Effect of sustained flow perturbations on stability and compensation of tubuloglomerular feedback

2003 ◽  
Vol 285 (5) ◽  
pp. F972-F989 ◽  
Author(s):  
Darren R. Oldson ◽  
Leon C. Moore ◽  
Harold E. Layton
Keyword(s):  
Mathematical Model ◽  
Proximal Tubule ◽  
Limit Cycle ◽  
Critical Value ◽  
Tubuloglomerular Feedback ◽  
Feedback Gain ◽  
Acta Physiol ◽  
Pressure Oscillations ◽  
Intratubular Pressure ◽  
Abrupt Changes

A mathematical model previously formulated by us predicts that limit-cycle oscillations (LCO) in nephron flow are mediated by tubuloglomerular feedback (TGF) and that the LCO arise from a bifurcation that depends heavily on the feedback gain magnitude, γ, and on its relationship to a theoretically determined critical value of gain, γc. In this study, we used that model to show how sustained perturbations in proximal tubule flow, a common experimental maneuver, can initiate or terminate LCO by changing the values of γ and γc, thus changing the sign of γ - γc. This result may help explain experiments in which intratubular pressure oscillations were initiated by the sustained introduction or removal of fluid from the proximal tubule (Leyssac PP and Baumbach L. Acta Physiol Scand 117: 415–419, 1983). In addition, our model predicts that, for a range of TGF sensitivities, sustained perturbations that initiate or terminate LCO can yield substantial and abrupt changes in both distal NaCl delivery and NaCl delivery compensation, changes that may play an important role in the response to physiological challenge.

Perturbation analysis of tubuloglomerular feedback in hydropenic and hemorrhaged rats

1983 ◽  
Vol 245 (5) ◽  
pp. F554-F563 ◽  
Author(s):  
L. C. Moore ◽  
J. Mason
Keyword(s):  
Proximal Tubule ◽  
Feedback Loop ◽  
Tubuloglomerular Feedback ◽  
Fluid Delivery ◽  
Intratubular Pressure ◽  
Fluid Load ◽  
Combined Action ◽  
Distal Delivery ◽  
Distal Flow ◽  
Variable Analysis

A closed-feedback-loop method was used to investigate regulation of SNGFR and distal fluid delivery by tubuloglomerular feedback (TGF) in hydropenic and hemorrhaged rats. Unblocked nephrons were perturbed by early proximal perfusion of previously collected, inulin-free, tubular fluid at 0, 7.5, and 15 nl/min, thereby increasing nephron fluid load. The resultant changes in SNGFR, tubular reabsorption, proximal intratubular pressure, and early distal flow were measured. During perfusion, SNGFR decreased and distal flow increased; the effect on reabsorption was variable. Analysis of the data indicated that the combined action of TGF and changes in proximal tubule and Henle's loop reabsorption were able to provide a maximum of 56% compensation for the effect of the perturbation on distal delivery in hydropenic rats and 70% compensation in hemorrhaged rats. In one group of hydropenic rats in which a significant fall in reabsorption was found, the total fluid load presented to the nephron, SNGFR plus the perfusion rate, was significantly better regulated than distal delivery. This result is consistent with the behavior of a model used to estimate the contribution of TGF to the observed regulation. The results indicated that TGF alone could provide 56% compensation for the perturbation in hydropenia and a significantly greater 72% compensation following hemorrhage. The conclusions are 1) that the properties of TGF are sufficient to result in significant regulation of distal fluid delivery and SNGFR, 2) that hemorrhage increases the strength of the TGF response, and 3) that TGF regulation of SNGFR and distal delivery is strongly influenced by changes in proximal tubule and loop of Henle reabsorption.

scholarly journals Assessment of Steady and Unsteady Friction Models in the Draining Processes of Hydraulic Installations

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1888
Author(s):  
Óscar E. Coronado-Hernández ◽  
Ivan Derpich ◽  
Vicente S. Fuertes-Miquel ◽  
Jairo R. Coronado-Hernández ◽  
Gustavo Gatica
Keyword(s):  
Mathematical Model ◽  
Turbulent Flow ◽  
Water Velocity ◽  
Experimental Facility ◽  
Governing Equations ◽  
Pressure Oscillations ◽  
Air Pocket ◽  
Friction Models ◽  
The Mathematical Model

The study of draining processes without admitting air has been conducted using only steady friction formulations in the implementation of governing equations. However, this hydraulic event involves transitions from laminar to turbulent flow, and vice versa, because of the changes in water velocity. In this sense, this research improves the current mathematical model considering unsteady friction models. An experimental facility composed by a 4.36 m long methacrylate pipe was configured, and measurements of air pocket pressure oscillations were recorded. The mathematical model was performed using steady and unsteady friction models. Comparisons between measured and computed air pocket pressure patterns indicated that unsteady friction models slightly improve the results compared to steady friction models.

