Symmetric Channel Research Articles

Sub-4.7 Scaling Exponent of Polar Codes

Polar codes approach channel capacity provably and empirically and are thereby a constituent code of the 5G standard. Compared to low-density parity-check codes, however, the performance of short-length polar codes have rooms for improvement that could hinder its adoption by a wider class of applications. As part of the program that addresses the performance issue at short length, it is crucial to understand how fast binary memoryless symmetric channels polarize. A number, called scaling exponent, was defined to measure the speed of polarization and several estimates of the scaling exponent were given in literature. As of 2022, the tightest overestimate is 4.714 made by Mondelli, Hassani, and Urbanke in 2015. We lower the overestimate to 4.63. The idea behind this improvement is that, instead of describing the relation between a channel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> and its children <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ◻ and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ⊛, we describe the relation between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> and its grandchildren <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ◻◻, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ◻⊛, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ⊛◻, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ⊛⊛. By doing so, the evolution of channels becomes “less Markovian” and hence more tighter inequalities can be obtained.

Flow inspection of micropolar nanofluids with motile gyrotactic microorganisms across symmetric channel in porous medium by quasi-linearization technique

The current article investigates the influence of radiation as well as gyrotactic microbes in the flow of micropolar nanoliquids through a channel. Flow is assumed to be symmetric across a channel having permeable walls. The work also focuses on the change in mass transport rate and density distribution of motile microbes across flow regimes in a porous channel. The governing nonlinear partial differential equations of the present problem are transformed into ODEs through dimensionless variables. The coupled nonlinear ODEs are numerically addressed by utilizing the quasi-linearization technique. Impacts of the pertinent parameters on the fluid flow are analyzed and demonstrated through tables as well as figures by using the powerful tool MATLAB. The velocity profiles escalate near both walls with an enhancement in Reynolds number. Moreover, an enhancement in values of heat radiation parameter causes declination in the fluid temperature. An evaluation of the comparison with existing results reveals an excellent harmony. The nanofluids possess marvelous characteristics subject to heat transport as compared to other ordinary fluids. We intend to elaborate the interaction of micropolar nanofluids with the microbes in a symmetric channel flow.

Ionic Current Rectification Induced by Charge Polarity in Janus Graphene Channels

Ionic current rectification (ICR) in nanofluidic diodes is determined by a combination of channel geometry and surface charge, where most of the previous works have focused on charged asymmetric channels. In this work, through a series of molecular dynamics simulations, we find a surprising ICR phenomenon in a Janus graphene channel, whose geometry is symmetric, while the surface charge is asymmetric by tuning the ratio of cationic and anionic surface modification. A key observation is that when the electric field changes from positive to negative direction, the ionic current exhibits a switchable on–off state depending on whether the dipole moment of the channel’s inner surface is parallel to the electrical force. Strikingly, the ICR ratio shows a maximum behavior with the increase in cationic modification, attributed to the change in the range of electrostatic repulsion under the negative electric field. Furthermore, for a given modification ratio, with the increase in graphene layer distance, the ICR ratio also displays a maximum behavior because of the reduced range of the electric double layer (EDL). For small layer distance, the EDL overlap leads to a Coulomb blockade effect under the positive electric field, corresponding to a small ionic current. However, the large layer distance reduces the influence of EDL on ion transport owing to the weakened electrostatic interactions, which ultimately leads to the decrease in ICR ratio. Our results shed light on the essential role of charge polarity in ICR performance, which could open a new window for the design of novel nanofluidic diodes based on symmetric Janus channels.

