to florescent lighting. They can be used as 121 volt DC light bulbs, flood lights, motion detecting lights among others. Led is also used in making toys and accessories such as glow sticks and it can also be used to light up jewelry for example necklaces, hair accessories, rings and bracelets. They are also used in making Christmas lights (Quinn,Lydia.). Advantages and disadvantages of LEDs Light emitting diodes are very efficient; they do not use a lot of electricity hence they are economical. The light emitted by an LED bulb is regarded to be a cool light therefore; one gets more light per watt as compared to an incandescent bulb. LED lights come in a wide range of sizes; they can be as small as 2mm or even less, unlike incandescent bulbs. They can therefore be used in instances where a regular bulb cannot be used. These bulbs also come in a range of colors without necessarily requiring filters so as to produce these colors. LED can come in almost any color one could think of; the color depends on the material of the semiconductor and is therefore easier to come up with different colors. LED lights have the ability to achieve their optimum level of brightness in a few micro seconds, in other words, they have a more efficient on/off time. Light emitting diodes last longer than incandescent bulbs. One can therefore get value for his money because of their lifetime. They also last longer and manage better for cycling; they dont burn out that quickly and they are therefore economical (ledlights.org) The main disadvantage of LEDs is their high cost. They are expensive on the basis of start up costs. These costs can be attributed to the low lumen output and power supplies that may be needed (ledlights.org) Conclusion Although the LEDs are expensive to use for the lighting applications because they are manufactured using the advanced semiconductor materials, they are the most cost effective lighting option in many situations. For instance, their long run lower costs make them better as compared to other light sources and they will play bigger role in the technology sector. Buy custom Light Emitting Diodes essay

Western Heritage Essay Example | Topics and Well Written Essays - 750 words

Western Heritage - Essay Example , women such as Bianca and Emilia are more open in their interpretation of obedience and may even go against the wishes and desired of their husbands/lovers to get what they want. Of course, this is certainly not the real world image of what women do or what a person does but in Shakespeare’s times such behavior would have been perfectly acceptable given the shape of the characters. It is certainly easy to compare Desdemona to other gentle and kind ladies who were in love with their lords from other plays of Shakespeare as they are the paragons of virtue and not at all led to enter into fights with their lovers as opposed to women who were evil who vexed their lovers justly or unjustly. At the same time, it must be noted that misogyny has been a part of literature for centuries and was part of the dramas presented by Shakespeare so again, it is difficult to fault him for thinking in a particular manner about the women he represents. The common man is essentially the mouthpiece in A Man for All Seasons simply because he says what the audience needs to hear concerning the progress of the play itself. There are a variety of roles assigned to the common man ranging from More’s jailer to More’s servant and even the individual who executes him. In all these roles the common man interacts with More in meaningful ways of which one example is at the execution the executor asks for More’s forgiveness which I feel is the common’s man apology for not rising up to help More and do what is right simply because the singular common man is too weak against the power of the state. The story and the acts of the common man clarify the position as well as the nature and the strength of the common man who is often nothing more than a spectator to the events of history, the corruption of the strong and the piety of those who stand up against them. The character is neither positive nor negative but only an element in the story which does not interact in any significant way

Advanced Fire Administration Essay Example | Topics and Well Written Essays - 1500 words - 2

Advanced Fire Administration - Essay Example These businesses range from groceries, computer shops, to supermarkets. These business organizations recruit their staff from all over America. The companies also have a quota system in their recruitment strategies aimed at recruiting local people, for purposes of appealing to the locals in relation to the sale of their products. Big business organizations within my community promote environmental and social initiatives. These are their strategies of creating a positive brand name, within the community. The literacy level of people within my community is over 70%, and this is because of huge investments in school, and other tertiary institutions that offer knowledge. This attracts investors because of the availability of labor and the necessary skills for running an organization (Varone, 47). The Federal and State government ensures that there is adequate security by building police stations, and setting up judicial court houses. This is for purposes of ensuring that the trial conducted is fair, and speedy (Grosshandler, 62). The government has invested on health care provision by building numerous hospitals, and staffing them with highly qualified health care providers. Because of this, my people are assured of better medical care attention. Politically, the environment within my community is stable, with the major political parties possessing an equal membership. That is the Democratic Party, and the Republican Party. On different occasions, political intolerance emanates amongst the residents of my community, and this might be on the different views the members of opposing political parties possess. My community also enjoys a number of social facilities built by the government, and private individuals. This includes stadiums, restaurants, night clubs and casinos. In identifying the issues that the fire department should focus on, the first step is to identify the activities within Oregon that might trigger an outbreak of fire. To effectively

