1,005 research outputs found
Sensibilidad a la colocación de los marcadores en el modelo convencional de análisis cinemático de la marcha
La correcta evaluación del movimiento articular a través de sistemas de análisis del movimiento depende, entre otros factores, de la correcta colocación de los marcadores reflectantes sobre los sujetos analizados. En el modelo convencional de marcha, de los 15 marcadores de miembro inferior, la mayorÃa se localizan en puntos anatómicos fáciles de localizar y que tienen poca posibilidad de error. Sin embargo, hay dificultad en otros, como el de la articulación de la rodilla y, sobre todo, en los del muslo y pierna.
En el estudio, se empleó un sistema VICON 460, con el que se analizó la cinemática de miembro inferior de 5 sujetos adultos sanos (2 mujeres, 3 varones). Para evaluar los movimientos articulares se empleó el modelo convencional de marcha. Determinada la posición correcta de los marcadores en cada sujeto, se procedió a la variación por separado de los marcadores de la rodilla, el muslo y la pierna, moviendo cada uno 15 mm anterior y posteriormente con relación a la posición inicial.
Estos pequeños desplazamientos producen importantes variaciones en los resultados cinemáticos obtenidos. Entre ellas en el varo-valgo de rodilla, parámetro que es de gran utilidad a la hora de detectar errores en la colocación de los marcadores
Do Omnivorous Shrimp Influence Mayfly Nymphs in a Tropical Island Stream?
Interspecific interactions can play an important role in determining habitat selection and resource use between competing species. We examined interactions between an omnivorous shrimp and a grazing mayfly, two co-dominant taxa found in Puerto Rican headwater streams, to assess how predator presence may influence mayfly resource use and instantaneous growth in a tropical rainforest ecosystem. We conducted a series of behavioral and growth experiments to determine the effects of the freshwater shrimp, Xiphocaris elongata, on the growth rate and resource selection of mayfly nymphs in the family Leptophlebiidae. For resource choice assessments, we conducted a series of five day laboratory experiments where mayflies were given access to two resource substrate choices (cobble vs. leaves) in the presence or absence of shrimp. To assess for the effects of shrimp on mayfly fitness, we measured mayfly growth in laboratory aquaria after five days using four treatments (cobble, leaves, cobble + leaves, no resource) in the presence or absence of shrimp. In resource choice experiments, mayflies showed preference for cobble over leaf substrata (p\u3c0.05) regardless of the presence of shrimps, however, the preference for cobble was significantly greater when shrimp were present in the leaf habitat. In growth experiments, there were no statistical differences in mayfly growth in the presence or absence of shrimp (p=0.07). However, we measured increased mayfly nymph growth in the absence of predators and when both cobble and leaves were available. Our results suggest that interspecific interactions between these taxa could potentially influence organic matter resource dynamics (e.g., leaf litter processing and export) in Puerto Rican streams
Stability of the phase motion in race-track microtrons
We model the phase oscillations of electrons in race-track microtrons by means of an area preserving map with a fixed point at the origin, which represents the synchronous trajectory of a reference particle in the beam. We study the nonlinear stability of the origin in terms of the synchronous phase —the phase of the synchronous particle at the injection. We estimate the size and shape of the stability domain around the origin, whose main connected component is enclosed by an invariant curve. We describe the evolution of the stability domain as the synchronous phase varies. We also clarify the role of the stable and unstable invariant curves of some hyperbolic (fixed or periodic) points.Peer ReviewedPostprint (author's final draft
NLTE determination of the aluminium abundance in a homogeneous sample of extremely metal-poor stars
Aims: Aluminium is a key element to constrain the models of the chemical
enrichment and the yields of the first supernovae. But obtaining precise Al
abundances in extremely metal-poor (EMP) stars requires that the non-LTE
effects be carefully taken into account.
Methods: The NLTE profiles of the blue resonance aluminium lines have been
computed in a sample of 53 extremely metal-poor stars with a modified version
of the program MULTI applied to an atomic model of the Al atom with 78 levels
of Al I and 13 levels of Al II, and compared to the observations.
