The Black Death known as the Pestilence, the Great Plague or the Plague, or less the Black Plague, was one of the most devastating pandemics in human history, resulting in the deaths of an estimated 75 to 200 million people in Eurasia, peaking in Europe from 1347 to 1351. The bacterium Yersinia pestis, which results in several forms of plague is believed to have been the cause; the Black Death was the first major European outbreak of the second plague pandemic. The plague created a number of religious and economic upheavals, with profound effects on the course of European history; the Black Death originated in East Asia, from where it travelled along the Silk Road, reaching Crimea by 1343. From there, it was most carried by fleas living on the black rats that traveled on Genoese merchant ships, spreading throughout the Mediterranean Basin, reaching the rest of Europe via the Italian peninsula. However, one study has suggested the opposite view, in which the Black Death originated in Europe and spread eastward.
The Black Death is estimated to have killed 30% to 60% of Europe's population. In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million in the 14th century, it took 200 years for Europe’s population to recover to its previous level and some regions like Florence only recovered by the 19th century. The plague recurred as outbreaks until the early 20th century; the plague disease, caused by Yersinia pestis, is enzootic in populations of fleas carried by ground rodents, including marmots, in various areas, including Central Asia, Western Asia, North India, Uganda. Due to climate change in Asia, rodents began to flee the dried-out grasslands to more populated areas, spreading the disease. Nestorian graves dating to 1338–1339 near Issyk-Kul in Kyrgyzstan have inscriptions referring to plague and are thought by many epidemiologists to mark the outbreak of the epidemic, from which it could have spread to China and India. In October 2010, medical geneticists suggested that all three of the great waves of the plague originated in China.
The 13th-century Mongol conquest of China caused a decline in trading. Economic recovery had been observed at the beginning of the fourteenth century. In the 1330s, many natural disasters and plagues led to widespread famine, starting in 1331, with a deadly plague arriving soon after. Epidemics that may have included the plague killed an estimated 25 million across Asia during the fifteen years before it reached Constantinople in 1347; the disease may have travelled along the Silk Road with Mongol armies and traders or it could have arrived via ship. By the end of 1346, reports of plague had reached the seaports of Europe: "India was depopulated, Mesopotamia, Armenia were covered with dead bodies". Plague was first introduced to Europe via Genoese traders from the port city of Kaffa in the Crimea in 1347. During a protracted siege of the city by the Mongol army under Jani Beg, whose army was suffering from the disease, the army catapulted infected corpses over the city walls of Kaffa to infect the inhabitants.
The Genoese traders fled, taking the plague by ship into Sicily the Italian mainland, whence it spread north. Whether or not this hypothesis is accurate, it is clear that several existing conditions such as war and weather contributed to the severity of the Black Death. Among many other culprits of plague contagiousness malnutrition if distantly had an effect as a contributor to such an immense loss in European population since it lead to weakened immune systems. There appear to have been several introductions into Europe; the plague reached Sicily in October 1347, carried by twelve Genoese galleys, spread all over the island. Galleys from Kaffa reached Genoa and Venice in January 1348, but it was the outbreak in Pisa a few weeks, the entry point to northern Italy. Towards the end of January, one of the galleys expelled from Italy arrived in Marseille. From Italy, the disease spread northwest across Europe, striking France, Spain and England by June 1348 spread east and north through Germany and Scandinavia from 1348 to 1350.
It was introduced into Norway in 1349 when a ship landed at Askøy spread to Bjørgvin and Iceland. It spread to northwestern Russia in 1351; the plague was somewhat more uncommon in parts of Europe with less developed trade with their neighbours, including the majority of the Basque Country, isolated parts of Belgium and the Netherlands, isolated alpine villages throughout the continent. According to some epidemiologists, periods of unfavorable weather decimated plague-infected rodent populations and forced their fleas onto alternative hosts, inducing plague outbreaks which peaked in the hot summers of the Mediterranean, as well as during the cool autumn months of the southern Baltic states. However, other researchers do not think that the plague became endemic in Europe or its rat population; the disease wiped out the rodent carriers, so that the fleas died out until a new outbreak from Central Asia repeated the process. The outbreaks have been shown to occur 15 years after a warmer and wetter period in areas where plague is endemic in other species, such as gerbils.