State Estimator of Flow as an Integrated Computational Method With the Feedback of Online Experimental Measurement

1997 ◽  
Vol 119 (4) ◽  
pp. 814-822 ◽  
Author(s):  
Toshiyuki Hayase ◽  
Satoru Hayashi
Keyword(s):  
Mathematical Model ◽  
Turbulent Flows ◽  
Experimental Measurement ◽  
Flow Simulation ◽  
Computational Method ◽  
Feedback Gain ◽  
State Estimator ◽  
Output Measurement ◽  
Real Flow ◽  
The Mathematical Model

This paper deals with a state estimator or simply an observer of flow field. The observer, being a fundamental concept in the control system theory, also has a potential in the analysis of flow related problems as an integrated computational method with the aid of experiment. In the framework of the observer, the state of physical flow is estimated from the mathematical model with the feedback of on-line experimental measurement. A SIMPLER based flow simulation algorithm is used as the mathematical model of the real flow and partial experimental measurement of flow is fed back to the boundary condition through the feedback controller. The existence of the feedback-loop essentially distinguishes the observer from ordinary flow simulations. Time variation of the computational result of the observer is expected to converge exactly to that of the physical flow in the whole flow domain even for unstable turbulent flows. A numerical experiment has been performed to confirm the validity of the proposed observer for a turbulent flow through a duct of square cross section. The physical flow to be estimated is modeled by a numerical solution. Appropriate choice for the proportional feedback gain of the observer results in accelerated convergence of the simulation by a factor of 0.012 and reduced error in estimation of the perturbation velocity by a factor of 0.6 in the whole domain or a factor of 0.3 behind the output measurement plane in comparison with the ordinary flow simulation without feedback.

scholarly journals Mathematical Analysis of Influenza A Dynamics in the Emergence of Drug Resistance

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Caroline W. Kanyiri ◽  
Kimathi Mark ◽  
Livingstone Luboobi
Keyword(s):  
Mathematical Model ◽  
Sensitivity Analysis ◽  
Drug Resistance ◽  
Stability Analysis ◽  
Influenza A ◽  
Reproduction Number ◽  
Critical Value ◽  
Backward Bifurcation ◽  
Transmission Dynamics ◽  
High Morbidity

Every year, influenza causes high morbidity and mortality especially among the immunocompromised persons worldwide. The emergence of drug resistance has been a major challenge in curbing the spread of influenza. In this paper, a mathematical model is formulated and used to analyze the transmission dynamics of influenza A virus having incorporated the aspect of drug resistance. The qualitative analysis of the model is given in terms of the control reproduction number,Rc. The model equilibria are computed and stability analysis carried out. The model is found to exhibit backward bifurcation prompting the need to lowerRcto a critical valueRc∗for effective disease control. Sensitivity analysis results reveal that vaccine efficacy is the parameter with the most control over the spread of influenza. Numerical simulations reveal that despite vaccination reducing the reproduction number below unity, influenza still persists in the population. Hence, it is essential, in addition to vaccination, to apply other strategies to curb the spread of influenza.

