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1
Sharma, Ajay Kumar, and Murli Manohar Verma. "Power-law Inflation in the f(R) Gravity." Astrophysical Journal 926, no. 1 (February 1, 2022): 29. http://dx.doi.org/10.3847/1538-4357/ac3ed7.
Повний текст джерелаАнотація:
Abstract We investigate a form of f ( R ) = R 1 + δ / R c δ and study the viability of the model for inflation in the Jordan and the Einstein frames. We have extended this form to f ( R ) = R + R 1 + δ / R c δ in an attempt to solve the problems of the former model. This model is further analyzed by using the power spectrum indices of inflation and the reheating temperature. During the inflationary evolution, the model predicts a value of the δ parameter very close to one (δ = 0.98), while the reheating temperature T re ∼ 10 16 GeV at δ = 0.98 is consistent with the standard approach to inflation and observations. We calculate the slow roll parameters for the minimally coupled scalar field within the framework of our models. It is found that the values of the scalar spectral index and tensor-to-scalar ratio are very close to the recent observational data, including those released by Planck. Further, we find the scalar spectral index and the tensor-to-scalar ratio are exactly the same in the first model because the Jordan and the Einstein frames are conformally equivalent. We also attempt to provide a constraint through the non-Gaussianity parameter.
2
Wang, Hao, Xiao-Yong Yan, and Jinshan Wu. "Free utility model for explaining the social gravity law." Journal of Statistical Mechanics: Theory and Experiment 2021, no. 3 (March 1, 2021): 033418. http://dx.doi.org/10.1088/1742-5468/abee18.
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GOSWAMI, UMANANDA DEV, and KABITA DEKA. "COSMOLOGICAL DYNAMICS OF f(R) GRAVITY SCALAR DEGREE OF FREEDOM IN EINSTEIN FRAME." International Journal of Modern Physics D 22, no. 14 (December 2013): 1350083. http://dx.doi.org/10.1142/s0218271813500831.
Повний текст джерелаАнотація:
f(R) gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as a manifestation of the large scale modification of the force of gravity. f(R) gravity models can be expressed in terms of a scalar degree of freedom by redefinition of model's variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law (ξRn) and the Starobinsky (disappearing cosmological constant) f(R) gravity models numerically in the Einstein frame. Both the models show interesting behavior of their scalar degree of freedom and could produce the accelerated expansion of the universe in the Einstein frame with the negative equation of state of the scalar field. However, the scalar field potential for the power-law model is the well-behaved function of the field, whereas the potential becomes flat for higher value of field in the case of the Starobinsky model. Moreover, the equation of state of the scalar field for the power-law model is always negative and less than -1/3, which corresponds to the behavior of the dark energy, that produces the accelerated expansion of the universe. This is not always the case for the Starobinsky model. At late times, the Starobinsky model behaves as cosmological constant Λ as behaves by power-law model for the values of n → 2 at all times.
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Sharif, M., and Ayesha Ikram. "Thermodynamics in f(G,T) Gravity." Advances in High Energy Physics 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/2563871.
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This paper explores the nonequilibrium behavior of thermodynamics at the apparent horizon of isotropic and homogeneous universe model in f(G,T) gravity (G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, resp.). We construct the corresponding field equations and analyze the first as well as generalized second law of thermodynamics in this scenario. It is found that an auxiliary term corresponding to entropy production appears due to the nonequilibrium picture of thermodynamics in first law. The universal condition for the validity of generalized second law of thermodynamics is also obtained. Finally, we check the validity of generalized second law of thermodynamics for the reconstructed f(G,T) models (de Sitter and power-law solutions). We conclude that this law holds for suitable choices of free parameters.
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Chen, Yanguang. "The distance-decay function of geographical gravity model: Power law or exponential law?" Chaos, Solitons & Fractals 77 (August 2015): 174–89. http://dx.doi.org/10.1016/j.chaos.2015.05.022.
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Wu, Qimeng, Melle T. J. J. M. Punter, Thomas E. Kodger, Luben Arnaudov, Bela M. Mulder, Simeon Stoyanov, and Jasper van der Gucht. "Gravity-driven syneresis in model low-fat mayonnaise." Soft Matter 15, no. 46 (2019): 9474–81. http://dx.doi.org/10.1039/c9sm01097a.
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We show that forced syneresis in model low fat mayonnaise, a colloid polymer mixture, can be described as a gravity-driven porous flow through the densely packed emulsion, explainable with a model based on Darcy's law.
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Fu, Yanbin, Xiuling Wang, Sizhan Zhang, and Yong Yang. "Modelling of Permeation Grouting considering Grout Self-Gravity Effect: Theoretical and Experimental Study." Advances in Materials Science and Engineering 2019 (November 27, 2019): 1–16. http://dx.doi.org/10.1155/2019/7968240.
Повний текст джерелаАнотація:
Self-gravity is one key parameter for behavior characterization of grout permeation and diffusion. This study proposes mathematical models for permeation grouting with consideration of grout self-gravity effect. The models concerning power law, Bingham, and Newtonian grouts are based on the generalized Darcy’s law and spherical diffusion theory. In addition, a prediction model of grout concretion dimension used for Bingham grout was developed. An analysis of the injection pressure distribution law and a comparative evaluation of diffusion radius considering self-gravity effect using established models were conducted subsequently. Moreover, grouting experiments were performed to check and verify the prediction model. The experimental results showed that injection pressure decreases linearly with increase of diffusion radius for the power-law grout, while nonlinear decrease of injection pressure was confirmed in Bingham and Newtonian grouts in this case. Three grouts approximately diffuse in an “ellipsoidal” shape, and it is confirmed that the diffusion radius is closely related to grout self-gravity. The Newtonian grout produces the maximum diffusion radius compared with the other two grouts whether the gravity effects were considered or not. The grout quantity under a smaller water-to-cement w/c ratio exhibits a significant difference and undergoes two increasing stages, whereas the quantity simply tends to be stable after it reaches its maximum in terms of the larger w/c ratios. The constructed dimension prediction model agrees well with the experimental results, which can be helpful for design and assessment of the grouting scheme.
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Moussa, Mohamed. "Constraining unparticle-inspired model parameters using dwarf stars." International Journal of Modern Physics D 30, no. 05 (February 23, 2021): 2150031. http://dx.doi.org/10.1142/s0218271821500310.
