Biomedical subjects

John E Franke

Publications and source records attributed to John E Franke.

3 recordsLinked to original sources

PubMed2006

Globally attracting attenuant versus resonant cycles in periodic compensatory Leslie models.

We use a periodically forced density-dependent compensatory Leslie model to study the combined effects of environmental fluctuations and age-structure on pioneer populations. In constant environments, the models have globally attracting positive fixed points. However, with the advent of periodic forcing, the models have globally attracting cycles. We derive conditions under which the cycle is attenuant, resonant, and neither attenuant nor resonant. These results show that the response of age-structured populations to environmental fluctuations is a complex function of the compensatory mechanisms at different life-history stages, the fertile age classes and the period of the environment.

Animals↗

PubMed2006

Signature function for predicting resonant and attenuant population 2-cycles.

Populations are either enhanced via resonant cycles or suppressed via attenuant cycles by periodic environments. We develop a signature function for predicting the response of discretely reproducing populations to 2-periodic fluctuations of both a characteristic of the environment (carrying capacity), and a characteristic of the population (inherent growth rate). Our signature function is the sign of a weighted sum of the relative strengths of the oscillations of the carrying capacity and the demographic characteristic. Periodic environments are deleterious for populations when the signature function is negative. However, positive signature functions signal favorable environments. We compute the signature functions of six classical discrete-time single species population models, and use the functions to determine regions in parameter space that are either favorable or detrimental to the populations. The two-parameter classical models include the Ricker, Beverton-Holt, Logistic, and Maynard Smith models.

Animals↗

PubMed2006

Personal dust exposures at a food processing facility.

A field study was performed to quantify personal dust exposures at a food processing facility. A review of the literature shows very little exposure information in the food processing industry. The processing area consisted of a series of four rooms, connected by a closed-loop ventilation system, housed within a larger warehouse-type facility. Workers were exposed to various fruit and vegetable dusts during the grinding, sieving, mixing and packaging of freeze-dried or air-dried products. Eight two-hour periods were monitored over two days. Personal total suspended particulate samples were collected on 37 mm PVC filters with 5 microm pore size according to National Institute for Occupational Safety and Health (NIOSH) Method 0500. The filters were analyzed gravimetrically. The two-hour task sampling personal dust exposures ranged from 0.33-103 mg/m3. For each worker, an eight-hour time weighted average (TWA) concentration was calculated, and these ranged from 3.08-59.8 mg/m3. Although there are no directly appropriate occupational exposure limits that may be used for comparison, we selected the Threshold Limit Value (TLV) for particulates not otherwise classified (PNOC) of 10 mg/m3 for inhalable particles. Neglecting the respiratory protection used, five out of eight of the worker time-weighted averages exceeded the TLV. It should be noted that the TLV is based on the inhalable fraction and in this study total suspended particulate was measured; additionally, the TLV is applicable for dusts that are insoluble or poorly soluble, and have low toxicity, which may have limited protective ability in this case due to the irritant nature of certain dusts (e.g., jalapeno peppers, aloe vera). Sieving resulted in significantly higher exposure than grinding and blending. Measuring area concentrations alone in this environment is not a sufficient method of estimating personal exposures due to work practices for some operations.

Dust↗