Models of Labour Services and Estimates of Total Factor Productivity

This paper examines the manner in which labour services are modelled in the aggregate production function, concentrating on the relationship between numbers employed and average hours worked. It argues that numbers employed and hours worked are not perfect substitutes and that conventional estimates of total factor productivity which, by using total hours worked as the measure of labour services, assume they are perfect substitutes, will be biased when there are marked changes in average hours worked. The relevance of the theoretical argument is illustrated using data for the United States and the United Kingdom.Labour Services, Production Function, Total Factor Productivity

The not-so-great moderation? Evidence on changing volatility from Australian regions

In this paper we examine Australian data on national and regional employment numbers, focusing in particular on whether there have been common national and regional changes in the volatility of employment. A subsidiary objective is to assess whether the results derived from traditional growth rate models are sustained when alternative filtering methods are used. In particular, we compare the results of the growth rate models with those obtained from Hodrick-Prescott models. Using frequency filtering methods in conjunction with autoregressive modeling, we show that there is considerable diversity in the regional pattern of change and that it would be wrong to suppose that results derived from the aggregate employment series are generally applicable across the regions. The results suggest that the so-called great moderation may have been less extensive than aggregate macro studies suggest.Regional employment, State business cycle, Structural change, Volatility

Poisson point process models solve the "pseudo-absence problem" for presence-only data in ecology

Presence-only data, point locations where a species has been recorded as being present, are often used in modeling the distribution of a species as a function of a set of explanatory variables---whether to map species occurrence, to understand its association with the environment, or to predict its response to environmental change. Currently, ecologists most commonly analyze presence-only data by adding randomly chosen "pseudo-absences" to the data such that it can be analyzed using logistic regression, an approach which has weaknesses in model specification, in interpretation, and in implementation. To address these issues, we propose Poisson point process modeling of the intensity of presences. We also derive a link between the proposed approach and logistic regression---specifically, we show that as the number of pseudo-absences increases (in a regular or uniform random arrangement), logistic regression slope parameters and their standard errors converge to those of the corresponding Poisson point process model. We discuss the practical implications of these results. In particular, point process modeling offers a framework for choice of the number and location of pseudo-absences, both of which are currently chosen by ad hoc and sometimes ineffective methods in ecology, a point which we illustrate by example.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS331 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Understanding soil nitrogen supply: organic matter quality and quantity

The soil organic matter (SOM) contents of organic and conventionally farmed soils were compared. Whilst the quantity of SOM was found to be similar with both systems, the quality of SOM differed in respect of higher amounts of N released by the organic soils under anaerobic incubation. This indicated a greater potential rate of mineralization and suggested that the inherent fertility of the organic soils had been improve

Structural trends in clusters of quadrupolar spheres

The influence of quadrupolar interactions on the structure of small clusters is investigated by adding a point quadrupole of variable strength to the Lennard-Jones potential. Competition arises between sheet-like arrangements of the particles, favoured by the quadrupoles, and compact structures, favoured by the isotropic Lennard-Jones attraction. Putative global potential energy minima are obtained for clusters of up to 25 particles using the basin-hopping algorithm. A number of structural motifs and growth sequences emerge, including star-like structures, tubes, shells and sheets. The results are discussed in the context of colloidal self-assembly.Comment: 8 pages, 6 figure

Towards a lightweight generic computational grid framework for biological research

Background: An increasing number of scientific research projects require access to large-scale computational resources. This is particularly true in the biological field, whether to facilitate the analysis of large high-throughput data sets, or to perform large numbers of complex simulations – a characteristic of the emerging field of systems biology. Results: In this paper we present a lightweight generic framework for combining disparate computational resources at multiple sites (ranging from local computers and clusters to established national Grid services). A detailed guide describing how to set up the framework is available from the following URL: http://igrid-ext.cryst.bbk.ac.uk/portal_guide/. Conclusion: This approach is particularly (but not exclusively) appropriate for large-scale biology projects with multiple collaborators working at different national or international sites. The framework is relatively easy to set up, hides the complexity of Grid middleware from the user, and provides access to resources through a single, uniform interface. It has been developed as part of the European ImmunoGrid project

The Cyclical Dynamics and Volatility of Australian Output and Employment

In this paper we examine the volatility of aggregate output and employment in Australia with the aid of a frequency filtering method (the Butterworth filter) that allows each time series to be decomposed into trend, cycle and noise components. This analysis is compared with more traditional methods based simply on the examination of first differences in the logs of the raw data using cointegration-VAR modelling. We show that the application of univariate AR and bivariate VECM methods to the data results in a detrended series which is dominated by noise rather than cyclical variation and gives break points which are not robust to alternative decomposition methods. Also, our conclusions challenge accepted wisdom in relation to output volatility in Australia which holds that there was a once and for all sustained reduction in output volatility in or around 1984. We do not find any convincing evidence for a sustained reduction in the cyclical volatility of the GDP (or employment) series at that time, but we do find evidence of a sustained reduction in the cyclical volatility of the GDP (and employment) series in 1993/4. We also find that there is a clear association between output volatility and employment volatility. We discuss the key features of the business cycle we have identified as well as some of the policy implications of our results.Business cycles, volatility, inflation targeting, Australia

Explicitly correlated plane waves: Accelerating convergence in periodic wavefunction expansions

We present an investigation into the use of an explicitly correlated plane wave basis for periodic wavefunction expansions at the level of second-order M{\o}ller-Plesset perturbation theory (MP2). The convergence of the electronic correlation energy with respect to the one-electron basis set is investigated and compared to conventional MP2 theory in a finite homogeneous electron gas model. In addition to the widely used Slater-type geminal correlation factor, we also derive and investigate a novel correlation factor that we term Yukawa-Coulomb. The Yukawa-Coulomb correlation factor is motivated by analytic results for two electrons in a box and allows for a further improved convergence of the correlation energies with respect to the employed basis set. We find the combination of the infinitely delocalized plane waves and local short-ranged geminals provides a complementary, and rapidly convergent basis for the description of periodic wavefunctions. We hope that this approach will expand the scope of discrete wavefunction expansions in periodic systems.Comment: 15 pages, 13 figure