3,714 research outputs found
Higher Descent Data as a Homotopy Limit
We define the 2-groupoid of descent data assigned to a cosimplicial
2-groupoid and present it as the homotopy limit of the cosimplicial space
gotten after applying the 2-nerve in each cosimplicial degree. This can be
applied also to the case of -groupoids thus providing an analogous
presentation of "descent data" in higher dimensions.Comment: Appeared in JHR
The hypertoric intersection cohomology ring
We present a functorial computation of the equivariant intersection
cohomology of a hypertoric variety, and endow it with a natural ring structure.
When the hyperplane arrangement associated with the hypertoric variety is
unimodular, we show that this ring structure is induced by a ring structure on
the equivariant intersection cohomology sheaf in the equivariant derived
category. The computation is given in terms of a localization functor which
takes equivariant sheaves on a sufficiently nice stratified space to sheaves on
a poset.Comment: Significant revisions in Section 5, with several corrected proof
Nitrogen storage and use of biochemical indices to assess nitrogen deficiency and growth rate in natural plankton populations
Various newly developed indicators of N deficiency, physiological state (approximate growth rate), and N source for growth were measured during five cruises to Dabob Bay, Washington from early spring to summer. Although nitrate and ammonium in the surface layer were depleted early in the spring, the plankton populations never became extremely N deficient, as indicated by high intracellular amino acid/protein ratios. However, growth rates, estimated from protein/DNA or RNA/DNA ratios, were usually low unless nitrate concentrations were high or had recently been high, as indicated by large intracellular nitrate pools or high nitrate reductase activities. High growth rates were observed during the spring bloom or as a result of the sporadic supply of nitrate to the euphotic zone, which was inferred from measurements of biochemical indicators on several cruises after the spring bloom. The sporadic supply of nitrate could account for the lack of N deficiency in these populations and mask diel periodicity in N utilization. These results demonstrate that biochemical indicators can be easily measured in the field and that variations in indicators such as intracellular amino acid/protein, protein/DNA, RNA/DNA ratios, NR activities and intracellular nitrate concentrations are an aid in understanding plankton dynamics
Leibniz 2-algebras and twisted Courant algebroids
In this paper, we give the categorification of Leibniz algebras, which is
equivalent to 2-term sh Leibniz algebras. They reveal the algebraic structure
of omni-Lie 2-algebras introduced in \cite{omniLie2} as well as twisted Courant
algebroids by closed 4-forms introduced in \cite{4form}.
We also prove that Dirac structures of twisted Courant algebroids give rise
to 2-term -algebras and geometric structures behind them are exactly
-twisted Lie algebroids introduced in \cite{Grutzmann}.Comment: 22 pages, to appear in Comm. Algebr
Glycoprotein Ib activation by thrombin stimulates the energy metabolism in human platelets
<div><p>Thrombin-induced platelet activation requires substantial amounts of ATP. However, the specific contribution of each ATP-generating pathway <i>i</i>.<i>e</i>., oxidative phosphorylation (OxPhos) versus glycolysis and the biochemical mechanisms involved in the thrombin-induced activation of energy metabolism remain unclear. Here we report an integral analysis on the role of both energy pathways in human platelets activated by several agonists, and the signal transducing mechanisms associated with such activation. We found that thrombin, Trap-6, arachidonic acid, collagen, A23187, epinephrine and ADP significantly increased glycolytic flux (3–38 times <i>vs</i>. non-activated platelets) whereas ristocetin was ineffective. OxPhos (33 times) and mitochondrial transmembrane potential (88%) were increased only by thrombin. OxPhos was the main source of ATP in thrombin-activated platelets, whereas in platelets activated by any of the other agonists, glycolysis was the principal ATP supplier. In order to establish the biochemical mechanisms involved in the thrombin-induced OxPhos activation in platelets, several signaling pathways associated with mitochondrial activation were analyzed. Wortmannin and LY294002 (PI3K/Akt pathway inhibitors), ristocetin and heparin (GPIb inhibitors) as well as resveratrol, ATP (calcium-release inhibitors) and PP1 (Tyr-phosphorylation inhibitor) prevented the thrombin-induced platelet activation. These results suggest that thrombin activates OxPhos and glycolysis through GPIb-dependent signaling involving PI3K and Akt activation, calcium mobilization and protein phosphorylation.</p></div
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