Yield conditions for deformation of amorphous polymer glasses

Shear yielding of glassy polymers is usually described in terms of the pressure-dependent Tresca or von Mises yield criteria. We test these criteria against molecular dynamics simulations of deformation in amorphous polymer glasses under triaxial loading conditions that are difficult to realize in experiments. Difficulties and ambiguities in extending several standard definitions of the yield point to triaxial loads are described. Two definitions, the maximum and offset octahedral stresses, are then used to evaluate the yield stress for a wide range of model parameters. In all cases, the onset of shear is consistent with the pressure-modified von Mises criterion, and the pressure coefficient is nearly independent of many parameters. Under triaxial tensile loading, the mode of failure changes to cavitation.Comment: 9 pages, 8 figures, revte

Larval case architecture and implications of host-plant associations for North American Coleophora (Lepidoptera; Coleophoridae)

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The Way and the Word: Science and Medicine in Early China and Greece, by Geoffrey Lloyd and Nathan Sivin, New Haven and London: Yale University Press, 2002,”

While it is evident that a metal ion in aqueous solution interacts electrostatically with water molecules and the anions present in the solution, it is equally apparent that often the metal ion chemically combines with varying numbers of ions or molecules to form complex species. This tendency towards coordination complexing is observed most often with the transition metals and results in a series of complex species MA with n being the number of ligand molecules A which are cpmplexed to the metal ion M and is equal to 1, 2, ..., N-1, N, where N is the maximum observed coordination number but not necessarily identical with Werner vs coordination number for the metal ion. A portion of the work abstracted in this paper was concerned with devising a simple method for the determination of kn2 where kn1 = (MAn)/(MAn-1)(A)

Cognitive Learning Styles and Digital Equity: Searching for the Middle Way

This research is driven by a desire to understand the lifelong learner in the context of styles of learning and the emerging implications of technology enhanced learning for digital equity. Recognizing cognitive learning styles is the first step educators need to take in order to be most effective in working with students of diversity and bridging across formal and informal settings. Learning environments as a characterising feature of learning styles have undergone unprecedented change over the past decade with learning environments now blending physical and virtual space. To support the increasing diversity of learners pedagogy has to be fair, culturally responsive, equitable and relevant to the ‘virtual generation’. This in turn will inform our understanding of the ‘middle way’ in recognising cognitive learning styles , associated cultural context, and the implications to digital pedagogy equity

Scaling of Nucleation Rates

The homogeneous nucleation rate, J, for T ≪ Tc can be cast into a corresponding states form by exploiting scaled expressions for the vapor pressure and for the surface tension, σ. In the vapor-to-liquid case with σ = σ0[Tc-T], the classical cluster energy of formation /kT = [16π/3]·Ω3[Tc/T-1]3/(ln S)2 ≡ [x0/x]2, where Ω ≡ σ0[k ñ2/3] and ñ is liquid number density. The Ω ≈ 2 for normal liquids. (A similar approach can be applied to homogeneous liquid to solid nucleation and to heterogeneous nucleation formalisms using appropriate modifications of σ and Ω.) The above [x0/x]2 is sufficiently tenable that in some cases, one can use it to extract approximate critical temperatures from experimental data. In this work, we point out that expansion cloud chamber data (for nonane, toluene, and water) are in excellent agreement with ln J ≈ const. - [x0/x]2 [centimeter-gram-second (cgs) units], and that the constant term is well approximated by ln (Γc), where Γc is the inverse thermal wavelength cubed per second at T = Tc. The ln (Γc) is ≈ 60 in cgs units (74 in SI units) for most materials. A physical basis for the latter form, which includes the behavior at small n, the discrete integer behavior of n, and a configurational entropy term, τ ln (n), is presented