Basic information.

Salt marshes occur on low-energy shorelines in temperate and high-latitudes which can be stable, emerging, or submerging depending if the sedimentation is greater, equal to, or lower than relative sea level rise (subsidence rate plus sea level change), respectively. Commonly these shorelines consist of mud or sand flats (known also as tidal flats or abbreviated to mudflats) which are nourished with sediment from inflowing rivers and streams. These typically include sheltered environments such as embankments, estuaries and the leeward side of barrier islands and spits. In the tropics and sub-tropics they are replaced by mangroves; an area that differs from a salt marsh in that instead of herbaceous plants, they are dominated by salt-tolerant trees.  Most salt marshes have a low topography with low elevations but a vast wide area, making them hugely popular for human populations. Salt marshes are located among different landforms based on their physical and geomorphological settings. Such marsh landforms include deltaic marshes, estuarine, back-barrier, open coast, embayments and drowned-valley marshes. Deltaic marshes are associated with large rivers where many occur in Southern Europe such

Worldwide occurrence.

Saltmarshes across 99 countries (essentially worldwide) were mapped by Mcowen et al. 2017. A total of 5,495,089 hectares of mapped saltmarsh across 43 countries and territories are represented in a Geographic Information

Formation.

The formation begins as tidal flats gain elevation relative to sea level by sediment accretion, and subsequently the rate and duration of tidal flooding decreases so that vegetation can colonize on the exposed surface. The arrival of propagules of pioneer species such as seeds or rhizome portions are combined with the development of suitable conditions for their germination and establishment in the process of colonisation. When rivers and streams arrive at the low gradient of the tidal flats, the discharge rate reduces and suspended sediment settles onto the tidal flat surface, helped by the backwater effect of the rising

Tidal flooding and vegetation zonation.

Coastal salt marshes can be distinguished from terrestrial habitats by the daily tidal flow that occurs and continuously floods the area. It is an important process in delivering sediments, nutrients and plant water supply to the marsh. At higher elevations in the upper marsh zone, there is much less tidal inflow, resulting in lower salinity levels. Soil salinity in the lower marsh zone is fairly constant due to everyday annual tidal flow. However, in the upper marsh, variability in salinity is shown as a result of less frequent flooding and climate variations. Rainfall can reduce salinity and evapotranspiration can increase levels during dry periods. As a result, there are microhabitats populated by different species of flora and fauna dependant on their physiological abilities. The flora of a salt marsh is differentiated into levels according to the plants' individual tolerance of salinity and water table levels. Vegetation found at the water must be able to survive high salt concentrations, periodical submersion, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower

Sediment trapping, accretion, and the role of tidal creeks.

The factors and processes that influence the rate and spatial distribution of sediment accretion within the salt marsh are numerous. Sediment deposition can occur when marsh species provide a surface for the sediment to adhere to, followed by deposition onto the marsh surface when the sediment flakes off at low tide. The amount of sediment adhering to salt marsh species is dependent on the type of marsh species, the proximity of the species to the sediment supply, the amount of plant biomass, and the elevation of the species. For example, in a study of the Eastern Chongming Island and Jiuduansha Island tidal marshes at the mouth of the Yangtze River, China, the amount of sediment adhering to the species "Spartina alterniflora", "Phragmites australis", and "Scirpus mariqueter" decreased with distance from the highest levels of suspended sediment concentrations (found at the marsh edge bordering tidal creeks or the mudflats); decreased with those species at the highest elevations, which experienced the lowest frequency and depth of tidal inundations; and increased with increasing plant biomass. "Spartina alterniflora", which had the most sediment adhering to it, may contribute >10% of the total marsh surface sediment accretion by this process.  Salt

Human impacts.

The coast is a highly attractive natural feature to humans through its beauty, resources, and accessibility. As of 2002, over half of the world's population was estimated to being living within 60 km of the coastal shoreline, making coastlines highly vulnerable to human impacts from daily activities that put pressure on these surrounding natural environments. In the past, salt marshes were perceived as coastal 'wastelands,' causing considerable loss and change of these ecosystems through land reclamation for agriculture, urban development, salt production and recreation. The indirect effects of human activities such as nitrogen loading also play a major role in the salt marsh area. Salt marshes can suffer from dieback in the high marsh and die-off in the low marsh.

Land reclamation.

Reclamation of land for agriculture by converting marshland to upland was historically a common practice. Dikes were often built to allow for this shift in land change and to provide flood protection further inland. In recent times intertidal flats have also been reclaimed. For centuries, livestock such as sheep and cattle grazed on the highly fertile salt marsh land. Land reclamation for agriculture has resulted in many changes such as shifts in vegetation structure, sedimentation, salinity, water flow, biodiversity loss and high nutrient inputs. There have been many attempts made to eradicate these problems for example, in New Zealand, the cordgrass "Spartina anglica" was introduced from England into the Manawatu River mouth in 1913 to try and reclaim the estuary land for farming. A shift in structure from bare tidal flat to

Upstream agriculture.

Cultivation of land upstream from the salt marsh can introduce increased silt inputs and raise the rate of primary sediment accretion on the tidal flats, so that pioneer species can spread further onto the flats and grow rapidly upwards out of the level of tidal

Urban development and nitrogen loading.

The conversion of marshland to upland for agriculture has in the past century been overshadowed by conversion for urban development. Coastal cities worldwide have encroached onto former salt marshes and in the U.S. the growth of cities looked to salt marshes for waste disposal sites. Estuarine pollution from organic, inorganic, and toxic substances from urban development or industrialisation is a worldwide problem and the sediment in salt marshes may entrain this pollution with toxic effects on floral and faunal species. Urban development of salt marshes has slowed since about 1970 owing to growing awareness by environmental groups that they provide beneficial ecosystem services. They are highly productive ecosystems, and when net productivity is measured in g m yr they are equalled only by tropical rainforests. Additionally, they can help reduce wave erosion on sea walls designed to protect low-lying areas of land from wave erosion.  De-naturalisation of the landward boundaries of salt marshes from urban or industrial encroachment can have negative effects. In the

Sea level rise.

Due to the melting of Arctic sea ice and thermal expansion of the oceans, as a result of global warming, sea levels have begun to rise. As with all coastlines, this rise in water levels is predicted to negatively affect salt marshes, by flooding and eroding them. The sea level rise causes more open water zones within the salt marsh. These zones cause erosion along their edges, further eroding the marsh into open water until the whole marsh disintegrates.  While salt marshes are susceptible to threats concerning sea level rise, they are also

Mosquito control.

Earlier in the 20th century, it was believed that draining salt marshes would help reduce mosquito populations, such as "Aedes taeniorhynchus", the black salt marsh mosquito. In many locations, particularly in the northeastern United States, residents and local and state

Crab herbivory and bioturbation.

Increased nitrogen uptake by marsh species into their leaves can prompt greater rates of length-specific leaf growth, and increase the herbivory rates of crabs. The burrowing crab "Neohelice granulata" frequents SW Atlantic salt marshes where high density populations can be found among populations of the marsh species "Spartina densiflora" and "Sarcocornia perennis". In Mar Chiquita lagoon, north of Mar del Plata, Argentina, "Neohelice granulata" herbivory increased as a likely response to the increased nutrient value of the leaves of fertilised "Spartina densiflora" plots, compared to non-fertilised plots. Regardless of whether the plots were fertilised or not, grazing by "Neohelice granulata" also reduced the length specific leaf growth rates of the leaves in summer, while increasing their length-specific senescence rates. This may have been assisted by the increased fungal effectiveness on the wounds left by the crabs.  The salt marshes of Cape Cod, Massachusetts (USA), are experiencing creek bank die-offs of "Spartina" spp. (cordgrass) that has been attributed to herbivory by the crab "Sesarma reticulatum". At 12 surveyed Cape Cod salt marsh sites, 10%

Restoration and management.

The perception of bay salt marshes as a coastal 'wasteland' has since changed, acknowledging that they are one of the most biologically productive habitats on earth, rivalling tropical rainforests. Salt marshes are ecologically important providing habitats for native migratory fish and acting as sheltered feeding and nursery grounds. They are now protected by legislation in many countries to look after these ecologically important habitats. In the United States and Europe, they are now accorded a high level of protection by the Clean Water Act and the Habitats Directive respectively. With the impacts of this habitat and its importance now realised, a growing interest in restoring salt marshes, through managed retreat or the reclamation of land has been established. However, many Asian countries such as China are still to recognise the value of marshlands. With their ever-growing populations and intense development along the coast, the value of salt marshes tends to be ignored and the land continues to be reclaimed.  Bakker et al. (1997) suggests two options available for restoring salt marshes. The first is to abandon all human interference and leave the salt marsh to complete its natural development. These types of restoration projects are often unsuccessful as vegetation tends to struggle to revert to its original structure and the natural tidal cycles are shifted due to land changes. The second option suggested by Bakker et al. (1997) is to restore the destroyed habitat into its natural state either at the original site or as a replacement at a different site. Under natural conditions, recovery can take 2–10 years or even longer depending on the nature and degree of the disturbance and the relative maturity of the marsh involved. Marshes in their pioneer stages of development will recover more rapidly than mature marshes as they are often first to colonize the land. It is important to note, that restoration can often be sped up through the replanting of native vegetation.  This last approach is often the most practiced and generally more successful than allowing the area to naturally recover on its own. The salt marshes in the state of Connecticut in the United States have long

Research methods.

There is a diverse range and combination of methodologies employed to understand the hydrological dynamics in salt marshes and their ability to trap and accrete sediment. Sediment traps are often used to measure rates of marsh surface accretion when short term deployments (e.g. less than one month) are required. These circular traps consist of pre-weighed filters that are anchored to the marsh surface, then dried in a laboratory and re-weighed to determine the total deposited sediment.  For longer term studies (e.g. more than one year) researchers may prefer to measure sediment accretion with marker horizon plots. Marker horizons consist of a mineral such as feldspar that is buried at a known depth within wetland substrates to record the increase in overlying substrate over long time periods. In order to gauge the amount of sediment suspended in the water column, manual or automated samples of tidal water can be poured through pre-weighed filters in a laboratory then dried to determine the amount of sediment per volume of water.  Another method for estimating suspended sediment concentrations is by measuring the turbidity of the water using optical backscatter probes, which can be calibrated against water samples containing a known suspended sediment concentration to establish a regression relationship between the two. Marsh surface elevations may be measured with a stadia rod and transit, electronic theodolite, Real-Time Kinematic Global Positioning System, laser level or electronic distance meter (total station). Hydrological dynamics include water depth, measured automatically with a pressure transducer, or with a marked wooden stake, and water velocity, often using electromagnetic current meters.

