10,632 research outputs found
Inflating magnetically charged braneworlds
Numerical solutions of Einstein, scalar, and gauge field equations are found
for static and inflating defects in a higher-dimensional spacetime. The defects
have -dimensional core and magnetic monopole configuration in
extra dimensions. For symmetry-breaking scale below the critical value
, the defects are characterized by a flat worldsheet geometry and
asymptotically flat extra dimensions. The critical scale is comparable
to the higher-dimensional Planck scale and has some dependence on the gauge and
scalar couplings. For , the extra dimensions degenerate into a
`cigar', and for all static solutions are singular. The
singularity can be removed if the requirement of staticity is relaxed and
defect cores are allowed to inflate. The inflating solutions have de Sitter
worldsheets and cigar geometry in the extra dimensions. Exact analytic
solutions describing the asymptotic behavior of these inflating monopoles are
found and the parameter space of these solutions is analyzed.Comment: 35 pages, revtex, 18 eps figure
Airborne measurements of launch vehicle effluent: Launch of Space Shuttle (STS-1) on 12 April 1981
Launch vehicle effluent environmental impact activities from the first space shuttle (STS-1) included airborne measurements within the exhaust cloud from about 9 min after launch (T + 9) to T + 120 min. Measurements included total hydrogen chloride (gaseous plus aqueous) concentrations, particulate concentrations, temperature, and dewpoint temperature. The airborne measurements are summarized. The physical growth and behavior of exhaust clouds is presented as well as the results of laboratory analysis of elemental composition of particulate samples collected by the aircraft. Observed results from the STS-1 launch are compared with earlier Titan III results. Shuttle effluent concentrations are found to be within the range of Titan III observations
Inertial range turbulence in kinetic plasmas
The transfer of turbulent energy through an inertial range from the driving
scale to dissipative scales in a kinetic plasma followed by the conversion of
this energy into heat is a fundamental plasma physics process. A theoretical
foundation for the study of this process is constructed, but the details of the
kinetic cascade are not well understood. Several important properties are
identified: (a) the conservation of a generalized energy by the cascade; (b)
the need for collisions to increase entropy and realize irreversible plasma
heating; and (c) the key role played by the entropy cascade--a dual cascade of
energy to small scales in both physical and velocity space--to convert
ultimately the turbulent energy into heat. A strategy for nonlinear numerical
simulations of kinetic turbulence is outlined. Initial numerical results are
consistent with the operation of the entropy cascade. Inertial range turbulence
arises in a broad range of space and astrophysical plasmas and may play an
important role in the thermalization of fusion energy in burning plasmas.Comment: 11 pages, 2 figures, submitted to Physics of Plasmas, DPP Meeting
Special Issu
Special Massive Spin-2 on de Sitter Space
The theory of a massive spin-2 state on the de Sitter space -- with the mass
squared equal to one sixth of the curvature -- is special for two reasons: (i)
it exhibits an enhanced local symmetry; (ii) it emerges as a part of the model
that gives rise to the self-accelerated Universe. The known problems of this
theory are: either it cannot be coupled to a non-conformal conserved
stress-tensor because of the enhanced symmetry, or it propagates a ghost-like
state when the symmetry is constrained by the Lagrange multiplier method. Here
we propose a solution to these problems in the linearized approximation.Comment: 9 pages, reference added, JCAP versio
Robustness of reserve selection procedures under temporal species turnover
Complementarity-based algorithms for the selection of reserve networks emphasize the need to represent biodiversity features efficiently, but this may not be sufficient to maintain those features in the long term. Here, we use data from the Common Birds Census in Britain as an exemplar data set to determine guidelines for the selection of reserve networks which are more robust to temporal turnover in features. The extinction patterns found over the 1981-1991 interval suggest that two such guidelines are to represent species in the best sites where they occur (higher local abundance) and to give priority to the rarer species. We tested five reserve selection strategies, one which finds the minimum representation set and others which incorporate the first or both guidelines proposed. Strategies were tested in terms of their efficiency (inversely related to the total area selected) and effectiveness (inversely related to the percentage of species lost) using data on eight pairs of ten-year intervals.
