Search Results (1,021)

We present results for the tidal deformability of neutron stars, the tidal Love number $k_2$, and the effective deformability of a binary system. The equation of state for cold $\beta$-stable neutron matter is based upon high-precision two-neutron forces and includes the chiral three-neutron forces required at each order. Although we show results at both the third (N²LO) and fourth (N³LO) orders of the chiral expansion, we emphasize that only the results at N²LO can be considered truly ab initio. This is because of standing problems with regularizing three-nucleon forces at N³LO and higher orders and maintaining chiral symmetry. Thus, the results at N³LO are for illustration purposes only. We review and motivate our choices for the high-density continuation of the microscopic equation of state. We discuss our predictions and observe that they are well within multimessenger constraints. In contrast, stiff equations of state that yield radii larger than about 13 km are ruled out by GW170817 constraints. One of the main contributions from this work is the finding that tidal properties are insensitive to the high-density continuation of the equation of state, suggesting that future tidal measurements can provide robust constraints on the equation of state in the medium-density region, where the predictions from chiral effective field theory are most reliable. Full article

Carbon dioxide water-alternating-gas (CO₂-WAG) flooding simultaneously enables carbon emission mitigation, improved oil displacement efficiency, and expanded gas sweep coverage. Nevertheless, the field performance of this technology remains significantly constrained by gravity override effects, especially in ultra-thick oil reservoirs. In this work, a synthetic heterogeneous dipping mechanistic reservoir model is constructed. Using a quantitative metric for gravity override index in WAG processes, the variation patterns of gravity override under various operational factors are systematically analyzed. Furthermore, the eXtreme Gradient Boosting (XGBoost) machine learning algorithm is employed to conduct feature importance analysis of the controlling factors, identifying parameters with the most substantial impacts. The results indicate that well spacing, oil production rate, WAG injection strategy, and WAG slug duration all exert pronounced effects on both gravity override index and oil recovery factor. Gravity override is confirmed as the dominant factor governing the production performance of WAG flooding in ultra-thick reservoirs. In addition, an optimal combination of operational parameters exists that counterbalances the adverse effects of gravitational and viscous forces, thereby maximizing gas sweep efficiency, delaying gas breakthrough, and enhancing oil recovery. This study provides valuable insights and technical guidance for gas channeling mitigation, vertical gas sweep improvement, and efficient development of analogous ultra-thick reservoirs. Full article

Merging galaxy clusters represent one of the most powerful macroscopic laboratories in the Universe for searching for new physics within the dark sector. High-velocity cosmic collisions inherently separate the dark matter and stellar components from the highly collisional, X-ray-emitting intracluster gas. These massive systems provide an ideal environment to probe the fundamental nature of dark matter, specifically testing whether it behaves as a strictly collisionless particle or exhibits non-zero self-interactions. While pioneering systems like the Bullet Cluster historically demonstrated the macroscopic decoupling of dark and ordinary matter, the field has evolved into a sophisticated discipline driven by multi-disciplinary methodologies. This review synthesizes recent theoretical and empirical advances in interpreting post-collision dynamics. It examines how the synergy of combined approaches—integrating multi-wavelength observations from gravitational lensing and X-ray mapping with high-fidelity N-body hydrodynamical simulations—allows the translation of macroscopic spatial observables into stringent constraints on microscopic particle properties. Through this synthesis, the work evaluates how leveraging heterogeneous merger ensembles can reliably advance the ongoing search for physics beyond the standard cosmological model. Full article

This paper investigates the constrained particle dynamics on rotational surfaces within the 4-dimensional pseudo-Euclidean space $E_2^4$, characterized by its second-order metric signature of index 2. A comprehensive Lagrangian and Hamiltonian formulation is developed to construct the specific energy and specific angular momentum as conserved Noetherian charges along timelike geodesics. By integrating Clairaut’s theorem into the geodesic flow equations, explicit analytical expressions for these fundamental physical invariants are obtained. This work explores the structural relationship between the surface’s continuous rotational symmetries and the mechanical stability of the geodesic flow. A mathematical resolution for the signature transitions manifested via the appearance of the imaginary unit i on elliptic surfaces is provided through analytic continuation and distinct coordinate charts. Furthermore, by reducing the second-order geodesic flow to a one-dimensional energy balance equation, the exact effective potentials ($V_{eff}$) are derived, and the local orbital stability zones are analytically verified via second-order radial derivatives (${\partial }_s^2{V}_{eff}>0$). These embedded geometric configurations are shown to share qualitative features with the equatorial slices of rotating relativistic spacetimes. Consequently, they can serve as potential geometric toy-models for studying the dynamics of photon spheres, ergosphere oscillations, and innermost stable circular orbits in extreme gravitational fields. Full article

