1,267 research outputs found
Equus Unbound: Fairman Rogers and the Age of the Horse (Panel Discussion)
Podcast introduction, Kristin Winch, 00:00-01:17
Welcome and introduction, H. Carton Rogers, 01:17-05:06:30
Remarks by panel moderator Ann N. Greene, 06:35-20:15
Remarks by Herbert Moelis, 20:33-28:58
Remarks by Ellen Moelis, 28:58-39:45
Remarks by Dean Richardson, 39:45-46:45
Remarks by Douglas Kemmerer, 46:45-1:07:45
Questions and answers, 1:07:45-1:10:18
Concluding remarks, Lynne Farrington, 1:10:18-1:11:19
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Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic
supernovae (collectively known as stripped-envelope supernovae) are studied by
collecting data on the apparent magnitude, distance, and interstellar
extinction of each event. Weighted and unweighted mean absolute magnitudes of
the combined sample as well as various subsets of the sample are reported. The
limited sample size and the considerable uncertainties, especially those
associated with extinction in the host galaxies, prevent firm conclusions
regarding differences between the absolute magnitudes of supernovae of Type Ib
and Ic, and regarding the existence of separate groups of overluminous and
normal-luminosity stripped-envelope supernovae. The spectroscopic
characteristics of the events of the sample are considered. Three of the four
overluminous events are known to have had unusual spectra. Most but not all of
the normal luminosity events had typical spectra. Light curves of
stripped-envelope supernovae are collected and compared. Because SN 1994I in
M51 was very well observed it often is regarded as the prototypical Type Ic
supernova, but it has the fastest light curve in the sample. Light curves are
modeled by means of a simple analytical technique that, combined with a
constraint on E/M from spectroscopy, yields internally consistent values of
ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A
The MAD-Related Protein Smad7 Associates with the TGFβ Receptor and Functions as an Antagonist of TGFβ Signaling
AbstractTGFβ signaling is initiated when the type I receptor phosphorylates the MAD-related protein, Smad2, on C-terminal serine residues. This leads to Smad2 association with Smad4, translocation to the nucleus, and regulation of transcriptional responses. Here we demonstrate that Smad7 is an inhibitor of TGFβ signaling. Smad7 prevents TGFβ-dependent formation of Smad2/Smad4 complexes and inhibits the nuclear accumulation of Smad2. Smad7 interacts stably with the activated TGFβ type I receptor, thereby blocking the association, phosphorylation, and activation of Smad2. Furthermore, mutations in Smad7 that interfere with receptor binding disrupt its inhibitory activity. These studies thus define a novel function for MAD-related proteins as intracellular antagonists of the type I kinase domain of TGFβ family receptors
A HST Census of Nuclear Star Clusters in Late-Type Spiral Galaxies: II. Cluster Sizes and Structural Parameter Correlations
We investigate the structural properties of nuclear star clusters in
late-type spiral galaxies. More specifically, we fit analytical models to HST
images of 39 nuclear clusters in order to determine their effective radii after
correction for the instrumental point spread function. We use the results of
this analysis to compare the luminosities and sizes of nuclear star clusters to
those of other ellipsoidal stellar systems, in particular the Milky Way
globular clusters. Our nuclear clusters have a median effective radius of r_e =
3.5 pc, with 50% of the sample falling between 2.4 pc < r_e < 5.0 pc. This
narrow size distribution is statistically indistinguishable from that of
Galactic globular clusters, even though the nuclear clusters are on average 4
magnitudes brighter than the old globulars. We discuss some possible
interpretations of this result. From a comparison of nuclear cluster
luminosities with various properties of their host galaxies, we confirm that
more luminous galaxies harbor more luminous nuclear clusters. It remains
unclear whether this correlation mainly reflects the influence of galaxy size,
mass, and/or star formation rate. Since the brighter galaxies in our sample
typically have stellar disks with a higher central surface brightness, nuclear
cluster luminosity also correlates with this property of their hosts. On the
other hand, we find no evidence for a correlation between the presence of a
nuclear star cluster and the presence of a large-scale stellar bar.Comment: 32 pages incl. 11 figures. Accepted for publication in AJ (Jan. 2004
issue
Pairing in nuclear systems: from neutron stars to finite nuclei
We discuss several pairing-related phenomena in nuclear systems, ranging from
superfluidity in neutron stars to the gradual breaking of pairs in finite
