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81.
Experimental results are presented on the measurements of thermal expansion (up to 1500°C), thermal conductivity (up to 1000°C), dielectric constant (up to 450 °C) and tan (up to 800 °C) of zirconyl phosphate compacts obtained by sintering at 1600°C. The thermal expansion coefficient of the samples at the temperature below 1100°C was less than 1.7 × 10–6°C–1. The samples showed a definite shrinkage at temperatures of 1110 and 1470°C due to the phase transformations. The expansion at 1500°C was less than that at 1100°C probably because of the phase transformation. The thermal conductivity at room temperature was a very small value (0.0046 to 0.0065 cal s–1 cm°C–1 cm–2). The dielectric constant was close to 9. The value of tan° (–0.0001) measured is one of the lowest values for ceramic materials. 相似文献
82.
风环境是评价人居生活质量好坏的重要指标,随着国民经济的快速发展,越来越多的高耸楼宇应运而生,这些楼宇会较大程度地改变已有小区的风环境,给小区居民正常生活带来困扰,而当前对该问题的针对性研究还十分匮乏。以长沙通用时代国际社区为研究背景,利用大尺度风洞(10 m×3 m×21 m)对新增高耸建筑后的小区风环境进行了全方位、多工况试验研究,并基于超越概率法对有无新增高耸建筑小区风环境舒适度与危险度进行定量评估。结果表明:城市小区平均风剖面与湍流度剖面指数值要远高于规范值,表明城市小区具有较大的地表粗糙度。新增高耸建筑会显著改变其邻近区域风环境,如高耸建筑对通用时代小区100、200、300 m范围内平均风速分别造成了25%、6%和2%的加速作用,在增加高耸建筑后小区风环境舒适度与危险度超越概率最大值分别增加了2倍和6倍。 相似文献
83.
Ming-Yen Hsiao Ya-Wen Wu Wen-Shiang Chen Yu-Ling Lin Po-Ling Kuo Chueh-Hung Wu 《International journal of molecular sciences》2021,22(7)
Entrapment neuropathy (EN) is a prevalent and debilitative condition caused by a complex pathogenesis that involves a chronic compression–edema–ischemia cascade and perineural adhesion that results in excessive shear stress during motion. Despite decades of research, an easily accessible and surgery-free animal model mimicking the mixed etiology is currently lacking, thus limiting our understanding of the disease and the development of effective therapies. In this proof-of-concept study, we used ultrasound-guided perineural injection of a methoxy poly(ethylene glycol)-b-Poly(lactide-co-glycoilide) carboxylic acid (mPEG-PLGA-BOX) hydrogel near the rat’s sciatic nerve to induce EN, as confirmed sonographically, electrophysiologically, and histologically. The nerve that was injected with hydrogel appeared unevenly contoured and swollen proximally with slowed nerve conduction velocities across the injected segments, thus showing the compressive features of EN. Histology showed perineural cellular infiltration, deposition of irregular collagen fibers, and a possible early demyelination process, thus indicating the existence of adhesions. The novel method provides a surgery-free and cost-effective way to establish a small-animal model of EN that has mixed compression and adhesion features, thus facilitating the additional elucidation of the pathophysiology of EN and the search for promising treatments. 相似文献
84.
Flexible memory devices are one of the most crucial elements in the wearable electronics. In this work, polyimides (PIs)-based flexible resistive memory devices with an excellent thermal and mechanical durability are demonstrated. Four kinds of functional PIs are derived from the heterocyclic diamines including 2,6-diaminodibenzo-p-dioxin (OODA) and 2,6-diaminothianthrene, and dianhydrides including 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride. PI with diamine of OODA and dianhydride of 6FDA (PI(OODA_6FDA)) possesses outstanding thermal and mechanical properties with a high glass transition temperature of 352 °C, a low coefficient of thermal expansion of 28.1 ppm K−1, and a high elongation at break of 10%. In addition, PI(OODA_6FDA)-based memory shows write-once-read-many behavior with a high on/off current ratio of 106 and a stable data retention, attributed to the donor–acceptor charge transfer between the polymer chains. The retained current levels at a low resistive state can be observed even with thermal treatment at 200 °C for 24 h or 1000 times cyclic bending at a bending radius of 5 mm. These results demonstrate the potential of heterocyclic PIs for flexible resistive memory. 相似文献
85.
PHASES IN HIGH ALLOY STEELS AND SUPERALLOYS 总被引:1,自引:0,他引:1
<正> 高温合金一般是指以铁、镍或钴形成的面心立方基体(γ)为基的在较高温度下使用的合金,有些合金靠碳化物强化,有些合金靠铝、钛、铌等与镍生成的中间相(γ′或γ″)强化。此外,还要加入一定数量的钼或钨强化固溶体γ,加入微量的硼或锆强化晶界,加入较多的铬以增强合金的抗氧化能力。由此可见,高温合金中的合金元素,无论从种类或数量上来看,都要比合金钢中复杂得多。但是,在奥氏体不锈耐热钢与铁基高温合金之间并无明显的界限,实际上铁基高温合金就是在镍铬不锈耐热钢中不断提高镍的含量和增添新的合金元素而发展出来的。因此,在讨论高温合金中的相时,我们把铬镍不锈耐热钢也包括在内。 相似文献
86.
