bluuebunny/crossref_metadata_2025 huggingface dataset:
Acceleration of plasma toroidal rotation driven by non-axisymmetric magnetic perturbation fields in the EAST tokamak
Authors: Sheng H. , Lyu B. , Sun Y. W. , Li H. H. , Li Y. Y. , Bae C. , Liu Y. Q. , Jin Y. F. , Mao S. F , Yan X. T. , Xie P. C. , Ma Q. , Wang H. H. , Shi T. H. , Zang Q. , Qian J. P. , Jia M. N. , Chu N. , Ye C. , Chang Y. Y. , Wu X. M. , Zhang Y. N. , Yang H. , Wu M. F. , Ye M. Y. ,   EAST Team
Published: March 2024

Plasma toroidal rotation acceleration in the co-current direction introduced by the n = 1 (toroidal mode number) static resonant magnetic perturbation (RMP) has been observed in the EAST tokamak. It strongly depends on the RMP coil configuration, which is manifested by its dependence on δϕUL (phase difference between upper and lower coils) and RMP current. Modeling results from NTVTOK based on the linear plasma response modeled by MARS-F shows that the Neoclassical Toroidal Viscosity (NTV) torque is in the co-current direction because of the dominant contribution from electrons with the condition that the electron normalized collisionality is much lower than that of ions in this experiment. The modeled dependence of core integrated NTV torque modulated by the magnitude of core magnetic perturbation on δϕUL is consistent with the experimental observations. Threshold condition related to normalized collisionality to achieve the transition from rotation braking to acceleration is obtained in the NTV modeling and agrees well with experimental observations. It is shown in the modeling that the discharges with rotation acceleration are located at the regime that electron contribution to NTV is dominant and the torque is in co-current direction, while others with rotation braking are located at the regime that ion contribution to NTV torque is dominant and the torque is in countercurrent direction. Though the modeling results are in qualitative agreement with the experimental results, there is quantity difference between the modeled NTV torque based on linear plasma response and the experimental values. Possible reason is that the 3D fields are underestimated by linear modeling, particularly in the case of RMP field penetration, as demonstrated by the RMP current threshold for the rotation acceleration observed in the experiments.
Accelerated evolution of Burgers' turbulence with coarse projective integration and deep learning
Authors: Dhingra Mrigank , San Omer , Staples Anne E.
Published: March 2024

The evolution of a turbulent flow to a statistically steady state can be cast as a multiscale problem involving energy redistribution processes that take place on the long, large eddy turnover timescale and chaotic processes that take place on the much shorter timescale of the turbulence fluctuations. But the absence of a way to perform super-resolution reconstructions of the instantaneous velocity field from its lower-dimensional moments has prevented the use of standard multiscale computational approaches for accelerating turbulence simulations. We introduce an encoder-decoder recurrent neural network model, an architecture typically used in natural language processing, for translating between the instantaneous velocity field and energy spectrum in a one-dimensional turbulent flow. We use the model in a multiscale simulation scheme to evolve the stochastic Burgers' equation and recover the final, statistically stationary turbulent Burgers' velocity field up to 443 times faster in wall-clock time than using direct numerical simulation alone.
Rapid generation of massive thermodynamic datasets using frequency comb spectroscopy
Authors: Karim Faisal , Scholten Sarah K. , Perrella Christopher , Luiten Andre N.
Published: March 2024

We demonstrate massively parallel spectroscopic measurements of 12C2H2 using an optical frequency comb. This allows for the rapid and simultaneous estimation of self-broadening and self-shifting of more than 50 optical transitions between 1512 and 1538 nm. The use of a temperature-controlled sealed gas cell allows us to measure both pressure- and temperature-mediated broadening and shifting. We present the results for the pressure-mediated self-broadening and self-shifting coefficients for 59 optical lines that make up the v1 + v3 combination band and a selection of hot bands. Our ability to measure the broadening of numerous transitions allows for the confirmation of prior work that shows that there is no measurable vibrational dependence across all acetylene bands, despite the strong dependence of the broadening coefficient on the rotational number. We also present an extensive measurement of the temperature dependence of the self-broadening for each of these 59 lines. This work shows the revolutionary power afforded by the frequency combs for rapid generation of large datasets related to thermodynamic variations of the key spectroscopic parameters of important gases.
Investigation of magnetization dynamics in trilayer width-modulated nanowires
Authors: Kuchibhotla Mahathi , Haldar Arabinda , Adeyeye Adekunle Olusola
Published: March 2024

