Reverse Mode Research Articles

Thermal Diode Films with Liquid Crystal Elastomer Microstructures

Thermal diodes enabling asymmetric heat flow via efficiently conducting heat in one direction while blocking it in the opposite direction have great potential for controlling and managing thermal energy. Here, a thermal diode film with a scalable and thin‐film form factor is presented, which utilizes thermal contact asymmetry that varies with the direction of heat flow. The proposed thermal diode film is fabricated using two liquid crystal elastomer (LCE) layers separated by an air gap: one surface has a pillar structure, and the other has a hexagonal honeycomb structure. In forward mode, heating the LCE layer with the hexagonal honeycomb structure causes the sidewalls to buckle and contact the pillar structure on the opposite side, facilitating efficient conductive heat transfer. In reverse mode, heating the LCE layer with a pillar structure causes it to contract, increasing the gap between the layers with the pillar and hexagonal structures. This increased gap reduces convective heat transfer across the air gap. The thermal contact asymmetry, depending on the direction of heat flow, enables the film to achieve a thermal rectification ratio of ≈2.0 over a wide temperature range of 60–100 °C.

Efficient evaluation of the Jacobian in the damped least-squares method for optical design problems using algorithmic differentiation.

The fast evaluation of the Jacobian is an essential part of the optimization of optical systems using the damped least-squares algorithm. While finite differences provide an intuitive way to approximate derivatives, algorithmic differentiation is a technique to evaluate them exactly. However, applying algorithmic differentiation to a ray tracing routine for optical systems with many parameters is computationally expensive, where the main costs are caused by the determination of the ray-surface intersection. To overcome this disadvantage, we present a mathematical analysis of the ray-surface intersection and its efficient differentiation in both forward and reverse mode algorithmic differentiation. Futhermore the structure of the optimization variables and operands is exploited to derive a method that allows computation of the Jacobian in the same order of computational complexity as the primal ray trace. The method is successfully tested for a rotationally symmetric lens system and a freeform design task.

Analog behavior of V-FET operating in forward and reverse mode

Analog behavior of V-FET operating in forward and reverse mode

Impact Ionization in LDMOS Transistors: Improved Compact Model and Asymmetry under Forward and Reverse Modes of Operation

Impact Ionization in LDMOS Transistors: Improved Compact Model and Asymmetry under Forward and Reverse Modes of Operation

METHODOLOGICAL APPROACHES TO DETERMINING THE GENERAL PARAMETERS OF SOLAR COLLECTORS AND GROUND HEAT ACCUMULATOR FOR A HEAT PUMP HEATING SYSTEM

In this article, the authors considered and described the principle of operation of a combined heat pump heating system of a building consisting of a heat pump, solar collectors and vertical ground heat exchangers. This heat pump system is an energy-efficient and environmentally friendly technology of using renewable energy sources from solar radiation and the ground, which will replace traditional organic fuel for heating the building. An analysis of the direct use of solar energy in heat pump heating systems as a low-potential heat source was carried out and it was found that its effective use in comparison with the natural heat of the ground is limited to the sunny period of the day. It is noted that it is necessary to take into account the difference in climatic conditions, solar insolation and thermal properties of the ground for different regions of the country, which affect the modes of operation and energy efficiency of the heat pump heating system. This heat pump heating system works in combination with solar collectors and a vertical ground heat exchanger in the reverse mode: in the summer, the energy of solar radiation is utilized by solar collectors and with the use of heat exchangers is accumulated in the ground, and in the winter (in the heating period) the accumulated heat is extracted from the ground using a heat pump. The authors conducted an analytical study of the balance energy equations and developed methodological approaches for calculating the required area of solar collectors and the total depth of wells that ensure the functioning of the heating system during the entire heating season, taking into account the influence of the average monthly values of the following factors: temperature coefficient, average heat flux of incident radiation, average the duration of insolation in the non-heating period, the specific heat flow from the ground, the average minimum specific consumption of external electricity for the operation of the electric motors of the heat pump and the circulation pump. The obtained results can be used in the further design development of heat pump heating systems using the renewable energy of the sun and ground for specific residential buildings with given initial data. Bibl. 24, Fig. 3, Tab. 4.

