Effect of Elastic Energy due to Atomic Size Factor on Ordering and Decomposition Behaviour of Binary Solid Solutions

A theory recently developed by the present authors is applied to the study of the effect of elastic energy due to atomic size factor on the transformation behaviour of binary solid solutions. lt is found that elastic interaction energy (EIE), which is a part of the total elastic energy plays a key role in both ordering elastic interaction ordering (EIO) and spinodal decomposition. The present study gives a reasonable explanation to the historical dilemmas, "elastic energy paradox" and "atomic size factor paradox . By solving these confusing problems, the coexistence of ordering (EIO) and decomposition, which has been regarded as impossible by conventional theories. can be well understood. The mechanism is as follows: lowering of elastic energy demands EIO, and such an ordering provides a driving force for spinodal decomposition. Therefore, in alloys with large atomic size factor, spinodal decomposition is preceded and induced by ordering. Ordering and spinodal decomposition are thus closely related processes to each other     

二元合金有序化反应研究进展

介绍了两个先进的二元合金有序化反应动力学模型、以及利用计算机对此类合金组织演化模拟取得的进展。先进的模型可成功地描述原子有序化及相分离 ,并将形核、长大和粗化在同一物理模型内加以考虑。利用此模型已对许多重要新型合金的相变动力学进行了模拟研究     

Macroscopic Elastic Studies of Orientational Ordering in Single-Crystal Fullerites

We give an overview on dynamic mechanic experiments in single-crystal fullerites C₆₀ and C₇₀. Elastic properties and thermal expansion in the vicinity of ordering phase transitions were studied. Landau theory and simple microscopic models are used to describe the experimental results.     

Molecular Orientational Ordering in Solid C60

Abstract

Single-crystal X-ray diffraction studies of the orientational ordering in solid C₆₀ are reviewed. The temperature dependence of selected Bragg reflections was carefully examined, allowing to obtain original information on the first-order orientational ordering transition at T_o = 259K, the unusual behavior of both fundamental and superstructure reflections below T_o and the freezing in of the C₆₀ reorientations at T_g ≈ 85K. The diffuse intensity due to orientational disorder of the C₆₀ molecules at room temperature is found to be strongly modulated, both radially and azimuthally. showing that the molecular orientations are indeed correlated. The corresponding intensity distribution has been calculated within a mean-field theory for different microscopic models of inter molecular interactions. It should allow a better understanding of these interactions.     

Molecular Orientational Ordering in Solid C60

Single-crystal X-ray diffraction studies of the orientational ordering in solid C₆₀ are reviewed. The temperature dependence of selected Bragg reflections was carefully examined, allowing to obtain original information on the first-order orientational ordering transition at T_o = 259K, the unusual behavior of both fundamental and superstructure reflections below T_o and the freezing in of the C₆₀ reorientations at T_g ≈ 85K. The diffuse intensity due to orientational disorder of the C₆₀ molecules at room temperature is found to be strongly modulated, both radially and azimuthally. showing that the molecular orientations are indeed correlated. The corresponding intensity distribution has been calculated within a mean-field theory for different microscopic models of inter molecular interactions. It should allow a better understanding of these interactions.     

Macroscopic Elastic Studies of Orientational Ordering in Single-Crystal Fullerites

Abstract

We give an overview on dynamic mechanic experiments in single-crystal fullerites C₆₀ and C₇₀. Elastic properties and thermal expansion in the vicinity of ordering phase transitions were studied. Landau theory and simple microscopic models are used to describe the experimental results.

     

SiC-Based Solid Solutions

The available data on the solubility of some chemical elements in SiC are analyzed, and the diffusion parameters of these elements are assessed using the compensation law.     

The Interaction of Economic Ordering Quantities and Marketing Policies

A general net profit model is developed consisting of the difference between the gross profit and the total inventory costs. This model considers that the demand is a function of the selling price, that the selling price depends on the pricing policy and on the unit cost which in its turn varies according to the order quantity. It is shown that the correct treatment of inventory problems is that which considers its interaction with problems of pricing since the obtainable net profit can be increased over the amounts achieved when inventory problems were regarded as independent subsystems. Further it has been found that there exists a critical demand elasticity such that the preferable pricing policy is different for prevailing elasticities above this value than for elasticities below it.     

