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Marine δ¹⁸O data reveal astronomical forcing of the climate and cryosphere during the Miocene, when atmosphericPco₂was on par with emissions scenarios over the next century. This inspired hypotheses for how Milankovitch cycles, ice-ocean interactions, and greenhouse gases influence ice volume. Mass balance controls for marine and terrestrial ice sheets differ, and proxy data collected far from Antarctica provide valuable but limited insight into regional processes. We evaluate clast abundance data from Antarctic marine sedimentary records, observing a strong signal of eccentricity and precession coincident with a terrestrial ice sheet and a clear obliquity signal at the margins of a marine ice sheet. These analyses are integrated with a synthesis of proxy data, and we argue that high variance in obliquity forcing (mediated and enhanced by the ocean and atmosphere) can inhibit ice sheet growth, even when insolation forcing is conducive to glaciation. This “obliquity disruption” explains cryosphere variability before the existence of large northern hemisphere ice sheets. 

Poly- and Perfluorinated alkyl substances (PFAS) pose environmental and public health concerns. While incineration remains the most common PFAS remediation method, the complete combustion and pyrolysis mechanism of PFAS is unknown. This study aims to expand our understanding of the kinetics of gas-phase PFAS incineration by measuring the effect of difluoromethane (CHF) on propane ignition delay times (IDTs). The ignition delay times were measured by OH* emission and end-wall pressure time histories behind the reflected shock wave. Different concentrations of CH2F2 were mixed with fuel-lean propane-oxygen mixtures diluted in argon. Experiments were conducted at a nominal reflected shock pressure of P5 = 1 atm and reflected shock temperatures of 1200 < T5 < 1800 K. A new detailed chemical kinetic mechanism is presented. 135 new rate constants were computed using RRKM/ME theory, based upon stationary points computed using ANL0. The new mechanism is in excellent agreement with the measured ignition delay time. A novel sensitivity analysis helps to explain the elementary steps by which CH2F2 increases the ignition delay time. 

Orb-weaver spiders produce upwards of seven different types of silk, each with unique material properties. We focus on the adhesive within orb-weaving spider webs, aggregate glue silk. These droplets are composed of three main components: water, glycoproteins, and a wide range of low molecular mass compounds (LMMCs). These LMMCs are known to play a crucial role in maintaining the material properties of the glycoproteins, aid in water absorption from the environment, and increase surface adhesion. Orb-weavers within the Cyrtarachninae subfamily are moth specialists and have evolved glue droplets with novel material properties. This study investigated the biochemical composition and diversity of the LMMCs present in the aggregate glue of eight moth-specialist species and compared them with five generalist orb-weavers using nuclear magnetic resonance (NMR) spectroscopy. We hypothesized that the novel drying ability of moth-specialist glue was accompanied by novel LMMCs and lower overall percentages by silk weight of LMMCs. We measured no difference in LMMC weight by the type of prey specialization, but observed novel compositions in the glue of all eight moth-catching species. Further, we quantified the presence of a previously reported but unidentified compound that appears in the glue of all moth specialists. These silks can provide insight into the functions of bioadhesives and inform our own synthetic adhesives. 

Abstract LetXbe acompact orientable non-Haken 3-manifold modeled on the Thurston geometry $\mathrm{Nil}${\operatorname{Nil}}. We show that the diffeomorphism group $\mathrm{Diff}\left(X\right)${\operatorname{Diff}(X)}deformation retracts to the isometry group $\mathrm{Isom}\left(X\right)${\operatorname{Isom}(X)}. Combining this with earlier work by many authors, this completes the determination the homotopy type of $\mathrm{Diff}\left(X\right)${\operatorname{Diff}(X)}for any compact, orientable, prime 3-manifoldX.