Subject insensitivity mechanisms

Polyolefin melts under excessive loads are subject to mechanically and oxidatively activated chain cleavage. Polyolefins do not depolymerize. Polyethylene and polypropylene are relatively insensitive to purely thermal degradation, but react easily with oxygen and radicals. Under mild conditions and the presence of oxygen, oxidation is preferred to thermal degradation due its lower level of activation energy (oxidation PE approx. 96 kj/mol vs. thermal degradation PE approx. 264 kj/mol) [20]. 

Returning now to the subject of the chapter, in addition to appropriate retentive characteristics, a potential stationary phase must have other key physical characteristics before it can be considered suitable for use in LC. It is extremely important that the stationary phase is completely insoluble (or virtually so) in all solvents that are likely to be used as a mobile phase. Furthermore, it must be insensitive to changes in pH and be capable of assuming the range of interactive characteristics that are necessary for the retention of all types of solutes. In addition, the material must be available as solid particles a few microns in diameter, so that it can be packed into a column and at the same time be mechanically strong enough to sustain bed pressures of 6,000 p.s.i. or more. It is clear that the need for versatile interactive characteristics, virtually universal solvent insolubility together with other critical physical characteristics severely restricts the choice of materials suitable for LC stationary phases. 

Benzoyl peroxide appears to decompose entirely by the radical mechanism, the reaction being rather insensitive either to solvent changes or to the addition of acid catalysts. The unsymmetrical peroxide, -methoxy-/> -nitrobenzoyl peroxide, behaves quite differently. It will decompose either by the polar mechanism or by the radical mechanism.821 The radical mechanism prevails in benzene and the acids produced are -nitrobenzoic and anisic in equal amounts. In the more polar solvents anisic acid is formed to a lesser extent than is >-nitrobenzoic acid, because the carboxy inversion reaction (rearrangement) competes successfully. The reaction is subject to acid catalysis... 

This book outlines the basic principles needed to understand the mechanism of explosions by chemical explosives. The history, theory and chemical types of explosives are introduced, providing the reader with information on the physical parameters of primary and secondary explosives. Thermodynamics, enthalpy, free energy and gas equations are covered together with examples of calculations, leading to the power and temperature of explosions. A very brief introduction to propellants and pyrotechnics is given, more information on these types of explosives should be found from other sources. This second edition introduces the subject of Insensitive Munitions (IM) and the concept of explosive waste recovery. Developments in explosive crystals and formulations have also been updated. This book is aimed primarily at A level students and new graduates who have not previously studied explosive materials, but it should prove useful to others as well. I hope that the more experienced chemist in the explosives industry looking for concise information on the subject will also find this book useful. 

We begin with an innocuous case. Consider a pendulum suspended in air and consequently subject to damping accompanied by a Langevin force. This force is, of course, the same as the one in equation (1.1) for the Brownian particle, because the collisions of the air molecules are the same. They depend on the instantaneous value of V, but they are insensitive to the fact that there is a mechanical force acting on the particle as well. Hence for small amplitudes the motion is governed by the linear equation (1.10). For larger amplitudes the equation becomes nonlinear ... 

In this paper we have derived expressions for the environment-induced correction to the Berry phase, for a spin coupled to an environment. On one hand, we presented a simple quantum-mechanical derivation for the case when the environment is treated as a separate quantum system. On the other hand, we analyzed the case of a spin subject to a random classical field. The quantum-mechanical derivation provides a result which is insensitive to the antisymmetric part of the random-field correlations. In other words, the results for the Lamb shift and the Berry phase are insensitive to whether the different-time values of the random-field operator commute with each other or not. This observation gives rise to the expectation that for a random classical field, with the same noise power, one should obtain the same result. For the quantities at hand, our analysis outlined above involving classical randomly fluctuating fields has confirmed this expectation. 

Equations (17.67)-(17.69) are based on the assumption that only the rate constants of the chemical step are subject to a kinetic solvent isotope effect. This assumption simplifies the derivation of rate equations, but one must always keep in mind that, though the substrate binding and product release are usually solvent isotope-insensitive, the entire mechanism may contain more than a single isotope sensitive step. 

The mechanism of stereoregulation in the polymerization of 3-lactones and lactams is a subject in which very little definitive information is available and, consequently, many unanswered questions exist. Little is known about the molecular basis for the apparent stereoregulatlon in these ring-opening polymerization reactions, and unfortunately there is even very little quantitative information on tactlclty in these families of polymers. Because of this lack of reliable tacticlty information (as a result of the insensitivity of NMR spectra to differences in configurational sequences), stereoregularity is often inferred from crystallinity measurements. Unfortunately, however, there are many anomalies in the relationships between polymer crystallinity and apparent stereoregularity in the polyesters and polyamides obtained from 3-lactones and lactams. 

Insensitive munitions are munitions which are stable enough to withstand mechanical shocks, fire, and impact by shrapnel, but that are still able to explode as intended in order to destroy their targets. Insensitive munitions will only bum (rather than explode) when subjected to fast or slow heating, bullets, shrapnel, shaped charges, or the detonation of another nearby munition. The term typically refers to warheads, bombs, and rocket motors. Insensitive munitions are munitions that are less sensitive to unplanned stimuli that might cause unplanned ignition of the munition. 

Another approach for dealing with the singularity points is to use a cohesive zone model (CZM). This approach is associated to interface elements and enable to predict crack initiation and crack growth. It is a combination of a stress limit and fracture mechanics approach and relatively mesh insensitive. Many researchers are using this tool with accurate results (de Moura et al. 2006). However, the parameters associated to the CZM require previous experimental tuning and the user needs to know beforehand where the failure is likely to occur. This subject is discussed in detail in O Chap. 25. 

Thus, several important mechanical properties of metals may be determined from tensile stress-strain tests. Table 6.2 presents some typical room-temperature values of yield strength, tensile strength, and ductility for several common metals. These properties are sensitive to any prior deformation, the presence of impurities, and/or any heat treatment to which the metal has been subjected. The modulus of elasticity is one mechanical parameter that is insensitive to these treatments. As with modulus of elasticity, the magnitudes of both yield and tensile strengths decline with increasing temperature just the reverse holds for ductility —it usually increases with temperature. Figure 6.14 shows how the stress-strain behavior of iron varies with temperature. 

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