The steady-state kinetics of parallel reaction networks

We infused 11 mmol/kg of intravenous ethanol into dogs with either intact renal function (n = 5) or ureteral ligation (n = 7), and studied by frequent blood sampling and by urine collection the time and mode of ethanol equilibration, the elimination parameters, and the comparison of observed equilibrated plasma ethanol levels to levels predicted either by linear or by nonlinear kinetics. Equilibration time was 25 min or less, renal fraction of elimination was less than 5% of total elimination, and both linear (elimination rate) and nonlinear (Vmax and Km) elimination parameters were not different between dogs with intact renal function and dogs with anuria. Serum sodium concentration did not change throughout the experiments, eliminating the hypothesis that acute ethanol load creates clinically significant temporary osmotic water transfer from the intracellular into the extracellular compartment. Distribution volumes of ethanol from linear kinetics were slightly, but not statistically, greater than volumes from nonlinear kinetics. Equilibrated plasma ethanol levels predicted by linear kinetics agreed closely with observed levels greater than 4 mmol/liter, but underestimated observed levels less than 4 mmol/liter. Equilibrated plasma ethanol levels predicted by nonlinear kinetics agreed with observed levels throughout the range of observed concentrations. The use of linear kinetics to predict blood ethanol levels should be limited to the pseudolinear portion of the blood alcohol curve.

Introduction to Circuit Analysis and Design

The linearity of the (AMT) kinetics of amitriptyline has been tested in 135 depressed dosed twice daily by measuring plasma. Their (AMT) and nortriptyline (NT) levels under steady-state conditions. The AMT concentration/dose ratios at low and high dosages were not significantly different and there was a linear relationship between the dose ratios and the concentration ratios. No change in the metabolic ratio (AMT/NT) was observed between the two dosages. Although the results are consistent with linear AMT kinetics, there may have been nonlinear kinetics in some patients as the ratio between the concentration/dose ratios in them at low and high dosages was greater than one. Those patients were characterized by a low concentration/dose ratio at low dosage. No clinical adverse effect appeared in the study.

Chapter 7 - Ohm's Law: Electric Current Is Driven by Emf, and Limited by Electrical Resistance

In this paper, the small signal stability of a Battery Energy Storage System (BESS) used in a low voltage islanded microgrid is investigated for an ohmic load case using eigenvalue sensitivity analysis. Two approaches namely Quasi Steady State (QSS) and Dynamic Phasor Modeling (DPM) are presented and compared for a reference BESS in a real microgrid. The QSS approach is considered as a traditional method to model system dynamics assuming that they are slow enough to apply steady state rules. The DPM approach on the other hand considers the electrical dynamics in the control feedback loop and the coupling between the parallel inverters. The evaluation of the mathematical models for both approaches as well as simulation and measurement results are presented. The classical QSS stability analysis applied to the BESS does not show the dependency of stability margins on droop parameters, smoothing time constant or load parameters. This problem can be overcome by the presented DPM method. The sensitivity of the BESS and load parameters on stability limits is studied in detail.

An analysis of reaction rate enhancements by forced concentration oscillations of reactants for an adsorption/desorption type model with Eley-Rideal surface kinetics, is presented. Under cycling conditions in which the cycle time approaches zero, there is considerable rate enhancement relative to optimal steady state for nonlinear kinetics but no improvement for linear kinetics. The presence of inerts or products from irreversible reactions deteriorates the rate enhancement. For cycle times approaching infinity, there is no rate enhancement for either linear or nonlinear kinetics.

Rapid adsorption of arsenate from water on a novel hybrid of zirconia oxide anchored rGO functionalised carbon foam

The methodology previously developed for determining the Flux Control Coefficients [Delgado & Liao (1992) Biochem. J. 282, 919-927] is extended to the calculation of metabolite Concentration Control Coefficients. It is shown that the transient metabolite concentrations are related by a few algebraic equations, attributed to mass balance, stoichiometric constraints, quasi-equilibrium or quasi-steady states, and kinetic regulations. The coefficients in these relations can be estimated using linear regression, and can be used to calculate the Control Coefficients. The theoretical basis and two examples are discussed. Although the methodology is derived based on the linear approximation of enzyme kinetics, it yields reasonably good estimates of the Control Coefficients for systems with non-linear kinetics.

