Quantum linear mutual information and classical correlations in globally pure bipartite systems

We investigate the correlations of initially separable probability distributions in a globally pure bipartite system with two degrees of freedom for classical and quantum systems. A classical version of the quantum linear mutual information is introduced and the two quantities are compared for a system of oscillators coupled with both linear and non-linear interactions. The classical correlations help to understand how much of the quantum loss of purity are due to intrinsic quantum effects and how much is related to the probabilistic character of the initial states, a characteristic shared by both the classical and quantum pictures. Our examples show that, for initially localized Gaussian states, the classical statistical mutual linear entropy follows its quantum counterpart for short times. For non-Gaussian states the behavior of the classical and quantum measures of information are still qualitatively similar, although the fingerprints of the non-classical nature of the initial state can be observed in their different amplitudes of oscillation.Comment: (16 pages, 4 figures

Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

We demonstrate a great improvement in the crystal quality of our semi-polar (11-22) GaN overgrown on regularly arrayed micro-rod templates fabricated using a combination of industry-matched photolithography and dry-etching techniques. As a result of our micro-rod configuration specially designed, an intrinsic issue on the anisotropic growth rate which is a great challenge in conventional overgrowth technique for semi-polar GaN has been resolved. Transmission electron microscopy measurements show a different mechanism of defect reduction from conventional overgrowth techniques and also demonstrate major advantages of our approach. The dislocations existing in the GaN micro-rods are effectively blocked by both a SiO2 mask on the top of each GaN micro-rod and lateral growth along the c-direction, where the growth rate along the c-direction is faster than that along any other direction. Basal stacking faults (BSFs) are also effectively impeded, leading to a distribution of BSF-free regions periodically spaced by BSF regions along the [-1-123] direction, in which high and low BSF density areas further show a periodic distribution along the [1-100] direction. Furthermore, a defect reduction model is proposed for further improvement in the crystalline quality of overgrown (11-22) GaN on sapphire

Microstructure investigation of semi-polar (11-22) GaN overgrown on differently designed micro-rod array templates

In order to realize semi-polar (11-22) GaN based laser diodes grown on sapphire, it is necessary to further improve the crystal quality of the (11-22) GaN obtained by using our overgrowth approach developed on regularly arrayed micro-rod templates [T. Wang, Semicond. Sci. Technol. 31, 093003 (2016)]. This can be achieved by carefully designing micro-rod templates. Based on transmission electron microscopy and photoluminescence measurements, it has been found that the micro-rod diameter plays a vital role in effectively reducing both the dislocation density and the basal staking fault (BSF) density of the overgrown (11-22) GaN, but in different manners. The BSF density reduces monotonically with increasing the micro-rod diameter from 2 to 5 μm, and then starts to be saturated when the micro-rod diameter further increases. In contrast, the dislocation density reduces significantly when the micro-rod diameter increases from 2 to 4 μm, and then starts to increase when the diameter further increases to 5 μm. Furthermore, employing shorter micro-rods is useful for removing additional BSFs, leading to further improvement in crystal quality. The results presented provide a very promising approach to eventually achieving (11-22) semi-polar III-nitride laser diodes

Feedback methods for inverse simulation of dynamic models for engineering systems applications

Inverse simulation is a form of inverse modelling in which computer simulation methods are used to find the time histories of input variables that, for a given model, match a set of required output responses. Conventional inverse simulation methods for dynamic models are computationally intensive and can present difficulties for high-speed applications. This paper includes a review of established methods of inverse simulation,giving some emphasis to iterative techniques that were first developed for aeronautical applications. It goes on to discuss the application of a different approach which is based on feedback principles. This feedback method is suitable for a wide range of linear and nonlinear dynamic models and involves two distinct stages. The first stage involves design of a feedback loop around the given simulation model and, in the second stage, that closed-loop system is used for inversion of the model. Issues of robustness within closed-loop systems used in inverse simulation are not significant as there are no plant uncertainties or external disturbances. Thus the process is simpler than that required for the development of a control system of equivalent complexity. Engineering applications of this feedback approach to inverse simulation are described through case studies that put particular emphasis on nonlinear and multi-input multi-output models

Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging

Taking advantage of electron diffraction based measurements, in a scanning electron microscope, can deliver non-destructive and quantitative information on extended defects in semiconductor thin films. In this work, we have studied a (11-22) semi-polar GaN thin film overgrown on regularly arrayed GaN micro-rod array templates grown by metal organic vapour phase epitaxy. We were able to optimise the diffraction conditions to image and quantify basal plane stacking faults (BSFs) and threading dislocations (TDs) using electron channelling contrast imaging (ECCI). Clusters of BSFs and TDs were observed with the same periodicity as the underlying micro-rod array template. The average BSF and TD densities were estimated to be ≈4 × 104 cm−1 and ≈5 × 108 cm−2, respectively. The contrast seen for BSFs in ECCI is similar to that observed for plan-view transmission electron microscopy images, with the only difference being the former acquiring the backscattered electrons and the latter collecting the transmitted electrons. Our present work shows the capability of ECCI for quantifying extended defects in semi-polar nitrides and represents a real step forward for optimising the growth conditions in these materials

Horava Gravity and Gravitons at a Conformal Point

Recently Horava proposed a renormalizable gravity theory with higher derivatives by abandoning the Lorenz invariance in UV. Here, I study the Horava model at $\lambda=1/3$, where an anisotropic Weyl symmetry exists in the UV limit, in addition to the foliation-preserving diffeomorphism. By considering linear perturbations around Minkowski vacuum, I show that the scalar graviton mode is completely disappeared and only the usual tensor graviton modes remain in the physical spectrum. The existence of the UV conformal symmetry is unique to the theory with the detailed balance and it is quite probable that $\lambda=1/3$ be the UV fixed point. This situation is analogous to $\lambda=1$, which is Lorentz invariant in the IR limit and is believed to be the IR fixed point.Comment: Added comments and references, Accepted in GER

Energy Conditions in f(G)f(G) Modified Gravity with Non-minimal Coupling to Matter

In this paper we study a model of modified gravity with non-minimal coupling between a general function of the Gauss-Bonnet invariant, $f(G)$, and matter Lagrangian from the point of view of the energy conditions. Such model has been introduced in Ref. [21] for description of early inflation and late-time cosmic acceleration. We present the suitable energy conditions for the above mentioned model and then, we use the estimated values of the Hubble, deceleration and jerk parameters to apply the obtained energy conditions to the specific class of modified Gauss-Bonnet models.Comment: 12 pages, no figur, Accepted for publication in Astrophysics and Space Scienc

On the mechanisms of heavy-quarkonium hadroproduction

We discuss the various mechanisms potentially at work in hadroproduction of heavy quarkonia in the light of computations of higher-order QCD corrections both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the inclusion of the contribution arising from the s-channel cut in the CS channel. We also discuss new observables meant to better discriminate between these different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June 2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses svjour.cls and svepj.clo (included

A Protocol for a Distributed Recommender System

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