1,098 research outputs found
Thermally activated exchange narrowing of the Gd3+ ESR fine structure in a single crystal of Ce1-xGdxFe4P12 (x = 0.001) skutterudite
We report electron spin resonance (ESR) measurements in the Gd3+ doped
semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the
temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and
hyperfine structures coalesce into a broad inhomogeneous single resonance. At T
= 200 K the line narrows and as T increases further, the resonance becomes
homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest
that the origin of these features may be associated to a subtle interdependence
of thermally activated mechanisms that combine: i) an increase with T of the
density of activated conduction-carriers across the T-dependent semiconducting
pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange
interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the
thermally activated conduction-carriers and; iii) a relatively weak confining
potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which
allows the rare-earths to become rattler Einstein oscillators above T = 148 K.
We argue that the rattling of the Gd3+ ions, via a motional narrowing
mechanism, also contributes to the coalescence of the ESR fine and hyperfine
structure.Comment: 7 pages, 9 figures, accepted for publication in Phys Rev
Optimality and Complexity in Measured Quantum-State Stochastic Processes
If an experimentalist observes a sequence of emitted quantum states via
either projective or positive-operator-valued measurements, the outcomes form a
time series. Individual time series are realizations of a stochastic process
over the measurements' classical outcomes. We recently showed that, in general,
the resulting stochastic process is highly complex in two specific senses: (i)
it is inherently unpredictable to varying degrees that depend on measurement
choice and (ii) optimal prediction requires using an infinite number of
temporal features. Here, we identify the mechanism underlying this
complicatedness as generator nonunifilarity -- the degeneracy between sequences
of generator states and sequences of measurement outcomes. This makes it
possible to quantitatively explore the influence that measurement choice has on
a quantum process' degrees of randomness and structural complexity using
recently introduced methods from ergodic theory. Progress in this, though,
requires quantitative measures of structure and memory in observed time series.
And, success requires accurate and efficient estimation algorithms that
overcome the requirement to explicitly represent an infinite set of predictive
features. We provide these metrics and associated algorithms, using them to
design informationally-optimal measurements of open quantum dynamical systems.Comment: 31 pages, 6 appendices, 22 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/qdic.ht
Bases socio-antropológicas del sistema de alimentación ticuna y huitoto
Se sabe poco sobre los hábitos alimenticios tradicionales y actuales de los pueblos indígenas amazónicos. Este documento ilustra la evolución de la gastronomía de los pueblos Ticuna y Huitoto que habitan la Amazonia colombiana.Gauza gutxi dakigu Amazoniako herri indigenen jateko ohitura tradizionalez eta oraingoez. Dokumentu honek Kolonbiako Amazonian bizi diren Tikuna eta Huitoto herrien gastronomiaren bilakaera azaltzen du.On ne sait pas grand chose sur les habitudes alimentaires traditionnelles et actuelles des peuples indigènes amazoniens. Ce document illustre l'évolution de la gastronomie des peuples Ticuna et Huitoto qui habitent l'Amazonie colombienne.Very little is known on the traditional and current food habit s of indigenous peoples in the Amazon region. This document illustrates the evolution of gastronomy of the Ticuna and Huitoto peoples that inhabit the Colombian Amazonia
Collapse of the ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor
Experiments on the Electron Spin Resonance (ESR) in the filled
skutterudite (), at temperatures
where the host resistivity manifests a smooth insulator-metal crossover,
provides evidence of the underlying Kondo physics associated with this system.
At low temperatures (below ), behaves
as a Kondo-insulator with a relatively large hybridization gap, and the
ESR spectra displays a fine structure with lorentzian line shape,
typical of insulating media. The electronic gap is attributed to the large
hybridization present in the coherent regime of a Kondo lattice, when Ce
4f-electrons cooperate with band properties at half-filling. Mean-field
calculations suggest that the electron-phonon interaction is fundamental at
explaining the strong 4f-electron hybridization in this filled skutterudite.
