Block-Transitive Designs in Affine Spaces

This paper deals with block-transitive $t$-$(v,k,\lambda)$ designs in affine spaces for large $t$, with a focus on the important index $\lambda=1$ case. We prove that there are no non-trivial 5-$(v,k,1)$ designs admitting a block-transitive group of automorphisms that is of affine type. Moreover, we show that the corresponding non-existence result holds for 4-$(v,k,1)$ designs, except possibly when the group is one-dimensional affine. Our approach involves a consideration of the finite 2-homogeneous affine permutation groups.Comment: 10 pages; to appear in: "Designs, Codes and Cryptography

Combined potential of future long-baseline and reactor experiments

We investigate the determination of neutrino oscillation parameters by experiments within the next ten years. The potential of conventional beam experiments (MINOS, ICARUS, OPERA), superbeam experiments (T2K, NOvA), and reactor experiments (D-CHOOZ) to improve the precision on the ``atmospheric'' parameters $\Delta m^2_{31}$, $\theta_{23}$, as well as the sensitivity to $\theta_{13}$ are discussed. Further, we comment on the possibility to determine the leptonic CP-phase and the neutrino mass hierarchy if $\theta_{13}$ turns out to be large.Comment: 4 pages, 4 figures, Talk given by T.S. at the NOW2004 workshop, Conca Specchiulla (Otranto, Italy), 11--17 Sept. 200

Tetravalent Colloids by Nematic Wetting

In an elegant paper, D. Nelson suggested a method to produce tetravalent colloids based on a tetrahedral configuration created on the surface of a spherical particle. It emerges from a two-dimensional nematic liquid crystal placed on a sphere due to the presence of four 1/2 disclinations, i.e., topological defects in the orientational order. In this paper we show that such a tetrahedral configuration also occurs in the wetting layers which form around spheres dispersed in a liquid crystal above the nematic-isotropic phase transition. Nematic wetting therefore offers an alternative route towards tetravalent colloids.Comment: 7 pages, 4 figures, submitted to Europhys. Let

Stimulated emission and excited-state absorption at room temperature on the 550 nm-laser transition in Er3+ doped YAlO3

A pump- and probe-beam technique is used for measuring time-resolved and cw-pumped excited-state absorption (ESA) and stimulated-emission (SE) spectra of Er3+:YAlO3 with high resolution. In combination with absorption and fluorescence spectra, detailed information on the wavelengths and cross-sections of ESA and SE at the 550 nm laser transition is provided

East African pholcid spiders: an overview, with descriptions of eight new species (Araneae, Pholcidae)

This paper summarizes current knowledge about East African pholcids. East Africa is defined as the area from 12°S to 5°N and from 28° to 42°E, including all of Uganda, Kenya, Burundi, Rwanda, and Tanzania. An annotated list of the 15 genera and 87 species recorded from this area is given, together with distribution maps and an identification key to genera. Most East African species (90%) belong to one of only six genera: Buitinga Huber, 2003 (21 species); Smeringopus Simon, 1890 (18); Pholcus Walckenaer, 1805 (17); Spermophora Hentz, 1841 (12); Leptopholcus Simon, 1893 (5) and Quamtana Huber, 2003 (4). Eight species for which DNA sequence data have been published recently are newly described: Buitinga batwa sp. nov., B. wataita sp. nov., Spermophora mau sp. nov., S. maathaiae sp. nov., S. bukusu sp. nov., S. kirinyaga sp. nov., S. kyambura sp. nov. and Quamtana nyahururu sp. nov. Crossopriza johncloudsleyi Deeleman-Reinhold & van Harten, 2001, previously only known from Yemen, is redescribed based on specimens from Kenya. Additional new records are given for 21 previously described species