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Historical thinking involves being able to conceptualize historical events from multiple perspectives and to relate historical data within these. Hypermedia has enormous potential for supporting the development of historical thinking because it is open, nonlinear, and heterogeneous in ways other media is not; it can physically represent information in ways that model the cognitive representations characteristic of critical thinking in ill-structured domains. Another advantage hypermedia has over traditional text-based materials for the development of historical thinking is its support of the integration of a variety of media, video in particular. "Set On Freedom" is a hypermedia application that combines text, graphics, and video footage in a collection of images and information about the American civil rights movement. It organizes information from four general perspectives in a single screen: people, places, events, and viewpoints; it also provides links to primary source documents. In May 1993, "Set On Freedom" was tested; subjects included seventh and eight grade students in a public school in rural Vermont. Students were interviewed before and after using this application on their impressions of and knowledge about civil rights and the civil rights movement. After using "Set On Freedom," students had much clearer conceptions of civil rights and the civil rights movement. There were implications that visual imagery might serve as a mnemonic device in students' mental representations of the material they covered. Students were found to perceive significantly more linkages between people, places, issues and events, even though they only identified slightly more items in the final interview. (Contains 15 references.) (AEF)

We present a new analysis of kinematic data of the young planetary nebula BD+30 3639. The data include spectroscopic long-slit and internal proper motion measurements. In this paper we also introduce a new type of mapping of kinematic proper motion data that we name "criss-cross" mapping. It basically consists of finding all points where extended proper motion vectors cross converge. From the crossing points a map is generated which helps to interpret the kinematic data. From the criss-cross mapping of BD+30 3639, we conclude that the kinematic center is approximately 0.5 arcsec offset to the South-East from the central star. The mapping does also show evidence for a non-homologous expansion of the nebula that is consistent with a disturbance aligned with the bipolar molecular bullets., Comment: 4 pages, to appear in the proceedings of the conference "Asymmetrical Planetary Nebulae V", eds. Zijlstra, et al., editorial: Ebrary

Aims. We study a new broad well-defined arc of optical nebulosity close to the cloud-shock interacting Criss-Cross Nebula, derive the basic physical properties of the former and revise those of the latter, and compare both objects to simulations of cloud-shock interactions from the literature. Methods. Deep optical, partly wide-field, images were used to reveal the intricate morphology and overall extent of the nebulosities. Optical spectroscopy enabled us to uncover their nature. Results. The two nebulosities obviously are physically linked, but are of different type; the Criss-Cross Nebula is, as was shown also in an earlier paper, excited via a slow shock from the expanding Orion-Eridanus Bubble, but the broad arc is definitely photo-ionized. The source for ionizing photons appears to be hot gas in this bubble. Some results of simulations of interactions of SNRs with interstellar clouds available from the literature bear a striking resemblance to our nebulae, which appear to represent an example - unrivalled in closeness and clarity - for an early to medium stage in the destruction of an isolated cloud over-run by a highly evolved SNR. Thereby the Criss-Cross Nebula is, when seen from the SNR, the rear disrupted part of the original small cloud, whereas the arc probably is its yet rather intact front part., Comment: 6 pages, 3 figures. Figures degraded because of size constraints. Accepted for publication in A&A

Given a non-uniform criss-cross partition of a rectangular domain $\Omega$, we analyse the error between a function $f$ defined on $\Omega$ and two types of $C^1$-quadratic spline quasi-interpolants (QIs) obtained as linear combinations of B-splines with discrete functionals as coefficients. The main novelties are the facts that supports of B-splines are contained in $\Omega$ and that data sites also lie inside or on the boundary of $\Omega$. Moreover, the infinity norms of these QIs are small and do not depend on the triangulation: as the two QIs are exact on quadratic polynomials, they give the optimal approximation order for smooth functions. Our analysis is done for $f$ and its partial derivatives of the first and second orders and a particular effort has been made in order to give the best possible error bounds in terms of the smoothness of $f$ and of the mesh ratios of the triangulation.