Evaluation of the potential of nonlinear gradients for separating a ternary mixture

The potential of applying nonlinear gradients in preparative chromatography is evaluated theoretically and experimentally. The second eluting component of a ternary model mixture is considered as the target component. Systematic gradient resolution experiments were conducted for this mixture using reversed phase chromatography. In preliminary experimental investigations the effect of the mobile phase composition on the specific distribution equilibria was quantified. Concave and convex solvent strength gradients were analysed and compared with conventional linear gradients. Main result of the study is the fact that significant improvement in productivity can be achieved if the gradient shapes are designed carefully.     

Fuzzy profit measures for a fuzzy economic order quantity model

Changing economic conditions make the selling price and demand quantity more and more uncertain in the market. The conventional inventory models determine the selling price and order quantity for a retailer’s maximal profit with exactly known parameters. This paper develops a solution method to derive the fuzzy profit of the inventory model when the demand quantity and unit cost are fuzzy numbers. Since the parameters contained in the inventory model are fuzzy, the profit value calculated from the model should be fuzzy as well. Based on the extension principle, the fuzzy inventory problem is transformed into a pair of two-level mathematical programs to derive the upper bound and lower bound of the fuzzy profit at possibility level α. According to the duality theorem of geometric programming, the pair of two-level mathematical programs is transformed into a pair of conventional geometric programs to solve. By enumerating different α values, the upper bound and lower bound of the fuzzy profit are collected to approximate the membership function. Since the profit of the inventory problem is expressed by the membership function rather than by a crisp value, more information is provided for making decisions.     

Multicommodity long-term hydrogeneration optimization with capacity and energy constraints

The work presented deals with long-term hydrogeneration optimization in integrated systems when there are no limitations on the availability of fuels for thermal units. A multicommondity network model represents hydrovariables. Hydrogeneration and its unavailability distribution is modeled as a multiblock distribution and a procedure is derived to convolve the hydropower unavailability distribution with the load duration curve. A suitable approximation of the expected production cost is minimized subject to multicommodity network constraints and to hydropower capacity and hydroenergy limit nonlinear constraints. It can be applied to systems with hydrogeneration regardless of its proportion of hydrothermal mix. A realistic case example is solved and the results are discussed. Simulation tests performed with many inflow sequences validate the results obtained.     

A proposal for a hybrid meta-strategy for combinatorial optimization problems

In this paper, we propose an algorithm named BDS (Bound-Driven Search) that combines features of exact and approximate methods. The proposed procedure may be seen as a local search algorithm that systematically explores (in a branch-and bound sense) the most promising nodes, thus preventing solutions from being reevaluated. Additionally, it can be regarded as an exact method as it may be able to guarantee that the solution found is optimal. We present the application of this new algorithm to a specific problem domain: the permutation flow shop scheduling problem with makespan objective. The subsequent computational experiments are encouraging, as the algorithm is able to yield exact or near exact solutions to most instances of the problem. Furthermore, the algorithm outperforms one of the best state-of-the-art algorithms for the problem.     

Optimization of supercritical fluid extraction of saikosaponins from Bupleurum falcatum with orthogonal array design

Supercritical fluid extraction (SFE) was used to extract saikosaponins a, c and d from the root of Bupleurum falcatum. An orthogonal array design L₉(3)⁴ was employed as a chemometric method for the optimization of the SFE conditions. The effects of four factors including pressure (30–40 MPa), temperature (40–50°C), ethanol concentration (60–100%) and time (2.5–3.5 h) on the yields of saikosaponins were investigated by a preparative SFE system in the SFE mode. Under the optimized conditions, namely 35 MPa of pressure, 45°C of temperature, 80% of ethanol concentration and 3.0 h of time, the yields of saikosaponin c, saikosaponin a, saikosaponin d, total saikosaponins and SFE extract were 0.16, 0.12, 0.96, 1.24 and 16.48 mg/g, respectively. Determinations of the saikosaponins were performed by HPLC.     

Optimization of simulated moving bed chromatography with fractionation and feedback: Part II. Fractionation of both outlets

A new improvement based on outlet fractionation and feedback has been developed for simulated moving bed (SMB) chromatography. In this contribution, this fractionation and feedback SMB (FF-SMB) concept is extended to the general scenario which integrates a simultaneous fractionation of both outlet streams. A model-based optimization approach, previously adopted to investigate single fractionation, is extended to consider this flexible fractionation policy. Quantitative optimization studies based on a specific separation problem reveal that the double fractionation is the most efficient operating scheme in terms of maximum feed throughput, while the two existing single fractionation modes discussed in our previous study are also significantly superior to the conventional SMB operation. The advantages of the double fractionation extension are further demonstrated in terms of several more detailed performance criteria. In order to evaluate the applicability of the fractionation and feedback modification, the effect of product purity, adsorption selectivity, column efficiency and column number on the relative potential of FF-SMB over SMB is examined.     

The optimization problem over a distributive lattice

In this paper we give a necessary and sufficient condition for existence of minimal solution(s) of the linear system A * X ≥ b where A, b are fixed matrices and X is an unknown matrix over a lattice. Next, an algorithm which finds these minimal solutions over a distributive lattice is given. Finally, we find an optimal solution for the optimization problem min {Z = C * X | A * X ≥ b} where C is the given matrix of coefficients of objective function Z. This research was completed while the author was a visitor of the Center for Informatics and Applied Optimization, University of Ballarat, Ballarat, Australia.     

基于空间光调制器的波面重建优化方法研究

针对不同非球面面形的实时检测需求,研究了基于空间光调制器的标准波面重建技术.基于空间光调制器波面重建的原理设计了干涉测量系统,依据空间光调制器的自身特点选取修正离轴计算全息编码方式实现对标准球波面的编码.针对实验中空间光调制器作为全息再现介质引起重建波面质量下降问题,提出了错位叠加优化方案,并将这一过程进行了模拟实验....     

高场超导MRI系统铁磁屏蔽的几何优化

磁共振成像（MRI）系统是一种重要的医学影像诊断设备,它根据核磁共振原理对处于静磁场中的人体器官进行成像,具有清晰度高和任意层面成像等优点,在医学检查和诊断方面有着重要的作用,与低场MRI相比,高场MRI系统可提高质子的磁化率,增加图像的信噪比,缩短MRI信号采集时间,从而使脑功能成像的信号变化更为明显;但是较高的背景...