Issues in designing learning by teaching systems

Abstract: Learning by teaching systems are a relatively recent approach to designing Intelligent Learning Environments that place learners in the role of tutors. These systems are based on the practice of peer tutoring where students take on defined roles of tutor and tutee. An architecture for learning by teaching systems is described that does not require the domain model of an Intelligent Tutoring System. However a mutual communication language is needed and is defined by a conceptual syntax that delimits the domain content of the dialogue. An example learning by teaching system is described for the domain of qualitative economics. The construction and testing of this system inform a discussion of the major design issues involved: the nature of the learnt model, the form of the conceptual syntax, the control of the interaction and the possible introduction of domain knowledge. 1

I’d like to complain about this software…

Software is often frustrating. You need only walk past a group of users to hear exclamations of annoyance as the users’ expectations and the software interface clash head on

Center-of-mass angular momentum and memory effect in asymptotically flat spacetimes

Gravitational-wave (GW) memory effects are constant changes in the GW strain and its time integrals, which are closely connected to changes in the charges that characterize asymptotically flat spacetimes. The first GW memory effect discovered was a lasting change in the GW strain. It can occur when GWs or massless fields carry away 4-momentum from an isolated source. Subsequently, it was shown that fluxes of intrinsic angular momentum can generate a new type of memory effect called the spin memory, which is an enduring change in a portion of the time integral of the GW strain. In this paper, we note that there is another new type of memory effect. We call it the center-of-mass (CM) memory effect, because it is related to changes in the CM part of the angular momentum of a spacetime. We first examine a few properties of the CM angular momentum. Specifically, we describe how it transforms under the supertranslation symmetry transformations of the Bondi-Metzner-Sachs group, and we compute a new expression for the flux of CM angular momentum carried by GWs in terms of a set of radiative multipole moments of the GW strain. We then turn to the CM memory effect. The CM memory effect appears in a quantity which has units of the time integral of the GW strain. We define the effect in asymptotically flat spacetimes that start in a stationary state, radiate, and settle to a different stationary state. We show that it is invariant under infinitesimal supertranslation symmetries in this context. To determine the magnitude of the flux of CM angular momentum and the CM memory effect, we compute these quantities for nonspinning, quasicircular compact binaries in the post-Newtonian approximation. The CM memory effect arises from terms in the gravitational waveform for such binaries beginning at third and fourth post-Newtonian order for unequal- and equal-mass binaries, respectively. [Abstract abridged]Comment: v2: 26 pages; updated to match version published in Phys. Rev.

Designing Interfaces to Support Collaboration in Information Retrieval

Information retrieval systems should acknowledge the existence of collaboration in the search process. Collaboration can help users to be more effective in both learning systems and in using them. We consider some issues of viewing interfaces to information retrieval systems as collaborative notations and how to build systems that more actively support collaboration. We describe a system that embodies just one kind of explicit support; a graphical representation of the search process that can be manipulated and discussed by the users. By acknowledging the importance of other people in the search process, we can develop systems that not only improve help-giving by people but which can lead to a more robust search activity, more able to cope with, and indeed exploit, the failures of any intelligent agents used

From punishment to universalism

Many philosophers have claimed that the folk endorse moral universalism. Some have taken the folk view to support moral universalism; others have taken the folk view to reflect a deep confusion. And while some empirical evidence supports the claim that the folk endorse moral universalism, this work has uncovered intra-domain differences in folk judgments of moral universalism. In light of all this, our question is: why do the folk endorse moral universalism? Our hypothesis is that folk judgments of moral universalism are generated in part by a desire to punish. We present evidence supporting this across three studies. On the basis of this, we argue for a debunking explanation of folk judgments of moral universalism. Our results not only further our understanding of the psychological processes underpinning folk judgments of moral universalism. They also bear on philosophical discussions of folk meta-ethics

Hybrid method for understanding black-hole mergers: Inspiralling case

We adapt a method of matching post-Newtonian and black-hole-perturbation theories on a timelike surface (which proved useful for understanding head-on black-hole-binary collisions) to treat equal-mass, inspiralling black-hole binaries. We first introduce a radiation-reaction potential into this method, and we show that it leads to a self-consistent set of equations that describe the simultaneous evolution of the waveform and of the timelike matching surface. This allows us to produce a full inspiral-merger-ringdown waveform of the l=2, m=±2 modes of the gravitational waveform of an equal-mass black-hole-binary inspiral. These modes match those of numerical-relativity simulations well in phase, though less well in amplitude for the inspiral. As a second application of this method, we study a merger of black holes with spins antialigned in the orbital plane (the superkick configuration). During the ringdown of the superkick, the phases of the mass- and current-quadrupole radiation become locked together, because they evolve at the same quasinormal-mode frequencies. We argue that this locking begins during the merger, and we show that if the spins of the black holes evolve via geodetic precession in the perturbed black-hole spacetime of our model, then the spins precess at the orbital frequency during the merger. In turn, this gives rise to the correct behavior of the radiation, and produces a kick similar to that observed in numerical simulations

Properties of an affine transport equation and its holonomy

An affine transport equation was used recently to study properties of angular momentum and gravitational-wave memory effects in general relativity. In this paper, we investigate local properties of this transport equation in greater detail. Associated with this transport equation is a map between the tangent spaces at two points on a curve. This map consists of a homogeneous (linear) part given by the parallel transport map along the curve plus an inhomogeneous part, which is related to the development of a curve in a manifold into an affine tangent space. For closed curves, the affine transport equation defines a "generalized holonomy" that takes the form of an affine map on the tangent space. We explore the local properties of this generalized holonomy by using covariant bitensor methods to compute the generalized holonomy around geodesic polygon loops. We focus on triangles and "parallelogramoids" with sides formed from geodesic segments. For small loops, we recover the well-known result for the leading-order linear holonomy ($\sim$ Riemann $\times$ area), and we derive the leading-order inhomogeneous part of the generalized holonomy ($\sim$ Riemann $\times$ area$^{3/2}$). Our bitensor methods let us naturally compute higher-order corrections to these leading results. These corrections reveal the form of the finite-size effects that enter into the holonomy for larger loops; they could also provide quantitative errors on the leading-order results for finite loops.Comment: 18 pages, 4 figures, new short section (Sec. 5) in v3; updated to match article published in GR