Low Channel Research Articles

Development of a composite MoS2/PEI nanofiltration membrane for radionuclides efficient removal from aquatic environments

The simultaneously efficient removal of radionuclides and heavy metals is an important and challenging topic for aquatic environmental protection. In this work, molybdenum disulfide (MoS2) with heavy metal ion adsorption capacity and positively charged polyethyleneimine (PEI) were used to fabricate a novel layer-by-layer (LbL) self-assembly composite membrane by a simple alternating immersion method. The unique structure with positive charge ensures high removal for toxic metals (RCs(I) = 99.83 %, RSr(II) = 100 %, RHg(II) = 99.2 %, RPb(II) = 98.13 %, RAs(III) = 98.5 %). The inherent low resistance channels in MoS2 provided the optimized composite membrane an elevated water flux. Long-term experiments and membrane regeneration also demonstrated that the membrane possesses exceptional stability and reusability in removing low levels of radionuclides Cs(I) and Sr(II) from water. This study confirms the feasibility of the MoS2-PEI composite membrane for the treatment of contaminated waters containing radionuclides and heavy metals.

Atomistic mechanism of coupling between cytosolic sensor domain and selectivity filter in TREK K2P channels

The two-pore domain potassium (K2P) channels TREK-1 and TREK-2 link neuronal excitability to a variety of stimuli including mechanical force, lipids, temperature and phosphorylation. This regulation involves the C-terminus as a polymodal stimulus sensor and the selectivity filter (SF) as channel gate. Using crystallographic up- and down-state structures of TREK-2 as a template for full atomistic molecular dynamics (MD) simulations, we reveal that the SF in down-state undergoes inactivation via conformational changes, while the up-state structure maintains a stable and conductive SF. This suggests an atomistic mechanism for the low channel activity previously assigned to the down state, but not evident from the crystal structure. Furthermore, experimentally by using (de-)phosphorylation mimics and chemically attaching lipid tethers to the proximal C-terminus (pCt), we confirm the hypothesis that moving the pCt towards the membrane induces the up-state. Based on MD simulations, we propose two gating pathways by which movement of the pCt controls the stability (i.e., conductivity) of the filter gate. Together, these findings provide atomistic insights into the SF gating mechanism and the physiological regulation of TREK channels by phosphorylation.

Study of the Impact of Fairness Concern on Low Carbon Dual Channel Supply Chain

A supplier-dominated secondary low-carbon dual channel supply chain is used as the object of study, and the expected demand function is constructed when the seller has the advantage of market information in the information asymmetry situation, in order to explore the impact of fairness concern on supply chain decision making. The utility functions in the three scenarios were analyzed and compared, and mathematical simulations were conducted according to market demand information available to the seller and the effort input of decision-making subject. Studies have shown that: Whichever decision-making subject has the fairness concern behavior does not affect the supplier as a higher profit maker; information on market demand also needs to be taken into account when considering the impact of the level of fairness concern on profits of the decision maker. When suppliers misjudge market demand, wholesale price increases are slowed if sellers have equity concerns, and sellers may engage in retaliatory behavior if equity demands are not met. In addition, low carbon demand is profitable for suppliers in supplier-led supply chains regardless of market demand, and low carbon sales efforts are not necessarily profitable for retailers.

Evaluation of plate heat exchangers comprising sections with different chevron angle arrangements

