Increase In Channel Width Research Articles

Localized insulator-conductor transformation of graphene oxide thin films via focused laser beam irradiation

By scanning a focused laser beam over graphene oxide (GO) film deposited on SiO2/Si substrates, conductive strips as small as 1 μm can be patterned directly either as a channel in the insulating matrix, or as a stand-alone micro belt. The conductivity was increased by at least two orders of magnitude with the mobility estimated in the range of 1–10 cm2/V s. Raman mapping and X-ray photoelectron spectroscopy studies demonstrated the reduction of GO in the laser-irradiated area. The conductance of the patterned channel was independent of the change in oxide-electrode contact resistance of the graphene, and increased linearly with increasing channel width. Increasing irradiation power by repeated scanning initially increased the conductivity of the irradiated area and saturated at a conductivity of ∼36 S/cm. Partial oxidative burning combined with photothermal reduction was identified as the underlying mechanism for the enhancement of the conductivity after laser irradiation on the GO film. Oxidative burning can be controlled by varying the film thickness and laser power.

Thermal modelling of a photovoltaic module under variable free convection conditions

A thermal model regarding a photovoltaic module has been developed and validated using experimental data. The aim of this study was to obtain the temperature field of a BP 585 F module mounted at different distances from a roof wall, as well as the temperature and velocity profiles of the air at the exit section between the panel and the wall. The influence of the mounting distance on the temperature and velocity values was also studied. The simulation is done by applying the Galerkin finite element method to the flow and energy equations, incorporating an implicit convective boundary condition. The results show a good accuracy of the model. ► A two-dimensional steady-state thermal model of a photovoltaic module is studied. ► The air flow in the channel formed by the module and the mounting wall is examined. ► Due to the radiation and convection two boundary layers are formed. ► Velocity and temperature profiles depend on the boundary layer interaction. ► Increasing channel width leads to unexpected shape of velocity and temperature.

High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects

A large magnetoresistance effect is obtained at room-temperature by using p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is the virtual elimination of thermal currents due to the presence of band gaps in the contacts. The current at B = 0 T is greatly decreased while the current at B > 0 T is relatively large due to the band-to-band tunneling effects, resulting in a high magnetoresistance ratio, even at room-temperature. Moreover, we explore the effects of edge-roughness, length, and width of GNR channels on device performance. An increase in edge-roughness and channel length enhances the magnetoresistance ratio while increased channel width can reduce the operating bias.

Numerical studies on the geometrical characterization of serpentine flow-field for efficient PEMFC

Geometrical characterization of the serpentine flow-field is one of the key issues to be solved to enhance the performance of PEMFC in relation to pressure drop, discharge of condensed water, maximization of cell voltage, and uniformity of current density over the entire surface area. Three different channel heights and widths were compared with the base flow-field design of the serpentine channel whose width is 1 mm and 0.34 mm in height, each through a detailed numerical study of the distribution of temperature, pressure, water content, and local current density. As the channel height increases higher than the base design, the total pressure drop decreases and results in reduced load of BOP and accumulation of liquid water at the outlet of both anode and cathode. The accumulation of anode liquid water at the outlet caused by back diffusion is accelerated as the channel height increases. As the channel width expands wider than the base design, the pressure drop is lowered and the removal rate of liquid water becomes faster. The effect of the channel width increase on the water removal is greater than that of the channel height increase. Which can influence the dehydration and temperature of the MEA and thus cell performance and lifetime of PEMFC. The results obtained in this work are expected to be applied in developing an efficient serpentine flow-field channel with sub-channels and by-passes.

Experimental studies on the three-dimensional effects of opposed-flow flame spread over thin solid materials

The three-dimensional effects of flame spread over thin solid materials were experimentally studied using a natural-convection-suppressing horizontal narrow-channel. In a sufficiently wide narrow-channel, the variation of flame spread against the width of the material sample showed different trends for different gas flow speeds and oxygen concentrations. The extent of three-dimensional effects was inversely proportional to the gas flow speed or its square. Near quenching extinction limits, the effects were significant because weak combustion is sensitive to a slight variation of heat loss and oxygen concentration. The effects may be due to different factors such as side heat loss, side oxygen diffusion, or both. Far away from quenching extinction limits, the effects were weak because vigorous combustion is insensitive to a small variation of oxygen concentration and heat loss. In all tests, the effects were limited to the samples of width less than 10 times of the diffusion length. Moreover, a higher oxygen concentration suppressed the effects at a lower gas flow speed. For sufficiently wide samples, in the most range of gas flow speeds, the channel width had almost no effect on flame spread. However, near extinction limits, the flame spread rate decreased with the increasing channel width.

