234 research outputs found
Influence of adaptive mesh refinement and the hydro solver on shear-induced mass stripping in a minor-merger scenario
We compare two different codes for simulations of cosmological structure
formation to investigate the sensitivity of hydrodynamical instabilities to
numerics, in particular, the hydro solver and the application of adaptive mesh
refinement (AMR). As a simple test problem, we consider an initially spherical
gas cloud in a wind, which is an idealized model for the merger of a subcluster
or galaxy with a big cluster. Based on an entropy criterion, we calculate the
mass stripping from the subcluster as a function of time. Moreover, the
turbulent velocity field is analyzed with a multi-scale filtering technique. We
find remarkable differences between the commonly used PPM solver with
directional splitting in the Enzo code and an unsplit variant of PPM in the Nyx
code, which demonstrates that different codes can converge to systematically
different solutions even when using uniform grids. For the test case of an
unbound cloud, AMR simulations reproduce uniform-grid results for the mass
stripping quite well, although the flow realizations can differ substantially.
If the cloud is bound by a static gravitational potential, however, we find
strong sensitivity to spurious fluctuations which are induced at the cutoff
radius of the potential and amplified by the bow shock. This gives rise to
substantial deviations between uniform-grid and AMR runs performed with Enzo,
while the mass stripping in Nyx simulations of the subcluster is nearly
independent of numerical resolution and AMR. Although many factors related to
numerics are involved, our study indicates that unsplit solvers with advanced
flux limiters help to reduce grid effects and to keep numerical noise under
control, which is important for hydrodynamical instabilities and turbulent
flows.Comment: 23 pages, 18 figures, accepted for publication by Astronomy and
Computin
Un-rooted grafted cuttings for eggplant plug-transplant production and shipping: simulated transportation and healing requirements
Vegetable grafting is one of the most effective eco-friendly techniques to overcome pests and soilborne diseases in modern cropping systems of fruiting vegetables. Due to the increased farmersâ preference for grafted seedlings of high quality and better performance, the use of vegetable grafted plants is rapidly spreading and expanding over the world and intensive researches on new commercial production systems are under way. However, in many areas of the world, due to the high cost of skilled manpower, the use of grafted plug plants is still limited causing a relatively slow development of the grafting nursery industry. The aim of this work was to evaluate a possible use of un-rooted grafted cuttings as means of propagation and distribution of eggplant transplants. In this experiment, un-rooted grafted eggplant cuttings (âBirgahâ eggplant scion with Solanum torvum rootstock) harvested after diverse healing times [0 (DIH 0), 1 (DIH 1), 3 (DIH 3), 5 (DIH 5), or 7 (DIH 7) days in healing] were exposed to 20, 14 and 8°C âsimulated transportation temperatureâ and dark condition in a growth chamber for 72 hours. After 72 hours of the simulated transportation treatment, all unârooted grafted cuttings were transferred into the greenhouse for rooting. The results showed that S. torvum is a suitable rootstock for applying the un-rooted grafted cutting propagation technique. All grafted cuttings reached the grafting success (100%) and all un-rooted grafted cuttings developed roots at the end of the rooting stage (100%). Regardless of the simulated shipping conditions, the treatment DIH 0 gave the best results in terms of number of leaves after rooting (3.8 leaves), shoot fresh and dry weight after 7 days of growth (3.92 and 0.46 g, respectively), fresh weight of the roots (1.34 g), and plantlet visual quality of the finished plug transplants (8.8). This innovative production/ shipping method might be successfully used in areas where local nurseries do not have high grafting ability
Turbulence in the ICM from mergers, cool-core sloshing and jets: results from a new multi-scale filtering approach
We have designed a simple multi-scale method that identifies turbulent
motions in hydrodynamical grid simulations. The method does not assmume ant
a-priori coherence scale to distinguish laminar and turbulent flows. Instead,
the local mean velocity field around each cell is reconstructed with a
multi-scale filtering technique, yielding the maximum scale of turbulent eddies
by means of iterations. The method is robust, fast and easily applicable to any
grid simulation. We present here the application of this technique to the study
of spatial and spectral properties of turbulence in the intra cluster medium,
measuring turbulent diffusion and anisotropy of the turbulent velocity field
for a variety of driving mechanisms: a) accretion of matter in galaxy clusters
(simulated with ENZO); b) sloshing motions around cool-cores (simulated with
FLASH); c) jet outflows from active galactic nuclei, AGN (simulated with
FLASH). The turbulent velocities driven by matter accretion in galaxy clusters
are mostly tangential in the inner regions (inside the cluster virial radius)
and isotropic in regions close to the virial radius. The same is found for
turbulence excited by cool core sloshing, while the jet outflowing from AGN
drives mostly radial turbulence motions near its sonic point and beyond.
