453 research outputs found
Foreground contamination of the WMAP CMB maps from the perspective of the matched circle test
WMAP has provided CMB maps of the full sky. The raw data is subject to
foreground contamination, in particular near to the Galactic plane. Foreground
cleaned maps have been derived, e.g., the internal linear combination (ILC) map
of Bennett et al. and the reduced foreground TOH map of Tegmark et al. Using S
statistics we examine whether residual foreground contamination is left over in
the foreground cleaned maps. In particular, we specify which parts of the
foreground cleaned maps are sufficiently accurate for the circle-in-the-sky
signature. We generalise the S statistic, called D statistic, such that the
circle test can deal with CMB maps in which the contaminated regions of the sky
are excluded with masks
Maass cusp forms for large eigenvalues
We investigate the numerical computation of Maass cusp forms for the modular
group corresponding to large eigenvalues. We present Fourier coefficients of
two cusp forms whose eigenvalues exceed r=40000. These eigenvalues are the
largest that have so far been found in the case of the modular group. They are
larger than the 130millionth eigenvalue.Comment: 24 pages, 7 figures, 3 table
Spectral resolution in hyperbolic orbifolds, quantum chaos, and cosmology
We present a few subjects from physics that have one in common: the spectral
resolution of the Laplacian.Comment: 24 pages. Contribution to the TSL Expository Lecture Series V
"Computational Physical Sciences 2006", Universiti Putra Malaysi
Linear and angular momentum of electromagnetic fields generated by an arbitrary distribution of charge and current densities at rest
Starting from Stratton-Panofsky-Phillips-Jefimenko equations for the electric
and magnetic fields generated by completely arbitrary charge and current
density distributions at rest, we derive far-zone approximations for the
fields, containing all components, dominant as well as sub-dominant. Using
these approximate formulas, we derive general formulas for the total
electromagnetic linear momentum and angular momentum, valid at large distances
from arbitrary, non-moving charge and current sources.Comment: Six pages, one figure. Errors correcte
Strategies for Improving Semi-automated Topic Classification of Media and Parliamentary documents
Since 1995 the techniques and capacities to store new electronic data and to make it available to many persons have become a common good. As of then, different organizations, such as research institutes, universities, libraries, and private companies (Google) started to scan older documents and make them electronically available as well. This has generated a lot of new research opportunities for all kinds of academic disciplines. The use of software to analyze large datasets has become an important part of doing research in the social sciences. Most academics rely on human coded datasets, both in qualitative and quantitative research. However, with the increasing amount of datasets and the complexity of the questions scholars pose to the datasets, the quest for more efficient and effective methods is now on the agenda. One of the most common techniques of content analysis is the Boolean key-word search method. To find certain topics in a dataset, the researcher creates first a list of keywords, added with certain parameters (AND, OR etc.). All keys are usually grouped in families and the entire list of keys and groups is called the ontology. Then the keywords are searched in the dataset, retrieving all documents containing the specified keywords. The online newspaper dataset, LexisNexis, provides the user with such a Boolean search method. However, the Boolean key-word search is not always satisfying in terms of reliability and validity. For that reason social scientists rely on hand-coding. Two projects that do so are the congressional bills project (www.congressionalbills.org ) and the policy agenda-setting project (see www.policyagendas.org ). They developed a topic code book and coded various different sources, such as, the state of the union speeches, bills, newspaper articles etcetera. The continuous improving automated coding techniques, and the increasing number of agenda setting projects (in especially European countries), however, has made the use of automated coding software a feasible option and also a necessity
Numerical computation of Maass waveforms and an application to cosmology
We compute numerically eigenvalues and eigenfunctions of the Laplacian in a
three-dimensional hyperbolic space. Applying the results to cosmology, we
demonstrate that the methods learned in quantum chaos can be used in other
fields of research.Comment: A version of the paper with high resolution figures is available at
http://www.physik.uni-ulm.de/theo/qc/publications.htm
The physics of angular momentum radio
Wireless communications, radio astronomy and other radio science applications
are predominantly implemented with techniques built on top of the
electromagnetic linear momentum (Poynting vector) physical layer. As a
supplement and/or alternative to this conventional approach, techniques rooted
in the electromagnetic angular momentum physical layer have been advocated, and
promising results from proof-of-concept radio communication experiments using
angular momentum were recently published. This sparingly exploited physical
observable describes the rotational (spinning and orbiting) physical properties
of the electromagnetic fields and the rotational dynamics of the pertinent
charge and current densities. In order to facilitate the exploitation of
angular momentum techniques in real-world implementations, we present a
systematic, comprehensive theoretical review of the fundamental physical
properties of electromagnetic angular momentum observable. Starting from an
overview that puts it into its physical context among the other Poincar\'e
invariants of the electromagnetic field, we describe the multi-mode quantized
character and other physical properties that sets electromagnetic angular
momentum apart from the electromagnetic linear momentum. These properties
allow, among other things, a more flexible and efficient utilization of the
radio frequency spectrum. Implementation aspects are discussed and illustrated
by examples based on analytic and numerical solutions.Comment: Fixed LaTeX rendering errors due to inconsistencies between arXiv's
LaTeX machine and texlive in OpenSuSE 13.
Using bijective maps to improve free energy estimates
We derive a fluctuation theorem for generalized work distributions, related
to bijective mappings of the phase spaces of two physical systems, and use it
to derive a two-sided constraint maximum likelihood estimator of their free
energy difference which uses samples from the equilibrium configurations of
both systems. As an application, we evaluate the chemical potential of a dense
Lennard-Jones fluid and study the construction and performance of suitable
maps.Comment: 17 pages, 11 figure
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