Analysis of Leptogenesis in Supersymmetric Triplet Seesaw Model

We analyze leptogenesis in a supersymmetric triplet seesaw scenario that explains the observed neutrino masses, adopting a phenomenological approach where the decay branching ratios of the triplets and the amount of CP--violation in its different decay channels are assumed as free parameters. We find that the solutions of the relevant Boltzmann equations lead to a rich phenomenology, in particular much more complex compared to the non--supersymmetric case, mainly due to the presence of an additional Higgs doublet. Several unexpected and counter--intuitive behaviors emerge from our analysis: the amount of CP violation in one of the decay channels can prove to be be irrelevant to the final lepton asymmetry, leading to successful leptogenesis even in scenarios with a vanishing CP violation in the leptonic sector; gauge annihilations can be the dominant effect in the determination of the evolution of the triplet density up to very high values of its mass, leading anyway to a sizeable final lepton asymmetry, which is also a growing function of the wash--out parameter K=Gamma_d/H, defined as usual as the ratio between the triplet decay amplitude Gamma_d and the Hubble constant H; on the other hand, cancellations in the Boltzmann equations may lead to a vanishing lepton asymmetry if in one of the decay channels both the branching ratio and the amount of CP violation are suppressed, but not vanishing. The present analysis suggests that in the supersymmetric triplet see-saw model successful leptogenesis can be attained in a wide range of scenarios, provided that an asymmetry in the decaying triplets can act as a lepton--number reservoir.Comment: 14 pages, 6 figure

Trade-offs between biomass use and soil cover. The case of rice-based cropping systems in the lake Alaotra region of Madagascar

Farmers in the Lake Alaotra region of Madagascar are currently evaluating a range of conservation agriculture (CA) cropping systems. Most of the expected agroecological functions of CA (weed control, erosion control and water retention) are related to the degree of soil cover. Under farmers’ conditions, the grain and biomass productivity of these systems is highly variable and the biomass is used for several purposes. In this study, we measured biomass production of cover crops and crops in farmers’ fields. Further, we derived relationships to predict the soil cover that can be generated for a particular quantity of mulch. We used these relationships to explore the variability of soil cover that can be generated in farmers’ fields, and to estimate howmuch of the biomass can be removed for use as livestock feed, while retaining sufficient soil cover. Three different kinds of cropping systems were investigated in 91 farmers’ fields. The first two cropping sequences were on the hillsides: (i) maize + pulse (Vigna unguiculata or Dolichos lablab) in year 1, followed by upland rice in year 2; (ii) the second crop sequence included several years of Stylosanthes guianensis followed by upland rice; (iii) the third crop sequence was in lowland paddy fields: Vicia villosa or D. lablab, which was followed by rice within the same year and repeated every year. The biomass available prior to rice sowing varied from 3.6 t ha-1 with S. guianensis to 7.3 t ha-1 with V. villosa. The relationship between the mulch quantity (M) and soil cover (C) was measured using digital imaging and was well described by the following equation: C = 1 - exp(-Am × M), where Am is an area-to-mass ratio with R2 > 0.99 in all cases. The calculated average soil cover varied from 56 to 97% for maize + V. unguiculata and V. villosa, respectively. In order to maintain 90% soil cover at rice sowing, the average amount of biomass of V. villosa that could be removed was at least 3 t ha-1 for three quarters of the fields. This quantity was less for other annual or biennial cropping systems. On average the V. villosa aboveground biomass contained 236 kg N ha-1. The study showed that for the conditions of farmers of Malagasy, the production and conservation of biomass is not always sufficient to fulfil all the above-cited agroecological functions of mulch. Inventory of the soil cover capacity for different types of mulch may help farmers to decide how much biomass they can remove from the fiel

A EDUCAÇÃO POPULAR NAS EXPERIÊNCIAS E PRÁTICAS DE INTEGRAÇÃO CURRICULAR NO PROEJA DO IFES

A questão problema que instigou esta investigação reporta ao modo como as experiências vividas nas práticas educativas do Proeja explicitam a busca pela integração curricular e a construção coletiva, na perspectiva da educação popular. Teve como objetivo geral analisar as experiências vividas junto aos sujeitos envolvidos no Proeja, no Ifes - CampusVitória, em contextos de práticas educativas diferenciadas, com vistas à integração curricular e à construção coletiva. Os fundamentos epistemológicos da educação popular, a partir da perspectiva libertadora, são tomados como principal aporte teórico-metodológico, para dialogar com as práticas e experiências no âmbito do Proeja, a partir do campo de estudos produzido no contexto latino-americano, caracterizado por um pensamento próprio e uma prática política e pedagógica de resistência à dominação e ao Pensamento hegemônico neoliberal, tendo como opção básica a transformação das condições que perpetuam a desigualdade, a injustiça e a exclusão social. Trabalhamos com a hipótese de que o Proeja, ao longo de 10 anos de sua implantação, produziu inúmeras experiências e apesar de suas contradições, essas experiências têm sido expressas nas mudanças observadas nas práticas educativas que incorporam alguns princípios da educação popular, na busca da integração curricular. Operamos com a sistematização de experiências como estratégia metodológica, respaldada pela abordagem epistemológica desconstrutiva e histórico-dialética, atentando para a postura crítica, analítica e o estranhamento de quem a realiza, e para as condições de contexto e do momento histórico de realização das experiências, que envolveu 25 educadores, 15 educandos e 5 gestores. As análises foram realizadas a partir da produção de dados oriunda dos registros das reuniões pedagógicas, do diário de campo, das entrevistas e observações in loco. As experiências aqui sistematizadas nos levam a reafirmar a tese de que os fundamentos epistemológicos e as práticas da educação popular se constituem em alternativa para se repensar os processos educativos no Proeja, no CampusVitória. Os resultados indicam o protagonismo dos sujeitos, suas reflexões críticas das práticas para compreendê-las e produzir interferências, no que demandam de transformação. Apesar das contradições, percebe-se o exercício do diálogo com um dos princípios do currículo integrado, na construção coletiva de conhecimentos gerais e específicos

Hyperfine magnetic field in ferromagnetic graphite

Information on atomic-scale features is required for a better understanding of the mechanisms leading to magnetism in non-metallic, carbon-based materials. This work reports a direct evaluation of the hyperfine magnetic field produced at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR). The experimental investigation was made possible by the results of first-principles calculations carried out in model systems, including graphene sheets with atomic vacancies and graphite nanoribbons with edge sites partially passivated by oxygen. A similar range of maximum hyperfine magnetic field values (18-21T) was found for all systems, setting the frequency span to be investigated in the NMR experiments; accordingly, a significant 13C NMR signal was detected close to this range without any external applied magnetic field in ferromagnetic graphite

Sensitivity plots for WIMP modulation searches

Prospects of WIMP searches using the annual modulation signature are discussed on statistical grounds, introducing sensitivity plots for the WIMP-nucleon scalar cross section.Comment: 3 pages, 2 figures, talk given at TAUP'99, september 199