9,161 research outputs found
Diamonds on the Hat: Globular Clusters in The Sombrero Galaxy (M104)
Images from the HST ACS are used to carry out a new photometric study of the
globular clusters (GCs) in M104, the Sombrero galaxy. The primary focus of our
study is the characteristic distribution function of linear sizes (SDF) of the
GCs. We measure the effective radii for 652 clusters with PSF-convolved King
and Wilson dynamical model fits. The SDF is remarkably similar to those
measured for other large galaxies of all types, adding strong support to the
view that it is a "universal" feature of globular cluster systems.
We develop a more general interpretation of the size distribution function
for globular clusters, proposing that the shape of the SDF that we see today
for GCs is strongly influenced by the early rapid mass loss during their star
forming stage, coupled with stochastic differences from cluster to cluster in
the star formation efficiency (SFE) and their initial sizes. We find that the
observed SDF shape can be accurately predicted by a simple model in which the
protocluster clouds had characteristic sizes of pc and SFEs of
. The colors and luminosities of the M104 clusters show the
clearly defined classic bimodal form. The blue sequence exhibits a
mass/metallicity relation (MMR), following a scaling of heavy-element abundance
with luminosity of very similar to what has been found in most
giant elliptical galaxies. A quantitative self-enrichment model provides a good
first-order match to the data for the same initial SFE and protocluster size
that were required to explain the SDF. We also discuss various forms of the
globular cluster Fundamental Plane (FP) of structural parameters, and show that
useful tests of it can be extended to galaxies beyond the Local Group.Comment: In press for MNRA
Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope
The onset of a solar eruption is formulated here as either a magnetic
catastrophe or as an instability. Both start with the same equation of force
balance governing the underlying equilibria. Using a toroidal flux rope in an
external bipolar or quadrupolar field as a model for the current-carrying flux,
we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for
several representative evolutionary sequences in the stable domain of parameter
space. We verify that this catastrophe and the torus instability occur at the
same point; they are thus equivalent descriptions for the onset condition of
solar eruptions.Comment: V2: update to conform to the published article; new choice for
internal inductance of torus; updated Fig. 2; new Figs. 3, 5, and
Vibration effects on heat transfer in cryogenic systems Quarterly progress report no. 1, Jun. 1 - Aug. 31, 1966
Vibration effects on natural convection and fluid transport properties in cryogenic system
The Potential of Erin Brokovitch to Introduce Organizaitonal Behavior Topics
Real organizational behavior is rich, and messy, and emotional, and at times painful, but at other times immensely rewarding. The movie, Erin Brockovich, captures this richness and provides an exciting means to introduce a variety of individual or micro- organizational behavior concepts (such as perception, personality, and motivation) typically covered at the beginning of the Organizational Behavior course. In this paper, we describe the use of the film, including a takehome viewing assignment, an in-class assignment, a description of clips and comments for in-class use, and suggestions for the types of issues to discuss in relation to the major topics and in relation to other potentially relevant areas. The richness of this film and the issues raised also provide the potential for more critical analyses of management and organizational practices
Kaon Condensation in a Nambu--Jona-Lasinio (NJL) Model at High Density
We demonstrate a fully self-consistent microscopic realization of a
kaon-condensed colour-flavour locked state (CFLK0) within the context of a
mean-field NJL model at high density. The properties of this state are shown to
be consistent with the QCD low-energy effective theory once the proper gauge
neutrality conditions are satisfied, and a simple matching procedure is used to
compute the pion decay constant, which agrees with the perturbative QCD result.
