476 research outputs found
Mutual information between reflected and transmitted speckle images
We study theoretically the mutual information between reflected and
transmitted speckle patterns produced by wave scattering from disordered media.
The mutual information between the two speckle images recorded on an array of N
detection points (pixels) takes the form of long-range intensity correlation
loops, that we evaluate explicitly as a function of the disorder strength and
the Thouless number g. Our analysis, supported by extensive numerical
simulations, reveals a competing effect of cross-sample and surface spatial
correlations. An optimal distance between pixels is proven to exist, that
enhances the mutual information by a factor Ng compared to the single-pixel
scenario.Comment: 5 pages, 4 figures, + S
Near-field interactions and non-universality in speckle patterns produced by a point source in a disordered medium
A point source in a disordered scattering medium generates a speckle pattern
with non-universal features, giving rise to the so-called C_0 correlation. We
analyze theoretically the relationship between the C_0 correlation and the
statistical fluctuations of the local density of states, based on simple
arguments of energy conservation. This derivation leads to a clear physical
interpretation of the C_0 correlation. Using exact numerical simulations, we
show that C_0 is essentially a correlation resulting from near-field
interactions. These interactions are responsible for the non-universality of
C_0, that confers to this correlation a huge potential for sensing and imaging
at the subwavelength scale in complex media
Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media
The propagation of monochromatic light through a scattering medium produces
speckle patterns in reflection and transmission, and the apparent randomness of
these patterns prevents direct imaging through thick turbid media. Yet, since
elastic multiple scattering is fundamentally a linear and deterministic
process, information is not lost but distributed among many degrees of freedom
that can be resolved and manipulated. Here we demonstrate experimentally that
the reflected and transmitted speckle patterns are correlated, even for opaque
media with thickness much larger than the transport mean free path, proving
that information survives the multiple scattering process and can be recovered.
The existence of mutual information between the two sides of a scattering
medium opens up new possibilities for the control of transmitted light without
any feedback from the target side, but using only information gathered from the
reflected speckle.Comment: 6 pages, 4 figure
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
Radiative and non-radiative local density of states on disordered plasmonic films
We present numerical calculations of the Local Density of Optical States
(LDOS) in the near field of disordered plasmonic films. The calculations are
based on an integral volume method, that takes into account polarization and
retardation effects, and allows us to discriminate radiative and non-radiative
contributions to the LDOS. At short distance, the LDOS is dominated by
non-radiative channels, showing that changes in the spontaneous dynamics of
dipole emitters are driven by non-radiative coupling to plasmon modes. Maps of
radiative and non-radiative LDOS exhibit strong fluctuations, but with
substantially different spatial distributions
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The exon junction complex senses energetic stress and regulates contractility and cell architecture in cardiac myocytes
The exon junction complex (EJC) is the main mechanism by which cells select specific mRNAs
for translation into protein. We hypothesized that the EJC is involved in the regulation
of gene expression during the stress response in cardiac myocytes, with implications for
the failing heart. In cultured rat neonatal myocytes, we examined the cellular distribution
of two EJC components eukaryotic translation initiation factor 4A isoform 3 (eIF4A3) and
mago nashi homologue (Mago) in response to metabolic stress. There was significant relocalization
of eIF4A3 and Mago from the nucleus to cytoplasm following 18 h of hypoxia.
Treating myocytes with 50 mM NaN3 for 4 h to mimic the metabolic stress induced by hypoxia
also resulted in significant relocalization of eIF4A3 and Mago to the cytoplasm. To
examine whether the effects of metabolic stress on the EJC proteins were dependent on
the metabolic sensor AMP kinase (AMPK), we treated myocytes with 1 ÎĽM dorsomorphin
(DM) in combination with NaN3. DM augmented the translocation of Mago and eIF4A3 from
the nucleus to the cytoplasm. Knockdown of eIF4A3 resulted in cessation of cell contractility
96 h post-treatment and a significant reduction in the number of intact sarcomeres.
Cell area was significantly reduced by both hypoxia and eIF4A3 knockdown, whilst eIF4A3
knockdown also significantly reduced nuclear size. The reduction in nuclear size is unlikely
to be related to apoptosis as it was reversed in combination with hypoxia. These data suggest
for the first time that eIF4A3 and potentially other EJC members play an important role
in the myocyte stress response, cell contractility and morphology
Characterization of ejecta in shock experiments with multiple light scattering
Upon impact, the free surface of a solid metal may eject a cloud of fast and
fine particles. Photon Doppler Velocimetry (PDV) is one of the optical
diagnostics used to characterize these ejecta. Although the technique provides
a direct way to estimate the particle velocities in the single scattering
regime, it has been shown that multiple scattering cannot be neglected in real
ejecta. Here we derive a model for PDV measurements starting from first
principles of wave scattering. We establish rigorously the relationship between
the specific intensity and the measured signal, as well as the radiative
transport equation (RTE) that describes the evolution of the specific intensity
upon scattering and absorption in a dynamic ejecta, including the effects of
inelastic scattering and inhomogenities in the optical properties. We also
establish rigorously the connection between the Monte-Carlo scheme used for
numerical simulations and the solution to the RTE. Using numerical simulations,
we demonstrate the crucial role of multiple scattering and inhomogeneities in
the particle density and size-velocity distribution. These results could
substantially impact the analysis of ejecta by PDV
Spatial coherence in complex photonic and plasmonic systems
The concept of cross density of states characterizes the intrinsic spatial
coherence of complex photonic or plasmonic systems, independently on the
illumination conditions. Using this tool and the associated intrinsic coherence
length, we demonstrate unambiguously the spatial squeezing of eigenmodes on
disordered fractal metallic films, thus clarifying a basic issue in plasmonics
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