1,646 research outputs found
Discovery of Solar Rieger Periodicities in Another Star
The Rieger periods are solar cycles with a time scale of months, which are
present in both flaring activity and sunspot occurrence. These short-term
periodicities, tentatively explained by equatorially trapped Rossby-type waves
modulating the emergence of magnetic flux at the surface, are considered a
peculiar and not yet fully understood solar phenomenon. We chose a stellar
system with solar characteristics, UX Arietis, and performed a timing analysis
of two 9-year datasets of radio and optical observations. The analysis reveals
a 294-day cycle. When the two 9-year datasets are folded with this period, a
synchronization of the peak of the optical light curve (i.e., the minimum spot
coverage) with the minimum radio flaring activity is observed. This close
relationship between two completly independent curves makes it very likely that
the 294-day cycle is real. We conclude that the process invoked for the Sun of
a periodical emergence of magnetic flux may also be applied to UX Arietis and
can explain the cyclic flaring activity triggered by interactions between
successive cyclic emergences of magnetic flux.Comment: 4 Pages, 1 table, 3 figures (quality of Fig. 1 degraded to match the
requested size), needs aa.cls, accepted to be published as a letter in
Astronomy & Astrophysic
Renormalization of modular invariant Coulomb gas and Sine-Gordon theories, and quantum Hall flow diagram
Using the renormalisation group (RG) we study two dimensional electromagnetic
coulomb gas and extended Sine-Gordon theories invariant under the modular group
SL(2,Z). The flow diagram is established from the scaling equations, and we
derive the critical behaviour at the various transition points of the diagram.
Following proposal for a SL(2,Z) duality between different quantum Hall fluids,
we discuss the analogy between this flow and the global quantum Hall phase
diagram.Comment: 10 pages, 1 EPS figure include
On the relevance of polyynyl-substituted PAHs to astrophysics
We report on the absorption spectra of the polycyclic aromatic hydrocarbon
(PAH) molecules anthracene, phenanthrene, and pyrene carrying either an ethynyl
(-C2H) or a butadiynyl (-C4H) group. Measurements were carried out in the mid
infrared at room temperature on grains embedded in CsI pellets and in the near
ultraviolet at cryogenic temperature on molecules isolated in Ne matrices. The
infrared measurements show that interstellar populations of
polyynyl-substituted PAHs would give rise to collective features in the same
way non-substituted PAHs give rise to the aromatic infrared bands. The main
features characteristic of the substituted molecules correspond to the
acetylenic CH stretching mode near 3.05 mum and to the almost isoenergetic
acetylenic CCH in- and out-of-plane bending modes near 15.9 mum.
Sub-populations defined by the length of the polyynyl side group cause
collective features which correspond to the various acetylenic CC stretching
modes. The ultraviolet spectra reveal that the addition of an ethynyl group to
a non-substituted PAH molecule results in all its electronic transitions being
redshifted. Due to fast internal energy conversion, the bands at shorter
wavelengths are significantly broadened. Those at longer wavelengths are only
barely affected in this respect. As a consequence, their relative peak
absorption increases. The substitution with the longer butadiynyl chain causes
the same effects with a larger magnitude, resulting in the spectra to show a
prominent if not dominating pi-pi* transition at long wavelength. After
discussing the relevance of polyynyl-substituted PAHs to astrophysics, we
conclude that this class of highly conjugated, unsaturated molecules are valid
candidates for the carriers of the diffuse interstellar bands.Comment: 29 pages, 9 figures, accepted for publication in ApJ 2 April 201
The concordance of MRI and arthroscopy in traumatic meniscal lesions in children
SummaryIntroductionTraumatic meniscal lesions in children must be diagnosed quickly and efficiently as a priority in order to conserve the meniscus and safeguard the future of the knee. They are often isolated and difficult to identify clinically. In the diagnostic work up stage, an excessive resort to diagnostic arthroscopy has given way to increasing use of MRI by radiologists without pediatric specialization. The present study examined the agreement between MRI aspect and arthroscopic exploration in traumatic meniscal lesions in children.Patients and methodsSixty-nine knees in children aged 9 to 16 years having undergone MRI followed by arthroscopy for knee trauma between 1995 and 2008 were included in a retrospective design. Discoid meniscus was excluded. Files were reviewed by a single clinician and MRI scans by a radiologist specialized in pediatric pathology. Cases of epiphyseal fusion were excluded. All files were analyzable. Agreement with arthroscopic findings as reference was assessed for presence, location and type of meniscal lesion.ResultsOverall agreement with arthroscopy was respectively 78% and 82% on first and second MRI readings: 77% and 80% for the medial, and 78% and 84% for the lateral meniscus. On the first reading, there were 13 false positives for the medial and 5 for the lateral meniscus, versus 9 and 0 respectively on second reading. Overall sensitivity was 70% on first reading and 64% on second, and overall specificity 81% and 90%, respectively.DiscussionThe present results, in line with the literature, may appear encouraging, but hide considerable disparity between analysis of the medial and of the lateral meniscus: MRI overestimated medial and underestimated lateral meniscus lesions.ConclusionMRI serves only as a support and does not provide sure diagnosis of meniscus lesion. Interpretation should take account of the clinical examination and the pediatric orthopedic specialist's experience.Level of evidenceLevel IV, retrospective study
How do roots respond to osmotic stress? A transcriptomic approach to address this question in a non-model crop
Drought is a complex phenomenon that is relevant for many crops. Performing high-throughput transcriptomics in non-model crops is challenging. The non-model crop where our workflow has been tested on is banana (Musa spp.), which ranks among the top ten staple foods (total production over 145 million tons in 2013 (FAOstat)[1]). Bananas need vast amounts of water and even mild-drought conditions are responsible for considerable yield losses[2]. To characterize drought in the roots of different banana genotypes, we designed a lab model based on osmotic stress (5% PEG treatment for 3 days) and performed mRNA-seq analysis[3]. Using Illumina technology, 18 cDNA libraries were sequenced producing around 568 million high quality reads, of which 70-84% were mapped to the diploid reference genome[4]. We show that the applied stress leads to a drop in energy levels inducing a metabolic shift towards (i) higher oxidative respiration, (ii) alternative respiration and (iii) fermentation. We also analyzed the expression patterns of paralogous genes belonging to the same gene families and detected possible cases of sub-functionalization
XY models with disorder and symmetry-breaking fields in two dimensions
The combined effect of disorder and symmetry-breaking fields on the
two-dimensional XY model is examined. The study includes disorder in the
interaction among spins in the form of random phase shifts as well as disorder
in the local orientation of the field. The phase diagrams are determined and
the properties of the various phases and phase transitions are calculated. We
use a renormalization group approach in the Coulomb gas representation of the
model. Our results differ from those obtained for special cases in previous
works. In particular, we find a changed topology of the phase diagram that is
composed of phases with long-range order, quasi-long-range order, and
short-range order. The discrepancies can be ascribed to a breakdown of the
fugacity expansion in the Coulomb gas representation.
Implications for physical systems such as planar Josephson junctions and the
faceting of crystal surfaces are discussed.Comment: 17 pages Latex with 5 eps figures, change: acknowledgment extende
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