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Articles 1 - 14 of 14
Full-Text Articles in Physics
Inhomogeneous Exclusion Processes With Extended Objects: The Effect Of Defect Locations, J. J. Dong, Beate Schmittmann, R. K. P. Zia
Inhomogeneous Exclusion Processes With Extended Objects: The Effect Of Defect Locations, J. J. Dong, Beate Schmittmann, R. K. P. Zia
Beate Schmittmann
We study the effects of local inhomogeneities, i.e., slow sites of hopping rate q<1, in a totally asymmetric simple exclusion process for particles of size ℓ⩾1 (in units of the lattice spacing). We compare the simulation results of ℓ=1 and ℓ>1 and notice that the existence of local defects has qualitatively similar effects on the steady state. We focus on the stationary current as well as the density profiles. If there is only a single slow site in the system, we observe a significant dependence of the current on the location of the slow site for both ℓ=1 and ℓ>1 cases. When two slow sites are introduced, more intriguing phenomena emerge, e.g., dramatic decreases in the current when the two are close together. In addition, …
Posterminaries: More Or Less Modern, Alexander H. King
Posterminaries: More Or Less Modern, Alexander H. King
Alexander H. King
It is yet another sign that I am aging. More and more often when young researchers hand me a written report of their research, I find myself criticizing their introductory section: “You need to start your literature survey with the original papers on this topic. Go and read…” followed by a citation to some classic of the learned literature.
Power Spectra Of The Total Occupancy In The Totally Asymmetric Simple Exclusion Process, D. `A. Adams, R. K. P. Zia, Beate Schmittmann
Power Spectra Of The Total Occupancy In The Totally Asymmetric Simple Exclusion Process, D. `A. Adams, R. K. P. Zia, Beate Schmittmann
Beate Schmittmann
As a solvable and broadly applicable model system, the totally asymmetric exclusion process enjoys iconic status in the theory of nonequilibrium phase transitions. Here, we focus on the time dependence of the total number of particles on a 1-dimensional open lattice and its power spectrum. Using both Monte Carlo simulations and analytic methods, we explore its behavior in different characteristic regimes. In the maximal current phase and on the coexistence line (between high and low density phases), the power spectrum displays algebraic decay, with exponents −1.62 and −2.00, respectively. Deep within the high and low density phases, we find pronounced …
Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King
Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King
Alexander H. King
We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF2), and calcium fluoride (CaF2) as a function of the substrate temperature for films deposited by thermal evaporation onto glass substrates. The amount of porosity in the thin films was measured using an atomic force microscope and a quartz crystal thickness monitor. The porosity was very sensitive to the substrate temperature and decreased as the substrate temperature increased. Consistent behavior was observed among all of the materials in this study.
Posterminaries: Full Circle, Alexander H. King
Posterminaries: Full Circle, Alexander H. King
Alexander H. King
A few years ago, I was walking near the old Union Station in Pittsburgh with a colleague only slightly younger than myself, when we happened upon some large-scale relics of the steel industry displayed for public viewing. “You don’t see too many of those in public parking lots,” I offered. “Um… what is it?” was the response. I suppose I was just a little surprised that a prominent materials scientist did not recognize a Bessemer converter—arguably the principal source of wealth during the U.S. industrial revolution—but this conversation took place back when steel was in decline, and many university Materials …
Controlling Surface Morphologies By Time-Delayed Feedback, M. Block, Beate Schmittmann, E. Schöll
Controlling Surface Morphologies By Time-Delayed Feedback, M. Block, Beate Schmittmann, E. Schöll
Beate Schmittmann
We propose a method to control the roughness of a growing surface via a time-delayed feedback scheme. The method is very general and can be applied to a wide range of nonequilibrium growth phenomena, from solid-state epitaxy to tumor growth. Possible experimental realizations are suggested. As an illustration, we consider the Kardar-Parisi-Zhang equation [Phys. Rev. Lett. 56, 889 (1986)] in 1+1 dimensions and show that the effective growth exponent of the surface width can be stabilized at any desired value in the interval [0.25, 0.33], for a significant length of time.
Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson
Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson
Duane D. Johnson
Because reactivity increases as particle size decreases and competition between numerous structures are possible, which affects catalytic and magnetic properties, we study the structural trends of late-transition-metal 13-atom clusters using density functional theory within the generalized gradient approximation to exchange-correlation functional. We consider open structural motifs, such as bilayer and cubic (recently found to have lower energy), and find new bilayer candidates that are even lower in energy. To study the influence of d-orbital filling on structural trends, we focus on Pt, Pd, and Rh clusters and find several new, low-energy structures for Pt13 and Pd13 from searches using a …
Coarsening Of “Clouds” And Dynamic Scaling In A Far-From-Equilibrium Model System, D. A. Adams, Beate Schmittmann, R. K. P. Zia
Coarsening Of “Clouds” And Dynamic Scaling In A Far-From-Equilibrium Model System, D. A. Adams, Beate Schmittmann, R. K. P. Zia
Beate Schmittmann
A two-dimensional lattice gas of two species, driven in opposite directions by an external force, undergoes a jamming transition if the filling fraction is sufficiently high. Using Monte Carlo simulations, we investigate the growth of these jams (‘‘clouds’’), as the system approaches a nonequilibrium steady state from a disordered initial state. We monitor the dynamic structure factor S(kx,ky;t) and find that the kx=0 component exhibits dynamic scaling, of the form S(0,ky;t)=tβS̃ (kytα). Over a significant range of times, we observe excellent data collapse with α=1/2 and β=1. The effects of varying filling fraction and driving force are discussed.
