Univariate versus multivariate modeling of panel data

Panel data can be arranged into a matrix in two ways, called 'long' and 'wide' formats (LFand WF). The two formats suggest two alternative model approaches for analyzing paneldata: (i) univariate regression with varying intercept; and (ii) multivariate regression withlatent variables (a particular case of structural equation model, SEM). The present papercompares the two approaches showing in which circumstances they yield equivalent?insome cases, even numerically equal?results. We show that the univariate approach givesresults equivalent to the multivariate approach when restrictions of time invariance (inthe paper, the TI assumption) are imposed on the parameters of the multivariate model.It is shown that the restrictions implicit in the univariate approach can be assessed bychi-square difference testing of two nested multivariate models. In addition, commontests encountered in the econometric analysis of panel data, such as the Hausman test, areshown to have an equivalent representation as chi-square difference tests. Commonalitiesand differences between the univariate and multivariate approaches are illustrated usingan empirical panel data set of firms' profitability as well as a simulated panel data.

Estratigrafia i evolució conceptual d'un paisatge de muntanya al massís del Garraf: la Maçana-Rovirós-Térmens (Begues)

En aquest estudi, l'aplicació regressiva de tècniques com la prospecció arqueològica, la foto i cartointerpretació, els SIG i el buidatge documental han permès la reconstrucció diacrònica del paisatge de l'àrea de la Maçana-Térmens-Rovirós (Begues). L'estudi paisatgístic del Garraf revesteix un singular interès per la seva condició muntanyenca i la seva intensa antropització. Els entorns de muntanya són medis especialment sensibles a processos de canvi, especialment en el cas del massís del Garraf, proper a importants nuclis d'habitació des de l'antiguitat. El nostre treball mostrarà com, en ocasions, el canvi paisatgístic ha estat irreversible al massís.

Integration in strategic alliances : a conceptual framework of IT use in marketing as NPD key factor

En una economia basada en el coneixement, la innovació del producte es considera un factor clau a l'hora de determinar la competitivitat, la productivitat i el creixement d'una companyia. No obstant això, l'experiència de les companyies demostra la necessitat d'un nou model de gestió de la innovació del producte: una gestió basada en el màrqueting, en què la cooperació i l'ús intensiu de les tecnologies de la informació i de la comunicació (TIC) són especialment importants. En els darrers anys, la bibliografia sobre màrqueting ha analitzat el paper de la cooperació en l'èxit del procés d'innovació. No obstant això, fins ara pocs treballs han estudiat el paper que té l'ús de les TIC en el màrqueting en l'èxit del desenvolupament de nous productes (NPD, New Product Development en anglès). És una omissió curiosa, tenint en compte que el nou entorn competitiu és definit per una economia i una societat basades principalment en l'ús intensiu de les TIC i del coneixement. L'objectiu d'aquest treball és investigar el paper que l'ús de les TIC en el màrqueting té en el procés de desenvolupament de nous productes, com a element que reforça la integració d'agents al projecte, afavorint l'establiment de relacions dirigides a la cooperació i l'adquisició d'intel·ligència de mercat útil en el procés de desenvolupament de nous productes. L'estudi d'una mostra de 2.038 companyies de tots els sectors de l'activitat econòmica a Catalunya ens permet contrastar hipòtesis inicials i establir un perfil de companyia innovadora basat en les importants relacions que hi ha entre la innovació, l'ús de TIC en el màrqueting i la integració. Sobresurten dues idees en la nostra anàlisi. En primer lloc, l'ús intensiu de les TIC en el màrqueting fa que la companyia sigui més innovadora, ja que percep que el seu ús ajuda a superar barreres a la innovació i accelera els processos, que es tornen més eficients. En segon lloc, incrementant l'ús de les TIC en el màrqueting es fa augmentar la predisposició de la companyia a integrar agents particulars en l'entorn de negoci en el desenvolupament del procés d'innovació i a col·laborar-hi, de manera que es millora el grau d'adaptació del nou producte a les demandes del mercat.

Study and modeling of the desintegration kinetics of coated paper

The disintegration of recovered paper is the first operation in the preparation of recycled pulp. It is known that the defibering process follows a first order kinetics from which it is possible to obtain the disintegration kinetic constant (KD) by means of different ways. The disintegration constant can be obtained from the Somerville index results (%lsv and from the dissipated energy per volume unit (Ss). The %slv is related to the quantity of non-defibrated paper, as a measure of the non-disintegrated fiber residual (percentage of flakes), which is expressed in disintegration time units. In this work, disintegration kinetics from recycled coated paper has been evaluated, working at 20 revise rotor speed and for different fiber consistency (6, 8, 10, 12 and 14%). The results showed that the values of experimental disintegration kinetic constant, Ko, through the analysis of Somerville index, as function of time. Increased, the disintegration time was drastically reduced. The calculation of the disintegration kinetic constant (modelled Ko), extracted from the Rayleigh’s dissipation function, showed a good correlation with the experimental values using the evolution of the Somerville index or with the dissipated energy

Reliability of the density functional approximation to describe the charge transfer and electrostatic complexes involved in the modeling of organic conducting polymers

Both the intermolecular interaction energies and the geometries for M ̄ thiophene, M ̄ pyrrole, M n+ ̄ thiophene, and M n+ ̄ pyrrole ͑with M = Li, Na, K, Ca, and Mg; and M n+ = Li+ , Na+ , K+ , Ca2+, and Mg2+͒ have been estimated using four commonly used density functional theory ͑DFT͒ methods: B3LYP, B3PW91, PBE, and MPW1PW91. Results have been compared to those provided by HF, MP2, and MP4 conventional ab initio methods. The PBE and MPW1PW91 are the only DFT methods able to provide a reasonable description of the M ̄ complexes. Regarding M n+ ̄ ␲ complexes, the four DFT methods have been proven to be adequate in the prediction of these electrostatically stabilized systems, even though they tend to overestimate the interaction energies.

