Non-equilibrium sorption performances for composite sorbents of chlorides–ammonia working pairs for refrigeration

The sorption/desorption characteristics under the non-equilibrium conditions are extremely important for the refrigeration. The experimental test unit is set up, and the p–T–x curves of different working pairs are tested under the non-equilibrium working conditions. The results show that non-equilibrium sorption/desorption processes are related with dual variables rather than a single variable. Then we tested the isobaric sorption/desorption processes of chlorides. Results show that the hysteresis phenomena are related with the desorption enthalpy. Sorption/desorption dynamic models are studied. For sorption process the model is in accord with D-A equation, but for the desorption process both D-A equation and Spinner model should be considered. The Arrhenius equation is used to fit the relation between reaction heat and desorption hysteresis. The results show that the non-equilibrium equations fit the refrigeration performance well, whereas the theoretical equilibrium curves have big error.     

High temperature low cycle fatigue

Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing (DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current design approaches employ linear summation of fatigue and creep damage with suitable factors on permissible damage to take care of uncertainties in interaction between cyclic and time-dependent processes. It is, therefore, important to develop a deeper understanding of the processes that occur during high temperature fatigue so that realistic life predictions could be made. Results on the high temperature fatigue behaviour of austenitic stainless steels, ferritic steels and nickel base alloys are presented here. The important mechanisms of interaction of high temperature time-dependent processes with fatigue under various conditions are discussed in detail. Emphasis is placed on cyclic stress response, fatigue life, deformation substructure and fracture behaviour. This is followed by a review of important life prediction techniques under combined creep-fatigue loading conditions. Life prediction techniques considered here include linear damage summation, strain range partitioning, ductility exhaustion approach, frequency modified and frequency separation methods, techniques based on hysteresis energy and damage rate models, and methods based on crack-cavitation interation models.     

型钢混凝土异形柱框架地震损伤分析

为实现对型钢混凝土异形柱框架的地震损伤分析,采用加权系数法建立了能够反映构件损伤、楼层损伤和整体框架损伤三者迁移演化的地震损伤模型,并对两榀型钢混凝土异形柱框架进行了地震损伤试验及有限元模拟,获得了梁的弯矩-转角滞回曲线和柱的水平荷载-位移滞回曲线,进而对试件的地震损伤指数进行了计算分析。结果表明,构件、楼层和整体框架的损伤指数变化规律与试件的破坏发展历程较为吻合,说明所建立的型钢混凝土异形柱框架地震损伤模型是合理的。基于试件的破坏状态及地震损伤分析结果,提出了型钢混凝土异形柱框架对应5个性能水平的损伤指数范围,为该类结构的震后损伤评估提供了依据。     

Interfacial Stresses and the Anomalous Character of Thermoelastic-Deformation Curves of a Cu–Al–Ni Shape-Memory Alloy

Thermoelastic-deformation curves of a single-crystalline Cu–13.5 wt % Al–4.0 wt % Ni shapememory (SM) alloy have been studied. Cyclic temperature variation in a 300–450 K interval revealed an anomalous character of thermoelastic hysteresis loops with regions of accelerated straining at both heating and cooling stages. The observed phenomenon can be used for increasing the response speed of SM-alloy based drive and sensor devices. Analysis of this phenomenon in the framework of the theory of diffuse martensitic transformations showed that the anomalous character of thermoelastic hysteresis loops may be related to the influence of interfacial stresses on the dynamics of martensitic transformations in these SM alloys.     

