13,098 research outputs found

    Low-frequency noise reduction of spacecraft structures

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    Low frequency noise reduction of spacecraft structure

    On the stability and growth of single myelin figures

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    Myelin figures are long thin cylindrical structures that typically grow as a dense tangle when water is added to the concentrated lamellar phase of certain surfactants. We show that, starting from a well-ordered initial state, single myelin figures can be produced in isolation thus allowing a detailed study of their growth and stability. These structures grow with their base at the exposed edges of bilayer stacks from which material is transported into the myelin. Myelins only form and grow in the presence of a driving stress; when the stress is removed, the myelins retract.Comment: 4 pages, 8 figures. Revised version, 1 new figure, additional reference

    The phase behaviour and structure of a fluid confined between competing (solvophobic and solvophilic) walls

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    We consider a model fluid with long-ranged, dispersion interparticle potentials confined between competing parallel walls. One wall is solvophilic and would be completely wet at bulk liquid-gas coexistence while the other is solvophobic and would be completely dry at bulk coexistence. When the wall separation L is large and the system is below the bulk critical temperature and close to bulk liquid-gas coexistence, a `delocalized interface' or `soft mode' phase forms with a liquid-gas interface near to the centre of the slit; this interacts with the walls via the power-law tails of the interparticle potentials. We use a coarse-grained effective Hamiltonian approach to derive explicit scaling expressions for the Gibbs adsorption, the surface tension, the solvation force and the total susceptibility. Using a non-local density functional theory (DFT) we calculate density profiles for the asymmetrically confined fluid at different chemical potentials and, for sufficiently large L, confirm the scaling predictions for the four thermodynamic quantities. Since the upper critical dimension for complete wetting with power-law potentials is <3 we argue that our (mean-field) scaling predictions should remain valid in treatments that incorporate the effects of interfacial fluctuations. As the wall separation L is decreased at bulk liquid-gas coexistence we predict a capillary evaporation transition from the `delocalized interface' phase to a dilute gas state with just a thin adsorbed film of liquid-like density next to the solvophilic wall. This transition is connected closely to the first order pre-wetting transition which occurs at the solvophilic wall in the semi-infinite system. We compare the phase diagram for the competing walls system with the phase diagrams for the fluid confined between identical solvophilic and identical solvophobic walls.Comment: 19 pages, 13 figure

    Critical holes in undercooled wetting layers

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    The profile of a critical hole in an undercooled wetting layer is determined by the saddle-point equation of a standard interface Hamiltonian supported by convenient boundary conditions. It is shown that this saddle-point equation can be mapped onto an autonomous dynamical system in a three-dimensional phase space. The corresponding flux has a polynomial form and in general displays four fixed points, each with different stability properties. On the basis of this picture we derive the thermodynamic behaviour of critical holes in three different nucleation regimes of the phase diagram.Comment: 18 pages, LaTeX, 6 figures Postscript, submitted to J. Phys.
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