Supreme court cases Essay Example | Topics and Well Written Essays - 1250 words

Supreme court cases - Essay Example A similar fact to the present case can be found in the case of Bowers v. Hardwick (1986). Hardwick was charged violating Georgia statute criminalizing sodomy by committing an act with another male in the bedroom. The court in Bowers v. Hardwick (1986) reversed the Court of Appeals decision and stated that the case does not require a judgment on whether laws against sodomy between consenting adults in general, or between homosexuals in particular, are wise or desirable. The issue presented in Bowers v. Hardwick (1986) is whether the Federal Constitution confers a fundamental right upon homosexuals to engage in sodomy and hence invalidates the laws of the many States that still make such conduct illegal and have done so for a very long time. In this case of Bower v. Hardwick (1986), the court declared their disagreement with the Court of Appeals and with respondent that the Court’s prior cases has construed the Constitution to confer a right of privacy that extends to homosexual sodomy and for all intents and purposes have decided this case. Bower v. Hardwick (1986) presented the reach of this line of cases was sketched in Carey v. Population Services International (1977). Pierce v. Society of Sisters (1925), and Meyer v. Nebraska (1923), were described as dealing with child rearing and education; Prince v. Massachusetts (1944), with family relationships; Skinner v. Oklahoma ex rel. Williamson (1942), with procreation; Loving v. Virginia (1967), with marriage; Griswold v. Connecticut, supra, and Eisenstadt v. Baird, supra, with contraception; and Roe v. Wade (1973), with abortion. The rulings in Bowers v. Hardwick (1986) settled that there is no connection between family, marriage, or procreation on the one hand and homosexual activity on the other has been demonstrated, either by the Court of Appeals or by respondent. However, I dissent in the decision stated above. I agree with Judge Blackmun (Bowers v. Hardwick, 1986) that this case is no more about "a fundamental right to engage in homosexual sodomy," as the Court purports to declare, ante, at 191, than Stanley v. Georgia (1969), was about a fundamental right to watch obscene movies, or Katz v. United States (1967), was about a fundamental right to place interstate bets from a telephone booth. Judge Blackmun said that this case is about "the most comprehensive of rights and the right most valued by civilized men," namely, "the right to be let alone" Olmstead v. United States (1928) (Brandeis, J., dissenting). It is very sad to know that we based our decisions to the rule of law laid down in ancient times. Justice Holmes, believed that "it is revolting to have no better reason for a rule of law than that so it was laid down in the time of Henry IV. It is still more revolting if the grounds upon which it was laid down have vanished long since, and the rule simply persists from blind imitation of the past." Thus it is very important when deciding the case to pay attention to the pre sent condition of the state. We may have laid down rules from the past centuries, but these rules were based on the condition of the state during those times. There are differences on how the people act, think, and decide before and on how they do at this present time. There are acts which were morally wrong before, that maybe right and acceptable today. As for the present case of Susan and Mary, it is

