Transient Response Curves Research Articles

Measurements of transient cataphoretic segregation in a discharge tube with large cylindrical end volumes

A study has been made of time-dependent cataphoresis in a binary gas mixture when a dc discharge is initiated in a tube with end volumes behind the electrodes. The gas separation in the positive column of the discharge is studied experimentally for a mixture of 0.025% argon in neon. The argon density is monitored at two locations in the positive column using a mass spectrometer. The experimental data are compared with computed transient response curves obtained using the theoretical model formulated by Ongena et al. A very good agreement between theory and experiment is obtained for the neon-argon mixture and the end-volume configuration under consideration.

Hydrogenation of ethylene on a Co-Mo/Al2O3 catalyst under transient conditions

Hydrogenation of ethylene on a Co-Mo/Al2O3 catalyst at 353 K and atmospheric pressure has been studied. The unsteady-state method was used, in which reactor feed-rate and feed-composition were changed in a defined way. The analysis of transient response curves proved negligible adsorption of hydrogen and ethane and confirmed the reaction mechanism of ethylene hydrogenation which involves reaction of adsorbed ethylene with hydrogen from gas phase in the rate determining step. Combined stationary and transient experimental data were used to calculate kinetic parameters: rate constant of ethylene hydrogenation, total concentration of active sites on the catalyst surface and equilibrium adsorption coefficient of ethylene.

Heterogeneity of a silver surface used in the oxidation of carbon monoxide

The mechanism of the oxidation of CO by nitrous oxide and oxygen over a silver catalyst has been studied by an analysis of the transient behaviour at 20 °C. Half of the total surface sites are active for the adsorption of oxygen and one-third of the active sites are active for the decomposition of N2O, indicating the heterogeneity of the silver surface. At a steady state of CO oxidation in the N2O + CO and the O2+ CO systems, the surface for the N2O + CO reaction is more reduced than that for the O2+ CO reaction. The activation energy is 14 kcal mol–1 for the O2+ CO reaction and 10 kcal mol–1 for the N2O + CO reaction, suggesting different rate-controlling steps.Adsorbed oxygen (presumed to be diatomic) formed from gaseous oxygen and not from N2O is responsible for the oxidation of CO. An Eley–Rideal-type mechanism is proposed and the rate of oxidation of CO by diatomic oxygen is estimated to be ca. 14 times faster than the rate of decomposition of N2O. Graphical analysis of the transient response curves obtained for the two reactions leads to the conclusion that the rate of formation of the diatomic oxygen species is the rate-determining step in the N2O + CO reaction.Computer simulation of the transient response curves proved the validity of the proposed reaction mechanism and gave estimates of the values of the kinetic parameters (kj) for all the elementary steps. Comparing the kj obtained for the two reactions, the dissociation of diatomic oxygen in the O2+ CO reaction was determined to be one hundred times faster than in the N2O + CO reaction, again indicating the heterogeneity of the working silver surface.

Discrimination of rival kinetic models in heterogeneous catalysis by the dynamic behaviour of products

AbstractThe transient response method has been applied to discriminate between rival kinetic models derived from the conventional Hougen‐Watson procedure in heterogeneous catalysis, by using some old data for the NO‐CO reaction, dehydrogenation of sec‐butanol, hydrogenation of phenol, and dehydrogenation of tert‐butanol. A computer technique is commonly used for the simulation of the transient response curves of products caused by the concentration jump of reactants in a flow type reactor. The shapes of the calculated response curves are of various characteristic types (depending on the given model) which allow for easy discrimination between rival kinetic models. The difficulty of the discrimination in some particular models is also discussed.