Gasketed Plate Heat Exchangers (GPHEs) are essential equipment for thermal control of oil facilities owing to their compactness and well-organized assembly concept. In order to satisfy heat loads of several megawatts, numerous and large plates are necessary. The application of GPHEs with plentiful plates yields flow maldistribution which affects GPHE thermal–hydraulic performance. With the purpose of matching different heat loads and processing conditions or as an alternative to reduce maldistribution effects, GPHEs with mixed arrangements, comprising sections where channels contain different geometrical features, may be selected. This works addresses the evaluation of flow and pressure distributions in GPHEs with mixed arrangements. The pressure drop in each GPHE section is initially approximated by the pressure drop in parallel pipes, neglecting the pressure drop in the ports. With this assumption, the inlet flow rate is divided into two different parts. The pressure distributions in each section are assumed to maintain flow features of m2-model for U-type arrangement. The friction factor for each GPHE segment was determined with independent experiments including only one section type and with a small number of channels as to avoid flow maldistribution. Friction factor correlations were determined for single section GPHEs where each channel can be formed with plates containing different chevron angles: 30°/30°, 60°/60°, 66°/66°, 30°/60° and 30°/66°, with channel Reynolds number ranging from 260 to 3,080. Subsequently, experiments with GPHEs containing mixed sections with high and low pressure drop channels were performed: 60°/60° and 30°/30°, 30°/30° and 66°/66°; with total number of channels up to 180. The channel pressure drop was measured in regularly spaced locations. The pressure drop in each GPHE segment has been predicted with the fractional RMS deviation equal to 2.2%. Although the mass flow rate per channel has not been measured, it is expected that the predicted flow rate distribution can reasonably stand for the real one and, therefore, assisting in proper thermal performance evaluation.

Hierarchical Training of Deep Neural Networks Using Early Exiting.

Deep neural networks (DNNs) provide state-of-the-art accuracy for vision tasks, but they require significant resources for training. Thus, they are trained on cloud servers far from the edge devices that acquire the data. This issue increases communication cost, runtime, and privacy concerns. In this study, a novel hierarchical training method for DNNs is proposed that uses early exits in a divided architecture between edge and cloud workers to reduce the communication cost, training runtime, and privacy concerns. The method proposes a brand-new use case for early exits to separate the backward pass of neural networks between the edge and the cloud during the training phase. We address the issues of most available methods that, due to the sequential nature of the training phase, cannot train the levels of hierarchy simultaneously or they do it with the cost of compromising privacy. In contrast, our method can use both edge and cloud workers simultaneously, does not share the raw input data with the cloud, and does not require communication during the backward pass. Several simulations and on-device experiments for different neural network architectures demonstrate the effectiveness of this method. It is shown that the proposed method reduces the training runtime for VGG-16 and ResNet-18 architectures by 29% and 61% in CIFAR-10 classification and by 25% and 81% in Tiny ImageNet classification, respectively, when the communication with the cloud is done over a low bit rate channel. This gain in the runtime is achieved, while the accuracy drop is negligible. This method is advantageous for online learning of high-accuracy DNNs on sensor-holding low-resource devices such as mobile phones or robots as a part of an edge-cloud system, making them more flexible in facing new tasks and classes of data.

Численно-аналитическая модель для интерпретации результатов индикаторных исследований нефтяных пластов: решение прямой задачи при наличии каналов низкого фильтрационного сопротивления

The article considers the problem of interpretation of tracer tests in oil reservoirs, into which a specific chemical substance - tracer - is injected via an injection well for flow monitoring and tracer concentration measurements in surrounding production wells. The testing data provide evidence of the existence of low resistance channels in the reservoirs, along which the tracer moves at velocities several orders of magnitude higher than in the reservoir. The nature and properties of these channels are unknown, and a semi-analytical model involving two small parameters is proposed to solve this problem. This makes it possible to construct two non-conjugate solutions: universal numerical and analytical. Such an approach allows us to solve both direct and inverse problems. The present article is devoted to solving the direct problem. The problem of pressure distribution in a rectangular reservoir pattern is solved in dimensionless coordinates and is universal, i.e., it does not depend on the size of the area and the pressure drop. This solution is approximated by power functions and is further used to determine the mass transfer between channel and reservoir. The problem of tracer slug propagation through the channel obeys the law of conservation of tracer mass and Darcy's law. Its solution is found by the methods of characteristics under the condition of smallness of the parameter reflecting the ratio of reservoir permeability to channel permeability. The results of the semi-analytical solution are compared with the numerical solutions previously obtained by other authors. The fundamental difference between these solutions is the presence of numerical diffusion when using the finite-difference method of solution, which leads to the «dissipation» of the trace slug edges.

