Modelling fibrillation potentials--analysis of time parameters in the muscle intracellular action potential.

A single fiber action potential (SFAP) can be modelled as the convolution of a biolectrical source and a filter impulse response. In the Dimitrov-Dimitrova (D-D) convolutional model, the first temporal derivative of the intracellular action potential (IAP) is used as the source, and Tspl is a time parameter related to the duration of the IAP waveform. This paper is centred on the relation between Tspl and the main spike duration (MSD), defined as the time interval between the first and third phases of the SFAP. We show that Tspl essentially determines the MSD parameter. As experimental data, we used fibrillation potentials (FPs) of two different muscles to study the D-D model. We found that Tspl should have a certain statistical variability in order to explain the variability in the MSD of our FPs. In addition, we present a method to estimate the Tspl values corresponding to a given SFAP from its measured MSD.     

Modeling the cardiac action potential using B-spline surfaces

This paper presents a new method for constructing empirical, two-state-variable models of cardiac cell membrane kinetics. The formulation is based on nonuniform rational B-spline surfaces that can be manipulated interactively to produce desired action potential (AP) properties. Using this new methodology, a model of the guinea pig ventricular action potential was constructed that reproduces experimentally measured relationships between pacing cycle length and action potential duration and conduction velocity. The model is computationally efficient, requiring about sixfold less CPU time than the Beeler-Reuter ionic model and only about twice as much time as a FitzHugh-Nagumo type empirical model. Thus, for modeling propagation phenomena, this method can produce models that improve on the quantitative accuracy of both simple empirical models and elaborate ionic models, with computational cost comparable to the simplest of empirical models.     

Novel ideas for fast muscle action potential simulations using the line source model

Using a signal processing approach, we analyze the line source model for muscle action potential (AP) modeling. We show that the original model presents a tradeoff between violating the Nyquist criterion on one hand and using a discretization frequency that is unnecessarily high with respect to the bandwidth of the generated AP on the other. Here, we present an improved line source model that, compared to the original, allows a lower discretization frequency while retaining the accuracy by simply introducing a continuous-time anti-aliasing filter. Moreover, a transfer function form of the transmembrane current is presented that promote the use of sophisticated signal processing methods on these type of signals. Both continuous-time and discrete-time models are presented. We also address and analyze the implications of the finite length of the muscle fibers. Including this in the model is straightforward, owing to the convolutional form of the line source model, and is manifested by a simple transformation of the associated weighting function. AP modeling is discussed for the three different electrode models: the concentric needle electrode, the single fiber electrode, and the macro electrode. The presented model is suitable for modeling large motor units, where both accuracy and computational efficiency are important factors. To simplify the selection of the discretization interval, we derive what we call the cumulative cutoff frequency that provides an estimate of the required Nyquist frequency.     

Modeling and performance analysis for wireless mobile networks: a new analytical approach

In wireless mobile networks, quantities such as call blocking probability, call dropping probability, handoff probability, handoff rate, and the actual call holding times for both complete and incomplete calls are very important performance parameters in the network performance evaluation and design. In the past, their analytical computations are given only when the classical exponential assumptions for all involved time variables are imposed. In this paper, we relax the exponential assumptions for the involved time variables and, under independence assumption on the cell residence times, derive analytical formulae for these parameters using a novel unifying analytical approach. It turns out that the computation of many performance parameters is boiled down to computing a certain type of probability, and the obtained analytical results can be easily applied when the Laplace transform of probability density function of call holding time is a rational function. Thus, easily computable results can be obtained when the call holding time is distributed with the mixed-Erlang distribution, a distribution model having universal approximation capability. More importantly, this paper develops a new analytical approach to performance evaluation for wireless networks and mobile computing systems.     

Nonlinear dynamic modeling of neuron action potential threshold during synaptically driven broadband intracellular activity

Activity-dependent variation of neuronal thresholds for action potential (AP) generation is one of the key determinants of spike-train temporal-pattern transformations from presynaptic to postsynaptic spike trains. In this study, we model the nonlinear dynamics of the threshold variation during synaptically driven broadband intracellular activity. First, membrane potentials of single CA1 pyramidal cells were recorded under physiologically plausible broadband stimulation conditions. Second, a method was developed to measure AP thresholds from the continuous recordings of membrane potentials. It involves measuring the turning points of APs by analyzing the third-order derivatives of the membrane potentials. Four stimulation paradigms with different temporal patterns were applied to validate this method by comparing the measured AP turning points and the actual AP thresholds estimated with varying stimulation intensities. Results show that the AP turning points provide consistent measurement of the AP thresholds, except for a constant offset. It indicates that 1) the variation of AP turning points represents the nonlinearities of threshold dynamics; and 2) an optimization of the constant offset is required to achieve accurate spike prediction. Third, a nonlinear dynamical third-order Volterra model was built to describe the relations between the threshold dynamics and the AP activities. Results show that the model can predict threshold accurately based on the preceding APs. Finally, the dynamic threshold model was integrated into a previously developed single neuron model and resulted in a 33% improvement in spike prediction.     

