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81.
This paper documents the first of the two interrelated studies that were conducted to more fundamentally understand the scalability of flame heat flux, the motivation being that it has been reported that flame heat flux back to the burning surface in bench‐scale experiments is not the same as for large‐scale fires. The key aspect was the use of real scale applied heat flux up to 200kW/m2 which is well beyond that typically considered in contemporary testing. The main conclusions are that decomposition kinetics needs to be included in the study of ignition and the energy balance for steady burning is too simplistic to represent the physics occurring. An unexpected non‐linear trend is observed in the typical plotting methods currently used in fire protection engineering for ignition and mass loss flux data for several materials tested and this non‐linearity is a true material response. Using measured temperature profiles in the condensed phase shows that viewing ignition as an inert material process is inaccurate at predicting the surface temperature at higher heat fluxes. The steady burning temperature profiles appear to be invariant with applied heat flux. This possible inaccuracy was investigated by obtaining the heat of gasification via the ‘typical technique’ using the mass loss flux data and comparing it to the commonly considered ‘fundamental’ value obtained from differential scanning calorimetry measurements. This comparison suggests that the ‘typical technique’ energy balance is too simplified to represent the physics occurring for any range of applied heat flux. Observed bubbling and melting phenomena provide a possible direction of study. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
82.
用WAXD和FT-IR对高温超高压处理前后的HDPE进行了研究。发现经5.0GPa的高压处理或200℃下4.0GPa的高压同时处理后的HDPE分子链的化学结构未发生变化。HDPE晶体中(200)面与(110)面衍射峰的峰高比(γ)随着压力的升高而增大,表明HDPE分子链在超高压作用下发生了取向排列,且升高温度更有利于这种取向排列,但当压力增大至5.0GPa及温度升高至200℃时,γ反而大幅度下降。 相似文献
83.
大小样品在液氮中的淬冷沸腾换热比较研究 总被引:1,自引:1,他引:0
分析了大小样品在液氮中的淬冷沸腾换热特性。大小样品的淬冷沸腾换热有着明显的差别,小样品的热流密度比大样品的明显高得多。小样品的淬冷沸腾有一起始段,其温降高达60K。从实验结果还可以看到,小样品的Leidenfrost点和临界热流点对应的壁面过热度明显比大样品的高。最后还分析了样品直径对临界热流密度的影响。 相似文献
84.
Journal of Electronic Materials - Low pressure chemical vapor deposition (LPCVD) of tungsten (W) by SiH4 reduction of WF6 on Si(100) surfaces was studied in a single-wafer, cold-wall reactor over a... 相似文献
85.
Current-voltage characteristics of Bi2Sr2Ca2Cu3O10 tapes and bulk samples with preferentially oriented crystallites have been measured in zero applied magnetic field and for temperatures close to the mean-field critical-temperature,T
c0. It was shown that the power-law dependence,V=AI
a, valid for two-dimensional systems, does not correctly describe the data, which clearly indicate the existence of a finite critical-current density,J
c. The experimentalI-V curves are fitted quite well with the model which attributes the finite critical-current density to the coupling between the CuO2 double layers. It was found thatJ
c vanishes at a temperature value belowT
c0. This behavior can result from the occurrence of vortex fluctuation-induced layer decoupling and/or from the contribution of entropy to the vortex unbinding process. 相似文献
86.
Dielectric properties andI–V characteristics of solution-gas interface-formed PbS thin-film capacitors (Al/PbS/Al) of various thicknesses have been studied
in the frequency range 10-106 Hz at various temperatures (300–443 K). Current-voltage (I–V) characteristics show space-charge-limited conduction. Dielectric constant (ε) increases with increasing film thickness and temperature and decreases with increase of frequency. The loss factor (tanδ) peaks observed in tanδ vs frequency and tanδ vs temperature reveal relaxation effect from dipolar orientation. These maxima shift to higher-temperature region with increasing
frequency. The large increase in capacitance (C) and dielectric constant (ε) towards low-frequency (f) region indicates the possibility of an interfacial polarization mechanism in this region. 相似文献
87.
魏登严 《石油化工管理干部学院学报》2007,9(4):42-43
随着社会主义和谐社会建设的提出和推进,企业和谐文化建设也成为当然的命题,并越来越重要。企业和谐文化建设内容很多,但核心建设理念必须是“以人为本”。以人为本思想有着深厚的历史渊源和现实意涵,只有坚持以人为本,企业和谐文化建设才会不断焕发生机与活力。 相似文献
88.
采用高含铬量超低碳不锈钢焊丝和专门研制的含铬陶质型焊剂两种方案研究了00Cr18Ni10不锈钢坦弧自动焊时焊缝的抗裂性,试验结果表明:以上两种途径,均可有效地防止焊缝金属中出现表面热裂缝。采用后者更为经济,现已用于生产。 相似文献
89.
Oscar Díaz 《Data & Knowledge Engineering》1995,16(3):223-240
In semantic data models, abstract relationship (e.g. generalization, aggregation, etc.) semantics are defined, specifying how insertion, deletion and modification operations made at a higher level of abstraction can affect the objects abstracted over and vice versa. These semantics, also known as structural constraints, are expressed through so-called update rules. This perspective has been somewhat lost in most object-oriented systems, where user-defined relationships are supported as simple pointers and their semantics are embedded, distributed and replicated within the operations accessing these pointers. This paper inherits and extends the treatment of relationships found in semantic data models to behavioural object-oriented models by presenting an approach to uniformly capture the update rules for user-defined relationships. The stress is not on supporting relationships as first-class objects, but on describing their update rules (or operational semantics) through a set of constructors namely, reaction, anticipation, delegation and exception. The approach has been borne out by an implementation in an active object-oriented database system. 相似文献
90.
Magnetization measurements were carried out on bulk Tl2Ba2CaCu2O8 (referred to as Tl-2212) and on various site-selective substituted Tl-2212 samples. At 5K between 0 and 4.5 T, the 5 at.
% Mg-doped Tl-2212 (Tl,Mg-2212) samples displayed enhanced pinning as demonstrated by a field dependent increase of the magnetic
critical-current density Jc by 18 to 25 percent over that of pristine Tl-2212. Excess Mg (10–15 at. %), however, is deleterious. Rietveld refinement
of the x-ray diffraction pattern showed Mg on the Tl sites. Auger electron spectroscopy analysis showed part of the Mg on
grain boundaries. The flux-creep activation energies are higher for flux expulsion than for flux penetration in both Tl-2212
and Tl,Mg-2212 samples; the latter displays higher individual values. Our results demonstrate an increase in the number density
of flux lines as a result of increased density of atomic-size-structural, defects by Mg (5 at. %) doping. In the Tl2−yBa2(Ca1−zYz)Cu2O8−x(z=0–0.3; single phase; x and y represent oxygen and thallium vacancies) system also studied, the Tc decreases as z increases. At z=0.3, the sample becomes an antiferromagnetic semiconductor. 相似文献