scholarly journals A Stochastic Model for Discrete Waves in the Limulus Photoreceptor

1971 ◽  
Vol 58 (3) ◽  
pp. 267-286 ◽  
Author(s):  
Richard Srebro ◽  
Mahmood Behbehani
Keyword(s):  
Stochastic Model ◽  
Mathematical Description ◽  
Initial Component ◽  
Limulus Photoreceptor ◽  
Lateral Eye ◽  
Time Courses

A stochastic model that links the absorption of a photon to the production of a discrete wave in the photoreceptor of the lateral eye of Limulus is proposed. By separating a discrete wave into an initial component due directly to the absorption of a photon, and a second quasi all-or-nothing component, a mathematical description of the latencies of discrete waves is deduced and some important features of their time courses are suggested. The predictions of the model are compared to observations from 60 different ommatidia.

Adaptive Changes in Motor Activity Associated With Functional Recovery Following Muscle Denervation in Walking Cats

1999 ◽  
Vol 82 (1) ◽  
pp. 370-381 ◽  
Author(s):  
K. G. Pearson ◽  
K. Fouad ◽  
J. E. Misiaszek
Keyword(s):  
Time Course ◽  
Biomechanical Properties ◽  
Afferent Feedback ◽  
Initial Component ◽  
Medial Gastrocnemius ◽  
Ground Contact ◽  
Late Component ◽  
Ankle Movement ◽  
Time Courses ◽  
Ankle Function

In this investigation we examined the changes in the pattern of activity in the medial gastrocnemius (MG) muscle in walking cats following transection of the nerves innervating synergist muscles (lateral gastrocnemius, soleus, and plantaris). Immediately following the nerve transections, there was a large increase in ankle flexion during early stance (from ∼10 to ∼30°) and a marked increase in the magnitude of the MG bursts during stance. We attribute this increase in the magnitude of the MG bursts to an increase in afferent feedback from the abnormally stretched MG muscle. During the week after the nerve transections, there was a progressive decrease in ankle yield. This improvement in ankle function was correlated with an increase in magnitude of two components of the MG bursts; the initial component starting during late swing and ending ∼40 ms after ground contact, and a late component associated with stance. The time courses of the increases in the initial and late components of the MG bursts were different. Large and significant increases in the late component occurred the day after the nerve transections, whereas increases in the initial component occurred more gradually. This difference in time course was reflected in the kinematics of ankle movement. Over the first few days after the nerve transections, improvement in ankle movement occurred primarily late in the stance phase, and there was little change in ankle yield during early stance. At 1 wk, however, there was a significant reduction in ankle yield during early stance. This decreased yield was most likely due to an increase in stiffness of the MG muscle at the time of ground contact resulting from the increase in magnitude of the initial component of the MG bursts. The increases in the magnitude of the initial and late components of the MG bursts, as well as the improvement in ankle function, depended on use of the leg. All these changes were delayed by immobilizing the leg for 6 days in an extended position. We discuss possible mechanisms underlying the increase in the magnitude of the MG bursts and propose that proprioceptive signals from the stretched MG muscles provide an error signal for rescaling the magnitude of the centrally generated initial component. Our data support the concept that proprioceptive feedback functions to scale the magnitude of feed-forward motor commands to ensure they are appropriate for the biomechanical properties of the musculoskeletal system.

A Fruitful Stochastic Model

1964 ◽  
Vol 9 (7) ◽  
pp. 273-276
Author(s):  
ANATOL RAPOPORT
Keyword(s):  
Stochastic Model

A Stochastic Model for Evolution of Altruistic Genes

1996 ◽  
Vol 6 (4) ◽  
pp. 445-453 ◽  
Author(s):  
Roberta Donato
Keyword(s):  
Stochastic Model

A Stochastic Model for the Inheritance of the Cancer Proneness Phenotype

1987 ◽  
Vol 26 (03) ◽  
pp. 117-123
Author(s):  
P. Tautu ◽  
G. Wagner
Keyword(s):  
Stochastic Model ◽  
Gaussian Process ◽  
Covariance Function ◽  
Neoplastic Disease ◽  
Disease Phenotype ◽  
Probabilistic Representation ◽  
Temporal Behaviour ◽  
Continuous Trait ◽  
Continuous Parameter ◽  
Level Zero

SummaryA continuous parameter, stationary Gaussian process is introduced as a first approach to the probabilistic representation of the phenotype inheritance process. With some specific assumptions about the components of the covariance function, it may describe the temporal behaviour of the “cancer-proneness phenotype” (CPF) as a quantitative continuous trait. Upcrossing a fixed level (“threshold”) u and reaching level zero are the extremes of the Gaussian process considered; it is assumed that they might be interpreted as the transformation of CPF into a “neoplastic disease phenotype” or as the non-proneness to cancer, respectively.

