Experiencias en la enseñanza de la matemática universitaria en ambientes de programación sobre asistentes matemáticos

El trabajo muestra las experiencias en la enseñanza de las matemáticas en carreras de perfil informático y matemático apoyado en un ambiente de programación sobre asistentes matemáticos durante dos años en las carreras de ingeniería informática en la universidad de Pinar del Río en Cuba y en las carreras de licenciatura en computación en la universidad estadual de Mato Groso Brasil. La metodología aplicada consistió en la construcción de conceptos y modelos matemáticos fundamentales pasando por las etapas gráfica, numérica y analítica apoyados en niveles de programación, el trabajo se desarrollo en equipos. Se pueden utilizar en esta metodología diferentes asistentes matemáticos siempre que permitan la programación

Human Head Natural Protection Against Electromagnetic Fields

In this paper we provide concluding evidence that the human skull acts as a dynamic barrier to electromagnetic fields (EMF) and temperature flow at 1800 MHz. This natural helmet e®ectively and dynamically protects brain tissue against safety-de¯ned threshold temperature increase due to external EMF induction. A half-wavelength dipole antenna has been employed as the EMF source. The human head is modelled by several coronal planes extracted from the Visible Human Project. Results described here have a great importance should thermal e®ects be directly used to derive basic restrictions to EM fields safety limits for human exposure.FUNDACIÓN SENECA. Plan de Ciencia y Tecnología de la Región de Murcia. Código: 05746/PI/07

Sobre Lyapunov y la Teoría de la Estabilidad

In this work some ideas about the history of the stability concept from  Lyapunov, its development until now and some open problems are presented. En este trabajo, presentamos algunas ideas sobre la historia del concepto estabilidad según Lyapunov, sus desarrollos actuales y problemas abiertos. &nbsp

Apuntes para la historia de la arquitectura y observaciones sobre la que se distingue con la denominación de gótica

Sign.: [ ]\p1\s, 1-9\p4\s, 10\p2\sLa h. de grab. lit. es un retr. de Manuel Fernández Varel

Learning strategies to raise the academic level of students of Medical Sciences in Pinar del Rio

The paper deals with learning strategies and their necessity in contemporary education as a way to provide lifelong learning to medical science students. It systematizes some of the most used theoretical positions in the understanding of the subject. It aims to present a theoretical position from a complex and dialectical approach in relation to the perception of learning strategies and the way in which these positions have evolved, highlighting the role that the teacher should play to promote their development. The intention of the present work, leads to the discussion of a detected problem and, above all, raises lines of action that lead to an improvement, however, this improvement is presented in an innovative way, since it starts from the theoretical support, from those arguments that characters of the psychology of learning and cognition have raised, through their explanations of how the process of learning occurs, from the process of teaching. The data reveal that high-performing students use more strategies than low-performing ones. Hence the importance of guiding students in the use of learning strategies so that they can perform a variety of tasks and facilitate the study of the different disciplines that make up the curriculum throughout their careers, helping them to be more autonomous and effective in their learning

MIMO TIS/TRP active testing with second-generation mode-stirred chambers

With the first 4G trials scheduled for 2010 and the compulsory use of MIMO into both WiMAX and LTE standards, MIMO technology has finally exploded. Mobile Internet Peripherals and Devices are said to take a market share of 30% of all handsets and non-handsets wireless devices by 2013. In this complex scenario, antenna engineering has gained a tremendous importance. While the use of multiple antennas in the base station or access point (AP) is usually feasible, user terminals have size and weight restrictions that make the use of conventional antenna elements such as dipoles or patch antennas problematic. Thus, novel array topologies and antenna elements for multi-antenna systems are of great interest. But not only new geometries and designs are required, but also the antenna engineer is faced with a novel way to evaluate performance. While the parameters to characterize antennas in general are well defined and worldwide accepted, the way to evaluate the performance of an antenna array for MIMO is still an open issue, since multiple new concepts have to be considered, such as pattern diversity, corrrelation among elements, fading environment or polarization diversity, among others. Typical active parameters being currently tested for 2G and 3G systems are Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS). 4G systems are already envisioned to require more complex active testing due their inherently embedded MIMO technology. In this article, the way of using a second generation mode-stirred chamber (EMITE Ing E300 MIMO Analyzer) connected to a rradiocommunications tester (Rohde & Schwarz CMU200) to characterize wireless devices by measuring TRP and TIS is decribed. Measurements have been perormed for the UMTS system, but are simply extende to other systems. Since second-generation mode-stirred chambers can emulate a wide variety of Rayleigh, Rician, isotropic and non-isotropic scenarios, the procedure described in this paper opens the door for more advanced evaluation of active parameters for a variety of fading scenarios, which is unheard of in the wireless communications arena.Ministerio de Educación y Cienci

