The tire-ice interaction is a highly complex phenomenon, which has a direct influence on the overall performance of the pneumatic tire. From tire-terrain interaction dynamics, it is evident that icy road conditions and tire operational parameters play a vital role in determining the overall performance of the vehicle. With the reduction of traction available at the surface in icy conditions, the dynamics of the vehicle becomes more unpredictable, as the system can become unstable. In order to design an appropriate safety system, the tire-ice interaction must be closely investigated. Since the tire is the part of the vehicle that is in direct contact with the terrain during operation, it is critical to have an in-depth understanding of the contact mechanics at the contact patch. This study has led to the development and validation of an existing tire-ice model to further improve the understanding of the contact phenomena at the tire-ice interface. Experimental investigations led to a novel measurement technique in order to validate the semi-empirical based tire-ice contact model. The Advanced Tire-Ice Interface Model serves to simulate the temperature rise at the contact patch based on the pressure distribution in the contact patch, thermal properties of the tread compound and of the ice surface. Since its initial development, the advanced model is now capable of simulating the thin water film created from the melted ice, the prediction of tractive performance, the estimation of the viscous friction due to the water layer, and the influence of braking operations including the locked wheel condition. Experimental studies, carried out at the Terramechanics, Multibody, and Vehicle Systems (TMVS) Laboratory, were performed on the Terramechanics Rig. The investigation included measuring the bulk temperature distribution at the contact patch in order to validate the temperature rise simulations of the original Tire-Ice Model. The tractive performance of a P225/60R16 97S Standard Reference Test Tire and a 235/55R-19 Pirelli Scorpion Verde All-Season Plus XL were also investigated during this study. A design of experiment was prepared to capture the tire tractive performance under various controlled operating conditions. / Ph. D.

Gravimetric analysis was used to determine the release rates and longevities of several designs of pheromone dispensers for mating disruption of leafrollers and codling moth, Cydia pomonella (Linneaus). Release rates were described by linear equations for at least four months, but by the end of the season release rates tended to become erratic. Biocontrol’s red-brown codling moth dispenser lasted for up to four months, and one application of the dispenser in early May should control codling moth for the entire season in Virginia apple orchards. Ecogen and Hercon leafroller dispensers lasted for a shorter time than the codling moth dispensers and would require two applications per season to provide the best control of their target pests. In a commercial northern Virginia apple orchard, the effects of pheromone trap height and pheromone dispenser height on captures of the tufted apple bud moth, Platynota idaeusalis (Walker), were studied. Low traps (2.0 m) were more sensitive than high traps (4.5 m) for monitoring tufted apple bud moth. The number of moths caught in 1994 and 1995 in a two-hectare mating disruption plot with pheromone dispensers placed in the upper third of the tree was not significantly different from the number caught in a plot with pheromone dispensers placed at head height. Fruit damage was very high in both pheromone plots in 1994, but by 1995 it appeared that mating disruption was able to reduce fruit damage due to leafroller larvae. / Master of Science

Work related musculoskeletal disorders (WMSD) remain the focus of research efforts as costs associated with these disorders range from 13 to 54 billion dollars annually. WMSDs associated with the back and neck compromise almost 27% of all reported WMSDs. Approximately 1/3 of visual display terminal (VDT) operators report back and neck pain annually (BLS, 1998). Physical risk factors of VDTs associated with low back and neck WMSDs include static work postures and workstation design. The objectives of this study were to assess the effects of monitor height, chair type and their interaction on task performance, back/neck electromyography (EMG), perceived discomfort, and number of posture shifts. Both monitor height and chair type were assessed using two levels (high and low). Participants, four male and four female college age students, performed two data entry tasks using a standard keyboard and monitor and a fully adjustable bi-level table. In addition to the experimenter defined workstation configurations, participants were allowed to adjust their workstation to their preferred settings. Analysis of variance was performed to assess differences in task performance, perceived level of discomfort, number of posture shifts, and EMG data associated with various combinations of monitor height and chair type. Correlation analysis was performed to assess the relationship between participant's perceived discomfort and measured muscle activity to help determine if these two measurements could be used interchangeably to assess workstation design. No effect of workstation configuration (monitor height/chair type) was found for the majority of dependent variables. An exception was that configuration of low monitor, high chair, and their interaction generated significantly more muscle activity for the low back. User preferred settings were not found to differ significantly from those investigated with respect to muscle activity, perceived discomfort, posture shifts, and performance. Additionally, it was found the participants chose to position the iii workstation according to guidelines suggested in the literature for reducing WMSD discomfort. Task effects were found for performance, posture shifts, and perceived level of discomfort. Higher levels of performance and posture shifts for the neck were associated with the typing task, as opposed to the math task. Higher levels of neck discomfort, posture shifts of the feet and posture shifts of the back were associated with the math task. Correlation analysis provided evidence that perceived discomfort reported by participants and muscle activity for job tasks may not be related. Observed muscle activity for the tasks investigated in this study was low and in some instances, close to resting activity. Due to low levels of EMG, participants may not have been cognizant of their back and neck muscle activity, offering an explanation for why participants experience a cumulative effect of workstation design and seated postures, but linking particular causal factors to the development of LBP and NP is difficult. The findings of this study suggest that there are no gross physical differences between the chair types or monitor heights as defined in this study. Other factors (such as user preferences, job task demands, specific chair parameters, etc.) may significantly effect chair selection. This study found that task was a significant effect for the majority of dependent variables, and therefore may need to be a major factor driving workstation design. Workstation configuration will help determine the type of static posture assumed at a workstation, but the "discomfort or number of posture shifts" associated with that workstation and posture might be more a result of the job task requirements. / Master of Science

