Bio-remediation of Oil Spills using Microbes Essay

Bio-remediation of Oil Spills using Microbes - Essay Example Apart from the above, people illegally may dump the pollutants such as the crude oil into the sea. Moreover, terrorists may also cause the oil spills just to destroy the country’s resources. The major victims of the oil spills occurring in the sea would be the aquatic animals and other marine living organisms which include plants under the sea. Thus, cleaning up and recovering from the oil spill are a major tasks and it is mainly based on the factors such as the nature of the oil that is being spilled, the quantity or the amount and the nature of the area being affected. There are different methods for cleaning up the oil spills which ensemble chemical treatment and Bioremediation. Bioremediation is the process of using the microorganisms to break down and remove the pollutants. â€Å"Bioremediation usually involves the use of biological agents to detoxify a contaminated environment† (Thangarajan et al., 2011). Thus, the noxious wastes of the oil spill can be effectivel y treated using microorganisms isolated and selected from the oil-contaminated environments to biodegrade the hydrocarbons in oil spill are a very promising technique for treatment of oil spills. This paper will feature the function of certain species of bacteria such as Pseudomonas aeruginosa and Bacillus subtilis and their role in Bio-remediation. Biodegradation by natural population of microorganisms can be considered as one of the primary mechanism by which the oil spills which are rich in petroleum hydrocarbons can be eradicated from the environment. The major success of the oil spills bioremediation mainly depends on the nature of the hydrocarbons and one’s ability to maintain and establish the conditions that favors the growth of the microorganisms in the particular contaminated environment. Therefore, the physical and the chemical characteristic of the oil and the oil spill area are the vital determinants in the bioremediation process. Thus, bioremediation encompasses the accelerated biodegradation in a natural way. Bioremediation techniques can be carried out in two different ways namely the in-situ or ex-situ methods. â€Å"In in-situ processes, the biological remediation is conducted at the contaminated site, whereas in ex-situ processes, the contaminated medium is extracted and processed off-site purification facilities.† (Rezende et al, n.d). Thus, bioremediation involves the processes of biostimulation and bioaugmentation. The Phenomenon of biostimulation comprises of addition of nutrients such as nitrogen, potassium and phosphorous and thereby enhancing the growth of the microorganisms through adjusting the environmental conditions such as the temperature, moisture and aeration etc. Thus, most of the bacterial species such as Pseudomonas, Bacillus and Cornybacterium are able to degrade the contaminants effectively under favorable environmental conditions and enriched nutrient supply. (Salami & Elum, 2008). On the other hand, the ot her phenomenon known as the bioaugmentaion where the microorganisms are able to degrade the specific oil spill contaminants namely the hydrocarbons are also being implemented. Therefore, bioremediation can be clearly understood as the phenomenon that exploits the microbial diversity and their metabolic versatility to convert noxious chemical oil spill contami

Lifestyle of blackfoot Essay Example | Topics and Well Written Essays - 1250 words

Lifestyle of blackfoot - Essay Example Buffalo hunting is their major hunting activity. â€Å"The Blackfoot Indian tribe displayed agility in hunting buffalo that outranked other tribes. Their nomadic lifestyle was aided by dogs and later horses. They seldom fought over land but were great warriors in their own right† (Blackfoot Indian Tribe). This paper analyses different aspects of Blackfoot’s life styles. Because of huge diversity in culture, the life styles of Blackfoot (Also known as Blackfeet) people are different. Different languages, clothing, hunting methods, worshipping methods, food habits and hobbies are prevailing among the Blackfoot community because of the differences in their ethnicity. â€Å"Mi'kmaq, Cree, Ojibwa, Arapaho, Shawnee, Fox, Algonquin† etc are some of the major languages in the Blackfoot community (Tribal Lifestyle, Gender Roles, Elders). â€Å"The members of a Blackfoot Indian tribe spoke a language called Pikunii. This is language was lyrical and musical to the ear with complex word formations. The language was learned by word of mouth and there was no written language† (Blackfoot Indian Tribe). ... In other words, inter-tribal marital relationship is also possible among some of the tribal groups of the Blackfoot community. â€Å"There are three main clans in the Blackfoot community: The Kainai (Many Leaders, also called the Blood); The Piikani (Amsskaapipiikani in Montana and Apatohsipiikani in southern Alberta also called the Peigan ); The Siksika (Blackfoot, also called northern Blackfoot)† (Tribal Lifestyle, Gender Roles, Elders). Even though, these clans have lot of differences in their life styles, the elements of a common culture can be seen in the life styles of these people. â€Å"Each tribe in Blackfoot community consisted of a number of hunting bands, which were the primary political units of the tribe† (Hanes & Pifer). Each hunting band may have two leaders; one for leading the group for hunting activities and the other for leading the group in other social and political activities. The hunting leader would be an expert hunter whereas the other leader w ould be a person with immense capabilities in solving the social problems. In case of any disputes occur, the final word comes from either the hunting leader or the civilian leader. During ancient period, arrows and lances were the major war weapons of the Blackfoot community. Blackfoot community had no hesitation in engaging in war with other tribal groups. They were clever warriors and their fighting spirit and better war strategy helped them to expand their territories. The Blackfoot or Siksikas were one of the most famous of the northern tribes, largely due to the fact that they were among the first to encounter and form relationships with European fur traders. Through this contact, the people of the Siksika nation became familiar with the objects, inventions and animals brought by these

