843 research outputs found
Ion structure in warm dense matter: benchmarking solutions of hypernetted-chain equations by first-principle simulations
We investigate the microscopic structure of strongly coupled ions in warm dense matter using ab initio simulations and hypernetted chain (HNC) equations. We demonstrate that an approximate treatment of quantum effects by weak pseudopotentials fails to describe the highly degenerate electrons in warm dense matter correctly. However, one-component HNC calculations for the ions agree well with first-principles simulations if a linearly screened Coulomb potential is used. These HNC results can be further improved by adding a short-range repulsion that accounts for bound electrons. Examples are given for recently studied light elements, lithium and beryllium, and for aluminum where the extra short-range repulsion is essential
The fragmentation of expanding shells II: Thickness matters
We study analytically the development of gravitational instability in an
expanding shell having finite thickness. We consider three models for the
radial density profile of the shell: (i) an analytic uniform-density model,
(ii) a semi-analytic model obtained by numerical solution of the hydrostatic
equilibrium equation, and (iii) a 3D hydrodynamic simulation. We show that all
three profiles are in close agreement, and this allows us to use the first
model to describe fragments in the radial direction of the shell. We then use
non-linear equations describing the time-evolution of a uniform oblate spheroid
to derive the growth rates of shell fragments having different sizes. This
yields a dispersion relation which depends on the shell thickness, and hence on
the pressure confining the shell. We compare this dispersion relation with the
dispersion relation obtained using the standard thin-shell analysis, and show
that, if the confining pressure is low, only large fragments are unstable. On
the other hand, if the confining pressure is high, fragments smaller than
predicted by the thin-shell analysis become unstable. Finally, we compare the
new dispersion relation with the results of 3D hydrodynamic simulations, and
show that the two are in good agreement.Comment: 9 pages, 9 figures, accepted by MNRA
Two-Dimensional Hydrodynamic Models of Super Star Clusters with a Positive Star Formation Feedback
Using the hydrodynamic code ZEUS, we perform 2D simulations to determine the
fate of the gas ejected by massive stars within super star clusters. It turns
out that the outcome depends mainly on the mass and radius of the cluster. In
the case of less massive clusters, a hot high velocity ( km
s) stationary wind develops and the metals injected by supernovae are
dispersed to large distances from the cluster. On the other hand, the density
of the thermalized ejecta within massive and compact clusters is sufficiently
large as to immediately provoke the onset of thermal instabilities. These
deplete, particularly in the central densest regions, the pressure and the
pressure gradient required to establish a stationary wind, and instead the
thermally unstable parcels of gas are rapidly compressed, by a plethora of
re-pressurizing shocks, into compact high density condensations. Most of these
are unable to leave the cluster volume and thus accumulate to eventually feed
further generations of star formation.
The simulations cover an important fraction of the parameter-space, which
allows us to estimate the fraction of the reinserted gas which accumulates
within the cluster and the fraction that leaves the cluster as a function of
the cluster mechanical luminosity, the cluster size and heating efficiency.Comment: Accepted for publication in ApJ; 27 pages, 9 figures, 1 tabl
The Carina Flare: What can fragments in the wall tell us?
CO(J=2--1) and CO(J=2--1) observations of the molecular cloud
G285.90+4.53 (Cloud~16) in the Carina Flare supershell (GSH287+04-17) with the
APEX telescope are presented. With an algorithm DENDROFIND we identify 51
fragments and compute their sizes and masses. We discuss their mass spectrum
and interpret it as being the result of the shell fragmentation process
described by the pressure assisted gravitational instability - PAGI. We
conclude that the explanation of the clump mass function needs a combination of
gravity with pressure external to the shell.Comment: 19 pages, 14 figures, accepted by A&
Identification and characterization of DAMs mutations associated with early blooming in sweet cherry, and validation of DNA-based markers for selection