Instabilities above critical current region in Bi-2223/Ag superconducting coils cooled by liquid nitrogen

A sudden drop of the coil voltage and a hysteresis of I-V curve were observed in measurement of one-layer Bi-2223/Ag coils cooled by liquid nitrogen at currents well above critical current region. Their temporal behavior indicates, that the improvement of the cooling and corresponding decrease of temperature after the jump takes place. To study this phenomenon we measured I-V curves of two Bi-2223/Ag coils made from tapes with various degree of critical current homogeneity and analogical curves of two non-superconducting coils made from thin Cu tapes having various widths. In Cu coils we really observed a sudden drop of the temperature, measured in parallel with Cu resistance drop, after reaching heat flux of about 0.4 W cm⁻² during current ramping up. In spite of non-superconducting character of the tape, the hysteresis, i.e. difference between increasing branch and decreasing branch of I-V curves, was observed too! Approximately the same value of heat flux, at current corresponding to the jump, was found also in superconducting coil on segment with least value of local critical current. We conclude that observed voltage drop of the Bi-2223/Ag does not bear upon superconducting nature of the coil and, as that for Cu coil, can be explained by dynamics of heat transfer to liquid nitrogen and its history.     

Structural Mechanisms of Dilatometric Processes

Temperature actions on metals and alloys usually stimulate the development of irreversible processes of structural evolution. Dilatometric hysteresis can be considered as the total effect of such processes. The elementary mechanisms affecting the sample size upon heating are known to be the thermal expansion of materials, the phase and structural transformations, the ductile flow under its own weight, and the creep stimulated by internal stresses. Each of these mechanisms has specific features, which are unavoidably reflected by the shape of the dilatometric curves in the corresponding temperature ranges. The thermal activation parameters of the mechanisms controlling the kinetics of the change in structural parameters and the development of the corresponding size effects have been determined by photometric analysis of structural images and directly from the dilatometric curves, and the results are discussed in this paper.     

<Emphasis Type="Italic">N-S</Emphasis> transition in nonisothermal characteristics of silicon diodes and thyristors

The results of numerical modeling of the stationary nonisothermal current-voltage (I-U) characteristics of forward-biased high-voltage diodes and thyristors in the interval of current densities J ～ 200–500 A/cm² revealed an N-S transition in the shape of these curves and a hysteresis in the constant current source regimes. It is established that the mechanism of these phenomena is related to a temperature-induced decrease in the coefficient of ambipolar diffusion under the conditions of enhanced recombination. Devices with such I-U characteristics can be irreversibly switched by short current pulses from stable states on the working branch to the states with high heat evolution, which leads to a risk of thermal breakdown.     

共聚改性尼龙MXD6的热解动力学

根据热解(TG)以及微分热解(DTG)曲线分析得出共聚改性聚间苯二甲胺己二酸(MXD6)的热解过程分为3个阶段,随着升温速率的增大,对应的失重峰温依次增大,且热传导和传质会有滞后。在共聚改性尼龙MXD6样品中首先断裂的为酰胺键,酰胺键中的C-N键断裂生成氨基自由基和羰基自由基碎片,最终在高温下生成稳定的小分子迅速离开体系,致使体系失重。热解反应还伴随着交联和水解反应,PA66单元主要热解为环状物。根据Kissinger方程、Ozawa方程和Grane方程以及TG-DTG曲线分析可知,共聚改性尼龙MXD6的热解反应级数均为0.94(近似于1级反应的复杂反应),并根据求得的热解活化能E、指前因子A和反应级数n模拟出热解动力学方程。     

Fatigue of Woven Composite Laminates in Off-Axis Loading I. The Mastercurves

The behaviour of woven orthotropic composite laminates in static and fatigue off-axis loading is described. It is shown that all phenomena: linear and nonlinear deformation; accumulation of damage, measured as change of cyclic modulus or hysteresis loop; and the static and cyclic strength can be described by single master curves using the generalized stress and strain functions. These functions always contain the quadratic expressions of invariants of orthotropy, but coefficients of the invariants depend on the severity of nonlinearity in the described processes or phenomena.     

