A new method of characterization for stratified thermal energy stores

A new method for characterization of stratified thermal energy stores (TES) that integrates both the first law and the second law concerns is presented here. The first law concern is incorporated into a quantity called energy response factor and the second law concern into an entropy generation ratio. A product of these two quantities is at the heart of the TES efficiency definitions. This approach removes the overemphasis of the existing methods either on the first or the second law of thermodynamics which often biases the characterization results. The information about the evolution of the temperature field of the system in time is the prerequisite of the new method. It may be obtained from experiments or from suitable numerical simulations. The current method can be easily integrated into computational fluid dynamic (CFD) simulations and thus facilitate CFD-based design analysis. As an example of such CFD-integrated analysis, a large-scale hot water seasonal heat store is numerically studied to identify the effects of aspect ratio, containment shape, internal structures, and containment size on their efficiency. The results suggest the effectiveness of the new method in deriving useful design insights.     

INTERFACIAL INTERACTIONS AND SECONDARY FLOWS IN STRATIFIED TWO-PHASE FLOW

In this paper are analysed the interactions between a surface wave field and the kinematic structures above and below the waves, in gas-liquid stratified flow in a rectangular cross sectional channel. The analysis is based on experimental data both on the local structure of the flows and on the deformation of the gas-liquid surface. The basic phenomena that have been observed are: on the one hand, the waves that propagates over the liquid surface can exhibit a crosswise distribution of amplitude; on the other hand, secondary flows can be generated both in the gas and in the liquid. A theoretical attempt is developed to explain the distribution to wave amplitude: in fact, the waves propagate over a non uniform liquid current. On the one hand, the wave field interact with the liquid current to generate secondary flows below the waves. On the other hand, the wave amplitude distribution interacts with the gas flow; the wave distribution can be considered as a non uniform interfacial roughness which generates Prandtl second type secondary flows above the waves. These physical mechanisms which are based on the analysis of experimental results are also validated with numerical simulations.     

基于粒计算与区分能力的属性约简算法?

传统的属性约简方法将整个数据集一次性装入内存,很难适应大数据背景下的数据分析。为此文中提出基于粒计算与区分能力的属性约简算法。该算法运用统计学中的分层抽样技术,拆分原始大数据集为多个样本子集(粒),在每个粒上运用属性的区分能力进行属性约简,最后将各粒约简结果进行加权融合,得到原始大数据集的属性约简结果。实验表明该算法对海量数据集进行属性约简的可行性和高效性。     

基于聚类方法的审计分层抽样算法研究

针对审计抽样中最复杂的抽样算法一分层抽样,从数据挖掘中“聚类”的角度出发,较好地运用了聚类思想于审计抽样的分层抽样算法之中,为该算法的实现提供了一种新的解决方案。AICPA39没有为分层抽样提供具体的实现方式,国内的学者曾从统计学角度有过实现,将从计算机科学角度实现方法与统计学实现方法进行分析比较,这是对分层抽样算法实现的有益新探索。     

Modelling concurrency with comtraces and generalized comtraces

Comtraces (combined traces) are extensions of Mazurkiewicz traces that can model the “not later than” relationship. In this paper, we first introduce the novel notion of generalized comtraces, extensions of comtraces that can additionally model the “non-simultaneously” relationship. Then we study some basic algebraic properties and canonical representations of comtraces and generalized comtraces. Finally we analyze the relationship between generalized comtraces and generalized stratified order structures. The major technical contribution of this paper is a proof showing that generalized comtraces can be represented by generalized stratified order structures.     

一种使用分量组合的彩色图像压缩方法

为了适应图像的存储和传输,需要对图像进行压缩以减少数据量。对于彩色图像而言,其色彩模式和数据组合直接影响了压缩效率,压缩时通常采用每个分量单独压缩后再统一编码,未考虑分量之间的组合关系。根据彩色图像的数据结构将图像的RGB分量排列组合成新的灰度图像,将其中一个分量作为基准实行粗细分层操作,汇同该分量与其他两个分量的差值图像分别按JPEG压缩标准进行压缩编码。实验表明,该算法得到的压缩图像在与JPEG同等质量的条件下,数据量要小于JPEG压缩的数据量,耗时短,同时可为快速的彩色图像搜索和预览提供技术参考。     

Evaluating the precision of eight spatial sampling schemes in estimating regional means of simulated yield for two crops

We compared the precision of simple random sampling (SimRS) and seven types of stratified random sampling (StrRS) schemes in estimating regional mean of water-limited yields for two crops (winter wheat and silage maize) that were simulated by fourteen crop models. We found that the precision gains of StrRS varied considerably across stratification methods and crop models. Precision gains for compact geographical stratification were positive, stable and consistent across crop models. Stratification with soil water holding capacity had very high precision gains for twelve models, but resulted in negative gains for two models. Increasing the sample size monotonously decreased the sampling errors for all the sampling schemes. We conclude that compact geographical stratification can modestly but consistently improve the precision in estimating regional mean yields. Using the most influential environmental variable for stratification can notably improve the sampling precision, especially when the sensitivity behavior of a crop model is known.     

Efficient computational method for transient EM response of large-loop source over layered earth

Calculations of the ElectroMagnetic （EM） response produced by a large horizontal loop placed over layered medium are rather complex because its integral expression contains the product of two Bessel functions and has a divergent term. In this paper, an improved fast Hankel and Gaver-Stehfest transforms are introduced to solve the strong-oscillation and slow-decay properties of the integrand, where one Bessel function in the product is substituted by a carefully chosen polynomial of high accuracy and the other used as the digital filter coefficients in the convolution integral. Comparisons prove the validity and the efficiency of the proposed method.     

分层扫气技术在小型二冲程汽油机上的应用

本文为应对欧洲、美国的汽油机排放法规,提出一种分层扫气技术,利用这项技术,可以最大限度降低小型二冲程汽油机在扫气时未燃烧混合气的短路损失和提高燃烧效率,从而实现减少汽油机的HC和NOx排放指标的目的,并能大幅降低汽油机燃油消耗率,达到使小型二冲程汽油机即环保又节能的目的,为小型二冲程汽油机进入欧美市场扫清技术障碍。     

缸内直接喷射式汽油机点火稳定性的数值分析

缸内直接喷射式汽油机的一个显著特点是依靠火花塞点燃喷入缸内的汽油油束。由于缸内混合气浓度极不均匀，所以其点火及火焰传播过程与普通均质燃烧式发动机有很大的不同。火焰核心的稳定形成及初始火焰发展对缸内的整个燃烧过程有极其重要的影响。本文利用二维两相混合模型模拟喷雾过程，利用一个详细的准维模型模拟火花塞的点火过程，并采用特殊处理方法使两个子模型相匹配，计算了缸内直接喷射式汽油机从喷雾到形成稳定火核的全过程，分析了多种因素对点火稳定性的影响，尤其是对涡流比、点火时刻和喷油定时之间的适当配合进行了模拟分析。计算结果对优化实验有明显的指导作用。