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In this study, the flow pattern and bubble behavior of R1233zd(E) during subcooled flow boiling in parallel channels are experimentally investigated with visualization and thermal measurement. The test section is composed of 21 rectangular mini channels with the hydraulic diameter of 1.5 mm and the length of 140 mm. Bubbly flow, slug flow, churn flow and wavy-annular flow occur in sequence with the increase of vapor quality, while transient flow pattern transition process involving multiple flow patterns are also captured. The distribution of flow pattern is non-synchronized and axial-asymmetric, with earlier flow pattern transitions observed in peripheral channels away from the center axis. The initial nucleate site in each channel also show a random and axial-asymmetric distribution, while faster bubble growth can be noted in some channel under the comprehensive effects of liquid evaporation and bubble coalescence. The variation of heat transfer coefficient is correspondence to the flow pattern transition, showing different trends along the flow direction. The increase of mass flux can lead to delayed flow pattern transition and variation of heat transfer coefficient. In addition, higher heat transfer coefficient can be noted in channels away from the center axis. [ABSTRACT FROM AUTHOR]

There is growing interest in multi-nozzle array printing, as it has the potential to increase productivity and produce more intricate products. However, a key challenge is ensuring consistent flow across each outlet. In the heat exchangers, achieving uniform distribution of flow in parallel channels is a classic goal. To address this issue in multi-nozzle array direct printing technology, high-viscosity slurry fluids can be utilized in place of water, and the structure of compact parallel channels can be employed. This study experimentally and numerically investigated the flow distribution law of Herschel-Bulkley fluids (high-viscosity slurry fluids) entering each manifold of the compact parallel channels, which contained a single circular inlet and multiple outlets. The research identified two types of factors that impact the non-uniformity flow coefficient (Φ), which reflects the uniformity of flow distribution in each channel of the structure: entrance and exit conditions (V, P1, P2) that have a negligible effect on Φ, and structural dimensions (D, S, L, N, A, d) that are the primary influence factors. By analyzing the experimental results, a prediction model was derived that could accurately calculate Φ (error < 0.05) based on three structural dimensions: A, S, and L. Through proper design of these structural dimensions, a consistent flow rate of each channel of the parallel channels can be ensured. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There is growing interest in multi-nozzle array printing, as it has the potential to increase productivity and produce more intricate products. However, a key challenge is ensuring consistent flow across each outlet. In the heat exchangers, achieving uniform distribution of flow in parallel channels is a classic goal. To address this issue in multi-nozzle array direct printing technology, high-viscosity slurry fluids can be utilized in place of water, and the structure of compact parallel channels can be employed. This study experimentally and numerically investigated the flow distribution law of Herschel-Bulkley fluids (high-viscosity slurry fluids) entering each manifold of the compact parallel channels, which contained a single circular inlet and multiple outlets. The research identified two types of factors that impact the non-uniformity flow coefficient (Φ), which reflects the uniformity of flow distribution in each channel of the structure: entrance and exit conditions (V, P1, P2) that have a negligible effect on Φ, and structural dimensions (D, S, L, N, A, d) that are the primary influence factors. By analyzing the experimental results, a prediction model was derived that could accurately calculate Φ (error < 0.05) based on three structural dimensions: A, S, and L. Through proper design of these structural dimensions, a consistent flow rate of each channel of the parallel channels can be ensured.

Emotional conversation generation model predicts the response according to the current words and the emotional words. However, the researchers only dedicated to adding more emotional words in the conversation generation model to retain the taste of chat users without considering whether the emotion of a response is suitable for human conversations or not. In this paper, we aim to address the issue of emotion drift which indicates the emotion of a response is not the same category as its post in human conversations. We propose a control unit framework, which consists of emotional channels and word-level attention mechanism, to incorporate natural and smooth emotional words into conversation generation. Emotional channel consists six channels, namely like, sadness, disgust, anger, happiness and other ones, which provides strategy choice control unit to generate emotional words. To improve the importance of emotional content, we use the word-level attention mechanism in emotional channel for acquiring a better emotional decoding response. Experimental results suggest that the proposed model is effective not only in generate content but also in emotion.

