Spherical diffuse Yukawa sources in relativity

1977 ◽  
Vol 55 (18) ◽  
pp. 1628-1632 ◽  
Author(s):  
J. A. Souza ◽  
A. F. da F. Teixeira
Keyword(s):  
Short Range ◽  
Mass Parameter ◽  
Scalar Fields ◽  
Gravitational Theory ◽  
The Other ◽  
Field Equations ◽  
Physical Systems ◽  
Simple Physical Interpretation ◽  
The Stability ◽  
Uniform Ratio

A system containing only two diffuse massless sources (bearing a uniform ratio) of two different short range scalar fields is studied, according to Einstein's gravitational theory. One field is attractive, the other is repulsive. The distribution is in static equilibrium with spherical symmetry. A class of solutions of the field equations is obtained, where the solutions are nonsingular and have simple physical interpretation. A Schwarzschild-type gravitation is found at infinity, with the mass parameter solely arising from the scalar fields; these rapidly disappear with a Yukawa-type behaviour. The stability of the system is briefly stated, and the applicability of the model to large or small physical systems is pointed out.

scholarly journals Thick brane structures in generalized hybrid metric-Palatini gravity

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
João Luís Rosa ◽  
D. A. Ferreira ◽  
Dionisio Bazeia ◽  
Francisco S. N. Lobo
Keyword(s):  
Scalar Field ◽  
Internal Structure ◽  
Zero Mode ◽  
Scalar Fields ◽  
Gravitational Theory ◽  
Tensor Representation ◽  
The Stability

AbstractIn this work, we study 5-dimensional braneworld scenarios in the scalar-tensor representation of the generalized hybrid metric-Palatini gravitational theory. We start by considering a model for a brane supported purely by the gravitational scalar fields of the theory and then consider other distinct cases where the models are also supported by an additional matter scalar field. We investigate the stability of the gravity sector and show that the models are all robust against small fluctuations of the metric. In particular, in the presence of the additional scalar field, we find that the profile of the gravitational zero mode may be controlled by the parameters of the model, being also capable of developing internal structure.

scholarly journals Metric-affine bumblebee gravity: classical aspects

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Adrià Delhom ◽  
J. R. Nascimento ◽  
Gonzalo J. Olmo ◽  
A. Yu. Petrov ◽  
Paulo J. Porfírio
Keyword(s):  
Physical Properties ◽  
Weak Field ◽  
The Other ◽  
Effective Theory ◽  
Field Equations ◽  
Field Limit ◽  
Weak Field Limit ◽  
Effective Metric ◽  
The Stability ◽  
Matter Fields

AbstractWe consider the metric-affine formulation of bumblebee gravity, derive the field equations, and show that the connection can be written as Levi-Civita of a disformally related metric in which the bumblebee field determines the disformal part. As a consequence, the bumblebee field gets coupled to all the other matter fields present in the theory, potentially leading to nontrivial phenomenological effects. To explore this issue we compute the post-Minkowskian, weak-field limit and study the resulting effective theory. In this scenario, we couple scalar and spinorial matter to the effective metric, and then we explore the physical properties of the VEV of the bumblebee field, focusing mainly on the dispersion relations and the stability of the resulting effective theory.

Two bodies at rest in general relativity

1959 ◽  
Vol 55 (1) ◽  
pp. 82-86 ◽  
Author(s):  
L. Marder
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
The Other ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Definite Sense ◽  
The Stability ◽  
Two Bodies

ABSTRACTIt is well known that there is no static axisymmetric two-body solution of Einstein's gravitational field equations, if it is assumed that the bodies are separated in a certain definite sense. In this paper it is shown, by the construction of a complete physically sensible model, that static two-body solutions do exist for systems in which one body is hollow and contains the other. The stability of the particular system described is briefly discussed.

scholarly journals Anisotropic power-law inflation in a two-scalar-field model with a mixed kinetic term

2017 ◽  
Vol 26 (07) ◽  
pp. 1750072 ◽  
Author(s):  
Tuan Q. Do ◽  
Sonnet Hung Q. Nguyen
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Field Model ◽  
Scalar Fields ◽  
Kinetic Term ◽  
Type I ◽  
Field Equations ◽  
Scalar Field Model ◽  
Phantom Scalar ◽  
The Stability

We examine whether an extended scenario of a two-scalar-field model, in which a mixed kinetic term of canonical and phantom scalar fields is involved, admits the Bianchi type I metric, which is homogeneous but anisotropic spacetime, as its power-law solutions. Then, we analyze the stability of the anisotropic power-law solutions to see whether these solutions respect the cosmic no-hair conjecture or not during the inflationary phase. In addition, we will also investigate a special scenario, where the pure kinetic terms of canonical and phantom fields disappear altogether in field equations, to test again the validity of cosmic no-hair conjecture. As a result, the cosmic no-hair conjecture always holds in both these scenarios due to the instability of the corresponding anisotropic inflationary solutions.

