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1. Nanoscale Surfactant Transport: Bridging Molecular and Continuum Models

Author

Rahman, Muhammad Rizwanur, Ewen, James P., Shen, Li, Heyes, D. M., Dini, Daniele, and Smith, E. R.

Subjects
Condensed Matter - Soft Condensed Matter, Physics - Fluid Dynamics
Abstract

Surfactant transport is central to a diverse range of natural phenomena, and for many practical applications in physics and engineering. Surprisingly, this process remains relatively poorly understood at the molecular scale. This study investigates the mechanism behind the transport of surfactant monolayers on flat and curved liquid vapor interfaces using nonequilibrium molecular dynamics simulations, which are compared with the continuum transport model. This approach not only provides fresh molecular level insight into surfactant dynamics, but also confirms the nanoscale mechanism of the lateral migration of surfactant molecules along a thin film that continuously deforms as surfactants spread. By connecting the continuum model where the long wave approximations prevail, to the molecular details where such approximations break down, we establish that the transport equation preserves substantial accuracy in capturing the underlying physics. Moreover, the relative importance of the different mechanisms of the transport process are identified. Consequently, we derive a novel, exact molecular equation for surfactant transport along a deforming surface. Finally, our findings demonstrate that the spreading of surfactants at the molecular scale adheres to expected scaling laws and aligns well with experimental observations., Comment: Submitted for journal publication

Published
2024

2. Life and Death of a Thin Liquid Film

Author

Rahman, Muhammad Rizwanur, Shen, Li, Ewen, James P., Heyes, D. M., Dini, Daniele, and Smith, E. R.

Subjects
Physics - Fluid Dynamics
Abstract

Thin films, bubbles and membranes are central to numerous natural and engineering processes, i.e., in thin-film solar cells, coatings, biosensors, electrowetting displays, foams, and emulsions. Yet, the characterization and an adequate understanding of their rupture is limited by the scarcity of atomic detail. We present here the complete life-cycle of freely suspended films using non-equilibrium molecular dynamics simulations of a simple atomic fluid free of surfactants and surface impurities, thus isolating the fundamental rupture mechanisms. Counter to the conventional notion that rupture occurs randomly, we discovered a short-term 'memory' by rewinding in time from a rupture event, extracting deterministic behaviors from apparent stochasticity. A comprehensive investigation of the key rupture-stages including both unrestrained and frustrated propagation is made - characterization of the latter leads to a first-order correction to the classical film-retraction theory. Furthermore, the highly resolved time window reveals that the different modes of the morphological development, typically characterized as heterogeneous nucleation and spinodal decomposition, continuously evolve seamlessly with time from one into the other.

Published
2023
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3. Thin Film Rupture from the Atomic Scale

Author

Rahman, Muhammad Rizwanur, Shen, Li, Ewen, James P., Collard, Benjamin, Heyes, D. M., Dini, Daniele, and Smith, E. R.

Subjects
Physics - Fluid Dynamics
Abstract

The retraction of thin films, as described by the Taylor-Culick (TC) theory, is subject to widespread debate, particularly for films at the nanoscale. We use non-equilibrium molecular dynamics simulations to explore the validity of the assumptions used in continuum models, by tracking the evolution of holes in a film. By deriving a new mathematical form for the surface shape and considering a locally varying surface tension at the front of the retracting film, we reconcile the original theory with our simulation data to recover a corrected TC speed valid at the nanoscale.

Published
2022
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4. The Intrinsic Fragility of the Liquid-Vapor Interface: A Stress Network Perspective

Author

Rahman, Muhammad Rizwanur, Shen, Li, Ewen, James P., Dini, Daniele, and Smith, E. R.

Subjects
Physics - Fluid Dynamics
Abstract

The evolution of the liquid-vapour interface of a Lennard-Jones fluid is examined with molecular dynamics simulations using the intrinsic sampling method. Results suggest, in agreement with capillary wave theory, clear damping of the density profiles as the temperature is increased. We identify a linear variation of the space-filling nature (fractal dimension) of the stress-clusters at the intrinsic surface with increasing surface tension, or equivalently, with decreasing temperature. A percolation analysis of these stress networks indicates that the stress field is more disjointed at higher temperatures. This leads to more fragile interfaces that result in a reduction in surface tension at higher temperature.

Published
2022
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5. Measuring Heat Flux Beyond Fourier's law

Author

Smith, E. R., Daivis, P. J., and Todd, B. D.

Subjects
Condensed Matter - Soft Condensed Matter, Physics - Computational Physics, Physics - Fluid Dynamics, 76A02, 74A25
Abstract

We use nonequilibrium molecular dynamics (NEMD) to explore the effect of shear flow on heat flux. By simulating a simple fluid in a channel bounded by tethered atoms, the heat flux is computed for two systems: a temperature driven one with no flow and a wall driven, Couette flow system. The results for the temperature driven system give the Fourier's law thermal conductivity, which is shown to agree well with experiments. Through comparison of the two systems, we quantify the additional components of the heat flux parallel and normal to the walls due to shear flow. To compute the heat flux in the flow direction, the Irving-Kirkwood equations are integrated over a volume, giving the so-called volume average form, and they are also manipulated to get expressions for the surface averaged and method of planes forms. The method of planes and volume average forms are shown to give equivalent results for the heat flux when using small volumes. The heat flux in the flow direction is obtained consistently over a range of simulations, and it is shown to vary linearly with strain rate, as predicted by theory. The additional strain rate dependent component of the heat flux normal to the wall is obtained by fitting the strain rate dependence of the heat flux to the expected form. As a result, the additional terms in the thermal conductivity tensor quantified in this work should be experimentally testable., Comment: 16 pages double column, 11 figures, one table

Published
2019
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6. Moving Contact Lines: Linking Molecular Dynamics and Continuum-Scale Modeling

Author

Smith, E. R., Theodorakis, P. E., Craster, R. V., and Matar, O. K.

Subjects
Condensed Matter - Soft Condensed Matter, Physics - Fluid Dynamics
Abstract

Despite decades of research, the modeling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide a link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which governs the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modeling and highlight the opportunities for future developments in this area., Comment: 54 pages, 11 figures

Published
2018
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9. A Molecular Dynamics Simulation of the Turbulent Couette Minimal Flow Unit

Author

Smith, E. R.

