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1

Density functional theory for Baxter's sticky hard spheres in confinement  

E-print Network

It has recently been shown that a free energy for Baxter's sticky hard sphere fluid is uniquely defined within the framework of fundamental measure theory (FMT) for the inhomogeneous hard sphere fluid, provided that it obeys scaled-particle theory and the Percus-Yevick (PY) result for the direct correlation function [Hansen-Goos and Wettlaufer, J. Chem. Phys. {\\bf 134}, 014506 (2011)]. Here, combining weighted densities from common versions of FMT with a new vectorial weighted density, we derive a regularization of the divergences of the associated strongly confined limit. Moreover, the simple free energy that emerges is exact in the zero-dimensional limit, leaves the underlying equation of state unaffected, and yields a direct correlation function distinct from the PY expression. Comparison with simulation data for both the bulk pair correlation function and the density profiles in confinement shows that the new theory is significantly more accurate than the PY-based results. Finally, the resulting free energy is applicable to a glass of adhesive hard spheres.

Hendrik Hansen-Goos; Mark A. Miller; J. S. Wettlaufer

2011-12-15

2

Equation of state and jamming density for equivalent bi-and polydisperse, smooth, hard sphere systems  

E-print Network

; equations of state; noncrystalline structure; solid-liquid transformations I. INTRODUCTION The hard-sphere- sions are instantaneous1,8 , like in the hard-sphere model. In this paper we study the high density reasonable model that re- lates the behavior of different hard sphere mixtures, even a)Electronic mail: v

Luding, Stefan

3

Density fluctuations and the structure of a nonuniform hard sphere fluid  

E-print Network

We derive an exact equation for density changes induced by a general external field that corrects the hydrostatic approximation where the local value of the field is adsorbed into a modified chemical potential. Using linear response theory to relate density changes self-consistently in different regions of space, we arrive at an integral equation for a hard sphere fluid that is exact in the limit of a slowly varying field or at low density and reduces to the accurate Percus-Yevick equation for a hard core field. This and related equations give accurate results for a wide variety of fields.

Kirill Katsov; John D. Weeks

2000-08-08

4

A Dynamic Hard Sphere Model  

Microsoft Academic Search

A simple two-dimensional model, in which uniform hard spheres are made to move steadily and apparently nearly at random, is described. At low sphere density the model exhibits ``gas-like'' behavior. As the density is increased the behavior becomes more ``liquid-like'' and then ``crystallization'' occurs. Many dynamic atomic phenomena, believed to occur in the gas, liquid, or solid state, are illustrated

D. Turnbull; R. L. Cormia

1960-01-01

5

Hard Sphere Gas Model  

NSDL National Science Digital Library

The Ejs Hard Sphere Gas model displays a three-dimensional (ideal) gas made out of hard disks. Particles are initialized with a random speed and in a random direction and move with constant velocity until a collision occurs. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. Ejs Hard Sphere Gas model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_newton_HardShpereGas.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for statistical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang

2008-07-06

6

Mode expansion for the density profiles of crystal-fluid interfaces: hard spheres as a test case.  

PubMed

We present a technique for analyzing the full three-dimensional density profiles of planar crystal-fluid interfaces in terms of density modes. These density modes can also be related to crystallinity order parameter profiles which are used in coarse-grained, phase field type models of the statics and dynamics of crystal-fluid interfaces and are an alternative to crystallinity order parameters extracted from simulations using local crystallinity criteria. We illustrate our results for the hard sphere system using finely resolved, three-dimensional density profiles from a density functional theory of fundamental measure type. PMID:23114279

Oettel, M

2012-11-21

7

Mode expansion for the density profile of crystal-fluid interfaces: Hard spheres as a test case  

E-print Network

We present a technique for analyzing the full three-dimensional density profiles of a planar crystal-fluid interface in terms of density modes. These density modes can also be related to crystallinity order parameter profiles which are used in coarse-grained, phase field type models of the statics and dynamics of crystal-fluid interfaces and are an alternative to crystallinity order parameters extracted from simulations using local crystallinity criteria. We illustrate our results for the hard sphere system using finely-resolved, three-dimensional density profiles from density functional theory of fundamental measure type.

M. Oettel

2012-03-16

8

Backward Clusters, Hierarchy and Wild Sums for a Hard Sphere System in a Low-Density Regime  

E-print Network

We study the statistics of backward clusters in a gas of hard spheres at low density. A backward cluster is defined as the group of particles involved directly or indirectly in the backwards-in-time dynamics of a given tagged sphere. We derive upper and lower bounds on the average size of clusters by using the theory of the homogeneous Boltzmann equation combined with suitable hierarchical expansions. These representations are known in the easier context of Maxwellian molecules (Wild sums). We test our results with a numerical experiment based on molecular dynamics simulations.

K. Aoki; M. Pulvirenti; S. Simonella; T. Tsuji

2014-08-27

9

Free energies, vacancy concentrations and density distribution anisotropies in hard--sphere crystals: A combined density functional and simulation study  

E-print Network

We perform a comparative study of the free energies and the density distributions in hard sphere crystals using Monte Carlo simulations and density functional theory (employing Fundamental Measure functionals). Using a recently introduced technique (Schilling and Schmid, J. Chem. Phys 131, 231102 (2009)) we obtain crystal free energies to a high precision. The free energies from Fundamental Measure theory are in good agreement with the simulation results and demonstrate the applicability of these functionals to the treatment of other problems involving crystallization. The agreement between FMT and simulations on the level of the free energies is also reflected in the density distributions around single lattice sites. Overall, the peak widths and anisotropy signs for different lattice directions agree, however, it is found that Fundamental Measure theory gives slightly narrower peaks with more anisotropy than seen in the simulations. Among the three types of Fundamental Measure functionals studied, only the White Bear II functional (Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)) exhibits sensible results for the equilibrium vacancy concentration and a physical behavior of the chemical potential in crystals constrained by a fixed vacancy concentration.

M. Oettel; S. Goerig; A. Haertel; H. Loewen; M. Radu; T. Schilling

2010-09-03

10

Density functional theory of liquid crystals and surface anchoring: Hard Gaussian overlap-sphere and hard Gaussian overlap-surface potentials  

NASA Astrophysics Data System (ADS)

This article applies the density functional theory to confined liquid crystals, comprised of ellipsoidal shaped particles interacting through the hard Gaussian overlap (HGO) potential. The extended restricted orientation model proposed by Moradi and co-workers [J. Phys.: Condens. Matter 17, 5625 (2005)] is used to study the surface anchoring. The excess free energy is calculated as a functional expansion of density around a reference homogeneous fluid. The pair direct correlation function (DCF) of a homogeneous HGO fluid is approximated, based on the optimized sum of Percus-Yevick and Roth DCF for hard spheres; the anisotropy introduced by means of the closest approach parameter, the expression proposed by Marko [Physica B 392, 242 (2007)] for DCF of HGO, and hard ellipsoids were used. In this study we extend an our previous work [Phys. Rev. E 72, 061706 (2005)] on the anchoring behavior of hard particle liquid crystal model, by studying the effect of changing the particle-substrate contact function instead of hard needle-wall potentials. We use the two particle-surface potentials: the HGO-sphere and the HGO-surface potentials. The average number density and order parameter profiles of a confined HGO fluid are obtained using the two particle-wall potentials. For bulk isotropic liquid, the results are in agreement with the Monte Carlo simulation of Barmes and Cleaver [Phys. Rev. E 71, 021705 (2005)]. Also, for the bulk nematic phase, the theory gives the correct density profile and order parameter between the walls.

Avazpour, A.; Avazpour, L.

2010-12-01

11

Exciting Hard Spheres  

E-print Network

We investigate the collision cascade that is generated by a single moving incident particle on a static hard-sphere gas. We argue that the number of moving particles at time t grows as t^{xi} and the number collisions up to time t grows as t^{eta}, with xi=2d/(d+2) and eta=2(d+1)/(d+2) and d the spatial dimension. These growth laws are the same as those from a hydrodynamic theory for the shock wave emanating from an explosion. Our predictions are verified by molecular dynamics simulations in d=1 and 2. For a particle incident on a static gas in a half-space, the resulting backsplatter ultimately contains almost all the initial energy.

T. Antal; P. L. Krapivsky; S. Redner

2008-05-25

12

Structural properties of dense hard sphere packings.  

