4,345 research outputs found
No-Go Theorem in Spacetimes with Two Commuting Spacelike Killing Vectors
Four-dimensional Riemannian spacetimes with two commuting spacelike Killing
vectors are studied in Einstein's theory of gravity, and found that no outer
apparent horizons exist, provided that the dominant energy condition holds.Comment: latex, 1 figure, version published in Gen. Relativ. Grav., 37,
1919-1926 (2005
Gene transcription analysis during interaction between potato and Ralstonia solanacearum
Bacterial wilt (BW) caused by Ralstonia solanacearum (Rs) is an important quarantine disease that spreads worldwide and infects hundreds of plant species. The BW defense response of potato is a complicated continuous process, which involves transcription of a battery of genes. The molecular mechanisms of potato-Rs interactions are poorly understood. In this study, we combined suppression subtractive hybridization and macroarray hybridization to identify genes that are differentially expressed during the incompatible interaction between Rs and potato. In total, 302 differentially expressed genes were identified and classified into 12 groups according to their putative biological functions. Of 302 genes, 81 were considered as Rs resistance-related genes based on the homology to genes of known function, and they have putative roles in pathogen recognition, signal transduction, transcription factor functioning, hypersensitive response, systemic acquired resistance, and cell rescue and protection. Additionally, 50 out of 302 genes had no match or low similarity in the NCBI databases, and they may represent novel genes. Of seven interesting genes analyzed via RNA gel blot and semi-quantitative RT-PCR, six were induced, one was suppressed, and all had different transcription patterns. The results demonstrate that the response of potato against Rs is rapid and involves the induction of numerous various genes. The genes identified in this study add to our knowledge of potato resistance to Rs
Rigidity of minimal submanifolds in hyperbolic space
We prove that if an -dimensional complete minimal submanifold in
hyperbolic space has sufficiently small total scalar curvature then has
only one end. We also prove that for such there exist no nontrivial
harmonic 1-forms on
Hidden symmetries for thermodynamics and emergence of relativity
Erik Verlinde recently proposed an idea about the thermodynamic origin of
gravity. Though this is a beautiful idea which may resolve many long standing
problems in the theories of gravity, it also raises many other problems. In
this article I will comment on some of the problems of Verlinde's proposal with
special emphasis on the thermodynamical origin of the principle of relativity.
It is found that there is a large group of hidden symmetries of thermodynamics
which contains the Poincare group of the spacetime for which space is emergent.
This explains the thermodynamic origin of the principle of relativity.Comment: V1: 4 pages, comments/criticisms welcomed; V2: references added; V3:
typos and minor corrections? V4? substantial changes in Section 3 and other
parts mad
Static Cylindrical Matter Shells
Static cylindrical shells composed of massive particles arising from matching
of two different Levi-Civita space-times are studied for the shell satisfying
either isotropic or anisotropic equation of state. We find that these solutions
satisfy the energy conditions for certain ranges of the parameters.Comment: 9 pages, 3 figures, Latex; Final version, To appear in General
Relativity and Gravitatio
3D Flapping Trajectory of a Micro-Air-Vehicle and its Application to Unsteady Flow Simulation
[[abstract]]A three-dimensional (3D) trajectory detection framework using two high-speed cameras for the flapping flexible wing of a micro-air-vehicle (MAV) is presented. This MAV, which is called the âGolden Snitchâ, has a successful flight record of 8 minutes. We embed the flexible wingskin with a nine light emitting diode (LED) array as the light enhancing marker and capsulate it with parylene (poly-para-xylylene) as the protection layer. We confirm an oblique figure of eight trajectory of this MAVâs wing with time-varying coordinate data. The corresponding aerofoil of the main wingsâ profiles was subjected to the time-varying coordinate data, yielding a resolution of a 1/70 wing beating cycle of 15Hz flapping. The trajectory information is first demonstrated as the moving boundaries of an unsteady flow simulation around a flapping flexible wing.[[notice]]èŁæŁćźçą[[journaltype]]ćć€[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]é»ćç[[booktype]]çŽæŹ[[countrycodes]]HR
Evolving Lorentzian Wormholes
Evolving Lorentzian wormholes with the required matter satisfying the Energy
conditions are discussed. Several different scale factors are used and the
corresponding consequences derived. The effect of extra, decaying (in time)
compact dimensions present in the wormhole metric is also explored and certain
interesting conclusions are derived for the cases of exponential and
Kaluza--Klein inflation.Comment: 10 pages( RevTex, Twocolumn format), Two figures available on request
from the first author. transmission errors corrected
Gravitational Collapse of Cylindrical Shells Made of Counter-Rotating Dust Particles
The general formulas of a non-rotating dynamic thin shell that connects two
arbitrary cylindrical regions are given using Israel's method. As an
application of them, the dynamics of a thin shell made of counter-rotating dust
particles, which emits both gravitational waves and massless particles when it
is expanding or collapsing, is studied. It is found that when the models
represent a collapsing shell, in some cases the angular momentum of the dust
particles is strong enough to halt the collapse, so that a spacetime
singularity is prevented from forming, while in other cases it is not, and a
line-like spacetime singularity is finally formed on the symmetry axis.Comment: To appear in Phys. Rev.
Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler shift and
line width simultaneously in a large field of view. By studying the Doppler
shift and line width we may explore more of the physical processes of CME
initiation and propagation. Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary analysis
shows that CMEs are usually associated with greatly increased Doppler shift and
enhanced line width. These new observations provide not only valuable
information to constrain CME models and probe various processes during the
initial propagation of CMEs in the low corona, but also offer a possible
cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism,
Sol. Phy
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