bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of alkali beam emission spectroscopy on NSTX-U
Authors: Lampert M. , Anda G. , Asztalos O. , Berkery J. W. , Diallo A. , Stratton B. , Zoletnik S.
Published: September 2024

Understanding fast pedestal dynamics and turbulent transport in the edge and scrape-off layer (SOL) plasma of spherical tokamaks is crucial for the design and operation of future fusion reactors. The alkali beam emission spectroscopy diagnostic technique offers a means to measure the absolute electron density radial profile and fluctuation amplitude in these regions. In this study, we demonstrate that injecting a sodium neutral beam radially into the plasma and analyzing the light emission from its 3p–3s atomic transition using near-orthogonal viewing angles allows for accurate measurement of the electron density profile and fluctuations in the National Spherical Torus Experiment (NSTX) Upgrade spherical tokamak. Our findings indicate a peak signal-to-noise ratio of 118 in the pedestal and 12 in the SOL under typical NSTX plasma conditions. The spatial resolution for the electron density profile is estimated to be between 2 and 8 mm, while for fluctuation measurements, it ranges from 12 to 15 mm.
High-n Rydberg transition spectroscopy for heavy impurity transport studies in W7-X (invited)
Authors: Swee Colin , Geiger Benedikt , Ford Oliver , O’Mullane Martin , Poloskei Peter , Reimold Felix , Romba Thilo , Wegner Thomas ,   W7-X Team
Published: September 2024

Here, we present a novel spectroscopy approach to investigate impurity transport by analyzing line-radiation following high-n Rydberg transitions. While high-n Rydberg states of impurity ions are unlikely to be populated via impact excitation, they can be accessed by charge exchange (CX) reactions along the neutral beams in high-temperature plasmas. Hence, localized radiation of highly ionized impurities, free of passive contributions, can be observed at multiple wavelengths in the visible range. For the analysis and modeling of the observed Rydberg transitions, a technique for calculating effective emission coefficients is presented that can well reproduce the energy dependence seen in datasets available on the OPEN-ADAS database. By using the rate coefficients and comparing modeling results with the new high-n Rydberg CX measurements, impurity transport coefficients are determined with well-documented 2σ confidence intervals for the first time. This demonstrates that high-n Rydberg spectroscopy provides important constraints on the determination of impurity transport coefficients. By additionally considering Bolometer measurements, which provide constraints on the overall impurity emissivity and, therefore, impurity densities, error bars can be reduced even further.
Numerical analysis of vortex dynamics in hyperbolic funnels using computational fluid dynamics
Authors: Donepudi Teja , van de Griend Maarten , Agostinho Luewton L. F. , Kroon Esther J. de , Klymenko Roman , Pecnik Rene , Woisetschläger Jakob , Fuchs Elmar C.
Published: September 2024

Experimental investigations into the characterization of vortices in hyperbolic funnels have shown efficient aeration properties. Certain regimes of vortices have been observed to exhibit high gas dissolution rates. This phenomenon has prompted inquiries into the underlying physical mechanisms at both micro and macroscopic scales. The present study employs computational fluid dynamics to numerically analyze the flow field organization inside these vortices, aiming to elucidate the observed high gas transfer rates. Transient simulations are performed on a three-dimensional radially structured hexahedral mesh, utilizing a multiphase Euler–Euler approach-based volume of fluid method for modeling, along with shear stress transport turbulence modeling based on k−ω equations with curvature correction. The evaluation of the two vortex regimes was conducted in terms of hydraulic retention time, water volume in the reactor, air–water interfacial area, and bulk mixing. Instabilities resembling Taylor vortices observed in Taylor–Couette flow systems emerge in the secondary flow field of these vortical structures, facilitating turbulent mixing. A qualitative analysis of the strength of these instabilities in terms of average vorticity per unit mass of water explains the high gas transfer efficiency. Despite high gas transfer rates, water exiting the funnel remains undersaturated under given operating conditions due to the short hydraulic retention time.
Optical force and torque in near-field excitation of C3H6: A first-principles study using RT-TDDFT
Authors: Amano Risa , Nishizawa Daisuke , Taketsugu Tetsuya , Iwasa Takeshi
Published: September 2024

Optical trapping is an effective tool for manipulating micrometer-sized particles, although its application to nanometer-sized particles remains difficult. The field of optical trapping has advanced significantly, incorporating more advanced techniques such as plasmonic structures. However, single-molecule trapping remains a challenge. To achieve a deeper understanding of optical forces acting on molecular systems, a first-principles approach to analyze the optical force on molecules interacting with a plasmonic field is crucial. In our study, the optical force and torque induced by the near-field excitation of C3H6 were investigated using real-time time-dependent density functional theory calculations on real-space grids. The near field from the scanning tunneling probe was adopted as the excitation source for the molecule. The optical force was calculated using the polarization charges induced in the molecule based on Lorentz force. While the optical force and torque calculated as functions of the light energy were in moderate agreement with the oscillator strengths obtained from the far-field excitation of C3H6, a closer correspondence was achieved with the power spectrum of the induced dipole moment using near-field excitation. Time-domain analysis of the optical force suggests that the simultaneous excitation of multiple excited states generally weakens the force because of mismatches between the directions of the induced polarization and the electric field. This study revealed a subtle damping mechanism for the optical force arising from intrinsic electronic states and the influence of beating.
Optical and microstructural studies of erbium-doped TiO2 thin films on silicon, SrTiO3, and sapphire
Authors: Singh Manish K. , Grant Gregory D. , Wolfowicz Gary , Wen Jianguo , Sullivan Sean E. , Prakash Abhinav , Dibos Alan M. , Joseph Heremans F. , Awschalom David D. , Guha Supratik
Published: September 2024

