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The processing of potential field datasets requires many steps; one of them is the inverse modeling of potential field data. Using a measurement dataset, the purpose is to evaluate the physical and geometric properties of an unidentified model in the subsurface. Because of the ill-posedness of the inverse problem, the determination of an acceptable solution requires the imposition of a regularization term to stabilize the inversion process. We also need a regularization parameter that determines the comparative weights of the stabilization and data fit terms. This work offers an evaluation of automated strategies for the estimation of the regularization parameter for underdetermined linear inverse problems. We look at the methods of generalized cross validation, active constraint balancing (ACB), the discrepancy principle, and the unbiased predictive risk estimator. It has been shown that the ACB technique is superior by applying the algorithms to both synthetic data and field data, which produces density models that are representative of real structures and demonstrate the method's supremacy. Data acquired over the chromite deposit in Camaguey, Cuba, are utilized to corroborate the procedures for the inversion of experimental data. The findings gathered from the three-dimensional inversion of gravity data from this region demonstrate that the ACB approach gives appropriate estimations of anomalous density structures and depth resolution inside the subsurface. [ABSTRACT FROM AUTHOR]

In the context of chameleon gravity, we present a semi-analytical solution of the chameleon field profile in an accurately modelled galaxy cluster's mass components, namely the stellar mass of the Brightest Cluster Galaxy (BCG), the baryonic mass in galaxies other than the BCG, the mass of the Intra-Cluster Medium (ICM) and the diffuse cold dark matter (CDM). The obtained semi-analytic profile is validated against the numerical solution of the chameleon field equation and implemented in the MG-MAMPOSSt code for kinematic analyses of galaxy clusters in modified gravity scenarios. By means of mock halos, simulated both in GR and in modified gravity, we show that the combination of the velocities and positions of cluster member galaxies, along with the data of the stellar velocity dispersion profile of the BCG, can impose constraints on the parameter space of the chameleon model; for a cluster generated in GR, these constraints are at the same level as a joint lensing+kinematics analysis of a cluster modelled with a single mass profile, without the BCG data. [ABSTRACT FROM AUTHOR]

The gravity gradient anomaly zone is produced due to density differences on both sides of a fault. Tracking of extreme points enables the characterization and description of fault locations. However, for some deep-seated faults with large burial depths and secondary faults with moderate burial depths, the gravity horizontal total gradient anomaly must be enhanced using the concept of dip angle to strengthen the weak anomaly extraction for the identification of more fault information. This method was used to predict five regional deep-seated faults and six secondary faults in the Miquan region. The fracture plane extends in a near north-northeast direction; that is, it mostly expands out of the study area, spreads out in a trumpet shape to the southwest, and converges to the northeast. Fracture activity is an important factor in controlling structural units or local structures. The Miquan block is located in a complex structural zone in front of the Bogeda Mountains, which have very complex surface and subsurface geological conditions, and seismic data are unideal. Therefore, fracture prediction results using gravity data are important in-depth understanding of the structure in this area. [ABSTRACT FROM AUTHOR]

The results of the visualization of the matter transfer processes in colored free-fall drops, which mix with a transparent target fluid are analyzed. The parametrization is carried out basing on the system of fundamental equations of fluid mechanics which includes the equations of state for the density and the Gibbs potential. The contribution of different mechanisms of energy transfer is discussed; these are the macroscopic (including flows, waves, and vortices) and microscopic (dissipative and conversional) ones. The radiation transfer effect is not considered. The technique of the present-day experiments is descried, which allows to record accompanying acoustic signals together with the highly-resolving videorecording of colored flow pictures. The flow structure, dynamics, and energetics are analyzed for different density ratios of the confluent fluids and the kinetic and potential surface energies (PSE) of the drop. The conditions of the establishment of certain selected regimes, such as intrusive drop inflow, impact breakdown in fibers, and an intermediate hovering and rebound regime, are determined. A drop flowing smoothly into the fluid thickness at a small contact velocity in the intrusive regime forms a connected body. Thin trickles containing the matter of both media are formed in the contact spot in the impact mode. The fibrous wakes of the trickles form lineate and reticular structures on the fluid surface and within its thickness. In the intermediate regime the drop can hover on the fluid surface, touch it, merge partially with it, and rebound with the loss of the matter. The evolution of gas cavities and bubbles radiating acoustic packets is traced. The necessity of taking account for all the mechanisms of total energy transfer in describing hydrodynamics and acoustics of drop flows is noted. [ABSTRACT FROM AUTHOR]

In a recent paper, black holes were viewed as topological thermodynamic defects using generalized off-shell free energy. The aforementioned work indicates that all black hole solutions in the pure Einstein–Maxwell gravity theory could be classified into three different topological classes for four and higher spacetime dimensions. In this paper, we investigate the topological number of BTZ black holes in distinct theories with different charges (Q) and rotational parameters (J) . Using generalized free energy and Duan's ϕ -mapping topological current theory, we found only two topological classes for BTZ spacetime. Particularly, for a BTZ black hole with rotation or in the Einstein–Power–Maxwell theory, there is only one zero point and the total topological number is 1. While for a BTZ black hole in new massive gravity, the global topological charge depends on the value of the specific parameter m, which provides a counter-example for the conjecture that the topological number is independent of the black hole's parameters. [ABSTRACT FROM AUTHOR]

