Ibadan is the capital and most populous city of Oyo State, Nigeria. With a population of over 3 million, it is the third most populous city in Nigeria after Lagos and Kano. At the time of Nigeria's independence in 1960, Ibadan was the largest and most populous city in the country, the second most populous in Africa behind Cairo. Ibadan is located in south-western Nigeria, 128 kilometres inland northeast of Lagos and 530 kilometres southwest of Abuja, the federal capital, is a prominent transit point between the coastal region and the areas in the hinterland of the country. Ibadan had been the centre of administration of the old Western Region since the days of the British colonial rule, parts of the city's ancient protective walls still stand to this day; the principal inhabitants of the city are the Yorubas, as well as various communities from other parts of the country. Ibadan, coined from the phrase "Eba Odan", which means'between the forest and plains', came into existence in 1829, during a period of turmoil that characterized Yorubaland at the time.

It was in this period that many old Yoruba cities such as old Oyo and Owu disappeared, newer ones such as Abeokuta, new Oyo and Ibadan sprang up to replace them. According to local historians, Lagelu founded the city, was intended to be a war camp for warriors coming from Oyo and Ijebu; as a forest site containing several ranges of hills, varying in elevation from 160 to 275 metres, the location of the camp offered strategic defence opportunities. Moreover, its location at the fringe of the forest promoted its emergence as a marketing centre for traders and goods from both the forest and grassland areas. In 1852 the Church Missionary Society sent Anna Hinderer to found a mission, they decided to build the mission and a church in Ibadan when they arrived in 1853. Ibadan thus had begun as a military state and remained so until the last decade of the 19th century; the city-state succeeded in building a large empire from the 1860s to the 1890s which extended over much of northern and eastern Yorubaland.

It was appropriately nicknamed "gun base", because of its unique military character. Unlike other Yoruba cities with traditional kingship institutions however, In Ibadan, the warrior class became the rulers of the city as well as the most important economic group. Ibadan grew into an impressive and sprawling urban center so much that by the end of 1829, Ibadan dominated the Yorùbá region militarily and economically; the military sanctuary expanded further when refugees began arriving in large numbers from northern Oyo following raids by Fulani warriors. After losing the northern portion of their region to the marauding Fulanis, many Oyo indigenes retreated deeper into the Ibadan environs; the Fulani Caliphate attempted to expand further into the southern region of modern-day Nigeria, but was decisively defeated by the armies of Ibadan in 1840, which halted their progress. The colonial period reinforced the position of the city in the Yoruba urban network. After a small boom in rubber business, cocoa became the main produce of the region and attracted European and Levantine firms, as well as southern and northern traders from Lagos, Ijebu-Ode and Kano among others.

The city became a major point of bulk trade. Its central location and accessibility from the capital city of Lagos were major considerations in the choice of Ibadan as the headquarters of the Western Provinces which ranged from the northernmost areas of Oyo State to Ekeremor and Patani, which were regions transferred from the old Delta province in the Old Western region and Mid-west to the old Rivers state and Bayelsa, in the redistricting of Nigeria carried out by the Yakubu Gowon administration shortly before the Nigerian civil war In 1893, Ibadan area became a British Protectorate after a treaty signed by Fijabi, the Baale of Ibadan with the British acting Governor of Lagos Colony, George C. Denton on 15 August. By the population had swelled to 120,000; the British developed the new colony to facilitate their commercial activities in the area, Ibadan shortly grew into the major trading center that it is today. Ibadan is located in south-western Nigeria in the southeastern part of Oyo State at about 119 kilometres northeast of Lagos and 120 kilometres east of the Nigerian international border with the Republic of Benin.

