Ronald E. Pitt

Fractal-based image texture analysis of trabecular bone architecture.

Fractal-based image analysis methods are investigated to extract textural features related to the anisotropic structure of trabecular bone from the X-ray images of cubic bone specimens. Three methods are used to quantify image textural features: power spectrum, Minkowski dimension and mean intercept length. The global fractal dimension is used to describe the overall roughness of the image texture. The anisotropic features formed by the trabeculae are characterised by a fabric ellipse, whose orientation and eccentricity reflect the textural anisotropy of the image. Tests of these methods with synthetic images of known fractal dimension show that the Minkowski dimension provides a more accurate and consistent estimation of global fractal dimension. Tests on bone x-ray (eccentricity range 0.25–0.80) images indicate that the Minkowski dimension is more sensitive to the changes in textural orientation. The results suggest that the Minkowski dimension is a better measure for characterising trabecular bone anisotropy in the x-ray images of thick specimens.

On Modelling the Statistical Strength of Yarns and Cables Under Localized Load-Sharing Among Fibers

This paper describes a statistical model for the strength of long, slender, fibrous structures such as yarns and cables. Emphasis is on the effect of strong mechanical interactions among fibers that arise from the presence of friction or a binding matrix. Basic features are that the structure is viewed as a long chain of statistically and structurally independent bundles whose lengths depend on the local mechanics of fibers at breaks. Within each bundle, localized load-sharing occurs among non-failed fiber elements depending on the local mechanics and fiber spatial geometry. The strengths of the fiber elements vary statistically and are modelled by a Weibull distribution. The analysis is for bundles with few fibers, though previous results under more idealized conditions suggest that the key features of the results will prevail also for much larger bundles. Key conclusions are that, for all practical purposes, a Weibull distribution describes the statistical strength of yarns and cables. The variability in fiber strength has a strong negative effect on the median strength of the yarn or cable and very little effect on its variability in strength. As the load-sharing becomes more diffuse, the median strength of the yarn or cable rises moderately. The size effect for the strength of the cable is very mild when compared to that for the fiber.

Use of in vitro gas production models in ruminal kinetics.

Physiological systems models for ruminant animals are used to predict the extent of ruminal carbohydrate digestion, based on rates of intake, digestion, and passage to the lower tract. Digestion of feed carbohydrates is described in these models by a first-order rate constant. Recently, an in vitro gas production technique has been developed to determine the digestion kinetics in batch fermentation, and nonlinear mathematical models have been fitted to the cumulative gas production data from these experiments. In this paper, we present an analysis that converts these gas production models to an effective first-order rate constant that can be used directly in rumen systems models. The analysis considers the digestion of an incremental mass of substrate entering the rumen. The occurrence of passage is represented probabilistically, and integration through time gives the total mass of substrate and total rate of digestion in the rumen. To demonstrate the analysis, several gas production models are fitted to a sample data set for corn silage, and the effective first-order rate constants are calculated. The rate constants for digestion depend on ruminal passage rate, an interaction that arises from the nonlinearity of the gas production models.

Osmometric behavior of Drosophila melanogaster embryos

The osmometric behavior of Drosophila melanogaster embryos in permeabilized eggs was studied in a microscope diffusion chamber designed to impose a rapid change in osmotic environment at various temperatures. A numerical model of NaCl diffusion in the chamber predicted that radial variations in concentration arising from the presence of a thin film of solution at the top of the chamber were negligible. On the basis of transient electrical conductance measurements in the chamber, characteristic time constants for the change in concentration averaged over the chamber depth occupied by the eggs were 0.99, 0.77, and 0.60 min at 0, 10, and 20 degrees C, respectively. The chamber response was sufficiently rapid that the characteristic response of the embryo was not masked. Equilibrium volumetric behavior of the embryos indicated that they behaved as nearly ideal osmometers over the range of 0.256 to 2.000 osm, and followed the relation FVeq = 0.123C-1 + 0.541, where FVeq is equilibrium fractional volume and C is osmolality. Nonlinear regression of volumetric data during osmotic contraction yielded an average Lp of 0.722 micron/(min.atm) at 20 degrees C and an apparent activation energy delta E of 8.11 kcal/mol. The coefficients of variation in the Lp estimates among individual embryos were 38, 18, and 47% at 0, 10, and 20 degrees C, respectively. With the use of probability rules and a model for volumetric behavior during freezing, it was determined that the observed variability in Lp (assuming delta E is fixed) considerably broadens the transition range of cooling rates over which the predicted probability of intracellular ice formation goes from 0 to 1. However, experimental observations (21) show the actual transition range is even wider, indicating that there exist other important sources of variability which determine the event of ice formation in D. melanogaster embryos.

