7,218 research outputs found
The application of interactive graphics to large time-dependent hydrodynamics problems
A written companion of a movie entitled "Interactive Graphics at Los Alamos Scientific Laboratory" was presented. While the movie presents the actual graphics terminal and the functions performed on it, the paper attempts to put in perspective the complexity of the application code and the complexity of the interaction that is possible
The rich cluster of galaxies ABCG~85. IV. Emission line galaxies, luminosity function and dynamical properties
This paper is the fourth of a series dealing with the cluster of galaxies
ABCG 85. Using our two extensive photometric and spectroscopic catalogues (with
4232 and 551 galaxies respectively), we discuss here three topics derived from
optical data. First, we present the properties of emission line versus
non-emission line galaxies, showing that their spatial distributions somewhat
differ; emission line galaxies tend to be more concentrated in the south region
where groups appear to be falling onto the main cluster, in agreement with the
hypothesis (presented in our previous paper) that this infall may create a
shock which can heat the X-ray emitting gas and also enhance star formation in
galaxies. Then, we analyze the luminosity function in the R band, which shows
the presence of a dip similar to that observed in other clusters at comparable
absolute magnitudes; this result is interpreted as due to comparable
distributions of spirals, ellipticals and dwarfs in these various clusters.
Finally, we present the dynamical analysis of the cluster using parametric and
non-parametric methods and compare the dynamical mass profiles obtained from
the X-ray and optical data.Comment: accepted for publication in A&
Semiclassical geons as solitonic black hole remnants
We find that the end state of black hole evaporation could be represented by
non-singular and without event horizon stable solitonic remnants with masses of
the order the Planck scale and up to 16 units of charge. Though these objects
are locally indistinguishable from spherically symmetric, massive electric (or
magnetic) charges, they turn out to be sourceless geons containing a wormhole
generated by the electromagnetic field. Our results are obtained by
interpreting semiclassical corrections to Einstein's theory in the first-order
(Palatini) formalism, which yields second-order equations and avoids the
instabilities of the usual (metric) formulation of quadratic gravity. We also
discuss the potential relevance of these solutions for primordial black holes
and the dark matter problem.Comment: 9 pages, 1 figur
Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys
The local structural distortions arising as a consequence of increasing Mn
content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on
martensitic transformation have been studied using Extended X-ray Absorption
Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni
and Mn K-edges in the above compositions, the changes associated with respect
to the local structure of these absorbing atoms are compared. It is seen that
in the alloys exhibiting martensitic transformation () there is a
significant difference between the Ni-In and Ni-Mn bond lengths even in the
austenitic phase indicating atomic volume to be the main factor in inducing
martensitic transformation in Ni-Mn-In Heusler alloys.Comment: 8 pages, 2 figure
An anti-Schwarzshild solution: wormholes and scalar-tensor solutions
We investigate a static solution with an hyperbolic nature, characterised by
a pseudo-spherical foliation of space. This space-time metric can be perceived
as an anti-Schwarzschild solution, and exhibits repulsive features. It belongs
to the class of static vacuum solutions termed "a degenerate static solution of
class A". In the present work we review its fundamental features, discuss the
existence of generalised wormholes, and derive its extension to scalar-tensor
gravity theories in general.Comment: 3 pages, contribution to the proceedings of the Spanish Relativity
Meeting-ERE200
Microscopic wormholes and the geometry of entanglement
It has recently been suggested that Einstein-Rosen (ER) bridges can be
interpreted as maximally entangled states of two black holes that form a
complex Einstein-Podolsky-Rosen (EPR) pair. This relationship has been dubbed
as the ER = EPR correlation. In this work, we consider the latter conjecture in
the context of quadratic Palatini theory. An important result, which stems from
the underlying assumptions about the geometry on which the theory is
constructed, is the fact that all the charged solutions of the quadratic
Palatini theory possess a wormhole structure. Our results show that spacetime
may have a foam-like microstructure with wormholes generated by fluctuations of
the quantum vacuum. This involves the spontaneous creation/annihilation of
entangled particle-antiparticle pairs, existing in a maximally entangled state
connected by a non-traversable wormhole. Since the particles are produced from
the vacuum and therefore exist in a singlet state, they are necessarily
entangled with one another. This gives further support to the ER=EPR claim.Comment: 5 pages. V2: minor changes and references adde
f(R,T) gravity
We consider f(R,T) modified theories of gravity, where the gravitational
Lagrangian is given by an arbitrary function of the Ricci scalar R and of the
trace of the stress-energy tensor T. We obtain the gravitational field
equations in the metric formalism, as well as the equations of motion for test
particles, which follow from the covariant divergence of the stress-energy
tensor. Generally, the gravitational field equations depend on the nature of
the matter source. The field equations of several particular models,
corresponding to some explicit forms of the function f(R,T), are also
presented. An important case, which is analyzed in detail, is represented by
scalar field models. We write down the action and briefly consider the
cosmological implications of the models, where is
the trace of the stress-energy tensor of a self-interacting scalar field. The
equations of motion of the test particles are also obtained from a variational
principle. The motion of massive test particles is non-geodesic, and takes
place in the presence of an extra force orthogonal to the four-velocity. The
Newtonian limit of the equation of motion is further analyzed. Finally, we
provide a constraint on the magnitude of the extra-acceleration by analyzing
the perihelion precession of the planet Mercury in the framework of the present
model.Comment: 14 pages. V2: minor corrections, to appear in PR
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