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‣ A Simple maxwell Based Model in Order to Represent the frequency-dependent viscosity measured by ultrasound

Franco, Ediguer E.; Adamowski, Julio C.; Higuti, Ricardo T.; Buiochi, Flávio
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1905-1907
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A previous work showed that viscosity values measured high frequency by ultrasound agreed with the values at low frequency by the rotational viscometer when conditions are met, such as relatively low frequency viscosity. However, these conditions strongly reduce the range of the measurement cell. In order to obtain a measurement range and sensitivity high frequency must used, but it causes a frequency-dependent decrease on the viscosity values. This work introduces a new simple in order to represent this frequency-dependent behavior.model is based on the Maxwell model for viscoelastic , but using a variable parameter. This parameter has physical meaning because it represents the linear behavior the apparent elasticity measured along with the viscosity by .Automotive oils SAE 90 and SAE 250 at 22.5±0.5oC viscosities at low frequency of 0.6 and 6.7 Pa.s, respectively,tested in the range of 1-5 MHz. The model was used in to fit the obtained data using an algorithm of non-linear in Matlab. By including the viscosity at low frequency an unknown fitting parameter, it is possible to extrapolate its . Relative deviations between the values measured by the and extrapolated using the model for the SAE 90 and SAE 250 oils were 5.0% and 15.7%...

‣ One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate

Carapau, Fernando
Fonte: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010. Publicador: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010.
Tipo: Artigo de Revista Científica
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Westudy the unsteady motion of a viscoelastic fluid modeled by a second-order fluid where normal stress coefficients and viscosity depend on the shear rate by using a power-law model. To study this problem, we use the one-dimensional nine-director Cosserat theory approach which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. Integrating the equation of conservation of linear momentum over the tube cross-section, with the velocity field approximated by the Cosserat theory, we obtain a one-dimensional system. The velocity field approximation satisfies both the incompressibility condition and the kinematic boundary condition exactly. From this one-dimensional system we obtain the relationship between average pressure and volume flow rate over a finite section of the tube with constant and variable radius. Also, we obtain the correspondent equation for the wall shear stress which enters directly in the formulation as a dependent variable. Attention is focused on some numerical simulation of unsteady/steady flows for average pressure, wall shear stress and on the analysis of perturbed flows.

‣ Aplicação de um modelo hedónico de avaliação a edifícios habitacionais no Concelho de Gaia

Neto, Fernando da Silva
Fonte: Instituto Superior de Economia e Gestão Publicador: Instituto Superior de Economia e Gestão
Tipo: Dissertação de Mestrado
Publicado em /11/2008 Português
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Mestrado em Gestão e Avaliação Imobiliária; A aplicação da Teoria dos Preços Hedónicos tem permitido a construção de inúmeros modelos visando, no essencial, explicar o comportamento dos consumidores face às características dos imóveis disponíveis, bem como a um conjunto de outros factores inerentes, quer aos compradores, quer aos mercados, e que influenciam directamente a formação de preços. Assim, o desenvolvimento e aplicação de Modelos Hedónicos para o Mercado Habitacional encontram múltiplos exemplos na literatura. Com o presente trabalho pretendeu-se sobretudo construir um modelo-base em que a maior parte das variáveis utilizadas fossem generalizáveis a todo o Território Nacional, e que, caso a caso, adoptasse ainda variáveis características de cada local. Por outro lado procurou suprimir-se a excessiva simplicidade que usualmente é utilizada para avaliar a qualidade da construção. Os modelos obtidos apresentam resultados interessantes explicando o comportamento da variável dependente escolhida (preço/m²) em percentagens em torno dos 95%, e evidenciando também uma capacidade de prever o valor médio dos imóveis com um erro máximo de cerca de 5% (nos testes efectuados). Apesar de estes bons resultados poderem não ser considerados completamente conclusivos...

