1,344 research outputs found
An Atlas of H-alpha and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies
Narrow-band H-alpha+[NII] and broadband R images and surface photometry are
presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within
a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral
galaxies of their Hubble classifications as determined from the Nearby Galaxies
Catalog (Tully 1987a).Comment: To appear in Astrophysical Journal Supplement Series. 17 pages,
including 8 atlas pages in JPEG format. Version with high resolution figures
available at http://www1.union.edu/~koopmanr/preprints.htm
Density Matrix Perturbation Theory
An expansion method for perturbation of the zero temperature grand canonical
density matrix is introduced. The method achieves quadratically convergent
recursions that yield the response of the zero temperature density matrix upon
variation of the Hamiltonian. The technique allows treatment of embedded
quantum subsystems with a computational cost scaling linearly with the size of
the perturbed region, O(N_pert.), and as O(1) with the total system size. It
also allows direct computation of the density matrix response functions to any
order with linear scaling effort. Energy expressions to 4th order based on only
first and second order density matrix response are given.Comment: 4 pages, 2 figure
Static Pressure of Hot Gas: Its Effect on the Gas Disks of Galaxies
The static pressure of the hot gas that fills clusters and groups of galaxies
can affect significantly the volume density and thickness of the gas disks in
galaxies. In combination with the dynamic pressure, the static pressure allows
several observed peculiarities of spiral galaxies surrounded by a hot medium to
be explained.Comment: 9 pages, 2 figures. This is a slightly modified version of the paper
published in Astronomy Letters 2008, Vol. 34, No 11, p. 73
Temporal variability and statistics of the Strehl ratio in adaptive-optics images
We have investigated the temporal variability and statistics of the
"instantaneous" Strehl ratio. The observations were carried out with the 3.63-m
AEOS telescope equipped with a high-order adaptive optics system. In this paper
Strehl ratio is defined as the peak intensity of a single short exposure. We
have also studied the behaviour of the phase variance computed on the
reconstructed wavefronts. We tested the Marechal approximation and used it to
explain the observed negative skewness of the Strehl ratio distribution. The
estimate of the phase variance is shown to fit a three-parameter Gamma
distribution model. We show that simple scaling of the reconstructed wavefronts
has a large impact on the shape of the Strehl ratio distribution.Comment: submitted to PAS
Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
Based on two models, we investigate the molecular-to-atomic gas ratio in
Virgo cluster galaxies in comparison with field galaxies. We show that the
enhanced metallicity for cluster members and the ram pressure stripping of
atomic gas from the disk periphery cannot fully explain the observed gas
component ratios. The additional environmental factors affecting the
interstellar medium and leading to an increase in the molecular gas fraction
should be taken into account for cluster galaxies.Comment: 11 pages, 4 figure
Recommended from our members
Pressure-induced suppression of ferromagnetism in the itinerant ferromagnet LaCrSb3
We have performed an extensive pressure-dependent structural, spectroscopic, and electrical transport study of LaCrSb3. The ferromagnetic phase (TC=120 K at p = 0 GPa) is fully suppressed by p = 26.5 GPa and the Cr moment decreases steadily with increasing pressure. The unit-cell volume decreases smoothly up to p = 55 GPa. We find that the bulk modulus and suppression of the magnetism are in good agreement with theoretical predictions, but the Cr moment decreases smoothly with pressure, in contrast to steplike drops predicted by theory. The ferromagnetic ordering temperature appears to be driven by the Cr moment
Ready ... Go: Amplitude of the fMRI Signal Encodes Expectation of Cue Arrival Time
What happens when the brain awaits a signal of uncertain arrival time, as when a sprinter waits for the starting pistol? And what happens just after the starting pistol fires? Using functional magnetic resonance imaging (fMRI), we have discovered a novel correlate of temporal expectations in several brain regions, most prominently in the supplementary motor area (SMA). Contrary to expectations, we found little fMRI activity during the waiting period; however, a large signal appears after the “go” signal, the amplitude of which reflects learned expectations about the distribution of possible waiting times. Specifically, the amplitude of the fMRI signal appears to encode a cumulative conditional probability, also known as the cumulative hazard function. The fMRI signal loses its dependence on waiting time in a “countdown” condition in which the arrival time of the go cue is known in advance, suggesting that the signal encodes temporal probabilities rather than simply elapsed time. The dependence of the signal on temporal expectation is present in “no-go” conditions, demonstrating that the effect is not a consequence of motor output. Finally, the encoding is not dependent on modality, operating in the same manner with auditory or visual signals. This finding extends our understanding of the relationship between temporal expectancy and measurable neural signals
Young Nuclei in Dwarf Elliptical Galaxies
We report discovery of young embedded structures in three diffuse elliptical
galaxies (dE) in the Virgo cluster: IC 783, IC 3468, and IC 3509. We performed
3D spectroscopic observations of these galaxies using the MPFS spectrograph at
the Russian 6-m telescope, and obtained spatially resolved distributions of
kinematical and stellar population parameters by fitting high-resolution
PEGASE.HR synthetic single stellar populations (SSP) in the pixel space. In all
three galaxies, the luminosity weighted age of the nuclei, about 4 Gyr, is
considerably younger than population in the outer regions of the galaxies. We
discuss two possibilities to acquire the observed structures -- dissipative
merger event and different ram pressure stripping efficiency during two
consequent crossings of the Virgo cluster centre.Comment: accepted to "Astronomy Letters". Version for astro-ph with colour
figures. 14 pages, 3 figures, 2 table
Fertility, Living Arrangements, Care and Mobility
There are four main interconnecting themes around which the contributions in this book are based. This introductory chapter aims to establish the broad context for the chapters that follow by discussing each of the themes. It does so by setting these themes within the overarching demographic challenge of the twenty-first century – demographic ageing. Each chapter is introduced in the context of the specific theme to which it primarily relates and there is a summary of the data sets used by the contributors to illustrate the wide range of cross-sectional and longitudinal data analysed
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