On January 1, 2000, the Amateur Softball Association of America (ASA) imposed maximum bat performance limitations on commercial softball bats. The ASA adopted a testing standard defined by the American Society of Testing and Materials (ASTM) to determine the bat performance factor (BPF), a normalized coefficient of restitution that must be less than 1.2 for the bat to be eligible for ASA sanctioned events. The ASTM standard requires that the softball strike the bat, which is free to rotate in the horizontal plane, at 26.8 mfs ± 0.3 mfs (88 ftfs ± 1 ftfs) with little or no spin. The central project goal was to develop the ASTM test apparatus, which consisted of a precision ball launcher, a pivoting stage for the bat, and instrumentation for velocity measurements. The key feature of the testing apparatus developed in this project was the ability to measure the rebound velocity of the ball directly-ASTM method derives the ball rebound velocity by assuming the bat behaves as a rigid body and applying conservation of angular momentum. Tests revealed a discrepancy in the BPF between the ASTM method and an alternative method,. termed the direct method, which uses the direct measurement of the ball rebound velocity. Furthermore, the ASTM method proved to be very sensitive to parameter errors, demonstrated by magnification factors between 2.0 and 3.0. The direct method was insensitive to parameter variation with magnification factors between o and 1.0. The ball rebound velocity discrepancy was also analyzed with mechanism simulation software. A three-degree-of-freedom model of the bat was used to test the effects of elasticity and pivot friction. The analysis determined that applying conservation of angular momentum on an elastic body caused transient errors in the derivation of the ball rebound velocity; and pivot friction significantly affected the motion of the bat and thus, the derived ball rebound velocity. The experimental results show that the direct method was more accurate than the ASTM method in calculating the BPF; and the conclusion of the analytical model shows that the ASTM method can be corrected by precisely identifying external moments in the system.

Thesis (PhD)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The emergence and re-emergence of viral human pathogens from wildlife sources in the recent past has led to increased studies and surveillance of wildlife for potentially zoonotic agents in order to gain a better understanding of the pathogens, their sources as well as events that may lead to viral emergence. Of the >1407 known human pathogens, 13% are classified as emerging or re-emerging, and 58% as zoonotic; 37% of the (re-)emerging and 19% of the zoonotic pathogens are RNA viruses, accounting for the majority of recently emerged infectious diseases with a zoonotic origin, such as HIV, Ebola, Hendra, Nipah, Influenza and SARS. This study focusses on potentially zoonotic viruses hosted by rodents (Muridae family), shrews (order previously known as Insectivora/Soricomorpha, now reclassified as Eulipotyphla) and bats (order Chiroptera). Rodents and bats represent the largest (~40%) and second largest (~25%) mammalian orders and both occur on every continent except Antarctica. Together, the three mammalian orders investigated represent the most relevant potential sources of new zoonoses. In this study I investigated the occurrence of astroviruses, arenaviruses, coronaviruses and hantaviruses in South African small mammal species belonging to the orders mentioned above. These viruses have either been implicated in recent emerging zoonotic events or are considered to have the potential to cause cross-species transmissions resulting in a zoonotic event. In the first part of the study specimens collected from various bat, rodent and shrew species were screened for viral sequences by broadly reactive PCRs; positive samples were characterised by sequencing and sequence analysis. A separate part of the study focussed on hantavirus disease in humans: a seroprevalance survey was conducted to determine the presence of hantavirus antibodies in the local population. Additionally, acutely ill patients with potential hantavirus disease were tested in an attempt to identify possible acute infections and define clinical hantavirus disease in South Africa. Screening of rodent and shrew specimens resulted in the identification of eight novel arenavirus sequences. Seven of the sequences are related to Merino Walk virus, a recently identified South African arenavirus, and the eighth sequence represents a novel lineage of Old World arenaviruses. Screening of bat specimens resulted in the identification of highly diverse novel astrovirus and coronavirus sequences in various South African bat species, including the identification of a viral sequence closely related to the recently emerged Middle East Respiratory Syndrome coronavirus. While the study did not identify hantavirus infections in any of the acutely ill patients, it found seroprevalences similar to those observed in Europe and West Africa. The results obtained highlight the importance of small mammals in the emergence of potential zoonoses and further reinforce the importance of viral surveillance of relevant wildlife species. Further in-depth studies of naturally infected reservoir host populations are required in order to gain a better understanding of virus-host dynamics and the events that lead to virus emergence. / German Research Foundation (DFG) (project number: KR1293/9-1/13-1) / The Polio Research Foundation and the NHLS Research / Harry Crossley Foundation, the Polio Research Foundation and Stellenbosch University for granting scholarships and bursaries for PhD.