Detection of human influence on twentieth-century precipitation trends

Human influence on climate has been detected in surface air temperature, sea level pressure, free atmospheric temperature, tropopause height and ocean heat content. Human-induced changes have not, however, previously been detected in precipitation at the global scale, partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal. Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation, increasing precipitation at high latitudes, decreasing precipitation at sub-tropical latitudes, and possibly changing the distribution of precipitation within the tropics by shifting the position of the Intertropical Convergence Zone. Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models. We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation, such as the Sahel.     

运动导体感应涡电流分布的解析计算与仿真验证

在电磁应用中,分析导体在电磁场激励作用下感应涡电流的分布有利于深入理解导体与激励源之间的相互作用。因其复杂性,运动导体在电磁场作用下涡电流分布的规律尚未得到充分研究。采用二维傅里叶变换方法,推导出圆形通电激励线圈作用下导电平板涡电流分布的积分形式表达式;该表达式与线圈的激励频率、导体的材料特性、形状及运动速度等参数有关。计算并分析了在相同线圈激励条件下,导体以不同速度运动时,表面涡电流密度分布特点,总结了导体运动速度对涡电流分布的影响规律;并用有限元方法对解析计算结果进行了验证。所采用的解析方法具有方便、快速的优点,该方法也可以用于其他涡电流问题的分析计算。     

Binding energies and interaction origins between nonclassical single-electron hydrogen,sodium and lithium bonds and neutral boron-containing radicals: a theoretical investigation

Nonclassical single electron hydrogen,sodium and lithium bonds(SEHBs,SENaBs and SELiBs)between single electron acceptors X–A(A=H,Na,Li;X=CN,HCC,HO,NC,CF3)and neutral radicals BY2(Y=H,OH,CH3)and have been systematically investigated by high level theoretical methods,such as second-order Mφller-Plesset perturbation theory(MP2),spin-component-scaled MφllerPlesset theory(SCS-MP2),the coupled cluster method with perturbative triples(CCSD(T)),and the correlation consistent composite approach(ccCA).Binding energies have been corrected for zero-point vibrational effects and(when applicable)basis set superposition error.The quantum theory of atoms in molecules(AIM)and natural bond orbital(NBO)analyses were also employed to qualitatively characterize the single electron bond interactions.The stabilization energy was partitioned via the localized molecular orbital energy decomposition analysis(LMOEDA)method,and both electrostatic and exchange interactions were seen to be major driving forces for the complex stabilization.Interestingly,the sum of the energy contributors of exchange(EEX),repulsion(EREP),polarization(EPOL),dispersion(EDIS)is close to zero and the changes in the interaction energy follow the trend of the electrostatic energy(EES).We observe several linear relationships among the optimized intermolecular parameters and the interaction energies of the various complexes.     

为什么《授时历》受外来的影响很小？

<授时历>受外来影响很少,不是因为中国人不喜欢外国人,也不是因为中国人对外来的专业知识不感兴趣,而是蒙古统治者的统治政策造成了这个结果.忽必烈及其后继者限制不同种族人员之间的知识交流,好让自己享有多种选择的特权,而不使不同种族的臣民联手反抗.尽管元初设有回回司天监,但回回天文学家与汉族天文学家之间没有什么交流.     

Introduction of new genetic material into pluripotent haematopoietic stem cells of the mouse

An infectious retrovirus vector has been used to transfer a bacterial gene encoding resistance to the neomycin analogue G418 into pluripotent haematopoietic stem cells present in explanted murine bone marrow tissue. Subsequent transplantation of the cells into lethally irradiated mice results in engraftment of the animals with donor haematopoietic tissue containing the bacterial gene. This approach affords an efficient and rapid means of re-introducing genetically modified tissue into intact organisms and provides a system whereby the expression and regulation of cloned genes can be followed within the context of a well characterized developmental programme.     

Observation of voice in the western collared lizard Crotaphytus collaris bicinctores

A noosed female Crotophytus collaris bicinclores Smith and Tanner voiced an alarm similar to that of C. wislizeni. &nbsp;     

The MLH1 D132H variant is associated with susceptibility to sporadic colorectal cancer

Most susceptibility to colorectal cancer (CRC) is not accounted for by known risk factors. Because MLH1, MSH2 and MSH6 mutations underlie high-penetrance CRC susceptibility in hereditary nonpolyposis colon cancer (HNPCC), we hypothesized that attenuated alleles might also underlie susceptibility to sporadic CRC. We looked for gene variants associated with HNPCC in Israeli probands with familial CRC unstratified with respect to the microsatellite instability (MSI) phenotype. Association studies identified a new MLH1 variant (415G-->C, resulting in the amino acid substitution D132H) in approximately 1.3% of Israeli individuals with CRC self-described as Jewish, Christian and Muslim. MLH1 415C confers clinically significant susceptibility to CRC. In contrast to classic HNPCC, CRCs associated with MLH1 415C usually do not have the MSI defect, which is important for clinical mutation screening. Structural and functional analyses showed that the normal ATPase function of MLH1 is attenuated, but not eliminated, by the MLH1 415G-->C mutation. The new MLH1 variant confers a high risk of CRC and identifies a previously unrecognized mechanism in microsatellite-stable tumors. These studies suggest that variants of mismatch repair proteins with attenuated function may account for a higher proportion of susceptibility to sporadic microsatellite-stable CRC than previously assumed.