制备(R)-2,2-二甲基四氢噻唑4-羧酸-L-酒石酸盐的新方法

发展了一种制备(R)-2,2-二甲基四氢噻唑4-羧酸-L-酒石酸盐(D-DMT·L-TA)的新方法,可以以73.0%的收率以及99%的光学纯度得到产品.     

基于复数FastICA算法的盲多用户检测

针对MIMO-OFDM系统,提出了一种基于复数FastICA的盲多用户检测算法.该算法首先利用复数FastICA算法的快速收敛特性来提高多用户的分离速度,同时利用信号的相关函数对复数FastICA算法引起的幅度不确定性和相位不确定性进行了修正,最后将所提出的改进算法与复数自然梯度学习算法(CNGLA)进行仿真比较.结果表明,相比于传统的自然梯度算法,所提算法不仅收敛速度较快,而且具有更低的误码率,另外随着接收天线的增多,信号的分离效果会更好.     

基于随机摄动法的齿轮系统动态响应及灵敏度分析

考虑时变啮合刚度、齿轮综合误差及齿侧间隙等非线性影响因素,建立了多级齿轮传动系统的动力学模型.将齿轮系统中的相关物理参数、几何参数和载荷参数看做随机变量,得到随机振动模型.当随机参数的随机部分比确定部分小得多时,采用随机摄动理论,将振动微分方程在随机参数向量的均值处按Taylor级数展开定理展开至一阶项,并对整理后的方程组进行数值求解.求解过程中结合Kronecker积的代数和矩阵微分理论,得到系统响应的前四阶矩.为了衡量系统的平稳性,对齿对的动态传递误差的前两阶矩进行求解,并与MonteCarlo法进行比较,同时分析了动态传递误差对随机参数的无量纲均值灵敏度,分析结果为提高系统的平稳性提供了依据.     

多道次搅拌摩擦加工对5083-O铝合金组织性能的影响

在不同轴肩直径、搅拌头转速和搅拌头行进速度下,对27mm厚5083-O铝合金进行了多道次搅拌摩擦加工(multi passfrictionstirprocessing),搭接率为100%,共进行3道次搅拌摩擦加工.研究结果表明,加工区由细小的再结晶组织组成;随着加工道次的增加,加工区内部缺陷体积减少,晶粒进一步细化,析出相细化并均匀分布,力学性能提高,加工区最高抗拉强度可达360MPa,延伸率也优于母材;其中,第二道次加工对材料组织和性能的影响最为明显.     

Characterization of cocrystals formed by grinding amino acids through terahertz time-domain spectroscopy

In this paper,we used terahertz time-domain spectroscopy(THz-TDS)over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids,formed by grinding mixtures of two different kinds of amino acids.For comparison,we prepared dual-layer samples,combined by pressing two single-component pellets together without grinding.In the ground-mixture samples,some extra absorption peaks appeared,different from the characteristic peaks of the pure components,but these peaks did not appear in the dual-layer samples.Thus,these extra absorption peaks in the THz range are unique features of cocrystals.From our results,we believe that THz-TDS is a promising technique to characterize cocrystals.     

Spatiotemporal characteristics of freezing and thawing of the active layer in the source areas of the Yellow River （SAYR）

Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils in the active layer were compared and contrasted for understanding the spatiotemporal variations.At the four studied sites,the thickness and mean annual temperature of permafrost are different.The temperatures at the top of permafrost(TTOP),i.e.,the maximum depth(s)of seasonal frost and/or thaw penetration,are-1.9°C at the Chalaping site(CLP),-0.9°C at the site on the southern bank of the Zhaling Lake(ZLH),-0.4°C at the Maduo Town site(MDX),and 1.1°C at the site on the northern bank of the Eling Lake(ELH).Differences in the mean annual ground temperature of permafrost and TTOPs may be responsible for the differentiations in the freeze–thaw processes of soils in the active layer.With rising TTOPs,the ground thawing started earlier:CLP in early June,ZLH in late May,MDX in early May,and ELH in mid-April,while the freezing began later:CLP in early October,ZLH in early to midOctober,MDX in mid-October,and ELH in the mid-to late October.With increasing TTOPs,the freeze-up periods for permafrost sites were shortened:202 days at CLP,130 days at ZLH,100 days at MDX,and the period of complete thaw was 89 days at ELH.At the CLP and ZLH sites,the two-directional ground freezing(downwards from ground surfaces and upwards from the permafrost table)and thawing finished in the same year,but the ground freezing at the MDX continued to the end of the nextJanuary,with very slow freezing rates in the end.At the ELH site,ground freezing kept on until early May when thawing began on the surface,and upward and downward thawing became increasingly stable in late June to early July.At each site,with rising TTOPs,the downward freezing accelerated in comparison with the upward freezing,and with an increasing proportion of downward frozen depth,and with the larger ratios of freezing to thawing duration.In summary,the patterns of thawing and freezing processes in the active layer in the SAYR differ from those in other parts of the Qinghai–Tibet Plateau to a noticeable extent.     

