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11.
Peter D. Olmsted 《Rheologica Acta》2008,47(3):283-300
In this review, I present an idiosyncratic view of the current state of shear banding in complex fluids. Particular attention
is paid to some of the outstanding issues and questions facing the field, including the applicability of models that have
“traditionally” been used to model experiments; future directions and challenges for experimentalists; and some of the issues
surrounding vorticity banding, which has been discussed theoretically and whose experiments are fewer in number yet, in many
ways, more varied in character. 相似文献
12.
David L. Olmsted Louis G. Hector Jr. 《Journal of the mechanics and physics of solids》2006,54(8):1763-1788
The strengthening of Al by Mg solute atoms is investigated using molecular dynamics (MD) studies of single dislocations moving through a field of randomly placed solutes. The MD method permits explicit treatment of “core” effects, dislocation pinning and deceleration, and dislocation unpinning by thermal activation, all under an applied load. Choice of an appropriate MD simulation cell size is assessed using analytic concepts developed by Labusch. The interaction energy of a single Mg atom with straight edge and screw dislocations is computed and compared with continuum models. Using the single Mg energies, a one-dimensional energy landscape for the motion of a straight edge dislocation through a random field of Mg solutes is computed. The minima in this landscape match well with those found in the MD simulations at zero temperature. The stress to unpin a straight edge dislocation trapped in a local energy minimum generated by the solutes is then predicted semi-analytically using the energy landscape, and good agreement is obtained with the MD results. At temperatures of 300 and 500 K, the thermally activated rate of unpinning vs. stress and temperature is calculated semi-analytically, and agreement with the full MD results is again obtained with the fitting of a single attempt frequency in a transition state model. The agreement of the semi-analytical models provides a basis for calculating yield stress vs. strain rate and temperature, resulting from statistical pinning, for the case of non-interacting dislocations on a single slip system, and for extending the analysis to study dynamic strain aging effects resulting from diffusion of Mg atoms around a pinned dislocation. 相似文献
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14.
A photochemical method for determining the oxygen concentration in air-saturated non-aqueous solvents has been developed. Solutions containing a sensitizer (Rose Bengal or Methylene Blue) and 1,3-diphenylisobenzofuran (DPIBF) as an oxygen acceptor are irradiated at 546 or 633 nm and the absorbance at 404 nm is monitored. The dissolved oxygen content is found from the change in absorbance and the known 1:1 stoichiometry of addition of singlet oxygen to DPIBF. The solubilities found, accurate to +/- 6%, for oxygen in air-equilibrated solvents, are (mM): acetone, 2.37; acetonitrile, 2.42; dimethylsulfoxide, 0.33; ethanol, 1.94; N-methylformamide, 1.31. Measurements on mixed acetone-N-methylformamide solvents showed that the solubility of oxygen does not vary with solvent composition in a predictable manner. 相似文献
15.
Craig K Comfort JR Allgower CE Bekrenev V Berger E Briscoe WJ Clajus M Draper B Grosnick D Isenhower D Knecht N Koetke D Koulbardis A Kozlenko N Kruglov S Lolos GJ Lopatin I Manley DM Manweiler R Marusić A McDonald S Nefkens BM Olmsted J Papandreou Z Peaslee D Phaisangittisakul N Prakhov S Price JW Pulver M Ramirez AF Sadler ME Shafi A Spinka H Stanislaus S Starostin A Supek I Staudenmaier HM Tippens WB;Crystal Ball Collaboration 《Physical review letters》2003,91(10):102301
Data are presented for the reaction pi(-)p-->pi(0)pi(0)n in the range from threshold to p(pi(-))=750 MeV/c. The systematics of the data and multipole analyses are examined for sensitivity to a f(0)(600) ("sigma") meson. A one-pion-exchange mechanism is found to be very weak, or absent. The reaction appears to become dominated by sequential pi(0) decays through the Delta(1232) resonance as the beam momentum increases, along with substantial interference effects from several competing mechanisms. 相似文献
16.
