Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Features of Reaction of Dialkyl Perfluoroadipic and Perfluoropimelic Acids with Alkyl(Aryl) Methyl Ketones

Reaction of dialkyl esters of perfluoroadipic and perfluoropimelic acids with ketones form diketo esters. The possibility of cyclization of the products is discussed.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 318–321.Original Russian Text Copyright © 2005 by Chapurkin, Litinskii, Baklanov, Leont’eva.     

Resonant Stimulated Raman Scattering from the 23S–11S Forbidden Transition in a Helium Atom

Optics and Spectroscopy - Resonant stimulated Raman scattering (SRS) from the $${{2}^{3}}S{-} {{1}^{1}}S$$ forbidden transition in a helium atom (62.6 nm) via the intermediate...     

A study of nucleation in supersaturated ibuprofen vapor in a flow diffusion chamber

Isothermal nucleation of supersaturated ibuprofen racemate vapor has been experimentally studied in a flow diffusion chamber at 293.3 and 301.2 K. Nucleation rates have been measured in the range of 10⁴?10⁴ cm^?3 s^?1 as functions of supersaturation. According to the first nucleation theorem, the numbers of molecules in critical nuclei have been found and used to determine the nucleation rate and supersaturation values as depending on the sizes of critical nuclei. The comparison of the experimental data with theoretical predictions has shown that the nucleation rates measured as functions of the numbers of molecules in critical nuclei are higher than the rates predicted by the classical theory by six to seven decimal orders of magnitude but, within one order of magnitude, coincide with the rates predicted by a theory previously proposed in a work by one of the authors, in which nucleation clusters were considered to be microscopic objects.     

The Breit equation as a zeroth-order approximation for calculation of the bound-state energy

An equation whose kernel is determined by the one-photon exchange between interacting particles is analyzed in the framework of the Bethe-Salpeter formalism. This equation is considered as a zeroth-order approximation in the calculation of the corrections to the energy levels. This is the Breit equation that takes into account additional small terms (with respect to the parameter (Zα)²). A procedure that employs the Brillouin-Wigner perturbation theory and makes it possible to sequentially take into account the corrections to the energy levels is considered.     

Mixing of two optical frequencies in atomic vapors

It is demonstrated that two optical frequencies can be mixed in a medium with a quadratic non-linearity. The radiation at the difference frequency can be tuned in a wide spectral range and can be generated at moderate pumping powers.     

Formation of an eutectic structure in Al-Mo-Zr alloy crystallization

A eutectic structure has been obtained in crystallization of an Al-Mo-Zr alloy. This structure is represented by lamellar eutectic colonies, consisting of Mo₃Al₈ and Al₂Zr solid solution, between which more disperse triple and double eutectics with Mo₃Al and Mo₂Zr are crystallized.