56 research outputs found
Static imaging of dynamic fluctuations in multiple light scattering media
Abstract Multiple light scattering experiments in backscattering geometry are performed on highly viscous and solid turbid media which contain macroscopic inclusions of a low viscosity colloidal suspension. We demonstrate that the intensity probability Ž . distribution P I of the multiple scattering speckle patterns can be used to image an inclusion even if its photon transport mean free path matches the value of the surrounding medium. The main difference between solid and liquid samples is discussed
MCL-1 promiscuity and the structural resilience of its binding partners
The allosteric protein MCL-1 and its natural inhibitors, the BH3-only proteins PUMA, BIM, and NOXA regulate apoptosis by interacting promiscuously within an entangled binding network. Little is known about the transient processes and dynamic conformational fluctuations that are the basis for the formation and stability of the MCL-1/BH3-only complex. In this study, we designed photoswitchable versions of MCL-1/PUMA and MCL-1/NOXA, and investigated the protein response after an ultrafast photo-perturbation with transient infrared spectroscopy. We observed partial α-helical unfolding in all cases, albeit on strongly varying timescales (1.6 ns for PUMA, 9.7 ns for the previously studied BIM, and 85 ns for NOXA). These differences are interpreted as a BH3-only-specific “structural resilience” to defy the perturbation while remaining in MCL-1’s binding pocket. Thus, the presented insights could help to better understand the differences between PUMA, BIM, and NOXA, the promiscuity of MCL-1, in general, and the role of the proteins in the apoptotic network
MCL-1 promiscuity and the structural resilience of its binding partners
MCL-1 and its natural inhibitors, the BH3-only proteins PUMA, BIM, and NOXA
regulate apoptosis by interacting promiscuously within an entangled binding
network. Little is known about the transient processes and dynamic
conformational fluctuations that are the basis for the formation and stability
of the MCL-1/BH3-only complex. In this study, we designed photoswitchable
versions of MCL-1/PUMA and MCL-1/NOXA, and investigated the protein response
after an ultrafast photo-perturbation with transient infrared spectroscopy. We
observed partial -helical unfolding in all cases, albeit on strongly
varying timescales (1.6~ns for PUMA, 9.7~ns for the previously studied BIM, and
85~ns for NOXA). These differences are interpreted as a BH3-only-specific
"structural resilience" to defy the perturbation while remaining in MCL-1's
binding pocket. Thus, the presented insights could help to better understand
the differences between PUMA, BIM, and NOXA, the promiscuity of MCL-1 in
general, and the role of the proteins in the apoptotic network
Quantitative modeling of laser speckle imaging
We have analyzed the image formation and dynamic properties in laser speckle
imaging (LSI) both experimentally and with Monte-Carlo simulation. We show for
the case of a liquid inclusion that the spatial resolution and the signal
itself are both significantly affected by scattering from the turbid
environment. Multiple scattering leads to blurring of the dynamic inhomogeneity
as detected by LSI. The presence of a non-fluctuating component of scattered
light results in the significant increase in the measured image contrast and
complicates the estimation of the relaxation time. We present a refined
processing scheme that allows a correct estimation of the relaxation time from
LSI data.Comment: submitted to Optics Letter
Nonuniversal correlations in multiple scattering
We show that intensity of a wave created by a source embedded inside a
three-dimensional disordered medium exhibits a non-universal space-time
correlation which depends explicitly on the short-distance properties of
disorder, source size, and dynamics of disorder in the immediate neighborhood
of the source. This correlation has an infinite spatial range and is
long-ranged in time. We suggest that a technique of "diffuse microscopy" might
be developed employing spatially-selective sensitivity of the considered
correlation to the disorder properties.Comment: 15 pages, 3 postscript figures, accepted to Phys. Rev.
Imaging in turbid media using quasi-ballistic photons
We study by means of experiments and Monte Carlo simulations, the scattering
of light in random media, to determine the distance upto which photons travel
along almost undeviated paths within a scattering medium, and are therefore
capable of casting a shadow of an opaque inclusion embedded within the medium.
Such photons are isolated by polarisation discrimination wherein the plane of
linear polarisation of the input light is continuously rotated and the
polarisation preserving component of the emerging light is extracted by means
of a Fourier transform. This technique is a software implementation of lock-in
detection. We find that images may be recovered to a depth far in excess of
what is predicted by the diffusion theory of photon propagation. To understand
our experimental results, we perform Monte Carlo simulations to model the
random walk behaviour of the multiply scattered photons. We present a new
definition of a diffusing photon in terms of the memory of its initial
direction of propagation, which we then quantify in terms of an angular
correlation function. This redefinition yields the penetration depth of the
polarisation preserving photons. Based on these results, we have formulated a
model to understand shadow formation in a turbid medium, the predictions of
which are in good agreement with our experimental results.Comment: LaTex 19 pages, 10 ps figures and 8 eps figures. psfig.sty included.
(submitted to Optics Commumications
Time-Resolved Diffusing Wave Spectroscopy for selected photon paths beyond 300 transport mean free paths
This paper is devoted to the theoretical and experimental demonstration of
the possibility to perform time-resolved diffusing wave spectroscopy: we
successfully registered field fluctuations for selected photon path lengths
that can overpass 300 transport mean free paths. Such a performance opens new
possibilities for biomedical optics applications.Comment: 12 pages, 3 figure
Diffusing-wave spectroscopy of nonergodic media
We introduce an elegant method which allows the application of diffusing-wave
spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on
the idea that light transmitted through a sandwich of two turbid cells can be
considered ergodic even though only the second cell is ergodic. If absorption
and/or leakage of light take place at the interface between the cells, we
establish a so-called "multiplication rule", which relates the intensity
autocorrelation function of light transmitted through the double-cell sandwich
to the autocorrelation functions of individual cells by a simple
multiplication. To test the proposed method, we perform a series of DWS
experiments using colloidal gels as model nonergodic media. Our experimental
data are consistent with the theoretical predictions, allowing quantitative
characterization of nonergodic media and demonstrating the validity of the
proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.
Recommended from our members
INVESTIGATION OF MULTI-MATERIAL LIQUID METAL JETTING WITH COPPER MATERIALS
Technical parts are typically subject to various requirements that may conflict with each
other. Multi-material parts can be a way to overcome such conflicting goals. Liquid Metal Jetting
(LMJ) can be a promising additive manufacturing process for the production of multi-material
copper parts with high geometric complexity. Since LMJ builds up a part droplet by droplet, there
are no mixed powders after printing. In addition, LMJ offers the possibility of changing materials
from droplet to droplet. In previous studies, we have shown that it is possible to produce copper
alloy parts using LMJ. In this work, we produced multi-material copper specimens at different
process parameters to investigate the manufacturing of multi-material copper parts. The
investigations show that the quality of the compound and the microstructure depend significantly
on the thermal process parameters used.Mechanical Engineerin
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