scholarly journals Modelling the effect of ephaptic coupling on spike propagation in peripheral nerve fibres

2021 ◽  
Author(s):  
Helmut Schmidt ◽  
Thomas Reiner Kn&oumlsche
Keyword(s):  
Peripheral Nerve ◽  
Realistic Model ◽  
Propagation Model ◽  
Biophysical Model ◽  
Computationally Efficient ◽  
Fibre Bundles ◽  
Dispersive Effect ◽  
Nerve Bundles ◽  
Different Diameters ◽  
Ephaptic Coupling

Experimental and theoretical studies have shown that ephaptic coupling leads to the synchronisation and slowing down of spikes propagating along the axons within peripheral nerve bundles. However, the main focus thus far has been on a small number of identical axons, whereas realistic peripheral nerve bundles contain numerous axons with different diameters. Here, we present a computationally efficient spike propagation model, which captures the essential features of propagating spikes and their ephaptic interaction, and facilitates the theoretical investigation of spike volleys in large, heterogeneous fibre bundles. The spike propagation model describes an action potential, or spike, by its position on the axon, and its velocity. The velocity is primarily defined by intrinsic features of the axons, such as diameter and myelination status, but it is also modulated by changes in the extracellular potential. These changes are due to transmembrane currents that occur during the generation of action potentials. The resulting change in the velocity is appropriately described by a linearised coupling function, which is calibrated with a biophysical model. We first lay out the theoretical basis to describe how the spike in an active axon changes the membrane potential of a passive axon. These insights are then incorporated into the spike propagation model, which is calibrated with a biophysically realistic model based on Hodgkin-Huxley dynamics. The fully calibrated model is then applied to fibre bundles with a large number of axons and different types of axon diameter distributions. One key insight of this study is that the heterogeneity of the axonal diameters has a dispersive effect, and that with increasing level of heterogeneity the ephaptic coupling strength has to increase to achieve full synchronisation between spikes. Another result of this study is that in the absence of full synchronisation, a subset of spikes on axons with similar diameter can form synchronised clusters. These findings may help interpret the results of noninvasive experiments on the electrophysiology of peripheral nerves.

Research on the Transmission Characteristics of Mechanical Vibration Signals in Optical Axis with Different Diameters

2014 ◽  
Vol 563 ◽  
pp. 233-236
Author(s):  
Xu Long Li ◽  
Hong Xian Ye ◽  
Xiao Ping Hu ◽  
Shuang Shuang Zhao ◽  
Chao Xu
Keyword(s):  
Optical Axis ◽  
Mechanical Vibration ◽  
Experimental System ◽  
Test Methods ◽  
Propagation Model ◽  
Vibration Source ◽  
Transmission Characteristics ◽  
Vibration Signals ◽  
Source Signal ◽  
Different Diameters

In view of the phenomenon that the complex transmission path of signals in the gear box and the lack of analysis and test methods for appropriate vibration source signals, the paper takes different-diameter optical axis as the research object, and firstly establishes the propagation model to analyze how the source signal changes and decays in the optical axis of different diameters from the perspective of wave equation. Then this paper builds proper text platforms to conduct experiment, and verify the correctness and validity of the theory. Besides, through the experiments, the paper analyzes the stress change of the optical axis transverse, the lowing trend of transmission speed of the stress wave in the axis, and the relationship between displacement and scope. At last, the paper aims to verity the rationality and generalization performance of the experimental system, which will support the future study on the transmission characteristics of mechanical vibration signals in optical axis theoretically and experimentally.

S-100 Immunoreactivity in Melanomas of Two Marsupials, a Bird, and a Reptile

1997 ◽  
Vol 34 (6) ◽  
pp. 615-618 ◽  
Author(s):  
D. F. Kusewitt ◽  
R. L. Reece ◽  
K. B. Miska
Keyword(s):  
Peripheral Nerve ◽  
Epithelioid Cells ◽  
Phalacrocorax Carbo ◽  
Primary Mass ◽  
Polyclonal Rabbit ◽  
Or Groups ◽  
Nerve Bundles ◽  
S 100 ◽  
Diagnostic Criterion

