Field Method Research Articles

Effect of Electric Fields on the Decomposition of Phosphate Esters.

Phosphate esters decompose on metal surfaces and form protective polyphosphate films. For many applications, such as in lubricants for electric vehicles and wind turbines, an understanding of the effect of electric fields on molecular decomposition is urgently required. Experimental investigations have yielded contradictory results, with some suggesting that electric fields improve tribological performance, while others have reported the opposite effect. Here, we use nonequilibrium molecular dynamics (NEMD) simulations to study the decomposition of tri-n-butyl phosphate (TNBP) molecules nanoconfined between ferrous surfaces (iron and iron oxide) under electrostatic fields. The reactive force field (ReaxFF) method is used to model the effects of chemical bonding and molecular dissociation. We show that the charge transfer with the polarization current equalization (QTPIE) method gives more realistic behavior compared to the standard charge equilibration (QEq) method under applied electrostatic fields. The rate of TNBP decomposition via carbon-oxygen bond dissociation is faster in the nanoconfined systems than that in the bulk due to the catalytic action of the surfaces. In all cases, the application of an electric field accelerates TNBP decomposition. When electric fields are applied to the confined systems, the phosphate anions are pulled toward the surface with high electric potential, while the alkyl cations are pulled to the surface with lower potential, leading to asymmetric film growth. Analysis of the temperature- and electric field strength-dependent dissociation rate constants using the Arrhenius equation suggests that, on reactive iron surfaces, the increased reactivity under an applied electric field is driven mostly by an increase in the pre-exponential factor, which is linked to the number of molecule-surface collisions. Conversely, the accelerated decomposition of TNBP on iron oxide surfaces can be attributed to a reduction in the activation energy with increasing electric field strength. Single-molecule nudged-elastic band (NEB) calculations also show a linear reduction in the energy barrier for carbon-oxygen bond breaking with electric field strength, due to stabilization of the charged transition state. The simulation results are consistent with experimental observations of enhanced and asymmetric tribofilm growth under electrostatic fields.

Neutral pion polarizabilities from four-point functions in lattice QCD

We report a proof-of-principle lattice QCD simulation of the electric and magnetic polarizabilities for a neutral pion in the four-point function method. The results are based on the same quenched Wilson ensembles on a 243×48 lattice at β=6.0 with pion mass from 1100 to 370 MeV previously used for a charged pion. For electric polarizability, the results are largely consistent with those from the background field method and ChPT. In contrast, there are significant differences for magnetic polarizability among the four-point function method, the background field method, and ChPT. The situation points to the important role of disconnected diagrams for a neutral pion. We elucidate a transparent quark decomposition in the four-point function method that can be used to shed light on the issue.

Understanding the Intellectual Approaches of the Archaeology of ‘Rōhaṇa’ from the 1840s to 1960s: A Literature Review

The archaeology of Rōhaṇa entails a focus on comprehending ‘Rōhaṇa’ from material perspectives. Originating in the mid-19th century CE, this approach evolved with diverse theoretical, methodological, and technological dimensions in alignment with the scholarly context of its time. This paper constitutes an investigation into the available sources explaining the progression of archaeological studies on Rōhaṇa from the 1840s to the 1960s, highlighting the contributions of individuals often identified as British Colonial Officers, Antiquarians, and Archaeologists. While extant research has predominantly centred on elucidating Rōhaṇa, it has overlooked an exploration of the intellectual practices of the scholars involved. Consequently, this paper aims to comprehend the intellectual approaches employed in existing scholarly works on Rōhaṇa. This study uses qualitative methods in secondary research to analyse sources such as published accounts and reports by British officers, archaeological field reports and other significant studies by local scholars. Examining the methodologies, findings, and conclusions of these selected studies reveals their collective contribution to the intellectual understanding of Rōhaṇa from a material perspective. In conclusion, antiquarian methods initially identified Rōhaṇa as the southern administrative division, with Māgama serving as its capital. Subsequently, archaeological initiatives expanded this knowledge through field methods, providing insights into regional settlement patterns. Over time, inquiries into the historicity of Rōhaṇa emerged, evolving the understanding of this region by the mid-20th century.