Results: With these new determinations, all the stars of the sample show a
ratio Al/Fe close to the solar value: [Al/Fe] =-0.06 +- 0.10 with a very small
scatter. These results are compared to the models of the chemical evolution of
the halo using different models of SN II and are compatible with recent
computations. The sodium-rich giants are not found to be also aluminium-rich
and thus, as expected, the convection in these giants only brings to the
surface the products of the Ne-Na cycle.Comment: To be published on A&
Low X-Ray Luminosity Galaxy Clusters: Main goals, sample selection, photometric and spectroscopic observations
We present the study of nineteen low X-ray luminosity galaxy clusters (L 0.5--45 erg s), selected from the ROSAT
Position Sensitive Proportional Counters (PSPC) Pointed Observations (Vikhlinin
et al. 1998) and the revised version of Mullis et al. (2003) in the redshift
range of 0.16 to 0.7. This is the introductory paper of a series presenting the
sample selection, photometric and spectroscopic observations and data
reduction. Photometric data in different passbands were taken for eight galaxy
clusters at Las Campanas Observatory; three clusters at Cerro Tololo
Interamerican Observatory; and eight clusters at the Gemini Observatory.
Spectroscopic data were collected for only four galaxy clusters using Gemini
telescopes. With the photometry, the galaxies were defined based on the
star-galaxy separation taking into account photometric parameters. For each
galaxy cluster, the catalogues contain the PSF and aperture magnitudes of
galaxies within the 90\% completeness limit. They are used together with
structural parameters to study the galaxy morphology and to estimate
photometric redshifts. With the spectroscopy, the derived galaxy velocity
dispersion of our clusters ranged from 507 km~s for [VMF98]022 to 775
km~s for [VMF98]097 with signs of substructure. Cluster membership has
been extensively discussed taking into account spectroscopic and photometric
redshift estimates. In this sense, members are the galaxies within a projected
radius of 0.75 Mpc from the X-ray mission peak and with cluster centric
velocities smaller than the cluster velocity dispersion or 6000 km~s,
respectively. These results will be used in forthcoming papers to study, among
the main topics, the red cluster sequence, blue cloud and green populations;
the galaxy luminosity function and cluster dynamics.Comment: 13 pages, 6 tables, 9 figures. Uses emulateapj. Accepted for
publication in The Astronomical Journal. Some formatting errors fixe
Influence of stress and depression on the immune system in patients evaluated in an anti-aging unit
Background: There is compelling evidence pointing out that stress and depression
produce a dramatic impact on human well-being mainly through impairing the regular
function of the immune system and producing a low-chronic inflammation status that
favors the occurrence of infections, metabolic diseases, and even cancer. The present
work aims to evaluate the stress/depression levels of some patients treated in an
antiaging unit and detect any potential relationship with their immune system status
prior of the implementation of a physical/psychological program designed to prevent
health deterioration.
Methods: We evaluated 48 patients (16 men and 32 women with a mean age of
55.11 ± 10.71 years) from middle-upper class from psychological and immunological
points of view. In particular, we analyzed neutrophil chemotaxis and phagocytosis;
lymphocyte chemotaxis and proliferation, and natural killer (NK) cell activity.
Results: Women showed more depressive symptoms than men. Chemotaxis levels of
lymphocytes and neutrophils in women showed a significant reduction compared with
those in men. We also found a strong negative correlation between depression and NK
cell function. This correlation was also significant independently of gender.
Conclusion: We conclude that NK activity is affected at least by depression state, and
we propose that a combined treatment consisting of cognitive behavioral therapy and
physical activity programs might improve patient health deterioration
Chemical similarities between Galactic bulge and local thick disk red giant stars
The evolution of the Milky Way bulge and its relationship with the other
Galactic populations is still poorly understood. The bulge has been suggested
to be either a merger-driven classical bulge or the product of a dynamical
instability of the inner disk. To probe the star formation history, the initial
mass function and stellar nucleosynthesis of the bulge, we performed an
elemental abundance analysis of bulge red giant stars. We also completed an
identical study of local thin disk, thick disk and halo giants to establish the
chemical differences and similarities between the various populations.
