Endo-epsilon-(gamma-Glu)Lys-isopeptidolysis as a sign of highly-specific proteolysis

Catalytic activity of destabilase has been studied in hydrolyses of synthetic and natural substrates. High specificity of the enzyme is shown in hydrolysis of endo-epsilon-(gamma-Glu)Lys isopeptide bonds.     

Hopping conductivity in polycrystalline photoconductive Pb3O4 layers

Ac conductivity has been studied in polycrystalline Pb₃O₄ layers in the frequency range f = 10²–10⁵ Hz at temperatures of 293–370 K; the conductivity has been measured in the dark and under illumination. Specific features of the charge-transport process are discussed. Analysis of the experimental data in terms of the Mott theory shows that the conduction is by the hopping mechanism and the charge transport occurs in the energy gap near the Fermi level. Microscopic parameters governing the conduction process, such as density of localized states and the average carrier’s hopping distance, are determined for different temperatures.     

Radionuclides in the Kara sea bottom sediments

The contents and distribution of natural (214Pb, 214Bi, 228Ac, and 208Tl) and technogenic (90Sr, 137Cs, and 60Co) radionuclides in the Kara Sea bottom sediments was analyzed by using the materials collected by R/V "Pomor" (Murmansk Marine Biological Institute). In 1994, no high (critical) concentrations of technogenic radioisotopes were found in the sea sediments, while the spots (regions) of elevated 137Cs content found in 1984 were not confirmed in 1994. It was proposed that the main sources of entry of technogenic radionuclides in the sea sediments in the last years are the flow of the Ob'-Yenisei waters and container burials of radioactive waste in the sea, which appeared to have been markedly corroded. The latter is confirmed by detection in some places of 60Co, which was not previously found in the sediments.     

Optical and electron energy loss spectra of cadmium dichloride and lead dichloride crystals

Experimental electron energy loss spectra of cadmium dichloride and reflection spectra of lead dichloride are used to calculate the complete sets of fundamental optical functions of the two highly ionic materials in a wide energy range (0–30 eV). Their cumulative permittivity and volume electron energy loss curves are decomposed into transverse and longitudinal elementary components of transitions, and their main parameters are evaluated. The effect of the nature of the cation on the key features of the optical spectra is examined.     

Nickel field-emission microcathode: Art of fabrication, properties, and applications

An effective method for mass production of field-emission microcathodes (μFECs) is suggested and described. The main properties of the μFECs are calculated using the actual geometric parameters of the system (emitting nanotip radius ∼15-20 nm, interelectrode distance ∼1.5-2 μm, etc.). It is shown that the electric field strength in the immediate vicinity of a nanotip is several units of at comparatively low (100-200 V) voltages applied. A series of probable applications taking advantage of the unique features of the μFECs are suggested.     

Hydrogenation of aromatic hydrocarbons in the presence of dibenzothiophene over platinum-palladium catalysts based on Al-SBA-15 aluminosilicates

The hydrogenation of a 2-methylnaphthalene solution in n-heptane in the presence of dibenzothiophene (400 ppm in terms of sulfur) over Pt-Pd catalysts containing Al-SBA-15 mesoporous aluminosilicates has been studied. Supports for the catalysts contained 35 wt % Al-SBA-15 and 65 wt % γ-Al₂O₃. The Pt and Pd contents of the catalysts was 0.25 and 1.0 wt %, respectively. Experiments with the model feedstock were conducted in an autoclave at 240–260°C, an initial hydrogen pressure of 30 atm, and a substrate/metal weight ratio of 30. It has been found that a catalyst based on Al-SBA-15 with Si/Al = 5 exhibits the highest activity under poisoning with 400 ppm sulfur. Thus, the conversion of 2-methylnaphthalene at 260°C after 3 h was 85% with the selectivity for methyltetralins of 97%. The dearomatization of a hydrotreated diesel fraction with 45 ppm sulfur at 260°C at a pressure of 30 atm and a space velocity of 2.4 h^?1 has made it possible to decrease the total aromatic content, in particular reduce the concentration of polycyclic aromatic compounds to a level of less than 1 wt %.     

THE THROMBORESISTANCE OF A HEPARIN-POLYVINYL ALCOHOL HYDROGEL†

Heparin immobilized onto polyvinyl alcohol (PVA) by action of glutaraldehyde has been shown to be biologically active in a novel parallel flow arteriovenous shunt in dogs. The hepann-PVA hydrogel originally devised by Merrill and his collaborators was applied as a coaling to chromic acid etched polyethylene lubing. A pair of Y-connectors was used to divert < 2% of the flow in the AV shunt through the heparinized tube, which remained patent for longer Ihan two hours while a control tube without heparin was occluded within 30 minutes at a main shunt flow rate of ～l50mL/min. This enhanced patency was achieved without significant release from the surface, consistent with earlier experiments attributing the thromboresistance of the heparin-PVA hydrogel to the formation of a surface bound inactive thrombin-antithrombin III complex. Radiolabelled thrombin adsorbed onto beads made from the gel was readily displaced by arvinized plasma, indicating that the inactive complex was not itself permanently bound to the surface.

These results demonstrate the utility of Merrill's hydrogel for preparing materials with potential long lerm thromboresistance and for testing the validity of the hypothesized limitations to the long term use of immobilized heparin.     

Hydrogenation of aromatic compounds in the presence of dibenzothiophene over bimetallic catalysts containing mesoporous aluminosilicates

The hydrogenation of a mixture of naphthalene, tetralin, and toluene (a solution in n-heptane) in the presence of dibenzothiophene (150 and 400 ppm on a sulfur basis) over Pt-Pd catalysts containing Al-HMS mesoporous aluminosilicates has been studied. The catalyst supports contained 35 wt % Al-HMS and 65 wt % γ-Al₂O₃. The Pt and Pd loadings in the catalysts were 0.2 and 0.8 wt %, respectively. The process was carried out at 200–240°C, a pressure of 30 atm, and a weight hourly space velocity of 1.7 h^?1. It has been found that the catalyst based on Al-HMS with Si/Al = 10 exhibits the highest activity. Thus, in the hydrogenation of a model mixture containing 150 and 400 ppm of sulfur, the conversion of toluene at 240°C was 22.2 and 10.9 wt %, respectively. In the presence of this catalyst, the concentration of aromatic hydrocarbons in the hydrotreated diesel fraction decreased from 28.4 to 6.8 wt %, and the sulfur content decreased from 45 to 5 ppm.     

IP电话：创新者的追求

早在１９９５年就有人预测Ｉｎｔｅｒｎｅｔ在某种意义上可能会对电话技术产生重要影响。短短几年间,ＩＰ电话技术的屡次重大突破为这一预言提供了不可辨驳的佐证,也使人们不再小看这一事物。目前,ＩＰ电话供应商已开发出大量应用：ＩＰ增强型服务、因特网呼叫等待／电话倍频器、基于ＩＰ的ＰＢＸ和基于Ｗｅｂ的呼叫中心等,ＩＰ电话正逐步改变着这个世界的交流方式。