Role of Chiral Configuration in the Photoinduced Interaction of D- and L-Tryptophan with Optical Isomers of Ketoprofen in Linked Systems

The study of the L- and D-amino acid properties in proteins and peptides has attracted considerable attention in recent years, as the replacement of even one L-amino acid by its D-analogue due to aging of the body is resulted in a number of pathological conditions, including Alzheimer’s and Parkinson’s diseases. A recent trend is using short model systems to study the peculiarities of proteins with D-amino acids. In this report, the comparison of the excited states quenching of L- and D-tryptophan (Trp) in a model donor–acceptor dyad with (R)- and (S)-ketoprofen (KP-Trp) was carried out by photochemically induced dynamic nuclear polarization (CIDNP) and fluorescence spectroscopy. Quenching of the Trp excited states, which occurs via two mechanisms: prevailing resonance energy transfer (RET) and electron transfer (ET), indeed demonstrates some peculiarities for all three studied configurations of the dyad: (R,S)-, (S,R)-, and (S,S)-. Thus, the ET efficiency is identical for (S,R)- and (R,S)-enantiomers, while RET differs by 1.6 times. For (S,S)-, the CIDNP coefficient is almost an order of magnitude greater than for (R,S)- and (S,R)-. To understand the source of this difference, hyperpolarization of (S,S)-and (R,S)- has been calculated using theory involving the electron dipole–dipole interaction in the secular equation.     

Separation of zirconium and hafnium fluorides by the sublimation–sorption method

A preparation method of zirconium tetrafluoride (ZTF) of the nuclear degree of purity for one separation stage is proposed and confirmed experimentally. For this purpose, initial ZTF vapors should be passed inside the powderlike zirconium dioxide layer 140–150 mm in height or above its layer 1000–1100 mm in length. A process cascade for the fabrication of nuclear-pure ZTF and HTF with the hafnium content higher than 99% for one separation stage in the absence of process wastes is developed and calculated. It is shown that the proposed process cascade for the separation and concentration of ZTF and HTF for one stage makes it possible to prepare ZTF with a hafnium content up to 0.01 wt % from the initial ZTF with a hafnium concentration of 2.0 wt % and a hafnium concentrate with a hafnium content higher than 99%.     

Investigation into the properties of electroerosive powders and hard alloy fabricated from them by isostatic pressing and sintering

Results of an investigation into the properties of the hard alloy fabricated by isostatic pressing and sintering of powders prepared by the electric discharge dispersal (EDD) of tungsten-containing waste of the T15K6 alloy in distilled water and burning kerosene are presented. An original installation developed and patented by the authors was used for the EDD of conductive materials. Isostatic pressing of the powder was performed using an EPSI press (Belgium) at a pressure of 300 MPa, and sintering was performed in a Nabertherm high-temperature furnace (Germany) in vacuum at 1500°C for 2 h. The content of main elements (W, Ti, Co), both in the powder and in the hard alloy fabricated from it, was established using electron probe microanalysis. The microhardness of the powder and alloy is investigated and it is shown that powder prepared by EDD in kerosene and the alloy made of it has increased HV compared with the samples fabricated using water as the working liquid.     

Standardization of sintered bearing materials part I

Conclusions The work carried out has demonstrated that in principle the existing grades of bearing materials can be reduced in number while still fulfilling all the requirements regarding their operating and physicomechanical properties.Translated from Poroshkovaya Metallurgiya, No. 2(170), pp. 44–48, February, 1977.     

Effect of zinc sulfide on the formation of an antiseizing layer in the sintered antifriction materials

Conclusions As a result of deformation and dispersion occuring under frictional conditions in the Fe-ZnS material, a colloid-type lubricating layer consisting of single crystals of ZnO (presumably) and finely dispersed Fe₃O₄ phase in its quasi-crystalline and crystalline states forms up to a depth of 100 nm.The high effectiveness of the lubricating layer may be due to the decreased degree of oxidation of the iron matrix, prevention of seizure of the contacting surfaces, and the easy dispersibility and the low shear strength of the iron oxides (Fe₃O₄).As a rule, wearing out of the Fe-ZnS material occurs through the embrittlement of the antiseizing layer and due to delamination of its individual sublayers.Translated from Poroshkovaya Metallurgiaya, No. 4, pp. 87–94, April, 1992.     

Cyclic behavior of ultrafast self-modulation of the light-absorption spectrum under conditions of pump and stimulated emission in GaAs

Under picosecond photogeneration of charge carriers in GaAs, accompanied by intense stimulated emission of the semiconductor itself, ultrafast self-modulation of its light-absorption spectrum takes place, which consists in the appearance of regions of local absorption enhancement (bumps) in the spectrum. The ultrafast self-modulation is found to exhibit a cyclic behavior; i.e., the pattern of the self-modulation of the spectrum (the number and spectral position of the bumps) is repeated after a certain time T _c falling in the picosecond range. The cycle period T _c varies over the time span of the pump pulse and depends on the pulse energy, which means that T _c is a function of the pump intensity. Assuming that self-modulation of the absorption reflects self-modulation of the charge-carrier energy distribution in GaAs under pumping, experimental results can be formulated as follows: in the process of the ultrafast self-modulation, deviations of the occupancies of different energy levels from the Fermi distribution evolve with time in a mutually related way; the distribution of the occupancy depletion in the conduction band repeats cyclically in time; and the cycle period decreases as the intensity of the pump increases.     

Wear Resistance of Hardened Components Produced from Electrospark Cobalt–Chromium Powder by Additive Manufacturing

Russian Engineering Research - The wear resistance of hardened additive products is studied experimentally. The products are made from electrospark cobalt–chromium powder obtained in alcohol....     

Microstructure and Elemental Composition of Powders Obtained Under Conditions of Electroerosive Metallurgy of Heat-Resistant Nickel Alloy ZhS6U Wastes in Water

Metallurgist - This work is based on experimental studies aimed at examining the microstructure and elemental composition of powders obtained under electroerosive metallurgy conditions of the...     

Relation between the Relaxation of Intrinsic Stimulated Picosecond Emission from GaAs with a Characteristic Charge-Carrier Cooling Time

Semiconductors - During the powerful picosecond optical pumping of a thin (~1 μm) GaAs layer, a stimulated intense (up to 1 GW/cm2) picosecond emission arises. It is found that the...