Elastic Properties of Polycrystalline Solid Helium

Recent experiments have shown that the shear modulus of solid helium undergoes a large temperature variation in the range 20 to 200 mK, possibly due to changes in the pinning of dislocations. In this note we report on computer simulations of the elastic properties of polycrystalline solid helium. We calculate how the elastic coefficients of a sample made up of a large number of randomly oriented grains are affected by the changes in the shear modulus c ₄₄ of the individual grains.     

Elastic Properties of Solid 4He

The shear modulus of solid ⁴He increases below 200 mK, with the same dependence on temperature, amplitude and ³He concentration as the frequency changes recently seen in torsional oscillator (TO) experiments. These have been interpreted as mass decoupling in a supersolid but the shear modulus behavior has a natural explanation in terms of dislocations. This paper summarizes early ultrasonic and elastic experiments which established the basic properties of dislocations in solid helium. It then describes the results of our experiments on the low temperature shear modulus of solid helium. The modulus changes can be explained in terms of dislocations which are mobile above 200 mK but are pinned by ³He impurities at low temperature. The changes we observe when we anneal or stress our crystals confirm that defects are involved. They also make it clear that the shear modulus measured at the lowest temperatures is the intrinsic value—it is the high temperature modulus which is reduced by defects. By measuring the shear modulus at different frequencies, we show that the amplitude dependence depends on stress in the crystal, rather than reflecting a superfluid-like critical velocity. The shear modulus changes shift to lower temperatures as the frequency decreases, showing that they arise from a crossover in a thermally activated relaxation process rather than from a true phase transition. The activation energy for this process is about 0.7 K but a wide distribution of energies is needed to fit the broad crossover. Although the shear modulus behavior can be explained in terms of dislocations, it is clearly related to the TO behavior. However, we made measurements on hcp ³He which show essentially the same modulus stiffening but there is no corresponding TO anomaly. This implies that the TO frequency changes are not simply due to mechanical stiffening of the oscillator—they only occur in the Bose solid. We conclude by pointing out some of the open questions involving the elastic and TO behavior of solid helium.     

二元固溶体型合金凝固过程中固相分数的变化规律

本文首先总结了前人在固相分数计算方面的研究工作。通过对几个主要影响因素的分析,指出了以前所用计算式的适用范围。进而通过对作者最近提出的局部溶质再分配方程修正式的求解,得出了板状技晶和柱状枝晶两种生长形态下适用范围更广的计算式。最后以Al—4.5％Cu合金枝晶生长过程为例,对各式的计算结果进行了对比讨论。并估算了非平衡共晶和θ相的析出量。     

Diametrical Elastic Relaxation During Ejection of Lactose-Cocoa Binary Tablets

This work investigates the diametrical elastic relaxation of a compacted binary powder mixture of lactose and cocoa. It has been observed that the addition of lactose improved the mechanical strength of the binary tablets at the higher compaction stresses used in this study. The tablets having the maximum tensile strengths have relatively low diametrical elastic relaxations, similar to the pure cocoa tablets. Meanwhile, pure lactose tablets displayed increasing diametrical elastic relaxations as the compaction stress increased.     

New Progressive Variable Ordering for Binary Decision Diagram Analysis of Fault Trees

The binary decision diagram (BDD) is the most efficient method currently available to analyse failure modes represented by fault trees. The fault tree is converted to this alternative structure representative of the failure mode as a Boolean equation. For the conversion the basic event variables within the fault tree are required to be placed in an order. The size of the resulting BDD and therefore the efficiency of the whole methodology is dependent upon the variable ordering chosen. Most commonly the order of variables is determined prior to the conversion using a structured or weighted approach and remains fixed during the process. Although there are several ordering heuristics available, no one heuristic has been found that will guarantee a minimal BDD for all fault trees. This paper proposes a new ordering methodology which seeks to select variables during the conversion process from a fault tree, allowing different potential ordering permutations on each path of the diagram. This method is simple to implement and is applied directly to the fault tree structure. When compared against the best sized BDD produced from 11 different methodologies, it produced a BDD of equal or smaller size in 82% of test cases. In addition, the technique has shown a 34% increase in the likelihood of producing the best BDD compared with the best individual heuristic from the 11 tested. Copyright © 2005 John Wiley & Sons, Ltd.     

