Field Model Research Articles

Relation between Electrostatic Charge Density and Spin Hamiltonian Models of Ligand Field in Lanthanide Complexes.

Understanding the ligand field interactions in lanthanide-containing magnetic molecular complexes is of paramount importance for understanding their magnetic properties, and simple models for rationalizing their effects are much desired. In this work, the equivalence between electrostatic models, which derive their results from calculating the electrostatic interaction energy of the charge density of the 4f electrons in an electrostatic potential representing the ligands, and the common quantum mechanical effective spin Hamiltonian in the space of the ground J multiplet is formulated in detail. This enables the construction of an electrostatic potential for any given ligand field Hamiltonian and discusses the effects of the ligand field interactions in terms of an interaction of a generalized 4f charge density with the electrostatic potential. Such models often allow for an easier rationalization of the ligand field interactions, and it can be hoped that the results in this work will help us to better understand the effects of ligand field in lanthanide complexes.

Evaluation of the Hydrodynamic Impacts of Tidal Turbine Arrays in Jiaozhou Bay

In this paper, a hydrodynamic model of Jiaozhou Bay was developed using the Regional Ocean Modeling System and validated against observed tidal levels and current data. The model accurately characterizes the tidal and current features of the region. Based on this model, the spatial and temporal distributions of flow fields and tidal energy resources were analyzed. A 100-turbine tidal power plant was simulated utilizing a momentum-based approach that accounts for resource distribution, bathymetry, topography, and turbine parameters. The resulting hydrodynamic changes, including velocity variations peaking at 0.5 m/s within the turbine deployment zone and tidal level shifts confined to the bay (maximum change in ~10 cm), emphasize the importance of localized environmental assessments. However, the findings also highlight broader considerations for the sustainable development of tidal energy in semi-enclosed bays worldwide, where strategic siting and design can mitigate larger ecological disturbances. These findings may provide a scientific foundation for balancing clean energy extraction with minimal environmental impact, thus contributing to global efforts to develop more resilient and sustainable coastal energy systems.

Institutional logics, social interactions and management of tensions in public-private partnership organizations.

We aim to understand the link between field-level institutional logics and practice-level social interactions and relationships between public and private actors and their influences on the responses and resolutions to the issues causing tensions. Adopting a multiple logics perspective with a focus on social interactions and relationships between public and private actors, we conducted a multiple case study in five city hospitals recently established under a public-private partnership model in the Turkish healthcare field. We found that the state and market logics that predominantly characterize the Turkish healthcare field were enacted in each of the five hospitals in different manners and constitute three different configurations as compatible, complementary and contradictory. The social interactions and relationships developed between the public and private actors occur based on these configurations, and they all together shape the responses and resolutions to the issues causing tensions. Since we did all analyses between the organizational actors at the partnership level, we did not consider possible differences arising from individual and positional roles in each partnership. It is therefore important to acknowledge that the interviews, which are central to the research results, might be influenced by the motivation and power dynamics of the participants in terms of their positions, roles and responsibilities. Thus, much work must be done to understand the management of tensions in public-private partnership organizations (PPPOs) influenced by institutional logics with a greater focus on individual, partnership, organizational and field-level interactions. Tensions arising between public and private actors in PPPOs can be understood better and managed more effectively when the enactment of institutional logics is considered together with their social interactions and relationships. The novelty of our study is that we advance the knowledge on the management of tensions in PPPOs by empirically showing the link between field-level institutional logics and practice-level social interactions and relationships and their influences on the responses and resolutions to the issues causing tensions. Our results indicate that tensions arising between public and private actors in PPPOs are primarily responded to by private actors mainly with avoidance, defiance or decoupling and subsequently resolved by their joint efforts through informal collaboration, formalization, formalized collaboration, enforcement or coercive pressure, depending on how the state and market logics are enacted within the hospitals and how social interactions and relationships between public and private side actors are formed accordingly.