Shutdown dose rate calculation for fission reactors: An application of the MS-CADIS method to OPAL

There have been considerable advances of shutdown dose rate (SDDR) calculation methods for fusion related problems, however applications of these methods in the fission reactor field have hitherto been sparse. The present study attempts to bridge this gap by investigating the applicability of SDDR calculation methods for fission reactor problems. Specifically, we aim to assess and validate whether recent advances in SDDR methods can be successfully applied in fission research reactors. To this end, we estimate the shutdown dose rate distribution at the Open Pool Australian Light water reactor (OPAL) using the rigorous two step (R2S) computational method, and we compare the calculated results with the experimental data. This method utilizes a 3D reactor model implemented in the Monte Carlo N-Particle (MCNP) transport code, the AutomeD VAriaNce reduction Generator (ADVANTG) code for geometry discretization and variance reduction calculations, and the Oak Ridge Isotope GENeration (ORIGEN) inventory code for activation calculations. To ensure robustness, we employ two variance reduction techniques, Forward Weighted Consistent Adjoint Driven Importance Sampling (FW-CADIS) and Multi-Step Consistent Adjoint Driven Importance Sampling (MS-CADIS). To the best of our knowledge, this is the first MS-CADIS method implementation for fission reactor problems. The SDDR is estimated at ten locations within the experimental hall, all situated more than 4 m away from the reactor core.The paper shows that, the experimental observations are within the lower and upper bounds of the simulation results for 4 out of 10 locations, while the remaining observations are within a factor of 7, with one significant outlier. The calculated average dose rate is within 5% of the nominal values of the experimental observations for 3 locations. The computational results are within statistical uncertainty by using two different variance reduction techniques, with significant computational advantage of MS-CADIS over FW-CADIS for SDDR calculations. The results indicate that the combination of SDDR distribution maps, estimated dose rate energy dependance, and activation information are powerful tools in identifying the radioisotopes and reactor components dominating the SDDR. These results can contribute to better radiation safety practices in contaminated areas, by enabling the minimal dose path planning or by improving radiation shielding.

An online prediction method of three-dimensional machining residual stress field based on IncepU-net

The magnitude and distribution of residual stress field inside thin-walled parts is a critical factor influencing machining deformation. Traditional methods relying on offline data struggle to rapidly and accurately predict evolutionary state of residual stress fields, due to the time-varying and nonlinear characteristics in machining. This paper presents an online prediction method for residual stress in machining thin-walled parts based on deep learning. The multi-channel vector model is proposed to incorporate geometric, physical, and process information as input for deep learning models. A deep learning framework utilizing the IncepU-net network is developed and trained using both experimental and finite element simulation data. Results indicate a mean error of 6.2 MPa compared to experimental values, with an overall prediction time of 0.17 s. The proposed method can online predict the magnitude and distribution of residual stress field in machining, which offers cost-effectiveness and strong generalization capabilities.

Effectiveness of the use of chickpea collection samples in breeding

Aim. To determine the breeding value the large number of collection chickpea (Cicer arietinum L.) varieties obtained from the International Crops Research Institute for the Semi-Arid Tropics (India, Patancheru, ICRISAT) and the National Center for Plant Genetic Resources of Ukraine (Kharkiv) was evaluated in 1995-2022 under the conditions of the steppe zone of Ukraine. Methods. Standard field and laboratory methods (phenological observations, hybridization, structural analysis, biochemical analysis of protein content in seeds according to the Kjeldahl method), statistical analysis. Results. Donors and sources of such economically valuable features as early maturity, increased productivity, protein content in seeds, large-seeded, resistance against pathogens on an artificially created infectious background were identified. The set of 12 varieties of chickpea were developed by artificial hybridization, which are recommended for cultivation in all zones of Ukraine. Conclusions.The characteristics of the created varieties are given, the most valuable collection genotypes for use in crossing programs are recommended.

Crack patterns in masonry structures using phase field method

This work aims to study the crack pattern in masonry-like structures by a simplified description of the mediumusing a variational damage model. In literature, when modeling fractures in masonry structures, capturingboth fracture types, cracks in units, and cracks at the interface simultaneously, usually requires a complicated scheme. The phase-field method has been widely used recently because of its robustness in capturing variousfracture types. In this work, we consider the mortar and the interface (between the mortar and units) as a thickinterface layer with pseudo-material properties. We conduct numerical tests on a bending beam and a tensilewall using strategies of material properties with a phase field model. As it is not distinguished the crack in themortar and the brick-mortar interface, it is shown in this work that both types of fracture, in the thick interfacelayer and the unit, can be captured just using the phase field method and the simplified micro model.

