Opposite Channel Research Articles

An asymmetric orifice-based active micromixer in the microfluidic chip with 3D microelectrode

The fluid mixing in microscale is central to the development of flow patterns in microfluidic chips for particles separation and biological analysis. Yet, as the size of the fluid decreases, the mixing becomes challenging to change this state of flow. In this work, a novel active micromixer for enhancing the mixing performance in the micromixer with asymmetric orifices is presented. To induce the electric-driven micromixing, an AC electric field is employed to the inserted 3D microelectrodes to produce the local electric field through the asymmetric orifices located on the opposite channel walls, which is perpendicular to the main microchannel. Then the mixing experiments were conducted in a microfluidic chip comprising microelectrode with asymmetric orifices, specifically exploiting the mixing efficiency varying with the asymmetric orifice pairs, applied electric potential and frequency of the AC electric field, and flow rate. The bending degree of the mixing interface was calculated and found increasing as a function of applied electric voltage at a given AC frequency, thus enabling effective mixing crossing the microelectrode's area. The predictions are confirmed by optical microscopy experiments and the micromixing can be significantly improved as they experience longer-exposed electrical forces. The integration of multiple asymmetric orifices leads a larger zone to increase mixing efficiency and makes it a promising method for rapid and stable fluid mixing in microscale.

Control of the magnetic anisotropy and Curie temperature of monolayer 1T-CrTe2 for room temperature application

Magnetic units with large magnetic anisotropy energy (MAE) and high Curie temperature (Tc) are crucial for spintronic and quantum computing devices, which are a persisting demand for miniaturization of magnetic units. Using first-principles calculations and Monte Carlo simulation, it is found that monolayer 1T-CrTe2 exhibits strong perpendicular magnetic anisotropy with a MAE of approximately 5.29 meV and high Tc of ∼136 K. Interestingly, we find that the MAE and Tc of monolayer 1T-CrTe2 are tunable through electron/hole doping, strain, and heterostructure engineering. The magnetic easy-axis can be adjusted from out of plane to in plane, which is mainly attributed to the coupling between Te atomic orbitals (px, py). Second-order perturbation theory reveals that the spin–orbit coupling interaction between the occupied px and unoccupied py orbitals in opposite spin channel near Fermi level gives rise to negative contribution of MAE. Moreover, Tc can be enhanced to ∼230 K through super–superexchange mechanism of heterostructure due to the electron hopping between t2g/eg orbitals of Cr4+ ions and e1/a1 orbitals of Fe2+ ions. Importantly, we find that Tc can be boosted above room temperature by applying moderate strain (6%), ascribing to significant enhancement of MAE and exchange coupling constant. The present work indicates that monolayer 1T-CrTe2-based two-dimensional materials are very promising for room temperature application in magnetic storage and information processing.

Chemically Controlled Reversible Magnetic Phase Transition in Two-Dimensional Organometallic Lattices.

Developing an efficient method to reversibly control materials' spin order is urgently needed but challenging in spintronics. Though various physical field control methods have been advancing, the chemical control of spin is little exploited. Here, we propose a chemical means for such spin manipulation, i.e., utilizing the well-known lactim-lactam tautomerization to reversibly modulate the magnetic phase transition in two-dimensional (2D) organometallic lattices. The proposal is verified by theoretically designing several 2D organometallic frameworks with antiferromagnetic to ferrimagnetic spin order transformation modulated by lactim-lactam tautomerization on organic linkers. The transition originates from the change in spin states of organic linkers (from singlet to doublet) via tautomerization. Such a transition further switches materials' electronic structures from normal semiconductors with zero spin polarization to bipolar magnetic semiconductors with valence and conduction band edges 100% spin polarized in opposite spin channels. Moreover, the magnitude of magnetic anisotropy energy also enhances by 5- to 9-fold.

Probing the structural, mechanical, phonon, thermal, and transport properties of magnetic halide perovskites XTiBr3 (X = Rb, Cs) through ab-initio results

