Phosphorus (P) inputs into water reservoirs are the primary cause for accelerated eutrophication affecting water quality. Attempts are underway to regulate inputs originating from concentrated animal feeding operations (CAFOs). The purpose of this research was to relate runoff dissolved (DP) and total P (TP) losses to site-specific characteristics from plots in CAFOs and compare them to their corresponding risk assessment using the Texas Phosphorus Index (PI). Initial studies showed that soil test P (STP) methods used in Texas by inductively coupled plasma were highly reproducible regardless of manure source or application rate. However, NH4OAc-EDTA extraction efficiency was increased with respect to other methods as soil conditions became less acidic, probably due to dissolution of the greater portion of Ca-bound P resulting in STP values that could be three times greater than those of Mehlich III for the same soil. Surface application of dairy manure to high pH soils were positively correlated to STP at various soil-sampling depths down to 15 cm. First order linear relationships between STP values and DP concentrations in runoff were statistically significant for extraction methods and sampling depths but were different among different soils under neutral to calcareous conditions. Attempts to reproduce this relationship on fields that received periodic applications of manure or effluent with various incubation periods failed, although there was a single highly significant relationship between STP and runoff DP for different soils when soil conditions were acid ( pH<6.5) with various sampling depths. Analyses of NH4OAc-EDTA extractable soil elements showed Mg was significantly correlated to DP concentration across various management and soils, indicating that Mg-bound P is a major component controlling P release into runoff. Use of the Texas PI reflected vegetation type closely, with grass-covered sites averaging the lowest risk rating, and having the lowest DP and TP losses, while conversely tilled sites had the highest. However, overall relationship was poor when estimates for erosion rates were used due to experimental design limitations. Use of measured erosion rates for plots and inclusion of extractable Mg improved correlations between PI rating to DP and TP losses, with r2 ranging from 0.60 to 0.87.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. J. Erik Loehr. Includes bibliographical references.

The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of such off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. This study is focused on the simulation of thunderstorm downbursts using a deterministic-stochastic hybrid model and the prediction of wind turbine loads resulting from these simulated downburst wind fields. The wind velocity field model for thunderstorm downburst simulation is first discussed; in this model, downburst winds are generated separately from non-turbulent and turbulent parts. The non-turbulent part is based on an available analytical model (with some modifications), while the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions. Tower and rotor loads are generated using simulation of the aeroelastic response for models of utility-scale wind turbines. The main objective is to improve our understanding from the point of view of design so that we may begin to address transient events such as thunderstorm downbursts based on the simulations carried out in this research study. The study discusses as well the role of control systems (for blade pitch and turbine yaw), of models for representing transient turbulence characteristics, and of correlated demand and loads on multiple units in turbine arrays during thunderstorm downbursts. / text

This dissertation examines the effects of instantaneous constant-power loads (CPLs) on power converters. These CPLs are prevalent in distributed power architectures and are also present in certain motor-drive applications. CPLs introduce a destabilizing nonlinear effect on power converters through an inverse voltage term that leads to significant oscillations in the main bus voltage or to its collapse. Boundary control is studied in order to stabilize dc-dc converters with instantaneous CPLs. The three basic topologies are studied: buck, boost, and buck-boost. Converter dynamics are analyzed in both switching states and the various operating regions of switch interaction with a first-order switching surface are identified. The analysis reveals important characteristics of CPLs. For non-minimum phase converters, in order to avoid issues related with the fact that the closed-loop state-dependent switching function is undefined on the switching surface, reflective mode solutions to both converter systems are defined in the sense of Filippov. Sufficient conditions for large-signal stability of the closed loop converter operating points are established. It is shown that first-order switching surfaces with negative slopes achieve large-signal stability, while positive slopes lead to instability. In particular, for the boost converter it is illustrated via simulations and experiments that positive slopes may lead to another closed-loop limit cycle. It is also shown that instability as well as system-stalling, which is termed the invariant-set problem, may still occur in reflective mode. However, a hysteresis band that contains the designed boundary may be used to prevent system-stalling, and also allow for a practical implementation of the controller by avoiding chattering. Regulation is also achieved. The dynamic behavior of single-phase full-wave uncontrolled rectifiers with instantaneous CPLs is also explored. Stable operation is shown to be dependent on initial condition and circuit parameters, which must fall within reasonable ranges that validate a CPL model. A necessary condition for stable operation of the rectifier system is thus derived. Furthermore, input and output characteristics of the rectifier with a CPL are investigated, and comparisons are made with the resistive case. A more complete model for the rectifier system that incorporates line-voltage distortion is also utilized to study the rectifier system. Simulations and experimental results are included for verification. / text

No description available.

Εξετάζεται με χρήση του προγράμματος σε Η/Υ PRAO, η δυνατότητα αντιμετώπισης των προβλημάτων αύξησης των ηλεκτρικών φορτίων την προσεχή δεκαπενταετία (έτος 2008 εως 2023) στην ευρύτερη περιοχή της πόλης της Πάτρας που αποτελείται από το αστικό τμήμα των Δήμων Πάτρας και Ρίου. / -

The main aim of this study was to analyse the long-term effects on epiphytic lichen dry mass development, diversity and community structure after exposure to a simulated nitrogen deposition gradient. A whole tree experiment was set up in a boreal forest in the County of Västerbotten in Sweden, whereby 15 trees were artificially irrigated and nitrogen fertilized during seven consecutive years (2006-2012). The treatments were equal to an additional deposition of 0.6, 6, 12.5, 25 and 50 kg N ha-1 yr-1. Branches from the trees were collected in October 2012 and the lichen material was harvested and further analysed during the spring 2013. The results from this study showed that the lichens were directly affected by the long-term increased nitrogen deposition. Generally, lichen dry mass and species richness declined at high nitrogen loads and the initial positive effects of low nitrogen loads reported in a preceding study had thus depressed with time. The results from this study also showed that the composition of the lichen community changed benefitting nitrogen-tolerant species, probably not because of competition but more likely because of nitrogen-sensitive species disappearance. This study strongly indicates that it takes more than a few years to detect changes in lichen communities exposed to enhanced nitrogen loads. In addition low concentrations seem to have a cumulative impact. Consequently, this study stresses the importance of also considering the cumulative effect of low nitrogen loads when determining critical values. The critical load for lichen communities in boreal forests might be below 6 kg N ha-1 yr-1.

No description available.

This is an investigation of the buckling characteristics of short, thin-walled cylinders. This study was required as large storage tanks, which were converted from Boating roof to fixed roofed tanks, were found to buckle when severe atmospheric temperature drops and thus pressure differentials occurred. These severe ambient temperature changes are characteristic of the Highveld in South Africa where the tanks in question are situated. Since this modification is an uncommon procedure, codes of practice for storage vessels do not cover this type of cylinder. For the same reason, research performed in this field is limited. Buckling due to axial loading, lateral external pressure, hydrostatic pressure and a combination of axial loading and hydrostatic pressure are explored in this study. To compare with and verify theory, existing research for each case is examined, and the Finite Element Analysis package MSC Nastran used to determine trends. In some cases, to the best of the author's knowledge, no research exists and numerical analysis is performed to establish the relationships present in those cases. The study is extended to include the design of imperfect cylinders, as defined in the tank code AD Merkblatter where it is stated as being dependant on the major and minor diameters of the imperfect section . The study is also extended to the case of variable wall thickness cylinders, where the thickness variation is symmetrical about the axis of the cylinder. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

No description available.