Stochastic Analysis of the LMS Algorithm for System Identification with Subspace Inputs

This paper studies the behavior of the low rank LMS adaptive algorithm for the general case in which the input transformation may not capture the exact input subspace. It is shown that the Independence Theory and the independent additive noise model are not applicable to this case. A new theoretical model for the weight mean and fluctuation behaviors is developed which incorporates the correlation between successive data vectors (as opposed to the Independence Theory model). The new theory is applied to a network echo cancellation scheme which uses partial-Haar input vector transformations. Comparison of the new model predictions with Monte Carlo simulations shows good-to-excellent agreement, certainly much better than predicted by the Independence Theory based model available in the literature

Stochastic analysis of an error power ratio scheme applied to the affine combination of two LMS adaptive filters

The affine combination of two adaptive filters that simultaneously adapt on the same inputs has been actively investigated. In these structures, the filter outputs are linearly combined to yield a performance that is better than that of either filter. Various decision rules can be used to determine the time-varying parameter for combining the filter outputs. A recently proposed scheme based on the ratio of error powers of the two filters has been shown by simulation to achieve nearly optimum performance. The purpose of this paper is to present a first analysis of the statistical behavior of this error power scheme for white Gaussian inputs. Expressions are derived for the mean behavior of the combination parameter and for the adaptive weight mean-square deviation. Monte Carlo simulations show good to excellent agreement with the theoretical predictions

Echo Cancellation : the generalized likelihood ratio test for double-talk vs. channel change

Echo cancellers are required in both electrical (impedance mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The optimum likelihood ratio test (LRT) for this problem was studied in a recent paper. The LRT requires a priori knowledge of the background noise and double-talk power levels. Instead, this paper derives a generalized log likelihood ratio test (GLRT) that does not require this knowledge. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a channel change, based upon a single look. However, detection based on about 200 successive samples yields a detection probability close to unity (0.99) with a small false alarm probability (0.01) for the theoretical GLRT model. Application of a GLRT-based echo canceller (EC) to real voice data shows comparable performance to that of the LRT-based EC given in a recent paper

An affine combination of two LMS adaptive filters - Transient mean-square analysis

This paper studies the statistical behavior of an affine combination of the outputs of two LMS adaptive filters that simultaneously adapt using the same white Gaussian inputs. The purpose of the combination is to obtain an LMS adaptive filter with fast convergence and small steady-state mean-square deviation (MSD). The linear combination studied is a generalization of the convex combination, in which the combination factor $\lambda(n)$ is restricted to the interval $(0,1)$. The viewpoint is taken that each of the two filters produces dependent estimates of the unknown channel. Thus, there exists a sequence of optimal affine combining coefficients which minimizes the MSE. First, the optimal unrealizable affine combiner is studied and provides the best possible performance for this class. Then two new schemes are proposed for practical applications. The mean-square performances are analyzed and validated by Monte Carlo simulations. With proper design, the two practical schemes yield an overall MSD that is usually less than the MSD's of either filter

Aplicando restricciones en un datawarehouse temporal utilizando UML/OCL

Un datawarehouse es una colección de datos no volátiles, variables en el tiempo y orientado a un tema específico utilizado para tomar decisiones. La necesidad de registrar valores que permitan evaluar tendencias, variaciones, máximos y mínimos, justifican considerar en el diseño la evolución temporal de atributos o interrelaciones. La determinación de restricciones que permitan mantener la consistencia de los datos almacenados e impidan los solapamientos de rangos temporales, permiten conservar la integridad de la base de datos. En la etapa de modelado la determinación de estas restricciones se realizan de manera informal.\nEstablecer sin ambigüedad las mismas no es posible sin un lenguaje apropiado.\nProponemos determinar restricciones en el modelo de datos transformando el esquema multidimensional temporal a UML y emplear OCL para documentar dichas limitaciones.Eje: Ingeniería de Software y Bases de Datos (ISBD

Exploring the Barriers, Opportunities, and Motivation for Agricultural Entrepreneurship of Rural Colombian Students Who Participated in Dual-Credit Programs

Rural Colombian college students may be interested in pursuing entrepreneurship activities to improve their future and livelihoods. College students who participated in a dual-credit program as high school students completed a questionnaire to assess their motivations to participate in agricultural entrepreneurship activities and the barriers and opportunities to participate in rural entrepreneurship activities. We found that students were motivated to participate in entrepreneurship activities because of their motivations to be their own boss and job security. At the same time, the rural students perceived political and structural barriers as important to be addressed to develop entrepreneurship projects. Finally, participants agreed that personal opportunities related to education were essential for developing rural entrepreneurship activities. These results are important to develop policies and methodologies to improve students\u27 preparation for their future and their communities

Towards two-stage service representation and reasoning: from lightweight annotations to comprehensive semantics

