2,784 research outputs found
The Partition Function and Level Density for Yang-Mills-Higgs Quantum Mechanics
We calculate the partition function and the asymptotic integrated
level density for Yang-Mills-Higgs Quantum Mechanics for two and three
dimensions (). Due to the infinite volume of the phase space
on energy shell for , it is not possible to disentangle completely the
coupled oscillators (-model) from the Higgs sector. The situation is
different for for which is finite. The transition from order
to chaos in these systems is expressed by the corresponding transitions in
and , analogous to the transitions in adjacent level spacing
distribution from Poisson distribution to Wigner-Dyson distribution. We also
discuss a related system with quartic coupled oscillators and two dimensional
quartic free oscillators for which, contrary to YMHQM, both coupling constants
are dimensionless.Comment: 10 pages, LaTeX; minor changes; version accepted for publication as a
Letter in J. Phys.
Spectroscopic analysis of finite size effects around a Kondo quantum dot
We consider a simple setup in which a small quantum dot is strongly connected
to a finite size box. This box can be either a metallic box or a finite size
quantum wire.The formation of the Kondo screening cloud in the box strongly
depends on the ratio between the Kondo temperature and the box level spacing.
By weakly connecting two metallic reservoirs to the quantum dot, a detailed
spectroscopic analysis can be performed. Since the transport channels and the
screening channels are almost decoupled, such a setup allows an easier access
to the measure of finite-size effects associated with the finite extension of
the Kondo cloud.Comment: contribution to Les Houches proceeding, ``Quantum magnetism'' 200
Tightrope walkers and solidarity sisters: critical workplace educators in the garment industry
Abstract: This article focuses on the complex negotiations of critical workplace educators positioned amongst contradictory agendas and discourses in the workplace. While philosophically aligned with critical pedagogical agendas of transformation and collective action for workplace change, these educators perform an array of pedagogic articulations in everyday practice to secure their continued presence in the workplace. What becomes evident in these seemingly opposing articulations are various strategic political positionings of educators alongside their juggling of demands, attachments and inter-identifications with both learners and managers. The pedagogy that emerges challenges conventional binaries of âtransformativeâ and âreproductiveâ learning. Dynamics of transformation and liberation as well as reproduction and subjugation appear to be interlinked, along with expanding nets of social relations that blur power hierarchies and spatial boundaries, in a pedagogy that ultimately appears to mobilise hope and agency among workers. The workplace educator works a delicate balance of these dynamics to survive. The argument is based on a case study of a garment factory in Canada in which an adult education programme managed to thrive for 17 years: both workers and educators were interviewed in depth
Kondo screening cloud effects in mesoscopic devices
We study how finite size effects may appear when a quantum dot in the Kondo
Coulomb blockade regime is embedded into a mesoscopic device with finite wires.
These finite size effects appear when the size of the mesoscopic device
containing the quantum dot is of the order of the size of Kondo cloud and
affect all thermodynamic and transport properties of the Kondo quantum dot. We
also generalize our results to the experimentally relevant case where the wires
contain several transverse modes/channels. Our results are based on
perturbation theory, Fermi liquid theory and slave boson mean field theory.Comment: 19 pages, 9 figure
Detecting the Kondo screening cloud around a quantum dot
A fundamental prediction of scaling theories of the Kondo effect is the
screening of an impurity spin by a cloud of electrons spread out over a
mesoscopic distance. This cloud has never been observed experimentally.
Recently, aspects of the Kondo effect have been observed in experiments on
quantum dots embedded in quantum wires. Since the length of the wire may be of
order the size of the screening cloud, such systems provide an ideal
opportunity to observe it. We point out that persistent current measurements in
a closed ring provide a conceptually simple way of detecting this fundamental
length scale.Comment: 4 pages, RevTex, 1 postscript figur
Argumentation in school science : Breaking the tradition of authoritative exposition through a pedagogy that promotes discussion and reasoning
The value of argumentation in science education has become internationally recognised and has been the subject of many research studies in recent years. Successful introduction of argumentation activities in learning contexts involves extending teaching goals beyond the understanding of facts and concepts, to include an emphasis on cognitive and metacognitive processes, epistemic criteria and reasoning. The authors focus on the difficulties inherent in shifting a tradition of teaching from one dominated by authoritative exposition to one that is more dialogic, involving small-group discussion based on tasks that stimulate argumentation. The paper builds on previous research on enhancing the quality of argument in school science, to focus on how argumentation activities have been designed, with appropriate strategies, resources and modelling, for pedagogical purposes. The paper analyses design frameworks, their contexts and lesson plans, to evaluate their potential for enhancing reasoning through foregrounding the processes of argumentation. Examples of classroom dialogue where teachers adopt the frameworks/plans are analysed to show how argumentation processes are scaffolded. The analysis shows that several layers of interpretation are needed and these layers need to be aligned for successful implementation. The analysis serves to highlight the potential and limitations of the design frameworks
