Don W. DeMichele

Reaction kinetics of poikilotherm development.

A stochastic thermodynamic model of poikilotherm development has been derived from the Eyring equation assuming multiple activity states of the underlying developmental control enzymes. This analysis brings together into a general model the day-degrees concept and the Arrhenius hypothesis as interpreted by Eyring. The compensating effect of enzyme inactivation at high and low temperatures incorporated into the model has the following consequences. 1. (i) It demonstrates the validity of the linear approximation (day-degree concept) in the mid-temperature region for some organisms. 2. (ii) It effectively establishes a low-temperature threshold for development. 3. (iii) It reduces the rate of development at higher temperatures, thereby establishing both an optimum and upper threshold for development. The resulting equation has been found applicable to a wide range of organisms.

Distribution model of organism development times.

Abstract It is shown in this analysis that the distribution of organism development times for constant and variable temperatures can be described based upon one simple assumption. This assumption is that the concentration of enzymes which are rate controlling for development are symmetrically distributed about some genetically determined mean concentration. It then follows mathematically that the skew in the distribution in development times, observed by Stinner, Butler, Bacheler & Tuttle (1975) and others, results naturally from the transformation from development rates to emergence times. The distribution model is shown to agree with observed data for (i) boll weevil, Anthonomus grandis Boheman, and (ii) cotton fleahopper, Pseudatomoscelis seriatus Reuter, reared under both constant and variable temperature regimes. The resulting model enables predictions of the distribution of emergence times for organisms reared under any set of variable temperature field conditions.

An analysis of the mechanics of guard cell motion

Abstract This paper presents a mechanical analysis of the cellular deformations which occur during the opening and closing of stomata. The aperture of the stomatal pore is shown to be a result of opposing pressures of the guard and adjacent epidermal cells. The analysis indicates that the epidermal cells have a mechanical advantage over the guard cells. With no mechanical advantage, an equal reduction in the turgor pressure of both guard and epidermal cells would have a neglible effect upon stomatal aperture. However, due to the mechanical advantage of the surrounding cells, the stomatal aperture increases with equal reductions in turgor, until the adjacent epidermal cells become flaccid. The minimum diffusion resistance of the pore occurs at this point. Further reductions in guard cell turgor lead to closure of the pore. The analysis further demonstrates how the shape, size, wall thickness and material properties of the guard cell walls influence their behavior.

Continuously produced, high specific activity 11C for studies of photosynthesis, transport and metabolism

Abstract A continuous supply of high specific activity 11CO2 was produced for studies of photosynthesis, transport, metabolic utilization, and storage in plants. The reaction 12C(p,d) 11C from a 35 MeV proton beam on a 300 cm3 gaseous 12CO2 target yielded 7.7 × 105 atoms/μA/sec in a flow of 1 cm3/sec, and yielded 2.1 × 10911C atoms/μA/sec from a dry ice target. The resultant 11CO was purified (in air), then oxidized to 11CO2, and 12CO2 was added in known amounts to produce the mixture air/12CO2/11CO2 of known concentration and specific activity. By analyzing pulse-fronts and steady-state labelling levels in an individual plant it is possible to extract considerably more information about uptake rates, product pool sizes and turnover rates, transport velocities and concentrations, metabolic sink strengths, and other parameters, than would be attainable by pulse methods alone. The high yields of 11C and potentially of 13N by these and related methods would also be of use in radiopharmaceuticals and biomedical tracers.

A general law for direct sunlight penetration

Abstract Under the assumption that foliage area distributions may be adequately approximated by probability distributions, a general law for the prediction of direct sunlight penetration of crop canopies is derived. It is shown that the Poisson (Beers) law is a special case of this more general law. Area and transect problems are treated, and stochastic variation in leaf sizes is considered. Numerical studies are presented which indicate that the Poisson law is not adequate in all cases for the prediction of sunlight penetration and that stochastic variation in leaf sizes is of less consequence than average leaf size and/or leaf-area index.

A time-dependent mathematical expression of the münch hypothesis of phloem transport

Abstract A time-dependent mathematical expression of the Munch, osmotically driven mass flow hypothesis of phloem transport is presented. The dependent variables include concentration of solutes, pressure, velocity of phloem sap, osmotic flux of water, and concentration dependent unloading of solutes. The model meets conservation requirements during all iterations, and responds realistically to changes in independent variables. Given the same set of independent variables the time-dependent model converges to the same values as the closed-form steady-state model of Goeschl et al. (1976) regardless of the initial conditions.

A parametric analysis of the anatomy and physiology of the stomata

ABSTRACT DeMichele, D. W. and Sharpe, P. J. H., 1974. A parametric analysis of the anatomy and physiology of the stomata. Agric. Meteorol., 14: 229–241. This paper highlights the stomatal dimensions and pressure relationships which might be genetically or environmentally altered to improve a plants water-use efficiency. A simplified mathematical model of the guard cell has been shown to be consistent with experimental observations, and based upon this model a parametric analysis has been carried out. The model presented herein has revealed that the following cellular characteristics affect stomatal response to water stress: (a) the osmotic potential of the guard cell; (b) the osmotic potential of the epidermal cells; (c) the semi-circumference of the pore; (d) the wall thickness of the guard cell; (e) the modulus of elasticity of the cell wall material; and (f) the size of the guard cell itself.

Modeling heat and moisture flow in soils

This paper describes a new model of the simultaneous flow of heat and moisture in soils. The model is a user-oriented experimental tool specifically designed for use in research. Computer optimization techni ques, numerical methods, and soil physics were used in developing the model. The model has been used in simulating the two-dimensional transfer of heat and moisture. It includes the effects of the environment and of subsurface sources and sinks.