353 research outputs found
Cooperative emission of a pulse train in an optically thick scattering medium
An optically thick cold atomic cloud emits a coherent flash of light in the
forward direction when the phase of an incident probe field is abruptly
changed. Because of cooperativity, the duration of this phenomena can be much
shorter than the excited lifetime of a single atom. Repeating periodically the
abrupt phase jump, we generate a train of pulses with short repetition time,
high intensity contrast and high efficiency. In this regime, the emission is
fully governed by cooperativity even if the cloud is dilute.Comment: 5 pages, 3 figure
Coherent flash of light emitted by a cold atomic cloud
When a resonant laser sent on an optically thick cold atomic cloud is
abruptly switched off, a coherent flash of light is emitted in the forward
direction. This transient phenomenon is observed due to the highly resonant
character of the atomic scatterers. We analyze quantitatively its
spatio-temporal properties and show very good agreement with theoretical
predictions. Based on complementary experiments, the phase of the coherent
field is reconstructed without interferometric tools.Comment: Submitted to Phys. Rev. Let
Cooperative Emission of a Coherent Superflash of Light
We investigate the transient coherent transmission of light through an
optically thick cold stron-tium gas. We observe a coherent superflash just
after an abrupt probe extinction, with peak intensity more than three times the
incident one. We show that this coherent superflash is a direct signature of
the cooperative forward emission of the atoms. By engineering fast transient
phenomena on the incident field, we give a clear and simple picture of the
physical mechanisms at play.Comment: 4 Fig., 5 page
Dynamic force spectroscopy on multiple bonds: experiments and model
We probe the dynamic strength of multiple biotin-streptavidin adhesion bonds
under linear loading using the biomembrane force probe setup for dynamic force
spectroscopy. Measured rupture force histograms are compared to results from a
master equation model for the stochastic dynamics of bond rupture under load.
This allows us to extract the distribution of the number of initially closed
bonds. We also extract the molecular parameters of the adhesion bonds, in good
agreement with earlier results from single bond experiments. Our analysis shows
that the peaks in the measured histograms are not simple multiples of the
single bond values, but follow from a superposition procedure which generates
different peak positions.Comment: to appear in Europhysics Letter
Bismuth coordination networks containing deferiprone: synthesis, characterisation, stability and antibacterial activity
A series of bismuthâdicarboxylateâdeferiprone coordination networks have been prepared and structurally characterised. The new compounds have been demonstrated to release the iron overload drug deferiprone on treatment with PBS and have also been shown to have antibacterial activity against H. pylori
Signatures of LeÂŽvy ïŹights with annealed disorder
We present theoretical and experimental results of LeÂŽvy ïŹights of light originating from a random walk of
photons in a hot atomic vapor. In contrast to systems with quenched disorder, this system does not present any
correlations between the position and the step length of the random walk. In an analytical model based on micro-
scopic ïŹrst principles including Doppler broadening we ïŹnd anomalous LeÂŽvy-type superdiffusion corresponding
to a single-step size distribution P (x) â xâ(1+α), with α â 1. We show that this step size distribution leads to a
violation of Ohmâs law [Tdiff â Lâα/2 ┏= Lâ1], as expected for a LeÂŽvy walk of independent steps. Furthermore,
the spatial proïŹle of the transmitted light develops power-law tails [Tdiff(r) â râ3âα]. In an experiment using a
slab geometry with hot Rb vapor, we measured the total diffuse transmission Tdiff and the spatial proïŹle of the
transmitted light Tdiff(r). We obtained the microscopic LeŽvy parameter α under macroscopic multiple scattering
conditions paving the way to investigation of LeÂŽvy ïŹights in different atomic physics and astrophysics systems.We thank Dominique Delande for fruitful discussions and we acknowledge funding for N.M. and Q.B. by the french Direction Generale de l'Armement. R.P acknowledges the support of LABEX WIFI (Laboratory of Excellence ANR-10-LABX-24) within the French Program "Investments for the Future" under reference ANR-10-IDEX-0001-02 PSL*. E.J.N. and R.K. acknowledge the FCT/CNRS exchange program (441.00 CNRS)
Developmental cascades of social inhibition and friendships in preterm and fullâterm children
Friendships are crucial to children's socioemotional development and quality of life. Children born preterm (<37 weeks gestation) have an increased risk for social relationship difficulties, including fewer friends, but the mechanisms underlying the link between lower gestational age and fewer friendships are not clear. The prospective Bavarian Longitudinal Study investigated potential cascading effects on N = 1,181 children's friendships at 8 years. Path modelling indicated that higher gestational age predicted good early parentâinfant relationship quality, good inhibitory control, and higher friendship scores. Good parentâinfant relationship quality predicted good inhibitory control, which subsequently predicted low social inhibition at 6 years and higher friendship scores at 8 years. There is evidence of cascading effects from gestational age to early parentâinfant relationships, to toddlers' inhibitory control, and to social inhibition, which partially explain differences in children's friendships at 8 years of age
Wet Granular Materials
Most studies on granular physics have focused on dry granular media, with no
liquids between the grains. However, in geology and many real world
applications (e.g., food processing, pharmaceuticals, ceramics, civil
engineering, constructions, and many industrial applications), liquid is
present between the grains. This produces inter-grain cohesion and drastically
modifies the mechanical properties of the granular media (e.g., the surface
angle can be larger than 90 degrees). Here we present a review of the
mechanical properties of wet granular media, with particular emphasis on the
effect of cohesion. We also list several open problems that might motivate
future studies in this exciting but mostly unexplored field.Comment: review article, accepted for publication in Advances in Physics;
tex-style change
High shear granulation: an investigation into the granule consolidation mechanism
The mechanisms of early granule growth are difficult to study and poorly understood. Consolidation and layering play a critical role in the growth process. However, little is known about the kinetics.
In this work, a novel consolidation-only granulator (COG) was used to study dynamic consolidation and layering only, eliminating other granulation mechanisms. Prenucleated granule growth was studied over time. Based on experimental data and literature models, a mechanistic layering kernel for population balance modelling was developed.
Granule growth kinetics were qualitatively predicted by a previously reported model; growth behaviour was linear with the square root of time to a certain critical size, after which growth stopped. X-ray computed tomography revealed that consolidation mainly occurred in the outer layers of the granules.
The results greatly advance understanding of consolidation and layered growth, and the new model opens the way for improved predictive modelling and design of granulation processes and products
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