38,118 research outputs found
Exchange coupling between magnetic layers across non-magnetic superlattices
The oscillation periods of the interlayer exchange coupling are investigated
when two magnetic layers are separated by a metallic superlattice of two
distinct non-magnetic materials. In spite of the conventional behaviour of the
coupling as a function of the spacer thickness, new periods arise when the
coupling is looked upon as a function of the number of cells of the
superlattice. The new periodicity results from the deformation of the
corresponding Fermi surface, which is explicitly related to a few controllable
parameters, allowing the oscillation periods to be tuned.Comment: 13 pages; 5 figures; To appear in J. Phys.: Cond. Matte
Transition on the entropic elasticity of DNA induced by intercalating molecules
We use optical tweezers to perform stretching experiments on DNA molecules
when interacting with the drugs daunomycin and ethidium bromide, which
intercalate the DNA molecule. These experiments are performed in the low-force
regime from zero up to 2 pN. Our results show that the persistence length of
the DNA-drug complexes increases strongly as the drug concentration increases
up to some critical value. Above this critical value, the persistence length
decreases abruptly and remains practically constant for larger drug
concentrations. The contour length of the molecules increases monotonically and
saturates as drugs concentration increases. Measured in- tercalants critical
concentrations for the persistence length transition coincide with reported
values for the helix-coil transition of DNA-drug complexes, obtained from
sedimentation experiments.Comment: This experimental article shows and discuss a transition observed in
the persistence length of DNA molecules when studied as a function of some
intercalating drug concentrations, like daunomycin and ethidium bromide. It
has 15 pages and 4 figures. The article presented here is in preprint forma
Faceted anomalous scaling in the epitaxial growth of semiconductor films
We apply the generic dynamical scaling theory (GDST) to the surfaces of CdTe
polycrystalline films grown in glass substrates. The analysed data were
obtained with a stylus profiler with an estimated resolution lateral resolution
of m. Both real two-point correlation function and power spectrum
analyses were done. We found that the GDST applied to the surface power spectra
foresees faceted morphology in contrast with the self-affine surface indicated
by the local roughness exponent found via the height-height correlation
function. This inconsistency is explained in terms of convolution effects
resulting from the finite size of the probe tip used to scan the surfaces. High
resolution AFM images corroborates the predictions of GDST.Comment: to appear in Europhysics Letter
Strategies for Optimize Off-Lattice Aggregate Simulations
We review some computer algorithms for the simulation of off-lattice clusters
grown from a seed, with emphasis on the diffusion-limited aggregation,
ballistic aggregation and Eden models. Only those methods which can be
immediately extended to distinct off-lattice aggregation processes are
discussed. The computer efficiencies of the distinct algorithms are compared.Comment: 6 pages, 7 figures and 3 tables; published at Brazilian Journal of
Physics 38, march, 2008 (http://www.sbfisica.org.br/bjp/files/v38_81.pdf
Exponential behavior of the interlayer exchange coupling across non-magnetic metallic superlattices
It is shown that the coupling between magnetic layers separated by
non-magnetic metallic superlattices can decay exponentially as a function of
the spacer thickness , as opposed to the usual decay. This effect
is due to the lack of constructive contributions to the coupling from extended
states across the spacer. The exponential behavior is obtained by properly
choosing the distinct metals and the superlattice unit cell composition.Comment: To appear in Phys. Rev.
Contact process on a Voronoi triangulation
We study the continuous absorbing-state phase transition in the contact
process on the Voronoi-Delaunay lattice. The Voronoi construction is a natural
way to introduce quenched coordination disorder in lattice models. We simulate
the disordered system using the quasistationary simulation method and determine
its critical exponents and moment ratios. Our results suggest that the critical
behavior of the disordered system is unchanged with respect to that on a
regular lattice, i.e., that of directed percolation
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