bluuebunny/crossref_metadata_2025 huggingface dataset:
Composite control of airfoil broadband noise based on the combination of porous material and serrated trailing edges
Authors: Hu Ya-Sen , Wan Zhen-Hua , Sun De-Jun , Lu Xi-Yun
Published: February 2024

Improving the noise reduction capability of airfoil broadband noise through serrated trailing edge design is a challenging task. To address this, we propose a novel porous-serrated trailing edge design where the gaps between the serrations are filled with porous media. Implicit large eddy simulations were conducted at Mach number Ma=0.1631 and Reynolds number Re=96 000 under a zero incidence angle. In addition to straight trailing edges and conventional serrated trailing edges, cutting-type porous-serrated (CPS) and insert-type porous-serrated (IPS) trailing edges with different porosities were designed. The flow in the porous media is described by Darcy's law, which is related to the pressure and velocity. The results indicate that the CPS trailing edges offer limited noise reduction compared to conventional serrated trailing edges, while IPS trailing edges achieve a significant noise reduction of approximately 5.21 dB. However, the drag force increases by 8.0% in the IPS case with maximum noise reduction. The composite control mainly affects flow structures near the trailing edges, especially inducing the flow penetration across the porous surface. To investigate the noise reduction mechanism, dynamic mode decomposition was conducted to show that both the CPS and IPS designs promote energy transferring significantly from the energetic mode to the modes at other frequencies, which would partly explain the difference in the noise reduction performance to some extent. Furthermore, the analysis of the wall pressure fluctuations reveals that the reduced convection velocity on the porous surface and enhanced destructive interference between the porous and the solid surfaces in IPS cases could be identified as the key factors contributing to lower noise radiation efficiency.
2-Gb/s ultraviolet-light optical wireless communication by InGaN/GaN multi-quantum well dual-function micro-photodetector
Authors: Park Tae-Yong , Wang Yue , Alkhazragi Omar , Min Jung-Hong , Ng Tien Khee , Ooi Boon S.
Published: February 2024

We demonstrate a series of multifunctional micro-photodetectors (μPDs) designed for high-speed ultraviolet-A-(UVA)-light detection and blue-light illumination based on InGaN/GaN triple-quantum-well devices grown on patterned sapphire substrates. At forward voltage bias, the device operated as a light-emitting diode with a peak emission wavelength of ∼450 nm. When switching to reverse voltage bias, the device exhibited a dual-band responsivity of 0.17 A/W at 370 nm and 0.14 A/W at 400 nm, indicating effective UVA light detection. Furthermore, size-dependent emission and detection behaviors were investigated with the device's active area having radii ranging from 15 to 50 μm. For μPDs, the −3-dB bandwidth increased with the reduced device radius and reached a maximum of 689 MHz for the 15-μm device under −10-V bias. High responsivity and fast modulation speed contributed to 2-Gb/s UVA optical wireless communication based on direct-current-biased optical orthogonal frequency-division multiplexing. The research offers a promising approach to simultaneous high-speed communication and illumination in the UVA-blue-light optical spectral regime, and the dual-band responsivity feature is potentially useful for increasing channel capacity.
On the integrable stretch-twist-fold flow: Bi-Hamiltonian structures and global dynamics
Authors: Xu Mingxing , Shi Shaoyun , Huang Kaiyin
Published: February 2024

The stretch-twist-fold (STF) flow is a variant of the dynamo model describing the generation and behavior of magnetic fields in celestial bodies such as stars and planets. This study seeks to provide fresh insights into the integrable STF flow within the framework of dynamical systems theory and Poisson geometry. Our results include (i) the establishment of Poisson structures, Hamilton–Poisson realizations, and a Lax formulation for the STF flow; (ii) a comprehensive classification of phase portraits for the STF flow restricted to its symplectic leaf; (iii) a description of the asymptotic behavior of the STF flow on the Poincaré sphere, revealing the occurrence of bifurcations at infinity; (iv) a characterization of the energy-Casimir mapping of the STF flow and its connections with dynamical elements. These findings have the potential to deepen our understanding of the intricate and diverse dynamics exhibited by the STF flow in the context of dynamo theory.
Multiphoton photocurrent in wide bandgap semiconductors for nonlinear optoelectronics: Comparison of GaP, GaN/InGaN, and SiC
Authors: Wang Chuanliang , Ali Ahsan , Karki Khadga Jung
Published: February 2024

Wide bandgap semiconductors are ideally suited for nonlinear optoelectronics. Because their bandgaps are larger than 2 eV, simultaneous absorption of two or more near-infrared photons is necessary to excite the electrons from the valence to the conduction band. Understanding of the processes that affect multiphoton absorption is important in the design and fabrication of optoelectronic devices. Here, we present an overview of the photocurrent response in photodetectors made from GaP, GaN, InGaN, and SiC when they are excited by photons at 1.2 eV. Recent measurements have shown that sub-bandgap absorptions contribute to photocurrent in GaP, and, thus, it is not a good material for nonlinear optoelectronics. Similarly, the response of GaN is affected by long-lived trapped charges. Photocurrents in InGaN and SiC are predominantly from three- and four-photon absorption, respectively. Moreover, these materials can withstand excitation intensities higher than 1011 W cm−2, making them appropriate platforms for nonlinear optoelectronics.
Dielectric conductivity and microwave heating behavior of NiO at high temperature
Authors: Yoshikawa Noboru , Sato Haruto
Published: February 2024