Herein, we have first reported the intrinsic properties, including structural, mechanical, electronic, magnetic, thermal, and transport properties of XTiBr3 (X = Rb, Cs) halide perovskites within the simulation scheme of density functional theory as integrated into Wien2k. First and foremost, the structural stability in terms of their ground state energies has been keenly evaluated from their corresponding structural optimizations, which advocate that XTiBr3 (X = Rb, Cs) has a stable ferromagnetic rather than the competing non-magnetic phase. Later on, the electronic properties have been computed within the mix of two applied potential schemes like Generalized Gradient Approximation (GGA) along with Trans-Bhala modified Becke Johnson (TB-mBJ), which thoroughly addresses the half-metallic behaviour with spin-up as metallic and in contrast to opposite spin-down channel signatures the semiconducting behaviour. Furthermore, the spin-splitting seen from their corresponding spin-polarised band structures offers a net magnetism of 2 µB which lends their opportunities to unlock the application branch of spintronics. In addition, these alloys have been characterised to show their mechanical stability describing the ductile feature. Moreover, phonon dispersions decisively certify the dynamical stability within the density functional perturbation theory (DFPT) context. Finally, the transport and thermal properties predicted within their specified packages have also been forwarded in this report.

Optimization and evaluation criteria of water-gas transport performance in wave flow channel for proton exchange membrane fuel cell

Flow channel optimization is an important method to improve the water-gas transport capacity and enhance the performance of proton exchange membrane fuel cells. In this study, the size ratio of the opposite sinusoidal wave flow channel (OSWFC) is optimized, and three-dimensional numerical models are developed to evaluate the comprehensive performance. The results show that OSWFCs obtain performance enhancement compared to the parallel flow channel. 1:1 wave channel has a maximum improvement of 19.53% in mass transfer capacity by the most frequent flow disturbance, while 1:3 has a maximum increasement of 37.5% in water removal performance by the virtue of gentle wave structure. Large pressure loss decreases the mass transfer efficiency, although it with the maximum mass transfer capacity, the mass transfer evaluation criterion of 1:1 wave channel is less than that of 1:3. Moreover, a significant correlation between water-gas transport capacity and electrochemical performance is demonstrated by Pearson correlation coefficient.

ENVIRONMENTAL EXTERNALITIES OF URBAN AGGLOMERATION IN CHINA: NEW EVIDENCE FROM THE PERSPECTIVE OF ECONOMIC DENSITY

In order to capture the environmental externalities of urban agglomeration, we use an agglomeration indicator referred to as economic density, which can be decomposed into the average population density and the concentration of population distribution. Our benchmark regressions use the ordinary least squares method and grid-level panel data for China and for the period 2000–2016. We find that economic density is positively correlated with PM2.5 concentration, and the effects of the two components of economic density are opposite. To address the endogeneity issues, the causal effect of economic density on PM2.5 concentration is estimated with an instrumental variable method. Empirical results show that the PM2.5 concentration increases with economic density, and the associated elasticity is between 0.045 and 0.079. The findings of our benchmark regressions are also supported by a variety of robustness checks. Moreover, while economic growth, the development of secondary industry, and the presence of coal-driven power plants explain why cities with more dense population are more polluted, residential energy use is an opposite channel through which cities with higher economic density can reduce air pollution. Overall, the total effect is a trade-off, and the negative environmental externalities of agglomeration are larger than positive environmental externalities.

Resonances and antiresonances in heat generation by spin current in a quantum dot

We study the heat generation in a quantum dot exposed to a rotating magnetic field and coupled to a normal lead. Both electron-phonon interaction and electron-electron interaction are considered in the dot. We show the emergence of resonances and antiresonances in the heat generation, which we attribute to constructive interference and destructive interference between phonon waves emitted from opposite spin channels in the dot.

Bandpass Filter and Diplexer Based on Short-Circuited Stub-Embedded Resonators and Novel Coupling Scheme

A novel coupling scheme is proposed based on short-circuited stub-embedded resonator (SCSER) for bandpass filters (BPFs). The BPF utilizing SCSER owns three transmission zeros (TZs) that are controlled by short-circuited and open-circuited stubs. Based on the proposed SCSER and coupling structure, a novel high-isolation diplexer is presented. When the TZ is allocated in the opposite channel and impedance transformation is carried out in the common port, the proposed diplexer can be realized by directly combining two different BPFs without an additional matching network. For the demonstration, a BPF and a diplexer based on SCSER are fabricated and measured. The measured results agree well with the simulated ones.

