25,866 research outputs found
The Far-Infrared Surveyor (FIS) for AKARI
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the
AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and
uses two kinds of array detectors. The FIS arrays and optics are designed to
sweep the sky with high spatial resolution and redundancy. The actual scan
width is more than eight arcmin, and the pixel pitch is matches the diffraction
limit of the telescope. Derived point spread functions (PSFs) from observations
of asteroids are similar to the optical model. Significant excesses, however,
are clearly seen around tails of the PSFs, whose contributions are about 30% of
the total power. All FIS functions are operating well in orbit, and its
performance meets the laboratory characterizations, except for the two longer
wavelength bands, which are not performing as well as characterized.
Furthermore, the FIS has a spectroscopic capability using a Fourier transform
spectrometer (FTS). Because the FTS takes advantage of the optics and detectors
of the photometer, it can simultaneously make a spectral map. This paper
summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
The High Arctic in Extreme Winters: Vortex, Temperature, and MLS and ACE-FTS Trace Gas Evolution
The first three Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns at Eureka (80° N, 86° W) were during two extremes of Arctic winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry, and Aura Microwave Limb Sounder (MLS), with meteorological analyses and Eureka lidar and radiosonde temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport and chemistry, and to provide a context for interpretation of campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, above where it could be accurately represented in the meteorological analyses. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with Eureka radiosondes, and with lidar data up to 50â60 km. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex during the 2004 and 2006 Eureka campaigns compared to that in 2005
Recommended from our members
Universality of Bayesian Predictions
Given the sequential update nature of Bayes rule, Bayesian methods find natural application to prediction problems. Advances in computational methods allow to routinely use Bayesian methods in econometrics. Hence, there is a strong case for feasible predictions in a Bayesian framework. This paper studies the theoretical properties of Bayesian predictions and shows that under minimal conditions we can derive finite sample bounds for the loss incurred using
Bayesian predictions under the Kullback-Leibler divergence. In particular, the concept of universality of predictions is discussed and universality is established for Bayesian predictions in a variety of settings. These include predictions under almost arbitrary loss functions, model
averaging, predictions in a non stationary environment and under model miss-specification.
Given the possibility of regime switches and multiple breaks in economic series, as well as the
need to choose among different forecasting models, which may inevitably be miss-specified, the
finite sample results derived here are of interest to economic and financial forecasting
Systematic characterisation of the Herschel SPIRE Fourier Transform Spectrometer
A systematic programme of calibration observations was carried out to monitor
the performance of the SPIRE FTS instrument on board the Herschel Space
Observatory. Observations of planets (including the prime point-source
calibrator, Uranus), asteroids, line sources, dark sky, and cross-calibration
sources were made in order to monitor repeatability and sensitivity, and to
improve FTS calibration. We present a complete analysis of the full set of
calibration observations and use them to assess the performance of the FTS.
Particular care is taken to understand and separate out the effect of pointing
uncertainties, including the position of the internal beam steering mirror for
sparse observations in the early part of the mission. The repeatability of
spectral line centre positions is <5km/s, for lines with signal-to-noise ratios
>40, corresponding to <0.5-2.0% of a resolution element. For spectral line
flux, the repeatability is better than 6%, which improves to 1-2% for spectra
corrected for pointing offsets. The continuum repeatability is 4.4% for the SLW
band and 13.6% for the SSW band, which reduces to ~1% once the data have been
corrected for pointing offsets. Observations of dark sky were used to assess
the sensitivity and the systematic offset in the continuum, both of which were
found to be consistent across the FTS detector arrays. The average point-source
calibrated sensitivity for the centre detectors is 0.20 and 0.21 Jy [1 sigma; 1
hour], for SLW and SSW. The average continuum offset is 0.40 Jy for the SLW
band and 0.28 Jy for the SSW band.Comment: 41 pages, 37 figures, 32 tables. Accepted for publication in MNRA
The Challenges of the European Automotive Industry at the Beginning of the 21st Century. Summary of the main findings of the CoCKEAS project
The paper presents the main conclusions of the CoCKEAS European project (Coordinating Competencies and Knowledge in the European Automobile System). It analyses the main changes in the organisation of the European automotive system, not only in the relationships between carmakers and their first tier suppliers, but also in the relations they have with the other actors (upstream and downstream). It discusses the issues associated to the intangible dimension of this industry (financialisation and services), its new geography, and, finally, its distinctivness compared with is competitors (USA and Japan).: automobile industry, Europe, financialisation, interfirm relationships, Japan, location, modular production, services, system, USA
Femtochemistry: the role of alignment and orientation
Some aspects of alignment and orientation have been considered for femtochemistry experiments. Elementary theoretical descriptions of the time evolution of alignment and angular momenta have been discussed and related to the radial and angular parts of the potential-energy surface. Applications to ICN unimolecular dissociation, H + CO2oriented bimolecular reaction, and crossings between different potential-energy curves in alkali-metal halide reactions (M + X) are give. Emphasis is on the femtosecond dynamics of the transition-state region and the clocking of fragment separation in real time
Method of Non-Data-Aided Carrier Recovery with Modulation Identification
A non-data aided carrier recovery technique using digital modulation format identification called multi-mode PLL (Phase Locked Loop) is proposed. This technique can be interpreted as a modulation identification method that is robust against static phase and frequency offsets. The performance of the proposed technique is studied and the analytical expressions are derived for the probability of lock detection, acquisition time over AWGN channel in the cases of M-PSK and M-QAM modulations with respect to frequency offset and signal-to-noise ratio
Partial separability revisited: Necessary and sufficient criteria
We extend the classification of mixed states of quantum systems composed of
arbitrary number of subsystems of arbitrary dimensions. This extended
classification is complete in the sense of partial separability and gives
1+18+1 partial separability classes in the tripartite case contrary to a former
1+8+1. Then we give necessary and sufficient criteria for these classes, which
make it possible to determine to which class a mixed state belongs. These
criteria are given by convex roof extensions of functions defined on pure
states. In the special case of three-qubit systems, we define a different set
of such functions with the help of the Freudenthal triple system approach of
three-qubit entanglement.Comment: v3: 22 pages, 5 tables, 1 figure, minor corrections (typos),
clarification in the Introduction. Accepted in Phys. Rev. A. Comments are
welcom
- âŠ