We present a unified model of shear-induced demixing and "mechanical" shear banding instabilities in polymeric and surfactant solutions, by combining a simple flow instability with a two-fluid approach to concentration fluctuations. Within this model, we calculate the "spinodal" limit of stability of initially homogeneous shear states to demixing/banding, and predict the selected length and time scales at which inhomogeneity first emerges after a shear start-up "quench" into the unstable region, finding qualitative agreement with experiment. Our analysis is the counterpart, for this driven phase transition, of the Cahn-Hilliard calculation for unsheared fluid-fluid demixing. 相似文献
17.
Nefkens BM Prakhov S Gårdestig A Allgower CE Bekrenev V Briscoe WJ Clajus M Comfort JR Craig K Grosnick D Isenhower D Knecht N Koetke D Koulbardis A Kozlenko N Kruglov S Lolos G Lopatin I Manley DM Manweiler R Marusić A McDonald S Olmsted J Papandreou Z Peaslee D Phaisangittisakul N Price JW Ramirez AF Sadler M Shafi A Spinka H Stanislaus TD Starostin A Staudenmaier HM Supek I Tippens WB;Crystal Ball Collaboration 《Physical review letters》2005,94(4):041601
We report on the first determination of upper limits on the branching ratio (BR) of eta decay to pi0pi0gamma and to pi0pi0pi0gamma. Both decay modes are strictly forbidden by charge conjugation (C) invariance. Using the Crystal Ball multiphoton detector, we obtained BR(eta-->pi0pi0gamma)<5 x 10(-4) at the 90% confidence level, in support of C invariance of isoscalar electromagnetic interactions of the light quarks. We have also measured BR(eta-->pi0pi0pi0gamma)<6 x 10(-5) at the 90% confidence level, in support of C invariance of isovector electromagnetic interactions. 相似文献
18.
N. G. Kozlenko V. V. Abaev V. S. Bekrenev S. P. Kruglov A. A. Koulbardis I. V. Lopatin A. B. Starostin B. Draper S. Hayden J. Huddleston D. Isenhower C. Robinson M. Sadler C. Allgower R. Cadman H. Spinka J. Comfort K. Craig A. Ramirez T. Kycia M. Clajus A. Marusic S. McDonald B. M. K. Nefkens N. Phaisangittisakul S. Prakhov J. W. Price W. B. Tippens J. Peterson W. J. Briscoe A. Shafi I. I. Strakovsky H. Staudenmaier D. M. Manley J. Olmsted D. Peaslee N. Knecht G. Lolos Z. Papandreou I. Supek I. Slaus A. Gibson D. Grosnic D. Koetke R. Manweiler S. Stanislaus 《Physics of Atomic Nuclei》2003,66(1):110-113
The first results obtained in 1998 by the Crystal Ball collaboration from a measurement of the total and differential cross sections for the reaction π ? p → ηn are presented. These new experimental results for the total cross sections are compared with the predictions of the K-matrix model for pion-nucleon scattering. The angular distribution at momenta near the reaction threshold (685 MeV/c) is determined by the S-wave contribution. The P-wave contribution begins to manifest itself from a momentum of 720 MeV/c. 相似文献
19.
The strain field of isolated screw and edge dislocation cores in aluminum are calculated using density-functional theory and a flexible boundary condition method. Nye tensor density contours and differential displacement fields are used to accurately bound Shockley partial separation distances. Our results of 5-7.5 A (screw) and 7.0-9.5 A (edge) eliminate uncertainties resulting from the wide range of previous results based on Peierls-Nabarro and atomistic methods. Favorable agreement of the predicted cores with limited experimental measurements demonstrates the need for quantum mechanical treatment of dislocation cores. 相似文献
20.
Calculations of the first density correction to the binary diffusion coefficient are presented for several mixtures. These calculations are based on the classical kinetic theory for mixtures developed by Bennett and Curtiss. The theoretical predictions agree well with experimental data. 相似文献