Anthropogenic Polycyclic Aromatic

Anthropogenic Polycyclic Aromatic Source Apportionment of Anthropogenic Polycyclic Aromatic Hydrocarbons (PAHs) by Molecular and Isotopic Characterization A dissertation submitted as part of the requirements for the Degree of Master of Science Abstract Polycyclic aromatic hydrocarbons (PAHs) are important, ubiquitous environmental pollutants known for their carcinogenic and mutagenic properties. They are released into the atmosphere, soil (which bears about 90% of the environmental PAH burden in the UK) and water by natural and anthropogenic processes. Today, anthropogenic combustion of fossil fuel is, by far, the most important source of PAH input into the environment. The importance of PAHs as environmental pollutants with a multiplicity of sources has resulted in considerable interest in source apportionment techniques. This study therefore investigated the PAH profiles in road dust samples around a high temperature carbonization plant (Barnsley, South Yorkshire) and used the combination of molecular methods and gas chromatography-isotope ratio mass spectrometry (d13C GC-IRMS) to identify their origin. Quantification of the sixteen U.S EPA priority PAHs extracted from the dust samples ranged from 2.65 to 90.82g/g. The PAH profiles were dominated by phenanthrene for 2-3 ring PAHs and by fluoranthene, pyrene, chrysene and benzo(b+k)flouranthene for PAHs with ring size ≠¥ 4. The fluoranthene to pyrene (Fl/(FL+P)) )) concentration ratio ranged from 0.51 to 0.55, while the indenol(1,2,3-cd)pyrene to benzo(ghi)perylene (IcdP/(IcdP+ BghiPer)) ratio ranged from 0.37 to 0.55; suggesting contributions from diesel combustion, most likely from heavy duty trucks. The ability of compound-specific stable isotope measurement, using d13C GC-IRMS, to source apportion environmental PAHs where significant input from coal is expected has been demonstrated. The PAH d13C isotope ratio values ranged from -25.5 to -29.7%o. Overall, the d13C isotope ratio, in conjunction with PAH molecular distribution/ratio, strongly suggest that PAHs in the study area have inputs from both high temperature coal carbonisation and transport fuels (mainly diesel combustion). Chapter One 1.0 Introduction Industrialization, centered on energy use, has been the driving force for many of the greatest advances in the 20th century and is central to our way of life in the modern world today. Energy improvements and the discovery of fossil fuel (coal and petroleum) have hastened industrialization and breakthroughs in areas such as travel, communication, agriculture and healthcare, in many parts of the world. Despite these achievements, industrialization has brought along with it global problems of environmental pollution and challenges. These include exploitation of natural resources, oil spillages, global warming due to rising emissions of carbon dioxide and other green house gases, disposal of wastes (industrial and domestic) and inorganic and organic emissions which ultimately affect air, water and land quality. The release of organics/organic effluents such as polycyclic aromatic hydrocarbons (PAHs), mainly from the use of fossil fuels; into the environment have particularly gained attention in recent times due to their toxicity and persistence. 1.1 Polycyclic Aromatic Hydrocarbons (PAHs) Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that are of great public concern due to their toxicity, carcinogenicity and/or mutagenicity (Fabbri et al., 2003; Sharma et al., 2007). They are continuously introduced into the environment by both natural processes, such as volcanic eruptions and forest fires; and anthropogenic sources which include various industrial processes such as coke production in the iron and steel industry, catalytic cracking in the petroleum industry, coal gasification, heating and power generation, open burning of vegetation and internal combustion engines used for various means of transportation (Suess, 1976; Morasch et al., 2007). Immense PAHs contaminations of the environment typically originate from anthropogenic sources. A natural balance existing between the production and natural degradation of PAH historically kept the background concentration of PAH in the environment low and fixed (Smith and Harrison, 1996). The ever-increasing industrial development and use of fossil fuels in many parts of the world released PAHs into the environment resulting in their universal occurrence in air, water, soil and sediments. This increase in the production rate of anthropogenic PAHs has disrupted the natural balance of PAHs in the environment, while their rate of decomposition remains more or less constant (Suess, 1976; Fetzer, 1988). PAHs are found in great abundance in fossil fuel materials such as shale oil, coal liquids, petroleum, asphalt and many other hydrocarbon based materials (Fetzer, 1988). Incomplete combustion of these fossil fuel materials produces fly ash, chimney soot and engine-derived air particulates which have higher levels of PAHs than the original materials (Chadwick et al., 1987; Fetzer, 1988). Generally, PAHs give rise to significant impact to the areas close to the nearest point sources (Ohkuchi et al., 1999). There are very high concentrations of atmospheric PAH in the urban environment which is accounted for by the various industrial processes earlier identified, increasing vehicular traffic and the scarce dispersion of the atmospheric pollutants. These PAHs are emitted to the atmosphere either in the gaseous phase or on very small particles, 70-90% of which are in the respirable range (et al., 1987). The risk associated with the human exposure to atmospheric PAH is therefore highest in the cities because of these factors and the density of population (Sharma et al., 2007). In view of the carcinogenic potential of many PAH compounds, their contribution to the mutagenic activity of ambient aerosols and range of sources of emission, their concentration in the environment is considered alarming and efforts should be made to reduce or even eliminate them wherever possible. To achieve this, a better understanding of their fate and associative transformation pathways in the environment is necessary and this has resulted in considerable interest in PAHs source apportionment. 