Basic rules for polarised cell growth.

Growth by cell elongation is a morphological process that transcends taxonomic kingdoms. Examples of this polarised growth form include hyphal tip growth in actinobacteria and filamentous fungi and pollen tube development. The biological processes required to produce polarisation in each of these examples are very different. However, commonality of the polarised growth habit suggests that certain "basic physical rules" of development are being followed. In this paper we are concerned with trying to further elucidate some of these basic rules. To this end, we focus on a simple and hence ubiquitous description of the polarised cell, its geometry, and using a mathematical model investigate how geometry and the deposition of new wall material could be related. We show that this simple model predicts both cell geometry and the location of maximal wall-deposition in a range of examples.

Effects of periodic input on the quasi-steady state assumptions for enzyme-catalysed reactions.

In this paper we investigate the validity of a quasi-steady state assumption in approximating Michaelis-Menten type kinetics for enzyme-catalysed biochemical reactions that are subject to periodic substrate input.

Quasi-steady state assumptions for non-isolated enzyme-catalysed reactions.

The nature and validity of the mathematical formulation of Michaelis-Menten type kinetics for enzyme-catalysed biochemical reactions is studied. Almost all previous work has concentrated on isolated reactions, i.e. those without input or other environmental influences. In this paper, we investigate the effects of substrate input on this formulation, in particular, on the nature and validity of the quasi-steady state assumptions.

Translocation induced outgrowth of fungi in nutrient-free environments.

The study of alternatives to chemical methods of nematode control in agriculture has received significant recent interest. One such method is biological control using nematode trapping fungi such as Arthrobotrys superba. To understand how these fungi can be implemented as effective nematicides, it is essential to study their outgrowth into soil from localized nutrient resources. In this paper, we use a mathematical model to investigate the outgrowth of fungi into an environment essentially without available nutrients capable of supporting net growth. By comparing model solutions with experimental results, we show that in such circumstances, continual mycelial expansion can only be obtained if internal metabolites are actively translocated through the mycelium. Predictions are made concerning the maximal extension possible from a given quantity of nutrients and a testable functional relationship between the two is derived. Using this modelling technique we are able to map not only biomass extent but also biomass distribution at each stage. The type of environmental heterogeneity investigated here is encountered by many species of fungi in nature and is of relevance for the introduction of specific fungi into soil for biological control or bioremediation purposes.

Hospitalization of patients with diabetes.

To determine annual hospitalization rates for patients with diabetes mellitus, we retrospectively analyzed the frequency of hospitalization among 905 patients with diabetes receiving primary care in a private practice outpatient program during a 20-month period (1,508 patient-years). We assessed the annual hospitalization rates stratified by diabetes clinical severity index, type of diabetes, type of treatment, age, sex, and mean glycosylated hemoglobin. The all-cause annual hospitalization rate was 211 per 1,000 patients (95% confidence interval, 184 to 238). Hospitalization rates were strongly correlated with measures of clinical severity; hospitalization rates did not vary significantly with type of diabetes, age, or sex. Among patients with type II diabetes, rates were higher in the group treated with insulin. A trend was noted for hospitalization rates to increase with mean glycosylated hemoglobin (not statistically significant in this sample). Overall, 14% of hospitalizations were for metabolic reasons, 45% were related to clinical complications of diabetes, and 41% were unrelated to the presence of diabetes. In analysis of hospitalization rates and therefore health-care expenditures for patients with diabetes, the characteristics of the patient population--and especially measures of clinical severity--must be considered. Interventions to reduce hospitalization can be targeted at high-risk groups.