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991.
Level set methods [Osher and Sethian. Fronts propagating with curvature-dependent speed: algorithms based on Hamilton–Jacobi formulations. J. Comput. Phys. 79 (1988) 12] have proved very successful for interface tracking in many different areas of computational science. However, current level set methods are limited by a poor balance between computational efficiency and storage requirements. Tree-based methods have relatively slow access times, whereas narrow band schemes lead to very large memory footprints for high resolution interfaces. In this paper we present a level set scheme for which both computational complexity and storage requirements scale with the size of the interface. Our novel level set data structure and algorithms are fast, cache efficient and allow for a very low memory footprint when representing high resolution level sets. We use a time-dependent and interface adapting grid dubbed the “Dynamic Tubular Grid” or DT-Grid. Additionally, it has been optimized for advanced finite difference schemes currently employed in accurate level set computations. As a key feature of the DT-Grid, the associated interface propagations are not limited to any computational box and can expand freely. We present several numerical evaluations, including a level set simulation on a grid with an effective resolution of 10243 相似文献
992.
993.
Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by To = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was Tp = 0.91B + 320, and the temperature at which degradation was completed was Tf = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), To = 0.96B + 308, Tp = 0.99B + 320, and Tf = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), To = 1.11B + 305, Tp = 1.10B + 319, and Tf = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures To, Tp, and Tf relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001 相似文献
994.
DECOMPOSITION BEHAVIOR AND MECHANISM OF CALCIUM SULFATE UNDER THE CONDITION OF O2/CO2 PULVERIZED COAL COMBUSTION 总被引:3,自引:0,他引:3
The decomposition behavior and mechanism of calcium sulfate in O2/CO2 pulverized coal combustion were studied in an entrained flow reactor. A reaction rate expression correlating the influence of various factors was proposed for CaS04 decomposition and it is able to predict CaS04 decomposition satisfactorily. Under the conditions investigated, the decomposition of CaS04 was found to be a regime of chemically controlled shrinking core reaction. A CO2-rich atmosphere enhances CaSO4 decomposition in absence of oxygen. CaSO4 particles have catalytic effect on formation of CO from CO2. A high SO2 concentration inhibits CaSO4 decomposition. The kinetics of CaSO4decomposition has obvious dependence on experimental facilities and conditions, whereas the activation energy has much lower dependence. The kinetics derived in this work is more appropriate for investigating desulfurization in O2/CO2 pulverized coal combustion because an entrained flow reactor has a much closer condition to that in O2/CO2 pulverized coal combustion than a TGA. 相似文献
995.
目的研究可降解材料聚乳酸(PLA)/聚丁二酸丁二醇酯-聚己二酸丁二醇酯共聚物(PBSA)薄膜在添加有机纳米蒙脱土(MMT)和精油后的抗氧化性和保鲜性能。方法采用挤出共混改性和挤出流延法加工制备出PLA/PBSA/MMT/精油纳米复合薄膜,对其力学性能、透湿性、透气性、抗氧化性等进行探讨,并研究对樱桃的保鲜作用。结果添加了DK4型号MMT的PLA/PBSA薄膜的抗拉强度得到提高,薄膜的水蒸气透过率、透气率得到降低,但是对樱桃保鲜的各项指标与对照组无明显差异。在此基础上添加丁香精油后,力学性能得到提升,抗氧化作用明显,并且对改善樱桃的保鲜效果显著增加。结论添加了DK4型MMT和丁香精油的PLA/PBSA薄膜有着较好的改性效果,并且有良好的保鲜效果。 相似文献
996.
预计算一个完整的数据立方可以获得最快的查询响应速度,但是对于一个大规模的数据立方,所需的存储空间非常大,因此通常只能预先计算数据立方中的部分聚集。文章提出了计算部分数据立方的算法PCC(PartialComputationofCube),它的特点是采用自底向上的划分方法,能根据需要计算的聚集确定维的划分路径,并裁减不必要的聚集和划分。实验表明,和利用完整数据立方的计算方法BUC来计算部分数据立方的方法比,PCC算法的效率更高。 相似文献
997.
