Fabrication and electroosmotic flow measurements in micro- and nanofluidic channels

An easy method for fabricating micro- and nanofluidic channels, entirely made of a thermally grown silicon dioxide is presented. The nanochannels are up to 1-mm long and have widths and heights down to 200 nm, whereas the microfluidic channels are 20-μm wide and 4.8-μm high. The nanochannels are created at the interface of two silicon wafers. Their fabrication is based on the expansion of growing silicon dioxide and the corresponding reduction in channel cross-section. The embedded silicon dioxide channels were released and are partially freestanding. The transparent and hydrophilic silicon dioxide channel system could be spontaneously filled with aqueous, fluorescent solution. The electrical resistances of the micro- and nanofluidic channel segments were calculated and the found values were confirmed by current measurements. Electrical field strengths up to 600 V/cm were reached within the nanochannels when applying a potential of only 10 V. Electroosmotic flow (EOF) measurements through micro- and nanofluidic channel systems resulted in electroosmotic mobilities in the same order of those encountered in regular, fused silica capillaries.     

Electrokinetic energy conversion in micrometer-length nanofluidic channels

In this study, we present a theoretical and numerical investigation of electrokinetic energy conversion in short-length nanofluidic channels, taking into account reservoir resistance and concentration polarization effects. The concentration polarization effect was demonstrated through numerical modeling using the Poisson–Nernst–Planck (PNP) model. In the absence of concentration polarization, the modified Onsager reciprocal relation for the electrokinetic flow through a one-dimensional (1D) nanochannel is derived from both Ohm’s law and Kirchhoff’s current law while considering the reservoir resistance. Based on this modified Onsager reciprocal relation and the Poisson–Boltzmann (PB) model, a theoretical model for electrokinetic energy conversion is proposed to address the importance of the reservoir resistance effect on electrokinetic energy conversion. The applicability of our proposed model is also verified through numerical modeling of the PNP model. The results calculated from our proposed model are shown to be in good agreement with those from the PNP model when the concentration polarization effect does not occur significantly at the reservoirs. The conversion efficiency and generation power are decreased when the channel resistance is not much larger than the reservoir resistance, especially for a shorter-length nanochannel (e.g., a channel several micrometers in length) with a lower electrolyte concentration and a higher surface charge density. After the concentration polarization effect becomes increased as a larger pressure gradient is applied through an ideal ion-selective nanochannel, the conversion efficiency/generation power is further decreased due to the ion depletion at the inlet reservoir, which increases the electrical resistance of the inlet reservoir or the equivalent electrical resistance of the electrokinetic energy conversion system. The onset pressure difference (or gradient) for a significant concentration polarization is identified both theoretically and numerically. In order to avoid decreases in the conversion efficiency/generation power mentioned above, some key factors such as the length of the nanochannel, the position of electrodes at the reservoirs, and the applied pressure gradient were noticed in this study.     

Electrokinetic characterization of individual nanoparticles in nanofluidic channels

We electrokinetically characterize properties of single 42-nm polystyrene nanoparticles (NP) in nanofluidic channels imaged with frustrated total internal reflection fluorescence microscopy (fTIRFM). Specifically, we demonstrate fTIRFM of individual NPs in nanofluidic channels shallower than the evanescent field and use the resultant illumination field to gain insight into the behavior and electrokinetic properties of individual NP transport in channels. We find that the electrophoretic mobility of nanoparticles in 100-nm channels is lower than in larger channels or in bulk, presumably due to hindrance effects. Furthermore, we notice a non-intuitive increase in mobility with buffer concentration, which we attribute to electric double layer interactions. Finally, since the evanescent field intensity decreases with distance from the channel wall, we use the measured fluorescence intensity to report probable transverse distributions of free-solution 42-nm polystyrene fluorescent particles. Our method promises to be useful for characterizing nanoscale molecules for many applications in drug discovery, bioanalytics, nanoparticle synthesis, viral targeting, and the basic science of understanding nanoparticle behavior.     

