Sensitivity, concentration temperature

Standardizing the Method Equations 10.32 and 10.33 show that the intensity of fluorescent or phosphorescent emission is proportional to the concentration of the photoluminescent species, provided that the absorbance of radiation from the excitation source (A = ebC) is less than approximately 0.01. Quantitative methods are usually standardized using a set of external standards. Calibration curves are linear over as much as four to six orders of magnitude for fluorescence and two to four orders of magnitude for phosphorescence. Calibration curves become nonlinear for high concentrations of the photoluminescent species at which the intensity of emission is given by equation 10.31. Nonlinearity also may be observed at low concentrations due to the presence of fluorescent or phosphorescent contaminants. As discussed earlier, the quantum efficiency for emission is sensitive to temperature and sample matrix, both of which must be controlled if external standards are to be used. In addition, emission intensity depends on the molar absorptivity of the photoluminescent species, which is sensitive to the sample matrix. 

Of all the characteristic points in the phase diagram, the composition of the middle phase is most sensitive to temperature. Point M moves in an arc between the composition of the bottom phase (point B) at and the composition of the top phase (point T) at reaching its maximum surfactant concentration near T = - -T )/2. (Points B and Tmove by much smaller amounts, also.) The complete nonionic-amphiphile—oh—water—temperature... 

Equation (10.12) is the simplest—and most generally useful—model that reflects heterogeneous catalysis. The active sites S are fixed in number, and the gas-phase molecules of component A compete for them. When the gas-phase concentration of component A is low, the k a term in Equation (10.12) is small, and the reaction is first order in a. When a is large, all the active sites are occupied, and the reaction rate reaches a saturation value of kjkd-The constant in the denominator, is formed from ratios of rate constants. This makes it less sensitive to temperature than k, which is a normal rate constant. 

Every reaction has its own characteristic rate constant that depends on the intrinsic speed of that particular reaction. For example, the value of k in the rate law for NO2 decomposition is different from the value of k for the reaction of O3 with NO. Rate constants are independent of concentration and time, but as we discuss in Section 15-1. rate constants are sensitive to temperature. 

Low temperature steam and formaldehyde Reactive chemical Indicator paper impregnated with a formaldehyde-, steam- and temperature-sensitive reactive chemical which changes colour during the sterilization process Gas concentration, temperature, time (selected cycles)... 

When using fluorophores of known lifetime, it is important to validate the lifetime used. Fluorescence lifetimes can be sensitive to concentration, temperature, pH, and other environmental variables. Fluorophores from different suppliers can have variable purity. As a result, one should not assume that a value reported in the literature will be exactly transferable to other labs and conditions. Users of the method should be particularly careful to use low concentrations of fluorophore (<10 /iM) to avoid a variety of processes which can perturb lifetimes in solution. There are a limited number of well characterized fluorophores. If one is not available for a particular wavelength this will require a change of filters leaving the method with nothing to recommend it over reflection and scatter. 

Steric Stabilization. Steric stabilization was a term first introduced by Heller to explain how adsorbed polyethylene oxide polymers increased the salt concentration required for flocculation of negatively charged aqueous suspensions.(6) Heller s systems were stabilized by both mechanisms, as are most commercial dispersions today, aqueous and non-aqueous. Much of the more recent literature on steric stabilizers has been preoccupied with solubility requirements, for the solubility of polymers is a delicate matter and very sensitive to temperature and solvent... 

Enzymes also are homogeneous catalysts, although they are sometimes attached to solid surfaces without degradation. They possess a different form of rate equation, for which the development may be found in problem P2.03.02. Their behavior is especially sensitive to temperature and to substrate concentration. 

Equation (48) e ees with experimental results in some circumstances. This does not mean the mechanism is necessarily correct. Other mechanisms may be compatible with the experimental data and this mechanism may not be compatible with experiment if the physical conditions (temperature and pressure etc.) are changed. Edelson and Allara [15] discuss this point with reference to the application of the steady state approximation to propane pyrolysis. It must be remembered that a laboratory study is often confined to a narrow range of conditions, whereas an industrial reactor often has to accommodate large changes in concentrations, temperature and pressure. Thus, a successful kinetic model must allow for these conditions even if the chemistry it portrays is not strictly correct. One major problem with any kinetic model, whatever its degree of reality, is the evaluation of the rate cofficients (or model parameters). This requires careful numerical analysis of experimental data it is particularly important to identify those parameters to which the model predictions are most sensitive. 

Note that the Henry s law constants given in Table 8.1 are generally for 25°C. At lower temperatures, the values will, of course, be larger due to the increased solubility. While the rate constants for most reactions, especially those in the liquid phase, decrease with decreasing temperature, the increased reactant concentrations tend to counterbalance this effect. Thus rates of reactant loss and product formation are not as sensitive to temperature as the rate constant alone. 

Here, K is sometimes referred to as the consistency index and has units that depend on the value of the power law index, n—for example, N-s"/m. The power law index is itself dimensionless. Typical values of K and n are listed in Table 4.4. In general, the power law index is independent of both temperature and concentration, although fluids tend to become more Newtonian (n approaches 1.0) as temperature increases and concentration decreases. The consistency factor, however, is more sensitive to temperature and concentration. To correct for temperature, the following relationship is often used ... 

The discharge of warm wastewaters into a surface receiver may have many adverse effects on aquatic life. The increase in temperature results in a decrease in the oxygen concentration in water and the elimination of the most sensitive species. Temperature changes may also cause changes in the reproductive periods of fishes, growth of parasites and diseases, or even thermal shock to the animals found in the thermal plume. 

Changing the initial mixture temperature affects stability. U0 for blow-off from burners increases with approximately the square of the absolute temperature, whether the flow is laminar or turbulent (17). The exact dependence on temperature is a function of fuel type and concentration, and may also be affected by wall temperature. The flash-back velocity is even more sensitive to temperature (17), so that raising the temperature may actually decrease the relative range of flow velocities that will permit stable flames on burners. As to supported flames, the correlations in Table IV show that blow-off in such systems is less dependent on initial temperature than is blow-off from burners (38) the exponent on 7 > is only 1.2, as compared with 2.0. 

The mass diffusive flux m, of Equation (3.2) generally depends on the operating conditions, such as reactant concentration, temperature and pressure and on the microstructure of material (porosity, tortuosity and pore size). Well established ways of describing the diffusion phenomenon in the SOFC electrodes are through either Fick s first law [21, 34. 48, 50, 51], or the Maxwell-Stefan equation [52-55], Some authors use more complex models, like for example the dusty-gas model [56] or other models derived from this [57, 58], A comparison between the three approaches is reported by Suwanwarangkul et al. [59], who concluded that the choice of the most appropriate model is very case-sensitive, and should be selected, according to the specific case under study. 

Since most conduction takes place in the pore space of soils, pore fluid conductivity is an important parameter. Many models relating fluid conductivity and pore fluid concentration are applicable only for low ionic concentrations, since at higher concentrations, ion-ion interactions reduce ionic mobility [15]. Additionally, ionic mobility is sensitive to temperature, increasing as temperat-... 

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