PubMed

We numerically study structural properties of mechanically stable packings of hard spheres (HS), in a wide range of packing fractions 0.53 ? ? ? 0.72. Detailed structural information is obtained from the analysis of orientational order parameters, which clearly reveals a disorder-order phase transition at the random close packing (RCP) density, ?c ? 0.64. Above ?c, the crystalline nuclei form 3D-like clusters, which upon further desification transform into alternating planar-like layers. We also find that particles with icosahedral symmetry survive only in a narrow density range in the vicinity of the RCP transition. PMID:25098389

Klumov, Boris A; Jin, Yuliang; Makse, Hernán A

2014-09-11

13

Structure the Hard Sphere Solid Charles Radin  

E-print Network

interested solid phase the sphere model, phase which is generally agreed exist based computer experimentsStructure the Hard Sphere Solid Charles Radin * Lorenzo Sadun Department of Mathematics, University (centers the) spheres. We be concerned with solid­fluid transi­ tion, associated d around 0

14

Collision statistics in sheared inelastic hard spheres  

E-print Network

The dynamics of sheared inelastic-hard-sphere systems are studied using non-equilibrium molecular dynamics simulations and direct simulation Monte Carlo. In the molecular dynamics simulations Lees-Edwards boundary conditions are used to impose the shear. The dimensions of the simulation box are chosen to ensure that the systems are homogeneous and that the shear is applied uniformly. Various system properties are monitored, including the one-particle velocity distribution, granular temperature, stress tensor, collision rates, and time between collisions. The one-particle velocity distribution is found to agree reasonably well with an anisotropic Gaussian distribution, with only a slight overpopulation of the high velocity tails. The velocity distribution is strongly anisotropic, especially at lower densities and lower values of the coefficient of restitution, with the largest variance in the direction of shear. The density dependence of the compressibility factor of the sheared inelastic hard sphere system is quite similar to that of elastic hard sphere fluids. As the systems become more inelastic, the glancing collisions begin to dominate more direct, head-on collisions. Examination of the distribution of the time between collisions indicates that the collisions experienced by the particles are strongly correlated in the highly inelastic systems. A comparison of the simulation data is made with DSMC simulation of the Enskog equation. Results of the kinetic model of Montanero et al. {[}Montanero et al., J. Fluid Mech. 389, 391 (1999){]} based on the Enskog equation are also included. In general, good agreement is found for high density, weakly inelastic systems.

Marcus N. Bannerman; Thomas E. Green; Paul Grassia; Leo Lue

2009-03-24

15

In Search of Colloidal Hard Spheres  

E-print Network

We recently reviewed the experimental determination of the volume fraction, $\\phi$, of hard-sphere colloids, and concluded that the absolute value of $\\phi$ was unlikely to be known to better than $\\pm 3$-6%. Here, in a second part to that review, we survey effects due to softness in the interparticle potential, which necessitates the use of an {\\em effective} volume fraction. We review current experimental systems, and conclude that the one that most closely approximates hard spheres remains polymethylmethacrylate spheres sterically stabilised by polyhydroxystearic acid `hairs'. For these particles their effective hard sphere diameter is around 1-10% larger than the core diameter, depending on the particle size. We argue that for larger colloids suitable for confocal microscopy, the effect of electrostatic charge cannot be neglected, so that mapping to hard spheres must be treated with caution.

C. Patrick Royall; Wilson C. K. Poon; Eric R. Weeks

2012-05-30

16

Point Defects in Hard Sphere Crystals  

E-print Network

We report numerical calculations of the concentration of interstitials in hard-sphere crystals. We find that, in a three-dimensional fcc hard-sphere crystal at the melting point, the concentration of interstitials is 2 * 10^-8. This is some three orders of magnitude lower than the concentration of vacancies. A simple, analytical estimate yields a value that is in fair agreement with the numerical results.

Sander Pronk; Daan Frenkel

2001-05-03

17

Hard spheres on the gyroid surface  

PubMed Central

We find that 48/64 hard spheres per unit cell on the gyroid minimal surface are entropically self-organized. Striking evidence is obtained in terms of the acceptance ratio of Monte Carlo moves and order parameters. The regular tessellations of the spheres can be viewed as hyperbolic tilings on the Poincaré disc with a negative Gaussian curvature, one of which is, equivalently, the arrangement of angels and devils in Escher's Circle Limit IV. PMID:24098841

Dotera, Tomonari; Kimoto, Masakiyo; Matsuzawa, Junichi

2012-01-01

18

Computational study of the melting-freezing transition in the quantum hard-sphere system for intermediate densities. II. Structural features.  

PubMed

The structural features of the quantum hard-sphere system in the region of the fluid-face-centered-cubic-solid transition, for reduced number densities 0.45hard spheres has been performed, and some interesting differences between the classical and quantum melting-freezing transition are observed. PMID:17477616

Sesé, Luis M; Bailey, Lorna E

2007-04-28

19

Description of hard sphere crystals and crystal-fluid interfaces: a critical comparison between density functional approaches and a phase field crystal model  

E-print Network

In materials science the phase field crystal approach has become popular to model crystallization processes. Phase field crystal models are in essence Landau-Ginzburg-type models, which should be derivable from the underlying microscopic description of the system in question. We present a study on classical density functional theory in three stages of approximation leading to a specific phase field crystal model, and we discuss the limits of applicability of the models that result from these approximations. As a test system we have chosen the three--dimensional suspension of monodisperse hard spheres. The levels of density functional theory that we discuss are fundamental measure theory, a second-order Taylor expansion thereof, and a minimal phase-field crystal model. We have computed coexistence densities, vacancy concentrations in the crystalline phase, interfacial tensions and interfacial order parameter profiles, and we compare these quantities to simulation results. We also suggest a procedure to fit the free parameters of the phase field crystal model.

M. Oettel; S. Dorosz; M. Berghoff; B. Nestler; T. Schilling

2012-06-22

20

Vortices in a Gas of Hard Spheres  

Microsoft Academic Search

We approximately describe the transition regime between two vortex-type flows in a gas of hard spheres. Such flows rotate as solid bodies about their axes, which in turn move translationally with arbitrary linear velocities. We study the asymptotic behavior of the integral norm of the discrepancy between the two sides of the Boltzmann equation under a special choice of hydrodynamic

V. D. Gordevsky

2003-01-01

21

Computational study of the melting-freezing transition in the quantum hard-sphere system for intermediate densities. I. Thermodynamic results.  

PubMed

The points where the fluid-solid (face-centered-cubic) transition takes place in the quantum hard-sphere system, for reduced densities 0.85>rhoN*>0.5 (reduced de Broglie wavelengths lambdaB*densities are arranged along a straight line rhoFCC*=rho(rhoF*), a behavior which at least holds even for lambdaB*<2, as revealed by completing the present analysis with data available in the literature. PMID:17477615

Sesé, Luis M

2007-04-28

22

Density anomaly of charged hard spheres of different diameters in a mixture with core-softened model solvent. Monte Carlo simulation results  

E-print Network

Very recently the effect of equisized charged hard sphere solutes in a mixture with core-softened fluid model on the structural and thermodynamic anomalies of the system has been explored in detail by using Monte Carlo simulations and integral equations theory [J. Chem. Phys., 2012, 137, 244502]. Our objective of the present short work is to complement this study by considering univalent ions of unequal diameters in a mixture with the same soft-core fluid model. Specifically, we are interested in the analysis of changes of the temperature of maximum density (TMD) lines with ion concentration for three model salt solutes, namely sodium chloride, potassium chloride and rubidium chloride models. We resort to Monte Carlo simulations for this purpose. Our discussion also involves the dependences of the pair contribution to excess entropy and of constant volume heat capacity on the temperature of maximum density line. Some examples of the microscopic structure of mixtures in question in terms of pair distribution functions are given in addition.

B. Hribar-Lee; O. Pizio

2013-12-16

23

Crystallizing hard-sphere glasses by doping with active particles.  

PubMed

Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as building blocks for novel functional materials with potential applications, e.g. photonic crystals. By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, we show that the crystallization of such hard-sphere glasses can be dramatically promoted by doping the system with small amounts of active particles. Surprisingly, even hard-sphere glasses of packing fraction up to ? = 0.635 crystallize, which is around 0.5% below the random close packing at ? ? 0.64. Our results suggest a novel way of fabricating crystalline materials from (colloidal) glasses. This is particularly important for materials that get easily kinetically trapped in glassy states, and the crystal nucleation hardly occurs. PMID:25079244

Ni, Ran; Cohen Stuart, Martien A; Dijkstra, Marjolein; Bolhuis, Peter G

2014-09-21

24

Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.  

PubMed

In this work we study a set of soft-sphere systems characterised by a well-defined variation of their softness. These systems represent an extension of the repulsive Lennard-Jones potential widely used in statistical mechanics of fluids. This type of soft spheres is of interest because they represent quite accurately the effective intermolecular repulsion in fluid substances and also because they exhibit interesting properties. The thermodynamics of the soft-sphere fluids is obtained via an effective hard-sphere diameter approach that leads to a compact and accurate equation of state. The virial coefficients of soft spheres are shown to follow quite simple relationships that are incorporated into the equation of state. The approach followed exhibits the rescaling of the density that produces a unique equation for all systems and temperatures. The scaling is carried through to the level of the structure of the fluids. PMID:22158949

Rodríguez-López, Tonalli; del Río, Fernando

2012-01-28

25

Regularized 13 moment equations for hard spheres  

NASA Astrophysics Data System (ADS)

The regularized 13 moment equations (R13) of rarefied gas dynamics for a monatomic hard sphere gas in the linear regime are presented. The equations are based on an extended Grad-type moment system, which was systematically reduced by means of the Order of Magnitude Method [Struchtrup, Phys. Fluids 16(11), 3921-3934 (2004)]. The linear Burnett and super-Burnett equations are derived from Chapman-Enskog expansion of the R13 equations. While the Burnett coefficients agree with literature values, this seems to be the first time that super-Burnett coefficients are computed for a hard sphere gas. The equations are considered for stability, and dispersion and damping of sound waves. Boundary conditions are given, and solutions of simple boundary value problems are briefly discussed.

Struchtrup, Henning; Torrilhon, Manuel

2012-11-01

26

Evolution of correlation functions in the hard sphere dynamics  

E-print Network

The series expansion for the evolution of the correlation functions of a finite system of hard spheres is derived from direct integration of the solution of the Liouville equation, with minimal regularity assumptions on the density of the initial measure. The usual BBGKY hierarchy of equations is then recovered. A graphical language based on the notion of collision history originally introduced by Spohn is developed, as a useful tool for the description of the expansion and of the elimination of degrees of freedom.

