1,021 research outputs found
Bounded repairability for regular tree languages
We study the problem of bounded repairability of a given restriction tree language R into a target tree language T. More precisely, we say that R is bounded repairable w.r.t. T if there exists a bound on the number of standard tree editing operations necessary to apply to any tree in R in order to obtain a tree in T. We consider a number of possible specifications for tree languages: bottom-up tree automata (on curry encoding of unranked trees) that capture the class of XML Schemas and DTDs. We also consider a special case when the restriction language R is universal, i.e., contains all trees over a given alphabet. We give an effective characterization of bounded repairability between pairs of tree languages represented with automata. This characterization introduces two tools, synopsis trees and a coverage relation between them, allowing one to reason about tree languages that undergo a bounded number of editing operations. We then employ this characterization to provide upper bounds to the complexity of deciding bounded repairability and we show that these bounds are tight. In particular, when the input tree languages are specified with arbitrary bottom-up automata, the problem is coNEXPTIME-complete. The problem remains coNEXPTIME-complete even if we use deterministic non-recursive DTDs to specify the input languages. The complexity of the problem can be reduced if we assume that the alphabet, the set of node labels, is fixed: the problem becomes PSPACE-complete for non-recursive DTDs and coNP-complete for deterministic non-recursive DTDs. Finally, when the restriction tree language R is universal, we show that the bounded repairability problem becomes EXPTIME-complete if the target language is specified by an arbitrary bottom-up tree automaton and becomes tractable (PTIME-complete, in fact) when a deterministic bottom-up automaton is used
A Next-to-Leading-Order Study of Dihadron Production
The production of pairs of hadrons in hadronic collisions is studied using a
next-to-leading-order Monte Carlo program based on the phase space slicing
technique. Up-to-date fragmentation functions based on fits to LEP data are
employed, together with several versions of current parton distribution
functions. Good agreement is found with data for the dihadron mass
distribution. A comparison is also made with data for the dihadron angular
distribution. The scale dependence of the predictions and the dependence on the
choices made for the fragmentation and parton distribution functions are also
presented. The good agreement between theory and experiment is contrasted to
the case for single production where significant deviations between
theory and experiment have been observed.Comment: 22 pages, 15 figures; 3 references added, one figure modified for
clarit
Ti–Si–C thin films produced by magnetron sputtering : correlation between physical properties, mechanical properties and tribological behavior
Ti–Si–C thin films were deposited onto silicon, stainless steel and high-speed steel substrates by magnetron sputtering, using different chamber configurations. The composition of the produced films was obtained by Electron Probe Micro-Analysis (EPMA) and the structure by X-ray diffraction
(XRD). The hardness and residual stresses were obtained by depth-sensing indentation and substrate deflection measurements (using Stoney’s equation), respectively. The tribological behavior of the produced films was studied by pin-on-disc. The increase of the concentration of non-metallic elements (carbon and silicon) caused significant changes in their properties. Structural analysis
revealed the possibility of the coexistence of different phases in the prepared films, namely Ti metallic phase ( alpha-Ti or beta-Ti) in the films with higher Ti content. The coatings with highest carbon contents, exhibited mainly a sub-stoichiometric fcc NaCl TiC-type structure. These structural changes were
also confirmed by resistivity measurements, whose values ranged from 10E3 Ohm/sq for low non-metal concentration, up to 10E6 Ohm /sq for the highest metalloid concentration. Astrong increase of hardness
and residual stresses was observed with the increase of the non-metal concentration in the films. The hardness (H) values ranged between 11 and 27 GPa, with a clear dependence on both crystalline structure and composition features. Following the mechanical behavior, the tribological results
showed similar trends, with both friction coefficients and wear revealing also a straight correlation with the composition and crystalline structure of the coatings
Optimization and thermal stability of TiAlN-Mo multilayers
In this work we focus on the optimization and thermal stability of nanocomposite TiAlN/Mo multilayers that were produced by reactive
magnetron sputtering on high-speed steel substrates, with modulation periods below 5 nm. These multilayers were annealed between 600–
900 ºC for 1 h in a vacuum furnace. Preliminary X-ray diffraction results reveal that these coatings are very stable up to 900 ºC, since the multilayer
chemical modulation is not severely affected. At intermediate annealing temperatures the modulation period decreases due to interdiffusion at
the interface, resulting in a thicker interface between metal/nitride and hence decreasing the thickness of those layers.Portuguese FCT/MCES scientific program
Photon tagged correlations in heavy ion collisions
A detailed study of various two-particle correlation functions involving
photons and neutral pions is presented in proton-proton and lead-lead
collisions at the LHC energy. The aim is to use these correlation functions to
quantify the effect of the medium (in lead-lead collisions) on the jet decay
properties. The calculations are carried out at the leading order in QCD but
the next-to-leading order corrections are also discussed. The competition
between different production mechanisms makes the connection between the jet
energy loss spectrum and the gamma-pi correlations somewhat indirect while the
gamma-gamma correlations have a clearer relation to the jet fragmentation
properties.Comment: 32 pages, 19 figures. Minor changes, published versio
Next-to-leading-order predictions for D^{*+-} plus jet photoproduction at DESY HERA
We study the photoproduction of a D^{*+-} meson in association with a hadron
jet at next-to-leading order in the parton model of QCD with non-perturbative
fragmentation functions extracted from LEP1 data of e^+e^- annihilation. The
transverse-momentum and rapidity distributions recently measured at DESY HERA
in various kinematic ranges nicely agree with our theoretical predictions. This
provides a useful test of the universality and the scaling violations of the
fragmentation functions predicted by the factorization theorem. These
comparisons also illustrate the significance of the charm component in the
resolved photon. This is elaborated by investigating the cross-section
distributions in x_obs^gamma and cos(theta^*).Comment: 20 pages, 10 figure
All-orders resummation for diphoton production at hadron colliders
We present a QCD calculation of the transverse momentum distribution of
photon pairs produced at hadron colliders, including all-orders soft-gluon
resummation valid at next-to-next-to-leading logarithmic accuracy. We specify
the region of phase space in which the calculation is most reliable, compare
our results with data from the Fermilab Tevatron, and make predictions for the
Large Hadron Collider. The uncertainty of predictions for production of
diphotons from fragmentation of final-state quarks is examined.Comment: 16 pages, 6 figures; minor change
Colour-Octet Effects in Radiative Decays
We investigate the effects of colour-octet contributions to the radiative
decay within the Bodwin, Braaten and Lepage NRQCD factorization
framework. Photons coming both from the coupling to hard processes (`direct')
and by collinear emission from light quarks (`fragmentation') are consistently
included at next-to-leading order (NLO) in . An estimate for the
non-perturbative matrix elements which enter in the final result is then
obtained. By comparing the NRQCD prediction at NLO for total decay rates with
the experimental data, it is found that the non-perturbative parameters must be
smaller than expected from the na\"\i ve scaling rules of NRQCD. Nevertheless,
colour-octet contributions to the shape of the photon spectrum turn out to be
significant.Comment: 25 pages, Latex, 8 figure
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