Durability of polyurethanes elastomers

The effect of thermal aging on three different elastomeric polyurethane adhesives was studied. Consequently, an attempt was made to predict the polyurethanes' service lifetimes from the changes in tensile properties, hardness of bulk specimens and adhesion strength properties (lap shear and butt joints) of polycarbonate bonded joints. Aging temperatures ranged from ambient to 70 °C (at 50% relative humidity) for durations from 20 days to 18 months. Experimental results were analyzed according to a kinetic rate theory and using limit values for the various properties. Consequently, service lifetimes were determined and compared to results from actual service life. Predictions of long-term performance from accelerated tests proved to be reasonable for the properties and materials studied.     

A Carbon-13 and nitrogen-15 NMR study of some nitrogen heterocycles

A number of phenyl-substituted nitrogen heterocycles and the corresponding 2,6-diethylphenyl derivatives were examined by 13 C nmr in order to verify that the heterocyclic ring system was the same in both series. The heterocyclic ring carbon shifts did not differ substantially between the phenyl and 2,6-diethylphenyl derivatives for all systems except one, where substantial differences were also seen in the ¹⁵N chemical shifts. Acetylated derivatives were prepared to confirm the cyclization mode in this latter case.     

The virtues of locking by symbolic names

We propose an algorithm for improving the concurrency of two phase locked transaction systems, which use symbolic-name locking. The algorithm determines by preanalysis which entities can be unlocked before all locks have been obtained, without comprising serializability. This extends the work we published (J. Algorithms 7 (1986) 146–156), in three ways. First, the transactions are not restricted to exclusive locks and may use shared locks as well. Second, a method is proposed to prevent the potential problem of cascading restarts, which results from unlocking of entities before commitment. Third, the transactions may be designed for a distributed database.     

Selective hydrogen transfer from formic acid to α,β-unsaturated ketones by polystyrene-bound IrCl(CO)(PPh3)2

Polytyrene-anchored chlorocarbonylbis(triphenylphosphine)iridium has been shown to be a highly stable and active catalyst for the selective transfer hydrogenation of α,β-unsaturated ketones by formic acid.     

Generating Signals with Multiscale Time Irreversibility: The Asymmetric Weierstrass Function

Time irreversibility (asymmetry with respect to time reversal) is an important property of many time series derived from processes in nature. Some time series (e.g., healthy heart rate dynamics) demonstrate even more complex, multiscale irreversibility, such that not only the original but also coarse-grained time series are asymmetric over a wide range of scales. Several indices to quantify multiscale asymmetry have been introduced. However, there has been no simple generator of model time series with "tunable" multiscale asymmetry to test such indices. We introduce an asymmetric Weierstrass function W(A) (constructed from asymmetric sawtooth functions instead of cosine waves) that can be used to construct time series with any given value of the multiscale asymmetry. We show that multiscale asymmetry appears to be independent of other multiscale complexity indices, such as fractal dimension and multiscale entropy. We further generalize the concept of multiscale asymmetry by introducing time-dependent (local) multiscale asymmetry and provide examples of such time series. The W(A) function combines two essential features of complex fluctuations, namely fractality (self-similarity) and irreversibility (multiscale time asymmetry); moreover, each of these features can be tuned independently. The proposed family of functions can be used to compare and refine multiscale measures of time series asymmetry.