Channel Behavior Research Articles

Influence of surface roughness on fluid flow and solute transport through 3D crossed rock fractures

The influence of surface roughness on fluid flow and solute transport through three-dimensional (3D) crossed rock fractures are investigated by numerical simulations. Three crossed fracture models with different degrees of surface roughness are established by two intersecting rough-walled fractures with four branches. The fracture surface morphological data are measured from three natural fractures in sandstone and granite rock samples. The fluid flow is simulated by solving the Navier-Stokes equations and solute transport is simulated by solving the advective-diffusion equation. By rotating one fracture plane while fixing the other, series of intersection models with different angles between the two crossed fractures are established to investigate the influence of the intersecting angle. Simulation results of the rough-walled fractures are compared with the smooth parallel-plate model, showing that the surface roughness significantly enhances channeling and mixing for fluid flow and solute transport at fracture intersections. The mechanism is that the complex geometry of the intersection for rough-walled models results in reallocation of fluid pathways at the intersection, which consequently affect the mixing behavior depending on the Peclet number. The intersecting angle affects the channeling and mixing behavior because it influences the geometrical structure of the fracture intersection. The correlation between the mixing ratio and the geometrical characteristics of intersections is quantified by a relative roughness parameter. The results reveal that the widely adopted smooth parallel-plate model may lead to significant uncertainty in predicting the solute transport in crossed fractures, especially at intersections with unmated fracture surfaces. The correlation between the mixing ratio and the roughness parameter developed in this study can be incorporated into discrete fracture network models to improve their performance in estimating solute transport in fractured rocks.

Characterization and modeling of the reverse behavior of a vertical power MOSFET

AbstractIn this work, the static and dynamic reverse behavior of a vertical structure Si power MOSFET is characterized. The BSIM3 model is adopted and extended to describe the channel current considering asymmetric channel behavior caused by the vertical structure. The diffusion capacitance of the body diode is analyzed, which is critical for the reverse recovery behavior but currently not precisely defined in power MOSFET models. To accurately depict the reverse recovery current, two diode models with diffusion capacitance definitions based on the solution of different methods are built into the MOSFET model and their performance is compared. The result shows that to describe the reverse recovery of the body diode for smaller current range simulation, the stored charge model is recommended, but when scalability is necessary, the carrier distribution model is more suitable.

The Role of Collapsed Bank Soil on Tidal Channel Evolution: A Process‐Based Model Involving Bank Collapse and Sediment Dynamics

AbstractWe develop a process‐based model to simulate the geomorphodynamic evolution of tidal channels, considering hydrodynamics, flow‐induced bank erosion, gravity‐induced bank collapse, and sediment dynamics. A stress‐deformation analysis and the Mohr‐Coulomb criterion, calibrated through previous laboratory experiments, are included in a model simulating bank collapse. Results show that collapsed bank soil plays a primary role in the dynamics of bank retreat. For bank collapse with small bank height, tensile failure in the middle of the bank (Stage I), tensile failure on the bank top (Stage II), and sectional cracking from bank top to the toe (Stage III) are present sequentially before bank collapse occurs. A significant linear relation is observed between bank height and the contribution of bank collapse to bank retreat. Contrary to flow‐induced bank erosion, bank collapse prevents further widening since the collapsed bank soil protects the bank from direct bank erosion. The bank profile is linear or slightly convex, and the planimetric shape of tidal channels (gradually decreasing in width landward) is similar when approaching equilibrium, regardless of the consideration of bank erosion and collapse. Moreover, the simulated width‐to‐depth ratio in all runs is comparable with observations from the Venice Lagoon. This indicates that the equilibrium configuration of tidal channels depends on hydrodynamic conditions and sediment properties, while bank erosion and collapse greatly affect the transient behavior (before equilibrium) of the tidal channels. Overall, this contribution highlights the importance of collapsed bank soil in investigating tidal channel morphodynamics using a combined perspective of geotechnics and soil mechanics.

