Multicycle fatigue resistance of brittle polymers

Conclusion A model of multicycle fatigue of polymers based on the hypothesis of self-simulation of the failure process was proposed and a method of predicting the durability was elaborated in the present study. It was found that in low-temperature conditions of self-heating, the crack is the basic cause of fatigue failure. A cyclic durability equation was obtained in the form of a modified time summation criterion for the stressed state in the failure zone in the vicinity of the apex of a fatigue crack. It was shown that in the case of brittle failure in multicycle fatigue, the maximum principal stresses which arise in the failure zone, one order of magnitude smaller than the size of the fatigue crack, are the criterion of failure.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 633–638, July–August, 1990.     

Thermoactivation theory of wear in plastics

It has been shown that wear, being a thermofluctuation process, can be described by an equation analogous to Zhurkov's law of simple fracture. In fatigue wear the maximum value of the activation energy u₀ is close to the u for the rupture of chemical bonds. Abrasive wear is an almost barrierless process, therefore in the case of mixed wear the presence of an abrasive component sharply reduced u₀. The thermoactivation equation describes the effect of temperature on wear only within the limits of one physical state of the polymer. In transition zones it is necessary to take into account the role of the sharp change in elongation at break, which introduces extrema into the temperature wear curve.Mekhanika Polimerov, Vol. 2, No. 6, pp. 867–874, 1966     

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.     

Intermediate structure of the giant dipole resonance in 54Fe and 56Fe

The cross sections for the (γ, n) reaction on ⁵⁴Fe and ⁵⁶Fe for the high-energy component of the neutron spectrum have been investigated using a neutron spectrometer and a synchrotron with a photon energy range from 5 to 26.3 MeV. Neutron energy spectra have been measured. It is shown that the intermediate structure in the (γ, n) reaction cross section is due to high-energy neutrons and correlates with the structure in the neutron spectrum.     

Horocycle flows are loosely Bernoulli

It is proved that horocycle flows associated with transitiveC ²-Anosov flows are loosely Bernoulli with respect to their unique ergodic measures. Partially supported by the Sloan Foundation and NSF Grant MCS74-19388.     

Application of a screened INDO model (INDO/S) to spectroscopic properties of TCNQ and its anions

Theoretical Chemistry Accounts - An INDO model Hamiltonian, incorporating screening within the π-system and parametrized particularly to describe dynamical properties (photoemission and...     

First-order model potential for optical dipole transitions: Application to the lithium isoelectronic sequence

We have constructed two first-order model potentials which were designed to yield dipole transition moments, and have applied them to the lithium isoelectronic sequence. The models contain two or three adjustable parameters, chosen so as to reproduce selected transition moment data on a single ion of the sequence. With negligible computational effort, they both yield other transition moments of high accuracy.