The Islamic Conquests Essay Example | Topics and Well Written Essays - 1000 words

The Islamic Conquests - Essay Example In Empire to Commonwealth (12-19), historian Garth Fowden has delineated three separate geographical, cultural, and political spheres in Eurasia: China, India, and the Near East (the Fertile Crescent and the adjacent Mediterranean coast). These areas were all ancient centers of civilization and because of the distances and geographical barriers involved, had little interaction with each other. This is why China, India, and the Near East/Mediterranean can be thought of as continuous discrete civilizations even though throughout much of their history they lacked the political unity to provide full national identity. Although Islam eventually spread to all three areas, it origin and center lay in the Near East and it was only there that it became fully dominant. The Near East is unique among the three in having close interaction with a wide variety of surrounding areas. The Fertile Crescent is "a vortex that pulls inward and fuses what lies around it. So not only can the Fertile Crescent never enjoy long-term autonomy, but its unity can only be realized on a secure bases as part of a wider unification of the Iranian Plateau with the Mediterranean" (Fowden, 18). This unity was only achieved twice, in the first instance by the Achaemenid Empire (Alexander's fleeting unification of an even larger territory was based on Achaemenid Iran) in the sixth to fourth centuries BC, and in the seventh century by the Umayyad Caliphate. The initial Arab conquests unified the entire Fertile Crescent region with Iran for the first time in centuries, providing a secure economic, political, and geographical base fo r further conquests, for instance by allowing the Islamic state to compete on an even footing with the Byzantine navy (Fowden, 140). It may well be that the impetus to sustain large scale conquests into the eighth century came from the Islamic practice of providing for the army from the income of conquered lands collectively, rather than distributing the lands. This tended to keep the army in being (Karsh, 24). How did the initial Arab conquest succeed so well The Arabs' opponents in the area, the Byzantine and Sassanian Empires, were exhausted after a generation of fruitless war with each other over the Fertile Crescent and were in internal states of near collapse. In Iran, ultimately the loosing party in this conflict, on which the pressure was increased by Turkish invasions from the north (Christian, 260-285), the aftermath of defeat had led to assassination, civil war, and by 633 a state of anarchy in the empire (Nafziger and Walton, 18). Rome was also riven with internal dissensions (see below). So, to a large degree from a military perspective, the rapid Arab conquest of the Iranian state and of nearly half the territory of the Byzantine state, is to be attributed to the internal weakness of the defeated Empires rather to any special qualities of Islam. Other possible purely military factors to explain the Islamic conquests have been proposed, though with less plausibility. In Islam at War, Nafziger and Walton suggest a 'great man' solution to the problem of the Arab conquest, arguing that Khalid ibn al Waleed was "one of the great [sic] natural military leaders in all of human history" (16-17). But this hardly seems plausible. However remarkable Khalid's successes were on an operation level, and as astounding as his victories were, the were (as above) due more to the