Sergio Simonella

2012-05-12

27

Haptic Search for Hard and Soft Spheres  

PubMed Central

In this study the saliency of hardness and softness were investigated in an active haptic search task. Two experiments were performed to explore these properties in different contexts. In Experiment 1, blindfolded participants had to grasp a bundle of spheres and determine the presence of a hard target among soft distractors or vice versa. If the difference in compliance between target and distractors was small, reaction times increased with the number of items for both features; a serial strategy was found to be used. When the difference in compliance was large, the reaction times were independent of the number of items, indicating a parallel strategy. In Experiment 2, blindfolded participants pressed their hand on a display filled with hard and soft items. In the search for a soft target, increasing reaction times with the number of items were found, but the location of target and distractors appeared to have a large influence on the search difficulty. In the search for a hard target, reaction times did not depend on the number of items. In sum, this showed that both hardness and softness are salient features. PMID:23056197

van Polanen, Vonne; Bergmann Tiest, Wouter M.; Kappers, Astrid M. L.

2012-01-01

28

Phase transitions of semiflexible hard-sphere chain liquids Hanif Bayat Movahed,1,2  

E-print Network

liquid and solid phases 1,3­7 . Studies of liquid-crystalline ordering in this model using densityPhase transitions of semiflexible hard-sphere chain liquids Hanif Bayat Movahed,1,2 Raul Cruz liquid-crystalline phase transitions in a fluid of semi- flexible hard-sphere chain molecules based

Sullivan, Donald E.

29

Crystallization Mechanism of Hard Sphere Glasses  

NASA Astrophysics Data System (ADS)

In supercooled liquids, vitrification generally suppresses crystallization. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystallization of monodisperse hard-sphere glasses at constant volume (as in a colloid experiment). Multiple crystalline patches appear without particles having to diffuse more than one diameter. As these patches grow, the mobility in neighboring areas is enhanced, creating dynamic heterogeneity with positive feedback. The future crystallization pattern cannot be predicted from the coordinates alone: Crystallization proceeds by a sequence of stochastic micronucleation events, correlated in space by emergent dynamic heterogeneity.

Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, W. C. K.; Pusey, P. N.; Cates, M. E.

2011-05-01

30

Aging dynamics of colloidal hard sphere glasses  

NASA Astrophysics Data System (ADS)

We report the results of dynamic light scattering measurements of the coherent intermediate scattering function (ISF) of glasses of colloidal hard spheres for several volume fractions and a range of scattering vectors around the primary peak of the static structure factor. The ISF shows a clear crossover from an initial fast decay to a slower nonstationary decay. Aging is quantified in several different ways. However, regardless of the method chosen, the perfect ``aged'' glass is approached in a power law fashion. In particular the coupling between the fast and slow decays, as measured by the degree of stretching of the ISF at the crossover, also decreases algebraically with waiting time. The nonstationarity of this coupling implies that even the fastest detectable processes are themselves nonstationary.

Martinez, V. A.; Bryant, G.; van Megen, W.

2010-09-01

31

Most stable structure for hard spheres Hans Koch,* Charles Radin,  

E-print Network

The hard sphere model is known to show a liquid-solid phase transition, with the solid expected s : 05.20.Gg, 05.10. a, 61.50.Ah, 82.70.Dd I. INTRODUCTION Computer simulations of the hard sphere model structure of that solid phase, since the model is one of the simplest possible showing both liquid and solid

Radin, Charles

32

Dynamics of hard sphere colloidal dispersions  

NASA Technical Reports Server (NTRS)

Our objective is to perform on homogeneous, fully equilibrated dispersions the full set of experiments characterizing the transition from fluid to solid and the properties of the crystalline and glassy solid. These include measurements quantifying the nucleation and growth of crystallites, the structure of the initial fluid and the fully crystalline solid, and Brownian motion of particles within the crystal, and the elasticity of the crystal and the glass. Experiments are being built and tested for ideal microgravity environment. Here we describe the ground based effort, which exploits a fluidized bed to create a homogeneous, steady dispersion for the studies. The differences between the microgravity environment and the fluidized bed is gauged by the Peclet number Pe, which measures the rate of convection/sedimentation relative to Brownian motion. We have designed our experiment to accomplish three types of measurements on hard sphere suspensions in a fluidized bed: the static scattering intensity as a function of angle to determine the structure factor, the temporal autocorrelation function at all scattering angles to probe the dynamics, and the amplitude of the response to an oscillatory forcing to deduce the low frequency viscoelasticity. Thus the scattering instrument and the colloidal dispersion were chosen such as that the important features of each physical property lie within the detectable range for each measurement.

Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.

1994-01-01

33

Multiple reentrant glass transitions in confined hard-sphere glasses  

NASA Astrophysics Data System (ADS)

Glass-forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro- and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition.

Mandal, Suvendu; Lang, Simon; Gross, Markus; Oettel, Martin; Raabe, Dierk; Franosch, Thomas; Varnik, Fathollah

2014-07-01

34

Multiple reentrant glass transitions in confined hard-sphere glasses  

E-print Network

Glass forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro- and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in-line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition.

S. Mandal; S. Lang; M. Gross; M. Oettel; D. Raabe; T. Franosch; F. Varnik

2014-06-20

35

Revisit of interfacial free energy of the hard sphere system near hard wall  

E-print Network

We propose a simple Monte Carlo method to calculate the interfacial free energy between the substrate and the material. Using this method we investigate the interfacial free energys of the hard sphere fluid and solid phases near a smooth hard wall. According to the obtained interfacial free energys of the coexisting fluid and solid phases and the Young equation we are able to determine the contact angle with high accuracy, cos$\\theta$ = 1:010(31), which indicates that a smooth hard wall can be wetted completely by the hard sphere crystal at the interface between the wall and the hard sphere fluid.

Mingcheng Yang; Hongru Ma

2008-06-23

36

Phase equilibria in polydisperse nonadditive hard-sphere systems  

NASA Astrophysics Data System (ADS)

Colloidal particles naturally exhibit a size polydispersity that can greatly influence their phase behavior in solution. Nonadditive hard-sphere (NAHS) mixtures are simple and well-suited model systems to represent phase transitions in colloid systems. Here, we propose an analytical equation of state (EOS) for NAHS fluid mixtures, which can be straightforwardly applied to polydisperse systems. For positive values of the nonadditivity parameter ? the model gives accurate predictions of the simulated fluid-fluid coexistence curves and compressibility factors. NPT Monte Carlo simulations of the mixing properties of the NAHS symmetric binary mixture with ?>0 are reported. It is shown that the enthalpy of mixing is largely positive and overcomes the positive entropy of mixing when the pressure is increased, leading to a fluid-fluid phase transition with a lower critical solution pressure. Phase equilibria in polydisperse systems are predicted with the model by using the density moment formalism [P. Sollich , Adv. Chem. Phys. 116, 265 (2001)]. We present predictions of the cloud and shadow curves for polydisperse NAHS systems composed of monodisperse spheres and polydisperse colloid particles. A fixed nonadditivity parameter ?>0 is assumed between the monodisperse and polydisperse spheres, and a Schulz distribution is used to represent the size polydispersity. Polydispersity is found to increase the extent of the immiscibility region. The predicted cloud and shadow curves depend dramatically on the upper cutoff diameter ?c of the Schulz distribution, and three-phase equilibria can occur for large values of ?c .

Paricaud, Patrice

2008-08-01

37

Structure and kinetics in the freezing of nearly hard spheres  

E-print Network

We consider homogeneous crystallisation rates in confocal microscopy experiments on colloidal nearly hard spheres at the single particle level. These we compare with Brownian dynamics simuations by carefully modelling the softness in the interactions with a Yukawa potential, which takes account of the electrostatic charges present in the experimental system. Both structure and dynamics of the colloidal fluid are very well matched between experiment and simulation, so we have confidence that the system simulated is close to that in the experiment. In the regimes we can access, we find reasonable agreement in crystallisation rates between experiment and simulations, noting that the larger system size in experiments enables the formation of critical nuclei and hence crystallisation at lower supersaturations than the simulations. We further examine the structure of the metastable fluid with a novel structural analysis, the topological cluster classification. We find that at densities where the hard sphere fluid becomes metastable, the dominant structure is a cluster of m=10 particles with five-fold symmetry. At a particle level, we find three regimes for the crystallisation process: metastable fluid (dominated by m=10 clusters), crystal and a transition region of frequent hopping between crystal-like environments and other (m\

Jade Taffs; Stephen R. Williams; Hajime Tanaka; C. Patrick Royall

2012-06-24

38

Thermodynamic properties of lattice hard-sphere models  

Microsoft Academic Search

Thermodynamic properties of several lattice hard-sphere models were obtained from grand canonical histogram- reweighting Monte Carlo simulations. Sphere centers occupy positions on a simple cubic lattice of unit spacing and exclude neighboring sites up to a distance ?. The nearestneighbor exclusion model, ?=&sqrt;2, was previously found to have a second-order transition. Models with integer values of ?=1 or 2 do

A. Z. Panagiotopoulos

2005-01-01

39

Most stable structure hard spheres Hans Koch,* Charles Radin,  

E-print Network

Mathematics, University Texas, Austin, Texas 78712, #Received 18 published July 2005# sphere model is known.20.Gg, 05.10.#a, 61.50.Ah, 82.70.Dd I. INTRODUCTION Computer simulations of hard sphere model late 1950s there been significant interest determin­ internal structure of solid phase, since model one simplest

Radin, Charles

40

Elasticity of a polydisperse hard-sphere crystal  

E-print Network

A general Monte Carlo simulation method of calculating the elastic constants of polydisperse hard-sphere colloidal crystal was developed. The elastic constants of a size polydisperse hard sphere fcc crystal is calculated. The pressure and three elastic constants(C11, C12 and C44) increase significantly with the polydispersity. It was also found from extrapolation that there is a mechanical terminal polydispersity above which a fcc crystal will be mechanically unstable.

