7,637 research outputs found
Cluster Monte Carlo Simulations of the Nematic--Isotropic Transition
We report the results of simulations of the Lebwohl-Lasher model of the
nematic-isotropic transition using a new cluster Monte Carlo algorithm. The
algorithm is a modification of the Wolff algorithm for spin systems, and
greatly reduces critical slowing down. We calculate the free energy in the
neighborhood of the transition for systems up to linear size 70. We find a
double well structure with a barrier that grows with increasing system size,
obeying finite size scaling for systems of size greater than 35. We thus obtain
an estimate of the value of the transition temperature in the thermodynamic
limit.Comment: 4 figure
Resolving the M2-brane
We construct deformed, T^2 wrapped, rotating M2-branes on a resolved cone
over Q^{1,1,1} and Q^{1,1,1}/Z_2, as well as on a product of two Eguchi-Hanson
instantons. All worldvolume directions of these supersymmetric and regular
solutions are fibred over the transverse space. These constitute gravity duals
of D=3, N=2 gauge theories. In particular, the deformed M2-brane on a resolved
cone over Q^{1,1,1} and the S^1 wrapped M2-brane on a resolved cone over
Q^{1,1,1}/Z_2 provide explicit realizations of holographic renormalization
group flows in M-theory for which both conformal and Lorentz symmetries are
broken in the IR region and restored in the UV limit. These solutions can be
dualized to supersymmetric type IIB pp-waves, which are rendered non-singular
either by additional flux or a twisted time-like direction.Comment: Latex, 23 pages, references adde
Does roflumilast decrease exacerbations in severe COPD patients not controlled by inhaled combination therapy? the REACT study protocol.
Many patients with chronic obstructive pulmonary disease (COPD) continue to suffer exacerbations, even when treated with maximum recommended therapy (eg, inhaled combinations of long-acting β(2)-agonist and high dose inhaled corticosteroids, with or without a long-acting anticholinergic [long-acting muscarinic antagonist]). Roflumilast is approved to treat severe COPD in patients with chronic bronchitis - and a history of frequent exacerbations - as an add-on to bronchodilators.PURPOSE:The REACT (Roflumilast in the Prevention of COPD Exacerbations While Taking Appropriate Combination Treatment) study (identification number RO-2455-404-RD, clinicaltrials. gov identifier NCT01329029) will investigate whether roflumilast further reduces exacerbations when added to inhaled combination therapy in patients still suffering from frequent exacerbations.PATIENTS AND METHODS:REACT is a 1-year randomized, double-blind, multicenter, phase III/IV study of roflumilast 500 μg once daily or placebo on top of a fixed long-acting β(2)-agonist/inhaled corticosteroid combination. A concomitant long-acting muscarinic antagonist will be allowed at stable doses. The primary outcome is the rate of moderate or severe COPD exacerbations. Using a Poisson regression model with a two-sided significance level of 5%, a sample size of 967 patients per treatment group is needed for 90% power. COPD patients with severe to very severe airflow limitation, symptoms of chronic bronchitis, and at least two exacerbations in the previous year will be recruited.CONCLUSION:It is hypothesized that because roflumilast (a phosphodiesterase-4 inhibitor) has a different mode of action to bronchodilators and inhaled corticosteroids, it may provide additional benefits when added to these treatments in frequent exacerbators. REACT will be important to determine the role of roflumilast in COPD management. Here, the design and rationale for this important study is described
The SPOrt Project: Cosmological and Astrophysical Goals
We present the cosmological and astrophysical objectives of the SPOrt
mission, which is scheduled for flying on the International Space Station (ISS)
in the year 2002 with the purpose of measuring the diffuse sky polarized
radiation in the microwave region. We discuss the problem of disentangling the
cosmic background polarized signal from the Galactic foregrounds.Comment: 10 pages; 5 PS figures; requires aipproc2.cls, aipproc2.sty,
epsfc.tex; to appear in Proc. of ``3K Cosmology'', Rome 5-10 Oct. 199
Deterministic direct growth of WS2 on CVD graphene arrays
The combination of the exciting properties of graphene with those of monolayer tungsten disulfide (WS2) makes this heterostack of great interest for electronic, optoelectronic and spintronic applications. The scalable synthesis of graphene/WS2 heterostructures on technologically attractive substrates like SiO2 would greatly facilitate the implementation of novel two-dimensional (2D) devices. In this work, we report the direct growth of monolayer WS2 via chemical vapor deposition (CVD) on single-crystal graphene arrays on SiO2. Remarkably, spectroscopic and microscopic characterization reveals that WS2 grows only on top of the graphene crystals so that the vertical heterostack is selectively obtained in a bottom-up fashion. Spectroscopic characterization indicates that, after WS2 synthesis, graphene undergoes compressive strain and hole doping. Tailored experiments show that such hole doping is caused by the modification of the SiO2 stoichiometry at the graphene/SiO2 interface during the WS2 growth. Electrical transport measurements reveal that the heterostructure behaves like an electron-blocking layer at large positive gate voltage, which makes it a suitable candidate for the development of unipolar optoelectronic components
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Italian Experience and Problems in Deep Geothermal Drilling