The basic problem of the calculus of variations consists of finding a function that minimizes an energy, like finding the fastest trajectory between two points for a point mass in a gravity field or finding the best shape of a wing. The existence of a solution may be established in quite abstract spaces, much larger than the space of smooth functions. An important practical problem is that of being able to approach the value of the infimum of the energy. However, numerical methods work with very "concrete" functions and sometimes they are unable to approximate the infimum: this is the surprising Lavrentiev phenomenon. The papers that ensure the nonoccurrence of the phenomenon form a recent saga, and the most general result formulated in the early '90s was actually fully proved just recently, more than 30 years later. Our aim here is to introduce the reader to the calculus of variations, to illustrate the Lavrentiev phenomenon with the simplest known example, and to give an elementary proof of the nonoccurrence of the phenomenon. [ABSTRACT FROM AUTHOR]

Recent years have seen the development of multiple in silico lung models, notably with the aim of improving patient care for pulmonary diseases. These models vary in complexity and typically only consider the implementation of pleural pressure, a depression that keeps the lungs inflated. Gravity, often considered negligible compared to pleural pressure, has been largely overlooked, also due to the complexity of formulating physiological boundary conditions to counterbalance it. However, gravity is known to affect pulmonary functions, such as ventilation. In this study, we incorporated gravity into a recent lung poromechanical model. To do so, in addition to the gravitational body force, we proposed novel boundary conditions consisting in a heterogeneous pleural pressure field constrained to counterbalance gravity to reach global equilibrium of applied forces. We assessed the impact of gravity on the global and local behavior of the model, including the pressure–volume response and porosity field. Our findings reveal that gravity, despite being small, influences lung response. Specifically, the inclusion of gravity in our model led to the emergence of heterogeneities in deformation and stress distribution, compatible with in vivo imaging data. This could provide valuable insights for predicting the progression of certain pulmonary diseases by correlating areas subjected to higher deformation and stresses with disease evolution patterns. [ABSTRACT FROM AUTHOR]

We consider the Bianchi type-VI0 space time with domain walls in the framework of the modified f (R, T) theory of gravitation. To solve the field equations, we assume that the shear scalar σ is proportional to the expansion scalar θ. We also consider the parametrization of the equation of the state parameter of barotropic fluid and discuss the effect on domain walls. It has been observed that the domain wall may behave like dark energy. Some physical parameters are also discussed in detail. [ABSTRACT FROM AUTHOR]

Understanding the effects of gravity on manufacturing processes is a pioneering extension of the process parameter space used to date. Until now, the improvement of manufacturing technologies has mainly focused on process parameters such as temperature, pressure, and material composition, as access to variable gravity environments is limited. The Einstein-Elevator opens up new possibilities for the variation of these process parameters and the development of in-space manufacturing technologies. Together with the research of innovative production processes for optical components within the PhoenixD Cluster of Excellence, this creates an entirely new field of research. The research presented here focuses on investigating gravity's effects on dispensed optical lens production. Using a jet dispenser, sessile droplets are produced during a flight phase in the Einstein-Elevator and cured directly by UV polymerization. As part of this study, optical lenses were produced and compared under microgravity and Earth's gravitational conditions. Geometric properties such as height and contact angle of the lenses produced were analyzed. It was found that lenses fabricated under microgravity have a larger contact angle than those fabricated under Earth gravity. Similarly, the height increases with decreasing gravity. These results are consistent with the theoretical assumptions described, although generalized theories to describe the morphology of a sessile droplet are not yet available. The case study findings on the influence of gravity as a process parameter on drop morphology represent a fundamental improvement for additive manufacturing technologies, especially for in-space manufacturing. [ABSTRACT FROM AUTHOR]

The application of the centrifugal pendulum vibration absorber (CPVA) has expanded from the aerospace sector to the automotive sector. To date, in most previous studies, viscous damping has been assumed to be present between the absorber and rotor, and damping has been neglected in other studies. To reflect and control the dynamic behaviour of the CPVA in vehicular applications realistically, a hybrid damping model incorporating viscous damping and rolling resistance was developed in this study and validated by conducting tests. Under the combined action of the centrifugal force, gravity, viscous resistance, and rolling resistance, an equation of motion of the CPVA was established using the Lagrangian function equation of the second type. The wear state of the kinematic pair between the absorber and rotor, which is common in practical applications, was included into a mathematical model in which the rolling resistance coefficient changes with the travel of the absorber, whereas the viscous resistance coefficient remains unchanged. A model was established to simulate the response of the absorber under a wide range of working conditions, and corresponding tests were performed. Compared with the results obtained using only viscous damping as reported in other studies, those of the proposed hybrid damping model are more consistent with the experimental results. This work fills the existing research gap and lays a foundation for further control of the dynamic behaviour of CPVAs in the gravitational field, particularly at low rotational speeds. [ABSTRACT FROM AUTHOR]

We construct exact analytical Taub-NUT solutions in the context of f(T) gravity. We study the physical properties of the solutions, and compare them with those of the Taub-NUT solution in Einstein gravity. [ABSTRACT FROM AUTHOR]

The strong gravitational potential of neutron stars (NSs) makes them ideal astrophysical objects for testing extreme gravity phenomena. We explore the potential of NS X-ray pulsed light curve observations to probe deviations from general relativity (GR) within the scalar–tensor theory (STT) of gravity framework. We compute the flux from a single, circular, finite-size hot spot, accounting for light bending, Shapiro time delay, and Doppler effect. We focus on the high-compactness regime, i.e., close to the critical GR value G M / (c 2 R) = 0.284 , over which multiple images of the spot appear and impact crucially the light curves. Our investigation is motivated by the increased sensitivity of the pulse to the scalar charge of the spacetime in such high compactness regimes, making these systems exceptionally suitable for scrutinizing deviations from GR, notably phenomena such as spontaneous scalarization, as predicted by STT. We find significant differences in NS observables, e.g., the flux of a single spot can differ up to 80% with respect to GR. Additionally, reasonable choices for the STT parameters that satisfy astrophysical constraints lead to changes in the NS radius relative to GR of up to approximately 10%. Consequently, scalar parameters might be better constrained when uncertainties in NS radii decrease, where this could occur with the advent of next-generation gravitational wave detectors, such as the Einstein Telescope and LISA, as well as future electromagnetic missions like eXTP and ATHENA. Thus, our findings suggest that accurate X-ray data of the NS surface emission, jointly with refined theoretical models, could constrain STTs. [ABSTRACT FROM AUTHOR]

