Non-uniform Channel Research Articles

Properties of cardiac conduction in a cell-based computational model.

The conduction of electrical signals through cardiac tissue is essential for maintaining the function of the heart, and conduction abnormalities are known to potentially lead to life-threatening arrhythmias. The properties of cardiac conduction have therefore been the topic of intense study for decades, but a number of questions related to the mechanisms of conduction still remain unresolved. In this paper, we demonstrate how the so-called EMI model may be used to study some of these open questions. In the EMI model, the extracellular space, the cell membrane, the intracellular space and the cell connections are all represented as separate parts of the computational domain, and the model therefore allows for study of local properties that are hard to represent in the classical homogenized bidomain or monodomain models commonly used to study cardiac conduction. We conclude that a non-uniform sodium channel distribution increases the conduction velocity and decreases the time delays over gap junctions of reduced coupling in the EMI model simulations. We also present a theoretical optimal cell length with respect to conduction velocity and consider the possibility of ephaptic coupling (i.e. cell-to-cell coupling through the extracellular potential) acting as an alternative or supporting mechanism to gap junction coupling. We conclude that for a non-uniform distribution of sodium channels and a sufficiently small intercellular distance, ephaptic coupling can influence the dynamics of the sodium channels and potentially provide cell-to-cell coupling when the gap junction connection is absent.

Low-Energy State Electron Beam in a Uniform Channel

In our earlier work, we showed that a low-energy state of an electron beam exists in a nonuniform channel between two virtual cathodes in a magnetron with diffraction output, which consists of three uniform sections with increasing radius. A uniform axial magnetic field fills the interaction space. This led to magnetron operation with >90% efficiency when combined with a magnetic mirror field at the output end. In this present paper, we show that a low-energy state of an electron beam can be realized in a uniform channel in which an increasing magnetic field is used in order to create a magnetic mirror at the output end. We consider two cases, one where the injected beam current slightly exceeds the space-charge-limiting current and the other where the injected beam current greatly exceeds the space-charge-limiting current. On the time scale of relevance to planned experiments (∼30 ns), when the injected current slightly exceeds the space-charge-limiting current a stationary virtual cathode forms and when the injected current greatly exceeds the space-charge-limiting current the virtual cathode oscillates back and forth.

Obstructed flow field designs for improved performance in vanadium redox flow batteries

In this study, we have investigated the effects of varying flow channel depths and addition of various channel obstructions on the electrochemical performance and pumping power requirements of vanadium redox flow batteries (VRFBs). Specifically, 3D-printed ramps and prismatic obstructions were inserted into the channels of interdigitated flow field (IDFF) and parallel flow field (PFF) designs to observe the effect of non-uniform channel depth on the mass transport properties of open- and closed-ended flow channels. Results were compared with conventional flow field geometries. Integration of ramps into the closed-ended (i.e., IDFF) flow channels resulted in 15% improvement in peak power density (PPD) at a flow rate of 50 mL min−1. Addition of ramps to IDFF has also resulted in a significant 40% drop in required pumping pressure due to guided and gradual delivery of the electrolyte to the electrode plane. In addition, the effects of varying channel depths in open-ended (i.e., PFF) channels were found to be much more drastic with improvements in PPD up to 150%. Overall, findings of this study highlight the significance of varying channel depths on improving the mass transport characteristics of VRFBs and offer an alternative approach for design of high-performance flow cells.

Power generation enhancement in direct methanol fuel cells using non-uniform cross-sectional serpentine channels

Non-uniform cross-sectional designs of serpentine channel in direct methanol fuel cells are systematically studied in the present work. A parametric design is proposed to describe and classify channel geometries whose effects on cell performance are numerically and experimentally analyzed. Numerical results show that the non-uniform converging designs are beneficial for both in- and through-plane methanol transportations, and thus to enhance the peak power generation performance as much as 12% at high-current-density operations. Effectiveness of non-uniform designs for power generation enhancements is also validated by experimental studies which consider various operating conditions, and significant enhancement of power generation (18.4%) is noticed by the usage of non-uniform converging design. Optimal application conditions for the non-uniform converging designs are determined to be the high-current-density operations with high temperatures.

