Characterization of AZ91D Granules Covered with a Flux during In‐Situ Melting

Oxidation and melting behaviors of AZ91D granules throughout the in‐situ melting process using flux were investigated. The granules were heated under unprotected environment at four different temperatures between 650 and 800 °C, for the durations of 30 and 60 min. The products of heating process were characterized macroscopically and the oxides formed on the granules were examined using field emission scanning electron microscope, energy dispersive X‐ray spectroscopy and X‐ray diffraction analysis. Thermal analysis was used to reveal the response of the granules to heating during the in‐situ melting. The results showed that the granules experienced severe oxidation even in the presence of the flux, and significant amount of them changed to a powdered state due to oxidation and combustion, especially at 800 °C. It was discovered that the granules melted during heating; however, oxides formed on their surface encapsulated the molten metal and prevented the liquids from merging. The results also revealed that increasing heating temperature and time enhanced mold‐magnesium reaction resulted in the entrance of mold materials into the oxidation residues.     

Temperature dependence of the Raman spectra of Bi2Te3 and Bi0.5Sb1.5Te3 thermoelectric films

The temperature dependence of the Raman spectra of Bi₂Te₃ and Bi_0.5Sb_1.5Te₃ thermoelectric films was investigated. The temperature coefficients of the E_g(2) peak positions were determined as –0.0137 cm^–1/°C and –0.0156 cm^–1/°C, respectively. The thermal expansion of the crystal caused a linear shift of the Raman peak induced by the temperature change. Based on the linear relation, a reliable and noninvasive micro‐Raman scattering method was shown to measure the thermal conductivity of the thermoelectric films. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Regular Binary Thermal Lattice-Gases

We analyze the power spectrum of a regular binary thermal lattice gas in two dimensions and derive a Landau–Placzek formula, describing the power spectrum in the long-wavelength, low frequency domain, for both the full mixture and a single component in the binary mixture. The theoretical results are compared with simulations performed on this model and show a perfect agreement. The power spectrums are found to be similar in structure as the ones obtained for the continuous theory, in which the central peak is a complicated superposition of entropy and concentration contributions, due to the coupling of the fluctuations in these quantities. Spectra based on the relative difference between both components have in general additional Brillouin peaks as a consequence of the equipartition failure.     

液体氦-3的热导率性质

揭示了低温流体~3He的热导率在液态区随温度和压力两个状态参数变化的反常规律。综合该反常规律以及热导率在临界点附近的突变特性,首次提出了~3He在0.003 K至临界温度3.3157 K温区内完整的饱和线热导率方程以及压力高至20 MPa的压缩液相区热导率方程。方程计算值与实验数据相对偏差小于±1.5%,与高精度实验数据偏差小于±0.4%,并且在极低温条件下光滑过渡为由量子理论预测的理论极限.     

两相颗粒多孔材料导热系数研究

对固-气两相颗粒多孔材料导热系数的预测,尚未见以实验数据对其各预测模型进行分析及验证其准确度的相关文献。本文利用断电热线法测定石英砂、碳化硅、工程沙以及煤灰的导热系数;将模型预测结果与实验数据进行对比分析,结果表明,Kunii and Smith模型误差小;考虑孔隙率的影响,利用实测数据对Kunii and Smith模型进行修正,给出新的预测模型;通过与国外学者给出的实测导热系数的对比,验证了本文给出的修正模型的准确性。     

Quantum phase transition and entanglement in Heisenberg XX spin chain with impurity

In this paper,we study the quantum phase transition and the effect of impurity on the thermal entanglement between any two lattices in three-qubit Heisenberg XX chain in a uniform magnetic field.We show that the quantum phase transition always appears when impurity parameter is an arbitrary constant and unequal to zero,the external magnetic field and impurity parameters have a great effect on it.Also,there exists a relation between the quantum phase transition and the entanglement.By modulating the temperature,magnetic field and the impurity parameters,the entanglement between any two lattices can exhibit platform-like behaviour,which can be used to realize entanglement switch.     

液态硝基甲烷热分解行为及压力效应的第一性原理研究

采用基于密度泛函理论的第一性原理分子动力学方法对液态硝基甲烷的热分解行为进行了模拟,结合各产物布居数随时间的演化,讨论了热分解初期可能发生的3种反应,即分子内/分子间的质子迁移反应和C—N键的断裂.在长时间（30 ps）的模拟过程中,H₂O是主要产物.研究了液态硝基甲烷在不同密度（压力）条件下热分解的动力学行为.发现不同密度（压力）条件下液态硝基甲烷热分解呈现明显不同的变化趋势,并给出了解释. 关键词： 硝基甲烷 分子动力学 热分解 压力效应     

Integrated Condition Monitoring of Large Captive Power Plants and Aluminum Smelters

Condition monitoring is implementation of the advanced diagnostic techniques to reduce downtime and to increase the efficiency and reliability. The research is for determining the usage of advanced techniques like Vibration analysis, Oil analysis and Thermography to diagnose ensuing problems of the Plant and Machinery at an early stage and plan to take corrective and preventive actions to eliminate the forthcoming breakdown and enhancing the reliability of the system. Nowadays, the most of the industries have adopted the condition monitoring techniques as a part of support system to the basic maintenance strategies. Major condition monitoring technique they follow is Vibration Spectrum Analysis, which can detect faults at a very early stage. However implementation of other techniques like Oil analysis or Ferrography, Thermography etc. can further enhance the data interpretation as they would detect the source of abnormality at much early stage thus providing us with a longer lead time to plan and take the corrective actions. In Large Captive Power Plants and Aluminium Smelters, Integrated Condition Monitoring techniques play an important role as stoppage of primary system and its auxiliaries (boiler, steam turbine, generator, coal and ash handling plants etc.) results into the stoppage of the entire plant, which in turn leads to loss of productivity. From economical and operational point of view, it is desirable to ensure optimum level of system availability.     

基于伴随方程法的材料热传导系数反演方法

建立利用材料内部温度场的测量结果反演材料热传导系数随时间和空间位置变化函数的伴随方程法,参考迭代正则化的思想在优化过程中给目标函数设置停止准则.对典型算例计算表明,方法在测量噪声较小情况下能得出较为合理的反演结果.但在有测量噪声的情况下,反演结果与真值在边界x=0和L处存在着一定偏差.当测量噪声较大时,反演结果与真值的偏差较为明显,且初值选取会对反演结果有相当大的影响.     

Phase transition at 204–250 K in the crystals of β-alanine: kinetically irreproduceable,or an artefact?

The crystals and the powder samples of β-alanine were studied in the wide temperature range by adiabatic calorimetry, differential scanning calorimetry, IR- and Raman spectroscopy and X-ray diffraction. No phase transitions could be observed. A small anomaly observed at about 256 K in the Cp(T) dependences measured for the samples re-crystallized from water was shown to be due to the presence of a small (about 0.14% of the total sample mass) amount of solvent inclusions. This anomaly was not observed in the solvent-free samples, either powders or single crystals.