Real-time monitoring of wind turbine aeroelastic damping is crucial for dynamically adjusting operational strategies and enhancing turbine stability and economic efficiency. However, since aeroelastic damping cannot be directly measured and effective industrial methodologies remain limited, this study proposes an innovative hybrid prediction framework for aeroelastic damping of wind turbine blades based on field-measured turbine data. First, a general model for calculating blade root reaction forces was developed using blade element momentum theory, considering multiple influencing factors such as motor torque, gravitational force, and centrifugal force. Linear regression and decision tree algorithms were employed to identify key coefficients in the theoretical model, thereby providing accurate hub load inputs for finite element (FE) calculations of tower aeroelastic damping through blade physical modeling. Second, a full-scale FE model of the wind turbine was constructed in Abaqus, where dynamic responses were computed using hub axial forces as inputs and compared with field data to obtain aeroelastic damping values, yielding high-quality labeled data for training machine learning models. Finally, an aeroelastic damping dataset was generated through data analysis and downsampling, and a long short-term memory recurrent neural network was trained as the prediction model. Simulation results demonstrated high accuracy, with mean prediction errors below 2.2% and maximum errors below 2.5% on real turbine datasets. In addition, experimental validation further confirmed the effectiveness of the proposed method. The model features a computationally efficient architecture, strong real-time applicability for high-dimensional inputs, and considerable potential for practical implementation. Full article

We model the vacuum as a discrete face-centered-cubic ($K=12$) tensor network with Bell-pair bonds and use it to predict a two-step quantum-to-classical threshold for macroscopic center-of-mass superpositions. A reversible dispersive deformation of the center-of-mass mode sets in at $m_{\mathrm{soft}}\approx 13.1$$\mu$g, and coherence becomes geometrically unsustainable at $m_{\mathrm{hard}}\approx 22.6\mu$g. The two scales are separated by the exact, parameter-free ratio $\sqrt{3}$, fixed by the edge-to-circumradius ratio of the cuboctahedral triangular face. Gravitational-collapse models predict a single scale of the same order, so the distinctive, falsifiable content is the two-step structure and the exact $\sqrt{3}$ separation, testable by a mass scan across the window; the recent $16.2\mu$g cat-state oscillator of Bild et al. falls between the thresholds, where coherence is not ruled out. The absolute window depends on the bond length $L=\sqrt{4ln2}{\mathsf{\ell }}_P\approx 1.665{\mathsf{\ell }}_P$, fixed by one calibration against the Bekenstein–Hawking area law. This calibration and the Compton representability hypothesis—that a mass excitation remains coherent only while its reduced Compton wavelength is resolvable by the lattice—are stated model inputs rather than derivations, motivated by the Compton frequency internal clock of massive excitations, the mass cutoff generic to lattice-regularized field theories, and the total-mass dependence observed in composite-object interferometry. Open problems are stated explicitly. Full article

This work aims to explore the gravitational consequences of a recently proposed black hole solution previously introduced, which incorporates quantum gravitational corrections of General Relativity. We initiate our analyses by taking into account the horizon structure, focusing on both the event and Cauchy horizons. Subsequently, we examine the quasinormal modes by considering all types of perturbations—scalar, vector, tensor, and spinorial. To strengthen these results, we also compute the time domain for each perturbation. Next, we turn to the study of optical properties of the black hole. In particular, we investigate null geodesics, the photon sphere and its stability, and the corresponding black hole shadows. Following this, we analyze gravitational lensing phenomena in two regimes: the weak-field limit, utilizing the Gauss–Bonnet theorem, and the strong deflection limit, employing Tsukamoto’s approach. In addition, we address the lensing observables with Event Horizon Telescope (EHT) data for $SgrA*$ and $M87*$. Finally, constraints on the parameter $\xi$—which is introduced by higher-order curvature–scalar gravity, thereby differing from the Schwarzschild solution—are estimated using Solar System measurements such as the precession of Mercury’s orbit, gravitational light bending, and time delay (or the Shapiro effect). Full article

