Acid-base properties of phosphorus compounds 12. Stereochemistry of H-bonded complexes of phosphorus compounds

Conclusions Measurements of the dipole moments of R₃P = O... HOR' type complexes with weak H-bonding (_H0) have shown that the angle of coordination of the phosphoryl group at the H-bond to be 109 ± 6°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1531–1534, July, 1977.     

Absorption saturation properties and laser Q-switch performance of Cr<Superscript>5+</Superscript>-doped YVO<Subscript>4</Subscript> crystal

The ground-state and excited-state absorption cross sections of a Cr⁵⁺:YVO₄ single crystal were determined by the intensity-dependant transmission measurements to be(2.0±0.4)×10^-18 cm² and less than 0.1×10^-18 cm² at 1.08 μm, respectively. The bleaching relaxation time of the Cr⁵⁺:YVO₄ crystal was estimated to be 3.5±1.5 ns. Passive Q-switching of a diode-pumped Yb³⁺:YVO₄ laser with the Cr⁵⁺:YVO₄ saturable absorber was realized. PACS 42.55.Xi; 42.60.Gd; 42.70.Hj     

Diode-pumped continuous-wave Nd:YVO<Subscript>4</Subscript> laser with self-frequency Raman conversion

Continuous-wave operation of a diode-pumped Nd:YVO₄ laser with self-frequency Raman conversion is demonstrated. The threshold of Raman generation was measured to be 1.3 W of laser diode power. The maximum output power of Stokes radiation at the wavelength of 1177 nm was up to 50 mW at a laser diode pump power of 2.3 W, corresponding to the slope efficiency of 5%. The beam quality M² of the Stokes radiation was about 1.4. The fluctuations of the Stokes power were minimised down to 4%. PACS 42.55.Ye; 42.60.Pk; 42.65.Dr     

Disruption of Shaped‐Charge Jets by a Pulsed Current

This paper gives results from experimental studies of the effect of electricpulse parameters on the development of current instability and disruption of shapedcharge jets. A simple physical model for the development of current instability and the decrease in the cavern depth in the target is proposed. Notations are introduced and analytical expressions are obtained for the critical current (critical linear current density) and the ideal shape of the current pulse required for the disruption of shapedcharge jets. It is shown that the estimate of the final cavern depths in steel target for the proposed model is in fairly good agreement with both experimental values of cavern depths in targets and with the results of numerical calculations using quasitwodimensional unsteady models of MHD instability and volume disruption.     

pH-Dependent Photoinduced Interconversion of Furocoumaric and Furocoumarinic Acids

Photo-controlled or photo-regulated molecules, especially biologically active and operating in physiological conditions, are in steady demand. Herein, furocoumaric and furocoumarinic acids being (Z/E)-isomers relative to each other were obtained in two stages starting from psoralen: the alkaline solvolysis of psoralen led to furocoumaric acid, which was further Z → E photoisomerized (365 nm) to furocoumarinic acid. The kinetics of Z → E photoisomerization was monitored by HPLC and UV-vis spectrophotometry. Photophysical characteristics in the aqueous phase for both acids, as well as the reversibility of (Z/E) photoisomerization process, were also assessed. Furocoumarinic acid was found to be visibly fluorescent at pH 2.0–12.0, with the maxima of fluorescence emission spectra being pH-dependent. The reverse E → Z photoisomerization predicted by quantum chemistry calculations as energetically favorable for the monoanionic form of furocoumarinic acid was proved in the experiment while being complicated by pyrone ring closure back to psoralen in acidic and neutral conditions. The preparative synthesis of furocoumarinic acid outlined in this work is particularly valuable in view of a wide range of pharmacological effects previously predicted for this compound.     

The stability of the set of equilibrium positions of autonomous mechanical systems with sliding friction

Problems of the stabiity of the set of equilibrium positions of autonomous differential equations, to which the equations of motion of mechanical systems with sliding friction can be reduced, are considered (see [1, 2]). The structure of the equations, due to the specific features of the system, is taken into account substantially and the general properties of motions, investigated previously in [3, 7], and the sets which arise when analysing the equations and which possess the properties of the absolute sector are used.