793 research outputs found
The multifrequency Siberian Radioheliograph
The 10-antenna prototype of the multifrequency Siberian radioheliograph is
described. The prototype consists of four parts: antennas with broadband
front-ends, analog back-ends, digital receivers and a correlator. The prototype
antennas are mounted on the outermost stations of the Siberian Solar Radio
Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom
by an analog fiber optical link, laid in an underground tunnel. After mixing,
all signals are digitized and processed by digital receivers before the data
are transmitted to the correlator. The digital receivers and the correlator are
accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz.
Currently the frequency switching observing mode is used. The prototype data
include both circular polarizations at a number of frequencies given by a list.
This prototype is the first stage of the multifrequency Siberian
radioheliograph development. It is assumed that the radioheliograph will
consist of 96 antennas and will occupy stations of the West-East-South subarray
of the SSRT. The radioheliograph will be fully constructed in autumn of 2012.
We plan to reach the brightness temperature sensitivity about 100 K for the
snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and
polarization measurement accuracy about a few percent.
First results with the 10-antenna prototype are presented of observations of
solar microwave bursts. The prototype abilities to estimate source size and
locations at different frequencies are discussed
Distinctive diets of eutherian predators in Australia
Introduction of the domestic cat and red fox has devastated Australian native fauna. We synthesized Australian diet analyses to identify traits of prey species in cat, fox and dingo diets, which prey were more frequent or distinctive to the diet of each predator, and quantified dietary overlap. Nearly half (45%) of all Australian terrestrial mammal, bird and reptile species occurred in the diets of one or more predators. Cat and dingo diets overlapped least (0.64 ± 0.27, n = 24 location/time points) and cat diet changed little over 55 years of study. Cats were more likely to have eaten birds, reptiles and small mammals than foxes or dingoes. Dingo diet remained constant over 53 years and constituted the largest mammal, bird and reptile prey species, including more macropods/potoroids, wombats, monotremes and bandicoots/bilbies than cats or foxes. Fox diet had greater overlap with both cats (0.79 ± 0.20, n = 37) and dingoes (0.73 ± 0.21, n = 42), fewer distinctive items (plant material, possums/gliders) and significant spatial and temporal heterogeneity over 69 years, suggesting the opportunity for prey switching (especially of mammal prey) to mitigate competition. Our study reinforced concerns about mesopredator impacts upon scarce/threatened species and the need to control foxes and cats for fauna conservation. However, extensive dietary overlap and opportunism, as well as low incidence of mesopredators in dingo diets, precluded resolution of the debate about possible dingo suppression of foxes and cats
Development of Proficiency Testing for Detection of Irradiated Food: Project E01068. Results of First Round PSL Trials, September 2005
Stellar Inversion Techniques
Stellar seismic inversions have proved to be a powerful technique for probing
the internal structure of stars, and paving the way for a better understanding
of the underlying physics by revealing some of the shortcomings in current
stellar models. In this lecture, we provide an introduction to this topic by
explaining kernel-based inversion techniques. Specifically, we explain how
various kernels are obtained from the pulsation equations, and describe
inversion techniques such as the Regularised Least-Squares (RLS) and Optimally
Localised Averages (OLA) methods.Comment: 20 pages, 8 figures. Lecture presented at the IVth Azores
International Advanced School in Space Sciences on "Asteroseismology and
Exoplanets: Listening to the Stars and Searching for New Worlds"
(arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in
July 201
The Basics of Water Waves Theory for Analogue Gravity
This chapter gives an introduction to the connection between the physics of
water waves and analogue gravity. Only a basic knowledge of fluid mechanics is
assumed as a prerequisite.Comment: 36 pages. Lecture Notes for the IX SIGRAV School on "Analogue
Gravity", Como (Italy), May 201
Self-Similar Factor Approximants
The problem of reconstructing functions from their asymptotic expansions in
powers of a small variable is addressed by deriving a novel type of
approximants. The derivation is based on the self-similar approximation theory,
which presents the passage from one approximant to another as the motion
realized by a dynamical system with the property of group self-similarity. The
derived approximants, because of their form, are named the self-similar factor
approximants. These complement the obtained earlier self-similar exponential
approximants and self-similar root approximants. The specific feature of the
self-similar factor approximants is that their control functions, providing
convergence of the computational algorithm, are completely defined from the
accuracy-through-order conditions. These approximants contain the Pade
approximants as a particular case, and in some limit they can be reduced to the
self-similar exponential approximants previously introduced by two of us. It is
proved that the self-similar factor approximants are able to reproduce exactly
a wide class of functions which include a variety of transcendental functions.
For other functions, not pertaining to this exactly reproducible class, the
factor approximants provide very accurate approximations, whose accuracy
surpasses significantly that of the most accurate Pade approximants. This is
illustrated by a number of examples showing the generality and accuracy of the
factor approximants even when conventional techniques meet serious
difficulties.Comment: 22 pages + 11 ps figure
Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"
``EIT waves" are large-scale coronal bright fronts (CBFs) that were first
observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging
Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}.
Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that
propagate pseudo-radially across the solar disk at velocities of 100--700 km
s with front widths of 50-100 Mm. As their speed is greater than the
quiet coronal sound speed (200 km s) and comparable to the
local Alfv\'{e}n speed (1000 km s), they were initially
interpreted as fast-mode magnetoacoustic waves ().