Semantics are used to mark up a wide variety of data-centric Web resources but are not used to annotate online functionality in significant numbers. That is despite considerable research dedicated to Semantic Web Services (SWS). This has led to the emergence of a new Linked Services approach with simplified and less costly to produce service models, which targets a wider audience and allows even non-SWS developers to annotate services. However, such models merely aim at enabling semantic search by humans or automated service clustering rather than automation of service tasks such as discovery or orchestration. Thus, more expressive solutions are still required to achieve automated discovery and orchestration of services. In this paper, we describe our investigation into combining the strengths of two distinct approaches to modeling semantic Web services – 'lightweight' Linked Services and 'heavyweight' SWS automation - into a coherent SWS framework. In our vision, such integration is achieved by means of model cross-referencing and model transformation and augmentation

Baseline and stress-induced levels of corticosterone in male and female Afrotropical and European temperate stonechats during breeding

Background: Latitudinal variation in avian life histories falls along a slow-fast pace of life continuum: tropical species produce small clutches, but have a high survival probability, while in temperate species the opposite pattern is found. This study investigated whether differential investment into reproduction and survival of tropical and temperate species is paralleled by differences in the secretion of the vertebrate hormone corticosterone (CORT). Depending on circulating concentrations, CORT can both act as a metabolic (low to medium levels) and a stress hormone (high levels) and, thereby, influence reproductive decisions. Baseline and stress-induced CORT was measured across sequential stages of the breeding season in males and females of closely related taxa of stonechats (Saxicola spp) from a wide distribution area. We compared stonechats from 13 sites, representing Canary Islands, European temperate and East African tropical areas. Stonechats are highly seasonal breeders at all these sites, but vary between tropical and temperate regions with regard to reproductive investment and presumably also survival. Results: In accordance with life-history theory, during parental stages, post-capture (baseline) CORT was overall lower in tropical than in temperate stonechats. However, during mating stages, tropical males had elevated post-capture (baseline) CORT concentrations, which did not differ from those of temperate males. Female and male mates of a pair showed correlated levels of post-capture CORT when sampled after simulated territorial intrusions. In contrast to the hypothesis that species with low reproduction and high annual survival should be more risk-sensitive, tropical stonechats had lower stress-induced CORT concentrations than temperate stonechats. We also found relatively high post-capture (baseline) and stress-induced CORT concentrations, in slow-paced Canary Islands stonechats. Conclusions: Our data support and refine the view that baseline CORT facilitates energetically demanding activities in males and females and reflects investment into reproduction. Low parental workload was associated with lower post-capture (baseline) CORT as expected for a slow pace of life in tropical species. On a finer resolution, however, this tropical-temperate contrast did not generally hold. Post-capture (baseline) CORT was higher during mating stages in particular in tropical males, possibly to support the energetic needs of mate-guarding. Counter to predictions based on life history theory, our data do not confirm the hypothesis that long-lived tropical populations have higher stress-induced CORT concentrations than short-lived temperate populations. Instead, in the predator-rich tropical environments of African stonechats, a dampened stress response during parental stages may increase survival probabilities of young. Overall our data further support an association between life history and baseline CORT, but challenge the role of stress-induced CORT as a mediator of tropical-temperate variation in life history

An Empirical Evaluation of a Historical Data Warehouse

Computing is widely regarded as a scientific discipline that emphasizes on three different perspectives: mathematics, present in the development of formalisms, theories and algorithms; engineering, linked to the goal of making things better, faster, smaller, cheaper and, finally, the science that can be defined as the activity to develop general and predictive theories that allow these theories to be evaluated and tested. However, research in software engineering rarely describes explicitly its research paradigms and standards to assess the quality of its results. Due to a growing understanding in the computer science community that empirical studies are needed to improve processes, methods and tools for the development and maintenance of software, an emerging area in software engineering is developed: the Empirical Software Engineering. This subarea is one step down in the claims of scientificity but it aims to address this shortcoming. The objective of this work is to conduct an empirical corroboration for developing a method of a Historical Data Warehouse, the temporal data model and the associated query interface.Sociedad Argentina de Informática e Investigación Operativa (SADIO

An Empirical Evaluation of a Historical Data Warehouse

Computing is widely regarded as a scientific discipline that emphasizes on three different perspectives: mathematics, present in the development of formalisms, theories and algorithms; engineering, linked to the goal of making things better, faster, smaller, cheaper and, finally, the science that can be defined as the activity to develop general and predictive theories that allow these theories to be evaluated and tested. However, research in software engineering rarely describes explicitly its research paradigms and standards to assess the quality of its results. Due to a growing understanding in the computer science community that empirical studies are needed to improve processes, methods and tools for the development and maintenance of software, an emerging area in software engineering is developed: the Empirical Software Engineering. This subarea is one step down in the claims of scientificity but it aims to address this shortcoming. The objective of this work is to conduct an empirical corroboration for developing a method of a Historical Data Warehouse, the temporal data model and the associated query interface.Sociedad Argentina de Informática e Investigación Operativa (SADIO