Pulse response technique

Pudjiono and Tavare (1993) used the pulse-response technique to study the residence time... 

Dogu and Smith [22,23] have given the theoretical basis for the dynamic pulse response technique. If the experimental conditions are identical to those described for the step injection and the injection time is much lower than the diffusion time L2/Z), the theoretical first moment is... 

Towell (T24, ), and Hikita and Kikukawa (Hll) have utilized a pulse response technique or step response and the rest of the data have been obtained by the steady back-mixing method. These are correlated as follows (M27). 

The basic steps of the experimental operation of the DC pulse response technique proposed for monitoring the environmental pollution level is as simple as follows... 

On the other hand, pulse response techniques have been useful for obtaining, these par< imeters for first order and reversible adsorption process - SMITH et col (2), (3). The objective of this communication is to apply this moment method to a chromatographic - type column in which the reacting gas flows and reacts in a stationary liquid phase. ... 

A frequency response technique was tried first and some results were received. The useful frequency domain was less than one order of magnitude, while in electrical problems five orders of magnitude can be scanned. The single pulse technique was more revealing, but evaluation by moments had the usual accumulation of errors. Fourier transform of the pulse test results was the final method. 

A square concentration pulse flow technique has been developed to study the kinetics of catalytic reactions over catalysts which change their stoichiometry in response to the reaction conditions. The technique makes it possible to obtain hysteresis-free kinetics data while greatly reducing the time during which the catalyst is exposed to the reaction mixture. 

This is a dynamic electrochemical technique, which can be used to study electron transfer reactions with solid electrodes. A voltammo-gram is the electrical current response that is due to applied excitation potential. Chapter 18b describes the origin of the current in steady-state voltammetry, chronoamperometry, cyclic voltammetry, and square wave voltammetry and other pulse voltammetric techniques. 

The realization that current sampling on a step pulse can increase the detection sensitivity by increasing the faradaic/charging ratio is the basis for the development of various pulse voltammetric (or polarographic) techniques. Also, the pulses can be applied when it is necessary and can reduce the effect of diffusion on the analyte. Figure 18b. 11 shows the waveform and response for three commonly used pulse voltammetric techniques normal pulse voltammetry (NPY), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). 

Knowledge of the dynamics of excited states is of major importance in understanding photophysical, photochemical and photobiological processes. Two time-resolved techniques, pulse fluorometry and phase-modulation fluorometry, are commonly used to recover the lifetimes, or more generally the parameters characterizing the S-pulse response of a fluorescent sample (i.e. the response to an infinitely short pulse of light expressed as the Dirac function S). 

Pulse fluorometry uses a short exciting pulse of light and gives the d-pulse response of the sample, convoluted by the instrument response. Phase-modulation fluorometry uses modulated light at variable frequency and gives the harmonic response of the sample, which is the Fourier transform of the d-pulse response. The first technique works in the time domain, and the second in the frequency domain. Pulse fluorometry and phase-modulation fluorometry are theoretically equivalent, but the principles of the instruments are different. Each technique will now be presented and then compared. 

The time of data collection depends on the complexity of the (5-pulse response. For a single exponential decay phase fluorometry is more rapid. For complex 5-pulse responses, the time of data collection is about the same for the two techniques in pulse fluorometry, a large number of photon events is necessary, and in phase fluorometry, a large number of frequencies has to be selected. It should be emphasized that the short acquisition time for phase shift and modulation ratio measurements at a given frequency is a distinct advantage in several situations, especially for lifetime-imaging spectroscopy. 

Thus we see that the stimulus-response technique using a step or pulse input function provides a convenient experimental technique for finding the age distribution of the contents and the residence-time distribution of material passing through a closed vessel. 

Today, ultrafast pulsed-laser techniques, high-speed computers, and other sophisticated instrumentation make it possible to measure the time evolutions of reactants, intermediates, transition structures, and products following an abrupt photoactivation of a starting material. Detailed theoretical calculations, experienced judgments based on the literature, and newly accessible femtosecond-domain experimental data providing observed intensities of chemical species versus time can provide insights on the atomic-scale events responsible for overall reaction outcomes. 