EEG source imaging of hand movement-related areas: an evaluation of the reconstruction and classification accuracy with optimized channels

The hand motor activity can be identified and converted into commands for controlling machines through a brain-computer interface (BCI) system. Electroencephalography (EEG) based BCI systems employ electrodes to measure the electrical brain activity projected at the scalp and discern patterns. However, the volume conduction problem attenuates the electric potential from the brain to the scalp and introduces spatial mixing to the signals. EEG source imaging (ESI) techniques can be applied to alleviate these issues and enhance the spatial segregation of information. Despite this potential solution, the use of ESI has not been extensively applied in BCI systems, largely due to accuracy concerns over reconstruction accuracy when using low-density EEG (ldEEG), which is commonly used in BCIs. To overcome these accuracy issues in low channel counts, recent studies have proposed reducing the number of EEG channels based on optimized channel selection. This work presents an evaluation of the spatial and temporal accuracy of ESI when applying optimized channel selection towards ldEEG number of channels. For this, a simulation study of source activity related to hand movement has been performed using as a starting point an EEG system with 339 channels. The results obtained after optimization show that the activity in the concerned areas can be retrieved with a spatial accuracy of 3.99, 10.69, and 14.29 mm (localization error) when using 32, 16, and 8 channel counts respectively. In addition, the use of optimally selected electrodes has been validated in a motor imagery classification task, obtaining a higher classification performance when using 16 optimally selected channels than 32 typical electrode distributions under 10–10 system, and obtaining higher classification performance when combining ESI methods with the optimal selected channels.

Low Complexity Deep Learning Augmented Wireless Channel Estimation for Pilot-Based OFDM on Zynq System on Chip

Low Complexity Deep Learning Augmented Wireless Channel Estimation for Pilot-Based OFDM on Zynq System on Chip

Ball Modular Advanced Cryocooler Control Electronics (MACCE)

To support the application of heritage aerospace coolers and modern tactical coolers to future mission architectures, Ball has developed the Modular Advanced Cryocooler Control Electronics (MACCE). This entirely new cryocooler electronics architecture is based on modularity and scalability in performance supporting a wide range of cryocoolers including 4K Hybrid Systems (J-T + Pre-Cooler), Pulse Tube Cryocoolers, and Stirling Cryocoolers. The MACCE design includes the primary CCE box and an Accelerometer Pre-Amp (APA) box that can be remote mounted. The MACCE architecture includes four high power drive channels and two low power channels supporting >500W of output power, three independent accelerometer feedback control loops for vibration cancellation, high efficiency using GaN FET technology, and a combination of six thermistors and six precision RTD circuits for telemetry. Operational modes include constant power, constant temperature, or open loop. An engineering model of MACCE has been completed and is currently going through qualification. Performance data is presented from box level testing.

An efficient training-from-scratch framework with BN-based structural compressor

Channel pruning is an effective way of compressing convolutional neural networks (CNNs) under constrained resources. The current pruning methods follow a progressive pretrain-prune-finetune pipeline, which is inefficient and computationally expensive. In this paper, we bypass the pretrain-prune-finetune pipeline and propose a novel and efficient model training framework based on online channel pruning, which automatically produces a compact well-performed sub-network in one training-from-scratch pass under a given budget condition. Specifically, we introduce a novel BN-based indicator and a sparsity regularization strategy in the early training stage to iteratively and greedily shrink the model layers, which encourages a high-quality architecture with low channel redundancy. To ensure training stability and promote the generalization ability of the resultant pruned network, we also skillfully incorporate a simple self-distillation framework into our training and pruning pipeline. Extensive experiments indicate that our method can effectively achieve competitive performance on the image classification task compared with the state-of-the-arts.