The role of polarization diversity for MIMO systems under rayleigh-fading environments

Polarization diversity techniques have not received as much attention as others due to the significant difference in mean signal level between copolarized and cross-polarized branches when one polarization is transmitted. However, multiple- input–multiple-output (MIMO) systems where the multipath fading is only partially correlated could use polarization diversity to provide a high diversity gain. Hence there is a need to fully understand the role of true polarization diversity in such systems. In this letter, progressive (true) polarization diversity performance for 3 3 MIMO systems under Rayleigh-fading environments is evaluated through simulations and measurements. True polarization diversity was found to be as significant as spatial diversity at improving diversity gain, and hence MIMO system capacity.This work was supported in part by Fundación Séneca, the R&D coordinating unit of the Autonomous Region of Murcia (Spain) under project reference 2I05SU0033. The authors wish to thank Bluetest AB for its generous educational discounting

Advances in mode-stirred reverberation chambers for wireless communication performance evaluation

Reverberation chambers (RC) are a popular tool for laboratory wireless communication performance evaluation, and their sandardization for Over-The-Air (OTA) measurements is underway. Yet, the inherent limitations of singlecavity RCs to emulate isotropic Rayleigh-fading scenarios with uniform phase distribution and high elevation angular spread put their representation of realistic scenarios into jeopardy. Recent advances in the last few years, however, have solved all these limitations by using more general mode-stirred reverberation chambers (MSC), wherein the number of cavities, their stirring and coupling mechanisms, and their software postprocessing algorithms is far from simple, representing a new era for wireless communications research, development, and over-the-air testing. This article highlights recent advances in the development of second-generation mode-stirred chambers for wireless communications performance evaluatio

Tunable dual-band printed tab monopole antennas for wireless communications

The advance of communication systems requires new antenna designs to comply with the ever-increasing demands of the wireless market. The antenna designs are being conditioned by miniaturization and migration to new frequencies (IEEE 802.11a/g), while keeping compatibility with other systems poses yet additional constrains. This contribution presents a novel monopole multi-band printed antenna design for WiFi systems, featuring the use of a spur-line filter to obtain dual-frequency operation. Design constrains are discussed, along with simulated and measured resultsThe authors would like to thank Bluetest AB for their generous educational discounting. This research work has been partially funded by The Spanish National R&D Programme under the FIT-330210-2005-2 project

The influence of efficiency on receive diversity and MIMO capacity for rayleigh-fading channels

A previously published guideline for MIMO antenna arrays is refuted. The influence of radiation efficiency on diversity gain and MIMO capacity of wireless communications systems is investigated through simulations and measurements using a reverberation chamber. Integrated antennas on a portable device have efficiencies low enough to disallow typical inter-element correlation assumptions. Both diversity gain and MIMO capacity depend on the number of antennas, SNR and efficiency in a complex way. When the efficiency of antennas is considered, certain system capacity losses are predicted and measured. These losses may be recovered through using more receive elements than commonly recommended or through the addition of a smaller number of more efficient antennas.This work was supported in part by the Fundación Séneca, the R&D unit of the Autonomous Region of Murcia (Spain) under project references TIC-TEC 06/01-0003, 07/02-0005 and 05746/PI/07, and in part by the Spanish National R&D Programme through TEC2007/63470/TCM