Molecular insight into the oil charging mechanism in tight reservoirs

Tight oil reservoirs are dominated by nano-pore throats that significantly impede the migration of crude oil. Understanding the oil charging behavior in these nanoscale channels is critical to assess the oil accumulation. In this work, molecular dynamics (MD) simulations were adopted to uncover molecular insights into the oil charging and migration through differently-sized hydrophilic nano-pore throats. On the one hand, the dynamic pathway and the energetic driving force of the oil charging process were clarified. On the other hand, with analyzing the force that the oil undergoes when going across nano-pore throats, the capillary pressure for different throat sizes was calculated; based on which, we propose an MD simulation method to assess the oil accumulation threshold of tight reservoirs. Taken together, this work expends our knowledge of the fluid migration through nano-pores, and it could facilitate future studies on the evaluation of tight oil reservoirs.

Thin metallic wave-like channel bipolar plates for proton exchange membrane fuel cells: Deformation behavior, formability analysis and process design

Metallic bipolar plates are one of the main components of proton exchange membrane fuel cells, and the selection of channel layout is a key point for the design of metal bipolar plate which affects both the performance and the manufacturability of bipolar plates directly. Among various design proposals, the wave-like channel is found as a promising layout to enhance the performance of the fuel cell stack. However, the forming rules of this channel layout are unclear and still to be investigated. In this paper, the influences of the various factors of die sets on the forming behavior of the wave-like channel are explored through experiments. The rules derived from experiments are verified by simulation and summarized as the empirical rule of thickness reduction and maximum pressing depth. For 316 stainless steel sheet, fracture occurs when the thickness reduction reaches around 30%. Before fracture, the relationship between the thickness reduction and the pressing depth can be described as an empirical exponential formula. Finally, guidance is also provided for the die set design of wave-like channels.

Doppler Shift in a Radiating Cable System in Tunnel Environments: A Theoretical Analysis

For many years, radiating cables have been used to provide coverage inside tunnels or underground venues. Due to the progress in transport technology and the increasing demand on mobile communications the necessity of having a clear understanding of the behaviour of the wireless channel in these environments is essential to successfully deploy radiating cable systems. In this context, the main objective of this paper is the study of the Doppler shift generated in a radiating cable system due to a mobile receiver changing positions along a defined path inside a tunnel. Doppler shift is an important effect in mobile communications as it degrades system performance. The study shows that a correct selection of the operating frequency used for the radiating cable can help reduce the Doppler shift and in turn the Doppler spread in the channel. At the same time the study reveals how the Doppler shift of a radiating cable generated by a fast-moving user is related to its radiation pattern, especially at the cable terminations. Finally, Doppler spread is accentuated when the cross section of the tunnel is reduced. These results can be used as a reference for improving the design of radiating cable systems applied in mobile communications with fast-moving vehicles, e.g. high-speed trains.

Towards the utilization of optical ground-to-space links for low earth orbiting spacecraft

The microwave spectrum has become a highly limited resource in satellite communications owing to an ever increasing demand for bandwidth and capacity. Therefore, a shift to the exploitation of optical carrier frequencies is currently underway. Focusing on high-rate transmissions of payload data from remote sensing satellites, operational systems, like the well-known European Data Relay Satellite system, are based on optical inter-satellite links. Besides, direct-to-earth free-space optical communications from low Earth orbiting spacecraft hold high potential for upcoming space missions through lower complexity. In that regard, we study the viability of the ground-to-space beacon laser signal of optical ground stations to be additionally modulated with tele-command tokens. Such an optical return channel could be variously put into use, for example to trigger automatic repeat requests of payload data downlinks, for jamming-free control of the spacecraft or for high-rate software uploads to its on-board processor. A particular challenge is posed by the unequal fading behavior of the optical channel regarding the down- and uplinks, which cover asymmetric optical pathways through the atmosphere.We define the end-to-end architecture of the communication chain including the transmitter on ground and the space-based receiver. Special attention is given to compatibility with established space data and system standards. Moreover, we examine the effects on the scheduling of satellite control, resulting from a constrained availability of the optical uplink due to cloud blockages. Our analysis aims at the employment of available space protocols for bidirectional optical communications with low earth orbiting spacecraft. Further on, we consider the adoption of upcoming standards to account for the optical fading channel. Certain applications like immediate automatic-repeat-requests for the downlink will require novel, optimized protocols.

