Obtaining Resistance

The most thoroughly studied mode of /3-lactam hydrolysis is that catalyzed by the enzyme /3-lactamase (EC 3.5.2.6). The elaboration of this enzyme is one of the three principal ways in which a bacterium can obtain resistance to a /3-lactam antibiotic (see Section 5.11.5.1), and much of the chemical work carried out on the penicillin molecule has been related to attempts to deal with this problem. A discussion of the /3-lactamases is beyond the scope of this work. The reader is referred to (B-79MI51101) for a recent review. 

Microbial Resistance to Drugs. Figure 2 Bacterial cells can obtain resistance genes in three ways ... 

Data analysis in the normal state of the superconductor is relatively straightforward, measurements of I, V, and T together with sample geometry are used to obtain resistivity vs temperature. 

Despite the uncertainty in the mechanism of hormone-induced lymphocytolysis, cultured cells of mouse and human origin have been very useful for obtaining resistant cell variants. Mostly, three cell culture lines have been used S49.1 and WEHI-7 mouse lymphoma cells of thymic origin [43,44] and human CEM-C7 lym-... 

The SAMPLE program (O was used to obtain resist profiles. Exposure at 248 nm with a lens of numerical aperture NA = 0.38 and partial coherence a = 0.7 was assumed. The substrate was 1200 A of Si02 on thick HB206 photoresist on silicon. That is, the sensitive resist is part of a trilevel structure. Exposure dose was set to 120 mj/cm, and development times were about 2 min. 

FIGURE 22.18 Plots used to obtain resistances and the average specific resistance. 

As a conclusion to this part, the modest selectivity of 12459 for G4 over duplex DNA may render questionable some of these findings, that is, the relationship between short-term effects and its molecular action against telomeres. Future work to obtain resistant cell lines from other sources and with more selective G-quadruplex ligands, such as telomestatin or pyridine dicarboxamide derivatives will aim to confirm some of the views presented here. 

Figure 10.11 is with a vertical slice with a resistivity 5 times that of the surrounding medium. It has little influence on the sensitivity field. Multiplying the sensitivity field with the local resistivity yields the volume resistance density field, as shown in Figure i0.i2. The result is quite different and illustrates that with respect to the overall transfer resistance of the system, the increased resistivity of the slice is very important. The transfer resistance is not determined by the sensitivity value alone, the sensitivity is to be multiplied by the resistivity to obtain resistance values. 

Fluoroelastomers provide excellent resistance to oils, fuels, lubricants, most mineral acids, many aliphatic and aromatic hydrocarbons (carbon tetrachloride, benzene, toluene, xylene) that act as solvents for other rubbers, gasoline, naphtha, chlorinated solvents, and pesticides. Special formulation can be produced to obtain resistance to hot mineral acids, steam, and hot water. 

Hakkinen et al. [51] investigated the filterability of sul-fathiazole crystals obtained by crystallization from one-solvent and two-solvent solutions. Their results showed that the choice of the mother-Uquor composition affected the obtained resistance of crystal cake. Lowering the cake resistance in a system usually decreases the moisture content of the cake that in turn facilitates the drying process. Organic compounds may also form amorphous solid particles that usually lead to low permeability of the solid bed due to the compression of the filter cake. 

By alloying nickel with both molybdenum and chromium, an alloy is obtained resistant to oxidizing media imparted by alloyed chromium, as well as to reducing media imparted by molybdenum. One such alloy, which also contains a few percent iron and tungsten (AUoy C), is immune to pitting and crevice corrosion in seawater (10-year exposure) and does not tarnish appreciably when exposed to marine atmospheres. Alloys of this kind, however, despite improved resistance to Cl, corrode more rapidly in hydrochloric acid than do the nickel-molybdenum alloys that do not contain chromium. 

The Ni-Fe-Cr system bridges the gap between the high-nickel austenitic stainless steels and the Ni-Cr-Fe alloy system. Alloy 825 is an upgrade from the 300 series stainless steels and is used to obtain resistance to localized corrosion and S.C.C. This alloy was developed from Alloy 800 by increasing the nickel content and by adding molybdenum (3%), copper (2%), and titanium (0.9%) for improved corrosion resistance in many media [20, 21]. 

Figure 31 illustrates the obtained resistance factors as a function of time in the experiments described in the Procedure section. In the first pack, the resistance factor buildup is much faster than in the second pack. The first stop in flow resulted in a significant recovery in permeability to polymer solution. After resuming the injection, several hours were required to regain the maximum polymer flow resistance... 

Equation (16.18) was fitted to the experimental data with D oh2 representing the unknown variable. The fit result is shown in Figure 16.16 (dashed hne). As can be seen, the model approximates very well the trend of the experimentally obtained resistance R a- From the fit, a reasonable effective diffusion coefficient D qjj = 4.12 X 10 m s is estimated. This result strongly supports the hypothesis that the low-frequency process Pia reflects the mass transfer resistance caused by the gas-phase diffusion in the pores of the Ni/YSZ anode substrate. 

Schematic diagram for obtaining resistance factcrs from pressure inorease tests on pipes [243]...

Suppose it is desired to obtain resistance of 20 anodes in parallel at 20 ft spacing in a soil of 3000ohm-cm, the following is a step-wise procedure. 

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