Characterization of DNA hybridization kinetics in a microfluidic flow channel

In this investigation we report on the influence of volumetric flow rate, flow velocity, complementary DNA concentration, height of a microfluidic flow channel and time on DNA hybridization kinetics. A syringe pump was used to drive Cy3-labeled target DNA through a polydimethylsiloxane (PDMS) microfluidic flow channel to hybridize with immobilized DNA from the West Nile Virus. We demonstrate that a reduction of channel height, while keeping a fixed volumetric flow rate or a fixed flow velocity, enhances mass transport of target DNA to the capture probes. Compared to a passive hybridization, the DNA hybridization in the microfluidic flow channel generates higher fluorescence intensities for lower concentration of target DNA during the same fixed period of time. Within a fixed 2 min time period the fastest DNA hybridization at a 50 pM concentration of target DNA is achieved with a continuous flow of target DNA at the highest flow rate and the lowest channel height.     

Effects of channel surface finish on blood flow in microfluidic devices

The behaviour of blood flow in relation to microchannel surface roughness has been investigated. Special attention was focused on the techniques used to fabricate the microchannels and on the apparent viscosity of the blood as it flowed through these microchannels. For the experimental comparison of smooth and rough surface channels, each channel was designed to be 10 mm long and rectangular in cross-section with aspect ratios of ≥100:1 for channel heights of 50 and 100 μm. Polycarbonate was used as the material for the device construction. The shims, which created the heights of the channels, were made of polyethylene terephthalate. Surface roughnesses of the channels were varied from R _z of 60 nm to 1.8 μm. Whole horse blood and filtered water were used as the test fluids and differential pressures ranged from 200 to 5,000 Pa. The defibrinated horse blood was treated further to prevent coagulation. The results indicate that a surface roughness above an unknown value lowers the apparent viscosity of blood dramatically due to boundary effects. Furthermore, the roughness seemed to influence both water and whole blood almost equally. A set of design rules for channel fabrication is also presented in accordance with the experiments performed.     

弹性支撑浅拱的非线性动力行为分析

本文研究了两端转角均为转动弹簧支撑的铰支浅拱在外激励作用下的非线性动力学行为.基于弹性支撑浅拱的基本动力控制方程,采用多尺度法对内共振进行了摄动分析,并得到了极坐标形式的平均方程.弹性约束的刚度通过特征方程影响结构的自振频率和模态,且与平均方程的相关系数一一对应,文中还以最低两阶模态之间1:1内共振为对象进行了数值分析.结果显示系统存在模态交叉与转向两种内共振形式,另一方面结构参数处于某一范围之内时外激励激发的模态作用可导致出现准周期运动和混沌运动.     

Identification of boundary conditions in a nonlinear shallow water flow

In this paper, we present sufficient smoothness results on the solution of a nonlinear shallow water problem in order to obtain an existence result for the associated adjoint problem. We introduce a necessary but not sufficient existence condition for the functional minimum. The control is made on the velocity boundary condition, in considering observations at isolated points. Moreover, we give a set of numerical results obtained in a real situation.     

Asymptotic nonlinear and dispersive pulsatile flow in elastic vessels with cylindrical symmetry

The asymptotic derivation of a new family of one-dimensional, weakly nonlinear and weakly dispersive equations that model the flow of an ideal fluid in an elastic vessel is presented. Dissipative effects due to the viscous nature of the fluid are also taken into account. The new models validate by asymptotic reasoning other non-dispersive systems of equations that are commonly used, and improve other nonlinear and dispersive mathematical models derived to describe the blood flow in elastic vessels. The new systems are studied analytically in terms of their basic characteristic properties such as the linear dispersion characteristics, symmetries, conservation laws and solitary waves. Unidirectional model equations are also derived and analysed in the case of vessels of constant radius. The capacity of the models to be used in practical problems is being demonstrated by employing a particular system with favourable properties to study the blood flow in a large artery. Two different cases are considered: A vessel with constant radius and a tapered vessel. Significant changes in the flow can be observed in the case of the tapered vessel.     

The dynamic stability of the flow in a meander channel

The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river dynamics.The transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent v...     

微沟道内两相流速比对液滴形成的影响

研究了流聚焦微沟道内不同两相流速比对单分散性液滴形成的影响.不相混容的两相系统能够快速、周期性地形成液滴,液滴的形态和生成率随着油相速度的变化而改变.研究采用模拟软件COMSOL Mutiphysics,模拟了不同流速下液滴的形成过程,并通过实验进行了验证,从流体动力学的角度解释了其物理机制.所得结论为在流聚焦微沟道内获得分散性良好且大小可控的液滴提供了理论和数据支持.     

Design of microfluidic channel networks with specified output flow rates using the CFD-based optimization method

We report an effective, easy-to-use, computational fluid dynamics-based optimization method for designing purely resistive microfluidic networks with desired flow rates at user-specified outlets. The detailed topology and shape of the microchannel networks are obtained by minimizing the fluidic resistance of channels under a fixed driving flow rate at the inlet. This proposed method allows flexibility in setting up the relative positions among the inlet and outlets so that the layout of channel networks can be compactly adjusted based on the specific design requirements.     

