6,378 research outputs found
D-Brane Probe and Closed String Tachyons
We consider a D-brane probe in unstable string background associated with
flux branes. The twist in spacetime metric reponsible for the supersymmetry
breaking is shown to manifest itself in mixing of open Wilson lines with the
phases of some adjoint matter fields, resulting in a nonlocal and
nonsupersymmetric form of Yang-Mills theory as the probe dynamics. This
provides a setup where one can study fate of a large class of unstable closed
string theories that include as a limit type 0 theories and various orbifolds
of type II and type 0 theories. We discuss the limit of orbifold
in some detail and speculate on couplings with closed string tachyons.Comment: LaTeX, 17 pages, typos fixed, references update
Closed String Tachyons and Semi-Classical Instabilities
We conjecture that the end point of bulk closed string tachyon decay at any
non-zero coupling, is the annihilation of space time by Witten's bubble of
nothing, resulting in a topological phase of the theory. In support of this we
present a variety of situations in which there is a correspondence between the
existence of perturbative tachyons in one regime and the semi-classical
annihilation of space-time. Our discussion will include many recently
investigated scenarios in string theory including Scherk-Schwarz
compactifications, Melvin magnetic backgrounds, and noncompact orbifolds. We
use this conjecture to investigate a possible web of dualities relating the
eleven-dimensional Fabinger-Horava background with nonsupersymmetric string
theories. Along the way we point out where our conjecture resolves some of the
puzzles associated with bulk closed string tachyon condensation.Comment: 31 pages, 5 figures 3 figures added, typos corrected and references
added. Discussion of Type 0/Heterotic s-duality extended and some other
points clarified Revision of discussion on Fabinger-Horava string
descendents, section on Scherk-Schwarz compactification of Horava-Witten
removed, some references adde
DMSO and Temperature Contributions to Synthesis of Silver Nano-Particles by the Bacterium Shewanella oneidensis
Nanomaterial are widely used in different areas such as optical device, drug delivery, chemicals, mechanics, magnetics, catalysis, energy science, Nano therapeutics and space industries depend on the special physical properties. However, most methods to produce nanoparticles are expensive or environmental unfriendly which can involve in toxic chemical. Another reason is that the nanoparticles from bio-based protocols are hydrophilic which is compatible with biological materials. In this project, we chose Shewanella oneidensis which is Gram-negative bacterium as the organism to produce sliver nanoparticles from sliver nitrate solution. The mechanism of bacterial of ion metal ion reduction to stable metal nanoparticles is unclear, but the NADH-dependent reeducates, quinines, and soluble electron-shuttles are thought to play an important role in metal reduction. This research focused on the temperature and DMSO affects the synthesis of silver nanoparticles by Shewanella Oneidensis. At various temperatures, the bio-activity of bacterium is different which can affect the silver nanoparticles reducing rate and the spherical size and nanoparticle geometry. DMSO is an aprotic, polar solvent which can penetrate skin and other membranes without damaging the cells. Due to this property of DMSO, DMSO was utilized as a co-solvent, which may change biosynthesis of silver nanoparticles. The synthesis processes were carried out at different temperatures and DMSO concentration and the nanoparticle formation monitored by using UV-vis spectrometer scans of the aqueous layer of reaction at 0 hr, 24 hr and 48 hr.https://ecommons.udayton.edu/stander_posters/1429/thumbnail.jp
Non-Singular Solutions for S-branes
Exact, non-singular, time-dependent solutions of Maxwell-Einstein gravity
with and without dilatons are constructed by double Wick rotating a variety of
static, axisymmetric solutions. This procedure transforms arrays of charged or
neutral black holes into s-brane (spacelike brane) solutions, i.e. extended,
short-lived spacelike defects. Along the way, new static solutions
corresponding to arrays of alternating-charge Reissner-Nordstrom black holes,
as well as their dilatonic generalizations, are found. Their double Wick
rotation yields s-brane solutions which are periodic in imaginary time and
potential large-N duals for the creation/decay of unstable D-branes in string
theory.Comment: 21 pages, 3 figure
The Bekenstein Formula and String Theory (N-brane Theory)
A review of recent progress in string theory concerning the Bekenstein
formula for black hole entropy is given. Topics discussed include p-branes,
D-branes and supersymmetry; the correspondence principle; the D- and M-brane
approach to black hole entropy; the D-brane analogue of Hawking radiation, and
information loss; D-branes as probes of black holes; and the Matrix theory
approach to charged and neutral black holes. Some introductory material is
included.Comment: 53 pages, LaTeX. v3: Typos fixed, minor updates, references added,
brief Note Added on AdS/CF
Cosmic Acceleration in Brans-Dicke Cosmology
We consider Brans-Dicke theory with a self-interacting potential in Einstein
conformal frame. We show that an accelerating expansion is possible in a
