1,265 research outputs found
What is the Entanglement Length in a Polymer Melt ?
We present results of molecular dynamics simulations of very long model
polymer chains analyzed by various experimentally relevant techniques. The
segment motion of the chains is found to be in very good agreement with the
repatation model. We also calculated the plateau-modulus G_N. The predicitions
of the entanglement length N_e from G_N and from the mean square displacements
of the chains segments disagree by a factor of about 2.2(2), indicating an
error in the prefactor in the standard formula for G_N. We show that recent
neutron spin echo measurements were carried out for chain lengths which are too
small for a correct determination of N_e.Comment: 5 pages, 4 figures, RevTe
h-deformation of Gr(2)
The -deformation of functions on the Grassmann matrix group is
presented via a contraction of . As an interesting point, we have seen
that, in the case of the -deformation, both R-matrices of and
are the same
Evaluating causal psychological models: A study of language theories of autism using a large sample
We used a large convenience sample (n = 22,223) from the Simons Powering Autism Research (SPARK) dataset to evaluate causal, explanatory theories of core autism symptoms. In particular, the data-items collected supported the testing of theories that posited altered language abilities as cause of social withdrawal, as well as alternative theories that competed with these language theories. Our results using this large dataset converge with the evolution of the field in the decades since these theories were first proposed, namely supporting primary social withdrawal (in some cases of autism) as a cause of altered language development, rather than vice versa.To accomplish the above empiric goals, we used a highly theory-constrained approach, one which differs from current data-driven modeling trends but is coherent with a very recent resurgence in theory-driven psychology. In addition to careful explication and formalization of theoretical accounts, we propose three principles for future work of this type: specification, quantification, and integration. Specification refers to constraining models with pre-existing data, from both outside and within autism research, with more elaborate models and more veridical measures, and with longitudinal data collection. Quantification refers to using continuous measures of both psychological causes and effects, as well as weighted graphs. This approach avoids “universality and uniqueness” tests that hold that a single cognitive difference could be responsible for a heterogeneous and complex behavioral phenotype. Integration of multiple explanatory paths within a single model helps the field examine for multiple contributors to a single behavioral feature or to multiple behavioral features. It also allows integration of explanatory theories across multiple current-day diagnoses and as well as typical development
h-deformation of GL(1|1)
h-deformation of (graded) Hopf algebra of functions on supergroup GL(1|1) is
introduced via a contration of GL_q (1|1). The deformation parameter h is odd
(grassmann). Related differential calculus on h-superplane is presented.Comment: latex file, 8 pages, minor change
Tensor Operators for Uh(sl(2))
Tensor operators for the Jordanian quantum algebra Uh(sl(2)) are considered.
Some explicit examples of them, which are obtained in the boson or fermion
realization, are given and their properties are studied. It is also shown that
the Wigner-Eckart's theorem can be extended to Uh(sl(2)).Comment: 11pages, LaTeX, to be published in J. Phys.
Deformed Minkowski spaces: clasification and properties
Using general but simple covariance arguments, we classify the `quantum'
Minkowski spaces for dimensionless deformation parameters. This requires a
previous analysis of the associated Lorentz groups, which reproduces a previous
classification by Woronowicz and Zakrzewski. As a consequence of the unified
analysis presented, we give the commutation properties, the deformed (and
central) length element and the metric tensor for the different spacetime
algebras.Comment: Some comments/misprints have been added/corrected, to appear in
Journal of Physics A (1996
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