The aim of the paper is to discuss a system of complex feedback queue model containing three subsystems; one is comprised with two biserial service channels and other with two parallel service channels. Both the subsystems are commonly connected with a central service channel. The customers have the facility to revisit any of the service channels at most once with different probability of leaving the server and moving from one server to another server. Mean queue length is derived in steady state condition. Particular values are given to the variables to check the validity of the model. The model is applicable to many real life situations such as in shopping malls, offices, communication networks etc. [ABSTRACT FROM AUTHOR]

Summary: Steam generator is the heat transfer component of sodium‐cooled fast reactor (SFR). It is possible to happen flow instability in the tubes of sodium heated once‐through steam generator (OTSG). In order to investigate the flow instability of parallel channels in sodium heated OTSG, a numerical analysis code called COSFIAS has been developed in Fortran language based on time‐domain method. The experimental data of parallel channels flow instability with uniform heating power condition and sodium heated condition have been applied to validate the code. The relative errors between calculation results and experimental data of uniform heating power condition are within 10%. The relative errors between calculation results and experimental data of sodium heated conditions are within 7%. The comparison results indicate that the COSFIAS program is reasonable and accurate for practical engineering application. In addition, the effects of important parameters on flow instability of parallel channels have been analyzed. From the calculation results some conclusions could be drawn: the decrease of water pressure would cause the increase of heat transfer power and destabilize the parallel channels system; in high subcooling region, the increase of inlet subcooling would stabilize the system; in low subcooling region, with the decrease of inlet subcooling, the parallel channels system would turn to be unstable and then return to be stable again; the increase of water mass flow rate could stabilize the parallel channels system.; the sodium heated condition is more stable than uniform heat flux condition in the same heat transfer power; the increase of sodium inlet temperature could destabilize the parallel channels system; the increase of sodium mass flow rate could destabilize the parallel channels system. In addition, the code could be applied to support the design work of sodium heated OTSG. [ABSTRACT FROM AUTHOR]

The flow field is an integral part of a proton exchange membrane fuel cell. In this work, three flow‐field designs, including straight parallel, multiple channel serpentine, and single channel serpentine, are studied systematically to investigate their effects on fuel cell performance. To evaluate the characteristics of each design, relative humidity and flow rate are parametrically adjusted to evaluate performance experimentally. A finite element‐based 3D steady state, single phase COMSOL computational model is employed to analyze reactant distribution and fuel cell performance. The single channel serpentine exhibits the best performance under the greatest variety of operating conditions, but also experiences the highest inlet‐outlet pressure differentials. This study shows that parallel channel design has more evenly distributed reactant concentration, but is prone to liquid water accumulation, which requires high flow rate to remain stable operation under wet conditions. In summary, the multiple channel serpentine design can provide a reasonable balance between pressure drop and flow distribution with robust fuel cell operation. [ABSTRACT FROM AUTHOR]

Summary: In this study, two‐phase density wave instability in parallel‐twin rectangular channels was investigated with axially nonuniform heat profiles in the reactor core combined with static and rolling conditions. A parallel‐channel thermal‐hydraulic model was built using the method of two‐phase homogeneous flow developed in previous work, while the drift‐flux approach for void fraction and profile‐fit model for subcooled boiling were implemented. Although the rolling condition was chosen as the typical motion in this work, the additional force caused by the motion with six degrees of freedom was derived. The theoretical analysis was performed based on the method of small power perturbation for parallel‐twin rectangular channels. The flow oscillation caused by rolling was studied for different system parameters, including inlet resistance, exit resistance, pressure, and axial heating profile. The influence on flow instability of rolling parameters such as period, amplitude, and distance between channels was analyzed. The results showed that it would destabilize the system if a larger additional force was generated by rolling parameters. The influence of different axial heat profiles on flow instability was also studied under inlet‐peaked, cosine‐shape, and outlet‐peaked heat fluxes. The coupling effect of rolling motion and axial nonuniform heating was finally studied. The stability boundaries under different conditions were compared to the inherent boundary under the static condition with uniform heating. The results indicated that the influence of nonuniform heating was more evident and should be paid more attention to. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A numerical model of the two-phase flow oscillation behavior was established. • The physical phenomenon of flow oscillation and its manifestations was proposed. • The heat transfer, pressure drop oscillation and volume fraction were analyzed. • Optimized parallel channel structure to mitigate flow oscillation was evaluated. The uniformity of two-phase flow distribution in a multi-channel heat sink is important for heat transfer performance. During flow boiling, flow oscillations such as transient reverse flow could cause severe flow mal-distribution, thus degrading heat transfer performance and thermal uniformity. Due to the shortcomings of experimental instruments, a 3D numerical simulation was conducted on a heat sink with 21 parallel micro-channels to study the transient flow oscillations and distributions during the subcooled flow boiling of R1233zd(E). The numerical model was validated by the flow pattern visualization experiments. The flow instability was studied on its cause and phenomenon like reversed flow and asymmetric flow. The two-phase flow pattern, heat transfer performance and pressure drop oscillation was also researched and a relationship between them was built. Based on the results, an optimized structure is conducted. The comparison between the optimized and original structure showed that the optimized structure could mitigate the reversed flow, meanwhile the uniformity of mass and temperature distribution were improved by 11.2 % and 8.89 %, respectively. The heat transfer performance of side channels was also enhanced, which in turn improved the overall heat transfer performance. [ABSTRACT FROM AUTHOR]

