Stability of rotation of a vane in a flow

The results of investigation of the stability of permanent rotation of a four-blade vane on a weightless rod in the flow of a homogeneous medium are discussed. The rod rotates about a fixed point where a spherical joint is situated. The vane rotates about the second joint fixed at the other end of the rod. The stability of permanent rotation of the vane is studied when the rod coincides with the dynamic symmetry axis of the vane. The results are compared with the one-joint case. It is shown that increasing the number of degrees of freedom leads to “diminishing” the stability domain projection onto the corresponding subspace of parameters. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 11, No. 7, pp. 73–95, 2005.     

An LGN-303 frequency-stabilized He-Ne laser with a modulating attachment

The operating principle and elements of the construction of an LGN-303 frequency-stabilized He-Ne laser with a modulating attachment are considered. The basic parameters of the laser are presented, and some recommendations are given concerning the use of a modulating attachment in He-Ne lasers stabilized with the aid of an iodine absorption cell.     

The effect of the back reflections in an optical discriminator of a double-mode laser

Lidar sounding of iodine molecules were performed at pressures lower than 1 torr. The differential cross-section of fluorescence and the absorption cross-section of iodine molecules at a wavelength of 532 nm were been obtained.     

Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride. Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer

Reaction of [2,3,4,5-Ph(4)(eta(5)-C(4)COH)Ru(CO)(2)H] (2) with different imines afforded ruthenium amine complexes at low temperatures. At higher temperatures in the presence of 2, the complexes decomposed to give [Ru(2)(CO)(4)(mu-H)(C(4)Ph(4)COHOCC(4)Ph(4))] (1) and free amine. Electron-rich imines gave ruthenium amine complexes with 2 at a lower temperature than did electron-deficient imines. The negligible deuterium isotope effect (k(RuHOH)/k(RuDOD) = 1.05) observed in the reaction of 2 with N-phenyl[1-(4-methoxyphenyl)ethylidene]amine (12) shows that neither hydride (RuH) nor proton (OH) is transferred to the imine in the rate-determining step. In the dehydrogenation of N-phenyl-1-phenylethylamine (4) to the corresponding imine 8 by [2,3,4,5-Ph(4)(eta(4)-C(4)CO)Ru(CO)(2)] (A), the kinetic isotope effects observed support a stepwise hydrogen transfer where the isotope effect for C-H cleavage (k(CHNH)/k(CDNH) = 3.24) is equal to the combined (C-H, N-H) isotope effect (k(CHNH)/k(CDND) = 3.26). Hydrogenation of N-methyl(1-phenylethylidene)amine (14) by 2 in the presence of the external amine trap N-methyl-1-(4-methoxyphenyl)ethylamine (16) afforded 90-100% of complex [2,3,4,5-Ph(4)(eta(4)-C(4)CO)]Ru(CO)(2)NH(CH(3))(CHPhCH(3)) (15), which is the complex between ruthenium and the amine newly generated from the imine. At -80 degrees C the reaction of hydride 2 with 4-BnNH-C(6)H(9)=NPh (18), with an internal amine trap, only afforded [2,3,4,5-Ph(4)(eta(4)-C(4)CO)](CO)(2)RuNH(Ph)(C(6)H(10)-4-NHBn) (19), where the ruthenium binds to the amine originating from the imine, showing that neither complex A nor the diamine is formed. Above -8 degrees C complex 19 rearranged to the thermodynamically more stable [Ph(4)(eta(4)-C(4)CO)](CO)(2)RuNH(Bn)(C(6)H(10)-4-NHPh) (20). These results are consistent with an inner sphere mechanism in which the substrate coordinates to ruthenium prior to hydrogen transfer and are difficult to explain with the outer sphere pathway previously proposed.     

On the Possibility of Conversion of Alcohols to Ketones and Aldehydes by Phosphinoboranes R2PBR′R′′: A Computational Study

Can phosphinoboranes promote hydrogenation of carbonyl moieties? By means of B3LYP and MPW1K density functional calculations the likelihood of the oxidation of alcohols by phosphinoboranes R₂PBR′₂ ( 1 ) was explored. As a proof‐of‐principle, a theoretical study that tests the reversibility of the alcohol oxidation is reported. The potential of 1 as a metal‐free hydrogenation mediator is discussed for a series of hydrogen sources such as primary and secondary alcohols.

     

Fluorine dynamics in BaF2 crystal lattice as an example of complex motion in a simple system

Fluorine relaxation profiles for a BaF₂ single crystal collected at several temperatures have been analyzed in terms of essentially different motional models: free rotational and free translational diffusion. The analysis has been performed to critically review the sensitivity of field dependent relaxation studies to mechanisms of molecular motions. The tested motional models do not realistically describe the fluorine dynamics within the crystal lattice. They have been chosen to attempt to answer quite fundamental questions regarding the feasibility of the field dependent nuclear spin relaxation studies to provide unique information on dynamic processes: 1. Is it possible to get information about the motional mechanisms by analyzing relaxation profiles collected in a broad frequency range? 2. To what extent is it possible to reasonably reproduce relaxation profiles in terms of unrealistic motional models?It has been concluded from the analysis that the rotational model leading to a single exponential correlation function explains the experimental data much better than the translational one. Validity regimes of the second order perturbation theory have been discussed in the context of the investigated system and the applied models.     

Electron transfer in uranyl(VI)-uranyl(V) complexes in solution

The rates and mechanisms of the electron self-exchange between U(V) and U(VI) in solution have been studied with quantum chemical methods. Both outer-sphere and inner-sphere mechanisms have been investigated; the former for the aqua ions, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligand. The calculated rate constant for the self-exchange reaction UO(2)(+)(aq) + UO(2)(2+)(aq) <=>UO(2)(2+)(aq) + UO(2)(+)(aq), at 25 degrees C, is k = 26 M(-1) s(-1). The lower limit of the rate of electron transfer in the inner-sphere complexes is estimated to be in the range 2 x 10(4) to 4 x 10(6) M(-1) s(-1), indicating that the rate for the overall exchange reaction may be determined by the rate of formation and dissociation of the binuclear complex. The activation energy for the outer-sphere model calculated from the Marcus model is nearly the same as that obtained by a direct calculation of the precursor- and transition-state energy. A simple model with one water ligand is shown to recover 60% of the reorganization energy. This finding is important because it indicates the possibility to carry out theoretical studies of electron-transfer reactions involving M(3+) and M(4+) actinide species that have eight or nine water ligands in the first coordination sphere.