Search

This study explores the combined effects of variable gravity and a uniform vertical throughflow on linear instability and nonlinear stability of thermal convection in a bidispersive porous medium (BDPM) characterized by relatively large macropores with single temperature field. The fluid flow in micropores and macropores is modelled using Darcy's and Brinkman's theories, respectively. The analysis encompasses three depth-dependent gravity laws: linear, quadratic, and exponential. The principle of exchange of stabilities is established. The numerically computed critical thresholds of linear instability and nonlinear stability are found to be different indicating the manifestation of subcritical instability and also the direction of throughflow dictates the stability of base flow. In particular, the upflow is found to be more stabilizing than downflow, highlighting the dominant influence of gravity variation over throughflow in determining the system's stability. Under a constant gravitational field, however, the linear instability threshold coincides precisely with the global nonlinear stability boundary in the absence of throughflow. Moreover, with throughflow, subcritical instability arises and the stability of the system remains unaffected by the direction of the throughflow. • Natural convection in a horizontal bidispersive porous layer is investigated. • Linear instability and nonlinear stability analyses are performed numerically. • The combined influence of a vertical throughflow and gravity variations on the onset of convection is examined. • The occurrence of subcritical instability is established. [ABSTRACT FROM AUTHOR]

The empirical Gravitational constant G is of fundamental interest in metrology, Newtonian physics, and the field equations in General Relativity, particle physics, geophysics, and astrophysics. The precise value of G has yet to be known with the desired level of accuracy. In the 233 years since Cavendish, hundreds of experiments sought more accurate results but produced inconsistent results. Although they have had much more advanced supporting technology, past experiments have mostly stayed the same from the Cavendish approach. This paper shows that a different method is feasible to enhance the accuracy of G. A sphere made of metal with a large uniform mass density having a channel through the center with a bead oscillating back and forth in a simple-harmonic fashion. Monitoring the positions of the bead experimentally and comparing the predictions of the channel model will allow refining the value of G. The study develops a gravitational force function for the bead in a channeled sphere to provide more accuracy in the prediction of the bead's motion. This study determines that the best place to perform future gravitation constant experiments is in space far away from interfering effects. A near-perfect place is likely to be in outer space at the Sun-Earth Lagrange point L1, located about 1.5 million kilometers from the Earth on a line toward the Sun where other probes reside. It is estimated that three to six significant figures may be added to the current value of G. • New way to increase the accuracy of the gravitational constant G. • The current value of G is orders of magnitude less accurate than all of the other physics constants. • Bead oscillates in a tunneled sphere with approximately Simple Harmonic Motion (SHM). • The bead oscillates with Quisi-Simple Harmonic Motion (QSHM) that accounts for loss of the matter in the tunnel of a sphere. • A concise force function on a bead oscillating in a tunnel for QSHM is derived. [ABSTRACT FROM AUTHOR]

The gravitational search algorithm (GSA) is widely used for solving optimization problems because it performs in a superior manner as compared to various competing evolutionary and swarm-based metaheuristics. However, GSA frequently gets trapped in local optima due to a lack of solution diversity. Although chaotic gravitational search algorithm (CGSA) can resolve this issue to some extent but its degraded exploitation rate and convergence speed may not result in desired outcome. To this end, diversity-based chaotic GSA (DCGSA) has exhibited its capability to resolve the issues encountered with GSA and CGSA to a certain extent for unconstrained problems. DCGSA achieves this characteristic through the use of an adaptive gravitational constant, which varies according to the diversity values of the population. Since most real-world problems are subjected to some constraints, it is prudent to improve the performance of GSA in solving constrained optimization problems. The present study integrates the enhanced search capability of DCGSA with a generalized constraint handling mechanism to improve the performance of GSA in solving constrained problems. It is observed that DCGSA significantly outperforms GSA on both CEC (Congress on evolutionary computation) 2006, 2010 and 2017 functions and competes strongly with CGSA. Diversity analysis shows that the capability to balance exploration and exploitation rates is enhanced using CGSA and DCGSA. Furthermore, DCGSA algorithms outperform GSA and CGSA on real-world machining and CEC 2020 mechanical design problems. Comparison with state-of-the-art algorithms is made to analyze the performance of the algorithms from a larger perspective. • Performance of gravitational search algorithm is improved on constrained problems. • The algorithms are tested on CEC 2006, 2010, 2017 functions. • Algorithm's performance is tested on machining and mechanical design problems. • Diversity-based chaotic gravitational search algorithms perform better. • Diversity analysis is reported to test algorithms' exploration and exploitation. [ABSTRACT FROM AUTHOR]

It has been suggested recently that the Hubble tension could be eliminated by a sharp, ∼ 10 % increase of the effective gravitational constant at z ∼ 0.01. This would decrease the luminosities of type 1a supernovae in just the needed amount to explain the larger value of the Hubble parameter. In the present paper we call attention to a dramatic effect of such transition on neutron stars. A neutron star that existed at z = 0.01 would contract, conserving the baryon mass but undergoing a mass reduction. We computed neutron star models, with a realistic equation of state, and obtained that this reduction is typically 0.04 M ⊙. This amounts to an energy of 7 × 10 52 erg. The transition will affect all neutron stars that formed along the history of each galaxy prior to the transition. Given the large number of neutron stars per galaxy, the liberated energy is huge. An estimate of the expected fluxes of neutrinos and x-rays yields values exceeding observational upper limits, thus rendering the late G transition scenario non-viable. [ABSTRACT FROM AUTHOR]