Effect of cathode channel dimensions on the performance of an air-breathing PEM fuel cell

A three dimensional, steady state, non-isothermal, single phase model was developed and simulations were carried out in order to find the effect of cathode channel dimensions (width, depth and height) on the performance of an air-breathing fuel cell. The model was solved using commercial CFD package Fluent (version 6.3). Separate user defined functions were written to solve the electrochemical equations and the water transport through the membrane along with the other governing equations. Analyses were carried out for three different channel widths (2, 4 and 6 mm), for three different channel depths (2, 6 and 10 mm) and for three different cell heights (15, 30 and 45 mm). Cell characteristics like current distribution, species distribution, oxygen mass transfer coefficient, cell temperature, cathode channel velocities and net water transport coefficients are reported. The results show that the cell performance improves with increase in cathode channel width, channel depth and with decrease in cell height. Maximum power density obtained was 240 mW/cm 2 for a channel width of 4 mm and channel depth of 6 mm. When the channel depth was 2 mm the performance was limited mainly due to the resistance offered by the channel for the buoyancy induced flow. For channel depths higher than 2 mm, the diffusion resistance of the porous GDL also contributed significantly to limit the performance to low current densities. At low current densities the fuel cell is prone to flooding whereas at high current densities ohmic overpotential due to dehydration of the membrane significantly contributes to the overall voltage loss.

Channel inception in cohesionless sediment by seepage erosion

This study presents a series of systematic experiments on channelization by seepage erosion with various sediment layer depths and chamber slopes. When the depth of the sediment layer increases, the threshold discharge for channel initiation decreases, but the channel width increases. This is due to the fact that an increase in the weight of sediment induces an increase in a gravitational driving force along the chamber bed. When the chamber slope increases, we also found a similar effect as an increase in the sediment layer depth that the threshold discharge decreases, but the width increases. While channel bifurcation was never found in the previous study using plastic pellets as sediment, it was observed in many experiments in the present study, in which very coarse sand was used. We hypothesized that the characteristics of groundwater flow field and the resistibility of sediment material to slope failure play important roles on the channel bifurcation.

Estimating parameters of the channel width–flow discharge relation using rill and gully channel junction data

AbstractEroding channels can usually be characterized by a power relationship between channel width (W) and channel discharge (Q). This paper examines the WQ relation using a recently developed channel junction approach to extend the validity of the WQ relation and to develop a procedure for estimating the WQ exponent and proportionality coefficient. Rill and gully channel data from the literature, and new data collected in different badland areas and in a few forest mountain streams, are analysed. Analysis shows that the WQ relation for channel width collected in badlands and forests agrees with trends observed for cropland. The exponent increases with increasing channel width in a continuous fashion rather than in a step‐like way and tends to a maximum whose value ranges between 0·5 and 0·6.The proportionality coefficient can be split into two terms, one expressing the case in which an eroding channel can broaden, the other reflecting the difficulties in removing the less erodible clods or rock fragments from the channel bed. Its splitting allows the development of a more correct form of the WQ relation in agreement with modern approaches of channel geometry: one part has the dimension of a discharge and makes the power base dimensionless, while the other brings the dimension of a length, needed for the channel width, into the WQ relation. The interpretation of the two constants is supported by data collected in rainfall‐runoff simulation experiments conducted in the field. Values characterizing the two constants in some environments are also given. Nevertheless the approach is not sufficiently parameterized yet to be of practical use (e.g. in models or for estimating peak discharge in areas where rill channels have formed). Copyright © 2009 John Wiley & Sons, Ltd.

Quantum Goos-Hänchen Effect in Graphene

The Goos-Hänchen (GH) effect is an interference effect on total internal reflection at an interface, resulting in a shift sigma of the reflected beam along the interface. We show that the GH effect at a p-n interface in graphene depends on the pseudospin (sublattice) degree of freedom of the massless Dirac fermions, and find a sign change of sigma at angle of incidence alpha=arcsin sqrt[sinalpha{c}] determined by the critical angle alpha{c} for total reflection. In an n-doped channel with p-doped boundaries the GH effect doubles the degeneracy of the lowest propagating mode, introducing a twofold degeneracy on top of the usual spin and valley degeneracies. This can be observed as a stepwise increase by 8e;{2}/h of the conductance with increasing channel width.

