Steady state response time

Response time of the biosensor is classified into steady state response time and transient response time. The time required to reach 95% of the steady state response of the biosensor is known as steady state response time. It is easily determined after the addition of each analyte into measurement cell. Transient response time corresponds to the first derivative of the output signal to reach its maximum value following the analyte addition. Both are dependent upon the analyte and the activity of the molecular recognition system, i.e., the higher activity, the shorter the response time. 

The root locus method provides a very powerful tool for control system design. The objective is to shape the loci so that closed-loop poles can be placed in the. v-plane at positions that produce a transient response that meets a given performance specification. It should be noted that a root locus diagram does not provide information relating to steady-state response, so that steady-state errors may go undetected, unless checked by other means, i.e. time response. 

The steady state is disturbed and the system exhibits transient behavior when at least one of its parameters is altered under an external stimulus (perturbation). Transitory processes that adjust the other parameters set in (response) and at the end produce a new steady state. The time of adjustment (transition time, relaxation time) is an important characteristic of the system. 

Heat fluxes in fire conditions have commonly been measured by steady state (fast time response) devices namely a Schmidt-Boelter heat flux meter or a Gordon heat flux meter. The former uses a thermopile over a thin film of known conductivity, with a controlled back-face temperature the latter uses a suspended foil with a fixed edge temperature. The temperature difference between the center of the foil and its edge is directly proportional to an imposed uniform heat flux. Because the Gordon meter does not have a uniform temperature over its surface, convective heat flux may not be accurately measured. 

Photodiodes occur in many different varieties and are useful in both steady-state and time-resolved fluorescence studies. Photodiodes designed for use in steady-state or on microsecond time-scales are inexpensive and have effective areas up to a few square millimeters, and are capable of efficiently matching to simple focusing optics. However, as the temporal resolution increases so does the cost, and the effective area has to be reduced. For example, APDs with response times in the 50 psec region have effective diameters ofca. 10 /small active area of high-speed devices is currently the primary drawback in fluorescence studies. Also, photodiodes other... 

In concluding, let us comment on the time needed to attain the steady state after establishing the surface activities. Two transient processes having different relaxation times occur I) the steady state vacancy concentration profile builds up and 2) the component demixing profile builds up until eventually the system becomes truly stationary. Even if the vacancies have attained a (quasi-) steady state, their drift flux is not stationary until the demixing profile has also reached its steady state. This time dependence of the vacancy drift is responsible for the difficulties that arise when the transient transport problem must be solved explicitly, see, for example, [G. Petot-Er-vas, et al. (1992)]. 

The actual solution for both transient and steady-state response of any zero-flux-boundary sensor can be obtained by solving (2.26) through (2.33) for the appropriate boundary and initial conditions. Fitting of the experimental calibration curves (Fig. 2.10) and of the time response curves (Fig. 2.11) to the calculated ones, validates the proposed model. 

In these electrode processes, the use of macroelectrodes is recommended when the homogeneous kinetics is slow in order to achieve a commitment between the diffusive and chemical rates. When the chemical kinetics is very fast with respect to the mass transport and macroelectrodes are employed, the electrochemical response is insensitive to the homogeneous kinetics of the chemical reactions—except for first-order catalytic reactions and irreversible chemical reactions follow up the electron transfer—because the reaction layer becomes negligible compared with the diffusion layer. Under the above conditions, the equilibria behave as fully labile and it can be supposed that they are maintained at any point in the solution at any time and at any applied potential pulse. This means an independent of time (stationary) response cannot be obtained at planar electrodes except in the case of a first-order catalytic mechanism. Under these conditions, the use of microelectrodes is recommended to determine large rate constants. However, there is a range of microelectrode radii with which a kinetic-dependent stationary response is obtained beyond the upper limit, a transient response is recorded, whereas beyond the lower limit, the steady-state response is insensitive to the chemical kinetics because the kinetic contribution is masked by the diffusion mass transport. In the case of spherical microelectrodes, the lower limit corresponds to the situation where the reaction layer thickness does not exceed 80 % of the diffusion layer thickness. 

The lag between density cell response and reactor events were considerably less for this example and the figures ignore any correction. After establishing a "steady state" response to the monomer feed (about 160 minutes into the reaction), the incremental increase of the feed rate is seen not to alter the overall fractional conversion since the rate of polymerization increases to parallel the monomer feed rate. At the end of this set of data the rate is 2-3 times that observed earlier before the feed. 

This simple RNA stemloop serves as an illustration of how both steady-state and time-resolved fluorescence together provide a detailed description of the properties of an RNA (Hall and Williams, 2004). The sequence of the iron response element (IRE) RNA hairpin loop [C6A7G8U9G10C11] is phylogenetically conserved (numbered from our construct). Cytidine 6 and... 

The time required for the electrode to attain a steady-state response after addition of an aliquot of NADH is of the order of seconds (—10 s for a film held at 0.1 V). Comparing this response time with those obtained in the mass transport-limited regime for a standard couple at a bare electrode, it is clear that the response time of the modified poly(aniline) electrodes is of the order of the mixing time for the system. 

An alternative approach, adopted by Albery et al. [59-61], is to determine the mechanism giving rise to the sensor response and to use this information together with the measured data at short times to calculate the final response. This was used for an electrochemical sensor system incorporating cytochrome oxidase where the steady-state responses of the measurement system were insufficiently fast for useful measurement of respiratory inhibitors such as cyanide, hydrogen sulphide, etc. By using mechanistic information, it was possible to successfully calculate the concentration in a test sample by real-time analysis of the sensor signals at short times after exposure to the test sample. The analysis could cope with the gradual loss of enzyme activity commonly found in these biosensor devices. 

The above discussion implies steady-state response in time. An equivalent reciprocal view of steady-state resonance response is that in the vicinity of resonance there is a dip in the force required to maintain a constant level of response. The force-reduction ratio is Q, and the fractional bandwidth of the force reduction is T. In contrast, a truly force-free response of a resonant system (once excited) would involve the exponential decay of vibration amplitude with time. As we have mentioned earlier, decay is also controlled by the system loss factor as follows ... 

Impedance, on the other hand, includes the transient response of the system as well as the long-term, steady-state response defined by Ohm s law. The entire time course of impedance is usually captured by transforming the measurement to the frequency domain. This is an inverse transform in which transient responses occur at high frequencies and long-term, steady-state responses are approached at low frequencies. 

Provided r, is small, then the critical inflow concentration for this branching-termination model under CSTR conditions differs slightly from the so-called pool chemical result which is obtained by assuming [A] = constant. For typical chemical systems the residence time will be such that k, > 1/fres, SO the two results are not significantly different but the extra influence of the flow is clearly evident in the above forms. In neither of the analyses above, however, is there a discontinuous jump in the steady-state response as the parameters are varied. 

A variety of operations can be performed on the sample as it flows through the reaction tube. In the simplest case, the sample merely disperses into an inert carrier stream. It is then measured directly at the detector, as in the determination of seawater pH. The contact time between the sample and the pH electrode is short so that only a fraction of the steady-state response is obtained. However, this fraction is very reproducible [ 0.002 pH, (i5)], which is the key to the success of FIA. 

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