Simulation of electrophoretic stretching of DNA in a microcontraction using an obstacle array for conformational preconditioning

Recently our group has reported experiments using an obstacle array to precondition the conformations of DNA molecules to facilitate their stretch in a microcontraction. Based upon previous successes simulating electrophoretic stretching in microcontractions without obstacles, we use our simulation model to study the deformation of DNA chains in a microcontraction preceded by an array of cylindrical obstacles. We compare our data to the experimental results and find good qualitative, and even quantitative, agreement concerning the behavior of the chains in the array; however, the simulations overpredict the mean stretch of the chains as they leave the contraction. We examine the amount of stretch gained between leaving the array and reaching the end of the contraction and speculate that the differences seen are caused by nonlinear electrokinetic effects that become important in the contraction due to a combination of field gradients and high field strengths.     

Simulation guided design of a microfluidic device for electrophoretic stretching of DNA

We have used Brownian dynamics-finite element method (BD-FEM) to guide the optimization of a microfluidic device designed to stretch DNA for gene mapping. The original design was proposed in our previous study [C. C. Hsieh and T. H. Lin, Biomicrofluidics 5(4), 044106 (2011)] for demonstrating a new pre-conditioning strategy to facilitate DNA stretching through a microcontraction using electrophoresis. In this study, we examine the efficiency of the original device for stretching DNA with different sizes ranging from 48.5 kbp (λ-DNA) to 166 kbp (T4-DNA). The efficiency of the device is found to deteriorate with increasing DNA molecular weight. The cause of the efficiency loss is determined by BD-FEM, and a modified design is proposed by drawing an analogy between an electric field and a potential flow. The modified device does not only regain the efficiency for stretching large DNA but also outperforms the original device for stretching small DNA.     

Simulation of single DNA molecule stretching and immobilization in a de-wetting two-phase flow over micropillar-patterned surface

We investigate single DNA stretching dynamics in a de-wetting flow over micropillars using Brownian dynamics simulation. The Brownian dynamics simulation is coupled with transient flow field computation through a numerical particle tracking algorithm. The droplet formation on the top of the micropillar during the de-wetting process creates a flow pattern that allows DNA to stretch across the micropillars. It is found that DNA nanowire forms if DNA molecules could extend across the stagnation point inside the connecting water filament before its breakup. It also shows that DNA locates closer to the top wall of the micropillar has higher chance to enter the flow pattern of droplet formation and thus has higher chance to be stretched across the micropillars. Our simulation tool has the potential to become a design tool for DNA manipulation in complex biomicrofluidic devices.     

Simulations of DNA stretching by flow field in microchannels with complex geometry

Recently, we have reported the experimental results of DNA stretching by flow field in three microchannels (C. H. Lee and C. C. Hsieh, Biomicrofluidics 7(1), 014109 (2013)) designed specifically for the purpose of preconditioning DNA conformation for easier stretching. The experimental results do not only demonstrate the superiority of the new devices but also provides detailed observation of DNA behavior in complex flow field that was not available before. In this study, we use Brownian dynamics-finite element method (BD-FEM) to simulate DNA behavior in these microchannels, and compare the results against the experiments. Although the hydrodynamic interaction (HI) between DNA segments and between DNA and the device boundaries was not included in the simulations, the simulation results are in fairly good agreement with the experimental data from either the aspect of the single molecule behavior or from the aspect of ensemble averaged properties. The discrepancy between the simulation and the experimental results can be explained by the neglect of HI effect in the simulations. Considering the huge savings on the computational cost from neglecting HI, we conclude that BD-FEM can be used as an efficient and economic designing tool for developing new microfluidic device for DNA manipulation.     

移动通信技术标准化的国家战略与企业战略

在移动通信发展过程中,技术标准的竞争是现代移动通信市场竞争的最重要方面。从移动通信技术标准化的发展历程来看,国家战略与企业战略存在着一定的相互影响和相互作用,其中国家战略发挥着关键的作用。本文通过理论分析和国际经验的比较研究,得出了中国3G技术标准化国家战略的政策性含义。     

Combined strategies for improving production of a thermo-alkali stable laccase in Pichia pastoris