1.2 Source Apportionment Most organic pollutants can be released into the environment from various sources. Hydrocarbon pollutants are particularly widespread in the environment due to the multiplicity of their sources such as synthesis by living organisms (biogenic origin), degradation of organic matter (diagenic origin), incomplete combustion of organic matter and natural and anthropogenic fossil fuel combustibles (petrogenic origin) (Mazeas et al., 2002). Due to the multiplicity of the sources of organic pollutants, source apportionment techniques are invaluable in the determination of the contributions of various pollution sources of a pollutant in the environment. Source apportionment generally refers to the quantitative assignment of a combination of distinct sources of a particular group of compounds put into a system (OMalley et al., 1994). Differences in emission profile, among emission sources, have been sufficiently used to develop fingerprints that can be identified and quantified at a particular site (Dallarosa et al., 2005). As mentioned earlier, most of the environmental PAHs have anthropogenic origins. Contributions from coal combustion and use of petroleum in internal combustion engines for transportation have increased over the years and have generated a lot of concern. It is therefore important to be able to distinguish different sources that contribute to PAH pollution of a particular environment using reliable source apportionment techniques. This project work is therefore aimed at contributing to the knowledge of reliable, unambiguous novel PAH source apportionment techniques by: (i) Identifying and quantifying contemporary PAHs fluxes in the environment around a coking works using molecular methods (ii) Demonstrating the ability of compound specific stable isotope measurement to source apportion environmental PAHs where significant input from coal is expected Chapter Two 2.0 Literature Review 2.1 General overview of the properties of PAHs Polycyclic aromatic hydrocarbon (PAH) compounds are a class of complex organic chemicals made up of carbon and hydrogen with a fused ring structure containing at least 2 benzene rings (Ravindra et al., 2008). They may also contain additional fused rings that are not six-sided (Figure 1). Pyrosynthesis and pyrolysis are two main mechanisms that can explain the formation of PAH from saturated hydrocarbons under oxygen-deficient conditions. Low molecular weight hydrocarbons like ethane form PAHs by pyrosynthesis (Figure 2). At a temperature greater than 5000C, carbon-hydrogen and carbon-carbon bond are broken to form free radicals which combine to form acetylene. Acetylene condenses further to form aromatic ring structures which are resistant to degradation (Figure 2). The ease with which hydrocarbons may form PAH structure varies in the order aromatics > cycloolefins > olefins > Paraffins (Ravindra et al., 2008). The higher molecular weight alkanes in fuel form PAH by pyrolysis: the cracking of organic compounds. The discovery of the fluorescence of a number of known carcinogenic tars and mineral oils in 1930 led to the investigation of the carcinogenic properties of PAHs. This spanned from the discovery that benz(a)anthracene and other compounds in its group possessed a similar fluorescence (Chadwick et al., 1987). Initial investigation for PAH carcinogenicity using dibenz(a,h)anthracene later resulted in the isolation of a powerful carcinogenic substance from coal tar: benzo(a)pyrene (Chadwick et al., 1987). Since the discovery of benzo(a)pyrene, various works have been done to identify other carcinogenic PAHs. Sixteen (16) parental PAHs have been designated by the US environmental protection agency (US EPA) as priority pollutants and most of the studies have focused on these (Figure 1 and Table 1). Seven (7) of these (Table 2) have been identified by the International Agency for Research on Cancer (IARC) as animal carcinogens and have been studied by the EPA as potential human carcinogens (EPA report, 1998). PAH can undergo metabolic transformation into mutagenic, carcinogenic and teratogenic agents in aquatic and terrestrial organisms. These metabolites, such as dihydrodiol epoxides, bind to, and disrupt, DNA and RNA, which is the basis for tumor formation (Wild and Jones, 1995). Although PAHs are renowned for their carcinogenic and mutagenic properties, not all of them are environmentally or biologically significant. Studies have been carried out on monitoring the levels of some of the important PAH in various parts of the world and the results of a number of these are summarized in Table 2. The carcinogenicity and/or mutagenicity of PAH, which require metabolic conversion and activation, is structurally dependent: while certain isomers can be very active, other similar ones are not (Fetzer, 1988). An example, as shown by Fetzer (1988), is found in the five PAHs with molecular weight of 288 and containing 4 rings. Chrysene, benz[a]anthracene and benzo[c]phenanthrene are mutagenic but the remaining two, napthacene and triphenylene are not. As molecular weight increases, the carcinogenic level of PAHs also increases and acute toxicity decreases (Ravindra et al., 2008). The p electron fused benzene rings in PAHs account for most of their physical properties and chemical stability (Lee et al., 1981). The 2-ring and 3-ring PAHs compounds, which are more volatile and water soluble, but less lipophilic than their higher molecular weight relatives, generally exist primarily in the gas phase in the atmosphere and will tend to be deposited to the surfaces via dry gaseous and/or wet deposition (Ravindra et al., 2008). On the other hand, the less volatile 5-6 ring PAHs tend to be deposited on