Single Stage to Orbit (SSTO) Propulsion System

Single Stage to Orbit (SSTO) Propulsion System This paper discusses the relevant selection criteria for a single stage to orbit (SSTO) propulsion system and then reviews the characteristics of the typical engine types proposed for this role against these criteria. The engine types considered include Hydrogen/Oxygen (H2/O2) rockets, Scramjets, Turbojets, Turborockets and Liquid Air Cycle Engines. In the authors opinion none of the above engines are able to meet all the necessary criteria for an SSTO propulsion system simultaneously. However by selecting appropriate features from each it is possible to synthesise a new class of engines which are specifically optimised for the SSTO role. The resulting engines employ precooling of the airstream and a high internal pressure ratio to enable a relatively conventional high pressure rocket combustion chamber to be utilised in both airbreathing and rocket modes. This results in a significant mass saving with installation advantages which by careful design of the cycle thermodynamics enable s the full potential of airbreathing to be realised. The SABRE engine which powers the SKYLON launch vehicle is an example of one of these so called Precooled hybrid airbreathing rocket engines and the conceptual reasoning which leads to its main design parameters are described in the paper. Keywords: Reusable launchers, SABRE, SKYLON, SSTO 1.Introduction Several organisations world-wide are studying the technical and commercial feasibility of reusable SSTO launchers. This new class of vehicles appear to offer the tantalising prospect of greatly reduced recurring costs and increased reliability compared to existing expendable vehicles. However achieving this breakthrough is a difficult task since the attainment of orbital velocity in a re-entry capable single stage demands extraordinary propulsive performance. Most studies to date have focused on high pressure hydrogen/oxygen (H2/O2) rocket engines for the primary propulsion of such vehicles. However it is the authors opinion that despite recent advances in materials technology such an approach is not destined to succeed, due to the relatively low specific impulse of this type of propulsion. Airbreathing engines offer a possible route forward with their intrinsically higher specific impulse. However their low thrust/weight ratio, limited Mach number range and high dynamic pressure trajectory have in the past cancelled any theoretical advantage. By design review of the relevant characteristics of both rockets and airbreathing engines this paper sets out the rationale for the selection of deeply precooled hybrid airbreathing rocket engines for the main propulsion system of SSTO launchers as exemplified by the SKYLON vehicle [1]. 2. Propulsion Candidates This paper will only consider those engine types which would result in politically and environmentally acceptable vehicles. Therefore engines employing nuclear reactions (eg: onboard fission reactors or external nuclear pulse) and chemical engines with toxic exhausts (eg: fluorine/oxygen) will be excluded. The candidate engines can be split into two broad groups, namely pure rockets and engines with an airbreathing component. Since none of the airbreathers are capable of accelerating an SSTO vehicle all the way to orbital velocity, a practical vehicle will always have an onboard rocket engine to complete the ascent. Therefore the use of airbreathing has always been proposed within the context of improving the specific impulse of pure rocket propulsion during the initial lower Mach portion of the trajectory. Airbreathing engines have a much lower thrust/ weight ratio than rocket engines (à ¢Ã¢â‚¬ °Ã‹â€ 10%) which tends to offset the advantage of reduced fuel consumption. Therefore vehicles with airbreathing engines invariably have wings and employ a lifting trajectory in order to reduce the installed thrust requirement and hence the airbreathing engine mass penalty. The combination of wings and airbreathing engines then demands a low flat trajectory (compared to a ballistic rocket trajectory) in order to maximise the installed performance (i.e. (thrust-drag)/fuel flow). This high dynamic pressure trajectory gives rise to one of the drawbacks of an airbreathing approach since the airframe heating and loading are increased during the ascent which ultimately reflects in increased structure mass. However the absolute level of mass growth depends on the relative severity of the ascent as compared with reentry which in turn is mostly dependant on the type of airbreathing engine selected. An a dditional drawback to the low trajectory is increased drag losses particularly since the vehicle loiters longer in the lower atmosphere due to the lower acceleration, offset to some extent by the much reduced gravity loss during the rocket powered ascent. Importantly however, the addition of a set of wings brings more than just performance advantages to airbreathing vehicles. They also give considerably increased abort capability since a properly configured vehicle can remain in stable flight with up to half of its propulsion systems shutdown. Also during reentry the presence of wings reduces the ballistic coefficient thereby reducing the heating and hence thermal protection system mass, whilst simultaneously improving the vehicle lift/drag ratio permitting greater crossrange. The suitability of the following engines to the SSTO launcher role will be discussed since these are representative of the main types presently under study within various organisations world-wide: Liquid Hydrogen/Oxygen rockets Ramjets and Scramjets Turbojets/Turborockets and variants Liquid Air Cycle Engines (LACE) and Air Collection Engines (ACE) Precooled hybrid airbreathing rocket engines (RB545/SABRE) 3.Selection Criteria The selection of an optimum propulsion system involves an assessment of a number of interdependant factors which are listed below. The relative importance of these factors depends on the severity of the mission and the vehicle characteristics. Engine performance Useable Mach number and altitude range. Installed specific impulse. Installed thrust/weight. Performance sensitivity to component level efficiencies. Engine/Airframe integration Effect on airframe layout (Cg/Cp pitch trim structural efficiency). Effect of required engine trajectory (Q and heating) on airframe technology/materials. Technology level Materials/structures/aerothermodynamic and manufacturing technology. Development cost Engine scale and technology level. Complexity and power demand of ground test facilities. Necessity of an X plane research project to precede the main development program. 