2,531 research outputs found
Ideal bandpasses for type Ia supernova cosmology
To use type Ia supernovae as standard candles for cosmology we need accurate
broadband magnitudes. In practice the observed magnitude may differ from the
ideal magnitude-redshift relationship either through intrinsic inhomogeneities
in the type Ia supernova population or through observational error. Here we
investigate how we can choose filter bandpasses to reduce the error caused by
both these effects. We find that bandpasses with large integral fluxes and
sloping wings are best able to minimise several sources of observational error,
and are also least sensitive to intrinsic differences in type Ia supernovae.
The most important feature of a complete filter set for type Ia supernova
cosmology is that each bandpass be a redshifted copy of the first. We design
practical sets of redshifted bandpasses that are matched to typical high
resistivity CCD and HgCdTe infra-red detector sensitivities. These are designed
to minimise systematic error in well observed supernovae, final designs for
specific missions should also consider signal-to-noise requirements and
observing strategy. In addition we calculate how accurately filters need to be
calibrated in order to achieve the required photometric accuracy of future
supernova cosmology experiments such as the SuperNova-Acceleration-Probe
(SNAP), which is one possible realisation of the Joint Dark-Energy mission
(JDEM). We consider the effect of possible periodic miscalibrations that may
arise from the construction of an interference filter.Comment: Accepted for publication in PASP, 22 pages (preprint format), 17
figure
Spectral diversity of Type Ia Supernovae
We use published spectroscopic and photometric data for 8 Type Ia supernovae
to construct a dispersion spectrum for this class of object, showing their
diversity over the wavelength range 3700A to 7100A. We find that the B and V
bands are the spectral regions with the least dispersion, while the U band
below 4100A is more diverse. Some spectral features such as the Si line at
6150A are also highly diverse. We then construct two objective measures of
'peculiarity' by (i) using the deviation of individual objects from the average
SN Ia spectrum compared to the typical dispersion and (ii) applying principle
component analysis. We demonstrate these methods on several SNe Ia that have
previously been classified as peculiar.Comment: 8 pages, 8 figures, uses mn2e.cls, accepted for publication by MNRA
Forces between a single atom and its distant mirror image
An excited-state atom whose emitted light is back-reflected by a distant
mirror can experience trapping forces, because the presence of the mirror
modifies both the electromagnetic vacuum field and the atom's own radiation
reaction field. We demonstrate this mechanical action using a single trapped
barium ion. We observe the trapping conditions to be notably altered when the
distant mirror is shifted by an optical wavelength. The well-localised barium
ion enables the spatial dependence of the forces to be measured explicitly. The
experiment has implications for quantum information processing and may be
regarded as the most elementary optical tweezers.Comment: 4 pages, 5 figures, published versio
Supernova Cosmology and the ESSENCE project
The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has
revolutionized cosmology, and added a new dominant component to the energy
density of the Universe, dark energy. Following the discovery and confirmation
era, the currently ongoing SNe Ia surveys aim to determine the properties of
the dark energy. ESSENCE is a five year ground-based supernova survey aimed at
finding and characterizing 200 SNe Ia in the redshift domain z=[0.2-0.8]. The
goal of the project is to put constraints on the equation of state parameter,
w, of the dark energy with an accuracy of <10%. This paper presents these
ongoing efforts in the context of the current developments in observational
cosmology.Comment: Submitted to EPS1
Theoretical interpretation of the experimental electronic structure of lens shaped, self-assembled InAs/GaAs quantum dots
We adopt an atomistic pseudopotential description of the electronic structure
of self-assembled, lens shaped InAs quantum dots within the ``linear
combination of bulk bands'' method. We present a detailed comparison with
experiment, including quantites such as the single particle electron and hole
energy level spacings, the excitonic band gap, the electron-electron, hole-hole
and electron hole Coulomb energies and the optical polarization anisotropy. We
find a generally good agreement, which is improved even further for a dot
composition where some Ga has diffused into the dots.Comment: 16 pages, 5 figures. Submitted to Physical Review
The Open Source GAITOR Suite for Rodent Gait Analysis
Locomotive changes are often associated with disease or injury, and these changes can be quantified through gait analysis. Gait analysis has been applied to preclinical studies, providing quantitative behavioural assessment with a reasonable clinical analogue. However, available gait analysis technology for small animals is somewhat limited. Furthermore, technological and analytical challenges can limit the effectiveness of preclinical gait analysis. The Gait Analysis Instrumentation and Technology Optimized for Rodents (GAITOR) Suite is designed to increase the accessibility of preclinical gait analysis to researchers, facilitating hardware and software customization for broad applications. Here, the GAITOR Suite’s utility is demonstrated in 4 models: a monoiodoacetate (MIA) injection model of joint pain, a sciatic nerve injury model, an elbow joint contracture model, and a spinal cord injury model. The GAITOR Suite identified unique compensatory gait patterns in each model, demonstrating the software’s utility for detecting gait changes in rodent models of highly disparate injuries and diseases. Robust gait analysis may improve preclinical model selection, disease sequelae assessment, and evaluation of potential therapeutics
Two-bands superconductivity with intra- and interband pairing for synthetic superlattices
We consider a model for superconductivity in a two-band superconductor,
having an anisotropic electronic structure made of two partially overlapping
bands with a first hole-like and a second electron-like fermi surface. In this
pairing scenario, driven by the interplay between interband and
intraband pairing terms, we have solved the two gap equations at the
critical temperature and calculate and the chemical potential
as a function of the number of carriers for various values of pairing
interactions, , , and . The results show the
complexity of the physics of condensates with multiple order parameters with
the chemical potential near band edges.Comment: 6 pages, 2 figure
Clinicians' use of breast cancer risk assessment tools according to their perceived importance of breast cancer risk factors: an international survey.
