Purely radiative irrotational dust spacetimes

We consider irrotational dust spacetimes in the full non-linear regime which are "purely radiative" in the sense that the gravitational field satisfies the covariant transverse conditions div(H) = div(E) = 0. Within this family we show that the Bianchi class A spatially homogeneous dust models are uniquely characterised by the condition that $H$ is diagonal in the shear-eigenframe.Comment: 6 pages, ERE 2006 conference, minor correction

Reversible implementation of a disrete linear transformation

Discrete linear transformations form important steps in processing information. Many such transformations are injective and therefore are prime candidates for a physically reversible implementation into hardware. We present here the first steps towards a reversible digital implementation of two different integer transformations on four inputs: The Haar wavelet and the H.264 transform

Birefringent filter design

A birefringent filter is provided for tuning the wavelength of a broad band emission laser. The filter comprises thin plates of a birefringent material having thicknesses which are non-unity, integral multiples of the difference between the thicknesses of the two thinnest plates. The resulting wavelength selectivity is substantially equivalent to the wavelength selectivity of a conventional filter which has a thinnest plate having a thickness equal to this thickness difference. The present invention obtains an acceptable tuning of the wavelength while avoiding a decrease in optical quality associated with conventional filters wherein the respective plate thicknesses are integral multiples of the thinnest plate

New sum rules for nucleon and trinucleon total photoproduction cross-sections

Two new sum rules are derived relating Dirac radii and anomalous magnetic moments of the considered strongly interacting fermions with the convergent integral over a difference of the total proton and neutron, as well as $He^3$ and $H^3$, photoproduction cross-sections.Comment: 1 eps figure. Contribution presented at the PHOTON'03, April 7-11, 2003, Frascati (Roma), Ital

Anàlisi comparativa de les diferents tipologies de xarxes de metro existents al món. Establiment d’uns paràmetres i metodologia de comparació

Un gran nombre de ciutats d’arreu del món disposen de sistemes ferroviaris metropolitans, coneguts popularment en molts indrets com a metro, que permeten transportar en general una gran quantitat de gent de forma més sostenible i eficient que amb el transport individual. Ara bé aquests sistemes són molt variats ja que presenten una gran diversitat de característiques tècniques i de prestacions de servei. La denominació dels diferents sistemes és molt confosa i sovint sistemes amb característiques ben diferents s’anomenen de la mateixa forma, alguns cops perquè la frontera entre els diferents modes no és molt clara i altres perquè es vol associar aquell mode a un transport ràpid, freqüent i que permeti transportar grans quantitats de gent, i aquestes tres qualitats per a molta gent estan associades a la paraula “metro”

H&H Committee Interest Responses

Survey responses as to the future of the H&H Committe