94,009 research outputs found
Semantic web-based document: editing and browsing in AktiveDoc
This paper presents a tool for supporting sharing and reuse of knowledge in document creation (writing) and use (reading). Semantic Web technologies are used to support the production of ontology based annotations while the document is written. Free text annotations (comments) can be added to integrate the knowledge in the document. In addition the tool uses external services (e.g. a Semantic Web harvester) to propose relevant content to writing
user, enabling easy knowledge reuse. Similar facilities are provided for readers when their task does not coincide with the author’s one. The tool is specifically designed for Knowledge Management in organisations. In this paper we present and discuss how Semantic Web technologies are designed and integrated in the system
Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number
Supercritical fluids near the critical point are characterized by liquid-like
densities and gas-like transport properties. These features are purposely
exploited in different contexts ranging from natural products
extraction/fractionation to aerospace propulsion. Large part of studies
concerns this last context, focusing on the dynamics of supercritical fluids at
high Mach number where compressibility and thermodynamics strictly interact.
Despite the widespread use also at low Mach number, the turbulent mixing
properties of slightly supercritical fluids have still not investigated in
detail in this regime. This topic is addressed here by dealing with Direct
Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van
der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number
conditions found in many industrial applications, the numerical model is based
on a suitable low-Mach number expansion of the governing equation. According to
experimental observations, the weakly supercritical regime is characterized by
the formation of finger-like structures-- the so-called ligaments --in the
shear layers separating the two streams. The mechanism of ligament formation at
vanishing Mach number is extracted from the simulations and a detailed
statistical characterization is provided. Ligaments always form whenever a high
density contrast occurs, independently of real or perfect gas behaviors. The
difference between real and perfect gas conditions is found in the ligament
small-scale structure. More intense density gradients and thinner interfaces
characterize the near critical fluid in comparison with the smoother behavior
of the perfect gas. A phenomenological interpretation is here provided on the
basis of the real gas thermodynamics properties.Comment: Published on Physics of Fluid
Positivity and strong ellipticity
We consider second-order partial differential operators in divergence
form on \Ri^d with a positive-semidefinite, symmetric, matrix of real
-coefficients and establish that is strongly elliptic if and only
if the associated semigroup kernel satisfies local lower bounds, or, if and
only if the kernel satisfies Gaussian upper and lower bounds.Comment: 9 page
Crystals for high-energy calorimetry in extreme environments
Crystals are used as a homogeneous calorimetric medium in many high-energy
physics experiments. For some experiments, performance has to be ensured in
very difficult operating conditions, like a high radiation environment, very
large particle fluxes, high collision rates, placing constraints on response
and readout time. An overview is presented of recent achievements in the field,
with particular attention given to the performance of Lead Tungstate (PWO)
crystals exposed to high particle fluxes.Comment: To be published in Proc. of the Meeting of the Division of Particles
and Fields of the American Physical Society, DPF2004 (Riverside, USA, August
26th to 31st, 2004
Structured Prediction of Sequences and Trees using Infinite Contexts
Linguistic structures exhibit a rich array of global phenomena, however
commonly used Markov models are unable to adequately describe these phenomena
due to their strong locality assumptions. We propose a novel hierarchical model
for structured prediction over sequences and trees which exploits global
context by conditioning each generation decision on an unbounded context of
prior decisions. This builds on the success of Markov models but without
imposing a fixed bound in order to better represent global phenomena. To
facilitate learning of this large and unbounded model, we use a hierarchical
Pitman-Yor process prior which provides a recursive form of smoothing. We
propose prediction algorithms based on A* and Markov Chain Monte Carlo
sampling. Empirical results demonstrate the potential of our model compared to
baseline finite-context Markov models on part-of-speech tagging and syntactic
parsing
Technological innovations at the onset of the Mid-Pleistocene Climate Transition in high-latitude East Asia
The interplay between Pleistocene climatic variability and hominin adaptations to diverse terrestrial ecosystems is a key topic in human evolutionary studies. Early and Middle Pleistocene environmental change and its relation to hominin behavioural responses has been a subject of great interest in Africa and Europe, though little information is available for other key regions of the Old World, particularly from Eastern Asia. Here we examine key Early Pleistocene sites of the Nihewan Basin, in high-latitude northern China, dating between ∼1.4 to 1.0 million years ago (Ma). We compare stone tool assemblages from three Early Pleistocene sites in the Nihewan Basin, including detailed assessment of stone tool refitting sequences at the ∼1.1 Ma-old site of Cenjiawan. Increased toolmaking skills and technological innovations are evident in the Nihewan Basin at the onset of the Mid-Pleistocene Climate Transition (MPT). Examination of the lithic technology of the Nihewan sites, together with an assessment of other key Palaeolithic sites of China, indicates that toolkits show increasing diversity at the outset of the MPT and in its aftermath. The overall evidence indicates the adaptive flexibility of early hominins to ecosystem changes since the MPT, though regional abandonments are also apparent in high-latitudes, likely owing to cold and oscillating environmental conditions. The view presented here sharply contrasts with traditional arguments that stone tool technologies of China are homogeneous and continuous over the course of the Early Pleistocene.Introduction Results - Stone-tool-knapping skills recorded in the Cenjiawan assemblage - Technological comparisons of the Nihewan Basin assemblages Discussio
Direct observation of irradiation-induced nanocavity shrinkage in Si
Nanocavities in Si substrates, formed by conventional H implantation and thermal annealing, are shown to evolve in size during subsequent Si irradiation. Both ex situ and in situ analytical techniques were used to demonstrate that the mean nanocavity diameter decreases as a function of Si irradiation dose in both the crystalline and amorphous phases. Potential mechanisms for this irradiation-induced nanocavity evolution are discussed. In the crystalline phase, the observed decrease in diameter is attributed to the gettering of interstitials. When the matrix surrounding the cavities is amorphized, cavity shrinkage may be mediated by one of two processes: nanocavities can supply vacancies into the amorphous phase and/or the amorphous phase may flow plastically into the nanocavities. Both processes yield the necessary decrease in density of the amorphous phase relative to crystalline material
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