The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
James M Bower - One of the best experts on this subject based on the ideXlab platform.
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an active Membrane Model of the cerebellar purkinje cell ii simulation of synaptic responses
Journal of Neurophysiology, 1994Co-Authors: E De Schutter, James M BowerAbstract:1. Both excitatory and inhibitory postsynaptic channels were added to a previously described complex compartmental Model of a cerebellar Purkinje cell to examine Model responses to synaptic inputs....
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an active Membrane Model of the cerebellar purkinje cell i simulation of current clamps in slice
Journal of Neurophysiology, 1994Co-Authors: E De Schutter, James M BowerAbstract:1. A detailed compartmental Model of a cerebellar Purkinje cell with active dendritic Membrane was constructed. The Model was based on anatomic reconstructions of single Purkinje cells and included 10 different types of voltage-dependent channels described by Hodgkin-Huxley equations, derived from Purkinje cell-specific voltage-clamp data where available. These channels included a fast and persistent Na+ channel, three voltage-dependent K+ channels, T-type and P-type Ca2+ channels, and two types of Ca(2+)-activated K+ channels. 2. The ionic channels were distributed differentially over three zones of the Model, with Na+ channels in the soma, fast K+ channels in the soma and main dendrite, and Ca2+ channels and Ca(2+)-activated K+ channels in the entire dendrite. Channel densities in the Model were varied until it could reproduce Purkinje cell responses to current injections in the soma or dendrite, as observed in slice recordings. 3. As in real Purkinje cells, the Model generated two types of spiking behavior. In response to small current injections the Model fired exclusively fast somatic spikes. These somatic spikes were caused by Na+ channels and repolarized by the delayed rectifier. When higher-amplitude current injections were given, sodium spiking increased in frequency until the Model generated large dendritic Ca2+ spikes. Analysis of Membrane currents underlying this behavior showed that these Ca2+ spikes were caused by the P-type Ca2+ channel and repolarized by the BK-type Ca(2+)-activated K+ channel. As in pharmacological blocking experiments, removal of Na+ channels abolished the fast spikes and removal of Ca2+ channels removed Ca2+ spiking. 4. In addition to spiking behavior, the Model also produced slow plateau potentials in both the dendrite and soma. These longer-duration potentials occurred in response to both short and prolonged current steps. Analysis of the Model demonstrated that the plateau potentials in the soma were caused by the window current component of the fast Na+ current, which was much larger than the current through the persistent Na+ channels. Plateau potentials in the dendrite were carried by the same P-type Ca2+ channel that was also responsible for Ca2+ spike generation. The P channel could participate in both Model functions because of the low-threshold K2-type Ca(2+)-activated K+ channel, which dynamically changed the threshold for dendritic spike generation through a negative feedback loop with the activation kinetics of the P-type Ca2+ channel. 5. These Model responses were robust to changes in the densities of all of the ionic channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Donald A Glaser - One of the best experts on this subject based on the ideXlab platform.
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slowly moving stimuli induce characteristic periodic activity waves in an excitable Membrane Model of visual motion processing
Neurocomputing, 2002Co-Authors: Donald A GlaserAbstract:Abstract A two-dimensional sheet of locally connected neural elements may be used to Model motion detection in visual cortex. External inputs applied to such a system give rise to activity waves, which propagate with a speed determined by the Membrane parameters. Membrane inputs which are moving at a speed less than this intrinsic propagation rate give rise to periodic activity waves, which outrun the stimulus. The spacing between these waves is compressed in front of the stimulus, and expanded behind it, in a Doppler-like fashion. The wave frequency may be used to characterize the speed of the stimulus.
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synaptic depression and facilitation can induce motion aftereffects in an excitable Membrane Model of visual motion processing
Neurocomputing, 2002Co-Authors: Donald A GlaserAbstract:Abstract A two-dimensional sheet of locally connected neural elements may be used to Model motion detection in visual cortex. Activity waves resulting from inputs representing objects in motion have distinctive amplitudes and shapes, which characterize the object's motion. Repeated application of moving stimuli to such a system may lead to depression and facilitation of connections in the Membrane. As a consequence, nonmoving stimuli may then give rise to activity waves like those characteristic of motion, but in the direction opposite to that of the conditioning stimulus. This effect may be used to Model translational and rotational motion aftereffects in visual cortex.