We have investigated the magnetization reversal processes and dynamic behavior of trilayered Py(50 nm)/Pd(tPd)/Py(20 nm) nanowires with periodic width modulation as a function of spacer layer thickness tPd in the range from 0 to 10 nm and compared them with single-layer nanowires. The ferromagnetic resonance spectra show more than three modes that result from a non-uniform demagnetizing field in width-modulated nanowires. We observe that the spacer layer thickness influenced the ferromagnetic resonance spectra, which showed different numbers and values of modes and frequencies due to the different magnetization configurations for different spacer layer thicknesses. We also found that the two ferromagnetic layers are exchange-coupled for tPd = 2 nm nanowire arrays, showing the sharp switching of magnetization from the static measurements and sharp frequency jump from 13.6 to 14.7 GHz around −18 mT from the dynamic measurements. However, for tPd = 10 nm, the two layers switch at different fields, indicating a gradual decrease in magnetization as the reversal is mediated through dipolar coupling. The origin of modes is well explained from the spatial mode profiles of top and bottom magnetic layers. The dynamic responses in this spin-valve-type structure are useful for designing microwave-based spintronic devices.
High-amplitude pressure pulsations induced by complex inter-blade flow during load rejection of ultrahigh-head prototype pump turbines
Authors: Fu Xiaolong , Li Deyou , Lv Jingwei , Yang Biao , Wang Hongjie , Wei Xianzhu
Published: March 2024

The flow pattern evolution is particularly complicated in the low specific speed impeller of ultrahigh-head pump turbines. To reveal the mechanism of pressure pulsation induced by the inter-blade flow, the load rejection process of an ultrahigh-head prototype pump turbine was numerically calculated using one- and three-dimensional coupled compressible flow simulation methods. The mechanism of pressure pulsation was analyzed using time-frequency analysis and visualization method of flow field. The investigation captured two high-amplitude low-frequency components of the pressure pulsations during load rejection of the ultrahigh-head prototype pump turbine. The investigation suggested that the first frequency components of the pressure pulsations were unique to the ultrahigh-head pump turbines. They were approximately one- to sevenfold impeller rotation frequency, which are caused by inter-blade separation vortices in the impeller. Other low-frequency components of the pressure pulsations near the first speed-no-load condition were induced by the unstable transitions of the flow separation and backflow vortices close to the high-pressure entrance of the impeller. This study first found that unstable transitions of the flow patterns in the impeller of ultrahigh-head prototype pump turbines could cause high-amplitude pressure pulsations. However, stable flow-vortex structures cannot cause apparent pressure pulsations. The findings of this investigation provide a theoretical basis for suppressing pressure pulsations and controlling complex flows in ultrahigh-head prototype pump turbines.
Perspective: Theory and simulation of highly mismatched semiconductor alloys using the tight-binding method
Authors: Broderick Christopher A. , O’Reilly Eoin P. , Schulz Stefan
Published: March 2024

The electronic structure of highly mismatched semiconductor alloys is characterized by carrier localization and strongly influenced by the local alloy microstructure. First-principles calculations can deliver valuable quantitative insight, but their associated computational expense limits alloy supercell size and imposes artificial long-range ordering, which can produce misleading results. The empirical tight-binding method (ETBM) provides a transparent approach to investigate large-scale supercells on an atomistic level, to quantitatively predict the electronic structure of semiconductor alloys. Here, we overview key aspects and considerations for establishing ETBMs. Additionally, we discuss and highlight, given that the ETBM matrix elements are described in the language of overlaps between localized atomic orbitals, that ETBMs have proven highly successful in analyzing the impact of localized and resonant impurity states, as well as disorder, on the optoelectronic properties of highly mismatched alloys. The ETBM continues to provide valuable insight for emerging material systems, including two-dimensional materials, perovskites and their heterostructures, and provides a framework to address technologically relevant questions including the importance of short-range disorder for loss mechanisms such as non-radiative Auger–Meitner recombination. Moreover, the ETBM furnishes a quantitative basis for continuum models such as k⋅p or localization landscape theories, allowing to explicitly incorporate disorder effects in nanostructures to underpin predictive device-level analysis.
Cluster perturbation theory IX: Perturbation series for the coupled cluster singles and doubles ground state energy
Authors: Hillers-Bendtsen Andreas Erbs , Jensen Frank , Mikkelsen Kurt V. , Olsen Jeppe , Jørgensen Poul
Published: March 2024

In this paper, we develop and analyze a number of perturbation series that target the coupled cluster singles and doubles (CCSD) ground state energy. We show how classical Møller–Plesset perturbation theory series can be restructured to target the CCSD energy based on a reference CCS calculation and how the corresponding cluster perturbation series differs from the classical Møller–Plesset perturbation series. Subsequently, we reformulate these series using the coupled cluster Lagrangian framework to obtain series, where fourth and fifth order energies are determined only using parameters through second order. To test the methods, we perform a series of test calculations on molecular photoswitches of both total energies and reaction energies. We find that the fifth order reaction energies are of CCSD quality and that they are of comparable accuracy to state-of-the-art approximations to the CCSD energy based on local pair natural orbitals. The advantage of the present approach over local correlation methods is the absence of user defined threshold parameters for neglecting or approximating contributions to the correlation energy. Fixed threshold parameters lead to discontinuous energy surfaces, although this effect is often small enough to be ignored, but the present approach has a differentiable energy that will facilitate derivation and implementation of gradients and higher derivatives. A further advantage is that the calculation of the perturbation correction is non-iterative and can, therefore, be calculated in parallel, leading to a short time-to-solution.
Investigating the influence of substrate orientation and temperature on Cu cluster deposition
Authors: He Yiwen , Zhang Shixu , Zheng Zhijun , Li Gongping
Published: March 2024