Rare-earth ion doped oxide thin films integrated on silicon substrates provide a route toward scalable, chip-scale platforms for quantum coherent devices. Erbium-doped TiO2 is an attractive candidate: the Er3+ optical transition is compatible with C-band optical fiber communications, while TiO2 is an insulating dielectric compatible with silicon process technology. Through structural and optical studies of Er-doped TiO2 thin films grown via molecular beam deposition on silicon, SrTiO3, and sapphire substrates, we have explored the impact of polycrystallinity and microstructure on the optical properties of the Er emission. Comparing polycrystalline TiO2(rutile)/Si with single-crystalline TiO2(rutile)/r-sapphire and polycrystalline TiO2(anatase)/Si with single-crystalline TiO2(anatase)/SrTiO3, we observe that the inhomogeneous linewidth (Γinh) of the most prominent peak in the Er spectrum (the Y1–Z1 transition, 1520 and 1533 nm in rutile and anatase TiO2) is significantly narrower in the polycrystalline case. This implies a relative insensitivity to extended structural defects and grain boundaries in such films (as opposed to, e.g., point defects). We show that the growth of an undoped, underlying TiO2 buffer on Si can reduce Γinh by a factor of 4–5. Expectedly, Γinh also reduces with decreasing Er concentrations: we observe a ∼2 order of magnitude reduction from ∼1000 ppm Er to ∼10 ppm Er. Γinh then gets limited to a residual value of ∼5 GHz that is insensitive to further reduction in the Er concentration. Based upon the above results, we argue that the optical properties in these thin films are limited by the presence of high “grown-in” point defect concentrations.
Numerical study of a self-propelled biomimetic robotic fish driven by pectoral fins in labriform mode
Authors: Feng Yikun , Su Yumin
Published: September 2024

In contrast to other swimming modes, the motions of fins in the labriform mode can be categorized into the drag-based mode and the lift-based mode, which differ in terms of the thrust generation mechanisms. This variance in thrust generation mechanisms gives the labriform mode unique advantages in underwater propulsion. The term labriform indicates that propulsion occurs due to oscillatory movements of pectoral fins. Herein, to identify the key features of labriform locomotion, numerical simulations of a self-propelled biomimetic robotic fish with a Reynolds number (Re) of up to 3 000 000 in the labriform mode are performed. This study includes a detailed analysis of swimming performance and hydrodynamic mechanisms and their connection to three-dimensional vortex dynamics. Compared with the drag-based mode, the fish is observed to cruise faster and swim more smoothly in the lift-based mode. This study also finds that the pectoral fin can produce continuous thrust during one cycle in lift-based mode but can only generate thrust during the power stroke in the drag-based mode. By connecting vortex dynamics and surface pressure, the results show that the leading-edge vortices generated by pectoral fins are associated with most of the thrust production in both motion modes. The analysis of the vortex structure shows that the pectoral fins shed one vortex ring in one cycle of the drag-based mode and two vortex rings in one cycle of the lift-based mode. Our results provide new insights regarding the self-propelled swimming mechanism of biomimetic robotic fish with different labriform propulsion modes.
Extending van der Waals equation of state by molecular potential theory to study nano-confined gas properties
Authors: Wu Shouya
Published: September 2024

Understanding the properties of nano-confined gas is essential for the effective utilization of unconventional natural gas, but the classical equation of state (EOS) for bulk gas does not apply to nano-confined gas. In this work, based on the potential energy of nano-confined gas molecules, the gas density distribution function on a nano-pore cross section is derived and subsequently, a novel van der Waals (vdW) EOS is proposed that modifies the “internal pressure” term and extends the “external pressure” term. In this proposed EOS, the gas/solid and porous media properties, such as pore size, gas molecular size, solid molecular number density, and the gas–solid molecular interaction parameter, are applied to characterize the nano-confinement effect. Using the experimental results of nano-confined gas critical temperature, the applicability of this proposed vdW EOS model is verified and it has the largest relative deviation of 7% for nanopores with sizes greater than 2 nm. The gas molecular size and gas–solid molecular interaction are found to be important factors contributing to the nano-confinement effect, and they influence the critical point shift and density of nano-confined gas. Also, the solid molecular number density greatly affects the compressibility of nano-confined gas. Using this model, the U-shaped density distribution curve described in molecular dynamic simulations is obtained, and the equation to calculate the adsorption layer thickness is also obtained. The nano-confinement effect induces gas liquefaction and incompressibility because of the increased gas density and increased compressibility factor of nano-confined gas.
Efficient simulation of open quantum systems coupled to a reservoir through multiple channels
Authors: Nuomin Hanggai , Wu Jiaxi , Zhang Peng , Beratan David N.
Published: September 2024

