5,231 research outputs found

    Weights in cohomology and the Eilenberg-Moore spectral sequence

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    We show that in the category of complex algebraic varieties, the Eilenberg--Moore spectral sequence can be endowed with a weight filtration. This implies that it degenerates if all involved spaces have pure cohomology. As application, we compute the rational cohomology of an algebraic GG-variety XX (GG being a connected algebraic group) in terms of its equivariant cohomology provided that HG(X)H_G(X) is pure. This is the case, for example, if XX is smooth and has only finitely many orbits. We work in the category of mixed sheaves; therefore our results apply equally to (equivariant) intersection homology.Comment: 17 pages, final version, to appear in Annales de l'Institute Fourie

    Sodium chloride transport of normal and dietary enlarged rat cecum in vitro

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    Sodium chloride transport across isolated cecum mucosa was investigated in normal rats and rats with adaptive cecum growth induced by dietary polyethylene glycol (PEG). The normal cecum absorbed CI in excess of Na with a small short-circuit current (Isc). Dietary adaptation led to large equivalent increments of Na and Cl net absorption without adequate Ise change. Inhibitor studies (mucosal amiloride 10(-3) and 10(-4) M; mucosal 4,4-diisolhiocyanatostilbene-2,2-disulfonic acid 5 x 10(-5) M;serosal furosemide 10(-3) M;serosal ouabain 10(-3) M) suggested that normal cecal NaCl absorption involves electroneutral Na/N and Cl/HCO3 exchange at the apical and Na-K-ATPase-mediated exit across the basolateral cell membrane. Dietary adaptation stimulates the loosely coupled antiports and possibly activates a small serosally located NaCl cotransport. Comparative histology showed flattening of all tissue layers and widening of crypts in PEG animals. Crypt widening may facilitate ion access to underutilized transport sites and, at least in part, explain the increased absorption of the enlarged cecum
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