52,192 research outputs found
A Fast and Accurate Algorithm for Spherical Harmonic Analysis on HEALPix Grids with Applications to the Cosmic Microwave Background Radiation
The Hierarchical Equal Area isoLatitude Pixelation (HEALPix) scheme is used
extensively in astrophysics for data collection and analysis on the sphere. The
scheme was originally designed for studying the Cosmic Microwave Background
(CMB) radiation, which represents the first light to travel during the early
stages of the universe's development and gives the strongest evidence for the
Big Bang theory to date. Refined analysis of the CMB angular power spectrum can
lead to revolutionary developments in understanding the nature of dark matter
and dark energy. In this paper, we present a new method for performing
spherical harmonic analysis for HEALPix data, which is a central component to
computing and analyzing the angular power spectrum of the massive CMB data
sets. The method uses a novel combination of a non-uniform fast Fourier
transform, the double Fourier sphere method, and Slevinsky's fast spherical
harmonic transform (Slevinsky, 2019). For a HEALPix grid with pixels
(points), the computational complexity of the method is , with an initial set-up cost of . This compares
favorably with runtime complexity of the current methods
available in the HEALPix software when multiple maps need to be analyzed at the
same time. Using numerical experiments, we demonstrate that the new method also
appears to provide better accuracy over the entire angular power spectrum of
synthetic data when compared to the current methods, with a convergence rate at
least two times higher
Atomic-phase interference devices based on ring-shaped Bose-Einstein condensates: Two ring case
We theoretically investigate the ground-state properties and quantum dynamics
of a pair of adjacent ring-shaped Bose-Einstein condensates that are coupled
via tunneling. This device, which is the analogue of a symmetric
superconducting quantum interference device, is the simplest version of what we
term an Atomic-Phase Interference Device (APHID). The two-ring APHID is shown
to be sensitive to rotation.Comment: 8 page
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Information, VARs and DSGE Models
How informative is a time series representation of a given vector of observables about the structural shocks and impulse response functions in a DSGE model? In this paper we refer to this econometricianâs problem as âE-invertibilityâ and consider the corresponding information problem of the agents in the assumed DGP, the DSGE model, which we refer to as âA-invertibilityâ We consider how the general nature of the agentsâ signal extraction problem under imperfect information impacts on the econometricianâs problem of attempting to infer the nature of structural shocks and associated impulse responses from the data. We also examine a weaker condition of recoverability. A general conclusion is that validating a DSGE model by comparing its impulse response functions with those of a data VAR is more problematic when we drop the common assumption in the literature that agents have perfect information as an endowment. We develop measures of approximate fundamentalness for both perfect and imperfect information cases and illustrate our results using analytical and numerical examples
Using visualization for visualization : an ecological interface design approach to inputting data
Visualization is experiencing growing use by a diverse community, with continuing improvements in the availability and usability of systems. In spite of these developments the problem of how first to get the data in has received scant attention: the established approach of pre-defined readers and programming aids has changed little in the last two decades. This paper proposes a novel way of inputting data for scientific visualization that employs rapid interaction and visual feedback in order to understand how the data is stored. The approach draws on ideas from the discipline of ecological interface design to extract and control important parameters describing the data, at the same time harnessing our innate human ability to recognize patterns. Crucially, the emphasis is on file format discovery rather than file format description, so the method can therefore still work when nothing is known initially of how the file was originally written, as is often the case with legacy binary data. Š 2013 Elsevier Ltd
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Reliability modeling of a 1-out-of-2 system: Research with diverse Off-the-shelf SQL database servers
Fault tolerance via design diversity is often the only viable way of achieving sufficient dependability levels when using off-the-shelf components. We have reported previously on studies with bug reports of four open-source and commercial off-the-shelf database servers and later release of two of them. The results were very promising for designers of fault-tolerant solutions that wish to employ diverse servers: very few bugs caused failures in more than one server and none caused failure in more than two. In this paper we offer details of two approaches we have studied to construct reliability growth models for a 1-out-of-2 fault-tolerant server which utilize the bug reports. The models presented are of practical significance to system designers wishing to employ diversity with off-the-shelf components since often the bug reports are the only direct dependability evidence available to them
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Noble gases from the planetary nebula stage of stellar evolution implanted in meteoritic SiC grains
Center-commissioned external review of International Water Management Institute: Consolidated report, 19-29 May 2003
Agricultural research / Research institutes / Research policy / Research priorities / Planning / Monitoring / Evaluation / Financial resources / Gender
Structural, vibrational and thermal properties of densified silicates : insights from Molecular Dynamics
Structural, vibrational and thermal properties of densified sodium silicate
(NS2) are investigated with classical molecular dynamics simulations of the
glass and the liquid state. A systematic investigation of the glass structure
with respect to density was performed. We observe a repolymerization of the
network manifested by a transition from a tetrahedral to an octahedral silicon
environment, the decrease of the amount of non-bridging oxygen atoms and the
appearance of three-fold coordinated oxygen atoms (triclusters). Anomalous
changes in the medium range order are observed, the first sharp diffraction
peak showing a minimum of its full-width at half maximum according to density.
The previously reported vibrational trends in densified glasses are observed,
such as the shift of the Boson peak intensity to higher frequencies and the
decrease of its intensity. Finally, we show that the thermal behavior of the
liquid can be reproduced by the Birch-Murnaghan equation of states, thus
allowing us to compute the isothermal compressibility
Combustion instability prediction using a nonlinear bipropellant vaporization model
Combustion instability prediction using nonlinear bipropellant vaporization mode
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