223 research outputs found
The Planck-LFI : a Study of Instrumental and Astrophysical Effects
No full textThis thesis aims to address some aspects of the Low Frequency Instrument (LFI) on board
the PLANCK satellite. As for any CMB experiment a great attention has to be devoted
to all the possible systematic effects. Previous experiences in CMB experiments have in
fact demonstrated that the more and the larger are systematic effects which contaminate
the data and which have to be scrubbed in the data analysis, the less robust the final
results will be. It is therefore of great importance, for not degrading the nominal angular
resolution and sensitivity per resolution element, to carefully address and quantify all
potential systematic effects. Through accurate and realistic simulations of PLANCK-LFI
observations we study how LFI performances are affected by some of these systematic
effects and how to control and further reduce these effects.
This thesis is organized as follows. We give a brief overview of the origin of microwave
sky fluctuations, including CMB anisotropy, foreground contaminations originated
within our Galaxy (synchrotron, free-free and dust emission) and extra-galactic
foregrounds (Sunyaev-Zel'dovich effect and point sources fluctuations). Since accurate
simulations are needed, they must include complete and realistic simulated microwave sky
at the various observing frequencies. Unfortunately our present knowledge of foreground
emissions (both galactic and extra-galactic) is far from complete and approximations have
to be made. All these problems are discussed in Chapter 2.
A presentation of the PLANCK mission and its scientific capabilities is reported in
Chapter 3: §3.2 reports on the selected orbit and scanning strategy; §3.3 describes the
adopted telescope configuration and actual focal plane arrangement; §3.4 briefly outlines
the LFI instrument and §3.5 reports LFI scientific capabilities. An introduction to the
systematic effects addressed in this thesis is in §3.6 and the Flight Simulator code is
presented in §3. 7. .
The rest of the work deals with the results from different kinds of PLAN9K-LFI :?imulations.
The off-axis position of the LFI instrument, as in the present baseline, results in
optical aberrations in the angular response function of the instrument. The effect of these
distortions (usually called main-beam distortions since they affect the very central part
of the response function) on the nominal angular resolution is addressed in Chapter 4,
firstly considering a pure CMB sky, and then a more realistic sky including galactic emission.
§4.l uses approximated response functions while "real" optical simulated ones are
considered in §4.4. The effective angular resolution is derived and the loss in capabilities
of cosmological parameters extraction properly quantified. The angular response function of the LFI instrument at large angles out of the central
part is extremely complex and depends not only on the telescope design but also on
the whole optical system (shields, supporting structures, focal plane assembly). Signal
and signal variations entering at large angles from the true direction of observation may
produce errors on CMB measurem~nts. Chapter 5 addresses this issue using a simulated
full pattern of the response function and considering signal coming from our Galaxy (§5.1
and §5.2). The level of this contamination and its spatial distribution on the sky are
discussed in §5.4.
As described in Chapter 2, PLANCK is a spinning space-craft with 1 minute period.
Instrumental drifts occurring on time scales less than the spinning period are possible
sources of systematic artifacts in final data. In general they produce "stripes" in the
final maps. Chapter 6 considers typical instrumental drifts which are mainly due to gain
fluctuations in the LFI amplifiers. A de-striping code for removing these artifacts is
described in §6.6; its performances and possible residual striping are evaluated in §6. 7.
Finally, Chapter 7 overviews simulations results and their implication on the optimization
of the PLANCK design
Cosmological dynamics: from the Eulerian to the Lagrangian frame. Part I. Newtonian approximation
No full textWe analyse the non-linear gravitational dynamics of a pressure-less fluid in the Newtonian limit of General Relativity in both the Eulerian and Lagrangian pictures. Starting from the Newtonian metric in the Poisson gauge, we transform to the synchronous and comoving gauge and obtain the Lagrangian metric within the Newtonian approximation. Our approach is fully non-perturbative, which implies that if our quantities are expanded according to the rules of standard perturbation theory, all terms are exactly recovered at any order in perturbation theory, only provided they are Newtonian. We explicitly show this result up to second order and in both gauges. Our transformation clarifies the meaning of the change of spatial and time coordinates from the Eulerian to the Lagrangian frame in the Newtonian approximation
Post-Newtonian cosmological dynamics of plane-parallel perturbations and back-reaction
No full textWe study the general relativistic non-linear dynamics of self-gravitating irrotational dust in a cosmological setting, adopting the comoving and synchronous gauge, where all the equations can be written in terms of the metric tensor of spatial hyper-surfaces orthogonal to the fluid flow. Performing an expansion in inverse powers of the speed of light, we obtain the post-Newtonian equations, which yield the lowest-order relativistic effects arising during the non-linear evolution. We then specialize our analysis to globally plane-parallel configurations, i.e. to the case where the initial perturbation field depends on a single coordinate. The leading order of our expansion, corresponding to the ``Newtonian background'', is the Zel'dovich approximation, which, for plane-parallel perturbations in the Newtonian limit, represents an exact solution. This allows us to find the exact analytical form for the post-Newtonian metric, thereby providing the post-Newtonian extension of the Zel'dovich solution: this accounts for some relativistic effects, such as the non-Gaussianity of primordial perturbations. An application of our solution in the context of the back-reaction proposal is eventually given, providing a post-Newtonian estimation of kinematical back-reaction, mean spatial curvature, average scale-factor and expansion rate
