96 research outputs found
Multi-Centered First Order Formalism
We propose a first order formalism for multi-centered black holes with flat
tree-dimensional base-space, within the stu model of N=2, D=4 ungauged
Maxwell-Einstein supergravity. This provides a unified description of first
order flows of this universal sector of all models with a symmetric scalar
manifold which can be obtained by dimensional reduction from five dimensions.
We develop a D=3 Cartesian formalism which suitably extends the definition of
central and matter charges, as well as of black hole effective potential and
first order "fake" superpotential, in order to deal with not necessarily
axisimmetric solutions, and thus with multi-centered and/or (under-)rotating
extremal black holes. We derive general first order flow equations for
composite non-BPS and almost BPS classes, and we analyze some of their
solutions, retrieving various single-centered (static or under-rotating) and
multi-centered known systems. As in the t^3 model, the almost BPS class turns
out to split into two general branches, and the well known almost BPS system is
shown to be a particular solution of the second branch.Comment: 1+22 pages; v2 : some typos fixes and Refs. adde
Fixed-time consensus algorithm for multi-agent systems with integrator dynamics
International audienceThe paper addresses the problem of exact average-consensus reaching in a prescribed time. The communication topology is assumed to be defined by a weighted undirected graph and the agents are represented by integrators. A nonlinear control protocol, which ensures a finite-time convergence, is proposed. With the designed protocol, any prescribed convergence time can be guaranteed regardless of the initial conditions
Superfield formulation of nonlinear N=4 supermultiplets
We propose a unified superfield formulation of N=4 off-shell supermultiplets in one spacetime dimension using the standard N=4 superspace. The main idea of our approach is a gluing together of two linear supermultiplets along their fermions. The functions defining such a gluing obey a system of equations. Each solution of this system provides a new supermultiplet, linear or nonlinear, modulo equivalence transformations. In such a way we reproduce all known linear and nonlinear N=4, d=1 supermultiplets and propose some new ones. Particularly interesting is an explicit construction of nonlinear N=4 hypermultiplets
Effect of electric field on the photoluminescence of polymer-inorganic nanoparticles composites
We report on the effect of electric field on the photoluminescence, PL, from
a composite consisting of a conjugated polymer mixed with zinc oxide
nanoparticles. We have found that in the absence of electric field PL emission
from the composite film has two maxima in the blue and green-yellow regions.
Application of a voltage bias to planar gold electrodes suppresses the
green-yellow emission and shifts the only PL emission maximum towards the blue
region. Current-voltage characteristics of the polymer-nanoparticles composite
exhibit the non-linear behavior typical of non-homogeneous polymer-inorganic
structures. Generation of excited states in the composite structure implies the
presence of several radiative recombination mechanisms including formation of
polymer-nanoparticle complexes including exciplex states and charge transfer
between the polymer and nanoparticle that can be controlled by an electric
field.Comment: 5 pages, 5 figures. accepted for publication in Solid State
Communication
Synthesis, Structural Characterization and Magnetic Properties of Iron Boride Nanoparticles with or without Silicon Dioxide Coating
Nanoparticles of iron boride (Fe2B, Fe2B coated in SiO2, FexCo2āxB coated in SiO2) were synthesized
using the reduction of metal ions by sodium borohydride. X-ray diffraction confirms the amorphicity
of the coated compounds and scanning electron microscope imaging revealed the nanoparticulated structure
of all compounds. The splitting between zero-field-cooled and field-cooled temperature dependent
magnetization curves point to the blocking of superparamagnetic particles magnetization. Magnetic hysteresis
loops are however consistent with the combined effects of blocked superparamagnetic and ferromagnetic
(multidomain) particles. The observed quite complex magnetic behaviour is in accordance with
structural studies, where additional phases and broad distribution of particle sizes were identified
Synthesis, Structural Characterization and Magnetic Properties of Iron Boride Nanoparticles with or without Silicon Dioxide Coating
Nanoparticles of iron boride (Fe2B, Fe2B coated in SiO2, FexCo2āxB coated in SiO2) were synthesized
using the reduction of metal ions by sodium borohydride. X-ray diffraction confirms the amorphicity
of the coated compounds and scanning electron microscope imaging revealed the nanoparticulated structure
of all compounds. The splitting between zero-field-cooled and field-cooled temperature dependent
magnetization curves point to the blocking of superparamagnetic particles magnetization. Magnetic hysteresis
loops are however consistent with the combined effects of blocked superparamagnetic and ferromagnetic
(multidomain) particles. The observed quite complex magnetic behaviour is in accordance with
structural studies, where additional phases and broad distribution of particle sizes were identified
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