scholarly journals Three-dimensional axisymmetric sources for Majumdar–Papapetrou type spacetimes

2018 ◽  
Vol 27 (07) ◽  
pp. 1850068
Author(s):  
Gonzalo García-Reyes ◽  
Kevin A. Hernández-Gómez
Keyword(s):  
Three Dimensional ◽  
Relativistic Effects ◽  
Dark Matter Halo ◽  
Energy Conditions ◽  
Newtonian Potential ◽  
Potential Density ◽  
Rayleigh Criterion ◽  
Test Particles ◽  
Radial Perturbation ◽  
The Stability

From Newtonian potential-density pairs, we construct three-dimensional axisymmetric relativistic sources for a Majumdar–Papapetrou type conformastatic spacetime. As simple examples, we build two families of relativistic thick disks from the first two Miyamoto–Nagai potential-density pairs used in Newtonian gravity to model flat galaxies, and a three-component relativistic model of galaxy (bulge, disk and dark matter halo). We study the equatorial circular motion of test particles around such structures. Also the stability of the orbits is analyzed for radial perturbation using an extension of the Rayleigh criterion. In all examples, the relativistic effects are analyzed and compared with the Newtonian approximation. The models are considered satisfying all the energy conditions.

scholarly journals Stability of thin-shell wormholes from noncommutative BTZ black hole

2015 ◽  
Vol 24 (05) ◽  
pp. 1550034 ◽  
Author(s):  
Piyali Bhar ◽  
Ayan Banerjee
Keyword(s):  
Black Hole ◽  
Thin Shell ◽  
Static Solution ◽  
Dynamical Analysis ◽  
Energy Conditions ◽  
Btz Black Hole ◽  
Wormhole Throat ◽  
Radial Perturbation ◽  
Thin Shell Wormholes ◽  
The Stability

In this paper, we construct thin-shell wormholes in (2 + 1)-dimensions from noncommutative BTZ black hole by applying the cut-and-paste procedure implemented by Visser. We calculate the surface stresses localized at the wormhole throat by using the Darmois–Israel formalism and we find that the wormholes are supported by matter violating the energy conditions. In order to explore the dynamical analysis of the wormhole throat, we consider that the matter at the shell is supported by dark energy equation of state (EoS) p = ωρ with ω < 0. The stability analysis is carried out of these wormholes to linearized spherically symmetric perturbations around static solutions. Preserving the symmetry we also consider the linearized radial perturbation around static solution to investigate the stability of wormholes which was explored by the parameter β (speed of sound).

scholarly journals Sawtooth-like oscillations of black hole accretion disks

2006 ◽  
Vol 2 (S238) ◽  
pp. 37-42
Author(s):  
Ryoji Matsumoto ◽  
Mami Machida
Keyword(s):  
Black Hole ◽  
Accretion Disks ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Relativistic Effects ◽  
Rotating Disk ◽  
Newtonian Potential ◽  
X Rays ◽  
Initial State ◽  
Magnetohydrodynamic Simulations

AbstractWe studied the origin of quasi-periodic oscillations (QPOs) of X-rays in black hole candidates by three-dimensional global resistive magnetohydrodynamic simulations of accretion disks. Initial state is a rotating disk threaded by weak toroidal magnetic fields. General relativistic effects are simulated by using the pseudo-Newtonian potential. When the temperature of the outer disk decreases, the accreting matter accumulates into an inner torus.We found that the inner torus is deformed into a crescent shape and that it shows sawtooth-like oscillations of magnetic energy with frequency 3-5Hz when the mass of the black hole is 10M⊙. The magnetic energy inside the torus is amplified until magnetic reconnection suddenly releases the accumulated magnetic energy. A new cycle of the oscillation starts when magnetic energy is amplified again. We found that high frequency QPOs with frequency around 100Hz in stellar mass black holes are excited when sawtooth-like oscillation appears in the inner torus.

