1,530 research outputs found
Epistemología y política en el discurso pedagógico
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Sistemas caóticos y su aplicación a la encriptación de señales
La sincronización y control de señales caóticas es una activa área de investigación por sus posibles aplicaciones en telecomunicaciones y transmisión de señales [1, 2, 3, 4]. En el presente trabajo se estudia un sistema de comunicación basado
en la sincronización de dos sistemas no lineales caóticos, cada uno modelado a partir de las ecuaciones de movimiento de un péndulo forzado amortiguado y que se encuentran en el mismo punto de operación del espacio de parámetros.
Synchronization and control of chaotic signals is an active research area because of its applications
in telecommunications and secure signal transmission [1,2,3,4]. In this work a communication system
based in the synchronization of two chaotic nonlinear systems, each one being modeled by the motion
equations of a driven damped pendulum and operated in the same parameter space region is shown. Two
communication channels were used: the first one for the synchronizing signal and the second one for the
sent message. By using two channels the initial conditions sensibility problem is solved. In the receiver
system a feedback loop as a proportional controller is used in order to drive quickly the error between the
decoder and encoder states to zero. The last two facts make the system to be robust to external pertubative
signals such as noise in the communication channels
Tratamiento quirúrgico en las cifosis congénitas: Revisión de 14 pacientes
Los autores efectúan una revisión de 14 pacientes con cifosis congénita,
intervenidos entre los años 1979-1989, con un seguimiento medio de 7 años. La edad
media preoperatoria fue de 11 años (todos ellos mayores de 5 años), con una cifosis media
de 7 9 . En 6 casos se realizó una artrodesis posterior y en 8 una anterior combinada
con una fusión posterior. Inicialmente obtuvieron una corrección media de la curva de
18° con la artrodesis posterior y 20° con la artrodesis combinada. La pérdida postoperatoria
final fue de 10° y 8° respectivamente. En un caso, se produjo una pseudoartrosis
por fusión corta. Como complicaciones postoperatorias en 5 pacientes, una radiculopatía,
una infección superficial y cuatro protusiones de material que requirieron su extracción.
Los autores analizan los factores que han podido influir en los resultados obtenidos,
comparándolos posteriormente con los conseguidos por otros centros hospitalarios importantes.Fourteen patients with congenital kyphosis treated surgically between 1979-
1989 were reviewed. All had a follow-up of 2 years or more, with an average follow-up of 7 years.
The average age at surgery was 11 and the average kyphosis was 79°. Six cases had
posterior fusion only and eigth had combined anterior and posterior fusion. The results showed
an average correction of the curve at surgery of 18° with posterior arthrodesis and 20°
with combined arthrodesis. There was thus an average loss of 10° and 8° respectively from
the time of surgery in both types of treatment. Pseudoarthrosis by short fusion ocurred in
one case. Other complications after surgery were 1 radiculopathy, one wound infection and
four rod protusion (six patients). The factors that have influence in this results were analysed.
A comparison from the results of treatment at other medical centers was also carried
out
Forage Yield and Nutritive Value of 30 Cultivars of Maize for Silage in the Highland Valleys of Central Mexico
In Mexico, the selection of maize cultivars for forage has mainly been based on dry matter (DM) yields, not considering nutritional quality as an important evaluation parameter. The objective of this study was to assess forage yield and nutritive value of Highland and Subtropical maize cultivars for silage in the Highland Valleys of Central México
Contribución al estudio polarográfico de la l-bencilidenamino-4,6-difenil-2-piridona
Polarographic behaviour of l-benzylideneamine4,6-diphenyl-2-pyridone was studied in ethanol-Britton and Robinson buffer solution mixtures. This paper is specially concerned with the wave appeared at basic media and the adsorption effects on the DME
Nueva plataforma dinamométrica para el análisis y valoración del rendimiento deportivo
Un nuevo modelo de plataforma dinamométrica ha
sido desarrollado por el Instituto de Biomecánica de
Valencia (IBV) y se han fabricado sus primeros prototipos.
