Effects of band filling in the Anderson-Falicov-Kimball model

In this work, we study the Anderson-Falicov-Kimball model within the dynamical mean field theory for the Bethe lattice, restricting our analysis to the nonmagnetic case. The one-particle density of states is obtained by both arithmetic and geometric averages over disorder, since only the latter can detect localization in the absence of an energy gap. Varying the strengths of Coulomb interaction and disorder at zero temperature, we construct phase diagrams for this model, where we distinguish spectral regions with localized states, with extended states, or with a correlation-induced gap. With this, we identify metal-insulator transitions driven by correlation and disorder, as well as the competition between these effects. This is done for various band fillings, since our main interest here is to study how the variation of the electron density affects the phase diagrams previously obtained for half-filling. The picture revealed by the density of states is further checked by evaluating the static and dynamic conductivities, including temperature effects

Searching for the roots of the first free African American community

San Basilio de Palenque is an Afro-descendant community near Cartagena, Colombia, founded in the sixteenth century. The recognition of the historical and cultural importance of Palenque has promoted several studies, namely concerning the African roots of its first inhabitants. To deepen the knowledge of the origin and diversity of the Palenque parental lineages, we analysed a sample of 81 individuals for the entire mtDNA Control Region as well as 92 individuals for 27 Y-STRs and 95 for 51 Y-SNPs. The results confirmed the strong isolation of the Palenque, with some degree of influx of Native American maternal lineages, and a European admixture exclusively mediated by men. Due to the high genetic drift observed, a pairwise FST analysis with available data on African populations proved to be inadequate for determining population affinities. In contrast, when a phylogenetic approach was used, it was possible to infer the phylogeographic origin of some lineages in Palenque. Contradicting previous studies indicating a single African origin, our results evidence parental genetic contributions from widely different African regions.We thank all sample donors for their contribution to this work and all the people who helped with sample collection, namely, Regina Miranda from the Community of San Basilio de Palenque, the personnel of the Benkos Biojó Rural school, and Miguel Obeso from the etnoeducación program. This work was supported by the University of Cartagena and FPIT—Fundación para la promoción de la investigación y la tecnología del Banco de la República, Colombia (FPIT-388) and partially financed by FEDER—Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020—Operacional Programme for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through FCT—Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Inovação in the framework of the projects “Institute for Research and Innovation in Health Sciences” (POCI-01-0145-FEDER-007274). FS was supported by Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro—FAPERJ (E-26/202.275/2019). LG was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq (ref. 306342/2019-7), and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro—FAPERJ (CNE-2018). VG was supported by FCT, under the program contract provided in Decree-Law no.57/2016 of August 29. The IPATIMUP integrates the i3S research unit, which is partially supported by the Portuguese Foundation for Science and Technology

Electronic and phononic states of the Holstein-Hubbard dimer of variable length

We consider a model Hamiltonian for a dimer including all the electronic one- and two-body terms consistent with a single orbital per site, a free Einstein phonon term, and an electron-phonon coupling of the Holstein type. The bare electronic interaction parameters were evaluated in terms of Wannier functions built from Gaussian atomic orbitals. An effective polaronic Hamiltonian was obtained by an unrestricted displaced-oscillator transformation, followed by evaluation of the phononic terms over a squeezed-phonon variational wave function. For the cases of quarter-filled and half-filled orbital, and over a range of dimer length values, the ground state was identified by simultaneously and independently optimizing the orbital shape, the phonon displacement and the squeezing effect strength. As the dimer length varies, we generally find discontinuous changes of both electronic and phononic states, accompanied by an appreciable renormalization of the effective electronic interactions across the transitions, due to the equilibrium shape of the wave functions strongly depending on the phononic regime and on the type of ground state.Comment: 11 pages, RevTeX, 10 PostScript figures; to appear in Phys. Rev.

Effect of band filling in the Kondo lattice: A mean-field approach

The usual Kondo-lattice, including an antiferromagnetic exchange interaction between nearest-neighboring localized spins, is treated here in a mean-field scheme that introduces two mean-field parameters: one associated with the local Kondo effect, and the other related to the magnetic correlations between localized spins. Phases with short-range magnetic correlations or coexistence between those and the Kondo effect are obtained. By varying the number of electrons in the conduction band, we notice that the Kondo effect tends to be suppressed away from half filling, while magnetic correlations can survive if the Heisenberg coupling is strong enough. An enhanced linear coefficient of the specific heat is obtained at low temperatures in the metallic state.Comment: 7 pages, ReVTeX two-column, 7 figure

Avaliação agronômica de linhagens de arroz irrigado de viveiros internacionais.

