Inertia of measurements with “auxiliary-wall” type heat meters

The article examines the problem of thermal inertia on the basis of an auxiliary-wall type heat meter, it demonstrates the boundaries of applicability of the approximate relationship for calculating non-steady-state heat fluxes.Notation q() non-steady-state heat flux through the heat meter - _i,a _i thermal conductivity, thermal diffusivity, and thickness of the heat meter, respectively - ₂,a ₂ thermal conductivity and thermal diffusivity, respectively, of the base of the heat meter - t() temperature gradient over the thickness of the heat meter - index of thermal inertia - time - s parameter of Laplace transform - t₁ (x, ) temperature of the heat meter at point x - t₂(x, ) temperature of the base - t_c ambient temperature - Y_q(s) transfer function from the heat flux q() to the temperature gradient t() Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 298–305, August, 1980.     

A guarded hot-plate apparatus for thermal conductivity measurements over the temperature range −75 to 200‡C

A guarded hot-plate apparatus for small circular samples has been developed for the temperature range from –75 to 200C. To avoid edge losses, the apparatus is immersed in a liquid whose temperature is a few degrees lower than the mean temperature of the samples. A detailed evaluation procedure with several correction calculations leads to a remaining uncertainty of measurement of 0.5% for measurements on glass samples. This has been confirmed by experiment. Measurements on glass and on insulation material showed that the developed apparatus and the evaluation procedure applied can be used in a relatively wide range of thermal conductivity values (factor 50).     

High-resolution measurements of the heat capacity of MnBr2·4H2O near its Néel temperature

The heat capacityC _P of the antiferromagnet MnBr₂ ·4H₂O has been measured for polycrystalline and single-crystal samples nearT _N(2.123 K) with temperature resolution of 1×10^–6 K. Similar rounding of the lambda anomaly is found in both cases. For |1 –T/T _N| 10^–1 all data can be well fitted by assuming the samples to consist of many independent subsystems obeying the same power laws but with a Gaussian distribution ofT _N's having a width of 1.1×10^–3 K. ForT>T _N, we findC _P ^–0.12, essentially as predicted for three-dimensional Ising models in the critical region. ForT<T _N and 10^–3 10^–1,C _P ln , which approximates Ising model behavior in this interval but is not expected to be valid for 10^–4. ForT>T _N and 2.5×10^–1, C_P agrees well with predictions for the classical Heisenberg model. This crossover at 10^–1 is consistent with the known anisotropy of the salt and with present theory. The data forT>T _N in the interval 10^–4 10^–3, while not in the range of obvious rounding, appear to be strongly influenced by the mechanism responsible for that rounding.Work supported by the National Science Foundation and the Office of Naval Research. Based on a thesis submitted by L.W.K. to Carnegie-Mellon University in partial fulfillment of the requirements for the Ph.D. degree. A preliminary account of this work was presented at the Atlantic City meeting of the American Physical Society, March 1972 [Bull. Am. Phys. Soc. 17, 299 (1972)].     

Precipitation–segregation mechanism for high temperature temper embrittlement of steels revealed by Auger electron spectroscopy and internal friction measurements

Abstract

A precipitation–segregation mechanism of high temperature (reversible) temper embrittlement has been suggested on the basis of Auger electron spectroscopy, internal friction measurements, and scanning and transmission electron microscopy (SEM, TEM) of 0·3C–Si–Mn–Cr steel after various heat treatments. It was found that P segregation takes place during heating for quenching and tempering. The intensity of P segregation does not change when the steel transforms from a ductile (600°C tempered for 2 h with water cooling) to a brittle (600°C tempered with furnace cooling) state. Isothermal aging at 500°C for 200 h leads to further segregation of P, but the intensity remains unchanged after a reductilising treatment (600°C reheating for 2 h with water cooling). (The term reductilising is used to describe the treatment employed to attempt to return the material to its original ductile state.) The internal friction measurements and TEM examinations indicated that the temper embrittlement of the steel is always accompanied by precipitation of very fine particles of Fe₃C(N) causing dead pinning of dislocations within the grains while the reductilised state corresponds to the re-solution of these fine particles back into the a solid solution which explains the reversibility of the phenomenon. Therefore, the P segregation is a necessary factor for grain boundary fracture of the steel in the temper embrittled state, but is still not sufficient for the actual appearance of this mode of fracture. The leading factor is the precipitation of Fe₃C(N) particles on dislocations and a precipitation–segregation mechanism is suggested which can be used to explain all the specific features of high temperature temper embrittlement.