Prediction of the flow stress of Al6061 at hot deformation conditions

Isothermal compression tests were carried out on Al6061 using a Gleeble-1500 thermal simulator at temperatures ranging from 573 to 723 K and strain rates from 0.5 to 30 s⁻¹. The flow stress of Al6061 was characterized based on an analysis of the true stress-true strain curves. A mathematical mode coupling flow stress with strain, strain rate and temperature for Al6061 has been proposed by using a hyperbolic sinusoidal type equation. The material constant α is 0.01 MPa⁻¹ in the model, whereas other material constants n, lnA and Q are found to be functions of strain. The predicted results from this proposed model are found to be in good agreement with the experimental flow stress curves which can be used to predict the required deformation forces in hot deformation processes.     

Role of dynamic strain ageing in low cycle fatigue

Low cycle fatigue (LCF) at elevated temperatures is known to be influenced by time-dependent processes like creep, oxidation and metallurgical instabilities. Another time-dependent phenomenon namely, dynamic strain ageing (DSA) has been found to exert an influence on LCF behaviour at high temperatures. Research activities carried out in the present author’s laboratory with a view to understanding the effects of DSA on LCF are highlighted in this paper. Occurrence of DSA manifests during total strain-controlled fatigue tests in the form of serrated plastic flow in stress-strain hysteresis loops, increased cyclic work hardening and reduced plastic strain range. Further, DSA causes localization of plastic flow leading to enhanced planarity of slip and widely-spaced slip bands. Impingement of slip bands on grain boundaries causes increased grain boundary decohesion, leading to reduced fatigue life. The influence of prior microstructure such as second phase particles and grain size on the effects of DSA on LCF is also discussed.     

Studies on initial permeability and loss factor in Ni-Zn ferrites synthesized by oxalate precursors

Ni_XZn_1−XFe₂O₄ ferrites with (X = 0.28-0.40 in step of 0.2) have been synthesized by oxalate precursor method and investigated for their, initial permeability and loss factor measurements. Initial permeability has been observed to increase with the increase in Ni²⁺ up to X = 0.32, beyond which it decreases. The variation of initial permeability has been explained by considering the factors such as grain size, saturation magnetization and anisotropy constant. Thermal variation of initial permeability reveals a peak height in μ_i-T curves which tends to increase with increase in Ni²⁺ content. μ_i-T curves also exhibit thermal hysteresis, which reveals the inverse relationship between the difference in heating and cooling curves at which hysteresis falls between Hopkinson peak and T_c with value of initial permeability. Loss factor values are small which is attributed to high density of the samples and processing techniques.     

Thermal Hysteresis in Thin-Film Platinum Resistance Thermometers

Thin-film platinum resistance thermometers (PRTs) are generally manufactured using the deposition of a thin platinum film on an alumina substrate and a laser-trimming method. Because of the strong adhesion between the platinum thin film and the alumina substrate, the PRTs inevitably have strain over the operating temperature range. This causes anomalies and instabilities in the resistance versus temperature characteristics (R?CT). The most prominent and observable effect of thermally induced strain is the thermal hysteresis in the R?CT characteristics. Thermal hysteresis is one of the main uncertainty factors in the calibration of industrial platinum resistance thermometers in laboratories. The thermal hysteresis for 30 thin-film PRTs was measured in the range of 0 °C to 500 °C in 100 °C steps. The thermal hysteresis was measured repeatedly using the same process, and the hysteresis decreased drastically with the repeated measurements. The thermal hysteresis was distributed from 16 mK to 156 mK for all sensors, and the lowest hysteresis was 1 mK to 11 mK in the test temperature range.     

Phase field simulations of low-dimensional ferroelectrics

A coupled theory of nonlinear electro-thermo-viscoelasticity with inclusion of hysteresis, aging and damage effects is developed based on non-equilibrium thermodynamics. In consideration of the Gibbs free energy including the contribution of the free electric field as a functional of the histories of stress, temperature, temperature gradient and electric field in the reference configuration with damage being introduced as an internal state variable, constitutive relations and kinetic laws are obtained from the energy balance equation and the entropy production inequality. Finite electro-thermo-viscoelasticity and nonlinear electro-thermo- elasticity can be taken as special cases. A superposition principle of time, aging, temperature, stress and electric field is proposed for materials with memory on an intrinsic time scale so that the long-term property functions may be represented with horizontal and vertical shifting of the momentary master curves. This formulation lays a foundation for the characterization of the short- and long-term behavior of time-dependent materials with evolving damage under combined electric, thermal and mechanical loadings.     