Subjects
Physics - Fluid Dynamics
Abstract

A molecular dynamics (MD) simulation of planar Couette flow is presented for the minimal channel in which turbulence structures can be sustained. Evolution over a single breakdown and regeneration cycle is compared to computational fluid dynamics (CFD) simulations. Qualitative similar structures are observed and turbulent statistics show excellent quantitative agreement. The molecular scale law of the wall is presented in which stick-slip molecular wall-fluid interactions replace the no-slip conditions. The impact of grid resolution is explored and the observed structures are seen to be dependant on averaging time and length scales. The kinetic energy spectra show a range of scales are present in the molecular system and that spectral content is dependent on the grid resolution employed. The subgrid velocity of the molecules is compared to spatial averaged velocity using joint probability density functions. Molecular trajectories, diffusions and Lagrangian statistics are presented. The importance of sub-grid scales, relevance of the Kolmogorov lengthscale and implications of molecular turbulence are discussed., Comment: 25 pages, 14 figures journal article under review by the Physics of Fluids

Published
2015
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10. Non-equilibrium molecular simulations of thin film rupture.

Author

Rahman, Muhammad Rizwanur, Shen, Li, Ewen, James P., Collard, Benjamin, Heyes, D. M., Dini, Daniele, and Smith, E. R.

Subjects
THIN films, MOLECULAR dynamics, SURFACE tension, MATHEMATICAL forms, MONOMOLECULAR films, GEOMETRIC shapes
Abstract

The retraction of thin films, as described by the Taylor–Culick (TC) theory, is subject to widespread debate, particularly for films at the nanoscale. We use non-equilibrium molecular dynamics simulations to explore the validity of the assumptions used in continuum models by tracking the evolution of holes in a film. By deriving a new mathematical form for the surface shape and considering a locally varying surface tension at the front of the retracting film, we reconcile the original theory with our simulation to recover a corrected TC speed valid at the nanoscale. [ABSTRACT FROM AUTHOR]

Published
2023
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12. Control-volume representation of molecular dynamics

Author

Smith, E. R., Heyes, D. M., Dini, D., and Zaki, T. A.

Subjects
Mathematical Physics, 76A02, 74A25
Abstract

A Molecular Dynamics (MD) parallel to the Control Volume (CV) formulation of fluid mechanics is developed by integrating the formulas of Irving and Kirkwood, J. Chem. Phys. 18, 817 (1950) over a finite cubic volume of molecular dimensions. The Lagrangian molecular system is expressed in terms of an Eulerian CV, which yields an equivalent to Reynolds' Transport Theorem for the discrete system. This approach casts the dynamics of the molecular system into a form that can be readily compared to the continuum equations. The MD equations of motion are reinterpreted in terms of a Lagrangian-to-Control-Volume (\CV) conversion function $\vartheta_{i}$, for each molecule $i$. The \CV function and its spatial derivatives are used to express fluxes and relevant forces across the control surfaces. The relationship between the local pressures computed using the Volume Average (VA, Lutsko, J. Appl. Phys 64, 1152 (1988)) techniques and the Method of Planes (MOP, Todd et al, Phys. Rev. E 52, 1627 (1995)) emerges naturally from the treatment. Numerical experiments using the MD CV method are reported for equilibrium and non-equilibrium (start-up Couette flow) model liquids, which demonstrate the advantages of the formulation. The CV formulation of the MD is shown to be exactly conservative, and is therefore ideally suited to obtain macroscopic properties from a discrete system., Comment: 19 pages, 15 figures

Published
2012
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13. Charge Transport in one Dimension:Dissipative and Non-Dissipative Space-Charge Limited Currents

Author

Holcombe, S. R. and Smith, E. R.

Subjects
Mathematical Physics, Condensed Matter - Other Condensed Matter, Physics - Classical Physics
Abstract

We consider charge transport in nanopores where the dielectric constant inside the nanopore is much greater than in the surrounding material, so that the flux of the electric fields due to the charges is almost entirely confined to the nanopore. That means that we may model the electric fields due to charge densities in the nanopore in terms of average properties across the nanopore as solutions of one dimensional Poisson equations. We develop basic equations for an M component system using equations of continuity to relate concentrations to currents, and flux equations relating currents to concentration gradients and conductivities. We then derive simplified scaled versions of the equations. We develop exact solutions for the one component case in a variety of boundary conditions using a Hopf-Cole transformation, Fourier series, and periodic solutions of the Burgers equation. These are compared with a simpler model in which the scaled diffusivity is zero so that all charge motion is driven by the electric field. In this non-dissipative case, recourse to an admissibility condition is utilised to obtain the physically relevant weak solution of a Riemann problem concerning the electric field. It is shown that the admissibility condition is Poynting's theorem., Comment: v2 contains the minor updates and corrections that have been incorporated into the published article

Published
2010
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15. On the trajectory of discrimination: A meta-analysis and forecasting survey capturing 44 years of field experiments on gender and hiring decisions

