Strain strong

Different mouse strains strongly differ in their degree of susceptibility to S. pneumoniae (7). While CBA/Ca and SJL are highly susceptible, BALB/c is highly resistant and C3H/He, FVB/n, NIH, AKR, C57BL/6, and DBA/2 exhibit intermediate resistance. 

Next, compressive and tensile biaxial strain effects are discussed, because biaxial strains are usually adopted to reduce the threshold carrier density in conventional ZB QWs. FIGURE 5 shows the maximum optical gain of biaxially strained ZB GaN/Alo.2Gao. N QWs with well width Lz = 60 A. The compressive biaxial strain strongly depresses the TM-mode optical gain and enhances the TE-mode optical gain. On the other hand, the effect of tensile biaxial strain is the reverse of that of compressive strain. These results can easily be understood from the feature of bulk ZB GaN, where compressive... 

The very satisfactory fit of the scaling predictions obtained by the tube model with deformation-dependent constraints to experimental results for various rubbers at small strains strongly supports the basic assumptions of this approach. Further, it seems worth noting that the small-strain behaviour of rubber-elastic networks considered here is well described by the theoretical results for the case of low crosslink density. This case shows a strong resemblance to that of the melt as there, the influence of topological constraints on the mechanical properties of the networks is important and is well reflected by the molecular field approach of the tube model. As mentioned already in Sect. 4.2, these conclusions are almost identical with the view of Graessley and co-workers and Macosko and co-workers who also extensively... 

Purified adipyI-7-ADCA and adipyl-7-ACA from culture broths could be readily deacylated by a Pseudumonos-derived gluiaryl amidase to produce, respectively, 7-AIX A and 7-ACA. Interestingly, production levek of adipyl-7-ADCA and adipyl-7-ACA by the recombinant strains were substantially enhanced by applying classical methods of strain improvement to the transformants. The production levels of 7-ACA and 7-ADCA by these strains strongly suggested the possibility for commercial development (167). 

On the other hand, the phosphorylative inactivation of kanamycin by the RF-mediated resistant E j coli strain does differ from that involved in the resistance of laborata y acquired strains of . coli 12. The RF-mediated enzyme of E. coli (ml 1629) responsible for the inactivation is absent in sensitive ,. coli 12 strains, strongly suggesting a direct relationship between this inactivating process and the observed resistance. Adenylation as a means for the inactivation of streptomycin by RF-resistant Ej coli has been reported from two additional laboratories Whether adenylation, rather than phosphorylation, is actually the first step of inactivation of aminoglycoside antibiotics other than streptomycin remains to be established. 

Another aspect of plasticity is the time dependent progressive deformation under constant load, known as creep. This process occurs when a fiber is loaded above the yield value and continues over several logarithmic decades of time. The extension under fixed load, or creep, is analogous to the relaxation of stress under fixed extension. Stress relaxation is the process whereby the stress that is generated as a result of a deformation is dissipated as a function of time. Both of these time dependent processes are reflections of plastic flow resulting from various molecular motions in the fiber. As a direct consequence of creep and stress relaxation, the shape of a stress—strain curve is in many cases strongly dependent on the rate of deformation, as is illustrated in Figure 6. 

Steels iu the AISI 400 series contain a minimum of 11.5% chromium and usually not more than 2.5% of any other aHoyiag element these steels are either hardenable (martensitic) or nonhardenable, depending principally on chromium content. Whereas these steels resist oxidation up to temperatures as high as 1150°C, they are not particularly strong above 700°C. Steels iu the AISI 300 series contain a minimum of 16% chromium and 6% nickel the relative amounts of these elements are balanced to give an austenitic stmcture. These steels caimot be strengthened by heat treatment, but can be strain-hardened by cold work. 

Although reasonably stable at room temperature under neutral conditions, tri- and tetrametaphosphate ions readily hydrolyze in strongly acidic or basic solution via polyphosphate intermediates. The hydrolysis is first-order under constant pH. Small cycHc phosphates, in particular trimetaphosphate, undergo hydrolysis via nucleophilic attack by hydroxide ion to yield tripolyphosphate. The ring strain also makes these stmctures susceptible to nucleophilic ring opening by other nucleophiles. 

Fig. 4. Types of stress—strain curves (a) soft and weak (b) hard and brittle (c) soft and tough (d) hard and strong and (e) hard and tough.

Deformation Under Loa.d. The mechanical behavior of coal is strongly affected by the presence of cracks, as shown by the lack of proportionahty between stress and strain in compression tests or between strength and rank. However, tests in triaxial compression indicate that as the confirming pressure is increased different coals tend to exhibit similar values of compressive strength perpendicular to the directions of these confining pressures. Except for anthracites, different coals exhibit small amounts of recoverable and irrecoverable strain underload. 

Proportion of Hard Segments. As expected, the modulus of styrenic block copolymers increases with the proportion of the hard polystyrene segments. The tensile behavior of otherwise similar block copolymers with a wide range of polystyrene contents shows a family of stress—strain curves (4,7,8). As the styrene content is increased, the products change from very weak, soft, mbbedike materials to strong elastomers, then to leathery materials, and finally to hard glassy thermoplastics. The latter have been commercialized as clear, high impact polystyrenes under the trade name K-Resin (39) (Phillips Petroleum Co.). Other types of thermoplastic elastomers show similar behavior that is, as the ratio of the hard to soft phase is increased, the product in turn becomes harder. 

The result is work-hardening the steeply rising stress-strain curve after yield, shown in Chapter 8. All metals and ceramics work-harden. It can be a nuisance if you want to roll thin sheet, work-hardening quickly raises the yield strength so much that you have to stop and anneal the metal (heat it up to remove the accumulated dislocations) before you can go on. But it is also useful it is a potent strengthening method, which can be added to the other methods to produce strong materials. 

Finally, mild steel can sometimes show an instability like that of polythene. If the steel is annealed, the stress/strain curve looks like that in Fig. 11.10. A stable neck, called a Luders Band, forms and propagates (as it did in polythene) without causing fracture because the strong work-hardening of the later part of the stress/strain curve prevents this. Luders Bands are a problem when sheet steel is pressed because they give lower precision and disfigure the pressing. 

Many fibrous composites are made of strong, brittle fibres in a more ductile polymeric matrix. Then the stress-strain curve looks like the heavy line in Fig. 25.2. The figure largely explains itself. The stress-strain curve is linear, with slope E (eqn. 25.1) until the matrix yields. From there on, most of the extra load is carried by the fibres which continue to stretch elastically until they fracture. When they do, the stress drops to the yield strength of the matrix (though not as sharply as the figure shows because the fibres do not all break at once). When the matrix fractures, the composite fails completely. 

The axial tensile strength of many woods is around 100 MPa - about the same as that of strong polymers like the epoxies. The ductility is low - typically 1% strain to failure. 

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