1,087 research outputs found
Analytic Framework for Students' Use of Mathematics in Upper-Division Physics
Many students in upper-division physics courses struggle with the
mathematically sophisticated tools and techniques that are required for
advanced physics content. We have developed an analytical framework to assist
instructors and researchers in characterizing students' difficulties with
specific mathematical tools when solving the long and complex problems that are
characteristic of upper-division. In this paper, we present this framework,
including its motivation and development. We also describe an application of
the framework to investigations of student difficulties with direct integration
in electricity and magnetism (i.e., Coulomb's Law) and approximation methods in
classical mechanics (i.e., Taylor series). These investigations provide
examples of the types of difficulties encountered by advanced physics students,
as well as the utility of the framework for both researchers and instructors.Comment: 17 pages, 4 figures, 3 tables, in Phys. Rev. - PE
Investigating teacher presence in courses using synchronous videoconferencing
This research examines teacher presence in high school distance courses that are delivered by synchronous videoconference. In rural and remote areas, many school districts are using videoconferencing as way to reach dispersed students. This collective case study uses mixed methods to unpack the notion of presence from the perspective of teachers and their students. This study reports four key findings which have implications for building presence in a videoconference course: teachers’ confidence and experience aligned with higher presence; teaching videoconference and face-to-face classes simultaneously led to challenges with developing presence; immediacy behaviors correlated with higher presence; and, students’ learning preference related to perceived teacher presence. These findings confirm many of the issues raised in the literature about technology integration but also contribute new perspectives on teaching presence in a videoconference
Complete Characterization of Quantum-Optical Processes
The technologies of quantum information and quantum control are rapidly
improving, but full exploitation of their capabilities requires complete
characterization and assessment of processes that occur within quantum devices.
We present a method for characterizing, with arbitrarily high accuracy, any
quantum optical process. Our protocol recovers complete knowledge of the
process by studying, via homodyne tomography, its effect on a set of coherent
states, i.e. classical fields produced by common laser sources. We demonstrate
the capability of our protocol by evaluating and experimentally verifying the
effect of a test process on squeezed vacuum.Comment: 5 pages, 4 figure
Excited States in Warm and Hot Dense Matter
Accurate modeling of warm and hot dense matter is challenging in part due to
the multitude of excited states that must be considered. In thermal density
functional theory, these excited states are averaged over to produce a single,
averaged, thermal ground state. Here we present a variational framework and
model that includes explicit excited states. In this framework an excited state
is defined by a set of effective one-electron occupation factors and the
corresponding energy is defined by the effective one-body energy with an
exchange and correlation term. The variational framework is applied to an
atom-in-plasma model (a generalization of the so-called average atom model).
Comparisons with a density functional theory based average atom model generally
reveal good agreement in the calculated pressure, but the new model also gives
access to the excitation energies and charge state distributions
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The role of gamma rays and freely-migrating defects in reactor pressure vessel embrittlement
Gamma ray effects are often neglected when evaluating reactor pressure vessel (RPV) embrittlement. However, recent analyses indicate that in newer style light water reactors, gamma damage can be a substantial fraction of the total displacement damage experienced by the (RPV); ignoring this damage will lead to errors in embrittlement predictions. Furthermore, gamma rays may be more efficient than fast neutrons at producing freely-migrating defects and as such can impact certain embrittlement mechanisms more effectively than fast neutrons. Consideration of these gamma effects are therefore essential for a more complete understanding of radiation embrittlement
Random perfect lattices and the sphere packing problem
Motivated by the search for best lattice sphere packings in Euclidean spaces
of large dimensions we study randomly generated perfect lattices in moderately
large dimensions (up to d=19 included). Perfect lattices are relevant in the
solution of the problem of lattice sphere packing, because the best lattice
packing is a perfect lattice and because they can be generated easily by an
algorithm. Their number however grows super-exponentially with the dimension so
to get an idea of their properties we propose to study a randomized version of
the algorithm and to define a random ensemble with an effective temperature in
a way reminiscent of a Monte-Carlo simulation. We therefore study the
distribution of packing fractions and kissing numbers of these ensembles and
show how as the temperature is decreased the best know packers are easily
recovered. We find that, even at infinite temperature, the typical perfect
lattices are considerably denser than known families (like A_d and D_d) and we
propose two hypotheses between which we cannot distinguish in this paper: one
in which they improve Minkowsky's bound phi\sim 2^{-(0.84+-0.06) d}, and a
competitor, in which their packing fraction decreases super-exponentially,
namely phi\sim d^{-a d} but with a very small coefficient a=0.06+-0.04. We also
find properties of the random walk which are suggestive of a glassy system
already for moderately small dimensions. We also analyze local structure of
network of perfect lattices conjecturing that this is a scale-free network in
all dimensions with constant scaling exponent 2.6+-0.1.Comment: 19 pages, 22 figure
One-dimensional phase transitions in a two-dimensional optical lattice
A phase transition for bosonic atoms in a two-dimensional anisotropic optical
lattice is considered. If the tunnelling rates in two directions are different,
the system can undergo a transition between a two-dimensional superfluid and a
one-dimensional Mott insulating array of strongly coupled tubes. The connection
to other lattice models is exploited in order to better understand the phase
transition. Critical properties are obtained using quantum Monte Carlo
calculations. These critical properties are related to correlation properties
of the bosons and a criterion for commensurate filling is established.Comment: 14 pages, 8 figure
Web-based participatory surveillance of infectious diseases: the Influenzanet participatory surveillance experience.
To overcome the limitations of the state-of-the-art influenza surveillance systems in Europe, we established in 2008 a European-wide consortium aimed at introducing an innovative information and communication technology approach for a web-based surveillance system across different European countries, called Influenzanet. The system, based on earlier efforts in The Netherlands and Portugal, works with the participation of the population in each country to collect real-time information on the distribution of influenza-like illness cases through web surveys administered to volunteers reporting their symptoms (or lack of symptoms) every week during the influenza season. Such a large European-wide web-based monitoring infrastructure is intended to rapidly identify public health emergencies, contribute to understanding global trends, inform data-driven forecast models to assess the impact on the population, optimize the allocation of resources, and help in devising mitigation and containment measures. In this article, we describe the scientific and technological issues faced during the development and deployment of a flexible and readily deployable web tool capable of coping with the requirements of different countries for data collection, during either a public health emergency or an ordinary influenza season. Even though the system is based on previous successful experience, the implementation in each new country represented a separate scientific challenge. Only after more than 5 years of development are the existing platforms based on a plug-and-play tool that can be promptly deployed in any country wishing to be part of the Influenzanet network, now composed of The Netherlands, Belgium, Portugal, Italy, the UK, France, Sweden, Spain, Ireland, and Denmark
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