The NJL model is used to compare the energies of the CFLK0 state to the parity
even CFL state, and to determine locations of the metal/insulator transition to
a phase with gapless fermionic excitations in the presence of a non-zero
hypercharge chemical potential and a non-zero strange quark mass. The
transition points are compared with results derived previously via effective
theories and with partially self-consistent NJL calculations. We find that the
qualitative physics does not change, but that the transitions are slightly
lower.Comment: 21 pages, ReVTeX4. Clarified discussion and minor change
A space division multiplexed free-space-optical communication system that can auto-locate and fully self align with a remote transceiver
Free-Space Optical (FSO) systems offer the ability to distribute high speed digital links into remote and rural communities where terrain, installation cost or infrastructure security pose critical hurdles to deployment. A challenge in any point-to-point FSO system is initiating and maintaining optical alignment from the sender to the receiver. In this paper we propose and demonstrate a low-complexity self-aligning FSO prototype that can completely self-align with no requirement for initial manual positioning and could therefore form the opto-mechanical basis for a mesh network of optical transceivers. The prototype utilises off-the-shelf consumer electrical components and a bespoke alignment algorithm. We demonstrate an eight fibre spatially multiplexed link with a loss of 15 dB over 210 m
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The effects of landscape modifications on the long-term persistence of animal populations
Background: The effects of landscape modifications on the long-term persistence of wild animal populations is of crucial
importance to wildlife managers and conservation biologists, but obtaining experimental evidence using real landscapes is
usually impossible. To circumvent this problem we used individual-based models (IBMs) of interacting animals in
experimental modifications of a real Danish landscape. The models incorporate as much as possible of the behaviour and
ecology of four species with contrasting life-history characteristics: skylark (Alauda arvensis), vole (Microtus agrestis), a
ground beetle (Bembidion lampros) and a linyphiid spider (Erigone atra). This allows us to quantify the population
implications of experimental modifications of landscape configuration and composition.
Methodology/Principal Findings: Starting with a real agricultural landscape, we progressively reduced landscape
complexity by (i) homogenizing habitat patch shapes, (ii) randomizing the locations of the patches, and (iii) randomizing the
size of the patches. The first two steps increased landscape fragmentation. We assessed the effects of these manipulations
on the long-term persistence of animal populations by measuring equilibrium population sizes and time to recovery after
disturbance. Patch rearrangement and the presence of corridors had a large effect on the population dynamics of species
whose local success depends on the surrounding terrain. Landscape modifications that reduced population sizes increased
recovery times in the short-dispersing species, making small populations vulnerable to increasing disturbance. The species
that were most strongly affected by large disturbances fluctuated little in population sizes in years when no perturbations
took place.
Significance: Traditional approaches to the management and conservation of populations use either classical methods of
population analysis, which fail to adequately account for the spatial configurations of landscapes, or landscape ecology,
which accounts for landscape structure but has difficulty predicting the dynamics of populations living in them. Here we
show how realistic and replicable individual-based models can bridge the gap between non-spatial population theory and
non-dynamic landscape ecology. A major strength of the approach is its ability to identify population vulnerabilities not
detected by standard population viability analyses
The X-ray Emission in Post-Merger Ellipticals
The evolution in X-ray properties of early-type galaxies is largely unconstrained. In particular, little is known about how, and if, remnants of mergers generate hot gas halos. Here we examine the relationship between X-ray luminosity and galaxy age for a sample of early-type galaxies. Comparing normalized X-ray luminosity to three different age indicators we find that L_X/L_B increases with age, suggesting an increase in X-ray halo mass with time after a galaxy's last major star-formation episode. The long-term nature of this trend, which appears to continue across the full age range of our sample, poses a challenge for many models of hot halo formation. We conclude that models involving a declining rate of type Ia supernovae, and a transition from outflow to inflow of the gas originally lost by galactic stars, offers the most promising explanation for the observed evolution in X-ray luminosity
Dependence of the Fundamental Plane Scatter on Galaxy Age
The fundamental plane (FP) has an intrinsic scatter that can not be explained
purely by observational errors. Using recently available age estimates for
nearby early type galaxies, we show that a galaxy's position relative to the FP
depends on its age. In particular, the mean FP corresponds to ellipticals with
an age of ~10 Gyr. Younger galaxies are systematically brighter with higher
surface brightness relative to the mean relation. Old ellipticals form an
`upper envelope' to the FP. For our sample of mostly non-cluster galaxies, age
can account for almost half of the scatter in the B band FP. Distance
determinations based on the FP may have a systematic bias, if the mean age of
the sample varies with redshift.
We also show that fundamental plane residuals, B-V colors and Mg_2 line
strength are consistent with an ageing central burst superposed on an old
stellar population. This reinforces the view that these age estimates are
tracing the last major episode of star formation induced by a gaseous merger
event. We briefly discuss the empirical `evolutionary tracks' of
merger-remnants and young ellipticals in terms of their key observational
parameters.Comment: 14 pages, Latex, 2 figures, accepted by ApJ Letter
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