BackgroundLaccases are copper-containing enzymes which have been used as green biocatalysts for many industrial processes. Although bacterial laccases have high stabilities which facilitate their application under harsh conditions, their activities and production yields are usually very low. In this work, we attempt to use a combinatorial strategy, including site-directed mutagenesis, codon and cultivation optimization, for improving the productivity of a thermo-alkali stable bacterial laccase in Pichia pastoris.ResultsA D500G mutant of Bacillus licheniformis LS04 laccase, which was constructed by site-directed mutagenesis, demonstrated 2.1-fold higher activity when expressed in P. pastoris. The D500G variant retained similar catalytic characteristics to the wild-type laccase, and could efficiently decolorize synthetic dyes at alkaline conditions. Various cultivation factors such as medium components, pH and temperature were investigated for their effects on laccase expression. After cultivation optimization, a laccase activity of 347 ± 7 U/L was finally achieved for D500G after 3 d of induction, which was about 9.3 times higher than that of wild-type enzyme. The protein yield under the optimized conditions was about 59 mg/L for D500G.ConclusionsThe productivity of the thermo-alkali stable laccase from B. licheniformis expressed in P. pastoris was significantly improved through the combination of site-directed mutagenesis and optimization of the cultivation process. The mutant enzyme retains good stability under high temperature and alkaline conditions, and is a good candidate for industrial application in dye decolorization.     

北京市私人载客小型和微型汽车的仿真模型及政策模拟

本文构建了系统动力学模型用以分析北京市私人载客小型和微型汽车的发展情况。首先,将模型细分为人口、经济、私人载客小汽车三个子模块,通过收入分布和汽车的年度使用成本预测私人汽车的拥有情况。其次,根据模型的模拟结果对2000年-2020年的车辆数量、车辆年龄、新车销量、车辆报废与淘汰进行分析。最后,通过情景分析模拟出不同政策下北京市私人载客小型和微型汽车的不同发展趋势,进一步探讨了了今后的政策建议。     

Influences of electric field on living cells in a charged water-in-oil droplet under electrophoretic actuation

We experimentally investigate the effects of high electric field on living cells inside a charged droplet under electrophoretic actuation. When an aqueous droplet suspended in a dielectric liquid contacts with electrified electrode, the droplet acquires charge. This charged droplet undergoes electrophoretic motion under strong electric field (1–3 kV/cm), which can be used as a droplet manipulation method in biomicrofluidic applications. However, because strong electric field and use of dielectric oil can be a harmful environment for living cells, the biological feasibilities have been tested. Trypan blue test and cell growth test have been performed to check the viability and proliferation of cells in a droplet under various electric field strengths and actuation times. We have not observed any noticeable influence of electric field and silicone oil on the viability and proliferation of cells, which indicates that electrophoresis could be safely used as a manipulation method for a droplet containing living biological system.     

错排问题的DNA计算方法

全错位排列问题是组合数学中最常见的一类问题，本文给出了它的一个运用图论和DNA计算的新方法。     

Numerical investigation on a new local preconditioning method for solving the incompressible inviscid, non-cavitating and cavitating flows

A locally power-law preconditioning algorithm is developed. This is applied to compute incompressible inviscid, steady-state, non-cavitating and cavitating flows. The preconditioning parameters are adapted automatically from the pressure of computational domain. This method suggests better convergence rates rather than the standard artificial compressibility and the standard preconditioning method. Single-fluid Euler equations, cast in their conservative form, along with the barotropic cavitation model are employed. The cell-centred Jameson's finite volume discretization technique is used to solve the preconditioned governing equations. The stabilization is achieved via the second and fourth, order artificial dissipation scheme. Explicit four-stage Runge-Kutta time integration is applied to find the steady-state condition. In this paper, the method is assessed through simulations of incompressible inviscid, steady-state, non-cavitating and cavitating flows over a 2D NACA0012 and a 2D NACA66(MOD)+a=0.8 hydrofoil section. The results show satisfactory agreement with others numerical and experimental works in pressure distribution and hydrodynamic forces. Using the power-law preconditioner decreases the convergence rate significantly. In addition, information such as the effects of the new locally power-law preconditioner, the effects of the artificial dissipation terms, and the effects of the artificial compressibility parameter, on convergence speed and solution accuracy is highlighted.     

