7,330 research outputs found
Cold Attractive Spin Polarized Fermi Lattice Gases and the Doped Positive U Hubbard Model
Experiments on polarized fermion gases performed by trapping ultracold atoms
in optical lattices, allow the study of an attractive Hubbard model for which
the strength of the on site interaction is tuned by means of a Feshbach
resonance. Using a well-known particle-hole transformation we discuss how
results obtained for this system can be reinterpreted in the context of a doped
repulsive Hubbard model. In particular we show that the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state corresponds to the striped state
of the two-dimensional doped positive U Hubbard model. We then use the results
of numerical studies of the striped state to relate the periodicity of the FFLO
state to the spin polarization. We also comment on the relationship of the
superconducting phase of the doped 2D repulsive Hubbard model to
a d-wave spin density wave state for the attractive case.Comment: 4 pages, 2 figure
Sources of sport confidence, imagery type and performance among competitive athletes: The mediating role of sports confidence
Aim: This study explored the mediating role of sport confidence upon (1) sources of sport confidence-performance relationship and (2) imagery-performance relationship. Methods: Participants were 157 competitive athletes who completed state measures of confidence level/sources, imagery type and performance within one hour after competition. Results: Among the current sample, confirmatory factor analysis revealed appropriate support for the nine-factor SSCQ and the five-factor SIQ. Mediational analysis revealed that sport confidence had a mediating influence upon the achievement source of confidence-performance relationship. In addition, both cognitive and motivational imagery types were found to be important sources of confidence, as sport confidence mediated imagery type-performance relationship. Conclusion: Findings indicated that athletes who construed confidence from their own achievements and report multiple images on a more frequent basis are likely to benefit from enhanced levels of state sport confidence and subsequent performance
Sources of sport confidence, imagery type and performance among competitive athletes: The mediating role of sports confidence
Aim: This study explored the mediating role of sport confidence upon (1) sources of sport confidence-performance relationship and (2) imagery-performance relationship. Methods: Participants were 157 competitive athletes who completed state measures of confidence level/sources, imagery type and performance within one hour after competition. Results: Among the current sample, confirmatory factor analysis revealed appropriate support for the nine-factor SSCQ and the five-factor SIQ. Mediational analysis revealed that sport confidence had a mediating influence upon the achievement source of confidence-performance relationship. In addition, both cognitive and motivational imagery types were found to be important sources of confidence, as sport confidence mediated imagery type-performance relationship. Conclusion: Findings indicated that athletes who construed confidence from their own achievements and report multiple images on a more frequent basis are likely to benefit from enhanced levels of state sport confidence and subsequent performance
Exotic superfluid states of lattice fermions in elongated traps
We present real-space dynamical mean-field theory calculations for
attractively interacting fermions in three-dimensional lattices with elongated
traps. The critical polarization is found to be 0.8, regardless of the trap
elongation. Below the critical polarization, we find unconventional superfluid
structures where the polarized superfluid and
Fulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core
region
A Double Hurdle Model of Preferences for a Proposed Capacity Reduction Program in the Atlantic Shark Fishery
The Atlantic shark fishery is considered to be overcapitalized. One approach to capacity management is the purchase and permanent retirement of fishing vessels, fishing permits, or both under voluntary buyback programs. Representatives of the commercial shark fishery have proposed such an approach to manage the overcapacity in their fishery in the Gulf of Mexico and Atlantic regions. This program would allow owners to submit willingness-to-accept (WTA) bids for their permits and vessels. This study uses econometric modeling to explain the potential participation and bid amounts from a survey of permit owners.Resource /Energy Economics and Policy,
Stability conditions and Fermi surface topologies in a superconductor
Candidate homogeneous, isotropic superfluid or superconducting states of
paired fermion species with different chemical potentials, can lead to
quasiparticle excitation energies that vanish at either zero, one, or two
spheres in momentum space. With no zeroes, we have a conventional BCS
superconductor. The other two cases, ``gapless'' superconductors, appear in
mean field theory for sufficiently large mismatches and/or sufficiently large
coupling strengths. Here we examine several stability criteria for those
candidate phases. Positivity of number susceptibility appears to provide the
most powerful constraint, and renders all the two-zero states that we have
examined mechanically unstable. Our results should apply directly to ultracold
fermionic atom systems.Comment: 18 pages, 7 figures; v2: some clarifications in Sec. IIC; references
added; version accepted for publication in Phys. Rev.