Fluctuation aftereffect in magnetic materials

Time dependence of magnetization under constant field conditions is exhibited by all materials subject to hysteresis. The phenomenon is a consequence of thermal activation of irreversible magnetization effects from metastable to stable states. Experimental observations of time dependence may be accounted for by considering distributions of the energy required for activation of the metastable states. Two simple cases are considered in this paper. The first involves a fixed value activation energy distribution; the second is concerned with magnetization events that all have the same value of activation energy. The latter is applicable to describing magnetization of magnetooptic films. It is shown that the results of measurements of time dependence of magnetization over wide ranges of time and field are useful in distinguishing between different mechanisms involved in magnetization reversal processes     

锈蚀钢筋混凝土构件基于地震损伤的恢复力模型研究

为建立锈蚀钢筋混凝土构件恢复力模型,本文通过对6个锈蚀钢筋混凝土受弯构件低周反复荷载试验,得到不同锈蚀程度的各试件的滞回曲线及骨架曲线,分析了钢筋锈蚀对试件抗震性能的影响。根据试验成果,结合钢筋锈蚀引起结构破坏形态的改变,综合考虑钢筋锈蚀后引起结构截面几何损伤、钢筋和混凝土力学性能降低、粘结滑移性能劣化以及结构刚度退化等各种耐久性损伤因素,并考虑箍筋锈蚀引起结构延性的影响,提出了锈蚀钢筋混凝土构件基于地震损伤的恢复力模型的确定方法。通过与试验进行对比分析表明模型描绘的骨架曲线和滞回曲线与试验结果总体吻合较好,所描述的现象与试验一致,该恢复力模型可在损伤钢筋混凝土结构地震反应分析中采用。     

基于迟滞耗散能的纤维增强陶瓷基复合材料疲劳寿命预测方法

纤维增强陶瓷基复合材料(CMCs)在疲劳载荷作用下,纤维相对基体在界面脱粘区往复滑移导致其出现疲劳迟滞现象,迟滞回线包围的面积,即迟滞耗散能,可用于监测纤维增强CMCs疲劳损伤演化过程。提出了一种基于迟滞耗散能的纤维增强CMCs疲劳寿命预测方法及考虑纤维失效的迟滞回线模型,建立了迟滞耗散能、基于迟滞耗散能的损伤参数、应力-应变迟滞回线与疲劳损伤机制(多基体开裂、纤维/基体界面脱粘、界面磨损与纤维失效)之间的关系。分析了疲劳峰值应力、疲劳应力比与纤维体积分数对纤维增强CMCs疲劳寿命S-N曲线、迟滞耗散能和基于迟滞耗散能的损伤参数随循环次数变化的影响。疲劳寿命随疲劳峰值应力增加而减小,随纤维体积含量增加而增加;迟滞耗散能随疲劳峰值应力增加而增加,随应力比和纤维体积分数增加而减小;基于迟滞耗散能的损伤参数随纤维体积分数增加而减小。      

On the readout of HT peaks in LiF:Mg,Ti by applying high rate gas heating

The main high temperature (HT) peaks in the glow curves of LiF:Mg,Ti, normally assigned as 6 and 7 are known to have higher response to high LET radiation than to low LET radiation. This effect can be used in principle to discriminate between neutrons and gamma rays in a mixed neutron–gamma field. In routine dosimetry, a high rate gas heating of Teflon coated chips is employed (mostly 25 °C/s), which may cause marginal thermal conditions. The fast heating rate readout process of the HT peaks and the practical consequences were studied, leading to the conclusion that in spite of the technical constraints, using high rate gas heating produces results which are not significantly different from those using a slow heating rate. Applying high heating rates seems to pose no practical obstacle in utilizing HT peaks information, which has the potential to be used for mixed neutron–gamma dosimetry.     

