Anisotropy in ac losses near the irreversibility field of Bi2Sr2CaCu2O8

The ac susceptibility under a biased dc field near the irreversibility field (H _irr) of a Bi₂Sr₂CaCu₂O₈ single crystal has been measured. The frequency dependence, the ac-power dependence, and the nearly lossless character of the vs.H _dc curve forHa-axis have been roughly explained from a reversible (elastic) fluxoid motion, while those forH c-axis have been explained from a thermally assisted flux-flow (TAFF) model. The obtained parameters are discussed in relation to anisotropic flux-pinning mechanisms in the layered structure of this compound.     

Modeling,numerical optimization,and irreversibility reduction of a triple-pressure reheat combined cycle

The main methods for improving the efficiency of the combined cycle are: increasing the inlet temperature of the gas turbine (TIT), reducing the irreversibility of the heat recovery steam generator (HRSG), and optimization. In this paper, modeling and optimization of the triple-pressure reheat combined cycle as well as irreversibility reduction of its HRSG are considered. Constraints were set on the minimum temperature difference for pinch points (PP_m), the temperature difference for superheat approach, the steam turbine inlet temperature and pressure, the stack temperature, and the dryness fraction at steam turbine outlet. The triple-pressure reheat combined cycle was optimized at 41 different maximum values of TIT using two different methods; the direct search and the variable metric. A feasible technique to reduce the irreversibility of the HRSG of the combined cycle was introduced. The optimized and the reduced-irreversibility triple-pressure reheat combined cycles were compared with the regularly designed triple-pressure reheat combined cycle, which is the typical design for a commercial combined cycle. The effects of varying the TIT on the performance of all cycles were presented and discussed. The results indicate that the optimized triple-pressure reheat combined cycle is up to 1.7% higher in efficiency than the reduced-irreversibility triple-pressure reheat combined cycle, which is 1.9–2.1% higher in efficiency than the regularly designed triple-pressure reheat combined cycle when all cycles are compared at the same values of TIT and PP_m. The optimized and reduced-irreversibility combined cycles were compared with the most efficient commercially available combined cycle at the same value of TIT.     

The role of intergrain junctions in transport critical current irreversibility

The magnetic field dependence of voltage at constant measuring currents of YBa₂Cu₃O_7– bulk ceramics and Bi(Pb)SrCaCuO screen printed films were studied at different temperatures so as to obtain information on critical current irreversibility. Two ranges of these curves were found to show sensitivity to magnetic field. They suggest that the two types of superconducting medium, i.e., the Josephson and Abrikosov medium, result in two different voltage generation mechanisms. It is shown that the Josephson medium plays a role in both low and high magnetic field critical current irreversibility.     

支持需求追踪的版本控制机制

版本控制是增强软件可维护性的重要方法,但目前常用的版本控制机制缺乏对需求的可追踪性支持。该文提出一种支持需求追踪的版本控制机制,能够有效追踪功能需求、功能设计、代码间的版本关联关系,确保开发人员可以正确获取所需程度的需求追踪信息,有利于软件产品的一致性维护。基于该机制,设计并实现了一个支持需求追踪的版本控制工具VCFQ,并对该工具实现中的一些关键技术进行了论述。     

_P 最大时不可逆卡诺热机的_和 P

本文在内可逆卡诺热机模型的基础上,引入不可逆程度Ⅰ来描述传热以外的其它不可逆性,从而建立了不可逆卡诺热机模型。并以η~λΡ作为目标函数讨论热机的最优化。导出了最大时不可逆卡诺热机的效率和功率,并对λ=0,λ=1和λ→∞三种情况作了较详细的讨论。     

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。     

Unearthing a Buried Memory: Duhem's Third Way to Thermodynamics. Part 2†

Duhem considered himself as the upholder of a ‘third way’ to Thermodynamics. His generalized Mechanics/Thermodynamics aimed at encompassing all kinds of transformations, from spatial changes to the change of physical qualities. From 1886 until 1896 he undertook a demanding design for the unification of physics. He translated Thermodynamics into the language of Analytical Mechanics, and conversely founded Mechanics on the principles of Thermodynamics. Step by step he widened the mathematical and conceptual structure of Analytic Mechanics, in order to hold together ‘local motion,’ thermal phenomena, electromagnetic phenomena, and many kinds of irreversible transformations. At the same time, he tried to recast methods and targets of physics: from the reductionist tradition of Mechanics he let a new interest in the complexity of the natural world emerge. Modern science had had to fight against the old physics of qualities, in order to supplant it: the complexity of the physical world was set aside, and replaced by a simplified geometrical world. Duhem endeavoured to retrieve and take that neglected complexity into the wide boundaries of a generalized Mechanics‐Thermodynamics. He aimed at widening the scope of physics: the new physics could not confine itself to ‘local motion’ but had to describe what Duhem labelled ‘motions of modification.’     

Performance comparison of CFCs with their substitutes using artificial neural network

In order to decrease global pollution due to chlorofluorocarbons (CFCs), the usage of HFC‐ and HC‐based refrigerants and their mixtures are considered instead of CFCs (R12, R22, and R502). This was confirmed by an international consensus (i.e. Montreal Protocol signed in 1987). This paper offers to determine coefficient of performance (COP) and total irreversibility (TI) values of vapour‐compression refrigeration system with different refrigerants and their mixtures mentioned above using artificial neural networks (ANN). In order to train the network, COPs and TIs of refrigerants and their some binary, ternary and quartet mixtures of different ratios have been calculated in a vapour‐compression refrigeration system with liquid/suction line heat exchanger. In the calculations thermodynamic properties of refrigerants have been taken from REFPROP 6.01 which was prepared based on Helmholtz energy equation of state. To achieve this, a new software has been written in FORTRAN programming language using sub‐programs of REFPROP, and all related calculations have been performed using this software using constant temperature method as reference. Scaled conjugate gradient, Pola–Ribiere conjugate gradient, and Levenberg–Marquardt learning algorithms and logistic sigmoid transfer function were used in the network. Mixing ratios of refrigerants, and evaporator temperature were used as input layer; COP and TI values were used as output layer. It is shown that R² values are about 0.9999, maximum errors for training and test data are smaller than 2 and 3%, respectively. It is concluded that, ANNs can be used for prediction of COP and TI as an accurate method in the systems. Copyright © 2004 John Wiley & Sons, Ltd.     

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...     

质漏对内可逆四源化学泵性能的影响

建立受传质不可逆性和质漏影响的一类不可逆四源化学泵的新循环模型,分析这些不可逆性对循环性能的影响,导出了循环的泵能率和性能系数间的基本优化关系,同时确定了一些重要参数的最优工作区域和性能界限。