The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar ma...The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar maximum and minimum phases. It emerges that foF2 diurnal variation graphs at Dakar station exhibits the different types of foF2 profiles in African EIA regions. The type of profile depends on solar activity, season and solar phase. During solar minimum and under quiet time condition, data show?the signature of a strength electrojet that is coupled with intense counter electrojet in the afternoon. Under disturbed conditions,?mean intense electrojet is observed in winter?during fluctuating and recurrent activities. Intense counter electrojet is seen under fluctuating and shock activities in all seasons coupled with strength electrojet in autumn. In summer?and spring under all geomagnetic activity condition, there is intense counter electrojet. During solar maximum, in summer and spring there is no electrojet under geomagnetic activity conditions.?Winter shows a mean intense electrojet. Winter and autumn are marked by the signature of the reversal electric field.展开更多
Two new diterpenes, 15-ethyl-18-methyl pinifolate （1） and 18-hydroxy-labda-8（17）, 13E-dien-15-acetate （2）, were isolated from the needles of Pinus sylvestris. Their structures were elucidated by spectroscopic me...Two new diterpenes, 15-ethyl-18-methyl pinifolate （1） and 18-hydroxy-labda-8（17）, 13E-dien-15-acetate （2）, were isolated from the needles of Pinus sylvestris. Their structures were elucidated by spectroscopic methods, including 2D-NMR spectra. Compound 1 exhibited the significant cytotoxic activity against the human carcinoma cell lines Hela, SK-N-SH and BEL-7402 in vitro.展开更多
E类放大器是磁共振无线电能传输(wireless power transmission,WPT)系统中常用的高频电源,其开关效率是评价WPT系统整体性能的关键指标。针对E类放大器中开关器件的效率和电压应力与负载的紧耦合关系导致其输出效率的不稳定,根据锂离子...E类放大器是磁共振无线电能传输(wireless power transmission,WPT)系统中常用的高频电源,其开关效率是评价WPT系统整体性能的关键指标。针对E类放大器中开关器件的效率和电压应力与负载的紧耦合关系导致其输出效率的不稳定,根据锂离子电池的充电特性和E类放大器的输出效率特性,选用合理的谐振补偿网络结构,提出了一种通过电容和电感阵列实现E类放大器零电压开关状态的主动控制策略。结果表明:在20 cm气隙条件下实现了功率输出为1.1 k W、逆变部分效率高于95%以上的WPT系统实验,大大提高了采用E类放大器的WPT系统的稳定性,验证了所提出控制策略的有效性。展开更多
Dear Editor,Human papillomaviruses(HPV)are a large group(>200genotypes)of small double-stranded DNA viruses(https://pave.niaid.nih.gov/).Although infections by most HPV types are asymptomatic,persistent infections ...Dear Editor,Human papillomaviruses(HPV)are a large group(>200genotypes)of small double-stranded DNA viruses(https://pave.niaid.nih.gov/).Although infections by most HPV types are asymptomatic,persistent infections in cervical and ano-genital epithelia by high-risk展开更多
Using a strong version of the Curve Selection Lemma for real semianalytic sets, we prove that for an arbitrary connected Lie group G, each connected component of the set E_n(G)of all elements of order n in G is a conj...Using a strong version of the Curve Selection Lemma for real semianalytic sets, we prove that for an arbitrary connected Lie group G, each connected component of the set E_n(G)of all elements of order n in G is a conjugacy class in G. In particular, all conjugacy classes of finite order in G are closed. Some properties of connected components of E_n(G) are also given.展开更多
文摘The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar maximum and minimum phases. It emerges that foF2 diurnal variation graphs at Dakar station exhibits the different types of foF2 profiles in African EIA regions. The type of profile depends on solar activity, season and solar phase. During solar minimum and under quiet time condition, data show?the signature of a strength electrojet that is coupled with intense counter electrojet in the afternoon. Under disturbed conditions,?mean intense electrojet is observed in winter?during fluctuating and recurrent activities. Intense counter electrojet is seen under fluctuating and shock activities in all seasons coupled with strength electrojet in autumn. In summer?and spring under all geomagnetic activity condition, there is intense counter electrojet. During solar maximum, in summer and spring there is no electrojet under geomagnetic activity conditions.?Winter shows a mean intense electrojet. Winter and autumn are marked by the signature of the reversal electric field.
文摘Two new diterpenes, 15-ethyl-18-methyl pinifolate （1） and 18-hydroxy-labda-8（17）, 13E-dien-15-acetate （2）, were isolated from the needles of Pinus sylvestris. Their structures were elucidated by spectroscopic methods, including 2D-NMR spectra. Compound 1 exhibited the significant cytotoxic activity against the human carcinoma cell lines Hela, SK-N-SH and BEL-7402 in vitro.
文摘E类放大器是磁共振无线电能传输(wireless power transmission,WPT)系统中常用的高频电源,其开关效率是评价WPT系统整体性能的关键指标。针对E类放大器中开关器件的效率和电压应力与负载的紧耦合关系导致其输出效率的不稳定,根据锂离子电池的充电特性和E类放大器的输出效率特性,选用合理的谐振补偿网络结构,提出了一种通过电容和电感阵列实现E类放大器零电压开关状态的主动控制策略。结果表明:在20 cm气隙条件下实现了功率输出为1.1 k W、逆变部分效率高于95%以上的WPT系统实验,大大提高了采用E类放大器的WPT系统的稳定性,验证了所提出控制策略的有效性。
基金supported by the Intramural Research Program of the National Institutes of HealthNational Cancer Institutethe Center for Cancer Research
文摘Dear Editor,Human papillomaviruses(HPV)are a large group(>200genotypes)of small double-stranded DNA viruses(https://pave.niaid.nih.gov/).Although infections by most HPV types are asymptomatic,persistent infections in cervical and ano-genital epithelia by high-risk
基金the 973 Project Foundation of China (Grant No. TG1999075102)
文摘Using a strong version of the Curve Selection Lemma for real semianalytic sets, we prove that for an arbitrary connected Lie group G, each connected component of the set E_n(G)of all elements of order n in G is a conjugacy class in G. In particular, all conjugacy classes of finite order in G are closed. Some properties of connected components of E_n(G) are also given.