Measurement of gap junction conductance (gj) with patch-clamp amplifiers can, due to series resistance problems, be subject to considerable errors when large currents are measured. Formulas developed to correct for these errors unfortunately depend on exact estimates of series resistance, which are not always easy to obtain. Discontinuous single-electrode voltage-clamp amplifiers (DSEVCs) were shown to overcome series resistance problems in single whole cell recording. With the use of two synchronized DSEVCs, the simulated gj in a model circuit can be measured with a maximum error of <5% in all recording situations investigated (series resistance, 5-47 MOmega; membrane resistance, 20-1,000 MOmega; gj, 1-100 nS). At a very low gj of 100 pS, the error sometimes exceeded 5% (maximum of 15%), but the error was always <5% when membrane resistance was >100 MOmega. The precision of the measurements is independent of series resistance, membrane resistance, and gj. Consequently, it is possible to calculate gj directly from Ohm's law, i.e., without using correction formulas. Our results suggest that DSEVCs should be used to measure gj if large currents must be recorded, i.e., if cells are well coupled or if membrane resistance is low.

Whole cell patch clamp has provided much insight into the function of voltage-gated ion channels in central neurons. However, voltage errors caused by the resistance of the recording electrode [series resistance (Rs)] limit its application to relatively small ionic currents. Ohm's law is often applied to estimate and correct the membrane potential for these voltage errors. We tested this assumption in brainstem motoneurons of adult frogs with dual patch-clamp recordings, one performing whole cell voltage clamp of K+ currents and the other directly recording the membrane potential. We hypothesized that Ohm's law-based correction would approximate the measured voltage error. We found that voltage errors averaged <5 mV for currents considered to be large for patch clamp (∼7-13 nA) and <10 mV for massive currents thought to be experimentally intractable (25-30 nA), each error falling within commonly accepted inclusion limits. In most cases Ohm's law-based correction overpredicted these measured voltage errors by roughly 2.5-fold. Consequently, the use of Ohm's law to correct for voltage errors led to erroneous current-voltage (I-V) relationships, showing the greatest distortion for inactivating currents. Finally, recordings with low electrode Rs compensated moderately by the amplifier circuitry appeared to have smaller voltage errors than those with larger Rs and high compensation despite the same "effective Rs" and current magnitude. Therefore, when Rs is low, large currents may be studied with better-than-expected voltage control. These results suggest that patch-clamp may be used to study ionic currents often interpreted to be off limits because of size.NEW & NOTEWORTHY Voltage errors occur in whole cell voltage clamp. We make, to our knowledge, the first direct measurements of these errors and find that voltage errors are far smaller than standard calculations would predict. Since voltage errors were often minimal during the measurement of large ion channel currents, this technique may be applied to large neurons of adults to gain insight into ion channel function across the life span and progression of disease.

