Precessing Jets and Molecular Outflows: A 3-D Numerical Study

We present 3-D numerical hydrodynamical simulations of precessing supersonic heavy jets to explore how well they serve as a model for generating molecular outflows from Young Stellar Objects. The dynamics are studied with a number of high resolution simulations on a Cartesian grid (128x128x128 zones) using a high order finite difference method. A range of cone angles and precession rates were included in the study. Two higher resolution runs (256x256x256 zones) were made for comparison in order to confirm numerical convergence of global flow characteristics. Morphological, kinematical and dynamical characteristics of precessing jets are described and compared to important properties of straight jets and also to observations of YSOs. In order to examine the robustness of precessing jets as a mean to produce molecular outflows around Young Stellar Objects, ``synthetic observations'' of the momentum distributions of the simulated precessing jets are compared to observations of molecular outflows. It is found that precessing jets match better the morphology, highly forward driven momentum and momentum distributions along the long axis of molecular outflows than do wind-driven or straight jet-driven flow models.Comment: Accepted by ApJ, 31 pages, using aasms.sty, Also available in postscript with figures via a gzipped tar file at ftp://s1.msi.umn.edu/pub/afrank/3DJet/3DJet.tar.gz . For information contact [email protected]

Oblique MHD cosmic-ray modified shocks: Two-fluid numerical simulations

We present the first results of time dependent, two-fluid, cosmic-ray (CR) modified, MHD shock simulations. The calculations were carried out with a new numerical code for 1-D ideal MHD. By coupling this code with the CR energy transport equation we can simulate the time-dependent evolution of MHD shocks including the acceleration of the CR and their feedback on the shock structures. We report tests of the combined numerical method including comparisons with analytical steady state results published earlier by Webb, as well as internal consistency checks for more general MHD CR shock structures after they appear to have converged to dynamical steady states. We also present results from an initial time dependent simulation which extend the parameter space domain of previous analytical models. These new results support Webb's suggestion that equilibrium oblique shocks are less effective than parallel shocks in the acceleration of CR. However, for realistic models of anisotropic CR diffusion, oblique shocks may achieve dynamical equilibrium on shorter timescale than parallel shocks

A Divergence-Free Upwind Code for Multidimensional Magnetohydrodynamic Flows

A description is given for preserving {\bmsy\nabla}\cdot{\vec B}=0 in a magnetohydrodynamic (MHD) code that employs the upwind, Total Variation Diminishing (TVD) scheme and the Strang-type operator splitting for multi-dimensionality. The method is based on the staggered mesh technique to constrain the transport of magnetic field: the magnetic field components are defined at grid interfaces with their advective fluxes on grid edges, while other quantities are defined at grid centers. The magnetic field at grid centers for the upwind step is calculated by interpolating the values from grid interfaces. The advective fluxes on grid edges for the magnetic field evolution are calculated from the upwind fluxes at grid interfaces. Then, the magnetic field can be maintained with {\bmsy\nabla}\cdot{\vec B}=0 exactly, if this is so initially, while the upwind scheme is used for the update of fluid quantities. The correctness of the code is demonstrated through tests comparing numerical solutions either with analytic solutions or with numerical solutions from the code using an explicit divergence-cleaning method. Also the robustness is shown through tests involving realistic astrophysical problems.Comment: 15 pages of text, 8 figures (in degraded gif format), to appear in The Astrophysical Journal (Dec. 10, 1998), original quality figures available via anonymous ftp at ftp://ftp.msi.umn.edu/pub/users/twj/mhddivb5.uu or ftp://canopus.chungnam.ac.kr/ryu/mhddivb5.u

Undergraduate Teaching Assistants and their Use of Nonverbal Immediacy Behaviors in the Basic Communication Course

Over the past two decades, perhaps no instructional communication topic has been researched as thoroughly as teacher immediacy. However, one important area of the existing teacher immediacy literature that remains underdeveloped is how undergraduate teaching assistants enact immediacy behaviors, and how, if at all, students respond to these teaching assistants differently based on the enactment of these behaviors. Thus, the purpose of this investigation was to gain a clearer understanding as to what, if any, immediacy behaviors are used by undergraduate teaching assistants in the basic communication course at a large Midwestern university. The researchers conducted 50 hours of observation in an attempt to determine the different types of immediacy behaviors being displayed by undergraduate teaching assistants in the instructional context as well as examine the effects those behaviors have on students. The results of this analysis are discussed