A Novel Multifin Dynamic Random Access Memory Periphery Transistor Technology Using a Spacer Patterning through Gate Polycrystalline Silicon Technique

A new technique that integrates the metal gate multifin field effect transistor (multi-FinFET) and the conventional polycrystalline silicon (poly-Si) gate planar FET is proposed. It solves the problems of the previous scheme, such as the complicated process integration due to the coexistence of TiN gate FinFETs and poly-Si gate planar FETs, the fin width consumption by multiple gate oxidation, the large fin pitch limited by the resolution of lithography, and the gap-filling ability of shallow trench isolation (STI). The newly proposed technique forms multifin structures by spacer patterning through the gate poly-Si electrode for planar FETs. The drain current gain due to an increase in effective channel width is estimated, and the basic electrical characteristics of a multi-FinFET are evaluated.

Channel width effect for organic thin film transistors using TIPS-pentacene employed as a dopant of poly-triarylamine

The effects of the physical channel width on the characteristics of organic thin film transistors (OTFTs), made with 6,13-bis(triisopropyl-silylethynyl)-pentacene (TIPS-pentacene) embedded into poly-triarylamine (PTAA, hole conductor within an active channel), have been examined in this paper. The devices are estimated by measuring the drain-source current ( I DS ) for different contact metals such as Au and Ag, at fixed gate and drain voltages. The results show that the threshold voltage ( V T ) and I DS increase with increasing channel width. Furthermore, it has been observed that the field effect mobility is dependent on V T, which is influenced by the channel width. The OTFTs, produced using Au and Ag contacts, exhibited the highest values of mobility in the saturation regime, namely 5.44 × 10 −2 and 1.33 × 10 −2 cm 2/Vs, respectively.

Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi-Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

Analyzing the effects of historical and recent floods on channel pattern and the environment in the Lower Omo basin of Ethiopia using satellite images and GIS

Previous accounts and recent observations indicate that the pattern and geometry of the Omo River meanders in the Lower Omo basin of Ethiopia had already been established in earlier times by large floods that took place after extended periods of drought. The cross-sectional changes resulted from floods in the nineteenth and twentieth centuries, were then simply limited to small degree channel widening and entrenchment, and floodplain erosion and deposition. The effects of the August 2006 flood, although widespread and destructive for the environment, were also modest as far as adjusting the channel pattern is concerned. Changes in channel profiles at short-term scales usually come in the form of aggradation and degradation. Interpretations of satellite images taken before and after the flood showed the accumulation of coarse sediments in the channel. There are also some sporadic indications for an increase in channel width. Widening in response to high amount of discharges can generally be expected during floods. Besides, signs of channel shortening were observed in some places. Apart from these minor changes, the dimension of meandering segments or the outline of the entire meander belt, and the basic morphology of the channel remained unaffected.

Electrokinetic instability effects in microchannels with and without nanofilm coatings

This paper presents a parametric experimental investigation into the electrokinetic instability (EKI) phenomenon within three different types of microfluidic device, namely T-type, cross-shaped, and cross-form with an expansion configuration. The critical electric field strength at which the EKI phenomenon is induced is examined as a function of the conductivity ratio, the microchannel width, the expansion ratio, and the surface treatment of the microchannel walls. It is found that the critical electric field strength associated with the onset of EKI is strongly dependent on the conductivity ratio of the two samples within the microfluidic device and reduces as the channel width increases. The surfaces of the microchannel walls are coated with hydrophilic or hydrophobic organic-based spin-on-glass (SOG) nanofilms for glass-based microchips. The experimental results indicate that no significant difference exists in the critical electric field strengths in the hydrophilic or hydrophobic SOG-coated microchannels, respectively. However, for a given conductivity ratio and microchannel width, the critical strength of the electric field is slightly lower in the SOG-coated microchannels than in the non-coated channels. In general, the results presented in this study demonstrate the potential for designing and controlling on-chip assays requiring the manipulation of samples with high conductivity gradients, and provide a useful general reference for avoiding EKI effects in capillary electrophoresis analysis applications.

A Bayesian analysis of physical habitat changes at tributary confluences in cobble‐bed upland streams of the Acheron River basin, Australia

Tributary confluences are known to affect downstream channel morphology and have the potential to increase downstream habitat heterogeneity. However, few studies have explicitly investigated the effect of tributaries on physical habitat. We used Bayesian modelling to investigate tributary effects on channel morphology, flow velocity, and bed particle size distribution at eight confluences in the Acheron River system in Victoria, Australia, under high‐flow and low‐flow conditions. Consistent tributary effects across sites and flow stages were a localized increase in channel depth at the confluence and a step increase in channel width in the postconfluence channel. Other tributary effects, such as increased or decreased flow velocity, the presence and placement of confluence bed forms (e.g., scours, pools, bars, and avalanche faces), and altered bed particle size distributions, varied between sites and flow conditions. These results provide evidence of changes to the physical habitat at confluences, which may affect stream biota.

