1,401 research outputs found
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
Human stromal cells are required for an anti-breast cancer effect of zoledronic acid
Previous studies suggested that bisphosphonate zoledronic acid exerts an antitumor effect by interacting with the microenvironment. In this study, we aimed to elucidate the mechanism behind the anti-breast cancer effect of zoledronic acid.Here we showed that zoledronic acid did not influence in vitro human breast cancer cell survival, but did affect human stromal cell survival. Breast cancer cell death in co-culture with stromal cells was analyzed in vitro by fluorescent microscopy and flowcytometry analysis. In co-culture, the addition of stromal cells to breast cancer cells induced tumor cell death by zoledronic acid, which was abolished by transforming growth factor (TGF)-beta. In the in vivo chicken chorioallantoic membrane model, zoledronic acid reduced the breast cancer cells fraction per tumor only in the presence of human stromal cells. Zoledronic acid decreased TGF-beta excretion by stromal cells and co-cultures. Moreover, supernatant of zoledronic acid treated stromal cells reduced phospho-Smad2 protein levels in breast cancer cells. Thus, zoledronic acid exerts an anti-breast cancer effect via stromal cells, accompanied by decreased stromal TGF-beta excretion and reduced TGF-beta signaling in cancer cells.</p
Limitations of the nested reverse transcriptase polymerase chain reaction on tyrosinase for the detection of malignant melanoma micrometastases in lymph nodes
The specificity and sensitivity of the nested reverse transcriptase polymerase chain reaction (RT-PCR) on tyrosinase was studied, for the detection of micrometastases of malignant melanoma. The specificity was assessed in the blood of six healthy donors, four patients with non-melanoma cancers of which one patient was treated with granulocyte-colony stimulating factor. Lymph nodes of nine patients without malignant melanoma were tested and four cell lines of various other tumours. Six of the nine non-melanoma lymph nodes were positive in this assay. The sensitivity was tested in a spike experiment in vitro, using a melanoma cell line. The detection limit was ten melanoma cells per 107peripheral blood lymphocytes. © 2000 Cancer Research Campaig
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]
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
PG 1211+143: probing high frequency lags in a high mass AGN
We present the timing analysis of the four archived XMM-Newton observations
of PG 1211+143. The source is well-known for its spectral complexity,
comprising a strong soft-excess and different absorption systems. Soft energy
band (0.3-0.7 keV) lags are detected over all the four observations, in the
frequency range \nu \lsim 6 \times 10^{-4} Hz, where hard lags, similar to
those observed in black hole X-ray binaries, are usually detected in smaller
mass AGN. The lag magnitude is energy-dependent, showing two distinct trends
apparently connectable to the two flux levels at which the source is observed.
The results are discussed in the context of disk- and/or corona-reprocessing
scenarios, and of disk wind models. Similarities with the high-frequency
negative lag of 1H 0707-495 are highlighted, and, if confirmed, they would
support the hypothesis that the lag in PG 1211+143 represents the signature of
the same underlying mechanism, whose temporal characteristics scale with the
mass of the central object.Comment: 6 pages, 6 figures, accepted for publication in MNRAS Letter
Critical temperature of non-interacting Bose gases on disordered lattices
For a non-interacting Bose gas on a lattice we compute the shift of the
critical temperature for condensation when random-bond and onsite disorder are
present. We evidence that the shift depends on the space dimensionality D and
the filling fraction f. For D -> infinity (infinite-range model), using results
from the theory of random matrices, we show that the shift of the critical
temperature is negative, depends on f, and vanishes only for large f. The
connections with analogous results obtained for the spherical model are
discussed. For D=3 we find that, for large f, the critical temperature Tc is
enhanced by disorder and that the relative shift does not sensibly depend on f;
at variance, for small f, Tc decreases in agreement with the results obtained
for a Bose gas in the continuum. We also provide numerical estimates for the
shift of the critical temperature due to disorder induced on a non-interacting
Bose gas by a bichromatic incommensurate potential.Comment: 18 pages, 8 figures; Fig. 8 improved adding results for another value
of q (q=830/1076
Better Nonlinear Models from Noisy Data: Attractors with Maximum Likelihood
A new approach to nonlinear modelling is presented which, by incorporating
the global behaviour of the model, lifts shortcomings of both least squares and
total least squares parameter estimates. Although ubiquitous in practice, a
least squares approach is fundamentally flawed in that it assumes independent,
normally distributed (IND) forecast errors: nonlinear models will not yield IND
errors even if the noise is IND. A new cost function is obtained via the
maximum likelihood principle; superior results are illustrated both for small
data sets and infinitely long data streams.Comment: RevTex, 11 pages, 4 figure
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