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The unparticle-inspired model of gravity suggested by Georgi is based on that the standard model (SM) may contain a massive but scale invariant particles, which can be exchanged between SM massive particles, leading to a new force called ungravity. This would add a perturbed term to the Newtonian law of gravity at low energy. We use the minimum mass of hydrogen burning (MMHB) to constrain the relevant parameters of unparticle inspired model of gravity, on scales [Formula: see text] and [Formula: see text].
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Kuiroukidis, A. "A class of simple bouncing and late-time accelerating cosmologies in f(R) gravity." International Journal of Modern Physics D 27, no. 05 (April 2018): 1850055. http://dx.doi.org/10.1142/s0218271818500554.
Повний текст джерелаАнотація:
We consider the field equations for a flat FRW cosmological model, given by Eq. (??), in an a priori generic [Formula: see text] gravity model and cast them into a, completely normalized and dimensionless, system of ODEs for the scale factor and the function [Formula: see text], with respect to the scalar curvature [Formula: see text]. It is shown that under reasonable assumptions, namely for power-law functional form for the [Formula: see text] gravity model, one can produce simple analytical and numerical solutions describing bouncing cosmological models where in addition there are late-time accelerating. The power-law form for the [Formula: see text] gravity model is typically considered in the literature as the most concrete, reasonable, practical and viable assumption [see S. D. Odintsov and V. K. Oikonomou, Phys. Rev. D 90 (2014) 124083, arXiv:1410.8183 [gr-qc]]. However even without assuming a power-law form for the [Formula: see text] gravity model, the formulation of the field equations, that is suggested in this paper, is according to the author’s viewpoint quite generic in order to analyze the resulting field equations, without any further assumptions. Possibility of extending these results is briefly discussed.
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Debnath, Partha Sarathi, and Bikash Chandra Paul. "Cosmological models in R2 gravity with hybrid expansion law." International Journal of Geometric Methods in Modern Physics 18, no. 09 (June 11, 2021): 2150143. http://dx.doi.org/10.1142/s0219887821501437.
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In this paper, evolution of a Friedmann–Robertson–Walker universe is studied in a higher derivative theory of gravity. The relativistic solutions admitting hybrid expansion law of the universe are explored here. Hybrid expansion law is a general form of scale factor from which one can recover both the power-law expansion and exponential expansion as a special case. The hybrid expansion law is interesting as it addresses the early deceleration phase and presents accelerating phase satisfactorily. It is found that an inflationary scenario with hybrid expansion law is permitted in the [Formula: see text] gravity fairly well. We consider universe filled with cosmic fluid that describes by an equation of state (EoS) parameter which varies with time. Consequently, we analyze the time variation of energy density parameter, cosmic pressure, equation of state parameter, deceleration parameter and jerk parameter in the cosmological model. The constraints of the model parameters imposed by the cosmological observational data set are determined. The present value of the deceleration parameter [Formula: see text], EoS parameter and the epoch at which the transition of decelerated phase to accelerated phase are estimated. In the higher derivative theory, we obtain some new and interesting cosmological solutions relevant for building cosmological models.
11
Johnson, Christopher G., and Andrew J. Hogg. "Entraining gravity currents." Journal of Fluid Mechanics 731 (August 19, 2013): 477–508. http://dx.doi.org/10.1017/jfm.2013.329.
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AbstractEntrainment of ambient fluid into a gravity current, while often negligible in laboratory-scale flows, may become increasingly significant in large-scale natural flows. We present a theoretical study of the effect of this entrainment by augmenting a shallow water model for gravity currents under a deep ambient with a simple empirical model for entrainment, based on experimental measurements of the fluid entrainment rate as a function of the bulk Richardson number. By analysing long-time similarity solutions of the model, we find that the decrease in entrainment coefficient at large Richardson number, due to the suppression of turbulent mixing by stable stratification, qualitatively affects the structure and growth rate of the solutions, compared to currents in which the entrainment is taken to be constant or negligible. In particular, mixing is most significant close to the front of the currents, leading to flows that are more dilute, deeper and slower than their non-entraining counterparts. The long-time solution of an inviscid entraining gravity current generated by a lock-release of dense fluid is a similarity solution of the second kind, in which the current grows as a power of time that is dependent on the form of the entrainment law. With an entrainment law that fits the experimental measurements well, the length of currents in this entraining inviscid regime grows with time approximately as ${t}^{0. 447} $. For currents instigated by a constant buoyancy flux, a different solution structure exists in which the current length grows as ${t}^{4/ 5} $. In both cases, entrainment is most significant close to the current front.
12
Elizalde, E., S. D. Odintsov, E. O. Pozdeeva, and S. Yu Vernov. "De Sitter and power-law solutions in non-local Gauss–Bonnet gravity." International Journal of Geometric Methods in Modern Physics 15, no. 11 (November 2018): 1850188. http://dx.doi.org/10.1142/s0219887818501888.
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The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d’Alembertian, is investigated. Casting the dynamical equations into local form, the fixed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows to describe the matter-dominated phase of the Universe evolution.
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Hewitt, Duncan R., and Neil J. Balmforth. "Thixotropic gravity currents." Journal of Fluid Mechanics 727 (June 14, 2013): 56–82. http://dx.doi.org/10.1017/jfm.2013.235.
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AbstractWe present a model for thixotropic gravity currents flowing down an inclined plane that combines lubrication theory for shallow flow with a rheological constitutive law describing the degree of microscopic structure. The model is solved numerically for a finite volume of fluid in both two and three dimensions. The results illustrate the importance of the degree of initial ageing and the spatio-temporal variations of the microstructure during flow. The fluid does not flow unless the plane is inclined beyond a critical angle that depends on the ageing time. Above that critical angle and for relatively long ageing times, the fluid dramatically avalanches downslope, with the current becoming characterized by a structured horseshoe-shaped remnant of fluid at the back and a raised nose at the advancing front. The flow is prone to a weak interfacial instability that occurs along the border between structured and de-structured fluid. Experiments with bentonite clay show broadly similar phenomenological behaviour to that predicted by the model. Differences between the experiments and the model are discussed.
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Shamir, M. Farasat, та Mushtaq Ahmad. "Power law f(𝒢,T) gravity models supporting wormhole solutions". International Journal of Geometric Methods in Modern Physics 15, № 05 (2 квітня 2018): 1850070. http://dx.doi.org/10.1142/s0219887818500706.
