17,456 research outputs found
A gallium phosphide high-temperature bipolar junction transistor
Preliminary results are reported on the development of a high temperature (350 C) gallium phosphide bipolar junction transistor (BJT) for geothermal and other energy applications. This four-layer p(+)n(-)pp(+) structure was formed by liquid phase epitaxy using a supercooling technique to insure uniform nucleation of the thin layers. Magnesium was used as the p-type dopant to avoid excessive out-diffusion into the lightly doped base. By appropriate choice of electrodes, the device may also be driven as an n-channel junction field-effect transistor. The initial design suffers from a series resistance problem which limits the transistor's usefulness at high temperatures
Fluctuation limits of strongly degenerate branching systems
Functional limit theorems for scaled fluctuations of occupation time
processes of a sequence of critical branching particle systems in with
anisotropic space motions and strongly degenerated splitting abilities are
proved in the cases of critical and intermediate dimensions. The results show
that the limit processes are constant measure-valued Wienner processes with
degenerated temporal and simple spatial structures.Comment: 15 page
Near Infrared Spectroscopy of Young Brown Dwarfs in Upper Scorpius
Spectroscopic follow-up is a pre-requisite for studies of the formation and
early evolution of brown dwarfs. Here we present IRTF/SpeX near-infrared
spectroscopy of 30 candidate members of the young Upper Scorpius association,
selected from our previous survey work. All 24 high confidence members are
confirmed as young very low mass objects with spectral types from M5 to L1,
15-20 of them are likely brown dwarfs. This high yield confirms that brown
dwarfs in Upper Scorpius can be identified from photometry and proper motions
alone, with negligible contamination from field objects (<4%). Out of the 6
candidates with lower confidence, 5 might still be young very low mass members
of Upper Scorpius, according to our spectroscopy. We demonstrate that some very
low mass class II objects exhibit radically different near infrared (0.6 -
2.5micron) spectra from class III objects, with strong excess emission
increasing towards longer wavelengths and partially filled in features at
wavelengths shorter than 1.25micron. These characteristics can obscure the
contribution of the photosphere within such spectra. Therefore, we caution that
near infrared derived spectral types for objects with discs may be unreliable.
Furthermore, we show that the same characteristics can be seen to some extent
in all class II and even a significant fraction of class III objects (~40%),
indicating that some of them are still surrounded by traces of dust and gas.
Based on our spectra, we select a sample of objects with spectral types of M5
to L1, whose near-infrared emission represents the photosphere only. We
recommend the use of these objects as spectroscopic templates for young brown
dwarfs in the future.Comment: 12 pages, 9 figures, Accepted in MNRA
Exclusive Higgs Boson Production with bottom quarks at Hadron Colliders
We present the next-to-leading order QCD corrected rate for the production of
a scalar Higgs boson with a pair of high p_T bottom and anti-bottom quarks at
the Tevatron and at the Large Hadron Collider. Results are given for both the
Standard Model and the Minimal Supersymmetric Standard Model. The exclusive
b-bbar-h production rate is small in the Standard Model, but it can be greatly
enhanced in the Minimal Supersymmetric Standard Model for large tan(beta),
making b-bbar-h an important discovery mode. We find that the next-to-leading
order QCD results are much less sensitive to the renormalization and
factorization scales than the lowest order results, but have a significant
dependence on the choice of the renormalization scheme for the bottom quark
Yukawa coupling.Comment: 27 pages, 17 figures, RevTeX
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Draft Genome Sequence of the Caffeine-Degrading Methylotroph Methylorubrum populi Pinkel.
A pink-pigmented facultative methylotroph, Methylorubrum populi Pinkel, was isolated from compost by selective enrichment with caffeine (3,5,7-trimethylxanthine) as the sole carbon, nitrogen, and energy source. We report here its high-quality draft genome sequence, assembled in 35 contigs totaling 5,630,907âbp. We identified 5,681 protein-coding sequences, including those putatively involved in caffeine degradation
BRAVO economic study of LANDSAT follow-on
The LANDSAT Follow-On satellite consists of two major systems: the instrument module and the Multi-Mission Modular Spacecraft (MMS). The instrument module contains the thematic mapper and the five-band multispectral scanner instruments. The instrument module also includes the solar array, the tracking and data relay satellite (TDRS) antenna, and the wideband data module. The MMS contains the modularized and standardized power, propulsion, attitude control, and command and data handling subsystems. The Shuttle will be supporting the LANDSAT Follow-On system. The LANDSAT Follow-On Project plans two Delta 3910 launches. The first is scheduled for 1981; the second Delta launch will occur as needed to keep one satellite operational on orbit. The second satellite will be ready six months after the first. It could be launched any time after that. Shuttle support of the system could begin in early 1983 but would be scheduled to start after the second Delta launch
The role of remote sensing in the development of SMART indicators for ecosystem services assessment
Human beings benefit from a wide range of goods and services from the natural environment that are collectively known as ecosystem services. However, rapid natural habitat loss, overexploitation and climate change is causing accelerating losses of populations and species, with largely unknown consequences on ecosystem functioning and the sustainable provision of ecosystem services. It is crucial, therefore, to develop a suite of indicators of the health and status of ecosystems, to monitor and quantify services delivery and to facilitate policy responses to stop and reverse negative trends. An effective framework to facilitate the development of suitable indicators is by using the SMART approach, which defines five criteria that could be applied to set monitoring and management goals, which are Specific, Measurable, Achievable, Realistic and Time-sensitive. Remote sensing provides a useful data source that can monitor ecosystems over multiple spatial and temporal scales. Although the development and application of landscape indicators (vegetation indices, for example) derived from remote sensing data are comparatively advanced, it is acknowledged that a number of organisms and ecosystem processes are not detectable by remote sensing. This paper explores several approaches to overcome this limitation, by examining the strong affinity of species with dominant habitat structures and through the coupling of remote sensing and ecosystem process models using examples drawn from a number of important ecosystems
Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study
Previous theoretical, along with early simulation and experimental, studies
have indicated that particles with a short-ranged attraction exhibit a range of
new dynamical arrest phenomena. These include very pronounced reentrance in the
dynamical arrest curve, a logarithmic singularity in the density correlation
functions, and the existence of `attractive' and `repulsive' glasses. Here we
carry out extensive molecular dynamics calculations on dense systems
interacting via a square-well potential. This is one of the simplest systems
with the required properties, and may be regarded as canonical for interpreting
the phase diagram, and now also the dynamical arrest. We confirm the
theoretical predictions for re-entrance, logarithmic singularity, and give the
first direct evidence of the coexistence, independent of theory, of the two
coexisting glasses. We now regard the previous predictions of these phenomena
as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.
Plausible responses to the threat of rapid sea-level rise for the Thames Estuary
This paper considers the perceptions and responses of selected stakeholders to a scenarion of rapid rise in sea-level due to the collapse of the West Antarctic ice sheet, which could produce a global rise in sea-level of 5 to 6 metres. Through a process of dialogue involving one-to one interviews and a one-day policy exercise, we addressed influences on decision-making when information is uncertain and our ability to plan, prepare for and implement effective ways of coping with this extreme scenario. Through these interactions we hoped to uncover plausible responses to the scenario and identify potential weaknesses in our current flood management approaches to dealing with such an occurrence. By undertaking this exploratory exercise we hoped to find out whether this was a feasible way to deal with such a low probability but high consequence scenario. It was the process of finding a solution that interested us rather than the technical merits of one solution over another. We were not intending to produce definitive set of recommendations on how to respond but to gain insights into the process of making a decision, specifically what influences it and what assumptions are made.Sea level rise, London
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