A Growth Model for Porous Sedimentary Rocks

A growth model for porous sedimentary rocks is proposed, using a simple computer simulation algorithm. We generate the structure by ballistic deposition of particles with a bimodal size distribution. Porosity and specific surface area are calculated varying the proportion of small and larger particles. Permeability and its variation with porosity are studied. The fractal nature of the pore space is also discussed.Comment: 11 pages, Latex format, figures available on reques

Driven Interface Depinning in a Disordered Medium

The dynamics of a driven interface in a medium with random pinning forces is analyzed. The interface undergoes a depinning transition where the order parameter is the interface velocity $v$, which increases as $v \sim (F-F_c)^\theta$ for driving forces $F$ close to its threshold value $F_c$. We consider a Langevin-type equation which is expected to be valid close to the depinning transition of an interface in a statistically isotropic medium. By a functional renormalization group scheme the critical exponents characterizing the depinning transition are obtained to the first order in $\epsilon=4-D>0$, where $D$ is the interface dimension. The main results were published earlier [T. Nattermann et al., J. Phys. II France {\bf 2} (1992) 1483]. Here, we present details of the perturbative calculation and of the derivation of the functional flow equation for the random-force correlator. The fixed point function of the correlator has a cusp singularity which is related to a finite value of the threshold $F_c$, similar to the mean field theory. We also present extensive numerical simulations and compare them with our analytical results for the critical exponents. For $\epsilon =1$ the numerical and analytical results deviate from each other by only a few percent. The deviations in lower dimensions $\epsilon = 2,3$ are larger and suggest that the roughness exponent is somewhat larger than the value $\zeta = \epsilon / 3$ of an interface in thermal equilibrium.Comment: 32 pages, 14 figures, REVTeX, to be published in Annalen der Physi

Self similar Barkhausen noise in magnetic domain wall motion

A model for domain wall motion in ferromagnets is analyzed. Long-range magnetic dipolar interactions are shown to give rise to self-similar dynamics when the external magnetic field is increased adiabatically. The power spectrum of the resultant Barkhausen noise is of the form $1/\omega^\alpha$, where $\alpha\approx 1.5$ can be estimated from the critical exponents for interface depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let

Pumping of Concrete: Understanding a Common Placement Method with Lots of Challenges

Several million cubic meters of concrete are pumped daily, as this technique permits fast concrete placement. Fundamental research has been performed and practical guidelines have been developed to increase the knowledge of concrete behavior in pipes. However, the pumping process and concrete behavior are not fully understood. This paper gives an overview of the current knowledge of concrete pumping. At first, the known physics governing the flow of concrete in pipes are introduced. A series of experimental techniques characterizing concrete flow behavior near a smooth wall to predict pressure-flow rate relationships are discussed, followed by recent developments in the use of numerical simulations of concrete behavior in pipes. The influence of the pumping process on concrete rheology and air-void system is reviewed, and the first developments in active rheology control for concrete pumping are introduced. The last section of this paper gives an overview of open research questions and challenges

Vortex dynamics in disordered Josephson junction arrays: from plastic flow to flux flow

We study the dynamics of Josephson junction arrays with positional disorder and driven by an external current. We consider weak magnetic fields, corresponding to a frustration $f=n+1/25$ with $n$ integer. We find that above the critical current $i_c$ there is a plastic flow of vortices, where most of the vortices are pinned and only a few vortices flow through channels. This dynamical regime is characterized by strong fluctuations of the total vorticity. The number of the flow channels grow with increasing bias current. At larger currents there is a dynamical regime characterized by the homogeneous motion of all the vortices, i.e. a flux flow regime. We find a dynamical phase transition between the plastic flow and the flux flow regimes when analyzing voltage-voltage correlation functions.Comment: 9 pages. 3 Figures available upon request. Presented in the Workshop on Josephson Junction Arrays, ICTP (August 1995). To appear in Physica B (1996

O ensino de arte na Educação de Jovens e Adultos e as metodologias em sala de aula

