48,788 research outputs found
A New Monte Carlo Method and Its Implications for Generalized Cluster Algorithms
We describe a novel switching algorithm based on a ``reverse'' Monte Carlo
method, in which the potential is stochastically modified before the system
configuration is moved. This new algorithm facilitates a generalized
formulation of cluster-type Monte Carlo methods, and the generalization makes
it possible to derive cluster algorithms for systems with both discrete and
continuous degrees of freedom. The roughening transition in the sine-Gordon
model has been studied with this method, and high-accuracy simulations for
system sizes up to were carried out to examine the logarithmic
divergence of the surface roughness above the transition temperature, revealing
clear evidence for universal scaling of the Kosterlitz-Thouless type.Comment: 4 pages, 2 figures. Phys. Rev. Lett. (in press
The origins of electromechanical indentation size effect in ferroelectrics
Metals exhibit a size-dependent hardening when subject to indentation.
Mechanisms for this phenomenon have been intensely researched in recent times.
Does such a size-effect also exist in the electromechanical behavior of
ferroelectrics?--if yes, what are the operative mechanisms? Our experiments on
BaTiO3 indeed suggest an electromechanical size-effect. We argue, through
theoretical calculations and differential experiments on another
non-ferroelectric piezoelectric (Quartz), that the phenomenon of
flexoelectricity(as opposed to dislocation activity) is responsible for our
observations. Flexoelectricity is the coupling of strain gradients to
polarization and exists in both ordinary and piezoelectric dielectrics. In
particular, ferroelectrics exhibit an unusually large flexoelectric response.Comment: in revie
Strain-driven light polarization switching in deep ultraviolet nitride emitters
Residual strain plays a critical role in determining the crystalline quality
of nitride epitaxial layers and in modifying their band structure; this often
leads to several interesting physical phenomena. It is found, for example, that
compressive strain in AlxGa1-xN layers grown on AlyGa1-yN (x<y) templates
results in an anti-crossing of the valence bands at considerably much higher Al
composition than expected. This happens even in the presence of large and
negative crystal field splitting energy for AlxGa1-xN layers. A judicious
magnitude of the compressive strain can support vertical light emission (out of
the c-plane) from AlxGa1-xN quantum wells up to x\approx 0.80, which is
desirable for the development of deep ultraviolet light-emitting diodes
designed to operate below 250nm with transverse electric polarization
characteristics
Overview and implications of obstructive sleep apnoea
Obstructive sleep apnoea (OSA) is a leading public health problem both in the developed and developing nations. However, awareness regarding diagnostic options, management and consequences of untreated OSA remains inadequate. In developing nations, the resources for adequate sleep medicine facilities are scarce. Therefore, there is a need for low cost, simple and accurate diagnostic and therapeutic modalities exists. Untreated OSA leads to excessive daytime sleepiness, diminished performance and an overall poor quality of life. The role of OSA in promoting insulin resistance, atherosclerosis, hypertension and a procoagulant state has now been established. Newer insights into the biochemical and genetic mediators of OSA have raised hopes regarding the development of a "cure". However, as of now, continuous positive airway pressure (CPAP) therapy remains the first-line treatment. Though its use improves the quality of life as well as metabolic derangements observed in OSA, patients' acceptance remains low. Its high cost and long-term use are also cumbersome. Newer modes of delivering CPAP, oral appliances and upper airway surgery are the other options available. It is hoped that their appropriate use to increase patients' compliance may improve the quality of life as well as provide a survival benefit
Production of nuclei and antinuclei in pp and Pb-Pb collisions with ALICE at the LHC
We present first results on the production of nuclei and antinuclei such as
(anti)deuterons, (anti)tritons, (anti)3He and (anti)4He in pp collisions at
\s = 7 TeV and Pb-Pb collisions at \sNN = 2.76 TeV. These particles are
identified using their energy loss (dE/dx) information in the Time Projection
Chamber of the ALICE experiment. The Inner Tracking System gives a precise
determination of the event vertex, by which primary and secondary particles are
separated. The high statistics of over 360 million events for pp and 16 million
events for Pb-Pb collisions give a significant number of light nuclei and
antinuclei (Pb-Pb collisions: \sim30,000 anti-deuterons() and \sim4
anti-alpha()). The predictions of various particle ratios from the
THERMUS model is also discussed.Comment: 4 pages, 5 figures, parallel talk at Quark Matter 2011, May 23rd-28th
2011, Annecy, Franc
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