Micron resolved Quantum precision measurement of magnetic field at Tesla level

Abstract We develop a quantum precision measurement method of magnetic field at Tesla level, utilizing a fiber diamond magnetometer. Central to our system is a micron-sized fiber diamond probe positioned on the surface of a coplanar waveguide made of nonmagnetic materials. Calibrated with the nuclear magnetic resonance (NMR) magnetometer, this probe demonstrates a broad magnetic field range from 10 mT to 1.5 T with a nonlinear error better than 0.0028% under standard magnetic field generator, and stability better than 0.0012% at a 1.5 T magnetic field. Finally, we demonstrate quantitative mapping of the vector magnetic field on the surface of a permanent magnet using the diamond magnetometer.

Three-loop renormalization of the quantum action for a five-dimensional scalar cubic model with the usage of the background field method and a cutoff regularization

Three-loop renormalization of the quantum action for a five-dimensional scalar cubic model with the usage of the background field method and a cutoff regularization

Factors of winter moisture movement in arable soils of the Ishim steppe

Based on the materials of long-term field observations in the southern regions of the Omsk region, the influence of the main factors on the winter movement of moisture in arable soils of the Ishim steppe was traced. The penetration depth of 0 °С determines the lower boundary and vertical thickness of the moisture freezing layer. The distance between its lower edge and the penetration depth of 0 °С is 20–40 cm. The penetration depth of 0 °С is predetermined by the air temperature and the thickness of the snow cover and reaches 170–240 cm. The forms of moisture dominant in the soil are associated with the granulometric composition. Film moisture prevails in the heavy loamy, highly silty soil-ground strata of the Ishim steppe. The content of capillary-backed and free gravitational water does not exceed 6% of the soil volume at full moisture capacity, which determines the small volume of moisture freezing (up to 50 mm). Thermogradient migration of moisture is determined by field methods in highly moistened soil-ground strata. High humidity of the soils and rocks of the Ishim steppe is associated with their granulometric composition and the close occurrence of groundwater. If in the second ten days of October groundwater is recorded at a depth of less than 3 m, the layer of moisture freezing at the end of March is noted in the depth range between 40–80 and 160–200 cm, the volume of cryogenic accumulation is 30–50 mm, including in the upper meter layer – 10–25 mm. If groundwater is detected at a depth of more than 3 m in the autumn, the freezing layer is fixed at 80 to 160–200 cm, the moisture gain in it is 15–30 mm, in the 0–100 cm layer the moisture content does not change. The role of cryogenic accumulation in replenishing the post-vegetation moisture deficit in the root layer of spring grains is modest. This process is significant for the formation of conditions for anaerobiosis and the development of modern hydromorphism in the lower soil horizons and in the subsoil strata.

NON-DESTRUCTIVE METHODS OF ESTABLISHING A CAUSE-AND-EFFECT RELATIONSHIP BETWEEN WATER SUPPLY NETWORK ACCIDENTS AND THE CONDITIONS FOR PRESERVING ARCHITECTURAL HERITAGE

Accidents on water supply networks have the most significant negative consequences on the state of the historical and architectural heritage, which was formed over many centuries. The paper analyzes the cause-and-effect relationship between accidents of water-carrying networks and the conditions of architectural heritage preservation using the example of the Kyiv-Pechersk Lavra. The results of determining waterlogging zones and their factors by non-destructive monitoring methods on the territory of the Metropolitan Garden of the Upper Lavra are given. This area combines complex engineering and geological conditions and technogenic mastering, creating conditions for developing dangerous engineering and geological processes and emergency situations. In terms of danger, the garden’s territory belongs to unstable areas for preserving historical monuments of the UNESCO world heritage. The last accident on the water supply networks occurred in October 2022. It caused sinkholes on the surface, rising groundwater levels, significant destruction of an underground structure of historical importance – the Metropolitan Cellar. The research was carried out using the methods of electrotomography and natural electric field. The results of electrotomography were interpreted using two- and three-dimensional models. The existence of an anomalous dome (soils of low resistance), which is observed in the central part of the site, is probably the focus of waterlogging of the soil massif as a result of an accident on the heating network. The analysis of the adapted 3D model based on the results of non-destructive methods of monitoring the geological environment made it possible to indirectly establish the places of unsatisfactory technical condition of engineering networks (cold water supply), where a wetted section with low values of apparent resistance was recorded. Research has confirmed the presence of an inflow of man-made waters (leaks) from main water supply networks in the western part of all profiles as a constant source and factor of waterlogging of the array of soil bases of architectural monuments – Monastyrski walls, Kushnyka tower, etc. Based on the research results, the need to develop compensatory measures to strengthen part of the fortress walls was proposed, and a safe distance for moving networks from historical objects was substantiated to preserve them.