We investigate self-gravitating solutions of the Einstein-Skyrme theory coupled to spin-isospin Dirac fermions and consider the dependence of the spectral flow on the effective gravitational coupling constant and on the Yukawa coupling. It is shown that the effects of the backreaction of the fermionic mode may strongly deform the configuration. Depending on the choice of parameters, solutions with positive, negative and zero ADM mass may arise. The occurrence of regular anti-gravitating asymptotically flat solutions with negative ADM mass is caused by the violation of the energy conditions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the cosmological implications and constraints of Weyl-type f (Q , T) gravity. This theory introduces a coupling between the non-metricity Q and the trace T of the energy–momentum tensor, using the principles of proper Weyl geometry. In this geometry, the scalar non-metricity Q , which characterizes the deviations from Riemannian geometry, is expressed in its standard Weyl form ∇ μ g α β = − w μ g α β and is determined by a vector field w μ. To study the implications of this theory, we propose a deceleration parameter with a single unknown parameter χ , which we constrain by using the latest cosmological data. By solving the field equations derived from Weyl-type f (Q , T) gravity, we aim to understand the behavior of the energy conditions within this framework. In the present work, we consider two well-motivated forms of the function f (Q , T) : (i) the linear model represented by f (Q , T) = α Q + β 6 κ 2 T , and (ii) the coupling model represented by f (Q , T) = γ 6 H 0 2 κ 2 Q T , where α , β , and γ are free parameters. Here, κ 2 = 1 16 π G represents the gravitational coupling constant. In both of the models considered, the strong energy condition is violated, indicating consistency with the present accelerated expansion. However, the null, weak, and dominant energy conditions are satisfied in these models. [ABSTRACT FROM AUTHOR]

We extend the adiabatic regularization method by introducing an arbitrary mass scale μ in the construction of the subtraction terms. This allows us to obtain, in a very robust way, the running of the coupling constants by demanding μ -invariance of the effective semiclassical (Maxwell-Einstein) equations. In particular, we get the running of the electric charge of perturbative quantum electrodynamics. Furthermore, the method brings about a renormalization of the cosmological constant and the Newtonian gravitational constant. The running obtained for these dimensionful coupling constants has new relevant (non-logarithmic) contributions, not predicted by dimensional regularization. [ABSTRACT FROM AUTHOR]

Abstract Gravitational search algorithm (GSA) inspired by the law of gravity is a swarm intelligent optimization algorithm. It utilizes the gravitational force to implement the interaction and evolution of individuals. The conventional GSA achieves several successful applications, but it still faces a premature convergence and a low search ability. To address these two issues, a hierarchical GSA with an effective gravitational constant (HGSA) is proposed from the viewpoint of population topology. Three contrastive experiments are carried out to analyze the performances between HGSA and other GSAs, heuristic algorithms and particle swarm optimizations (PSOs) on function optimization. Experimental results demonstrate the effective property of HGSA due to its hierarchical structure and gravitational constant. A component-wise experiment is also established to further verify the superiority of HGSA. Additionally, HGSA is applied to several real-world optimization problems so as to verify its good practicability and performance. Finally, the time complexity analysis is discussed to conclude that HGSA has the same computational efficiency in comparison with other GSAs. [ABSTRACT FROM AUTHOR]

The gravitational constant variation means the breakdown of the strong equivalence principle. As the cornerstone of general relativity, the validity of general relativity can be examined by studying the gravitational constant variation. Such variations have the potential to affect both the generation and propagation of gravitational waves. Here, our focus lies on the effect of gravitational constant variation specifically on the propagation of gravitational waves. In a previous paper (An et al., 2023 [13]) we have studied such effect based on a Maxwell-like equation. That work admits two drawbacks. The assumption that describing gravitational waves with Maxwell-like equation is not solid. And more such treatment can only deal with space dependent gravitational constant. In the current paper we will remedy these two issues. We employ two analytical methods, namely based on the Fierz-Pauli action and the perturbation of Einstein-Hilbert action around Minkowski spacetime, both leading to the same gravitational wave equation. By solving this equation, we find the effects of gravitational constant variation on gravitational wave propagation. The result is consistent with previous investigations based on Maxwell-like equations for gravitational waves for space dependent gravitational constant cases. In addition we can constrain the time variation of the gravitational constant via the propagation of gravitational waves based on GW170817 data. And more, we find that small variations in the gravitational constant result in an amplitude correction at the leading order and a phase correction at the sub-leading order for gravitational waves. These results provide valuable insights for probing gravitational constant variation and can be directly applied to gravitational wave data analysis. [ABSTRACT FROM AUTHOR]

A massive particle under the influence of a constant gravitational force that is bouncing inside an ideal reflecting mirror described by some function f (x) is considered. For the associated flight trajectories we derive the parametric curves, named foci curves. All foci points of the parabolas for a given initial position and energy lie on these curves. From these foci curves the associated flight parabola envelopes are derived resulting, together with the mirror surface, in a confined domain for all possible particle trajectories in the non-periodic orbit case. The general results are briefly discussed and visualized for three concrete mirror surfaces. • Foci curves of flight parabolas. • Confined domains. • Application to various examples. [ABSTRACT FROM AUTHOR]

