Comprehensive modeling of diffused quantum-well vertical-cavity surface-emitting lasers

A numerical model for investigating the thermal, electrical, and optical characteristics of vertical-cavity surface-emitting: lasers (VCSELs) with a diffused quantum-well (QW) structure is presented. In the model, the quasi-three-dimensional (quasi-3-D) distribution of temperature, voltage and optical fields as well as the quasi-two-dimensional (quasi-2-D) diffusion and recombination of carrier concentration inside the QW active layer are calculated in a self-consistent manner. In addition, the quasi-3-D distribution of implanted ions before and after thermal annealing are computed. The variation of electrical conductivity and absorption loss as well as the influence of impurity induced compositional disordering on the optical gain and refractive index of the QW active layer are also taken into consideration. Using this model, the steady-state characteristics of diffused QW VCSELs are studied theoretically. It is shown that significant improvement of stable single-mode operation can be obtained using diffused QW structure.published_or_final_versio

Effect of non-uniform distribution of electric field on diffusedquantum well lasers

The influence of non-uniform distribution of electric field on the steady state and dynamic behavior of diffused quantum well lasers is studied by a self-consistent model. The energy band structure of the quantum well can be distorted significantly by the non-uniform distribution of electric field, especially for devices with diffused quantum well structure. Hence, the evaluation on the optical gain as well as the modulation responses of diffused quantum well lasers using flat band approximation can be deviated significantly with nonuniform distribution of electric field taken into consideration.published_or_final_versio

Active anti-guide vertical cavity surface emitting lasers with diffused quantam wells structure

The enhancement of single transverse mode operation in vertical cavity surface emitting lasers by using interdiffused quantum wells is proposed and analyzed. It is observed that the influence of self-focusing (arising from carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized by introducing a step diffused quantum wells structure inside the core region of quantum-well active layer. Stable single-mode operation in vertical cavity surface emitting lasers can also be maintained.published_or_final_versio

Analyzing ranking data using decision tree

Ranking/preference data arises from many applications in marketing, psychology and politics. We establish a new decision tree model for the analysis of ranking data by adopting the concept of classification and regression tree [2]. We modify the existing splitting criteria, Gini and entropy, which can precisely measure the impurity of a set of ranking data. Two types of impurity measures for ranking data are introduced, namely n-wise and top-k measures. Minimal cost-complexity pruning is used to find the optimum-sized tree. In model assessment, the area under the ROC curve (AUC) is applied to evaluate the tree performance. The proposed methodology is implemented to analyze a partial ranking dataset of Inglehart's items collected in the 1993 International Social Science Programme survey. Change in importance of item values with country, age and level of education are identified.postprintThe European Conference on Machine Learning and Principles and Practice of Knowledge Discovery in Databases (ECML PKDD 2008), Antwerp, Belgium, 15-19 September 2008. In Proceedings of ECML PKDD 2008, p. 139-15

Quantitative Chevalley-Weil theorem for curves

The classical Chevalley-Weil theorem asserts that for an \'etale covering of projective varieties over a number field K, the discriminant of the field of definition of the fiber over a K-rational point is uniformly bounded. We obtain a fully explicit version of this theorem in dimension 1.Comment: version 4: minor inaccuracies in Lemma 3.4 and Proposition 5.2 correcte

On the voltage dependence of sensitivity for Schottky-type gas sensor

published_or_final_versio

Evidence of the influence of phonon density on Tm³⁺ upconversion luminescence in tellurite and germanate glasses

Author name used in this publication: C. L. MakAuthor name used in this publication: W. L. TsuiAuthor name used in this publication: K. H. Wong2001-2002 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Quantifying Robotic Swarm Coverage

In the field of swarm robotics, the design and implementation of spatial density control laws has received much attention, with less emphasis being placed on performance evaluation. This work fills that gap by introducing an error metric that provides a quantitative measure of coverage for use with any control scheme. The proposed error metric is continuously sensitive to changes in the swarm distribution, unlike commonly used discretization methods. We analyze the theoretical and computational properties of the error metric and propose two benchmarks to which error metric values can be compared. The first uses the realizable extrema of the error metric to compute the relative error of an observed swarm distribution. We also show that the error metric extrema can be used to help choose the swarm size and effective radius of each robot required to achieve a desired level of coverage. The second benchmark compares the observed distribution of error metric values to the probability density function of the error metric when robot positions are randomly sampled from the target distribution. We demonstrate the utility of this benchmark in assessing the performance of stochastic control algorithms. We prove that the error metric obeys a central limit theorem, develop a streamlined method for performing computations, and place the standard statistical tests used here on a firm theoretical footing. We provide rigorous theoretical development, computational methodologies, numerical examples, and MATLAB code for both benchmarks.Comment: To appear in Springer series Lecture Notes in Electrical Engineering (LNEE). This book contribution is an extension of our ICINCO 2018 conference paper arXiv:1806.02488. 27 pages, 8 figures, 2 table

MiR-637 maintains the balance between adipocytes and osteoblasts by directly targeting Osterix

Bone development is dynamically regulated by homeostasis, in which a balance between adipocytes and osteoblasts is maintained. Disruption of this differentiation balance leads to various bone-related metabolic diseases, including osteoporosis. In the present study, a primate-specific microRNA (miR-637) was found to be involved in the differentiation of human mesenchymal stem cells (hMSCs). Our preliminary data indicated that miR-637 suppressed the growth of hMSCs and induced S-phase arrest. Expression of miR-637 was increased during adipocyte differentiation (AD), whereas it was decreased during osteoblast differentiation (OS), which suggests miR-637 could act as a mediator of adipoosteogenic differentiation. Osterix (Osx), a significant transcription factor of osteoblasts, was shown to be a direct target of miR-637, which significantly enhanced AD and suppressed OS in hMSCs through direct suppression of Osx expression. Furthermore, miR-637 also significantly enhanced de novo adipogenesis in nude mice. In conclusion, our data indicated that the expression of miR-637 was indispensable for maintaining the balance of adipocytes and osteoblasts. Disruption of miR-637 expression patterns leads to irreversible damage to the balance of differentiation in bone marrow. © 2011 Zhang et al.published_or_final_versio

Fine Structure of the Sensilla and Immunolocalisation of Odorant Binding Proteins in the Cerci of the Migratory Locust, Locusta migratoria

Using light and electron microscopy (both scanning and transmission), we observed the presence of sensilla chaetica and hairs on the cerci of the migratory locust, Locusta migratoria L. (Orthoptera: Acrididae). Based on their fine structures, three types of sensilla chaetica were identified: long, medium, and short. Males presented significantly more numbers of medium and short sensilla chaetica than females (p<0.05). The other hairs can also be distinguished as long and short. Sensilla chaetica were mainly located on the distal parts of the cerci, while hairs were mostly found on the proximal parts. Several dendritic branches, enveloped by a dendritic sheath, are present in the lymph cavity of the sensilla chaetica. Long, medium, and short sensilla chaetica contain five, four and three dendrites, respectively. In contrast, no dendritic structure was observed in the cavity of the hairs. By immunocytochemistry experiments only odorant-binding protein 2 from L. migratoria (LmigOBP2) and chemosensory protein class I from the desert locust, Schistocerca gregaria Forsskål (SgreCSPI) strongly stained the outer lymph of sensilla chaetica of the cerci. The other two types of hairs were never labeled. The results indicate that the cerci might be involved in contact chemoreception processes