Chih-Wei Chang Chun-Pao Kuo 《International Journal of Machine Tools and Manufacture》2007,47(3-4):452-461
Laser-assisted machining (LAM), an alternative method of fabricating difficult-to-machine materials, uses primarily laser power to heat the local area (without necessarily evaporating or melting any material) before the material is removed. It not only efficiently reduces the cutting force during the manufacturing process but also improves the machining characteristics and geography with regard to difficult-to-machine materials, especially structural ceramics.This study on the application of laser-assisted machining to Al2O3 ceramics examines the measurements of cutting force and workpiece surface temperature as well as surface integrity and tool wear. Specifically, it uses the lattice Boltzmann method (LBM) to calculate the temperature distribution inside the ceramic workpiece during the LAM process and ensure that the laser energy causes no subsurface damage. The experimental results reveal that the LAM process efficiently reduces the cutting force by 22% (feed force) and 20% (thrust force) and produces better workpiece surface quality than conventional planing. 相似文献
87.
W. R. Vogler A. C. Olson S. Okamoto M. Shoji R. L. Raynor J. F. Kuo W. E. Berdel H. Eibl J. Hajdu H. Nomura 《Lipids》1991,26(12):1418-1423
Alkyl lysophospholipids have been shown to be cytooxic to a number of neoplastic tissues. One, ET-18-OCH3, has been used to selectively purge leukemic cells from mixtures with normal marrow progenitor cells,in vitro andin vivo. We have measured the 50% inhibitory (IC50) effect of a series of ether, lipids (EL) on leukemic cells (HL60, K562, Daudi, KG-1, KG-1a) and normal marrow progenitor
cells. Cells were incubated with varying concentrations of EL for 4 hr and assayed for viability, [3H]thymidine incorporation and clonogenicity in semi-solid media. The effect on protein kinase C (PKC) activity was assayed
for each compound. Compounds tested included three glycerophosphocholine analogs-ET-18-OCH3, ET-16-NHCOCH3, and BM 41.440. In addition, a lipoidal amine, CP 46665, an ethyleneglycolphospholipid, AEPL, and four single chain alkylphosphocholine
analogs, HePC2, HePC3, HePC4 and HePC6 were also tested. During the period of incubation, the cells remained viable (>70%) as judged by trypan blue dye exclusion.
The glycerophosphocholines were the most active and showed the highest therapeutic index. The lipoidal amine was active, but
toxic to normal marrow progenitor cells. The ethyleneglycolphospholipid was active against HL60, but not against the other
cell lines. The single chain alkylphosphocholine analogs were less active. All of the compounds inhibited PKC activity; however,
the glycerophosphocholines were the most inhibitory.
Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989. 相似文献
88.
A series of new alkene and octenyloxy monomers containing 4′-[oligo(ethylene oxide)] n monomethyl ether 4-biphenyl ether carboxyl benzoate [MS3BDBEn] (n = to 3) and 1- (p-methoxydiphenyl)–(carboxyl benzoate) [oligo(ethylene oxide)]n [MSm+2BEnDB] (m = 1, 6; n = 1 to 3) as end groups were synthesized. The molecular structure of the monomers was charaterized using nuclear magnetic resonance (NMR) spectroscopy. These monomers were grafted onto poly(methylhydrosiloxane)s (PMHS) by the platinun-catalyzed hydrosilylation process. The thermal transition temeratures and mesophase textures of the monomers and the polysiloxane polymers have been determined by diffential scanning calorimetry (DSC) and by polarized optical microscopy. The effect of changes in chemical structure on the mesophase properties, glass transition temperature, isotropic temperature, and mesophase texture of the monomers and the polysiloxane polymers is discussed. Polymers PS3BDBEn showed smectic and nematic phases which were not analogous to their precursor nematic monomers MS3BDBEn. Both monomers MSm+2BEnDB and their polymeric homologous PSm+2BEnDB did not exhibit mesophase properties. This demonstrated that the polymer effect could not stabilize the mesophase obtained from mesogenic core which contained a flexible oligo(ethylene oxide) unit interconnecting aromatic group. © 1995 John Wiley & Sons, Inc. 相似文献
89.
This paper examines the linear elastic tensile and fracture behavior of biaxial plain weave SiC/SiC ceramic woven fabric composites. Iso-phase mode and random-phase mode have been adopted to simulate multilayer stacking and to predict the initial linear elastic constants. It has been found that both modes predict very close results. Porosities in the composite affect the stiffness significantly, while fiber undulation shows only minimal effect. The nonlinear stress-strain relation of the composite is due to transverse cracks, which initiate mainly from interyarn pores. In the second part of this paper, two methods, classical fracture mechanics and energy balance approach, have been used to examine the crack initiation and growth. A finite element method and a modified shear-lag method have been developed to evaluate the stress distribution in the yarn with transverse cracks. The composite stiffness reduction due to transverse cracking has been obtained by both the finite element and shear-lag methods. Strain energy release rates of the growth of transverse cracks have been studied by the crack-closure procedure, using finite element methods. Effects of the yarn size and crack position on the strain energy release rate have been quantified. It is concluded that thinner yarns lead to higher critical strains for transverse cracking. 相似文献
90.
Poly(vinyl pyrrolidone‐co‐isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP–POSS) were synthesized by one‐step polymerization and characterized using FTIR, high‐resolution 1H‐NMR, solid‐state 13C‐NMR, 29Si‐NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The Tg of the PVP–POSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self‐association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low POSS content, the role as diluent dominates, resulting in a decrease in Tg. At a relatively high POSS content, the last two factors dominate and result in Tg increase of the PVP–POSS hybrid. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2208–2215, 2004 相似文献