Analysis of polymer drag reduction mechanisms from energy budgets

The transfer of energy in drag reducing viscoelastic flows is analyzed through a sequence of energetic budgets that include the mean and turbulent kinetic energy, and the mean polymeric energy and mean elastic potential energy. Within the context of single-point statistics, this provides a complete picture of the energy exchange between the mean, turbulent and polymeric fields. The analysis utilizes direct simulation data of a fully developed channel flow at a moderately high friction Reynolds number of 1000 and at medium (30%) and high (58%) drag reduction levels using a FENE-P polymeric model.Results show that the primary effect of the interaction between the turbulent and polymeric fields is to transfer energy from the turbulence to the polymer, and that the magnitude of this transfer does not change between the low and high drag reduction flows. This one-way transfer, with an amplitude independent of the drag reduction regime, comes in contradiction with the purely elastic coupling which is implicit within the elastic theory of the polymer drag reduction phenomenon by Tabor and De Gennes (Europhys. Lett. 2, pp. 519–522, 1986).     

贴牌生产供应链混合渠道构建基础及优化机理研究

研究由制造商和品牌商组成的混合渠道贴牌生产供应链渠道结构优化问题,制造商通过直销和贴牌两条渠道销售产品.通过与单一渠道比较,分别推导出制造商和品牌商选择混合渠道的依据和优越性,进而归纳出双方共同接受混合渠道的制造商生产成本和品牌商品牌溢价优化条件,分析了渠道转移系数对双方构建混合渠道结构条件的影响,得出了制造商生产成本和品牌商品牌溢价作为竞争要素的互动决策改进贴牌供应链整体绩效的优化机理.     

一种抗高阶旁路攻击的LED密码算法

LED密码算法是2011年提出的超轻量级密码算法,主要是为资源受限下物联网加密应用研发的.轻量级密码算法结构相对简单,更容易被旁路攻击成功.随机掩码是一种有效抗旁路攻击的方法,在深入LED密码算法结构研究的基础上,提出一种全随机掩码的LED密码算法CMLED.论述了CMLED算法的设计方法,从形式化方面给出了抗高阶旁路攻击选择掩码的原则.同时,对全随机掩码的CMLED与原始算法进行了硬件资源占用与加密效率对比,实验表明CMLED仍然可以高效地在智能卡上实现.     

基于非适应性组合群测的多路存取信道模型的构作

在多路存取信道中当前用户的信息传输是计算机通信网络的一个重要内容,基于组合群测理论构作了多路存取信道模型,介绍了它在多路存取信道中当前用户信息传输方面的应用.     

Population Monte Carlo

Importance sampling methods can be iterated like MCMC algorithms, while being more robust against dependence and starting values. The population Monte Carlo principle consists of iterated generations of importance samples, with importance functions depending on the previously generated importance samples. The advantage over MCMC algorithms is that the scheme is unbiased at any iteration and can thus be stopped at any time, while iterations improve the performances of the importance function, thus leading to an adaptive importance sampling. We illustrate this method on a mixture example with multiscale importance functions. A second example reanalyzes the ion channel model using an importance sampling scheme based on a hidden Markov representation, and compares population Monte Carlo with a corresponding MCMC algorithm.     

Advertising coordination games of a manufacturer and a retailer while introducing a new product

Two kinds of vertical cooperative advertising program are considered in a distribution channel constituted by a manufacturer and a retailer, where the manufacturer pays part of the retailer’s advertising costs. In the first participation scheme, the manufacturer chooses his/her advertising participation rate in the retailer’s advertising effort and then each player determines the advertising effort that maximizes his/her profit. In the second scheme, the retailer chooses the manufacturer’s participation rate and then the manufacturer determines the advertising efforts of both players with the objective of maximizing the manufacturer’s profit. Each participation scheme corresponds to a special Stackelberg game: the manufacturer is the leader of the first, while the retailer is the leader of the second. The Stackelberg equilibrium advertising efforts and participation rate in both games are provided. Then the equilibrium strategies of the two players in the analyzed scenarios are compared with the Nash equilibrium in the competitive framework. Finally, the conditions which suggest a special kind of agreement to a player are analyzed. This work was supported by the Italian Ministry of University and Research and the University of Padua.     

Effect of Deborah number and phase difference on peristaltic transport of a third-order fluid in an asymmetric channel

The effect of a third-order fluid on the peristaltic transport in an asymmetric channel is studied. The wavelength of the peristaltic waves is assumed to be large compared to the varying channel width, whereas the wave amplitudes need not be small compared to the varying channel width. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The flow is investigated in a wave frame of reference moving with velocity of the wave. The effects of Deborah number, phase difference, varying channel width and wave amplitudes on the pumping characteristics, streamline pattern and trapping phenomena are investigated. It is observed that the trapping regions increase as the channel becomes more and more symmetric and the trapped bolus volume decreases for increasing Deborah number, phase difference and varying channel width whereas it increases for increasing flow rate and wave amplitudes. Furthermore, the obtained results could also have applications to a range of peristaltic flows for a variety of non-Newtonian fluids such as aqueous solutions of high-molecular weight polyethylene oxide and polyacrylamide.     

Sum rates for multi-user MIMO vector perturbation precoding with regularization

In this paper, we analyze the sum rate performance of multiuser multi-antenna downlink channel. We consider Rayleigh fading environment when regularized vector perturbation precoding (R-VPP) method is used at the transmitter. We derive expressions for the sum rate in terms of the variance of the received signal. We also provide a closed form approximation for the mean squared error (MSE) which is shown to work well for the whole range of SNR. Further, we also propose a simpler expression for R-VPP sum rate based on MSE. The simulation results show that the proposed expressions for R-VPP sum rate closely match the sum rate found by the entropy estimation. Our results show that when compared with other linear and non-linear precoding methods (like zero-forcing precoder, linear minimum mean square error (MMSE) precoder and VPP), R-VPP sum rate performance is very close to DPC for all SNR values. It is also noted that the sum rate performance of the linear MMSE precoder is very close to the R-VPP at low to medium SNR range. Finally we also compared the merits of performing regularization for VPP as compared to the greedy rate maximizing user scheduling. It turns out that the R-VPP with or without user selection performs better than the VPP systems with user selection.