8,237 research outputs found
Hadron Masses and Screening from AdS Wilson Loops
We show that in strongly coupled N=4 SYM the binding energy of a heavy and a
light quark is independent of the strength of the coupling constant. As a
consequence we are able to show that in the presence of light quarks the analog
of the QCD string can snap and color charges are screened. The resulting
neutral mesons interact with each other only via pion exchange and we estimate
the massesComment: 4 pages, revte
Oscillations of solar and atmospheric neutrinos
Motivated by recent results from SuperKamiokande, we study both solar and
atmospheric neutrino fluxes in the context of oscillations of the three known
neutrinos. We aim at a global view which identifies the various possibilities,
rather than attempting the most accurate determination of the parameters of
each scenario. For solar neutrinos we emphasise the importance of performing a
general analysis, independent of any particular solar model and we consider the
possibility that any one of the techniques --- chlorine, gallium or water
Cerenkov --- has a large unknown systematic error, so that its results should
be discarded. The atmospheric neutrino anomaly is studied by paying special
attention to the ratios of upward and downward going nu_e and nu_mu fluxes.
Both anomalies can be described in a minimal scheme where the respective
oscillation frequencies are widely separated or in non-minimal schemes with two
comparable oscillation frequencies. We discuss explicit forms of neutrino mass
matrices in which both atmospheric and solar neutrino fluxes are explained. In
the minimal scheme we identify only two `zeroth order' textures that can result
from unbroken symmetries. Finally we discuss experimental strategies for the
determination of the various oscillation parameters.Comment: 20 pages, 7 figures. Final version: one reference added; fit of
atmospheric neutrinos improve
Transform-limited pulses are not optimal for resonant multiphoton transitions
Maximizing nonlinear light-matter interactions is a primary motive for
compressing laser pulses to achieve ultrashort transform limited pulses. Here
we show how, by appropriately shaping the pulses, resonant multiphoton
transitions can be enhanced significantly beyond the level achieved by
maximizing the pulse's peak intensity. We demonstrate the counterintuitive
nature of this effect with an experiment in a resonant two-photon absorption,
in which, by selectively removing certain spectral bands, the peak intensity of
the pulse is reduced by a factor of 40, yet the absorption rate is doubled.
Furthermore, by suitably designing the spectral phase of the pulse, we increase
the absorption rate by a factor of 7.Comment: 4 pages, 3 figure
Success Attributions and More: Multidimensional Extensions of the Sexual Attribution Bias to Failure Attributions, Social Emotions, and the Desire for Social Interaction
According to the recently discovered sexual attribution bias (SAB), young adults attribute the success of same-aged, same-sex attractive stimulus persons in a more derogative way than the success of less attractive same-sex persons, whereas this pattern is reversed for members of the opposite sex. Because this bias has so far only been investigated with respect to attributions in success scenarios, two studies examined its potential transferability to other psychological variables and settings: Study 1 (N = 419)demonstrated analogous biases for emotions and the desire for social interaction, and Study 2 (N = 509) revealed that the SAB can also be extended to failure scenarios
Is gastro-oesophageal reflux a factor in exercise-induced asthma?
AbstractExercise-induced bronchoconstriction (EIB) occurs in the majority of patients with asthma. The relationship between asthma and gastro-oesophageal reflux (GER) is well defined, and the reports of exertional gastro-oesophageal acid reflux in healthy subjects, prompted us to study the relationship between EIB and GER.Following an overnight fast and medication withholding, 15 asthmatics and 15 normal subjects were placed on continuous monitoring of oesophageal pH and ECG. After baseline monitoring of oesophageal pH, at rest, for 30 min, spirometry was performed. Thereafter, the subjects underwent rigorous treadmill exercise for 8 min followed by spirometry, 10 min after running.Twelve out of 15 asthmatics and none in the control group demonstrated significant fall in FEV1 in response to exercise. However, only six out of 15 normal subjects and three in the asthmatic group had evidence of GER during or following exercise.We concluded that there is no significant correlation between EIB and GER in patients with asthma
Finite Higgs mass without Supersymmetry
We identify a class of chiral models where the one-loop effective potential
for Higgs scalar fields is finite without any requirement of supersymmetry. It
corresponds to the case where the Higgs fields are identified with the
components of a gauge field along compactified extra dimensions. We present a
six dimensional model with gauge group U(3)xU(3) and quarks and leptons
accomodated in fundamental and bi-fundamental representations. The model can be
embedded in a D-brane configuration of type I string theory and, upon
compactification on a T^2/Z_2 orbifold, it gives rise to the standard model
with two Higgs doublets.Comment: 28 pages, 4 figures, uses axodraw. Some typos corrected and
references rearrange
Cerebral Amyloid and Hypertension are Independently Associated with White Matter Lesions in Elderly.
