Materials Literature
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In this paper we report the results from a transmission electron microscope study of α-iron after irradiation with heavy ions. No visible damage was observed following a low dose of self-ions in the energy range 40–240 keV. This is in contrast to the results from other pure metals where visible damage is produced afte…
Abstract The occurrence of polymers branched in a random fashion is common. Chain transfer reactions can cause short- and long-chain branching in polymerizations such as the high-pressure polymerization of ethylene. Branching can also be introduced intentionally by the use of a polyfunctional monomer in end-linking po…
A technique is described for applying flexible boundaries to an atomic region in computer simulation of dislocations or other line defects. The method results in continuity of equilibrium, under the chosen interatomic potential, across the interface between the atomic region and the outer region described in terms of…
Abstract Conformational energy calculations are used to investigate molecular motions in polyethylene crystals. From these a model is derived for the motion that accomplishes the net rotation translation that is believed to underlie the nuclear magnetic resonance (NMR) and dielectric α processes in polyethylenes and p…
The stable tetrahedrane derivative (3)—the very first alkyl-substituted tetrahedrane—has now been synthesized photochemically from the cyclopentadienone (1). 1H-NMR, 13C-NMR, mass, and IR spectra, as well as the reversible isomerization to (2), are compatible with the tetrahedrane structure. The unexpected stability o…
A series of experiments are reported which demonstrate that donors or acceptors can dope polyacetylene to n type or p type, respectively, and that the two kinds of dopants can compensate one another. The formation of a rectifying p-n junction is demonstrated. These results suggest the possibility of utilizing doped po…
We describe a computer model for predicting ductile-fracture initiation and propagation. The model is based on plastic strain. Fracture starts or a crack extends when the integrated product of the equivalent plastic-strain increment and a function of the mean stress exceeds a critical value over a critical length. Thi…
Polyacetylene film and bulk samples were prepared by polymerization of acetylene in the presence of a μ- (η1:η5-cyclopentadienyl) -tris (η-cyclopentadienyl) dititanium (Ti–Ti) catalyst in hexane. Conducting films (σR.T.∼25 Ω−1⋅cm−1), or bulk polymer samples (σR.T.∼1 Ω−1⋅ cm−1) were prepared by treatment of the nascent…
Abstract The term dynamic properties as applied to elastomers refers to the response to periodic or transient forces which do not cause failure or appreciable fatigue (permanent change of properties) during the investigation. Generally this is limited to vulcanizates subjected to deformations not exceeding about 25%;…
Abstract The Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The…
Considerable evidence has recently been presented for anomalous mois ture diffusion in epoxy matrix composites. In an earlier paper we noted that there is no a priori reason why moisture should obey simple diffusion theory rather than Kirkwood's (linear) generalization of the Boltzmann transport equation. With the int…
The present state of the theory of volume effects in a polymer chain is reviewed. The theory of coils (i.e., chains with predominately repulsive volume interaction of monomers) and the analogy between the excluded volume problem and the theory of second-order phase transitions are briefly described. The theory of glob…
A method is described which produces sensible estimates of structure factor moduli from intensity observations, whether the latter are positive or negative. Preliminary applications of the method to data from the protein phosphorylase b are summarized.
A quantitative method is described for the measurement of intralysosomal pH in living cells. Fluorescein isothiocyanate-labeled dextran (FD) is endocytized and accumulates in lysosomes where it remains without apparent degradation. The fluorescence spectrum of this compound changes with pH in the range 4-7 and is not…
The anisotropic properties of some chalcogenide glassy semiconductors changed under the influence of temperature and laser radiation of 0.63 μ wavelength. The induced anisotropy was found to be a function of the composition and previous history of a sample, and was associated with the appearance of nuclei of a new pha…
All the diverse types of liquid-crystalline states can be described in a unified manner by analogy with the group-theoretical description of the symmetry and properties of crystals. The symmetry properties of liquid crystals with respect to the orientation of the molecules, and the conditions for the appearance of a m…
The deformation and conditions for breakup of a single slender drop placed symmetrically in a uniaxial extensional flow are examined theoretically. For the case of an inviscid drop in zero-Reynolds-number flow, Buckmaster (1972) showed, using slender-body analysis, that the shape of the drop is given by r ≡ε R ( z )=ε…
Abstract Ausgehend von Monoaminen (I) und Diaminen (V) werden in einer Kaskaden‐Reaktion durch Cyanethylierung und Reduktion zu Aminen polyfunktionelle Derivate (IV) bzw. (VI) erhalten.
The internal friction (Q−1) in KH2PO4, RbH2PO4, and RbH2AsO4 crystals is investigated using the torsion pendulum technique at frequencies of some Hz in the temperature range from −240°C to the crystal decomposition temperature. The low frequency mechanism of the Q−1 in the vicinity of the Curie point for the crystals…
Abstract This paper discusses the transition in a nematic liquid crystal from a strongly distorted orientation of the anisotropic axis to uniform alignment in a situation of some practical interest. If a nematic with positive dielectric or diamagnetic anisotropy is initially at rest between parallel plates with the an…