Self-generated Field Research Articles

Active electrolocation in pulse gymnotids: sensory consequences of objects’ mutual polarization

We examined non-linear effects of the presence of one object on the electric image of another placed at the foveal region in Gymnotus omarorum. The sensory consequences of object mutual polarization on electric images were also depicted using behavioral procedures. Image measurements show that objects whose electric image is not detectable may modify the electric image of another placed closer to the fish and suggest that detection range and discrimination parameters used for one object may be affected when the presence of others enriches the scene. Behavioral experiments confirm that these changes in object images resulting from mutual polarization may be exploited for improving perception. While conductive objects close to the skin allow the fish to detect other objects placed out of the active electrodetection range, non-conductive objects may hide objects that otherwise show clear electric images. This suggests that fish movements may orient the self-generated field to exploit object mutual polarization, increasing or decreasing the active electrolocation range. In addition, images of a nearby object may be modulated by the presence of another object placed outside the detection range and the corresponding behavioral responses suggest that a moving or impedance-changing context may modify a fish's discrimination abilities for closer objects.

Scott Correction for Large Atoms and Molecules in a Self-Generated Magnetic Field

We consider a large neutral molecule with total nuclear charge $Z$ in non-relativistic quantum mechanics with a self-generated classical electromagnetic field. To ensure stability, we assume that $Z\al^2\le \kappa_0$ for a sufficiently small $\kappa_0$, where $\al$ denotes the fine structure constant. We show that, in the simultaneous limit $Z\to\infty$, $\al\to 0$ such that $\kappa =Z\al^2$ is fixed, the ground state energy of the system is given by a two term expansion $c_1Z^{7/3} + c_2(\kappa) Z^2 + o(Z^2)$. The leading term is given by the non-magnetic Thomas-Fermi theory. Our result shows that the magnetic field affects only the second (so-called Scott) term in the expansion.

Time evolution of filamentation and self-generated fields in the coronae of directly driven inertial-confinement fusion capsules

Time-gated radiography with monoenergetic 15-MeV protons, 3-MeV protons, and 4-MeV alpha particles has revealed a rich and complex evolution of electromagnetic field structures in and around imploding, directly driven inertial-confinement fusion (ICF) targets at the OMEGA laser facility. Plastic-shell capsules and solid plastic spheres were imaged during and after irradiation with ICF-relevant laser drive (up to 6 × 1014 W/cm2). Radial filaments appeared while the laser was on; they filled, and were frozen into, the out-flowing corona, persisting until well after the end of the laser drive. Data from specially designed experiments indicate that the filaments were not generated by two-plasmon-decay instabilities or by Rayleigh-Taylor instabilities associated with shell acceleration. Before the onset of visible filamentation, quasi-spherical field structures appeared outside the capsule in the images in a form that suggests outgoing shells of net positive charge. We conjecture that these discrete shells are related to multiple peaks seen previously in the spectra of protons ablated from the targets.

Numerical Techniques for the Analysis of Charge Transport and Electrodynamics in Graphene Nanoribbons

In this paper, we report on multiphysics full-wave techniques in the frequency (energy)-domain and the time-domain, aimed at the investigation of the combined electromagnetic-coherent transport problem in carbon based on nano-structured materials and devices, e.g., graphene nanoribbons. The frequency-domain approach is introduced in order to describe a Poisson/Schrödinger system in a quasi static framework. An example of the self-consistent solution of laterally coupled graphene nanoribbons is shown. The time-domain approach deals with the solution of the combined Maxwell/Schrödinger system of equations. The propagation of a charge wavepacket is reported, showing the effect of the self-generated electromagnetic field that affects the dynamics of the charge wavepacket.

