Let D be a symmetric design admitting a null polarity such that either all singular lines, or all nonsingular lines, have size (v − λ)/(k − λ); assume that this number is greater than λ in the case of singular lines. Then D is either a projective space or an orthogonal symmetric design. © 2003 Elsevier Ltd. All rights reserved. The Dembowski–Wagner Theorem [3] characterizes projective spaces as...

The X-ray binary system 4U 1907+09 contains an accretion-powered X-ray pulsar in an eccentric orbit around a massive early-type companion star. It has been previously suggested that a trailing gas stream along with strong stellar winds could describe the orbital variations in X-ray flux. In this work, 12 yr of X-ray observations from the Rossi X-ray Timing Explorer/ All-Sky Monitor are analysed...

We show that the spectral properties of a self-amplified spontaneous emission x-ray free-electron laser can be controlled by modulating the gain in magnetic undulators, thus producing one or several spectral lines within a single few femtosecond pulse. By varying the magnetic field along the undulator and the electron beam transport line, the system we demonstrate can tailor the x-ray spectrum ...

We report on a recent Chandra ACIS-S observation of the Circinus galaxy. These observations confirm that the nuclear spectrum results from reflection of a hard X-ray continuum by “neutral” matter. The nuclear X-ray emission is extended by ∼ 60 pc in the general direction of the optical “ionization cone”. An image in the Fe Kα line has been made and shows that this emission extends up to 200 pc ...

Determination of the structure of biological particles, randomly oriented in solution, from spatial correlation analysis of fluctuations in x-ray scattering has recently been proposed. The feasibility of scattering fluctuation measurements was evaluated by using an x-ray synchrotron radiation camera to obtain the spatial correlation for a solution of tobacco mosaic virus along a line. The exper...

Let X be a smooth projective curve over C, and let M X be the moduli space of stable Higgs bundles on X (with genus g > 1), with rank n and fixed determinant ξ, with n and deg(ξ) coprime. Let X ′ and ξ′ be another such curve and line bundle. We prove that if M X and M n,ξ X are isomorphic as algebraic varieties, then X and X ′ are isomorphic.