13,841 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
Composição florÃstica e análise fitossociológica da floresta com araucária presente na reserva florestal Embrapa/Epagri, Caçador, SC, Brasil.
EVINCI. Resumo 036
Pressure measurements on a rectangular wing with a NACA0012 airfoil during conventional flutter
The Structural Dynamics Division at NASA LaRC has started a wind tunnel activity referred to as the Benchmark Models Program. The primary objective of the program is to acquire measured dynamic instability and corresponding pressure data that will be useful for developing and evaluating aeroelastic type CFD codes currently in use or under development. The program is a multi-year activity that will involve testing of several different models to investigate various aeroelastic phenomena. The first model consisted of a rigid semispan wing having a rectangular planform and a NACA 0012 airfoil shape which was mounted on a flexible two degree-of-freedom mount system. Two wind-tunnel tests were conducted with the first model. Several dynamic instability boundaries were investigated such as a conventional flutter boundary, a transonic plunge instability region near Mach = 0.90, and stall flutter. In addition, wing surface unsteady pressure data were acquired along two model chords located at the 60 to 95-percent span stations during these instabilities. At this time, only the pressure data for the conventional flutter boundary is presented. The conventional flutter boundary and the wing surface unsteady pressure measurements obtained at the conventional flutter boundary test conditions in pressure coefficient form are presented. Wing surface steady pressure measurements obtained with the model mount system rigidized are also presented. These steady pressure data were acquired at essentially the same dynamic pressure at which conventional flutter had been encountered with the mount system flexible
NACA0012 benchmark model experimental flutter results with unsteady pressure distributions
The Structural Dynamics Division at NASA Langley Research Center has started a wind tunnel activity referred to as the Benchmark Models Program. The primary objective of this program is to acquire measured dynamic instability and corresponding pressure data that will be useful for developing and evaluating aeroelastic type computational fluid dynamics codes currently in use or under development. The program is a multi-year activity that will involve testing of several different models to investigate various aeroelastic phenomena. This paper describes results obtained from a second wind tunnel test of the first model in the Benchmark Models Program. This first model consisted of a rigid semispan wing having a rectangular planform and a NACA 0012 airfoil shape which was mounted on a flexible two degree of freedom mount system. Experimental flutter boundaries and corresponding unsteady pressure distribution data acquired over two model chords located at the 60 and 95 percent span stations are presented
Determination of masses and other properties of extra-solar planetary systems with more than one planet
Recent analysis of the Doppler shift oscillations of the light from
extra-solar planetary systems indicate that some of these systems have more
than one large planet. In this case it has been shown that the masses of these
planets can be determined without the familiar ambiguity due to the unknown
inclination angle of the plane of the orbit of the central star provided,
however, that its mass is known. A method is presented here which determines
also a lower limit to the mass of this star from these observations. As an
illustration, our method is applied to the Keck and Lick data for GJ876.Comment: 10 pages, 17 figures. Accepted for publication in Astrophysical
Journa
Are low-frequency songs sexually selected, and do they lose their potency in male–female interactions under noisy conditions?
ABSTRACT: We agree with Halfwerk et al. on the importance of including the receivers when studying the impact of anthropogenic noise. However, we find the conclusion that the use of lowfrequency song is sexually selected in great tits and that noisy conditions affect male–female communication premature for several reasons
Extinction and Distance to Anomalous X-ray Pulsars from X-ray Scattering Halos
We analyze the X-ray scattering halos around three Galactic Anomalous X-ray
Pulsars (AXPs) in order to constrain the distance and the optical extinction of
each source. We obtain surface brightness distributions from EPIC-pn data
obtained with XMM-Newton, compare the profiles of different sources, and fit
them with a model based on the standard theory of X-ray scattering by dust
grains, both for a uniform distribution of dust along the line of sight, and
for dust distributions constrained by previous measurements. Somewhat
surprisingly, we find that for all three sources, the uniform distribution
reproduces the observed surface brightness as well as or better than the
distributions that are informed by previous constraints. Nevertheless, the
inferred total dust columns are robust, and serve to confirm that previous
measurements based on interstellar edges in high-resolution X-ray spectra and
on modelling of broad-band X-ray spectra were reliable. Specifically, we find
Av ~= 4, 6, and 8 mag for 4U 0142+61, 1E 1048.1-5937, and 1RXS
J170849.0-400910, respectively. For 1E 1048.1-5937, this is well in excess of
the extinction expected towards a HI bubble along the line of sight, thus
casting further doubt on the suggested association with the source.Comment: 8 pages, 6 figure
Condiciones orgánicas y correlaciones de fuerza del movimiento estudiantil chileno.: Una aproximación desde la Confech (2011-2015)*
This paper aims at analyzing the organizational changes in the Confederation of Chilean Students (CONFECH) in the period 2011-2015 and the complexities of the process of institutionalization in the context of the government of Sebastián Piñera and the subsequent administration of Michelle Bachelet. It argues, in the main, that the processes of growth and fragmentation of space CONFECH have generated an increase in the cost of decision-making and collective coordination has become more complex political management capacity of the Executive Board
The benchmark aeroelastic models program: Description and highlights of initial results
An experimental effort was implemented in aeroelasticity called the Benchmark Models Program. The primary purpose of this program is to provide the necessary data to evaluate computational fluid dynamic codes for aeroelastic analysis. It also focuses on increasing the understanding of the physics of unsteady flows and providing data for empirical design. An overview is given of this program and some results obtained in the initial tests are highlighted. The tests that were completed include measurement of unsteady pressures during flutter of rigid wing with a NACA 0012 airfoil section and dynamic response measurements of a flexible rectangular wing with a thick circular arc airfoil undergoing shock boundary layer oscillations
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