8,358 research outputs found
Development and Validation of the Colorado Learning Attitudes about Science Survey for Experimental Physics
As part of a comprehensive effort to transform our undergraduate physics
laboratories and evaluate the impacts of these efforts, we have developed the
Colorado Learning Attitudes about Science Survey for Experimental Physics
(E-CLASS). The E-CLASS assesses the changes in students' attitudes about a
variety of scientific laboratory practices before and after a lab course and
compares attitudes with perceptions of the course grading requirements and
laboratory practices. The E-CLASS is designed to give researchers insight into
students' attitudes and also to provide actionable evidence to instructors
looking for feedback on their courses. We present the development, validation,
and preliminary results from the initial implementation of the survey in three
undergraduate physics lab courses.Comment: 8 pages, 4 figures, 1 table, submitted to 2012 PERC Proceeding
A numerical finite size scaling approach to many-body localization
We develop a numerical technique to study Anderson localization in
interacting electronic systems. The ground state of the disordered system is
calculated with quantum Monte-Carlo simulations while the localization
properties are extracted from the ``Thouless conductance'' , i.e. the
curvature of the energy with respect to an Aharonov-Bohm flux. We apply our
method to polarized electrons in a two dimensional system of size . We
recover the well known universal one
parameter scaling function without interaction. Upon switching on the
interaction, we find that is unchanged while the system flows toward
the insulating limit. We conclude that polarized electrons in two dimensions
stay in an insulating state in the presence of weak to moderate
electron-electron correlations.Comment: 5 pages, 4 figure
Development and results from a survey on students views of experiments in lab classes and research
The Colorado Learning Attitudes about Science Survey for Experimental Physics
(E-CLASS) was developed as a broadly applicable assessment tool for
undergraduate physics lab courses. At the beginning and end of the semester,
the E-CLASS assesses students views about their strategies, habits of mind, and
attitudes when doing experiments in lab classes. Students also reflect on how
those same strategies, habits-of-mind, and attitudes are practiced by
professional researchers. Finally, at the end of the semester, students reflect
on how their own course valued those practices in terms of earning a good
grade. In response to frequent calls to transform laboratory curricula to more
closely align it with the skills and abilities needed for professional
research, the E-CLASS is a tool to assess students' perceptions of the gap
between classroom laboratory instruction and professional research. The E-CLASS
has been validated and administered in all levels of undergraduate physics
classes. To aid in its use as a formative assessment tool, E-CLASS provides all
participating instructors with a detailed feedback report. Example figures and
analysis from the report are presented to demonstrate the capabilities of the
E-CLASS. The E-CLASS is actively administered through an online interface and
all interested instructors are invited to administer the E-CLASS their own
classes and will be provided with a summary of results at the end of the
semester
An epistemology and expectations survey about experimental physics: Development and initial results
In response to national calls to better align physics laboratory courses with
the way physicists engage in research, we have developed an epistemology and
expectations survey to assess how students perceive the nature of physics
experiments in the contexts of laboratory courses and the professional research
laboratory. The Colorado Learning Attitudes about Science Survey for
Experimental Physics (E-CLASS) evaluates students' epistemology at the
beginning and end of a semester. Students respond to paired questions about how
they personally perceive doing experiments in laboratory courses and how they
perceive an experimental physicist might respond regarding their research.
Also, at the end of the semester, the E-CLASS assesses a third dimension of
laboratory instruction, students' reflections on their course's expectations
for earning a good grade. By basing survey statements on widely embraced
learning goals and common critiques of teaching labs, the E-CLASS serves as an
assessment tool for lab courses across the undergraduate curriculum and as a
tool for physics education research. We present the development, evidence of
validation, and initial formative assessment results from a sample that
includes 45 classes at 20 institutions. We also discuss feedback from
instructors and reflect on the challenges of large-scale online administration
and distribution of results.Comment: 31 pages, 9 figures, 3 tables, submitted to Phys. Rev. - PE
Derivation of the Quantum Probability Rule without the Frequency Operator
We present an alternative frequencists' proof of the quantum probability rule
which does not make use of the frequency operator, with expectation that this
can circumvent the recent criticism against the previous proofs which use it.
We also argue that avoiding the frequency operator is not only for technical
merits for doing so but is closely related to what quantum mechanics is all
about from the viewpoint of many-world interpretation.Comment: 12 page
Four-Probe Measurements of Carbon Nanotubes with Narrow Metal Contacts
We find that electrons in single-wall carbon nanotubes may propagate
substantial distances (tens of nanometers) under the metal contacts. We perform
four-probe transport measurements of the nanotube conductance and observe
significant deviations from the standard Kirchhoff's circuit rules. Most
noticeably, injecting current between two neighboring contacts on one end of
the nanotube, induces a non-zero voltage difference between two contacts on the
other end.Comment: 4 pages, 5 figures; submitte
New constraints on dust emission and UV attenuation of z=6.5-7.5 galaxies from millimeter observations
We have targeted two recently discovered Lyman break galaxies (LBGs) to
search for dust continuum and [CII] 158 micron line emission. The strongly
lensed z~6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703, and the
spectroscopically confirmed z=7.508 LBG z8-GND-5296 in the GOODS-N field have
been observed with the Plateau de Bure interferometer (PdBI) at 1.2mm. These
observations have been combined with those of three z>6.5 Lya emitters (named
HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained
with the PdBI and ALMA. [CII] is undetected in both galaxies, providing a deep
upper limit for Abell1703-zD1, comparable to recent ALMA non-detections. Dust
continuum emission from Abell1703-zD1 and z8-GND-5296 is not detected with an
rms of 0.12 and 0.16 mJy/beam. From these non-detections we derive upper limits
on their IR luminosity and star formation rate, dust mass, and UV attenuation.
Thanks to strong gravitational lensing the limit for Abell1703-zD1 is probing
the sub-LIRG regime ( Lsun) and very low dust
masses ( Msun). We find that all five galaxies are
compatible with the Calzetti IRX- relation, their UV attenuation is
compatible with several indirect estimates from other methods (the UV slope,
extrapolation of the attenuation measured from the IR/UV ratio at lower
redshift, and SED fits), and the dust-to-stellar mass ratio is not incompatible
with that of galaxies from z=0 to 3. For their stellar mass the high-z galaxies
studied here have an attenuation below the one expected from the mean relation
of low redshift (z<1.5) galaxies. More and deeper (sub)-mm data are clearly
needed to directly determine the UV attenuation and dust content of the
dominant population of high-z star-forming galaxies and to establish more
firmly their dependence on stellar mass, redshift, and other properties.Comment: 10 pages, 7 figures. Minor revisions. Accepted for publication in A&
Localized to extended states transition for two interacting particles in a two-dimensional random potential
We show by a numerical procedure that a short-range interaction induces
extended two-particle states in a two-dimensional random potential. Our
procedure treats the interaction as a perturbation and solve Dyson's equation
exactly in the subspace of doubly occupied sites. We consider long bars of
several widths and extract the macroscopic localization and correlation lengths
by an scaling analysis of the renormalized decay length of the bars. For ,
the critical disorder found is , and the critical
exponent . For two non-interacting particles we do not find any
transition and the localization length is roughly half the one-particle value,
as expected.Comment: 4 two-column pages, 4 eps figures, Revtex, to be published in
Europhys. Let
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