Monografia (graduação)—Universidade Aberta do Brasil, Universidade de Brasília, Instituto de Artes, Departamento de Artes Visuais, 2012. Curso de Licenciatura em Artes Visuais a Distância.Este trabalho de conclusão de curso enfatiza a importância da Arte na formação do jovem e adulto bem como as práticas pedagógicas utilizadas na modalidade de ensino da EJA (8º ano do 2º segmento) da escola pública do Município Mestre Francisco, localizada na cidade de Peixe - Tocantins, a fim de verificar sua adequação ao contexto dos alunos. Há décadas, buscam-se métodos e práticas educativas adequadas à realidade cultural e ao nível de subjetividade dos jovens e adultos, no entanto, é com as atividades da disciplina de Arte que esta busca se encurta. A pesquisa perpassa a história e o parâmetro legal da Educação de Jovens e Adultos. Fundamenta-se com Freire (1981), Barbosa (2003), Arslan (2009), Duarte Junior (2008), na Lei de Diretrizes e Bases da Educação Nacional, na Proposta Curricular para a EJA/TO, Ferraz e Siqueira (2003) e ainda um olhar sobre os Parâmetros Curriculares Nacionais de Arte. Os resultados desse estudo apontam a disciplina de Arte como um elo entre as outras disciplinas do currículo e que é tão importante quanto as demais no que tange a sua contribuição ao aprendizado e formação do aluno, da mesma forma se deve pensar sobre as práticas pedagógicas, que de fato prendem a atenção dessa clientela em sala de aula. Portanto, esse estudo contribuirá para um repensar do educador que atua frente à disciplina de Arte nas classes da Educação de Jovens e Adultos, fazendo-os refletir sobre sua prática pedagógica e também sobre as reais contribuições da disciplina de Arte para/na formação de educandos cônscios de seu papel na sociedade. ___________________________________________________________________________ ABSTRACTThis work emphasizes the importance of art in the formation of young and adult as well as pedagogical practices used in the teaching mode of the EJA (8th grade 2nd segment) public school Master Francisco Municipality, located in the city of fish-Tocantins, in order to verify their suitability to the context of the students. For decades, seek out educational methods and practices appropriate to the cultural reality and the level of subjectivity of youth and adults, however, is with the activities of the art discipline that seeks to shorten. Research permeates the history and the legal parameter of adult and youth education. It rests with Freire (1981), Babu (2003), Arslan (2009), Duarte Junior (2008), in the law of Guidelines and Bases for national education in the Curricular Proposal for EJA/TO, Fernandez; Servin (2003) and even a glance at the art curriculum parameters. The results of this study indicate the discipline of art as a link between the other disciplines of the curriculum and that is just as important as the other in terms of their contribution to student learning, likewise one should think about pedagogical practices, which is in fact who holds the attention of this clientele in the classroom. Therefore, this study will contribute to a rethinking of the educator, who plays opposite art discipline in classes of adult and youth education, causing them to reflect on their teaching practice and also on the actual contributions of Art to/in formation of learners aware of their role in society

Using force covariance to derive effective stochastic interactions in dissipative particle dynamics

There exist methods for determining effective conservative interactions in coarse grained particle based mesoscopic simulations. The resulting models can be used to capture thermal equilibrium behavior, but in the model system we study do not correctly represent transport properties. In this article we suggest the use of force covariance to determine the full functional form of dissipative and stochastic interactions. We show that a combination of the radial distribution function and a force covariance function can be used to determine all interactions in dissipative particle dynamics. Furthermore we use the method to test if the effective interactions in dissipative particle dynamics (DPD) can be adjusted to produce a force covariance consistent with a projection of a microscopic Lennard-Jones simulation. The results indicate that the DPD ansatz may not be consistent with the underlying microscopic dynamics. We discuss how this result relates to theoretical studies reported in the literature.Comment: 10 pages, 10 figure

Anisotropic Scaling in Threshold Critical Dynamics of Driven Directed Lines

The dynamical critical behavior of a single directed line driven in a random medium near the depinning threshold is studied both analytically (by renormalization group) and numerically, in the context of a Flux Line in a Type-II superconductor with a bulk current $\vec J$. In the absence of transverse fluctuations, the system reduces to recently studied models of interface depinning. In most cases, the presence of transverse fluctuations are found not to influence the critical exponents that describe longitudinal correlations. For a manifold with $d=4-\epsilon$ internal dimensions, longitudinal fluctuations in an isotropic medium are described by a roughness exponent $\zeta_\parallel=\epsilon/3$ to all orders in $\epsilon$, and a dynamical exponent $z_\parallel=2-2\epsilon/9+O(\epsilon^2)$. Transverse fluctuations have a distinct and smaller roughness exponent $\zeta_\perp=\zeta_\parallel-d/2$ for an isotropic medium. Furthermore, their relaxation is much slower, characterized by a dynamical exponent $z_\perp=z_\parallel+1/\nu$, where $\nu=1/(2-\zeta_\parallel)$ is the correlation length exponent. The predicted exponents agree well with numerical results for a flux line in three dimensions. As in the case of interface depinning models, anisotropy leads to additional universality classes. A nonzero Hall angle, which has no analogue in the interface models, also affects the critical behavior.Comment: 26 pages, 8 Postscript figures packed together with RevTeX 3.0 manuscript using uufiles, uses multicol.sty and epsf.sty, e-mail [email protected] in case of problem

Permeability Estimates of Self-Affine Fracture Faults Based on Generalization of the Bottle Neck Concept

We propose a method for calculating the effective permeability of two-dimensional self-affine permeability fields based on generalizing the one-dimensional concept of a bottleneck. We test the method on fracture faults where the local permeability field is given by the cube of the aperture field. The method remains accurate even when there is substantial mechanical overlap between the two fracture surfaces. The computational efficiency of the method is comparable to calculating a simple average and is more than two orders of magnitude faster than solving the Reynolds equations using a finite-difference scheme

Novel type of phase transition in a system of self-driven particles

A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation ($\eta$) added. We present numerical evidence that this model results in a kinetic phase transition from no transport (zero average velocity, $| {\bf v}_a | =0$) to finite net transport through spontaneous symmetry breaking of the rotational symmetry. The transition is continuous since $| {\bf v}_a |$ is found to scale as $(\eta_c-\eta)^\beta$ with $\beta\simeq 0.45$