Field In Space Research Articles

A novel hybrid superposition method for predicting ship seismic wave in shallow sea

A hybrid superposition method (HSM) is developed for predicting seismic wave in elastic seabed excited by low frequency noise from ship submerged in shallow sea. In the scheme of HSM, an array of distributed equivalent sources interior to a radiator are employed to represent this radiator based on wave superposition principle. The equivalent sources that satisfy the boundary conditions of shallow sea are constructed by making inverse Hanker transform to the depth-dependent Green’s function corresponding to displacement potential by aid of wavenumber integration algorithm. The strengths of equivalent sources are determined by matching normal velocities on the boundary surface of radiator and then modified for ship seismic wave computation. The ship seismic wave is conveniently calculated using the superposition of the fields from the equivalent sources. It is the key feature of HSM that truncating and discretizing the field space are not required for the prediction, which reduces original problem by one dimension, while accurate results are achieved. The performance of the present method including accuracy, stability, and convergence is studied numerically. Simulations indicate that this novel method is outstanding and competitive at predicting ship seismic wave in shallow sea.

Vapor-liquid phase transition in fluctuating hydrodynamics: The most probable transition path and its computation

In this paper, we consider transition events between metastable states in fluid systems modeled by two-phase Navier-Stokes equations with thermal noise. The vapor-liquid phase transition which occurs during the vapor condensation is such an example. We propose a numerical method to compute the transition pathway. We first approximate the continuum hydrodynamics model by the smoothed particle hydrodynamics (SPH). In the SPH formulation, the dynamics of the system take the form of Langevin equations. This allows us to derive conditions that characterize the most probable transition pathway. Then we compute the most probable transition pathway by solving these conditions in the space of mass and momentum density fields using the string method. The force, which is needed to evolve the string in the space of the density fields, is computed by discretizing the deterministic model using the finite difference method. The numerical method is applied to study the condensation of vapor in a periodic cell and the Cassie-Wenzel transition on pillared solid substrates.

Chevalley-Eilenberg algebraic cohomology space of polynomial vector fields Lie algebras on the line

Chevalley-Eilenberg algebraic cohomology space of polynomial vector fields Lie algebras on the line

Theory of In-Cloud Activation of Aerosols and Microphysical Quasi-Equilibrium in a Deep Updraft

Abstract The microphysical quasi-equilibrium in an ascending adiabatic parcel is elucidated by an analytical theory in 0D with drastic simplifications. The theory predicts how in-cloud activation is most likely to be triggered by the onset of precipitation during sufficient ascent, with the ascent only needing to approach almost twice the cloud-base updraft speed aloft. The precipitation and cloud condensate mass fields are coupled in a closed system in a simplified version of the model. The initial state of no precipitation is unstable with respect to a perturbation. In the 2D phase space of both mass fields, there is a neutral line. Unstable growth of precipitation mass drives the system to cross the line into a regime of stability. An attractor is then approached consisting of precipitation mass balanced by accretion of cloud mass and fallout. The cloud-particle number concentration also approaches a stable equilibrium governed by the balance between in-cloud activation aloft from the inexorably increasing supersaturation during vertical acceleration and accretion of cloud droplets by precipitation. Dimensionless numbers characterizing the microphysical equilibria and their stability are derived mathematically, including a condensation–precipitation efficiency and an in-cloud activation efficiency. The theory explains common observations of the orders of magnitude of liquid water content in convective and stratiform clouds. Finally, sensitivity tests of the numerically integrated theoretical equations are documented with respect to variations in cloud condensation nucleus (CCN) aerosols and updraft speed. It is shown that this theory of in-cloud activation, with an increasing supersaturation during ascent, applies to both ice-only and liquid-only cloud. Significance Statement The purpose of the study is to create a theory for how equilibria among cloud-microphysical properties are attained during ascent. Continual initiation of fresh cloud droplets far above cloud base in the free troposphere is explained. The theory proposes a balance between creation and depletion of such droplets, in relation to a balance between creation and fallout of precipitation. The transition from positive feedbacks of instability toward negative feedbacks of stability when the equilibria are approached is elucidated. The theory explains why the mass content of cloud liquid in regions of ascent is typically about an order of magnitude lower in layer clouds with weak ascent than in convective clouds with faster ascent. Any future work could extend the theory to treat dilute parcels or coexistence of supercooled liquid and ice.

