507 research outputs found
Frustrated multiband superconductivity
We show that a clean multiband superconductor may display one or several
phase transitions with increasing temperature from or to frustrated
configurations of the relative phases of the superconducting order parameters.
These transitions may occur when more than two bands are involved in the
formation of the superconducting phase and when the number of repulsive
interband interactions is odd. These transitions are signalled by slope changes
in the temperature dependence of the superconducting gaps.Comment: 5 pages, 3 figure
Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago
The earliest tin bronze artefacts in Eurasia are generally believed to have appeared in the Near East in the early third millennium BC. Here we present tin bronze artefacts that occur far from the Near East, and in a significantly earlier period. Excavations at Pločnik, a Vinča culture site in Serbia, recovered a piece of tin bronze foil from an occupation layer dated to the mid fifth millennium BC. The discovery prompted a reassessment of 14 insufficiently contextualised early tin bronze artefacts from the Balkans. They too were found to derive from the smelting of copper-tin ores. These tin bronzes extend the record of bronze making by c. 1500 years, and challenge the conventional narrative of Eurasian metallurgical development
L-Arginine Intake Effect on Adenine Nucleotide Metabolism in Rat Parenchymal and Reproductive Tissues
L-arginine is conditionally essetcial amino acid, required for normal cell growth, protein synthesis, ammonia detoxification, tissue growth and general performance, proposed in the treatment of men sterility and prevention of male impotence. The aim of the present paper was to estimate the activity of the enzymes of adenine nucleotide metabolism: 5′-nucleotidase (5′-NU), adenosine deaminase (ADA), AMP deaminase, and xanthine oxidase (XO), during dietary intake of L-arginine for a period of four weeks of male Wistar rats. Adenosine concentration in tissues is maintained by the relative activities of the adenosine-producing enzyme, 5′-NU and the adenosine-degrading enzyme-ADA adenosine deaminase. Dietary L-arginine intake directed adenine nucleotide metabolism in liver, kidney, and testis tissue toward the activation of adenosine production, by increased 5′-NU activity and decreased ADA activity. Stimulation of adenosine accumulation could be of importance in mediating arginine antiatherosclerotic, vasoactive, immunomodulatory, and antioxidant effects. Assuming that the XO activity reflects the rate of purine catabolism in the cell, while the activity of AMP deaminase is of importance in ATP regeneration, reduced activity of XO, together with the increased AMP-deaminase activity, may suggest that adenine nucleotides are presumably directed to the ATP regenerating process during dietary L-arginine intake
Application of semidefinite programming to maximize the spectral gap produced by node removal
The smallest positive eigenvalue of the Laplacian of a network is called the
spectral gap and characterizes various dynamics on networks. We propose
mathematical programming methods to maximize the spectral gap of a given
network by removing a fixed number of nodes. We formulate relaxed versions of
the original problem using semidefinite programming and apply them to example
networks.Comment: 1 figure. Short paper presented in CompleNet, Berlin, March 13-15
(2013
Single Impurity Problem in Iron-Pnictide Superconductors
Single impurity problem in iron-pnictide superconductors is investigated by
solving Bogoliubov-de Gennes (BdG) equation in the five-orbital model, which
enables us to distinguish s and s superconducting states. We
construct a five-orbital model suitable to BdG analysis. This model reproduces
the results of random phase approximation in the uniform case. Using this
model, we study the local density of states around a non-magnetic impurity and
discuss the bound-state peak structure, which can be used for distinguishing
s and s states. A bound state with nearly zero-energy is found
for the impurity potential eV, while the bound state peaks stick to
the gap edge in the unitary limit. Novel multiple peak structure originated
from the multi-orbital nature of the iron pnictides is also found.Comment: 5 page
Superconducting gap structure of the 115's revisited
Density functional theory calculations of the electronic structure of Ce- and
Pu-based heavy fermion superconductors in the so-called 115 family are
performed. The gap equation is used to consider which superconducting order
parameters are most favorable assuming a pairing interaction that is peaked at
(\pi,\pi,q_z) - the wavevector for the antiferromagnetic ordering found in
close proximity. In addition to the commonly accepted order
parameter, there is evidence that an extended s-wave order parameter with nodes
is also plausible. We discuss whether these results are consistent with current
observations and possible measurements that could help distinguish between
these scenarios.Comment: 8 pages, 4 figures; Accepted for publication in JPC
Electronic structure of optimally doped pnictide BaKFeAs: a comprehensive ARPES investigation
We have conducted a comprehensive angle-resolved photoemission study on the
normal state electronic structure of the Fe-based superconductor
BaKFeAs. We have identified four dispersive bands which
cross the Fermi level and form two hole-like Fermi surfaces around and
two electron-like Fermi surfaces around M. There are two nearly nested Fermi
surface pockets connected by an antiferromagnetic (, ) wavevector.
The observed Fermi surfaces show small dispersion and a total volume
consistent with Luttinger theorem. Compared to band structure calculations, the
overall bandwidth is reduced by a factor of 2. However, many low energy
dispersions display stronger mass renormalization by a factor of 4,
indicating possible orbital (energy) dependent correlation effects. Using an
effective tight banding model, we fitted the band structure and the Fermi
surfaces to obtain band parameters reliable for theoretical modeling and
calculations of the important physical quantities, such as the specific heat
coefficient.Comment: 13 pages, 4 figure
Identification and Characterization of Potential Discharge Areas for Radionuclide Transport by Groundwater from a Nuclear Waste Repository in Sweden
Role of Hund's coupling in stabilization of the (0,pi) ordered SDW state within the minimal two-band model for iron pnictides
Spin wave excitations and stability of the (0,pi) ordered SDW state are
investigated within the minimal two-band model for iron pnictides including a
Hund's coupling term. The SDW state is shown to be stable in two distinct
doping regimes --- finite hole doping in the lower SDW band for small second
neighbour hoppings, and small electron doping in the upper SDW band for
comparable first and second neighbour hoppings. In both cases, Hund's coupling
strongly stabilizes the SDW state due to generation of additional ferromagnetic
spin couplings involving the inter-orbital part of the particle-hole
propagator. Spin wave energies for the two-band model are very similar to the
one-band t-t' Hubbard model results obtained earlier, and are in agreement with
inelastic neutron scattering studies of iron pnictides.Comment: 9 pages, 4 figure
Spectral Simplicity of Apparent Complexity, Part I: The Nondiagonalizable Metadynamics of Prediction
Virtually all questions that one can ask about the behavioral and structural
complexity of a stochastic process reduce to a linear algebraic framing of a
time evolution governed by an appropriate hidden-Markov process generator. Each
type of question---correlation, predictability, predictive cost, observer
synchronization, and the like---induces a distinct generator class. Answers are
then functions of the class-appropriate transition dynamic. Unfortunately,
these dynamics are generically nonnormal, nondiagonalizable, singular, and so
on. Tractably analyzing these dynamics relies on adapting the recently
introduced meromorphic functional calculus, which specifies the spectral
decomposition of functions of nondiagonalizable linear operators, even when the
function poles and zeros coincide with the operator's spectrum. Along the way,
we establish special properties of the projection operators that demonstrate
how they capture the organization of subprocesses within a complex system.
Circumventing the spurious infinities of alternative calculi, this leads in the
sequel, Part II, to the first closed-form expressions for complexity measures,
couched either in terms of the Drazin inverse (negative-one power of a singular
operator) or the eigenvalues and projection operators of the appropriate
transition dynamic.Comment: 24 pages, 3 figures, 4 tables; current version always at
http://csc.ucdavis.edu/~cmg/compmech/pubs/sdscpt1.ht
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