The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, with the funding from this NASA program, we concentrated on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we developed unique global models that allowed us to study the coupling between the different regions. These results are highlighted in the next section. Another important aspect of our NASA Theory Program concerned the effect that localized 'structure' had on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkland current patterns) or time variations in these input due to storms and substorms. Also, some of the plasma flows that we predicted with our macroscopic models could be unstable, and another one of our goals was to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another goal of our NASA Theory Program was to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This could involve a detailed comparison of kinetic, semi-kinetic, and hydrodynamic predictions for a given polar wind scenario or it could involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations provides insight into when the various models can be used with confidence

GOMA - A full-Newton finite element program for free and moving boundary problems with coupled fluid/solid momentum, energy, mass, and chemical species transport: User`s guide

GOMA is a two- and three-dimensional finite element program which excels in analyses of manufacturing processes, particularly those involving free or moving interfaces. Specifically, the full-Newton-coupled heat, mass, momentum, and pseudo-solid mesh motion algorithm makes GOMA ideally suited for simulating processes in which the bulk fluid transport is closely coupled to the interfacial physics. Examples include, but are not limited to, coating and polymer processing flows, soldering, crystal growth, and solid-network or solution film drying. The code is based on the premise that any boundary can be (1) moving or free, with an apriori unknown position dictated by the distinguishing physics, (2) fixed, according to a global analytical representation, or (3) moving in time and space under user-prescribed kinematics. The goal is to enable the user to predict boundary position or motion simultaneously with the physics of the problem being analyzed and to pursue geometrical design studies and fluid-structure interaction problems. The moving mesh algorithm treats the entire domain as a computational Lagrangian solid that deforms subject to the physical principles which dictate boundary position. As an added benefit, the same Lagrangian solid mechanics can be exploited to solve multi-field problems for which the solid motion and stresses interact with other transport phenomena, either within the same material phase (e.g. shrinking coating) or in neighboring material phases (e.g. flexible blade coating). Thus, analyses of many fluid-structure interaction problems and deformable porous media problems are accessible. This document serves as a user`s guide and reference for GOMA and provides a brief overview of GOMA`s capabilities, theoretical background, and classes of problems for which it is targeted

Academic achievement : the role of praise in motivating students

The motivation of students is an important issue in higher education, particularly in the context of the increasing diversity of student populations. A social-cognitive perspective assumes motivation to be dynamic, context-sensitive and changeable, thereby rendering it to be a much more differentiated construct than previously understood. This complexity may be perplexing to tutors who are keen to develop applications to improve academic achievement. One application that is within the control of the tutor, at least to some extent, is the use of praise. Using psychological literature the article argues that in motivating students, the tutor is not well served by relying on simplistic and common sense understandings of the construct of praise and that effective applications of praise are mediated by students' goal orientations, which of themselves may be either additive or interactive composites of different objectives and different contexts

Finite-element analyses of blade and slot coating flows using an implicit pseudo-solid domain mapping technique coupled with unstructured grids

In coating processes (e.g. in blade coating) the flow domain inherently contains free surfaces and three-phase contact lines, and characteristic length scales of flow features in the dimension transverse to the web-movement vary by an order of magnitude or more from a fraction of a millimeter or more to tens of microns or less). The presence of free surfaces and three-phase contact lines, and the sudden changes of flow geometry and directions create difficulties in theoretical analyses of such flows. Though simulations of coating flows via finite-element methods using structured grids have been reportedly demonstrated in the literature, achieving high efficiency of such numerical experiments remains a grand challenge -- mainly due to difficulties in local mesh-refinement and in avoiding unacceptably distorted grids. High efficiency of computing steady flow fields under various process conditions is crucial in shortening turn-around time in design and optimization of coating-flow processes. In this paper we employ a fully-implicit, pseudo-solid, domain mapping technique coupled with unstructured meshes to analyze blade and slot coating flows using Galerkin`s method with finite element basis functions. We demonstrate the robustness and efficiency of our unique technique in circumventing shortcomings of mesh-motion schemes currently being used in the coating-flow research community. Our goal is to develop an efficient numerical tool, together with a suitable optimization toolkit, that can be used routinely in design and optimization of coating-flow processes

A Multi-Ion, Flux-Corrected Transport Based Hydrodynamic Model for the Plasmasphere Refilling Problem

