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  • 1
    Publication Date: 2015-04-25
    Description: Understanding the relative motion between the Pacific plate and its neighboring plates in the Paleogene has important consequences for deciphering the relationship between absolute and relative plate motions in the Pacific Ocean basin, the history of circum-Pacific subduction, and the cause of the Hawaiian-Emperor bend (HEB). We quantitatively model the Farallon/Vancouver-Pacific-Antarctic seafloor spreading history from 67 to 33 Ma based on a comprehensive synthesis of magnetic anomaly and fracture identifications. We find a well-constrained increase from 75 ± 5 mm/yr to 101 ± 5 mm/yr in Pacific-Farallon full spreading rates between 57.6 Ma and 55.9 Ma, followed by a stepwise increase to 182 ± 2 mm/yr from 49.7 to 40.1 Ma. The increases in Pacific-Farallon spreading rates are not accompanied by any statistically significant change in spreading direction. The 57.6–55.9 Ma surge of Pacific-Farallon spreading reflects an eastward acceleration in Farallon plate motion, as it precedes west Pacific subduction initiation and is not associated with any significant change in Pacific-Antarctic spreading. We interpret the increase in Pacific-Farallon spreading rates after ca. 50 Ma as a consequence of further acceleration in Farallon plate motion. We find no indication of a major change in Pacific plate absolute motion at this time. Our model suggests that changes in relative motion direction between the Pacific and Farallon and Pacific and Antarctic plates were insignificant around the formation time of the HEB (ca. 47.5 Ma), and the bend is largely a consequence of Hawaiian hotspot motion, which ceased rapid motion after 47 Ma.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 2
    Publication Date: 2014-04-19
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 3
    Publication Date: 2013-07-23
    Description: Global oceans are known to have alternated between aragonite and calcite seas. These oscillations reflect changes in the Mg/Ca ratios of seawater that control biomineralization and the composition of marine carbonates, and are thought to be caused mainly by the time dependence of crustal accretion at mid-ocean ridge crests and the associated high-temperature mid-ocean ridge fluid flux. Here we use global ocean basin reconstructions to demonstrate that the fluctuations in hydrothermal ocean inputs are instead caused by the gradual growth and destruction of mid-ocean ridges and their relatively cool flanks during long-term tectonic cycles, thus linking ocean chemistry to off-ridge low-temperature hydrothermal exchange. Early Jurassic aragonite seas were a consequence of supercontinent stability and a minimum in mid-ocean ridge length and global basalt alteration. The breakup of Pangea resulted in a gradual doubling in ridge length and a 50% increase in the ridge flank area, leading to an enhanced volume of basalt to be altered. The associated increase in the total global hydrothermal fluid flux by as much as 65%, peaking at 120 Ma, led to lowered seawater Mg/Ca ratios and marine hypercalcification from 140 to 35 Ma. A return to aragonite seas with preferential aragonite and high-Mg calcite precipitation was driven by pronounced continental dispersal, leading to progressive subduction of ridges and their flanks along the Pacific rim.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 4
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    Geological Society of America (GSA)
    Publication Date: 2013-03-29
    Description: The topography of Earth is primarily controlled by lateral differences in the density structure of the crust and lithosphere. In addition to this isostatic topography, flow in the mantle induces deformation of its surface leading to dynamic topography . This transient deformation evolves over tens of millions of years, occurs at long wavelength, and is relatively small (〈2 km) in amplitude. Here, we review the observational constraints and modeling approaches used to understand the amplitude, spatial pattern, and time dependence of dynamic topography. The best constraint on the present-day dynamic topography induced by sublithospheric mantle flow is likely the residual bathymetry calculated by removing the isostatic effect of oceanic lithospheric structure from observed bathymetry. Increasing knowledge of the thermal and chemical structure of the lithosphere is important to better constrain present-day mantle flow and dynamic topography. Nevertheless, at long wavelengths (〉5000 km), we show that there is good agreement between published residual topography fields, including the one described here, and present-day dynamic topography predicted from mantle flow models, including a new one. Residual and predicted fields show peak-to-peak amplitudes of roughly ±2 km and a dominant degree two pattern with high values for the Pacific Ocean, southern Africa, and the North Atlantic and low values for South America, western North America, and Eurasia. The flooding of continental interiors has long been known to require both larger amplitudes and to be temporally phase-shifted compared with inferred eustatic changes. Such long-wavelength inferred vertical motions have been attributed to dynamic topography. An important consequence of dynamic topography is that long-term global sea-level change cannot be estimated at a single passive margin. As a case study, we compare the results of three published models and of our model to the subsidence history of well COST-B2 offshore New Jersey. The 〈400 ± 45 m amount of anomalous subsidence of this well since 85 Ma is best explained by models that predict dynamic subsidence of the New Jersey margin during that period. Explicitly including the lithosphere in future global mantle flow models should not only facilitate such comparisons between model results and data, but also further constrain the nature of the coupling between the mantle and the lithosphere.
