1,087 research outputs found
Old Inflation in String Theory
We propose a stringy version of the old inflation scenario which does not
require any slow-roll inflaton potential and is based on a specific example of
string compatification with warped metric. Our set-up admits the presence of
anti-D3-branes in the deep infrared region of the metric and a false vacuum
state with positive vacuum energy density. The latter is responsible for the
accelerated period of inflation. The false vacuum exists only if the number of
anti-D3-branes is smaller than a critical number and the graceful exit from
inflation is attained if a number of anti-D3-branes travels from the
ultraviolet towards the infrared region. The cosmological curvature
perturbation is generated through the curvaton mechanism.Comment: 31 pages, 3 figures; typos corrected and reference adde
Kondo Effect of Quantum Dots in the Quantum Hall Regime
Quantum dots in the quantum Hall regime can have pairs of single Slater
determinant states that are degenerate in energy. We argue that these pairs of
many body states may give rise to a Kondo effect which can be mapped into an
ordinary Kondo effect in a fictitious magnetic field. We report on several
properties of this Kondo effect using scaling and numerical renormalization
group analysis. We suggest an experiment to investigate this Kondo effect.Comment: To appear in Phys. Rev. B (5 pages, 4 figures); references added;
several changes in tex
Magnetothermopower and Nernst effect in unconventional charge density waves
Recently we have shown that the striking angular dependent magnetoresistance
in the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 is
consistently described in terms of unconventional charge density wave (UCDW).
Here we investigate theoretically the thermoelectric power and the Nernst
effect in UDW. The present results account consistently for the recent data of
magnetothermopower in alpha-(BEDT-TTF)_2KHg(SCN)_4 obtained by Choi et al.
(Phys. Rev. B, 65, 205119 (2002)). This confirms further our identification of
LTP in this salt as UCDW. We propose also that the Nernst effect provides a
clear signature of UDW.Comment: 4 pages, 4 figure
Applications of scalar attractor solutions to Cosmology
We develop a framework to study the phase space of a system consisting of a
scalar field rolling down an arbitrary potential with varying slope and a
background fluid, in a cosmological setting. We give analytical approximate
solutions of the field evolution and discuss applications of its features to
the issues of quintessence, moduli stabilisation and quintessential inflation.Comment: 9 pages, 7 figures. Accepted for publication in PR
D*-->Dpi and D*-->Dgamma decays: Axial coupling and Magnetic moment of D* meson
The axial coupling and the magnetic moment of D*-meson or, more specifically,
the couplings g(D*Dpi) and g(D*Dgamma), encode the non-perturbative QCD effects
describing the decays D*-->Dpi and D*-->Dgamma. We compute these quantities by
means of lattice QCD with Nf=2 dynamical quarks, by employing the Wilson
("clover") action. On our finer lattice (a=0.065 fm) we obtain: g(D*Dpi)=20 +/-
2, and g(D0*D0gamma)=[2.0 +/- 0.6]/GeV. This is the first determination of
g(D0*D0gamma) on the lattice. We also provide a short phenomenological
discussion and the comparison of our result with experiment and with the
results quoted in the literature.Comment: 22 pages, 3 figure
Quantum Iterated Function Systems
Iterated functions system (IFS) is defined by specifying a set of functions
in a classical phase space, which act randomly on an initial point. In an
analogous way, we define a quantum iterated functions system (QIFS), where
functions act randomly with prescribed probabilities in the Hilbert space. In a
more general setting a QIFS consists of completely positive maps acting in the
space of density operators. We present exemplary classical IFSs, the invariant
measure of which exhibits fractal structure, and study properties of the
corresponding QIFSs and their invariant states.Comment: 12 pages, 1 figure include
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
We propose a cosmological scenario in which the hot big bang universe is
produced by the collision of a brane in the bulk space with a bounding orbifold
plane, beginning from an otherwise cold, vacuous, static universe. The model
addresses the cosmological horizon, flatness and monopole problems and
generates a nearly scale-invariant spectrum of density perturbations without
invoking superluminal expansion (inflation). The scenario relies, instead, on
physical phenomena that arise naturally in theories based on extra dimensions
and branes. As an example, we present our scenario predominantly within the
context of heterotic M-theory. A prediction that distinguishes this scenario
from standard inflationary cosmology is a strongly blue gravitational wave
spectrum, which has consequences for microwave background polarization
experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde
Stress corrosion cracking in Al-Zn-Mg-Cu aluminum alloys in saline environments
Copyright 2013 ASM International. This paper was published in Metallurgical and Materials Transactions A, 44A(3), 1230 - 1253, and is made
available as an electronic reprint with the permission of ASM International. One print or electronic copy may
be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via
electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or
