10 research outputs found

    TLISMNI/Adams algorithm for the solution of the differential/algebraic equations of constrained dynamical systems

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    This paper examines the performance of the 3rd and 4th order implicit Adams methods in the framework of the two-loop implicit sparse matrix numerical integration method in solving the differential/algebraic equations of heavily constrained dynamical systems. The variable-step size two-loop implicit sparse matrix numerical integration/Adams method proposed in this investigation avoids numerical force differentiation, ensures satisfying the nonlinear algebraic constraint equations at the position, velocity, and acceleration levels, and allows using sparse matrix techniques for efficiently solving the dynamical equations. The iterative outer loop of the two-loop implicit sparse matrix numerical integration/Adams method is aimed at achieving the convergence of the implicit integration formulae used to solve the independent differential equations of motion, while the inner loop is used to ensure the convergence of the iterative procedure used to satisfy the algebraic constraint equations. To solve the independent differential equations, two different implicit Adams integration formulae are examined in this investigation; a 3rd order implicit Adams-Moulton formula with a 2nd order explicit predictor Adams Bashforth formula, and a 4th order implicit Adams-Moulton formula with a 3rd order explicit predictor Adams Bashforth formula. A standard Newton–Raphson algorithm is used to satisfy the nonlinear algebraic constraint equations at the position level. The constraint equations at the velocity and acceleration levels are linear, and therefore, there is no need for an iterative procedure to solve for the dependent velocities and accelerations. The algorithm used for the error check and step-size change is described. The performance of the two-loop implicit sparse matrix numerical integration/Adams algorithm developed in this investigation is evaluated by comparison with the explicit predictor-corrector Adams method which has a variable-order and variable-step size. Simple and heavily constrained dynamical systems are used to evaluate the accuracy, robustness, damping characteristics, and effect of the outer-loop iterations of the proposed implicit schemes. The results obtained in this investigation show that the two-loop implicit sparse matrix numerical integration methods proposed in this study can be more efficient for stiff systems because of their ability to damp out high-frequency oscillations. Explicit integration methods, on the other hand, can be more efficient in the case of non-stiff systems

    Nondestructive Functionalization of Graphene by Surface-Initiated Atom Transfer Radical Polymerization: An Ideal Nanofiller for Poly(<i>p</i>‑phenylene benzobisoxazole) Fibers

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    A direct and nondestructive strategy for growing polymers from the surface of graphene is demonstrated. The technique involves the covalent attachment of an initiator via one-step cycloaddition of a diarylcarbene, followed by the polymerization of 2-hydroxyethyl methacrylate (HEMA) using atom transfer radical polymerization (ATRP). The functionalization strategy is shown to significantly increase the solubility of the resulting materials (PHEMA-G) and leave the structure of the graphene largely intact. Importantly, the PHEMA-G/poly­(<i>p</i>-phenylene benzobisoxazole) (PBO) composite fibers could be obtained by a one-pot polymerization and dry-jet wet spinning process. The nanocomposite fibers exhibited a tensile strength of 3.22 GPa (51.2% higher than PBO) and Young’s modulus of 139.3 GPa (33.7% higher than PBO) at very low PHEMA-G loading (1.0 wt %). This represents an excellent reinforcing efficiency, better than other reports of the graphene/PBO fibers system, and indicates that this material is suitable for applications in composite science

    Petrogenesis and timing of emplacement of porphyritic monzonite, dolerite, and basalt associated with the Kuoerzhenkuola Au deposit, Western Junggar, NW China: implications for early Carboniferous tectonic setting and Cu–Au mineralization prospectivity

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    <p>The Kuoerzhenkuola epithermal Au deposit is located in the northern part of the West Junggar region of NW China and is underlain by a recently discovered porphyritic monzonite intrusion that contains Cu–Au mineralization. Zircon LA-ICP-MS U–Pb dating of this intrusion yielded an age of 350 ± 4.7 Ma. The porphyritic monzonite is calc-alkaline and is characterized by high concentrations of Sr (583–892 ppm), significant depletions in the heavy rare earth elements (HREE; e.g. Yb = 0.96–2.57 ppm) and Y (10.4–23.3 ppm), and primitive mantle-normalized multi-element variation diagram patterns with positive Sr and Ba and negative Nb and Ti anomalies, all of which indicate that this intrusion is compositionally similar to adakites elsewhere. The composition of the porphyritic monzonite is indicative of the derivation from magmas generated by the melting of young subducted slab material. The area also contains Nb-enriched basalts that are enriched in sodium (Na<sub>2</sub>O/K<sub>2</sub>O = 1.20–3.90) and have higher Nb, Zr, TiO<sub>2</sub>, and P<sub>2</sub>O<sub>5</sub> concentrations and Nb/La and Nb/U ratios than typical arc basalts. The juxtaposition of adakitic rocks, Nb-enriched basalts, and dolerites in this region suggests that the oceanic crust of the expansive oceans within the West Junggar underwent early Carboniferous subduction. Magnetite is widespread throughout the Kuoerzhenkuola Au deposit, as evidenced by the volcanic breccias cemented by late hydrothermal magnetite and pyrite. In addition, the zoned potassic, quartz-sericite alteration, and propylitic and kaolin alteration in the deeper parts of the porphyritic monzonite are similar to those found in porphyry Cu–Au deposits. These findings, coupled with the mineralogy and geochemistry of the alteration associated with the Kuoerzhenkuola Au deposit, suggest that the mineralization in this area is not purely epithermal, with the geology and geochemistry of the porphyritic monzonite in this area suggesting that a porphyry Cu–Au deposit is probably located beneath the Kuoerzhenkuola Au deposit.</p