This paper focuses on understanding the effect of reticulated porous cathode flow fields in real scale close and open cathode polymer electrolyte membrane fuel cells (PEMFCs) in terms of their thermo-electrical performance. This research contributes to addressing challenges with PEMFCs linked to oxygen supply to the cathode and proper mixing of gasses as well as water removal issues. Parallel channel and porous cathode flow fields in both open and closed cathode PEMFCs of medium scale (active area of 15 × 15 cm2) have been investigated. The porous material consisted of 20 pores per inch with a porosity level of 80%. The cells' polarisation and impedance characteristics have been analysed. The porous flow field has been found providing better electrical performance in closed cathode PEMFC compared to the open cathode. Improvements in gas diffusion and temperature uniformity were observed with porous flow field; however, water removal has been observed challenging, which need to be addressed before the benefits of using porous flow field are fully realised. • Metal foam cathode flow field outperformed parallel channel cathode flow field in a medium scale closed cathode PEMFC. • Parallel channel cathode flow field outperformed metal foam cathode flow field in a medium scale open cathode PEMFC. • Gas diffusion towards electrode is improved by using metal foam flow field. • Water removal from metal foam is challenging in both open and closed cathode PEMFCs. [ABSTRACT FROM AUTHOR]

Abstract It is frequently observed that long cracks in sea-ice tend to form between parallel channels during ice management operations. The long cracks that develop play an important role in reducing the size of the managed ice floes, which is one of the main goals in an ice management operation. However, the fracture mechanism behind these long cracks remains unclear. To address this issue, a comprehensive study is reported here in two associated papers. In the current paper (i.e., Paper I), an edge-crack theoretical model is proposed to elucidate the parallel channels' fracture mechanism. The proposed theoretical model is partially based on theories regarding ship – level ice interactions and partially based on previous studies on the general ice fracturing mechanism. The edge-crack theoretical model is extensively examined using a separately developed numerical scheme based on the eXtended Finite Element Method (XFEM), which allows for the existence of a singularity field and displacement jump within conventional Finite Elements (i.e., FEM). The numerical scheme is benchmarked against known asymptotic analytical solutions and field experiments. Afterwards, with the developed numerical scheme, through fitting numerical simulation results in terms of the edge crack's Stress Intensity Factors (SIFs) and a relevant asymptotical analysis, we managed to derive a group of closed-form formulae with wide application ranges. For the current engineering problem, this set of formulae quantifies the maximum parallel channel spacing h max , beyond which the observed parallel channels' fracturing events cease to occur. Moreover, the same numerical scheme is utilised to study parallel channels' fracturing paths. Based on the XFEM-based crack path simulations, a second group of formulae and a numerical recipe were obtained to characterise a simplified crack path. This set of equations enables us to quantify the maximum floe size L MCD that can be generated between two parallel channels and its corresponding floe size ratio. In the sequel paper (i.e., Paper II), these equations are validated by a series of well-controlled field experiments undertaken during the Oden Arctic Technology Research Cruise of 2015 (OATRC2015). Highlights • Analytical formulas to calculate Stress Intensity Factors of a quarter plane with an edge crack are developed. • Maximum ice floe size and channel spacing for ice management operations are predicted by the edge crack model. [ABSTRACT FROM AUTHOR]

