169 research outputs found
Recommended from our members
Visualization methods for high-resolution, transient, 3-D, finite element situations
Scientific visualization is the process whereby numerical data is transformed into a visual form to augment the process of discovery and understanding. Visualizing the data generated by large-scale, transient, three-dimensional finite element simulations poses many challenges due to geometric complexity, the presence of multiple materials and multiple element types, and the inherent unstructured nature of the meshes. In this paper, the direct use of finite element data structures, nodal assembly procedures, and element interpolants for volumetric adaptive surface extraction, surface rendering, vector grids and particle tracing is discussed. A brief description of a {open_quotes}direct-to-disk{close_quotes} animation system is presented, and case studies which demonstrate the use of isosurfaces, vector plots, cutting planes, reference surfaces and particle tracing are then discussed in the context of several case studies for transient incompressible viscous flow, and acoustic fluid-structure interaction simulations. An overview of the implications of massively parallel computers on visualization is presented to highlight the issues in parallel visualization methodology, algorithms. data locality and the ultimate requirements for temporary and archival data storage and network bandwidth
Generalised-Lorentzian Thermodynamics
We extend the recently developed non-gaussian thermodynamic formalism
\cite{tre98} of a (presumably strongly turbulent) non-Markovian medium to its
most general form that allows for the formulation of a consistent thermodynamic
theory. All thermodynamic functions, including the definition of the
temperature, are shown to be meaningful. The thermodynamic potential from which
all relevant physical information in equilibrium can be extracted, is defined
consistently. The most important findings are the following two: (1) The
temperature is defined exactly in the same way as in classical statistical
mechanics as the derivative of the energy with respect to the entropy at
constant volume. (2) Observables are defined in the same way as in Boltzmannian
statistics as the linear averages of the new equilibrium distribution function.
This lets us conclude that the new state is a real thermodynamic equilibrium in
systems capable of strong turbulence with the new distribution function
replacing the Boltzmann distribution in such systems. We discuss the ideal gas,
find the equation of state, and derive the specific heat and adiabatic exponent
for such a gas. We also derive the new Gibbsian distribution of states. Finally
we discuss the physical reasons for the development of such states and the
observable properties of the new distribution function.Comment: 13 pages, 1 figur
Revisiting the role of magnetic field fluctuations in nonadiabatic acceleration of ions during dipolarization
Using energetic (9–212 keV/e) ion flux data obtained by the Geotail spacecraft, Ono et al. (2009) statistically examined changes in the energy density of H+ and O+ ions in the near-Earth plasma sheet during substorm-associated dipolarization. They found that ions are nonadiabatically accelerated by the electric field induced by the magnetic field fluctuations whose frequencies are close to their gyrofrequencies. The present paper revisits this result and finds it still holds
Recommended from our members
Laminar backward-facing step flow using the finite element method
Laminar, incompressible flow over a backward-facing step is calculated using a finite element spatial discretization with a piecewise continuous pressure approximation and an explicit time marching algorithm. The time-accurate evolution to steady state is demonstrated for both two-dimensional (2D) and three-dimensional (3D) simulations. This approach is shown to accurately predict the lengths of the recirculation zone on the top wall and at the step for various meshes and domain lengths, for a Reynolds number of 800 based on the average inlet velocity and twice the inlet channel height. The instantaneous and steady-state results are investigated. The steady-state solutions are evaluated by comparison to published numerical and experimental results
Banded electron structure formation in the inner magnetosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94985/1/grl10936.pd
Disparities in the Clinical Encounter: Virginia's African American Children with Special Health Care Needs
This study analyzed Virginia data from the most recent National Survey of Children with Special Health Care Needs. Logistic regression models were run for six Maternal and Child Health Bureau core outcomes and included demographics, child characteristics, health care providers, and health care access variables as predictors. Race/ethnicity disparities were judged to be present if the race/ethnicity variable was a significant predictor in the final model. Examining the components of disparate outcomes, African American children were found to be less likely than their white counterparts to have a usual source for sick and preventive care and to have a personal doctor or nurse. Their parents were less likely to say that doctors spent enough time, listened carefully, were sensitive to values and customs, and made them feel like a partner. These findings emphasize the need to examine health care disparities at a state level in order to guide efforts at remediation
Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si
Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin.publishedVersio
The electromagnetic ion-cyclotron instability in bi-Kappa distributed plasmas
Context. Observations regularly show low-frequency fluctuations of the interplanetary magnetic field (IMF), which are attributed to the electromagnetic ion-cyclotron (EMIC) waves generated either locally and self-consistently by the kinetic anisotropies of ions, or closer to the Sun (through a nonlinear cascade from long to short wavelengths), and transported by the super-Alfvenic solar wind. As a back reaction, ions can be pitch-angle scattered and accelerated, leading to the observed suprathermal populations, which are invariably anisotropic and are well described by the generalized Kappa models. Aims. A refined analysis is proposed for the EMIC wave instability as one of the most plausible constraints for the proton temperature anisotropy T p, < T p, where and denote directions relative to the stationary IMF. In the context of a strong, but not clear competition with the mirror instability that can develop in the same conditions, an advanced Kappa model is expected to provide the first realistic insights into the EMIC instability conditions in the solar wind. Methods. Because the solar wind is a poor-collisional plasma, the dispersion/stability formalism is based on the fundamental kinetic Vlasov-Maxwell equations for an nonthermal bi-Kappa distributed plasma. EMIC solutions are derived exactly numerically, providing accurate physical correlations between the maximum growth rates and the instability threshold conditions, which are here derived for the full range of values of the plasma beta, including the solar wind and magnetospheric plasma conditions. Results. The lowest thresholds (close to the marginal stability), which are the most relevant for the instability conditions, decrease with the increase in density of suprathermal populations. This is contrary to what was found before in a less general model, but it is fully predicted by the enhanced fluctuations of this instability for sufficiently low temperature anisotropies. These results furthermore support a fast and efficient EMIC instability involving the relaxation of kinetic anisotropies and (re)heating plasma particles. © 2012 ESO.status: publishe
Electron Surfing Acceleration in Magnetic Reconnection
We discuss that energetic electrons are generated near the X-type magnetic
reconnection region due to a surfing acceleration mechanism. In a thin plasma
sheet, the polarization electric fields pointing towards the neutral sheet are
induced around the boundary between the lobe and plasma sheet in association
with the Hall electric current. By using a particle-in-cell simulation, we
demonstrate that the polarization electric fields are strongly enhanced in an
externally driven reconnection system, and some electrons can be trapped by the
electrostatic potential well of the polarization field. During the trapping
phase, the electrons can gain their energies from the convection/inductive
reconnection electric fields. We discuss that relativistic electrons with MeV
energies are quickly generated in and around the X-type neutral region by
utilizing the surfing acceleration
- …