Impact of Shale Gas on Seismic Activity

Impact of Shale Gas on Seismic Activity Is shale gas development responsible for increased seismic activity? 1. Introduction In recent years, shale gas has become the notorious poster child of the fossil fuel industry (Sovacool, 2014). Proponents tout it as being the answer to current energy needs given that it is available in abundance and has a lower carbon footprint than other fossil fuels e.g. coal and oil (Sovacool, 2014). Contrary to this, opponents have a firm stance against shale gas development, having concerns about its environmental impact. Shale gas has come under fire once again as a link between fracking and earthquakes has stirred up public emotions (Walsh, 2014). There has been a dramatic increase in the number of seismic events in the central and eastern regions of the United States. The US has seen over 300 earthquakes of magnitude 3.0 on the Richter scale over a period of three years (2010 to 2012) in comparison to an average of 21 events per year over the last three decades (Ellsworth, 2013). In several states such as Oklahoma, Colorado, Texas, Arkansas and Ohio these increased seismic events have been linked to underground injection of waste water from shale gas developments (Ellsworth, 2013). In the United Kingdom hydraulic fracturing at Preese Hall near Blackpool has been linked to two earthquakes of magnitude 2.3 and 1.5 on the Richter scale (Green, Styles Baptie, 2012). There are a number of procedural steps required for shale gas development that include the following: road and well pad construction, well drilling, casing, perforating, hydraulic fracturing, completion, production, abandonment and reclamation. This essay focuses on the underlying potential of hydraulic fracturing and underground waste water disposal to trigger seismic activities. Despite seismic activities being recorded at only a handful of the numerous shale gas development sites, the evidence indicates that increased seismic activity can be linked to shale gas development (Ellsworth, 2013). Even though the magnitude of these earthquakes are on the scale of being nuisances rather than catastrophes (Sovacool, 2014), there is a growing interest into understanding the cause of these events and the mitigation strategies to avoid larger catastrophes in terms of earthquakes or surface damage. 2. Induced Seismicity Induced seismic events are earthquakes triggered by human activity such as injecting fluids into rock formations for waste water disposal and hydraulic fracturing (National Research Council, 2013). Induced events have a much smaller magnitude than naturally occurring events and are therefore not usually felt on the Earth’s surface (Davies et al, 2013). Induced earthquakes take place when changes occur in the pore pressure-the pressure of fluid in the pores and fractures of rock-due to injection or withdrawal of fluids from the Earth’s subsurface. This change in pressure alters the stress on nearby faults, causing them to slip creating a seismic event. There are many factors that contribute to the magnitude and likelihood of an induced earthquake which include the injection rate, fluid pressure, fluid volume and injection duration (Davies et al, 2013). Since there is no physical difference between naturally occurring earthquakes and induced earthquakes it is difficult to determine the origin of a seismic event (National Research Council, 2013). A study conducted by Davis and Frohlich (1993) proposed criteria that have to be met in order to consider an earthquake as induced. These are: 1. Are these events the first known earthquakes of this character in the region? 2. Is there a clear correlation between injection and seismicity? 3. Are epicentres near wells (within 5km)? 4. Do some earthquakes occur at or near injection depths? 5. If not, are there known geologic structures that may channel flow to sites of earthquakes? 6. Are changes in fluid pressures at well bottoms sufficient to encourage seismicity? Based on these criterion the seismic activity in Dallas Fort Worth, USA was attributed to disposal of waste water from fracking activities (Frohlich et al, 2010) and the earthquakes at Preese Hall, UK were linked to hydraulic fracturing (Green, Styles Baptie, 2012). Figure 1 shows the 198 recorded global induced seismic events (Davies et al, 2013:p.178). Out of the 198 examples of induced seismicity hydraulic fracturing accounts for only 3 instances of ‘felt seismicity’ (seismic activity above magnitude 2.0 on the Richter scale) and waste water disposal, specifically from shale gas activities, also accounts for only 3 ‘felt’ seismic events (Davies et al, 2013). Figure 1. Frequency vs. magnitude for 198 published examples of induced seismicity (Davies et al, 2013:p.178) 3. Seismic activity due to hydraulic fracturing Hydraulic fracturing is the technique used to extract gas from ‘shale rock’ formations. Shale rock has large quantities of methane which are trapped in it due to its low permeability (The Royal Society and The Royal Academy of Engineering, 2012). In order to release the gas, fracking fluid is injected at high pressures to create fractures, increasing permeability of the rock and allowing gas to flow out. Micro-seismic events (less than magnitude 2 on the Richter scale) are often associated with the creation of faults in hydraulic fracturing, however their magnitude is too small to be felt on the surface (Davies et al, 2013). In the event of the presence of a pre-stressed fault near the fracked well a larger seismic event can occur although its magnitude will have an upper limit of 3 on the Richter scale (Green, Styles Baptie, 2012). The magnitude of induced seismicity is directly proportional to the surface area of the fault and degree of stress on the fault (The Royal Society and The Royal Academy of Engineering, 2012). The magnitude also depends on the pressure in the well, which is determined by the following factors (The Royal Society and The Royal Academy of Engineering, 2012): Volume of injected fracking fluid Volume of flow back fluid Injection rate Flow back rate The importance of controlling the well pressure can help mitigate seismicity, as seismic events have occurred only at wells where large volumes of fluid have been injected with little or no flow back leading to pressure build up (de Pater Baisch, 2011). The seismic activity observed at Blackpool, UK was linked to the hydraulic fracturing operations underway at Preese Hall due to spatial and temporal correlation (Green, Styles Baptie, 2012). Eisner et al (2011) conducted a study to look into the reasons behind the earthquakes, which concluded that the earthquakes were caused by injection of fracking fluid directly into an adjacent fault. The fluid injection had changed the pore pressure, reduced stress on the fault and caused it to slip resulting in a series of earthquakes. The earthquakes were also measured against the criteria suggested by Davis and Frohlich (1993) to determine whether they were induced or natural events (Eisner et al, 2011): Table 1. Criteria proposed by Davis and Frohlich (1993) to help differentiate between induced and natural seismicity applied to events at Preese Hall (Eisner et al, 2011:p. 21) The table above shows that the criteria were met and hence the events at Blackpool were classified as having been induced by hydraulic fracturing activities at Preese Hall. Mitigation: In order to avoid such events the Department of Energy and Climate Change introduced the following controls and checks for well operators (Department of Energy and Climate Change, 2014): Utilise all geological information available to determine the location of faults before drilling wells to ensure wells are at a distance from existing fault lines. Inject minimum amounts of fracking fluid Constantly monitor seismic activity Introduce ‘traffic light monitoring system’, which determines whether to proceed with injection or not on the basis of seismic activity magnitude. The implementation of these mitigation strategies would help operators assess location of faults before fracking, monitor seismic activity and stop even if minor tremors occur. 