Design and Analysis of a Novel Opposite Trapezoidal Flow Channel for Solid Oxide Electrolysis Cell Stack

High efficiency, raw material availability, and compatibility with downstream systems will enable the Solid Oxide Electrolysis Cell (SOEC) to play an important role in the future energy transition. However, the SOEC stack’s performance should be improved further by utilizing a novel flow-field design, and the channel shape is a key factor for enhancing gas transportation. To investigate the main effects of the novel channel design with fewer calculations, we assumed ideal gas laminar flows in the cathode channel. Furthermore, the cathode support layer thickness and electrical contact resistance are ignored. The conventional channel flow is validated first with mesh independence, and then the performance difference between the conventional and novel designs is analyzed using COMSOL Multiphysics. The process parameters such as velocity, pressure, current density, and mole concentration are compared between the conventional and novel designs, demonstrating that the novel design significantly improves electrolysis efficiency. Furthermore, it directly increased the concentration of product hydrogen in the novel channel. In addition to enhancing convection and diffusion of reaction gases in neighboring channels, the simple structure makes it easy to manufacture, which is advantageous for accelerating commercial use of the novel design.

Numerical modeling and performance analysis of an acid-alkaline aluminum-air cell

The imminent threat of climate change has prompted a global effort to decarbonize the transport sector through the adoption of electric vehicles. Aluminum-air cells have been utilized for this purpose due to their massive energy density, which can be boosted even further by employing an acidic catholyte and an alkaline anolyte. A numerical model of this system would be valuable for designing these cells, but none have been proposed thus far. In this work, we investigated the design of a dual-electrolyte aqueous acid-alkaline aluminum-air cell via numerical modeling to determine potential performance improvements under practical operating conditions. The model was implemented in COMSOL Multiphysics® and validated with experimental voltage and power density curves reported in literature. Afterwards, the performance of the cell was evaluated from its voltage and power density curves, concentration profiles, and ion fluxes. A sensitivity analysis of the cell performance was then conducted with respect to various design parameters and operating conditions to infer possible refinements in the cell's design. Lastly, we simulated cells that were redesigned following observations from the sensitivity analysis. The proposed model showed good agreement with experimental data, most notably at moderate applied current densities and near the maximum power point. H+ and OH− ions are consumed by the electrochemical reactions and a parasitic acid-base neutralization reaction, although the latter is discouraged at higher applied current densities. K+ and HSO4− served as the charge carriers and crossed over to their opposite electrolyte channel to retain electroneutrality whenever H+ or OH− were depleted by the reactions. Lowering the inlet flowrate and employing a thicker separator can reduce the extent of acid-base neutralization without sacrificing the maximum power output. Moreover, enlarging the cathode area can raise the maximum power output while also discouraging acid-base neutralization. Incorporating all three design changes resulted in a 4% increase in the maximum power output and 39% decrease in acid-base neutralization. We also simulated an alternative design that uses a cation exchange membrane, so that electrolyte separation does not rely on the flow pattern, and this yielded an 80% decrease in acid-base neutralization with minimal effect on the power output. The model was based on a proof-of-concept acid-alkaline aluminum-air cell, but it can serve as a baseline for improving the performance of similar cells with more practical designs or geometries.

Asymmetric Method of Heat Transfer Intensification in Radial Channels of Gas Turbine Blades

Loop and semi-loop cooling schemes are widely used for the high-temperature gas turbine blades. In such schemes, the mid-chord airfoil parts are traditionally cooled by radial channels with ribbed walls. The blades with a small specific span, or “short” blades, have different heat flux amounts on pressure and suction sides, which results in a temperature difference in these sides of 100–150 °K. This difference causes thermal stresses and reduces the long-term strength margins. This paper presents a new method of heat transfer intensification in the ribbed radial cooling channels. The method is based on air streams’ injection through holes in the ribs that split channels. The streams are directed along the walls into the stagnation zones behind the ribs. The results of a 3D coolant flow simulation with ANSYS CFX code show the influence of the geometry parameters upon the channel heat transfer asymmetry. In the Reynolds number within a range of 6000–20,000, the method provides the heat transfer augmentation difference by up to 40% on the opposite channel walls. Test results presented in the criteria relations form allow for the calculation of mean the heat transfer coefficient along the channel length.

A novel opposite sinusoidal wave flow channel for performance enhancement of proton exchange membrane fuel cell

The optimized design of the flow field structure helps to enhance the mass transfer and water removal capacity of the proton exchange membrane fuel cell (PEMFC). A novel opposite sinusoidal wave flow channel is proposed in this study, and the influence of amplitudes and periods of the sinusoidal function on performance of PEMFC is explored by numerical simulation. The research results show that the mass transfer capacity of the opposite sinusoidal wave channel is better than that of the straight channel. By increasing the amplitude, combined with decreasing the period, the mass transfer capacity and the performance of the PEMFC can be effectively enhanced. Compared with the straight channel, for an amplitude of 0.8 mm and a period of 0.5Π mm at 2.0 A cm−2, the net power density is increased by 16.61% and 12.01% respectively. Moreover, based on the volume of fluid model, the transport process and distribution characteristics of liquid water in the straight channel and the opposite sinusoidal wave channel are compared and analyzed. The results show the drainage period of the opposite sinusoidal wave channel is half shorter compared to the straight channel. Therefore, the proposed opposite sinusoidal wave channel has better water removal capacity.

