A density functional theory study on size-dependent structures, stabilities, and electronic properties of the bimetallic MnAgm (M=Na, Li; n+m ≤ 7) clusters

The equilibrium geometries, relative stabilities, and electronic properties of M_nAg_m (M=Na, Li; n+m≤ 7) as well as pure Ag_n, Na_n, Li_n (n≤ 7) clusters are systematically investigated by means of density functional theory. The optimized geometries reveal that for 2≤ n ≤ 7, there are significant similarities in geometry among pure Ag_n, Na_n, and Li_n clusters, and the transitions from planar to three-dimensional configurations occur at n=7, 7, and 6, respectively. In contrast, the first three-dimensional (3D) structures are observed at n+m=5 for both Na_nAg_m and Li_nAg_m cluters. When n+m ≥ 5, a striking feature is that the trigonal bipyramid becomes the main subunit of Li_nAg_m. Furthermore, dramatic odd-even alternative behaviours are obtained in the fragmentation energies, second-order difference energies, highest occupied and lowest unoccupied molecular orbital energy gaps, and chemical hardness for both pure and doped clusters. The analytic results exhibit that clusters with even electronic configuration (2, 4, 6) possess weakest chemical reactivity and more enhanced stability.     

Intrinsic Self‐Trapped Emission in 0D Lead‐Free (C4H14N2)2In2Br10 Single Crystal

Low‐dimensional lead halide perovskite materials recently have drawn much attention owing to the intriguing broadband emissions; however, the toxicity of lead will hinder their future development. Now, a lead‐free (C₄H₁₄N₂)₂In₂Br₁₀ single crystal with a unique zero‐dimensional (0D) structure constituted by [InBr₆]^3? octahedral and [InBr₄]^? tetrahedral units is described. The single crystal exhibits broadband photoluminescence (PL) that spans almost the whole visible spectrum with a lifetime of 3.2 μs. Computational and experimental studies unveil that an excited‐state structural distortion in [InBr₆]^3? octahedral units enables the formation of intrinsic self‐trapped excitons (STEs) and thus contributing the broad emission. Furthermore, femtosecond transient absorption (fs‐TA) measurement reveals that the ultrafast STEs formation together with an efficient intersystem crossing has made a significant contribution to the long‐lived and broad STE‐based emission behavior.     

Self‐Assembled Gold Arrays That Allow Rectification by Nanoscale Selectivity

The deposition of a monolayer nanoarray on the surface of a micrometer‐thick substrate is demonstrated, producing rectification characteristics at the nanoscale. The experimental results show that the heterogeneity of the structure and the charge density are the two key factors affecting rectification, which was confirmed with molecular dynamic (MD) and finite element simulations. Moreover, by altering the asymmetric electrolyte environment, the fabricated heterogeneous membrane can be used in energy conversion. This study provides insights into the mechanism underlying the generation of rectification and related factors, providing a theoretical basis for the characteristics of rectification.     

Photothermal performance of MFe2O4 nanoparticles

Photothermal therapy (PTT) has emerged as one of the promising cancer therapy approaches. As a representative photothermal agent (PTA), magnetite possesses many advantages such as biodegradability and biocompatibility. However, photothermal instability hampers its further application. Herein, we systematically synthesized three kinds of ferrite nanoparticles and detailedly investigated their photothermal effect. Compared with Fe₃O₄ and MnFe₂O₄ nanoparticles, ZnFe₂O₄ nanoparticles exhibited a superior photothermal effect. After preservation for 70 days, the photothermal effect of Fe₃O₄ and MnFe₂O₄ nanoparticles observably declined while ZnFe₂O₄ nanoparticles showed slight decrease. Furthermore, in vitro experiment, ZnFe₂O₄ nanoparticles showed little toxicity to cells and achieved outstanding effect in killing cancer cells under NIR laser irradiation. Overall, through synthesizing and studying three kinds of ferrite MFe₂O₄ nanoparticles, we obtained ferrites as PTAs and learned about their changing trend in photothermal effect, expecting it can inspire further exploration of photothermal agents.     

Applications of α, ω‐telechelic polydimethylsiloxane as cross‐linkers for preparing high‐temperature vulcanized silicone rubber

Multiamino‐terminated telechelic polydimethylsiloxane (MATTPS) was synthesized via aza‐Micheal reaction and amidation reaction and subsequently employed as cross‐linkers of polysiloxane containing γ‐chloropropyl groups (CPPS) for preparing a series of high‐temperature vulcanized silicone rubber (MCSR/MATTPS). The curing, mechanical, and thermal properties of MCSR/MATTPS were studied through rheometry, mechanical testing, and thermogravimetric analysis (TGA). MCSR/MATTPS exhibits optimal mechanical properties with a tensile strength of 9.52 MPa and tear strength of 45.4 kN/m when the molar ratio of [N–H]/[CH₂CH₂CH₂Cl] is of 1, which is attributed to the formation of concentrative cross‐linking in the three‐dimensional polymer networks. The thermal behaviors of MCSR/MATTPS display a two‐step weight loss process by heating in nitrogen whereas more than two weight loss process in air. TGA results indicate that the introduction of aliphatic long chain and carbonyl groups in the structure of MATTPS has little negative effect on the thermal stability of MCSR/MATTPS.     

