Bayesian and regularization approaches to multivariable linear system identification: the role of rank penalties

Recent developments in linear system identification have proposed the use of non-parameteric methods, relying on regularization strategies, to handle the so-called bias/variance trade-off. This paper introduces an impulse response estimator which relies on an $\ell_2$-type regularization including a rank-penalty derived using the log-det heuristic as a smooth approximation to the rank function. This allows to account for different properties of the estimated impulse response (e.g. smoothness and stability) while also penalizing high-complexity models. This also allows to account and enforce coupling between different input-output channels in MIMO systems. According to the Bayesian paradigm, the parameters defining the relative weight of the two regularization terms as well as the structure of the rank penalty are estimated optimizing the marginal likelihood. Once these hyperameters have been estimated, the impulse response estimate is available in closed form. Experiments show that the proposed method is superior to the estimator relying on the "classic" $\ell_2$-regularization alone as well as those based in atomic and nuclear norm.Comment: to appear in IEEE Conference on Decision and Control, 201

Estimating effective connectivity in linear brain network models

Contemporary neuroscience has embraced network science to study the complex and self-organized structure of the human brain; one of the main outstanding issues is that of inferring from measure data, chiefly functional Magnetic Resonance Imaging (fMRI), the so-called effective connectivity in brain networks, that is the existing interactions among neuronal populations. This inverse problem is complicated by the fact that the BOLD (Blood Oxygenation Level Dependent) signal measured by fMRI represent a dynamic and nonlinear transformation (the hemodynamic response) of neuronal activity. In this paper, we consider resting state (rs) fMRI data; building upon a linear population model of the BOLD signal and a stochastic linear DCM model, the model parameters are estimated through an EM-type iterative procedure, which alternately estimates the neuronal activity by means of the Rauch-Tung-Striebel (RTS) smoother, updates the connections among neuronal states and refines the parameters of the hemodynamic model; sparsity in the interconnection structure is favoured using an iteratively reweighting scheme. Experimental results using rs-fMRI data are shown demonstrating the effectiveness of our approach and comparison with state of the art routines (SPM12 toolbox) is provided

Classical vs. Bayesian methods for linear system identification: point estimators and confidence sets

This paper compares classical parametric methods with recently developed Bayesian methods for system identification. A Full Bayes solution is considered together with one of the standard approximations based on the Empirical Bayes paradigm. Results regarding point estimators for the impulse response as well as for confidence regions are reported.Comment: number of pages = 8, number of figures =

A importância da ética para o profissional da área contábil: caso Sauer Contabilidade S/S Ltda.

TCC (Graduação) - Universidade Federal de Santa Catarina. Centro Socioeconômico. Curso de Ciências ContábeisEste trabalho teve como tema Identificar a importância da ética para o profissional da área contábil, por meio de uma pesquisa de campo realizada na Empresa Contábil: Ildomar Sauer, localizada no Município de Sananduva/RS. A pesquisa configurou-se como qualitativa e exploratória. Para atingir os objetivos propostos neste trabalho, a coleta dos dados foi mediante a pesquisa de campo, onde foi aplicado 01 (um) questionário composto por perguntas fechadas e abertas, envolvendo os 06 colaboradores da empresa estudada. No entanto, o resultado da pesquisa mostrou que os colaboradores entrevistados, buscam realizar suas atividades dentro dos valores éticos, trabalhando com honestidade e comprometimento em suas ações. Embora, nem todos os colaboradores possuam conhecimento sobre o código de ética, realizam suas atividades dentro da boa conduta, discutindo situações nas quais poderiam afetar a dignidade profissional antes de haver envolvimento total. Além de preservarem as informações confidencias, nas quais são atribuídas em seu ambiente de trabalho, buscam cumprir com o seu dever da forma mais correta possível. Portanto, pode-se dizer que a ética é um dos fatores primordiais na profissão da área contábil

