6,142 research outputs found
Van der Waals contribution to the inelastic atom-surface scattering
A calculation of the inelastic scattering rate of Xe atoms on Cu(111) is
presented. We focus in the regimes of low and intermediate velocities, where
the energy loss is mainly associated to the excitation electron-hole pairs in
the substrate. We consider trajectories parallel to the surface and restrict
ourselves to the Van der Waals contribution. The decay rate is calculated
within a self-energy formulation. The effect of the response function of the
substrate is studied by comparing the results obtained with two different
approaches: the Specular Reflection Model and the Random Phase Approximation.
In the latter, the surface is described by a finite slab and the wave functions
are obtained from a one-dimensional model potential that describes the main
features of the surface electronic structure while correctly retains the
image-like asymptotic behaviour. We have also studied the influence of the
surface state on the calculation, finding that it represents around 50% of the
total probability of electron-hole pairs excitation.Comment: 7 pages, 4 figure
Ab initio study of the double row model of the Si(553)-Au reconstruction
Using x-ray diffraction Ghose et al. [Surf. Sci. {\bf 581} (2005) 199] have
recently produced a structural model for the quantum-wire surface Si(553)-Au.
This model presents two parallel gold wires located at the step edge. Thus, the
structure and the gold coverage are quite different from previous proposals. We
present here an ab initio study using density functional theory of the
stability, electronic band structure and scanning tunneling microscopy images
of this model.Comment: Submitted to Surface Science on December 200
Kato's square root problem in Banach spaces
Let be an elliptic differential operator with bounded measurable
coefficients, acting in Bochner spaces of -valued functions
on . We characterize Kato's square root estimates and the -functional calculus of in
terms of R-boundedness properties of the resolvent of , when is a Banach
function lattice with the UMD property, or a noncommutative space. To
do so, we develop various vector-valued analogues of classical objects in
Harmonic Analysis, including a maximal function for Bochner spaces. In the
special case , we get a new approach to the theory of square roots
of elliptic operators, as well as an version of Carleson's inequality.Comment: 44 page
INSA scientific activities in the space astronomy area
Support to Astronomy operations is an important and long-lived activity
within INSA. Probably the best known (and traditional) INSA activities are
those related with real-time spacecraft operations: Ground station maintenance
and operation (Ground station engineers and operators); spacecraft and payload
real-time operation (spacecraft and instruments controllers); computing
infrastructure maintenance (operators, analysts) and general site services.In
this paper, we'll show a different perspective, probably not so well-known,
presenting some INSA recent activities at the European Space Astronomy Centre
(ESAC) and NASA Madrid Deep Space Communication Complex (MDSCC) directly
related to scientific operations. Basic lines of activity involved include:
Operations support for science operations; system and software support for real
time systems; technical administration and IT support; R \& D activities,
radioastronomy (at MDSCC and ESAC) and scientific research projects. This paper
is structured as follows: first, INSA activities in two ESA cornerstone
astrophysics missions, XMM-Newton and Herschel, will be outlined. Then, our
activities related to Science infrastructure services, represented by the
Virtual Observatory (VO) framework and the Science Archives development
facilities are briefly shown. Radio Astronomy activities will be described
afterwards, and finally, a few research topics in which INSA scientists are
involved will be also described.Comment: 6 pages. Highlights of Spanish Astrophysics V Proceedings of the VIII
Scientific Meeting of the Spanish AstronomicalSociety (SEA) held in
Santander, 7-11 July, 200
Conical square function estimates and functional calculi for perturbed Hodge-Dirac operators in L^p
Perturbed Hodge-Dirac operators and their holomorphic functional calculi, as
investigated in the papers by Axelsson, Keith and the second author, provided
insight into the solution of the Kato square-root problem for elliptic
operators in spaces, and allowed for an extension of these estimates to
other systems with applications to non-smooth boundary value problems. In this
paper, we determine conditions under which such operators satisfy conical
square function estimates in a range of spaces, thus allowing us to apply
the theory of Hardy spaces associated with an operator, to prove that they have
a bounded holomorphic functional calculus in those spaces. We also obtain
functional calculi results for restrictions to certain subspaces, for a larger
range of . This provides a framework for obtaining results on
perturbed Hodge Laplacians, generalising known Riesz transform bounds for an
elliptic operator with bounded measurable coefficients, one Sobolev
exponent below the Hodge exponent, and bounds on the square-root of
by the gradient, two Sobolev exponents below the Hodge exponent. Our proof
shows that the heart of the harmonic analysis in extends to for all
, while the restrictions in come from the
operator-theoretic part of the proof. In the course of our work, we
obtain some results of independent interest about singular integral operators
on tent spaces, and about the relationship between conical and vertical square
functions.Comment: 45 pages; mistake correcte
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