478 research outputs found
Evaluation of innovative sprayed-concrete-lined tunnelling
The front-shunt tunnel was the first tunnel of the Terminal 5 project at Heathrow to be constructed, and was the first section of sprayed-concrete-lined (SCL) tunnel to be constructed using the method known as LaserShell. This innovation represented a significant deviation from the methods previously used in SCL construction. Therefore it was subjected to a careful examination before and during construction using sophisticated 3D numerical modelling and monitoring during construction. The paper presents typical results from surface settlement levelling, inclinometers and extensometers, pressure cells and tunnel lining displacement measurements, and comments on the performance of the methods and instruments used. The paper then presents the methodology and typical results of the numerical modelling, and shows that the predictions of displacements and stresses compared well with the field measurements. In terms of the control of ground deformations and structural safety the tunnel performed well
Integration over quantum permutation groups
We find a combinatorial formula for the Haar measure of quantum permutation
groups. This leads to a dynamic formula for laws of diagonal coefficients,
explaining the Poisson/free Poisson convergence result for characters.Comment: 15 page
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Limiting homologous recombination at stalled replication forks is essential for cell viability: DNA2 to the rescue
The disease-associated nuclease–helicase DNA2 has been implicated in DNA end-resection during DNA double-strand break repair, Okazaki fragment processing, and the recovery of stalled DNA replication forks (RFs). Its role in Okazaki fragment processing has been proposed to explain why DNA2 is indispensable for cell survival across organisms. Unexpectedly, we found that DNA2 has an essential role in suppressing homologous recombination (HR)-dependent replication restart at stalled RFs. In the absence of DNA2-mediated RF recovery, excessive HR-restart of stalled RFs results in toxic levels of abortive recombination intermediates that lead to DNA damage-checkpoint activation and terminal cell-cycle arrest. While HR proteins protect and restart stalled RFs to promote faithful genome replication, these findings show how HR-dependent replication restart is actively constrained by DNA2 to ensure cell survival. These new insights disambiguate the effects of DNA2 dysfunction on cell survival, and provide a framework to rationalize the association of DNA2 with cancer and the primordial dwarfism disorder Seckel syndrome based on its role in RF recovery
Blind component separation for polarized observations of the CMB
We present in this paper the PolEMICA (Polarized Expectation-Maximization
Independent Component Analysis) algorithm which is an extension to polarization
of the SMICA (Spectral Matching Independent Component Analysis) temperature
multi-detectors multi-components (MD-MC) component separation method
(Delabrouille et al. 2003). This algorithm allows us to estimate blindly in
harmonic space multiple physical components from multi-detectors polarized sky
maps. Assuming a linear noisy mixture of components we are able to reconstruct
jointly the anisotropies electromagnetic spectra of the components for each
mode T, E and B, as well as the temperature and polarization spatial power
spectra, TT, EE, BB, TE, TB and EB for each of the physical components and for
the noise on each of the detectors. PolEMICA is specially developed to estimate
the CMB temperature and polarization power spectra from sky observations
including both CMB and foreground emissions. This has been tested intensively
using as a first approach full sky simulations of the Planck satellite
polarized channels for a 14-months nominal mission assuming a simplified linear
sky model including CMB, and optionally Galactic synchrotron emission and a
Gaussian dust emission. Finally, we have applied our algorithm to more
realistic Planck full sky simulations, including synchrotron, realistic dust
and free-free emissions.Comment: 20 pages, 21 figures, 1 table, TeX file, accepted for publication in
MNRA
Synthesis and Luminescence Modulation of Pyrazine-Based Gold(III) Pincer Complexes
The first examples of pyrazine-based gold(III) pincer complexes have been synthesized; their intense photoemissions can be modified by interactions with the non-coordinating pyrazine-N atom. Luminescence modulation is possible without the need for altering the ligand framework. Emissions shift from red (77 K) to blue (298 K) due to thermally activated delayed fluorescence (TADF
Measurement of the response of heat-and-ionization germanium detectors to nuclear recoils
The heat quenching factor Q' (the ratio of the heat signals produced by
nuclear and electron recoils of equal energy) of the heat-and-ionization
germanium bolometers used by the EDELWEISS collaboration has been measured. It
is explained how this factor affects the energy scale and the effective
quenching factor observed in calibrations with neutron sources. This effective
quenching effect is found to be equal to Q/Q', where Q is the quenching factor
of the ionization yield. To measure Q', a precise EDELWEISS measurement of Q/Q'
is combined with values of Q obtained from a review of all available
measurements of this quantity in tagged neutron beam experiments. The
systematic uncertainties associated with this method to evaluate Q' are
discussed in detail. For recoil energies between 20 and 100 keV, the resulting
heat quenching factor is Q' = 0.91+-0.03+-0.04, where the two errors are the
contributions from the Q and Q/Q' measurements, respectively. The present
compilation of Q values and evaluation of Q' represent one of the most precise
determinations of the absolute energy scale for any detector used in direct
searches for dark matter.Comment: 28 pages, 7 figures. Submitted to Phys. Rev.
