95 research outputs found
A Classification of random Dirac fermions
We present a detailed classification of random Dirac hamiltonians in two
spatial dimensions based on the implementation of discrete symmetries. Our
classification is slightly finer than that of random matrices, and contains
thirteen classes. We also extend this classification to non-hermitian
hamiltonians with and without Dirac structure.Comment: 15 pages, version2: typos in the table of classes are correcte
Strong Coupling Fixed Points of Current Interactions and Disordered Fermions in 2D
The all-orders beta function is used to study disordered Dirac fermions in
2D. The generic strong coupling fixed `points' of anisotropic current-current
interactions at large distances are actually isotropic manifolds corresponding
to subalgebras of the maximal current algebra at short distances. The IR
theories are argued to be current algebra cosets. We illustrate this with the
simple example of anisotropic su(2), which is the physics of
Kosterlitz-Thouless transitions. We work out the phase diagram for the
Chalker-Coddington network model which is in the universality class of the
integer Quantum Hall transition. One massless phase is in the universality
class of dense polymers.Comment: published version (Phys. Rev. B
Gauge Invariance and the Critical Properties of Quantum Hall Plateaux Transitions
A model consisting of a single massless scalar field with a topological
coupling to a pure gauge field is defined and studied. It possesses an SL(2,Z)
symmetry as a consequence of the gauge invariance. We propose that by adding
impurities the model can be used to describe transitions between Quantum Hall
plateaux. This leads to a correlation length exponent of 20/9, in excellent
agreement with the most recent experimental measurements.Comment: 25 pages, minor changes in data discussion, Section V on connection
with staircase model is expanded References added. Interpretive comments
added in section 3 about the critical condition. with improved terminolog
Investigation of an international water polo tournament in Czechia as a potential source for early introduction of the SARS-CoV-2 Omicron variant into Belgium, Switzerland and Germany, November 2021
Background: The earliest recognised infections by the SARS-CoV-2 Omicron variant (Pango lineage B.1.1.529) in Belgium and Switzerland suggested a connection to an international water polo tournament, held 12-14 November 2021 in Brno, Czechia.AimTo study the arrival and subsequent spread of the Omicron variant in Belgium and Switzerland, and understand the overall importance of this international sporting event on the number of infections in the two countries.
Methods: We performed intensive forward and backward contact tracing in both countries, supplemented by phylogenetic investigations using virus sequences of the suspected infection chain archived in public databases.
Results: Through contact tracing, we identified two and one infected athletes of the Belgian and Swiss water polo teams, respectively, and subsequently also three athletes from Germany. In Belgium and Switzerland, four and three secondary infections, and three and one confirmed tertiary infections were identified. Phylogenetic investigation demonstrated that this sporting event played a role as the source of infection, but without a direct link with infections from South Africa and not as a superspreading event; the virus was found to already be circulating at that time in the countries involved.
Conclusion: The SARS-CoV-2 Omicron variant started to circulate in Europe several weeks before its identification in South Africa on 24 November 2021. Accordingly, it can be assumed that travel restrictions are usually implemented too late to prevent the spread of newly detected SARS-CoV-2 variants to other regions. Phylogenetic analysis may modify the perception of an apparently clear result of intensive contact tracing
Accuracy and quality assessment of 454 GS-FLX Titanium pyrosequencing
<p>Abstract</p> <p>Background</p> <p>The rapid evolution of 454 GS-FLX sequencing technology has not been accompanied by a reassessment of the quality and accuracy of the sequences obtained. Current strategies for decision-making and error-correction are based on an initial analysis by Huse <it>et al. </it>in 2007, for the older GS20 system based on experimental sequences. We analyze here the quality of 454 sequencing data and identify factors playing a role in sequencing error, through the use of an extensive dataset for Roche control DNA fragments.</p> <p>Results</p> <p>We obtained a mean error rate for 454 sequences of 1.07%. More importantly, the error rate is not randomly distributed; it occasionally rose to more than 50% in certain positions, and its distribution was linked to several experimental variables. The main factors related to error are the presence of homopolymers, position in the sequence, size of the sequence and spatial localization in PT plates for insertion and deletion errors. These factors can be described by considering seven variables. No single variable can account for the error rate distribution, but most of the variation is explained by the combination of all seven variables.</p> <p>Conclusions</p> <p>The pattern identified here calls for the use of internal controls and error-correcting base callers, to correct for errors, when available (e.g. when sequencing amplicons). For shotgun libraries, the use of both sequencing primers and deep coverage, combined with the use of random sequencing primer sites should partly compensate for even high error rates, although it may prove more difficult than previous thought to distinguish between low-frequency alleles and errors.</p