Jamming avoidance trajectory planning and load balancing user association in mmWave UAV-assisted HetECN

Emergency communication network (ECN) can provide fast, efficient and high-capacity communication services for specific areas by using mmWave transmission and unmanned aerial vehicles (UAVs) serving as aerial base stations (ABSs) or relay nodes. Now, in order to satisfy diverse demands, ECN should support different types of nodes, access methods, and traffic distributions, which is referred to as heterogeneous ECN (HetECN). Therefore, inappropriate trajectory planning and unbalanced traffic loading can lead to UAV flight collisions and network congestion. In this article, we jointly optimize UAV jamming avoidance trajectory and user association strategy aimed to load balancing, to maximize the utilization of HetECN. Specifically, an improved artificial potential field (APF) method along with mmWave beam forming technology is used to obtain the jamming avoidance trajectory of UAVs, and the optimal deployment location of UAVs are determined based on the distribution of ground users (GUs). Subsequently, the matching game and alliance game are comprehensively used to determine the load balancing based GU-UAV associated strategy under various GU demands, thereby ensuring traffic load balancing and resource optimization allocation. In addition, altitude fine-tuning have been made to further power consumption, thereby improving overall network efficiency. Simulation results demonstrate that the proposed method can achieve the expected performance in network utilities such as coverage rate, network capacity, load balancing effect of mmWave UAV-assisted HetECNs.

Efficient large-scale scene representation with a hybrid of high-resolution grid and plane features

Existing neural radiance fields (NeRF) methods for large-scale scene modeling require days of training using multiple GPUs, hindering their applications in scenarios with limited computing resources. Radiance field models based on explicit dense or hash grid features have been proposed for fast optimization, but their effectiveness has mainly been demonstrated in the context of object-scale scene representation. In this paper, we point out that the low feature resolution in explicit representation is the bottleneck for large-scale unbounded scene representation. To address this problem, we introduce a new and efficient hybrid feature representation for NeRF that fuses the 3D hash-grids and high-resolution 2D dense plane features. Compared with the dense-grid representation, the resolution of a dense 2D plane can be scaled up more efficiently. Based on this hybrid representation, we propose a fast optimization NeRF variant, called GP-NeRF, that achieves better rendering results while maintaining a compact model size. Extensive experiments on multiple large-scale unbounded scene datasets show that our model can converge in 1.5 h using a single GPU while achieving results comparable to or even better than the existing method that requires about one day’s training with 8 GPUs. Our code can be found at https://zyqz97.github.io/GP_NeRF/.

A Pseudo-Exponential-Based Artificial Potential Field Method for UAV Cluster Control under Static and Dynamical Obstacles

A Pseudo-Exponential-Based Artificial Potential Field Method for UAV Cluster Control under Static and Dynamical Obstacles

A comprehensive literature review and bibliometric analysis on shape grammar theory and applications in architecture

Shape Grammar is a systematic tool used in the logical argumentive method in research for interpreting spatial design and activities. Shape grammar applies a group of shape rules in stages to create a set or a language of design. Researchers worldwide have used this method in various fields including architecture, arts, graphical design, and pattern recognition. Even in the case of architecture, researchers worldwide have implemented the shape grammar method to analyze patterns in various architectural fields. This study analyzed publication trends in the shape grammar domain using “Bibliometrix”, an open-source tool that uses the R package. Research papers from the Web of Science and Scopus (WoS) database were identified and assessed in terms of annual publication trends, contributions of various authors, countries, citation counts of authors, universities, popular keywords, journal trends, etc. A comprehensive literature review of all relevant research papers available in the WoS and Scopus academic databases on shape grammar and its application in architecture was also conducted as part of this study. The research paper concludes with the possible research opportunities in the domain of shape grammar.