Within the Boussinesq approximation an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame in a central gravitational field is formulated and explored numerically. The self-acceleration is sustained by the intrinsic Rayleigh-Taylor instability until the Deshaies-Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. The present study is an extension of the preceding models dealing with constant gravitational fields. [ABSTRACT FROM AUTHOR]

The f ( R ) gravity can be cast into the form of a scalar–tensor theory, and scalar degree of freedom can be suppressed in high-density regions by the chameleon mechanism. In this article, for the general f ( R ) gravity, using a scalar–tensor representation with the chameleon mechanism, we calculate the parametrized post-Newtonian parameters γ and β , the effective gravitational constant G eff , and the effective cosmological constant Λ eff . In addition, for the general f ( R ) gravity, we also calculate the rate of orbital period decay of the binary system due to gravitational radiation. Then we apply these results to specific f ( R ) models (Hu–Sawicki model, Tsujikawa model and Starobinsky model) and derive the constraints on the model parameters by combining the observations in solar system, cosmological scales and the binary systems. [ABSTRACT FROM AUTHOR]

Gravitational search algorithm (GSA), a recent meta-heuristic algorithm inspired by Newton's law of gravity and mass interactions, shows good performance in various optimization problems. In GSA, the gravitational constant attenuation factor alpha ( α ) plays a vital role in convergence and the balance between exploration and exploitation. However, in GSA and most of its variants, all agents share the same α value without considering their evolutionary states, which has inevitably caused the premature convergence and imbalance of exploration and exploitation. In order to alleviate these drawbacks, in this paper, we propose a new variant of GSA, namely stability constrained adaptive alpha for GSA (SCAA). In SCAA, each agent's evolutionary state is estimated, which is then combined with the variation of the agent's position and fitness feedback to adaptively adjust the value of α . Moreover, to preserve agents’ stable trajectories and improve convergence precision, a boundary constraint is derived from the stability conditions of GSA to restrict the value of α in each iteration. The performance of SCAA has been evaluated by comparing with the original GSA and four alpha adjusting algorithms on 13 conventional functions and 15 complex CEC2015 functions. The experimental results have demonstrated that SCAA has significantly better searching performance than its peers do. [ABSTRACT FROM AUTHOR]

Satellite orbits require periodical maintenance due to the presence of perturbations. However, random errors caused by inaccurate orbit determination and thrust implementation may lead to failure of the orbit control strategy. Therefore, it is necessary to analyze the robustness of the orbit control methods. Feasible strategies which are tolerant to errors of a certain magnitude can be developed to perform reliable orbit control for the satellite. In this paper, first, the orbital dynamic model is formulated by Gauss’ form of the planetary equation using the mean orbit elements; the atmospheric drag and the Earth's non-spherical perturbations are taken into consideration in this model. Second, an impulsive control strategy employing the differential correction algorithm is developed to maintain the satellite trajectory parameters in given ranges. Finally, the robustness of the impulsive control method is analyzed through Monte Carlo simulations while taking orbit determination error and thrust error into account. [ABSTRACT FROM AUTHOR]

In its weak field limit, Scalar-tensor-vector gravity theory introduces a Yukawa-correction to the gravitational potential. Such a correction depends on the two parameters, α which accounts for the modification of the gravitational constant, and μ ⁎ − 1 which represents the scale length on which the scalar field propagates. These parameters were found to be universal when the modified gravitational potential was used to fit the galaxy rotation curves and the mass profiles of galaxy clusters, both without Dark Matter. We test the universality of these parameters using the temperature anisotropies due to the thermal Sunyaev–Zeldovich effect. In our model the intra-cluster gas is in hydrostatic equilibrium within the modified gravitational potential well and it is described by a polytropic equation of state. We predict the thermal Sunyaev–Zeldovich temperature anisotropies produced by Coma cluster, and we compare them with those obtained using the Planck 2013 Nominal maps. In our analysis, we find α and the scale length, respectively, to be consistent and to depart from their universal values. Our analysis points out that the assumption of the universality of the Yukawa-correction to the gravitational potential is ruled out at more than 3.5 σ at galaxy clusters scale, while demonstrating that such a theory of gravity is capable to fit the cluster profile if the scale dependence of the gravitational potential is restored. [ABSTRACT FROM AUTHOR]

We review the paradigm of holographic dark energy (HDE), which arises from a theoretical attempt of applying the holographic principle (HP) to the dark energy (DE) problem. Making use of the HP and the dimensional analysis, we derive the general formula of the energy density of HDE. Then, we describe the properties of HDE model, in which the future event horizon is chosen as the characteristic length scale. We also introduce the theoretical explorations and the observational constraints for this model. Next, in the framework of HDE, we discuss various topics, such as spatial curvature, neutrino, instability of perturbation, time-varying gravitational constant, inflation, black hole and big rip singularity. In addition, from both the theoretical and the observational aspects, we introduce the interacting holographic dark energy scenario, where the interaction between dark matter and HDE is taken into account. Furthermore, we discuss the HDE scenario in various modified gravity (MG) theories, such as Brans–Dicke theory, braneworld theory, scalar–tensor theory, Horava–Lifshitz theory, and so on. Besides, we introduce the attempts of reconstructing various scalar-field DE and MG models from HDE. Moreover, we introduce other DE models inspired by the HP, in which different characteristic length scales are chosen. Finally, we make comparisons among various HP-inspired DE models, by using cosmological observations and diagnostic tools. [ABSTRACT FROM AUTHOR]

