Lorentz-violating dimension-five operator contribution to the black body radiation

We investigate the thermodynamics of a photon gas in an effective field theory model that describes Lorentz violations through dimension-five operators and Horava-Lifshitz theory. We explore the electrodynamics of the model which includes higher order derivatives in the Lagrangian that can modify the dispersion relation for the propagation of the photons. We shall focus on the deformed black body radiation spectrum and modified Stefan-Boltzmann law to address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL

The Casimir spectrum revisited

We examine the mathematical and physical significance of the spectral density sigma(w) introduced by Ford in Phys. Rev. D38, 528 (1988), defining the contribution of each frequency to the renormalised energy density of a quantum field. Firstly, by considering a simple example, we argue that sigma(w) is well defined, in the sense of being regulator independent, despite an apparently regulator dependent definition. We then suggest that sigma(w) is a spectral distribution, rather than a function, which only produces physically meaningful results when integrated over a sufficiently large range of frequencies and with a high energy smooth enough regulator. Moreover, sigma(w) is seen to be simply the difference between the bare spectral density and the spectral density of the reference background. This interpretation yields a simple `rule of thumb' to writing down a (formal) expression for sigma(w) as shown in an explicit example. Finally, by considering an example in which the sign of the Casimir force varies, we show that the spectrum carries no manifest information about this sign; it can only be inferred by integrating sigma(w).Comment: 10 pages, 4 figure

Equivalence between the Lovelock-Cartan action and a constrained gauge theory

We show that the four-dimensional Lovelock-Cartan action can be derived from a massless gauge theory for the $SO(1,3)$ group with an additional BRST trivial part. The model is originally composed by a topological sector and a BRST exact piece and has no explicit dependence on the metric, the vierbein or a mass parameter. The vierbein is introduced together with a mass parameter through some BRST trivial constraints. The effect of the constraints is to identify the vierbein with some of the additional fields, transforming the original action into the Lovelock-Cartan one. In this scenario, the mass parameter is identified with Newton's constant while the gauge field is identified with the spin-connection. The symmetries of the model are also explored. Moreover, the extension of the model to a quantum version is qualitatively discussed.Comment: 17 pages. No figures. Final version accepted for publication at the EPJ

Principal component analysis as a tool to correlate properties of different laboratorial papers

We measured fibre morphological properties and corresponding handsheet paper properties in pulps obtained from Eucalyptus globulus, Acacia dealbata and Acacia melanoxylon wood samples. The three wood samples were chipped, cooked, and bleached according to standard procedures. The basic chip densities of the samples obtained from the three species studied were 0.351g/cm3, 0.387g/cm3 and 0.536g/cm3, respectively for A. dealbata, A. melanoxylon and E. globulus. All species were submitted to cooking with the following reaction conditions: active alkali charge = 22% (as NaOH); sulfidity index = 30%; liquor/wood ratio = 4/1; time to temperature = 90 min; time at temperature (160 ºC) = 120 min. Acacia species show higher pulp yield than the E. globulus sample used as a reference and cooking selectivity is higher in the Acacia species investigated. The three pulps were beaten in a PFI mill at 500, 2500 and 4500 revolutions under a refining intensity of 3.33 N/mm, and laboratory paper sheets were produced, including the unbeaten pulps, which made up 4 samples per species. The corresponding fibre characteristics in suspension were also determined. We used principal components analysis to investigate the differences in fibre characteristics and paper properties, as well as their interaction. Each value of these variables represents a mean of 10 tests, for the paper sheets. This methodology allowed us to determine how close, or how independent, the study variables were. We conclude there is a group of paper characteristics which depend strongly on each other - paper density, smoothness, tensile index, stretch, burst index, Schopper Riegler degree, internal cohesion and WRV – and are negatively correlated with the light scattering coefficient, opacity and brightness. On the other hand, intrinsic paper fibre resistance is strongly affected by fibre length and coarseness. On the basis of the properties we studied, it is clear that paper produced from Eucalyptus fibre has different properties from that produced from Acacia fibre. Papers produced from both species of Acacia are similar

Wood and pulp properties of two Eucalyptus globulus wood samples

This paper reports experimental data about wood chemical composition (extractives and lignin content), fibre characteristics, kraft cooking behaviour and papermaking potential of two wood samples of Eucalyptus globulus (one industrial chip sample and another obtained from a clone tree). The samples were submitted to the kraft cooking and bleaching processes in order to evaluate its pulping potential. The experimental results showed that the clone tree requires milder cooking conditions and exhibits higher pulp yield. The pulp fibres obtained from the clone have higher fibre length and fibre width and lower coarseness, which give higher fibre flexibility and collapsibility. In consequence, structural, mechanical and optical properties of paper are significantly different. In addition, we observed that the fibres from the clone tree are weaker than the corresponding fibres from the industrial sample

Efeito do teor de hemiceluloses na qualidade de papel produzido com fibra de eucalipto

Este estudo analisa o efeito do teor de hemiceluloses das pastas de eucalipto nas características do papel produzido. Para o efeito, utilizaram-se aparas industriais de Eucalyptus globulus, com massa volúmica básica de 536 ± 4 kg/m3. As aparas crivadas foram sujeitas ao processo kraft, convencional e modificado, para a produção das respectivas pastas cruas com teores de hemiceluloses diferentes. Os cozimentos realizaram-se num digestor descontínuo de circulação forçada, com 1000g de madeira. A pasta crua foi submetida a um branqueamento ECF com dióxido de cloro, segundo uma sequência de cinco estágios (D0E1D1E2D2). As duas pastas, convencional e modificada, apresentaram teores de hemiceluloses da ordem dos 19% e 14%, respectivamente. Posteriormente, a pasta branca foi caracterizada em termos biométricos e papeleiro. Para este fim, a pasta foi refinada em PFI (ISO 5264/2-79) a diversas revoluções e com uma carga específica de bordo de 2 Nmm-1, tendo-se contabilizado o consumo de energia. Caracterizou-se a suspensão fibrosa e o potencial papeleiro. Para um dado número de revoluções em PFI, a resistência à drenagem, a densidade e a resistência à tracção das folhas aumentam com o incremento do teor de hemiceluloses. Assim, para produzir papéis com a mesma densidade, as pastas com menor teor de hemiceluloses requerem mais energia de refinação