It is challenging to simulate open quantum systems that are connected to a reservoir through multiple channels. For example, vibrations may induce fluctuations in both energy gaps and electronic couplings, which represent two independent channels of system–bath couplings. Systems of this kind are ubiquitous in the processes of excited state radiationless decay. Combined with density matrix renormalization group (DMRG) and matrix product states (MPS) methods, we develop an interaction-picture chain mapping strategy for vibrational reservoirs to simulate the dynamics of these open systems, resulting in time-dependent spatially local system–bath couplings in the chain-mapped Hamiltonian. This transformation causes the entanglement generated by the system–bath interactions to be restricted within a narrow frequency window of vibrational modes, enabling efficient DMRG/MPS dynamical simulations. We demonstrate the utility of this approach by simulating singlet fission dynamics using a generalized spin-boson Hamiltonian with both diagonal and off-diagonal system–bath couplings. This approach generalizes an earlier interaction-picture chain mapping scheme, allowing for efficient and exact simulation of systems with multi-channel system–bath couplings using matrix product states, which may further our understanding of nonlocal exciton–phonon couplings in exciton transport and the non-Condon effect in energy and electron transfer.
Effect of four-phonon scattering on thermal transport of γ-graphyne revealed by atomic cluster expansion
Authors: Cui Chunfeng , Zhang Yuwen , Ouyang Tao , Tang Chao , He Chaoyu , Li Jin , Zhong Jianxin
Published: September 2024

In this work, we systematically explore the effect of four-phonon (4ph) scattering on the lattice thermal conductivity (κl) of γ-graphyne based on the atomic cluster expansion potential for carbon (C-ACE) combined with a phonon Boltzmann transport equation. The reliability of C-ACE in assessing the thermal transport properties of γ-graphyne is confirmed through comparing the results of phonon dispersion relation and κ3ph (only considering 3ph scattering) derived from C-ACE and density functional theory calculations. Regular residual analysis indicates that there might exist a strong 4ph interaction in γ-graphyne, and calculations further demonstrate κ3ph+4ph (considering 3ph scattering in an iterative solution and 4ph scattering in relaxation time approximation) is indeed reduced by 69.8% relative to κ3ph. From the analysis of scattering rates in γ-graphyne, one can intuitively observed that the 4ph scattering occupies a highly significant position in total phonon scattering, which greatly suppresses the κl. The strong 4ph scattering in γ-graphyne is primarily due to the reflection symmetry selection rule less restricts 4ph scattering process for an out-of-plane flexural acoustic mode. The findings presented in this work demonstrate the reliability of C-ACE based accelerated calculations on the κl of γ-graphyne, as well as reveal that the strong 4ph scattering in γ-graphyne significantly reduces its κl, which will greatly promote the application of γ-graphyne and graphyne family in the field of thermoelectricity.
Calibration of roughness coefficient for long-distance water supply systems with multi-branch pipelines
Authors: Shi Lin , Zhang Jian , Yu Xiaodong , Chen Sheng , He Wei , Chen Nan
Published: September 2024

Hydraulic models are essential for predicting, estimating, analyzing, and optimizing long-distance water supply systems. Accurate calibration of these models is crucial for effectively representing the behavior of such complex systems and achieving a comprehensive understanding. However, the limited availability of measured data in actual systems often leads to an ill-posed problem characterized by more variables than equations. This paper proposes a calibration framework based on artificial neural networks (ANN) and adaptive particle swarm optimization to address this challenge. The influence of the number of measurement points and the measurement errors on the calibration results is analyzed within an actual long-distance water supply system featuring multi-branch pipelines. Results showed that ANNs can accurately reconstruct flow rates and pressures at unmeasured nodes, even with very limited measurement data. Compared to conventional calibration methods, the proposed framework can reduce the influence of measurement data uncertainty on calibration results, achieving better calibration accuracy. Additionally, by introducing regularization into the loss function, the constraints of physical laws are incorporated into the neural network's training process, further enhancing the calibration accuracy of the model.
An asymptotic theory formulating the surface ablation impact on Mack modes in high-enthalpy hypersonic boundary layers
Authors: Yuan Qingjiang , Dong Ming
Published: September 2024

Surface ablation induced by aerodynamic heating is a common phenomenon for high-speed cruising vehicles, impacting surface geometry, temperature distribution, and mass injection, all of which play crucial roles in the perturbation evolution and boundary-layer transition. This paper presents a high-Reynolds-number asymptotic theory to formulate the impact of a local surface ablation on the Mack-mode evolution in high-enthalpy hypersonic boundary layers. The mean-flow distortion induced by ablation is formulated by the compressible triple-deck formalism, incorporating the chemical non-equilibrium effect. Simultaneously, the distortion of the Mack mode is formulated by the multi-scale analysis, with an amplification factor quantifying the overall impact of the ablation. The asymptotic model distinctly separates the effects of the mean-flow distortion and the Mack instability property. The amplification factor is attributed to two main factors: a local scattering effect at the ablation region, primarily contributed by the indentation, and a successive adjustment of the Mack growth rate, mainly contributed by the temperature distribution. The study reveals that the Mack mode experiences enhancement by ablation when its frequency falls below a critical threshold but is suppressed for higher frequencies. Remarkably, the critical frequency aligns closely with the most unstable frequency within the second-mode frequency band.
Scour due to circular jets in cohesive soils: Physical evidence from three-dimensional laboratory tests
Authors: Palermo Michele , Di Nardi Jessica , Bombardelli Fabián A. , Pagliara Stefano
Published: September 2024