Using the dynamical systems approach together with the cosmographic parameters, we present a model-independent dynamical system formulation for cosmology in f(R) gravity. The formulation is model-independent in the sense that one needs to specify not a particular functional form of f(R) a-priori, but rather a particular cosmological evolution, which fixes the cosmography. In a sense, our approach is the way around the reconstruction method. This is shown using both non-compact and compact dynamical variables. The focus in this paper is on the compact analysis since we demonstrate the applicability of this formulation using examples of bouncing and cyclic cosmology. In particular, our analysis reveals, in a model-independent manner, the problem of achieving such cosmologies when the universe is globally spatially flat and devoid of matter. [ABSTRACT FROM AUTHOR]

In this paper, we investigate one of the established methods for reconstructing modified gravity models from a dark energy model, with the aim of discovering relationships between these theories. In this study, we focus on the f(R, T) modified gravity theory, where R denotes the Ricci scalar and T represents the trace of the energy–momentum tensor. We employ Barrow's holographic dark energy model, derived from fractal surfaces of black holes, to investigate the reconstruction process. The numerical results are subsequently presented for various infrared cutoffs, such as the Hubble horizon, future event horizon, and Granda–Oliveros cutoff. [ABSTRACT FROM AUTHOR]

We study the Energy Conditions in modified f (G) gravity, with G being the topological Gauss–Bonnet term. Then we use the cosmographic parameters to constrain the functional form of the gravitational action and investigate the possibility to have standard inflation in the early time. Specifically, we select models containing symmetries within the modified f (G) theory and obtain conditions for which (i) the energy conditions can be violated and (ii) the magnitude of the slow-roll parameters is small, thus suggesting that under given limits the analyzed theory can potentially trace the cosmic history both at early and at the late times. [ABSTRACT FROM AUTHOR]

We analyse neutral and charged matter distributions in second order Lovelock gravity, also known as Einstein–Gauss–Bonnet gravity, in arbitrary dimensions for a static, spherically symmetric spacetime. We first transform the charged condition of pressure isotropy, an Abel differential equation of the second kind, into canonical form. We then determine a systematic approach to integrate the condition of pressure isotropy by showing that the canonical form is a Chini differential equation. The Chini invariant, which allows the master differential equation to be separable, is identified. This enables us to find three new general solutions, in implicit form, to the condition of pressure isotropy. We also show that previously obtained exact specific solutions arise as special cases in our general class of models. The Chini invariant does not arise in general relativity; it is a distinguishing feature of Einstein–Gauss–Bonnet gravity. [ABSTRACT FROM AUTHOR]

We explore wormhole solutions sourced by Casimir energy density involving generalized uncertainty principle corrections within the framework of Rastall–Rainbow gravity. The questions of traversability and stability, as well as the presence of exotic matter, are carefully investigated. In particular, the stability issue is addressed via an approach that has not been previously employed in the context of wormholes. This method, which represents an improved version of the so-called Herrera cracking technique, has the potential to yield novel insights in the field of wormhole geometries. [ABSTRACT FROM AUTHOR]

In this paper, we explore a stationary BTZ space-time within the framework of modified gravity theory, specifically focusing on Ricci-inverse gravity. It is important to clarify that "Ricci-inverse" refers to the inverse of the Ricci tensor, not the Ricci scalar. We consider a general class of this gravity theory, where the function f is defined by f (R , A , A μ ν A μ ν) , with R and A representing the Ricci and anti-curvature scalars, respectively and A μ ν is the anti-curvature tensor. We demonstrate that stationary BTZ space-time is a valid solution in this gravity theory, wherein the cosmological constant undergoes modifications due to the coupling constants. Moreover, we study another modified gravity theory known as f (R) -gravity and analyze the stationary BTZ space-time. Subsequently, we fully integrate the geodesic equations for BTZ space-time constructed within the Ricci-Inverse gravity, expressing the solutions in terms of elementary functions and compared with the GR result. We classify different types of geodesics, including null and time-like geodesics, under three conditions: (i) nonzero mass and angular momentum, M ≠ 0 , J ≠ 0 , (ii) massless BTZ space-time, M = 0 and J = 0 , and (iii) M = - 1 , J = 0 , that is A d S 3 -type, and analyze the results in modified gravity theories and compare with the general relativity case. [ABSTRACT FROM AUTHOR]

The Tolman–Ehrenfest criterion for the thermal equilibrium of a fluid at rest in a static general-relativistic geometry is generalized to scalar–tensor gravity. Surprisingly, the gravitational scalar field, which fixes the strength of the effective gravitational coupling, does not play a role in determining thermal equilibrium. As a result, heat does not sink more in a gravitational field where gravity is stronger. [ABSTRACT FROM AUTHOR]

