374 research outputs found
A Sensitivity Analysis for Quality Measures of Quantitative Association Rules
There exist several fitness function proposals based on a combination
of weighted objectives to optimize the discovery of association
rules. Nevertheless, some differences in the measures used to assess the
quality of association rules could be obtained according to the values of
such weights. Therefore, in such proposals it is very important the user’s
decision in order to specify the weights or coefficients of the optimized objectives.
Thus, this work presents an analysis on the sensitivity of several
quality measures when the weights included in the fitness function of the
existing QARGA algorithm are modified. Finally, a comparative analysis
of the results obtained according to the weights setup is provided.MICYT TIN2011-28956-C02-00Junta de Andalucía P11-TIC-752
Study of Nonlinear Periodic Optical System
We give a brief review of some results of our study on one-dimensional shallow nonlinear Bragg grating with nonlinear modulation and deep nonlinear Bragg grating
Superconductivity and hybrid soft modes in TiSe
The competition between superconductivity and other ground states of solids
is one of the challenging topics in condensed matter physics. Apart from
high-temperature superconductors [1,2] this interplay also plays a central role
in the layered transition-metal dichalcogenides, where superconductivity is
stabilized by suppressing charge-density-wave order to zero temperature by
intercalation [3] or applied pressure [4-7]. 1T-TiSe forms a prime example,
featuring superconducting domes on intercalation as well as under applied
pressure. Here, we present high energy-resolution inelastic x-ray scattering
measurements of the CDW soft phonon mode in intercalated CuTiSe and
pressurized 1T-TiSe along with detailed ab-initio calculations for the
lattice dynamical properties and phonon-mediated superconductivity. We find
that the intercalation-induced superconductivity can be explained by a solely
phonon-mediated pairing mechanism, while this is not possible for the
superconducting phase under pressure. We argue that a hybridization of phonon
and exciton modes in the pairing mechanism is necessary to explain the full
observed temperature-pressure-intercalation phase diagram. These results
indicate that 1T-TiSe under pressure is close to the elusive state of the
excitonic insulator
Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite
Lead halide perovskites such as methylammonium lead triiodide (MAPI) have
outstanding optical and electronic properties for photovoltaic applications,
yet a full understanding of how this solution processable material works so
well is currently missing. Previous research has revealed that MAPI possesses
multiple forms of static disorder regardless of preparation method, which is
surprising in light of its excellent performance. Using high energy resolution
inelastic X-ray (HERIX) scattering, we measure phonon dispersions in MAPI and
find direct evidence for another form of disorder in single crystals: large
amplitude anharmonic zone-edge rotational instabilities of the PbI_6 octahedra
that persist to room temperature and above, left over from structural phase
transitions that take place tens to hundreds of degrees below. Phonon
calculations show that the orientations of the methylammonium couple strongly
and cooperatively to these modes. The result is a non-centrosymmetric,
instantaneous local structure, which we observe in atomic pair distribution
function (PDF) measurements. This local symmetry breaking is unobservable by
Bragg diffraction, but can explain key material properties such as the
structural phase sequence, ultra low thermal transport, and large minority
charge carrier lifetimes despite moderate carrier mobility.Comment: 30 pages, 11 figure
Dose-Response Curve of Chromosome Aberrations in Human Lymphocytes Induced by Gamma-Rays
Chromosome aberration is a biomarker to predict the level of cell damage caused by exposure to ionizing radiation on human body. Dicentric chromosome is a specific chromosome aberration caused by ionizing radiation and is used as a gold standard biodosimetry of individuals over exposed to ionizing radiation.In radiation accident the dicentric assays has been applied as biological dosimetry to estimate radiation absorbed dose and also to confirm the radiation dose received to radiation workers.The purpose of this study was to generate a dose response curve of chromosome aberration (dicentric) in human lymphocyte inducedbygamma radiation. Peripheral blood samplesfrom three non smoking healthy volunteers aged between 25-48 years old with informed consent were irradiated with dose between 0.1-4.0Gy and a control using gamma teletherapy source. The culture procedure was conducted following the IAEA standard procedures with slight modifications. Analysis of dose-response curves used was LQ model Y = a + αD + βD2. The result showed that α and β values of the curve obtained were 0.018± 0.006 and 0.013 ± 0.002,respectively. Dose response calibration curve for dicentric chromosome aberrations in human lymphocytes induced by gamma-radiation fitted to linear quadratic model. In order to apply the dose response curve of chromosome aberration disentric for biodosimetry, this standar curve still need to be validatedReceived: 8 November 2013; Revised: 27 December 2013; Accepted: 31 December 201
Intrinsic Localized Modes Observed in the High Temperature Vibrational Spectrum of NaI
Inelastic neutron measurements of the high-temperature lattice excitations in
NaI show that in thermal equilibrium at 555 K an intrinsic mode, localized in
three dimensions, occurs at a single frequency near the center of the spectral
phonon gap, polarized along [111]. At higher temperatures the intrinsic
localized mode gains intensity. Higher energy inelastic neutron and x-ray
scattering measurements on a room-temperature NaI crystal indicate that the
creation energy of the ground state of the intrinsic localized mode is 299 meV.Comment: 17 pages, 5 figures Revised version; final versio
- …