Gate-tunable high-responsivity photodiode based on 2D ambipolar semiconductor

Abstract Electrically tunable homojunctions based on ambipolar two-dimensional materials have attracted widespread attention in the field of intelligent vision. These devices exhibit inherent switchable positive and negative photovoltaic properties, that effectively mimic the behavior of human retinal cells. However, the photovoltaic responsivity of most electrically tunable homojunctions remain significantly low due to the weak light absorption, making it challenging to meet the application requirements for high-sensitivity target detection in the field of intelligent vision. Here, we propose a gate-tunable photodiode based on two-dimensional ambipolar WSe2 with an asymmetric gate electrode, achieving high photovoltaic responsivity. By adjusting the gate voltage and keeping bias voltage zero, we can dynamically realize reconfigurable n--p and n--n homojunction states, as well as gate-tunable photovoltaic response characteristics that range from positive to negative. The maximum photovoltaic responsivity of the electrically tunable WSe2 homojunction is approximately 0.4 A/W, which is significantly larger than the previously reported value ~0.1 A/W in homojunction devices. In addition, the responsivity can be further enhanced to approximately 1.0 A/W when the n--p photodiode operates in reverse bias mode, enabling high-sensitivity detection of targets. Our work paves the way for developing gate-tunable photodiodes with high photovoltaic responsivity and advancing high-performance intelligent vision technology.

The Fluorescent Amyloid Ligand X34 Binding to Transthyretin (TTR) Tetramer and Fibrils: FRET and Binding Constants of a Sequential Two‐step Process

AbstractThe amyloidogenic homotetrameric plasma protein transthyretin (TTR) has an affinity for bicyclic small molecule ligands in its two thyroxine (T4) binding sites. We have shown that native tetrameric TTR binds to amyloid ligands based on the trans‐stilbene scaffold. The fluorescent Congo‐red analogue, X34, is a symmetric bi‐trans‐stilbene that contains two salicylic acid motifs. We used fluorescence spectroscopy methods to interrogate X34 binding to the TTR tetramer and fibril. We discovered two binding sites in both TTR forms by tryptophan FRET, ligand self‐quenching, Stern‐Volmer plots and binding curves, for the latter including the competitive ligand diflunisal. X34 binds with the similar affinity as diflunisal in the first binding site (Kd1=150 nM), and negative cooperativity renders the binding to the second site with lower affinity very similar compared to diflunisal (Kd2= 1.1 μM). This behavior is coherent with the salicylic acid moiety of diflunisal binding into the binding pocket of TTR (reverse mode). Interestingly X34 binding to TTR fibrils was also well fitted to two binding sites, however with overall lower affinity (Kd1=1.2 μM; Kd2=2.1 μM) compared to binding to the native tetramer. X34 fluorescence when bound to TTR‐fibrils was significantly blue shifted compared to binding to the TTR‐tetramer.

Investigation on coupling vibration characteristics of asymmetric rails with variable cross-sections based on modal separation

In railway turnouts, asymmetric switch rails with variable cross-sections are designed for wheel load transitions. However, the dynamic characteristics of these specially shaped switch rails are not yet fully understood. This paper investigates the vibration characteristics of switch rails through theoretical simulations, on-site admittance tests, and operational deflection shape (ODS) measurements. The study reveals that the modes of the switch rail involve multi-directional coupling vibrations, making the mode types indiscernible through direct observation. To address this, a modal separation method is proposed, based on the calculation of modal mass. The vertical vibration of the switch rail can be categorized into three types: torsional mode, vertical bending mode, and reverse torsion mode of the rail head and base above 600 Hz. As the position approaches the switch rail point, the degree of cross-sectional asymmetry increases, which consequently intensifies torsional vibration. Cross-sectional asymmetry is identified as the primary factor causing the coupling of bending-torsional vibrations, while variable cross-sections contribute to mode shape asymmetry and the gradual alteration of natural frequency along the rail.

A novel Zero Back Power Flow (ZBPF) controlled DAB for DC bus stability and energy storage integrations in hybrid DC/AC off-grid systems

A novel Zero Back Power Flow (ZBPF) controlled DAB for DC bus stability and energy storage integrations in hybrid DC/AC off-grid systems

Investigation of Water Dissociation Catalyst Layer Configurations for Bipolar Membrane Water Electrolzyers