Investigation of impact of gate underlap/overlap on the analog/RF performance of composite channel double gate MOSFETs

The influence of gate overlap and underlap on the DC/RF behavior of a composite channel based double gate MOSFET (DG MOSFET) that can be used for RF/analog applications is investigated using the 2D Sentaurus TCAD tool in this work. An InAs-inserted In07Ga0.3As composite channel, double silicon delta doping technology, n+-In0.53Ga0.47As source and drain regions, and Si3N4 passivation are some of the key features of the proposed device. 2D-Sentaurus Technology Computer Aided Design (TCAD) simulation has been performed using the hydrodynamic model. Interface trap models have also been incorporated to increase the accuracy of TCAD simulations carried out at room temperature. Key RF/analog figures of merit such as drain current (ID), transconductance (gm), gate leakage current (IGS), subthreshold current, drain induced barrier lowering, electron velocity in the quantum well, cutoff frequency (fT), and maximum oscillation frequency (fmax) have been explored to analyze the RF/analog performance of the proposed device. TCAD simulations reveal the fact that reducing the gate length and employing a gate underlap strategy can improve the analog and RF performance of the proposed DG MOSFET.

River sensitivity and sediment connectivity as tools for assessing future geomorphic channel behavior

ABSTRACT The science of geomorphology is increasingly used to inform river management efforts; however, the complexity of fluvial systems makes predictions of future channel adjustment difficult at best. The geomorphic concepts of landform sensitivity and sediment connectivity are well suited to aid river managers in assessing the probability and variability of river channel responses. This can be especially helpful in planning for impacts of future climate change or changes in management activity. River sensitivity and sediment connectivity datasets provide a necessary reach-in-catchment perspective to inform geomorphic interpretations of river behaviour. Such interpretations constitute a first step towards providing the contextual geomorphic understanding necessary to establish expectations of future channel behaviour. In this paper, we use geomorphic interpretations based on river sensitivity and sediment connectivity datasets to describe the historical trajectory and future adjustment possibilities for four channel reaches in the Lockyer Valley, southeast Queensland (SEQ). We apply our interpretations to three different scenarios of future climate and river management conditions to constrain what forms of geomorphic adjustment are possible for resilient-disconnected, resilient-connected, sensitive-connected, and sensitive-disconnected channels. Using scenario-building exercises to forecast possibilities of river adjustment can aid river managers by establishing expectations of future channel behaviour. This information can then be fed into the decision-making process regarding where to prioritize management actions as part of catchment action planning that works with, not against, the natural behaviour of riverine environments.

Analytical modelling of dielectric engineered strained dual‐material double‐gate‐tunnelling field effect transistor

In this endeavour, the fruition of a resurrected tunnel field effect transistor has been investigated incorporating the idea of strained channel engineering along with the implementation of dielectric modulation technique. A non-homogeneous pattern of gate oxide layer is considered with hetero-dielectric architecture at the front gate and linearly graded oxide at the back gate. The buried oxide (BOX) thickness is kept intentionally double that of front oxide one to reduce electric field lines penetrating from drain to source, thus minimising fringing field effect. The surface potential function has been deduced with the help of 2D Poisson's equation assuming appropriate boundary conditions. Lateral electric field and hence total electric field have been computed from channel potential to study tunnelling efficiency, hot carrier effect and drain induced barrier lowering for the aimed device. Finally drain current has been derived with the help of Kane's model upon integration of band-to-band tunnelling rate and the results have been compared with previously published reports to corroborate the eminence of the proposed model. All analytical corollaries are in adroit amity with Silvaco ATLAS simulated data for avowal of the developed modelin terms of sublime short channel behaviour.

Electrical Field Regulation of Ion Transport in Polyethylene Terephthalate Nanochannels.

