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...     

Anticorrelation between the Intensity of Stimulated Picosecond Emission in GaAs and the Characteristic Time of Charge-Carrier Cooling

Semiconductors - During the powerful picosecond optical pumping, intense stimulated picosecond emission arises in a thin GaAs layer. It is found that, first, the maximum emission intensity...     

Elemental Composition of the Powder Particles Produced by Electric Discharge Dispersion of the Wastes of a VK8 Hard Alloy

The powder fabricated by electric discharge dispersion of the wastes of a VK8 hard alloy is studied by electron-probe microanalysis. This powder formed by electric discharge dispersion in kerosene mainly contains tungsten and carbon and has low contents of oxygen, cobalt, and iron.     

Electroerosion micro- and nanopowders for the production of hard alloys

The shape and the surface morphology of the powder particles fabricated by the electroerosion dispersion of tungsten-containing wastes in illuminating oil are studied. The hard alloy fabricated from these powder particles is analyzed by electron-probe microanalysis. The powder synthesized by the electroerosion dispersion of the wastes of sintered hard alloys is found to consist of particles of a spherical or elliptical shape, an irregular shape (conglomerates), and a fragment shape. It is shown that W, Ti, and Co are the main elements in the hard alloy fabricated from the powder synthesized by electroerosion dispersion in illuminating oil.     

Self-synchronization of the modulation of energy-levels population with electrons in GaAs induced by picosecond pulses of probe radiation and intrinsic stimulated emission

Picosecond optical pumping leads to the initiation of intrinsic picosecond stimulated emission in GaAs. As was established previously, due to the interaction of pulses of probe radiation with those of intrinsic emission, the dependence of the absorption α of the probe pulse on its delay τ with respect to the pump pulse is modulated with oscillations. It is found that the oscillatory dependences α(τ) have a similar shape only in the case of certain combinations of energies of the interacting pulses. As a result, it is assumed that the above interaction is, in fact, a synchronization of modulations (formed by pulses) of charge-carrier populations at energy levels; this synchronization occurs in the direction of the reconstruction of detailed equilibrium. The real-time picosecond self-modulation of the absorption α is measured for the first time. The characteristics of this self-modulation as well as absorption α and intrinsic emission self-modulation characteristics measured previously by correlation methods are now accounted for by the concept of synchronization.     

Chiral Linked Systems as a Model for Understanding D-Amino Acids Influence on the Structure and Properties of Amyloid Peptides

In this review, we provide an illustration of the idea discussed in the literature of using model compounds to study the effect of substitution of L- for D-amino acid residues in amyloid peptides. The need for modeling is due to the inability to study highly disordered peptides by traditional methods (high-field NMR, X-ray). At the same time, the appearance of such peptides, where L-amino acids are partially replaced by D-analogs is one of the main causes of Alzheimer’s disease. The review presents examples of the use diastereomers with L-/D-tryptophan in model process—photoinduced electron transfer (ET) for studying differences in reactivity and structure of systems with L- and D-optical isomers. The combined application of spin effects, including those calculated using the original theory, fluorescence techniques and molecular modeling has demonstrated a real difference in the structure and efficiency of ET in diastereomers with L-/D-tryptophan residues. In addition, the review compared the factors governing chiral inversion in model metallopeptides and Aβ42 amyloid.     

Investigation of the mechanism and kinetics of dissolution of nickel(II) and nickel(III) oxides in sulfuric acid

Based on the experimental data on the effect of pH and the H₂SO₄ concentration on the dissolution rate of nickel oxides, the nature of the limiting stage is revealed, which consists in the formation of surface compounds and their subsequent transfer into the electrolyte solution. The intermediate products of dissolution of nickel(II) oxide in sulfuric acid are identified.