Measurement and modeling of pulsatile flow in microchannel

An experimental study of pulsatile flow in microchannel is reported in this paper. Such a study is important because time-varying flows are frequently encountered in microdevices. The hydraulic diameter of the microchannel is 144 μm and deionized water is the working fluid. The pressure drop across the microchannel as a function of time is recorded, from which the average and r.m.s. pressure drops are obtained. The experiments have been performed in the quasi-steady flow regime for a wide range of flow rate, frequency of pulsations, and duty cycle. The results suggest that the pressure with pulsations lies between the minimum and maximum steady state pressure values. The average pressure drop with pulsation is approximately linear with respect to the flow rate. The theoretical expression for pressure has also been derived wherever possible and the experimental data is found to lie below the corresponding theoretical values. The difference with respect to the theoretical value increases with an increase in frequency and a decrease in flow rate, with a maximum difference of 32.7%. This is attributed to the small size of the microchannel. An increase in frequency of square waveform leads to a larger reduction in pressure drop as compared to rectangular waveform, irrespective of the duty cycle. The results can be interpreted with the help of a first-order model proposed here; the model results are found to compare well against the experimental results. A correlation for friction factor in terms of the other non-dimensional governing parameters is also proposed. Experimental study of mass-driven pulsatile flow in microchannel is being conducted for the first time at these scales and the results are of both fundamental and practical importance.     

Size-selective separation of magnetic nanospheres in a microfluidic channel

This paper reported an efficient method to size-selective separate magnetic nanospheres using a self-focusing microfluidic channel equipped with a permanent magnet. Under external magnetic field, the magnetophoresis force exerted on particles leads to size-dependent deflections from their laminar flow paths and results in effective particles separation. By adjusting the distance between magnet and main path of channel, we obtained two monodisperse nanosphere samples (Ca. 90 nm, Ca. 160 nm) from polydispersing particles solution whose diameters varied from 40 to 280 nm. Based on the magnetostatic and laminar flow models, numerical simulations were also used to predict and optimize the nanospheres migrations. Two thresholds of particles diameters were obtained by the simulations and diverse at each position of magnet. Therefore, appropriate position of the magnet could be determined at a certain particle sizes’ range when the flow rate of the two inlets remains unchanged.     

Self-organization in the basal ganglia with modulation of reinforcement signals

Self-organization is one of fundamental brain computations for forming efficient representations of information. Experimental support for this idea has been largely limited to the developmental and reorganizational formation of neural circuits in the sensory cortices. We now propose that self-organization may also play an important role in short-term synaptic changes in reward-driven voluntary behaviors. It has recently been shown that many neurons in the basal ganglia change their sensory responses flexibly in relation to rewards. Our computational model proposes that the rapid changes in striatal projection neurons depend on the subtle balance between the Hebb-type mechanisms of excitation and inhibition, which are modulated by reinforcement signals. Simulations based on the model are shown to produce various types of neural activity similar to those found in experiments.     

稀疏信道下OFDM信号的迭代检测方法

提出了一种适用于稀疏信道环境的OFDM信号迭代检测方法。该方法采用导频进行初始化信道估计,使用数学期望最大（EM）算法迭代检测OFDM信号。该方法需要已知信道的路径时延信息、噪声方差和信道冲击响应的协方差矩阵,因此同时给出了这些参数的估计方法。仿真结果证明了这种迭代算法的有效性,而且使用估计的信道参数时的系统性能和理想参数条件下的性能接近。     

卫星非线性信道下非对称MAPSK优化设计

为了克服非线性失真对卫星通信系统的影响,首先论述了卫星非线性信道的特性,提出了在调制端对MAPSK映射星座进行非对称设计,在解调端采用标准的解映射星座进行解调的方法。通过仿真试验验证了此方法能够补偿非线性失真对MAPSK调制信号带来的相位和幅度的影响。     

Transient flow behavior of complex fluids in microfluidic channels

The ongoing development of microfluidic devices involves the use of highly complex fluids, even of multiphase systems. Despite the great achievements in the development of numerous applications, there is still a lack in the complete understanding of the underlying physics of the observed macroscopic effects. One prominent example is the flow through benchmark contractions where micro- and even macroscopic explanations of some of the occurring flow patterns are still missing. Here, we study the development of the flow profiles of shear thinning semi-dilute polymer solutions in microfluidic planar abrupt contraction geometries. Flow profiles along the narrow channel part are obtained by μ-PIV measurements, whereby the pressure drop along the microfluidic channel as well as the local transient viscosities downstream to the orifice are computed. A relaxation process of the flow profiles from an initially parabolic shape to the flattened steady-state flow profile is observed and traced back to the polymer relaxation.     

