Measurement of the working parameters of an air-post vertical-cavity surface-emitting laser

We present a complete experimental evaluation of the effective parameters necessary to describe the dynamical behavior of an air-post vertical-cavity surface-emitting lasers, on the basis of theoretical equations which are also derived in this paper. The experimental investigation is composed of several steps, including power versus current measurement, noise spectrum analysis, linewidth evaluation. The complete set of parameters derived, in particular the linewidth-enhancement factor and the spontaneous emission factor, is particularly important for accurate comparisons of theoretical models on the laser dynamics with experiments.     

Soluble interleukin-2 receptor levels in lupus nephritis

Soluble interleukin-2 receptor (IL-2R) levels were measured and correlated prospectively with clinical, histologic and serologic findings over a 9-month period in 62 lupus patients. Initially, 39 patients had clinical nephritis and 23 patients did not have nephritis. The 62 lupus patients has significantly higher IL-2R than 15 normal controls, most of this difference attributable to patients with nephritis. During lupus nephritis flare 9 of 10 patients showed significant elevations of IL-2R while only 6 of the 10 patients showed either elevation of anti-DNA antibody or decrease in CH50. During disease remission or stable clinical activity changes in IL-2R levels paralleled changes in anti-DNA antibody and CH50. Nephritis patients with cellular proliferative histology had significantly higher IL-2R levels than those with membranous or mesangial nephropathy. IL-2R correlated strongly with histologic activity and chronicity indices, IgG and C3 deposition whereas anti-DNA antibody and CH50 levels did not. IL-2R levels did not correlate with serum creatinine suggesting that elevations of IL-2R were not simply due to decreased clearance. These observations suggest that serum IL-2R level is a useful marker of disease activity in lupus nephritis and may serve as a helpful adjunct in management of this disorder.     

Attentional mechanisms driven adaptive quantization and selective bit allocation scheme for H.264/AVC

Rate control algorithm adopted in H.264/AVC reference software shows several shortcomings that have been highlighted by different studies. For instance, in the baseline profile, the frame target bit-rate estimation assumes similar characteristics for all frames and the quantization parameter determination uses the Mean Absolute Difference for complexity estimation. Consequently, an inefficient bit allocation is performed leading to important quality variation of decoded sequences. A saliency-based rate-control is proposed in this paper to achieve bit-rate saving and improve perceived quality. The saliency map of each frame, simulating the human visual attention by a bottom-up approach, is used at the frame level to adjust the quantization parameter and at the macroblock level to guide the bit allocation process. Simulation results show that the proposed attentional model is well correlated to human behavior. When compared to JM15.0 reference software, at the frame level, the saliency map exploitation achieves bit-rate savings of up to 26%. At the MB level and under the same quality constraint, bit-rate improvement is up to 42% and buffer level variation is reduced by up to 71%.     

Growth and morphological transformations of Helicobacter pylori in broth media

Helicobacter pylori, a cause of peptic ulcer disease and certain types of gastric cancers, has usually been cultured on diverse agar-based media, resulting in a requirement for 2 to 4 days of growth at 37 degrees C. We have developed a novel broth medium consisting of a base medium supplemented with 2% newborn calf serum, Mg2+, Cu2+, Fe2+, Zn2+, Mn2+, and 1 mg of lysed human erythrocytes per ml. This medium supports rapid growth of H. pylori, with a doubling time of about 50 min. Optimal growth was obtained in a pH range higher than that supporting most other gram-negative bacteria (at pH 8.5). H. pylori cultured in this supplemented broth retains the spiral morphology seen in both histological sections and cultures from agar-based media and also retains a high urease activity. After 18 h in this broth, H. pylori transforms to a coccal form with a complete loss of urease activity. Previously these cocci have been reported to be senescent, since they could not be subcultured on agar medium. Our experiments suggest that some of the cocci can revert back to the spiral morphology with full recovery of urease activity when subcultured in fresh microaerobic broth medium.     

Single-mode operation and transverse-mode control in VCSELs induced by frequency-selective feedback

An experimental study of a vertical-cavity surface-emitting laser with frequency-selective feedback is reported. We show that we can force the laser to emit in its fundamental transverse mode or in a higher order transverse mode and that we can also control the polarization emitted in the fundamental one. We obtain single fundamental-mode operation within a large range of injection current values (almost /spl ap/2.5 I/sub th/) and a maximum optical power of 2.7 mW. In this current range, the output is found to be stable.     

Clinically occult avascular necrosis of the hip in systemic lupus erythematosus

OBJECTIVE: To study the natural history of clinically occult avascular necrosis (AVN) of the hip in patients with systemic lupus erythematosus (SLE). METHODS: Sixty-six patients with SLE (without symptoms referable to the hip) receiving at least 5 mg/day prednisone for > or = 6 months were screened by magnetic resonance imaging (MRI) for AVN of the hip. A complete MRI evaluating class and percentage of femoral head involvement, AP and lateral radiographs of the hips, bone scan, and physical examination were performed for patients with positive MRI. Medical records were reviewed for serologic and clinical variables that might predict AVN. Repeat MRI were obtained at 3, 6, and 12 months to assess possible progression or resolution of the lesion. Patients with negative screening MRI underwent repeat screening after one year to assess the one year incidence rate. RESULTS: Eleven asymptomatic hips (8%) in 8 patients (12%) had MRI documented AVN. The percentage of femoral head involvement ranged from 1 to 46%. One lesion was MRI class B, the remaining lesions were class A. The radiographic stage of 10 hips was stage 1, the MRI class B hip was stage 2. Risk factors for clinically occult AVN included Afro-American origin, Raynaud's phenomenon, migraine headaches, and a maximal corticosteroid dose of at least 30 mg/day. After 12 months, 43 of 58 patients with an initially negative MRI underwent repeat screening examinations; no new lesions were observed. CONCLUSION: Clinically occult AVN of the hip is common in patients with SLE. The short term natural history of these lesions appears stable without spontaneous healing or clinical or radiographic progression. Risk factors for these asymptomatic lesions are similar to the risks for symptomatic AVN and surgical intervention appears not to be indicated in these patients.     

Optimization of the switch-on and switch-off transition in a commercial laser

The response of a Class B laser to a rapid change in one of its parameters is known to be accompanied by delay and ringing. It has been theoretically and numerically shown that the transition can be modified by using adequate functional shapes for the control parameter (e.g., the laser pump) in order to steer the laser from one point of operation to another. Here we experimentally show the implementation of these ideas in a commercial device: a semiconductor laser. We establish a procedure for optimizing a controlled switch-on and switch-off and obtain a clean, fast, and reliable square pulse, either in a single shot or in a repetitive sequence. The generality of this procedure promises a wide field of application for a variety of laser systems.     

Cavity solitons in a driven VCSEL above threshold

We experimentally demonstrate the existence and the control of cavity solitons in externally driven vertical-cavity semiconductor lasers above threshold. A model including material polarization dynamics is used to predict and confirm the experimental findings.     

Low-frequency fluctuations in vertical-cavity surface-emitting lasers with polarization selective feedback: experiment and theory

We present theory and measurements on a vertical-cavity surface-emitting laser (VCSEL) biased close to its solitary threshold and subject to polarization selective external optical feedback. The system shows low-frequency fluctuations (LFF) in the selected polarization mode (PM). Below solitary laser threshold, the orthogonal PM remains silent, while it only responds after a dropout event in the main mode above threshold. Our calculations show good agreement with the measurements and identify a type of synchronization between the low-frequency dynamics of the two PMs.