Maximum Entropy Vector Kernels for MIMO system identification

Recent contributions have framed linear system identification as a nonparametric regularized inverse problem. Relying on $\ell_2$-type regularization which accounts for the stability and smoothness of the impulse response to be estimated, these approaches have been shown to be competitive w.r.t classical parametric methods. In this paper, adopting Maximum Entropy arguments, we derive a new $\ell_2$ penalty deriving from a vector-valued kernel; to do so we exploit the structure of the Hankel matrix, thus controlling at the same time complexity, measured by the McMillan degree, stability and smoothness of the identified models. As a special case we recover the nuclear norm penalty on the squared block Hankel matrix. In contrast with previous literature on reweighted nuclear norm penalties, our kernel is described by a small number of hyper-parameters, which are iteratively updated through marginal likelihood maximization; constraining the structure of the kernel acts as a (hyper)regularizer which helps controlling the effective degrees of freedom of our estimator. To optimize the marginal likelihood we adapt a Scaled Gradient Projection (SGP) algorithm which is proved to be significantly computationally cheaper than other first and second order off-the-shelf optimization methods. The paper also contains an extensive comparison with many state-of-the-art methods on several Monte-Carlo studies, which confirms the effectiveness of our procedure

A view from inside iron-based superconductors

Muon spin spectroscopy is one of the most powerful tools to investigate the microscopic properties of superconductors. In this manuscript, an overview on some of the main achievements obtained by this technique in the iron-based superconductors (IBS) are presented. It is shown how the muons allow to probe the whole phase diagram of IBS, from the magnetic to the superconducting phase, and their sensitivity to unravel the modifications of the magnetic and the superconducting order parameters, as the phase diagram is spanned either by charge doping, by an external pressure or by introducing magnetic and non-magnetic impurities. Moreover, it is highlighted that the muons are unique probes for the study of the nanoscopic coexistence between magnetism and superconductivity taking place at the crossover between the two ground-states.Comment: 28 pages, 18 figure

Anomalous lattice contraction and emergent electronic phases in Bi-doped Eu2_2Ir2_2O7_7

We study the pyrochlore series (Eu$_{1-x}$Bi$_x$)$_2$Ir$_2$O$_7$ for $0 \leq x \leq 1$. We show that for small $x$, the lattice undergoes an anomalous contraction but the all-in/all-out and metal-to-insulator transitions remain robust, and the resistivity approaches a $1/T$ dependence at low-T, suggesting proximity to the Weyl semimetallic phase, as previously predicted theoretically. At the boundary between Eu$_2$Ir$_2$O$_7$ and Bi$_2$Ir$_2$O$_7$ a qualitatively different ground state emerges, which is characterized by its unusual metallic behavior and absence of magnetic ordering at least down to $0.02$ K.Comment: 5 Pages, 4 figure

Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study

$^{19}$F NMR measurements in SmFeAsO$_{1-x}$F$_x$, for $0.15\leq x\leq 0.2$, are presented. The nuclear spin-lattice relaxation rate $1/T_1$ increases upon cooling with a trend analogous to the one already observed in CeCu$_{5.2}$Au$_{0.8}$, a quasi two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground-state. In particular, the behaviour of the relaxation rate either in SmFeAsO$_{1-x}$F$_x$ or in CeCu$_{5.2}$Au$_{0.8}$ can be described in the framework of the self-consistent renormalization theory for weakly itinerant electron systems. Remarkably, no effect of the superconducting transition on $^{19}$F $1/T_1$ is detected, a phenomenon which can hardly be explained within a single band model.Comment: 4 figure

Processamentos linguístico, perceptivo auditivo e executivo em crianças: o papel da idade, do tipo de escola e do TDAH