Spontaneous scalarization in Einstein-scalar-Gauss–Bonnet theory admits both vacuum-general relativity (GR) and scalarized hairy black holes as valid solutions, which provides a distinctive signature of new physics in strong gravity regime. In this paper, we shall examine the optical features of Gauss–Bonnet black holes with spontaneous scalarization, which is governed by the coupling parameter λ . We find that the photon sphere, critical impact parameter and innermost stable circular orbit all decrease as the increasing of λ . Using observable data from Event Horizon Telescope, we establish the upper limit for λ . Then we construct the optical appearances of the scalarized black holes illuminated by various thin accretions. Our findings reveal that the scalarized black holes consistently exhibit smaller shadow sizes and reduced brightness compared to Schwarzschild black holes. Notably, in the case of thin spherical accretion, the shadow of the scalarized black hole is smaller, but the surrounding bright ring is more pronounced. Our results highlight the observable features of the scalarized black holes, providing a distinguishable probe from their counterpart in GR in strong gravity regime. [ABSTRACT FROM AUTHOR]

A particular extension of Einstein's General Relativity up to and including quartic terms in the curvature tensor is minimal in the sense that it has a unique maximally symmetric vacuum and only a massless spin-2 excitation in its spectrum around the vacuum. We study the inflation phase of the universe in this minimal quartic extension of Einstein's gravity in the presence of trace anomaly terms coming from the Standard Model fields and the fields of the Minimal Supersymmetric Standard Model. We show that the theory allows a quasi-de Sitter phase with sufficient e-foldings. [ABSTRACT FROM AUTHOR]

In various fields of mathematical research, the Brouwer degree is a potent tool for topological analysis. By using the Brouwer degree defined in one-dimensional space, we interpret the equation of state for temperature in black hole thermodynamics, T = T (V , x i) , as a spinodal curve, with its derivative defining a new function f. The sign of the slope of f indicates the topological charge of the black hole's critical points, and the total topological charge can be deduced from the asymptotic behavior of the function f. We analyze a spherical hairy black hole within the framework of Lovelock gravity, paying particular attention to the topological structure of black hole thermodynamics under Gauss–Bonnet gravity. Here, the sign of the scalar hair parameter influences the topological classification of uncharged black holes. When exploring the thermodynamic topological properties of hairy black holes under cubic Lovelock gravity, we find that the spherical hairy black hole reproduces the thermodynamic topological classification results seen under Gauss–Bonnet gravity. [ABSTRACT FROM AUTHOR]

This "vision document" is about what the future has in store for tests of general relativity with gravitational wave detectors. I will make an honest attempt to answer this question by addressing the role of inspiral-based and ringdown-based tests; recent progress on quasinormal modes in modified theories of gravity; the complementarity between light ring tests and ringdown tests; and the interesting possibility of observing some of the nonlinear effects predicted by general relativity. I may well prove to be wrong. To quote Yogi Berra: "It's hard to make predictions, especially about the future". [ABSTRACT FROM AUTHOR]

In this work, we have obtained new phantom fluid-type traversable wormhole (WH) solutions in the context of f (R , T) modified gravity. We investigate the potential that some equations of state (EoS), specifically phantom energy, which describes the accelerated expansion of the universe, could support the existence of traversable wormholes. This cosmic fluid thus offers us a plausible explanation for the occurrence of WH geometries. We construct two WH models with matter Lagrangian density L m = - (- ρ + P r + 2 P t) and inspect numerous characteristics of these models under the WH geometry. The first WH solution (WH-I) is discovered by utilising a linear barotropic equation of state (EoS) connected with phantom energy ω < - 1 indicating the presence of the phantom fluid and pointing to the Universe's expansion, while in the second WH (WH-II) solution, we take into account an interesting EoS ρ = η (P t - P r) to generate a WH model. Additionally, it showed that the phantom fluid WH-I solution violates the radial null energy condition (NEC) while tangential NEC is satisfied. On the other hand, for the WH-II solution, NEC is violated. Extensive detailed discussions of the matter components have been done via graphical analysis. The obtained WH geometries satisfy a stable WH's physically acceptable criteria. [ABSTRACT FROM AUTHOR]

In the field of complex network analysis, accurately identifying key nodes is crucial for understanding and controlling information propagation. Although several local centrality methods have been proposed, their accuracy may be compromised if interactions between nodes and their neighbors are not fully considered. To address this issue, this paper proposes a key node identification method based on multilayer neighbor node gravity and information entropy (MNNGE). The method works as follows: First, the relative gravity of the nodes is calculated based on their weights. Second, the direct gravity of the nodes is calculated by considering the attributes of neighboring nodes, thus capturing interactions within local triangular structures. Finally, the centrality of the nodes is obtained by aggregating the relative and direct gravity of multilayer neighbor nodes using information entropy. To validate the effectiveness of the MNNGE method, we conducted experiments on various real-world network datasets, using evaluation metrics such as the susceptible-infected-recovered (SIR) model, Kendall τ correlation coefficient, Jaccard similarity coefficient, monotonicity, and complementary cumulative distribution function. Our results demonstrate that MNNGE can identify key nodes more accurately than other methods, without requiring parameter settings, and is suitable for large-scale complex networks. [ABSTRACT FROM AUTHOR]

This paper presents the discontinuous energy fields-field, which is the replacement for spacetime in discontinuum physics, the conservation of the absorption and emission process discontinuity, of Bohr's atomic model, as an emitted electromagnetic radiation discontinuity, and Einstein's theory that electromagnetic radiation transfers inertia from an emitting body to an absorbing body leads to a dark, nonordinary matter that has the property of gravity. [ABSTRACT FROM AUTHOR]