A model of the muscle action potential for describing the leadingedge, terminal wave, and slow afterwave

The leading edge, terminal wave, and slow afterwave of the motor-unit action potential (MUAP) are produced by changes in the strength of electrical sources in the muscle fibers rather than by movement of sources. The latencies and shapes of these features are, therefore, determined primarily by the motor-unit (MU) architecture and the intracellular action potential (IAP), rather than by the volume-conduction characteristics of the limb. We present a simple model to explain these relationships. The MUAP is modeled as the convolution of a source function related to the IAP and a weighting function related to the MU architecture. The IAP waveform is modeled as the sum of a spike and a slow repolarization phase. The MU architecture is modeled by assuming that the individual fibers lie along a single equivalent axis but that their action potentials have dispersed initiation and termination times. The model is illustrated by simulating experimentally recorded MUAPs and compound muscle action potentials.     

板料激光弯曲成形角度的解析研究

采用解析方法建立了板料激光弯曲角度的解析表达式,其包含了能量(光束功率、吸收系数、扫描速度、光斑直径)、几何(板料厚度)和材料性能参数(热膨胀系数、热传导系数、比热、密度、弹性模量、屈服强度)等因素。实验验证表明,其具有较高的准确度。得到了激光弯曲成形时能量密度应满足的临界条件,可较准确地预测板料产生弯曲变形所需的最小能量密度。     

A new analytical model for the dual-banyan ATM switch throughputcalculation

Dual-banyan is a buffered banyan asynchronous transfer mode (ATM) switch encompassing multiple input-queueing (bifurcated queueing) as its buffering strategy. This paper describes a new analytical model for a throughput evaluation of the dual-banyan switch under different traffic patterns. the model developed and presented enables the computation of buffer state probability and the switch normalized throughput by iterative calculations. The efficiency of the given model is verified through a comparison with simulation results     

On the analytical description of ageing kinetics in ceramic manganite-based NTC thermistors

Experimental results on thermally induced degradation tests carried out at the relatively low ageing temperatures less than 200 °C in NTC ceramic thermistors based on mixed transition-metal manganites (Cu,Ni,Co,Mn)₃O₄ are discussed. It is first established that, despite of chemical composition and technological features of the investigated ceramics, the stretched-exponential relaxation function of DeBast–Gillard or Williams–Watts is the unique analytical expression describing kinetics of the observed degradation processes.     

A model analysis of aftereffects of high-intensity DC stimulationon action potential of ventricular muscle

The mechanism for aftereffects of high-intensity dc stimulation on ventricular muscle was studied by using Beeler-Reuter's action potential model. A leak conductance (G_pore maximal value from 40 to 80 μS for 1 cm² of membrane), which mimics reversible dielectric breakdown of the cell membrane by the shock, was incorporated into the model. To simulate resealing process, G_pore was assumed to decrease after the shock exponentially at a time constant (τ_pore) of 5-50 s. The simulation results are qualitatively consistent with the authors' experimental observations in guinea pig papillary muscle (Amer. J. Physiol., vol. 267, p. H248-58, 1994); they include prolonged depolarization, diastolic depolarization or oscillation of membrane potential leading to a single or multiple spontaneous excitation. The phase-independence and shock intensity-dependence can also be reproduced. Analysis of current components has revealed that: (1) a large inward leak current (l_leak) is responsible for the prolonged depolarization (2) time-dependent decay of outward current (I_X1) in combination with I_leak and slow inward current (I_s) results in diastolic depolarization or oscillation of membrane potential; (3) spontaneous excitation depends on an activation of I_s. These findings support the authors' hypothesis that strong shocks (>15 V/cm) will produce abnormal arrhythmogenic responses in ventricular muscle through a transient rupture of sarcolemmal membrane     

Matrix analysis of discontinuities in nonreciprocal waveguides: analytical description for magnetooptical slab waveguides

A new analytical formalism to study the effect of discontinuities in a nonreciprocal waveguide has been developed. The analysis is based on 1) the general orthogonality relation obtained from the reciprocity theorem, 2) the modal expansion of the transverse electromagnetic fields within the waveguide, and 3) the continuity of the tangential components of such electromagnetic fields at both sides of the discontinuity. The formalism is presented in a matrix form, which allows the treatment of several discontinuities as a simple summation and product of coupling and propagation matrices. The matrix formalism is developed for magnetooptic waveguides in the three different orientations of the magnetization, and, within this context, two practical applications of magnetooptic isolators are studied.     