Mingcheng Yang; Hongru Ma

2008-06-19

41

Stochastic model of a dense spinless hard-sphere gas  

Microsoft Academic Search

Summary  The motion of a spinless quantum particle subjected to random hard-sphere scatterings is studied in the framework of stochastic\\u000a mechanics. The result is applied to the case of a generic particle of a dense spinless hard-sphere gas leading to a description\\u000a that displays the competition between the thermal and the quantum noise. Finally, the model is discussed in connection with

L. M. Morato; G. Galilei

1991-01-01

42

Gibbs ensemble Monte Carlo of nonadditive hard-sphere mixtures.  

PubMed

In this article, we perform Gibbs ensemble Monte Carlo (GEMC) simulations of liquid-liquid phase coexistence in nonadditive hard-sphere mixtures (NAHSMs) for different size ratios and non-additivity parameters. The simulation data are used to provide a benchmark to a number of theoretical and mixed theoretical/computer simulation approaches which have been adopted in the past to study phase equilibria in NAHSMs, including the method of the zero of the Residual Multi-Particle Entropy, Integral Equation Theories (IETs), and classical Density Functional Theory (DFT). We show that while the entropic criterium is quite accurate in predicting the location of phase equilibrium curves, IETs and DFT provide at best a semi-quantitative reproduction of GEMC demixing curves. PMID:25084927

Pellicane, Giuseppe; Pandaram, Owen D

2014-07-28

43

Thermodynamic properties of lattice hard-sphere models  

Microsoft Academic Search

Thermodynamic properties of several lattice hard-sphere models were obtained from grand canonical histogram- reweighting Monte Carlo simulations. Sphere centers occupy positions on a simple cubic lattice of unit spacing and exclude neighboring sites up to a distance sigma. The nearestneighbor exclusion model, sigma=&surd;2, was previously found to have a second-order transition. Models with integer values of sigma=1 or 2 do

A. Z. Panagiotopoulos

2005-01-01

44

Free volume distribution of nearly jammed hard sphere packings  

NASA Astrophysics Data System (ADS)

We calculate the free volume distributions of nearly jammed packings of monodisperse and bidisperse hard sphere configurations. These distributions differ qualitatively from those of the fluid, displaying a power law tail at large free volumes, which constitutes a distinct signature of nearly jammed configurations, persisting for moderate degrees of decompression. We reproduce and explain the observed distribution by considering the pair correlation function within the first coordination shell for jammed hard sphere configurations. We analyze features of the equation of state near jamming, and discuss the significance of observed asphericities of the free volumes to the equation of state.

Maiti, Moumita; Sastry, Srikanth

2014-07-01

45

Slip and flow of hard-sphere colloidal glasses  

E-print Network

We study the flow of concentrated hard-sphere colloidal suspensions along smooth, non-stick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the `solid' microstructure during full slip and the local nature of the `slip to shear' transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.

P. Ballesta; R. Besseling; L. Isa; G. Petekidis; W. C. K. Poon

2008-07-09

46

Local order variations in confined hard-sphere fluids  

E-print Network

Pair distributions of fluids confined between two surfaces at close distance are of fundamental importance for a variety of physical, chemical, and biological phenomena, such as interactions between macromolecules in solution, surface forces, and diffusion in narrow pores. However, in contrast to bulk fluids, properties of inhomogeneous fluids are seldom studied at the pair-distribution level. Motivated by recent experimental advances in determining anisotropic structure factors of confined fluids, we analyze theoretically the underlying anisotropic pair distributions of the archetypical hard-sphere fluid confined between two parallel hard surfaces using first-principles statistical mechanics of inhomogeneous fluids. For this purpose, we introduce an experimentally accessible ensemble-averaged local density correlation function and study its behavior as a function of confining slit width. Upon increasing the distance between the confining surfaces, we observe an alternating sequence of strongly anisotropic versus more isotropic local order. The latter is due to packing frustration of the spherical particles. This observation highlights the importance of studying inhomogeneous fluids at the pair-distribution level.

Kim Nygård; Sten Sarman; Roland Kjellander

2013-10-31

47

Criticality in charge-asymmetric hard-sphere ionic fluids  

NASA Astrophysics Data System (ADS)

Phase separation and criticality are analyzed in z:1 charge-asymmetric ionic fluids of equisized hard spheres by generalizing the Debye-Hückel approach combined with ionic association, cluster solvation by charged ions, and hard-core interactions, following lines developed by Fisher and Levin for the 1:1 case (i.e., the restricted primitive model). Explicit analytical calculations for 2:1 and 3:1 systems account for ionic association into dimers, trimers, and tetramers and subsequent multipolar cluster solvation. The reduced critical temperatures, Tc* (normalized by z ), decrease with charge asymmetry, while the critical densities increase rapidly with z . The results compare favorably with simulations and represent a distinct improvement over all current theories such as the mean spherical approximation, symmetric Poisson-Boltzmann theory, etc. For z?1 , the interphase Galvani (or absolute electrostatic) potential difference, ??(T) , between coexisting liquid and vapor phases is calculated and found to vanish as ?T-Tc?? when T?Tc —with, since our approximations are classical, ?=(1)/(2) . Above Tc , the compressibility maxima and so-called k -inflection loci (which aid the fast and accurate determination of the critical parameters) are found to exhibit a strong z dependence.

Aqua, Jean-Noël; Banerjee, Shubho; Fisher, Michael E.

2005-10-01

48

Local order variations in confined hard-sphere fluids  

NASA Astrophysics Data System (ADS)

Pair distributions of fluids confined between two surfaces at close distance are of fundamental importance for a variety of physical, chemical, and biological phenomena, such as interactions between macromolecules in solution, surface forces, and diffusion in narrow pores. However, in contrast to bulk fluids, properties of inhomogeneous fluids are seldom studied at the pair-distribution level. Motivated by recent experimental advances in determining anisotropic structure factors of confined fluids, we analyze theoretically the underlying anisotropic pair distributions of the archetypical hard-sphere fluid confined between two parallel hard surfaces using first-principles statistical mechanics of inhomogeneous fluids. For this purpose, we introduce an experimentally accessible ensemble-averaged local density correlation function and study its behavior as a function of confining slit width. Upon increasing the distance between the confining surfaces, we observe an alternating sequence of strongly anisotropic versus more isotropic local order. The latter is due to packing frustration of the spherical particles. This observation highlights the importance of studying inhomogeneous fluids at the pair-distribution level.

Nyga?rd, Kim; Sarman, Sten; Kjellander, Roland

2013-10-01

49

Enhanced stability of layered phases in parallel hard spherocylinders due to addition of hard spheres  

E-print Network

.30.Cz I. INTRODUCTION In hard particle fluids all allowed configurations have the same energy . In microphase separation the system starts sepa- rating into liquidlike regions that are rich in either spheres or rods. However, unlike bulk demixing, where rod and sphere rich regions grow until reaching macroscopic

Fraden, Seth

50

Physics of Hard Spheres Experiment: Significant and Quantitative Findings Made  

NASA Technical Reports Server (NTRS)

Direct examination of atomic interactions is difficult. One powerful approach to visualizing atomic interactions is to study near-index-matched colloidal dispersions of microscopic plastic spheres, which can be probed by visible light. Such spheres interact through hydrodynamic and Brownian forces, but they feel no direct force before an infinite repulsion at contact. Through the microgravity flight of the Physics of Hard Spheres Experiment (PHaSE), researchers have sought a more complete understanding of the entropically driven disorder-order transition in hard-sphere colloidal dispersions. The experiment was conceived by Professors Paul M. Chaikin and William B. Russel of Princeton University. Microgravity was required because, on Earth, index-matched colloidal dispersions often cannot be density matched, resulting in significant settling over the crystallization period. This settling makes them a poor model of the equilibrium atomic system, where the effect of gravity is truly negligible. For this purpose, a customized light-scattering instrument was designed, built, and flown by the NASA Glenn Research Center at Lewis Field on the space shuttle (shuttle missions STS 83 and STS 94). This instrument performed both static and dynamic light scattering, with sample oscillation for determining rheological properties. Scattered light from a 532- nm laser was recorded either by a 10-bit charge-coupled discharge (CCD) camera from a concentric screen covering angles of 0 to 60 or by sensitive avalanche photodiode detectors, which convert the photons into binary data from which two correlators compute autocorrelation functions. The sample cell was driven by a direct-current servomotor to allow sinusoidal oscillation for the measurement of rheological properties. Significant microgravity research findings include the observation of beautiful dendritic crystals, the crystallization of a "glassy phase" sample in microgravity that did not crystallize for over 1 year in 1g (Earth's gravity), and the emergence of face-centered-cubic (FCC) crystals late in the coarsening process (as small crystallites lost particles to the slow ripening of large crystallites). Significant quantitative findings from the microgravity experiments have been developed describing complex interactions among crystallites during the growth process, as concentration fields overlap in the surrounding disordered phase. Time-resolved Bragg scattering under microgravity captures one effect of these interactions quite conclusively for the sample at a volume fraction of 0.528. From the earliest time until the sample is almost fully crystalline, the size and overall crystallinity grow monotonically, but the number of crystallites per unit volume (number density) falls. Apparently nucleation is slower than the loss of crystallites because of the transfer of particles from small to large crystals. Thus, coarsening occurs simultaneously with growth, rather than following the completion of nucleation and growth as is generally assumed. In the same sample, an interesting signature appears in the apparent number density of crystallites and the volume fraction within the crystallites shortly before full crystallinity is reached. A brief upturn in both indicates the creation of more domains of the size of the average crystallite simultaneous with the compression of the crystallites. Only the emergence of dendritic arms offers a reasonable explanation. The arms would be "seen" by the light scattering as separate domains whose smaller radii of curvature would compress the interior phase. In fiscal year 1999, numerous papers, a doctoral dissertation, and the PHaSE final report were produced. Although this flight project has been completed, plans are in place for a follow-on colloid experiment by Chaikin and Russel that employs a light microscope within Glenn's Fluids and Combustion Facility on the International Space Station. PHaSE is providing us with a deeper understanding of the nure of phase transitions. The knowledge derived has added to the understandin

