88 research outputs found
Efficiency in Public Works Engineering--Alternative Arrangements for the Delivery of Municipal Services
Cosmological Simulations of Massive Compact High-z Galaxies
In order to investigate the structure and dynamics of the recently discovered
massive (M_* > 10^11 M_sun) compact z~2 galaxies, cosmological
hydrodynamical/N-body simulations of a proto-cluster region have been
undertaken. At z=2, the highest resolution simulation contains ~5800 resolved
galaxies, of which 509, 27 and 5 have M_* > 10^10 M_sun, > 10^11 M_sun and >
4x10^11 M_sun, respectively. Effective radii and characteristic stellar
densities have been determined for all galaxies. At z=2, for the definitely
well resolved mass range of M_* > 10^11 Msun, the mass-size relation is
consistent with observational findings for the most compact z~2 galaxies. The
very high velocity dispersion recently measured for a compact z~2 galaxy (~510
km/s; van Dokkum et al 2009) can be matched at about the 1-sigma level,
although a somewhat larger mass than the estimated M_* ~ 2 x 10^11 M_sun is
indicated. For the above mass range, the galaxies have an average axial ratio
= 0.64 +/- 0.02 with a dispersion of 0.1, an average rotation to 1D
velocity dispersion ratio = 0.46 +/- 0.06 with a dispersion of 0.3,
and a maximum value of v/sigma ~ 1.1. Rotation and velocity anisotropy both
contribute in flattening the compact galaxies. Some of the observed compact
galaxies appear flatter than any of the simulated galaxies. Finally, it is
found that the massive compact galaxies are strongly baryon dominated in their
inner parts, with typical dark matter mass fractions of order only 20% inside
of r=2R_eff.Comment: 10 pages, 8 figures, submitted to Ap
Noise-driven oscillations in microbial population dynamics
Microbial populations in the natural environment are likely to experience
growth conditions very different from those of a typical laboratory xperiment.
In particular, removal rates of biomass and substrate are unlikely to be
balanced under realistic environmental conditions. Here, we consider a single
population growing on a substrate under conditions where the removal rates of
substrate and biomass are not necessarily equal. For a large population, with
deterministic growth dynamics, our model predicts that this system can show
transient (damped) oscillations. For a small population, demographic noise
causes these oscillations to be sustained indefinitely. These oscillations
arise when the dynamics of changes in biomass are faster than the dynamics of
the substrate, for example, due to a high microbial death rate and/or low
substrate flow rates. We show that the same mechanism can produce sustained
stochastic oscillations in a two-species, nutrient-cycling microbial ecosystem.
Our results suggest that oscillatory population dynamics may be a common
feature of small microbial populations in the natural environment, even in the
absence of complex interspecies interactions.Comment: 25 pages, 11 figure
Cluster galaxies in XMMU J2235-2557: galaxy population properties in most massive environments at z~1.4
We present a multi-wavelength study of galaxy populations in the core of the
massive, X-ray luminous cluster XMMU J2235 at z=1.39, based on VLT and HST
optical and near-infrared photometry. Luminosity functions in the z, H, and Ks
bands show a faint-end slope consistent with being flat, and a characteristic
magnitude M* close to passive evolution predictions of M* of local massive
clusters, with a formation redshift z>2. The color-magnitude and color-mass
diagrams show evidence of a tight red sequence of massive galaxies, with
overall old stellar populations, generally early-type morphology, typically
showing early-type spectral features and rest-frame far-UV emission consistent
with very low star formation rates (SFR<0.2Msun/yr). Star forming spectroscopic
members, with SFRs of up to ~100Msun/yr, are all located at clustercentric
distances >~250kpc, with the central cluster region already appearing
effectively quenched. Massive galaxies in the core of this cluster appear to be
in an advanced evolutionary stage in terms of both star formation and mass
assembly. The high-mass end of the galaxy stellar mass function is essentially
already in place, and the stellar mass fraction estimated within r500 (~1%,
Kroupa IMF) is already similar to that of local massive clusters. On the other
hand, morphological analysis of the massive red sequence galaxies suggests that
they are smaller than similarly massive local early-types. While possibly
affected by systematics and biases, this result might imply that, in spite of
the overall early assembly of these sources, their evolution is not complete,
and processes like minor (and likely dry) merging might still shape their
structural properties to resemble those of their local counterparts, without
substantially affecting their stellar mass or host stellar
populations.[abridged]Comment: 14 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Primordialists and Constructionists: a typology of theories of religion
This article adopts categories from nationalism theory to classify theories of religion. Primordialist explanations are grounded in evolutionary psychology and emphasize the innate human demand for religion. Primordialists predict that religion does not decline in the modern era but will endure in perpetuity. Constructionist theories argue that religious demand is a human construct. Modernity initially energizes religion, but subsequently undermines it. Unpacking these ideal types is necessary in order to describe actual theorists of religion. Three distinctions within primordialism and constructionism are relevant. Namely those distinguishing: a) materialist from symbolist forms of constructionism; b) theories of origins from those pertaining to the reproduction of religion; and c) within reproduction, between theories of religious persistence and secularization. This typology helps to make sense of theories of religion by classifying them on the basis of their causal mechanisms, chronology and effects. In so doing, it opens up new sightlines for theory and research
CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62
We discuss the structural and morphological properties of galaxies in a
z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope
Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology
relation: galaxies with colors of quiescent stellar populations generally have
morphologies consistent with spheroids, and galaxies with colors consistent
with ongoing star formation have disk-like and irregular morphologies. The size
distribution of the quiescent cluster galaxies shows a deficit of compact (<
1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a
result the cluster quiescent galaxies have larger average effective sizes
compared to field galaxies at fixed mass at greater than 90% significance.