In a population-based meta-heuristic, the search process is divided into two main phases: exploration versus exploitation. In the exploration phase, a random behavior is fruitful to explore the search space as extensive as possible. In contrast, a fast exploitation toward the promising regions is the main objective of the latter phase. It is really challenging to find a proper balance between these two phases because of the stochastic nature of population-based meta-heuristic algorithms. The literature shows that chaotic maps are able to improve both phases. This work embeds ten chaotic maps into the gravitational constant ( G ) of the recently proposed population-based meta-heuristic algorithm called Gravitational Search Algorithm (GSA). Also, an adaptive normalization method is proposed to transit from the exploration phase to the exploitation phase smoothly. As case studies, twelve shifted and biased benchmark functions evaluate the performance of the proposed chaos-based GSA algorithms in terms of exploration and exploitation. A statistical test called Wilcoxon rank-sum is done to judge about the significance of the results as well. The results demonstrate that sinusoidal map is the best map for improving the performance of GSA significantly. [ABSTRACT FROM AUTHOR]

Since the first detection of gravitational waves, they have been used to investigate various fundamental problems, including the variation of physical constants. Regarding the gravitational constant, previous works focused on the effect of the gravitational constant variation on the gravitational wave generation. In this paper, we investigate the effect of the gravitational constant variation on the gravitational wave propagation. The Maxwell-like equation that describes the propagation of gravitational waves is extended in this paper to account for situations where the gravitational constant varies. Based on this equation, we find that the amplitude of gravitational waves will be corrected. Consequently the estimated distance to the gravitational wave source without considering such a correction may be biased. Applying our correction result to the well known binary neutron star coalescence event GW170817, we get a constraint on the variation of the gravitational constant. Relating our result to the Yukawa deviation of gravity, we for the first time get the constraint of the Yukawa parameters in 10 Mpc scale. This scale corresponds to a graviton mass m g ∼ 10 − 31 eV. [ABSTRACT FROM AUTHOR]

Recently, gravitational search algorithm (GSA) has been successfully applied to solve various optimization problems. However, GSA tends to fall into local optimum because it ignores the environmental heterogeneity of agents. Therefore, locally informed gravitational search algorithm (LIGSA) based on neighborhood structure is proposed to balance exploration and exploitation. However, LIGSA ignores the differences in the evolutionary states between agents in the same neighborhood, and also ignores the differences in the evolutionary states between neighbors, which affects the performance of the algorithm. Therefore, a hierarchical locally informed gravitational search algorithm (HLIGSA) is proposed in this paper. This algorithm designs a hierarchical topology. In the lower layer, there are several non-overlapping neighborhoods, which constitute the whole population. Each agent in the neighborhood adaptively adjusts the gravitational constant according to its evolutionary state, so as to fully search the region of the neighborhood. The upper layer is a population composed of the best agents in each neighborhood, which performs gravity strategy or merging strategy for those neighborhoods that have lost the evolutionary capability, so as to balance the algorithm's exploration and exploitation. The two layers work together to complete the entire search process. Experimental results show that HLIGSA outperforms many variants of GSA and many current state-of-the-art heuristic algorithms. [ABSTRACT FROM AUTHOR]

We consider the standard Einstein-Hilbert-Higgs action where the Higgs field couples nonminimally with gravity via the term ξ h 2 R , and investigate the stability of the electroweak vacuum in the presence of gravitational corrections in both the metric and Palatini formulations of gravity. In order to identify the differences between the two formalisms analytically, we follow a perturbative approach in which the gravitational corrections are taken into consideration via a leading order expansion in the gravitational coupling constant. Our analysis shows that in the Palatini formalism, the well-known effect of gravity suppressing the vacuum decay probability, becomes milder in comparison with the metric case for any value of the nonminimal coupling ξ. Furthermore, we have found that in the Palatini formalism, the positivity of the gravitational corrections, which is a necessary requirement for the unitarity of the theory, entails the lower bound ξ > − 1 / 12. [ABSTRACT FROM AUTHOR]

We introduce Weyl's scale-invariance as an additional global symmetry in the standard model of electroweak interactions. A natural consequence is the introduction of general relativity coupled to scalar fields à la Dirac, that includes the Higgs doublet and a singlet σ -field required for implementing global scale-invariance. We introduce a mechanism for ‘spontaneous breaking’ of scale-invariance by introducing a coupling of the σ -field to a new metric-independent measure Φ defined in terms of four scalars ϕ i ( i = 1 , 2 , 3 , 4 ) . Global scale-invariance is regained by combining it with internal diffeomorphism of these four scalars. We show that once the global scale-invariance is broken, the phenomenon (a) generates Newton's gravitational constant G N and (b) triggers spontaneous symmetry breaking in the normal manner resulting in masses for the conventional fermions and bosons. In the absence of fine-tuning the scale at which the scale-symmetry breaks can be of order Planck mass. If right-handed neutrinos are also introduced, their absence at present energy scales is attributed to their mass terms tied to the scale where scale-invariance breaks. [ABSTRACT FROM AUTHOR]

