34,849 research outputs found

    Nutritional characteristics of moon dust for soil microorganisms

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    Approximately 46% of the lunar sample (10084,151), 125.42 mg, was solubilized in 680 ml 0.01 M salicylic acid. Atomic absorption spectroscopic analysis of the solubilized lunar sample showed the following amount of metal ions: Ca, 3.1; Mg, 4.0; K, 0.09; Na, 0.67; Fe, 7.3; Mn, 1.6; Cu, Ni, Cr, less than 0.1 each. All are in ppm. Salicylic acid used to solubilize the lunar sample was highly inhibitory to the growth of mixed soil microbes. However, the mineral part of the lunar extract stimulated the growth. For optimal growth of the soil microbes the following nutrients must be added to the moon extract; sources of carbon, nitrogen, sulfur, phosphorus, and magnesium in addition to water

    Global modeling study of potentially bioavailable iron input from shipboard aerosol sources to the ocean

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    Iron (Fe) is an essential element for phytoplankton. The majority of iron is transported from arid and semiarid regions to the open ocean, but it is mainly in an insoluble form. Since most aquatic organisms can take up iron only in the dissolved form, aerosol iron solubility is a key factor that can influence the air-sea CO2 fluxes and thus climate. Field observations have shown relatively high iron solubility in aerosols influenced by combustion sources, but specific emissions sources and their contributions to deposition fluxes largely remain uncertain. Here, a global chemical transport model is used to investigate the effect of aerosol emissions from ship plumes on iron solubility in particles from the combustion and dust sources. The model results reveal that the oil combustion from shipping mainly contributes to high iron solubility (> 10%) at low iron loading (1-110 ng m-3) observed over the high latitude North Atlantic Ocean, rather than the other combustion sources from continental industrialized regions. Due to continuing growth in global shipping and no regulations regarding particles emissions over the open ocean, the input of potentially bioavailable iron from ship plumes is likely to increase during the next century. The model results suggest that deposition of soluble iron from ships in 2100 contributes 30-60% of the soluble iron deposition over the high latitude North Atlantic and North Pacific

    Reconfiguration of Dominating Sets

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    We explore a reconfiguration version of the dominating set problem, where a dominating set in a graph GG is a set SS of vertices such that each vertex is either in SS or has a neighbour in SS. In a reconfiguration problem, the goal is to determine whether there exists a sequence of feasible solutions connecting given feasible solutions ss and tt such that each pair of consecutive solutions is adjacent according to a specified adjacency relation. Two dominating sets are adjacent if one can be formed from the other by the addition or deletion of a single vertex. For various values of kk, we consider properties of Dk(G)D_k(G), the graph consisting of a vertex for each dominating set of size at most kk and edges specified by the adjacency relation. Addressing an open question posed by Haas and Seyffarth, we demonstrate that DΓ(G)+1(G)D_{\Gamma(G)+1}(G) is not necessarily connected, for Γ(G)\Gamma(G) the maximum cardinality of a minimal dominating set in GG. The result holds even when graphs are constrained to be planar, of bounded tree-width, or bb-partite for b3b \ge 3. Moreover, we construct an infinite family of graphs such that Dγ(G)+1(G)D_{\gamma(G)+1}(G) has exponential diameter, for γ(G)\gamma(G) the minimum size of a dominating set. On the positive side, we show that Dnm(G)D_{n-m}(G) is connected and of linear diameter for any graph GG on nn vertices having at least m+1m+1 independent edges.Comment: 12 pages, 4 figure

    Reconfiguration on sparse graphs

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    A vertex-subset graph problem Q defines which subsets of the vertices of an input graph are feasible solutions. A reconfiguration variant of a vertex-subset problem asks, given two feasible solutions S and T of size k, whether it is possible to transform S into T by a sequence of vertex additions and deletions such that each intermediate set is also a feasible solution of size bounded by k. We study reconfiguration variants of two classical vertex-subset problems, namely Independent Set and Dominating Set. We denote the former by ISR and the latter by DSR. Both ISR and DSR are PSPACE-complete on graphs of bounded bandwidth and W[1]-hard parameterized by k on general graphs. We show that ISR is fixed-parameter tractable parameterized by k when the input graph is of bounded degeneracy or nowhere-dense. As a corollary, we answer positively an open question concerning the parameterized complexity of the problem on graphs of bounded treewidth. Moreover, our techniques generalize recent results showing that ISR is fixed-parameter tractable on planar graphs and graphs of bounded degree. For DSR, we show the problem fixed-parameter tractable parameterized by k when the input graph does not contain large bicliques, a class of graphs which includes graphs of bounded degeneracy and nowhere-dense graphs

    Momentum-Dependent Hybridization Gap and dispersive in-gap state of The Kondo Semiconductor SmB6

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    We report the temperature-dependent three-dimensional angle-resolved photoemission spectra of the Kondo semiconductor SmB6_6. We found a difference in the temperature dependence of the peaks at the X and Γ\Gamma points, due to hybridization between the Sm 5d conduction band and the nearly localized Sm 4f state. The peak intensity at the X point has the same temperature dependence as the valence transition below 120 K, while that at the Γ\Gamma point is consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This suggests that the hybridization with the valence transition mainly occurs at the X point, and the initial state of the magnetic excitation is located at the Γ\Gamma point.Comment: 5 pages, 3 figure

    Formation of Hot Planets by a combination of planet scattering, tidal circularization, and Kozai mechanism

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    We have investigated the formation of close-in extrasolar giant planets through a coupling effect of mutual scattering, Kozai mechanism, and tidal circularization, by orbital integrations. We have carried out orbital integrations of three planets with Jupiter-mass, directly including the effect of tidal circularization. We have found that in about 30% runs close-in planets are formed, which is much higher than suggested by previous studies. We have found that Kozai mechanism by outer planets is responsible for the formation of close-in planets. During the three-planet orbital crossing, the Kozai excitation is repeated and the eccentricity is often increased secularly to values close enough to unity for tidal circularization to transform the inner planet to a close-in planet. Since a moderate eccentricity can remain for the close-in planet, this mechanism may account for the observed close-in planets with moderate eccentricities and without nearby secondary planets. Since these planets also remain a broad range of orbital inclinations (even retrograde ones), the contribution of this process would be clarified by more observations of Rossiter-McLaughlin effects for transiting planets.Comment: 15 pages, 16 figures, Accepted for publication in Ap