867 research outputs found
Geodesic motions in extraordinary string geometry
The geodesic properties of the extraordinary vacuum string solution in (4+1)
dimensions are analyzed by using Hamilton-Jacobi method. The geodesic motions
show distinct properties from those of the static one. Especially, any freely
falling particle can not arrive at the horizon or singularity. There exist
stable null circular orbits and bouncing timelike and null geodesics. To get
into the horizon {or singularity}, a particle need to follow a non-geodesic
trajectory. We also analyze the orbit precession to show that the precession
angle has distinct features for each geometry such as naked singularity, black
string, and wormhole.Comment: 15 pages, 11 figure
Evolution of electromagnetic and Dirac perturbations around a black hole in Horava gravity
The evolution of electromagnetic and Dirac perturbations in the spacetime
geometry of Kehagias-Sfetsos(KS) black hole in the deformed Horava-Lifshitz(HL)
gravity is investigated and the associated quasinormal modes are evaluated
using time domain integration and WKB methods. We find a considerable deviation
in the nature of field evolution in HL theory from that in the Schwarzschild
spacetime and QNMs region extends over a longer time in HL theory before the
power-law tail decay begins. The dependence of the field evolution on the HL
parameter are studied. In the time domain picture we find that the
length of QNM region increases with . But the late time decay of field
follows the same power-law tail behavior as in the case of Schwarzschild black
hole.Comment: The article was fully rewritten, references added, to appear in MPL
Counteracting Selfish Nodes Using Reputation Based System in Mobile Ad Hoc Networks
A mobile ad hoc network (MANET) is a group of nodes constituting a network of mobile nodes without predefined and pre-established architecture where mobile nodes can communicate without any dedicated access points or base stations. In MANETs, a node may act as a host as well as a router. Nodes in the network can send and receive packets through intermediate nodes. However, the existence of malicious and selfish nodes in MANETs severely degrades network performance. The identification of such nodes in the network and their isolation from the network is a challenging problem. Therefore, in this paper, a simple reputation-based scheme is proposed which uses the consumption and contribution information for selfish node detection and cooperation enforcement. Nodes failing to cooperate are detached from the network to save resources of other nodes with good reputation. The simulation results show that our proposed scheme outperforms the benchmark scheme in terms of NRL (normalized routing load), PDF (packet delivery fraction), and packet drop in the presence of malicious and selfish attacks. Furthermore, our scheme identifies the selfish nodes quickly and accurately as compared to the benchmark scheme
Creation of a black hole pair with a domain wall
We study the creation of a black hole (BH) pair separated by a domain wall,
in the presence of a cosmological constant. We construct the solution
representing a BH pair with a domain wall and compute the Euclidean action to
evaluate the probability of the pair creation in the background with a
preexisting domain wall. The BHs can be either neutral or magnetically charged
ones. We compare the results of the charged case with those of the neutral case
with the same cosmological constant. We find that the production rate of a
charged BH pair is always suppressed in comparison with that of the neutral one
in both four and five dimensions, irrespective of the sign of the cosmological
constant. The Euclidean action is equal to the minus of the entropy. Since the
horizon area of a BH is decreased as the magnitude of its charge is increased
in general, the decreasing creation rate can be understood in terms of the
increasing charge. We obtain the explicit confirmation on the relation between
the pair creation rate of the charged BHs and the area of horizons in both the
four- and five-dimensional cases in the presence of a cosmological constant.
The singularity of the domain wall universe with charged BHs, as distinct from
that with neutral BHs, can be avoided.Comment: 23 pages, 11 figures, Some typos corrected and references added with
respect to the published versio
Particle Probe of Horava-Lifshitz Gravity
Kehagias-Sfetsos black hole in Ho\v{r}ava-Lifshitz gravity is probed through
particle geodesics. Gravitational force of KS black hole becomes weaker than
that of Schwarzschild around horizon and interior space. Particles can be
always scattered or trapped in new closed orbits, unlike those falling forever
in Schwarzschild black. The properties of null and timelike geodesics are
classified with values of coupling constants. The precession rates of the
orbits are evaluated. The time trajectories are also classified under different
values of coupling constants for both null and timelike geodesics. Physical
phenomena that may be observable are discussed.Comment: 10 pages, 8 figure
Wall-thickness-dependent strength of nanotubular ZnO
We fabricate nanotubular ZnO with wall thickness of 45, 92, 123 nm using nanoporous gold (np-Au) with ligament diameter at necks of 1.43 mu m as sacrificial template. Through micro-tensile and micro-compressive testing of nanotubular ZnO structures, we find that the exponent m in (sigma) over bar proportional to (rho) over bar (m), where (sigma) over bar is the relative strength and (rho) over bar is the relative density, for tension is 1.09 and for compression is 0.63. Both exponents are lower than the value of 1.5 in the Gibson-Ashby model that describes the relation between relative strength and relative density where the strength of constituent material is independent of external size, which indicates that strength of constituent ZnO increases as wall thickness decreases. We find, based on hole-nanoindentation and glazing incidence X-ray diffraction, that this wall-thickness-dependent strength of nanotubular ZnO is not caused by strengthening of constituent ZnO by size reduction at the nanoscale. Finite element analysis suggests that the wall-thickness-dependent strength of nanotubular ZnO originates from nanotubular structures formed on ligaments of np-Au
Semiclassical strings in AdS(3) X S^2
In this paper, we investigate the semiclassical strings in AdS(3)XS^2, in
which the string configuration of AdS(3) is classified to three cases depending
on the parameters. Each of these has a different anomalous dimension
proportional to logS, S^(1/3) and S, where S is a angular momentum on AdS(3).
Further we generalize the dispersion relations for various string configuration
on AdS(3)XS^2.Comment: 15 pages, added reference
The Baryonic Phase in Holographic Descriptions of the QCD Phase Diagram
We study holographic models of the QCD temperature-chemical potential phase
diagram based on the D3/D7 system with chiral symmetry breaking. The baryonic
phase may be included through linked D5-D7 systems. In a previous analysis of a
model with a running gauge coupling a baryonic phase was shown to exist to
arbitrarily large chemical potential. Here we explore this phase in a more
generic phenomenological setting with a step function dilaton profile. The
change in dilaton generates a linear confining potential and opposes
the screening effect of temperature. We show that the persistence of the
baryonic phase depends on the step size and that QCD-like phase diagrams can be
described. The baryonic phase's existence is qualitatively linked to the
existence of confinement in Wilson loop computations in the background.Comment: 21 pages, 7 figure
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