modification of the content of this paper are prohibited.Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack (“pop-in” vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies (E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under- and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak- and over-aged tempers, and for high-copper alloys in under- and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor
Weak Isospin Violations in Charged and Neutral Higgs Couplings from SUSY Loop Corrections
Supersymmetric QCD and supersymmetric electroweak loop corrections to the
violations of weak isospin to Yukawa couplings are investigated. Specifically
it involves an analysis of the supersymmetric loop corrections to the Higgs
couplings to the third generation quarks and leptons. Here we analyze the SUSY
loop corrections to the charged Higgs couplings which are then compared with
the supersymmetric loop corrections to the neutral Higgs couplings previously
computed. It is found that the weak isospin violations can be quite
significant, i.e, as much as 40-50% or more of the total loop correction to the
Yukawa coupling. The effects of CP phases are also studied and it is found that
these effects can either enhance or suppress the weak isospin violations. We
also investigate the weak isospin violation effects on the branching ratio
and show that the effects
are sensitive to CP phases. Thus an accurate measurement of this branching
ratio along with the branching ratio of the neutral Higgs boson decays can
provide a measure of weak isospin violation along with providing a clue to the
presence of supersymmetry.Comment: 20 pages, 9 figure
Prenatal phthalate exposures and executive function in preschool children
Background: Prenatal phthalate exposure has been linked with altered neurodevelopment, including externalizing behaviors and attention-deficit hyperactivity disorder (ADHD). However, the implicated metabolite, neurobehavioral endpoint, and child sex have not always been consistent across studies, possibly due to heterogeneity in neurodevelopmental instruments. The complex set of findings may be synthesized using executive function (EF), a construct of complex cognitive processes that facilitate ongoing goal-directed behaviors. Impaired EF can be presented with various phenotypes of poor neurodevelopment, differently across structured conditions, home/community, or preschool/school. We evaluated the relationship between prenatal phthalate exposure and comprehensive assessment of preschool EF. Methods: Our study comprised 262 children with clinically significant/subthreshold ADHD symptoms and 78 typically developing children who were born between 2003 and 2008 and participated in the Preschool ADHD Substudy, which is nested within a population-based prospective cohort study, the Norwegian Mother, Father, and Child Cohort (MoBa). Twelve phthalate metabolites were measured from urine samples that their mothers had provided during pregnancy, at 17 weeks’ gestation. All children, at approximately 3.5-years, took part in a detailed clinical assessment that included parent-and teacher-rated inventories and administered tests. We used instruments that measured constructs related to EF, which include a parent-and teacher-reported Behavior Rating Inventory of Executive Function-Preschool (BRIEF-P) and three performance-based tests: A Developmental NEuroPSYchological Assessment (NEPSY), Stanford-Binet intelligence test V (SB5), and the cookie delay task (CDT). The standard deviation change in test score per interquartile range (IQR) increase in phthalate metabolite was estimated with multivariable linear regression. We applied weighting in all models to account for the oversampling of children with clinically significant or subthreshold symptoms of ADHD. Additionally, we assessed modification by child sex and potential co-pollutant confounding. Results: Elevated exposure to mono-benzyl phthalate (MBzP) during pregnancy was associated with poorer EF, across all domains and instruments, in both sex. For example, an IQR increase in MBzP was associated with poorer working memory rated by parent (1.23 [95% CI: 0.20, 2.26]) and teacher (1.13 [0.14, 2.13]) using BRIEF-P, and administered tests such as SB5 (no-verbal: 0.19 [0.09, 0.28]; verbal: 0.13 [0.01, 0.25]). Adverse associations were also observed for mono-n-butyl phthalate (MnBP) and mono-iso-butyl phthalate (MiBP), although results varied by instruments. EF domains reported by parents using BRIEF-P were most apparently implicated, with stronger associations among boys (e.g., MnBP and inhibition: 2.74 [1.77, 3.72]; MiBP and inhibition: 1.88 [0.84, 2.92]) than among girls (e.g., MnBP and inhibition: −0.63 [−2.08, 0.83], interaction p-value: 0.04; MiBP and inhibition: −0.15 [−1.04, 0.74], interaction p-value: 0.3). Differences by sex, however, were not found for the teacher-rated BRIEF-P or administered tests including NEPSY, SB5, and CDT. Conclusion and relevance: Elevated mid-pregnancy MBzP, MiBP, and MnBP were associated with more adverse profiles of EF among preschool-aged children across a range of instruments and raters, with some associations found only among boys. Given our findings and accumulating evidence of the prenatal period as a critical window for phthalate exposure, there is a timely need to expand the current phthalate regulations focused on baby products to include pregnancy exposures
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