720 research outputs found
The Planck-LFI instrument: analysis of the 1/f noise and implications for the scanning strategy
We study the impact of the 1/f noise on the PLANCK Low Frequency Instrument
(LFI) osbervations (Mandolesi et al 1998) and describe a simple method for
removing striping effects from the maps for a number of different scanning
stategies. A configuration with an angle between telescope optical axis and
spin-axis just less than 90 degrees (namely 85 degress) shows good destriping
efficiency for all receivers in the focal plane, with residual noise
degradation < 1-2 %. In this configuration, the full sky coverage can be
achieved for each channel separately with a 5 degrees spin-axis precession to
maintain a constant solar aspect angle.Comment: submitted to Astronomy and Astrophysics, 12 pages, 15 PostSript
figure
LFI 30 and 44 GHz receivers Back-End Modules
The 30 and 44 GHz Back End Modules (BEM) for the Planck Low Frequency
Instrument are broadband receivers (20% relative bandwidth) working at room
temperature. The signals coming from the Front End Module are amplified, band
pass filtered and finally converted to DC by a detector diode. Each receiver
has two identical branches following the differential scheme of the Planck
radiometers. The BEM design is based on MMIC Low Noise Amplifiers using GaAs
P-HEMT devices, microstrip filters and Schottky diode detectors. Their
manufacturing development has included elegant breadboard prototypes and
finally qualification and flight model units. Electrical, mechanical and
environmental tests were carried out for the characterization and verification
of the manufactured BEMs. A description of the 30 and 44 GHz Back End Modules
of Planck-LFI radiometers is given, with details of the tests done to determine
their electrical and environmental performances. The electrical performances of
the 30 and 44 GHz Back End Modules: frequency response, effective bandwidth,
equivalent noise temperature, 1/f noise and linearity are presented
Validation of the italian version of the behavioral inhibition questionnaire (Biq) for preschool children
Behavioral Inhibition (BI) is a temperamental trait characterized by fear and wariness in reaction to new and unfamiliar stimuli, both social and non-social. BI has been recognized as possible forerunner of anxiety disorders, especially social anxiety and phobia; therefore, its assessment is clinically relevant. The present study aimed to examine the psychometric properties of the Italian adaptation of the Behavioral Inhibition Questionnaire (BIQ), which measures BI in preschool children. The BIQ was completed by 417 Italian parents (230 mothers, 187 fathers) of 270 preschoolers aged 3–5. Confirmatory factor analysis showed a good internal validity: the factorial structure was corresponding to the original six-factor version. Results showed excellent internal consistency, significant item-total correlations, good inter-rater reliability, convergent validity (by correlating the BIQ with the Italian Questionnaires of Temperament-QUIT, the Anxiety-Shy Conner’s Scale and the Laboratory Temperament Assessment Battery) and discriminant validity (i.e., no correlation with Conners’ ADHD scale). Significant correlations emerged between BI indexes and total BIQ scores of parents and maternal (but not paternal) versions of the questionnaire. Altogether, the results are promising and consistent with previous validation studies, suggesting the BIQ as a reliable and valid measure for evaluating parents’ perception of BI in Italian preschoolers
Upper Limits on the Continuum Emission from Geminga at 74 and 326 MHz
We report a search for radio continuum emission from the gamma-ray pulsar
Geminga. We have used the VLA to image the location of the optical counterpart
of Geminga at 74 and 326 MHz. We detect no radio counterpart. We derive upper
limits to the pulse-averaged flux density of Geminga, taking diffractive
scintillation into account. We find that diffractive scintillation is probably
quenched at 74 MHz and does not influence our upper limit, S < 56 mJy
(2\sigma), but that a 95% confidence level at 326 MHz is S < 5 mJy. Owing to
uncertainties on the other low-frequency detections and the possibility of
intrinsic variability or extrinsic variability (refractive interstellar
scintillation) or both, our non-detections are nominally consistent with these
previous detections.Comment: 8 pages, LaTeX2e with AASTeX 4.0, 3 figures; to be published in Ap
High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths
We report on the design, fabrication and testing of a set of high performance
corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced
prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission.