Micropuncture analysis of single-nephron function in NHE3-deficient mice

1999 ◽  
Vol 277 (3) ◽  
pp. F447-F453 ◽  
Author(s):  
John N. Lorenz ◽  
Patrick J. Schultheis ◽  
Timothy Traynor ◽  
Gary E. Shull ◽  
Jürgen Schnermann
Keyword(s):  
Proximal Tubule ◽  
Filtration Rate ◽  
Distal Tubule ◽  
Transport Processes ◽  
Tubuloglomerular Feedback ◽  
Thick Ascending Limb ◽  
Fluid Reabsorption ◽  
Fluid Delivery ◽  
Single Nephron ◽  
Flow Pressure

The Na/H exchanger isoform 3 (NHE3) is expressed in the proximal tubule and thick ascending limb and contributes to the reabsorption of fluid and electrolytes in these segments. The contribution of NHE3 to fluid reabsorption was assessed by micropuncture in homozygous ( Nhe3 −/−) and heterozygous ( Nhe3 +/−) knockout mice, and in their wild-type (WT, Nhe3 +/+) littermates. Arterial pressure was lower in the Nhe3 −/−mice (89 ± 6 mmHg) compared with Nhe3 +/+ (118 ± 4) and Nhe3 +/−(108 ± 5). Collections from proximal and distal tubules demonstrated that proximal fluid reabsorption was blunted in both Nhe3 +/− and Nhe3 −/−mice (WT, 4.2 ± 0.3; Nhe3 +/−, 3.4 ± 0.2; and Nhe3 −/−, 2.6 ± 0.3 nl/min; P < 0.05). However, distal delivery of fluid was not different among the three groups of mice (WT, 3.3 ± 0.4 nl/min; Nhe3 +/−, 3.3 ± 0.2 nl/min; and Nhe3 −/−, 3.0 ± 0.4 nl/min; P < 0.05). In Nhe3 −/−mice, this compensation was largely attributable to decreased single-nephron glomerular filtration rate (SNGFR): 10.7 ± 0.9 nl/min in the Nhe3 +/+ vs. 6.6 ± 0.8 nl/min in the Nhe3 −/−, measured distally. Proximal-distal SNGFR differences in Nhe3 −/−mice indicated that much of the decrease in SNGFR was due to activation of tubuloglomerular feedback (TGF), and measurements of stop-flow pressure confirmed that TGF is intact in Nhe3 −/−animals. In contrast to Nhe3 −/−mice, normalization of early distal flow rate in Nhe3 +/−mice was not related to decreased SNGFR (9.9 ± 0.7 nl/min), but rather, to increased fluid reabsorption in the loop segment ( Nhe3 +/+, 2.6 ± 0.2; Nhe3 +/−, 3.6 ± 0.5 nl/min). We conclude that NHE3 is a major Na/H exchanger isoform mediating Na+ and fluid reabsorption in the proximal tubule. In animals with NHE3 deficiency, normalization of fluid delivery to the distal tubule is achieved through alterations in filtration rate and/or downstream transport processes.

Modeling Unsteady Flow of a Lean Partially Premixed Flame on a Dry Low NOx Combustion System

2013 ◽  
Author(s):  
Salvatore Matarazzo ◽  
Hannes Laget ◽  
Evert Vanderhaegen ◽  
Jim B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Limit Cycle ◽  
Gas Turbines ◽  
Premixed Flame ◽  
Computational Domain ◽  
Pressure Oscillations ◽  
Combustion Dynamics ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Limit Cycle Behavior

The phenomenon of combustion dynamics (CD) is one of the most important operational challenges facing the gas turbine (GT) industry today. The Limousine project, a Marie Curie Initial Training network funded by the European Commission, focuses on the understanding of the limit cycle behavior of unstable pressure oscillations in gas turbines, and on the resulting mechanical vibrations and materials fatigue. In the framework of this project, a full transient CFD analysis for a Dry Low NOx combustor in a heavy duty gas turbine has been performed. The goal is to gain insight on the thermo-acoustic instability development mechanisms and limit cycle oscillations. The possibility to use numerical codes for complex industrial cases involving fuel staging, fluid-structure interaction, fuel quality variation and flexible operations has been also addressed. The unsteady U-RANS approach used to describe the high-swirled lean partially premixed flame is presented and the results on the flow characteristics as vortex core generation, vortex shedding, flame pulsation are commented on with respect to monitored parameters during operations of the GT units at Electrabel/GDF-SUEZ sites. The time domain pressure oscillations show limit cycle behavior. By means of Fourier analysis, the coupling frequencies caused by the thermo-acoustic feedback between the acoustic resonances of the chamber and the flame heat release has been detected. The possibility to reduce the computational domain to speed up computations, as done in other works in literature, has been investigated.