High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in
the solar neighborhood were acquired with Gemini/Phoenix. All stars have
similar stellar parameters but cover a broad range in metallicity. A standard
1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O
and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk
and thick disk stars ensured that systematic errors were minimized. We confirm
the well-established differences for [O/Fe] (at a given metallicity) between
the local thin and thick disks. For the elements investigated, we find no
chemical distinction between the bulge and the local thick disk, which is in
contrast to previous studies relying on literature values for disk dwarf stars
in the solar neighborhood. Our findings suggest that the bulge and local thick
disk experienced similar, but not necessarily shared, chemical evolution
histories. We argue that their formation timescales, star formation rates and
initial mass functions were similar.Comment: Accepted for publication in A&A, 5 page
Microstructure and mechanical properties of high temperature protonic conductors fabricated by melt growth
Se han estudiado conductores protónicos de alta temperatura (CPAT) fabricados por fusión de zona flotante asistida por láser (SrCe0.9Y0.1O3-δ
,
SrCe0.8Y0.2O3-δ
, SrZr0.9Y0.1O3-δ
, SrZr0.8Y0.2O3-δ
, Sr3
(Ca1.18Nb1.82)O9-δ
y SrTi0.95Sc0.05O3-δ
). La caracterización microestructural se ha realizado mediante
MicroscopÃa Electrónica de Barrido y Transmisión (MEB, MET). Los materiales tienen una estructura celular, con células de anchuras entre
10-50 µm y regiones intercelulares superiores a 1 µm de espesor. El análisis de difracción indica que las células son cristalinas y que la región
intercelular es amorfa. La MET revela que las células presentan múltiples defectos planares, separadas por regiones rotadas con la misma
estructura cristalográfica. Las propiedades mecánicas a altas temperaturas fueron estudiadas a partir de ensayos de compresión bajo velocidad
de deformación y carga constantes. Nuestros materiales resisten tensiones de 500 MPa a 700 ºC, 400 MPa a 1100 ºC y 370 MPa a 1300 ºC,
observándose deformación plástica a 1100 ºC y 1300 ºC. El mejor comportamiento mecánico fue obtenido para los sistemas Sr3
(Ca1.18Nb1.82)O9-
δ
_ y SrZr0.9Y0.1O3-δ
. Las tensiones y resistencias en fluencia de estos sistemas son mejores que las de las cerámicas policristalinas CPAT de
similar estructura y composición. Después de los ensayos mecánicos, las muestras fueron estudiadas por MEB y MET. La fractura comenzó a
propagarse siguiendo las regiones intercelulares. En las muestras deformadas plásticamente se detecta la actividad de dislocaciones.High temperature protonic conductors (HTPC) were successfully fabricated by melt growth using the laser heated floating zone method
(SrCe0.9Y0.1O3-δ
, SrCe0.8Y0.2O3-δ
, SrZr0.9Y0.1O3-δ
, SrZr0.8Y0.2O3-δ
, Sr3
(Ca1.18Nb1.82)O9-δ
and SrTi0.95Sc0.05O3-δ
). Microstructural characterization was
performed by scanning and transmission electron microscopy (SEM, TEM). The materials have a cellular microstructure, with cell width
ranging between 10-50 µm and intercellular regions up to 1 µm thick. The diffraction analysis indicates that the cells are crystalline, and
the intercellular regions are amorphous. TEM reveals that the cells present multiple planar defects, separating rotated regions with of same
crystallographic structure. The high temperature mechanical properties were studied by compression tests performed under constant
strain rate and constant load. Remarkable high temperature strengths of 500 MPa at 700 o
C, 400 MPa at 1100 o
C and 370 MPa at 1300 o
C
were measured, being the plastic deformation evident at 1100 ºC and 1300 ºC. The best mechanical behavior was obtained for the systems
Sr3
(Ca1.18Nb1.82)O9-δ and SrZr0.9Y0.1O3-δ
. The strengths and creep resistance of these systems are better than the ones of polycrystalline HTPC
ceramics of similar structure and composition. After the mechanical tests, the samples were studied by SEM and TEM. The fracture started to
propagate following the intercellular regions. In the plastically deformed samples, dislocation activity was found
Linfangioma QuÃstico del Mesenterio. Reporte de un caso clÃnico radiológico
Los linfangiomas intraabdominales constituyen una patologÃa poco frecuente, que en la mayorÃa de los casosestá presente antes de los 5 años de edad, aunque en el 75% de las ocasiones se manifiestan en la edadadulta. Su incidencia se calcula en uno de cada 140.000 ingresos hospitalarios. Se localizan en cualquierregión del mesenterio gastrointestinal, aunque con mayor frecuencia se presentan en el intestino delgado.Representan el 2% de las lesiones benignas del intestino delgado y muy raramente se transforman enmalignos. El método diagnóstico de elección es la ecografÃa, en la que se determina su consistencia ycontenido. El estudio debe ser completado con otras pruebas de diagnóstico mediante imagen, como TC oRMN, que nos proporcionan información de la localización, el tamaño y las relaciones con los órganosvecinos. El tratamiento recomendado es la exéresis quirúrgica. Se presenta el caso de un hombre de 47 añoscon tumor localizado en mesenterio, tratado quirúrgicamente. El estudio histopatológico reveló LinfangiomaquÃstico del mesenterio. Se analizan los aspectos más relevantes de este tipo de tumor, con énfasis en eldiagnóstico por imágene
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