Despite its widespread appearance, the scour of cohesive materials has received relatively less attention than the granular counterpart. In particular, the different modes of erosion of cohesive soils, its long-term temporal evolution, and the effect of the impinging angle and jet regime on scour features still represent open questions. To shed light on these aspects, a series of long-term experiments were conducted involving a circular jet impinging on a clay bed at angles of 45°, 60°, 75°, and 90°. Experimental evidence allowed us to provide unprecedented insights into the peculiar evolution of the scour process, as well as empirical formulas to estimate the main geometrical features of the scour hole. Scour evolution is distinguished between continuous or discontinuous. These two modes differ for scour evolution kinetics and scour profile similitude. Distinct erosion mechanisms are documented, including the formation of a peculiar ring scour shape. The transition between strongly and weakly deflected jet regimes is investigated and, for the first time, related to the soil friction angle. Overall, the analysis of physical evidence allowed us to reach the following main conclusions: (1) the inclination of the jet and the tailwater depth affect the scour process and its evolution and (2) the long-term scour behavior should not be disregarded to provide trustable predicting tools.
Fast-adaption thrust optimization by cluster-based control for a pitching foil
Authors: Wang Zhangyuan , Deng Nan , Cornejo Maceda Guy Y. , Xu Wenhua , Noack Bernd R. , Li Ruipeng , Cui Weicheng , Fan Dixia
Published: September 2024

To optimize flapping motion for pitching foil dynamics, we significantly expand the search space to include non-periodic feedback laws through the application of the cluster-based control method, which is integrated with interpolation and machine learning optimization techniques. This approach allows for dynamic adjustment between transient and steady-state conditions, leading to an 18% increase in thrust efficiency compared to traditional sinusoidal waveforms. By clustering flow field dynamics into two cycle categories with eight clusters and optimizing closed-loop control laws, we achieve accelerated convergence to the optimal thrust cycle. The proposed approach not only refines control strategies for pitching foil dynamics but also ensures robustness and efficiency in the system performance.
Effect of Reynolds number on the coherent structure and dynamics of vortex in double-stage counter-rotating swirling flows
Authors: Liu Chang , Yang Jianzhi , Dong Qixuan , Lai Canlong , Zhao Jingyi , Lin Jiayu , Liu Minghou
Published: September 2024

In this paper, the isothermal swirling flow in a combustion chamber equipped with a double-stage swirler is studied by a combination of experiments and numerical simulations at the Reynolds number (Re) ranging from 2712 to 43 396. The swirl numbers of the inside and outside entrances of the swirler are 0.81 and 0.89, respectively. The effect of Re on the mean flow field, the oscillation and evolution characteristics of instantaneous vortex structures such as vortex breakdown and precessing vortex core (PVC) are systematically analyzed. It is found that there is a significant difference between low and high Re numbers, with the critical Re number occurring at a value of 16 273. After the critical Re, the mean axial and tangential velocity indicates the presence of Reynolds self-similarity. The precession intensity of the PVC increases significantly, while the helical diameter of the PVC decreases with the increase in Re number. The characteristic frequency of the PVC in the swirling field increases linearly with the Re number, and the second characteristic frequency appears at Re = 16 273, which is confirmed to be related to the combined effects of the PVC and shear layer (SL) thermoacoustic instability, which is caused by a regular high-frequency vortex shedding along the SL.
Efficient control of magnetization dynamics via W/CuOX interface
Authors: Sahoo Antarjami , Mallick Sagar , Rath Ashutosh , Ding Haifeng , Azevedo Antonio , Bedanta Subhankar
Published: September 2024

Magnetization dynamics, which determine the speed of magnetization switching and spin information propagation, play a central role in modern spintronics. Gaining its control will satisfy the different needs of various spintronic devices. In this work, we demonstrate that the surface oxidized Cu (CuOX) can be employed for the tunability of magnetization dynamics of ferromagnet/heavy metal (HM) bilayer system. The capping CuOX layer in CoFeB/W/CuOX trilayer reduces the magnetic damping value in comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower than that of the CoFeB/CuOX by ∼ 16% inferring the stabilization of anti-damping phenomena. Further, the reduction in damping is accompanied by a very small reduction in the spin pumping-induced output DC voltage in the CoFeB/W/CuOX trilayer. The simultaneous observation of anti-damping and spin-to-charge current conversion could be attributed to the orbital Rashba effect observed at the HM/CuOX interface. Our experimental findings illustrate that the cost-effective CuOX can be employed as an integral part of modern spintronics devices owing to its rich underneath spin–orbital physics.
Analysis of non-immersed cavitation jet fluid–solid coupling microforming
Authors: Yu Liang , He Peiyu , Wang Yun , Li Fuzhu , Zhang Linqiang , Liu Weili
Published: September 2024