Rectified ion transport in nanochannels is the basis of ion channels in biological cells and has inspired emerging nanochannel applications in ion separation, Coulter counters, and biomolecule detection and nanochannel energy harvesters. In this work we fabricated a polyethylene terephthalate (PET) conical nanochannel using latent ion track etching technique and then systematically studied the ion transport and influence of cation species on the nanochannel surface with cyclic I-V measurement. We discovered the electrical regulation of the reversible and irreversible modification of the nanochannel transportation by bivalent and trivalent cations, revealing the existence of the switching threshold voltage which can control the current rectification in bivalent solution. The proposed mechanism of the transport state transition in the PET nanochannel mimics behaviors of voltage-gated biological ion channels. These findings provide new insight into the understanding of the ion channel signaling and translocation control of charged particles in nanochannel applications.

Modulation of osmotic stress-induced TRPV1 expression rescues human iPSC-derived retinal ganglion cells through PKA

BackgroundTransient receptor potential vanilloid 1 (TRPV1), recognized as a hyperosmolarity sensor, is a crucial ion channel involved in the pathogenesis of neural and glial signaling. Recently, TRPV1 was determined to play a role in retinal physiology and visual transmission. In this study, we sought to clarify the role of TRPV1 and the downstream pathway in the osmotic stress-related retina ganglion cell (RGC) damage.MethodsFirst, we modified the RGC differentiation protocol to obtain a homogeneous RGC population from human induced pluripotent stem cells (hiPSCs). Subsequently, we induced high osmotic pressure in the hiPSC-derived RGCs by administering NaCl solution and observed the behavior of the TRPV1 channel and its downstream cascade.ResultsWe obtained a purified RGC population from the heterogeneous retina cell population using our modified method. Our findings revealed that TRPV1 was activated after 24 h of NaCl treatment. Upregulation of TRPV1 was noted with autophagy and apoptosis induction. Downstream protein expression analysis indicated increased phosphorylation of CREB and downregulated brain-derived neurotrophic factor (BDNF). However, hyperosmolarity-mediated defective morphological change and apoptosis of RGCs, CREB phosphorylation, and BDNF downregulation were abrogated after concomitant treatment with the PKA inhibitor H89.ConclusionCollectively, our study results indicated that the TRPV1–PKA pathway contributed to cellular response under high levels of osmolarity stress; furthermore, the PKA inhibitor had a protective effect on RGCs exposed to this stress. Therefore, our findings may assist in the treatment of eye diseases involving RGC damage.

Noncanonical Ion Channel Behaviour in Pain.

Ion channels contribute fundamental properties to cell membranes. Although highly diverse in conductivity, structure, location, and function, many of them can be regulated by common mechanisms, such as voltage or (de-)phosphorylation. Primarily considering ion channels involved in the nociceptive system, this review covers more novel and less known features. Accordingly, we outline noncanonical operation of voltage-gated sodium, potassium, transient receptor potential (TRP), and hyperpolarization-activated cyclic nucleotide (HCN)-gated channels. Noncanonical features discussed include properties as a memory for prior voltage and chemical exposure, alternative ion conduction pathways, cluster formation, and silent subunits. Complementary to this main focus, the intention is also to transfer knowledge between fields, which become inevitably more separate due to their size.

Consumer behavior in the omni-channel supply chain under social networking services

PurposeThe purpose of this paper is to analyze how social networking services (SNSs) affect consumers’ behaviors on the omni-channel supply chain by using a reverse research method.Design/methodology/approachInitially, a questionnaire was administered to obtain data on the relationship between the perception factors of channels and consumer behavior. Subsequently, a structural equation model was constructed, and consumer behavior were determined in the omni-channel supply chain. Finally, the importance of various factors that affected consumer behavior in the omni-channel supply chain under SNSs was determined.FindingsConclusions affirm that a positive effect on consumer channel behaviors occurs when buyers obtain information from social network platforms. However, regardless of online, offline, or mobile terminal, shortcomings are indicated in consumers’ lack of feedback on purchased goods and the bias of feedback.Originality/valueThe study explored ways to efficiently apply SNSs in building the omni-channel supply chain. Meanwhile, corresponding suggestions were provided such that companies will know about consumer needs.

