13,741 research outputs found
New Limits on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
We update the limit from the 90 GHz PIQUE ground-based polarimeter on the
magnitude of any polarized anisotropy of the cosmic microwave radiation. With a
second year of data, we have now limited both Q and U on a ring of 1 degree
radius. The window functions are broad: for E-mode polarization, the effective
l is = 191 +143 -132. We find that the E-mode signal can be no greater than
8.4 microK (95% CL), assuming no B-mode polarization. Limits on a possible
B-mode signal are also presented.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
Conformational Dependence of a Protein Kinase Phosphate Transfer Reaction
Atomic motions and energetics for a phosphate transfer reaction catalyzed by
the cAMP-dependent protein kinase (PKA) are calculated by plane-wave density
functional theory, starting from structures of proteins crystallized in both
the reactant conformation (RC) and the transition-state conformation (TC). In
the TC, we calculate that the reactants and products are nearly isoenergetic
with a 0.2 eV barrier; while phosphate transfer is unfavorable by over 1.2 eV
in the RC, with an even higher barrier. With the protein in the TC, the motions
involved in reaction are small, with only P and the catalytic proton
moving more than 0.5 \AA. Examination of the structures reveals that in the RC
the active site cleft is not completely closed and there is insufficient space
for the phosphorylated serine residue in the product state. Together, these
observations imply that the phosphate transfer reaction occurs rapidly and
reversibly in a particular conformation of the protein, and that the reaction
can be gated by changes of a few tenths of an \AA in the catalytic site.Comment: revtex4, 7 pages, 4 figures, to be submitted to Scienc
Discovery of a redshift 6.13 quasar in the UKIRT infrared deep sky survey
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO) DOI: 10.1051/0004-6361/200811161Optical and near-infrared (NIR) spectra are presented for ULAS J131911.29+095051.4â(hereafter ULAS J1319+0950), a new redshift z = 6.127 0.004 quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared Deep Sky Survey (UKIDSS). The source has = 19.10 0.03, corresponding to = -27.12, which is comparable to the absolute magnitudes of the z 6 quasars discovered in the Sloan Digital Sky Survey (SDSS). ULAS J1319+0950âwas, in fact, registered by SDSS as a faint source with = 20.13 0.12, just below the signal-to-noise ratio limit of the SDSS high-redshift quasar survey. The faint z-band magnitude is a consequence of the weak Lyâ/NâVâemission line, which has a rest-frame equivalent width of ~20Ă
âand provides only a small boost to the z-band flux. Nevertheless, there is no evidence of a significant new population of high-redshift quasars with weak emission lines from this UKIDSS-based search. The Lyââoptical depth to ULAS J1319+0950âis consistent with that measured towards similarly distant SDSS quasars, implying that results from optical- and NIR-selected quasars may be combined in studies of cosmological reionization. Also presented is a new NIR-spectrum of the previously discovered UKIDSS quasar ULAS J020332.38+001229.2, which reveals the object to be a broad absorption line quasar. The new spectrum shows that the emission line initially identified as Lyââis actually NâV, leading to a revised redshift of z = 5.72, rather than z = 5.86 as previously estimatedPeer reviewe
Revealing Cosmic Rotation
Cosmological Birefringence (CB), a rotation of the polarization plane of
radiation coming to us from distant astrophysical sources, may reveal parity
violation in either the electromagnetic or gravitational sectors of the
fundamental interactions in nature. Until only recently this phenomenon could
be probed with only radio observations or observations at UV wavelengths.