4.Hydrogen/Oxygen Rocket Engines Hydrogen/oxygen rocket engines achieve a very high thrust/weight ratio (60-80) but relatively low specific impulse (450-475 secs in vacuum) compared with conventional airbreathing engines. Due to the relatively large à ¢Ã‹â€ Ã¢â‚¬  V needed to reach low earth orbit (approx 9 km/s including gravity and drag losses) in relation to the engine exhaust velocity, SSTO rocket vehicles are characterised by very high mass ratios and low payload fractions. The H2/O2 propellant combination is invariably chosen for SSTO rockets due to its higher performance than other alternatives despite the structural penalties of employing a very low density cryogenic fuel. In order to maximise the specific impulse, high area ratio nozzles are required which inevitably leads to a high chamber pressure cycle in order to give a compact installation and reduce back pressure losses at low altitude. The need to minimise back pressure losses normally results in the selection of some form of altitude compensating nozzle since conventional bell nozzles have high divergence and overexpansion losses when running in a separated condition. The high thrust/weight and low specific impulse of H2/O2 rocket engines favours vertical takeoff wingless vehicles since the wing mass and drag penalty of a lifting trajectory results in a smaller payload than a steep ballistic climb out of the atmosphere. The ascent trajectory is therefore extremely benign (in terms of dynamic pressure and heating) with vehicle material selection determined by re-entry. Relative to airbreathing vehicles a pure rocket vehicle has a higher density (gross take off weight/volume) due to the reduced hydrogen consumption which has a favourable effect on the tankage and thermal protection system mass. In their favour rocket engines represent broadly known (current) technology, are ground testable in simple facilities, functional throughout the whole Mach number range and physically very compact resulting in good engine/airframe integration. Abort capability for an SSTO rocket vehicle would be achieved by arranging a high takeoff thrust/weight ratio (eg: 1.5) and a large number of engines (eg: 10) to permit shutdown of at least two whilst retaining overall vehicle control. From an operational standpoint SSTO rockets will be relatively noisy since the high takeoff mass and thrust/weight ratio results in an installed thrust level up to 10 times higher than a well designed airbreather. Reentry should be relatively straightforward providing the vehicle reenters base first with active cooling of the engine nozzles and the vehicle base. However the maximum lift/drag ratio in this attitude is relatively low (approx 0.25) limiting the maximum achievable crossrange to around 250 km. Having reached a low altitude some of the main engines would be restarted to control the subsonic descent before finally effecting a tailfirst landing on legs. Low crossrange is not a particular problem providing the vehicle operator has adequate time to wait for the orbital plane to cross the landing site. However in the case of a military or commercial operator this could pose a serious operational restriction and is consequently considered to be an undesirable characteristic for a new launch vehicle. In an attempt to increase the crossrange capability some designs attempt nosefirst re-entry of a blunt cone shaped vehicle or alternatively a blended wing/body configuration. This approach potentially increases the lift/drag ratio by reducing the fuselage wave drag and/or increasing the aerodynamic lift generation. However the drawback to this approach is that the nosefirst attitude is aerodynamically unstable since the aft mounted engine package pulls the empty center of gravity a considerable distance behind the hypersonic center of pressure. The resulting pitching moment is difficult to trim without adding nose ballast or large control surfaces projecting from the vehicle base. It is expected that the additional mass of these components is likely to erode the small payload capability of this engine/vehicle combination to the point where it is no longer feasible. Recent advances in materials technology (eg: fibre reinforced plastics and ceramics) have made a big impact on the feasibility of these vehicles. However the payload fraction is still very small at around 1-2% for an Equatorial low Earth orbit falling to as low as 0.25% for a Polar orbit. The low payload fraction is generally perceived to be the main disadvantage of this engine/vehicle combination and has historically prevented the development of such vehicles, since it is felt that a small degree of optimism in the preliminary mass estimates may be concealing the fact that the real payload fraction is negative. One possible route forward to increasing the average specific impulse of rocket vehicles is to employ the atmosphere for both oxidiser and reaction mass for part of the ascent. This is an old idea dating back to the 1950s and revitalised by the emergence of the BAe/Rolls Royce HOTOL project in the 1980s [2]. The following sections will review the main airbreathing engine candidates and trace the design background of precooled hybrid airbreathing rockets. 