4,738 research outputs found
The Hausdorff Dimension of Surfaces in Two-Dimensional Quantum Gravity Coupled to Ising Minimal Matter
Within the framework of string field theory the intrinsic Hausdorff dimension
d_H of the ensemble of surfaces in two-dimensional quantum gravity has recently
been claimed to be 2m for the class of unitary minimal models (p = m+1,q = m).
This contradicts recent results from numerical simulations, which consistently
find d_H approximatly 4 in the cases m = 2, 3, 5 and infinity. The string field
calculations rely on identifying the scaling behavior of geodesic distance and
area with respect to a common length scale l. This length scale is introduced
by formulating the models on a disk with fixed boundary length l. In this paper
we study the relationship between the mean area and the boundary length for
pure gravity and the Ising model coupled to gravity. We discuss how this
relationship is modified by relevant perturbations in the Ising model. We
discuss how this leads to a modified value for the Hausdorff dimension.Comment: 12 pages, Latex. Revised to deal only with Ising matter. Clarifying
discussion adde
Spin/disorder correlations and duality in the c=1/2 string
We use the method of discrete loop equations to calculate exact correlation
functions of spin and disorder operators on the sphere and on the boundary of a
disk in the string, both in the Ising and dual Ising matrix model
formulations. For both the Ising and dual Ising theories the results on the
sphere are in agreement with the KPZ/DDK scaling predictions based on Liouville
theory; the results on the disk agree with the scaling predictions of Martinec,
Moore, and Seiberg for boundary operators. The calculation of Ising disorder
correlations on the sphere requires the use of boundary variables introduced in
[hep-th/9510199], which have no matrix model analog. A subtlety in the
calculation on the disk arises because the expansions of the correlation
functions have leading singular terms which are nonuniversal; we show that this
issue may be resolved by using separate cosmological constants for each
boundary domain. These results give evidence that the Kramers-Wannier duality
symmetry of the conformal field theory survives coupling to quantum
gravity, implying a duality symmetry of the string even in the
presence of boundary operators.Comment: 19 pages, LaTeX; final publication versio
Minimal Dynamical Triangulations of Random Surfaces
We introduce and investigate numerically a minimal class of dynamical
triangulations of two-dimensional gravity on the sphere in which only vertices
of order five, six or seven are permitted. We show firstly that this
restriction of the local coordination number, or equivalently intrinsic scalar
curvature, leaves intact the fractal structure characteristic of generic
dynamically triangulated random surfaces. Furthermore the Ising model coupled
to minimal two-dimensional gravity still possesses a continuous phase
transition. The critical exponents of this transition correspond to the usual
KPZ exponents associated with coupling a central charge c=1/2 model to
two-dimensional gravity.Comment: Latex, 9 pages, 3 figures, Published versio
Cosmological Birefringence: an Astrophysical test of Fundamental Physics
We review the methods used to test for the existence of cosmological
birefringence, i.e. a rotation of the plane of linear polarization for
electromagnetic radiation traveling over cosmological distances, which might
arise in a number of important contexts involving the violation of fundamental
physical principles. The main methods use: (1) the radio polarization of radio
galaxies and quasars, (2) the ultraviolet polarization of radio galaxies, and
(3) the cosmic microwave background polarization. We discuss the main results
obtained so far, the advantages and disadvantages of each method, and future
prospects.Comment: To appear in the Proceedings of the JENAM 2010 Symposium "From
Varying Couplings to Fundamental Physics", held in Lisbon, 6-10 Sept. 201
Prevalence of human papillomavirus in head and neck cancers in European populations: a meta-analysis.
BACKGROUND: Infection with human papillomavirus (HPV) is necessary for the development of cervical carcinoma. By contrast, the role of HPV in the pathogenesis of other malignancies, such as head and neck cancers, is less well characterised. This study aimed to address key information gaps by conducting a systematic review and meta-analysis of the prevalence of HPV infection in head and neck cancers, focusing on data for European populations. METHODS: MEDLINE, Embase and grey literature sources were systematically searched for primary studies that were published in English between July 2002 and July 2012, and which reported on the prevalence of HPV infection in head and neck cancers in European populations. Studies on non-European populations, those not published in English, and those assessing patients co-infected with human immunodeficiency virus were excluded. Eligible studies were combined in a meta-analysis. In addition, the potential statistical association between the head and neck cancers and certain HPV types was investigated. RESULTS: Thirty-nine publications met the inclusion criteria. The prevalence of HPV of any type in 3,649 patients with head and neck cancers was 40.0% (95% confidence interval, 34.6% to 45.5%), and was highest in tonsillar cancer (66.4%) and lowest in pharyngeal (15.3%) and tongue (25.7%) cancers. There were no statistically significant associations between the HPV types analysed and the geographical setting, type of sample analysed or type of primer used to analyse samples in head and neck cancers. CONCLUSIONS: The prevalence of HPV infection in European patients with head and neck cancers is high but varies between the different anatomical sites of these malignancies. There appears to be no association between HPV type and geographical setting, type of samples analysed or type of primer used to analyse samples in such cancers
Does Institutional Context Affect CSR Disclosure? A Study on Eurostoxx 50
We propose to investigate the relationship between corporate social responsibility disclosure and institutional/environmental factors among a sample of European listed companies. We find that, by using several traditional explicative variables, institutional factors affect the level of CSR disclosure, in a context where the EU Commission has been paying growing attention to social and environmental accountability of listed companies (see the EU Dir. 95/2014). Our findings are further supported by multivariate regression, where ESG score (measure of CSR disclosure) is regressed on nine variables which represent the expression of institutional factors. By looking at the institutional
determinants of CSR disclosure, we are seeking to pose a challenge for future research agenda, in order to understand whether CSR does actually reflect an effective commitment of firms to accounting practices and rules, as a form of social behavior, or whether it is just a tool to manage stakeholders’ perception and to comply with regulation
Hyperpolarized 13C Spectroscopic Evaluation of Oxidative Stress in a Rodent Model of Steatohepatitis.
