Closed-form equation for natural frequencies of beams under full range of axial loads modeled with a spring-mass system

A new simple closed-form equation that accurately predicts the effect of an arbitrarily large constant axial load, residual stress or temperature shift on the natural frequencies of an uniform single-span beam, with various end conditions, is presented. Its accuracy and applicability range are studied by comparing its predictions with numerical simulations and with the approximate Galef’s and Bokaian’s formulas. The new equation may be understood as a refinement or extension of these two approximate formulas. Significant accuracy and applicability range improvements are achieved, especially near the buckling point and for large and moderate axial load. The new closed-form equation is applicable in the full range of axial load, i.e., from the buckling load to the tensioned-string limit. It also models well the beam-to-string transition region for the eight boundary conditions studied. It works remarkably well in the free-free and sliding-free cases, where it is a near-exact solution. In addition, it yields the natural frequencies of a 1-D spring-mass system that may be used to model tensioned beams, and potentially, more complex systems.Peer ReviewedPostprint (published version

Discussion on “Assessing the goodness of fit of logistic regression models in large samples: A modification of the Hosmer-Lemeshow test” by Giovanni Nattino, Michael L. Pennell, and Stanley Lemeshow

This work was supported by the Marsden Fund (Award Num-ber E2987-3648) administrated by the Royal Society of NewZealand and also supported by grant RTI2018-100927-J-I00 administrated by Ministerio de Ciencia e Innovación (MCI,Spain), by the Agencia Estatal de Investigación (AEI, Spain),and by the European Regional Development Fund FEDER(FEDER, UE). We are grateful to Dr Louise McMillan for helpful comments.Peer ReviewedPostprint (author's final draft

On two mixture-based clustering approaches used in modeling an insurance portfolio

We review two complementary mixture-based clustering approaches for modeling unobserved heterogeneity in an insurance portfolio: the generalized linear mixed cluster-weighted model (CWM) and mixture-based clustering for an ordered stereotype model (OSM). The latter is for modeling of ordinal variables, and the former is for modeling losses as a function of mixed-type of covariates. The article extends the idea of mixture modeling to a multivariate classification for the purpose of testing unobserved heterogeneity in an insurance portfolio. The application of both methods is illustrated on a well-known French automobile portfolio, in which the model fitting is performed using the expectation-maximization (EM) algorithm. Our findings show that these mixture-based clustering methods can be used to further test unobserved heterogeneity in an insurance portfolio and as such may be considered in insurance pricing, underwriting, and risk management.Peer ReviewedPostprint (published version

Categorising count data into ordinal responses with application to ecological communities

Count data sets may involve overdispersion from a set of species and underdispersion from another set which would require fitting different models (e.g. a negative binomial model for the overdispersed set and a binomial model for the underdispersed one). Additionally, many count data sets have very high counts and very low counts. Categorising these counts into ordinal categories makes the actual counts less influential in the model fitting, giving broad categories which enable us to detect major broadly based patterns of turnover or nestedness shown by groups of species. In this paper, a strategy of categorising count data into ordinal data was carried out and also we implemented measures to compare different cluster structures. The application of this categorising strategy and a comparison of clustering results between count and categorised ordinal data in two ecological community data sets are shown. A major advantage of using our ordinal approach is that it allows for the inclusion of all different levels of dispersion in the data in one methodology, without treating the data differently. This reduction of the parameters on modelling different levels of dispersion does not substantially change the results in clustering structure. In the two data sets used in this paper, we observed ordinal clustering structure up to 93.1 % similar to those from the count data approaches. This has the important implication of supporting simpler, faster data collection using ordinal scales only.Peer ReviewedPostprint (author's final draft

Curvature of BEOL cantilevers in CMOS-MEMS processes

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents the curvature characterization results of released back-end-of-line 5 µm-wide cantilevers for two different 0.18-µm 1P6M complementary metal-oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers.Peer ReviewedPostprint (author's final draft

Translinear signal processing circuits in standard CMOS FPAA

In this paper, the implementation of signal processing circuits on a novel translinear Field-Programmable Analog Array (FPAA) testchip is reported. The FPAA testchip is based on a 0.35-micron, fully CMOS translinear element, which is the core block of a reconfigurable analog cell. The FPAA embeds a 5 5 cell array. As implementation examples, a four-quadrant multiplier with five decade dynamic range and a programmable fourth-order low-pass filter with up to 7 MHz bandwidth have been mapped on the translinear FPAA. 14 cells have been used for the four-quadrant multiplier while 18 cells were needed for the fourth-order low-pass filter.Postprint (published version