5.Ramjet and Scramjet Engines A ramjet engine is from a thermodynamic viewpoint a very simple device consisting of an intake, combustion and nozzle system in which the cycle pressure rise is achieved purely by ram compression. Consequently a separate propulsion system is needed to accelerate the vehicle to speeds at which the ramjet can takeover (Mach 1-2). A conventional hydrogen fuelled ramjet with a subsonic combustor is capable of operating up to around Mach 5-6 at which point the limiting effects of dissociation reduce the effective heat addition to the airflow resulting in a rapid loss in nett thrust. The idea behind the scramjet engine is to avoid the dissociation limit by only partially slowing the airstream through the intake system (thereby reducing the static temperature rise) and hence permitting greater useful heat addition in the now supersonic combustor. By this means scramjet engines offer the tantalising prospect of achieving a high specific impulse up to very high Mach numbers. The consequent de crease in the rocket powered à ¢Ã‹â€ Ã¢â‚¬  V would translate into a large saving in the mass of liquid oxygen required and hence possibly a reduction in launch mass. Although the scramjet is theoretically capable of generating positive nett thrust to a significant fraction of orbital velocity it is unworkable at low supersonic speeds. Therefore it is generally proposed that the internal geometry be reconfigured to function as a conventional ramjet to Mach 5 followed by transition to scramjet mode. A further reduction of the useful speed range of the scramjet results from consideration of the nett vehicle specific impulse ((thrust-drag)/fuel flow) in scramjet mode as compared with rocket mode. This tradeoff shows that it is more effective to shut the scramjet down at Mach 12-15 and continue the remainder of the ascent on pure rocket power. Therefore a scramjet powered launcher would have four main propulsion modes: a low speed accelerator mode to ramjet followed by scramjet and finally rocket mode. The proposed low speed propulsor is often a ducted ejector rocket system employing the scramjet injector struts as both ejector nozzles to entrain air at low speeds and later as the rocket combustion chambers for the final ascent. Whilst the scramjet engine is thermodynamically simple in conception, in engineering practice it is the most complex and technically demanding of all the engine concepts discussed in this paper. To make matters worse many studies including the recent ESA Winged Launcher Concept study have failed to show a positive payload for a scramjet powered SSTO since the fundamental propulsive characteristics of scramjets are poorly suited to the launcher role. The low specific thrust and high specific impulse of scramjets tends to favour a cruise vehicle application flying at fixed Mach number over long distances, especially since this would enable the elimination of most of the variable geometry. Scramjet engines have a relatively low specific thrust (nett thrust/airflow) due to the moderate combustor temperature rise and pressure ratio, and therefore a very large air mass flow is required to give adequate vehicle thrust/weight ratio. However at constant freestream dynamic head the captured air mass flow reduces for a given intake area as speed rises above Mach 1. Consequently the entire vehicle frontal area is needed to serve as an intake at scramjet speeds and similarly the exhaust flow has to be re-expanded back into the original streamtube in order to achieve a reasonable exhaust velocity. However employing the vehicle forebody and aftbody as part of the propulsion system has many disadvantages: The forebody boundary layer (up to 40% of the intake flow) must be carried through the entire shock system with consequent likelihood of upsetting the intake flow stability. The conventional solution of bleeding the boundary layer off would be unacceptable due to the prohibitive momentum drag penalty. The vehicle undersurface must be flat in order to provide a reasonably uniform flowfield for the engine installation. The flattened vehicle cross section is poorly suited to pressurised tankage and has a higher surface area/volume than a circular cross section with knock-on penalties in aeroshell, insulation and structure mass. Since the engine and airframe are physically inseparable little freedom is available to the designer to control the vehicle pitch balance. The single sided intake and nozzle systems positioned underneath the vehicle generate both lift and pitching moments. Since it is necessary to optimise the intake and nozzle system geometry to maximise the engine performance it is extremely unlikely that the vehicle will be pitch balanced over the entire Mach number range. Further it is not clear whether adequate CG movement to trim the vehicle could be achieved by active propellant transfer. Clustering the engines into a compact package underneath the vehicle results in a highly interdependant flowfield. An unexpected failure in one engine with a consequent loss of internal flow is likely to unstart the entire engine installation precipitating a violent change in vehicle pitching moment. In order to focus the intake shock system and generate the correct duct flow areas over the whole Mach range, variable geometry intake/combustor and nozzle surfaces are required. The large variation in flow passage shape forces the adoption of a rectangular engine cross section with flat moving ramps thereby incurring a severe penalty in the pressure vessel mass. Also to maximise the installed engine performance requires a high dynamic pressure trajectory which in combination with the high Mach number imposes severe heating rates on the airframe. Active cooling of significant portions of the airframe will be necessary with further penalties in mass and complexity. Further drawbacks to the scramjet concept are evident in many areas. The nett thrust of a scramjet engine is very sensitive to the intake, combustion and nozzle efficiencies due to the exceptionally poor work ratio of the cycle. Since the exhaust velocity is only slightly greater than the incoming freestream velocity a small reduction in pressure recovery or combustion efficiency is likely to convert a small nett thrust into a small nett drag. This situation might be tolerable if the theoretical methods (CFD codes) and engineering knowledge were on a very solid footing with ample correlation of theory with experiment. However the reality is that the component efficiencies are dependant on the detailed physics of poorly understood areas like flow turbulence, shock wave/boundary layer interactions and boundary layer transition. To exacerbate this deficiency in the underlying physics existing ground test facilities are unable to replicate the flowfield at physically representative sizes , forcing the adoption of expensive flight research vehicles to acquire the necessary data. Scramjet development could only proceed after a lengthy technology program and even then would probably be a risky and expensive project. In 1993 Reaction Engines estimated that a 130 tonne scramjet vehicle development program would cost $25B (at fixed prices) assuming that the program proceeded according to plan. This program would have included two X planes, one devoted to the subsonic handling and low supersonic regime and the other an air dropped scramjet research vehicle to explore the Mach 5-15 regime. 