Some rheological properties of highly crosslinked polysiloxanes

Seven crosslinked polydimethylsiloxanes were prepared from carboxyl-terminated siloxane oligomers of different average lengths and a trifunctional imine. The 10-sec torsion modulus was measured as a function of temperature, and compression-deflection data were obtained on swollen specimens. Polymer-solvent interaction parameters were calculated from equilibrium swelling ratios and modulus data. The plots of modulus versus temperature show two distinct transitions for all the crosslinked polymers. The low-temperature transition corresponds to the siloxane chains, whereas the high-temperature transition should be attributed to the portion of the network chain derived from the crosslinking agent and the organic part of the oligosiloxane. On shortening the siloxane blocks, both transitions shift to successively higher temperatures and higher modulus levels. However, the siloxane transition temperature shows only a limited rise even when the average block length becomes quite small. The low siloxane polymers seem to exhibit two swelling maxima, each corresponding to one of the constituents. The studied materials from nonrandom copolymeric structures typical of block polymers. Such microphase systems can probably be expected in crosslinked polymers whenever the crosslinking agent participates significantly in the network chains and its compatibility with the flexible chains species is poor.     

The reactions of ureas with glyoxylic acid and methyl glyoxylate

The reactions of urea, methylurea and dimethylureas with glyoxylic acid and its methyl ester to give α-substituted hydantoic acid derivatives (4, 5, 6, 7) and substituted allantoic acid derivatives (8) is discussed. The cyclization of the hydantoates and allantoates to 5-substituted hydantoins (11, 12) is also described.     

Advertising Budgeting,Wearout and Copy Replacement

In this paper we offer a formulation for the "Copy Life Cycle" phenomenon. In particular, we introduce simultaneously three decision variables, the optimal advertising expenditures during a given planning horizon, the optimal times for copy replacements and the optimal investments in the new copies. The analysis and the solution of the problem is carried out by a mixed optimization technique based on dynamic programming and optimal control theory.     

Analytic Calculi for Product Logics

Product logic is an important t-norm based fuzzy logic with conjunction interpreted as multiplication on the real unit interval [0,1], while Cancellative hoop logic CHL is a related logic with connectives interpreted as for but on the real unit interval with 0 removed (0,1]. Here we present several analytic proof systems for and CHL, including hypersequent calculi, co-NP labelled calculi and sequent calculi.     

Semihard scattering unraveled from collective dynamics by two-pion azimuthal correlations in 158A GeV/c Pb+Au collisions

Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.     

Exactly solvable model for driven dissipative systems

We introduce a solvable stochastic model inspired by granular gases for driven dissipative systems. We characterize far from equilibrium steady states of such systems through the non-Boltzmann energy distribution and compare different measures of effective temperatures. As an example we demonstrate that fluctuation-dissipation relations hold, however, with an effective temperature differing from the effective temperature defined from the average energy.     

LIGHT-DRIVEN MOVEMENTS IN THE SOLAR TRACKING LEAF OF Lupinus palaestinus Boiss. (Fabaceae)

Abstract— The palmatcly-compound leaf lamina of Lupinus palaestinus Boiss. tracks the sun by independent diaphototropic movements of its individual leaflets, operated by the appropriate flexing of their pulvinules. The lamina also exhibits two additional, light-dependent nastic movements, that can operate concurrently with the diaphototropic response: (1) a nyctinastic response to light/dark transitions bv which all the leaflets fold down simultaneously and at equal rates, and which is reversed by a photonastic response to dark/light transitions by which all the leaflets unfold into a co-planar configuration; (2) a photonastic upward folding ("cupping"), which all the leaflets exhibit simultaneously and at equal rates in response to high irradiance. thereby modulating their diaphototropic response to reduce light interception and evade over-exposure. Although the individual leaflets can sense all these tight-signals and respond to them independently, they do so simultaneously, so that the entire lamina responds in a co-ordinated manner, as a unit. The photoreceptors for the two nastic responses are localized in the individual pulvinules and may or may not be the same. The photoreceptors for the diaphototropic perception are localized in the proximal segment of the lamina of the individual leaflets, adjacent to but outside the pulvinule. The separation of the sites of perception for the tropic and nastic responses allows these responses to operate concurrently. The capacity of the diaphototropic response to occur concurrently with one or the other of the two nastic responses may be accounted for by its inductive nature.