Simple Summary: Animal species show marked variations in their cerebrovascular responses to substances that affect blood vessel tone, like noradrenaline, histamine, acetylcholine, 5-hydroxytryptamine, angiotensin II, and bradykinin. These variations may result from the receptor subtype distribution in smooth muscle or endothelial cells, and reflect the interplay of evolutionary and genetic influences for different animal species. Recently, we have investigated whether and how the response to one of these substances, noradrenaline, is related to deviations from an even heart-to-head alignment in an animal's normal posture (which has implications for the gravitational effect on blood flow), for multiple species. Sika deer are even-toed ungulates, closely related to cattle. Close phylogenetic relatives have often been found to show similar cerebrovascular responses, but deer and cattle have a very different heart-to-head alignment. Accordingly, we compared the cerebrovascular responses between sika deer and other ungulates. We found that deer and other even-toed ungulates have similar cerebrovascular responses to histamine, bradykinin, Nω-nitro-L-arginine, and indomethacin (evaluated with cattle), but different responses to noradrenaline and acetylcholine (evaluated with pigs and cattle). We considered that cerebrovascular responses to noradrenaline may positively correlate with gravity (as it affects blood flow in a normal posture) in quadrupedal animals. Gravity may exert species-specific effects on quadrupedal vasoreactivity, reflecting variations in the vertical displacement of the cardiocranial axis from the dorsal plane. Deer show markedly displaced cardiocranial axes compared to their closest phylogenetic relatives, but their relative cerebrovascular responses remain unelucidated. Accordingly, we investigated the responses to noradrenaline (NA), acetylcholine (ACh), 5-hydroxytryptamine (5-HT), histamine, angiotensin (Ang) II, and bradykinin (BK) in cervine basilar arterial rings. NA and 5-HT induced slight contraction, and ACh induced relaxation, which contrasts with the findings reported in pigs and cattle. The cumulative response to ACh was abolished by endothelial denudation and inhibited by Nω-nitro-L-arginine (a nitric oxide synthase inhibitor), atropine (a nonselective muscarinic antagonist), and p-fluoro-hexahydro-sila-difenidol (an M3 antagonist). Pirenzepine (an M1 antagonist) and methoctramine (an M2 antagonist) showed no significant effects. Histamine induced contractions, with its concentration–response curve shifted to the right in parallel by diphenhydramine (an H1 antagonist). However, cimetidine (an H2 antagonist) showed no significant effects. Ang II and BK had no vasomotive effects. NA and ACh induced different cerebrovascular responses in sika deer versus cattle, but histamine and BK did not. Our findings suggest that cerebrovascular responses are influenced by the similarity of animal species and the head and heart positions relative to gravity. [ABSTRACT FROM AUTHOR]

As a key component of remote-sensing technology, satellite gravity observation offers extensive coverage and high accuracy, effectively compensating for the shortcomings of terrestrial gravity measurements. Three-dimensional gravity data inversion can predict the physical property and spatial distribution of geological formations beneath the surface by analyzing the gravity data. In this paper, the heat source position within the Gonghe Basin's geothermal system is identified through the analysis of satellite gravity data, and a constrained deep-learning inversion method is proposed. This method adds the fitting data constraints and depth-weighting function into the network model establishment of deep learning, and trains the network through a large number of datasets, so that the network is constrained by physical information in the training process to obtain the results with a better data-fitting accuracy and higher depth resolution. The proposed method is employed to verify the synthetic model data, and the inversion results indicated that, compared to other methods, the deep-learning gravity inversion method with the addition of physical information constraints has a higher inversion accuracy and depth resolution. Finally, the inversion results based on satellite gravity data revealed the presence of numerous low-density bodies in the underground range of 10–35 km in the research area. It is speculated that this part could be the heat source of the geothermal system in the Gonghe Basin. The findings from this study are expected to contribute to a deeper comprehension of the formation of the geothermal system in the region. [ABSTRACT FROM AUTHOR]

Accurate subsurface imaging is crucial for understanding complex geological structures. Traditional approaches often involve separate inversion of different geophysical datasets, which may not fully capture the structural similarities between the models. Joint inversion, integrating multiple datasets, offers a more comprehensive view by enhancing the resolution and the accuracy of subsurface models. In this study, we propose a joint inversion technique for DC resistivity and vertical gravity gradient data, leveraging the cross-gradient constraint to enforce structural similarities between the resulting models. This method is applied to both synthetic and real datasets, including case studies involving qanats in Iran and a dolerite dyke in South Africa. The results demonstrate that joint inversion significantly improves the accuracy of resistivity and density models compared to independent inversion, particularly in resolving intricate geological features. This approach has proven effective in enhancing subsurface mapping for multi-disciplinary purposes, including resource exploration, heritage conservation, and risk mitigation for the built environment. [ABSTRACT FROM AUTHOR]

There is ongoing interest in the nonmetricity formulation of gravity. The nonlinear extension of the theory, called f (Q) gravity, has recently been proposed and offers a promising avenue for addressing some of the long-standing challenges in cosmology and fundamental physics. A number of solutions have already been found that have confirmed the usefulness of the theory for astrophysics and cosmology. Motivated by earlier work on Gödel-type spacetimes, we investigate whether f (Q) gravity admits such cosmological solutions, which entail causality violation. In the coincident gauge, which is shown to be a legitimate gauge because the connection field equations are satisfied, we find that Gödel-type metrics are allowed by this modified gravity theory for any function f (Q). Noncausal and causal solutions exist depending on the matter content. For a perfect fluid, out of all Gödel-type metrics only Gödel's original model is allowed in f (Q) gravity, implying violation of causality. The requirement that energy conditions be obeyed by the fluid leads to mild restrictions on f (Q). For a massless scalar field in the presence of a cosmological constant, there are causal solutions for any reasonable function f (Q). [ABSTRACT FROM AUTHOR]