surfaces bound to particles in wet and dry deposition; while compounds of intermediate vapor pressure will have a temperature-dependent gas/particle partitioning of PAHs leading to both wet and dry deposition in gaseous and particle-bound form (Mannino and Orecchio, 2008). PAHs have a tendency to sorb on hydrophobic surfaces and this tendency increases with the number of aromatic rings (Morasch et al., 2007). Thus, PAHs are primarily found/present in the environment in soils and sediments, rather than water and air. Their high hydrophobic tendency and high lipophilic properties make them easily bio-accumulated to such an extent that can threaten the safety of food chains for both man and animals (Sun et al., 2003). Compounds Chemical formula Molecular weight Melting point, oC Boiling point,oC Particle/gas phase distribution Napthalene C10H8 128.19 80.5 218 Acenaphthylene C12H8 152.21 Gas phase Acenaphthene C12H10 154.21 96.2 279 Gas phase Fluorene C13H10 166.22 116 -117 295 Gas phase Phenanthrene C14H10 178.24 100 101 340 Particle phase Anthracene C14H10 178.24 216.5 217.2 339.9 Particle phase Fluoranthene C16H10 202.26 110.6 111.0 393 Particle phase Pyrene C16H10 202.66 152.2 152.9 360 Particle phase Benz(a)anthracene* C18H12 228.30 159.5 160.5 435 Particle phase Chrysene* C18H12 228.30 250 254 448 Particle phase Benzo(b)fluoranthene* C20H12 252.32 Particle phase Benzo(K)fluoranthene* C20H12 252.32 215.5 216 Particle phase Benzo(a)pyrene* C20H12 252.32 176.5 -177.5 311 Particle phase Indeno(1,2,3-cd)pyrene* C20H12 276.34 Particle phase Dibenz(a,h)anthracene* C22H14 278.34 205 Particle phase Benzo(ghi)perylene C20H12 276.34 273 Particle phase *PAHs identified animal carcinogens and as potential human carcinogens Table 1: Physical properties of 16 priority PAHs on US EPA listing (Adapted from EPA REPORT, 1998, Ravindra et al., 2008) S/N Total PAHs Mean (ngm-3) Cities 1 à ¥ 15 PAHs 56 Columbia (USA) 2 à ¥ 15 PAHs 412 Austria 3 B (a) P 4.99-9.56a Delhi 4 à ¥ 12 PAHs 93 Denver (USA) 5 à ¥ 8 PAHs 150-1800a Delhi 6 à ¥ 15 PAHs 166 London 7 à ¥ 15 PAHs 59 Cardiff 8 à ¥ 11 PAHs 90-195 (I)a, 20-70 (R)a Ahmedabad 9 à ¥ 12 PAHs 22.9-190.96a Kolkata 10 à ¥ 12 PAHs 20-95a, 125-190a Mumbai, Nagpur 11 à ¥ 13 PAHs 90.37 57.04 Coimbatore 12 à ¥ 11 PAHs 310 (60-910)a Mexico city 13 à ¥ 15 PAHs 8.94-62.5a Camo Grande city 14 à ¥ 16 PAHs 13-1865a Chicago I= industrial site, R = residential site, a Range Table 2: A summary of mean concentrations (ng/m3) of total PAHs in various cities of the world (Sharma et al., 2007) 2.2 Anthropogenic sources of PAHS The high concentration of PAHs in the environment, as shown in Table 2, suggests the extent of anthropogenic contribution (Sharma et al., 2007). It is, however, difficult to estimate the amount of anthropogenic PAHS on the yearly input of the various sources on a global basis. An approximate quantification has been made, based on the annual consumption of fossil fuel, that while the global annual release of PAHs to the atmosphere is of an order of 105 tonnes, including 103 tonnes of benzo(a)pyrene; the annual input of crude and processed oil containing 1-3% PAHs to the oceans of the world is 1.1106 tonnes (Ivwurie, 2004). The main anthropogenic sources of carcinogenic PAHs are emissions from fossil fuel combustion in industrial and power plants, automobile emissions, biomass burning, agricultural burning and natural gas utilization. Fossil fuel utilization is the major cause of anthropogenic PAH occurrence in the environment. Hence, emphasis is placed on these sources below. 2.2.1 PAHs from Coal Combustion and Conversion Processes Coal, an organic rock formed from the accumulation and burial of partially decomposed vegetation in previous geologic ages through a series of physical, biological and biochemical changes; is a major fossil fuel for heating and power generation. The predominant organic components in coal have resulted from the formation and condensation of polynuclear carboxylic and heterocyclic ring compounds containing carbon, hydrogen, oxygen, nitrogen and sulphur (United Nations, 1973). Due to its chemical composition (heterogeneous macro-molecular matrix, including hydrocarbons and hetero-atomic moieties) various coal conversion and utilizations are significant contributors of PAHs to the environment. Coal combustion emissions 47 PAH compounds resulting from coal combustion residing in fly ash, grate ash or the stack emissions were identified in the work of Junk and Ford (1980, cited in Chadwick et al., 1987). However, these PAH emissions are a function of the efficiency of the coal combustion plant. On the whole, large, efficient coal-burning, electricity-generating plants, with high combustion temperatures, emit relatively low total amounts of PAH and contribute very little to PAH emissions when operated properly (Chadwick et al., 1987). PAH emission factors for coal-fired plants were put at 32ugkg-1 and 41ugkg-1 coal by Ramdahl et al. (1983) and Masclet et al. (1987) respectively. 70% of the total PAH emission flux from power plants is made up of 3-4 ring PAHs and their alkylated counterparts (Wild and Jones, 1995). 5-6 ring PAHs and their heteroatom-containing derivatives are emitted from coke ovens during coal carbonisation (Kirton et al., 1991) Coal carbonization emissions Coal carbonization, the pyrolytic decomposition of coal in the absence of oxygen, can be classified according to the temperature to which the coal is heated, as shown in Table 3. This process yields char or coke, tar and oven or coal gas as the major products. Coke is by far the most important product in terms of yield and revenue. However, leakages from coke ovens are sources of release of high levels of PAHs and other organics to the environment. Emissions from coke ovens range from volatile monoaromatics (alkyl benzenes) to 5-6 ring PAHs together with their substituted heteroatom derivatives such as O-PAHs, NPAHs and S-PAHs (Lao et al., 1975; Kirton et al., 1991). Anderson et al. (1983) determine

