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 $1024^2$ 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

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

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

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($\bar{d}$) and \sim4 anti-alpha($\bar{^4He}$)). 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