published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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Controlled Start Transmissions (CST) can be described as a mechanical transmission combined with a wet clutch for controlled torque output. CST:s are commonly used to start up heavy loads for example mining conveyors. Several CST:s can work together to share the load. The transferred torque is controlled by a hydraulic wet clutch which is a proven technology for high torque transfer and low wear. This thesis is a part of a project to increase the knowledge and improve the CST design and control performance. The heat generation in the wet clutch is the focus of this thesis. Literature review shows that most research is done in order to get high accuracy for smaller clutches and most of the high torque engagements have very short transients.Models for the CST clutch heat generation together with thermal behavior have been developed and investigated. This includes a temperature model together with a kinetic model of the gearbox and a clutch torque model. Validation of separate model components and sensitivity analysis of the parameters are made. The developed model is then analyzed by comparing measurements from a commission site and simulations to get an idea of how much heat is generated.

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Rice is the leading staple for half the world’s population. Climate change, expanding populations and loss of agricultural land are projected to reduce rice yields by upwards of 30%. Significantly, rice yields decline by 10% for every 1°C increase in temperature. Temperatures ≥ 32°C can cause failure in male reproductive development and eliminate yields in some cultivars. This dissertation determined the developmental features and mechanisms associated with failure in male reproduction at temperatures of 32 °C and 36 °C in temperature tolerant and sensitive cultivars of O. sativa and O. glaberrima. Temperatures of 32 °C impaired anther dehiscence in the temperature sensitive cultivar of O. sativa by preventing septum cell wall degradation, which is essential for pollen dispersal. Temperatures of 36 °C induced abortion in pollen development either during meiosis primarily in O. sativa or at the uninucleate stage in O. glaberrima. Abortion during meiosis was associated with autophagic programmed cell death, whereas failure at the uninucleate stage of pollen development was associated with features of necrosis such as cytoplasmic shrinkage and cell wall collapse. Increased hydrogen peroxide production was detected in aborting meiocytes and uninucleate microspores at 36 °C, indicating that this reactive oxygen species may contribute to the failure of male reproductive development in rice during high temperature stress. Identification of the timing of failure in male reproductive development, and the cellular features associated with these processes in rice, form the basis for the identification of molecular mechanisms that control yield responses to high temperature stress.