Non-immersed cavitation jets represent an advanced surface treatment technology, characterized by their ability to generate cavitation in an air environment. Owing to their simple structure, these jets have found widespread application. In this study, both numerical and experimental investigations of non-immersed cavitation jets, incorporating fluid–solid coupling, are conducted. The microforming effects on T2 copper foils, induced by non-immersed cavitation jets, are analyzed by comparing simulation results with the experimental data, thereby validating the efficacy of this technique in foil microforming. Additionally, the flow field characteristics of the non-immersed cavitation jet are examined, focusing on the transient distributions of velocity, vortex structures, cavitation bubbles, and pressure at various dimensionless impact distances. The findings confirm that non-immersed cavitation jets are effective for microforming T2 copper foils, with an optimal dimensionless impact distance of 40 under the specified process parameters. The study also reveals that the non-immersed cavitation jet flow is inherently unstable, with the impact distance significantly influencing the evolution of vortex structures and cavitation bubbles. This research offers critical insights into the physical mechanisms underlying non-immersed cavitation jet microforming and provides both a theoretical foundation and experimental guidance for optimizing jet parameters to enhance microforming precision in future applications.
Imaging study of O3 photodissociation in the Huggins band
Authors: Shuber Nicholas J. , Fast Megan E. , North Simon W.
Published: September 2024

We report a velocity-mapped ion imaging study of the photodissociation of O3 in the Huggins band. The O(3PJ) images show evidence for three electronic channels producing O2(X3Σg−), O2(a1∆g), and O2(b1Σg+) state fragments, with the latter two arising from the spin-forbidden photodissociation of O3. Forward convolution simulations of the derived total translational energy distributions permit extraction of the vibrational state distribution for each O2 electronic state. All these distributions peak near v = 0 and decrease monotonically with the vibrational state. The wavelength-dependent branching of the three electronic channels has been determined and is approximately constant over the wavelength region studied (322–328 nm). We have observed that the O2 electronic state branching ratios depend on the coincident O(3PJ) spin–orbit state, and the O2(b1Σg+) state is particularly sensitive. These results are qualitatively consistent with previous calculations on the coupling of the initially excited state to dissociative states by Rosenwaks and Grebenshchikov [J. Phys. Chem. A. 114, 9809–9819 (2010)]. The spatial anisotropy of the three dissociation channels has been determined through analysis of the O(3P0) angular distributions. The results are consistent with recent calculations but differ from previous experimental reports. The experimental results provide detailed information on the dissociation dynamics and should motivate new calculations.
Effects of porous wall on deflagration to detonation transition and detonation wave propagation
Authors: Jiang Yuguang , Lin Yong , Wang Qi , Fang Xiaojia , Jiang Xudong , Fan Wei
Published: September 2024

To study the influence of a porous wall on the initiation and propagation of the detonation wave, experiments with ethylene and oxygen-rich air are carried out. The effects of oxygen content (β) on oxidant, pore density of porous media, and equivalent ratio are analyzed with technologies like chemiluminescence, schlieren, and soot foil. The results show that the detonation wave bends due to the mass divergence into the porous wall. With the increase in oxygen content in the mixture, the curvature of the wave surface decreases, and the local decoupling and re-initiation of detonation disappear. Regarding the pore density, porous walls with smaller pores (10 ppi) have the strongest flame acceleration capability. The deflagration to detonation transition distance is the shortest and the velocity deficit is the largest. As for the equivalent ratio (ϕ), a deflagration wave is observed in the condition β = 0.5, ϕ = 0.5. Successful detonation is observed in the range ϕ = 0.6–2.2. The detonation capability of the gas mixture is highest with ϕ = 1.4. As the equivalent ratio decreases from 1.4 to the fuel-lean conditions, the detonation wave is attenuated by the porous wall much more obviously. Detonation fails at ϕ = 0.6.
Impact of electro-hydrodynamics on combined convection in an opposed ventilation system
Authors: Navaneethakrishnan V. , Muthtamilselvan M. , Yeom Eunseop
Published: September 2024

In this study, numerical experimentation was performed to explore the impact of electro-thermo-convection on unsteady combined convection flow within a square chamber driven by dual ventilation channels with opposing flow. An electrical emitter was placed on the left wall to influence the hot wall, with a collector electrode on the other wall, while the remaining walls were thermally and electrically insulated. The equations which govern the system were solved using the finite difference method with an alternate direction implicit scheme and an iterative successive under-relaxation (SUR) technique. Key physical parameters, including Reynolds number (50≤Re≤500), Richardson number (0.1≤Ri≤20), and a range of electrical Rayleigh numbers (0≤Rae≤1200), were examined for their effects on charge density distribution, streamlines, isotherms, and the mean Nusselt number. The study reveals that electrical effects significantly boost heat transfer, with an 88% increase in the mean Nusselt number under low forced convection and buoyancy (Ri=0.1, Re=50). However, as buoyancy (Ri=20) and forced ventilation (Re=500) intensify, this enhancement decreases to 25% and 33%, indicating that these forces moderate the influence of electrical effects. Additionally, Richardson and Reynolds numbers strongly affect heat transfer, with rates increasing by 52% and 126%, respectively, under pure thermal convection. The numerical model results align well with previous research, suggesting the potential application of advanced cooling techniques to enhance the heat transfer efficiency in an electronic devices and similar systems.
Correlations between adhesion and molecular interactions at buried interfaces of model polymer systems and in commercial multilayer barrier films
Authors: Rossi Daniel , Wu Yuchen , Dong Yifan , Paradkar Rajesh , Chen Xiaoyun , Kuo Tzu-Chi , Chen Zhan
Published: September 2024