Doherty, Michael P.

2000-01-01

51

Clustering and gelation of hard spheres induced by the Pickering effect  

E-print Network

A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, Science 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.

Andrea Fortini

2012-03-23

52

Solidification of a colloidal hard sphere like model system approaching and crossing the glass transition.  

PubMed

We investigated the process of vitrification and crystallization in a model system of colloidal hard spheres. The kinetics of the solidification process was measured using time resolved static light scattering, while the time evolution of the dynamic properties was determined using time resolved dynamic light scattering. By performing further analysis we confirm that solidification of hard sphere colloids is mediated by precursors. Analyzing the dynamic properties we can show that the long time dynamics and thus the shear rigidity of the metastable melt is highly correlated with the number density of solid clusters (precursors) nucleated. In crystallization these objects convert into highly ordered crystals whereas in the case of vitrification this conversion is blocked and the system is (temporarily) locked in the metastable precursor state. From the early stages of solidification one cannot clearly conclude whether the melt will crystallize or vitrify. Furthermore our data suggests that colloidal hard sphere glasses can crystallize via homogeneous nucleation. PMID:24926966

Franke, Markus; Golde, Sebastian; Schöpe, Hans Joachim

2014-08-01

53

Clustering and gelation of hard spheres induced by the Pickering effect.  

PubMed

A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, Science 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids. PMID:22680411

Fortini, Andrea

2012-04-01

54

Dynamic equivalences in the hard-sphere dynamic universality class.  

PubMed

We perform systematic simulation experiments on model systems with soft-sphere repulsive interactions to test the predicted dynamic equivalence between soft-sphere liquids with similar static structure. For this we compare the simulated dynamics (mean squared displacement, intermediate scattering function, ?-relaxation time, etc.) of different soft-sphere systems, between them and with the hard-sphere liquid. We then show that the referred dynamic equivalence does not depend on the (Newtonian or Brownian) nature of the microscopic laws of motion of the constituent particles, and hence, applies independently to colloidal and to atomic simple liquids. Finally, we verify another more recently proposed dynamic equivalence, this time between the long-time dynamics of an atomic liquid and its corresponding Brownian fluid (i.e., the Brownian system with the same interaction potential). PMID:24229166

López-Flores, Leticia; Ruíz-Estrada, Honorina; Chávez-Páez, Martín; Medina-Noyola, Magdaleno

2013-10-01

55

Dynamic equivalences in the hard-sphere dynamic universality class  

NASA Astrophysics Data System (ADS)

We perform systematic simulation experiments on model systems with soft-sphere repulsive interactions to test the predicted dynamic equivalence between soft-sphere liquids with similar static structure. For this we compare the simulated dynamics (mean squared displacement, intermediate scattering function, ?-relaxation time, etc.) of different soft-sphere systems, between them and with the hard-sphere liquid. We then show that the referred dynamic equivalence does not depend on the (Newtonian or Brownian) nature of the microscopic laws of motion of the constituent particles, and hence, applies independently to colloidal and to atomic simple liquids. Finally, we verify another more recently proposed dynamic equivalence, this time between the long-time dynamics of an atomic liquid and its corresponding Brownian fluid (i.e., the Brownian system with the same interaction potential).

López-Flores, Leticia; Ruíz-Estrada, Honorina; Chávez-Páez, Martín; Medina-Noyola, Magdaleno

2013-10-01

56

Comparison of structure and transport properties of concentrated hard and soft sphere fluids.  

PubMed

Using Newtonian and Brownian dynamics simulations, the structural and transport properties of hard and soft spheres have been studied. The soft spheres were modeled using inverse power potentials (V approximately r(-n), with 1n the potential softness). Although, at constant density, the pressure, diffusion coefficient, and viscosity depend on the particle softness up to extremely high values of n, we show that scaling the density with the freezing point for every system effectively collapses these parameters for n > or = 18 (including hard spheres) for large densities. At the freezing points, the long range structure of all systems is identical, when length is measured in units of the interparticle distance, but differences appear at short distances (due to the different shapes of the interaction potential). This translates into differences at short times in the velocity and stress autocorrelation functions, although they concur to give the same value of the corresponding transport coefficient (for the same density to freezing ratio); the microscopic dynamics also affects the short time behavior of the correlation functions and absolute values of the transport coefficients, but the same scaling with the freezing density works for Newtonian or Brownian dynamics. For hard spheres, the short time behavior of the stress autocorrelation function has been studied in detail, confirming quantitatively the theoretical forms derived for it. PMID:19425812

Lange, Erik; Caballero, Jose B; Puertas, Antonio M; Fuchs, Matthias

2009-05-01

57

A density functional calculation of the liquid-solid phase diagram of a charged-hard-spheres model of a salt  

Microsoft Academic Search

The density functional theory of freezing is applied to the calculation of the liquid-solid phase diagram of the restricted primitive model of a molten salt. As the temperature is lowered, the structure of the solid changes from a disordered, face-centred cubic (FCC) structure to a caesium chloride (CsCl) structure, with a triple point at about 2500 K for ions of

J.-L. Barrat

1987-01-01

58

Density-Temperature-Softness Scaling of the Dynamics of Glass-forming Soft-sphere Liquids  

E-print Network

The principle of dynamic equivalence between soft-sphere and hard-sphere fluids [Phys. Rev. E \\textbf{68}, 011405 (2003)] is employed to describe the interplay of the effects of varying the density n, the temperature T, and the softness (characterized by a softness parameter {\

Pedro E. Ramírez-González; Leticia López-Flores; Heriberto Acuña-Campa; Magdaleno Medina-Noyola

2011-03-24

59

Complex oscillatory yielding of model hard-sphere glasses.  

PubMed

The yielding behavior of hard sphere glasses under large-amplitude oscillatory shear has been studied by probing the interplay of Brownian motion and shear-induced diffusion at varying oscillation frequencies. Stress, structure and dynamics are followed by experimental rheology and Browian dynamics simulations. Brownian-motion-assisted cage escape dominates at low frequencies while escape through shear-induced collisions at high ones, both related with a yielding peak in G''. At intermediate frequencies a novel, for hard sphere glasses, double peak in G'' is revealed reflecting both mechanisms. At high frequencies and strain amplitudes a persistent structural anisotropy causes a stress drop within the cycle after strain reversal, while higher stress harmonics are minimized at certain strain amplitudes indicating an apparent harmonic response. PMID:23679786

Koumakis, N; Brady, J F; Petekidis, G

2013-04-26

60

Complex Oscillatory Yielding of Model Hard-Sphere Glasses  

NASA Astrophysics Data System (ADS)

The yielding behavior of hard sphere glasses under large-amplitude oscillatory shear has been studied by probing the interplay of Brownian motion and shear-induced diffusion at varying oscillation frequencies. Stress, structure and dynamics are followed by experimental rheology and Browian dynamics simulations. Brownian-motion-assisted cage escape dominates at low frequencies while escape through shear-induced collisions at high ones, both related with a yielding peak in G''. At intermediate frequencies a novel, for hard sphere glasses, double peak in G'' is revealed reflecting both mechanisms. At high frequencies and strain amplitudes a persistent structural anisotropy causes a stress drop within the cycle after strain reversal, while higher stress harmonics are minimized at certain strain amplitudes indicating an apparent harmonic response.

Koumakis, N.; Brady, J. F.; Petekidis, G.

2013-04-01

61

Anomalous dynamics at the hard-sphere glass transition.  

PubMed

We use X-ray photon correlation spectroscopy to study the dynamics of hard sphere suspensions and report the emergence of ergodicity restoring anomalous intermittent relaxation modes in the highest concentration suspension that is estimated to be above the glass transition concentration. We associate these phenomena with non-thermal stress induced relaxations and support our interpretation by a direct comparison of the results with predictions of the mode coupling theory. PMID:25255771

Kwa?niewski, Pawe?; Fluerasu, Andrei; Madsen, Anders

2014-10-15

62

Structure characterization of hard sphere packings in amorphous and crystalline states  

E-print Network

,13 , or the amorphous solid phase transition14. One of the main reasons for us- ing the hard-sphere model over classical The hard-sphere particle interaction limit is a tremendously versatile physical model, being widely used with the nucleation and growth of the crystalline phase11. Hard-sphere models are known to successfully reproduce

Luding, Stefan

63

Passive and active microrheology of hard-sphere colloids.  