spatially flat universe for large values of the Brans-Dicke parameter
consistent with local gravity experiments.Comment: 10 Pages, 3 figures, To appear in General Relativity and Gravitatio
Interacting model of new agegraphic dark energy: observational constraints and age problem
Many dark energy models fail to pass the cosmic age test because of the old
quasar APM 08279+5255 at redshift , the CDM model and
holographic dark energy models being no exception. In this paper, we focus on
the topic of age problem in the new agegraphic dark energy (NADE) model. We
determine the age of the universe in the NADE model by fitting the
observational data, including type Ia supernovae (SNIa), baryon acoustic
oscillations (BAO) and the cosmic microwave background (CMB). We find that the
NADE model also faces the challenge of the age problem caused by the old quasar
APM 08279+5255. In order to overcome such a difficulty, we consider the
possible interaction between dark energy and dark matter. We show that this
quasar can be successfully accommodated in the interacting new agegraphic dark
energy (INADE) model at the level under the current observational
constraints.Comment: 12 pages, 5 figures; typos corrected; version for publication in
SCIENCE CHINA Physics, Mechanics & Astronom
Of cattle, sand flies and men : a systematic review of risk factor analyses for South Asian visceral leishmaniasis and implications for elimination
Background: Studies performed over the past decade have identified fairly consistent epidemiological patterns of risk
factors for visceral leishmaniasis (VL) in the Indian subcontinent.
Methods and Principal Findings: To inform the current regional VL elimination effort and identify key gaps in knowledge,
we performed a systematic review of the literature, with a special emphasis on data regarding the role of cattle because
primary risk factor studies have yielded apparently contradictory results. Because humans form the sole infection reservoir,
clustering of kala-azar cases is a prominent epidemiological feature, both at the household level and on a larger scale.
Subclinical infection also tends to show clustering around kala-azar cases. Within villages, areas become saturated over a
period of several years; kala-azar incidence then decreases while neighboring areas see increases. More recently, post kalaazar
dermal leishmaniasis (PKDL) cases have followed kala-azar peaks. Mud walls, palpable dampness in houses, and peridomestic
vegetation may increase infection risk through enhanced density and prolonged survival of the sand fly vector.
Bed net use, sleeping on a cot and indoor residual spraying are generally associated with decreased risk. Poor micronutrient
status increases the risk of progression to kala-azar. The presence of cattle is associated with increased risk in some studies
and decreased risk in others, reflecting the complexity of the effect of bovines on sand fly abundance, aggregation, feeding
behavior and leishmanial infection rates. Poverty is an overarching theme, interacting with individual risk factors on multiple
levels.
Conclusions: Carefully designed demonstration projects, taking into account the complex web of interconnected risk
factors, are needed to provide direct proof of principle for elimination and to identify the most effective maintenance
activities to prevent a rapid resurgence when interventions are scaled back. More effective, short-course treatment
regimens for PKDL are urgently needed to enable the elimination initiative to succeed
Cork oak and climate change: disentangling drought effects on cork chemical composition
Climate change induces in the Mediterranean region more frequent and extreme events, namely, heat
waves and droughts, disturbing forest species and affecting their productivity and product quality.
The cork oak (Quercus suber) is present along the western Mediterranean basin and its outer bark
(cork) is sustainably collected and used for several products, mainly wine bottle stoppers. Since most
cork properties arise from its chemical composition, this research studies the effect of drought on cork
chemical composition (suberin, lignin, polysaccharides and extractives) and on polysaccharide and
suberin monomeric composition. Three sets of cork samples, from the same site, were examined: in one
set the cork grew without drought; in another two drought events occurred during cork growth and in
the third one drought event happened. The results show that, in general, drought does not affect the
proportion of the main components of cork, the monomers of suberin or of polysaccharides, with few
exceptions e.g. drought increased ethanol extractives and xylose in polysaccharides and decreased
arabinose in polysaccharides. The variability associated to the tree is much more relevant than the
effect of drought conditions and affects all the parameters analyzed. Therefore, our research suggests
that the tree genetic information, or its expression, plays a much more important role on the chemical
composition of cork than the drought conditions occurring during cork growth. In practical terms, the
potential increased occurrence of droughts arising from climatic changes will not compromise the
performance of cork as a sealant for wine bottlesinfo:eu-repo/semantics/publishedVersio
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
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