Este trabalho tem por objetivo apresentar à comunidade científica e acadêmica em agronomia os resultados da avaliação de dois Viveiros Internacionais de Observação de Arroz Irrigado conduzidos na Embrapa Arroz e Feijão.bitstream/CNPAF-2009-09/27609/1/doc_223.pd

Dinâmica do crescimento de Brachiaria ruziziensis cv. BRS Integra, sob três severidades de desfolha.

Resumo: O objetivo deste estudo foi avaliar as características morfogênicas e o acúmulo de forragem de cultivares de B. ruziziensis (Kenedy e BRS Integra), manejadas sob cortes, com três severidades de desfolha (40, 50 e 70% de rebaixamento em relação à altura inicial). O estudo foi realizado no Campo Experimental da Embrapa Gado de Leite, durante a época chuvosa. Foi adotado o delineamento de blocos casualizados, com três repetições, em esquema fatorial 2x3 (duas cultivares e três severidades de desfolha). As taxas de alongamento e aparecimento de folhas e o filocrono não variaram com os tratamentos, enquanto as taxas de senescência foliar e alongamento de colmos foram maiores na Kenedy. A percentagem de folha foi maior na BRS Integra. O rebaixamento de 40% da altura inicial resultou em maiores número de folhas por perfilho e tempo de vida da folha, especialmente quando comparado ao rebaixamento de 70% da altura. As taxas de crescimento, senescência e acúmulo de forragem não variaram com os tratamentos. As vantagens da cv. BRS Integra em relação à cv. Kenedy estão relacionadas às menores taxas de alongamento de colmos e de senescência foliar, associadas às maiores proporções de folhas. Devem-se preconizar rebaixamentos entre 40 e 50% da altura inicial.Editor Técnico: Leônidas Paixão Passos, Embrapa Gado de Leite

Reconstructing the Indian Origin and Dispersal of the European Roma: A Maternal Genetic Perspective

Previous genetic, anthropological and linguistic studies have shown that Roma (Gypsies) constitute a founder population dispersed throughout Europe whose origins might be traced to the Indian subcontinent. Linguistic and anthropological evidence point to Indo-Aryan ethnic groups from North-western India as the ancestral parental population of Roma. Recently, a strong genetic hint supporting this theory came from a study of a private mutation causing primary congenital glaucoma. In the present study, complete mitochondrial control sequences of Iberian Roma and previously published maternal lineages of other European Roma were analyzed in order to establish the genetic affinities among Roma groups, determine the degree of admixture with neighbouring populations, infer the migration routes followed since the first arrival to Europe, and survey the origin of Roma within the Indian subcontinent. Our results show that the maternal lineage composition in the Roma groups follows a pattern of different migration routes, with several founder effects, and low effective population sizes along their dispersal. Our data allowed the confirmation of a North/West migration route shared by Polish, Lithuanian and Iberian Roma. Additionally, eleven Roma founder lineages were identified and degrees of admixture with host populations were estimated. Finally, the comparison with an extensive database of Indian sequences allowed us to identify the Punjab state, in North-western India, as the putative ancestral homeland of the European Roma, in agreement with previous linguistic and anthropological studies

Unveiling oxygen vacancy impact on lizardite thermo and mechanical properties

Here, we performed a systematic DFT study assisted by the workflow framework SimStack for the mechanical and thermodynamic properties of the clay mineral lizardite in pristine and six different types of O vacancies configurations. In most cases, the defect caused a structural phase transition in the lizardite from the trigonal (pristine) to the triclinic phase. The results show that oxygen vacancies in lizardite significantly reduce the lattice thermal conductivity, accompanied by an elastic moduli reduction and an anisotropy index increase. Through the P–V relation, an increase in compressibility was evidenced for vacancy configurations. Except for the vacancy with the same crystalline structure as pristine lizardite, the sound velocities of the other vacancy configurations produce a decrease in these velocities, and it is essential to highlight high values for the Grüneisen parameter. We emphasize the great relevance of the punctual-defects introduction, such as O vacancies, in lizardite, since this microstructural design is responsible for the decrease of the lattice thermal conductivity in comparison with the pristine system by decreasing the heat transfer ability, turning lizardite into a promising candidate for thermoelectric materials