545 research outputs found
Environmental Effects in the Evolution of Galactic Bulges
We investigate possible environmental trends in the evolution of galactic
bulges over the redshift range 0<z<0.6. For this purpose, we construct the
Fundamental Plane (FP) for cluster and field samples at redshifts =0.4 and
=0.54 using surface photometry based on HST imaging and velocity dispersions
based on Keck spectroscopy. As a reference point for our study we include data
for pure ellipticals, which we model as single-component Sersic profiles;
whereas for multi-component galaxies we undertake decompositions using Sersic
and exponential models for the bulge and disk respectively. Although the FP for
both distant cluster and field samples are offset from the local relation,
consistent with evolutionary trends found in earlier studies, we detect
significant differences in the zero point of ~=0.2 dex between the field and
cluster samples at a given redshift. For both clusters, the
environmentally-dependent offset is in the sense expected for an accelerated
evolution of bulges in dense environments. By matching the mass range of our
samples, we confirm that this difference does not arise as a result of the
mass-dependent downsizing effects seen in larger field samples. Our result is
also consistent with the hypothesis that - at fixed mass and environment - the
star formation histories of galactic bulges and pure spheroids are
indistinguishable, and difficult to reconcile with the picture whereby the
majority of large bulges form primarily via secular processes within spiral
galaxies.Comment: 5 pages, 3 figures, accepted for publication in ApJ Letter
Supergravity on R4 x S1/Z2 and singular Calabi-Yaus
We discuss the moduli space singularities that are generally present in
five-dimensional vector-coupled supergravity on a spactime of the form R4 x
S1/Z2, with vector fields surviving on the Z2 fixed planes. The framework of
supergravity is necessarily ambiguous when it comes to the non-singular
embedding theory, so we focus on those models coming from Calabi-Yau
three-folds with wrapped membranes.Comment: 13 p
A Migration Study of \u3ci\u3eStelidota Geminata\u3c/i\u3e (Coleoptera: Nitidulidae)
The strawberry sap beetle, Stelidota geminata (Say), is a major pest of strawberries in the northeastern United States. Further knowledge of the migratory habits of this insect pest can enhance the effectiveness of pest management strategies. This nitidulid was shown to migrate from its overwintering sites to one of its primary reproductive sites, strawberry fields, in late May. The beetle population peaked in the third week in July, 1993 in the strawberry field and then gradually declined. In 1994, the peak, as well as the total population, was much greater than in 1993. Furthermore, S. geminata was concentrated in the transition areas surrounding the strawberry fields prior to the ripening of the fruit
Evolution of the Stellar Mass--Metallicity Relation - I: Galaxies in the z~0.4 Cluster Cl0024
We present the stellar mass-stellar metallicity relationship (MZR) in the
Cl0024+1654 galaxy cluster at z~0.4 using full spectrum stellar population
synthesis modeling of individual quiescent galaxies. The lower limit of our
stellar mass range is , the lowest galaxy mass at which
individual stellar metallicity has been measured beyond the local universe. We
report a detection of an evolution of the stellar MZR with observed redshift at
dex per Gyr, consistent with the predictions from
hydrodynamical simulations. Additionally, we find that the evolution of the
stellar MZR with observed redshift can be explained by an evolution of the
stellar MZR with their formation time, i.e., when the single stellar population
(SSP)-equivalent ages of galaxies are taken into account. This behavior is
consistent with stars forming out of gas that also has an MZR with a
normalization that decreases with redshift. Lastly, we find that over the
observed mass range, the MZR can be described by a linear function with a
shallow slope, (). The slope suggests
that galaxy feedback, in terms of mass-loading factor, might be
mass-independent over the observed mass and redshift range.Comment: 22 pages, 10 figures. Accepted for publication in Ap
The Dynamical Distinction between Elliptical and Lenticular Galaxies in Distant Clusters: Further Evidence for the Recent Origin of S0 Galaxies
We examine resolved spectroscopic data obtained with the Keck II telescope
for 44 spheroidal galaxies in the fields of two rich clusters, Cl0024+16
(z=0.40) and MS0451-03 (z=0.54), and contrast this with similar data for 23
galaxies within the redshift interval 0.3<z<0.65 in the GOODS northern field.