Combined with data from the literature, the size evolution of quiescent cluster
galaxies is relatively slow from z~1.6 to the present, growing as
(1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that
physical processes associated with the denser cluster region seems to have
caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower
subsequent growth at z<1.6 compared to galaxies in the lower density field. The
quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower
redshift samples at fixed mass, and their surface-brightness profiles suggest
that they contain extended stellar disks. We argue the cluster galaxies require
dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk
material and to match the relations for ellipticity, stellar mass, size, and
color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format.
Replacement includes improvements from referee report, and updates and
additions to reference
CANDELS: The progenitors of compact quiescent galaxies at z~2
We combine high-resolution HST/WFC3 images with multi-wavelength photometry
to track the evolution of structure and activity of massive (log(M*) > 10)
galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact,
star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star
formation rates qualify them as likely progenitors of compact, quiescent,
massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific
star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at
the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently.
These properties suggest that cSFGs are formed by gas-rich processes (mergers
or disk-instabilities) that induce a compact starburst and feed an AGN, which,
in turn, quench the star formation on dynamical timescales (few 10^8 yr). The
cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5.
After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs.
Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs
in size, while less-gas-rich mergers and other secular mechanisms shepherd
(larger) SFGs as later arrivals to the red sequence. In summary, we propose two
evolutionary scenarios of QG formation: an early (z > 2), fast-formation path
of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the
quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs
without passing through a compact state.Comment: Submitted to the Astrophysical Journal Letters, 6 pages, 4 figure
Output-based assessment of herd-level freedom from infection in endemic situations:Application of a Bayesian Hidden Markov model
International audienceCountries have implemented control programmes (CPs) for cattle diseases such as bovine viral diarrhoea virus (BVDV) that are tailored to each country-specific situation. Practical methods are needed to assess the output of these CPs in terms of the confidence of freedom from infection that is achieved. As part of the STOC free project, a Bayesian Hidden Markov model was developed, called STOC free model, to estimate the probability of infection at herd-level. In the current study, the STOC free model was applied to BVDV field data in four study regions, from CPs based on ear notch samples. The aim of this study was to estimate the probability of herd-level freedom from BVDV in regions that are not (yet) free. We additionally evaluated the sensitivity of the parameter estimates and predicted probabilities of freedom to the prior distributions for the different model parameters. First, default priors were used in the model to enable comparison of model outputs between study regions. Thereafter, country-specific priors based on expert opinion or historical data were used in the model, to study the influence of the priors on the results and to obtain country-specific estimates.The STOC free model calculates a posterior value for the model parameters (e.g. herd-level test sensitivity and specificity, probability of introduction of infection) and a predicted probability of infection. The probability of freedom from infection was computed as one minus the probability of infection. For dairy herds that were considered free from infection within their own CP, the predicted probabilities of freedom were very high for all study regions ranging from 0.98 to 1.00, regardless of the use of default or country-specific priors. The priors did have more influence on two of the model parameters, herd-level sensitivity and the probability of remaining infected, due to the low prevalence and incidence of BVDV in the study regions. The advantage of STOC free model compared to scenario tree modelling, the reference method, is that actual data from the CP can be used and estimates are easily updated when new data becomes availabl
Mantle plume capture, anchoring, and outflow during GalĂĄpagos plume-ridge interaction
Compositions of basalts erupted between the main zone of GalĂĄpagos plume upwelling and adjacent GalĂĄpagos Spreading Center (GSC) provide important constraints on dynamic processes involved in transfer of deep-mantle-sourced material to mid-ocean ridges. We examine recent basalts from central and northeast GalĂĄpagos including some that have less radiogenic Sr, Nd, and Pb isotopic compositions than plume-influenced basalts (E-MORB) from the nearby ridge. We show that the location of E-MORB, greatest crustal thickness, and elevated topography on the GSC correlates with a confined zone of low-velocity, high-temperature mantle connecting the plume stem and ridge at depths of âŒ100 km. At this site on the ridge, plume-driven upwelling involving deep melting of partially dehydrated, recycled ancient oceanic crust, plus plate-limited shallow melting of anhydrous peridotite, generate E-MORB and larger amounts of melt than elsewhere on the GSC. The first-order control on plume stem to ridge flow is rheological rather than gravitational, and strongly influenced by flow regimes initiated when the plume was on axis (>5 Ma). During subsequent northeast ridge migration material upwelling in the plume stem appears to have remained âanchoredâ to a contact point on the GSC. This deep, confined NE plume stem-to-ridge flow occurs via a network of melt channels, embedded within the normal spreading and advection of plume material beneath the Nazca plate, and coincides with locations of historic volcanism. Our observations require a more dynamically complex model than proposed by most studies, which rely on radial solid-state outflow of heterogeneous plume material to the ridge.We thank GalĂĄpagos National Park authorities and CDRS for permitting fieldwork in GalĂĄpagos. D. Villagomez and D. Toomey generously shared their extensive seismic data set for GalĂĄpagos, and D. McKenzie kindly provided help with temperature calculations. End-member compositions of GalĂĄpagos mantle reservoirs in Figure 4 were estimated from principal component analysis; data related to these calculations are available in the supporting information. We are grateful to Kaj Hoernle and two anonymous reviewers for their constructive comments on an earlier version of this manuscript. The research was funded by the University of Cambridge, Geological Society of London, NERC (RG57434), and NSF (EAR 0838461, EAR 0944229, and EAR-11452711).This is the final published version of the article. It first appeared at http://dx.doi.org/10.1002/2015GC00572
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