Non-Equilibium Al-Ga interdiffusion in MOCVD reactor annealed AIGaAs quantum well heterostructures

AlGaAs-GaAs quantum well heterostructures have been annealed in an atmospheric pressure MOCVD reactor under an AsH₃/H₂ ambient. Photoluminescence spectra show a uniform and reproducible increase in the effective quantum well band-gap. Energy shift data indicate that Al-Ga interdiffusion occurs under “non-equilibrium” conditions resulting in depth-dependent Al-Ga interdiffusion such that quantum wells close to the surface disorder less than those further away. Activation energies vary from approximately 5.1–5.2 eV for the “equilibrium” case to 3.2–3.6 eV for the “non-equilibrium” case. These results suggest that caution must be exercised in using reported activation energies to characterize Al-Ga interdiffusion for photonic device fabrication. IBM Graduate Fellow Howard Hughes Doctoral Fellow     

Hapten-tagged plasma proteins as immunocytochemical probes for the study of vascular permeability.

Bovine serum albumin and transferrin were covalently coupled with fluorescein isothiocyanate and digoxigenin, respectively, and intravenously co-injected in equal amounts in mouse. The derivation of the two proteins induces minor alterations of their physicochemical properties as well as of their physiological functions. The two tracers were revealed within vascular and extravascular compartments of diaphragm by quantitative postembedding immunocytochemistry, using antibodies against each of the haptens in conjunction with the protein AG-gold complexes. The influence of different fixatives and embedding protocols on the immunodetectability of the hapten-tagged proteins was assessed. Both resist reasonably well to osmication and embedding in Epon. None of the haptens reacted with the heterologous antibody. At 30 minutes after injection, the tracers were detected in blood plasma, interstitium, and endothelial plasmalemmal vesicles. The presence of both proteins within the interendothelial clefts was inconspicuous. The ratios between the labeling densities found over endothelium, interstitial space, and vascular lumen were similar for both tracers. This suggests that the endothelium of mouse diaphragm capillaries might exhibit comparable permeabilities towards serum albumin and transferrin which are similar in size and charge. The study shows that hapten-tagged polypeptides are close to the corresponding native macromolecules, and represent interesting tools for the morphological study of dynamic processes such as transcytosis.     

Optical properties of strained layer (111)B Al0.15Ga0.85As-In0.04Ga0.96as quantum well heterostructures

Data presented here demonstrate that strained-layer (111)B Al_0.15Ga_0.85As-In_0.04Ga_0.96As quantum wells exhibit unique optical properties when compared to otherwise identical (100) oriented strained layers. Photoluminescence measurements identify a strain-induced electric field of order 6.7 Vμm^-1 within the (111)B quantum well that is not present for the (100) case. Photoluminescence excitation spectroscopy measurements show that the heavy-hole to light-hole energy band splitting is approximately 7 meV larger for the (111)B structure than for the (100) structure. Howard Hughes Doctoral Fellow IBM Graduate Fellow     

Detection of astroviruses in feces of a cat with diarrhea. Brief report

Astroviruses were detected by electron microscopy in the feces from a 4 month old kitten with diarrhea. The mean diameter of the viral particles was 28.7 nm, and they showed characteristic five- or six-pointed star-shaped surface configurations. The clinical disease manifested by the cat and the observed morphology of the viral particles are consistent with previous reports on astroviruses of other species.     

Lipid abnormalities in pancreatic tissue of streptozotocin-induced diabetic rats

Pancreatic lipid and fatty acid composition was determined in streptozotocin-induced diabetic rats and compared to control and insulin-treated diabetic rats. A pronounced decrease of total fatty acids was recorded and mainly accounted for by a drop of fatty acids in glycerides. Cholesterol, on the other hand, was significantly increased two- to three-fold, leading to an elevated cholesterol/phospholipid ratio. Morpho-cytochemical studies confirmed these findings because the multiple lipid droplets present in acinar cells of diabetic animals were found to be of cholesterol nature. The major alterations in phospholipid-fatty acid composition were characterized by an increase of linoleate coupled to a decrease of monounsaturates and arachidonate, suggesting defective metabolism of saturates and of linoleate. This was further supported by fatty acid ratios that suggested low Δ5 and Δ9 desaturation. Daily administration of insulin for 10 days restored and overcorrected the various lipid alterations. This study suggests that there are alterations in lipid composition and metabolism in the exocrine pancreas of chronic streptozotocin-induced diabetic rats. Their possible role in the mechanism regulating pancreatic function and secretion remains to be elucidated.     

Long-term neurodevelopmental outcome after intrauterine transfusion for the treatment of fetal hemolytic disease

OBJECTIVE: The aim of the study was to assess the developmental outcome of neonatal survivors of hemolytic disease of the neonate treated with modern intrauterine transfusion techniques. STUDY DESIGN: In this prospective, observational study, auditory evoked-response tests were performed in the nursery. Neurodevelopmental evaluation with the Gesell Developmental Schedules was performed between 9 and 18 months of corrected age to assess motor skills, language development, comprehension capacity, and social skills. The McCarthy Scales of Children's Abilities were administered between 36 and 62 months. RESULTS: Forty children who survived severe fetal hemolytic disease were followed up until 62 months old. Demographic data included gestational age at first intrauterine transfusion (26.4 +/- 3.7 weeks), median number of intrauterine transfusions (4, range 1-8), lowest fetal hematocrit (20.2% +/- 7.8%), peak fetal bilirubin (7.1 +/- 2.1 mg/dL), incidence of hydrops fetalis (45%), and mean gestational age at delivery (35.6 +/- 2.2 weeks). One case of severe bilateral deafness and 1 case of right spastic hemiplegia were diagnosed. The Gesell Developmental Schedules score was assessed between 9 and 18 months of corrected age in 22 infants. The global developmental quotient was 101.9 +/- 9.5 (mean for normal population is 100). Regression analysis revealed no correlation between the global developmental quotient and gestational age at the first intrauterine transfusion, gestational age at birth, or the severity of the fetal hemolytic disease (fetal hematocrit, fetal bilirubin, presence of hydrops fetalis, total number of intrauterine transfusions, duration of neonatal phototherapy, and number of neonatal exchange transfusions). Eleven of the 40 children were followed up until they were 62 months old, and the McCarthy Scales of Children's Abilities were administered. The mean cognitive index was 107.6 +/- 9.4 (90-109 is considered average). CONCLUSION: Despite severe fetal hemolytic disease, normal developmental outcome can be expected for children treated with intrauterine transfusions.     

Introduction of the protein G—gold complex for high-resolution immunocytochemistry

Protein G, an immunoglobulin G-binding molecule, was tagged with colloidal gold particles and was applied in immunocytochemistry. The present study reports the conditions required for the preparation of the protein G–gold complex and for its application in electron microscopy. Once used in combination with specific primary antibodies, the protein G–gold complex was able to yield highly specific labelings over particular tissue compartments. Various control experiments confirmed the specificity of the labelings obtained. Since the IgG-binding properties of protein G are superior to those displayed by protein A, the protein G–gold appears a far better tool for high-resolution immunocytochemistry.