1H spin-lattice relaxation and observation of interfacial material in solid polyethylenes

The ¹H NMR laboratory- and rotating-frame (LF,RF) spin-lattice relaxation (SLR) behaviour in solid polyethylenes is reviewed in light of the two region spin diffusion coupled model. Highly crystalline high-density materials show single T¹ values indicative of the fast diffusion limit whilst RFSLR is close to the slow diffusion limit, allowing direct determination of the dimensions of the crystalline and disordered regions. The LFSLR and RFSLR of the HDPE's suggest the existence of an interfacial material which the SLR behaviour includes as part of the crystalline region in contrast to XRD and DSC. ¹³C CPMAS measurements of ¹H RFSLR in a LLDPE provide an additional insight into this problem. The ¹H RFSLR is best represented by a superposition of two exponentials, measured by either ¹H or ¹³C NMR. The ¹H RFSLR, measured at different chemical shifts in the ¹³C NMR spectrum, provides direct evidence of the interfacial material. The possible use of spin-locking at angles other than 90° in the rotating frame to scale the spin diffusion rates is reviewed and its possible utility for LLDPE materials explored.     

Cosheaves and connectedness in formal topology

The localic definitions of cosheaves, connectedness and local connectedness are transferred from impredicative topos theory to predicative formal topology. A formal topology is locally connected (has base of connected opens) iff it has a cosheaf π₀ together with certain additional structure and properties that constrain π₀ to be the connected components cosheaf. In the inductively generated case, complete spreads (in the sense of Bunge and Funk) corresponding to cosheaves are defined as formal topologies. Maps between the complete spreads are equivalent to homomorphisms between the cosheaves. A cosheaf is the connected components cosheaf for a locally connected formal topology iff its complete spread is a homeomorphism, and in this case it is a terminal cosheaf.A new, geometric proof is given of the topos-theoretic result that a cosheaf is a connected components cosheaf iff it is a “strongly terminal” point of the symmetric topos, in the sense that it is terminal amongst all the generalized points of the symmetric topos. It is conjectured that a study of sites as “formal toposes” would allow such geometric proofs to be incorporated into predicative mathematics.     

Nanostructures in Physical Materials Chemistry: An Exploratory Laboratory

The blend of nanotechnology and material science is often beyond the scope of undergraduate laboratories. Through undergraduate research, graphite-intercalated compounds have been incorporated in the production of carbon-based nanostructures. Based on this work a series of exploratory exercises were designed for the undergraduate physical chemistry laboratory emphasizing nanostructure material science. This rapidly expanding area of science and technology can be introduced at an undergraduate level using a high temperature oven to produce nanostructure samples that are analyzed by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy at research university laboratories, infrared spectroscopy, and a bomb calorimeter. In these experiments we use samples of pure graphite, fluorinated graphite, and lanthanum oxide to induce the formation of nanostructures. An overview of fullerenes, nanotubes, boron nitride and Si nanostructures, other carbon forms, graphite-intercalated compounds, and the storage of hydrogen in nanotubes are provided in an appendix. Several extensions of the laboratory are proposed.     

100 mK bolometers for the submillimetre common-user bolometer array (scuba) I. Design and construction

We describe the design and construction of bolometric detectors for SCUBA - the Submillimetre Common-User Bolometer Array for the James Clerk Maxwell Telescope in Hawaii. The instrument contains 131 individual detectors, in two arrays, optimized for the submillimetre atmospheric transmission windows. The detectors are cooled by dilution refrigeration to a temperature of 100 mK, so that the receiver performance will be limited by photon noise from the sky and telescope background in all wavebands. A future paper will describe the performance of the detectors with reference to typical data obtained during the laboratory commissioning period.     

Thermoset polyester as an alternative material for microchip electrophoresis/electrochemistry

Microchip CE coupled with electrochemical detection (MCE-EC) is a good method for the direct detection of many small molecule analytes because the technique is sensitive and readily miniaturized. Polymer materials are being increasingly used with MCE due to their affordability and ease of fabrication. While PDMS has become arguably the most widely used material in MCE-EC due to the simplicity of microelectrode incorporation, it suffers from a lack of separation efficiency, lower surface stability, and a tendency for analyte sorption. Other polymers, such as poly(methylmethacrylate) (PMMA) and poly(carbonate) (PC), have higher separation efficiencies but require more difficult fabrication techniques for electrode incorporation. In this report, thermoset polyester (TPE) was characterized as an alternative material for MCE-EC. TPE microchips were characterized in their native and plasma oxidized forms and after coating with polyelectrolyte multilayers (PEMs). TPE provides higher separation efficiencies when compared to PDMS microchips, while still using simple fabrication protocols. In this work, separation efficiencies as high as 295,000 N/m were seen when using TPE MCE-EC devices. Furthermore, the EOF was higher and more consistent as a function of pH for both native and plasma-treated TPE than PDMS. Finally, TPE is amenable to modification using simple PEM coatings as another way to control surface chemistry and surface charge.     

Laser Excited Raman and Fluorescence Spectra of Some Important Pesticides

The detection of residual pesticide levels in air and soils by remotely sensing their Raman Spectra is the objective of a recently initiated research program in the department. A necessary preliminary step in the endeavor has been to obtain data on the spectral distribution of scattered laser light from pure samples, under laboratory conditions.     

An approach to an asymmetric synthesis of stemofoline

A stereoselective Mannich reaction between an (S)-tert-butylsulfinimine and methyl (S)-4-benzyloxy-3-methylbutanoate followed by treatment with acid and N-protection was used to prepare methyl (2R,3S)-2-[(S)-2-benzyloxy-1-methylethyl]-3-tert-butoxycarbonylamino-6-methylenedecanoate. This was taken through to methyl (4R,5S)-4-[(S)-2-benzyloxy-1-methylethyl]-5-tert-butoxycarbonylamino-3,8-dioxododecanoate which on treatment with trifluoroacetic acid cyclised stereoselectively to give (1R,2S,4R,5S)-4-[(S)-2-benzyloxy-1-methylethyl]-1-butyl-2-methoxycarbonyl-8-tert-butoxycarbonyl-3-oxo-8-azabicyclo[3.2.1]octane, a potential precursor of stemofoline. Reduction and N-deprotection of this ketone gave (1R,2S,3R,4R,5S)-4-[(S)-2-benzyloxy-1-methylethyl]-1-butyl-2-methoxycarbonyl-8-azabicyclo[3.2.1]octan-3-ol the structure of which was confirmed by X-ray diffraction.     

A localic theory of lower and upper integrals

An account of lower and upper integration is given. It is constructive in the sense of geometric logic. If the integrand takes its values in the non‐negative lower reals, then its lower integral with respect to a valuation is a lower real. If the integrand takes its values in the non‐negative upper reals, then its upper integral with respect to a covaluation and with domain of integration bounded by a compact subspace is an upper real. Spaces of valuations and of covaluations are defined. Riemann and Choquet integrals can be calculated in terms of these lower and upper integrals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of part-per-milliard concentrations of mercury by atomic- fluorescence flame spectrometry

A method is reported for the determination of mercury in the range 0.002-1 microg/ml . Mercury is extracted by dithizone from aqueous solutions into chloroform or isobutyl methyl ketone, the organic solution is aspirated into a hydrogen-oxygen name, and the intensity of atomic-fluorescence of mercury is measured. The method should be particularly useful for the determination of mercury in urine and for the determination of organic-bound mercury without prior decomposition.