Integration of visual and electrosensory information in a discrimination task

Event Abstract Back to Event Integration of visual and electrosensory information in a discrimination task Anatoli Ender1*, Jan Benda1, 2 and Jan Grewe1 1 Ludwig-Maximilians Universität München, Biologie II, Germany 2 Eberhard Karls Universität Tübingen, Institut für Neurobiologie, Germany Weakly electric fish (Apteronotus albifrons) possess an electric sense that is employed to guide their behavior under low visibility conditions. The animals produce and electric organ discharge (EOD) which leads to an electric field surrounding the fish. With cutaneous electroreceptors distributed all over their body which are tuned to the own electric field they can sense distortions of the self-generated field and use this information. Any object having a conductivity different from the surrounding medium (water) will distort the field. Strongly conductive objects locally increase the field intensity and less conductive objects locally reduce the electric field amplitude. While animals of this species are a widely used model system for studies on sensory processing. These, however, have been concentrated on the processing of electrosensory information, their visual sense has been largely neglected. Here we set out to establish a behavioral paradigm to assess learning and the integration of visual and electrosensory information. In a two-alternative-forced-choice discrimination task animals were trained to certain combinations of electrosensory and visual cues. In test experiments these cues were set into conflict. Our results show that fish of this species are well able to learn such a discrimination task yielding discrimination performances of 100% correct choices. They further can discriminate objects using visual or electrosensory information alone. In conflict situations the animals show decreased discrimination performance indicating that both senses contribute in approximately equal shares. We thus have established a behavioral paradigm that will in the future allow us to relate physiological findings back to behavior and vice versa. Keywords: behaviour, Learning, object discrimination, Perception, sensory integration, weakly electric fish Conference: Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012. Presentation Type: Poster Topic: Sensory processing and perception Citation: Ender A, Benda J and Grewe J (2012). Integration of visual and electrosensory information in a discrimination task. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference 2012. doi: 10.3389/conf.fncom.2012.55.00055 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 May 2012; Published Online: 12 Sep 2012. * Correspondence: Miss. Anatoli Ender, Ludwig-Maximilians Universität München, Biologie II, Planegg-Martinsried, Germany, anatolie@gmx.at Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Anatoli Ender Jan Benda Jan Grewe Google Anatoli Ender Jan Benda Jan Grewe Google Scholar Anatoli Ender Jan Benda Jan Grewe PubMed Anatoli Ender Jan Benda Jan Grewe Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Fish geometry and electric organ discharge determine functional organization of the electrosensory epithelium.

Active electroreception in Gymnotus omarorum is a sensory modality that perceives the changes that nearby objects cause in a self generated electric field. The field is emitted as repetitive stereotyped pulses that stimulate skin electroreceptors. Differently from mormyriformes electric fish, gymnotiformes have an electric organ distributed along a large portion of the body, which fires sequentially. As a consequence shape and amplitude of both, the electric field generated and the image of objects, change during the electric pulse. To study how G. omarorum constructs a perceptual representation, we developed a computational model that allows the determination of the self-generated field and the electric image. We verify and use the model as a tool to explore image formation in diverse experimental circumstances. We show how the electric images of objects change in shape as a function of time and position, relative to the fish's body. We propose a theoretical framework about the organization of the different perceptive tasks made by electroreception: 1) At the head region, where the electrosensory mosaic presents an electric fovea, the field polarizing nearby objects is coherent and collimated. This favors the high resolution sampling of images of small objects and perception of electric color. Besides, the high sensitivity of the fovea allows the detection and tracking of large faraway objects in rostral regions. 2) In the trunk and tail region a multiplicity of sources illuminate different regions of the object, allowing the characterization of the shape and position of a large object. In this region, electroreceptors are of a unique type and capacitive detection should be based in the pattern of the afferents response. 3) Far from the fish, active electroreception is not possible but the collimated field is suitable to be used for electrocommunication and detection of large objects at the sides and caudally.

Modulational Instability for Gravitoelectromagnetic Perturbations with Longitudinal and Transverse Modes

The modulational instability for longitudinal and transverse gravitoelectromagnetic (GEM) perturbations is investigated on the basis of the self-generated gravitomagnetic field equations in a self-gravitating system. Analytical results indicate that the instability may lead the initially uniformly distributed matter collapse into a small region where the density of matter and the quasi-static self-generated gravitomagnetic field are strongly enhanced. There will be a pancake-like structure because the characteristic scale of longitudinal perturbation is much larger than the transverse one. The anisotropic accumulation of matter and the generation of a gravitomagnetic field are in favor of the formation of a rotationally pancake-like structure.

An integrated model of fixational eye movements and microsaccades

When we fixate a stationary target, our eyes generate miniature (or fixational) eye movements involuntarily. These fixational eye movements are classified as slow components (physiological drift, tremor) and microsaccades, which represent rapid, small-amplitude movements. Here we propose an integrated mathematical model for the generation of slow fixational eye movements and microsaccades. The model is based on the concept of self-avoiding random walks in a potential, a process driven by a self-generated activation field. The self-avoiding walk generates persistent movements on a short timescale, whereas, on a longer timescale, the potential produces antipersistent motions that keep the eye close to an intended fixation position. We introduce microsaccades as fast movements triggered by critical activation values. As a consequence, both slow movements and microsaccades follow the same law of motion; i.e., movements are driven by the self-generated activation field. Thus, the model contributes a unified explanation of why it has been a long-standing problem to separate slow movements and microsaccades with respect to their motion-generating principles. We conclude that the concept of a self-avoiding random walk captures fundamental properties of fixational eye movements and provides a coherent theoretical framework for two physiologically distinct movement types.

