1,119 research outputs found
Spin polarons in triangular antiferromagnets
The motion of a single hole in a 2D triangular antiferromagnet is
investigated using the t-J model. The one-hole states are described by strings
of spin deviations around the hole. Using projection technique the one-hole
spectral function is calculated. For large J/t we find low-lying
quasiparticle-like bands which are well separated from an incoherent background
by a gap of order J. However, for small J/t this gap vanishes and the spectrum
becomes broad over an energy range of several t. The results are compared with
SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR
Extraction of chemical-induced diseases using prior knowledge and textual information
We describe our approach to the chemical-disease relation (CDR) task in the BioCreative V challenge. The CDR task consists of two subtasks: Automatic disease-named entity recognition and normalization (DNER), and extraction of chemical-induced diseases (CIDs) from Medline abstracts. For the DNER subtask, we used our concept recognition tool Peregrine, in combination with several optimization steps. For the CID subtask, our system, which we named RELigator, was trained on a rich feature set, comprising features derived from a graph database containing prior knowledge about chemicals and diseases, and linguistic and statistical features derived from the abstracts in the CDR training corpus. We describe the systems that were developed and present evaluation results for both subtasks on the CDR test set. For DNER, our Peregrine system reached an F-score of 0.757. For CID, the system achieved an F-score of 0.526, which ranked second among 18 participating teams. Several post-challenge modifications of the systems resulted in substantially improved F-scores (0.828 for DNER and 0.602 for CID)
Supersymmetric IIB Solutions with Schr\"{o}dinger Symmetry
We find a class of non-relativistic supersymmetric solutions of IIB
supergravity with non-trivial B-field that have dynamical exponent n=2 and are
invariant under the Schrodinger group. For a general Sasaki-Einstein internal
manifold with U(1)^3 isometry, the solutions have two real supercharges. When
the internal manifold is S^5, the number of supercharges can be four. We also
find a large class of non-relativistic scale invariant type IIB solutions with
dynamical exponents different from two. The explicit solutions and the values
of the dynamical exponents are determined by vector eigenfunctions and
eigenvalues of the Laplacian on an Einstein manifold.Comment: 28 pages, LaTe
Cosmic opacity to CMB photons and polarization measurements
Anisotropy data analysis leaves a significant degeneracy between primeval
spectral index (n_s) and cosmic opacity to CMB photons (\tau). Low--l
polarization measures, in principle, can remove it. We perform a likelihood
analysis to see how cosmic variance possibly affects such a problem. We find
that, for a sufficiently low noise level (\sigma_{pix}) and if \tau is not
negligibly low, the degeneracy is greatly reduced, while the residual impact of
cosmic variance on n_s and \tau determinations is under control. On the
contrary, if \sigma_{pix} is too high, cosmic variance effects appear to be
magnified. We apply general results to specific experiments and find that, if
favorable conditions occur, it is possible that a 2--\sigma detection of a
lower limit on \tau is provided by the SPOrt experiment. Furthermore, if the
PLANCK experiment will measure polarization with the expected precision, the
error on low--l harmonics is adequate to determine \tau, without significant
magnification of the cosmic variance. This however indicates that high
sensitivity might be more important than high resolution in \tau
determinations. We also outline that a determination of \tau is critical to
perform detailed analyses on the nature of dark energy and/or on the presence
of primeval gravitational waves.Comment: 17 pages, 11 figures, to be published on New Astronom
Pion double charge exchange on 4He
The doubly differential cross sections for the He
reaction were calculated using both a two-nucleon sequential single charge
exchange model and an intranuclear cascade code. Final state interactions
between the two final protons which were the initial neutrons were included in
both methods. At incident pion energies of 240 and 270 MeV the low-energy peak
observed experimentally in the energy spectrum of the final pions can be
understood only if the contribution of pion production is included. The
calculated cross sections are compared with data.Comment: 25 pages, 9 figure
LARGE Volume String Compactifications at Finite Temperature
We present a detailed study of the finite-temperature behaviour of the LARGE
Volume type IIB flux compactifications. We show that certain moduli can
thermalise at high temperatures. Despite that, their contribution to the
finite-temperature effective potential is always negligible and the latter has
a runaway behaviour. We compute the maximal temperature , above which
the internal space decompactifies, as well as the temperature , that is
reached after the decay of the heaviest moduli. The natural constraint
implies a lower bound on the allowed values of the internal
volume . We find that this restriction rules out a significant
range of values corresponding to smaller volumes of the order , which lead to standard GUT theories. Instead, the bound favours
values of the order , which lead to TeV scale
SUSY desirable for solving the hierarchy problem. Moreover, our result favours
low-energy inflationary scenarios with density perturbations generated by a
field, which is not the inflaton. In such a scenario, one could achieve both
inflation and TeV-scale SUSY, although gravity waves would not be observable.