The main goal of the present thesis was to explore the development and relationship between language and executive functions (EF), a topic of extreme relevance both for research and clinical practice. Given the scarcity of studies of the association between language and executive abilities in typically developing children, there is an absence of assessment instruments with norms for children of different ages and education levels. Verbal fluency (VF) tasks are some of the most commonly used tools in the neuropsychological assessment of linguistic and executive processing. As such, these tasks may be able to satisfy the research and clinical demands for a further understanding of these abilities in patients with Attention Deficit/Hyperactivity Disorder (ADHD), a highly prevalent condition in childhood. The relationship between EF and language in children with this disorder were examined through two empirical studies and a literature review. The first study assessed the impact of age and type of school in the performance of 6-to-12-year old children in unconstrained, phonemic and semantic VF tasks (abbreviated as UVF, PVF and SVF, respectively). A total of 378 participants (177 from private schools) with a mean age of 9. 03 years (SD=1. 91) completed the UVF task, while 403 children (186 from private schools) with a mean age of 9. 12 years (SD=1. 88) completed were administered the PVF task and 385 children (168 from private schools) with a mean age of 9. 01 years (SD=1. 86) completed the SVF task. The effect of age and type of school on children’s VF performance was assessed using a Two-Way ANOVA, and group differences were investigated using Bonferroni post-hoc tests. Main effects of age and type of school were observed in UVF and PVF scores, while the interaction between these two variables had an effect on SVF. Overall, performance tended to improve with age, and was better in children who attended private schools than in those recruited from public institutions. The second study aimed to perform a review of studies addressing the clinical and/or neuropsychological assessment of linguistic and auditory processing (AP) in children with ADHD. The PubMed database was searched for articles published between 2000 and 2012 using the following keywords [language or linguistic] and [auditory processing or auditory perception] and [attention deficit or hyperactivity]. All abstracts returned were analyzed in parallel by two independent researchers, using a third reviewer for consensus. A total of 46. 7% of the studies included in the reviewed focused on language assessment at word and sentence levels, while 33. 33% investigated AP and 13. 33% assessed both variables. Reading disorders were the most prevalent condition in the samples studied, and, interestingly, the assessments of language and AP were not conducted with the aim of achieving any specific neuropsychological goals. Lastly, the third study in this thesis assessed the impact of the intensity of symptoms of inattention and/or hyperactivity/impulsivity on language, AP, working memory (WM) and the EF of children with ADHD, as well as the relationships and interactions between these variables. Forty-four children with a diagnosis of ADHD took part in the study (33 from private schools, with a mean age of 9. 07 years (SD = 1. 71)). Correlation analysis was used to select variables for inclusion in a linear regression model. The following results were obtained from this investigation: (1) the intensity of inattention symptoms accounted for a significant portion of the variability reading and writing performance, especially phonological reading and spelling in a writing-to-dictation task; (2) the intensity of hyperactivity/impulsivity symptoms had a significant impact on children’s EF (processing speed, cognitive flexibility and inhibitory control), corroborating other findings in the literature; (3) oral language and AP were associated with measures of EF and WM, suggesting that these components are interdependent, although the directionality of their relationship needs to be further explored. In conclusion, the present studies contributed to the understanding of relationships between language and EF in typical childhood development and in children with psychiatric disorders. These findings also have important implications for the neuropsychological assessment and rehabilitation of patients with ADHD.A presente tese tem como eixo principal a avaliação de funções cognitivas e suas interrelações, como componentes linguísticos lexicais, sintáticos e discursivos, de funções executivas (FE) e de percepção auditiva, no desenvolvimento típico e atípico (Transtorno de Déficit de Atenção e Hiperatividade – TDAH). Na medida em que as investigações sobre a interface entre componentes linguísticos e executivos em crianças em desenvolvimento típico ainda são escassas, levanta-se a necessidade de ferramentas adaptadas e normatizadas para esta população, considerando as variáveis