Theoretical investigation of enzymatic hydrolysis of polypeptides in nanofluidic channels

Label-free detection of enzymes using nanofluidic channels requires enzymes to diffuse into a nanochannel and react with substrates already immobilized on the nanochannel surfaces. A theoretical model is necessary to predict the reaction progress in the confined space and translate it to the electrical readouts of the nanochannel. In this paper, enzymatic hydrolysis of polypeptides in nanofluidic channels is considered and a 1-D model is developed that accounts for various reaction kinetics, enzyme diffusion and non-specific adsorption. The polypeptides have multiple cleavage sites which can be cleaved in different orders depending on the type of enzyme. Here it is shown that this process creates two types of reaction fronts inside the nanochannel which advance linearly with time once they are fully developed. Such constant reaction rates can be predicted by an analytical model. The numerical simulations are validated against the experimental results of trypsin–polylysine reaction in nanochannels, and a good agreement between the two is observed. This study deepens our understandings of enzymatic reactions in nanoscale-confined spaces and can guide the development of a fast-response, label-free enzyme sensor based on nanochannels.     

Remote stabilization over fading channels

In this paper, we study the problem of remote mean square stabilization of a MIMO system when independent fading channels are dedicated to each actuator and sensor. We show that the stochastic variables responsible for the fading can be seen as a source of model uncertainty. This view leads to robust control analysis and synthesis problems with a deterministic nominal system and a stochastic, structured, model uncertainty. As a special case, we consider the stabilization over Erasure or drop-out channels. We show that the largest probability of erasure tolerable by the closed loop is obtained from solving a robust control synthesis problem. In more general terms, we establish that the set of plants which can be stabilized by linear controllers over fading channels is fundamentally limited by the channel generated uncertainty. We show that, the notion of mean square capacity, defined for a single channel in the loop, captures this limitation precisely and characterizes equivalence classes of channels within the class of memoryless fading channels.     

基于高通量显微成像及分析技术的 DNA 重排研究

直接的重复序列广泛地存在于真核和原核细胞基因组中,并且与多种疾病（如遗传性神经肌肉神经退行性疾病等）相关,因此定量重复序列的删除变得非常重要。结合高通量显微成像和分析技术,该文设计了基于三色荧光报告系统的方法来定量重复序列删除的发生。结果显示,在铜绿假单胞菌中,重复序列的删除频率在 recA 基因缺失突变株中明显降低,而 RadA 蛋白和 UvrD 蛋白的缺失则会提高重复序列的删除频率,并且重复序列的删除与细菌的生长率和启动子等因素无关。该研究有助于加深对直接重复序列相关问题的理解,并为直接重复序列删除定量提供了新的方法。     

Detection of oscillations in control loops in irrigation channels

Oscillation in irrigation channels have many undesired consequences such as increased erosion on channel banks, reduced level of service to farmers, increased wear and tear on mechanical equipments, etc. It is therefore important to detect oscillations early. In this paper computationally inexpensive algorithms for detection of oscillatory control loops are applied to operational data from six consecutive pools of an irrigation channel. The algorithms performed well and detected the control loops which gave oscillatory responses. Moreover, the controller which caused the oscillations was also identified. As there can be many control loops in an irrigation channel, methods which are able to detect and locate the cause of oscillations are of great value in the operation of irrigation channels.     

DNA计算与DNA计算机研究进展与展望

DNA computing is a new method based on biochemical reactions and molecular biology technology.The paper first introduces the basic principle and advantages of DNA computing, and then surveys DNA computing and DNA computer, finally, points out current existing problems and future search directions of DNA computing and DNA computer.     

Molecular dynamics simulations of oscillatory flows in microfluidic channels

In this paper we apply the direct non-equilibrium molecular dynamics technique to oscillatory flows of fluids in microscopic channels. Initially, we show that the microscopic simulations resemble the macroscopic predictions based on the Navier–Stokes equation very well for large channel width, high density and low temperature. Further simulations for high temperature and low density show that the non-slip boundary condition traditionally used in the macroscopic equation is greatly compromised when the fluid–wall interactions are the same as the fluid–fluid interactions. Simulations of a system with very narrow channel width confirm earlier findings of Poiseuille flow, namely, that the velocity profiles are modulated. We find that these modulations cannot be explained by the local area density model.