Sum frequency generation vibrational spectroscopy (SFG) was applied to characterize the interfacial adhesion chemistry at several buried polymer interfaces in both model systems and blown multilayer films. Anhydride/acid modified polyolefins are used as tie layers to bond dissimilar polymers in multilayer barrier structures. In these films, the interfacial reactions between the barrier polymers, such as ethylene vinyl alcohol (EVOH) or nylon, and the grafted anhydrides/acids provide covalent linkages that enhance adhesion. However, the bonding strengths vary for different polymer–tie layer combinations. Here, using SFG, we aim to provide a systematic study on four common polymer–tie interfaces, including EVOH/polypropylene–tie, EVOH/polyethylene–tie, nylon/polypropylene–tie, and nylon/polyethylene–tie, to understand how the adhesion chemistry varies and its impact on the measured adhesion. Our SFG studies suggest that adhesion enhancement is driven by a combination of reaction kinetics and the interfacial enrichment of the anhydride/acid, resulting in stronger adhesion in the case of nylon. This observation matches well with the higher adhesion observed in the nylon/tie systems in both lap shear and peel test measurements. In addition, in the polypropylene–tie systems, grafted oligomers due to chain scission may migrate to the interface, affecting the adhesion. These by-products can react or interfere with the barrier–tie chemistry, resulting in reduced adhesion strength in the polypropylene–tie system.
Tailoring Li assisted CZTSe film growth under controllable selenium partial pressure and solar cells
Authors: Liu Yue , Zhang Huamei , Meng Rutao , Dong Jiabin , Xu Xuejun , Zhang Jincheng , Zhang Yi
Published: September 2024

It is still critical to prepare a high-quality absorber layer for high-performance Cu2ZnSnSe4 (CZTSe) multi-component thin film solar cell. The gas pressure during the selenization process is commonly referred to as the pressure of inert gas in the tube furnace, while the exact selenium partial pressure is difficult to be controlled. Therefore, the grain growth under different selenium partial pressures cannot be made clear, and the film quality cannot be controlled as well. In this work, we use a sealed quartz tube as the selenization vessel, which can provide a relatively high and controllable selenium partial pressure during the selenization process. To further tailor the grain growth, lithium doping is also utilized. We find that lithium can greatly promote the growth of CZTSe films as the selenium partial pressure is controlled near the selenium saturation vapor pressure. Combined with ALD-Al2O3, the crystallization quality of CZTSe absorber films is significantly enhanced and the efficiency of CZTSe solar cells achieved a significant improvement. This work clarifies the effect of controllable Se pressure on CZTSe film growth and can lead to better results in CZTSe and other multi-compound thin film solar cells.
Resistive anisotropy in the charge density wave phase of Kagome superconductor CsV3Sb5 thin films
Authors: Lou Han-Xin , Ye Xing-Guo , Liao Xin , Zhao Tong-Yang , Wang An-Qi , Yu Da-Peng , Liao Zhi-Min
Published: September 2024

We investigate the resistive anisotropy in CsV3Sb5 thin films within the charge density wave phase. Using a device structure with twelve electrodes symmetrically distributed in a circular shape, we measure the resistivity anisotropy by varying the current direction. A twofold resistivity anisotropy modulated by temperature is found, which is fully consistent with the electronic nematicity in CsV3Sb5, that is, the spontaneous rotational symmetry breaking by electronic degree of freedom. Additionally, the resistivity anisotropy also shows modest changes by applying magnetic fields, implying the possible chiral charge orders with time-reversal symmetry breaking. These findings provide deep insights into the correlated electronic states in Kagome materials and highlight the unique properties of CsV3Sb5 in the two-dimensional regime.
Numerical investigation of unsteady leading edge cavitation in a double-suction centrifugal pump
Authors: Du Yuxin , Zhang Shijie , Lu Hongzhong , Xiao Ruofu , Wang Fujun , Yao Zhifeng
Published: September 2024

This paper aims to analyze the leading edge cavitation of a double-suction centrifugal pump, focusing on its periodic evolution process and unsteady characteristics. The calculation of external characteristics and the simulation of the leading edge cavitation in the double-suction centrifugal pump were performed based on the turbulent viscosity correction model. The cavitation was studied under three working conditions (0.5, 0.9, and 1.2 times the design flow rate). The position and structural characteristics of the leading edge cavitation were identified. The instability phenomenon and vortex motion in the impeller passage caused by cavitation were analyzed. The results indicate the inlet flow of the impeller and the pressure distribution on the blade surface are the primary factors influencing the characteristics of the leading edge cavitation. The inlet flow of the impeller determines the position of the leading edge cavitation, while the pressure distribution on the blade surface dictates the specific shape and structure of the cavitation. Throughout the development cycle of cavitation, the position of the flow instability region within the impeller shifts from the off-flow area of the leading edge to the tail of the cavitation region.
Message-Passing Monte Carlo: Generating low-discrepancy point sets via graph neural networks
Authors: Rusch T. Konstantin , Kirk Nathan , Bronstein Michael M. , Lemieux Christiane , Rus Daniela
Published: September 2024

