Channel Regime Research Articles

Linear and non-linear stability analysis of double-diffusive Hadley-Prats flow through horizontal porous layer with non-uniform thermal and solutal gradients

A scientific model is devised to understand the onset of double-diffusion Hadley-Prats flow through an infinite parallel permeable channel with non-uniform thermal, solutal gradients, and concentration based internal heat generation under the influence of convection conditions is considered. Darcy’s model is implemented in the context of a porous medium, which is characterized as isotropic and homogeneous. A linear and nonlinear stability analysis is conducted with the help of energy functional method and longitudinal roll perturbations are examined. The emerged dimensionless eigenvalue problem in the linear and nonlinear stability analysis is solved numerically by utilizing fourth order Runge-Kutta method (RK-4) method and shooting scheme. The critical values of wave and vertical thermal Rayleigh numbers are examined. A comprehensive analysis of solutions concerning the onset of convection mechanism is conducted. The produced results are discussed for the various values of emerged physical parameters. It is evident that, the presence of non-uniform thermal and solutal gradients and the internal heat generation mechanism causes the significant variations in the critical values of vertical thermal Rayleigh number in the channel regime.

Dynamical chaos and level splitting under the channeling of the high energy positrons in [100] direction of the silicon crystal

The motion of charged particles in a crystal in the axial channeling regime can be both regular and chaotic. The chaos in quantum case manifests itself in the statistical properties of the energy levels set. These properties have been studied previously for the electrons channeling along [110] direction of the silicon crystal, in the case when the classical motion was completely chaotic, as well as for the ones channeling along [100] direction, when the classical motion can be both regular and chaotic for the same energy depending on the initial conditions. Here we study the positrons channeling in [100] direction. This case is of special interest due to the substantial tunneling probability between dynamically isolated regular motion domains in the phase space. The interaction of the energy levels via tunneling distinctly changes the level spacing statistics. All transverse motion energy levels as well as corresponding stationary wave functions are computed numerically for the 30 GeV positrons channeling in [100] direction of the silicon crystal. The values of the matrix elements for the tunnel transitions areextractedfrom these data. These results confirm the chaos assistance for the tunneling and the level splitting. These values will be used in the further researches of the quantum chaos manifestations in the channeling phenomenon.

Numerical heat and mass transfer in magnetized Williamson liquid motion over a sensor wall engulfed in a micro-cantilever system: An application to thin-film fluidic cells

Central focus of this numerical analysis is to investigate the influence of magnetic body force and thermal radiation on the time-dependent electrically conducting two-dimensional viscous incompressible boundary layer flow of non-Newtonian Williamson fluid over a microcantilever sensor surface suspended in a squeezed regime numerically. A novel heat source/sink and Soret effects are included in the respective governing equations. The constructed time-dependent nonlinear coupled partial differential equations are solved by using a bobust RK-4 technique. Increasing magnetic number increases the velocity distribution and decreases the temperature and concentration profiles in the flow regime.Enhancing Soret number increases the mass diffusion profile. Increasing magnetic number suppress the skin-friction coefficient. Heat transport rate booted with rising radiation number and Sherwood number decreased with enlarged Schmidt number in the channel regime. Finally, the numerical accuracy of the present similarity solutions and used numerical method is validated with existing results and observed a remarkable agreement.

Evolution characteristics of mid‐channel bars with a typical high/low bank structure in the Middle Yangtze River