Transient cataphoresis in a discharge tube with end volumes

A theoretical and experimental study has been made of time-dependent cataphoresis in a binary gas mixture when a dc discharge is initiated in a tube with end volumes behind the electrodes. The theoretical models as proposed by Shair et al. and Metze and Chanin are compared. Transient response curves of the impurity density, computed in accordance with the two models, are presented and discussed. The gas separation in the positive column of a dc discharge is also studied experimentally for a mixture of 0.025% argon in neon. The argon density is monitored at two locations within the positive column of the discharge using a mass spectrometer. The experimental data are compared with calculations based on the model formulated by Metze and Chanin. A good agreement between theory and experiment is obtained for the end-volume configuration under consideration.

Transient and steady state phase response curves of limit cycle oscillators

The experiment of phase shifts resulting from discrete perturbations of stable biological rhythms has been carried out to study entrainment behavior of oscillators. There are two kinds of phase response curves, which are measured in experiments, according to as one measures the phase shifts immediately or long after the perturbation. The former is the first transient phase response curve and the latter is the steady state phase response curve. We redefine both curves within the framework of dynamical system theory and homotopy theory. Several topological properties of both curves are clarified. Consequently, it is shown that we must compare the shapes of both two phase response curves to investigate the inner structures of biological oscillators. Moreover, we prove that a single limit cycle oscillator involving only two variables cannot simulate transient resetting behavior reported by Pittendrigh and Minis (1964). In other words, the circadian oscillator of Drosophila pseudoobscura does not consist of a single oscillator of two variables. Finally we show that a model which consists of two limit cycle oscillators is able to simulate qualitatively the phase response curves of Drosophila.

Characterization of transient response curves in heterogeneous catalysis—I Classification of the curves

The first step in the search for a general rule has been conducted in order to predict the reaction mechanism in heterogeneous catalysis, based on the mode of the transient response curves of products caused by the concentration jump of the reactants. The response curves based on typical model reactions were simulated using a digital computer and the simulated responses revealed characteristic modes in accordance with the mechanism of the reactions. The modes can be classified into the following six different types: (I) Instantaneous response: surface reaction controlling or adsorption of reactants controlling. (II) Monotonic response: slow desorption of products or the combination of two or more factors. (III) Overshoot response: slow regeneration of active sites or active species on the surface, or competitive adsorption of reactants. (IV) S-shape response: the slow transformation of certain stable intermediates in the course of the reaction. (V) False start response: self-inhibition of adsorbed reactants to the reaction. And (VI) complex response: the superposition of two (or more) different types of responses due to dual reaction paths forming the same product or the existence of more than two rate controlling steps. Other factors contributing to the mode of the response curves have also been discussed.

Characterization of transient response curves in heterogeneous catalysis—II Estimation of the reaction mechanism in the oxidation of ethylene over a silver catalyst from the mode of the transient response curves

The reaction mechanism and the kinetic structure of the oxidation of ethylene over a silver catalyst at 91°C have roughly been elucidated from the mode of the transient response curves of ethylene oxide, carbon dioxide and water, due to the concentration jump of reactants. The typical overshoot mode with an instantaneous maximum for C 2H 4O clearly indicates two things. First that the surface reaction controlling in the reaction between adsorbed diatomic oxygen species and gaseous C 2H 4 (an Eley—Rideal type mechanism) with the rapid desorption of C 2H 4O formed and, second, that the slower regeneration of the adsorbed oxygen species. The typical S-shape mode with an overshoot for CO 2 strongly suggests the existence of an intermediate ( In) and, the presence of the ( In) has been actually confirmed by the transient response of its decomposition in an O 2-He stream. The ( In) can desorb as acetic acid only when the surface is reduced by H 2. Much transient data seems to suggest that the ( In) is formed from the reaction of adsorbed monoatomic oxygen species with C 2H 4 and, is decomposed by the reaction with diatomic oxygen species. The false start mode for the response curve of ( In) decomposition indicates the inhibitory effect of adsorbed ethylene on the reaction.

Reaction mechanism of NO-NH3-O2 system,elucidated by transient response technique.