It lies within the tropical forest zone but close to the boundary between the forest and the derived savanna. The city ranges in elevation from 150 m in the valley area, to 275 m above sea level on the major north-south ridge which crosses the central part of the city; the city covers a total area of the largest in Nigeria. The city of Ibadan is drained by four rivers with many tributaries: Ona River in the North and West. Ogunpa River, a third-order stream with a channel length of 12.76 km and a catchment area of 54.92 km2. Lake Eleyele is located at the northwestern part of the city, while the Osun River and the Asejire Lake bounds the city to the east. Ibadan has a tropical wet and dry climate, with a lengthy wet season and constant temperatures throughout the course of the year. Ibadan’s wet season runs from March through October, though August sees somewhat of a lull in precipitation; this lull nearly divides the wet season into two different wet seasons. November to February forms the city’


A derailment occurs when a vehicle such as a train runs off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are seriously hazardous to human health and safety; the derailment of a train can be caused by a collision with another object, an operational error, the mechanical failure of tracks, such as broken rails, or the mechanical failure of the wheels. In emergency situations, deliberate derailment with derails or catch points is sometimes used to prevent a more serious accident. Railroad wrecks in the 19th century were sensational, the newspapers claimed them to be due to human failure or the consequence of corporate greed, it took railroads several decades to improve train-control practices and adopt safety devices sufficient to make railroad travel safe. Few passengers were killed in train wrecks in the US before 1853; the early trains ran and made short trips, night travel was rare, there were not many of them in operation.

While trains were convenient for travel and for transporting goods, they had become a greater danger over the years as their speed had increased. While fatal railway accidents occurred about once a year there was a sudden 800 percent increase in accidents in 1853; some railroad accidents were caused by human error, but other causes included derailment, explosions on board, equipment failures, bridge collapses. Thereafter, the rate of accidents returned to its former level. Boiler explosions had been noted in locomotive-type fire tube boilers when the top of the firebox failed; this had to be covered with a significant layer of water at all times or the heat of the fire would weaken it to the point of failure at normal working pressures. Low water levels in the boiler when traversing a significant grade could expose parts of the crown sheet. A well-maintained firebox could fail explosively if the water level in the boiler was allowed to fall far enough to leave the top plate of the firebox uncovered.

Due to the constant expansion and contraction of the firebox a form of "stress corrosion" could take place at the ends of the firebox plates. This corrosion was accelerated by the build-up of boiler scale. A fuel explosion within the confines of the firebox could damage the pressurized boiler tubes and interior shell triggering a structural failure; the majority of locomotive explosions were found to be related to these circumstances, constant attention to the engine was found to be the best defense against catastrophe. On 6 January 1853, the Boston & Maine express, traveling from Boston to Lawrence, MA, derailed at forty miles per hour when an axle broke, the single coach went down an embankment breaking in two. Only one person was killed, the eleven-year-old son of President-elect Franklin Pierce, on board but was only badly bruised. A few days on 23 January 1853, at Glen Rock, PA, the conductor B. A. Stells was lost; the body of the man and the car were not found until Spring. On 6 May 1853, a New Haven Railroad train ran through an open drawbridge at Norwalk, CT and plunged into the Norwalk River.

Forty-six passengers were drowned. This was the first major railroad drawbridge accident. On 17 July 1856, at Fort Washington, PA, there was one of the most infamous train wrecks to occur in the US and the deadliest in the world up to that time. Known as the Great Train Wreck, two North Pennsylvania Railroad trains, one of them carrying 1,500 Sunday School children to a picnic, collided. Upon impact, the boiler of the passenger train exploded and the train carrying the children derailed. Fifty-nine people were killed, dozens more died from their injuries; the conductor of the passenger train committed suicide the same day, although he was absolved of any responsibility. In this sampling, on 11 May 1858, at Utica, NY, two New York Central trains, a westbound freight and the eastbound Cincinnati Express, passed on parallel tracks on a forty-foot wooden trestle over Sauquoit Creek, it collapsed under their combined weight, utterly destroying the passenger train, killing nine and injuring 55 persons.

