Differential cross section for neutron-proton bremsstrahlung

The neutron-proton bremsstrahlung process $(np \to np\gamma)$ is known to be sensitive to meson exchange currents in the nucleon-nucleon interaction. The triply differential cross section for this reaction has been measured for the first time at the Los Alamos Neutron Science Center, using an intense, pulsed beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered neutrons were observed at six angles between 12$^\circ$ and 32$^\circ$, and the recoil protons were observed in coincidence at 12$^\circ$, 20$^\circ$, and 28$^\circ$ on the opposite side of the beam. Measurement of the neutron and proton energies at known angles allows full kinematic reconstruction of each event. The data are compared with predictions of two theoretical calculations, based on relativistic soft-photon and non-relativistic potential models.Comment: 5 pages, 3 figure

Lifetime Analysis of Reliable Wireless Sensor Networks

A wireless sensor network is comprised of a large number of battery-limited sensor nodes communicating with unreliable radio links. The nodes are deployed in an ad hoc fashion and a reverse multicast tree is formed in the target domain. The sink node disseminates a query and collects responses from the sensors over pre-established links. Survivability in wireless sensor networks reflects the ability of the network to continue to detect events in the case of individual node failures. We present a sender initiated path switching algorithm that enables the immediate sender to change the packet's route dynamically when its parent on the reverse path is down. The overall effect of path switching on the survivability is analyzed as a measure of reliable event delivery. Using independent battery capacities, an analytical model of a multihop network is derived. The model is used to predict the maximum network lifetime in terms of total transmitted messages; which is in turn used to verify the correctness of our simulations. The results have revealed that dynamic path switching has a better performance than static multipath routing and salvaging schemes. It has also been shown that the proposed approach enhances reliability up to 30% in some topologies