Bounds on heat transfer by incompressible flows between balanced sources and sinks

Internally heated convection involves the transfer of heat by fluid motion between a distribution of sources and sinks. Focusing on the balanced case where the total heat added by the sources matches the heat taken away by the sinks, we obtain \emph{a priori} bounds on the minimum mean thermal dissipation $\langle |\nabla T|^2\rangle$ as a measure of the inefficiency of transport. In the advective limit, our bounds scale with the inverse mean kinetic energy of the flow. The constant in this scaling law depends on the source--sink distribution, as we explain both in a pair of examples involving oscillatory or concentrated heating and cooling, and via a general asymptotic variational principle for optimizing transport. Key to our analysis is the solution of a pure advection equation, which we do to find examples of extreme heat transfer by cellular and `pinching' flows. When the flow obeys a momentum equation, our bound is re-expressed in terms of a flux-based Rayleigh number $Ra$ yielding $\langle |\nabla T|^2\rangle\geq CRa^{-\alpha}$. The power $\alpha$ is $0, 2/3$ or $1$ depending on the arrangement of the sources and sinks relative to gravity.Comment: Minor revisions from review, figure adde

Balanced Heat Transport and Optimal Cooling

In this dissertation, we study the problem of designing an optimal incompressible fluid flow to achieve the most efficient heat transfer between a pair of balanced heat source and sink. We obtain a priori bounds on the heat transfer in terms of various measures of bulk flow intensity, such as the mean kinetic energy. A key question in our analysis is how the choice of source–sink function should enter into the optimization. We begin in Chapter III by presenting our results on the two-dimensional version of this problem from [SFT23], where we obtained a general bound on heat transfer in terms of a Hardy norm of the source–sink function, and introduced a ‘pinching’ flow design to saturate the scaling law of this bound for a pair of point-like sources and sinks. We discuss the implications of our bounds for physical, buoyancy-driven internally heated convection, which is a cousin of the more famous Rayleigh–B´enard problem. Chapter IV extends our bounds on heat transfer in various directions, to higher dimensions as well as to a dumbbell-shaped domain with a pair of point source and sink separated by a thin neck. Chapter V improves our analysis of the point source–sink problem by finding the optimal prefactor in our bound on heat transfer, for a subclass of radially symmetric heat profiles. Interestingly, we find that the bulk properties of the fluid flow do not enter into the leading order optimization of heat transfer in this setup. Instead, the heat transfer is set first and foremost by the particular choice of pinching flow profile nearby the sources and sinks. We end with a short conclusion section that provides some suggestions for future work.PhDMathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/192350/1/bingsong_1.pd

Effect of N fertilization rate on soil alkali-hydrolyzable N, subtending leaf N concentration, fiber yield, and quality of cotton

Soil alkali-hydrolyzable nitrogen, which is sensitive to N fertilization rate, is one of the indicators of soil nitrogen supplying capacity. Two field experiments were conducted in Dongtai (120°19″ E, 32°52″ N), Jiangsu, China in 2009 and Dafeng (120°28″ E, 33°12″ N), Jiangsu province, China in 2010. Six nitrogen rates (0, 150, 300, 375, 450, and 600 kg ha−1) were used to study the effect of N fertilization rate on soil alkali-hydrolyzable nitrogen content (SAHNC), subtending leaf nitrogen concentration (SLNC), yield, and fiber quality. In both Dongtai and Dafeng experiment station, the highest yield (1709 kg ha−1), best quality (fiber length 30.6 mm, fiber strength 31.6 cN tex−1, micronaire 4.82), and highest N agronomic efficiency (2.03 kg kg−1) were achieved at the nitrogen fertilization rate of 375 kg ha−1. The dynamics of SAHNC and SLNC could be simulated with a cubic and an exponential function, respectively. The changes in SAHNC were consistent with the changes in SLNC. Optimal average rate (0.276 mg day−1) and duration (51.8 days) of SAHNC rapid decline were similar to the values obtained at the nitrogen rate of 375 kg ha−1 at which cotton showed highest fiber yield, quality, and N agronomic efficiency. Thus, the levels and strategies of nitrogen fertilization can affect SAHNC dynamics. The N fertilization rate that optimizes soil alkali-hydrolyzable nitrogen content would optimize the subtending leaf nitrogen concentration and thereby increase the yield and quality of the cotton fiber

Degradation of zirconia in moisture

Zirconia especially stabilized by Y2O3 (YSZ) is an important and popularly used material. We have observed the degradation of YSZ in moisture, and have also revealed the degradation mechanism which could be related to the following three chemical processes: (1) reaction of water with the residual Y2O3 which is not incorporated into the crystal lattice of ZrO2; (2) corrosion of YSZ by water; (3) depletion of Y3+ from the crystal lattice by water molecule due to oxygen vacancies. A core/shell structure of ZrO2/Y2O3 in YSZ crystalline grains has been proved. Calcination of YSZ above 1100 °C can prevent the degradation

Targeted Mutagenesis of NAC Transcription Factor Gene, OsNAC041, Leading to Salt Sensitivity in Rice

Salinity is a major abiotic stress factor that seriously affects plant growth. Many genes are involved in the response to salt stress with various metabolism pathways. A number of plant transcription factor family genes have been found to be involved in the salt stress response, and NAM, ATAF and CUC (NAC) transcription factors are thought to act as active regulators during abiotic stress, especially salt stress. In this study, we detected a rice NAC transcription factor coding gene, OsNAC041, and confirmed that it influenced the germination of seeds under salt stress and salt tolerance of plants. OsNAC041 was primarily expressed in the leaves and located in the nucleus. Furthermore, the CRISPR/Cas9 method was used to obtain a targeted osnac041 mutant, of which the plant height was higher than that of the wild-type, showing increased salt sensitivity. Moreover, RNA-seq analysis revealed a number of differentially expressed genes (DEGs) involved in several important signaling pathways in the osnac041 mutant. Subsequently, Kyoto Encyclopedia of Genes and Genomes annotation also revealed differential expression of DEGs associated with mitogen-activated protein kinase signaling, peroxisome, eukaryotic- type ABC transporters, photosynthesis and plant hormones, which are involved in stress-related signaling pathways. Overall, our study suggested that OsNAC041 was involved in the salt stress response in rice. These findings not only provide empirical evidence of OsNAC041 function, but also provide new insight into its potential application in rice resistance breeding. Keywords: rice, NAC transcription factor, CRISPR, Cas9, RNA-seq, salinit

Magnetic and electronic properties of single-crystalline BaCoSO

Magnetic and electronic properties of single-crystalline BaCoS