Dispersion in electroosmotic flow generated by oscillatory electric field interacting with oscillatory wall potentials

An analytical study is presented in this article on the dispersion of a neutral solute released in an oscillatory electroosmotic flow (EOF) through a two-dimensional microchannel. The flow is driven by the nonlinear interaction between oscillatory axial electric field and oscillatory wall potentials. These fields have the same oscillation frequency, but with disparate phases. An asymptotic method of averaging is employed to derive the analytical expressions for the steady-flow-induced and oscillatory-flow-induced components of the dispersion coefficient. Dispersion coefficients are functions of various parameters representing the effects of electric double-layer thickness (Debye length), oscillation parameter, and phases of the oscillating fields. The time–harmonic interaction between the wall potentials and electric field generates steady as well as time-oscillatory components of electroosmotic flow, each of which will contribute to a steady component of the dispersion coefficient. It is found that, for a thin electric double layer, the phases of the oscillating wall potentials will play an important role in determining the magnitude of the dispersion coefficient. When both phases are zero (i.e., full synchronization of the wall potentials with the electric field), the flow is nearly a plug flow leading to very small dispersion. When one phase is zero and the other phase is π,?the flow will be sheared to the largest possible extent at the center of the channel, and such a sharp velocity gradient will lead to the maximum possible dispersion coefficient.     

Micromixing and flow manipulation with polymer microactuators

Polymer actuators based on Gold/PolyPyrrole bilayers were microfabricated and their properties tested for flow promoting in the microdomain. When implemented in microchannels these actuators behaved as efficient micromixers for both, flow-through and stagnant conditions. Particle tracking experiments and numerical simulations of cross-sectional domains verified the capacity of these devices to promote complex, high velocity flows with chaotic advection properties in microscopic environments. Thinner devices could be actuated at higher frequencies than thicker devices, up to 10 Hz for 10 nm thick Gold layers with voltages not over 0.6 V (vs. Ag/AgCl), which led to enhanced flow generation properties. The results herein demonstrate that these actuators are practical candidates for fluid manipulation in the microdomain (for applications such as micromixing and pumping, and possibly even for propelling of swimming microdevices).     

An electrokinetic mixer driven by oscillatory cross flow

An electrokinetic mixer driven by oscillatory cross flow has been studied numerically as a means for generating chaotic mixing in microfluidic devices for both confined and throughput mixing configurations. The flow is analyzed using numerical simulation of the unsteady Navier–Stokes equations combined with the tracking of single and multi-species passive tracer particles. First, the case of confined flow mixing is studied in which flow in the perpendicular channels of the oscillatory mixing element is driven sinusoidally, and 90° out of phase. The flow is shown to be chaotic by means of positive effective (finite time) Lyapunov exponents, and the stretching and folding of material lines leading to Lagrangian tracer particle dispersion. The transition to chaotic flow in this case depends strongly on the Strouhal number (St), and weakly on the ratio of the cross flow channel length to width (L/W). For L/W = 2, the flow becomes appreciably chaotic as evidenced by visual particle dispersion at approximately St = 0.32, and the transitional value of St increases slightly with increasing aspect ratio. A peak degree of mixing on the order of 85% is obtained for the range of parameter values explored here. In the second phase of the analysis, the effect of combining a fixed throughput flow with the oscillatory cross channel motion for use in a continuous mixing operation is examined in a star cell geometry. Chaotic mixing is again observed, and the characteristics of the downstream dispersion patterns depend mainly on the Strouhal number and the (dimensionless) throughput rate. In the star cell, the flow becomes appreciably chaotic as evidenced by visual particle dispersion at approximately St = 1, slightly higher than for the case of cross cell. The star cell mixing behavior is marked by the convergence of the degree of mixing to a plateau level as the Strouhal number is increased at fixed flow rate. Degree of mixing values from 70 to 80% are obtained indicating that the continuous flow is bounded by the maximum degree of mixing obtained from the confined flow configuration.