Their propagation is now known to be modified by regions where the magnetosonic
sound speed varies, such as active regions and coronal holes, but there is also
evidence for stationary CBFs at coronal hole boundaries. The latter has led to
the suggestion that they may be a manifestation of a processes such as Joule
heating or magnetic reconnection, rather than a wave-related phenomena. While
the general morphological and kinematic properties of CBFs and their
association with coronal mass ejections have now been well described, there are
many questions regarding their excitation and propagation. In particular, the
theoretical interpretation of these enigmatic events as magnetohydrodynamic
waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure
Prevalence of diffuse pancreatic beta islet cell disease with hyperinsulinism: Problems in recognition and management
Among 77 patients with endogenous hyperinsulinism seen in 2 medical centers, diffuse islet cell disease accounted for 17 (22%) patients. Since diffuse islet cell disease poses special problems in management, its prevalence is emphasized in this report. Among these patients with diffuse islet cell disease, there were 11 patients with adenomatosis, 4 with nesidioblastosis, and 2 with islet cell hyperplasia. Six of the 77 patients were found in multiple endocrine neoplasia, type I kindreds; diffuse islet cell disease was documented in 4 of these patients. We outline principles of management in patients with diffuse islet cell disease. Frozen section microscopy failed to identify nesidioblastosis or islet cell hyperplasia. Chez 77 malades, provenant de 2 centres médicaux, qui présentaient un hyperinsulinisme endogène, 17 cas de lésions diffuses des îlots de Langerhans ont été dénombrés. Ce fait est donc loin d'être exceptionnel et cette étude a pour but de le souligner. Parmi ces 17 malades, 11 présentaient des adénomes multiples (adénomatoses), 4 des nésidoblastomes (anomalies tissulaires multifocales), 2 des hyperplasies cellulaires insulaires. Chez ces 77 malades, 6 cas de MEN type I furent individualisés, 4 d'entre eux présentaient une maladie insulaire diffuse. Les auteurs, forts de cette expériences insistent sur les principes du traitement de ce type d'affection. Ils insistent sur le fait que l'étude histologique extemporanée ne permet pas d'identifier les nésidoblastomes et les hyperplasies cellulaires insulaires et que dans 70%–80% des cas les résections pancréatiques ne permettent pas d'obtenir la guérison. Un problema constante para el cirujano que opera pacientes con hiperinsulinismo endógeno es el de qué hacer cuando no se encuentre patologÃa en el curso de la operación una vez realizada la exploración preliminar del páncreas. Los adenomas solitarios de células beta pueden pasar desapercibidos cuando no son palpables; la identificación de la enfermedad difusa de las células insulares plantea muchos problemas. Reconocemos tres alteraciones principales de tipo difuso: adenomatosis de células beta, nesidioblastosis e hiperplasia pancreática de células beta. Además, múltiples macroadenomas pueden coexistir o no con microadenomatosis o con hiperplasia en ciertos pacientes con hiperinsulinismo. Los desórdenes de células insulares de tipo multifocal son particularmente frecuentes en pacientes con Neoplasia Endocrina Multiple Tipo I.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41314/1/268_2005_Article_BF01654942.pd
Reptiles as food: Predation of Australian reptiles by introduced red foxes compounds and complements predation by cats
Context: Invasive species are a major cause of biodiversity loss across much of the world, and a key threat to Australia’s diverse reptile fauna. There has been no previous comprehensive analysis of the potential impact of the introduced European red fox, Vulpes vulpes, on Australian reptiles.
Aims: We seek to provide an inventory of all Australian reptile species known to be consumed by the fox, and identify characteristics of squamate species associated with such predation. We also compare these tallies and characteristics with reptile species known to be consumed by the domestic cat, Felis catus, to examine whether predation by these two introduced species is compounded (i.e. affecting much the same set of species) or complementary (affecting different groups of species).
Methods: We collated records of Australian reptiles consumed by foxes in Australia, with most records deriving from fox dietary studies (tallying >35 000 samples). We modelled presence or absence of fox predation records against a set of biological and other traits, and population trends, for squamate species.
Key results: In total, 108 reptile species (~11% of Australia’s terrestrial reptile fauna) have been recorded as consumed by foxes, fewer than that reported for cats (263 species). Eighty-six species have been reported to be eaten by both predators. More Australian turtle species have been reported as consumed by foxes than by cats, including many that suffer high levels of predation on egg clutches. Twenty threatened reptile species have been reported as consumed by foxes, and 15 by cats. Squamate species consumed by foxes are more likely to be undergoing population decline than those not known to be consumed by foxes. The likelihood of predation by foxes increased with squamate species’ adult body mass, in contrast to the relationship for predation by cats, which peaked at ~217 g. Foxes, but not cats, were also less likely to consume venomous snakes.
Conclusions: The two introduced, and now widespread, predators have both compounding and complementary impacts on the Australian reptile fauna.
Implications: Enhanced and integrated management of the two introduced predators is likely to provide substantial conservation benefits to much of the Australian reptile fauna
Asteroseismology of Eclipsing Binary Stars in the Kepler Era
Eclipsing binary stars have long served as benchmark systems to measure
fundamental stellar properties. In the past few decades, asteroseismology - the
study of stellar pulsations - has emerged as a new powerful tool to study the
structure and evolution of stars across the HR diagram. Pulsating stars in
eclipsing binary systems are particularly valuable since fundamental properties
(such as radii and masses) can determined using two independent techniques.
Furthermore, independently measured properties from binary orbits can be used
to improve asteroseismic modeling for pulsating stars in which mode
identifications are not straightforward. This contribution provides a review of
asteroseismic detections in eclipsing binary stars, with a focus on space-based
missions such as CoRoT and Kepler, and empirical tests of asteroseismic scaling
relations for stochastic ("solar-like") oscillations.Comment: 28 pages, 12 figures, 2 tables; Proceedings of the AAS topical
conference "Giants of Eclipse" (AASTCS-3), July 28 - August 2 2013, Monterey,
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