On-Line Student Modeling for Coached Problem Solving Using Bayesian Networks

This paper describes the student modeling component of ANDES, an Intelligent Tutoring System for Newtonian physics. ANDES' student model uses a Bayesian network to do long-term knowledge assessment, plan recognition and prediction of students' actions during problem solving. The network is updated in real time, using an approximate anytime algorithm based on stochastic sampling, as a student solves problems with ANDES.The information in the student model is used by ANDES' Help system to tailor its support when the student reaches impasses in the problem solving process. In this paper, we describe the knowledge structures represented in the student model and discuss the implementation of the Bayesian network assessor. We also present a preliminary evaluation of the time performance of stochastic sampling algorithms to update the network

Lasing on the third harmonic

The Los Alamos Free-Electron Laser has recently lased near 4 {mu}m on the third harmonic of the fundamental frequency of about 12 {mu}m. By choice of intercavity apertures and cavity length, lasing can be forced to occur on both frequencies simultaneously or on either one alone. 8 refs., 3 figs., 1 tab

Numerical simulations of free-electron laser oscillators

A numerical simulation capability has been developed to model the physics and realistic design constraints of free electron laser oscillators driven by rf linear accelerators. Two computer codes have been written FELEX and FELP. The code FELP is a one spatial dimension code with essentially unlimited time or spectral resolution. The codes are complementary and their use is dependent upon the problem being addressed. The code FELP is used to model optical and electron micropulse structure, broadband noise, and the sideband instability. The code FELEX models accelerator generated electron beam distributions, the transport of these distributions through wigglers with misalignments and field errors, self-consistent interaction with the optical field, and propagation of the optical field through resonators with realistically modelled components. FELEX is routinely used to match resonator designs to the optical parameters of the electron beam, and used to investigate the physics of 3-D micropulse effects. Some details of the codes will be presented along with various examples of simulation results. 22 refs., 10 figs., 1 tab