290 research outputs found
Characteristics and energy dependence of recurrent galactic cosmic-ray flux depressions and of a forbush decrease with LISA Pathfinder
The final publication is available at IOS Press through http://dx.doi.org/10.3847/1538-4357/aaa774Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder, meant for subsystems diagnostics, was devoted to the measurement of GCR and solar energetic particle integral fluxes above 70 MeV n-1 up to 6500 counts s-1. PD data were gathered with a sampling time of 15 s. Characteristics and energy dependence of GCR flux recurrent depressions and of a Forbush decrease dated 2016 August 2 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections is also discussed.Peer ReviewedPreprin
Measuring the LISA test mass magnetic proprieties with a torsion pendulum
Achieving the low frequency LISA sensitivity requires that the test masses
acting as the interferometer end mirrors are free-falling with an unprecedented
small degree of deviation. Magnetic disturbances, originating in the
interaction of the test mass with the environmental magnetic field, can
significantly deteriorate the LISA performance and can be parameterized through
the test mass remnant dipole moment and the magnetic susceptibility
. While the LISA test flight precursor LTP will investigate these effects
during the preliminary phases of the mission, the very stringent requirements
on the test mass magnetic cleanliness make ground-based characterization of its
magnetic proprieties paramount. We propose a torsion pendulum technique to
accurately measure on ground the magnetic proprieties of the LISA/LTP test
masses.Comment: 6 pages, 3 figure
Forbush decreases and <2 day GCR flux non-recurrent variations studied with LISA pathfinder
Non-recurrent short-term variations of the galactic cosmic-ray (GCR) flux above 70 MeV n-1 were observed between 2016 February 18 and 2017 July 3 on board the European Space Agency LISA Pathfinder (LPF) mission orbiting around the Lagrange point L1 at 1.5 × 106 km from Earth. The energy dependence of three Forbush decreases is studied and reported here. A comparison of these observations with others carried out in space down to the energy of a few tens of MeV n-1 shows that the same GCR flux parameterization applies to events of different intensity during the main phase. FD observations in L1 with LPF and geomagnetic storm occurrence are also presented. Finally, the characteristics of GCR flux non-recurrent variations (peaks and depressions) of duration <2 days and their association with interplanetary structures are investigated. It is found that, most likely, plasma compression regions between subsequent corotating high-speed streams cause peaks, while heliospheric current sheet crossing causes the majority of the depressions.Peer ReviewedPostprint (published version
An automated method based on LATEX for the realization of accessible PDF documents containing formulae
Time domain maximum likelihood parameter estimation in LISA Pathfinder Data Analysis
LISA is the upcoming space-based Gravitational Wave telescope. LISA
Pathfinder, to be launched in the coming years, will prove and verify the
detection principle of the fundamental Doppler link of LISA on a flight
hardware identical in design to that of LISA. LISA Pathfinder will collect a
picture of all noise disturbances possibly affecting LISA, achieving the
unprecedented pureness of geodesic motion necessary for the detection of
gravitational waves. The first steps of both missions will crucially depend on
a very precise calibration of the key system parameters. Moreover, robust
parameters estimation is of fundamental importance in the correct assessment of
the residual force noise, an essential part of the data processing for LISA. In
this paper we present a maximum likelihood parameter estimation technique in
time domain being devised for this calibration and show its proficiency on
simulated data and validation through Monte Carlo realizations of independent
noise runs. We discuss its robustness to non-standard scenarios possibly
arising during the real-life mission, as well as its independence to the
initial guess and non-gaussianities. Furthermore, we apply the same technique
to data produced in mission-like fashion during operational exercises with a
realistic simulator provided by ESA.Comment: 16 pages (two columns), 15 figures, 5 tables, submitted to Phys. Rev.
Axessibility: a LaTeX Package for Mathematical Formulae Accessibility in PDF Documents
Accessing mathematical formulae within digital documents is challenging for blind people. In particular, document formats designed for printing, such as PDF, structure math content for visual access only. While accessibility features exist to present PDF content non-visually, formulae support is limited to providing replacement text that can be read by a screen reader or displayed on a braille bar. However, the operation of inserting replacement text is left to document authors, who rarely provide such content. Furthermore, at best, description of the formulae are provided. Thus, conveying detailed understanding of complex formulae is nearly impossible. In this contribution we report our ongoing research on Axessibility, a LATEX package framework that automates the process of making mathematical formulae accessible by providing the formulae LATEX code as PDF replacement text. Axessibility is coupled with external scripts to automate its integration in existing documents, expand user shorthand macros to standard LATEX representation, and custom screen reader dictionaries that improve formulae reading on screen readers
Parameter estimation in LISA Pathfinder operational exercises
The LISA Pathfinder data analysis team has been developing in the last years
the infrastructure and methods required to run the mission during flight
operations. These are gathered in the LTPDA toolbox, an object oriented MATLAB
toolbox that allows all the data analysis functionalities for the mission,
while storing the history of all operations performed to the data, thus easing
traceability and reproducibility of the analysis. The parameter estimation
methods in the toolbox have been applied recently to data sets generated with
the OSE (Off-line Simulations Environment), a detailed LISA Pathfinder
non-linear simulator that will serve as a reference simulator during mission
operations. These operational exercises aim at testing the on-orbit experiments
in a realistic environment in terms of software and time constraints. These
simulations, so called operational exercises, are the last verification step
before translating these experiments into tele-command sequences for the
spacecraft, producing therefore very relevant datasets to test our data
analysis methods. In this contribution we report the results obtained with
three different parameter estimation methods during one of these operational
exercises.Comment: 10 pages, 3 figures, prepared for the Proceedings of the 9th Edoardo
Amaldi Conference on Gravitational Waves, JPC
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