PubMed

We performed passive and active microrheology using probe particles in a bath of well-characterized, model hard-sphere colloids in the fluid state over the whole range of volume fractions below the glass transition. The probe and bath particles have nearly the same size. Passive tracking of probe particles yields short-time self-diffusion coefficients. Comparison with literature data demonstrates that the interaction between probe and bath particles is hard-sphere-like. The short-time diffusivities yield one set of microviscosities as a function of volume fraction, which agrees with previous macrorheological measurements of the high-frequency viscosity of hard-sphere colloids. Using optical tweezers, we measure the force on a trapped probe particle as the rest of the sample is translated at constant velocity. This yields a second set of microviscosities at high Péclet numbers. These agree with previous macrorheological measurements of the high-shear viscosity of similar colloids, at shear-rates below the onset of shear-thickening. PMID:19673070

Wilson, L G; Harrison, A W; Schofield, A B; Arlt, J; Poon, W C K

2009-03-26

64

Self-consistent phonon theory of the crystallization and elasticity of attractive hard spheres.  

PubMed

We propose an Einstein-solid, self-consistent phonon theory for the crystal phase of hard spheres that interact via short-range attractions. The approach is first tested against the known behavior of hard spheres, and then applied to homogeneous particles that interact via short-range square well attractions and the Baxter adhesive hard sphere model. Given the crystal symmetry, packing fraction, and strength and range of attractive interactions, an effective harmonic potential experienced by a particle confined to its Wigner-Seitz cell and corresponding mean square vibrational amplitude are self-consistently calculated. The crystal free energy is then computed and, using separate information about the fluid phase free energy, phase diagrams constructed, including a first-order solid-solid phase transition and its associated critical point. The simple theory qualitatively captures all the many distinctive features of the phase diagram (critical and triple point, crystal-fluid re-entrancy, low-density coexistence curve) as a function of attraction range, and overall is in good semi-quantitative agreement with simulation. Knowledge of the particle localization length allows the crystal shear modulus to be estimated based on elementary ideas. Excellent predictions are obtained for the hard sphere crystal. Expanded and condensed face-centered cubic crystals are found to have qualitatively different elastic responses to varying attraction strength or temperature. As temperature increases, the expanded entropic solid stiffens, while the energy-controlled, fully-bonded dense solid softens. PMID:23464163

Shin, Homin; Schweizer, Kenneth S

2013-02-28

65

On the jamming phase diagram for frictionless hard-sphere packings.  

PubMed

We computer-generated monodisperse and polydisperse frictionless hard-sphere packings of 10(4) particles with log-normal particle diameter distributions in a wide range of packing densities ? (for monodisperse packings ? = 0.46-0.72). We equilibrated these packings and searched for their inherent structures, which for hard spheres we refer to as closest jammed configurations. We found that the closest jamming densities ?(J) for equilibrated packings with initial densities ? ? 0.52 are located near the random close packing limit ?(RCP); the available phase space is dominated by basins of attraction that we associate with liquid. ?(RCP) depends on the polydispersity and is ? 0.64 for monodisperse packings. For ? > 0.52, ?(J) increases with ?; the available phase space is dominated by basins of attraction that we associate with glass. When ? reaches the ideal glass transition density ?(g), ?(J) reaches the ideal glass density (the glass close packing limit) ?(GCP), so that the available phase space is dominated at ?(g) by the basin of attraction of the ideal glass. For packings with sphere diameter standard deviation ? = 0.1, ?(GCP) ? 0.655 and ?(g) ? 0.59. For monodisperse and slightly polydisperse packings, crystallization is superimposed on these processes: it starts at the melting transition density ?(m) and ends at the crystallization offset density ?(off). For monodisperse packings, ?(m) ? 0.54 and ?(off) ? 0.61. We verified that the results for polydisperse packings are independent of the generation protocol for ? ? ?(g). PMID:25155116

Baranau, Vasili; Tallarek, Ulrich

2014-10-21

66

Parameterizing the surface free energy and excess adsorption of a hard-sphere fluid at a planar hard wall  

E-print Network

he inhomogeneous structure of a fluid at a wall can be characterized in several ways. Within a thermodynamic description the surface free energy $\\gamma$ and the excess adsorption $\\Gamma$ are of central importance. For theoretical studies closed expression of $\\gamma$ and $\\Gamma$ can be very valuable; however, even for a well-studied model system such as a hard-sphere fluid at a planar hard wall, the accuracy of existing expressions for $\\gamma$ and $\\Gamma$, compared to precise computer simulation data, can still be improved. Here, we compare several known expressions for $\\gamma$ and $\\Gamma$ to the most precise computer simulation data. While good agreement is generally found at low to intermediate fluid densities, the existing parameterizations show significant deviation at high density. In this work, we propose new parameterizations for $\\gamma$ and $\\Gamma$ that agree with the simulation data within statistical error over the entire fluid density range.

Davidchack, Ruslan L; Roth, Roland

2014-01-01

67

The velocity autocorrelation function of nanoparticles in a hard-sphere molecular system  

Microsoft Academic Search

The diffusion of nanoparticles in a dense molecular medium representing a fluid (liquid or gas) composed of hard absolutely\\u000a elastic spheres was studied by the molecular dynamics method in a broad range of the medium density. It was established that\\u000a relaxation of the velocity autocorrelation function of the particles is well described by a superposition of two exponents\\u000a with different

V. Ya. Rudyak; G. V. Kharlamov; A. A. Belkin

2000-01-01

68

Simulation of Gas-Solid Flow in Vertical Pipe by Hard-Sphere Model  

Microsoft Academic Search

This article presents a two-dimensional study of the gas-solid flow in a vertical pneumatic conveying pipe by means of a hard-sphere model where the motion of individual particles can be traced. Simulations were performed for a pipe of height 0.9 m and width 0.06 m, with air as gas phase and particles of density 900 kg\\/m and diameter 0.003 m as solid phase.

J. OUYANG; A. B. YU; R. H. PAN

2005-01-01

69

Solid phase in helium 4 based on the hard-sphere model  

Microsoft Academic Search

In this letter we extended our numerical computations of a hard-sphere Boson system to the solid phase density. These computations are based on a former paper [1] devoted to the superfluid phase. The core diameter was taken as 2.1 Å and the trial wave function used was a simple pair-wise form as used in the liquid phase. The crystal structure

K. W. Wong

1969-01-01

70

Density-temperature-softness scaling of the dynamics of glass-forming soft-sphere liquids.  

PubMed

We employ the principle of dynamic equivalence between soft-sphere and hard-sphere fluids [Phys. Rev. E 68, 011405 (2003)] to describe the interplay of the effects of varying the density n, the temperature T, and the softness (characterized by a softness parameter ?(-1)) on the dynamics of glass-forming soft-sphere liquids in terms of simple scaling rules. The main prediction is the existence of a dynamic universality class associated with the hard-sphere fluid, constituted by the soft-sphere systems whose dynamic parameters depend on n, T, and ? only through the reduced density n*?n?(HS)(T*,?). A number of scaling properties observed in recent experiments and simulations involving glass-forming fluids with repulsive short-range interactions are found to be a direct manifestation of this general dynamic equivalence principle. PMID:22107301

Ramírez-González, Pedro E; López-Flores, Leticia; Acuña-Campa, Heriberto; Medina-Noyola, Magdaleno

2011-10-01

71

Fifth to eleventh virial coefficients of hard spheres  

NASA Astrophysics Data System (ADS)

Virial coefficients Bn of three-dimensional hard spheres are reported for n=5 to 11, with precision exceeding that presently available in the literature. Calculations are performed using the recursive method due to Wheatley, and a binning approach is proposed to allow more flexibility in where computational effort is directed in the calculations. We highlight the difficulty as a general measure that quantifies performance of an algorithm that computes a stochastic average and show how it can be used as the basis for optimizing such calculations.

Schultz, Andrew J.; Kofke, David A.

2014-08-01

72

Hard-sphere interactions in velocity jump models  

E-print Network

Group-level behaviour of particles undergoing a velocity jump process with hard-sphere interactions is investigated. We derive $N$-particle transport equations that include the possibility of collisions between particles and apply different approximation techniques to get expressions for the dependence of the collective diffusion coefficient on the number of particles and their diameter. The derived approximations are compared with numerical results obtained from individual-based simulations. The theoretical results compare well with Monte Carlo simulations providing the excluded volume fraction is small.