A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.

盐碱滩,又称盐沼,是沿海潮间带和陆地间的一种生态系统,海水或咸水有规律地涌入流出地带。这一地带主要生长盐土植物。这些植物是陆生植物且耐盐碱。在水域食物链及海陆营养交换中盐碱滩扮演着重要的地位,此外次地带也为一些陆地生物的生存提供了支持。同时它起著海岸保护的作用。


Early years.

Mohamed Siad Barre was born on October 6, 1919, Bardhere, a town in the Italian Somaliland, into the Somali Marehan Darod clan and the sub-clan of Rer Dini. Barre's parents died when he was ten years old, and after receiving his primary education in the town of Luuq in southern Italian Somalia he moved to the capital Mogadishu to pursue his secondary education. Barre seems to have probably participated as a Zaptié in the southern theatre of the Italian conquest of Ethiopia in 1936, and later joined the colonial police force during the British Somaliland military administration, rising to major general, the highest possible rank. In 1946, Barre supported the Somali Conference (), a political group of parties and clan associations that were hostile to the Somali Youth League and were supported by the local Italian farmers. The group presented a petition to the "Four Powers" Investigation Commission in order to allow that the administration of the United Nations Trust Territory could be entrusted for thirty years to Italy. In 1950, shortly after Italian Somaliland became a United Nations Trust Territory under Italian administration for ten years, Barre (who was fluent in Italian) attended the Carabinieri police school in Florence for two years. Upon his return to Somalia, Barre remained with the military and eventually became Vice Commander of the Somali Army when the country gained its independence in 1960 as the Somali Republic.  In the early 1960s, after spending time with Soviet officers in joint training exercises, Barre became an advocate of Soviet-style Marxist-Leninist government, believing in a socialist government and a stronger sense of Somali nationalism.

Seizure of power.

In 1969, following the assassination of Somalia's second president, Abdirashid Ali Shermarke, the military staged the 1969 coup d'état on October 21, the day after Shermarke's funeral, overthrowing the Somali Republic's government. The Supreme Revolutionary Council (SRC), a military junta led by Major General Barre, Lieutenant Colonel Salaad Gabeyre Kediye and Chief of Police Jama Ali Korshel, assumed power and filled the top offices of the government, with Kediye officially holding the title of "Father of the Revolution," although Barre shortly afterwards became the head of the SRC. The SRC subsequently renamed the country the Somali Democratic Republic, arrested members of the former government, banned political parties, dissolved the parliament and the Supreme Court, and suspended the constitution.

Presidency.

Barre assumed the position of President of Somalia, styled the "Victorious Leader" ("Guulwade"), and fostered the growth of a personality cult with portraits of him in the company of Marx and Lenin lining the streets on public occasions. Barre advocated a form of scientific socialism based on the Qur'an and Marxism, with heavy influences of Somali nationalism.

Supreme Revolutionary Council.

The Supreme Revolutionary Council established large-scale public works programs and successfully implemented an urban and rural literacy campaign, which helped dramatically increase the literacy rate. Barre began a program of nationalising industry and land, and the new regime's foreign policy placed an emphasis on Somalia's traditional and religious links with the Arab world, eventually joining the Arab League in 1974. That same year, Barre also served as chairman of the Organization of African Unity (OAU), the predecessor of the African Union (AU).  In July 1976, Barre's SRC disbanded itself and established in its place the Somali Revolutionary Socialist Party (SRSP), a one-party government based on scientific socialism and Islamic tenets. The SRSP was an attempt to reconcile the official state ideology with the official state religion by adapting Marxist precepts to local circumstances. Emphasis was placed on the Muslim principles of social progress, equality and justice, which the government argued formed the core of scientific socialism and its own accent on self-sufficiency, public participation and popular control, as well as direct ownership of the means of production. While the SRSP encouraged private investment on a limited scale, the administration's overall direction was essentially communist.  A new constitution was promulgated in 1979 under which elections for a People's Assembly were held. However, the Politburo of Barre's Somali Revolutionary Socialist Party continued to rule. In October 1980, the SRSP was disbanded, and the Supreme Revolutionary Council was re-established in its place.

Language and anti-clanism.

One of the first and principal objectives of the revolutionary regime was the adoption of a standard national writing system. Barre supported the official use of Latin script for the Somali language, replacing Arabic script and Wadaad writing that had been used for centuries. Shortly after coming to power, Barre introduced the Somali language ("Af Soomaali") as the official language of education, and selected the modified Somali Latin alphabet developed by the Somali linguist Shire Jama Ahmed as the nation's standard orthography. From then on, all education in government schools had to be conducted in Somali, and in 1972, all government employees were ordered to learn to read and write Somali within six months. The reason given for this was to decrease a growing rift between those who spoke the colonial languages, Italian or English, and those who did not, as many of the high ranking positions in the former government were given to people who spoke either Italian or English.  Additionally, Barre also sought to eradicate the importance of the Somali clan system ("qabil") within Somalia's government and civil society. The inevitable first question that Somalis asked one another when they met was, '"What is your clan?", but when this was considered to be against to the purpose of a modern state, Somalis began to pointedly ask, "What is your ex-clan?". Barre outlawed this question and a broad range of other activities classified as "clanism", with informers reporting "qabilists", those considered to propagate the clan system, to the government, leading to arrests and imprisonment.  On a more symbolic level, Barre had repeated a number of times, "Whom do you know? is changed to: What do you know?", and this incantation became part of a popular street song in Somalia. He also promoted a number of favored greetings, such as the singular "jaalle" (comrade) or the plural "jaalleyaal" (comrades).

Nationalism and Greater Somalia.

Barre advocated the concept of a Greater Somalia ("Soomaaliweyn"), which refers to those regions in the Horn of Africa in which ethnic Somalis reside and have historically represented the predominant population. Greater Somalia encompasses Somalia, Djibouti, the Ogaden in Ethiopia, and Kenya's former North Eastern Province, regions of the Horn of Africa where Somalis form the majority of the population to some proportion. In July 1977, the Ogaden War broke out after the Barre's government sought to incorporate the various Somali-inhabited territories of the region into a Greater Somalia, beginning with the Ogaden. The Somali national army invaded Ethiopia, which was now under communist rule of the Soviet-backed Derg, and was successful at first, capturing most of the territory of the Ogaden. The invasion reached an abrupt end with the Soviet Union's shift of support to Ethiopia, followed by almost the entire communist world siding against Somalia. The Soviets halted their previous supplies to Barre's regime and increased the distribution of aid, weapons, and training to the Ethiopian government, and also brought in around 15,000 Cuban troops to assist the Ethiopian regime. In 1978, the Somali troops were ultimately pushed out of the Ogaden.

Foreign relations.

Control of Somalia was of great interest to both the Soviet Union and the United States due to the country's strategic location at the mouth of the Red Sea. After the Soviets broke with Somalia in the late 1970s, Barre subsequently expelled all Soviet advisers, tore up his friendship treaty with the Soviet Union, and switched allegiance to the West, announcing this in a televised speech in English. Somalia also broke all ties with the Soviet Bloc and the Second World (except China and Romania). The United States stepped in and until 1989, was a strong supporter of the Barre government for whom it provided approximately US$100 million per year in economic and military aid, meeting in 1982 with Ronald Reagan to announce the new relationship between the US and Somalia.  In September 1972 Tanzanian-sponsored rebels attacked Uganda. Ugandan President Idi Amin requested Barre's assistance, and he subsequently mediated a non-aggression pact between Tanzania and Uganda. For his actions, a road in Kampala was named after Barre.  On October 17 and 18, 1977, a Popular Front for the Liberation of Palestine (PFLP) group hijacked Lufthansa Flight 181 to Mogadishu, holding 86 hostages. West German Chancellor Helmut Schmidt and Barre negotiated a deal to allow a GSG 9 anti-terrorist unit into Mogadishu to free the hostages.

Domestic programs.

During the first five years, Barre's government set up several cooperative farms and factories of mass production such as mills, sugar cane processing facilities in Jowhar and Afgooye, and a meat processing house in Kismayo.  Another public project initiated by the government was the Shalanbood Sanddune Stoppage: from 1971 onwards, a massive tree-planting campaign on a nationwide scale was introduced by Barre's administration to halt the advance of thousands of acres of wind-driven sand dunes that threatened to engulf towns, roads, and farm land. By 1988, 265 hectares of a projected 336 hectares had been treated, with 39 range reserve sites and 36 forestry plantation sites established.  Between 1974 and 1975, a major drought referred to as the "Abaartii Dabadheer" ("The Lingering Drought") occurred in the northern regions of Somalia. The Soviet Union, which at the time maintained strategic relations with the Barre government, airlifted some 90,000 people from the devastated regions of Hobyo and Caynaba. New settlements of small villages were created in the Jubbada Hoose (Lower Jubba) and Jubbada Dhexe (Middle Jubba) regions, with these new settlements known as the "Danwadaagaha" or "Collective Settlements". The transplanted families were introduced to farming and fishing, a change from their traditional pastoralist lifestyle of livestock herding. Other such resettlement programs were also introduced as part of Barre's effort to undercut clan solidarity by dispersing nomads and moving them away from clan-controlled land.

Economic policies.

As part of Barre's socialist policies, major industries and farms were nationalised, including banks, insurance companies and oil distribution farms. By the mid-to-late-1970s, public discontent with the Barre regime was increasing, largely due to corruption among government officials as well as poor economic performance. The Ogaden War had also weakened the Somali army substantially and military spending had crippled the economy. Foreign debt increased faster than export earnings, and by the end of the decade, Somalia's debt of 4 billion shillings equaled the earnings from seventy-five years' worth of banana exports.  By 1978, manufactured goods exports were almost non-existent, and with the lost support of the Soviet Union the Barre government signed a structural adjustment agreement with the International Monetary Fund (IMF) during the early 1980s. This included the abolishment of some government monopolies and increased public investment. This and a second agreement were both cancelled by the mid-1980s, as the Somali army refused to accept a proposed 60 percent cut in military spending. New agreements were made with the Paris Club, the International Development Association and the IMF during the second half of the 1980s. This ultimately failed to improve the economy which deteriorated rapidly in 1989 and 1990, and resulted in nationwide commodity shortages.

Car collision.