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This work provides some feasible regions for the existence of traversable wormhole geometries in modified [Formula: see text] gravity. For this purpose, three different matter contents have been studied with special emphasis on anisotropic fluid by considering a specific [Formula: see text] gravity power law model. It has been shown that the null energy conditions for the effective energy–momentum tensor are widely violated for the ordinary matter content. However, some small feasible regions to support the wormhole solutions have been noted. Furthermore, the stability of the anisotropic feasible regions for the wormhole solutions has been discussed. It is concluded that the wormhole geometries threaded by the ordinary matter actually exist and are well stable in [Formula: see text] gravity.
15
Manzoor, Rubab, Abdul Jawad, and Shamaila Rani. "Dynamics of evolving self-gravitating models in extended teleparallel gravity." International Journal of Modern Physics D 28, no. 02 (January 2019): 1950043. http://dx.doi.org/10.1142/s0218271819500433.
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The self-gravitating spherically symmetric fluid models are being studied taking power-law model in extended teleparallel (or [Formula: see text]) gravity. We form a set of governing equations which describes the dynamics of stellar evolution in the presence of torsion scalar (dark energy candidate) by incorporating power-law model in [Formula: see text] gravity along with dynamical terms like shear tensor, anisotropy, expansion scalar, dissipation, Weyl tensor and energy inhomogeneity. We explore some particular models of fluid according to various dynamical scenarios for particular values of model parameter [Formula: see text]. It is found that torsion terms associated with [Formula: see text], govern stellar evolution and provide deviation from theory of general relativity (GR). For the case, [Formula: see text], tetrad field is almost negligible and the evolving models are consistent with GR model having cosmological constant. We obtain practicable rate of change of expansion and deformation of fluid models at [Formula: see text].
16
Wirth, A. "Estimation of friction parameters in gravity currents by data assimilation in a model hierarchy." Ocean Science 7, no. 2 (April 15, 2011): 245–55. http://dx.doi.org/10.5194/os-7-245-2011.
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Abstract. This paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, 2009) and on the estimation of friction laws by data assimilation (Wirth and Verron, 2008) are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model. I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compares well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connecting models within a model hierarchy.
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Wirth, A. "Estimation of friction parameters in gravity currents by data assimilation in a model hierarchy." Ocean Science Discussions 8, no. 1 (January 24, 2011): 159–87. http://dx.doi.org/10.5194/osd-8-159-2011.
Повний текст джерелаАнотація:
Abstract. This paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, 2009) and on the estimation of friction laws by data assimilation (Wirth and Verron, 2008) are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model. I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compare well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connection models within a model hierarchy.
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Wei, Jin, Wenbin Shen, Hui Li, and Liu Ziwei. "Nonlinear Drift of the Spring Gravimeter Caused by Air Pressure from the Kunming GS15 Gravimeters." Polish Maritime Research 23, s1 (October 1, 2016): 180–86. http://dx.doi.org/10.1515/pomr-2016-0063.
Повний текст джерелаАнотація:
Abstract In order to monitor and correct the meteorological factors of the spring gravity meter, the characteristics of the time varying gravity changes caused by meteorological factors were analyzed. Kunming GS15 gravity meter from 2007 continuous gravity observation has been carried out with the sampling rate of the pressure observation. In this study, we first compare the effects of 4 types of gravity meter and 3 different types of stations on the gravity observed seasonal gravity signals. It is indicated that the observed seasonal gravity signal of the cave is only 1/10, and there is a constant temperature and constant pressure device. Compared with the same time, the gravity signal of the gravity signal is about 100 times smaller. The influence of the pressure load of the gravity meter is tested by using the theory of pressure. The results show that only the actual value of 2cpd - 3cpd pressure load varies from -0.395 to -0.280×10-8ms-2 , and the 1cpd to 1 cpm periodic partial type gravity meter is also in accordance with the law of gravity and air pressure. And with the characteristics of time lag. In this paper, the nonlinear zero drift parameters of the linear regression model with time lag and the time series of the GS15 gravity meter are used to simulate the nonlinear zero drift parameters of the gravity meter. The results show that the gravity signal contains time lag 35 hours, and the air pressure admittance is 0.8 × 10-8ms-2/mbar. The correlation can reach 79%. The gravity changes signal and satellite gravity as well as the gravity water load signal of the land water model are the same as the gravity water load signal in the autumn as the minimum value, and the seasonal variation of the maximum value of gravity in summer.
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Sharif, M., та Ayesha Ikram. "Inflationary dynamics in f(𝒢) gravity". International Journal of Modern Physics D 26, № 04 (17 лютого 2017): 1750030. http://dx.doi.org/10.1142/s0218271817500304.
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This paper investigates inflationary dynamics for isotropic and homogeneous universe model in the background of [Formula: see text] gravity. We construct Hubble-flow functions, slow-roll parameters, amplitude of scalar power spectrum, spectral index and tensor–scalar ratio for a particular form of equation of state which describes quasi-de Sitter expansion. The dynamics of inflationary epoch is analyzed for scalar field as well as fluid cosmology with viable power-law [Formula: see text] model. We obtain different potential functions that correspond to chaotic inflation and Starobinsky type models. The graphical behavior of these parameters shows compatible results with observational Planck 2015 data in this gravity.
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Demirci, Beyda, and Mustafa Sevüktekin. "The evaluation of Turkey's foreign trade with different country groups within the framework of the gravity model." Volume 2, Issue 2 2, no. 2 (December 29, 2022): 52–65. http://dx.doi.org/10.53753/jame.2.2.02.
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The gravity model is based on the law known as the gravitational law discovered by Newton and was first used by Tinbergen to explain the foreign trade flow. It assumes that the size of the countries affects the foreign trade flow positively and the distance variable affects the foreign trade flow negatively. After the collapse of the Soviet Union, the Black Sea Economic Cooperation Organization was established under the leadership of Turkey to develop foreign trade with the countries that declared their autonomy. Similar to the story of the disintegrating Soviets, the Balkan Countries also declared their independence by leaving Yugoslavia. This study aims to investigate whether the gravity model is appropriate to explain Turkey’s exports and imports to the Black Sea Economic Cooperation (BSEC), Balkan and selected countries during the 1996-2019 period. Export and import were used as dependent variables. Gravity model variables such as GDP, distance, population, language and common border variables were used to explain the exports and imports of the respective countries. For all these models, panel data analysis techniques were employed; pooled, random and fixed effects models were estimated and then tests for the model selection were carried out to choose the most appropriate model. After the appropriate models were determined, the assumption tests were executed. As a result of the study, it was concluded that the gravity model was suitable to explain Turkey’s imports to the Balkan countries and exports to the selected country groups. The results of the study suggested that while the gravity model was suitable for explaining the factors affecting Turkey’s trade flow for some country groups, it further suggested that it was not suitable for some countries.
