Functional Analysis of MicroRNA Pathway Genes in the Somatic Gonad and Germ Cells During Ovulation in \u3cem\u3eC. Elegans\u3c/em\u3e

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression that play critical roles in animal development and physiology, though functions for most miRNAs remain unknown. Worms with reduced miRNA biogenesis due to loss of Drosha or Pasha/DGCR8 activity are sterile and fail to ovulate, indicating that miRNAs are required for the process of oocyte maturation and ovulation. Starting with this penetrant sterile phenotype and using new strains created to perform tissue specific RNAi, we characterized the roles of the C. elegans Pasha, pash-1, and two miRNA-specific Argonautes, alg-1 and alg-2, in somatic gonad cells and in germ cells in the regulation of ovulation. Conditional loss of pash-1activity resulted in a reduced rate of ovulation and in basal and ovulatory sheath contractions. Similarly, knockdown of miRNA-specific Argonautes in the cells of the somatic gonad by tissue-specific RNAi results in a reduction of the ovulation rate and in basal and ovulatory sheath contractions. Reduced miRNA pathway gene activity resulted in a range of defects, including oocytes that were pinched upon entry of the oocyte into the distal end of the spermatheca in about 42% of the ovulation events observed following alg-1 RNAi. This phenotype was not observed on worms exposed to control RNAi. In contrast, knockdown of alg-1 and alg-2 in germ cells results in few defects in oocyte maturation and ovulation. These data identify specific steps in the process of ovulation that require miRNA pathway gene activity in the somatic gonad cells

Unit organization of four topics in English literature for the ninth school year.

Thesis (M.A.)--Boston Universit

Permafrost in a warmer world: net ecosystem carbon imbalance

Thesis (Ph.D.) University of Alaska Fairbanks, 2014Arctic tundra and boreal forest have accumulated a vast pool of organic carbon, twice as large as the atmospheric carbon pool and three times as large as the carbon contained by all living things. As the permafrost region warms, more of this carbon will be exposed to decomposition, combustion, and hydrologic export. This permafrost carbon feedback has been described as the largest terrestrial feedback to climate change as well as one of the most likely to occur; however, estimates of its strength vary by a factor of thirty. Models predict that some portion of this release will be offset by increased arctic and boreal biomass, but the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets with serious societal and environmental consequences. In this dissertation I investigate the potential and actual response of Arctic and boreal carbon balance to climate change. First, I present estimates from 98 permafrost-region experts of the response of circumarctic biomass, wildfire, and hydrologic carbon flux to warming over the next several centuries. Because precise estimates of the factors driving arctic and boreal carbon balance are unlikely in the near future, these qualitative estimates provide a holistic summary of current scientific understanding and provide a framework for assessing uncertainty and risk. Assessments indicate that little agreement exists on the magnitude and even sign of change in high-latitude biomass, and that end-of-the-century organic carbon release from arctic rivers and collapsing coastlines could increase three-fold while carbon loss via burning could increase seven-fold. Second, I test the impact of permafrost collapse (thermokarst) on carbon and nutrient release from upland tundra on the North Slope of Alaska. The biogeochemical consequences of thermokarst are not adequately conceptualized or characterized to incorporate into numerical models, though thermokarst may impact a third of the permafrost region by the end of the century. I employ a coupled aquatic and terrestrial experimental design to address this knowledge gap, measuring the displacement of soil organic carbon, surface flux of CO₂, CH₄, and N₂O, and hydrologic export of dissolved carbon and nutrients. Results show that thermokarst can stimulate or suppress ecosystem respiration depending on feature morphology; remove a large portion of ecosystem carbon; mobilize highly biodegradable dissolved organic carbon; disrupt the nitrogen cycle resulting in N₂O production and hydrologic nitrogen losses; and influence offsite organic matter decomposition by the release of labile dissolved organic carbon nitrogen, and other nutrients. Spatial patterns of carbon and nutrient export from thermokarst suggest that upland thermokarst may be a dominant linkage between terrestrial and aquatic ecosystems as the permafrost region warms. I conclude that the strength of the permafrost climate feedback depends largely on coupled carbon and nutrient dynamics, which will interact with disturbance such as wildfire and thermokarst. My results indicate that three-quarters of permafrost carbon release could be avoided if human emissions are actively reduced, though the window of opportunity to keep that carbon in the ground is rapidly closing

Analyzing the Edges of a Snowboard

No Abstrac

Choosing low-cost institutions in global governance

Contemporary global governance takes place not only through formal inter-governmental organizations and treaties, but increasingly through diverse institutional forms including informal inter-governmental organizations, trans-governmental networks, and transnational public–private partnerships. Although these forms differ in many ways, they are all what we call ‘low-cost institutions’ (LCIs): the costs of creating, operating, changing, and exiting them, and the sovereignty costs they impose, are substantially lower on average than those of treaty-based institutions. LCIs also provide substantive and political governance benefits based on their low costs, including reduced risk, malleability, and flexibility, as well as many of the general cooperation benefits provided by all types of institutions. LCIs are poorly-suited for creating and enforcing binding commitments, but can perform many other governance functions, alone and as complements to treaty-based institutions. We argue that the availability of LCIs changes the cost–benefit logic of institutional choice in a densely institutionalized international system, making the creation of new institutions, which existing research sees as the ‘last resort’, more likely. In addition, LCIs empower executive, bureaucratic, and societal actors, incentivizing those actors to favor creating LCIs rather than treaty-based institutions. The availability of LCIs affects global governance in multiple ways. It reduces the status quo bias of governance, changes its institutional and actor composition, enables (modest) cooperation in times of polarization and gridlock, creates beneficial institutional divisions of labor, and expands governance options. At the same time, the proliferation of LCIs reduces the focality of incumbent institutions, increasing the complexity of governance

Quantum Parrondo's Games

Parrondo's Paradox arises when two losing games are combined to produce a winning one. A history dependent quantum Parrondo game is studied where the rotation operators that represent the toss of a classical biased coin are replaced by general SU(2) operators to transform the game into the quantum domain. In the initial state, a superposition of qubits can be used to couple the games and produce interference leading to quite different payoffs to those in the classical case.Comment: LateX, 10 pages, 2 figures, submitted to Physica A special issue (Gene Stanley Conference, Sicily, 2001), v2 minor correction to equations, v3 corrections to results section and table, acknowledgement adde

Apodization of Surface Acoustic Wave Three Phase Unidirectional Transducers

This thesis presents an introduction to surface acoustic wave (SAW unidirectional transducer (UDT) apodization. An unbalanced apodization structure is described. The structure is shown to suffer from an unbalanced capacitive effects, significant apodization losses and passband ripple. A balanced UDT structure is developed for the purpose of improving performance and minimizing undesirable effects associated with the unbalanced structure. Each apodization structure is analyzed and compared using a typical impulse response of a SAW transducer. The analysis is accomplished using SAWCAD2, a unidirectional Surface Acoustic Wave Computer Aided Design FORTRAN-77 program developed at the University of Central Florida. Having shown the balanced structure to be superior in performance, this structure is described in greater detail and a short summary of UDT fabrication is given