Accelerating phase field simulations through a hybrid adaptive Fourier neural operator with U-net backbone

Prolonged contact between a corrosive liquid and metal alloys can cause progressive dealloying. For one such process as liquid-metal dealloying (LMD), phase field models have been developed to understand the mechanisms leading to complex morphologies. However, the LMD governing equations in these models often involve coupled non-linear partial differential equations (PDE), which are challenging to solve numerically. In particular, numerical stiffness in the PDEs requires an extremely refined time step size (on the order of 10−12s or smaller). This computational bottleneck is especially problematic when running LMD simulation until a late time horizon is required. This motivates the development of surrogate models capable of leaping forward in time, by skipping several consecutive time steps at-once. In this paper, we propose a U-shaped adaptive Fourier neural operator (U-AFNO), a machine learning (ML) based model inspired by recent advances in neural operator learning. U-AFNO employs U-Nets for extracting and reconstructing local features within the physical fields, and passes the latent space through a vision transformer (ViT) implemented in the Fourier space (AFNO). We use U-AFNOs to learn the dynamics of mapping the field at a current time step into a later time step. We also identify global quantities of interest (QoI) describing the corrosion process (e.g., the deformation of the liquid-metal interface, lost metal, etc.) and show that our proposed U-AFNO model is able to accurately predict the field dynamics, in spite of the chaotic nature of LMD. Most notably, our model reproduces the key microstructure statistics and QoIs with a level of accuracy on par with the high-fidelity numerical solver, while achieving a significant 11, 200 × speed-up on a high-resolution grid when comparing the computational expense per time step. Finally, we also investigate the opportunity of using hybrid simulations, in which we alternate forward leaps in time using the U-AFNO with high-fidelity time stepping. We demonstrate that while advantageous for some surrogate model design choices, our proposed U-AFNO model in fully auto-regressive settings consistently outperforms hybrid schemes.

Stability of stationary states for mean field models with multichromatic interaction potentials

Abstract We consider weakly interacting diffusions on the torus, for multichromatic interaction potentials. We consider interaction potentials that are not $H$-stable, leading to phase transitions in the mean field limit. We show that the mean field dynamics can exhibit multipeak stationary states, where the number of peaks is related to the number of nonzero Fourier modes of the interaction. We also consider the effect of a confining potential on the structure of non-uniform steady states. We approach the problem by means of analysis, perturbation theory and numerical simulations for the interacting particle systems and the PDEs.

The mechanistical principles and engineering application of roof- cutting for roadway protection in advance of the working face

In coal mining operations, it is often challenging to control the deformation of the roadway in front of the working face. The excessive stress from the surrounding rock of the working face and the difficulties in caving the goaf roof have led to a prominent factor that hinders safe and efficient production in coal mines. For this reason, a mechanical model of the stress field in the advance roadway of the working face is established, and the stress evolution law of the surrounding rock before and after cutting the roof of the roadway is analyzed. Key parameters such as cutting depth, cutting angle, and hole spacing are determined through theoretical calculation, numerical simulation with 3DEC numerical software, and field testing. A kind of roof cutting and pressure relief techniques (TCPAF) for enhanced roadway safeguarding in advance mining face is proposed, and its effectiveness is verified through field testing. The results indicate that the stress on the low-stress side of the leading roadway remains slightly increased, while on the high-stress side, stress decreases significantly, optimizing the stress environment of the surrounding rock. In addition, the research results provide a scientific basis for similar conditions of roadway deformation.

Study on the performance of laser cladding Ni-based WC60 composite coatings

Nickel-based Tungsten Carbide (WC) materials have excellent wear resistance and high temperature stability. They are prone to cracking during laser cladding due to the rapid cooling and heating characteristics. The sensitivity of cracking differs when cladding different substrates, which is a bottleneck for the industry. Quantitatively revealing the laser cladding mechanism of nickel-based WC is significant for optimizing the process. In this paper, a coupling model of the thermal field, flow field, and stress field was established for the laser cladding of nickel-based WC60 on a 42CrMo substrate. The model considered the influence of the powder absorption, surface tension and buoyancy on the flow for liquid metal and focused on analyzing the transient evolution during laser cladding. Cladding samples were prepared and subjected to the X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and microhardness characterization experiments. The morphology and mechanical properties of WC60 based on nickel were observed, and its solidification characteristics were analyzed. The calculations show that the maximum temperature during laser cladding reaches 2529 K, forming an upward Marangoni flow with a maximum velocity of 0.25 m/s. The thermal stress of the cladding layer reaches 616 MPa, and the residual stress reaches 647 MPa. The experiments show that WC particles are spherical and exist in the cladding layer as hard phases, deposited in the middle and lower parts of the cladding layer, which effectively enhances the hardness of cladding layer. WC particles impede columnar crystal growth, and some WC particle boundaries undergo melting, leading to the diffusion of tungsten elements into the cladding layer. This study provides a theoretical basis for optimizing the laser cladding process of nickel-based WC and improving the coating performance.

