Poling effect on distribution of quenched random fields in a uniaxial relaxor ferroelectric

The frequency dependence of the dielectric permitivity's maximum has been studied for poled and unpoled doped relaxor strontium barium niobate $Sr_{0.61}Ba_{0.39}Nb_{2}O_{6}:Cr^{3+}$ (SBN-61:Cr). In both cases the maximum found is broad and the frequency dispersion is strong. The present view of random fields compensation in the unpoled sample is not suitable for explaining this experimental result. We propose a new mechanism where the dispersion of quenched random electric fields, affecting the nanodomains, is minimized after poling. We test our proposal by numerical simulations on a random field Ising model. Results obtained are in agreement with the polarization's measurements presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].Comment: 7 pages, 4 figure

TOKES studies of the thermal quench heat load reduction in mitigated ITER disruptions

Disruption mitigation by massive gas injection (MGI) of Ne gas has been simulated using the 3D TOKES code that includes the injectors of the Disruption Mitigation System (DMS) as it will be implemented in ITER. The simulations have been done using a quasi-3D approach, which gives an upper limit for the radiation heat load (notwithstanding possible asymmetries in radial heat flux associated with MHD). The heating of the first wall from the radiation flash has been assessed with respect to injection quantity, the number of injectors, and their location for an H-mode ITER discharge with 280 MJ of thermal energy. Simulations for the maximum quantity of Ne (8 kPa m3) have shown that wall melting can be avoided by using solely the three injectors in the upper ports, whereas shallow melting occurred when the midplane injector had been added. With all four injectors, melting had been avoided for a smaller neon quantity of 250 Pa m3 that provides still a sufficient radiation level for thermal load mitigation

BRAZILIAN INSECURITY

The position papers below formed the basis for a roundtable on “Brazilian Insecurity,” sponsored by the American Portuguese Studies Association at the Convention of the Modern Language Association of America, in New York City, January 4-7, 2018, in response to the presidential theme for the convention, “States of Insecurity.” The papers deal with such issues as the shape of undergraduate education, the training of graduate students, faculty hiring and promotion, and the future of the humanities in the American academy. The authors represent three different types of academic institutions in the United States: a private research university (Brown University), a private liberal arts college (Smith College) and a public research university (University of New Mexico).[1][1] On July 1, 2018 Professor Leila M. Lehnen will join the faculty of Brown University as Associate Professor of Portuguese and Brazilian Studies