944,740 research outputs found
The Case for Dynamic Models of Learners' Ontologies in Physics
In a series of well-known papers, Chi and Slotta (Chi, 1992; Chi & Slotta,
1993; Chi, Slotta & de Leeuw, 1994; Slotta, Chi & Joram, 1995; Chi, 2005;
Slotta & Chi, 2006) have contended that a reason for students' difficulties in
learning physics is that they think about concepts as things rather than as
processes, and that there is a significant barrier between these two
ontological categories. We contest this view, arguing that expert and novice
reasoning often and productively traverses ontological categories. We cite
examples from everyday, classroom, and professional contexts to illustrate
this. We agree with Chi and Slotta that instruction should attend to learners'
ontologies; but we find these ontologies are better understood as dynamic and
context-dependent, rather than as static constraints. To promote one
ontological description in physics instruction, as suggested by Slotta and Chi,
could undermine novices' access to productive cognitive resources they bring to
their studies and inhibit their transition to the dynamic ontological
flexibility required of experts.Comment: The Journal of the Learning Sciences (In Press
Experimental Test of an Event-Based Corpuscular Model Modification as an Alternative to Quantum Mechanics
We present the first experimental test that distinguishes between an
event-based corpuscular model (EBCM) [H. De Raedt et al.: J. Comput. Theor.
Nanosci. 8 (2011) 1052] of the interaction of photons with matter and quantum
mechanics. The test looks at the interference that results as a single photon
passes through a Mach-Zehnder interferometer [H. De Raedt et al.: J. Phys. Soc.
Jpn. 74 (2005) 16]. The experimental results, obtained with a low-noise
single-photon source [G. Brida et al.: Opt. Expr. 19 (2011) 1484], agree with
the predictions of standard quantum mechanics with a reduced of 0.98
and falsify the EBCM with a reduced of greater than 20
Searches for Scalar Top and Bottom Quarks at the Tevatron
Searches for the supersymmetric partners of top and bottom quarks using data
up to 340 pb taken at the Tevatron collider are described. We
report on searches for scalar top quarks in the decays
and and for
scalar bottom quarks in the decay . No evidence for a signal has been found, but improved
exclusion regions have been derived in the framework of a generic minimal
superymmetric extension of the standard model.Comment: For the D0 and CDF Collaborations. Presented at HEP2005 International
Europhysics Conference on High Energy Physics, July 21st - 27th 2005, Lisboa,
Portugal (4 pages, 4 figures
Zero-norm states and stringy symmetries
We identify spacetime symmetry charges of 26D open bosonic string theory from
an infinite number of zero-norm states (ZNS) with arbitrary high spin in the
old covariant first quantized string spectrum. We give various evidences to
support this identification. These include massive sigma-model calculation,
Witten string field theory calculation, 2D string theory calculation and, most
importantly, three methods of high-energy stringy scattering amplitude
calculations. The last calculations explicitly prove Gross's conjectures in
1988 on high energy symmetry of string theory.Comment: 6 pages. Talks presented by Jen-Chi Lee at XXVIII Spanish Relativity
Meeting (ERE2005),"A Century of Relativity Physics",Oviedo,Spain,6-10 Sep
2005 and "4th Meeting on constrained Dynamics and Quantum Gravity",Cala
Gonone,Sardinia,Italy,12-16 Sep 2005. To appear in the Journal of Physics:
Conference Serie
The effects of parental input on the early development of bei2 dative constructions in Cantonese children
Also available in print.A dissertation submitted in partial fulfilment of the requirements for the Bachelor of Science (Speech and Hearing Sciences), The University of Hong Kong, June 30, 2005.Thesis (B.Sc)--University of Hong Kong, 2005.published_or_final_versionSpeech and Hearing SciencesBachelorBachelor of Science in Speech and Hearing Science
Relations Between the Luminosity, Mass, and Age Distributions of Young Star Clusters
We derive and interpret some relations between the luminosity, mass, and age
distributions of star clusters, denoted here by phi(L), psi(M), and chi(tau),
respectively. Of these, phi(L) is the easiest to determine observationally,
whereas psi(M) and chi(tau) are more informative about formation and disruption
processes. For populations of young clusters, with a relatively wide range of
ages, phi(L) depends on both psi(M) and chi(tau) and thus cannot serve as a
proxy for psi(M) in general. We demonstrate this explicitly by four
illustrative examples with specific forms for either psi(M) or chi(tau). In the
special case in which psi(M) is a power law and is independent of chi(tau),
however, phi(L) is also a power law with the same exponent as psi(M). We
conclude that this accounts for the observed similarity between phi(L) and
psi(M) for the young clusters in the Antennae galaxies. This result reinforces
our picture in which clusters form with psi(M) propto M^{-2} and are then
disrupted rapidly at a rate roughly independent of their masses. The most
likely disruptive process in this first stage is the removal of interstellar
matter by the energy and momentum input from young stars (by photoionization,
winds, jets, and supernovae). The few clusters that avoid this "infant
mortality" are eventually disrupted in a second stage by the evaporation of
stars driven by two-body relaxation, a process with a strong dependence on
mass. We suspect this picture may apply to many, if not all, populations of
star clusters, but this needs to be verified observationally by determinations
of psi(M) and chi(tau) in more galaxies.Comment: Ten pages. Astrophysical Journal. Submitted 2005 October 20. Accepted
2006 August 15. V2--Minor improvements for consistency with published articl
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