GEOCRYOLOGICAL CONDITIONS OF THE FORMATION OF GIANT SPRING AUFEIS AT THE ANMANGYNDA RIVER (MAGADAN REGION) ACCORDING TO GEOPHYSICAL DATA

Giant aufeis fields, common in the Northeast of Russia, are the indicators of water exchange processes in cryosphere. The development of ideas about icing processes is relevant both from the fundamental point of view of studying the permafrost evolution, and from the practical point of view – for the development of aufeis hazard measures. The aufeis in the Anmangynda River basin (aufeis glade area 7 km2) is considered representative of the region, and its studies have been carried out since 1962. In 2022, during the period of maximum thawing of the active layer Electrical Resistivity Tomography (ERT) soundings were carried out at the aufeis glade aiming to identify underchannel taliks and flooded fault zones in bedrock, including local areas of groundwater discharge. It was found that within the main river channels there are underchannel taliks up to 30 m deep. According to the results of 2D inversion, local anomalies of low electrical resistivity mark groundwater filtration channels. In 3D geoelectrical models, pipe-like anomalies of low resistivity are identified in the areas of groundwater discharge, interpreted as filtration channels in the alluvium and the zone of exogenous fracturing in bedrock formed by sandy-clay shales, as well as linear vertical anomalies of low resistivity, interpreted as faults. On vertical sections of 3D resistive models, a connection between faults and filtration channels in alluvium and a layer of exogenous fracturing is traced. In the right bank of the valley, geoelectric signs of taliks in the bedrock, presumably associated with fault tectonics, have been established. It is assumed that the identified faults are the additional transit routes for groundwater in the Anmangynda River valley, along with the alluvial aquifer and the zone of exogenous fracturing of bedrock.

Resource-Efficient Multicast URLLC Service in 5G Systems.

Many emerging applications, such as factory automation, electric power distribution, and intelligent transportation systems, require multicast Ultra-Reliable Low-Latency Communications (mURLLC). Since 3GPP Release 17, 5G systems natively support multicast functionality, including multicast Hybrid Automatic Repeat Request and various feedback schemes. Although these features can be promising for mURLLC, the specifications and existing studies fall short in offering guidance on their efficient usage. This paper presents the first comprehensive system-level evaluation of mURLLC, leveraging insights from 3GPP specifications. It points out (i) how mURLLC differs from traditional multicast broadband wireless communications, and (ii) which approaches to provide mURLLC require changing the paradigm compared with the existing solutions. Finally, the paper provides recommendations on how to satisfy strict mURLLC requirements efficiently, i.e., with low channel resource consumption, which increases the capacity of 5G systems for mURLLC. Simulation results show that proper configuration of multicast mechanisms and the corresponding algorithms for mURLLC traffic can reduce resource consumption up to three times compared to the baseline solutions proposed for broadband multicast traffic, which significantly increases the system capacity.

Numerical investigation on thermal-hydraulic performance of variable cross section printed circuit heat exchanger

CO2 transcritical power cycle (CTPC) systems have attracted considerable research focus in the fields of thermoelectric conversion and waste heat recovery. The regenerator is a key component affecting the CTPC system's efficiency. To improve the comprehensive performance of the regenerator, extensive research has been conducted to optimize the regenerator flow channel design. However, the optimization of the traditional Z-channel printed circuit heat exchanger structure (ZPCHE) is limited to constant cross-sectional configurations along the flow direction, which can lead to low channel space utilization. To solve this problem, an efficient variable cross section Z-channel structure (UAPCHE) is proposed in this study. The structure is designed with different cross-sectional shapes along the flow direction to fit the flow path of the main fluid. UAPCHE achieves a coordinated optimization of the heat transfer (Nu), flow (dP), and compactness performance (Q/V) by increasing the effective utilization of the channel space and weakening the damage to the fluid boundary layer. The design principle of the UAPCHE is introduced, and based on this, the structural parameters of the UAPCHE are optimized to achieve the best comprehensive performance. The results show that, compared with the ZPCHE, Nu of UAPCHE can be increased by 16.79%, dP can be reduced by 19.48%, and Q/V can be increased by 22.65%.