A new approach to model virtual channels in interconnection networks

Dealing with virtual channels has always been a critical issue in developing analytical performance models for interconnection networks. Almost all previous studies relied on a method proposed by Dally to capture the effect of virtual channels multiplexing in the performance of interconnection networks. This paper presents a new method to model the effect of virtual channel multiplexing in high-speed wormhole-switched interconnection networks. Dally's method loses its accuracy as the traffic load increases due to blocking nature of wormhole-switched networks. Our new method is based on a finite capacity queue, M/G/1/V and comparing to Dally's method achieves a higher degree of accuracy under low, moderate and high traffic loads. Furthermore, its simplicity eases its employment under different network conditions and setup. The presented model is validated by means of an event driven simulator and a detailed comparison with Dally's method is presented.     

Algorithms for leak detection, estimation, isolation and localization in open water channels

In this paper, a methodology for leak detection and isolation in open water channels is proposed. It consists of on-line leak detection and off-line leak isolation, estimation and localization. The on-line leak detection is carried out pool by pool using local information only, and a comparison between three leak detection methods in terms of detection performance and ease of implementation is presented. Information from neighboring pools is used to distinguish the effect of a leak from sensor faults. The proposed methods were tested on real experimental data from the Coleambally Channel no. 6 in Australia and showed good performance.     

Threading splines through 3D channels

Given a polygonal channel between obstacles in the plane or in space, we present an algorithm for generating a parametric spline curve with few pieces that traverses the channel and stays inside. While the problem without emphasis on few pieces has trivial solutions, the problem for a limited budget of pieces represents a nonlinear and continuous (‘infinite’) feasibility problem. Using tight, two-sided, piecewise linear bounds on the potential solution curves, we reformulate the problem as a finite, linear feasibility problem whose solution, by standard linear programming techniques, is a solution of the channel-fitting problem. The algorithm allows the user to specify the degree and smoothness of the solution curve and to minimize an objective function, for example, to approximately minimize the curvature of the spline. We describe in detail how to formulate and solve the problem, as well as the problem of fitting parallel curves, for a spline in Bernstein-Bézier form.     

DNA计算中的数据与计算模型

对DNA计算的通用性及单链、双链、粘性末端、发夹、质粒、k-臂DNA分子等各种数据作了简单介绍,并对基于DNA分子结构特性和基于DNA计算机研制过程两个方面的DNA计算模型进行了分析对比。针对各种不同的DNA数据及特性,提出了混合DNA计算模型的研究思路,并从不同角度论述了混合DNA计算模型的可行性。     

Control of LTI plants over erasure channels

This paper studies linear time-invariant (LTI) control architectures for LTI plants when communication takes place over a scalar erasure channel. Assuming i.i.d. data dropouts, we first show that such a channel is equivalent, in a second order moment sense, to an additive white noise channel subject to an instantaneous signal-to-noise ratio constraint. This key result is then exploited in two ways: First, we use it to characterize the set of all LTI controllers that achieve mean square stability in control architectures closed over scalar erasure channels. Second, we use it to show that the optimal design of LTI controllers over scalar erasure channels can be carried out by using tools from standard quadratic optimal control theory. We finally apply our results to the dynamic output feedback control of LTI single-input single-output (SISO) plants subject to data dropouts. In this case, we are able to establish closed form necessary and sufficient conditions on the minimal successful transmission probability that allows one to design mean square stabilizing controllers.     

Application of continuum mechanics to fluid flow in nanochannels

A fundamental understanding of the transport phenomena in nanofluidic channels is critical for systematic design and precise control of such miniaturized devices towards the integration and automation of Lab-on-a-chip devices. The goal of this study is to develop a theoretical model of electroosmotic flow in nano channels to gain a better understanding of transport phenomena in nanofluidic channels. Instead of using the Boltzmann distribution, the conservation condition of ion number and the Nernst equation are used in this new model to find the ionic concentration field of an electrolyte solution in nano channels. Correct boundary conditions for the potential field at the center of the nanochannel and the concentration field at the wall of the channel are developed and applied to this model. It is found that the traditional plug-like velocity profile is distorted in the center of the channel due to the presence of net charges in this region opposite to that in the electrical double layer region. The developed model predicted a trend similar to that observed in experiments reported in the literature for the area-average velocity versus the ratio of Debye length to the channel height.     

