48,162 research outputs found
Pressure and isotope effect on the anisotropy of MgB
We analyze the data for the pressure and boron isotope effect on the
temperature dependence of the magnetization near . Invoking the
universal scaling relation for the magnetization at fixed magnetic field it is
shown that the relative shift of , induced by pressure or boron isotope
exchange, mirrors essentially that of the anisotropy. This uncovers a novel
generic property of anisotropic type II superconductors, inexistent in the
isotropic case. For MgB it implies that the renormalization of the Fermi
surface topology due to pressure or isotope exchange is dominated by a
mechanism controlling the anisotropy.Comment: 7 pages, 3 figure
Formation of nanocrystals based on decomposition in the amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy
Primary crystallization and decomposition in the bulk amorphous alloy Ar41.2Ti13.8Cu12.5Ni10Be22.5 have been studied by small angle neutron scattering (SANS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). SANS data of samples annealed isothermally at 623 K exhibit an interference peak centered at q=0.46 nm(^-1) after an incubation time of about 100 min. TEM and DSC investigations confirm that the respective periodic variation in the scattering length density is due to the formation of nanocrystals embedded in the amorphous matrix. These observations suggest that during the incubation time a chemical decomposition process occurs and the related periodic composition fluctuations give rise to the observed periodic arrangement of the nanocrystals
Generalized Robba rings
We prove that any projective coadmissible module over the locally analytic
distribution algebra of a compact -adic Lie group is finitely generated. In
particular, the category of coadmissible modules does not have enough
projectives. In the Appendix a "generalized Robba ring" for uniform pro-
groups is constructed which naturally contains the locally analytic
distribution algebra as a subring. The construction uses the theory of
generalized microlocalization of quasi-abelian normed algebras that is also
developed there. We equip this generalized Robba ring with a self-dual locally
convex topology extending the topology on the distribution algebra. This is
used to show some results on coadmissible modules.Comment: with an appendix by Peter Schneider; revised; new titl
Kondo effect of Co adatoms on Ag monolayers on noble metal surfaces
The Kondo temperature of single Co adatoms on monolayers of Ag on Cu
and Au(111) is determined using Scanning Tunneling Spectroscopy. of Co on
a single monolayer of Ag on either substrate is essentially the same as that of
Co on a homogenous Ag(111) crystal. This gives strong evidence that the
interaction of surface Kondo impurities with the substrate is very local in
nature. By comparing found for Co on Cu, Ag, and Au (111)-surfaces we
show that the energy scale of the many-electron Kondo state is insensitive to
the properties of surface states and to the energetic position of the projected
bulk band edges.Comment: 4 pages, 3 figure
Qualitative Theory for Lensed QSOs
We show that some characteristics of multiply-imaged QSO systems are very
model-independent and can be deduced accurately by simply scrutinizing the
relative positions of images and galaxy-lens center. These include the
time-ordering of the images, the orientation of the lens potential, and the
rough morphology of any ring. Other features can differ considerably between
specific models; H_0 is an example. Surprisingly, properties inherited from a
circularly symmetric lens system are model-dependent, whereas features that
arise from the breaking of circular symmetry are model-independent. We first
develop these results from some abstract geometrical ideas, then illustrate
them for some well-known systems (the quads Q2237+030, H1413+117,
HST14113+5211, PG1115+080, MG0414+0534, B1608+656, B1422+231, and RXJ0911+0551,
and the ten-image system B1933+507), and finally remark on two systems
(B1359+154 and PMN J0134-0931) where the lens properties are more complex. We
also introduce a Java applet which produces simple lens systems, and helps
further illustrate the concepts.Comment: 26 pages, incl. 15 figs; accepted to AJ; java applet available at
http://ankh-morpork.maths.qmw.ac.uk/~saha/astron/lens
Small-angle x-ray-scattering study of phase separation and crystallization in the bulk amorphous Mg62Cu25Y10Li3 alloy
We report on a small-angle x-ray-scattering (SAXS) and differential scanning calorimetry study of phase separation and crystallization in rapidly quenched amorphous Mg62Cu25Y10Li3 alloy samples. Differential scanning calorimetry demonstrates the occurrence of crystallization and grain growth upon isothermal annealing of these samples at 135 °C. The SAXS studies show the presence of large inhomogeneities even in the rapidly quenched as-prepared Mg62Cu25Y10Li3 alloy that is attributed to phase separation in the undercooled liquid during the cooling process. After isothermal annealing at 135 °C for longer than 30 min the samples exhibit a strong SAXS intensity that monotonically increases with increasing annealing time. During heat treatment, crystallization and growth of a nanocrystalline bcc-Mg7Li3 phase occurs in the Y-poor and MgLi-rich domains. The initially rough boundaries of the nanocrystals become sharper with increasing annealing time. Anomalous small-angle x-ray-scattering investigations near the Cu K edge indicate that while Cu is distributed homogeneously in the as-prepared sample, a Cu composition gradient develops between the matrix and the bcc-Mg7Li3 nanocrystals in the annealed sample
Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction
The electronic and vibrational density of states of a semiconducting carbon
nanotube in a crossed junction was investigated by elastic and inelastic
scanning tunneling spectroscopy. The strong radial compression of the nanotube
at the junction induces local metallization spatially confined to a few nm. The
local electronic modifications are correlated with the observed changes in the
radial breathing and G-band phonon modes, which react very sensitively to local
mechanical deformation. In addition, the experiments reveal the crucial
contribution of the image charges to the contact potential at nanotube-metal
interfaces
Query processing of spatial objects: Complexity versus Redundancy
The management of complex spatial objects in applications, such as geography and cartography,
imposes stringent new requirements on spatial database systems, in particular on efficient
query processing. As shown before, the performance of spatial query processing can be improved
by decomposing complex spatial objects into simple components. Up to now, only decomposition
techniques generating a linear number of very simple components, e.g. triangles or trapezoids, have
been considered. In this paper, we will investigate the natural trade-off between the complexity of
the components and the redundancy, i.e. the number of components, with respect to its effect on
efficient query processing. In particular, we present two new decomposition methods generating
a better balance between the complexity and the number of components than previously known
techniques. We compare these new decomposition methods to the traditional undecomposed representation
as well as to the well-known decomposition into convex polygons with respect to their
performance in spatial query processing. This comparison points out that for a wide range of query
selectivity the new decomposition techniques clearly outperform both the undecomposed representation
and the convex decomposition method. More important than the absolute gain in performance
by a factor of up to an order of magnitude is the robust performance of our new decomposition
techniques over the whole range of query selectivity
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