6,795 research outputs found
Vortex Viscosity in Magnetic Superconductors Due to Radiation of Spin Waves
In type-II superconductors that contain a lattice of magnetic moments,
vortices polarize the magnetic system inducing additional contributions to the
vortex mass, vortex viscosity, and vortex-vortex interaction. Extra magnetic
viscosity is caused by radiation of spin waves by a moving vortex. Like in the
case of Cherenkov radiation, this effect has a characteristic threshold
behavior and the resulting vortex viscosity may be comparable to the well-known
Bardeen-Stephen contribution. The threshold behavior leads to an anomaly in the
current-voltage characteristics, and a drop in dissipation for a current
interval that is determined by the magnetic excitation spectrum.Comment: 4 pages, 1 figur
Produção e qualidade de frutos de cultivares de melancia em ecossistema de "terra firme" do Estado do Amazonas.
Neste trabalho, avaliaram-se diferentes cultivares de melancia e dois espaçamentos, para a produção de melancia na terra firme do Amazonas. O ensaio foi conduzido na Embrapa Amazônia Ocidental, Iranduba-AM, em Argissolo Amarelo distrófico, textura média, de junho a agosto de 2010
Electron Spin Resonance of SrCu2(BO3)2 at High Magnetic Field
We calculate the electron spin resonance (ESR) spectra of the
quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of magnetic
field B. Using the standard Lanczos method, we solve a Shastry-Sutherland
Hamiltonian with additional Dzyaloshinsky-Moriya (DM) terms which are crucial
to explain different qualitative aspects of the ESR spectra. In particular, a
nearest-neighbor DM interaction with a non-zero D_z component is required to
explain the low frequency ESR lines for B || c. This suggests that crystal
symmetry is lowered at low temperatures due to a structural phase transition.Comment: 4 pages, 4 b&w figure
Crescimento e nutrição na abobrinha-de-moita em plantio direto utilizando cobertura do solo com fitomassa de leguminosa arbustiva com e sem uréia.
Objetivou-se estudar aspectos do crescimento inicial e nutricional da abobrinha com uso de fitomassa da leguminosa arbustiva flemíngia cobrindo o solo (CF), com e sem uréia, em plantio direto sobre um Latossolo Amarelo muito argiloso, em Manaus-AM (julho de 2011), utilizando delineamento experimental em blocos casualizados com quatro repetições.Edição dos Resumos do 52º Congresso Brasileiro de Olericultura, Salvador, jul. 2012
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
Quantum Cosmology of Fab Four John Theory with Conformable Fractional Derivative
We study a quantization via fractional derivative of a nonminimal derivative coupling cosmological theory, namely, the Fab Four John theory. Its Hamiltonian version presents the issue of fractional powers in the momenta. That problem is solved here by the application of the so-called conformable fractional derivative. This leads to a Wheeler\u2013DeWitt equation of second order, showing that a Bohm\u2013de Broglie interpretation can be constructed. That combination of fractional quantization and Bohmian interpretation provides us a new quantization method, in which the quantum potential is the criterion to say if a quantum solution is acceptable or not to be further studied. We show that a wide range of solutions for the scale factor is possible. Among all of those, a bouncing solution analogous to the perfect fluid cosmology seems to deserve special attention
Vortex-induced dissipation in narrow current-biased thin-film superconducting strips
A vortex crossing a thin-film superconducting strip from one edge to the
other, perpendicular to the bias current, is the dominant mechanism of
dissipation for films of thickness d on the order of the coherence length XI;
and of width w much narrower than the Pearl length LAMBDA >> w >> XI. At high
bias currents, I* < I < Ic, the heat released by the crossing of a single
vortex suffices to create a belt-like normal-state region across the strip,
resulting in a detectable voltage pulse. Here Ic is the critical current at
which the energy barrier vanishes for a single vortex crossing. The belt forms
along the vortex path and causes a transition of the entire strip into the
normal state. We estimate I* to be roughly Ic/3. Further, we argue that such
"hot" vortex crossings are the origin of dark counts in photon detectors, which
operate in the regime of metastable superconductivity at currents between I*
and Ic. We estimate the rate of vortex crossings and compare it with recent
experimental data for dark counts. For currents below I*, i.e., in the stable
superconducting but resistive regime, we estimate the amplitude and duration of
voltage pulses induced by a single vortex crossing.Comment: 9 pages, 3 figure
Non Abelian Sugawara Construction and the q-deformed N=2 Superconformal Algebra
The construction of a q-deformed N=2 superconformal algebra is proposed in
terms of level 1 currents of quantum affine
Lie algebra and a single real Fermi field. In particular, it suggests the
expression for the q-deformed Energy-Momentum tensor in the Sugawara form. Its
constituents generate two isomorphic quadratic algebraic structures. The
generalization to is also proposed.Comment: AMSLATEX, 21page
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