The identification of multiple outliers in arima models

The presence of outliers causes biases in the estimation of ARIMA models. In this work we present a procedure for detecting outliers and obtaining a robust estimator of the parameters in univariate ARIMA time series models. There are three main problems in the existing procedures for detecting outliers in ARIMA time series models. The first one is the confusion between level shifts and innovative outliers when a level shift is present in a time series. The procedure ineludes a possible solution to avoid this problem based on not comparing the statistics for level shifts and innovative outliers together, because the critical values under the null hypothesis of no outliers can be quite different. The second problem is the biased estimation of the initial parameter values. In the existing procedures, this initial estimation is done under the hypotheses of no outliers in the data, which may lead to begin the search for outliers using a very biased set of parameters and, therefore, these procedures may fail. In order to solve this problem, we use two measures of influence in the first stage of the proposed procedure; one measure for individually influential observations, and an additional measure for level shifts and sequences of outliers. The third problem is masking. This problem appears when there is a sequence of additive outliers, because the usual one by one outlier identification method may fail in the identification of sorne of the members of the group. The proposed procedure seems to solve the aforementioned problems and obtains food parameter estimates when the time series has isolated outliers and/or multiple adjacent outliers. The performance of the proposed procedure is analyzed and an example is shown

Band-pass filtering of the time sequences of spectral parameters for robust wireless speech recognition

In this paper we address the problem of automatic speech recognition when wireless speech communication systems are involved. In this context, three main sources of distortion should be considered: acoustic environment, speech coding and transmission errors. Whilst the first one has already received a lot of attention, the last two deserve further investigation in our opinion. We have found out that band-pass filtering of the recognition features improves ASR performance when distortions due to these particular communication systems are present. Furthermore, we have evaluated two alternative configurations at different bit error rates (BER) typical of these channels: band-pass filtering the LP-MFCC parameters or a modification of the RASTA-PLP using a sharper low-pass section perform consistently better than LP-MFCC and RASTA-PLP, respectively.Publicad

Uncertainty decoding on Frequency Filtered parameters for robust ASR

The use of feature enhancement techniques to obtain estimates of the clean parameters is a common approach for robust automatic speech recognition (ASR). However, the decoding algorithm typically ignores how accurate these estimates are. Uncertainty decoding methods incorporate this type of information. In this paper, we develop a formulation of the uncertainty decoding paradigm for Frequency Filtered (FF) parameters using spectral subtraction as a feature enhancement method. Additionally, we show that the uncertainty decoding method for FF parameters admits a simple interpretation as a spectral weighting method that assigns more importance to the most reliable spectral components. Furthermore, we suggest combining this method with SSBD-HMM (Spectral Subtraction and Bounded Distance HMM), one recently proposed technique that is able to compensate for the effects of features that are highly contaminated (outliers). This combination pursues two objectives: to improve the results achieved by uncertainty decoding methods and to determine which part of the improvements is due to compensating for the effects of outliers and which part is due to compensating for other less deteriorated features.Publicad

Los productos forestales no maderables como complemento económico en zonas forestales de países en desarrollo. Caso de El Merendón, en San Pedro Sula. Honduras. CA.

Se analizan las posibilidades que tiene el cultivo de mariposas y la utilización de las plantas en la alimentación, sanidad y otros usos en el medio rural de Honduras, como complemento para su desarrollo

Desarrollo de competencias geoespaciales en educación al aire libre: ejemplo de aplicación en Linköping (Suecia)

El desarrollo de competencias geoespaciales es fundamental como materia transversal en numerosas disciplinas y como destreza fundamental dentro de la educación permanente. En esta comunicación se presenta el desarrollo de esta metodología con un grupo de estudiantes de Máster de la Universidad de Linköping (Suecia). Tras algunas sesiones introductorias en clase y salidas de campo, se han desarrollado actividades prácticas que fomenten el uso de las nuevas tecnologías en conexión con la geolocalización espacial y la sensibilización patrimonial. Al final de la experiencia se llevó a cabo un análisis de resultados a partir de cuestionarios con el grupo participante

Aprendo a convivir, comunicándome en las reuniones de aula en una institución educativa de Comas

