243 research outputs found
Unstable Disk Galaxies. I. Modal Properties
I utilize the Petrov-Galerkin formulation and develop a new method for
solving the unsteady collisionless Boltzmann equation in both the linear and
nonlinear regimes. In the first order approximation, the method reduces to a
linear eigenvalue problem which is solved using standard numerical methods. I
apply the method to the dynamics of a model stellar disk which is embedded in
the field of a soft-centered logarithmic potential. The outcome is the full
spectrum of eigenfrequencies and their conjugate normal modes for prescribed
azimuthal wavenumbers. The results show that the fundamental bar mode is
isolated in the frequency space while spiral modes belong to discrete families
that bifurcate from the continuous family of van Kampen modes. The population
of spiral modes in the bifurcating family increases by cooling the disk and
declines by increasing the fraction of dark to luminous matter. It is shown
that the variety of unstable modes is controlled by the shape of the dark
matter density profile.Comment: Accepted for publication in The Astrophysical Journa
Global Spiral Modes in NGC 1566: Observations and Theory
We present an observational and theoretical study of the spiral structure in
galaxy NGC 1566. A digitized image of NGC 1566 in I-band was used for
measurements of the radial dependence of amplitude variations in the spiral
arms. We use the known velocity dispersion in the disk of NGC 1566, together
with its rotation curve, to construct linear and 2D nonlinear simulations which
are then compared with observations. A two-armed spiral is the most unstable
linear global mode in the disk of NGC 1566. The nonlinear simulations are in
agreement with the results of the linear modal analysis, and the theoretical
surface amplitude and the velocity residual variations across the spiral arms
are in qualitative agreement with the observations. The spiral arms found in
the linear and nonlinear simulations are considerably shorter than those
observed in the disk of NGC 1566. We argue therefore, that the surface density
distribution in the disk of the galaxy NGC 1566 was different in the past, when
spiral structure in NGC 1566 was linearly growing.Comment: 41 pages, 20 figures, to be published in the Astrophysical Journa
Potentially inappropriate prescribing in multimorbid and polymedicated older adults with AF:A Systematic Review and Meta-Analysis
Aim: Polypharmacy in multimorbid older patients with atrial fibrillation (AF) is a risk factor for potentially inappropriate prescribing (PIP). We aimed to systematically assess the evidence on the prevalence of PIP and its impact on adverse health outcomes in this patient group. Methods: A systematic search of the published peer-reviewed literature describing the prevalence of PIP and/or its association with adverse health outcomes in multimorbid (AF plus one comorbidity) and polymedicated (≥ 2 drugs) adults ≥ 65 years was done up to March 2023. A meta-analysis of the prevalence of PIP of (direct) oral anticoagulants ((D)OACs) was conducted using a random-effects model. Leave-one-out analysis was performed with R (version 4.2.2) and RStudio (version 2022.12.0+353).Results: Of the 12 studies included, only one reported on the prevalence of overall PIP (65%). The meta-analysis of 10 studies assessing PIP of (D)OACs produced a pooled prevalence [95% confidence interval (CI)] of 35% [30–40%], with significant heterogeneity between the included studies (I2 95%). No statistically significant association was reported in three studies between PIP of (D)OACs, cardiovascular (CV) and all-cause mortality, hospital readmission, CV hospitalisation and stroke. Reported associations between PIP and major bleeding differed, with one study demonstrating a significant association (odds ratio 2.17; 95% CI 1.14–4.12) and the other study not showing such association. Conclusion: This systematic review highlights the scarce evidence regarding the prevalence of PIP and its association with adverse health outcomes in multimorbid older adults with AF. Large, prospective and better-designed studies are needed.</p
Nonlinear Effects in Models of the Galaxy: 1. Midplane Stellar Orbits in the Presence of 3D Spiral Arms
With the aim of studying the nonlinear stellar and gaseous response to the
gravitational potential of a galaxy such as the Milky Way, we have modeled 3D
galactic spiral arms as a superposition of inhomogeneous oblate spheroids and
added their contribution to an axisymmetric model of the Galactic mass
distribution. Three spiral loci are proposed here, based in different sets of
observations. A comparison of our model with a tight-winding approximation
shows that the self-gravitation of the whole spiral pattern is important in the
middle and outer galactic regions. As a first step to full 3D calculations the
model is suitable for, we have explored the stellar orbital structure in the
midplane of the Galaxy. We present the standard analysis in the pattern
rotating frame, and complement this analysis with orbital information from the
Galactic inertial frame. Prograde and retrograde orbits are defined
unambiguously in the inertial frame, then labeled as such in the Poincar\'e
diagrams of the non-inertial frame. In this manner we found a sharp separatrix
between the two classes of orbits. Chaos is restricted to the prograde orbits,
and its onset occurs for the higher spiral perturbation considered plausible in
our Galaxy.Comment: 23 pages, 22 Figures. Latex. Submitted to Ap
Properties of odd nuclei and the impact of time-odd mean fields: A systematic Skyrme-Hartree-Fock analysis
We present a systematic analysis of the description of odd nuclei by the
Skyrme-Hartree-Fock approach augmented with pairing in BCS approximation and
blocking of the odd nucleon. Current and spin densities in the Skyrme
functional produce time-odd mean fields (TOMF) for odd nuclei. Their effect on
basic properties (binding energies, odd-even staggering, separation energies
and spectra) is investigated for the three Skyrme parameterizations SkI3, SLy6,
and SV-bas. About 1300 spherical and axially-deformed odd nuclei with 16 < Z <
92 are considered. The calculations demonstrate that the TOMF effect is
generally small, although not fully negligible. The influence of the Skyrme
parameterization and the consistency of the calculations are much more
important. With a proper choice of the parameterization, a good description of
binding energies and their differences is obtained, comparable to that for even
nuclei. The description of low-energy excitation spectra of odd nuclei is of
varying quality depending on the nucleus
The Leo I Cloud: Secular nuclear evolution of NGC 3379, NGC 3384, and NGC 3368?
