Waveguiding in vertical cavity quantum-well structure defined by ion implantation

A theoretical model is presented for investigating AlGaAs-GaAs quantum-well (QW) vertical cavity waveguides defined by impurity-induced disordering. This model is based on a two-dimensional (2-D) description of the implantation profile to produce quantum-well intermixing. The modal propagation constant, power, and field evolution along the nonuniform circular waveguide is analyzed in terms of the coupled-mode equation. The influence of varying the mask dimension and length of cavity on the fundamental mode operation is studied. In a long cavity, guided mode can be supported by using higher implantation energy, however, a larger mask diameter should be used to maintain strong guiding. Result shows that optical lateral confinement is accomplished, with more than 70% of the power gathered in the cavity. The fraction of power confined in the waveguide is shown to improve by 30% after annealing. In addition, waveguide loss is estimated to be less than 40 cm-1 which results in less than 1 dB for our structure.published_or_final_versio

A novel dead-time vector approach to analysis of DC link current inPWM inverter drives

An analysis on the DC link current of space-vector PWM AC drives using novel dead-time vector (DTV) concept has been presented. By employing the DTV, a bi-value function to quantify the polarities of three phase winding currents, inverter output voltages and DC link current at dead time state can be expressed in close vectored forms. Thus, the entire drive system is considered as a whole to investigate the characteristics of DC link current at both normal and dead time states during steady and transient operations, increasingly, a phenomenon of negative spikes on DC link current caused by dead time effect is newly observed and highlighted. This phenomenon can be accurately predicted and mathematically characterized by using the proposed DTV approach. Both computer simulation and experimental results have been used for verification.published_or_final_versio

Optimization of Textured-surface Light Emitting Diode

We present an analysis of the efficiency and radiation pattern of the textured-surface LED by tracing the light rays that emits from the active layer. Through simulation, we discover that the efficiency depends on the thickness of the textured layer and its separation distance from the active layer. By carefully choosing these two parameters, maximum efficiency an be achieved. The radiation pattern of a texture-surface LED is found to be different from the flat-surfaced LED in that the textured surface has a wider angular spread.published_or_final_versio

Designing an external efficieny of over 30% for light emittingdiode

In designing high intensity LED's, substantial increase in efficiency can be achieved with the use of a textured surface, which is characterized by its external quantum efficiency and radiation pattern. We have found that the randomness of the inclined facade surfaces contributes substantially to the enhanced efficiency substantially. Such efficiency is strongly dependent upon the textured surface layer's thickness and its distance to the active layer of the diode. To attain the maximum efficiency, an optimal range for these parameters is required.published_or_final_versio

Epidemiology of acute primary angle-closure glaucoma in the Hong Kong Chinese population: prospective study.

OBJECTIVES: To determine the incidence of acute primary angle-closure glaucoma in the Hong Kong Chinese population, and to identify risk factors for this condition. DESIGN: Prospective study. SETTING: University teaching hospital, Hong Kong. PARTICIPANTS: Patients with acute primary angle-closure glaucoma presenting between 1 March 1998 and 29 February 2000. MAIN OUTCOME MEASURES: Demographic data, presenting symptoms and signs, temporal details of the presentation, and precipitating factors. The crude regional incidence was calculated according to the Hong Kong population census of 1991 and the age-specific incidence was calculated. RESULTS: Seventy-two cases (72 eyes of 72 patients) of acute primary angle-closure glaucoma were recruited. The crude incidence was 10.4 per 100,000 per year in the population aged 30 years and older. Patients at higher risk of attacks were those aged 70 years or older (age-specific incidence, 58.7 per 100,000 per year) and females, who had a relative risk of 3.8 compared with males (95% confidence interval, 1.7-8.4). Only four (5.6%) patients had a positive family history of acute primary angle-closure glaucoma. Seventeen (23.6%) patients were noted to have an upper respiratory tract infection before the attack, and 25 (34.7%) patients had taken antitussive agents. There was a statistically significant inverse correlation between the monthly attack rate and the monthly rate of influenza (Spearman's rank correlation coefficient = -0.388; P=0.031). CONCLUSION: There is a high incidence of acute primary angle-closure glaucoma among Chinese residents of Hong Kong, with elderly females at highest risk. A significant proportion of patients reported upper respiratory tract infection or the use of antitussive medication prior to attacks.published_or_final_versio

A unified analysis of DC link current in space-vector PWM drives

A unified analysis of the DC link current in space-vector PWM drives, comprising induction motor, inverter and space-vector PWM scheme, is presented. The DC link current is investigated in a unified way, whether the inverter is operating at normal or dead-time switching modes. The key is to introduce a dead-time vector, which is mathematically similar to the well-known space voltage vector, to express the DC link current and inverter output voltages into a unified form. Moreover, the formation of positive and negative spikes on the DC link current is discussed. In particular, the occurrence of negative spikes is mathematically formulated. The proposed unified approach is verified by means of both computer simulation and experimental results. The occurrence of positive and negative spikes is also verified by using circuit-oriented and device-oriented computer simulations as well as experimental results.published_or_final_versio

