Problems in Acute Head Injuries

A CAJM article on acute head injuries

Purchasing Power Parity and Emerging South East Asian Nations

This paper provides a test of purchasing power parity (PPP) as an explanation for longterm foreign exchange rate movements. It essentially extends the analysis of Cheung and Lai (1993) to the South East Asian nations, Indonesia, the Philippines, Malaysia, South Korea, and Thailand. Consistent with Cheung and Lai, we impose symmetry and proportionality restrictions flowing from the absolute form of purchasing power parity (PPP) as well as applying the less restrictive Johansen test of PPP to data drawn from the period 1972 through 1997. The tests are also run for sub-periods with similar results. Symmetry and proportionality restrictions find little support in the unit root tests though the Johansen tests suggest that the foreign exchange rate and inflation rates are linked in a long run sense. Error correction models are then estimated on the basis of the assumption that the USA inflation rate is exogenous with respect to the selected emerging South East Asian nations. The error correction models vary considerably across the countries though one consistent result is the negative relation between the foreign exchange rate and the error correction parameter and the generally positive relation between the local CPI and the error correction parameter. The impact of the USA CPI on the countries varies considerably, ranging from no impact in the case of Indonesia through to a statistically significant impact on both the foreign exchange rate and local CPI for South Korea

Deviations and Mean Reversion to Purchasing Power in the Asian Currency Crisis of 1997

We analyse the process of mean reversion towards purchasing power parity (PPP) for a sample of Asian countries around the 1997 crisis. It is found that appreciation relative to PPP is evident prior to the 1997 crash period. Correction occurs from 1997 onwards, a period marked by extreme movements in exchange rates with both appreciation and depreciation relative to the PPP rate over relatively short periods. The key result of this paper is that although reversion towards PPP is apparent for mean, though not statistically significant, it is clear that there is a substantial, statistically significant change in variance from 1997 onwards. This result has implications both for economic modelling of crash periods and for appropriate choice of statistical tests

The Shareholder Wealth Effects of Director Departure Announcements

While executive directors are responsible for superior performance, their behaviour may not always be aligned with shareholder interests. Non-executive directors provide one method of monitoring and controlling these and other agency costs. An event study focusing on director departure provides some insight into the economic importance of directors to shareholders. Initial results highlight both the importance of non-executive directors relative to other directors and the possibility of performance and size impacts. Multivariate tests suggest that non-executive director departures, especially when combined with resignation, explain the cross-sectional variation in share returns associated with director departure even after controlling for performance and size

Forest-Pest Interaction Dynamics: The Simplest Mathematical Models

This paper is devoted to the investigation of the simplest mathematical models of non-even-aged forests affected by insect pests. Two extremely simple situations are considered: (1) the pest feeds only on young trees; (2) the pest feeds only on old trees. The parameter values of the second model are estimated for the case of balsam fir forests and the eastern spruce budworm. It is shown that an invasion of a small number of pests into a steady-state forest ecosystem could result in intensive oscillations of its age structure. Possible implications of environmental changes on forest ecosystems are also considered

The role of forest genetic resources in responding to biotic and abiotic factors in the context of anthropogenic climate change

The current distribution of forest genetic resources on Earth is the result of a combination of natural processes and human actions. Over time, tree populations have become adapted to their habitats including the local ecological disturbances they face. As the planet enters a phase of human-induced climate change of unprecedented speed and magnitude, however, previously locally-adapted populations are rendered less suitable for new conditions, and ‘natural’ biotic and abiotic disturbances are taken outside their historic distribution, frequency and intensity ranges. Tree populations rely on phenotypic plasticity to survive in extant locations, on genetic adaptation to modify their local phenotypic optimum or on migration to new suitable environmental conditions. The rate of required change, however, may outpace the ability to respond, and tree species and populations may become locally extinct after specific, but as yet unknown and unquantified, tipping points are reached. Here, we review the importance of forest genetic resources as a source of evolutionary potential for adaptation to changes in climate and other ecological factors. We particularly consider climate-related responses in the context of linkages to disturbances such as pests, diseases and fire, and associated feedback loops. The importance of management strategies to conserve evolutionary potential is emphasised and recommendations for policy-makers are provided

