Low Channel Research Articles

Design optimization of noise reduction for labyrinth control valve in secondary circuit flow regulation system

The labyrinth control valve has been widely used in the secondary circuit flow regulation system of nuclear power field for good pressure reduction and cavitation suppression characteristics. The design of the labyrinth channel is a key to realizing pressure regulation and cavitation suppression for the labyrinth control valve. However, an unreasonable labyrinth flow channel design will be challenging to meet the requirements and aggravate the noise problem under severe operating conditions. This paper proposes a hybrid labyrinth flow channel structure (HLS) that combines the traditional labyrinth flow channel (TLS) and orifice plate structure. The cavitation volume and maximum flow velocity are used as evaluation parameters of the labyrinth flow channel noise. The flow characteristics analysis show that compared with the TLS, the HLS can reduce flow velocity, decrease cavitation volume, improve transmission loss, and lower sound power levels. In addition, the influence between the HLS structural parameters and the noise evaluation parameters is clarified by correlation coefficient analysis. A low noise HLS based on the adaptive NSGA-II algorithm is established. The experimental results indicate that the optimized HLS reduces air noise by 4.21 dB(A) compared to the TLS. The optimized HLS can effectively reduce noise, and help the design of low noise labyrinth flow channels for nuclear power field.

Experimental investigation of varying design parameters on the production rate and temperature polarisation of a DCMD system

Much of the research in the analysis of Temperature polarisation (TP) and the productivity of a membrane distillation (MD) system tends to concentrate on operational conditions. However, substantial enhancements in permeate flux can be realised through the incorporation of fundamental design modifications. This research showed that TP can be successfully mitigated almost to a level of non-existence, by manipulating the module orientation and flow channel height of an in-house designed direct contact membrane distillation (DCMD) system. Notably, at higher flow channel heights, changing the module orientation from the default horizontal position with the feed side on top (FST) to a sideway orientation led to a remarkable 90% increase in the permeate flux of the DCMD module. Permeate side on top (PST) and sideways orientations performed significantly better than FST for larger channel heights, while at low channel heights, the improvement was slight. Temperature measurements proved that thermal convective currents and secondary flows played a vital role in assisting or opposing TP and cannot be disregarded when investigating the hydrodynamics of a DCMD system. The impact of flow directions was insignificant with different channel heights, while the proximity of the flow inlets played a pivotal role in shaping the temperature profiles along the membrane.

Household energy price resilience in the face of gas and electricity market crises

Despite the provision of financial support by the Government in response to the recent energy crisis, the resilience of households to the ensuing high energy prices remains to be established. In this study we propose a new definition of resilience, specifically ‘energy price resilience’, and put forward an empirical approach to capture low energy price resilience (LENRES). We also assess its associated socio-economic and demographic factors using a representative UK panel. Using models that account for time-invariant unobserved heterogeneity, we further explore the association between LENRES and a rich set of health, disability, and wellbeing outcomes for adults and children through two fundamental routes: (1) the low energy and thermal affordability channel (LEA); and (2) the low energy and financial solvency channel (LES). We find that employment status, housing tenure, inability to save, energy prepayment methods, and household composition are systematic socio-economic correlates of LENRES. Moreover, LENRES is associated with worse health, disability, and wellbeing outcomes for adults; these associations are primarily driven by the LES component. On the other hand, in the case of children, LENRES at home is only systematically associated with life satisfaction, rather than general health. Our results suggest that targeted energy interventions could generate wider societal benefits.

The rainstorm waterlogging resistance of a novel fiber-reinforced self-compacting recycled pervious concrete after freeze-thaw cycles

