Climate-Driven Impacts of Warming and Grazing on Sub-Arctic Coastal Wetlands in Alaska

Climate change is rapidly warming the Arctic, especially at lower latitudes. Warmer temperatures and earlier springs are altering the timing of plants and animals, especially for long-distance migratory herbivores. Changes in the timing of both plants and herbivores have the potential to impact plant productivity and nutrient cycling, while also altering plant community diversity and composition. In chapter 2, I conducted a field experiment to investigate how earlier growing seasons and differences in arrival times of migratory geese influence physical traits of sedge forage species. I found that both an earlier growing season and late grazing by geese had similar effects on plant traits but delays in grazing had a greater effect than a change in spring. In chapter 3, I examined how earlier springs and differences in timing of goose herbivores affect soil nitrogen availability in sedge grazing lawns. I found that both earlier growing season and early grazing by geese increased soil nitrogen, while late grazing decreased soil nitrogen. However, early grazing resulted in a greater increase in soil nitrogen than an earlier growing season. In chapter 4, I investigated how warming and grazing interact to affect plant community diversity and composition in three different coastal wetland plant communities. I found that both warming and grazing increase community diversity but can also interact to mediate or synergistically increase community effects. Grazing decreased dominant grasses but increased low-lying forbs, while warming had little effect on functional groups across different communities

Controlling Singlet Fission with Coordination Chemistry-Induced Assembly of Dipyridyl Pyrrole Bipentacenes

Singlet fission has the potential to surpass current efficiency limits in next-generation photovoltaics and to find use in quantum information science. Despite the demonstration of singlet fission in various materials, there is still a great need for fundamental design principles that allow for tuning of photophysical parameters, including the rate of fission and triplet lifetimes. Here, we describe the synthesis and photophysical characterization of a novel bipentacene dipyridyl pyrrole (HDPP-Pent) and its Li- and K-coordinated derivatives. HDPP-Pent undergoes singlet fission at roughly 50% efficiency (τ_(SF) = 730 ps), whereas coordination in the Li complex induces significant structural changes to generate a dimer, resulting in a 7-fold rate increase (τ_(SF) = 100 ps) and more efficient singlet fission with virtually no sacrifice in triplet lifetime. We thus illustrate novel design principles to produce favorable singlet fission properties, wherein through-space control can be achieved via coordination chemistry-induced multipentacene assembly

Controlling Singlet Fission with Coordination Chemistry-Induced Assembly of Dipyridyl Pyrrole Bipentacenes

Singlet fission has the potential to surpass current efficiency limits in next-generation photovoltaics and to find use in quantum information science. Despite the demonstration of singlet fission in various materials, there is still a great need for fundamental design principles that allow for tuning of photophysical parameters, including the rate of fission and triplet lifetimes. Here, we describe the synthesis and photophysical characterization of a novel bipentacene dipyridyl pyrrole (HDPP-Pent) and its Li- and K-coordinated derivatives. HDPP-Pent undergoes singlet fission at roughly 50% efficiency (τ_(SF) = 730 ps), whereas coordination in the Li complex induces significant structural changes to generate a dimer, resulting in a 7-fold rate increase (τ_(SF) = 100 ps) and more efficient singlet fission with virtually no sacrifice in triplet lifetime. We thus illustrate novel design principles to produce favorable singlet fission properties, wherein through-space control can be achieved via coordination chemistry-induced multipentacene assembly

Breaking the Chain: Liberation from the Temporal Markov Assumption for Tracking Human Poses

We present an approach to multi-target tracking that has expressive potential beyond the capabilities of chain-shaped hidden Markov models, yet has significantly reduced complexity. Our framework, which we call tracking-by-selection, is similar to tracking-by-detection in that it sepa-rates the tasks of detection and tracking, but it shifts tempo-ral reasoning from the tracking stage to the detection stage. The core feature of tracking-by-selection is that it reasons about path hypotheses that traverse the entire video instead of a chain of single-frame object hypotheses. A traditional chain-shaped tracking-by-detection model is only able to promote consistency between one frame and the next. In tracking-by-selection, path hypotheses exist across time, and encouraging long-term temporal consistency is as sim-ple as rewarding path hypotheses with consistent image fea-tures. One additional advantage of tracking-by-selection is that it results in a dramatically simplified model that can be solved exactly. We adapt an existing tracking-by-detection model to the tracking-by-selection framework, and show im-proved performance on a challenging dataset (introduced in [18]). 1