Using the unique spectral signature of guano to identify unknown seabird colonies

Despite the threats faced by seabirds in both terrestrial and marine habitats, even basic knowledge of the locations of colonies, population sizes and trends is lacking for many remote areas of the world. Recent studies have shown that the guano of Adélie penguins can be identified from Landsat Enhanced Thematic Mapper (ETM) imagery and used to map colonies on coasts around continental Antarctica. Our study highlights a new technique based on the unique spectral signature of guano that can be used to discriminate seabird colonies from background geology and vegetation in a wider range of natural environments, including the vegetated and zoologically-diverse region of the Antarctic Peninsula; moreover, the method was effective for all densely colonial, surface-nesting seabirds. Using Landsat ETM imagery, we correctly identified all known seabird colonies of over 50 pairs in the area of Marguerite Bay. Almost all other areas with a similar spectral signature that were outside known breeding areas were single pixels that were readily distinguishable from genuine colonies. If these were excluded, only 4.1% of pixels appeared to represent unknown breeding or roosting sites, and warrant further investigation. The spatial extent of the guano provided a general guide to the number of individuals present, but further work would be required to determine the accuracy of this method for estimating population size. Spectral profiles of guano collected by satellite and hand-held spectrometers were compared with available data in spectral libraries and did not match with any known geological profile. There may also be potential for discriminating colonies of different species that differ in phenology and show seasonal changes in diet by the carefully-timed acquisition of suitable satellite imagery. We conclude that the remotely-sensed guano signature is a good indicator of the location of seabird breeding or roosting sites, with potentially wide application to other areas of the world

The Response of the Balsam Fir Forest to a Spruce Budworm Invasion: A Simple Dynamical Model

The parameter values of a simple dynamical model of a non-even age forest-insect ecosystem are estimated for the case of balsam fir forests and the eastern spruce budworm. It is shown that, despite its extreme simplicity, the model can reproduce time series of a real budworm outbreak and can be considered a compact presentation of available forest data. Strengths and weaknesses of the model are discussed and some directions for further research proposed

Forest-Pest Interaction Dynamics: The Simplest Mathematical Models

This report is devoted to the investigation of the simplest mathematical models of non-even-aged forests affected by insect pests. Two extremely simple situations are considered: (1) the pest feeds only on young trees; (2) the pest feeds only on old trees. The parameter values of the second model are estimated for the case of balsam fir forests and the eastern spruce budworm. It is shown that an invasion of a small number of pests into a steady-state forest ecosystem could result in intensive oscillations of its age structure. Possible implications of environmental changes in forest ecosystems are also considered

CaMEL and ADCIRC storm surge models-A comparative study

The Computation and Modeling Engineering Laboratory (CaMEL), an implicit solver-based storm surge model, has been extended for use on high performance computing platforms. An MPI (Message Passing Interface) based parallel version of CaMEL has been developed from the previously existing serial version. CaMEL uses hybrid finite element and finite volume techniques to solve shallow water conservation equations in either a Cartesian or a spherical coordinate system and includes hurricane-induced wind stress and pressure, bottom friction, the Coriolis effect, and tidal forcing. Both semi-implicit and fully-implicit time stepping formulations are available. Once the parallel implementation is properly validated, CaMEL is evaluated against ADCIRC, an established storm surge model, using a hindcast of storm surge due to Hurricane Katrina. Observed high water marks are used to verify that both models have comparable accuracy. The effects of time step on the stability and accuracy of the models are investigated and indicate that the semi- and fully-implicit solvers in CaMEL allow the use of larger timesteps than ADCIRC's explicit and semi-implicit solvers. However, ADCIRC outperforms CaMEL in parallel scalability and execution wall clock times. Wall times of CaMEL improve significantly when the largest stable time step sizes are used in respective models, although ADCIRC still is faster