Measurement transient rapid response

This technique provides an opportunity to examine the "adsorption" and "reaction" steps sequentially at reaction temperatures and pressures. How sharply the individual steps can be separated depends largely upon the magnitude of the differences in rates and upon the data resolution capability of the experimental apparatus. Interpretation of the transient rapid response measurements in terms of steady state operation is needed if these results are to be most useful. Recent studies in this laboratory indicate that this approach holds some promise and it is the purpose of this paper to describe the adsorber-reactor system and its performance capabilities. The most recent design provides rapid gas-solid contact in a constant volume cell with transient rates for temperature and pressure measurements in the millisecond region. 

Transport properties of biological membranes and tissues are commonly determined through classical flux experiments. However, the experimental setup and analytical procedures involved in such studies are laborious and time-consuming. Furthermore, transient flux responses are difficult to measure accurately. Alternatively, impedance spectroscopy allows rapid experimental determination of the transient and steady-state conduction properties of materials. 

Evaluation of the data requires time constants for both the heat transfer and diffusion under nonisothermal conditions. It turns out that the initial part of the response curve is mainly determined by the mass transport (transport diffusion), whereas the descending part is mainly governed by the heat transfer. The STIR technique avoids intrusion by the evolution of heat, in that it measures the transient temperature, and has a rapid response (time constant about 10 s). Results obtained for the diffusion of CH3OH into Na-X were essentially consistent with those derived from the ZLC and PFG NMR... 

The examples of catalyst screening cited above mainly demonstrate the concept of MSRs for fuel reforming processes. In addition, MSRs show some additional experimental benefits such as rapid response times for transient experiments and the coupling ofendo- and exothermic reactions. Note, however, thatas already stressed, if all studies claim excellent adherence and catalyst activity, key information is usually missing, such as a comparison of different catalyst synthesis methods, catalyst characterization or measurement of the temperature inside the reaction channels. 

Transient, or time-resolved, techniques measure tire response of a substance after a rapid perturbation. A swift kick can be provided by any means tliat suddenly moves tire system away from equilibrium—a change in reactant concentration, for instance, or tire photodissociation of a chemical bond. Kinetic properties such as rate constants and amplitudes of chemical reactions or transfonnations of physical state taking place in a material are tlien detennined by measuring tire time course of relaxation to some, possibly new, equilibrium state. Detennining how tire kinetic rate constants vary witli temperature can further yield infonnation about tire tliennodynamic properties (activation entlialpies and entropies) of transition states, tire exceedingly ephemeral species tliat he between reactants, intennediates and products in a chemical reaction. 

Gal-Or and Hoelscher (G5) have recently developed a fast and simple transient-response method for the measurement of concentration and volumetric mass-transfer coefficients in gas-liquid dispersions. The method involves the use of a transient response to a step change in the composition of the feed gas. The resulting change in the composition of the liquid phase of the dispersion is measured by means of a Clark electrode, which permits the rapid and accurate analysis of oxygen or carbon dioxide concentrations in a gas, in blood, or in any liquid mixture. 

It is the essence of transient measurements that a certain perturbation is applied to the electrode and then the response is recorded as a function of time. Usually, the transition times are short (fractions of a second), and the transient measurements are performed very rapidly with automated data acquisition. 

The 1,4,5-IP3 hypothesis has been extensively tested in smooth muscle. In skinned smooth muscle, physiological concentrations of 1,4,5-IP3 have been shown to release sufficient Ca + rapidly enough to account for transient contractions (Somlyo et al, 1985 Suematsu et al., 1984 Walker et al, 1987 Baron et al., 1989 Abdel-Latif, 1989). This response can be blocked by intracellular heparin (Kobayashi et al., 1988b), a competitive blocker of cerebellar 1,4,5-IP3 receptors (Worley et al., 1987). Agonist stimulation increased the apparent concentration of 1,4,5-IP3 when measured as either [ HJIPg in cells (Griendling etal., 1986) or tissues (Howe etal., 1986 Long and Stone, 1987 Takuwa etal., 1986 Miller-Hance et al., 1988 Salmon and Bolton,... 

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