Zugl.: Duisburg, Essen, University, Diss., 2006.

München, Techn. Univ., Diss., 2002. / Computerdatei im Fernzugriff.

München, Techn. Univ., Diss., 2002. / Computerdatei im Fernzugriff.

München, Techn. Universiẗat, Diss., 2004.

München, Techn. Universiẗat, Diss., 2002.

The purpose of this research is to identify socio-economic factors which may influence the adoption of auto-steer technologies by row crop farmers in Mississippi. The variables of geographic location, size of farm, age of the farmer, and educational level of the farmer were analyzed using a binary logistic regression analysis to determine if those variables could be used as predictors in the farmer’s adoption of auto-steer. Analysis revealed that the size of the farm and the age of the farmer are both statistically significant predictors of the probability of a farmer adopting auto-steer in the state of Mississippi. Geographic location and level of education were both included in the model but failed to indicate significant predictive ability. Among farmers who adopted auto-steer respondents ranked the importance of saving time and profitability as the most important and second most important factor in their decision to adopt auto-steer. Future research involving precision agriculture technologies should also include advances in the fields of beef production, forestry, and aquaculture. These can provide helpful insight into the reasons why a producer would adopt a particular precision agriculture technology.

Master of Science / Department of Animal Sciences and Industry / Evan C. Titgemeyer / Two experiments were conducted to determine effects of postruminal amino acid (AA) supplementation on protein deposition and signaling of the mammalian target of rapamycin (mTOR) pathway. For both experiments, 7 ruminally cannulated Holstein steers (172.7 ± 3.7 and 201.7 ± 3.8 kg initial BW in Exp. 1 and 2, respectively) were utilized in 6  6 Latin square designs with 7 d periods. A basal AA solution containing all essential AA, with the exception of lysine, were provided to all steers in each study in order to meet growth requirements, while making lysine the only limiting AA. Steers were fed 2.8 kg/d of a pelleted soyhull diet designed to be low in ruminally undegradable protein. Glucose was infused abomasally and volatile fatty acids were infused ruminally to prevent energy from being limiting. Steers were housed in metabolism crates to obtain total collection of both urine and feces. Blood and muscle biopsies of the longissimus lumborum were collected on the last day of each period. In experiment 1, treatments consisted of 2 levels of lysine (0 or 6 g/d) and 3 levels of leucine (0, 15, or 30 g/d) infused abomasally. Nitrogen retention increased with supplemental lysine. Leucine linearly decreased plasma concentrations of total AA. Plasma urea N (PUN) decreased with supplemental lysine. Total, phosphorylated, and the percent phosphorylated Akt were unaffected by treatments. The percentage of 4E-BP1 phosphorylated decreased linearly when leucine was supplemented. A tendency for a lysine x quadratic leucine effect was observed for the ratio of phosphorylated RPS6²⁴⁰/²⁴⁴ in which the intermediate level of leucine led to a decrease in the percent of RPS6²⁴⁰/²⁴⁴ phosphorylated when no lysine was supplied but increased when 6 g lysine/d was supplied. No differences were observed in the abundance of total, phosphorylated, or percent phosphorylated mTOR or in total abundance of E3 ubiquitin ligase proteins, MuRF1 or MAFbx. Experiment 2 was conducted similarly as experiment 1. Treatments consisted of 2 levels of lysine (0 or 6 g/d) and 3 mixtures of supplemental essential AA [none (control), 103 g/d essential AA (EAA), or EAA plus 30 g/d leucine (EL)] abomasally infused. Supplementation with essential AA, with or without leucine, increased the percentage of RPS6 phosphorylated, with a greater increase when leucine was included as part of the supplement. A lysine x (control vs. EAA+EL) interaction was observed for N retention in which the EAA and EL treatments did not improve N retention when no lysine was supplemented, but they increased it when 6 g lysine/d was provided. PUN increased above control when EAA or EL was provided, but PUN decreased when lysine was supplied. Supplementation of EAA or EL increased plasma total AA concentrations, but EL led to lower total plasma AA than EAA; however, concentrations were greater for EL than for control. In summary, leucine supplementation alone did not yield effects on whole-body protein deposition or on regulatory factors known to affect muscle protein synthesis, whereas a mixture of excess essential AA improved both lysine utilization and phosphorylation of RPS6²⁴⁰/²⁴⁴. These studies demonstrate the effects of essential AA, both limiting and nonlimiting, on protein deposition in growing cattle.

