387 research outputs found
Probing non-Gaussianities on Large Scales in WMAP5 and WMAP7 Data using Surrogates
Probing Gaussianity represents one of the key questions in modern cosmology,
because it allows to discriminate between different models of inflation. We
test for large-scale non-Gaussianities in the cosmic microwave background (CMB)
in a model-independent way. To this end, so-called first and second order
surrogates are generated by first shuffling the Fourier phases belonging to the
scales not of interest and then shuffling the remaining phases for the length
scales under study. Using scaling indices as test statistics we find highly
significant signatures for both non-Gaussianities and asymmetries on large
scales for the WMAP data of the CMB. We find remarkably similar results when
analyzing different ILC-maps based on the WMAP five and seven year data. Such
features being independent from the map-making procedure would disfavor the
fundamental principle of isotropy as well as canonical single-field slow-roll
inflation - unless there is some undiscovered systematic error in the
collection or reduction of the CMB data or yet unknown foreground
contributions.Comment: 4 pages, 3 figures, to appear in the Proceedings of Moriond Cosmology
201
Supersonic dislocations observed in a plasma crystal
Experimental results on the dislocation dynamics in a two-dimensional plasma
crystal are presented. Edge dislocations were created in pairs in lattice
locations where the internal shear stress exceeded a threshold and then moved
apart in the glide plane at a speed higher than the sound speed of shear waves,
. The experimental system, a plasma crystal, allowed observation of this
process at an atomistic (kinetic) level. The early stage of this process is
identified as a stacking fault. At a later stage, supersonically moving
dislocations generated shear-wave Mach cones
Correlating Fourier phase information with real-space higher order statistics
We establish for the first time heuristic correlations between harmonic space
phase information and higher order statistics. Using the spherical full-sky
maps of the cosmic microwave background as an example we demonstrate that known
phase correlations at large spatial scales can gradually be diminished when
subtracting a suitable best-fit (Bianchi-) template map of given strength. The
weaker phase correlations lead in turn to a vanishing signature of anisotropy
when measuring the Minkowski functionals and scaling indices in real-space and
comparing them with surrogate maps being free of phase correlations. Those
investigations can open a new road to a better understanding of signatures of
non-Gaussianities in complex spatial structures by elucidating the meaning of
Fourier phase correlations and their influence on higher order statistics.Comment: 6 pages plus 1 supplemental page, 4 figures, submitte
Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes
In semiconductor manufacturing, contamination due to particulates
significantly decreases the yield and quality of device fabrication, therefore
increasing the cost of production. Dust particle clouds can be found in almost
all plasma processing environments including both plasma etching devices and in
plasma deposition processes. Dust particles suspended within such plasmas will
acquire an electric charge from collisions with free electrons in the plasma.
If the ratio of inter-particle potential energy to the average kinetic energy
is sufficient, the particles will form either a liquid structure with short
range ordering or a crystalline structure with long range ordering. Otherwise,
the dust particle system will remain in a gaseous state. Many experiments have
been conducted over the past decade on such colloidal plasmas to discover the
character of the systems formed, but more work is needed to fully understand
these structures. The preponderance of previous experiments used monodisperse
spheres to form complex plasma systems
Probing non-Gaussianities in the CMB on an incomplete sky using surrogates
We demonstrate the feasibility to generate surrogates by Fourier-based
methods for an incomplete data set. This is performed for the case of a CMB
analysis, where astrophysical foreground emission, mainly present in the
Galactic plane, is a major challenge. The shuffling of the Fourier phases for
generating surrogates is now enabled by transforming the spherical harmonics
into a new set of basis functions that are orthonormal on the cut sky. The
results show that non-Gaussianities and hemispherical asymmetries in the CMB as
identified in several former investigations, can still be detected even when
the complete Galactic plane (|b| < 30{\deg}) is removed. We conclude that the
Galactic plane cannot be the dominant source for these anomalies. The results
point towards a violation of statistical isotropy.Comment: 9 pages, 13 figures, accepted by Physical Review
Dusty Plasma Correlation Function Experiment
Dust particles immersed within a plasma environment, such as those in
protostellar clouds, planetary rings or cometary environments, will acquire an
electric charge. If the ratio of the inter-particle potential energy to the
average kinetic energy is high enough the particles will form either a "liquid"
structure with short-range ordering or a crystalline structure with long range
ordering. Many experiments have been conducted over the past several years on
such colloidal plasmas to discover the nature of the crystals formed, but more
work is needed to fully understand these complex colloidal systems. Most
previous experiments have employed monodisperse spheres to form Coulomb
crystals. However, in nature (as well as in most plasma processing
environments) the distribution of particle sizes is more randomized and
disperse. This paper reports experiments which were carried out in a GEC rf
reference cell modified for use as a dusty plasma system, using varying sizes
of particles to determine the manner in which the correlation function depends
upon the overall dust grain size distribution. (The correlation function
determines the overall crystalline structure of the lattice.) Two dimensional
plasma crystals were formed of assorted glass spheres with specific size
distributions in an argon plasma. Using various optical techniques, the pair
correlation function was determined and compared to those calculated
numerically.Comment: 6 pages, Presented at COSPAR '0
A model-independent test for scale-dependent non-Gaussianities in the CMB
We present a model-independent method to test for scale-dependent
non-Gaussianities in combination with scaling indices as test statistics.