Noise generated by turbulent flow over forward facing steps

In this study, aeroacoustical characteristics of forward facing steps (FFSs) subject to turbulent freestream are assessed by means of linearized Euler equations (LEE). The investigated parameters are the velocity scaling of SPL and the different construction of sharp edge of FFSs. In addition to numerical simulation, an analytical vortex injection method and flow measurement are also utilized for validation purposes. It is found that the sound signal obtained from the simulation and from the theoretical approach at prescribed positions are of same phases and have comparable amplitudes. Moreover, it is reported that sound intensity scales with 5.8th power of freestream velocity. This result agrees well with the theoretical result of Curle et al. Sound radiation pattern is found to have dipole character lying horizontally. Finally, it is shown that one gains reduction in SPL by replacing sharp edged FFS with the half round edged one. Furthermore, round edged FFS, i.e. r=h, is more silent than half round edged FFS at the same frequency level.     

A second-order analytic solution for oscillatory wind-induced flow in an idealized shallow lake

We present a second-order analytic solution to the nonlinear depth-integrated shallow water equations for free-surface oscillatory wind-driven flow in an idealized lake. Expressing the solution as an asymptotic expansion in the dimensionless wave amplitude (ζ/h), which is considered to be a small parameter, enables simplification of the governing equations and permits the use of a perturbation approach to solve them.This analytic solution provides a benchmark for testing numerical models. In particular, the main merit of this solution is that it accounts for advective effects, which are typically omitted from analytic solutions of two-dimensional free surface flow. In order to retain these effects in an analytic solution, we restrict our attention to forcing from a monochromatic wind stress, consider a constant depth rectangular lake, and simplify the governing equations by omitting the Coriolis and eddy viscosity terms and using a linearised friction factor. As such, the analytic solution is of limited use for considering real world problems. Due to the complexity of the analytic solution computer code for this solution is available online.Our solution is valid for cases where changes in the water surface level are small compared with the depth of the lake, and the advective terms in the momentum equations are small compared with acceleration terms. We examine the validity of these assumptions for three test cases, and compare the second-order analytic solution to numerical results to verify an existing hydrodynamic model.     

Advanced control of a continuous oscillatory flow crystalliser

This paper presents the application and challenges of achieving Model Predictive Control (MPC) on two continuous oscillatory baffled crystallisation reactors, delivering precise product quality control in the face of raw material fluctuations. A key advantage of MPC is that it effectively deals with multivariable interactions and constraints that appear within the continuous crystallisation process. Using a flexible real-time software package, a control scheme is proposed that incorporates three MPC blocks for controlling reactor cooling profile, API (Active Pharmaceutical Ingredient) concentration and crystal size distribution, respectively. Furthermore, the solution is customisable and transferable to different crystallisation reactors as well as various APIs.     

Micromixing by pneumatic agitation on continually rotating centrifugal microfluidic platforms

A highly effective pneumatic technique for mixing liquids on centrifugal microfluidic platforms is demonstrated and characterized. While a centrifugal platform is rotating, a stream of compressed gas is used to agitate liquids on the platform. This technique is implemented in a non-contact fashion and allows mixing without the need to alter the rotational frequency or direction of the centrifugal platform. Pneumatic agitation causes rapid mixing of the liquids and achieves homogeneity in 11.2?±?1.2?s while rotating at 450?rpm (7.5?Hz), a 30-fold improvement compared to conventional mixing by interfacial diffusion. The mixing operation is shown to be equally effective when implemented over a range of rotational frequencies from 450?rpm (7.5?Hz) to 1,500?rpm (25?Hz).     

