131 research outputs found
Analysis of self--averaging properties in the transport of particles through random media
We investigate self-averaging properties in the transport of particles
through random media. We show rigorously that in the subdiffusive anomalous
regime transport coefficients are not self--averaging quantities. These
quantities are exactly calculated in the case of directed random walks. In the
case of general symmetric random walks a perturbative analysis around the
Effective Medium Approximation (EMA) is performed.Comment: 4 pages, RevTeX , No figures, submitted to Physical Review E (Rapid
Communication
Giant Optical Polarization Rotation Induced by Spin-Orbit Coupling in Polarons
We have uncovered a giant gyrotropic magneto-optical response for doped
ferromagnetic manganite La2/3Ca1/3MnO3 around the near room-temperature
paramagnetic-to-ferromagnetic transition. At odds with current wisdom, where
this response is usually assumed to be fundamentally fixed by the electronic
band structure, we point to the presence of small polarons as the driving force
for this unexpected phenomenon. We explain the observed properties by the
intricate interplay of mobility, Jahn-Teller effect and spin-orbit coupling of
small polarons. As magnetic polarons are ubiquitously inherent to many strongly
correlated systems, our results provide an original, general pathway towards
the generation of gigantic gyrotropic responses that can be harnessed for
nonreciprocal devices that exploit the polarization of light
A Unified Framework for Reservoir Computing and Extreme Learning Machines based on a Single Time-delayed Neuron
In this paper we present a unified framework for extreme learning machines and reservoir computing (echo state networks), which can be physically implemented using a single nonlinear neuron subject to delayed feedback. The reservoir is built within the delay-line, employing a number of “virtual” neurons. These virtual neurons receive random projections from the input layer containing the information to be processed. One key advantage of this approach is that it can be implemented efficiently in hardware. We show that the reservoir computing implementation, in this case optoelectronic, is also capable to realize extreme learning machines, demonstrating the unified framework for both schemes in software as well as in hardware
Multiple strain-induced phase transitions in LaNiO3 thin films
Strain effects on epitaxial thin films of LaNiO3 grown on different single
crystalline substrates are studied by Raman scattering and first-principles
simulation. New Raman modes, not present in bulk or fully-relaxed films, appear
under both compressive and tensile strains, indicating symmetry reductions.
Interestingly, the Raman spectra and the underlying crystal symmetry for
tensile and compressively strained films are different. Extensive mapping of
LaNiO3 phase stability is addressed by simulations, showing that a variety of
crystalline phases are indeed stabilized under strain which may impact the
electronic orbital hierarchy. The calculated Raman frequencies reproduce the
principal features of the experimental spectra, supporting the validity of the
multiple strain-driven structural transitions predicted by the simulations.Comment: 18 pages, 7 figure
Elevational and local climate variability predicts thermal breadth of mountain tropical tadpoles
The climate variability hypothesis posits that increased environmental thermal variation should select for thermal generalists, while stable environments should favor thermal specialists. This hypothesis has been tested on large spatial scales, such as latitude and elevation, but less so on smaller scales reflective of the experienced microclimate. Here, we estimated thermal tolerance limits of 75 species of amphibian tadpoles from an aseasonal tropical mountain range of the Ecuadorian Andes, distributed along a 3500 m elevational range, to test the climatic variability hypothesis at a large (elevation) and a small (microhabitat) scale. We show how species from less variable thermal habitats, such as lowlands and those restricted to streams, exhibit narrower thermal tolerance breadths than highland and pond-dwelling species respectively. Interestingly, while broader thermal tolerance breadths at large scales are driven by higher cold tolerance variation (heat-invariant hypothesis), at local scales they are driven by higher heat tolerance variation. This contrasting pattern may result from divergent selection on both thermal limits to face environmental thermal extremes at different scales. Specifically, within the same elevational window, exposure to extreme maximum temperatures could be avoided through habitat shifts from temporary ponds to permanent ponds or streams, while minimum peak temperatures remained invariable between habitats but steadily decreased with elevation. Therefore an understanding of the effects of habitat conversion is crucial for future research on resilience to climate change
Approach to predictability via anticipated synchronization
Predictability of chaotic systems is limited, in addition to the precision of the knowledge of the initial conditions, by the error of the models used to extract the nonlinear dynamics from the time series. In this paper, we analyze the predictions obtained from the anticipated synchronization scheme using a chain of slave neural network approximate replicas of the master system. We compare the maximum prediction horizons obtained with those attainable using standard prediction techniques
Voltage-driven displacement of magnetic vortex cores
Magnetic vortex cores in polycrystalline Ni discs underwent non-volatile displacements due to voltage-driven ferroelectric domain switching in single-crystal BaTiO3. This behaviour was observed using photoemission electron microscopy to image both the ferromagnetism and ferroelectricity, while varying in-plane sample orientation. The resulting vector maps of disc magnetization match well with micromagnetic simulations, which show that the vortex core is translated by the transit of a ferroelectric domain wall, and thus the inhomogeneous strain with which it is associated. The non-volatility is attributed to pinning inside the discs. Voltage-driven displacement of magnetic vortex cores is novel, and opens the way for studying voltage-driven vortex dynamics
Exact expression for the diffusion propagator in a family of time-dependent anharmonic potentials
We have obtained the exact expression of the diffusion propagator in the
time-dependent anharmonic potential . The
underlying Euclidean metric of the problem allows us to obtain analytical
solutions for a whole family of the elastic parameter a(t), exploiting the
relation between the path integral representation of the short time propagator
and the modified Bessel functions. We have also analyzed the conditions for the
appearance of a non-zero flow of particles through the infinite barrier located
at the origin (b<0).Comment: RevTex, 19 pgs. Accepted in Physical Review
VISIR: experiences and challenges
It is of crucial importance the integration of practical
sessions in engineering curricula owing to their significant
role in understanding engineering concepts and scientific
phenomena. However, the lack of practical sessions due
to the high costs of the equipment and the unavailability of
instructors has caused a significant declination in experimentation
in engineering education. Remote laboratories
have tackled this issues providing online reusable and
shared workbenches unconstrained by neither geographical
nor time considerations. Thereby, they have extremely proliferated
among universities and integrated into engineering
curricula over the last decade. This contribution compiles
diverse experiences based on the deployment of the remote
laboratory, Virtual Instrument Systems in Reality (VISIR),
on the practices of undergraduate engineering grades at
various universities within the VISIR community. It aims to
show the impact of its usage on engineering education concerning
the assessments of students and teachers as well. In
addition, the paper address the next challenges and future
works carried out at several universities within the VISIR
community
Wax worm saliva and the enzymes therein are the key to polyethylene degradation by Galleria mellonella
Plastic degradation by biological systems with re-utilization of the by-products could be a future solution to the global threat of plastic waste accumulation. Here, we report that the saliva of Galleria mellonella larvae (wax worms) is capable of oxidizing and depolymerizing polyethylene (PE), one of the most produced and sturdy polyolefin-derived plastics. This effect is achieved after a few hours’ exposure at room temperature under physiological conditions (neutral pH). The wax worm saliva can overcome the bottleneck step in PE biodegradation, namely the initial oxidation step. Within the saliva, we identify two enzymes, belonging to the phenol oxidase family, that can reproduce the same effect. To the best of our knowledge, these enzymes are the first animal enzymes with this capability, opening the way to potential solutions for plastic waste management through bio-recycling/up-cycling
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