2,597 research outputs found
Examining electron-boson coupling using time-resolved spectroscopy
Nonequilibrium pump-probe time domain spectroscopies can become an important
tool to disentangle degrees of freedom whose coupling leads to broad structures
in the frequency domain. Here, using the time-resolved solution of a model
photoexcited electron-phonon system we show that the relaxational dynamics are
directly governed by the equilibrium self-energy so that the phonon frequency
sets a window for "slow" versus "fast" recovery. The overall temporal structure
of this relaxation spectroscopy allows for a reliable and quantitative
extraction of the electron-phonon coupling strength without requiring an
effective temperature model or making strong assumptions about the underlying
bare electronic band dispersion.Comment: 23 pages, 4 figures + Supplementary Material and movies, to appear in
PR
What do Teens Make of Personal Informatics?: Young People's Responses to Self-Tracking Practices for Self-Determined Motives
Personal informatics (PI) technologies allow users to collect data about aspects of their lifestyle like mood or step count. Though teens increasingly encounter and use such technologies, little is known about how they ascribe meaning to their own PI activities. We report a qualitative study of the PI experiences of eighteen teens (aged 14 – 17). Following a learning phase focused on interpreting PI data, participants chose a personal goal that interested them and a PI tool to track it for 4-8 weeks in everyday contexts. Participants proved to be competent, flexible users of PI tools, tracking a range of meaningful life factors, from ‘worries’ to ‘exercise’; they valued learning about ‘natural patterns’ in their lives and were motivated to manage their emotions and evaluate whether they were doing the right thing. Our findings contribute to understanding how young people can engage in appropriation and interpretation of PI data – suggesting opportunities for educational interventions and design
Age-specific incidence of A/H1N1 2009 influenza infection in England from sequential antibody prevalence data using likelihood-based estimation.
Estimating the age-specific incidence of an emerging pathogen is essential for understanding its severity and transmission dynamics. This paper describes a statistical method that uses likelihoods to estimate incidence from sequential serological data. The method requires information on seroconversion intervals and allows integration of information on the temporal distribution of cases from clinical surveillance. Among a family of candidate incidences, a likelihood function is derived by reconstructing the change in seroprevalence from seroconversion following infection and comparing it with the observed sequence of positivity among the samples. This method is applied to derive the cumulative and weekly incidence of A/H1N1 pandemic influenza in England during the second wave using sera taken between September 2009 and February 2010 in four age groups (1-4, 5-14, 15-24, 25-44 years). The highest cumulative incidence was in 5-14 year olds (59%, 95% credible interval (CI): 52%, 68%) followed by 1-4 year olds (49%, 95% CI: 38%, 61%), rates 20 and 40 times higher respectively than estimated from clinical surveillance. The method provides a more accurate and continuous measure of incidence than achieved by comparing prevalence in samples grouped by time period
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
Ohio Conservation Plan: Plains gartersnake, Thamnophis radix
This plan outlines strategies and methods used in an ongoing study initiated in 1999 to restore a selfsustaining population of the Plains gartersnake (Thamnophis radix) in Ohio. Restoring a self-sustaining population would require increases in the current population to where the ratios of T. radix to T. sirtalis are approximately 1:1 in multiple locations in Killdeer Plains Wildlife Area (KPWA). This ratio would be similar to what was seen earlier by Reichenbach and Dalrymple (1986) at one site in KPWA.
The plan was developed by a team of enthusiastic conservationists representing, the Division of Wildlife (ODW), the Columbus and Cleveland Zoos, Westerville North High School Field Study Class, Liberty University, Northern Illinois University, and the University of Tennessee. A thorough review of the plan will be made in 2012 with revisions and updates as needed
Protoclusters associated with z > 2 radio galaxies. I. Characteristics of high redshift protoclusters
[Abridged] We present the results of a large program conducted with the Very
Large Telescope and Keck telescope to search for forming clusters of galaxies
near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and
broad-band images of nine radio galaxies and their surroundings. The imaging
was used to select candidate Lyman alpha emitting galaxies in ~3x3 Mpc^2 areas
near the radio galaxies. A total of 337 candidate emitters were found with a
rest-frame Lyman alpha equivalent width of EW_0 > 15 A and Sigma = EW_0/Delta
EW_0 > 3. Follow-up spectroscopy confirmed 168 Lyman alpha emitters near eight
radio galaxies. The success rate of our selection procedure is 91%. At least
six of our eight fields are overdense in Lyman alpha emitters by a factor 3-5.