多信道无线通信功率分配的最优化决策

研究了基于有损Gilbert-Elliott信道的多信道无线通信功率分配的最优化决策问题,利用部分可观测的马尔可夫决策过程（POMDP）和数学语言建立并描述理论模型,提出了具有一般性的功率分配方案,并给出问题的最优决策的各项性质和特征。在三维信道的通信系统上,进一步给出最优决策的空间结构,利用线性规划仿真验证了其正确性,并分析了最优决策随信道转移概率的变化趋势。     

Scheduler-based state estimation over multiple channels networks

We investigate the remote state estimation problem for networked systems over parallel noise-free communication channels. Due to limited network capabilities in practical network environments, communication schedulers are implemented at the transmit side of each subchannel to promote resource efficiency. Specifically, the processed signals are transmitted only when it is necessary to provide the real-time measurements to the remote estimator. The recursive approximate minimum mean-square error estimator is established to restore the state vector of a target plant by utilizing the scheduled transmission signals. All the information coming from the individual subchannels, even if no measurement is sent, will contribute to improve the estimation performance in an analytical form. Finally, a numerical example is given to illustrate the effectiveness of the main results.     

混合信道下译码转发中继系统性能研究

针对中继协作系统,研究瑞利信道和Nakagami-◢m◣信道的混合信道下解码转发（decode-and-forward）中继系统性能。结合信息传输过程中可能发生的数据平均误包率,推导出以源节点和中继节点的调制等级为设计变量的双中继端到端频谱效率表达式以及系统稳定性表达式,同时还分析了不同信道参数◢m◣对于链路频谱效率以及系统稳定性的影响,对表达式进行高阶变量推导演变可得出多中继频谱效率表达式及系统稳定性表达式,最后通过仿真验证了端到端表达式所得结果优于传统的自适应算法。     

DNA 数据存储中 DNA 保存技术的研究进展与挑战

数据信息的规模呈指数级增长与现有存储介质储存能力不足的矛盾日益凸显,亟需通过开发新型介质解决相应问题。DNA 基于其数据存储密度超高、能耗低及寿命长等特点,作为一种新兴的数据存储媒介备受关注,尤其在海量“冷数据”存储方面,有望替代现有存储方式。在数据存储过程中,DNA 的有效保存是其中重要的一环,该环节直接影响数据的存储密度、稳定性、存储时间,以及数据的写入和读取。针对目前文献中关于 DNA 保存技术的介绍较少,该文综述了数据存储中 DNA 保存技术的研究进展和策略,讨论了现有的 DNA 保存技术应用在 DNA 数据存储中面临的困难与挑战,对 DNA 数据存储的实现方式进行了展望。     

Multiplying with DNA

A functional machine is not only an assembly of parts, but also an assembly of processes. The processing of each part must obey laws that respect to the property of this part. For example, building any kind of computer entails selecting appropriate components and assembling their properties to function in computation. Here, we describe computation using a DNA strand as the basic unit and we have used this unit to achieve the function of multiplication. We exploit the phenomenon of DNA hybridization, in which each strand can represent two individual units that can pair to form a single unit. We represent the numbers we multiply in binary, with different lengths representing each digit present in the number. In principle, all combinations of the numbers will be present in solution. Following hybridization, there is present a collection of duplex molecules that are tailed by single-stranded ends. These intermediates are converted to fully duplex molecules by filling in the ends with DNA polymerase. The lengths that are present represent the digits that are present, and they may be separated by denaturing PAGE. The results give a series of bands for each power of two. The number of bands in the size domain for a particular power of two is converted to binary and the sum of all present bands is then added together. Experimentally, the result of this process always yields the correct answer.