A Mixed-Strategy based Gravitational Search Algorithm (MS-GSA) is proposed in this paper, in which three improvement strategies are mixed and integrated in the standard GSA to enhance the optimization ability. The first improvement strategy is introducing elite agent's guidance into movement function to accelerate convergence speed. The second one is designing an adaptive gravitational constant function to keep a balance between the exploration and exploitation in the searching process. And the third improvement strategy is the mutation strategy based on the Cauchy and Gaussian mutations for overcoming the shortages of premature. The MS-GSA has been verified by comparing with 7 popular meta-heuristics algorithms on 23 typical basic benchmark functions and 7 CEC2005 composite benchmark functions. The results on these benchmark functions show that the MS-GSA has achieved significantly better performance than other algorithms. The effectiveness and significance of the results have been verified by Wilcoxon's test. Finally, the MS-GSA is employed to solve the parameter identification problem of Hydraulic turbine governing system (HTGS). It is shown that the MS-GSA is able to identify the parameters of HTGS effectively with higher accuracy compared with existing methods. [ABSTRACT FROM AUTHOR]

We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector. [ABSTRACT FROM AUTHOR]

Multilevel image segmentation is an important technique and indispensable process in vision inspection on semiconductor packages to sort out defective products from the qualified ones, classify and identify the defect types. Conventional multilevel image segmentation methods are computationally expensive, and lack accuracy and stability. To address this issue, this paper proposes a novel gravitational search algorithm (NGSA) for multilevel image segmentation. Two major improvements to the update mechanism (UM) have been made in NGSA, i.e., adaptive gravitational constant and normal mutation of global best agent, to help agents jump out of local optima and improve the calculation accuracy. The experimental results based on multilevel Otsu criterion demonstrate that the proposed NGSA can obtain optimal multilevel thresholds for the quad flat non-lead (QFN) defect images and the segmentation results are promising. Three different methods, firefly algorithm (FA), cuckoo search (CS) and gravitational search algorithm (GSA), are compared with the proposed method. Numerical illustrations show that the proposed NGSA outperforms FA and GSA, and performs as well as, or is better than CS in solution quality, computational efficiency, and operation stability. Hence, NGSA in combination with multilevel Otsu criterion can be accurately and efficiently used in multilevel image segmentation of vision inspection on semiconductor packages. [ABSTRACT FROM AUTHOR]

White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other relevant ingredients are needed to compare theory and observations. In this review we summarize the recent attempts to empirically determine the white dwarf luminosity function for the different Galactic populations. We also discuss the biases that may affect its interpretation. Finally, we elaborate on the theoretical ingredients needed to model the white dwarf luminosity function, paying special attention to the remaining uncertainties, and we comment on some applications of the white dwarf cooling theory. Astrophysical problems for which white dwarf stars may provide useful leverage in the near future are also discussed. [ABSTRACT FROM AUTHOR]

We demonstrate that renormalization-group effects of scale-running propagator-coupling constants due to classical fluctuations can induce antiscreening/screening and multifractal symmetry breakings among various helical and other ordered states of generalized Lifshitz character leading to novel phase-transition associated complexities in condensed matter physics and gravitational evolution. Such phenomenon can exhibit the sporadic and localized appearance of virtual particles and in the context of cosmological evolution, the coarse-grained scale-running of the gravitational constant G due to classical fluctuations may provide a partial explanation to the dark matter mystery. [ABSTRACT FROM AUTHOR]

Despite the scientific effort, the experimental values of the gravitational constant are still not consistent within their expanded uncertainties. The paper suggests so far undiscovered systematic errors of two previously obtained results that do not match the CODATA 2014 value, namely the results obtained from the JILA and the BIPM experimental setups. The suggested corrections are towards the CODATA value and they could significantly suppress the longstanding inconsistency in the experimental values. The experimental investigations using both setups are still possible, and thus this paper may open a way to establish a consistent value of the gravitational constant. [ABSTRACT FROM AUTHOR]

This paper introduces an Improved Artificial Bee Colony algorithm for modeling and managing Micro Grid (MG) connected system. IABC differs from ABC because of its inclusion of Gravitational search algorithm (GSA) in the scout bee phase. Hence, the scout bee phase is substantially improved as the gravitational constant of GSA increases searching accuracy. As already ABC works with memory, IABC tackles drawbacks occur due to memory-less search entertained by GSA. In the proposed technique, optimal MG’s configuration is determined based on load demand by reducing the fuel cost, emission factors, operating and maintenance cost. By using the input of MG’s configuration such as Wind Turbine (WT), Photovoltaic array (PV), Fuel Cell (FC), Micro Turbine (MT), Diesel Generator (DG) and battery storage and the corresponding cost functions, the proposed method achieves the required multi-objective function. The performance of the proposed method is examined by comparing with other techniques that are recently reported in the literature. The comparison results demonstrate the superiority of the proposed technique and confirm its potential to solve the problem. [ABSTRACT FROM AUTHOR]

In this paper we have derived the equipartition law of energy using Tsallis formalism and the Kaniadakis power law statistics in order to obtain a modified gravitational constant. We have applied this result in the gravothermal collapse phenomenon. We have discussed the equivalence between Tsallis and the Kaniadakis statistics in the context of Verlinde’s entropic formalism. In the same way we have analyzed the negative heat capacities in the light of gravothermal catastrophe. The relative deviations of the modified gravitational constants are derived. [ABSTRACT FROM AUTHOR]

