Coupled Vlasov and two-fluid codes on GPUs

We present a way to combine Vlasov and two-fluid codes for the simulation of a collisionless plasma in large domains while keeping full information of the velocity distribution in localized areas of interest. This is made possible by solving the full Vlasov equation in one region while the remaining area is treated by a 5-moment two-fluid code. In such a treatment, the main challenge of coupling kinetic and fluid descriptions is the interchange of physically correct boundary conditions between the different plasma models. In contrast to other treatments, we do not rely on any specific form of the distribution function, e.g. a Maxwellian type. Instead, we combine an extrapolation of the distribution function and a correction of the moments based on the fluid data. Thus, throughout the simulation both codes provide the necessary boundary conditions for each other. A speed-up factor of around 20 is achieved by using GPUs for the computationally expensive solution of the Vlasov equation and an overall factor of at least 60 using the coupling strategy combined with the GPU computation. The coupled codes were then tested on the GEM reconnection challenge

A Lagrangian model for the evolution of turbulent magnetic and passive scalar fields

In this paper we present an extension of the \emph{Recent Fluid Deformation (RFD)} closure introduced by Chevillard and Meneveau (2006) which was developed for modeling the time evolution of Lagrangian fluctuations in incompressible Navier-Stokes turbulence. We apply the RFD closure to study the evolution of magnetic and passive scalar fluctuations. This comparison is especially interesting since the stretching term for the magnetic field and for the gradient of the passive scalar are similar but differ by a sign such that the effect of stretching and compression by the turbulent velocity field is reversed. Probability density functions (PDFs) of magnetic fluctuations and fluctuations of the gradient of the passive scalar obtained from the RFD closure are compared against PDFs obtained from direct numerical simulations

Applying the Grinblatt-Titman and the Conditional (Ferson-Schadt) Performance Measures: The Case of Industry Rotation Via the Dynamic Investment Model.

Nearly any standard financial model concludes that two assets with identical cash flows must sell for the same price. Alas, closed-end mutual fund company share prices seem to violate this fundamental tenant. Even when one considers several standard frictions, such as taxes and agency costs, classical financial models cannot explain the large persistent discounts found within the data. While the standard financial markets model may not explain the existence of large closed-end fund discounts, this paper shows that a rather close version of it does. In an otherwise frictionless market, if asset supplies vary randomly over time and agents possess finite lives, a closed-end mutual fund's stock price may not track its net asset value. Furthermore, the analysis provides a number of conditions under which these discrepancies will lead to the existence of systematic discounts for the mutual fund's shares. In addition, the model provides predictions regarding the correlation between current closed-end fund discounts and current changes in stock prices and future changes in corporate productivity. As the analysis shows, the same parameter values that lead to systematic discounts also lead to other fund price characteristics that resemble many of the results found within empirical studies.

Lagrangian Statistics of Navier-Stokes- and MHD-Turbulence

We report on a comparison of high-resolution numerical simulations of Lagrangian particles advected by incompressible turbulent hydro- and magnetohydrodynamic (MHD) flows. Numerical simulations were performed with up to $1024^3$ collocation points and 10 million particles in the Navier-Stokes case and $512^3$ collocation points and 1 million particles in the MHD case. In the hydrodynamics case our findings compare with recent experiments from Mordant et al. [1] and Xu et al. [2]. They differ from the simulations of Biferale et al. [3] due to differences of the ranges choosen for evaluating the structure functions. In Navier-Stokes turbulence intermittency is stronger than predicted by a multifractal approach of [3] whereas in MHD turbulence the predictions from the multifractal approach are more intermittent than observed in our simulations. In addition, our simulations reveal that Lagrangian Navier-Stokes turbulence is more intermittent than MHD turbulence, whereas the situation is reversed in the Eulerian case. Those findings can not consistently be described by the multifractal modeling. The crucial point is that the geometry of the dissipative structures have different implications for Lagrangian and Eulerian intermittency. Application of the multifractal approach for the modeling of the acceleration PDFs works well for the Navier-Stokes case but in the MHD case just the tails are well described.Comment: to appear in J. Plasma Phy

Review of \u3ci\u3eArt of West Texas Women: A Celebration\u3c/i\u3e by Kippra D. Hopper and Laurie J. Churchill

