Large Channel Width Research Articles

Water wicking in phosphorene-based nanochannels: Effect of surface texture

The imbibition dynamics of water in a nanochannel made of two-dimensional phosphorene are explored using Molecular Dynamics. The partial wetting behavior of water nanodroplets on phosphorene sheets is examined first. The initial spreading of the wetted area (A) and internal energy (ΔE) are found to follow the power law, A ∼ t1/2 and ΔE-t1/2. Additionally, the Laplace pressure and equilibrium contact angle, determined from water plugs confined within nanoslits, verify the applicability of the Young-Laplace equation at the nanoscale. For water wicking in channels with a width of N layers of phosphorene sheets, the rate of change of both the penetration length and internal energy is proportional to t1/2. However, the imbibition rate in narrow nanoslits (N = 2 ∼ 5) depends on the orientation (armchair and zigzag) of the walls. This effect gradually diminishes as N increases. It was observed that, except for N = 1, the imbibition rate decreases with increasing channel width, which contradicts the prediction of Lucas-Washburn equation. Compared to smooth graphene-based channels, the imbibition rate is lower in phosphorene-based channels. Nonetheless, this difference decreases as the channel width increases, suggesting that the impact of surface roughness becomes less pronounced with larger channel widths.

Augmentation of multi-stage Tesla valve design cold plate with reverse flow to enhance thermal management of pouch batteries

With the active promotion of the green energy vehicle sector in recent years, electric vehicles have garnered widespread attention as their future direction. The operating temperature substantially influences the functioning of power batteries, as being one of the key components of electric vehicles. Battery thermal management is vital for improving electric vehicles' performance and durability. Concerning this, a novel 4-channelled liquid cooling plate with reverse flow multi-stage Tesla valve (MSTV) design developed in our previous work is further analysed to effectively manage an undesirable temperature distribution in a cell. The effects of structural parameters, including channel width, outer curve radius, and valve angle, are investigated numerically for a wide range of Reynolds number by applying heat flux on the cooling plate's upper and lower surfaces using COMSOL Multiphysics software. Results indicate that a large channel width, a large outer curve radius, and a small valve angle in MSTV can effectively reduce peak temperature rise of a standard 20Ah pouch li-ion battery of 160 mm × 227 mm × 7.25 mm dimension. Alongside, the variation in pressure drop is minimal with the increase of outer curve radius and valve angle except for the channel width for a given Reynolds number.

A predictive model of velocity for local hydrokinetic power assessment based on remote sensing data

Hydrokinetic power is a small-scale, zero-head form of hydropower with the potential to address renewable energy needs for many communities, including those in the Arctic. An impediment to its wide deployment is the ability to screen suitable stream reaches for adequate power generation. Remote resource assessment of streams, particularly the estimation of mean velocity, is valuable for assessing the potential of new locations prior to field visits. Many studies have investigated remote sensing techniques for stream velocity prediction through machine learning and empirical relations, but most of these studies relied at least partly on in-situ data and were not suitable for small width streams. This study addresses these gaps with a Random Forest machine learning model that uses only remotely sensible data to estimate velocities of small and large streams at locations across Alaska. The developed model, validated by velocity gage readings, had a mean prediction error of 24%, at the lower end of error rates (20–30%) found for large channel widths. Novel geometric and temporal parameters were developed and found to importantly influence predictive accuracy (e.g. slope, stream meanders). Remotely sensible data enables future model expansion by those interested in assessing new sites for community energy planning.

Micro pin fins with topologically optimized configurations enhance flow boiling heat transfer in manifold microchannel heat sinks

The manifold microchannel heat sink (MMCHS) is a promising design for heat dissipation in high power electronics. However, the configuration of the microchannels in MMCHS is generally rectangular straight channels, which would limit the further improvement of heat transfer performance. Topology optimization has been proven to be an effective approach to design single-phase heat sinks, which only depends on the iterative algorithm. In this work, we first design three single-phase heat transfer structures (2D) by a density-based topology optimization method, and then systematically investigate the two-phase flow and heat transfer characteristics of MMCHS (3D configurations that are converted based on 2D designs). The thermohydraulic performances of three topologically optimized MMCHS obtained by varying the constrained pressure drop (named TOC-I, TOC-II and TOC-III for simplicity) and the baseline rectangular MMCHS are compared. The results show that the flow paths in the TOCs exhibit root-like configurations and the number of pin fins increases with the increase in constrained pressure drop (i.e., TOC-III has the most complex flow path). Due to the differences in velocity distribution and channel width among various configurations, churn flow and confined bubbly flow are observed in BC and TOCs, respectively. Compared to BC, the maximum average heat transfer coefficients of TOC-I, TOC-II and TOC-III are increased by 40%, 62% and 87%, respectively. The TOC-I has the lowest pressure drop due to the minimum number of pin fins and the relatively large channel width. The maximum values of Figure of Merit (FOM), a parameter usually employed to analyze the comprehensive performance of MMCHS, for TOC-I, TOC-II and TOC-III are 1.72, 1.77 and 1.8 at Qb= 1000 W/cm2, respectively. Moreover, TOC-I and TOC-III have the best comprehensive performance at 300 W/cm2≤ Qb ≤ 800 W/cm2 and 900 W/cm2 ≤ Qb ≤ 1000 W/cm2, respectively.