In May 1986, President Barre suffered serious injuries in a life-threatening automobile collision near Mogadishu, when the car that was transporting him smashed into the back of a bus during a heavy rainstorm. He was treated in a hospital in Saudi Arabia for head injuries, broken ribs and shock over a period of a month. Lieutenant General Mohamed Ali Samatar, then Vice President, subsequently served as de facto head of state for the next several months. Although Barre managed to recover enough to present himself as the sole presidential candidate for re-election over a term of seven years on December 23, 1986, his poor health and advanced age led to speculation about who would succeed him in power. Possible contenders included his son-in-law General Ahmed Suleiman Abdille, who was at the time the Minister of the Interior, in addition to Barre's Vice President Lt. Gen. Samatar.

Human rights abuses.

Part of Barre's time in power was characterized by oppressive dictatorial rule, including persecution, jailing and torture of political opponents and dissidents. The United Nations Development Programme stated that "the 21-year regime of Siyad Barre had one of the worst human rights records in Africa." In January 1990, the Africa Watch Committee, a branch of Human Rights Watch organizational released an extensive report titled ""Somalia A Government At War with Its Own People"" composing of 268 pages, the report highlights the widespread violations of basic human rights in the northern regions of Somalia. The report includes testimonies about the killing and conflict in northern Somalia by newly arrived refugees in various countries around the world. Systematic human rights abuses against the dominant Isaaq clan in the north was described in the report as "state sponsored terrorism" "both the urban population and nomads living in the countryside [were] subjected to summary killings, arbitrary arrest, detention in squalid conditions, torture, rape, crippling constraints on freedom of movement and expression and a pattern of psychological intimidation. The report estimates that 50,000 to 60,000 people were killed from 1988 to 1989." Amnesty International went on to report that torture methods committed by Barre's National Security Service (NSS) included executions and "beatings while tied in a contorted position, electric shocks, rape of woman prisoners, simulated executions and death threats."  In September 1970, the government introduced the National Security Law No. 54, which granted the NSS the power to arrest and detain indefinitely those who expressed critical views of the government, without ever being brought to trial. It further gave the NSS the power to arrest without a warrant anyone suspected of a crime involving "national security". Article 1 of the law prohibited "acts against the independence, unity or security of the State", and capital punishment was mandatory for anyone convicted of such acts.  From the late 1970s, and onwards Barre faced a shrinking popularity and increased domestic resistance. In response, Barre's elite unit, the Red Berets ("Duub Cas"), and the paramilitary unit called the Victory Pioneers carried out systematic terror against the Majeerteen, Hawiye, and Isaaq clans. The Red Berets systematically smashed water reservoirs to deny water to the Majeerteen and Isaaq clans and their herds. More than 2,000 members of the Majeerteen clan died of thirst, and an estimated 5,000 Isaaq were killed by the government. Members of the Victory Pioneers also raped large numbers of Majeerteen and Isaaq women, and more than 300,000 Isaaq members fled to Ethiopia.  By the mid-1980s, more resistance movements supported by Ethiopia's communist Derg administration had sprung up across the country. Barre responded by ordering punitive measures against those he perceived as locally supporting the guerillas, especially in the northern regions. The clampdown included bombing of cities, with the northwestern administrative center of Hargeisa, a Somali National Movement (SNM) stronghold, among the targeted areas in 1988. The bombardment was led by General Mohammed Said Hersi Morgan, Barre's son-in-law, and resulted in the deaths of 50,000 people in the north.

Rebellion and ouster.

After fallout from the unsuccessful Ogaden campaign, Barre's administration began arresting government and military officials under suspicion of participation in the 1978 coup d'état attempt. Most of the people who had allegedly helped plot the putsch were summarily executed. However, several officials managed to escape abroad and started to form the first of various dissident groups dedicated to ousting Barre's regime by force.  A new constitution was promulgated in 1979 under which elections for a People's Assembly were held. However, Barre and the Politburo of his Somali Revolutionary Socialist Party continued to rule. In October 1980, the SRSP was disbanded, and the Supreme Revolutionary Council was re-established in its place. By that time, the moral authority of Barre's ruling Supreme Revolutionary Council had begun to weaken. Many Somalis were becoming disillusioned with life under military dictatorship. The regime was further weakened in the 1980s as the Cold War drew to a close and Somalia's strategic importance was diminished. The government became increasingly totalitarian, and resistance movements, supported by Ethiopia's communist Derg administration, sprang up across the country. This eventually led in 1991 to the outbreak of the civil war, the toppling of Barre's regime and the disbandment of the Somali National Army (SNA). Among the militia groups that led the rebellion were the Somali Salvation Democratic Front (SSDF), United Somali Congress (USC), Somali National Movement (SNM) and the Somali Patriotic Movement (SPM), together with the non-violent political oppositions of the Somali Democratic Movement (SDM), the Somali Democratic Alliance (SDA) and the Somali Manifesto Group (SMG). Siad Barre escaped from his palace towards the Kenyan border in a tank. Many of the opposition groups subsequently began competing for influence in the power vacuum that followed the ouster of Barre's regime. In the south, armed factions led by USC commanders General Mohamed Farah Aidid and Ali Mahdi Mohamed, in particular, clashed as each sought to exert authority over the capital.

Exile and death.

After fleeing Mogadishu in January 1991, Barre temporarily remained in Burdhubo, in southwestern Somalia, his family's stronghold. From there, he launched a military campaign to return to power. He twice attempted to retake Mogadishu, but in May 1991 was overwhelmed by General Mohamed Farrah Aidid's army and forced into exile.  Barre initially moved to Nairobi, Kenya, but opposition groups there protested his arrival and the Kenyan government's support for him. In response to the pressure and hostilities, he moved two weeks later to Nigeria. Barre died of a heart attack on January 26, 1995, in Lagos. He was buried in Garbaharey, Somalia.

Jaalle Mohamed Siad Barre (; ; October 6, 1919 – January 2, 1995) was a Somali politician who served as the President of the Somali Democratic Republic from 1969 to 1991.

贾莱·穆罕默德·西亚德·巴雷(索马里语:;;1919年-10月6日-1995年-1月2日)是索马里的政治家及军人,曾任该国第三任总统。


History and etymology.

The discovery of Wnt signaling was influenced by research on oncogenic (cancer-causing) retroviruses. In 1982, Roel Nusse and Harold Varmus infected mice with mouse mammary tumor virus in order to mutate mouse genes to see which mutated genes could cause breast tumors. They identified a new mouse proto-oncogene that they named int1 (integration 1).  Int1 is highly conserved across multiple species, including humans and "Drosophila". Its presence in "D. melanogaster" led researchers to discover in 1987 that the int1 gene in "Drosophila" was actually the already known and characterized "Drosophila" gene known as Wingless (Wg). Since previous research by Christiane Nüsslein-Volhard and Eric Wieschaus (which won them the Nobel Prize in Physiology or Medicine in 1995) had already established the function of Wg as a segment polarity gene involved in the formation of the body axis during embryonic development, researchers determined that the mammalian int1 discovered in mice is also involved in embryonic development.  Continued research led to the discovery of further int1-related genes; however, because those genes were not identified in the same manner as int1, the int gene nomenclature was inadequate. Thus, the int/Wingless family became the Wnt family and int1 became Wnt1. The name Wnt is a portmanteau of int and Wg and stands for "Wingless-related integration site".

Proteins.

Wnt comprises a diverse family of secreted lipid-modified signaling glycoproteins that are 350–400 amino acids in length. The lipid modification of all Wnts is palmitoleoylation of a single totally conserved serine residue. Palmitoleoylation is necessary because it is required for Wnt to bind to its carrier protein Wntless (WLS) so it can be transported to the plasma membrane for secretion and it allows the Wnt protein to bind its receptor Frizzled Wnt proteins also undergo glycosylation, which attaches a carbohydrate in order to ensure proper secretion. In Wnt signaling, these proteins act as ligands to activate the different Wnt pathways via paracrine and autocrine routes.<ref name="doi10.1016/0092-8674(92)90630-U"></ref>  These proteins are highly conserved across species. They can be found in mice, humans, "Xenopus", zebrafish, "Drosophila" and many others.

Mechanism.

Foundation.

Wnt signaling begins when a Wnt protein binds to the N-terminal extra-cellular cysteine-rich domain of a Frizzled (Fz) family receptor. These receptors span the plasma membrane seven times and constitute a distinct family of G-protein coupled receptors (GPCRs). However, to facilitate Wnt signaling, co-receptors may be required alongside the interaction between the Wnt protein and Fz receptor. Examples include lipoprotein receptor-related protein (LRP)-5/6, receptor tyrosine kinase (RTK), and ROR2. Upon activation of the receptor, a signal is sent to the phosphoprotein Dishevelled (Dsh), which is located in the cytoplasm. This signal is transmitted via a direct interaction between Fz and Dsh. Dsh proteins are present in all organisms and they all share the following highly conserved protein domains: an amino-terminal DIX domain, a central PDZ domain, and a carboxy-terminal DEP domain. These different domains are important because after Dsh, the Wnt signal can branch off into multiple pathways and each pathway interacts with a different combination of the three domains.

Canonical and noncanonical pathways.

The three best characterized Wnt signaling pathways are the canonical Wnt pathway, the noncanonical planar cell polarity pathway, and the noncanonical Wnt/calcium pathway. As their names suggest, these pathways belong to one of two categories: canonical or noncanonical. The difference between the categories is that a canonical pathway involves the protein β-catenin while a noncanonical pathway operates independently of it.

Canonical pathway.