The poor permeability of pervious concrete after freeze-thaw (F-T) cycles is a difficult issue in the face of frequent extreme rainstorms, causing urban rainstorm waterlogging problems (stagnant water depth exceeds 150 mm). A novel fiber-reinforced self-compacting recycled pervious concrete (NSPC) with low tortuosity artificial pore channel (APC) is a pervious material with high permeability and strength, and has potential application in pervious pavement at the coupling action of F-T cycles and rainstorm. In this study, the frost resistance, mechanical properties and permeability of C60 NSPC (pore diameter of 3 mm, porosity of 1.13%) with various steel fiber contents (0 vol%, 0.5 vol%, 1 vol%, 1.5 vol% and 2 vol%) were investigated, and then the rainstorm waterlogging resistance of NSPC after 300 F-T cycles was examined under 20-, 50- and 100-year rainstorm. Results showed that the macroscopic destruction of NSPC surface after F-T cycles always started near the APCs, and the existence of APCs aggravated the mass loss and the decrease of the relative dynamic modulus of elasticity. As the increase of steel fiber content, the compressive strength loss of NSPC decreased first and then increased after F-T cycles. The use of steel fiber enhanced the integrality inside the APCs of NSPC and reduced the APC clogging rate, which improved hydraulic-conductivity properties after F-T cycles. After 300 F-T cycles, NSPC with 2% steel fiber achieved an excellent rainstorm waterlogging resistance (stagnant water depth of 0 mm), regardless of the rainstorm return period. Through F-T damage analysis, in order to cope with waterlogging, the maximum FT failure thresholds of NSPC to prevent stagnant water of 50, 70 and 100 mm are 0.097, 0.125 and 0.161 respectively, equivalent to 196, 243 and 264 F-T cycles. This study designed a NSPC that can dissipate stagnant water after F-T cycles, which provided a promising route towards solving urban rainstorm waterlogging.

Timescale of the Morphodynamic Feedback Between Planform Geometry and Lateral Migration of Meandering Rivers

AbstractAcross varied environments, meandering channels evolve through a common morphodynamic feedback: the sinuous channel shape causes spatial variations in boundary shear stress, which cause lateral migration rates to vary along a meander bend and change the shape of the channel. This feedback is embedded in all conceptual models of meandering channel migration, and in numerical models, it occurs over an explicit timescale (i.e., the model time step). However, the sensitivity of modeled channel trajectory to the time step is unknown. In numerical experiments using a curvature‐driven model of channel migration, we find that channel trajectories are consistent over time if the channel migrates ≤10% of the channel width over the feedback timescale. In contrast, channel trajectories diverge if the time step causes migration to exceed this threshold, due to the instability in the co‐evolution of channel curvature and migration rate. The divergence of channel trajectories accumulates with the total run time. Application to hindcasting of channel migration for 10 natural rivers from the continental US and the Amazon River basin shows that the sensitivity of modeled channel trajectories to the time step is greatest at low (near‐unity) channel sinuosity. A time step exceeding the criterion causes over‐prediction of the width of the channel belt developed over millennial timescales. These findings establish a geometric constraint for predicting channel migration in landscape evolution models for lowland alluvial rivers, upland channels coupled to hillslopes and submarine channels shaped by turbidity currents, over timescales from years to millennia.

On the Performance of Noma Systems with Different User Grouping Strategies

This paper investigates several critical issues on the ergodic sum capacity and system outage performance of downlink non-orthogonal multiple access (NOMA) systems with different numbers of users per cluster sharing the same resource. The outcomes from this work suggest that NOMA systems with more users per cluster perform better under a low channel gain, while those with fewer users per cluster perform better under a high channel gain. It discloses a fact that a traditional NOMA system with a fixed user grouping scheme may not be a good choice to deal with complex channel conditions with diverse applications. To address the issue, this paper introduces a concept of mixed user grouping NOMA, which outperforms OMA and traditional NOMA significantly. The work in this paper lays a foundation for more further investigations on mixed user grouping NOMA systems.

MR-SFAMA-Q: A MAC Protocol based on Q-Learning for Underwater Acoustic Sensor Networks