Перенос аврорального километрового радиоизлучения посредством каналов с пониженной плотностью на границе плазмосферы

We present the results of Auroral Kilometric Radiation (AKR) measurements near the plasmapause on the ERG (Arase) satellite. The apogee of the satellite's orbit is located near the ecliptic plane, at latitudes ±30°. According to the generally accepted point of view, AKR observation is impossible in this region since it is shielded by the plasmasphere. Simultaneous measurements of AKR and local plasma density made it possible to determine that AKR in near-equatorial regions occur in plasma channels — density inhomogeneities elongated along magnetic field lines. AKR from sources located in the auroral magnetosphere is transferred by these channels to the equatorial region. This work analyzes the conditions for the capture and propagation of AKR in low plasma density channels. In the geometrical optics approximation, we have simulated the conditions for the radiation capture and propagation. The calculation results show that the proposed scheme for AKR capture into plasma channels can explain the measurement results — the radiation transfer from the auroral region to the near-equatorial region.

Transfer of auroral kilometric radiation through low-density channels at the boundary of plasmasphere

We present the results of Auroral Kilometric Radiation (AKR) measurements near the plasmapause on the ERG (Arase) satellite. The apogee of the satellite's orbit is located near the ecliptic plane, at latitudes ±30°. According to the generally accepted point of view, AKR observation is impossible in this region since it is shielded by the plasmasphere. Simultaneous measurements of AKR and local plasma density made it possible to determine that AKR in near-equatorial regions occur in plasma channels — density inhomogeneities elongated along magnetic field lines. AKR from sources located in the auroral magnetosphere is transferred by these channels to the equatorial region. This work analyzes the conditions for the capture and propagation of AKR in low plasma density channels. In the geometrical optics approximation, we have simulated the conditions for the radiation capture and propagation. The calculation results show that the proposed scheme for AKR capture into plasma channels can explain the measurement results — the radiation transfer from the auroral region to the near-equatorial region.

Inverse design of a silicon-based ultra-compact four-channel mode splitter with dual polarizations

We adopt the inverse-designed method and demonstrate an ultra-compact four-channel mode splitter with dual polarizations, which enables mode division multiplexing and polarization division multiplexing simultaneously without changing the mode orders and suitable for fabrication and integration based on silicon-on-insulator platform. The four TE0, TM0, TE1 and TM1 modes at the central wavelength of 1550 nm can be efficiently split with low insertion loss (<1.9 dB), low channel crosstalk (<−17 dB), low reflection loss (<−18 dB). Moreover, the proposed mode splitter has the potential of incorporating the wavelength division multiplexing for mass data transmission and high computing parallelism.

Mg activation anneal of the p-GaN body in trench gate MOSFETs and its effect on channel mobility and threshold voltage stability

This work addresses the impact of the Mg activation anneal step and the resulting acceptor concentration on the channel mobility and VT stability of vertical MOSFETs. Increasing the annealing time with N2 only ambient and the annealing temperature with O2 in the ambient is shown to be effective in increasing the channel acceptor concentration. When the effective acceptor concentration is increased, the mobility is degraded due to a transition in the main scattering mechanism from Coulomb to surface roughness scattering. Degradation of the on-state current and maximum transconductance at high operating temperatures was linked to bulk mobility degradation of the drift layer due to lattice scattering. The two Mg activation annealing conditions considered here show different trends with regard to the threshold voltage stability, while N2 only ambient did not impact this parameter, including O2 increased threshold voltage instability. It is shown that increasing the Mg chemical concentration in the p-GaN layer degrades channel mobility and threshold voltage stability, irrespectively of the effective acceptor concentration, providing evidence for degradation of the channel/dielectric interface characteristics with higher Mg chemical concentration. This study shows that it is possible to achieve very low threshold voltage hysteresis and high channel mobility by reducing the Mg chemical concentration while maintaining high effective acceptor concentration. These results provide key insights for the development of vertical GaN FETs.

