23,685 research outputs found
A surface force apparatus for nanorheology under large shear strain
We describe a surface force apparatus designed to probe the rheology of a
nanoconfined medium under large shear amplitudes (up to 500 m). The
instrument can be operated in closed-loop, controlling either the applied
normal load or the thickness of the medium during shear experiments. Feedback
control allows to greatly extend the range of confinement/shear strain
attainable with the surface force apparatus. The performances of the instrument
are illustrated using hexadecane as the confined medium
Non-linear rheology of a nanoconfined simple fluid
We probe the rheology of the model liquid octamethylcyclotetrasiloxane
(OMCTS) confined into molecularly thin films, using a unique Surface Forces
Apparatus allowing to explore a large range of shear rates and confinement. We
thus show that OMCTS under increasing confinement exhibits the viscosity
enhancement and the non-linear flow properties characteristic of a sheared
supercooled liquid approaching its glass transition. Besides, we study the
drainage of confined OMCTS via the propagation of "squeeze-out" fronts. The
hydrodynamic model proposed by Becker and Mugele [Phys. Rev. Lett. {\bf 91},
166104 (2003)] to describe such front dynamics leads to a conclusion in
apparent contradiction with the dynamical slowdown evidenced by rheology
measurements, which suggests that front propagation is not controlled by large
scale flow in the confined films
Secular evolution in action: central values and radial trends in the stellar populations of boxy bulges
We determine central values and radial trends in the stellar populations of
the bulges of a sample of 28 edge-on S0-Sb disk galaxies, 22 of which are
boxy/peanut-shaped (and therefore barred). Our principal findings are the
following. (1) At a given velocity dispersion, the central stellar populations
of galaxies with boxy/peanut-shaped bulges are indistinguishable from those of
early-type (elliptical and S0) galaxies. Either secular evolution affects
stellar populations no differently to monolithic collapse or mergers, or
secular evolution is not important in the central regions of these galaxies,
despite the fact that they are barred. (2) The radial metallicity gradients of
boxy/peanut-shaped bulges are uncorrelated with velocity dispersion and are, on
average, shallower than those of unbarred early-type galaxies. This is
qualitatively consistent with chemodynamical models of bar formation, in which
radial inflow and outflow smears out pre-existing gradients.Comment: MNRAS Letters accepted. 5 page
HI and Hot Gas in the Outskirts of the M81 Group
Results are presented from a wide area, high resolution HI synthesis survey
of the outer regions of the nearby M81 group, where internal (galactic) and
external (group-related) evolution processes can be studied simultaneously in
great detail. The survey encompasses the star forming dwarf galaxies M81dwA,
UGC4483, and HoII, where evidence of ram pressure stripping was recently
discovered. The data do not reveal any intergalactic HI, but the outer parts of
HoII are reminiscent of tidal tails. We argue however that those structures are
equally consistent with the latest ram pressure models including cooling. The
case for a hot intergalactic medium in this poor, spiral-only group is thus
still open. The survey also puts tight constraints on possible counterparts to
the local high velocity cloud population in an external group, reaching a 3
sigma column density of 10^19 atom/cm^2 and a 6 sigma limiting mass of 1.5x10^5
M_sun.Comment: 6 pages, 3 figures, to be published in "Recycling Intergalactic and
Interstellar Matter," eds. P.-A. Duc, J. Braine, & E. Brinks (ASP: San
Francisco
Frictional dissipation of polymeric solids vs interfacial glass transition
We present single contact friction experiments between a glassy polymer and
smooth silica substrates grafted with alkylsilane layers of different coverage
densities and morphologies. This allows us to adjust the polymer/substrate
interaction strength. We find that, when going from weak to strong interaction,
the response of the interfacial junction where shear localizes evolves from
that of a highly viscous threshold fluid to that of a plastically deformed
glassy solid. This we analyse as resulting from an interaction-induced
``interfacial glass transition'' helped by pressure
Rate effects on layering of a confined linear alkane
We perform drainage experiments of a linear alkane fluid (n-hexadecane) down
to molecular thicknesses, and focus on the role played by the confinement rate.
We show that molecular layering is strongly influenced by the velocity at which
the confining walls are approached: under high enough shear rates, the confined
medium behaves as a structureless liquid of enhanced viscosity for film
thickness below 10 nm. Our results also lead us to conclude that a
rapidly confined film can be quenched in a metastable disordered state, which
might be related with recent intriguing results on the shear properties of
confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett.
{\bf 93}, 096101 (2004)]
WTO accession, the changing competitiveness of foreign-financed firms and regional development in Guangdong of southern China
This paper investigates the changing competitiveness of foreign-financed manufacturing firms and its implications for regional development in Guangdong province of southern China in the run-up to World Trade Organization (WTO) accession. It is argued that transnational corporations (TNCs) and some competitive, large-scale, locally-funded firms in Guangdong will triumph after WTO accession. The crowding-out process of small and medium sized enterprises (SMEs) in Guangdong will be accelerated in the near future, as they are competing directly with TNCs, and as their competitive advantages are diminishing, due to bureaucratic red tape and the rigorous enforcement of new government policies. Due to close business linkages with local privately-funded firms, the competitiveness and vitality of foreign-financed enterprises will have profound long term effects on the economic development of Guangdong, before and after WTO accession
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