Measurement of high-temperature physical properties at microwave frequency is important to interpret the heating behavior of NiO observed in the author’s previous studies. In this study, the impedance (4 Hz–5 MHz) and permittivity [at the microwave frequency (2.45 GHz)] of NiO powder particles were measured from room temperature (RT) to 800 °C. At high frequency above 100 kHz, the conductivity is almost independent of temperature up to a certain temperature (Ti). Above Ti, the conductivity showed a strong positive dependence on the temperature. In this region, the apparent activation energy is determined to be 0.51 eV, which is close to that of the previously reported large polaron transport mechanism (band-like conduction). It was also shown that the conductivity increased linearly with frequency and that a dielectric conductivity relation (σ = ωε″) holds, which is different from the hopping mechanism of the small polaron. Considering these results, it was understood that the temperature increase occurred preferentially in the microwave E-field. The slow increase from the room temperature is due to a small but finite dielectric loss at room temperature, and because of the low conductivity, induction current is not effectively generated in the H-field. On the other hand, after a certain time, the temperature rises to reach the large temperature-dependent conductivity, and then, a significant temperature rise occurs.
Path selection of liquid fronts in junctions of branching channels
Authors: Jung Sohyun , Kim Tae Jeong , Lee Jae Hong , Jung Wonjong , Kim Ho-Young
Published: February 2024

We consider how a liquid front propagating through an initially dry channel network selects its path when encountering branch junctions. We employ both experimental observation and theoretical analysis to investigate the path selection dynamics depending on liquid properties, pressure-driven flow rate, and channel geometry. We identify three distinct front propagation types at the junction, namely, straight, diverging, and diverting flows, and construct their regime map with theoretical regime boundaries. These flow types at the junction determine the subsequent channel-filling patterns, which we also identify and categorize. Our results allow us to design small-scale channel networks to precisely deliver or distribute functional liquids, which can be applied to lab-on-a-chip systems, liquid sculpture, and porous flow control.
Effect of sulfate erosion on shear characteristics of slurry-reinforced coal body structural faces
Authors: Ren Zhiwei , Wang Jun , Ning Jianguo , Zhang Shuai , Hu Hao , Bian Yongtian
Published: February 2024

To study the effect of sulfate ion erosion on grouted reinforced coal bodies, downhole grouting reinforcement was simulated by artificially prefabricating regular serrated structural surfaces and grouting them with cement. In addition, sulfate erosion tests were carried out at three erosion ion concentrations (3%, 5%, and 10%) and four erosion times (7d, 14d, 28d, and 40d) at a pressure of 0.2 MPa using self-developed constant pressure accelerated erosion equipment, and then, mechanical property tests were conducted using an MTS816 rock mechanics shear tester, which is the most effective way to test the mechanical properties of coal. The test results are as follows: (1) the shear stress–displacement curves of the specimens were of slip type at lower normal stresses and of peak shear type at higher normal stresses, (2) the shear strength of the specimen was linearly negatively correlated with the erosion time and erosion ion concentration, (3) the effect of erosion time was greater than the effect of erosion concentration on the specimen shear strength parameters, (4) sulfate erosion can only affect the degree of shear shrinkage and shear rise and cannot change the damage behavior, and (5) with an increase in erosion ion concentration and the prolongation of the erosion time, the damage morphology of the specimen was shown as the “coal body destruction–nipping fracture–climbing nipping fracture” (coal–pulp interfacial separation) damage form.
Numerical study of Taylor bubble breakup in counter-current flow using large eddy simulation
Authors: Kren Jan , Frederix E. M. A. , Tiselj Iztok , Mikuž Blaž
Published: February 2024

This paper investigates dynamics of Taylor bubble in counter-current flows, leveraging large eddy simulations combined with the volume of fluid method. Utilizing the OpenFOAM framework, we have implemented a high-order Runge–Kutta time-integration scheme, along with a piecewise linear interface calculation method for precise geometric reconstruction of the bubble interface. We examine the performance of algebraic vs geometric capturing techniques in the context of Taylor bubble breakup, focusing specifically on the transitional flow regime with a liquid Reynolds number of 1400. Our results reveal that the geometric capturing technique offers superior accuracy, improving our understanding of the breakup process and providing valuable insight for multiphase flow simulations in various engineering fields. Our study also reveals the emergence of a secondary vortex in the turbulent wake region behind the Taylor bubble, a phenomenon most prominent at finer mesh resolutions. This vortex represents a novel discovery in counter-current Taylor bubble flows.
Tunable magnetic anisotropy of Os-Ru dimer on 2D transition metal chalcogenides substrates
Authors: Zhao Bo , Xing Jianpei , Wang Peng , Jiang Xue , Zhao Jijun
Published: February 2024