sociodemográficas, como idade e escolaridade. Nesse contexto, destaca-se o paradigma da fluência verbal (FV), sendo uma das tarefas mais utilizadas na avaliação neuropsicológica das FE que contempla a análise do processamento linguístico e executivo. Este tema vem ao encontro da demanda clínica e de pesquisa sobre o entendimento destes construtos em associação com o quadro clínico de TDAH, que é frequente na população infantil. Foram desenvolvidos dois estudos empíricos e um de revisão sistemática da literatura. O primeiro estudo investigou, preliminarmente, o impacto da idade e do tipo de escola no desempenho de crianças de 6 a 12 anos em tarefas de fluência verbal livre (FVL), fonêmico-ortográfica (FVF) e semântica (FVS). Para responder as questões de pesquisa participaram da avaliação da FVL, 378 participantes (177 de escolas privadas) com média de idade de 9,03 anos (dp=1,91); da FVF, foram 403 crianças (186 de escolas privadas) com idade média de 9,12 (dp=1,88); e da FVS, 385 participantes (168 de escolas privadas) com idade média de 9,01 anos (dp=1,86). O efeito da idade, do tipo de escola e interação foi analisado pelo teste Two-Way ANOVA e as diferenças entre os grupos foram verificadas por análise post-hoc Bonferroni. Observaram-se efeitos principais da idade e do tipo de escola na FVL e FVF e interação entre os fatores na FVS. De modo geral, o desempenho melhora de acordo com o aumento da idade e as crianças de escolas privadas tendem a apresentar melhores escores. O segundo estudo objetivou identificar na literatura pesquisas que investigaram o processamento linguístico e auditivo (PA) na avaliação clínica e/ou neuropsicológica de crianças/adolescentes com TDAH. Realizou-se uma busca na base de dados PubMed de 2000 a 2012 com keywords dos construtos [language or linguistic] e [auditory processing or auditory perception] e [attention deficit or hyperactivity]. Os abstracts foram analisados por double blind review com terceiro juiz para consenso. Os resultados mostraram que 46,67% dos estudos avaliaram a linguagem (nível da palavra e sentença), 33,33% processamento auditivo (PA) e 13,33%, ambos. O transtorno de leitura foi a comorbidade mais prevalente e o desempenho linguístico e de PA não foram analisados nos estudos para fins neuropsicológicos específicos. Por fim, o terceiro estudo analisou o impacto da intensidade de sintomas de desatenção e/ou hiperatividade/impulsividade de crianças com TDAH em desfechos de linguagem, PA, memória de trabalho (MT), componentes das FE, e as suas relações e influências mútuas. Participaram do estudo 44 crianças com diagnóstico de TDAH (33 de escolas privadas, com idade média de 9,07 anos (dp=1,71)).As variáveis que se correlacionaram significativamente participaram no modelo de análise de regressão linear. Concluiu-se, com dados preliminares, que: (1) a intensidade de sintomas de desatenção explicou aspectos relacionados à leitura e escrita, mais especificamente o processamento ortográfico em tarefa de ditado e a leitura por via fonológica; (2) a intensidade dos sintomas de hiperatividade/impulsividade apresentou maior impacto em subcomponentes das FE (velocidade de processamento, flexibilidade cognitiva e controle inibitório) das crianças investigadas, estando de acordo com outras pesquisas já realizadas e (3) o processamento de linguagem oral e do PA relacionam-se com as medidas de FE e de MT, sugerindo a interdependência entre esses componentes, embora a direcionalidade destas influências necessitem ser mais exploradas. Em suma, os estudos desenvolvidos contribuíram para a reflexão sobre relação entre a linguagem e as FE no desenvolvimento típico infantil, bem como, para o entendimento de suas manifestações clínicas e implicações para avaliação e reabilitação neuropsicológica de indivíduos com TDAH

Superconducting phase fluctuations in SmFeAsO0.8_{0.8}F0.2_{0.2} from diamagnetism at low magnetic field above TcT_{c}

Superconducting fluctuations (SF) in SmFeAsO$_{0.8}$F$_{0.2}$ (characterized by superconducting transition temperature $T_{c} \simeq 52.3$ K) are investigated by means of isothermal high-resolution dc magnetization measurements. The diamagnetic response to magnetic fields up to 1 T above $T_{c}$ is similar to what previously reported for underdoped cuprate superconductors and it can be justified in terms of metastable superconducting islands at non-zero order parameter lacking of long-range coherence because of strong phase fluctuations. In the high-field regime ($H \gtrsim 1.5$ T) scaling arguments predicted on the basis of the Ginzburg-Landau theory of conventional SF are found to be applicable, at variance with what observed in the low-field regime. This fact enlightens that two different phenomena are simultaneously present in the fluctuating diamagnetism, namely the phase SF of novel character and the conventional SF. High magnetic fields (1.5 T $\lesssim H \ll H_{c2}$) are found to suppress the former while leaving unaltered the latter one.Comment: 7 pages, 5 figure