Occupants in manifolds

Let K be a subset of a smooth manifold M. In some cases functor calculus methods lead to a homotopical formula for M minus K in terms of the subspaces M minus S, where S runs through the finite subsets of K.Comment: There is a sequel to this paper: title "Configuration categories and homotopy automorphisms". v2: some typos corrected, v3: some errors in section 1 corrected. v4: more errors corrected and therefore number of authors increased from 1 to 2. v5: more errors corrected especially in section 3. v6: just a few typos corrected and pointers adde

Dry Friction in the Frenkel-Kontorova-Tomlinson Model: Dynamical Properties

Wearless friction is investigated in a simple mechanical model called Frenkel-Kontorova-Tomlinson model. We have introduced this model in [Phys. Rev. B, Vol. 53, 7539 (1996)] where the static friction has already been considered. Here the model is treated for constant sliding speed. The kinetic friction is calculated numerically as well as analytically. As a function of the sliding velocity it shows many structures which can be understood by varies kinds of phonon resonances (normal, superharmonic and parametric) caused by the so-called "washboard wave". For increasing interaction strength the regular motion becomes chaotic (fluid-sliding state). The fluid sliding state is mainly determined by the density of decay channels of m washboard waves into n phonons. We also find strong bistabilities and coherent motions with superimposed dark envelope solitons which interact nondestructively.Comment: Written in RevTeX, figures in PostScript, appears in Z. Phys.

More Guidance, Better Results? Three-Year Effects of an Enhanced Student Services Program at Two Community Colleges

In a program at Lorain County Community College and Owens Community College in Ohio, low-income students received enhanced counseling and advising services and were eligible to receive a modest stipend for two semesters. The program improved academic outcomes during the second semester and continued to have a positive effect on registration rates in the semester that followed, but it did not have any meaningful effects on academic outcomes in subsequent semesters