管内变密度流体的充分发展流动与换热

本文提出了圆管内变密度流体流动与换热充分发展的概念及其相关假设.在所提出的概念和假设基础上给出了摩擦阻力系数Cf与Nusselt数Nu的定义式和计算式.通过对圆管内密度随温度变化的氩气的流动与换热所进行的数值模拟,验证了在本文的计算条件范围内,圆管内变密度流体充分发展流动与换热的概念是合理的,并且CfRe=16,Nu=4.36.     

Quantum speedup via engineering multiple environments

Evolution speed of an open quantum system is vividly influenced by the structure of environments. The strong system‐environment coupling is found to be able to accelerate quantum evolution. In this work, we propose a different method of governing the quantum speedup via engineering multiple environments. It is shown that, with a judicious choice of the number of coupling environments, the quantum speedup of an open system can be achieved even under weak system‐environment coupling conditions. The mechanism for the speedup is due to the switch between Markovian and non‐Markovian regions by manipulating the number of the surrounding environments. In addition, we verify the above phenomena by using quantum dots embedded in a planar photonic crystal under current technologies. These results provide a new degree of freedoms to accelerate quantum evolution of open systems. The strong system‐environment coupling can speed up the quantum evolution process. This work shows that, via engineering multiple environments, one can speed up the evolution process even under weak coupling conditions.     

计及污垢影响的换热器热优化

本文利用熵产生数方法研究了气体和液体传热介质的顺流、逆流换热器的热力学完善性，结果表明，如给定冷、热流体的入口温度，在综合考虑传热、流动阻力和污垢的情况下，可用优化方法确定其它参数。     

A fixed point theorem for eventually nonexpansive semigroups of mappings

Let K be a subset of a Banach space X. A semigroup $\text{F}$ = {?_α ∥ α ∞ A} of Lipschitz mappings of K into itself is called eventually nonexpansive if the family of corresponding Lipschitz constants $\text{{k}{}_{\mathrm{\alpha }}\text{¦ α ? A}}$ satisfies the following condition: for every ? > 0, there is a γ?A such that k_β < 1 + ? whenever ?_β ? ?_γ$\text{F}$ = {?_gg?_α ¦ ?_α ? $\text{F}$}. It is shown that if K is a nonempty, closed, convex, and bounded subset of a uniformly convex Banach space, and if $\text{F}$:K → K is an eventually nonexpansive, commutative, linearly ordered semigroup of mappings, then $\text{F}$ has a common fixed point. This result generalizes a fixed point theorem by Goebel and Kirk.     

封闭圆内开缝圆自然对流换热的振荡特性

本文通过数值计算探讨了封闭圆内开缝圆自然对流换热的振荡特性。数值计算以整个圆为计算区域,采用了非稳态的数学模型和具有QUICK差分格式的SIMPLE算法。在相同条件下计算结果和实验结果符合很好。数值结果显示, 当几何结构一定时,Rayleigh数Ra小于某个临界值时,流动和换热处于稳态,并且关于垂直中心线对称;Ra大于这个临界值时,流动和换热是振荡的,非对称的。数值实验还表明,流动和换热出现振荡时的临界Rayleigh数Rac与开缝圆的开缝度有关,且流动和换热的振荡会出现对称振荡和非对称振荡两种情形。     

InxGa1-xN薄膜的弯曲因子及斯托克斯移动研究

采用常压金属有机化学汽相沉积(MOCVD)技术以Al2O3为衬底在GaN膜上生长了InxGa1-xN薄膜。以卢瑟福背散射／沟道技术、光透射谱、光致发光光谱对InxGa1-xN／GaN／AI2O3样品进行了测试。研究了InxGa1-xN薄膜的弯曲因子及斯托克斯移动。结果表明，采用光透射谱、光致发光光谱得到的InxGa1-xN薄膜的禁带宽度一致，InxGa1-xN薄膜并不存在斯托克斯移动。InxGa1-xN薄膜的In组分分别为0．04，0．06，0．24，0．26时，其弯曲因子分别为3．40,2．36，1．82，3．70。随In组分变化。InxGa1-xN薄膜的弯曲因子的变化并没有一定的规律，表明InxGa1-xN薄膜的禁带宽度随In组分的变化关系复杂。     

各向异性磁化等离子体JEC-FDTD算法

将色散介质的电流密度卷积-时域有限差分(JEC-FDTD)算法推广到各向异性磁化等离子体色散介质.该算法同时解决了电磁波在各向异性和频率色散介质中传播的难题，给出了各向异性磁化等离子体JEC-FDTD算法的公式.计算磁化等离子体平板对平行于磁场传播的电磁波的反射和透射系数，通过与解析结果的比较，验证了该算法的高效性和高精度. 关键词： 色散介质 FDTD算法 各向异性 磁化等离子体     

Measurements of cavitation bubble dynamics based on a beam-deflection probe

We present an optodynamic measurement of a laser-induced cavitation bubble and its oscillations based on a scanning technique using a laser beam-deflection probe. The deflection of the beam was detected with a fast quadrant photodiode which was built into the optical probe. The applied experimental setup enabled us to carry out one- or two-dimensional scanning of the cavitation bubble, automatic control of the experiment, data acquisition and data processing. Shadow photography was used as a comparative method during the experiments.