Resummation of infrared divergences in the free-energy of spin-two fields

We derive a closed form expression for the sum of all the infrared divergent contributions to the free-energy of a gas of gravitons. An important ingredient of our calculation is the use of a gauge fixing procedure such that the graviton propagator becomes both traceless and transverse. This has been shown to be possible, in a previous work, using a general gauge fixing procedure, in the context of the lowest order expansion of the Einstein-Hilbert action, describing non-interacting spin two fields. In order to encompass the problems involving thermal loops, such as the resummation of the free-energy, in the present work, we have extended this procedure to the situations when the interactions are taken into account.Comment: 12 pages, 25 figure

Impacto do inseticida imidacloprido em aspectos biológicos de adultos de Mononychellus planki (McGregor) (Acari: Tetranychidae).

É amplamente conhecido o efeito deletério de agrotóxicos e de práticas de manejo cultural que prejudicam os inimigos naturais em campo e favorecem indiretamente os ácaros-praga em diferentes cultivos. Por outro lado, o efeito direto ou indireto de agrotóxicos na soja sobre ácaros fitófagos, favorecendo o seu desenvolvimento, precisa ser mais amplamente estudado. Tendo em vista a utilização de imidacloprido na cultura da soja em mistura comercial com um piretróide e a relação entre aumento na fecundidade de fêmeas de Tetranychus urticae Koch (Acari: Tetranychidae) com a utilização desse produto estudou-se a possibilidade deste mesmo princípio ativo causar efeito semelhante no ácaro verde Mononychellus planki. Foram testadas três formulações, Connect (100g i.a. imidacloprido/L de formulação + 12,5g i.a. beta-ciflutrina/L de formulação) e Provado 200SC (200g i.a. imidacloprido/L de formulação) e Kohinor 200SC (200g i.a. imidacloprido /L de formulação) em duas dosagens do ingrediente ativo imidacloprido, 0,013% e metade da dose (0,0065%). Ensaios com Bulldock 125 SC foram realizados para verificar a ação da beta-ciflutrina isoladamente, com dosagens de 100μL p.c./L (Diluição A) e 100μL p.c./L (Diluição B). Não foi observada diferença significativa na longevidade e fecundidade das fêmeas submetidas a ambas as dosagens de Connect, Kohinor e Provado; para aquelas tratadas com a diluição A de Bulldock 125SC observou-se longevidade e fecundidade média menor do que a obtida para testemunha. Entretanto a longevidade das fêmeas pulverizadas com a diluição B foi de 8,12 dias e fecundidade de 17,81 ovos/fêmea semelhantes às médias obtidas para a testemunha. Nos tratamentos com Connect, Kohinor e Provado constatou-se maior taxa de oviposição nos primeiros sete dias, consequentemente há possibilidade de estímulo ao aumento populacional de M. planki em campo após utilização de agrotóxicos com imidacloprido em sua composição

Possible chiral phase transition in two-dimensional solid 3^3He

We study a spin system with two- and four-spin exchange interactions on the triangular lattice, which is a possible model for the nuclear magnetism of solid $^3$He layers. It is found that a novel spin structure with scalar chiral order appears if the four-spin interaction is dominant. Ground-state properties are studied using the spin-wave approximation. A phase transition concerning the scalar chirality occurs at a finite temperature, even though the dimensionality of the system is two and the interaction has isotropic spin symmetry. Critical properties of this transition are studied with Monte Carlo simulations in the classical limit.Comment: 4 pages, Revtex, 4 figures, to appear in Phys.Rev.Let

Magnetization plateau in a two-dimensional multiple-spin exchange model

We study a multiple-spin exchange model on a triangular lattice, which is a possible model for low-density solid 3He films. Due to strong competitions between ferromagnetic three-spin exchange and antiferromagnetic four-spin one, the ground states are highly degenerate in the classical limit. At least 2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the SO(3) symmetry. In the magnetization process, we found a plateau at m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state with four sublattices). The 1/2-plateau appears due to the strong four-spin exchange interaction. This plateau survives against both quantum and thermal fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a phase transition occurs at a finite temperature. We predict that low-density solid 3He thin films may show the 1/2-plateau in the magnetization process. Experimental observation of the plateau will verify strength of the four-spin exchange. It is also discussed that this magnetization plateau can be understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos, to be published in Phys.Rev.B (01 APR 99

Indicações de gestão para um laboratório, a partir do cadastro de clientes e de serviços: estudo de caso da clínica fitossanitária Embrapa Clima Temperado.

bitstream/item/31621/1/comunicado91.pd

Composição química das sementes de algumas cultivares de algodão do nordeste brasileiro.

bitstream/item/118239/1/composicao-quimica-das-sementes-nordeste.pd

Microscopic Conductivity of Lattice Fermions at Equilibrium - Part I: Non-Interacting Particles

We consider free lattice fermions subjected to a static bounded potential and a time- and space-dependent electric field. For any bounded convex region $\mathcal{R}\subset \mathbb{R}^{d}$ ($d\geq 1$) of space, electric fields $\mathcal{E}$ within $\mathcal{R}$ drive currents. At leading order, uniformly with respect to the volume $\left| \mathcal{R}\right|$ of $\mathcal{R}$ and the particular choice of the static potential, the dependency on $\mathcal{E}$ of the current is linear and described by a conductivity distribution. Because of the positivity of the heat production, the real part of its Fourier transform is a positive measure, named here (microscopic) conductivity measure of $\mathcal{R}$, in accordance with Ohm's law in Fourier space. This finite measure is the Fourier transform of a time-correlation function of current fluctuations, i.e., the conductivity distribution satisfies Green-Kubo relations. We additionally show that this measure can also be seen as the boundary value of the Laplace-Fourier transform of a so-called quantum current viscosity. The real and imaginary parts of conductivity distributions satisfy Kramers-Kronig relations. At leading order, uniformly with respect to parameters, the heat production is the classical work performed by electric fields on the system in presence of currents. The conductivity measure is uniformly bounded with respect to parameters of the system and it is never the trivial measure $0\,\mathrm{d}\nu$. Therefore, electric fields generally produce heat in such systems. In fact, the conductivity measure defines a quadratic form in the space of Schwartz functions, the Legendre-Fenchel transform of which describes the resistivity of the system. This leads to Joule's law, i.e., the heat produced by currents is proportional to the resistivity and the square of currents