503 research outputs found
Generalized Vaidya Solutions and Misner-Sharp mass for -dimensional massive gravity
Dynamical solutions are always of interest to people in gravity theories. We
derive a series of generalized Vaidya solutions in the -dimensional de
Rham-Gabadadze-Tolley (dRGT) massive gravity with a singular reference metric.
Similar to the case of the Einstein gravity, the generalized Vaidya solution
can describe shining/absorbing stars. Moreover, we also find a more general
Vaidya-like solution by introducing a more generic matter field than the pure
radiation in the original Vaidya spacetime. As a result, the above generalized
Vaidya solution is naturally included in this Vaidya-like solution as a special
case. We investigate the thermodynamics for this Vaidya-like spacetime by using
the unified first law, and present the generalized Misner-Sharp mass. Our
results show that the generalized Minser-Sharp mass does exist in this
spacetime. In addition, the usual Clausius relation holds on
the apparent horizon, which implicates that the massive gravity is in a
thermodynamic equilibrium state. We find that the work density vanishes for the
generalized Vaidya solution, while it appears in the more general Vaidya-like
solution. Furthermore, the covariant generalized Minser-Sharp mass in the
-dimensional de Rham-Gabadadze-Tolley massive gravity is also derived by
taking a general metric ansatz into account.Comment: 10 pages, no figure, version published in PR
Lopsidedness of self-consistent galaxies by the external field effect of clusters
Adopting Schwarzschild's orbit-superposition technique, we construct a series
of self-consistent galaxy models, embedded in the external field of galaxy
clusters in the framework of Milgrom's MOdified Newtonian Dynamics. These
models represent relatively massive ellipticals with a Hernquist radial profile
at various distances from the cluster centre. Using -body simulations, we
perform a first analysis of these models and their evolution. We find that
self-gravitating axisymmetric density models, even under a weak external field,
lose their symmetry by instability and generally evolve to triaxial
configurations. A kinematic analysis suggests that the instability originates
from both box and non-classified orbits with low angular momentum. We also
consider a self-consistent isolated system which is then placed in a strong
external field and allowed to evolve freely. This model, just as the
corresponding equilibrium model in the same external field, eventually settles
to a triaxial equilibrium as well, but has a higher velocity radial anisotropy
and is rounder. The presence of an external field in MOND universe generically
predicts some lopsidedness of galaxy shapes.Comment: 24 pages, 20 figures. Accepted for publication in Ap
Extraordinary surface voltage effect in the invisibility cloak with an active device inside
The electromagnetic field solution for a spherical invisibility cloak with an
active device inside is established. Extraordinary electric and magnetic
surface voltages are induced at the inner boundary of a spherical cloak, which
prevent electromagnetic waves from going out. The phase and handness of
polarized waves obliquely incident on such boundaries is kept in the reflected
waves. The surface voltages due to an electric dipole inside the concealed
region are found equal to the auxiliary scalar potentials at the inner
boundary, which consequently gain physical counterparts in this case
Cylindrical Cloak with Axial Permittivity/Permeability Spatially Invariant
In order to reduce the difficulties in the experimental realizations of the
cloak but still keep good performance of invisibility, we proposed a perfect
cylindrical invisibility cloak with spatially invariant axial material
parameters. The advantage of this kind of TE (or TM) cloak is that only rho and
phi components of mu (or epsilon) are spatially variant, which makes it
possible to realize perfect invisibility with two-dimensional (2D) magnetic (or
electric) metamaterials. The effects of perturbations of the parameters on the
performance of this cloak are quantitatively analyzed by scattering theory. Our
work provides a simple and feasible solution to the experimental realization of
cloaks with ideal parameters
The Galactic potential and the asymmetric distribution of hypervelocity stars
In recent years several hypervelocity stars (HVSs) have been observed in the
halo of our Galaxy. Such HVSs have possibly been ejected from the Galactic
center and then propagated in the Galactic potential up to their current
position. The recent survey for candidate HVSs show an asymmetry in the
kinematics of candidate HVSs (position and velocity vectors), where more
outgoing stars than ingoing stars (i.e. positive Galactocentric velocities vs.
negative ones) are observed. We show that such kinematic asymmetry, which is
likely due to the finite lifetime of the stars and Galactic potential
structure, could be used in a novel method to probe and constrain the Galactic
potential, identify the stellar type of the stars in the survey and estimate
the number of HVSs. Kinematics-independent identification of the stellar types
of the stars in such surveys (e.g. spectroscopic identification) could further
improve these results. We find that the observed asymmetry between ingoing and
outgoing stars favors specific Galactic potential models. It also implies a
lower limit of ~54+-8 main sequence HVSs in the survey sample (>=648+-96 in the
Galaxy), assuming that all of the main sequence stars in the survey originate
from the Galactic center. The other stars in the survey are likely to be hot
blue horizontal branch stars born in the halo rather than stars ejected from
the Galactic center.Comment: 7 pages, 3 figures. Added an appendix. Accepted to Ap
Effects of transgenic Cry1Ac + CpTI cotton on non-target mealybug pest Ferrisia virgata and its predator Cryptolaemus montrouzieri
Recently, several invasive mealybugs (Hemiptera: Pseudococcidae) have rapidly spread to Asia and have become a serious threat to the production of cotton including transgenic cotton. Thus far, studies have mainly focused on the effects of mealybugs on non-transgenic cotton, without fully considering their effects on transgenic cotton and trophic interactions. Therefore, investigating the potential effects of mealybugs on transgenic cotton and their key natural enemies is vitally important. A first study on the effects of transgenic cotton on a non-target mealybug, Ferrisia virgata (Cockerell) (Hemiptera: Pseudococcidae) was performed by comparing its development, survival and body weight on transgenic cotton leaves expressing Cry1Ac (Bt toxin) + CpTI (Cowpea Trypsin Inhibitor) with those on its near-isogenic non-transgenic line. Furthermore, the development, survival, body weight, fecundity, adult longevity and feeding preference of the mealybug predator Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) was assessed when fed F. virgata maintained on transgenic cotton. In order to investigate potential transfer of Cry1Ac and CpTI proteins via the food chain, protein levels in cotton leaves, mealybugs and ladybirds were quantified. Experimental results showed that F. virgata could infest this bivalent transgenic cotton. No significant differences were observed in the physiological parameters of the predator C. montrouzieri offered F. virgata reared on transgenic cotton or its near-isogenic line. Cry1Ac and CpTI proteins were detected in transgenic cotton leaves, but no detectable levels of both proteins were present in the mealybug or its predator when reared on transgenic cotton leaves. Our bioassays indicated that transgenic cotton poses a negligible risk to the predatory coccinellid C. montrouzieri via its prey, the mealybug F.virgata
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