The Experts below are selected from a list of 130596 Experts worldwide ranked by ideXlab platform
Anton V. Chizhov - One of the best experts on this subject based on the ideXlab platform.
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Orientation hypercolumns of the visual cortex: Ring Model
Biophysics, 2011Co-Authors: E. Yu. Smirnova, Anton V. ChizhovAbstract:A hypercolumn of the visual cortex is a functional unit formed of neighboRing columns whose neurons respond to a stimulus of particular orientation. The function of the hypercolumn is to amplify the orientation tuning of visually evoked responses. According to the conventional simple Model of a hypercolumn, neuronal populations with different orientation preferences are distributed on a Ring. Every population is described by a fiRing rate (FR) Model. To determine the limitations of the FR-Ring Model, it was compared with a more detailed Ring Model, which takes into account the distribution of neurons of each population according to their voltage values. In the case of leaky integrate-and-fire neurons, every neuronal population is described by the Fokker-Planck equation (FPE). The mapping of parameters was obtained. The simulations revealed differences in the behavior of the two Models. The FPE-based Model reacts faster to a change in stimulus orientation. The FPE Ring Model gives a steady-state solution in the form of waves of activity traveling on the Ring, whereas the FR Ring Model presents amplitude instability for the same parameter set. The FPE Ring Model reproduces the characteristic effects of the FR Ring Model: virtual rotation and symmetry breaking.
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Orientation hypercolumns of the visual cortex: Ring Model
Biofizika, 2011Co-Authors: E Iu Smirnova, Anton V. ChizhovAbstract:A hypercolumn of the visual cortex is a functional unit formed of the neighbouRing columns whose neurons respond to a stimulus of particular orientation. The function of the hypercolumn is to amplify the orientation tuning of visually evoked responses. According to the conventional simple Model of a hypercolumn, neuronal populations with different orientation preferences are distributed on a Ring. Every population is described by the frequency (FR) Model. To determine the limitations of the FR-Ring Model, it was compared with a more detailed Ring Model, which takes into account the distribution of neurons of each population according to their voltage values. In the case of the leaky integrate-and-fire neurons, every neural population is described by the Fokker-Planck (FP) equation. The mapping of parameters was obtained. The simulations revealed differences in the behaviour of the two Models. Contrary to the FR Model, the Model based on the Fokker-Planck equation reacts faster to a change in stimulus orientation. The Fokker-Planck Ring Model gives a steady-state solution in the form of waves of activity travelling on the Ring, whereas the FR Ring Model presents amplitude instability for the same parameter set. The FR Ring Model reproduces the characteristic effects of the Ring Model: the virtual rotation and the symmetry breaking.
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Mapping between V1 Models of orientation selectivity: From a distributed multi-population conductance-based refractory density Model to a fiRing-rate Ring Model
BMC Neuroscience, 2009Co-Authors: Anton V. Chizhov, Elena Y. Smirnova, Lyle J. GrahamAbstract:To study the selectivity of neurons in primary visual cortex to the orientation of visual stimuli, we have built a detailed Model consideRing neuronal populations distributed along the cortex and receiving a thalamic input according to a classic pinwheel architecture. The Model is based on the refractory density (RD) approach developed in [1,2] for a population of conductance-based adaptive neurons, where "population" implies an infinite number of similar neurons receiving a common input with an implicit noise term that is distinct for each neuron. While in its full form this type of Model can be compared with experimental intracellular recordings, for mathematical analysis of the dynamics of feature selectivity the Model must undergo considerable reductions. To this end we have constructed a hierarchy of reduced Models, at one extreme arriving at the classical fiRing-rate (FR) Ring Model [3]. Specifically, we 1) simplify the conductance-based adaptive and fast spiking neuron Models to leaky integrate-and-fire neurons, 2) approximate pinwheel architecture by a Ring, 3) replace realistic synaptic kinetics by instantaneous kinetics, 4) reduce the number of neuronal populations to one, 5) replace the refractory density approach by the Kolmogorov-Fokker-Planck (KFP) equation describing voltage phase space, 6) substitute the KFP by an artificial relaxation equation for the fiRing rate driven by its stationary dependence on the input conductance and current (f-g-I-function), and 7) approximate the f-g-I-function by a threshold linear f-I-curve, thus arriving to the classical FR Ring Model as described in [3]. With the appropriate analytical expressions we map the parameters of the various Models to the four parameters of the FR Ring Model. We compare the behaviors of the Models with the parameter sets corresponding to different domains on a two-parameter plane of the FR Ring Model corresponding to the intracortical connection strengths. For a range of parameter sets, the comparison shows a consistency for steady-state solutions, whereas the Models derived from the probability density approach (RD and KFP) possess a larger variety of solutions, similar to that of the FR Ring Model with a delay [4]. We then compare the transient solutions of the Models when the stimulus orientation changes abruptly. The transient behavior of the RD and KFP-based Models differs significantly from that of the FR Model, showing a faster reaction of the cortex. The results of the comparison demonstrate that the constructed hierarchy of Models can serve as a useful instrument for fitting mathematical Models to experimental data, and their subsequent analysis.