Спектральные характеристики рельефа: расчет и использование в морфометрическом картографировании

A methodology for calculating eight spectral terrain characteristics by DEM is given. Their geomorphological meaning and mathematical definition are described. The generalized results of the spectral terrain characteristics calculation for five continents (except for Antarctica and a number of large and small islands and archipelagos) by DEM with a resolution of 1000 m, a step of a moving window of 10 km and its various sizes from 40 to 100 km are presented. The total covered area was 119.3 million sq. km. The results of the continents landform clustering on a small scale by its periodicity are shown – 10 clusters are distinguished using Kohonen neural networks and subsequent hierarchical clustering, which separate different patterns of topographic dissection. The spectral characteristics of the relief that distinguish various areas reflect the typical elevation difference between the watersheds and the bottoms of the valleys, their frequency in space, the unidirectional or multidirectional oscillations of the altitude field, and the prevailing direction itself, etc. Corresponding general map is made.

Cultural Spaces as Political Spaces: The Musical Field of the German Democratic Republic

This article examines the relationship between music and politics in the German Democratic Republic (GDR), departing from the crucial role the State played there in organizing, and controlling all fields of cultural production. Much of the literature on the subject either depicts the interaction between the State and artists as unidirectional or represents their relationship as highly conflictual due to contrasting understandings of culture and its functions. In both cases, this tendency to dichotomize makes it hard to explain, for instance, how music genres that had arisen in Western countries could flourish in the GDR despite the official understanding of ‘socialist music’ propagated by the Socialist Unity Party (SED). Conversely, by adopting a field perspective, this article aims to highlight how musicians, the State, and Party representatives competed to shape the symbolic space of the GDR musical field. Hence, instead of understanding Party and State decisions as merely applications of ideological principles, a field perspective enables us to consider them as resulting from strategies, depending on both the objective position occupied in the musical field and its spatial-material dimension, and as aimed at maintaining their own power within it. The political elite succeeded, then, in actualizing its strategy of legitimating emerging music genres which were potentially disrupting until it was able to provide musicians with physical cultural spaces for developing their careers and, at the same time, expressing criticisms. On the other hand, from the 1950s, localized music scenes were created which proposed an alternative understanding of music to the official one without, however, refusing the core principles which structured the GDR musical field. After the end of the 1970s, though, new music scenes were formed which positioned themselves outside the institutionalized music spaces and places, refusing in this way the rules of the GDR musical field and questioning its very existence.

A combined first- and second-order optimization method for improving convergence of Hartree–Fock and Kohn–Sham calculations

In this work, we investigate the optimization of Hartree-Fock (HF) orbitals with our recently proposed combined first- and second-order (SO-SCI) method, which was originally developed for multi-configuration self-consistent field (MCSCF) and complete active space SCF (CASSCF) calculations. In MCSCF/CASSCF, it unites a second-order optimization of the active orbitals with a Fock-based first-order treatment of the remaining closed-virtual orbital rotations. In the case of the single-determinant wavefunctions, the active space is replaced by a preselected "second-order domain," and all rotations involving orbitals in this subspace are treated at second-order. The method has been implemented for spin-restricted and spin-unrestricted Hartree-Fock (RHF, UHF), configuration-averaged Hartree-Fock (CAHF), as well as Kohn-Sham (KS) density functional theory (RKS, UKS). For each of these cases, various choices of the second-order domain have been tested, and appropriate defaults are proposed. The performance of the method is demonstrated for several transition metal complexes. It is shown that the SO-SCI optimization provides faster and more robust convergence than the standard SCF procedure but requires, in many cases, even less computation time. In difficult cases, the SO-SCI method not only speeds up convergence but also avoids convergence to saddle-points. Furthermore, it helps to find spin-symmetry broken solutions in the cases of UHF or UKS. In the case of CAHF, convergence can also be significantly improved as compared to a previous SCF implementation. This is particularly important for multi-center cases with two or more equal heavy atoms. The performance is demonstrated for various two-center complexes with different lanthanide atoms.