The crystal orientation and the temperature of the substrate are crucial factors that influence clusters deposition and, consequently, the properties of thin films. In this study, the molecular dynamics simulation method was employed to investigate the deposition of Cu55 clusters on Fe(001), Fe(011), and Fe(111) substrates with varying crystal orientations. The incident energies used ranged from 0.1 to 20.0 eV/atom, and the substrates were maintained at temperatures of 300, 500, and 800 K. Analysis of cluster and substrate atom snapshots, along with the physical properties of clusters, revealed how the crystal orientation of Fe substrates affects the morphology and structure of the cluster at different temperatures. Additionally, specific microscopic mechanisms responsible for these effects were identified. The simulation results demonstrate that the crystal orientation of Fe substrate significantly influences the deposition of Cu55 clusters. The structures of the clusters on the three crystal substrates undergo similar changes as the substrate temperature increases, with the Cu55 clusters on the Fe(111) substrate exhibiting the most significant changes in response to the temperature rise.
Discrete element analysis on impact failure mechanism of “Zhengzhou 7.20” catastrophic flood for coal gangue railway subgrade
Authors: Li Xianquan , Ren Lianwei , Chen Xinming , Yang Quanwei
Published: March 2024

Limited research has been conducted on the failure mechanism of coal gangue railway subgrade structures during catastrophic flood disasters, including the impact of varying flood impact heights and load sizes. This study investigates the process and mechanism of coal gangue railway subgrade failure in the coal mining subsidence area, in conjunction with the “7.20” catastrophic flood in Zhengzhou. First, various factors such as impact forms, impact height, flow velocity, water depth, and wave height are considered, and a wave-water flow coupling calculation method is proposed to determine the catastrophic flood load acting on inclined slopes. The maximum impact load calculated is then applied to simulate the impact process of the catastrophic flood using Particle Flow Code 2D. As the flood-related parameters increase, the maximum impact load on the subgrade slope also increases, leading to the breakdown of the subgrade and causing fatal damage. Finally, the failure process of the coal gangue railway subgrade under the impact and scour of a catastrophic flood is divided into three stages: erosion weakening, potential failure surface formation, and overall failure. The main failure mechanisms of each stage are revealed. These research result findings offer valuable insights for the design of railway subgrade reinforcement under catastrophic flood conditions.
Droplet electrohydrodynamic deformation in a shear flow field
Authors: Hao Guanqiu , Lv Le , Yu Wei , Liu Xiangdong , Chen Yongping
Published: March 2024

The electrohydrodynamic deformation characteristics of a leaky dielectric droplet in combined shear flow field (SFF) and electric field (EF) are investigated by a three-dimensional numerical simulation. Based on the investigation, the cooperation and competition of the two fields on the droplet electrohydrodynamic deformation degree D and orientation angle ϕd are revealed. The influences of SFF strength, EF strength, viscosity, electrophysical parameters, and confinement degree on the droplet deformation morphologies are analyzed. Particularly, theoretical prediction models for droplet electrohydrodynamic deformation and rotation with consideration of domain confinement are proposed. It is found that the two fields collaborate with each other in promoting droplet deformation while they are competing or cooperating with each other in rotating the droplet when Ω > 0 and Ω < 0 (Ω is Taylor's deformation characteristic function). In addition, for a given condition, with increasing conductivity ratio R, the effect of permittivity ratio S turns to diminish and the droplet steady-state D and ϕd converge to a constant. Otherwise, a larger permittivity ratio S leads to a larger D and a smaller ϕd, respectively. The domain confinement promotes D when Ω > 0, while it first reduces D and then promotes it when Ω < 0. For the droplet orientation, the droplet is rotated to the EF direction with the increasing confinement degree when R < S, while it is rotated to the direction perpendicular to the EF when R > S. Furthermore, theoretical prediction models for droplet deformation and rotation with consideration of domain confinement are proposed, which are proved to be accurate and reliable based on the current simulation results and available data.
Manipulation of the flow induced by afterbody vortices using sweeping jets
Authors: Chen Xiaodong , Zhong Shan , Liu Tanghong , Ozer Ozgun , Gao Guangjun
Published: March 2024

In this study, the impact of oscillatory fluids on the flow induced by afterbody vortices, resembling those of a high-speed train, was investigated in wind tunnel experiments. The afterbody vortices were generated by a cylindrical model with a slanted base at Reynolds numbers ranging from 87 000 to 200 000. A fluidic oscillator was utilized to produce sweeping jets (SWJ) acting on the vortical flow, which is similar to those observed over the rear of a typical high-speed train. Our particle image velocimetry measurements on cross-stream planes reveal that the oscillatory flow produced by the sweeping jet significantly reduces the magnitude of induced flow, resulting in a 17.7% and 15.9% decrease in the total velocity and horizontal slipstream, respectively, at a velocity ratio of 6.4. This is attributed to the injection of the kinetic energy of sweeping jets into the core of the afterbody vortices, which leads to a higher dispersion of vorticity and incoherent energy distributions. The iso-surfaces of resultant velocities reveal that the fluid injection by the sweeping jet increased local velocities, resulting in a spanwise shrinkage of the induced velocity structure downstream. The study demonstrates the capability of sweeping jets in decreasing induced flow by manipulating afterbody vortices and their potential for reducing the slipstream produced by high-speed trains at the tracksides.
Thermo-hydrodynamic lubrication and energy dissipation mechanism of a pump-turbine thrust bearing in load-rejection process
Authors: Cao Jingwei , Luo Yongyao , Deng Liwei , Liu Xin , Yan Shu , Zhai Liming , Wang Zhengwei
Published: March 2024

