Electrohydrodynamic (EHD) stimulation of jet breakup

Electrohydrodynamic (EHD) excitation of liquid jets offers an alternative to piezoelectric excitation without the complex frequency response caused by piezoelectric and mechanical resonances. In an EHD exciter, an electrode near the nozzle applies an alternating Coulomb force to the jet surface, generating a disturbance which grows until a drop breaks off downstream. This interaction is modelled quite well by a linear, long wave model of the jet together with a cylindrical electric field. The breakup length, measured on a 33 micrometer jet, agrees quite well with that predicted by the theory, and increases with the square of the applied voltage, as expected. In addition, the frequency response is very smooth, with pronounced nulls occurring only at frequencies related to the time which the jet spends inside the exciter

J.R.R. Tolkien: the Forest and the City (2013), edited by Helen Conrad-O’Briain and Gerard Hynes.

J.R.R. Tolkien: the Forest and the City (2013), edited by Helen Conrad-O’Briain and Gerard Hynes. Book Review by Kelley M. Wickham-Crowle

How do you make a time series sing like a choir? Using the Hilbert-Huang transform to extract embedded frequencies from economic or financial time series

The Hilbert-Huang transform (HHT) was developed late last century but has still to be introduced to the vast majority of economists. The HHT transform is a way of extracting the frequency mode features of cycles embedded in any time series using an adaptive data method that can be applied without making any assumptions about stationarity or linear data-generating properties. This paper introduces economists to the two constituent parts of the HHT transform, namely empirical mode decomposition (EMD) and Hilbert spectral analysis. Illustrative applications using HHT are also made to two financial and three economic time series.business cycles; growth cycles; Hilbert-Huang transform (HHT); empirical mode decomposition (EMD); economic time series; non-stationarity; spectral analysis

A single currency for Asia? Evaluation and comparison using hierarchical and model-based cluster analysis

Today, there is increased speculation on the possibility of an Asian currency, as the region begins to show increased promise as a region of nascent economic activity. Any monetary integration scheme in East Asia would likely have to include both China and India though, so this paper attempts to assess the evolution of convergence among the East Asian countries, including China and India, according to the optimum currency area theory criteria, which is operationalized through the use of cluster analysis. In this paper we use both traditional "hierarchical" clustering as well as the more recently developed "model-based" clustering techniques and compare the outcome in each case. As the East Asian crisis of 1997-98 is likely to a¤ect the results, the exercise is done for pre-crisis, crisis, and post-crisis periods. The results reveal some structure among the countries, an increase in the degree of subregional homogeneity, and a robust relationship between Malaysia and Singapore

Evaluating the stresses from ECB monetary policy in the euro area

This paper investigates the extent to which euro area monetary policy has responded to evolving economic conditions in individual member states as opposed to the euro area as a whole. Based on a forward-looking Taylor rule-type policy reaction function, we conduct counterfactual exercises that compare the monetary policy behaviour of the ECB under alternative hypothetical scenarios: (1) the euro member states make individual policy decisions, and (2) the ECB responds to the economic conditions of individual members. Stress measures are then constructed to evaluate the degree of divergence of member state economies under these two hypothetical scenarios. The results we obtain reflect the extent of heterogeneity among the national economies in the monetary union, indicating that euro area policy rates have been particularly close to the ‘counterfactual’ interest rates of the largest euro members and countries with similar economic conditions, namely Germany, Austria, Belgium and France.European Central Bank; monetary policy reaction; Taylor rule; counterfactual analysis

The great moderation under the microscope: decomposition of macroeconomic cycles in US and UK aggregate demand

In this paper the relationship between the growth of real GDP components is explored in the frequency domain using both static and dynamic wavelet analysis. This analysis is carried out separately for the US and UK using quarterly data, and the results are found to be substantially different for the two countries. One of the key findings of this research is that the ‘great moderation’ shows up only at certain frequencies, and not in all components of real GDP. We use these results to explain why the incidence of the great moderation has been so patchy across GDP components, countries and time periods. This also explains why it has been so hard to detect periods of moderation (or other periods) reliably in the aggregate data. We argue this cannot be done without separating the GDP components into their frequency components over time. Our results show why: the predictions of traditional real business cycle theory often appear not to be upheld in the data.business cycles; growth cycles; discrete wavelet analysis; US real GDP; UK real GDP

Parameter identification in continuum models

Approximation techniques for use in numerical schemes for estimating spatially varying coefficients in continuum models such as those for Euler-Bernoulli beams are discussed. The techniques are based on quintic spline state approximations and cubic spline parameter approximations. Both theoretical and numerical results are presented

Public health and landfill sites

Landfill management is a complex discipline, requiring very high levels of organisation, and considerable investment. Until the early 1990’s most Irish landfill sites were not managed to modern standards. Illegal landfill sites are, of course, usually not managed at all. Landfills are very active. The traditional idea of ‘put it in the ground and forget about it’ is entirely misleading. There is a lot of chemical and biological activity underground. This produces complex changes in the chemistry of the landfill, and of the emissions from the site. The main emissions of concern are landfill gases and contaminated water (which is known as leachate). Both of these emissions have complex and changing chemical compositions, and both depend critically on what has been put into the landfill. The gases spread mainly through the atmosphere, but also through the soil, while the leachate (the water) spreads through surface waters and the local groundwater. Essentially all unmanaged landfills will discharge large volumes of leachate into the local groundwater. In sites where the waste accepted has been properly regulated, and where no hazardous wastes are present, there is a lot known about the likely composition of this leachate and there is some knowledge of its likely biological and health effects. This is not the case for poorly regulated sites, where the composition of the waste accepted is unknown. It is possible to monitor the emissions from landfills, and to reduce some of the adverse health and environmental effects of these. These emissions, and hence the possible health effects, depend greatly on the content of the landfill, and on the details of the local geology and landscape. There is insufficient evidence to demonstrate a clear link between cancers and exposure to landfill, however, it is noted that there may be an association with adverse birth outcomes such as low birth weight and birth defects. It should be noted, however, that modern landfills, run in strict accordance with standard operation procedures, would have much less impact on the health of residents living in proximity to the site