13,098 research outputs found
Low-frequency noise reduction of spacecraft structures
Low frequency noise reduction of spacecraft structure
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The development of the passé composé in lower-intermediate learners of French as a second language
In this study we tracked the development of the passe compose in second-language learners of French whose first language is English. Although the passe compose is a highly used tense among native speakers of French and it appears to present particular difficulty for first-language English speakers, its second-language development has been surprisingly under-researched. In order to trace developmental patterns of the passe compose we obtained a corpus of obligatory context use of this tense by 30 Year-12 (lower-intermediate) students at two time points six months apart and analysed the data both quantitatively and qualitatively. Our findings suggest that these students used remarkably few memorized formulas, that they passed through five distinct stages in their acquisition of the passe compose, that those early stages were characterized by transfer errors, and that the presence of the auxiliary, whether correct or incorrect, formed a crucial stage in the development of the tense. Theoretical explanations for the findings are presented together with some tentative pedagogical implications
On the stability and growth of single myelin figures
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
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
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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