16,339 research outputs found
Finite Temperature Phase Diagramm of QCD with improved Wilson fermions
We present first results of a study of two flavour QCD with Wilson fermions
at finite temperature. We have used tree level Symanzik improvement in both the
gauge and fermion part of the action. In a first step we explore the phase
diagramm on an lattice, with particular emphasis on checking
Aoki's conjecture with an improved action.Comment: Talk presented at LATTICE97(finite temperature), 3 pages, 3
Postscript figure
Passing through the `chiral limit' in quenched QCD with Wilson fermions
We investigate the limit of vanishing quark mass in quenched lattice QCD with
unimproved Wilson fermions at . Exploiting the correlations of
propagators at different time slices we extract pion masses extremely close to
the `chiral limit', despite the presence of `exceptional configurations'. With
this at hand, the existence of quenched chiral logarithms can be demonstrated,
provided, finite size effects are small. With reference to the phase diagram
proposed by Aoki also the range is investigated. The width
of a potential parity-flavor violating phase can, if at all, hardly be
resolved.Comment: LATTICE98(spectrum
A small tabletop experiment for a direct measurement of the speed of light
A small tabletop experiment for a direct measurement of the speed of light to
an accuracy of few percent is described. The experiment is accessible to a wide
spectrum of undergraduate students, in particular to students not majoring in
science or engineering. The experiment may further include a measurement of the
index of refraction of a sample. Details of the setup and equipment are given.
Results and limitations of the experiment are analyzed, partly based on our
experience in employing the experiment in our student laboratories. Safety
considerations are also discussed.Comment: 4pages, 5fig
Itinerant ferromagnetism in the multiorbital Hubbard model: a dynamical mean-field study
In order to resolve the long-standing issue of how the itinerant
ferromagnetism is affected by the lattice structure and Hund's coupling, we
have compared various three-dimensional lattice structures in the single- and
multiorbital Hubbard models with the dynamical mean-field theory with an
improved quantum Monte Carlo algorithm that preserves the spin-SU(2) symmetry.
The result indicates that {\it both} the lattice structure and the d-orbital
degeneracy are essential for the ferromagnetism in the parameter region
representing a transition metal. Specifically, (a) Hund's coupling, despite the
common belief, is important, which is here identified to come from
particle-hole scatterings, and (b) the ferromagnetism is a correlation effect
(outside the Stoner picture) as indicated from the band-filling dependence.Comment: 4 pages, 5 figure
Spontaneous Parity Violation in QCD At Finite Temperature: On the Inapplicability of the Vafa-Witten Theorem
The generalization of the Vafa-Witten theorem ruling out parity violation to
QCD at finite temperature is considered. It is shown that this generalization
of the theorem rules out Lorentz-invariant parity violating operators from
spontaneously acquiring vacuum expectation values. However, it does not rule
out Lorentz-noninvariant parity-violating operators from acquiring expectation
values. Other situations where the theorem is inapplicable are also discussed.Comment: Minor typos correcte
Practical Strategies for Integrating a Conversation Analyst in an Iterative Design Process
We present a case study of an iterative design process that includes a
conversation analyst. We discuss potential benefits of conversation analysis
for design, and we describe our strategies for integrating the conversation
analyst in the design process. Since the analyst on our team had no previous
exposure to design or engineering, and none of the other members of our team
had any experience with conversation analysis, we needed to build a foundation
for our interaction. One of our key strategies was to pair the conversation
analyst with a designer in a highly interactive collaboration. Our tactics have
been effective on our project, leading to valuable results that we believe we
could not have obtained using another method. We hope that this paper can serve
as a practical guide to those interested in establishing a productive and
efficient working relationship between a conversation analyst and the other
members of a design team.Comment: 11 page
Self-Consistent Perturbation Theory for Thermodynamics of Magnetic Impurity Systems
Integral equations for thermodynamic quantities are derived in the framework
of the non-crossing approximation (NCA). Entropy and specific heat of 4f
contribution are calculated without numerical differentiations of thermodynamic
potential. The formulation is applied to systems such as PrFe4P12 with
singlet-triplet crystalline electric field (CEF) levels.Comment: 3 pages, 2 figures, proc. ASR-WYP-2005 (JAERI
Electronic structure of solid coronene: differences and commonalities to picene
We have obtained the first-principles electronic structure of solid coronene,
which has been recently discovered to exhibit superconductivity with potassium
doping. Since coronene, along with picene, the first aromatic superconductor,
now provide a class of superconductors as solids of aromatic compounds, here we
compare the two cases in examining the electronic structures. In the undoped
coronene crystal, where the molecules are arranged in a herringbone structure
with two molecules in a unit cell, the conduction band above an insulating gap
is found to comprise four bands, which basically originate from the lowest two
unoccupied molecular orbitals
(doubly-degenerate, reflecting the high symmetry of the molecular shape) in
an isolated molecule but the bands are entangled as in solid picene. The Fermi
surface for a candidate of the structure of Kcoronene with , for which
superconductivity is found, comprises multiple sheets, as in doped picene but
exhibiting a larger anisotropy with different topology.Comment: 5 pages, to be published in Phys. Rev.
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