A quantitatively verifiable expression for the gravitational constant is derived in terms of quantum mechanical quantities. This derivation appears to be possible by selecting a suitable physical process in which the transformation of the equation of motion into a quantum mechanical wave equation can be obtained by Einstein’s geodesic approach. The selected process is the pi-meson, modeled as the one-body equivalent of a two-body quantum mechanical oscillator in which the vibrating mass is modeled as the result of the two energy fluxes from the quark and the antiquark. The quantum mechanical formula for the gravitational constant appears to show a quantitatively verifiable relationship with the Higgs boson as conceived in the Standard Model. [ABSTRACT FROM AUTHOR]

With a basic varying space-time cutoff l, we study a regularized and quantized Einstein-Cartan gravitational field theory and its domains of ultraviolet-unstable fixed point gir≳0 and ultraviolet-stable fixed point guv≈4/3 of the gravitational gauge coupling g = (4/3)G/G Newton. Because the fundamental op-erators of quantum gravitational field theory are dimension-2 area operators, the cosmological constant is inversely proportional to the squared correlation length σ ∝ξ-2. The correlation length ξcharacterizes an infrared size of a causally correlate patch of the universe. The cosmological constant and the gravita-tional constant Gare related by a generalized Bianchi identity. As the basic space-time cutoff l decreases and approaches to the Planck length lpl, the universe undergoes inflation in the domain of the ultraviolet-unstable fixed point gir, then evolves to the low-redshift universe in the domain of ultraviolet-stable fixed point guv. We give the quantitative description of the low-redshift universe in the scaling-invariant domain of the ultraviolet-stable fixed point guv, and its deviation from the ΛCDM can be examined by low-redshift (z1)cosmological observations, such as supernova Type Ia. [ABSTRACT FROM AUTHOR]

Many precision measurements of G have produced a spread of results incompatible with measurement errors. Clearly an unknown source of systematic errors is at work. It is proposed here that most of the discrepancies derive from subtle deviations from Hooke's law, caused by avalanches of entangled dislocations. The idea is supported by deviations from linearity reported by experimenters measuring G, similarly to what is observed, on a larger scale, in low-frequency spring oscillators. Some mitigating experimental apparatus modifications are suggested. [ABSTRACT FROM AUTHOR]

Recent work has proposed that the interaction between ordinary matter and a stochastic gravitational background can lead to the decoherence of large aggregates of ordinary matter. In this work we point out that these arguments can be carried over to a stochastic neutrino background but with the Planck scale of the gravitational decoherence replaced by the weak scale. This implies that it might be possible to observe such neutrino induced decoherence on a small, microscopic system rather than a macroscopic system as is the case for gravitationally induced decoherence. In particular we suggest that neutrino decoherence could be linked with observed variations in the decay rates of certain nuclei. Finally we point out that this proposed neutrino induced decoherence can be considered the complement of the Mikheev–Smirnov–Wolfenstein (MSW) effect. [ABSTRACT FROM AUTHOR]

We propose a sequence of steps and a generic transformation for connecting common thermodynamic quantities considered in asymptotically anti-de Sitter black hole thermodynamics in the bulk and those that are appropriate for CFT thermodynamics in the boundary. We do this by constructing a "varying- G map", where G is the gravitational constant, and demonstrate its usefulness by considering various examples. [ABSTRACT FROM AUTHOR]

The design of a globally convergent position observer for feature points from visual information is a challenging problem, especially for the case with only inertial measurements and without assumptions of uniform observability, which remained open for a long time. We give a solution to the problem in this paper assuming that only the bearing of a feature point, and biased linear acceleration and rotational velocity of a robot – all in the body-fixed frame – are available. Further, in contrast to existing related results, we do not need the value of the gravitational constant either. The proposed approach builds upon the parameter estimation-based observer recently developed in Ortega et al. (2015) and its extension to matrix Lie groups in our previous work. Conditions on the robot trajectory under which the observer converges are given, and these are strictly weaker than the standard persistency of excitation and uniform complete observability conditions. Finally, as an illustration, we apply the proposed design to the visual inertial navigation problem. [ABSTRACT FROM AUTHOR]

• The pose of the end-effector can be better controlled by IGPEF. • DGC can help solve the local minimum problem. • PRF can solve the issues that the robot can not reach the target nearby obstacles. • PDNN is used to solve the kinematics problem under safety constraints. • RTPVS is applied to prevent the accumulation of position errors. Safety and accuracy are essential for path planning in a surgical navigation system. In this paper, an improved path planning algorithm is proposed to increase the autonomous level of spine surgery robots for higher safety and accuracy. Firstly, the dynamic gravitational constant and piecewise repulsion function are adopted to improve the traditional Artificial Potential Field algorithm to solve the common issues of path planning, including local minimum, unable to reach the target near obstacles. To better control the pose of the end-effector in an operation space, the positions of the two endpoints of the end-effector are further constrained. Secondly, an improved Primal-Dual Neural Network with multiple constraints is proposed to minimize the joint angular velocity norm. The multiple constraints are formulated according to the planned path, the obstacle avoidance of the robot and the joint limits. Moreover, a real-time planned velocity scheme is applied to prevent the accumulation of position errors. The simulation results of the pedicle screw implantation demonstrate that the robot can find the collision-free trajectory and arrive at the target position in various complicated situations. More specifically, the error between two endpoints of the end-effector and the target pose is below 0.1 mm in reaching the surgical tool pose, while the maximum position error is around 0.05 mm when performing the planned path. Moreover, two experiments are conducted in the real-world to verify the proposed algorithm is effective in practice. [ABSTRACT FROM AUTHOR]

