5,798 research outputs found
The Great Eruption of Eta Carinae
During the years 1838-1858, the very massive star {\eta} Carinae became the
prototype supernova impostor: it released nearly as much light as a supernova
explosion and shed an impressive amount of mass, but survived as a star.1 Based
on a light-echo spectrum of that event, Rest et al.2 conclude that "a new
physical mechanism" is required to explain it, because the gas outflow appears
cooler than theoretical expectations. Here we note that (1) theory predicted a
substantially lower temperature than they quoted, and (2) their inferred
observational value is quite uncertain. Therefore, analyses so far do not
reveal any significant contradiction between the observed spectrum and most
previous discussions of the Great Eruption and its physics.Comment: To appear in Nature, a brief communication arising in response to
Rest et al. 2012. Submitted to Nature February 17, 201
Aspects of management options for pasture-based dairy production stocked at two cows per hectare
End of project reportWhite clover in association with Rhizobium bacteria have the capacity to fix or convent atmospheric N into plant available N. This can make a considerable contribution to sward productivity. One of the objectives of this experiment was to determine the upper carrying capacity of grass-white clover swards receiving 90 kg fertilizer N/ha. A second objective was to examine the impact of grass-clover swards on mineral-N in the soil and losses of nitrate-N from soil to drainage water during the winter. This experiment was conducted at Solohead Research Farm. There were three treatments: (i) A grass-only treatment (FN) stocked at 2.0 cows per ha in 2003 and 2.2 cows per ha during 2004, 2005 and 2006. This treatment received an average of 226 kg per ha of fertilizer N per year during these years. (ii) A grass-clover treatment (WC) stocked at the same rates as FN and received an average of 90 kg per ha of fertilizer N per year during the experiment. (iii) A grass-only treatment (CC) that was gradually converted over to grass-clover during the experiment and stocked at 2.0 cows per ha throughout the experiment. Fertilizer N input was gradually lowered from 150 kg per ha in 2003 to a target of 90 kg per ha in 2005 and 2006
Morphological instability, evolution, and scaling in strained epitaxial films: An amplitude equation analysis of the phase field crystal model
Morphological properties of strained epitaxial films are examined through a
mesoscopic approach developed to incorporate both the film crystalline
structure and standard continuum theory. Film surface profiles and properties,
such as surface energy, liquid-solid miscibility gap and interface thickness,
are determined as a function of misfit strains and film elastic modulus. We
analyze the stress-driven instability of film surface morphology that leads to
the formation of strained islands. We find a universal scaling relationship
between the island size and misfit strain which shows a crossover from the
well-known continuum elasticity result at the weak strain to a behavior
governed by a "perfect" lattice relaxation condition. The strain at which the
crossover occurs is shown to be a function of liquid-solid interfacial
thickness, and an asymmetry between tensile and compressive strains is
observed. The film instability is found to be accompanied by mode coupling of
the complex amplitudes of the surface morphological profile, a factor
associated with the crystalline nature of the strained film but absent in
conventional continuum theory.Comment: 16 pages, 10 figures; to be published in Phys. Rev.
Non-linear Microwave Surface Impedance of Epitaxial HTS Thin Films in Low DC Magnetic Fields
We have carried out non-linear microwave (8 GHz) surface impedance
measurements of three YBaCuO thin films in dc magnetic fields
(parallel to c axis) up to 12 mT using a coplanar resonator technique. In zero
dc field the three films, deposited by the same method, show a spread of
low-power residual surface resistance, and penetration depth,
(T=15 K) within a factor of 1.9. However, they exhibit dramatically
different microwave field, dependences of the surface resistance,
, but universal dependence. Application of a dc field was
found to affect not only absolute values of and , but the functional
dependences and as well. For some of the samples
the dc field was found to decrease below its zero-field low-power value.Comment: 4 pages, 4 figures. To be published in IEEE Trans. Appl. Supercond.,
June 199
Terahertz Microstrip Elevated Stack Antenna Technology on GaN-on-Low Resistivity Silicon Substrates for TMIC
In this paper we demonstrate a THz microstrip stack antenna on GaN-on-low resistivity silicon substrates (Ï < 40 Ω.cm). To reduce losses caused by the substrate and to enhance performance of the integrated antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold in addition to a layer of benzocyclobutene (BCB). A second circular patch is elevated in air using gold posts, making this design a stack configuration. The demonstrated antenna shows a measured resonance frequency in agreement with the modeling at 0.27 THz and a measured S11 as low as â18 dB was obtained. A directivity, gain and radiation efficiency of 8.3 dB, 3.4 dB, and 32% respectively was exhibited from the 3D EM model. To the authors' knowledge, this is the first demonstrated THz integrated microstrip stack antenna for TMIC (THz Monolithic Integrated Circuits) technology; the developed technology is suitable for high performance III-V material on low resistivity/high dielectric substrates
