Microstructure investigation of dynamic recrystallization in hard machining: From thermodynamic irreversibility perspective

Frontiers of Mechanical Engineering - The drastically changed thermal, mechanical, and chemical energies within the machined surface layer during hard machining tend to initiate microstructural...     

沿轴向截面突变的圆柱形钉肋肋列传热的熵产分析

对沿轴向截面突变的圆柱形钉肋的热力学性能做了综合理论分析,研究了其传热过程因传热和摩擦损失引起的不可逆熵产的变化特点,对３种肋结构做了比较。     

First-cycle irreversibility of layered Li-Ni-Co-Mn oxide cathode in Li-ion batteries

The first-cycle irreversibility of Li_1.048(Ni_1/3Co_1/3Mn_1/3)_0.952O₂ (LiMO₂) cathode material in lithium and lithium-ion cells has been studied using galvanostatic cycling and in situ synchrotron X-ray diffraction. The so-called “lost capacity” of a Li/LiMO₂ cell observed during initial cycle in conventional voltage ranges (e.g., 3.0-4.3 V) could be completely recovered by discharging the cell to low voltages (<2 V). During the deep discharge, the lithium cell exhibited an additional voltage plateau, which is believed to result from the formation of Li₂MO₂-like phase on the oxide particle surface due to very sluggish lithium diffusion in Li_1−ΔMO₂ with Δ → 0 (i.e., near the end of discharge). Voltage relaxation curve and in situ X-ray diffraction patterns, measured during relaxation of the lithium cell after deep discharge to obtain 100% cycle efficiency, suggested that the oxide cathode returned to its original state after the following two-step relaxation processes: relatively quick disappearance of the Li₂MO₂-like phase on the particle surface, followed by slow lithium diffusion in the layered structure. Experiments conducted in Li₄Ti₅O₁₂/LiMO₂ lithium-ion cells confirmed that the physical loss of lithium (via surface film formation or parasitic electrochemical reactions, etc.) from LiMO₂ was negligible up to an oxide voltage of 4.3 V vs. Li⁺/Li.     

评海伍德的第三可逆功原理以及第三和第四功损原理

介绍并讨论了海伍德提出的第三可逆功原理以及第三和第四功损原理。对这些原理的论证方法、热力学模型以及适用范围也作了评述。着重说明了功损与损(不可逆性)之间的区别。     

相变贮热系统的热力学分析

本文基于热力学第二定律,对相变贮热系统进行了分析,得到了两个热力学优化参数,即最佳贮热介质温度和最佳传热单元数;同时运用了压朋损失和焓朋损失这两个不同的概念,讨论了由此而对最佳传热单元数(即换热器尺寸大小)的影响;还比较了显热贮存系统和相变贮热系统之间贮热性能的差别。     

换热器肋片的最小熵产优化研究

<正>肋片作为一种非常高效的强化传热技术,不仅是作为二次传热面,扩大传热面积,并促进流体介质扰动来强化换热,同时其增加的传热面积也会造成相对增加的流动阻力.关于肋片强化传热与增大流阻的综合评判准则在文献[1]中已有论述     

Improving thermal comfort conditions by accounting for the mean radiant temperature

The environment in many air conditioned spaces is often determined by the air dry bulb temperature alone. However, in certain circumstances, ignoring the consequences of the mean radiant temperature is not acceptable. A strategy is proposed, therefore, in which the operative temperature, which accounts for radiant effects, is employed as the parameter for control purposes. It is based primarily upon the ASHRAE comfort chart and results in improved thermal comfort.     

LONG-RANGE DEPENDENCE, NON-LINEARITY AND TIME IRREVERSIBILITY

Abstract. A rather general class of stationary processes with long-range dependence is introduced by mixing independent processes with short-range dependence. The class is used to study the relation between non-linearity and time irreversibility of the long-range dependence process and the corresponding features of the component processes.     

Y0.75Ca0.25MnO3体系的自旋玻璃行为与输运特性研究

研究了Y0.75Ca0.25MnO3体系的结构和电磁特性,结果表明,场冷(FC)和零场冷(ZFC)直流磁化曲线在低温下存在典型的分叉现象,相应的Tcusp=34K;不同频率下交流磁化测量表明了随着频率的增加自旋冻结温度Tf=Tcusp向高温区移动,结合电输运测量,证明Y0.75Ca0.25MnO3体系为一典型的自旋玻璃绝缘(SGI)体系.     

论动态规划方法在不确定性投资理论中的应用

不确定性条件下的经济问题非常重要,采取动态规划方法研究不确定性投资理论的应用现实意义重大。本文介绍了动态规划及其基本方程———贝尔曼方程,然后应用贝尔曼方程和处理不确定性问题的基本引理———伊藤引理,阐释了一个著名的不可逆性投资模型及其现实应用,由此抛砖引玉,推进该领域的研究。