12,930 research outputs found
Ab initio Evidence for Giant Magnetoelectric Responses Driven by Structural Softness
We show that inducing structural softness in regular magnetoelectric (ME)
multiferroics -- i.e., tuning the materials to make their structure strongly
reactive to applied fields -- makes it possible to obtain very large ME
effects. We present illustrative first-principles results for BiFeO3 thin
films.Comment: 4 pages with 3 figures embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
MCMC Bayesian Estimation in FIEGARCH Models
Bayesian inference for fractionally integrated exponential generalized
autoregressive conditional heteroskedastic (FIEGARCH) models using Markov Chain
Monte Carlo (MCMC) methods is described. A simulation study is presented to
access the performance of the procedure, under the presence of long-memory in
the volatility. Samples from FIEGARCH processes are obtained upon considering
the generalized error distribution (GED) for the innovation process. Different
values for the tail-thickness parameter \nu are considered covering both
scenarios, innovation processes with lighter (\nu2) tails
than the Gaussian distribution (\nu=2). A sensitivity analysis is performed by
considering different prior density functions and by integrating (or not) the
knowledge on the true parameter values to select the hyperparameter values
Periodic Gravitational Waves From Small Cosmic String Loops
We consider a population of small, high-velocity cosmic string loops. We
assume the typical length of these loops is determined by the gravitational
radiation scale and use the results of \cite{Polchinski:2007rg} which pointed
out their highly relativistic nature. A study of the gravitational wave
emission from such a population is carried out. The large Lorentz boost
involved causes the lowest harmonics of the loops to fall within the frequency
band of the LIGO detector. Due to this feature the gravitational waves emitted
by such loops can be detected in a periodic search rather than in burst or
stochastic analysis.
It is shown that, for interesting values of the string tension
(10^{-10}\lsim G\mu\lsim 10^{-8}) the detector can observe loops at
reasonably high redshifts and that detection is, in principle, possible. We
compute the number of expected observations produced by such a process. For a
10 hour search we find that this number is of order . This is a
consequence of the low effective number density of the loops traveling along
the line of sight. However, small probabilities of reconnection and longer
observation times can improve the result.Comment: 1+15 pages, 7 figure
Magnetoelectric response of multiferroic BiFeO3 and related materials
We present a first-principles scheme for computing the magnetoelectric
response of multiferroics. We apply our method to BiFeO3 (BFO) and related
compounds in which Fe is substituted by other magnetic species. We show that
under certain relevant conditions -- i.e., in absence of incommensurate spin
modulation, as in BFO thin films and some BFO-based solid solutions -- these
materials display a large linear magnetoelectric response. Our calculations
reveal the atomistic origin of the coupling and allow us to identify the most
promising strategies to enhance it.Comment: 4 pages with 1 figure embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
Chemical abundances for the transiting planet host stars OGLE-TR-10, 56, 111, 113, 132 and TrES-1. Abundances in different galactic populations
We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution
spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111,
113, 132 and TrES-1. The spectra are now used to derive and discuss the
chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni,
Cu and Zn. Abundances were derived in LTE, using 1-D plane-parallel Kurucz
model atmospheres. For S, Zn and Cu we used a spectral synthesis procedure,
while for the remaining cases the abundances were derived from measurements of
line-equivalent widths. The resulting abundances are compared with those found
for stars in the solar neighborhood. Distances and galactic coordinates are
estimated for the stars. We conclude that besides being particularly
metal-rich, with small possible exceptions OGLE-TR-10, 56, 111, 113, 132 and
TrES-1 are chemically undistinguishable from the field (thin disk) stars
regarding their [X/Fe] abundances. This is particularly relevant for the most
distant of the targets, located at up to ~2 Kpc from the Sun. We also did not
find any correlation between the abundances and the condensation temperature of
the elements, an evidence that strong accretion of planetary-like material,
tentatively connected to planetary migration, did not occur.Comment: Accepted for publication in Astronomy & Astrophysics (June 2006
Desenvolvimento de ferramenta de extração de atributos para gabarito eletrônico para valoração de frutas e hortaliças frescas.
Classification of algebras with minimal quadratic growth of identities
The main goal of this paper is to prove that the five algebraswhich were used in [3] to classify (up to PI-equivalence) thealgebras whose sequence of codimensions is bounded by a linear functiongenerate the only five minimal varieties of quadratic growth
Tuning the atomic and domain structure of epitaxial films of multiferroic BiFeO3
Recent works have shown that the domain walls of room-temperature
multiferroic BiFeO3 (BFO) thin films can display distinct and promising
functionalities. It is thus important to understand the mechanisms underlying
domain formation in these films. High-resolution x-ray diffraction and
piezo-force microscopy, combined with first-principles simulations, have
allowed us to characterize both the atomic and domain structure of BFO films
grown under compressive strain on (001)-SrTiO3, as a function of thickness. We
derive a twining model that describes the experimental observations and
explains why the 71o domain walls are the ones commonly observed in these
films. This understanding provides us with a new degree of freedom to control
the structure and, thus, the properties of BiFeO3 thin films.Comment: RevTeX; 4 two-column pages; 4 color figures. Figure 2b does not seem
to display well. A proper version can be found in the source fil
Characterization of Plum Procyanidins by Thiolytic Depolymerization
The phenolic compounds of ?Green Gage? (GG) plums (Prunus domestica L.), ?Rainha Cla?udia Verde?, from a ?protected designation of origin? (PDO), in Portugal, were quantified in both flesh and skin tissues of plums collected in two different orchards (GG-V and GG-C). Analyzes of phenolic compounds were also performed on another GG European plum obtained in France (GG-F) and two other French plums, ?Mirabelle? (M) and ?Golden Japan? (GJ). Thiolysis was used for the first time in the analysis of plum phenolic compounds. This methodology showed that the flesh and skin contain a large proportion of flavan-3-ols, which account, respectively, for 92 and 85% in GJ, 61 and 44% in GG-V, 62 and 48% in GG-C, 54 and 27% in M, and 45 and 37% in GG-F. Terminal units of procyanidins observed in plums are mainly (+)-catechin (54?77% of all terminal units in flesh and 57?81% in skin). The GJ plums showed a phenolic composition different from all of the others, with a lower content of chlorogenic acid isomers and the presence of A-type procyanidins as dimers and terminal residues of polymerized forms. The average degree of polymerization (DPn) of plum procyanidins was higher in the flesh (5?9 units) than in the skin (4?6 units). Procyanidin B7 was observed in the flesh of all GG plums and in the skin of the Portuguese ones. Principal component analysis of the phenolic composition of the flesh and skin of these plums obtained after thiolysis allowed their distinction according to the variety and origin, opening the possibility of the use of phenolic composition for variety/origin identification
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