Characterization of intracellular ice formation in Drosophila melanogaster embryos

Cryomicroscopy and differential scanning calorimetry (DSC) were used to characterize the incidence of intracellular ice formation (IIF) in 12- to 13-hr-old embryos of Drosophila melanogaster (Oregon-R strain P2) as influenced by the state of the eggcase (untreated, dechorionated, or permeabilized), the composition of the suspending medium (with and without cryoprotectants), and the cooling rate. Untreated eggs underwent IIF over a very narrow temperature range when cooled at 4 or 16 degrees C/min with a median temperature of intracellular ice formation (TIIF50) of -28 degrees C. The freezable water volume of untreated eggs was approximately 5.4 nl as determined by DSC. IIF in dechorionated eggs occurred over a much broader temperature range (-13 to -31 degrees C), but the incidence of IIF increased sharply below -24 degrees C, and the cumulative incidence of IIF at -24 degrees C decreased with cooling rate. In permeabilized eggs without cryoprotectants (CPAs), IIF occurred at much warmer temperatures and over a much wider temperature range than in untreated eggs, and the TIIF50 was cooling rate dependent. At low cooling rates (1 to 2 degrees C/min), TIIF50 increased with cooling rate; at intermediate cooling rates (2 to 16 degrees C/min), TIIF50 decreased with cooling rate. The total incidence of IIF in permeabilized eggs was 54% at 1 degree C/min, and volumetric contraction almost always occurred during cooling. Decreasing the cooling rate to 0.5 degree C/min reduced the incidence of IIF to 43%. At a cooling rate of 4 degrees C/min, ethylene glycol reduced the TIIF50 by about 12 degrees C for each unit increase in molarity of CPA (up to 2.0 M) in the suspending medium. The TIIF50 was cooling rate dependent when embryos were preequilibrated with 1.0 M propylene glycol or ethylene glycol, but was not so in 1.0 M DMSO. For embryos equilibrated in 1.5 M ethylene glycol and then held at -5 degrees C for 1 min before further cooling at 1 degree C/min, the incidence of IIF was decreased to 31%. Increasing the duration of the isothermal hold to 10 min reduced the incidence of IIF to 22% and reduced the volume of freezable water in embryos when intracellular ice formation occurred. If the isothermal hold temperature was -7.5 or -10 degrees C, a 10- to 30-min holding time was required to achieve a comparable reduction in the incidence of IIF.

Performance of a kinetic model for intracellular ice formation based on the extent of supercooling

Cryomicroscopy was used to study the incidence of intracellular ice formation (IIF) in protoplasts isolated from rye (Secale cereale) leaves during subfreezing isothermal periods and in in vitro mature bovine oocytes during cooling at constant rates. IIF in protoplasts occurred at random times during isothermal periods, and the kinetics of IIF were faster as isothermal temperature decreased. Mean IIF times decreased from approximately 1700 s at -4.0 degrees C to less than 1 s at -18.5 degrees C. Total incidence of IIF after 200 s increased from 4% at -4.0 degrees C to near 100% at -15.5 degrees C. IIF behavior in protoplasts was qualitatively similar to that for Drosophila melanogaster embryos over the same temperature ranges (Myers et al., Cryobiology 26, 472-484, 1989), but the kinetics of IIF were about five times faster in protoplasts. IIF observations in linear cooling of bovine oocytes indicated a median IIF temperature of -11 degrees C at 16 degrees C/min and total incidences of 97%, 50%, and 19% at 16, 8, and 4 degrees C/min, respectively. A stochastic model of IIF was developed which preserved certain features of an earlier model (Pitt et al. Cryobiology 28, 72-86, 1991), namely Weibull behavior in IIF temperatures during rapid linear cooling, but with a departure from the concept of a supercooling tolerance. Instead, the new model uses the osmotic state of the cell, represented by the extent of supercooling, as the independent variable governing the kinetics of IIF. Two kinetic parameters are needed for the model: a scale factor tau 0 dictating the sensitivity to supercooling, and an exponent rho dictating the strength of time dependency. The model was fit to the data presented in this study as well as those from Myers et al. and Pitt et al. for D. melanogaster embryos with and without cryoprotectant, and from Toner et al. (Cryobiology 28, 55-71, 1991) for mouse oocytes. In protoplasts, D. melanogaster embryos, and mouse oocytes, the parameters were estimated from IIF times in the early stages of isothermal periods, while the osmotic state of the cell was relatively constant. In bovine oocytes, the parameters were estimated from linear cooling data. Without further calibration, the model was used to predict total IIF incidence under different cooling regimes. For protoplasts, D. melanogaster embryos, and bovine oocytes, the models predictions were quite accurate compared to the actual data. In mouse oocytes, adjustment of the hydraulic permeability coefficient (Lp) at 0 degree C was required to yield realistic behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Temperature Sensitivity of Near-Infrared Scattering Transmittance Spectra of Water-Adsorbed Starch and Cellulose

