Quantum Perfect-Fluid Kaluza-Klein Cosmology

The perfect fluid cosmology in the 1+d+D dimensional Kaluza-Klein spacetimes for an arbitrary barotropic equation of state $p= n \rho$ is quantized by using the Schutz's variational formalism. We make efforts in the mathematics to solve the problems in two cases. For the first case of the stiff fluid $n=1$ we exactly solve the Wheeler-DeWitt equation when the $d$ space is flat. After the superposition of the solutions we analyze the Bohmian trajectories of the final-stage wave-packet functions and show that the flat $d$ spaces and the compact $D$ spaces will eventually evolve into finite scale functions. For the second case of $n \approx 1$, we use the approximated wavefunction in the Wheeler-DeWitt equation to find the analytic forms of the final-stage wave-packet functions. After analyzing the Bohmian trajectories we show that the flat $d$ spaces will be expanding forever while the scale function of the contracting $D$ spaces would not become zero within finite time. Our investigations indicate that the quantum effect in the quantum perfect-fluid cosmology could prevent the extra compact $D$ spaces in the Kaluza-Klein theory from collapsing into a singularity or that the "crack-of-doom" singularity of the extra compact dimensions is made to occur at $t=\infty$.Comment: Latex 18 pages, add section 2 to introduce the quantization of perfect flui

Does Quantum Cosmology Predict a Constant Dilatonic Field?

Quantum cosmology may permit to determine the initial conditions of the Universe. In particular, it may select a specific model between many possible classical models. In this work, we study a quantum cosmological model based on the string effective action coupled to matter. The Schutz's formalism is employed in the description of the fluid. A radiation fluid is considered. In this way, a time coordinate may be identified and the Wheeler-DeWitt equation reduces in the minisuperspace to a Schr\"odinger-like equation. It is shown that, under some quite natural assumptions, the expectation values indicate a null axionic field and a constant dilatonic field. At the same time the scale factor exhibits a bounce revealing a singularity-free cosmological model. In some cases, the mininum value of the scale factor can be related to the value of gravitational coupling.Comment: Latex file, 14 page

Influência da relação altura/comprimento de pórticos metálicos na rigidez lateral de estruturas compostas de pórticos preenchidos com alvenaria : avaliação experimental

Uma solução bastante freqüente para preenchimento de pórticos de aço é a utilização de painéis de alvenaria de blocos de concreto celular autoclavados. Esta associação produz efeitos benéficos relacionados à resistência, rigidez e ductilidade da estrutura composta resultante. Neste trabalho apresenta-se um estudo experimental da influência da relação altura/comprimento (H/L) de pórticos metálicos na rigidez de estruturas compostas de pórticos preenchidos com alvenaria. Foram utilizados dois pórticos de aço de perfis soldados, de dimensões em cm 322x275 e 522x275, correspondendo às relações altura/comprimento (H/L) iguais a 0,83 e 0,51, respectivamente. Para preenchimento dos pórticos foram utilizados painéis de blocos de alvenaria estrutural de concreto celular autoclavados, enquanto nas juntas entre blocos e na interface pórtico-painel utilizou-se argamassa colante. O conjunto pórtico-painel foi submetido a uma ação horizontal aplicada no eixo da viga superior do pórtico, que trabalhou em regime elástico, enquanto a alvenaria foi ensaiada até o colapso, a fim de obter o modo de ruptura para a mesma. Os resultados obtidos comprovam que quanto menor a relação H/L dos pórticos preenchidos, menor a rigidez e maior a carga de ruptura por fissuração da diagonal, embora surjam fissuras verticais

Anomalous metamagnetic-like transition in a FeRh/Fe3_3Pt interface occurring at T120 K in the field-cooled-cooling curves for low magnetic fields

We report on the magnetic properties of a special configuration of a FeRh thin film. An anomalous behavior on the magnetisation vs. temperature was observed when low magnetic fields are applied in the plane of a thin layer of FeRh deposited on ordered Fe$_3$Pt. The anomalous effect resembles a metamagnetic transition and occur only in the field-cooled-cooling magnetisation curve at temperatures near 120 K in samples without any heat treatment.Comment: 7 pages, 5 figures. arXiv admin note: text overlap with arXiv:1008.195

Iinfluencia de micropartículas de residuos de vidrio soda-lime en la trabajabilidad y propiedades térmicas de compuestos de cemento portland

Numerous studies have investigated the use of waste glass as a partial substitution in Portland cement. Nonetheless, it seems there is no consensus about the influence of particle size and color on the behavior of the compounds. This work investigates the influence of soda-lime glass microparticles on the properties of cement and mortar in both fresh and hardened states. The effects of partial substitution (10 and 20%) of the cement by colorless and amber glass particles with dimensions of approximately 9.5 mm were investigated. The results revealed that the substitutions did not significantly affect the setting times, nor the mechanical properties of mortar at longer curing times. The influence of glass content and chemical composition on workability and hydration heat was also observed. The waste glass samples showed lower thermal diffusivity than the control sample. Thermal emissivity was not influenced by the presence of glass microparticles.Diferentes estudios han investigado el uso de residuos de vidrio como un sustituto parcial del cemento Portland. Sin embargo, parece no haber consenso sobre la influencia del tamaño o del color de la partícula en el comportamiento de los compuestos. Este trabajo aborda la influencia de micropartículas de vidrio soda-lime en las propiedades del cemento y de los morteros tanto en estado fresco como endurecido. Se han investigado los efectos de la sustitución parcial del 10 y 20% del cemento por partículas de vidrio incoloro o color ámbar con dimensiones alrededor de 9.5 mm. Los resultados revelaron que las sustituciones no afectan notablemente los tiempos de fraguado, tampoco las propiedades mecánicas de los morteros en los tiempos más largos de curado. Se observó la influencia del contenido y composición química del vidrio en la trabajabilidad y calor de hidratación. Las muestras con residuos vítreos mostraron una difusividad térmica más baja que la muestra sin residuos. La emisividad termica no se vió afectada por la presencia de micropartículas de vidrio