Transient response technique was applied to elucidate the roles of oxygen in NO-NH3-O2 reaction system at low concentrations of NO and NH3 (ca. 500 ppm). Reaction hardly takes place in the absence of oxygen. Analyses of transient response curves of such reaction system indicated that the reaction involves consumption of surface oxygen. High activity of CuSO4-Active Carbon catalyst is due to its high affinity for oxygen.

Transient behavior of the oxidation of propylene over a modified silver oxide

AbstractThe oxidation of propylene over a silver oxide containing sodium chloride and sodium hydrogensulfate has been studied by using a transient response method at temperatures ranging from 150 to 175°C. An overshoot behavior for the transient response of propylene oxide indicates the mechanism of Eley‐Rideal type with a rapid desorption of propylene oxide and a slow regeneration of surface oxygen. The activation energy estimated at the transient state was 58.6 kJ/mol.A characteristic S‐shape mode for the transient response of carbon dioxide reveals the presence of a stable intermediate (In). The (In) can produce equimolar amounts of H2O and CO2 by the reaction with oxygen without producing propylene oxide, indicating that the ratio of C:H in the structure of (In) is 1:2. The amount of (In) estimated under the steady state of reaction is a linear relation to the rate of CO2 formation. The estimated apparent rate constant for the formation of CO2 is in good agreement with that for (In) decomposition estimated from the transient response curves of (In) decomposition. From this agreement, it is concluded that the (In) is a reaction intermediate through which carbon dioxide and water are produced.

Methods of Interpreting Transient Response Curves from Dynamic Sorption Experiments

Methods of Interpreting Transient Response Curves from Dynamic Sorption Experiments

Resonance phenomena in the nonlinear vibration of plates governed by Duffing's equation

This paper presents a theoretical and experimental study of the resonance phenomena of a nonlinear system, the time dependent part of which is governed by Duffing's equation. The method of Krylov, Bogoliubov and Mitropolsky is applied to analyze the transient motion near resonance, and the amplitude of the system is shown to change rapidly, during a short time duration, at certain critical driving frequencies. During this transitional period, the instantaneous response frequency of the system differs from the driving frequency, and the variation of amplitude vs response frequency is bounded by the usual steady-state nonlinear response curve. Experimental results are presented for a clamped circular plate driven into large amplitude oscillations by a magnetic force, during the downward and upward “jumps”. The transient nonlinear response curves during the jumps, and the free vibration (skelton) curves of the plate are determined experimentally. Methods for measuring the damping coefficient, linear frequency and nonlinear stiffness of the plate are also discussed.

Fundamental Studies on Rhizosphere Environment Control (2)

The applicability of the P.I.D. control algorithm for an identified soil temperature system1) was investigated using both experiments and computer simulations.Results:1) The P.I.D. soil temperature control experiments showed that although every four optimally adjusted P.I.D. parameter sets lead the controlled variable, (the soil temperature at the logarithmical middle point) to the stepwise desired value in the steady state, the transient response curves are differ greatly when four sets of optimal P.I.D. parameters from the C.H.R. method are used. The simulated P.I.D. soil temperature controls were similar to the above experiments except for slight differences in detail. This implies that investigations of P.I.D. soil temperatue control systems can be carried out using computer simulations composed of the mathematical model for a soil temperature system developed in a previous paper1) .2) Not only was it determined that P.I.D. soil temperature control can be performed using a digital computer, but that the P.I.D. soil temperature control system, itself, and the soil temperature distributions can be investigated with computer simulations while the soil temperature is P.I.D. controlled, if the digital computer possesses the state space simulation model of the P.I.D. soil temperature control system developed in the present paper.

Convergence of stimuli in arterial chemoreceptors.