Near-infrared spectroscopy was used to examine unmodified wheat starch and microcrystalline cellulose (MCC) at temperatures of −80 to 60°C and water activities of 0.22−0.94 aw. A commercially available liquid transmittance cell was modified to permit collection of scattering transmittance spectra of powdered samples. Changes to the shape, peak location, and intensity of the 1400–1500 and 1900–2000 nm water absorption bands were measured as temperature varied. Results indicated that frozen water was not detected at any of the temperatures or aw examined. All water was strongly associated with the carbohydrate matrix so that bulk water was absent. Sharpening of spectral features was not evident at low temperature. However, temperature changes resulted in slight changes to the water absorption bands in the 1400–1500 nm and 1900–2000 nm regions. From −80 to 60°C, the 1900–2000 nm band shifted approximately 10 nm and 15 nm toward shorter wavelengths in starch and MCC, respectively. The direction of shift is consistent with the hypothesis that an increase in temperature results in a decreased proportion of hydrogen bonded water-to-water molecules.

Subfreezing volumetric behavior and stochastic modeling of intracellular ice formation in Drosophila melanogaster embryos

Cryomicroscopic observations were made of the volumetric behavior and kinetics of intracellular ice formation (IIF) in Drosophila melanogaster embryos in a modified cell culture medium (BD.20) or BD.20 + 2 M ethylene glycol. After rapid cooling to a given temperature, transient volumetric contraction of the embryos during the isothermal period was quantified by computerized video image analysis. Fitting these data to the numerical solution of the volume flux equation yielded estimates of the hydraulic permeability coefficient (Lp) for individual embryos at various subfreezing temperatures. Lp approximately followed an Arrhenius relation between -2 and -9 degrees C, with a value of 0.168 microns/(min-atm) extrapolated to 0 degrees C and an apparent activation energy delta E of 38.9 kcal/mol. IIF during an isothermal period occurred at random times whose characteristic temperature range and kinetics were affected by the presence of ethylene glycol. A stochastic process model developed to fit these data indicated the influence of both time-dependent and instantaneous components of IIF, presumed to be the result of seeding and heterogeneous nucleation, respectively. The presence of 2 M ethylene glycol depressed the characteristic temperature of instantaneous IIF by about 12 degrees C and reduced the rate constant for time-dependent IIF. Comparison with observed incidences of IIF yielded an estimate of the supercooling tolerance of 3 to 5 degrees C.

Cryobiology of Drosophila Melanogaster Embryos

The common fruit fly Drosophila melanogaster is the subject of investigation in many diverse areas of biology. It has been studied intensively by geneticists, developmental and molecular biologists, neurobiologists, population and evolutionary biologists, entomologists, and chronobiologists. Currently, interest in D. melanogaster is most intense among molecular biologists, but studies of D. melanogaster have a long and distinguished history, dating back to Thomas Hunt Morgan in the first decade of this century. As a result of both past and present activity, there is an enormous number of D. melanogaster genetic stocks. In 1985 it was estimated that the number of different stocks was in excess of 30,000 and was rapidly increasing because of the increased number of investigators studying Drosophila, the increased number of large scale mutant screens, and the generation of new stocks by DNA transformation. Since then, the number of mutant stocks is even greater, especially since so many germ line transformants have been obtained; for example, in Drosophila Information Service (June 1988), some 1350 entries were recorded in the “clone list.” Many of these clones have been reinserted in several different places in the germ line via P-element mediated transformation. We estimate that over 50,000 different genetic lines of D. melanogaster are now maintained in national and international stock centers and in the laboratories of individual investigators.

Simulation of Soil Loss and Available Water Content to Assess the Sustainability of Selected Farm Practices

ABSTRACT One consequence of unsustainable farming practices is considered to be the deterioration of soil quality; however, finding a measure of soil quality in relation to sustainability has proven elusive. Defining soil quality in terms of productivity is problematic because of the numerous factors affecting productivity, including use of managed inputs that can mask soil deterioration. This paper explores, as one measure of soil quality, the consistency of the soil water content available for crop growth. By comparing soil water content under different cropping practices with that for a known sustainable system, a mature forested soil, we show how variation in water content can be used as an indicator of sustainability. The model CENTURY was used to simulate changes in soil organic matter content over time, and the Generalized Watershed Loading Function was used to simulate soil erosion and fluctuations in water content. Effects of soil type, initial soil organic matter content, slope, cropping system, tillage, and manure application were considered. Generally, only small differences were predicted in the mean available water content among these systems, but the coefficient of variation in available water content was higher in the cropped systems than in the mature system. Systems with higher rates of soil erosion also exhibited greater variability in available water content. This finding suggests that variability in available water, as compared with that of a mature system, is an indicator of the sustainability of farm practices.