379 research outputs found
Electronic theory for superconductivity in SrRuO: triplet pairing due to spin-fluctuation exchange
Using a two-dimensional Hubbard Hamiltonian for the three electronic bands
crossing the Fermi level in SrRuO we calculate the band structure and
spin susceptibility in quantitative agreement with
nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS)
experiments. The susceptibility has two peaks at {\bf Q}
due to the nesting Fermi surface properties and at {\bf q}
due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange
theory as in layered cuprates we determine from ,
electronic dispersions, and Fermi surface topology that superconductivity in
SrRuO consists of triplet pairing. Combining the Fermi surface topology
and the results for we can exclude and wave
symmetry for the superconducting order parameter. Furthermore, within our
analysis and approximations we find that -wave symmetry is slightly favored
over p-wave symmetry due to the nesting properties of the Fermi surface.Comment: 5 pages, 5 figures, misprints correcte
Contribution of Freshwater Bivalves to Muskrat Diets in the Green River, Mammoth Cave National Park, Kentucky
Muskrats (Ondatra zibethicus) are known to prey on freshwater bivalves (mussels and clams) and can negatively impact imperiled mussel species. However, factors that infl uence muskrat predation on bivalves are poorly understood. We evaluated the feeding ecology of muskrats at Mammoth Cave National Park, Kentucky by using stable isotope analysis of muskrat hair samples and by monitoring bivalve shell deposition at muskrat middens. Bayesian mixing-model analysis of stable isotope ÎŽ15N and ÎŽ13C ratios revealed that the median muskrat biomass derived from bivalves was 51.4% (5th and 95th percentiles were 39.1 to 63.4%, respectively), a much higher dietary proportion than previously reported. Shell depositions by muskrats at middens decreased with the availability of seasonal emergent vegetation, suggesting that the consumption of animal matter is in response to a scarcity of plant foods. Our results add to the growing body of evidence that muskrats have the potential to impact mussel population growth and recovery in some environments
Spin-triplet superconductivity due to antiferromagnetic spin-fluctuation in Sr_2RuO_4
A mechanism leading to the spin-triplet superconductivity is proposed based
on the antiferromagnetic spin fluctuation. The effects of anisotropy in spin
fluctuation on the Cooper pairing and on the direction of d vector are examined
in the one-band Hubbard model with RPA approximation. The gap equations for the
anisotropic case are derived and applied to Sr_2RuO_4. It is found that a
nesting property of the Fermi surface together with the anisotropy leads to the
triplet superconductivity with the d=z(sin{k_x}\pm isin{k_y}), which is
consistent with experiments.Comment: 4 pages, 3 eps figures, revte
Model Flames in the Boussinesq Limit: The Effects of Feedback
We have studied the fully nonlinear behavior of pre-mixed flames in a
gravitationally stratified medium, subject to the Boussinesq approximation. Key
results include the establishment of criterion for when such flames propagate
as simple planar flames; elucidation of scaling laws for the effective flame
speed; and a study of the stability properties of these flames. The simplicity
of some of our scalings results suggests that analytical work may further
advance our understandings of buoyant flames.Comment: 11 pages, 14 figures, RevTex, gzipped tar fil
Developing Antidote Controlled Antiplatelet Therapies By Targeting The Vwf â Gp IbâIxâV Interaction
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106054/1/jth02400.pd
Spin-triplet superconducting pairing due to local (Hund's rule, Dirac) exchange
We discuss general implications of the local spin-triplet pairing among
fermions induced by local ferromagnetic exchange, example of which is the
Hund's rule coupling. The quasiparticle energy and their wave function are
determined for the three principal phases with the gap, which is momentum
independent. We utilize the Bogolyubov-Nambu-De Gennes approach, which in the
case of triplet pairing in the two-band case leads to the four-components wave
function. Both gapless modes and those with an isotropic gap appear in the
quasiparticle spectrum. A striking analogy with the Dirac equation is briefly
explored. This type of pairing is relevant to relativistic fermions as well,
since it reflects the fundamental discrete symmetry-particle interchange. A
comparison with the local interband spin-singlet pairing is also made.Comment: 16 pages, LaTex, submitted to Phys. Rev.
The Cold Big-Bang Cosmology as a Counter-example to Several Anthropic Arguments
A general Friedmann big-bang cosmology can be specified by fixing a
half-dozen cosmological parameters such as the photon-to-baryon ratio Eta, the
cosmological constant Lambda, the curvature scale R, and the amplitude Q of
(assumed scale-invariant) primordial density fluctuations. There is currently
no established theory as to why these parameters take the particular values we
deduce from observations. This has led to proposed `anthropic' explanations for
the observed value of each parameter, as the only value capable of generating a
universe that can host intelligent life. In this paper, I explicitly show that
the requirement that the universe generates sun-like stars with planets does
not fix these parameters, by developing a class of cosmologies (based on the
classical `cold big-bang' model) in which some or all of the cosmological
parameters differ by orders of magnitude from the values they assume in the
standard hot big-bang cosmology, without precluding in any obvious way the
existence of intelligent life. I also give a careful discussion of the
structure and context of anthropic arguments in cosmology, and point out some
implications of the cold big-bang model's existence for anthropic arguments
concerning specific parameters.Comment: 13 PRD-style pages, 2 postscript figures. Reference 26 corrected.
Accepted to Phys. Rev.
Ionization Potential of the Helium Atom
Ground state ionization potential of the He^4 atom is evaluated to be 5 945
204 221 (42) MHz. Along with lower order contributions, this result includes
all effects of the relative orders alpha^4, alpha^3*m_e/m_alpha and
alpha^5*ln^2(alpha).Comment: 4 page
Calculation of the Electron Self Energy for Low Nuclear Charge
We present a nonperturbative numerical evaluation of the one-photon electron
self energy for hydrogenlike ions with low nuclear charge numbers Z=1 to 5. Our
calculation for the 1S state has a numerical uncertainty of 0.8 Hz for hydrogen
and 13 Hz for singly-ionized helium. Resummation and convergence acceleration
techniques that reduce the computer time by about three orders of magnitude
were employed in the calculation. The numerical results are compared to results
based on known terms in the expansion of the self energy in powers of (Z
alpha).Comment: 10 pages, RevTeX, 2 figure
Electron Self Energy for the K and L Shell at Low Nuclear Charge
A nonperturbative numerical evaluation of the one-photon electron self energy
for the K- and L-shell states of hydrogenlike ions with nuclear charge numbers
Z=1 to 5 is described. Our calculation for the 1S state has a numerical
uncertainty of 0.8 Hz in atomic hydrogen, and for the L-shell states (2S and
2P) the numerical uncertainty is 1.0 Hz. The method of evaluation for the
ground state and for the excited states is described in detail. The numerical
results are compared to results based on known terms in the expansion of the
self energy in powers of (Z alpha).Comment: 21 pages, RevTeX, 5 Tables, 6 figure
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