26,006 research outputs found
Diagrammatic perturbation theory and the pseudogap
We study a model of quasiparticles on a two-dimensional square lattice
coupled to Gaussian distributed dynamical fields. The model describes
quasiparticles coupled to spin or charge fluctuations and is solved by a Monte
Carlo sampling of the molecular field distributions. The non-perturbative
solution is compared to various approximations based on diagrammatic
perturbation theory. When the molecular field correlations are sufficiently
weak, the diagrammatic calculations capture the qualitative aspects of the
quasiparticle spectrum. For a range of model parameters near the magnetic
boundary, we find that the quasiparticle spectrum is qualitatively different
from that of a Fermi liquid in that it shows a double peak structure, and that
the diagrammatic approximations we consider fail to reproduce, even
qualitatively, the results of the Monte Carlo calculations. This suggests that
the pseudogap induced by a coupling to antiferromagnetic fluctuations and the
spin-splitting of the quasiparticle peak induced by a coupling to ferromagnetic
spin-fluctuations lie beyond diagrammatic perturbation theory
Locally critical point in an anisotropic Kondo lattice
We report the first numerical identification of a locally quantum critical
point, at which the criticality of the local Kondo physics is embedded in that
associated with a magnetic ordering. We are able to numerically access the
quantum critical behavior by focusing on a Kondo-lattice model with Ising
anisotropy. We also establish that the critical exponent for the q-dependent
dynamical spin susceptibility is fractional and compares well with the
experimental value for heavy fermions.Comment: 4 pages, 3 figures; published versio
A Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation. Part 2: Program Description Document
For abstract, see N75-32026
Reply to the comment by Carmelo Anile on the paper "Complexity analysis of the cerebrospinal fluid pulse waveform during infusion studies"
Veterinary technology is an emerging profession within the veterinary and allied animal health fields in Australia and affords graduates the opportunity to contribute to the small but growing body of literature within this discipline. This study describes the introduction of a contextualised assessment task to develop students’ research capability, competence and confidence in professional writing, and to engage them with the academic publishing process. Students worked in self-selected dyads to author a scientific case report, of publishable standard, based on authentic cases from their clinical practicum. Intrinsic to the task, students attended a series of workshops that explored topics such as critiquing the literature, professional writing styles and oral presentation skills. Assessment was multi-staged with progressive feedback, including peer review, and culminated with students presenting their abstracts at a mock conference. Students reported the task to be an enjoyable and valuable learning experience which improved their competence and confidence in scientific writing; supported by a comparison of previously submitted work. Linking scientific writing skills to clinical practice experiences enhanced learning outcomes and may foster the professionalisation of students within this emerging discipline
Magnetic latitude effects in the solar wind
The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of high electrical conductivity, rotational symmetry, the polytropic relation between pressure and density, and a flow-alined field in a system rotating with the sun, are retained. An approximate solution to the resulting equations for spherical boundary conditions at the base of the corona indicates a small component of latitudinal flow toward the solar poles at large distances from the sun as result of latitudinal magnetic forces
Vacuum Decay in Theories with Symmetry Breaking by Radiative Corrections
The standard bounce formalism for calculating the decay rate of a metastable
vacuum cannot be applied to theories in which the symmetry breaking is due to
radiative corrections, because in such theories the tree-level action has no
bounce solutions. In this paper I derive a modified formalism to deal with such
cases. As in the usual case, the bubble nucleation rate may be written in the
form . To leading approximation, is the bounce action obtained by
replacing the tree-level potential by the leading one-loop approximation to the
effective potential, in agreement with the generally adopted {\it ad hoc}
remedy. The next correction to (which is proportional to an inverse power
of a small coupling) is given in terms of the next-to-leading term in the
effective potential and the leading correction to the two-derivative term in
the effective action. The corrections beyond these (which may be included in
the prefactor) do not have simple expressions in terms of the effective
potential and the other functions in the effective action. In particular, the
scalar-loop terms which give an imaginary part to the effective potential do
not explicitly appear; the corresponding effects are included in a functional
determinant which gives a manifestly real result for the nucleation rate.Comment: 39 pages, CU-TP-57
Local Moments in an Interacting Environment
We discuss how local moment physics is modified by the presence of
interactions in the conduction sea. Interactions in the conduction sea are
shown to open up new symmetry channels for the exchange of spin with the
localized moment. We illustrate this conclusion in the strong-coupling limit by
carrying out a Schrieffer Wolff transformation for a local moment in an
interacting electron sea, and show that these corrections become very severe in
the approach to a Mott transition. As an example, we show how the Zhang Rice
reduction of a two-band model is modified by these new effects.Comment: Latex file with two postscript figures. Revised version, with more
fully detailed calculation
Treatment and secondary prevention of venous thromboembolism in cancer
Patients with cancer who develop venous thromboembolism (VTE) are at elevated
risk for recurrent thrombotic events, even during anticoagulant therapy. The
clinical picture is further complicated because these patients are also at
increased risk of bleeding while on anticoagulants. In general, there are four
key goals of treatment for VTE: preventing fatal pulmonary embolism (PE);
reducing short-term morbidities associated with acute leg or lung thrombus;
preventing recurrent VTE; and preventing the long-term sequelae of VTE (e.g.,
post-thrombotic syndrome and chronic thromboembolic pulmonary hypertension). A
fifth goal – minimising the risk for bleeding while on anticoagulation
– is particularly warranted in patients with cancer. Traditionally,
pharmacological treatment of VTE has two phases, with the transition between
phases marked by a switch from a rapid-acting, parenterally administered
anticoagulant (such as unfractionated heparin (UFH), low-molecular-weight
heparin (LMWH), or fondaparinux) to an oral vitamin K antagonist (e.g.,
warfarin). Recent clinical trials of established agents and the advent of new
pharmacological options are changing this paradigm. Low-molecular-weight heparin
continued for 6 months is more effective than warfarin in the secondary
prevention of VTE in cancer patients without increasing the risk of bleeding and
is now the preferred treatment option. Given the impact of VTE on short-term and
long-term outcomes in patients with cancer, a group of health-care providers
based in the United Kingdom gathered in London in 2009 to discuss recent data on
cancer-associated thrombosis and to evaluate how these recommendations can be
integrated or translated into UK clinical practice. This article, which is the
third of four articles covering key topics in cancer thrombosis, focuses on
treatment and secondary prevention of VTE in cancer patients
New measure of electron correlation
We propose to quantify the "correlation" inherent in a many-electron (or
many-fermion) wavefunction by comparing it to the unique uncorrelated state
that has the same single-particle density operator as it does.Comment: Final version to appear in PR
- …