-The dynamics of polymer melts is well reflected in the complex shear compliance J*(o,T,M) measured in wide ranges of frequency and temperature and f o r various molecular weights. In the frame of the meander model all typical features of J * ( U ,T,M) are quantitatively described:(1) J&N is due to intra-meander shear, and decreases by incorporating pairs of chain ends within the superstructure folds, i.e. with decreasing M. (2) This shear motion is guaranteed by a certain amount of edge-dislocations (with Burgers vector b equal to the chain distance d -for some polymers equal to d/2). The glass relaxation and its activation diagram are understood by asking f o r the probability for just this amount of dislocation segments to be present. The dielectric relaxation strengths and those of the thermal properties support the chosen segment lengths. Neglecting flow,the stress-strain curves of uncrosslinked high molecular weight polymer melts can be derived by taking into account intra-and inter-meander shear deformation.
INTRODUCTIONIn this paper experimental data shall be summarized which characterize the two main relaxations in uncrosslinked amorphous polymers, the glass process and the viscoelastic flow relaxation. These data (among others) should be explained by any molecular model of the levels of order in amorphous polymers to establish its availability for an understanding of more complex macroscopic properties. Here a quantitative interpretation will be given in the frame of the meander model, the suppositions and derivation of which are discussed elsewhere ( 1 , Z ) . The main topic will be the linear viscoelastic behavior in shear of polymer melts, which is best represented by the complex shear compliance J* (w,T,M) in the range between the glassy state (higho or low T) and the viscous flow region ( l o w w or high T). In fig. 1 -3
In recent years research on active safety systems with the main focus on environment sensing has been done. Therefore vehicles are equipped with sensors which record information about the nearby traffic situation and possible hazards. For anticipatory driving additional information outside of the range of the sensors' area needs to be collected. This can be done by introducing data transfer between vehicles, which allows to gather data of a larger area and therefore improves the anticipatory capabilities of the system.One main aspect in the data exchange between vehicles is the organization of the access to the medium. It has to be able to cope with all the problems of mobile ad-hoc networks. Especially the hidden station problem is an important factor in vehicular ad-hoc networks (VANETs). But also the high density of nodes, high dynamics and a limited data rate require a fair and efficient access to the medium.In this paper we present a medium access scheme for vehicular ad-hoc networks which is based on clustering of the vehicles. Thus the effect of hidden stations can be minimized, which leads to a more reliable data transfer than IEEE 802.11 based systems can provide.
A simple method for incorporating bond-length constraints in Monte Carlo simulations of cyclic and linear molecules is described. As an example, the conformational behavior of five even-numbered cyclic alkanes is studied using Monte Carlo simulation and the MM2 force field. 0 1994
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