The objective of this paper is the application of a newly-developed Flux-Corrected Transport (FCT) based hydrodynamic solution methodology to the plasmasphere refilling problem following a geomagnetic storm. The FCT method is extremely well-suited to the solution of nonlinear partial differential equations with shocks and discontinuities. In this solution methodology, every ion species is modeled as two separate fluids originating from the northern and southern hemispheres. We present refilling results that includes three ion (H+, He+ and O+) species and two neutrals (H and O). We believe that with additional modifications, the model can be adapted to the solution of other ionosphere-magnetosphere coupling problems

A Finite Element Method for Free-Surface Flows of Incompressible Fluids in Three Dimensions, Part II: Dynamic Wetting Lines

To date, few researchers have solved three-dimensional free-surface problems with dynamic wetting lines. This paper extends the free-surface finite element method described in a companion paper [Cairncross, R.A., P.R. Schunk, T.A. Baer, P.A. Sackinger, R.R. Rao, "A finite element method for free surface flows of incompressible fluid in three dimensions, Part I: Boundary-Fitted mesh motion.", to be published (1998)] to handle dynamic wetting. A generalization of the technique used in two dimensional modeling to circumvent double-valued velocities at the wetting line, the so-called kinematic paradox, is presented for a wetting line in three dimensions. This approach requires the fluid velocity normal to the contact line to be zero, the fluid velocity tangent to the contact line to be equal to the tangential component of web velocity, and the fluid velocity into the web to be zero. In addition, slip is allowed in a narrow strip along the substrate surface near the dynamic contact line. For realistic wetting-line motion, a contact angle which varies with wetting speed is required because contact lines in three dimensions typically advance or recede a different rates depending upon location and/or have both advancing and receding portions. The theory is applied to capillary rise of static fluid in a corner, the initial motion of a Newtonian droplet down an inclined plane, and extrusion of a Newtonian fluid from a nozzle onto a moving substrate. The extrusion results are compared to experimental visualization. Subject Categorie

A self‐consistent model of helium in the thermosphere

We have found that consideration of neutral helium as a major species leads to a more complete physics‐based modeling description of the Earth's upper thermosphere. An augmented version of the composition equation employed by the Thermosphere‐Ionosphere‐Electrodynamic General Circulation Model (TIE‐GCM) is presented, enabling the inclusion of helium as the fourth major neutral constituent. Exospheric transport acting above the upper boundary of the model is considered, further improving the local time and latitudinal distributions of helium. The new model successfully simulates a previously observed phenomenon known as the “winter helium bulge,” yielding behavior very similar to that of an empirical model based on mass spectrometer observations. This inclusion has direct consequence on the study of atmospheric drag for low‐Earth‐orbiting satellites, as well as potential implications on exospheric and topside ionospheric research.Key PointsTIE‐GCM has been modified to account for neutral heliumSeasonal behavior is successfully capturedNeutral densities from the new model agree well with previous observationsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113723/1/jgra51979.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/113723/2/jgra51979_am.pd

Ionospheric Assimilation Techniques for ARGOS Low-Resolution Airglow and Aurora Spectrograph (LORAAS) Tomographically Reconstructed Equatorial Electron Density Profiles

The LORAAS instrument aboard the ARGOS satellite observes line-of-sight ultraviolet limb intensities from ionosphere and thermosphere airglow. This study uses tomographically reconstructed electron density profiles (EDPs) from the nightside emissions. The ionospheric reconstruction is performed using a two-dimensional O+ 1356Å radiative recombination forward model and discrete inverse theory. The forward model assumes a Chapman layer for the vertical electron density distribution from which h m F 2, N m F 2, and topside scale height are derived for every 90 s limb scan, which is equivalent to 5° resolution in latitude. Since ARGOS is in a near Sun-synchronous orbit, these EDPs form a latitude slice through the equatorial anomaly structures at approximately 0230 LT. These data reflect ongoing ionospheric processes, and it is necessary to assimilate or compare with a model that contains appropriate ionospheric evolution such as the ionospheric forecast model (IFM). This study addresses the reasonableness of both the reconstructed EDPs and the IFM in describing the equatorial anomalies\u27 diurnal and weather variability. The comparison of the LORASS EDPs with those of IFM for October 2000 show that the EDP reconstruction results compare favorably to the IFM EDPs in peak height and topside scale height. Additionally, the sector-to-sector climatology of the observed and modeled equatorial anomalies is similar to within the resolution of the instrument and model. The variability observed in each pass of the satellite is much larger than the IFM variability. The LORASS observation variability indicates that careful assessment of the representation error of the observations should be addressed through supplemental observations