Low-dimensional modelling of dynamics via computer algebra

I describe a method, particularly suitable to implementation by computer algebra, for the derivation of low-dimensional models of dynamical systems. The method is systematic and is based upon centre manifold theory. Computer code for the algorithm is relatively simple, robust and flexible. The method is applied to two examples: one a straightforward pitchwork bifurcation, and one being the dynamics of thin fluid films.     

National and regional corporate spatial structure

Much is known about the macro-impacts of business activities on national and regional economies; however, comparatively little is known at the micro level about the impact spatial agglomeration of corporate wealth and performance has on urban systems. This paper reports on a collaborative research project between the Australian Housing and Urban Research Institute and Dun and Bradstreet, an international financial credit agency, to analyse the spatial implications of corporate structure in metropolitan regions. This paper analyses spatial patterns of medium to large businesses in three Australian State capital cities at the postcode level in order to assess the agglomeration of corporate capital, sales, and performance. The research indicates that ratio analysis can provide a useful insight into the competitiveness of metropolitan regions and the control corporate headquarters have over decision making and investment processes. The findings of this research are of special interest to capital markets, business and urban researchers in the Asia Pacific Region. Received: September 1997/Accepted: September 2001     

What influences patients' reports of three aspects of hospital services?

OBJECTIVES: Market forces make it essential to know what policies and actions influence patients' reports of hospital services. No studies have examined the role of patient characteristics, labor quality and staff characteristics, nonlabor resources, managerial practices, and employee attitudes within a single investigation. METHODS: The authors collected, simultaneously, data about labor, management and service processes, nonlabor resources, and employee attitudes on 117 nonintensive medical-surgical inpatient units in 17 hospitals selected from a pool of 69 institutions within a metropolitan area by a stratified random sample. Of the 2,595 patients who agreed to participate, 2,051 (79%) completed telephone interviews regarding their experiences with physical care, education, and pain management services within 26 days of hospital discharge. RESULTS: A significant amount of variation in patients' service reports was explained (adjusted R2 = 0.41 physical care, 0.35 pain management, 0.44 education). Although the predictors varied for each service report, patient characteristics, especially those related to personal resources, had a large explanatory role. A labor assignment pattern that could explain why earlier studies found labor quality and staff characteristics to have only a weak role in the prediction of patients' service reports was noted. CONCLUSIONS: The results related to patient characteristics may indicate opportunities to improve care by confronting service design strategies that erroneously rely on a homogeneous patient population. Measurement challenges identified by this study must be addressed to determine the role of labor quantity and staff characteristics.     

Stereological estimation of the total volume of MR visible brain lesions in patients with multiple sclerosis

Point counting represents a convenient and efficient technique for estimating the area of transects through multiple sclerosis (MS) lesions on magnetic resonance (MR) images obtained for sections through the brain. When sectioning has been performed according to the Cavalieri method, unbiased estimates of the total volume of MR-visible MS plaques can be obtained with a precision of 3–5% in 5–10 min.     

Production of the 19-kDa antigen of Mycobacterium tuberculosis in Escherichia coli and its purification

The 19-kDa antigen (19Ag) of Mycobacterium tuberculosis (Mt) is a lipoprotein which is released from the organism during growth. In order to study the possible involvement of this antigen in the host protective response against Mt infection, it would be helpful to obtain high-level production of 19Ag from a recombinant organism. We have found that overexpression of the native 19Ag gene in Escherichia coli or yeast leads to products which are aggregated and insoluble. By site-directed mutagenesis of the 19Ag lipoprotein leader sequence, we have generated a mutant gene which directs the production of 19Ag into the periplasmic space of E. coli, from where it can be easily purified in high yield. 19Ag obtained from this mutant construct lacks the lipid-modified N-terminal Cys residue found in the native 19Ag, and is not glycosylated, but is otherwise indistinguishable from 19Ag isolated from Mt culture supernatant.     

Hydrolysis of 4-methylumbelliferyl butyrate: A convenient and sensitive fluorescent assay for lipase activity

A rapid, sensitive and convenient fluorescent assay was developed to screen for lipase activity. The non-fluorescent substrate, 4-methylumbelliferyl butyrate (4-MUB), solubilized in either liposomal dispersions or bile salt/lecithin mixed micelles, is hydrolyzed to butyric acid and the highly fluorescent compound, 4-methylumbelliferone (4-MU). Assays are run at 37 C for 10 min, terminated, and the changes in fluorescence quantitated with a Turner III fluorometer. Both lingual and pancreatic lipases exhibit activity against this artificial substrate. The assay has several advantages: nmoles 4 MU/ml/hr are measured allowing the detection of very low lipolytic activity; multiple samples may be simultaneously assayed, and only a brief incubation period is required.