Extended scalar–tensor theory and thermodynamics in teleparallel framework

2016 ◽  
Vol 31 (33) ◽  
pp. 1650185 ◽  
Author(s):  
Mustafa Salti ◽  
Oktay Aydogdu ◽  
Irfan Acikgoz
Keyword(s):  
Lagrangian Density ◽  
Scalar Fields ◽  
Teleparallel Gravity ◽  
The Other ◽  
Field Energy ◽  
Field Equations ◽  
Energy Effect ◽  
Tensor Theory ◽  
Equilibrium Profiles ◽  
Friedmann Robertson Walker

We present here a new modified gravitation theory for the galactic dark energy effect by using a general Lagrangian density which is represented by an arbitrary function f(T, [Formula: see text], X) where T describes the torsion scalar in teleparallel gravity while X shows the kinetic scalar field energy. While the function is in general form, once reduced, the model can be transformed into some of the other well-known gravitation theories. After deriving the corresponding field equations and considering the flat Friedmann–Robertson–Walker type universe which is filled with ordinary cosmic matter, we discuss both the non-equilibrium and equilibrium profiles of galactic thermodynamics. We find that there exists an equilibrium picture of thermodynamics. Additionally, we also generalize ordinary f(T, [Formula: see text], X) model’s action to the case in which there exists an interaction between the chameleon and scalar fields.

Uniformity of Magnification from Different Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 32-33
Author(s):  
Godfrey C. Hoskins ◽  
V. Williams ◽  
V. Allison
Keyword(s):  
Diffraction Grating ◽  
The Other ◽  
Carbon Replica ◽  
Electron Microscopes ◽  
The Stability

The method demonstrated is an adaptation of a proven procedure for accurately determining the magnification of light photomicrographs. Because of the stability of modern electrical lenses, the method is shown to be directly applicable for providing precise reproducibility of magnification in various models of electron microscopes.A readily recognizable area of a carbon replica of a crossed-line diffraction grating is used as a standard. The same area of the standard was photographed in Phillips EM 200, Hitachi HU-11B2, and RCA EMU 3F electron microscopes at taps representative of the range of magnification of each. Negatives from one microscope were selected as guides and printed at convenient magnifications; then negatives from each of the other microscopes were projected to register with these prints. By deferring measurement to the print rather than comparing negatives, correspondence of magnification of the specimen in the three microscopes could be brought to within 2%.

scholarly journals Black Hole Algorithm for Sustainable Design of Counterfort Retaining Walls

2020 ◽  
Vol 12 (7) ◽  
pp. 2767 ◽  
Author(s):  
Víctor Yepes ◽  
José V. Martí ◽  
José García
Keyword(s):  
Black Hole ◽  
Sustainable Design ◽  
Retaining Walls ◽  
The Other ◽  
Trade Off ◽  
Construction Company ◽  
Geometric Variables ◽  
The Stability ◽  
The Cost ◽  
Black Hole Algorithm

The optimization of the cost and CO 2 emissions in earth-retaining walls is of relevance, since these structures are often used in civil engineering. The optimization of costs is essential for the competitiveness of the construction company, and the optimization of emissions is relevant in the environmental impact of construction. To address the optimization, black hole metaheuristics were used, along with a discretization mechanism based on min–max normalization. The stability of the algorithm was evaluated with respect to the solutions obtained; the steel and concrete values obtained in both optimizations were analyzed. Additionally, the geometric variables of the structure were compared. Finally, the results obtained were compared with another algorithm that solved the problem. The results show that there is a trade-off between the use of steel and concrete. The solutions that minimize CO 2 emissions prefer the use of concrete instead of those that optimize the cost. On the other hand, when comparing the geometric variables, it is seen that most remain similar in both optimizations except for the distance between buttresses. When comparing with another algorithm, the results show a good performance in optimization using the black hole algorithm.

