First-order phase transitions: equivalence between bimodalities and the Yang–Lee theorem

First-order phase transitions in finite systems can be defined through the bimodality of the distribution of the order parameter. This definition is equivalent to the one based on the inverted curvature of the thermodynamic potential. Moreover we show that it is in a one-to-one correspondence with the Yang–Lee theorem in the thermodynamic limit. Bimodality is a necessary and sufficient condition for zeroes of the partition sum in the control intensive variable complex plane to be distributed on a line perpendicular to the real axis with a uniform density, scaling like the number of particles.     

新模式热电联产系统:联产供热的一个发展

1前言经济的迅猛发展，能源与水源的供需矛盾的突出，环保形势的严峻要求用能的“文明化”。文明用能应是跨世纪和新世纪用能战略的基本原则。文明用能的一个极重要方面就是对热能的文明利用问。热电联产是热能文明利用不可替代的途径。本文提出一种热电联产的新模式，旨在通过这种模式把联产供热规模化，大幅度地节约能源和水资源，减轻电能与热能的生产对环境的不利影响。最近中央提出的可持续发展战略，应成为我们今后技术研究的一个指导性方针。节约能源、水源和保护环境是这一战略的重要组成部分。在世界范围内，对节约资源保护环境问…     

细长竖直管路内自然对流沸腾临界热通量研究

l引言管内或窄小流路内的自然对流沸腾CHF的研究比较少。文献［1～41对水及氟里昂系等液体进行了实验，在Kutataladze【’］的池内沸腾无量式基础上，提出如下经验公式当L／De－－＋0时上式退化为池内沸腾公式。式中qm。x是临界热通量；Hi。是蒸发潜热；。是汽液界面张力；尸l和p。分别是液体和蒸汽的密度；9是重力加速度；c是实验常数；不同研究者之间相差很大。当L／De较大时各经验公式的计算值会相差l～2倍。式（1）没有任何物理机理的支持，仅以J和L／De之间的无量纲关系对实验值进行统计整理，对物性的实际影响、De独立于L／De的…     

相变乳状液的储冷模型与参数分析

本文建立了一种乳化的非牛顿相变功能流体的循环储冷模型,对影响其储冷性能的各项参数进行了模拟计算和分析。得出了描述不同储冷条件下与初始温度相关联的显热段和与乳液浓度相关联的潜热段储冷性能特征的无量纲关联式,以及储冷速率的相对比较。计算结果与有限条件下的测试结果基本吻合。该研究结果对采用潜热型功能相变流体储冷装置的设计具有参考价值。     

Design of square-shaped heat flux cloaks and concentrators using method of coordinate transformation

A square-shaped heat flux cloak and a square-shaped heat flux concentrator have been designed theoretically according to the invariance symmetry of steady state thermal conductive equation. The direction of heat flux in these devices can be modulated as desired. Using the method of coordinate transformation, the inhomogeneous and anisotropic thermal conductivity in the transformation region have been acquired. Two-dimensional finite element simulations were performed to confirm the theoretical results.     

Characterization and oxidation behavior of NiCoCrAlY coating fabricated by electrophoretic deposition and vacuum heat treatment

Electrophoretic deposition (EPD) was showed to be a feasible and convenient method to fabricate NiCoCrAlY coatings on nickel based supperalloys. The microstructure and composition of the NiCoCrAlY coatings after vacuum heat treatment were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX). Isothermal-oxidation test was performed at 1100 °C in static air for 100 h. The results show that the major phases in electrophoretic deposited and vacuum heat treated NiCoCrAlY coating are γ-Ni and γ′-Ni₃Al phases, also there is an extremely small quantity of Al₂O₃ in the coating. Composition fluctuations occur in the coating and a certain amount of titanium diffuse from the superalloy substrate to the top of the coating during vacuum heat treatment. The oxidation test results exhibit that the oxidation kinetics of this coating has two typical stages. The protective oxide layer is mainly formed in the initial linear growth stage and then the oxide layer hinders further oxidation of the coating in the subsequent parabolic growth stage. The coating can effectively protect the superalloy substrate from oxidation. A certain amount of rutile TiO₂ is formed in the coating during oxidation and it is adverse to the oxidation resistance of the coating.     

高温及超高温热管的启动特性和传热极限

根据局部高温、高热流加热等特殊场合的需求,设计、加工了钠高温热管及锂超高温热管,并对热管的启动和极限特性进行了研究。高温及超高温热管能够顺利启动,但启动时应注意可能到来的声速传热极限。端部加热启动时,端部附近管体部分会形成一段等效的加热段,可以将工质从启动时的固体状态到全部熔化形成相变传热及流动循环的时间确定为启动时间。热管的传热极限特性表明,超高温热管应工作在更高的温度和更大的热流密度。热管的结构和工艺优化有利于启动和运行。     

LOM and HOM damping study in a superconducting deflecting cavity for ALS at LBNL

Superconducting deflecting cavities can be used in synchrotron light source to generate subpicosecond X-ray pulses while the impedance of the lower order modes (LOM) and higher order modes (HOM) in the cavity should be kept below an accepted level to avoid beam instability. These modes can be damped by adding waveguide on beam pipe. Detailed simulation of Q in CST Microwave Studio is introduced and experiment results on an aluminum model cavity with damping waveguide are reported to make a comparison.     

Quantum gauge fields and flat connections in 2-dimensional BF theory

The 2-dimensional BF theory is both a gauge theory and a topological Poisson σ-model corresponding to a linear Poisson bracket. In [3], Torossian discovered a connection which governs correlation functions of the BF theory with sources for the B-field. This connection is flat, and it is a close relative of the KZ connection in the WZW model. In this Letter, we show that flatness of the Torossian connection follows from (properly regularized) quantum equations of motion of the BF theory.     

基于单色捕捉技术的透平导叶传热系数测量

采用窄带热敏液晶瞬态单色捕捉技术测量叶片全表面传热系数,以预先加热被测叶片并在主流中快速冷却的方法引入温度阶跃,利用3台3CCD（电荷耦合元件）相机对叶片表面的不同区域进行图像采集记录,将图像坐标转换至叶片空间坐标,通过后处理得到叶片表面传热系数。由实验结果分析可知,叶片前缘区域传热系数最大值位于加速最剧烈处,在吸力面...