VLBA Determination of the Distance to Nearby Star-forming Regions. IV. A Preliminary Distance to the Proto-Herbig AeBe Star EC 95 in the Serpens Core

Using the Very Long Base Array, we observed the young stellar object EC 95 in the Serpens cloud core at eight epochs from 2007 December to 2009 December. Two sources are detected in our field and are shown to form a tight binary system. The primary (EC 95a) is a 4-5 M_⊙ proto-Herbig AeBe object (arguably the youngest such object known), whereas the secondary (EC 95b) is most likely a low-mass T Tauri star. Interestingly, both sources are non-thermal emitters. While T Tauri stars are expected to power a corona because they are convective while they go down the Hayashi track, intermediate-mass stars approach the main sequence on radiative tracks. Thus, they are not expected to have strong superficial magnetic fields, and should not be magnetically active. We review several mechanisms that could produce the non-thermal emission of EC 95a and argue that the observed properties of EC 95a might be most readily interpreted if it possessed a corona powered by a rotation-driven convective layer. Using our observations, we show that the trigonometric parallax of EC 95 is π = 2.41 ± 0.02 mas, corresponding to a distance of 414.9^(+4.4)_ (–4.3) pc. We argue that this implies a distance to the Serpens core of 415 ± 5 pc and a mean distance to the Serpens cloud of 415 ± 25 pc. This value is significantly larger than previous estimates (d ~ 260 pc) based on measurements of the extinction suffered by stars in the direction of Serpens. A possible explanation for this discrepancy is that these previous observations picked out foreground dust clouds associated with the Aquila Rift system rather than Serpens itself

An object-oriented approach to task tree management in the TANGOW system

This paper describes the object-oriented features of TANGOW (Task-based Adaptive learNer Guidance On the WWW), a tool for developing Internet-based courses. This system facilitates the construction of adaptive learning environments for the WWW and is able to guide the students during their learning process based on student profiles and previous actions. In the TANGOW system, the course contents is modelled in terms of objects and relationships among them. This allows the course designer to reuse the same descriptive objects in different sections of the same course, or even in completely different courses. In addition, information about the student and his/her actions when interacting with the system is also stored as dynamic objects, which are instantiated at runtime. This makes it easy to access and update student related data.This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project number TEL97-0306

Reconfigurable switched-current ΣΔ power amplifier

Trabajo presentado al XIV Iberchip celebrado en Puebla (México) del 20 al 22 de febreo de 2008.In this paper a reconfigurable switched-current sigma delta modulator for power amplifier is shown, which is a suitable topology to save energy and integrated area in portable applications. Results have shown the correct operation of a 1.8V , 0.18¿ m CMOS reconfigurable switched-current sigma delta modulator with 11bits dynamic range within 1MHz and 7.8bits within 3.8MHz bandwidth.One of the authors Rosalino Rodríguez Calderon thanks the economic support received from CONACYT (México).Peer Reviewe

Creación de cursos adaptativos en TANGOW mediante tareas, reglas y elementos multimedia

En este artículo se describe, en términos generales, el proceso de diseño de un curso adaptativo accesible a través de Internet mediante el sistema TANGOW. En este proceso de diseño se establece una clara separación entre la estructura del curso, para cuya construcción se utilizan tareas y reglas docentes, y la asociación de contenidos a esta estructura. A continuación se analizan los distintos tipos de adaptación que pueden definirse durante el diseño de un curso entre las que se incluyen la adaptación en función del perfil del estudiante, las dependencias teóricas y prácticas entre tareas y la creación de distintas versiones de un mismo fragmento de contenido. Se describen, también, distintas aproximaciones metodológicas que facilitan la labor de di-seño de cursos adaptativos. El artículo termina con algunas conclusiones y trabajo futuro.Este trabajo ha sido financiado por la Comisión Interministerial de Ciencia y Tecnología (CICYT), con los números de proyecto TEL97-0306 y TEL1999-0181

An adaptive driving course based on HTML dynamic generation

Reprinted from the Proceedings of WebNet World Conference on the WWW and Internet 1999 with permission of AACE (http://www.aace.org).This is an electronic version of the paper presented at the World Conference on the WWW and Internet (WebNet '99) held in Honolulu (United States) on 1999In this paper we describe a new approach for developing adaptive Web based courses. These courses are defined by means of teaching tasks which correspond to basic knowledge units, and rules which describe how teaching tasks are divided into subtasks. Both tasks and rules are used at execution time to guide the students during their learning process by determining the set of achievable tasks to be presented to the student at every step. Adaptivity is implemented by presenting students with different HTML pages depending on their profile, their previous actions, and the active learning strategy. The HTML pages presented to the students are generated dynamically from general information about the type of media elements associated to each task and their layout. The whole approach is exemplified by means of a course on traffic signs