Discovering traffic congestion through traffic flow patterns generated by moving object trajectories

The discovery of moving object trajectory patterns representing high traffic density has been covered in various works using diverse approaches. These models are useful in areas such as transportation planning, traffic monitoring, and advertising on public roads. However, though studies tend to recognize the importance of these types of patterns in utility, they usually do not consider traffic congestion as a particular condition of high traffic. In this work, we present a model for the discovery of high traffic flow patterns in relation to traffic congestion. This relationship is represented in terms of traffic that is shared between different sectors of the pattern, making it possible to identify traffic flow situations causing congestion. We also complement this model by discovering alternative paths for the severe traffic depicted in these patterns. These alternative paths depend on traffic level and location inside the road network. Depending on the traffic conditions, alternative paths are commonly sought by drivers when they are approaching a traffic jam, in order to mitigate the effects of traffic congestion. We compare these models with related work from similar areas and validate them by conducting experiments using real data. We describe discovered patterns related to the main elements of the road network in the dataset and show their advantages in comparison to related models. Based on the displayed metrics, the algorithms’ implementation offers good performance execution for the given dataset volume. The results presented confirm the usefulness of the proposed patterns as a tool that helps to improve traffic, allowing the identification of problems and possible alternatives.     

Scattering of seismic waves generated by an irregular seabed

The changes in the seismic response due to the presence of an irregular elastic seabed, and/or the presence of a water-filled inclusion located under the elastic seabed surface, in the presence of a dilatational spatially harmonic line source, is assessed. The seabed surface deformations and the water-filled inclusions are bi-dimensional.The solution is obtained using the Boundary Elements Method for a wide range of frequencies and spatially harmonic line sources, which are then used to compute the time series by means of fast inverse Fourier transforms.     

Numerical study of the viscous flow in oscillatory spherical annuli

The method of fractional steps is applied for investigating the viscous flow field in the oscillatory spherical annuli. The numerical solution obtained enlarges the intervals of the frequency parameter M and amplitude of the torsional oscillations ε in comparison with known solutions. Typical flow fields are shown graphically.     

Determining three-dimensional motion and structure from optical flow generated by several moving objects

A new approach for the interpretation of optical flow fields is presented. The flow field, which can be produced by a sensor moving through an environment with several independently moving, rigid objects, is allowed to be sparse, noisy, and partially incorrect. The approach is based on two main stages. In the first stage, the flow field is partitioned into connected segments of flow vectors, where each segment is consistent with a rigid motion of a roughly planar surface. In the second stage, segments are grouped under the hypothesis that they are induced by a single, rigidly moving object. Each hypothesis is tested by searching for three-dimensional (3-D) motion parameters which are compatible with all the segments in the corresponding group. Once the motion parameters are recovered, the relative environmental depth can be estimated as well. Experiments based on real and simulated data are presented.     

Relative similarity preserving bitwise weights generated by an adaptive mechanism

Due to its high query speed and low storage cost, binary hashing has been widely used in approximate nearest neighbors (ANN) search. However, the binary bits are generally considered to be equal, which causes data points with different codes to share the same Hamming distance to the query sample. To solve the above distance measure ambiguity, bitwise weights methods were proposed. Unfortunately, in most of the existing methods, the bitwise weights and the binary codes are learnt separately in two stages, and their performances cannot be further improved. In this paper, to effectively address the above issues, we propose an adaptive mechanism that jointly generate the bitwise weights and the binary codes by preserving different types of similarity relationship. As a result, the binary codes are utilized to obtain the initial retrieval results, and they are further re-ranked by the weighted Hamming distance. This ANN search mechanism is termed AR-Rank in this paper. First, this joint mechanism allows the bitwise weights and the binary codes to be used as mutual feedback during the training stage, and they are well adapted to one other when the algorithm converges. Furthermore, the bitwise weights are required to preserve the relative similarity which is consistent with the nature of ANN search task. Thus, the data points can be accurately re-sorted based on the weighted Hamming distances. Evaluations on three datasets demonstrate that the proposed AR-Rank retrieval system outperforms nine state-of-the-art methods.

