185,510 research outputs found
The risks of mixing dependency lengths from sequences of different length
Mixing dependency lengths from sequences of different length is a common
practice in language research. However, the empirical distribution of
dependency lengths of sentences of the same length differs from that of
sentences of varying length and the distribution of dependency lengths depends
on sentence length for real sentences and also under the null hypothesis that
dependencies connect vertices located in random positions of the sequence. This
suggests that certain results, such as the distribution of syntactic dependency
lengths mixing dependencies from sentences of varying length, could be a mere
consequence of that mixing. Furthermore, differences in the global averages of
dependency length (mixing lengths from sentences of varying length) for two
different languages do not simply imply a priori that one language optimizes
dependency lengths better than the other because those differences could be due
to differences in the distribution of sentence lengths and other factors.Comment: Laguage and referencing has been improved; Eqs. 7, 11, B7 and B8 have
been correcte
Unconventional superconducting pairing symmetry induced by phonons
The possibility of non-s-wave superconductivity induced by phonons is
investigated using a simple model that is inspired by SrRuO. The model
assumes a two-dimensional electronic structure, a two-dimensional
spin-fluctuation spectrum, and three-dimensional electron-phonon coupling.
Taken separately, each interaction favors formation of spin-singlet pairs (of s
symmetry for the phonon interaction and d symmetry for the spin
interaction), but in combination, a variety of more unusual singlet and triplet
states are found, depending on the interaction parameters. This may have
important implications for SrRuO, providing a plausible explanation of
how the observed spin fluctuations, which clearly favor d pairing,
may still be instrumental in creating a superconducting state with a different
(e.g., p-wave) symmetry. It also suggests an interpretation of the large
isotope effect observed in SrRuO. These results indicate that phonons
could play a key role in establishing the order-parameter symmetry in
SrRuO, and possibly in other unconventional superconductors.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Localization of fermionic fields on braneworlds with bulk tachyon matter
Recently, Pal and Skar in [arXiv:hep-th/0701266] proposed a mechanism to
arise the warped braneworld models from bulk tachyon matter, which are endowed
with a thin brane and a thick brane. In this framework, we investigate
localization of fermionic fields on these branes. As in the 1/2 spin case, the
field can be localized on both the thin and thick branes with inclusion of
scalar background. In the 3/2 spin extension, the general supergravity action
coupled to chiral supermultiplets is considered to produce the localization on
both the branes as a result.Comment: 9 pages, no figure
On the geometry of double field theory
Double field theory was developed by theoretical physicists as a way to
encompass -duality. In this paper, we express the basic notions of the
theory in differential-geometric invariant terms, in the framework of
para-Kaehler manifolds. We define metric algebroids, which are vector bundles
with a bracket of cross sections that has the same metric compatibility
property as a Courant bracket. We show that a double field gives rise to two
canonical connections, whose scalar curvatures can be integrated to obtain
actions. Finally, in analogy with Dirac structures, we define and study
para-Dirac structures on double manifolds.Comment: The paper will appear in J. Math. Phys., 201
Identification of photons in double beta-decay experiments using segmented germanium detectors - studies with a GERDA Phase II prototype detector
The sensitivity of experiments searching for neutrinoless double beta-decay
of germanium was so far limited by the background induced by external
gamma-radiation. Segmented germanium detectors can be used to identify photons
and thus reduce this background component.
The GERmanium Detector Array, GERDA, will use highly segmented germanium
detectors in its second phase. The identification of photonic events is
investigated using a prototype detector. The results are compared with Monte
Carlo data.Comment: 20 pages, 7 figures, to be submitted to NIM-
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