Simple microfluidic device for spectroelectrochemistry

The design, fabrication, and performance of a simple microfluidic device permitting spectroelectrochemical measurements on submicroliter samples are described. Planar electrode chips were prepared from cast epoxy and assembled to yield a device with a single flow channel of approximate dimensions 25 mm × 1.3 mm × 0.2 mm. Spectral measurements were made by passing the light beam parallel to the 1.3-mm channel dimension, resulting in a relatively high optical sensitivity. Bare disk electrodes embedded in opposing channel walls permit spectroelectrochemical measurements on sample volumes as low as approximately 3 µL, corresponding to a solution plug just long enough to contact all three electrodes. Adding a solution-cast ionomeric film to the channel wall containing reference and auxiliary electrodes provided an effective salt bridge to significantly smaller sample volumes in contact with a bare working electrode on the opposite channel wall. As demonstration of submicroliter sample analysis, spectroelectrochemical measurements were carried out on a ∼ 0.3 µL aqueous ferricyanide solution and showed near exhaustive electrolysis of the optically sampled volume is achieved in approximately 3 min.

Free fermions, KdV charges, generalised Gibbs ensembles and modular transforms

In this paper we consider the modular properties of generalised Gibbs ensembles in the Ising model, realised as a theory of one free massless fermion. The Gibbs ensembles are given by adding chemical potentials to chiral charges corresponding to the KdV conserved quantities. (They can also be thought of as simple models for extended characters for the W-algebras). The eigenvalues and Gibbs ensembles for the charges can be easily calculated exactly using their expression as bilinears in the fermion fields. We re-derive the constant term in the charges, previously found by zeta-function regularisation, from modular properties. We expand the Gibbs ensembles as a power series in the chemical potentials and find the modular properties of the corresponding expectation values of polynomials of KdV charges. This leads us to an asymptotic expansion of the Gibbs ensemble calculated in the opposite channel. We obtain the same asymptotic expansion using Dijkgraaf’s results for chiral partition functions. By considering the corresponding TBA calculation, we are led to a conjecture for the exact closed-form expression of the GGE in the opposite channel. This has the form of a trace over multiple copies of the fermion Fock space. We give analytic and numerical evidence supporting our conjecture.

Foreign Demand, Competition Strategy, and Export Markups: Evidence from Chinese Multi‐Product Exporters

AbstractUsing Chinese microdata from 2000 to 2013, we document how demand shocks in export markets lead multi‐product exporters to adjust markups across products. We find that, in response to positive demand shocks, quality‐based competitive multi‐product firms increase product markups significantly, particularly for core products, whereas cost‐based competitive multi‐product firms respond by reducing product markups. The reason for this is that positive foreign demand affects markups through two opposite channels: pro‐innovative effects and pro‐competitive effects. Pro‐innovative effects are predominant among quality‐based competitive multi‐product firms, and these firms respond to positive foreign demand shocks by increasing product quality, prices, and markups. Pro‐competitive effects are predominant among cost‐based competitive multi‐product firms, and these firms respond to positive foreign demand shocks by lowering product cost, prices, and markups. We demonstrate the presence of these mechanisms empirically. The results imply that firms with different competition strategies should adopt different measures in response to foreign demand shocks.

Application of a newly developed radial directional electron probe to the edge unidirectional electron current measurement in EAST

• A newly developed radial directional electron probe (DEP) has been applied on EAST. • DEP can measure the amplitude and structure of SOL unidirectional electron current. • This is the first application of DEP to unidirectional electron current in experiment. • The SOL unidirectional electron current driven by LHW is directly measured. A newly developed radial directional electron probe (DEP) has been applied to the unidirectional electron current measurement on EAST tokamak. The DEP consists of two radial arrays of channels which have opposite directions and align along the local magnetic field line. Each radial array has 6 holes with a radial interval of 5 mm. Every channel has a hole with 0.5 mm radial width, 3 mm depth and 15° poloidal opening angle. The graphite collector embedded inside the hole is biased to positive potential to repel low energy ions, and high energy ions are blocked by the hole surface because their Larmor radii are larger than the radial width of hole. In consequence, the ion current collected by the DEP collector can be ignored in contrast with the electron current, as demonstrated by the I - V characteristics in a DEP commissioning experiment. The difference of collected current between two opposite channels signifies the unidirectional electron current in the flux tube. In a lower hybrid wave (LHW) modulation experiment, the amplitude and radial structure of unidirectional electron current induced by LHW is measured directly by this radial DEP array, and the LHW filament current covers over 20 mm radial region with a maximum of 20 A/cm 2 .