Modeling of PZT Ferroelectric Ceramic Depolarization Driven by Shock Stress

Shock-induced phase transition of ferroelectric ceramic PZT 95/5 causes elastic stiffening and depolarization, releasing stored electrostatic energy into the load circuit. We develop a model to describe the response of the PZT ferroelectric ceramic and implement it into simulation codes. The model is based on the phenomenological theory of phase transition dynamics and takes into account the effects of the self-generated intensive electrical field and stress. Connected with the discharge model and external circuit, the whole transient process of PZT ceramic depoling can be investigated. The results show the finite transition velocity of the ferroelectric phase and the double wave structure caused by phase transition. Simulated currents are compared with the results from experiments with shock pressures varying from 0.4 to 2.8 GPa.

Anomalous self-generated electrostatic fields in nanosecond laser-plasma interaction

Electrostatic (E) fields associated with the interaction of a well-controlled, high-power, nanosecond laser pulse with an underdense plasma are diagnosed by proton radiography. Using a current three-dimensional wave propagation code equipped with nonlinear and nonlocal hydrodynamics, we can model the measured E-fields that are driven by the laser ponderomotive force in the region where the laser undergoes filamentation. However, strong fields of up to 110 MV/m measured in the first millimeter of propagation cannot be reproduced in the simulations. This could point to the presence of unexpected strong thermal electron pressure gradients possibly linked to ion acoustic turbulence, thus emphasizing the need for the development of full kinetic collisional simulations in order to properly model laser-plasma interaction in these strongly nonlinear conditions.

Comparison between time-of-flight measurements and numerical simulations for laser-generated plasmas

The modeling of laser-generated plasmas can be carried out by means of different theoretical approaches. Hydrodynamic simulations have the advantage of treating the plasma as a continuous fluid that expands in vacuum with a high Mach number. We used the analytical Anisimov model for the numerical simulations of a plasma expanding at supersonic velocities. The model describes the plume by means of a special solution of the gas dynamical equations on the hypothesis that the flow expands adiabatically. Here, we carry out a comparative analysis between experimental and numerical results: the model fits the experimental data for monoatomic plumes quite well. More specifically, the numerical data have been tested by comparing the time-of-flight signals obtained at the INFN-LNS in Catania from a pure metallic target. A Coulomb drift velocity was added to the expansion velocity, and only in this way was it possible to explain the experimental results, thus confirming the presence of self-generated electrostatic fields inside the expanding plasma plume.

Spatial stimulation of the electrosensory system of mormyrid electric fish

The long-term goal of this project is to understand adaptive processing in sensory systems. Our work focuses on the electrosensory system of the mormyrid electric fish, a system uniquely suited for the study of adaptive sensory processing. The electrosensory lateral line lobe (ELL) of the mormyrid electric fish presents a special opportunity for examining the influence adaptation on sensory processing because much of the physiology [1] and anatomy [2] has been well characterized. The mormyrid electric fish senses its environment by emitting an electric organ discharge (EOD) and detecting the perturbations that nearby objects cause in the self-generated electric field. Specialized mormyromast electroreceptors sense the self-generated field and its distortions. Afferent fibers from these electroreceptors respond to the fish’s own EOD, and the field strength of the electric field is encoded in the latency of the afferent spike response [3,4]. The electrosensory responses are conveyed with somatotopic precision to the ELL where the fibers terminate [5]. Previous research on electrosensory adaptation has concentrated on point-like electrical fields on the skin. Since the purpose of the electrosensory system is to analyze changes in spatial patterns, we expect that presenting a spatially distributed electrical pattern will lead to a better understanding of adaptive aspects of electrosensory processing in ELL. Thus, we have begun construction of a stimulus device that can present a spatially distributed electrical pattern on the skin of a mormyrid fish. By controlling the patterns that we present, we can simultaneously record from principal cells of ELL to observe changes in responses to spatial patterns. The first phase of our stimulus development program has been to present a low-resolution, 1-dimensional pattern on the fish’s skin. The design was based on an array of vertical rectangles that could be independently controlled to present a spatially varying electrical image along the fish’s skin. We developed electrostatic models to predict fields that would be generated by an array of stimulator pads in water. We have developed an electrical pattern design algorithm that will approximate any given electrical pattern by imposing a set of electrical potentials on the stimulator array. The algorithm will allow flexibility in electrophysiological experimental design to test hypotheses about spatial effects on sensory processing. A cellular modeling component of this study has been developed to predict the responses of individual neurons to stimulation by spatial patterns. Results of our neuronal network models will be compared with experimental measurements of cell responses to the same stimulation to iteratively improve our understanding of mechanisms of electrosensory processing.

