Taylor-Görtler vortices in the flow driven by a rotating magnetic field in a cylindrical container

Taylor-Görtler vortices play an important role in the flow driven by rotating magnetic field in a closed cylindrical container. The visualization of these structures is essential to understand their physics and their impact on the dynamics of the flow. We present a study of various methods for identifying vortex cores, including the so-called λ₂ andQriteria. While λ₂ is, probably, the better indicator it is more sensitive to numerical noise and thus less effective in devising 3D vortex structures. Here, the Q criterion proved particularly useful when applied to the fluctuation velocity field.     

Multinuclear enantiopure titanium self‐assembly complexes—synthesis,characterization and application to organic synthesis

Hexa‐ and nonanuclear titanium complexes were obtained by self‐assembly of titanium(IV)‐tert‐butoxide and D ‐mandelic acid. Suitable single crystals of these complexes were characterized by X‐ray structure analysis. When used with these complexes, aldol adducts were isolated with a high degree of regioselectivity in direct aldol additions of aromatic and aliphatic aldehydes to functionalized unsymmetrical ketones. High syn‐diastereoselectivities were obtained in aldol additions of enolizable aldehydes with hydroxyacetone and methoxyacetone. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical study of the electric field effect on ion-molecule reactions in diluted gases and solutions

In diluted gases the rate coefficients of ion-molecule reactions in an electric field depend on the characteristic ratio $\text{E}{}_{\mathrm{<mtext>P</mtext>}}\text{k}{}_{\mathrm{<mtext>B</mtext>}}\text{Θ}$ where E_P represents the energetic threshold for the reaction and k_BΘ is the mean kinetic energy summarizing both electric field effects and collision processes within a two-temperature model. Using the Lorentz-gas concept the model can be precised from a microscopic point of view by solving a kinetic equation for the ionic component.In diluted solutions like in gases the field effect on ion-molecule reactions depends on the energy gain of the ions by the electric field. However, the field effect is considerably reduced here because of the small magnitude of the mean free path in liquids. In addition the rate constant modification by the field depends on the ratio of the ion diffusion coefficient to the sum of the diffusion coefficients of both the reactants.     

Scalar dynamic nuclear polarization of protons in trifluoroacetic acid solutions

Strongly scalar ¹H intermolecular dynamic nuclear polarization (DNP) of solvent ¹H nuclei in solutions of organic free radicals has now been observed at room temperature. Transient protonation of the CF₃COOH/pyridyl imidazoline-1-oxyl radical system accounts for the observed effects.     

Martinaxiom und die Beschreibung gewisser Homomorphismen in der Theorie der ℵ1-freien abelschen Gruppen

P(I) denotes the abelian group of integer-valuated functions defined on the set I, P_κ (I) its subgroup consisting of all elements, which support has size less than the infinite cardinal κ and Q_κ (I) the quotient P(I)/P_κ(I). We formulate a statement I(κ) in the following way: For an arbitrary set I you can lift every homomorphism from P (?) to Q_κ(I) to a homomorphism from P(?) to P(I). Using Martin's Axiom we show, that L(?) is independent of ZFC.     

Microwave spectrum and structure of cyanamide: Semirigid bender treatment

An extensive study of the microwave spectrum of cyanamide has been undertaken, the analysis being based in part on semirigidbender calculations by the methods of Bunker and Szalay. Inversion lines of NH₂CN, $\text{K}{}_{\mathrm{?1}}\text{= 2}{}^{\mathrm{a}}\text{Q}$ branches and a number of vibrational satellites of the J = 2?1 transition were observed. A two-vibrational-state Hamiltonian was used to fit simultaneously the 0⁺ and 0^? microwave data and yielded rotational constants X, Y, Z, D_J, D_JK, d₁, H_JK as well as the inversion splitting and the μ_yz-connecting matrix element. Vibrational satellite data of seven isotopic species and infrared frequencies of NH₂CN were included in the semirigid bender calculations: The NCN spine is nonlinear by ca. 5° in the equilibrium structure of the molecule. Also, $\text{r}{}_{\mathrm{<mtext>NH</mtext>}}\text{A}\text{?}\text{= 0.9994 + 0.0144?}{}^2$; <HNH/2 = 60.39° ? 0.1134?²; $\text{r}{}_{\mathrm{<mtext>NC</mtext>}}\text{A}\text{?}\text{= 1.3301 + 0.0327?}{}^2$ (? is the inversion angle in rad); $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.1645}\text{A}\text{?}$ fixed. The inclusion of the NC bond flexing was necessary in order to reproduce the observed vibrational satellite patterns of NH₂CN, NHDCN, and ND₂CN. The barrier to inversion of the amino group is 510 ± 6 cm^?1 with minima at ±45.0 ±0.2°. The inversion dipole moment is 0.91 ± 0.02 Debye.