Discrepancy is a well-known measure for the irregularity of the distribution of a point set. Point sets with small discrepancy are called low discrepancy and are known to efficiently fill the space in a uniform manner. Low-discrepancy points play a central role in many problems in science and engineering, including numerical integration, computer vision, machine perception, computer graphics, machine learning, and simulation. In this work, we present a machine learning approach to generate a new class of low-discrepancy point sets named Message-Passing Monte Carlo (MPMC) points. Motivated by the geometric nature of generating low-discrepancy point sets, we leverage tools from Geometric Deep Learning and base our model on graph neural networks. We further provide an extension of our framework to higher dimensions, which flexibly allows the generation of custom-made points that emphasize the uniformity in specific dimensions that are primarily important for the particular problem at hand. Finally, we demonstrate that our proposed model achieves state-of-the-art performance superior to previous methods by a significant margin. In fact, MPMC points are empirically shown to be either optimal or near-optimal with respect to the discrepancy for low dimension and small number of points, i.e., for which the optimal discrepancy can be determined.
KSW criterion in large field models
Authors: Janssen Oliver
Published: September 2024

We extend the analytic description of complex no-boundary solutions in the context of inflation to large field models. We discuss the Kontsevich–Segal–Witten (KSW) criterion and find it is satisfied in small field models, while in large field models it depends on an integral involving

V

′

(
ϕ
)

over the range of inflation. It follows that although particular models are ruled out, e.g. quadratic inflation, the criterion does not truly constrain inflationary phenomenology since any inflation potential can be completed beyond observable scales so as to satisfy KSW.
Multifunctional 2D MoTe2: Recent developments and future perspectives
Authors: Sunny Fency , C S Chitra Lekha , Kalarikkal Nandakumar , Rout C S , Chakraborthy Brahmananda
Published: September 2024

Two-dimensional (2D) transition metal dichalcogenides (TMDs), especially molybdenum ditelluride (MoTe2), are an attractive topic in the modern era due to their unique properties. Although research progress on 2D materials has gained a lot of attention due to new synthesis methods and their extraordinary properties compared to their bulk counterparts, there is room for modification for large-scale production and tailoring the output performance in specific applications, such as solar cells, energy storage and conversion devices. Compared to other 2D TMDs, MoTe2 offers a lower band gap, which in turn gives the possibility to replace Si in many applications. This review is an attempt to assemble and encapsulate the physical properties, recent developments in the fabrication of 2D MoTe2 and its different applications in the field of batteries, transistors, energy conversion, solar cells, etc. This review will help to provide a deep insight into the research on MoTe2 for modifying the structure and enhancing the properties of these layered materials.
Fabrication and formation mechanisms of ohmic conducts with low annealing temperature for GaN/AlN superlattice barrier HEMTs
Authors: Li Shanjie , Wu Changtong , Zeng Fanyi , Wu Nengtao , Luo Ling , Cao Ben , Wang Wenliang , Li Guoqiang
Published: September 2024

This work investigates the Ohmic contact mechanism and low resistance Ohmic contact preparation for GaN-based high electron mobility transistors (HEMTs) with GaN/AlN superlattice (SL) barriers. The electrical and microstructural characterization of Ti/Al/Ni/Au contacts shows that the formation of Ohmic contacts primarily depends on the TiN islands formed by Ti diffusion in the barrier layer, which is the main reason for the high contact resistance of GaN/AlN SLs HEMTs under conventional high-temperature annealing. A grid deep-recess technique is proposed to establish direct contact between TiN interfacial layer, the barrier, and the two-dimensional electron gas through the sidewalls. This novel technique achieves an Ohmic contact with a low contact resistance of 0.31 Ω mm at low temperatures (700 °C). Furthermore, increased grid deep-recess density effectively reduces contact resistance due to the additional contribution from the conduction width. It is also noteworthy that after complete removal of the barrier layer, the impact of recess depth on contact characteristics is minimal, greatly reducing the process complexity of grid deep-recess technique. Consequently, GaN/AlN SLs HEMTs fabricated using the grid deep-recess technique exhibit significant improvements in on-resistance, transconductance and saturation current. These results are expected to expand the potential application of GaN/AlN SL barrier layers in radio frequency and power devices.
Tunable interfacial properties of monolayer GeSb2Te4 on metal surfaces
Authors: Li Jiahui , Zhang Chengqi , Wan Xiaoying , Zhang Zhaofu , Wang Qingbo , Wang Hai , Liu Jun , Zhong Hongxia
Published: September 2024

Atomically thin monolayer (ML)

