319 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
Hybrids and allied species as potential rootstocks for eggplant: Effect of grafting on vigour, yield and overall fruit quality traits
Grafting of fruiting vegetables is an effective technique to overcome pests and diseases in modern cropping
systems and it is often used to improve yield and fruit quality. Eggplant is an important vegetable crop that
benefits significantly from grafting. In this regards, the exploitation, valorization and breeding of new rootstock
genotypes as possible substitute to those commonly used (Solanum torvum and tomato hybrids) would permit an
intensive eggplant crop system in those situations where a rootstock rotation is required. In the present article,
we study the effects of several potential rootstocks including both wild/allied species of eggplant [S. torvum
(STO), S. macrocarpon (SMA), S. aethiopicum (accession SASI), S. aethiopicum (accession SASa2), S. paniculatum
(jurubeba) (SPA) and S. indicum (SIN)] and Msa 2/2 E7 and 460 CAL. eggplant hybrids on plant vigor, yield and
fruit characteristics of eggplant F1 hybrid (âBirgahâ), in two spring-summer growing seasons (2014 and 2015).
SPA and the hybrids Msa 2/2 E7 and 460 CAL. displayed a high percentage of grafting success. âBirgahâ scion
grafted onto the two above-mentioned rootstocks showed a notable vigour and yield. Both rootstocks did not
promote any unfavorable effects on apparent fruit quality traits and overall fruit composition. Furthermore, the
concentration of glycoalkaloids in the fruit remained below the recommended safety value (200 mg/100 g of
dw). These results suggest that SPA and Msa 2/2 E7 and 460 CAL. eggplant hybrids might represent a potential
rootstock alternative to S. torvum
Uncertainties and robustness of the ignition process in type Ia supernovae
It is widely accepted that the onset of the explosive carbon burning in the
core of a CO WD triggers the ignition of a SN Ia. The features of the ignition
are among the few free parameters of the SN Ia explosion theory. We explore the
role for the ignition process of two different issues: firstly, the ignition is
studied in WD models coming from different accretion histories. Secondly, we
estimate how a different reaction rate for C-burning can affect the ignition.
Two-dimensional hydrodynamical simulations of temperature perturbations in the
WD core ("bubbles") are performed with the FLASH code. In order to evaluate the
impact of the C-burning reaction rate on the WD model, the evolution code
FLASH_THE_TORTOISE from Lesaffre et al. (2006) is used. In different WD models
a key role is played by the different gravitational acceleration in the
progenitor's core. As a consequence, the ignition is disfavored at a large
distance from the WD center in models with a larger central density, resulting
from the evolution of initially more massive progenitors. Changes in the C
reaction rate at T < 5e8 K slightly influence the ignition density in the WD
core, while the ignition temperature is almost unaffected. Recent measurements
of new resonances in the C-burning reaction rate (Spillane et al. 2007) do not
affect the core conditions of the WD significantly. This simple analysis,
performed on the features of the temperature perturbations in the WD core,
should be extended in the framework of the state-of-the-art numerical tools for
studying the turbulent convection and ignition in the WD core. Future
measurements of the C-burning reactions cross section at low energy, though
certainly useful, are not expected to affect dramatically our current
understanding of the ignition process.Comment: 7 pages, 5 figures, A&A accepte
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