Influences of some engineered factors on IVR-ERVC limits

In-vessel retention (IVR) through passive external reactor vessel cooling (ERVC) has been adopted as one of the key severe accident mitigation strategies for Chinese-designed large-scale advanced passive pressurized water reactor. From the view of thermal load effectiveness, critical heat flux (CHF) of reactor pressure vessel (RPV) out wall has been taken as one of the key criteria for IVR-ERVC feasibility. In order to investigate the ERVC limits, as well as its performance during IVR-ERVC process, a campaign of CHF tests under real plant conditions is conducted on the full-height REPEC-II facility, which has been designed according to the prototypic ERVC configuration and verified following an integrated, hierarchical scaling approach. Based on the abundant results acquired in the tests, it is attempted, in this paper, to summarize and evaluate ERVC performances and trends under various practical engineered conditions. The main evaluation results includes: influences on CHF of RPV out wall with various non-uniform heat load distribution and ERVC channel configurations, effects of subcooling, heating surface conditions (prototypic surface material and its oxidization) and water chemistry on external cooling limits, etc. These are expected to help designers with reliable estimation on impact of some related engineered factors on real IVR-ERVC performance.

Mass transfer and cell performance of a unitized regenerative fuel cell with nonuniform depth channel in oxygen‐side flow field

Mass transfer and cell performance of a unitized regenerative fuel cell with nonuniform depth channel in oxygen‐side flow field

Peristaltic motion of Sisko fluid in an inclined asymmetric tapered channel with nonlinear radiation

Peristaltic pumping of Sisko fluid through the non-uniform asymmetric channel is addressed. Main motivations are given to nonlinear radiation and inclined magnetic field. The perturbation technique and lubrication approach are utilized for development of governing problems and solutions. Resulting equations are solved for velocity, temperature, pressure and stream function. Trapping phenomenon is also observed. Variation of pertinent parameters is plotted and illustrated physically. The larger inclination of the magnetic field leads to a rise in velocity. Moreover, the size of trapping bolus tends to reduce and finally disappears for the larger fluid parameter. To our knowledge, such attempt for linear radiation and without inclined magnetic field does not exist even for both symmetric and asymmetric channels. Further it should be noted that problem remains nonlinear even after utilizing long wavelength and low Reynolds number assumptions.

ECCO: A Novel End-to-End Congestion Control Scheme in Multi-Hop Cognitive Radio Ad Hoc Networks

End-to-end congestion control, aiming to find out how much traffic load offered by the source can be handled by a network, is an essential function of a transport layer protocol. Although various efforts have been made to address the end-to-end congestion control issue in traditional wireless ad hoc networks, these approaches usually lead to excessively long delay for the source node to react to the congestion in cognitive radio (CR) ad hoc network because of the non-uniform channel availability. Thus, the end-to-end throughput suffers significant degradation. In this paper, a novel end-to-end congestion control scheme named ECCO is proposed that considers the unique features in multi-hop CR ad hoc networks, such as spectrum sensing, channel rendezvous, and licensed user activities. The average packet round trip time for multi-hop CR ad hoc networks is derived. In addition, through extensive simulation, it is shown that our proposed novel end-to-end congestion control scheme outperforms the existing congestion control mechanisms in terms of higher end-to-end throughput. To the best of our knowledge, this is the first paper that investigates the end-to-end congestion control issue in multi-hop CR ad hoc networks.

Optimal Design of Multiplier-Less Non-uniform Channel Filters with Successive Approximation of Vectors

Applications such as software-defined radio (SDR) receivers utilize channel filters to isolate the individual frequency bands of different communication standards present in a wideband input signal. Low complexity and sharp transition width are the two important design constraints of channel filters in SDR receivers. Frequency response masking (FRM) with the multiplier-less design is an effective approach for designing sharp filters with low complexity. This paper presents an optimal design for multiplier-less implementation of FRM-based non-uniform channel filters. In the proposed design, multiplier-less channel filters are realized basing upon decomposing their impulse response values in generalized bit planes. This decomposition is based on a vector successive approximation technique in which impulse responses are successively approximated using a dictionary of vectors. The resulting coefficients of channel filters belong to signed sums of powers of two form. The proposed channel filter designs are simulated using MATLAB R2017b, and the results have been compared with the existing ones in order to signify the effectiveness of the proposed design. The simulations show that the proposed channel filter design has low complexity (number of adders) and the design time is considerably low.

