662 research outputs found
Excitability in a nonlinear magnetoacoustic resonator
We report a nonlinear acoustic system displaying excitability. The considered
system is a magnetostrictive material where acoustic waves are parametrically
generated. For a set of parameters, the system presents homoclinic and
heteroclinic dynamics, whose boundaries define a excitability domain. The
excitable behaviour is characterized by analyzing the response of the system to
different external stimuli. Single spiking and bursting regimes have been
identified.Comment: 4 pages, 5 figure
Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms
Ultra-low density polymers, metals, and ceramic nanofoams are valued for
their high strength-to-weight ratio, high surface area and insulating
properties ascribed to their structural geometry. We obtain the labrynthine
internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging.
Finite element analysis from the structure reveals mechanical properties
consistent with bulk samples and with a diffusion limited cluster aggregation
model, while excess mass on the nodes discounts the dangling fragments
hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference
The stability of modified gravity models
Conditions for the existence and stability of de Sitter space in modified
gravity are derived by considering inhomogeneous perturbations in a
gauge-invariant formalism. The stability condition coincides with the
corresponding condition for stability with respect to homogeneous
perturbations, while this is not the case in scalar-tensor gravity. The
stability criterion is applied to various modified gravity models of the early
and the present universe.Comment: 22 pages, LaTeX, to appear in Phys. Rev.
Who are you talking to? The role of addressee identity in utterance comprehension
Issue online: 30 March 2020Experimental evidence suggests that speaker and addressee quickly adapt to each
other from the earliest moments of sentence processing, and that interlocutor-related
information is rapidly integrated with other sources of nonpragmatic information
(e.g., semantic, morphosyntactic, etc.). These findings have been taken as support
for one-step models of sentence comprehension. The results from the present eventrelated
potential study challenge this theoretical framework providing a case where
discourse level information is integrated only at a late stage of processing, when
morphosyntactic analysis has been already initiated. We considered the case of
Basque allocutive agreement, where information about addressee gender is encoded
in verbal inflection. Two different types of Basque grammatical violations were presented
together with the corresponding control conditions: one could be detected
based on a morphosyntactic mismatch (person agreement violation), while the other
could be detected only if the addressee's gender was considered (allocutive violation).
Morphosyntactic violations elicited greater N400 effects followed by P600
effects, while allocutive violations elicited only P600 effects. These results provide
new constraints to one-step accounts as they represent a case where speakers do not
immediately adjust to the addressee's perspective. We propose that the relevance of
discourse-level information might be a crucial variable to reconcile the dichotomy
between one- and two-step models.Horizon 2020 Framework Programme,
Grant/Award Number: H2020-MSCAIF-
2018-837228; Fundación BBVA, Grant/
Award Number: IN[18]_HMS_LIN_0058;
Ministerio de Economía y Competitividad,
Grant/Award Number: IJCI-2016-27702,
PSI2014-54500, RYC 2017-22015 and
SEV-2015-490; Eusko Jaurlaritza, Grant/
Award Number: PI_2015_1_25; Gipuzkoa
Fellowship Program, Grant/Award Number:
FFI2016-76432-P. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 83722
Kneadings, Symbolic Dynamics and Painting Lorenz Chaos. A Tutorial
A new computational technique based on the symbolic description utilizing
kneading invariants is proposed and verified for explorations of dynamical and
parametric chaos in a few exemplary systems with the Lorenz attractor. The
technique allows for uncovering the stunning complexity and universality of
bi-parametric structures and detect their organizing centers - codimension-two
T-points and separating saddles in the kneading-based scans of the iconic
Lorenz equation from hydrodynamics, a normal model from mathematics, and a
laser model from nonlinear optics.Comment: Journal of Bifurcations and Chaos, 201
Analysis of the shearing instability in nonlinear convection and magnetoconvection
Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced
Experience-based behavioral and chemosensory changes in the generalist insect herbivore Helicoverpa armigera exposed to two deterrent plant chemicals
Behavioral and electrophysiological responses of larvae of the polyphagous moth species Helicoverpa armigera to two plant-derived allelochemicals were studied, both in larvae that had been reared on a diet devoid of these compounds and in larvae previously exposed to these compounds. In dual-choice cotton leaf disk and pepper fruit disk arena assays, caterpillars reared on a normal artificial diet were strongly deterred by strychnine and strophanthin-K. However, caterpillars reared on an artificial diet containing strychnine were insensitive to strychnine and strophanthin-K. Similarly, caterpillars reared on an artificial diet containing strophanthin-K were also desensitized to both deterrent chemicals. Electrophysiological tests revealed that the deterrent-sensitive neurons in taste sensilla on the maxillae of caterpillars reared on each deterrent-containing diet displayed reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets. We conclude that the experience-dependent behavioral plasticity was partly based on the reduced sensitivity of taste receptor neurons and that the desensitization of taste receptor neurons contributed to the cross-habituation to the two chemicals
Microbiota in exhaled breath condensate and the lung
The lung microbiota is commonly sampled using relatively invasive bronchoscopic procedures. Exhaled breath condensate (EBC) collection potentially offers a less invasive alternative for lung microbiota sampling. We compared lung microbiota samples retrieved by protected specimen brushings (PSB) and exhaled breath condensate collection. We also sought to assess whether aerosolized antibiotic treatment would influence the lung microbiota and whether this change could be detected in EBC. EBC was collected from 6 conscious sheep and then from the same anesthetized sheep during mechanical ventilation. Following the latter EBC collection, PSB samples were collected from separate sites within each sheep lung. On the subsequent day, each sheep was then treated with nebulized colistimethate sodium. Two days after nebulization, EBC and PSB samples were again collected. Bacterial DNA was quantified using 16S rRNA gene quantitative PCR. The V2-V3 region of the 16S rRNA gene was amplified by PCR and sequenced using Illumina MiSeq. Quality control and operational taxonomic unit (OTU) clustering were performed with mothur. The EBC samples contained significantly less bacterial DNA than the PSB samples. The EBC samples from anesthetized animals clustered separately by their bacterial community compositions in comparison to the PSB samples, and 37 bacterial OTUs were identified as differentially abundant between the two sample types. Despite only low concentrations of colistin being detected in bronchoalveolar lavage fluid, PSB samples were found to differ by their bacterial compositions before and after colistimethate sodium treatment. Our findings indicate that microbiota in EBC samples and PSB samples are not equivalent
Rigorous Theory of Optical Trapping by an Optical Vortex Beam
We propose a rigorous theory for the optical trapping by optical vortices,
which is emerging as an important tool to trap mesoscopic particles. The common
perception is that the trapping is solely due to the gradient force, and may be
characterized by three real force constants. However, we show that the optical
vortex trap can exhibit complex force constants, implying that the trapping
must be stabilized by ambient damping. At different damping levels, particle
shows remarkably different dynamics, such as stable trapping, periodic and
aperiodic orbital motions
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