Linear response time-dependent density functional theory for van der Waals coefficients

A linear response time-dependent density functional theory is described and used to calculate the dynamic polarizabilities and van der Waals C(6) coefficients of complex atom pairs. We present values of C(6) for dimers of main group atoms and the first row of transition metal atoms.     

Pyrimido[5,4-b]quinolines. II. Reactions at the heterocyclic ring-carbon and nitrogen atoms

10-Chloro-7,8-dimethylpyrimido[5,4-b]quinolin-2,4(1H,3H)dione (I) was unreactive toward ammonia but it reacted with 2 molecules of n-butylamine, presumably via Dimroth-type ring-opening and closure, to give the N₃-butyl, N₁₀-butylamino derivative (IV). In similar reactions of 10-chloro-2,4-dimethoxy-7,8-dimethylpyrimido[5,4-b]quinoline (II) only the 4-meth-oxyl was displaced by either ammonia or n-butylamine. Alkyllithium reagents also displaced the 4-methoxyl as well as added to the 3,4 double bond of II to yield the corresponding gem-dialkyl substituted (C₄) derivatives; the C₁₀ chlorine remained unreactive. 2,4-Dimethoxy-7,8-di-methylpyrimido[5,4-b]quinoline-10-one (III) could be alkylated only in the form of the thallium salt. Treatment of the benzyl derivative of III with methylmagnesium bromide led only to the displacement of the 4-methoxyl by a methyl group.     

A cut-and-solve based algorithm for the single-source capacitated facility location problem

In this paper, we present a cut-and-solve (CS) based exact algorithm for the Single Source Capacitated Facility Location Problem (SSCFLP). At each level of CS’s branching tree, it has only two nodes, corresponding to the Sparse Problem (SP) and the Dense Problem (DP), respectively. The SP, whose solution space is relatively small with the values of some variables fixed to zero, is solved to optimality by using a commercial MIP solver and its solution if it exists provides an upper bound to the SSCFLP. Meanwhile, the resolution of the LP of DP provides a lower bound for the SSCFLP. A cutting plane method which combines the lifted cover inequalities and Fenchel cutting planes to separate the 0–1 knapsack polytopes is applied to strengthen the lower bound of SSCFLP and that of DP. These lower bounds are further tightened with a partial integrality strategy. Numerical tests on benchmark instances demonstrate the effectiveness of the proposed cutting plane algorithm and the partial integrality strategy in reducing integrality gap and the effectiveness of the CS approach in searching an optimal solution in a reasonable time. Computational results on large sized instances are also presented.     

Influence of the illumination on the subband structure and?occupation in AlxGa1?xN/GaN heterostructures

The subband structure and occupation in the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination.     

HIAF高能辐照终端感生放射性

本工作是基于蒙特卡罗模拟软件FLUKA对高能强流重离子加速器（HIAF）高能辐照终端感生放射性进行初步研究。该终端可运行质子最高能量为9.3 GeV,最大流强是1.45×1012 pps（particle per second）。研究内容包括:（1）预测高能辐照终端内活化物质的放射性活度特性;（2）预测不同冷却时间高能辐照终端内残余剂量率分布。研究结果表明,HIAF正常运行时高能辐照终端内的感生放射性主要受束流垃圾桶活化产生的放射性核素影响。当加速器连续运行100天冷却4小时,垃圾桶表面残余剂量率为2.375 mSv·h-1。终端内空气中13N和15O动态饱和比浓度大于其对应的导出空气浓度。冷却水中13N和15O的活度大于对应的ALI_min。该研究是HIAF辐射防护基础研究以及加速器环境影响评价的一项重要内容。The Monte Carlo code FLUKA was used to predict the induced radioactivity of high-energy irradiation terminal of HIAF. The maximum energy of proton is 9.3 GeV, and the maximum current is 1.45×1012 pps (particle per second). In this study we were to predict:(1) the activity properties of activated substances in the experimental terminal; (2) the residual dose rate distribution in the experimental terminal at different cooling time. The results indicate that the induced radioactivity in the high energy irradiation terminal of the HIAF is mainly affected by the radionuclide induced in the beam dump. The residual dose rate on the surface of the beam dump is 2.375 mSv·h-1, after 100 d irradiation and 4 h cooling. The dynamic saturation ratio of 13N and 15O induced in the air inside the terminal is higher than its corresponding derived air concentration. The activity of 13 N and15O induced in cooling water is higher than its ALI_min. This study is a part of radiation protection basic research and environmental impact assessment for HIAF.     

Nonlinear optical properties of stimulated Brillouin scattering process in submerged object detection

Nonlinear optical properties of stimulated Brillouin scattering(SBS)to signal detection in water are analyzed.With the threshold characteristics,SBS only occnrs when the high power laser is focused in the SBS cell.When there is an object present in front of the focus,it leads to lower incident intensity and then SBS does not occur.The backward SBS signal depends on the focusing location.The nonlinear optical properties of SBS process in the focusing regime axe analyzed theoretically.With the object coming near to the focusing center,the backward Stokes signal rises up from zero to a maximum,and then grows to saturation.The delay time of the echo signal to pump signal can give the object location.In experiment,the peak position of varying rate of energy can give object location.     

Dynamics of an enzymatic substitution reaction in haloalkane dehalogenase

Reactive flux molecular dynamics simulations have been carried out using a combined QM/MM potential to study the dynamics of the nucleophilic substitution reaction of dichloroethane by a carboxylate group in haloalkane dehalogenase and in water. We found that protein dynamics accelerates the reaction rate by a factor of 2 over the uncatalyzed reaction. Compared to the thermodynamic effect in barrier reduction, protein dynamic contribution is relatively small. However, analyses of the friction kernel reveal that the origins of the reaction dynamics in water and in the enzyme are different. In aqueous solution, there is significant electrostatic solvation effect, which is reflected by the slow reorganization relaxation of the solvent. On the other hand, there is no strong electrostatic coupling in the enzyme and the major effect on reaction coordinate motion is intramolecular energy relaxation.     

Aerobic oxidation assisted by ligand-free palladium catalysts

Aerobic oxidation of electron-rich benzylic and phenyl allylic alcohols was achieved with high yields with only 0.1 mol.% of Pd(OAc)2 catalyst in the absence of any ligand. This procedure was expected to be valuable for realistic industrial-scale applications from both economic as well as environmental points of view.     

One‐dimensional polymeric chain structure of bis­(aniline)­di­thio­cyanato­cadmium(II)

In the title compound, catena‐poly­[[bis­(aniline‐N)cadmium(II)]‐di‐μ‐thio­cyanato‐S:N;N:S], [Cd­(SCN)₂­(C₆H₇N)₂], the Cd^II atom lies on an inversion centre and is in a distorted octahedral geometry. The coordination sphere contains two thio­cyanate (SCN) S atoms, two iso­thio­cyanate (NCS) N atoms and two aniline N atoms. The six‐coordinated Cd atoms run parallel to the b axis and are doubly bridged with neighbouring Cd atoms by SCN and NCS ligands. Thus, this complex has a one‐dimensional coordination polymeric chain structure in which the aniline ligand is in the trans conformation.