Texas historians, acknowledging women as art pioneers in Texas, rely on the old saw that while men were settling the state, women led the charge for cultural pursuits. Groups of women-trained artists among them-began organizing art activities in all parts of the state in the early 1880s on the heels of settlement, recognizing the importance of an appreciation of aesthetics and beauty to the development of a significant culture. Since most public school teachers in Texas were female, teaching art and bringing art to students were natural developments; women also founded Texas\u27s first public art museums. While scholars have acknowledged women\u27s contributions to the areas of art appreciation and art education in Texas, the accomplishments and importance of Texas\u27s women artists are rarely addressed. Old patterns persist, however, and in recent historic Texas art exhibitions, women artists continue to be discussed as late comers or second-tier members of the artistic community. Experimentation became almost de rigeur for women artists as they fought their way out from under the shadows of their male counterparts. Ironically, many were taken more seriously in their own time than in our enlightened present

Instanton filtering for the stochastic Burgers equation

We address the question whether one can identify instantons in direct numerical simulations of the stochastically driven Burgers equation. For this purpose, we first solve the instanton equations using the Chernykh-Stepanov method [Phys. Rev. E 64, 026306 (2001)]. These results are then compared to direct numerical simulations by introducing a filtering technique to extract prescribed rare events from massive data sets of realizations. Using this approach we can extract the entire time history of the instanton evolution which allows us to identify the different phases predicted by the direct method of Chernykh and Stepanov with remarkable agreement

An exact relation between Eulerian and Lagrangian velocity increment statistics

We present a formal connection between Lagrangian and Eulerian velocity increment distributions which is applicable to a wide range of turbulent systems ranging from turbulence in incompressible fluids to magnetohydrodynamic turbulence. For the case of the inverse cascade regime of two-dimensional turbulence we numerically estimate the transition probabilities involved in this connection. In this context we are able to directly identify the processes leading to strongly non-Gaussian statistics for the Lagrangian velocity increments.Comment: 5 pages, 3 figure

Think Globally, Act Locally: A Delphi Study of Educational Leadership through the Development of International Resources in the Local Community

The probable future of international resource development in the local school community for the years leading up to 2000 was researched using the Delphi method--the best available tool for building consensus in emerging fields. A panel of 28 identified experts in elementary and secondary schools and districts from Southern California in the field of school-community relations with demonstrable experience in international education completed three rounds of surveys. The surveys served to identify (1) educational resource people who could bring constructive change communitywide, (2) program developments and school-community partnerships, (3) practical and philosophical goals for fusing international, national, community and academic educational values, and (4) competing demands and pressures. Results show specific, readily apparent trends in each area. Trends from all areas fell into one of four models, each reflecting a distinct perspective of international education. The perspectives are Model I, involving curriculum and instruction values, Model II, involving local multicultural and political values, Model III, involving national economic security values and Model IV, involving more universal, globally shared values. Model IV unites the fundamental values of all four models and complements the findings in the literature on leadership. The strongest trend was towards Model IV, although there was no single, unified consensus the respondents. Model II concerns formed the second strongest trend and provided the basic diversion towards the achievement of Model IV. The author concludes that the emergence of Model IV will have a unifying influence on the traditionally fragmented field of global education

Identification of Bare-Airframe Dynamics from Closed-Loop Data Using Multisine Inputs and Frequency Responses

Amethod is presented for computing multiple-input multiple-output frequency responses of bare-airframe dynamics for systems excited using orthogonal phase-optimized multisines and including correlated data arising from control mixing or feedback control. The estimation was posed as the solution to an underdetermined system of linear equations, for which additional information was supplied using interpolation of the frequency responses. A simulation model of the NASA T-2 aircraft having two inputs and two outputs was used to investigate the method in the open-loop configuration and under closed-loop control. The method was also applied to flight test data from the X-56A aeroelastic demonstrator having five inputs and ten outputs and flying under closed-loop control with additional control allocation mixing. Results demonstrated that the proposed method accurately estimates the bare airframe frequency responses in the presence of correlated data from control mixing and feedback control. Results also agreed with estimates obtained using different methods that are less sensitive to correlated inputs