AbstractAdjustments in mid‐channel bars (MCBs) often influence the stability of channel regime and the safety of river navigation in anabranching reaches. This study aims to investigate the evolution characteristics of the low and high parts of MCBs (L‐MCBs and H‐MCBs) in the Middle Yangtze River (MYR) and reveal the main factors influencing the deformation of these two components. Results show that the total exposed area of L‐MCBs decreased from 305 to 288 km2 in 2003–2019, whereas the H‐MCBs remained relatively stable. Taking the Nanyang bar with a typical high/low bank structure as an example, the deformation of the L‐MCB mainly occurred in the head zone, while the deformation of the H‐MCB was characterised by bank retreat in the tail zone and floodplain deposition on the top of the H‐MCB. In terms of influencing factors, the impacts of the altered flow–sediment conditions and the MCB's properties (soil composition and morphology characteristics) on the Nanyang bar deformation were investigated. On the one hand, the reduction in sediment concentration was the most direct factor causing the shrinkage of L‐MCBs, and the decrease in flood occurrence frequency made the deformation of H‐MCB less significant. On the other hand, the soil composition of the L‐MCB primarily consisted of fine sand with weak erosion resistance, while the large content of cohesive sediment made the H‐MCB difficult to be eroded by overbank flows; moreover, the riverbank of the H‐MCB in the bar‐tail zone was much steeper than that in the bar‐head zone, causing the deformation of the high part to mainly occur in the tail zone. Furthermore, the deformation of the high part was simulated using a bank erosion model at section scale, and the calculated safety factors of riverbank at a typical cross‐section show that the riverbank of the H‐MCB was the most unstable during the receding period.

The international space station packed bed reactor experiment: capillary effects in gas-liquid two-phase flows

Experimental data on flow patterns and pressure drop in two-phase gas-liquid flows through a packed bed obtained aboard the International Space Station (ISS) are analyzed in the limit of low flow rates. Four distinct flow regimes (dispersed bubble, pulse, elongated or large bubble, and gas continuous) are observed and the transition boundaries are identified by a change in the slope of the pressure gradient versus flow rate. It is found that the pressure drop is a function of flow history with the relative magnitude of the hysteresis decreasing with increasing gas or liquid flow rates. Pressure drop (or friction factor) correlations are presented for each of the flow regimes. The capillary or interfacial contribution to the pressure gradient is found to be dominant in the gas channeling regime but comparable to the viscous contribution in the large bubble regime. Preliminary data indicating the slow accumulation of the gas in the bed in the large bubble regime over a longer time period and the intermittent nature of this regime are also presented.

Channeling is a distinct class of dissolution in complex porous media

The traditional model of solid dissolution in porous media consists of three dissolution regimes (uniform, compact, wormhole)—or patterns—that are established depending on the relative dominance of reaction rate, flow, and diffusion. In this work, we investigate the evolution of pore structure using numerical simulations during acid injection on two models of increasing complexity. We investigate the boundaries between dissolution regimes and characterize the existence of a fourth dissolution regime called channeling, where initially fast flow pathways are preferentially widened by dissolution. Channeling occurs in cases where the distribution in pore throat size results in orders of magnitude differences in flow rate for different flow pathways. This focusing of dissolution along only dominant flow paths induces an immediate, large change in permeability with a comparatively small change in porosity, resulting in a porosity–permeability relationship unlike any that has been previously seen. This work suggests that the traditional conceptual model of dissolution regimes must be updated to incorporate the channeling regime for reliable forecasting of dissolution in applications like geothermal energy production and geologic carbon storage.

Channel Morphology and Flow Distribution between Islands in Complex Parallel-Branch Bifurcation in the Lower Lena and Their Long-Term Variations

The first full morphological–hydrological characteristic is given to complex parallel-branch bifurcations of the lower Lena, which have formed at the total (taken with islands) channel width in individual links from 12.6 to 28 km and their length from 36 to 45 km. The number of islands in the branching links is 29 in the Upper Monastyrskii and more than 40 in the Cherpalskii bifurcations. It is shown that, all over the length, two branches with largest water abundance can be identified—the left and the right—of which the latter, navigable in all links and more abundant in water, runs along or near the right, bedrock bank. The left branch concentrates the runoff of water and sediments from the Vilyui, the left tributary of the Lena; this, along with the sediment-removing role, determines its shallowness and higher secondary branching. The links of the branches are separated by short segments of channel narrowing down to 5–8 km, in which two-midstream flow persists. It is shown that groups of islands (archipelagoes) in the middle of the river between the main branches are separated by relatively low-flow central branches subparallel to them (overall, within 10–15% of river flow), numerous transverse channels between islands and divided into into two parts (upstream and downstream) by diagonal branches, through which water partly redistributes between the main branches. It was shown that, at many-year scale and at seasonal runoff variations, the water abundance in the main and subparallel branches is practically constant, while the discharge in diagonal branches varies periodically from 10–15 to 30–35%, depending on channel transformations in the right main branch. This coincides with the periodic redistribution of water discharges, the development and shallowing of channels in secondary branching of the main channel, which lie near the sites of separation of diagonal branches from them. The revealed regularities for the first time give data on the channel regime of parallel-branch bifurcation of the channel of a large river, which is of great importance for the improvement of navigation in the Lower Lena