6.Turbojets, Turborockets and Variants In this section are grouped those engines that employ turbocompressors to compress the airflow but without the aid of precoolers. The advantage of cycles that employ onboard work transfer to the airflow is that they are capable of operation from sea level static conditions. This has important performance advantages over engines employing solely ram compression and additionally enables a cheaper development program since the mechanical reliability can be acquired in relatively inexpensive open air ground test facilities. 6.1 Turbojets Turbojets (Fig. 1) exhibit a very rapid thrust decay above about Mach 3 due to the effects of the rising compressor inlet temperature forcing a reduction in both flow and pressure ratio. Compressors must be operated within a stable part of their characteristic bounded by the surge and choke limits. In addition structural considerations impose an upper outlet temperature and spool speed limit. As inlet temperature rises (whilst operating at constant Wà ¢Ã‹â€ Ã… ¡T/P and N/à ¢Ã‹â€ Ã… ¡T) the spool speed and/or outlet temperature limit is rapidly approached. Either way it is necessary to throttle the engine by moving down the running line, in the process reducing both flow and pressure ratio. The consequent reduction in nozzle pressure ratio and mass flow results in a rapid loss in nett thrust. However at Mach 3 the vehicle has received an insufficient boost to make up for the mass penalty of the airbreathing engine. Therefore all these cycles tend to be proposed in conjunction with a subsonic combustion ramjet mode to higher Mach numbers. The turbojet would be isolated from the hot airflow in ramjet mode by blocker doors which allow the airstream to flow around the core engine with small pressure loss. The ramjet mode provides reasonable specific thrust to around Mach 6-7 at which point transition to rocket propulsion is effected. Despite the ramjet extension to the Mach number range the performance of these systems is poor due mainly to their low thrust/weight ratio. An uninstalled turbojet has a thrust/weight ratio of around 10. However this falls to 5 or less when the intake and nozzle systems are added which compares badly with a H2/O2 rocket of 60+. 6.2 Turborocket The turborocket (Fig. 2) cycles represent an attempt to improve on the low thrust/weight of the turbojet and to increase the useful Mach number range. The pure turborocket consists of a low pressure ratio fan driven by an entirely separate turbine employing H2/O2 combustion products. Due to the separate turbine working fluid the matching problems of the turbojet are eased since the compressor can in principle be operated anywhere on its characteristic. By manufacturing the compressor components in a suitable high temperature material (such as reinforced ceramic) it is possible to eliminate the ramjet bypass duct and operate the engine to Mach 5-6 whilst staying within outlet temperature and spool speed limits. In practice this involves operating at reduced nondimensional speed N/à ¢Ã‹â€ Ã… ¡T and hence pressure ratio. Consequently to avoid choking the compressor outlet guide vanes a low pressure ratio compressor is selected (often only 2 stages) which permits operation over a wider flow range. The turborocket is considerably lighter than a turbojet. However the low cycle pressure ratio reduces the specific thrust at low Mach numbers and in conjunction with the preburner liquid oxygen flow results in a poor specific impulse compared to the turbojet. 6.3 Expander Cycle Turborocket This cycle is a variant of the turborocket whereby the turbine working fluid is replaced by high pressure regeneratively heated hydrogen warmed in a heat exchanger located in the exhaust duct (Fig. 3). Due to heat exchanger metal temperature limitations the combustion process is normally split into two stages (upstream and downstream of the ma- LHLH LOx/LH2 Fig. 1 Turbo-ramjet Engine (with integrated rocket engine). LOx/LH2LH2 LOx/LH2 Fig. 2 Turborocket. LH2LOx/LH2 Fig. 3 Turbo-expander engine. trix) and the turbine entry temperature is quite low at around 950K. This variant exhibits a moderate improvement in specific impulse compared with the pure turborocket due to the elimination of the liquid oxygen flow. However this is achieved at the expense of additional pressure loss in the air ducting and the mass penalty of the heat exchanger. Unfortunately none of the above engines exhibit any performance improvement over a pure rocket approach to the SSTO launcher problem, despite the wide variations in core engine cycle and machinery. This is for the simple reason that the core engine masses are swamped by the much larger masses of the intake and nozzle systems which tend to outweigh the advantage of increased specific impulse. Due to the relatively low pressure ratio ramjet modes of these engines, it is essential to provide an efficient high pressure recovery variable geometry intake and a variable geometry exhaust nozzle. The need for high pressure recovery forces the adoption of 2 dimensional geometry for the intake system due to the requirement to focus multiple oblique shockwaves over a wide mach number range. This results in a very serious mass penalty due to the inefficient pressure vessel cross section and the physically large and complicated moving ramp assembly with its high actuation loads. Similarly the exhaust nozzle geometry must be capable of a wide area ratio variation in order to cope with the widely differing flow conditions (Wà ¢Ã‹â€ Ã… ¡T/P and pressure ratio) between transonic and high Mach number flight. A further complication emerges due to the requirement to integrate the rocket engine needed for the later ascent into the airbreathing engine nozzle. This avoids the prohibitive base drag penalty that would result from a separate dead nozzle system as the vehicle attempted to accelerate through transonic. 