Abstract This work focuses on forced convection through asymmetrically heated rectangular confined porous flow passage of aspect ratio of 50 (width/height = 150/3). Heat transfer characteristics of the porous flow passage were investigated with four different open-cell aluminium metal foams (MF) as porous media. Two sets (four samples) of aluminium foams of 20 ppi and 40 ppi pore densities with each set had two different relative densities (RD) of 9–11% and 12–16% (as per supplier's specification). One set of MFs was uncompressed (9–11% relative density) while another set was obtained by unidirectional compressing the MFs of 6–8% RD and 6 mm height flow passages. The study was systemically conducted with constant heat flux at the bottom surface of the flow passage, and on the basis of compact heat transfer surface analogy. Steady state condition was achieved before acquiring data. Temperature distribution along flow direction was investigated to study thermal development of air flow through it. It was found that thermally developed flow exists in such confined flow passages. Moreover, as a case study of a potential application, a systematic method was followed to obtain performance curves for all the flow passages as compact heat transfer surfaces for use in a Polymer Electrolyte Membrane Fuel Cell(PEMFC). The performance curves were utilised to obtain the best compact heat transfer surface for its possible use in a PEMFC. [ABSTRACT FROM AUTHOR]

The safety boundary of flow instability and critical heat flux(CHF) for parallel channels was theoretically investigated in static and motion. For flow instability, a parallel-channel instability mechanistic model was adopted. For CHF, the liquid sublayer dryout mechanism model was used. Also, a unified form of additional forces caused by motion was derived for both flow instability and CHF model. An in-house code was developed combining the flow instability model and the CHF model in motion. The safety boundary of twin rectangular parallel channels with length of 40 mm, width of 2 mm and height of 1 m was calculated in static, inclination, heaving, pitching and rolling motions. The results show that the safety boundary consists of CHF lines and instability boundary. The heating power of the parallel channels is limited by flow instability or CHF depending on the mass flux. All the motions have little influence on the instability boundary. The effects of longitudinal inclination, heaving and pitching motions on the safety boundary are no more than 1%. However, the CHF is obviously reduced in transverse inclination due to flow maldistribution and in rolling motion due to pulsating flow. [ABSTRACT FROM AUTHOR]

Direct methanol fuel cells are a potential candidate to replace traditional power sources for portable applications. The flow field design, manufacture, and optimization are of great significance to the cell performance. When the scale of flow channels decreases to the level of submillimeter‐scale, it is favourable to the reactant and product management. This paper focuses on the effectiveness of using a multi‐tooth planing technique to create submillimeter‐scale parallel channels in a graphite sheet. Besides the structural parameters of flow channels, a series of operating parameters are experimentally investigated, including methanol concentration, methanol feed rate, oxygen feed rate, cathode backpressure, and environmental temperature. Results indicate that the prepared channels promote a higher cell performance than the traditional design with a larger scale. It is beneficial to both the anode and cathode performances, but it has a more prominent effect at the anode. The methanol concentration of 4 mol/L yields the best performance. Using a relatively lower methanol feed rate below 0.5 mL/min has a more obvious effect on the fuel cell. The cell performance is insensitive to the change of cathode oxygen feed rate and backpressure especially when the oxygen can be sufficiently supplied. In this case we can use lower levels of oxygen feed rate and cathode backpressure. The cell temperatures and influence of environmental temperature are also discussed. [ABSTRACT FROM AUTHOR]