In cognitively normal (CN) elderly individuals, white matter hyperintensities (WMH) are commonly viewed as a marker of cerebral small vessel disease (SVD). SVD is due to exposure to systemic vascular injury processes associated with highly prevalent vascular risk factors (VRFs) such as hypertension, high cholesterol, and diabetes. However, cerebral amyloid accumulation is also prevalent in this population and is associated with WMH accrual. Therefore, we examined the independent associations of amyloid burden and VRFs with WMH burden in CN elderly individuals with low to moderate vascular risk. Participants (n = 150) in the Alzheimer's Disease Neuroimaging Initiative (ADNI) received fluid attenuated inversion recovery (FLAIR) MRI at study entry. Total WMH volume was calculated from FLAIR images co-registered with structural MRI. Amyloid burden was determined by cerebrospinal fluid Aβ1-42 levels. Clinical histories of VRFs, as well as current measurements of vascular status, were recorded during a baseline clinical evaluation. We tested ridge regression models for independent associations and interactions of elevated blood pressure (BP) and amyloid to total WMH volume. We found that greater amyloid burden and a clinical history of hypertension were independently associated with greater WMH volume. In addition, elevated BP modified the association between amyloid and WMH, such that those with either current or past evidence of elevated BP had greater WMH volumes at a given burden of amyloid. These findings are consistent with the hypothesis that cerebral amyloid accumulation and VRFs are independently associated with clinically latent white matter damage represented by WMHs. The potential contribution of amyloid to WMHs should be further explored, even among elderly individuals without cognitive impairment and with limited VRF exposure
Theoretical characterization of a model of aragonite crystal orientation in red abalone nacre
Nacre, commonly known as mother-of-pearl, is a remarkable biomineral that in
red abalone consists of layers of 400-nm thick aragonite crystalline tablets
confined by organic matrix sheets, with the crystal axes of the
aragonite tablets oriented to within 12 degrees from the normal to the
layer planes. Recent experiments demonstrate that this orientational order
develops over a distance of tens of layers from the prismatic boundary at which
nacre formation begins.
Our previous simulations of a model in which the order develops because of
differential tablet growth rates (oriented tablets growing faster than
misoriented ones) yield patterns of tablets that agree qualitatively and
quantitatively with the experimental measurements. This paper presents an
analytical treatment of this model, focusing on how the dynamical development
and eventual degree of order depend on model parameters. Dynamical equations
for the probability distributions governing tablet orientations are introduced
whose form can be determined from symmetry considerations and for which
substantial analytic progress can be made. Numerical simulations are performed
to relate the parameters used in the analytic theory to those in the
microscopic growth model. The analytic theory demonstrates that the dynamical
mechanism is able to achieve a much higher degree of order than naive estimates
would indicate.Comment: 20 pages, 3 figure
Higher-order corrections to the short-pulse equation
Using renormalization group techniques, we derive an extended short- pulse
equation as approximation to a nonlinear wave equation. We investigate the new
equation numerically and show that the new equation captures efficiently
higher- order effects on pulse propagation in cubic nonlinear media. We
illustrate our findings using one- and two-soliton solutions of the first-order
short-pulse equation as initial conditions in the nonlinear wave equation
The Biotechnology Cluster in Vancouver
There is a strong biotechnology cluster in Vancouver yet there is no major manufacturing facility. The Vancouver cluster is unlike other biotech clusters in that its output is solely intellectual property. This ongoing study not only examines the usual structure of a cluster, but also will focus on the issue of intellectual environment, and seek to determine whether a strong cluster can be built without the presence of a large, globally-competitive, manufacturer
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