Approximate kinetic quasiequilibrium distributions for intense beam propagation through a periodic focusing quadrupole lattice

The transverse dynamics of an intense charged particle beam propagating through a periodic quadrupole focusing lattice is described by the nonlinear Vlasov-Maxwell system of equations, where the propagation distances play the role of time. To determine matched-beam quasiequilibrium distribution functions, one needs to determine a dynamical invariant for the beam particles moving in the combined applied and self-generated fields. In this paper, a perturbative Hamiltonian transformation method is developed which is an expansion in the particle’s vacuum phase advance � � � � v=2� , treated as a small parameter, which is used to transform away the fast particle orbit oscillations and obtain the average Hamiltonian accurate to order � � 3 . The average Hamiltonian is an approximate invariant of the original system, and can be used to determine self-consistent beam quasiequilibrium solutions that are matched to the focusing channel. The equation determining the average self-field potential is derived for general boundary conditions by taking into account the average contribution of the charges induced on the boundary. It is shown for a cylindrical conducting boundary that the average self-field potential acquires an octupole component, which results in the average motion of some beam particles being nonintegrable and their trajectories chaotic. This chaotic behavior of the beam particles may significantly change the nature of the Landau damping (or growth) of collective excitations supported by an intense charged particle beam.

Stability of an electron beam in a two-frequency wiggler with a self-generated field

AbstractWe investigate the relativistic electron motions in a two-frequency wiggler magnetic field with self-generated fields. The equations of motion are derived from the Hamiltonian which include the self-generated field, and we find the steady-state orbit from the equations of motion. The stability of electron motion in a two-frequency wiggler is examined by the numerical simulation. We analyze the a dynamical systems using the fast Fourier transformation and the Poincarè surface of section to find the critical value which have the periodical electron motion and to optimize the two-frequency wiggler.

Angular distribution of emitted electrons due to intense p-polarized laser foil interaction

The angular distribution of electrons emitting from a foil surface illuminated by p-polarized laser pulses is studied using particle-in-cell simulation for incident angles of θ1=22.5°, 45°, 67.5° and laser amplitudes of a=0.5, 1, 2. Theoretical prediction of the emission direction, based on canonical momentum conservation along the target surface, is verified. Surface ablation, the Alfvén current limit, as well as self-generated electromagnetic fields on the surface are numerically investigated and found to play important roles in the modulation of the angular distribution of the emitted electrons. The emitted electrons of higher energy are found to be directly accelerated to near the polarization direction of the incident laser light. The simulation results agree very well with the recent experimental results from Al targets irradiated by a 60 fs, 180 mJ laser pulse.

Feed forward inhibition: a possible player in the adaptive filtering mechanism of sensory information in the shark's electroreception

Event Abstract Back to Event Feed forward inhibition: a possible player in the adaptive filtering mechanism of sensory information in the shark's electroreception Naama Rotem1, 2*, Emanuel Sestieri2, Yosef Yarom1, 2 and J Hounsgaard3 1 Hebrew University of Jerusalem, Dept. Neurobiology, Israel 2 Inter-University Inst, Otto Loewi Minerva Ctr, Israel 3 Panum Inst, INF, Denmark Sharks sense the peripheral electric field generated by their own activity and the activity of other animals in their vicinity. The self-generated electrical field is filtered at the first synapse in the CNS in the Dorsal Octavolateral Nucleus (DON). However, the filter mechanism is poorly understood. Previously, we demonstrated the high fidelity of transmission from the peripheral nerve to the principal neurons in the DON (Ascending Efferent Neurons; AENs). Here we describe a powerful feed-forward inhibitory mechanism activated by the efferent input and exclusively acting on afferent sensory input. Intracellular recordings were obtained from AENs in the isolated DON of Iago omanensis sharks. The response to afferent and central synaptic input was investigated by stimulating the afferent electrosensory nerve (AFF) and parallel fibers (PF). Paired-pulse stimulation of the AFF showed a robust decrease in the response to the second stimulus. This decrease reached a maximum (up to 80%) at an interval of 30 msec, was relatively insensitive to stimulus intensity and was reversibly blocked by the selective GABAA blocker gabazine (300 nmol l–1). Surprisingly the response of AENs to PF stimulation was unaffected by preceding AFF stimulation. Hence the feed-forward inhibition to AENs was limited to its AFF input. Furthermore, inhibitory postsynaptic potentials were rarely observed in response to AFF stimulation. These results indicate that the feed-forward inhibition of the principal neurons in the DON, activated by peripheral input and mediated by GABAA receptors, is pre-synaptic. We hypothesize that this powerful feed forward inhibition serves as a mechanism to remove predictable self-generated electrical fields and highlight unpredictable novel sensory signals. Keywords: Cerebellum Conference: The Cerebellum: from neurons to higher control and cognition, Pavia, Italy, 8 Jul - 9 Jul, 2010. Presentation Type: Short Communication Topic: The Cerebellum: from neurons to higher control and cognition Citation: Rotem N, Sestieri E, Yarom Y and Hounsgaard J (2010). Feed forward inhibition: a possible player in the adaptive filtering mechanism of sensory information in the shark's electroreception. Front. Neurosci. Conference Abstract: The Cerebellum: from neurons to higher control and cognition. doi: 10.3389/conf.fnins.2010.83.00015 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 13 Oct 2010; Published Online: 13 Oct 2010. * Correspondence: Ms. Naama Rotem, Hebrew University of Jerusalem, Dept. Neurobiology, Jerusalem, Israel, naama.rotem@mail.huji.ac.il Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Naama Rotem Emanuel Sestieri Yosef Yarom J Hounsgaard Google Naama Rotem Emanuel Sestieri Yosef Yarom J Hounsgaard Google Scholar Naama Rotem Emanuel Sestieri Yosef Yarom J Hounsgaard PubMed Naama Rotem Emanuel Sestieri Yosef Yarom J Hounsgaard Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