The precise manipulation of atoms enables the creation of distinct materials from the bottom up to construct devices with breakthrough performance, especially in the field of quantum technologies. A large magnetic anisotropy energy (MAE) is important to realize bit storage of information in magnetic memory devices. As the smallest magnetic nanostructure, substrate-supported transition metal dimers are potential atomic-scale storage medium to obtain large MAEs. Using high-throughput first-principles calculations, we have performed a systematic investigation of the MAE of 76 heterodimensional systems consisting of zero-dimensional Os-Ru dimer and experimentally synthesized two-dimensional transition metal dichalcogenides (TMDs). Huge MAEs in the range of 102.09–247.69 meV were found in 13 of these heterodimensional systems. In particular, the Os-Ru@T-ZrSe2 with the largest MAE of 247.69 meV corresponds to a theoretical blocking temperature (67 K) in terms of a relaxation time of 10 years and a storage density of 281 Tb·inch−2. The underlying mechanism for the significant enhancement of MAE is attributed to the rearrangement of the in-plane molecular orbitals near the Fermi level, which is closed relative to the electron transfer capability between the Os-Ru dimer and the TMD substrates. In addition, we have also constructed a heat map for TMD-supported Os-Ru dimer, showing the degree of correlation between MAEs and feature descriptors. Our work not only suggests an effective way to improve MAE of transition metal dimers but also extracts relatively simple rules for substrate selection.
Correlation between spin state and activity for hydrogen evolution of PtN2 monolayer
Authors: Zhang Tao , Li Lei , Huang Tao , Wan Hui , Chen Wu-Yu , Yang Zi-Xuan , Huang Gui-Fang , Hu Wangyu , Huang Wei-Qing
Published: February 2024

Spin plays a key role in physical and chemical reactions, such as oxygen evolution and hydrogen evolution reactions (OER/HER), but the spin–activity correlation has remained unclear. Based on a transition metal (TM)-doped PtN2 monolayer model with a well-defined spin center as an adsorption site, we here reveal that only an active spin state can enhance the strength of hydrogen adsorption, while an inert spin state offers very little influence. Specifically, the an unpaired electron along the out-of-plane direction such as in the dz2 orbital, acting as an active spin state, will strongly hybridize with hydrogen, resulting in enhanced hydrogen binding energy because the dz2 orbital is just enough to accommodate two electrons to form a bonding orbital. While the in-plane unpaired electron such as in the dx2−y2 orbital plays a negligible role in an adsorbing hydrogen atom. This is verified by a series of single atom catalysts comprising of PtN2 monolayer by replacing a Pt atom with a TM (Fe, Co, Ni, Ru, Rh, Pd, Os, or Ir) atom or subsequent adsorbing a Cl atom. One of the most promising materials is Pd@PtN2-Cl that offers superior HER activity, even better than pure Pt. This work uncovers the nature of spin–activity correlation, thus paving the way for the design of high-performance catalysts through spin-engineering.
Polarized Raman scattering and magnetic ordering in Mn lightly doped van der Waals Cr1−xMnxGeTe3 crystals
Authors: Xie Qiyun , Zeng Shuai , Chen Yalong , Chen Limin , Wang Wei , Ma Ligang , Cheng Guofeng
Published: February 2024

A layered van der Waals ferromagnet CrGeTe3 has attracted considerable interest due to the great potential for exploring low-power functional spintronic devices. However, research on the incorporation of chemical substitution in CrGeTe3 to tune the lattice vibrations and magnetic interactions is still lacking. In this work, an understanding of the phonon property and magnetic orders in Mn lightly doped Cr1−xMnxGeTe3 single crystals has been reported. It is found that the phonon symmetries are preserved over the studied Mn substitution content, as confirmed by angle-resolved polarized Raman spectroscopy and first-principles calculations. Furthermore, clear signatures of improved ferromagnetic Curie–Weiss temperature and magnetic moment are observed by detailed magnetic measurements. The higher magnetic moment of Mn ions, the variation of Mn–Te–Cr angle, Mn-induced hole doping, and the concomitant strain effect may all contribute to the enhanced ferromagnetism. Overall, our results demonstrate that chemical substitution is an effective pathway to engineering the lattice and magnetism of CrGeTe3.
The role of porous structure on airfoil turbulence interaction noise reduction
Authors: Bowen L. , Celik A. , Westin M. F. , Azarpeyvand M.
Published: February 2024

Experiments are performed to investigate the effect of porous treatment structure used at the leading edge on the aerodynamic and aeroacoustic characteristics of a National Advisory Committee for Aeronautics (NACA) 0012 airfoil. Three different triply periodic minimal surface porous structures of constant porosity are studied to explore their effect on the flow field and the relationship between airfoil response and far-field noise. The results show that the ratio between the porous structure pore size and the length scale of the turbulent flow plays an important role in the noise reduction capability of a porous leading edge. Changes to the turbulent flow properties in the vicinity of the airfoil are assessed to characterize the contributing physical behavior responsible for far-field noise manipulation. Velocity field analysis in front of the leading edge demonstrates a pronounced difference among porous structures. Furthermore, close to the airfoil surface and off from the stagnation line, all porous leading edges demonstrate a marked reduction in the low-frequency content of the velocity fluctuations. These results demonstrate the importance of the airfoil leading edge region and not just the stagnation line. The strong link evident in pressure–velocity coherence analysis of the solid airfoil is broken by the introduction of the porous leading edge. Furthermore, the porous leading edges reduce the near-field to far-field pressure coherence in both magnitude and frequency range.
A bond swap algorithm for simulating dynamically crosslinked polymers
Authors: Rao Peilin , Xia Xiuyang , Ni Ran
Published: February 2024

