Building the analytical response in frequency domain of AC biased bolometers Application to Planck/HFI

Context: Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for {\nu} < 1 Hz, and secondly the Analog To digital Converter (ADC) component had been insufficiently characterized on-ground. These two problems require an exquisite knowledge of detector response. However bolometers have highly nonlinear characteristics, coming from their electrical and thermal coupling making them very difficult to modelize. Goal: We present a method to build the analytical transfer function in frequency domain which describe the voltage response of an Alternative Current (AC) biased bolometer to optical excitation, based on the standard bolometer model. This model is built using the setup of the Planck/HFI instrument and offers the major improvement of being based on a physical model rather than the currently in use had-hoc model based on Direct Current (DC) bolometer theory. Method: The analytical transfer function expression will be presented in matrix form. For this purpose, we build linearized versions of the bolometer electro thermal equilibrium. And a custom description of signals in frequency is used to solve the problem with linear algebra. The model performances is validated using time domain simulations. Results: The provided expression is suitable for calibration and data process- ing. It can also be used to provide constraints for fitting optical transfer function using real data from steady state electronic response and optical response. The accurate description of electronic response can also be used to improve the ADC nonlinearity correction for quickly varying optical signals.Comment: 20 pages, 10 figure

A novel estimator of the polarization amplitude from normally distributed Stokes parameters

We propose a novel estimator of the polarization amplitude from a single measurement of its normally distributed $(Q,U)$ Stokes components. Based on the properties of the Rice distribution and dubbed 'MAS' (Modified ASymptotic), it meets several desirable criteria:(i) its values lie in the whole positive region; (ii) its distribution is continuous; (iii) it transforms smoothly with the signal-to-noise ratio (SNR) from a Rayleigh-like shape to a Gaussian one; (iv) it is unbiased and reaches its components' variance as soon as the SNR exceeds 2; (v) it is analytic and can therefore be used on large data-sets. We also revisit the construction of its associated confidence intervals and show how the Feldman-Cousins prescription efficiently solves the issue of classical intervals lying entirely in the unphysical negative domain. Such intervals can be used to identify statistically significant polarized regions and conversely build masks for polarization data. We then consider the case of a general $[Q,U]$ covariance matrix and perform a generalization of the estimator that preserves its asymptotic properties. We show that its bias does not depend on the true polarization angle, and provide an analytic estimate of its variance. The estimator value, together with its variance, provide a powerful point-estimate of the true polarization amplitude that follows an unbiased Gaussian distribution for a SNR as low as 2. These results can be applied to the much more general case of transforming any normally distributed random variable from Cartesian to polar coordinates.Comment: Accepted by MNRA

Apoyo social percibido por familiares de niños con Leucemia Linfoblástica Aguda

Introduction: social support has a great impact on the processes of adaptation to illness, recovery and rehabilitation. The perceived dimension of this category is a cognitive assessment that describes the degree to which the subject perceives the existence of sufficient and adequate support-providing relationships.Objective: to study in depth the contribution of social support perceived by family members to the comprehensive care of the child with acute lymphoblastic leukemia.Methods:  a bibliographic review was carried out using national and international sources specialized in the subject based on a reflexive analysis from a theoretical point of view.Results: many investigations agree that the true social support is the perceived one, arguing that if the subject does not perceive the help offered or the external resources that are available to him/her, these will hardly influence his/her health and well-being, especially in the case of relatives of children with diseases such as Acute Lymphoblastic Leukemia.Conclusions: knowledge of the social support perceived by relatives allows us to obtain a more realistic view of the felt needs of families and children with acute lymphoblastic leukemia and contributes to the improvement of comprehensive care. Introducción: el apoyo social tiene un gran impacto en los procesos de adaptación a la enfermedad, la recuperación y rehabilitación. La dimensión percibida de esta categoría es una valoración cognitiva que describe el grado en que el sujeto percibe la existencia de relaciones proveedoras de apoyo suficientes y adecuadas.Objetivo: profundizar en la contribución del apoyo social percibido por familiares, a la atención integral del niño con leucemia linfoblástica aguda.Métodos: se realizó una revisión bibliográfica a través de fuentes nacionales e internacionales especializadas en el tema, se tomó como punto de partida un análisis reflexivo desde una visión teórica.Resultados: muchas investigaciones coinciden que el verdadero apoyo social es el percibido, argumentan que si el sujeto no percibe la ayuda ofrecida o los recursos externos que están a su disposición, difícilmente influirán sobre su salud y bienestar, especialmente en el caso de familiares de niños con enfermedades como la leucemia linfoblástica aguda.Conclusiones: el conocimiento del apoyo social percibido por familiares permite obtener la visión más real de las necesidades sentidas de las familias y los niños con leucemia linfoblástica aguda y contribuye al perfeccionamiento de la atención integral

Simulating the impact of dust cooling on the statistical properties of the intracluster medium

From the first stages of star and galaxy formation, non-gravitational processes such as ram pressure stripping, SNs, galactic winds, AGNs, galaxy-galaxy mergers, etc... lead to the enrichment of the IGM in stars, metals as well as dust, via the ejection of galactic material into the IGM. We know now that these processes shape, side by side with gravitation, the formation and the evolution of structures. We present here hydrodynamic simulations of structure formation implementing the effect of the cooling by dust on large scale structure formation. We focus on the scale of galaxy clusters and study the statistical properties of clusters. Here we present our results on the $T_X-M$ and the $L_X-M$ scaling relations which exhibit changes on both the slope and normalization when adding cooling by dust to the standard radiative cooling model. For example, the normalization of the $T_X-M$ relation changes only by a maximum of 2% at $M=10^{14}$ M$_\odot$ whereas the normalization of the $L_X-T_X$ changes by as much as 10% at $T_X=1$ keV for models that including dust cooling. Our study shows that the dust is an added non-gravitational process that contributes shaping the thermodynamical state of the hot ICM gas.Comment: 11 pages, 4 figures, ASR in pres

Henri Cartier-Bresson, ‘Public Intellectual’?

