2,147 research outputs found
Lagrangian fibrations of holomorphic-symplectic varieties of K3^[n]-type
Let X be a compact Kahler holomorphic-symplectic manifold, which is
deformation equivalent to the Hilbert scheme of length n subschemes of a K3
surface. Let L be a nef line-bundle on X, such that the 2n-th power of c_1(L)
vanishes and c_1(L) is primitive. Assume that the two dimensional subspace
H^{2,0}(X) + H^{0,2}(X), of the second cohomology of X with complex
coefficients, intersects trivially the integral cohomology. We prove that the
linear system of L is base point free and it induces a Lagrangian fibration on
X. In particular, the line-bundle L is effective. A determination of the
semi-group of effective divisor classes on X follows, when X is projective. For
a generic such pair (X,L), not necessarily projective, we show that X is
bimeromorphic to a Tate-Shafarevich twist of a moduli space of stable torsion
sheaves, each with pure one dimensional support, on a projective K3 surface.Comment: 34 pages. v3: Reference [Mat5] and Remark 1.8 added. Incorporated
improvement to the exposition and corrected typos according to the referees
suggestions. To appear in the proceedings of the conference Algebraic and
Complex Geometry, Hannover 201
JMASM40: Monte Carlo Simulations For Structural Equation Modelling (Revolution R)
Revolution R code is presented to setup Structural Equation Model (SEM) for a Monte Carlo study. The example is a comparison of different fit indices
Does Peer Ability Affect Student Achievement?
Empirical analysis of peer effects on student achievement has been open to question because of the difficulties of separating peer effects from other confounding influences. While most econometric attention has been directed at issues of simultaneous determination of peer interactions, we argue that issues of omitted and mismeasured variables are likely to be more important. We control for the most important determinants of achievement that will confound peer estimates by removing student and school-by-grade fixed effects in addition to observable family and school characteristics. The analysis also addresses the reciprocal nature of peer interactions and the interpretation of estimates based upon models using past achievement as the measure of peer group quality. The results indicate that peer achievement has a positive effect on achievement growth. Moreover, students throughout the school test score distribution appear to benefit from higher achieving schoolmates. On the other hand, the variance in achievement appears to have no systematic effect.
Limitations in the Systematic Analysis of Structural Equation Model Fit Indices
The purpose of this study was to evaluate the sensitivity of selected fit index statistics in determining model fit in structural equation modeling (SEM). The results indicated a large dependency on correlation magnitude of the input correlation matrix, with mixed results when the correlation magnitudes were low and a primary indication of good model fit. This was due to the default SEM method of Maximum Likelihood that assumes unstandardized correlation values. However, this warning is not well-known, and is only obscurely mentioned in some textbooks. Many SEM computer software programs do not give appropriate error indications that the results are unsubstantiated when standardized correlation values are provided
Matrix String Theory and its Moduli Space
The correspondence between Matrix String Theory in the strong coupling limit
and IIA superstring theory can be shown by means of the instanton solutions of
the former. We construct the general instanton solutions of Matrix String
Theory which interpolate between given initial and final string configurations.
Each instanton is characterized by a Riemann surface of genus h with n
punctures, which is realized as a plane curve. We study the moduli space of
such plane curves and find out that, at finite N, it is a discretized version
of the moduli space of Riemann surfaces: instead of 3h-3+n its complex
dimensions are 2h-3+n, the remaining h dimensions being discrete. It turns out
that as tends to infinity, these discrete dimensions become continuous, and
one recovers the full moduli space of string interaction theory.Comment: 30 pages, LaTeX, JHEP.cls class file, minor correction
Multi-Hamiltonian structures for r-matrix systems
For the rational, elliptic and trigonometric r-matrices, we exhibit the links
between three "levels" of Poisson spaces: (a) Some finite-dimensional spaces of
matrix-valued holomorphic functions on the complex line; (b) Spaces of spectral
curves and sheaves supported on them; (c) Symmetric products of a surface. We
have, at each level, a linear space of compatible Poisson structures, and the
maps relating the levels are Poisson. This leads in a natural way to Nijenhuis
coordinates for these spaces. At level (b), there are Hamiltonian systems on
these spaces which are integrable for each Poisson structure in the family, and
which are such that the Lagrangian leaves are the intersections of the
symplective leaves over the Poisson structures in the family. Specific examples
include many of the well-known integrable systems.Comment: 26 pages, Plain Te
Probing F-theory With Multiple Branes
We study multiple 3-branes on an F theory orientifold. The world-volume
theory of the 3-branes is d=4, N=2 Sp(2k) gauge theory with an antisymmetric
tensor and four flavors of matter in the fundamental. The solution of this
gauge theory is found for vanishing bare mass of the antisymmetric tensor
matter, and massive fundamental matter. The integrable system underlying this
theory is constructed.Comment: 9 pages, harvma
Recommended from our members
Loss of testosterone impairs anti-tumor neutrophil function.
In men, the incidence of melanoma rises rapidly after age 50, and nearly two thirds of melanoma deaths are male. The immune system is known to play a key role in controlling the growth and spread of malignancies, but whether age- and sex-dependent changes in immune cell function account for this effect remains unknown. Here, we show that in castrated male mice, neutrophil maturation and function are impaired, leading to elevated metastatic burden in two models of melanoma. Replacement of testosterone effectively normalized the tumor burden in castrated male mice. Further, the aberrant neutrophil phenotype was also observed in prostate cancer patients receiving androgen deprivation therapy, highlighting the evolutionary conservation and clinical relevance of the phenotype. Taken together, these results provide a better understanding of the role of androgen signaling in neutrophil function and the impact of this biology on immune control of malignancies
Curve classes on irreducible holomorphic symplectic varieties
We prove that the integral Hodge conjecture holds for 1-cycles on irreducible
holomorphic symplectic varieties of K3 type and of Generalized Kummer type. As
an application, we give a new proof of the integral Hodge conjecture for cubic
fourfolds.Comment: 15 page
Looking Beyond Looks: Comments on Sloutsky, Kloos, and Fisher (2007)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75080/1/j.1467-9280.2007.01937.x.pd
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