Nonalcoholic fatty liver disease (NAFLD) has become highly prevalent, now considered the most common liver disease in the western world. Approximately one-third of patients with NASH develop non-alchoholic steatohepatitis (NASH), histologically defined by lobular and portal inflammation, and accompanied by marked oxidative stress. Patients with NASH are at increased risk for cirrhosis and hepatocellular carcinoma, and diagnosis currently requires invasive biopsy. In animal models of NASH, particularly the methionine-choline deficient (MCD) model, profound changes are seen in redox enzymes and key intracellular antioxidants. To study antioxidant status in NASH non-invasively, we applied the redox probe hyperpolarized [1-13C] dehydroascorbic acid (HP DHA), which is reduced to Vitamin C (VitC) rapidly in the normal liver. In MCD mice, we observed a significant decrease in HP DHA to VitC conversion that accompanied hepatic fat deposition. When these animals were subsequently placed on a normal diet, resonance ratios reverted to those seen in control mice. These findings suggest that HP DHA, a potentially clinically translatable imaging agent, holds special promise in imaging NASH and other metabolic syndromes, to monitor disease progression and response to targeted therapies
The 2003 eclipse of EE Cep is coming. A review of past eclipses
EE Cep is an eclipsing binary with a period of 5.6 years. The next eclipse
will occur soon, in May-June 2003, and all available past eclipses were
collected and briefly analysed. EE Cep shows very large changes of the shape
and the depth of minima during different eclipses, however it is possible to
single out some persistent features. The analysis suggests that the eclipsing
body should be a long object surrounded by an extended semi-transparent
envelope. As an explanation, a model of a precessing optically thick disc,
inclined to the plane of the binary orbit, is invoked. The changes of its
spatial orientation, which is defined by the inclination of the disc and the
tilt, induced most probably by precession of the disc spin axis with a period
of about 50 years, produce strange photometric behaviour of this star. The
H_alpha emission, and possibly the NaI absorptions, show significant changes
during several months outside of the eclipse phase.Comment: 7 pages, 7 figures, LaTeX2e, accepted by A&
Quintessence and tachyon dark energy models with a constant equation of state parameter
In this work we determine the correspondence between quintessence and tachyon
dark energy models with a constant dark energy equation of state parameter,
. Although the evolution of both the Hubble parameter and the scalar field
potential with redshift is the same, we show that the evolution of
quintessence/tachyon scalar fields with redshift is, in general, very
different. We explicity demonstrate that if the potentials need
to be very fine-tuned for the relative perturbation on the equation of state
parameter, , to be very small around the present
time. We also discuss possible implications of our results for the
reconstruction of the evolution of with redshift using varying couplings.Comment: 9 pages, 2 figures, published version with two extra references
include
A geometric approach to free variable loop equations in discretized theories of 2D gravity
We present a self-contained analysis of theories of discrete 2D gravity
coupled to matter, using geometric methods to derive equations for generating
functions in terms of free (noncommuting) variables. For the class of discrete
gravity theories which correspond to matrix models, our method is a
generalization of the technique of Schwinger-Dyson equations and is closely
related to recent work describing the master field in terms of noncommuting
variables; the important differences are that we derive a single equation for
the generating function using purely graphical arguments, and that the approach
is applicable to a broader class of theories than those described by matrix
models. Several example applications are given here, including theories of
gravity coupled to a single Ising spin (), multiple Ising spins (), a general class of two-matrix models which includes the Ising theory and
its dual, the three-state Potts model, and a dually weighted graph model which
does not admit a simple description in terms of matrix models.Comment: 40 pages, 8 figures, LaTeX; final publication versio
- …