Also, the emitters show significant clustering in velocity space. In the
overdense fields, the width of the velocity distributions of the emitters is a
factor 2-5 smaller than the width of the narrow-band filters. Taken together,
we conclude that we have discovered six forming clusters of galaxies
(protoclusters). We estimate that roughly 75% of powerful (L_2.7GHz > 10^33
erg/s/Hz/sr) high redshift radio galaxies reside in a protocluster, with a
sizes of at least 1.75 Mpc. We estimate that the protoclusters have masses in
the range 2-9 x 10^14 Msun and they are likely to be progenitors of present-day
(massive) clusters of galaxies. For the first time, we have been able to
estimate the velocity dispersion of cluster progenitors from z~5 to ~2. The
velocity dispersion of the emitters increases with cosmic time, in agreement
with the dark matter velocity dispersion in numerical simulations of forming
massive clusters.Comment: 30 pages, 20 figures. Published in A&A. The article with high
resolution figures is available at
http://www.ast.cam.ac.uk/~venemans/research/datapaper/index.htm
The Nascent Red Sequence at z~2
We present new constraints on the evolution of the early-type galaxy
color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy
protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space
Telescope. This field contains a spectroscopically confirmed space-overdensity
of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio
galaxy MRC 1138-262. Using these NICMOS data we identify a significant
surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram
(when compared with deep NICMOS imaging from the HDF-N and UDF). The
optical-NIR colors of these prospective red-sequence galaxies indicate the
presence of on-going dust-obscured star-formation or recently formed (<~ 1.5
Gyr)stellar populations in a majority of the red galaxies. We measure the slope
and intrinsic scatter of the CMR for three different red galaxy samples
selected by a wide color cut, and using photometric redshifts both with and
without restrictions on rest-frame optical morphology. In all three cases both
the rest-frame slope and intrinsic color scatter are considerably higher
than corresponding values for lower redshift galaxy clusters. These results
suggest that while some relatively quiescent galaxies do exist in this
protocluster both the majority of the galaxy population and hence the
color-magnitude relation are still in the process of forming, as expected.Comment: 8 pages, 7 figures, accepted for publication in ApJ (to appear June
1, 2008, v679n2
The WIRCAM Deep Infrared Cluster Survey I: Groups and Clusters at z > 1.1
We use CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) NIR data and XMM
data to identify z>1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to
such clusters can not be identified without deep NIR data and as such the total
of =1deg2 of J , H & Ks band imaging provided by WIRDS is an indispensable tool
in such work. Using public XMM X-ray data, we identify extended X-ray sources
in the two fields. The resulting catalogue of extended X-ray sources was
analyzed for optical/NIR counterparts, using a red-sequence algorithm.
Redshifts of candidate groups and clusters were estimated using the median
photometric redshifts of detected counterparts and where available
spectroscopic data. Additionally, we surveyed X-ray point sources for potential
group systems at the limit of our detection range in the X-ray data. A
catalogue of z > 1.1 cluster candidates in the two fields has been compiled and
cluster masses, radii and temperatures have been estimated using the scaling
relations. The catalogue consists of 15 z > 1.1 candidates. Three of the
detections are previously published extended X-ray sources. Of note is JKSC 041
for which we identify possible structures at z = 0.8, z = 0.96, z = 1.13 and z
= 1.49. We also make an independent detection of the massive cluster, XMMXCS
J2215.9-1738. We use the z > 1.1 catalogue to compare the cluster number counts
in these fields with models based on WMAP 7-year cosmology and find that the
models slightly over-predict the observations, whilst at z>1.5 we do not detect
any clusters. We note that cluster number counts at z > 1.1 are highly
sensitive to the cosmological model, however a significant reduction in present
statistical (due to available survey area) and systematic (due to cluster
scaling relations) uncertainties is required in order to confidently constrain
cosmological parameters using cluster number counts at high redshift.Comment: 22 pages, 22 figures, Accepted 4 August 201
C. trachomatis pgp3 antibody prevalence in young women in England, 1993-2010
Seroepidemiology of chlamydia can offer study opportunities and insights into cumulative risk of exposure that may contribute to monitoring the frequency of, and control of, genital chlamydia-the most commonly diagnosed STI in England. We undertook retrospective anonymous population-based cross-sectional surveys using an indirect IgG ELISA for chlamydia Pgp3 antibody. Sera from 4,732 women aged 17-24 years were tested. Samples were taken at 3-yearly intervals between 1993 and 2002, a period during which other data suggest chlamydia transmission may have been increasing, and from each year between 2007 and 2010. Seroprevalence increased in 17-24 year olds over time between 1993 and 2002. Between 2007 and 2010, age-standardised seroprevalence among 17-24 year olds decreased from 20% (95% CI: 17-23) to 15% (95%CI 12-17) (p = 0.0001). The biggest drop was among 20 to 21 year olds, where seroprevalence decreased from 21% in 2007 to 9% in 2010 (p = 0.002). These seroprevalence data reflect some known features of the epidemiology of chlamydia infection, and show that exposure to antibody-inducing chlamydia infection has declined in recent years. This decline was concurrent with increasing rates of screening for asymptomatic chlamydia. Serology should be explored further as a tool for evaluation of chlamydia control, including chlamydia screening programmes
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