A blocking quadruple (BQ) is a quadruple of vertices of a graph such that any two vertices of the quadruple either miss (have no neighbours on) some path connecting the remaining two vertices of the quadruple, or are connected by some path missed by the remaining two vertices. This is akin to the notion of asteroidal triple used in the classical characterization of interval graphs by Lekkerkerk...

In recent work, planar configurations of permanent magnets were proposed as substitutes for conventional current-driven iron quadruples in applications limited by small apefiure sizes and featuring small beam occupation diameters. Important examples include the configuring of focusing lattices in -.. small-gap insetiion devices, and the implementation of compact mini-beta sections on linear or ...

Not a great deal is known about the electrophysiology of category learning. In our study, one group of participants learned novel categories of tropical fish, an exposure group viewed the same stimuli without learning any categories, and a control group did not see the stimuli. All three groups then viewed a sequence of quadruples of fish while their EEG was recorded. In half the quadruples (”d...

Let B(n, ≤ 4) denote the subsets of [n] := {1, 2,. .. , n} of at most 4 elements. Suppose that F is a set system with the property that every member of B can be written as a union of (at most) two members of F. (Then F is called a 2-base of B.) Here we answer a question of Erd˝ os proving that |F | ≥ 1 + n + n 2 − 4 3 n, and this bound is best possible for n ≥ 8.

ABSTRACT Double-close-binary quadruples (2 + 2 systems) are hierarchical systems of four stars where two short-period binary move around their common centre mass on a wider orbit. Using Gaia Early Data Release 3, we search for comoving pairs both components eclipsing binaries. We present eight quadruple with inner orbital periods <0.4 d and outer separations ?1000 au. All these but one n...