Franz, Benjamin; Yates, Christian; Erban, Radek

2014-01-01

73

Structure of the Hard Sphere Solid Charles Radin* and Lorenzo Sadun  

E-print Network

.--We are interested in the solid phase of the hard sphere model, a phase which is generally agreed to exist basedStructure of the Hard Sphere Solid Charles Radin* and Lorenzo Sadun Department of Mathematics of each sphere impinges slightly less on the motion of its nearest neighbors than in the other structures

Radin, Charles

74

THE STRUCTURE OF THE HARD SPHERE SOLID Charles Radin * and Lorenzo Sadun **  

E-print Network

. Introduction. We are interested in the solid phase of the hard sphere gas model, a phase which is generallyTHE STRUCTURE OF THE HARD SPHERE SOLID by Charles Radin * and Lorenzo Sadun ** Abstract We show between motions of nearest neighbors. In the HCP structure random motion of each sphere impinges slightly

75

A Monte Carlo study of the freezing transition of hard spheres  

NASA Astrophysics Data System (ADS)

A simulation method for fluid-solid transitions, which is based on a modification of the constrained cell model of Hoover and Ree, is developed and tested on a system of hard spheres. In the fully occupied constrained cell model, each particle is confined in its own Wigner-Seitz cell. Constant-pressure simulations of the constrained cell model for a system of hard spheres indicate a point of mechanical instability at a density which is about 64% of the density at the close packed limit. Below that point, the solid is mechanically unstable since without the confinement imposed by the cell walls it will disintegrate to a disordered, fluid-like phase. Hoover and Ree proposed a modified cell model by introducing an external field of variable strength. High values of the external field variable favor configurations with one particle per cell and thus stabilize the solid phase. In this work, the modified cell model of a hard-sphere system is simulated under constant-pressure conditions using tempering and histogram reweighting techniques. The simulations indicate that as the strength of the field is reduced, the transition from the solid to the fluid phase is continuous below the mechanical instability point and discontinuous above. The fluid-solid transition of the hard-sphere system is determined by analyzing the field-induced fluid-solid transition of the modified cell model in the limit in which the external field vanishes. The coexistence pressure and densities are obtained through finite-size scaling techniques and are in good accord with previous estimates.

Nayhouse, Michael; Amlani, Ankur M.; Orkoulas, G.

2011-08-01

76

A Monte Carlo study of the freezing transition of hard spheres.  

PubMed

A simulation method for fluid-solid transitions, which is based on a modification of the constrained cell model of Hoover and Ree, is developed and tested on a system of hard spheres. In the fully occupied constrained cell model, each particle is confined in its own Wigner-Seitz cell. Constant-pressure simulations of the constrained cell model for a system of hard spheres indicate a point of mechanical instability at a density which is about 64% of the density at the close packed limit. Below that point, the solid is mechanically unstable since without the confinement imposed by the cell walls it will disintegrate to a disordered, fluid-like phase. Hoover and Ree proposed a modified cell model by introducing an external field of variable strength. High values of the external field variable favor configurations with one particle per cell and thus stabilize the solid phase. In this work, the modified cell model of a hard-sphere system is simulated under constant-pressure conditions using tempering and histogram reweighting techniques. The simulations indicate that as the strength of the field is reduced, the transition from the solid to the fluid phase is continuous below the mechanical instability point and discontinuous above. The fluid-solid transition of the hard-sphere system is determined by analyzing the field-induced fluid-solid transition of the modified cell model in the limit in which the external field vanishes. The coexistence pressure and densities are obtained through finite-size scaling techniques and are in good accord with previous estimates. PMID:21795778

Nayhouse, Michael; Amlani, Ankur M; Orkoulas, G

2011-08-17

77

Branching points in the low-temperature dipolar hard sphere fluid.  

PubMed

In this contribution, we investigate the low-temperature, low-density behaviour of dipolar hard-sphere (DHS) particles, i.e., hard spheres with dipoles embedded in their centre. We aim at describing the DHS fluid in terms of a network of chains and rings (the fundamental clusters) held together by branching points (defects) of different nature. We first introduce a systematic way of classifying inter-cluster connections according to their topology, and then employ this classification to analyse the geometric and thermodynamic properties of each class of defects, as extracted from state-of-the-art equilibrium Monte Carlo simulations. By computing the average density and energetic cost of each defect class, we find that the relevant contribution to inter-cluster interactions is indeed provided by (rare) three-way junctions and by four-way junctions arising from parallel or anti-parallel locally linear aggregates. All other (numerous) defects are either intra-cluster or associated to low cluster-cluster interaction energies, suggesting that these defects do not play a significant part in the thermodynamic description of the self-assembly processes of dipolar hard spheres. PMID:24116579

Rovigatti, Lorenzo; Kantorovich, Sofia; Ivanov, Alexey O; Tavares, José Maria; Sciortino, Francesco

2013-10-01

78

Branching points in the low-temperature dipolar hard sphere fluid  

NASA Astrophysics Data System (ADS)

In this contribution, we investigate the low-temperature, low-density behaviour of dipolar hard-sphere (DHS) particles, i.e., hard spheres with dipoles embedded in their centre. We aim at describing the DHS fluid in terms of a network of chains and rings (the fundamental clusters) held together by branching points (defects) of different nature. We first introduce a systematic way of classifying inter-cluster connections according to their topology, and then employ this classification to analyse the geometric and thermodynamic properties of each class of defects, as extracted from state-of-the-art equilibrium Monte Carlo simulations. By computing the average density and energetic cost of each defect class, we find that the relevant contribution to inter-cluster interactions is indeed provided by (rare) three-way junctions and by four-way junctions arising from parallel or anti-parallel locally linear aggregates. All other (numerous) defects are either intra-cluster or associated to low cluster-cluster interaction energies, suggesting that these defects do not play a significant part in the thermodynamic description of the self-assembly processes of dipolar hard spheres.

Rovigatti, Lorenzo; Kantorovich, Sofia; Ivanov, Alexey O.; Tavares, José Maria; Sciortino, Francesco

2013-10-01

79

The Boltzmann-Grad Limit of a Hard Sphere System: Analysis of the Correlation Error  

E-print Network

We present a quantitative analysis of the Boltzmann-Grad (low-density) limit of a hard sphere system. We introduce and study a set of functions (correlation errors) measuring the deviations in time from the statistical independence of particles (propagation of chaos). In the context of the BBGKY hierarchy, a correlation error of order $k$ measures the event where $k$ tagged particles are connected by a chain of interactions preventing the factorization. We prove that, provided $k$ is not too large, such an error flows to zero with the hard spheres diameter $\\varepsilon$, for short times, as $\\varepsilon^{\\gamma k}$, for some $\\gamma>0$. This requires a new analysis of many-recollision events, and improves previous estimates of high order correlation functions.

Mario Pulvirenti; Sergio Simonella

2014-05-19

80

Compact Collision Kernels for Hard Sphere and Coulomb Cross Sections; Fokker-Planck Coefficients  

SciTech Connect

A compact collision kernel is derived for both hard sphere and Coulomb cross sections. The difference between hard sphere interaction and Coulomb interaction is characterized by a parameter {eta}. With this compact collision kernel, the calculation of Fokker-Planck coefficients can be done for both the Coulomb and hard sphere interactions. The results for arbitrary order Fokker-Planck coefficients are greatly simplified. An alternate form for the Coulomb logarithm is derived with concern to the temperature relaxation in a binary plasma.

Chang Yongbin; Shizgal, Bernie D. [Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1 (Canada)

2008-12-31

81

Nature of the breakdown in the Stokes-Einstein relationship in a hard sphere fluid  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations of high density hard sphere fluids clearly show a breakdown of the Stokes-Einstein equation (SE). This result has been conjectured to be due to the presence of mobile particles, i.e., ones which have the propensity to "hop" distances that are integer multiples of the interparticle distance. We conclusively show that the sedentary particles, i.e., ones complementary to the "hoppers," obey the SE relationship to a good approximation, even though the fluid as a whole violates the SE equation at high densities. These results support the notion that the unusual diffusive behavior of supercooled liquids is dominated by the hopping particles.

Kumar, Sanat K.; Szamel, Grzegorz; Douglas, Jack F.

2006-06-01

82

A simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres  

E-print Network

A recent proposal in which the equation of state of a polydisperse hard-sphere mixture is mapped onto that of the one-component fluid is extrapolated beyond the freezing point to estimate the jamming packing fraction $\\phi_\\text{J}$ of the polydisperse system as a simple function of $M_1M_3/M_2^2$, where $M_k$ is the $k$th moment of the size distribution. An analysis of experimental and simulation data of $\\phi_\\text{J}$ for a large number of different mixtures shows a remarkable general agreement with the theoretical estimate. To give extra support to the procedure, simulation data for seventeen mixtures in the high-density region are used to infer the equation of state of the pure hard-sphere system in the metastable region. An excellent collapse of the inferred curves up to the glass transition and a significant narrowing of the different out-of-equilibrium glass branches all the way to jamming are observed. Thus, the present approach provides an extremely simple criterion to unify in a common framework and to give coherence to data coming from very different polydisperse hard-sphere mixtures.

Andrés Santos; Santos B. Yuste; Mariano López de Haro; Gerardo Odriozola; Vitaliy Ogarko

2014-02-14

83

Simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres  

NASA Astrophysics Data System (ADS)

A recent proposal in which the equation of state of a polydisperse hard-sphere mixture is mapped onto that of the one-component fluid is extrapolated beyond the freezing point to estimate the jamming packing fraction ?J of the polydisperse system as a simple function of M1M3/M22, where Mk is the kth moment of the size distribution. An analysis of experimental and simulation data of ?J for a large number of different mixtures shows a remarkable general agreement with the theoretical estimate. To give extra support to the procedure, simulation data for seventeen mixtures in the high-density region are used to infer the equation of state of the pure hard-sphere system in the metastable region. An excellent collapse of the inferred curves up to the glass transition and a significant narrowing of the different out-of-equilibrium glass branches all the way to jamming are observed. Thus, the present approach provides an extremely simple criterion to unify in a common framework and to give coherence to data coming from very different polydisperse hard-sphere mixtures.