Author

Schaerer, M, Plessis, C, Nguyen, M, Aert, R, Tiokhin, L, Lakens, D, Clemente, E, Pfeiffer, T, Dreber, A, Johannesson, M, Clark, C, Uhlmann, E, Abraham, A, Adamus, M, Akinci, C, Alberti, F, Alsharawy, A, Alzahawi, S, Anseel, F, Arndt, F, Balkan, B, Baskin, E, Bearden, C, Benotsch, E, Bernritter, S, Black, S, Bleidorn, W, Boysen, A, Brienza, J, Brown, M, Brown, S, Brown, J, Buckley, J, Buttliere, B, Byrd, N, Cigler, H, Capitan, T, Cherubini, P, Chong, S, Ciftci, E, Conrad, C, Conway, P, Costa, E, Cox, J, Cox, D, Cruz, F, Dawson, I, Demiral, E, Derrick, J, Doshi, S, Dunleavy, D, Durham, J, Elbaek, C, Ellis, D, Ert, E, Espinoza, M, Fullbrunn, S, Fath, S, Furrer, R, Fiala, L, Fillon, A, Forsgren, M, Fytraki, A, Galarza, F, Gandhi, L, Garrison, S, Geraldes, D, Ghasemi, O, Gjoneska, B, Gothilander, J, Gruhn, D, Grieder, M, Hafenbradl, S, Halkias, G, Hancock, R, Hantula, D, Harton, H, Hoffmann, C, Holzmeister, F, Horak, F, Hosch, A, Imada, H, Ioannidis, K, Jaeger, B, Janas, M, Janik, B, Kc, R, Keel, P, Keeley, J, Keller, L, Kenrick, D, Kiely, K, Knutsson, M, Kovacheva, A, Kovera, M, Krivoshchekov, V, Krumrei-Mancuso, E, Kulibert, D, Lacko, D, Lemay, E, Leung, D, Li, F, Lin, H, Lorenzo, K, Lorenzo-Luaces, L, Lou, N, Lovakov, A, Luzardo, A, Macaulay, S, Madan, C, Mahmoud, O, Makel, M, Mari, S, Fages, D, Marsh, A, Mccarthy, R, Mercier, B, Milfont, T, Mittlaender, S, Montoya, A, Moyer, A, Myrseth, K, Navarro-Martinez, D, Nelson, A, Neyse, L, Minghui, N, Niszczota, P, Obrecht, N, Otterbring, T, Panlilio, Z, Park, L, Pauer, S, Pavlov, Y, Pentek, I, Pereyra, J, Perkowski, P, Pew, E, Peynircioglu, Z, Pezzo, M, Pirrone, A, Plonsky, O, Porfirio, J, Pownall, M, Prochnicki, M, Protzko, J, Roer, J, Rahnev, D, Reis, H, Rios, K, Rodrigues, D, Rodriguez, P, Roth, Y, Ruffle, B, Samahita, M, Schmidt, A, Schoemann, M, Schoenegger, P, Schwebel, D, Segovia, A, Sherman, J, Siegenthaler, S, Siem, B, Sirota, M, Smith, E, Stamatogiannakis, A, Stewart-Williams, S, Storage, D, Su, Y, Talbert, E, Todd, A, Tonin, M, Trautmann, S, Travaglino, G, Tsang, J, Veldhuizen, R, Varnum, M, Walf, A, Wallrich, L, Wang, K, Ward, D, Waugh, C, Wingen, T, Woike, J, Wollbrant, C, Wu, S, Wylie, K, Xiao, Q, Xue, S, Yakobi, O, Zayas, V, Zheng, J, Zhong, Y, Zogmaister, C, Zolopa, C, Lisa, N, Chin Wen, O, Dmitry, G, Schaerer M., Plessis C. D., Nguyen M. H. B., Aert R. C. M. V., Tiokhin L., Lakens D., Clemente E. G., Pfeiffer T., Dreber A., Johannesson M., Clark C. J., Uhlmann E. L., Abraham A. T., Adamus M., Akinci C., Alberti F., Alsharawy A. M., Alzahawi S., Anseel F., Arndt F., Balkan B., Baskin E., Bearden C. E., Benotsch E. G., Bernritter S., Black S. R., Bleidorn W., Boysen A. P., Brienza J. P., Brown M., Brown S. E. V., Brown J. W., Buckley J., Buttliere B., Byrd N., Cigler H., Capitan T., Cherubini P., Chong S. Y., Ciftci E. E., Conrad C. D., Conway P., Costa E., Cox J. A., Cox D. J., Cruz F., Dawson I. G. J., Demiral E. E., Derrick J. L., Doshi S., Dunleavy D. J., Durham J. D., Elbaek C. T., Ellis D. A., Ert E., Espinoza M. P., Fullbrunn S. C., Fath S., Furrer R., Fiala L., Fillon A. A., Forsgren M., Fytraki A. T., Galarza F. B., Gandhi L., Garrison S. M., Geraldes D., Ghasemi O., Gjoneska B., Gothilander J., Gruhn D., Grieder M., Hafenbradl S., Halkias G., Hancock R., Hantula D. A., Harton H. C., Hoffmann C. P., Holzmeister F., Horak F., Hosch A. -K., Imada H., Ioannidis K., Jaeger B., Janas M., Janik B., Kc R. P., Keel P. K., Keeley J. W., Keller L., Kenrick D. T., Kiely K. M., Knutsson M., Kovacheva A., Kovera M. B., Krivoshchekov V., Krumrei-Mancuso E. J., Kulibert D., Lacko D., Lemay E. P., Leung D. W., Li F., Lin H., Lorenzo K. E., Lorenzo-Luaces L., Lou N. M., Lovakov A., Luzardo A., MacAulay S. C., Madan C. R., Mahmoud O., Makel M. C., Mari S., Fages D. M., Marsh A. A., McCarthy R. J., Mercier B., Milfont T. L., Mittlaender S., Montoya A. K., Moyer A., Myrseth K. O. R., Navarro-Martinez D., Nelson A. J., Neyse L., Minghui N., Niszczota P., Obrecht N. A., Otterbring T., Panlilio Z. A., Park L. E., Pauer S., Pavlov Y. G., Pentek I., Pereyra J. S., Perkowski P., Pew E., Peynircioglu Z. F., Pezzo M. V., Pirrone A., Plonsky O., Porfirio J. C. C., Pownall M., Prochnicki M. M., Protzko J., Roer J. P., Rahnev D., Reis H. T., Rios K., Rodrigues D. L., Rodriguez P., Roth Y., Ruffle B. J., Samahita M., Schmidt A., Schoemann M., Schoenegger P., Schwebel D. C., Segovia A. M., Sherman J. W., Siegenthaler S., Siem B., Sirota M., Smith E. R., Stamatogiannakis A., Stewart-Williams S., Storage D., Su Y., Talbert E. J., Todd A. R., Tonin M., Trautmann S. T., Travaglino G. A., Tsang J. -A., Veldhuizen R. V., Varnum M. E. W., Walf A. A., Wallrich L., Wang K., Ward D. E., Waugh C. E., Wingen T., Woike J. K., Wollbrant C. E., Wu S., Wylie K., Xiao Q., Xue S. Y., Yakobi O., Zayas V., Zheng J., Zhong Y., Zogmaister C., Zolopa C. S., Lisa N., Chin Wen O., Dmitry