A single chemoreeeptor fibre of the carotid sinus nerve responds both to hypoxia and to hypercapnia/acidity of the arterial blood. These reactions have been well brought out by such recent studies as those of Lahiri1 which he has illustrated in a figure in his paper at this symposium. If reactions to CO2 are presented as a series of CO2 response curves at various intensities of hypoxia, the curves appear as a fan of approximately straight lines which have a steeper slope the more intense the hypoxia. It is when there is some degree of hypoxia that the effects of CO2 become marked in the steady state, as Neil2 has always emphasised, but if the PCO2 arterial blood is changing, the effects of CO2 on discharge are more striking, for adaptation of the response to a sudden change of PCO2 marked, particularly in hyperoxia. Thus if a receptor is discharging at some steady initial level and the PaCO2 is suddenly raised, the discharge immediately rises along a steep transient response curve and then adapts down to lie upon the steady state curve.

Thermal Response of Microwave Transistors Under Pulsed Power Operation

The transient temperature response and thermal profiles near the junction of a transistor or other semiconductor device are nearly impossible to measure experimentally. These response characteristics can be accurately predicted, however, through the use of computeraided simulation. In this paper results from the simulation of two microwave power transistors are presented and discussed. In particular, the first device contains a single large junction area, and the second contains multiple junction areas. Thermal characteristics within the chip itself, that is, from the transistor junction to the chip .carrier, are emphasized. This region usually contains, by far, the greatest fraction of the total <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Delta</tex> T between the junction and the final heat sink, especially under pulsed power operation. Transient temperature response curves, internal temperature distributions and the effects of temperature dependent material properties are described. The effects of varying the power dissipation rate, pulse length and duty cycle are shown, and final1y, methods of improving heat transfer, such as the use of a diamond heat-spreader, are discussed.

A programme for on-line process identification

A hybrid/analog computer programme is presented for the automatic on-line computation of the time ratios necessary for the implementation of Strejc's method of indicial response analysis. The method, which does not require the recording of the transient response, avoids the difficulty of accurately constructing the tangent of maximum slope on the experimentally determined transient response curve.

Distributed amplifiers with paired-plate connections

It is shown that, in pairing the plates of a conventional distributed amplifier, it not only improves the frequency response but also the transient response. The transient response curves are normalized with respect to both amplitude and time, and may be applied to specific situations by resealing the axes. Also, a comparison with the conventional amplifier is presented.

Dynamic simulation of gas chromatographic column

The dynamic behavior of a gas—liquid chromatographic column was investigated to develop methods for estimation of the pulse response and dead time. A mathematical model describing the column behavior was proposed and the resulting response curves compared with the experimental column behavior. This study indicated that the models based on assumptions of perfect mixing and plug flow could be used to predict the dead time which could represent the residence time of the solute gas through the column if enough subdivisions were used for the simulation. Van Deemter's model was verified experimentally and adequately describes the gas—liquid chromatographic column in process control computer simulation of the system. The values of the system parameters characterizing the dynamic behavior were obtained from the simulation. The pulse response curve simulation is unique for the estimation of dead time just as is the transient response curve for the steady-state time.

Dynamics of Pressure in Forced-Flow Evaporator System

Theoretical solutions are here presented which may be available to the understanding of dynamics in the forced-flow evaporator system. Some basic forms of various transient response curves are illustrated by using these solutions. As a main result, it was made clear that the dynamic behavior of system pressure is composed by two factors. The first factor shows the effect as lumped-parameter, and the second as distributed-parameter. It was found, moreover, that the transient response of pressure is almost determined by the lumped-parameter effect.

Dynamics of Pressure in Forced-Flow Evaporator System

Some theoretical solutions are here intrcduced which may be applied to the analysis of dynamics in forced-flow evaporator systems. Some basic forms of the various transient response curves are illustrated by using the above solutions. As a main result, it was made clear that the dynamic behavior of system pressure is subjected to two factors. The first factor has such a physical meaning as a lumped parameter corresponding to drum-type boilers, and the second as a distributed parameter. It is found, however, that the transient response of pressure is almost determined by the lumped parameter.