The Evolution and Efficiency of Oblique MHD Cosmic-Ray Shocks: Two-Fluid Simulations

Using a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic ray (CR) modified plane shock evolution using the two-fluid model for diffusive particle acceleration. The numerical shocks evolve to published analytical steady state properties. In order to probe the dynamical role of magnetic fields we have explored for these time asymptotic states the parameter space of upstream fast mode Mach number, $M_f$, and plasma $\beta$, compiling the results into maps of dynamical steady state CR acceleration efficiency, $\epsilon_c$. These maps, along with additional numerical experiments, show that $\epsilon_c$ is reduced through the action of compressive work on tangential magnetic fields in CR-MHD shocks. Thus $\epsilon_c$ in low $\beta$, moderate $M_f$ shocks tends to be smaller in quasi perpendicular shocks than it would be high $\beta$ shocks of the same $M_f$. This result supports earlier conclusions that strong, oblique magnetic fields inhibit diffusive shock acceleration. For quasi parallel shocks with $\beta < 1$, on the other hand, $\epsilon_c$ seems to be increased at a given $M_f$ when compared to high $\beta$ shocks. The apparent contradiction to the first conclusion results, however, from the fact that for small $\beta$ quasi parallel shocks, the fast mode Mach number is not a good measure of compression through the shock. That is better reflected in the sonic Mach number, which is greater. Acceleration efficiencies for high and low $\beta$ having comparable sonic Mach numbers are more similar. Time evolution of CR-MHD shocks is qualitatively similar to CR-gasdynamical shocks. However, several potentially interesting differences are apparent.Comment: 23 pages with 8 figures (uuencoded compressed tar file of text and figures available via anonymous ftp from directory /pub at sirius.chungnam.ac.kr), submitted to The Astrophysical Journal, CNU-AST-94-

Numerical Magnetohydrodynamics in Astrophysics: Algorithm and Tests for Multi-Dimensional Flow

We present for astrophysical use a multi-dimensional numerical code to solve the equations for ideal magnetohydrodynamics (MHD). It is based on an explicit finite difference method on an Eulerian grid, called the Total Variation Diminishing (TVD) scheme, which is a second-order-accurate extension of the Roe-type upwind scheme. Multiple spatial dimensions are treated through a Strang-type operator splitting. The constraint of a divergence-free field is enforced exactly by calculating a correction via a gauge transformation in each time step. Results from two-dimensional shock tube tests show that the code captures correctly discontinuities in all three MHD waves families as well as contact discontinuities. The numerical viscosities and resistivity in the code, which are useful in order to understand simulations involving turbulent flows, are estimated through the decay of two-dimensional linear waves. Finally, the robustness of the code in two-dimensions is demonstrated through calculations of the Kelvin-Helmholtz instability and the Orszag-Tang vortex.Comment: ApJ accepted, 20 pages, uuencoded, compressed postscript file, 8 figures available by anonymous ftp at ftp://sirius.chungnam.ac.kr/pub/mhd2d/ or available upon request to [email protected]

National Outreach Programming for Landowners—Natural Resource Enterprises

We conducted a survey of Mississippi landowners to determine revenues collected and expenditures incurred during 1996-1998 for fee hunting on their properties (inflated to 2011 estimates). Study findings revealed that respondents diversified incomes derived through fee hunting enterprises on their lands. This information has been used to design a series of multi-state landowner workshops about natural resource enterprises development and conservation practices on private lands. With state and local collaborator assistance, we have conducted over 50 landowner workshops in nine U.S. states and Sweden and have received requests to expand outreach programming to other U.S. states

Faculty Observables and Self-Reported Responsiveness to Academic Dishonesty

Prior to 2009, a mid-sized public institution in the southeast had a faculty-driven honor policy characterized by little education about the policy and no tracking of repeat offenders. An updated code, implemented in August of 2009, required that students sign an honor pledge, created a formal student honor board, and developed a process to track and hold accountable, repeat offenders. Self-reported data on faculty vigilance to detect and punish cheating is collected both prior to and after a change in the honor code at a mid-sized public institution in the southeast. We find that, at the time of the first survey, full professors and faculty with a longer duration of employment were more likely to claim vigilance in cheating detection and harshness in punishing cheaters than newer, untenured faculty. The relationship between these factors and detection and harshness diminished when the honor code was enhanced