Singer quadrangles

[no abstract available

On a homotopy relation between the 2-local geometry and the Bouc complex for the sporadic group Co3

We study the homotopy relation between the standard 2-local geometry and the Bouc complex for the sporadic group Co3. We also give a result concerning the relative projectivity of the reduced Lefschetz module associated to the aformentioned 2-local geometry.Comment: 20 page

On two new classes of semibiplanes

AbstractTwo new infinite classes of semibiplanes are defined by considering for any q = 2h, h > 1, a point-plane pair (p, π) in PG(3, q), a hyperoval O in the star of p and a dual hyperoval O∗ in the plane π in suitable mutual position. These geometries are called of flag type or anti-flag type according to p and π are incident or not. By deleting some suitable elements from the semibiplanes of flag type we obtain another family of semibiplanes. In all of cases some quotients are defined. For q = 4, the semibiplane of anti-flag type is a flag-transitive geometry already given by Pasini and Yoshiara

Microwave properties of (PrxY1−x)Ba2Cu3O7−δ(Pr_xY_{1-x})Ba_2Cu_3O_{7-\delta} : Influence of magnetic scattering

We report measurements of the surface impedance $Z_s=R_s+iX_s$ of $(Pr_xY_{1-x})Ba_2Cu_3O_{7-\delta}$, $(x=0,0.15,0.23,0.3,0.4,0.5)$. Increasing $Pr$ concentration leads to some striking results not observed in samples doped by non-magnetic constituents. The three principal features of the $R_s(T)$ data - multiple structure in the transition, a high residual resistance and, at high $Pr$ concentrations, an upturn of the low $T$ data, are all characteristic of the influence of magnetic scattering on superconductivity, and appear to be common to materials where magnetism and superconductivity coexist. The low $T$ behavior of $\lambda (T)$ appears to change from $T$ to $T^4$ at large $Pr$ doping, and provides evidence of the influence of magnetic pairbreaking of the $Pr$.Comment: 5 pages, 3 eps figures, Revtex, 2-column format, uses graphicx. To appear in Physica C. Postscript version also available at http://sagar.physics.neu.edu/preprints.htm

Flag-transitive L_h.L*-geometries

The classification of finite flag-transitive linear spaces, obtained by Buekenhout, Delandtsheer, Doyen, Kleidman, Liebeck and Saxl [20] at the end of the eighties, gave new impulse to the program of classifying various classes of locally finite flag-transitive geometries belonging to diagrams obtained from a Coxeter diagram by putting a label L or L ∗ on some (possibly, all) of the singlebond strokes for projective planes

Universal and homogeneous embeddings of dual polar spaces of rank 3 defined over quadratic alternative division algebras

Suppose O is an alternative division algebra that is quadratic over some subfield K of its center Z(O). Then with (O, K), there is associated a dual polar space. We provide an explicit representation of this dual polar space into a (6n + 7)-dimensional projective space over K, where n D dim(K)(O). We prove that this embedding is the universal one, provided vertical bar K vertical bar > 2. When O is not an inseparable field extension of K, we show that this universal embedding is the unique polarized one. When O is an inseparable field extension of K, then we determine the minimal full polarized embedding, and show that all homogeneous embeddings are either universal or minimal. We also provide explicit generators of the corresponding projective representations of the little projective group associated with the ( dual) polar space