The United States share of the exported flue-cured tobacco market has decreased over the last decade as other countries have increased production of improved quality tobacco. Such tobacco is available at a substantially lower price than U. S. tobacco and thus desirable for the manufacture of less expensive discount cigarettes. Although world consumption of American style cigarettes is increasing, demand is not sufficient to maintain current production levels of premium quality U. S. flue-cured tobacco. Production systems that increase yields of suitable quality tobacco for discount cigarette manufacture without increasing production costs would allow tobacco to be offered competitively on the world market while maintaining current income. A study of ten management systems was conducted evaluating the influence of plant spacing, topping height, and harvest method on yield and quality of flue-cured tobacco. Leaf populations of 538,000/ha harvested once-over resulted in a 6.5%, 11.0%, 6.0%, and 13.5% increase in yield, value, price, and grade index, respectively, compared to the standard treatment. An expert panel showed no preference among systems and judged all systems acceptable in quality. A study conducted as a randomized complete block in a split plot arrangement evaluated the influence of row spacing and plant spacing on the yield and quality of flue-cured tobacco harvested once-over. Yield, value, and grade index increased while price per kg was unchanged as plant population increased. Flue-cured tobacco harvested in a single harvest produced cured leaf of acceptable quality; however, increased leaf populations are required to maintain acceptable yields. / Master of Science

<p dir="ltr">The s<i>patial-musical association of response code</i><i> </i>(SMARC) effect is the name given to a phenomenon for which responses to low and high pitch tones are faster when they correspond with lower and upper response locations, or left and right response locations, respectively, than when they do not. The SMARC effect was observed consistently when responses were located at lower or higher locations on the vertical dimension (the vertical SMARC effect). However, when the responses were located on the left or right to the center of the body on the horizontal dimension, the horizontal SMARC effect was observed among musicians consistently, but for nonmusicians, the horizontal SMARC effect was only observed under certain conditions (e.g., in pitch-height judgment tasks, or in color judgment tasks with a reference tone). Two theories, the direct mapping theory and intermediate mapping theory, can account for the horizontal SMARC effect. These theories indicate that musicians automatically code pitch to horizontal locations based on a direct mapping established through their musical training. In contrast, the horizontal SMARC effect for nonmusicians is based on an indirect mapping, which needs to be established via extra reference cues to associate the pitch height with the horizontal response locations.</p><p dir="ltr">The current study consists of four experiments designed to investigate the differences in conditions where the horizontal SMARC effect occurs for musicians versus nonmusicians, and how to elicit the horizontal SMARC effect among nonmusicians. Experiments 1 and 2 examined two factors that have been previously shown to influence the horizontal SMARC effect, tone laterality and musical experience, when properties of the tones were task irrelevant. It was found that only musicians showed horizontal SMARC effect when tones were presented binaurally, but both musicians and nonmusicians showed horizontal SMARC effect when tones were presented monaurally on all trials. The horizontal SMARC effect was eliminated among nonmusicians by diluting monaural tone’s lateral information by intermixing monaural and binaural trials. However, with monaural cue presentation, the auditory Simon effect was present regardless of whether the binaural trials were intermixed. Experiment 3 examined if the pitch-height was made a relevant stimulus dimension, would it evoke the horizontal SMARC effect among nonmusicians and decrease the differences in SMARC effect sizes between musicians and nonmusicians. No significant horizontal SMARC effect was found among nonmusicians in Experiment 3, which may have been attributed to other spatial congruity effects, such as the Simon effect, being present. Experiment 4 showed that 600 trials of practice with compatible mapping of low pitch to left location and high pitch to right location was sufficient to elicit the horizontal SMARC effect in a transfer session among nonmusicians.</p><p dir="ltr">The results of this study confirmed that musicians are able to associate the pitch height and the left-right locations on the horizontal dimension directly but nonmusicians do not have this ability. For nonmusicians, a horizontal reference frame, provided via tone laterality or extensive training to associate pitch to left-right responses is needed for the horizontal SMARC effect to emerge.</p>

