42,420 research outputs found
Empirical Methods for Compound Splitting
Compounded words are a challenge for NLP applications such as machine
translation (MT). We introduce methods to learn splitting rules from
monolingual and parallel corpora. We evaluate them against a gold standard and
measure their impact on performance of statistical MT systems. Results show
accuracy of 99.1% and performance gains for MT of 0.039 BLEU on a
German-English noun phrase translation task.Comment: 8 pages, 2 figures. Published at EACL 200
Segmentation algorithm for non-stationary compound Poisson processes
We introduce an algorithm for the segmentation of a class of regime switching
processes. The segmentation algorithm is a non parametric statistical method
able to identify the regimes (patches) of the time series. The process is
composed of consecutive patches of variable length, each patch being described
by a stationary compound Poisson process, i.e. a Poisson process where each
count is associated to a fluctuating signal. The parameters of the process are
different in each patch and therefore the time series is non stationary. Our
method is a generalization of the algorithm introduced by Bernaola-Galvan, et
al., Phys. Rev. Lett., 87, 168105 (2001). We show that the new algorithm
outperforms the original one for regime switching compound Poisson processes.
As an application we use the algorithm to segment the time series of the
inventory of market members of the London Stock Exchange and we observe that
our method finds almost three times more patches than the original one.Comment: 11 pages, 11 figure
First-principles Study of the Luminescence of Eu2+-doped Phosphors
The luminescence of fifteen representative Eu-doped phosphors used for
white-LED and scintillation applications is studied through a Constrained
Density Functional Theory. Transition energies and Stokes shift are deduced
from differences of total energies between the ground and excited states of the
systems, in the absorption and emission geometries. The general applicability
of such methodology is first assessed: for this representative set, the
calculated absolute error with respect to experiment on absorption and emission
energies is within 0.3 eV. This set of compounds covers a wide range of
transition energies that extents from 1.7 to 3.5 eV. The information gained
from the relaxed geometries and total energies is further used to evaluate the
thermal barrier for the crossover, the full width at half-maximum of
the emission spectrum and the temperature shift of the emission peak, using a
one-dimensional configuration-coordinate model. The former results indicate
that the crossover cannot be the dominant mechanism for the thermal
quenching behavior of Eu-doped phosphors and the latter results are
compared to available experimental data and yield a 30 mean absolute
relative error. Finally, a semi-empirical model used previously for
Ce-doped hosts is adapted to Eu-doped hosts and gives the
absorption and emission energies within 0.9 eV of experiment, underperforming
compared to the first-principles calculation.Comment: 17 pages, 13 figures, (Phys. Rev. B 2017 Accept
Dutch compound splitting for bilingual terminology extraction
Compounds pose a problem for applications that rely on precise word alignments such as bilingual terminology extraction. We therefore developed a state-of-the-art hybrid compound splitter for Dutch that makes use of corpus frequency information and linguistic knowledge. Domain-adaptation techniques are used to combine large out-of-domain and dynamically compiled in-domain frequency lists. We perform an extensive intrinsic evaluation on a Gold Standard set of 50,000 Dutch compounds and a set of 5,000 Dutch compounds belonging to the automotive domain. We also propose a novel methodology for word alignment that makes use of the compound splitter. As compounds are not always translated compositionally, we train the word alignment models twice: a first time on the original data set and a second time on the data set in which the compounds are split into their component parts. The obtained word alignment points are then combined
Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds
The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.Comment: 38 pages, 15 figure
Thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies
The thermal and magnetic properties of spin-1 magnetic chain compounds with
large single-ion and in-plane anisotropies are investigated via the integrable
su(3) model in terms of the quantum transfer matrix method and the recently
developed high temperature expansion method for exactly solved models. It is
shown that large single-ion anisotropy may result in a singlet gapped phase in
the spin-1 chain which is significantly different from the standard Haldane
phase. A large in-plane anisotropy may destroy the gapped phase. On the other
hand, in the vicinity of the critical point a weak in-plane anisotropy leads to
a different phase transition than the Pokrovsky-Talapov transition. The
magnetic susceptibility, specific heat and magnetization evaluated from the
free energy are in excellent agreement with the experimental data for the
compounds NiC_2H_8N_2)_2Ni(CN)_4 and Ni(C_{10}H_8N_2)_2Ni(CN)_4.H_2O.Comment: 18 pages, 6 figures, to appear in PR
First-principles study of Ce doped lanthanum silicate nitride phosphors: Neutral excitation, Stokes shift, and luminescent center identification
We study from first principles two lanthanum silicate nitride compounds,
LaSiN and LaSiN, pristine as well as doped with
Ce ion, in view of explaining their different emission color, and
characterising the luminescent center. The electronic structures of the two
undoped hosts are similar, and do not give a hint to quantitatively describe
such difference. The neutral excitation of the Ce
ions is simulated through a constrained density-functional theory method
coupled with a SCF analysis of total energies, yielding absorption
energies. Afterwards, atomic positions in the excited state are relaxed,
yielding the emission energies and Stokes shifts. Based on these results, the
luminescent centers in LaSiN:Ce and LaSiN:Ce are
identified. The agreement with the experimental data for the computed
quantities is quite reasonable and explains the different color of the emitted
light. Also, the Stokes shifts are obtained within 20\% difference relative to
experimental data.Comment: 12 pages, 10 figure
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