‣ Application of alternative regression models to deal with proportions as dependent variables

Marques, José Lourenço Pires
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em 09/03/2012 Português
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Mestrado em Finanças; The main purpose of this thesis is to consider different approaches to deal with proportions as dependent variables in regression models. The Classical Linear Regression Model (CLRM) is the approach that most researchers apply to their data. However, the CLRM is inappropriate to deal with bounded variables whose response is restricted into the interval (0, 1) as dependent variables since it may possibly yield fitted values for the variable of interest that surpass its lower and upper limits. Due to the CLRM weaknesses, in this thesis we will consider some alternative parametric regression models that include the additive logistic normal distribution, the censored normal distribution, the Beta distribution and the normal distribution with nonlinear response function. A quasi-parametric regression approach will also be considered. In the empirical case we consider a dataset with financial information from US firms. The dependent variable of the models we intend to estimate is the debt to maturity, which is measured as a proportion of the total debt of the firm that has a maturity larger than three years. The explanatory variables are the abnormal earnings, the asset maturity and the size of the firm. To compare the above models will be used the Akaike’s information criterion (AIC) and Schwarz criterion (SBC). The distribution that displays the lowest values on both criteria is the best to study proportions as dependent variables. We will also study the adjusted value of each model.; Com esta tese pretendem-se considerar vários modelos de regressão alternativos ao lidar com proporções...

‣ Bayesian Approaches for Limited Dependent Variable Change Point Problems

Spirling, Arthur P
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
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Limited dependent variable (LDV) data are common in political science, and political methodologists have given much good advice on dealing with them. We review some methods for LDV "change point problems" and demonstrate the use of Bayesian approaches for count, binary, and duration-type data. Our applications are drawn from American politics, Comparative politics, and International Political Economy. We discuss the tradeoffs both philosophically and computationally. We conclude with possibilities for multiple change point work.; Government

‣ Coordinating global software development activities: requisite variety in information systems as a dependent variable

Wiredu, Gamel O.
Fonte: University of Limerick Publicador: University of Limerick
Tipo: Conference item; all_ul_research; ul_published_reviewed; none
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peer-reviewed; In this paper, I explain how globally-distributed software development subunits can coordinate their activities with information systems (IS). The basis of this explanation lies in the contemporary proliferation of global software development (GSD) activities which suggests an unexplained reality: that organizations practicing GSD are somehow regulating their IS to cope with increasing and varied uncertainties. Through an empirical example of an organization’s subunit’s regulating and coping, I make the case that requisite variety in a subunit’s information systems is a dependent variable for managing uncertainties leading to optimal coordination. In this example, I show varied uncertainties that faced the subunit; and I explain how variety in its information system was requisite for managing the uncertainties satisfactorily. Based on these explanations, I suggest four characteristics of variety in IS that will be requisite for managing uncertainties in GSD – developers’ agility, developers’ continuity and travelling, high frequency of communications, and varied communication modes and technologies.

‣ The Effects on Growth of Commodity Price Uncertainty and Shocks

Dehn, Jan
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
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The author estimates the effects on growth of commodity price shocks, and uncertainty within an established empirical growth model. Ex-post shocks, and ex-ante uncertainty have been treated in the empirical literature as if they were synonymous. But they are distinct concepts, and it is both theoretically, and empirically inappropriate to treat them as synonymous. He shows that the interaction between policy, and aid is robust to the inclusion of variables capturing commodity price movements. More important, his approach departs in three ways from earlier empirical studies of the subject: 1) It deals with issues of endogeneity, without incurring an excessive loss of efficiency. 2) It defines the dependent variable to allow an assessment of the longer-term implications of temporary trade shocks. 3) It imposes no priors on how commodity price movements affect growth, but compares and contrasts a range of competing shock, and uncertainty specifications. The author resolves the disagreement about the long-run effect of positive shocks on growth...