ZnO-WS2Nano-heterojunction/ITO photodetector for detection of visible light

Recently, large-area photodetectors fabricated with low-cost techniques have gained tremendous attention. Herein, efforts have been made to study the photodetector parameters for different concentration variations of the ZnO-WS2 heterostructure. The device was fabricated using a drop-casting method on an ITO glass substrate with a large area channel width. It has higher electrical stability and stable photoresponse with Responsivity ∼10.6 mA/W, Detectivity ∼1011 Jones and EQE% ∼1.96% under 670 nm with an intensity of 110 μW/cm2illumination at bias 5 V, respectively. Present findings will advocate the huge development of simple, low-cost and large-area photodetectors with high performance in the nearest future.

River Response to Melting Cryosphere Since Late Quaternary in the Pir Panjal Range of NW Himalaya

Rambiara River basin, a sub-basin of the Upper Indus, is dotted with fluvial and glacial geomorphic landforms. The presence of large number of glacial landforms like moraines, cirques, aretes, U-shaped valleys, etc. reflects the enormous erosive power of the past glaciers. During the Last Glacial Maximum (LGM), glaciers on average were 200 m thick and extended more than 10 km from the present-day cirque marks. Rock glaciers outnumber the clean glaciers that cover an area of 0.22 and 1.25 km2, respectively, in the basin. Glacial lakes are the prominent features in the higher reaches of the basin and occupy an area ranging from 0.01 to 0.70 km2. Downstream, the river is characterized by large channel width, anomalous sinuosity, braided pattern, and the presence of unpaired fluvial terraces. The large channel width depicts the enormous discharge from the glacial- and snow-melt during the Late Pleistocene when glaciers covered most of the Pir Panjal. After LGM, the glacier cover and the river discharge significantly decreased as highlighted by a large number of braided bars and the narrow stream to which the river is reduced. The warming trends observed across the Himalayas encompassing the Pir Panjal Range since the last century has further contributed significantly to the glacier recession in the basin.

Controlling anisotropy of porous B4C structures through magnetic field-assisted freeze-casting

Anisotropic porous boron carbide (B4C) structures were successfully produced, for the first time, using the magnetic field-assisted freeze casting method. The effect of the magnetic field on the structure and mechanical strength of the formed porous B4C was compared for two different magnetic field directions that were either aligned with ice growth (vertical), or perpendicular to the ice growth direction (horizontal). It was shown that applying even a weak horizontal magnetic field of 0.1–0.3 T noticeably affected the alignment of mineral bridges between lamellar walls. Both the porosity and the channel widths decreased with increasing horizontal magnetic field strength. In the case of a vertical magnetic field, a larger strength of 0.4 T was required for highly aligned lamellar walls and larger channel widths. Compression strength tests indicated that the application of magnetic fields led to more homogeneously aligned channels, which resulted in increased compression strength in the longitudinal (parallel to the ice growth) direction. Applying a vertical magnetic field of 0.4 T with a cooling rate of 2 °C/min during the freezing step of the magnetic field-assisted freeze-casting method was found to result in the best conditions for producing highly anisotropic structures with large channel widths and fewer mineral bridges, which led to an increase in the mechanical strength.

Carbon Nanotube Based Radio Frequency Transistors for K-Band Amplifiers.

