2,104 research outputs found
Recommended from our members
Cosmic choruses: Metaphor and performance
In this chapter, Renaud Gagné pursues a chronologically wide-ranging study of how the motion of the heavenly bodies was thought about through the idea of choral dance. This chapter compares various unrelated, self-reflexive usages of the astral chorus metaphor in three genres of poetry and briefly considers how each illuminates the others. Instead of a teleological narrative, a dialogue of commonalities and contrasts is sought in the juxtaposition of comparable case studies. The striking image of the astral chorus was, among many other things, a powerful catalyst for thinking mimesis in action. A vision of the cosmic order is used in all three texts to reflect on the boundaries of poetic representation. The first text is a short epigram from Marcus Argentarius (AP 9.270 = G.-P. XXVI). The second passage is the ecphrasis of Dionysus’s shield in the Dionysica of Nonnus of Panopolis (25.380-572). The third text is another shield ecphrasis, that one from the first stasimon of Euripides’ Electra (432-486). The readings illustrate how a key figure of cosmic harmony was revisited to ponder the limits of poetic representation. Projecting itself on the cosmos, the idea of the choral dance could also reflect the cosmos back on song itself
Gold( i )-catalyzed addition of aldehydes to cyclopropylidene bearing 6-aryl-1,5-enynes
A diastereoselective, gold-catalyzed cascading cycloisomerization of alkylidene cyclopropane bearing 1,5-enynes that terminates in a cyclo-addition of aldehydes has been developed
Diagnostics Of Disks Around Hot Stars
We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars
Influence of permafrost extent on photochemical reactivity, functional group composition, and geochemical cycling of a subarctic discontinuous permafrost Alaskan watershed
Thesis (Ph.D.) University of Alaska Fairbanks, 2020Sub-Arctic Alaskan boreal forests are currently extremely susceptible to permafrost thaw caused by increases in atmospheric temperatures in the region. Upon thaw, permafrost soil organic matter can leach out organic matter, nitrogen, and metals. It is important to observe the effects the leaching of permafrost may have on photoreactivity, functional group composition, and metal introduction. Photoproduced reactive oxygen species may affect metal fate and transport through mechanisms such as the photo-Fenton reaction. Functional group analysis allows for differences in natural organic matter source and ability to complex metals throughout a watershed. Additionally, permafrost soils may have the ability to leach in metals through lateral flow of surface waters as observed in other studies. These metals could then complex to organic matter and alter the geochemical cycling within the watershed. Organic matter is a nutrient source, and metals (e.g., As) may increase the toxicity of surface waters through the thaw of permafrost. The influx of sequestered organic matter and metals to surface waters has the potential to drastically alter ecosystem processes. This study observes how permafrost leaching affects water composition, including its overall photoreactivity and functional group composition. The data obtained was then used to observe and deduce conclusions on how permafrost thaw influences surface water photoreactivity and functional group composition. Finally, trace metal analysis was conducted on a whole watershed scale over three years to observe how permafrost influences the geochemical composition of three main thermokarst surface waters with varying degrees of permafrost degradation. Overall, permafrost was determined to be heterogeneous and highly photoreactive both inter- and intra- watershed. Additionally, the functional group composition of surface waters influenced by permafrost thaw was different between summer and winter, indicating that winter is an important period to sample. Due to this change in functional group composition, the photoreactivity of winter samples was higher than summer with regard to the production of reactive oxygen species. Metal concentrations also increased during the winter for lakes identified to be undergoing active permafrost thaw. Finally, this case study found that metal concentration data combined with optical indices provided important information for resolving the possible extent of permafrost beneath thermokarst lakes.Chapter 1. Composition and photoreactivity of natural organic matter leached from discontinuous permafrost in sub-Arctic Alaska -- Chapter 2. Permafrost thaw impact on natural organic matter photoreactivity and chemical composition in sub-Arctic Alaskan thermokarst lakes -- Chapter 3. Seasonal geochemistry cycles in a sub-Arctic watershed underlain by discontinuous permafrost -- General conclusions
{Bis[2-(diphenylphosphanyl)ethyl]phenylphosphane-κ3 P,P′,P′′}[(Z)-8-mesitylcyclooct-4-en-1-yl]platinum(II) tetrafluoridoborate dichloromethane disolvate
In the title ionic compound, [Pt(C17H23)(C34H33P3)](BF4)·2CH2Cl2, the PtII atom adopts a square-planar coordination geometry with the large (Z)-8-mesitylcyclooct-4-en-1-yl group occupying the fourth coordination site. The (triphos)Pt moiety and the mesityl group are attached to the cyclooct-4-ene motif at the 1- and 8-position in a syn configuration. The (BF4)− anion and one of the dichloromethane solvate molecules each are disordered over two sets of sites
Dinuclear Gold−Silver Resting States May Explain Silver Effects in Gold(I)-Catalysis
The resting state of the gold(I)-catalyzed hydroarylation of 1 changes in the presence of Ag+, with silver free catalysts resting at the dinuclear gold structure 5 and Ag+ containing solutions resting at a heteronuclear species like 6. Adventitious Ag+ (typically from LAuCl activation) can therefore intercept key organogold intermediates and effect the catalysis even when it does not effect the reaction in Au free control experiments
Pd(0)/Au(i) redox incompatibilities as revealed by Pd-catalyzed homo-coupling of arylgold(i)-complexes
A Pd(ii)-catalyzed homo-coupling of Au(i)-aryls is reported. The reaction is driven by a Pd(0)/Au(i) redox reaction that generates a gold mirror and Pd(ii), and illustrates one of the challenges for developing dual catalytic Au–Pd systems
Enantioselective Cascade Cyclization/Protodemetalation of Polyenes with N 3 Pt 2+ Catalysts
The combination of the N-based pincer ligand PyBOX with Pt2+ leads to new catalysts for the enantioselective cycloisomerization of dienyl- and trienyl-ols. The mechanistic combination of electrophilic cyclization followed by rapid protodemetalation is surprising and leads to a powerful construct for developing new reactions
σ–π-Diauration as an alternative binding mode for digold intermediates in gold( i ) catalysis
While investigating the gold(i)-catalyzed intramolecular hydroarylation of allenes, the structure of a digoldvinyl intermediate was verified. Instead of the previously proposed geminally diaurated binding mode for the digold when L = PPh3, an alternative σ–π-diauration mode was observed with the bulkier ligand L = P(o-Tol)3. Reactivity studies indicate the σ–π-mode has a disproportionate effect on protonolysis reactivity
- …