组织中的学习战略演化及其案例研究

经济的全球化、商业环境的剧烈变化促使组织采取相应的学习战略来提高自身的学习能力。由于商业环境的不同、组织自身的条件各异,组织采取的学习战略会各不相同。文章讨论了一个组织内学习战略演化的三阶段模型,这三个阶段是：职工开发、逼近的商业需要、未知的商业开发。然后,对Motorola大学在公司内战略地位的变化历程进行了剖析。最后得出了一些有借鉴意义的经验和结论。     

航空发动机控制系统设计课程教学用仿真试验平台建设的思考与建议

本文对航空发动机控制系统设计课程实验教学提出了新的建议和思考。随着国际先进航空发动机控制新技术的发展,基于快速原型的发动机控制系统以及系统综合控制规律设计方法已成为必然趋势,航空发动机控制系统设计专业教学必须做出适应性的对策与措施,以满足教学内容对专业发展需求。借助一些关键发动机仿真试验平台的建设,通过课程实验环节使得学生熟悉了解航空发动机控制系统设计新方法,是一条可行的航空发动机控制专业教学改革途径。     

试析高校财务风险成因及防范措施

近年,高校财务风险剧增。通过对不同财务风险成因分析,建立财务预警系统、提高创收能力、硬化预算约束来防范财务状况失衡风险;建立贷款监督机制、加强贷款资金管理、制定还款计划来防范债务风险;提出了防范财务风险的措施。     

The cognitive selection framework for knowledge acquisition strategies in virtual communities

As a significant source of knowledge, virtual communities have stimulated interest in knowledge management research. Nonetheless, very few studies to date have examined the demand-side knowledge perspective such as knowledge acquisition in virtual communities. In order to explore the knowledge acquisition process within virtual communities, this study proposes the cognitive selection framework of knowledge acquisition strategy in virtual communities. The proposed framework takes a cognitive perspective, to identify how knowledge recipients select their strategy for acquiring specialized knowledge, emphasizing their cognitive goals (e.g., cognitive replication and innovation) and cognitive motivators (e.g., virtual community self-efficacy, heightened enjoyment, and time resources). Our results suggest that knowledge recipients’ cognitive motivators differentially influence their cognitive goals (cognitive replication and innovation), which, in turn, are related to their selection of knowledge acquisition strategy (static and dynamic acquisition strategy), respectively.     

应对我国水资源问题适应性战略研究

文章在论述中国水资源“水多、水少、水脏”主要问题基础上,阐述了水资源问题引发的生态影响,提出了建立节水型社会、建立利水型社会和走绿色水利之路的适应性战略。     

西部地区创新性人才开发战略研究

本文从人才知识结构、软硬件设施、科研创新能力以及创新教育等方面剖析了西部地区创新性人才开发存在的问题,提出西部地区创新性人才开发与培养的新思维（包括树立“以才为本”、“不求留其人但求用其才”、自我开发和可持续开发的人才开发等）和多元化留才、育才、用才与引才战略（如培育并留住现有人才、开发潜在人才、引、用外来人才等）。     

我国企业如何应对反倾销诉讼

针对我国厂商对国际反倾销法规的不熟悉以及反倾销抗辩意识的淡漠,不仅导致我国企业常被处以不公正的判决,受到高额反倾销税的制裁,而且破坏中国贸易形象。从4个方面探讨我国企业如何应对国际反倾销诉讼,如何以法律的手段保护自己的合法权益。     

医学科技期刊网络化的现状和发展对策分析

医学科技期刊网络化建设日益成为期刊发展的焦点问题。根据现有的研究结果分析了医学期刊网络化建设的现状,并在此基础上讨论了医学期刊网络化的发展对策。     

微重力条件下腔体内竖板火蔓延的三维非稳态数值模拟

本文用数值求解基本控制微分方程组的方法研究了微重力条件下腔体内部固体可燃物表面火焰传播的三维非稳态过程。建立的理论模型考虑了气相有限速率化学反应，以及固相的传热和热解过程，阐明了微重力场中固体表面火蔓延过程可燃表面热解的“表面燃料喷射”效应的重要作用，并建立了相应的数学处理方法。数值模拟的结果反映了微重力大小对竖板火蔓延过程形成重要影响的特点，结果基本合理。     

我国国家知识产权战略的研究与思考——基于国外政府及跨国公司知识产权战略的比较

全球经济一体化下,知识产权的国际化会对我国的经济发展产生巨大的影响。在国家知识产权战略管理中,政府要充分发挥其职能作用,制定出合理有效的知识产权战略。本文分析、研究了一些发达国家政府及其跨国公司的知识产权战略,提出了我国知识产权战略的构想。