4,888 research outputs found
Q-based design equations for resonant metamaterials and experimental validation
Practical design parameters of resonant metamaterials, such as loss tangent,
are derived in terms of the quality factor of the resonant effective medium
permeability or permittivity. Through electromagnetic simulations of loop-based
resonant particles, it is also shown that the of the effective medium
response is essentially equal to the of an individual resonant particle.
Thus, by measuring the of a single fabricated metamaterial particle, the
effective permeability or permittivity of a metamaterial can be calculated
simply and accurately without requiring complex simulations, fabrication, or
measurements. Experimental validation shows that the complex permeability
analytically estimated from the measured of a single fabricated
self-resonant loop agrees with the complex permeability extracted from
parameter measurements of a metamaterial slab to better than 20%. This
equivalence reduces the design of a metamaterial to meet a given loss
constraint to the simpler problem of the design of a resonant particle to meet
a specific constraint. This analysis also yields simple analytical
expressions for estimating the loss tangent of a planar loop magnetic
metamaterial due to ohmic losses. It is shown that
is a strong lower bound for magnetic loss tangents for frequencies not too far
from 1 GHz. The ohmic loss of the metamaterial varies inversely with the
electrical size of the metamaterial particle, indicating that there is a loss
penalty for reducing the particle size at a fixed frequency
High temperature ferromagnetism of Li-doped vanadium oxide nanotubes
The nature of a puzzling high temperature ferromagnetism of doped
mixed-valent vanadium oxide nanotubes reported earlier by Krusin-Elbaum et al.,
Nature 431 (2004) 672, has been addressed by static magnetization, muon spin
relaxation, nuclear magnetic and electron spin resonance spectroscopy
techniques. A precise control of the charge doping was achieved by
electrochemical Li intercalation. We find that it provides excess electrons,
thereby increasing the number of interacting magnetic vanadium sites, and, at a
certain doping level, yields a ferromagnetic-like response persisting up to
room temperature. Thus we confirm the surprising previous results on the
samples prepared by a completely different intercalation method. Moreover our
spectroscopic data provide first ample evidence for the bulk nature of the
effect. In particular, they enable a conclusion that the Li nucleates
superparamagnetic nanosize spin clusters around the intercalation site which
are responsible for the unusual high temperature ferromagnetism of vanadium
oxide nanotubes.Comment: with some amendments published in Europhysics Letters (EPL) 88 (2009)
57002; http://epljournal.edpsciences.or
THE VALUATION OF THE ENTERPRISES AND PRODUCTS COMPETITIVENESS
The increase of the enterprise competitiveness in the enlarged European Union imposes, firstly, a good knowledge of the competitiveness factors and a pragmatic rigorous valuation of the competitiveness at the micro level (cluster, firm, business, and product), in correlation with the competitiveness at the macro level (continent, country, and region) and the mezzo level (county, zone, and locality). New concepts, models and methods have been analysed and developed in this field: the competitiveness typology; the competitiveness metaperformances (flexibility, value, liquidity, efficiency) and factors at the micro level; the competitive capacity of enterprises; integrated valuations of the competitiveness (value in
the market/segment/niche, competitiveness profile, score)
Do Search for Dibaryonic De - Excitations in Relativistic Nuclear Reactions
Some odd characteristics are observed in the single particle distributions
obtained from interactions at momenta which are
explained as the manifestation of a new mechanism of strangeness production via
dibaryonic de-excitations. A signature of the formation of hadronic and
baryonic clusters is also reported. The di-pionic signals of the dibaryonic
orbital de-excitations are analyzed in the frame of the MIT - bag Model and a
Monte Carlo simulation.The role played by the dibaryonic resonances in
relativistic nuclear collisions could be a significant one.
Key words: Relativistic nuclear interactions negative pions, negative kaons,
di-pions , streamer chamber, dibaryons, MIT - bag model
PACS codes: 25.75.+r,14.40.Aq,14.20.Pt,12.40.AsComment: 17 pages,LATEX, preprint ICTP -243 1993,figures available by reques
The magnetoelectrochemical switch
In the field of spintronics, the archetype solid-state two-terminal device is the spin valve, where the resistance is controlled by the magnetization configuration. We show here how this concept of spin-dependent switch can be extended to magnetic electrodes in solution, by magnetic control of their chemical environment. Appropriate nanoscale design allows a huge enhancement of the magnetic force field experienced by paramagnetic molecular species in solutions, which changes between repulsive and attractive on changing the electrodes' magnetic orientations. Specifically, the field gradient force created within a sub-100-nm-sized nanogap separating two magnetic electrodes can be reversed by changing the orientation of the electrodes' magnetization relative to the current flowing between the electrodes. This can result in a breaking or making of an electric nanocontact, with a change of resistance by a factor of up to 103. The results reveal how an external field can impact chemical equilibrium in the vicinity of nanoscale magnetic circuits
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