A Liquid Metal Flow Between Two Coaxial Cylinders System

2019 ◽  
Vol 11 (1) ◽  
pp. 79-86
Author(s):  
Abdelkrim Merah ◽  
Ridha Kelaiaia ◽  
Faiza Mokhtari
Keyword(s):  
Couette Flow ◽  
Metal Flow ◽  
Three Dimensional ◽  
Liquid Sodium ◽  
Taylor Vortex ◽  
Turbulent Regime ◽  
Coaxial Cylinders ◽  
Concentric Cylinders ◽  
Ideal Tool ◽  
The Stability

Abstract The Taylor-Couette flow between two rotating coaxial cylinders remains an ideal tool for understanding the mechanism of the transition from laminar to turbulent regime in rotating flow for the scientific community. We present for different Taylor numbers a set of three-dimensional numerical investigations of the stability and transition from Couette flow to Taylor vortex regime of a viscous incompressible fluid (liquid sodium) between two concentric cylinders with the inner one rotating and the outer one at rest. We seek the onset of the first instability and we compare the obtained results for different velocity rates. We calculate the corresponding Taylor number in order to show its effect on flow patterns and pressure field.

Handheld Laser Scanner Research

2019 ◽  
Vol 952 (10) ◽  
pp. 47-54
Author(s):  
A.V. Komissarov ◽  
A.V. Remizov ◽  
M.M. Shlyakhova ◽  
K.K. Yambaev
Keyword(s):  
Point Cloud ◽  
Three Dimensional ◽  
Laser Scanner ◽  
Test Site ◽  
Optical Systems ◽  
Advantages And Disadvantages ◽  
Site Survey ◽  
Laser Scanners ◽  
Three Dimensional Models ◽  
The Stability

The authors consider hand-held laser scanners, as a new photogrammetric tool for obtaining three-dimensional models of objects. The principle of their work and the newest optical systems based on various sensors measuring the depth of space are described in detail. The method of simultaneous navigation and mapping (SLAM) used for combining single scans into point cloud is outlined. The formulated tasks and methods for performing studies of the DotProduct (USA) hand-held laser scanner DPI?8X based on a test site survey are presented. The accuracy requirements for determining the coordinates of polygon points are given. The essence of the performed experimental research of the DPI?8X scanner is described, including scanning of a test object at various scanner distances, shooting a test polygon from various scanner positions and building point cloud, repeatedly shooting the same area of the polygon to check the stability of the scanner. The data on the assessment of accuracy and analysis of research results are given. Fields of applying hand-held laser scanners, their advantages and disadvantages are identified.

scholarly journals Gum Tragacanth (GT): A Versatile Biocompatible Material beyond Borders

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1510 ◽  
Author(s):  
Mohammad Ehsan Taghavizadeh Yazdi ◽  
Simin Nazarnezhad ◽  
Seyed Hadi Mousavi ◽  
Mohammad Sadegh Amiri ◽  
Majid Darroudi ◽  
...  
Keyword(s):  
Tissue Engineering ◽  
Food Packaging ◽  
Three Dimensional ◽  
Great Promise ◽  
Anionic Polymer ◽  
Gum Tragacanth ◽  
New Horizons ◽  
Tissue Healing ◽  
The Stability ◽  
Therapeutic Substance

The use of naturally occurring materials in biomedicine has been increasingly attracting the researchers’ interest and, in this regard, gum tragacanth (GT) is recently showing great promise as a therapeutic substance in tissue engineering and regenerative medicine. As a polysaccharide, GT can be easily extracted from the stems and branches of various species of Astragalus. This anionic polymer is known to be a biodegradable, non-allergenic, non-toxic, and non-carcinogenic material. The stability against microbial, heat and acid degradation has made GT an attractive material not only in industrial settings (e.g., food packaging) but also in biomedical approaches (e.g., drug delivery). Over time, GT has been shown to be a useful reagent in the formation and stabilization of metal nanoparticles in the context of green chemistry. With the advent of tissue engineering, GT has also been utilized for the fabrication of three-dimensional (3D) scaffolds applied for both hard and soft tissue healing strategies. However, more research is needed for defining GT applicability in the future of biomedical engineering. On this object, the present review aims to provide a state-of-the-art overview of GT in biomedicine and tries to open new horizons in the field based on its inherent characteristics.

scholarly journals Earth-size planet formation in the habitable zone of circumbinary stars

