Automatic generation of signals and systems exercises

A computer based training tool has been developed for Signals and Systems undergraduate course students. It consists in an automatic exercise generator and an automatic self assessment system that can be used by the students as many times as they want. The students use the tool to generate numerical variation of the problem, they solve it and afterword use again the tool to answer a series of questions that are automatically assessed. The proposed problem comprised a continuous time domain characterization of a linear and time invariant system and its Fourier domain and Laplace domain analysis. The automatic exercise generator is based on a simple algorithm that varies the parameters that defined the exercise in a controlled way, so the students can be trained to analyze different kind of first and second order filters. The proposed algorithm requires only an arbitrary input number to generate a new exercise. More than 2000 numerically different exercises are automatically generated and assessed. This tool can also be used as a computer based assessment system when used in an environment that guarantees the identification of the student. When used as assessment system, it has the advantage that the teacher can select the difficulty of the exercise (all the student are required to analyze the same order and type filter but with different parameters, so the cheating is quite difficult). The algorithm can be easily transferred to almost any kind of problem in Signal and Systems and other engineering disciplines

Peer Assessment and Self-assessment: Effective Learning Tools in Higher Education.

When used appropriately, self- and peer-assessment are very effective learning tools. In the present work, instructor formative assessment and feedback, self-assessment (SA), and peer-assessment (PA) have been compared. During the first part of a semester, the students followed a continuous formative assessment. Subsequently, they were divided into two subgroups based on similar performances. One subgroup performed SAs, and the other followedPAduring the last part of the course. The performances of the two groups in solving problems were compared. Results suggest that PA is a more effective learning tool than SA, and both are more effective than instructor formative assessment. However, a survey that was conducted at the end of the experiment showed higher student confidence in instructor assessment than in PA. The students recognized the usefulness of acting as peer assessors, but believed that SA helped them more than PA

Computer based trainer for signal and systems undergraduate students

University students demand many exercises for practicing during their undergraduate courses. Although there are many resources where they can find proposed exercises, specially for basic courses, these resources include a fixed and limited set of proposed exercises. The students usually want to repeat similar exercises till they are sure they have the skill to solve it. Additionally they demand fast feedback about their trials. With the development of the European Higher Education Area, the work of the students must be assessed and this could be seen as a higher workload for the instructors, so the development of tools that help in the assignment and assessment of students work is necessary. Here, a tool that automatically generates thousands of numerical and wording variations of the same exercise and automatically assesses the solution given by the student is presented. The selected exercise is the convolution of two signals, a basic exercise for Signals and Systems undergraduate course for Electrical and Electronic Engineering students. Wording variations of the exercise include discrete time and continuous time signals, to find the output of a linear and invariant system for a given input and different presentations of the signals (analytic expressions, graphical or tabulated representation for the time span where the signals have non zero values). Both wording and numerical variations are obtained from a single seed. The remainders of division of the seed by different divisors are calculated and used to obtain a large set of variations of the exercise. One of these remainders is used to group the variations of the exercise by difficulty grade. The teacher can use this tool to automatically assign personalized exercises for each student that attends his/her course. This personalized assignment makes the cheating among students more difficult than when the same exercise is assigned to all the students. The teacher can be sure that all the assignments are in the same difficulty group. Moreover, this tool automatically grades the solution given by the student, so can be used as an assessment tool by the teacher. The basic algorithm to generate the variations in this exercise could be extended to almost all typical exercises in Signal and Systems cours

Fenómenos de transporte en bismuto : Influencia de los Portadores bombeados a una banda metaestable

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Óptica, leída el 16-05-1994En estos trabajos se ha medido el efecto nernst-ettingshausen en muestras policristalinas de bismuto y a partir de su estudio se han determinado los tiempos de relajación de los distintos portadores, sus masas efectivas y sus potenciales químicos. También se ha estudiado la evolución temporal del efecto termoeléctrico transverso en láminas gruesas de bismuto al ser irradiadas con pulsos láser de dos longitudes de onda distinta: una capaz de bombear portadores a una posible banda metaestable y otra no. Los resultados de este experimento corroboran la existencia de una banda metaestable en bismuto. Se ha desarrollado una técnica para la medida de señales fotoinducidas débiles y de corta duración. Utilizando esta técnica se ha detectado por primera vez un efecto fotoconductivo en bismuto. Además se ha encontrado un efecto de superficie debido al calentamiento no uniforme que produce el pulso láser.Depto. de ÓpticaFac. de Ciencias FísicasTRUEpu

Signals and Systems Students trainer.

