1,332 research outputs found
FAKTOR-FAKTOR YANG MEMPENGARUHI EFEKTIVITAS GABUNGAN KELOMPOK TANI (GAPOKTAN) DALAM PROGRAM PENGEMBANGAN USAHA AGRIBISNIS PERDESAAN (PUAP) DI KECAMATAN PEDAN KABUPATEN KLATEN
n this paper we give the full classification of curves of genus such that a Brill--Noether locus , strictly contained in the jacobian of , contains a variety stable under translations by the elements of a positive dimensional abelian subvariety and such that , i.e., the maximum possible dimension for such a
On the Hilbert scheme of curves in higher-dimensional projective space
In this paper we prove that, for any , there exist infinitely many
and for each of them a smooth, connected curve in such
that lies on exactly irreducible components of the Hilbert scheme
\hilb(\P^r). This is proven by reducing the problem to an analogous statement
for the moduli of surfaces of general type.Comment: latex, 12 pages, no figure
Prym varieties and the canonical map of surfaces of general type
Let X be a smooth complex surface of general type such that the image of the
canonical map of X is a surface and that has degree
. Let be a desingularization of
and assume that the geometric genus of S is not zero. Beauville has
proved that in this case S is of general type and is the canonical
map of S. Beauville has also constructed the only infinite series of examples
with the above properties that was known up to now. Starting
from his construction, we define a {\em good generating pair}, namely a pair
where h is a finite morphism of surfaces and L is a nef and big
line bundle of W satisfying certain assumptions. We show that by applying a
construction analogous to Beauville's to a good generating pair one obtains an
infinite series of surfaces of general type whose canonical map is 2-to-1 onto
a canonically embedded surface. In this way we are able to construct more
infinite series of such surfaces. In addition, we show that good generating
pairs have bounded invariants and that there exist essentially only 2 examples
with . The key fact that we exploit for obtaining these results is
that the Albanese variety P of V is a Prym variety and that the fibre of the
Prym map over P has positive dimension.Comment: 40 pages, LaTeX 2.0
Spin-stiffness of anisotropic Heisenberg model on square lattice and possible mechanism for pinning of the electronic liquid crystal direction in YBCO
Using series expansions and spin-wave theory we calculate the spin-stiffness
anisotropy in Heisenberg models on the square lattice
with anisotropic couplings . We find that for the weakly anisotropic
spin-half model (), deviates
substantially from the naive estimate . We
argue that this deviation can be responsible for pinning the electronic liquid
crystal direction, a novel effect recently discovered in YBCO. For
completeness, we also study the spin-stiffness for arbitrary anisotropy
for spin-half and spin-one models. In the limit of ,
when the model reduces to weakly coupled chains, the two show dramatically
different behavior. In the spin-one model, the stiffness along the chains goes
to zero, implying the onset of Haldane-gap phase, whereas for spin-half the
stiffness along the chains increases monotonically from a value of
for towards for . Spin-wave theory is
extremely accurate for spin-one but breaks down for spin-half presumably due to
the onset of topological terms.Comment: 6 pages, 3 figure
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