Non-Steady-State Methods

In steady state experiments, time-dependent effects are deliberately elimented by waiting, often for an hour or even longer, until all 

Enzyme degradation can be measured after the removal of an inducing stimulus by following the time course of enzyme loss. If the 

Degradation rate constants may also be obtained from the decrease in enzyme activity after protein synthesis has been inhibited (Fig. 2b). This simple method should give reliable measurements of provided enzyme activity is equivalent to enzyme content, the protein synthesis inhibitor is totally effective, and side effects of the inhibitor are not seen over the time course of the experiment. Of these assumptions, the first is the easiest to satisfy since the only examples reported in which an inactive enzyme protein is present in vivo are those in which an apoenzyme accumulates during a deficiency of the required coenzyme (see Section VII.C). 

The change in enzyme activity or content from a low to a high level can also be used to calculate the degradation rate constant (Schimke and Doyle, 1970), but, as mentioned above for measurements on the reduc- 

In most cases, measurements made at steady-state concentrations of enzymes are far more precise than those dependent on changes in steady states. Yet the simplicity of detecting activity changes has made the methods very attractive, and even the rough information so obtained is useful. 

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Only ratios of rate constants of autoxidation can be determined by ordinary steady-state velocity measurements. Non-steady state methods, notably the sector method, have been used to evaluate the individual or absolute rate constants. We have devised a method for measuring the change in rate of autoxidation under non-stationary conditions directly, by means of sensitive manometric apparatus, and for deriving individual rate constants from these measurements. 

The build-up is often very fast, e.g. over in 10 4 s, and not observed experimentally under normal steady state conditions. Special fast reaction techniques are required to study the build-up, and analysis of the data requires non-steady state methods. If build-up continues after the steady state concentrations occur, the rate of reaction continues to increase and explosion can occur. 

As a mater of fact, before a series of papers were published by Kosaka et a ., a procedure to calculate the value of (S of an arbitrary solid, which is based on a concept near that of Kosaka et aL, had been presented in a book edited by Tye as one of the so-called non-steady state methods to measure a few thermal constants [48]. Fig. 64 is quoted from page 186 of Tye s book. Two experiments [49, 50], in which the values of at of solid ZrOi, Ta, ZrC and TiC were each calculated at considerably high temperatures, are also introduced in the same book. 

THERMODYNAMICS. A NON-STEADY-STATE METHOD FOR THE MEASUREMENT OF THE THERMAL CONDUCTIVITIES OF LIQUID AND GASES. FROM PROC. INTERN. CONGRESS OF REFRIGERATION, 11TH, MUNICH, 1963. 

The techniques for characterizing the kinetics of electrode reactions can be classified into steady-state and transient methods. The steady-state methods involve the measurement of the current-potential relationships at constant current (galvanoslatic control) or constant potential (potentiostatic control) conditions and measuring the response, which is either the potential or the current after a steady state is achieved. The non-steady-state methods involve the perturbation of the system from an equilibrium or a steady-state condition, and follow the response of the system as a function of time using current, potential, charge, impedance, or any other accessible property of the interface. Relaxation methods are a subclass of perturbation methods. 

In non-steady-state methods [56,57], the system is perturbed by a signal and then aUowed to relax to the equilibrium value or to another steady state. During these measurements, the double layer is charged lirst, as any change in the electrical state of an electrochemical system results in the rearrangement of charges at the electrical double layer. The resulting displacement current density can be expressed by ... 

Non-Steady-State methods such as cyclic or single-sweep voltammetry are able to give both kinetic and (implicit) mechanistic information on organic electrode reactions in the following ways. 

Non-steady-state methods can be used to measure thermal conductivity according to... 

Grassman P., Jobst W. A non-steady-state method for the thermal conductivity of liquid and gases.—In Proc. XI Intemat. congr. of refr. Munich, 1963 London, Pergamon Press, 1965, v. I, p. 301—305. 

Both FRAP and microinjection are non-steady-state methods of measuring the diffusivity at a particular location in the hiofihn. The value obtained is the molecular diffusivity, corrected for the tortuosity of the matrix (D ) but not the porosity (Libicki et al. 1988). For determination of Deff (D, /j), flux measurements during steady-state transport are needed. 

From this we can see that knowledge of k f and Rp in a conventional polymerization process readily yields a value of the ratio kp jkt. In order to obtain a value for ky we require further information on kp. Analysis of Rp data obtained under nonsteady-state conditions (when there is no continuous source of initiator radicals) yields the ratio kp/ky Various non-steady-state methods have been developed including the rotating sector method, SIP, and PEP. The classical approach for deriving the individual values of kp and fet by combining values of kp fky with kp/kt obtained in separate experiments can, however, be problematical because the values of fet are strongly dependent on the polymerization conditions (Section 3.04.4.1.1(iv)). These issues are thought to account for much of the scatter apparent in literature values of PEP and related methods yield... 

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