Intramural, collaborative learning systems

This thesis focuses on three related concepts: problem-based collaborative learning; the use of multimedia tools in learning systems; and participatory design as a software engineering methodology to create multimedia tools to be used in learning systems. A literature review of the three areas is followed by an overview of the pedagogical, technological, and business trends that affect the direction of innovation in education, including problem-based learning. A discussion of a software engineering project to develop a multimedia application that enhances the learning of geography skills and puts the programming, interface design and multimedia systems capabilities of college students into action ensues. The project results are presented, and suggestions for future research are proposed

Topological Censorship

All three-manifolds are known to occur as Cauchy surfaces of asymptotically flat vacuum spacetimes and of spacetimes with positive-energy sources. We prove here the conjecture that general relativity does not allow an observer to probe the topology of spacetime: any topological structure collapses too quickly to allow light to traverse it. More precisely, in a globally hyperbolic, asymptotically flat spacetime satisfying the null energy condition, every causal curve from \scri^- to {\scri}^+ is homotopic to a topologically trivial curve from \scri^- to {\scri}^+. (If the Poincar\'e conjecture is false, the theorem does not prevent one from probing fake 3-spheres).Comment: 12 pages, REVTEX; 1 postscript figure in a separate uuencoded file. Our earlier version (PRL 71, 1486 (1993)) contained a secondary result, mistakenly attributed to Schoen and Yau, regarding ``passive topological censorship'' of a certain class of topologies. As Gregory Burnett has pointed out (gr-qc/9504012), this secondary result is false. The main topological censorship theorem is unaffected by the erro

Relativistic Diskoseismology. I. Analytical Results for 'Gravity Modes'

We generalize previous calculations to a fully relativistic treatment of adiabatic oscillations which are trapped in the inner regions of accretion disks by non-Newtonian gravitational effects of a black hole. We employ the Kerr geometry within the scalar potential formalism of Ipser and Lindblom, neglecting the gravitational field of the disk. This approach treats perturbations of arbitrary stationary, axisymmetric, perfect fluid models. It is applied here to thin accretion disks. Approximate analytic eigenfunctions and eigenfrequencies are obtained for the most robust and observable class of modes, which corresponds roughly to the gravity (internal) oscillations of stars. The dependence of the oscillation frequencies on the mass and angular momentum of the black hole is exhibited. These trapped modes do not exist in Newtonian gravity, and thus provide a signature and probe of the strong-field structure of black holes. Our predictions are relevant to observations which could detect modulation of the X-ray luminosity from stellar mass black holes in our galaxy and the UV and optical luminosity from supermassive black holes in active galactic nuclei.Comment: 31 pages, 6 figures, uses style file aaspp4.sty, prepared with the AAS LATEX macros v4.0, significant revision of earlier submission to include modes with axial index m>

Cross Border State Sales and Use Taxation After \u3ci\u3eSouth Dakota v. Wayfair\u3c/i\u3e: A New Paradigm for E-Commerce

For over 50 years, U.S. Supreme Court precedents held that state sales taxes could not be constitutionally applied against retailers with no physical presence in the taxing states. As a result, many states implemented use tax laws to supplement sales tax laws, essentially requiring each resident consumer to self-report and pay taxes on purchases made from out of state retailers. However, these use tax laws were largely ignored. Moreover, with the advent of online retail (“e-tail”), many sales on which states previously collected sales tax from local stores essentially converted to “tax-free” sales because many online sellers (“e-tailers”) had no physical nexus to the states in which the products were delivered. As online sales continued to take up a larger percentage of all purchases, states struggled to secure sales and use tax revenue consistent with the physical nexus standard. In recent years, many states implemented laws that required e-tailers to collect sales taxes not based upon physical presence, but upon annual dollar value or number of sales into the states (called, “economic nexus”). However, enforceability of the economic nexus laws was questionable in light of past U.S. Supreme Court decisions. Additionally, with more than 9,600 sales taxing jurisdictions with varying rules and rates, many argued that compliance would create an undue burden on interstate commerce in violation of the Commerce Clause of the U.S. Constitution. South Dakota was one of the states to implement an economic nexus law, and it was challenged on constitutional grounds. In June 2018, in the matter of South Dakota v. Wayfair, et al., the U.S. Supreme Court held in favor of South Dakota, overturning the physical nexus standard and allowing economic nexus sales taxation of online sales based upon dollar value or number of sales alone. This article summarizes state sales and use tax laws, prior Supreme Court precedent, and the South Dakota v. Wayfair decision. It then examines current economic nexus and similar laws, compliance issues, and possible solutions for the e-tailer client