Numerical study of the flow over shallow cavities

This paper reports on a series of numerical simulations of both laminar and turbulent flows over shallow cavities. For the turbulent case the influences of the following parameters were considered: (i) cavity aspect ratios, (ii) turbulence level of the oncoming flow, and (iii) Reynolds number. Several important results and conclusions are reported. We have found that for the turbulent case the external flow touches the floor of the cavity, and this depends on a specific value of each of these parameters. This condition has an important impact upon convective effects inside the cavity. The mathematical model corresponds to the incompressible, Reynolds-averaged, Navier-Stokes equations plus a high-Reynolds κ-ε model of turbulence, and the numerical computation is performed using the SIMPLER algorithm.     

Effect of channel geometry on solute dispersion in pressure-driven microfluidic systems

Pressure-driven transport of fluid and solute samples is often desirable in microfluidic devices, particularly where sufficient electroosmotic flow rates cannot be realized or the use of an electric field is restricted. Unfortunately, this mode of actuation also leads to hydrodynamic dispersion due to the inherent fluid shear in the system. While such dispersivity is known to scale with the square of the Peclet number based on the narrower dimension of the conduit (often the channel depth), the proportionality constant can vary significantly depending on its actual cross section. In this article, we review previous studies to understand the effect of commonly microfabricated channel cross sections on the Taylor–Aris dispersion of solute slugs in simple pressure-driven flow systems. We also analyze some recently proposed optimum designs which can reduce the contribution to this band broadening arising from the presence of the channel sidewalls. Finally, new simulation results have been presented in the last section of this paper which describe solutal spreading due to bowing of microchannels that can occur from stresses developed during their fabrication or operation under high-pressure conditions.     

Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation

We demonstrate controlled guiding of nanoliter emulsion droplets of polar liquids suspended in oil along shallow hydrophilic tracks fabricated at the base of microchannels located within microfluidic chips. The tracks for droplet guiding are generated by exposing the glass surface of polydimethylsiloxane (PDMS)-coated microscope slides via femtosecond laser ablation. The difference in wettability of glass and PDMS surfaces together with the shallow step-like transverse topographical profile of the ablated tracks allows polar droplets wetting preferentially the glass surface to follow the track. In this study, we investigate guiding of droplets of two different polar liquids (water/ethylene glycol) with and without surfactant suspended in an oil medium along surface tracks of different depths of 1, 1.5, and 2 \(\upmu\)m. The results of experiments are also verified with computational fluid dynamics simulations. Guiding of droplets along the tracks as a function of the droplet composition and size and the surface profile depth is evaluated by analyzing the trajectories of moving droplets with respect to the track central axis, and conditions for stable guiding are identified. The experiments and numerical simulations indicate that while the track topography plays a role in droplet guiding using 1.5- and 2-\(\upmu\)m deep tracks, for the case of the smallest track depth of 1 \(\upmu\)m, droplet guiding is mainly caused by surface energy modification along the track rather than the presence of a topographical step on the surface. Our results can be exploited to sort passively different microdroplets mixed in the same microfluidic chip, based on their inherent wetting properties, and they can also pave the way for guiding of droplets along reconfigurable tracks defined by surface energy modifications obtained using other external control mechanisms such as electric field or light.     

Numerical simulations of pulsatile non-Newtonian flow in an end-to-side anastomosis model

A potential interaction between the local hemodynamics and the artery wall response has been suggested for vascular graft failure by intimal hyperplasia (IH). Among the various hemodynamic factors, wall shear has been implicated as the primary factor responsible for the development of IH. In order to explore the role of hemodynamics in the formation of IH in end-to-side anastomosis, computational fluid dynamics is employed. To validate the numerical simulations, comparisons with existing experimental data are performed for both steady and pulsatile flows. Generally, good agreement is observed with the velocity profiles whereas some discrepancies are found in wall shear stress (WSS) distributions. Using the same end-to-side anastomosis geometry, numerical simulations are extended using a femoral artery waveform to identify the possible role of unsteady hemodynamics. In the current simulations, Carreau–Yasuda model is used to account for the non-Newtonian nature of the blood. Computations indicated a disturbed flow field at the artery-graft junction leading to locally elevated shear stresses on the vascular wall. Furthermore, the shear stress distribution followed the same behavior with oscillating magnitude over the entire flow cycle. Thus, distal IH observed in end-to-side artery-graft models may be caused by the fluctuations in WSS’s along the wall.     

基于深度学习的通信信号自动调制识别技术

基于特征提取和模式识别的多体制通信信号自动调制识别技术是软件无线电领域中的重要研究课题,是复杂电磁环境下频谱管理、频谱检测等非协作通信领域的关键技术之一。提出一种基于深度学习的通信信号调制模式识别算法,应用自编码技术进行特征提取,获得具有较好的抗干扰能力的特征集,然后使用BP神经网络对经过筛选的特征进行分类识别,实现了MQAM通信信号调制模式自动识别。仿真实验结果表明,所提出的方法分类识别效果好,有效提高了数字调制信号自动识别的抗干扰能力。