Weber-like interactions and energy conservation

Velocity dependent forces varying as $k(\hat{r}/r)(1 - \mu \dot{r}^2 + \gamma r \ddot{r})$ (such as Weber force), here called Weber-like forces, are examined from the point of view of energy conservation and it is proved that they are conservative if and only if $\gamma=2\mu$. As a consequence, it is shown that gravitational theories employing Weber-like forces cannot be conservative and also yield both the precession of the perihelion of Mercury as well as the gravitational deflection of light.Comment: latex, 11 pages, no figure

The saga of the Ising susceptibility

We review developments made since 1959 in the search for a closed form for the susceptibility of the Ising model. The expressions for the form factors in terms of the nome $q$ and the modulus $k$ are compared and contrasted. The $\lambda$ generalized correlations $C(M,N;\lambda)$ are defined and explicitly computed in terms of theta functions for $M=N=0,1$.Comment: 19 pages, 1 figur

Experimental Observation of Quantum Correlations in Modular Variables

We experimentally detect entanglement in modular position and momentum variables of photon pairs which have passed through $D$-slit apertures. We first employ an entanglement criteria recently proposed in [Phys. Rev. Lett. {\bf 106}, 210501 (2011)], using variances of the modular variables. We then propose an entanglement witness for modular variables based on the Shannon entropy, and test it experimentally. Finally, we derive criteria for Einstein-Podolsky-Rosen-Steering correlations using variances and entropy functions. In both cases, the entropic criteria are more successful at identifying quantum correlations in our data.Comment: 7 pages, 4 figures, comments welcom

Equações para estimar biomassa e volume de madeira em cerradões do Pantanal da Nhecolândia, MS.

A quantidade e a distribuição da biomassa e do volume de madeira são aspectos importantes para o uso sustentável e para a conservação dos ecossitemas. Apesar da sua importância, estes aspectos são poucos conhecidos e estudados nas áreas de cerradão do Brasil. Anderson & Ingram (1993) recomendam que a estimativa da biomassa em florestas nativas, com grandes número de espécies, seja obtida pela estimativa da biomassa direta (amostra destrutivabitstream/item/37487/1/CT50.pd

Self-Interacting Electromagnetic Fields and a Classical Discussion on the Stability of the Electric Charge

The present work proposes a discussion on the self-energy of charged particles in the framework of nonlinear electrodynamics. We seek magnet- ically stable solutions generated by purely electric charges whose electric and magnetic fields are computed as solutions to the Born-Infeld equa- tions. The approach yields rich internal structures that can be described in terms of the physical fields with explicit analytic solutions. This suggests that the anomalous field probably originates from a magnetic excitation in the vacuum due to the presence of the very intense electric field. In addition, the magnetic contribution has been found to exert a negative pressure on the charge. This, in turn, balances the electric repulsion, in such a way that the self-interaction of the field appears as a simple and natural classical mechanism that is able to account for the stability of the electron charge.Comment: 8 pages, 1 figur

Spacetime Defects: von K\'arm\'an vortex street like configurations

A special arrangement of spinning strings with dislocations similar to a von K\'arm\'an vortex street is studied. We numerically solve the geodesic equations for the special case of a test particle moving along twoinfinite rows of pure dislocations and also discuss the case of pure spinning defects.Comment: 9 pages, 2figures, CQG in pres

The Pauli equation with complex boundary conditions

We consider one-dimensional Pauli Hamiltonians in a bounded interval with possibly non-self-adjoint Robin-type boundary conditions. We study the influence of the spin-magnetic interaction on the interplay between the type of boundary conditions and the spectrum. A special attention is paid to PT-symmetric boundary conditions with the physical choice of the time-reversal operator T.Comment: 16 pages, 4 figure

Caracterização fenológica da espécie Hybanthus ipecacuanha (L.) Saill.

A falsa-ipeca (Hybanthus ipecacuanha (L.) Saill.) é uma espécie medicinal muito utilizada no nordeste brasileiro como amebicida e expectorante. Herbácea anual ou perene apresenta folhas simples, alternas opostas e flores solitárias, geralmente brancas e com uma pétala grande. Apresenta distribuição neotropical, com distribuição na América do sul. Identificar os períodos de floração e frutificação torna-se importante para o cultivo, a coleta, o beneficiamento e a comercialização da espécie, através de cronogramas montados a partir de observações feitas em campo. O objetivo do trabalho foi avaliar o período de floração e frutificação da espécie H. ipecacuanha, cultivada no horto e plantas medicinais da Embrapa Amazônia Oriental. Os dados foram coletados diariamente nos períodos de janeiro de 2010 a dezembro de 2013, no horto de plantas medicinais da Embrapa Amazônia Oriental. Na primeira fenofase, foi observado ocorrência de floração de janeiro à março, em julho e de outubro a dezembro, sendo então, registrado a maior média do número de dias de floração no mês de novembro, com 16 dias. A frutificação ocorreu nos meses de janeiro a março e de setembro a dezembro, onde as maiores médias de dias foram registradas nos meses de outubro e novembro, respectivamente com 6 e 10 dias