Therefore, surrogate data sets are generated, in which the power spectrum of
the original data is preserved, while the higher order correlations are partly
randomised by applying a scale-dependent shuffling procedure to the Fourier
phases. We apply this method to the WMAP data of the cosmic microwave
background (CMB) and find signatures for non-Gaussianities on large scales.
Further tests are required to elucidate the origin of the detected anomalies.Comment: accepted for publication in PRL, minor revisions, results unchanged,
l(cut)-dependency adde
Dust in the Local Interstellar Wind
The gas-to-dust mass ratios found for interstellar dust within the Solar
System, versus values determined astronomically for the cloud around the Solar
System, suggest that large and small interstellar grains have separate
histories, and that large interstellar grains preferentially detected by
spacecraft are not formed exclusively by mass exchange with nearby interstellar
gas. Observations by the Ulysses and Galileo satellites of the mass spectrum
and flux rate of interstellar dust within the heliosphere are combined with
information about the density, composition, and relative flow speed and
direction of interstellar gas in the cloud surrounding the solar system to
derive an in situ value for the gas-to-dust mass ratio, . Hubble observations of the cloud surrounding the solar system
yield a gas-to-dust mass ratio of Rg/d=551+61-251 when B-star reference
abundances are assumed. The exclusion of small dust grains from the heliosheath
and heliosphere regions are modeled, increasing the discrepancy between
interstellar and in situ observations. The shock destruction of interstellar
grains is considered, and comparisons are made with interplanetary and presolar
dust grains.Comment: 87 pages, 9 figures, 6 tables, accepted for publication in
Astrophysical Journal. Uses AASTe
Separation of VUV/UV photons and reactive particles in the effluent of a He/O2 atmospheric pressure plasma jet
Cold atmospheric pressure plasmas can be used for treatment of living tissues
or for inactivation of bacteria or biological macromolecules. The treatment is
usually characterized by a combined effect of UV and VUV radiation, reactive
species, and ions. This combination is usually beneficial for the effectiveness
of the treatment but it makes the study of fundamental interaction mechanisms
very difficult. Here we report on an effective separation of VUV/UV photons and
heavy reactive species in the effluent of a micro scale atmospheric pressure
plasma jet (-APPJ). The separation is realized by an additional flow of
helium gas under well-defined flow conditions, which deflects heavy particles
in the effluent without affecting the VUV and UV photons. Both components of
the effluent, the photons and the reactive species, can be used separately or
in combination for sample treatment. The results of treatment of a model plasma
polymer film and vegetative Bacillus subtilis and Escherichia coli cells are
shown and discussed. A simple model of the He gas flow and reaction kinetics of
oxygen atoms in the gas phase and at the surface is used to provide a better
understanding of the processes in the plasma effluent. The new jet
modification, called X-Jet for its appearance, will simplify the investigation
of interaction mechanisms of atmospheric pressure plasmas with biological
samples.Comment: 10 pages, 7 figures, submitted to Journal of Physics D: Applied
Physic
Radiometric force in dusty plasmas
A radiofrequency glow discharge plasma, which is polluted with a certain
number of dusty grains, is studied. In addition to various dusty plasma
phenomena, several specific colloidal effects should be considered. We focus on
radiometric forces, which are caused by inhomogeneous temperature distribution.
Aside from thermophoresis, the role of temperature distribution in dusty
plasmas is an open question. It is shown that inhomogeneous heating of the
grain by ion flows results in a new photophoresis like force, which is specific
for dusty discharges. This radiometric force can be observable under conditions
of recent microgravity experiments.Comment: 4 pages, amsmat
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