4,130 research outputs found
Addressing student models of energy loss in quantum tunnelling
We report on a multi-year, multi-institution study to investigate student
reasoning about energy in the context of quantum tunnelling. We use ungraded
surveys, graded examination questions, individual clinical interviews, and
multiple-choice exams to build a picture of the types of responses that
students typically give. We find that two descriptions of tunnelling through a
square barrier are particularly common. Students often state that tunnelling
particles lose energy while tunnelling. When sketching wave functions, students
also show a shift in the axis of oscillation, as if the height of the axis of
oscillation indicated the energy of the particle. We find inconsistencies
between students' conceptual, mathematical, and graphical models of quantum
tunnelling. As part of a curriculum in quantum physics, we have developed
instructional materials to help students develop a more robust and less
inconsistent picture of tunnelling, and present data suggesting that we have
succeeded in doing so.Comment: Originally submitted to the European Journal of Physics on 2005 Feb
10. Pages: 14. References: 11. Figures: 9. Tables: 1. Resubmitted May 18 with
revisions that include an appendix with the curriculum materials discussed in
the paper (4 page small group UW-style tutorial
Self-Diffusion of a Polymer Chain in a Melt
Self-diffusion of a polymer chain in a melt is studied by Monte Carlo
simulations of the bond fluctuation model, where only the excluded volume
interaction is taken into account. Polymer chains, each of which consists of
segments, are located on an simple cubic lattice
under periodic boundary conditions, where each segment occupies unit cells. The results for
and 512 at the volume fraction are reported, where
for and L=192 for . The -dependence of the
self-diffusion constant is examined. Here, is estimated from the mean
square displacements of the center of mass of a single polymer chain at the
times larger than the longest relaxation time. From the data for , 384
and 512, the apparent exponent , which describes the apparent power
law dependence of on as , is estimated as
. The ratio seems to be a
constant for and 512, where and
denote the longest relaxation time and the mean square end-to-end distance,
respectively.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp
Using resource graphs to represent conceptual change
We introduce resource graphs, a representation of linked ideas used when
reasoning about specific contexts in physics. Our model is consistent with
previous descriptions of resources and coordination classes. It can represent
mesoscopic scales that are neither knowledge-in-pieces or large-scale concepts.
We use resource graphs to describe several forms of conceptual change:
incremental, cascade, wholesale, and dual construction. For each, we give
evidence from the physics education research literature to show examples of
each form of conceptual change. Where possible, we compare our representation
to models used by other researchers. Building on our representation, we
introduce a new form of conceptual change, differentiation, and suggest several
experimental studies that would help understand the differences between
reform-based curricula.Comment: 27 pages, 14 figures, no tables. Submitted for publication to the
Physical Review Special Topics Physics Education Research on March 8, 200
The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations
The contrast of granulation is an important quantity characterizing solar
surface convection. We compare the intensity contrast at 630 nm, observed using
the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative
MHD simulations of V{\"o}gler & Sch{\"u}ssler (2007). A synthetic image from
the simulation is degraded using a theoretical point-spread function of the
optical system, and by considering other important effects. The telescope
aperture and the obscuration by the secondary mirror and its attachment spider,
reduce the simulated contrast from 14.4 % to 8.5 %. A slight effective defocus
of the instrument brings the simulated contrast down to 7.5 %, close to the
observed value of 7.0 %. A proper consideration of the effects of the optical
system and a slight defocus, lead to sufficient degradation of the synthetic
image from the MHD simulation, such that the contrast reaches almost the
observed value. The remaining small discrepancy can be ascribed to straylight
and slight imperfections of the instrument, which are difficult to model.
Hence, Hinode SP data are consistent with a granulation contrast which is
predicted by 3D radiation MHD simulations.Comment: 5 pages, 4 figures, to be published in A&
Graduate Quantum Mechanics Reform
We address four main areas in which graduate quantum mechanics education can
be improved: course content, textbook, teaching methods, and assessment tools.
We report on a three year longitudinal study at the Colorado School of Mines
using innovations in all these areas. In particular, we have modified the
content of the course to reflect progress in the field in the last 50 years,
used textbooks that include such content, incorporated a variety of teaching
techniques based on physics education research, and used a variety of
assessment tools to study the effectiveness of these reforms. We present a new
assessment tool, the Graduate Quantum Mechanics Conceptual Survey, and further
testing of a previously developed assessment tool, the Quantum Mechanics
Conceptual Survey. We find that graduate students respond well to
research-based techniques that have been tested mainly in introductory courses,
and that they learn much of the new content introduced in each version of the
course. We also find that students' ability to answer conceptual questions
about graduate quantum mechanics is highly correlated with their ability to
solve calculational problems on the same topics. In contrast, we find that
students' understanding of basic undergraduate quantum mechanics concepts at
the modern physics level is not improved by instruction at the graduate level.Comment: accepted to American Journal of Physic
OpenFLUX: efficient modelling software for 13C-based metabolic flux analysis
Background: The quantitative analysis of metabolic fluxes, i. e., in vivo activities of intracellular enzymes and pathways, provides key information on biological systems in systems biology and metabolic engineering. It is based on a comprehensive approach combining (i) tracer cultivation on C-13 substrates, (ii) C-13 labelling analysis by mass spectrometry and (iii) mathematical modelling for experimental design, data processing, flux calculation and statistics. Whereas the cultivation and the analytical part is fairly advanced, a lack of appropriate modelling software solutions for all modelling aspects in flux studies is limiting the application of metabolic flux analysis
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