Direct Numerical Simulation of Involute Channel Turbulence

Abstract A direct numerical simulation (DNS) study was performed on turbulent flow in the high flux isotope reactor involute channel geometry to develop a numerical database and determine the differences compared with a flat parallel channel. The varying channel curvature along the walls was studied for differences in mean profiles. Parameters of interest include streamwise velocity, turbulent kinetic energy (TKE), and turbulence dissipation rate, as well as Reynolds stresses and turbulence transport terms. Profile sampling was carried out at 10 locations along the span of the involute. Additional DNS studies were performed on smaller domains of comparable curvature to the involute domain: a high curvature channel (high circular), a low curvature channel (low circular), and a flat channel (flat). Each of these four cases was compared against each other and to other DNS studies performed on parallel flows. The results indicate that the bulk involute channel flow does not differ significantly from a flat parallel channel flow and that the curvature of the walls does not significantly alter the mean flow parameters. However, the regions of the involute channel near the side walls exhibit relatively low magnitude twin recirculation structures driven toward the side walls from the centerline of the channel, which warrants further study.

Transmit beam design for tissue harmonic volume imaging of muscular tissues with a row-column array

Row-Column-addressed Arrays (RCAs), which have recently become commercially available, transmit along the rows and receive along columns of a 2D array in order to produce 3D volume images with low channel count. Imaging of the inherently three-dimensional, layered, and fibrous structure of muscular tissues in 3D using an RCA can improve evaluations of muscle function and disease compared to conventional 2D cross-sectional imaging, but volume images obtained using an RCA suffer from low lateral spatial resolution, low contrast, and grating lobe artifacts. Tissue harmonic imaging (THI) employs nonlinear acoustic effects to image at twice the transmit frequency, and can yield increased spatial resolution, increased contrast, and decreased artifacts from grating lobes. Here we investigate transmission considerations for THI in muscular tissues using a commercially available RCA (Vermon RC6gV). The parameter space is explored efficiently with frequency domain simulations of the 3D Westervelt equation. Pulse inversion imaging is applied experimentally using both steered plane wave and focused transmits to evaluate THI with an RCA in tissue phantoms and in muscular tissue. Pulse inversion volume images are compared to conventional images in terms of signal-to-noise, contrast, and ability to identify layers and fibrous structures in muscle in 3D. [Work supported by NIH HEAL Initiative R61AT012282.]

Exploiting Successive Interference Cancellation for Spectrum Sharing Over Unlicensed Bands

Harmonious coexistence among different unlicensed wireless technologies has became increasingly important due to the spectrum shortage problem. As a representative case, we focus on addressing LTE-LAA and WiFi coexistence in unlicensed bands. Traditionally, collision avoidance-based medium access control (MAC) protocols adopted by both LAA and WiFi have led to low channel utilization and fairness. In this paper, we explore physical-layer interference suppression techniques (e.g., successive interference cancellation, SIC) to enhance the spectrum utilization of coexisting LAA and WiFi networks. We propose a SIC-aware MAC protocol that embraces concurrent transmissions and optimizes the channel access strategy at the MAC layer, so as to mitigate the interference (same-technology or cross-technology) due to excess channel contentions. We theoretically analyze the network throughput by extending Bianchi's Markov model, considering the impact of concurrent transmissions and SIC. We also extend the analysis to consider MIMO and MU-MIMO links with SIC. We validate our theoretical analysis and the effectiveness of the proposed MAC protocol via extensive simulations. We also implement a prototype LAA/WiFi SIC receiver on USRP devices to demonstrate the feasibility of cross-technology SIC and the proposed MAC protocol.