Switching characteristics and efficiency improvement with auxiliaryresonant snubber based soft-switching inverters

The auxiliary resonant snubber inverter (RSI) has demonstrated superiority in reduction of switching losses and dv/dt. It was found that the overall inverter system efficiency might not be improved if the resonant current was not controlled in accordance with the load current. This paper proposes an improved control scheme to minimize the operation of auxiliary circuit for efficiency improvement. The principle of this control scheme is to vary the resonant current with variable timing control based on the load current magnitude and to disable the auxiliary circuit operation when diode freewheeling occurs after switching. To illustrate the operation of this control scheme, this paper compares the switching characteristics and inverter power loss of hard-switching inverter, RSI with fixed-timing and variable-timing control and RSI with the proposed control scheme. Experimental results fully agree with the analyses and prove that the proposed control scheme is suitable for RSI to achieve better operating conditions.published_or_final_versio

Influence of gaseous annealing environment on the properties of indium-tin-oxide thin films

The influence of postannealing in different gaseous environments on the optical properties of indiu-tin-oxide (ITO) thin films deposited on glass substrates using e-beam evaporation has been systematically investigated. It is found that the annealing conditions affect the optical and electrical properties of the films. Atomic force microscopy, x-ray diffraction, and x-ray photoemission spectroscopy (XPS) were employed to obtain information on the chemical state and crystallization of the films. These data suggest that the chemical states and surface morphology of the ITO film are strongly influenced by the gaseous environment during the annealing process. The XPS data indicate that the observed variations in the optical transmittance can be explained by oxygen incorporation into the film, decomposition of the indium oxide phases, as well as the removal of metallic In. © 2005 American Institute of Physics.published_or_final_versio

Patients' satisfaction and prevalence of complications on surgical extraction of third molar.

OBJECTIVES: To study patients' satisfaction and prevalence of complications in surgical extraction of impacted third molar by senior dentists and recently graduated dentists in a university dental clinic. METHOD: Patients who had impacted third molar extraction in a university dental clinic by two associate dentists who had 15 years of experience were evaluated in this study. Patients' age, sex, history of pericoronitis, tooth extracted, and radiographic assessment of the impacted tooth were recorded. Immediately after suture removal, the patients were invited to indicate their satisfaction on a Likert scale of 1-5. RESULTS: A total of 546 patients received extraction, and 251 patients were operated by associate dentists. Patient satisfaction was higher among those who had noncomplicated surgery (P=0.007), short treatment time (P<0.001), and had no postsurgical emergency appointments (P<0.001). The prevalence of seeking postsurgical emergency appointments was 9.2%. The reasons were severe pain (4.8%), swelling (2.6%), bleeding (2.4%), alveolar osteitis (0.9%), paresthesia (0.9), and trismus (0.5%). The prevalence of postsurgical complication(s) in associate dentists and senior dentists was 11.6% and 7.1%, respectively (P=0.050). The mean satisfaction scores for associate dentists and senior dentists were 4.17 and 3.95, respectively (P=0.002). CONCLUSION: Although a higher rate of postsurgical complications was observed among the patients treated by the recently graduated dentists, their patients' satisfaction scores were higher than that of the senior dentists. Around 9% of patients attended postsurgical emergency appointments, and their common reason was severe pain.published_or_final_versio

Learning Optimal Deep Projection of 18^{18}F-FDG PET Imaging for Early Differential Diagnosis of Parkinsonian Syndromes

Several diseases of parkinsonian syndromes present similar symptoms at early stage and no objective widely used diagnostic methods have been approved until now. Positron emission tomography (PET) with $^{18}$F-FDG was shown to be able to assess early neuronal dysfunction of synucleinopathies and tauopathies. Tensor factorization (TF) based approaches have been applied to identify characteristic metabolic patterns for differential diagnosis. However, these conventional dimension-reduction strategies assume linear or multi-linear relationships inside data, and are therefore insufficient to distinguish nonlinear metabolic differences between various parkinsonian syndromes. In this paper, we propose a Deep Projection Neural Network (DPNN) to identify characteristic metabolic pattern for early differential diagnosis of parkinsonian syndromes. We draw our inspiration from the existing TF methods. The network consists of a (i) compression part: which uses a deep network to learn optimal 2D projections of 3D scans, and a (ii) classification part: which maps the 2D projections to labels. The compression part can be pre-trained using surplus unlabelled datasets. Also, as the classification part operates on these 2D projections, it can be trained end-to-end effectively with limited labelled data, in contrast to 3D approaches. We show that DPNN is more effective in comparison to existing state-of-the-art and plausible baselines.Comment: 8 pages, 3 figures, conference, MICCAI DLMIA, 201