221 research outputs found
On the k-Symplectic, k-Cosymplectic and Multisymplectic Formalisms of Classical Field Theories
The objective of this work is twofold: First, we analyze the relation between
the k-cosymplectic and the k-symplectic Hamiltonian and Lagrangian formalisms
in classical field theories. In particular, we prove the equivalence between
k-symplectic field theories and the so-called autonomous k-cosymplectic field
theories, extending in this way the description of the symplectic formalism of
autonomous systems as a particular case of the cosymplectic formalism in
non-autonomous mechanics. Furthermore, we clarify some aspects of the geometric
character of the solutions to the Hamilton-de Donder-Weyl and the
Euler-Lagrange equations in these formalisms. Second, we study the equivalence
between k-cosymplectic and a particular kind of multisymplectic Hamiltonian and
Lagrangian field theories (those where the configuration bundle of the theory
is trivial).Comment: 25 page
Invariant Forms and Automorphisms of Locally Homogeneous Multisymplectic Manifolds
It is shown that the geometry of locally homogeneous multisymplectic
manifolds (that is, smooth manifolds equipped with a closed nondegenerate form
of degree > 1, which is locally homogeneous of degree k with respect to a local
Euler field) is characterized by their automorphisms. Thus, locally homogeneous
multisymplectic manifolds extend the family of classical geometries possessing
a similar property: symplectic, volume and contact. The proof of the first
result relies on the characterization of invariant differential forms with
respect to the graded Lie algebra of infinitesimal automorphisms, and on the
study of the local properties of Hamiltonian vector fields on locally
multisymplectic manifolds. In particular it is proved that the group of
multisymplectic diffeomorphisms acts (strongly locally) transitively on the
manifold. It is also shown that the graded Lie algebra of infinitesimal
automorphisms of a locally homogeneous multisymplectic manifold characterizes
their multisymplectic diffeomorphisms.Comment: 25 p.; LaTeX file. The paper has been partially rewritten. Some
terminology has been changed. The proof of some theorems and lemmas have been
revised. The title and the abstract are slightly modified. An appendix is
added. The bibliography is update
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
c-axis penetration depth in BiSrCaCuO single crystals measured by ac-susceptibility and cavity perturbation technique
The -axis penetration depth in
BiSrCaCuO (BSCCO) single crystals as a function of
temperature has been determined using two techniques, namely, measurements of
the ac-susceptibility at a frequency of 100 kHz and the surface impedance at
9.4 GHz. Both techniques yield an almost linear function
in the temperature range T<0.5 T_c.
Electrodynamic analysis of the impedance anisotropy has allowed us to estimate
m in BSCCO crystals overdoped with oxygen
( K) and m at the optimal doping
level ( K).Comment: 5 pages, 4 figure
Glycoprotein Ib activation by thrombin stimulates the energy metabolism in human platelets
<div><p>Thrombin-induced platelet activation requires substantial amounts of ATP. However, the specific contribution of each ATP-generating pathway <i>i</i>.<i>e</i>., oxidative phosphorylation (OxPhos) versus glycolysis and the biochemical mechanisms involved in the thrombin-induced activation of energy metabolism remain unclear. Here we report an integral analysis on the role of both energy pathways in human platelets activated by several agonists, and the signal transducing mechanisms associated with such activation. We found that thrombin, Trap-6, arachidonic acid, collagen, A23187, epinephrine and ADP significantly increased glycolytic flux (3–38 times <i>vs</i>. non-activated platelets) whereas ristocetin was ineffective. OxPhos (33 times) and mitochondrial transmembrane potential (88%) were increased only by thrombin. OxPhos was the main source of ATP in thrombin-activated platelets, whereas in platelets activated by any of the other agonists, glycolysis was the principal ATP supplier. In order to establish the biochemical mechanisms involved in the thrombin-induced OxPhos activation in platelets, several signaling pathways associated with mitochondrial activation were analyzed. Wortmannin and LY294002 (PI3K/Akt pathway inhibitors), ristocetin and heparin (GPIb inhibitors) as well as resveratrol, ATP (calcium-release inhibitors) and PP1 (Tyr-phosphorylation inhibitor) prevented the thrombin-induced platelet activation. These results suggest that thrombin activates OxPhos and glycolysis through GPIb-dependent signaling involving PI3K and Akt activation, calcium mobilization and protein phosphorylation.</p></div
The CARMENES search for exoplanets around M dwarfs: Wing asymmetries of H, Na I D, and He I lines