The research on the interfacial area transport equation in rectangular channels: Interfacial characteristics distribution and bubbles interaction mechanism

The interfacial area transport equation (IATE) is employed to describe the evolution of interfacial structure and evaluate the interfacial area concentration of two-phase flow. However, the interaction mechanisms among bubbles change in different rectangular channels, significantly impacting interfacial characteristics and source terms in IATE. In order to study the interface characteristics and mechanism of bubble interaction in rectangular channels with different gap sizes, an experimental study was conducted on the upward mixture flow of air and water in an adiabatic vertical channel under atmospheric pressure. Two channels with cross-sections of 4 × 66 mm and 8 × 66 mm were selected. The superficial velocities of water and air were 0.5–3 and 0–1.12 m/s, respectively, almost at the transitional region of bubbly to slug flow. Flat electrodes and the four-sensor probes measured the interfacial characteristics. This study analyzes the development of interface and mechanism of interaction among bubbles. The result shows that the evolution in the distribution of void fraction and interfacial area concentration significantly depends on the flow regime, flow rate, and cross-sectional geometric size of channels. Under the condition of a lower liquid flow rate, the gap size of the channel plays a vital role in the efficiency of bubble coalescence, influencing the mechanisms of the random collision and wake entrainment among bubbles. However, the interfacial parameter distribution under higher liquid rate conditions is dominated by turbulence intensity and flow regime, and the mechanisms of bubble interaction become identical. Finally, the mechanisms of interaction among bubbles (random collision and wake entrainment) are analyzed based on the development of interfacial characteristics. In a word, based on the conclusions specified in this research, the new models of source terms of ITAE in rectangular channels will be predictably established in the future.

Thermal Condition in the Channels of Plate Heat Exchangers

Equipping heat points with plate-type heat exchangers is an integral structural element of the 3rd generation heat and power network and a component of the reliability of the heat supply system as a whole. It has been established that the optimization calculations of heat exchangers of this type are difficult due to the absence of dependences on heat transfer and hydraulic resistance between the channels in the structural space of the heat exchanger.Purpose of research. To clarify the method of calculating plate heat exchangers, excluding the equality of thermal and hydraulic conditions from the generally accepted assumptions.Methods. The research methodology is based on the use of the law of conservation of mass in order to determine the temperature parameters of working fluids in each channel. The solution of this problem is proposed in the form of a system of equations, each of the equations of which characterizes the thermal balance of the channel under consideration. A computer model of the heat exchanger is constructed in order to conduct a numerical study of the thermal regime of the heat exchanger.Results. It is indicated that as an assumption in the well-known mathematical model for calculating the thermal regime of a plate-type heat exchanger, the condition of equal distribution of fluid flows between channels is accepted. This restriction leads to equalization of liquid temperatures in each channel. Taking into account the geometric arrangement of the channels, the excess of the final temperature of the heating and heated coolant in the first and last channels with respect to known data is up to 10%. The results of the study confirm the hypothesis of uneven heating of the coolant along the length of the plate package due to the uneven flow distribution between the channels.Conclusion. The results of analytical calculation and modeling in the SolidWorks environment of the temperature regime in the channels of a plate-type heat exchanger indicate a significant influence of the geometric arrangement on the thermal regime in the channels. The formulated provisions of the mathematical description of the unevenness of the thermal regime of heat exchange channels, taking into account the location of the plates, are recommended to be used when improving the design parameters of plate-type heat exchangers.

