Superconducting Kondo phase in an orbitally-separated bilayer

The nature of superconductivity in heavy-fermion materials is a subject under intense debate, and controlling this many-body state is central for its eventual understanding. Here, we examine how proximity effects may change this phenomenon, by investigating the effects of an additional metallic layer on the top of a Kondo-lattice, and allowing for pairing in the former. We analyze a bilayer Kondo Lattice Model with an on-site Hubbard interaction, $-U$, on the additional layer, using a mean-field approach. For $U=0$, we notice a drastic change in the density-of-states due to multiple-orbital singlet resonating combinations. It destroys the well-known Kondo insulator at half filling, leading to a metallic ground state, which, in turn, enhances antiferromagnetism through the polarization of the conduction electrons. For $U\neq 0$, a superconducting Kondo state sets in at zero temperature, with the occurrence of unconventional pairing amplitudes involving $f$-electrons. We establish that this remarkable feature is only possible due to the proximity effects of the additional layer. At finite temperatures we find that the critical superconducting temperature, $T_c$, decreases with the interlayer hybridization. We have also established that a zero temperature superconducting amplitude tracks $T_c$, which reminisces the BCS proportionality between the superconducting gap and $T_c$.Comment: 11 pages, 10 figure

The half-filled extended Hubbard model on a square lattice: Phase boundaries from determinant quantum Monte Carlo simulations

The extended Hubbard model (EHM) describes fermions on a lattice coupled through on-site, $U$, and first-neighbor, $V$, interactions. In the context of high-$T_c$ cuprates, antiferromagnetic fluctuations may lead to an attractive channel, hence to superconductivity. Despite interest in the two-dimensional version of the model, the current knowledge about the phase diagram is still far from complete. Here, we report on the results of extensive determinant quantum Monte Carlo simulations for this model at half filling, in which we have used the average sign of the product of fermionic determinants as an additional observable to locate critical points. We arrive at a ground state phase diagram in the $U$-$V$ plane in which the boundaries involving antiferromagnetic, charge-ordered, $s$- and $d$-wave superconductivity, and phase-separated phases are quantitatively set with good accuracy. We have also proposed a partial phase diagram, $T_c(U,V)$, featuring critical temperatures for the CDW and $s$-wave superconducting phases

Magnetic impurities in a charge-ordered background

We investigate how magnetic impurities may affect a system exhibiting charge-density wave (CDW) in its ground state. We consider a disordered Hubbard-Holstein model with a homogeneous electron-phonon interaction, but with a (randomly chosen) fraction of sites displaying a non-zero Coulomb repulsion, $U$, and perform state-of-the-art finite-temperature quantum Monte Carlo simulations. For a single magnetic impurity, charge-charge correlations hamper the spin-spin ones around the repulsive site, thus requiring a strong enough value of $U$ to create non-negligible antiferromagnetic (AFM) correlations. As the number of magnetic impurities increases, these AFM correlations become deleterious to CDW order and its features. First, the critical temperature is drastically reduced, and seems to vanish around 40$\%$ of impurities (for fixed $U/\lambda=2$), which we correlate with the classical percolation threshold. We also notice that just a small amount of disorder suffices to create a \textit{bad insulating} state, with the suppression of both Peierls and spin gaps, even within the charge-ordered phase. Finally, we have also found that pairing correlations are enhanced at large doping, driven by the competition between CDW and AFM tendencies

Agricultura familiar e políticas públicas: o impacto do Pronaf no Rio Grande do Sul.

A aparição do Programa Nacional de Fortalecimento da Agricultura Familiar (PRONAF) marca um momento singular na trajetória do processo de intervenção estatal na agricultura e no mundo rural do Brasil. Apesar de avanços no aperfeiçoamento e ampliação do universo de cobertura, o programa permanece ancorado numa ambigüidade básica tanto em termos do público-alvo a ser beneficiado quanto aos objetivos essenciais que persegue, onde, na retórica oficial, mesclam-se orientações tipicamente produtivistas com compromissos mais amplos, como a geração de empregos, a inclusão social e o desenvolvimento territorial. O artigo em questão desenvolve uma análise do PRONAF à luz de recente pesquisa realizada no Estado do Rio Grande do Sul, inserida no contexto de um convênio firmado entre o PCT/IICA-PRONAF e a Fundação de Economia de Campinas - FECAMP para montar um sistema de acompanhamento das ações do Ministério do Desenvolvimento Agrário e avaliar os impactos deste programa. Os dados finais mostram fortes evidências de diferenciação social dentre os produtores familiares

Voice Interaction for Augmented Reality Navigation Interfaces with Natural Language Understanding

Voice interaction with natural language understanding (NLU) has been extensively explored in desktop computers, handheld devices, and human-robot interaction. However, there is limited research into voice interaction with NLU in augmented reality (AR). There are benefits of using voice interaction in AR, such as high naturalness and being hands-free. In this project, we introduce VOARLA, an NLU-powered AR voice interface, which navigate courier driver delivery a package. A user study was completed to evaluate VOARLA against an AR voice interface without NLU to investigate the effectiveness of NLU in the navigation interface in AR. We evaluated from three aspects: accuracy, productivity, and commands learning curve. Results found that using NLU in AR increases the accuracy of the interface by 15%. However, higher accuracy did not correlate to an increase in productivity. Results suggest that NLU helped users remember the commands on the first run when they were unfamiliar with the system. This suggests that using NLU in an AR hands-free application can make the learning curve easier for new users

Aplicação da microextração em fase sólida na determinação de resíduos de agrotóxicos em alimentos.

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Efeito da adicao de hidroretentores de agua em Argissolo Amarelo Eutrofico.

Estudou-se o eleito da absorcao de agua proporcionada por tres hidroretentores utilizados em duas concentracoes, em um solo do tipo Argissolo Amarelo Eutrofico, sobre a germinacao e emergencia de plantulas de milho (Zea mays, L.) variedade Assum Preto. Os tratamentos utilizados foram: TO = Solo (Testemunha); T1 = Amido retrogradado + Solo; T2 = Acetato de celulose e poliester + Solo; T3 = Vermiculita expandida + Solo, com os hidroretentores na concentracao de 3,35g.Kg-1; T4 = Amido retrogradado + Solo; T5 = Acetato de celulose e poliester + Solo; T6 = Vermiculita expandida + Solo, com os hidroretentores na proporcao de 6,70g.Kg-1 de solo. Apos irrigacao dos substratos com um volume de 18,45 mm de agua, efetuou-se a semeadura do milho em potes plasticos a uma profundidade de 2 cm. Os tratamentos T2 e T4, 25% dos potes apresentaram e emergencia de plantulas de milho, seguido de 75% em T6 e 100% no tratamento T5. Nao houve germinacao e emergencia de plantulas de milho nos tratamentos TO, T1 e T3

Zoneamento de riscos climáticos para a cultura de feijão no estado do Rio Grande do Sul: períodos favoráveis de semeadura por município, safra 2003-2004.

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