Solutions of the quasi-vector wave equation for optical waveguides in a mapped infinite domains by the Galerkin's method

Galerkin's method is employed to analyze the quasi-vector wave equation for optical waveguides with arbitrary refractive index profile in a mapped infinite domains. Results are presented for a range of waveguide structures which include rectangular core, circular core, rib, and multiple quantum well. Solutions are compared favorably to exact vector solution and numerical results using Fourier operator transform method and beam-propagation method.published_or_final_versio

Cutoff frequency of the quasi-vector mode of optical waveguide with arbitrary refractive index profile

Based on the Galerkin's method, a numerical method is developed to analysis the cutoff frequencies of guided modes of optical waveguides with arbitrary refractive index profile. Solutions are presented in the quasi-vector regime. Optical waveguide structures with single core of arbitrary shape are considered in this paper. The calculated results are compared favorably with exact vector solution and circular-harmonic expansion method.published_or_final_versio

Phase modulator defined by impurities induced disordering

Optical waveguide type phase modulators defined by impurities induced disordering (IID) are investigated. To achieve a better optical confinement, a two steps ion implantation process is carried out to introduce additional impurities with respect to depth in the cladding region. A more uniform refractive index profile in deeper lateral confined region is obtained after thermal annealing. The refractive index different between the core and cladding can be adjusted by controlling the extension of interdiffusion in the cladding. This provide tuning of single mode operating region. For present IID phase modulator with 25 period of 100 angstroms/100 angstroms Al0.3Ga0.7As/GaAs multiple quantum wells single mode operating at 0.88 μm, a normalized phase shift of 362°/Vmm, chirping parameter of 47, and absorption loss less than 120 cm-1 are achieved theoretically.published_or_final_versio

High-power single-mode operation in DFB and FP lasers using diffused quantum-well structure

Distributed feedback (DFB) and Fabry-Perot (FP) semiconductor lasers with step and periodic interdiffusion quantum-well structures are proposed for high-power single-longitudinal-mode operation. It is shown that the phase-adjustment region formed by the diffusion step (i.e., step change in optical gain and refractive index) counteracts the influence of spatial hole burning, especially for DFB lasers with large coupling-length products biased at high injection current. Furthermore, it is found that with careful design of the diffusion grating (i.e., grating period and amount of diffusion extent) of FP lasers, side-mode suppression ratio can be enhanced and threshold current density can be minimized to a satisfied level.published_or_final_versio

Vertical-cavity surface-emitting semiconductor lasers with diffusedquantum wells

A self-consistent dynamic model is developed including the current distribution, carrier diffusion rate and spatial hole burning effects to investigate the modulation response of vertical-cavity surface-emitting lasers with diffused quantum wells structure. It is found that the overall performance including relaxation oscillation frequency and modulation bandwidth is improved.published_or_final_versio

Impurity induced disordering produced lateral optical confinement in AlGaAs and InGaAs (on GaAs) quantum well waveguides

The impurity induced disordering technique is employed on an AlGaAs/GaAs quantum well optical waveguide to provide lateral optical confinement. The modal propagation constant and field profile are analysed using an improved Fourier decomposition method. The single mode operating region is given in terms of thickness of quantum well layers.published_or_final_versio

Fabry Perot semiconductor lasers with periodic diffused quantum wells structure

Fabry Perot semiconductor laser with periodic change in the extent of interdiffusion along the longitudinal direction of the quantum well active region is proposed to improve the discrimination between cavity modes.published_or_final_versio

Negative parental responses to coming out and family functioning in a sample of lesbian and gay young adults

