2,262 research outputs found
Scaling graphs of heart rate time series in athletes demonstrate the VLF, LF and HF regions
Scaling analysis of heart rate time series has emerged as an useful tool for
assessment of autonomic cardiac control. We investigate the heart rate time
series of ten athletes (five males and five females), by applying detrended
fluctuation analysis (DFA). High resolution ECGs are recorded under
standardized resting conditions over 30 minutes and subsequently heart rate
time series are extracted and artefacts filtered. We find three distinct
regions of scale-invariance, which correspond to the well-known VLF, LF, and HF
bands in the power spectra of heart rate variability. The scaling exponents
alpha are alphaHF: 1.15 [0.96-1.22], alphaLF: 0.68 [0.57-0.84], alphaVLF:
0.83[0.82-0.99]; p<10^-5). In conclusion, DFA scaling exponents of heart rate
time series should be fitted to the VLF, LF, and HF ranges, respectively
Combining visibilities from the Giant Meterwave Radio Telescope and the Nancay Radio Heliograph: High dynamic range snapshot images of the solar corona at 327 MHz
We report first results from an ongoing program of combining visibilities
from the Giant Meterwave Radio Telescope (GMRT) and the Nancay Radio Heliograph
(NRH) to produce composite snapshot images of the sun at meter wavelengths. We
describe the data processing, including a specific multi-scale CLEAN algorithm.
We present results of a) simulations for two models of the sun at 327 MHz, with
differing complexity b) observations of a complex noise storm on the sun at 327
MHz on Aug 27 2002. Our results illustrate the capacity of this method to
produce high dynamic range snapshot images when the solar corona has structures
with scales ranging from the image resolution of 49" to the size of the whole
sun.
We find that we cannot obtain reliable snapshot images for complex objects
when the visibilities are sparsely sampled.Comment: Accepted for publication in Astronomy & Astrophysics. Version with
high resolution figures available from
ftp://ftp.iucaa.ernet.in/in.coming/gmrtnr
Limits on I-band microvariability of the Galactic Bulge Miras
We search for microvariability in a sample of 485 Mira variables with high
quality I-band light curves from the second generation Optical Gravitational
Lensing Experiment (OGLE-II). Rapid variations with amplitudes in the ~0.2-1.1
mag range lasting hours to days were discovered in Hipparcos data by de Laverny
et al. (1998). Our search is primarily sensitive to events with time-scales of
about 1 day, but retains a few percent efficiency (per object) for detecting
unresolved microvariability events as short as 2 hours. We do not detect any
candidate events. Assuming that the distribution of the event time profiles is
identical to that from the Hipparcos light curves we derive the 95% confidence
level upper limit of 0.038 per year per star for the rate of such events (1 per
26 years per average object of the ensemble). The high event rates of the order
of 1 per year per star implied by the Hipparcos study in the H_P band are
excluded with high confidence by the OGLE-II data in the I band. Our
non-detection could still be explained by much redder spectral response of the
I filter compared to the H_P band or by population differences between the
bulge and the solar neighborhood. In any case, the OGLE-II I-band data provide
the first limit on the rate of the postulated microvariability events in Mira
stars and offer new quantitative constraints on their properties. Similar
limits are obtained for other pulse shapes and a range of the assumed
time-scales and size-frequency distributions.Comment: Accepted for publication in Ap
Simulating spatial and temporal evolution of multiple wing cracks around faults in crystalline basement rocks
Fault zones are structurally highly spatially heterogeneous and hence extremely complex. Observations of fluid flow through fault zones over several scales show that this structural complexity is reflected in the hydrogeological properties of faults. Information on faults at depth is scarce, hence, it is highly valuable to understand the controls on spatial and temporal fault zone development. In this paper we increase our understanding of fault damage zone development in crystalline rocks by dynamically simulating the growth of single and multiple splay fractures produced from failure on a pre-existing fault. We present a new simulation model, MOPEDZ (Modeling Of Permeability Evolution in the Damage Zone surrounding faults), that simulates fault evolution through solution of Navier's equation with a combined Mohr-Coulomb and tensile failure criteria. Simulations suggest that location, frequency, mode of failure and orientation of splay fractures are significantly affected both by the orientation of the fault with respect to the maximum principal compressive stress and the conditions of differential stress. Model predictions compare well with published field outcrop data, confirming that this model produces realistic damage zone geometries
Metronidazole (Flagyl): characterization as a cytotoxic drug specific for hypoxic tumour cells.