Materials incorporating covalent adaptive networks (CAN), e.g., vitrimers, have received significant scientific attention due to their distinctive attributes of self-healing and stimuli-responsive properties. Different from direct crosslinked systems, bivalent and multivalent systems require a bond swap algorithm that respects detailed balance, considering the multiple equilibria in the system. Here, we propose a simple and robust algorithm to handle bond swap in multivalent and multi-species CAN systems. By including a bias term in the acceptance of Monte Carlo moves, we eliminate the imbalance from the bond swap site selection and multivalency effects, ensuring the detailed balance for all species in the system.
Evaporation dynamics of a binary mixture droplet subjected to forced convection
Authors: Wang Xiaoyu , Zhang Ningkang , Ye Xuemin , Li Chunxi
Published: February 2024

Evaporation of binary mixture droplets (BMDs) is a ubiquitous natural phenomenon with numerous industrial applications. In this study, a theoretical model of BMD evaporation under forced convection is established by considering the influence of evaporative cooling, thermal and Marangoni effects, convection, and a Stefan flow. The dynamic evaporation of a binary ethanol–water droplet on a heated substrate is simulated, and the internal and external flow structures of the droplets and their interactions are investigated. The influence of temperature-dependent physical properties on the evaporation dynamics is analyzed, and the effect of the forced convection intensity on the exclusion distance and Marangoni instability is explored. Our findings reveal that, during the stable flow stage, a single vortex flow pattern prevails, characterized by a circulating zone with low ethanol concentration within the droplets. However, in the Marangoni instability-driven flow (MIF) stage, a complex multi-vortex flow appears inside the droplets, with a heterogeneous ethanol distribution. Under the action of the Stefan flow, external forced convection cannot directly affect the flow inside the droplets through viscous shear but indirectly impacts the internal flow through heat and mass transfer. The temperature-dependence of physical properties significantly influences the internal flow and delays the onset of the MIF stage. Forced convection affects the heat and mass transfer by changing the thickness of the thermal and concentration boundary layers. Compared with BMD evaporation under natural convection, the heat and mass transfer rate are significantly higher under forced convection, particularly in the MIF stage.
Probing avoided crossings and conical intersections by two-pulse femtosecond stimulated Raman spectroscopy: Theoretical study
Authors: Qiang Yijia , Sun Kewei , Palacino-González Elisa , Shen Kaijun , Rao B. Jayachander , Gelin Maxim F. , Zhao Yang
Published: February 2024

This study leverages two-pulse femtosecond stimulated Raman spectroscopy (2FSRS) to characterize molecular systems with avoided crossings (ACs) and conical intersections (CIs) in their low-lying excited electronic states. By simulating 2FSRS spectra of microscopically inspired ACs and CIs models, we demonstrate that 2FSRS not only delivers valuable information on the molecular parameters characterizing ACs and CIs but also helps distinguish between these two systems.
Competition between the source and loss processes of radiation belt source, seed, and relativistic electrons induced by a magnetic cloud event
Authors: Zou Zhengyang , Zuo Pingbing , Ni Binbin , Wei Jiayun , Zhou Wentao , Huang Hanyu , Xie Yanqiong
Published: February 2024

The radiation belt energetic electrons that are trapped by the geomagnetic field are one kind of space plasma and magnetic fluid. We quantitatively study the competition process between source and loss processes of radiation belt “source” (a few to tens of keV), “seed” (hundreds of keV), and “relativistic” (>1 MeV) electrons when a typical magnetic cloud (MC) event impinged on the magnetosphere on 19–20 July 2016. A very weak geomagnetic storm with SymHmin = −32 nT was driven by this magnetic cloud event. With the MC-driven shock arrival, the relativistic electrons experienced a “one-kick” energization at lower L-shells while having a moderate dropout at higher L-shells. The dropout became pronounced during the weak storm main phase. However, the seed electrons had a slight depletion after the shock and recovered to the pre-event level in the main phase, while the source electrons continued increasing during the entire event. Further analysis demonstrates that the loss processes (magnetopause shadowing and ultralow-frequency waves-driven outward transport) were competing with the source processes (shock-induced energization, substorm ejections, and wave–particle interactions), which are strongly sensitive to electron energy and L-shells. It is found that L*= ∼ 4 and μ =  102–102.5 MeV/G could be typical values at which the source and loss processes arrived at dynamic equilibrium. Our study first provides the “balance lines” in both energy channels and L* of the radiation belt source, seed, and relativistic electrons in response to magnetic cloud events. The quantitative results could be a key factor when investigating MC–magnetosphere coupling.
Exploring flow transition induced by surface-mounted riblets using large eddy simulations
Authors: Jain Ishita , Sarkar S.
Published: February 2024