nuclei. We focus on the links between many-body pairing as it evolves from the
underlying nucleon-nucleon interaction and the eventual experimental and
theoretical manifestations of superfluidity in infinite nuclear matter and of
pairing in finite nuclei. We analyse the nature of pair correlations in nuclei
and their potential impact on nuclear structure experiments. We also describe
recent experimental evidence that points to a relation between pairing and
phase transitions (or transformations) in finite nuclear systems. Finally, we
discuss recent investigations of ground-state properties of random two-body
interactions where pairing plays little role although the interactions yield
interesting nuclear properties such as 0+ ground states in even-even nuclei.Comment: 74 pages, 33 figs, uses revtex4. Submitted to Reviews of Modern
Physic
Cell Cycle Re-Entry and Mitochondrial Defects in Myc-Mediated Hypertrophic Cardiomyopathy and Heart Failure
While considerable evidence supports the causal relationship between increases in c-Myc (Myc) and cardiomyopathy as a part of a “fetal re-expression” pattern, the functional role of Myc in mechanisms of cardiomyopathy remains unclear. To address this, we developed a bitransgenic mouse that inducibly expresses Myc under the control of the cardiomyocyte-specific MHC promoter. In adult mice the induction of Myc expression in cardiomyocytes in the heart led to the development of severe hypertrophic cardiomyopathy followed by ventricular dysfunction and ultimately death from congestive heart failure. Mechanistically, following Myc activation, cell cycle markers and other indices of DNA replication were significantly increased suggesting that cell cycle-related events might be a primary mechanism of cardiac dysfunction. Furthermore, pathological alterations at the cellular level included alterations in mitochondrial function with dysregulation of mitochondrial biogenesis and defects in electron transport chain complexes I and III. These data are consistent with the known role of Myc in several different pathways including cell cycle activation, mitochondrial proliferation, and apoptosis, and indicate that Myc activation in cardiomyocytes is an important regulator of downstream pathological sequelae. Moreover, our findings indicate that the induction of Myc in cardiomyocytes is sufficient to cause cardiomyopathy and heart failure, and that sustained induction of Myc, leading to cell cycle re-entry in adult cardiomyocytes, represents a maladaptive response for the mature heart
A full Bayesian hierarchical mixture model for the variance of gene differential expression
<p>Abstract</p> <p>Background</p> <p>In many laboratory-based high throughput microarray experiments, there are very few replicates of gene expression levels. Thus, estimates of gene variances are inaccurate. Visual inspection of graphical summaries of these data usually reveals that heteroscedasticity is present, and the standard approach to address this is to take a log<sub>2 </sub>transformation. In such circumstances, it is then common to assume that gene variability is constant when an analysis of these data is undertaken. However, this is perhaps too stringent an assumption. More careful inspection reveals that the simple log<sub>2 </sub>transformation does not remove the problem of heteroscedasticity. An alternative strategy is to assume independent gene-specific variances; although again this is problematic as variance estimates based on few replications are highly unstable. More meaningful and reliable comparisons of gene expression might be achieved, for different conditions or different tissue samples, where the test statistics are based on accurate estimates of gene variability; a crucial step in the identification of differentially expressed genes.</p> <p>Results</p> <p>We propose a Bayesian mixture model, which classifies genes according to similarity in their variance. The result is that genes in the same latent class share the similar variance, estimated from a larger number of replicates than purely those per gene, i.e. the total of all replicates of all genes in the same latent class. An example dataset, consisting of 9216 genes with four replicates per condition, resulted in four latent classes based on their similarity of the variance.</p> <p>Conclusion</p> <p>The mixture variance model provides a realistic and flexible estimate for the variance of gene expression data under limited replicates. We believe that in using the latent class variances, estimated from a larger number of genes in each derived latent group, the <it>p</it>-values obtained are more robust than either using a constant gene or gene-specific variance estimate.</p
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