[ Instrument Network Instrument R & D ] Wei Xiaoman and Li Xiang, members of the Cui Jie research group of the Shanghai Pasteur Institute of the Chinese Academy of Sciences and the Shanghai Branch of the Biosafety Science Center of the Chinese Academy of Sciences, based on the results of the new coronavirus (2019-nCoV) analysis and The results of genome comparison uploaded from the public database were comprehensively analyzed, and the early evolution mechanism of the new coronavirus was estimated to provide a scientific basis for the prevention and control of the pneumonia epidemic of new coronavirus infection.
2019-nCoV is different from any of the previously known six types of coronaviruses that can infect humans, including HCoV-229E, HCoV-OC43, SARS-CoV, HCoV-NL63, HCoV-HKU1, and MERS-CoV. Infects human coronavirus and can cause pneumonia. Genomics analysis of 2019-nCoV showed that it is significantly different from SARS and MERS viruses, with genomic differences of 21% and 50%, respectively. Although both belong to Beta coronavirus, 2019-nCoV is not the same as SARS and MERS coronavirus. It can be considered a distant relative of SARS coronavirus, and it is definitely not a variant of SARS coronavirus or a resurgence of SARS.
Coronaviruses are systematically classified as Coronaviridae (Coronaviridae). Coronavirus is a positive-stranded single-stranded RNA virus with an envelope of about 80 to 120 nm in diameter. Its genetic material is the largest of all RNA viruses and infects humans, mice, pigs, cats, dogs, wolves, Vertebrates of chicken, cattle and poultry. A variant of coronavirus is the pathogen that causes atypical pneumonia and belongs to the RNA virus. Coronavirus was isolated from chickens in 1937. The diameter of the virus particles is 60-200nm, and the average diameter is 100nm. It is spherical or oval and has polymorphism. The virus has an envelope, and there are spinous processes on the envelope. The entire virus looks like a corona, and the spinous processes of different coronaviruses are significantly different. Tubular inclusions are sometimes seen in coronavirus-infected cells.
Research suggests that under long-term coexistence of the coronavirus and the host, the virus usually spreads in the same species, such as bats, due to host restrictions, but in a few cases, different viruses recombine after infecting the same host cell, resulting in a series of Recombinants with different genetic material. Some of these newly recombined viruses have the ability to infect new hosts (other animals or humans). Judging from the available data, the new coronavirus showed weak infectivity in early evolution and can also be transmitted from person to person, but its ability to transmit cannot be ignored. Phylogenetic analysis showed that the virus lacked topology and clustering was not obvious. However, analysis of 2019-nCoV found that at least 17 sites on different proteins involved amino acid changes, and several of these mutations were more common in clustered cases of Guangdong families.
Coronavirus is one of the main pathogens of the common cold in adults. It can cause upper respiratory tract infections in children, and rarely affects the lower respiratory tract. The incubation period for coronavirus infection is usually 2 to 5 days, with an average of 3 days. Typical coronavirus infections have cold symptoms such as runny nose and discomfort. Different types of viruses have different pathogenicity and cause different clinical manifestations. The symptoms caused by OC43 strain are generally more severe than those of 229E virus. Coronavirus infection can cause fever, chills, and vomiting. The course of disease is usually about 1 week, the clinical course is mild, and there are no sequelae.
As for whether the virus has undergone adaptive evolution, it is not yet conclusive, and more viral genome analysis and subsequent functional experiment verification of mutation sites are needed. In the future, researchers will focus on analyzing the evolutionary pattern of viruses in nature and in the population, and clarify the origin of 2019-nCoV and the evolutionary mechanism of its interaction with intermediate hosts. Researchers also called for close monitoring of the mutations, evolution and spread of the virus, which is necessary to guide the control of the epidemic.
There is specific prevention for its prevention, that is, targeted preventive measures (the development of vaccines and vaccines is possible, but it takes a long time to solve the problem of virus reproduction is its problem) and non-specific preventive measures (that is, prevention of spring respiratory diseases) Measures such as keeping warm, washing hands, ventilating, avoiding excessive fatigue and contacting patients, and going to less public places, etc.).
Source: Encyclopedia, Chinese Academy of Sciences
Low-pressure Casting Parts
Low-pressure casting was the earliest anti-gravity casting technology, which was first used in industrial production in the 1940s. Nowadays, low-pressure casting is mainly used in the production of aluminum alloy and magnesium alloy parts, such as the automotive hub of the automobile industry, the cylinder body, cylinder head, piston, missile shell, impeller, air guide wheel and other castings with complex shapes and high quality requirements.
The common material of low-pressure casting is A356\ZL101\ZL101A,this kind of material is usually applied to auto part, storage part,transformation part,etc.
The pressure on the surface of the molten metal is 0.06~0.12Mpa.This processing has good shrinkage, casting tissue is dense, easy to produce the large thin-walled complex parts, the casting head is not needed , metal yield can be up to 95%.
Low pressure casting can adopt sand type, metal type, graphite type, etc. The filling process is not only different from gravity casting such as metal casting and sand casting, but also different from high pressure and high speed filling pressure casting, which has the following advantages:
1) Pure metal liquid filling type, which improves the purity of the casting. Because the slag generally floats on the surface of the metal liquid, and the low pressure casting by the metal liquid in the lower part of the crucible realizes the filling through the lifting pipe, which completely avoids the possibility of the slag into the cast cavity.
2) The metal liquid filling type is smooth, reducing or avoiding the turnover, impact and splashing phenomenon of the metal liquid when filling the type, thus reducing the formation of less oxide slag.
3) The casting molding performance is good, the metal liquid filling under the pressure action, can improve the fluidity of the metal liquid, is conducive to the formation of clear outline, smooth surface casting, for the formation of large thin-wall casting is more favorable.
4) The casting crystallizes and solidifies under pressure, which can be fully condensed, and the casting structure is compact.
5) Improve the yield of metal liquid, generally do not need to burst, and the same metal in the lifting tube can be returned to the crucible, reuse, so that the yield of metal liquid greatly increased, the yield can generally reach 90%.
6) Convenient production and operation, good working conditions, high production efficiency, easy to achieve mechanization and automation.
Low pressure casting also has some disadvantages, equipment and mold investment is large; in the production of aluminum alloy casting, crucible and lift pipe long time with metal liquid contact, easy to erosion and scrap, will also make the metal liquid iron and performance deterioration.
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