经典极限下量子卡诺制冷机有限时间热力学性能界限和优化准则

研究了量子卡诺制冷机的最优性能和有限时间热力学优化准则，得到了量子制冷机制冷率与致冷系数之间的优化关系以及制冷的有限时间热力学性能界限。     

超薄铋薄膜的量子尺寸效应

采用基于密度泛函理论的第一性原理方法,研究了2～16层Bi(111)薄膜的表面能和功函数,它们展现出量子尺寸效应引起的奇偶振荡.解释这种振荡需要考虑表面投影能带结构,振荡周期与量子阱态在二维布里渊区中高对称点费米能级处的穿越有关,量子阱态穿越费米能级亦引起态密度在费米能级处振荡,预示传导性质的振荡转变.     

侧向约束GFRP筋混凝土板内压缩薄膜效应的研究

当混凝土板受到平面内的侧向约束时, 由于压缩薄膜效应(Compressive Membrane Action-CMA)的存在, 板的极限承载力和工作性能将显著提高. 为了正确认识纤维增强材料(FRP)筋混凝土桥面结构的工作性能, 建立了一组带有横向约束的玻璃纤维增强筋材混凝土板带来分析板内压缩薄膜效应对这一非金属筋材混凝土结构的影响. 试验中发现GFRP筋混凝土板带的工作性能主要受到横向约束刚度和混凝土强度的影响, 而配筋率的影响却不明显. 现行的设计规范(ACI440R-06)由于没有考虑板内压缩薄膜效应的作用严重低估了GFRP筋混凝土板带的承载能力. 因此基于过去对钢筋混凝土桥梁面板的研究, 建立了一套考虑板内压缩薄膜效应的GFRP筋混凝土桥梁面板承载力计算模型. 通过与多个试验结果进行对比后发现, 该理论算法与试验结果有着良好的吻合.     

一般费米量子信道的经典容量

文章在费米子平均占据数受限的情况下 ,利用费米型量子高斯加性噪声的球谐函数展开方法 ,给出单模费米子在一般费米量子加性信道上传输经典信息的经典容量     

波导光子晶体的态密度

令方形波导内的电介质介电常数沿波导方向周期变化,实际上是非周期方向受限的一维光子晶体,不妨称为波导光子晶体。本文利用经典电动力学的方法计算了波导光子晶体的态密度,发现当波导宽度与其内部一维光子晶体晶的格常数可比拟时,会出现光子带隙;而且,波导宽度对系统的态密度有明显影响,随着波导宽度的增大光子带隙逐渐闭合。     

应变量子阱中杂质态结合能的压力效应

对应变闪锌矿(001)取向GaN-AlxGa1-xN量子阱系统,采用变分法讨论了流体静压力对束缚于界面附近的浅杂质态结合能的影响。计算结果表明,考虑压力对单轴、双轴应变的调制及电子有效质量,材料介电常数及禁带宽度的影响,杂质态的结合能随压力呈线性变化。由简化相干势近似法讨论了垒材料AlxGa1-xN中Al组分对杂质态结合能的影响。结果表明,在阱宽和压力固定时,当Al组分增加时杂质态结合能会逐渐增加;且压力较大时结合能随组分的增加更加显著。Al组分的增加使电子的二维特性增强,从而使结合能增大。     

基于压缩感知的旋转声源多普勒效应消除方法EI北大核心CSCD

消除旋转声源的多普勒效应是监测旋转机械工作状态和定位旋转声源的前提。当前用于消除旋转声源多普勒效应的方法分为频域和时域两种,但是这两种方法都需要在周向均匀布置大量传声器,这不仅增加了测量成本,而且增加了测量工作量。针对上述问题提出了一种基于压缩感知的多普勒效应消除方法,该方法通过在周向随机布置少量传声器完成周向模态幅值的重构,并根据静止柱坐标系与随声源同步旋转的旋转柱坐标系之间的相对运动关系完成多普勒效应的消除。数值仿真和试验研究都表明采用较少传声器随机布置的方法同基于采样定理均匀布置传声器的方法在消除多普勒效应的效果上基本一致,且所提方法可有效降低测量成本和测量工作量。     

C/C复合材料压缩破坏的应变率效应研究

研究了碳布叠层/碳复合材料在四种不同应变率下的压缩性能, 对其在准静态、动态载荷下的压缩破坏机理进行了初步的探讨. 研究结果表明: C/C复合材料的压缩破坏强度具有较强的应变率效应, 与准静态(10^-4/s)相比, 复合材料的动态(1.5×10²/s)压缩强度可提高70%左右; 复合材料在准静态、动态载荷下力学性能的差异可归结为纤维与基体界面特性的应变率效应以及不同应变率下破坏模式的不同.     

超微粒子量子振动理论及其应用研究评述

自我们在本刊发表系列文章之后 ,收到许多同仁和读者来信 ,或口头询问。在此 ,我们首先对他们的关心和支持表示衷心的谢意 !此外 ,对于他们提出的一些不理解或不明之处 ,本文将做简要的说明和补充。在现有的原子和分子理论中 ,人们认为原子和分子的能量 (动能和势能之和 )是一个守恒量 ,以此为前提得到原子和分子能级的表示。实际上 ,与经典谐振系统性质完全不同 ,量子谐振系统本身是一个开放系统 ,它与外界存在能量交换 ,系统在运动过程中会受到非保守内力的作用 ,因此 ,量子谐振系统的哈密顿量就不再是一个守恒量。海森堡 (Ｗ Ｈｉｓｅｎ…     