With the recent push towards autonomous cars, a traditional steering wheel with its mechanical connection between the road and driver may soon be unnecessary. To facilitate interior design and lower production costs whilst still maintaining a manual alternative for maneuvering, an alternative steering input device relying on Steer-by-Wire technology is investigated. In order to finish the investigation and development of the steering device within the time-span of a master thesis, the limitation to only investigate the design of a hand wheel was established. The finished alternative steering device utilises an optical encoder for position measurement and a brushless direct current (DC) motor with a planetary gearbox for force feedback. Open-loop speed control proved to be insufficient with the available hardware. Instead, an approach of two PD-controllers regulating the angular error between the steering rack and the steering device was implemented successfully. Initially, mathematical models of the system components were derived and implemented in Mathworks Simulink. The transition from models to test rig implementation proved to be difficult due to unknown parameters in the hardware components such as embedded controllers in the steering gear and the internal works of the sensor emulator used to control the steering gear. By modifying parameters in accordance with system identification measurements performed on the test rig, the models could be validated. At the end of the project, a Volvo S60 was made available and the steering device was tested with real world driving. It was discovered that controllers tuned only for good reference following in the test rig did not translate to good driveability as the controller allowed for overly aggressive maneuvers. Following some in vehicle tuning, the proposed solution performed well during testing with surprisingly high drive-ability. For future iterations of similar hand wheel design projects, a user study was performed with regards to user experience, hand wheel size and perceived driveability.

A skid steer loader is a machine used in construction for multiple tasks. Its small size and versatility makesit a use-full addition to any work site. The machine is driven by a combustion engine that in turn powers ahydraulic pump. This hydraulic fluid from the pump is then directed to either motor to propel the vehicle. Twospeed motors are used to allow high-speed operation. A problem present in the current design of the hydraulicsystem for a skid steer loader is its tendency to jerk when shifting speed at low temperatures. In an effort toidentify potential problems and rectify those, two models will be constructed in Simulink. One is a model ofthe whole system, where the pump and both motors are included as well as the machine itself. The other modelis designed to predict the system behaviour of one motor and a pump in a flywheel test rig. Also auxiliarycomponents are included in the models, including the two-speed shifting valve and pressure release valves. Bothmodels will predict the system behaviour from a set of input variables, including temperature, oil viscosity andgeometrical parameters. Improvements to the design where identified by analysing the simulation data. It wasfound that system performance could be enhanced by switching to an alternative notch shape of the two-speedshifting valve.

Improving prediction of P availability necessitates understanding of P digestion and absorption mechanism in ruminants. Greater knowledge of the interaction of P with other nutrients and the utilization of dietary P in the digestive tract will improve our ability to optimize P feeding and reduce P runoff in agricultural areas. In vivo experiments were performed and the data were used to reparamterize a model regarding P digestion and metabolism. The interaction of P and iron was investigated in lactating dairy cows by infusing 0, 200, 500, or 1250 mg/d Fe (equivalent to 0, 2, 5, or 12.5 mg Fe/L in drinking water) in the form of ferrous lactate solution into the abomasum of lactating cows. Phosphorus absorption was not negatively influenced by abomasally infused ferrous lactate, and the highest infusion (1250 mg Fe/d) approximates a drinking water iron content far above that found in most samples from the field. In the second study the effects of dietary P intake on intestinal P absorption was evaluated in eight growing Holstein steers fitted with permanent duodenal and ileal cannulas. Diets varying in P content (0.15%, 0.27%, 0.36% and 0.45%, DM basis) were fed , and increasing P intake increased the quantity of P absorbed from the small intestine linearly without affecting the absorption efficiency (mean = 59.6%). Only a small portion of P absorption occurred in large intestine and this was not affected by dietary P concentration. An absence of change of salivary P secretion at low dietary P suggested rumen function was prioritized during short-term P deficiency. Finally the data from these experiments along with four other studies were used to parameterize the P digestion and metabolism model of Hill et al. (2008) to provide a better understanding of the digestion and metabolism of P fractions in cattle. The data used were adequate to parameterize the digestive elements of the model with good precision, and the model structure appears to be appropriate with no significant mean or slope bias. The resulting model could be used to derive P bio-availabilities of commonly used feedstuffs in cattle production. Although the model explained the data used with no apparent bias, this does not guarantee that the model parameters are valid for all conditions. Additional data are needed to evaluate this model in a wider range of scenarios. / Ph. D.