10,902 research outputs found
Validity of the Adiabatic Approximation
We analyze the validity of the adiabatic approximation, and in particular the
reliability of what has been called the "standard criterion" for validity of
this approximation. Recently, this criterion has been found to be insufficient.
We will argue that the criterion is sufficient only when it agrees with the
intuitive notion of slowness of evolution of the Hamiltonian. However, it can
be insufficient in cases where the Hamiltonian varies rapidly but only by a
small amount. We also emphasize the distinction between the adiabatic {\em
theorem} and the adiabatic {\em approximation}, two quite different although
closely related ideas.Comment: 4 pages, 1 figur
A new perturbative approach to the adiabatic approximation
A new and intuitive perturbative approach to time-dependent quantum mechanics
problems is presented, which is useful in situations where the evolution of the
Hamiltonian is slow. The state of a system which starts in an instantaneous
eigenstate of the initial Hamiltonian is written as a power series which has a
straightforward diagrammatic representation. Each term of the series
corresponds to a sequence of "adiabatic" evolutions, during which the system
remains in an instantaneous eigenstate of the Hamiltonian, punctuated by
transitions from one state to another. The first term of this series is the
standard adiabatic evolution, the next is the well-known first correction to
it, and subsequent terms can be written down essentially by inspection.
Although the final result is perhaps not terribly surprising, it seems to be
not widely known, and the interpretation is new, as far as we know. Application
of the method to the adiabatic approximation is given, and some discussion of
the validity of this approximation is presented.Comment: 9 pages. Added references, discussion of previous results, expanded
upon discussion of main result and application of i
Interplay of Spin-Orbit Interaction and Electron Correlation on the Van Vleck Susceptibility in Transition Metal Compounds
We have studied the effects of electron correlation on Van Vleck
susceptibility () in transition metal compounds. A typical
crossover behavior is found for the correlation effect on as
sweeping spin-orbit interaction, . For a small , orbital
fluctuation plays a dominant role in the correlation enhancement of
; however, the enhancement rate is rather small. In contrast,
for an intermediate , shows a substantial increase,
accompanied by the development of spin fluctuation. We will discuss the
behavior of in association with the results of Knight-shift
experiments on SrRuO and an anomalously large magnetic susceptibility
observed for Ir compounds.Comment: 5 pages, 3 figures, to appear in J. Phys. Soc. Jp
From double Lie groupoids to local Lie 2-groupoids
We apply the bar construction to the nerve of a double Lie groupoid to obtain
a local Lie 2-groupoid. As an application, we recover Haefliger's fundamental
groupoid from the fundamental double groupoid of a Lie groupoid. In the case of
a symplectic double groupoid, we study the induced closed 2-form on the
associated local Lie 2-groupoid, which leads us to propose a definition of a
symplectic 2-groupoid.Comment: 23 pages, a few minor changes, including a correction to Lemma 6.
Photoemission Quasi-Particle Spectra of SrRuO
Multi-band quasi-particle calculations based on perturbation theory and
dynamical mean field methods show that the creation of a photoemission hole
state in SrRuO is associated with a highly anisotropic self-energy.
Since the narrow Ru-derived bands are more strongly distorted by
Coulomb correlations than the wide band, charge is partially
transferred from to , thereby shifting the van
Hove singularity close to the Fermi level.Comment: 4 pages, to be published in PRB Rapid Com
A Novel Use for the Rigid Cystoscope: The Removal of Sacral Tacks after a Coloanal Anastamosis Dehiscence
A 69-year-old female presented as an emergency with atrial fibrillation, which was treated with warfarin. She subsequently developed fresh rectal bleeding and after further investigations a Dukes B adenocarcinoma of the rectum was found. She subsequently underwent a low anterior resection, coloanal anastamosis and a defunctioning ileostomy. Three sterile surgical metallic tacks (pins) were inserted into the sacrum to stop brisk bleeding from the presacral venous plexus. Following discharge, she was readmitted with septic shock and a CT scan revealed a presacral fluid collection in the area surrounding the sacral tacks (pins) and an anastamotic dehiscence. The patient was not fit for further pelvic surgery to remove the tacks, so an alternative minimally invasive cystoscopic procedure was performed. The sacral tacks (pins) were removed by the urologist using a rigid cystoscope and cold cup biopsy forceps. To our knowledge, this is the first reported case in the literature
Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs
If strong electron-electron interactions between neighboring Fe atoms mediate
the Cooper pairing in iron-pnictide superconductors, then specific and distinct
anisotropic superconducting energy gaps \Delta_i(k) should appear on the
different electronic bands i. Here we introduce intra-band Bogoliubov
quasiparticle scattering interference (QPI) techniques for determination of
\Delta_i(k) in such materials, focusing on LiFeAs. We identify the three
hole-like bands assigned previously as \gamma, \alpha_2 and \alpha_1, and we
determine the anisotropy, magnitude and relative orientations of their
\Delta_i(k). These measurements will advance quantitative theoretical analysis
of the mechanism of Cooper pairing in iron-based superconductivity
The de Haas-van Alphen effect across the metamagnetic transition in SrRuO
We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant
metamagnet SrRuO. Extremely high sample purity allows the
observation of dHvA oscillations both above and below the metamagnetic
transition field of 7.9 T. The quasiparticle masses are fairly large away from
the transition, and are enhanced by up to an extra factor of three as the
transition is approached, but the Fermi surface topography change is quite
small. The results are qualitatively consistent with a field-induced Stoner
transition in which the mass enhancement is the result of critical
fluctuations.Comment: 4 pages, 3 figure
Upper critical field in layered superconductors
The theoretical statements about a restoration of a superconductivity at
magnetic fields higher than the quasiclassical upper critical field and a
reentrance of superconductivity at temperatures in the
superconductors with open Fermi surfaces are reinvestigated taking into account
a scattering of quasiparticles on the impurities.
The system of integral equations for determination of the upper critical
field parallel to the conducting planes in a layered conventional and
unconventional superconductors with impurities are derived. The
values for the "clean" case in the Ginzburg-Landau regime and at any
temperature in the "dirty" case are found analytically. The upper limit of the
superconductor purity when the upper critical field definately has a finite
value is established.Comment: 10 page
What factors facilitate the engagement with flipped classrooms used in the preparation for postgraduate medical membership examinations?
Background: The “flipped classroom,” a pedagogical model where typical lecture and homework elements are reversed, is being advocated in medical education to support the teaching of a large curriculum. However, research into the use of this model in postgraduate medical education, which requires the application of acquired knowledge, is limited. The aim of this study was to explore the barriers and facilitators to engagement with the flipped classroom model in preparation for the written element of postgraduate membership examinations.
Methods: Three focus groups (n=14) were held between February and June 2016. Participants were drawn from a membership examination preparation course, run by the University of Sheffield. Two of the groups (n=10) involved “students” (public health registrars) while the other focus group (n=4) was held with “tutors” (experienced registrars and consultants). The focus groups were audiorecorded and transcribed verbatim. Transcripts were thematically analyzed by using both predetermined and emergent themes.
Results: Key themes that emerged from the data included variation in learning and teaching styles of individuals as well as the feasibility and flexibility of the overall course design. However, management of students’ expectations was found to be the fundamental factor, which underpinned the engagement.
Conclusion: The complex interaction of factors affecting engagement in this study highlights the need to consider the appropriateness of the flipped classroom model. However, this must be balanced by the potential benefits of the approach for delivering a large curriculum. Recognizing the central importance of managing expectations at the outset would be useful when considering this model in postgraduate medical education
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