161,739 research outputs found
Expensive control of long-time averages using sum of squares and its application to a laminar wake flow
No full textThe paper presents a nonlinear state-feedback control design approach for long-time average cost control, where the control effort is assumed to be expensive. The approach is based on sum-of-squares and semi-definite programming techniques. It is applicable to dynamical systems whose right-hand side is a polynomial function in the state variables and the controls. The key idea, first described but not implemented in (Chernyshenko et al., Phil. Trans. R. Soc. A, 372, 2014), is that the difficult problem of optimizing a cost function involving long-time averages is replaced by an optimization of the upper bound of the same average. As such, controller design requires the simultaneous optimization of both the control law and a tunable function, similar to a Lyapunov function. The present paper introduces a method resolving the well-known inherent non-convexity of this kind of optimization. The method is based on the formal assumption that the control is expensive, from which it follows that the optimal control is small. The resulting asymptotic optimization problems are convex. The derivation of all the polynomial coefficients in the controller is given in terms of the solvability conditions of state-dependent linear and bilinear inequalities. The proposed approach is applied to the problem of designing a full-information feedback controller that mitigates vortex shedding in the wake of a circular cylinder in the laminar regime via rotary oscillations. Control results on a reduced-order model of the actuated wake and in direct numerical simulation are reported
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Flow regimes in a simplified Taylor-Couette-type flow model
No full textIn this paper we introduce a simplified variant of the well-known Taylor-Couette flow. The aim is to develop and investigate a model problem which is as simple as possible while admitting a wide range of behaviour, and which can be used for further study into stability, transition and ultimately control of flow. As opposed to models based on ordinary differential equations, this model is fully specified by a set of partial differential equations that describe the evolution of the three velocity components over two spatial dimensions, in one meridian plane between the two counter-rotating coaxial cylinders. We assume axisymmetric perturbations of the flow in a narrow gap limit of the governing equations and, considering the evolution of the flow in a narrow strip of fluid between the two cylinders, we assume periodic boundary conditions along the radial and axial directions, with special additional symmetry constraints. In the paper, we present linear stability analysis of the first bifurcation, leading to the well known Taylor vortices, and of the secondary bifurcation, which, depending on the type of symmetries imposed on the solution, can lead to wave-like solutions travelling along the axial direction. In addition, we show results of numerical simulations to highlight the wide range of flow structures that emerge, from simple uni-directional flow to chaotic motion, even with the restriction placed on the flow
Adaptação e evidências de validade da Escala Chernyshenko de Conscienciosidade para brasileiros
No full textEsta dissertação teve como principal objetivo adaptar e validar para o contexto brasileiro a The Chernyshenko Conscientiousness Scales (Cheryshenko, 2002), a qual se propõe a ser uma medida mais ampla do que as anteriores para acessar a conscienciosidade. O instrumento subdivide o fator conscienciosidade em seis facetas: industrialidade, ordem, autocontrole, tradicionalismo, virtude e responsabilidade. Sabendo que a conscienciosidade correlaciona-se de forma positiva com importantes variáveis associadas ao bem-estar (especialmente no contexto profissional e acadêmico), também idealizou-se, como objetivo secundário, identificar como a conscienciosidade se relaciona em nível de faceta com algumas variáveis critério em uma amostra de estudantes universitários. As variáveis critério escolhidas para fazerem parte deste estudo foram afetos positivos, afetos negativos, satisfação com a vida, e envolvimento acadêmico. A amostra obtida foi de 320 participantes, estudantes de graduação e de pós-graduação. Os resultados demonstraram que uma solução de cinco fatores emergiu dos itens da escala, que são: industrialidade, ordem, virtude, tradicionalismo e autocontrole. No entanto, a faceta responsabilidade não se estruturou como um fator independente e requer investigações em estudos posteriores. Em relação ao estudo correlacional, com exceção da faceta responsabilidade, todas as outras apresentaram correlações positivas com as variáveis associadas ao bem-estar: satisfação com a vida, envolvimento acadêmico e afetos positivos. No entanto, a faceta que apresentou a correlação mais forte com essas variáveis e que, consequentemente, destacou-se neste estudo foi industrialidade. De modo geral, a Escala Chernyshenko de Conscienciosidade (ECC) se mostrou como um bom e amplo instrumento para medir a conscienciosidade em nível de faceta. Sugere-se que mais estudos sejam feitos a fim de compreender melhor o funcionamento da faceta responsabilidade.This master thesis had as main objective to adapt and to validate to the Brazilian context The Chernyshenko Conscientiousness Scale (Cheryshenko, 2002), which is intended to be a broader measure to access conscientiousness. The instrument subdivide the conscientiousness factor into six facets: industriousness, order, self-control, traditionalism, virtue and responsability. Knowing that conscientiousness correlates positively with important variables associated to wellbeing (specially in the academic and professional contexts), also it was idealized, as a secondary objective, to identify how conscientiousness relates, at a facet level, with some criterion variables in a sample of college students. The criterion variables chosen to be part of this research were positive affect, negative affect, life satisfaction and academic involvement. The sample obtained was 320 participants, undergraduate and graduate students. The results showed that a five factors solution emerged from the items, which are: industriousness, order, self-control, traditionalism and virtue. However, the responsability facet was not structured as an independent factor and requires future investigations. In relation to the correlational study, with the exception of the responsibility facet, all others showed positive correlations with the variables associated with well-being: satisfaction with life, academic involvement and positive affects. However, the facet that showed the strongest correlation with these variables and that, consequently, stood out in this study was industriousness. In general, the Escala Chernyshenko de Conscienciosidade proved to be a good and complete instrument to measure conscientiousness at a facet level. It is suggested that more studies should be done in order to better understand the functioning of the responsibility facet