Peter Kindt - One of the best experts on this subject based on the ideXlab platform.
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a modified complex modal testing technique for a rotating tire with a flexible Ring Model
Mechanical Systems and Signal Processing, 2015Co-Authors: Semyung Wang, Bert Pluymers, Wim Desmet, Peter KindtAbstract:Abstract Natural frequencies, mode shapes and modal damping values are the most important parameters to describe the noise and vibration behavior of a mechanical system. For rotating machinery, however, the directivity of the propagation wave of each mode should also be taken into account. For rotating systems, this directivity can be determined by complex modal testing. In this paper, a rolling tire is represented as a flexible Ring Model. The limitation of application of the complex modal testing which requires two directional measurements at a certain point, which is difficult to measure in practice, has been overcome through a modified complex modal testing which requires only one directional measurements at any two points. The technique is described in detail and applied to both a numerical example and to an experimental data set of a real rotating tire.
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damping analysis with respect to rolling speed by analytic solution of a flexible Ring Model and its frequency response function derivation by modal summation method
International Journal of Applied Mechanics, 2014Co-Authors: Semyung Wang, Bert Pluymers, Peter Kindt, Wim DesmetAbstract:In this research, a modal approach has been adopted to analyze the dynamic characteristics of the rolling tire by a Ring Model. Previously, most of the researchers focused on the changes in natural frequencies with respect to the rotational speed (in global coordinate) only. In this research, the change in the damping has also been taken into account by including a damping term in the Ring Model equations. The bi-orthogonal property which is used to obtain the Frequency Response Functions (FRFs) of a rotor/beaRing system described in Cartesian coordinate has been applied to the Ring Model described in cylindrical coordinate to obtain the FRFs. The obtained damping values and FRFs from the analytic Model are then compared with experimental results. Moreover, the physical meanings of the results are analyzed, based on experimental data of a stationary tire and a rolling tire at 60 km/h and 100 km/h.
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Analytic Formula Derivation for a Rolling Tire with a Ring Model
Topics in Modal Analysis Volume 7, 2013Co-Authors: Jongsuh Lee, Peter Kindt, Bert Pluymers, Paul Sas, Semyung WangAbstract:This paper analyzes the dynamic characteristics of a rolling tire with a modal approach. A Ring Model is adopted to Model a tire and this Model is substituted in a general transfer function and considers the rolling condition to make a transfer function of a rolling tire in the Laplace domain and an corresponding impulse response function in the time domain. From this transfer function it is clearly confirmed that the shifting effect, the so-called Doppler Effect, shifts not only the natural frequencies but also the damping ratios.
Semyung Wang - One of the best experts on this subject based on the ideXlab platform.
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a modified complex modal testing technique for a rotating tire with a flexible Ring Model
Mechanical Systems and Signal Processing, 2015Co-Authors: Semyung Wang, Bert Pluymers, Wim Desmet, Peter KindtAbstract:Abstract Natural frequencies, mode shapes and modal damping values are the most important parameters to describe the noise and vibration behavior of a mechanical system. For rotating machinery, however, the directivity of the propagation wave of each mode should also be taken into account. For rotating systems, this directivity can be determined by complex modal testing. In this paper, a rolling tire is represented as a flexible Ring Model. The limitation of application of the complex modal testing which requires two directional measurements at a certain point, which is difficult to measure in practice, has been overcome through a modified complex modal testing which requires only one directional measurements at any two points. The technique is described in detail and applied to both a numerical example and to an experimental data set of a real rotating tire.