Computational thermodynamics,computational kinetics,and materials design

Computational thermodynamics, known as CALPHAD method when dawned in 1950s, aimed at cou- pling phase diagrams with thermochemistry by computa- tional techniques. It eventually evolves toward kinetic simulations integrated with thermodynamic calculations, i.e., computational kinetics, including diffusion-controlled phase transformation, precipitation simulation, and phase- field simulation. In the meantime, thermodynamic, mobility, and physical property databases for multi-component and multi-phase materials, served as basic knowledge for materials design, are critically evaluated by CALPHAD approach combining key experiments, first-principles cal- culations, statistic methods, and empirical theories. The combination of these computational techniques with their conjugated databases makes it possible to simulate phase transformations and predict the microstructure evolution in real materials in a foreseeable future. Further links to micro- and macro-scale simulations lead to a multi-scale compu- tational framework, and aid the search for the quantitative relations among chemistry, process, microstructures, and materials properties in order to accelerate materials devel- opment and deployment. This is a new route of materials and process design pursued by Integrated Computational Materials Engineering （ICME） and Materials Genome Ini- tiative （MGI）. This article presents a review on the basic theories and applications, the state of the art and perspective of computational thermodynamics and kinetics.     

Effect of ytterbium on sodium current and its kinetics in rat hippocampal neurons

This study addressed the effects of Yb3＋ on voltage-gated sodium currents in rat hippocampal neurons using the whole-cell patch-clamp technique. Voltage-clamp recordings in single neurons were filtered and stored in a computer. Yb3＋ increased the amplitude of sodium currents in a concentration-dependent and voltage-dependent man- ner. The 50 % enhancement concentration of Yb3＋ on sodium currents was about 8.97 μmol/L, which was dif- ferent from the inhibitory effects of Yb3＋ on potassium current. The analysis on the activation and inactivation kinetics of Na＋ current showed that 100 μmol/L Yb3＋ did not change the process of activation and inactivation. In addition, the times reaching the peak of current （t） and inactivated time constant （τ） were voltage dependent. 100 μmol/L Yb3＋ significantly prolonged the time to peak at -70 and -80 mV. The effect disappeared at the positive direction of -70 mV. Furthermore, Yb3＋ decreased r val- ues to more positive values than -80 mV. In total, Yb3＋ did not change the process of activation, but impelled inacti- vated process. Yb3＋ mainly increased the Na＋ current through changing its conductance. It might be one of the mechanisms that Yb3＋ affected the hippocampal neurons.     

Millennial climate changes since MIS 3 revealed by element records in deep-sea sediments from northern South China Sea

High resolution elemental MD05-2903 from the northern South records in core China Sea were obtained from XRF scanning and grain size and mineral component analyses. The K/Ti curve reveals climate changes since MIS 3 on a millennial scale, representing one of the best such records so far from deep-sea sediments of the South China Sea. When compared our K/Ti record with other climate records from high latitude ice cores and from East Asia stalagmites, variations in the K/Ti record show some typical saw-shaped features of rapid climate changes in the Northern Hemisphere. Grain size analysis reveals a close relationship between variations in K/Ti and in the fine end-member grain size. XRD analysis confirms that high K/Ti layers were dominated by K-rich weathering minerals, especially illite, while low K/Ti layers contain low illite but high abundance of Ti-rich heavy minerals. Therefore, the K/Ti record reflects changes in the input and deposition of fine weathering minerals and heavy minerals in the northern South China Sea region during stadials and interstadials. These elemental changes were largely con- trolled by variations in rainfall, erosion, and fluvial trans- portation induced by East Asia Monsoon.     

Progress in the research of radical anion ligands and their complexes

Recent progress in the research of radical anion ligands and their complexes with metals were summarized in this review. Radical anions were sorted into several types including iminosemiquinonate and iminoquinonate radical, nitroxide radical, heterocycle radical etc. Structural characteristics and properties of the corresponding complexes were introduced. The complexes exhibited novel properties and possibility for applications in organic magnetic materials and transition metal catalysis.