783 research outputs found
Discrimination against Turkish minorities in Germany and the Netherlands: field experimental evidence on the effect of diagnostic information on labour market outcomes.
Discrimination against Turkish minorities in Germany and the Netherlands: field experimental evidence on the effect of diagnostic information on labour market outcomes.
Spatially Resolved Excitation of Rydberg Atoms and Surface Effects on an Atom Chip
We demonstrate spatially resolved, coherent excitation of Rydberg atoms on an
atom chip. Electromagnetically induced transparency (EIT) is used to
investigate the properties of the Rydberg atoms near the gold coated chip
surface. We measure distance dependent shifts (~10 MHz) of the Rydberg energy
levels caused by a spatially inhomogeneous electric field. The measured field
strength and distance dependence is in agreement with a simple model for the
electric field produced by a localized patch of Rb adsorbates deposited on the
chip surface during experiments. The EIT resonances remain narrow (< 4 MHz) and
the observed widths are independent of atom-surface distance down to ~20 \mum,
indicating relatively long lifetime of the Rydberg states. Our results open the
way to studies of dipolar physics, collective excitations, quantum metrology
and quantum information processing involving interacting Rydberg excited atoms
on atom chips
Bicontinuous Soft Solids with a Gradient in Channel Size
We present examples of bicontinuous interfacially jammed emulsion gels
("bijels") with a designed gradient in the channel size along the sample. These
samples are created by quenching binary fluids which have a gradient in
particle concentration along the sample, since the channel size is determined
by the local particle concentration. A gradient in local particle concentration
is achieved using a two-stage loading process, with different particle volume
fractions in each stage. Confocal microscopy and image analysis were used to
quantitatively measure the channel size of the bijels. Bijels with a gradient
in channel size of up to 2.8%/mm have been created. Such tailored soft
materials could act as templates for energy materials optimised for both high
ionic transport rates (high power) and high interfacial area (high energy
density), potentially making them useful in novel energy applications.Comment: 9 pages, 5 figure
Emulsification in binary liquids containing colloidal particles: a structure-factor analysis
We present a quantitative confocal-microscopy study of the transient and
final microstructure of particle-stabilised emulsions formed via demixing in a
binary liquid. To this end, we have developed an image-analysis method that
relies on structure factors obtained from discrete Fourier transforms of
individual frames in confocal image sequences. Radially averaging the squared
modulus of these Fourier transforms before peak fitting allows extraction of
dominant length scales over the entire temperature range of the quench. Our
procedure even yields information just after droplet nucleation, when the
(fluorescence) contrast between the two separating phases is scarcely
discernable in the images. We find that our emulsions are stabilised on
experimental time scales by interfacial particles and that they are likely to
have bimodal droplet-size distributions. We attribute the latter to coalescence
together with creaming being the main coarsening mechanism during the late
stages of emulsification and we support this claim with (direct)
confocal-microscopy observations. In addition, our results imply that the
observed droplets emerge from particle-promoted nucleation, possibly followed
by a free-growth regime. Finally, we argue that creaming strongly affects
droplet growth during the early stages of emulsification. Future investigations
could clarify the link between quench conditions and resulting microstructure,
paving the way for tailor-made particle-stabilised emulsions from binary
liquids.Comment: http://iopscience.iop.org/0953-8984/22/45/455102
Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations
Recent experiments have shown that the superconducting energy gap in some
cuprates is spatially inhomogeneous. Motivated by these experiments, and using
exact diagonalization of a model d-wave Hamiltonian, combined with Monte Carlo
simulations of a Ginzburg-Landau free energy functional, we have calculated the
single-particle density of states LDOS of a model high-T
superconductor as a function of temperature. Our calculations include both
quenched disorder in the pairing potential and thermal fluctuations in both
phase and amplitude of the superconducting gap. Most of our calculations assume
two types of superconducting regions: , with a small gap and large
superfluid density, and , with the opposite. If the regions are
randomly embedded in an host, the LDOS on the sites still has
a sharp coherence peak at , but the component does not, in
agreement with experiment. An ordered arrangement of regions leads to
oscillations in the LDOS as a function of energy. The model leads to a
superconducting transition temperature well below the pseudogap
temperature , and has a spatially varying gap at very low , both
consistent with experiments in underdoped Bi2212. Our calculated
LDOS shows coherence peaks for , in agreement with previous work considering phase but not amplitude
fluctuations in a homogeneous superconductor. Well above , the gap in the
LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01
Nov 200
Conditional phase shift from a quantum dot in a pillar microcavity
Large conditional phase shifts from coupled atom-cavity systems are a key
requirement for building a spin photon interface. This in turn would allow the
realisation of hybrid quantum information schemes using spin and photonic
qubits. Here we perform high resolution reflection spectroscopy of a quantum
dot resonantly coupled to a pillar microcavity. We show both the change in
reflectivity as the quantum dot is tuned through the cavity resonance, and
measure the conditional phase shift induced by the quantum dot using an ultra
stable interferometer. These techniques could be extended to the study of
charged quantum dots, where it would be possible to realise a spin photon
interface
Phase transition in ultrathin magnetic films with long-range interactions: Monte Carlo simulation of the anisotropic Heisenberg model
Ultrathin magnetic films can be modeled as an anisotropic Heisenberg model
with long-range dipolar interactions. It is believed that the phase diagram
presents three phases: An ordered ferromagnetic phase I, a phase characterized
by a change from out-of-plane to in-plane in the magnetization II, and a
high-temperature paramagnetic phase III. It is claimed that the border lines
from phase I to III and II to III are of second order and from I to II is first
order. In the present work we have performed a very careful Monte Carlo
simulation of the model. Our results strongly support that the line separating
phases II and III is of the BKT type.Comment: 7 page
The counterintuitive role of exercise in the prevention and cause of atrial fibrillation.
Atrial fibrillation (AF) is the most common cardiac arrhythmia characterised by irregular atrial activity. AF is related to increased risk of thromboembolic events, heart failure, and premature mortality. Recent advances in our understanding of its pathophysiology include a potentially central role for inflammation and presence of cardiovascular risk factors. The role of physical activity and exercise in the development and progression of AF, however, are not yet fully understood. Physical activity is protective for modifiable cardiovascular risk factors, including those associated with AF. Indeed, emerging research has demonstrated beneficial effects of exercise on AF-specific outcomes, including AF recurrence post-ablation. Counterintuitively, the prevalence of AF in veteran endurance athletes seems higher compared to the general population. In this review, we discuss the novel evidence and underlying mechanisms underpinning the role of exercise as medicine in the development and management of AF, but also the counterintuitive detrimental role of excessive endurance exercise. Finally, we advocate regular (but not long-term high-intensity endurance) exercise training as a safe and effective strategy to reduce the risk of incident AF, and to minimise the associated risk of secondary cardiovascular events
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