38 research outputs found
Commutants of Toeplitz operators with separately radial polynomial symbols on the Fock space
No full textMy talk concerns commuting Toeplitz operators on the Fock space . Let be a separately radial polynomial in and in . Then the Toeplitz operator is diagonal with respect to the standard orthonormal basis of . We obtain a characterization of polynomially bounded functions for which commutes with . Substantially different from the radial case, the characterization depends highly on the behavior of the polynomial . I will discuss several examples and consequences of our result. This is joint work with Amila Appuhamy
Algebraic properties of Toeplitz operators on weighted Bergman spaces
No full textsummary:We study algebraic properties of two Toeplitz operators on the weighted Bergman space on the unit disk with harmonic symbols. In particular the product property and commutative property are discussed. Further we apply our results to solve a compactness problem of the product of two Hankel operators on the weighted Bergman space on the unit bidisk
Effects of diet and manure storage method on carbon and nitrogen dynamics during storage and plant nitrogen uptake
No full textAltering dairy cattle diets to reduce both enteric methane (CH4) production and nitrogen (N) excretion are valuable tools for mitigating the environmental impact of dairy production. We examined the impact of altering diets on changes in physicochemical properties of manure during storage, short term plant N availability, and overall system N use efficiency. Manure collected from cattle fed diets with differing forage and crude protein (CP) content were stored via three methods (slurry, static pile, turned pile) for 29 weeks and sampled at week 0, 1, 2, 3, 4, 9, 14, 19, 24, and 29. Mass losses of total carbon (C) ranged from 28 to 50% and followed the trend static pile > slurry > turned pile (P < 0.01). Total N losses ranged from 20 to 47% with the slurry and static pile treatments having larger (but similar) losses than the turned pile treatment (P < 0.01). The soil 2-week plant available N was similar in the static pile and turned pile treatments and were 67% less than the slurry treatment. The short-term plant N use efficiency was similar for both the static pile and slurry treatments (22-24%), which were greater than that of the turned pile treatment (16%). Overall estimated system N use efficiencies were 5% greater for lower CP diets compared to high CP diets. While rapidly drying manure may conserve C and N, there may be a tradeoff with plant N utilization which could affect overall system efficiencies
Development of mathematical models to predict volume and nutrient composition of fresh manure from lactating Holstein cows.
No full textOrganic compounds in dairy manure undergo a series of reactions producing pollutants such as ammonia and methane. Because various organic compounds have different reaction rates, the emissions could be accurately determined if amounts and concentrations of individual nutrients in manure are known. A set of empirical models were developed for predicting faecal and urinary water, carbon (C), nitrogen (N), acid detergent fibre and neutral detergent fibre output (kg/day) from lactating Holstein cows. Dietary nutrient contents, milk yield and composition, bodyweight, age and days in milk were used with or without dry matter intake (DMI) as potential predictor variables. Multi-collinearity, goodness of fit, model complexity, and random study and animal effects were taken into account during model development, which used 742 measured faecal or urinary nutrient output observations (kg/day). The models were evaluated with an independent dataset (n = 364). When DMI was used as a predictor variable, the models predicted faecal and urinary nutrient outputs successfully with root mean square prediction error as a percentage of average observed values (RMSPE%) ranging from 9.1% to 20.7%. All the predictions except urine output had RMSPE% ranging from 18.3% to 24.6% when DMI was not used. The nutrient output predictions were in reasonable agreement with observed values throughout the data range (systematic bias \u3c14% of total bias). Fresh manure C : N ratio predictions were acceptable (RMSPE% = 14.3–15.2%) although the systematic bias were notable (17.1–20.7% of total bias). The models could be integrated successfully with process-based manure or soil models to assess nutrient transformation in dairy production systems