A 2D channel potential modelling of symmetric double-gate MOSFET at onset of threshold condition

ABSTRACT A two-dimensional (2D) channel potential distribution is analytically derived for lightly doped double-gate MOSFET at turn-on condition of the device by solving 2D Poisson’s equation with the application of suitable boundary condition. Threshold voltage roll-off is also modelled to predict the short channel behaviour of the device at sub-threshold condition. Our derived model closely follows the 2D numerical simulation without the inclusion of any fitting parameters. It also serves as a basic step towards computing the compact modelling of DG MOSFET at threshold condition.

DEVELOPMENT OF AN EFFICIENT SMART GRID WITH ERROR CONTROL ALGORITHM

The in capabilities of the current power grid in distributing monitoring and managing due to the rising needs in the energy consumption and the aging infrastructure of the prevailing power grid, has led to the emergence of the grid that is smart in managing distributing and monitoring . The smart grid incorporating controls, computer, automation along innovative technologies and tools are able to provide an enhanced performance by being extra proficient, secure, reliable and greener. The smart grid also provides with the two way communication between the users and the utilities on the terms of electricity and information with the usage being completely monitored using the wireless sensor networks. The communication between the user and the utilities are often affected due to the noise, fading and path loss etc. experienced by the communication path. So the paper proffers an error control method that is adaptive to the changing behavior of the communication channels to make have an error less communication making the smart grid efficient. The result obtained based on the bit error rate, delay and the throughput evince the capability of the proposed scheme.

Device Structure and Passivation Options for the Integration of Scaled IGZO TFTs

The focus of this work is on the performance dependence of scaled IGZO TFTs with variations in gate electrode configuration and passivation options. A conservative process for the fabrication of long channel length devices (i.e. L ≥ 2 µm) exhibits long-channel behavior and excellent stability in both bottom-gate (BG) and double-gate (DG) configurations [1,2]. As the devices are scaled to shorter channel lengths, limitations of the device electrostatics begin to give way to short channel behavior. Dielectrics used for the gate and back-channel regions are typically adjusted to overcome short-channel effects as lateral dimensions are reduced. However certain interaction effects require additional process modifications for the desired device response and to accommodate the details of process integration. Scaled devices with channel lengths L < 2 µm are under investigation, with process conditions evaluated by quantitative measures on the materials properties, electrostatic behavior, and stability when subjected to bias and thermal stress. Process recipes for PECVD passivation layers, oxygen ambient annealing, and ALD capping materials are under reevaluation for their impact on short-channel devices. TCAD simulation is used as a resource to refine material and device models [3], and provide insight on the details which establish the limits of device operation. Design rule scaling and self-aligned gate device structures are also being studied for reduced parasitic capacitance and stage delay, and a reduction in overhead real estate. [1] T. Mudgal, N. Edwards, P. Ganesh, A. Bharadwaj, Eli Powell, M.S. Pierce, R. G. Manley, and K. D. Hirschman, “Investigation on the Gate Electrode Configuration of IGZO TFTs for Improved Channel Control and Suppression of Bias-Stress Induced Instability”, ECS Trans. 75 (10), 189-197 (2016) [2] M.S. Kabir, P. Ganesh, R.R. Chowdhury, H. Sethupathi, J. Okvath, J. Konowitch, R.G. Manley and K.D. Hirschman, “Channel-length dependent performance degradation of thermally stressed IGZO TFTs”, ECS Trans. 86 (11), 125-133 (2018) DOI: 10.1149/08611.0125ecst [3] K.D. Hirschman, T. Mudgal, E. Powell and R.G. Manley, “A 2D empirical model for on-state operation of scaled IGZO TFTs exemplifying the physical response of TCAD simulation”, ECS Trans. 86 (11), 153-166 (2018) DOI: 10.1149/08611.0153ecst Figure 1