Chemically reactive MHD peristaltic flow of Jeffrey nanofluid via a vertical porous conduit with complaint walls under the effects of bioconvection and double diffusion

Inspired by significant physiological applications of peristaltic transport, a mathematical model for the peristaltic pumping of a Jeffrey nanofluid containing gyrotactic microorganisms through a flexible and vertical symmetric channel is investigated, along with the effects of thermal radiation, heat source/sink, chemical reaction, porous medium and Hall current. Swimming microorganisms in a model of non-Newtonian fluid has several biological and ecological benefits, including in the pharmaceutical industry, biofertilizers, biofuel technology, biosensors, etc. With these presumptions in mind, a conducting Jeffery fluid flow containing microorganisms via a porous vertical conduit is proposed. The expressions for the flow quantities are established by solving the governing equations of this study analytically using the homotopy perturbation method (HPM). A detailed examination is performed using the tables and graphical representations to comprehend the impact of significant components on this analysis. In addition, the results for Newtonian nanofluid are obtained as a special case and discovered that its velocity is lower than the Jeffrey nanofluid. It is observed that the best velocity distribution can be seen at larger thermal Grashof number and Darcy number. The size of the trapped bolus enhances with the increase of the Hall parameter. Furthermore, the density of the motile microorganism distribution declines for higher bioconvection Peclet number and bioconvection constant.

An electroosmotic peristaltic flow of graphene-lubrication oil nanofluid through a symmetric channel

The purpose of this manuscript is to analyze the electroosmotic peristaltic motion of graphene-lubrication oil nanofluid. Rheological characteristics of such fluids are predicted by using the Carreau’s model. Effects of magnetic field, electric field, viscous dissipation, Joule heating, Brownian motion and thermophoresis are also reckoned. Debye-Hückel linearization and lubrication approach are employed in mathematical modeling. Obtained non-linear system of equations are analytically solved by using the builtin command NdSolve and parametric study is carried out to visualize the variation in temperature, velocity, heat transfer rate, concentration profiles, pressure gradient and pressure rise per wavelength. Results unveil that strong electroosmotic parameter enhances both velocity and temperature. Temperature and velocity decline on the enlargement of the Helmholtz-Smoluchowski velocity. Variation in electroosmotic parameter decreases and Helmholtz-Smoluchowski velocity increases mass transfer rate. Pumping region can also be maintained by thickening and thinning the Electric Double Layer (EDL). Present study has useful applications in industries, defect sensor, energy saving, domestic air conditioning, cooling power electronic components and heat extraction and heat transportation.

Using a lightweight Siamese neural network for generating a feature vector in a vascular authentication system

The article analyzes the possibility of using a Siamese convolutional neural network to solve the problem of vascular authentication on an embedded hardware platform with limited computing resources (Orange Pi One). The authors give a brief review of modern methods for calculating image feature vectors used in the tasks of classifying, comparing or searching for images by content: based on variational series (histograms), local descriptors, singular point descriptors, descriptors based on hash functions, neural network descriptors. They suggest using the architecture of a biometric authentication system (BAS) based on images of palms in the visible and near-IR spectra based on a Siamese convolutional neural network. The developed software solution allows using the Siamese neural network in the "full network" (both symmetrical channels of the neural network are used) and "half of the neural network" (only one channel is used) modes to reduce the time for comparing biometric data vectors - images of the palms of registered BAS users. The authors demonstrate advantages of the neural network features: universality, scalability and competitiveness, including on embedded hardware and software solutions with limited computing resources without graphics accelerators. The studies have shown that using the Siamese neural network, the "overall accuracy" of palm image classification can be improved from 0.929 to 0.968 when compared with the image vectorization method based on a perceptual hash, while showing a comparable authentication time for individuals registered in BAS. In the experiments, the authors use a database of 2,000 images for 400 people.

Reinforcement learning for performance improvement in cooperative spectrum sensing