The canonical Wnt pathway (or Wnt/β-catenin pathway) is the Wnt pathway that causes an accumulation of β-catenin in the cytoplasm and its eventual translocation into the nucleus to act as a transcriptional coactivator of transcription factors that belong to the TCF/LEF family. Without Wnt, β-catenin would not accumulate in the cytoplasm since a destruction complex would normally degrade it. This destruction complex includes the following proteins: Axin, adenomatosis polyposis coli (APC), protein phosphatase 2A (PP2A), glycogen synthase kinase 3 (GSK3) and casein kinase 1α (CK1α). It degrades β-catenin by targeting it for ubiquitination, which subsequently sends it to the proteasome to be digested. However, as soon as Wnt binds Fz and LRP5/6, the destruction complex function becomes disrupted. This is due to Wnt causing the translocation of the negative Wnt regulator, Axin, and the destruction complex to the plasma membrane. Phosphorylation by other proteins in the destruction complex subsequently binds Axin to the cytoplasmic tail of LRP5/6. Axin becomes de-phosphorylated and its stability and levels decrease. Dsh then becomes activated via phosphorylation and its DIX and PDZ domains inhibit the GSK3 activity of the destruction complex. This allows β-catenin to accumulate and localize to the nucleus and subsequently induce a cellular response via gene transduction alongside the TCF/LEF (T-cell factor/lymphoid enhancing factor) transcription factors. β-catenin recruits other transcriptional coactivators, such as BCL9, Pygopus and Parafibromin/Hyrax. The complexity of the transcriptional complex assembled by β-catenin is beginning to emerge thanks to new high-throughput proteomics studies. The extensivity of the β-catenin interacting proteins complicates our understanding: β-catenin may be directly phosphorylated at Ser552 by Akt, which causes its disassociation from cell-cell contacts and accumulation in cytosol, thereafter 14-3-3ζ interacts with β-catenin (pSer552) and enhances its nuclear translocation. BCL9 and Pygopus have been reported, in fact, to possess several β-catenin-independent functions (therefore, likely, Wnt signaling-independent).

Noncanonical pathways.

The noncanonical planar cell polarity (PCP) pathway does not involve β-catenin. It does not use LRP-5/6 as its co-receptor and is thought to use NRH1, Ryk, PTK7 or ROR2. The PCP pathway is activated via the binding of Wnt to Fz and its co-receptor. The receptor then recruits Dsh, which uses its PDZ and DIX domains to form a complex with Dishevelled-associated activator of morphogenesis 1 (DAAM1). Daam1 then activates the small G-protein Rho through a guanine exchange factor. Rho activates Rho-associated kinase (ROCK), which is one of the major regulators of the cytoskeleton. Dsh also forms a complex with rac1 and mediates profilin binding to actin. Rac1 activates JNK and can also lead to actin polymerization. Profilin binding to actin can result in restructuring of the cytoskeleton and gastrulation. The noncanonical Wnt/calcium pathway also does not involve β-catenin. Its role is to help regulate calcium release from the endoplasmic reticulum (ER) in order to control intracellular calcium levels. Like other Wnt pathways, upon ligand binding, the activated Fz receptor directly interacts with Dsh and activates specific Dsh-protein domains. The domains involved in Wnt/calcium signaling are the PDZ and DEP domains. However, unlike other Wnt pathways, the Fz receptor directly interfaces with a trimeric G-protein. This co-stimulation of Dsh and the G-protein can lead to the activation of either PLC or cGMP-specific PDE. If PLC is activated, the plasma membrane component PIP2 is cleaved into DAG and IP3. When IP3 binds its receptor on the ER, calcium is released. Increased concentrations of calcium and DAG can activate Cdc42 through PKC. Cdc42 is an important regulator of ventral patterning. Increased calcium also activates calcineurin and CaMKII. CaMKII induces activation of the transcription factor NFAT, which regulates cell adhesion, migration and tissue separation. Calcineurin activates TAK1 and NLK kinase, which can interfere with TCF/ß-Catenin signaling in the canonical Wnt pathway. However, if PDE is activated, calcium release from the ER is inhibited. PDE mediates this through the inhibition of PKG, which subsequently causes the inhibition of calcium release.

Integrated Wnt pathway.

The binary distinction of canonical and non-canonical Wnt signaling pathways has come under scrutiny and an integrated, convergent Wnt pathway has been proposed. Some evidence for this was found for one Wnt ligand (Wnt5A). Evidence for a convergent Wnt signaling pathway that shows integrated activation of Wnt/Ca2+ and Wnt/ß-catenin signaling, for multiple Wnt ligands, was described in mammalian cell lines.

Other pathways.

Wnt signaling also regulates a number of other signaling pathways that have not been as extensively elucidated. One such pathway includes the interaction between Wnt and GSK3. During cell growth, Wnt can inhibit GSK3 in order to activate mTOR in the absence of β-catenin. However, Wnt can also serve as a negative regulator of mTOR via activation of the tumor suppressor TSC2, which is upregulated via Dsh and GSK3 interaction. During myogenesis, Wnt uses PA and CREB to activate MyoD and Myf5 genes. Wnt also acts in conjunction with Ryk and Src to allow for regulation of neuron repulsion during axonal guidance. Wnt regulates gastrulation when CK1 serves as an inhibitor of Rap1-ATPase in order to modulate the cytoskeleton during gastrulation. Further regulation of gastrulation is achieved when Wnt uses ROR2 along with the CDC42 and JNK pathway to regulate the expression of PAPC. Dsh can also interact with aPKC, Pa3, Par6 and LGl in order to control cell polarity and microtubule cytoskeleton development. While these pathways overlap with components associated with PCP and Wnt/Calcium signaling, they are considered distinct pathways because they produce different responses.

Regulation.

In order to ensure proper functioning, Wnt signaling is constantly regulated at several points along its signaling pathways.<ref name="doi:10.1016/j.sbi.2014.10.003"></ref> For example, Wnt proteins are palmitoylated. The protein "porcupine" mediates this process, which means that it helps regulate when the Wnt ligand is secreted by determining when it is fully formed. Secretion is further controlled with proteins such as GPR177 (wntless) and evenness interrupted and complexes such as the retromer complex.<ref name="doi10.1016/j.devcel.2009.06.016"></ref> Upon secretion, the ligand can be prevented from reaching its receptor through the binding of proteins such as the stabilizers Dally and glypican 3 (GPC3), which inhibit diffusion. In cancer cells, both the heparan sulfate chains and the core protein of GPC3 are involved in regulating Wnt binding and activation for cell proliferation. Wnt recognizes a heparan sulfate structure on GPC3, which contains IdoA2S and GlcNS6S, and the 3-O-sulfation in GlcNS6S3S enhances the binding of Wnt to the heparan sulfate glypican. A cysteine-rich domain at the N-lobe of GPC3 has been identified to form a Wnt-binding hydrophobic groove including phenylalanine-41 that interacts with Wnt. Blocking the Wnt binding domain using a nanobody called HN3 can inhibit Wnt activation. At the Fz receptor, the binding of proteins other than Wnt can antagonize signaling. Specific antagonists include Dickkopf (Dkk), Wnt inhibitory factor 1 (WIF-1), secreted Frizzled-related proteins (SFRP), Cerberus, Frzb, Wise, SOST, and Naked cuticle. These constitute inhibitors of Wnt signaling. However, other molecules also act as activators. Norrin and R-Spondin2 activate Wnt signaling in the absence of Wnt ligand. Interactions between Wnt signaling pathways also regulate Wnt signaling. As previously mentioned, the Wnt/calcium pathway can inhibit TCF/β-catenin, preventing canonical Wnt pathway signaling. Prostaglandin E2 is an essential activator of the canonical Wnt signaling pathway. Interaction of PGE2 with its receptors E2/E4 stabilizes β-catenin through cAMP/PKA mediated phosphorylation. The synthesis of PGE2 is necessary for Wnt signaling mediated processes such as tissue regeneration and control of stem cell population in zebrafish and mouse. Intriguingly, the unstructured regions of several oversized Intrinsically disordered proteins play crucial roles in regulating Wnt signaling.

Induced cell responses.

Embryonic development.

Wnt signaling plays a critical role in embryonic development. It operates in both vertebrates and invertebrates, including humans, frogs, zebrafish, "C. elegans", "Drosophila" and others. It was first found in the segment polarity of Drosophila, where it helps to establish anterior and posterior polarities. It is implicated in other developmental processes. As its function in "Drosophila" suggests, it plays a key role in body axis formation, particularly the formation of the anteroposterior and dorsoventral axes. It is involved in the induction of cell differentiation to prompt formation of important organs such as lungs and ovaries. Wnt further ensures the development of these tissues through proper regulation of cell proliferation and migration. Wnt signaling functions can be divided into axis patterning, cell fate specification, cell proliferation and cell migration.

Axis patterning.

In early embryo development, the formation of the primary body axes is a crucial step in establishing the organism's overall body plan. The axes include the anteroposterior axis, dorsoventral axis, and right-left axis. Wnt signaling is implicated in the formation of the anteroposterior and dorsoventral (DV) axes. Wnt signaling activity in anterior-posterior development can be seen in mammals, fish and frogs. In mammals, the primitive streak and other surrounding tissues produce the morphogenic compounds Wnts, BMPs, FGFs, Nodal and retinoic acid to establish the posterior region during late gastrula. These proteins form concentration gradients. Areas of highest concentration establish the posterior region while areas of lowest concentration indicate the anterior region. In fish and frogs, β-catenin produced by canonical Wnt signaling causes the formation of organizing centers, which, alongside BMPs, elicit posterior formation. Wnt involvement in DV axis formation can be seen in the activity of the formation of the Spemann organizer, which establishes the dorsal region. Canonical Wnt signaling β-catenin production induces the formation of this organizer via the activation of the genes twin and siamois. Similarly, in avian gastrulation, cells of the Koller's sickle express different mesodermal marker genes that allow for the differential movement of cells during the formation of the primitive streak. Wnt signaling activated by FGFs is responsible for this movement.  Wnt signaling is also involved in the axis formation of specific body parts and organ systems later in development. In vertebrates, sonic hedgehog (Shh) and Wnt morphogenetic signaling gradients establish the dorsoventral axis of the central nervous system during neural tube axial patterning. High Wnt signaling establishes the dorsal region while high Shh signaling indicates the ventral region. Wnt is involved in the DV formation of the central nervous system through its involvement in axon guidance. Wnt proteins guide the axons of the spinal cord in an anterior-posterior direction. Wnt is also involved in the formation of the limb DV axis. Specifically, Wnt7a helps produce the dorsal patterning of the developing limb.  In the embryonic differentiation waves model of development Wnt plays a critical role as part a signalling complex in competent cells ready to differentiate. Wnt reacts to the activity of the cytoskeleton, stabilizing the initial change created by a passing wave of contraction or expansion and simultaneously signals the nucleus through the use of its different signalling pathways as to which wave the individual cell has participated in. Wnt activity thereby amplifies mechanical signalling that occurs during development.

Cell fate specification.

