3,355 research outputs found
Casimir Energy and Entropy between perfect metal Spheres
We calculate the Casimir energy and entropy for two perfect metal spheres in
the large and short separation limit. We obtain nonmonotonic behavior of the
Helmholtz free energy with separation and temperature, leading to parameter
ranges with negative entropy, and also nonmonotonic behavior of the entropy
with temperature and with the separation between the spheres. The appearance of
this anomalous behavior of the entropy is discussed as well as its
thermodynamic consequences.Comment: 10 pages and 8 figures. Accepted for publication in the Proceedings
of the tenth conference on Quantum Field Theory under the influence of
external conditions - QFEXT'1
The role of sign in students' modeling of scalar equations
We describe students revising the mathematical form of physics equations to
match the physical situation they are describing, even though their revision
violates physical laws. In an unfamiliar air resistance problem, a majority of
students in a sophomore level mechanics class at some point wrote Newton's
Second Law as F = -ma; they were using this form to ensure that the sign of the
force pointed in a direction consistent with the chosen coordinate system while
assuming that some variables have only positive value. We use one student's
detailed explanation to suggest that students' issues with variables are
context-dependent, and that much of their reasoning is useful for productive
instruction.Comment: 5 pages, 1 figure, to be published in The Physics Teache
Understanding and Affecting Student Reasoning About Sound Waves
Student learning of sound waves can be helped through the creation of
group-learning classroom materials whose development and design rely on
explicit investigations into student understanding. We describe reasoning in
terms of sets of resources, i.e. grouped building blocks of thinking that are
commonly used in many different settings. Students in our university physics
classes often used sets of resources that were different from the ones we wish
them to use. By designing curriculum materials that ask students to think about
the physics from a different view, we bring about improvement in student
understanding of sound waves. Our curriculum modifications are specific to our
own classes, but our description of student learning is more generally useful
for teachers. We describe how students can use multiple sets of resources in
their thinking, and raise questions that should be considered by both
instructors and researchers.Comment: 23 pages, 4 figures, 3 tables, 28 references, 7 notes. Accepted for
publication in the International Journal of Science Educatio
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
Solving the Einstein-Podolsky-Rosen puzzle: the origin of non-locality in Aspect-type experiments
So far no mechanism is known, which could connect the two measurements in an
Aspect-type experiment. Here, we suggest such a mechanism, based on the phase
of a photon's field during propagation. We show that two polarization
measurements are correlated, even if no signal passes from one point of
measurement to the other. The non-local connection of a photon pair is the
result of its origin at a common source, where the two fields acquire a well
defined phase difference. Therefore, it is not actually a non-local effect in
any conventional sense. We expect that the model and the detailed analysis it
allows will have a major impact on quantum cryptography and quantum
computation.Comment: 5 pages 1 figure. Added an analysis of quantum steering. The result
is that under certain conditions the experimental result at B can be
predicted if the polarization angle and the result at A are known. The paper
has been accepted for publication in Frontiers of Physics. arXiv admin note:
substantial text overlap with arXiv:1108.435
Casimir forces between arbitrary compact objects
We develop an exact method for computing the Casimir energy between arbitrary
compact objects, either dielectrics or perfect conductors. The energy is
obtained as an interaction between multipoles, generated by quantum current
fluctuations. The objects' shape and composition enter only through their
scattering matrices. The result is exact when all multipoles are included, and
converges rapidly. A low frequency expansion yields the energy as a series in
the ratio of the objects' size to their separation. As an example, we obtain
this series for two dielectric spheres and the full interaction at all
separations for perfectly conducting spheres.Comment: 4 pages, 1 figur
Improving marketing success: The role of tacit knowledge exchange between sales and marketing
Successful organizations adapt their marketing strategies to marketplace changes. Boundary spanners, such as salespeople, because they are able to embed themselves in social networks outside the organization, play a key role in developing marketplace knowledge. However, if this knowledge remains solely with the boundary spanners, it cannot be used effectively to improve firm performance. This study investigates tacit knowledge exchange between sales and marketing and its ability to enhance marketing success (i.e., marketing program innovativeness, relative efficiency, and relative effectiveness). In addition, by examining five antecedents hypothesized to influence tacit knowledge exchange, it provides guidance to sales and marketing managers, who desire to improve tacit knowledge exchange, and, in turn, marketing success. Published by Elsevier Inc
The Object Coordination Class Applied to Wavepulses: Analysing Student Reasoning in Wave Physics
Detailed investigations of student reasoning show that students approach the
topic of wave physics using both event-like and object-like descriptions of
wavepulses, but primarily focus on object properties in their reasoning.
Student responses to interview and written questions are analysed using diSessa
and Sherin's coordination class model which suggests that student use of
specific reasoning resources is guided by possibly unconscious cues. Here, the
term reasoning resources is used in a general fashion to describe any of the
smaller grain size models of reasoning (p-prims, facets of knowledge, intuitive
rules, etc) rather than theoretically ambiguous (mis)conceptions. Student
applications of reasoning resources, including one previously undocumented, are
described. Though the coordination class model is extremely helpful in
organising the research data, problematic aspects of the model are also
discussed.Comment: 20 pages, 8 figures, 27 reference
A Deeper Look at Student Learning of Quantum Mechanics: the Case of Tunneling
We report on a large-scale study of student learning of quantum tunneling in
4 traditional and 4 transformed modern physics courses. In the transformed
courses, which were designed to address student difficulties found in previous
research, students still struggle with many of the same issues found in other
courses. However, the reasons for these difficulties are more subtle, and many
new issues are brought to the surface. By explicitly addressing how to build
models of wave functions and energy and how to relate these models to real
physical systems, we have opened up a floodgate of deep and difficult questions
as students struggle to make sense of these models. We conclude that the
difficulties found in previous research are the tip of the iceberg, and the
real issue at the heart of student difficulties in learning quantum tunneling
is the struggle to build the complex models that are implicit in experts'
understanding but often not explicitly addressed in instruction.Comment: v2, v3 updated with more detailed analysis of data and discussion;
submitted to Phys. Rev. ST: PE
- …