300 research outputs found
A Bistatic Ground Station for Concurrent Spacecraft Operations
It is common for SmallSat and CubeSat operators to implement telecommunication systems using a half-duplex UHF system to reduce the cost and complexity of spcecraft hardware. This half-duplex configuration requires transmission and reception of the spacecraft signals at the same frequency, with the 402 MHz to 403 MHz band being a popular choice.
Due to practical filter limitations, it is impossible to produce an analogue filter for a ground-based receiver which can sufficiently attenuate transmissions from neighboring transmitters also operating in the same 402-403 MHz, band while still retaining a sufficiently low insertion loss to clearly receive tranmissions from a spacecraft. As a result, only one such half-duplex ground station can operate in the 402-403 MHZ frequency band in any local area at any one time.
We developed a bi-static station where the transmitting station is some 15 kilometers distant from the receiving station, allowing multiple concurrent spacecraft passes. Such an approach makes supporting UHF missions economic for ground station providers
A New Approach to High Reliability UHF Controllers
Many available UHF antenna positioners lack reliability for high-intensity commercial use. Similarly, many UHF antenna controllers lack appropriate interfaces for remote and automated control.
We present a number of ways to simplify UHF ground station design and improve reliability. We also describe an improved antenna controller we have designed, with Ethernet connectivity, human- and machine-friendly interfaces, detailed metrics for fault diagnosis, and an improved control algorithm designed to minimise gearbox stresses and improve pointing accuracy
Marine baseline and monitoring strategies for Carbon Dioxide Capture and Storage (CCS)
The QICS controlled release experiment demonstrates that leaks of carbon dioxide (CO2) gas can be detected by monitoring acoustic, geochemical and biological parameters within a given marine system. However the natural complexity and variability of marine system responses to (artificial) leakage strongly suggests that there are no absolute indicators of leakage or impact that can unequivocally and universally be used for all potential future storage sites. We suggest a multivariate, hierarchical approach to monitoring, escalating from anomaly detection to attribution, quantification and then impact assessment, as required. Given the spatial heterogeneity of many marine ecosystems it is essential that environmental monitoring programmes are supported by a temporally (tidal, seasonal and annual) and spatially resolved baseline of data from which changes can be accurately identified. In this paper we outline and discuss the options for monitoring methodologies and identify the components of an appropriate baseline survey
Photographic identification of individuals of a free-ranging, small terrestrial vertebrate
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.Recognition of individuals within an animal population is central to a range of
estimates about population structure and dynamics. However, traditional methods
of distinguishing individuals, by some form of physical marking, often rely
on capture and handling which may affect aspects of normal behavior. Photographic
identification has been used as a less-invasive alternative, but limitations
in both manual and computer-automated recognition of individuals are
particularly problematic for smaller taxa (<500 g). In this study, we explored
the use of photographic identification for individuals of a free-ranging, small
terrestrial reptile using (a) independent observers, and (b) automated matching
with the Interactive Individual Identification System (I3S Pattern) computer
algorithm. We tested the technique on individuals of an Australian skink in the
Egernia group, Slater’s skink Liopholis slateri, whose natural history and varied
scale markings make it a potentially suitable candidate for photo-identification.
From ‘photographic captures’ of skink head profiles, we designed a multichoice
key based on alternate character states and tested the abilities of observers
— with or without experience in wildlife survey — to identify individuals
using categorized test photos. We also used the I3S Pattern algorithm to match
the same set of test photos against a database of 30 individuals. Experienced
observers identified a significantly higher proportion of photos correctly (74%)
than those with no experience (63%) while the I3S software correctly matched
67% as the first ranked match and 83% of images in the top five ranks. This
study is one of the first to investigate photo identification with a free-ranging
small vertebrate. The method demonstrated here has the potential to be applied
to the developing field of camera-traps for wildlife survey and thus a wide
range of survey and monitoring applications
Foreground Subtraction in Intensity Mapping with the SKA
21cm intensity mapping experiments aim to observe the diffuse neutral
hydrogen (HI) distribution on large scales which traces the Cosmic structure.
