2,958 research outputs found
Caracterización del xilema de 352 conÃferas
Following the traditional methods of preparation and description of wood at microscopy level, 352 descriptions of the woods of conifers were made. For the characterisation of each wood a multiple entry key was prepared, with a total of 81 features divided into four groups: tracheids with 29 features, axial parenchyma with 8, wood rays with 37 and resin canals with 7.Siguiendo los métodos tradicionales de preparación y descripción de la madera a nivel microscópico, se han realizado 352 descripciones de maderas de coníferas. Para la caracterización de cada madera se ha elaborado una clave de múltiple entrada con un total de 81 caracteres dividida en cuatro grupos: traqueidas con 29 caracteres, parénquima axial 8, radios leñosos 37 y canales resiníferos 7
Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star
We report the detection of an unusually high lithium content in HD 232862, a
field giant classified as a G8II star, and hosting a magnetic field. With the
spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high
resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg
and HD 21018. From spectral synthesis we have inferred stellar parameters and
measured lithium abundances that we have compared to predictions from
evolutionary models. We have also analysed Stokes V signatures, looking for a
magnetic field on these giants. HD 232862, presents a very high abundance of
lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value
expected at this spectral type and for this luminosity class (i.e, G8II). The
evolutionary stage of HD 232862 has been precised, and it suggests a mass in
the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0
solar mass, at the bottom of the Red Giant Branch. Besides, a time variable
Stokes V signature has been detected in the data of HD 232862 and KU Peg,
pointing to the presence of a magnetic field at the surface of these two
rapidly rotating active stars.Comment: 11 pages, 9 figures ; accepted by Astronomy and Astrophysic
Redes neuronales artificiales en el control de procesos por variables: aplicación en la fabricación de tableros de partÃculas
Artificial neural networks are an efficient tool for modelling production control processes using data from the actual production as well as simulated or design of experiments data. In this study two artificial neural networks were combined with the control process charts and it was checked whether the data obtained by the networks were valid for variable process control in particleboard manufacture. The networks made it possible to obtain the mean and standard deviation of the internal bond strength of the particleboard within acceptable margins using known data of thickness, density, moisture content, swelling and absorption. The networks obtained met the acceptance criteria for test values from non-standard test methods, as well as the criteria for using these values in statistical process control.Las redes neuronales artificiales son una herramienta eficaz para el modelado de los procesos de control de producción, tanto partiendo de datos de la propia producción como de datos simulados o procedentes de diseños de experimentos. En este estudio se han combinado dos redes neuronales artificiales con los gráficos de control de procesos y se ha comprobado si los datos obtenidos con ellas eran válidos para el control de producción por variables en la fabricación de tableros de partículas. Las redes han permitido obtener valores de la media y la desviación típica de la cohesión interna del tablero de partículas dentro de unos márgenes aceptables a partir de datos conocidos de espesor, densidad, contenido de humedad, hinchazón y absorción. Las redes obtenidas han cumplido con los requisitos de aceptación de valores de ensayo por métodos alternativos al normalizado y con los requisitos impuestos para su utilización en el control estadístico de procesos
Long time universality of black-hole lasers
For flowing quantum gases, it has been found that at long times an initial
black-hole laser (BHL) configuration exhibits only two possible states: the
ground state or a periodic self-oscillating state of continuous emission of
solitons. So far, all the works on this subject are based on a highly idealized
model, quite difficult to implement experimentally. Here we study the
instability spectrum and the time evolution of a recently proposed realistic
model of a BHL, thus providing a useful theoretical tool for the clear
identification of black-hole lasing in future experiments. We further confirm
the existence of a well-defined phase diagram at long times, which bespeaks
universality in the long-time behavior of a BHL. Additionally, we develop a