Etoposide Reduces Peroxynitrite-Induced Cytotoxicity via Direct Scavenging Effect

Previously, we reported that glucose-deprived astrocytes are more vulnerable to the cytotoxicity of peroxynitrite, the reaction product of nitric oxide and superoxide anion. The augmented vulnerability of glucose-deprived astrocytes to peroxynitrite cytotoxicity was dependent on their proliferation rate. Inhibition of cell cycle progression has been shown to inhibit the apoptotic cell death occurring in cerebral ischemia-reperfusion. In the present study, we demonstrate that the increased death of glucose-deprived astrocytes by peroxynitrte was largely blocked by the cell cycle phase G2/M transition blocker etoposide. However, the cytoprotective effect of etoposide was not associated with its inhibition of cell cycle progression. Instead, etoposide effectively scavenged peroxynitrite. However, etoposide did not scavenge individual nitric oxide and superoxide anion and it did not prevent the hydrogen peroxide-induced cytotoxicity. The present results indicate that etoposide prevents the toxicity of peroxynitrite in astrocytes by directly scavenging peroxynitrite, not by inhibiting cell cycle progression

Development of a Multi-material Stereolithography System

Researchers continue to explore possibilities for expanding additive manufacturing (AM) technologies into direct product manufacturing. One limitation is in the materials available for use in AM that can meet the needs of end-use applications. Stereolithography (SL) is an AM technology well known for its precision and high quality surface finish capabilities. SL builds parts by selectively crosslinking or solidifying photo-curable liquid resins, and the resin industry has been continuously developing new resins with improved performance characteristics. This paper introduces a unique SL machine that can fabricate parts out of multiple SL materials. The technology is based on using multiple vats positioned on a rotating vat carousel that contain different photo-curable materials. To change the material during the process, the build platform is raised out of the current vat, a new vat with a different material is rotated under the platform, and the platform is submerged into the new vat so that the new material can be used. This paper introduces a new vat exchange mechanism, cleaning process, recoating process, resin leveling mechanism and process planning technologies for the implementation of multiple material SL. An overview of the system framework is provided and the system integration and control software is described. In addition, several multiple material test parts are designed, fabricated, and described

Reactions of Hydroxylamine with Metal Porphyrins

The reaction of hydroxylamine with a series of metal porphyrins was examined in methanol/chloroform media. The reductive nitrosylation reaction was observed for the manganese and iron porphyrins, leading to a nitrosyl complex that precipitated out of the solution in good isolatable yield (80−90%). This reaction could be used synthetically for the generation of iron and manganese porphyrin nitrosyl complexes and was particularly useful for making isotopically labeled nitrosyl complexes. On the other hand, CoII(TPP) and Cr(TPP)(Cl) did not react with hydroxylamine under anaerobic conditions. With trace amounts of oxygen, the reaction of CoII(TPP) with hydroxylamine led to the formation of a stable cobalt(III)−bis(hydroxylamine) complex. The infrared, resonance Raman, and proton NMR spectra were consistent with a cobalt(III)−bis(hydroxylamine) complex. The cyclic voltammetry and visible spectroelectrochemistry of this complex were examined. The one-electron reduction of CoIII(TPP)(NH2OH)2+ formed CoII(TPP), for which there was no evidence for the coordination of hydroxylamine. Further reduction led to CoI(TPP)-, which reacted with the halogenated solvent to form a cobalt−alkyl complex. The difference in the reactivity of these four metal porphyrins with hydroxylamine correlated well with their E1/2 values. Iron(III) and manganese(III) porphyrins were relatively easy to reduce and readily underwent the reductive nitrosylation reaction, while cobalt(II) and chromium(III) porphyrins are unreactive. The one-electron oxidation of the hydroxylamine complex with a M(III) porphyrin would be expected to oxidize the N-atom in the coordinated hydroxylamine. The oxidation of MIII(NH2OH) with the loss of a proton would form MII(NIH2O)+ by an internal electron transfer, which will eventually lead to M(NO). The relationship between the reductive nitrosyl reaction and the enzymatic interconversion of NO and hydroxylamine was discusse

Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e. magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling (SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at atomic scale. Magnetic easy axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin-orbit state within the nominally paramagnetic SIO.Comment: Proceedings of the National Academy of Sciences, May 201