Development of a plasma panel radiation detector: recent progress and key issues

A radiation detector based on plasma display panel technology, which is the principal component of plasma television displays is presented. Plasma Panel Sensor (PPS) technology is a variant of micropattern gas radiation detectors. The PPS is conceived as an array of sealed plasma discharge gas cells which can be used for fast response (O(5ns) per pixel), high spatial resolution detection (pixel pitch can be less than 100 micrometer) of ionizing and minimum ionizing particles. The PPS is assembled from non-reactive, intrinsically radiation-hard materials: glass substrates, metal electrodes and inert gas mixtures. We report on the PPS development program, including simulations and design and the first laboratory studies which demonstrate the usage of plasma display panels in measurements of cosmic ray muons, as well as the expansion of experimental results on the detection of betas from radioactive sources.Comment: presented at IEEE NSS 2011 (Barcelona

The Detection of Ionizing Radiation by Plasma Panel Sensors: Cosmic Muons, Ion Beams and Cancer Therapy

The plasma panel sensor is an ionizing photon and particle radiation detector derived from PDP technology with high gain and nanosecond response. Experimental results in detecting cosmic ray muons and beta particles from radioactive sources are described along with applications including high energy and nuclear physics, homeland security and cancer therapeuticsComment: Presented at SID Symposium, June 201

Type II Supernova Light Curves and Spectra From the CfA

We present multiband photometry of 60 spectroscopically-confirmed supernovae (SN): 39 SN II/IIP, 19 IIn, one IIb and one that was originally classified as a IIn but later as a Ibn. Forty-six have only optical photometry, six have only near infrared (NIR) photometry and eight have both optical and NIR. The median redshift of the sample is 0.016. We also present 192 optical spectra for 47 of the 60 SN. All data are publicly available. There are 26 optical and two NIR light curves of SN II/IIP with redshifts z > 0.01, some of which may give rise to useful distances for cosmological applications. All photometry was obtained between 2000 and 2011 at the Fred Lawrence Whipple Observatory (FLWO), via the 1.2m and 1.3m PAIRITEL telescopes for the optical and NIR, respectively. Each SN was observed in a subset of the $u'UBVRIr'i'JHK_s$ bands. There are a total of 2932 optical and 816 NIR light curve points. Optical spectra were obtained using the FLWO 1.5m Tillinghast telescope with the FAST spectrograph and the MMT Telescope with the Blue Channel Spectrograph. Our photometry is in reasonable agreement with other samples from the literature. Comparison with Pan-STARRS shows that two-thirds of our individual star sequences have weighted-mean V offsets within $\pm$0.02 mag. In comparing our standard-system SN light curves with common Carnegie Supernova Project objects using their color terms, we found that roughly three-quarters have average differences within $\pm$0.04 mag. The data from this work and the literature will provide insight into SN II explosions, help with developing methods for photometric SN classification, and contribute to their use as cosmological distance indicators.Comment: Accepted to ApJS. TAR of light curves and star sequences here: https://www.cfa.harvard.edu/supernova/fmalcolm2017/cfa_snII_lightcurvesndstars.june2017.tar ... Spectra can be found here: https://www.cfa.harvard.edu/supernova/fmalcolm2017/cfaspec_snII.tar.gz ... Passbands and plot of spectra can be found here: https://www.cfa.harvard.edu/supernova/SNarchive.htm

Plasma Panel Sensors for Particle and Beam Detection

The plasma panel sensor (PPS) is an inherently digital, high gain, novel variant of micropattern gas detectors inspired by many operational and fabrication principles common to plasma display panels (PDPs). The PPS is comprised of a dense array of small, plasma discharge, gas cells within a hermetically-sealed glass panel, and is assembled from non-reactive, intrinsically radiation-hard materials such as glass substrates, metal electrodes and mostly inert gas mixtures. We are developing the technology to fabricate these devices with very low mass and small thickness, using gas gaps of at least a few hundred micrometers. Our tests with these devices demonstrate a spatial resolution of about 1 mm. We intend to make PPS devices with much smaller cells and the potential for much finer position resolutions. Our PPS tests also show response times of several nanoseconds. We report here our results in detecting betas, cosmic-ray muons, and our first proton beam tests.Comment: 2012 IEEE NS