1,233 research outputs found
Correlated X-ray and Optical Variability in Mkn 509
We present results of a 3 year monitoring campaign of the Seyfert 1 galaxy
Markarian 509, using X-ray data from the Rossi X-ray Timing Explorer (RXTE) and
optical data taken by the SMARTS consortium. Both light curves show significant
variations, and are strongly correlated with the optical flux leading the X-ray
flux by 15 days. The X-ray power spectrum shows a steep high-frequency slope of
-2.0, breaking to a slope of -1.0 at at timescale of 34 days. The lag from
optical to X-ray emission is most likely caused by variations in the accretion
disk propagating inward.Comment: 13 pages, 3 figures. Accepted for publication in the Astrophysical
Journa
Characterization of the Crab Pulsar's Timing Noise
We present a power spectral analysis of the Crab pulsar's timing noise,
mainly using radio measurements from Jodrell Bank taken over the period
1982-1989. The power spectral analysis is complicated by nonuniform data
sampling and the presence of a steep red power spectrum that can distort power
spectra measurement by causing severe power ``leakage''. We develop a simple
windowing method for computing red noise power spectra of uniformly sampled
data sets and test it on Monte Carlo generated sample realizations of red
power-law noise. We generalize time-domain methods of generating power-law red
noise with even integer spectral indices to the case of noninteger spectral
indices. The Jodrell Bank pulse phase residuals are dense and smooth enough
that an interpolation onto a uniform time series is possible. A windowed power
spectrum is computed revealing a periodic or nearly periodic component with a
period of about 568 days and a 1/f^3 power-law noise component with a noise
strength of 1.24 +/- 0.067 10^{-16} cycles^2/sec^2 over the analysis frequency
range 0.003 - 0.1 cycles/day. This result deviates from past analyses which
characterized the pulse phase timing residuals as either 1/f^4 power-law noise
or a quasiperiodic process. The analysis was checked using the Deeter
polynomial method of power spectrum estimation that was developed for the case
of nonuniform sampling, but has lower spectral resolution. The timing noise is
consistent with a torque noise spectrum rising with analysis frequency as f
implying blue torque noise, a result not predicted by current models of pulsar
timing noise. If the periodic or nearly periodic component is due to a binary
companion, we find a companion mass > 3.2 Earth masses.Comment: 53 pages, 9 figures, submitted to MNRAS, abstract condense
The role of remote engagement in supporting boundary chain networks across Alaska
AbstractBoundary organizations serve multiple roles in linking science and decision making, including brokering knowledge, supporting local- and cross-level networks, facilitating the co-production of knowledge, and negotiating conflict. Yet they face several challenges in providing services for an ever-increasing number of actors and institutions interested in climate information and adaptation. This study evaluates how the Alaska Center for Climate Assessment and Policy (ACCAP) innovated its boundary spanning role to improve outcomes by partnering with other boundary organizations through its ongoing climate webinar series. We utilize the concept of boundary chains to investigate outcomes associated with different extended network connections. Our evaluation is based on the analysis three datasets, including interviews (2013) and two web-based questionnaires (2010 and 2013–2015). Findings from the evaluation reveal several ways that remote engagement via the ACCAP webinar series facilitates learning, decision application, and cross-level network building, and overcomes barriers associated with large geographic distances between communities. In an organic evolution and innovation of the climate webinar series, ACCAP partnered with other boundary organizations to establish satellite hub sites to facilitate in-person gatherings at remote locations, thereby increasing the number and diversity of participants served and supporting local networking within organizations, agencies, and communities. Leveraging complementary resources through the satellite hub sites provided mutual benefits for ACCAP and partnering boundary organizations. These findings advance our understanding of the value of remote engagement in supporting boundary spanning processes and how boundary organizations innovate their roles to build capacity and increase the usability of climate information
A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft -ray and Sub-millimeter Emission
(abridged) We describe highlights of the results of two observing campaigns
in 2004 to investigate the correlation of flare activity in Sgr A* in different
wavelength regimes, using a total of nine ground and space-based telescopes. We
report the detection of several new near-IR flares during the campaign based on
{\it HST} observations. The level of near-IR flare activity can be as low as
mJy at 1.6 m and continuous up to about 40% of the total
observing time. Using the NICMOS instrument on the {\it HST}, the {\it
XMM-Newton} and CSO observatories, we also detect simultaneous bright X-ray and
near-IR flare in which we observe for the first time correlated substructures
as well as simultaneous submillimeter and near-IR flaring. X-ray emission is
arising from the population of near-IR-synchrotron-emitting relativistic
particles which scatter submillimeter seed photons within the inner 10
Schwarzschild radii of Sgr A* up to X-ray energies. In addition, using the
inverse Compton scattering picture, we explain the high energy 20-120 keV
emission from the direction toward Sgr A*, and the lack of one-to-one X-ray
counterparts to near-IR flares, by the variation of the magnetic field and the
spectral index distributions of this population of nonthermal particles. In
this picture, the evidence for the variability of submillimeter emission during
a near-IR flare is produced by the low-energy component of the population of
particles emitting synchrotron near-IR emission. Based on the measurements of
the duration of flares in near-IR and submillimeter wavelengths, we argue that
the cooling could be due to adiabatic expansion with the implication that flare
activity may drive an outflow.Comment: 48 pages, 12 figures, ApJ (in press
Parameter estimation in spatially extended systems: The Karhunen-Loeve and Galerkin multiple shooting approach
Parameter estimation for spatiotemporal dynamics for coupled map lattices and
continuous time domain systems is shown using a combination of multiple
shooting, Karhunen-Loeve decomposition and Galerkin's projection methodologies.
