Multipartite entanglement in the interaction system between a single-mode microwave cavity field and superconducting charge qubits

This paper proposes a method of generating multipartite entanglement through using d.c. superconducting quantum interference devices (SQUID) inside a standing wave cavity. In this scheme, the d.c. SQUID works in the charge region. It is shown that, a large number of important multipartite entangled states can be generated by a controllable interaction between a cavity field and qubits. It is even possible to produce entangled states involving different cavity modes based on the measurement of charge qubits states. After such superpositions states are created, the interaction can be switched off by the classical magnetic field through the SQUID, and there is no information transfer between the cavity field and the charge qubits.     

The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

F _A1:Ag⁺ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K⁺ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.      

Room-temperature fluorescence of a charge-transfer complex of reserpine in aqueous and aqueous–ethanol media

The room-temperature fluorescence of a charge-transfer (CT) complex different from those of the component donor/acceptor in polar organic solvent is not very common. The phenomenon is even rarer in aqueous medium. The present work demonstrates that a CT complex formed between reserpine (Res) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in aqueous and aqueous–ethanol media exhibits fluorescence at room temperature that is entirely different from those of the components, Res and DDQ. With decreasing polarity of the medium on the addition of ethanol, the fluorescence intensity and also the fluorimetrically determined formation constant of the complex increase, but the fluorescence emission wavelength does not change significantly. The quantum yield of fluorescence of the CT complex systematically decreases with increasing ethanol content of the medium. That the observed fluorescence is due to the CT complex is established by the constancy of the assumed proportionality constant (β) between the fluorescence intensity and the complex concentration measured using different equilibrium concentrations of the complex and also by demonstrating the mirror image relationship between its excitation and emission spectra in aqueous medium. To our knowledge, this is the first report on the room-temperature fluorescence of a CT complex in aqueous solution.     

质子辐照空间级硅橡胶的正电子淹没寿命谱研究

 用正电子淹没寿命谱方法（PALS）研究了质子辐照对空间级硅橡胶KH-L-Y微观结构的影响。试验结果表明，PALS谱所揭示的最长寿命成分的t₃, I₃及自由体积分数Vf随辐照剂量的增加开始明显下降；而当辐照剂量大于10¹⁵cm^-2后，随剂量的增加平缓上升。辐照剂量小于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积减小，分子链间堆砌紧密；辐照剂量大于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积增大。交联密度及DMA测试结果同样表明，质子辐照在剂量较小时硅橡胶的交联密度及玻璃化转变温度增加，辐照以交联效应为主；而剂量较大时辐照降解占优势。     

Effects of substituents on activation parameters in SN2 reactions at aliphatic carbon in solution

Changes of the activation parameters in aliphatic S_N2 reactions with anionic and neutral nucleophiles in various solvents, ΔH^≠ and ΔS^≠, were correlated with σ constants of the substituents. The resultant δΔH^≠ and δΔS^≠ reaction constants are linearly related for variations of substituents at the substrate, leaving group and nucleophile. Correlations of δΔH^≠ versus δΔS^≠ allow the estimation of the contribution of changes of the internal enthalpy, δΔH, to the enthalpy reaction constant, δΔH^≠, which gives a single linear dependence on the Hammett ρ reaction constants. The deviations from the dependence of δΔH versus ρ can be interpreted in terms of changes in the transition state structure in S_N2 reactions. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH. Copyright © 2009 John Wiley & Sons, Ltd.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough.A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform.In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance.With the uniform driving laser and the unbalanced RF gun,the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm.mrad.     

柱状装药预制破片缩比战斗部爆炸冲击波和破片的作用时序

针对柱状装药的周向预制破片战斗部,结合无量纲分析方法和爆炸驱动理论,确定了影响破片和冲击波相遇位置的关键参数,给出了由缩比战斗部推广预测原型战斗部爆炸产生的破片冲击波作用时序的方法。采用ANSYS/LS-DYNA有限元软件进行数值模拟,对比验证了理论分析和数值试验结果,分析了战斗部缩比比例对冲击波和破片作用时序的影响。结果表明:缩比模型与原型战斗部爆炸产生的破片和冲击波的相遇位置之比和相遇时间之比主要取决于两模型的质量比,在不考虑破片速度衰减时,两模型中载荷相遇位置之比和相遇时间之比等于其质量比的0.33次方。受破片速度衰减影响,该方法仅适用于质量缩比不小于0.2的模型。     

Enhancing hydrogen evolution of MoS2 basal planes by combining single-boron catalyst and compressive strain

MoS₂ is a promising candidate for hydrogen evolution reaction (HER), while its active sites are mainly distributed on the edge sites rather than the basal plane sites. Herein, a strategy to overcome the inertness of the MoS₂ basal surface and achieve high HER activity by combining single-boron catalyst and compressive strain was reported through density functional theory (DFT) computations. The ab initio molecular dynamics (AIMD) simulation on B@MoS₂ suggests high thermodynamic and kinetic stability. We found that the rather strong adsorption of hydrogen by B@MoS₂ can be alleviated by stress engineering. The optimal stress of −7% can achieve a nearly zero value of ΔG_H (~ −0.084 eV), which is close to that of the ideal Pt–SACs for HER. The novel HER activity is attributed to (i) the B– doping brings the active site to the basal plane of MoS₂ and reduces the band-gap, thereby increasing the conductivity; (ii) the compressive stress regulates the number of charge transfer between (H)–(B)–(MoS₂), weakening the adsorption energy of hydrogen on B@MoS₂. Moreover, we constructed a SiN/B@MoS₂ heterojunction, which introduces an 8.6% compressive stress for B@MoS₂ and yields an ideal ΔGH. This work provides an effective means to achieve high intrinsic HER activity for MoS₂.     

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C(66). The shear failure under {110}{111} shear deformation occurring in process of tension may result in a small ideal tensile strength(~ 2 GPa) for NiTi. The unlikeness in the ideal strength of Ni Al and Ni Ti alloys is discussed based on the charge density difference.