The central regions of the three brightest members of the Leo I galaxy group
-- NGC 3368, NGC 3379, and NGC 3384 -- are investigated by means of 2D
spectroscopy. In all three galaxies we have found separate circumnuclear
stellar and gaseous subsystems -- more probably, disks -- whose spatial
orientations and spins are connected to the spatial orientation of the
supergiant intergalactic HI ring reported previously by Schneider et al. (1983)
and Schneider (1985, 1989). In NGC 3368 the global gaseous disk seems also to
be inclined to the symmetry plane of the stellar body, being probably of
external origin. Although the rather young mean stellar age and spatial
orientations of the circumnuclear disks in NGC 3379, NGC 3384, and NGC 3368
could imply their recent formation from material of the intergalactic HI cloud,
the time scale of these secondary formation events, of order 3 Gyr, does not
support the collision scenario of Rood & Williams (1985), but is rather in line
with the ideas of Schneider (1985, 1989) regarding tidal interactions of the
galaxies with the HI cloud on timescales of the intergroup orbital motions.Comment: Accepted to ApJ, 46 pages (figs 18 and 22 are low resolution
Sensing and adhesion are adaptive functions in the plant pathogenic xanthomonads
<p>Abstract</p> <p>Background</p> <p>Bacterial plant pathogens belonging to the <it>Xanthomonas </it>genus are tightly adapted to their host plants and are not known to colonise other environments. The host range of each strain is usually restricted to a few host plant species. Bacterial strains responsible for the same type of symptoms on the same host range cluster in a pathovar. The phyllosphere is a highly stressful environment, but it provides a selective habitat and a source of substrates for these bacteria. Xanthomonads colonise host phylloplane before entering leaf tissues and engaging in an invasive pathogenic phase. Hence, these bacteria are likely to have evolved strategies to adapt to life in this environment. We hypothesised that determinants responsible for bacterial host adaptation are expressed starting from the establishment of chemotactic attraction and adhesion on host tissue.</p> <p>Results</p> <p>We established the distribution of 70 genes coding sensors and adhesins in a large collection of xanthomonad strains. These 173 strains belong to different pathovars of <it>Xanthomonas </it>spp and display different host ranges. Candidate genes are involved in chemotactic attraction (25 genes), chemical environment sensing (35 genes), and adhesion (10 genes). Our study revealed that candidate gene repertoires comprised core and variable gene suites that likely have distinct roles in host adaptation. Most pathovars were characterized by unique repertoires of candidate genes, highlighting a correspondence between pathovar clustering and repertoires of sensors and adhesins. To further challenge our hypothesis, we tested for molecular signatures of selection on candidate genes extracted from sequenced genomes of strains belonging to different pathovars. We found strong evidence of adaptive divergence acting on most candidate genes.</p> <p>Conclusions</p> <p>These data provide insight into the potential role played by sensors and adhesins in the adaptation of xanthomonads to their host plants. The correspondence between repertoires of sensor and adhesin genes and pathovars and the rapid evolution of sensors and adhesins shows that, for plant pathogenic xanthomonads, events leading to host specificity may occur as early as chemotactic attraction by host and adhesion to tissues.</p
Evolutionary and Experimental Assessment of Novel Markers for Detection of Xanthomonas euvesicatoria in Plant Samples
BACKGROUND: Bacterial spot-causing xanthomonads (BSX) are quarantine phytopathogenic bacteria responsible for heavy losses in tomato and pepper production. Despite the research on improved plant spraying methods and resistant cultivars, the use of healthy plant material is still considered as the most effective bacterial spot control measure. Therefore, rapid and efficient detection methods are crucial for an early detection of these phytopathogens. METHODOLOGY: In this work, we selected and validated novel DNA markers for reliable detection of the BSX Xanthomonas euvesicatoria (Xeu). Xeu-specific DNA regions were selected using two online applications, CUPID and Insignia. Furthermore, to facilitate the selection of putative DNA markers, a customized C program was designed to retrieve the regions outputted by both databases. The in silico validation was further extended in order to provide an insight on the origin of these Xeu-specific regions by assessing chromosomal location, GC content, codon usage and synteny analyses. Primer-pairs were designed for amplification of those regions and the PCR validation assays showed that most primers allowed for positive amplification with different Xeu strains. The obtained amplicons were labeled and used as probes in dot blot assays, which allowed testing the probes against a collection of 12 non-BSX Xanthomonas and 23 other phytopathogenic bacteria. These assays confirmed the specificity of the selected DNA markers. Finally, we designed and tested a duplex PCR assay and an inverted dot blot platform for culture-independent detection of Xeu in infected plants. SIGNIFICANCE: This study details a selection strategy able to provide a large number of Xeu-specific DNA markers. As demonstrated, the selected markers can detect Xeu in infected plants both by PCR and by hybridization-based assays coupled with automatic data analysis. Furthermore, this work is a contribution to implement more efficient DNA-based methods of bacterial diagnostics
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