Stability of the operation of SCWR at the supercritical conditions has become a major concern to the nuclear engineers worldwide, especially around the pseudo-critical point where dramatic changes of the fluid properties are experienced. This concern of addressing supercritical flow instability is due to various studies showing that the efficiency of light water reactors can be improved considerably from 33% at subcritical pressures to 45% at supercritical pressures. This work investigates effect of axial power distribution on flow instability in parallel channels with water at supercritical pressures. The axial power distributions considered include axially decreased and homogeneous axial power shapes. The study also seeks to examine the performance of the 3D numerical tool STAR-CCM+ in predicting flow instability at supercritical pressures. The effects of parameters such as mass flow rate, pressure and gravity on flow instability were also discussed. Sensitivity analysis of some selected turbulence models and time steps were initially carried out with the aim of selecting suitable turbulence model and time step for the numerical simulations. For a system operated exclusively at two different pressures 23 MPa and 25 MPa with 125 kg/h mass flow rate, inlet temperatures from 180 °C to 360 °C and with gravity influence, stability of the system with axially decreased or homogeneous power shape decreases and increases respectively below and above a particular threshold power with inlet temperature. The system was found more stable with homogeneous Axial Power Shape (HAPS) than that of axially decreased power shape (ADPS). Similar observation was made for a system operated at mass flow rate of 125 kg/h, system pressure of 23 MPa, and with or without gravity influence. When the system is operated at 23 MPa pressure, 145 kg/h mass flow rate and with gravity influence, there is a threshold power below which stability decreases and above which stability increases with inlet temperature for HAPS. In this case, there is no inflection point for ADPS and the stability deceases with inlet temperature. At low inlet temperatures, the system is more stable with ADPS but at high inlet temperatures the system is more stable with HAPS for the system operated at 23 MPa pressure and 145 kg/h mass flow rate. The system with ADPS or HAPS becomes more stable with the change of the system operated with gravity influence to the system operated without gravity influence, and also with the change of system pressure from 23 MPa to 25 MPa. With the change of the system mass flow rate from 125 kg/h to 145vkg/h, the system with ADPS becomes more stable at low inlet temperatures and less stable at high inlet temperatures, whereas the system with HAPS becomes less stable for the various inlet temperatures. For a system operated under experimental conditions of 125 kg/h mass flow rate, 23 MPa pressure, inlet temperatures from 180 °C to 260 °C and with gravity influence, the trends of the numerical instability boundary results agree quite well with the trends of the experimental instability boundary results for most of the inlet temperatures, but there is no inflection point for experimental HAPS as it is the case for numerical HAPS. The system with HAPS is more stable than that with ADPS, a finding also obtained for the experimental results. The dynamics characteristics such as amplitude and period were also compared with experimental results for ADPS at mass flow rate of 125 kg/h, 23 MPa, and with gravity influence. The experimental amplitude was largely under-predicted and the experimental period was quite well predicted by the numerical tool adopted. The results of this study show that the type of axial power shape adopted in supplying heat to the fluid flowing through heat transfer system has significant effect on the stability of the system. From the comparison of the numerical and experimental results, the 3D numerical tool, STAR-CCM+ code could predict flow instability in the parallel channels irrespective of the type of axial power shape adopted. However, there is an evidence that the presence of heating structures in the geometrical model adopted may change the predicted behavior, as shown in previous works. More relevant experiments at supercritical pressures should be carried out for validation of numerical tools adopted for similar studies. [ABSTRACT FROM AUTHOR]

A general calculation model based on the time-domain method is established for analyzing flow instability in parallel channels. In this model, the governing equations of mass, momentum, and energy are discretized and solved using the first-order upwind scheme. A numerical computational program called Dynsys is developed in Fortran language to analyze the flow instability occurring in the water wall of an ultra-supercritical CFB boiler with annular furnace. Comparing the calculation results of Dynsys with the experimental results shows that the model is reasonable and accurate for practical engineering application. On the basis of the validated model, the typical parallel channels in water wall of ultra-supercritical CFB boiler are simulated. Results show that, under the condition of invariable inlet pressure, temperature, and total mass flow rate, as well as 1.2 times heat flux disturbance applied on the parallel channels of ultra-supercritical CFB boiler, the fluctuation of inlet flow rate versus time in two channels is out of phase. In addition, the amplitude of flow pulsation decreases with time first and then returns to the steady state. Therefore, the flow in the parallel channels of ultra-supercritical CFB boiler with annular furnace is stable. Compared with the flow instability in single channel, the calculating results show that the flow in parallel channels was more stable within the range of parameters in the present paper. [ABSTRACT FROM AUTHOR]

Distributing reactant gases uniformly within a cell to ensure proper delivery of reactants is one the crucial requirements for better performance of a Proton Exchange Membrane fuel cell (PEMFC). This investigation was focused on enhancing flow uniformity and distribution of cathode air in parallel channel flow field of a fuel cell. 2D Computational Fluid Dynamic (CFD) simulations (i.e. using ANSYS) were performed to solve continuity and momentum equations across the cathode flow field. Two main designs with modified headers that provide (i) Z-type, and (ii) combination of Z and U-types parallel channel configurations, were investigated for uniform distribution of gases. Our presented designs were able to allow 60–70% of total flow through frontal 80% of total gas flow field area which was just reversed case compared to conventional design where nearly 80% of flow passes through 20% of total area at the end portion of the gas flow field. Further improvement in flow distributions was observed by segmenting the flow field. [ABSTRACT FROM AUTHOR]