Permite la medida de la fuerza de reaccipón tridimensional,
en momento torsor y el punto de aplicación
de la fuerza, a una velocidad de muestre0 de hasta 1000
Hz (500 Hz para dos plataformas).
El nuevo diseño se caracteriza por poseer cuatro captadores
bidimensionales octogonales mecánicamente
desacoplados, placa superior de rigidez optimizada y
sensibilidad cruzada mínima
Genetic structure of Tetraclinis articulata, an endangered conifer of the western Mediterranean basin
Tetraclinis articulata (Vahl) Masters is a tree distributed throughout the western Mediterranean basin. It is included in the IUCN (International Union for Conservation of Nature) red list, and protected by law in several of the countries where it grows. In this study we examined the genetic diversity and genetic structure of 14 populations of T. articulata in its whole geographic range using ISSR (inter simple sequence repeat) markers. T. articulata showed moderate genetic diversity at intrapopulation level and high genetic differentiation. The distribution of genetic diversity among populations did not exhibit a linear pattern related to geographic distances, since all analyses (principal coordinate analysis, Unweighted pair group method with arithmetic mean dendrogram and Bayesian structure analysis) revealed that spanish population grouped with Malta
and Tunisia populations. Although it is possible that T. articulata earlier was natural in Southeast Spain, results suggest that the current population has been reintroduced into the Iberian Peninsula in historical times, due to its utility in mining and building. In addition, results could be used to propose management guidelines for the conservation of T. articulata.peer-reviewe
Productive Performance of Growing Cattle Grazing a Silvopastoral System with \u3cem\u3eLeucaena leucocephala\u3c/em\u3e
In tropical regions, the feeding of cattle is usually based on the grazing of medium to low quality grasses. Low fertility of soils, changing climatic conditions and the poor management of pastures, have further reduced the quality and forage yield of pastures. The low availability and quality of grasses gives modest weight gains for grazing cattle and this in-turn causes low economical efficiency of cattle production systems (Campos et al. 2011). Silvopastoral systems represent a sustainable option for meat and milk production in the tropics. The association of grasses with legumes such as Leucaena leucocephala (leucaena) supply forage with high concentration of crude protein (Barros et al. 2012). There are reports in the scientific literature which show that intake of leucaena can result in good rates of growth in cattle (e.g. Shelton and Dalzell 2007); however the presence of the free amino acid mimosine and its metabolites (3,4-DHP and 2,3-DHP) in leucaena when the anaerobic bacteria Synergistes jonesii (Allison et al. 1992) is absent from the rumen, may induce subclinical toxicity in grazing ruminants (Graham 2007; Dalzell et al. 2012; Phaikaew et al. 2012). There are no reports in Mexico regarding the rate of growth of cattle grazing silvopastoral systems with leucaena.
The aim of the present work was to evaluate the rate of growth of cattle grazing an association of Panicum maximum and leucaena compared to that of cattle fed a high grain ration (feedlot)
The Chemical Evolution Carousel of Spiral Galaxies : Azimuthal Variations of Oxygen Abundance in NGC1365
19 pages, 13 figures. Accepted to ApJThe spatial distribution of oxygen in the interstellar medium of galaxies is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a galaxy. We present here a case study in the nearby spiral galaxy NGC1365 using 3D optical data obtained in the TYPHOON Program. We find systematic azimuthal variations of the HII region oxygen abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal variations occur over a wide radial range of 0.3 to 0.7 R25 and peak at the two spiral arms in NGC1365. We show that the azimuthal variations can be explained by two physical processes: gas undergoes localized, sub-kpc scale self-enrichment when orbiting in the inter-arm region, and experiences efficient, kpc scale mixing-induced dilution when spiral density waves pass through. We construct a simple chemical evolution model to quantitatively test this picture and find that our toy model can reproduce the observations. This result suggests that the observed abundance variations in NGC1365 are a snapshot of the dynamical local enrichment of oxygen modulated by spiral-driven, periodic mixing and dilution.Peer reviewedFinal Published versio
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