Cognitive radio (CR) can provide a promising solution to the spectrum scarcity issue for upcoming wireless communication technologies. Cooperative spectrum sensing (CSS) is generally adopted to improve spectrum utilization and minimize interference to primary users (PUs). The performance of CSS is significantly affected by imperfect reporting channels, and it is an easy target for Byzantine attackers. This paper studies CSS under imperfect reporting channels and Byzantine attacks. We have considered centralized CSS with a hard combining fusion rule. The binary symmetric channel (BSC) is used to model the imperfect reporting channels, and a centralized independent probabilistic small scale attack model is chosen to model Byzantine attackers. We first analyze the traditional CSS (T-CSS) under the imperfect reporting channel and the Byzantine attack. The performance of T-CSS is found to be greatly affected in the considered scenarios. We propose a reinforcement learning-based algorithm to detect cooperating secondary users (CSUs) experiencing weak reporting channels and Byzantine attackers. Generally, in literature, the detected malicious users (MUs) are removed to improve the performance. However, in case there are CSUs with weak reporting channels, the genuine CSUs may be detected as Byzantine attackers and hence removed. To overcome this issue, we propose a weighted sum-based CSS (WS-CSS) algorithm that can improve the CSS performance under weak reporting channels and attacks from Byzantine attackers. It is demonstrated using plots that the proposed WS-CSS algorithm significantly improves the CSS performance.

Scaling of secondary flows with surface parameters: A linear approach

Secondary flows are generated when a lateral variation of the topography, such as streamwise aligned ridges, is imposed upon a turbulent wall-bounded flow. In this case, the time-averaged flow field is characterized by streamwise vortices known as Prandtl’s vortices of the second kind (Prandtl, 1952). As demonstrated in previous experimental and numerical works, the strength and flow organization of these vortices depend on the ridge shape. In this paper, the effect of the ridge geometry on the generation of secondary flows is investigated using the linearized RANS-based model proposed by Zampino et al. (2022). The model is derived from the assumption that the ridges are shallow, with height smaller than any other length scale, e.g. the viscous length scale. Symmetric channels with rectangular, triangular, elliptical and trapezoidal ridges are studied. The model predicts that the strength of secondary flows can be scaled with the mean ridge height, regardless of the ridge shape, when the ridges are narrower than the half channel height and isolated, i.e. when the lateral separation between the ridges is much larger than the ridge width. Finally, the appearance of tertiary flows and the effect of the ridge shape on the flow organization is studied in detail for trapezoidal geometries. It is observed that tertiary flows emerge for ridge configurations where the scaling behaviour does not hold.

Channel polarization of two-dimensional-input quantum symmetric channels

Channel polarization of two-dimensional-input quantum symmetric channels

Splitting of microbubble mediated by power-law carrier fluid inside a symmetric bifurcating channel

We investigate the dynamics of bubble propagation in a symmetric bifurcating Y-channel by varying the power-law index (n) of the carrier fluid from 0.3 to 1.5, in the presence of gravity. To characterize the bubble evolution, the unsteady two-phase flow is solved numerically, employing a suitable phase-field model. Based on the flow rate ratio between the upper and lower branch channels and the neck-width evolution, the bubble bifurcation process is divided into three distinct stages, namely, squeezing, transition, and pinch-off. Temporal variation of neck-width demonstrates that the bubble pinch-off is somewhat delayed for shear-thickening (n &amp;gt; 1) fluids, while a shear-thinning carrier fluid (n &amp;lt; 1) triggers faster pinch-off. Our study reveals that for a large n (say, n = 1.5), viscous force strongly counters the buoyancy effect, resulting in symmetric (equal) bifurcation of the bubble. Conversely, for shear-thinning fluids, the bubble evolution is dictated primarily by the buoyancy force, leading to an asymmetric bubble breakup. We investigate the role of n on wall shear variation and determine the wall-location that is susceptible to the maximum damage. Performing simulations over wide ranges of capillary numbers (Ca) and Bond numbers (Bo), we unveil important regimes of bubble splitting phenomena, e.g., symmetric breakup, asymmetric breakup, buoyancy dominated no-breakup, and surface tension dominated no-breakup regimes. Numerically predicted regime plots, which comprehensively illustrate the roles of Ca, Bo and, n on various breakup regimes, may act as fundamental design basis of branching networks in classic applications, such as microfluidics, biofluid mechanics, and flow through porous media.

