1,290 research outputs found
Canonical connection on a class of Riemannian almost product manifolds
The canonical connection on a Riemannian almost product manifold is an
analogue to the Hermitian connection on an almost Hermitian manifold. In this
paper we consider the canonical connection on a class of Riemannian almost
product manifolds with non-integrable almost product structure. We construct
and characterize an example by a Lie group.Comment: 19 pages, some corrections in the example; J. Geom. (2012
Nanosecond photochromic molecular switching of a biphenyl-bridged imidazole dimer revealed by wide range transient absorption spectroscopy
We demonstrate that a biphenyl-bridged imidazole dimer exhibits fast photochromism with a thermal recovery time constant of similar to 100 ns, which is the fastest thermal back reaction in all reported imidazole dimers. Sub-ps transient absorption spectroscopy reveals that the generation process of the colored species occurs within 1 ps
Linking the beneficial effects of current therapeutic approaches in diabetes to the vascular endothelin system
The rising epidemic of diabetes worldwide is of significant concern. Although the ultimate objective is to prevent the development and find a cure for the disease, prevention and treatment of diabetic complications is very important. Vascular complications in diabetes, or diabetic vasculopathy, include macro- and microvascular dysfunction and represent the principal cause of morbidity and mortality in diabetic patients. Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vasculopathy. Endothelin-1 (ET-1), an endothelial cell-derived peptide, is a potent vasoconstrictor with mitogenic, pro-oxidative and pro-inflammatory properties that are particularly relevant to the pathophysiology of diabetic vasculopathy. Overproduction of ET-1 is reported in patients and animal models of diabetes and the functional effects of ET-1 and its receptors are also greatly altered in diabetic conditions. The current therapeutic approaches in diabetes include glucose lowering, sensitization to insulin, reduction of fatty acids and vasculoprotective therapies. However, whether and how these therapeutic approaches affect the ET-1 system remain poorly understood. Accordingly, in the present review, we will focus on experimental and clinical evidence that indicates a role for ET-1 in diabetic vasculopathy and on the effects of current therapeutic approaches in diabetes on the vascular ET-1 system
Spectroscopy by frequency entangled photon pairs
Quantum spectroscopy was performed using the frequency-entangled broadband
photon pairs generated by spontaneous parametric down-conversion. An absorptive
sample was placed in front of the idler photon detector, and the frequency of
signal photons was resolved by a diffraction grating. The absorption spectrum
of the sample was measured by counting the coincidences, and the result is in
agreement with the one measured by a conventional spectrophotometer with a
classical light source.Comment: 11 pages, 5 figures, to be published in Phys. Lett.
Description of surfaces associated with sigma models on Minkowski space
The objective of this paper is to construct and investigate smooth orientable
surfaces in by analytical methods. The structural equations of
surfaces in connection with sigma models on Minkowski space are
studied in detail. This is carried out using moving frames adapted to surfaces
immersed in the algebra. The first and second fundamental forms of this
surface as well as the relations between them as expressed in the
Gauss-Weingarten and Gauss-Codazzi-Ricci equations are found. The Gaussian
curvature, the mean curvature vector and the Willmore functional expressed in
terms of a solution of sigma model are obtained. An example of a
surface associated with the model is included as an illustration of the
theoretical results.Comment: 19 pages, 1 figure; shorter version, some typos and minor mistakes
correcte
Building GUTs from strings
We study in detail the structure of Grand Unified Theories derived as the
low-energy limit of orbifold four-dimensional strings. To this aim, new
techniques for building level-two symmetric orbifold theories are presented.
New classes of GUTs in the context of symmetric orbifolds are then constructed.
