4,449 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
Productive resources in studentsâ ideas about energy: An alternative analysis of Wattsâ original interview transcripts
For over 30 years, researchers have investigated studentsâ ideas about energy with the intent of reforming instructional practice. In this pursuit, Watts contributed an influential study with his 1983 paper âSome alternative views of energyâ [Phys. Educ. 18, 213 (1983)]. Wattsâ âalternative frameworksâ continue to be used for categorizing studentsâ non-normative ideas about energy. Using a resources framework, we propose an alternate analysis of student responses from Wattsâ interviews. In our analysis, we show how studentsâ activated resources about energy are disciplinarily productive. We suggest that fostering seeds of scientific understandings in studentsâ ideas about energy may play an important role in their development of scientific literacy
Students Talk about Energy in Project- Based Inquiry Science
We examine the types of emergent language eighth grade students in rural Maine middle schools use when they discuss energy in their first experiences with Project-Based Inquiry Science: Energy, a research-based curriculum that uses a specific language for talking about energy. By comparative analysis of the language used by the curriculum materials to studentsâ language, we find that studentsâ talk is at times more aligned with a Stores and Transfer model of energy than the Forms model supported by the curriculum
Kerncraft: A Tool for Analytic Performance Modeling of Loop Kernels
Achieving optimal program performance requires deep insight into the
interaction between hardware and software. For software developers without an
in-depth background in computer architecture, understanding and fully utilizing
modern architectures is close to impossible. Analytic loop performance modeling
is a useful way to understand the relevant bottlenecks of code execution based
on simple machine models. The Roofline Model and the Execution-Cache-Memory
(ECM) model are proven approaches to performance modeling of loop nests. In
comparison to the Roofline model, the ECM model can also describes the
single-core performance and saturation behavior on a multicore chip. We give an
introduction to the Roofline and ECM models, and to stencil performance
modeling using layer conditions (LC). We then present Kerncraft, a tool that
can automatically construct Roofline and ECM models for loop nests by
performing the required code, data transfer, and LC analysis. The layer
condition analysis allows to predict optimal spatial blocking factors for loop
nests. Together with the models it enables an ab-initio estimate of the
potential benefits of loop blocking optimizations and of useful block sizes. In
cases where LC analysis is not easily possible, Kerncraft supports a cache
simulator as a fallback option. Using a 25-point long-range stencil we
demonstrate the usefulness and predictive power of the Kerncraft tool.Comment: 22 pages, 5 figure
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
Preliminary results of passive microwave snow experiment during February and March 1978
The purpose of the experiment was to determine if remote microwave sensing of snowpack data could be used to predict runoff, thereby allowing more efficient management of the water supply. A four-frequency microwave radiometer system was attached to a truck-mounted aerial lift and was used to gather data on snowpacks at three different sites in the Colorado Rocky Mountains. Ground truth data measurements (density, temperature, grain size, hardness, and free-liquid water content) were taken at each site corresponding to each microwave scan
Olfactory Sensor Processing in Neural Networks: Lessons from Modeling the Fruit Fly Antennal Lobe
The insect olfactory system can be a model for artificial olfactory devices. In particular, Drosophila melanogaster due to its genetic tractability has yielded much information about the design and function of such systems in biology. In this study we investigate possible network topologies to separate representations of odors in the primary olfactory neuropil, the antennal lobe. In particular we compare networks based on stochastic and homogeneous connection weight distributions to connectivities that are based on the input correlations between the glomeruli in the antennal lobe. We show that moderate homogeneous inhibition implements a soft winner-take-all mechanism when paired with realistic input from a large meta-database of odor responses in receptor cells (DoOR database). The sparseness of representations increases with stronger inhibition. Excitation, on the other hand, pushes the representation of odors closer together thus making them harder to distinguish. We further analyze the relationship between different inhibitory network topologies and the properties of the receptor responses to different odors. We show that realistic input from the DoOR database has a relatively high entropy of activation values over all odors and receptors compared to the theoretical maximum. Furthermore, under conditions in which the information in the input is artificially decreased, networks with heterogeneous topologies based on the similarity of glomerular response profiles perform best. These results indicate that in order to arrive at the most beneficial representation for odor discrimination it is important to finely tune the strength of inhibition in combination with taking into account the properties of the available sensors
Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond
The coherent behavior of the single electron and single nuclear spins of a
defect center in diamond and a 13C nucleus in its vicinity, respectively, are
investigated. The energy levels associated with the hyperfine coupling of the
electron spin of the defect center to the 13C nuclear spin are analyzed.
Methods of magnetic resonance together with optical readout of single defect
centers have been applied in order to observe the coherent dynamics of the
electron and nuclear spins. Long coherence times, in the order of microseconds
for electron spins and tens of microseconds for nuclear spins, recommend the
studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure
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
- âŠ