A gated deuterium lamp which has a full width at half-maximum (FWHM) ofabout2nsanddecay time of 1 ns has been used. The decay curves are deconvolved by numerical convolution technique with the assumption that the delta-pulse response is a single exponential function. A programme is used that varies the lifetime until the sum oi the squares or tne deviations between the observed and the calculated decay curves is a minimum (Fig. 11.5). If t0 = unquenched fluorescence lifetime and t = lifetime of quenched... 

The development of a mixed time-frequency representation in which both characteristics of the field and the response function are highlighted is currently receiving considerable attention. This activity is triggered by the rapid progress in pulse-shaping techniques, which made it possible to control the temporal profiles as well as the phases of optical fields with a remarkable accuracy [1-4]. These developments have further opened up the possibility of coherent control of dynamics in condensed phases [5-7]. 

A complete comprehension of Single Pulse electrochemical techniques is fundamental for the study of more complex techniques that will be analyzed in the following chapters. Hence, the concept of half-wave potential, for example, will be defined here and then characterized in all electrochemical techniques [1, 3, 8]. Moreover, when very small electrodes are used, a stationary current-potential response is reached. This is independent of the conditions of the system prior to each potential step and even of the way the current-potential was obtained (i.e., by means of a controlled potential technique or a controlled current one) [9, 10]. So, the stationary solutions deduced in this chapter for the current-potential curves for single potential step techniques are applicable to any multipotential step or sweep technique such as Staircase Voltammetry or Cyclic Voltammetry. Moreover, many of the functional dependences shown in this chapter for different diffusion fields are maintained in the following chapters when multipulse techniques are described if the superposition principle can be applied. 

This chapter addresses more complex electrode processes than one-electron reversible electrochemical reactions in single potential pulse techniques. The concepts given here set the basis for tackling the current-potential response in multipotential pulse electrochemical techniques (see Chaps. 4—7), which are more powerful, but also present greater theoretical complexity. 

Finally, we note that the time scale for the PE experiment is determined by the dephasing times, which are very short in proteins ( 300 fs) (41). Other complementary 2D techniques were proposed in Ref. 17. In particular, energy relaxation, which occurs in proteins and polypeptides on a large time scale ( 2-15 ps) (15,41), can be studied by utilizing the transient grating and the three pulse PE techniques. These can be calculated as well using the third-order response function presented here. 

Clements also estimated the frequency response from the pulse response. A frequency-response method is also suggested by Kramers and Alberda.52 Schwartz et al.9S suggested a new, two-tracer technique for simultaneous determination of liquid holdup and Peclet number. 

The 10-membered ring zeolites (ZSM-22 and ZSM-23) were kindly provided by Prof. Martens (COK, KULeuven). Both of the zeolites have unidimensional pore structures without any intersection. The crystals are needle-like shaped for both materials. Zeolite ZSM-22 (belonging to the TON fhmily) has free pore dimensions of 0.44 X 0.55 nm and zeolite ZSM-23 (MTT fiimily) has free pore diameters of 0.45 X 0.42 nm. The framework structures are sketched in Figure 2. The low coverage adsorption properties were determined with the pulse chromatographic technique. The details of the experimental method are discussed elsewhere. The Henry constant was determined from the first moment of the response curve on the TCD detector alter injection of an alkane trace. Adsorption enthalpy and entropy were obtained by fitting the temperature dependence of the Henry constant to the van t Hoff equation. 

In the present study, supercritical CO2 chromatograph packed with MSC was again used to detect the pulse responses of organics, and the moment analysis technique was used to analyze. Equilibrium and dynamics were studied for benzene, toluene and m-xylene, respectively, -MSC systems in the supercritical CO2 mixed with organics which were different from that used in the form of pulse. Furthermore, the dependence of adsorption of the organics on the amount adsorbed of other organics was discussed. 

Figure 3. Experimental geometry for dephasing measurements by three-pulse scattering technique. Pump pulses (1 and 2) produce a grating response that diffracts probe pulse (3) into two orders. In grating experiments described in Section III (nuclear phase coherence), t = 0 and probe pulse is incident at the phase-matching angle for Bragg diffraction into only one order.

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