The dynamic behavior of the pump-turbine thrust bearing is important to the safety operation of the unit. This paper analyzed the lubrication and energy dissipation mechanism of pump-turbine thrust bearing during load-rejection based on the thermo-hydrodynamic model. The results show that the variation of the axial force and the maximum pad surface pressure is basically consistent with that of the inclination of the pad surface. The change of the friction loss is consistent with the change of rotational speed, while the change of pad surface temperature is affected by the combination of pad inclination and rotational speed. The chaotic flow in the oil tank is accompanied by different forms of vortices, such as Taylor vortices, vortex pairs, and Karman vortices, and results in a significant asymmetry in the pressure distribution. The flow in the bearing pad groove has an effect on the energy dissipation in the oil film. This paper provides a theoretical basis for the design and optimization of thrust bearings, and provides a reference for solving the problems of wear, oil mist, and other related problems of thrust bearings in engineering.
New higher-order accurate super-compact scheme for three-dimensional natural convection and entropy generation
Authors: Punia Ashwani , Ray Rajendra K.
Published: March 2024

Exploring natural convection in three dimensions through numerical analysis has become essential for gaining a deeper understanding of this process compared to studying it in just two dimensions. This paper presents an enhanced analysis of three-dimensional (3D) natural convection phenomena within an air-filled cubical cavity, with a primary focus on heat transfer characteristics. The distinguishing feature of this research lies in the pioneering application of the newly developed higher-order accurate super-compact finite difference scheme to study 3D natural convection and entropy generation. This numerical method is renowned for its fourth-order spatial accuracy and second-order temporal accuracy. The super-compact scheme employs 19 grid points at the current time level (nth time level) while utilizing just seven grid points from the subsequent time level [(n+1)th time level. The flow is considered to be 3D, time-varying, laminar, and incompressible. First, the newly developed numerical code has undergone validation through quantitative and qualitative comparisons with existing results. Then, we analyze the flow phenomena and heat transfer dynamics within the cavity for various Rayleigh numbers (102≤Ra≤105) with a fixed Prandtl number (Pr = 0.71) by using this scheme. Various parameters such as local Nusselt numbers, averaged Nusselt numbers, local entropy, Bejan number, streamlines, and isotherm dispersion are studied in this work. It is found that as the Rayleigh number (Ra) increases, the Bejan number (Be) decreases, while the total entropy increases. When the Ra is less than or equal to 104, the Be remains above 0.5, indicating that irreversibility primarily arises from heat transfer. However, as we transition to Ra=105, the Be falls below 0.5, signaling that irreversibility is now predominantly driven by viscous effects. To the best of our knowledge, this research marks a pioneering effort by introducing the application of the higher order super-compact (HOSC) scheme for the examination of heat transfer within a 3D cubic cavity, thus endowing our work with a truly novel and pioneering character. It is worth mentioning that, before this study, there has been no precedent in the exploration of heat transfer using the super-compact scheme, thus endowing our work with a truly novel and pioneering character.
Vortex synchronization-enabled heat-transfer enhancement in a channel with backward- and forward-facing steps
Authors: Ma Yuan , Ren Feng , Tang Hui , Wang Chenglei
Published: March 2024

A channel with one backward-facing step and one forward-facing step is a typical configuration in engineering applications. In the channel, good heat transfer performance is often required, and the enhancement is usually achieved by employing different passive control methods, such as modification of geometric configuration or application of nanofluid. However, the other control method, i.e., active flow control (AFC), which is likely more effective, has been rarely applied in such a scenario. This study aims to bridge this gap by exploring how a rigid plate affects the heat transfer of the channel. The plate either is stationary or actively rotates, corresponding to passive flow control or AFC. The influences of the horizontal position of the plate (S) and its orientation angle (θ) on the heat transfer performance are studied when the plate is stationary to provide a baseline. Compared to the baseline, the effects of S, θ, and the rotation frequency (fr) are revealed when the plate undergoes a sinusoidal rotation. Such a thermo-fluid dynamic problem is numerically simulated by the immersed-boundary lattice Boltzmann method. The results show that the plate can improve the heat transfer performance no matter whether it rotates or not, compared to the case without a plate. The rotating plate outperforms the stationary one when θ and fr are properly chosen at each S. Substantial improvement can be achieved when vortex synchronization or resonance occurs in the channel, i.e., when the natural vortex shedding frequency is close or equal to fr.
Gas dynamics at starting and terminating phase of a supersonic exhaust diffuser with a conical nozzle
Authors: Afkhami Sina , Fouladi Nematollah
Published: March 2024

