1,083 research outputs found
Discontinuous shear modulus determines the glass transition temperature
A solid - amorphous or crystalline - is defined by a finite shear modulus
while a fluid lacks such. We thus experimentally investigate the elastic
properties of a colloidal glass former near the glass transition: spectroscopy
of vibrational excitations yields the dispersion relations of longitudinal and
transverse phonons in the glassy state. From the long wavelength limit of the
dispersion relation we extract the bulk and the shear modulus. As expected, the
latter disappear in a fluid and we measure a clearly resolved discontinuous
behaviour of the elastic moduli at the glass transition. This not only
determines the transition temperature T_G of the system but also directly
addresses recent discussions about elasticity during vitrification. We show
that low frequency excitations in our system are plane waves such that
continuum elasticity theory can be used to describe the macroscopic behaviour.Comment: 8 pages, 6 figure
Glycolaldehyde in Perseus young solar analogs
Aims: In this paper we focus on the occurrence of glycolaldehyde (HCOCH2OH)
in young solar analogs by performing the first homogeneous and unbiased study
of this molecule in the Class 0 protostars of the nearby Perseus star forming
region. Methods: We obtained sub-arcsec angular resolution maps at 1.3mm and
1.4mm of glycolaldehyde emission lines using the IRAM Plateau de Bure (PdB)
interferometer in the framework of the CALYPSO IRAM large program. Results:
Glycolaldehyde has been detected towards 3 Class 0 and 1 Class I protostars out
of the 13 continuum sources targeted in Perseus: NGC1333-IRAS2A1,
NGC1333-IRAS4A2, NGC1333-IRAS4B1, and SVS13-A. The NGC1333 star forming region
looks particularly glycolaldehyde rich, with a rate of occurrence up to 60%.
The glycolaldehyde spatial distribution overlaps with the continuum one,
tracing the inner 100 au around the protostar. A large number of lines (up to
18), with upper-level energies Eu from 37 K up to 375 K has been detected. We
derived column densities > 10^15 cm^-2 and rotational temperatures Trot between
115 K and 236 K, imaging for the first time hot-corinos around NGC1333-IRAS4B1
and SVS13-A. Conclusions: In multiple systems glycolaldehyde emission is
detected only in one component. The case of the SVS13-A+B and IRAS4-A1+A2
systems support that the detection of glycolaldehyde (at least in the present
Perseus sample) indicates older protostars (i.e. SVS13-A and IRAS4-A2), evolved
enough to develop the hot-corino region (i.e. 100 K in the inner 100 au).
However, only two systems do not allow us to firmly conclude whether the
primary factor leading to the detection of glycolaldehyde emission is the
environments hosting the protostars, evolution (e.g. low value of Lsubmm/Lint),
or accretion luminosity (high Lint).Comment: A&A, in pres
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
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
First results from the CALYPSO IRAM-PdBI survey - III. Monopolar jets driven by a proto-binary system in NGC1333-IRAS2A
Context: The earliest evolutionary stages of low-mass protostars are
characterised by hot and fast jets which remove angular momentum from the
circumstellar disk, thus allowing mass accretion onto the central object.
However, the launch mechanism is still being debated. Aims: We would like to
exploit high-angular (~ 0.8") resolution and high-sensitivity images to
investigate the origin of protostellar jets using typical molecular tracers of
shocked regions, such as SiO and SO. Methods: We mapped the inner 22" of the
NGC1333-IRAS2A protostar in SiO(5-4), SO(65-54), and the continuum emission at
1.4 mm using the IRAM Plateau de Bure interferometer in the framework of the
CALYPSO IRAM large program. Results: For the first time, we disentangle the
NGC1333-IRAS2A Class 0 object into a proto-binary system revealing two
protostars (MM1, MM2) separated by ~ 560 AU, each of them driving their own
jet, while past work considered a single protostar with a quadrupolar outflow.
