561 research outputs found
Assembly of the SIR Complex and Its Regulation by O-Acetyl-ADP-Ribose, a Product of NAD-Dependent Histone Deacetylation
SummaryAssembly of silent chromatin domains in budding yeast involves the deacetylation of histone tails by Sir2 and the association of the Sir3 and Sir4 proteins with hypoacetylated histone tails. Sir2 couples deacetylation to NAD hydrolysis and the synthesis of a metabolite, O-acetyl-ADP-ribose (AAR), but the functional significance of NAD hydrolysis or AAR, if any, is unknown. Here we examine the association of the Sir2, Sir3, and Sir4 proteins with each other and histone tails. Our analysis reveals that deacetylation of histone H4-lysine 16 (K16), which is critical for silencing in vivo, is also critical for the binding of Sir3 and Sir4 to histone H4 peptides in vitro. Moreover, AAR itself promotes the association of multiple copies of Sir3 with Sir2/Sir4 and induces a dramatic structural rearrangement in the SIR complex. These results suggest that Sir2 activity modulates the assembly of the SIR complex through both histone deacetylation and AAR synthesis
Smoking Profile of Woodside Juvenile Detention Center and Interventional Goal-Setting Workshop
Abstract: We studied smoking status among teenage residents at the Woodside Juvenile Rehabilitation Center (Woodside) in Vermont. Using a modified CDC survey and focus groups, we found that short-term detention residents (S group) were significantly more likely to be âsmokersâ than the long-term treatment residents (L group). All residents reported that stress had an important impact on their lives. Based on our findings, we implemented a goal setting workshop for both L and S groups.https://scholarworks.uvm.edu/comphp_gallery/1002/thumbnail.jp
Transformations between 2MASS, SDSS and BVI photometric systems for late-type giants
We present colour transformations from Two Micron All Sky Survey (2MASS)
photometric system to Johnson-Cousins system and to Sloan Digital Sky Survey
(SDSS) system for late-type giants and vice versa. The giant star sample was
formed using surface gravity constraints () to Cayrel de
Strobel et al.\rq s (2001) spectroscopic catalogue. 2MASS, SDSS and
Johnson-Cousins photometric data was taken from Cutri et al. (2003), Ofek
(2008) and van Leeuwen (2007), respectively. The final sample was refined
applying the following steps: (1) the data were dereddened, (2) the sample
stars selected are of the highest photometric quality. We give two--colour
dependent transformations as a function of metallicity as well as independent
of metallicity. The transformations provide absolute magnitudes and distance
determinations which can be used in space density evaluations at relatively
short distances where some or all of the SDSS magnitudes of late-type giants
are saturated.Comment: The variables and "f" parameters in the equations 15-17 and 27-29
were change
Three-Point Correlation Functions of SDSS Galaxies: Luminosity and Color Dependence in Redshift and Projected Space
The three-point correlation function (3PCF) provides an important view into
the clustering of galaxies that is not available to its lower order cousin, the
two-point correlation function (2PCF). Higher order statistics, such as the
3PCF, are necessary to probe the non-Gaussian structure and shape information
expected in these distributions. We measure the clustering of spectroscopic
galaxies in the Main Galaxy Sample of the Sloan Digital Sky Survey (SDSS),
focusing on the shape or configuration dependence of the reduced 3PCF in both
redshift and projected space. This work constitutes the largest number of
galaxies ever used to investigate the reduced 3PCF, using over 220,000 galaxies
in three volume-limited samples. We find significant configuration dependence
of the reduced 3PCF at 3-27 Mpc/h, in agreement with LCDM predictions and in
disagreement with the hierarchical ansatz. Below 6 Mpc/h, the redshift space
reduced 3PCF shows a smaller amplitude and weak configuration dependence in
comparison with projected measurements suggesting that redshift distortions,
and not galaxy bias, can make the reduced 3PCF appear consistent with the
hierarchical ansatz. The reduced 3PCF shows a weaker dependence on luminosity
than the 2PCF, with no significant dependence on scales above 9 Mpc/h. On
scales less than 9 Mpc/h, the reduced 3PCF appears more affected by galaxy
color than luminosty. We demonstrate the extreme sensitivity of the 3PCF to
systematic effects such as sky completeness and binning scheme, along with the
difficulty of resolving the errors. Some comparable analyses make assumptions
that do not consistently account for these effects.Comment: 27 pages, 21 figures. Updated to match accepted version. Published in
Ap
Neutral hydrogen surveys for high redshift galaxy clusters and proto-clusters
We discuss the possibility of performing blind surveys to detect large-scale
features of the universe using 21cm emission. Using instruments with approx.