‣ The Effect of Aid on Growth : Evidence from a Quasi-Experiment

Galiani, Sebastian; Knack, Stephen; Xu, Lixin Colin; Zou, Ben
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
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The literature on aid and growth has not found a convincing instrumental variable to identify the causal effects of aid. This paper exploits an instrumental variable based on the fact that since 1987, eligibility for aid from the International Development Association (IDA) has been based partly on whether or not a country is below a certain threshold of per capita income. The paper finds evidence that other donors tend to reinforce rather than compensate for reductions in IDA aid following threshold crossings. Overall, aid as a share of gross national income (GNI) drops about 59 percent on average after countries cross the threshold. Focusing on the 35 countries that have crossed the income threshold from below between 1987 and 2010, a positive, statistically significant, and economically sizable effect of aid on growth is found. A one percentage point increase in the aid to GNI ratio from the sample mean raises annual real per capita growth in gross domestic product by approximately 0.35 percentage points. The analysis shows that the main channel through which aid promotes growth is by increasing physical investment.

‣ Rethinking the Dependent Variable in Electoral Behavior - on the measurement and analysis of electoral utilities

VAN DER EIJK, Cees; VAN DER BRUG, Wouter; KROH, Martin; FRANKLIN, Mark N.
Fonte: Instituto Universitário Europeu Publicador: Instituto Universitário Europeu
Tipo: Artigo de Revista Científica
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As a dependent variable, party choice did not lend itself to analysis by means of powerful multivariate methods until the coming of discrete-choice models, most notably conditional logit and multinomial logit. These methods involve estimating effects on party preferences (utilities) that are post hoc derived from the data, but such estimates are plagued by a number of difficulties. These difficulties do not apply if advanced statistical procedures are used to analyze utilities directly measured with survey data. Such variables have been employed for a number of years and have been extensively validated in past research. Analysis of party choice on the basis of measured utilities is less hampered by restrictions and (often implausible) assumptions than discrete-choice modeling is. Particularly problematic is the inability of discrete-choice models to analyze small-party voting. The resulting elimination of voters of small parties results in strong biases of the coefficients of explanatory variables. No such need for eliminating cases arises when analyzing empirically observed utilities, so parameter estimates from these analyses do not contain this bias. Finally, observed utilities provide opportunities to answer research questions that cannot be answered with discrete-choice models...

‣ Regression Models for Binary Dependent Variables Using Stata, SAS, R, LIMDEP, and SPSS

Park, Hun Myoung
Fonte: Universidade de Indiana Publicador: Universidade de Indiana
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A categorical variable here refers to a variable that is binary, ordinal, or nominal. Event count data are discrete (categorical) but often treated as continuous variables. When a dependent variable is categorical, the ordinary least squares (OLS) method can no longer produce the best linear unbiased estimator (BLUE); that is, OLS is biased and inefficient. Consequently, researchers have developed various regression models for categorical dependent variables. The nonlinearity of categorical dependent variable models makes it difficult to fit the models and interpret their results.

‣ Regression Models for Ordinal and Nominal Dependent Variables Using SAS, Stata, LIMDEP, and SPSS

Park, Hun Myoung
Fonte: Universidade de Indiana Publicador: Universidade de Indiana
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A categorical variable here refers to a variable that is binary, ordinal, or nominal. Event count data are discrete (categorical) but often treated as continuous variables. When a dependent variable is categorical, the ordinary least squares (OLS) method can no longer produce the best linear unbiased estimator (BLUE); that is, OLS is biased and inefficient. Consequently, researchers have developed various regression models for categorical dependent variables. The nonlinearity of categorical dependent variable models makes it difficult to fit the models and interpret their results.

‣ The probability of non-purchasing tobacco of a smoker

Miles, Daniel
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho em Andamento Formato: application/octet-stream; application/octet-stream; application/pdf
Publicado em /10/1998 Português
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This paper addresses the problem of zeroes in tobacco expenditure. Generally, tobacco demand is estimated using limited dependent variable models, i.e. Tobit or Double Hurdle Models, which take into account the zero expenditure problem under the assumption that a relatively important number of smokers declared a zero in tobacco expenditure. Clearly, if all zeroes where from non-smokers then demand estimation could be done using traditional methods over the positive expenditure observations. Based on the Spanish Expenditure Survey we estimate the conditional probability of non-expenditure by a smoker, finding that such probability is extremely small. This suggests that smokers buy quite regularly and hence it is possible to estimate the tobacco demand using only the positive observations.