Surface induced crystallization/amorphization of phase change materials.

Surface-induced crystallization/amorphization of a Germanium-antimony-tellurium nanolayer is investigated using the phase field model. A Ginzburg-Landau (GL) equation introduces an external surface layer (ESL) within which the surface energy and elastic properties are adequately distributed. Next, the coupled GL and elasticity equations for the crystallization/ amorphization are solved. For the initial surface crystalline nucleus, unphysical crystallization along the ESL appears for the ESL widthΔξ⩾2nmwhile oval growth occurs forΔξ⩽1nm. The ESL results in a faster surface nucleus growth than the sharp surface model but does not affect the crystallization rate inside the bulk. Initial homogeneous conditions cause a simultaneous crystallization in the bulk and later in the ESL. The ESL effect on amorphization is studied to determine the ESL width more precisely. For both the initial amorphous nucleus and homogenous conditions, the amorphization temperature shows a reduction from the sharp surface model to the ESL model withΔξ=0.5nmand then remains almost constant for largerΔξ. Combining the above results gives0.5⩽Δξ⩽1nmas a proper range for the ESL width. The ratio of the effective ESL width to the interface width (Δsat/Δη) and the ratio of the difference between the surface energies of transforming phases to the surface energy of the initial phase (Δγ/γin) are considered crucial parameters in determining the ESL effect on the phase transformation and a linear relation asΔsat/Δη≅6.235Δγ/γinis found based on current and previous works, which can help estimate the effective ESL width for any surface-induced transformations.

QPRF: A system to accelerate population receptive field modeling.

BOLD response can be fitted using the population receptive field (PRF) model to reveal how visual input is represented on the cortex (Dumoulin and Wandell, 2008). Fitting the PRF model costs considerable time, often requiring days to analyze BOLD signals for a small cohort of subjects. We introduce the qPRF ("quick PRF"), a system for accelerated PRF modeling that reduced the computation time by a factor >1,000 without losing goodness-of-fit when compared to another widely available PRF modeling package (Kay et al., 2013) on a benchmark of data from the Human Connectome Project (HCP; Van Essen et al. (2013). The system achieves this level of acceleration by pre-computing a tree-like data structure, which it rapidly searches during the fitting step for an optimal parameter combination. We tested the method on a constrained four-parameter version of the PRF model (Strategy 1 herein) and an unconstrained five-parameter PRF model, which the qPRF fitted at comparable speed (Strategy 2). We show how an additional search step can guarantee optimality of qPRF solutions with little additional time cost (Strategy 3). To assess the quality of qPRF solutions, we compared our Strategy 1 solutions to those provided by Benson et al. (2018) who performed a similar four-parameter fit. Both hemispheres of the 181 subjects in the HCP dataset (a total of 10,753,572 vertices, each with a unique BOLD time series of 1800 frames) were analyzed by qPRF in 12.82 h on an ordinary CPU. The absolute difference in R2 achieved by the qPRF compared to Benson et al. (2018) was negligible, with a median of 0.025% (R2 units being between 0% and 100%). In general, the qPRF yielded a slightly better fitting solution, achieving a greater R2 on 70.2% of vertices. We also assess the qPRF method's model-recovery ability using a simulated dataset. The qPRF may facilitate the development and use of more elaborate models based on the PRF framework and may pave the way for novel clinical applications.

Bearing Fault Diagnosis Based on the Markov Transition Field and SE-IShufflenetV2 Model

Bearing Fault Diagnosis Based on the Markov Transition Field and SE-IShufflenetV2 Model

Identifying Disease Associated Multi-Omics Network With Mixed Graphical Models Based on Markov Random Field Model.

