Stability of the advective flow in a horizontal rectangular channel with adiabatic boundaries

The steady-state advective flow in a long horizontal rectangular channel with rigid adiabatic boundaries in the presence of a uniform longitudinal pressure gradient is investigated. The stability of this flow with respect to perturbations of various types is studied. The dependence of the critical Rayleigh number on the Prandtl number is found for various aspect ratios.     

Effect of normal vibrations of a flat horizontal heater on the second boiling crisis

The effect of normal vibrations of a flat horizontal heater on the second boiling crisis is considered within the framework of the hydrodynamic theory of boiling crises. The critical heat flux is estimated by characteristics of growth of the most dangerous disturbances destroying the liquid-vapor interface. As the vibration intensity increases, the interface can be destroyed either owing to the Rayleigh-Taylor instability or by virtue of parametrically excited disturbances with wavelengths corresponding to resonance zones. In the domain of parameters where the parametric instability in the first resonance zone is the most dangerous factor, it is possible to significantly reduce the critical heat flux, as compared with the value corresponding to the case with no vibrations. With a further increase in vibration intensity, the critical heat flux increases as a whole. The nonmonotonic character of the critical heat flux as a function of vibration intensity allows an effective control of the critical heat flux whose value can be made higher or lower than the value in the case without vibrations. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 4, pp. 88–97, July–August, 2006.     

Effect of high-frequency vibrations on oriented crystallization of binary alloys

The effect of high-frequency rotational vibrations with small amplitude on the oriented crystallization of binary alloys has been numerically studied. The calculations have been made in the framework of the quasi-static approach for succinonitrile-acetone and succinonitrile-salol binary systems. It has been shown that at a large solidification rate and/or high impurity concentration both for a lighter impurity (acetone) and for a heavier one (salol) a pit is formed on the axis of symmetry during growth which accelerates the development of morphological instability. Rotational vibrations make a strong stabilizing effect. The threshold for morphological instability increases with an increase in the vibration intensity, the radial segregation of an impurity decreases, and the pit is not formed.     

Laboratory Service at the Fedorovskii All-Russia Institute of Mineral Resources

This paper briefly outlines the history of analytical laboratories at the Fedorovskii All-Russia Institute of Mineral Resources (VIMS). These laboratories have recently been affiliated with the Federal Guidance Center of Laboratory Research and Certification of the Ministry of Natural Resources of Russia.     

The polymerization of acryl pentaerythrol derivatives initiated by visible light

The photopolymerization of pentaerythrol triacrylate and its chloroacetyl derivative under the action of visible light in the presence of a camphorquinone initiator was studied in real time. Photopolymerization occurred at a low rate with a 40% monomer conversion. The introduction of the chloroacetate group accelerated polymerization only insignificantly, but monomer conversion remained unchanged. The use of donor-acceptor initiating systems (tert-aminocamphorquinone) increased the rate of polymerization by approximately an order of magnitude. The main reason for this effect was an increase in the quantum yield of initiator photodissociation in the presence of tert-amines. The rate of the polymerization of monomers did not correlate with the ionization potentials of amines and, therefore, the rate of radical generation. The camphorquinone-amine system formed a quaternary salt with pentaerythrol triacrylatechloroacetate. This salt hindered exciplex formation.     

Flow induced by a vibrating heated sphere

Mean flows induced by a heated or cold sphere vibrating in a liquid are studied. The cases of a sphere immersed in an unbounded liquid and a liquid layer of finite thickness, bounded by two rigid coaxial spheres, are considered. An analytical solution is obtained in the creeping flow approximation for small values of the governing parameters. The vibrating flow structure is shown to depend to a considerable extent on the clearance and to be fairly complex for small clearances. For a fixed clearance, the creeping flow structure is determined by a single parameter, the ratio of the vibrating Grashof number to the pulsating Reynolds number (Schlichting parameter). For large values of the parameters, the vibrating flow structure is determined by the vibrating Grashof number and the Schlichting parameter separately. The changes in the flow structure with increase in the values of the governing parameters are studied numerically by a finite difference method.Krasnoyarsk. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 31–39, January–February, 1996.     

Control of Thermo- and Solutocapillary Flows in FZ Crystal Growth by High-Frequency Vibrations

The paper deals with the numerical investigation of the possibilities to control convective flows in the liquid bridge in zero gravity conditions applying axial vibrations. The surface tension is assumed to be dependent both on the temperature and on the solute concentration. The free surface deformations and the curvature of the phase change surfaces are neglected but pulsational deformations of the free surface are accounted for. The first part of the paper concerns axisymmetric steady flows. The calculations show that the evolution of convective flow with the variation of thermal Marangoni number at a fixed value of the solutal Marangoni number is accompanied by the hysteresis phenomenon, which is related to the existence of two stable steady regimes in a certain parameter range. One of these regimes is thermocapillary dominated, it corresponds to the two-vortex flow, and the other is solutocapillary dominated, it corresponds to the single-vortex flow. Under vibrations, the range of the Marangoni numbers where hysteresis is observed becomes narrower and is shifted to the area of larger values. The second part of the paper concerns the stability of axisymmetric thermo-and solutocapillary flows and the transition to three-dimensional regimes. Significant mutual influence of flows generated by each process on the stability of the other is discovered. Stability maps in the parametric plane for the thermal Marangoni number, the solutal Marangoni number, are obtained for different values of vibration parameters. It is shown, that vibrations exert a stabilizing effect, increasing critical Marangoni numbers for all modes of instability. However, this effect is different for different modes and at high vibration intensity destabilization is possible. Consequently, vibrations can modify the scenario of the transition to the three-dimensional mode.     

Electronic structure and spectra of binuclear bridged nitrosyl ruthenium complexes

The B3LYP method in the LanL2DZ basis set was used to carry out geometry optimization for the binuclear bridged complexes [RuCl₄(NO)(μ-Pyz)Ru(P)(CO)]^?, [Ru(Bipy)₂(NO)(μ-Pyz)Ru(NH₃)₅]⁵⁺, and [(NC)Ru(Py)₄(μ-CN)Ru(Py)₄NO]³⁺ (Pyz is pyrazine). The electronic spectra of the complexes were calculated by the TDDFT and CINDO-CI methods with allowance for solvation effects. The ground-state electronic configurations of the two ruthenium atoms in these compounds were shown to be different. Among the lower excited states of all complexes, states with essentially weakened Ru-NO bonds were found. The strong absorption in the visible region of the spectrum of [Ru(Py)₄NO-CN-Ru(Py)₄CN]³⁺ is due to the interfragment electron transfer Ru^II → {RuNO} accompanied by weakening of the bond between nitrogen oxide and the complex.