Recently, there is a substantial effort to constrain such non-standard models
using observations of the rotation of the polarization plane of cosmic
microwave background (CMB) radiation. This can be done via measurements of the
-modes of the CMB or by measuring its TB and EB correlations which vanish in
the standard model. In this paper we show that correlations-based
estimator is the best for upcoming polarization experiments. The based
estimator surpasses other estimators because it has the smallest noise and of
all the estimators is least affected by systematics. Current polarimeters are
optimized for the detection of -mode polarization from either primordial
gravitational waves or by large scale structure via gravitational lensing. In
the paper we also study optimization of CMB experiments for the detection of
cosmological birefringence, in the presence of instrumental systematics, which
by themselves are capable of producing correlations; potentially mimicking
CB.Comment: 10 pages, 3 figures, 2 table
A general scheme for modeling gamma-ray burst prompt emission
We describe a general method for modeling gamma-ray burst prompt emission. We
find that for the burst to be produced via the synchrotron process unphysical
conditions are required -- the distance of the source from the center of the
explosion () must be larger than cm and the source
Lorentz factor \gta 10^3; for such a high Lorentz factor the deceleration
radius () is less than even if the number density of particles
in the surrounding medium is as small as cm. The result,
, is in contradiction with the early x-ray and optical
afterglow data. The synchrotron-self-Compton (SSC) process fares much better.
There is a large solution space for a typical GRB prompt emission to be
produced via the SSC process. The prompt optical emission accompanying the
burst is found to be very bright (\lta 14 mag; for ) in the SSC
model, which exceeds the observed flux (or upper limit) for most GRBs.
Continuous acceleration of electrons can significantly reduce the optical flux
and bring it down to the observed limits. (Abridged)Comment: Published in MNRAS Jan 2008, 56 page
A revised edition of the readiness to change questionnaire (treatment version)
The UK Alcohol Treatment Trial provided an opportunity to examine the factor structure of the Readiness to Change Questionnaire-Treatment Version (RCQ[TV]) in a large sample (N = 742) of individuals in treatment for alcohol problems who were given the RCQ[TV] at baseline, 3-months and 12-months follow-up. Confirmatory factor analysis of the previously reported factor structure (5 items for each of Precontemplation, Contemplation and Action scales) resulted in a relatively poor fit to the data. Removal of one item from each of the scales resulted in a 12-item instrument for which goodness-of-fit indices were improved, without loss of internal consistency of the three scales, on all three measurement occasions. Inspection of relationships between stage allocation by the new instrument and negative alcohol outcome expectancies provided evidence of improved construct validity for the revised edition of the RCQ[TV]. There was also a strong relationship between stage allocation at 3-months follow-up and outcome of treatment at 12 months. The revised edition of the RCQ[TV] offers researchers and clinicians a shorter and improved measurement of stage of change in the alcohol treatment population
What do women undergoing in vitro fertilization (IVF) understand about their chance of IVF success?
Funding No external funding was used for this study. S.L. is supported by a NHMRC Investigator Grant (APP1195189). R.W. is supported by a NHMRC Investigator Grant (GNT2009767). B.W.M. is supported by a NHMRC Investigator Grant (GNT1176437) and has received research funding and travel funding from MerckPeer reviewedPublisher PD
No excess of bright galaxies around the redshift 7.1 quasar ULAS J1120+0641
We present optical and near-infrared imaging of the field of the z = 7.0842 quasar ULAS J112001.48+064124.3 taken with the Hubble Space Telescope. We use these data to search for galaxies that may be physically associated with the quasar, using the Lyman break technique, and find three such objects, although the detection of one in Spitzer Space Telescope imaging strongly suggests it lies at z ⌠2. This is consistent with the field luminosity function and indicates that there is no excess of >Lâ
galaxies within 1 Mpc of the quasar. A detection of the quasar shortwards of the Lyα line is consistent with the previously observed evolution of the intergalactic medium at z > 5.5.SC acknowledges support from the NSF grant AST-1010004 and NASA HST grant GO-13033.06-A, RJM acknowledges ERC funding via the award of a consolidator grant, and BV has been supported by the ERC grant âCosmic Dawnâ.This is the final published version. It originally appeared in MNRAS at http://www.mnras.org/content/442/4/3454.full
Recommended from our members
GAP WORK project report: training for youth practitioners on tackling gender-related violence
This project sought to challenge gender-related violence against (and by) children and young people by developing training for practitioners who have everyday contact with general populations of children and young people (âyouth practitionersâ). Through improved knowledge and understanding practitioners can better identify and challenge sexist, sexualising, homophobic or controlling language and behaviour, and know when and how to refer children and young people to the most appropriate support services. This summary outlines the Project and our initial findings about the success of the four training programmes developed and piloted.Co-funded by the DAPHNE III programme of the EU
- âŠ