G., Schaerer, M, Plessis, C, Nguyen, M, Aert, R, Tiokhin, L, Lakens, D, Clemente, E, Pfeiffer, T, Dreber, A, Johannesson, M, Clark, C, Uhlmann, E, Abraham, A, Adamus, M, Akinci, C, Alberti, F, Alsharawy, A, Alzahawi, S, Anseel, F, Arndt, F, Balkan, B, Baskin, E, Bearden, C, Benotsch, E, Bernritter, S, Black, S, Bleidorn, W, Boysen, A, Brienza, J, Brown, M, Brown, S, Brown, J, Buckley, J, Buttliere, B, Byrd, N, Cigler, H, Capitan, T, Cherubini, P, Chong, S, Ciftci, E, Conrad, C, Conway, P, Costa, E, Cox, J, Cox, D, Cruz, F, Dawson, I, Demiral, E, Derrick, J, Doshi, S, Dunleavy, D, Durham, J, Elbaek, C, Ellis, D, Ert, E, Espinoza, M, Fullbrunn, S, Fath, S, Furrer, R, Fiala, L, Fillon, A, Forsgren, M, Fytraki, A, Galarza, F, Gandhi, L, Garrison, S, Geraldes, D, Ghasemi, O, Gjoneska, B, Gothilander, J, Gruhn, D, Grieder, M, Hafenbradl, S, Halkias, G, Hancock, R, Hantula, D, Harton, H, Hoffmann, C, Holzmeister, F, Horak, F, Hosch, A, Imada, H, Ioannidis, K, Jaeger, B, Janas, M, Janik, B, Kc, R, Keel, P, Keeley, J, Keller, L, Kenrick, D, Kiely, K, Knutsson, M, Kovacheva, A, Kovera, M, Krivoshchekov, V, Krumrei-Mancuso, E, Kulibert, D, Lacko, D, Lemay, E, Leung, D, Li, F, Lin, H, Lorenzo, K, Lorenzo-Luaces, L, Lou, N, Lovakov, A, Luzardo, A, Macaulay, S, Madan, C, Mahmoud, O, Makel, M, Mari, S, Fages, D, Marsh, A, Mccarthy, R, Mercier, B, Milfont, T, Mittlaender, S, Montoya, A, Moyer, A, Myrseth, K, Navarro-Martinez, D, Nelson, A, Neyse, L, Minghui, N, Niszczota, P, Obrecht, N, Otterbring, T, Panlilio, Z, Park, L, Pauer, S, Pavlov, Y, Pentek, I, Pereyra, J, Perkowski, P, Pew, E, Peynircioglu, Z, Pezzo, M, Pirrone, A, Plonsky, O, Porfirio, J, Pownall, M, Prochnicki, M, Protzko, J, Roer, J, Rahnev, D, Reis, H, Rios, K, Rodrigues, D, Rodriguez, P, Roth, Y, Ruffle, B, Samahita, M, Schmidt, A, Schoemann, M, Schoenegger, P, Schwebel, D, Segovia, A, Sherman, J, Siegenthaler, S, Siem, B, Sirota, M, Smith, E, Stamatogiannakis, A, Stewart-Williams, S, Storage, D, Su, Y, Talbert, E, Todd, A, Tonin, M, Trautmann, S, Travaglino, G, Tsang, J, Veldhuizen, R, Varnum, M, Walf, A, Wallrich, L, Wang, K, Ward, D, Waugh, C, Wingen, T, Woike, J, Wollbrant, C, Wu, S, Wylie, K, Xiao, Q, Xue, S, Yakobi, O, Zayas, V, Zheng, J, Zhong, Y, Zogmaister, C, Zolopa, C, Lisa, N, Chin Wen, O, Dmitry, G, Schaerer M., Plessis C. D., Nguyen M. H. B., Aert R. C. M. V., Tiokhin L., Lakens D., Clemente E. G., Pfeiffer T., Dreber A., Johannesson M., Clark C. J., Uhlmann E. L., Abraham A. T., Adamus M., Akinci C., Alberti F., Alsharawy A. M., Alzahawi S., Anseel F., Arndt F., Balkan B., Baskin E., Bearden C. E., Benotsch E. G., Bernritter S., Black S. R., Bleidorn W., Boysen A. P., Brienza J. P., Brown M., Brown S. E. V., Brown J. W., Buckley J., Buttliere B., Byrd N., Cigler H., Capitan T., Cherubini P., Chong S. Y., Ciftci E. E., Conrad C. D., Conway P., Costa E., Cox J. A., Cox D. J., Cruz F., Dawson I. G. J., Demiral E. E., Derrick J. L., Doshi S., Dunleavy D. J., Durham J. D., Elbaek C. T., Ellis D. A., Ert E., Espinoza M. P., Fullbrunn S. C., Fath S., Furrer R., Fiala L., Fillon A. A., Forsgren M., Fytraki A. T., Galarza F. B., Gandhi L., Garrison S. M., Geraldes D., Ghasemi O., Gjoneska B., Gothilander J., Gruhn D., Grieder M., Hafenbradl S., Halkias G., Hancock R., Hantula D. A., Harton H. C., Hoffmann C. P., Holzmeister F., Horak F., Hosch A. -K., Imada H., Ioannidis K., Jaeger B., Janas M., Janik B., Kc R. P., Keel P. K., Keeley J. W., Keller L., Kenrick D. T., Kiely K. M., Knutsson M., Kovacheva A., Kovera M. B., Krivoshchekov V., Krumrei-Mancuso E. J., Kulibert D., Lacko D., Lemay E. P., Leung D. W., Li F., Lin H., Lorenzo K. E., Lorenzo-Luaces L., Lou N. M., Lovakov A., Luzardo A., MacAulay S. C., Madan C. R., Mahmoud O., Makel M. C., Mari S., Fages D. M., Marsh A. A., McCarthy R. J., Mercier B., Milfont T. L., Mittlaender S., Montoya A. K., Moyer A., Myrseth K. O. R., Navarro-Martinez D., Nelson A. J., Neyse L., Minghui N., Niszczota P., Obrecht N. A., Otterbring T., Panlilio Z. A., Park L. E., Pauer S., Pavlov Y. G., Pentek I., Pereyra J. S., Perkowski P., Pew E., Peynircioglu Z. F., Pezzo M. V., Pirrone A., Plonsky O., Porfirio J. C. C., Pownall M., Prochnicki M. M., Protzko J., Roer J. P., Rahnev D., Reis H. T., Rios K., Rodrigues D. L., Rodriguez P., Roth Y., Ruffle B. J., Samahita M., Schmidt A., Schoemann M., Schoenegger P., Schwebel D. C., Segovia A. M., Sherman J. W., Siegenthaler S., Siem B., Sirota M., Smith E. R., Stamatogiannakis A., Stewart-Williams S., Storage D., Su Y., Talbert E. J., Todd A. R., Tonin M., Trautmann S. T., Travaglino G. A., Tsang J. -A., Veldhuizen R. V., Varnum M. E. W., Walf A. A., Wallrich L., Wang K., Ward D. E., Waugh C. E., Wingen T., Woike J. K., Wollbrant C. E., Wu S., Wylie K., Xiao Q., Xue S. Y., Yakobi O., Zayas V., Zheng J., Zhong Y., Zogmaister C., Zolopa C. S., Lisa N., Chin Wen O., and Dmitry G.

