An Analysis of the Influence of Students´ Technological Culture on Their Technology

decade has raised the interest among the research community on the acceptance and use of these systems by both teachers and students. At first, the implementation of LMS was based on their technical design and the adaptation of the learning processes to the virtual environment, neglecting students’ characteristics when the systems were deployed, which led to expensive and failing implementations. The Unified Theory of Acceptance and Use of Technology (UTAUT) proposes a framework which allows the study of the acceptance and use of technology that takes into consideration the students’ characteristics and how they affect the acceptance and the degree of use of educational technology. This study questions the role of the user’s attitude towards use of LMS and uses the UTAUT to examine the moderating effect of technological culture in the adoption of LMS in Spain. The results from the comparison and analysis of three different models confirm the relevance of attitude towards use as an antecedent of intention to use the system, as well as the important moderating effect of gender and technological culture. The discussion of results suggests the need for a more in-depth analysis and interrelations of cultural dimensions in the adoption of educational technologies and learning management system

Pre-Calculated Duty Cycle Control Implemented in FPGA for Power Factor Correction

A power factor correction (PFC) technique based on pre-calculated duty cycle values is presented in this paper. In this method the duty ratios for half a line period are calculated in advance and stored in a memory. By synchronizing the memory with the line, near unity power factors can be achieved in a specific operating point. The main advantage of this technique is that neither current measurement nor current loop are needed. To obtain stable output voltages a voltage loop is included. A boost converter prototype controlled by an FPGA evaluation board has been implemented in order to verify the functionality of the proposed method. Both the simulation and experimental results show that near unity power factor can be achieved with this PFC strategy

CMOS SPADs selection, modeling and characterization towards image sensors implementation

The selection, modeling and characterization of Single Photon Avalanche Diodes (SPADs) are presented. Working with the standard 180nm UMC CMOS process, different SPAD structures are proposed in combination with several quenching circuits in order to compare their relative performances. Various configurations for the active region and the prevention of the premature edge breakdown are tested, looking for a miniaturization of the devices to implement image sensor arrays without loses in their performance

On the development of a MODEM for data transmission and control of electrical household appliances using the low-voltage power-line

This paper presents a CMOS 0,6μm mixed-signal MODEM ASIC for data transmission on the low-voltage power line. The circuit includes all the analog circuitry needed for input interfacing and modulation/demodulation (PLL-based frequency synthesis, slave filter banks with PLL master VCO for tuning, decision circuitry, etc.) plus the logic circuitry needed for control purposes. The circuit operates correctly in the whole industrial temperature range, from -45 to 80°C, under 5% variations of the 3.3V supply voltage.Comisión Interministerial de Ciencia y Tecnología FD97-1611(TIC)Ministerio de Ciencia y Tecnología TIC200 1-092

CMOS mixed-signal MODEM for data transmission and control of electrical household appliances using the low-voltage power-line

This paper presents a CMOS 0.6μm mixed-signal MODEM ASIC for data transmission using the low-voltage power line. This circuit includes all the analog blocks needed for input interfacing and modulation/demodulation (PLL-based frequency synthesis, slave filter banks with PLL master VCO for tuning, and decision circuitry) plus the logic circuitry needed for control purposes. The circuit operates correctly within the industrial temperature range, from -45 to 80°C, under 5% variations of the 3.3V supply voltage.Comisión Interministerial de Ciencia y Tecnología 1FD97-1611(TIC)Ministerio de Ciencia y Tecnología TIC2001-092

Error control in simplification before generation algorithms for symbolic analysis of large analogue circuits

Circuit reduction is a fundamental first step in addressing the symbolic analysis of large analogue circuits. A new algorithm for simplification before generation is presented which is very efficient in terms of speed and the amount of circuit reduction, and solves the accuracy problems of previously reported approaches