This research investigates the process of starting and breakdown of second throat diffuser during high-altitude test of conical nozzle with a high expansion ratio. The subscale experimental setup includes a conical nozzle with an expansion ratio of 53, plus a second throat diffuser with a contraction ratio of 1.85, using compressed air as the working fluid. Numerical simulation has been employed to identify the flow physics during the unsteady process of diffuser startup and breakdown. According to the results, the starting process is divided into three distinct stages. In the first stage, the exhausted flow from the nozzle enters the vacuum chamber, leading to an increase in vacuum chamber pressure. The second stage, corresponding to the period before full flow establishment in the conical nozzle, exhibits a relatively constant slope. In the final stage, associated with the transition from over-expanded to under-expanded states, the slope of the rate of evacuation development descends. Next, the vacuum degradation in termination process has been analyzed, and it has been found to include three stages: high slope, middle slope, and low slope. The flow physics during the start process, similar to the results observed in other conical nozzles, exhibits only a Mach reflection structure. However, during the termination process, the flow physics involve a combination of both structures, including Mach reflection and Cap Shock. The results indicate that during the start, an internal shock only interacts with the separation shock, and no special change occurs in the Mach reflection structure. In contrast, during the termination process, unlike what has been reported in previous studies on conical nozzles, the structure of cap shock waves and restricted shock separation patterns are also observed. Another distinction between the starting and termination processes is related to the pressure distribution in the diffuser wall. The wall pressure at the diffuser inlet during the termination process has been reported to be 90% higher than during the starting process.
The effect of contact angle hysteresis on a droplet in a viscoelastic two-phase system
Authors: Bazesefidpar Kazem , Tammisola Outi
Published: March 2024

We investigate the dynamic behavior of a two-dimensional droplet adhering to a wall in Poiseuille flow at low Reynolds numbers, in a system where one of the phases is viscoelastic represented by a Giesekus model. The Cahn–Hilliard Phase-Field method is used to capture the interface between the two phases. The presence of polymeric molecules alters the viscoelastic drop's deformation over time, categorizing it into two stages before contact line depinning. In the first stage, the viscoelastic droplet deforms faster, while in the second stage, the Newtonian counterpart accelerates and its deformation outpaces the viscoelastic droplet. The deformation of viscoelastic drop is retarded significantly in the second stage with increasing Deborah number De. The viscous bending of viscoelastic drop is enhanced on the receding side for small De, but it is weakened by further increase in De. On the advancing side, the viscous bending is decreased monotonically for Ca < 0.25 with a non-monotonic behavior for Ca = 0.25. The non-monotonic behavior on the receding side is attributed to the emergence of outward pulling stresses in the vicinity of the receding contact line and the inception of strain-hardening at higher De, while the reduction in the viscous bending at the advancing side is the result of just strain-hardening. Finally, when the medium is viscoelastic, the viscoelasticity suppresses the droplet deformation on both receding and advancing sides, and this effect becomes more pronounced with increasing De. Increasing the Giesekus mobility parameter enhances the weakening effect of viscous bending on the advancing side.
On-the-fly simulation of time-resolved fluorescence spectra and anisotropy
Authors: Xu Chao , Lin Congru , Peng Jiawei , Zhang Juanjuan , Lin Shichen , Gu Feng Long , Gelin Maxim F. , Lan Zhenggang
Published: March 2024

We combine on-the-fly trajectory surface hopping simulations and the doorway–window representation of nonlinear optical response functions to create an efficient protocol for the evaluation of time- and frequency-resolved fluorescence (TFRF) spectra and anisotropies of the realistic polyatomic systems. This approach gives the effective description of the proper (e.g., experimental) pulse envelopes, laser field polarizations, and the proper orientational averaging of TFRF signals directly from the well-established on-the-fly nonadiabatic dynamic simulations without extra computational cost. To discuss the implementation details of the developed protocol, we chose cis-azobenzene as a prototype to simulate the time evolution of the TFRF spectra governed by its nonadiabatic dynamics. The results show that the TFRF is determined by the interplay of several key factors, i.e., decays of excited-state populations, evolution of the transition dipole moments along with the dynamic propagation, and scaling factor of the TFRF signals associated with the cube of emission frequency. This work not only provides an efficient and effective approach to simulate the TFRF and anisotropies of realistic polyatomic systems but also discusses the important relationship between the TFRF signals and the underlining nonadiabatic dynamics.
Reproductive dynamics of striped marlin (Kajikia audax) in the central North Pacific
Authors: Humphreys Robert L. , Brodziak Jon K. T.
Published: March 2024