Abstract

A preregistered meta-analysis, including 244 effect sizes from 85 field audits and 361,645 individual job applications, tested for gender bias in hiring practices in female-stereotypical and gender-balanced as well as male-stereotypical jobs from 1976 to 2020. A “red team” of independent experts was recruited to increase the rigor and robustness of our meta-analytic approach. A forecasting survey further examined whether laypeople (n = 499 nationally representative adults) and scientists (n = 312) could predict the results. Forecasters correctly anticipated reductions in discrimination against female candidates over time. However, both scientists and laypeople overestimated the continuation of bias against female candidates. Instead, selection bias in favor of male over female candidates was eliminated and, if anything, slightly reversed in sign starting in 2009 for mixed-gender and male-stereotypical jobs in our sample. Forecasters further failed to anticipate that discrimination against male candidates for stereotypically female jobs would remain stable across the decades.

Published
2023

16. Parenteral iron polymaltose changes i:c-terminal FGF23 ratios in iron deficiency, but not in dialysis patients

Author

Tan, S-J, Satake, S, Smith, E R, Toussaint, N D, Hewitson, T D, and Holt, S G

Subjects
Chronic kidney failure -- Care and treatment -- Complications and side effects, Iron deficiency diseases -- Diet therapy, Hemodialysis patients -- Diet therapy -- Physiological aspects, Fibroblast growth factors -- Physiological aspects -- Health aspects, Food/cooking/nutrition, Health
Abstract

Background/Objectives: Iron and phosphate are both vital to many biological cellular processes with central roles in energy metabolism, cellular proliferation and nucleic acid synthesis. Regulatory pathways in some of these metabolic pathways may intersect at fibroblast growth factor 23 (FGF23), a major phosphate regulatory hormone. Iron is reported to induce hypophosphataemia in rare cases, and recent reports suggest that iron deficiency may upregulate FGF23 synthesis by mechanisms involving hypoxia-inducible factor 1[alpha] (HIF1[alpha]). Our objective was to evaluate the effect of administration of intravenous iron polymaltose on intact and c-terminal FGF23 (i:cFGF23) ratios in two independent cohorts of patients, iron-deficient but non-inflamed patients and haemodialysis (HD)-dependent patients, and to examine the balance of synthesis and degradation. Subjects/Methods: We studied biochemical effects of intravenous iron polymaltose on both iFGF23 and cFGF23 fragments and their ratios in two patient groups: iron-deficient patients with normal renal function (ID-norm) and HD patients receiving iron supplementation (HD-ESKD) at a single institution. Patients were tested at baseline, day 4 and day 12 post iron administration. Results: Parenteral iron polymaltose resulted in increased i:cFGF23 ratios in ID-norm patients where circulating cFGF23 levels decreased with no appreciable effect on iFGF23, whereas no significant changes in i:cFGF23 ratios were observed in HD-ESKD patients following intravenous administration of 100mg iron polymaltose. Conclusions: Dysregulation of intracellular FGF23-processing mechanisms may be related to iron deficiency per se rather than iron repletion with iron polymaltose. In ID-norm, i:cFGF23 ratios altered with iron administration without significant clinical alterations in mineral parameters, implying that other regulatory mechanisms may be important. Finally, iron supplementation in HD-ESKD patients does not appear to significantly affect i:cFGF23 ratios already disturbed by a chronic inflammatory or functionally iron-deficient state., Author(s): S-J Tan [sup.1] [sup.2] , S Satake [sup.1] , E R Smith [sup.1] , N D Toussaint [sup.1] [sup.2] , T D Hewitson [sup.1] [sup.2] , S G Holt [...]

Published
2017
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17. Viscuit and the fluctuation theorem investigation of shear viscosity by molecular dynamics simulations: The information and the noise.

Author

Heyes, D. M., Dini, D., and Smith, E. R.

Subjects
VISCOSITY, MOLECULAR dynamics, STANDARD deviations, DISTRIBUTION (Probability theory), SHEARING force, NOISE
Abstract

The shear viscosity, η, of model liquids and solids is investigated within the framework of the viscuit and Fluctuation Theorem (FT) probability distribution function (PDF) theories, following Heyes et al. [J. Chem. Phys. 152, 194504 (2020)] using equilibrium molecular dynamics (MD) simulations on Lennard-Jones and Weeks–Chandler–Andersen model systems. The viscosity can be obtained in equilibrium MD simulation from the first moment of the viscuit PDF, which is shown for finite simulation lengths to give a less noisy plateau region than the Green–Kubo method. Two other formulas for the shear viscosity in terms of the viscuit and PDF analysis are also derived. A separation of the time-dependent average negative and positive viscuits extrapolated from the noise dominated region to zero time provides another route to η. The third method involves the relative number of positive and negative viscuits and their PDF standard deviations on the two sides for an equilibrium system. For the FT and finite shear rates, accurate analytic expressions for the relative number of positive to negative block average shear stresses is derived assuming a shifted Gaussian PDF, which is shown to agree well with non-equilibrium molecular dynamics simulations. A similar treatment of the positive and negative block average contributions to the viscosity is also shown to match the simulation data very well. [ABSTRACT FROM AUTHOR]

Published
2021
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18. Single trajectory transport coefficients and the energy landscape by molecular dynamics simulations.

Author

Heyes, D. M., Dini, D., and Smith, E. R.

Subjects
BULK viscosity, DISTRIBUTION (Probability theory), STANDARD deviations, DENSITY of states, THERMAL conductivity, DIFFUSION coefficients, MOLECULAR dynamics
Abstract

The Green–Kubo (GK) method is widely used to calculate the transport coefficients of model liquids by Molecular Dynamics (MD) simulation. A reformulation of GK was proposed by Heyes et al. [J. Chem. Phys. 150, 174504 (2019)], which expressed the shear viscosity in terms of a probability distribution function (PDF) of "single trajectory (ST) viscosities," called "viscuits." This approach is extended here to the bulk viscosity, thermal conductivity, and diffusion coefficient. The PDFs of the four STs expressed in terms of their standard deviations (calculated separately for the positive and negative sides) are shown by MD to be statistically the same for the Lennard-Jones fluid. This PDF can be represented well by a sum of exponentials and is independent of system size and state point in the equilibrium fluid regime. The PDF is not well reproduced by a stochastic model. The PDF is statistically the same as that derived from the potential energy, u, and other thermodynamic quantities, indicating that the transport coefficients are determined quantitatively by and follow closely the time evolution of the underlying energy landscape. The PDFs of out-of-equilibrium supercooled high density states are quite different from those of the equilibrium states. [ABSTRACT FROM AUTHOR]

Published
2020
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22. Fumonisin Toxicity and Sphingolipid Biosynthesis

Author

Merrill, A. H., Jr., Wang, E., Vales, T. R., Smith, E. R., Schroeder, J. J., Menaldino, D. S., Alexander, C., Crane, H. M., Xia, J., Liotta, D. C., Meredith, F. I., Riley, R. T., Jackson, Lauren S., editor, DeVries, Jonathan W., editor, and Bullerman, Lloyd B., editor

Published
1996
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23. Incremental viscosity by non-equilibrium molecular dynamics and the Eyring model.

Author

Heyes, D. M., Dini, D., and Smith, E. R.

