718 research outputs found
Foundation Rehabilitation of Bridge over Danube: the Role of Pile Integrity Testing
The construction of the bridge near Pöchlarn over Danube, in Austria was begun 1998 and completed in 2002. The four middle piers of the bridge consist of sink caissons made of pre-cast reinforced concrete elements. Each caisson is founded on 18 bored piles of 1.2 m diameter. In a first step, two pilot piles of about 40 m length are installed for each caisson. After the pilot piles were completed, an accident happened in April 1999. A cargo ship collided with the pier no 3 and damaged the two pilot piles. Since the piles were below water level, it was very difficult to inspect the damage. Therefore, integrity tests were carried out to know the level of damage. The possible scenarios range from local repair to installation of new pilot piles. The paper describes a case study of the repair works of the damaged piles, where under water pile integrity tests were carried out
On the Minimum Degree up to Local Complementation: Bounds and Complexity
The local minimum degree of a graph is the minimum degree reached by means of
a series of local complementations. In this paper, we investigate on this
quantity which plays an important role in quantum computation and quantum error
correcting codes. First, we show that the local minimum degree of the Paley
graph of order p is greater than sqrt{p} - 3/2, which is, up to our knowledge,
the highest known bound on an explicit family of graphs. Probabilistic methods
allows us to derive the existence of an infinite number of graphs whose local
minimum degree is linear in their order with constant 0.189 for graphs in
general and 0.110 for bipartite graphs. As regards the computational complexity
of the decision problem associated with the local minimum degree, we show that
it is NP-complete and that there exists no k-approximation algorithm for this
problem for any constant k unless P = NP.Comment: 11 page
Oxygen vacancy diffusion in alumina: New atomistic simulation methods applied to an old problem
Understanding diffusion in alumina is a long-standing challenge in ceramic science. The present article applies a novel combination of metadynamics and kinetic Monte Carlo simulation approaches to the investigation of oxygen vacancy diffusion in alumina. Three classes of diffusive jumps with different activation energies were identified, the resulting diffusion coefficient being best fitted by an Arrhenius equation having a pre-exponential factor of 7.88 x 10-2 m2 s-1 and an activation energy of 510.83 kJ mol-1. This activation energy is very close to values for the most pure aluminas studied experimentally (activation energy 531 kJ mol-1). The good agreement indicates that the dominating atomic-scale diffusion mechanism in alumina is vacancy diffusion
Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by
time resolved x-ray diffraction after photo excitation over the band gap. By
monitoring the diffraction intensity of a superlattice reflection that is
directly related to the structural order parameter of the soft-mode driven
antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a
0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be
independent of the initial temperaure despite large changes in the
corresponding soft-mode frequency. A further, much smaller reduction on a
slower picosecond timescale is attributed to thermal effects. Time-dependent
density-functional-theory calculations show that the fast response can be
ascribed to an ultrafast displacive modification of the soft-mode potential
towards the normal state, induced by holes created in the oxygen 2p states
Polygonal tessellations as predictive models of molecular monolayers
Molecular self-assembly plays a very important role in various aspects of
technology as well as in biological systems. Governed by the covalent, hydrogen
or van der Waals interactions - self-assembly of alike molecules results in a
large variety of complex patterns even in two dimensions (2D). Prediction of
pattern formation for 2D molecular networks is extremely important, though very
challenging, and so far, relied on computationally involved approaches such as
density functional theory, classical molecular dynamics, Monte Carlo, or
machine learning. Such methods, however, do not guarantee that all possible
patterns will be considered and often rely on intuition. Here we introduce a
much simpler, though rigorous, hierarchical geometric model founded on the
mean-field theory of 2D polygonal tessellations to predict extended network
patterns based on molecular-level information. Based on graph theory, this
approach yields pattern classification and pattern prediction within
well-defined ranges. When applied to existing experimental data, our model
provides an entirely new view of self-assembled molecular patterns, leading to
interesting predictions on admissible patterns and potential additional phases.