A well-resolved large eddy simulation is employed to study the transition of spatially developing boundary layer when excited by distributed blade-riblets that are arranged in different configurations: one is two-dimensional spanwise riblets (denoted as R1), and the other being three-dimensional herringbone pattern of alternating converging and diverging riblets (denoted as R2). The inlet Reynolds number based on momentum thickness and freestream velocity is 360. The flow characteristics vary considerably between the two configurations. A transition delay is observed over R1-riblets owing to the recirculation bubbles occupying the entire cavity space between the consecutive riblets. The appearance of T–S waves over R1-riblets is manifested through the modal analysis, which, in concurrence with streaks, leads to the development of Λ-vortices and, thereby, exhibiting characteristics associated with the mixed-mode transition. Contradictorily, the T–S waves are bypassed when subjected to R2-riblets attributed to enhanced spanwise disturbances. The roughness-induced streaks destabilize via a lift-up mechanism and interact with background disturbances, leading to flow transition. Post-transition conditions for self-similarity are met for both configurations, albeit earlier for R2-riblets.
Scaling laws for near-wall flows of thixo-elasto-viscoplastic fluids in a millifluidic channel
Authors: Amini Kasra , Mishra Ases Akas , Sivakumar Amit Kumar , Arlov Dragana , Innings Fredrik , Kádár Roland , Tammisola Outi , Lundell Fredrik
Published: February 2024

Thixo-elasto-viscoplastic (TEVP) fluids are very complex fluids. In addition to elasticity and viscoplasticity, they exhibit thixotropy, i.e., time-dependent rheology due to breakdown and recovery of internal structures at different length- and timescales. General and consistent methods for a priori flow prediction of TEVP fluids based on rheological characteristics are yet to be developed. We report a combined study of the rheology and flow of 18 samples of different TEVP fluids (three yogurts and three concentrations of Laponite and Carbopol, respectively, in water in both the unstirred and a stirred state). The rheology is determined both with standard protocols and with an ex situ protocol aiming at reproducing the shear history of the fluid in the flow. Micrometer resolution flow measurements in a millimeter scale rectangular duct are performed with Doppler Optical Coherence Tomography (D-OCT). As expected, the results show the existence of a plug flow region for samples with sufficiently high yield stress. At low flow rates, the plug extends almost all the way to the wall and the extent of the plug decreases not only with increased flow rate but also with increased thixotropy. The ex situ rheology protocol enables estimation of the shear rate and shear stress close to the wall, making it possible to identify two scaling laws that relates four different non-dimensional groups quantifying the key properties wall-shear stress and slip velocity. The scaling laws are suggested as an ansatz for a priori prediction of the near-wall flow of TEVP fluids based on shear flow-curves obtained with a rheometer.
An investigation of the heat transfer characteristics of a droplet impacting a compressor blade
Authors: Tang Jie , Li Lansong , Zhang Yue , Lu Xin , Wang Liwen
Published: February 2024

In this study, the effects of the heat transfer characteristics of jet droplets impacting compressor blades during the on-line washing process of an aero engine are investigated. A three-dimensional transient model of a droplet impinging on a blade is established, the heat transfer effectiveness calculation formula is modified, and the heat transfer process of the impact is numerically simulated using the volume-of-fluid method. The results show that the effective heat transfer area and heat transfer effectiveness increase with increasing blade curvature. The higher the droplet temperature, the higher the average heat flux and the higher the heat transfer effectiveness. For every 10 °C rise in the droplet temperature, the peak average wall heat flux increases by about 0.47 MW/m2, and the heat transfer effectiveness increases by about 0.01. The heat transfer effectiveness is inversely proportional to the diameter of the droplet, and an increase in the diameter reduces the heat transfer effectiveness. The increase in velocity causes the droplet to quickly detach from the blade and the effective heat transfer area to decrease, resulting in a decrease in the amount of heat transfer between the droplet and the blade, and thus a decrease in the heat transfer effectiveness.
Hydrodynamic performance of a periodic array of flap-type devices installed on the stepped bottom topography in the front of the coastal wall
Authors: Zhang Yang , Li Yuanjie , Zhu Wenjin , Xu Qing , Dong Xiaotian , Meng Yujie
Published: February 2024

Harnessing wave energy stands as a promising method to mitigate carbon dioxide emissions and address the global energy shortage. The strategic placement of wave energy converters (WECs) in offshore areas is contingent upon the distinctive features of the coastline and the topographical layout. This study is dedicated to scrutinizing the hydrodynamic characteristics and the wave energy absorption of a periodic array of flap-type WECs situated on a stepped bottom topography, strategically positioned in front of a straight coast. The coastline is modeled as a fully reflecting vertical wall. To analyze the oblique wave interaction with this system, we have developed a semi-analytical solution grounded in the linear potential flow theory. We evaluated key performance metrics, including hydrodynamic efficiency, reflection coefficient, wave excitation torque, added inertia torque, and radiation damping. Case studies were conducted to assess the impacts of varying parameters, such as the distance between the flap and the wall, the wave depth above the step, the incident angle, and the step length on the hydrodynamic performance of the current system. The results underscore the substantial influence of the distance between the flap and the coastal wall on wave power efficiency. The trigger condition's frequency downshift, indicative of the standing wave field between the flap and the coastal wall, is observed with a reduction in the wave depth above the step, in contrast to scenarios without the step. In addition, wave resonance above the stepped bottom topography amplifies wave power extraction, albeit with the caveat of a diminished hydrodynamic efficiency due to the presence of Rayleigh–Bloch waves.
Customizing the luminescent properties of compositionally disordered ceramics (Gd, Y, Yb, Tb, Ce)3Al2Ga3O12: From an ultra-fast scintillator to bright, wide-spectrum phosphor
Authors: Dubov Valery , Bondarau Aliaksei , Lelekova Daria , Komendo Ilya , Malashkevich Georgii , Kouhar Viktoryia , Pustovarov Vladimir , Tavrunov Dmitry , Korzhik Mikhail
Published: February 2024