Subjects
MOLECULAR dynamics, MATHEMATICAL models of viscoelasticity, MEASUREMENT of shear (Mechanics), SHEARING force, DISTRIBUTION (Probability theory), STRESS relaxation (Mechanics), MATHEMATICAL models
Abstract

The viscoelastic behavior of sheared fluids is calculated by Non-Equilibrium Molecular Dynamics (NEMD) simulation, and complementary analytic solutions of a time-dependent extension of Eyring’s model (EM) for shear thinning are derived. It is argued that an “incremental viscosity,” ηi, or IV which is the derivative of the steady state stress with respect to the shear rate is a better measure of the physical state of the system than the conventional definition of the shear rate dependent viscosity (i.e., the shear stress divided by the strain rate). The stress relaxation function, Ci(t), associated with ηi is consistent with Boltzmann’s superposition principle and is computed by NEMD and the EM. The IV of the Eyring model is shown to be a special case of the Carreau formula for shear thinning. An analytic solution for the transient time correlation function for the EM is derived. An extension of the EM to allow for significant local shear stress fluctuations on a molecular level, represented by a gaussian distribution, is shown to have the same analytic form as the original EM but with the EM stress replaced by its time and spatial average. Even at high shear rates and on small scales, the probability distribution function is almost gaussian (apart from in the wings) with the peak shifted by the shear. The Eyring formula approximately satisfies the Fluctuation Theorem, which may in part explain its success in representing the shear thinning curves of a wide range of different types of chemical systems. [ABSTRACT FROM AUTHOR]

Published
2018
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26. Association between convalescent plasma treatment and mortality in COVID-19: a collaborative systematic review and meta-analysis of randomized clinical trials

Author

Axfors, C., Janiaud, P., Schmitt, A. M., van't Hooft, J., Smith, E. R., Haber, N. A., Abayomi, A., Abduljalil, M., Abdulrahman, A., Acosta-Ampudia, Y., Aguilar-Guisado, M., Al-Beidh, F., Alejandria, M. M., Alfonso, R. N., Ali, M., Alqahtani, M., Alzamrooni, A., Anaya, J. -M., Ang, M. A. C., Aomar, I. F., Argumanis, L. E., Averyanov, A., Baklaushev, V. P., Balionis, O., Benfield, T., Berry, S., Birocco, N., Bonifacio, L. B., Bowen, A. C., Bown, A., Cabello-Gutierrez, C., Camacho, B., Camacho-Ortiz, A., Campbell-Lee, S., Cao, D. H., Cardesa, A., Carnate, J. M., Castillo, G. J. J., Cavallo, R., Chowdhury, F. R., Chowdhury, F. U. H., Ciccone, G., Cingolani, Antonella, Climacosa, F. M. M., Compernolle, V., Cortez, C. F. N., Costa Neto, A., D'Antico, S., Daly, J., Danielle, F., Davis, J. S., De Rosa, F. G., Denholm, J. T., Denkinger, C. M., Desmecht, D., Diaz-Coronado, J. C., Diaz Ponce-Medrano, J. A., Donneau, A. -F., Dumagay, T. E., Dunachie, S., Dungog, C. C., Erinoso, O., Escasa, I. M. S., Estcourt, L. J., Evans, A., Evasan, A. L. M., Fareli, C. J., Fernandez-Sanchez, V., Galassi, C., Gallo, J. E., Garcia, P. J., Garcia, P. L., Garcia, J. A., Garigliany, M., Garza-Gonzalez, E., Gauiran, D. T. V., Gaviria Garcia, P. A., Giron-Gonzalez, J. -A., Gomez-Almaguer, D., Gordon, A. C., Gothot, A., Grass Guaqueta, J. S., Green, C., Grimaldi, D., Hammond, N. E., Harvala, H., Heralde, F. M., Herrick, J., Higgins, A. M., Hills, T. E., Hines, J., Holm, K., Hoque, A., Hoste, E., Ignacio, J. M., Ivanov, A. V., Janssen, M., Jennings, J. H., Jha, V., King, R. A. N., Kjeldsen-Kragh, J., Klenerman, P., Kotecha, A., Krapp, F., Labanca, L., Laing, E., Landin-Olsson, M., Laterre, P. -F., Lim, L. -L., Lim, J., Ljungquist, O., Llaca-Diaz, J. M., Lopez-Robles, C., Lopez-Cardenas, S., Lopez-Plaza, I., Lucero, J. A. C., Lundgren, M., Macias, J., Maganito, S. C., Malundo, A. F. G., Manrique, R. D., Manzini, P. M., Marcos, M., Marquez, I., Martinez-Marcos, F. J., Mata, A. M., Mcarthur, C. J., Mcquilten, Z. K., Mcverry, B. J., Menon, D. K., Meyfroidt, G., Mirasol, M. A. L., Misset, B., Molton, J. S., Mondragon, A. V., Monsalve, D. M., Moradi Choghakabodi, P., Morpeth, S. C., Mouncey, P. R., Moutschen, M., Muller-Tidow, C., Murphy, E., Najdovski, T., Nichol, A. D., Nielsen, H., Novak, R. M., O'Sullivan, M. V. N., Olalla, J., Osibogun, A., Osikomaiya, B., Oyonarte, S., Pardo-Oviedo, J. M., Patel, M. C., Paterson, D. L., Pena-Perez, C. A., Perez-Calatayud, A. A., Perez-Alba, E., Perkina, A., Perry, N., Pouladzadeh, M., Poyato, I., Price, D. J., Quero, A. K. H., Rahman, M. M., Rahman, M. S., Ramesh, M., Ramirez-Santana, C., Rasmussen, M., Rees, M. A., Rego, E., Roberts, J. A., Roberts, D. J., Rodriguez, Y., Rodriguez-Bano, J., Rogers, B. A., Rojas, M., Romero, A., Rowan, K. M., Saccona, F., Safdarian, M., Santos, M. C. M., Sasadeusz, J., Scozzari, G., Shankar-Hari, M., Sharma, G., Snelling, T., Soto, A., Tagayuna, P. Y., Tang, A., Tatem, G., Teofili, Luciana, Tong, S. Y. C., Turgeon, A. F., Veloso, J. D., Venkatesh, B., Ventura-Enriquez, Y., Webb, S. A., Wiese, L., Wiken, C., Wood, E. M., Yusubalieva, G. M., Zacharowski, K., Zarychanski, R., Khanna, N., Moher, D., Goodman, S. N., Ioannidis, J. P. A., Hemkens, L. G., Cingolani A. (ORCID:0000-0002-3793-2755), Teofili L. (ORCID:0000-0002-7214-1561), Axfors, C., Janiaud, P., Schmitt, A. M., van't Hooft, J., Smith, E. R., Haber, N. A., Abayomi, A., Abduljalil, M., Abdulrahman, A., Acosta-Ampudia, Y., Aguilar-Guisado, M., Al-Beidh, F., Alejandria, M. M., Alfonso, R. N., Ali, M., Alqahtani, M., Alzamrooni, A., Anaya, J. -M., Ang, M. A. C., Aomar, I. F., Argumanis, L. E., Averyanov, A., Baklaushev, V. P., Balionis, O., Benfield, T., Berry, S., Birocco, N., Bonifacio, L. B., Bowen, A. C., Bown, A., Cabello-Gutierrez, C., Camacho, B., Camacho-Ortiz, A., Campbell-Lee, S., Cao, D. H., Cardesa, A., Carnate, J. M., Castillo, G. J. J., Cavallo, R., Chowdhury, F. R., Chowdhury, F. U. H., Ciccone, G., Cingolani, Antonella, Climacosa, F. M. M., Compernolle, V., Cortez, C. F. N., Costa Neto, A., D'Antico, S., Daly, J., Danielle, F., Davis, J. S., De Rosa, F. G., Denholm, J. T., Denkinger, C. M., Desmecht, D., Diaz-Coronado, J. C., Diaz Ponce-Medrano, J. A., Donneau, A. -F., Dumagay, T. E., Dunachie, S., Dungog, C. C., Erinoso, O., Escasa, I. M. S., Estcourt, L. J., Evans, A., Evasan, A. L. M., Fareli, C. J., Fernandez-Sanchez, V., Galassi, C., Gallo, J. E., Garcia, P. J., Garcia, P. L., Garcia, J. A., Garigliany, M., Garza-Gonzalez, E., Gauiran, D. T. V., Gaviria Garcia, P. A., Giron-Gonzalez, J. -A., Gomez-Almaguer, D., Gordon, A. C., Gothot, A., Grass Guaqueta, J. S., Green, C., Grimaldi, D., Hammond, N. E., Harvala, H., Heralde, F. M., Herrick, J., Higgins, A. M., Hills, T. E., Hines, J., Holm, K., Hoque, A., Hoste, E., Ignacio, J. M., Ivanov, A. V., Janssen, M., Jennings, J. H., Jha, V., King, R. A. N., Kjeldsen-Kragh, J., Klenerman, P., Kotecha, A., Krapp, F., Labanca, L., Laing, E., Landin-Olsson, M., Laterre, P. -F., Lim, L. -L., Lim, J., Ljungquist, O., Llaca-Diaz, J. M., Lopez-Robles, C., Lopez-Cardenas, S., Lopez-Plaza, I., Lucero, J. A. C., Lundgren, M., Macias, J., Maganito, S. C., Malundo, A. F. G., Manrique, R. D., Manzini, P. M., Marcos, M., Marquez, I., Martinez-Marcos, F. J., Mata, A. M., Mcarthur, C. J., Mcquilten, Z. K., Mcverry, B. J., Menon, D. K., Meyfroidt, G., Mirasol, M. A. L., Misset, B., Molton, J. S., Mondragon, A. V., Monsalve, D. M., Moradi Choghakabodi, P., Morpeth, S. C., Mouncey, P. R., Moutschen, M., Muller-Tidow, C., Murphy, E., Najdovski, T., Nichol, A. D., Nielsen, H., Novak, R. M., O'Sullivan, M. V. N., Olalla, J., Osibogun, A., Osikomaiya, B., Oyonarte, S., Pardo-Oviedo, J. M., Patel, M. C., Paterson, D. L., Pena-Perez, C. A., Perez-Calatayud, A. A., Perez-Alba, E., Perkina, A., Perry, N., Pouladzadeh, M., Poyato, I., Price, D. J., Quero, A. K. H., Rahman, M. M., Rahman, M. S., Ramesh, M., Ramirez-Santana, C., Rasmussen, M., Rees, M. A., Rego, E., Roberts, J. A., Roberts, D. J., Rodriguez, Y., Rodriguez-Bano, J., Rogers, B. A., Rojas, M., Romero, A., Rowan, K. M., Saccona, F., Safdarian, M., Santos, M. C. M., Sasadeusz, J., Scozzari, G., Shankar-Hari, M., Sharma, G., Snelling, T., Soto, A., Tagayuna, P. Y., Tang, A., Tatem, G., Teofili, Luciana, Tong, S. Y. C., Turgeon, A. F., Veloso, J. D., Venkatesh, B., Ventura-Enriquez, Y., Webb, S. A., Wiese, L., Wiken, C., Wood, E. M., Yusubalieva, G. M., Zacharowski, K., Zarychanski, R., Khanna, N., Moher, D., Goodman, S. N., Ioannidis, J. P. A., Hemkens, L. G., Cingolani A. (ORCID:0000-0002-3793-2755), and Teofili L. (ORCID:0000-0002-7214-1561)