Essay on Names in The Odyssey and The Bible -- comparison compare cont

Importance of Names in The Odyssey and The Bible      Ã‚   Two of the most widely studied ancient works are Homer’s Odyssey and the book of Genesis from the Bible.   Each of these texts provides a unique viewpoint of an early civilization.   In both of the texts, one can learn not only stories about great heroes, but also about the way that these peoples lived and what they believed.   Many interesting parallels can be drawn between the two developing societies shown in the Odyssey and the book of Genesis.   One parallel is the importance placed on names by each culture. Although viewed as important in different ways, the value placed on a name shows a striking similarity between the evolving cultures of both the Greeks and the Hebrews.   Ã‚  Ã‚  Ã‚   In the Odyssey, Homer’s characters frequently allude to the importance of names.   For these ancient Greeks, a name symbolizes one’s identity, ancestry, and honor.   It is the one thing a man always owns, even if he possesses nothing else.   This is clearly shown through the hero, Odysseus.   While traveling home from the Trojan War, Odysseus, in effect, loses his title, land, and power for twenty years.   He remains with nothing but his name to speak for his character and person.   As he himself says at the beginning of Book IX when beginning to tell his story to the Phaiacians, â€Å"First of all I will tell you my name, and then you may count me one of your friends if I live to reach my home, although that is far away.   I am Odysseus Laertiades, a name well known in the world as one who is ready for any event.†Ã‚   Although away from his home and all things that could speak well of him, Odysseus is still in possession of his nam e, which clearly shows his good character.   This speech of Odysseus also show... ... to be carefully guarded, for if everything else is lost, it remains forever.   Thus, there is nothing more precious to a man than to have a name that carries intrinsic honor and meaning throughout his whole life.   A man is defined by who he is, and that is shown best through his name.   As clearly shown in the texts, to have a good name and to be remembered by it ought to be the main goal for any and every man.    Works Cited and Consulted Bloom, Harold ,   Homer's Odyssey: Edited and with an Introduction, NY, Chelsea House 1988 Heubeck, Alfred, J.B. Hainsworth, et al. A commentary on Homer's Odyssey. 3 Vols. Oxford PA4167 .H4813 1988 Homer. The Odyssey. Trans. Robert Fitzgerald. New York: Vintage Books, 1989. Tracy, Stephen V. ,The Story of the Odyssey Princeton UP 1990 The Holy Bible. New Revised Standard Version. Grand Rapids: Zondervan, 1989.

Factors Affecting Fermentation of Glucose by Yeast

Fermentation is anaerobic respiration whereby food is altered into more simple compounds and energy in the form of chemicals is produced, an example being adenosine triphosphate (biology-online. org/dictionary/Fermentation). All this occurs with the lack of atmospheric oxygen. At the end of the day alcohol and carbon dioxide are the end products when yeast is used in the fermentation procedure. But end products like acetic acid or lactic acid can also be gained depending on the circumstances. The salinity, air conditions, temperature, pH of the system, the enzyme systems of microorganisms, and the type of sugars being fermented can show a variety in the type of end products produced. In this study the tube with the highest amount of chlorine is added, an increase in the rate of fermentation should be observed. Methods and Materials: 100ml of the stock solution of 10% glucose was placed into four separate beakers. Each beaker was labeled â€Å"1 (control),† â€Å"2 (5 drops),† â€Å"3 (10 drops),† and â€Å"4 (15 drops)†. Five drops of 6% sodium hypochlorite was added to beaker #2, 10 drops to beaker #3, and 15 drops to beaker #4. The contents of the yeast suspension were then stirred thoroughly to be sure the yeast cells were suspended and not settled at the bottom and to each solution 50ml of the yeast suspension was added. The contents of each beaker were stirred with a glass stirring rod to mix the solutions thoroughly. Each of the four fermentation tube bowls were filled with one of the solutions and the tubes were tilted so that the vertical arm was full, but the bowl was nearly empty. Each fermentation tube was labeled in order to indicate its contents. The tubes were placed in a warm place (in an incubator or near a heat lamp). Every 10 minutes for 90 minutes a measurement was made and the amount of gas produced in each of the four fermentation tubes was recorded and graphed. Results: Figure 1 As shown in figure 1, this study revealed that when chlorine was added there was a decline in the fermentation tubes excluding group â€Å"two,† the five drop tube. Therefore this observation concluded that when there’s a large amount of chlorine the fermentation rate slowed down. But when there was a little amount of chlorine there was increase in the rate of fermentation. An average of about 15 additional minutes were spared in order to equal the amount of fermentation in the control tube and five drop tube when large amounts of chlorine were evident. Discussion: All four beakers were evaporated by the 60 minute mark. The solution with five drops was the first to completely evaporate, following with the control group, the 10 drops and finally the 15 drops. No real conclusions could be drawn from this study because of the order in which the evaporation was completed. This lab also generates questions that could not have been asked before the lab. Why do some fermentation tubes have all their solution evaporate and not others? What would have happened if more yeast solution were added to the fermentation tubes? With the information discovered, experimenters know some of the different factors affecting fermentation of glucose by yeast. This information will help alcoholic fermentation in the wine and beer industries.

