Modelling of synchrotron SAXS patterns of silicalite-1 zeolite during crystallization

Synchrotron small angle X-ray scattering (SAXS) was used to characterize silicalite-1 zeolite crystallization from TEOS/TPAOH/water clear sol. SAXS patterns were recorded over a broad range of length scales, enabling the simultaneous monitoring of nanoparticles and crystals occurring at various stages of the synthesis. A simple two-population model accurately described the patterns. Nanoparticles were modeled by polydisperse core-shell spheres and crystals by monodisperse oblate ellipsoids. These models were consistent with TEM images. The SAXS results, in conjunction with in situ light scattering, showed that nucleation of crystals occurred in a short period of time. Crystals were uniform in size and shape and became increasingly anisotropic during growth. In the presence of nanoparticles, crystal growth was fast. During crystal growth, the number of nanoparticles decreased gradually but their size was constant. These observations suggested that the nanoparticles were growth units in an aggregative crystal growth mechanism. Crystals grown in the presence of nanoparticles developed a faceted habit and intergrowths. In the final stages of growth, nanoparticles were depleted. Concurrently, the crystal growth rate decreased significantly.     

Job assignment in large-scale service systems with affinity relations

We consider load balancing in service systems with affinity relations between jobs and servers. Specifically, an arriving job can be assigned to a fast, primary server from a particular selection associated with this job or to a secondary server to be processed at a slower rate. Such job–server affinity relations can model network topologies based on geographical proximity, or data locality in cloud scenarios. We introduce load balancing schemes that assign jobs to primary servers if available, and otherwise to secondary servers. A novel coupling construction is developed to obtain stability conditions and performance bounds. We also conduct a fluid limit analysis for symmetric model instances, which reveals a delicate interplay between the model parameters and load balancing performance.

     

Lines,Trees, and Branch Spaces

In this paper we examine the interactions between the topology of certain linearly ordered topological spaces (LOTS) and the properties of trees in whose branch spaces they embed. As one example of the interaction between ordered spaces and trees, we characterize hereditary ultraparacompactness in a LOTS (or GO-space) X in terms of the possibility of embedding the space X in the branch space of a certain kind of tree.     

Effect of collision and magnetic field on quantum beat in biacetyl

Molecular quantum beats are shown for the case of biacetyl, to vary strongly under the influence of weak magnetic fields. Values for dephasing constants for a gas-phase molecular system were determined. Information on sub-Doppler level splittings in the intersystem-crossing process is obtained.     

Mathematics Assessment: Practices and Reporting Methods

The curriculum, teaching, and assessment Standards of the National Council of Teachers of Mathematics advocate the use of various assessment techniques in mathematics, K-12. Practitioners from 35 school districts in two regions of a midwestern state completed a questionnaire and reported information about their assessment practices, reporting methods, and other issues that affect change in mathematics. The results of the survey suggest that current reporting practices are limiting the use of alternative classroom assessment practices. Delays in the use of alternative mathematics assessment practice can probably be expected until the reporting systems used in school districts become consistent with the assessment systems and teachers participate in ongoing professional development programs to learn more about alternative assessment practices.     

NMR-Untersuchungen über inter- und intramolekulare Wechselwirkungen in substituierten Trifluormethylphenylisocyanaten,Fluorphenylisocyanaten, in Fluoranilin und Fluornitrobenzol

The temperature and solvent concentration (carbon tetrachloride) dependence of the chemical shifts of the fluorine and proton signals of substituted trifluoromethylphenylisocyanate, fluorophenylisocyanate, fluoroaniline and fluoronitrobenzene are investigated. The temperature effect on the chemical shifts of the fluorine signals of the ortho-substituted trifluoromethylphenylisocyanate originates from the intramolecular interaction of the trifluoromethyl groups and the ortho-substituents, resulting in an increase of the chemical shifts with rising temperature. The temperature dependence of the electron distribution of meta- and para-substituted trifluoromethylphenylisocyanates is mainly attributed to intermolecular interactions, causing a decrease of the chemical shifts of fluorine signals with increasing temperature. The protons of the investigated compounds, being localized on the ‘molecular surface’, show a temperature dependence of the chemical shifts due to the van der Waals effect. Increasing the amount of the solvent (carbon tetrachloride) leads to a weakening of the anisotropy effect and causes an increase of the chemical shifts of the fluorine and proton signals of all investigated compounds.