Revisiting small-scale fluctuations in α-attractor models of inflation

Cosmological α-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate α-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. We study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space.In the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non-geodesic motion in field space. The two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. These enhanced scalar perturbations can lead to primordial black hole (PBH) production and second-order gravitational wave (GW) generation.Due to the existence of universal predictions in α-attractors, consistency with current CMB constraints on the large-scale spectral tilt implies that PBHs can only be produced with masses smaller than 108 g and are accompanied by ultra-high frequency GWs, with a peak expected to be at frequencies of order 10 kHz or above.

At the end of the world: Local Dynamical Cobordism

The Cobordism Conjecture states that any Quantum Gravity configuration admits, at topological level, a boundary ending spacetime. We study the dynamical realization of cobordism, as spacetime dependent solutions of Einstein gravity coupled to scalars containing such end-of-the-world ‘branes’. The latter appear in effective theory as a singularity at finite spacetime distance at which scalars go off to infinite field space distance. We provide a local description near the end-of-the-world branes, in which the solutions simplify dramatically and are characterized in terms of a critical exponent, which controls the asymptotic profiles of fields and the universal scaling relations among the spacetime distance to the singularity, the field space distance, and the spacetime curvature. The analysis does not rely on supersymmetry. We study many explicit examples of such Local Dynamical Cobordisms in string theory, including 10d massive IIA, the 10d non-supersymmetric USp(32) theory, Bubbles of Nothing, 4d \U0001d4a9 = 1 cosmic string solutions, the Klebanov-Strassler throat, Dp-brane solutions, brane configurations related to the D1/D5 systems, and small black holes. Our framework encompasses diverse recent setups in which scalars diverge at the core of defects, by regarding them as suitable end-of-the-world branes. We explore the interplay of Local Dynamical Cobordisms with the Distance Conjecture and other swampland constraints.

Spatiotemporal Analysis of Electromagnetic Field Coherence in Complex Media

We study the coherence in time and space of electromagnetic fields propagated through complex media. Whether for localization, imaging, or telecommunication, the development of dedicated numerical techniques is generally based on the exploitation of simplified models considering either coherent or diffuse fields. The optimization of such applications in conditions of partial coherence can therefore be particularly challenging, requiring the development of hybrid algorithms adaptable to prior knowledge on the processed fields. The objective of this work is to provide numerical techniques for decomposing an electromagnetic field into subspaces that can then be filtered according to their level of spatial and temporal coherence. In contrast to the studies carried out on space-space transfer matrices notably used for the calculation of Wigner-Smith operators, these decompositions are carried out on space-time matrices in order to facilitate the study of temporal dispersion. The theory is developed for illustrative purposes using experimental results from a leaky resonant system, but seem to be applicable to any scattering and reverberating media capable of transforming localized and coherent excitations into complex and diffuse distributions. To conclude this work, the proposed technique is exploited to improve image reconstruction in a millimeter-wave computational imaging demonstration. In the studied context and from a more general perspective, we propose a technique to select the most suitable subspaces for each application operating under conditions of partial coherence, whether these correspond in the most extreme cases to ballistic paths or to diffuse fields.

Trocar layouts in laparoscopic liver surgery.

Since the first laparoscopic wedge resection reported by Reich, laparoscopic liver resection (LLR) has been progressively developed, acquiring safety and feasibility. The time has witnessed a milestone leap for laparoscopic hepatectomy from pure laparoscopic partial hepatectomy to anatomical hepatectomy and from minor liver resection to major liver resection. The numerous previous studies have paid more attention to the short-time and long-time surgical outcomes caused by surgical techniques corresponding to various segments and approaches. However, focus on trocar layouts remains poorly described, but it plays an indispensable role in surgical process. We have searched PubMed for English language articles with the key words "trocar," "laparoscopic liver resection," and "liver resection approaches." This review highlighted each type of trocar layouts corresponding to specific circumstances, including targeted resection segments with various approaches. Notably, surgeon preferences and patients body habitus affect the trocar layouts to some extent as well. Although there were fewer researches focus on trocar layouts, they determine the operation field and manipulation space and be likely to have an impact on outcomes of surgery. Therefore, further studies are warranted to firm the role of trocar layouts in LLR.