The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70
GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and
by electro-formation at higher frequencies. The measured performances on side
lobes and return loss meet the stringent Planck requirements over the large
(20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape
and side lobes levels of the dual profiled designs has been demonstrated.Comment: 16 pages, 7 figures, accepted for publication in Experimental
Astronom
Probing Cosmic Strings with Satellite CMB measurements
We study the problem of searching for cosmic string signal patterns in the
present high resolution and high sensitivity observations of the Cosmic
Microwave Background (CMB). This article discusses a technique capable of
recognizing Kaiser-Stebbins effect signatures in total intensity anisotropy
maps, and shows that the biggest factor that produces confusion is represented
by the acoustic oscillation features of the scale comparable to the size of
horizon at recombination. Simulations show that the distribution of null
signals for pure Gaussian maps converges to a distribution, with
detectability threshold corresponding to a string induced step signal with an
amplitude of about 100 \muK which corresponds to a limit of roughly . We study the statistics of spurious detections caused by
extra-Galactic and Galactic foregrounds. For diffuse Galactic foregrounds,
which represents the dominant source of contamination, we derive sky masks
outlining the available region of the sky where the Galactic confusion is
sub-dominant, specializing our analysis to the case represented by the
frequency coverage and nominal sensitivity and resolution of the Planck
experiment.Comment: 14 pages, 3 figures, to be published in JCA
Planck LFI: Comparison Between Galaxy Straylight Contamination and other Systematic Effects
The straylight contamination due to the Galactic emission (GSC, Galaxy
Straylight Contamination) entering at large angles from the antenna centre
direction may be one of the most critical sources of systematic effects in
observations of the cosmic microwave background (CMB) anisotropies by future
satellite missions like {\sc Planck} and MAP. We describe here different
methods to evaluate the impact of this effect and compare it with other
systematics of instrumental and astrophysical origin. The contributions within
few degrees from the beam centre dominate the GSC near the Galaxy plane. The
antenna sidelobes at intermediate and large angles from the beam centre
dominate the GSC at medium and high Galactic latitudes. We find a GSC peak at
K and a GSC angular power spectrum above that of the white noise
for multipoles \ell \lsim 10 albeit smaller than that of CMB anisotropies by
a factor larger than . Although the GSC is largest at low Galactic
latitudes, the contamination produced by far pattern features at medium and
high Galactic latitudes, peaking at K, has to be carefully
investigated, because the combination of low amplitude of Galaxy emission in
those regions with the extremely good nominal {\sc Planck} sensitivity
naturally makes high Galactic latitude areas the targets for unprecedentedly
precise estimation of cosmological CMB anisotropy.Comment: 15 pages, submitted to A&
On the performance of Planck-like telescopes versus mirror aperture
Future space mission like MAP and PLANCK will be able to shade new light on our knowledge of the Universe thanks to their unprecedented angular resolution and sensitivity. The far sub-degree angular resolution is obtained coupling usual detectors, radiometers and/or bolometers, to an optical system, namely a telescope. The wealth of cosmological information is encoded at high l values (~1000) which can be reached with resolution of about 10′. Distortions of the main beam resulting from the current focal plane arrangement and the optical design of the PLANCK satellite will degrade angular resolution and sensitivity per resolution element possibly compromising the final results. The detailed design of the PLANCK telescope is continuously changing with the aim of optimizing its performance. In the present work we present a methodological study on the relation between telescope optical design, focal plane arrangement and optical performances, focussing on the dependence of angular resolution on primary mirror aperture. Different independent approaches have been developed to quantify the impact of main beam distortions on cosmic microwave background (CMB) science yielding nearly the same results. The so-called PHASE-A telescope is unacceptable with respect mission main goals. Larger telescopes (namely with effective aperture ≳ 1.5 m) are therefore preferable. This paper is based on the PLANCK LFI activities.
Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument
We give a description of the design, construction and testing of the 30 and
44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the
Planck mission to be launched in 2009. The scientific requirements of the
mission determine the performance parameters to be met by the FEMs, including
their linear polarization characteristics.
The FEM design is that of a differential pseudo-correlation radiometer in
which the signal from the sky is compared with a 4-K blackbody load. The Low
Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High
Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel
phase-switch design which gives excellent amplitude and phase match across the
band.
The noise temperature requirements are met within the measurement errors at
the two frequencies. For the most sensitive LNAs, the noise temperature at the
band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively.
For some of the FEMs, the noise temperature is still falling as the ambient
temperature is reduced to 20 K. Stability tests of the FEMs, including a
measurement of the 1/f knee frequency, also meet mission requirements.
The 30 and 44 GHz FEMs have met or bettered the mission requirements in all
critical aspects. The most sensitive LNAs have reached new limits of noise
temperature for HEMTs at their band centres. The FEMs have well-defined linear
polarization characteristcs.Comment: 39 pages, 33 figures (33 EPS files), 12 tables. Planck LFI technical
papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
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