960 research outputs found
The fundamental plane of evolving red nuggets
We present an exploration of the mass structure of a sample of 12 strongly
lensed massive, compact early-type galaxies at redshifts to provide
further possible evidence for their inside-out growth. We obtain new ESI/Keck
spectroscopy and infer the kinematics of both lens and source galaxies, and
combine these with existing photometry to construct (a) the fundamental plane
(FP) of the source galaxies and (b) physical models for their dark and luminous
mass structure. We find their FP to be tilted towards the virial plane relative
to the local FP, and attribute this to their unusual compactness, which causes
their kinematics to be totally dominated by the stellar mass as opposed to
their dark matter; that their FP is nevertheless still inconsistent with the
virial plane implies that both the stellar and dark structure of early-type
galaxies is non-homologous. We also find the intrinsic scatter of their FP to
be comparable to the local value, indicating that variations in the stellar
mass structure outweight variations in the dark halo in the central regions of
early-type galaxies. Finally, we show that inference on the dark halo structure
-- and, in turn, the underlying physics -- is sensitive to assumptions about
the stellar initial mass function (IMF), but that physically-motivated
assumptions about the IMF imply haloes with sub-NFW inner density slopes, and
may present further evidence for the inside-out growth of compact early-type
galaxies via minor mergers and accretion.Comment: 10 pages, 3 figures, 3 tables; submitted to MNRA
Red nuggets grow inside-out: evidence from gravitational lensing
We present a new sample of strong gravitational lens systems where both the
foreground lenses and background sources are early-type galaxies. Using imaging
from HST/ACS and Keck/NIRC2, we model the surface brightness distributions and
show that the sources form a distinct population of massive, compact galaxies
at redshifts , lying systematically below the
size-mass relation of the global elliptical galaxy population at those
redshifts. These may therefore represent relics of high-redshift red nuggets or
their partly-evolved descendants. We exploit the magnifying effect of lensing
to investigate the structural properties, stellar masses and stellar
populations of these objects with a view to understanding their evolution. We
model these objects parametrically and find that they generally require two
S\'ersic components to properly describe their light profiles, with one more
spheroidal component alongside a more envelope-like component, which is
slightly more extended though still compact. This is consistent with the
hypothesis of the inside-out growth of these objects via minor mergers. We also
find that the sources can be characterised by red-to-blue colour gradients as a
function of radius which are stronger at low redshift -- indicative of ongoing
accretion -- but that their environments generally appear consistent with that
of the general elliptical galaxy population, contrary to recent suggestions
that these objects are predominantly associated with clusters.Comment: 21 pages; accepted for publication in MNRA
Probing the Catalytic Roles of Arg548 and Gln552 in the Carboxyl Transferase Domain of the \u3cem\u3eRhizobium etli\u3c/em\u3e Pyruvate Carboxylase by Site-directed Mutagenesis
The roles of Arg548 and Gln552 residues in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase were investigated using site-directed mutagenesis. Mutation of Arg548 to alanine or glutamine resulted in the destabilization of the quaternary structure of the enzyme, suggesting that this residue has a structural role. Mutations R548K, Q552N, and Q552A resulted in a loss of the ability to catalyze pyruvate carboxylation, biotin-dependent decarboxylation of oxaloacetate, and the exchange of protons between pyruvate and water. These mutants retained the ability to catalyze reactions that occur at the active site of the biotin carboxylase domain, i.e., bicarbonate-dependent ATP cleavage and ADP phosphorylation by carbamoyl phosphate. The effects of oxamate on the catalysis in the biotin carboxylase domain by the R548K and Q552N mutants were similar to those on the catalysis of reactions by the wild-type enzyme. However, the presence of oxamate had no effect on the reactions catalyzed by the Q552A mutant. We propose that Arg548 and Gln552 facilitate the binding of pyruvate and the subsequent transfer of protons between pyruvate and biotin in the partial reaction catalyzed in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase
Clustering of multiple specific genes and gene-rich R-bands around SC-35 domains: evidence for local euchromatic neighborhoods
Typically, eukaryotic nuclei contain 10–30 prominent domains (referred to here as SC-35 domains) that are concentrated in mRNA metabolic factors. Here, we show that multiple specific genes cluster around a common SC-35 domain, which contains multiple mRNAs. Nonsyntenic genes are capable of associating with a common domain, but domain “choice” appears random, even for two coordinately expressed genes. Active genes widely separated on different chromosome arms associate with the same domain frequently, assorting randomly into the 3–4 subregions of the chromosome periphery that contact a domain. Most importantly, visualization of six individual chromosome bands showed that large genomic segments (∼5 Mb) have striking differences in organization relative to domains. Certain bands showed extensive contact, often aligning with or encircling an SC-35 domain, whereas others did not. All three gene-rich reverse bands showed this more than the gene-poor Giemsa dark bands, and morphometric analyses demonstrated statistically significant differences. Similarly, late-replicating DNA generally avoids SC-35 domains. These findings suggest a functional rationale for gene clustering in chromosomal bands, which relates to nuclear clustering of genes with SC-35 domains. Rather than random reservoirs of splicing factors, or factors accumulated on an individual highly active gene, we propose a model of SC-35 domains as functional centers for a multitude of clustered genes, forming local euchromatic “neighborhoods.
