Structure of Ca–Sr–Ba Sodium–Borosilicate Glasses according to <Superscript>11</Superscript>B and <Superscript>29</Superscript>Si NMR Spectroscopy

The structure of borosilicate glasses is studied with ¹¹B and ²⁹Si NMR spectroscopy in order to investigate the influence of replacement of Na₂O by oxides of alkali earth metals on their local structure. The quantitative data are analyzed with respect to their correspondence to the criterion of the average charge of the structural unit. The reasons for the deviation between the experimental results and this criterion are considered. It is shown that, in the case of glass devoid of borate structural units with nonbridging oxygen atoms, the corrected contents of these units are consistent with the predictions of thermodynamic modeling of the structure and properties of oxide glasses.     

Structure of high-alkali melts in the lithium borate system from vibrational spectroscopic data

Melts of the compositions Li₂O · B₂O₃, 3Li₂O · 2B₂O₃, 2Li₂O · B₂O₃, and 3Li₂O · B₂O₃ (asbatched) are investigated using high-temperature Raman spectroscopy in the temperature range 973–1373 K. The IR and Raman spectra of polycrystalline samples of the corresponding compositions are measured. The Raman spectra of the melts and the products of their crystallization are compared, and the frequencies of characteristic vibrations of the structural units are determined. The regularities of the changes in the structure of the melts are established as a function of the composition and temperature.     

Thermal Behavior of Alkali Zinc Phosphates

Alkali zinc phosphates Na₂ZnP₂O₇, K₂ZnP₂O₇, LiNaZnP₂O₇, LiKZnP₂O₇, NaKZnP₂O₇, and Li₁₂Zn₄(P₂O₇)₅, which can be prepared both by the solid-phase synthesis and through crystallization from a glass, are studied using high-temperature X-ray powder diffraction. The unit cell parameters as functions of the temperature in the range 20–700°C are analyzed, and the linear anisotropic thermal expansion coefficients are determined. The majority of these compounds are characterized by strong anisotropy of thermal expansion. It is found that the LiKZnP₂O₇ compound exists in two polymorphic modifications, namely, the low-temperature monoclinic modification and the high-temperature orthorhombic modification.     

Optimization of the composition of nitridic ceramic tool material by tribotechnical tests

Translated from Poroshkovaya Metallurgiya, No. 4, pp. 46–51, April, 1992.     

Safety of bacteria of the genus Bacillus, forming the base of some probiotics]

The study of the safety of bacillary strains forming the base of new probiotics (biosporin and subalin) was made. For control, the safety of Bacillus sp. IP5832 (the base of the preparation of bactisubtil) was studied. The results obtained in this investigation demonstrated that the strains contained in biosporin and subalin were safe when injected intravenously and intraperitoneally into animals in dose of 5 x 10(9) cells per 0.5 ml of physiological saline. The introduction of Bacillus sp. IP5832 in the same dose produced 100% lethal effect.     

Molecular genetic analysis of DNA structure of pFra plasmids in plague pathogen of varying biovar]

OBJECTIVE: To clarify the mechanism of the suppressive effect of 2-buten-4-olide (2-B4O), an endogenous feeding suppressant, on the pulsatile secretion of luteinizing hormone (LH), by studying whether endogenous opioid peptides are involved in this suppressive effect. METHODS: Using ovariectomized (ovx) rats, blood samples were taken every 6 min for 2 h after administration of 2-B4O or saline into the third cerebroventricle (3V) and sequential i.v. injection of naloxone (0. 5 mg/kg per h) or saline. Rats were divided into three experimental groups: group 1: 3V saline + i.v. saline (control); group 2: 3V 2-B4O + i.v. saline; group 3: 3V 2-B4O + i.v. naloxone. Serum LH concentrations were determined by double-antibody RIA. To determine whether 2-B4O affected the biosynthetic activity of the opioidergic neurons within the ovx rat arcuate nucleus, we measured the concentrations of pro-opiomelanocortin (POMC) mRNA, a precursor of beta-endorphin, in the rostral arcuate nucleus using non-radioactive in situ hybridization and a computerized image-analysis system. RESULTS: 2-B4O significantly suppressed the pulse frequency of LH (group 2: 1.5+/-0.33 pulses/2 h, group 1: 2.43+/-0.2 pulses/2 h; P < 0.05), but naloxone blocked its suppressive effect and restored the pulse frequency (group 3: 3.29+/-0.36 pulses/2 h, group 2: 1.5+/-0.33 pulses/2 h: P < 0.01). There were no significant changes in the mean LH concentrations and amplitude. Furthermore, 2-B4O significantly stimulated the expression of POMC mRNA in the rostral arcuate nucleus. CONCLUSION: These results suggest that 2-B4O may impair the pulsatile secretion of LH by activating the opioid pathway within the hypothalamus.