957 research outputs found
The amplitude of solar oscillations using stellar techniques
The amplitudes of solar-like oscillations depend on the excitation and
damping, both of which are controlled by convection. Comparing observations
with theory should therefore improve our understanding of the underlying
physics. However, theoretical models invariably compute oscillation amplitudes
relative to the Sun, and it is therefore vital to have a good calibration of
the solar amplitude using stellar techniques. We have used daytime spectra of
the Sun, obtained with HARPS and UCLES, to measure the solar oscillations and
made a detailed comparison with observations using the BiSON helioseismology
instrument. We find that the mean solar amplitude measured using stellar
techniques, averaged over one full solar cycle, is 18.7 +/- 0.7 cm/s for the
strongest radial modes (l=0) and 25.2 +/- 0.9 cm/s for l=1. In addition, we use
simulations to establish an equation that estimates the uncertainty of
amplitude measurements that are made of other stars, given that the mode
lifetime is known. Finally, we also give amplitudes of solar-like oscillations
for three stars that we measured from a series of short observations with HARPS
(gamma Ser, beta Aql and alpha For), together with revised amplitudes for five
other stars for which we have previously published results (alpha Cen A, alpha
Cen B, beta Hyi, nu Ind and delta Pav).Comment: 8 pages, accepted by ApJ. Minor wording changes and added a referenc
The BIOMASS mission — An ESA Earth Explorer candidate to measure the BIOMASS of the earth's forests
Molecular and morphometric variation in European populations of the articulate brachiopod <i>Terebeatulina retusa</i>
Molecular and morphometric variation within and between population samples of the articulate brachiopod <i>Terebratulina</i> spp., collected in 1985-1987 from a Norwegian fjord, sea lochs and costal sites in western Scotland, the southern English Channel (Brittany) and the western Mediterranean, were measured by the analysis of variation in the lengths of mitochondrial DNA (mtDNA) fragments produced by digestion with nine restriction endonucleases and by multivariate statistical analysis of six selected morphometric parameters. Nucleotide difference within each population sample was high. Nucleotide difference between population samples from the Scottish sites, both those that are tidally contiguous and those that appear to be geographically isolated, were not significantly different from zero. Nucleotide differences between the populations samples from Norway, Brittany, Scotland and the western Mediterranean were also very low. Morphometric analysis confirmed the absence of substantial differentiation
How a spin-glass remembers. Memory and rejuvenation from intermittency data: an analysis of temperature shifts
The memory and rejuvenation aspects of intermittent heat transport are
explored theoretically and by numerical simulation for Ising spin glasses with
short-ranged interactions. The theoretical part develops a picture of
non-equilibrium glassy dynamics recently introduced by the authors. Invoking
the concept of marginal stability, this theory links irreversible
`intermittent' events, or `quakes' to thermal fluctuations of record magnitude.
The pivotal idea is that the largest energy barrier surmounted prior
to by thermal fluctuations at temperature determines the rate of the intermittent events occurring near . The idea leads
to a rate of intermittent events after a negative temperature shift given by
, where the `effective age' has
an algebraic dependence on , whose exponent contains the temperatures
before and after the shift. The analytical expression is verified by numerical
simulations. Marginal stability suggests that a positive temperature shift could erase the memory of the barrier . The simulations show
that the barrier controls the intermittent dynamics,
whose rate is hence .
Additional `rejuvenation' effects are also identified in the intermittency
data for shifts of both signs.Comment: Revised introduction and discussion. Final version to appear in
Journal of Statistical Mechanics: Theory and Experimen
Inferring phytoplankton carbon and eco-physiological rates from diel cycles of spectral particulate beam-attenuation coefficient
The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coefficient (cp) measured at multiple wavelengths. The method is based on fitting observations with a size-structured population model coupled to an optical model to infer the particle size distribution and physiologically relevant parameters of the cells responsible for the measured diel cycle in cp. Results show that the information related to size and contained in the spectral data can be exploited to independently estimate growth and loss rates during the day and night. In addition, the model can characterize the population of particles affecting the diel variability in cp. Application of this method to spectral cp measured at a station in the oligotrophic Mediterranean Sea suggests that most of the observed variations in cp can be ascribed to a synchronized population of cells with an equivalent spherical diameter around 4.6-1.5 1/4μm. The inferred carbon biomass of these cells was about 5.2-6.0 mg mg -\u273 and accounted for approximately 10% of the total particulate organic carbon. If successfully validated, this method may improve our in situ estimates of primary productivity
When the spatial networks split?
We consider a three dimensional spatial network, where nodes are randomly
distributed within a cube . Each two nodes are connected if
their mutual distance does not excess a given cutoff . We analyse
numerically the probability distribution of the critical density
, where one or more nodes become separated; is
found to increase with as , where is between 20 and 300. The
results can be useful for a design of protocols to control sets of wearable
sensors.Comment: 7 pages, 6 figures, prepared for the Physical, Biological and Social
Networks - Workshop in the International Conference on Computational Science
ICCS 200
Solar-like oscillations in the G2 subgiant beta Hydri from dual-site observations
We have observed oscillations in the nearby G2 subgiant star beta Hyi using
high-precision velocity observations obtained over more than a week with the
HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb
structure, as expected for solar-like oscillations, but with several l=1 modes
being strongly affected by avoided crossings. The data, combined with those we
obtained five years earlier, allow us to identify 28 oscillation modes. By
scaling the large frequency separation from the Sun, we measure the mean
density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations
are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison
of the mixed l=1 modes with theoretical models should allow a precise estimate
of the age of the star.Comment: 13 pages, 14 figures, accepted by ApJ. Fixed minor typo (ref to Fig
14
New early Triassic Lingulidae (Brachiopoda) genera and species from South China
Two new genera, Sinolingularia gen. nov. and Sinoglottidia gen. nov., together with three new species, Sinolingularia huananensis gen. et sp. nov., Sinolingularia yini gen. et sp. nov. and Sinoglottidia archboldi gen. et sp. nov., are described on the basis of a large collection of well-preserved specimens from several sections straddling the Permian - Triassic boundary in South China. <br /
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