11,891 research outputs found
Fragmented many-body ground states for scalar bosons in a single trap
We investigate whether the many-body ground states of bosons in a generalized
two-mode model with localized inhomogeneous single-particle orbitals and
anisotropic long-range interactions (e.g. dipole-dipole interactions), are
coherent or fragmented. It is demonstrated that fragmentation can take place in
a single trap for positive values of the interaction couplings, implying that
the system is potentially stable. Furthermore, the degree of fragmentation is
shown to be insensitive to small perturbations on the single-particle level.Comment: 4 pages of RevTex4, 3 figures; as published in Physical Review
Letter
Multiple origins for the DLA at toward PKS 1127145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn
We investigate the dust depletion properties of optically thick gas in and
around galaxies and its origin we study in detail the dust depletion patterns
of Ti, Mn, and Ca in the multi-component damped Lyman- (DLA) absorber
at toward the quasar PKS 1127145.} We performed a
detailed spectral analysis of the absorption profiles of CaII, MnII, TiII, and
NaI associated with the DLA toward PKS 1127145, based on optical
high-resolution data obtained with the UVES instrument at the Very Large
Telescope (VLT). We obtained column densities and Doppler-parameters for the
ions listed above and determine their gas-phase abundances, from which we
conclude on their dust depletion properties. We compared the Ca and Ti
depletion properties of this DLA with that of other DLAs. One of the six
analyzed absorption components shows a striking underabundance of Ti and Mn in
the gas-phase, indicating the effect of dust depletion for these elements and a
locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers,
the MnII abundance follows that of TiII very closely, implying that both ions
are equally sensitive to the dust depletion effects. Our analysis indicates
that the DLA toward PKS 1127145 has multiple origins. With its narrow line
width and its strong dust depletion, component 3 points toward the presence of
a neutral gas disk from a faint LSB galaxy in front of PKS 1127145, while
the other, more diffuse and dust-poor, absorption components possibly are
related to tidal gas features from the interaction between the various,
optically confirmed galaxy-group members. In general, the Mn/CaII ratio in
sub-DLAs and DLAs possibly serves as an important indicator to discriminate
between dust-rich and dust-poor in neutral gas in and around galaxies.Comment: 10 pages, 8 figures, accepted for A&
The Draft Genome of the Invasive Walking Stick, Medauroidea extradendata, Reveals Extensive Lineage-Specific Gene Family Expansions of Cell Wall Degrading Enzymes in Phasmatodea.
Plant cell wall components are the most abundant macromolecules on Earth. The study of the breakdown of these molecules is thus a central question in biology. Surprisingly, plant cell wall breakdown by herbivores is relatively poorly understood, as nearly all early work focused on the mechanisms used by symbiotic microbes to breakdown plant cell walls in insects such as termites. Recently, however, it has been shown that many organisms make endogenous cellulases. Insects, and other arthropods, in particular have been shown to express a variety of plant cell wall degrading enzymes in many gene families with the ability to break down all the major components of the plant cell wall. Here we report the genome of a walking stick, Medauroidea extradentata, an obligate herbivore that makes uses of endogenously produced plant cell wall degrading enzymes. We present a draft of the 3.3Gbp genome along with an official gene set that contains a diversity of plant cell wall degrading enzymes. We show that at least one of the major families of plant cell wall degrading enzymes, the pectinases, have undergone a striking lineage-specific gene family expansion in the Phasmatodea. This genome will be a useful resource for comparative evolutionary studies with herbivores in many other clades and will help elucidate the mechanisms by which metazoans breakdown plant cell wall components
Nonequilibrium dynamical mean-field theory for bosonic lattice models
We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium "phase diagrams" which map out the different dynamical
regimes.Comment: 18 pages, 8 figure
On high-order pressure-robust space discretisations, their advantages for incompressible high Reynolds number generalised Beltrami flows and beyond
An improved understanding of the divergence-free constraint for the
incompressible Navier--Stokes equations leads to the observation that a
semi-norm and corresponding equivalence classes of forces are fundamental for
their nonlinear dynamics. The recent concept of {\em pressure-robustness}
allows to distinguish between space discretisations that discretise these
equivalence classes appropriately or not. This contribution compares the
accuracy of pressure-robust and non-pressure-robust space discretisations for
transient high Reynolds number flows, starting from the observation that in
generalised Beltrami flows the nonlinear convection term is balanced by a
strong pressure gradient. Then, pressure-robust methods are shown to outperform
comparable non-pressure-robust space discretisations. Indeed, pressure-robust
methods of formal order are comparably accurate than non-pressure-robust
methods of formal order on coarse meshes. Investigating the material
derivative of incompressible Euler flows, it is conjectured that strong
pressure gradients are typical for non-trivial high Reynolds number flows.
Connections to vortex-dominated flows are established. Thus,
pressure-robustness appears to be a prerequisite for accurate incompressible
flow solvers at high Reynolds numbers. The arguments are supported by numerical
analysis and numerical experiments.Comment: 43 pages, 18 figures, 2 table
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