Iain MacLaren

Corrections to virial estimates of molecular cloud masses

The application of the virial theorem to the determination of giant molecular cloud masses is reconsidered. It is argued that it is necessary to transform the results to equivalent velocity widths for the optically thin line of (C-13)O rather than that of (C-12)O. The results lead to a substantial lowering of H2 mass and values of X closer to that of the gamma-ray analysis of Bhat et al. (1986). The total mass of H2 in the Inner Galaxy is significantly less than that of atomic hydrogen. 27 references.

The Contradictions of Policy and Practice: Creativity in Higher Education.

Whilst much of the rhetoric of current educational policy champions creativity and innovation, structural reforms and new management practices in higher education run counter to the known conditions under which creativity flourishes. As a review of recent literature suggests, surveillance, performativity, the end of tenure and rising levels of workplace stress are all closing off the space for real creative endeavour, characterised as it is by risk-taking, collaborative exploration and autonomy. Innovation, as conceived in this policy context, is narrow in scope and leaves little room for critical re-examination of the nature of education itself or radical reconceptions of curriculum, raising the question as to whether such are more likely to arise extra mural, from new forms of organisation.

The size-line width relation and the mass of molecular hydrogen

Some difficulties associated with the problem of cloud definition are considered, with particular regard to the crowded distribution of clouds and the difficulty of choosing an appropriate boundary in such circumstances. A number of tests carried out on the original data suggest that the delta(v) - S relation found by Solomon et al. (1987) is not a genuine reflection of the dynamical state of Giant Molecular Clouds. The Solomon et al. parameters, are insensitive to the actual cloud properties and are unable to distinguish true clouds from the consequences of sampling any crowded region of emission down to a low threshold temperature. The overall effect of such problems is to overestimate both the masses of Giant Molecular Clouds and the number of very large clouds. 24 refs.

Neural network based methods for cloud classification on AVHRR images

Artificial neural networks trained on spectral and textural features extracted from Advanced Very High Resolution Radiometer (AVHRR) images have been used to develop an automated cloud classification system. Selection of the optimum combination of features was achieved by using statistical methods presented in earlier work by Gu et al. and by running large numbers of neural network simulations on test datasets. The performance of these methods surpasses that of other approaches such as the use of Gabor filters for texture segmentation and the maximum likelihood classifier. A particular architecture for an operational classification system is presented based on a two-stage multiple network configuration which is shown to segment complex images to a high degree of accuracy and achieves an overall accuracy on an independent, representative test set of 91%.

Neural networks and cloud classification

The development of an efficient and accurate automated cloud classification method for use on satellite Images will be of great benefit to operational meteorology and climate studies. We have examined the possible use of neural networks as a classification tool for spectral and textural data extracted from Meteosat images. A large number of back-propagation neural network configurations were run and many were found to be highly effective, outperforming more traditional statistical classifiers. A Kohonen type competitive learning network was also tried, but was found to be considerably less successful on this data set. Some suggestions are made for future development based on the experience gained in this project.

Cosmic rays and the masses of giant molecular clouds

The use of cosmic gamma rays in elucidating the spatial density of cosmic rays in the Galaxy depends crucially on knowledge of the distribution of the target gas. There has been argument as to the latter quantity and a new analysis is timely. In the present work we make a critical analysis of the various methods of determining the masses of local giant molecular clouds with particular emphasis being placed on the use of far-infrared data in examining the Taurus and Orion GMCS. Consistent results are found for the conversion factor, X, in coverting the 12CO signal ( integral T(12CO)d nu ) to the column density of molecular gas (in 1020 H molecules cm-2): X approximately=1.5. A notable result is that the far-infrared method applied to the nearest and coldest GMC (Taurus) reveals no evidence for the presence of significant quantities of very cold dust (and associated gas). There is thus support for the validity of the authors use of this method in the Inner Galaxy and their previous work in this field (Broadbent et al. 1989); in that work they found a slightly lower value of X ( approximately=1.0) in the Inner Galaxy. The reasons for other workers having found higher values of X in the Inner Galaxy are examined and it is concluded that problems of cloud definition and confusion in this crowded region are responsible. Returning to the question of the cosmic-ray distribution, the confirmation of their previous gas estimates indicates that their claim (e.g. in Bhat et al. 1986) that there is a significant dependence of cosmic-ray intensity on Galactocentric distance is well founded. The significance of the result is that the majority of the observed cosmic rays at Earth are of Galactic origin.

The 'cosmic ray gradient' and far infrared observations as a tracer of molecular material in the Galaxy

The derivation of the spatial distribution of cosmic rays from an analysis of cosmic gamma rays requires a knowledge of the distribution of gas in the inner Galaxy most notably that of molecular hydrogen. There has been considerable argument about the amount of this gas, an argument manifested by disagreement over the magnitude of the conversion factor, X, used in converting the strength of the 12CO line to the column density of molecular hydrogen. A promising technique has been to study the far infrared radiation from dust associated with gas but here, too, there have been differences. The authors analyse the situation in detail and conclude that virtually all the differences can be understood and that the best estimate in the inner Galaxy is XMS approximately 1, in units of 1020 H2 molecules cm-2, the CO data used being those from the Massachusetts-Stony Brook survey of Sanders et al. (1986).