To analyse the steady state behaviour and dynamic density wave instabilities (DWIs) of super-critical pressure fluid (SCF) inside a natural circulation loop (NCL) for a heated section with parallel channels, a numerical thermal-hydraulic (TH) model is developed. The capability of the TH model to simulate the above mentioned aspects for a two channel heated section is validated with the existing numerical results and experimental data points. Steady state analysis is performed mainly to find the loop mass flow rate at different operating conditions. It is also aimed to correlate the loop mass flow rate with the driving head, i.e., with the difference in pressure drops due to gravity and friction. Next, the transient model is integrated with that of the steady state to analyse DWI. The model accounts for compressible flow dynamics of SCF and can deal with any number of parallel channels in the heated section while analysing DWIs. With the transient simulations, it is aimed to bifurcate the operating regime into stable and unstable regions, and find the marginal stability boundary (MSB). Extensive simulations are, next, performed to determine the effect of different parameters on the MSB and the findings are reported accordingly. • This work demonstrates the development of TH model for parallel channel NCL. • The model performs the steady–state and dynamic density wave instability analysis. • The TH model accounts for compressible flow dynamics of supercritical pressure fluid. • Simulates any number of parallel channels by treating boundary conditions naturally. • Identifies the core-wide and regional modes of DWOs in parallel channel NCL. [ABSTRACT FROM AUTHOR]

• Conventional springback model works in micro bending using the surface layer model. • The model underestimates the channel height in microforming of parallel channels. • The transverse stress is found to play an important role. • An improved model was developed considering the transverse stress. • The shift distance of the neutral plane and channel height are better captured. To satisfy the higher accuracy requirement in the microforming of thin-walled structures, the springback behavior under miniaturizing dimensions need to be accurately predicted and controlled. However, as the feature size approaches the thickness in microforming, many assumptions in conventional springback model for macroforming are not valid making these models can hardly provide effective springback analysis in microforming. In the present work, the applicability of a springback analytical framework of conventional stretch-bending was first explored via bending tests of 0.1 mm-thick SS316L sheets under different holding conditions with a punch radius from 3 to 5 mm which is much greater than the thickness. The analytical springback angle results agree with the experimental ones with the maximum error of 4.2% for different punch radii, grain sizes and stretching forces conditions, indicating the correctness of the model. The model was further verified in the microforming of parallel channels with a fillet radius of 0.15 mm. Finite element simulations were conducted to obtain the stretching loads for each channel. However, a significant underestimation of the channel height after springback for over 15% was found especially for the middle channel. The transverse stress is revealed to be no longer neglectable due to the strong stretching load and the small die radius during the microforming of parallel channels, which substantially contributes to yielding, hardening and thickness reduction in the stretch-bending area. In addition, the uneven stretching also affects the springback angle and channel height, which is caused by the nonuniform plastic deformation of the adjacent channels. By incorporating the effects of the transverse stress and the non-uniform stretching loads, an improved springback model was developed for microforming of parallel channels in this work. The shift distance of the neutral plane is better estimated by the improved model than by the conventional one. The predictive heights by the improved model are also revealed to agree with the experimental ones during the microforming of parallel channels with a maximum error of less than 5%. [Display omitted] [ABSTRACT FROM AUTHOR]

We bring out a passive droplet sorting perspective engendered by emulsion flow in a parallel microchannel with converging–diverging branches and varying channel constriction ratios (CR) and throat lengths (TL). In one microdevice, the value of TL in both the branches was fixed at 300 μ m, while the CR were varied between 0.50 and 0.75. The other microdevice had a constant CR of 0.50, but the TL was changed between 300 μ m and 600 μ m. Three different emulsions containing mean droplet sizes of 25.65 μ m, 36.72 μ m, and 39.18 μ m are analyzed at three different flow rates of 2 μ l/min, 10 μ l/min, and 30 μ l/min. Depending on the difference in geometric constriction induced flow resistances in two arms, bigger droplets are observed to flow through the less resistive path and smaller droplets move across the other branch. Our results demonstrate that droplet sorting efficacy can be more effectively tuned with constriction ratio instead of the throat length variation keeping other geometric and rheological properties constant. Moreover, droplet separation is found to be facilitated by decreasing the emulsion flow rate and increasing the dispersed phase viscosity from 20 cSt to 350 cSt. • Influence of channel constriction on emulsion flow-mediated droplet sorting. • Effect of downstream channel captivity on asymmetrical droplet separation. • Construction ratio and throat length dictate the droplet sorting. • Inlet flow rate and the droplet viscosity critically guide the sorting process. [ABSTRACT FROM AUTHOR]

