Regular and anomalous-type conversion of p-CdTe during Cd-rich annealing

The kinetics of the p-to-n conversion and effect of the anomalous n-to-p reconversion of p-CdTe during annealing at 400–700°C under Cd-rich overpressure have been investigated. The p-to-n conversion is related to diffusion of Cd interstitials together with gettering of foreign fast diffusing acceptors to the center of the sample. The propagation of the n-type layer during annealing at 500°C was found to be significantly slower then the standard square-root dependence on annealing time. The anomalous n-to-p reconversion of the converted n-type sample was observed after sufficient long time annealing at 600°C.     

Amphiphilic networks. XIV

Summary The synthesis and characterization of novel amphiphilic networks based on dimethylacrylamide and crosslinked by methacrylate telechelic three-arm star polyisobutylene (?(PIB-MA)₃) are reported. The networks are characterized by two M _c's and possess “homogeneous” and “heterogeneous” crosslinks. The networks swell both in water and n-heptane which indicates a cocontinuous hydrophobic-hydrophilic microarchitecture. Water-swollen networks exhibit higher tensile strengths and elongations, than those made previously with linear MA-PIB-MA's of similar overall compositions (i.e., ∼1.0 versus ∼0.5 Mpa, and ∼300% versus ∼200%, respectively). The enhanced mechanical properties of the new networks are being exploited in biomedical applications. Received: 28 July 1999/Revised version: 25 October 1999/Accepted: 27 October 1999     

Effect of trace additives on the efficiencyof peroxydisulfate regeneration

Direct chemical oxidation (DCO) is an emerging technology in which the organic components of hazardous or mixed waste streams are mineralized to carbon dioxide by the nearly omnivorous oxidant peroxydisulfate. Following treatment, the expended oxidant may be electrochemically regenerated to lower costs and minimize secondary waste; however, due to the varied contents of potential waste streams, trace chemical species may slowly accumulate in the system. To verify that the electrochemical recycling step was not adversely affected, the effect that several species have on the efficiency of this peroxydisulfate regeneration step has been measured. The organic additives formaldehyde, formic acid, and oxalic acid were tested, as well as the inorganic ions phosphate, nitrate, fluoride, chloride and thiocyanate. Changes in the peroxydisulfate formation potential in the presence of these additives were measured using chronopotentiometry, with current densities from 0.5 to 2.0 Acm–2, and additive concentrations of 0.1mm to 0.1m. Also, a real-time technique using a rotating disc electrode was developed to measure these additives' effect on the formation kinetics of peroxydisulfate. In addition, the effect that various additives had on the rate of electrochemical peroxydisulfate generation was measured in a large-scale electrolysis cell. None of the additives caused a significant reduction in the potential or the efficiency of the peroxydisulfate generation step, although the presence of formic acid appeared to increase the efficiency. In addition, the presence of thiocyanate completely blocks the reduction of peroxydisulfate on platinum. This information is currently being applied in scale-up testing of this technology for use in treating hazardous waste or the organic components of mixed waste.     

Retinoprotective Effects of PACAP Eye Drops in Microbead-Induced Glaucoma Model in Rats

Glaucoma is associated with increased intraocular pressure (IOP), causing the apoptosis of retinal ganglion cells (RGCs) and the loss of their axons leading to blindness. Pituitary adenylate cyclase activating polypeptide (PACAP) is neuroprotective in several neural injuries, including retinopathies. The aim of this study was to investigate the effects of PACAP1-38 eye drops in a model of glaucoma. IOP was elevated bilaterally by injections of microbeads to block the aqueous humor outflow. The control groups received the same volume of saline. Animals were treated with PACAP1-38 (1 µg/drop, 3 × 1 drop/day) or vehicle for 4 weeks starting one day after the injections. Retinal morphology by histology and optical coherence tomography, function by electroretinography, and IOP changes were analyzed. Animals were sacrificed 8 weeks after the injections. Microbeads injections induced a significant increase in the IOP, while PACAP1-38 treatment lowered it to normal levels (~10 mmHg). Significant retinal degeneration and functional impairment were observed in the microbead-injected group without PACAP1-38 treatment. In the microbeads + PACAP1-38 group, the retinal morphology and functionality were close to the normal values. In summary, our results show that PACAP1-38, given in form of eye drops, is neuroprotective in glaucoma, providing the basis for potential future therapeutic administration.     

Complementary optical and electron microanalysis of high-temperature superconductors

Scanning electron microscopy coupled to quantitative energy-dispersive x-ray spectroscopy provides an excellent tool for determining the compositions of various cuprate superconducting phases in the course of processing from insulator to superconductor. When coupled with a new room temperature optical microscopy technique for the identification of individual superconducting grains, it provides a complete picture of the processed state of the material. The techniques are complementary. Two different materials were examined with both optical and electron microscopy: (1) a Tl-Sr-Ca-Cu-O system superconducting material doped with Hg and (2) a metallic, but not superconducting La-Sr-Cu-O system material. The results and the complementary nature of optical and electron microscopy in assessing the stoichiometry and homogeneity of these materials are described.