A series of (Gd, Y, Yb, Tb, Ce)3Al2Ga3O12 compositionally disordered compounds with a garnet structure were prepared in the form of ceramics by sintering in oxygen at 1650 °C for 2 h and studied for the luminescent properties and interaction of ions entering the matrix host. The luminescence features of Ce3+ ions were found to be strongly dependent on the Yb concentration. Photoluminescence and scintillation kinetics are characterized by subnanosecond kinetics when the Yb index in the compound exceeds X = 0.3. It opens an opportunity to create an extremely fast and dense scintillation material emitting in a visible range. A further decrease in the Yb index in the compound leads to an increase in the intensity of Yb3+ infrared (IR) emission, whereas Ce3+ and Tb3+ ions contribute to the luminosity of the material by overlapping intra- and intereconfiguration luminescence bands in the spectral range of 300–700 nm. This finding opens an opportunity to create converter materials tolerant to the corpuscular radiation of isotope sources, providing a high efficiency of electric current production when coupled with a silicon photovoltaic element. The compounds were engineered at the nanoscale level, providing control over electronic excitation transfer between luminescent ions.
The ultraviolet and vacuum ultraviolet absorption spectrum of gamma-pyrone; the singlet states studied by configuration interaction and density functional calculations
Authors: Palmer Michael H. , Hoffmann Søren Vrønning , Jones Nykola C. , Coreno Marcello , de Simone Monica , Grazioli Cesare , Aitken R. Alan , Perrault Loëlia , Patterson Iain L. J.
Published: February 2024

A synchrotron based vacuum ultraviolet absorption spectrum for γ-pyrone has been interpreted in terms of singlet excited electronic states using a variety of coupled cluster, configuration interaction, and density functional calculations. The extremely weak spectral onset at 3.557 eV shows eight vibrational peaks, which following previous analyses, are attributed to a forbidden 1A2 state. A contrasting broad peak with a maximum at 5.381 eV has a relatively high cross-section of 30 Mb; this arises from three overlapping states, where a 1A1 state dominates over progressively weaker 1B2 and 1B1 states. After fitting the second band to a polynomial Gaussian function and plotting the regular residuals over 20 vibrational peaks, we have had limited success in analyzing this fine structure. However, the small separation between these three states clearly shows that their vibrational satellites must overlap. Singlet valence and Rydberg state vibrational profiles were determined by configuration interaction using the CAM-B3LYP density functional. Vibrational analysis using both the Franck–Condon and Herzberg–Teller procedures showed that both procedures contributed to the profiles. Theoretical Rydberg states were evaluated by a highly focused CI procedure. The superposition of the lowest photoelectron spectral band on the vacuum ultraviolet spectrum near 6.4 eV shows that the 3s and 3p Rydberg states based on the 2B2 ionic state are present; those based on the other low-lying ionic state (X2B1) are destroyed by broadening; this is a dramatic extension of the broadening previously witnessed in our studies of halogenobenzenes.
Electron transfer in a crystalline cytochrome with four hemes
Authors: Parson William W. , Huang Jingcheng , Kulke Martin , Vermaas Josh V. , Kramer David M.
Published: February 2024

Diffusion of electrons over distances on the order of 100 μm has been observed in crystals of a small tetraheme cytochrome (STC) from Shewanella oneidensis [J. Huang et al. J. Am. Chem. Soc. 142, 10459–10467 (2020)]. Electron transfer between hemes in adjacent subunits of the crystal is slower and more strongly dependent on temperature than had been expected based on semiclassical electron-transfer theory. We here explore explanations for these findings by molecular-dynamics simulations of crystalline and monomeric STC. New procedures are developed for including time-dependent quantum mechanical energy differences in the gap between the energies of the reactant and product states and for evaluating fluctuations of the electronic-interaction matrix element that couples the two hemes. Rate constants for electron transfer are calculated from the time- and temperature-dependent energy gaps, coupling factors, and Franck–Condon-weighted densities of states using an expression with no freely adjustable parameters. Back reactions are considered, as are the effects of various protonation states of the carboxyl groups on the heme side chains. Interactions with water are found to dominate the fluctuations of the energy gap between the reactant and product states. The calculated rate constant for electron transfer from heme IV to heme Ib in a neighboring subunit at 300 K agrees well with the measured value. However, the calculated activation energy of the reaction in the crystal is considerably smaller than observed. We suggest two possible explanations for this discrepancy. The calculated rate constant for transfer from heme I to II within the same subunit of the crystal is about one-third that for monomeric STC in solution.
Translocation of a daughter vesicle in a model system of self-reproducing vesicles
Authors: Klawtanong Manit , Sakuma Yuka , Imai Masayuki , Kawakatsu Toshihiro , Khunpetch Petch
Published: February 2024