    Genesis of late carboniferous granitoid intrusions in the Dayinsu area, West Junggar, Northwest China: evidence of an arc setting for the western CAOB

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    <p>The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO<sub>2</sub> contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K<sub>2</sub>O + Na<sub>2</sub>O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.</p

    Multiple alignment of GH2 β-galactosidases (a) and the homology model of the whole BgaL3 (b) and its enlarged active center (c).

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    <p>The amino residues in the black boxing region are parallel to the <i>E</i>. <i>coli</i> W999. The putative catalytic residues of BgaL3, Glu465 and Glu532, locate at the bottom of the active center (in red), while the crucial residue involved in substrate specificity, W980, stands at the entrance of the active center (in blue).</p

    Multistimuli-Responsive Intrinsic Self-Healing Epoxy Resin Constructed by Host–Guest Interactions

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    The self-healing abilities inside polymeric materials are desirable functions in materials science. Host–guest chemistry, combined with excellent properties of graphene, was used for the construction of multistimuli-responsive intrinsic self-healing epoxy materials. By ultraviolet (UV) curing, the unsaturated epoxy resin was connected with β-cyclodextrin/graphene complex through free radical copolymerization. The introduced complex, acting as macro-cross-linker and photothermal agent, can reconnect the damage-induced broken bonds through dynamic host–guest interaction. In this work, the epoxy composites exhibited a high healing efficiency of up to 79.2% and tensile strength of up to 20.8 MPa under heating or near-infrared stimulation, which represent relatively excellent values among all the reported intrinsic self-healing epoxy resin and host–guest self-healing systems

    Transglycosylation reactions catalyzed by 19 mutants.

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    <p>(a) Lactose self-condensation. Lane 1, standard glucose plus galactose; lane 2, galactose plus lactose; lane 3, lactose. (b) Transglycosylation toward hydroquinone using lactose as donor. Lane 1, lactose; lane 2, hydroquinone (invisible in the plate); lane 3 and 4, reactions by the wild type and the W980F mutant only in the presence of the lactose, respectively. The capital letters ‘W’ to ‘P’ represent the results from crude enzymes bearing relevant amino-acid substitutions at the 980 site.</p

    Glycosylation of Phenolic Compounds by the Site-Mutated β-Galactosidase from <i>Lactobacillus bulgaricus</i> L3

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    <div><p>β-Galactosidases can transfer the galactosyl from lactose or galactoside donors to various acceptors and thus are especially useful for the synthesis of important glycosides. However, these enzymes have limitations in the glycosylation of phenolic compounds that have many physiological functions. In this work, the β-galactosidase from <i>Lactobacillus bulgaricus</i> L3 was subjected to site-saturation mutagenesis at the W980 residue. The recombinant pET-21b plasmid carrying the enzyme gene was used as the template for mutation. The mutant plasmids were transformed into <i>Escherichia coli</i> cells for screening. One recombinant mutant, W980F, exhibited increased yield of glycoside when using hydroquinone as the screening acceptor. The enzyme was purified and the effects of the mutation on enzyme properties were determined in detail. It showed improved transglycosylation activity on novel phenolic acceptors besides hydroquinone. The yields of the glycosides produced from phenol, hydroquinone, and catechol were increased by 7.6% to 53.1%. Moreover, it generated 32.3% glycosides from the pyrogallol that could not be glycosylated by the wild-type enzyme. Chemical structures of these glycoside products were further determined by MS and NMR analysis. Thus, a series of novel phenolic galactosides were achieved by β-galactosidase for the first time. This was a breakthrough in the enzymatic galactosylation of the challenging phenolic compounds of great values.</p></div
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