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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.

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The goal of this thesis is to determine power counting rules at next-to-leading order (NLO) in the hard thermal loop (HTL) resummation. The original paper by Braaten and Pisarski discusses NLO HTL resummation and argues that there are potentially three types of contributions. We start by studying these terms in the specific case of the boson and fermion self energies in QED and QCD, as these quantities have been calculated in previous literature. For the real and imaginary parts of the fermion and gluon self energies, one needs to calculate only one type of term, as the other two are found to be subleading. However, for the real and imaginary parts of the photon self energy, all types of terms need to be calculated.

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This dissertation investigates three topics concerning high clouds: 1) convectively coupled equatorial wave (CCEW) signals derived from cloud top temperature (CTT) and cirrus optical thickness retrieved from satellite observations; 2) investigation of the physical mechanism governing the fixed anvil temperature (FAT) hypothesis and test of FAT hypothesis with CTT measurements; and 3) the intercomparison of cloud fraction and radiative effects between satellite-based observations and reanalysis product and simulations from general circulation models (GCMs). A wealth of information on CCEWs is derived from Aqua/MODIS cloud-top properties. We apply space-time spectral analysis on more than 6 years of CTT and isolate various modes of CCEWs including Kelvin, n = 1 equatorial Rossby, mixed Rossby-gravity, n = 0 eastward inertio-gravity waves, and the Madden-Julian oscillation. The successful application of the same method to cirrus cloud optical thickness confirms robust convective signals at upper troposphere. Consistent with the physical governing mechanism of the FAT hypothesis, the peak clear-sky diabatic subsidence, convergence and cloud fraction are located at roughly the same level (200 hPa), which is fundamentally determined by the rapid decrease of water vapor concentration above this level. The geographical maxima of cloud fraction agree well with that of water vapor, clear-sky cooling rates, diabatic subsidence and convergence at 200 hPa. An analysis of the response of the tropical mean CTT anomaly time series to sea surface temperature indicates that a possible negative relationship is present. In addition, we suggest interpreting the FAT hypothesis, and the more recent proportionately higher anvil temperature (PHAT) hypothesis, by using the temperature at the maximum cloud detrainment level instead of the CTT. Simulations of cloud fraction and radiative properties using two versions of the NCAR CAM models indicate that an overall improvement is observed in CAM5 compared to CAM3. However, an apparent bias in CAM5 shortwave (SW) cloud radiative forcing (CRF) simulation is shown in boreal winter southern mid latitude. This bias is primarily due to the underestimation of fraction-weighted SW CRF related to both high and middle top clouds. Additionally, apparent compensation errors are observed in models.

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<p> Recent advances in the development of intense short pulse lasers are significant. It is available now to access laser with intensity 10²¹ W/cm² by focusing a petawatt class laser, at which intensity hot dense plasmas with relativistic electrons, energy greater than 100 MeV, are produced. High energy x-rays, so called &gamma;-rays, are emitted strongly from such plasmas via Bremsstrahlung. </p><p> In a few years the laser intensity is expected to exceed 10²² W/cm². In such extreme intense laser-matter interaction, the radiative damping is significant, namely, electrons accelerated by the laser fields lose their energies and emit &gamma;-rays. So that we will see intense &gamma;-ray flash from the laser produced plasmas via two competing processes, Bremsstrahlung and radiative damping. However It is not clearly understood which process is dominant at what laser or what target conditions. My research is focus on making the radiation models to understand the &gamma;-ray emissions and studying the extremely intense laser-matter interaction to optimize the &gamma;-ray emissions under the given laser and target conditions. </p><p> Since these relativistic plasmas are non-thermal and non-equilibriated, it is necessary to develop a kinetic plasma code with the radiation physics. We had developed a collisional particle-in-cell code, PICLS, coupled to a radiation transport module to consider the &gamma;-ray emissions. The emissivities of &gamma;-rays had been derived for the relativistic Bremsstrahlung and the radiative damping. In the radiative damping, especially, not only the first order damping term, but up to 4-th order damping terms had been derived from the Lorentz-Dirac equation for the first time. Especially, the 2nd term is found to be important since it is a damping term of the Lorentz force, indicating the particle acceleration including ions would be much less efficient than that what we expected when the laser intensity become greater than 10²³ W/cm². </p><p> The laser energy dependence of the &gamma;-ray energy and the intensity dependence of the angular distribution of &gamma;-rays are studied. By solving the emission and transport of &gamma;-ray it was found that the radiative damping is not significant until the laser intensity exceeds 10²³ W/cm². While the Bremsstrahlung is dominant &gamma;-rays emission process, which can also boost by changing the target with higher Z material or increasing the mass (volume) of the target. As an application of &gamma;-ray production, the pair creation, forming a pair plasma, is attractive. The number of positrons via pair creation from the Bethe-Heitler process is also computed in the code. The optimal parameters of laser and target to increase &gamma;-ray yields as well as positrons yields are identified.</p>