Social-like bacteria, fungi, and protozoa communicate chemical and behavioral signals to coordinate their specializations into an ordered group of individuals capable of fitter ecological performance. Examples of microbial “social” behaviors include sporulation and dispersion, kin recognition, and nonclonal or paired reproduction. Paired reproduction by ciliates is believed to involve intra- and intermate selection through pheromone-stimulated “courting” rituals. Such social maneuvering minimizes survival-reproduction tradeoffs while sorting superior mates from inferior ones, lowering the vertical spread of deleterious genes in geographically constricted populations and possibly promoting advantageous genetic innovations. In a previous article, I reported findings that the heterotrich Spirostomum ambiguum can out-complete mating rivals in simulated social trials by learning behavioral heuristics which it then employs to store and select sets of altruistic and deceptive signaling strategies. Frequencies of strategy use typically follow Maxwell-Boltzmann (MB), Fermi-Dirac (FD), or Bose-Einstein (BE) statistical distributions. For ciliates most adept at social decision making, a brief classical MB computational phase drives signaling behavior into a later quantum BE computational phase that condenses or favors the selection of a single fittest strategy. Appearance of the network analogue of BE condensation coincides with Hebbian-like trial-and-error learning and is consistent with the idea that cells behave as heat engines, where loss of energy associated with specific cellular machinery critical for mating decisions effectively reduces the temperature of intracellular enzymes cohering into weak Fröhlich superposition. I extend these findings by showing the rates at which ciliates switch serial behavioral strategies agree with principles of chemical reactions exhibiting linear and nonlinear Arrhenius kinetics during respective classical and quantum computational phases. Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from quantum tunneling in social information processing.

In this paper, an efficient numerical procedure for calculating the solution of the non–linear neutron point kinetics equations in the field of nuclear reactor dynamics is presented. The explicit finite difference method is applied to solve the non–linear neutron point kinetics equations with temperature feedback reactivity. The numerical solution obtained by explicit finite difference scheme is an approximate solution based on neutron density, the precursor's concentration of multi–group delayed neutrons, and the reactivity function. The method is investigated over data of nuclear reactor–type compositions, with appropriate initial conditions applying in three types of reactivity: step, ramp and temperature feedback. The computational results show that this numerical approximation method is straightforward and effective for solving the non–linear point kinetics equations. Numerical results addressing the time behaviour of neutron density and results of this method with different types of reactivity are presented graphically. The comparisons of results with other referred methods are also discussed.

Photodegradation of organic and inorganic pollutants by L-tyrosine@AC/Fe3O4 nanocomposites under visible light: Evaluation of linear and nonlinear kinetics, isotherm models, scavengers effect, and antibacterial activity

This study presents a structural analysis of NiO and the fabrication of Al/NiO/p-Si isotype heterojunction photodiode (PD) as well as an investigation of the photo-response and photovoltaic (PV) properties of the PD in the various illumination intensities. The series resistance (RS) value of the Al/NiO/p-Si was calculated to be 0.11 kΩ using Ohm's Law at 2 V. This result corroborates the assertion that RS is the pivotal parameter for attaining optimal performance in a PD. The NiO has made a notable improvement to the electrical parameters such as ideality factor, barrier height, and series resistance. The spectral responsivity R value of the PD was calculated as 1.59 A/W at -2 V. The Al/NiO/p-Si exhibited a short-circuit current density (JSC) of 60.38 mA.cm-2, an open-circuit voltage (VOC) of 149.0 mV, a fill factor (FF) of 27.67%, and a power conversion efficiency (PCE) of 2.49%. In view of the experimental results, it can be concluded that NiO represents a promising material for the optimization of heterojunction photodiode applications.

Quasi-steady state (QSS) reduction is a commonly used method to lower the dimension of a differential equation model of a chemical reaction network. From a mathematical perspective, QSS reduction is generally interpreted as a special type of singular perturbation reduction, but in many instances the correspondence is not worked out rigorously, and the QSS reduction may yield incorrect results. The present paper contains a thorough discussion of QSS reduction and its relation to singular perturbation reduction for the special, but important, case when the right-hand side of the differential equation is linear in the variables to be eliminated (but the differential equation model might otherwise be nonlinear). For this class we give necessary and sufficient conditions for a singular perturbation reduction (in the sense of Tikhonov and Fenichel) to exist, and to agree with QSS reduction. We then apply the general results to chemical reaction networks with noninteracting species, generalizing earlier results and methods for steady states to QSS scenarios. We provide easy-to-check graphical conditions to select parameter values for which the singular perturbation reduction applies, and additionally, we identify when the singular perturbation reduction agrees with the QSS reduction. Finally we consider a number of examples.