Characterization of qutrit channels in terms of their covariance and symmetry properties
We characterize the completely positive trace-preserving maps on qutrits
(qutrit channels) according to their covariance and symmetry properties. Both
discrete and continuous groups are considered. It is shown how each symmetry
group restricts arbitrariness in the parameters of the channel to a very small
set. Although the explicit examples are related to qutrit channels, the
formalism is sufficiently general to be applied to qudit channels
On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events
We describe and analyze Hubble Space Telescope (HST) observations of
transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner &
Damineli (2004). If, as seems probable, this is He II 4687, then it is
a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several
aspects of this feature support a mass-ejection model of the observed
spectroscopic events, and not an eclipse model. The He II emission appeared in
early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and
then abruptly disappeared. It did not appear in any other HST spectra before or
after the event. The peak brightness was larger than previously reported, and
is difficult to explain even if one allows for an uncertainty factor of order
3. The stellar wind must provide a temporary larger-than-normal energy supply,
and we describe a special form of radiative amplification that may also be
needed. These characteristics are consistent with a class of mass-ejection or
wind-disturbance scenarios, which have implications for the physical structure
and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3
tables; submitted to Astrophysical Journal (2005 March 29), accepted for
publication in Ap
Updated recommendations for HER2 testing in the UK
This paper serves to update previously published guidance on rationale and methodology for HER2 laboratory testing following the recommendation for the use of HER2 targeted treatment in the management of advanced breast cancer in the UK. Emphasis is placed on the standardisation of methodology and assessment and strategies to achieve high quality performance. A two phase testing algorithm based on first line immunocytochemistry evaluation and second line fluorescence in situ hybridisation assessment of borderline cases is recommended. To ensure maintenance of expertise, an annual caseload volume of at least 250 cases is recommended for laboratories providing a testing service
Application of Real-time AMDF Pitch Detection in a Voice Gender Normalisation System
Traditionally the interest in voice gender conversion was of a more theoretical nature rather than founded in real-life applications. However, with the increase in mobile communication and the resulting limitation in transmission bandwidth new approaches to minimising data rates have to be developed. Here voice gender normalisation (VGN) presents an efficient method of achieving higher compression rates by using the VGN algorithm to remove gender specific components of a speech signal and thus enhancing the information content to be transmitted. A second application for VGN is in the field of speech controlled systems, where current speech recognition algorithms have to deal with the voice characteristics of a speaker as well as the information content. Here again the use of VGN can remove the speaker's voice gender characteristics and thus enhance the message contents. Therefore, such a system would be capable of achieving higher recognition rates while being independent of the speaker. This paper presents the theory of a VGN system and furthermore, outlines an efficient real-time hardware implementation for the use in portable communications equipment
On the multiplicity of ALMA Compact Array counterparts of far-infrared bright quasars
We present ALMA Atacama Compact Array (ACA) 870 micron continuum maps of 28
infrared-bright SDSS quasars with Herschel/SPIRE detections at redshifts 2-4,
the largest such sample ever observed with ALMA. The ACA detections are centred
on the SDSS coordinates to within 1 arcsec for about 80 per cent of the sample.
Larger offsets indicate that the far-infrared (FIR) emission detected by
Herschel might come from a companion source. The majority of the objects (about
70 per cent) have unique ACA counterparts within the SPIRE beam down to 3-4
arcsec resolution. Only 30 per cent of the sample shows clear evidence for
multiple sources with secondary counterparts contributing to the total 870
micron flux within the SPIRE beam to at least 25 per cent. We discuss the
limitations of the data based on simulated pairs of point-like sources at the
resolution of the ACA and present an extensive comparison of our findings with
recent works on the multiplicities of sub-millimetre galaxies. We conclude
that, despite the coarse resolution of the ACA, our data support the idea that,
for a large fraction of FIR-bright quasars, the sub-mm emission comes from
single sources. Our results suggest that, on average, optically bright quasars
with strong FIR emission are not triggered by early-stage mergers but are,
instead, together with their associated star formation rates, the outcome of
either late-stage mergers or secular processes.Comment: 16 pages, 10 figure
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