22,917 research outputs found
IMAGES I, MD101: A coring cruise of the R/V Marion Dufresne in the North Atlantic Ocean and Norwegian Sea
IMAGES coordinated a first international cruise in June and July 1995 over the North Atlantic and Norwegian sea on board the French RN Mm'ion Dufresne (MD 10 I, Brest - Stornoway (Lewis Island) - St-Pierre - Azores - Marseille). Its main scientific objective was the collection of giant piston cores on rapidly sedimenting drifts and continental margins of the North Atlantic ocean and Norwegian Sea, along the track of the main thermohaline circulation. The cruise crossed the North-East Atlantic margins, the Feni Drift, the Scottish, North Faeroes and Norwegian margins (to nON), the Iceland South-East margins, the Gardar Drift, the NAMOC Channel, the Newfoundland margin, the Bermuda rise, the mid Atlantic ridge, and the Azores and Iberian margins. Additional objectives covered: - the contribution of Mediterranean waters to the North Atlantic intermediate waters, with 5 cores recovered across the slopes of the Iberian margin; - the evolution of the NAMOC channel, in the deep North-West Atlantic basin, in relation to the growths and decays of the Laurentide ice sheet (8 Kullenberg and gravity cores). This was the maiden cruise of the new Mm'ion Dujresne, just 2 weeks out from her Le Havre shipyard. The ship had a very small number of problems, taking into account the number of things which were not ready just a few days before the departure. Two days were lost for engine problems. 70 scientists, students and technicians from 22 institutions (13 countries) participated to at least one of the three legs. 43 cores (mean length over 30 meters) have been retrieved during the cruise, described and measured for magnetic susceptibility, p-wave velocity, y density and spectral light reflectance. The longest core, MD 95-2036 (52.64 m) was retrieved at 4461 m water depth on the Bermuda Rise. It covers about 150 kyr with a sedimentation rate over 30 cm/kyr. The Calypso corer worked properly, once a few problems encountered at the be"innin" of the cruise had been solved (i.e. sliced or imploded PVC liner). This report presents preliminary results, mostly obtained on board: core descriptions, physical properties and micro-paleontological stratigraphy. Color reflectance (between 40° and 55°N) and magnetic susceptibility (between 50° and 700N) have been used for direct tuning of the time scales by cyclo-stratigraphy in the precession and obliquity bands. Ocean-wide correlations have been established over the last 250 kyr
Anomalous quantum Hall effect induced by disorder in topological insulators
We investigate a transition between a two-dimensional topological insulator
conduction state, characterized by a conductance (in fundamental units
) and a Chern insulator with , induced by polarized magnetic
impurities. Two kinds of coupling, ferro and antiferromagnetic, are considered
with the electron and hole subbands. We demonstrate that for strong disorder, a
phase exists even for ferromagnetic order, in contrast with the
prediction of the mean field approximation. This result is supported by direct
numerical computations using Landauer transport formula, and by analytical
calculations of the chemical potential and mass renormalization as a function
of the disorder strength, in the self-consistent Born approximation. The
transition is related to the suppression of one of the spin conduction
channels, for strong enough disorder, by selective spin scattering and
localization.Comment: 9 pages, 4 figures (figs. 2 and 3 in low resolution
Liquid bridging of cylindrical colloids in near-critical solvents
Within mean field theory, we investigate the bridging transition between a
pair of parallel cylindrical colloids immersed in a binary liquid mixture as a
solvent which is close to its critical consolute point . We determine the
universal scaling functions of the effective potential and of the force between
the colloids. For a solvent which is at the critical concentration and close to
, we find that the critical Casimir force is the dominant interaction at
close separations. This agrees very well with the corresponding Derjaguin
approximation for the effective interaction between the two cylinders, while
capillary forces originating from the extension of the liquid bridge turn out
to be more important at large separations. In addition, we are able to infer
from the wetting characteristics of the individual colloids the first-order
transition of the liquid bridge connecting two colloidal particles to the
ruptured state. While specific to cylindrical colloids, the results presented
here provide also an outline for identifying critical Casimir forces acting on
bridged colloidal particles as such, and for analyzing the bridging transition
between them.Comment: 23 pages, 12 figure
Dimensionality of Local Minimizers of the Interaction Energy
In this work we consider local minimizers (in the topology of transport
distances) of the interaction energy associated to a repulsive-attractive
potential. We show how the imensionality of the support of local minimizers is
related to the repulsive strength of the potential at the origin.Comment: 27 page
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