In this article, we proposed a new method named fused mixed graphical model (FMGM), which can infer network structures associated with dichotomous phenotypes. FMGM is based on a pairwise Markov random field model, and statistical analyses including the proposed method were conducted to find biological markers and underlying network structures of the atopic dermatitis (AD) from multiomics data of 6-month-old infants. The performance of FMGM was evaluated with simulations by using synthetic datasets of power-law networks, showing that FMGM had superior performance for identifying the differences of the networks compared to the separate inference with the previous method, causalMGM (F1-scores 0.550 vs. 0.730). Furthermore, FMGM was applied to identify multiomics profiles associated with AD, and significance association was found for the correlation between carotenoid biosynthesis and RNA degradation, suggesting the importance of metabolism related to oxidative stress and microbial RNA balance. R codes can be accessed as an R package "fusedMGM," and an example data set and a script for analyses can be found at http://figshare.com/articles/dataset/FMGM_synthetic_data_example_zip/20509113.

Fracture behaviors of microstructured dentin using a phase field model dominated by volume change energy

Fracture behaviors of microstructured dentin using a phase field model dominated by volume change energy

Atomistic-informed phase field modeling of magnesium twin growth by disconnections

The nucleation and propagation of disconnections play an essential role during twin growth. Atomistic methods can reveal such small structural features on twin facets and model their motion, yet are limited by the simulation length and time scales. Alternatively, mesoscale modeling approaches (such as the phase field method) address these constraints of atomistic simulations and can maintain atomic-level accuracy when integrated with atomic-level information. In this work, a phase field model is used to simulate the disconnection-mediated twinning, informed by molecular dynamics (MD) simulations. This work considers the specific case of the growth of {101¯2} twin in magnesium. MD simulations are first conducted to obtain the orientation-dependent interface mobility and motion threshold, and to simulate twin embryo growth and collect facet velocities, which can be used for calibrating the continuum model. The phase field disconnections model, based on the principle of minimum dissipation potential, provides the theoretical framework. This model incorporates a nonconvex grain boundary energy, elasticity and shear coupling, and simulates disconnections as a natural emergence under the elastic driving force. The phase field model is further optimized by including the anisotropic interface mobility and motion threshold suggested by MD simulations. Results agree with MD simulations of twin embryo growth in the aspects of final twin thickness, twin shape, and twin size, as well as the kinetic behavior of twin boundaries and twin tips. The simulated twin microstructure is also consistent with experimental observations, demonstrating the fidelity of the model.

Constraints on axion-like particles from the gamma-ray observation of the Galactic Center

High energy photons originating from the Galactic Center (GC) region have the potential to undergo significant photon-axion-like particle (ALP) oscillation effects, primarily induced by the presence of intense magnetic fields in this region. Observations conducted by imaging atmospheric Cherenkov telescopes have detected very high energy gamma-rays originating from a point source known as HESS J1745-290, situated in close proximity to the GC. This source is conjectured to be associated with the supermassive black hole Sagittarius A*. The GC region contains diverse structures, including molecular clouds and non-thermal filaments, which collectively contribute to the intricate magnetic field configurations in this region. By utilizing a magnetic field model specific in the GC region, we explore the phenomenon of photon-ALP oscillations in the gamma-ray spectrum of HESS J1745-290. Our analysis does not reveal any discernible signature of photon-ALP oscillations, yielding significant constraints that serve as a complement to gamma-ray observations of extragalactic sources across a broad parameter region. The uncertainties arising from the outer Galactic magnetic field models have minor impacts on our results, except for ALP masses around 10-7 eV, as the dominant influence originates from the intense magnetic field strength in the inner GC region.

An adaptive incremental solution scheme for the phase field model of fracture

An adaptive incremental solution scheme for the phase field model of fracture

Impact of parameters in the toroidal blazar jet magnetic field model on axion-like particle constraints

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the γ-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. Many studies focus on a simple jet magnetic field model with a toroidal component exerting a predominant influence on regions far from the central region. While many investigations have explored the effects of ALP-photon oscillations using typical parameter values in this model, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy γ-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the simple toroidal balazar jet magnetic field model, and investigate their impacts on the ALP constraints.

