Aging of as-prepared gels based on tetraethoxysilane in the presence of boric acid

The influence of additions of boric acid on the aging of as-prepared gels from water-alcohol solutions of tetraethoxysilane has been investigated by the kinetic spectrophotometric method using the reaction between silica and ammonium molybdate with the formation of a colored β-silicomolybdate heteropolyanion as the reaction product. The distribution of silica over different molecular species at different instants of time after the gel formation point has been determined within the framework of the kinetic model.     

Kinetics of the early stages of the sol-gel process: III. Evolution of silica associates

A kinetic scheme is proposed for the processes of hydrolysis of alkoxysilanes and polycondensation of the hydrolysis products represented as monomers, dimers, trimers, oligomers, and polymers. A kinetic model that makes it possible to evaluate the weight fractions of silica associates at different instants of time after the beginning of the hydrolysis and to determine the kinetic characteristics of these processes is constructed. The evolution of silica associates at different pH values and dilutions at the early stages of the hydrolytic polycondensation of silicon alkoxides is analyzed. It is noted that the structuring of silica in the case of tetraethoxysilane differs from the structuring for tetramethoxysilane.     

Thin film deposition for permeability increase of gas being implanted (theoretical consideration)

A theoretical model has been developed for diffusive permeation of gas injected by ion bombardment through thin metallic targets, including membranes with thin films deposited onto the surface. The film material differs from the substrate material. Calculations for gas atom distribution in the film and substrate have been carried out, as well as gas fluxes to the source and sink sides in such a system in a quasi-stationary régime. The possibility of a permeability increase is revealed under implantation of gas ions both with low (～ keV) and higher energies (of the order of tens of keV) by deposition onto an irradiated target surface having a film of material with a lower diffusion coefficient for the gas being implanted than the substrate material itself. It has been shown that the most significant effect may be obtained under relatively high energy implantation for deposited film thicknesses markedly less than the mean ion range, and where the film permeability (diffusion coefficient and/or gas solubility) is much smaller than that of the substrate material itself. Periodic or simultaneous with implantation film renewal on the target surface has been suggested to compensate for sputtering.     

Influence of monoatomic alcohols on hydrolysis and condensation of tetraethoxysilane

The influence of some monoatomic alcohols (ethanol, isopropanol, and butanol) on the kinetics of hydrolysis and condensation of water-alcohol solutions of tetraethoxysilane at the early stages of the process has been investigated using a technique developed by the authors, which is based on the investigation of the kinetics of interaction of various silica associates with ammonium molybdate.     

An ethnographic, controlled study of the use of a computer-based histology atlas during a laboratory course

Data regarding future residential plans were collected from 141 mothers of adult children with mental retardation. Results demonstrate that greater caregiving burden was associated with more extensive planning for residence within the formal service system and less planning for residence with a family member. More frequent service use also predicted greater planning for future residence within the formal system. Planning for residence with a family member and higher functional ability on the part of the child significantly decreased the sense of worry mothers had about the child's future whereas plans for the child to reside within the formal system had no association with worry about the future.     

Effects of lead exposure on GnRH and LH secretion in male rats: response to castration and alpha-methyl-p-tyrosine (AMPT) challenge

Duchenne and Becker muscular dystrophies are X-linked genetic disorders characterized by dystrophin gene defects. We have studied 250 families with Duchenne and Becker muscular dystrophies (D/BMD) by molecular genetic methods since 1992. Nineteen exons of the dystrophin gene were analyzed for deletion. In families with no deletion, linkage analysis was performed to follow the inheritance of mutant alleles in the affected families. Twenty of these families requested prenatal diagnosis. Six mothers were found to be non-carriers (99% accuracy), thus fetuses were examined in the remaining 14. Two fetuses were affected and terminated. We report our experience and our current clinical practice in providing prenatal studies for D/BMD.     

Proposed recommendations for research on biochemical markers for problematic drinking

Successful eradication of Helicobacter pylori infection in children has required long treatment regimens that may result in noncompliance with failure to eradicate this organism. Despite full compliance with shorter therapeutic regimens, such as amoxycillin and omeprazole for 2 wk, the H. pylori eradication rate is poor in children. OBJECTIVES: The aim of this study was to evaluate the efficacy of, and compliance with, a 2-wk treatment with metronidazole, omeprazole, and clarithromycin in eradicating H. pylori disease in children. METHODS: Over a 15-month period, children diagnosed to be H. pylori positive by Steiner's stain of gastric antral biopsy specimens were treated with metronidazole, omeprazole, and clarithromycin. Follow-up upper GI endoscopy was performed 6-8 wk after completion of therapy. RESULTS: Of 15 patients with H. pylori-positive antral gastritis, 11 had duodenal ulcer disease; three patients with severe abdominal pain and one with vomiting had H. pylori gastritis only. H. pylori eradication was seen in 11 of 11 (100%) patients with duodenal ulcer disease and in three of four (75%) with gastritis only; the overall success rate was 93%. Duodenal ulcer disease healed when H. pylori was eradicated in all but one patient, who at presentation had a penetrating ulcer with a duodenobiliary fistula. Fourteen of 15 patients (93%) were fully compliant, and no adverse reactions were reported. CONCLUSIONS: Two weeks of therapy with metronidazole, omeprazole, and clarithromycin is effective H. pylori therapy in children. It is well tolerated, and full compliance can be achieved.     

Implantable hearing device performance measured by laser Doppler interferometry

Recent application of the Doppler principle laser interferometry to audiology, acoustics and otology has facilitated the development of implantable hearing devices (IHDs). During the design and testing of two different electromagnetic middle ear implants for sensorineural hearing loss, we used single-point laser Doppler interferometry (LDI). A commercially available interferometer, internally calibrated and validated against a National Institute for Standards and Technology (NIST) standard, was used with both mechanical fixtures and fresh temporal bones to evaluate implant mass, shape and orientation, attachment, electromagnetic coupling and acoustic properties. At both Hough Ear Institute and Symphonix Devices, Inc., we have shown that high fidelity and amplitudes can be recorded in vitro over a frequency range of 500 Hz to 10 kHz. These data can provide greater assurance of safety and efficacy to regulatory agencies before entering clinical trials. We propose that LDI be considered as an international standard for accurate, consistent comparison of performances of all IHDs during development. Furthermore, the future availability of human IHD data will allow for the extrapolation of a mechanical bench model of the middle ear transfer function for use in quality control during manufacturing and diagnosis of failure in IHDs.