Breakdown of the Fermi-liquid regime in the 2D Hubbard model from a two-loop field-theoretical renormalization group approach

We analyze the particle-hole symmetric two-dimensional Hubbard model on a square lattice starting from weak-to-moderate couplings by means of the field-theoretical renormalization group (RG) approach up to two-loop order. This method is essential in order to evaluate the effect of the momentum-resolved anomalous dimension $\eta(\textbf{p})$ which arises in the normal phase of this model on the corresponding low-energy single-particle excitations. As a result, we find important indications pointing to the existence of a non-Fermi liquid (NFL) regime at temperature $T\to 0$ displaying a truncated Fermi surface (FS) for a doping range exactly in between the well-known antiferromagnetic insulating and the $d_{x^2-y^2}$-wave singlet superconducting phases. This NFL evolves as a function of doping into a correlated metal with a large FS before the $d_{x^2-y^2}$-wave pairing susceptibility finally produces the dominant instability in the low-energy limit.Comment: 9 pages, 9 figures; published in Phys. Rev.

Utilizacao do parasitoide de ovos Trissolcus basalis (Wollaston) no controle de percevejos da soja.

Incidencia natural dos parasitoides de ovos de percevejos. Biologia de Trissolcus basalis, tempo de desenvolvimento,longevidade, comportamento de acasalamento e oviposicao, capacidade reprodutiva, razao sexual; Producao massal do parasitoide Trissocus basalis, criacao do hospedeiro, criacao em laboratorio, criacao em casa-de-vegetacao, armazenamento dos ovos, multiplicacao do parasitoide. Uso e eficiencia de controle; Programa ao nivel de agricultor.bitstream/item/50285/1/11.pd

Ocorrência, danos e estratégias de manejo de percevejos na cultura da soja.

Em função da ocorrência de elevadas populações de percevejos, a resistência comprovada da praga a inseticidas organofosforados e aplicações indiscriminadas de agrotóxicos que levam ao desequilíbrio, o problema percevejo na cultura da soja tem aumentado a cada safra. Na soja várias espécies compõem o complexo de pentatomídeos sugadores, cuja distribuição varia nas diferentes regiões produtoras, com predomínio acentuado hoje do percevejo marrom, Euschistus heros (F.). Embora estejam presentes nas lavouras desde o período vegetativo, por se alimentarem das vagens sugando diretamente os grãos de soja, é no período reprodutivo que os percevejos causam prejuízos. Portanto, para o melhor manejo desses insetos medidas integradas dentro do sistema produtivo precisam ser adotadas. Com o uso de procedimentos de monitoramento e a utilização de forma correta dos produtos indicados para o controle desses sugadores, considerando os níveis de ação pré-estabelecidos é possível manejá-los de forma eficiente e com sustentabilidade. Segundo o manejo integrado de pragas, o pano-de-batida é o método indicado para o monitoramento dos percevejos e o seu controle, considerando ninfas e adultos, deve ser realizado a partir do início do desenvolvimento de vagens, quando a população atinge os níveis de um ou dois percevejos por metro para lavouras de produção de sementes e grãos, respectivamente. Resultados têm mostrado que mesmo frente às mudanças ocorridas no cenário produtivo da soja destacando o predomínio no uso de cultivares de crescimento indeterminado e precoces, o reduzido número de ingredientes ativos disponíveis e as elevadas densidades populacionais de percevejos presentes na soja, os critérios recomendados pelo MIP-Soja são viáveis. Entretanto, deve-se, cada vez mais, considerar o sistema produtivo de forma integrada, onde o manejo de outras pragas, o desenvolvimento da planta e sua capacidade de tolerar danos e as culturas que antecedem ou são semeadas após a soja assumem fundamental importância

Welfare guarantees for proportional allocations

According to the proportional allocation mechanism from the network optimization literature, users compete for a divisible resource -- such as bandwidth -- by submitting bids. The mechanism allocates to each user a fraction of the resource that is proportional to her bid and collects an amount equal to her bid as payment. Since users act as utility-maximizers, this naturally defines a proportional allocation game. Recently, Syrgkanis and Tardos (STOC 2013) quantified the inefficiency of equilibria in this game with respect to the social welfare and presented a lower bound of 26.8% on the price of anarchy over coarse-correlated and Bayes-Nash equilibria in the full and incomplete information settings, respectively. In this paper, we improve this bound to 50% over both equilibrium concepts. Our analysis is simpler and, furthermore, we argue that it cannot be improved by arguments that do not take the equilibrium structure into account. We also extend it to settings with budget constraints where we show the first constant bound (between 36% and 50%) on the price of anarchy of the corresponding game with respect to an effective welfare benchmark that takes budgets into account.Comment: 15 page

Negative-energy perturbations in cylindrical equilibria with a radial electric field

The impact of an equilibrium radial electric field $E$ on negative-energy perturbations (NEPs) (which are potentially dangerous because they can lead to either linear or nonlinear explosive instabilities) in cylindrical equilibria of magnetically confined plasmas is investigated within the framework of Maxwell-drift kinetic theory. It turns out that for wave vectors with a non-vanishing component parallel to the magnetic field the conditions for the existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D. Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for the existence of perpendicular NEPs, which are found to be the most important perturbations, is modified. For $|e_i\phi|\approx T_i$ ($\phi$ is the electrostatic potential) and $T_i/T_e > \beta_c\approx P/(B^2/8\pi)$ ($P$ is the total plasma pressure), a case which is of operational interest in magnetic confinement systems, the existence of perpendicular NEPs depends on $e_\nu E$, where $e_\nu$ is the charge of the particle species $\nu$. In this case the electric field can reduce the NEPs activity in the edge region of tokamaklike and stellaratorlike equilibria with identical parabolic pressure profiles, the reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late

Twist Deformations of the Supersymmetric Quantum Mechanics

The N-extended Supersymmetric Quantum Mechanics is deformed via an abelian twist which preserves the super-Hopf algebra structure of its Universal Enveloping Superalgebra. Two constructions are possible. For even N one can identify the 1D N-extended superalgebra with the fermionic Heisenberg algebra. Alternatively, supersymmetry generators can be realized as operators belonging to the Universal Enveloping Superalgebra of one bosonic and several fermionic oscillators. The deformed system is described in terms of twisted operators satisfying twist-deformed (anti)commutators. The main differences between an abelian twist defined in terms of fermionic operators and an abelian twist defined in terms of bosonic operators are discussed.Comment: 18 pages; two references adde

Nonlinear Supersymmetry as a Hidden Symmetry

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