Die Nusseltsche Zahl für laminare Strömung im zylindrischen Rohr mit konstanter Wandtemperatur

Summary The Nusselt modulus for laminar flow through a pipe with constant temperature of the walls has been determined as a function of the Peclet modulus. This function is represented by a diagram.     

X-ray mapping of freeze-dried cryosections from biological cells

Elemental mapping of freeze-dried cryosections from biological cells was done using the energy window mode and the quantitative mode. Quantitative mapping requires long measuring times and high electron exposure resulting in inhomogeneous shrinkage and distortion of the cryosection. Collection of X-ray spectra for quantitative analysis of intracellular structures and compartments combined with energy window mapping was found to be sufficiently fast and reliable to reveal inhomogeneities of the element distribution in cells. However, this method is suitable only for mapping elements without overlapping peaks in the X-ray spectrum.     

Spatially resolved ultra-trace analysis of elements combining resonance ionization with a MALDI-TOF spectrometer

A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented. This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry (RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure, laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective of the setup is given and future investigations are outlined.     

Femtodynamics reflected in nanoseconds: bimolecular free electron transfer in nonpolar media

The (free) electron transfer (FET) from electron donor molecules to parent solvent radical cations of alkanes and alkyl chlorides exhibits mechanistic peculiarities that are conditioned by the low polarity of these solvents. Because of the negligible solvation of ions in such systems and the almost complete lack of an activation barrier, the electron jump takes place at the very first encounter of the reactants and, as such, in extremely short times of 相似文献   

On Estimates of the Boltzmann Collision Operator with Cut-off

We present new estimates of the Boltzmann collision operator in weighted Lebesgue and Bessel potential spaces. The main focus is put on hard potentials under the assumption that the angular part of the collision kernel fulfills some weighted integrability condition. In addition, the proofs for some previously known -estimates have been considerably shortened and carried out by elementary methods. For a class of metric spaces, the collision integral is seen to be a continuous operator into the same space. Furthermore, we give a new pointwise lower bound as well as asymptotic estimates for the loss term without requiring that the entropy is finite.     

Comparative study of p‐amino benzhydrazide and m‐amino benzhydrazide by free radicals and free electron transfer

The bimolecular electron transfer from p‐amino benzhydrazide (PABH) and its meta‐derivative (m‐amino benzhydrazide (MABH)) to specific one‐electron oxidant results in the formation of anilino radical. In case of PABH, reaction with ^?OH radicals results in the synchronous formation of adduct as well as anilino radical. The interesting observation is that the yield of the anilino radical increases with increase in pH. The effect of substitution also has a significant effect on the formation of adduct. In case of MABH, significant yield of anilino radical gets form on reaction with ^?OH radical. The free radical electron transfer from PABH and MABH to parent radical cation of non‐polar solvent also results in the formation of anilino radical only suggesting that the radical cation of PABH and MABH has short life time. The above results were supported by quantum chemical calculations. Copyright © 2013 John Wiley & Sons, Ltd.     

The formation of biaxial nematic phases in binary mixtures of thermotropic liquid-crystals composed of uniaxial molecules

ABSTRACT

Monte Carlo simulations in the isothermal-isobaric ensemble are used to investigate the formation of an ordered, biaxial nematic phase in a binary mixture of thermotropic liquid crystals. The orientational dependence of the interaction between molecules of each pure component is the same as in the well-known Maier-Saupe model; each pure component of the mixture is therefore capable of forming a uniaxial nematic phase. For the interaction between molecules of different components, we use the same Maier-Saupe model but change the sign of the coupling constant. As a consequence a T-shaped arrangement of these molecules is energetically favoured. The formation of the biaxial phase occurs in two steps. At higher temperatures T, one of the components forms a uniaxial nematic phase whereas the other is in a quasi two-dimensional restricted isotropic liquid state. We develop a simple theoretical model to understand the high degree of (ostensible) nematic order in the latter. At lower T, the second component becomes nematic and then the entire mixture of the two compounds has biaxial symmetry. The biaxial nematic phase does not demix into domains rich in molecules of one or the other species.