Crystallization of Zircon in Stoneware Glazes

High levels of zircon are required to impart opacity in glazes. Zircon additions of <3 wt% dissolve into the glassy phase; additions of >12% cause all the zircon to crystallize from the glaze. Dynamic high-temperature X-ray diffraction has shown that, during heating, a portion of the zircon dissolves and subsequently recrystallizes, using undissolved zircon crystals as seeds. This recrystallization does not occur at lesser zircon levels, because of a lack of seed crystals. When zirconia is added to the glaze, zircon is formed as elongated crystals at the glaze surface. Lesser zircon levels have been observed in the glazes that have zirconia additions.     

High-throughput method for the production and analysis of large natural product libraries for drug discovery

High-throughput methods were applied to the production, analysis, and characterization of libraries of natural products in order to accelerate the drug discovery process for high-throughput screening in the pharmaceutical and biotechnology industries. Library production integrates automated flash chromatography, solid-phase extraction, filtration, and high-throughput parallel four-channel preparative high-performance liquid chromatography to obtain the libraries in 96- or 384-well plates. Libraries consist of purified fractions with approximately one to five compounds per well. Libraries are analyzed prior to biological screening by a high-throughput parallel eight-channel liquid chromatography-evaporative light scattering detection-mass spectrometry system to determine the molecular weight, number, and quantity of compounds in a fraction. After biological screening, active fractions are rapidly purified at the microgram level and individual compounds are rescreened for confirmation of activity. Structures of active compounds are elucidated by NMR spectroscopy and mass spectrometry. Utilization of a novel microcoil probe allows NMR data to be gathered on 50 microg. As a demonstration, a library was made from the stem bark of Taxus brevifolia. Biological screening in the National Cancer Institute's in vitro panel of three cancer cell lines demonstrates that the process enables the discovery of active anticancer compounds not detected in the flash fractions from which the library originates.     

Laser chemical vapor deposition of TiC on tantalum

Laser chemical vapor deposition (LCVD) of titanium carbide (TiC) coatings onto tantalum substrates using hydrogen gas, titanium tetrachloride (TiCl₄) and either methane (CH₄) or acetylene (C₂H₂) source gasses was investigated. The influences of the molar ratio of the source gases and the deposition temperature on the phase assemblage, composition, and morphology of the coatings was examined. Using C₂H₂, nearly stoichiometric coatings were produced at 1000°C and at a TiCl₄/C₂H₂ ratio of 1/0.4. Stoichiometric coatings were also produced using CH₄ but the deposition temperature was 400°C higher and a much larger fraction of the carbon source was required compared to C₂H₂. Although deposition rates were much slower when using CH₄, the coatings exhibited a smoother surface finish and had a higher density compared to those produced using C₂H₂. The suitability of CH₄ and C₂H₂ as carbon sources for depositing stoichiometric, phase-pure coatings is discussed in light of these results.     

Strategies to improve electrode positioning and safety in cochlear implants

An injection-molded internal supporting rib has been produced to control the flexibility of silicone rubber encapsulated electrodes designed to electrically stimulate the auditory nerve in human subjects with severe to profound hearing loss. The rib molding dies, and molds for silicone rubber encapsulation of the electrode, were designed and machined using AutoCad and MasterCam software packages in a PC environment. After molding, the prototype plastic ribs were iteratively modified based on observations of the performance of the rib/silicone composite insert in a clear plastic model of the human scala tympani cavity. The rib-based electrodes were reliably inserted farther into these models, required less insertion force and were positioned closer to the target auditory neural elements than currently available cochlear implant electrodes. With further design improvements the injection-molded rib may also function to accurately support metal stimulating contacts and wire leads during assembly to significantly increase the manufacturing efficiency of these devices. This method to reliably control the mechanical properties of miniature implantable devices with multiple electrical leads may be valuable in other areas of biomedical device design.     

The expectation-maximization algorithm for symbol unsynchronizedsequence detection

The expectation-maximization (EM) algorithm for maximizing likelihood functions, combined with the Viterbi algorithm, is applied to the problem of sequence detection when symbol timing information is not present. Although the EM algorithm is noncausal, results obtained using the algorithm on the problem of nonsynchronized sequence detection indicate that it converges most of the time in three iterations, making it both of theoretical and of practical interest. A practical algorithm based on the EM algorithm is introduced. It reduces the computational burden and improves performance by making use of timing estimates in previous observation windows     

Identification and purification of diphosphoinositol pentakisphosphate kinase, which synthesizes the inositol pyrophosphate bis(diphospho)inositol tetrakisphosphate

Diphosphoinositol pentakisphosphate (PP-IP5) and bis(diphospho)inositol tetrakisphosphate (bis-PP-IP4) were recently identified as inositol phosphates which possess pyrophosphate bonds. The molecular mechanisms that regulate the cellular levels of these compounds are not yet characterized. To pursue this question, we have previously purified an inositol hexakisphosphate (IP6) kinase from rat brain supernatants [Voglmaier, S. M., et al. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 4305-4310]. We now report the identification and purification of another novel kinase, diphosphoinositol pentakisphosphate (PP-IP5) kinase, which uses PP-IP5 as a substrate to form bis(diphospho)inositol tetrakisphosphate (bis-PP-IP4) in soluble fractions of rat forebrain. The purified protein, a monomer of 56 kDa, displays high affinity (Km = 0.7 microM) and selectivity for PP-IP5 as a substrate. The purified enzyme also can transfer a phosphate from bis-PP-IP4 to ADP to form ATP. This ATP synthase activity is an indication of the high phosphoryl group transfer potential of bis-PP-IP4 and may represent a physiological role for PP-IP5 and bis-PP-IP4.