Review of Channel Estimation for Candidate Waveforms of Next Generation Networks

The advancement in wireless communication applications encourages the use of effective and efficient channel estimation (CE) techniques because of the varying behaviour of the Rayleigh fading channel. In most cases, the emphasis of most proposed CE schemes is to improve the CE performance and complexity for ensuring quality signal reception and improved system throughput. Candidate waveforms whose designs are based on filter bank multi-carrier (FBMC) modulation techniques such as filter bank orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM), universal filtered multicarrier (UFMC) and generalised frequency division multiplexing based on offset quadrature amplitude modulation (GFDM-OQAM) are no exception to the use of these proposed CE techniques in the literature. These schemes are considered as potential waveform candidates for the physical/media access control layer of the emerging fifth generation (5G) networks. Therefore, pinpoint CE techniques represent an important requirement for these waveforms to attain their full potentials. In this regard, this paper reviews the concept of CE as applicable to these waveforms as well as other waveform candidates under consideration in the emerging 5G networks. Since the design of the majority of the waveform candidates is filter based, a review of the general filter design considerations is presented in this paper. Secondly, we review general CE techniques for candidate waveforms of next generation networks and classify some of the studied CE techniques. In particular, we classify the CE schemes used in filter bank OFDM-OQAM and GFDM-OQAM based transceivers and present a performance comparison of some of these CE schemes. Besides, the paper reviews the performances of two linear CE schemes and three adaptive based CE schemes for two FBMC based waveform candidates assuming near perfect reconstruction (NPR) and non-perfect reconstruction (Non-PR) filter designs over slow and fast frequency selective Rayleigh fading channels. The results obtained are documented through computer simulations, where the performances of the studied CE schemes in terms of the normalised mean square error (NMSE) are analysed. Lastly, we summarise the findings of this work and suggest possible research directions in order to improve the potentials of the studied candidate waveforms over Rayleigh fading channels.

Structural Dynamics of the Paddle Motif Loop in the Activated Conformation of KvAP Voltage Sensor

Voltage-dependent potassium (Kv) channels play a fundamental role in neuronal and cardiac excitability and are potential therapeutic targets. They assemble as tetramers with a centrally located pore domain surrounded by a voltage-sensing domain (VSD), which is critical for sensing transmembrane potential and subsequent gating. Although the sensor is supposed to be in “Up” conformation in both n-octylglucoside (OG) micelles and phospholipid membranes in the absence of membrane potential, toxins that bind VSD and modulate the gating behavior of Kv channels exhibit dramatic affinity differences in these membrane-mimetic systems. In this study, we have monitored the structural dynamics of the S3b-S4 loop of the paddle motif in activated conformation of KvAP-VSD by site-directed fluorescence approaches, using the environment-sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD). Emission maximum of NBD-labeled loop region of KvAP-VSD (residues 110–117) suggests a significant change in the polarity of local environment in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) membranes compared to OG micelles. This indicates that S3b-S4 loop residues might be partitioning to membrane interface, which is supported by an overall increased mean fluorescence lifetimes and significantly reduced water accessibility in membranes. Further, the magnitude of red edge excitation shift (REES) supports the presence of restricted/bound water molecules in the loop region of the VSD in micelles and membranes. Quantitative analysis of REES data using Gaussian probability distribution function clearly indicates that the sensor loop has fewer discrete equilibrium conformational states when reconstituted in membranes. Interestingly, this reduced molecular heterogeneity is consistent with the site-specific NBD polarization results, which suggest that the membrane environment offers a relaxed/dynamic organization for most of the S3b-S4 loop residues of the sensor. Overall, our results are relevant for understanding toxin-VSD interaction and gating mechanisms of Kv channels in membranes.

Impact of H-Doping on n-Type TMD Channels for Low-Temperature Band-Like Transport.

Band-like transport behavior of H-doped transition metal dichalcogenide (TMD) channels in field effect transistors (FET) is studied by conducting low-temperature electrical measurements, where MoTe2 , WSe2 , and MoS2 are chosen for channels. Doped with H atoms through atomic layer deposition, those channels show strong n-type conduction and their mobility increases without losing on-state current as the measurement temperature decreases. In contrast, the mobility of unintentionally (naturally) doped TMD FETs always drops at low temperatures whether they are p- or n-type. Density functional theory calculations show that H-doped MoTe2 , WSe2 , and MoS2 have Fermi levels above conduction band edge. It is thus concluded that the charge transport behavior in H-doped TMD channels is metallic showing band-like transport rather than thermal hopping. These results indicate that H-doped TMD FETs are practically useful even at low-temperature ranges.