Two issues of Paris Match and the book Moscou vu par Henri Cartier-Bresson feature some of the photographer’s most striking reportages, made during a visit to the Soviet Union. That the trip in question took place in 1954, a few weeks after Jean-Paul Sartre and Simone de Beauvoir traveled to the USSR themselves, is not completely fortuitous. At the time, an apparent convergence of political history, the history of photojournalism, and the history of ideas resulted in a kind of cross-collaboration between the figures of the writer/public intellectual and the artist/photographer. Generic and axiological conditions coalesced around the literary genre of the travelogue in the Soviet Union and Sartre’s idea of the responsibility of the writer confronting his times. From that standpoint, a reporter or photographer had to be more than a visual witness: a full participant in the debates on history and a full-fledged intellectual figure, without, at the same time, ever ceasing to be an artist. Was Cartier-Bresson a privileged protagonist in this convergence

The Infrared Luminosity of Galaxy Clusters

The aim of this study is to quantify the infrared luminosity of clusters as a function of redshift and compare this with the X-ray luminosity. This can potentially constrain the origin of the infrared emission to be intracluster dust and/or dust heated by star formation in the cluster galaxies. We perform a statistical analysis of a large sample of galaxy clusters selected from existing databases and catalogues.We coadd the infrared IRAS and X-ray RASS images in the direction of the selected clusters within successive redshift intervals up to z = 1. We find that the total infrared luminosity is very high and on average 20 times higher than the X-ray luminosity. If all the infrared luminosity is to be attributed to emission from diffuse intracluster dust, then the IR to X-ray ratio implies a dust-to-gas mass abundance of 5e-4. However, the infrared luminosity shows a strong enhancement for 0.1 < z < 1, which cannot be attributed to cluster selection effects. We show that this enhancement is compatible with a star formation rate in the member galaxies that is typical of the central Mpc of the Coma cluster at z = 0 and evolves with the redshift as (1+z)^5. It is likely that most of the infrared luminosity that we measure is generated by the ongoing star formation in the member galaxies. From theoretical predictions calibrated on extinction measurements (dust mass abundance equal to 1e-5), we expect only a minor contribution, of a few percent, from intracluster dust.Comment: 9 pages, 7 figures, accepted july 31st 2008 for publication in Astronomy and Astrophysics, language improved for this versio

Three-Dimensional GPU-Accelerated Active Contours for Automated Localization of Cells in Large Images

Cell segmentation in microscopy is a challenging problem, since cells are often asymmetric and densely packed. This becomes particularly challenging for extremely large images, since manual intervention and processing time can make segmentation intractable. In this paper, we present an efficient and highly parallel formulation for symmetric three-dimensional (3D) contour evolution that extends previous work on fast two-dimensional active contours. We provide a formulation for optimization on 3D images, as well as a strategy for accelerating computation on consumer graphics hardware. The proposed software takes advantage of Monte-Carlo sampling schemes in order to speed up convergence and reduce thread divergence. Experimental results show that this method provides superior performance for large 2D and 3D cell segmentation tasks when compared to existing methods on large 3D brain images

Polarization measurements analysis II. Best estimators of polarization fraction and angle

With the forthcoming release of high precision polarization measurements, such as from the Planck satellite, it becomes critical to evaluate the performance of estimators for the polarization fraction and angle. These two physical quantities suffer from a well-known bias in the presence of measurement noise, as has been described in part I of this series. In this paper, part II of the series, we explore the extent to which various estimators may correct the bias. Traditional frequentist estimators of the polarization fraction are compared with two recent estimators: one inspired by a Bayesian analysis and a second following an asymptotic method. We investigate the sensitivity of these estimators to the asymmetry of the covariance matrix which may vary over large datasets. We present for the first time a comparison among polarization angle estimators, and evaluate the statistical bias on the angle that appears when the covariance matrix exhibits effective ellipticity. We also address the question of the accuracy of the polarization fraction and angle uncertainty estimators. The methods linked to the credible intervals and to the variance estimates are tested against the robust confidence interval method. From this pool of estimators, we build recipes adapted to different use-cases: build a mask, compute large maps, and deal with low S/N data. More generally, we show that the traditional estimators suffer from discontinuous distributions at low S/N, while the asymptotic and Bayesian methods do not. Attention is given to the shape of the output distribution of the estimators, and is compared with a Gaussian. In this regard, the new asymptotic method presents the best performance, while the Bayesian output distribution is shown to be strongly asymmetric with a sharp cut at low S/N.Finally, we present an optimization of the estimator derived from the Bayesian analysis using adapted priors