Water electrolysis is a promising technology for the production of sustainable green hydrogen. Alkaline exchange membrane water electrolyzers (AEMWEs) operate at low current densities (<1.0 Acm-2) and low pressures (<30 bars), and have very long operating lifetimes (over 100,000 h) [1]. On the other hand, proton exchange membrane water electrolyzers (PEMWEs) are able to operate at high current densities (>2.0 Acm-2) and pressures (>300 bars), but rely on expensive platinum group metal (PGM) catalysts (Pt, Ir) with a shorter lifetime (80,000 h, 2026 DoE target) [1, 2]. In order to bridge this gap, a newer, under-investigated configuration may have significant advantages: bipolar membranes.Bipolar membranes (BPMs) for water electrolysis consist of two membrane layers: a cation exchange layer (CEL) and anion exchange layer (AEL). This allows the electrolyzer to operate with a high pH gradient with an acidic cathode and basic anode (reverse bias) [3]. Operation in reverse bias mode allows for optimal pH conditions for the half-cell reaction kinetics for a BPM electrolyzer. The BPM aims to maximize OH- and H+ transport, promoting kinetically favorable conditions.BPMs face significant challenges with respect to both performance and durability. BPMs have demonstrated low operational current density compared to PEMWEs [4-6]. Traditional BPMs experienced catalyst layer delamination, failure due to “ballooning”, and significant ohmic resistance, all of which drastically limit cell performance and durability. One method for mitigating all three failure modes is the inclusion of a water dissociation (WD) catalyst at the interlayer. The WD interlayer can mitigate water buildup at the CEL—AEL interface, and can reduce the ionic resistance between the two dissimilar layers. It is vitally important to have a mechanically stable membrane configuration while achieving high performance. BPMs without a well-designed ionomer junction cannot operate effectively without the inclusion of a catalyst at the interlayer junction [7].In this work, reactive spray deposition technology (RSDT) was used to fabricate low loaded, high electrochemically active surface area (ECSA) catalysts as WD interlayers for BPMs. Polarization, electrochemical impedance spectroscopy, and distribution of relaxation times are used to investigate cell performance and short-term durability.

Solving Inverse PDE Problems using Grid-Free Monte Carlo Estimators

Partial differential equations can model diverse physical phenomena including heat diffusion, incompressible flows, and electrostatic potentials. Given a description of an object's boundary and interior, traditional methods solve such PDEs by densely meshing the interior and then solving a large and sparse linear system derived from this mesh. Recent grid-free solvers take an alternative approach and avoid this complexity in exchange for randomness: they compute stochastic solution estimates and generally bear a striking resemblance to physically-based rendering algorithms. In this article, we develop algorithms targeting the inverse form of this problem: given an already existing solution of a PDE, we infer parameters characterizing the boundary and interior. In the grid-free setting, there are again significant connections to rendering, and we show how insights from both fields can be combined to compute unbiased derivative estimates that enable gradient-based optimization. In this process, we encounter new challenges that must be addressed to obtain practical solutions. We introduce acceleration and variance reduction strategies and show how to differentiate branching random walks in reverse mode. We finally demonstrate our approach on both simulated data and a real-world electrical impedance tomography experiment, where we reconstruct the position of a conducting object from voltage measurements taken in a saline-filled tank.

Demonstration of normally OFF beta-gallium oxide monolithic bidirectional switch for AC switching applications

In this work, we report on the beta-gallium oxide (β-Ga2O3) monolithic bidirectional switch. The as-fabricated switch works on enhancement mode operation with a threshold voltage of ∼4 V. Maximum drain current density of 1.93 mA/mm is obtained with a drain voltage of 5 V. The bidirectional switch in a bidirectional mode has an ON/OFF current ratio of ∼107 with ON-resistance of 1.11 and 1.09 kΩ · mm in forward and reverse direction, respectively. However, in diode mode, the device shows an ON/OFF current ratio of 1.6 × 108 and 1.4 × 108 in forward and reverse conduction modes, respectively. The fabricated β-Ga2O3 monolithic bidirectional switch is then used to chop a 60 Hz Alternating Current signal at a chopping frequency of 1 kHz, indicating its potential applications in a range of converters.

