Measurement of the spectral brightness of terahertz radiation in the process of nonlinear-optical detection

A method has been proposed for the absolute measurement of the spectral brightness of terahertz radiation in the process of the parametric frequency conversion to the optical range. The method has a low threshold flux and does not require extrinsic references. The method simultaneously allows for the calibration of thermal fluctuations and the determination of the absolute local temperature of a nonlinear converter crystal.     

Dependence of the thermodynamic characteristics of forms of hydrogen adsorbed on a porous nickel surface on the degree of deactivation

Thermodynamic characteristics of the adsorption equilibria of individual forms of adsorbed hydrogen are calculated using data from adsorption-calorimetric studies of liquid-phase hydrogenation in a model of a surface with discrete nonuniformity in the ideal adsorption layer approximation under conditions of liquid-phase hydrogenation. It is shown that partial deactivation raises the fraction of the molecular α form via the atomic β form of adsorbed hydrogen and increases the adsorbate-adsorbent binding energy.     

Effect of low molecular additives on the electrospinning of nonwoven materials from a polyamide-6 melt

The effect of low molecular additives on the structure and properties of polyamide-6-based nonwoven materials obtained via electrospinning from a melt is studied. The introduction of up to 10% salts of higher fatty acids into the polymer melt leads to a decrease in its viscosity and to an increase in its electrical conductivity, thereby making it possible to produce nonwoven materials with an average fiber diameter of <1.5 µm. With the use of DSC, IR spectroscopy, and X-ray diffraction, it is shown that, in nonwoven materials based on polyamide-6, the metastable γ form of crystals prevails, while, in the native polymer, the stable a form predominates. The resulting materials demonstrate high filtration characteristics, and their surface properties are close to superhydrophobic.     

N-Lithium derivatives of aliphatic amines in the synthesis of 1-alkyl-2-phenyldiazene 2-oxides

Magnesium derivatives of aliphatic amines containing -hydrogen atoms, in contrast to t-BuNHMgBr, do not form phenylaliphatic diazene oxides upon reaction with nitrobenzene, but rather reduce it to azobenzene and azoxybenzene. Asymmetric diazene oxides are formed when the magnesium derivatives are replaced by lithium derivatives. The reaction of t-BuNHLi with dimethylnitramine gives 1,3,5-trimethyl-1,3,5-triazacyclohexane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1452–1454, June, 1991.     

Generation of nanosecond terahertz pulses by the optical rectification method

The possibility of the generation of quasi-cw terahertz radiation by the optical rectification method for broad-band Fourier unlimited nanosecond laser pulses has been experimentally demonstrated. The broadband radiation of a LiF dye-center laser is used as a pump source of a nonlinear optical oscillator. The energy efficiency of terahertz optical frequency conversion in a periodically polarized lithium niobate crystal is 4 × 10⁻⁹ at a pump power density of 7 MW/cm².     

Observation of the quasar 3C47 with the interferometer URAN at decametric wavelengths

Preliminary results of the observation of the angular structure of the quasar 3C47 at 20 and 25 MHz using the URAN-1 interferometer are presented. The most probable model of the brightness distribution of this source at decameter wavelengths has been determined. This model consists of two extended components having angular dimensions about 22 arcsec and separated by about 50 arcsec.Radioastronomical Institute, Ukrainian Academy of Sciences, Khar'kov. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 6, pp. 511–521, June, 1995.     

Superelasticity and the propagation of shock waves in crystals

The separation of a shock wave into an elastic precursor and a plastic wave is a characteristic phenomenon occurring only in solid media. The existence of the elastic shock wave at pressures p ≈ 10 GPa, which is one or two orders of magnitude higher than the dynamic elastic limit, has been detected in recent numerical calculations and a femtosecond laser experiment. The plastic shock wave has no time to be formed in these ultrashort waves at p ≈ 10 GPa. The processes of the formation and propagation of the elastic and plastic waves in aluminum at higher pressures obtained by means of femtosecond lasers have been analyzed in this work. It has been found that the elastic precursor survives even under the conditions when the pressure behind the plastic front reaches a giant value p ∼ 1 Mbar at which the melting of the metal begins. It has been shown that superelasticity should be taken into account to correctly interpret the preceding laser experiments.