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Item Response Models for Forced-Choice Questionnaires: A Common Framework
No full textIn forced-choice questionnaires, respondents have to make choices between two or more items presented at the same time. Several IRT models have been developed to link respondent choices to underlying psychological attributes, including the recent MUPP (Stark, Chernyshenko & Drasgow, 2005) and Thurstonian IRT (Brown & Maydeu-Olivares, 2011) models. In the present article, a common framework is proposed that describes forced-choice models along three axes: 1) the forced-choice format used; 2) the measurement model for the relationships between items and psychological attributes they measure; and 3) the decision model for choice behavior. Using the framework, fundamental properties of forced-choice measurement of individual differences are considered. It is shown that the scale origin for the attributes is generally identified in questionnaires using either unidimensional or multidimensional comparisons. Both dominance and ideal point models can be used to provide accurate forced-choice measurement; and the rules governing accurate person score estimation with these models are remarkably similar
Blood coagulation parameters in rats with acute radiation syndrome receiving activated carbon as a preventive remedy
No full textRadiation-induced coagulopathy (RIC) is one of the major causes of death during acute radiation syndrome (ARS). The aim of this study was to characterize the responses of the hemostasis system to ARS of a moderate level on the 1st and 9th days after irradiation. We aimed to identify molecular markers of the blood coagulation system that are most affected by ARS and to estimate the enterosorption effect on the development of irradiation-induced changes. Platelet aggregation rate, activated partial thromboplastin time (APTT) and fibrinogen concentration were determined by standard methods. Level of protein C (PC) was measured using chromogenic substrate S2366 (p-Glu-Pro-Arg-pNa) and Agkistrodon halys halys snake venom activating enzyme. Functionally inactive forms of prothrombin (FIFPs) were determined using two activators in parallel – thromboplastin or prothrombin activator from Echis multisqumatis venom. Rats of both irradiated groups had a higher risk of intravascular clotting in comparison to both control groups. Statistically significant shortening of clotting time in the APTT test (24 ± 4 s vs. 33 ± 5 s) and increased fibrinogen concentration (4.2 ± 0.6 mg/ml vs. 3.2 ± 0.3 mg/ml) were detected. Both parameters were normalized on the 9th day after irradiation. However the platelet count was decreased (0.3∙106 ± 0.05∙106 1/μl vs. 0.145∙106 ± 0.04∙106 1/μl) due to the impaired megakaryocytic function. The level of PC was decreased after X-ray irradiation (70 ± 10%) and partly restored on the 9th day after irradiation (87 ± 10%). Administration of activated carbon (AC) inhibited the drop in the PC concentration after X-ray irradiation (86 ± 15%) and accelerated its restoration on the 9th day (103 ± 14%). The statistically significant accumulation of FIFPs was detected in blood plasma of irradiated rats at the 1st and 9th days after irradiation. No FIFPs were found in any irradiated rat treated with AC. Characterization of the hemostasis system of rats that were exposed to a semilethal dose of X-rays allowed us to select parameters that can be used for monitoring of ARS development. Apart of from basic coagulation tests (APTT) and the measurement of platelet aggregation, fibrinogen and protein C level we can recommend the determination of FIFPs as a useful tool for estimation of the hemostasis response after irradiation with X-rays. This test indicates the intravascular thrombin generation and can help predict thrombotic complication or disseminated intravascular coagulation. Determination of FIFPs in blood plasma of irradiated rats allowed us to study the enterosorption effect on the development of irradiation-induced changes. It was shown that enterosorption with AC prevented accumulation of FIFPs which appears to be a newly discovered anti-thrombotic effect of therapy with AC. ARS influenced hemostasis by inducing thrombin generation (indicated by FIFPs generation), low-grade inflammation (indicated by PC concentration decrease) and thrombocytopenia. Enterosorption with AC minimizes inflammation and pro-coagulant processes caused by a moderate dose of X-ray irradiation. Accumulation of FIFPs can be assumed to be one of the most sensitive markers of the blood coagulation response to X-ray irradiation
Modeling forced-choice response formats
No full textTo counter response distortions associated with the use of rating scales in personality and similar assessments, test items may be presented in so-called ‘forced-choice’ formats. Respondents may be asked to rank-order a number of items, or distribute a fixed number of points between several items – therefore they are forced to make a choice. Until recently, basic classical scoring methods were applied to such formats, leading to scores relative to the person’s mean (ipsative scores). While interpretable in intra-individual assessments, ipsative scores are problematic when used for inter-individual comparisons. Recent advances in estimation methods enabled rapid development of item response models for comparative data, including the Thurstonian IRT model (Brown & Maydeu-Olivares, 2011a), the Multi-Unidimensional Pairwise Preference model (Stark, Chernyshenko & Drasgow, 2005), and others. Appropriate item response modeling enables estimation of person scores that are directly interpretable for inter-individual comparisons, without the distortions and artifacts produced by ipsative scoring
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