1前言
Mahakam褶皱带位于Borneo岛东部边缘第三纪Kutai盆地的滨岸区部分内(图1).褶皱带内的Sanga Sanga区有四个大到巨大的烃类富集区:Mutiara,Semberah、Nilam和Badak油田(Bates,1996)还有许多其它的小油田(图2),在kutai盆地发现的烃类估计有25亿桶油(总采收率或简称EUR)和28万亿立方英尺天然气(EUR)(Paterson等人,1997).…… 相似文献
998.
Neuropsychological evidence suggests that face recognition based on configural (holistic) information can occur in isolation from recognition based on local feature cues. The present study shows that configural processing can be isolated experimentally in normal subjects. A phenomenon is reported that exists only for upright whole faces, namely categorical perception (CP) of face identity in noise. Three discrimination tasks (ABX, better likeness, and similarity ratings) were used to test for perceptual distortion across the category boundary predicted from binary classification of face morphs. Noise was added such that any single local region provided unreliable cues to identity. Under these conditions, CP was found for upright faces but not for inverted faces or single features, even with more than 10,000 trials. The CP-in-noise signature phenomenon was then used to show that configural processing survives image plane rotations of 45°–90°. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Milk fats as ingredients 总被引:1,自引:0,他引:1
Ken J Burgess 《International Journal of Dairy Technology》2001,54(2):56-60
This paper reviews aspects of the use of milk fats as food ingredients from a technico-marketing perspective. Good marketing involves matching the needs of the market place with the strengths of the supplier relative to those needs. A practical approach to using milk fats as ingredients is therefore based on understanding the background science and technology of milk fats, and on appreciating where the attributes of milk fat in its various forms can deliver real benefits to food manufacturers. These considerations have been addressed in three key areas: what are the characteristics of milk fats; how can the properties of milk fats be modified; and what are the typical milk fat ingredients and their applications. 相似文献
1000.
Raoul S. Pereira Gerald Wisenberg Frank S. Prato Ken Yvorchuk 《Magma (New York, N.Y.)》2000,11(2):104-113
This study assessed the accuracy and feasibility of magnetic resonance imaging (MRI) during a constant infusion of gadolinium
diethylenetriaminepentaacetic acid (Gd-DTPA) for the determination of myocardial viability in patients with recent acute myocardial
infarction (AMI). Nine patients were studied within 10 days of AMI. Rest-redistribution201Thallium (201Tl) single photon emission computed tomography (SPECT) was used as a gold standard for viability. Using MRI, regional perfusion
was assessed using dynamic imaging during a bolus injection of Gd-DTPA and viability was assessed during a continuous infusion.
Finally, cine MR images were acquired at baseline, during low-dose dobutamine infusion and after recovery. To assess viability,
the left ventricle was divided into 16 segments and signal intensity in corresponding MRI and redistribution SPECT segments
were compared. Wall thickening index (WTI) was determined at each step during the dobutamine study. The results revealed that
in five patients, reduced perfusion in infarcted regions was observed qualitatively during dynamic first pass imaging. There
was a significant inverse correlation between201Tl uptake and MRI signal intensity, i.e. infarcted tissue (low201Tl uptake) had increased MR signal intensity. Segments were separated into normal (201Tl uptake >90%) and infarcted (<60%). Infarcted MRI segments had greater signal intensity than normal segments (179±50 vs.
102±14%;P<0.0001). WTI in normal segments increased by 18±8.5% (P<0.0001) from baseline to 10 μg/kg per min of dobutamine while infarcted tissue WTI decreased 2.8±7.2% (P=0.17). Thus regions of myocardium that were infarcted as defined by reduced201Tl uptake and absent contractile reserve showed greatly increased MRI signal intensity during a constant infusion of Gd-DTPA.
The use of MRI during a constant infusion of Gd-DTPA is accurate and feasible for the determination of myocardial necrosis
in a clinical setting. 相似文献