錝,5″S)-2-{3′-Methoxy-2′-propoxy-5′-[5″-(3,4,5-trimethoxyphenyl)tetrahydrofuran-2″-yl] phenylsulfonyl}ethanol(MK-287) which was potent PAF antagonist, was enantioselectively synthesized in eight steps by a...錝,5″S)-2-{3′-Methoxy-2′-propoxy-5′-[5″-(3,4,5-trimethoxyphenyl)tetrahydrofuran-2″-yl] phenylsulfonyl}ethanol(MK-287) which was potent PAF antagonist, was enantioselectively synthesized in eight steps by addition, oxidation, hot decomposition, hydrogenation and so on from (-)-4,10-dioxatricyclo-[5.2.1.0 2,6]-decene-3-ole(1). Asymmetry was introduced using the nucleophilic addition of the triisopropoxytitanium to the lactol 1. The second asymmetric center was installed by a highly stereocontrolled acid-assisted reduction with sodium cyanoborohydride of the hemiketal formed. The product MK-287 was optically pure.展开更多
With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-...With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon （EASM） over the northeastern Tibet-Qinghai Plateau during the lastdeglacial.The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies.Smectite/kaolinite and smectite/（illite＋chlorite） ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin.Before 12.9 Cal ka BP,both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase.After 12.9 Cal ka BP,an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate.The beginning of Holocene is characterized by high smectite/（illite＋chlorite） and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae,implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP.The time interval after 5.0 Cai ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin.Comparing variations of clay mineral assemblages with previous pollen results,we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.展开更多
The authors consider the finite volume approximation of a reaction-diffusion system with fast reversible reaction.It is deduced from a priori estimates that the approximate solution converges to the weak solution of t...The authors consider the finite volume approximation of a reaction-diffusion system with fast reversible reaction.It is deduced from a priori estimates that the approximate solution converges to the weak solution of the reaction-diffusion problem and satisfies estimates which do not depend on the kinetic rate.It follows that the solution converges to the solution of a nonlinear diffusion problem,as the size of the volume elements and the time steps converge to zero while the kinetic rate tends to infinity.展开更多
A non-conventional positron source using the intense y radiation from an axially oriented monocrys- tal which materializes into e^＋e^- pairs in a granular amorphous converter is described. The enhancement of photon r...A non-conventional positron source using the intense y radiation from an axially oriented monocrys- tal which materializes into e^＋e^- pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its 〈111〉 axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also re- ported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and correspond- ing heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.展开更多
文摘錝,5″S)-2-{3′-Methoxy-2′-propoxy-5′-[5″-(3,4,5-trimethoxyphenyl)tetrahydrofuran-2″-yl] phenylsulfonyl}ethanol(MK-287) which was potent PAF antagonist, was enantioselectively synthesized in eight steps by addition, oxidation, hot decomposition, hydrogenation and so on from (-)-4,10-dioxatricyclo-[5.2.1.0 2,6]-decene-3-ole(1). Asymmetry was introduced using the nucleophilic addition of the triisopropoxytitanium to the lactol 1. The second asymmetric center was installed by a highly stereocontrolled acid-assisted reduction with sodium cyanoborohydride of the hemiketal formed. The product MK-287 was optically pure.
基金financially supported by the Natural Science Foundation of China (Grant No. 41061022)China Scholarship Council
文摘With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon （EASM） over the northeastern Tibet-Qinghai Plateau during the lastdeglacial.The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies.Smectite/kaolinite and smectite/（illite＋chlorite） ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin.Before 12.9 Cal ka BP,both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase.After 12.9 Cal ka BP,an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate.The beginning of Holocene is characterized by high smectite/（illite＋chlorite） and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae,implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP.The time interval after 5.0 Cai ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin.Comparing variations of clay mineral assemblages with previous pollen results,we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.
基金supported by a Marie Curie Transfer of Knowledge Fellowship of the European Community’s Sixth Framework Programme(No. MTKD-CT-2004-013389)
文摘The authors consider the finite volume approximation of a reaction-diffusion system with fast reversible reaction.It is deduced from a priori estimates that the approximate solution converges to the weak solution of the reaction-diffusion problem and satisfies estimates which do not depend on the kinetic rate.It follows that the solution converges to the solution of a nonlinear diffusion problem,as the size of the volume elements and the time steps converge to zero while the kinetic rate tends to infinity.
文摘A non-conventional positron source using the intense y radiation from an axially oriented monocrys- tal which materializes into e^＋e^- pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its 〈111〉 axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also re- ported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and correspond- ing heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.
