单层2H-MoTe2光电效应的理论研究

材料的禁带宽度是影响光电探测器探测范围的重要因素.单层2H-MoTe2因具有合适的禁带宽度引起了科研人员广泛的研究兴趣.本文基于非平衡态格林函数-密度泛函理论,采用第一性原理方法,研究了单层2H-MoTe2的光电效应.结果表明:在线性偏振光照射下,MoTe2产生的光电流函数与唯象理论相吻合;在光子能量范围1.6～1.8...     

A model of melting of rare gases within bubbles of crystalline metal matrix

Abstract

On the basis of experimental results obtained in the present and some other works a model of melting of rare gas solids within bubbles formed in a crystalline metal matrix as a result of ion implantation is proposed. Rare gas solid is supposed to melt on heating at the expense of the bubble volume expansion by emission of a dislocation loop. On this basis the melting temperature can be estimated as one which is enough to provide for a pressure inside a bubble sufficient for the initiation of the dislocation loop punching. Values of melting temperatures obtained in this way are in good agreement with available experimental data.     

Conductance of KCI-Glycerol Solutions: Test of the Fuoss Paired Ion Model

Abstract

The electrical conductance of KC1 in glycerol solutions has been measured at concentrations between 1.5 mol m^?3 and 353 mol m^?3 at 22°C. The results are compared with the Fuoss paired ion model and fits to the data are obtained assuming a Gurney co-sphere having a radius in the approximate range 6 ± 10^?10 m to 9 ± 10^?10 m. The model leads to an estimate of ionic association which is less than that given by the theory of Bjerrum.     

Preparation of Chiral Amino Esters by Asymmetric Phase‐Transfer Catalyzed Alkylations of Schiff Bases in a Ball Mill

The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified.     

Broadband excitation pulses for high‐field solid‐state nuclear magnetic resonance spectroscopy

In nuclear magnetic resonance spectroscopy, experimental limits due to the radiofrequency transmitter and/or coil means that conventional radiofrequency pulses (“hard pulses”) are sometimes not sufficiently powerful to excite magnetization uniformly over a desired range of frequencies. Effects due to nonuniform excitation are most frequently encountered at high magnetic fields for nuclei with a large range of chemical shifts. Using optimal control theory, we have designed broadband excitation pulses that are suitable for solid‐state samples under magic‐angle‐spinning conditions. These pulses are easy to implement, robust to spinning frequency variations, and radiofrequency inhomogeneities, and only four times as long as a corresponding hard pulse. The utility of these pulses for uniformly exciting ¹³C nuclei is demonstrated on a 900 MHz (21.1 T) spectrometer. Copyright © 2012 John Wiley & Sons, Ltd.     

Polymer electrolyte membranes based on polystyrenes with phosphonic acid via long alkyl side chains

A series of polystyrenes with phosphonic acid ( 5 ) via long alkyl side chains (4, 6, and 8 methylene units) were prepared by the radical polymerization of the corresponding diethyl ω‐(4‐vinylphenoxy)alkylphosphonates, followed by the hydrolysis with trimethylsilyl bromide. The resulting phosphonated polystyrene membranes had a high oxidative stability against Fenton's reagent at room temperature. The membranes prepared from 5 exhibited a very low water uptake, similar to that of Nafion 117 over the wide range of 30 to 80% relative humidity (RH). The proton conductivities of these membranes are lower than that of Nafion 117 in the range of 30 to 90% RH, but comparable or higher than those of the reported phosphonated polymers with higher IEC values, such as the phosphonated poly(N‐phenylacrylamide) (PDPAA, IEC: 6.72 mequiv/g) and fluorinated polymers with pendant phosphonic acids (M47, IEC: 8.5 mequiv/g), at low RH conditions despite the much lower IEC values (3.0–3.8 mequiv/g) of these membranes. These results suggest that the flexible pendant side chains of 5 would contribute to the formation of hydrogen‐bonding networks by considering the very low water uptake of these polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A1Ⅱ离子3snp^1p1序列能级辐射寿命的非单调变化

本文考虑了一价铝离子双激发干扰态３ｐ４ｓ＾１ｐ１＾０对ｓｎｐ＾１Ｐ１＾０Ｒｙｄｂｅｒｇ序列的强相互作用，多组态ＨＦＲ自洽场方法计算了Ａ１Ⅱ３ｓｎｐ＾１Ｐ１０（ｎ＝３－１０）序列能级的辐射寿命，与已有的实验和理论计算结果进行了比较，结果表明该序列能级寿命随主量子数ｎ呈现非单调变化。     

High-order squeezing of pure superposition states

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