Faizan Ahmad - One of the best experts on this subject based on the ideXlab platform.
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hollow fiber Membrane Model for gas separation process simulation experimental validation and module characteristics study
Journal of Industrial and Engineering Chemistry, 2015Co-Authors: Faizan Ahmad, Kok Keon Lau, Serene Sow Mu Lock, Sikander Rafiq, Asad Ullah Khan, Moonyong LeeAbstract:Abstract Conceptual process simulations and optimization are essential in the design, operation and troubleshooting stages of a Membrane-based gas separation system. Despite this, there are few mathematical Models/tools associated with a hollow fiber Membrane module available in a commercial process simulator. A mathematical Model dealing with the hollow fiber module characteristics that can be included within a commercial process simulator is needed to examine the performance and economics of a gas separation system. In this study, a hollow fiber Membrane Model was incorporated in Aspen HYSYS as a user defined unit operation for the study of carbon dioxide separation from methane. The hollow fiber Membrane Model was validated experimentally. The study of a double stage Membrane module with a permeate recycle, which was proposed to be the optimal configuration in previous studies, was extended to consider the effects of the module characteristics (such as the fiber length, radius of the fiber bundle, diameter of the fibers, and porosity) on the process performance and economics. The gas processing cost (GPC) increased with increasing fiber length and bundle radius, and decreased with increasing outer diameter of the fibers and porosity. At the same time, the separation efficiency (product quality) was also dependent on these module parameters. Therefore, the tradeoff for the hollow fiber Membrane module characteristics needs to be determined based on the minimum GPC with respect to the desired product purity.
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temperature and pressure dependence of Membrane permeance and its effect on process economics of hollow fiber gas separation system
Journal of Membrane Science, 2013Co-Authors: Faizan Ahmad, Kok Keon Lau, Azmi Muhamma Shariff, Yin Fong YeongAbstract:Abstract Conventional hollow fiber Models in process simulators usually assume constant Membrane permeance i.e., independent of pressure and temperature. In this work, hollow fiber Membrane Model has been proposed to cater the effects of temperature and pressure on Membrane permeance. The proposed Model is incorporated with Aspen HYSYS as a user defined unit operation in order to study the performance of gas separation system. The simulated Model is validated by experimental and published data. The temperature drop due to Joule Thomson effect and its contribution to the change in Membrane permeance has also been investigated. Similarly, the effect of pressure on Membrane permeance has been studied. The influence of these effects on the separation performance and process economics has been investigated for the separation of CO 2 from natural gas. The proposed hollow fiber Membrane Model has potential to be applied for design, optimization and scale up of wide range of gas separation systems.
E De Schutter - One of the best experts on this subject based on the ideXlab platform.
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an active Membrane Model of the cerebellar purkinje cell ii simulation of synaptic responses
Journal of Neurophysiology, 1994Co-Authors: E De Schutter, James M BowerAbstract:1. Both excitatory and inhibitory postsynaptic channels were added to a previously described complex compartmental Model of a cerebellar Purkinje cell to examine Model responses to synaptic inputs....