The Needlet CMB Trispectrum
No full textWe propose a computationally feasible estimator for the needlet trispectrum, which develops earlier work on the bispectrum by Donzelli et al. (2012). Our proposal seems to enjoy a number of useful properties, in particular a) the construction exploits the localization properties of the needlet system, and hence it automatically handles masked regions; b) the procedure incorporates a quadratic correction term to correct for the presence of instrumental noise and sky-cuts; c) it is possible to provide analytic results on its statistical properties, which can serve as a guidance for simulations. The needlet trispectrum we present here provides the natural building blocks for the efficient estimation of nonlinearity parameters on CMB data, and in particular for the third order constants g(N) (L) and tau(N) (L)
IMPACT OF THE 1/fNOISE AND THE ASYMMETRIC BEAM ON NON-GAUSSIANITY SEARCHES WITHPLANCK
No full textWe study the impact of correlated instrumental noise and non-circular antenna beam patterns on primordial non-Gaussianity analysis. The two systematic effects are reproduced in the case of the Planck mission, using Planck-like realistic simulations. The non-Gaussian analysis is conducted with different approaches. First we adopt a blind approach, using the Spherical Mexican Hat Wavelet and the Minkowski functionals, and then a fNL estimator. We look respectively for false primordial non-Gaussian detections and for bias or variance increase in the estimated fNL value. Even if some slight effects are present, we can not observe any significant impact of the 1/f noise and the asymmetric beam on non-Gaussianity searches in the context of the Planck mission
Developing, Validating and Using Internal Ratings: Methodologies and Case Studies
No full textWith a focus on practical applications of biophysical techniques, Biophysical Methods for Biotherapeutics helps formulation and analytical scientists in pharma and biotech better understand and use biophysical methods. Author Tapan K. Das links fundamental biophysics to the process of biopharmaceutical development using a chapter organization according to the steps of the drug development process. The text provides information to help organizations develop short- and long-term strategies for resource investment in biophysical research. © 2010 John Wiley & Sons, Ltd
Secure document management and distribution in an open network environment
No full textThis paper analyzes the problem of secure document management and distribution in an open network environment. Reader and author authentication, document integrity, origin, and privacy are addressed by a public-key based solution which exploits a combination of the PEM format with SSL-enhanced FTP and HTTP servers and clients. The solution is being implemented as part of a project to provide network security to the Italian public administratio
The integration of orthodontic miniscrews under mechanical loading: a pre-clinical study in rabbit
No full textIntroduction:
Orthodontic miniscrews are an increasingly popular choice to achieve absolute anchorage. The temporary use of miniscrews and their recent introduction have limited the debate over the biological aspect of the materials to that of the surface that permeates the field of dental implants. The aim of the present study was to investigate the integration of grade 5 titanium mini-implants with machined or sand blasted acid etched surface (SAE) under mechanical load in a rabbit tibia model of implant integration.
Methods:
A total of 64 miniscrews (Ti6Al4V) of 1.5 mm diameter and 6.5 mm length were inserted in the proximal medial surface of each tibia in eight male rabbits aged 6 months. Each tibia received four miniscrews. A 100 g nickel-titanium coil spring (Neosentalloy) was applied between two miniscrews along the main axis while two miniscrews were left unloaded. The removal torque was measured for loaded and unloaded miniscrews after 12 weeks. Two miniscrews were harvested for histology.
Results:
Removal torque was significantly higher for SAE mini-implants than for machined screws, under both loading conditions. Although no difference in bone to implant contact was observed among the groups, cortical area significantly decreased with both surfaces under loading.
Conclusions:
Our data indicate that SAE miniscrews have higher bone retention than MA miniscrews, although the effects of mechanical loading of these devices on cortical bone require further investigations
Applications of the Gaussian kinematic formula to CMB data analysis
No full textThe Gaussian Kinematic Formula (GKF, see Adler and Taylor (2007,2011)) is an extremely powerful tool allowing for explicit analytic predictions of expected values of Minkowski functionals under realistic experimental conditions for cosmological data collections. In this paper, we implement Minkowski functionals on multipoles and needlet components of CMB fields, thus allowing a better control of cosmic variance and extraction of information on both harmonic and real domains; we then exploit the GKF to provide their expected values on spherical maps, in the presence of arbitrary sky masks, and under nonGaussian circumstances. All our results are validated by numerical experiments, which show a perfect agreement between theoretical predictions and Monte Carlo simulations
Cross-sectional imaging after pancreatic surgery: The dialogue between the radiologist and the surgeon
No full textPancreatic surgery is nowadays considered one of the most complex surgical approaches and not unscathed from complications. After the surgical procedure, cross-sectional imaging is considered the non-invasive reference standard to detect early and late compilations, and consequently to address patients to the best management possible. Contras-enhanced computed tomography (CECT) should be considered the most important and useful imaging technique to evaluate the surgical site. Thanks to its speed, contrast, and spatial resolution, it can help reach the final diagnosis with high accuracy. On the other hand, magnetic resonance imaging (MRI) should be considered as a second-line imaging approach, especially for the evaluation of biliary findings and late complications. In both cases, the radiologist should be aware of protocols and what to look at, to create a robust dialogue with the surgeon and outline a fitted treatment for each patient
- …
