Calculation and comparison of the acid-base equilibrium constants for nickel(II) oxide determined by various methods

Methods for determining acid-base equilibrium constants at the nickel-electrolyte interface are developed. The methods are based on the principles of potentiometric titration, “powder addition”, and dependence of electrokinetic potential on pH. A correlation between the values of the constants determined by the different methods is found.     

Modelling the transverse magnetic field generated by equipment in arc welding

The design of equipment for generating the transverse magnetic field in arc welding can be optimised by modelling the direct magnetic field produced by the device for generating (GD) the transverse magnetic field (TMF) by the electric field of the current flowing in flat models made of electrically conducting materials. The lines of force of the electric field in the flow of the current in the modelling medium correspond to the lines of force (induction lines) of the magnetic field generated by GD TMF. Using these modelling methods, it is shown that to obtain the maximum values of the transverse component of the induction of the magnetic field in the zone of the welding arc of the electrode droplet and liquid metal of the weld pool, the optimum design of GD TMF is the one in which the angle of inclination of the bars to the vertical is equal to 45° and the end surfaces have chamfers parallel to the plane of the welded sheets.     

“LO-Phonon” correlation between picosecond superluminescence spectrum and special features of absorption spectrum in GaAs for non-Fermi distribution of carriers induced by picosecond light pulse

Dense electron-hole plasma (EHP) was generated in a GaAs layer by a picosecond light pulse. Superluminescence phenomenon and local deviations of the light-absorption spectrum from that calculated for the Fermi distribution of EHP were observed. Deviations in the enhancement region, where the measured gain is less than the calculated one, and in the absorption region, where the opposite relation takes place, were named the “hole” and the “protrusion”, respectively. The shape of the hole was similar to the shape of the superluminescence spectrum in the spectral region of the hole, as well as to the shape of the protrusion in the absorption spectrum. Both the spectral width of the spike, which was roughly equal to that of the hole, and its spectral position with respect to the superluminescence spectrum were governed by the energy of the longitudinal optical phonon. These correlations were attributed to superluminescence-induced depletion of levels at the conduction-band bottom and their filling with electrons due to the emission of longitudinal optical phonons.     

Modulation of the characteristics of intense picosecond stimulated emission from GaAs

Intense picosecond stimulated emission from the face of a thin GaAs film is studied. The emission is observed when GaAs is pumped with high-power picosecond optical pulses. It is found that the dependences of the emission energy on the photon energy, the picosecond delay between two pump pulses, and the distance between the active region and the face are modulated. Modulation is taken to mean the appearance of protrusions or peaks in any of the mentioned dependences. The modulation parameters for the dependences under consideration are found to be related by expressions that make it possible to suggest the following. The modulation of characteristics is caused by a common (not yet conclusively identified) mechanism of self-modulation of the emission spectrum. This mechanism is related to an ultrafast nonlinear interaction between a highly photoexcited semiconductor and the pump radiation and stimulated emission. There is indirect evidence that this mechanism also gives rise to an amplitude modulation of the emission in a picosecond time interval.     

A local specific feature of variation in the spectrum of picosecond superluminescence upon adding excited carriers to a non-Fermi electron-hole plasma in GaAs

Semiconductors - A dense hot electron-hole plasma and picosecond superluminescence appeared upon pumping of a GaAs layer by a picosecond (ex) optical pulse. The distribution of electrons over the...     

Repetition of the shape of the ultrafast self-modulation of the optical absorption spectrum upon varying the energy of pulse of GaAs pumping

Ultrafast self-modulation of the fundamental optical absorption emerges during intense picosecond optical pumping of GaAs and, according to the main assumption, reflects self-oscillations of depletion of electron populations in the conduction band. In this study, the quantitatively confirmed explanation of previously experimentally found cyclic repetition of the form of ultrafast self-modulation of the absorption spectrum upon varying the energy of the pumping pulse and fixed delay between pumping and probing (the measurement of absorption) is given. Repetition of the shape is explained by varying the phase of self-oscillations of the optical absorption. The explanation is based on the previously found experimentally dependence of the frequency of self-oscillations of absorption on the pumping energy. Therefore, this is also a new confirmation of the mentioned dependence (which satisfactorily coincides with a similar calculated dependence of the frequency of self-oscillations of depletion of populations).     

Transition from an Exponential to Linear Increase in the Energy Density of the Spectral Component of Picosecond Stimulated Emission by GaAs upon Gain Saturation

Semiconductors - At the beginning of high-power optical picosecond pumping of the GaAs layer of the AlxGa1 – xAs–GaAs–AlxGa1 – xAs...     

Changes in the spectra of picosecond stimulated emission from GaAs accompanied by signs of electron-phonon interaction

A nonmonotonic variation in the width of the emission spectra ?????_s of GaAs as the energy of the pump photon ???_ex is varied is observed at a fixed energy of a picosecond pump pulse W _ex giving rise to intrinsic stimulated emission. In the case of this nonmonotonic variation, the largest width of the spectra has been found to be close to the parameter ??, which is determined by the energy of a longitudinal optical (LO) phonon and by the masses of an electron and a heavy hole. As the nonmonotonicity of the dependence ?????_s = f(???_ex) becomes more pronounced, modulation of this dependence and the dependence of the spectrum amplitude on ???_ex are observed. The modulation features signs of relation to the electron-LO-phonon interaction. The observed evolution of the modulation is not inconsistent with published suggestions concerning the development and destruction of screening of the electron-LO-phonon interaction in the case of a dense electron-hole plasma. The level of radiation losses in the sample affects the modulation and nonmonotonicity.