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Abdul Rahim, Razinda Tasnim, Mohd Faizuddin Muhammad Zuki, and Nur Syamilah Md Noor. "Perspective Of Gravity Model Towards Halal Export: A Conceptual Study." Journal of Fatwa Management and Research 27, no. 2-SE (November 30, 2022): 56–67. http://dx.doi.org/10.33102/jfatwa.vol27no2-se.483.
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The first fundamental in Islam is that all things created by the almighty Allah s.w.t. are permissible or halal, except those that are explicitly prohibited in the Holy Quran or hadith. Another interesting concept closely connected with the halal concept is the safety and quality products and conducts better known as toyyiban. Hence, the halal concept should include toyyiban, or the better terms are Halalan Toyyiban, which can be translated as permissible and wholesomeness Meanwhile, the Halal industry is defined as an industry that produces and offer good quality products and services which under Sharia law. Sharia law is the law that governs Muslims' everyday conducts. The Halal industry includes sectors such as food, cosmetics, ingredients, pharmaceutical, chemicals, livestock, logistics, tourism, and most notably the Islamic finance and banking sector Halal exports are growing steadily while the performance is still very far from the targeted growth. Thus, an understanding of the determinants of Halal export flows is essential. This study aims to investigate the nexus between Gross Domestic Product (GDP), Muslim population, Halal Certificate, and distance of Halal export. The method employed in this study is the Qualitative method. Content analysis is formed to prove the relationship between those independent variables with Halal export. Limitations and future study recommendations were discussed at the end of this research.
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Sharif, M., and Kanwal Nazir. "Cosmological reconstruction and stability in F(T,TG) gravity." International Journal of Modern Physics D 27, no. 02 (January 2018): 1850001. http://dx.doi.org/10.1142/s0218271818500013.
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This study investigates the reconstruction scheme and stability of some well-known cosmological models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] represent the torsion scalar and Gauss–Bonnet invariant torsion term, respectively. For this purpose, we consider isotropic homogeneous universe model and develop the corresponding field equations. It is found that we can reproduce cosmological evolution for power-law, de Sitter solutions, phantom/nonphantom era and [Formula: see text] cold dark matter by applying reconstruction scheme in this gravity. Finally, we discuss stability of the reconstructed power-law and de Sitter solutions as well as two well-known [Formula: see text] models. It is concluded that all these models provide stable solutions for suitable choices of the constants except power-law solutions.
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Singh, S. Surendra, and Yohenba Soibam. "Anisotropic models with generalized hybrid expansion in Brans–Dicke theory of gravity." International Journal of Geometric Methods in Modern Physics 18, no. 09 (June 4, 2021): 2150141. http://dx.doi.org/10.1142/s0219887821501413.
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The hybrid expansion law (HEL) for average scale factor that yields power-law and exponential-law cosmologies is considered in spatially homogenous and anisotropic Bianchi type-I model in the context of Brans–Dicke (BD) Theory of gravitation. The solutions of the field equations have been calculated by assuming the power-law expression between the average scale factor [Formula: see text] and scalar field ([Formula: see text]). We studied both interacting and non-interacting forms of dark energy and dark matter and obtained respective solutions. The energy density [Formula: see text] decreases with time while energy densities [Formula: see text] increases with time. In both the cases, the physical acceptability and stability of the models are also studied. The coincidence problem in [Formula: see text]CDM model can be ruled out with proper choice of coupling between dark matter (DM) and dark energy (DE). We also discussed the physical behaviors of the derived models with the current observations applied to late-time acceleration and beginning of the universe. In this model, it is observed that our HEL Bianchi type I universe is highly anisotropic in the beginning of universe and becomes isotropic and overlaps with flat [Formula: see text]CDM model at late times.
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Kibaroğlu, Salih, and Mustafa Senay. "Effects of bosonic and fermionic q-deformation on the entropic gravity." Modern Physics Letters A 34, no. 31 (October 7, 2019): 1950249. http://dx.doi.org/10.1142/s0217732319502493.
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In this paper, we study thermodynamical contributions to the theory of gravity under the q-deformed boson and fermion gas models. According to Verlinde’s proposal, the law of gravity is not based on a fundamental interaction but it emerges as an entropic force from the changes of entropy associated with the information on the holographic screen. In addition, Strominger shows that the extremal quantum black holes obey neither boson nor fermion statistics, but they obey deformed statistic. Using these notions, we find q-deformed entropy and temperature functions. We also present the contributions that come from the q-deformed model to the Poisson equation, Newton’s law of gravity and Einstein’s field equations.
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da Silva, J. G., and S. C. Ulhoa. "On gravitational energy in conformal teleparallel gravity." Modern Physics Letters A 32, no. 21 (June 21, 2017): 1750113. http://dx.doi.org/10.1142/s0217732317501139.
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The paper deals with the definition of gravitational energy in conformal teleparallel gravity. The total energy is defined by means of the field equations which allow a local conservation law. Then such an expression is analyzed for a homogeneous and isotropic Universe. This model is implemented by the Friedmann–Robertson–Walker (FRW) line element. The energy of the Universe in the absence of matter is identified with the dark energy, however it can be expanded for curved models defining such an energy as the difference between the total energy and the energy of the perfect fluid which is the matter field in the FRW model.
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Chen, Yanguang, Yajing Li, Shuo Feng, Xiaoming Man, and Yuqing Long. "Gravitational scaling analysis on spatial diffusion of COVID-19 in Hubei Province, China." PLOS ONE 16, no. 6 (June 11, 2021): e0252889. http://dx.doi.org/10.1371/journal.pone.0252889.