Context Within the western and central North Pacific Ocean stock of striped marlin (Kajikia audax), reproductive information is lacking for the central North Pacific. Aims To derive estimates of sex-specific functional maturity ogives, eye-to-fork length at 50% maturity, reproductive phase composition, spawning season and sex ratios by sampling the Hawaii-based pelagic longline fishery. Methods Gonad histology was exclusively used to confirm sex and estimate all reproductive life history traits. Key results Females spawn in May–July; males are capable of spawning year-round. Best length at 50% maturity estimates were based on datasets restricted to the female spawning season (eye–fork length for females 152.2 cm and for males 109.0 cm). Length distributions and sex ratios are seasonally dynamic around Hawaii and differ from those in other Pacific regions. Conclusions Length-at-maturity estimates for the central North Pacific are lower than all sex-specific estimates reported from other Pacific regions. Implications The new maturity estimates will improve determinations of stock resilience and productivity in upcoming international assessments.
4D microvelocimetry reveals multiphase flow field perturbations in porous media
Authors: Bultreys Tom , Ellman Sharon , Schlepütz Christian M. , Boone Matthieu N. , Pakkaner Gülce Kalyoncu , Wang Shan , Borji Mostafa , Van Offenwert Stefanie , Moazami Goudarzi Niloofar , Goethals Wannes , Winardhi Chandra Widyananda , Cnudde Veerle
Published: March 2024

Many environmental and industrial processes depend on how fluids displace each other in porous materials. However, the flow dynamics that govern this process are still poorly understood, hampered by the lack of methods to measure flows in optically opaque, microscopic geometries. We introduce a 4D microvelocimetry method based on high-resolution X-ray computed tomography with fast imaging rates (up to 4 Hz). We use this to measure flow fields during unsteady-state drainage, injecting a viscous fluid into rock and filter samples. This provides experimental insight into the nonequilibrium energy dynamics of this process. We show that fluid displacements convert surface energy into kinetic energy. The latter corresponds to velocity perturbations in the pore-scale flow field behind the invading fluid front, reaching local velocities more than 40 times faster than the constant pump rate. The characteristic length scale of these perturbations exceeds the characteristic pore size by more than an order of magnitude. These flow field observations suggest that nonlocal dynamic effects may be long-ranged even at low capillary numbers, impacting the local viscous-capillary force balance and the representative elementary volume. Furthermore, the velocity perturbations can enhance unsaturated dispersive mixing and colloid transport and yet, are not accounted for in current models. Overall, this work shows that 4D X-ray velocimetry opens the way to solve long-standing fundamental questions regarding flow and transport in porous materials, underlying models of, e.g., groundwater pollution remediation and subsurface storage of CO
2
and hydrogen.
A tale of two topological isomers: Uptuning [Fe
IV
(O)(Me
4
cyclam)]
2+
for olefin epoxidation
Authors: Chandra Bittu , Ahsan Faiza , Sheng Yuan , Swart Marcel , Que Lawrence
Published: March 2024

TMC-
anti
and TMC-
syn,
the two topological isomers of [Fe
IV
(O)(TMC)(CH
3
CN)]
2+
(TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, or Me
4
cyclam), differ in the orientations of their Fe
IV
=O units relative to the four methyl groups of the TMC ligand framework. The Fe
IV
=O unit of TMC-
anti
points away from the four methyl groups, while that of TMC-
syn
is surrounded by the methyl groups, resulting in differences in their oxidative reactivities. TMC-
syn
reacts with HAT (hydrogen atom transfer) substrates at 1.3- to 3-fold faster rates than TMC-
anti
, but the reactivity difference increases dramatically in oxygen-atom transfer reactions. R
2
S substrates are oxidized into R
2
S=O products at rates 2-to-3 orders of magnitude faster by TMC-
syn
than TMC-
anti
. Even more remarkably, TMC-
syn
epoxidizes all the olefin substrates in this study, while TMC-
anti
reacts only with
cis
-cyclooctene but at a 100-fold slower rate. Comprehensive quantum chemical calculations have uncovered the key factors governing such reactivity differences found between these two topological isomers.
Interpreting chemisorption strength with AutoML-based feature deletion experiments
Authors: Li Zhuo , Zhao Changquan , Wang Haikun , Ding Yanqing , Chen Yechao , Schwaller Philippe , Yang Ke , Hua Cheng , He Yulian
Published: March 2024

The chemisorption energy of reactants on a catalyst surface,

E

ads

, is among the most informative characteristics of understanding and pinpointing the optimal catalyst. The intrinsic complexity of catalyst surfaces and chemisorption reactions presents significant difficulties in identifying the pivotal physical quantities determining

E

ads

. In response to this, the study proposes a methodology, the feature deletion experiment, based on Automatic Machine Learning (AutoML) for knowledge extraction from a high-throughput density functional theory (DFT) database. The study reveals that, for binary alloy surfaces, the local adsorption site geometric information is the primary physical quantity determining

E

ads

, compared to the electronic and physiochemical properties of the catalyst alloys. By integrating the feature deletion experiment with instance-wise variable selection (INVASE), a neural network-based explainable AI (XAI) tool, we established the best-performing feature set containing 21 intrinsic, non-DFT computed properties, achieving an MAE of 0.23 eV across a periodic table-wide chemical space involving more than 1,600 types of alloys surfaces and 8,400 chemisorption reactions. This study demonstrates the stability, consistency, and potential of AutoML-based feature deletion experiment in developing concise, predictive, and theoretically meaningful models for complex chemical problems with minimal human intervention.
Critical Opalescence and Its Impact on the Jet Quenching Parameter
q^
Authors: Wu 武 Jing 警 , Cao 曹 Shanshan 杉杉 , Li 李 Feng 峰
Published: March 2024

