1,524 research outputs found
Multi-Wavelength Variability of the Synchrotron Self-Compton Model for Blazar Emission
Motivated by recent reports of strongly correlated radio and X-ray
variability in 3C279 (Grandi, etal 1995), we have computed the relative
amplitudes of variations in the synchrotron flux at and the self-Compton
X-ray flux at 1 keV () for a homogeneous sphere of relativistic
electrons orbiting in a tangled magnetic field. Relative to synchrotron
self-Compton scattering without induced Compton scattering, stimulated
scattering reduces the amplitude of by as much as an order of
magnitude when \tau_T \gtwid 1. When varies in a fixed magnetic
field, increases monotonically from 0.01 at , the
self-absorption turnover frequency, to at . The relative
amplitudes of the correlated fluctuations in the radio-mm and X-ray fluxes from
3C279 are consistent with the synchrotron self-Compton model if varies
in a fixed magnetic field and induced Compton scattering is the dominant source
of radio opacity. The variation amplitudes are are too small to be produced by
the passage of a shock through the synchrotron emission region unless the
magnetic field is perpendicular to the shock front.Comment: 21 pages, 4 fig
On the Reliability of Cross Correlation Function Lag Determinations in Active Galactic Nuclei
Many AGN exhibit a highly variable luminosity. Some AGN also show a
pronounced time delay between variations seen in their optical continuum and in
their emission lines. In effect, the emission lines are light echoes of the
continuum. This light travel-time delay provides a characteristic radius of the
region producing the emission lines. The cross correlation function (CCF) is
the standard tool used to measure the time lag between the continuum and line
variations. For the few well-sampled AGN, the lag ranges from 1-100 days,
depending upon which line is used and the luminosity of the AGN. In the best
sampled AGN, NGC 5548, the H_beta lag shows year-to-year changes, ranging from
about 8.7 days to about 22.9 days over a span of 8 years. In this paper it is
demonstrated that, in the context of AGN variability studies, the lag estimate
using the CCF is biased too low and subject to a large variance. Thus the
year-to-year changes of the measured lag in NGC 5548 do not necessarily imply
changes in the AGN structure. The bias and large variance are consequences of
finite duration sampling and the dominance of long timescale trends in the
light curves, not due to noise or irregular sampling. Lag estimates can be
substantially improved by removing low frequency power from the light curves
prior to computing the CCF.Comment: To appear in the PASP, vol 111, 1999 Nov; 37 pages; 10 figure
The Effects of Periodically Gapped Time Series on Cross-correlation Lag Determinations
The three bright TeV blazars Mrk 421, Mrk 501 and PKS 2155-404 are highly
variable in synchrotron X-ray emission. In particular, these sources may
exhibit variable time lags between flux variations at different X-ray energy
bands. However, there are a number of issues that may significantly bias lag
determinations. Edelson et al. (2001) recently proposed that the lags on
timescales of hours, discovered by ASCA and BeppoSAX, could be an artifact of
periodic gaps in the light curves introduced by the Earth occultation every
\~1.6 hr. Using Monte Carlo simulations, in this paper we show that the lags
over timescales of hours can not be the spurious result of periodic gaps, while
periodic gaps indeed introduces uncertainty larger than what present in the
evenly sampled data. The results also show that time lag estimates can be
substantially improved by using evenly sampled light curves with large lag to
bin-size ratio. Furthermore, we consider an XMM-Newton observation without
interruptions and re-sample the light curves using the BeppoSAX observing
windows, and then repeat the same cross correlation function (CCF) analysis on
both the real and fake data. The results also show that periodic gaps in the
light curves do not significantly distort the CCF characters, and indeed the
CCF peak ranges of the real and fake data overlap. Therefore, the lags
discovered by ASCA and BeppoSAX are not due to periodic gaps in the light
curves.Comment: 13 pages, 6 figures, accepted for publication in Ap
Test result communication in primary care : clinical and office staff perspectives
OBJECTIVE. To understand how the results of laboratory tests are communicated to patients in primary care and perceptions on how the process may be improved. DESIGN. Qualitative study employing staff focus groups. SETTING. Four UK primary care practices. PARTICIPANTS. Staff involved in the communication of test results. FINDINGS. Five main themes emerged from the data: (i) the default method for communicating results differed between practices; (ii) clinical impact of results and patient characteristics such as anxiety level or health literacy influenced methods by which patients received their test result; (iii) which staff member had responsibility for the task was frequently unclear; (iv) barriers to communicating results existed, including there being no system or failsafe in place to determine whether results were returned to a practice or patient; (v) staff envisaged problems with a variety of test result communication methods discussed, including use of modern technologies, such as SMS messaging or online access. CONCLUSIONS. Communication of test results is a complex yet core primary care activity necessitating flexibility by both patients and staff. Dealing with the results from increasing numbers of tests is resource intensive and pressure on practice staff can be eased by greater utilization of electronic communication. Current systems appear vulnerable with no routine method of tracing delayed or missing results. Instead, practices only become aware of missing results following queries from patients. The creation of a test communication protocol for dissemination among patients and staff would help ensure both groups are aware of their roles and responsibilities
Unbiased Functional Proteomics Strategy for Protein Kinase Inhibitor Validation and Identification of bona fide Protein Kinase Substrates: Application to Identification of EEF1D as a Substrate for CK2
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Measurement of the Neutrino Mass Splitting and Flavor Mixing by MINOS
Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25×10^(20) protons on target. A fit to neutrino oscillations yields values of |Δm^2|=(2.32_(-0.08)^(+0.12))×10^(-3) eV^2 for the atmospheric mass splitting and sin^2(2θ)>0.90 (90% C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively
Measurement of the neutrino mass splitting and flavor mixing by MINOS
Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of protons on target. A fit to neutrino oscillations yields values of ,eV for the atmospheric mass splitting and m sin^2!(2 heta) > 0.90 (90%,C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively
Treating Solar Model Uncertainties: A Consistent Statistical Analysis of Solar Neutrino Models and Data
We describe how to consistently incorporate solar model uncertainties, along
with experimental errors and correlations, when analyzing solar neutrino data
to derive confidence limits on parameter space for proposed solutions of the
solar neutrino problem. Our work resolves ambiguities and inconsistencies in
the previous literature. As an application of our methods we calculate the
masses and mixing angles allowed by the current data for the proposed MSW
solution using both Bayesian and frequentist methods, allowing purely for solar
model flux variations, to compare with previous work. We consider the effects
of including metal diffusion in the solar models and also discuss implications
for future experiments.Comment: 29 pages (incl figs), latex, 6 figures (appended as separate
uuencoded file. To embed figures in text, uncomment 6 \epsfysize lines which
appear before bibliography), CWRU-P5-94, CfPA-94-TTH-29,
Fermilab-Pub-94/176-
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New constraints on muon-neutrino to electron-neutrino transitions in MINOS
This paper reports results from a search for ν_μ → ν_e transitions by the MINOS experiment based on a 7×10^(20) protons-on-target exposure. Our observation of 54 candidate ν_e events in the far detector with a background of 49.1±7.0(stat)±2.7(syst) events predicted by the measurements in the near detector requires 2sin^2(2θ_(13))sin^2θ_(23)<0.12(0.20) at the 90% C.L. for the normal (inverted) mass hierarchy at δ_(CP)=0. The experiment sets the tightest limits to date on the value of θ_(13) for nearly all values of δ_(CP) for the normal neutrino mass hierarchy and maximal sin^2(2θ_(23))
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