Повний текст джерелаАнотація:
The spatial diffusion of epidemic disease follows distance decay law in geography and social physics, but the mathematical models of distance decay depend on concrete spatio-temporal conditions. This paper is devoted to modeling spatial diffusion patterns of COVID-19 stemming from Wuhan city to Hubei province, China. The modeling approach is to integrate analytical method and experimental method. The local gravity model is derived from allometric scaling and global gravity model, and then the parameters of the local gravity model are estimated by observational data and least squares calculation. The main results are as below. The local gravity model based on power law decay can effectively describe the diffusion patterns and process of COVID-19 in Hubei Province, and the goodness of fit of the gravity model based on negative exponential decay to the observational data is not satisfactory. Further, the goodness of fit of the model to data entirely became better and better over time, the size elasticity coefficient increases first and then decreases, and the distance attenuation exponent decreases first and then increases. Moreover, the significance of spatial autoregressive coefficient in the model is low, and the confidence level is less than 80%. The conclusions can be reached as follows. (1) The spatial diffusion of COVID-19 of Hubei bears long range effect, and the size of a city and the distance of the city to Wuhan affect the total number of confirmed cases. (2) Wuhan direct transmission is the main process in the spatial diffusion of COVID-19 in Hubei at the early stage, and the horizontal transmission between regions is not significant. (3) The effect of spatial lockdown and isolation measures taken by Chinese government against the transmission of COVID-19 is obvious. This study suggests that the role of urban gravity (size and distance) should be taken into account to prevent and control epidemic disease.
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FU, XIANGYUN, PUXUN WU, and HONGWEI YU. "THE GROWTH OF MATTER PERTURBATIONS IN f(T) GRAVITY." International Journal of Modern Physics D 20, no. 07 (July 15, 2011): 1301–11. http://dx.doi.org/10.1142/s0218271811019372.
Повний текст джерелаАнотація:
In this paper, we study the growth index of matter density perturbations for the power law model in f(T) gravity. Using the parametrization γ(z) = γ0+ γ1(z/1 + z) for the growth index, which approximates the real evolution of γ(z) very well, and the observational data of the growth factor, we find that, at the 1σ confidence level, the power law model in f(T) gravity is consistent with the observations, since the obtained theoretical values of γ0and γ1are in the allowed region.
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Boko, R. D., M. J. S. Houndjo, and J. Tossa. "Stability and phase space analysis in f(R) theory with generalized exponential f(R) model." International Journal of Modern Physics D 25, no. 10 (August 25, 2016): 1650098. http://dx.doi.org/10.1142/s021827181650098x.
Повний текст джерелаАнотація:
We have studied in this paper, the stability of dynamical system in [Formula: see text] gravity. We have considered the [Formula: see text] [Formula: see text]-gravity and explored its dynamical analysis. We found six critical points among which only one describes a universe filled of both matter and dominated dark energy. It is shown that these critical points present specific phase spaces described by the corresponding fluids. Furthermore, we have investigated the stability conditions of these critical points and find that these conditions are dependent of the model parameters. We also study the stability of a new power-law [Formula: see text] model with de Sitter and power law solutions.
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Feng, Yinghua, and Wei Yang. "Packet loss rate monitoring model of IoT based on differential evolution algorithm." Web Intelligence 19, no. 3 (December 16, 2021): 215–26. http://dx.doi.org/10.3233/web-210468.
Повний текст джерелаАнотація:
In order to overcome the problems of high energy consumption and low execution efficiency of traditional Internet of things (IoT) packet loss rate monitoring model, a new packet loss rate monitoring model based on differential evolution algorithm is proposed. The similarity between each data point in the data space of the Internet of things is set as the data gravity. On the basis of the data gravity, combined with the law of gravity in the data space, the gravity of different data is calculated. At the same time, the size of the data gravity is compared, and the data are classified. Through the classification results, the packet loss rate monitoring model of the Internet of things is established. Differential evolution algorithm is used to solve the model to obtain the best monitoring scheme to ensure the security of network data transmission. The experimental results show that the proposed model can effectively reduce the data acquisition overhead and energy consumption, and improve the execution efficiency of the model. The maximum monitoring efficiency is 99.74%.
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Mishra, B., Sankarsan Tarai, and S. K. Tripathy. "Dynamics of an Anisotropic Universe inf(R,T)Theory." Advances in High Energy Physics 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/8543560.
Повний текст джерелаАнотація:
Dynamics of an anisotropic universe is studied inf(R,T)gravity using a rescaled functionalf(R,T), whereRis the Ricci Scalar andTis the trace of energy-momentum tensor. Three models have been constructed assuming a power law expansion of the universe. Physical features of the models are discussed. The model parameters are constrained from a dimensional analysis. It is found from the work that the anisotropic Bianchi typeVIh(BVIh) model in the modified gravity generally favours a quintessence phase when the parameterhis either-1or0. We may not get viable models in conformity with the present day observation forh=1.
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Chepigo, L. S., I. V. Lygin, and A. A. Bulychev. "Forward two-dimensional gravity problem for a parabolic density polygon." Moscow University Bulletin. Series 4. Geology, no. 4 (August 28, 2019): 89–93. http://dx.doi.org/10.33623/0579-9406-2019-4-89-93.
Повний текст джерелаАнотація:
The article describes the formula of gravity of a polygon with a density varying according to a parabolic law (two-dimensional model). Calculation of gravity according to the described formula can be made for both external and internal area.
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Liang, Lin, Tao Guo, Shi Qi Su, and Bing Bai. "Model and Dynamics Analysis of a New Oscillator under Gravity." Advanced Materials Research 694-697 (May 2013): 105–8. http://dx.doi.org/10.4028/www.scientific.net/amr.694-697.105.
Повний текст джерелаАнотація:
A mathematical modal for a new oscillator under Gravity is gived by The Second Law of Neton and proved the correctness by The Energy Method .We obtained a equation for the equilibrium point of system by the definition .We observe the dynamics action by the Hamilton function.Meanwhile the phase trajectories and the Poincaré sections are also presented. The analysis shows the complicated nonlinear dynamics with periodic motion in some special case.
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Farag Ali, Ahmed, and A. Tawfik. "Modified Newton's Law of Gravitation due to Minimal Length in Quantum Gravity." Advances in High Energy Physics 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/126528.
Повний текст джерелаАнотація:
A recent theory about the origin of the gravity suggests that the gravity is originally an entropic force. In this work, we discuss the effects of generalized uncertainty principle (GUP) which is proposed by some approaches to quantum gravity such as string theory, black hole physics, and doubly special relativity theories (DSR), on the area law of the entropy. This leads to aarea-type correction to the area law of entropy which implies that the number of bitsNis modified. Therefore, we obtain a modified Newton’s law of gravitation. Surprisingly, this modification agrees with different sign with the prediction of Randall-Sundrum II model which contains one uncompactified extra dimension. Furthermore, such modification may have observable consequences at length scales much larger than the Planck scale.
