Off-forward parton distributions and impact parameter dependence of parton structure

The connection between parton distributions as a function of the impact parameter and off-forward parton distributions is discussed in the limit of vanishing skewedness parameter $\zeta$, i.e. when the off-forwardness is purely transverse. For the $2^{nd}$ moment it is also illustrated how to relate $\zeta\neq 0$ data to $\zeta=0$ data, which is important for experimental measurements of these observables.Comment: invited talk presented at `Light-Cone Meeting on Non-Perturbative QCD and Hadron Phenomenology', Heidelberg, June 2000, 10 pages, elsart.st

Well-rounded equivariant deformation retracts of Teichm\"uller spaces

In this paper, we construct spines, i.e., \Mod_g-equivariant deformation retracts, of the Teichm\"uller space \T_g of compact Riemann surfaces of genus $g$. Specifically, we define a \Mod_g-stable subspace $S$ of positive codimension and construct an intrinsic \Mod_g-equivariant deformation retraction from \T_g to $S$. As an essential part of the proof, we construct a canonical \Mod_g-deformation retraction of the Teichm\"uller space \T_g to its thick part \T_g(\varepsilon) when $\varepsilon$ is sufficiently small. These equivariant deformation retracts of \T_g give cocompact models of the universal space \underline{E}\Mod_g for proper actions of the mapping class group \Mod_g. These deformation retractions of \T_g are motivated by the well-rounded deformation retraction of the space of lattices in $\R^n$. We also include a summary of results and difficulties of an unpublished paper of Thurston on a potential spine of the Teichm\"uller space.Comment: A revised version. L'Enseignement Mathematique, 201

A Comparison of Teaching Models in the West and in China

Models of teaching commonly used in the West and in China are analyzed and compared, using an analytical approach that systematically considers different aspects of the models. The purpose of the exploration is three-fold: (a) to create better understanding of both Chinese and Western models, for mutual insight and to strengthen the development of pedagogical theory building in China; (b) to guide a joint project between the Netherlands and China relative to the development computer-related learning resources for China; and (c) to contribute to better overall understanding of how instructional resources can be adapted for use in both Western and Chinese situations. The analysis provides a contribution for each of these goals