Dormancy release and bloom time of sweet cherry cultivars depend on the environment and the genotype. The knowledge of these traits is essential for cultivar adaptation to different growing areas, and to ensure fruit set in the current climate change scenario. In this work, the major sweet cherry bloom time QTL qP-BT1.1m (327 Kbs; Chromosome 1) was scanned for candidate genes in the Regina cv genome. Six MADS-box genes (PavDAMs), orthologs to peach and Japanese apricot DAMs, were identified as candidate genes for bloom time regulation. The complete curated genomic structure annotation of these genes is reported. To characterize PavDAMs intra-specific variation, genome sequences of cultivars with contrasting chilling requirements and bloom times (N = 13), were then mapped to the ‘Regina’ genome. A high protein sequence conservation (98.8–100%) was observed. A higher amino acid variability and several structural mutations were identified in the low-chilling and extra-early blooming cv Cristobalina. Specifically, a large deletion (694 bp) upstream of PavDAM1, and various INDELs and SNPs in contiguous PavDAM4 and -5 UTRs were identified. PavDAM1 upstream deletion in ‘Cristobalina’ revealed the absence of several cis-acting motifs, potentially involved in PavDAMs expression. Also, due to this deletion, a non-coding gene expressed in late-blooming ‘Regina’ seems truncated in ‘Cristobalina’. Additionally, PavDAM4 and -5 UTRs mutations revealed different splicing variants between ‘Regina’ and ‘Cristobalina’ PavDAM5. The results indicate that the regulation of PavDAMs expression and post-transcriptional regulation in ‘Cristobalina’ may be altered due to structural mutations in regulatory regions. Previous transcriptomic studies show differential expression of PavDAM genes during dormancy in this cultivar. The results indicate that ‘Cristobalina’ show significant amino acid differences, and structural mutations in PavDAMs, that correlate with low-chilling and early blooming, but the direct implication of these mutations remains to be determined. To complete the work, PCR markers designed for the detection of ‘Cristobalina’ structural mutations in PavDAMs, were validated in an F2 population and a set of cultivars. These PCR markers are useful for marker-assisted selection of early blooming seedlings, and probably low-chilling, from ‘Cristobalina’, which is a unique breeding source for these traits. © Copyright © 2021 Calle, Grimplet, Le Dantec and Wünsch
Self-Consistent Pushing and Cranking Corrections to the Meson Fields of the Chiral Quark-Loop Soliton
We study translational and spin-isospin symmetry restoration for the
two-flavor chiral quark-loop soliton. Instead of a static soliton at rest we
consider a boosted and rotating hedgehog soliton. Corrected classical meson
fields are obtained by minimizing a corrected energy functional which has been
derived by semi-classical methods ('variation after projection'). We evaluate
corrected meson fields in the region 300 MeV \le M \le 600 MeV of constituent
quark masses M and compare them with the uncorrected fields. We study the
effect of the corrections on various expectation values of nuclear observables
such as the root-mean square radius, the axial-vector coupling constant,
magnetic moments and the delta-nucleon mass splitting.Comment: 19 pages, LaTeX, 7 postscript figures included using 'psfig.sty', to
appear in Int.J.Mod.Phys.
The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae
We study the impact of stellar winds and supernovae on the multi-phase
interstellar medium using three-dimensional hydrodynamical simulations carried
out with FLASH. The selected galactic disc region has a size of (500 pc) x
5 kpc and a gas surface density of 10 M/pc. The simulations
include an external stellar potential and gas self-gravity, radiative cooling
and diffuse heating, sink particles representing star clusters, stellar winds
from these clusters which combine the winds from indi- vidual massive stars by
following their evolution tracks, and subsequent supernova explosions. Dust and
gas (self-)shielding is followed to compute the chemical state of the gas with
a chemical network. We find that stellar winds can regulate star (cluster)
formation. Since the winds suppress the accretion of fresh gas soon after the
cluster has formed, they lead to clusters which have lower average masses
(10 - 10 M) and form on shorter timescales (10 -
10 Myr). In particular we find an anti-correlation of cluster mass and
accretion time scale. Without winds the star clusters easily grow to larger
masses for ~5 Myr until the first supernova explodes. Overall the most massive
stars provide the most wind energy input, while objects beginning their
evolution as B-type stars contribute most of the supernova energy input. A
significant outflow from the disk (mass loading 1 at 1 kpc) can be
launched by thermal gas pressure if more than 50% of the volume near the disc
mid-plane can be heated to T > 3x10 K. Stellar winds alone cannot create a
hot volume-filling phase. The models which are in best agreement with observed
star formation rates drive either no outflows or weak outflows.Comment: 23 pages; submitted to MNRA
THz-range free-electron laser ESR spectroscopy: techniques and applications in high magnetic fields
The successful use of picosecond-pulse free-electron-laser (FEL) radiation
for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy
has been demonstrated. The combination of two linac-based FELs (covering the
wavelength range of 4 - 250 m) with pulsed magnetic fields up to 70 T
allows for multi-frequency ESR spectroscopy in a frequency range of 1.2 - 75
THz with a spectral resolution better than 1%. The performance of the
spectrometer is illustrated with ESR spectra obtained in the
2,2-diphenyl-1-picrylhydrazyl (DPPH) and the low-dimensional organic material
(CHN)CuCl.Comment: 9 pages, 9 figures. Rev. Sci. Instrum., accepte
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