complementary model in which the same potential profile is applied to a
subsonic homogeneous flowing condensate that, despite not forming a BHL,
evolves towards the same phase diagram as the associated BHL model. This result
reveals an even stronger form of robustness in the long-time behavior with
respect to the transient, which goes beyond what has been described in the
previous literature.Comment: 14 pages, 8 figures. Final version of the manuscrip
AnatomÃa de la madera de Abies spp. del área mediterránea: aproximación filética
An analysis was made of the wood anatomy of seven species, one subspecies and two varieties of the genus Abies from the Mediterranean area (A. alba, A. borisii-regis, A. cephalonica, A. cilicica, A. nordmanniana, A. nordmanniana subsp. equi-trojani, A. numidica, A. pinsapo, A. pinsapo var. marocana and A. pinsapo var. tazaotana) in order to find phyletically relevant features to help clarify and complement the evolutionary patterns based on molecular studies. The wood structure within the genus was qualitatively similar, except for specific features characteristic of certain provenances. However, the wood biometry allowed the different taxa to be grouped in accordance with their anatomical similarity. A. alba, A. pinsapo, A. pinsapo var. marocana and A. pinsapo var. tazaotana possess biometric features which distinguish them from the other Mediterranean firs. Furthermore, A. numidica showed biometric features which distinguish it from the eastern firs (A. borisii-regis, A. cephalonica, A. cilicica, A. nordmanniana and A. nordmanniana subsp. equi-trojani) and place it closer to certain Iberian populations of A. pinsapo. The maximum ray height in number of cells, frequency of rays with more than 30 cells and tracheid length can be regarded as specific patterns of the Mediterranean fir phylum.En este trabajo se ha analizado la anatomía de la madera de siete especies, una subespecie y dos variedades del género Abies procedentes del área mediterránea (A. alba, A. borisii-regis, A. cephalonica, A. cilicica, A. nordmanniana, A. nordmanniana subsp. equi-trojani, A. numidica, A. pinsapo, A. pinsapo var. marocana y A. pinsapo var. tazaotana) con el fin de buscar caracteres filéticamente relevantes que ayuden a clarificar y complementar los patrones evolutivos basados en estudios moleculares. Las maderas estudiadas fueron cualitativamente similares, exceptuando ciertos caracteres propios de algunas procedencias. No obstante, la biometría de la madera permitió agrupar los diferentes taxones según su afinidad anatómica. A. alba, A. pinsapo, A. pinsapo var. marocana y A. pinsapo var. tazaotana mostraron caracteres biométricos afines que los distinguen del resto de abetos mediterráneos. Por otro lado, A. numidica mostró caracteres biométricos que lo distinguen de los abetos orientales (A. borisii-regis, A. cephalonica, A. cilicica, A. nordmanniana y A. nordmanniana subsp. equi-trojani) y lo asemejan a determinadas poblaciones ibéricas de A. pinsapo. La altura máxima de radios en número de células, la frecuencia de radios de más de 30 células y la longitud de traqueidas, pueden ser considerados como patrones específicos del phylum de los abetos mediterráneos
An effective lowest Landau level treatment of demagnetization in superconducting mesoscopic disks
Demagnetization, which is inherently present in the magnetic response of
small finite-size superconductors, can be accounted for by an effective
within a two-dimensional lowest Landau level approximation of the
Ginzburg-Landau functional. We show this by comparing the equilibrium
magnetization of superconducting mesoscopic disks obtained from the numerical
solution of the three-dimensional Ginzburg-Landau equations with that obtained
in the ``effective'' LLL approximation.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Mesoscopic superconducting disks
Using the non-linear Ginzburg-Landau (GL) eqs. type I superconducting disks
of finite radius () and thickness () are studied in a perpendicular
magnetic field. Depending on and , first or second order phase
transitions are found for the normal to superconducting state. For sufficiently
large several transitions in the superconducting phase are found
corresponding to different angular momentum giant vortex states. In increasing
magnetic field the superconductor is in its ground state, while in field down
sweep it is possible to drive the system into metastable states. We also
present a quantitative analysis of the relation between the detector output and
the sample magnetization. The latter, and the incorporation of the finite
thickness of the disks, are essential in order to obtain quantitative agreement
with experiment.Comment: A brief review with new result
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