Optimized design procedure for small-scale Pumped Hydro Energy Storage systems based on the use of pumps as turbines

Abstract Pumped Hydro Energy Storage (PHES) is a well-established technology offering large storage capacities. In recent years, small-scale PHES plants are becoming more interesting, due to their possibility of being integrated with renewable-based microgrids. However, the high capital costs represent the most critical economic factor for such storage systems. The cost of the hydraulic machines can be mitigated by using commercial centrifugal pumps in reverse mode (the so called Pump as Turbine, PAT, technology) in place of small hydro-turbines. One of the main issues in PHES systems that operate with a single machine is the procedure followed to select the optimal PAT for a given case study. In this study, an automatic selection method was developed, utilizing commercial pump data and optimization algorithms in MATLAB to identify the optimal PAT configuration based on site-specific characteristics and user load profiles. To test the effectiveness of the proposed procedure, the case study of a small-scale PHES located in Sardinia (Italy) coupled with a photovoltaic plant is considered. Results demonstrated that while the choice of the PAT closest to the theoretical best efficiency point exhibit higher nominal efficiencies, their actual operational efficiencies showed considerable variation. This underscores the importance of both developing an algorithm capable of comparing different PATs and defining a method to determine an adequate group of PAT candidates. Additionally, the number of PATs installed significantly impacts the performance of PHES systems. Increasing the number of PATs generally enhances flexibility and efficiency in energy usage during the charging phase, leading to greater energy output during discharge phases. However, operating an excessive number of PATs far from their nominal conditions can result in efficiency losses.

On Hysteresis In A Variable Pitch Fan Transitioning To Reverse Thrust Mode And Back

Abstract A novel hysteresis phenomenon during the transition to and back from the reverse thrust mode in a Variable Pitch Fan (VPF) is identified and characterised in this work. This is done by using a three-dimensional (3D) fully transient Unsteady Reynolds averaged Navier?Stokes (URANS) with the transitioning fan blade aerofoils simulated by an adaptation of the mesh displacement method. The VPF is modelled to be transitioning in a modern 40000 lbf geared high bypass ratio turbofan engine architecture at "Approach Idle" engine power setting in a typical twin-engine airframe with the flaps, slats, and spoilers set for an aircraft touchdown airspeed of 140 knots. The transition to reverse thrust mode involves flow starvation into the engine, formation of recirculation zones in the bypass duct and the establishment of the reverse stream, all of which occurs in the opposing presence of the free stream flow at aircraft touchdown velocity. The transition back to forward flow mode involves the gradual re-establishment of the free stream which is opposed by the presence of the reverse stream within the engine. It is quantified that in the transition to reverse thrust, the blockage develops with a larger time delay than the disappearance of the blockage during the transition back due to the interplay of the temporal dynamics of fan blade motion and flow field response. The hysteresis phenomena described in this work are critical in properly developing control schedules to adapt for potential bi-stable flow field development during the landing run.

Structure of G protein-coupled receptor GPR1 bound to full-length chemerin adipokine reveals a chemokine-like reverse binding mode.

Chemerin is an adipokine with chemotactic activity to a subset of leukocytes. Chemerin binds to 3 G protein-coupled receptors, including chemokine-like receptor 1 (CMKLR1), G protein-coupled receptor 1 (GPR1), and C-C chemokine receptor-like 2 (CCRL2). Here, we report that GPR1 is capable of Gi signaling when stimulated with full-length chemerin or its C-terminal nonapeptide (C9, YFPGQFAFS). We present high-resolution cryo-EM structures of Gi-coupled GPR1 bound to full-length chemerin and to the C9 peptide, respectively. C9 insertion into the transmembrane (TM) binding pocket is both necessary and sufficient for GPR1 signaling, whereas the full-length chemerin uses its bulky N-terminal core for interaction with a β-strand located at the N-terminus of GPR1. This interaction involves multiple β-strands of full-length chemerin, forming a β-sheet that serves as a "lid" for the TM binding pocket and is energetically expensive to remove as indicated by molecular dynamics simulations with free energy landscape analysis. Combining results from functional assays, our structural model explains why C9 is an activating peptide at GPR1 and how the full-length chemerin uses a "two-site" model for enhanced interaction with GPR1.

Experimental Investigation of a Vertical Axis Savonius Wind Turbine

Wind turbines are machines that convert wind energy into energy usable by humans. These include wind turbines that produce electricity or those that pump water. There are many models of wind turbines.This report proposes to study an experimental part of a Savonius vertical axis wind turbine. We then define the efficiency of our Savonius wind turbine by its energy (the electrical output power over the kinetic power of the input wind). The parameters studied are varied: geometric configuration of the rotor, influence of the speed of the wind, influence of the generator, The study was carried out using a blower (reverse mode of a vacuum cleaner), The one of the shortcomings of the Savonius model is its relatively low efficiency, it is interesting to know which energy transformations (transformation of wind energy into mechanical energy of rotation, and transformation of mechanical energy of rotation into electrical energy) lead to yields so weak.