No / In many countries, routine data relating to growth of infants are collected as a means of tracking health and illness up to school age. These have potential to be used in research. For health monitoring and research, data should be accurate and reliable. This study aimed to determine the agreement between length/height and weight measurements from routine infant records and researcher-collected data. Methods Height/length and weight at ages 6, 12 and 24 months from the longitudinal UK birth cohort (born in Bradford; n=836–1280) were compared with routine data collected by health visitors within 2 months of the research data (n=104–573 for different comparisons). Data were age adjusted and compared using Bland Altman plots. Results There was agreement between data sources, albeit weaker for height than for weight. Routine data tended to underestimate length/height at 6 months (0.5 cm (95% CI −4.0 to 4.9)) and overestimate it at 12 (−0.3 cm (95% CI −0.5 to 4.0)) and 24 months (0.3 cm (95% CI −4.0 to 3.4)). Routine data slightly overestimated weight at all three ages (range −0.04 kg (95% CI −1.2 to 0.9) to −0.04 (95% CI −0.7 to 0.6)). Limits of agreement were wide, particularly for height. Differences were generally random, although routine data tended to underestimate length in taller infants and underestimate weight in lighter infants. Conclusions Routine data can provide an accurate and feasible method of data collection for research, though wide limits of agreement between data sources may be observed. Differences could be due to methodological issues; but may relate to variability in clinical practice. Continued provision of appropriate training and assessment is essential for health professionals responsible for collecting routine data. / Open Access article

Yes / Background A recent Genome-wide association meta-analysis (GWAS) of refractive error reported shared genetics with anthropometric traits such as height, BMI and obesity. To explore a potential relationship with refractive error and ocular structure we performed a life-course analysis including both maternal and child characteristics using data from the Avon Longitudinal Study of Parents and Children cohort. Methods Measures collected across the life-course were analysed to explore the association of height, weight, and BMI with refractive error and ocular biometric measures at age 15 years from 1613children. The outcome measures were the mean spherical equivalent (MSE) of refractive error (dioptres), axial length (AXL; mm), and radius of corneal curvature (RCC; mm). Potential confounding variables; maternal age at conception, maternal education level, parental socio-economic status, gestational age, breast-feeding, and gender were adjusted for within each multi-variable model. Results Maternal height was positively associated with teenage AXL (0.010 mm; 95% CI: 0.003, 0.017) and RCC (0.005 mm; 95% CI: 0.003, 0.007), increased maternal weight was positively associated with AXL (0.004 mm; 95% CI: 0.0001, 0.008). Birth length was associated with an increase in teenage AXL (0.067 mm; 95% CI: 0.032, 0.10) and flatter RCC (0.023 mm; 95% CI: 0.013, 0.034) and increasing birth weight was associated with flatter RCC (0.005 mm; 95% CI: 0.0003, 0.009). An increase in teenage height was associated with a lower MSE (− 0.007 D; 95% CI: − 0.013, − 0.001), an increase in AXL (0.021 mm; 95% CI: 0.015, 0.028) and flatter RCC (0.008 mm; 95% CI: 0.006, 0.010). Weight at 15 years was associated with an increase in AXL (0.005 mm; 95% CI: 0.001, 0.009). Conclusions At each life stage (pre-natal, birth, and teenage) height and weight, but not BMI, demonstrate an association with AXL and RCC measured at age 15 years. However, the negative association between refractive error and an increase in height was only present at the teenage life stage. Further research into the growth pattern of ocular structures and the development of refractive error over the life-course is required, particularly at the time of puberty.