Sb2Te3/MoS2 Van der Waals Junctions with High Thermal Stability and Low Contact Resistance

AbstractTwo‐dimensional transition metal dichalcogenides (TMDCs) demonstrate great potential in nanoelectronics devices owing to their high carrier mobility in the atomically thin channel regime. However, high contact resistance between source/drain electrodes and TMDC channels hinders the TMDCs applications in the very‐large‐scale integration (VLSI) field. Here, this work reports atomically aligned van der Waals (vdW) junction fabrications through thermal‐induced crystallization of layered Sb2Te3 electrodes on monolayer MoS2 using VLSI‐compatible physical vapor deposition and annealing processes. Due to Fermi‐level unpinning with a small band offset between Sb2Te3 and MoS2 and small density of state of Sb2Te3, better device performance is demonstrated on MoS2 MOSFETs with Sb2Te3/W contact than that of Sb/W contact. Moreover, the ideal vdW junctions are found to demonstrate extreme high‐thermal robustness. No intermixing at the Sb2Te3/MoS2 interface or crystallinity degradation of Sb2Te3 is observed after 450 °C annealing, leading to higher thermal stability than its Sb counterpart. Sb2Te3 is a promising candidate as an n‐type contact material for TMDC‐based devices such as MoS2, MoSe2, and WS2 in future VLSI electronics and various other applications.

Electrical/flow heterogeneity of gas diffusion layer and inlet humidity induced performance variation in polymer electrolyte fuel cells

A three-dimensional single-flow channel computational model is used to investigate the performance characteristics of polymer electrolyte fuel cells (PEFC). The combined influence of non-uniform interfacial contact resistance (ICR) and inlet relative humidity (RH), along with the heterogeneous flow properties of the gas diffusion layer (GDL) on the PEFC performance is evaluated. The study considers combinations of full and partial humidification of anode and cathode reactants. Results reveal heterogeneous GDL with non-uniform ICR distribution results in a slight ∼4.4% reduction in current density at 0.3V compared to the homogeneous case. However, under same electrical/flow heterogeneities, the current density is observed to increase by ∼19% to ∼1.3A/cm2 under fully humidified anode and partially humidified cathode (i.e., RHa|RHc = 100%|60%) as compared to ∼1.1A/cm2 under symmetric RHa|RHc = 100%|100%. Interesting observations are made on the temperature distribution and cathodic water fractions. The variation in anodic inlet humidity is observed to have no impact on temperature distribution in the membrane, whereas variation in cathodic inlet humidity is effective in reducing the temperature in the channel regime with a 4K (kelvin) difference among all the cases. It is noted here that the overpotential map is not an indicator for performance loss, at least at full inlet humidity. This parameter is observed to depend on water concentration in the cathode. The study provides a detailed analysis of the distribution of reactant mass fraction, water concentration, current density, temperature, cathodic overpotential, and cell performance for all the simulated cases.

Specific of transmission mechanism of monetary policy in Ukraine in the conditions of martial law

Introduction. The current state of the Ukrainian economy is determined by the unfolding of crisis as a result of full-scale military aggression, which determines the need to optimize the regulatory influence of monetary policy in order to ensure the stability of the economy against the negative consequences of the war, minimize and localize the impact of the negative consequences of the crisis for the real sector of the economy. Under such circumstances, the study of problems related to the choice of the most optimal monetary policy strategy, which is implemented in practice through the appropriate channels of monetary transmission, which operate on the basis of the selected targeting regime, is especially relevant. At the same time, military actions determine the need to reassess the system of economic coordinates, in which the central bank, defending its institutional independence, could focus monetary regulation exclusively on price stability, ignoring other strategic goals of state influence on the economy, related to the urgent need to save economic activity and prevent unfolding recession precisely with the help of monetary policy instruments. Goal. The purpose of the study is to find out the features of practical implementation and to identify problematic aspects of the transmission mechanism of monetary regulation, as well as to determine on this basis the most optimal channels of monetary transmission, suitable for use in conditions of martial law, external shocks and the unfolding of the economic crisis. Methodology. General scientific techniques and tools, methods of analysis and synthesis, comparison, summary and grouping, scientific abstraction are used. The results. The article examines the action of the main monetary transmission channels and their impact on key macroeconomic parameters. The features and effectiveness of the transmission mechanism of monetary policy in the conditions of unfolding economic crisis during the period of martial law are analyzed. Problematic aspects of the practical implementation of the channels of monetary policy transmission mechanism have been identified. The fallacy of certain actions of the NBU regarding use of interest rate channel and inflation targeting regime while rejecting the exchange rate stability is emphasized. The advantages of using the exchange rate channel as more effective in the system of central bank transmission of monetary impulses to the economy in order to achieve the goals of financial stabilization, maintenance of economic growth and employment are substantiated.