A Rank-Iteration Based Blind Identification Method for Convolutional Codes

A blind identification technology of channel coding has received increasing attentions in recent years. In this letter, we focus on blind identification of convolutional codes without a candidate set. To improve the blind identification accuracy, a novel rank-iteration based blind identification algorithm for convolutional codes is proposed in this paper. Specifically, a weight-dependent threshold for the Binary Symmetric Channel (BSC) channel is firstly proposed to calculate the rank of a received data matrix more accurately. Then, we propose a new iterative operation that repeats the Gauss-Jordan Elimination Through Pivoting (GJETP) algorithm for several times, and select the smallest rank as the rank of the data matrix. Employing this strategy, the rank of a rank-deficient matrix in noisy environments can be close to its noiseless rank. Further, a rank-deficient threshold is introduced to amend the rank of the full-rank matrix after the end of the whole iterative process, which can reduce the rank deviation of the full-rank matrix. Finally, the effectiveness of the proposed method is verified by simulations and comparisons.

Characteristics of a composite flow field with drop-shaped gas distribution zones and a honeycomb-like staggered channel for proton exchange membrane fuel cells

ABSTRACT On the basis of previous studies, a staggered honeycomb-like flow field with drop-shaped gas distribution zone is proposed in this paper, and the staggered honeycomb-like flow channel can make the oxygen concentration higher, and the drop-shaped gas distribution zone can improve the uniformity of reaction gas in the flow field. A three-dimensional (3D), non-isothermal two-phase numerical model is established to study the flow field performance. First, the reaction gases in the flow field are analyzed, and it is found that the proposed flow field structure can effectively improve the concentration and uniformity of reactants. Second, the volume fraction of liquid water at the (GDL)/channel (CH) interface is analyzed, and it is found that compared with the model of the symmetrical honeycomb channel without considering the gas distribution zone, the proposed model has better water removal effect at the cathode. Finally, the effects of the proposed flow field structure on the membrane properties are discussed. In addition, the temperature uniformity and liquid water removal of PEMFC are improved under the condition of reverse flow of cathode and anode reaction gases.

Rotation and Magnetic Force Effects on Peristaltic Transport of Non -Newtonian Fluid in a Symmetric Channel

In this paper, the impact of magnetic force, rotation, and nonlinear heat radiation on the peristaltic flow of a hybrid bio -nanofluids through a symmetric channel are investigated. Under the assumption of a low Reynolds number and a long wavelength, the exact solution of the expression for stream function, velocity, heat transfer coefficient, induced magnetic field, magnetic force, and temperature are obtained by using the Adomian decomposition method. The findings show that the magnetic force contours improve when the magnitude of the Hartmann number M is high and decreases when rotation increases. Lastly, the effects of essential parameters that appear in the problem are analyzed through a graph. Plotting all figures is done using the MATHEMATICA software.

Influence of Both Ohmic Dissipation and Activation Energy on Peristaltic Transport of Jeffery Nanofluid through a Porous Media

The theme of this study is to investigate the influence of the chemical reaction and activation energy on MHD peristaltic flow of Jeffery nanofluids in an inclined symmetric channel through a porous medium. Joule heating, radiation, viscous dissipation, heat generation/absorption, activation energy, and thermal diffusion and diffusion thermo effects are involved. The long wavelength and low Reynolds number approximations are used to simplify the non-linear equations that govern the flow. Then, the simplified equations are solved by using the homotopy perturbation method (HPM). We have depicted the velocity, temperature, solute concentration, and nanoparticles volume friction graphically. Physical explanations for the results are provided. The influence of interest parameters on entropy generation is also observed. Numerical results for the heat transfer coefficient, Nusselt number, and Sherwood number are presented. The results revealed that an increase in the value of the ratio of relaxation to retardation times of Jeffery nanofluid enhances the velocity distribution, while a reduction in the solute concentration distribution occurs by increasing the activation energy parameter and the temperature difference parameter . We also discovered that an increase of the chemical reaction parameter increases the temperature profile and decreases the velocity and solute concentration profiles. Furthermore, the velocity becomes lower along the normal axis y and ends up with the minimum value near the upper wall of the channel. Also, the maximum and minimum values of the velocity increase with an increase of the second order slip parameter , while they decrease as Darcy number increases