Inclined Magnetic Field of Non-uniform and Porous Medium Channel on Couple Stress Peristaltic Flow and application in medical treatment (Knee Arthritis)

The present study analyzes the effect of couple stress fluid (CSF) with the activity of connected inclined magnetic field (IMF) of a non-uniform channel (NUC) through a porous medium (PM), taking into account the sliding speed effect on channel walls and the effect of nonlinear particle size, applying long wavelength and low Reynolds count estimates. The mathematical expressions of axial velocity, stream function, mechanical effect and increase in pressure have been analytically determined. The effect of the physical parameter is included in the present model in the computational results. The results of this algorithm have been presented in chart form by applying the mathematical program.

Practical Pulse-Shaping Waveforms for Reduced-Cyclic-Prefix OTFS

In this paper, we model $M\times N$ orthogonal time frequency space modulation (OTFS) over a $P$ -path doubly dispersive channel with delays less than $\tau _{\max }$ and Doppler shifts in the range $(\nu _{\min },\nu _{\max })$ . We first derive in a simple matrix form the input–output relation in the delay-Doppler domain for practical (e.g., rectangular) pulse-shaping waveforms, next generalize it to arbitrary waveforms. This relation extends the original OTFS input–output approach, which assumes ideal pulse-shaping waveforms that are bi-orthogonal in both time and frequency. We show that the OTFS input–output relation has a simple sparse structure that enables one to use low-complexity detection algorithms. Different from previous work, only a single cyclic prefix is added at the end of the OTFS frame, significantly reducing the overhead, without incurring any penalty from the loss of bi-orthogonality of the pulse-shaping waveforms. Finally, we compare the OTFS performance with different pulse-shaping waveforms, and show that the reduction of out-of-band power may introduce nonuniform channel gains for the transmitted symbols, thus impairing the overall error performance.

Corrigendum to “Optimization of SWCNTs and MWCNTs (single and multi-wall carbon nanotubes) in peristaltic transport with thermal radiation in a non-uniform channel” [J. Mol. Liq. 273(2019) 383–391

• Carbon nanotubes are considered. • Viscosity is taken as a function of temperature. • Effective heat transfer at lower and upper walls are discussed. • Velocity and thermal slip conditions comprises at peristaltic walls. • Thermal radiation effects are taken.

Effect of joule heating and MHD on peristaltic blood flow of Eyring–Powell nanofluid in a non-uniform channel

This paper examines the effect of joule heating and MHD on peristaltic blood flow of a Eyring–Powell nanofluid in a non-uniform channel. The transport equations involve the combined effects of Brownian and Thermophoresis diffusion of nanoparticles. The mathematical modelling is carried out by utilizing long wavelength and low Reynolds number assumptions. The energy equation is modelled by taking joule heating effect. The resulting nonlinear system of partial differential equations is solved for the stream function, velocity, pressure gradient, concentration and temperature distributions with the help of the Homotopy Analysis Method. The effect of various physical parameters on the flow characteristics is shown and discussed with the help of graphs. Pressure gradient gives opposite behaviour with increasing values of Eyring–Powell fluid parameters A and B. Pressure gradient decreases by increasing Hartman number and joule heating. Nanoparticle concentration increases with increasing thermophoresis parameter, but the reverse trend is observed with the effect of Brownian motion parameter.

Transient peristaltic diffusion of nanofluids: A model of micropumps in medical engineering

Peristaltic micro-pumps offer an excellent mechanism for delivery of a variety of medicines including drugs, corneal solutions etc. The surge in deployment of nanoparticles in medicine has provided new potential for such pumps. In light of this we investigate the time-dependent peristaltic flow of nanofluids with diffusive effects through a finite non-uniform channel, this geometry being more representative of real micro-pumps. Creeping flow is taken into account (inertial forces are small compared with viscous forces) i.e., Reynolds number is low (Re <1) and wavelength is also taken to be very large. The Buongiorno formulation for nanofluids is employed with an Oberbeck-Boussinesq approximation. Closed-form solutions are developed for the non-dimensional governing equations subject to physically realistic boundary conditions. Mathematica symbolic software is employed to evaluate the evolution of nanoparticle fraction, temperature, axial velocity, transverse velocity and pressure difference distribution along the length of the pump channel with variation in thermal Grashof number, basic-density (species i.e., mass) Grashof number, Brownian motion parameter and thermophoresis parameter.