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an active Membrane Model of the cerebellar purkinje cell i simulation of current clamps in slice
Journal of Neurophysiology, 1994Co-Authors: E De Schutter, James M BowerAbstract:1. A detailed compartmental Model of a cerebellar Purkinje cell with active dendritic Membrane was constructed. The Model was based on anatomic reconstructions of single Purkinje cells and included 10 different types of voltage-dependent channels described by Hodgkin-Huxley equations, derived from Purkinje cell-specific voltage-clamp data where available. These channels included a fast and persistent Na+ channel, three voltage-dependent K+ channels, T-type and P-type Ca2+ channels, and two types of Ca(2+)-activated K+ channels. 2. The ionic channels were distributed differentially over three zones of the Model, with Na+ channels in the soma, fast K+ channels in the soma and main dendrite, and Ca2+ channels and Ca(2+)-activated K+ channels in the entire dendrite. Channel densities in the Model were varied until it could reproduce Purkinje cell responses to current injections in the soma or dendrite, as observed in slice recordings. 3. As in real Purkinje cells, the Model generated two types of spiking behavior. In response to small current injections the Model fired exclusively fast somatic spikes. These somatic spikes were caused by Na+ channels and repolarized by the delayed rectifier. When higher-amplitude current injections were given, sodium spiking increased in frequency until the Model generated large dendritic Ca2+ spikes. Analysis of Membrane currents underlying this behavior showed that these Ca2+ spikes were caused by the P-type Ca2+ channel and repolarized by the BK-type Ca(2+)-activated K+ channel. As in pharmacological blocking experiments, removal of Na+ channels abolished the fast spikes and removal of Ca2+ channels removed Ca2+ spiking. 4. In addition to spiking behavior, the Model also produced slow plateau potentials in both the dendrite and soma. These longer-duration potentials occurred in response to both short and prolonged current steps. Analysis of the Model demonstrated that the plateau potentials in the soma were caused by the window current component of the fast Na+ current, which was much larger than the current through the persistent Na+ channels. Plateau potentials in the dendrite were carried by the same P-type Ca2+ channel that was also responsible for Ca2+ spike generation. The P channel could participate in both Model functions because of the low-threshold K2-type Ca(2+)-activated K+ channel, which dynamically changed the threshold for dendritic spike generation through a negative feedback loop with the activation kinetics of the P-type Ca2+ channel. 5. These Model responses were robust to changes in the densities of all of the ionic channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Chyuanhwan Jeng - One of the best experts on this subject based on the ideXlab platform.
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unified softened Membrane Model for torsion in hollow and solid reinforced concrete members Modeling precracking and postcracking behavior
Journal of Structural Engineering-asce, 2015Co-Authors: Chyuanhwan JengAbstract:AbstractThe softened Membrane Model for torsion (SMMT) was the first rational theory to incorporate the precracking and postcracking torsional behavior of solid RC members. A series of theoretical and experimental investigations were conducted in Taiwan to extend the SMMT to hollow RC members. This paper proposes a generalized SMMT based on the results of these investigations, determines the constitutive relationships of concrete for thin- and thick-walled hollow RC members, and develops a unified SMMT theory for hollow and solid RC members. The proposed SMMT for hollow RC members (SMMT-H) is also employed to derive a rational Tcr and θcr formula for such members, completing a unified set of noniterative rational Tcr-θcr formulas for both hollow and solid RC members. In the experiment, the proposed SMMT-H analyzed the torsional responses of the specimens reasonably well, and predicted the cracking points and precracking torque-twist curves almost perfectly. The proposed rational formula for hollow RC memb...
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a softened Membrane Model for torsion in reinforced concrete members
Engineering Structures, 2009Co-Authors: Chyuanhwan Jeng, Thomas T C HsuAbstract:Abstract The Softened Membrane Model (SMM), developed for predicting the behavior of reinforced concrete (RC) Membrane elements under shear, is extended to RC members subjected to torsion. This new analytical method, referred to as the Softened Membrane Model for Torsion (SMMT), takes into account the strain gradient of concrete struts in the shear flow zone by making two modifications to the constitutive relationships of concrete. First, in the tensile stress–strain relationship of concrete, the pre-cracking stiffness and the strain at peak stress should each be increased by 45%. Second, the Hsu/Zhu ratio for torsion is taken as 80% of the Hsu/Zhu ratio for shear. Similar to the case of the SMM Model for shear, this new SMMT Model can predict the entire torque–twist curve, including the ranges before and after cracking, as well as the ascending and descending branches. The theoretical predictions from the SMMT compare very well with the test data on torsion available in the literature.