All region analytical modeling of 2-D transition metal dichalcogenide FET by considering effect of fringing field and region-wise mobility

In this paper, for the first time an analytical all region model of Transition metal dichalcogenide based FET has been developed to represent the current–voltage characteristics of the device in ultra-short channel regime. Starting from Gauss’s law, Poisson’s equation is formulated and short channel subthreshold current model is developed subsequently. In order to include fringing field effect, the gaussian box is considered for top and bottom oxides along with channel. Next, Velocity saturation model is developed by considering mobile charges due to top-bottom gates and region-wise field dependent mobility in the channel utilizing the drift diffusion approach. Both the models are then unified by finding the natural points of transition from one model to other. The intraband source to drain tunneling has also been incorporated to develop generalized 2-D material based FET model. Veracity of the model has been verified with NEGF simulations for different device parameters and excellent congruence is observed. The effect of the interface trap charge density has also been included in the model and its effects on the transfer characteristics are investigated. • Analytical modeling of I-V characteristics for TMD materials applicable for all channel lengths. • Validation of model with atomistic simulator data for Sub 10 nm channel length. • Effects of double gate and fringing field have been included. • Source to drain tunneling has been included to increase model applicability for any 2D materials.

ANALYSIS AND ASSESSMENT OF THE HYDROMORPHOLOGICAL SITUATION AT THE CONSTRUCTION SITE OF A BRIDGE CROSSING OVER THE ZEYA RIVER IN BLAGOVESHCHENSK USING MATHEMATICAL MODELING OF WATER MOVEMENT CHARACTERISTICS

The hydromorphological situation at the site of bridge construction is analyzed in the paper; the analysis results are presented. The issues of ensuring the channel geometry stability are considered. The impact of a temporary construction embankment on the f low kinematics is estimated. The level regime of the river and the channel reformations in the alignment of the bridge crossing and on the upstream section of the river are studied at the calculated level and water flow. The results obtained make it possible to determine and establish the values of the permissible degree of impact of the designed hydraulic structures and measures on the channel regime of the near-mouth section of the Zeya River in the area of the projected bridge crossing over the river in Blagoveshchensk, within which the natural and anthropogenic-induced conditions of the statistical stability of the “flow-moving channel” system are realized by the river flow. The studies were carried out in 2 stages: the first one, a test stage, was carried out for the initial everyday state of the riverbed in the section of the Zeya River in the area of the bridge crossing, according to which the model was calibrated in accordance with the specified boundary conditions in the area under study; the second one, on the model, was carried out for three options of the construction dam length, erected from the left bank to the 15th pillar of the bridge, to the middle of the span between the 15th and 16th pillars and up to the 16th pillar of the bridge crossing, which made it possible to assess the impact of the structure with different options of its length on the flow hydraulics in the area of the bridge crossing. The research method applied is the mathematical 2-D modeling of the water movement characteristics, for which the “FLOOD” software package is used.

Investigation of the current state of the tailwater of the Nizhny Novgorod hydroelectric power station, taking into account channel deformations and the effect of dredging

Integrated waterworks on rivers have a great impact on the state of natural waterways. With the commissioning of hydroelectric facilities and reservoirs that regulate river flow, a new hydrological and channel regime is created; the intensity and nature of channel processes change. The regulation of the runoff by hydropower systems introduces changes in the travel and navigation conditions of the river in question, especially in the lower pools. In this paper, an assessment is made of the current state of the lower pool of the Nizhny Novgorod hydroelectric power station, which is one of the areas limiting navigation throughout the entire unified deep-water system of the Russian Federation. The results of studies of the effect of dredging on the level regime of the tailwater are also presented.