While developed for hydrogen-bonded systems, an extension to covalently bonded
graphene-derived materials or 3D structures such as fullerenes is possible,
significantly opening the range of potential future applications
Polaronic metal state at the LaAlO3/SrTiO3 interface
Interplay of spin, charge, orbital and lattice degrees of freedom in oxide
heterostructures results in a plethora of fascinating properties, which can be
exploited in new generations of electronic devices with enhanced
functionalities. The paradigm example is the interface between the two band
insulators LaAlO3 and SrTiO3 (LAO/STO) that hosts two-dimensional electron
system (2DES). Apart from the mobile charge carriers, this system exhibits a
range of intriguing properties such as field effect, superconductivity and
ferromagnetism, whose fundamental origins are still debated. Here, we use
soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the
LAO overlayer and access charge carriers at the buried interface. The
experimental spectral function directly identifies the interface charge
carriers as large polarons, emerging from coupling of charge and lattice
degrees of freedom, and involving two phonons of different energy and thermal
activity. This phenomenon fundamentally limits the carrier mobility and
explains its puzzling drop at high temperatures
The central nervous system of sea cucumbers (Echinodermata: Holothuroidea) shows positive immunostaining for a chordate glial secretion
<p>Abstract</p> <p>Background</p> <p>Echinoderms and chordates belong to the same monophyletic taxon, the Deuterostomia. In spite of significant differences in body plan organization, the two phyla may share more common traits than was thought previously. Of particular interest are the common features in the organization of the central nervous system. The present study employs two polyclonal antisera raised against bovine Reissner's substance (RS), a secretory product produced by glial cells of the subcomissural organ, to study RS-like immunoreactivity in the central nervous system of sea cucumbers.</p> <p>Results</p> <p>In the ectoneural division of the nervous system, both antisera recognize the content of secretory vacuoles in the apical cytoplasm of the radial glia-like cells of the neuroepithelium and in the flattened glial cells of the non-neural epineural roof epithelium. The secreted immunopositive material seems to form a thin layer covering the cell apices. There is no accumulation of the immunoreactive material on the apical surface of the hyponeural neuroepithelium or the hyponeural roof epithelium. Besides labelling the supporting cells and flattened glial cells of the epineural roof epithelium, both anti-RS antisera reveal a previously unknown putative glial cell type within the neural parenchyma of the holothurian nervous system.</p> <p>Conclusion</p> <p>Our results show that: a) the glial cells of the holothurian tubular nervous system produce a material similar to Reissner's substance known to be synthesized by secretory glial cells in all chordates studied so far; b) the nervous system of sea cucumbers shows a previously unrealized complexity of glial organization. Our findings also provide significant clues for interpretation of the evolution of the nervous system in the Deuterostomia. It is suggested that echinoderms and chordates might have inherited the RS-producing radial glial cell type from the central nervous system of their common ancestor, i.e., the last common ancestor of all the Deuterostomia.</p
Entanglement purification of multi-mode quantum states
An iterative random procedure is considered allowing an entanglement
purification of a class of multi-mode quantum states. In certain cases, a
complete purification may be achieved using only a single signal state
preparation. A physical implementation based on beam splitter arrays and
non-linear elements is suggested. The influence of loss is analyzed in the
example of a purification of entangled N-mode coherent states.Comment: 6 pages, 3 eps-figures, using revtex
A 64k pixel CMOS-DEPFET module for the soft X-rays DSSC imager operating at MHz-frame rates
: The 64k pixel DEPFET module is the key sensitive component of the DEPFET Sensor with Signal Compression (DSSC), a large area 2D hybrid detector for capturing and measuring soft X-rays at the European XFEL. The final 1-megapixel camera has to detect photons with energies between [Formula: see text] and [Formula: see text], and must provide a peak frame rate of [Formula: see text] to cope with the unique bunch structure of the European XFEL. This work summarizes the functionalities and properties of the first modules assembled with full-format CMOS-DEPFET arrays, featuring [Formula: see text] hexagonally-shaped pixels with a side length of 136 μm. The pixel sensors utilize the DEPFET technology to realize an extremely low input capacitance for excellent energy resolution and, at the same time, an intrinsic capability of signal compression without any gain switching. Each pixel of the readout ASIC includes a DEPFET-bias current cancellation circuitry, a trapezoidal-shaping filter, a 9-bit ADC and a 800-word long digital memory. The trimming, calibration and final characterization were performed in a laboratory test-bench at DESY. All detector features are assessed at [Formula: see text]. An outstanding equivalent noise charge of [Formula: see text]e-rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV ([Formula: see text]). At [Formula: see text] and [Formula: see text], a noise of [Formula: see text] e-rms and a dynamic range of [Formula: see text] are obtained. The highest dynamic range of [Formula: see text] is reached at [Formula: see text] and [Formula: see text]. These values can fulfill the specification of the DSSC project
Domain-specific textual meta-modelling languages for model driven engineering
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-31491-9_20Proceedings of 8th European Conference, ECMFA 2012, Kgs. Lyngby, Denmark, July 2-5, 2012Domain-specific modelling languages are normally defined through general-purpose meta-modelling languages like the MOF. While this is satisfactory for many Model-Driven Engineering (MDE) projects, several researchers have identified the need for domain-specific meta-modelling (DSMM) languages providing customised meta-modelling primitives aimed at the definition of modelling languages in a specific domain, as well as the construction of meta-model families.
In this paper, we discuss the potential of multi-level meta-modelling for the systematic engineering of DSMM architectures. For this purpose, we present: (i) several primitives and techniques to control the meta-modelling facilities offered to the users of the DSMM languages, (ii) a flexible approach to define textual concrete syntaxes for DSMM languages, (iii) extensions to model management languages enabling the practical use of DSMM in MDE, and (iv) an implementation of these ideas in the metaDepth tool.This work was funded by the Spanish Ministry of Economy and Competitivity (project “Go Lite” TIN2011-24139) and the R&D programme of the Madrid Region (project “e-Madrid” S2009/TIC-1650
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