Cell fate specification or cell differentiation is a process where undifferentiated cells can become a more specialized cell type. Wnt signaling induces differentiation of pluripotent stem cells into mesoderm and endoderm progenitor cells. These progenitor cells further differentiate into cell types such as endothelial, cardiac and vascular smooth muscle lineages. Wnt signaling induces blood formation from stem cells. Specifically, Wnt3 leads to mesoderm committed cells with hematopoietic potential. Wnt1 antagonizes neural differentiation and is a major factor in self-renewal of neural stem cells. This allows for regeneration of nervous system cells, which is further evidence of a role in promoting neural stem cell proliferation. Wnt signaling is involved in germ cell determination, gut tissue specification, hair follicle development, lung tissue development, trunk neural crest cell differentiation, nephron development, ovary development and sex determination. Wnt signaling also antagonizes heart formation, and Wnt inhibition was shown to be a critical inducer of heart tissue during development, and small molecule Wnt inhibitors are routinely used to produce cardiomyocytes from pluripotent stem cells.

Cell proliferation.

In order to have the mass differentiation of cells needed to form the specified cell tissues of different organisms, proliferation and growth of embryonic stem cells must take place. This process is mediated through canonical Wnt signaling, which increases nuclear and cytoplasmic β-catenin. Increased β-catenin can initiate transcriptional activation of proteins such as cyclin D1 and "c-myc", which control the G1 to S phase transition in the cell cycle. Entry into the S phase causes DNA replication and ultimately mitosis, which are responsible for cell proliferation. This proliferation increase is directly paired with cell differentiation because as the stem cells proliferate, they also differentiate. This allows for overall growth and development of specific tissue systems during embryonic development. This is apparent in systems such as the circulatory system where Wnt3a leads to proliferation and expansion of hematopoietic stem cells needed for red blood cell formation.  The biochemistry of cancer stem cells is subtly different than that of other tumor cells. These so-called Wnt-addicted cells hijack and depend on constant stimulation of the Wnt pathway to promote their uncontrolled growth, survival and migration. In cancer, Wnt signaling can become independent of regular stimuli, through mutations in downstream oncogenes and tumor suppressor genes that become permanently activated even though the normal receptor has not received a signal. β-catenin binds to transcription factors such as the protein TCF4 and in combination the molecules activate the necessary genes. LF3 strongly inhibits this binding "in vitro," in cell lines and reduced tumor growth in mouse models. It prevented replication and reduced their ability to migrate, all without affecting healthy cells. No cancer stem cells remained after treatment. The discovery was the product of "rational drug design", involving AlphaScreens and ELISA technologies.

Cell migration.

Cell migration during embryonic development allows for the establishment of body axes, tissue formation, limb induction and several other processes. Wnt signaling helps mediate this process, particularly during convergent extension. Signaling from both the Wnt PCP pathway and canonical Wnt pathway is required for proper convergent extension during gastrulation. Convergent extension is further regulated by the Wnt/calcium pathway, which blocks convergent extension when activated. Wnt signaling also induces cell migration in later stages of development through the control of the migration behavior of neuroblasts, neural crest cells, myocytes, and tracheal cells.  Wnt signaling is involved in another key migration process known as the epithelial-mesenchymal transition (EMT). This process allows epithelial cells to transform into mesenchymal cells so that they are no longer held in place at the laminin. It involves cadherin down-regulation so that cells can detach from laminin and migrate. Wnt signaling is an inducer of EMT, particularly in mammary development.

Insulin sensitivity.

Insulin is a peptide hormone involved in glucose homeostasis within certain organisms. Specifically, it leads to upregulation of glucose transporters in the cell membrane in order to increase glucose uptake from the bloodstream. This process is partially mediated by activation of Wnt/β-catenin signaling, which can increase a cell's insulin sensitivity. In particular, Wnt10b is a Wnt protein that increases this sensitivity in skeletal muscle cells.

Clinical implications.

Cancer.

Since its initial discovery, Wnt signaling has had an association with cancer. When Wnt1 was discovered, it was first identified as a proto-oncogene in a mouse model for breast cancer. The fact that Wnt1 is a homolog of Wg shows that it is involved in embryonic development, which often calls for rapid cell division and migration. Misregulation of these processes can lead to tumor development via excess cell proliferation.  Canonical Wnt pathway activity is involved in the development of benign and malignant breast tumors. Its presence is revealed by elevated levels of β-catenin in the nucleus and/or cytoplasm, which can be detected with immunohistochemical staining and Western blotting. Increased β-catenin expression is correlated with poor prognosis in breast cancer patients. This accumulation may be due to factors such as mutations in β-catenin, deficiencies in the β-catenin destruction complex, most frequently by mutations in structurally disordered regions of APC, overexpression of Wnt ligands, loss of inhibitors and/or decreased activity of regulatory pathways (such as the Wnt/calcium pathway). Breast tumors can metastasize due to Wnt involvement in EMT. Research looking at metastasis of basal-like breast cancer to the lungs showed that repression of Wnt/β-catenin signaling can prevent EMT, which can inhibit metastasis.  Wnt signaling has been implicated in the development of other cancers. Changes in CTNNB1 expression, which is the gene that encodes β-catenin, can be measured in breast, colorectal, melanoma, prostate, lung, and other cancers. Increased expression of Wnt ligand-proteins such as Wnt1, Wnt2 and Wnt7A were observed in the development of glioblastoma, oesophageal cancer and ovarian cancer respectively. Other proteins that cause multiple cancer types in the absence of proper functioning include ROR1, ROR2, SFRP4, Wnt5A, WIF1 and those of the TCF/LEF family.  The link between PGE2 and Wnt suggests that a chronic inflammation-related increase of PGE2 may lead to activation of the Wnt pathway in different tissues, resulting in carcinogenesis.

Type II diabetes.

Diabetes mellitus type 2 is a common disease that causes reduced insulin secretion and increased insulin resistance in the periphery. It results in increased blood glucose levels, or hyperglycemia, which can be fatal if untreated. Since Wnt signaling is involved in insulin sensitivity, malfunctioning of its pathway could be involved. Overexpression of Wnt5b, for instance, may increase susceptibility due to its role in adipogenesis, since obesity and type II diabetes have high comorbidity. Wnt signaling is a strong activator of mitochondrial biogenesis. This leads to increased production of reactive oxygen species (ROS) known to cause DNA and cellular damage. This ROS-induced damage is significant because it can cause acute hepatic insulin resistance, or injury-induced insulin resistance. Mutations in Wnt signaling-associated transcription factors, such as TCF7L2, are linked to increased susceptibility.

The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans.

Wnt信号通路是一个复杂的蛋白质作用网络,其功能最常见于胚胎发育和癌症,但也参与成年动物的正常生理过程。 现在已鉴别出三种Wnt信号通路:经典Wnt通路(canonical Wnt pathway)、非经典Wnt/平面细胞极化通路(noncanonical Wnt/planar cell polarity pathway,PCP)和非经典Wnt/钙离子通路(noncanonical Wnt/calcium pathway)。所有这三种Wnt信号通路都由Wnt蛋白配体与其受体卷曲受体的结合来激活,将信号传给胞内的散乱蛋白。经典Wnt信号通路参与基因表达的调控,非经典平面细胞极化通路调控细胞骨架控制细胞形状,非经典Wnt/钙离子通路调控细胞内钙离子的浓度。Wnt信号通路常用于临近的细胞之间的通信(旁分泌)或同个细胞自身的通信(自分泌信号传送)。Wnt信号通路在动物中高度保守,从果蝇到人类都非常类似<ref name=doi10.1016/0092-8674(92)90630-U>。


Overview.

One of the early computer networking designs, development of the ALOHA network was begun in September 1968 at the University of Hawaii under the leadership of Norman Abramson along with Thomas Gaarder, Franklin Kuo, Shu Lin, Wesley Peterson and Edward ("Ned") Weldon. The goal was to use low-cost commercial radio equipment to connect users on Oahu and the other Hawaiian islands with a central time-sharing computer on the main Oahu campus. The first packet broadcasting unit went into operation in June 1971. Terminals were connected to a special purpose "terminal connection unit" using RS-232 at 9600 bit/s.  The initial purpose of the ALOHA System was to provide a systematically different designer interaction for radio communications. This alternative method allows the system to determine when and where radio communications are "preferable" to wired communications. It made practical means of communication and made accessibility of differing networks plausible.  The original version of ALOHA used two distinct frequencies in a hub configuration, with the hub machine broadcasting packets to everyone on the "outbound" channel, and the various client machines sending data packets to the hub on the "inbound" channel. If data was received correctly at the hub, a short acknowledgment packet was sent to the client; if an acknowledgment was not received by a client machine after a short wait time, it would automatically retransmit the data packet after waiting a randomly selected time interval. This acknowledgment mechanism was used to detect and correct for "collisions" created when two client machines both attempted to send a packet at the same time.  ALOHAnet's primary importance was its use of a shared medium for client transmissions. Unlike the ARPANET where each node could only talk directly to a node at the other end of a wire or satellite circuit, in ALOHAnet all client nodes communicated with the hub on the same frequency. This meant that some sort of mechanism was needed to control who could talk at what time. The ALOHAnet solution was to allow each client to send its data without controlling when it was sent, with an acknowledgment/retransmission scheme used to deal with collisions. This approach radically reduced the complexity of the protocol and the networking hardware, since nodes do not need negotiate "who" is allowed to speak (see: Token Ring).  This solution became known as a pure ALOHA, or random-access channel, and was the basis for subsequent Ethernet development and later Wi-Fi networks. Various versions of the ALOHA protocol (such as Slotted ALOHA) also appeared later in satellite communications, and were used in wireless data networks such as ARDIS, Mobitex, CDPD, and GSM.  Also important was ALOHAnet's use of the outgoing hub channel to broadcast packets directly to all clients on a second shared frequency, using an address in each packet to allow selective receipt at each client node. Two frequencies were used so that a device could both receive acknowledgments regardless of transmissions. The Aloha network introduced the mechanism of randomized multiple access, which resolved device transmission collisions by transmitting a package immediately if no acknowledgement is present, and if no acknowledgment was received, the transmission was repeated after a random waiting time.

ALOHA protocol.

Pure ALOHA.