We introduce a theoretical framework to alleviate the Hubble tension. This framework is based on dynamics of a minimally coupled scalar field which either belongs to the Brans–Dicke theory with a self-interacting potential or is the scalar partner of f (R) gravity. These two theories are dynamically equivalent when the Brans–Dicke parameter is zero. We will use the dynamical equivalence to interpret the Hubble tension in the same theoretical framework. For both theories, we write one set of field equations in which the value of a parameter distinguishes between the two theories. We will show that H 0 actually evolves with redshift so that its value is consistent with that measured from the local distance ladder and then drops to the value measured from CMB at high redshift. We argue that even though both theories exhibit this behavior, Brans–Dicke theory with an exponential potential is more successful than power-law f (R) gravity to relieve the Hubble tension. [ABSTRACT FROM AUTHOR]

We put forward a novel method of constructing unfolded formulations of field theories, which is based on initial fixation of the form of an unfolded field and subsequent looking for the corresponding unfolded equation as an identity that this field satisfies. Making use of this method, we find an unfolded formulation for 4d scalar electrodynamics. By considering a symmetry-breaking scalar potential, we study the implementation of the Higgs mechanism within the framework of the unfolded dynamics approach. We explore a deformation of unfolded modules in the symmetry-broken phase and identify a non-invertible unfolded-field redefinition that diagonalizes the higgsed system. [ABSTRACT FROM AUTHOR]

We consider some of the epistemic benefits of exploring "theory space" in the context of modifications of general relativity with intended applications in cosmology. We show how studying modifications of general relativity can help in assessing the robustness of empirical inferences, particularly in inaccessible regimes. We also discuss challenges to sharply distinguishing apparently distinct directions in theory space. [ABSTRACT FROM AUTHOR]

Teleparallel gravity, an empirically equivalent counterpart to general relativity, represents the influence of gravity using torsional forces. It raises questions about theory interpretation and underdetermination. To better understand the torsional forces of teleparallel gravity, we consider a context in which forces are better understood: classical spacetimes. We propose a method of incorporating torsion into the classical spacetime context that yields a classical theory of gravity with a closed temporal metric and spacetime torsion. We then prove a result analogous to the Trautman degeometrization theorem: that every model of Newton–Cartan theory gives rise, non-uniquely, to a model of this theory. [ABSTRACT FROM AUTHOR]

Background/Objectives: The flexibility deficits of hip flexors have been identified as potential biomechanical risk factors for the lumbo–pelvic–hip complex, with postural repercussions on the trunk and lower limbs. The purpose of this study was to conduct a single gravity stretching experiment and to monitor its acute and prolonged effects. Methods: The sample comprised 14 healthy participants (8 females and 6 males). Data were collected during two-day measurement sessions. These analyzed via Kinovea software. The single intervention (i.e., gravity stretching) was performed on the first day. A modified Thomas test was used at the same time in two ways, both as a measurement and as an intervention tool. Stretching was achieved by relaxing in a position to perform the modified Thomas test where, each participant lies completely relaxed for 3 min, allowing gravity to stretch the hip flexors of the examined limb. Results: After intervention, a significant acute increase in hip extension range of motion and a decrease in knee extension range of motion were found. We did not find any significant prolonged effects; moreover, after 48 h, the hip range of motion almost returned to the initial value. Conclusions: A single 3 min stretch is very effective in terms of achieving immediate changes in the range of motion, but insufficient for long-term improvements in flexibility. [ABSTRACT FROM AUTHOR]

This paper presents a finite‐differences 3D numerical model that simulates the gravity and thermal structure of the Corsica‐Sardinia Block (CSB), an apparently stable lithospheric domain characterized by cryptic tectonic activity. In the experiments, we change the density and heat production rate of the model crust within a range of geologically realistic values to fit the measured Bouguer gravity anomaly and surface heat flow pattern. The discrepancy between the observed geophysical structure and the outcomes of numerical modelling are discussed in relation to the composition of the CSB crust and finally recast in the geodynamic framework of the western Mediterranean region. [ABSTRACT FROM AUTHOR]

The control of bilateral teleoperation systems with time-varying delays is a challenging problem that is frequently addressed with advanced control techniques. Widely known controllers, like Proportional-Derivative (PD) and Proportional-Integral-Derivative (PID), are seldom employed independently and are typically combined with other approaches, or at least with gravity compensation. This work aims to address a gap in the analysis of bilateral systems by demonstrating that the standard PID control law alone can achieve regulation in these systems when a human operator moves any of the robots while exchanging delayed positions. Experimental results are consistent with the theoretical analysis. Additionally, to illustrate the high degree of robustness of the standard PID, further experiments are conducted in constrained motion, both with and without force feedback. [ABSTRACT FROM AUTHOR]

The introductory paper sets the stage for the research essays in the special issue. It provides an overview of the concepts of minilateralism and the context in which minilateralism has become an alternative form of collective action by states in the international arena, in particular in the Indo-Pacific region that has emerged as the new centre of gravity in world politics. How has minilateralism become a prominent feature of inter-state cooperation in the early twenty-first century, and how is it often used to complement (and in some cases, even substitute for) traditional international organisations, which are based on more liberal and inclusive multilateral norms and principles, but suffering from functional deficits? In a world of more diffuse power, how can minilateralism offer states an expanded toolset for pursuing their policy preferences and advancing their interests? At the same time, the paper also highlights the potential negatives of (or challenges to) minilateralism, including difficulties emanating from a narrowly framed agenda that perpetuates certain narratives, a leadership vacuum that could emerge from non-hierarchical arrangements, and questions about how to achieve support and legitimacy with low institutionalisation. [ABSTRACT FROM AUTHOR]

A new coordinate system on the tangent space to planar configurations is introduced to simplify some calculations on central configurations and relative equilibria in the N-body problem with a homogeneous potential, which includes the case of Newtonian gravity. These coordinates are applied to some problems on four-body central configurations to illustrate their utility. [ABSTRACT FROM AUTHOR]

