872 research outputs found
Effect of inelasticity on the phase transitions of a thin vibrated granular layer
We describe an experimental and computational investigation of the ordered
and disordered phases of a vibrating thin, dense granular layer composed of
identical metal spheres. We compare the results from spheres with different
amounts of inelasticity and show that inelasticity has a strong effect on the
phase diagram. We also report the melting of an ordered phase to a homogeneous
disordered liquid phase at high vibration amplitude or at large inelasticities.
Our results show that dissipation has a strong effect on ordering and that in
this system ordered phases are absent entirely in highly inelastic materials.Comment: 5 pages, 5 figures, published in Physical Review E. Title of first
version slightly change
The dynamics of thin vibrated granular layers
We describe a series of experiments and computer simulations on vibrated
granular media in a geometry chosen to eliminate gravitationally induced
settling. The system consists of a collection of identical spherical particles
on a horizontal plate vibrating vertically, with or without a confining lid.
Previously reported results are reviewed, including the observation of
homogeneous, disordered liquid-like states, an instability to a `collapse' of
motionless spheres on a perfect hexagonal lattice, and a fluctuating,
hexagonally ordered state. In the presence of a confining lid we see a variety
of solid phases at high densities and relatively high vibration amplitudes,
several of which are reported for the first time in this article. The phase
behavior of the system is closely related to that observed in confined
hard-sphere colloidal suspensions in equilibrium, but with modifications due to
the effects of the forcing and dissipation. We also review measurements of
velocity distributions, which range from Maxwellian to strongly non-Maxwellian
depending on the experimental parameter values. We describe measurements of
spatial velocity correlations that show a clear dependence on the mechanism of
energy injection. We also report new measurements of the velocity
autocorrelation function in the granular layer and show that increased
inelasticity leads to enhanced particle self-diffusion.Comment: 11 pages, 7 figure
Performance characterization and near-realtime monitoring of MUSE adaptive optics modes at Paranal
The Multi Unit Spectroscopic Explorer (MUSE) is an integral field
spectrograph on the Very Large Telescope Unit Telescope 4, capable of laser
guide star assisted and tomographic adaptive optics using the GALACSI module.
Its observing capabilities include a wide field (1 square arcmin), ground layer
AO mode (WFM-AO) and a narrow field (7.5"x7.5"), laser tomography AO mode
(NFM-AO). The latter has had several upgrades in the 4 years since
commissioning, including an optimisation of the control matrices for the AO
system and a new sub-electron noise detector for its infra-red low order
wavefront sensor. We set out to quantify the NFM-AO system performance by
analysing 230 spectrophotometric standard star observations taken over
the last 3 years. To this end we expand upon previous work, designed to
facilitate analysis of the WFM-AO system performance. We briefly describe the
framework that will provide a user friendly, semi-automated way for system
performance monitoring during science operations. We provide the results of our
performance analysis, chiefly through the measured Strehl ratio and full width
at half maximum (FWHM) of the core of the point spread function (PSF) using two
PSF models, and correlations with atmospheric conditions. These results will
feed into a range of applications, including providing a more accurate
prediction of the system performance as implemented in the exposure time
calculator, and the associated optimization of the scientific output for a
given set of limiting atmospheric conditions.Comment: SPIE proceedings (2022), Observatory Operations: Strategies,
Processes, and Systems I
Thermal Segregation Beyond Navier-Stokes
A dilute suspension of impurities in a low density gas is described by the
Boltzmann and Boltzman-Lorentz kinetic theory. Scaling forms for the species
distribution functions allow an exact determination of the hydrodynamic fields,
without restriction to small thermal gradients or Navier-Stokes hydrodynamics.
The thermal diffusion factor characterizing sedimentation is identified in
terms of collision integrals as functions of the mechanical properties of the
particles and the temperature gradient. An evaluation of the collision
integrals using Sonine polynomial approximations is discussed. Conditions for
segregation both along and opposite the temperature gradient are found, in
contrast to the Navier-Stokes description for which no segregation occurs.Comment: 9 figure
Non-Newtonian Couette-Poiseuille flow of a dilute gas
The steady state of a dilute gas enclosed between two infinite parallel
plates in relative motion and under the action of a uniform body force parallel
to the plates is considered. The Bhatnagar-Gross-Krook model kinetic equation
is analytically solved for this Couette-Poiseuille flow to first order in the
force and for arbitrary values of the Knudsen number associated with the shear
rate. This allows us to investigate the influence of the external force on the
non-Newtonian properties of the Couette flow. Moreover, the Couette-Poiseuille
flow is analyzed when the shear-rate Knudsen number and the scaled force are of
the same order and terms up to second order are retained. In this way, the
transition from the bimodal temperature profile characteristic of the pure
force-driven Poiseuille flow to the parabolic profile characteristic of the
pure Couette flow through several intermediate stages in the Couette-Poiseuille
flow are described. A critical comparison with the Navier-Stokes solution of
the problem is carried out.Comment: 24 pages, 5 figures; v2: discussion on boundary conditions added; 10
additional references. Published in a special issue of the journal "Kinetic
and Related Models" dedicated to the memory of Carlo Cercignan
Salinity impairs photosynthetic capacity and enhances carotenoid-related gene expression and biosynthesis in tomato (Solanum lycopersicum L. cv. Micro-Tom)
Indexación: ScopusCarotenoids are essential components of the photosynthetic antenna and reaction center complexes, being also responsible for antioxidant defense, coloration, and many other functions in multiple plant tissues. In tomato, salinity negatively affects the development of vegetative organs and productivity, but according to previous studies it might also increase fruit color and taste, improving its quality, which is a current agricultural challenge. The fruit quality parameters that are increased by salinity are cultivar-specific and include carotenoid, sugar, and organic acid contents. However, the relationship between vegetative and reproductive organs and response to salinity is still poorly understood. Considering this, Solanum lycopersicum cv. Micro-Tom plants were grown in the absence of salt supplementation as well as with increasing concentrations of NaCl for 14 weeks, evaluating plant performance from vegetative to reproductive stages. In response to salinity, plants showed a significant reduction in net photosynthesis, stomatal conductance, PSII quantum yield, and electron transport rate, in addition to an increase in non-photochemical quenching. In line with these responses the number of tomato clusters decreased, and smaller fruits with higher soluble solids content were obtained. Mature-green fruits also displayed a salt-dependent higher induction in the expression of PSY1, PDS, ZDS, and LYCB, key genes of the carotenoid biosynthesis pathway, in correlation with increased lycopene, lutein, _- carotene, and violaxanthin levels. These results suggest a key relationship between photosynthetic plant response and yield, involving impaired photosynthetic capacity, increased carotenoid-related gene expression, and carotenoid biosynthesis.https://peerj.com/articles/9742
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