The version of the protocol (now called "Pure ALOHA", and the one implemented in ALOHAnet) was quite simple:  Note that the first step implies that Pure ALOHA does not check whether the channel is busy before transmitting. Since collisions can occur and data may have to be sent again, ALOHA cannot use 100% of the capacity of the communications channel. How long a station waits until it transmits, and the likelihood a collision occurs are interrelated, and both affect how efficiently the channel can be used. This means that the concept of "transmit later" is a critical aspect: the quality of the backoff scheme chosen significantly influences the efficiency of the protocol, the ultimate channel capacity, and the predictability of its behavior.  To assess Pure ALOHA, there is a need to predict its throughput, the rate of (successful) transmission of frames. (This discussion of Pure ALOHA's performance follows Tanenbaum.) First, let's make a few simplifying assumptions: Let ""T"" refer to the time needed to transmit one frame on the channel, and let's define "frame-time" as a unit of time equal to "T". Let ""G"" refer to the mean used in the Poisson distribution over transmission-attempt amounts: that is, on average, there are "G" transmission-attempts per frame-time.  Consider what needs to happen for a frame to be transmitted successfully. Let ""t"" refer to the time at which it is intended to send a frame. It is preferable to use the channel for one frame-time beginning at "t", and all other stations to refrain from transmitting during this time.  For any frame-time, the probability of there being "k" transmission-attempts during that frame-time is:  formula_1  The average amount of transmission-attempts for 2 consecutive frame-times is 2"G". Hence, for any pair of consecutive frame-times, the probability of there being "k" transmission-attempts during those two frame-times is:  formula_2  Therefore, the probability (formula_3) of there being zero transmission-attempts between "t-T" and "t+T" (and thus of a successful transmission for us) is:  formula_4  The throughput can be calculated as the rate of transmission-attempts multiplied by the probability of success, and it can be concluded that the throughput (formula_5) is:  formula_6 Vulnerable time=2*T.  The maximum throughput is "0.5/e" frames per frame-time (reached when "G" = 0.5), which is approximately 0.184 frames per frame-time. This means that, in Pure ALOHA, only about 18.4% of the time is used for successful transmissions.  Another simple way to establish the equation for throughput in Pure ALOHA (and in Slotted ALOHA) is as follows:  Consider what needs to happen for frames to be transmitted successfully. Let T represent the frame time. For simplicity, it is assumed that the contention begins at t=0. Then if exactly one node sends during interval t=0 to t=T and no node tries between t=T to t=2T, then the frame will be transmitted successfully. Similarly during all next time intervals t=2nT to t=(2n+1)T, exactly one node sends and during t=(2n+1)T to t=(2n+2)T no node tries to send where n=1,2,3,..., then the frames are successfully transmitted. But in pure ALOHA, the nodes begin transmission whenever they want to do so without checking that what other nodes are doing at that time. Thus sending frames are independent events, that is, transmission by any particular node neither affects nor is affected by the time of start of transmission by other nodes. Let G be the average number of nodes that begin transmission within period T (the frame time). If a large number of nodes is trying to transmit, then by using Poisson distribution, the probability that exactly x nodes begin transmission during period T is  formula_7  Therefore, the probability that during any particular period from t=2nT to t=(2n+1)T, (that is for any particular non-zero integer value of n) exactly one node will begin transmission is  formula_8  And the probability that during any particular period t=(2n+1)T to t=(2n+2)T, no node will begin transmission is  formula_9  But for successful transmission of a frame, both the events should occur simultaneously. That is during period t=2nT to t=(2n+1)T, exactly one node begins transmission and during t=(2n+1)T to t=(2n+2)T no node begins transmission. Hence the probability that both the independent events will occur simultaneously is  formula_10  This is the throughput. Throughput is intended to mean the probability of successful transmission during minimum possible period. Therefore, the throughput in pure ALOHA,  formula_6  Suppose:  1) There are N nodes attempt to send data at time T. 2) The probability of successful transmission of one node is formula_12.  Then, the probability of successful transmission like following:  formula_13  Similarly for slotted ALOHA, a frame will be successfully transmitted, if exactly one node will begin transmission at the beginning of any particular time slot (equal to frame time T). But the probability that one node will begin during any particular time slot is  formula_14  This is the throughput in slotted ALOHA. Thus,  formula_15  Disadvantages of Pure ALOHA:  1) Time is wasted  2) Data is lost

Slotted ALOHA.

An improvement to the original ALOHA protocol was "Slotted ALOHA", which introduced discrete timeslots and increased the maximum throughput. A station can start a transmission only at the beginning of a timeslot, and thus collisions are reduced. In this case, only transmission-attempts within 1 frame-time and not 2 consecutive frame-times need to be considered, since collisions can only occur during each timeslot. Thus, the probability of there being zero transmission-attempts by other stations in a single timeslot is:  formula_16  the probability of a transmission requiring exactly k attempts is (k-1 collisions and 1 success):  formula_17  The throughput is:  formula_18  The maximum throughput is "1/e" frames per frame-time (reached when "G" = 1), which is approximately 0.368 frames per frame-time, or 36.8%.  Slotted ALOHA is used in low-data-rate tactical satellite communications networks by military forces, in subscriber-based satellite communications networks, mobile telephony call setup, set-top box communications and in the contactless RFID technologies.

Other protocol.

The use of a random-access channel in ALOHAnet led to the development of carrier sense multiple access (CSMA), a "listen before send" random-access protocol that can be used when all nodes send and receive on the same channel. The first implementation of CSMA was Ethernet. CSMA in radio channels was extensively modeled. The AX.25 packet radio protocol is based on the CSMA approach with collision recovery, based on the experience gained from ALOHAnet.  ALOHA and the other random-access protocols have an inherent variability in their throughput and delay performance characteristics. For this reason, applications which need highly deterministic load behavior sometimes used polling or token-passing schemes (such as token ring) instead of contention systems. For instance ARCNET was popular in embedded data applications in the 1980 network.

Design.

Network architecture.

Two fundamental choices which dictated much of the ALOHAnet design were the two-channel star configuration of the network and the use of random accessing for user transmissions.  The two-channel configuration was primarily chosen to allow for efficient transmission of the relatively dense total traffic stream being returned to users by the central time-sharing computer. An additional reason for the star configuration was the desire to centralize as many communication functions as possible at the central network node (the Menehune), minimizing the cost of the original all-hardware terminal control unit (TCU) at each user node.  The random-access channel for communication between users and the Menehune was designed specifically for the traffic characteristics of interactive computing. In a conventional communication system a user might be assigned a portion of the channel on either a frequency-division multiple access (FDMA) or time-division multiple access (TDMA) basis. Since it was well known that in time-sharing systems [circa 1970], computer and user data are bursty, such fixed assignments are generally wasteful of bandwidth because of the high peak-to-average data rates that characterize the traffic.  To achieve a more efficient use of bandwidth for bursty traffic, ALOHAnet developed the random-access packet switching method that has come to be known as a "pure ALOHA" channel. This approach effectively dynamically allocates bandwidth immediately to a user who has data to send, using the acknowledgment/retransmission mechanism described earlier to deal with occasional access collisions. While the average channel loading must be kept below about 10% to maintain a low collision rate, this still results in better bandwidth efficiency than when fixed allocations are used in a bursty traffic context.  Two 100 kHz channels in the experimental UHF band were used in the implemented system, one for the user-to-computer random-access channel and one for the computer-to-user broadcast channel. The system was configured as a star network, allowing only the central node to receive transmissions in the random-access channel. All user TCUs received each transmission made by the central node in the broadcast channel. All transmissions were made in bursts at 9600 bit/s, with data and control information encapsulated in packets.  Each packet consisted of a 32-bit header and a 16-bit header parity check word, followed by up to 80 bytes of data and a 16-bit parity check word for the data. The header contained address information identifying a particular user so that when the Menehune broadcast a packet, only the intended user's node would accept it.

Menehune.

The central node communications processor was an HP 2100 minicomputer called the Menehune, which is the Hawaiian language word for "imp", or dwarf people, and was named for its similar role to the original ARPANET Interface Message Processor (IMP) which was being deployed at about the same time. In the original system, the Menehune forwarded correctly received user data to the UH central computer, an IBM System 360/65 time-sharing system. Outgoing messages from the 360 were converted into packets by the Menehune, which were queued and broadcast to the remote users at a data rate of 9600 bit/s. Unlike the half-duplex radios at the user TCUs, the Menehune was interfaced to the radio channels with full-duplex radio equipment.

Remote units.

The original user interface developed for the system was an all-hardware unit called an ALOHAnet Terminal Control Unit (TCU), and was the sole piece of equipment necessary to connect a terminal into the ALOHA channel. The TCU was composed of a UHF antenna, transceiver, modem, buffer and control unit. The buffer was designed for a full line length of 80 characters, which allowed handling of both the 40- and 80-character fixed-length packets defined for the system. The typical user terminal in the original system consisted of a Teletype Model 33 or a dumb CRT user terminal connected to the TCU using a standard RS-232C interface. Shortly after the original ALOHA network went into operation, the TCU was redesigned with one of the first Intel microprocessors, and the resulting upgrade was called a PCU (Programmable Control Unit).  Additional basic functions performed by the TCU's and PCU's were generation of a cyclic-parity-check code vector and decoding of received packets for packet error-detection purposes, and generation of packet retransmissions using a simple random interval generator. If an acknowledgment was not received from the Menehune after the prescribed number of automatic retransmissions, a flashing light was used as an indicator to the human user. Also, since the TCU's and PCU's did not send acknowledgments to the Menehune, a steady warning light was displayed to the human user when an error was detected in a received packet. Thus it can be seen that considerable simplification was incorporated into the initial design of the TCU as well as the PCU, making use of the fact that it was interfacing a human user into the network.

Later developments.

In later versions of the system, simple radio relays were placed in operation to connect the main network on the island of Oahu to other islands in Hawaii, and Menehune routing capabilities were expanded to allow user nodes to exchange packets with other user nodes, the ARPANET, and an experimental satellite network. More details are available in and in the technical reports listed in the Further Reading section below.

ALOHAnet, also known as the ALOHA System, or simply ALOHA, was a pioneering computer networking system developed at the University of Hawaii. ALOHAnet became operational in June, 1971, providing the first public demonstration of a wireless packet data network. ALOHA originally stood for Additive Links On-line Hawaii Area.

ALOHA网络(英语:ALOHAnet,或英语:ALOHA),也称为ALOHA系统(英语:ALOHA system),是由美国夏威夷大学所开发的实验性电脑网络系统。在1971年6月开始成功运作,是世界上第一个无线资料网络。


Background.