Procalcitonin guided antibiotic therapy and hospitalization in patients with lower respiratory tract infections: a prospective, multicenter, randomized controlled trial
<p>Abstract</p> <p>Background:</p> <p>Lower respiratory tract infections like acute bronchitis, exacerbated chronic obstructive pulmonary disease and community-acquired pneumonia are often unnecessarily treated with antibiotics, mainly because of physicians' difficulties to distinguish viral from bacterial cause and to estimate disease-severity. The goal of this trial is to compare medical outcomes, use of antibiotics and hospital resources in a strategy based on enforced evidence-based guidelines versus procalcitonin guided antibiotic therapy in patients with lower respiratory tract infections.</p> <p>Methods and design:</p> <p>We describe a prospective randomized controlled non-inferiority trial with an open intervention. We aim to randomize over a fixed recruitment period of 18 months a minimal number of 1002 patients from 6 hospitals in Switzerland. Patients must be >18 years of age with a lower respiratory tract infections <28 days of duration. Patients with no informed consent, not fluent in German, a previous hospital stay within 14 days, severe immunosuppression or chronic infection, intravenous drug use or a terminal condition are excluded. Randomization to either guidelines-enforced management or procalcitonin-guided antibiotic therapy is stratified by centre and type of lower respiratory tract infections. During hospitalization, all patients are reassessed at days 3, 5, 7 and at the day of discharge. After 30 and 180 days, structured phone interviews by blinded medical students are conducted. Depending on the randomization allocation, initiation and discontinuation of antibiotics is encouraged or discouraged based on evidence-based guidelines or procalcitonin cut off ranges, respectively. The primary endpoint is the risk of combined disease-specific failure after 30 days. Secondary outcomes are antibiotic exposure, side effects from antibiotics, rate and duration of hospitalization, time to clinical stability, disease activity scores and cost effectiveness. The study hypothesis is that procalcitonin-guidance is non-inferior (i.e., at worst a 7.5% higher combined failure rate) to the management with enforced guidelines, but is associated with a reduced total antibiotic use and length of hospital stay.</p> <p>Discussion:</p> <p>Use of and prolonged exposure to antibiotics in lower respiratory tract infections is high. The proposed trial investigates whether procalcitonin-guidance may safely reduce antibiotic consumption along with reductions in hospitalization costs and antibiotic resistance. It will additionally generate insights for improved prognostic assessment of patients with lower respiratory tract infections.</p> <p>Trial registration:</p> <p>ISRCTN95122877</p
Adiabatic transport in nanostructures
A confined system of non-interacting electrons, subject to the combined
effect of a time-dependent potential and different external
chemical-potentials, is considered. The current flowing through such a system
is obtained for arbitrary strengths of the modulating potential, using the
adiabatic approximation in an iterative manner. A new formula is derived for
the charge pumped through an un-biased system (all external chemical potentials
are kept at the same value); It reproduces the Brouwer formula for a
two-terminal nanostructure. The formalism presented yields the effect of the
chemical potential bias on the pumped charge on one hand, and the modification
of the Landauer formula (which gives the current in response to a constant
chemical-potential difference) brought about by the modulating potential on the
other. Corrections to the adiabatic approximation are derived and discussed.Comment: 8 pages, 2 figure
Temperature and Field Dependence of the Energy Gap of MgB2/Pb planar junction
We have constructed MgB2/Pb planar junctions for both temperature and field
dependence studies. Our results show that the small gap is a true bulk property
of MgB2 superconductor, not due to surface effects. The temperature dependence
of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect
of magnetic field on junctions suggests that the energy gap of MgB2 depends
non-linearly on the magnetic field. Moreover, MgB2 has an upper critical field
of 15 T, in agreement with some reported Hc2 from transport measurements.Comment: 5 pages, 5 figures. Submitted to Phys. Rev.
The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
Observations indicate that nearly all galaxies contain supermassive black
holes (SMBHs) at their centers. When galaxies merge, their component black
holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves
(GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the
recently-released North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits.
As we did not find strong evidence for GWs in our data, we placed 95\% upper
limits on the strength of GWs from such sources as a function of GW frequency
and sky location. We placed a sky-averaged upper limit on the GW strain of at nHz. We also developed a
technique to determine the significance of a particular signal in each pulsar
using ``dropout' parameters as a way of identifying spurious signals in
measurements from individual pulsars. We used our upper limits on the GW strain
to place lower limits on the distances to individual SMBHBs. At the
most-sensitive sky location, we ruled out SMBHBs emitting GWs with
nHz within 120 Mpc for , and
within 5.5 Gpc for . We also determined that
there are no SMBHBs with emitting
GWs in the Virgo Cluster. Finally, we estimated the number of potentially
detectable sources given our current strain upper limits based on galaxies in
Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris
cosmological simulation project. Only 34 out of 75,000 realizations of the
local Universe contained a detectable source, from which we concluded it was
unsurprising that we did not detect any individual sources given our current
sensitivity to GWs.Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send
any comments/questions to S. J. Vigeland ([email protected]
- âŠ