Influence of Structural Anisotropy on the Irreversibility Line of High-Tc Cuprates

From zero-field-cooled and field-cooled magnetic response, we have determined the irreversibility lines for a number of high-T _c oxides, viz., La(Sr)-214, Nd-223, Dy(Tb)-124, (Tl, Pb)-1212, and Tl-11112, in the H–T plane, which fit the relation H=A(1 –T/T _c ) ⁿ . Our results are consistent with a correlation between the anisotropy of the structure and the value of n, is in agreement with the Josephson decoupling model [1].     

Comparative Study of Dense Bulk MgB2 Materials Prepared by Different Methods

We report on the results of a comparative investigation of highly dense bulk MgB₂ samples prepared by three methods: (i) hot deformation; (ii) high pressure sintering; and (iii) mechanical alloying of Mg and B powders with subsequent hot compaction. All types of samples were studied by AC susceptibility, DC magnetization, and resistivity measurements in magnetic fields up to ₀ H = 160 kOe. A small but distinct anisotropy of the upper critical field connected with some texture of MgB₂ grains was found for the hot deformed samples. The samples prepared by high pressure sintering as well as by mechanical alloying show improved superconducting properties, including high upper critical fields H _c2 (₀ H _c2 (0) 23 T), irreversibility fields H _irr which are strongly shifted towards higher values H _irr(T) 0.8 H _c2(T) and high critical current J _c (J _c = 10⁵ A/cm² at 20 K and 1 T).     

Influence of Sr Substitution on Structure, Hole Concentration in CuO2 Planes, and Irreversibility Line in (Hg,Pb)(Ba,Sr)2Ca2Cu3O8+δ Single Crystals

Single crystals of HgBa₂Ca₂Cu₃O₈₊ compound with partial substitution of Sr and Pb have been grown at high gas pressure. Bond valence sum calculations show that the substitution of Sr for Ba leads to a more homogeneous distribution of holes between nonequivalent CuO₂ planes. In nonsubstituted crystals, the density of holes is significantly higher in the inner CuO₂ planes. The irreversibility field increases on Sr substitution. The thickness of the charge reservoir decreases with Sr substitution by 0.7 Å.     

Finite-time thermodynamic modelling and analysis of an irreversible Otto-cycle

The performance of an air standard Otto-cycle is analyzed using finite-time thermodynamics. In the irreversible cycle model, the non-linear relation between the specific heat of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and the heat-transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are indicated by numerical examples. Moreover, the effects of internal irreversibility, heat-transfer loss and friction loss on the cycle performance are analyzed. The results obtained in this paper may provide guidance for the design of practical internal-combustion engines.     

试论非平衡统计物理基本方程

由于从刘维方程不能严格统一推导出不可逆性、熵增加原理和流体力学方程，本文提出时间反演不对称的刘维空间反常朗之万方程或其等价的广义刘维方程，作为统计物理的基本方程。这个方程反映了统计热力学的运动规律是随机性的而非确定性的。由它出发推导出了非平衡熵、熵增加原理、平衡态系综、ＢＢＧＤＹ扩散方程链，流体力学方程，如质量漂移扩散方程、广义Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程等。所有这一切都是统一的严格的，不需增补任何假设．但是难以证明所有非均匀的远离平衡态的孤立系统内各处的熵产生密度σ≥０。     

On the life-controlling microstructural fatigue mechanisms in ductile metals and alloys in the gigacycle regime

The high-cycle fatigue (HCF) behaviour of ductile metals and alloys, and the life-controlling microstructural fatigue mechanisms known from HCF are reviewed critically with respect to their possible role in the gigacycle or ultra-high-cycle fatigue (UHCF) regime. Arguments are presented to support the hypothesis that, at the very low amplitudes of the UHCF regime, fatigue crack initiation, resulting from cyclic strain localization, and slow early Stage I fatigue crack propagation are the life-controlling mechanisms and that these processes can essentially be described in terms of the microstructurally irreversible portion of the cumulative cyclic plastic strain. Emphasis is placed on the important role of the so-called slip irreversibility which decreases as the amplitude becomes lower and lower. Finally, the Manson–Coffin law is reformulated for very low amplitudes in terms of microstructurally relevant parameters, and a fatigue life diagram is developed, based on these preceding microstructural considerations. Important features of this diagram are: (i) the plastic strain fatigue limit in the HCF regime which is related to the threshold for cyclic strain localization in persistent slip bands; and (ii) the transition from this plastic strain fatigue limit to a threshold of negligible slip irreversibility at still lower amplitudes in the UHCF regime.     

_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。     

等截面钉肋的熵产优化研究

从热力学熵产的角度出发,以熵产最小为目标,建立了肋片的熵产分析理论模型,并对在强迫对流条件下的熵产最小时的圆柱形钉肋进行了讨论。     

不可逆汽机热泵有限时间热力学优化

本文建立了汽机热泵系统的模型并基于有限时间热力学考虑汽机热泵系统内部不可逆和外部不可逆性对系统性能进行了分析研究。汽机热泵系统由不可逆汽机循环和不可逆压缩式热泵循环组成。分别对汽机侧和热泵的蒸发器与冷凝器进行了优化面积分配和优化时间分配研究,得到了系统热负荷与系统性能系数的数学关系。研究中引入两个不可逆参数RΔS、RΔS＇。算例研究显示内不可逆参数对汽机热泵系统的性能比外部不可逆因素有更大的影响。研究还发现热泵侧不可逆因素对系统的影响大于汽机侧不可逆因素对系统的影响。     

钉肋肋列传热的最小熵产优化分析

应用热力学的熵产概念对钉肋肋列的传热问题进行了研究,从如何使各种不可逆损失最小着手,分析了肋列的肋间距,肋片的直径,换热介质与热负荷等不同参数对熵产的影响,发现在不同参数条件下,熵产数都会存在一个最小值以及与此对应的最优的Ｒｅｄｏｐｔ数,并对顺列和错列两种常用肋片布置方式作了对比,研究结果将有助于节能型钉肋的设计。