Explaining Monetary Spillovers: The Matrix Reloaded

AbstractThis paper relies on a high‐frequency identification approach to provide new insights into monetary policy spillovers by major central banks. Our long and broad sample (1999–2019, from four major economies to 47 advanced and emerging market economies) allows us to accurately identify the properties of spillovers and to shed light on different transmission channels. We find that spillovers by the Fed to foreign interest rates are economically large, but more surprisingly, document an intensification of spillovers by the European Central Bank over time. Spillovers are more significant to bond yields in advanced economies than they are to those in emerging markets. Differentiating across key spillover channels, we find strongest support for a financial links channel, but weaker evidence for the macroeconomic links channel and foreign exchange regime channel.

End-To-End Capacities of Hybrid Quantum Networks

Future quantum networks will be hybrid structures, constructed from complex architectures of quantum repeaters interconnected by quantum channels that describe a variety of physical domains; predominantly optical-fiber and free-space links. In this hybrid setting, the interplay between the channel quality within network sub-structures must be carefully considered, and is pivotal for ensuring high-rate end-to-end quantum communication. In this work, we combine recent advances in the theory of point-to-point free-space channel capacities and end-to-end quantum network capacities in order to develop critical tools for the study of hybrid, free-space quantum networks. We present a general formalism for studying the capacities of arbitrary, hybrid quantum networks, before specifying to the regime of atmospheric and space-based quantum channels. We then introduce a class of modular quantum network architectures which offer a realistic and readily analysable framework for hybrid quantum networks. By considering a physically motivated, highly connected modular structure we are able to idealize network performance and derive channel conditions for which optimal performance is guaranteed. This allows us to reveal vital properties for which distance-independent rates are achieved, so that the end-to-end capacity has no dependence on the physical separation between users. Our analytical method elucidates key infrastructure demands for a future satellite-based global quantum internet, and for hybrid wired/wireless metropolitan quantum networks.

Who Gets Exposed to Political Misinformation in a Hybrid Media Environment? The Case of the 2019 Indonesian Election

In the wake of the US 2016 Presidential Election, concerns about misinformation traversing on social media have heightened. Since then, much of the public discourse has been on developing effective strategies to combat the spread of misinformation online. While several studies have focused on the effects of a mixed/hybrid regime of information channels on political participation and campaigns, we know little about how the existence of a hybrid media system exposes people to misinformation during an election cycle. Using a nationally representative survey administered during the 2019 Indonesian election ( N = 1,820), we find evidence for the prominence of traditional media as well as face-to-face discussions: political use of traditional media such as newspapers and TV as well as sharing of political information through face-to-face discussions are found to be positively associated with at least one measure of misinformation exposure. As for the social media communicative pathways, only political use of WhatsApp and Instagram are found to be positively associated with misinformation exposure; that no similar effects are observed for Facebook and Twitter attests, to some extent, to the efficacy of strategies aimed at combating misinformation implemented on such platforms. By considering social media, traditional media, and face-to-face communication in a context of a less digitalized hybrid media environment, this article provides a more comprehensive framework and novel empirical data to study misinformation exposure beyond the context of Western democracies.

P‐141: Student Poster: Modulation of Subthreshold Current in In‐Ga‐Zn‐O Thin‐film Transistor for OLED Display using Electrohydrodynamic Jet Printing

Here, we suggest simple method for multi value slope In‐Ga‐Zn O (IGZO) thin‐film transistors (TFTs) using electrohydrodynamic (EHD) jet printing. To induce multi value slope, parasitic channel was intentionally formed on top of IGZO main channel using EHD jet printing. By precisely controlling parasitic channel regime with EHD jet printing, multi value slope could be realized without degradation in electrical performance of original IGZO TFTs.

Modeling and analysis of changes in the channel regime of the Kama river within the boundaries of 1639,0-1644,5 km during the development of the channel part of the Sidorovskoye occurrence

The problem studied in the framework of this work is devoted to issues related to the projected excavation of soil from the channel part of the Sidorovskoye sand and gravel deposit on the river. Kama. The channel part of the deposit is located at 1639.0-1644.5 km of the Nizhnekamsk sluice–mouth of the river. Vyatka, which is the upper part of the Kuibyshev reservoir. The paper presents the results of the analysis of channel reformations of the studied section of the river according to field data and hydraulic calculations performed to model the channel process in the section of the river. Kama, is located in the downstream of the N. Kamskaya HPP, taking into account the planned engineering measures related to the extraction of river alluvium from the channel open pit.