Eine im unteren Theile aus Milchglas bestehende Kochflasche

Ohne Zusammenfassung     

{Δ‐1,4,7,10‐Tetrakis[(S)‐2‐hydroxy­propyl‐κO]‐1,4,7,10‐tetra­aza­cyclo­do­dec­ane‐κ4N}cad­mium(II) 4‐nitrophenolate per­chlor­ate hydrate

Crystallization of [Cd(S‐thpc12)](ClO₄)₂·H₂O {S‐thpc12 is 1,4,7,10‐tetra­kis[(S)‐2‐hy­drox­y­propyl]‐1,4,7,10‐tetra­aza­cy­clo‐do­dec­ane} in the presence of sodium p‐nitrophenolate forms the title complex, [Cd(C₂₀H₄₄N₄O₄)](C₆H₄NO₃)(ClO₄)·H₂O, in which p‐nitrophenolate and water separately hydrogen bond to a different pair of cis‐related pendant hydroxyl groups which, together with the four N atoms, are themselves bound to Cd^II in an approximately square antiprismatic arrangement. The diastereoselectivity of the complex‐forming process is apparent from the fact that both different disymmetric cations in the asymmetric unit have the same Δ helicity.     

Morse�CSmale theory for flows on covering spaces of compact manifolds

For a dynamical system X on a compact differentiable manifold M and for the dynamical system X(ρ) induced from X by a covering map r :  [(M)\tilde] ?  M{\rho \, : \, \widetilde{M}\, \rightarrow \, M}, we develop algebraic topology methods for estimating the lower bounds on the number of codimension-1 surfaces (i.e., on the number of index-1 equilibria of flows and their stable manifolds) on the boundary of regions of stability on [(M)\tilde]{\widetilde{M}}. We also develop methods for estimating the number of equilibria on the boundaries of stability regions of noncompact manifolds with very general assumptions. Our methods allow us to obtain results for noncompact manifolds in cases when Morse–Smale approach does not work.     

Synthesis of alkylpyrroles by use of a vinamidinium salt

The synthesis of alkyl-substituted 2-pyrrolecarboxylate esters has been accomplished by the condensation reaction of a symmetrical vinamidinium salt and glycine ester derivatives.     

Modelling the Flow of Carbon Dioxide Through Beds of Cereal Grains

The insect population in grain stores can be kept under control by maintaining a high concentration of CO₂ gas (greater than 35%) throughout the grain bed. In this paper the initial phase of this process is considered, where the gas is introduced into the bed. The flow of CO₂ through the grain bulk is modelled as fluid flow in a porous medium and the effect of advection, dispersion, sorption and curvilinear isobars and streamlines are considered. An analytic solution to this problem is developed using perturbation expansions and the analysis is restricted to the dominant term in each expansion. In curvilinear flow, a useful variable is the traverse time; the time taken for the gas to travel from the inlet duct. It is shown that lines of constant traverse time are also lines of constant CO₂ concentration throughout the grain bed except in the narrow region called the front, where the concentration gradient is large. For most grain stores the isobars have a negative curvature and in these situations the front moves more slowly than in uniform flow and the width of the front increases more rapidly as it travels through the grain bed. It is shown that sorption has an effect on the CO₂ concentration in the air for some grains such as canola but not for others such as wheat.     

Performance-based design of permeation test cells for reliable evaluation of chemical protective materials

The test cell constitutes the core functionality of a permeation testing system. Accuracy of an experimental methodology depends on the ability of the test cell to efficiently deliver the challenge agents to the test material, collect all the transported permeate compounds from the test material and transfer those analytes to the online detector. Common test cell designs used in the US and internationally form the basis of their respective testing procedures. However, widespread usage does not necessarily equate to defensible assurance of analytical reliability. Consequently, chemical protective materials characterized with these cells may provide inadequate protection to users whose health and safety depend on barrier garments such as gloves and suits. Permeation test data, including those acquired in our laboratory, have emphasized the significance of test cell design on the accuracy of permeation measurements. This paper describes the key considerations necessary to ensure analytical reliability for a test cell, illustrates quantitative improvements demonstrated by existing prototypes and, finally, proposes a design which further advances the technology of permeation testing.     

Formation of simple organic molecules in the interstellar medium

In this work we present a methodology for the synthesis of simple molecules from basic formaldehyde (H₂CO) precursors. We have approached this challenging problem by considering a basic dimerization scheme that eventually leads to diose and methyl formate, using an HCO⁺ proton source. This species was chosen due to its ample abundance in the atmosphere. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Stress effects on the anisotropic thermal expansions of “martensitic” A15 compounds

Precision capacitance dilatometry provides a sensitive measure of the thermal strain developed in a sample undergoing a structural distortion with its varying temperature. The A15 structure compounds, V₃Si and Nb₃Sn, are well known to undergo distortion from their cubic structures at room temperature to tetragonal structures (c/a > 1 for V₃Si and c/a < 1 for Nb₃Sn) at low temperatures. In the past, highly anomalous thermal expansion behaviour recorded for these materials has been attributed to a strongly anharmonic lattice potential manifesting itself in unusually high, and strongly temperature-dependent, Grüneisen parameters. Further studies on polycrystalline material revealed this anomalous expansion to be highly anisotropic at temperatures for which, according to conventional diffraction data, the materials are cubic. This behaviour was linked to control of sample morphology by a residual stress field resulting from sample preparation.

More recent experiments, in which the transformation morphology has been controlled by the application of external stresses to single crystal V₃Si and polycrystalline samples of Nb₃Sn and Nb₃(Sn_1-x Sb _x ), have confirmed the occurrence of significant anisotropy in the thermal strain in the cubic phase, well above the structural transformation.

We link this departure from cubic symmetry with the well-known soft-mode character of these materials and the associated “central peak” scattering which is also observed well above the transformation temperature. We are led to propose that the “central peak” is the precursor to a Bragg reflection for the transformation structure. This coincidence between “central peak” scattering and the reciprocal lattice for the transformed phase in Ti-Ni has been termed a “ghost lattice”.