Department of Mathematics and Statistics

We study the joint distribution of stochastic events described by (X,Y,N), where N has a 1-inflated (or deflated) geometric distribution and X, Y are the sum and the maximum of N exponential random variables. Models with similar structure have been used in several areas of applications, including actuarial science, finance, and weather and climate, where such events naturally arise. We provide basic properties of this class of multivariate distributions of mixed type, and discuss their applications. Our results include marginal and conditional distributions, joint integral transforms, moments and related parameters, stochastic representations, estimation and testing. An example from finance illustrates the modeling potential of this new model.

Summary  The implications of bias due to previous inbreeding of parents and genotype x environmental interaction on narrow sense heritability (h2) estimates by parent-offspring regression are enumerated. To remove the bias caused by genotype x environment interaction, an analysis of covariance model could be used. In special cases, where phenotypic expression is a result of two organisms interacting, such as in symbiotic N2 fixation, an analysis of covariance model with a test of heterogeneity of slopes is recommended. When host genotype x strain interactions are significant, separate heritability estimates for each strain are suggested to take advantage of genotype x strain interaction, which may be a major factor contributing to the expression of N2 fixation traits.

Twenty geldings (five groups; similar age and BW) were used in a completely randomized design experiment to determine effects of grain supplementation of an alfalfa-cube diet on apparent nutrient digestibility and hindgut fermentation. The geldings were housed individually, fed their diets in two equal meals (0600 and 1800), and adapted to five dietary treatments over 6 wk. The treatments were alfalfa cubes (1% of BW; DM basis) without (control) or with one of four rolled cereal grains (i.e., barley, corn, naked oats, or oats) to provide a target level of 0.4% of BW as total nonstructural carbohydrates (TNC). Due to acute laminitis, three geldings (one in the control group and two in the barley group) were excluded. Because of this and multiple incidents of gas colic, TNC level was decreased to 0.2% of BW to ensure the geldings' health throughout the adaptation (7 d) and sample collection (5 d) periods. Grain intakes varied (P < 0.05) and reflected the different TNC concentra...

The air-surface exchange of mercury (Hg) was measured, using a dynamic polycarbonate flux chamber, for soils with low or "background" Hg concentrations (<0.1 mg/kg) at eleven locations across the contiguous United States. Sampling locations included agricultural, desert, grassland, mixed and pine forest ecosystems (n=1326 soil flux measurements at 46 individual sites). An overall soil Hg flux of 0.9+/-0.2 ng/m2/h for these background soils was obtained by averaging the means for the different locations. Soil Hg fluxes were significantly lower in dark conditions than in the light for all but the grassland sites. Mean inlet air Hg concentrations were 1.0+/-0.1 ng/m3 in the dark and 1.3+/-0.2 ng/m3 in the light. Soil temperature inside and outside of the chamber, air temperature, relative humidity, and irradiance were measured concurrently with soil Hg flux. Soil-air Hg exchange was weakly predicted by environmental variables (R2 from 0.07 to 0.52). For a single location, ...

Competition between native and nonnative species can change the composition and structure of plant communities, but in deserts, the highly variable timing of resource availability also influences non-native plant establishment, thus modulating their impacts on native species. In a field experiment, we varied densities of the nonnative annual grass Bromus madritensis ssp. rubens around individuals of three native Mojave Desert perennials-Larrea tridentata, Achnatherum hymenoides, and Pleuraphis rigida-in either winter or spring. For comparison, additional plots were prepared for the same perennial species and seasons, but with a mixture of native annual species as neighbors. Growth of perennials declined when Bromus was established in winter because Bromus stands had 2-3 months of growth and high water use before perennial growth began. However, water potentials for the perennials were not significantly reduced, suggesting that direct competition for water may not be the major mechanism driving reduced perennial growth. The impact of Bromus on Larrea was lower than for the two perennial grasses, likely because Larrea maintains low growth rates throughout the year, even after Bromus has completed its life cycle. This result contrasts with the perennial grasses, whose phenology completely overlaps with (Achnatherum) or closely follows (Pleuraphis) that of Bromus. In comparison, Bromus plants established in spring were smaller than those established in winter and thus did not effectively reduce growth of the perennials. Growth of perennials with mixed annuals as neighbors also did not differ from those with Bromus neighbors of equivalent biomass, but stands of these native annuals did not achieve the high biomass of Bromus stands that were necessary to reduce perennial growth. Seed dormancy and narrow requirements for seedling survivorship of native annuals produce densities and biomass lower than those achieved by Bromus; thus, impacts of native Mojave Desert annuals on perennials are expected to be lower than those of Bromus.

The mungbean [Vigna radiata (L.) Wilczek] is an important short-duration annual grain legume. Mungbean is grown principally for its edible dry seeds, which are high in protein, easily digested, and prepared in numerous forms for human consumption; e.g., as a green vegetable and for sprouts. Other attributes of the crop include drought tolerance, high lysine content as compared to cereal grains, low production of flatulence, and wide adaptability. Commercial production occurs throughout Asia, Australia, the West Indies, South America, and tropical and subtropical Africa. In North America, production is centered in northern Texas and Oklahoma. Annual world mungbean production is estimated at 1.4 million t harvested from ≈3.4 million ha (1). In the United States >50 million kg of bean sprouts are produced annually from 8.3 million kg of mungbean seeds (4).

The activable proacrosin/acrosin levels in bovine sperm were examined using fluorescent staining and flow cytometry. The proportion of sperm with active acrosin were determined using the biotinylated isocoumarin serine protease inhibitor, Bi-Aca-Aca-OMe-IC (BIC). The presence of bound inhibitor on sperm was then determined by secondary labeling with avidin fluorescein conjugate. The proportion of sperm with activable proacrosin/acrosin was assessed by using detergent treatment to expose the active acrosin in intact sperm. The difference between untreated and detergent-treated aliquots was used to estimate the proportion of sperm with activable proacrosin/acrosin. In the 24-h stored samples from six bulls, the mean proportion of sperm with activable proacrosin/acrosin was 78.8 + 2.8%, whereas the mean proportion with exposed acrosin after cryopreservation of these samples was 55.8 4.1%. Significant differences (p < 0.05) were found among bulls in the proportion of sperm with activable proacrosin/acrosin both before and after cryopreservation. Activable proacrosin/acrosin levels in samples of cryopreserved sperm from five bulls were not correlated with fertility. These results do indicate, however, that the irreversible isocoumarin serine protease inhibitor BIC can be used to determine the proportion of sperm cells that retain activable proacrosin/acrosin after cryopreservation and thawing.