Free-energy distribution functions for the randomly forced directed polymer
We study the -dimensional random directed polymer problem, i.e., an
elastic string subject to a Gaussian random potential and
confined within a plane. We mainly concentrate on the short-scale and
finite-temperature behavior of this problem described by a short- but
finite-ranged disorder correlator and introduce two types of
approximations amenable to exact solutions. Expanding the disorder potential
at short distances, we study the
random force (or Larkin) problem with as well as the shifted
random force problem including the random offset ; as such, these
models remain well defined at all scales. Alternatively, we analyze the
harmonic approximation to the correlator in a consistent manner.
Using direct averaging as well as the replica technique, we derive the
distribution functions and of free energies
of a polymer of length for both fixed () and free boundary
conditions on the displacement field and determine the mean
displacement correlators on the distance . The inconsistencies encountered
in the analysis of the harmonic approximation to the correlator are traced back
to its non-spectral correlator; we discuss how to implement this approximation
in a proper way and present a general criterion for physically admissible
disorder correlators .Comment: 16 pages, 5 figure
Site-Competition Epitaxy for N-Type and P-Type Dopant Control in CVD Sic Epilayers
The use of site-competition epitaxy, which is based on intentional variation of the Si/C ratio during epitaxy, has now been reproduced in numerous national and international laboratories. However, previous reports have only considered dopant incorporation control for epitaxy on the Si-face 6H-SiC(OOO1) substrates. Presented in this paper is the extension of this technique for control of phosphorous incorporation and also a comparison of controlled doping on C-face 6H-SiC(OOO1) versus Si-face 6H-SiC(OOO1) substrates for aluminum, boron, nitrogen, and phosphorous
Theory of quantum paraelectrics and the metaelectric transition
We present a microscopic model of the quantum paraelectric-ferroelectric
phase transition with a focus on the influence of coupled fluctuating phonon
modes. These may drive the continuous phase transition first order through a
metaelectric transition and furthermore stimulate the emergence of a textured
phase that preempts the transition. We discuss two further consequences of
fluctuations, firstly for the heat capacity, and secondly we show that the
inverse paraelectric susceptibility displays T^2 quantum critical behavior, and
can also adopt a characteristic minimum with temperature. Finally, we discuss
the observable consequences of our results.Comment: 5 pages, 2 figure
Dopant Incorporation Efficiency in CVD Silicon Carbide Epilayers
In order to ensure reproducible and reliable SiC semiconductor device characteristics, controlled dopant incorporation must be accomplished. Some of the many factors which greatly influence dopant incorporation are the site-competition effect, SiC(0001) substrate polarity, substrate temperature, and the dopant-source reactor concentration. In this paper, dopant incorporation is considered and compared for various dopants in the context of dopant incorporation efficiency. By using secondary ion mass spectrometry (SIMS), the relative dopant incorporation efficiencies were calculated by dividing the SIMS determined dopant concentration in the resulting epitaxial layer by the intentional gas phase dopant concentration used during the SiC CVD. Specifically, the relative magnitudes of dopant incorporation efficiencies for nitrogen, phosphorus, and boron in 6H-SiC (0001) Si-face epitaxial layers are compared as a function of the site-competition effect and the dopant-source reactor concentrations. This serves as a first approximation for comparison of the relative 'doping potencies' of some common dopants used in SiC CVD epitaxial growth
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