320 research outputs found
Risk-bounded formation of fuzzy coalitions among service agents.
Cooperative autonomous agents form coalitions in order ro share and combine resources and services to efficiently respond to market demands. With the variety of resources and services provided online today, there is a need for stable and flexible techniques to support the automation of agent coalition formation in this context. This paper describes an approach to the problem based on fuzzy coalitions. Compared with a classic cooperative game with crisp coalitions (where each agent is a full member of exactly one coalition), an agent can participate in multiple coalitions with varying degrees of involvement. This gives the agent more freedom and flexibility, allowing them to make full use of their resources, thus maximising utility, even if only comparatively small coalitions are formed. An important aspect of our approach is that the agents can control and bound the risk caused by the possible failure or default of some partner agents by spreading their involvement in diverse coalitions
The mean energy, strength and width of triple giant dipole resonances
We investigate the mean energy, strength and width of the triple giant dipole
resonance using sum rules.Comment: 12 page
Ultrasonic attenuation in magnetic fields for superconducting states with line nodes in Sr2RuO4
We calculate the ultrasonic attenuation in magnetic fields for
superconducting states with line nodes vertical or horizontal relative to the
RuO_2 planes. This theory, which is valid for fields near Hc2 and not too low
temperatures, takes into account the effects of supercurrent flow and Andreev
scattering by the Abrikosov vortex lattice. For rotating in-plane field
H(theta) the attenuation alpha(theta)exhibits variations of fourfold symmetry
in the rotation angle theta. In the case of vertical nodes, the transverse T100
sound mode yields the weakest(linear)H and T dependence of alpha, while the
longitudinal L100 mode yields a stronger (quadratic) H and T dependence. This
is in strong contrast to the case of horizontal line nodes where alpha is the
same for the T100 and L100 modes (apart from a shift of pi/4 in field
direction) and is roughly a quadratic function of H and T. Thus we conclude
that measurements of alpha in in-plane magnetic fields for different in-plane
sound modes may be an important tool for probing the nodal structure of the gap
in Sr_2RuO_4.Comment: 5 pages, 6 figures, replaced in non-preprint form, to appear in Phys.
Rev.
Mechanism of spin-triplet superconductivity in Sr2RuO4
The unique Fermi surfaces and their nesting properties of Sr2RuO4 are
considered. The existence of unconventional superconductivity is shown
microscopically, for the first time, from the magnetic interactions (due to
nesting) and the phonon-mediated interactions. The odd-parity superconductivity
is favored in the and sheets of the Fermi surface, and the
various superconductivities are possible in the sheet. There are a
number of possible odd-parity gaps, which include the gaps with nodes, the
breaking of time-reversal symmetry and .Comment: 4 pages, 3 figure
Possible unconventional superconductivity in iron-based layered compound LaFePO: Study of heat capacity
Heat capacity measurements were performed on recently discovered iron based
layered superconductors, non doped LaFePO and fluorine doped LaFePO. A
relatively large electronic heat capacity coefficient and a small normalized
heat capacity jump at Tc = 3.3 K were observed in LaFePO. LaFePO0.94F0.06 had a
smaller electronic heat capacity coefficient and a larger normalized heat
capacity jump at Tc = 5.8 K. These values indicate that these compounds have
strong electron electron correlation and magnetic spin fluctuation, which are
the signatures of unconventional superconductivity mediated by spin
fluctuation.Comment: 15 Pages, 3 Figure
Gap Structure of the Spin-Triplet Superconductor Sr2RuO4 Determined from the Field-Orientation Dependence of Specific Heat
We report the field-orientation dependent specific heat of the spin-triplet
superconductor Sr2RuO4 under the magnetic field aligned parallel to the RuO2
planes with high accuracy. Below about 0.3 K, striking 4-fold oscillations of
the density of states reflecting the superconducting gap structure have been
resolved for the first time. We also obtained strong evidence of multi-band
superconductivity and concluded that the superconducting gap in the active
band, responsible for the superconducting instability, is modulated with a
minimum along the [100] direction.Comment: 4 pages, 4 figure
Interlayer Coupling and p-wave Pairing in Strontium Ruthenate
On the basis of a three orbital model and an effective attractive interaction
between electrons we investigate the possible superconducting states, with
and -wave internal symmetry, of SrRuO. For an orbital dependent
interaction which acts between in plane and out of plane nearest neighbour
Ruthenium atoms we find a state for which the gap in the quasi-particle spectra
has a line node on the and sheets of the Fermi Surface, but
it is complex with no nodes on the -sheet. We show that this state is
consistent with all the available experimental data. In particular, we present
the results of our calculations of the specific heat and penetration depth as
functions of the temperature.Comment: 4 pages, 5 figure
Evidence for incommensurate spin fluctuations in Sr_2RuO_4
We report first inelastic neutron scattering measurements in the normal state
of Sr_2RuO_4 that reveal the existence of incommensurate magnetic spin
fluctuations located at . This
finding confirms recent band structure calculations that have predicted
incommensurate magnetic responses related to dynamical nesting properties of
its Fermi surface
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