Simulation of input electron noise in the free-electron laser

We present a calculation of the shot noise to be used as initial condition for the electron-beam phase-variables in numerical simulations of the free-electron laser

Efficient upwind algorithms for solution of the Euler and Navier-stokes equations

An efficient three-dimensionasl tructured solver for the Euler and Navier-Stokese quations is developed based on a finite volume upwind algorithm using Roe fluxes. Multigrid and optimal smoothing multi-stage time stepping accelerate convergence. The accuracy of the new solver is demonstrated for inviscid flows in the range 0.675 :5M :5 25. A comparative grid convergence study for transonic turbulent flow about a wing is conducted with the present solver and a scalar dissipation central difference industrial design solver. The upwind solver demonstrates faster grid convergence than the central scheme, producing more consistent estimates of lift, drag and boundary layer parameters. In transonic viscous computations, the upwind scheme with convergence acceleration is over 20 times more efficient than without it. The ability of the upwind solver to compute viscous flows of comparable accuracy to scalar dissipation central schemes on grids of one-quarter the density make it a more accurate, cost effective alternative. In addition, an original convergencea cceleration method termed shock acceleration is proposed. The method is designed to reduce the errors caused by the shock wave singularity M -+ 1, based on a localized treatment of discontinuities. Acceleration models are formulated for an inhomogeneous PDE in one variable. Results for the Roe and Engquist-Osher schemes demonstrate an order of magnitude improvement in the rate of convergence. One of the acceleration models is extended to the quasi one-dimensiona Euler equations for duct flow. Results for this case d monstrate a marked increase in convergence with negligible loss in accuracy when the acceleration procedure is applied after the shock has settled in its final cell. Typically, the method saves up to 60% in computational expense. Significantly, the performance gain is entirely at the expense of the error modes associated with discrete shock structure. In view of the success achieved, further development of the method is proposed

Engineering faculty views of teaching quality, accreditation, and institutional climate and how they influence teaching practices

There is wide agreement that teaching quality matters in higher education, but faculty have varied ideas about the definition of quality. This dissertation examined data from a survey administered in 1997, 1999, and 2002 at institutions of the Southeastern University and College Coalition for Engineering Education (SUCCEED) supplemented by a survey administered more recently to a subset of those institutions and two additional institutions. All participating institutions are large public universities. The data collected included faculty teaching practices and three influences on those practices—the faculty member’s definition of quality teaching, their perspective on ABET accreditation processes, and the climate for teaching at their institution, resulting in a dissertation in a three-paper format.^“Engineering Faculty Perspectives on the Nature of Quality Teaching” examines definitions of quality teaching. Using thematic analysis, these were coded according to a framework for quality in higher education by Harvey and Greene. Multinomial logistic regression showed that views on quality teaching were associated with faculty teaching practices. The most common definition of teaching quality (held by 49 percent of participants) is associated with elitism and restricted access—the best way to improve education is to admit better students. These faculty focus on education as “knowledge transfer” and “learning content.” Another 38 percent of faculty had a transformational perspective, more focused on process than content, valuing “empowering students,” “developing students,” and “creating an environment for learning.” These faculty refer pedagogies of engagement such as active learning. The only other prevalent definition of quality (30 percent of faculty) focused on “fitness for purpose,” characterized by terms such as “ability to meet specific legitimate learning objectives” and “mastery of learning outcomes.” This work provides guidance to faculty development efforts. ^ “The Influence of ABET Accreditation Practices on Faculty Approaches to Teaching” explores the effect of ABET accreditation on quality teaching as described in faculty comments from 2014 using thematic analysis. Multinomial logistic regression related faculty perspectives on accreditation terminology and processes to faculty teaching practices. Faculty had overwhelmingly negative views regarding accreditation, believing that it adds to their workload, stifles their creativity, and distracts them from other important objectives including teaching. Faculty who express various negative views of either the goals or the practice of accreditation are less likely to engage in certain student-centered teaching practices. More positively, our findings show that faculty who tend agree with the student-outcomes focus of the ABET criteria engage in richer educational experiences—they give students more writing assignments and allow students to learn collaboratively. ^ “Faculty Perspectives and Institutional Climate for Teaching Quality in Engineering” analyzes faculty comments from the earlier surveys using thematic analysis. Comments from the 2014 survey were classified by teaching practices (traditional vs. non-traditional) and institutional climate (traditional vs. non-traditional), creating four cases. These comments were then analyzed using a collective case study approach. The study of the two collections of open-ended comments was supplemented by multinomial logistic regression of survey items from the 2014 administration relating faculty teaching practices and the institutional climate for teaching. In the historical data, faculty views of student evaluations evolved from seeing it as a negative burden to describing is as positive evidence of student learning. Faculty comments included many references to administrators who only “pay lip service” to the importance of teaching, although some faculty spoke positively about their campus’ commitment to quality teaching. Faculty awareness of and pressure to use student-centered methods increased with time. The collective case study identified faculty in all four conditions, although they were not equally prevalent, and illustrates the experience in each condition using faculty comments

