The severe acute respiratory syndrome COVID-19 was discovered on December 31,2019 in China.Subsequently,many COVID-19 cases were reported in many other countries.However,some positive COVID-19 samples had been reporte...The severe acute respiratory syndrome COVID-19 was discovered on December 31,2019 in China.Subsequently,many COVID-19 cases were reported in many other countries.However,some positive COVID-19 samples had been reported earlier than those officially accepted by health authorities in other countries,such as France and Italy.Thus,it is of great importance to determine the place where SARS-CoV-2 was first transmitted to human.To this end,we analyze genomes of SARS-CoV-2 using k-mer natural vector method and compare the similarities of global SARS-CoV-2 genomes by a new natural metric.Because it is commonly accepted that SARS-CoV-2 is originated from bat coronavirus RaTG13,we only need to determine which SARS-CoV-2 genome sequence has the closest distance to bat coronavirus RaTG13 under our natural metric.From our analysis,SARS-CoV-2 most likely has already existed in other countries such as France,India,Netherland,England and United States before the outbreak at Wuhan,China.展开更多
Economic decide taxes and taxes have an adverse effect on the economy. To achieve a sustained development of economy, we must require the taxes which are closely related to economy meet the requirements of its own dev...Economic decide taxes and taxes have an adverse effect on the economy. To achieve a sustained development of economy, we must require the taxes which are closely related to economy meet the requirements of its own development. That is tax receipts raised by government meeting functional needs as much as possible, while reducing the facts that will damage the future needs and development of economy. Therefore, we need to analyze various factors that affect revenue. If we make a very good understanding on how structure impacting on tax revenues, that will help us to use policy tools tax making impacts on revenue and optimize the structure of the tax. For this theme, many domestic scholars have done correlation research, and their research paper provides a good reference, but we believe their research can be further refined. Through theoretical analysis, we can select appropriate indicators letting tax revenue to be explained variable. Each possible influencing factor of tax revenues establish measurement model for explaining variable using stepwise regression models, and make a rigorous statistical test on the model. On the base of fully proving the effectiveness of the model, we can make relevant economic analysis.展开更多
基金supported by Tsinghua University Spring Breeze Fund(2020Z99CFY044)Tsinghua University start-up fundTsinghua University Education Foundation fund(042202008)。
文摘The severe acute respiratory syndrome COVID-19 was discovered on December 31,2019 in China.Subsequently,many COVID-19 cases were reported in many other countries.However,some positive COVID-19 samples had been reported earlier than those officially accepted by health authorities in other countries,such as France and Italy.Thus,it is of great importance to determine the place where SARS-CoV-2 was first transmitted to human.To this end,we analyze genomes of SARS-CoV-2 using k-mer natural vector method and compare the similarities of global SARS-CoV-2 genomes by a new natural metric.Because it is commonly accepted that SARS-CoV-2 is originated from bat coronavirus RaTG13,we only need to determine which SARS-CoV-2 genome sequence has the closest distance to bat coronavirus RaTG13 under our natural metric.From our analysis,SARS-CoV-2 most likely has already existed in other countries such as France,India,Netherland,England and United States before the outbreak at Wuhan,China.
文摘Economic decide taxes and taxes have an adverse effect on the economy. To achieve a sustained development of economy, we must require the taxes which are closely related to economy meet the requirements of its own development. That is tax receipts raised by government meeting functional needs as much as possible, while reducing the facts that will damage the future needs and development of economy. Therefore, we need to analyze various factors that affect revenue. If we make a very good understanding on how structure impacting on tax revenues, that will help us to use policy tools tax making impacts on revenue and optimize the structure of the tax. For this theme, many domestic scholars have done correlation research, and their research paper provides a good reference, but we believe their research can be further refined. Through theoretical analysis, we can select appropriate indicators letting tax revenue to be explained variable. Each possible influencing factor of tax revenues establish measurement model for explaining variable using stepwise regression models, and make a rigorous statistical test on the model. On the base of fully proving the effectiveness of the model, we can make relevant economic analysis.
