1,720,964 research outputs found
Chaos in a Periodically Perturbed Second-Order Equation with Signum Nonlinearity
No full textWe study the periodically perturbed Duffing-type equation g(x) = e(t) and its damped counterpart + g(x) = e(t). The main feature of our model is the presence of a "signum term" in g(x). We prove the existence of infinitely many subharmonic solutions as well as the presence of chaotic dynamics for some T-periodic forcing terms
Analysis of the period map for a singular ODE related to the Liebau phenomenon
No full textWe study the positive periodic solutions of a periodically perturbed second-order nonlinear equation with a singularity, related to the so-called Liebau phenomenon, which has received great deal of interest in the past decade. Our main contribution concerns a global theorem about the monotonicity of the period map for the equation with constant coefficients. Then, as applications, we prove new bifurcation results for periodic solutions (harmonic and subharmonic), as well as the presence of complex dynamics for some periodic coefficients which are meaningful from a physical point of view
Chaotic dynamics in a vertically driven planar pendulum
No full textUsing elementary phase-plane analysis, combined with results from the theory of
topological horseshoes and linked twist maps, we prove the presence of chaos-like
dynamics for a vertically driven planar pendulum and other, more general, related
equations
A topological approach to the problem of chaotic tides
No full textWe study the existence of subharmonic solutions and solutions with complicated dynamics in a Duffing-type equation which arises from the study of forced tides. This is a model which involves an almost enclosed basin, connected to the sea by a narrow strait. Such a basin turns out to be a nonlinear Helmholtz resonator. The proofs are based on developments of the theory of topological horseshoes in connection with some geometric features associated to linked twist maps
Monotonicity of the period function and chaotic dynamics in a class of singular ODEs
No full textThe present article deals with the positive solutions of a periodically perturbed Duffing type equation with singularity of the form u′′−u−α=e(t) and its damped counterpart u′′+cu′−u−α=e(t), for α≥1. Using a result on monotonicity for the period function of an associated planar autonomous system, we prove the existence of infinitely many subharmonic solutions, as well as the presence of chaotic dynamics, for some T-periodic forcing terms with negative mean value
Do households substitute mileage across their cars?
No full textUnderstanding the driving behavior of multi-car households is crucial to evaluate the effectiveness of policies aimed at reducing fuel consumption in the passenger car fleet. In this paper, we investigate whether households adjust their vehicle miles traveled (VMT) among their cars in response to changes in fuel prices. We use data from the 2017 National Household Travel Survey (NHTS) on two-car households, where both cars are powered by gasoline, and estimate econometric models that distinguish cars based on their fuel economy. Our results show that an increase in per-mile driving cost significantly reduces the demand for driving the same car and increases demand for driving the other car, with little to no evidence of overall substitution at the daily or annual level. However, further investigation using artificial monthly travel diary data revealed a pronounced substitution towards the most fuel-efficient car only when there is a large and sustained increase in gas price
Counting vehicle miles traveled: What can we learn from the NHTS?
No full textAn accurate estimate of vehicle miles traveled (VMT) is an essential input into a variety of emissions, climate change, energy and infrastructure-planning models. We examine different measures of annual miles driven from the 2017 National Household Travel Survey (NHTS), which includes a self-reported and an imputed measure of annual VMT for a nationally representative sample of U.S. households. We compute two additional estimates from the odometer reading, and the trip diary information contained in the NHTS, respectively. We compare these four measures of annual VMT, seek to identify low/high mileage segments of the fleet, and examine the quality of the data and their internal validity. The price elasticity of VMT (−0.275 to −0.20) is comparable across these four measures. Quantile regressions indicate that the households with higher driving intensity are less responsive to the fuel cost per mile. As cars get older, the difference between the four VMT measures tends to increase; this implies large discrepancies in the CO2 emissions that would be saved, for example, when older cars are removed from the fleet, due to natural turnover or when “cash for clunkers” programs are implemented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
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