Search results for "Filter"
showing 10 items of 1019 documents
Implications of the Semigeostrophic Nature of Rossby Waves for Rossby Wave Packet Detection
2015
Abstract Upper-tropospheric Rossby wave packets have received increased attention recently. In most previous studies wave packets have been detected by computing the envelope of the meridional wind field using either complex demodulation or a Hilbert transform. The latter requires fewer choices to be made and appears, therefore, preferable. However, the Hilbert transform is fraught with a significant problem, namely, a tendency that fragments a single wave packet into several parts. The problem arises because Rossby wave packets show substantial deviations from the almost-plane wave paradigm, a feature that is well represented by semigeostrophic dynamics. As a consequence, higher harmonics …
More on the determination of the coronal heating function from Yohkoh data
2002
Two recent works have analyzed a solar large and steady coronal loop observed with Yohkoh/SXT in two filter passbands to infer the distribution of the heating along it. Priest et al. (2000) modelled the distribution of the temperature obtained from filter ratio method with an analytical approach, and concluded that the heating was uniform along the loop. Aschwanden (2001) found that a uniform heating led to an unreasonably large plasma column depth along the line of sight, and, using a two component loop model, that a footpoint-heated model loop (with a minor cool component) yields more acceptable physical solutions. We revisit the analysis of the same loop system, considering conventional …
On the importance of background subtraction in the analysis of coronal loops observed with TRACE
2010
In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably differen…
Analysis of a multi-wavelength time-resolved observation of a coronal loop
2005
Several items on the diagnostics and interpretation of coronal loop observations are under debate. In this work, we analyze a well-defined loop system detected in a time-resolved observation in several spectral bands. The dataset includes simultaneous images in the TRACE 171 A, 195 A and 284 A bands, and Yohkoh/SXT, and two rasters taken with SoHO/CDS in twelve relevant lines. The loop is initially best visible in the TRACE 195 A filter band, and later in the 171 A filter band, with correspondence with the CDS raster images at log T \~ 6.0-6.1. We have taken as pixel-by-pixel background the latest TRACE, Yohkoh and CDS images where the loop has faded out. We examine the loop morphology evol…
Solc filters in a reflective geometry
2017
We present the realization of a bulk optics birefringent Solc filter in a reflective geometry. This geometry reduces by half the number of required retarders, ensures the same spectral retardance function in pairs of retarders, and helps to make more compact filters. The key element is a quarter-wave Fresnel rhomb located in between the set of retarders and a mirror. Two cases are considered: the first Solc filter uses multiple-order quartz retarders, and the second one uses two liquid-crystal retarders. The latter has the advantage of being tunable via an applied voltage. Experimental results show how to filter the spectral content of a supercontinuum laser.
Improved determination of the β−ν¯e angular correlation coefficient a in free neutron decay with the aSPECT spectrometer
2020
We report on a precise measurement of the electron-antineutrino angular correlation ($a$ coefficient) in free neutron beta-decay from the $a$SPECT experiment. The $a$ coefficient is inferred from the recoil energy spectrum of the protons which are detected in 4$\pi$ by the $a$SPECT spectrometer using magnetic adiabatic collimation with an electrostatic filter. Data are presented from a 100 days run at the Institut Laue Langevin in 2013. The sources of systematic errors are considered and included in the final result. We obtain $a = -0.10430(84)$ which is the most precise measurement of the neutron $a$ coefficient to date. From this, the ratio of axial-vector to vector coupling constants is …
Preliminary Mechanical Characterization of Thermal Filters for the X-IFU Instrument on Athena
2018
The X-ray Integral Field Unit (X-IFU) is one of the two instruments of the Athena astrophysics space mission approved by ESA in the Cosmic Vision Science Program. The X-IFU consists of a large array of TES microcalorimeters that will operate at ~ 50 mK inside a sophisticated cryostat. A set of thin filters, highly transparent to X-rays, will be mounted on the cryostat thermal shields in order to attenuate the IR radiative load, to attenuate RF electromagnetic interferences, and to protect the detector from contamination. In this paper, we present the current thermal filters design, describe the filter samples developed/procured so far, and present preliminary results from the ongoing charac…
Far-field light imaging in the presence of atmospheric turbulence with rotating anti-phase apertures: Theoretical investigation
2017
We investigated the diffraction of far-field light objects in the presence of turbulence formed by an optical system with a rotating anti-phase mask. This mask facilitates to detect the position of faint companion in every direction around the bright companion. In the presence of atmospheric turbulence, diffraction images of distant objects are beyond the diffraction limits, the proposed phase shift mask has a merit to compensate the turbulence results high contrast astronomical imaging under partially coherent light illumination and it is proficient to increase the resolution limits in a Sparrow criterion sense. In this approach, we demonstrated the mask fabrication in laboratory condition…
Hybrid (refractive-diffractive) Fourier processor: A novel optical architecture for achromatic processing with broadband point-source illumination
1998
We report on an achromatic Fourier processor constituted basically by a quasi-wavelength-independent imaging forming system whose first half performs an achromatic Fourier transform of the colour input. The novel optical architecture, only formed by a small number of diffractive and refractive lenses, works under white-light point-source illumination and provides an intermediate achromatic real Fraunhofer plane and a final colour image without chromatic distortion. In this way, our optical processor performs simultaneously, with a single filter, the same spatial filtering operation for all the spectral components of the broadband illumination. The practical capabilities of our proposal are …
Implementation and Performance of the Signal Reconstruction in the ATLAS Hadronic Tile Calorimeter
2012
AbstractThe Tile Calorimeter (TileCal) for the ATLAS experiment at the CERN Large Hadron Collider (LHC) is currently taking data with proton-proton collisions. The Tile Calorimeter is a sampling calorimeter with steel as absorber and scintillators as active medium. The scintillators are read-out by wavelength shifting fibers coupled to photomultiplier tubes (PMT). The analogue signals from the PMTs are amplified, shaped and digitized by sampling the signal every 25ns. The TileCal front-end electronics allows to read-out the signals produced by about 10000 channels measuring energies ranging from ∼30 MeV to ∼2 TeV. The read-out system is designed to reconstruct the data in real-time fulfilli…