1,056 research outputs found
Avalanche statistics and time-resolved grain dynamics for a driven heap
We probe the dynamics of intermittent avalanches caused by steady addition of
grains to a quasi-two dimensional heap. To characterize the time-dependent
average avalanche flow speed v(t), we image the top free surface. To
characterize the grain fluctuation speed dv(t), we use Speckle-Visibility
Spectroscopy. During an avalanche, we find that the fluctuation speed is
approximately one-tenth the average flow speed, and that these speeds are
largest near the beginning of an event. We also find that the distribution of
event durations is peaked, and that event sizes are correlated with the time
interval since the end of the previous event. At high rates of grain addition,
where successive avalanches merge into smooth continuous flow, the relationship
between average and fluctuation speeds changes to dv Sqrt[v]
Multispeckle diffusing-wave spectroscopy: a tool to study slow relaxation and time-dependent dynamics
A multispeckle technique for efficiently measuring correctly
ensemble-averaged intensity autocorrelation functions of scattered light from
non-ergodic and/or non-stationary systems is described.
The method employs a CCD camera as a multispeckle light detector and a
computer-based correlator, and permits the simultaneous calculation of up to
500 correlation functions, where each correlation function is started at a
different time.
The correlation functions are calculated in real time and are referenced to a
unique starting time.
The multispeckle nature of the CCD camera detector means that a true ensemble
average is calculated; no time averaging is necessary.
The technique thus provides a "snapshot" of the dynamics, making it
particularly useful for non-stationary systems where the dynamics are changing
with time.
Delay times spanning the range from 1 ms to 1000 s are readily achieved with
this method.
The technique is demonstrated in the multiple scattering limit where
diffusing-wave spectroscopy theory applies.
The technique can also be combined with a recently-developed two-cell
technique that can measure faster decay times.
The combined technique can measure delay times from 10 ns to 1000 s.
The method is peculiarly well suited for studying aging processes in soft
glassy materials, which exhibit both short and long relaxation times,
non-ergodic dynamics, and slowly-evolving transient behavior.Comment: 11 pages 13 figures Accepted in Review of Scientific Instrument (june
02
Elastic Behavior of a Two-dimensional Crystal near Melting
Using positional data from video-microscopy we determine the elastic moduli
of two-dimensional colloidal crystals as a function of temperature. The moduli
are extracted from the wave-vector-dependent normal mode spring constants in
the limit and are compared to the renormalized Young's modulus of the
KTHNY theory. An essential element of this theory is the universal prediction
that Young's modulus must approach at the melting temperature. This is
indeed observed in our experiment.Comment: 4 pages, 3 figure
Non-collinear magnetism in Al-Mn topologically disordered systems
We have performed the first ab-initio calculations of a possible complex
non-collinear magnetic structure in aluminium-rich Al-Mn liquids within the
real-space tight-binding LMTO method. In our previous work we predicted the
existence of large magnetic moments in Al-Mn liquids [A.M. Bratkovsky, A.V.
Smirnov, D. N. Manh, and A. Pasturel, \prb {\bf 52}, 3056 (1995)] which has
been very recently confirmed experimentally. Our present calculations show that
there is a strong tendency for the moments on Mn to have a non-collinear
(random) order retaining their large value of about 3~. The d-electrons
on Mn demonstrate a pronounced non-rigid band behaviour which cannot be
reproduced within a simple Stoner picture. The origin of the magnetism in these
systems is a topological disorder which drives the moments formation and
frustrates their directions in the liquid phase.Comment: 10 pages, RevTex 3.0, 24kb. 3 PS figures available on request from
[email protected] The work has been presented at ERC
``Electronic Structire of Solids'' (Lunteren, The Netherlands, 9-14 September
1995
Quantum theory of dynamic multiple light scattering
We formulate a quantum theory of dynamic multiple light scattering in
fluctuating disordered media and calculate the fluctuation and the
autocorrelation function of photon number operator for light transmitted
through a disordered slab. The effect of disorder on the information capacity
of a quantum communication channel operating in a disordered environment is
estimated and the use of squeezed light in diffusing-wave spectroscopy is
discussed.Comment: Revised text, additional figur
GGD 37: An Extreme Protostellar Outflow
We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom
BOSS Great Wall: morphology, luminosity, and mass
We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift . We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with .
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than . This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional for the richer BGW superclusters (
and ) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of , and masses in the range of . Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.Comment: Comments: 10 pages, 2 figures, A&A, in pres
Contact dynamics in a gently vibrated granular pile
We use multi-speckle diffusive wave spectroscopy (MSDWS) to probe the
micron-scale dynamics of a granular pile submitted to discrete gentle taps. The
typical time-scale between plastic events is found to increase dramatically
with the number of applied taps. Furthermore, this microscopic dynamics weakly
depends on the solid fraction of the sample. This process is strongly analogous
to the aging phenomenon observed in thermal glassy systems. We propose a
heuristic model where this slowing down mechanism is associated with a slow
evolution of the distribution of the contact forces between particles. This
model accounts for the main features of the observed dynamics.Comment: 4 pages, 4 figure
Biochemistry of mobile zinc and nitric oxide revealed by fluorescent sensors
Biological mobile zinc and nitric oxide (NO) are two prominent examples of inorganic compounds involved in numerous signaling pathways in living systems. In the past decade, a synergy of regulation, signaling, and translocation of these two species has emerged in several areas of human physiology, providing additional incentive for developing adequate detection systems for Zn(II) ions and NO in biological specimens. Fluorescent probes for both of these bioinorganic analytes provide excellent tools for their detection, with high spatial and temporal resolution. We review the most widely used fluorescent sensors for biological zinc and nitric oxide, together with promising new developments and unmet needs of contemporary Zn(II) and NO biological imaging. The interplay between zinc and nitric oxide in the nervous, cardiovascular, and immune systems is highlighted to illustrate the contributions of selective fluorescent probes to the study of these two important bioinorganic analytes.National Science Foundation (Grant Number CHE-0907905)National Institutes of Health (U.S.) (Grant Number GM065519)National Institutes of Health (U.S.) (Grant Number K99GM092970
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