Parental responses to youths' coming out (CO) are crucial to the subsequent adjustment of children and family. The present study investigated the negative parental reaction to the disclosure of same-sex attraction and the differences between maternal and paternal responses, as reported by their homosexual daughters and sons. Participants' perceptions of their parents' reactions (evaluated through the Perceived Parental Reactions Scale, PPRS), age at coming out, gender, parental political orientation, and religiosity involvement, the family functioning (assessed through the Family Adaptability and Cohesion Evaluation Scales, FACES IV), were assessed in 164 Italian gay and lesbian young adults. Pearson correlation coefficients were calculated to assess the relation between family functioning and parental reaction to CO. The paired sample t-test was used to compare mothers and fathers' scores on the PPRS. Hierarchical multiple regression was conducted to analyze the relevance of each variable. No differences were found between mothers and fathers in their reaction to the disclosure. The analysis showed that a negative reaction to coming out was predicted by parents' right-wing political conservatism, strong religious beliefs, and higher scores in the scales Rigid and Enmeshed. Findings confirm that a negative parental reaction is the result of poor family resources to face a stressful situation and a strong belief in traditional values. These results have important implications in both clinical and social fields

Linear, Deterministic, and Order-Invariant Initialization Methods for the K-Means Clustering Algorithm

Over the past five decades, k-means has become the clustering algorithm of choice in many application domains primarily due to its simplicity, time/space efficiency, and invariance to the ordering of the data points. Unfortunately, the algorithm's sensitivity to the initial selection of the cluster centers remains to be its most serious drawback. Numerous initialization methods have been proposed to address this drawback. Many of these methods, however, have time complexity superlinear in the number of data points, which makes them impractical for large data sets. On the other hand, linear methods are often random and/or sensitive to the ordering of the data points. These methods are generally unreliable in that the quality of their results is unpredictable. Therefore, it is common practice to perform multiple runs of such methods and take the output of the run that produces the best results. Such a practice, however, greatly increases the computational requirements of the otherwise highly efficient k-means algorithm. In this chapter, we investigate the empirical performance of six linear, deterministic (non-random), and order-invariant k-means initialization methods on a large and diverse collection of data sets from the UCI Machine Learning Repository. The results demonstrate that two relatively unknown hierarchical initialization methods due to Su and Dy outperform the remaining four methods with respect to two objective effectiveness criteria. In addition, a recent method due to Erisoglu et al. performs surprisingly poorly.Comment: 21 pages, 2 figures, 5 tables, Partitional Clustering Algorithms (Springer, 2014). arXiv admin note: substantial text overlap with arXiv:1304.7465, arXiv:1209.196

Structure and boosting activity of a starch-degrading lytic polysaccharide monooxygenase.

Lytic polysaccharide monooxygenases (LPMOs) are recently discovered enzymes that oxidatively deconstruct polysaccharides. LPMOs are fundamental in the effective utilization of these substrates by bacteria and fungi; moreover, the enzymes have significant industrial importance. We report here the activity, spectroscopy and three-dimensional structure of a starch-active LPMO, a representative of the new CAZy AA13 family. We demonstrate that these enzymes generate aldonic acid-terminated malto-oligosaccharides from retrograded starch and boost significantly the conversion of this recalcitrant substrate to maltose by β-amylase. The detailed structure of the enzyme's active site yields insights into the mechanism of action of this important class of enzymes.This work was supported by a grant from the European Research Agency—Industrial Biotechnology Initiative as financed by the national research councils: Biotechnology and Biological Sciences Research Council (grant number BB/L000423) and Agence Française de l'Environnement et de la Maîtrise de l'Energie (grant number 1201C102). The Danish Council for Strategic Research (grant numbers 12-134923 and 12-134922). The Danish Ministry of Higher Education and Science through the Instrument Center DANSCATT and the European Community’s Seventh Framework Programme (FP7/2007-2013) under BioStruct-X (grant agreement N°283570) funded travel to synchrotrons. P.H.W. acknowledges the experimental assistance of Rebecca Gregory and Dr Victor Chechik. L.L.L. acknowledges the experimental assistance of Dorthe Boelskifte and the ESRF and MAXLAB staff for assistance with data collection.This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/ncomms696