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排序方式: 共有477条查询结果,搜索用时 31 毫秒
1.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
2.
脉冲激光沉积SrBi2Ta2O9铁电薄膜电容特性研究 总被引:2,自引:0,他引:2
用PLD方法成功地制备了SBT铁电薄膜,并制作成Pt/SBT/Pt薄膜电容器。SBT薄膜的晶面取向以(008)和(115)为主。在5V电压下,极化反转,并且得到较饱和的电滞回线,剩余极化强度和矫顽电场分别为84μC/cm2和57kv/cm。IV特性测试显示两个对称的双稳峰,并得到零电压下,面积为314×104μm2,厚度为035μm的电容器,电容约为560pF,介电常数约为600。疲劳测试表明Pt/SBT/Pt具有优良的抗疲劳特性。 相似文献
3.
Metabolism and biochemical effects of 3,3',4,4'-tetrachlorobiphenyl in pregnant and fetal rats 总被引:1,自引:0,他引:1
DC Morse EK Wehler M van de Pas AT de Bie PJ van Bladeren A Brouwer 《Canadian Metallurgical Quarterly》1995,95(1-2):41-56
The metabolism and distribution of a single oral dose of 25 mumol 14C-labelled 3,3',4,4'-tetrachlorobiphenyl (14C-TCB) were investigated in pregnant female Wistar rats and their fetuses. TCB was administered on day 13 of gestation and the elimination was followed for 7 days. Non-pregnant rats were treated similarly for comparison. Fecal elimination of 14C-TCB derived radioactivity was significantly lower in pregnant rats than in non-pregnant rats. The major metabolite found in adult liver and plasma, placental tissue, whole fetuses and fetal plasma was 3,3',4',5-tetrachloro-4-biphenylol (4-OH-TCB). Tissue levels (liver, abdominal fat, skin, skeletal muscle, kidney and plasma) of 14C-TCB-derived radioactivity declined by 65-85% over a 7-day period following administration in the adult animals. However, 14C-TCB-derived radioactivity accumulated more than 100-fold in the fetuses over the same time period, and GC/MS analysis revealed that the fetal accumulation in radioactivity was due primarily to 4-OH-TCB, and not the parent compound. On day 20 of gestation, concentrations of 4-OH-TCB were 14 times greater in fetal plasma than maternal plasma. Treatment with 14C-TCB significantly reduced plasma thyroxine levels by at least 28% up to 7 days after administration in non-pregnant animals and up to 4 days after administration in pregnant rats (31% decrease). By 7 days after administration plasma thyroxine levels had returned to control levels in the TCB-treated pregnant rats. However, fetal plasma thyroxine levels were significantly decreased by 35% in fetuses from 14C-TCB-treated dams 7 days after TCB administration. Hepatic microsomal ethoxyresorufin-O-deethylase (EROD) activity was significantly induced in TCB-treated dams relative to controls at 4 and 7 days after administration, while no EROD activity was detected in hepatic microsomes from control or TCB treated fetal rats at day 20 of gestation. These data suggest that hydroxylated metabolites of polychlorinated biphenyls may play a role in the development toxicity of these compounds. 相似文献
4.
Z Zhu J Yao T Johns K Fu I De Bie C Macmillan AP Cuthbert RF Newbold J Wang M Chevrette GK Brown RM Brown EA Shoubridge 《Canadian Metallurgical Quarterly》1998,20(4):337-343
A drug with cationic characteristics such as procaine can be conveyed in a Carbomer hydrogel in two different ways: (i) in the form of salt in solution in the aqueous phase, and (ii) in the base form salified with the same polymer. Introduction of the drug into the hydrogel with different concentrations of polymer produced, in both cases, a reduction in viscosity in relation to drug concentration. The gels with procaine salified with the polymer showed greater viscosity. The drug release rate, in general, diminished with the increase in polymer concentration. Nevertheless, when this concentration was maintained, there was no variation in release rate when the viscosity produced as a consequence of drug concentration was changed. Gels with procaine salified with the carboxyvinylic polymer had a faster release rate than those with procaine in the hydrochloride form dissolved in the aqueous phase. These results have also been confirmed by a simulated absorption test. 相似文献
5.
