Accurate and approximate integrations of Drucker–Prager plasticity with linear isotropic and kinematic hardening

Up to now, some explicit approximate integration schemes based on exponential maps, for non-hardening material obeying Drucker–Prager’s criterion, have been presented. Two new exponential-based approximate formulations, for associative Drucker–Prager plasticity are developed in this article. Both are consistent and explicit algorithms. The linear isotropic and Prager’s kinematic hardening behavior are assumed. Furthermore, an accurate solution for the constitutive equations is derived. The accuracies of the suggested approximate algorithms are assessed by creating related iso-error maps. In addition, by using piecewise strain load histories, and calculating computation times, the robustness and efficiency of the formulations are demonstrated.     

In situ vinylindole synthesis. Diels-alder reactions with maleimides to give tetrahydrocarbazoles

Tetrahydrocarbazoles have been prepared in one-flask syntheses from indoles, ketones or aldehydes, and maleimides, with acid catalysis. The reactions involve a condensation of the indole with the ketone or aldehyde, followed by an in situ trapping of the vinylindole in a Diels-Alder addition with a maleimide. Isomerization of the double bond into the indole nucleus gave the tetrahydrocarbazoles which were isolated ( 6, 9 , and 10 ). Variation of the indole, carbonyl compound, and maleimide has been explored. The predominant stereochemistry of the tetrahydro ring in the products is all-cis, although a second stereoisomer has been isolated. Two regioisomers were generated from all unsymmetrical 2-alkanones, except 2-butanone, which gave the single isomer 9a . Aromatization of tetrahydrocarbazoles 6 to carbazoles 7 was accomplished with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.     

Material symmetry and the evolution of anisotropies in a simple material—I. Change of reference configuration

Noll's rule is used to determine the structure of a material symmetry group written with respect to one reference configuration when the representation of the symmetry with respect to another configuration is the traditional material symmetry group associated with isotropy, transverse isotropy or orthotropy, and for an arbitrary deformation gradient relating the two configurations. It is shown that the former symmetry group can contain an orthogonal subgroup. It is determined whether this subgroup is that for isotropic, transversely isotropic, orthotropic, monoclinic, or triclinic response, and the preferred directions of the symmetry are determined.     

The use of Chebyshev cardinal functions for the solution of a partial differential equation with an unknown time-dependent coefficient subject to an extra measurement

A numerical technique is presented for the solution of a parabolic partial differential equation with a time-dependent coefficient subject to an extra measurement. The method is derived by expanding the required approximate solution as the elements of Chebyshev cardinal functions. Using the operational matrix of derivative, the problem can be reduced to a set of algebraic equations. From the computational point of view, the solution obtained by this method is in excellent agreement with those obtained by previous works and also it is efficient to use.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.     

On selecting portfolio of international mutual funds using goal programming with extended factors

This paper proposes and investigates the use of several factors for portfolio selection of international mutual funds. Three of the selected factors are specific to mutual funds, additional three factors are taken from Macroeconomics and one factor represents regional and country preferences. Each factor is treated as an objective in the multiple objective approach of goal programming. Three variants of goal programming are utilized.     

Atomic scale design and control of cation distribution in hexagonal ferrite

Using a novel alternating target laser ablation deposition technique, Mn cations were placed in specific interstitial sites of BaFe12O19 thin films as opposed to being distributed throughout the unit cell as in conventional bulk materials. The distribution of Mn cations has been confirmed experimentally and predicted theoretically. As a result of site selection, the saturation magnetization increased 12%-22%, and the Néel temperature increased by 40-60 K compared to bulk materials. This technique implies a new methodology to design and process a new generation of ferrite, oxide, and alloy materials.     

Synergistic Biophysical Techniques Reveal Structural Mechanisms of Engineered Cationic Antimicrobial Peptides in Lipid Model Membranes

In the quest for new antibiotics, two novel engineered cationic antimicrobial peptides (eCAPs) have been rationally designed. WLBU2 and D8 (all 8 valines are the d -enantiomer) efficiently kill both Gram-negative and -positive bacteria, but WLBU2 is toxic and D8 nontoxic to eukaryotic cells. We explore protein secondary structure, location of peptides in six lipid model membranes, changes in membrane structure and pore evidence. We suggest that protein secondary structure is not a critical determinant of bactericidal activity, but that membrane thinning and dual location of WLBU2 and D8 in the membrane headgroup and hydrocarbon region may be important. While neither peptide thins the Gram-negative lipopolysaccharide outer membrane model, both locate deep into its hydrocarbon region where they are primed for self-promoted uptake into the periplasm. The partially α-helical secondary structure of WLBU2 in a red blood cell (RBC) membrane model containing 50 % cholesterol, could play a role in destabilizing this RBC membrane model causing pore formation that is not observed with the D8 random coil, which correlates with RBC hemolysis caused by WLBU2 but not by D8.     

Rapid Learning-Based and Geologically Consistent History Matching

Various types of data become available at different stages of a reservoir’s life. The production data are integrated into the flow simulation models through a process referred to as history matching. The history-matching process is iterative, and it usually involves a large number of simulation runs. Hence, this process requires significant computational time. In most history-matching methods, the initial geological assumptions in the reservoir model are destroyed or significantly altered in the process. Furthermore, they do not account for the information obtained during the previous trials, and lack learning from the previous failures. In this paper, we introduce a new methodology that maintains the geological realism. The candidate realizations are selected through a learning-based history-matching (LHM) algorithm by which all the previously successful patterns are preserved and used to assist the construction of the next realizations. The various pieces of matching regions are assembled together to make a pool of the successful candidates. Such regions are then utilized for making an auxiliary dataset in a multiscale framework by which the next model is generated. To prevent from trapping in local minima, ideas from the genetic algorithm is adapted. The LHM algorithm can be applied to both categorical and continuous distributions. The LHM provides a conditional map by which the new production data are immediately incorporated into the existing reservoir models. We apply the LHM algorithm to various 2D and 3D examples with very complex binary and continuous properties. The algorithm is shown to produce history-matched models with significantly smaller CPU times.