The resulting electronic structure is strongly temperature dependent, and at
about the system undergoes an insulator-to-metal
transition induced by the withdrawal of 4f-electrons from the Fermi volume, the
system becoming metallic and non-magnetic. The ESR fine structure
coalesces into a single dysonian resonance, as in metals. Still, our
simulations suggest that exchange-narrowing via the usual Korringa mechanism,
alone, is not capable of describing the thermal behavior of the ESR spectra in
the entire temperature region ( - K). We propose that temperature
activated fluctuating-valence of the Ce ions is the missing ingredient that,
added to the usual exchange-narrowing mechanism, fully describes this unique
temperature dependence of the ESR fine structure observed in
.Comment: 19 pages, 6 figure
Nonlinear dynamics of coupled transverse-rotational waves in granular chains
The nonlinear dynamics of coupled waves in one-dimensional granular chains with and without a substrate
is theoretically studied accounting for quadratic nonlinearity. The multiple time scale method is used to derive
the nonlinear dispersion relations for infinite granular chains and to obtain the wave solutions for semiinfinite
systems. It is shown that the sum-frequency and difference-frequency components of the coupled
transverse-rotational waves are generated due to their nonlinear interactions with the longitudinal wave.
Nonlinear resonances are not present in the chain with no substrate where these frequency components have
low amplitudes and exhibit beating oscillations. In the chain positioned on a substrate two types of nonlinear
resonances are predicted. At resonance, the fundamental frequency wave amplitudes decrease and the
generated frequency component amplitudes increase along the chain, accompanied by the oscillations due to
the wave numbers asynchronism. The results confirm the possibility of a highly efficient energy transfer
between the waves of different frequencies, which could find applications in the design of acoustic devices
for energy transfer and energy rectification
Long-term magnetic anomalies and their possible relationship to the latest greater Chilean earthquakes in the context of the seismo-electromagnetic theory
Several magnetic measurements and theoretical developments from different
research groups have shown certain relationships with worldwide geological
processes. Secular variation in geomagnetic cutoff rigidity, magnetic
frequencies, or magnetic anomalies have been linked with spatial properties
of active convergent tectonic margins or earthquake occurrences during
recent years. These include the rise in similar fundamental frequencies in
the range of microhertz before the Maule 2010, Tōhoku 2011, and Sumatra–Andaman 2004
earthquakes and the dramatic rise in the cumulative number of magnetic
anomalous peaks before several earthquakes such as Nepal 2015 and Mexico (Puebla) 2017. Currently, all of these measurements have been physically
explained by the microcrack generation due to uniaxial stress change in rock
experiments. The basic physics of these experiments have been used to
describe the lithospheric behavior in the context of the
seismo-electromagnetic theory. Due to the dramatic increase in experimental
evidence, physical mechanisms, and the theoretical framework, this paper analyzes
vertical magnetic behavior close to the three latest main earthquakes in
Chile: Maule 2010 (Mw 8.8), Iquique 2014 (Mw 8.2), and Illapel 2015 (Mw 8.3).
The fast Fourier transform (FFT), wavelet transform, and daily cumulative number of anomalies methods
were used during quiet space weather time during 1 year before and after
each earthquake in order to filter space influence. The FFT method confirms the
rise in the power spectral density in the millihertz range 1 month before each
earthquake, which decreases to lower values some months after
earthquake occurrence. The cumulative anomaly method exhibited an increase
prior to each Chilean earthquake (50–90 d prior to earthquakes) similar
to those found for Nepal 2015 and Mexico 2017. The wavelet analyses also
show similar properties to FFT analysis. However, the lack of
physics-based constraints in the wavelet analysis does not allow conclusions that are
as strong as those made by FFT and cumulative methods. By using these results and previous
research, it could be stated that these magnetic features could give seismic
information about impending events. Additionally, these results could be
related to the lithosphere–atmosphere–ionosphere coupling (LAIC effect) and
the growth of microcracks and electrification in rocks described by the
seismo-electromagnetic theory.</p
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