Owing to the combination of high carrier mobility and saturation velocity, low intrinsic capacitance, and excellent stability, the carbon nanotube (CNT) has been considered as a perfect semiconductor to construct radio frequency (RF) field-effect transistors (FETs) and circuits with an ultrahigh frequency band. However, the reported CNT RF FETs usually exhibited poor real performance indicated by the as-measured maximum oscillation frequency (fmax), and then the amplifiers, which are the most important and fundamental RF circuits, suffered from a low power gain and a low frequency band. In this work, we build RF transistors on solution-derived randomly orientated CNT films with improved quality and uniformity. The randomly orientated CNT film FETs exhibit the record as-measured maximum fmax of 90 GHz, demonstrating the potential for over 28 GHz (at least one-third of 90 GHz) 5G mmWave (frequency range 2) applications. Benefiting from the large-scale uniformity of CNT films, FETs are designed and fabricated with a large channel width to present low internal resistance for the standard 50 Ω impedance matching guide line, which is critical to construct an RF amplifier. Furthermore, we first demonstrate amplifiers with a maximum power gain up to 11 dB and output third-order intercept point (OIP3) of 15 dBm, both at the K-band, which represents the record of a CNT amplifier and is even comparable with a commercial amplifier based on III-V RF transistors.

An Automated Setup for the Characterization of Time-Based Degradation Effects Including the Process Variability in 40-nm CMOS Transistors

This article reports a test chip design in commercial 40-nm process technology to characterize the level of time-based degradation in metal-oxide-semiconductor field-effect transistors (MOSFETs). The two phenomena that have been concentrated on are the bias temperature instability (BTI) and the hot carrier injection (HCI). Stress tests have been carried out on both n- and p-MOSFETs with large channel widths and shorter channel lengths, as practically observed in analog and radio frequency circuits. Reliability characterization has been extended to cover the body effect and the impact of process variations both at prestress and poststress stages. The results demonstrate that the designed test chip has been instrumental in observing the extent of degradation due to BTI and HCI. Furthermore, both the body effect and the poststress variability have been found to affect the transistor and circuit performance significantly.

River Network and Reach‐Scale Controls on Habitat for Lamprey Larvae in the Umpqua River Basin, Oregon

AbstractThis study developed a spatially explicit framework to support the conservation of Western Brook Lamprey Lampetra richardsoni and Pacific Lamprey Entosphenus tridentatus in the Umpqua River basin, Oregon. This framework identified locations within the river network likely to support “potential burrowing habitat” for lamprey larvae based on geomorphic conditions and evaluated the overlap of potential burrowing habitat with water temperatures suitable for the nonnative, piscivorous Smallmouth Bass Micropterus dolomieu. The study also documented reach‐scale factors that create heterogeneity in potential burrowing habitat to guide on‐the‐ground habitat restoration. Based on criteria for mean annual suspended sediment loads and channel slope, 18% of the Umpqua River network was classified as potential burrowing habitat. Existing mean August water temperatures of ≥20°C were suitable for Smallmouth Bass for 32% of the potential burrowing habitat. This percentage increased to 41% of the potential burrowing habitat using projected mean August water temperatures for year 2040, suggesting that water temperatures in the future will facilitate upstream expansion of Smallmouth Bass into the potential burrowing habitat. At finer spatial scales, potential burrowing habitat was influenced by channel features, such as large wood, pools, and local channel slope and width. These results provide an initial template for identifying locations in river networks likely to have potential burrowing habitat, considering the overlap between threats and lamprey habitats, and planning conservation actions to support native lampreys.

Features of Heat Transfer during Pool Boiling of Nitrogen on Surfaces with Capillary-Porous Coatings of Various Thicknesses

An experimental investigation has been carried out regarding the effect of microstructural parameters of capillary porous coatings produced by directed plasma spraying on the heat transfer and critical heat fluxes during boiling of nitrogen at steady-state heat generation on horizontally-oriented tubular heaters of 3 and 16 mm in diameter. For both the tube diameters, the highest increase in the critical heat flux by a factor of 1.8 as compared with smooth heaters is observed for coatings with the highest porosity. The maximum heat transfer coefficients were observed in three-dimensional capillary-porous (TCP) coatings with large channel widths. Those were more than 3.5 times as high as the heat transfer coefficients on a smooth heater at low heat fluxes. The influence of the thickness of residual layer of microstructured capillary-porous coatings on the heat transfer during nucleate boiling has been shown. Based on the data of high-speed video recording, it has been shown that enhancement of heat transfer during boiling on structured capillary-porous surfaces is not associated with increase in the nucleation site density, but is caused by enhancement of liquid inlet and vapor phase removal in the macrolayer between the ridges of the coating.

Label-Free, High-Throughput Assay of Human Dendritic Cells from Whole-Blood Samples with Microfluidic Inertial Separation Suitable for Resource-Limited Manufacturing.

