RESUMEN
Direct production of electron-positron pairs in two-photon collisions, the Breit-Wheeler process, is one of the basic processes in the universe. However, it has never been directly observed in the laboratory because of the absence of the intense γ-ray sources. Laser-induced synchrotron sources emission may open a way to observe this process. The feasibility of an experimental setup using a MeV photon source is studied in this paper. We compare several γ-ray sources and estimate the expected number of electron-positron pairs and competing processes by using numerical simulations including quantum electrodynamic effects.
RESUMEN
We report on the first self-consistent numerical study of the feasibility of laser-driven relativistic pair shocks of prime interest for high-energy astrophysics. Using a QED-particle-in-cell code, we simulate the collective interaction between two counterstreaming electron-positron jets driven from solid foils by short-pulse (~60 fs), high-energy (~100 kJ) lasers. We show that the dissipation caused by self-induced, ultrastrong (>10^{6} T) electromagnetic fluctuations is amplified by intense synchrotron emission, which enhances the magnetic confinement and compression of the colliding jets.
RESUMEN
Morbidity registration by a network of sentinel general practitioners (SGPs) in Belgium raises a number of problems related to possible biases in the network procedure, such as unequal geographical distribution, non-participation of a segment of the target population of practitioners and difficulties in the estimation of the denominator population at risk for the health problems under study. Through the application of two hierarchical clustering procedures, the initial number of 43 districts in the country has been reduced to 15 homogeneous district clusters. These represent the new geographical framework from which the geographical spread of the network is checked. This network is subsequently corrected for such socio-demographic parameters as age, sex and occupation in order to match more closely the total population of Belgian general practitioners (GPs). The population covered by the network is estimated on the basis of the annual number of patient contacts. Application of the described procedures should result in a network allowing valid estimations for a number of health issues as seen by Belgian GPs.
