Strain sensitivity of thick resistive films based on BaB6 and SnO2-Sb after laser irradiation

We study the influence of laser irradiation on the strain sensitivity of thick films based on BaB₆ and SnO₂-Sb and analyze the behavior of their electric resistance depending the duration of laser pulses. It is shown that the laser treatment of thick films based on SnO₂-Sb with nanosecond pulses increases the coefficient of strain sensitivity by about 40%. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 95–100, July–August, 2006.     

D-lactate-selective amperometric biosensor based on the mitochondrial fraction of Ogataea polymorpha recombinant cells

During the recent decades, a lot of data about the significance of D-lactate determination in food technology and quality control have been accumulated. Nowadays, the development of new methods for the determination of D-lactate is very relevant, especially with regard to biosensors. To construct a D-lactate-selective biosensor, we suggest using the mitochondria of recombinant yeast cells of Ogataea (Hansenula) polymorpha “tr6” (gcr1 catX/Δcyb2, prAOX_DLDH) overproducing D-lactate: cytochrome c-oxidoreductase (DLDH, EC 1.1.2.4) and lacking an L-lactate-specific enzyme (flavocytochrome b₂, E.C. 1.1.2.3). The usage of the pure enzyme is problematic due to the complexity of its isolation and stabilization because of the intramembranous localization of DLDH. The enzyme catalyzes D-lactate oxidation to pyruvate coupled with ferricytochrome c reduction to ferrocytochrome c. The constructed biosensor is characterized by high sensitivity (18.5 А·М⁻¹·m⁻²), a low detection limit (3 μM of D-lactate), wide linear ranges, good selectivity, and sufficient stability. The real samples' analysis of D-lactate in dairy products was performed, and high correlation of the obtained results with the reference approach (0.7 < r < 1) and literature data was demonstrated.     

Effective removal of nonmetallic inclusions by continuous refining of liquid steel in the intermediate ladle of the continuous-casting machine

The influence of modification of the liquid-metal flow by various structural elements (barriers, thresholds, etc.) and bottom injection on the removal of nonmetallic inclusions in the intermediate ladle of a continuous-casting machine is investigated.     

Low-Cycle Fatigue of Steels After Ion Nitriding in Hydrogen-Free Atmospheres

We present the results of investigation of low-cycle fatigue in bending for different types of steel after ion nitriding in hydrogen-free saturating atmospheres. The recommendations concerning the field of applicability of this technology of surface hardening in the process of operation are given. We make a conclusion that the procedure of ionic hardening in hydrogen-free atmospheres makes it possible to change the physicomechanical properties of the surface layers in broad ranges and substantially increase the low-cycle fatigue strength of structural steels. The maximum durability is attained by optimizing the parameters of the process of diffusion saturation.     

Cytochrome c peroxidase from a methylotrophic yeast: physiological role and isolation

Mutant strains of the methylotrophic yeast Hansenula polymorpha defective in catalase (cat) and in glucose repression of alcohol oxidase synthesis (gcr1) have been isolated following multiple UV mutagenesis steps. One representative gcr1 cat mutant C-105 grows during batch cultivation in a glucose/methanol medium. However, growth is preceded by a prolonged lag period. C-105 and other gcr1 cat mutants do not grow on methanol medium without an alternative carbon source. A large collection of second-site suppressor catalase-defective (scd) revertants were isolated with restored ability for methylotrophic growth (Mth+) in the absence of catalase activity. These Mth+ gcr1 cat scd strains utilize methanol as a sole source of carbon and energy, although biomass yields are reduced relative to the wild-type strain. In contrast to the parental C-105 strain, H2O2 does not accumulate in the methanol medium of the revertants. We show that restoration of methylotrophic growth in the suppressor strains is strongly correlated with increased levels of the alternative H2O2-destroying enzyme, cytochrome c peroxidase. Cytochrome c peroxidase from cell-free extracts of one of the scd revertants has been purified to homogeneity and crystallized.     

Ultralow concentrations of ibuprofen activate cell prostaglandin synthesis

The interest in the prostaglandin (PG) synthesis by animal cells today grows steadily because of the difficulties in obtaining them by any other way. Murine peritoneal macrophages can under certain conditions synthesize large amounts of PGs. The effect of well-known nonsteroidal anti-inflammatory drug ibuprofen on PG synthesis by the cells using a high-performance liquid chromatography (HPLC) method with fluorescence detection of 4-bromomethyl-7-methoxy-coumarin (BrMMC) derivatives was studied. In our case, the main metabolites were PGE2 and PGF2a. The PG synthesis activation effect was shown by ibuprofen concentrations in the 10(-10)-10(-14) M range with the maximum effect of 10(-12)M. In this case, the ibuprofen effect was comparable in value with the effect of well-known cell PG synthesis activator--calcium ionophore A23187. Although the exact mechanism of such an effect is not clear at the moment, at low concentration, ibuprofen itself is able to activate PG synthesis in murine peritoneal macrophages.     

Effect of Residual Stresses on Electrophysical Properties of High-Ohmic Thick Films Based on SnO 2 ― Sb

We have studied the effect of a mismatch between the thermal coefficients of linear expansion for the current-conducting phase and the glass on the electrical properties of composite thick films based on Sn_0.93Sb_0.07O₂. The physical explanation of the results obtained is connected with the appearance of residual stresses in the film on cooling during heat treatment.     

Rheological properties of concentrated solutions of cellulose and its mixtures with other polymers in orthophosphoric acid

We have investigated the specific features of the steady shear flow of concentrated spinning solutions of cellulose and its mixtures with polyvinyl alcohol, chitosan, and polyacrylonitryl in orthophosphoric acid in the temperature range of 303–323 K. Rheological curves including highest- and lowest-viscosity regions have been obtained. The influence of the nature of the polymer additive and its content on the profile of rheological curves of the cellulose solution has been established.