Actualmente, la convivencia en nuestro país se agudiza por la presencia de conductas agresivas, reclamos en las calles, toma de pistas por parte de vecinos problemas entre gremio de trabajadores y empleadores. Este escenario macro se reproduce en la convivencia cotidiana con los estudiantes, debido a que en las aulas también encontramos conductas agresivas que impiden el normal desarrollo de los aprendizajes e influyen negativamente en el clima de clase.Trabajo académic

The synergy between bounded-distance HMM and spectral subtraction for robust speech recognition

Additive noise generates important losses in automatic speech recognition systems. In this paper, we show that one of the causes contributing to these losses is the fact that conventional recognisers take into consideration feature values that are outliers. The method that we call bounded-distance HMM is a suitable method to avoid that outliers contribute to the recogniser decision. However, this method just deals with outliers, leaving the remaining features unaltered. In contrast, spectral subtraction is able to correct all the features at the expense of introducing some artifacts that, as shown in the paper, cause a larger number of outliers. As a result, we find that bounded-distance HMM and spectral subtraction complement each other well. A comprehensive experimental evaluation was conducted, considering several well-known ASR tasks (of different complexities) and numerous noise types and SNRs. The achieved results show that the suggested combination generally outperforms both the bounded-distance HMM and spectral subtraction individually. Furthermore, the obtained improvements, especially for low and medium SNRs, are larger than the sum of the improvements individually obtained by bounded-distance HMM and spectral subtraction.Publicad

XIV Foro Internacional sobre la Evaluación de la Calidad de la Investigación y de la Educación Superior (FECIES)

Introducción. El Proceso de Bolonia ha impulsado un nuevo modelo educativo que pretende centrar las metodologías docentes en el aprendizaje de los estudiantes, priorizando el manejo de herramientas por encima de la mera acumulación de conocimientos. Objetivo. El objetivo de este trabajo es evaluar la eficacia del aprendizaje colaborativo en la asignatura “Sistemas de Comunicación”, que se imparte en la E.T.S. Ingenieros de Telecomunicación de la Universidad de Valladolid. Método. Se emplearon diferentes herramientas basadas en el aprendizaje colaborativo dentro de la “Práctica sobre telefonía móvil de cuarta generación”. Dicha práctica está compuesta por diferentes actividades: (i) Trabajo escrito individual; (ii) Actividad de revisión por pares; (iii) Debate; (iv) Actividad puzle; (v) Trabajo escrito grupal; y (vi) Exposición y defensa del trabajo grupal. Resultados. Las encuestas realizadas a los alumnos mostraron que están muy satisfechos con esta práctica, puesto que les ha permitido desarrollar diferentes competencias transversales. Además, los alumnos obtuvieron una mayor calificación en el examen final de la asignatura en la pregunta sobre telefonía móvil de cuarta generación (Calificación sobre 1 punto = 0.59 0.33 puntos, media desviación estándar) que en la pregunta análoga sobre telefonía móvil de tercera generación, tema impartido utilizando una metodología docente tradicional (Calificación sobre 1 punto = 0.51 0.34 puntos). Conclusiones. El aprendizaje colaborativo no sólo permite a los alumnos adquirir competencias transversales, sino que además les permite interiorizar más conocimientos teóricos que la docencia tradicional

Late Quaternary palaeoenvironmental controls on concentric talus evolution in the Central Ebro Basin (NE Spain)

The polyphasic evolution of the testimonial buttes in the central area of the Ebro basin (Los Monegros) is analysed. This is a semiarid area that favours high erosion rates. An evolutionary model of the Jubierre hills is presented that shows the environmental cycles represented by aggradational and degradative processes on the slopes that resulted in the present arrangement of talus flatiron rings. In the four studied cases, talus relicts are composed of detritic material from a disappeared caprock pediment. Four slope stages (S4 to S1) that formed under stable climate conditions are identified. Older stages (S4 and S3) are estimated by comparison with other talus flatirons in the region. The S2 stage contains Bronze Age archaeological remains and the radiocarbon age obtained was 1608-1446 years cal BC (2 sigma), while S1 is younger. A palaeoenvironmental interpretation was made for these aggradational stages (S4 to S1). The active erosion of these hills led to a relief inversion, and talus flatirons remain as the only features revealing the presence of the relict hills and past human occupations