The plague struck various regions in the Middle East during the pandemic, leading to serious depopulation and permanent change in both economic and social structures. It spread from China with the Mongols to a trading post in Crimea, called Kaffa, controlled by the Republic of Genoa; as infected rodents infec
Hywel ap Rhys was a king of Glywysing in South Wales. His sons Arthfael and Owain were responsible for the reünification of the realm of Morgannwg. A third son may have fallen assisting Rhodri the Great resist a Mercian invasion of Anglesey around 843. A cross in the collection of ancient stones at St Illtyd's Church, Llantwit Major has been identified with Hywel; the Houelt Cross has a Latin inscription written in half-uncial Latin, interpreted as a memorial cross raised by Hywel for his father. R. A. Stewart Macalister read the inscription as: "NINOMINEDIPATRISE/TS | PERETUSSANTDIANC | --]UCEMHOUELTPROPE | --]BITPROANIMARESPA | --]ESEUS" In 1950 Victor Erle Nash-Williams translated it as "In the Name of God the Father and of the Son and of the Holy Spirit; this cross Houelt prepared for the soul of Res his father" while in 1976 the Royal Commission on the Ancient and Historical Monuments of Wales translated it as "In the name of God, the Father and the Holy Spirit, Houelt prepared this cross for the soul of Res his father".
The Cross itself is a striking example of a Celtic wheel cross and features interlacing carvings, the work is a lasting reminder of Hywel's wealth and influence. Arthfael Owain Ermithridd Nest
Fanno flow is the adiabatic flow through a constant area duct where the effect of friction is considered. Compressibility effects come into consideration, although the Fanno flow model also applies to incompressible flow. For this model, the duct area remains constant, the flow is assumed to be steady and one-dimensional, no mass is added within the duct; the Fanno flow model is considered an irreversible process due to viscous effects. The viscous friction causes the flow properties to change along the duct; the frictional effect is modeled as a shear stress at the wall acting on the fluid with uniform properties over any cross section of the duct. For a flow with an upstream Mach number greater than 1.0 in a sufficiently long enough duct, deceleration occurs and the flow can become choked. On the other hand, for a flow with an upstream Mach number less than 1.0, acceleration occurs and the flow can become choked in a sufficiently long duct. It can be shown that for flow of calorically perfect gas the maximum entropy occurs at M = 1.0.
Fanno flow is named after Gino Girolamo Fanno. The Fanno flow model begins with a differential equation that relates the change in Mach number with respect to the length of the duct, dM/dx. Other terms in the differential equation are the heat capacity ratio, γ, the Fanning friction factor, f, the hydraulic diameter, Dh: d M 2 M 2 = γ M 2 1 − M 2 4 f D h d x Assuming the Fanning friction factor is a constant along the duct wall, the differential equation can be solved easily. One must keep in mind, that the value of the Fanning friction factor can be difficult to determine for supersonic and hypersonic flow velocities; the resulting relation is shown below where L* is the required duct length to choke the flow assuming the upstream Mach number is supersonic. The left-hand side is called the Fanno parameter. 4 f L ∗ D h = + ln Equally important to the Fanno flow model is the dimensionless ratio of the change in entropy over the heat capacity at constant pressure, cp. Δ S = Δ s c p = ln The above equation can be rewritten in terms of a static to stagnation temperature ratio, for a calorically perfect gas, is equal to the dimensionless enthalpy ratio, H: H = h h 0 = c p T c p T 0 = T T 0 Δ S = Δ s c p = ln [ γ − 1 2 γ γ − 1 2