On Decoder Ties for the Binary Symmetric Channel with Arbitrarily Distributed Input

The error probability of block codes sent under a non-uniform input distribution over the memoryless binary symmetric channel (BSC) and decoded via the maximum a posteriori (MAP) decoding rule is investigated. It is proved that the ratio of the probability of MAP decoder ties to the probability of error grows most linearly in blocklength when no MAP decoding ties occur, thus showing that decoder ties do not affect the code's error exponent. This result generalizes a similar recent result shown for the case of block codes transmitted over the BSC under a uniform input distribution.

A double tangential flow filtration-based microfluidic device for highly efficient separation and enrichment of exosomes

Recently, exosomes have been recognized as important disease biomarkers due to the essential roles they played in disease development. Nevertheless, the highly efficient isolation and enrichment of exosomes from complex body fluids continues to hinder the research and application of exosomes for clinical use. In this work, we developed a double tangential flow filtration-based microfluidic device for exosome isolation from cell supernatants and human serum. The microfluidic device contained two modules. Each module included two polymethylmethacrylate (PMMA) plates with symmetrical serpentine channels and a nanoporous membrane with 200 nm or 30 nm pore diameter and was used to separate larger vesicles, exosomes and free biomolecules. The design of double tangential flow filtration in symmetrical serpentine channels largely increased the contact area between the filtrate and the nanoporous membranes, thus improved the separation efficiency and prevented the clogging of the membrane. Compared with standard separation method, i.e. ultracentrifugation (UC), the microfluidic chip-based separation (Chip) of exosomes showed the advantages of much lower instrumental cost, lower consumable cost, shorter time (<120 min), higher purity (82.8%) and significantly higher recovery rate (77.8%). In addition, due to the label-free separation, the microfluidic device-collected exosomes could be directly used for downstream analysis such as proteomics analysis. The proteomics analysis results of exosomes isolated from the sera of clinical patients with different diseases by the chip revealed richer disease-related information comparing with those exosomes isolated by UC, demonstrating the good practicability of this chip for future clinical research and applications.

Metachronal ciliary wave motion analysis on peristaltic flow of hyperbolic tangent nanofluid through an inclined magnetic field in a symmetric channel

ABSTRACT The phenomenon of metachronal wave of artificial cilia activated by the influence of magnetic field has many biological applications. The main aim of the present investigation is to show the effect of magnetic field on peristaltic-ciliary flow of hyperbolic tangent nanofluid through an inclined symmetric channel with surface roughness. The dimensional equations were converted into a non-dimensional form by suitable dimensionless parameters, which are solved by using the transformation method combined with perturbation technique. Impact of different physical characteristics on velocity, different wave forms, volume fraction, trapping phenomenon and temperature has been analysed. From the study we can observe that the fluid flow can be controlled by varying the power law index. The angle of inclination of the channel enhances the fluid velocity. It is also observed that the Darcy number and peristaltic-ciliary flow increase the fluid flow in the system. Whereas, the shape of the waves remains the same for both multi-sinusoidal waves and triangular waves when the pressure gradient is taken into account. The outcomes of this study can be utilised to detect the illnesses in biological tissues, and cilia that actively move fluid and suspended nanoparticles by pumping in a metachronous manner through biological organs.

Analysis of Joule heating and Hall effects on the electro-osmotic flow of third-grade nanofluid regulated by peristaltic waves through a porous medium with double diffusion

The current analysis is based on the third-grade nanofluid flow triggered by the combined effects of peristaltic pumping and an external electric field. The effects of double diffusion convection and viscous dissipation in nanofluids across a porous symmetric channel were explored. Thermal radiation, the Hall effect and Joule heating are the key phenomena discussed in the flow problem. The governing model is modified by using the Lubrication theory and Debye-Hückel linearization. A highly non-linear system of equations was solved by Mathematica software to scrutinize the effects of Joule heating, Hall effect, electro-osmotic velocity, Grashof numbers, thermophoresis, and Brownian motion on the flow characteristics. Brinkman number and the thermal radiation show opposite characteristics on the temperature profile.