MST/707     

Low-Field microwave measurements of YBa2Cu3O7?x near the superconducting transition temperature

Novel microwave absorption and dispersion measurements have been performed on well-characterized single-crystal platelets of the high-T _c superconductor YBa₂Cu₃O_7–x . The results are explained in terms of the rapid variation of the penetration depth near and belowT _c . Since EPR measurements are very sensitive to small changes in absorption and dispersion, this technique should be very useful in the understanding of the transition temperature region in both new and old superconducting materials.     

Analysis of the temperature field in the capillary structure of an “antigravity” heat pipe

The authors analyze the influence of the geometric parameters and the technical and physical properties of the capillary structure on the operating temperature of the antigravity heat pipe.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 2, pp. 203–207, August, 1986.     

Prediction on temperature dependent elastic constants of “soft” metal Al by AIMD and QHA

First-principles methods based on density functional theory(DFT) are nowadays routinely applied to calculate the elastic constants of materials at temperature of 0 K. Nevertheless, the first-principles calculations of elastic constants at finite temperature are not straightforward. In the present work, the feasibility of the ab initio molecular dynamic(AIMD) method in calculations of the temperature dependent elastic constants of relatively soft metals, taking face centered cubic(FCC) aluminum(Al) as example, is explored. The AIMD calculations are performed with carefully selected strain tensors and strain magnitude. In parallel with the AIMD calculations, first-principles calculations with the quasiharmonic approximation(QHA) are performed as well. We show that all three independent elastic constant components(C_(11), C_(12) and C_(44)) of Al from both the AIMD and QHA calculations decrease with increasing temperature T, in good agreement with those from experimental measurements. Our work allows us to quantify the individual contributions of the volume expansion, lattice vibration(excluding those contributed to the volume expansion), and electronic temperature effects to the temperature induced variation of the elastic constants. For Al with stable FCC crystal structure, the volume expansion effect contributes the major part(about 75%～80%) in the temperature induced variation of the elastic constants.The contribution of the lattice vibration is minor(about 20%～25%) while the electronic temperature effect is negligible. Although the elastic constants soften with increasing temperature, FCC Al satisfies the Born elastic stability criteria with temperature up to the experimental melting point.     

Engineered flux pinning centres in Pb-doped high temperature superconducting “Bi2Sr2CaCu2O8” ceramics

The Pb solubility of Bi₂Sr₂CaCu₂O₈ is determined within the concentration range Bi_2.18-x Pb _x Sr₂CaCu_8+d with 0 x 0.6 and the temperature range from 800 to 900°C. From a consideration of the Pb solubility in Bi₂Sr₂CaCu₂O₈ a simple annealing procedure was developed to precipitate (Pb,Bi)₄(Sr,Ca)₅Cu0_10+d (451 phase) in high-temperature superconducting Pb-rich Bi₂Sr₂CaCu₂O₈ ceramics. The precipitation results in a two-fold increase of the critical current density which is believed to express improved pinning properties of the superconducting ceramics. The microstructures of the samples with increased critical current density were studied with respect to the grain size and volume content of the 451 phase.     

“学院院长”“杰出人才”“高层次人才”招聘

<正>广东工业大学坐落在美丽的南国花城广州,是一所具有50多年历史的以工为主、多科性协调发展的省属重点大学。借助于毗邻港澳的地理优势,在广东经济蓬勃发展的带动下,学校的办学水平、科研能力和核心竞争力得到了快速提升。学校现有全日制在校生47 000余人;设有19个学院和4个公共课教学部(中心),75个本科专业。具有广东省重点建设的3个攀峰学科和12个优     

“低碳研究”不要“热”后“亡”

最近。从媒体上看到这样一条消息，哥本哈根气候大会后。“低碳”成了全球公众关注的热点。继清华大学、对外经济贸易大学成立低碳研究所后，4月2日，北京交通大学也成立了“低碳研究与教育中心”。北京备高校日前正掀起一股“低碳研究”热潮。（4月4日《北京晚报》）     

“桥”和“家”

这次作为代表,被邀参加由中国包装技术协会主办、包装世界杂志社承办的“纪念小平同志对包装工作批示20周年座谈会”,感触很深、浮想联翩。这次座谈会充分体现了中国包装技术协会高举邓小平理论伟大旗帜,沿着总设计师设计的实现中国四个现代化的道路前进的坚定不移的决心,也是我国包装走向世界的希望。20年眨眼过去了。以前,由于我国没成立包装工作领导机构,致使落后的包装、野蛮的装卸随处可见,因而给国家造成了极大的损失。