Overloading coefficient

As it is known [1, 2], the dilation concept of solid bodies fracture process assumes negative fluctuation density formation - dilaton, length of which is defined by phonons free run length A. In this case the overloading coefficient K on breaking bonds can be expressed as follows [3] ... 

TABLE 7.1 The Local Overloading Coefficients (Kj and Kj) and Necessary For Their Calculation Parameters [5]... 

In insertion of Fig. 7.1 the dependence of overloading coefficient mean values k (k = 0.5(Kj + k )) on value D l is adduced. As one can see, a good linear correlation between the indicated parameters is observed, with the exception of only two polymers (PTFE and PSF) which have considerable, although symmetrical, scatter. This gives the possibility to express as function as follows [9] ... 

FIGURE 7.1 The dependence of local overloading coefficient (the Eq. (7.3)) on fractal dimension of chain part between clusters for 10 pol5aners, pointed out in Table 7.1. 1 - results of impact tests of HOPE samples with sharp notch, where figures indicated notch length in mm. In insertion the dependence is shown for the same 10 polymers [9]... 

FIGURE 7.2 The dependence of local overloading coefficient k, calculated according to the Eq. (7.3), on molecular draw ratio l j for UHMPE (1) and UHMPE/Al (2). The shaded region indicates literary values range [10]. 

Available Chlorine Test. The chlorine germicidal equivalent concentration test is a practical-type test. It is called a capacity test. Under practical conditions of use, a container of disinfectant might receive many soiled, contaminated instniments or other items to be disinfected. Eventually, the capacity of the disinfectant to serve its function would be overloaded due to reaction with the accumulated organic matter and organisms. The chlorine germicidal equivalent concentration test compares the load of a culture of bacteria that a concentration of a disinfectant will absorb and still kill bacteria, as compared to standard concentrations of sodium hypochlorite tested similarly. In the test, 10 successive additions of the test culture are added to each of 3 concentrations of the hypochlorite. One min after each addition a sample is transferred to the subculture medium and the next addition is made 1.5 min after the previous one. The disinfectant is then evaluated in a manner similar to the phenol coefficient test. For equivalence, the disinfectant must yield the same number of negative tubes as one of the chlorine standards. 

The lower isotherm represents the overload condition that can occur in liquid/liquid or gas/liquid systems under somewhat unique circumstances. If the interactions between solute molecules with themselves is stronger than the interactions between the solute molecules and the stationary phase molecules, then, as the concentration of solute molecules increases, the distribution coefficient of the solute with respect to the stationary phase also increases. This is because the solute molecules interact more strongly with a solution of themselves in the stationary phase than the stationary phase alone. Thus, the higher concentrations of solute in the chromatographic... 

Positive temperature coefficient (PCT) thermistors are solids, usually consisting of barium titanate, BaTiOi, in which the electrical resistivity increases dramatically with temperature over a narrow range of temperatures (Fig. 3.38). These devices are used for protection against power, current, and thermal overloads. When turned on, the thermistor has a low resitivity that allows a high current to flow. This in turn heats the thermistor, and if the temperature rise is sufficiently high, the device switches abruptly to the high resisitvity state, which effectively switches off the current flow. 

Compute the valve flow coefficient The valve flow coefficient C is a function of the maximum steam flow rate through the valve and the pressure drop that occurs at this flow rate. When choosing a control valve for a process control system, the usual procedure is to assume a maximum flow rate for the valve based on a considered judgment of the overload the system may carry. Usual overloads do not exceed 25 percent of the maximum rated capacity of the system. Using this overload range as a guide, assume that the valve must handle a 20 percent overload, or 0.20(1500) = 300 lb/h (0.038 kg/s). Hence, the rated capacity of this valve should be 1500 + 300 = 1800 lb/h (0.23 kg/s). 

Figure 5.13 shows overloaded elution profiles obtained for three different injection volumes of solutions of the same concentrations of the two enantiomers of PA (dashed lines). The solid lines in these figures show the band profiles numerically calculated for a concentration dependent mass transfer coefficient k( (main figure), a low concentration value of (upper inset) and a high concentration value of kf (lower inset). For the r-enantiomer, the best fit of the data is obtained using the concentration dependent rate constant, while for the o-enantiomer the best fit is obtained using a constant value of k equal to 35/min (low concentration value). 

All these parameters depend on the mass loadability of the column and change significantly when a critical loadability is reached. The critical mass loadability of analytical columns is usually reached at a 10% reduction of the retention coefficient or at 50 % decrease of column plate number. At higher values the column is, in chromatographic terms, overloaded. 

The goal is to obtain the unknown parameters for a selected isotherm equation. Special parameters of nearly all types of isotherms are the Henry coefficient as well as the saturation capacities for large concentrations. It is advisable to check the validity of the single-component isotherm equation before determining the component interaction parameters. In general the decision on a certain isotherm equation should be made on the basis of the ability to predict the experimental overloaded concentration profiles rather than fitting the experimental isotherm data. In any case, consistency with the Henry coefficient determined from initial pulse experiments with very low sample amounts must be fulfilled. 

Haarhoff and Van der Linde [68] have given a more direct mathematical demonstration of this result in the case of a moderately overloaded column, with a parabohc isotherm. It leads to the fundamental equation of the equilibriiun-dispersive model, in which the diffusion coefficient in the diffusive term of the mass balance equation (Eq. 2.2) is replaced by the apparent dispersion coefficient (Eq. 2.38). 

Previous work [126] had shown that the FOR model accounted well for the overloaded band profiles of samples of mixtures of various compositions of the enantiomers of indanol on cellulose tribenzoate, in a wide range of sizes. However, this was possible only by letting the effective diffusion coefficients of the two enantiomers float. The best values of these coefficients depended on the sample size. This suggested an important model error, the influence of surface diffusion... 

In the equilibrium-dispersive model of chromatography, however, we assume that Eq. 10.4 remains valid. Thus, we use Eq. 10.10 as the mass balance equation of the component, and we assume that the apparent dispersion coefficient Da in Eq. 10.10 is given by Eq. 10.11. We further assume that the HETP is independent of the solute concentration and that it remains the same in overloaded elution as the one meastued in linear chromatography. As shown by the previous discussion this assxunption is an approximation. However, as we have shown recently [6], Eq. 10.4 is an excellent approximation as long as the column efficiency is greater than a few hundred theoretical plates. Thus, the equilibriiun-dispersive model should and does account well for band profiles under almost all the experimental conditions used in preparative chromatography. In the cases in which the model breaks down because the mass transfer kinetics is too slow, and the column efficiency is too low, a kinetic model or, better, the general rate model (Chapter 14) should be used. 

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