1,424 research outputs found

    Causes of the 2000s food price surge: Insights from structural VAR

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    In 2001 began a rise in the prices of food commodities not seen since the 1970s. The prices of grains - the major staple foods - increased fivefold between 2003 and 2008, leading to the additional malnutrition of millions around the world. Many observers attribute the strong increase in part to speculation in derivatives markets. We examine this hypothesis by comparing the impact of speculation to that of fundamental supply and demand forces. We estimate the share of the price increase attributable to the respective market forces using a sign identified structural vector autoregressive model. Speculation is identifid using storage data, though a residual price shock is allowed to ensure the robustness of the findings

    Causes of the 2000s Food Price Surge: New Evidence fromStructural VAR

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    In 2001 began a rise in the prices of food commodities not seen since the 1970s. Some observers attribute the increase in part to food commodity spec- ulation. This hypothesis is examined by disentangling the impact of specu- lation on grain prices from that of fundamental supply and demand forces. Even though results point to a generally stabilising in uence of speculation on prices, speculation is shown to have pushed prices further up during crisis years. The analysis is based on a structural vector autoregressive model identified by sign and zero restrictions. The model is estimated for global corn, wheat and rice markets

    Skewness-Adjusted Bootstrap Confidence Intervals and Confidence Bands for Impulse Response Functions

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    This article investigates the construction of skewness-adjusted con�dence intervals and joint confidence bands for impulse response functions from vector autoregressive models. Three different implementations of the skewness adjustment are investigated. The methods are based on a bootstrap algorithm that adjusts mean and skewness of the bootstrap distribution of the autoregressive coeffcients before the impulse response functions are computed. Using extensive Monte Carlo simulations, the methods are shown to improve the coverage accuracy in small and medium sized samples and for unit root processes for both known and unknown lag orders

    Drag reduction in pipe flows with polymer additives

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    Polyethylene Oxides (PEO) with molecular weights of 4 and 6 million and a Polyacrylamide (PAM) with a molecular weight of 15 million, were added to a turbulent pipe flow (15000 \u3c Re \u3c 50000) for drag reduction. The polymer was injected directly into the test section in one scenario, premixed in a tank and then pumped through the test section in the second. The injection addition method was found to be optimal because it subjected the polymer to lower amounts of shear stresses than the premixed addition method. A maximum of 75% reduction in drag was obtained. Even trace concentrations, as low as 2.5 WPPM (weight parts per million) , resulted in as high as 37% reduction in drag. Long thin high molecular weight polymers (PEO) were more effective than coiled high molecular weight polymer (PAM) . For the same molecular structure it was found that the polymer with heavier molecules had better drag reducing characteristics. The polymer with coiled molecules, however, is more resistant to shear stresses which break down the polymer into smaller less effective molecules. It was found that there is a critical concentration for the greatest drag reduction. This concentration is approximately 375 WPPM (.0375% byweight) of PEO for the injection method, and 500 WPPM of PEO for the premixed method. At greater concentrations, the viscosity of the solution increases such that the drag reduction characteristics of the polymer can no longer compensate

    Skewness-Adjusted Bootstrap Confidence Intervals and Confidence Bands for Impulse Response Functions

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    This Article Investigates The Construction Of Skewness-Adjusted Confidence Intervals And Joint Confidence Bands For Impulse Response Functions From Vector Autoregressive Models. Three Different Implementations Of The Skewness Adjustment Are Investigated. The Methods Are Based On A Bootstrap Algorithm That Adjusts Mean And Skewness Of The Bootstrap Distribution Of The Autoregressive Coefficients Before The Impulse Response Functions Are Computed. Using Extensive Monte Carlo Simulations, The Methods Are Shown To Improve The Coverage Accuracy In Small And Medium Sized Samples And For Unit Root Processes For Both Known And Unknown Lag Orders

    Empirical comparison of diffusion kurtosis imaging and diffusion basis spectrum imaging using the same acquisition in healthy young adults

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    As diffusion tensor imaging gains widespread use, many researchers have been motivated to go beyond the tensor model and fit more complex diffusion models, to gain a more complete description of white matter microstructure and associated pathology. Two such models are diffusion kurtosis imaging (DKI) and diffusion basis spectrum imaging (DBSI). It is not clear which DKI parameters are most closely related to DBSI parameters, so in the interest of enabling comparisons between DKI and DBSI studies, we conducted an empirical survey of the interrelation of these models in 12 healthy volunteers using the same diffusion acquisition. We found that mean kurtosis is positively associated with the DBSI fiber ratio and negatively associated with the hindered ratio. This was primarily driven by the radial component of kurtosis. The axial component of kurtosis was strongly and specifically correlated with the restricted ratio. The joint spatial distributions of DBSI and DKI parameters are tissue-dependent and stable across healthy individuals. Our contribution is a better understanding of the biological interpretability of the parameters generated by the two models in healthy individuals

    Time Constrained Verification of Analog Circuits using Model-Checking Algorithms

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    In this contribution we present algorithms for model checking of analog circuits enabling the specification of time constraints. Furthermore, a methodology for defining time-based specifications is introduced. An already known method for model checking of integrated analog circuits has been extended to take into account time constraints. The method will be presented using three industrial circuits. The results of model checking will be compared to verification by simulation

    Pragmatic Rigor: Principles and Criteria for Conducting and Evaluating Practitioner Scholarship

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    Practitioner scholarship is a promising avenue for addressing the gap between academic research and practice. To advance the objective of publishing the findings of practitioner scholarship, we develop the concept of pragmatic rigor, which is intended to complement but not replace scientific rigor. We propose four principles of pragmatic rigor: relevance, actionability, comprehensibility, and ethical reasoning. For each principle, we develop associated criteria for conducting and evaluating practical research. Pragmatic principles are relevant to the research process, from choice of topic to final evaluation by journal reviewers. We believe that applying these principles can advance the practical value of studies and help to bridge the gap between scholars and practitioners

    Joaquim: o periódico que ousou trazer o mundo para a província

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    Neste artigo analisamos a produção textual do periódico Joaquim, publicado na década de 1940 em Curitiba. Estudamos as discussões quanto ao movimento modernista que perpassou os meios artísticos paranaenses, especialmente o grupo de intelectuais e artistas que faziam parte do periódico citado. Com isso observamos a constituição de discursos críticos aos paradigmas de arte paranense vigentes até o momento, especialmente o paranismo, em prol de uma arte que não se limite apenas a dialogar e exaltar elementos locais. Damos especial atenção à crítica a Emiliano Perneta formulada por Dalton Trevisan. A forma com que o primeiro se apropria de elementos simbolistas é criticada pelo segundo na medida em que dessa apropriação resulta uma poesia demasiadamente comportada. Tentamos assim contrapor elementos da própria poesia simbolista (Rimbaud é nosso exemplo) à forma com que Perneta formulou sua poesia. Nossa hipótese é que, em Rimbaud, há uma forte crítica à noção de identidade, a qual é mitigada na poesia criticada por Trevisan
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