Turbulence leads to a diffusivity in the range =10^29-10^30 cm^2/s in the intra
cluster medium. On average, the energetically dominant mechanism of turbulence
driving in the intra cluster medium is represented by accretion of matter and
major mergers during clusters evolution.Comment: 19 pages, 20 figures. Astronomy and Astrophysics, in pres
GUT microbiota change and time of restore in intensive care therapy : a case report
Exposure of gut microbiota to antibiotics can promote antibiotic resistance and development of diseases caused by multi-drug-resistant organisms. Here we present a case of a 54-year-old male patient with a diagnosis of acute cholecystitis with significant biliary duct leakage, admitted to Intensive Care Unit (ICU) due to a septic syndrome after surgery. Fecal microbial population was analyzed by DGGE and Real Time PCR during and after a combined antibiotic therapy and enteral nutritional feeding. Gut microbiota dysbiosis was demonstrated during ICU recovery. After antibiotic therapy discontinuation and the switch to normal diet, microbial gut population gradually increased up to values comparable with those of a healthy subject. Bifidobacterium spp. took longer to re-stabilize, reaching normal value after two weeks. Our case report corroborates the resilient nature of gut microbiota, but points out the long time needed to recover after antibiotic treatment, paving the way to supplementation with key probiotic species
Cluster magnetic fields through the study of polarized radio halos in the SKA era
Galaxy clusters are unique laboratories to investigate turbulent fluid
motions and large scale magnetic fields. Synchrotron radio halos at the center
of merging galaxy clusters provide the most spectacular and direct evidence of
the presence of relativistic particles and magnetic fields associated with the
intracluster medium. The study of polarized emission from radio halos is
extremely important to constrain the properties of intracluster magnetic fields
and the physics of the acceleration and transport of the relativistic
particles. However, detecting this polarized signal is a very hard task with
the current radio facilities.We use cosmological magneto-hydrodynamical
simulations to predict the expected polarized surface brightness of radio halos
at 1.4 GHz. We compare these expectations with the sensitivity and the
resolution reachable with the SKA1. This allows us to evaluate the potential
for studying intracluster magnetic fields in the surveys planned for SKA1.Comment: 11 pages, 4 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)10
Evolution of shocks and turbulence in major cluster mergers
We performed a set of cosmological simulations of major mergers in galaxy
clusters to study the evolution of merger shocks and the subsequent injection
of turbulence in the post-shock region and in the intra-cluster medium (ICM).
The computations were done with the grid-based, adaptive mesh refinement hydro
code Enzo, using an especially designed refinement criteria for refining
turbulent flows in the vicinity of shocks. A substantial amount of turbulence
energy is injected in the ICM due to major merger. Our simulations show that
the shock launched after a major merger develops an ellipsoidal shape and gets
broken by the interaction with the filamentary cosmic web around the merging
cluster. The size of the post-shock region along the direction of shock
propagation is about 300 kpc h^-1, and the turbulent velocity dispersion in
this region is larger than 100 km s^-1. Scaling analysis of the turbulence
energy with the cluster mass within our cluster sample is consistent with
M^(5/3), i.e. the scaling law for the thermal energy in the self-similar
cluster model. This clearly indicates the close relation between virialization
and injection of turbulence in the cluster evolution. We found that the ratio
of the turbulent to total pressure in the cluster core within 2 Gyr after the
major merger is larger than 10%, and it takes about 4 Gyr to get relaxed, which
is substantially longer than typically assumed in the turbulent re-acceleration
models, invoked to explain the statistics of observed radio halos. Striking
similarities in the morphology and other physical parameters between our
simulations and the "symmetrical radio relics" found at the periphery of the
merging cluster A3376 are finally discussed. In particular, the interaction
between the merger shock and the filaments surrounding the cluster could
explain the presence of "notch-like" features at the edges of the double
relics.Comment: 16 pages, 19 figures, Published in Astrophysical Journal (online) and
printed version will be published on 1st January, 201
Lung response to prone positioning in mechanically-ventilated patients with COVID-19
Background: Prone positioning improves survival in moderate-to-severe acute respiratory distress syndrome (ARDS) unrelated to the novel coronavirus disease (COVID-19). This benefit is probably mediated by a decrease in alveolar collapse and hyperinflation and a more homogeneous distribution of lung aeration, with fewer harms from mechanical ventilation. In this preliminary physiological study we aimed to verify whether prone positioning causes analogue changes in lung aeration in COVID-19. A positive result would support prone positioning even in this other population. Methods: Fifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography in the supine and prone position with a constant positive end-expiratory pressure (PEEP) within three days of endotracheal intubation. Using quantitative analysis, we measured the volume of the non-aerated, poorly-aerated, well-aerated, and over-aerated compartments and the gas-to-tissue ratio of the ten vertical levels of the lung. In addition, we expressed the heterogeneity of lung aeration with the standardized median absolute deviation of the ten vertical gas-to-tissue ratios, with lower values indicating less heterogeneity. Results: By the time of the study, PEEP was 12 (10â14) cmH2O and the PaO2:FiO2 107 (84â173) mmHg in the supine position. With prone positioning, the volume of the non-aerated compartment decreased by 82 (26â147) ml, of the poorly-aerated compartment increased by 82 (53â174) ml, of the normally-aerated compartment did not significantly change, and of the over-aerated compartment decreased by 28 (11â186) ml. In eight (53%) patients, the volume of the over-aerated compartment decreased more than the volume of the non-aerated compartment. The gas-to-tissue ratio of the ten vertical levels of the lung decreased by 0.34 (0.25â0.49) ml/g per level in the supine position and by 0.03 (â 0.11 to 0.14) ml/g in the prone position (p < 0.001). The standardized median absolute deviation of the gas-to-tissue ratios of those ten levels decreased in all patients, from 0.55 (0.50â0.71) to 0.20 (0.14â0.27) (p < 0.001). Conclusions: In fifteen patients with COVID-19, prone positioning decreased alveolar collapse, hyperinflation, and homogenized lung aeration. A similar response has been observed in other ARDS, where prone positioning improves outcome. Therefore, our data provide a pathophysiological rationale to support prone positioning even in COVID-19
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