7. Liquid Air Cycle Engines (LACE) and Air Collection Engines (ACE) Liquid Air Cycle Engines were first proposed by Marquardt in the early 1960s. The simple LACE engine exploits the low temperature and high specific heat of liquid hydrogen in order to liquify the captured airstream in a specially designed condenser (Fig. 4). Following liquifaction the air is relatively easily pumped up to such high pressures that it can be fed into a conventional rocket combustion chamber. The main advantage of this approach is that the airbreathing and rocket propulsion systems can be combined with only a single nozzle required for both modes. This results in a mass saving and a compact installation with efficient base area utilisation. Also the engine is in principle capable of operation from sea level static conditions up to perhaps Mach 6-7. LH2 LO2 Liquid Air Turbopump Fig. 4 Liquid Air Cycle Engine (LACE). The main disadvantage of the LACE engine however is that the fuel consumption is very high (compared to other airbreathing engines) with a specific impulse of only about 800 secs. Condensing the airflow necessitates the removal of the latent heat of vaporisation under isothermal conditions. However the hydrogen coolant is in a supercritical state following compression in the turbopump and absorbs the heat load with an accompanying increase in temperature. Consequently a temperature pinch point occurs within the condenser at around 80K and can only be controlled by increasing the hydrogen flow to several times stoichiometric. The air pressure within the condenser affects the latent heat of vaporisation and the liquifaction temperature and consequently has a strong effect on the fuel/air ratio. However at sea level static conditions of around 1 bar the minimum fuel/air ratio required is about 0.35 (ie: 12 times greater than the stoichiometric ratio of 0.029) assuming that the hydrogen had been compressed to 200 bar. Increasing the air pressure or reducing the hydrogen pump delivery pressure (and temperature) could reduce the fuel/ air ratio to perhaps 0.2 but nevertheless the fuel flow remains very high. At high Mach numbers the fuel flow may need to be increased further, due to heat exchanger metal temperature limitations (exacerbated by hydrogen embrittlement limiting the choice of tube materials). To reduce the fuel flow it is sometimes proposed to employ slush hydrogen and recirculate a portion of the coolant flow back into the tankage. However the handling of slush hydrogen poses difficult technical and operational problems. From a technology standpoint the main challenges of the simple LACE engine are the need to prevent clogging of the condenser by frozen carbon dioxide, argon and water vapour. Also the ability of the condenser to cope with a changing g vector and of designing a scavenge pump to operate with a very low NPSH inlet. Nevertheless performance studies of SSTOs equipped with LACE engines have shown no performance gains due to the inadequate specific impulse in airbreathing mode despite the reasonable thrust/weight ratio and Mach number capability. The Air Collection Engine (ACE) is a more complex variant of the LACE engine in which a liquid oxygen separator is incorporated after the air liquifier. The intention is to takeoff with the main liquid oxygen tanks empty and fill them during the airbreathing ascent thereby possibly reducing the undercarriage mass and installed thrust level. The ACE principal is often proposed for parallel operation with a ramjet main propulsion system. In this variant the hydrogen fuel flow would condense a quantity of air from which the oxygen would be separated before entering the ramjet combustion chamber at a near stoichiometric mixture ratio. The liquid nitrogen from the separator could perform various cooling duties before being fed back into the ramjet airflow to recover the momentum drag. The oxygen separator would be a complex and heavy item since the physical properties of liquid oxygen and nitrogen are very similar. However setting aside the engineering details, the basic thermodynamics of the ACE principal are wholly unsuited to an SSTO launcher. Since a fuel/air mixture ratio of approximately 0.2 is needed to liquify the air and since oxygen is 23.1% of the airflow it is apparent that a roughly equal mass of hydrogen is required to liquify a given mass of oxygen. Therefore there is no saving in the takeoff propellant loading and in reality a severe structure mass penalty due to the increased fuselage volume needed to contain the low density liquid hydrogen. 8. Precooled Hybrid Airbreathing Rocket Engines This last class of engines is specifically formulated for the SSTO propulsion role and combines some of the best features of the previous types whilst simultaneously overcoming their faults. The first engine of this type was the RB545 powerpla

Floods of 1998 in Bangladesh and Shrewsbury :: Papers

Floods of 1998 in Bangladesh and Shrewsbury Causes, Effects and responses to flooding In Shrewsbury The Severn Valley floods, Shrewsbury, UK 1998: Causes ====== The human causes of the floods were summed up by the then Shadow Countryside Minister Tim Yeo MP, he said 'the flooding had increased because of the housing developments on Greenfield sites.' By this he means that by covering the land with tarmac in urban areas humans have increased the rate of surface runoff and decreased the saturation levels of the ground. When surface runoff is high rainwater reaches the river faster. It would appear that the speed in which the water reached the river was too fast for the river to handle. The river filled up reaching bank-full discharge and then overflowing its banks onto the flood plain. The flood plain of the River Severn is built on, therefore, when the river floods it floods onto residential areas. With the building of these urban areas the amount of vegetation in the area surrounding the river was reduced, this affects the river two ways. It reduces the amount of interception, which in turn increases the speed of runoff into the river. The lack of vegetation also leads to the saturation of the ground. During the months of October and November the rainfall in the Severn Valley was high, as the water soaked into the ground it became saturated. More vegetation in the area would have meant the vegetation using the water would have decreased the amount of water in ground storage. Physical factors of the flood in 1998 are many; however, the most important one was the amount of rainfall. In October 1998 many areas received record amounts of rainfall caused by a 'hurricane'. This 'hurricane' brought very heavy rain and strong winds. The fact the rain was heavy means that the river did not have time to dissipate the water quick enough and the runoff was too fast, making the river rise t such an extent that it flooded.