Abstract

Background: Convalescent plasma has been widely used to treat COVID-19 and is under investigation in numerous randomized clinical trials, but results are publicly available only for a small number of trials. The objective of this study was to assess the benefits of convalescent plasma treatment compared to placebo or no treatment and all-cause mortality in patients with COVID-19, using data from all available randomized clinical trials, including unpublished and ongoing trials (Open Science Framework, https://doi.org/10.17605/OSF.IO/GEHFX). Methods: In this collaborative systematic review and meta-analysis, clinical trial registries (ClinicalTrials.gov, WHO International Clinical Trials Registry Platform), the Cochrane COVID-19 register, the LOVE database, and PubMed were searched until April 8, 2021. Investigators of trials registered by March 1, 2021, without published results were contacted via email. Eligible were ongoing, discontinued and completed randomized clinical trials that compared convalescent plasma with placebo or no treatment in COVID-19 patients, regardless of setting or treatment schedule. Aggregated mortality data were extracted from publications or provided by investigators of unpublished trials and combined using the Hartung–Knapp–Sidik–Jonkman random effects model. We investigated the contribution of unpublished trials to the overall evidence. Results: A total of 16,477 patients were included in 33 trials (20 unpublished with 3190 patients, 13 published with 13,287 patients). 32 trials enrolled only hospitalized patients (including 3 with only intensive care unit patients). Risk of bias was low for 29/33 trials. Of 8495 patients who received convalescent plasma, 1997 died (23%), and of 7982 control patients, 1952 died (24%). The combined risk ratio for all-cause mortality was 0.97 (95% confidence interval: 0.92; 1.02) with between-study heterogeneity not beyond chance (I2 = 0%). The RECOVERY trial had 69.8% and the unpublished evidence 25.3% of

Published
2021

32. Equilibrium fluctuations of liquid state static properties in a subvolume by molecular dynamics.

Author

Heyes, D. M., Dini, D., and Smith, E. R.

Subjects
MOLECULAR dynamics, FLUCTUATIONS (Physics), CHEMICAL equilibrium, THERMODYNAMICS, STOCHASTIC processes
Abstract

System property fluctuations increasingly dominate a physical process as the sampling volume decreases. The purpose of this work is to explore how the fluctuation statistics of various thermodynamic properties depend on the sampling volume, using molecular dynamics (MD) simulations. First an examination of various expressions for calculating the bulk pressure of a bulk liquid is made, which includes a decomposition of the virial expression into two terms, one of which is the Method of Planes (MOP) applied to the faces of the cubic simulation cell. Then an analysis is made of the fluctuations of local density, temperature, pressure, and shear stress as a function of sampling volume (SV). Cubic and spherical shaped SVs were used within a spatially homogeneous LJ liquid at a state point along the melting curve. It is shown that the MD-generated probability distribution functions (PDFs) of all of these properties are to a good approximation Gaussian even for SV containing only a few molecules (~10), with the variances being inversely proportional to the SV volume, O. For small subvolumes the shear stress PDF fits better to a Gaussian than the pressure PDF. A new stochastic sampling technique to implement the volume averaging definition of the pressure tensor is presented, which is employed for cubic, spherical, thin cubic, and spherical shell SV. This method is more efficient for less symmetric SV shapes. [ABSTRACT FROM AUTHOR]

Published
2016
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39. A localized momentum constraint for non-equilibrium molecular dynamics simulations.