Interface Reorientation During Coherent Phase Transformations, Valery I. Levitas, I. B. Ozsoy, D. L. Preston
Interface Reorientation During Coherent Phase Transformations, Valery I. Levitas, I. B. Ozsoy, D. L. Preston
Valery I. Levitas
The universal thermodynamic driving force for coherent plane interface reorientation (IR) during first-order phase transformations (PT) in solids is derived. The relation between the rates of IR and interface propagation (IP) and the corresponding driving forces are derived for combined athermal and drag interface friction. The coupled evolution of IR and IP during cubic-tetragonal and tetragonal-orthorhombic PTs under three-dimensional loading is studied. An instability in the interface orientation is shown to have the features of a first-order PT.
First-Principles Prediction Of Phase-Segregating Alloy Phase Diagrams And A Rapid Design Estimate Of Their Transition Temperatures, Nikolai A. Zarkevich, Teck L. Tan, Duane D. Johnson
First-Principles Prediction Of Phase-Segregating Alloy Phase Diagrams And A Rapid Design Estimate Of Their Transition Temperatures, Nikolai A. Zarkevich, Teck L. Tan, Duane D. Johnson
Nikolai A. Zarkevich
We calculate the transition temperature versus concentration (Tc vs c) phase diagrams of several phase-segregating alloys [fcc Ca-Sr, Au-Pt, and Rh-(Pd,Cu,Ag,Au)] using a multiscale method combining first-principles calculations and Monte Carlo via the cluster expansion (CE). We study Pd-Rh, with its well-known high-T miscibility gap, to verify the method’s reliability. We predict that Ca-Sr segregates at low temperatures. We then show that a rapid estimate of Tc is obtained from enthalpies analytically derived from a CE, and, using thermodynamic integration, we determine under what circumstances this mean-field estimate is accurate compared to Monte Carlo results. Also, we discuss how an …
Thermal Effects On Mechanical Grinding-Induced Surface Texture In Tetragonal Piezoelectrics, Wonyoung Chang, Alexander H. King, Keith J. Bowman
Thermal Effects On Mechanical Grinding-Induced Surface Texture In Tetragonal Piezoelectrics, Wonyoung Chang, Alexander H. King, Keith J. Bowman
Alexander H. King
The effect of temperature on grinding-induced texture in tetragonal lead zirconate titanate (PZT) and lead titanate (PT) has been investigated using in situ x-ray diffraction (XRD) with an area detector. In contrast with previous results on electrical poling, mechanically-ground PT and soft PZT materials retain strong ferroelastic textures during thermal cycling, even after excursions to temperatures slightly above the Curie temperature. The relationship between the residual stresses in the surface region, caused by grinding, and those resulting from domain wall motion is elucidated by in situ texture measurements obtained during thermal cycling.
How Surface Stresses Lead To Size-Dependent Mechanics Of Tensile Deformation In Nanowires, M. Ravi Shankar, Alexander H. King
How Surface Stresses Lead To Size-Dependent Mechanics Of Tensile Deformation In Nanowires, M. Ravi Shankar, Alexander H. King
Alexander H. King
It has been proposed that surface and interface stresses can modify the elastic behavior in nanomaterials such as nanowires. The authors show that surface stresses modify the tensile response of nanowires only when nonlinear elastic effects become important leading to cross terms between the applied stress and the surface stress. These effects are only significant when the radius of the nanowire is of the order of a few nanometers. The resulting alteration of tensile stiffness, though effected in part by the nonlinear elastic modulus, is particularly wrought by a modification of the stress state in the deformed nanowire.
Energy Pathways And Directionality In Deformation Twinning, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Energy Pathways And Directionality In Deformation Twinning, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Duane D. Johnson
We present ab initiodensity functional theory calculations of twinning energy pathways for two opposite twinning modes, (111)[112¯] and (111)[1¯1¯2], in fcc materials to examine the directional nature of twinning which cannot be explained by classical twin nucleationmodels or the “twinnability” criterion. By accounting for these energy pathways in a multiscale model, we quantitatively predict the critical twinning stress for the (111)[1¯1¯2] mode to be substantially higher compared to the favorable (111)[112¯] mode (whose predicted stresses are in agreement with experiment), thus, ruling out twinning in the (111)[1¯1¯2] mode.
Markov Chain Monte Carlo Defect Identification In Nde Images, Aleksandar Dogandžić, Benhong Zhang
Markov Chain Monte Carlo Defect Identification In Nde Images, Aleksandar Dogandžić, Benhong Zhang
Aleksandar Dogandžić
We derive a hierarchical Bayesian method for identifying elliptically‐shaped regions with elevated signal levels in NDE images. We adopt a simple elliptical parametric model for the shape of the defect region and assume that the defect signals within this region are random following a truncated Gaussian distribution. Our truncated‐Gaussian model ensures that the signals within the defect region are higher than the baseline level corresponding to the noise‐only case. We derive a closed‐form expression for the kernel of the posterior probability distribution of the location, shape, and defect‐signal distribution parameters (model parameters). This result is then used to develop Markov …