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Tunneling conductance of graphene ferromagnet-insulator-superconductor junctions

We study the transport properties of a graphene ferromagnet-insulator superconductor (FIS) junction within the Blonder-Tinkham-Klapwijk formalism by solving spin-polarized Dirac-Bogoliubov-de-Gennes equation. We find that the retro and specular Andreev reflections in the graphene FIS junction are drastically modified in the presence of exchange interaction and that the spin-polarization ($P_T$) of tunneling current can be tuned from the positive to negative value by bias voltage ($V$). In the thin-barrier limit, the conductance $G$ of a graphene FIS junction oscillates as a function of barrier strength $\chi$. Both the amplitude and phase of the conductance oscillation varies with the exchange energy $E_{ex}$. For $E_{ex}<E_F$ (Fermi energy), the amplitude of oscillation decreases with $E_{ex}$. For $E_{ex}^{c}>E_{ex}>E_F$, the amplitude of oscillation increases with $E_{ex}$, where $E_{ex}^{c}=2E_{F}+U_{0}$ ($U_{0}$ is the applied electrostatic potential on the superconducting segment of the junction). For $E_{ex} > E_{ex}^{c}$, the amplitude of oscillation decreases with $E_{ex}$ again. Interestingly, a universal phase difference of $\pi/2$ in $\chi$ exists between the $G-\chi$ curves for $E_{ex}>E_F$ and $E_{ex}<E_F$. Finally, we find that the transitions between retro and specular Andreev reflections occur at $eV=|E_{F}-E_{ex}|$ and $eV=E_{ex}+E_{F}$, and hence the singular behavior of the conductance near these bias voltages results from the difference in transport properties between specular and retro Andreev reflections.Comment: Accepted for publication in Physical Review

ANÁLISE CONJUNTURAL DA PREDIÇÃO DE IMPACTOS AMBIENTAIS RELACIONADOS ÀS CENTRAIS HIDRELÉTRICAS

O contexto energético brasileiro depende das fontes hídricas de maneira evidente. Impactos ambientais inerentes às Centrais Hidrelétricas devem ser previstos de forma eficaz, assegurando o controle ambiental e a qualidade do meio ambiente preconizada constitucionalmente. A Avaliação de Impactos Ambientais compreende inúmeras dificuldades e, por esse motivo, no contexto energético surge a Avaliação Ambiental Integrada como ferramenta auxiliar de predição das condições futuras de bacias hidrográficas. Este trabalho compreende uma pesquisa bibliográfica como procedimento técnico, com vistas à análise dos principais impactos de centrais hidrelétricas arrolados na literatura pertinente, evidenciando a cumulatividade e sinergia destes, ausentes na maioria dos estudos ambientais. Analisa a situação recorrente na predição de impactos no cenário energético, contemplando um estudo do contexto integrado empregado pela Empresa de Pesquisa Energética na Bacia Hidrográfica do Rio Uruguai. Objetiva, dessa maneira, elucidar os vieses que urgem com a preocupação de uma análise insuficiente, comprometendo a sustentabilidade futura. Chega-se a termo sobre a necessidade de ferramentas que contemplem empreendimentos de pequeno porte e certo nível de detalhamento, capazes de assegurar sustentabilidade das bacias hidrográficas, a visão integrada dos recursos, respeitos aos usos dissidentes e resolução de conflitos sociais, promovendo a estruturação de projetos mais sustentáveis ecológica e economicamente

Black-wattle growth in reponse to application of nitrogen, phosphorus and potassium

Due to the lack of information about Black-wattle fertilization, this study evaluated black-wattle plants growth in response to different fertilization levels of nitrogen, phosphorus and potassium six years after implantation. The statistical design used was a randomized blocks with trifatorial distribution. Total height (m), diameter at breast height (DBH) (cm) and stem volume with bark (m³ ha-1) were evaluated. Black-wattle showed a positive and significant growth response to N and P (interaction) fertilizations and absence for K. m To obtain the maximum development of black-wattle, for the soil and climate condition studied, it is required the use of the maximum dose of nitrogen (40.0 kg ha-1 N) and 78.9 kg ha-1 phosphorus, not requiring the addition of potassium

Photodissociation of small carbonaceous molecules of astrophysical interest

Astronomical observations have shown that small carbonaceous molecules can persist in interstellar clouds exposed to intense ultraviolet radiation. Current astrochemical models lack quantitative information on photodissociation rates in order to interpret these data. We here present ab initio multi-reference configuration-interaction calculations of the vertical excitation energies, transition dipole moments and oscillator strengths for a number of astrophysically relevant molecules: C3, C4, C2H, l- and c-C3H, l- and c-C3H2, HC3H, l-C4H and l-C5H. Highly excited states up to the 9'th root of each symmetry are computed, and several new states with large oscillator strengths are found below the ionization potentials. These data are used to calculate upper limits on photodissociation rates in the unattenuated interstellar radiation field by assuming that all absorptions above the dissociation limit lead to dissociation.Comment: Full tables, rates and cross sections are posted at http://www.strw.leidenuniv.nl/~ewine/phot