Magnetovoltage Measurements and Hysteresis Effects in Polycrystalline Superconducting Y1Ba2Cu3O7−x /Ag in Weak Magnetic Fields

The magnetovoltage measurements (V–H curves) with different sweeping rates (dH/dt) of the external magnetic field in Ag-added polycrystalline YBa₂Cu₃O_7?x sample (YBCO/Ag) were investigated. The measurements of V–H curves were carried out as functions of the transport current (I) and temperature (T). Upon cycling H, all V–H curves measured for different values of I exhibit a clockwise hysteresis effects in forward region. The hysteresis effects in the V–H curve were interpreted in terms of two-level magnetic system, which considers the superposition of the external magnetic field and the local magnetic fields in the intergrain boundaries induced by magnetic dipole moment of neighbor superconducting grains. The analysis of magnetovoltage data showed that the flux trapping in the junction network has a negligible effect on the evolution of the V–H curves and the irreversibilities arise mainly from the flux trapping inside the grains. It is shown that the width of V–H curves shows a universal scaling behavior with respect to the applied current below the critical temperature T _c . The comparison of V–H curves of the YBCO/Ag sample with those of YBCO shows that adding Ag to the superconducting structure weakens the pinning properties of Josephson medium and provokes the instabilities in measured dissipation. The presence of Ag in the superconducting matrix causes marked decrease in hysteresis effects and makes the V–H curves dH/dt dependent. At high values of dH/dt, the instabilities and plateau regions in V–H curves increase significantly as compared to those of observed in YBCO. In addition, the interrelation between the evolution of V–H curves obtained for different values of I and the critical current I _c was demonstrated experimentally.     

DNA double-strand break repair: a theoretical framework and its application

DNA double-strand breaks (DSBs) are formed as a result of genotoxic insults, such as exogenous ionizing radiation, and are among the most serious types of DNA damage. One of the earliest molecular responses following DSB formation is the phosphorylation of the histone H2AX, giving rise to γH2AX. Many copies of γH2AX are generated at DSBs and can be detected in vitro as foci using well-established immuno-histochemical methods. It has previously been shown that anti-γH2AX antibodies, modified by the addition of the cell-penetrating peptide TAT and a fluorescent or radionuclide label, can be used to visualize and quantify DSBs in vivo. Moreover, when labelled with a high amount of the short-range, Auger electron-emitting radioisotope, ¹¹¹In, the amount of DNA damage within a cell can be increased, leading to cell death. In this report, we develop a mathematical model that describes how molecular processes at individual sites of DNA damage give rise to quantifiable foci. Equations that describe stochastic mean behaviours at individual DSB sites are derived and parametrized using population-scale, time-series measurements from two different cancer cell lines. The model is used to examine two case studies in which the introduction of an antibody (anti-γH2AX-TAT) that targets a key component in the DSB repair pathway influences system behaviour. We investigate: (i) how the interaction between anti-γH2AX-TAT and γH2AX effects the kinetics of H2AX phosphorylation and DSB repair and (ii) model behaviour when the anti-γH2AX antibody is labelled with Auger electron-emitting ¹¹¹In and can thus instigate additional DNA damage. This work supports the conclusion that DSB kinetics are largely unaffected by the introduction of the anti-γH2AX antibody, a result that has been validated experimentally, and hence the hypothesis that the use of anti-γH2AX antibody to quantify DSBs does not violate the image tracer principle. Moreover, it provides a novel model of DNA damage accumulation in the presence of Auger electron-emitting ¹¹¹In that is supported qualitatively by the available experimental data.