Superconductivity and its Properties: Cooper Pairs, Meissner Effect, London Moment, Gravitomagnetic and Gravitoelectric Processes

The following properties of superconductivity are considered in this work: the creation and destruction of Cooper pairs, “mass defect”, Meissner effect, London moment, gravitomagnetic and gravitoelectric processes. The conducted research has shown that for explanation of the above-mentioned properties of superconductivity it is necessary to investigate the characteristics of physical vacuum. With this aim, the following physical models of physical vacuum are analyzed in the work. The Feynman model of creating of virtual photons by quantum objects, explaining the creation and destruction of Cooper pairs, “mass defect” and partly Meissner effect. The model of physical vacuum consisting of quantum oscillators by A. Einstein and O. Stern and the model of magnetic field by L. I. Sedov. The latter two models are basic for interpretation of Meissner effect, London moment, gravitomagnetic and gravitoelectric processes.

A Novel Map Matching Method Based on Improved Hidden Markov and Conditional Random Fields Model

ABSTRACT Aiming at the inherent “labeling bias” problem of Hidden Markov Models (HMMs) in the process of low-frequency sampling rate GPS trajectory map matching, this paper proposes a map matching method that combines HMMs and Conditional Random Field Models (CRFs). Various features including vehicle driving direction, direction change between candidate roads, shortest path, and spatial localization accuracy of trajectory points are integrated to optimize the state transfer process in the HMM model. The Viterbi algorithm was then employed to calculate the joint probability values of all candidate paths and the path with maximum probability value was selected as the matching path. The proposed map matching method was validated using publicly available Global Positioning System (GPS) vehicle trajectories from Guangzhou, Dongguan, and field-collected vehicle trajectory data from Ganzhou, China. The results demonstrated that the proposed method achieves high matching accuracy while maintaining efficient matching efficiency. The percentage of correct matching of GPS sampling points remains above 95%, and the average calculation time for each candidate road segment is kept within 50 ms. These advancements can greatly benefit location-based services that rely on map matching technology.

Noncommutative Reissner–Nordström Black Hole from Noncommutative Charged Scalar Field

Within the framework of noncommutative (NC) deformation of gauge field theory by the angular twist, we first rederive the NC scalar and gauge field model from our previous papers, and then generalize it to the second order in the Seiberg–Witten (SW) map. It turns out that SW expansion is finite and that it ceases at the second order in the deformation parameter, ultimately giving rise to the equation of motion for the scalar field in the Reissner–Nordström (RN) metric that is nonperturbative and exact at the same order. As a further step, we show that the effective metric put forth and constructed in our previous work satisfies the equations of Einstein–Maxwell gravity, but only within the first order of deformation and when the gauge field is fixed by the Coulomb potential of the charged black hole. Thus, the obtained NC deformation of the Reissner–Nordström (RN) metric appears to have an additional off-diagonal element which scales linearly with a deformation parameter. We analyze various properties of this metric.

Kaons and antikaons in isospin asymmetric dense resonance matter at finite temperature

We study the in-medium properties of kaons and antikaons in isospin asymmetric hot and dense resonance matter within the chiral SU(3) hadronic mean field model. Along with nucleons and hyperons, the interactions of K and K¯ mesons with all decuplet baryons (Δ++,+,0,−,Σ*±,0,Ξ*0,−,Ω−) are explicitly considered in the dispersion relations. The properties of mesons in the chiral SU(3) model are modified at finite density and temperature of asymmetric resonance matter through the exchange of scalar fields σ, ζ, and δ and the vector fields ω, ρ, and ϕ. The presence of resonance baryons in the medium at finite temperature is observed to modify significantly the effective masses of K and K¯ mesons. We also calculated the optical potentials of kaons and antikaons as a function of momentum in resonance matter. The present study of in-medium masses and optical potentials of kaons and antikaons will be important for understanding the experimental observables from the heavy-ion collision experiments where hot and dense matter may be produced. Our results indicate that when resonance baryons are present within the medium at finite baryonic density, the mass reduction of kaons and antikaons becomes more pronounced as the temperature of the medium increases from zero to 100 and 150 MeV. The study of the optical potentials of kaons and antikaons reveals a stronger correlation with strangeness fraction compared to isospin asymmetry. Published by the American Physical Society 2024