Effects of characteristics of Mo dispersions on the plasticity of Mg-based bulk metallic glass composites

The Mg₅₈Cu_28.5Gd₁₁Ag_2.5 bulk metallic glass composites (BMGCs) dispersion strengthened by porous Mo particles with different volume fractions and particle sizes were synthesized by casting and characterized. The presence of porous Mo particles could restrict the shear band propagation. It was found for a given volume fraction of Mo particles, smaller particles would lead to more interfacial areas, shorter inter-particle free spacings, smaller confinement zone sizes than the larger particles, and consequently the improvement of compression plasticity from 10% up to 27%. Also, for a given Mo particle size, higher volume fraction would lead to larger compression plasticity. The inter-particle free spacing, as well as the confinement zone size (mean free path of shear bands), appears to be the controlling factor in limiting the propagation of shear bands which in turn affecting the plasticity of BMGCs.     

Simulation of Swirling Turbulent Heat Transfer in a Vortex Heat Exchanger

ABSTRACT

This article presents a numerical simulation of swirling turbulent flow and heat transfer in a novel vortex heat exchanger. A new algebraic Reynolds stress/heat flux model (ASM/AFM) is applied to the simulation. The computation is performed under different air flow rates for both swirling and nonswirling flows. The calculated mean heat transfer coefficients on both inner and outer walls of the annular duct are compared with the measured data. They are generally improved over the results predicted by the new ASM/k–? model. The effects of swirl on enhancing heat transfer in the annular duct are illustrated. The heat transfer performance of the vortex heat exchanger under different air flow rates is obtained.     

Area dependence of TDDB characteristics for HfO/sub 2/ gate dielectrics

Weibull slopes, area scaling factors, and lifetime projection have been investigated for both soft breakdown and hard breakdown for the first time, in order to gain a better understanding of, the breakdown mechanism of HfO/sub 2/ gate dielectrics. The Weibull slope /spl beta/ of the hard breakdown for both the area dependence and the time-to-dielectric-breakdown distribution was found to be /spl beta/ = 2, whereas that of the soft breakdown was about 1.4. Estimated ten-year lifetime has been projected to be -2 V.     

火灾高温后混凝土剩余强度及本构方程研究

为了深入研究工程建设中几种C25～C40强度等级混凝土经历火灾高温后的力学性能变化规律,提出了相对精确的剩余强度计算方法和受压本构方程,以经历温度、混凝土强度等级、恒温时间为变化参数,设计并完成了120个棱柱体试件的轴压试验,分析了各变化参数对其峰值应力、轴压刚度及耗能能力的影响规律,并给出了相应的剩余强度计算公式和轴...     

Dynamic Grain Growth During Superplastic Deformation of Yttria-Stabilized Tetragonal Zirconia Polycrystals

Both static and dynamic grain growth were studied during superplastic deformation of fine-grained yttria-stabilized tetragonal zirconia. It was found that significant grain growth does not take place below 1300°C. Both static and dynamic growth were found to obey a similar equation of the form D³−D³₀=kt, where D and D₀ are the instantaneous and initial grain sizes, respectively, t is the annealing time, and k is the kinetic constant for either static or dynamic grain growth. The activation energies were approximately 580 and 520 kJ/mol for static and dynamic grain growth, respectively.     

Thermal analysis of black liquid cylindrical parabolic collector

In the present paper a simple theoretical analysis and an experiment are carried out for a modified concentrating collector which consists of a cylindrical parabolic reflector, a transparent glass tube centered along the focal line, and a highly absorbent black liquid which flows in the glass tube to directly absorb the concentrated solar beam radiation. The analytical results are presented in normalized form and proved to be in very good agreement with the experimental results.     

INTERACTION OF GRAVITY AND ELECTROSTATIC EFFECTS IN PIPE FLOW OF A GAS-PARTICLE SUSPENSION

The interaction of gravity and electrostatic effects in isothermal, fully developed, horizontal turbulent pipe flow of dilute suspensions has been examined. Experimental study has validated the fact that, in the presence of gravity, increased space charge associated with increased local concentration due to gravity accentuates the asymmetry in mass flux and particles density distributions in the vertical plane passing through the pipe centerline. The space charge effect on the particle mass flux distribution near the pipe bottom is enhanced by increased particle density. Measurements were made with air suspensions of monodispensed particles of alumina and latex with non-uniform particle charge in pipes of 51 mm and 127 mm diameters.     

Responsiveness to inhibitory signals changes as a function of colony size in honeybees (Apis mellifera)

Biological collectives, like honeybee colonies, can make intelligent decisions and robustly adapt to changing conditions via intricate systems of excitatory and inhibitory signals. In this study, we explore the role of behavioural plasticity and its relationship to network size by manipulating honeybee colony exposure to an artificial inhibitory signal. As predicted, inhibition was strongest in large colonies and weakest in small colonies. This is ecologically relevant for honeybees, for which reduced inhibitory effects may increase robustness in small colonies that must maintain a minimum level of foraging and food stores. We discuss evidence for size-dependent plasticity in other types of biological networks.