基于细观模拟的轻骨料混凝土动态压缩破坏及尺寸效应分析

轻骨料混凝土由于其轻质及保温隔热性能好等优点,越来越多被应用于实际工程结构。采用细观数值模拟方法,将轻骨料混凝土看作由骨料颗粒、砂浆基质及两者间界面过渡区组成的三相复合材料,采用塑性损伤本构关系模型,考虑应变率效应的影响,建立了对应的细观随机骨料模型,研究了轻骨料混凝土在动态压缩作用下的破坏行为及尺寸效应规律。发现：随着应变率的增加,惯性效应逐渐成为主导效应,动态压缩强度的尺寸效应逐渐被削弱,达到临界应变率时,尺寸效应被完全抑制。此外,结合率效应影响机制与规律,揭示了轻骨料混凝土动态压缩强度的尺寸效应机理,建立了“静动态统一”的尺寸效应半经验-半理论公式。     

单模光纤偏振状态在线控制器

研制了一种单模光纤偏振状态在线控制器,通过线性双折射和圆形双折射改变单模光纤中光的偏振状态,实验结果与理论分析一致     

Investigation of the Stressed State and Edge Effects in a Three-Layer Cylinder

We study an axisymmetric problem of determination of the zones of stress concentration in a three-layer circular cylinder with isotropic layers. The cylinder is subjected to uniform axial loading. An approximate solution of the problem of the linear theory of elasticity is obtained by the net method. We present a solution of this sort as an example and analyze the results.     

Squeezed vacuum,coherent and dc field effects on optical multistability via decay-induced quantum beats

Effect of the relative control phase as well as the squeezed phase parameter on the optical switching process of the optical bi-multistable behaviour are investigated in detail for a four-level Y-type atomic system; in the presence of a control field (coherent + dc fields) with squeezed vacuum field and quantum interference from spontaneous emission. The results indicated that (a) the quantum interference assists to decrease the rate of switching via the relative phase of the control field and makes the switching on/off points more rapid in squeezed vacuum compared to a normal vacuum case, and (b) the phase switching effects between the output field and the relative control phase increases the switching on/off processes in normal vacuum more than the squeezed vacuum case. In addition, we have demonstrated the possibility of displaying quantum beats with a novel type of bi-multistable behaviour in the cooperative switching diagram.     

Interface‐state density and noise behavior of gamma‐irradiated MOSFET'S

Abstract

MOSFET's and MOS memory devices suffer the increase of interface state density and oxide trapped charge density after ionization radiation such as gamma rays. The drain‐current dependence and the gate‐voltage dependence of the flicker noise of the irradiated MOSFET's are illustrated in this paper. The annealing effect, the bias effect, and the total dose effect on the noise behavior are shown. It is also shown that the change of the interface state density is essential to the noise change and the change of oxide trapped charge density may cause the “apparent” change of MOSFET's flicker noise after gamma irradiation.     

Effects of processing parameters on microstructure and mechanical properties of squeeze-cast Mg–12Zn–4Al–0.5Ca alloy

In this paper, a new magnesium alloy Mg–12Zn–4Al–0.5Ca (ZAX12405) was prepared by squeeze casting. The effects of processing parameters including applied pressure, pouring temperature and dwell time on the microstructure and mechanical properties of squeeze-cast ZAX12405 alloy were investigated. It was found that squeeze-cast ZAX12405 alloy exhibited finer microstructure and much better mechanical properties than gravity casting alloy. Increasing the applied pressure led to significant cast densification and a certain extent of grain refinement in the microstructure, along with obvious promotion in mechanical properties. Lowering the pouring temperature refined the microstructure of ZAX12405 alloy, but deteriorated the cast densification, resulting in that the mechanical properties firstly increased and then decreased. Increasing the dwell time promoted cast densification and mechanical properties just before the solidification process ended. A combination of highest applied pressure (120 MPa), medium pouring temperature (650 °C) and dwell time (30 s) brought the highest mechanical properties, under which the ultimate tensile strength (UTS), yield strength (YS) and elongation to failure (E_f) of the alloy reached 211 MPa, 113 MPa and 5.2% at room temperature. Comparing with the gravity casting ZAX12405 alloy, the UTS and E_f increased 40% and 300%, respectively. For squeeze-cast Mg–12Zn–4Al–0.5Ca alloy, cast densification was considered more important than microstructure refinement for the promotion of mechanical properties.     

Stress Field Effects on Phonon Properties in Spatially Confined Semiconductor Nanostructures

The phonon properties of spatially confined nanofilms under the preexisting stress fields are investigated theoretically by accounting for the confinement effects and acoustoelastic effects. Due to the spatial confinement in low-dimensional structures, the phonon dispersion relations, phonon group velocities as well as the phonon density of states are of significant difference with the ones in bulk structures. Here, the continuum elasticity theory is made use of to determine the phonon dispersion relations of shear modes (SH), dilatational modes (SA) and the flexural modes (AS), thus to analyze the contribution of stress fields on the phonon performance of confined nanofilms. Our numerical calculations indicate that the phonon properties can be modified by the preexisting stress fields significantly. The influence of the stress field on the phonon energy, phonon group velocity and the phonon density of states are sensitive to the strength and the direction of stress fields. The results in this paper can offer an alternative and applicable approach for phonon engineering to control the phonon properties in semiconductor nanostructures.     

光子计数特性反常效应的实验观测与研究

本文首次报道了PMT光子计数系统光电特性的反常现象,介绍了观测与研究其反常效应的实验装置与方法,给出了相应的实验结果,并就PMT阳极电压、入射光波长、偏振特性等对反常效应的影响进行了初步的实验研究。     

Effects of self heating when using a continuous bridge voltage for strain gauging epoxy models

One source of concern when strain gauging epoxy materials, is that if the gauges are continuously energised at high power densities, then the heat generated by the strain gauges will cause large apparent strains and will reduce the modulus of the underlying material. The magnitude and significance of the heating effect are discussed and methods of reducing this effect are indicated.