Polarization Phenomena in Small-Angle Photoproduction of e+e- Pairs and the Gerasimov-Drell-Hearn Sum Rule

Photoproduction of $e^+e^-$ pairs at small angles is investigated as a tool to determine the functions $f_1$ and $f_2$ entering the real-photon forward Compton scattering amplitude. The method is based on an interference of the Bethe-Heitler and the virtual Compton scattering mechanisms, generating an azimuthal asymmetry in the $e^+$ versus $e^-$ yield. The general case of a circularly polarized beam and a longitudinally polarized target allows one to determine both the real and imaginary parts of $f_1$ as well as $f_2$. The imaginary part of $f_2$ requires target polarization only. We calculate cross sections and asymmetries of the reaction $p(\gamma,e^+e^-)p$, estimate corrections and backgrounds, and propose suitable kinematical regions to perform the experiment. Our investigation shows that photoproduction of $e^+e^-$-pairs off the proton and light nuclei may serve as a rather sensitive test of the validity of the Gerasimov-Drell-Hearn sum rule.Comment: 22 pages; revtex; 5 postscript figures included in submission; submitted to Phys. Rev.

Real-Time PCR in HIV/Trypanosoma cruzi Coinfection with and without Chagas Disease Reactivation: Association with HIV Viral Load and CD4+ Level

Chagas disease is endemic in Latin America and is caused by the flagellate protozoan T. cruzi. The acute phase is asymptomatic in the majority of the cases and rarely causes inflammation of the heart or the central nervous system. Most infected patients progress to a chronic phase, characterized by cardiac or digestive involvement when not asymptomatic. However, when patients are also exposed to an immunosuppressant (such as chemotherapy), neoplasia, or other infections such as HIV, T. cruzi infection may develop into a severe disease (Chagas disease reactivation) involving the heart and central nervous system. The current microscopic methods for diagnosing Chagas disease reactivation are not sensitive enough to prevent the high rate of death observed in these cases. Therefore, we propose a quantitative method to monitor blood levels of the parasite, which will allow therapy to be administered as early as possible, even if the patient has not yet presented symptoms

Re-evaluating syndicalist opposition to the First World War

It has been argued that support for the First World War by the important French syndicalist organisation, the Confédération Générale du Travail (CGT) has tended to obscure the fact that other national syndicalist organisations remained faithful to their professed workers’ internationalism: on this basis syndicalists beyond France, more than any other ideological persuasion within the organised trade union movement in immediate pre-war and wartime Europe, can be seen to have constituted an authentic movement of opposition to the war in their refusal to subordinate class interests to those of the state, to endorse policies of ‘defencism’ of the ‘national interest’ and to abandon the rhetoric of class conflict. This article, which attempts to contribute to a much neglected comparative historiography of the international syndicalist movement, re-evaluates the syndicalist response across a broad geographical field of canvas (embracing France, Italy, Spain, Ireland, Britain and America) to reveal a rather more nuanced, ambiguous and uneven picture. While it highlights the distinctive nature of the syndicalist response compared with other labour movement trends, it also explores the important strategic and tactical limitations involved, including the dilemma of attempting to translate formal syndicalist ideological commitments against the war into practical measures of intervention, and the consequences of the syndicalists’ subordination of the political question of the war to the industrial struggle