Kenneth Grahame was born on 8 March 1859 in Edinburgh. When he was 5, his mother died from puerperal fever, and his father, who had a drinking problem, gave the care of his four children over to their grandmother, who lived in Cookham Dean in Berkshire. There they lived in a spacious but dilapidated home, "The Mount", in extensive grounds by the River Thames, and were introduced to the riverside and boating by their uncle, David Ingles, curate at Cookham Dean church.  At Christmas 1865 the chimney of the house collapsed and the children moved to Fern Hill Cottage in Cranbourne, Berkshire. In 1866, their father tried to overcome his drinking problem and took the children back to live with him in Argyll, Scotland, but after a year they returned to their grandmother's house in Cranbourne, where Kenneth lived until he entered St Edward's School, Oxford in 1868. During his early years at St. Edwards the boys were free to explore the old city with its quaint shops, historic buildings, and cobbled streets, St Giles' Fair, the idyllic upper reaches of the River Thames, and the nearby countryside.  Grahame married Elspeth Thomson in 1899, when he was 40; the next year they had their only child, a boy named Alastair (whose nickname was "Mouse") born premature, blind in one eye, and plagued by health problems throughout his life. When Alastair was about four years old, Grahame would tell him bedtime stories, some of which were about a toad, and on his frequent boating holidays without his family he would write further tales of Toad, Mole, Ratty, and Badger in letters to Alastair.  In 1908 Grahame took early retirement from his job at the Bank of England and moved with his wife and son to an old farmhouse in Blewbury, where he used the bedtime stories he had told Alastair as a basis for the manuscript of "The Wind in the Willows".

Plot summary.

Mole meets Rat.

With the arrival of spring and fine weather outside, the good-natured Mole loses patience with spring cleaning. He has fled his underground home, emerging to take in the air and ends up at the river, which he has never seen before. Here he meets Rat (a water vole), who at this time of year spends all his days in, on and close by the river. Rat takes Mole for a ride in his rowing boat. They get along well and spend many more days boating, with “Ratty” teaching Mole the ways of the river, with the two friends living together in Ratty's riverside home.

Toad.

One summer day, Rat and Mole disembark near the grand Toad Hall and pay a visit to Toad. Toad is rich, jovial, friendly and kind-hearted, but aimless and conceited; he regularly becomes obsessed with current fads, only to abandon them abruptly. Having recently given up boating, Toad's current craze is his horse-drawn caravan. He persuades the reluctant Rat and willing Mole to join him on a trip. Toad soon tires of the realities of camp life, and sleeps in the following day to avoid chores. Later that day, a passing motorcar scares the horse, causing the caravan to overturn into a ditch. Rat threatens to have the law on the car driver, while Mole calms the horse, but Toad's craze for caravan travel is immediately replaced by an obsession with motorcars.

The Wild Wood and Badger.

Mole wants to meet the respected but elusive Badger, who lives deep in the Wild Wood, but Rat – knowing that Badger does not appreciate visits – tells Mole to be patient and wait for Badger to pay them a visit himself. Nevertheless, on a snowy winter's day, while the seasonally somnolent Rat dozes, Mole impulsively goes to the Wild Wood to explore, hoping to meet Badger. He gets lost in the woods, sees many "evil faces" among the wood's less-welcoming denizens, succumbs to fright and panic and hides, trying to stay warm, among the sheltering roots of a tree.  Rat wakes to find Mole gone. Guessing his mission from the direction of Mole's tracks and equipping himself with two pistols and a stout cudgel, Rat goes in search, finding him as snow begins to fall in earnest. Attempting to find their way home, Rat and Mole quite literally stumble across Badger's home – Mole barks his shin on the boot scraper on Badger's doorstep. Badger – en route to bed in his dressing-gown and slippers – nonetheless warmly welcomes Rat and Mole to his large and cosy underground home, providing them with hot food, dry clothes, and reassuring conversation: "It takes all sorts to make a world."

Toad and motorcars.

Badger learns from his visitors that Toad has crashed seven cars, has been in hospital three times, and has spent a fortune on fines. Though nothing can be done at the moment (it being winter), they resolve that when the time is right they will make a plan to protect Toad from himself; they are, after all, his friends, and are worried about his well-being.  With the arrival of spring, Badger visits Mole and Rat to take action over Toad's self-destructive obsession. The three of them go to Toad Hall, and Badger tries talking Toad out of his behavior, to no avail. They put Toad under house arrest, with themselves as the guards, until Toad changes his mind. Feigning illness, Toad bamboozles Rat (who is on guard duty at the time) and escapes.  Badger and Mole are cross with Rat for his gullibility, but draw comfort because they need no longer waste their summer guarding Toad. However, Badger and Mole continue to live in Toad Hall in the hope that Toad may return. Meanwhile, Toad orders lunch at The Red Lion Inn, and then sees a motorcar pull into the courtyard. Taking the car, he drives it recklessly and is caught by the police. He is sent to prison for 20 years.

Toad escapes from prison.

In prison, Toad gains the sympathy of the gaoler's daughter, who helps him to escape disguised as a washerwoman. Though free again, Toad is without money or possessions other than the clothes upon his back. He manages to board a railway engine manned by a sympathetic driver, which is then pursued by a special train loaded with policemen, detectives and prison warders. Toad jumps from the train and, still disguised as a washerwoman, comes across a horse-drawn barge. The barge's female owner offers him a lift in exchange for Toad's services as a washerwoman. After he botches the wash, Toad gets into a fight with the barge-woman, who tosses him into the canal. In revenge, Toad makes off with the barge horse, which he then sells to a gypsy.  Toad subsequently flags down a passing car, which happens to be the very one he stole earlier. The car owners, not recognising Toad in his disguise, permit him to drive their car. Once behind the wheel, he is repossessed by his former exuberance and drives furiously, declaring his true identity to the passengers who try to seize him. This leads to the car landing in a horse-pond, after which Toad flees once more. Pursued by police, he runs accidentally into a river, which carries him by sheer chance to the house of Rat.

Recapture of Toad Hall.

Toad now hears from Rat that Toad Hall has been taken over by weasels and stoats from the Wild Wood, who have driven out Mole and Badger. Although upset at the loss of his house, Toad realizes what good friends he has and how badly he has behaved. Badger then arrives and announces that he knows of a secret tunnel into Toad Hall through which the enemies may be attacked. Armed to the teeth, Badger, Rat, Mole and Toad enter through the tunnel and pounce upon the unsuspecting Wild-Wooders who are holding a celebratory party. Having driven away the intruders, Toad holds a banquet to mark his return, during which (for a change) he behaves both quietly and humbly. He makes up for his earlier excesses by seeking out and compensating those he has wronged, and the four friends live out their lives happily ever after.

Short stories.

In addition to the main narrative, the book contains several independent short stories featuring Rat and Mole. These appear for the most part between the chapters chronicling Toad's adventures, and are often omitted from abridgements and dramatisations. The chapter "Dulce Domum" describes Mole's return to his home with Rat where he rediscovers, with Rat's help, a familiar comfort, despite finding it in a terrible mess after his abortive spring clean. "The Piper at the Gates of Dawn" tells how Mole and Rat search for Otter's missing son Portly, whom they find in the care of the god Pan. (Pan removes their memories of this meeting ""lest the awful remembrance should remain and grow, and overshadow mirth and pleasure"".) Finally, in "Wayfarers All", Ratty shows a restless side to his character when he is sorely tempted to join a Sea Rat on his travelling adventures.

Editions.

The original publication of the book was plain text, with a frontispiece illustrated by Graham Robertson, but many illustrated, comic, and annotated versions have been published over the years. Notable illustrators include Paul Bransom (1913), Nancy Barnhart (1922), Wyndham Payne (1927), Ernest H. Shepard (1931), Arthur Rackham (1940), Richard Cuffari (1966), Tasha Tudor (1966), Michael Hague (1980), Scott McKowen (2005), and Robert Ingpen (2007).

Reception.

A number of publishers rejected the manuscript. It was published in the UK by Methuen and Co., and later in the US by Scribner. The critics, who were hoping for a third volume in the style of Grahame's earlier works; "The Golden Age" and "Dream Days", generally gave negative reviews. The public loved it, however, and within a few years it sold in such numbers that many reprints were required. In 1909, then sitting US President Theodore Roosevelt wrote to Grahame to tell him that he had "read it and reread it, and have come to accept the characters as old friends".  In "The Enchanted Places", Christopher Robin Milne wrote of "The Wind in the Willows":

Adaptations.

Television.

Unproduced

Radio.

The BBC has broadcast a number of radio productions of the story. Dramatisations include:  Abridged readings include:  Other presentation formats:

Inspiration.

Mapledurham House in Oxfordshire was an inspiration for Toad Hall, although Hardwick House and Fawley Court also make this claim.  The village of Lerryn, Cornwall claims to be the setting for the book.  Simon Winchester suggested that the character of Ratty was based on Frederick Furnivall, a keen oarsman and acquaintance of Kenneth Grahame. However, Grahame himself said that this character was inspired by his good friend, the writer Sir Arthur Quiller-Couch. Grahame wrote this in a signed copy he gave to Quiller-Couch's daughter, Foy Felicia.  "The Scotsman" and "Oban Times" suggested was inspired by the Crinan Canal because Grahame spent some of his childhood in Ardrishaig.  There is a proposal that the idea for the story arose when its author saw a water vole beside the River Pang in Berkshire, southern England. A 29 hectare extension to the nature reserve at Moor Copse, near Tidmarsh Berkshire, was acquired in January 2007 by the Berks, Bucks, and Oxon Wildlife Trust.  Peter Ackroyd in his book "Thames: sacred river" asserts that "Quarry Wood, bordering on the river [Thames] at Cookham Dean, is the original of [the] 'Wild Wood'...."

The Wind in the Willows is a children's novel by Scottish novelist Kenneth Grahame, first published in 1908. Alternatingly slow-moving and fast-paced, it focuses on four anthropomorphised animals: Mole, Rat (a European water vole), Toad, and Badger. They live in a pastoral version of Edwardian England. The novel is notable for its mixture of mysticism, adventure, morality, and camaraderie, and celebrated for its evocation of the nature of the Thames Valley.

《柳林风声》(英语:The Wind in the Willows)或译「柳林中的风声」,是英国小说家肯尼思·格拉姆的代表作,也是经典的儿童文学作品,出版于1908年。


Development.