Higher education students demand fast feedback about their assignments and the opportunity to repeat them in case they do in a wrong way. Here a computer based trainer for Signals and Systems students is presented. An application, that automatically generates and assesses thousands of numerically different versions of several Signals and Systems problems have been developed. This applet guides the students to find the solution and automatically assesses and grades the students proposed solution. The students can use the application to practice in solving several types of Signals and Systems basic problems. After selecting the problem type, the student introduces a seed and the application generates a numerical version of the selected problem. Then the application presents a sequence of questions that the students must solve and the application automatically assess their answers. After solving a given problem, the students can repeat the same numerical variation of the problem by introducing the same seed to the application. In this way, they can review their solution with the help of the hints given by the application for wrong solutions. This application can also be used as an automatic assessment tool by the instructor. When the assessment is made in a controlled environment (examination classroom or laboratory) the instructor can use the same seed for all students. Otherwise, different seeds can be assigned to different students and in this way they solve different numerical variation of the proposed problem, so cheating becomes an arduous task. Given a problem type, the mathematical or conceptual difficulty of the problem can vary depending on the numerical values of the parameters of the problem. The application permits to easily select groups of seeds that yield to numerical variations with similar mathematical or conceptual difficulty. This represents an advantage over a randomised task assignment where students are asked to solve tasks with different difficulty

Terapia por láser de baja potencia: consideraciones óptico-físicas y biológicas determinantes en su aplicación clínica.

Objetivos : Analizar la distribución de energía en un tejido cuando se emplea terapia por láser de baja potencia y estudiar las especificaciones mínimas de equipos de terapia láser para estimar la dosis. Material y métodos: Se ha empleado el método de Monte Carlo para obtener la distribución de energía absorbida por la piel para dos tipos de láser y la teoría de la difusión para estimar la longitud de penetración y el recorrido libre medio. Se ha estudiado la variación de esa distribución en función de la raza (caucásico, asiático, afroamericano) y para dos localizaciones anatómicas distintas. Se ha analizado la información facilitada por diversos fabricantes de equipos comerciales para determinar si es necesario adaptar la dosimetría recomendada. Resultados: La radiación láser infrarroja (810nm) se absorbe mayoritariamente en un espesor de piel de 1,9±0,2mm para caucásicos, entre 1,73±0,08mm (volar del antebrazo) y 1,80±0,11mm (palma) para asiáticos y entre 1,25±0,09mm (volar del antebrazo) y 1,65±0,2mm (palma) para afroamericanos. El recorrido libre medio de la luz siempre es menor que 0,69±0,09mm. Para los equipos comerciales analizados la única característica geométrica del haz láser que se menciona es la superficie que oscila entre 0,08 y 1cm2, pero no se especifica cómo es la distribución de energía, la divergencia del haz, forma de la sección transversal, etc. Conclusiones:Dependiendo del equipo de terapia por láser de baja potencia utilizado, el tipo de paciente y la zona a tratar, el clínico debe adaptar las dosis recomendadas. Abstract: Objectives: To analyze the distribution of energy deposited in a tissue when this is irradiated with a low power laser and to study the minimum characteristics that manufacturers of low power laser therapy equipments should include to estimate the dosage. Material and methods: Monte Carlo simulation was performed to determine the absorption location of the laser energy. The diffusion theory was used to estimate penetration depth and mean free path. Variation of this distribution was studied based on three different skin types (Caucasians, Asians and Afroamericans) and for two different anatomic locations: palm and volar forearm. Information given by several manufactures of low power laser therapy equipments has been analyzed. Results: Infrared (810 nm) laser radiation is mainly absorbed in a skin layer of thickness 1.9±0.2mm for Caucasians, from 1.73±0.08mm (volar forearm) to 1.80±0.11mm (palm) for Asians, and from 1.25±0.09mm (volar forearm) to 1.65±0.2mm (palm) for Afroamericans. The light mean free path is lower than 0.69±0.09mm for all cases. The laser beam characteristics (beam shape, energy distribution on a transversal section, divergence, incidence angle,etc.) are not usually specified by the manufacturers. Only beam size (ranging from 0.08 to 1cm2) is given in some cases. Discussion and conclusions: Depending on the low power laser therapy equipment, on the patient and on the anatomic area to be treated, the staff should adapt the recommended dosage for each individual case

Mueller Matrix Polarimetry by Means of Azimuthally Polarized Beams and Adapted Commercial Polarimeter

A simple method for Mueller matrix polarimetry is proposed. The experimental set up is based on using an azimuthally polarized input beam, which presents all possible linearly polarized states across its transverse section, and an adapted commercial light polarimeter for analyzing the polarization state of the output beam. It will be shown that by measuring the Stokes parameters at only three different positions across the output beam section, the complete Mueller matrix of linear deterministic samples can be easily determined

Polarization changes at Lyot depolarizer output for different types of input beams

Lyot depolarizers are optical devices made of birefringent materials used for producing unpolarized beams from totally polarized incident light. The depolarization is produced for polychromatic input beams due to the different phase introduced by the Lyot depolarizer for each wavelength. The effect of this device on other types of incident fields is investigated. In particular two cases are analyzed: (i) monochromatic and nonuniformly polarized incident beams and (ii) incident light synthesized by superposition of two monochromatic orthogonally polarized beams with different wavelengths. In the last case, it is theoretically and experimentally shown that the Lyot depolarizer increases the degree of polarization instead of depolarizes

The Diffusion Process of Metastable Carrieres in Bismuth

The diffusion process of electrons and holes which have been pumped into a metastable band in bismuth films by a 1.064‐μm laser pulse is considered in the calculation of the induced thermal gradient. The fit between the temporal evolution of this calculated thermal gradient and that of the thermoelectric response of films to the laser excitation allows us to estimate an upper limit of the ambipolar diffusion coefficient of metastable carrier