副阀部的用途有哪些？它由哪几部分组成？
参考答案：
副阀的用途有以下几点：
（1）在缓解状态时，使制动管，工作风缸，降压风缸三者相通，缩短了工作风缸的充风时间，克服了由于工作风缸充气止回阀弹簧作用而造成的工作风缸压力不足，而且能使工作风缸、降压风缸的过充压力随制动管一起消除。
（2）初制动时起局减作用.
（3）控制机车制动机的一次缓解和阶段缓解。副阀部是由副阀，充气阀，保持阀，局减止回阀，一次缓解逆流止回阀及转换盖板组成的.
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| Each year a million cows in Africa die from east coast fever.The disease is spread by tick bites.Young cows are most at risk；they can die within days.Farmers and herders can lose up to half or more of their calves to east coast fever. The disease is widespread in eleven countries.And experts say it now threatens ten million more animals in new areas including southern Sudan. Researchers first developed an experimental vaccine against east coast fever thirty years ago.The vaccine works by a process called "infection and treatment"．The animals are infected with whole parasites and treated with antibiotics at the same time.This keeps the disease from developing. Controlling east coast fever has meant a better life in areas that have gotten the vaccine. For example,the vaccine has been available for a group of Maasai herders in northern Tanzania for about seven years.They used to lose threefourths of their newborn calves each year.Now,most survive.As a result,many people have extra cattle to sell,and use the money to pay for school for their children. But making the vaccine more widely available-especially in rural areas-has been difficult. Farmers have been using supplies produced in the nineteen nineties.Recently there was a shortage.The International Livestock Research Institute made one million doses at the request of African officials.But that supply is only temporary.Another problem is that the vaccine must be kept extremely cold. Now,the nonprofit Global Alliance for Livestock Veterinary Medicines is trying to expand production and lower the cost.GALVmed spokesman Hameed Nuru says mobile phones have helped lower some barriers to distribution. HAMEED NURU:"Now,with the advent of cellular technology,most of the people we do reach,such as the Maasai pastoralists,they all have cell phones.And they now call the delivery agent who can now come and meet them at a particular place and do the vaccination for them." The vaccine is not cheap.But Hameed Nuru says the herders get together to sell a bull and use the money to vaccinate all their animals.They understand that they are getting value for their money:A cow is worth nearly twice as much if it is vaccinated. A goal is to have local people develop businesses supplying the vaccine. HAMEED NURU:"People are now seeing that they can actually make a business from supplying this vaccine and getting out to the very rural areas where there is a market for this." The efforts are supported by the Bill and Melinda Gates Foundation and the British government. East Coast Fever
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