The chebop system for automatic solution of differential equations

In MATLAB, it would be good to be able to solve a linear differential equation by typing u = L\f, where f, u, and L are representations of the right-hand side, the solution, and the differential operator with boundary conditions. Similarly it would be good to be able to exponentiate an operator with expm(L) or determine eigenvalues and eigenfunctions with eigs(L). A system is described in which such calculations are indeed possible, based on the previously developed chebfun system in object-oriented MATLAB. The algorithms involved amount to spectral collocation methods on Chebyshev grids of automatically determined resolution

High-speed data search

The high-speed data search system developed for KSC incorporates existing and emerging information retrieval technology to help a user intelligently and rapidly locate information found in large textual databases. This technology includes: natural language input; statistical ranking of retrieved information; an artificial intelligence concept called semantics, where 'surface level' knowledge found in text is used to improve the ranking of retrieved information; and relevance feedback, where user judgements about viewed information are used to automatically modify the search for further information. Semantics and relevance feedback are features of the system which are not available commercially. The system further demonstrates focus on paragraphs of information to decide relevance; and it can be used (without modification) to intelligently search all kinds of document collections, such as collections of legal documents medical documents, news stories, patents, and so forth. The purpose of this paper is to demonstrate the usefulness of statistical ranking, our semantic improvement, and relevance feedback

Thermally excited Trivelpiece–Gould modes as a pure electron plasma temperature diagnostic

Thermally excited plasma modes are observed in trapped, near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05<kT<5 eV. The modes are excited and damped by thermal fluctuations in both the plasma and the receiver electronics. The thermal emission spectra together with a plasma-antenna coupling coefficient calibration uniquely determine the plasma (and load) temperature. This calibration is obtained from the mode spectra themselves when the receiver-generated noise absorption is measurable; or from separate wave reflection/absorption measurements; or from kinetic theory. This nondestructive temperature diagnostic agrees well with standard diagnostics, and may be useful for expensive species such as antimatter

Thermally excited fluctuations as a pure electron plasma temperature diagnostic

Thermally excited charge fluctuations in pure electron plasma columns provide a diagnostic for the plasma temperature over a range of 0.05 0.2, so that Landau damping is dominant and well modeled by theory. The third method compares the total (frequency-integrated) number delta N of fluctuating image charges on the wall antenna to a simple thermodynamic calculation. This method works when lambda(D)/R-p > 0.2

What’s in a Name: Exposing Gender Bias in Student Ratings of Teaching

Student ratings of teaching play a significant role in career outcomes for higher education instructors. Although instructor gender has been shown to play an important role in influencing student ratings, the extent and nature of that role remains contested. While difficult to separate gender from teaching practices in person, it is possible to disguise an instructor’s gender identity online. In our experiment, assistant instructors in an online class each operated under two different gender identities. Students rated the male identity significantly higher than the female identity, regardless of the instructor’s actual gender, demonstrating gender bias. Given the vital role that student ratings play in academic career trajectories, this finding warrants considerable attention

What’s in a Name: Exposing Gender Bias in Student Ratings of Teaching

Student ratings of teaching play a significant role in career outcomes for higher education instructors. Although instructor gender has been shown to play an important role in influencing student ratings, the extent and nature of that role remains contested. While difficult to separate gender from teaching practices in person, it is possible to disguise an instructor’s gender identity online. In our experiment, assistant instructors in an online class each operated under two different gender identities. Students rated the male identity significantly higher than the female identity, regardless of the instructor’s actual gender, demonstrating gender bias. Given the vital role that student ratings play in academic career trajectories, this finding warrants considerable attention

What’s in a Name: Exposing Gender Bias in Student Ratings of Teaching

Student ratings of teaching play a significant role in career outcomes for higher education instructors. Although instructor gender has been shown to play an important role in influencing student ratings, the extent and nature of that role remains contested. While difficult to separate gender from teaching practices in person, it is possible to disguise an instructor’s gender identity online. In our experiment, assistant instructors in an online class each operated under two different gender identities. Students rated the male identity significantly higher than the female identity, regardless of the instructor’s actual gender, demonstrating gender bias. Given the vital role that student ratings play in academic career trajectories, this finding warrants considerable attention

AAA rational approximation on a continuum

AAA rational approximation has normally been carried out on a discrete set, typically hundreds or thousands of points in a real interval or complex domain. Here we introduce a continuum AAA algorithm that discretizes a domain adaptively as it goes. This enables fast computation of high-accuracy rational approximations on domains such as the unit interval, the unit circle, and the imaginary axis, even in some cases where resolution of singularities requires exponentially clustered sample points, support points, and poles. Prototype MATLAB (or Octave) and Julia codes aaax, aaaz, and aaai are provided for these three special domains; the latter two are equivalent by a Möbius transformation. Execution is very fast since the matrices whose SVDs are computed have only three times as many rows as columns. The codes include a AAA-Lawson option for improvement of a AAA approximant to minimax, so long as the accuracy is well above machine precision. The result returned is pole-free in the approximation domain