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SHARIF, M., and SHAMAILA RANI. "ENTROPY CORRECTED HOLOGRAPHIC DARK ENERGY f(T) GRAVITY MODEL." Modern Physics Letters A 29, no. 02 (January 20, 2014): 1450015. http://dx.doi.org/10.1142/s0217732314500151.
Повний текст джерелаАнотація:
This paper is devoted to study the power-law entropy corrected holographic dark energy (ECHDE) model in the framework of f(T) gravity. We assume infrared (IR) cutoff in terms of Granda–Oliveros (GO) length and discuss the constructed f(T) model in interacting as well as in non-interacting scenarios. We explore some cosmological parameters like equation of state (EoS), deceleration, statefinder parameters as well as ωT–ωT′ analysis. The EoS and deceleration parameters indicate phantom behavior of the accelerated expansion of the universe. It is mentioned here that statefinder trajectories represent consistent results with ΛCDM limit, while evolution trajectory of ωT–ωT′ phase plane does not approach to ΛCDM limit for both interacting and non-interacting cases.
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Tuan, Do Quoc, and Nguyen Sonnet Hung Q. "No Small Hairs in Anisotropic Power-law Gauss-Bonnet Inflation." Communications in Physics 29, no. 2 (May 14, 2019): 173. http://dx.doi.org/10.15625/0868-3166/29/2/13677.
Повний текст джерелаАнотація:
We will examine whether anisotropic hairs exist in a string-inspired scalar-Gauss-Bonnet gravity model with the absence of potential of scalar field during the inflationary phase. As a result, we are able to obtain the Bianchi type I power-law solution to this model under the assumption that the scalar field acts as the phantom field, whose kinetic is negative definite. However, the obtained anisotropic hair of this model turns out to be large, which is inconsistent with the observational data. We will therefore introduce a nontrivial coupling between scalar and vector fields such as \(f^2(\phi)F_{\mu\nu}F^{\mu\nu}\) into the scalar-Gauss-Bonnet model with the expectation that the anisotropic hair would be reduced to a small one. Unfortunately, the magnitude of the obtained anisotropic hair is still large. These results indicate that the scalar-Gauss-Bonnet gravity model with the absence of potential of scalar field might not be suitable to generate small anisotropic hairs during the inflationary phase.
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Godonou, A. E., M. J. S. Houndjo, and J. Tossa. "Holographic dark energy model in unimodular f(T) gravity." International Journal of Geometric Methods in Modern Physics 16, no. 01 (January 2019): 1950003. http://dx.doi.org/10.1142/s0219887819500038.
Повний текст джерелаАнотація:
This work deals with holographic dark energy in the context of unimodular [Formula: see text] gravity, which is a modification of teleparallel gravity. We develop the general reconstruction procedure of the [Formula: see text] form that can yield the holographic feature of the dark energy. We fit the reconstructed model with the [Formula: see text] data and our results show a perfect agreement with the WMAP9 cosmological observational data, at least for the range [Formula: see text]. We investigate the consistency of the reconstructed model by studying its stability against linear gravitational and matter perturbations, fixing [Formula: see text] to [Formula: see text]. The model presents stability for both de Sitter and power-law solutions and we conclude that it is a good candidate as alternative viable model for characterizing holographic dark energy.
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Xiao, Dong, Yingfeng Meng, Xiangyang Zhao, Gao Li, and Jiaxin Xu. "Liquid–liquid gravity displacement in a vertical fracture during drilling: Experimental study and mathematical model." Energy Exploration & Exploitation 38, no. 2 (September 7, 2019): 533–54. http://dx.doi.org/10.1177/0144598719874467.
Повний текст джерелаАнотація:
Gravity displacement often occurs when drilling a vertical fractured formation, causing a downhole complexity with risk of blowout and reservoir damage, well control difficulty, drilling cycle prolongation, and increased costs. Based on an experimental device created for simulating the gravity displacement, various factors affecting the displacement quantity were quantitatively evaluated by simulating the fracture width, asphalt viscosity, drilling fluid density, and viscosity under different working conditions, and a liquid–liquid displacement law was obtained. Using the theories of rock mechanics, fluid mechanics, and seepage mechanics, based on conformal mapping, as well as a fracture-pore double substrate fluid flow model, we established a steady-state mathematical model of fractured formation liquid–liquid gravity displacement by optimizing the shape factors and using a combination of gravity displacement experiments to verify the feasibility of the mathematical model. We analyzed the influence of drilling fluid density, fracture height and length, and asphalt viscosity on displacement rate, and obtained the corresponding laws. The results show that when the oil–fluid interface is stable, the fracture width is the most important factor affecting the gravity displacement, and plugging is the most effective means of managing gravity displacement.
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Pan, Yulin, Brian K. Arbic, Arin D. Nelson, Dimitris Menemenlis, W. R. Peltier, Wentao Xu, and Ye Li. "Numerical Investigation of Mechanisms Underlying Oceanic Internal Gravity Wave Power-Law Spectra." Journal of Physical Oceanography 50, no. 9 (September 1, 2020): 2713–33. http://dx.doi.org/10.1175/jpo-d-20-0039.1.
Повний текст джерелаАнотація:
AbstractWe consider the power-law spectra of internal gravity waves in a rotating and stratified ocean. Field measurements have shown considerable variability of spectral slopes compared to the high-wavenumber, high-frequency portion of the Garrett–Munk (GM) spectrum. Theoretical explanations have been developed through wave turbulence theory (WTT), where different power-law solutions of the kinetic equation can be found depending on the mechanisms underlying the nonlinear interactions. Mathematically, these are reflected by the convergence properties of the so-called collision integral (CL) at low- and high-frequency limits. In this work, we study the mechanisms in the formation of the power-law spectra of internal gravity waves, utilizing numerical data from the high-resolution modeling of internal waves (HRMIW) in a region northwest of Hawaii. The model captures the power-law spectra in broad ranges of space and time scales, with scalings ω−2.05±0.2 in frequency and m−2.58±0.4 in vertical wavenumber. The latter clearly deviates from the GM76 spectrum but is closer to a family of induced-diffusion-dominated solutions predicted by WTT. Our analysis of nonlinear interactions is performed directly on these model outputs, which is fundamentally different from previous work assuming a GM76 spectrum. By applying a bicoherence analysis and evaluations of modal energy transfer, we show that the CL is dominated by nonlocal interactions between modes in the power-law range and low-frequency inertial motions. We further identify induced diffusion and the near-resonances at its spectral vicinity as dominating the formation of power-law spectrum.