Collaborative explicit plasticity framework: a conceptual scheme for the generation of plastic and group-aware user interfaces

The advent of new advances in mobile computing has changed the manner we do our daily work, even enabling us to perform collaborative activities. However, current groupware approaches do not offer an integrating and efficient solution that jointly tackles the flexibility and heterogeneity inherent to mobility as well as the awareness aspects intrinsic to collaborative environments. Issues related to the diversity of contexts of use are collected under the term plasticity. A great amount of tools have emerged offering a solution to some of these issues, although always focused on individual scenarios. We are working on reusing and specializing some already existing plasticity tools to the groupware design. The aim is to offer the benefits from plasticity and awareness jointly, trying to reach a real collaboration and a deeper understanding of multi-environment groupware scenarios. In particular, this paper presents a conceptual framework aimed at being a reference for the generation of plastic User Interfaces for collaborative environments in a systematic and comprehensive way. Starting from a previous conceptual framework for individual environments, inspired on the model-based approach, we introduce specific components and considerations related to groupware.

El debat i l"evolució conceptual de la carpeta d"aprenentatge universitària: un reflex del procès de canvi del model educatiu

[cat] La carpeta d'aprenentatge representa un punt de trobada dels grans temes que han ocupat la Didàctica d'ençà dels anys 90 del segle passat: el caràcter formatiu de l'avaluació, l'assumpte de les competències, la metacognició i el pensament crític de l'estudiant, el paper desenvolupat per les TIC, i la concepció d'un aprenentatge col·laboratiu i plantejat a llarg termini. En aquest article de revisió, hom estudia com aquests temes s'han concretat en la carpeta d'aprenentatge i n'han determinat la seva evolució. [eng] The learning portofolio represents a meeting point for the big questions than have concernend teaching since the 1990s: the formative character of the assessment, the issue of competencies, metacognition and the students's critical thinking, the role played by ICTs, and the idea of collaborative learning considered in the long term. The article looks at how these subjects have taken shape in the learning portofolio and how they have determinded its evolutin.

Spontaneous Speech and Emotional Response modeling based on One-class classifier oriented to Alzheimer Disease diagnosis

The purpose of our project is to contribute to earlier diagnosis of AD and better estimates of its severity by using automatic analysis performed through new biomarkers extracted from non-invasive intelligent methods. The methods selected in this case are speech biomarkers oriented to Sponta-neous Speech and Emotional Response Analysis. Thus the main goal of the present work is feature search in Spontaneous Speech oriented to pre-clinical evaluation for the definition of test for AD diagnosis by One-class classifier. One-class classifi-cation problem differs from multi-class classifier in one essen-tial aspect. In one-class classification it is assumed that only information of one of the classes, the target class, is available. In this work we explore the problem of imbalanced datasets that is particularly crucial in applications where the goal is to maximize recognition of the minority class as in medical diag-nosis. The use of information about outlier and Fractal Dimen-sion features improves the system performance.

Sectors i àmbits d'intervenció de l"Educació Social. Aproximació conceptual

En aquest article desenvolupem una aproximació als sectors i àmbits d'intervenció de l'educació social. Pensem, però, que és bo que, en primer lloc, intentem definir què és el que entenem per educació social i pedagogia social.

Una referencia conceptual para la disciplina

Es comprensible que cuando hablamos de los diagnósticos enfermeros se produzcan confusiones terminológicas puesto que, según el Diccionario de la Real Academia de la Lengua Española, la primera acepción de la palabra diagnóstico es «perteneciente o relativo a la diagnosis. Conjunto de signos que sirven para fijar la naturaleza de una enfermedad». Por tanto, debemos...

Theoretical modeling of photon and electron-stimulated Na and K desorption from SiO2

The mechanism of generation of atomic Na and K from SiO2 samples has been studied using explicitly correlated wave function and density functional theory cluster calculations. Possible pathways for the photon and electron stimulated desorption of Na and K atoms from silicates are proposed, thus providing new insight on the generation of the tenuous Na and K atmosphere of the Moon.

Modeling and manufacturability assessment of bistable quantum-dot cells

We have investigated the behavior of bistable cells made up of four quantum dots and occupied by two electrons, in the presence of realistic confinement potentials produced by depletion gates on top of a GaAs/AlGaAs heterostructure. Such a cell represents the basic building block for logic architectures based on the concept of quantum cellular automata (QCA) and of ground state computation, which have been proposed as an alternative to traditional transistor-based logic circuits. We have focused on the robustness of the operation of such cells with respect to asymmetries derived from fabrication tolerances. We have developed a two-dimensional model for the calculation of the electron density in a driven cell in response to the polarization state of a driver cell. Our method is based on the one-shot configuration-interaction technique, adapted from molecular chemistry. From the results of our simulations, we conclude that an implementation of QCA logic based on simple ¿hole arrays¿ is not feasible, because of the extreme sensitivity to fabrication tolerances. As an alternative, we propose cells defined by multiple gates, where geometrical asymmetries can be compensated for by adjusting the bias voltages. Even though not immediately applicable to the implementation of logic gates and not suitable for large scale integration, the proposed cell layout should allow an experimental demonstration of a chain of QCA cells.