Ferdinandea Island, part of a shallow-water submarine volcanic field, emerged in the Sicily Channel between Italy and Tunisia in July 1831 and was eroded below sea level within months; its submerged remnant forms the shallowest water depth region of Graham Bank. Here, we review nearly two centuries of historical accounts, geological interpretations and geomorphological data analysis and reassess them against high-resolution multibeam bathymetry, sub-bottom profiles (CHIRP) and published multichannel seismic data. The field comprises six volcanic edifices (V1–V6), 100–170 m high, located along structural trends characteristic of the Sicily Channel Rift. V3, the shallowest edifice, is the remnant of Ferdinandea Island formed during the 1831 Surtseyan eruption. Its flat summit, wave-reworked terrace and steep flanks record rapid post-eruptive modification. Historical observations and hydrographic surveys document the destruction of the emergent island and a further ~6 m lowering of its shallowest point between 1883 and 2012–2015; the separate contributions of wave erosion, subsidence and gravitational adjustment cannot be resolved from the available data. The same regional structural framework appears to have governed the distribution of the other volcanic centres, pockmarks, erosional escarpments and mass-transport deposits of the study area. Seventeen pockmarks, up to ~540 m wide and 22 m deep, occur as isolated, clustered and locally aligned depressions; they are associated with subsurface concave-upward reflectors and local water-column acoustic anomalies, consistent with focused fluid escape. Failures of volcanic and sedimentary slopes are widespread, with the largest debris-avalanche deposit covering ~2.2 km². Taken together, these observations indicate that tectonics, volcanism, fluid migration, wave- and bottom-current reworking, and gravitational instability have operated over different timescales to shape Graham Bank. Ferdinandea thus offers a rare historical and geological reference for investigating the rapid construction, degradation and long-term evolution of shallow-water volcanic edifices and highlights the still-open questions regarding the evolution and fate of ephemeral volcanic islands. Full article

Background: External and internal forces and tissue energy influence the structure and function of mammalian tissues during life in a gravitational field. Changing force (stress) and energy equilibria provide a dynamic means to regulate cell and tissue growth during development and maturation. However, genetic mutations and changes in expression of macromolecules involved in cell and extracellular matrix (ECM) equilibria lead to tumor formation. Methods: A model is presented illustrating connections between ECM, cell membranes, cell cyto- and nucleoskeletons, cell nucleus, and cell–cell junctions that promote energy storage, transmission, and dissipation. The effects of mutations involving changes in P53 and Coll 11A1 genes and changes in expression of collagens and collagen receptors, integrins, ILK, FAK, Talin, Paxillin, Kindlins, c-SRC, Actin, myosin light chain, Filamin A, E-cadherin, and beta catenin that have been reported to occur in cancerous lesions are examined. Results: When mutations or altered component expressions occur, mechanotransduction pathways are activated that lead to modified epithelial–mesenchymal (EMT) and endothelial–mesenchymal (ENT) transitions resulting in new cell division and deposition of ECM. Conclusions: It is hypothesized that changes in genes and expression of proteins in the connections between ECM and bound cells alter energy storage and dissipation. This leads to local stress concentrations that alter force and energy dynamic equilibria required to maintain homeostasis. Excess energy associated with broken connections within cells is dissipated through changes in myosin structure and function. Full article

Recently, several studies have investigated the validity of General Relativity’s predictions. Gravitational waves provide an ideal probe for testing the theory in the strong-field regime. In this work, we consider a class of modified-gravity theories, specifically $f\left(R\right)$, and scrutinize their predictions for the gravitational-wave emission from the coalescence of two astrophysical compact objects. We also assess the impact of next-generation gravitational-wave detectors on the ability to test these extensions of General Relativity. Full article

