ESTUDIO DE PROCESOS DE REVERSIÓN A LA MEDIA

Existen diversos procesos estocásticos adaptados para modelar comportamientos naturales, tales como biológicos, sociales, financieros, económicos… en delante se centrará la atención en presentar una descripción de un proceso particular, el de los procesos estocásticos con reversión a la media, los cuales han sido utilizados, por ejemplo, para representar el comportamiento de algunos mercados, como es el caso del mercado energético. El principal objetivo cuando se modela el comportamiento de alguna variable como un proceso con reversión a la media, consiste en determinar los parámetros presentes en el modelo, los cuales pueden o no tener algún significado “realista” o pueden representar simplemente algunos valores particulares. En el presente trabajo se mostrará una metodología en la estimación de parámetros en procesos con reversión a la media a partir de una revisión bibliográfica e implementación de algoritmos en MATLAB abarcando una amplia gama de situaciones con las cuales se hace evidente la importancia de la estimación de parámetros es la modelación de dichos procesos

Análisis, Descripción y Simulación de Modelos Estocásticos de Tasas de Interés

Los estudios acerca de los modelos de tasas de interés tienen una gran cantidad de aplicaciones en los campos económico, financiero, energético, productivo, entre otros. El descubrir la estructura que determina el comportamiento de las tasas de interés permite realizar análisis de una manera más eficiente, conociendo los potenciales y limitaciones los modelos desarrollados. Muchos modelos, tanto en el campo discreto como en el campo continuo, han sido propuestos para modelar el comportamiento de las tasas de interés, algunas veces partiendo de conocimientos a priori y algunas otras veces utilizando metodologías que permitan inferir particularidades del proceso. Los modelos de series de tiempo (en desarrollos discretos) y las ecuaciones diferenciales estocásticas (en los casos continuos) han sido dos de las metodologías más usadas tanto en la modelación como en el análisis de los procesos de tasas de interés. En este trabajo se presentan diferentes modelos teniendo como base las ecuaciones diferenciales estocásticas, aunque muchos de los análisis relacionados con ellos se desarrollen en el campo discreto, como se verá más adelante..

Heterogeneity in Kv2 Channel Expression Shapes Action Potential Characteristics and Firing Patterns in CA1 versus CA2 Hippocampal Pyramidal Neurons.

The CA1 region of the hippocampus plays a critical role in spatial and contextual memory, and has well-established circuitry, function and plasticity. In contrast, the properties of the flanking CA2 pyramidal neurons (PNs), important for social memory, and lacking CA1-like plasticity, remain relatively understudied. In particular, little is known regarding the expression of voltage-gated K+ (Kv) channels and the contribution of these channels to the distinct properties of intrinsic excitability, action potential (AP) waveform, firing patterns and neurotransmission between CA1 and CA2 PNs. In the present study, we used multiplex fluorescence immunolabeling of mouse brain sections, and whole-cell recordings in acute mouse brain slices, to define the role of heterogeneous expression of Kv2 family Kv channels in CA1 versus CA2 pyramidal cell excitability. Our results show that the somatodendritic delayed rectifier Kv channel subunits Kv2.1, Kv2.2, and their auxiliary subunit AMIGO-1 have region-specific differences in expression in PNs, with the highest expression levels in CA1, a sharp decrease at the CA1-CA2 boundary, and significantly reduced levels in CA2 neurons. PNs in CA1 exhibit a robust contribution of Guangxitoxin-1E-sensitive Kv2-based delayed rectifier current to AP shape and after-hyperpolarization potential (AHP) relative to that seen in CA2 PNs. Our results indicate that robust Kv2 channel expression confers a distinct pattern of intrinsic excitability to CA1 PNs, potentially contributing to their different roles in hippocampal network function

The health from the humanist perspective of Blas Álvarez de Miraval

A pesar de que existen diferentes estudios en las Ciencias de la Actividad Física y del Deporte sobre autores humanistas, el objetivo del presente trabajo es poner en valor la obra de una de las figuras más importantes del humanismo español, Blas Álvarez de Miraval, insigne médico y teólogo, a través del análisis pormenorizado de su obra cumbre, titulada De la conservación de la salud del cuerpo y el alma, cuyos resultados arrojan una visión única y diferente de lo que ha de ser la conservación de la salud desde una perspectiva integral por parte del individuoIn spite of the fact that there are different studies in the Sciences of the Sport on humanist authors, the aim of the present work is to put of relevancy the work of one of the most important figures of the Spanish humanism, Blas Álvarez de Miraval, celebrated doctor and theologian, with regard to the Sciences of the Physical Activity and of the Sport by means of the study detailed of his greatest work, "Of the conservation of the health of the body and the soul", which results throw an only and different vision from what has to be the conservation of the health from the integral care of the individua

Development and evaluation of a geographic information retrieval system using fine grained toponyms

Geographic information retrieval (GIR) is concerned with returning information in response to an information need, typically expressed in terms of a thematic and spatial component linked by a spatial relationship. However, evaluation initiatives have often failed to show significant differences between simple text baselines and more complex spatially enabled GIR approaches. We explore the effectiveness of three systems (a text baseline, spatial query expansion, and a full GIR system utilizing both text and spatial indexes) at retrieving documents from a corpus describing mountaineering expeditions, centred around fine grained toponyms. To allow evaluation, we use user generated content (UGC) in the form of metadata associated with individual articles to build a test collection of queries and judgments. The test collection allowed us to demonstrate that a GIR-based method significantly outperformed a text baseline for all but very specific queries associated with very small query radii. We argue that such approaches to test collection development have much to offer in the evaluation of GIR

