Structural features of martensitic transformations upon the low-temperature deformation of metastable austenitic Fe-Cr-Ni alloy single crystals

The features of martensitic transformations upon the low-temperature (1.8–300 K) deformation of metastable Fe-18Cr-10Ni and Fe-18Cr-15Ni alloy single crystals with low stacking-fault energies were studied. It was shown that the γ → ɛ and γ → α martensitic transformations play the main role in increasing strength and plasticity when the deformation temperature is reduced to 4.2 K.     

Errors in the determination of the amplitude and arrival times of acoustic pulses under their incomplete resolution

By the example of two overlapping pulses with a sinusoidal carrier and a gaussian envelope, errors in the determination of their amplitudes and positions on the time axis as functions of the extent of their overlapping are investigated. It is shown that, in the case of a considerable overlapping, the errors in the amplitude determination can exceed 100% (the pulses disappear); the greatest shifts of the maxima of the pulse envelopes are of the order of their half-width in the case of a half-pulse overlapping.     

Correlation characteristics and travel time differences for hydroacoustic signals under directional reception at different depths

Experimental data are presented for the cross-correlation coefficients and travel time differences of audible signals measured at distances of ～60 and ～120 km in an oceanic waveguide. The signals are received simultaneously by two highly directional vertical arrays (with a main lobe width of ～2°) whose centers are at depths of 200 and 450 m. The radiation depths of the pseudonoise signals were 200 and 400 m. The high correlation coefficients (0.75–0.94) obtained for the signals received at different depths suggest that the changes in the frequency spectra of signals arriving over different paths are almost identical. The small fluctuations of the travel time differences (≤0.43 ms for the “water” signals and ≤0.63 ms for the signals reflected from the sea surface) testify to their high stability.     

Hyperbranched polylysines: Mechanism of formation

To gain insight into the mechanism treating formation of hyperbranched polylysines through the polymerization of N ^?-carbobenzoxylysine N-carboxyanhydride under conditions of the reductive removal of a N ^?-carbobenzoxy group, hyperbranched polylysine has been synthesized with the use of trifluoroacetic acid as a terminator in the polymerization of N-carboxyanhydride. The structure of the polymers is studied by capillary electrophoresis, low-pressure gel-permeation chromatography, circular dichroism, and enzymatic hydrolysis with trypsin. At the first stage of synthesis, a low-molecular-mass strongly branched core of the polymer is formed. At the second stage, polylysine chains are grafted via one point onto amino groups of N-terminal lysine moieties of the low-molecular-mass core through their carboxyl ends.     

Characteristic features of the sound field formation near the bottom of a shallow sea

Detailed calculated data are presented for the angular, temporal, and energy structures of the sound field at the points of localtion of a horizontal line array of receivers (at 250-m intervals) in a shallow sea. The array is deployed near the bottom of a 200-m-deep waveguide along a sound propagation track, at distances from 20 to 30 km from a source generating a signal in the kilohertz frequency range. The influence of a sand or mud bottom on the intensity of signals arriving along single rays is numerically estimated for winter and summer conditions of sound propagation in a specific region of the Barents Sea.     

Molecular mass characteristics and hydrodynamic and conformational properties of hyperbranched poly-L-lysines

Hydrodynamic and conformational properties of hyperbranched poly(amino acids) based on lysine have been studied by static and dynamic light scattering, velocity sedimentation, translational diffusion, and viscometry in dilute aqueous-saline solutions (0.2 M NaCl). The effects of synthesis conditions of hyperbranched poly(amino acids), modification of their end groups by histidine fragments, and incorporation of diacylated lysine residues between branching points of oligomers and polymers composed of lysine and glutamic acid on the molecular mass characteristics of the hyperbranched polymers have been ascertained. The hydrodynamic properties of the hyperbranched poly(amino acids) differ appreciably from the behavior of both linear polylysine and lysine dendrimers due to conformational features of their macromolecules.     

Crystal structure of <Emphasis Type="Italic">L</Emphasis>-alanine phosphate

The crystal structure of L-alanine phosphate (C₃O₂NH₇ · H₃PO₄) is determined by the single-crystal diffraction technique; a = 11.918(1) Å, b = 9.117(1) Å, c = 7.285(1) Å, γ = 104.7(1)°, space group P2₁, and Z = 4. The amino group of the alanine is protonated by the hydrogen atom of the phosphoric acid. Pairs of H₂PO ₄ ^? hydrogen-bonded ions are packed into layers alternating with layers of alanine molecules in the crystal. No hydrogen bonds are formed immediately between the alanine molecules.     

On the thermal decomposition of [Ni(H2O)6](NO3)2 and its deuterated analogue

The methods of TG, DTA and DSC were used to study the thermal decompositions of [Ni(H₂O)₆](NO₃)₂ and [Ni(D₂O)₆](NO₃)₂ in an atmospheric air medium. Intermediates were isolated at 145, 230 and 245°, and were identified by quantitative analysis and IR spectroscopy. The following phase transitions were observed under the conditions of the experiment: melting of the salts, partial dehydration to the tetrahydrate, formation of basic nickel nitrate hydrate stable within a narrow temperature interval, and formation of NiO.

---

Zusammenfassung Mittels TG, DTA und DSC wurde die thermische Zersetzung von [Ni(H₂O)₆](NO₃)₂ und [Ni(D₂O)₆](NO₃)₂ in Luft untersucht. Bei Temperaturen von T=145°C, 230°C un 245°C konnten Intermediäre festgestellt werden, welche mittels quantitativer Analyse und IR-Spektroskopie identifiziert wurden. Unter den gegebenen experimentellen Bedingungen wurden folgende Phasenumwandlungen beobachtet: Schmelzen der Salze, partielle Dehydratation zu Tetrahydrat, Bildung von basishem Nickelnitrat-hydrat (stabil innerhalb eines schmalen Temperaturintervalles), schließliche Bildung von NiO.Aus den DSC-Daten wurden die Enthalpien der Phasenumwaldungen berechnet. DTA- und DSC-Daten zeigen, daß die Phasenunwandlungen bei [Ni(H₂O)₆](NO₃)₂ bei etwas niedrigeren Temperaturen liegen als bei [Ni(D₂O)₆](NO₃)₂.

     

Crystal Structure of di-(L-alanine)Monophosphite Monohydrate [{\rm C}_3{\rm O}_2{\rm NH}_7 ]_2 \cdot {\rm H}_3 {\rm PO}_3 \cdot {\rm H}_2{\rm O}

An X-ray analysis of the crystal structure of di-(L-alanine)monophosphite monohydrate was carried out. The symmetrically nonequivalent L-alanine molecules were found to be present in the structure in two different forms coupled by a strong hydrogen bond: monoprotonated positively charged [CH₃CH(NH₃)COOH] molecule and CH₃CH(NH₃)COO zwitterion. Two layers are distinguished in the structure: one is a positively charged layer formed by L-alanine molecules and the other is a negatively charged layer composed of phosphite ions and water molecules. These layers, alternating along the a axis, are connected to each other by a network of hydrogen bonds.