Self-aligned chemically assisted ion-beam-etched GaAs/(Al,Ga)Asturning mirrors for photonic applications

It is shown that totally reflecting turning mirrors can be fabricated in GaAs/(Al,Ga)As graded-index separate-confinement-heterostructure single-quantum-well (GRIN-SCH SQW) material using Ti metal masking and Cl₂ chemically assisted ion-beam-etching (CAIBE). Combined with ridge waveguides, these techniques have been used to make turning-mirror cleaved-facet lasers that have acceptable external slope efficiencies with a modest estimated increase in threshold current. Scanning electron microscope examination of the mirrors indicates some residual roughness attributed to the edge definition of the deposited titanium film. The mirror loss is estimated to be 68% for these particular turning mirrors. These components, which continue to be developed and improved, are being applied to increasingly sophisticated and demanding photonic programs     

Analytical performance of the Tandem-R free PSA immunoassay measuring free prostate-specific antigen

The analytical performance of the Tandem-R free PSA assay available from Hybritech Inc. was evaluated. Comparison of recoveries of purified free (unbound) prostate-specific antigen (PSA) diluted in female serum in the Tandem-R free PSA assay and the Tandem-R (total) PSA assay demonstrated a link in calibration between the assays and an accurate determination of percent free PSA. The cross-reactivity of the assay to purified PSA-alpha 1-antichymotrypsin was determined to be < 1%. The minimum-detectable concentration was < 0.05 microgram/L. The within-run and between-day CVs were < or = 5% for samples with > 0.3 microgram/L free PSA. Dilution and recovery showed no significant deviations from linearity across the assay range. The assay was insensitive to interference from blood components. The Tandem-R free PSA kit was shown to be an accurate, precise, and reliable assay for the measurement of free PSA.     

A method for quantization scale factor selection in MPEG2 videosequence encoding using a bilayer fuzzy expert system

This paper presents a method for intelligent selection of the quantization scale factor used for varying bit rate and quality in the MPEG2 video encoding standard. The goal is to select the quantization scale factor, above which noticeable quality degradation occurs. This method uses a bilayer fuzzy logic system to aggregate measurements taken on the block level. The rulebases are designed around the characteristics of the human visual system (HVS). A qualitatively sensitive quantization scale factor can be chosen by taking advantage of the HVS characteristics     

Two types of intraoral distribution of fluorotic enamel

Assessment of body composition remains a goal for the routine assessment of nutritional status of patients on long-term dialysis. Methods generally available for estimation of body fat in healthy individuals are limited by practicality and availability for use in this patient population. Anthropometry, which is cost effective and easy to perform, is limited by the lack of appropriate reference standards for patients on dialysis and artifact caused by hydration status. Bioelectrical impedance affords new opportunities for non-invasive assessment of fluid volume, its distribution, and body cell mass; estimation of fat-free mass and body fat can be affected by hydration status. Dual x-ray absorptiometry permits estimation of bone status and fat mass because changes in hydration status are reflected in estimates of fat-free mass. Evaluation of validity of techniques for fluid status and body composition assessment requires the use of appropriate reference methods and proper statistical procedures to examine error, not only between groups, but by individual. Use of body composition assessment methods together with biochemical measurements will enhance the nutritional assessment of end-stage renal disease patients on long-term hemodialysis.     

Relationships between gastric emptying, intragastric meal distribution and blood glucose concentrations in diabetes mellitus

The aim of this study was to evaluate the prevalence of disordered intragastric meal distribution and the relationships between gastric emptying, intragastric distribution, glycemic control and gastrointestinal symptoms in diabetes mellitus. METHODS: Eighty-six patients with diabetes mellitus had measurements of gastric emptying and intragastric distribution of a radioisotopically labeled solid/liquid meal (100 g beef and 150 ml 10% dextrose), glycemic control (plasma glucose concentrations), upper gastrointestinal symptoms (questionnaire) and autonomic nerve function (cardiovascular reflexes). Results were compared to those obtained in 20 normal volunteers. RESULTS: Solid and liquid gastric emptying were delayed in the diabetic patients and correlated weakly. Intragastric meal distribution was also often abnormal, with increased retention of both solid and liquid in the proximal stomach and increased retention of solid but not liquid in the distal stomach. In all patients with increased retention of solid in the proximal stomach, emptying from the total stomach was delayed. Gastric emptying of liquid was slower in those subjects who had a mean plasma glucose > 15 mmol/liter during the gastric emptying measurement, when compared to the remainder of the group. CONCLUSION: In patients with diabetes mellitus, there is poor relationship between solid and liquid gastric emptying and intragastric meal distribution is frequently abnormal. Interpretation of the results of gastric emptying measurements should consider meal composition and plasma glucose concentrations.     

Osteocalcin and osteonectin immunoreactivity in the diagnosis of osteosarcoma

Osteosarcomas (OSAs) can be difficult to distinguish histologically from tumors with significantly different biologic potentials and treatment protocols. The correct diagnosis of OSA relies on identification of malignant osteoblasts that are capable of producing neoplastic bone. To determine the use of immunohistochemistry for the diagnosis of OSA, 106 tumors from the Massachusetts General Hospital and the University of Vermont were immunostained with monoclonal antiosteocalcin (OC) and antiosteonectin (ON) antibodies. They included 42 OSAs, 25 non-bone-forming sarcomas, 24 other malignant tumors including lymphomas, carcinomas, and melanomas, and 15 benign bone tumors. Cytoplasmic staining with OC showed 70% sensitivity and 100% specificity, while staining with ON showed 90% sensitivity and 54% specificity for bone-forming tumors, consistently staining cell types other than osteoblasts. Of the OSAs, 83% demonstrated matrix staining with one or both antibodies, whereas dense collagen was negative for both antibodies in all tumors. We conclude that tumor cell cytoplasmic staining with monoclonal OC may be helpful in distinguishing OSAs from other malignancies, and staining of extracellular matrix for OC and ON antibodies concurrently may help distinguish bone matrix from dense collagen.     

The effect of alterations to action potential duration on beta-adrenoceptor-mediated aftercontractions in human and guinea-pig ventricular myocytes

Aftercontractions induced by beta-adrenoceptor stimulation in human and guinea-pig cardiomyocytes may be related to changes in action potential duration (APD). We investigated the effects of altering APD during the occurrence of isoproterenol-induced aftercontractions, using the KATP channel openers cromakalim and lemakalim or the action potential voltage clamp technique, in guinea-pig and human ventricular cardiomyocytes. Contractile responses were measured at 32 degrees C using a video-based edge-detection system. In guinea-pig myocytes, action potentials, Indo-1 fluorescence and contraction were measured at 22 degrees C. Isoproterenol (< or = 12 nM) had variable effects on APD but induced aftercontractions, the majority (14/19 cells) of which occurred during the action potential. Short action potentials were produced using K+ channel openers. These compounds reduced or completely abolished the isoproterenol-induced aftercontractions. Increasing isoproterenol in the presence of K+ channel opener restored the main contraction to a level similar to or above those with isoproterenol alone, but without the reappearance of aftercontractions. When cells were stimulated to contract under action potential voltage clamp, isoproterenol-induced aftercontractions were abolished by voltage clamping with action potentials of short duration. It was possible to induce aftercontractions in some cells without application of isoproterenol if voltage clamp-imposed action potentials of very long duration were used. These aftercontractions were also abolished by shortening action potential duration. We conclude that K+ channel openers or the imposition of action potentials of short duration can dissociate positively inotropic beta-adrenoceptor stimulation from aftercontraction formation and that action potentials of long duration can be pro-arrhythmic.