836 research outputs found
PSRCHIVE and PSRFITS: Definition of the Stokes Parameters and Instrumental Basis Conventions
This paper defines the mathematical convention adopted to describe an
electromagnetic wave and its polarisation state, as implemented in the PSRCHIVE
software and represented in the PSRFITS definition. Contrast is made between
the convention that has been widely accepted by pulsar astronomers and the
IAU/IEEE definitions of the Stokes parameters. The former is adopted as the
PSR/IEEE convention, and a set of useful parameters are presented for
describing the differences between the PSR/IEEE standard and the conventions
(either implicit or explicit) that form part of the design of observatory
instrumentation. To aid in the empirical determination of instrumental
convention parameters, well-calibrated average polarisation profiles of PSR
J0304+1932 and PSR J0742-2822 are presented at radio wavelengths of
approximately 10, 20, and 40 cm.Comment: 7 pages, 2 figures, to be published in PAS
The MeqTrees software system and its use for third-generation calibration of radio interferometers
The formulation of the radio interferometer measurement equation (RIME) by
Hamaker et al. has provided us with an elegant mathematical apparatus for
better understanding, simulation and calibration of existing and future
instruments. The calibration of the new radio telescopes (LOFAR, SKA) would be
unthinkable without the RIME formalism, and new software to exploit it.
MeqTrees is designed to implement numerical models such as the RIME, and to
solve for arbitrary subsets of their parameters. The technical goal of MeqTrees
is to provide a tool for rapid implementation of such models, while offering
performance comparable to hand-written code. We are also pursuing the wider
goal of increasing the rate of evolution of radio astronomical software, by
offering a tool for rapid experimentation and exchange of ideas.
MeqTrees is implemented as a Python-based front-end called the meqbrowser,
and an efficient (C++-based) computational back-end called the meqserver.
Numerical models are defined on the front-end via a Python-based Tree
Definition Language (TDL), then rapidly executed on the back-end. The use of
TDL facilitates an extremely short turn-around time for experimentation with
new ideas. This is also helped by unprecedented visualization capabilities for
all final and intermediate results. A flexible data model and a number of
important optimizations in the back-end ensures that the numerical performance
is comparable to that of hand-written code.
MeqTrees is already widely used as the simulation tool for new instruments
(LOFAR, SKA) and technologies (focal plane arrays). It has demonstrated that it
can achieve a noise-limited dynamic range in excess of a million, on WSRT data.
It is the only package that is specifically designed to handle what we propose
to call third-generation calibration (3GC), which is needed for the new
generation of giant radio telescopes.Comment: 15 pages; 14 figure
Modeling Affect Dynamics:State of the Art and Future Challenges
The current article aims to provide an up-to-date synopsis of available techniques to study affect dynamics using intensive longitudinal data (ILD). We do so by introducing the following eight dichotomies that help elucidate what kind of data one has, what process aspects are of interest, and what research questions are being considered: (1) single- versus multiple-person data; (2) univariate versus multivariate models; (3) stationary versus nonstationary models; (4) linear versus nonlinear models; (5) discrete time versus continuous time models; (6) discrete versus continuous variables; (7) time versus frequency domain; and (8) modeling the process versus computing descriptives. In addition, we discuss what we believe to be the most urging future challenges regarding the modeling of affect dynamics
Casimir forces in modulated systems
For the first time we present analytical results for the contribution of
electromagnetic fluctuations into thermodynamic properties of modulated
systems, like cholesteric or smectic liquid crystalline films. In the case of
small dielectric anisotropy we have derived explicit analytical expressions for
the chemical potential of such systems. Two limiting cases were specifically
considered: (i) the Van der Waals (VdW) limit, i.e., in the case when the
retardation of the electromagnetic interactions can be neglected; and (ii) the
Casimir limit, i.e. when the effects of retardation becomes considerable. It
was shown that in the Casimir limit, the film chemical potential oscillates
with the thickness of the film. This non-monotonic dependence of the chemical
potential on the film thickness can lead to step-wise wetting phenomena,
surface anchoring reorientation and other important effects. Applications of
the results may concern the various systems in soft matter or condensed matter
physics with multilayer or modulated structures.Comment: 13 page
Modeling Nonstationary Emotion Dynamics in Dyads using a Time-Varying Vector-Autoregressive Model
Interaction potentials for soft and hard ellipsoids
Using results from colloid science we derive interaction potentials for
computer simulations of mixtures of soft or hard ellipsoids of arbitrary shape
and size. Our results are in many respects reminicent of potentials of the
Gay-Berne type but have a well-defined microscopic interpretation and no
adjustable parameters. Since our potentials require the calculation of similar
variables, the modification of existing simulation codes for Gay-Berne
potentials is straightforward. The computational performance should remain
unaffected.Comment: 8 pages, 4 figure
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