Spatially-Coupled Codes for Channels with SNR Variation

Spatially-Coupled Codes for Channels with SNR Variation

MHD Peristaltic Flow of Fractional Jeffrey Model through Porous Medium

The magnetohydrodynamic (MHD) peristaltic flow of the fractional Jeffrey fluid through porous medium in a nonuniform channel is presented. The fractional calculus is considered in Darcy’s law and the constitutive relationship which included the relaxation and retardation behavior. Under the assumptions of long wavelength and low Reynolds number, the analysis solutions of velocity distribution, pressure gradient, and pressure rise are investigated. The effects of fractional viscoelastic parameters of the generalized Jeffrey fluid on the peristaltic flow and the influence of magnetic field, porous medium, and geometric parameter of the nonuniform channel are presented through graphical illustration. The results of the analogous flow for the generalized second grade fluid, the fractional Maxwell fluid, are also deduced as special cases. The comparison among them is presented graphically.

Optimization of SWCNTs and MWCNTs (single and multi-wall carbon nanotubes) in peristaltic transport with thermal radiation in a non-uniform channel

Here peristalsis of Carbon nanotubes is performed between non-uniform propagating waves channel/tube. Viscosity of the material is considered dependent upon temperature here. Thermally radiative aspects are considered through linear term of heat flux. Channel boundaries retain the momentum and thermal slip characteristics. Iijima suggested physical quantities for single and multiple WCNTS are taken. Conservation principles (i.e. Mass, momentum and energy) are used to modeled the flow. Later on lubrication assumptions are utilized to simplified such equations. Exact solution for stream function, velocity and temperature is carried out. Further pressure rise per wavelength is plotted via numerical integration. Effective heat transfer rate is analyzed through bar charts.

Development of in/outflow boundary conditions for MPM simulation of uniform and non-uniform open channel flows

This paper describes the development and application of inflow and outflow boundary conditions (BCs) for the material point method (MPM) in order to simulate fluid flow problems. This corresponds to velocity and pressure controlled BCs. Due to the coupled Lagrangian and Eulerian description of the fluid motion in MPM it is necessary to add and remove material points, with appropriate kinematic properties, to and from the computational domain. The newly-developed BCs have been used to simulate uniform open channel flow and the phenomenon of free overfall in open channels, which is transient conditions leading to non-uniform flow due to a sudden bed level drop. It is shown that the numerical results predict well the flow geometry including end depth ratio, pressure distribution and accelerations, therefore the velocities and displacements.

Wall Properties and Slip Consequences on Peristaltic Transport of a Casson Liquid in a Flexible Channel with Heat Transfer

Abstract In this paper, the peristaltic wave propagation of a Non-Newtonian Casson liquid in a non-uniform (flexible)channel with wall properties and heat transfer is analyzed. Long wavelength and low Reynolds number approximations are considered. Analytical solution for velocity, stream function and temperature in terms of various physical parameters is obtained. The impact of yield stress, elasticity, slip and non-uniformity parameters on the peristaltic flow of Casson liquidare observed through graphs and discussed. The important outcome is that an increase in rigidity, stiffness and viscous damping force of the wall results in the enhancement of the size and number of bolus formed in the flow pattern.

Influence of Inclined Magnetic Field on the Peristaltic Flow of a Jeffrey Fluid in an Inclined Porous Channel

In this paper we have studied the effects of inclined magnetic field, porous medium and wall properties on the peristaltic transport of a Jeffry fluid in an inclined non-uniform channel. The basic governing equations are solved by using the infinite wave length and small Reynolds number assumptions. The analytical solutions have obtained for velocity and stream function. The variations in velocity for different values of important parameters have presented in graphs. The results are discussed for both uniform and non-uniform channels.