<p>In recent years, with the rapid development of science and technology, many new technologies have made people’s exploration of the ocean deeper and deeper, and due to the requirements of national defense and marine development, the underwater acoustic sensor network (UASN) has been paid more and more attention. Nevertheless, the underwater acoustic channel has the properties of considerable propagation delay, limited bandwidth, and unstable network topology. In order to improve the performance of the medium access control (MAC) protocol in UASN, we propose a new MAC protocol based on the Slotted-FAMA of Multiple Reception (MR-SFAMA) protocol. The protocol uses the Q-Learning algorithm to optimize the multi-receiver handshake mechanism. The current state is judged according to the received node request, and the Q-table is established. Through the multi-round interaction between the node and the environment, the Q-table is continuously updated to obtain the optimal strategy and determine the optimal data transmission scheduling scheme. The reward function is set according to the total back-off time and frame error rate, which can reduce the packet loss rate during network data transmission while reducing the delay. In addition, the matching asynchronous operation and uniform random back-off algorithm are used to solve the problem of long channel idle time and low channel utilization. This new protocol can be well applied to unstable network topology. The simulation results show that the protocol performs better than Slotted-FAMA and MR-SFAMA regarding delay and normalized throughput.</p> <p> </p>

A CPW THz-MIMO antenna with reduced mutual coupling using Frequency Selective Surface for future wireless applications

In this article, we propose a novel THz-MIMO antenna system for future wireless applications. The performance of THz systems is prominently influenced by the MIMO configuration of the antenna. Increased signal attenuation and bit error rate (BER) are major hurdles to system performance at THz frequencies. MIMO antenna diversity techniques at the RF front end can significantly improve system performance. Toward this aim, this work attempts to develop a new THz-MIMO antenna system for future wireless applications. The proposed antenna uses a modified version of a traditional rectangular patch as the radiating element. The combination of a co-planar waveguide (CPW) feed structure and a modified stair-case radiator with an inverted L-shaped arch achieves excellent impedance matching between the feed line and the radiator, resulting in a broad bandwidth in the THz range. To evaluate the diversity performance of the antenna, both spatial and orthogonal 2-port antenna systems are designed and analyzed. Furthermore, isolation is enhanced by placing a frequency-selective surface (FSS) between the radiators of the proposed 4-port antenna. This design offers dual bandwidth, covering the ranges of 2.3–2.7 THz and 5.5–8.9 THz. The proposed antenna achieves very low mutual coupling (less than −30 dB), an extremely low envelope correlation coefficient (ECC) of 0.00001, and a low channel capacity loss (CCL) of 0.1 bps/Hz.

Performance analysis of OSSK-UWOC systems considering pointing errors and channel estimation errors.

In this paper, we present the bit error rate (BER) performance of the underwater wireless optical communication (UWOC) systems using the optical space shift keying (OSSK) on the gamma-gamma turbulent fading channel, which also considers pointing errors and channel estimation errors. Firstly, we develop the new expressions for the probability density function (PDF) based on the Gamma-Gamma distribution with error factors. Subsequently, we analyze the statistical characteristic of the difference in attenuation coefficients between two channels in the OSSK system, by which we provide analytical results for evaluating the average BER performance. The results show that the effective improvement of spectral efficiency (SE) and BER performance is achieved by rationally allocating the number of lasers and detectors in the system. The OSSK-UWOC system performs better when a narrow beam waist is used. Furthermore, the presence of channel estimation error brings the BER performance advantage to the system, and the system with a high channel estimation error (ρ = 0.7) shows a 4 dB improvement in signal-to-noise ratio (SNR) gain compared to the system with a low channel estimation error (ρ = 0.95). The findings in this paper can be used for the UWOC system design.

A Secure Emergency Data Handling in Wireless Body Area Network Using Channel Allocation Schema

ABSTRACT: The Wireless Body Area Network is universal tool based on block chain storage as ledgers to handle patient Database confidentially and avoid loss of data in recent data handling technologies with distributed storage. This solves the major drawback of wireless nodes with high degree of security with highly confidential data transmission among the Wireless Body Area Network also called WBAN nodes. The major challenge is to handle emergency data from the patients at any time. Hence this research work aims to focus the emergency data handling with channel sensation and data fixation in ledgers based on channel allocation. [1] The simulated output shows the data transmission with low delay and high channel utilization and enhanced throughput. Key Terms: WBAN, block chain, channel utilization, emergency data

Impact of nanoparticle agglomeration on thermal conductivity of molten salt based nanofluids: Insights from molecular dynamics and lattice Boltzmann methods