GeSb
2

Te
4

(GST) holds promising prospects in non-volatile memory applications because of its high non-homogeneous crystallization rate. In GST-based devices, the interaction between GST and metals is crucial, as it affects the electronic properties. Herein, based on first-principles calculations, we investigate the interaction and Schottky barrier height of contacts formed by the combination of ML GST with various metals. It is found that the interfaces of GST with Pt, Pd, Ir and W exhibit strong interaction, characterized by large binding energies ranging from 1.394 to 1.015 

eV

, and the interfaces between GST and Cu, Ag and Au display weak interaction. For the seven contacts, Ag and W form Ohmic contacts with ML GST, while Cu, Au, Pd, Ir, and Pt form n-type Schottky contacts, with Schottky barrier heights ranging from 0.029 to 0.353 

eV

. The strong Fermi level pinning at GST-metal interface is observed with a pinning factor of 0.378. Additionally, altering the interfacial distance and optimizing the layers of GST enable a transition from Ohmic contact to Schottky contact. These findings provide crucial guidance for the design and optimization of electronic devices based on phase change materials like GST.
Theoretical design and simulation of uncooled PbSe/Ge mid-wavelength infrared avalanche photodetector
Authors: Liu Yun , Su Leisheng , Fu Yu , Luo Yingmin , Yang Yiming , Qiu Jijun
Published: September 2024

To comply with SWaP3 specifications in infrared detectors, a novel uncooled mid-wavelength infrared avalanche photodetector (MWIR-APD) architecture based on PbSe/Ge heterojunction was proposed. A maximum high gain of 40.8 was achieved, which is comparable with cooled MWIR-APDs, including HgCdTe, and type II superlattices. The theoretical simulation shows that it is the significant difference in permittivity between PbSe and Ge that results in a sufficient electric field contrast between the absorption and multiplication layers, which facilitates the structural design of this APD. Additionally, a structural parameter limit was established by investigating the variation in the punch-through and breakdown voltages. Furthermore, the decreasing PbSe thickness will improve the device’s gain but at the expense of decreasing frequency response and quantum efficiency. This PbSe/Ge APD architecture provides a new solution for the MWIR detection at room temperature.
Large magnetocrystalline anisotropic energy and its impact on magnetostriction of L10-FePt
Authors: Das Tilak , Nieves Pablo , Legut Dominik
Published: September 2024

The origin of magnetocrystalline anisotropic energy (MAE) guided by spin–orbit coupling in the L10-FePt alloy was analyzed. Correlation of MAE with the calculated magnetoelastic constants in the single and polycrystal model was determined by means of first-principles calculations using density functional theory (DFT). More specifically, a systematic analysis of the large MAE and magnetostriction coefficients (λ’s) were done by means of post-processing of eigenvalues (orbital energies) and eigenfunctions (orbital occupancies). Our numerical analysis includes the convolution of the projected wave-function (density of states) of each orbital of the Fe and Pt sub-lattices into their orbital energies, which in principle should be valid for any solid regardless of the strength of the MAE. The determined anisotropic magnetostriction coefficients are of the

λ
∼

10

−
4

–10–3 order for several crystallographic directions; which is in accord to the known experimental data. However, the polycrystalline model based on the uniform stress approximation leads to a decrease of the λ by two orders in the overall magnetostrictive behavior (

λ
∼

10

−
5

). Such a large difference is not unexpected as the magnetostriction for polycrystalline FePt thin films were recorded as very low, thus validating the robustness of the current theoretical proposition of analyzing MAE.
Perspective on the spin field-effect transistor
Authors: Ciorga Mariusz
Published: September 2024

The spin field effect transistor (sFET), proposed by Datta and Das (1990 Appl. Phys. Lett.
56 665–7), has long been regarded as a model semiconductor spintronic device, offering potential for new, more energy-efficient functionalities in electronic devices. Here, the overview is given how the pursuit of meeting the requirements for implementing the sFET concept has influenced spintronic research, leading to a greater understanding of spin phenomena in solids and resulting in numerous exciting effects. After looking back, based on the recent developments, the possible future directions of the sFET-related research are described.
Influence of sulfurization process in tin sulfide and sulfur mixed vapors on the morphology of Cu2SnS3 thin films
Authors: Igarashi Yuki , Ohashi Ray , Kanai Ayaka , Tanaka Kunihiko
Published: September 2024

Cu2SnS3 (CTS) is expected to be an absorber material for next-generation solar cells because it is composed of nontoxic, low-cost elements and has an absorption coefficient of >104 cm−1. In this study, the effects of sulfurization in tin sulfide (Sn
x
S
y
) and S mixed vapors on various properties of CTS were investigated by using a 3-zone tube furnace to suppress carrier recombination at the grain boundaries and control the composition of the CTS. The CTS deposited via sulfurization in S vapor only (1-zone CTS) contained different monoclinic and tetragonal CTS structures. The grain size of the CTS thin films deposited via sulfurization in Sn
x
S
y
and S mixed vapors was not increased. On the other hand, crystal structure analysis revealed that the CTS had grown to single-phase monoclinic CTS. The results suggest that precipitation in Sn
x
S
y
and S mixed vapors contributes to the growth of monoclinic CTS with suitable power-generation characteristics. This finding is important for realizing high-efficiency CTS-based solar cells.