Stellar activity is ubiquitously encountered in M dwarfs and often
characterised by the H line. In the most active M dwarfs, H is
found in emission, sometimes with a complex line profile. Previous studies have
reported extended wings and asymmetries in the H line during flares. We
used a total of 473 high-resolution spectra of 28 active M dwarfs obtained by
the CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths
with Near-infrared and optical Echelle Spectrographs) spectrograph to study the
occurrence of broadened and asymmetric H line profiles and their
association with flares, and examine possible physical explanations. We
detected a total of 41 flares and 67 broad, potentially asymmetric, wings in
H. The broadened H lines display a variety of profiles with
symmetric cases and both red and blue asymmetries. Although some of these line
profiles are found during flares, the majority are at least not obviously
associated with flaring. We propose a mechanism similar to coronal rain or
chromospheric downward condensations as a cause for the observed red
asymmetries; the symmetric cases may also be caused by Stark broadening. We
suggest that blue asymmetries are associated with rising material, and our
results are consistent with a prevalence of blue asymmetries during the flare
onset. Besides the H asymmetries, we find some cases of additional line
asymmetries in \ion{He}{i} D, \ion{Na}{i}~D lines, and the \ion{He}{i}
line at 10830\,\AA\, taken all simultaneously thanks to the large wavelength
coverage of CARMENES. Our study shows that asymmetric H lines are a
rather common phenomenon in M~dwarfs and need to be studied in more detail to
obtain a better understanding of the atmospheric dynamics in these objects.Comment: 28 pages, 67 figures, accepted to A&
The CARMENES search for exoplanets around M dwarfs. Period search in H, Na I D, and Ca II IRT lines
We use spectra from CARMENES, the Calar Alto high-Resolution search for M
dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs, to
search for periods in chromospheric indices in 16 M0 to M2 dwarfs. We measure
spectral indices in the H, the Ca II infrared triplet (IRT), and the Na
I D lines to study which of these indices are best-suited to find rotation
periods in these stars. Moreover, we test a number of different period-search
algorithms, namely the string length method, the phase dispersion minimisation,
the generalized Lomb-Scargle periodogram, and the Gaussian process regression
with quasi-periodic kernel. We find periods in four stars using H and
in five stars using the Ca II IRT, two of which have not been found before. Our
results show that both H and the Ca II IRT lines are well suited for
period searches, with the Ca II IRT index performing slightly better than
H. Unfortunately, the Na I D lines are strongly affected by telluric
airglow, and we could not find any rotation period using this index. Further,
different definitions of the line indices have no major impact on the results.
Comparing the different search methods, the string length method and the phase
dispersion minimisation perform worst, while Gaussian process models produce
the smallest numbers of false positives and non-detections.Comment: 14 pages + 17 pages appendix, 9+16 figures, accepted to A&
Geometric Approach to Pontryagin's Maximum Principle
Since the second half of the 20th century, Pontryagin's Maximum Principle has
been widely discussed and used as a method to solve optimal control problems in
medicine, robotics, finance, engineering, astronomy. Here, we focus on the
proof and on the understanding of this Principle, using as much geometric ideas
and geometric tools as possible. This approach provides a better and clearer
understanding of the Principle and, in particular, of the role of the abnormal
extremals. These extremals are interesting because they do not depend on the
cost function, but only on the control system. Moreover, they were discarded as
solutions until the nineties, when examples of strict abnormal optimal curves
were found. In order to give a detailed exposition of the proof, the paper is
mostly self\textendash{}contained, which forces us to consider different areas
in mathematics such as algebra, analysis, geometry.Comment: Final version. Minors changes have been made. 56 page
Photoacclimation strategies in northeastern Atlantic seagrasses: Integrating responses across plant organizational levels
Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels (meadow, shoot, leaf and chloroplast level). Yet, comparative studies, to identify species' strategies, and integration of the relative importance of photoacclimatory adjustments at different levels are still missing. The variation in photoacclimatory responses at the chloroplast and leaf level were studied along individual leaves of Cymodocea nodosa, Zostera marina and Z. noltei, including measurements of variable chlorophyll fluorescence, photosynthesis, photoprotective capacities, non-photochemical quenching and D1-protein repair, and assessments of variation in leaf anatomy and chloroplast distribution. Our results show that the slower-growing C. nodosa expressed rather limited physiological and biochemical adjustments in response to light availability, while both species of faster-growing Zostera showed high variability along the leaves. In contrast, the inverse pattern was found for leaf anatomical adjustments in response to light availability, which were more pronounced in C. nodosa. This integrative plant organizational level approach shows that seagrasses differ in their photoacclimatory strategies and that these are linked to the species' life history strategies, information that will be critical for predicting the responses of seagrasses to disturbances and to accordingly develop adequate management strategies.Fundacao para a Ciencia e Tecnologia (FCT), Portugal [PTDC/MAR-EST/4257/2014
Características del líquido sinovial en pacientes con artritis idiopática juvenil
Introducción: El análisis del líquido sinovial (LS) es una herramienta importante en el diagnóstico de pacientes con artritis idiopática juvenil (AIJ). Pacientes y métodos: Análisis retrospectivo de las características citológicas del LS obtenido de pacientes con AIJ en el periodo 2008-2016. Resultados: Se analizaron 102 LS de 59 pacientes. El 66% fueron mujeres y la forma clínica más frecuente fue la AIJ oligoarticular persistente (52,5%). La mediana de edad al inicio fue de 5 años (RIC 2,4-11,8). El LS generalmente era de características inflamatorias (mediana leucocitos 11.757/mm3; RIC 4.543-18.800) con predominio de polimorfonucleares (PMN, 61%; RIC 30-75). Ocho pacientes (14%) presentaron recuentos inferiores a 2.000 cél/mm3, con predominio de mononucleares (80%), mientras que 3 pacientes (5%) presentaron recuentos superiores a 50.000 cél/mm3, con predominio de PMN (90%). No se encontraron diferencias en los recuentos celulares entre las distintas formas de AIJ. La mediana del recuento de leucocitos de pacientes positivos para ANA fue un 20% inferior a la de niños negativos para ANA (9.340 vs. 11.600/mm3; p = 0,23). La proporción de PMN en LS tendía a aumentar conforme se incrementaba la VSG (p < 0,001) y/o la PCR (p = 0,03). No existe correlación del índice JADAS-10 con el recuento en LS (p = 0,4). El LS en artrocentesis simultáneas de diferentes articulaciones mostró una correlación significativa (p = 0,001). Conclusiones: El LS de pacientes con AIJ generalmente tiene características inflamatorias, aunque un 19% presentó recuentos inferiores a 2.000 o superiores a 50.000 cél/mm3. Los recuentos en pacientes positivos para ANA tendían a ser menores que en los negativos para ANA (no significativo). La proporción de PMN aumentaba con los reactantes.Introduction: Synovial fluid (SF) analysis is an important tool for the diagnosis of patients with juvenile idiopathic arthritis (JIA).
Patients and methods: A retrospective analysis was carried out of cytological features of SF samples obtained from patients with JIA during the period 2008-2016.
Results: A total of 102 SF samples from 59 patients were analysed. JIA was more common in females (66%). The most frequent form was persistent oligoarticular JIA (52.5%). The median age at onset was 5 years (IQR 2.4-11.8). SF usually showed an inflammatory pattern (median white blood cells count 11,757/mm3; IQR 4,543-18,800), with a predominance of polymorphonuclear (PMN) cells (61%; IQR 30-75). Eight patients (14%) had white blood cells counts of less than 2,000 cells/mm3, with predominance of mononuclear cells (80%), whereas 3 patients (5%) had white blood cells counts higher than 50,000 cells/mm3, with a predominance of PMN cells (90%). Synovial white blood cells count did not show significant differences among the different forms of JIA. The median synovial white blood cells count in ANA-positive patients was 20% lower than in ANA-negative (9,340 vs. 11,600/mm3; P=.23). The proportion of PMN increased with increasing levels of ESR (P<.001) and/or CRP (P=.03). No significant correlation was found between JADAS-10 and synovial white blood cells count (P=.4). SF obtained from different joints in simultaneous arthrocentesis showed a significant correlation P=.001).
Conclusion: SF from JIA patients usually had inflammatory characteristics, although 19% of the patients showed white blood cells counts below 2,000cells/mm3 or higher than 50,000cells/mm3. SF cell count was non-significantly lower in ANA-positive patients, and the proportion of PMN increased with increasing levels of ESR/CRP
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