17,381 research outputs found
phi-meson production in proton-antiproton annihilation
Apparent channel-dependent violations of the OZI rule in nucleon-antinucleon
annihilation reactions are discussed in the presence of an intrinsic
strangeness component in the nucleon. Admixture of strange-antistrange quark
pairs in the nucleon wave function enables the direct coupling to the phi-meson
in the annihilation channel without violating the OZI rule. Three forms are
considered in this work for the strangeness content of the proton wave
function, namely, the uud cluster with a strange-antistrange sea quark
component, kaon-hyperon clusters based on a simple chiral quark model, and the
pentaquark picture. Nonrelativistic quark model calculations reveal that the
strangeness magnetic moment and the strangeness contribution to the proton spin
from the first two models are consistent with recent experimental data. For the
third model, the uuds subsystem with the configurations FS[31]F[211]S[22] and
FS[31]F[31]S[22] leads to negative values for the strangeness magnetic moment
and the strangeness contribution to the proton spin. With effective quark line
diagrams incorporating the 3P0 quark model we give estimates for the branching
ratios of the proton-antiproton annihilation reactions at rest to two mesons.
Results for the branching ratios of phi-meson production from atomic
proton-antiproton s-wave states are for the first and third model found to be
strongly channel dependent, in good agreement with measured rates.Comment: 12 pages, 1 figur
Weak local rules for planar octagonal tilings
We provide an effective characterization of the planar octagonal tilings
which admit weak local rules. As a corollary, we show that they are all based
on quadratic irrationalities, as conjectured by Thang Le in the 90s.Comment: 23 pages, 6 figure
Zeeman smearing of the Coulomb blockade
Charge fluctuations of a large quantum dot coupled to a two-dimensional lead
via a single-mode good Quantum Point Contact (QPC) and capacitively coupled to
a back-gate, are investigated in the presence of a parallel magnetic field. The
Zeeman term induces an asymmetry between transmission probabilities for the
spin-up and spin-down channels at the QPC, producing noticeable effects on the
quantization of the grain charge already at low magnetic fields. Performing a
quantitative analysis, I show that the capacitance between the gate and the
lead exhibits - instead of a logarithmic singularity - a reduced peak as a
function of gate voltage. Experimental applicability is discussed.Comment: 5 pages, 3 figures (Final version
In an Ising model with spin-exchange dynamics damage always spreads
We investigate the spreading of damage in Ising models with Kawasaki
spin-exchange dynamics which conserves the magnetization. We first modify a
recent master equation approach to account for dynamic rules involving more
than a single site. We then derive an effective-field theory for damage
spreading in Ising models with Kawasaki spin-exchange dynamics and solve it for
a two-dimensional model on a honeycomb lattice. In contrast to the cases of
Glauber or heat-bath dynamics, we find that the damage always spreads and never
heals. In the long-time limit the average Hamming distance approaches that of
two uncorrelated systems. These results are verified by Monte-Carlo
simulations.Comment: 5 pages REVTeX, 4 EPS figures, final version as publishe
Cathodoluminescence Mapping of Cherenkov-Radiation Generated Bloch-Modes in Planar Photonic Crystals by Fast Electrons
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
Variable range hopping and quantum creep in one dimension
We study the quantum non linear response to an applied electric field of
a one dimensional pinned charge density wave or Luttinger liquid in presence of
disorder. From an explicit construction of low lying metastable states and of
bounce instanton solutions between them, we demonstrate quantum creep as well as a sharp crossover at towards a linear response
form consistent with variable range hopping arguments, but dependent only on
electronic degrees of freedom
Specific detection and quantification of the marine flavobacterial genus Zobellia on macroalgae using novel qPCR and CARD-FISH assays
The flavobacterial genus Zobellia is considered as a model to study macroalgal polysaccharide degradation. The lack of data regarding its prevalence and abundance in coastal habitats constitutes a bottleneck to assess its ecological strategies. To overcome this issue, real-time quantitative PCR (qPCR) and fluorescence in situ hybridization (FISH) methods targeting the 16S rRNA gene were optimized to specifically detect and quantify Zobellia on the surface of diverse macroalgae. The newly designed qPCR primers and FISH probes targeted 98 and 100% of the Zobellia strains in silico and their specificity was confirmed using pure bacterial cultures. The dynamic range of the qPCR assay spanned 8 orders of magnitude from 10 to 108 16S rRNA gene copies and the detection limit was 0.01% relative abundance of Zobellia in environmental samples. Zobellia-16S rRNA gene copies were detected on all surveyed brown, green and red macroalgae, in proportion varying between 0.1 and 0.9% of the total bacterial copies. The absolute and relative abundance of Zobellia varied with tissue aging on the kelp Laminaria digitata. Zobellia cells were successfully visualized in Ulva lactuca and stranded Palmaria palmata surface biofilm using CARD-FISH, representing in the latter 10(5) Zobellia cells.cm(2) and 0.43% of total bacterial cells. Overall, qPCR and CARD-FISH assays enabled robust detection, quantification and localization of Zobellia representatives in complex samples, underlining their ecological relevance as primary biomass degraders potentially cross-feeding other microorganisms. (C) 2021 Elsevier GmbH. All rights reserved
Evidence of Titan's Climate History from Evaporite Distribution
Water-ice-poor, 5-m-bright material on Saturn's moon Titan has
previously been geomorphologically identified as evaporitic. Here we present a
global distribution of the occurrences of the 5-m-bright spectral unit,
identified with Cassini's Visual Infrared Mapping Spectrometer (VIMS) and
examined with RADAR when possible. We explore the possibility that each of
these occurrences are evaporite deposits. The 5-m-bright material covers
1\% of Titan's surface and is not limited to the poles (the only regions with
extensive, long-lived surface liquid). We find the greatest areal concentration
to be in the equatorial basins Tui Regio and Hotei Regio. Our interpretations,
based on the correlation between 5-m-bright material and lakebeds, imply
that there was enough liquid present at some time to create the observed
5-m-bright material. We address the climate implications surrounding a
lack of evaporitic material at the south polar basins: if the south pole basins
were filled at some point in the past, then where is the evaporite
Grating-assisted superresolution of slow waves in Fourier space
We present a far-ïŹeld optical technique allowing measurements of the dispersion relation of electromagnetic ïŹelds propagating under the light cone in photonic nanostructures. It relies on the use of a one-dimensional grating to probe the evanescent tail of the guided ïŹeld in combination with a high-numerical-aperture Fourier- space imaging setup. A high-resolution spectroscopy of the far-ïŹeld emission diagram allows us to accurately and efïŹciently determine the dispersion curve and the group-index dispersion of planar photonic crystal waveguides operating in the slow-light regime
Differences between regular and random order of updates in damage spreading simulations
We investigate the spreading of damage in the three-dimensional Ising model
by means of large-scale Monte-Carlo simulations. Within the Glauber dynamics we
use different rules for the order in which the sites are updated. We find that
the stationary damage values and the spreading temperature are different for
different update order. In particular, random update order leads to larger
damage and a lower spreading temperature than regular order. Consequently,
damage spreading in the Ising model is non-universal not only with respect to
different update algorithms (e.g. Glauber vs. heat-bath dynamics) as already
known, but even with respect to the order of sites.Comment: final version as published, 4 pages REVTeX, 2 eps figures include
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