We provide a complete description of normal affine varieties with effective algebraic torus action in terms of what we call proper polyhedral divisors on semiprojective varieties. Our approach extends classical cone constructions of Dolgachev, Demazure and Pinkham to the multigraded case, and it comprises the theory of affine toric varieties.
Given a lattice polytope Q ⊆ IR n , we define an affine schemeM that reflects the possibilities of splitting Q into a Minkowski sum.On the other hand, Q induces a toric Gorenstein singularity Y , and we construct a flat family overM with Y as special fiber. In case Y has an isolated singularity only, this family is versal.Using coordinates of IR n the g ε,k (t) turn into regular polynomials -for each pair (ε, k) we will get two linearly independent ones.We obtain an idealwhich defines an affine closed subschemeExample: For our hexagon Q 6 introduced in (2.1) we obtainOf course, finally many equations are sufficient to generate the ideal J -but we can
We have studied the binding of 1 ,lo-phenanthroline to specifically active-site cobalt(I1)-substituted horse-liver alcohol dehydrogenase [Co(II)-LADH]. The dissociation constant is a factor of 6500 smaller than in the native enzyme. Spectral evidence is given which shows that 1 ,lo-phenanthroline does not remove the catalytic Co(I1) ion and that binding of 1 ,I 0-phenanthroline renders the catalytic metal ion pentacoordinate. The maximum limiting rate constant for the association of 1,lO-phenanthroline to Co(I1)-LADH is about 60 s -' . This is about a third of the value (1 69 s-') determined for native horse-liver alcohol dehydrogenase, Zn(1I)LADH [Frolich et al. (1978) Arch. Biochem. Biuphys. 189,471 -4801. For cadmium(l1)-substituted horse-liver alcohol dehydrogenase, [Cd(II)LADH] the maximum limiting rate constant for association of 1 ,lo-phenanthroline increased to 590 s-'. These findings demonstrate that the rate-limiting step is strongly dependent on the chemical nature of the catalytic metal ion and its immediate environment. 1,lO-Phenanthroline is shown to bind to the Co(I1)-LADH . NAD' complex in the open conformation. The maximum limiting rate constant remains unchanged in the presence of NAD'. The data have been used to derive a kinetic scheme for the formation of ternary complexes including NAD' that involves a slow intermediary step.
Generalizing the passage from a fan to a toric variety, we provide a combinatorial approach to construct arbitrary effective torus actions on normal, algebraic varieties. Based on the notion of a "proper polyhedral divisor" introduced in earlier work, we develop the concept of a "divisorial fan" and show that these objects encode the equivariant gluing of affine varieties with torus action. We characterize separateness and completeness of the resulting varieties in terms of divisorial fans, and we study examples like C * -surfaces and projectivizations of (nonsplit) vector bundles over toric varieties.
SUMMARYThe production of cytokines by lymphoid cells, isolated from non-infected and Haemonchus contortus-infected lambs, was investigated. Particular attention was paid to differences in T helper 1-(Th1) and Th2-type immune pro®les between genetically resistant and random-bred animal groups. Non-infected resistant and random-bred lambs produced equivalent levels of interferon-c (IFN-c) and interleukin-5 (IL-5), from isolated abomasal lymph node cells (ALN), mesenteric lymph node cells (MLN) and spleen cells (SC), in response to in vitro stimulation with T-cell mitogen (concanavalin A) or larval parasite antigen. ALN and MLN cells derived from infected resistant and random-bred lambs produced relatively lower levels of IFN-c, following in vitro stimulation with parasite antigen, when compared with their uninfected counterparts. In contrast, infected lambs of both groups showed enhanced mitogen-and antigen-stimulated production of IL-5, in comparison with uninfected controls, at days 5 and 28 postinfection (p.i.). Mitogen-and antigenstimulated IL-5 responses were higher among resistant lambs compared with random-bred lambs, with the highest overall production of IL-5 by parasite antigen-stimulated ALN and MLN cells. Among day 28 p.i. lambs, levels of cell culture-derived parasite-speci®c immunoglobulin G1 (IgG1) and IgE antibodies were higher in resistant lambs than in random-bred lambs, following in vitro stimulation of SC or ALN cells with parasite antigen. Finally, after 28 days p.i., histological examination of abomasal tissue revealed higher densities of mast cells and eosinophils in the mucosa of resistant lambs than in random-bred lambs. Taken together, these data support the notion of a strong Th2-type immune response to Haemonchus infection in genetically resistant sheep, and support the claim for a Th1/Th2 dichotomy in ruminants.
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