Dynamics tacticity effects

Honer, O.P., Wachter, B., East, M.L., Runyoro, V.A. and Hofer, H. (2005) The effect of prey abundance and foraging tactics on the population dynamics of a social, territorial carnivore, the spotted hyena. Oikos 108, 544-554. 

Nuclear magnetic resonance (NMR) spectroscopy is a most effective and significant method for observing the structure and dynamics of polymer chains both in solution and in the solid state [1]. Undoubtedly the widest application of NMR spectroscopy is in the field of structure determination. The identification of certain atoms or groups in a molecule as well as their position relative to each other can be obtained by one-, two-, and three-dimensional NMR. Of importance to polymerization of vinyl monomers is the orientation of each vinyl monomer unit to the growing chain tacticity. The time scale involved in NMR measurements makes it possible to study certain rate processes, including chemical reaction rates. Other applications are isomerism, internal relaxation, conformational analysis, and tautomerism. 

Although syndiotactic polystyrene (SPS) consists of pure polystyrene, the tacticity has a dramatic effect on chain dynamics and causes crystallization to occur. This will be examined in a separate chapter. 

This chapter discusses the dynamic mechanical properties of polystyrene, styrene copolymers, rubber-modified polystyrene and rubber-modified styrene copolymers. In polystyrene, the experimental relaxation spectrum and its probable molecular origins are reviewed further the effects on the relaxations caused by polymer structure (e.g. tacticity, molecular weight, substituents and crosslinking) and additives (e.g. plasticizers, antioxidants, UV stabilizers, flame retardants and colorants) are assessed. The main relaxation behaviour of styrene copolymers is presented and some of the effects of random copolymerization on secondary mechanical relaxation processes are illustrated on styrene-co-acrylonitrile and styrene-co-methacrylic acid. Finally, in rubber-modified polystyrene and styrene copolymers, it is shown how dynamic mechanical spectroscopy can help in the characterization of rubber phase morphology through the analysis of its main relaxation loss peak. 

The above-described contributions address the tactical/strategic levels of the decisionmaking process in centralized FISCs. However, such models are not appropriate as operational decision support tools, which need be able to capture the real dynamic behavior of the system to effectively aid in the operational instance of the FISC. FISCs possess particular operational features as compared with typical chains, that makes... 

The alteration of ships silhouettes to render them unrecognisable, a tactic known as dynamic camouflage, was another technique widely used by the combatants of both World Wars. Apart from the addition or subtraction of funnels, a particularly ingenious trick was to create the effect of a symmetrical, double-ended vessel, with navigation bridges and... 

Another key challenge at the tactical level is to take into account the dynamics of the supply chain. Indeed, in recent years many suppliers and retailers have observed that while customer demand for specific products does not vary much, inventory and back-order levels fluctuate considerably across their supply chain. For instance, examining the demand for Pampers disposal diapers, executives at Procter Gamble noticed an interesting phenomenon. As expected, retail sMes of the product were fairly uniform there is no particular day or month in which the demand is significantly smaller or larger than any other. However, the distributors placed orders to the factory that fluctuated much more than retail sales. In addition, P G s orders to its supphers fluctuated even more. This increase in variability as we travel up in the supply chain is referred to as the Bullwhip effect. For more on this effect, see Simchi-Levi et al. (1999). 

The above mentioned models can be used to support operational distribution decisions under consideration of the available capacities. On the tactical and strategical level such capacities are subjects of interest. To be able to find improved SC configurations, the effects of alterations of the system s capacities have to be measured. These effects are hard to anticipate since stochastic processes often complicate theoretical deductions which also affect the planning at the operational level. Therefore, this work advocates simulation models as an appropriate approach to model complex chemical SCs with multiple stochastic processes and multiple objectives. This modelling approach integrates operational planning models in a stochastic environment to accurately reflect the dynamic effects of alternative SC configurations. 

Relaxations below the glass transition have received widespread study, using principally dynamical mechanical or dielectric relaxation techniques (2). Some effects of tacticity have been noted but will not be discussed here. The effect of configuration on the properties of the quasi-isolated macromolecule, i.e. in dilute solution under e-condition, is also of great interest but is outside the scope of this report. 

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