The method of permutation modding is further explored and SO(10) GUTs with both
or -plets are obtained. SU(5) models are also found through this
method. It is shown that, in the context of symmetric orbifold GUTs,
only a single GUT-Higgs, either a or a , can be present and it always
resides in an order-two untwisted sector. Very restrictive results also hold in
the case of . General properties and selection rules for string GUTs are
described. Some of these selection rules forbid the presence of some particular
GUT-Higgs couplings which are sometimes used in SUSY-GUT model building. Some
semi-realistic string GUT examples are presented and their properties briefly
discussed.Comment: 40 pages, no figures, Late
Evidence for orbital ordering in LaCoO3
We present powder and single crystal X-ray diffraction data as evidence for a
monoclinic distortion in the low spin (S=0) and intermediate spin state (S=1)
of LaCoO3. The alternation of short and long bonds in the ab plane indicates
the presence of eg orbital ordering induced by a cooperative Jahn-Teller
distortion. We observe an increase of the Jahn-Teller distortion with
temperature in agreement with a thermally activated behavior of the Co3+ ions
from a low-spin ground state to an intermediate-spin excited state.Comment: Accepted to Phys. Rev.
AdS/CFT Equivalence Transformation
We show that any conformal field theory in d-dimensional Minkowski space, in
a phase with spontaneously broken conformal symmetry and with the dilaton among
its fields, can be rewritten in terms of the static gauge (d-1)-brane on
AdS_(d+1) by means of an invertible change of variables. This nonlinear
holographic transformation maps the Minkowski space coordinates onto the brane
worldvolume ones and the dilaton onto the transverse AdS brane coordinate. One
of the consequences of the existence of this map is that any (d-1)-brane
worldvolume action on AdS_(d+1)\times X^m (with X^m standing for the sphere S^m
or more complicated curved manifold) admits an equivalent description in
Minkowski space as a nonlinear and higher-derivative extension of some
conventional conformal field theory action, with the conformal group being
realized in a standard way. The holographic transformation explicitly relates
the standard realization of the conformal group to its field-dependent
nonlinear realization as the isometry group of the brane AdS_(d+1) background.
Some possible implications of this transformation, in particular, for the study
of the quantum effective action of N=4 super Yang-Mills theory in the context
of AdS/CFT correspondence, are briefly discussed.Comment: LaTeX, 19 pages, minor correction in Abstrac
Uncorrelated scattering approximation for the scattering and break-up of weakly bound nuclei on heavy targets
The scattering of a weakly bound (halo) projectile nucleus by a heavy target
nucleus is investigated. A new approach, called the Uncorrelated Scattering
Approximation, is proposed. The main approximation involved is to neglect the
correlation between the fragments of the projectile in the region where the
interaction with the target is important. The formalism makes use of
hyper-spherical harmonics, Raynal-Revay coefficients and momentum-localized
wave functions to expand projectile channel wave functions in terms of products
of the channel wave function of the individual fragments. Within this approach,
the kinetic energy and angular momentum of each fragment is conserved during
the scattering process. The elastic, inelastic and break-up S-matrices are
obtained as an analytic combination involving the bound wave function of the
projectile and the product of the S-matrices of the fragments. The approach is
applied to describe the scattering of deuteron on Ni at several
energies. The results are compared with experimental data and
continuum-discretized coupled-channels calculations.Comment: 34 pages, 5 figures, accepted for publication in Nucl. Phys.
Universality in Bacterial Colonies
The emergent spatial patterns generated by growing bacterial colonies have
been the focus of intense study in physics during the last twenty years. Both
experimental and theoretical investigations have made possible a clear
qualitative picture of the different structures that such colonies can exhibit,
depending on the medium on which they are growing. However, there are
relatively few quantitative descriptions of these patterns. In this paper, we
use a mechanistically detailed simulation framework to measure the scaling
exponents associated with the advancing fronts of bacterial colonies on hard
agar substrata, aiming to discern the universality class to which the system
belongs. We show that the universal behavior exhibited by the colonies can be
much richer than previously reported, and we propose the possibility of up to
four different sub-phases within the medium-to-high nutrient concentration
regime. We hypothesize that the quenched disorder that characterizes one of
these sub-phases is an emergent property of the growth and division of bacteria
competing for limited space and nutrients.Comment: 12 pages, 5 figure
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