5,963 research outputs found
Explicit Global Coordinates for Schwarzschild and Reissner-Nordstroem
We construct coordinate systems that cover all of the Reissner-Nordstroem
solution with m>|q| and m=|q|, respectively. This is possible by means of
elementary analytical functions. The limit of vanishing charge q provides an
alternative to Kruskal which, to our mind, is more explicit and simpler. The
main tool for finding these global charts is the description of highly
symmetrical metrics by two-dimensional actions. Careful gauge fixing yields
global representatives of the two-dimensional theory that can be rewritten
easily as the corresponding four-dimensional line elements.Comment: 12 pages, 3 Postscript figures, sign error in Eq. (37) and below
corrected, references and Note added; to appear in Class. Quantum Gra
Analytical study of the fracture of liquid- filled tanks impacted by hypervelocity particles
Shock waves in water and stress waves in tank walls of water-filled fuel tanks impacted by hypervelocity particle
A strong constitutive ethylene-response phenotype conferred on Arabidopsis plants containing null mutations in the ethylene receptors ETR1 and ERS1
Background: The ethylene receptor family of Arabidopsis consists of five members, falling into two subfamilies. Subfamily 1 is composed of ETR1 and ERS1, and subfamily 2 is composed of ETR2, ERS2, and EIN4. Although mutations have been isolated in the genes encoding all five family members, the only previous insertion allele of ERS1 (ers1-2) is a partial loss-of-function mutation based on our analysis. The purpose of this study was to determine the extent of signaling mediated by subfamily-1 ethylene receptors through isolation and characterization of null mutations.
Results: We isolated new T-DNA insertion alleles of subfamily 1 members ERS1 and ETR1 (ers1-3 and etr1-9, respectively), both of which are null mutations based on molecular, biochemical, and genetic analyses. Single mutants show an ethylene response similar to wild type, although both mutants are slightly hypersensitive to ethylene. Double mutants of ers1-3 with etr1-9, as well as with the previously isolated etr1-7, display a constitutive ethylene-response phenotype more pronounced than that observed with any previously characterized combination of ethylene receptor mutations. Dark-grown etr1-9;ers1-3 and etr1-7;ers1-3 seedlings display a constitutive triple-response phenotype. Light-grown etr1-9;ers1-3 and etr1-7;ers1-3 plants are dwarfed, largely sterile, exhibit premature leaf senescence, and develop novel filamentous structures at the base of the flower. A reduced level of ethylene response was still uncovered in the double mutants, indicating that subfamily 2 receptors can independently contribute to signaling, with evidence suggesting that this is due to their interaction with the Raf-like kinase CTR1.
Conclusion: Our results are consistent with the ethylene receptors acting as redundant negative regulators of ethylene signaling, but with subfamily 1 receptors playing the predominant role. Loss of a single member of subfamily 1 is largely compensated for by the activity of the other member, but loss of both subfamily members results in a strong constitutive ethylene-response phenotype. The role of subfamily 1 members is greater than previously suspected and analysis of the double mutant null for both ETR1 and ERS1 uncovers novel roles for the receptors not previously characterized
Classical and Quantum Gravity in 1+1 Dimensions, Part III: Solutions of Arbitrary Topology
All global solutions of arbitrary topology of the most general 1+1
dimensional dilaton gravity models are obtained. We show that for a generic
model there are globally smooth solutions on any non-compact 2-surface. The
solution space is parametrized explicitly and the geometrical significance of
continuous and discrete labels is elucidated. As a corollary we gain insight
into the (in general non-trivial) topology of the reduced phase space.
The classification covers basically all 2D metrics of Lorentzian signature
with a (local) Killing symmetry.Comment: 39 pages, 22 figures, uses AMSTeX, extended version of former chapter
7 (Gravitational Kinks) now available as gr-qc/9707053, problem with figure 6
fixe
Gravity's Relentless Pull: An interactive, multimedia website about black holes for Education and Public Outreach
We have created a website, called "Black Holes: Gravity's Relentless Pull",
which explains the physics and astronomy of black holes for a general audience.
The site emphasizes user participation and is rich in animations and
astronomical imagery. It won the top prize of the 2005 Pirelli INTERNETional
Awards competition for the best communication of science and technology using
the internet. This article provides a brief overview of the site. The site
starts with an opening animation that introduces the basic concept of a black
hole. The user is then invited to embark on a journey from a backyard view of
the night sky to a personal encounter with a singularity. This journey proceeds
through three modules, which allow the user to: find black holes in the night
sky; travel to a black hole in an animated starship; and explore a black hole
from up close. There are also five "experiments" that allow the user to: create
a black hole; orbit around a black hole; weigh a black hole; drop a clock into
a black hole; or fall into a black hole. The modules and experiments offer
goal-based scenarios tailored for novices and children. The site also contains
an encyclopedia of frequently asked questions and a detailed glossary that are
targeted more at experts and adults. The overall result is a website where
scientific knowledge, learning theory, and fun converge. Despite its focus on
black holes, the site also teaches many other concepts of physics, astronomy
and scientific thought. The site aims to instill an appreciation for learning
and an interest in science, especially in the younger users. It can be used as
an aid in teaching introductory astronomy at the undergraduate level.Comment: STScI Newsletter, 2006, vol. 23, number 2, in press; 5 pages and 2
figures. The black hole website described in this article is located at
http://hubblesite.org/go/blackholes/ . We welcome all feedback and
suggestions, which can be submitted through the "Contact Us" button of the
sit
Poisson sigma models and symplectic groupoids
We consider the Poisson sigma model associated to a Poisson manifold. The
perturbative quantization of this model yields the Kontsevich star product
formula. We study here the classical model in the Hamiltonian formalism. The
phase space is the space of leaves of a Hamiltonian foliation and has a natural
groupoid structure. If it is a manifold then it is a symplectic groupoid for
the given Poisson manifold. We study various families of examples. In
particular, a global symplectic groupoid for a general class of two-dimensional
Poisson domains is constructed.Comment: 34 page
Generalized 2d dilaton gravity with matter fields
We extend the classical integrability of the CGHS model of 2d dilaton gravity
[1] to a larger class of models, allowing the gravitational part of the action
to depend more generally on the dilaton field and, simultaneously, adding
fermion- and U(1)-gauge-fields to the scalar matter. On the other hand we
provide the complete solution of the most general dilaton-dependent 2d gravity
action coupled to chiral fermions. The latter analysis is generalized to a
chiral fermion multiplet with a non-abelian gauge symmetry as well as to the
(anti-)self-dual sector df = *df (df = -*df) of a scalar field f.Comment: 37 pages, Latex; typos and Eqs. (44,45) corrected; paragraph on p.
26, referring to a work of S. Solodukhin, reformulated; references adde
Quantum Equilibration under Constraints and Transport Balance
For open quantum systems coupled to a thermal bath at inverse temperature
, it is well known that under the Born-, Markov-, and secular
approximations the system density matrix will approach the thermal Gibbs state
with the bath inverse temperature . We generalize this to systems where
there exists a conserved quantity (e.g., the total particle number), where for
a bath characterized by inverse temperature and chemical potential
we find equilibration of both temperature and chemical potential. For
couplings to multiple baths held at different temperatures and different
chemical potentials, we identify a class of systems that equilibrates according
to a single hypothetical average but in general non-thermal bath, which may be
exploited to generate desired non-thermal states. Under special circumstances
the stationary state may be again be described by a unique Boltzmann factor.
These results are illustrated by several examples.Comment: 8 pages, 1 figure, leaner presentation, to appear in PR
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