3D Numerical modelling of flow divisions at open channel junctions with or without vegetation

The flow division at an open channel junction is affected by the inflow discharge and the downstream water depths of the junction. The growth of vegetation in a channel system is environmental friendly, but its effect on the flow in an open channel junction can be significant. In this work a 3D RANS (Reynolds Averaged Navier–Stokes equation) model has been implemented to investigate the flow phenomena in channel junctions with or without vegetation. The model is first validated by two cases: flow in an open channel T-junction without vegetation, and flow in a single open channel with vegetation. The model is then applied to simulate flow in an open channel T-junction with varying width ratio and vegetation density of the branch channel. The results quantitatively predict the trend of increasing flow in the branch channel with the increase in branch channel width and/or the decrease in vegetation density. The overall energy loss coefficient of the system, however, decreases with the amount of flow in the branch channel.

A Vertical Thin Film Transistor Based on Low Temperature Technology (T

A new concept of vertical Thin Film Transistor (TFT) family called Thin Film Transistor Comb (TFTC) using only low temperature process (less than 600{degree sign}C) based on polycrystalline silicon (polysilicon) has been fabricated. This structure, compatible with glass substrate, can have up to 5 teeth and allows increasing channel width simultaneously to a better control and reduction of channel length, leading to an increase of the average current and device densities. In contrast to other vertical TFTs, the channel of TFTCs is made of non-intentionally doped silicon between two layers in-situ doped polysilicon, all deposited by low pressure chemical vapor deposition. Analyses of characteristics of main studied pattern, a comb with 3 teeth, show a high on-current, a threshold voltage of 1.6V, a transconductance of 97µS, a very low gate leakage current, but in the first layout a high off-current due to the large area of the drain and source overlapping.

Transport properties of liquid argon in krypton nanochannels: Anisotropy and non-homogeneity introduced by the solid walls

In this work we calculate the transport properties of liquid argon flowing through a nanochannel formed by krypton walls. Non-equilibrium molecular dynamics (NEMD) simulations are performed assuming flow conditions corresponding to the macroscopic equivalent of planar Poiseuille flow. We examine the effect of channel width and system temperature on diffusion coefficient, shear viscosity and thermal conductivity. The results show clearly the existence of a critical width, in the range 7–18 σ, below which the behavior of transport properties is affected in comparison to bulk properties. In fact for small width values, diffusion coefficient is highly anisotropic, the component normal to the wall being the smaller one. For the same width range, diffusivities along all directions are higher in the central layers than those close to the walls. Similarly, shear viscosity increases for small channel width values while thermal conductivity decreases. All properties approach bulk values as the channel width increases. The layers close to the walls always present distinctly different behavior due to the interaction with the wall atoms. The observed behavior is of particular importance in the design of nanofluidic devices.

An electrokinetic pressure sensor

A new concept for a micro pressure sensor is demonstrated. The pressure difference between the inlet and the outlet of glass nanochannels is obtained by measuring the electrokinetically generated electric potential. To demonstrate the proposed concept, experimental investigations are performed for 100 nm wide nanochannels with sodium chloride solutions having various concentrations. The proposed pressure sensor is able to measure the pressure difference within a 10% deviation from linearity. The sensitivity of the electrokinetic pressure sensor with 10−5 M sodium chloride solution is 18.5 µV Pa−1, which is one order of magnitude higher than that of typical diaphragm-based pressure sensors. A numerical model is presented for investigating the effects of the concentration and the channel width on the sensitivity of the electrokinetic pressure sensor. Numerical results show that the sensitivity increases as the concentration decreases and the channel width increases.

Simulations of a Turbulent Flow Past a Sudden Expansion: A Sensitivity Analysis

Large eddy simulation is used to study the flow behind a pair of symmetric backward-facing steps. As reported in the literature, the flow exhibits an asymmetric pattern characterized by the deflection of the jet toward one of the walls. The large eddy simulation results are compared with laser Doppler anemometry measurements showing the ability of the present numerical tool to capture the complex features of the flow. Furthermore, a sensitivity study is conducted to assess the influence of the grid resolution, the inflow boundary, the channel width, and the step size on the flowfield. The flow was found to be only weakly sensitive to the grid, assuring the quality of the simulation results. The inflow boundary influences the mean results only marginally unless low-frequency fluctuations are applied. In this case, the flowfield recovers a mean symmetry with suppression of the jet bending. The jet mean bending has also been shown to increase with the step size h and to decrease with increasing channel width.