Jet quenching parameter

q
^

is essential for characterizing the interaction strength between jet partons and nuclear matter. Based on the quark-meson model, we develop a new framework for calculating

q
^

at finite chemical potentials, in which

q
^

is related to the spectral function of the chiral order parameter. A mean field perturbative calculation up to the one-loop order indicates that the momentum broadening of jets is enhanced at both high temperature and high chemical potential, and approximately proportional to the parton number density in the partonic phase. We further investigate the behavior of

q
^

in the vicinity of the critical endpoint (CEP) by coupling our calculation with a recently developed equation of state that includes a CEP in the universality class of the Ising model, from which we discover the partonic critical opalescence, i.e., the divergence of scattering rate of jets and their momentum broadening at the CEP, contributed by scatterings via the σ exchange process. Hence, for the first time, jet quenching is connected with the search of CEP.
Nonlinear dynamics study of freestanding triboelectric nanogenerator system
Authors: Cao Jingyu , Bao Jiusheng , Yin Yan , Cao Ting
Published: March 2024

As a nonlinear dynamic system, the dynamic equation of triboelectric nanogenerator system is not only difficult to accurately establish, but also difficult to solve. The output signals of triboelectric nanogenerator system depends on the initial conditions of the system, which reflects the dynamic behavior of the system. Currently, there is little research on using the output signals to study the dynamic behavior of triboelectric nanogenerator system. Therefore, a dynamic simulation model of a freestanding triboelectric nanogenerator (F-TENG) system was established using COMSOL software. The mathematical model of the F-TENG system was fitted. Using chaos theory and its phase-space reconstruction technology, the phase-space trajectories of the F-TENG system were reconstructed through voltage signals under external factors, and the dynamic behavior of the F-TENG system was discussed and studied. Finally, validation experiments were carried out. The research shows that with the variation of internal factors and operating frequency, the mathematical model of the F-TENG system remains basically unchanged, and the variation law of output characteristics also remains basically unchanged. The F-TENG system is in periodic motion; with the variation of external factors such as resistance and friction layer spacing, the mathematical model of the F-TENG system will evolve in a complex direction, and the output characteristics will gradually distort. The F-TENG system will evolve from periodic motion to chaotic motion. The research results not only reveal the dynamic behavior and enrich the nonlinear dynamic theory of triboelectric nanogenerator system, but also provide theoretical guidance for increasing the working bandwidth and stability of triboelectric nanogenerator system.
Magnetization reversal of ferromagnetic nanosample by circularly polarized radiation pulse under resonance condition
Authors: Lobachev Andrew V , Ye Zhuravlev Mikhail , Vedyayev Anatoly V
Published: March 2024

We consider the problem of the magnetization dynamics of a nanosized ferromagnetic sample caused by the spin–orbit interaction of electrons arising in the field of an incident electromagnetic wave. We discuss the case when the frequency of the incident electromagnetic radiation is close to the frequency of the interband transitions. We show that with the use of high-power lasers, this mechanism causes the appearance of a magnetization component perpendicular to the initial magnetization of the sample. This component shows oscillations with a frequency lower than that of incident electromagnetic waves. These dynamics make possible the magnetization reversal of the sample.
Underwater wideband coherent signals DOA estimation using sparse representation and deconvolution
Authors: Fan Jingjing , Tao Quan , Qian Zhiwen , Fu Xiaomei
Published: March 2024

The beamforming-based direction of arrival (DOA) estimation method is widely used because of its advantages of robustness, which requires a large array aperture to ensure high spatial resolution. The deconvolution beam-forming method has high-resolution DOA estimation without increasing the array aperture. However, it is based on the assumption of incoherent narrowband signals. When the signals are coherent, the high cross-term sidelobes result in large estimation errors. In this paper, a new sparse deconvolution beamforming is proposed to estimate the DOA of wideband coherent signals. First, extend the deconvolution beamforming method to the wideband case by matrix transformation. Second, solve the problem that the traditional deconvolution algorithm is not applicable to coherent signals by sparse representation. Numerical simulations and underwater experiments are presented to verify the effectiveness of the proposed method. The results show that even at low signal-to-noise ratio and blind environment parameters, the proposed method can obtain better performance compared with other coherent signals DOA estimation algorithms.
Multisource elevations strategy obtaining robust seed points and reference surfaces for ground points extraction in complex terrain area
Authors: Li Jingyu , Wang Lei , Sun Liying , Zou Xin
Published: March 2024

The appearance of unmanned aerial vehicle photogrammetry and airborne lidar makes it possible to obtain measurement data for complex terrains such as gullies and mountainous regions. However, extracting ground points from these abundant and massive measurement datasets is challenging. In traditional extractions, their essence is to determine the surfaces that can describe the terrain from the seed points in the grid and use them as the basis for separating non-ground points. For effective extraction, this study proposes a multisource elevations strategy (MES) obtaining robust seed points and reference surfaces. First, two-level extended grids were constructed as the basic units. Then, to select more robust values between measurement and interpolation elevations, an elevation-determination rule was established for seed points. After, based fitting and interpolation elevations of grid nodes, the correction range is determined and the elevation is corrected for reference surfaces. In two representative complex terrain areas, when non-ground points were marked as seed points, the MES effectively reduced the phenomenon of seed points moving away from the ground. Reference surfaces can also accurately represent the global change trend and local elevation of the ground in areas where the terrain changes rapidly. This strategy provides a new thinking for ground point extraction from point cloud.
Numerical study of the Serre–Green–Naghdi equations in 2D
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Authors: Gavrilyuk Sergey , Klein Christian
Published: March 2024

