958 research outputs found
Atmospheric extinction coefficients in the band for several major international observatories: Results from the BiSON telescopes, 1984 to 2016
Over 30 years of solar data have been acquired by the Birmingham Solar
Oscillations Network (BiSON), an international network of telescopes used to
study oscillations of the Sun. Five of the six BiSON telescopes are located at
major observatories. The observational sites are, in order of increasing
longitude: Mount Wilson (Hale) Observatory (MWO), California, USA; Las Campanas
Observatory (LCO), Chile; Observatorio del Teide, Iza\~{n}a, Tenerife, Canary
Islands; the South African Astronomical Observatory (SAAO), Sutherland, South
Africa; Carnarvon, Western Australia; and the Paul Wild Observatory, Narrabri,
New South Wales, Australia. The BiSON data may be used to measure atmospheric
extinction coefficients in the band (approximately 700-900 nm),
and presented here are the derived atmospheric extinction coefficients from
each site over the years 1984 to 2016.Comment: 15 pages, 10 figures, 4 tables. Accepted by Astronomical Journal:
2017 July 2
Quasi-Neutral theory of epidemic outbreaks
Some epidemics have been empirically observed to exhibit outbreaks of all
possible sizes, i.e., to be scalefree or scale-invariant. Different
explanations for this finding have been put forward; among them there is a
model for "accidental pathogens" which leads to power-law distributed outbreaks
without apparent need of parameter fine tuning. This model has been claimed to
be related to self-organized criticality, and its critical properties have been
conjectured to be related to directed percolation. Instead, we show that this
is a (quasi) neutral model, analogous to those used in Population Genetics and
Ecology, with the same critical behavior as the voter-model, i.e. the theory of
accidental pathogens is a (quasi)-neutral theory. This analogy allows us to
explain all the system phenomenology, including generic scale invariance and
the associated scaling exponents, in a parsimonious and simple way.Comment: 13 pages, 6 figures Accepted for publication in PLoS ONE the text
have been modified in orden to improve the figure's resolutio
Comparison of large-scale flows on the Sun measured by time-distance helioseismology and local correlation tracking technique
We present a direct comparison between two different techniques time-distance
helioseismology and a local correlation tracking method for measuring mass
flows in the solar photosphere and in a near-surface layer: We applied both
methods to the same dataset (MDI high-cadence Dopplergrams covering almost the
entire Carrington rotation 1974) and compared the results. We found that after
necessary corrections, the vector flow fields obtained by these techniques are
very similar. The median difference between directions of corresponding vectors
is 24 degrees, and the correlation coefficients of the results for mean zonal
and meridional flows are 0.98 and 0.88 respectively. The largest discrepancies
are found in areas of small velocities where the inaccuracies of the computed
vectors play a significant role. The good agreement of these two methods
increases confidence in the reliability of large-scale synoptic maps obtained
by them.Comment: 14 pages, 6 figures, just before acceptance in Solar Physic
Single Molecule Statistics and the Polynucleotide Unzipping Transition
We present an extensive theoretical investigation of the mechanical unzipping
of double-stranded DNA under the influence of an applied force. In the limit of
long polymers, there is a thermodynamic unzipping transition at a critical
force value of order 10 pN, with different critical behavior for homopolymers
and for random heteropolymers. We extend results on the disorder-averaged
behavior of DNA's with random sequences to the more experimentally accessible
problem of unzipping a single DNA molecule. As the applied force approaches the
critical value, the double-stranded DNA unravels in a series of discrete,
sequence-dependent steps that allow it to reach successively deeper energy
minima. Plots of extension versus force thus take the striking form of a series
of plateaus separated by sharp jumps. Similar qualitative features should
reappear in micromanipulation experiments on proteins and on folded RNA
molecules. Despite their unusual form, the extension versus force curves for
single molecules still reveal remnants of the disorder-averaged critical
behavior. Above the transition, the dynamics of the unzipping fork is related
to that of a particle diffusing in a random force field; anomalous,
disorder-dominated behavior is expected until the applied force exceeds the
critical value for unzipping by roughly 5 pN.Comment: 40 pages, 18 figure
Mixing patterns and the spread of close-contact infectious diseases
Surprisingly little is known regarding the human mixing patterns relevant to the spread of close-contact infections, such as measles, influenza and meningococcal disease. This study aims to estimate the number of partnerships that individuals make, their stability and the degree to which mixing is assortative with respect to age. We defined four levels of putative at-risk events from casual (physical contact without conversation) to intimate (contact of a sexual nature), and asked university student volunteers to record details on those they contacted at these levels on three separate days. We found that intimate contacts are stable over short time periods whereas there was no evidence of repeat casual contacts with the same individuals. The contacts were increasingly assortative as intimacy increased. Such information will aid the development and parameterisation of models of close contact diseases, and may have direct use in outbreak investigations
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