2020 ◽  
Vol 494 (1) ◽  
pp. 1045-1057 ◽  
Author(s):  
G O Barbosa ◽  
O C Winter ◽  
A Amarante ◽  
A Izidoro ◽  
R C Domingos ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Planet Formation ◽  
Terrestrial Planet ◽  
Close Binary ◽  
Habitable Zone ◽  
Density Profiles ◽  
Habitable Planets ◽  
Habitable Zones ◽  
Test Particles ◽  
The Stability

ABSTRACT This work investigates the possibility of close binary (CB) star systems having Earth-size planets within their habitable zones (HZs). First, we selected all known CB systems with confirmed planets (totaling 22 systems) to calculate the boundaries of their respective HZs. However, only eight systems had all the data necessary for the computation of HZ. Then, we numerically explored the stability within HZs for each one of the eight systems using test particles. From the results, we selected five systems that have stable regions inside HZs, namely Kepler-34,35,38,413, and 453. For these five cases of systems with stable regions in HZ, we perform a series of numerical simulations for planet formation considering discs composed of planetary embryos and planetesimals, with two distinct density profiles, in addition to the stars and host planets of each system. We found that in the case of the Kepler-34 and 453 systems, no Earth-size planet is formed within HZs. Although planets with Earth-like masses were formed in Kepler-453, they were outside HZ. In contrast, for the Kepler-35 and 38 systems, the results showed that potentially habitable planets are formed in all simulations. In the case of the Kepler-413system, in just one simulation, a terrestrial planet was formed within HZ.

Propagation of cosmic rays and their secondaries in the intracluster medium

2020 ◽  
Vol 15 (S359) ◽  
pp. 178-179
Author(s):  
Saqib Hussain ◽  
Rafael Alves Batista ◽  
Elisabete Maria de Gouveia Dal Pino ◽  
Klaus Dolag
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Intergalactic Medium ◽  
Three Dimensional ◽  
High Energy ◽  
Intracluster Medium ◽  
High Energy Cosmic Rays ◽  
Test Particles

AbstractWe present results of the propagation of high-energy cosmic rays (CRs) and their secondaries in the intracluster medium (ICM). To this end, we employ three-dimensional cosmological magnetohydrodynamical simulations of the turbulent intergalactic medium to explore the propagation of CRs with energies between 1014 and 1019 eV. We study the interaction of test particles with this environment considering all relevant electromagnetic, photohadronic, photonuclear, and hadronuclear processes. Finally, we discuss the consequences of the confinement of high-energy CRs in clusters for the production of gamma rays and neutrinos.

scholarly journals Emergent chiral symmetry in a three-dimensional interacting Dirac liquid

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
András L. Szabó ◽  
Bitan Roy
Keyword(s):  
Fixed Points ◽  
Chiral Symmetry ◽  
Rotational Symmetry ◽  
Three Dimensional ◽  
Spatial Dimension ◽  
Dirac Fermions ◽  
Electronic Interactions ◽  
Emergent Phenomena ◽  
Ordered Phases ◽  
The Stability

Abstract We compute the effects of strong Hubbardlike local electronic interactions on three-dimensional four-component massless Dirac fermions, which in a noninteracting system possess a microscopic global U(1) ⊗ SU(2) chiral symmetry. A concrete lattice realization of such chiral Dirac excitations is presented, and the role of electron-electron interactions is studied by performing a field theoretic renormalization group (RG) analysis, controlled by a small parameter ϵ with ϵ = d−1, about the lower-critical one spatial dimension. Besides the noninteracting Gaussian fixed point, the system supports four quantum critical and four bicritical points at nonvanishing interaction couplings ∼ ϵ. Even though the chiral symmetry is absent in the interacting model, it gets restored (either partially or fully) at various RG fixed points as emergent phenomena. A representative cut of the global phase diagram displays a confluence of scalar and pseudoscalar excitonic and superconducting (such as the s-wave and p-wave) mass ordered phases, manifesting restoration of (a) chiral U(1) symmetry between two excitonic masses for repulsive interactions and (b) pseudospin SU(2) symmetry between scalar or pseudoscalar excitonic and superconducting masses for attractive interactions. Finally, we perturbatively study the effects of weak rotational symmetry breaking on the stability of various RG fixed points.

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Energy Conditions ◽  
Late Time ◽  
Swiss Cheese ◽  
Black Strings ◽  
The Stability

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

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