We reveal (i) a clumpy, fast (up to |V-VLSR| > 50 km/s), and blueshifted jet
emerging from the brightest MM1 source, and (ii) a slower redshifted jet,
driven by MM2. Silicon monoxide emission is a powerful tracer of
high-excitation (Tkin > 100 K; n(H2) > 10^5 cm-3) jets close to the launching
region. At the highest velocities, SO appears to mimic SiO tracing the jets,
whereas at velocities close to the systemic one, SO is dominated by extended
emission, tracing the cavity opened by the jet. Conclusions: Both jets are
intrinsically monopolar, and intermittent in time. The dynamical time of the
SiO clumps is < 30-90 yr, indicating that one-sided ejections from protostars
can take place on these timescales.Comment: Astronomy & Astrophysics Letter, in pres
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
Transcriptional and Metabolic Response of Wine-Related Lactiplantibacillus plantarum to Different Conditions of Aeration and Nitrogen Availability
Lactic acid bacteria (LAB) perform the process of malolactic fermentation (MLF) in wine. Availability of oxygen and nitrogen nutrients could influence LAB growth, malolactic activity, and other metabolic pathways, impacting the subsequent wine quality. The impact of these two factors has received limited investigation within LAB, especially on a transcriptome level. The aim of this study was to evaluate metabolic changes in the strain Lactiplantibacillus plantarum IWBT B063, growing in synthetic grape juice medium (GJM) under different oxygen exposure conditions, and with low availability of nitrogen-based nutrients. Next-generation sequencing was used to analyze expression across the transcriptome (RNA-seq), in combination with conventional microbiological and chemical analysis. L. plantarum consumed the malic acid present in all the conditions evaluated, with a slight delay and impaired growth for nitrogen limitation and for anaerobiosis. Comparison of L. plantarum transcriptome during growth in GJM with and without O-2 revealed differential expression of 148 functionally annotated genes, which were mostly involved in carbohydrate metabolism, genetic information processing, and signaling and cellular processes. In particular, genes with a protective role against oxidative stress and genes related to amino acid metabolism were differentially expressed. This study confirms the suitability of L. plantarum IWBT B063 to carry out MLF in different environmental conditions due to its potential adaption to the stress conditions tested and provides a better understanding of the genetic background of an industrially relevant strain
Evolution of skewness and kurtosis of cosmic density fields
Methods. We perform numerical simulations of the evolution of the cosmic web
for the conventional LCDM model. The simulations cover a wide range of box
sizes L = 256 - 4000 Mpc/h, mass and force resolutions and epochs from very
early moments z = 30 to the present moment z = 0. We calculate density fields
with various smoothing lengths to find the dependence of the density field on
smoothing scale. We calculate PDF and its moments - variance, skewness and
kurtosis. Results. We focus on the third (skewness S) and fourth (kurtosis K)
moments of the distribution functions: their dependence on the smoothing scale,
the amplitude of fluctuations and the redshift. During the evolution the
reduced skewness and reduced kurtosis present
a complex behaviour: at a fixed redshift curves of and
steeply increase with at and then flatten
out and become constant at . If we fix the smoothing scale ,
then after reaching the maximum at , the curves at large
start to gradually decline. We provide accurate fits for the evolution
of . Skewness and kurtosis approach at early epochs constant
levels, depending on smoothing length: and . Conclusions. Most of statistics of dark matter clustering (e.g.,
halo mass function or concentration-mass relation) are nearly universal: they
mostly depend on the with the relatively modest correction to explicit
dependence on the redshift. We find just the opposite for skewness and
kurtosis: the dependence of moments on evolutionary epoch and smoothing
length is very different, together they determine the evolution of
uniquely. The evolution of and cannot be
described by current theoretical approximations.Comment: 17 pages, 14 figures, revised version accepted by Astronomy and
Astrophysic
The Structural Colors of Photonic Glasses
The color of materials usually originates from a combination of wavelength-dependent absorption and scattering. Controlling the color without the use of absorbing dyes is of practical interest, not only because of undesired bleaching properties of dyes but also regarding minimization of environmental and health issues. Color control without dyes can be achieved by tuning the material's scattering properties in controlling size and spatial arrangement of scatterers. Herein, calibrated photonic glasses (PGs), which are isotropic materials made by random aggregation of nonabsorbing, monodisperse colloidal polystyrene spheres, are used to generate a wide spectral range of purely structural, angular-independent colors. Experimental reflectance spectra for different sized spheres compare well with a recent theoretical model, which establishes the latter as a tool for color mapping in PGs. It allows to determine the range of visible colors accessible in PGs as function of size, packing fraction, and refractive index of scatterers. It also predicts color saturation on top of the white reflectance as function of the sample's optical thickness. Blue, green, and red are obtained even with low index, while saturated green, cyan, yellow, and magenta can be reached in higher index PGs over several orders of magnitude of sample thickness.Deutsche Forschungsgemeinschaft. Grant Number: SFB1214
Swiss National Science Foundation. Grant Number: 200020M_162846
Alexander von Humboldt Foundatio
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
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