The nanoparticle aggregation has significant influence on heat transfer properties. The contradictions between different researches exist and the underlying mechanisms of heat conduction remain unclear. To address these issues, the thermal conductivity of solar salt-SiO2 nanofluids in the non-aggregated and aggregated states was investigated, based on the combination of the advantages of molecular dynamics (MD) in revealing physical insights and lattice Boltzmann method (LBM) in simulating properties for complex structures. LBM models were simplified on the basic of MD results. Different heat transfer physics in nanofluids at nanoscale and mesoscale were compared. The results show that the thermal conductivity of aggregated nanofluid is higher than the non-aggregated nanofluid. By analyzing the diffusion coefficient, number density and vibrational density of states, we found that the previous hypotheses (such as Brownian motion, interfacial layer and interfacial thermal resistance) cannot explain the enhanced thermal conductivity induced by the nanoparticle agglomeration. The heat transfer mechanisms of aggregated nanofluid were further analyzed from new perspectives, i.e., the contributions of different material components and fluctuation modes to heat flux. It is found that the nanoparticle aggregation leads to the nanoparticle contribution increase, indicating the formation of low thermal resistance channels within the aggregates. The heat conduction contributed by collision decreases in the aggregated state, while that contributed by potential energy increases. Moreover, the thermal conductivity of aggregated nanofluid is negatively correlated with temperature, aggregate size and fractal dimension of agglomerates, and positively correlated with mass fraction of nanoparticles, degree of agglomeration, and backbone length of each aggregate.

Channel Expansion Strategies in the Presence of Asymmetric Competitive Retail Platforms

The success of online retail platforms with hybrid reselling and agency selling has been well documented. Recently, manufacturers are expanding channels in competitive retail platforms (such as JingDong and Tmall) on the basis of reselling. Considering two asymmetric competitive retail platforms, we investigate the incentive for channel expansion under various strategies: agency selling in the incumbent platform, agency selling, or reselling in the asymmetric competing platform. Our analysis shows that the manufacturer's channel expansion strategies depend on the market potential ratio, competition intensity, and agency channel costs. Manufacturers prefer channel expansion when agency channel costs are small or the market potential ratio is above a threshold. Interestingly, even the competing platform has a smaller market potential, manufacturers may still prefer to expand the agency selling channel in the competing platform rather than the incumbent platform. When the market potential ratio is large, under low agency channel costs, the impact of competition on channel expansion strategies is nonmonotonic, and moderate competition motivates manufacturers to expand the channel by reselling rather than agency selling in the competing platform. Furthermore, we find moderate slotting fee or commission rate could make manufacturers and the incumbent platform better off when the market potential ratio is small.

Low Complexity Hybrid-Field Channel Estimation Based on Simultaneous Weighted OMP Algorithm in Extreme Large-Scale MIMO Systems

Low Complexity Hybrid-Field Channel Estimation Based on Simultaneous Weighted OMP Algorithm in Extreme Large-Scale MIMO Systems

Curved toroidal row column addressed transducer for 3D ultrafast ultrasound imaging.

3D Imaging of the human heart at high frame rate is of major interest for various clinical applications. Electronic complexity and cost has prevented the dissemination of 3D ultrafast imaging into the clinic. Row column addressed (RCA) transducers provide volumetric imaging at ultrafast frame rate by using a low electronic channel count, but current models are ill-suited for transthoracic cardiac imaging due to field-of-view limitations. In this study, we proposed a mechanically curved RCA with an aperture adapted for transthoracic cardiac imaging (24 × 16 mm²). The RCA has a toroidal curved surface of 96 elements along columns (curvature radius rC = 4.47 cm) and 64 elements along rows (curvature radius rR = 3 cm). We implemented delay and sum beamforming with an analytical calculation of the propagation of a toroidal wave which was validated using simulations (Field II). The imaging performance was evaluated on a calibrated phantom. Experimental 3D imaging was achieved up to 12 cm deep with a total angular aperture of 30° for both lateral dimensions. The Contrast-to-Noise ratio increased by 12 dB from 2 to 128 virtual sources. Then, 3D Ultrasound Localization Microscopy (ULM) was characterized in a sub-wavelength tube diameter. Finally, 3D ULM was demonstrated on a perfused ex-vivo swine heart to image the coronary microcirculation.

