3,992 research outputs found
Supernova Constraints and Systematic Uncertainties from the First Three Years of the Supernova Legacy Survey
We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = â0.91^(+0.16)_(â0.20)(stat)^(+0.07)_(â0.14)(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems
The Radio Spectrum of TVLM513-46546: Constraints on the Coronal Properties of a Late M Dwarf
We explore the radio emission from the M9 dwarf, TVLM513-46546, at multiple
radio frequencies, determining the flux spectrum of persistent radio emission,
as well as constraining the levels of circular polarization. Detections at both
3.6 and 6 cm provide spectral index measurement (where S) of . A detection at 20 cm suggests that the
spectral peak is between 1.4 and 5 GHz. The most stringent upper limits on
circular polarization are at 3.6 and 6 cm, with 15%. These
characteristics agree well with those of typical parameters for early to mid M
dwarfs, confirming that magnetic activity is present at levels comparable with
those extrapolated from earlier M dwarfs. We apply analytic models to
investigate the coronal properties under simple assumptions of dipole magnetic
field geometry and radially varying nonthermal electron density distributions.
Requiring the spectrum to be optically thin at frequencies higher than 5 GHz
and reproducing the observed 3.6 cm fluxes constrains the magnetic field at the
base to be less than about 500 G. There is no statistically significant
periodicity in the 3.6 cm light curve, but it is consistent with low-level
variability.Comment: 11 pages, 2 figures Accepted for publication in the Astrophysical
Journa
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Requirements Engineering as Creative Problem Solving: A Research Agenda for Idea Finding
This vision paper frames requirements engineering as a creative problem solving process. Its purpose is to enable requirements researchers and practitioners to recruit relevant theories, models, techniques and tools from creative problem solving to understand and support requirements processes more effectively. It uses 4 drivers to motivate the case for requirements engineering as a creative problem solving process. It then maps established requirements activities onto one of the longest-established creative problem solving processes, and uses these mappings to locate opportunities for the application of creative problem solving in requirements engineering. The second half of the paper describes selected creativity theories, techniques, software tools and training that can be adopted to improve requirements engineering research and practice. The focus is on support for problem and idea finding - two creative problem solving processes that our investigation revealed are poorly supported in requirements engineering. The paper ends with a research agenda to incorporate creative processes, techniques, training and tools in requirements projects
A macro-realism inequality for opto-electro-mechanical systems
We show how to apply the Leggett-Garg inequality to opto-electro-mechanical
systems near their quantum ground state. We find that by using a dichotomic
quantum non-demolition measurement (via, e.g., an additional circuit-QED
measurement device) either on the cavity or on the nanomechanical system
itself, the Leggett-Garg inequality is violated. We argue that only
measurements on the mechanical system itself give a truly unambigous violation
of the Leggett-Garg inequality for the mechanical system. In this case, a
violation of the Leggett-Garg inequality indicates physics beyond that of
"macroscopic realism" is occurring in the mechanical system. Finally, we
discuss the difficulties in using unbound non-dichotomic observables with the
Leggett-Garg inequality.Comment: 9 pages, 2 figures. Added additional figure (2b), and associated
conten
Detecting non-Markovian plasmonic band gaps in quantum dots using electron transport
Placing a quantum dot close to a metal nanowire leads to drastic changes in
its radiative decay behavior because of evanescent couplings to surface
plasmons. We show how two non-Markovian effects, band-edge and retardation,
could be observed in such a system. Combined with a quantum dot p-i-n junction,
these effects could be readout via current-noise measurements. We also discuss
how these effects can occur in similar systems with restricted geometries, like
phononic cavities and photonic crystal waveguides. This work links two
previously separate topics: surface-plasmons and current-noise measurements.Comment: 8 page
Detecting Bose-Einstein condensation of exciton-polaritons via electron transport
We examine the Bose-Einstein condensation of exciton-polaritons in a
semiconductor microcavity via an electrical current. We propose that by
embedding a quantum dot p-i-n junction inside the cavity, the tunneling current
through the device can reveal features of condensation due to a one-to-one
correspondence of the photons to the condensate polaritons. Such a device can
also be used to observe the phase interference of the order parameters from two
condensates.Comment: 5 Pages, 3 Figure
The quark fragmentation fractions at LHCb and meson decays with heavy quark spectators
We study the current estimates of to extract the
fragmentation fraction at the LHCb. A rather robust estimate of
based on factorization and lattice results for the form
factor gives with a error. We also revisit the
extraction of using instead of the theoretical cleaner
but more suppressed channel . We also find a tension on the
predictions of and considering the
measurements of these modes at LHCb, and find that, within a
uncertainty, only the lower end of the current prediction range would be consistent with the LHCb measurements.Comment: 11 pages, 2 figure
Hypergolic ignitor
An ignitor for use with the MC-1 rocket engine has a cartridge bounded by two end caps with rupture disc assemblies connected thereto. A piston assembly within the cartridge moves from one end of the cartridge during the ignition process. The inlet of the ignitor communicates with a supply taken from the discharge of the fuel pump. When the pump is initially started, the pressure differential bursts the first rupture disc to begin the movement of the piston assembly toward the discharge end. The pressurization of the cartridge causes the second rupture disc to rupture and hypergolic fluid contained within the cartridge is discharged out the ignitor outlet
Why are acute admissions to hospital of children under 5 years of age increasing in the UK?
Childrenâs use of hospital services in the UK has been increasing rapidly since the late 1990s.1â6 Findings from the latest QualityWatch report show significant increases in emergency hospital admissions for infants (23%) and young children aged 1â4 years (11%) between 2006/2007 and 2015/2016 (data have been adjusted for population increases in each childhood age group), while children over the age of 15 years showed a decrease in emergency admissions
Preparing the foundations for video-based, practice-placement support: establishing the role from a studentsâ perspective
Currently, many placement-based health programme students within the UK are supported through face-to-face visits from university staff. Whilst cited in literature as being of value, the face-to-face nature of this contact is not supported. Alternatives including video-based communications methods offer the potential for cost effective, environmentally responsible support. However, in order to establish the fitness for purpose of alternative approaches, the content and purpose of current support needs to be understood. This project aimed to investigate student perceptions of the ideal content and purpose of clinical support visits, and alternatives to the current face-to-face approach. Fifty-six Physiotherapy undergraduate students responded to questionnaires with a further nine participating in a follow-up focus group. Participants emphasised the value of the visit in guiding learning, ensuring progression and resolving arising issues, and highlighted concerns over alternative approaches. Focus group participants discussed the importance of personal and professional confidence in directing requirements for support, and went on to propose a menu of options for methods of communication.Whilst limited in some applications, video technologies may be one of the options. Overall, however, this project supports the need for consideration of individualised learning journeys within curriculum planning
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