A detailed numerical study of solutions to the Serre–Green–Naghdi (SGN) equations in 2D with vanishing curl of the velocity field is presented. The transverse stability of line solitary waves, 1D solitary waves being exact solutions of the 2D equations independent of the second variable, is established numerically. The study of localized initial data as well as crossing 1D solitary waves does not give an indication of existence of stable structures in SGN solutions localized in two spatial dimensions. For the numerical experiments, an approach based on a Fourier spectral method with a Krylov subspace technique is applied.
IWNeXt: an image-wavelet domain ConvNeXt-based network for self-supervised multi-contrast MRI reconstruction
Authors: Yan Yanghui , Yang Tiejun , Jiao Chunxia , Yang Aolin , Miao Jianyu
Published: March 2024

Objective. Multi-contrast magnetic resonance imaging (MC MRI) can obtain more comprehensive anatomical information of the same scanning object but requires a longer acquisition time than single-contrast MRI. To accelerate MC MRI speed, recent studies only collect partial k-space data of one modality (target contrast) to reconstruct the remaining non-sampled measurements using a deep learning-based model with the assistance of another fully sampled modality (reference contrast). However, MC MRI reconstruction mainly performs the image domain reconstruction with conventional CNN-based structures by full supervision. It ignores the prior information from reference contrast images in other sparse domains and requires fully sampled target contrast data. In addition, because of the limited receptive field, conventional CNN-based networks are difficult to build a high-quality non-local dependency. Approach. In the paper, we propose an Image-Wavelet domain ConvNeXt-based network (IWNeXt) for self-supervised MC MRI reconstruction. Firstly, INeXt and WNeXt based on ConvNeXt reconstruct undersampled target contrast data in the image domain and refine the initial reconstructed result in the wavelet domain respectively. To generate more tissue details in the refinement stage, reference contrast wavelet sub-bands are used as additional supplementary information for wavelet domain reconstruction. Then we design a novel attention ConvNeXt block for feature extraction, which can capture the non-local information of the MC image. Finally, the cross-domain consistency loss is designed for self-supervised learning. Especially, the frequency domain consistency loss deduces the non-sampled data, while the image and wavelet domain consistency loss retain more high-frequency information in the final reconstruction. Main results. Numerous experiments are conducted on the HCP dataset and the M4Raw dataset with different sampling trajectories. Compared with DuDoRNet, our model improves by 1.651 dB in the peak signal-to-noise ratio. Significance. IWNeXt is a potential cross-domain method that can enhance the accuracy of MC MRI reconstruction and reduce reliance on fully sampled target contrast images.
3D whole heart k-space-based super-resolution cardiac T1 mapping using rotated stacks
Authors: Hufnagel Simone , Schuenke Patrick , Schulz-Menger Jeanette , Schaeffter Tobias , Kolbitsch Christoph
Published: March 2024

Objective. To provide three-dimensional (3D) whole-heart high-resolution isotropic cardiac T1 maps using a k-space-based through-plane super-resolution reconstruction (SRR) with rotated multi-slice stacks. Approach. Due to limited SNR and cardiac motion, often only 2D T1 maps with low through-plane resolution (4–8 mm) can be obtained. Previous approaches used SRR to calculate 3D high-resolution isotropic cardiac T1 maps. However, they were limited to the ventricles. The proposed approach acquires rotated stacks in long-axis orientation with high in-plane resolution but low through-plane resolution. This results in radially overlapping stacks from which high-resolution T1 maps of the whole heart are reconstructed using a k-space-based SRR framework considering the complete acquisition model. Cardiac and residual respiratory motion between different breath holds is estimated and incorporated into the reconstruction. The proposed approach was evaluated in simulations and phantom experiments and successfully applied to ten healthy subjects.Main results. 3D T1 maps of the whole heart were obtained in the same acquisition time as previous methods covering only the ventricles. T1 measurements were possible even for small structures, such as the atrial wall. The proposed approach provided accurate (P > 0.4; R
2 > 0.99) and precise T1 values (SD of 64.32 ± 22.77 ms in the proposed approach, 44.73 ± 31.9 ms in the reference). The edge sharpness of the T1 maps was increased by 6.20% and 4.73% in simulation and phantom experiments, respectively. Contrast-to-noise ratios between the septum and blood pool increased by 14.50% in in vivo measurements with a k-space compared to an image-space-based SRR. Significance. The proposed approach provided whole-heart high-resolution 1.3 mm isotropic T1 maps in an overall acquisition time of approximately three minutes. Small structures, such as the atrial and right ventricular walls, could be visualized in the T1 maps.