Analysis of flow and heat transfer performance of different types of flow channels in printed circuit heat exchangers for pre-coolers

The shape of fins in flow channels of printed circuit heat exchangers (PCHE) significantly affects the heat exchanger performance. In the pre-cooler condition of the marine supercritical CO2 Brayton cycle power generation system, this study focuses on three typical discontinuous flow channel printed circuit heat exchangers. The investigation involves a numerical analysis of flow and heat transfer performance using CFD method. The comparative consequences illuminate that the rectangular fin channel exhibits the optimal heat transfer performance, and temperature drops are 1.18 times and 1.23 times, exceeding those of airfoil and rhombic fin channels, respectively. All three flow channels show different degrees of temperature drop reduction along the direction of fluid-flow. However, the rectangular fin channel demonstrates the worst flow performance, as pressure drops are 16.6 times and 17.8 times, higher than those of airfoil and rhombic fin channels, respectively. By calculating the values of Nu/f and Q/?p, the comprehensive performance of each flow channel is ranked from high to low airfoil fin channel, rhombic fin channel, and rectangular fin channel. This research provides guidance for optimizing the design and applying PCHE in engineering for marine supercritical CO2 Brayton cycle pre-coolers.

Low Complexity Channel Tracking for Hybrid Beamforming Systems

Low Complexity Channel Tracking for Hybrid Beamforming Systems

Enhancing Row-column array (RCA)-based 3D ultrasound vascular imaging with spatial-temporal similarity weighting.

Ultrasound vascular imaging (UVI) is a valuable tool for monitoring the physiological states and evaluating the pathological diseases. Advancing from conventional two-dimensional (2D) to three-dimensional (3D) UVI would enhance the vasculature visualization, thereby improving its reliability. Row-column array (RCA) has emerged as a promising approach for cost-effective ultrafast 3D imaging with a low channel count. However, ultrafast RCA imaging is often hampered by high-level sidelobe artifacts and low signal-to-noise ratio (SNR), which makes RCA-based UVI challenging. In this study, we propose a spatial-temporal similarity weighting (St-SW) method to overcome these challenges by exploiting the incoherence of sidelobe artifacts and noise between datasets acquired using orthogonal transmissions. Simulation, in vitro blood flow phantom, and in vivo experiments were conducted to compare the proposed method with existing orthogonal plane wave imaging (OPW), row-column-specific frame-multiply-and-sum beamforming (RC-FMAS), and XDoppler techniques. Qualitative and quantitative results demonstrate the superior performance of the proposed method. In simulations, the proposed method reduced the sidelobe level by 31.3 dB, 20.8 dB, and 14.0 dB, compared to OPW, XDoppler, and RC-FMAS, respectively. In the blood flow phantom experiment, the proposed method significantly improved the contrast-to-noise ratio (CNR) of the tube by 26.8 dB, 25.5 dB, and 19.7 dB, compared to OPW, XDoppler, and RC-FMAS methods, respectively. In the human submandibular gland experiment, it not only reconstructed a more complete vasculature but also improved the CNR by more than 15 dB, compared to OPW, XDoppler, and RC-FMAS methods. In summary, the proposed method effectively suppresses the side-lobe artifacts and noise in images collected using an RCA under low SNR conditions, leading to improved visualization of 3D vasculatures.

Geoecological and economic consequences of creation, drainage and possible variants of restoration the Kakhovsky reservoir

