Analysis of Yield-Density Models for Intercropping Experiments

Yield density models are used to describe the relationship between the yield of one or more crops and densities of planting. In this paper, we propose a correlated error structure for a linear yield-density model for intercopping and competition experiments. Four possible estimators of the parameters of the error structure are evaluated using a Monte Carlo study. The estimators are compared on the basis of gain in efficiency as measured by the generalized variance. An example is provided.     

Variation in stereotypic behavior related to restraint in circus elephants

The purpose of this study was to determine the effect of penning and chaining on circus elephant behavior. The behaviors of 10 Asian elephants (Elephas maximus) and three African elephants (Loxodonta africana) were videotaped for at least 24 hours at each of six performance locations. At four of these locations, the elephants were restrained in electric‐wire pens on turf and at two locations the elephants were restrained via leg chains on macadam. Instantaneous scan sampling at 5‐minute intervals during each observation period was conducted to determine the frequency of occurrence of seven behavior categories: aggression, comfort, ingestion, locomotion, resting, social, and stereotypy. Stereotypies and social interaction (P < 0.0008) were more likely with chained restraint; comfort, ingestion, and locomotion activities were less likely (P < 0.0037) with chained restraint, whereas aggression and resting activities were not affected by type of restraint (P > 0.6254). Variation in stereotypic activity was related to age (P = 0.0001), with younger elephants more likely to show stereotypic activity than older elephants. Zoo Biol 19:209–221, 2000. © 2000 Wiley‐Liss, Inc.     

Dynamics of the exotic Daphnia lumholtzii and native macro-zooplankton in a subtropical chain-of-lakes in Florida, U.S.A.

1. Seasonal dynamics of the exotic Daphnia lumholtzii and native macro-zooplankton species were studied for 2 years in six inter-connected lakes in Florida, U.S.A. The lakes ranged widely in pH, colour and trophic status, and were dominated by copepods.
2. All six lakes contained both D. lumholtzii and the native D. ambigua , but the two species did not overlap in time. D. ambigua was dominant in autumn–spring, coinciding with lower water temperature, higher transparency and lower nutrient and chlorophyll a (Chl a ) concentrations than in summer, when D. lumholtzii was dominant.
3. Based on the field observations, temperature optima were 24 °C for D. ambigua and 29 °C for D. lumholtzii , suggesting that temperature plays a role in determining dominance among the daphnids of subtropical Florida lakes.
4.  D. lumholtzii has not displaced native cladocerans but occupies a 'vacant' seasonal niche, unexploited due to the inability of native taxa to tolerate high temperature. Furthermore, D. lumholtzii did not significantly alter algal–zooplankton interactions. There was evidence of top–down control by grazing, but it was primarily attributable to the native taxa.     

Aerobically generated CO(2) stored during early exercise.

Previous studies have shown that a metabolic alkalosis develops in the muscle during early exercise. This has been linked to phosphocreatine hydrolysis. Over a similar time frame, the femoral vein blood pH and plasma K(+) and HCO(-)(3) concentrations increase without an increase in PCO(2). Thus CO(2) from aerobic metabolism is converted to HCO(-)(3) rather than being eliminated by the lungs. The purpose of this study was to quantify the increase in early CO(2) stores and the component due to the exercise-induced metabolic alkalosis (E-I Alk). To avoid masking the increase in CO(2) stores by CO(2) released as HCO(-)(3) buffers lactic acid, the transient increase in CO(2) stores was measured only for work rates (WRs) below the lactic acidosis threshold (LAT). The increase in CO(2) stores was evident at the airway starting at approximately 15 s; the increase reached a peak at approximately 60 s and was complete by approximately 3 min of exercise. The increase in CO(2) stores was greater, but the kinetics were unaffected at the higher WR. Three components of the change in aerobically generated CO(2) stores were considered relevant: the carbamate component of the Haldane effect, the increase in CO(2) stores due to increase in tissue PCO(2), and the E-I Alk. The Haldane effect was calculated to be approximately 5%. Physically dissolved CO(2) in the tissues was approximately 30% of the store increase. The remaining E-I Alk CO(2) stores averaged 61 and 68% for 60 and 80% LAT WRs, respectively. The kinetics of O(2) uptake correlated with the time course of the increase in CO(2) stores; the size of the O(2) deficit correlated with the size of the E-I Alk component of the CO(2) stores. We conclude that a major component of the aerobically generated increase in CO(2) stores is the new HCO(-)(3) generated as phosphocreatine is converted to creatine.     

A combined phenolic extraction and fermentation reactor engineering model for multiphase red wine fermentation

Red wine production begins with a simultaneous fermentation and solid-phase extraction process. Red wine color and mouthfeel is the result of the extraction of phenolics from grape skins and seeds during fermentation, where extraction is a strong function of temperature and ethanol concentration. During fermentation, grape solids form a porous “cap” at the top of the fermentor, resulting in a heterogeneous fermentation system with significant temperature and concentration gradients. In this work, we present a spatial, time-variant reactor engineering model for phenolic extraction during red wine fermentation, incorporating fermentation kinetics, mass transfer, heat transfer, compressible fluid flow, and phenolic extraction kinetics. The temperature and ethanol concentration profiles predicted by this model allow for the calculation of phenolic extraction rates over the course of fermentation. Phenolic extraction predictions were validated against prior experimental data to good agreement and compared to a well-mixed model's predictions to show the utility of a spatial model over well-mixed models.     

The effect of culture conditions on colony morphology and proliferative capacity in human prostate cancer cell lines

Primary cultures and cell lines form three types of colonies, termed holoclones, meroclones and paraclones by Barrandon and Green (Proc Natl Acad Sci U S A 84:2302-2306, 1987). They suggested that the three types correspond to colonies derived from stem, transit-amplifying and terminally differentiated cells. We determined the effect of culture conditions (seeding density, serum concentration, type of medium and substrate) on the proportion of each colony type and the cell number of individual colonies, using three prostate cancer cell lines, DU145, LNCaP and PC-3. In less favourable culture conditions, stem cell (SC) colonies tended to be lost; but in more favourable conditions, only modest increases in the proportion of SC colonies were observed. Under some conditions, cell number, but not colony-forming ability, was altered, indicating that colony cell number is controlled, at least in part, by different factors to colony formation. Colony-forming ability of individual cell lines is remarkably stable and there is little evidence for clonal evolution in culture, which might be expected and would result in more aggressive, faster-growing cells. Better understanding of how colony-forming efficiency is controlled could lead to the identification of drug targets that control SC growth and modify the progression of cancer.