6,292 research outputs found
Dynamical Locking of the Chiral and the Deconfinement Phase Transition in QCD
We study the fixed-point structure of four-fermion interactions in two-flavor
QCD with Nc colors close to the finite-temperature phase boundary. In
particular, we analyze how the fixed-point structure of four-fermion
interactions is related to the confining dynamics in the gauge sector. We show
that there exists indeed a mechanism which dynamically locks the chiral phase
transition to the deconfinement phase transition. This mechanism allows us to
determine a window for the values of physical observables in which the two
phase transitions lie close to each other.Comment: 14 pages, 5 figure
Thermodynamically Stable One-Component Metallic Quasicrystals
Classical density-functional theory is employed to study finite-temperature
trends in the relative stabilities of one-component quasicrystals interacting
via effective metallic pair potentials derived from pseudopotential theory.
Comparing the free energies of several periodic crystals and rational
approximant models of quasicrystals over a range of pseudopotential parameters,
thermodynamically stable quasicrystals are predicted for parameters approaching
the limits of mechanical stability of the crystalline structures. The results
support and significantly extend conclusions of previous ground-state
lattice-sum studies.Comment: REVTeX, 13 pages + 2 figures, to appear, Europhys. Let
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
On the example of exceptional families of viruses we i) show the existence of
a completely new type of matter organization in nanoparticles, in which the
regions with a chiral pentagonal quasicrystalline order of protein positions
are arranged in a structure commensurate with the spherical topology and
dodecahedral geometry, ii) generalize the classical theory of quasicrystals
(QCs) to explain this organization, and iii) establish the relation between
local chiral QC order and nonzero curvature of the dodecahedral capsid faces.Comment: 8 pages, 3 figure
Neutrinos from Accreting Neutron Stars
The magnetospheres of accreting neutron stars develop electrostatic gaps with
huge potential drops. Protons and ions, accelerated in these gaps along the
dipolar magnetic field lines to energies greater than 100 TeV, can impact onto
a surrounding accretion disc. A proton-induced cascade so develops, and
-emission is produced from charged pion decays. Using GEANT4, a computer
code that tracks particles produced in high energy collisions, we have
calculated the resulting -spectrum with extensive disc shower simulations.
We show that the -spectrum produced out of the proton beam is a power law.
We use this result to propose accretion-powered X-ray binaries (with highly
magnetized neutron stars) as a new population of point-like -sources for
km-scale detectors, such as ICECUBE. As a particular example we discuss the
case of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic
-source: one for which the formation and loss of its accretion disc can be
fully detected. Finally, we briefly comment on the possibility that smaller
telescopes, like AMANDA, could also detect A0535+26 by folding observations
with the orbital period.Comment: 7 pages, 5 figures. Updates to match accepted version in Astrophys.
Icosahedral multi-component model sets
A quasiperiodic packing Q of interpenetrating copies of C, most of them only
partially occupied, can be defined in terms of the strip projection method for
any icosahedral cluster C. We show that in the case when the coordinates of the
vectors of C belong to the quadratic field Q[\sqrt{5}] the dimension of the
superspace can be reduced, namely, Q can be re-defined as a multi-component
model set by using a 6-dimensional superspace.Comment: 7 pages, LaTeX2e in IOP styl
The Entropy of Square-Free Words
Finite alphabets of at least three letters permit the construction of
square-free words of infinite length. We show that the entropy density is
strictly positive and derive reasonable lower and upper bounds. Finally, we
present an approximate formula which is asymptotically exact with rapid
convergence in the number of letters.Comment: 18 page
Identifying and Indexing Icosahedral Quasicrystals from Powder Diffraction Patterns
We present a scheme to identify quasicrystals based on powder diffraction
data and to provide a standardized indexing. We apply our scheme to a large
catalog of powder diffraction patterns, including natural minerals, to look for
new quasicrystals. Based on our tests, we have found promising candidates
worthy of further exploration.Comment: 4 pages, 1 figur
The variability behavior of CoRoT M-giant Stars
For 6 years the Convection, Rotation, and Planetary Transits (CoRoT) space
mission has acquired photometric data from more than one hundred thousand point
sources towards and directly opposite from the inner and outer regions of the
Galaxy. The high temporal resolution of the CoRoT data combined with the wide
time span of the observations has enabled the study of short and long time
variations in unprecedented detail. From the initial sample of 2534 stars
classified as M-giants in the CoRoT databasis, we selected 1428 targets that
exhibit well defined variability, using visual inspection. The variability
period and amplitude of C1 stars (stars having Teff < 4200 K) were computed
using Lomb-Scargle and harmonic fit methods. The trends found in the V-I vs J-K
color-color diagram are in agreement with standard empirical calibrations for
M-giants. The sources located towards the inner regions of the Galaxy are
distributed throughout the diagram while the majority of the stars towards the
outer regions of the Galaxy are spread between the calibrations of M-giants and
the predicted position for Carbon stars. The stars classified as supergiants
follow a different sequence from the one found for giant stars. We also
performed a KS test of the period and amplitude of stars towards the inner and
outer regions of the Galaxy. We obtained a low probability that the two samples
come from the same parent distribution. The observed behavior of the
period-amplitude and period-Teff diagrams are, in general, in agreement with
those found for Kepler sources and ground based photometry, with pulsation
being the dominant cause responsible for the observed modulation. We also
conclude that short-time variations on M-Giant stars do not exist orare very
rare and the few cases we found are possibly related to biases or background
stars.Comment: 11 pages, 6 figure
Affine extension of noncrystallographic Coxeter groups and quasicrystals
Unique affine extensions H^{\aff}_2, H^{\aff}_3 and H^{\aff}_4 are
determined for the noncrystallographic Coxeter groups , and .
They are used for the construction of new mathematical models for quasicrystal
fragments with 10-fold symmetry. The case of H^{\aff}_2 corresponding to
planar point sets is discussed in detail. In contrast to the cut-and-project
scheme we obtain by construction finite point sets, which grow with a model
specific growth parameter.Comment: (27 pages, to appear in J. Phys. A
Norine, the knowledgebase dedicated to nonribosomal peptides, is now open to crowdsourcing
International audienceSince its creation in 2006, Norine remains the unique knowledgebase dedicated to non-ribosomal pep-tides (NRPs). These secondary metabolites, produced by bacteria and fungi, harbor diverse interesting biological activities (such as antibiotic, anti-tumor, siderophore or surfactant) directly related to the diversity of their structures. The Norine team goal is to collect the NRPs and provide tools to analyze them efficiently. We have developed a user-friendly interface and dedicated tools to provide a complete bioinformatics platform. The knowledgebase gathers abundant and valuable annotations on more than 1100 NRPs. To increase the quantity of described NRPs and improve the quality of associated annotations , we are now opening Norine to crowdsourc-ing. We believe that contributors from the scientific community are the best experts to annotate the NRPs they work on. We have developed MyNorine to facilitate the submission of new NRPs or modifications of stored ones. This article presents MyNorine and other novelties of Norine interface released since the first publication. Norine is freely accessible from the following URL: http://bioinfo.lifl.fr/NRP
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