11,235 research outputs found
Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO
Neutron scattering studies of single-crystal LiNiPO reveal a spontaneous
first-order commensurate-incommensurate magnetic phase transition. Short- and
long-range incommensurate phases are intermediate between the high temperature
paramagnetic and the low temperature antiferromagnetic phases. The modulated
structure has a predominant antiferromagnetic component, giving rise to
satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg
reflection, and a ferromagnetic component giving rise to peaks at small
momentum-transfers around the origin at . The wavelength of the
modulated magnetic structure varies continuously with temperature. It is argued
that the incommensurate short- and long-range phases are due to
spin-dimensionality crossover from a continuous to the discrete Ising state.
These observations explain the anomalous first-order transition seen in the
magnetoelectric effect of this system
Impact of noise on a dynamical system: prediction and uncertainties from a swarm-optimized neural network
In this study, an artificial neural network (ANN) based on particle swarm
optimization (PSO) was developed for the time series prediction. The hybrid
ANN+PSO algorithm was applied on Mackey--Glass chaotic time series in the
short-term . The performance prediction was evaluated and compared with
another studies available in the literature. Also, we presented properties of
the dynamical system via the study of chaotic behaviour obtained from the
predicted time series. Next, the hybrid ANN+PSO algorithm was complemented with
a Gaussian stochastic procedure (called {\it stochastic} hybrid ANN+PSO) in
order to obtain a new estimator of the predictions, which also allowed us to
compute uncertainties of predictions for noisy Mackey--Glass chaotic time
series. Thus, we studied the impact of noise for several cases with a white
noise level () from 0.01 to 0.1.Comment: 11 pages, 8 figure
Quasi-energy spectra of graphene dots under intense ac field: field anisotropy and photon dressed quantum rings
A graphene quantum dot under intense ac field and static low magnetic field
is investigated. From a tight-binding perspective, applying a Fourier-Floquet
transformation and renormalization process, we observe that graphene
-intrinsically anisotropic- reveals field polarization signatures in the
quasi-density of states. For the ac field polarized along the armchair
direction, the dressed electronic structure shows an emergent property: an ac
field induced quantum ring. This is inferred by the orientation-dependent
formation of a miniband of energy states periodically modulated with increasing
magnetic field, exactly analogous to the behavior of a quantum ring spectrum.Comment: 6 pages, 6 figure
The Stable Poor and Criticism of Poverty Area Agencies
International and cross-cultural research concerning populations living in poverty have uncovered similarities in attitudes and behaviors associated with participation in society\u27s institutional systems. One of these similarities is that feelings of alienation are an inevitable reaction of the poor to their marginal position in a class-stratified, highly individuated, capitalistic society (Lewis, 1966:21). These feelings, in turn, have led poor people in general to withdraw from participation in community life, including the community\u27s institutions charged with the task of delivering services associated with physical welfare. The central task of this paper is to report findings that suggest that the degree of social stability among a poverty sample is inversely associated with favorable attitudes toward a public clinic\u27s nurse practitioner program charged with the task of treating infants
On the Proof of Dark Matter, the Law of Gravity and the Mass of Neutrinos
We develop a new method to predict the density associated with weak lensing
maps of (un)relaxed clusters in a range of theories interpolating between GR
and MOND (General Relativity and Modified Newtonian Dynamics). We apply it to
fit the lensing map of the bullet merging cluster 1E0657-56, in order to
constrain more robustly the nature and amount of collisionless matter in
clusters {\it beyond} the usual assumption of spherical equilibrium
(Pointecouteau & Silk 2005) and the validity of GR on cluster scales (Clowe et
al. 2006). Strengthening the proposal of previous authors we show that the
bullet cluster is dominated by a collisionless -- most probably non-baryonic --
component in GR as well as in MOND, a result consistent with the dynamics of
many X-ray clusters. Our findings add to the number of known pathologies for a
purely baryonic MOND, including its inability to fit the latest data from the
Wilkinson Microwave Anisotropy Probe. A plausible resolution of all these
issues and standard issues of Cold Dark Matter with galaxy rotation curves is
the "marriage" of MOND with ordinary hot neutrinos of 2eV. This prediction is
just within the GR-independent maximum of neutrino mass from current
-decay experiments, and is falsifiable by the Karlsruhe Tritium Neutrino
(KATRIN) experiment by 2009. Issues of consistency with strong lensing arcs and
the large relative velocity of the two clusters comprising the bullet cluster
are also addressed.Comment: 4 pages, 1 figure, accepted for publication in ApJL. Added a simple
model of the bullet cluster's high velocity in TeVeS, and discussions of
sterile neutrinos and of non-uniqueness of the lensing deprojectio
Determination of seismogenic interplate contact zone and crustal seismicity around Antofagasta, Northern Chile using local data
International audienc
Inverse velocity statistics in two dimensional turbulence
We present a numerical study of two-dimensional turbulent flows in the
enstrophy cascade regime, with different large-scale forcings and energy sinks.
In particular, we study the statistics of more-than-differentiable velocity
fluctuations by means of two recently introduced sets of statistical
estimators, namely {\it inverse statistics} and {\it second order differences}.
We show that the 2D turbulent velocity field, , cannot be simply
characterized by its spectrum behavior, . There
exists a whole set of exponents associated to the non-trivial smooth
fluctuations of the velocity field at all scales. We also present a numerical
investigation of the temporal properties of measured in different
spatial locations.Comment: 9 pages, 12 figure
Seismic source study of the 1989, October 29, Chenoua (Algeria) earthquake from aftershocks, broad-band and strong ground motion records
The broad-band teleseismics records of the earthquake of October 29,1989 in Algeria (MW = 6.0) allow a detailed
study of the rupture process of this earthquake. The focal mechanism obtained by P and SH modeling corresponds
to reverse faulting with a small amount of left-lateral movement along a fault striking 246° and dipping 56°. The
rupture is found to be complex with two sub-events separated in time but occurring on the same plane. The lowfrequency
records of an accelerometer located some 25 km to the west of the main shock are also better fi tted when
the rupture is composed of a double pulse. In the two cases, there is strong evidence for the rupture to propagate
from south-west towards north-east.The relocalisation of the main shock by using a master-event technique and
the data from Italian and Spanish stations led to the same conclusions. Soon after the main event, a temporary
seimic network was installed in the epicentral area. The aftershock clouds defi ne a SW-NE fault dipping to the NW
compatible with the results of the modelisations of the teleseismic body-waves and the accelerogram. The focal
mechanisms correspond mainly to reverse faulting. The maximum principal direction of the stress tensor obtained
from the inversion is about N-S and the minimum is vertical, typical of a compressive regime. The Chenoua
earthquake took place on a fault which was not recognized as active. Repeated comparable seismic events on this
fault and on the fault that borders the massif to the south explain this intriguing topographic feature
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