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 473-482 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rates of mass and momentum transport in narrow flow channels (gaps 0.2-0.5 mm) have been determined over a wide range of flow velocities, 220-7,700 cm/sec (Re 1,300 to 22,000). Existing correlations that apply to smooth channels of much larger hydraulic diameter were found to be valid for the narrow channels as well. However, in the turbulent regime the condition of hydraulic smoothness could be satisfied only when the walls were optically smooth. Transport rates to rough walls were also measured. The ratio of the mass transport to the momentum transport in the form of jD/(f/2) - a measure of the improved mass transfer compared to the increased pressure drop - is given for the smooth and rough-wall cells over the Re range studied.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 289-303 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dynamic shear experiments in the linear range of deformation and extensional tests at constant strain rate have been carried out on a linear low-density polyethylene (LLDPE) melt and on two branched low-density polyethylene (LDPE) melts with different amounts of long-chain branching. Both the dynamic shear moduli and the tensile stress obey the time-temperature superposition principle. A simple model based on a nonaffine generalized Maxwell model with two relaxation times is proposed to describe the rheological behavior in elongation of these melts. Close agreement between the model and the experimental data can be obtained by adjusting the two relaxation times and the “slip parameter” of entanglements. The variations of these parameters with strain rate and their relationship with molecular structure are discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The fast tautomeric equilibrium of (N15)-4-phenylisoxazolin-5-one (2) has been investigated by a study of 2J(N15—H3) coupling. Comparison of the observed values for 2 and for the two fixed forms (N15)-2-methyl-4-phenylisoxazolin-5-one (3) and (N15)-4-phenyl-5-methoxyisoxazol (4) indicates a considerable amount of enolic type structure for 2 in basic media.
    Notes: La comparasion des constantes de couplage 2J(N15—H3) présentées par la (N15)-4-phénylisoxazoline-5-one (2) et par deux de ses formes fixes, la (N15)-2-méthyl-4-phénylisoxazoline-5-one (3) et le (N15)-4-phényl-5-méthoxyisoxazole (4), indique une participation élevée de structure énolique (et/ou ionique) dans les milieux basiques.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 301-308 
    ISSN: 1042-7147
    Keywords: polymer blends ; melt rheology ; crosslinked rubber ; structured latex ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 933-943 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Viscoelastic properties of styrene-co-methyl methacrylate random copolymers have been determined over a temperature range covering the glass transition, the rubbery plateau, and the terminal zone and compared with polystyrene and polymethyl methacrylate homopolymers. Nonlinear behavior was observed in the variations of most of the physical and rheological characteristics with the methyl methacrylate content in the copolymer. Results are interpreted in terms of the rupture of polar-polar intermolecular interactions between ester groups due to the presence of styrene units.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 295-310 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extensional tests at constant strain rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} have been carried out on polystyrene melts with different molecular weight distributions at various temperatures and strain rates. The true tensile stress is found to be well approximated by the sum of two contributions: (1) a neo-Hookean expression involving the recoverable strain and (2) a contribution rapidly reaching a steady-state value. Two experimental parameters can be defined: an elasticity modulus \documentclass{article}\pagestyle{empty}\begin{document}$ G(\dot \varepsilon ) $\end{document} from (1) and a viscosity \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{\rm v} (\dot \varepsilon ) $\end{document} from (2). It is further shown that time-temperature equivalence applies not only to the stress but also to the recoverable strain and to G and ηv. The dependence of G and ηv on strain rate is then discussed. For high strain rates, G is close to the linear viscoelastic plateau modulus of PS melts and decreases with decreasing strain rate. The value of ηv is found to a good approximation to be equal to three times the shear viscosity taken at a shear rate equivalent to the elongational strain rate.
    Additional Material: 13 Ill.
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