Physical Properties of (2) Pallas
We acquired and analyzed adaptive-optics imaging observations of asteroid (2)
Pallas from Keck II and the Very Large Telescope taken during four Pallas
oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km
(image scales 13-20 km/pix). We improve our determination of the size, shape,
and pole by a novel method that combines our AO data with 51 visual
light-curves spanning 34 years of observations as well as occultation data.
The shape model of Pallas derived here reproduces well both the projected
shape of Pallas on the sky and light-curve behavior at all the epochs
considered. We resolved the pole ambiguity and found the spin-vector
coordinates to be within 5 deg. of [long, lat] = [30 deg., -16 deg.] in the
ECJ2000.0 reference frame, indicating a high obliquity of ~84 deg., leading to
high seasonal contrast. The best triaxial-ellipsoid fit returns radii of a=275
km, b= 258 km, and c= 238 km. From the mass of Pallas determined by
gravitational perturbation on other minor bodies [(1.2 +/- 0.3) x 10-10 Solar
Masses], we derive a density of 3.4 +/- 0.9 g.cm-3 significantly different from
the density of C-type (1) Ceres of 2.2 +/- 0.1 g.cm-3. Considering the spectral
similarities of Pallas and Ceres at visible and near-infrared wavelengths, this
may point to fundamental differences in the interior composition or structure
of these two bodies.
We define a planetocentric longitude system for Pallas, following IAU
guidelines. We also present the first albedo maps of Pallas covering ~80% of
the surface in K-band. These maps reveal features with diameters in the 70-180
km range and an albedo contrast of about 6% wrt the mean surface albedo.Comment: 16 pages, 8 figures, 6 table
Functional characterization of SlscADH1, a fruit-ripening associated short-chain alcohol dehydrogenase of tomato
A tomato short-chain dehydrogenase-reductase (SlscADH1) is preferentially expressed in fruit with a maximum expression at the breaker stage while expression in roots, stems, leaves and flowers is very weak. It represents a potential candidate for the formation of aroma volatiles by interconverting alcohols and aldehydes. The SlscADH1 recombinant protein produced in Escherichia coli exhibited dehydrogenase-reductase activity towards several volatile compounds present in tomato flavour with a strong preference for the NAD/NADH co-factors. The strongest activity was observed for the reduction of hexanal (Km = 0.175 mM) and phenylacetaldehyde (Km = 0.375 mM) in the presence of NADH. The oxidation process of hexanol and 1-phenylethanol was much less efficient (Kms of 2.9 and 23.0 mM, respectively), indicating that the enzyme preferentially acts as a reductase. However activity was observed only for hexanal, phenylacetaldehyde, (E)-2-hexenal and acetaldehyde and the corresponding alcohols. No activity could be detected for other aroma volatiles important for tomato flavour, such as methyl-butanol/methyl-butanal, 5-methyl-6-hepten-2-one/5-methyl-6-hepten-2-ol, citronellal/citronellol, neral/nerol, geraniol. In order to assess the function of the SlscADH1 gene, transgenic plants have been generated using the technique of RNA interference (RNAi). Constitutive down-regulation using the 35S promoter resulted in the generation of dwarf plants, indicating that the SlscADH1 gene, although weakly expressed in vegetative tissues, had a function in regulating plant development. Fruitspecific down-regulation using the 2A11 promoter had no morphogenetic effect and did not alter the aldehyde/alcohol balance of the volatiles compounds produced by the fruit. Nevertheless, SlscADH1-inhibited fruit unexpectedly accumulated higher concentrations of C5 and C6 volatile compounds of the lipoxygenase pathway, possibly as an indirect effect of the suppression of SlscADH1 on the catabolism of phospholipids and/or integrity of membranes
Random graph states, maximal flow and Fuss-Catalan distributions
For any graph consisting of vertices and edges we construct an
ensemble of random pure quantum states which describe a system composed of
subsystems. Each edge of the graph represents a bi-partite, maximally entangled
state. Each vertex represents a random unitary matrix generated according to
the Haar measure, which describes the coupling between subsystems. Dividing all
subsystems into two parts, one may study entanglement with respect to this
partition. A general technique to derive an expression for the average
entanglement entropy of random pure states associated to a given graph is
presented. Our technique relies on Weingarten calculus and flow problems. We
analyze statistical properties of spectra of such random density matrices and
show for which cases they are described by the free Poissonian
(Marchenko-Pastur) distribution. We derive a discrete family of generalized,
Fuss-Catalan distributions and explicitly construct graphs which lead to
ensembles of random states characterized by these novel distributions of
eigenvalues.Comment: 37 pages, 24 figure
Natural language processing
Beginning with the basic issues of NLP, this chapter aims to chart the major research activities in this area since the last ARIST Chapter in 1996 (Haas, 1996), including: (i) natural language text processing systems - text summarization, information extraction, information retrieval, etc., including domain-specific applications; (ii) natural language interfaces; (iii) NLP in the context of www and digital libraries ; and (iv) evaluation of NLP systems
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