Translocation of a daughter vesicle from a mother vesicle through a pore is experimentally studied by many groups using a model system of self-reproducing vesicles. However, the theoretical formulation of the problem is not fully understood. In the present study, we present a theoretical formulation of the process based on our previous work [P. Khunpetch et al., Phys. Fluids 33, 077103 (2021)]. In our previous work, we considered the daughter vesicle as a rigid body. In the present work, however, we allow the daughter vesicle to deform during the expulsion process. We thus derive the free energy constituting of the elastic moduli of both the mother and daughter vesicles, and of pressure-driven contribution. The minimum energy path of the translocation is searched by using the string method. With use of experimentally reasonable values of the elastic moduli, our improved model successfully reproduced the progress of the birthing process where there is no free energy barrier between the initial and the final states. The equations of motion of the daughter vesicle have been derived within the framework of the Onsager principle. We found that the translocation time of the daughter vesicle can be reduced when the pressure inside the mother vesicle increases, or the initial size of the daughter vesicle decreases.
Motion states identification of underwater glider based on complex networks and graph convolutional networks
Authors: Guo Wei , Sun Xinlin , Lv Dongmei , Ma Wei , Niu Wendong , Gao Zhongke , Wang Yanhui
Published: February 2024

Underwater glider (UG) plays an important role in ocean observation and exploration for a more efficient and deeper understanding of complex ocean environment. Timely identifying the motion states of UG is conducive for timely attitude adjustment and detection of potential anomalies, thereby improving the working reliability of UG. Combining limited penetrable visibility graph (LPVG) and graph convolutional networks (GCN) with self-attention mechanisms, we propose a novel method for motion states identification of UG, which is called as visibility graph and self-attention mechanism-based graph convolutional network (VGSA-GCN). Based on the actual sea trial data of UG, we chose the attitude angle signals of motion states related sensors collected by the control system of UG as the research object and constructed complex networks based on the LPVG method from pitch angle, roll angle, and heading angle data in diving and climbing states. Then, we build a self-attention mechanism-based GCN framework and classify the graphs under different motion states constructed by a complex network. Compared with support vector machines, convolutional neural network, and GCN without self-attention pooling layer, the proposed VGSA-GCN method can more accurately distinguish the diving and climbing states of UG. Subsequently, we analyze the variation of the transitivity coefficient corresponding to these two motion states. The results suggest that the coordination of the various sensors in the attitude adjustment unit during diving becomes closer and more efficient, which corresponds to the higher network measure of the diving state compared to the climbing state.
Role of angular velocity on Marangoni convection shifting, heat accumulation, and microstructure evolution using laser directed energy deposition
Authors: Dai Donghua , Li Yanze , Gu Dongdong , Zhao Wentai , Long Yuhang , Shi Xinyu , Zhang Han , Lin Kaijie , Xi Lixia
Published: February 2024

In this study, laser Directed Energy Deposition technology is employed to fabricate internal structures within the hollow interiors of rotating parts such as tubes and cylinders. A three-dimensional transient multiphysics model for C276 material was developed, which anticipated the impact of angular velocity from tube rotation on various aspects. This model, validated by experiments, focused on the melt pool morphology, Marangoni convection, oriented crystal microevolution, and deposited material microhardness. It was found that at 150 ms deposition, the dimensions of the melt pool stabilized. With an increase in the Peclet number, heat transfer within the melt pool transitioned from conduction to convection. A rise in angular velocity reduced the melt pool deposition height, limited by the volume of the deposited material. Additionally, this angular velocity generated tangential forces, leading to an asymmetric melt distribution in the longitudinal section of the melt pool and a movement of the melt toward the melting front. At the bottom of the melt pool, the growth of C276 columnar crystals was notably inclined toward the center of Marangoni convection. The microhardness of the deposited material showed a stable distribution along the inclined crystal direction, whereas significant fluctuations were observed perpendicular to the cylinder substrate. These findings highlighted the considerable effect of Marangoni convection on microstructural evolution.
Formation and evolution of vortex breakdown consequent to post design flow increase in a Francis turbine
Authors: Masoodi Faiz Azhar , Salehi Saeed , Goyal Rahul
Published: February 2024

Draft tube flow instability encountered under off-design operating conditions in hydraulic turbines significantly limits their operational flexibility. The instability arises consequent to a higher than threshold swirl content in the runner outflow and leads to vortex breakdown phenomenon in the draft tube cone. At high load condition, the phenomenon presents as an enlarged vortex core counter-rotating with respect to the runner. The flow situation is known to compromise the turbine efficiency besides the generation of unwanted effects such as power swings and large-scale pressure fluctuations. The present paper is the first to encapsulate a thorough numerical investigation on the formation and evolution of the enlarged vortex core alongside the consequent effects. A transient operating sequence between best efficiency and high load operating points in a model Francis turbine is simulated. Turbulence closure has been attained using the shear stress transport-scale adaptive simulations turbulence model. Dynamic meshing based on a Laplacian smoothing scheme has been used to account for mesh deformation arising from guide vane motion during load change. The pressure and velocity fields have been determined and analyzed to elucidate the physics of vortex breakdown, the phenomenon underlying the formation of the enlarged vortex core. Furthermore, pressure fluctuations at salient points in the domain have been analyzed using Fourier and short-time Fourier transforms. Finally, the enlarged vortex core formed in the draft tube has been visualized through the λ2 criterion. The core takes the shape of a cork-screw like compactly wound spiral structure extending up to the draft tube elbow.
Development of a real-time impedance matching system for ion cyclotron resonance heating in experimental advanced superconducting tokamak
Authors: Chen Q. Q. , Liu L. N. , Qin C. M. , Zhang X. J. , Mao Y. Z. , Yuan S. , Zhang W. , Yang H. , Wang L. , Cheng Y. , Zhang K. , Guo Y. Y. , Sun Y. P.
Published: February 2024