All American Jazz Music essays

All American Jazz Music essays Jazz music came about in the city of New Orleans, Louisiana. It is considered to be Americas Music. People call it this because of the way it was developed. In the mid 1800s, during the times of slavery and segregation, the art of jazz music swept over the south. Particularly Louisiana. Blacks, whites, men and women of all ages and backgrounds came together and created a new, more artsy form of music that is known as jazz. What makes jazz music so special is that it is one of a kind and that it is unpredictable. People would just get together and play their instruments, usually the bass, trumpet or piano, and make beats and play any sporadic melody that came to them. The music was enjoyed by many, and was a sort of doorway for many other kinds of music to be developed from. These other kinds of music include the blues and ragtime. During the time period that jazz was developed, it was a way for both the musicians and the listeners to forget their problems and just enjoy what they were hearing. Jazz spread quickly and was soon spread throughout the south and became popular with all kinds of people. Slaves would sing and doo-wop on their plantations to help pass time. Many believe that this was also partly responsible for the birth of Jazz music. Throughout the jazz era, slavery was in full gear in the south. Within a few years, the civil war broke out. Jazz was not only played for listening pleasure, jazz was played as a way to express feelings and tell stories. This was called the blues. The blues was a form of jazz in which there would be a slow beat and a rhythmic story being told in sync with the beat. The sudden wave of another form of jazz called ragtime brought about mixed feelings. This was upbeat music and caught the attention of many of the younger listeners. This brought on the age of Flappers. Flappers were young women who felt free and wore shorter skirts and had shorter hair. Th ...

Overview of Spanish Verb Tenses

Overview of Spanish Verb Tenses It almost goes without saying that the tense of a verb depends upon when the verbs action takes place. So it shouldnt be surprising that the Spanish word for tense in the grammatical sense is tiempo, the same as the word for time. In the simplest sense, there are three tenses: the past, present, and future. Unfortunately for anyone learning most languages, including English and Spanish, it is seldom that simple. Spanish also has a tense not connected to time, as well as two types of simple past tenses. Overview of Spanish Tenses Although both Spanish and English have complex tenses that use auxiliary verbs, students often begin by learning four types of simple tenses: The present tense is the most common tense and the one invariably learned first in Spanish classes.The future tense is most often used to refer to events that havent happened yet, but it can also be used for emphatic commands and, in Spanish, to indicate uncertainty about current happenings.The past tenses of Spanish are known as the preterite and the imperfect. To simplify, the first is usually used to refer to something that happened at a specific point in time, while the latter is used to describe events where the time period isnt specific.The conditional tense, also known in Spanish as el futuro hipotà ©tico, the future hypothetical, is different than the others in that it isnt clearly connected with a particular time period. As the name implies, this tense is used to refer to events that are conditional or hypothetical in nature. This tense should not be confused with the subjunctive mood, a verb form that also can refer to actions that arent necessarily real. Verb Conjugation In Spanish, verb tenses are formed by changing the endings of verbs, a process known as conjugation. We sometimes  conjugate verbs  in English, for example adding -ed to indicate the past tense. In Spanish, the process is much more extensive. For example, the future tense is expressed using conjugation rather than by using an additional word such as will or shall in English. There are five types of conjugation for simple tenses: Present tenseImperfectPreteriteFutureConditional In addition to the simple tenses already listed, it is possible in both Spanish and English to form what is known as the perfect tense by using a form of the verb haber in Spanish, to have in English, with the past participle. These compound tenses are known as present perfect, the pluperfect or past perfect, the preterite perfect (limited mostly to literary use), the future perfect and the conditional perfect. A Closer Look at Spanish Tenses Although the tenses of Spanish and English are very much alike- after all, the two languages share a common ancestor, Indo-European, with origins dating to prehistoric times- Spanish has some peculiarities in its tense usage: The differences in the past tenses of ser and estar can be especially subtle.Sometimes, the word used to translate a Spanish verb can vary depending on the tense used.It is possible to describe events that will happen in the future without using the future tense.While the English auxiliary verb would is often an indication that the conditional tense is being used, such isnt always the case.Although the conditional tense is a common one, there are also  conditional sentences that use other forms of verbs.By using estar as an auxiliary verb in the various tenses, it is possible to form progressive verbs that can be used in various tenses.