A comparative analysis of sleep spindle characteristics of sleep-disordered patients and normal subjects.

Spindles differ in density, amplitude, and frequency, and these variations reflect different physiological processes. Sleep disorders are characterized by difficulty in falling asleep and maintaining sleep. In this study, we proposed a new spindle wave detection algorithm, which was more effective compared with traditional detection algorithms such as wavelet algorithm. Besides, we recorded EEG data from 20 subjects with sleep disorders and 10 normal subjects, and then we compared the spindle characteristics of sleep-disordered subjects and normal subjects (those without any sleep disorder) to assess the spindle activity during human sleep. Specifically, we scored 30 subjects on the Pittsburgh Sleep Quality Index and then analyzed the association between their sleep quality scores and spindle characteristics, reflecting the effect of sleep disorders on spindle characteristics. We found a significant correlation between the sleep quality score and spindle density (p = 1.84 × 10-8, p-value <0.05 was considered statistically significant.). We, therefore, concluded that the higher the spindle density, the better the sleep quality. The correlation analysis between the sleep quality score and mean frequency of spindles yielded a p-value of 0.667, suggesting that the spindle frequency and sleep quality score were not significantly correlated. The p-value between the sleep quality score and spindle amplitude was 1.33 × 10-4, indicating that the mean amplitude of the spindle decreases as the score increases, and the mean spindle amplitude is generally slightly higher in the normal population than in the sleep-disordered population. The normal and sleep-disordered groups did not show obvious differences in the number of spindles between symmetric channels C3/C4 and F3/F4. The difference in the density and amplitude of the spindles proposed in this paper can be a reference characteristic for the diagnosis of sleep disorders and provide valuable objective evidence for clinical diagnosis. In summary, our proposed detection method can effectively improve the accuracy of sleep spindle wave detection with stable performance. Meanwhile, our study shows that the spindle density, frequency and amplitude are different between the sleep-disordered and normal populations.

Dual optimization of the geometric design and inductor parameters of the induction heating tundish based on numerical simulations

Based on the application of electromagnetism and hydrodynamics in metallurgy, the selection of the number of inductors as well as the direction of inductor current access is investigated for channel-type induction heating (IH) tundish with dual-channel (D-Ch), three-channel (T-Ch) and four-channel (F-Ch) tundish designs. The results show that when a single inductor is used, the Joule heat power (JHP) and electromagnetic force (EMF) are essentially the same within the two channels of the D-Ch tundish, but in the T-Ch tundish and the F-Ch tundish, the JHP and EMF of channel No.1 (Ch1) is much larger than other channels, which is extremely asymmetric. This will further be reflected in the influence on the flow and temperature consistency of the molten steel in the tundish. When a single inductor is used in the T-Ch or F-Ch tundish, the molten steel flow velocity in Ch1 is 4.2 and 7.4 times higher than that in the symmetric channel, respectively, and the temperature difference at the symmetric strand can be as high as 11 K or more. However, the maximum flow velocity of the molten steel in Ch1 and channel No.2 (Ch2) of the D-Ch tundish is 0.21 and 0.19 m⋅s−1, respectively, and the maximum temperature difference at the symmetrical strand is only 2.3 K. For the tundish with double inductors, the influence of the direction of the access current of the inductors should be taken into account. The inductors of a D-Ch tundish can effectively heat the molten steel only by accessing the same direction current. The physical fields in the intermediate and side channels are significantly different when the same or opposite current is accessed to the dual inductors of T-Ch tundish. The temperature rise rate of the molten steel is 36% higher when the dual inductors of the F-Ch tundish are accessed to the opposite current than when they are accessed to the same current. Therefore, a D-Ch design should be used for the channel-type tundish with a single inductor. And for the channel-type tundish with dual inductors, the same direction current should be accessed under the D-Ch design, and the opposite current should be accessed under the F-Ch design.