The resulting advantages in estimating parameters have been studied and
discussed for chaotic and turbulent dynamics using small amounts of data from
subsystems, availability of only scalar and noisy time series data, effects of
space-time parameter variations, and in the presence of multiple time-scales.Comment: 11 pages, 5 figures, 4 Tables Corresponding Author - V. Ravi Kumar,
e-mail address: [email protected]
Altered expression of immune-associated genes in first-trimester human decidua of pregnancies later complicated with hypertension or foetal growth restriction
During pregnancy the maternal immune system has to coordinate uterine spiral-artery remodelling, trophoblast invasion, and acceptance of the semi-allogenic fetus simultaneously. As dysregulation of the immune system is associated with adverse pregnancy outcomes, we analysed first-trimester deciduas of pregnancies for immune parameters in later complicated pregnancies. Higher IL6 and macrophage mRNA expression, and lower ratios of regulatory macrophages were found in first-trimester deciduas of pregnancies later complicated with pregnancy-induced hypertension. Lower Gata3 (Th2) mRNA expression was found in deciduas of pregnancies with later foetal growth restriction. Our results suggest that adverse pregnancy outcomes are associated with immunological disturbances in first-trimester deciduas. (C) 2012 Elsevier Ltd. All rights reserved
Point process model of 1/f noise versus a sum of Lorentzians
We present a simple point process model of noise, covering
different values of the exponent . The signal of the model consists of
pulses or events. The interpulse, interevent, interarrival, recurrence or
waiting times of the signal are described by the general Langevin equation with
the multiplicative noise and stochastically diffuse in some interval resulting
in the power-law distribution. Our model is free from the requirement of a wide
distribution of relaxation times and from the power-law forms of the pulses. It
contains only one relaxation rate and yields spectra in a wide
range of frequency. We obtain explicit expressions for the power spectra and
present numerical illustrations of the model. Further we analyze the relation
of the point process model of noise with the Bernamont-Surdin-McWhorter
model, representing the signals as a sum of the uncorrelated components. We
show that the point process model is complementary to the model based on the
sum of signals with a wide-range distribution of the relaxation times. In
contrast to the Gaussian distribution of the signal intensity of the sum of the
uncorrelated components, the point process exhibits asymptotically a power-law
distribution of the signal intensity. The developed multiplicative point
process model of noise may be used for modeling and analysis of
stochastic processes in different systems with the power-law distribution of
the intensity of pulsing signals.Comment: 23 pages, 10 figures, to be published in Phys. Rev.
Motor development in children 0-2 years pre- and post-LTX, a prospective study
To determine prospectively gross and fine motor development of childre
Data driven optimal filtering for phase and frequency of noisy oscillations: application to vortex flowmetering
A new method for extracting the phase of oscillations from noisy time series
is proposed. To obtain the phase, the signal is filtered in such a way that the
filter output has minimal relative variation in the amplitude (MIRVA) over all
filters with complex-valued impulse response. The argument of the filter output
yields the phase. Implementation of the algorithm and interpretation of the
result are discussed. We argue that the phase obtained by the proposed method
has a low susceptibility to measurement noise and a low rate of artificial
phase slips. The method is applied for the detection and classification of mode
locking in vortex flowmeters. A novel measure for the strength of mode locking
is proposed.Comment: 12 pages, 10 figure
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