Genetically Modified Foods and the Labeling Debate Essay

There has been an ongoing debate between consumers and the government regarding the use of Genetically Modified Foods in the market today. â€Å"Since the introduction of the â€Å"Flavr Savr† tomato, biotechnology companies continue to introduce genetically engineered agricultural products to consumers† (Whittaker). The â€Å"Flavr Savor† tomato was the first food available to consumers that was produced using technology involving the recombinant DNA techniques in 1993. This was the dawn of a new generation in food production, and thus a whole new world of genetically engineered foods. At the present time the government, more specifically, the United States Food and Drug Administration (FDA) has not regulated labeling products that contain genetically engineered foods. Currently the policy for labeling all consumer products must meet the standards of the safety and nutritional assessment. The evaluations of genetically engineered foods by legal authority require that bioengineered foods must meet the same standards set forth for all imported and exported foods marked for human and animal consumption and according to the US FDA genetically modified (GM) foods meet these guidelines. Since the early 1990’s scientists has been researching new and improved techniques to bring plumper, juicer and insecticide resistant agricultural products to all consumers. But research such as this is nothing new to the scientific community and for over 50 years techniques have been used to create strains of wheat, rice, pears and many more crop species to create high yielding products that are capable of growing anywhere and anytime of the year. Currently, only one tenth of the world actually uses GM plants with the countries of Canada, US, Brazil and Argentina growing 90 percent of the GM crops (Freedman). With the majority of these crops being produced in North America, the US is seeing GM foods everywhere and this is drawing attention to different agencies and groups pushing to educate the public by labeling any products that contain genetically engineered foods. The US Food and Drug Administration has been dealing with the battle against labeling products with genetically modified organisms (GMO) for years, but regardless of the consistent scrutiny the FDA sticks firmly to the current regulations that govern the labeling of all foods for human and animal consumption. Under the Federal Food, Drug and Cosmetic (FD&C) Act, which drives the FDA’s safety regulations for food and food ingredients, â€Å"unless a significant safety risk exists or there is a sincere need for consumers to distinguish between food products before purchase, the FDA hesitates to mandate labeling of food products† (Leggio). Joseph A. Levitt, Director of the Center for Food Safety and Applied Nutrition with the US Food and Drug Administration states in his â€Å"Should the FDA Adopt a Stricter Policy on Genetically Engineered Foods? † testimony that â€Å"bioengineered foods and food ingredients must adhere to the same standards of safety under the FD&C act that apply to their conventionally bred counterparts† (Levitt, 81). With the strict laws set forth, the FDA remains consistent with its decision to maintain their current labeling program as it adheres to all safety standards of any food for consumption. The US FDA also assures the public that they have done significant research for decades on biotechnology foods to ensure it is safe for consumers, and additional testing is conducted years prior to the release of a GM product to the shelves. Scientists address all of the potential concerns to include the potential to adding new allergy causing proteins, removing vital nutrients and the possibility of introducing toxins, in these studies to ensure that unexpected results do not occur, â€Å"this testing provides a way to detect such changes at the development stage† (Levitt, 79) and it will also delay any release of products until they are able to find a solution. The FDA takes such precautions and studying all aspects of this technology to be confident that the risks are non-existent. Although the government has provided the public with research, publications, testimonies and scientific proof that the current law governing the labeling of food and animal products is appropriate and doesn’t require change, there is still much concern of the risks that the technology poses to humans. Barbara Boxer, a US Senator from California, introduced the Genetically Engineered Food Right-To-Know Act in 2001 in her testimony in â€Å"Should the FDA Adopt a Stricter Policy on Genetically Engineered Foods? † which states â€Å"all foods containing or produced with genetically engineered material bear a neutral label† (Boxer, 76). This act was created based on the lack of data and concerns that GM products are introducing risks of exposure to many health issues to include food allergens, lack of nutrition and toxic ailments. These claims are legitimate, however, the US FDA does take precautions as stated by Joseph A. Levitt, specifically with these risks while conducting trials during the developing stages of the product. In 2011 there was a petition filed against the FDA which warranted the need for labeling of GM products. According to this petition â€Å"consumers are misled when food labels do not differentiate foods with known health properties from novel foods with unknown health consequences† (Burgaard). An example of such health concerns come from a study performed in Scotland at the Rowett Institute in 1998. A plant biochemist named Arpad Pusztai conducted an experiment on rats who consumed a genetically engineered potato and his experiment concluded that the rats that were fed the modified potato â€Å"suffered growth and immune system-related changes† (Freedman). Ironically, the genetically modified potato used in this study â€Å"was not intended for human consumption — it was, in fact, designed to be toxic for research purposes,† (Freedman) discrediting the research altogether. Additionally, â€Å"American Medical Association, the National Academy of Sciences, the World Health Organization, and more than twenty-five Nobel Prize-winning scientists have concluded that there is no scientific evidence that GM food carries any risk to human health and that genetically engineered crops are safe,† (Burgaard) which ties into the overall nutrition and safety assessment that genetically engineered foods meet the same standards that imported and exported foods at held too. In the end, the US Food and Drug Administration stands by the current law governing the policy on labeling genetically modified foods. They maintain their standing on mandated labeling even under the microscope of doubters, but most importantly the â€Å"FDA’s process for evaluating bioengineered foods is one in which the public can have confidence that food biotechnology products must meet the law’s safety standards† (Maryanski). The FDA cares deeply of the health and wellbeing of the consumers in America and strive to meet the needs of the public in both food and nutrition education. Until the studies show significant risks or changes in the GM products warranting the need to readdress the process, the government and the US Food and Drug Administration believe their approach is relevant and remain firm to the present policies. Annotated Bibliography Whittaker, Michael A. â€Å"Reevaluating The Food And Drug Administration’s Stand On Labeling Genetically Engineered Foods. † San Diego Law Review 35. 