4. Seismic activity due to waste water disposal Waste water is a by-product of fracking and is often disposed of by being injected, under pressure, into disposal wells. Waste water injection increases underground pore pressure and weakens nearby faults, lubricating them, and causing them to slip resulting in an earthquake. The magnitude of induced seismic activity from waste water disposal is larger than that of fracking because it involves injection of larger volumes of fluid over a timespan of months or years (as opposed to a few days for fracking) causing greater pressures to build up (The Royal Society and The Royal Academy of Engineering, 2012). The upper limit of magnitude of seismicity induced by disposal in 5 on the Richter scale (Majer et al, 2007). In the USA links between waste water disposal and seismicity were drawn when a cluster of earthquakes were noticed in the Guy-Greenbrier area of Arkansas. Since the first disposal wells became operational in April 2009 this area experienced an increase in the number of magnitude 2.5 (or greater) earthquakes, with one in 2007, two in 2008, ten in 2009 and fifty four in 2010 (Horton, 2012). Horton (2012) reports that 98% of the earthquakes occurred within 6 km of one of the disposal wells, began post-injection, increased when the rate of injection increased and tapered off when the well was shutdown. After an extensive study of the area it was noted that the waste water was being injected into an aquifer from where it increased pore pressure on an unknown fault triggering the earthquakes (Horton, 2012). Similar activity was observed in the Dallas Fort Worth area, where 11 ‘non-felt’ (magnitude less than 2 on the Richter scale) seismic events were recorded during the period between the 20th of November and 2nd of December 2008 (Frohlich et al, 2010). The epicentre of all 11 events was less than 0.5 km away from a disposal well thereby causing them to be classified as induced seismic events (Frohlich et al, 2010). Out of the thousands of disposal wells in the US only a handful have displayed seismic activity (Frohlich et al, 2010). The reason for this could be that most of the wells are drilled into porous, permeable rocks suitable for accommodating fluids and that injection induced triggering occurs only if the fluid reaches a favourably oriented fault (Frohlich et al, 2010). Mitigation: The Royal Society and The Royal Academy of Engineering (2012) have suggested steps that could be taken to mitigate the seismic activity due to waste water disposal: 1. Injection into active faults and brittle, non-porous rocks should be avoided 2. Pressure changes at depth should be minimised by reducing volume of fluid to be disposed. This could be done by building more wells to accommodate smaller volumes of fluid or injecting into highly permeable rocks. 3. A ‘traffic light monitoring system’ should be deployed to respond to seismicity. 5. Conclusion After analysis of data from shale gas plays in the US and UK it can be concluded that shale gas development is responsible for the increased seismic activity felt in these regions. It must be noted however that most cases of seismic activity had magnitudes well below what could be felt at the surface (Davies et al, 2013). According to the National Research Council (2013) hydraulic fracturing does not pose a high risk for inducing seismic activity while disposal of waste water into underground wells poses a greater risk due to the injection of larger volumes of waste water for longer durations of time. However, of the 30,000 wells in operation in the US, only 3 wells have displayed ‘felt’ seismic activity (Davies et al, 2013). A balanced approach should be taken while addressing this matter as other human activities (mining and oil recovery) are responsible for far greater incidences of induced seismicity (Davies et al, 2013). In order to allay public concerns and reduce risks associated with seismic activity the government should enforce certain regulations e.g. geological assessment of rock system at well site, deployment of ‘traffic monitoring system’, limitations on volume and rate of fluid injected and limitations on the proximity of wells to active seismic zones or critical facilities (hospitals, schools, nuclear power plants etc.). Coordinated efforts should be made between the government and industry to put in place a mechanism to respond to induced seismic events and gather comprehensive geological data from shale gas development sites to better understand why, how and where these events occur. References Davies, R., Foulger, G., Bindley, A. Styles, P. (2013) Induced seismicity and hydraulic fracturing for the recovery of hydrocarbons. Marine and Petroleum Geology. 45 (0), 171-185. Davis, S. D. Frohlich, C. (1993) Did (or will) fluid injection cause earthquakes? -criteria for a rational assessment. Seismological Research Letters. 64 (3-4), 207-224. de Pater, C.J,Baish,S. (2011) Geomechanical Study of Bowland Shale Seismicity. Eisner,L.,Janskà ¡,E., OprÃ… ¡al,I.,MatouÃ… ¡ek,P. (2011) Seismic analysis of the events in the vicinity of the Preese Hall well. Cuadrilla Resources Ltd. Ellsworth, W. L. (2013) Injection-Induced Earthquakes. Science. 341 (6142). Frohlich, C., Potter, E., Hayward, C. Stump, B. (2010) Dallas-Fort Worth earthquakes coincident with activity associated with natural gas production. The Leading Edge. 29 (3), 270-275. Green,C.A.,Styles,P.,Baptie, B.J. (2012) Preese Hall Shale Gas Fracturing Review and Recommendations for Induced Seismic Mitigation. Horton, S. (2012) Disposal of Hydrofracking Waste Fluid by Injection into Subsurface Aquifers Triggers Earthquake Swarm in Central Arkansas with Potential for Damaging Earthquake. Seismological Research Letters. 83 (2), 250-260. Majer, E. L., Baria, R., Stark, M., Oates, S., Bommer, J., Smith, B. Asanuma, H. (2007) Induced seismicity associated with Enhanced Geothermal Systems. Geothermics. 36 (3), 185-222. National Research Council. (2013) Induced Seismicity Potential in Energy Technologies. Washington, DC, The National Academies Press. Sovacool, B. K. (2014) Cornucopia or curse? Reviewing the costs and benefits of shale gas hydraulic fracturing (fracking). Renewable and Sustainable Energy Reviews. 37 (0), 249-264.