Microfluidics technology has not impacted the delivery and accessibility of point-of-care health services, like diagnosing infectious disease, monitoring health or delivering interventions. Most microfluidics prototypes in academic research are not easy to scale-up with industrial-scale fabrication techniques and cannot be operated without complex manipulations of supporting equipment and additives, such as labels or reagents. We propose a label- and reagent-free inertial spiral microfluidic device to separate red blood, white blood and dendritic cells from blood fluid, for applications in health monitoring and immunotherapy. We demonstrate that using larger channel widths, in the range of 200 to 600 µm, allows separation of cells into multiple focused streams, according to different size ranges, and we utilize a novel technique to collect the closely separated focused cell streams, without constricting the channel. Our contribution is a method to adapt spiral inertial microfluidic designs to separate more than two cell types in the same device, which is robust against clogging, simple to operate and suitable for fabrication and deployment in resource-limited populations. When tested on actual human blood cells, 77% of dendritic cells were separated and 80% of cells remained viable after our assay.

Megahertz operation of vertical organic transistors for ultra-high resolution active-matrix display

Organic field-effect transistors (OFETs) are the technology of choice for flexible electronic devices such as active-matrix (AM) displays. However, despite the continuous improvement of charge carrier mobility in organic semiconductors, the performance of conventional OFETs is too poor for demanding electronic applications. Furthermore, hero-devices reported in literature often make use of processes (shadow mask fabrication, large channel width devices) which cannot be adapted in production lines, e.g. for AM displays. Here we present an OFET with a novel vertical device structure. It has static and dynamic transistor performance superior over conventional lateral organic transistors with regard to application in AM displays. We show that these vertical transistors can be integrated using processes well-established in the micro-electronic industry and thus offer seamless transfer into production lines. We discuss that these transistors obey scaling laws for footprint and capacitance which make them superior over other planar transistor devices. In combination with excellent device stability and uniformity, vertical OFET might enable ultra-high resolution flexible displays of the future.

P‐1.3: Comparision of two different a‐IGZO TFT Gate Driving Circuits for 32‐in FHD TFT‐LCD

Two different a‐IGZO gate driving circuits (GOA) which used long channel length (GOA_A) and STT (GOA_B) structures were designed and compared. GOA_B shows better performance than that of GOA_A, while the Vth of T53 in GOA_B circuit would shift to a very positive voltage after life test. The large channel width size ratio between T53 and T54 would bring about bigger Vds voltage of T53 which induces large current stress of T53 in GOA_B, so the Vth voltage of T53 in GOA_B would shift to a very positive voltage at life test. The phenomenon which T53 devices were easy to shift to positive bias can be restrained and improved by new design of its pull down holding part in GOA_B by spice simulated results.

Transport and escape in a deformable channel driven by fractional Gaussian noise.

Fractional Gaussian noise (FGN) with the Hurst exponent H is an important tool to model various phenomena in biophysical systems, like subdiffusion in a single protein molecule. Considering that there also exists a confined structure which can be modeled as a channel in these systems, transport and escape driven by FGN in a deformable channel are investigated in this paper. By calculating the mean velocity, and the mean first passage time (MFPT) for crossing the nearest bottleneck and the probability distribution of the final position, effects of FGN and channel structure on the system dynamics are illustrated. Our results indicate that FGN has a complex influence mechanism under different combinations of H and the noise intensity. For a persistence case (H>0.5), the mean velocity decreases but MFPT increases with the increase of the noise intensity and H. While for an antipersistence case (H<0.5), when H is small, the relationships among the mean velocity, MFPT and the noise intensity are exactly the opposite to persistence cases. When H has a large value, the mean velocity tends to first decrease and then increase. Moreover, effects of the bottleneck and channel asymmetry are investigated. It is shown that a small H and a large channel width can lead to a large mean velocity and fast crossing. Besides, a channel asymmetry can affect the system dynamics by inducing asymmetric structure and adjusting the width of bottleneck. However, the effect of the bottleneck is the main factor. Therefore, a combination of channel with wide bottleneck and FGN in an antipersistence regime is the optimal choice to promote the transport and escape. These results provide a basis for the explanation of molecular activity in living organisms and the design of particle mixture separators.

