53,683 research outputs found
Experiments with repeating weighted boosting search for optimization in signal processing applications
Enhanced Kerr nonlinearity for self-action via atomic coherence in a four-level atomic system
Enhancement of optical Kerr nonlinearity for self-action by
electro-magnetically induced transparency in a four-level atomic system
including dephasing between the ground states is studied in detail by solving
the density matrix equations for the atomic levels. We discern three major
contributions, from energy shifts of the ground states induced by the probe
light, to the third-order susceptibility in the four-level system. In this
four-level system with the frequency-degenerate probes, quantum interference
amongst the three contributions can, not only enhance the third-order
susceptibility more effectively than in the three-level system with the same
characteristic parameters, but also make the ratio between its real and
imaginary part controllable. Due to dephasing between the two ground states and
constructive quantum interference, the most effective enhancement generally
occurs at an offset that is determined by the atomic transition frequency
difference and the coupling Rabi frequency.Comment: Permanent email address: [email protected]. Accepted by Optics
Communication
NARX-based nonlinear system identification using orthogonal least squares basis hunting
An orthogonal least squares technique for basis hunting (OLS-BH) is proposed to construct sparse radial basis function (RBF) models for NARX-type nonlinear systems. Unlike most of the existing RBF or kernel modelling methods, whichplaces the RBF or kernel centers at the training input data points and use a fixed common variance for all the regressors, the proposed OLS-BH technique tunes the RBF center and diagonal covariance matrix of individual regressor by minimizing the training mean square error. An efficient optimization method isadopted for this basis hunting to select regressors in an orthogonal forward selection procedure. Experimental results obtained using this OLS-BH technique demonstrate that it offers a state-of-the-art method for constructing parsimonious RBF models with excellent generalization performance
Manipulating Synchronous Optical Signals with a Double Atomic Ensemble
We analyze a double atomic configuration interacting with two
signal beams and two control beams. Because of the quantum interference between
the two channels, the four fields are phase-matched in
electromagnetically induced transparency. Our numerical simulation shows that
this system is able to manipulate synchronous optical signals, such as
generation of optical twin signals, data correction, signal transfer and
amplification in the atomic storage.Comment: 5 pages, 7 figure
Sparse support vector regression based on orthogonal forward selection for the generalised kernel model
Summary of Results on Hard Probes
Results on observables related to hard scattering processes as presented at
this conference are reviewed. This includes in particular measurements related
to jet quenching, a phenomenon which has been predicted as a signature for the
hot and dense early phase of strongly interacting matter.Comment: Summary talk at Quark Matter 2002, Nantes, Proceedings to be
published in Nucl. Phys. A, 10 pages, 6 figures, (one figure added in this
version
Glucocorticoid Receptor and Adipocyte Biology.
Glucocorticoids are steroid hormones that play a key role in metabolic adaptations during stress, such as fasting and starvation, in order to maintain plasma glucose levels. Excess and chronic glucocorticoid exposure, however, causes metabolic syndrome including insulin resistance, dyslipidemia, and hyperglycemia. Studies in animal models of metabolic disorders frequently demonstrate that suppressing glucocorticoid signaling improves insulin sensitivity and metabolic profiles. Glucocorticoids convey their signals through an intracellular glucocorticoid receptor (GR), which is a transcriptional regulator. The adipocyte is one cell type that contributes to whole body metabolic homeostasis under the influence of GR. Glucocorticoids' functions on adipose tissues are complex. Depending on various physiological or pathophysiological states as well as distinct fat depots, glucocorticoids can either increase or decrease lipid storage in adipose tissues. In rodents, glucocorticoids have been shown to reduce the thermogenic activity of brown adipocytes. However, in human acute glucocorticoid exposure, glucocorticoids act to promote thermogenesis. In this article, we will review the recent studies on the mechanisms underlying the complex metabolic functions of GR in adipocytes. These include studies of the metabolic outcomes of adipocyte specific GR knockout mice and identification of novel GR primary target genes that mediate glucocorticoid action in adipocytes
Mechanical Characterization of Fourth Generation Composite Humerus
Mechanical data on upper extremity surrogate bones, supporting use as biomechanical tools, is limited. The objective of this study was to characterize the structural behaviour of the fourth-generation composite humerus under simulated physiologic bending, specifically, stiffness, rigidity, and mid-diaphysial surface strains. Three humeri were tested in four-point bending, in anatomically defined anteroposterior (AP) and mediolateral (ML) planes. Stiffness and rigidity were derived using load–displacement data. Principal strains were determined at the anterior, posterior, medial, and lateral surfaces in the humeral mid-diaphysial transverse plane of one specimen using stacked rosettes. Linear structural behaviour was observed within the test range. Average stiffness and rigidity were greater in the ML (918 ± 18 N/mm; 98.4 ± 1.9 Nm2) than the AP plane (833 ± 16 N/mm; 89.3 ± 1.6 Nm2), with little inter-specimen variability. The ML/AP rigidity ratio was 1.1. Surface principal strains were similar at the anterior (5.41 µε/N) and posterior (5.43 µε/N) gauges for AP bending, and comparatively less for ML bending, i.e. 5.1 and 4.5 µε/N, at the medial and lateral gauges, respectively. This study provides novel strain and stiffness data for the fourth-generation composite humerus and also adds to published construct rigidity data. The presented results support the use of this composite bone as a tool for modelling and experimentation
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