1,170 research outputs found
Artifacts with uneven sampling of red noise
The vast majority of sampling systems operate in a standard way: at each tick
of a fixed-frequency master clock a digitizer reads out a voltage that
corresponds to the value of some physical quantity and translates it into a bit
pattern that is either transmitted, stored, or processed right away. Thus
signal sampling at evenly spaced time intervals is the rule: however this is
not always the case, and uneven sampling is sometimes unavoidable.
While periodic or quasi-periodic uneven sampling of a deterministic signal
can reasonably be expected to produce artifacts, it is much less obvious that
the same happens with noise: here I show that this is indeed the case only for
long-memory noise processes, i.e., power-law noises with . The resulting artifacts are usually a nuisance although they can be
eliminated with a proper processing of the signal samples, but they could also
be turned to advantage and used to encode information.Comment: 5 figure
Probing X-ray burst -- accretion disk interaction in low mass X-ray binaries through kilohertz quasiperiodic oscillations
The intense radiation flux of Type I X-ray bursts is expected to interact
with the accretion flow around neutron stars. High frequency quasiperiodic
oscillations (kHz QPOs), observed at frequencies matching orbital frequencies
at tens of gravitational radii, offer a unique probe of the innermost disk
regions. In this paper, we follow the lower kHz QPOs, in response to Type I
X-ray bursts, in two prototypical QPO sources, namely 4U 1636-536 and 4U
1608-522, as observed by the Proportional Counter Array of the Rossi X-ray
Timing Explorer. We have selected a sample of 15 bursts for which the kHz QPO
frequency can be tracked on timescales commensurable with the burst durations
(tens of seconds). We find evidence that the QPOs are affected for over ~200 s
during one exceptionally long burst and ~100 s during two others (although at a
less significant level), while the burst emission has already decayed to a
level that would enable the pre-burst QPO to be detected. On the other hand,
for most of our burst-kHz QPO sample, we show that the QPO is detected as soon
as the statistics allow and in the best cases, we are able to set an upper
limit of ~20 s on the recovery time of the QPO. This diversity of behavior
cannot be related to differences in burst peak luminosity. We discuss these
results in the framework of recent findings that accretion onto the neutron
star may be enhanced during Type I X-ray bursts. The subsequent disk depletion
could explain the disappearance of the QPO for ~100 s, as possibly observed in
two events. However, alternative scenarios would have to be invoked for
explaining the short recovery timescales inferred from most bursts. Clearly the
combination of fast timing and spectral information of Type I X-ray bursts
holds great potential in the study of the dynamics of the inner accretion flow
around neutron stars.Comment: 8 pages, 9 figures, appears in Astronomy & Astrophysics, Volume 567,
id.A80, published 07/201
Toll-Like Receptor mRNA Expression Is Selectively Increased in the Colonic Mucosa of Two Animal Models Relevant to Irritable Bowel Syndrome
Background: Irritable bowel syndrome (IBS) is largely viewed as a stress-related disorder caused by aberrant brain-gut–
immune communication and altered gastrointestinal (GI) homeostasis. Accumulating evidence demonstrates that stress
modulates innate immune responses; however, very little is known on the immunological effects of stress on the GI tract.
Toll-like receptors (TLRs) are critical pattern recognition molecules of the innate immune system. Activation of TLRs by
bacterial and viral molecules leads to activation of NF-kB and an increase in inflammatory cytokine expression. It was our
hypothesis that innate immune receptor expression may be changed in the gastrointestinal tract of animals with stressinduced
IBS-like symptoms.
Methodology/Principal Findings: In this study, our objective was to evaluate the TLR expression profile in the colonic
mucosa of two rat strains that display colonic visceral hypersensivity; the stress-sensitive Wistar-Kyoto (WKY) rat and the
maternally separated (MS) rat. Quantitative PCR of TLR2-10 mRNA in both the proximal and distal colonic mucosae was
carried out in adulthood. Significant increases are seen in the mRNA levels of TLR3, 4 & 5 in both the distal and proximal
colonic mucosa of MS rats compared with controls. No significant differences were noted for TLR 2, 7, 9 & 10 while TLR 6
could not be detected in any samples in both rat strains. The WKY strain have increased levels of mRNA expression of TLR3,
4, 5, 7, 8, 9 & 10 in both the distal and proximal colonic mucosa compared to the control Sprague-Dawley strain. No
significant differences in expression were found for TLR2 while as before TLR6 could not be detected in all samples in both
strains.
Conclusions: These data suggest that both early life stress (MS) and a genetic predisposition (WKY) to stress affect the
expression of key sentinels of the innate immune system which may have direct relevance for the molecular
pathophysiology of IBS
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
OT FE-Box Test Procedures
The OT FE readout requirements is the precise (~0.5 ns) and efficient drift time measurement at an occupancy of ~4% to ensure single hit resolution. The acquired achievement of such performance on an assembled FE-Box is verify through a final test performed using a special FE-Tester. In this note the test procedures are described
Quantitative analysis by renormalized entropy of invasive electroencephalograph recordings in focal epilepsy
Invasive electroencephalograph (EEG) recordings of ten patients suffering
from focal epilepsy were analyzed using the method of renormalized entropy.
Introduced as a complexity measure for the different regimes of a dynamical
system, the feature was tested here for its spatio-temporal behavior in
epileptic seizures. In all patients a decrease of renormalized entropy within
the ictal phase of seizure was found. Furthermore, the strength of this
decrease is monotonically related to the distance of the recording location to
the focus. The results suggest that the method of renormalized entropy is a
useful procedure for clinical applications like seizure detection and
localization of epileptic foci.Comment: 10 pages, 5 figure
Current lifestyles in the context of future climate targets: analysis of long-term scenarios and consumer segments for residential and transport
The carbon emissions of individuals strongly depend on their lifestyle, both between and within regions. Therefore, lifestyle changes could have a significant potential for climate change mitigation. This potential is not fully explored in long-term scenarios, as the representation of behaviour change and consumer heterogeneity in these scenarios is limited. We explore the impact and feasibility of lifestyle and behaviour changes in achieving climate targets by analysing current per-capita emissions of transport and residential sectors for different regions and consumer segments within one of the regions, namely Japan. We compare these static snapshots to changes in per-capita emissions from consumption and technology changes in long-term mitigation scenarios. The analysis shows less need for reliance on technological solutions if consumption patterns become more sustainable. Furthermore, a large share of Japanese consumers is characterised by consumption patterns consistent with those in scenarios that achieve ambitious climate targets, especially regarding transport. The varied lifestyles highlight the importance of representing consumer heterogeneity in models and further analyses
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.
Researching the use of force: The background to the international project
This article provides the background to an international project on use of force by the police that was carried out in eight countries. Force is often considered to be the defining characteristic of policing and much research has been conducted on the determinants, prevalence and control of the use of force, particularly in the United States. However, little work has looked at police officers’ own views on the use of force, in particular the way in which they justify it. Using a hypothetical encounter developed for this project, researchers in each country conducted focus groups with police officers in which they were encouraged to talk about the use of force. The results show interesting similarities and differences across countries and demonstrate the value of using this kind of research focus and methodology
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