Modelling and application of a new method to measure the non-thermal electron current in the edge of magnetically confined plasma

The non-thermal electrons could form considerable current in the edge plasma of tokamak and stellarator. A new method, named directional electron probe (DEP), is proposed to measure the edge non-thermal electron current in magnetically confined plasma. The DEP consists of two opposite channels whose connection line aligns with the local magnetic field line. Each channel has a hole with small radial width and enough thickness to block high energy ions due to their large Larmor radii, and at the end of the hole the collector is biased to positive voltage to repel low energy ions. In this way, the collected current of DEP is mainly contributed by electrons. A particle orbit simulation is performed based on the Boris algorithm, which demonstrates the validity and rationality of the DEP. According to the simulation, the ion collection probability is quite small if compared with the electron collection probability, consequently the collected current is mainly contributed by electrons. The collected currents of thermal electrons under Maxwell–Boltzmann distribution from both channels are almost equal, and the net current is driven by non-thermal electrons. A radial array of DEP has been successfully applied to the scrape-off layer (SOL) non-thermal electron current measurement in EAST. The amplitude and structure of the non-thermal electron current are observed during the lower hybrid wave heating phase. The experimental SOL net current is compared with the simulated net current from a rough estimation, revealing the same radial structure of SOL current and demonstrating the validity of DEP.

Bipolar magnetic semiconducting behavior in VNbRuAl

We report the theoretical prediction of a class of spintronic materials, namely, bipolar magnetic semiconductors (BMSs), also supported by our experimental data. BMSs possess a unique band structure with unequal band gaps for spin-up and spin-down channels and thus are useful for tunable spin-transport-based applications such as spin filters. The valence band and conduction band in BMSs approach the Fermi level through opposite spin channels and hence facilitate reversible spin polarization that is controllable via applied gate voltage. We report the quaternary Heusler alloy VNbRuAl to exactly possess the band structure of a BMS. A rigorous normal x-ray diffraction (XRD) fitting along with synchrotron XRD data confirms that this alloy crystallizes in the LiMgPdSn structure with partial $\mathrm{B}2$ disorder. Transport measurements show a two-channel semiconducting behavior and a quasilinear dependence of negative magnetoresistance, indicating the possible semiconducting nature. The thermoelectric power data not only confirm the semiconducting nature but also give a strong indication of the BMS nature. Interestingly, VNbRuAl also appears to show features of a fully compensated ferrimagnetic (FCF) behavior with vanishing magnetization and significantly high ordering temperature ($>900 \mathrm{K}$). Theoretical simulations of the special quasirandom structure predict partial B2 disorder to be mainly responsible for the coexistent BMS and FCF-like behavior. This study opens up the possibility of finding another class of materials for antiferromagnetic spintronics, with great significance for both fundamental and applied fronts.

Electric-Field Tunable Magnetism in van der Waals Bilayers with A-Type Antiferromagnetic Order: Unipolar versus Bipolar Magnetic Semiconductor

Uncovering the physics behind the electrical manipulation of low-dimensional magnetic materials remains a fundamental issue in practical application of nanoscale spintronics. Here, we propose a strategy to transform A-type antiferromagnetic (AFM) semiconductors into asymmetric AFM unipolar or bipolar magnetic semiconductors by applying perpendicular electric fields in van der Waals bilayer systems. Electric fields lifting energy levels of electrons within same spin channel from consistent layers in opposite direction enables unipolar magnetic semiconductor, whereas electrons within opposite spin channel enable bipolar magnetic semiconductor. A comprehensive study demonstrates this discrepancy originates from spatial distributions of spin density of valence band and conduction band edges in two layers of systems. The electric field induced unipolar or bipolar magnetic semiconducting behavior represents great potential of nanoscale AFM spintronics for information storage and processing.

A Double-Envelope Mitral Inflow Spectral Doppler Profile After MitraClip

A Double-Envelope Mitral Inflow Spectral Doppler Profile After MitraClip