Differential nitrogen cycling in semiarid sub-shrubs with contrasting leaf habit

Nitrogen (N) is, after water, the most limiting resource in semiarid ecosystems. However, knowledge on the N cycling ability of semiarid woody plants is still very rudimentary. This study analyzed the seasonal change in the N concentrations and pools of the leaves and woody organs of two species of semiarid sub-shrubs with contrasting leaf habit. The ability of both species to uptake, remobilize and recycle N, plus the main storage organ for N during summer drought were evaluated. We combined an observational approach in the field with experimental 15N labelling of adult individuals grown in sand culture. Seasonal patterns of N concentrations were different between species and organs and foliar N concentrations of the summer deciduous Lepidium subulatum were almost double those of the evergreen Linum suffruticosum. L. subulatum up took ca. 60% more external N than the evergreen and it also had a higher N resorption efficiency and proficiency. Contrastingly, L. suffruticosum relied more on internal N remobilization for shoot growth. Differently to temperate species, the evergreen stored N preferentially in the main stem and old trunks, while the summer deciduous stored it in the foliage and young stems. The higher ability of L. subulatum to uptake external N can be related to its ability to perform opportunistic growth and exploit the sporadic pulses of N typical of semiarid ecosystems. Such ability may also explain its high foliar N concentrations and its preferential storage of N in leaves and young stems. Finally, L. suffruticosum had a lower ability to recycle N during leaf senescence. These strategies contrast with those of evergreen and deciduous species from temperate and boreal areas, highlighting the need of further studies on semiarid and arid plants

Pressure-induced structural phase transitions in the AMnF4 series (A=Cs, Rb, K) studied by synchrotron x-ray powder diffraction: Correlation between hydrostatic and chemical pressure

The effect of applying hydrostatic pressure in the layered-perovskite AMnF4 (A=Cs, Rb, K) series has been studied using energy-dispersive synchrotron x-ray powder diffraction at pressures between ambient and 20 GPa. At ambient pressure CsMnF4 is tetragonal with space group P4/n, RbMnF4 is orthorhombic with space group Pmab and KMnF4 is monoclinic with space group P21/a. CsMnF4 was found to undergo a first-order structural phase transition, from tetragonal to orthorhombic symmetry at Pc1=1.4±0.2 GPa. At pressures in excess of Pc2=6.3±1 GPa, for the Cs derivative, and Pc3.=4.5±1 GPa, for the Rb derivative, the symmetry appears to be monoclinic. Moreover, the critical unit-cell volumes associated with Pc1, Pc2, and Pc3 are slightly higher than the ambient pressure unit-cell volumes of RbMnF4 for Pc1 and KMnF4 for Pc2 and Pc3. Hydrostatic pressure has been found to have a similar effect on the crystal symmetry of the series as the decreasing of the radius of the alkaline ion from Cs to Rb and K. A correlation between hydrostatic and chemical pressure can therefore be established from the structural point of view for the AMnF4 series. The tetragonal to orthorhombic transition of CsMnF4 has been found to be inhibited when NaCl is used as an internal pressure calibrant. The partial substitution of Cs by Na in CsMnF4 at Pc1 has been shown to be a likely explanation for this behavior. The anisotropic broadening of the Bragg peaks for pressures higher than Pc1 has been analyzed in terms of microstrain affecting the CsMnF4 lattice due to Na incorporation. A substitutional reaction has been shown to be a competitive process, versus a structural phase transition, that enables the system to return to equilibrium after applying pressure on it. Finally, the equation of state associated with the different high-pressure phases has been calculated including compressibilities.We would like to thank the C.I.C.Y.T. for Grants No. MAT91-681, MAT94-43, and MAT95-1490-E, and U.K. Science & Engineering Research Council for providing Synchrotron Radiation beam time under the E.C. Large Scale Facilities Programme.Peer Reviewe

Wireless internet architecture and testbed for wineglass

One of the most challenging issues in the area of mobile communication is the deployment of IPbased wireless multimedia networks in public and business environments. The public branch may involve public mobile networks, like UMTS as 3G system, while the business branch introduces local radio access networks by means of W-LANs. Conventional mobile networks realise mobile specific functionality, e.g. mobility management or authentication and accounting, by implementing appropriate mechanisms in specific switching nodes (e.g. SGSN in GPRS). In order to exploit the full potential of IP networking solutions a replacement of these mechanisms by IP-based solutions might be appropriate. In addition current and innovative future services in mobile environments require at least soft-guaranteed, differentiated QoS. Therefore the WINE GLASS project investigates and implements enhanced IP-based techniques supporting mobility and QoS in a wireless Internet architecture. As a means to verify the applicability of the implemented solutions, location-aware services deploying both IP-mobility and QoS mechanisms will be implemented and demonstratedPeer ReviewedPostprint (published version

Shifted loops and coercivity from field imprinted high energy barriers in ferritin and ferrihydrite nanoparticles

We show that the coercive field in ferritin and ferrihydrite depends on the maximum magnetic field in a hysteresis loop and that coercivity and loop shifts depend both on the maximum and cooling fields. In the case of ferritin we show that the time dependence of the magnetization also depends on the maximum and previous cooling fields. This behavior is associated to changes in the intra-particle energy barriers imprinted by these fields. Accordingly, the dependence of the coercive and loop shift fields with the maximum field in ferritin and ferrihydrite can be described within the frame of a uniform-rotation model considering a dependence of the energy barrier with the maximum and the cooling fields.Comment: 8 pages, 5 figures. Accepted for publication in Phys. Rev. B. Final version with improved writing and figure