Finally, we pose a two-fold challenge for the solution of the cosmological
moduli problem. First, we show that the heavy moduli decay before they can
begin to dominate the energy density of the Universe. Hence they are not able
to dilute any unwanted relics. And second, we argue that, in order to obtain
thermal inflation in the closed string moduli sector, one needs to go beyond
the present EFT description.Comment: 54 pages + appendix, 5 figures; v2: minor corrections, references and
footnotes added, version published on JCA
Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity
We study Berry phase effects on conductance properties of diffusive
mesoscopic conductors, which are caused by an electron spin moving through an
orientationally inhomogeneous magnetic field. Extending previous work, we start
with an exact, i.e. not assuming adiabaticity, calculation of the universal
conductance fluctuations in a diffusive ring within the weak localization
regime, based on a differential equation which we derive for the diffuson in
the presence of Zeeman coupling to a magnetic field texture. We calculate the
field strength required for adiabaticity and show that this strength is reduced
by the diffusive motion. We demonstrate that not only the phases but also the
amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the
Berry phase. In particular, we show that these amplitudes are completely
suppressed at certain magic tilt angles of the external fields, and thereby
provide a useful criterion for experimental searches. We also discuss Berry
phase-like effects resulting from spin-orbit interaction in diffusive
conductors and derive exact formulas for both magnetoconductance and
conductance fluctuations. We discuss the power spectra of the
magnetoconductance and the conductance fluctuations for inhomogeneous magnetic
fields and for spin-orbit interaction.Comment: 18 pages, 13 figures; minor revisions. To appear in Phys. Rev.
User-informed marketing versus standard description to drive demand for evidence-based therapy: A randomized controlled trial.
Direct-to-consumer (DTC) marketing represents a vital strategy to disseminate evidence-based therapies (EBTs). This 3-phase research program, informed by the marketing mix, developed and evaluated user-informed DTC materials for parents concerned about adolescent substance use (SU). Phases 1 and 2 consisted of qualitative interviews (n = 29 parents) and a quantitative survey (n = 411), respectively, to elicit parentsâ preferred terms and strategies to disseminate EBT. Building upon prior phases, the current study (Phase 3) developed a user-informed infographic (128 words, 7th-grade level) focused on SU therapy. Parents were randomly assigned to view the user-informed infographic (n = 75) or a standard EBT description (n = 77) from the American Psychological Association (529 words, 12th-grade level). Logistic regressions examined the effect of marketing condition on parent-reported behavioral intentions and actual requests for EBT information, controlling for correlates of parent preferences in Phase 2 (parent education level; adolescent internalizing, externalizing, legal, and SU problems). Counter to hypotheses, condition did not have a main effect on either outcome. However, there was a significant interaction between condition and adolescent SU problems: among parents whose adolescents had SU problems, the user-informed infographic predicted 3.7 times higher odds of requesting EBT information than the standard description. Additionally, parents whose adolescents had legal problems were more likely to request EBT information than parents whose adolescents did not. The infographic was 4 times shorter and written at 5 grade levels lower, thereby providing a highly disseminable alternative. Findings highlight the value of specificity in DTC marketing, while advancing methods to create tailored marketing materials and communicate knowledge about psychological science
Sugars of pearl millet [Pennisetum americanum (L.) Leeke] grains
The sugars in the grains of nine pearl millet cultivars were fractionated through a Biogel column. Five different sugarsâ(stachyose, raffinose, sucrose, glucose, and fructose) were identified. Sucrose was predominant in all the cultivars. Raffinose content was high as compared to other cereals, and maltose was absen
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