Recently, Damour computed the radiation reaction on gravitational scattering as the (linear) response to the angular momentum loss which he found to be of O (G 2) in the gravitational constant. This is a puzzle because any amplitude calculation would predict both radiated energy and radiated angular momentum to start only at O (G 3). Another puzzle is that the resultant radiation reaction, of O (G 3) , is nevertheless correct and confirmed by a number of direct calculations. We ascribe these puzzles to the BMS ambiguity in defining angular momentum. The loss of angular momentum is to be counted out from the ADM value and, therefore, should be calculated in the so-called canonical gauge under the BMS transformations in which the remote-past limit of the Bondi angular momentum coincides with the ADM angular momentum. This calculation correctly gives the O (G 3) radiative loss. On the other hand, we introduce a gauge in which the Bondi light cones tend asymptotically to those emanating from the center of mass world line. We find that the angular momentum loss in this gauge is precisely the one used by Damour for his radiation reaction result. We call this new gauge "intrinsic" and argue that, although the radiated angular momentum is to be computed in the canonical gauge, any mechanical calculation of gauge-dependent quantities – such as angular momentum – gives the result in the intrinsic gauge. Therefore, it is this gauge that should be used in the linear response formula. This solves the puzzles and establishes the correspondence between the intrinsic mechanical calculations and the Bondi formalism. [ABSTRACT FROM AUTHOR]

Compact binaries are an important class of gravitational-wave (GW) sources that can be detected by current and future GW observatories. They provide a testbed for general relativity (GR) in the highly dynamical strong-field regime. Here, we use GWs from inspiraling binary neutron stars and binary black holes to investigate dipolar gravitational radiation (DGR) and varying gravitational constant predicted by some alternative theories to GR, such as the scalar-tensor gravity. Within the parametrized post-Einsteinian framework, we introduce the parametrization of these two effects simultaneously into compact binaries' inspiral waveform and perform the Fisher-information-matrix analysis to estimate their simultaneous bounds. In general, the space-based GW detectors can give a tighter limit than ground-based ones. The tightest constraints can reach σ B < 3 × 10 − 11 for the DGR parameter B and σ G ˙ / G < 7 × 10 − 9 yr − 1 for the varying G , when the time to coalescence of the GW event is close to the lifetime of space-based detectors. In addition, we analyze the correlation between these two effects and highlight the importance of considering both effects in order to arrive at more realistic results. [ABSTRACT FROM AUTHOR]

We first derive the boundary theory from the U(1) Chern-Simons theory. The boundary action on an n -sheet manifold appears from its back-reaction of the Wilson line. The reason is that the U(1) Chern-Simons theory can provide an exact effective action when introducing the Wilson line. The Wilson line in the pure AdS 3 Einstein gravity is equivalent to entanglement entropy in the boundary theory up to classical gravity. The U(1) Chern-Simons theory deviates by a self-interaction term from the gauge formulation on the boundary. We also compare the Hayward term in the SL(2) Chern-Simons formulation to the Wilson line approach. Introducing two wedges can reproduce the entanglement entropy for a single interval at the classical level. We propose quantum generalization by combining the bulk and Hayward terms. The quantum correction of the partition function vanishes. In the end, we calculate the entanglement entropy for a single interval. The pure AdS 3 Einstein gravity theory shows a shift of central charge by 26 at the one-loop level. The U(1) Chern-Simons theory does not show a shift from the quantum effect. The result is the same in the weak gravitational constant limit. The non-vanishing quantum correction shows that the Hayward term is incorrect. [ABSTRACT FROM AUTHOR]

We confront the big bang for the beginning of the universe with an equivalent picture of a slow freeze — a very cold and slowly evolving universe. In the freeze picture the masses of elementary particles increase and the gravitational constant decreases with cosmic time, while the Newtonian attraction remains unchanged. The freeze and big bang pictures both describe the same observations or physical reality. We present a simple “crossover model” without a big bang singularity. In the infinite past space–time is flat. Our model is compatible with present observations, describing the generation of primordial density fluctuations during inflation as well as the present transition to a dark energy-dominated universe. [ABSTRACT FROM AUTHOR]

It is shown that multiply distributed cosmic strings arise in the product Abelian gauge field theory of Tong and Wong where vortices generated from an extra gauge sector are used to realize magnetic impurities. It is seen that, in view of the fully coupled Einstein and gauge-matter equations, the presence of such cosmic strings in the form of topological defects is essential for gravitation. Asymptotic behavior of the string solutions can be precisely described to allow the derivation of a necessary and sufficient condition for the gravitational metric to be geodesically complete and an explicit calculation of the deficit angle proportional to the string tension, both stated in terms of string numbers, energy levels of broken symmetries, and the universal gravitational constant. [ABSTRACT FROM AUTHOR]

The question whether the invariant speed c, Planck constant h, and gravitational constant G can be put equal to 1 is analyzed. The discussion is based on fundamental considerations concerning the notion of physical quantity, it is found that the issue is not a matter of appropriate unit selection. Further it is shown that classical space-time geometry and quantum mechanics can be formulated in such a way that the invariant speed and the action quantum are truly one and do not have to be set equal to one. [ABSTRACT FROM AUTHOR]

A comparative review of the different systems of units that are most usual in electromagnetism leads to the proposal of a new system of units. In this system, the gravitational constant acquires the role of an interaction constant, both for gravitational and electromagnetic interaction, as a result of a redefinition of electric charge. In this way, the new system of units extends in a natural manner to mechanics. The comparison between the gravitational and electromagnetic interactions is of particular relevance. [ABSTRACT FROM AUTHOR]