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damping analysis with respect to rolling speed by analytic solution of a flexible Ring Model and its frequency response function derivation by modal summation method
International Journal of Applied Mechanics, 2014Co-Authors: Semyung Wang, Bert Pluymers, Peter Kindt, Wim DesmetAbstract:In this research, a modal approach has been adopted to analyze the dynamic characteristics of the rolling tire by a Ring Model. Previously, most of the researchers focused on the changes in natural frequencies with respect to the rotational speed (in global coordinate) only. In this research, the change in the damping has also been taken into account by including a damping term in the Ring Model equations. The bi-orthogonal property which is used to obtain the Frequency Response Functions (FRFs) of a rotor/beaRing system described in Cartesian coordinate has been applied to the Ring Model described in cylindrical coordinate to obtain the FRFs. The obtained damping values and FRFs from the analytic Model are then compared with experimental results. Moreover, the physical meanings of the results are analyzed, based on experimental data of a stationary tire and a rolling tire at 60 km/h and 100 km/h.
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Analytic Formula Derivation for a Rolling Tire with a Ring Model
Topics in Modal Analysis Volume 7, 2013Co-Authors: Jongsuh Lee, Peter Kindt, Bert Pluymers, Paul Sas, Semyung WangAbstract:This paper analyzes the dynamic characteristics of a rolling tire with a modal approach. A Ring Model is adopted to Model a tire and this Model is substituted in a general transfer function and considers the rolling condition to make a transfer function of a rolling tire in the Laplace domain and an corresponding impulse response function in the time domain. From this transfer function it is clearly confirmed that the shifting effect, the so-called Doppler Effect, shifts not only the natural frequencies but also the damping ratios.
Genji Yamazaki - One of the best experts on this subject based on the ideXlab platform.
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Approximate analysis of a slotted Ring Model with symmetric stations
Mathematical and Computer Modelling, 1995Co-Authors: Genji Yamazaki, R. W. Wolff, H. Sakasegawa, Kunio AndoAbstract:This paper presents an approximate method for the throughput and average delay characteristics in a slotted Ring Model in which the buffer sizes of all stations are finite and equal and the arrival process of new messages at each station is Poisson. The approximation is based on an independence assumption. The approximation is examined for various system parameters and the results show that it is very fine. This approximation requires to solve only a set of equations whose order is the buffer size plus one. Therefore, it is very useful even for large-scale systems.
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Analysis of a slotted Ring Model with Cambridge type protocol
Computers & Industrial Engineering, 1994Co-Authors: Kunio Ando, Takahiro Iwata, Genji YamazakiAbstract:Abstract This paper considers a Cambridge Ring type slotted Ring Model. We propose an approximate method for the throughput and average delay characteristics in the slotted Ring Model in which the buffer sizes of all stations are finite and same and the arrival process of new messages at each station is Poisson. The approximation is based on an independence assumption. The approximation is examined for various system parameters and the results show that it is very fine. This approximation requires to solve only a set of equations whose order is the buffer size plus one.
D Baldacchino - One of the best experts on this subject based on the ideXlab platform.
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verifying the blade element momentum method in unsteady radially varied axisymmetric loading using a vortex Ring Model
Wind Energy, 2017Co-Authors: W Yu, Carlos Simao Ferreira, Gijs Van Kuik, D BaldacchinoAbstract:Although the Blade Element Momentum method has been derived for the steady conditions, it is used for unsteady conditions by using corrections of engineeRing dynamic inflow Models. Its applicability in these cases is not yet fully verified. In this paper, the validity of the assumptions of quasi-steady state and annuli independence of the blade element momentum theory for unsteady, radially varied, axi-symmetric load cases is investigated. Firstly, a free wake Model that combines a vortex Ring Model with a semi-infinite cylindrical vortex tube was developed and applied to an actuator disc in three load cases: (i) steady uniform and radially varied, (ii) two types of unsteady uniform load and (iii) unsteady radially varied load. Results from the three cases were compared with Momentum Theory and also with two widely used engineeRing dynamic inflow Models—the Pitt-Peters and the Oye for the unsteady load cases. For unsteady load, the free wake vortex Ring Model predicts different hysteresis loops of the velocity at the disc or local annuli, and different aerodynamic work from the engineeRing dynamic inflow Models. Given that the free wake vortex Ring Model is more physically representative, the results indicate that the engineeRing dynamic inflow Models should be improved for unsteady loaded rotor, especially for radially varied unsteady loads. © 2016 The Authors. Wind Energy Published by John Wiley & Sons, Ltd.