The BOADICEA breast cancer (BC) risk assessment model and its associated Web Application v3 (BWA) tool are being extended to incorporate additional genetic and non-genetic BC risk factors. From an online survey through the BOADICEA website and UK, Dutch, French and Swedish national genetic societies, we explored the relationships between the usage frequencies of the BWA and six other common BC risk assessment tools and respondents' perceived importance of BC risk factors. Respondents (N = 443) varied in age, country and clinical seniority but comprised mainly genetics health professionals (82%) and BWA users (93%). Oncology professionals perceived reproductive, hormonal (exogenous) and lifestyle BC risk factors as more important in BC risk assessment compared to genetics professionals (p values < 0.05 to 0.0001). BWA was used more frequently by respondents who gave high weight to breast tumour pathology and low weight to personal BC history as BC risk factors. BWA use was positively related to the weight given to hormonal BC risk factors. The importance attributed to lifestyle and BMI BC risk factors was not associated with the use of BWA or any of the other tools. Next version of the BWA encompassing additional BC risk factors will facilitate more comprehensive BC risk assessment in genetics and oncology practice
Flaring Behavior of the Quasar 3C~454.3 across the Electromagnetic Spectrum
We analyze the behavior of the parsec-scale jet of the quasar 3C~454.3 during
pronounced flaring activity in 2005-2008. Three major disturbances propagated
down the jet along different trajectories with Lorentz factors 10. The
disturbances show a clear connection with millimeter-wave outbursts, in 2005
May/June, 2007 July, and 2007 December. High-amplitude optical events in the
-band light curve precede peaks of the millimeter-wave outbursts by 15-50
days. Each optical outburst is accompanied by an increase in X-ray activity. We
associate the optical outbursts with propagation of the superluminal knots and
derive the location of sites of energy dissipation in the form of radiation.
The most prominent and long-lasting of these, in 2005 May, occurred closer to
the black hole, while the outbursts with a shorter duration in 2005 Autumn and
in 2007 might be connected with the passage of a disturbance through the
millimeter-wave core of the jet. The optical outbursts, which coincide with the
passage of superluminal radio knots through the core, are accompanied by
systematic rotation of the position angle of optical linear polarization. Such
rotation appears to be a common feature during the early stages of flares in
blazars. We find correlations between optical variations and those at X-ray and
-ray energies. We conclude that the emergence of a superluminal knot
from the core yields a series of optical and high-energy outbursts, and that
the mm-wave core lies at the end of the jet's acceleration and collimation
zone.Comment: 57 pages, 23 figures, 8 tables (submitted to ApJ
Memory for expectation-violating concepts:The effects of agents and cultural familiarity
Previous research has shown that ideas which violate our expectations, such as schema-inconsistent concepts, enjoy privileged status in terms of memorability. In our study, memory for concepts that violate cultural (cultural schema-level) expectations (e.g., "illiterate teacher", "wooden bottle", or "thorny grass") versus domain-level (ontological) expectations (e.g., "speaking cat", "jumping maple", or "melting teacher") was examined. Concepts that violate cultural expectations, or counter-schematic, were remembered to a greater extent compared with concepts that violate ontological expectations and with intuitive concepts (e.g., "galloping pony", "drying orchid", or "convertible car"), in both immediate recall, and delayed recognition tests. Importantly, concepts related to agents showed a memory advantage over concepts not pertaining to agents, but this was true only for expectation-violating concepts. Our results imply that intuitive, everyday concepts are equally attractive and memorable regardless of the presence or absence of agents. However, concepts that violate our expectations (cultural-schema or domain-level) are more memorable when pertaining to agents (humans and animals) than to non-agents (plants or objects/artifacts). We conclude that due to their evolutionary salience, cultural ideas which combine expectancy violations and the involvement of an agent are especially memorable and thus have an enhanced probability of being successfully propagated. © 2014 Porubanova et al
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