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Fomin, Igor, and Sergey Chervon. "Exact and Slow-Roll Solutions for Exponential Power-Law Inflation Connected with Modified Gravity and Observational Constraints." Universe 6, no. 11 (October 29, 2020): 199. http://dx.doi.org/10.3390/universe6110199.
Повний текст джерелаАнотація:
We investigate the ability of the exponential power-law inflation to be a phenomenologically correct model of the early universe. We study General Relativity (GR) scalar cosmology equations in Ivanov–Salopek–Bond (or Hamilton–Jacobi like) representation where the Hubble parameter H is the function of a scalar field ϕ. Such approach admits calculation of the potential for given H(ϕ) and consequently reconstruction of f(R) gravity in parametric form. By this manner the Starobinsky potential and non-minimal Higgs potential (and consequently the corresponding f(R) gravity) were reconstructed using constraints on the model’s parameters. We also consider methods for generalising the obtained solutions to the case of chiral cosmological models and scalar-tensor gravity. Models based on the quadratic relationship between the Hubble parameter and the function of the non-minimal interaction of the scalar field and curvature are also considered. Comparison to observation (PLANCK 2018) data shows that all models under consideration give correct values for the scalar spectral index and tensor-to-scalar ratio under a wide range of exponential-power-law model’s parameters.
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Borgade, Kailas R., S. R. Bhoyar, and Vineeta Basotia. "Dynamics of Bulk Viscous String Cosmological Model in f(R,G) Theory of Gravity." International Journal of Research in Engineering, Science and Management 4, no. 4 (April 24, 2021): 89–97. http://dx.doi.org/10.47607/ijresm.2021.654.
Повний текст джерелаАнотація:
Existing investigations dedicated to the self-propelling investigation of dynamics of bulk viscous string in LRS Bianchi type-I cosmological model within the circumstance of alternative theory of gravity with Langrangian be the impulsive perform of Ricci scalar R and Gouss-Bonnet invariant G , say f(R,G) gravity. Exact solutions of the field equations correspond to special law of variation which provides singular model. Also some physical and kinematical aspects and its behavior with the present day universe of the cosmological model have been discussed.
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Asimakis, Petros, Emmanuel N. Saridakis, Spyros Basilakos, and Kuralay Yesmakhanova. "Big Bang Nucleosynthesis Constraints on f(T,TG) Gravity." Universe 8, no. 9 (September 14, 2022): 486. http://dx.doi.org/10.3390/universe8090486.
Повний текст джерелаАнотація:
We confront f(T,TG) gravity, with big bang nucleosynthesis (BBN) requirements. The former is obtained using both the torsion scalar, as well as the teleparallel equivalent of the Gauss–Bonnet term, in the Lagrangian, resulting to modified Friedmann equations in which the extra torsional terms constitute an effective dark energy sector. We calculate the deviations of the freeze-out temperature Tf, caused by the extra torsion terms in comparison to ΛCDM paradigm. Then, we impose five specific f(T,TG) models and extract the constraints on the model parameters in order for the ratio |ΔTf/Tf| to satisfy the observational BBN bound. As we find, in most of the models the involved parameters are bounded in a narrow window around their general relativity values as expected, asin the power-law model, where the exponent n needs to be n≲0.5. Nevertheless, the logarithmic model can easily satisfy the BBN constraints for large regions of the model parameters. This feature should be taken into account in future model building.
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Sefiedgar, Akram Sadat, and Majid Daghigh. "Thermodynamics of the FRW universe in rainbow gravity." International Journal of Modern Physics D 26, no. 13 (October 22, 2017): 1750139. http://dx.doi.org/10.1142/s0218271817501395.
Повний текст джерелаАнотація:
Rainbow gravity can be a suitable model to study the Friedmann–Robertson–Walker (FRW) universe in the realm of high energy physics. In rainbow gravity the radius of the apparent horizon is modified and it is used to derive the surface gravity and the temperature on the horizon. Inspired by the modified Friedmann equation in rainbow gravity and adopting the viewpoint that there is a deep connection between Friedmann equation and the first law of thermodynamics, the entropy on the horizon is obtained. It is interesting to be noted that the thermodynamical properties of the FRW universe depend on the energy of the probe, which is used by an observer to investigate the spacetime. Finally, it is shown that the validity of the generalized second law (GSL) of thermodynamics can be considered as a useful instrument to restrict the choice of rainbow gravity functions.
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Wang, Zihan, and Yanguang Chen. "Exploring Spatial Patterns of Interurban Passenger Flows Using Dual Gravity Models." Entropy 24, no. 12 (December 8, 2022): 1792. http://dx.doi.org/10.3390/e24121792.
Повний текст джерелаАнотація:
Geographical gravity models can be employed to quantitatively describe and predict spatial flows, including migration flows, passenger flows, daily commuting flows, etc. However, how to model spatial flows and reveal the structure of urban traffic networks in the case of missing partial data is still a problem to be solved. This paper is devoted to characterizing the interurban passenger flows in the Beijing–Tianjin–Hebei region of China using dual gravity models and Tencent location big data. The method of parameter estimation is the least squares regression. The main results are as follows. First, both the railway and highway passenger flows can be effectively described by dual gravity models. A small part of missing spatial data can be compensated for by predicted values. Second, the fractal properties of traffic flows can be revealed. The railway passenger flows follow the gravity scaling law better than the highway passenger flows. Third, the prediction residuals indicate the changing trend of interurban connections in the study area in recent years. The center of gravity of the spatial dynamics has shifted from the Beijing–Tianjin–Tangshan triangle to the Beijing–Baoding–Shijiazhuang axis. A conclusion can be reached that the dual gravity model is an effective tool for analyzing spatial structures and dynamics of traffic networks and flows. Moreover, the model provides a new approach to estimating the fractal dimensions of traffic networks and spatial flow patterns.
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Filippo, Sergio De, Filippo Maimone, Adele Naddeo, and Giovanni Scelza. "Microscopic foundation of the second law of thermodynamics within nonunitary Newtonian gravity." International Journal of Quantum Information 17, no. 08 (December 2019): 1941006. http://dx.doi.org/10.1142/s0219749919410065.
Повний текст джерелаАнотація:
The quest for a microscopic foundation of thermodynamics is addressed within the Nonunitary Newtonian Gravity (NNG) model through the study of a specific closed system, namely, a three-dimensional harmonic nanocrystal. A numerical calculation of the nanocrystal von Neumann entropy as a function of time is performed, showing a sharp monotonic increase, followed by a stabilization at late times. This behavior is consistent with the emergence of a microcanonical ensemble within the initial energy levels, signaling, in this way, the establishment of a nonunitary gravity-induced thermal equilibrium.