Variational damage model: A novel consistent approach to fracture

The computational modeling of fractures in solids using damage mechanics faces challenge when dealing with complex crack topologies. One effective approach to address this challenge is by reformulating damage mechanics within a variational framework. In this paper, we present a novel variational damage model that incorporates a threshold value to prevent damage initiation at low energy levels. The proposed model defines fracture energy density (ϕ˜) and damage field (s) based on the energy density (ϕ), crack energy release rate (Gc), and crack length scale (ℓ). Specifically, if ϕ≤Gc2ℓ, then ϕ˜=ϕ and s=0; otherwise, ϕ˜=−Gc24ℓ21ϕ+Gcℓ and s=1−Gc2ℓ1ϕ. Furthermore, we extend the model with a threshold value to a higher-order version. Utilizing this functional, we derive the governing equation for fractures that evolve automatically with ease. The formulation can be seamlessly integrated into conventional finite element methods for elastic solids with minimal modifications. The proposed formulation offers sharper crack interfaces compared to phase field methods using the same mesh density. We demonstrate the capabilities of our approach through representative numerical examples in both 2D and 3D, including static fracture problems, cohesive fractures, and dynamic fractures. The open-source code is available on GitHub via the link https://github.com/hl-ren/vdm.

Research on the Safety Design and Trajectory Planning for a New Dual Upper Limb Rehabilitation Robot

The increasing utilization of upper limb rehabilitation robots in rehabilitation therapy has brought to light significant safety concerns regarding their mechanical structures and control systems. This study focuses on a six degrees of freedom (DOF) upper limb rehabilitation robot, which has been designed with an emphasis on safety through careful consideration of its mechanical structure and trajectory planning. Various parameter schemes for the shoulder joint angles were proposed, and the robotic arm’s structure was developed by analyzing the spatial motion trajectories of the shoulder joint motor. This design successfully achieves the objective of minimizing the installation space while maximizing the range of motion. Additionally, an enhanced artificial field method is introduced to facilitate the planning of self-collision avoidance trajectories for dual-arm movements. This approach effectively mitigates the risk of collisions between the robotic arm and the human body, as well as between the two robotic arms, during movement. The efficacy of this method has been validated through experimental testing.

An influence of electronic structure theory method, thermodynamic and implicit solvation corrections on the organic carbonates conformational and binding energies.

An impact of an electronic structure or force field method, gas-phase thermodynamic correction, and continuum solvation model on organic carbonate clusters (S)n conformational and binding energies is explored. None of the tested force field (GFN-FF, GAFF, MMFF94) and standard semiempirical methods (PM3, AM1, RM1, PM6, PM6-D3, PM6-D3H4, PM7) can reproduce reference RI-SCS-MP2 conformational energies. Tight-binding GFNn-xTB methods provide more realistic conformational energies which are accurate enough to discard the least stable conformers. The effect of thermodynamic correction is moderate and can be ignored if the gas phase conformational stability ranking is a goal. The influence of continuum solvation is stronger, especially if reinforced with the Gibbs free energy thermodynamic correction, and results in the reduced spread of conformational energies. The cluster formation binding energies strongly depend on a particular approach to vibrational thermochemistry with the difference between traditional harmonic and modified scaled rigid - harmonic oscillator approximations reaching 10 kcal mol-1.

Numerical Simulation of Thermal–Mechanical Coupling in Laser–Metal Inert Gas Hybrid Welding Considering Grain Heterogeneity and Study of Phase Field Method during Solidification Process

Numerical Simulation of Thermal–Mechanical Coupling in Laser–Metal Inert Gas Hybrid Welding Considering Grain Heterogeneity and Study of Phase Field Method during Solidification Process

High-Efficiency Forward Modeling of Gravitational Fields in Spherical Harmonic Domain with Application to Lunar Topography Correction

Gravity forward modeling as a basic tool has been widely used for topography correction and 3D density inversion. The source region is usually discretized into tesseroids (i.e., spherical prisms) to consider the influence of the curvature of planets in global or large-scale problems. Traditional gravity forward modeling methods in spherical coordinates, including the Taylor expansion and Gaussian–Legendre quadrature, are all based on spatial domains, which mostly have low computational efficiency. This study proposes a high-efficiency forward modeling method of gravitational fields in the spherical harmonic domain, in which the gravity anomalies and gradient tensors can be expressed as spherical harmonic synthesis forms of spherical harmonic coefficients of 3D density distribution. A homogeneous spherical shell model is used to test its effectiveness compared with traditional spatial domain methods. It demonstrates that the computational efficiency of the proposed spherical harmonic domain method is improved by four orders of magnitude with a similar level of computational accuracy compared with the optimized 3D GLQ method. The test also shows that the computational time of the proposed method is not affected by the observation height. Finally, the proposed forward method is applied to the topography correction of the Moon. The results show that the gravity response of the topography obtained with our method is close to that of the optimized 3D GLQ method and is also consistent with previous results.