4,999 research outputs found
Extended Bose-Hubbard model with incompressible states at fractional numbers
The Bose-Hubbard model is extended to include nearest and far neighbor
interactions and is related to the fractional quantum Hall effect (FQHE). Both
models may be studied in optical lattices with quantum gases. The ground state
is calculated for the extended Bose-Hubbard model with strong repulsive
interactions (weak hopping). Incompressible Mott insulator states are found at
rational filling fractions compatible with the principal and secondary FQHE
filling fractions of the lowest Landau levels observed experimentally. It is
discussed to which extent these states at fractional filling survive or
undergoes a Mott insulator transition to a superfluid as hopping terms are
included.Comment: Revised version, to appear in PR
Gas of self-avoiding loops on the brickwork lattice
An exact calculation of the phase diagram for a loop gas model on the
brickwork lattice is presented. The model includes a bending energy. In the
dense limit, where all the lattice sites are occupied, a phase transition
occuring at an asymmetric Lifshitz tricritical point is observed as the
temperature associated with the bending energy is varied. Various critical
exponents are calculated. At lower densities, two lines of transitions (in the
Ising universality class) are observed, terminated by a tricritical point,
where there is a change in the modulation of the correlation function. To each
tricritical point an associated disorder line is found.Comment: 19 pages, 6 figures. to appear in J. Phys. A : Math. & Ge
Effective Field Theory of the Zero-Temperature Triangular-Lattice Antiferromagnet: A Monte Carlo Study
Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.Comment: 26 pages, 9 figure
Multichannel oscillations and relations between LSND, KARMEN and MiniBooNE, with and without CP violation
We show by examples that multichannel mixing can affect both the parameters
extracted from neutrino oscillation experiments, and that more general
conclusions derived by fitting the experimental data under the assumption that
only two channels are involved in the mixing. Implications for MiniBooNE are
noted and an example based on maximal CP violation displays profound
implications for the two data sets (muon-neutrino and muon-antineutrino) of
that experiment.Comment: 5 pages 4 figure
Damage spreading in two dimensional geometrically frustrated lattices: the triangular and kagome anistropic Heisenberg model
The technique of damage spreading is used to study the phase diagram of the
easy axis anisotropic Heisenberg antiferromagnet on two geometrically
frustrated lattices. The triangular and kagome systems are built up from
triangular units that either share edges or corners respectively. The
triangular lattice undergoes two sequential Kosterlitz-Thouless transitions
while the kagome lattice undergoes a glassy transition. In both cases, the
phase boundaries obtained using damage spreading are in good agreement with
those obtained from equilibrium Monte Carlo simulations.Comment: 7 pages, 4 figure
Factors that contribute to the process of reporting concussion symptoms experienced by Canadian Football League players
Background: Concussions continue to be at the forefront of research today and are still an ongoing problem for athletes across sporting domains. Further investigation is warranted to achieve a greater understanding of concussions. Purpose: The purpose of this dissertation was to explore research related to sports-related concussions, how concussions affect athletes and those surrounding the athletes at all levels of sport, with a particular focus on Canadian Football League players and the underreporting of concussions. This dissertation also reviews qualitative research methodologies, and how they are applied within concussion research. Research Questions: a) What is my own personal relationship with concussions? In particular, what was my experience with the culture of the CFL while I was playing professional football, and later, during my transition out of professional football? b) What is the extent, range, and nature of the peer-reviewed qualitative research literature on concussions in sport? c) What factors contribute to the process of reporting concussion symptoms in Canadian Football League players? Methodology: I utilized an autoethnography to for the first question, a scoping review to address the second question, and a constructivist grounded theory study (in a sample of ten current and retired CFL players) to approach the third question. Findings: Within the autoethnography presented herein, several factors were identified as influencing the way I interpreted my experiences throughout my playing career, and my subsequent transition from professional sport. The scoping review of qualitative research in sport-related concussion suggested that qualitative research is useful for exploring all levels and types of sports. It further suggested that qualitative methodologies provide researchers with a lens that can be used to view the athletes going through the concussions, and also the other people in their lives such as physicians, parents, coaches, care-takers, teammates and equipment personnel. Different methodologies highlighted several different areas such as barriers to reporting concussions, lived experiences, media portrayal of concussions, coping strategies and effected relationships. Finally, the empirical data collected within the grounded theory study that formed the primary study within this dissertation suggested several factors that influenced the underreporting of concussions in the CFL, within three contexts: a) premeditated thoughts during the pre-game b) assessing the hit on the field and c) during the recovery process of a concussion. Implications: Findings show the current state of concussion research and highlights several factors that influence professionals to underreport their concussions. Implications for future research are discussed
Vortex-induced topological transition of the bilinear-biquadratic Heisenberg antiferromagnet on the triangular lattice
The ordering of the classical Heisenberg antiferromagnet on the triangular
lattice with the the bilinear-biquadratic interaction is studied by Monte Carlo
simulations. It is shown that the model exhibits a topological phase transition
at a finite-temperature driven by topologically stable vortices, while the spin
correlation length remains finite even at and below the transition point. The
relevant vortices could be of three different types, depending on the value of
the biquadratic coupling. Implications to recent experiments on the triangular
antiferromagnet NiGaS is discussed
Sound Diffraction Modeling of Rotorcraft Noise Around Terrain
A new computational technique, Wave Confinement (WC), is extended here to account for sound diffraction around arbitrary terrain. While diffraction around elementary scattering objects, such as a knife edge, single slit, disc, sphere, etc. has been studied for several decades, realistic environments still pose significant problems. This new technique is first validated against Sommerfeld's classical problem of diffraction due to a knife edge. This is followed by comparisons with diffraction over three-dimensional smooth obstacles, such as a disc and Gaussian hill. Finally, comparisons with flight test acoustics data measured behind a hill are also shown. Comparison between experiment and Wave Confinement prediction demonstrates that a Poisson spot occurred behind the isolated hill, resulting in significantly increased sound intensity near the center of the shadowed region
Monte Carlo Study of the Anisotropic Heisenberg Antiferromagnet on the Triangular Lattice
We report a Monte Carlo study of the classical antiferromagnetic Heisenberg
model with easy axis anisotropy on the triangular lattice. Both the free energy
cost for long wavelength spin waves as well as for the formation of free
vortices are obtained from the spin stiffness and vorticity modulus
respectively. Evidence for two distinct Kosterlitz-Thouless types of
defect-mediated phase transitions at finite temperatures is presented.Comment: 8 pages, 10 figure
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