Analysis and optimization of dynamic and static thermal rectification in shell-and-tube phase change thermal rectifiers

Analysis and optimization of dynamic and static thermal rectification in shell-and-tube phase change thermal rectifiers

Caution for Multidrug Therapy: Significant Baroreflex Afferent Neuroexcitation Coordinated by Multi-Channels/Pumps Under the Threshold Concentration of Yoda1 and Dobutamine Combination

Multi-drug therapies are common in cardiovascular disease intervention; however, io channel/pump coordination has not been tested electrophysiologically. Apparently, inward currents were not elicited by Yoda1/10 nM or Dobutamine/100 nM alone in Ah-type baroreceptor neurons, but were by their combination. To verify this, electroneurography and the whole-cell patch-clamp technique were performed. The results showed that Ah- and C-volley were dramatically increased by the combination at 0.5 V and 5 V, in contrast to A-volley, as consistent with repetitive discharge elicited by step and ramp with markedly reduced current injection/stimulus intensity. Notably, a frequency-dependent action potential (AP) duration was increased with Iberiotoxin-sensitive K+ component. Furthermore, an increased peak in AP measured in phase plots suggested enhanced Na+ influx, cytoplasmic Ca2+ accumulation through reverse mode of Na+/Ca2+ exchanger, and, consequently, functional KCa1.1 up-regulation. Strikingly, the Yoda1- or Dbtm-mediated small/transient Na+/K+-pump currents were robustly increased by their combination, implying a quick ion equilibration that may also be synchronized by hyperpolarization-induced voltage-sag, enabling faster repetitive firing. These novel findings demonstrate multi-channel/pump collaboration together to integrate neurotransmission at the cellular level for baroreflex, providing an afferent explanation in sexual dimorphic blood pressure regulation, and raising the caution regarding the individual drug concentration in multi-drug therapies to optimize efficacy and minimize toxicity.

Study on the transient performance of textured water-lubricated bearings considering different acceleration conditions

This study analyses the transient friction dynamics behavior of water-lubricated bearings (WLBs) with a textured structure, which explains the mechanism of texture structure influencing the hydrodynamic effect of WLB in the physical aspect. A comparison of experimental and numerical data is carried out to validate the proposed mixed lubrication model with a textured structure for WLBs. The effects of texture type, texture angle, acceleration mode, and acceleration time on the nonlinear friction dynamics properties of WLBs are investigated. The result shows that various texture structures exhibit distinct pumping effects and that the optimal friction dynamics performance of WLBs can be achieved by adopting the right herringbone texture and an acceptable texture angle. It is advisable to utilize the reverse S-shaped acceleration mode, as it may efficiently mitigate hydrodynamic shock, minimize frictional contact at the initial startup stage, and control the rotor's vibration in later stages. The brief acceleration time may result in a transient shock that hampers proper lubrication, consequently affecting the stable operation of WLBs. The study's findings offer helpful suggestions for the enhanced design of WLB structures and the mitigation of wear and vibration.

A novel multi-excitation transient vibration framework for coupling three- and one-dimensional pumped storage hydropower shafting systems

In vibration models of shafting systems, the hydraulic excitation is difficult to characterize due to the complex and changeable hydraulic factors. Thus, hydropower units are not well understood in terms of their dynamics and stability control under transient processes. A hydraulic–mechanical–electric multi-excitation transient vibration calculation framework is developed for analyzing the relationship between shafting vibration and internal flow regimes. First, the boundary data from penstocks, tailraces, and hydro-turbine are interacted with using one-dimensional and three-dimensional (1D–3D) coupling; Second, user-defined function secondary development is applied to achieve two-stage guide vane closure and the runner's variable speed rotation; Third, based on the computational fluid dynamics results, a multi-excitation vibration model is established to analyze shafting system characteristics. There is less than 1.2% error between the algorithm and the field test in terms of speed peak values. Under braking or reverse pumping modes, various vortice clusters are generated in the blade channel as well as the cascade, blocking the flow passage and leading to the runner's unbalanced force. Three sudden increases in vibration amplitudes of the shafting system have occurred in the radial direction under load rejection, each corresponded to the runner's stall rotations. The change trend in axial vibration amplitudes, however, is closely related to the change in axial hydraulic thrust. Furthermore, in braking and reverse pumping conditions, the axis trajectory is more complex under the action of multiple coupling factors than when only hydraulic factors are considered.