4 (1998): 1215. Academic Search Premier. Web. 2 Jan. 2014. This journal review argues that the United States Food and Drug Administration (FDA) must reconsider its position on the labeling of genetically engineered food as well as consumer perceptions of the threat posed by genetically engineered foods. Freedman, David H. â€Å"Are Engineered Foods Evil?. † Scientific American 309. 3 (2013): 80-85. Environment Complete. Web. 2 Jan. 2014. This article discusses the debate over the safety of genetically modified (GM) crops. It covers comments from agricultural and environmental economist at the University of California, Berkeley, David Zilberman, on the benefits of GM foods compared to their health risks, a ban on GM crops by the European Union (EU), and the difference between selective plant breeding and mutagenic techniques. Leggio, Kelly A. â€Å"Limitations On The Consumer’s Right To Know: Settling The Debate Over Labeling Of Genetically Modified Foods In The United States. † San Diego Law Review 38. 3 (2001): 893. Academic Search Premier. Web. 3 Jan. 2014. This journal review supports the decision of the United States Food and Drug Administration (FDA) to reject mandatory labeling of genetically modified foods as a solution to accommodate consumer fears. There is a description of an approach designed to evaluate whether mandatory initiatives are appropriate to protect consumer’s right to know and the importance for states to follow guidelines established by the FDA. â€Å"Should The FDA Adopt A Stricter Policy On Genetically Engineered Foods? PRO/CON. † Congressional Digest 80. 3 (2001): Pages 76-95. Academic Search Premier. Web. 2 Jan. 2014. This is a two part article that discusses genetically engineered foods and the potential need to adopt a more strict policy. The articles provided information from the perspective of the US Food and Drug Administration (FDA) Joseph A. Levitt, the director of the Center of Food Safety and Applied Nutrition and US Senator, Barbara Boxer who speaks on behalf of the Genetically Engineered Food Right-to-Know Act and additional interviews that were conducted to give the audience an overall understanding of both sides of the debate. Burgaard, Sudhir. â€Å"The Labeling Of Genetically Modified Foods Debate. † Natural Resources & Environment 28. 1 (2013): 55-57. Environment Complete. Web. 2 Jan. 2014. This article focuses on the debate on labeling of genetically modified (GM) food which reflects food safety concerns in the U. S. It highlights various legal issues related to use of GM foods which includes increased risk of antibiotic resistant bacteria, increased use of pesticides, and environmental effects. It briefs the audience about the Center for Food Safety filing a legal petition with the U. S. Food and Drug Administration regarding labeling of genetically engineered food. Maryanski, . James H. , Ph D. â€Å"News & Events. † Genetically Engineered Foods. US Food and Drug Administration, 19 Oct. 1999. Web. 2 Jan. 2014. This testimony is from the perspective of the Biotechnology Coordinator with the US Food and Drug Administration (FDA) that discusses the current regulations governing genetically engineered foods and the process that dictates what and how determines what a DNA derived food is labeled. It includes a variety of examples that justifies the current labeling regulations and why GM Foods may not require additional information for the consumers.

Late payment/collections

Dear Sir/Madam, I found my credit rating to be really poor because of a few late payments and collections that happened on my accounts. Even though there were a few mistakes and over sights from my side, most of the recent late payments were due to technical difficulties faced by the concerned banks. I made payment arrangements for $3869 to clear the account with Citi Financial retail. But the payment was delayed since the concerned department could not locate my account in their system.I faced problems with payments to WEB Bank and Qwest, since I was out of town. However I had an arrangement to pay $100 per month to WEB Bank and settle the remaining amount by January 2011. I was never intimated by Qwest regarding any outstanding amount whatsoever despite updating them about the change of address. I am ready to settle with Telenational Communications, although I never maintained an account with them.I had rented out my house after clearing all the bills with Colorado Springs Utilitie s till July 2010. The outstanding amount of $55 was supposed to be settled by the tenant. I have missed few payment deadlines due to oversight. The PAID accounts to THD/CBSD, Colorado Springs Utilities and the credit card accounts with Chase and Service credit Union have been cleared and the recent late payment was in September 2008.The accounts with Service Credit Union, ENT Federal CU, USAA, Military star, Chase Mortgage and Capital One Note Loan have been settled completely and in many cases the payment was late by a couple of days. But the numbers of such instances are few and most of them have occurred during my re-deployment. Since all the above mentioned outstanding has been cleared and considering the circumstances under which many of the incidents happened, I request you to kindly re-evaluate my credit score and update my credit report with the relevant details.

Serian Synogoges essays

Serian Synogoges essays Architecture plays a very important role in a culture, and from its remains, historians can gain a wealth of information. It determines the wealth of the community, the weather conditions and many other things. Not only can historians learn what it was like in that area at that time, but also they can learn from it to improve our area now. For example, the Romans built curved roads and sewers to prevent flooding and currently we also build our roads similarly. Another example can be the columns the Greeks used to build; now the White house and many other buildings are built in a Greek style. In fact, the entire Washington D.C. is built just like Paris; it is built in a circle around the White House, as Paris is built around the Eiffel Tower. Architecture and the arts have such power over people that Jews are thought to have horns because of a misinterpretation by Leonardo Divenchi, who portrayed Moses with horns. Now well take a look at architecture from a religious point of view. During the late Fifteenth century, refugees from Spain escaped to Muslim countries, mainly the Ottoman Empire. With them they brought the Sephardic traditions and culture and it quickly spread throughout the Mediterranean region. The Sephardic tradition eventually dominated the Syrian synagogue design and its architecture. Today, this beautiful architecture still remains in the Syrian community in Brooklyn. During the Ottoman period, the basilica form was popular. The Syrian synagogue usually had a wide central aisle and two side aisles. Arcades supported by columns separate it. Different parts of the room would be elevated, especially the tevah for illumination purposes. Many of the synagogues of Syria were very decorative; even the mandatory utensils of the synagogue, such as the lightbox, which was used to give off light to read the torah, would be very fancy. ...