‣ On the use of variable-separation method for the analysis of vibration problems with time-dependent boundary conditions

Aranda-Ruiz, Josué; Fernández-Sáez, José
Fonte: Sage Publications Publicador: Sage Publications
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article
Publicado em /12/2012 Português
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In this article, the axial vibrations of a rod with a clamped end and the transversal vibrations of a cantilever beam, both with a time-dependent and non-harmonic force applied on their free ends, are analysed. These are problems in which the traction and the shear, for the rod and the beam, respectively, prescribed in the boundaries of the bodies vary with time. The problems can be solved by the method proposed by Mindlin and Goodman. However, it is usual to solve this problem by the classic variable-separation method (which does not properly fulfil the time-dependent boundary conditions). The displacements and the forces along the systems are derived from both cited methods, and the results are compared. These results highlight the importance of using the proper solution method for the vibration problems with time-dependent boundary conditions.; Comisión Interministerial de Ciencia y Tecnología of the Spanish Government and to the Comunidad Autónoma de Madrid for partial support of this work through the research projects DPI2011-23191 and CCG10-UC3M-DPI-5596, respectively.

‣ Regression Methods for Categorical Dependent Variables: Effects on a Model of Student College Choice

Rapp, Kelly E.
Fonte: [Bloomington, Ind.] : Indiana University Publicador: [Bloomington, Ind.] : Indiana University
Tipo: Doctoral Dissertation
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Thesis (Ph.D.) - Indiana University, School of Education, 2012; The use of categorical dependent variables with the classical linear regression model (CLRM) violates many of the model's assumptions and may result in biased estimates (Long, 1997; O'Connell, Goldstein, Rogers, & Peng, 2008). Many dependent variables of interest to educational researchers (e.g., professorial rank, educational attainment) are categorical in nature but are analyzed using the CLRM (Harwell & Gatti, 2001) even though alternate regression techniques for categorical dependent variables are recommended (Agresti, 1996; Long, 1997). Data obtained from ACT®, Inc., on 5,200 high school seniors in Illinois and Colorado were used to analyze effects of regression method on a model of ascriptive and academic influences on selectivity of postsecondary institution attended. The dependent variable was measured in rank-ordered categories based on self-reported institutional admissions policies and analyzed with classical linear, multinomial logistic, and ordered logistic regressions. Choice of regression method did not affect overall model performance as evidenced by significant F and Likelihood Ratio χ2 tests. The full CLRM was fit moderately-well to the data (R2 = .391)...

‣ Six reasons to turn sixty: NATO as a case study of Walt's five reasons for alliance endurance, revealing a sixth variable

Luhmann, Sybille
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Relatório
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In 1949 tensions were high - and shared. Concerns about the power vacuum created through the collapse of Germany and fears of the Soviet threat, soon united previous wartime enemies. Realizing their shared threat perceptions, Italy and the United States together with the remaining ten founding members\ met in Washington to sign the North Atlantic Treaty on 9 April 1949 and call the North Atlantic Treaty Organization (NATO) into existence. Sixty years have passed since that day and the security environment within Europe has changed considerably. No longer facing a uniting enemy like the Soviet Union, NATO has been criticized for its fractures, its inadequate force generation, and its divergent threat perceptions. The disagreement concerning the Y om Kippur war in 1973, the war in Bosnia Herzegovina in 1996, and NATO's ongoing operation in Afghanistan have all highlighted these critiques. Ironically though, the Yorn Kippur war, even though adhering to the criticism, disproves it, as the discord occurred before the collapse of the Soviet Union in 1991. If, however, these perpetual critiques have accompanied the alliance, the inimitability of NATO does not seem to be defined by its critics and their continuing predictions of certain collapse...

‣ Same Technology, Different Outcome? Lessons on Dummy Variables & Dependent Variable Transformations

Hunter, Starling David
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Trabalho em Andamento Formato: 159683 bytes; application/pdf
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There is long-standing body of empirical research concerned with the consequences of information technology for organization structure and processes. Several of those studies have reported that the same technology, when implemented in similar organizational settings, can be associated with vastly different, even diametrically opposing, organizational consequences. The seminal study in this stream of research is Barley's (1986) article entitled "Technology as an Occasion for Structuring: Evidence from Observations of CT Scanners and the Social Order of Radiology Departments." That study reported that two similarly-composed radiology departments implemented the same technology yet experienced different structural outcomes, i.e. that the two departments experienced different rates of decentralization and that they evolved through a different number of distinct phases of structuring. This difference in outcomes was attributed to differences between each departments' distribution of relevant expertise and "specific historical processes" (Barley...