The effect of gravity based on the vector sum of gravity and buoyancy forces working spontaneously for all species was introduced into capillary electrophoresis (CE) as another important force which cooperated with electrophoretic flow and electro-osmotic flow. Their portion was adjusted by simply tilting the whole of the capillary at an angle during CE running. The related formula was proposed and verified through a series of experiments. After investigating the related parameters, results showed that the gravity effect was significantly affected by additives in the buffer, the length, and the inner diameter of the capillary, and the size of the sample molecule. This made the different ions with opposite or significantly different mobilities to be observed at a CE run. It significantly improved separation efficiencies of some small molecules, chiral compounds, macromolecules and cells when the tilt angles of the capillary were adjusted to a special range predicted through the fitting curve. In addition, micrometer level microspheres and cells were firstly separated by the new CE strategy and the resolutions were more than 1.0. After ingeniously designing the gradient of the tilting angle with time, we were able to further enhance the separation efficiency of the targets. For example, the resolution of lysozyme and ribonuclease A could be increased from 3.691 to 7.342. These indicated the huge potential of the new CE strategy and its gradient mode in separation. [ABSTRACT FROM AUTHOR]

We describe the development and assessment of a new terrestrial reference frame (TRF) based on a combination of geodetic techniques at the observation level over the period 2010–2022. Included in the solution are observations from the Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). A key feature of our solution strategy is the use of space ties in low‐Earth orbit to connect SLR to GPS. Though the resulting TRF solution is based on only 12.6 years of data, it is competitive with the international (ITRF2020) standard in terms of fundamental frame parameters (origin and scale) and their temporal evolution, both linear and seasonal. The relative rates of origin (3D) and scale (at Earth's surface) are 0.2 mm yr−1 ${\text{yr}}^{-1}$ and 0.1 mm yr−1 ${\text{yr}}^{-1}$ respectively. Absolute scale and 3D origin (at epoch 2015.0) both differ by 2–3 mm. In addition to station positions and velocities, our combined solution includes Earth orientation parameters (EOP), low‐degree zonal coefficients (J2 and J3) of the geopotential and precise orbit solutions for all participating satellites (GPS, GRACE and GRACE Follow‐on tandems, Jason 2 and 3, and LAGEOS 1 and 2). We discuss potential benefits of our solution strategy and characterize the impacts of our new TRF on estimates of geocenter motion and sea level change from satellite altimetry. Plain Language Summary: An accurate terrestrial reference frame (TRF) provides a stable and enduring foundation for many metric observations of the changing Earth, whether they are collected by instruments on the ground or satellites in orbit. Powerful new measurements of changing sea levels, ice sheets, crustal motion and ground deformations are placing significant demands on the accuracy of the TRF. We describe an efficient method for realizing the frame which combines different geodetic techniques at the observation level, taking advantage of elemental tracking data from a diverse network of ground stations, artificial satellites at various altitudes and even super massive black holes (quasars) representing point sources at infinity. Our approach opens up new avenues for improving the TRF and also answering fundamental science questions that depend on it. Key Points: An accurate and stable terrestrial reference frame (TRF) is realized by combining geodetic techniques at the observation levelIn linking satellite geodetic techniques, traditional ground survey ties are replaced by space ties from low‐Earth orbitersAlternative approach to TRF is efficient and robust, providing the basis for accurate monitoring of geocenter motion and sea level [ABSTRACT FROM AUTHOR]

In this work, we study scalar field perturbations for a three-dimensional hairy black hole and gravitational soliton, both asymptotically dS3. These spacetimes are three-dimensional backgrounds of New Massive Gravity. We analytically calculate their quasinormal frequencies, where in the case of the hairy black hole the quasinormal modes are stable and we find normal modes on the gravitational soliton, which corresponds to a non-dissipative system. [ABSTRACT FROM AUTHOR]

This paper considers the case where multiple tariff schemes (e.g. general and preferential schemes) are available between trading countries. We incorporate these tariffs into gravity equations and estimate them by the Pseudo-Poisson maximum likelihood technique. The results show that omitting either tariff type leads to significant estimates biases. If fixed effects to control other tariffs are not included in the model, both preferential and general tariffs are to be introduced in the gravity equation. Indeed, some estimation results for precision metals show that reducing both types of tariffs contributes to significantly increasing trade values. However, reducing general tariffs does not always have a trade-enhancing effect. In leather products, for example, its impact was insignificant. Nevertheless, the reduction of preferential tariffs was again found to increase trade values significantly. [ABSTRACT FROM AUTHOR]

The hypergravity centrifugal shaking table (HCST) is the most effective means for studying the disaster effects of rock and soil earthquakes, and the accurate control of acceleration waveform recurrence is the critical problem. This paper compares the dynamic characteristics of the normal gravity shaking table (NGST) and the HCST, highlighting the latter's particularities, and analyzes the limitations of the existing control strategy. Meanwhile, a hypergravity unidirectional airborne shaking table (HUAST) is designed, and a data-driven iterative learning control and two-degree-of-freedom control-based acceleration waveform reproduction strategy is proposed and experimentally verified. • The research object is based on the hypergravity shaking table. • A 2-DOF servo control structure of shaking table is proposed. • The iterative learning was combined with the data-driven identification algorithm. • The shaking table is used to verify the effectiveness and advancement of the proposed composite control strategy. [ABSTRACT FROM AUTHOR]

