Formation of TiC-core, Graphitic-mantle Grains from CO Gas

We demonstrate a new formation route for TiC-core, graphitic-mantle spherules that does not require c-atom addition and the very long timescales associated with such growth (Bernatowicz et al. 1996). Carbonaceous materials can also be formed from C2H2 and its derivatives, as well as from CO gas. In this paper, we will demonstrate that large cage structure carbon particles can be produced from CO gas by the Boudouard reaction. Since the sublimation temperature for such fullerenes is low, the large cages can be deposited onto previously-nucleated TiC and produce TiC-core, graphitic-mantle spherules. New constraints for the formation conditions and the timescale for the formation of TiC-core, graphitic-mantle spherules are suggested by the results of this study. In particular, TiC-core, graphitic-mantle grains found in primitive meteorites that have never experienced hydration could be mantled by fullerenes or carbon nanotubes rather than by graphite. In situ observations of these grains in primitive anhydrous meteoritic matrix could confirm or refute this prediction and would demonstrate that the graphitic mantle on such grains is a metamorphic feature due to interaction of the pre-solar fullerenes with water within the meteorite matrix

Is the 21-micron Feature Observed in Some Post-AGB Stars Caused by the Interaction Between Ti Atoms and Fullerenes?

Recent measurements of fullerenes and Ti atoms recorded in our laboratory have demonstrated the presence of an infrared feature near 21 pm. The feature observed has nearly the same shape and position as is observed for one of the most enigmatic features in post-asymptotic giant blanch (AGB) stars. In our experimental system large cage carbon particles, such as large fullerenes, were produced from CO gas by the Boudouard reaction. Large-cage carbon particles intermixed with Ti atoms were produced by the evaporation of a Ti metal wrapped carbon electrode in CO gas. The infrared spectra of large fullerenes interacting with Ti atoms show a characteristic feature at 20.3 micron that closely corresponds to the 20.1 micron feature observed in post-AGB stars. Both the lab- oratory and stellar spectra also show a small but significant peak at 19.0 micron, which is attributed to fullerenes. Here, we propose that the interaction between fullerenes and Ti atoms may be a plausible explanation for the 21-micron feature seen in some post-AGB stars

Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments

Effect of GTP and Ca2+ on inositol 1,4,5-trisphosphate induced Ca2+ release from permeabilized rat exocrine pancreatic acinar cells

The effects of Ca2+ and GTP on the release of Ca2+ from the inositol 1,4,5-trisphosphate (IP3) sensitive Ca2+ compartment were investigated with digitonin permeabilized rat pancreatic acinar cells. The amount of Ca2+ released due to IP3 directly correlated with the amount of stored Ca2+ and was found to be inversely proportional to the medium free Ca2+ concentration. Ca2+ release induced by 0.18 μM IP3 was half maximally inhibited at 0.5 μM free Ca2+, i.e. at concentrations observed in the cytosol of pancreatic acinar cells. GTP did not cause Ca2+ release on its own, but a single addition of GTP (20 μM) abolished the apparent desensitization of the Ca2+ release which was observed during repeated IP3 applications. This effect of GTP was reversible. GTPγS could not replace GTP. Desensitization still occurred when GTPγS was added prior to GTP. The reported data indicate that GTP, stored Ca2+ and cytosolic free Ca2+ modulate the IP3 induced Ca2+ release. EGTA, Ethylene-glycol-bis (2-aminoethylether)-N,N,N′,N′- tetra acetic acid; GTPγS, Guanosine 5′-O-[3-thio]triphosphate; GDPβS, Guanosine 5′-O-[2-thio]diphosphate; IP3, Inositol 1,4,5-trisphosphate; IP2, Inositol 1,4-bisphosphate; IP4, Inositol 1,3,4,5-tetrakisphosphate; MOPS, Morpholinopropane sulfonic acid; HEPES, 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid; pHMB, Parahydroxymercuribenzoat

Additional experimental evidence for a solar influence on nuclear decay rates

Additional experimental evidence is presented in support of the recent hypothesis that a possible solar influence could explain fluctuations observed in the measured decay rates of some isotopes. These data were obtained during routine weekly calibrations of an instrument used for radiological safety at The Ohio State University Research Reactor using Cl-36. The detector system used was based on a Geiger-Mueller gas detector, which is a robust detector system with very low susceptibility to environmental changes. A clear annual variation is evident in the data, with a maximum relative count rate observed in January/February, and a minimum relative count rate observed in July/August, for seven successive years from July 2005 to June 2011. This annual variation is not likely to have arisen from changes in the detector surroundings, as we show here.Comment: 8 pages, 6 figure

How Many Subpopulations is Too Many? Exponential Lower Bounds for Inferring Population Histories

Reconstruction of population histories is a central problem in population genetics. Existing coalescent-based methods, like the seminal work of Li and Durbin (Nature, 2011), attempt to solve this problem using sequence data but have no rigorous guarantees. Determining the amount of data needed to correctly reconstruct population histories is a major challenge. Using a variety of tools from information theory, the theory of extremal polynomials, and approximation theory, we prove new sharp information-theoretic lower bounds on the problem of reconstructing population structure -- the history of multiple subpopulations that merge, split and change sizes over time. Our lower bounds are exponential in the number of subpopulations, even when reconstructing recent histories. We demonstrate the sharpness of our lower bounds by providing algorithms for distinguishing and learning population histories with matching dependence on the number of subpopulations. Along the way and of independent interest, we essentially determine the optimal number of samples needed to learn an exponential mixture distribution information-theoretically, proving the upper bound by analyzing natural (and efficient) algorithms for this problem.Comment: 38 pages, Appeared in RECOMB 201

Photo-responsive polymeric structures based on spiropyran

Spiropyrans are one of the most popular classes of photochromic compounds that change their optical and structural properties in response to external inputs such as light, protons and metal ions, making them ideal molecules for the fabrication of multifunctional stimuli-responsive materials. Nowadays, the emphasis in polymeric materials incorporating spiropyran units, focuses on the effectiveness of their reversible response to external photonic stimuli. Photo-control of a range of key characteristics for flow systems, such as wettability, permeability, photo-modulation of flow by photo-actuation of valves, photonic control of uptake and release of guests using films and coatings, and colorimetric sensing of various species, are highlighted and discussed

Vasopressin and oxytocin receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Vasopressin (AVP) and oxytocin (OT) receptors (nomenclature as recommended by NC-IUPHAR [92]) are activated by the endogenous cyclic nonapeptides vasopressin and oxytocin. These peptides are derived from precursors which also produce neurophysins (neurophysin I for oxytocin; neurophysin II for vasopressin). Vasopressin and oxytocin differ at only 2 amino acids (positions 3 and 8). There are metabolites of these neuropeptides that may be biologically active [67]