THE VLASOV CONTINUUM LIMIT FOR THE CLASSICAL MICROCANONICAL ENSEMBLE

For classical Hamiltonian N-body systems with mildly regular pair interaction potential (in particular, [Formula: see text] integrability is required), it is shown that when N → ∞ in a fixed bounded domain Λ ⊂ ℝ3, with energy [Formula: see text] scaling as [Formula: see text], then Boltzmann's ergodic ensemble entropy [Formula: see text] has the asymptotic expansion SΛ(N,N2ε) = - N ln N + sΛ(ε) N + o(N). Here, the N ln N term is combinatorial in origin and independent of the rescaled Hamiltonian, while sΛ(ε) is the system-specific Boltzmann entropy per particle, i.e. –sΛ(ε) is the minimum of Boltzmann's H function for a perfect gas of energy ε subjected to a combination of externally and self-generated fields. It is also shown that any limit point of the n-point marginal ensemble measures is a linear convex superposition of n-fold products of the H-function-minimizing one-point functions. The proofs are direct, in the sense that (a) the map [Formula: see text] is studied rather than its inverse [Formula: see text]; (b) no regularization of the microcanonical measure [Formula: see text] is invoked, and (c) no detour via the canonical ensemble. The proofs hold irrespective of whether microcanonical and canonical ensembles are equivalent or not.

Lorentz Mapping of Magnetic Fields in Hot Dense Plasmas

Unique detection of electromagnetic fields and identification of field type and strength as a function of position were used to determine the nature of self-generated fields in a novel experiment with laser-generated plasma bubbles on two sides of a plastic foil. Field-induced deflections of monoenergetic 15-MeV probe protons passing through the two bubbles, measured quantitatively with proton radiography, were combined with Lorentz mapping to provide separate measurements of magnetic and electric fields. The result was absolute identification and measurement of a toroidal magnetic field around each bubble and determination that any electric field component parallel to the foil was below measurement uncertainties.

Ground State Energy of Large Atoms in a Self-Generated Magnetic Field

We consider a large atom with nuclear charge $Z$ described by non-relativistic quantum mechanics with classical or quantized electromagnetic field. We prove that the absolute ground state energy, allowing for minimizing over all possible self-generated electromagnetic fields, is given by the non-magnetic Thomas-Fermi theory to leading order in the simultaneous $Z\to \infty$, $\al\to 0$ limit if $Z\al^2\leq \kappa$ for some universal $\kappa$, where $\al$ is the fine structure constant.

Gravitoelectromagnetic cavitons in the kinetic regime

The interactions of gravitational waves with interstellar matter, dealing with resonant wave-particle and wave-wave interactions, are considered on the basis of magnetic-type Maxwell-Vlasov equations. It is found that the behavior of the fields, involving the "gravitoelectromagnetic" or "GEM " fields, the perturbed density field and self-generated gravitomagnetic field with low frequency,can be described by the nonlinear coupling equations Eqs. (6.10)-(6.12). Numerical results show that they may collapse. In other words, due to self-condensing, a stronger GME fields could be produced; and they could appear as the gravitational waves with high energy reaching on Earth. In this case, Weber's results, perhaps, are acceptable.