The cytocidal properties of metronidazole against hypoxic mammalian cells are described. This chemotherapeutic action has been shown to be dependent on drug concentration and duration of exposure. The x-ray TCD50 for a murine anaplastic carcinoma was reduced from 6081 rad to 4643 rad when animals were given metronidazole orally for 36 h before radiation treatment. The effect is attributed to the direct killing of hypoxic tumour cells by a mechanism analogous to that proposed for the action of the drug on anaerobic micro-organisms. It is concluded that further work with metronidazole as a cytotoxin specific for hypoxic cells is warranted, particularly in view of the reported lack of toxicity associated with the preliminary clinical use of the drug as a radiosensitizer in man
Follow the Plume: Organic Molecules and Habitable Conditions in the Subsurface Ocean of Enceladus
This white paper describes the astrobiological significance of the Enceladus plume, and makes a series of scientific and technological recommendations that would lead to a future mission that samples and analyzes plume materials, and searches for evidence of life
Combined analysis of solar neutrino and solar irradiance data: further evidence for variability of the solar neutrino flux and its implications concerning the solar core
A search for any particular feature in any single solar neutrino dataset is
unlikely to establish variability of the solar neutrino flux since the count
rates are very low. It helps to combine datasets, and in this article we
examine data from both the Homestake and GALLEX experiments. These show
evidence of modulation with a frequency of 11.85 yr-1, which could be
indicative of rotational modulation originating in the solar core. We find that
precisely the same frequency is prominent in power spectrum analyses of the
ACRIM irradiance data for both the Homestake and GALLEX time intervals. These
results suggest that the solar core is inhomogeneous and rotates with sidereal
frequency 12.85 yr-1. We find, by Monte Carlo calculations, that the
probability that the neutrino data would by chance match the irradiance data in
this way is only 2 parts in 10,000. This rotation rate is significantly lower
than that of the inner radiative zone (13.97 yr-1) as recently inferred from
analysis of Super-Kamiokande data, suggesting that there may be a second, inner
tachocline separating the core from the radiative zone. This opens up the
possibility that there may be an inner dynamo that could produce a strong
internal magnetic field and a second solar cycle.Comment: 22 pages, 9 tables, 10 figure
Further Evidence Suggestive of a Solar Influence on Nuclear Decay Rates
Recent analyses of nuclear decay data show evidence of variations suggestive
of a solar influence. Analyses of datasets acquired at the Brookhaven National
Laboratory (BNL) and at the Physikalisch-Technische Bundesanstalt (PTB) both
show evidence of an annual periodicity and of periodicities with sidereal
frequencies in the neighborhood of 12.25 year^{-1} (at a significance level
that we have estimated to be 10^{-17}). It is notable that this implied
rotation rate is lower than that attributed to the solar radiative zone,
suggestive of a slowly rotating solar core. This leads us to hypothesize that
there may be an "inner tachocline" separating the core from the radiative zone,
analogous to the "outer tachocline" that separates the radiative zone from the
convection zone. The Rieger periodicity (which has a period of about 154 days,
corresponding to a frequency of 2.37 year^{-1}) may be attributed to an r-mode
oscillation with spherical-harmonic indices l=3, m=1, located in the outer
tachocline. This suggests that we may test the hypothesis of a solar influence
on nuclear decay rates by searching BNL and PTB data for evidence of a
"Rieger-like" r-mode oscillation, with l=3, m=1, in the inner tachocline. The
appropriate search band for such an oscillation is estimated to be 2.00-2.28
year^{-1}. We find, in both datasets, strong evidence of a periodicity at 2.11
year^{-1}. We estimate that the probability of obtaining these results by
chance is 10^{-12}.Comment: 12 pages, 6 figures, v2 has a color corrected Fig 6, a corrected
reference, and a corrected typ
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