‣ Semiparametric estimators for limited dependent variable (LDV) models with endogenous regressors

Lee, Myoung-Jae
Fonte: Marcel Dekker Inc. Publicador: Marcel Dekker Inc.
Tipo: Artigo de Revista Científica
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This article reviews semiparametric estimators for limited dependent variable (LDV) models with endogenous regressors, where nonlinearity and nonseparability pose difficulties. We first introduce six main approaches in the linear equation system literatur

‣ Spatial Discrete Choice and Spatial Limited Dependent Variable Models: a review with an emphasis on the use in Regional Health Economics

Billé, A. G.; Arbia, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/02/2013 Português
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Despite spatial econometrics is now considered a consolidated discipline, only in recent years we have experienced an increasing attention to the possibility of applying it to the field of discrete choices (e.g. Smirnov, 2010 for a recent review) and limited dependent variable models. In particular, only a small number of papers introduced the above-mentioned models in Health Economics. The main purpose of the present paper is to review the different methodological solutions in spatial discrete choice models as they appeared in several applied fields by placing an emphasis on the health economics applications.; Comment: 38 pages

‣ Global existence of critical nonlinear wave equation with time dependent variable coefficients

Zhou, Yi; Lai, Ning-An
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/03/2010 Português
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In this paper, we establish global existence of smooth solutions for the Cauchy problem of the critical nonlinear wave equation with time dependent variable coefficients in three space dimensions {equation}\partial_{tt}\phi-\partial_{x_i}\big(g^{ij}(t,x)\partial_{x_j}\phi\big)+\phi^5=0, mathbb{R}_t \times \mathbb{R}_x^3,{equation} where $\big(g_{ij}(t,x)\big)$ is a regular function valued in the spacetime of $3\times3$ positive definite matrix and $\big(g^{ij}(t,x)\big)$ its inverse matrix. Here and in the sequence, a repeated sum on an index in lower and upper position is never indicated. In the constant coefficients case, the result of global existence is due to Grillakis \cite{Grillakis1}; and in the time-independent variable coefficients case, the result of global existence and regularity is due to Ibrahim and Majdoub \cite{Ibrahim}. The key point of our proofs is to show that the energy cannot concentrate at any point. For that purpose, following Christodoulou and Klainerman \cite{Chris}, we use a null frame associated to an optical function to construct a geometric multiplier similar to the well-known Morawetz multiplier. Then we use comparison theorem originated from Riemannian Geometry to estimate the error terms. Finally, using Strichartz inequality due to \cite{Smith} as Ibrahim and Majdoub \cite{Ibrahim}...

‣ Common Correlated Effects Estimation of Heterogeneous Dynamic Panel Data Models with Weakly Exogenous Regressors

Pesaran, M. Hashem; Chudik, Alexander
Fonte: Faculty of Economics, University of Cambridge Publicador: Faculty of Economics, University of Cambridge
Tipo: Working Paper; not applicable
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This paper extends the Common Correlated Effects (CCE) approach developed by Pesaran (2006) to heterogeneous panel data models with lagged dependent variable and/or weakly exogenous regressors. We show that the CCE mean group estimator continues to be valid but the following two conditions must be satisfied to deal with the dynamics: a sufficient number of lags of cross section averages must be included in individual equations of the panel, and the number of cross section averages must be at least as large as the number of unobserved common factors. We establish consistency rates, derive the asymptotic distribution, suggest using co- variates to deal with the effects of multiple unobserved common factors, and consider jackknife and recursive de-meaning bias correction procedures to mitigate the small sample time series bias. Theoretical findings are accompanied by extensive Monte Carlo experiments, which show that the proposed estimators perform well so long as the time series dimension of the panel is sufficiently large.