The Helmholtz decomposition of a space of vector fields with bounded mean oscillation in a bounded domain

We introduce a space of vector fields with bounded mean oscillation whose “tangential” and “normal” components to the boundary behave differently. We establish its Helmholtz decomposition when the domain is bounded. This substantially extends the authors’ earlier result for a half space.

Efficiently rejecting and concentrating Li+ by nanofiltration membrane under a reversed electric field

Efficiently concentrating dilute lithium ion (Li+) solution is very important for the synthesis of Li+ products after Li+ extraction from salt lake brine. In this work, a reversed electric field coupling nanofiltration membrane (RENF) was designed to reject and concentrate Li+ solution from a low concentration feed. The effects of membrane pore structure, electric field and electrode spacing, and feed properties on Li+ rejection of RENF process were investigated. The concentration performance and energy consumption of the RENF process were also explored. Results showed that the NF membrane with a small structural coefficient under an electric field of >8 V/cm exhibited high Li+ rejection. A Li+ rejection of 97.01% by RENF and a high permeation flux were achieved. Likewise, the RENF showed a stable concentrating performance with a high Li+ recovery for dilute Li+ solution. The energy consumption of the RENF process only has a 0.17% increase as compared with the NF process, an order of magnitude lower than that of the RO process. The high rejection performance of RENF was resulted from the synergistic effects of the reversed EF dragging force to cations and sieving effect of the NF membrane with a small structural coefficient.

Bulk reconstruction in moduli space holography

It was recently suggested that certain UV-completable supersymmetric actions can be characterized by the solutions to an auxiliary non-linear sigma-model with special asymptotic boundary conditions. The space-time of this sigma-model is the scalar field space of these effective theories while the target space is a coset space. We study this sigma-model without any reference to a potentially underlying geometric description. Using a holographic approach reminiscent of the bulk reconstruction in the AdS/CFT correspondence, we then derive its near-boundary solutions for a two-dimensional space-time. Specifying a set of Sl(2, ℝ) boundary data we show that the near-boundary solutions are uniquely fixed after imposing a single bulk-boundary matching condition. The reconstruction exploits an elaborate set of recursion relations introduced by Cattani, Kaplan, and Schmid in the proof of the Sl(2)-orbit theorem. We explicitly solve these recursion relations for three sets of simple boundary data and show that they model asymptotic periods of a Calabi-Yau threefold near the conifold point, the large complex structure point, and the Tyurin degeneration.

Geometric structure of multi-form-field isotropic inflation and primordial fluctuations

An inflationary scenario is expected to be embedded into an ultraviolet (UV) complete theory such as string theory. The effect of UV complete theories may appear as nontrivial kinetic terms in the low energy effective field theory, which provides a nontrivial geometry in field space. In this paper, we study the effect of the geometry of multi-form-field space on an inflationary scenario. In particular, we focus on the geometric destabilization mechanism which induces the phase transition from the conventional slow-roll inflation to a novel inflationary scenario. Anisotropic inflation is a typical example of the new phase. To conform to observations, we restrict us to isotropic configuration of form fields. We clarify the conditions for the onset of the destabilization and reveal the geometric structure of attractors after the destabilization. We classify the viable models from the observational point of view. We also investigate the features of the primordial fluctuations and find the similarity to hyperbolic inflation. By calculating the power spectrum, we make several phenomenological predictions which are useful to discriminate our models from others inflation models. We found the scalar-to-tensor r will be suppressed by large one-form gauge fields, while it has the same order as the slow roll parameter r ∼ \U0001d4aa(1)ϵ for large two-from gauge fields.

The motivation and teaching strategies in pre-service physical education teachers

Coronavirus disease 2019 (COVID-19) pandemics significantly affect teaching and learning. Especially physical education teaching that emphasizes practice in the field or large space. On the other hand, physical education classes must do online teaching, which leads to students not being interested in learning. This reason affects the teacher's motivation, making most teachers bored to teach without motivation. Specifically, in the pre-service physical educators who have low experience in teaching and leads to unenjoyed in their class. Consequently, pre-service physical educators need to find new strategies to teach students to be of greater interest. Thus, this study examined the relationship between teachers' motivation (intrinsic and external motivation) towards teaching strategies among pre-service physical educators. The instruments were regarding teachers' motivation in terms of intrinsic and external motivation and teaching strategies. The respondents were 157 pre-service physical educators in five universities in the border provinces of Southern Thailand. The result showed that there is a relationship between intrinsic and external motivation towards teaching strategies among the participants. These results provide guidelines for pre-service physical educators to improve their teaching and enhance students' achievement in the future through online physical education classes.