To achieve stable operation of an ion cyclotron resonance heating (ICRH) system in the Experimental Advanced Superconducting Tokamak (EAST), a real-time impedance matching system needs to be established to respond to antenna load variation during long pulse discharges. A new impedance matching method based on capacitors was proposed in this study. By considering the reflected voltage of the transmission line as the feedback parameter, the real-time impedance-matching system can quickly control the motors based on a programmable logic controller to determine the minimum reflection voltage. A real-time impedance matching system was successfully used on the test platform in the laboratory and on the ICRH system in EAST. A significant result is that we can match the variable impedance within 1 s by suitably adjusting the motor controller to ensure high-power and long-pulse operation of the ICRH system to satisfy the requirements of the EAST experiment.
Effect of head on the flow state of water in tailwater channel of the hydropower station
Authors: Xue Yulin , Lu Yanlin , Meng Bangjie , Wu Liersha , Li Hongjuan , Ye Xunyun
Published: February 2024

Hydropower station tailwater channel is often prone to elevated water levels and insufficient energy consumption, which leads to the influence of the output of the unit. To study the intrinsic connection between the water flow state and elevated water level in the tailwater channel, this paper investigates the water flow characteristics inside the tailwater channel of the Mupo Hydropower Station under different heads and verifies the accuracy of numerical calculations by constructing a physical model test platform. The results show that the maximum velocity at the bottom of the fluid domain near the anti-slope section of the tailwater channel decreases with the increase of head, while the velocity at the top of the fluid domain near the anti-slope section of the tailwater channel does not change much with the increase of head; a large vortex is formed in the middle of the upper part of the fluid domain in the anti-slope section of the tailwater channel; and the lower the head, the more obvious the vortex is. The results provide guidance for the design of tailwater channels at hydropower stations.
Parametric investigation of slurry transport: Computational insight into the impact of particle composition and Prandtl numbers
Authors: Joshi Tanuj , Parkash Om , Gallegos Ralph Kristoffer B. , Krishan Gopal
Published: February 2024

In this study, a sophisticated three-dimensional computational model was developed to investigate the kinetic and thermal characteristics of a bi-model slurry. This model utilized the Eulerian–Eulerian Re-Normalization Group k–ε turbulence approach in conjunction with the kinetic theory of granular flow. The slurry, composed of different combinations of silica sand and fly ash, was transported through a straight pipeline under varying Prandtl numbers. Five different mixture combinations were considered, ranging from 65% silica sand and 35% fly ash to 100% silica sand. The slurry was transported using four different Prandtl fluids with varying temperatures. The pipe wall was maintained at a constant temperature of 400 K. The computational results yielded significant findings. A mixture with a higher proportion of fly ash (65:35) exhibited superior flow characteristics when combined with a low-viscosity Prandtl fluid (Pr = 2.88), resulting in a minimal pressure gradient and specific energy consumption. Enhanced energy efficiency was observed at lower Reynolds numbers and reduced efflux concentrations. Additionally, the 95:05 mixture demonstrated the highest heat transfer coefficient, with further improvements as flow Reynolds numbers and efflux concentrations increased. These results provide valuable insight into optimizing the transportation of bi-model slurries for various industrial applications, emphasizing the importance of composition and Prandtl numbers.
Mechanical properties of Xe-ion-irradiated high-entropy-alloy-based multilayers
Authors: G. Rao Smita , Shu Rui , Wang Ji , Chai Jianlong , Zhu Yabin , le Febvrier Arnaud , Eklund Per
Published: February 2024

In this Letter, we investigate the mechanical stability of HEA-based multilayers after Xe-ion irradiation. CrFeCoNi/TiNbZrTa metallic and nitride thin films with a bilayer thickness of 30 nm were grown by reactive dc-magnetron sputtering on Al2O3(0001) substrates for irradiation studies and on Si(100) substrates for other characterizations. The films were subjected to 3-MeV Xe-ion irradiation at room temperature (RT) and at 500 °C. The crystal structure and mechanical properties of the films before and after irradiation were studied by x-ray diffraction and nanoindentation. Before irradiation, both the metallic and nitride multilayers displayed a lower hardness (7 and 20 GPa, respectively). Annealing at 500 °C for 150 min increased the hardness of the multilayer samples, but it also induced intermixing of elements between the sublayers of the metallic multilayer. Irradiation hardening was observed only in the metallic multilayer at room temperature. When comparing the effects of irradiation damage vs the effects of annealing on the mechanical properties, it was observed that annealing the multilayers had a more pronounced effect.