scholarly journals A Fractional SAIDR Model in the Frame of Atangana–Baleanu Derivative

2021 ◽  
Vol 5 (2) ◽  
pp. 32
Author(s):  
Esmehan Uçar ◽  
Sümeyra Uçar ◽  
Fırat Evirgen ◽  
Necati Özdemir
Keyword(s):  
Existence And Uniqueness ◽  
Laplace Transformation ◽  
Cell Phones ◽  
Mobile Network ◽  
The Other ◽  
Banach Fixed Point Theorem ◽  
Propagation Models ◽  
Computer Worms ◽  
Computer Viruses ◽  
The Stability

It is possible to produce mobile phone worms, which are computer viruses with the ability to command the running of cell phones by taking advantage of their flaws, to be transmitted from one device to the other with increasing numbers. In our day, one of the services to gain currency for circulating these malignant worms is SMS. The distinctions of computers from mobile devices render the existing propagation models of computer worms unable to start operating instantaneously in the mobile network, and this is particularly valid for the SMS framework. The susceptible–affected–infectious–suspended–recovered model with a classical derivative (abbreviated as SAIDR) was coined by Xiao et al., (2017) in order to correctly estimate the spread of worms by means of SMS. This study is the first to implement an Atangana–Baleanu (AB) derivative in association with the fractional SAIDR model, depending upon the SAIDR model. The existence and uniqueness of the drinking model solutions together with the stability analysis are shown through the Banach fixed point theorem. The special solution of the model is investigated using the Laplace transformation and then we present a set of numeric graphics by varying the fractional-order θ with the intention of showing the effectiveness of the fractional derivative.

scholarly journals Competing Conventions with Costly Information Acquisition

Games ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 53
Author(s):  
Roberto Rozzi
Keyword(s):  
Information Acquisition ◽  
Evolutionary Model ◽  
Equilibrium Selection ◽  
The Other ◽  
Group Interactions ◽  
Social Coordination ◽  
Long Run ◽  
Stochastic Stability Analysis ◽  
The Stability ◽  
The Cost

We consider an evolutionary model of social coordination in a 2 × 2 game where two groups of players prefer to coordinate on different actions. Players can pay a cost to learn their opponent’s group: if they pay it, they can condition their actions concerning the groups. We assess the stability of outcomes in the long run using stochastic stability analysis. We find that three elements matter for the equilibrium selection: the group size, the strength of preferences, and the information’s cost. If the cost is too high, players never learn the group of their opponents in the long run. If one group is stronger in preferences for its favorite action than the other, or its size is sufficiently large compared to the other group, every player plays that group’s favorite action. If both groups are strong enough in preferences, or if none of the groups’ sizes is large enough, players play their favorite actions and miscoordinate in inter-group interactions. Lower levels of the cost favor coordination. Indeed, when the cost is low, in inside-group interactions, players always coordinate on their favorite action, while in inter-group interactions, they coordinate on the favorite action of the group that is stronger in preferences or large enough.

A Biomechanical Evaluation of Three Forms of Internal Fixation Used in Ankle Arthrodesis

1994 ◽  
Vol 15 (6) ◽  
pp. 297-300 ◽  
Author(s):  
Michael P. Dohm ◽  
James B. Benjamin ◽  
Jeffrey Harrison ◽  
John A. Szivek
Keyword(s):  
Internal Fixation ◽  
Plate Fixation ◽  
Ankle Arthrodesis ◽  
Biomechanical Study ◽  
The Other ◽  
Fixation Failure ◽  
Plate Group ◽  
Biomechanical Evaluation ◽  
The Stability ◽  
Fibular Strut

A biomechanical study was undertaken to evaluate the relative stability of three types of internal fixation used for ankle arthrodesis. Crossed screw fixation, RAF fibular strut fixation, and T-plate fixation were tested in 30 cadaver ankles using an MTS machine. T-plate fixation consistantly provided the stiffest construct when compared with the other types of fixation. Failure occurred by distraction of bony surfaces, posterior to the plane of fixation, in the crossed screw and RAF groups. In contrast, failure in the T-plate group occurred through compression of bone anterior to the midcoronal plane of the tibia. Although the stability of fixation is only one factor in determining the success or failure of ankle arthrodesis, the results of this study would support T-plate fixation over the other forms tested.

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