For each galaxy we examine the case for systemic rotation, derive central
stellar velocity dispersions sigma and photometric ellipticities, epsilon.
Using morphological classifications obtained via Hubble Space Telescope imaging
as the basis, we explore the utility of our kinematic quantities in
distinguishing between pressure-supported ellipticals and
rotationally-supported lenticulars (S0s). We demonstrate the reliability of
using the v/(1-epsilon) vs sigma and v/sigma vs epsilon distributions as
discriminators, finding that the two criteria correctly identify 63%+-3% and
80%+-2% of S0s at z~0.5, respectively, along with 76%+8-3% and 79%+-2% of
ellipticals. We test these diagnostics using equivalent local data in the Coma
cluster, and find that the diagnostics are similarly accurate at z=0. Our
measured accuracies are comparable to the accuracy of visual classification of
morphologies, but avoid the band-shifting and surface brightness effects that
hinder visual classification at high redshifts. As an example application of
our kinematic discriminators, we then examine the morphology-density relation
for elliptical and S0 galaxies separately at z~0.5. We confirm, from kinematic
data alone, the recent growth of rotationally-supported spheroidals. We discuss
the feasibility of extending the method to a more comprehensive study of
cluster and field galaxies to z~1, in order to verify in detail the recent
density-dependent growth of S0 galaxies.Comment: 7 pages, 4 figures, updated with version accepted to Ap
Estimating the active space of male koala bellows: propagation of cues to size and identity in a Eucalyptus forest
Examining how increasing distance affects the information content of vocal signals is fundamental for determining the active space of a given species’ vocal communication system. In the current study we played back male koala bellows in a Eucalyptus forest to determine the extent that individual classification of male koala bellows becomes less accurate over distance, and also to quantify how individually distinctive acoustic features of bellows and size-related information degrade over distance. Our results show that the formant frequencies of bellows derived from Linear Predictive Coding can be used to classify calls to male koalas over distances of 1–50 m. Further analysis revealed that the upper formant frequencies and formant frequency spacing were the most stable acoustic features of male bellows as they propagated through the Eucalyptus canopy. Taken together these findings suggest that koalas could recognise known individuals at distances of up to 50 m and indicate that they should attend to variation in the upper formant frequencies and formant frequency spacing when assessing the identity of callers. Furthermore, since the formant frequency spacing is also a cue to male body size in this species and its variation over distance remained very low compared to documented inter-individual variation, we suggest that male koalas would still be reliably classified as small, medium or large by receivers at distances of up to 150 m
How to make a traversable wormhole from a Schwarzschild black hole
The theoretical construction of a traversable wormhole from a Schwarzschild
black hole is described, using analytic solutions in Einstein gravity. The
matter model is pure phantom radiation (pure radiation with negative energy
density) and the idealization of impulsive radiation is employed.Comment: 4 pages, 4 figure
Quantitative Assessment of Magnetic Resonance Spectroscopy Data Reconstruction Methods: Region-of-Interest Averaging and Spectral Localization by Imaging
The aim of this dissertation was to compare two magnetic resonance spectroscopy (MRS) localization techniques: Fourier based region-of-interest (ROI) averaging, and the non-Fourier based spectral localization by imaging (SLIM). Unlike ROI-averaging, SLIM provides a technique for calculating the metabolite spectra of a compartmental region without the need for averaging voxels of spectral data to estimate that region. Because of this, SLIM has the potential to greatly reduce the acquisition time needed to acquire compartmental spectra. SLIM was processed over multiple k-space sizes and over an assortment of brain regions and then these results were compared to their equivalent ROI-averaged regions. The assorted k-space sizes were used to demonstrate SLIM operating with different amounts of available data, which was used to compare the process to ROI-averaging. The results of this study validate SLIM as a valuable localization tool that will shorten scan times and improve accuracy in spectral localization. The dissertation is divided into five main chapters: (1) Introduction, which addresses magnetic resonance background concepts and applications of MRS techniques; (2) Methods, which describes the processes involved in developing a programming pipeline designed to produce metabolite data for the localization techniques; (3) Results, which provides statistical measures of the localization methods; (4) Discussion, where comparisons were drawn from the datasets based on the results section; (5) Conclusions, which evaluates the thesis work and addresses possible research directions for the future
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