Investigation of Asymmetric Consequent-Pole Hybrid Excited Flux Reversal Machines

This article proposes and investigates two asymmetric consequent-pole hybrid excited flux reversal machine (AS-CP-HEFRM) topologies, which have same numbers of iron poles and permanent magnets (PMs) with concentrated ac and dc windings on each stator pole and a salient pole rotor. If PM number on one stator pole is larger than 1, PMs are magnetized radially in the same direction on one stator pole, while opposite on adjacent stator poles. The phenomenon of the phase shift between the flux linkages of dc and PM excitations in the AS-CP-HEFRMs is revealed for the first time, which will weaken the regulation of dc excitation field to PM produced field. The elimination condition of the phase shift is derived and verified by finite-element analysis in this article, which can be considered as design guidelines in AS-CP-HEFRMs. Airgap magnetic field space harmonics of AS-CP-HEFRM are also investigated and verified by finite-element analyses. Meanwhile, the relationship between the rotor pole number and the stator pole arc (PM ratio) is derived and verified by global optimization based on genetic algorithm for maximum average torque. The influence of stator/rotor pole number combinations is also studied and compared in terms of torque, torque ripple, and flux regulation capability. The torque components produced by airgap magnetic field space harmonics are calculated and compared. A prototype has been built and tested to validate the finite element calculations.

Embeddings and Integrable Charges for Extended Corner Symmetry.

We revisit the problem of extending the phase space of diffeomorphism-invariant theories to account for embeddings associated with the boundary of subregions. We do so by emphasizing the importance of a careful treatment of embeddings in all aspects of the covariant phase space formalism. In so doing we introduce a new notion of the extension of field space associated with the embeddings which has the important feature that the Noether charges associated with all extended corner symmetries are in fact integrable, but not necessarily conserved. We give an intuitive understanding of this description. We then show that the charges give a representation of the extended corner symmetry via the Poisson bracket, without central extension.

Multiple field ultraslow-roll inflation: Primordial black holes from straight bulk and distorted boundary

We study a model of two-field ultra-slow-roll (USR) inflation bounded by a curve in the field space. Curvature perturbations and non-Gaussianities can be enhanced both during the USR phase and from the inhomogeneities at the boundary. We employ the full non-linear $\delta N$ formalism to calculate the probability distribution function (PDF) for curvature perturbation non-perturbatively and show that the non-linear effects can significantly enhance the abundance of the primordial black holes (PBHs). For large curvature perturbations, the PDF has a universal exponential tail, but for the intermediate values, the PDF -- and, therefore, the abundance of the PBHs -- depend sensitively on the geometry of the boundary.

Four coupled SYK models and nearly AdS2 gravities: phase transitions in traversable wormholes and in bra-ket wormholes

We study four coupled Sachdev–Ye–Kitaev (SYK) models and nearly AdS2 gravities. In the SYK model side, we construct a model that couples two copies of two coupled SYK models. In nearly AdS2 gravity side, we entangle matter fields in two copies of traversable wormholes. In both cases, the systems show first order phase transitions at zero temperature by changing couplings, which is understood as the exchange of traversable wormhole configurations. In nearly AdS2 gravity cases, by exchanging the role of space and time the wormholes are interpreted as bra-ket wormholes. In Lorentzian signature, these bra-ket wormholes lead to two closed universes that are entangled with each other as well as matter fields in the flat space where we do not have dynamical gravity. We study the effect of projection or entangling operation for matters on flat spaces and they cause phase transitions in bra-ket wormholes, which leads to the pair annihilation of closed universes. Using these bra-ket wormholes, we discuss the way to embed states in 2D holographic CFTs into Hilbert space of many 2D free fields.