Baby Sitting :: essays research papers

Four-year-olds can be a nightmare or a gold mine if you know what to do. Most of us have had encounters with a few of them whether they be our brother's and sisters or our neighbors' children. Next time you have an encounter with one you might want to consider the following tips. Toddlers have LOTS of energy, they might run you around the table for hours before they tire. I can honestly say that every child has some sort of favorite character from Batman to Barbie to tellietubbies they will always have one. It might help to find in advance what their favorite TV Show is and there favorite characters so you can plan to watch a video or play with some figures of there favorite character. To help the kids to get into their nightclothes you might want to bribe them into it. Like for example you might say "I'll let you have a pop-sickle or some popcorn if you can get ready for bed." But one thing you must ALWAYS remember is to never ever ever under any circumstance give them sugar before bedtime. Now that you understand how to get them calmed down you should relax by letting them watch a Disney movie or a TV show. Kids under five should be in bed by no later than eight thirty no matter what the kids say. I think parents and any experienced baby-sitter will agree this is the most difficult task of the night. Almost all kids will fight to the death to avoid going to sleep. Some methods can vary from child to child depending on the attitude of the kids. First things first to avoid some conflict you should tell them at least an hour in advance when they will be going to bed, this gets rid of the argument "you never told me I had to go to bed at eight o clock." Next as bedtime arrives you should make sure they are ready for bed, teeth brushed, is your bed ready do you have your nightclothes on? Now for the most dreaded thing "Okay Marco and Amy its time for bed," is the way it should sound in a nice calm soothing voice.

Removal of tea breaks in the company Essay

It has been noted that many employees have been taking their tea break for more than an hour. The tea break is only supposed to be for thirty minutes, from 10h00-10h30. The customers have been complaining about poor service and it has come to my attention that the reason poor service is being provided to our customers is because of the long tea break hours. This gives a very bad impression to the customers and visitors and it reflects badly on the company. Staffs are reminded that tea breaks will no longer be taken as from 10 September 2012 until further notice. The decision to remove the tea breaks was taken by 70% of the staff members, who all voted to remove tea breaks. Staff should note the following points: * Because of the removal of the tea breaks, lunch has been extended for an extra thirty minutes. As from 10 September 2012, lunch will begin at 12h30 -14h00. * All employees are expected to be in their offices at all times, from 08h00 until lunch time. Should any of the employees feel like taking a break during working hours, permission should be asked from their immediate supervisors. * The company kitchen will be open and available for use at all hours, however, employees are asked not to stand around and chat in the kitchen during working hours. * No eating is permitted in the offices during working hours. Please do not hesitate to contact me should you have any questions.

Advantage and Disadvantage Being a Police Officer

I would love to be a police officer. I, have wanted to do this type of work because, it is an exciting career that will allow me to make a difference in my community. I know that being a police officer can be a dangerous, difficult and stressful job. However, it can also be a rewarding in doing what I'd love to do. Two definite challenges in being a police officer will be dangerous nature of the work and the long hours along with shift work.In addition each day you got to work, risking your life to protect the community, so you often put your own safety at the back of your mind. Racing through traffic to crime scenes, risking being shot and approaching unsuspecting criminals are just some of the daily activities that make the job dangerous and unpredictable. While there are bound to be lots of challenges, the rewards should outweigh them. First of all you can meet a variety of people, it can be a grate alternative to a boring desk job.It is immensely satisfying to save lives every da y and also to help people make better choices. Most often you will encounter people at their worst (drug addicts, gang members, thieves). The most satisfying aspect of working as a police officer is the unique opportunity you have to show these people a better way. Working as a police officer would not always be easy. Every day would be sure to bring its challenges. Whatever the challenges, the ultimate reward would be following my dream and helping keep my community peaceful and safe.