During the 19th century derailments were commonplace, but progressively improved safety measures have resulted in a stable lower level of such incidents. In the US, derailments have dropped since 1980 from over 3,000 annually to 1,000 or so in 1986, to about 500 in 2010. Derailments result from one or more of a number of distinct causes. A traditional track structure consists of two rails, fixed at a designated distance apar

Magnetic resonance angiography

Magnetic resonance angiography is a group of techniques based on magnetic resonance imaging to image blood vessels. Magnetic resonance angiography is used to generate images of arteries in order to evaluate them for stenosis, aneurysms or other abnormalities. MRA is used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, the legs. A variety of techniques can be used to generate the pictures of blood vessels, both arteries and veins, based on flow effects or on contrast; the most applied MRA methods involve the use intravenous contrast agents those containing gadolinium to shorten the T1 of blood to about 250 ms, shorter than the T1 of all other tissues. Short-TR sequences produce bright images of the blood. However, many other techniques for performing MRA exist, can be classified into two general groups:'flow-dependent' methods and'flow-independent' methods. One group of methods for MRA is based on blood flow; those methods are referred to as flow dependent MRA.

They take advantage of the fact that the blood within vessels is flowing to distinguish the vessels from other static tissue. That way, images of the vasculature can be produced. Flow dependent MRA can be divided into different categories: There is phase-contrast MRA which utilizes phase differences to distinguish blood from static tissue and time-of-flight MRA which exploits that moving spins of the blood experience fewer excitation pulses than static tissue, e.g. when imaging a thin slice. Time-of-flight or inflow angiography, uses a short echo time and flow compensation to make flowing blood much brighter than stationary tissue; as flowing blood enters the area being imaged it has seen a limited number of excitation pulses so it is not saturated, this gives it a much higher signal than the saturated stationary tissue. As this method is dependent on flowing blood, areas with slow flow or flow, in plane of the image may not be well visualized; this is most used in the head and neck and gives detailed high-resolution images.

It is the most common technique used for routine angiographic evaluation of the intracranial circulation in patients with ischemic stroke. Phase-contrast can be used to encode the velocity of moving blood in the magnetic resonance signal's phase; the most common method used to encode velocity is the application of a bipolar gradient between the excitation pulse and the readout. A bipolar gradient is formed by two symmetric lobes of equal area. By definition, the total area of a bipolar gradient, G bip, is null: ∫ G bip d t = 0 The bipolar gradient can be applied along any axis or combination of axes depending on the direction along which flow is to be measured. Δ Φ, the phase accrued during the application of the gradient, is 0 for stationary spins: their phase is unaffected by the application of the bipolar gradient. For spins moving with a constant velocity, v x, along the direction of the applied bipolar gradient: Δ Φ = γ v x Δ m 1 The accrued phase is proportional to both v x and the 1st moment of the bipolar gradient, Δ m 1, thus providing a means to estimate v x.

Γ is the Larmor frequency of the imaged spins. To measure Δ Φ, of the MRI signal is manipulated by bipolar gradients that are preset to a maximum expected flow velocity. An image acquisition, reverse of the bipolar gradient is acquired and the difference of the two images is calculated. Static tissues such as muscle or bone will subtract out, however moving tissues such as blood will acquire a different phase since it moves through the gradient, thus giving its speed of the flow. Since phase-contrast can only acquire flow in one direction at a time, 3 separate image acquisitions in all three directions must be computed to give the complete image of flow. Despite the slowness of this method, the strength of the technique is that in addition to imaging flowing blood, quantitative measurements of blood flow can be obtained. Whereas most of techniques in MRA rely on contrast agents or flow into blood to generate contrast, there are non-contrast enhanced flow-independent methods; these methods, as the name suggests, do not rely on flow, but are instead based on the differences of T1, T2 and chemical shift of the different tissues of the voxel.

One of the main advantages of this kind of techniques is that we may image the regions of slow flow found in patients with vascular diseases more easily. Moreover, non-contrast enhanced methods do not require the administration of additional contrast agent, which have been linked to nephrogenic systemic fibrosis in patients with chronic kidney disease and kidney failure. Contrast-enhanced magnetic resonance angiography uses injection of MRI contrast agents and is the most common method of performing M