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"Wave motion"
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Direction-selective motion discrimination by traveling waves in visual cortex
The majority of neurons in primary visual cortex respond selectively to bars of light that have a specific orientation and move in a specific direction. The spatial and temporal responses of such neurons are non-separable. How neurons accomplish that computational feat without resort to explicit time delays is unknown. We propose a novel neural mechanism whereby visual cortex computes non-separable responses by generating endogenous traveling waves of neural activity that resonate with the space-time signature of the visual stimulus. The spatiotemporal characteristics of the response are defined by the local topology of excitatory and inhibitory lateral connections in the cortex. We simulated the interaction between endogenous traveling waves and the visual stimulus using spatially distributed populations of excitatory and inhibitory neurons with Wilson-Cowan dynamics and inhibitory-surround coupling. Our model reliably detected visual gratings that moved with a given speed and direction provided that we incorporated neural competition to suppress false motion signals in the opposite direction. The findings suggest that endogenous traveling waves in visual cortex can impart direction-selectivity on neural responses without resort to explicit time delays. They also suggest a functional role for motion opponency in eliminating false motion signals.
Journal Article
Some Characteristics of Nonlinear Potential Surface Waves in an Ideal Fluid
A potential wave motion along a free surface of a deep ideal fluid has been studied. The exact solutions of the equations of motion with the physically validated boundary conditions on a free surface have been obtained. The shape of the free surface has been studied as a function of the amplitude and the surface characteristics have been highlighted. The characteristics of waves as a function of the nonlinearity parameter have been studied.
Journal Article
Accessible Solitons
Solitons are ubiquitous. Their description involves abstruse mathematics and is limited to a two-dimensional idealization. A nonlocal model is presented that provides a radical simplification and allows for an elegant description of soliton collisions, interactions, and deformations in two and three dimensions. The model reveals an intimate connection between solitons and the linear harmonic oscillator. It foreshadows a photonic switch in which a bright beam can steer a distant dim beam, and it predicts the existence of noncircularly symmetric solitons.
Journal Article
Sound and light waves investigations
How do bats use echolocation? Why does a siren's sound change as an ambulance drives by? Why can't we see colors in a dark place? See how scientists apply the scientific method to test theories about sound and light waves.
Book
A repeating fast radio burst
Observations of repeated fast radio bursts, having dispersion measures and sky positions consistent with those of FRB 121102, show that the signals do not originate in a single cataclysmic event and may come from a young, highly magnetized, extragalactic neutron star.
FRB 121102's repeat performance
Fast radio bursts (FRBs) are transient radio pulses that last a few milliseconds. They are thought to be extragalactic, and are of unknown physical origin. Many FRB models have proposed the cause to be one-time-only cataclysmic events. Follow-up monitoring of detected bursts did not reveal repeat bursts, consistent with such models. However, this paper reports ten additional bursts from the direction of FRB 121102, demonstrating that its source survived the energetic events that caused the bursts. Although there may be multiple physical origins for the burst, the repeating bursts seen from FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.
Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances
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. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections
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. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events
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. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst
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. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star
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Journal Article