5'-10' resolution currently in the planning stage, it should be possible to
detect virialized galaxy clusters at intermediate redshifts using the combined
emission from their constituent galaxies, as well as less overdense structures,
such as proto-clusters and the `cosmic web', at higher redshifts. Using
semi-analytic methods we compute the number of virialized objects and those at
turnaround which might be detected by such surveys. We find a surprisingly
large number of objects might be detected even using small (approx. 5%)
bandwidths and elaborate on some issues pertinent to optimising the design of
the instrument and the survey strategy. The main uncertainty is the fraction of
neutral gas relative to the total dark matter within the object. We discuss
this issue in the context of the observations which are currently available.Comment: 10 pages, 6 figure
Evidence of Gunn-Peterson damping wings in high-z quasar spectra: strengthening the case for incomplete reionization
The spectra of several high-redshift (z>6) quasars have shown evidence for a
Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen
fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However,
previous analyses assumed that the IGM was uniformly ionized outside of the
quasar's HII region. Here we relax this assumption and model patchy
reionization scenarios for a range of IGM and quasar parameters. We quantify
the impact of these differences on the inferred x_HI, by fitting the spectra of
three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112
(z=6.247). We find that the best-fit values of x_HI in the patchy models agree
well with the uniform case. More importantly, we confirm that the observed
spectra favor the presence of a GP damping wing, with peak likelihoods
decreasing by factors of > few - 10 when the spectra are modeled without a
damping wing. We also find that the Ly alpha absorption spectra, by themselves,
cannot distinguish the damping wing in a relatively neutral IGM from a damping
wing in a highly ionized IGM, caused either by an isolated neutral patch, or by
a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized
universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI
> few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable
prior probabilities for the line of sight (LOS) to intercept either a neutral
patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the
quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI >
0.1 (at 95% confidence). This strengthens earlier claims that a substantial
global fraction of hydrogen in the z~6 IGM is in neutral form.Comment: 18 pages, 7 figures, version accepted for publication in the MNRA
âA nation of town criersâ: civic publicity and historical pageantry in inter-war Britain
Historical pageantry emerged in 1905 as the brainchild of the theatrical impresario Louis Napoleon Parker. Large casts of volunteers re-enacted successive scenes of local history, as crowds of thousands watched on, in large outdoor arenas. As the press put it, Britain had caught âpageant feverâ. Towards the end of the 1920s, there was another outburst of historical pageantry. Yet, in contrast to the Edwardian period, when pageants took place in small towns, this revival was particularly vibrant in large industrial towns and cities. This article traces the popularity of urban pageantry to an inter-war âcivic publicityâ movement. In doing so, it reassesses questions of local cultural decline; the role of local government; and the relationship of civic responsibility to popular theatre
Fundamental Parameters and Abundances of Metal-Poor Stars: The SDSS Standard BD +17 4708
The atmospheric parameters and iron abundance of the Sloan Digital Sky Survey
(SDSS) spectrophotometric standard star BD +17 4708 are critically examined
using up-to-date Kurucz model atmospheres, LTE line formation calculations, and
reliable atomic data. We find Teff = 6141+-50 K, log g = 3.87+-0.08, and
[Fe/H]=-1.74+-0.09. The line-of-sight interstellar reddening, bolometric flux,
limb-darkened angular diameter, stellar mass, and the abundances of Mg, Si, and
Ca are also obtained. This star is a unique example of a moderately metal-poor
star for which the effective temperature can be accurately constrained from the
observed spectral energy distribution (corrected for reddening). Such analysis
leads to a value that is higher than most spectroscopic results previously
reported in the literature (~5950 K). We find that the ionization balance of Fe
lines is satisfied only if a low Teff (~5950 K) is adopted. With our preferred
Teff (6141 K), the mean iron abundance we obtain from the FeII lines is lower
by about 0.15 dex than that from the FeI lines, and therefore, the discrepancy
between the mean iron abundance from FeI and FeII lines cannot be explained by
overionization by UV photons as the main non-LTE effect. We also comment on
non-LTE effects and the importance of inelastic collisions with neutral H atoms
in the determination of oxygen abundances in metal-poor stars from the 777 nm
OI triplet. (Abridged)Comment: A&A in pres
A Mismatch in the Ultraviolet Spectra between Low-Redshift and Intermediate-Redshift Type Ia Supernovae as a Possible Systematic Uncertainty for Supernova Cosmology
We present Keck high-quality rest-frame ultraviolet (UV) through optical
spectra of 21 Type Ia supernovae (SNe Ia) in the redshift range 0.11 < z < 0.37
and a mean redshift of 0.22 that were discovered during the Sloan Digital Sky
Survey-II (SDSS-II) SN Survey. Using the broad-band photometry of the SDSS
survey, we are able to reconstruct the SN host-galaxy spectral energy
distributions (SEDs), allowing for a correction for the host-galaxy
contamination in the SN Ia spectra. Comparison of composite spectra constructed
from a subsample of 17 high-quality spectra to those created from a
low-redshift sample with otherwise similar properties shows that the Keck/SDSS
SNe Ia have, on average, extremely similar rest-frame optical spectra but show
a UV flux excess. This observation is confirmed by comparing synthesized
broad-band colors of the individual spectra, showing a difference in mean
colors at the 2.4 - 4.4 sigma level for various UV colors. We further see a
slight difference in the UV spectral shape between SNe with low-mass and
high-mass host galaxies. Additionally, we detect a relationship between the
flux ratio at 2770 and 2900 A and peak luminosity that differs from that
observed at low redshift. We find that changing the UV SED of an SN Ia within
the observed dispersion can change the inferred distance moduli by ~0.1 mag.
This effect only occurs when the data probe the rest-frame UV. We suggest that
this discrepancy could be due to differences in the host-galaxy population of
the two SN samples or to small-sample statistics.Comment: 28 pages, 21 figures, accepted by AJ, spectra are available at
http://www.cfa.harvard.edu/~rfoley/data
- âŠ