We study gravitational lensing by $k-n$ generalized black-bounce space-times both in regimes of weak and strong field approximations. These metrics interpolate between regular black holes and one-way or traversable wormholes. First, we investigate the light-like geodesic trajectories and derive an analytical expression for the deflection angle in terms of the bounce parameter in the weak-field gravitational regime. We then turn to the strong-field gravitational regime and display the behavior of the bending angle as a function of both the impact parameter and the bounce parameter. Next, using the lens equations, we analyze how the observables for Sagittarius A* behave concerning the bounce parameter. We obtain the shadow’s radii for some black-bounce metrics and plot the graph of their sizes, comparing them with the Schwarzschild one. Full article

Acoustically levitated thin reflective plates provide a promising approach for contactless optical beam steering by eliminating mechanical hinges, sliding interfaces, and the associated wear and friction losses. However, unlike conventional spherical particles or droplets, thin planar reflectors exhibit highly geometry-dependent acoustic force distributions and are highly susceptible to lateral drift and angular destabilization when the acoustic field is dynamically reconfigured for beam steering. Here, we present a theoretical and simulation-based stability analysis of an acoustically levitated thin reflective plate driven by a phase-controlled dual-array acoustic field. A reduced-order model based on the Gor’kov potential is developed to characterize the acoustic potential landscape, escape-barrier depth, and local restoring stiffness during phase-gradient-induced mirror tilting. The simulations reveal that increasing the phase gradient progressively distorts the trapping potential and reduces the available trapping stability margin. Among the translational degrees of freedom, the lateral restoring stiffness deteriorates much more rapidly than the axial stiffness, indicating that lateral slippage is the primary instability pathway during continuous steering. Parametric analysis further shows that thinner mirrors with larger radii can improve trapping stability by increasing the effective acoustic interaction area while reducing gravitational and inertial penalties. The influence of non-ideal acoustic driving conditions is also evaluated to determine practical operating limits for stable operation. These results clarify the stability mechanisms governing acoustically suspended planar reflectors and provide theoretical design guidelines for robust contactless optical beam-steering systems. Full article

This research examines the fundamental autonomous inertial navigation formulas for aircraft. The study aims to identify analytical errors arising from the use of approximate gravity field models and proposes corrections for horizontal inertial components relative to changes in flight altitude. GPS measurements of ground speed and its total and relative derivatives are transformed into compensations for Coriolis and centrifugal accelerations, with flight altitude taken into account. This type of compensation corresponds to a precisely defined gravitational field model, assumed to be accurate to the second degree of eccentricity. Full article

Path planning for unmanned ships has become an important research topic in recent years. To enhance navigation safety and reduce collision risk, this study proposes an improved artificial potential field (IAPF) method. A route gravitational force is introduced to guide the ship back to the planned route after collision avoidance, while the repulsive force is optimized to improve path smoothness and obstacle-avoidance stability. A collision-risk-index-based repulsive force is further developed for dynamic obstacle avoidance, and its direction is modified according to the COLREGs. In addition, a time-sequential rolling path-planning framework integrating the APF and velocity obstacle algorithms is proposed to suppress path oscillation and adapt to target-ship maneuvers. The method is validated in head-on, crossing, and multiple-obstacle scenarios. The minimum passing distances are 1064.07 m, 1072.98 m, and 1109.66 m, respectively, and the maximum decision time is 148 ms. The results demonstrate that the proposed method can generate smooth, COLREGs-compliant paths, avoid local minima, adapt to dynamic encounters, and satisfy real-time collision-avoidance requirements. Full article

In this work, a closed isotropic universe with scalar and spinor fields is considered within the framework of the extended phase space approach. Unlike conventional canonical quantization that yields the Wheeler–DeWitt equation, our method allows us to derive the Schrödinger equation for the wave function of the Universe directly from the path integral constructed with the Faddeev–Popov effective action, including gauge-fixing and ghost terms. We employ a mixed representation in the path integral: a coordinate representation for gravitational variables (lapse function and scale factor) and ghost fields, together with a holomorphic representation for matter fields. Assuming a conformally coupled scalar field as a first step, we obtain exact solutions to the Schrödinger equation under specific gauge conditions. To address the problem of vacuum divergences, we introduce supersymmetric multiplets of scalar and spinor fields, which systematically cancel the divergences and yield a finite vacuum energy in the closed universe. The resulting finite vacuum energy is interpreted as a topological Casimir effect. Full article