Freezing line of the Lennard-Jones fluid: a Phase Switch Monte Carlo study

We report a Phase Switch Monte Carlo (PSMC) method study of the freezing line of the Lennard-Jones (LJ) fluid. Our work generalizes to soft potentials the original application of the method to hard sphere freezing, and builds on a previous PSMC study of the LJ system by Errington (J. Chem. Phys. {\bf 120}, 3130 (2004)). The latter work is extended by tracing a large section of the Lennard-Jones freezing curve, the results for which we compare to a previous Gibbs-Duhem integration study. Additionally we provide new background regarding the statistical mechanical basis of the PSMC method and extensive implementation details.Comment: 18 pages, 6 figure

Multiple-Purpose Subsonic Naval Aircraft (MPSNA): Multiple Application Propfan Study (MAPS)

Study requirements, assumptions and guidelines were identified regarding carrier suitability, aircraft missions, technology availability, and propulsion considerations. Conceptual designs were executed for two missions, a full multimission aircraft and a minimum mission aircraft using three different propulsion systems, the UnDucted Fan (UDF), the Propfan and an advanced Turbofan. Detailed aircraft optimization was completed on those configurations yielding gross weight performance and carrier spot factors. Propfan STOVL conceptual designs were exercised also to show the effects of STOVL on gross weight, spot factor and cost. An advanced technology research plan was generated to identify additional investigation opportunities from an airframe contractors standpoint. Life cycle cost analysis was accomplished yielding a comparison of the UDF and propfan configurations against each other as well as against a turbofan with equivalent state of the art turbo-machinery

Short-Interval Cortical Inhibition and Intracortical Facilitation during Submaximal Voluntary Contractions Changes with Fatigue

This study determined whether short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) change during a sustained submaximal isometric contraction. On 2 days, 12 participants (6 men, 6 women) performed brief (7-s) elbow flexor contractions before and after a 10-min fatiguing contraction; all contractions were performed at the level of integrated electromyographic activity (EMG) which produced 25 % maximal unfatigued torque. During the brief 7-s and 10-min submaximal contractions, single (test) and paired (conditioning–test) transcranial magnetic stimuli were applied over the motor cortex (5 s apart) to elicit motor-evoked potentials (MEPs) in biceps brachii. SICI and ICF were elicited on separate days, with a conditioning–test interstimulus interval of 2.5 and 15 ms, respectively. On both days, integrated EMG remained constant while torque fell during the sustained contraction by ~51.5 % from control contractions, perceived effort increased threefold, and MVC declined by 21–22 %. For SICI, the conditioned MEP during control contractions (74.1 ± 2.5 % of unconditioned MEP) increased (less inhibition) during the sustained contraction (last 2.5 min: 86.0 ± 5.1 %; P \u3c 0.05). It remained elevated in recovery contractions at 2 min (82.0 ± 3.8 %; P \u3c 0.05) and returned toward control at 7-min recovery (76.3 ± 3.2 %). ICF during control contractions (conditioned MEP 129.7 ± 4.8 % of unconditioned MEP) decreased (less facilitation) during the sustained contraction (last 2.5 min: 107.6 ± 6.8 %; P \u3c 0.05) and recovered to 122.8 ± 4.3 % during contractions after 2 min of recovery. Both intracortical inhibitory and facilitatory circuits become less excitable with fatigue when assessed during voluntary activity, but their different time courses of recovery suggest different mechanisms for the fatigue-related changes of SICI and ICF

Kaon Condensation in a Nambu--Jona-Lasinio (NJL) Model at High Density

We demonstrate a fully self-consistent microscopic realization of a kaon-condensed colour-flavour locked state (CFLK0) within the context of a mean-field NJL model at high density. The properties of this state are shown to be consistent with the QCD low-energy effective theory once the proper gauge neutrality conditions are satisfied, and a simple matching procedure is used to compute the pion decay constant, which agrees with the perturbative QCD result. The NJL model is used to compare the energies of the CFLK0 state to the parity even CFL state, and to determine locations of the metal/insulator transition to a phase with gapless fermionic excitations in the presence of a non-zero hypercharge chemical potential and a non-zero strange quark mass. The transition points are compared with results derived previously via effective theories and with partially self-consistent NJL calculations. We find that the qualitative physics does not change, but that the transitions are slightly lower.Comment: 21 pages, ReVTeX4. Clarified discussion and minor change