In the present paper, we investigate the cosmic behavior of particle creation (PC) in (d+2) dimensional FLRW (Friedmann–Lemaitre–Robertson–Walker) models with time dependent gravitational constant and cosmological constant. The gravitational field equations are solved by assuming a periodically time-varying deceleration parameter (PTVDP) i.e. q = m cos k t − 1 (Shen and Zhao, 2014) which produces a scale factor a (t) = a 0 tan k t 2 1 m , where a 0 shows current scale factor and k displays the PTVDP periodicity and can be regarded as a parameter of cosmic frequency, m is an enhancement element that increases the PTVDP peak. Here, we studied the periodic time-varying behavior of a few quantities, such as the deceleration parameter q , the energy density ρ , the entropy S , PC rate ψ , the cosmological constant Λ , Newton's gravitational constant G and discuss their physical significance. We have also discussed the density parameter, proper distance, angular distance, luminosity distance, apparent magnitude, age of the Universe, and the look-back time with redshift z and have observed the role of particle formation in universe evolution in early and late times. The periodic nature of various physical parameters is also discussed which are supporting the recent observations. • Cosmic behavior of particle creation in (d+2) dimensional FLRW model with time-dependent G and Lambda. • The model presents a transition from early deceleration to late acceleration during its evolution. • Derived model is based on the experimental data: OHD+JLA observation. • Discussed the physical parameters like luminosity distance, age of the universe etc. [ABSTRACT FROM AUTHOR]

This study investigated multiple skydiving jumps and applied the unscented Kalman filter (UKF) to develop a real-time state estimation of the skydiving physics model with gravitational and drag forces. In addition, experimental datasets were prepared by measuring the altitude change with the skydiving duration. Subsequently, the UKF and measured datasets were compared to assess the performance of the UKF according to fluctuations in the falling velocity or missing dataset. We observed that the UKF could predict the falling altitudes with various error ranges (−122.5−1.2 m) against the measured values at the end of skydiving points. Based on classical physics incorporated into the estimation model, the falling velocity should be monotonously increased, primarily owing to constant gravitational acceleration. Meanwhile, velocity fluctuation can be generated from the variation in drag forces due to the vertical air current. The UKF estimation was influenced by fluctuations in the falling velocity (8.8–20.3 m/s), missing datasets for 0–44 s, and/or the specifications of the initial estimates. Additionally, this study monitored the wind velocity approaching the skydiver vertically and the skydiver's heart rate. The measured wind velocity exhibited similar trends to the falling velocity with overall errors of 6.7 and 11.9 m/s (0.2% and 0.4%). Low correlations (R 2 ≈ 0.11–0.47) were observed between the skydiving activities as falling speeds and the heart rates of the skydiver. Based on the measured and modeled data, the pressures at the terminal free falling and parachute descent were approximately 1500 and 6 N/m2, respectively. • Vertical falling was investigated in multiple skydiving jumps. • Objective was to develop real-time state estimation and prediction skydiving model. • Measured and model data predicted using an unscented Kalman filter are compared. • The developed model can predict actual pressure and movements during skydiving with the altitude error ranges of −122.5−1.2 m. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we have analyzed the nonextensive Tsallis statistical mechanics in the light of Verlinde’s formalism. We have obtained, with the aid of a noncommutative phase–space entropic gravity, a new bound for Tsallis nonextensive (NE) parameter (TNP) that is clearly different from the ones present in the current literature. We derived the Friedmann equations in a NE scenario. We also obtained here a relation between the gravitational constant and the TNP. [Copyright &y& Elsevier]

Abstract: A general comparison is made between two methods of measuring the gravitational constant G. The angular acceleration method can avoid the anelasticity effect since the torsion fiber is not twisted. The dynamic deflection method is similar in principle but it does not use feedback, therefore a major noise introduced by the feedback control system in the angular acceleration method can be avoided. Both methods have their advantages and can be performed with the same device. Based on different expressions of G, we have expressed the signal-to-noise ratio and calculated the thermal noise limit for both methods. In order to get a lower thermal noise limit, the dynamic deflection method should avoid resonance. [Copyright &y& Elsevier]

Abstract: A novel stochastic optimization approach to solve optimal bidding strategy problem in a pool based electricity market using fuzzy adaptive gravitational search algorithm (FAGSA) is presented. Generating companies (suppliers) participate in the bidding process in order to maximize their profits in an electricity market. Each supplier will bid strategically for choosing the bidding coefficients to counter the competitors bidding strategy. The gravitational search algorithm (GSA) is tedious to solve the optimal bidding strategy problem because, the optimum selection of gravitational constant (G). To overcome this problem, FAGSA is applied for the first time to tune the gravitational constant using fuzzy “IF/THEN” rules. The fuzzy rule-based systems are natural candidates to design gravitational constant, because they provide a way to develop decision mechanism based on specific nature of search regions, transitions between their boundaries and completely dependent on the problem. The proposed method is tested on IEEE 30-bus system and 75-bus Indian practical system and compared with GSA, particle swarm optimization (PSO) and genetic algorithm (GA). The results show that, fuzzification of the gravitational constant, improve search behavior, solution quality and reduced computational time compared against standard constant parameter algorithms. [Copyright &y& Elsevier]