3,833 research outputs found
Servicing the federation : the case for metadata harvesting
The paper presents a comparative analysis of data harvesting and distributed computing as complementary models of service delivery within large-scale federated digital libraries. Informed by requirements of flexibility and scalability of federated services, the analysis focuses on the identification and assessment of model invariants. In particular, it abstracts over application domains, services, and protocol implementations. The analytical evidence produced shows that the harvesting model offers stronger guarantees of satisfying the identified requirements. In addition, it suggests a first characterisation of services based on their suitability to either model and thus indicates how they could be integrated in the context of a single federated digital library
Heralded Entanglement of Arbitrary Degree in Remote Qubits
Incoherent scattering of photons off two remote atoms with a Lambda-level
structure is used as a basic Young-type interferometer to herald long-lived
entanglement of an arbitrary degree. The degree of entanglement, as measured by
the concurrence, is found to be tunable by two easily accessible experimental
parameters. Fixing one of them to certain values unveils an analog to the
Malus' law. An estimate of the variation in the degree of entanglement due to
uncertainties in an experimental realization is given.Comment: published version, 4 pages and 2 figure
Reactivity and structure of CF3I on Ru(001)
A variety of surface-sensitive techniques are used to elucidate the reaction pathways, as well as adsorbate structures, associated with thermal activation of CF3J following adsorption on Ru(001) at 100 K. XPS shows that the C-I bond of CF3I dissociates below 200 K to form CF3(ad) and I(ad); the subsequent reactions of CF2 are best viewed as being regulated by the availability of surface sites. CF3(ad) dissociates to CF2(ad) below 200 K. Further CF3 dissociation, some of which is activated by H(ad), occurs between 200 and 400 K until all available sites are filled. Desorption of the remaining CF3, peaking at 705 K, once again opens surface sites for decomposition. This is followed by recombination of the products to form CF3(g). No evidence for CF(ad) is ever observed. Hydrogen coadsorption studies explain interesting features associated with fluorine evolution. HREELS and ESDIAD results indicate that CF3 adopts a tilted configuration on Ru(001)
Phosphate concentration in artificial tears
Background: Irrigating solutions and eye drops may contain phosphates as part of their buffer system. In the presence of epithelial keratopathy, a high concentration of phosphate favours corneal calcification. Knowledge of the phosphate concentration in artificial tear products helps to prevent this sight-threatening complication. This study gives an overview on the amount of phosphate contained in artificial tears. Methods: Fifty-nine samples of commercially available artificial tear preparations were tested. The quantification of phosphate was performed using the molybdate method on a Modular P autoanalyzer. Results: Twenty-six of 59 (44%) artificial tear products had a phosphate concentration above physiological levels (>1.45mmol/l). A phosphate concentration above 25mmol/l was found in nine products (15%), a concentration higher than 50mmol/l in three (5%). Conclusions: Many artificial tear formulations contain unphysiological levels of phosphate, but very high concentrations are found only in a few products. These preparations have the potential to favour the formation of insoluble crystalline calcium phosphate deposits when used on a damaged corneal surface, and should therefore be used cautiousl
Generation of Total Angular Momentum Eigenstates in Remote Qubits
We propose a scheme enabling the universal coupling of angular momentum of
remote noninteracting qubits using linear optical tools only. Our system
consists of single-photon emitters in a -configuration that are
entangled among their long-lived ground-state qubits through suitably designed
measurements of the emitted photons. In this manner, we present an
experimentally feasible algorithm that is able to generate any of the
symmetric and nonsymmetric total angular momentum eigenstates spanning the
Hilbert space of the -qubit compound.Comment: 5 pages, 4 figures, improved presentation. Accepted in Physical
Review
A versatile source of polarization-entangled photons
We propose a method for the generation of a large variety of entangled
states, encoded in the polarization degrees of freedom of N photons, within the
same experimental setup. Starting with uncorrelated photons, emitted from N
arbitrary single photon sources, and using linear optical tools only, we
demonstrate the creation of all symmetric states, e.g., GHZ- and W-states, as
well as all symmetric and non-symmetric total angular momentum eigenstates of
the N qubit compound.Comment: 4 pages, 3 figure
Interferon-alpha 2b early phase chronic Lymphocytic Leukemia with high risk for progression-first results of a randomized multicenter AIO-Study
On the feasibility of pentamode mechanical metamaterials
Conceptually, all conceivable three-dimensional mechanical materials can be
built from pentamode materials. Pentamodes also enable to implement
three-dimensional transformation acoustics - the analogue of transformation
optics. However, pentamodes have not been realized experimentally to the best
of our knowledge. Here, we investigate inasmuch the pentamode theoretical ideal
suggested by Milton and Cherkaev in 1995 can be approximated by a metamaterial
with current state-of-the-art lithography. Using numerical calculations
calibrated by our fabricated three-dimensional microstructures, we find that
the figure of merit, i.e., the ratio of bulk modulus to shear modulus, can
realistically be made as large as about 1,000.Comment: 4 pages and 5 figure
Polar catastrophe and electronic reconstructions at the LaAlO3/SrTiO3 interface: evidence from optical second harmonic generation
The so-called "polar catastrophe", a sudden electronic reconstruction taking
place to compensate for the interfacial ionic polar discontinuity, is currently
considered as a likely factor to explain the surprising conductivity of the
interface between the insulators LaAlO3 and SrTiO3. We applied optical second
harmonic generation, a technique that a priori can detect both mobile and
localized interfacial electrons, to investigating the electronic polar
reconstructions taking place at the interface. As the LaAlO3 film thickness is
increased, we identify two abrupt electronic rearrangements: the first takes
place at a thickness of 3 unit cells, in the insulating state; the second
occurs at a thickness of 4-6 unit cells, i.e., just above the threshold for
which the samples become conducting. Two possible physical scenarios behind
these observations are proposed. The first is based on an electronic transfer
into localized electronic states at the interface that acts as a precursor of
the conductivity onset. In the second scenario, the signal variations are
attributed to the strong ionic relaxations taking place in the LaAlO3 layer
Coherent photon bremsstrahlung and dynamics of heavy-ion collisions: comparison of different models
Differential spectra of coherent photon bremsstrahlung in relativistic heavy
ion collisions are calculated within various schematic models of the
projectile-target stopping. Two versions of the degradation length model, based
on a phenomenological deceleration law, are considered. The simple shock wave
model is studied analytically. The predictions of these models agree in the
soft photon limit, where the spectrum is determined only by the final velocity
distribution of charged particles. The results of these models in the case of
central Au+Au collisions at various bombarding energies are compared with the
predictions of the microscopic transport model UrQMD. It is shown that at the
AGS energy the coherent photon bremsstrahlung exceeds the photon yield from
-decays at photon energies \omega\loo 50 MeV.Comment: 23 pages RevTeX, 9 eps Figure
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