Introducing spaced mosaic plots

Informe de com fer spaced mosaic plots en RRecent research has developed a group of likelihood-based finite mixture mod- els for a data matrix with ordinal data, establishing likelihood-based multivari- ate methods which applies fuzzy clustering via finite mixtures to the ordered stereotype model. There are many visualisation tools which depict reduction of dimensionality in matrices of ordinal data. This technical report introduces the spaced mosaic plot which is one new graphical tool for ordinal data when the or- dinal stereotype model is used. It takes advantage of the fitted score parameters to determine the spacing between two adjacent ordinal categories. We develop a function in R and its documentation is presented. Finally, the description of a spaced mosaic plot is shown.Preprin

Mixture-based Clustering for the Ordered Stereotype Model

Many of the methods which deal with the reduction of dimensionality in matrices of data are based on mathematical techniques. In general, it is not possible to use statistical inferences or select the appropriateness of a model via information criteria with these techniques because there is no underlying probability model. Furthermore, the use of ordinal data is very common (e.g. Likert or Braun-Blanquet scale) and the clustering methods in common use treat ordered categorical variables as nominal or continuous rather than as true ordinal data. Recently a group of likelihood-based finite mixture models for binary or count data has been developed (Pledger and Arnold, 2014). This thesis extends this idea and establishes novel likelihood-based multivariate methods for data reduction of a matrix containing ordinal data. This new approach applies fuzzy clustering via finite mixtures to the ordered stereotype model (Fernández et al., 2014a). Fuzzy allocation of rows and columns to corresponding clusters is achieved by performing the EM algorithm, and also Bayesian model fitting is obtained by performing a reversible jump MCMC sampler. Their performances for one-dimensional clustering are compared. Simulation studies and three real data sets are used to illustrate the application of these approaches and also to present novel data visualisation tools for depicting the fuzziness of the clustering results for ordinal data. Additionally, a simulation study is set up to empirically establish a relationship between our likelihood-based methodology and the performance of eleven information criteria in common use. Finally, clustering comparisons between count data and categorising the data as ordinal over a same data set are performed and results are analysed and presented

Arquitecturas y circuitos CMOS para el control, generación y procesado de señal de MEMS

En esta tesis se muestran arquitecturas y circuitos CMOS para el control de actuadores electroestáticos MEMS y para la generación y procesado de las señales proveniente de microsistemas. En el primer capítulo se introducen dos circuitos para la estimación de distancia o capacidad entre armaduras de actuadores electroestáticos y se muestran aplicaciones de los mismos, incluyendo la caracterización de la estática y dinámica de los actuadores, la detección de fallos y envejecimiento y su aplicación dentro de osciladores digitales pulsados y como parte de un sistema de actuación resonante de baja tensión. En el segundo capítulo se muestra un estudio sobre la viabilidad de la fabricación monolítica de actuadores electroestáticos dentro del proceso CMOS utilizando un sencillo proceso de wet etching de bajo coste para liberar las estructuras. En el tercer capítulo se presentan dos elementos translineales CMOS de alto ancho de banda y alta precisión y su aplicación como multiplicadores, divisores, filtros y como parte integrante de una celda reconfigurable con la que construir una FPAA capaz de realizar numerosas funciones del procesado analógico de señal. En el cuarto capítulo se muestran diseños adicionales como una ley para el control de la dinámica de actuadores electroestáticos con la que se pueden ajustar eléctricamente todos los parámetros que gobiernan su movimiento y un convertidor de potencia integrado con control digital basado en una máquina de estados asíncrona. Finalmente, en el capítulo cinco, se presentan las conclusiones finales de este trabajo

Aplicación de procesamiento y análisis de medidas

Treball Final de Grau en Enginyeria Informàtica. Codi: EI1054. Curs acadèmic: 2019/2020En este documento se describe el proyecto realizado como Trabajo de Final de Grado durante la estancia en practicas en la empresa IoTsens, el cual consiste en desarrollar una serie de módulos que amplíen la funcionalidad de la plataforma ya existente en la empresa, la cual permite obtener información de distintos sensores y realizar acciones sobre ellos, entre otras funciones. En concreto, se han creado dos módulos, uno encargado de procesar y almacenar las medidas de los sensores pertenecientes a diversas organizaciones, y otro encargado de utilizar dichas medidas para mostrar cálculos relacionados con los costes y gastos asociados a mantener estos sensores. Para realizar la plani ficación y el desarrollo del proyecto se ha utilizado una metodología ágil, en concreto Scrum. Además de esto, en este documento se describen las fases de análisis, diseño, implementación y pruebas del proyecto. Por ultimo, se muestran brevemente las conclusiones tras la realización de este Trabajo de Final de Grado y un anexo que describe una prueba de rendimiento realizada sobre una de las bases de datos de la empresa