Loading Studies

In experimental load studies, the measurable variables are often surface strain, acceleration, weight, pressure or temperature (Haugen, 1980). A discussion of the techniques on how to measure the different types of load parameters can be found in Figliola and Beasley (1995). The measurement of stress directly would be advantageous, you would assume, for use in subsequent calculations to predict reliability. However, no translation of the dimensional variability of the part could then be accounted for in the probabilistic model to give the stress distribution. A better test would be to output the load directly as shown and then use the appropriate probabilistic model to determine the stress distribution. 

The ramp of pressure to about 3 GPa observed in shock-loaded fused quartz has been used very effectively in acceleration-pulse loading studies of viscoelastic responses of polymers by Schuler and co-workers. The loading rates obtained at various thicknesses of fused quartz have been accurately characterized and data are summarized in Fig. 3.6. At higher peak pressures there are no precise standard materials to produce ramp loadings, but materials such as the ceramic pyroceram have been effectively employed. (See the description of the piezoelectric polymer in Chap. 5.)... 

Figure 1. Polystyrene loading study on one column (Part 1).

Metal loading studies of this type serve to enlighten the factors which control the impregnation of organometallics into zeolites, as well as providing an indirect probe of internal versus external location of the metal guests. In the following, a direct spectroscopic probe of this kind of process is presented. 

Figure 5. In situ FT-FAR-IR spectra of Co2+ ion-exchanged NaseY containing 6, 14 and 17 Co2 + cations per unit cell. (S represents a residual Na+ site II cation mode, I, III" and I designate the respective Co2+ cation site modes. Higher loading studies show that site II Co2+ lies in the same region as site II Na+).

For this example a loading study, similar to that described above, performed on the crude mixture suggested that a good separation would be achieved at loadings equivalent to 20 mg on an analytical column (4.6 mm X 250 mm). The required component of the mixture, shown on the analytical HPLC trace in Figure 5.7, was the more retained peak. 

In Figure 1 we show the coke selectivity of a series of Mo/A12C>3 catalysts with varying Mo load (ranging from 0 to 10 Mo/100 A1203). Without any Mo present a large amount of coke is deposited onto the alumina, whilst a tiny amount of Mo decreases the coke formed by a factor of almost three. As the Mo load increased further, we were surprised to observe an increase in the coke deposition. The HDS activity, on the other hand, increases monotonically over the entire range of Mo loads studied. 

Two children with the late-onset form initially were reported as having a defect in intestinal transport of biotin. This conclusion was supported by finding low plasma biotin concentrations when these children were administered oral biotin compared to the concentrations of plasma biotin of unaffected control subject. In 1983, it was demonstrated that the primary biochemical defect in most patients with late-onset multiple carboxylase deficiency was a deficiency of serum biotinidase activity. The two children with a putative defect in intestinal biotin transport both were confirmed to have biotinidase deficiency. This disparity was reconciled by demonstrating that, in both cases, the children were biotin depleted at the time the biotin-loading studies were performed. Therefore, when the children initially were given biotin, although the vitamin was transported into the blood normally, it was rapidly taken up... 

Home, R. A., R. H. Holm, and M. D. Meyers. 1957. The adsorption of zinc(II) on anion-exchange resins. II. Stoichiometry, thermodynamics, loading studies, Dowex-2 adsorption and factors influencing the rate of the adsorption process. J. Phys. Chem. 61 1655-1661. 

Perform a systematic loading study (as part of the isolation process). 

Barbi, V., Funari, S., Gehrke, R., Scharnagl, N., Stribeck, N. (2003). Nanostructure of Nafion membrane material as a function of mechanical load studied by SAXS. Polymer 44,4853-4861. 

The addition of Pd in the form of physical mixtures enhanced COj conversion to methanol, which increased with the higher Pd content. The activity was even greater in the case of the impregnated catalysts, although the two Pd loadings studied gave very similar results. Figure 1 shows the observed promotion in methanol production relative to Cu/Zn/Al-1. A promotion of approximately 35% was found for the two Pd/Cu/Zn/Al catalysts at... 

Once loading studies have been performed, scale-up can take place. First, the amount of feed material needed to yield the desired quantity of impurity must be determined. An FIPLC assay or other chemical assay can be used to determine the potency of the feed with respect to the desired impurity. If an assay is not available, the impurity potency can be approximated from analytical peak collection. Additionally, an estimation of the recovery yield (percentage of impurity present in feed that is recovered from the separation) can be obtained from a mass balance on the high-loading peak collection experiments. Off-cuts, fractions collected from the column that contain the impurity but do not meet purity, can often be recycled into the feed for the next run, increasing the recovery yield. The required preparative column volume can then be calculated as follows ... 

The same particle-size resin as used for the loading studies should be used for scaleup. The choice of particle size is a trade-off between resolution, which decreases with an increase in particle size, and pressure drop, which also decreases with an increase in particle size. Often, bulk resins are not offered in the full range of particle sizes that analytical columns are. Additionally, a size should be selected so that the column pressure drop does not exceed the resin limitations. 

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