Author

Smith, E. R., Heyes, D. M., Dini, D., and Zaki, T. A.

Subjects
*LOCALIZATION (Mathematics), *NON-equilibrium reactions, *MOLECULAR dynamics, *GAUSSIAN processes, *ITERATIVE methods (Mathematics)
Abstract

The article presents an overview of localized momentum constraint for non-equilibrium molecular dynamics simulations, which is used to control momentum evolution in sub-regions in molecular dynamics simulations, is derived from Gauss’s principle of least constraint and is based on the physics equations of Irving and Kirkwood. A discussion of the practical uses of the constraint, which can can prescribe arbitrary flow fields in non-equilibrium molecular dynamics simulations and can form a mathematical framework for introducing coupling constraints at the boundary between continuum and discrete systems in the field of physics, is presented.

Published
2015
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40. Fumonisin Toxicity and Sphingolipid Biosynthesis

Author

Merrill, A. H., primary, Wang, E., additional, Vales, T. R., additional, Smith, E. R., additional, Schroeder, J. J., additional, Menaldino, D. S., additional, Alexander, C., additional, Crane, H. M., additional, Xia, J., additional, Liotta, D. C., additional, Meredith, F. I., additional, and Riley, R. T., additional

Published
1996
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45. The method of planes pressure tensor for a spherical subvolume.

Author

Heyes, D. M., Smith, E. R., Dini, D., and Zaki, T. A.

Subjects
*MOLECULAR dynamics, *GEOMETRY, *DISTRIBUTION (Probability theory), *CALCULUS of tensors, *PRESSURE
Abstract

The article presents research on formulas to compute planes pressure or stress tensor for a spherical subvolume of radius (R). Topics include the Method of Planes (MoP) spherical geometry formula by Todd et al. in a 1995 issue of "Physics Review;" the proposed Control Volume formulation by E. R. Smith, D. M. Heyes, D. Dini, and T. A. Zaki in a 2012 issue of "Physics Review;" the radial-dependence of the pressure tensor calculated y the Molecular Dynamics simulation; and the Radial Irving-Kirkwood formula.

Published
2014
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48. The equivalence between volume averaging and method of planes definitions of the pressure tensor at a plane.

Author

Heyes, D. M., Smith, E. R., Dini, D., and Zaki, T. A.

Subjects
*PLANE geometry, *EQUILIBRIUM, *COMPUTER simulation, *MOLECULAR dynamics, *SHEAR flow, *DEVIATION (Statistics), *MATHEMATICAL analysis
Abstract

It is shown analytically that the method of planes (MOP) [Todd, Evans, and Daivis, Phys. Rev. E 52, 1627 (1995)] and volume averaging (VA) [Cormier, Rickman, and Delph, J. Appl. Phys. 89, 99 (2001)] formulas for the local pressure tensor, Pα, y(y), where α ≡ x, y, or z, are mathematically identical. In the case of VA, the sampling volume is taken to be an infinitely thin parallelepiped, with an infinite lateral extent. This limit is shown to yield the MOP expression. The treatment is extended to include the condition of mechanical equilibrium resulting from an imposed force field. This analytical development is followed by numerical simulations. The equivalence of these two methods is demonstrated in the context of non-equilibrium molecular dynamics (NEMD) simulations of boundary-driven shear flow. A wall of tethered atoms is constrained to impose a normal load and a velocity profile on the entrained central layer. The VA formula can be used to compute all components of Pαβ(y), which offers an advantage in calculating, for example, Pxx(y) for nano-scale pressure-driven flows in the x-direction, where deviations from the classical Poiseuille flow solution can occur. [ABSTRACT FROM AUTHOR]

Published
2011
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49. Optimal composition of europium gallium oxide thin films for device applications.

Author

Wellenius, P., Smith, E. R., LeBoeuf, S. M., Everitt, H. O., and Muth, J. F.

Subjects
*PHYSICS research, *THIN films, *SEMICONDUCTOR doping, *SEMICONDUCTOR industry, *EUROPIUM, *GALLIUM, *PULSED laser deposition, *PHOTOLUMINESCENCE
Abstract

The article discusses research in which europium gallium oxide (EuxGa1-x)2O3 thin films were deposited on sapphire substrates by pulsed laser deposition with varying Eu content from x=2.4 to 20 mol %. Researchers studied the optical and physical effects of high europium concentration on these thin films using photoluminescence (PL) spectroscopy, x-ray diffraction (XRD), and Rutherford backscattering spectrometry. They found that the PL spectra demonstrate that emission due to the 5D0 to 7FJ transitions in Eu3+ grows linearly with Eu content up to 10 mol %. They also concluded that time-resolved PL indicates decay parameters remain similar for films with up to 10 mol % Eu and at 20 mol %, but that PL intensity decreases substantially and PL decay accelerates, indicative of parasitic energy transfer processes. XRD shows films to be polycrystalline and beta-phase for low Eu compositions. They determined that increasing Eu content beyond 5 mol % does not continue to modify the film structure and thus, changes in PL spectra and decay cannot be attributed to structural changes in the host. They concluded that the optimal doping for optoelectronic devices based on (EuxGa1-x)2O3 thin films is between 5 and 10 mol %.

Published
2010
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50. Electrostatic potentials in systems periodic in one, two, and three dimensions.

Author

Smith, E. R.

Subjects
*ELECTROSTATICS, *CONDENSED matter, *PARTICLES, *POISSON'S equation, *BOUNDARY value problems, *SIMULATION methods & models
Abstract

We consider the electrostatic potential in a unit cell containing N point charges Qj with positions rj inside the cell. The cell is replicated periodically in one, two, and three dimensions. The purpose is to give representations for the potential which contain only lattice sums which are absolutely convergent and uniformly convergent in the sampling position r. These representations are derived using variants of the Ewald method and are primarily intended for use in evaluating the accuracy of any algorithm to evaluate electrostatic energies and forces in simulations of dense matter, rather than necessarily for use of themselves in simulations. In reduced dimensionality the Ewald representations can be numerically inefficient and other representations are also provided with careful specification which allows two forms to be used for the potential functions in order to improve numerical performance. These mixed representations may be satisfactory in simulations. [ABSTRACT FROM AUTHOR]

Published
2008
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