Budding and Domain Shape Transformations in Mixed Lipid Films and Bilayer Membranes

We study the stability and shapes of domains with spontaneous curvature in fluid films and membranes, embedded in a surrounding membrane with zero spontaneous curvature. These domains can result from the inclusion of an impurity in a fluid membrane, or from phase separation within the membrane. We show that for small but finite line and surface tensions and for finite spontaneous curvatures, an equilibrium phase of protruding circular domains is obtained at low impurity concentrations. At higher concentrations, we predict a transition from circular domains, or "caplets", to stripes. In both cases, we calculate the shapes of these domains within the Monge representation for the membrane shape. With increasing line tension, we show numerically that there is a budding transformation from stable protruding circular domains to spherical buds. We calculate the full phase diagram, and demonstrate a two triple points, of respectively bud-flat-caplet and flat-stripe-caplet coexistence.Comment: 14 pages, to appear in Phys Rev

Distribution and Character of Naleds in Northeastern Alaska

Satellite imagery and high- and low-altitude aerial photography of the North Slope of Alaska indicate that naleds (features formed during river icing) are widespread east of the Colville River but less abundant to its west. Where naleds occur, stream channels are wide and often braided. Their distribution can be related to changes in stream gradient and to the occurrence of springs. Large naleds, such as occur on the Kongakut River, often survive the summer melt season to form the nucleus of icing in the succeeding winter. Major naleds also are likely to significantly influence the nature of permafrost in their immediate vicinity. A map of naleds may serve as a guide to sources of perennially flowing water

A structural and spectroscopic investigation of some tin- and titania-based pigments

Two types of pigments suitable for colouring ceramic materials were investigated structurally and spectroscopically. The two types of pigments investigated were firstly yttrium/tin (Y 2Sn20 7) and yttrium/titanium (Y2Ti2O7) pyrochlores doped with calcium and vanadium, and secondly, malayaite (CaSnSiO5 - and related compounds) doped with chromium and cobalt. The synthesis techniques of the two types of pigments were investigated and optimised based on a two-fold approach; the physical and asthetic properties of the pigments and the economic implication of the synthesis techniques. The structures of the host materials of both pigment types were investigated using the following sophisticated techniques. Scanning electron microscopy, X-ray powder diffraction, Raman spectroscopy, infrared spectroscopy and electronic spectroscopy. The chemical state of the dopants and their structure in relation to their host materials were investigated spectroscopically using Raman spectroscopy, infrared spectroscopy, and electronic spectroscopy.Dissertation (MSc (Chemistry))--University of Pretoria, 1995.ChemistryMSc (Chemistry)Unrestricte

The Solid-State Chemistry of Some Titania-And Tin Pigments

Natural inorganic pigments have been known since prehistoric times. Initially they were obtained from natural sources, but later synthetic pigments were produced empirically. The modern ceramic pigment industry began early in the18th century and since then, ceramic pigments have been the subject of scientific studies to the point where today research makes use of the latest techniques in solid state chemistry and physics to try to understand their properties. Over and above the all-important colour properties of any colouring material, ceramic pigments require additional properties including exceptional thermal and chemical stability. It is through a better understanding of the nature of ceramic pigments and their extraordinary properties that new and improved pigments, and related materials will be synthesised. In the current investigation, a number of Titania- and tin materials suitable for colouring ceramic articles were investigated using a twofold approach. Firstly, their synthesis was investigated and optimised, and secondly, they were investigated structurally. The synthesis focused on their physical and aesthetic properties, and the economic implications of the synthesis techniques. The structural investigation was two dimensional. Firstly, the macroscopic details of the host materials were investigated using scanning electron microscopy (SEM) and x-ray techniques. This is important since it is the host lattice which provides the extraordinary properties required of a ceramic pigment. Secondly, the microscopic structural details of the interaction of the host lattice with the small quantities of dopant(s) were investigated using SEM, vibrational and electronic spectroscopy. This interaction is of paramount importance since it is the interaction between the host lattice and guest chromophore that results in the all-important colour of the pigment. Pigments investigated include chromium doped malayaite, Cr4+ :CaSnOSiO4 , and its titanium analogue titanite, Cr4+:CaTiOSiO4. The chemical state of the chromium in both materials was investigated. In both cases, the chromium was found to be in its fourth oxidation state. Other properties investigated include the chromium coordination states, bond lengths, bond orders and force constants. InCr4+:CaTiOSiO4, the chromium was used as a probe to investigate the paraelectric-antiferroelectric temperature phase transition which titanite undergoes at ~500 K using resonance Raman spectroscopy. This technique was also used to investigate the high-pressure phase transition of titanite. This transition was shown to occur at ~27 kbar. Other pigments investigated include two minerals with the pyrochlore structure 2 Ti2O7 and Y 2Sn2O7, co-doped with calcium and vanadium. The coordination states and chemical states of the calcium and vanadium in these host lattices were investigated. The vanadium was found to be in its fifth oxidation state. The bond lengths and bond orders of the vanadium were determined for these compounds .Following the investigation of these doped mixed metal oxides, various other compounds were synthesised which were found to have potential for use as pigmentsThesis (DPhil (Chemistry))--University of Pretoria, 1998.ChemistryDPhil (Chemistry)Unrestricte

Hand-portable gas chromatography-ion mobility spectrometer for the determination of the freshness of fish

A hand-held, portable gas chromatography-ion mobility spectrometer (GC-IMS) device was used to detect the presence of volatile amine compounds in the headspace of decomposing fish. The Food and Drug Administration (FDA) largely relies on olfactory discrimination with respect to fresh and spoiled, frozen and unfrozen fish. The fish are delivered at ship docks on pallets, and each pallet of fish can range from 30-40 thousand dollars in value. Fresh fish were placed in a teflon bag and the direct headspace was interrogated. In the first three days, only low molecular weight volatile amines were detected. On the fourth day, a number of spectral signatures were observed which indicated the presence of 1,5-diaminopentane, cadaverine. Analyses typically took from 0.5-1 minute

Transition from pediatric to adult renal services: a consensus statement by the International Society of Nephrology (ISN) and the International Pediatric Nephrology Association (IPNA)

The transfer of young patients from pediatric to adult renal care takes place after a transition process which involves both sides. It is important that it is individualized for each young person, focusing on self-management skills as well as assessing support structures. The consensus statement has been developed by the panel of adult and pediatric nephrologists and endorsed by the councils of both ISN and IPNA. It is hoped that the statement will provide a basis for the development of locally appropriate recommendations for clinical practice

The MERG Suite: Tools for discovering competencies and associated learning resources

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