An error-controlled methodology for approximate hierarchical symbolic analysis

Limitations of existing approaches for symbolic analysis of large analog circuits are discussed. To address their solution, a new methodology for hierarchical symbolic analysis is introduced. The combination of a hierarchical modeling technique and approximation strategies, comprising circuit reduction, graph-based symbolic solution of circuit equations and matrix-based error control, provides optimum results in terms of speech and quality of results.European Commission ESPRIT 21812Comisión Interministerial de Ciencia y Tecnología TIC97-058

Characterization-Based Modeling of Retriggering and Afterpulsing for Passively Quenched CMOS SPADs

The current trend in the design of systems based on CMOS SPADs is to adopt smaller technological nodes, allowing the co-integration of additional electronics for the implementation of complex digital systems on chip. Due to their simplicity, a way to reduce the area occupied by the integrated electronics is the use of passive quenching circuits (PQCs) instead of active (AQCs) or mixed (MQCs) ones. However, the recharge phase in PQCs is slower, so the device can be retriggered before this phase ends. This paper studies the phenomena of afterpulsing and retriggering, depending on the characteristics of the SPADs and the working conditions. In order to do that, a test chip containing SPADs of different size has been characterized in several operating environments. A mathematical model has been proposed for fitting afterpulsing phenomenon. It is shown that retriggering can be also described in terms of this model, suggesting that it is linked to carriers trapped in the shallow levels of the semiconductor and that should be taken into account when considering the total amount of afterpulsing events.Junta de Andalucía TIC 233

Corrección del factor de potencia, sin medida de corriente, mediante implementación en FPGA de one-cycle control

En este artículo se presenta una técnica de control digital de correctores de factor de potencia (CFP) trabajando en modo de conducción continua en la que no es necesario el uso de sensor de corriente ni de convertidor analógico-digital de alta velocidad. La corriente de entrada al CFP se estima a partir de la descripción del modelo en VHDL de un convertidor elevador y de las muestras digitales de las tensiones de entrada y salida del convertidor. El objetivo final es desarrollar un controlador universal para CFP, con posibilidad de trabajar varios convertidores idénticos en paralelo y así aumentar la potencia. En este trabajo se abordan las diferentes soluciones ante los problemas que aparecen en el desarrollo del prototipo de laboratorio y se presentan resultados en diferentes condiciones, comparando el contenido armónico de la corriente con los límites establecidos por la normativa vigente más restrictiv

A new whitefly species, Aleuropleurocelus petenensis sp. nov. (Hemiptera: Aleyrodidae), from Guatemala

A new species of whitefly, Aleuropleurocelus petenensis sp. nov. Carapia-Ruiz & García-Ochaeta, found on leaves of a plant belonging to the genus Acalypha (Euphorbiaceae) in Petén, Guatemala, is described based on characteristics of the pupa. This new species exhibits a black venter and has microtubercles on the subdorsal and submedian areas, whereas the most closely related species, A. mixtecus Carapia-Ruiz, presents a pale venter and has not microtubercles on the corresponding areas. In both species the transverse suture of the molt ends before the apparent margin and the dorsal surface presents folds; these features support the close relationship between these species. Microphotographs of morphological structures of the new species puparium are provided.Una nueva especie de mosca blanca, Aleuropleurocelus petenensis sp. nov. Carapia-Ruiz & García-Ochaeta, encontrada sobre hojas de una planta perteneciente al género Acalypha (Euphorbiaceae) en Petén, Guatemala, es descrita basada en características de la pupa. La nueva especie presenta vientre negro y tiene microtubérculos en el área subdorsal y submediana, mientras que la especie más cercanamente relacionada, Aleuropleurocelus mixtecus Carapia-Ruiz, tiene el vientre pálido y no presenta microtubérculos en las áreas correspondientes. En ambas especies la sutura transversa de la muda termina antes de margen aparente y la superficie dorsal presenta pliegues; estas características apoyan la cercana relación entre estas especies. Microfotografías de estructuras morfológicas del pupario de la nueva especie son presentadas