Weak Decay of Hypernuclei

The focus of these Lectures is on the weak decay modes of hypernuclei, with special attention to Lambda-hypernuclei. The subject involves many fields of modern theoretical and experimental physics, from nuclear structure to the fundamental constituents of matter and their interactions. The various weak decay modes of Lambda-hypernuclei are described: the mesonic mode and the non-mesonic ones. The latter are the dominant decay channels of medium--heavy hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli blocking effect on the outgoing nucleon. In particular, one can distinguish between one-body and two-body induced decays. Theoretical models employed to evaluate the (partial and total) decay widths of hypernuclei are illustrated, and their results compared with existing experimental data. Open problems and recent achievements are extensively discussed, in particular the determination of the ratio Gamma_n/Gamma_p, possible tests of the Delta I=1/2 rule in non-mesonic decays and the puzzling asymmetric non-mesonic decay of polarized hypernuclei.Comment: 59 pages, 13 figures Lectures given at the International School of Physics "Enrico Fermi" Course on: HADRON PHYSICS, Varenna (Lake Como), June 22nd - July 2nd, 200

Hydrostatic pressure to trigger and assist magnetic transitions: baromagnetic refrigeration

The possible application of the barocaloric effect to produce solid state refrigerators is a topic of interest in the field of applied physics. In this work, we present experimental data about the influence of external pressure on the magnetic properties of a manganite with phase separation. Using the Jahn Teller effect associated with the presence of the charge ordering we were able to follow the transition to the ferromagnetic state induced by pressure. We also demonstrated that external pressure can assist the ferromagnetic state, decreasing the magnetic field necessary to generate the magnetic transition.Comment: Acepted to be published in Applied Physics Letter

Weak decays of medium and heavy Lambda-hypernuclei

We have made a new evaluation of the Lambda decay width in nuclear matter within the Propagator Method. Through the Local Density Approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the N-N and Lambda-N short range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths in a wide range of mass numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure

MANAGEMENT OF AFRICA’S RARE EARTH MINING SECTORS

Africa’s rare earth mining sectors are growing rapidly due to the international strategic significance of these minerals. Whether or not countries privatize or nationalize their rare earth sectors has important strategic implications for U.S. access to these minerals. At present, most African countries have adopted privatized models of rare earth mining. What motivations have prompted African countries not to nationalize their rare earth industries? This thesis examines five potential drivers of Africa’s rare earth management: international pressures, economic viability, weak state capacity, political/public pressures, and environmental concerns, and investigates these hypotheses using two case studies from South Africa and Zambia. In both countries, economic viability is the most important guiding factor, while political pressures have also influenced Zambia’s resource management model. The remaining three factors exhibited weak explanatory evidence. In order to diversify U.S. rare earth supply outside of China, the strength of the economic viability hypothesis suggests the U.S. must implement programs that support private investment in Africa’s rare earth projects to ensure sustainable production and supply of these strategic minerals. U.S. policy objectives should promote privatization by incentivizing investment in Africa’s rare earth industries to ensure operations remain economically viable for the host nation.Lieutenant, United States NavyApproved for public release. Distribution is unlimited

Bell's inequality tests: from photons to B-mesons

We analyse the recent claim that a violation of a Bell's inequality has been observed in the $B$--meson system [A. Go, {\em Journal of Modern Optics} {\bf 51} (2004) 991]. The results of this experiment are a convincing proof of quantum entanglement in $B$--meson pairs similar to that shown by polarization entangled photon pairs. However, we conclude that the tested inequality is not a genuine Bell's inequality and thus cannot discriminate between quantum mechanics and local realistic approaches.Comment: 5 page

Evidence for polarons in iron pnictides of the Ln-1111 and AE-122 families

Examination of the electrical resistivities of iron pnictides shows that they can be accounted by conduction by polarons. Their activation energies show a linear behaviour with the critical temperatures of the spin density waves (SDW), T*, as both vary with pressure. The slope matches the ratio SDW gap to T*, while the intercept can be related to the transition temperature of the lattice distortion, T0. An adapted Landau free energy predicts the observed order of the transitions, according to which is higher, T* or T0. Simple arguments favour combined Jahn-Teller antiferromagnetic bipolarons.Comment: 14 pages with 4 Figure

Kurt Schwitters' An Anna Blume and the gendered politics of printmaking in Weimar Germany

Prominent German modernist Kurt Schwitters indulged in fragmented and nonsense aspects of art for most of his career. While Schwitters' collages and assemblages are his best-known works, what is missing from current scholarship is a comprehensive investigation of Schwitters' prints within the socio-historical context of the Weimar Republic. This thesis demonstrates how the print medium can add to our understanding of Schwitters' artistic career. The first chapter explores Schwitters as a printmaker, and how he aligned printmaking techniques with his artistic project titled "Merz." The second and third chapters address the apparent connection between Schwitters' print Komposition mit Kopf im Linksprofil, his renowned poem An Anna Blume, and numerous other works he created between 1919 and 1924. By bringing Schwitters' prints to the foreground, even his secondary works shed interesting light on modern artistic printmaking, Merz theory, and the politics of gender during the Weimar Republic. Largely due to the consequences of the First World War, this thesis argues that the graphic arts played an inevitable role in the history of Schwitters' artistic career

Pressure effects in the triangular layered cobaltites NaxCoO2

We have measured transport properties as a function of temperature and pressure up to 30GPa in the NaxCoO2 system. For the x=0.5 sample the transition temperature at 53K increases with pressure, while paradoxically the sample passes from an insulating to a metallic ground state. A similar transition is observed in the x=0.31 sample under pressure. Compression on the x=0.75 sample transforms the sample from a metallic to an insulating state. We discuss our results in terms of interactions between band structure effects and Na+ order.Comment: 18 pages, 5 figure