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Fayaz, V., H. Hossienkhani, A. Aghamohammadi, and M. Amirabadi. "Ghost dark energy models in Bianchi I cosmologies with modified gravity." Canadian Journal of Physics 92, no. 2 (February 2014): 168–72. http://dx.doi.org/10.1139/cjp-2013-0434.
Повний текст джерелаАнотація:
A ghost dark energy model has been recently put forward to explain the current accelerated expansion of the universe. In this model, we develop the general scheme for modified f(R) gravity reconstruction from realistic anisotropic Bianchi type I cosmology. Power-law volumetric expansion is used to obtain exact solutions of the field equations. We discuss the physical behavior of the solutions and anisotropy behavior of the fluid, the expansion parameter, and the model in future evolution of the universe. We reconstruct corresponding f(R) gravities and obtain the equation of state parameter. We show that the corresponding f(R) gravity of the ghost dark energy model can behave like phantom or quintessence of the selected models that describe accelerated expansion of the universe.
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Abdolmaleki, A., and T. Najafi. "Generalized second law of thermodynamics on the apparent horizon in modified Gauss–Bonnet gravity." International Journal of Modern Physics D 25, no. 04 (March 10, 2016): 1650040. http://dx.doi.org/10.1142/s0218271816500401.
Повний текст джерелаАнотація:
Modified gravity (MG) and generalized second law (GSL) of thermodynamics are interesting topics in the modern cosmology. In this regard, we investigate the GSL of gravitational thermodynamics in the framework of modified Gauss–Bonnet (GB) gravity or [Formula: see text]-gravity. We consider a spatially FRW universe filled with the pressureless matter and radiation enclosed by the dynamical apparent horizon with the Hawking temperature. For two viable [Formula: see text] models, we first numerically solve the set of differential equations governing the dynamics of [Formula: see text]-gravity. Then, we obtain the evolutions of the Hubble parameter, the GB curvature invariant term, the density and equation of state (EoS) parameters as well as the deceleration parameter. In addition, we check the energy conditions for both models and finally examine the validity of the GSL. For the selected [Formula: see text] models, we conclude that both models have a stable de Sitter attractor. The EoS parameters behave quite similar to those of the [Formula: see text]CDM model in the radiation/matter dominated epochs, then they enter the phantom region before reaching the de Sitter attractor with [Formula: see text]. The deceleration parameter starts from the radiation/matter dominated eras, then transits from a cosmic deceleration to acceleration and finally approaches a de Sitter regime at late times, as expected. Furthermore, the GSL is respected for both models during the standard radiation/matter dominated epochs. Thereafter when the universe becomes accelerating, the GSL is violated in some ranges of scale factor. At late times, the evolution of the GSL predicts an adiabatic behavior for the accelerated expansion of the universe.
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LEE, TAE HOON, and SUNNYEO LEE. "BULK SCALAR-FIELD INFLUENCED FRW UNIVERSE MODEL." Modern Physics Letters A 27, no. 01 (January 10, 2012): 1250003. http://dx.doi.org/10.1142/s0217732312500034.
Повний текст джерелаАнотація:
We consider a nonlinear sigma-model-like theory of bulk scalar fields coupled to the five-dimensional Einstein gravity. In Robertson–Walker spacetimes, we find some power-law cosmological solutions for the scale factor when the expansion rate of an extra dimension is proportional to one of our (3+1)-dimensional universe. Among them, the solution with a decreasing warp factor could be related to the one-brane model of Randall and Sundrum.
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Sharif, Muhammad, and Ayesha Ikram. "Study of GSLT in Curvature-Matter Coupling Gravity." EPJ Web of Conferences 168 (2018): 03007. http://dx.doi.org/10.1051/epjconf/201816803007.
Повний текст джерелаАнотація:
In this work, we study the first and generalized second laws of thermodynamics at the apparent horizon of homogeneous and isotropic universe model in the context of f (G, T) gravity (G and T represent the Gauss-Bonnet invariant and trace of the energymomentum tensor, respectively). We formulate the corresponding field equations as well as determine the radius, temperature and entropy to analyze these laws. An extra term associated with entropy production is appeared in the first law due to the non-equilibrium treatment of thermodynamics. It is found that the universal condition is obtained to preserve the generalized second law of thermodynamics.
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Munawaroh, L. W., V. Serevina, and B. H. Iswanto. "MIX Reality Based Media Prototype For Learning Physics of Gravity And Kepler’s Law." Journal of Physics: Conference Series 2019, no. 1 (October 1, 2021): 012054. http://dx.doi.org/10.1088/1742-6596/2019/1/012054.
Повний текст джерелаАнотація:
Abstract Gravity and Kepler’s Laws are materials that study natural phenomena, events or phenomena that reveal all the secrets of the universe. Based on the observations of several schools, there are difficulties for students understanding gravity and Kepler’s laws because they can not directly present 3D learning media in interactive classes. This study aims to develop a mixed reality-based media prototype for learning gravity physics and Kepler’s laws using special VR box glasses and markers to display 3D objects equipped with audio explanations, 3D animations, and evaluation questions. The research was conducted using the ADDIE development model (Analyze, design, develop, implement, and evaluate). To make it easier for students to use mix reality applications, the mix reality software design employs blender version 2.78, unity 5.1, Photoshop, the vuforia AR extension for unity, and the c # programming language. The trial of the feasibility of mix reality media was conducted by averaging the results of the validator’s assessment of each aspect of the assessment. Mixed reality media prototypes can help students understand gravity and Kepler’s laws.
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Mitra, Saugata, Subhajit Saha, and Subenoy Chakraborty. "Modified Hawking temperature and entropic force: A prescription in FRW model." Modern Physics Letters A 30, no. 13 (April 13, 2015): 1550058. http://dx.doi.org/10.1142/s0217732315500583.
Повний текст джерелаАнотація:
The idea of Verlinde that gravity is an entropic force caused by information changes associated with the positions of material bodies, is used in the present work for the Friedmann–Robertson–Walker (FRW) model of the Universe. Using modified Hawking temperature, the Friedmann equations are derived on any horizon. For the validity of the first law of thermodynamics (i.e. Clausius relation) it is found that there is modification of Bekenstein entropy on the horizon. However, using equipartition law of energy, Bekenstein entropy is recovered.