S-100 proteins are abundant in melanocytes of the skin; thus, S-100 immunoreactivity has been used as a diagnostic criterion for melanoma in humans and other placental mammals. We tested cutaneous melanomas of two marsupials, a bird, and a snake for S-100 immunoreactivity, using a polyclonal rabbit antibovine S-100 antibody. The tumor from a Tasmanian Pademelon ( Thylogale billardierii) was composed of large epithelioid cells, most of which had S-100–positive cytoplasm. In general, there were only scattered individual spindle-shaped S-100–positive cells or groups of cells in the primary mass from a Spotted-tailed Quoll ( Dasyurus maculates); S-100 staining was primarily nuclear. Cells comprising the melanomas of the Australian Cormorant ( Phalacrocorax carbo) and the Death Adder ( Acanthophis antarcticus) were S-100–negative, although peripheral nerve bundles in both were S-100–positive.

scholarly journals The Effect of Wake-Passing and Free-Stream Turbulence on Laminar Gas Turbine Blade Boundary Layers

1993 ◽  
Author(s):  
David Greenblatt
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
Free Stream ◽  
Leading Edge ◽  
Computational Procedure ◽  
Realistic Model ◽  
Computationally Efficient ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Wake Passing

A computational procedure has been developed which accounts for the combined time-mean effect of wake-passing and free-stream turbulence on laminar turbine blade boundary layers. The procedure has the advantage of being computationally efficient as well as providing a realistic model of the unsteady nature of the flow. The procedure yielded the parameter TuReD/σD/2 for characterizing the time-mean flow in the leading edge region and the parameter Γ≡2T~u2σx/γ for describing the flow downstream of the stagnation point. A provisional comparison with stagnation flow experimental data showed that the procedure may be more general than initially expected.

scholarly journals Flexible Computationally Efficient Platform for Simulating Scan Formation in Optical Coherence Tomography with Accounting for Arbitrary Motions of Scatterers

2021 ◽  
Vol 7 (1) ◽  
pp. 010304
Author(s):  
Alexey Zykov ◽  
Alexander Matveyev ◽  
Lev Matveev ◽  
Alexander Sovetsky ◽  
Vladimir Zaitsev
Keyword(s):  
Optical Coherence Tomography ◽  
Numerical Simulations ◽  
Biological Tissues ◽  
Realistic Model ◽  
Spectral Domain ◽  
Optical Coherence ◽  
Computationally Efficient ◽  
Proposed Model ◽  
Speckle Patterns ◽  
Rotational Motions

A computationally efficient and fairly realistic model of OCT-scan formation in spectral-domain optical coherence tomography is described. The model is based on the approximation of discrete scatterers and ballistic character of scattering, these approximations being widely used in literature. An important feature of the model is its ability to easily account for arbitrary scatterer motions and computationally efficiently generate large sequences of OCT scans for gradually varying configurations of scatterers. This makes the proposed simulation platform very convenient for studies related to the development of angiographic processing of OCT scans for visualization of microcirculation of blood, as well as for studies of decorrelation of speckle patterns in OCT scans due to random (Brownian type) motions of scatterers. Examples demonstrating utilization of the proposed model for generation OCT scans imitating perfused vessels in biological tissues, as well as evolution of speckles in OCT scans due to random translational and rotational motions of localized (but not-point-like) scatterers are given. To the best of our knowledge, such numerical simulations of large series of OCT scans in the presence of various types of motion of scatterers have not been demonstrated before.

scholarly journals A Through-the-Wall Radar Imaging Method Based on a Realistic Model

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Tian Jin ◽  
Alexander Yarovoy
Keyword(s):  
Multiple Input Multiple Output ◽  
Image Formation ◽  
Real Data ◽  
Radar Imaging ◽  
Realistic Model ◽  
Imaging Method ◽  
Computationally Efficient ◽  
Localization Accuracy ◽  
Multiple Input ◽  
Input Multiple Output

An image focusing method based on a realistic model for a wall is proposed for through-the-wall radar imaging using a multiple-input multiple-output array. A technique to estimate the wall parameters (i.e., position, thickness, and permittivity) from the radar returns is developed and tested. The estimated wall properties are used in the developed penetrating image formation to form images. The penetrating image formation developed is computationally efficient to realize real-time imaging, which does not depend on refraction points. The through-the-wall imaging method is validated on simulated and real data. It is shown that the proposed method provides high localization accuracy of targets concealed behind walls.