During the 1970s the world's commuter airline market began to evolve from the 20-seat class to larger and more comfortable cabins. Short Brothers of Northern Ireland had created the Skyvan in 1962, followed by the related but larger Short 330 in 1974. The Short 360 development was announced in 1980, with the prototype's first flight on 1 June 1981 and type certification awarded on 3 September 1981.  The first production Short 360 had its maiden flight on 19 August 1982 and entered service with Suburban Airlines (later merged with Allegheny Airlines/US Airways) in November 1982.  After initiating production with the basic model, Short marketed a number of 360 developments. First was the "360 Advanced", in late 1985, with 1,424 shp (1,062 kW) PT6A-65-AR engines. That was followed by the "360/300", in March 1987, with six-blade propellers, more powerful PT6A-67R engines, and aerodynamic improvements, giving a higher cruise speed and improved "hot and high" performance. The 360/300 was also built in 360/300F freighter configuration.  Production of the 360 ceased in 1991 after 165 deliveries.

Design.

The Short 360 is a 36-seat derivative of the 30–33 seat Short 330. In high density configuration, 39 passengers could be carried. The two Short airliners have a high degree of commonality and are very close in overall dimensions. The later 360 is easily identified by a larger, swept tail unit mounted on a revised rear fuselage. The 360 has a 3'0" (91 cm) fuselage "plug" which gave sufficient additional length for two more seat rows (six more passengers), while the extra length smoothed out the aerodynamic profile and reduced drag. Seating is arranged with two seats on the starboard side of the cabin and one seat on the port side. The 360's power is supplied by two Pratt & Whitney PT6A-65Rs.  Building on the strengths and reputation of its 330 antecedent, the 360s found a niche in regional airline use worldwide, being able to operate comfortably from 4,500 ft (1,400 m) runways – opening up hundreds of airfields that would otherwise be inaccessible to airliners. With a cruise speed about 215 mph (370 km/h), at an altitude of 10,000 ft (3,048 m), the unpressurized 360 was not the fastest turboprop in its market but it offered acceptable performance at a reasonable price combined with ease of service and maintainability. The PT6A turboprops are fully ICAO Stage 3 noise-compliant, making the 360 one of the quietest turboprop aircraft operating today.

Operators.

In 1998, approximately 110 360s were in service. In 2017 there were 42 Short 360 in service: 17 with Air Cargo Carriers, 6 with TransAir, 4 with Skyway Enterprises, 3 with Air Flamenco, 2 with Benair, Deraya Air Taxi and Freedom Air (Guam), 1 with Ayit Aviation, Comeravia, Gryphon Airlines, International Trans Air Business, Malu Aviation and Nightexpress. The Short 360 specifically proved very popular with the UK's regional airlines including the Isle of Man-based-Manx. This fed passengers into larger hubs in England, Scotland and Ireland.  Current and previous operators have included:

Civil operators.

A number of small air cargo airlines have also operated the Short 360 in freight operations in the U.S.

Accidents and incidents.

The Short 360 has been involved in 15 hull-loss accidents, resulting in the loss of 16 airframes.

The Short 360 (also SD3-60; also Shorts 360) is a commuter aircraft that was built by Northern Irish manufacturer Short Brothers during the 1980s. The Short 360 seats up to 39 passengers and was introduced into service in November 1982. It is a larger version of the Short 330.

肖特360(英语:Short 360,又名:英语:SD3-60),由肖特兄弟公司研发,以肖特330为基础的小飞机,载客量达39人,于1981年投入服务,是肖特330的延长版。


卡拉科尔 (吉尔吉斯斯坦)

History.

A Russian military outpost founded on 1 July 1869, Karakol grew in the 19th century after explorers came to map the peaks and valleys separating Kyrgyzstan from China. In the 1880s Karakol's population surged with an influx of Dungans, Chinese Muslims fleeing warfare in China.  In 1888, the Russian explorer Nicholay Przhevalsky died in Karakol of typhoid, while preparing for an expedition to Tibet, the city was renamed Przhevalsk in his honor. After local protests, the town was given its original name back in 1921—a decision reversed in 1939 by Stalin to celebrate the centenary of the explorer's birth. Karakol then remained Przhevalsk until the demise of the Soviet Union in 1991. However the name has been retained by nearby Pristan'-Przheval'sk.  Nearby Issyk Kul Lake was used by the Soviet military as a testing site for torpedo propulsion and guidance systems and Karakol was thus home to a sizable population of military personnel and their families. Karakol continues to be a major hub for visitors of Issyk Kul Lake.

Demographics.

Karakol is fourth largest town in Kyrgyzstan after Bishkek, Osh and Jalal-Abad. The population of Karakol, according to the Population and Housing Census of 2009, was 67,100.

Geography.

Climate.

Karakol features a humid continental climate ("Dfb") according to the Köppen climate classification.

Sights.

Karakol is one of Kyrgyzstan's major tourist destinations, serving as a good starting point for the excellent hiking, trekking, skiing and mountaineering in the high central Tian Shan to the south and east. Also this city is culturally rich by different ethnic groups that live here such as Dungan, Uighur, Kalmak, Uzbek, Russians and of course Kyrgyz. The city offers a great opportunity to discover other nationalities and cultures within the city.  Przhevalsky's grave, a memorial park and a small museum dedicated to his and other Russian explorations in Central Asia are some north of Karakol at Pristan Przhevalsky, overlooking the Mikhailovka inlet of Issyk Kul Lake where the former Soviet torpedo testing facilities were located. Facilities themselves are still a closed, military area.  Karakol has Central Asia's highest ski resort, with 20 km of slopes, situated just 20 minutes from the town. Unlike Shymbulak resort, the riding at Karakol includes forest areas as well as cleared trails.

Russian Orthodox cathedral.

The cathedral was originally built of stone in 1872, when Karakol was a garrison town established as an outpost on the edges of the Tsarist Russian Empire. It was destroyed in 1890 by an earthquake and the current cathedral was built out of wood on a brick base. It took six years to complete, and was finally completed in 1895. During the period of construction, a yurt served the congregation as a church. It has seen considerable service, not just as a church. During an anti-Russian uprising in 1916 its monks were brutally murdered.  Over the years, particularly following the Revolution in 1917, it has been used as an educational center housing a school, ladies' gymnasium and an institution of Higher Education; a Sports Hall; a Theater; a Dance Hall and even as a Coal Store. Then, in 1991, following the collapse of the Soviet Union and the Independence of Kyrgyzstan, the local authority once again gave the building back to the church, with the proviso that all further restorations were their responsibility.

Dungan mosque.

The Issyk-kul Central Mosque of Karakol city was built for the local Dungan community by an initiative of Ibrahim Aji. He invited the famous Beijing architect Chou Seu and 20 carvers with the skills of traditional Chinese architecture and composition techniques for building the mosque. The construction of outbuildings and other work involved local craftsmen. Construction of the mosque began in 1904 and was completed in 1910. Ingenious techniques allowed the builders to build the mosque with no nails. The mosque holds 42 based pillars and encircling the building is multi-tiered wooden cornice, decorated with images of plants like grapes, pomegranates, pears and peaches. From 1929 to 1947 (during the Soviet era) the mosque was used as a storehouse. In 1947, the building was given to the Muslim community and continues to function as a mosque. It is registered as a historical monument and protected by law. Today the mosque is open to visitors.

Przhevalsky Museum.

Nikolay Przhevalsky was one of the first Russian Scientist-Geographer to start detailed studies of the geography, flora and fauna of the Central Asian countries. Beginning from 1870, he arranged four large expeditions to Mongolia, China and Tibet. During his expeditions he revealed the exact directions of the mountain ranges and borders of the Tibet Mountains. He described the nature, relief, climate, flora and fauna in the territories under his study and discovered over 200 plant species. Przhevalsky also collected an enormous zoological collection which comprised several thousand species of plants, animals, birds, fishes and insects. In the year of 1888, he died from typhoid fever on the eve of his fifth expedition to Central Asia; he was buried on the Issyk-Kul lakeside not far from the city of Karakol. The Memorial Museum of N. M. Przhevalsky was opened on 29 April 1957 in Karakol.

Karakol Historical Museum.

This small museum was the pre-revolutionary summer home of the Iliana merchant family. During the turbulent years of 1918–20 the building earned its socialist stripes as headquarters of the Regional Revolutionary Committee, and was subsequently transformed into a museum by order of the Soviet Council of Ministers in 1948. Scythian artifacts include enormous bronze pots retrieved from Lake Issyk-Kul, displayed alongside exhibits on petroglyphs in the area. Besides a comprehensive display of traditional Kyrgyz punched leather work, felt wall hangings and woven yurt decorations, the museum has a colorful collection of national costumes, examples of finely worked silver jewellery and a good exhibition of Kyrgyz applied art. One hall covers the region's flora and fauna – much of which is endangered and listed in the 'Red Book' (a Soviet inventory of protected species). The museum is also worth visiting to gain a Soviet perspective of history in the region. A couple of walls relating to Kyrgyz union with Russia and the subsequent revolution are now historical artifacts in themselves.

Bugu-Ene Zoo.

Karakol Zoological Park was founded in 1987. This is the only zoo in Kyrgyzstan. After the demise of the Soviet Union, the economics of the country collapsed, and it concerned the newly created object culture. In 2001, closing the zoo was considered. However, sponsors were found, which not only allowed to preserve the wildlife area, but also allowed to keep it in a relatively prosperous state. Nowadays the buildings, cages and cells are not new, but in very good condition. There are Japanese macaques, bears, wolf, deer, camels, lamas, Przewalski's horse, peacock, lions and many others.

Animal Market.

Early on Sunday mornings one of Kyrgyzstan's biggest animal markets takes place around 2 km north of central Karakol. Locals loading and unloading sheep into the back of a sedan is not an uncommon sight. The setting amid semi-derelict flour mills might seem unprepossessing, but on clear days the backdrop of white-topped mountains is more striking from here than from the town center. A series of earthen unloading platforms lead north. Jostle through the chaos to reach a bigger main compound one block north, where horses and embossed leather saddlery are for sale. On foot the bazaar is about 25 minutes' walk from City Center.

Karakol (, "Qaraqol"/"Karakol", قاراقول, ; formerly Przhevalsk) is the fourth largest city in Kyrgyzstan, near the eastern tip of Lake Issyk-Kul in Kyrgyzstan, about from the Kyrgyzstan–China border and from the capital Bishkek. It is the administrative capital of Issyk-Kul Region. Its area is and its resident population was 66,294 in 2009 (both including Pristan'-Przheval'sk). To the north, on highway A363, is Tyup and to the southwest Jeti-Ögüz resort.

卡拉科尔(吉尔吉斯语: Каракол),吉尔吉斯斯坦东部城市,距离首都380公里。卡拉科尔为伊塞克湖州首府所在地。总人口75,000。