Generativity in College Students: Comparing and Explaining the Impact of Mentoring
Preparing college students to be active contributors to the next generation is an important function of higher education. This assumption about generativity forms a cornerstone in this mixed methods study that examined generativity levels among 273 college students at a 4-year public university. MANCOVA results indicated that college students who mentor demonstrated significantly higher generativity than nonmentoring students. Interviews with 9 mentoring students revealed that, although a “seed of generativity” may have already been planted, their mentoring experience served as a “lab” for learning how to be generative. The integrated findings offer important contributions relative to leadership and social responsibility
Generativity in College Students: Comparing and Explaining the Impact of Mentoring
Preparing college students to be active contributors to the next generation is an important function of higher education. This assumption about generativity forms a cornerstone in this mixed methods study that examined generativity levels among 273 college students at a 4-year public university. MANCOVA results indicated that college students who mentor demonstrated significantly higher generativity than nonmentoring students. Interviews with 9 mentoring students revealed that, although a “seed of generativity” may have already been planted, their mentoring experience served as a “lab” for learning how to be generative. The integrated findings offer important contributions relative to leadership and social responsibility
USING THE RESERVOIR WAVE APPROACH TO STUDY THE HORIZON EFFECT
INTRODUCTION Differing theories and models have been explored in the field of arterial hemodynamics in an effort to better understand how the blood flows in the body. The existence of discrete reflection sites remains a source of disagreement. As a wave proceeds along an artery, any local change in impedance will result in partial reflection. Thus, because of the great complexity of the arterial system, it has been suggested that no distinct reflector sites should exist. On the other hand, there is recent experimental evidence using the reservoir-wave approach (RWA) that implies discrete positive and negative reflection sites. The pattern of wave propagation and reflection is plausible, as are the modifications produced by pharmacologic interventions [1]. The classical, frequency-domain, “impedance analysis” approach uses Fourier analysis to break down pressure and flow waveforms into summations of sinusoids, resulting in an impedance spectrum [2]. The RWA is a novel alternative, positing that measured pressures and flows are the instantaneous sums of “excess” (wave-related) and reservoir (volume-related) components [2]. The “Horizon Effect” (HE) [3] implies that a reflector site can never be reached no matter how far into the periphery one measures (Figure 1). As such, it supports the idea that there are no distinct reflector sites. Measuring peripheral pressure and flow and using the RWA, the purpose of this study was to evaluate the HE and the question of fixed reflector sites. METHODS Eight anesthetized pigs were catheterized and pressure and flow were measured simultaneously at 4 locations: the aortic root and the brachial, carotid and renal arteries. Pharmacologic interventions were used to manipulate propagation and reflection patterns. MatLab (The MathWorks Inc., Natick, MA) was used to calculate the reservoir pressure, the local wave speed and to carry out wave intensity analysis (WIA) to obtain the forwards and backwards components of pressure. RESULTS Analysis has been completed on 4 of the 8 animals studied. Each showed minimal backward wave activity at the aortic root and in the carotid artery. However, in the brachial and renal arteries, no backward waves could be detected. DISCUSSION AND CONCLUSIONS Backward waves were scarcely detected in the periphery using either the RWA or classical analysis. This may suggest that the pig model was inappropriate to study the HE. Porcine anatomy does not allow measurement at remote peripheral sites and reflection sites cannot be studied if no reflections are to be found. Further analysis of the data is needed before more definitive conclusions can be made
The Milky Way's Kiloparsec Scale Wind: A Hybrid Cosmic-Ray and Thermally Driven Outflow
We apply a wind model, driven by combined cosmic-ray and thermal-gas
pressure, to the Milky Way, and show that the observed Galactic diffuse soft
X-ray emission can be better explained by a wind than by previous static gas
models. We find that cosmic-ray pressure is essential to driving the observed
wind. Having thus defined a "best-fit" model for a Galactic wind, we explore
variations in the base parameters and show how the wind's properties vary with
changes in gas pressure, cosmic-ray pressure and density. We demonstrate the
importance of cosmic rays in launching winds, and the effect cosmic rays have
on wind dynamics. In addition, this model adds support to the hypothesis of
Breitschwerdt and collaborators that such a wind may help explain the
relatively small gradient observed in gamma-ray emission as a function of
galactocentric radius.Comment: 14 pages, 11 figures; Accepted to Ap
Listen to Nice
In describing Humphrey Jennings’ wartime documentary propaganda film, 'Listen to Britain' (1942), a film with an overtly poetic sensibility and dominantly musical soundtrack, John Corner asserts that ‘through listening to
Britain, we are enabled to properly look at it'. This idea of sound leading our attention to the images has underpinned much of the collaborative
work between composer and sound designer, Geoffrey Cox, and documentary filmmaker, Keith Marley. It is in this context that the article will analyse an extract of A Film About Nice (Marley and Cox 2010), a contemporary
re-imagining of Jean Vigo’s silent documentary, 'A propos de Nice' (1930). Reference will be made throughout to the historical context, and the filmic and theoretical influences that have informed the way music and creative sound design have been used to place emphasis on hearing a place, as much as seeing it
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