665 research outputs found
Cosmic shear requirements on the wavelength dependence of telescope point spread functions
Cosmic shear requires high precision measurement of galaxy shapes in the presence of the observational point spread function (PSF) that smears out the image. The PSF must therefore be known for each galaxy to a high accuracy. However, for several reasons, the PSF is usually wavelength dependent; therefore, the differences between the spectral energy distribution of the observed objects introduce further complexity. In this paper, we investigate the effect of the wavelength dependence of the PSF, focusing on instruments in which the PSF size is dominated by the diffraction limit of the telescope and which use broad-band filters for shape measurement. We first calculate biases on cosmological parameter estimation from cosmic shear when the stellar PSF is used uncorrected. Using realistic galaxy and star spectral energy distributions and populations and a simple three-component circular PSF, we find that the colour dependence must be taken into account for the next generation of telescopes. We then consider two different methods for removing the effect: (i) the use of stars of the same colour as the galaxies and (ii) estimation of the galaxy spectral energy distribution using multiple colours and using a telescope model for the PSF. We find that both of these methods correct the effect to levels below the tolerances required for per cent level measurements of dark energy parameters. Comparison of the two methods favours the template-fitting method because its efficiency is less dependent on galaxy redshift than the broad-band colour method and takes full advantage of deeper photometr
Cosmic shear requirements on the wavelength-dependence of telescope point spread functions
Cosmic shear requires high precision measurement of galaxy shapes in the
presence of the observational Point Spread Function (PSF) that smears out the
image. The PSF must therefore be known for each galaxy to a high accuracy.
However, for several reasons, the PSF is usually wavelength dependent,
therefore the differences between the spectral energy distribution of the
observed objects introduces further complexity. In this paper we investigate
the effect of the wavelength-dependence of the PSF, focusing on instruments in
which the PSF size is dominated by the diffraction-limit of the telescope and
which use broad-band filters for shape measurement.
We first calculate biases on cosmological parameter estimation from cosmic
shear when the stellar PSF is used uncorrected. Using realistic galaxy and star
spectral energy distributions and populations and a simple three-component
circular PSF we find that the colour-dependence must be taken into account for
the next generation of telescopes. We then consider two different methods for
removing the effect (i) the use of stars of the same colour as the galaxies and
(ii) estimation of the galaxy spectral energy distribution using multiple
colours and using a telescope model for the PSF. We find that both of these
methods correct the effect to levels below the tolerances required for per-cent
level measurements of dark energy parameters. Comparison of the two methods
favours the template-fitting method because its efficiency is less dependent on
galaxy redshift than the broad-band colour method and takes full advantage of
deeper photometry.Comment: 10 pages, 8 figures, version accepted for publication in MNRA
CMB component separation by parameter estimation
We propose a solution to the CMB component separation problem based on
standard parameter estimation techniques. We assume a parametric spectral model
for each signal component, and fit the corresponding parameters pixel by pixel
in a two-stage process. First we fit for the full parameter set (e.g.,
component amplitudes and spectral indices) in low-resolution and high
signal-to-noise ratio maps using MCMC, obtaining both best-fit values for each
parameter, and the associated uncertainty. The goodness-of-fit is evaluated by
a chi^2 statistic. Then we fix all non-linear parameters at their
low-resolution best-fit values, and solve analytically for high-resolution
component amplitude maps. This likelihood approach has many advantages: The
fitted model may be chosen freely, and the method is therefore completely
general; all assumptions are transparent; no restrictions on spatial variations
of foreground properties are imposed; the results may be rigorously monitored
by goodness-of-fit tests; and, most importantly, we obtain reliable error
estimates on all estimated quantities. We apply the method to simulated Planck
and six-year WMAP data based on realistic models, and show that separation at
the muK level is indeed possible in these cases. We also outline how the
foreground uncertainties may be rigorously propagated through to the CMB power
spectrum and cosmological parameters using a Gibbs sampling technique.Comment: 20 pages, 10 figures, submitted to ApJ. For a high-resolution
version, see http://www.astro.uio.no/~hke/docs/eriksen_et_al_fgfit.p
Mecanismos de tolerância da variedade de milho "Saracura" (BRS 4154) ao alagamento.
Esta revisao tem por objetivo discutir mecanismos de tolerancia desenvolvidos por plantula da variedade de milho "Saracura" (BRS 4154), que possui, como principal caracteristica, tolerancia a periodos intermitentes de encharcamento do solo. Os primeiros estudos de analise de tolerancia a baixa disponibilidade de oxigenio no meio, sob condicoes controladas, em sala de crescimento, confirmaram essa caracteristica, ao revelar que as plantulas suportam ate quatro dias de hipoxia sem nenhum dano aparente. A partir dai, apresentaram na regiao do mesocotilo, uma regiao translucida, caracteristica de lise celular, a qual evoluiu para uma constricao, como o prolongamento do estresse, causando murcha, tombamento e morte das plantulas. Estudos posteriores revelaram que a deficiencia de oxigenio provocou uma intensa e irreversiviel degradacao da parede, como resultado de uma elevacao na acao, principalmente, das enzimas poligalacturonase de celulase. As causas da tolerancia do milho "Saracura" foram atribuidas a uma resistencia ao ataque de enzimas de degradacao da parede celular, ao desenvolvimento de aerenquimas tanto no colmo quanto nas raizes e a uma alta capacidade de recuperacao da fotossintese apos periodos de alagamento. Foi observado que, na germinacao, o calcio diminuiu o tamanho das plantulas e aumentou a sua tolerancia ao alagamento, retardando o aparecimento da constricao do mesocotilo. Durante a germinacao, na presenca desse elemento, as reservas de carboidratos ficaram preservadas na cariopse, atrasando o desenvolvimento das plantulas e, quando em condicoes de alagamento, essas foram alocadas e utilizadas, permitindo a manutencao do metabolismo celular por mais tempo. Ficou constatado, tambem, que o calcio aumentou a estabilidade da parede celular e induziu um ajustamento osmotico, pelo aumento na concentracao de aminoacidos, principalmente a prolina
Wide-Field InfraRed Survey Telescope (WFIRST) Final Report
In December 2010, NASA created a Science Definition Team (SDT) for WFIRST,
the Wide Field Infra-Red Survey Telescope, recommended by the Astro 2010
Decadal Survey as the highest priority for a large space mission. The SDT was
chartered to work with the WFIRST Project Office at GSFC and the Program Office
at JPL to produce a Design Reference Mission (DRM) for WFIRST. Part of the
original charge was to produce an interim design reference mission by mid-2011.
