96,633 research outputs found
Finite element analysis of non-isothermal multiphase porous media in dynamics
This work presents a mathematical and a numerical model for the analysis of the
thermo-hydro-mechanical (THM) behavior of multiphase deformable porous materials
in dynamics. The fully coupled governing equations are developed within the
Hybrid Mixture Theory. To analyze the THM behavior of soil structures in the low
frequency domain, e.g. under earthquake excitation, the u-p-T formulation is advocated
by neglecting the relative acceleration of the fluids and their convective terms.
The standard Bubnov-Galerkin method is applied to the governing equations for the
spatial discretization, whereas the generalized Newmark scheme is used for the time
discretization. The final non-linear and coupled system of algebraic equations is
solved by the Newton method within the monolithic approach. The formulation and
the implemented solution procedure are validated through the comparison with
other finite element solutions or analytical solutions
Macroscopic models of local field potentials and the apparent 1/f noise in brain activity
The power spectrum of local field potentials (LFPs) has been reported to
scale as the inverse of the frequency, but the origin of this "1/f noise" is at
present unclear. Macroscopic measurements in cortical tissue demonstrated that
electric conductivity (as well as permittivity) is frequency dependent, while
other measurements failed to evidence any dependence on frequency. In the
present paper, we propose a model of the genesis of LFPs which accounts for the
above data and contradictions. Starting from first principles (Maxwell
equations), we introduce a macroscopic formalism in which macroscopic
measurements are naturally incorporated, and also examine different physical
causes for the frequency dependence. We suggest that ionic diffusion primes
over electric field effects, and is responsible for the frequency dependence.
This explains the contradictory observations, and also reproduces the 1/f power
spectral structure of LFPs, as well as more complex frequency scaling. Finally,
we suggest a measurement method to reveal the frequency dependence of current
propagation in biological tissue, and which could be used to directly test the
predictions of the present formalism
The Speed of Gravity in General Relativity and Theoretical Interpretation of the Jovian Deflection Experiment
Recent measurements of the propagation of the quasar's radio signal past
Jupiter are directly sensitive to the time-dependent effect from the geometric
sector of general relativity which is proportional to the speed of propagation
of gravity but not the speed of light. It provides a first confirmative
measurement of the fundamental speed of the Einstein general principle of
relativity for gravitational field.Comment: 45 pages, 6 figures, publishe
Sub-Microarcsecond Astrometry and New Horizons in Relativistic Gravitational Physics
Attaining the limit of sub-microarcsecond optical resolution will completely
revolutionize fundamental astrometry by merging it with relativistic
gravitational physics. Beyond the sub-microarcsecond threshold, one will meet
in the sky a new population of physical phenomena caused by primordial
gravitational waves from early universe and/or different localized astronomical
sources, space-time topological defects, moving gravitational lenses, time
variability of gravitational fields of the solar system and binary stars, and
many others. Adequate physical interpretation of these yet undetectable
sub-microarcsecond phenomena can not be achieved on the ground of the
"standard" post-Newtonian approach (PNA), which is valid only in the near-zone
of astronomical objects having a time-dependent gravitational field. We
describe a new, post-Minkowskian relativistic approach for modeling astrometric
observations having sub-microarcsecond precision and briefly discuss the
light-propagation effects caused by gravitational waves and other phenomena
related to time-dependent gravitational fields. The domain of applicability of
the PNA in relativistic space astrometry is explicitly outlined.Comment: 5 pages, the talk given at the IAU Colloquium 180 "Towards Models and
Constants for Sub-Microarcsecond Astrometry", Washington DC, March 26 - April
2, 200
Strain injection techniques in dynamic fracture modeling
A computationally affordable modeling of dynamic fracture phenomena is performed in this study by using strain injection techniques and Finite Elements with Embedded strong discontinuities (E-FEM). In the present research, classical strain localization and strong discontinuity approaches are considered by injecting discontinuous strain and displacement modes in the finite element formulation without an increase of the total number of degrees of freedom. Following the Continuum Strong Discontinuity Approach (CSDA), stress–strain constitutive laws can be employed in the context of fracture phenomena and, therefore, the methodology remains applicable to a wide number of continuum mechanics models. The position and orientation of the displacement discontinuity is obtained through the solution of a crack propagation problem, i.e. the crack path field, based on the distribution of localized strains. The combination of the above mentioned approaches is envisaged to avoid stress-locking and directional mesh bias phenomena. Dynamic simulations are performed increasing the loading rate up to the appearance of crack branching, and the variation in terms of failure modes is investigated as well as the influence of the strain injection together with the crack path field algorithm. Objectivity of the presented methodology with respect to the spatial and temporal discretization is analyzed in terms of the dissipated energy during the fracture process. The dissipation at the onset of branching is studied for different loading rate conditions and is linked to the experimental maximum velocity observed before branching takes place.Fil: Lloberas Valls, Oriol. Universidad Politecnica de Catalunya; España. Centre Internacional de Metodes Numerics en Enginyeria; EspañaFil: Huespe, Alfredo Edmundo. Centre Internacional de Metodes Numerics en Enginyeria; España. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Santa Fe. Centro de Investigaciones en MĂ©todos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en MĂ©todos Computacionales; ArgentinaFil: Oliver, J.. Centre Internacional de Metodes Numerics en Enginyeria; España. Universidad Politecnica de Catalunya; EspañaFil: Dias, I.F.. LaboratĂłrio Nacional de Engenharia Civil; Portuga
Fast Escape from Quantum Mazes in Integrated Photonics
Escaping from a complex maze, by exploring different paths with several
decision-making branches in order to reach the exit, has always been a very
challenging and fascinating task. Wave field and quantum objects may explore a
complex structure in parallel by interference effects, but without necessarily
leading to more efficient transport. Here, inspired by recent observations in
biological energy transport phenomena, we demonstrate how a quantum walker can
efficiently reach the output of a maze by partially suppressing the presence of
interference. In particular, we show theoretically an unprecedented improvement
in transport efficiency for increasing maze size with respect to purely quantum
and classical approaches. In addition, we investigate experimentally these
hybrid transport phenomena, by mapping the maze problem in an integrated
waveguide array, probed by coherent light, hence successfully testing our
theoretical results. These achievements may lead towards future bio-inspired
photonics technologies for more efficient transport and computation.Comment: 13 pages, 10 figure
Planning Curricular Proposals on Sound and Music with Prospective Secondary-School Teachers
Sound is a preferred context to build foundations on wave phenomena, one of
the most important disciplinary referents in physics. It is also one of the
best-set frameworks to achieve transversality, overcoming scholastic level and
activating emotional aspects which are naturally connected with every day life,
as well as with music and perception. Looking at sound and music by a
transversal perspective - a border-line approach between science and art, is
the adopted statement for a teaching proposal using meta-cognition as a
strategy in scientific education. This work analyzes curricular proposals on
musical acoustics, planned by prospective secondary-school teachers in the
framework of a Formative Intervention Module answering the expectation of
making more effective teaching scientific subjects by improving creative
capabilities, as well as leading to build logical and scientific
categorizations able to consciously discipline artistic activity in music
students. With this aim, a particular emphasis is given to those concepts -
like sound parameters and structural elements of a musical piece, which are
best fitted to be addressed on a transversal perspective, involving
simultaneously physics, psychophysics and music.Comment: 12 pages with 5 figures. Submitted for publication in Physics
Curriculum Design, Development and Validation - GIREP 2008 book of selected
papers, 200
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