Geothermal exploration at depth is being conducted in the Larderello area of Italy, in order to ascertain whether it is possible to extract geothermal fluids from the layers which underlie the reservoir now being exploited. The main operating problems are caused by the high thermality and the chemical corrosiveness of the fluids encountered; and by the practical problems involved in drilling without circulation to the surface in mainly hard but anhomogeneous fractured formations. The technology employed for deep geothermal well drilling plays an important role in this research. In deep geothermal well drilling it is essential that the equipment and the materials employed are suitable for use in areas which are characterized by high thermality and chemical corrosiveness. The results of the experiences gained in Italy concerning the materials and tools employed in deep geothermal exploration are presented. The various problems involved are described in detail and particular mention is made of drift control, fishing operations, cementation of the deep casing, control of the circulation fluid, and choice of the tubular materials
Damping of Tensor Modes in Cosmology
An analytic formula is given for the traceless transverse part of the
anisotropic stress tensor due to free streaming neutrinos, and used to derive
an integro-differential equation for the propagation of cosmological
gravitational waves. The solution shows that anisotropic stress reduces the
squared amplitude by 35.6 % for wavelengths that enter the horizon during the
radiation-dominated phase, independent of any cosmological parameters. This
decreases the tensor temperature and polarization correlation functions for
these wavelengths by the same amount. The effect is less for wavelengths that
enter the horizon at later times. At the longest wavelengths the decrease in
the tensor correlation functions due to neutrino free streaming ranges from
10.7% for to 9.0% for . An Appendix gives a
general proof that tensor as well as scalar modes satisfy a conservation law
for perturbations outside the horizon, even when the anisotropic stress tensor
is not negligible.Comment: 14 pages. The original version of this paper has been expanded to
deal with perturbations of any wavelength. While for wavelengths short enough
to enter the horizon during radiation dominance, temperature and polarization
correlations are damped by 35.6%, at the longest wavelengths the damping is
from 9.0% to 11%. An added Appendix gives a general proof that tensor as well
as scalar modes satisfy a conservation law outside the horizon, even during
neutrino decoupling. Some references are also adde
Prolonged remission of disseminated atypical adenomatous hyperplasia under gefitinib.
Abstract:Atypical adenomatous hyperplasia (AAH) is a putative precursor of bronchioloalveolar carcinoma (BAC) and adenocarcinoma of the lung, developing from terminal respiratory unit cells. AAH and BAC lesions typically present as ground-glass opacities at spiral chest computed tomography. Epidermal growth factor receptor polysomy/mutations, conferring higher sensitivity to Gefitinib, are frequent in BAC but less common in AAH. We describe an interesting case of disseminated AAH showing a sustained remission under Gefitinib therapy
Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits
The ability to generate particles from the quantum vacuum is one of the most
profound consequences of Heisenberg's uncertainty principle. Although the
significance of vacuum fluctuations can be seen throughout physics, the
experimental realization of vacuum amplification effects has until now been
limited to a few cases. Superconducting circuit devices, driven by the goal to
achieve a viable quantum computer, have been used in the experimental
demonstration of the dynamical Casimir effect, and may soon be able to realize
the elusive verification of analogue Hawking radiation. This article describes
several mechanisms for generating photons from the quantum vacuum and
emphasizes their connection to the well-known parametric amplifier from quantum
optics. Discussed in detail is the possible realization of each mechanism, or
its analogue, in superconducting circuit systems. The ability to selectively
engineer these circuit devices highlights the relationship between the various
amplification mechanisms.Comment: 27 pages, 10 figures, version published in Rev. Mod. Phys. as a
Colloquiu
Can the evolution of music be analyzed in a quantitative manner?
We propose a methodology to study music development by applying multivariate
statistics on composers characteristics. Seven representative composers were
considered in terms of eight main musical features. Grades were assigned to
each characteristic and their correlations were analyzed. A bootstrap method
was applied to simulate hundreds of artificial composers influenced by the
seven representatives chosen. Afterwards we quantify non-numeric relations like
dialectics, opposition and innovation. Composers differences on style and
technique were represented as geometrical distances in the feature space,
making it possible to quantify, for example, how much Bach and Stockhausen
differ from other composers or how much Beethoven influenced Brahms. In
addition, we compared the results with a prior investigation on philosophy.
Opposition, strong on philosophy, was not remarkable on music. Supporting an
observation already considered by music theorists, strong influences were
identified between composers by the quantification of dialectics, implying
inheritance and suggesting a stronger master-disciple evolution when compared
to the philosophy analysis.Comment: 8 pages, 6 figures, added references for sections 1 and 4.C, better
mathematical description on section 2. New values and interpretation, now
considering a bootstrap metho
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