Renal effects of endogenous prostaglandin synthesis promoter ONO-3122

1992 ◽  
Vol 262 (6) ◽  
pp. F1047-F1054
Author(s):  
T. Takabatake ◽  
H. Hara ◽  
Y. Ishida ◽  
H. Ohta ◽  
K. Kobayashi
Keyword(s):  
Proximal Tubule ◽  
Prostaglandin Synthesis ◽  
Fluid Replacement ◽  
Tubuloglomerular Feedback ◽  
Loop Of Henle ◽  
Distal Nephron ◽  
Water Reabsorption ◽  
Renal Vasculature ◽  
Renal Effects ◽  
Collecting Tubules

The renal effects of a prostaglandin synthesis agonist, 1-iodo-3-aminomethyl-5,6,7,8-tetrahydro-2-naphthol (ONO-3122), were investigated in anesthetized rats. ONO-3122 (0.3 mg/kg + 0.3 mg.kg-1.h-1 iv) doubled the urinary excretion of the main metabolites of prostaglandin F, and induced transient increases in renal blood flow and glomerular filtration rate (GFR) with a marked, stable natriuresis. Indomethacin suppressed the natriuresis. When the diuretic fluid losses were replaced, micropuncture showed an unaltered reabsorption of sodium in the proximal tubule but reductions in the loop of Henle (86 +/- 1 vs. 76 +/- 1%) and in the more distal segments (98 +/- 1 vs. 83 +/- 3%) with comparable reductions in water reabsorption. Potassium secretion was seen in the distal and collecting tubules. Without fluid replacement, sodium reabsorption was reduced in the loop and more distal nephron but increased in the proximal tubule. Differences between proximal and distal nephron GFR were unaffected by systemic ONO-3122. Loop perfusion with ONO-3122 did not change tubuloglomerular feedback responses, which were, however, completely suppressed by furosemide. It is concluded that ONO-3122 stimulates renal prostaglandin biosynthesis, transiently dilates renal vasculature, and induces natriuresis mainly by suppressing sodium and water reabsorption in the loop of Henle and the more distal nephron. Luminal ONO-3122 does not affect the tubuloglomerular feedback.

scholarly journals Analytical calculation of time of reaching specific values based on visibility loss during a fire

2018 ◽  
Vol 193 ◽  
pp. 03007 ◽  
Author(s):  
Sergei Kolodyazhniy ◽  
Vladimir Kozlov
Keyword(s):  
Mathematical Model ◽  
Analytical Solutions ◽  
Ventilation System ◽  
Analytical Calculation ◽  
Critical Time ◽  
Original Data ◽  
Critical Value ◽  
Time Intervals ◽  
Evacuation Time ◽  
Analytical Formulas

Using an integral mathematical model of a fire considering the assumptions typical of a starting stage of a fire, analytical dependencies were obtained for determining the time of reaching a critical value of the density of a smoke screen in a premises with a fire epicenter and adjoining premises. By means of analytical formulas for determining critical evacuation time intervals based on visibility loss, table values for different parameters that are included in the original equations were obtained. Simple engineering analytical solutions that describe the dynamics of smoke formation in premises in case of a fire when used in a certain combination are presented. The obtained dependencies allow one to identify the critical time of evacuation with no use of special PC software as well as to obtain original data without calculating an anti-smoke ventilation system.

Effect of joint stiffness on the dynamic stability of a one-link force-controlled manipulator

Robotica ◽  
1989 ◽  
Vol 7 (4) ◽  
pp. 339-342
Author(s):  
Bing C. Chiou ◽  
M. Shahinpoor
Keyword(s):  
Dynamic Stability ◽  
Closed Loop ◽  
Force Feedback ◽  
Joint Stiffness ◽  
Stable Limit Cycle ◽  
Critical Value ◽  
Interaction Process ◽  
Feedback Gain ◽  
Stable Limit ◽  
Damping Force

SUMMARYStudies are the effects of joint flexibility on the dynamic stability of a one-link force-controlled manipulator. The closed-loop dynamic equation with the explicit force controller and the damping force controller are first derived. Stability analysis is then carried out by computing the system eigenvalues. Results indicate a conditionally stable system. Due to the presence of discontinuous contacts with the environment during the interaction process, the system exhibits a stable limit cycle when the force feedback gain goes beyond the critical value.

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