The Square Kilometre Array (SKA) will have the capacity to measure the 21cm
signal over a large fraction of the sky. However, the redshifted 21cm signal in
the respective frequencies is faint compared to the Galactic foregrounds
produced by synchrotron and free-free electron emission. In this article, we
review selected foreground subtraction methods suggested to effectively
separate the 21cm signal from the foregrounds with intensity mapping
simulations or data. We simulate an intensity mapping experiment feasible with
SKA phase 1 including extragalactic and Galactic foregrounds. We give an
example of the residuals of the foreground subtraction with a independent
component analysis and show that the angular power spectrum is recovered within
the statistical errors on most scales. Additionally, the scale of the Baryon
Acoustic Oscillations is shown to be unaffected by foreground subtraction.Comment: This article is part of the 'SKA Cosmology Chapter, Advancing
Astrophysics with the SKA (AASKA14), Conference, Giardini Naxos (Italy), June
9th-13th 2014
Polyphyly and gene flow between non-sibling Heliconius species
BACKGROUND: The view that gene flow between related animal species is rare and evolutionarily unimportant largely antedates sensitive molecular techniques. Here we use DNA sequencing to investigate a pair of morphologically and ecologically divergent, non-sibling butterfly species, Heliconius cydno and H. melpomene (Lepidoptera: Nymphalidae), whose distributions overlap in Central and Northwestern South America. RESULTS: In these taxa, we sequenced 30–45 haplotypes per locus of a mitochondrial region containing the genes for cytochrome oxidase subunits I and II (CoI/CoII), and intron-spanning fragments of three unlinked nuclear loci: triose-phosphate isomerase (Tpi), mannose-6-phosphate isomerase (Mpi) and cubitus interruptus (Ci) genes. A fifth gene, dopa decarboxylase (Ddc) produced sequence data likely to be from different duplicate loci in some of the taxa, and so was excluded. Mitochondrial and Tpi genealogies are consistent with reciprocal monophyly, whereas sympatric populations of the species in Panama share identical or similar Mpi and Ci haplotypes, giving rise to genealogical polyphyly at the species level despite evidence for rapid sequence divergence at these genes between geographic races of H. melpomene. CONCLUSION: Recent transfer of Mpi haplotypes between species is strongly supported, but there is no evidence for introgression at the other three loci. Our results demonstrate that the boundaries between animal species can remain selectively porous to gene flow long after speciation, and that introgression, even between non-sibling species, can be an important factor in animal evolution. Interspecific gene flow is demonstrated here for the first time in Heliconius and may provide a route for the transfer of switch-gene adaptations for Müllerian mimicry. The results also forcefully demonstrate how reliance on a single locus may give an erroneous picture of the overall genealogical history of speciation and gene flow
Signalling changes to individuals who show resistance to change can reduce challenging behaviour
BACKGROUND & OBJECTIVES: Several neurodevelopmental disorders are associated with resistance to change and challenging behaviours - including temper outbursts - that ensue following changes to routines, plans or expectations (here, collectively: expectations). Here, a change signalling intervention was tested for proof of concept and potential practical effectiveness.METHODS: Twelve individuals with Prader-Willi syndrome participated in researcher- and caregiver-led pairing of a distinctive visual-verbal signal with subsequent changes to expectations. Specific expectations for a planned subset of five participants were systematically observed in minimally manipulated natural environments. Nine caregivers completed a temper outburst diary during a four week baseline period and a two week signalling evaluation period.RESULTS: Participants demonstrated consistently less temper outburst behaviour in the systematic observations when changes imposed to expectations were signalled, compared to when changes were not signalled. Four of the nine participants whose caregivers completed the behaviour diary demonstrated reliable reductions in temper outbursts between baseline and signalling evaluation.LIMITATIONS: An active control group for the present initial evaluation of the signalling strategy using evidence from caregiver behaviour diaries was outside the scope of the present pilot study. Thus, findings cannot support the clinical efficacy of the present signalling approach.CONCLUSIONS: Proof of concept evidence that reliable pairing of a distinctive cue with a subsequent change to expectation can reduce associated challenging behaviour is provided. Data provide additional support for the importance of specific practical steps in further evaluations of the change signalling approach.</p
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