198 research outputs found
Bounds on the dimension of linear series on stable curves
We study the dimension of linear series on stable curves. In the first part,
we show that a general linear series with semistable multidegree is not
special, and obtain results on the dimension of the special loci in the Picard
scheme. In the process, we give a new characterization of semistability when
the total degree equals the genus of the curve. In the second part, we give a
generalization of Clifford's inequality to linear series of uniform multidegree
and show that the new bound is achieved on every stable curve.Comment: 23 pages, 4 Figure
Combinatorics of compactified universal Jacobians
We use orientations on stable graphs to express the combinatorial structure
of the compactified universal Jacobians in degrees g-1 and g over the moduli
space of stable curves, \Mgb, and construct for them graded stratifications
compatible with the one of \Mgb. In particular, for a stable curve we exhibit
graded stratifications of the compactified Jacobians in terms of totally
cyclic, respectively rooted, orientations on subgraphs of its dual graph.Comment: Final version, to appear in Advances in Mathematics. 41 page
On the Severi problem in arbitrary characteristic
We show that Severi varieties parametrizing irreducible reduced planar curves
of given degree and geometric genus are either empty or irreducible in any
characteristic. As a consequence, we generalize Zariski's theorem to positive
characteristic and show that a general reduced planar curve of given geometric
genus is nodal. As a byproduct, we obtain the first proof of the irreducibility
of the moduli space of smooth projective curves of given genus in positive
characteristic, that does not involve a reduction to the characteristic zero
case.Comment: 34 pages, 9 figures. Comments are welcome
A Clifford inequality for semistable curves
Let be a semistable curve and a line bundle whose multidegree is
uniform, i.e., in the range between those of the structure sheaf and the
dualizing sheaf of . We establish an upper bound for , which
generalizes the classic Clifford inequality for smooth curves. The bound
depends on the total degree of and connectivity properties of the dual
graph of . It is sharp, in the sense that on any semistable curve there
exist line bundles with uniform multidegree that achieve the bound.Comment: This was formerly the second part of arxive:2005.12817. It is
rewritten to fix a gap in the previous proof. Main results are unchanged, but
auxiliary ones have been replaced. 17 pages, 4 Figure
The Inositol- 1,4,5=Trisphosphate System Is Involved in Rapid Effects of Aldosterone in Human Mononuclear Leukocytes
There is increasing evidence for rapid steroid action on electrolyte transport in human mononuclear leukocytes (HML). In HML, aldosterone stimulates the Na+/H+ antiporter within a few minutes. Because a variety of hormones and growth factors activate the Na+/H+ antiporter via protein kinase C and inositol phospholipids, a possible involvement of inositol-1,4,5-trisphosphate (IP3) in the rapid effects of aldosterone in HML was investigated. The stimulation of IP3 generation was started by the addition of aldosterone, concanavalin A, or other steroids. A significant increase in IP3 levels by aldosterone (1 nmol/L, P < 0.05) was found after 1 min, similar to that found after concanavalin A (25 micrograms/mL). Aldosterone caused a concentration-dependent elevation of IP3 levels, with an apparent EC50 of approximately 0.1 nmol/L. Fludrocortisone stimulated IP3 generation at similar concentrations, whereas a weaker IP3 stimulation by glucocorticoids (hydrocortisone, dexamethasone) occurred at micromolar concentrations only. Canrenone, a potent inhibitor of classical aldosterone action, was not effective up to a concentration of 100 nmol/L. These findings show kinetic and pharmacological similarities with both the functional data on Na+/H+ antiport stimulation by aldosterone and the studies of 125I-aldosterone binding to plasma membranes of HML. Thus, these data are the first to indicate an involvement of the phosphoinositide pathway in the rapid membrane effects of aldosterone
Degeneration of curves on some polarized toric surfaces
We address the following question: Given a polarized toric surface (S,L), and
a general integral curve C of geometric genus g in the linear system |L|, do
there exist degenerations of C in |L| to general integral curves of smaller
geometric genera? We give an affirmative answer to this question for surfaces
associated to h-transverse polygons, provided that the characteristic of the
ground field is large enough. We give examples of surfaces in small
characteristic, for which the answer to the question is negative. In case the
answer is affirmative, we deduce that a general curve C as above is nodal. In
characteristic 0, we use the result to show irreducibility of Severi varieties
of a large class of polarized toric surfaces with h-transverse polygon.Comment: v1: 34 pages, 11 figures. v2: improved the bound on the
characteristic, the result is now sharp for characteristic at least 3. 35
pages, 12 figures. Comments are welcome
Compactified Jacobians as Mumford models
We show that relative compactified Jacobians of one-parameter smoothings of a
nodal curve of genus g, as constructed by Caporaso, Esteves, and Simpson, are
Mumford models of the generic fiber. Each such model is given by an admissible
polytopal decomposition of the skeleton of the Jacobian. We describe the
decompositions corresponding to compactified Jacobians explicitly in terms of
the auxiliary stability data and find, in particular, that the Simpson
compactified Jacobian in degree g is induced by the tropical break divisor
decomposition.Comment: 23 page
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