Lane-changing behavior plays an important role in characterizing urban arterial road traffic dynamics. This paper investigates efficiency-driven and objective-driven motives for drivers to change lanes on arterial roads. The former motive is determined by the circumstances of the surrounding traffic flow, whereas the latter depends on position. A location-dependent lane changing model is then established by weighing the two motives for lane changing. Both continuous and discrete versions of the arterial traffic model are obtained using the LWR (Lighthill–Whitham–Richards) model with the two types of lane changing. Simulations show that the proposed model can reproduce macroscopic traffic phenomena such as spillover and a decrease in the concomitant departure flow, which is the reason for capacity loss. It is concluded that 1) there exists a critical condition under which there is no capacity loss and that 2) a different flow composition could result in a different capacity loss, which varies according to the flow direction. Hence, traffic management and control should take this loss into account. 相似文献
6.
论高等教育大众化与农村人口转移 总被引:3,自引:0,他引:3
促进我国农村人口转移是当前解决“三农”问题、促进经济腾飞和社会进步的重大的战略之一。然而,农村人口素质低是制约着转移的“瓶颈”。高等教育要充分发挥提高农村人口素质,促进农村人口转移的积极作用,应逐渐完善大众化高等教育体系。具体而言,可采取以下改革举措:高等教育资源向农村地区倾斜;大力发展高等职业教育;调整、优化学科结构;发展农村高等教育等。 相似文献
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9.
Phase Separation Derived Core/Shell Structured Cu11V6O26/V2O5 Microspheres: First Synthesis and Excellent Lithium‐Ion Anode Performance with Outstanding Capacity Self‐Restoration
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Jian Pei Gang Chen Qiang Zhang Changfeng Bie Jingxue Sun 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(17)
Novel amorphous vanadium oxide coated copper vanadium oxide (Cu11V6O26/V2O5) microspheres with 3D hierarchical architecture have been successfully prepared via a microwave‐assisted solution method and subsequent annealing induced phase separation process. Pure Cu11V6O26 microspheres without V2O5 coating are also obtained by an H2O2 solution dissolving treatment. When evaluated as an anode material for lithium‐ion batteries (LIBs), the as‐synthesized hybrid exhibits large reversible capacity, excellent rate capability, and outstanding capacity self‐recovery. Under the condition of high current density of 1 A g?1, the 3D hierarchical Cu11V6O26/V2O5 hybrid maintains a reversible capacity of ≈1110 mA h g?1. Combined electrochemical analysis and high‐resolution transmission electron microscopy observation during cycling reveals that the amorphous V2O5 coating plays an important role on enhancing the electrochemical performances and capacity self‐recovery, which provides an active amorphous protective layer and abundant grain interfaces for efficient inserting and extracting of Li‐ion. As a result, this new copper vanadium oxide hybrid is proposed as a promising anode material for LIBs. 相似文献
10.
Maximum entropy models and subjective interestingness: an application to tiles in binary databases 总被引:3,自引:3,他引:0
Tijl De Bie 《Data mining and knowledge discovery》2011,23(3):407-446
Recent research has highlighted the practical benefits of subjective interestingness measures, which quantify the novelty
or unexpectedness of a pattern when contrasted with any prior information of the data miner (Silberschatz and Tuzhilin, Proceedings
of the 1st ACM SIGKDD international conference on Knowledge discovery and data mining (KDD95), 1995; Geng and Hamilton, ACM Comput Surv 38(3):9, 2006). A key challenge here is the formalization of this prior information in a way that lends itself to the definition of a subjective
interestingness measure that is both meaningful and practical. In this paper, we outline a general strategy of how this could be achieved, before working out the details for a use case that is important in its own right. Our general strategy is based on considering prior information as constraints on a probabilistic
model representing the uncertainty about the data. More specifically, we represent the prior information by the maximum entropy
(MaxEnt) distribution subject to these constraints. We briefly outline various measures that could subsequently be used to
contrast patterns with this MaxEnt model, thus quantifying their subjective interestingness. We demonstrate this strategy
for rectangular databases with knowledge of the row and column sums. This situation has been considered before using computation
intensive approaches based on swap randomizations, allowing for the computation of empirical p-values as interestingness measures (Gionis et al., ACM Trans Knowl Discov Data 1(3):14, 2007). We show how the MaxEnt model can be computed remarkably efficiently in this situation, and how it can be used for the same
purpose as swap randomizations but computationally more efficiently. More importantly, being an explicitly represented distribution,
the MaxEnt model can additionally be used to define analytically computable interestingness measures, as we demonstrate for
tiles (Geerts et al., Proceedings of the 7th international conference on Discovery science (DS04), 2004) in binary databases. 相似文献