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The oil recovery from the water-alternating-gas (WAG) injection process is significantly impacted by gravity, viscous fingering, and the permeability heterogeneity of the reservoir. Therefore, the combined effect of these parameters cannot be neglected in the WAG injection process. This article presents the development of a mathematical model of oil recovery and its solution for the WAG injection process that takes into account the combined effects of miscibility change, viscous fingering, gravity, and permeability heterogeneity in an inclined stratified reservoir. First, the governing equations and fractional flow functions were explained in relation to the effects of gravity, permeability heterogeneity, viscous fingering, and miscibility change in an inclined stratified porous medium. Then, a mathematical model was developed using fractional flow functions and conservation equations for both injected water and solvent. The model was generated in the form of a quasi-linear first-order partial differential equation, which was solved analytically in two dimensions (2-D) utilizing vector calculus. Next, this model was solved analytically by applying wave theory to practical constant pressure boundary conditions, which generate distinct waves at different times to provide pressure and saturation at the displacement front location. The total volumetric flux and breakthrough time are calculated from the analytical solution at various times. The presented analytical solutions can be used to predict different parameters for stratified porous media in a fast and efficient way. Finally, the results of analytical solution validated with high-resolution numerical simulation for a wide range of permeability heterogeneity, which shows excellent agreement for breakthrough time, saturation, and pressure versus displacement location of different waves at different times. This analytical solution will save time and money by offering guidance to engineers for analyzing the saturation and pressure distribution at different times and predicting oil recovery. It will also improve the understanding of the physics underlying the multiphase flow WAG injection process in heterogeneous reservoirs. [ABSTRACT FROM AUTHOR]

Purpose: The main objective of this paper is to examine the impact of COVID-19 on the tourism flows of eight Asia-Pacific Countries: Australia, Hong Kong, Malaysia, New Zealand, the Philippines, Singapore, Taiwan and Thailand. Design/methodology/approach: Using monthly data from 2019M1 to 2021M10 and 48 origin and eight destination countries in a panel Poisson pseudo-maximum likelihood (PPML) estimation technique and gravity equation framework, this paper finds that after controlling for gravity determinants, COVID-19 periods have a 0.689% lower tourism inflow than in non-COVID-19 periods. The total observations in this paper are 12,138. Findings: A 1% increase in COVID-19 transmission in the origin country leads to a 0.037% decline in tourism flow in the destination country, while the reduction is just 0.011% from the destination. On the mortality side, the corresponding decline in tourism flows from origin countries is 0.030%, whereas it is 0.038% from destination countries. A 1% increase in vaccine intensity in the destination country leads to a 0.10% improvement in tourism flows, whereas vaccinations at the source have no statistically significant effect. The results are also robust at a 1% level in a pooled OLS and random-effects specification for the same model. Research limitations/implications: The findings provide insights into managing tourism flows concerning transmission, death and vaccination coverage in destination and origin countries. Practical implications: The COVID-19-induced tourism decline may also be considered another channel through which the global recession has been aggravated. If we convert this decline in terms of loss of GDP, the global figure will be huge, and airline industries will have to cut down many service products for a long time to recover from the COVID-19-induced tourism decline. Social implications: It is to be realized by the policymaker and politicians that infectious diseases have no national boundary, and the problem is not local or national. That's why it is to be faced globally with cooperation from all the countries. Originality/value: This is the first paper to address tourism disruption due to COVID-19 in eight Asia-Pacific countries using a gravity model framework. Highlights: Asia-Pacific countries are traditionally globalized through tourism channels This pattern was severely affected by COVID-19 transmission and mortality and improved through vaccination The gravity model can be used to quantify the loss in the tourism sector due to COVID-19 shocks Transmission and mortality should be controlled both at the origin and the destination countries Vaccinations in destination countries significantly raise tourism flows [ABSTRACT FROM AUTHOR]

This study proposes the threshold level of steering effort to reduce rollover accidents. There is much research about the causes of rollover behavior during driving. The center of gravity height, tread length of road wheels, tire properties, and ESC is among the leading causes of rollover of vehicles. An enormous amount of research was done on those factors. First, the steering effort threshold value, which leads to loss of wheel grip, was tested. Second dynamic maneuver tests were done in a virtual environment with the help of CarMaker® vehicle dynamics software. By doing that, steering effort could be measured to understand how much effort is needed in those risky situations. [ABSTRACT FROM AUTHOR]

Bayan Obo is the second largest niobium deposit in the world, and has been developed and utilized as iron ore for a long time because of its low niobium content and complex mineral composition. During the high-temperature reduction process, the recovery rate of niobium is low, and most niobium cannot be effectively recovered and utilized. Therefore, a new technology of slag iron separation via super gravity and preconcentration of niobium is proposed in this paper. Firstly, the reduction conditions of niobium concentrate at different temperatures, C/O, and reduction time have been studied to explore the optimal reduction conditions. The results show that the reduction effect was the best at 1200°C, C/O = 1.2 and a reduction time of 60 min. Secondly, under optimal reduction conditions, the super gravity realizes the low-temperature separation of slag and iron. We then studied the effect of C/O, gravity coefficient, and centrifugal time on the super gravity separation of niobium concentrate. The niobium content in slag increased from 4.05% to 15.7%, and the recovery of Nb2O5 reached 94.43%, which greatly improves the niobium grade and is beneficial to the deep processing of niobium concentrate. [ABSTRACT FROM AUTHOR]

This work is focused on studying the cosmology of variable modified Chaplygin gas (VMCG) in the framework of exponential and logarithmic f (T) theory. The equation of state (EoS) for VMCG in exponential and logarithmic f (T) gravity shows quintom behavior. Primordial perturbations were studied for VMCG in both exponential and logarithmic f (T) gravity, and it was observed that the potential increases with cosmic time t, and the scalar field decreases toward the minimum value of the potential. The squared speed of sound was positive, meaning that VMCG in both exponential and logarithmic f (T) gravity shows stability against small gravitational perturbations. [ABSTRACT FROM AUTHOR]