The Endothelial Cell and the Factor VIII Bypassing Activity of Prothrombin Complex Concentrate

1988 ◽  
Vol 60 (02) ◽  
pp. 226-229 ◽  
Author(s):  
Jerome M Teitel ◽  
Hong-Yu Ni ◽  
John J Freedman ◽  
M Bernadette Garvey
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Factor Viii ◽  
Prothrombin Complex Concentrate ◽  
Vascular Endothelial Cells ◽  
Vascular Endothelial ◽  
Monolayer Cultures ◽  
Coagulant Activity ◽  
Time Courses ◽  
Privileged Site

SummarySome classical hemophiliacs have a paradoxical hemostatic response to prothrombin complex concentrate (PCC). We hypothesized that vascular endothelial cells (EC) may contribute to this “factor VIII bypassing activity”. When PCC were incubated with suspensions or monolayer cultures of EC, they acquired the ability to partially bypass the defect of factor VIII deficient plasma. This factor VIII bypassing activity distributed with EC and not with the supernatant PCC, and was not a general property of intravascular cells. The effect of PCC was even more dramatic on fixed EC monolayers, which became procoagulant after incubation with PCC. The time courses of association and dissociation of the PCC-derived factor VIII bypassing activity of fixed and viable EC monolayers were both rapid. We conclude that EC may provide a privileged site for sequestration of constituents of PCC which express coagulant activity and which bypass the abnormality of factor VIII deficient plasma.

Stochastic Model of Traffic Jam and Traffic Signal Control

2011 ◽  
Vol 131 (2) ◽  
pp. 303-310
Author(s):  
Ji-Sun Shin ◽  
Cheng-You Cui ◽  
Tae-Hong Lee ◽  
Hee-hyol Lee
Keyword(s):  
Stochastic Model ◽  
Traffic Signal ◽  
Signal Control ◽  
Traffic Signal Control ◽  
Traffic Jam

Study on the Modes of Operation of a Multi-Machine Installations with Mechanical Reduction

2019 ◽  
pp. 12-22
Author(s):  
A. M. Oleynikov ◽  
L. N. Kanov
Keyword(s):  
Mathematical Description ◽  
Reactive Power ◽  
Maximum Efficiency ◽  
Wind Flow ◽  
System Of Equations ◽  
Mechanical Equilibrium ◽  
Synchronous Generators ◽  
Electromagnetic Excitation ◽  
Number Of Generators ◽  
Wide Range

The paper gives the description of the original wind electrical installation with mechanical reduction in which the output of vertical axis wind turbine with rather low rotation speed over multiplicator is distributed to a certain number of generators. The number of acting generators is determined by the output of actual operating wind stream at each moment. According to this constructive scheme, it is possible to provide effective and with maximum efficiency installation work in a wide range of wind speeds and under any schedule issued to the consumer of electricity. As there are no any experience in using such complexes, mathematical description of its main elements is given, namely windwheels, generators with electromagnetic excitation of magnetic electrical type, then their interaction with windwheel, and also the results of mathematical modeling of work system regimes under using the offered system of equations. The basis for the mathematical description of the main elements of the installation – synchronous generators – are the system of equations of electrical and mechanical equilibrium in relative units in rotating coordinates without considering saturation of the magnetic circuit. The equation of mechanical equilibrium systems includes torque and brake windwheel electromagnetic moments of generators with taking into account the reduction coefficients and friction. In addition, we specify the alternator rotor dynamics resulting from continuous torque of windwheel fluctuations under the influence of unsteady wind flow and wind speed serving as the original variable is modeled by a set of sinusoids. Model simplification is achieved by equivalization of similar generators and by disregarding these transitions with a small time constant. Calculation the installation with synchronous generators of two types of small and medium capacity taking into account the operational factors allowed us to demonstrate the logic of interactions in the main elements of the reported complex in the process of converting wind flow into the generated active and reactive power. We have shown the possibility of stable system work under changeable wind stream condition by regulating of the plant blade angle and with simultaneous varying of generator number of different types. All these are in great interest for project organizations and power producers.

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