141,176 research outputs found
Forecast B-modes detection at large scales in presence of noise and foregrounds
We investigate the detectability of the primordial CMB polarization B-mode
power spectrum on large scales in the presence of instrumental noise and
realistic foreground contamination. We have worked out a method to estimate the
errors on component separation and to propagate them up to the power spectrum
estimation. The performances of our method are illustrated by applying it to
the instrumental specifications of the Planck satellite and to the proposed
configuration for the next generation CMB polarization experiment COrE. We
demonstrate that a proper component separation step is required in order
achieve the detection of B-modes on large scales and that the final sensitivity
to B-modes of a given experiment is determined by a delicate balance between
noise level and residual foregrounds, which depend on the set of frequencies
exploited in the CMB reconstruction, on the signal-to-noise of each frequency
map, and on our ability to correctly model the spectral behavior of the
foreground components. We have produced a flexible software tool that allows
the comparison of performances on B-mode detection of different instrumental
specifications (choice of frequencies, noise level at each frequency, etc.) as
well as of different proposed approaches to component separation.Comment: 7 pages, 2 tables, 1 figure, accepted by MNRA
Dealing with Structural Changes in the Common Dynamic Factor Model : Deterministic Mechanism
Composite economic indicator is a very useful tool designed to trace and predict the business cycle conditions. In this paper we study possible extensions of this approach intended to cope with the potential data problems caused by various structural breaks affecting both level and volatility of the component series. The structural shifts are introduced in the composite economic indicator model via deterministic dummies capturing breaks in the observed variablesâintercepts and in the residual variances of the specific factors. As an illustration the Post-World War II US monthly macroeconomic series are utilized for which different specifications of the single-factor linear and regime-switching model are evaluated.composite economic indicator;Markov switching;structural break;turning points;NBER dating
Inferring Concise Specifications of APIs
Modern software relies on libraries and uses them via application programming
interfaces (APIs). Correct API usage as well as many software engineering tasks
are enabled when APIs have formal specifications. In this work, we analyze the
implementation of each method in an API to infer a formal postcondition.
Conventional wisdom is that, if one has preconditions, then one can use the
strongest postcondition predicate transformer (SP) to infer postconditions.
However, SP yields postconditions that are exponentially large, which makes
them difficult to use, either by humans or by tools. Our key idea is an
algorithm that converts such exponentially large specifications into a form
that is more concise and thus more usable. This is done by leveraging the
structure of the specifications that result from the use of SP. We applied our
technique to infer postconditions for over 2,300 methods in seven popular Java
libraries. Our technique was able to infer specifications for 75.7% of these
methods, each of which was verified using an Extended Static Checker. We also
found that 84.6% of resulting specifications were less than 1/4 page (20 lines)
in length. Our technique was able to reduce the length of SMT proofs needed for
verifying implementations by 76.7% and reduced prover execution time by 26.7%
Evaluation of the ALMA Prototype Antennas
The ALMA North American and European prototype antennas have been evaluated
by a variety of measurement systems to quantify the major performance
specifications. Nearfield holography was used to set the reflector surfaces to
17 microns RMS. Pointing and fast switching performance was determined with an
optical telescope and by millimeter wavelength radiometry, yielding 2 arcsec
absolute and 0.6 arcsec offset pointing accuracies. Path length stability was
measured to be less than or approximately equal to 20 microns over 10 minute
time periods using optical measurement devices. Dynamical performance was
studied with a set of accelerometers, providing data on wind induced tracking
errors and structural deformation. Considering all measurements made during
this evaluation, both prototype antennas meet the major ALMA antenna
performance specifications.Comment: 83 pages, 36 figures, AASTex format, to appear in PASP September 2006
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Manufacturing requirements in design: The RTM process in aeronautics
A sub-unit of an aeronautical structure (fuselage, fin, wing, etc.) consists of a set of components fixed rigidly together. One of todayâs major industrial challenges is to produce these sub-units out of composite materials in order to increase the level of integration and reduce and cost. This article describes a procedure to assist in the industrialisation of aeronautical components produced from composite materials in a design for manufacturing context. In a multi-expertise approach, the problem of optimising integration is combined with the feasibility of injection for the Resin Transfer Molding process. This approach then takes into account admissible manufacturing deviations, defined from a classification of the structure parts. The limits set for admissible deviations guarantee the mechanical behaviour of the assembled component and the requirements of the assembly as a whole. Finally, an industrialisation solutions space is defined. A constraint satisfaction problem solver is used to carry out this research with a spar from a horizontal plane in an aircraft used to illustrate the procedure
Robust forecasts on fundamental physics from the foreground-obscured, gravitationally-lensed CMB polarization
[Abridged] Recent results from the BICEP, Keck Array and Planck
Collaborations demonstrate that Galactic foregrounds are an unavoidable
obstacle in the search for evidence of inflationary gravitational waves in the
cosmic microwave background (CMB) polarization. Beyond the foregrounds, the
effect of lensing by intervening large-scale structure further obscures all but
the strongest inflationary signals permitted by current data. With a plethora
of ongoing and upcoming experiments aiming to measure these signatures, careful
and self-consistent consideration of experiments' foreground- and
lensing-removal capabilities is critical in obtaining credible forecasts of
their performance. We investigate the capabilities of instruments such as
Advanced ACTPol, BICEP3 and Keck Array, CLASS, EBEX10K, PIPER, Simons Array,
SPT-3G and SPIDER, and projects as COrE+, LiteBIRD-ext, PIXIE and Stage IV, to
clean contamination due to polarized synchrotron and dust from raw
multi-frequency data, and remove lensing from the resulting co-added CMB maps
(either using iterative CMB-only techniques or through cross-correlation with
external data). Incorporating these effects, we present forecasts for the
constraining power of these experiments in terms of inflationary physics, the
neutrino sector, and dark energy parameters. Made publicly available through an
online interface, this tool enables the next generation of CMB experiments to
foreground-proof their designs, optimize their frequency coverage to maximize
scientific output, and determine where cross-experimental collaboration would
be most beneficial. We find that analyzing data from ground, balloon and space
instruments in complementary combinations can significantly improve component
separation performance, delensing, and cosmological constraints over individual
datasets.Comment: 37 pages plus appendices, 15 figures; first two authors contributed
equally to this work; forecasting tool available at http://turkey.lbl.gov.
v4: matches version published in JCAP (with extended dark energy constraints
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