1,783 research outputs found
Conjunctive queries with negation over DL-Lite: a closer look
While conjunctive query (CQ) answering over DL-Lite has been studied extensively, there have been few attempts to analyse CQs with negated atoms. This paper deepens the study of the problem. Answering CQs with safe negation and CQs with a single inequality over DL-Lite with role inclusions is shown to be undecidable, even for a fixed TBox and query.Without role inclusions, answering CQs with one inequality is P-hard and with two inequalities CoNP-hard in data complexity
On the evolution of a large class of inhomogeneous scalar field cosmologies
The asymptotic behaviour of a family of inhomogeneous scalar field
cosmologies with exponential potential is studied. By introducing new variables
we can perform an almost complete analysis of the evolution of these
cosmologies. Unlike the homogeneous case (Bianchi type solutions), when k^2<2
the models do not isotropize due to the presence of the inhomogeneitiesComment: 23 pages, 1 figure. Submitted to Classical and Quantum Gravit
Evidences of evanescent Bloch waves in Phononic Crystals
We show both experimentally and theoretically the evanescent behaviour of
modes in the Band Gap (BG) of finite Phononic Crystal (PC). Based on
experimental and numerical data we obtain the imaginary part of the wave vector
in good agreement with the complex band structures obtained by the Extended
Plane Wave Expansion (EPWE). The calculated and measured acoustic field of a
localized mode out of the point defect inside the PC presents also evanescent
behaviour. The correct understanding of evanescent modes is fundamental for
designing narrow filters and wave guides based on Phononic Crystals with
defects.Comment: 8 pages, 3 figure
The Exact MSSM Spectrum from String Theory
We show the existence of realistic vacua in string theory whose observable
sector has exactly the matter content of the MSSM. This is achieved by
compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau
threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line.
Specifically, the observable sector is N=1 supersymmetric with gauge group
SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons,
each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair.
Importantly, there are no extra vector-like pairs and no exotic matter in the
zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge
instanton moduli in the observable sector. The holomorphic SU(4) vector bundle
of the observable sector is slope-stable.Comment: 15 pages, LaTeX; v2: Hidden sector is unstable, symbol typesetting
error corrected, clarifications and references added; v3: New discussion of
hidden secto
Fast determination of toxic diethylene glycol in toothpaste by ultra-performance liquid chromatography–time of flight mass spectrometry
A rapid method for determining diethylene
glycol (DEG) in toothpaste based on the use of ultraperformance
liquid chromatography (UPLC) coupled to
time-of-flight mass spectrometry (TOF-MS) has been
developed. The method has been validated in toothpaste
samples spiked at different levels, 0.005, 0.1 and 5%,
obtaining satisfactory recoveries (74–98%) and relative
standard deviations (<4%). Quantification was carried out
by using matrix-matched standards calibration. The developed
method was applied to several types of toothpaste,
making identification and quantification of DEG and other
polyethylene glycols (PEG) feasible with very little sample
manipulation, as only extraction with water is required. The
excellent sensitivity of TOF-MS analysis performed in fullscan
acquisition mode allowed the determination of DEG at
concentration levels as low as 0.005% in samples and its
reliable identification via the mass accuracy measurements
provided by this instrument (<5 ppm
Gravitational lensing by spherically symmetric lenses with angular momentum
Following Sereno (2002a), we discuss the bending of light rays by spherically
symmetric lenses with angular momentum. For several astrophysical systems, such
as white dwarfs and galaxies, gravitomagnetism induces a correction on the
deflection angle as large as 0.1%.Comment: 6 pages, To appear in A&
A new scenario for string unification
We present a new scenario for gauge coupling unification in flipped SU(5)
string models, which identifies the scale of SU(3) and SU(2)
unification with the empirical ~GeV scale, and the
scale of SU(5) and U(1) unification with the theoretical ~GeV string unification scale. The vacuum shift
necessary for the cancellation of the anomalous and an SU(4)
hidden sector with fractionally-charged particles, play a crucial role in the
dynamical determination of all intermediate mass scales in this scenario.Comment: 8 pages, LaTeX, 2 figures (uuencoded
Análisis del decaimiento de Quercus Suber a escala regional en Andalucía: aplicación para una gestión eficaz
1 página. Comunicación oral presentada en la Sesión Ecología y Ecofisiología de la referida Reunión, celebrada en Huelva, 9-11, noviembre, 2011.Los sistemas forestales se están viendo afectados por el cambio global, uno de cuyos principales
impulsores es el cambio climático. Actualmente estos cambios ocurren a mayor velocidad de la
experimentada hasta ahora a lo largo de la evolución, lo que provoca una gran incertidumbre sobre
la capacidad de adaptación de muchas especies. Como consecuencia es necesario conocer la
dinámica de los sistemas forestales y los efectos del cambio global para dirigir todos los esfuerzos
de gestión hacia objetivos alcanzables para la conservación de estos sistemas y sus valores.Peer reviewe
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