Effects of a congested match period on countermovement jump height (CMJ) and match performance variables were examined over the course of a D-I female soccer season. Twenty-one female collegiate soccer players (20.3 ± 1.8 yrs, body mass (kg): 62.3 ± 7.3, height (cm): 168.9 ± 6.1, body fat (%): 23.0 ± 3.7. performed CMJ testing prior to regular season matches. Global Positioning System (GPS) was used to assess physical match performance, while pre- and post-season lab and field-based testing was also performed. Analysis of variance trend analyses (ANOVA) were conducted using a linear mixed-effects model (LMM) to examine trends in mean CMJ height and match performance variables over the course of the season. Post hoc comparisons (Cohen’s d) were conducted to clarify trend analysis and to compare and quantify the magnitude of change between consecutive matches. LMM were used to examine relationships between two match performance variables and match-to-match changes in CMJ height. ANOVA was also performed using LMM to examine changes in lab and field-based fitness measures from pre to post-season. Cohen’s d effect sizes focused on pre to post season comparisons. Pre-match CMJ height decreased over time and between consecutive matches separated by 42-92 hours season (p < 0.05). Distance per minute and high-speed running distance per minute fluctuated over the season but did not demonstrate a linear trend (p > 0.5). Match relative volume and intensity were inversely related to pre-match jump height changes in the subsequent match (p < 0.05). Pre and post season lab and field-based testing showed no signs of detraining, suggesting decreases in jump height over the season are unlikely related to loss of fitness components. Decreased jump height between consecutive matches, suggests players are unable to fully recover from previous physical match demands.

The electrical properties of ZnO and contacts to ZnO have been investigated using different techniques. Temperature dependent Hall (TDH) effect measurements have been used to characterize the as-received melt grown ZnO samples in the 20 – 330 K temperature range. The effect of argon annealing on hydrogen peroxide treated ZnO samples has been investigated in the 200 – 800oC temperature range by the TDH effect measurement technique. The experimental data has been analysed by fitting a theoretical model written in Matlab to the data. Donor concentrations and acceptor concentrations together with the associated energy levels have been extracted by fitting the models to the experimentally obtained carrier concentration data by assuming a multi-donor and single charged acceptor in solving the charge balance equation. TDH measurements have revealed the dominance of surface conduction in melt grown ZnO in the 20 – 40 K temperature range. Surface conduction effects have proved to increase with the increase in annealing temperature. Surface donor volume concentrations have been determined in the 200 – 800oC by use of theory developed by D. C. Look. Good rectifying Schottky contacts have been fabricated on ZnO after treating the samples with boiling hydrogen peroxide. Electrical properties of these Schottky contacts have been investigated using current-voltage (IV) and capacitance-voltage (CV) measurements in the 60 – 300 K temperature range. The Schottky contacts have revealed the dominance of predominantly thermionic emission at room temperature and the existence of other current transport mechanisms at temperatures below room temperature. Polarity effects on the Schottky contacts deposited on the O-polar and Zn-polar faces of ZnO have been demonstrated by the IV technique on the Pd and Au Schottky contacts at room temperature. Results obtained indicate a strong dependence of the Schottky contact quality on the polarity of the samples at room temperature. The quality of the Schottky contacts have also indicated their dependence on the type of metal used with the Pd producing contacts with the better quality as compared to the Au. Schottky barrier heights determined using temperature dependent IV measurements have been observed to increase with increasing temperature and this has been explained as an effect of barrier inhomogeneities, while the ones obtained from CV measurements have proved to follow the negative temperature coefficient of the II – VI semiconductor material, i.e. a decrease in barrier height with increasing temperature. However, the values have proved to be larger than the energy gap of ZnO, an effect that has been explained as caused by an inversion layer. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Physics / unrestricted

Work chair is considered as an important element for the users to improve comfort in work environment. An ergonomic chair design and engineering is therefore considered very important for its usability and comfort view of point for the users. The aim of the thesis is to improve the mobility and ergonomics of the existing chair in all aspects. Ergonomically designed chairs are important for long time seated workers to increase their productivity and also to reduce low back injuries which arise due to the poor design chairs in ergonomic aspects. In addition, ergonomically designed chairs help to increase the seating comfortability of the chair users. QFD and waterfall model was followed for the work execution. In this paper, we discuss a design of an ergonomically efficient chair with simple adjustments which gives more comfortability. This will give us a better likelihood to stay in a neutral position. The Ergonomics of the chair is improved in various steps. This thesis focuses on many ideas in which some of them are implemented and evaluated.