A new analytical model for the two-terminal MOS capacitor on SOIsubstrate

An analytical model for the two-terminal metal-oxide-semiconductor-oxide-semiconductor (MOSOS) structure, which takes into account the width of the accumulation layer in the SOI film and the space-charge region in the underlying Si substrate, is presented. The results of the model are compared with results one-dimensional (1-D) numerical simulations for a uniformly doped Si film and substrate, showing considerable improvement in accuracy compared to traditional models     

A new analytical model for the GaAs MESFET in the saturation region

A model that provides the static characteristics and the elements of the equivalent electrical scheme is presented. It is based on an approximate quadratic form for the depleted region under the gate when the electron velocity reaches the saturation velocity. The potential in the channel is calculated using Poisson's equation and taking into account the variation of the electron density inside it. The main physical phenomena such as edge effects, overshoot velocity, and carrier injection in the buffer layer are also taken into account. Theoretical and experimental results for the I-V characteristics, transconductance, output conductance, gate-source capacitance, and gate-drain capacitance are presented for a submicrometer-gate MESFET. The results calculated using this model agree well with experimental data     

A new simple analytical emitter model for bipolar transistors

An accurate analytic evaluation of emitter injection into an arbitrarily doped emitter (including a polysilicon-contacted emitter) is presented taking into account position-dependent quantities such as bandgap narrowing, Auger recombination and mobility. Two newly defined dimensionless parameters are introduced that are very useful for emitter design. These parameters are proposed to replace the conventional emitter Gummel number which becomes less useful when appreciable recombination takes place in the emitter. Universal emitter design curves are presented for devices made in silicon, GaAs and InGaAsP or in any other semiconductor for which a newly introduced lifetime model holds good. Numerical simulations show the accuracy and usefulness of the analytical model developed.     

基于关键点梯度特征描述的人体行为识别算法

提出一种新的人体行为识别方案并进行了算法实现。通过对视频序列在空间上高斯滤波,在时间轴向上Gabor滤波,提取出视频序列的关键点,对每个关键点邻域20×20的区域使用梯度位置朝向直方图进行描述,描述的序列可以表征视频序列的特征。与其他人体行为识别算法比较,不需要标记特定的特征区域和比较耗时的聚类算法,构建单个支持向量分类器即可达到好的识别率,算法简单有效。     

An accurate, analytical, and technology-mapped definition of the surface potential at threshold and a new postulate for the threshold voltage of MOSFETs

A novel approach of defining the threshold voltage for long channel MOSFETs has been presented in this paper, where it has been proposed that it corresponds to the gate-to-source voltage for which the drift and diffusion components of the total drain current become equal to each other. In order to avoid the greater computation time associated with the numerical solution of these two components, an analytical expression of the surface potential, corresponding to the threshold condition, is given here, which has the same functional form as the one proposed by Tsividis. The fuzzy parameter n, appearing in this expression of the surface potential, is expressed as a function of the substrate doping density (N_A) and the oxide thickness (t_ox). The threshold voltage values, obtained analytically from the relation between the surface potential at the threshold condition and the closed-form technology-mapped expression of the fuzzy parameter n, show an excellent match with those obtained from SILVACO simulations for a wide range of N_A and t_ox, with the maximum error being only about 4%. The comparison of the percent error values of the threshold voltage obtained from this proposed model with those obtained from the other two recently proposed methods, all with respect to SILVACO simulation results, further verifies the validity of our completely analytical, mathematically simple, and straight-forward approach, proposed in this work here.     

A new analytical model for the thermal resistance of deep-trench bipolar transistors

A new analytical model for the thermal resistance, temperature profile, and heat flow of deep-trench isolated (DTI) transistors is presented by taking the finite heat flow through the trenches into account. The new model is able to distinguish between the different contributions to the thermal resistance of the DTI structure and allows identification of the most dominant component. A detailed analysis of the substrate contribution shows that the substrate thermal resistance is overestimated in existing models. Results are compared with experimental data as well as numerical simulations and show a good agreement. The model can be used for process optimization and in a circuit simulator.