Tests for nonlinearity in short stationary time series

To compare direct tests for detecting determinism in chaotic time series, data from Henon, Lorenz, and Mackey-Glass equations were contaminated with various levels of additive colored noise. These data were analyzed with a variety of recently developed tests for determinism, and the results compared. (c) 1995 American Institute of Physics.     

New Synthesis of Pyrido[2,3-d] and [3,2-d]Oxazines

N-Hydroxyquinolinimide 1 reacts with each of aromatic amines, hydrazine hydrate and aromatic hydrocarbons to give arylcarbamoyl pyridines 2, pyrrolopyridines 3, pyridopyridazines 4 and pyridooxazinones 5 and 6. The heterocycles 5 and 6 can be transformed to the condensed systems, triazolopyridopyridazines 14 and 15 through series of reactions.     

Influence of pressure on yield and fracture in polymers

Some new data on the effects of pressure on a poly(p-oxybenzoyl) polymer are presented and existing data on various other polymers are reviewed and analyzed. It is demonstrated that the effect of pressure on the elastic response of a polymer depends on the location of T_g relative to room temperature, and that the modulus-pressure data can be used to estimate the pressure shift of T_g. Also, the pressure coefficient of the modulus increase can be deduced from considerations of finite strain elasticity theory. There is a marked increase of tensile and compressive yield strengths with pressure and this can be interpreted in terms of a Mohr-Coulomb type of yield criterion. In some polymers, hydrostatic pressure inhibits cold drawing and reduces the elongation to fracture. However, in other polymers which at atmospheric pressure fracture prior to yielding, increasing the pressure above some critical value can cause significant increases in ductility. This effect is utilized to show that even rigid high-temperature polymers, like polymide, can be successfully cold extruded at room temperature if a proper high-pressure environment is present. The nature of the changes occurring near the brittle-ductile transition pressure have been investigated by use of the scanning electron microscope and the possible influence of the pressure medium has been examined. SEM pictures of fracture surfaces and fracture modes of various polymers will be presented.     

Surface tension of polystyrene blends: Theory and experiment

Surface tension of linear–linear and star/linear polystyrene blends were measured using a modified Wilhelmy method. Our results show that for both polystyrene blend systems, the surface tension‐composition profile is convex, indicating a strong surface excess of the component with lower surface energy. Star/linear blends display more convex surface tension profiles than their linear–linear counterparts, indicative of stronger surface segregation of the branched‐component relative to linear chains. As a first step toward understanding the physical origin of enhanced‐surface segregation of star polymers, self‐consistent field (SCF) lattice simulations (both incompressible and compressible models) and Cahn‐Hilliard theory were used to predict surface tension‐composition profiles. Results from the lattice simulations indicate that the highly convex surface tension profiles observed in the star/linear blend systems are only possible if an architecture‐dependent, Flory interaction parameter (χ = 0.004) is assumed. This conclusion is inconsistent with results from bulk differential scanning calorimetry (DSC) measurements, which indicate sharp glass transitions in both the star/linear and linear/linear homopolymer blends and a simple linear relationship between the bulk glass transition temperature and blend composition. To implement the Cahn‐Hilliard theory, pressure‐volume‐temperature (PVT) data for each of the pure components in the blends were first measured and the data used as input for the theory. Consistent with the experimental data, Cahn‐Hilliard theory predicts a larger surface excess of star molecules in linear hosts over a wide composition range. Significantly, this result is obtained assuming a nearly neutral interaction parameter between the linear and star components, indicating that the surface enrichment of the stars is not a consequence of complex phase behavior in the bulk. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1666–1685, 2009