X-ray Pulsar/Starlight Doppler Deeply-integrated Navigation Method

2017 ◽  
Vol 70 (4) ◽  
pp. 829-846 ◽  
Author(s):  
Yidi Wang ◽  
Wei Zheng ◽  
Dapeng Zhang
Keyword(s):  
Estimation Method ◽  
Propagation Model ◽  
Phase Estimation ◽  
Integrated Navigation ◽  
Computationally Efficient ◽  
Doppler Measurement ◽  
X Ray ◽  
Pulse Phase ◽  
The Cost ◽  
Navigation Method

An X-ray pulsar/starlight Doppler deeply-integrated navigation method is proposed in this paper. A starlight Doppler measurement-aided phase propagation model, which can remove the orbital effect within the recorded photon Time Of Arrivals (TOAs), is derived, and guarantees that the pulse phase can be extracted from the converted photon TOAs using computationally efficient methods. Some simulations are performed by a hardware-in-loop system to verify the performance of the integrated pulse phase estimation method as well as of the integrated navigation method. The integrated pulse phase estimation method could achieve an estimation performance similar to the existing method for orbiting vehicles at the cost of much less computational complexity, is capable of handling the signals of millisecond pulsars, and is applicable to various vehicles. In addition, the proposed integrated navigation method could provide reliable positioning results for various vehicles.

Synaptic Relations in the Atrial Nervous System of Amphioxus

1958 ◽  
Vol s3-99 (46) ◽  
pp. 243-261
Author(s):  
QUENTIN BONE
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Peripheral Nerve ◽  
Dorsal Root ◽  
Nerve Cells ◽  
Nerve Fibres ◽  
Nerve Bundles ◽  
Analogous Manner ◽  
The Central Nervous System ◽  
Dorsal Nerve

A detailed description of the system of peripheral nerve-cells upon the gut and diverticulum of amphioxus (Branchiostoma) is given; it is shown experimentally by means of degeneration experiments that these cells are connected with the central nervous system by their own axons, which run in the dorsal-root nerves. The form and connexion of the cells are described, special attention is paid to the problems of the multinucleate cells in the plexus, and to the occurrence of possible asynaptic connexion between neighbouring nerve-cells. No sheath-cells have been observed upon the peripheral nerve-fibres, either within the atrial plexus or upon the dorsal-root nerve bundles; earlier misinterpretations of the nuclei of the cells of the epineurium around the dorsal nerve bundles are discussed. The origin of the atrial system in ontogeny is discussed; it is suggested that it arises in an analogous manner to the enteric plexuses of vertebrates, by outgrowth from the central nervous system. The part that this system of nerve-cells plays in the life of the animal is not known. Finally, the relation of this system of cells to that found upon the guts of other groups of animals is discussed, and it is concluded that the system is not homologous with the enteric systems of nerve-cells in the vertebrates.

Curvature effects in the dynamic propagation of wildfires

2016 ◽  
Vol 25 (12) ◽  
pp. 1238 ◽  
Author(s):  
J. E. Hilton ◽  
C. Miller ◽  
J. J. Sharples ◽  
A. L. Sullivan
Keyword(s):  
Propagation Model ◽  
Computationally Efficient ◽  
Local Curvature ◽  
Fire Propagation ◽  
Curvature Effects ◽  
Dynamic Propagation ◽  
Rate Of Spread ◽  
Complex Interactions ◽  
Curvature Parameter ◽  
Curvature Dependence

The behaviour and spread of a wildfire are driven by a range of processes including convection, radiation and the transport of burning material. The combination of these processes and their interactions with environmental conditions govern the evolution of a fire’s perimeter, which can include dynamic variation in the shape and the rate of spread of the fire. It is difficult to fully parametrise the complex interactions between these processes in order to predict a fire’s behaviour. We investigate whether the local curvature of a fire perimeter, defined as the interface between burnt and unburnt regions, can be used to model the dynamic evolution of a wildfire’s progression. We find that incorporation of curvature dependence in an empirical fire propagation model provides closer agreement with the observed evolution of field-based experimental fires than without curvature dependence. The local curvature parameter may represent compounded radiation and convective effects near the flame zone of a fire. Our findings provide a means to incorporate these effects in a computationally efficient way and may lead to improved prediction capability for empirical models of rate of spread and other fire behaviour characteristics.

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