In this paper, we extend the concept of adaptive spatial modulation to the parallel Gaussian channel with finite alphabet input and propose a transmit scheme called adaptive index modulation (AIM). In the proposed scheme, the transmitter adaptively selects the index modulation pattern, consisting of the active channel subset and the associated signal constellations, according to the criterion of maximizing the minimum squared Euclidean distance. To reduce the complexity, first, the number of candidate patterns in the selection procedure is reduced by employing the relation of the normalized signal constellations with different modulation orders. Second, a simple lookup table method is presented. Finally, the performance of the proposed scheme is demonstrated in both the scenarios of multicarrier transmission and multiantenna transmission by computer simulations. [ABSTRACT FROM AUTHOR]

A two-way active parallel channel refers to a communication link between two transceivers, where the subchannel gains between the two transceivers can be adjusted such that a given performance criterion is optimized. A two-way active channel can have reciprocal subchannels, meaning that the subchannel gains in both communication directions are identical. Otherwise, if the gains of each subchannel in the two communication directions are different, the active channel is referred to as non-reciprocal. In this paper, we consider the problem of sum-rate maximization for reciprocal and non-reciprocal two-way active channels under two constraints on the transceivers’ transmit powers and a third constraint on the channel power (i.e., the sum of squared of the subchannel gains). We prove rigorously that for such active channels, in order to maximize the sum-rate, only a subset of the subchannels will have to be active. We also provide the optimal values of the subchannel gains and the optimal values of the transceivers’ transmit powers over different subchannels in closed forms. Simulation results show that parallel active channels can outperform their passive counterparts, where the subchannel gains are fixed, and thus, they cannot be adjusted. [ABSTRACT FROM PUBLISHER]

State-dependent parallel networks with a common state-cognitive helper is studied, in which $K$ transmitters wish to send $K$ messages to their corresponding receivers over $K$ state-corrupted parallel channels, and a helper who knows the state information noncausally wishes to assist these receivers to cancel state interference. Furthermore, the helper also has its own message to be sent simultaneously to its corresponding receiver. Since the state information is known only to the helper, but not to other transmitters, transmitter-side state cognition and receiver-side state interference are mismatched. Our focus is on the high state power regime, i.e., the state power goes to infinity. Three (sub)models are studied. Model I serves as a basic model, which consists of only one transmitter–receiver (with state corruption) pair in addition to a helper that assists the receiver to cancel state in addition to transmitting its own message. Model II consists of two transmitter–receiver pairs in addition to a helper, and only one receiver is interfered by a state sequence. Model III generalizes model I to include multiple transmitter–receiver pairs with each receiver corrupted by independent state. For all models, the inner and outer bounds on the capacity region are derived, and comparison of the two bounds yields characterization of either full or partial boundary of the capacity region under various channel parameters. [ABSTRACT FROM PUBLISHER]

We develop an approximation for the outage probability of a parallel channel where the subchannel statistics satisfy mild conditions. The main result is in the form of a functional of the density function that describes the statistics of the subchannel powers. The error of the approximation is quantified to be O(\gamma^-n(q+1)-2), where $\gamma$ is the end-to-end SNR of a given subchannel, $n$ is the number of subchannels, and $q$ represents the inherent subchannel diversity. We illustrate the versatility and accuracy of the approximation by studying different statistical subchannel models, which reflect practical wireless communication systems, including line-of-sight links (Rician fading), transmissions affected by interference, and relay systems subject to amplifier distortion. [ABSTRACT FROM PUBLISHER]

Parallel‐computing‐based implementation of the two recent fast parallel algorithms for the discrete Gabor transform (DGT) is presented in this paper. First of all, the first existing block time‐recursive DGT algorithm with parallel lattice structure is analysed, and then an improved implementation method under a parallel computing environment is presented. Each parallel channel (i.e. process in parallel computing) in the improved method is independent, thereby reducing the interprocess communication by 99.2% on average over the original algorithm. Second, the second existing fast parallel DGT algorithm based on multirate filtering is analysed. Through the use of parallel computing, the communication overhead of the multirate filtering‐based parallel DGT algorithm is optimised and its time efficiency is raised from 31.26 times to 54.52 times faster than the serial fast DGT algorithm in processing of long sequences. Finally, the experimental results are compared and analysed, which indicate that the proposed fast DGT implementation methods are attractive for real‐time signal processing. [ABSTRACT FROM AUTHOR]