That document was delivered to NASA and widely circulated within the
astronomical community. In late 2011 the Astrophysics Division augmented its
original charge, asking for two design reference missions. The first of these,
DRM1, was to be a finalized version of the interim DRM, reducing overall
mission costs where possible. The second of these, DRM2, was to identify and
eliminate capabilities that overlapped with those of NASA's James Webb Space
Telescope (henceforth JWST), ESA's Euclid mission, and the NSF's ground-based
Large Synoptic Survey Telescope (henceforth LSST), and again to reduce overall
mission cost, while staying faithful to NWNH. This report presents both DRM1
and DRM2.Comment: 102 pages, 57 figures, 17 table
Software defect prediction: do different classifiers find the same defects?
Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.During the last 10 years, hundreds of different defect prediction models have been published. The performance of the classifiers used in these models is reported to be similar with models rarely performing above the predictive performance ceiling of about 80% recall. We investigate the individual defects that four classifiers predict and analyse the level of prediction uncertainty produced by these classifiers. We perform a sensitivity analysis to compare the performance of Random Forest, Naïve Bayes, RPart and SVM classifiers when predicting defects in NASA, open source and commercial datasets. The defect predictions that each classifier makes is captured in a confusion matrix and the prediction uncertainty of each classifier is compared. Despite similar predictive performance values for these four classifiers, each detects different sets of defects. Some classifiers are more consistent in predicting defects than others. Our results confirm that a unique subset of defects can be detected by specific classifiers. However, while some classifiers are consistent in the predictions they make, other classifiers vary in their predictions. Given our results, we conclude that classifier ensembles with decision-making strategies not based on majority voting are likely to perform best in defect prediction.Peer reviewedFinal Published versio
Planck pre-launch status: Low Frequency Instrument calibration and expected scientific performance
We give the calibration and scientific performance parameters of the Planck
Low Frequency Instrument (LFI) measured during the ground cryogenic test
campaign. These parameters characterise the instrument response and constitute
our best pre-launch knowledge of the LFI scientific performance. The LFI shows
excellent stability and rejection of instrumental systematic effects;
measured noise performance shows that LFI is the most sensitive instrument of
its kind. The set of measured calibration parameters will be updated during
flight operations through the end of the mission.Comment: Accepted for publications in Astronomy and Astrophysics. Astronomy &
Astrophysics, 2010 (acceptance date: 12 Jan 2010
Angular Power Spectra of the Millimeter Wavelength Background Light from Dusty Star-forming Galaxies with the South Pole Telescope
We use data from the first 100 square-degree field observed by the South Pole
Telescope (SPT) in 2008 to measure the angular power spectrum of temperature
anisotropies contributed by the background of dusty star-forming galaxies
(DSFGs) at millimeter wavelengths. From the auto and cross-correlation of 150
and 220 GHz SPT maps, we significantly detect both Poisson distributed and, for
the first time at millimeter wavelengths, clustered components of power from a
background of DSFGs. The spectral indices between 150 and 220 GHz of the
Poisson and clustered components are found to be 3.86 +- 0.23 and 3.8 +- 1.3
respectively, implying a steep scaling of the dust emissivity index beta ~ 2.
The Poisson and clustered power detected in SPT, BLAST (at 600, 860, and 1200
GHz), and Spitzer (1900 GHz) data can be understood in the context of a simple
model in which all galaxies have the same graybody spectrum with dust
emissivity index of beta = 2 and dust temperature T_d = 34 K. In this model,
half of the 150 GHz background light comes from redshifts greater than 3.2. We
also use the SPT data to place an upper limit on the amplitude of the kinetic
Sunyaev-Zel'dovich power spectrum at l = 3000 of 13 uK^2 at 95% confidence.Comment: 18 pages, 9 figure
Field propagation-induced directionality of carrier-envelope phase-controlled photoemission from nanospheres
Near-fields of non-resonantly laser-excited nanostructures enable strong localization of ultrashort light fields and have opened novel routes to fundamentally modify and control electronic strong-field processes. Harnessing spatiotemporally tunable near-fields for the steering of sub-cycle electron dynamics may enable ultrafast optoelectronic devices and unprecedented control in the generation of attosecond electron and photon pulses. Here we utilize unsupported sub-wavelength dielectric nanospheres to generate near-fields with adjustable structure and study the resulting strong-field dynamics via photoelectron imaging. We demonstrate field propagation-induced tunability of the emission direction of fast recollision electrons up to a regime, where nonlinear charge interaction effects become dominant in the acceleration process. Our analysis supports that the timing of the recollision process remains controllable with attosecond resolution by the carrier-envelope phase, indicating the possibility to expand near-field-mediated control far into the realm of high-field phenomena
- …