Precise patterning of organic semiconductors by reactive ion etching

Abstract Minimizing the off-state current is mandatory for the development of low power consumption circuits based on organic thin-film transistors (OTFTs). Small OTFTs which are required for compact circuits suffer from parasitic current pathways through the semiconductor and hence precise patterning of the semiconductor film is essential. Since state-of-the-art patterning techniques such as oxygen based reactive ion etching usually severely damage the organic transistors, usually OTFTs with a large channel width W are discussed in the literature in order to circumvent this problem. Here we demonstrate that precise patterning of organic semiconductor films for OTFT using reactive ion etching is possible without compromising the transistor performance. If adequate etching conditions and appropriate masks are chosen, oxygen radicals do not affect the organic transistor because lateral diffusion as well as vertical bombardment of ions through the etching mask do not occur. With the method presented here, we show small footprint OTFTs with W / L = 25 μm/10 μm and leakage current levels as low as 10 fA/μm which enable organic transistors to be used for demanding electronic applications such as high resolution active-matrix displays or photo detector arrays.

Fabrication and characterization of micro-channels on Al2O3/TiC ceramic produced by nanosecond laser

In this paper, a nanosecond laser with wavelength of 1064 nm is used to fabricate micro-channels on Al2O3/TiC ceramic, the influence of laser process parameters (voltage, scanning speed, frequency and the number of overscans) on surface quality and dimensions of micro-channels is investigated. The surface morphology, channel width and depth, and surface composition in ablated zone are measured by scanning electron microscope (SEM), optical profiler, energy dispersive X-ray (EDX) and X-ray diffraction (XRD). Results show that the heat-affected zone is formed surrounding the micro-channels with the oxidation reactions, and the surface morphologies and dimensions of micro-channels are strongly dependent on the laser process parameters. The high voltage, low scanning speed, high frequency and high number of overscans are prone to create large channel width and depth within a certain range induced by higher energy accumulation, however, excessive energy accumulation may lead to the reduced channel width and depth. Based on the experimental results, the optimal laser process parameters for better surface quality of micro-channels are obtained, accordingly, the desired micro-channels with the width of about 50 µm and depth of about 43 µm are fabricated.

Photochemical Molecular Tailoring for Efficient Diffusion and Reorganization of Organic Nanocrystals for Ultra-Flexible Organic Semiconductor Arrays.

Solution-processed organic single crystals with high carrier mobility have been actively investigated for diverse applications such as displays, sensors, and next generation electronics on a flexible platform. However, the lack of precise alignment and growth control of organic single crystals impedes the widespread adoption of organic materials in an industrial perspective. Here, a photochemical modification approach is reported tailoring the solubility and molecular diffusivity of polymeric sacrificial layer and sequential batch-type vapor annealing to implement high-performance (average saturation mobility: 8.01 cm2 V-1 s-1 ) organic single-crystal thin film transistors with large channel width including multiple aligned single crystals. Additionally, the mechanical properties of the organic single crystals are systematically investigated with extreme strain conditions such as bending radius of 150 μm.

Experimental study of the influence of cold heat exchanger geometry on the performance of a co-axial pulse tube cooler

Improving the performance of the pulse tube cooler is one of the important objectives of the current studies. Besides the phase shifters and regenerators, heat exchangers also play an important role in determining the system efficiency and cooling capacity. A series of experiments on a 10W @ 77K class co-axial type pulse tube cooler with different cold heat exchanger geometries are presented in this paper. The cold heat exchangers are made from a copper block with radial slots, cut through using electrical discharge machining. Different slot widths varying from 0.12mm to 0.4mm and different slot numbers varying from around 20–60 are investigated, while the length of cold heat exchangers are kept the same. The cold heat exchanger geometry is classified into three groups, namely, constant heat transfer area, constant porosity and constant slot width. The study reveals that a large channel width of 0.4mm (about ten times the thermal penetration depth of helium gas at 77K, 100Hz and 3.5MPa) shows poor performance, the other results show complicated interaction effects between slot width and slot number. These systematic comparison experiments provide a useful reference for selecting a cold heat exchanger geometry in a practical cooler.

Decay of counterflow turbulence in superfluid 4He

We summarize recent experiments on thermal counterflow turbulence in superfluid 4He, emphasizing the observation of turbulence in the normal fluid and its effect on the decay process when the heat flux is turned off. We argue that what is observed as turbulence in the normal fluid is a novel form of coupled turbulence in the superfluid and normal components, with injection of energy on the scales of both the (large) channel width and the (small) spacing between quantized vortices. Although an understanding of this coupled turbulence remains challenging, a theory of its decay is developed which accounts for the experimental observations.