The Temporal Dynamics of Voluntary Emotion Regulation
Background: Neuroimaging has demonstrated that voluntary emotion regulation is effective in reducing amygdala activation to aversive stimuli during regulation. However, to date little is known about the sustainability of these neural effects once active emotion regulation has been terminated. Methodology/Principal Findings: We addressed this issue by means of functional magnetic resonance imaging (fMRI) in healthy female subjects. We performed an active emotion regulation task using aversive visual scenes (task 1) and a subsequent passive viewing task using the same stimuli (task 2). Here we demonstrate not only a significantly reduced amygdala activation during active regulation but also a sustained regulation effect on the amygdala in the subsequent passive viewing task. This effect was related to an immediate increase of amygdala signal in task 1 once active emotion regulation has been terminated: The larger this peak postregulation signal in the amygdala in task 1, the smaller the sustained regulation effect in task 2. Conclusions/Significance: In summary, we found clear evidence that effects of voluntary emotion regulation extend beyond the period of active regulation. These findings are of importance for the understanding of emotion regulation i
The G9.62+0.19-F Hot Molecular Core - The infrared view on very young massive stars
(abridged) We present the results of an extensive infrared study of the
massive star-forming region G9.62+0.19. The data cover information from broad-
and narrow-band filters in the wavelength range from 1 to 19 micrometer and are
obtained with ESO's infrared cameras ISAAC and TIMMI2 and with SpectroCam-10
(Mt. Palomar). The high sensitivity and resolution provided by these facilities
revealed intriguing new details of this star-forming region and especially
about the embedded hot molecular core (HMC) - component F. We analyse the newly
found infrared sub-structure of four objects in this HMC region. While one of
these objects (F2) is probably a foreground field star, the nature of the
brightest object in the near-infrared there (F1) remains somewhat enigmatic.
Our new astrometry proves that this object is not coincident with the peak of
the molecular line emission of the HMC, but displaced by 1.7 arcsecs (nearly
10000 AU on a linear scale). We estimate this object to be an additional
embedded object with a dense dust shell. Very near the HMC location we find L'
band emission which strongly rises in flux towards longer wavelengths. We
presume that this emission (F4) arises from the envelope of the HMC which is
known to be associated with a molecular outflow roughly aligned along the line
of sight. Thus, the clearing effect of this outflow causes strong deviations
from spherical symmetry which might allow infrared emission from the HMC to
escape through the outflow cavities. This presents the first direct detection
of an HMC at a wavelength as short as 3.8 micron. At 11.7 and 18.75 micron, the
HMC counterpart F4 ultimately proves to be the most luminous IR source within
the G9.62+0.19-F region.Comment: 39 pages, 10 figures, accepted for publication in Astronomy &
Astrophysics. The paper contains several colour images. It is highly
advisable to go to the following website to get a high-resolution version of
this preprint:
http://www.tls-tautenburg.de/research/tls-research/papers/linz/G9.62.htm
A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
A study of gas-phase element abundances reported in the literature for 17
different elements sampled over 243 sight lines in the local part of our Galaxy
reveals that the depletions into solid form (dust grains) are extremely well
characterized by trends that employ only three kinds of parameters. One is an
index that describes the overall level of depletion applicable to the gas in
any particular sight line, and the other two represent linear coefficients that
describe how to derive each element's depletion from this sight-line parameter.
The information from this study reveals the relative proportions of different
elements that are incorporated into dust at different stages of grain growth.
An extremely simple scheme is proposed for deriving the dust contents and
metallicities of absorption-line systems that are seen in the spectra of
distant quasars or the optical afterglows of gamma-ray bursts. Contrary to
presently accepted thinking, the elements sulfur and krypton appear to show
measurable changes in their depletions as the general levels of depletions of
other elements increase, although more data are needed to ascertain whether or
not these findings truly compelling. Nitrogen appears to show no such increase.
The incorporation of oxygen into solid form in the densest gas regions far
exceeds the amounts that can take the form of silicates or metallic oxides;
this conclusion is based on differential measurements of depletion and thus is
unaffected by uncertainties in the solar abundance reference scale.Comment: 166 pages, 21 figures, pages 116-166 contain detailed tabulations
that may not be of interest to most readers. Accepted for publication in the
Astrophysical Journa
- âŠ