Coexisting Pulses in a Model for Binary-Mixture Convection

We address the striking coexistence of localized waves (`pulses') of different lengths which was observed in recent experiments and full numerical simulations of binary-mixture convection. Using a set of extended Ginzburg-Landau equations, we show that this multiplicity finds a natural explanation in terms of the competition of two distinct, physical localization mechanisms; one arises from dispersion and the other from a concentration mode. This competition is absent in the standard Ginzburg-Landau equation. It may also be relevant in other waves coupled to a large-scale field.Comment: 5 pages revtex with 4 postscript figures (everything uuencoded

Phase Diffusion in Localized Spatio-Temporal Amplitude Chaos

We present numerical simulations of coupled Ginzburg-Landau equations describing parametrically excited waves which reveal persistent dynamics due to the occurrence of phase slips in sequential pairs, with the second phase slip quickly following and negating the first. Of particular interest are solutions where these double phase slips occur irregularly in space and time within a spatially localized region. An effective phase diffusion equation utilizing the long term phase conservation of the solution explains the localization of this new form of amplitude chaos.Comment: 4 pages incl. 5 figures uucompresse

Detecting Spatial Orientation Demands during Virtual Navigation using EEG Brain Sensing

This study shows how brain sensing can offer insight to the evaluation of human spatial orientation in virtual reality (VR) and establish a role for electroencephalogram (EEG) in virtual navigation. Research suggests that the evaluation of spatial orientation in VR benefits by goingbeyond performance measures or questionnaires to measurements of the user’s cognitive state. While EEG has emerged as a practical brain sensing technology in cognitive research, spatial orientation tasks often rely on multiple factors (e.g., reference frame used, ability to update simulated rotation, and/or left-right confusion) which may be inaccessible to this measurement. EEG has been shown to correlate with human spatial orientation in previous research. In this paper, we use convolutional neural network (CNN), an advanced technique in machine learning, to train a detection model that can identify moments in which VR users experienced some increase in spatial orientation demands in real-time. Our results demonstrate that we can indeed use machine learning technique to detect such cognitive state of increasing spatial orientation demands in virtual reality research with 96% accurate on average

Attractive Interaction Between Pulses in a Model for Binary-Mixture Convection

Recent experiments on convection in binary mixtures have shown that the interaction between localized waves (pulses) can be repulsive as well as {\it attractive} and depends strongly on the relative {\it orientation} of the pulses. It is demonstrated that the concentration mode, which is characteristic of the extended Ginzburg-Landau equations introduced recently, allows a natural understanding of that result. Within the standard complex Ginzburg-Landau equation this would not be possible.Comment: 7 pages revtex with 3 postscript figures (uuencoded

Dynamic visual information facilitates object recognition from novel viewpoints

Normally, people have difficulties recognizing objects from novel as compared to learned views, resulting in increased reaction times and errors. Recent studies showed, however, that this "view-dependency" can be reduced or even completely eliminated when novel views result from observer's movements instead of object movements. This observer movement benefit was previously attributed to extra-retinal (physical motion) cues. In two experiments, we demonstrate that dynamic visual information (that would normally accompany observer's movements) can provide a similar benefit and thus a potential alternative explanation. Participants performed sequential matching tasks for Shepard-Metzler-like objects presented via head-mounted display. As predicted by the literature, object recognition performance improved when view changes (45-or 90-) resulted from active observer movements around the object instead of object movements. Unexpectedly, however, merely providing dynamic visual information depicting the viewpoint change showed an equal benefit, despite the lack of any extra-retinal/physical self-motion cues. Moreover, visually simulated rotations of the table and hidden target object (table movement condition) yielded similar performance benefits as simulated viewpoint changes (scene movement condition). These findings challenge the prevailing notion that extra-retinal (physical motion) cues are required for facilitating object recognition from novel viewpoints, and highlight the importance of dynamic visual cues, which have previously received little attention

Parametric Forcing of Waves with Non-Monotonic Dispersion Relation: Domain Structures in Ferrofluids?

Surface waves on ferrofluids exposed to a dc-magnetic field exhibit a non-monotonic dispersion relation. The effect of a parametric driving on such waves is studied within suitable coupled Ginzburg-Landau equations. Due to the non-monotonicity the neutral curve for the excitation of standing waves can have up to three minima. The stability of the waves with respect to long-wave perturbations is determined $via$ a phase-diffusion equation. It shows that the band of stable wave numbers can split up into two or three sub-bands. The resulting competition between the wave numbers corresponding to the respective sub-bands leads quite naturally to patterns consisting of multiple domains of standing waves which differ in their wave number. The coarsening dynamics of such domain structures is addressed.Comment: 23 pages, 6 postscript figures, composed using RevTeX. Submitted to PR

Worm Structure in Modified Swift-Hohenberg Equation for Electroconvection

A theoretical model for studying pattern formation in electroconvection is proposed in the form of a modified Swift-Hohenberg equation. A localized state is found in two dimension, in agreement with the experimentally observed ``worm" state. The corresponding one dimensional model is also studied, and a novel stationary localized state due to nonadiabatic effect is found. The existence of the 1D localized state is shown to be responsible for the formation of the two dimensional ``worm" state in our model

Whirling Hexagons and Defect Chaos in Hexagonal Non-Boussinesq Convection

We study hexagon patterns in non-Boussinesq convection of a thin rotating layer of water. For realistic parameters and boundary conditions we identify various linear instabilities of the pattern. We focus on the dynamics arising from an oscillatory side-band instability that leads to a spatially disordered chaotic state characterized by oscillating (whirling) hexagons. Using triangulation we obtain the distribution functions for the number of pentagonal and heptagonal convection cells. In contrast to the results found for defect chaos in the complex Ginzburg-Landau equation and in inclined-layer convection, the distribution functions can show deviations from a squared Poisson distribution that suggest non-trivial correlations between the defects.Comment: 4 mpg-movies are available at http://www.esam.northwestern.edu/~riecke/lit/lit.html submitted to New J. Physic

Direct Hopf Bifurcation in Parametric Resonance of Hybridized Waves

We study parametric resonance of interacting waves having the same wave vector and frequency. In addition to the well-known period-doubling instability we show that under certain conditions the instability is caused by a Hopf bifurcation leading to quasiperiodic traveling waves. It occurs, for example, if the group velocities of both waves have different signs and the damping is weak. The dynamics above the threshold is briefly discussed. Examples concerning ferromagnetic spin waves and surface waves of ferro fluids are discussed.Comment: Appears in Phys. Rev. Lett., RevTeX file and three postscript figures. Packaged using the 'uufiles' utility, 33 k