The minimum set strategy was always the most efficient, but suffered higher species loss than the others, suggesting that there is a trade-off between efficiency and effectiveness. A desirable compromise can be achieved by embedding the concerns about the long-term maintenance of the biodiversity features of interest in the complementarity-based algorithms
Equation-free implementation of statistical moment closures
We present a general numerical scheme for the practical implementation of
statistical moment closures suitable for modeling complex, large-scale,
nonlinear systems. Building on recently developed equation-free methods, this
approach numerically integrates the closure dynamics, the equations of which
may not even be available in closed form. Although closure dynamics introduce
statistical assumptions of unknown validity, they can have significant
computational advantages as they typically have fewer degrees of freedom and
may be much less stiff than the original detailed model. The closure method can
in principle be applied to a wide class of nonlinear problems, including
strongly-coupled systems (either deterministic or stochastic) for which there
may be no scale separation. We demonstrate the equation-free approach for
implementing entropy-based Eyink-Levermore closures on a nonlinear stochastic
partial differential equation.Comment: 7 pages, 2 figure
Summary of aircraft results for 1978 southeastern Virginia urban plume measurement study of ozone, nitrogen oxides, and methane
Ozone production was determined from aircraft and surface in situ measurements, as well as from an airborne laser absorption spectrometer. Three aircraft and approximately 10 surface stations provided air-quality data. Extensive meteorological, mixing-layer-height, and ozone-precursor data were also measured. Approximately 50 hrs (9 flight days) of data from the aircraft equipped to monitor ozone, nitrogen oxides, dewpoint temperature, and temperature are presented. In addition, each experiment conducted is discussed
Calli Essential Oils Synergize with Lawsone against Multidrug Resistant Pathogens.
The fast development of multi-drug resistant (MDR) organisms increasingly threatens global health and well-being. Plant natural products have been known for centuries as alternative medicines that can possess pharmacological characteristics, including antimicrobial activities. The antimicrobial activities of essential oil (Calli oil) extracted from the Calligonum comosum plant by hydro-steam distillation was tested either alone or when combined with lawsone, a henna plant naphthoquinone, against MDR microbes. Lawsone showed significant antimicrobial activities against MDR pathogens in the range of 200-300 µg/mL. Furthermore, Calli oil showed significant antimicrobial activities against MDR bacteria in the range of 180-200 µg/mL, Candida at 220-240 µg/mL and spore-forming Rhizopus fungus at 250 µg/mL. Calli oil's inhibition effect on Rhizopus, the major cause of the lethal infection mucormycosis, stands for 72 h, followed by an extended irreversible white sporulation effect. The combination of Calli oil with lawsone enhanced the antimicrobial activities of each individual alone by at least three-fold, while incorporation of both natural products in a liposome reduced their toxicity by four- to eight-fold, while maintaining the augmented efficacy of the combination treatment. We map the antimicrobial activity of Calli oil to its major component, a benzaldehyde derivative. The findings from this study demonstrate that formulations containing essential oils have the potential in the future to overcome antimicrobial resistance
Nonsingular global string compactifications
We consider an exotic `compactification' of spacetime in which there are two
infinite extra dimensions, using a global string instead of a domain wall. By
having a negative cosmological constant we prove the existence of a nonsingular
static solution using a dynamical systems argument. A nonsingular solution also
exists in the absence of a cosmological constant with a time-dependent metric.
We compare and contrast this solution with the Randall-Sundrum universe and the
Cohen-Kaplan spacetime, and consider the options of using such a model as a
realistic resolution of the hierarchy problem.Comment: 8 pages revtex, 1 figure : References added and equation correcte
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
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