7,578 research outputs found
Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface
We propose a new mechanism for surface-induced magnetic anisotropy to explain
the thickness-dependence of the Kondo resistivity of thin films of dilute
magnetic alloys. The surface anisotropy energy, generated by spin-orbit
coupling on the magnetic impurity itself, is an oscillating function of the
distance d from the surface and decays as 1/d^2. Numerical estimates based on
simple models suggest that this mechanism, unlike its alternatives, gives rise
to an effect of the desired order of magnitude.Comment: 4 pages, 4 figure
Restricted dog leucocyte antigen (DLA) class II haplotypes and genotypes in Beagles
AbstractBeagles are commonly used in vaccine trials as part of the regulatory approval process. Genetic restriction within this breed and the impact this might have on vaccine responses are rarely considered. This study was designed to characterise diversity of dog leucocyte antigen (DLA) class II genes in a breeding colony of laboratory Beagles, whose offspring are used in vaccine studies. DLA haplotypes were determined by PCR and sequence-based typing from genomic DNA extracted from blood. Breeding colony Beagles had significantly different DLA haplotype frequencies in comparison with pet Beagles and both groups showed limited DLA diversity. Restricted DLA class II genetic variability within Beagles might result in selective antigen presentation and vaccine responses that are not necessarily representative of those seen in other dog breeds
Reversible enhancement of the magnetism of ultrathin Co films by H adsorption
By means of ab initio calculations, we have investigated the effect of H
adsorption in the structural, electronic and magnetic properties of ultrathin
Co films on Ru(0001). Our calculations predict that H occupies hollow sites
preserving the two-dimensional 3-fold symmetry. The formation of a complete H
overlayer leads to a very stable surface with strong H-Co bonds. H tends to
suppress surface features, in particular, the enhancement of the magnetic
moments of the bare film. The H-induced effects are mostly confined to the Co
atoms bonded to H, independent of the H coverage or of the thickness and the
structure of the Co film. However, for partial H coverages a significant
increase occurs in the magnetic moment for the surface Co atoms not bonded to
H, leading to a net enhancement of surface magnetism.Comment: 6 pages, 4 figures, 3 table
Robustness of Device Independent Dimension Witnesses
Device independent dimension witnesses provide a lower bound on the
dimensionality of classical and quantum systems in a "black box" scenario where
only correlations between preparations, measurements and outcomes are
considered. We address the problem of the robustness of dimension witnesses,
namely that to witness the dimension of a system or to discriminate between its
quantum or classical nature, even in the presence of loss. We consider the case
when shared randomness is allowed between preparations and measurements and we
provide a threshold in the detection efficiency such that dimension witnessing
can still be performed.Comment: 8 pages, 5 figures, published versio
Pseudospectral versus finite-differences schemes in the numerical integration of stochastic models of surface growth
We present a comparison between finite differences schemes and a
pseudospectral method applied to the numerical integration of stochastic
partial differential equations that model surface growth. We have studied, in
1+1 dimensions, the Kardar, Parisi and Zhang model (KPZ) and the Lai, Das Sarma
and Villain model (LDV). The pseudospectral method appears to be the most
stable for a given time step for both models. This means that the time up to
which we can follow the temporal evolution of a given system is larger for the
pseudospectral method. Moreover, for the KPZ model, a pseudospectral scheme
gives results closer to the predictions of the continuum model than those
obtained through finite difference methods. On the other hand, some numerical
instabilities appearing with finite difference methods for the LDV model are
absent when a pseudospectral integration is performed. These numerical
instabilities give rise to an approximate multiscaling observed in the
numerical simulations. With the pseudospectral approach no multiscaling is seen
in agreement with the continuum model.Comment: 13 single column pages, RevTeX, 6 eps fig
Renormalization Group and Grand Unification with 331 Models
By making a renormalization group analysis we explore the possibility of
having a 331 model as the only intermediate gauge group between the standard
model and the scale of unification of the three coupling constants. We shall
assume that there is no necessarily a group of grand unification at the scale
of convergence of the couplings. With this scenario, different 331 models and
their corresponding supersymmetric versions are considered, and we find the
versions that allow the symmetry breaking described above. Besides, the allowed
interval for the 331 symmetry breaking scale, and the behavior of the running
coupling constants are obtained. It worths saying that some of the
supersymmetric scenarios could be natural frameworks for split supersymmetry.
Finally, we look for possible 331 models with a simple group at the grand
unification scale, that could fit the symmetry breaking scheme described above.Comment: 18 pages. 3 figures. Some results reinterpreted, a new section and
references added. Version to appear in International Journal of Modern
Physics
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