CN~+离子电子结构和跃迁性质的理论研究

采用多组态参考相互作用方法和AV5Z-DK基组对CN~+离子的两个解离极限C~+(~2P_u)+N(~2D_u)和C~+(~2P_u)+N(~4S_u)下的X~1Σ~+、a~3Π、~1Δ和A~1四个电子态的势能曲线、永久偶极矩和振动能级进行了计算.为保证计算结果的精确性,在计算中考虑了Davidson修正.基于求得的势能曲线,数值求解一维径向薛定谔方程得到了各个电子态的光谱数据,并与实验值和已有的理论值吻合较好.除此之外,对A~1Π→X~1Σ~+和1~1Δ?A1~Π的跃迁性质进行了研究,同时通过跃迁的弗兰克-康登因子及辐射寿命,对CN~+离子激光冷却的可行性进行了分析.     

Nanomechanical resonator coupling with a double quantum dot: quantum state engineering

We propose a theoretical scheme to realize quantum state engineering of a nanomechanical resonator (NAMR) through the coupling between the NAMR and a double quantum dot (DQD). Hybrid entangled states between the NAMR and the DQD and superposed coherent states of the NAMR are created explicitly. It is shown that quantum state tomography for the NAMR can be implemented through carrying out unitary operations on the NAMR and the DQD. It is indicated that the scheme is feasible at the reach of the present technology.     

A Conservative Formulation and a Numerical Algorithm for the Double-Gyre Nonlinear Shallow-Water Model

We present a conservative formulation and a numerical algorithm for the reduced-gravity shallow-water equations on a beta plane, subjected to a constant wind forcing that leads to the formation of double-gyre circulation in a closed ocean basin. The novelty of the paper is that we reformulate the governing equations into a nonlinear hyperbolic conservation law plus source terms. A second-order fractional-step algorithm is used to solve the reformulated equations. In the first step of the fractional-step algorithm, we solve the homogeneous hyperbolic shallow-water equations by the wave-propagation finite volume method. The resulting intermediate solution is then used as the initial condition for the initial-boundary value problem in the second step. As a result, the proposed method is not sensitive to the choice of viscosity and gives high-resolution results for coarse grids, as long as the Rossby deformation radius is resolved. We discuss the boundary conditions in each step, when no-slip boundary conditions are imposed to the problem. We validate the algorithm by a periodic flow on an $f$-plane with exact solutions. The order-of-accuracy for the proposed algorithm is tested numerically. We illustrate a quasi-steady-state solution of the double-gyre model via the height anomaly and the contour of stream function for the formation of double-gyre circulation in a closed basin. Our calculations are highly consistent with the results reported in the literature. Finally, we present an application, in which the double-gyre model is coupled with the advection equation for modeling transport of a pollutant in a closed ocean basin.     

物理变分原理及其在电磁介质中的应用

和数学变分原理的意义不同,物理变分原理是物理界的客观规律,是基本规律.热力学定律是能量守恒定律,指任一自然过程的能量总是守恒的;但同时又是物理变分原理,指从一种状态变化到另一无限接近的状态,在所有可能的稳定过程中,真实过程的能量取极小值,因而又是动量定律.特别是对于存在迁移变分的过程和偏离平衡态不大的不可逆过程,物理变分原理特别有效,可以用来推求连续介质的控制方程,且尚未完全研究透彻.本文对这一原理及其在电磁介质中的某些应用进行了一些研究.     

黑腔中等离子体相互作用的流体力学现象观测

激光间接驱动惯性约束聚变实验中,黑腔内情况复杂,在激光烧蚀和辐射烧蚀等的驱动下,光斑区、冕区、纯辐射烧蚀区、射流区的多种等离子体以不同规律运动.发展了X光双能段窄能带的时间分辨成像方法,用以观测黑腔内多种等离子体的运动情况.在真空黑腔中观测到清晰的射流,分析了射流产生机制及其速度;在黑腔中充气,能有效消除射流和抑制冕区等离子体运动,但两种物质界面处可能会出现流体力学不稳定性等现象,分析了界面处的压力平衡关系和密度陡变情况.