In the article, in the aspect of engineering and geological safety of structures and communications, the long-term hydrogeological consequences of the support and drainage effects at coastal areas of destroyed Kakhovsky hydro node reservoir as a leading eco-forming component of a giant natural and man-made geosystem are considered. In particular, it included Zaporizhia NPP, the largest in Europe, and the largest irrigation systems in Ukraine. The consequences of the hydrodynamic disaster due to explosion of Kakhovskaya HPP, the dynamics and current state of drainage of the bed of its reservoir are briefly described, according to the data of GIS analysis of space images. And also – the state of hydrogeological and engineering-geological conditions in the reservoir support zone at the time of disaster and in retrospect. A calculated assessment of changes in hydrogeological conditions for the next 10-15 years has been carried out. Long-term natural and man-made threats that arose as a result of such changes in hydrogeological (geofiltration and geodynamic) conditions are named. The set of socio-economic threats that arose due to the negative consequences of Kakhovsky reservoir existence and draining is described. It is emphasized that the restoration of hydrotechnical and water management parameters of the reservoir in the previous values (according to the conservative version) will lead to secondary geospatial water saturation of subsiding loess-loamy silty-clay floatingable rocks that have already undergone deformations due to a decrease in geotechnical stability during the initial flooding and subsequent drainage. This will start a new stage in the formation of dangerous violations of stress-deformed state of coastal slopes, of Zaporizhzhya NPP responsible structures foundation and in nearby cities and towns. A socially and ecologically favorable option for the rehabilitation of affected region is possible only on the modern European ideological and technological basis of taking into account the maximum permissible changes in the hydrological network, i.e. by means of: creating a cascade of low support channel reservoirs with locks and small hydroelectric power stations, reconstruction of riverside ponds and water supply systems, transfer of domestic water supply to underground sources, irrigated lands – for drip irrigation, ecological reclamation and afforestation of drained lands.

Citrus sinensis manganese tolerance: Insight from manganese-stimulated secretion of root exudates and rhizosphere alkalization

We used manganese (Mn)-tolerant ‘Xuegan’ (Citrus sinensis) seedlings as materials and examined the characterization of Mn uptake and Mn-activated-release of root exudates under hydroponic conditions. We observed that root and shoot Mn bioaccumulation factor (BCF) reduced with the increase of Mn supply, and that Mn transfer factor (Tf) reduced greatly as Mn supply increased from 0 to 500 μM, beyond which Tf slightly increased with increasing Mn supply, suggesting that Mn supply reduced the ability to absorb and accumulate Mn in roots and shoots, as well as root-to-shoot Mn translocation. Without Mn, roots alkalized the solution pH from 5.0 to above 6.2, while Mn supply reduced root-induced alkalization. As Mn supply increased from 0 to 2000 μM, the secretion of root total phenolics (TPs) increased, while the solution pH decreased. Mn supply did not alter the secretion of root total free amino acids, total soluble sugars, malate, and citrate. Mn-activated-release of TPs was inhibited by low temperature and anion channel inhibitors, but not by protein biosynthesis inhibitor. Using widely targeted metabolome, we detected 48 upregulated [35 upregulated phenolic compounds + 13 other secondary metabolites (SMs)] and three downregulated SMs, and 39 upregulated and eight downregulated primary metabolites (PMs). These findings suggested that reduced ability to absorb and accumulate Mn in roots and shoots and less root-to-shoot Mn translocation in Mn-toxic seedlings, rhizosphere alkalization, and Mn-activated-release of root exudates (especially phenolic compounds) contributed to the high Mn tolerance of C. sinensis seedlings.

Stopping Microfluidic Flow.

A cross-comparison of three stop-flow configurations-such as low-pressure (LSF), high-pressure open-circuit (OC-HSF), and high-pressure short-circuit (SC-HSF) stop-flow-is presented to rapidly bring a high velocity flow O(m s-1) within a microchannel to a standstill O(µm s-1). The performance of three stop-flow configurations is assessed by measuring residual flow velocities within microchannels having three orders of magnitude different flow resistances. The LSF configuration outperforms the OC-HSF and SC-HSF configurations within a high flow resistance microchannel and results in a residual velocity of <10µms-1. The OC-HSF configuration results in a residual velocity of <150µms-1 within a low flow resistance microchannel. The SC-HSF configuration results in a residual velocity of <200µms-1 across the three orders-of-magnitude different flow resistance microchannels, and <100µms-1 for the low flow resistance channel. It is hypothesized that residual velocity results from compliance in fluidic circuits, which is further investigated by varying the elasticity of microchannel walls and connecting tubing. A numerical model is developed to estimate the expanded volumes of the compliant microchannel and connecting tubings under a pressure gradient and to calculate the distance traveled by the sample fluid. A comparison of the numerically and experimentally obtained traveling distances confirms the hypothesis that the residual velocities are an outcome of the compliance in the fluidic circuit.