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

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

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

Improvement of surface ECG recording in adult zebrafish reveals that the value of this model exceeds our expectation

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Attenuation of proinflammatory responses by S -[6]-Gingerol via inhibition of ROS/NF-Kappa B/COX2 activation in HuH7 cells

Introduction. Hepatic inflammation underlies the pathogenesis of chronic diseases such as insulin resistance and type 2 diabetes mellitus. S-[6]-Gingerol has been shown to have anti-inflammatory properties. Important inflammatory mediators of interleukins include nuclear factor B (NFB) and cyclooxygenase 2 (COX2). We now explore the mechanism of anti-inflammatory effects of S-[6]-gingerol in liver cells. Methods. HuH7 cells were stimulated with IL1β to establish an in vitro hepatic inflammatory model. Results. S-[6]-Gingerol attenuated IL1β-induced inflammation and oxidative stress in HuH7 cells, as evidenced by decreasing mRNA levels of inflammatory factor IL6, IL8, and SAA1, suppression of ROS generation, and increasing mRNA levels of DHCR24. In addition, S-[6]-gingerol reduced IL1β-induced COX2 upregulation as well as NFB activity. Similar to the protective effects of S-[6]-gingerol, both NS-398 (a selective COX2 inhibitor) and PDTC (a selective NFB inhibitor) suppressed mRNA levels of IL6, IL8, and SAA1. Importantly, PDTC attenuated IL1β-induced overexpression of COX2. Of particular note, the protective effect of S-[6]-gingerol against the IL1β-induced inflammatory response was similar to that of BHT, an ROS scavenger. Conclusions. The findings of this study demonstrate that S-[6]-gingerol protects HuH7 cells against IL1β-induced inflammatory insults through inhibition of the ROS/NFB/COX2 pathway. © 2013 Xiao-Hong Li et al

Acceptors in undoped gallium antimonide

Undoped GaSb materials were studied by temperature dependent Hall (TDH) measurements and photoluminescence (PL). The TDH data reveals four acceptor levels (having ionization energies of 7meV, 32meV, 89meV and 123meV) in the as-grown undoped GaSb samples. The 32meV and the 89meV levels were attributed to the GaSb defect and the VGa-related defect. The Ga Sb defect was found to be the important acceptor responsible for the p-type nature of the present undoped GaSb samples because of its abundance and its low ionization energy. This defect was thermally stable after the 500°C annealing. Similar to the non-irradiated samples, the 777meV and the 800meV PL signals were also observed in the electron irradiated undoped GaSb samples. The decrease of the two peaks' intensities with respect to the electron irradiation dosage reveals the introduction of a non-radiative defect during the electron irradiation process, which competes with the transition responsible for the 777meV and the 800meV PL peaks.published_or_final_versio

Autosomal recessive disease in children of consanguineous parents: inferences from the proportion of compound heterozygotes

This short communication deals with the questions of how to calculate the expected proportion of compound heterozygous patients among affected offspring of consanguineous parents, and how, from an observed proportion of compound heterozygotes, to calculate both the proportion of homozygotes not identical by descent and the frequency of pathogenic alleles in the population. This estimate of allele frequency may be useful when dealing with populations with a considerable number of consanguineous matings