Behavior Management Project Research Paper Example | Topics and Well Written Essays - 3500 words

Behavior Management Project - Research Paper Example At some point, Brian has difficulties in interpreting academic instructions more particularly in absence of an adult help. When presented with academic instructions or exams, Brian would progressively become angry, uneasy, breaking down and crying profusely. In order to help Brian deal with these problems, the following behaviour intervention plan was designed. For a period of two weeks, Brian will be required to have a full time company of an adult helper while in class who will help him read questions whenever he is unable to read or finds it difficult. The adult will leave at a scheduled three time period every hour. Each break will last utmost 3 minutes in duration. It is expected that during this period, Brian will most likely face individual reading exam and would either get angry or cry uncontrollably causing a halt in exam administration. In addition, he may fail to complete his exam. The behavioural plan designed is aimed at teaching him the essence of self-control in his co nduct while dealing stressful situations in school and life after. During the interaction session, he will be taught how to manage his behaviour. In this regard, on the event he faces difficulty and senses a feeling of anger he will be required to stop whatever he does and raise up his hand for a short break. This would then be followed by a support schedule that would be given consistently and then slowly withdrawn. This is important in instilling in him the expected end behaviour without necessarily using reinforcement. After numerous weeks of implementing the intervention plan, it was found that on average the difficulties experienced in reading reduced considerably. However, some traces of anger would still be witnessed for example Brian would occasionally be noticed frowning during or after the exam or a reading session in class. If this recommended plan is continued, the end result would be desirable. Introduction Target behaviour Brian, a third grade student, is a normal stud ent like others except that he has difficulties in reading and working out questions by himself. This behaviour normally begins some few minutes after the start of examination session and worsens as it nears the end. The tension first rises then followed by a show of frustration and anger and eventual loud cry sobbing uncontrollably. The crying can last for a period of between 5 and 10 minutes and always happens whenever examinations are administered across all subjects. Hypothesis It is hypothesized from his behaviour that Brian engages in crying when he fails to recall what was taught in class prior to exam administration. He therefore thinks the exam given is too difficult and meant to frustrate him. He engages in crying as a means of letting off stress and as a show of frustration on the teachers. This behaviour is normally caused by inadequate preparation and excessive parental expectation. At the beginning of every examination, he actually needs the presence of one of the pare nts or an equivalent helper whose work is to acknowledge every simple step he makes in doing the exam. Rationale In order to assist Brian to do his work independently and deal adequately with his unworthy behaviour, there is a need to design and teach him necessary tools required to enhance self-control. His behaviour of crying whenever he fails to memorize what was earlier taught in class can effectively be minimized by teaching

Supply Chain Risk Management Essay Example | Topics and Well Written Essays - 3750 words

Supply Chain Risk Management - Essay Example Therefore, the significance of supply chain management theories and their usage in all industry types has increased greatly. Supply chains are evolved by companies for fulfilling business needs and functions. Supply chains help business to survive and grow. Each business is a part of the supply chain completing the assigned task. A multi-tier supply chain includes various flows i.e. financial flow, Information flow and material flow. Third party logistics (3PL) services providers who manage and perform specific logistic functions for other companies arrange the inbound and outbound logistic functions of the suppliers or owners (Khan et al., 2010). The term â€Å"supply chain management† came into usage in the 1990s for earlier used terms like â€Å"logistics† and â€Å"operations management†. â€Å"A supply chain is a network of facilities and distribution options that performs the functions of procurement of materials, transformation of these materials into int ermediate and finished products, and the distribution of these finished products to customers.†Ã¢â‚¬â€Ganeshan and Harrison (1995)). ... The first level is completed via internal supply chain management activities associated with logistics and procurement. Procurement for companies’ stock can stockpile high inventory levels and additional transport costs if the inventory is not consumed due to lack of demand (Kannegiesser et al., 2007). The second echelon can help companies in optimizing supply chain processes via integrated management of supply chains. The central focus of supply chain management is to manage the risk of overflowing inventories and inefficient handling of information not only within the company but among all supply chain members, which could be original equipment manufacturers (OEM), maintenance, repair and overhauling (MROs) or third-party logistics (3PL) partners to minimize stock levels and achieving optimization in resource usage (Kannegiesser et al., 2007). As such, the aim of supply chain management is to cover the cost risk, to offer the desired service level and fulfill customer expect ations. Production and distribution functions have to be integrated to achieve optimum performance volumes. As decisions on quantity and price of stock can not be taken beforehand, any drawback in integrated approach can reduce the profit margins although cost-cutting has been used as a tool in supply chain management (Kannegiesser et al., 2007). Research Background -- Theory Before discussing the study outcomes on total logistic costs based on general modeling approach, some theoretical background on current literature is necessary. There are two types of studies on logistic costs. One type deals with strategic parts of logistics and the other with optimal logistic decisions. This is the second type, which helps in mitigating risks, the leading purpose of which is finding system costs, which