42,219 research outputs found
Radial Velocity Curves of Ellipsoidal Red Giant Binaries in the Large Magellanic Cloud
Ellipsoidal red giant binaries are close binary systems where an unseen,
relatively close companion distorts the red giant, leading to light variations
as the red giant moves around its orbit. These binaries are likely to be the
immediate evolutionary precursors of close binary planetary nebula and
post-asymptotic giant branch and post-red giant branch stars. Due to the MACHO
and OGLE photometric monitoring projects, the light variability nature of these
ellipsoidal variables has been well studied. However, due to the lack of radial
velocity curves, the nature of their masses, separations, and other orbital
details has so far remained largely unknown. In order to improve this
situation, we have carried out spectral monitoring observations of a large
sample of 80 ellipsoidal variables in the Large Magellanic Cloud and we have
derived radial velocity curves. At least 12 radial velocity points with good
quality were obtained for most of the ellipsoidal variables. The radial
velocity data are provided with this paper. Combining the photometric and
radial velocity data, we present some statistical results related to the binary
properties of these ellipsoidal variables.Comment: 10 pages, 8 figures, 3 table
A microcontroller system for investigating the catch effect: Functional electrical stimulation of the common peroneal nerve
Correction of drop foot in hemiplegic gait is achieved by electrical stimulation of the common peroneal nerve with a series of pulses at a fixed frequency. However, during normal gait, the electromyographic signals from the tibialis anterior muscle indicate that muscle force is not constant but varies during the swing phase. The application of double pulses for the correction of drop foot may enhance the gait by generating greater torque at the ankle and thereby increase the efficiency of the stimulation with reduced fatigue. A flexible controller has been designed around the Odstock Drop Foot Stimulator to deliver different profiles of pulses implementing doublets and optimum series. A peripheral interface controller (PIC) microcontroller with some external circuits has been designed and tested to accommodate six profiles. Preliminary results of the measurements from a normal subject seated in a multi-moment chair (an isometric torque measurement device) indicate that profiles containing doublets and optimum spaced pulses look favourable for clinical use
A newly discovered stellar type: dusty post-red giant branch stars in the Magellanic Clouds
Context: We present a newly discovered class of low-luminosity, dusty,
evolved objects in the Magellanic Clouds. These objects have dust excesses,
stellar parameters, and spectral energy distributions similar to those of dusty
post-asymptotic giant branch (post-AGB) stars. However, they have lower
luminosities and hence lower masses. We suggest that they have evolved off the
red giant branch (RGB) instead of the AGB as a result of binary interaction.
Aims: In this study we aim to place these objects in an evolutionary context
and establish an evolutionary connection between RGB binaries (such as the
sequence E variables) and our new sample of objects. Methods: We compared the
theoretically predicted birthrates of the progeny of RGB binaries to the
observational birthrates of the new sample of objects. Results: We find that
there is order-of-magnitude agreement between the observed and predicted
birthrates of post-RGB stars. The sources of uncertainty in the birthrates are
discussed; the most important sources are probably the observational
incompleteness factor and the post-RGB evolution rates. We also note that
mergers are relatively common low on the RGB and that stars low on the RGB with
mid-IR excesses may recently have undergone a merger. Conclusions: Our sample
of dusty post-RGB stars most likely provides the first observational evidence
for a newly discovered phase in binary evolution: post-RGB binaries with
circumstellar dust.Comment: Accepted for publication in Astronomy and Astrophysics Letter
On the interpretation of lateral manganin gauge stress measurements in polymers
Encapsulated wire-element stress gauges enable changes in lateral stress during
shock loading to be directly monitored. However, there is substantial debate
with regards to interpretation of observed changes in stress behind the shock
front; a phenomenon attributed both to changes in material strength and shock-
dispersion within the gauge-encapsulation. Here, a pair of novel techniques
which both modify or remove the embedding medium where such stress gauges are
placed within target materials have been used to try and inform this debate. The
behavior of three polymeric materials of differing complexity was considered,
namely polystyrene, the commercially important resin transfer moulding RTM 6
resin and a commercially available fat lard. Comparison to the response of
embedded gauges has suggested a possible slight decrease in the absolute
magnitude of stress. However, changing the encapsulation has no detectable
effect on the gradient behind the shock in such polymeric systems
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Mechanical Properties and Biological Responses of Bioactive Glass Ceramics Processed using Indirect SLS
This paper will report on research which aims to generate bone replacement components by
processing bioactive glass-ceramic powders using indirect selective laser sintering. The indirect
SLS route has been chosen as it offers the ability to tailor the shape of the implant to the
implantation site, and two bioactive glass ceramic materials have been processed through this
route: apatite-mullite and apatite-wollostanite. The results of bend tests, to investigate
mechanical properties, and in vitro and in vivo experiments to investigate biological responses of
the materials will be reported, and the suitability of completed components for implant will be
assessed.Mechanical Engineerin
Soft-tissue specimens from pre-European extinct birds of New Zealand
We provide the first complete review of soft tissue remains from New Zealand birds that became extinct prior to European settlement (c. AD 1800). These rare specimens allow insights into the anatomy and appearance of the birds that are not attainable from bones. Our review includes previously unpublished records of ‘lost’ specimens, and descriptions of recently discovered specimens such as the first evidence of soft tissues from the South Island goose (Cnemiornis calcitrans). Overall, the soft tissue remains are dominated by moa (with specimens from each of the six genera), but also include specimens from Finsch's duck (Chenonetta finschi) and the New Zealand owlet-nightjar (Aegotheles novaezealandiae). All desiccated soft tissue specimens that have radiocarbon or stratigraphic dates are late Holocene in age, and most have been found in the semi-arid region of Central Otago
Proximity Drawings of High-Degree Trees
A drawing of a given (abstract) tree that is a minimum spanning tree of the
vertex set is considered aesthetically pleasing. However, such a drawing can
only exist if the tree has maximum degree at most 6. What can be said for trees
of higher degree? We approach this question by supposing that a partition or
covering of the tree by subtrees of bounded degree is given. Then we show that
if the partition or covering satisfies some natural properties, then there is a
drawing of the entire tree such that each of the given subtrees is drawn as a
minimum spanning tree of its vertex set
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