Formation of IPN organic-inorganic polymer hybrids utilizing the photodimerization of thymine

Summary Formation of an interpenetrating polymer network (IPN) composed of organic polymer gel and silica gel in the form of polymer hybrids was conducted by utilizing the photodimerization of thymine bases. Thymine-modified poly(2-methyl-2-oxazoline) (POZO-T) was synthesized by the condensation reaction of partially hydrolyzed polyoxazoline and 1-(2-carboxyethyl)thymine. Organic-inorganic polymer hybrids were prepared from POZO-T and tetramethoxysilane (TMOS). Transparent and homogeneous polymer hybrids could be obtained. The photodimerization and the reverse reaction of thymine in the polymer hybrids were monitored by the UV absorption spectroscopy. Received: 27 March 2000/Revised version: 5 June 2000/Accepted: 15 June 2000     

Effect of bonding parameters on microstructure and properties of Si_3N_4/Si_3N_4 joint brazed by Cu-Zn-Ti filler alloy

1INTRODUCTION Si3N4ceramichashighthermalandwearingresistanceandisapromisingmaterialforhightem peratureapplications.However,itisdifficultto manufacturetheSi3N4ceramicworkpieceswithla gerdimensionsandcomplicatedshapesduetoitspoorworkabilityandlowductility.Inrecent20years,manystudieshavebeenfocusedonthetech niquesofceramicjoining,becausethejoiningtech niquescanbeusednotonlyforlow costandhigh reliabilitymanufacturingofceramicpartswith complicatedshapesbutalsoforrepairingofthece ramicpartsinw…     

Spatio-Temporal Receptive Field Measurement of Retinal Neurons by Random Pattern Stimulation and Cross Correlation

A method is developed for the measurement of the spatio-temporal receptive field (STRF) of neurons in the retina. The test input is an unsteady visual pattern randomly modulated in both space and time, and the output is the stochastic time course of the intracellular response. The STRF is expressed in terms of the spatio-temporal Wiener kernels calculated through a special cross-correlation algorithm between the response and the stimulus-related information. The method is an extension of existing white-noise identification techniques to include the spatial domain. Consideration is given to the practical implementation of the required stimulus pattern, and has led to several alternative approaches.     

Isolation and conformational analysis of fragment peptide corresponding to the heparin-binding site of hepatocyte growth factor

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes. The mitogenic activity of HGF is mediated by its binding to a high-affinity receptor, c-Met. Heparan sulfate is an initial binding site for HGF, based on its relative abundance on the cell surface. The binding of HGF to heparin or heparin-like molecules may induce oligomerization of HGF and facilitate c-Met-dependent mitogenesis [Zioncheck et al. (1995) J. Biol.Chem. 270, 16871-16878]. Thus, heparin binding is important for the biological activity of HGF. To identify the heparin-binding site of HGF, we isolated fragment peptides corresponding to the site by limited proteolysis and chemical degradation of recombinant human HGF (rhHGF). The heparin-binding ability of the peptides was expressed as their elution positions on heparin-affinity column chromatography with NaCl gradient elution. Because all of the heparin-binding peptides obtained in this study were isolated from the N-terminal hairpin-loop region (PyrGlu32-Asn127) of HGF, the region was identified as the heparin-binding site of HGF. One of the isolated peptides, Phe42-Glu111, containing the N-terminal hairpin-loop structure, was considered a suitable model peptide for the heparin-binding site of HGF. From the observation using circular dichroism spectroscopy, it was indicated that the secondary structure of the peptide changed from a random structure to a beta-sheet-like structure upon heparin binding. In addition, oligomerization of HGF in the presence of heparin was observed by dynamic light scattering. Based on our evidence, it is considered that the conformational change in the heparin-binding site may induce the oligomerization of HGF.     

Azide-phenolic resin UV resist (MRL) for microlithography

Poly(4-vinylphenol) sensitized by an aromatic monoazide compound (4-azidochalcone), called MRL (Micro Resist for Longer wavelengths), has been prepared and evaluated as a negative UV resist. The resist is sensitive to radiation in the 300 to 400 nm region. The sensitivity of MRL is comparable to that of a positive quinonediazide photoresist under exposure to unfiltered light from a high pressure Hg lamp. An aqueous base developer removes the unexposed areas of MRL with no evidence of swelling of the exposed areas, indicating its high resolution capability. The main products in the exposure of MRL films are found to be primary and secondary amines. It is concluded that the formation of secondary amines attached to the polymer chain is responsible for the insolubilization of the exposed MRL in the base developer.     

Crystallite orientation in polycrystalline graphites made from glass-like carbons under high pressure

The preferred orientation of crystallites was investigated on polycrystalline graphites made from the glass-like carbons with spherical particles under a pressure of 5 kbar at 1300 to 2000? C. The glassy carbon spheres 40 to 70 Μm diameter which were pre-heated at 1000? C under normal pressure, gave sintered discs with a bulk density of 1.5 g cm^?3 and a relatively high degree of orientation. However, spheres of the same type pre-heated at 2000? C gave the high bulk density of 1.9 g cm^?3 and a very low degree of orientation. The carbon beads 40 to 70 Μm diameter gave a relatively low degree of orientation and pre-heating at 2000? C reduced the degree very remarkably. Carbon beads with a smaller particle size, <20 Μm, gave a lower degree of orientation. Pre-heating of the initial carbon of small particle size at temperatures as high as 2000? C resulted in a low degree of preferred orientation of the crystallites in the sintered discs, the temperature dependence being the strongest.     

Optimum parameter guidelines for 10 Gbit/s, multi-megametre transmission systems considering the nonlinear effect

The impact of the nonlinear effect, combined with group velocity dispersion, on cascaded amplifier transmission systems is clarified experimentally using a 10 Gbit/s transmission system. Based on the results, the optimum amplifier output power is presented as a function of amplifier spacing 3000 km transmission is feasible at 10 Gbit/s if the spacing is 100 km.<>     

Application of antisense human telomerase RNA toward cancer therapy

We overviewed recent results of anti-tumor effects and inhibition of telomerase activity in tumor cells through antisense human telomerase RNA(hTR). By introducing antisense hTR expression construct into tumor cells, reduction of telomeric DNAs and crisis or cellular senescence occurred in several human cancer cell lines. Antisense oligonucleotides to hTR synthesized with peptide nucleic acids and phosphorothioate deoxyribonucleic acids(PS) also inhibited telomerase activity in vitro. Furthermore, PS antisense hTR had significant effect to decrease tumor size and a number of metastatic nodules in a xenograft human cancer-nude mouse model. Taken together, the telomerase inhibitors targeting to hTR are expected to be novel anti-tumor agents.