     

Sequence memory based on an oscillatory neural network

In the brain,the discrete elements in a temporal order is encoded as a sequence memory.At the neural level,the reproducible sequence order of neural activity is very crucial for many cases.In this paper,a mechanism for oscillation in the network has been proposed to realize the sequence memory.The mechanism for oscillation in the network that cooperates with hetero-association can help the network oscillate between the stored patterns,leading to the sequence memory.Due to the oscillatory mechanism,the firing history will not be sampled,the stability of the sequence is increased,and the evolvement of neurons’states only depends on the current states.The simulation results show that neural network can effectively achieve sequence memory with our proposed model.     

Wall profile of thick photoresist generated via contact printing

High-aspect-ratio patterns generated by direct contact or proximity printing in LIGA and other similar processes have recently gained great interest in the field of MEMS. One key issue for a successful thick-film lithography Is the control of wall profile. This paper deals with this issue based on an approximation including the effects of Fresnel diffraction and exposure kinetics for various types of photoresist. This approach leads to simple but practical formulas for estimating the wall profile and resolution for the near-field lithography of thick photoresist     

Simulation of surface generated in abrasive flow machining process

For the control of abrasive flow machining (AFM) process, it is important to understand the mechanics of generation of its surface profile. This paper describes the analysis and simulation of profile of finished surface and material removal by the interaction of abrasive grains with workpiece. The abrasive grains are randomly distributed in media depending upon their percentage concentration and mesh size. The results predicted from simulation and obtained from response surface analysis (or experiments) are compared to explain the relative importance of AFM parameters. The generated surface profile and material removal are the function of number of cycles, percentage concentration and mesh size of abrasives, reduction ratio and extrusion pressure applied.     

Numerical study on onset of oscillatory thermocapillary flow in rectangular liquid pool

Thermocapillary flow in a rectangular liquid pool of large Prandtl fluid(Pr=105.6) is numerically studied in microgravity.Oscillatory thermocapillary flow arises when the imposed temperature difference between the sidewalls exceeds a critical value.The fluctuations of the oscillatory flow,accompanied by the propagation of the hydrothermal wave from the cold sidewall to the hot one,are much smaller than the time-averaged velocity and temperature fields.The corresponding disturbance cells arise in the centre ...     

The study of atmospheric ice-nucleating particles via microfluidically generated droplets

Ice-nucleating particles (INPs) play a significant role in the climate and hydrological cycle by triggering ice formation in supercooled clouds, thereby causing precipitation and affecting cloud lifetimes and their radiative properties. However, despite their importance, INP often comprise only 1 in 10³–10⁶ ambient particles, making it difficult to ascertain and predict their type, source, and concentration. The typical techniques for quantifying INP concentrations tend to be highly labour-intensive, suffer from poor time resolution, or are limited in sensitivity to low concentrations. Here, we present the application of microfluidic devices to the study of atmospheric INPs via the simple and rapid production of monodisperse droplets and their subsequent freezing on a cold stage. This device offers the potential for the testing of INP concentrations in aqueous samples with high sensitivity and high counting statistics. Various INPs were tested for validation of the platform, including mineral dust and biological species, with results compared to literature values. We also describe a methodology for sampling atmospheric aerosol in a manner that minimises sampling biases and which is compatible with the microfluidic device. We present results for INP concentrations in air sampled during two field campaigns: (1) from a rural location in the UK and (2) during the UK’s annual Bonfire Night festival. These initial results will provide a route for deployment of the microfluidic platform for the study and quantification of INPs in upcoming field campaigns around the globe, while providing a benchmark for future lab-on-a-chip-based INP studies.     

On the instability of an oscillatory distributed parameter system

An oscillatory distributed. parameter system with state dependent Gaussian white noise is dealt with. By using a stochastic Liapunov’-type functional, it is shown that the oscillations of the system diverge. Also On estimate on the rate of divergence is given.