Reaction Driven Elastic Waves in Solid Media

Chemical reactions and phase transformations couple in solid systems with the stress fields. When reaction rates become of the same order as the rate of relaxation of mechanical perturbations, the reactions can stabilize elastic waves in the system. Density varies with temperature and conversion and since the elastic waves are driven by the gradients in temperature and conversion, these source terms travel with the same speed as the reaction front. A model is presented for elastic waves in solid media, driven by a moving source term that is well approximated by a delta function. The propagation velocity of this source is constant, but it can propagate either subsonically or supersonically. The effects of precompressing the sample, applying a force at one boundary, and varying the strength of the source term with time are included in the discussion. The model is useful to study transformation reactions under shock-compression, ultrafast deflagrations, and detonations in the solid phase.     

Characterization and Dissolution Study of Oxodipine from Solid Binary Systems

Thennomicroscopy and differential scanning calorimetry were employed to characterize solid binary systems prepared with oxodipine and PEG 6000, 2-hydroxypropyl-β-cyclodextrin or mannitol. DSC curves did not allow to diferentiate physical mixtures from solid dispersions. Thennomicroscopy revealed the interactions that can be produced between drug and each carrier, due to heat contribution, when the physical mixtures were observed; also this thermal technique permited us to ascertain the composition of particles that constitute the solid dispersions. Dissolution studies showed that the amelioration obtained in oxodipine dissolution from physical mixtures was due to the dessagregant action of the carriers, which obtained an increase of the drug surface in contact with the dissolution medium. The proportions and carrier nature influence the oxodipine dissolution, fundamentally from solid dispersions, where the interaction drug/carrier is stronger than in physical mixtures.     

Elastic Low Temperature Anomalies of Solid Hydrogen Crystallites

The property of solid hydrogen (H₂, HD and D₂) not to wet an attractive substrate, can be used to prepare micron sized hydrogen crystals. We used surface acoustic waves (SAW) in the range from 100 MHz to 1 GHz to study the elastic properties of the crystallite-substrate system. The growth of crystallites at temperatures around 3 K can be monitored by the resonant coupling of elastic eigenmodes to the SAW. We observed drastic changes of the resonant coupling for all isotopes when the temperature was varied between 0.15 K and 2.4 K. Possible origins of this unexpecied effect are discussed including a temperature variation of the wetting behavior. For H₂ the impact of the ordering transition of ortho-H₂ was also investigated.     

Elastic Coupling Through Flux Lines and Magnetic Interaction

We show that elastic coupling through flux lines gives an interaction energy between two superconductors or magnetic pieces, which is inversely proportional to the distance between the two bodies. First, we present some details on the penetration depth of the magnetic field in layered superconductors and, especially, on the vortex lines.     

Dy-黄长石固溶体的氧化行为研究

本 工 作 选 取 了 四 个 Dy-黄 长 石 固 溶 体 Dy₂Si_3-xAl_xO_3+xN_4-x(Dy-M’, x=0, 0.3, 0.6 和 1.0) 组 份, 试 样 由 热 压 工 艺 制 成, 并 置 于 马 弗 炉 中 于 1000℃ 氧 化 20 h. 随 着 固 溶 度 x 的 增 加, 氧 化 增 重 的 行 为呈 现 出：Dy-M’(x=0.6)<< Dy-M’(x=0.3)2Si₂O₇ 晶 粒 的 硅 酸 盐 层, 其 中 α-Dy₂Si₂O₇ 晶 粒 在 氧 化 表 面 具 有 择 优 取 向.     

二元阳离子表面活性剂的CMC及相互作用

采用紫外法和荧光法测定了二元阳离子混合表面活性剂体系(十六烷基三甲基溴化铵和十二烷基三甲基溴化铵、十六烷基三甲基溴化铵和十四烷基三甲基溴化铵)的临界胶束浓度(CMC)。在正规溶液理论的基础上计算出形成胶束时的相互作用参数βm、超额自由能ΔGex和胶束组成xi,分析结果表明,两种二元体系的CMC值介于纯组分之间,胶束中的组成都与理想混合有一定偏差;胶束相中两组分间的作用力为吸引力;当胶束相中CTAB的摩尔分数增大时,吸引力增强。