8,805 research outputs found
Nuclear DNA contents, rDNAs, and karyotype evolution in subgenus Vicia: III. The heterogeneous section Hypechusa.
Abstract: Nuclear DNA contents, automated karyotype analyses, and sequences of internal transcribed spacers from ribosomal genes have been determined in the species belonging to section Hypechusa of the sub-genus Vicia. Karyomorphological results and phylogenetic data generated from the comparison of rDNA ( genes coding for rRNA) sequences showed that sect. Hypechusa is not monophyletic; however, some monophyletic units are apparent ( one including Vicia galeata, V. hyrcanica, V. noeana, and V. tigridis, another including V. assyriaca, V. hybrida, V. melanops, V. mollis, and V. sericocarpa), which partly correspond to morphology-based infrasectional groups. The relationships among these species and the species in sections Faba, Narbonensis, Bithynicae, and Peregrinae have been also investigated. Nuclear DNA contents, automated karyotype analyses, and sequences of internal transcribed spacers from ribosomal genes have been determined in the species belonging to section Hypechusa of the subgenus Vicia. Karyomorphological results and phylogenetic data generated from the comparison of rDNA (genes coding for rRNA) sequences showed that sect. Hypechusa is not monophyletic; however, some monophyletic units are apparent (one including Vicia galeata, V. hyrcanica, V. noeana, and V. tigridis, another including V. assyriaca, V. hybrida, V. melanops, V. mollis, and V. sericocarpa), which partly correspond to morphology-based infrasectional groups. The relationships among these species and the species in sections Faba, Narbonensis, Bithynicae, and Peregrinae have been also investigated
Triggering the Formation of Halo Globular Clusters with Galaxy Outflows
We investigate the interactions of high-redshift galaxy outflows with
low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While
atomic cooling allows star formation in larger primordial objects, such
"minihalos" are generally unable to form stars by themselves. However, the
large population of high-redshift starburst galaxies may have induced
widespread star formation in these objects, via shocks that caused intense
cooling both through nonequilibrium H2 formation and metal-line emission. Using
a simple analytic model, we show that the resulting star clusters naturally
reproduce three key features of the observed population of halo globular
clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to
the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the
momentum imparted in such interactions is sufficient to strip the gas from its
associated dark matter halo, explaining why GCs do not reside in dark matter
potential wells. Finally, the mixing of ejected metals into the primordial gas
is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a
given GC, while at the same time allowing for a large spread in metallicity
between different clusters. To study this possibility in detail, we use a
simple 1D numerical model of turbulence transport to simulate mixing in
cloud-outflow interactions. We find that as the shock shears across the side of
the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched
material into > 20% of the cloud. Such estimates ignore the likely presence of
large-scale vortices, however, which would further enhance turbulence
generation. Thus quantitative mixing predictions must await more detailed
numerical studies.Comment: 21 pages, 11 figures, Apj in pres
Fourier mode dynamics for the nonlinear Schroedinger equation in one-dimensional bounded domains
We analyze the 1D focusing nonlinear Schr\"{o}dinger equation in a finite
interval with homogeneous Dirichlet or Neumann boundary conditions. There are
two main dynamics, the collapse which is very fast and a slow cascade of
Fourier modes. For the cubic nonlinearity the calculations show no long term
energy exchange between Fourier modes as opposed to higher nonlinearities. This
slow dynamics is explained by fairly simple amplitude equations for the
resonant Fourier modes. Their solutions are well behaved so filtering high
frequencies prevents collapse. Finally these equations elucidate the unique
role of the zero mode for the Neumann boundary conditions
Creep, Relaxation and Viscosity Properties for Basic Fractional Models in Rheology
The purpose of this paper is twofold: from one side we provide a general
survey to the viscoelastic models constructed via fractional calculus and from
the other side we intend to analyze the basic fractional models as far as their
creep, relaxation and viscosity properties are considered. The basic models are
those that generalize via derivatives of fractional order the classical
mechanical models characterized by two, three and four parameters, that we
refer to as Kelvin-Voigt, Maxwell, Zener, anti-Zener and Burgers. For each
fractional model we provide plots of the creep compliance, relaxation modulus
and effective viscosity in non dimensional form in terms of a suitable time
scale for different values of the order of fractional derivative. We also
discuss the role of the order of fractional derivative in modifying the
properties of the classical models.Comment: 41 pages, 8 figure
Raman solitons in transient SRS
We report the observation of Raman solitons on numerical simulations of
transient stimulated Raman scattering (TSRS) with small group velocity
dispersion. The theory proceeds with the inverse scattering transform (IST) for
initial-boundary value problems and it is shown that the explicit theoretical
solution obtained by IST for a semi-infinite medium fits strikingly well the
numerical solution for a finite medium. We understand this from the rapid
decrease of the medium dynamical variable (the potential of the scattering
theory). The spectral transform reflection coefficient can be computed directly
from the values of the input and output fields and this allows to see the
generation of the Raman solitons from the numerical solution. We confirm the
presence of these nonlinear modes in the medium dynamical variable by the use
of a discrete spectral analysis.Comment: LaTex file, to appear in Inverse Problem
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