21,581 research outputs found
Analysis of the Kondo effect in ferromagnetic atomic-sized contacts
Atomic contacts made of ferromagnetic metals present zero-bias anomalies in
the differential conductance due to the Kondo effect. These systems provide a
unique opportunity to perform a statistical analysis of the Kondo parameters in
nanostructures since a large number of contacts can be easily fabricated using
break-junction techniques. The details of the atomic structure differ from one
contact to another so a large number of different configurations can be
statistically analyzed. Here we present such a statistical analysis of the
Kondo effect in atomic contacts made from the ferromagnetic transition metals
Ni, Co and Fe. Our analysis shows clear differences between materials that can
be understood by fundamental theoretical considerations. This combination of
experiments and theory allow us to extract information about the origin and
nature of the Kondo effect in these systems and to explore the influence of
geometry and valence in the Kondo screening of atomic-sized nanostructures.Comment: 17 pages, 11 figure
Scaling properties in the production range of shear dominated flows
Recent developments in turbulence are focused on the effect of large scale
anisotropy on the small scale statistics of velocity increments. According to
Kolmogorov, isotropy is recovered in the large Reynolds number limit as the
scale is reduced and, in the so-called inertial range, universal features
-namely the scaling exponents of structure functions - emerge clearly. However
this picture is violated in a number of cases, typically in the high shear
region of wall bounded flows. The common opinion ascribes this effect to the
contamination of the inertial range by the larger anisotropic scales, i.e. the
residual anisotropy is assumed as a weak perturbation of an otherwise isotropic
dynamics. In this case, given the rotational invariance of the Navier-Stokes
equations, the isotropic component of the structure functions keeps the same
exponents of isotropic turbulence. This kind of reasoning fails when the
anisotropic effects are strong as in the production range of shear dominated
flows. This regime is analyzed here by means of both numerical and experimental
data for a homogeneous shear flow. A well defined scaling behavior is found to
exist, with exponents which differ substantially from those of classical
isotropic turbulence. Contrary to what predicted by the perturbation approach,
such a deep alteration concerns the isotropic sector itself. The general
validity of these results is discussed in the context of turbulence near solid
walls, where more appropriate closure models for the coarse grained
Navier-Stokes equations would be advisable.Comment: 4 pages, 4 figure
Orbital Kondo effect in Cobalt-Benzene sandwich molecules
We study a Co-benzene sandwich molecule bridging the tips of a Cu nanocontact
as a realistic model of correlated molecular transport. To this end we employ a
recently developed method for calculating the correlated electronic structure
and transport properties of nanoscopic conductors. When the molecule is
slightly compressed by the tips of the nanocontact the dynamic correlations
originating from the strongly interacting Co 3d shell give rise to an orbital
Kondo effect while the usual spin Kondo effect is suppressed due to Hund's rule
coupling. This non-trivial Kondo effect produces a sharp and
temperature-dependent Abrikosov-Suhl resonance in the spectral function at the
Fermi level and a corresponding Fano line shape in the low bias conductance
Copulatory behavior and web of Indicoblemma lannaianum from Thailand (Arachnida, Araneae, Tetrablemmidae)
The Computational Power of Minkowski Spacetime
The Lorentzian length of a timelike curve connecting both endpoints of a
classical computation is a function of the path taken through Minkowski
spacetime. The associated runtime difference is due to time-dilation: the
phenomenon whereby an observer finds that another's physically identical ideal
clock has ticked at a different rate than their own clock. Using ideas
appearing in the framework of computational complexity theory, time-dilation is
quantified as an algorithmic resource by relating relativistic energy to an
th order polynomial time reduction at the completion of an observer's
journey. These results enable a comparison between the optimal quadratic
\emph{Grover speedup} from quantum computing and an speedup using
classical computers and relativistic effects. The goal is not to propose a
practical model of computation, but to probe the ultimate limits physics places
on computation.Comment: 6 pages, LaTeX, feedback welcom
Near infrared spectroscopy of the type IIn SN 2010jl: evidence for high velocity ejecta
The Type IIn supernova SN 2010jl was relatively nearby and luminous, allowing
detailed studies of the near-infrared (NIR) emission. We present 1 - 2.4 micron
spectroscopy over the age range of 36 - 565 days from the earliest detection of
the supernova. On day 36, the H lines show an unresolved narrow emission
component along with a symmetric broad component that can be modeled as the
result of electron scattering by a thermal distribution of electrons. Over the
next hundreds of days, the broad components of the H lines shift to the blue by
700 km/s, as is also observed in optical lines. The narrow lines do not show a
shift, indicating they originate in a different region. He I 1.0830 and 2.0587
micron lines both show an asymmetric broad emission component, with a shoulder
on the blue side that varies in prominence and velocity from -5500 km/s on day
108 to -4000 km/s on day 219. This component may be associated with the higher
velocity flow indicated by X-ray observations of the supernova. The absence of
the feature in the H lines suggests that this is from a He rich ejecta flow.
The He I 1.0830 micron feature has a narrow P Cygni line, with absorption
extending to ~100 km/s and strengthening over the first 200 days, and an
emission component which weakens with time. At day 403, the continuum emission
becomes dominated by a blackbody spectrum with a temperature of ~1900 K,
suggestive of dust emission.Comment: 17 pages, 18 figure
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