877 research outputs found
High-Fidelity Spectroscopy at the Highest Resolutions
High-fidelity spectroscopy presents challenges for both observations and in
designing instruments. High-resolution and high-accuracy spectra are required
for verifying hydrodynamic stellar atmospheres and for resolving intergalactic
absorption-line structures in quasars. Even with great photon fluxes from large
telescopes with matching spectrometers, precise measurements of line profiles
and wavelength positions encounter various physical, observational, and
instrumental limits. The analysis may be limited by astrophysical and telluric
blends, lack of suitable lines, imprecise laboratory wavelengths, or
instrumental imperfections. To some extent, such limits can be pushed by
forming averages over many similar spectral lines, thus averaging away small
random blends and wavelength errors. In situations where theoretical
predictions of lineshapes and shifts can be accurately made (e.g., hydrodynamic
models of solar-type stars), the consistency between noisy observations and
theoretical predictions may be verified; however this is not feasible for,
e.g., the complex of intergalactic metal lines in spectra of distant quasars,
where the primary data must come from observations. To more fully resolve
lineshapes and interpret wavelength shifts in stars and quasars alike, spectral
resolutions on order R=300,000 or more are required; a level that is becoming
(but is not yet) available. A grand challenge remains to design efficient
spectrometers with resolutions approaching R=1,000,000 for the forthcoming
generation of extremely large telescopes.Comment: 6 pages, 4 figures, to appear in Reviews in Modern Astronomy vol. 22
(2010
Evolutionary dynamic optimisation of airport security lane schedules
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Reducing costs whilst maintaining passenger satisfaction is an important problem for airports. One area this can be applied is the security lane checks at the airport. However, reducing costs through reducing lane openings typically increases queue length and hence passenger dissatisfaction. This paper demonstrates that evolutionary methods can be used to optimise airport security lane schedules such that passenger dissatisfaction and staffing costs can be minimised. However, it is shown that these schedules typically over-fit the forecasts of passenger arrivals at security such that in actuality significant passenger delays can occur with deviations from the forecast. Consequently, this paper further demonstrates that dynamic evolutionary re-optimisation of these schedules can significantly mitigate this over-fitting problem with much reduced passenger delays
Attention-dependent modulation of cortical taste circuits revealed by granger causality with signal-dependent noise
We show, for the first time, that in cortical areas, for example the insular, orbitofrontal, and lateral prefrontal cortex, there is signal-dependent noise in the fMRI blood-oxygen level dependent (BOLD) time series, with the variance of the noise increasing approximately linearly with the square of the signal. Classical Granger causal models are based on autoregressive models with time invariant covariance structure, and thus do not take this signal-dependent noise into account. To address this limitation, here we describe a Granger causal model with signal-dependent noise, and a novel, likelihood ratio test for causal inferences. We apply this approach to the data from an fMRI study to investigate the source of the top-down attentional control of taste intensity and taste pleasantness processing. The Granger causality with signal-dependent noise analysis reveals effects not identified by classical Granger causal analysis. In particular, there is a top-down effect from the posterior lateral prefrontal cortex to the insular taste cortex during attention to intensity but not to pleasantness, and there is a top-down effect from the anterior and posterior lateral prefrontal cortex to the orbitofrontal cortex during attention to pleasantness but not to intensity. In addition, there is stronger forward effective connectivity from the insular taste cortex to the orbitofrontal cortex during attention to pleasantness than during attention to intensity. These findings indicate the importance of explicitly modeling signal-dependent noise in functional neuroimaging, and reveal some of the processes involved in a biased activation theory of selective attention
Conformance-based doping detection for cyber-physical systems
We present a novel and generalised notion of doping cleanness for cyber-physical systems that allows for perturbing the inputs and observing the perturbed outputs both in the time– and value–domains. We instantiate our definition using existing notions of conformance for cyber-physical systems. We show that our generalised definitions are essential in a data-driven method for doping detection and apply our definitions to a case study concerning diesel emission tests
Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an <i>in vitro</i> model of CNS tuberculosis
Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB
Robustness and evolutionary dynamic optimisation of airport security schedules
Reducing security lane operations whilst minimising passenger waiting times in unforseen circumstances is important for airports. Evolutionary methods can design optimised schedules but these tend to over-fit passenger arrival forecasts resulting in lengthy waiting times for unforeseen events. Dynamic re-optimisation can mitigate for this issue but security lane schedules are an example of a constrained problem due to the human element preventing major modifications. This paper postulates that for dynamic re-optimisation to be more effective in constrained circumstances consideration of schedule robustness is required. To reduce over-fitting a simple methodology for evolving more robust schedules is investigated. Random delays are introduced into forecasts of passenger arrivals to better reflect actuality and a range of these randomly perturbed forecasts are used to evaluate schedules. These steps reduced passenger waiting times for actual events for both static and dynamic policies with minimal increases in security operations
Limits on the spin-dependent WIMP-nucleon cross-sections from the first science run of the ZEPLIN-III experiment
We present new experimental constraints on the WIMP-nucleon spin-dependent elastic cross-sections using data from the first science run of ZEPLIN-III, a two-phase xenon experiment searching for galactic dark matter WIMPs based at the Boulby mine. Analysis of 450 kgdays fiducial exposure revealed a most likely signal of zero events, leading to a 90%-confidence upper limit on the pure WIMP-neutron cross-section of pb at 55 GeV/ WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn CD nucleon-nucleon potential were used for the odd-neutron isotopes Xe and Xe. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction is much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of 2
Measurement and simulation of the muon-induced neutron yield in lead
A measurement is presented of the neutron production rate in lead by high energy cosmic-ray muons at a depth of 2850 m water equivalent (w.e.) and a mean muon energy of 260 GeV. The measurement exploits the delayed coincidences between muons and the radiative capture of induced neutrons in a highly segmented tonne scale plastic scintillator detector. Detailed Monte Carlo simulations reproduce well the measured capture times and multiplicities and, within the dynamic range of the instrumentation, the spectrum of energy deposits. By comparing measurements with simulations of neutron capture rates a neutron yield in lead of (View the MathML source) ×10-3 neutrons/muon/(g/cm2) has been obtained. Absolute agreement between simulation and data is of order 25%. Consequences for deep underground rare event searches are discussed
'Ultimate' Information Content in Solar and Stellar Spectra: Photospheric line asymmetries and wavelength shifts
CONTEXT: Spectral-line asymmetries and wavelength shifts are signatures of
hydrodynamics in solar and stellar atmospheres. Theory may precisely predict
idealized lines, but observed spectra are limited by blends, too few suitable
lines, imprecise laboratory wavelengths, and by instrumental imperfections.
AIMS: Bisectors and shifts are extracted until the 'ultimate' accuracy limits
in highest-quality solar and stellar spectra, to understand limits set by
stellar physics, observational techniques, and limitations in laboratory data.
METHODS: Spectral atlases of the Sun and bright solar-type stars were
examined for thousands of 'unblended' lines with the most accurate laboratory
wavelengths, yielding bisectors and shifts as averages over groups of similar
lines, thus minimizing effects of photometric noise and of random blends.
RESULTS: For solar spectra, bisector shapes and shifts were extracted for
previously little-studied species (Fe II, Ti I, Ti II, Cr II, Ca I, C I), using
recently determined very accurate laboratory wavelengths. In Procyon and other
F-type stars, a blueward bend in the bisector near the spectral continuum
reveals line saturation and damping wings in upward-moving photospheric
granules. Accuracy limits set by 'astrophysical' noise, finite instrumental
resolution, superposed telluric absorption, and inaccurate wavelengths,
together limit absolute lineshift studies to approximately 50-100 m/s.
CONCLUSIONS: Spectroscopy with resolutions R = 300,000 will enable bisector
studies for many stars. Circumventing remaining limits of astrophysical noise
in line-blends and rotationally smeared profiles may ultimately require
spectroscopy across spatially resolved stellar disks.Comment: 15 pages, 11 figures, 6 tables; accepted for publication in Astronomy
& Astrophysic
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