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排序方式: 共有3419条查询结果,搜索用时 15 毫秒
31.
32.
We determined the optimal reaction conditions to minimize the energy cost and the quantities of by‐products for a poly(ethylene terephthalate) process by using the iterative dynamic programming (IDP) algorithm. Here, we employed a sequence of three reactor models: the semibatch transesterification reactor model, the semibatch prepolymerization reactor model, and the rotating‐disc‐type polycondensation reactor model. We selectively chose or developed the reactor models by incorporating experimentally verified kinetic models reported in the literature. We established the model for the entire reactor system by connecting the three reactor models in series and by resolving some joint problems arising when different types of reactor models were interconnected. On the basis of the simulation results of the reactor system, we scrutinized the cause and effect between the reaction conditions and the final quality of the polymer product. Here, we set up the optimization strategy by using IDP on the basis of the integrated reactor model, and the process variables with significant influence on the properties of polymer were selected as control variables with the help of a simulation study. With this method, we could refine the reaction conditions at the end of each iteration step by contracting the spectra of control regions, and the iteration process finally stopped when the profile of the optimal trajectory converged. We also took the constraints on the control variables into account to guarantee polymer quality and to suppress side reactions. Constituting six different strategies by setting weighting vectors differently, we examined the differences in optimal trajectories, the trend of optimality, and the quality of the final polymer product. For each of the strategies, we conducted the optimization to examine whether the number‐average degree of polymerization approached the desired value. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 993–1008, 2002 相似文献
33.
Carsten Dachsbacher Jaroslav Křivánek Miloš Hašan Adam Arbree Bruce Walter Jan Novák 《Computer Graphics Forum》2014,33(1):88-104
Recent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering. 相似文献
34.
In this paper, we propose a new fully computerized image analysis method for measuring the thickness of muscles from ultrasound image obtained by muscle endurance test using morphological information of fascia and thoracic vertebra. Firstly, we divide the image into lumbar region and thoracolumbar region by the difference of density in image for measuring the thickness of muscles. In lumbar region, we notice that the intensity of fascia is relatively higher than other parts. Thus, we measure the thickness of muscles surrounding the fascia area. In the process, we apply median filter to candidate fascia areas for extracting candidate muscle layers between fascias. Then, the thickness of muscles we measure is that of the third layer. In thoracolumbar region, we apply region expansion method for classifying the region into subcutaneous fat part and part including thoracic vertebra. Then, we apply counting method and evolutionary computation search model to find the measuring location that is in between subcutaneous fat area and thoracic vertebra. In experiment, the proposed method is effective in measuring the thickness of muscles and avoids failures of previous studies. The performance of this approach is sufficiently comparable to that of medical experts. 相似文献
35.
Graft copolymerization of acrylonitrile (AN) and methyl methacrylate (MMA) onto polychloroprene (CR) was carried out using benzoyl peroxide as initiator. The effects of mole ratio of AN to MMA, reaction temperature, reaction time, solvent, and initiator concentration on the graft copolymerization were examined. It was found that the thermal stability and weatherability of the AN—CR—MMA graft copolymer (ACM) were considerably better than those of CR. 相似文献
36.
Copolymerizations of ethylene with 1-decene were carried out with a series of
stereospecific metallocene compounds, rac–(EBI)Zr(NMe2)2 [ 1, EBI = ethylene–1,2–bis( 1–indenyl)], rac–(EBI)Hf(NMe2 (2), rac–Me2Si( 1–C5H2–2–Me–4–
t
Bu)2Zr(NMe2)2
(3), ethylidene(cyclopentadienyl)(9-fluorenyl)ZrMe2 [4, Et(Flu)(Cp)ZrMe2] and isopropylidene(cyclopentadienyl)(9–fluorenyl)ZrMe2 [5, iPr(Flu)(Cp)ZrMe2], combined
with Al(i–Bu)3/[CPh3] [B(C6F5)4] cocatalyst. All catalyst systems showed very high
copolymerization rates and the 1–decene reactivity decreased in the order of 2 > 5 > 1 4 > 3. The reactivity product of ethylene and 1–decene (r
E x r
D) was below 1 except
3 catalyst, corresponding to random copolymer structures with an alternating
character. The melting point (Tm), crystallinity (XC), intrinsic viscosity ([] and
density of the 1–decene/ethylene copolymers decreased markedly with an increase in
the 1–decene content, regardless of the type of catalytic system. 相似文献
37.
The key to the success of flip‐chip technology lies in the availability of sucessful underfill materials. However, the reliability of flip‐chip technology using current underfill materials is generally found to be lower than that of conventional wire‐bond connection packaging materials such as epoxy molding compound (EMC) because of the high coefficients of thermal expansion (CTE) and moisture absorption of cured underfill material. In this study desbimide (DBMI), which has a low melting point (about 80°C), was used in the underfill materials as a cohardener. As a result, DBMI‐added underfill can show excellent thermal reliability, which is due to the superior properties of the CTE, the elastic modulus, and water resistance. When the properties of a 2 wt % DBMI‐added underfill were compared with those of a typical underfill (epoxy/anhydride), the CTE value was reduced to less than one‐half at the solder reflow temperature (about 200°C), the elastic modulus was reduced to less than one‐half in the temperature region below the glass‐transition temperature, and the water resistance was improved twofold. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2617–2624, 2002 相似文献
38.
J. H. Kim J. H. Park J. H. Kim T. V. Cao T. Y. Lee H. J. Ban K. Yang H. G. Kim P. B. Ha Y. H. Kim 《中南工业大学学报(英文版)》2009,16(4):621-628
A power management unit (PMU) chip supplying dual panel supply voltage, which has a low electro-magnetic interference (EMI)
characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor
increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up
circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator
used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area.
The PMU chip is designed with MagnaChip’s 0.25 μm high-voltage process. The driving currents of ELVDD and ELVSS are more than
50 mA when a SPICE simulation is done. 相似文献
39.
The peel and tack properties of mixtures of polystyrene-block-polybutadiene-block-polystyrene (SBS) and a tackifier were investigated after these were crosslinked by ultraviolet (UV) irradiation at various amounts of benzophenone (BP) as a photoinitiator and trimethylolpropane mercaptopropionate (TRIS) as a crosslinking agent.The degree of crosslinking of polybutadiene (PB) block in the SBS mixture was qualitatively estimated from the amount of gel fraction as well as the change in the glass transition temperature of the PB block. The crosslinking of the PB block was done within 3 min after UV irradiation and the peel strength of crosslinked specimens was as low as 45[percnt] of specimens without crosslinking. Nano-tack and bulk tack properties as well as the surface tension of mixtures were measured depending upon amounts of BP and TRIS. 相似文献
40.
根据沧州市92个雨量监测站2006~2016年间的春季大到暴雨资料,研究了11年来沧州市春季大到暴雨的特征指标、时间变化规律以及空间变化趋势.研究发现:沧州市11年间春季大到暴雨强度(站点数)的时间变化呈抛物线趋势,与沧州市年降水量变化趋势非常接近;沧州市春季大到暴雨的空间分布情况为各县市均有发生,但分布不均匀,子牙新河沿岸出现高值区,以子牙新河为界,向两侧递减. 相似文献