2,474 research outputs found
Reinventing College Physics for Biologists: Explicating an epistemological curriculum
The University of Maryland Physics Education Research Group (UMd-PERG)
carried out a five-year research project to rethink, observe, and reform
introductory algebra-based (college) physics. This class is one of the Maryland
Physics Department's large service courses, serving primarily life-science
majors. After consultation with biologists, we re-focused the class on helping
the students learn to think scientifically -- to build coherence, think in
terms of mechanism, and to follow the implications of assumptions. We designed
the course to tap into students' productive conceptual and epistemological
resources, based on a theoretical framework from research on learning. The
reformed class retains its traditional structure in terms of time and
instructional personnel, but we modified existing best-practices curricular
materials, including Peer Instruction, Interactive Lecture Demonstrations, and
Tutorials. We provided class-controlled spaces for student collaboration, which
allowed us to observe and record students learning directly. We also scanned
all written homework and examinations, and we administered pre-post conceptual
and epistemological surveys. The reformed class enhanced the strong gains on
pre-post conceptual tests produced by the best-practices materials while
obtaining unprecedented pre-post gains on epistemological surveys instead of
the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material
Multi-transmission-line-beam interactive system
We construct here a Lagrangian field formulation for a system consisting of
an electron beam interacting with a slow-wave structure modeled by a possibly
non-uniform multiple transmission line (MTL). In the case of a single line we
recover the linear model of a traveling wave tube (TWT) due to J.R. Pierce.
Since a properly chosen MTL can approximate a real waveguide structure with any
desired accuracy, the proposed model can be used in particular for design
optimization. Furthermore, the Lagrangian formulation provides for: (i) a clear
identification of the mathematical source of amplification, (ii) exact
expressions for the conserved energy and its flux distributions obtained from
the Noether theorem. In the case of uniform MTLs we carry out an exhaustive
analysis of eigenmodes and find sharp conditions on the parameters of the
system to provide for amplifying regimes
Disfluency in dialogue:an intentional signal from the speaker?
Disfluency is a characteristic feature of spontaneous human speech, commonly seen as a consequence of problems with production. However, the question remains open as to why speakers are disfluent: Is it a mechanical by-product of planning difficulty, or do speakers use disfluency in dialogue to manage listeners' expectations? To address this question, we present two experiments investigating the production of disfluency in monologue and dialogue situations. Dialogue affected the linguistic choices made by participants, who aligned on referring expressions by choosing less frequent names for ambiguous images where those names had previously been mentioned. However, participants were no more disfluent in dialogue than in monologue situations, and the distribution of types of disfluency used remained constant. Our evidence rules out at least a straightforward interpretation of the view that disfluencies are an intentional signal in dialogue. © 2012 Psychonomic Society, Inc
An Intense Gamma-Ray Flare of PKS1622-297
We report the observation by the Compton Gamma Ray Observatory of a
spectacular flare of radio source PKS 1622-297. A peak flux of 17E-6 cm^-2 s^-1
(E > 100 MeV) was observed. The corresponding isotropic luminosity is 2.9E49
erg/s. We find that PKS 1622-297 exhibits gamma-ray intra-day variability. A
flux increase by a factor of at least 3.6 was observed to occur in less than
7.1 hours (with 99% confidence). Assuming an exponential rise, the
corresponding doubling time is less than 3.8 hours. A significant flux decrease
by a factor of ~2 in 9.7 hours was also observed. Without beaming, the rapid
flux change and large isotropic luminosity are inconsistent with the
Elliot-Shapiro condition (assuming that gas accretion is the immediate source
of power for the gamma-rays). This inconsistency suggests that the gamma-ray
emission is beamed. A minimum Doppler factor of 8.1 is implied by the observed
lack of pair-production opacity (assuming x-rays are emitted co-spatially with
the gamma-rays). Simultaneous observation by EGRET and OSSE finds a spectrum
adequately fit by a power law with photon index of -1.9. Although the
significance is not sufficient to establish this beyond doubt, the high-energy
gamma-ray spectrum appears to evolve from hard to soft as a flare progresses.Comment: 14 pages, 4 figures, 1 tabl
Unravelling the nature of HD 81032 - a new RS CVn Binary
BVR photometric and quasi-simultaneous optical spectroscopic observations of
the star HD 81032 have been carried out during the years 2000 - 2004. A
photometric period of d has been detected for this star. A
large group of spots with a migration period of years is
inferred from the first three years of the data. H and Ca II H and K
emissions from the star indicate high chromospheric activity. The available
photometry in the BVRIJHK bands is consistent with spectral type of K0 IV
previously found for this star. We have also examined the spectral energy
distribution of HD 81032 for the presence of an infrared colour excess using
the 2MASS JHK and IRAS photometry, but found no significant excess in any band
abovethe normal values expected for a star with this spectral type. We have
also analyzed the X-ray emission properties of this star using data obtained by
the ROSAT X-ray observatory during its All-Sky Survey phase. An X-ray flare of
about 12 hours duration was detected during the two days of X-ray coverage
obtained for this star. Its X-ray spectrum, while only containing 345 counts,
is inconsistent with a single-temperature component solar-abundance coronal
plasma model, but implies either the presence of two or more plasma components,
non-solar abundances, or a combination of both of these properties. All of the
above properties of HD 81032 suggest that it is a newly identified, evolved RS
CVn binary.Comment: 18 pages, 10 figures, 3 tables, Accepted for the publication in JAp
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