Santos, Andrés; Yuste, Santos B.; López de Haro, Mariano; Odriozola, Gerardo; Ogarko, Vitaliy

2014-04-01

84

Tunable long range forces mediated by self-propelled colloidal hard spheres  

E-print Network

Most colloidal interactions can be tuned by changing properties of the medium. Here we show that activating the colloidal particles with random self-propulsions can mediate giant effective interactions between the objects thereby. By performing Brownian dynamics simulations, we systematically study the effective force between two hard walls in a 2D suspension of self-propelled (active)colloidal hard spheres. We find that at relatively high densities, the active colloidal hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing the density of active colloids, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction dominates the effective interaction between the two walls. These two long range forces suppress each other, and the effective interaction can be tuned from a long range repulsion into a long range attraction by reducing the density of active particles. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.

Ran Ni; Martien A. Cohen Stuart; Peter G. Bolhuis

2014-03-06

85

Most stable structure for hard spheres Hans Koch, # Charles Radin, + and Lorenzo Sadun #  

E-print Network

of the hard sphere model in the late 1950's (see [1] for a review) showed a liquid/solid phase transition of Mathematics, University of Texas, Austin, TX 78712 (Dated: April 18, 2005) The hard sphere model is known in determining the internal structure of that solid phase, since the model is one of the simplest possible

86

Random-close packing limits for monodisperse and polydisperse hard spheres.  

PubMed

We investigate how the densities of inherent structures, which we refer to as the closest jammed configurations, are distributed for packings of 10(4) frictionless hard spheres. A computational algorithm is introduced to generate closest jammed configurations and determine corresponding densities. Closest jamming densities for monodisperse packings generated with high compression rates using Lubachevsky-Stillinger and force-biased algorithms are distributed in a narrow density range from ? = 0.634-0.636 to ?? 0.64; closest jamming densities for monodisperse packings generated with low compression rates converge to ?? 0.65 and grow rapidly when crystallization starts with very low compression rates. We interpret ?? 0.64 as the random-close packing (RCP) limit and ?? 0.65 as a lower bound of the glass close packing (GCP) limit, whereas ? = 0.634-0.636 is attributed to another characteristic (lowest typical, LT) density ?LT. The three characteristic densities ?LT, ?RCP, and ?GCP are determined for polydisperse packings with log-normal sphere radii distributions. PMID:24723008

Baranau, Vasili; Tallarek, Ulrich

2014-06-01

87

Direct calculation of the hard-sphere crystal/melt interfacial free energy  

E-print Network

.4 3 10 23 JH20862m 2 . In recent years, the primary theoretical approach to studying the structure and thermodynamics of the crystalH20862melt interface has been density-functional theory (DFT) [11–16]. For these studies, the hard-sphere system has....10.–a, 05.70.Np, 68.35.Md A detailed microscopic description of the interface be- tween a crystal and its melt is necessary for a full under- standing of such important phenomena as homogeneous nucleation and crystal growth [1–3]. Computer simula- tion...

Laird, Brian Bostian; Davidchack, R. L.

2000-11-27

88

An efficient approach to approximating the pair distribution function of the inhomogeneous hard-sphere fluid  

E-print Network

We introduce an approximation for the pair distribution function of the inhomogeneous hard sphere fluid. Our approximation makes use of our recently published averaged pair distribution function at contact which has been shown to accurately reproduce the averaged pair distribution function at contact for inhomogeneous density distributions. This approach achieves greater computational efficiency than previous approaches by enabling the use of exclusively fixed-kernel convolutions and thus allowing an implementation using fast Fourier transforms. We compare results for our pair distribution approximation with two previously published works and Monte-Carlo simulation, showing favorable results.

Paho Lurie-Gregg; Jeff B. Schulte; David Roundy

2014-03-26

89

Using Fundamental Measure Theory to Treat the Correlation Function of the Inhomogeneous Hard-Sphere Fluid  

E-print Network

We investigate the value of the correlation function of an inhomogeneous hard-sphere fluid at contact. This quantity plays a critical role in Statistical Associating Fluid Theory (SAFT), which is the basis of a number of recently developed classical density functionals. We define two averaged values for the correlation function at contact, and derive formulas for each of them from the White Bear version of the Fundamental Measure Theory functional, using an assumption of thermodynamic consistency. We test these formulas, as well as two existing formulas against Monte Carlo simulations, and find excellent agreement between the Monte Carlo data and one of our averaged correlation functions.

Jeff Schulte; Patrick Kreitzberg; Chris Haglund; David Roundy

2012-08-31

90

Using fundamental measure theory to treat the correlation function of the inhomogeneous hard-sphere fluid  

NASA Astrophysics Data System (ADS)

We investigate the value of the correlation function of an inhomogeneous hard-sphere fluid at contact. This quantity plays a critical role in statistical associating fluid theory, which is the basis of a number of recently developed classical density functionals. We define two averaged values for the correlation function at contact and derive formulas for each of them from the White Bear version of the fundamental measure theory functional, using an assumption of thermodynamic consistency. We test these formulas, as well as two existing formulas, against Monte Carlo simulations and find excellent agreement between the Monte Carlo data and one of our averaged correlation functions.

Schulte, Jeff B.; Kreitzberg, Patrick A.; Haglund, Chris V.; Roundy, David

2012-12-01

91

Interfacial free energy calculation of a binary hard-sphere fluid at a hard wall by Gibbs-Cahn Integration  

NASA Astrophysics Data System (ADS)

The interfacial free energy, ?, of fluids at surfaces is a parameter that is central to a number of technologically important phenomena, such as wetting, nucleation and the stability and self assembly of colloidal particles in solution. In recent years, our group has developed techniques to determine ? from atomistic simulation. In this work, we apply one of these methods, Gibbs-Cahn Integration, to determine ? for a model two-component (binary) mixture of hard spheres. Molecular dynamics simulation is used to characterize a hard-sphere fluid mixture in a slit-pore confined geometry as packing fraction, mole fraction, and diameter ratio are varied. We find that recent theoretical predictions from the White Bear II classical density functional theory [Roth et al., J. Phys.: Condens. Matter, 18, 8413, (2006)] agree well with our computational results We also observe that, for this model system, the preferential adsorption of one particle species over the other contributes negligibly to the interfacial free energy at modest diameter ratios.

Kern, Jesse; Laird, Brian

2013-03-01

92

A CONTINUUM HARD-SPHERE MODEL OF PROTEIN ADSORPTION.  

PubMed

Protein adsorption plays a significant role in biological phenomena such as cell-surface interactions and the coagulation of blood. Two-dimensional random sequential adsorption (RSA) models are widely used to model the adsorption of proteins on solid surfaces. Continuum equations have been developed so that the results of RSA simulations can be used to predict the kinetics of adsorption. Recently, Brownian dynamics simulations have become popular for modeling protein adsorption. In this work a continuum model was developed to allow the results from a Brownian dynamics simulation to be used as the boundary condition in a computational fluid dynamics (CFD) simulation. Brownian dynamics simulations were used to model the diffusive transport of hard-sphere particles in a liquid and the adsorption of the particles onto a solid surface. The configuration of the adsorbed particles was analyzed to quantify the chemical potential near the surface, which was found to be a function of the distance from the surface and the fractional surface coverage. The near-surface chemical potential was used to derive a continuum model of adsorption that incorporates the results from the Brownian dynamics simulations. The equations of the continuum model were discretized and coupled to a CFD simulation of diffusive transport to the surface. The kinetics of adsorption predicted by the continuum model closely matched the results from the Brownian dynamics simulation. This new model allows the results from mesoscale simulations to be incorporated into micro- or macro-scale CFD transport simulations of protein adsorption in practical devices. PMID:23729843

Finch, Craig; Clarke, Thomas; Hickman, James J

2013-07-01

93

Short-time diffusion in concentrated bidisperse hard-sphere suspensions  

E-print Network

Diffusion in bidisperse Brownian hard-sphere suspensions is studied by Stokesian Dynamics (SD) computer simulations and a semi-analytical theoretical scheme for colloidal short-time dynamics, based on Beenakker and Mazur's method [Physica 120A, 388 (1983) & 126A, 349 (1984)]. Two species of hard spheres are suspended in an overdamped viscous solvent that mediates the salient hydrodynamic interactions among all particles. In a comprehensive parameter scan that covers various packing fractions and suspension compositions, we employ numerically accurate SD simulations to compute the initial diffusive relaxation of density modulations at the Brownian time scale, quantified by the partial hydrodynamic functions. A revised version of Beenakker and Mazur's $\\delta\\gamma$-scheme for monodisperse suspensions is found to exhibit surprisingly good accuracy, when simple rescaling laws are invoked in its application to mixtures. The so-modified $\\delta\\gamma$ scheme predicts hydrodynamic functions in very good agreement with our SD simulation results, for all densities from the very dilute limit up to packing fractions as high as $40\\%$.

Mu Wang; Marco Heinen; John F. Brady

2014-10-31

94

Structure and anomalous solubility for hard spheres in an associating lattice gas model  

E-print Network

Structure and anomalous solubility for hard spheres in an associating lattice gas model Marcia M://jcp.aip.org/about/rights_and_permissions #12;THE JOURNAL OF CHEMICAL PHYSICS 137, 064905 (2012) Structure and anomalous solubility for hard July 2012; published online 13 August 2012) In this paper we investigate the solubility of a hard

Barbosa, Marcia C. B.

95

Free-energy functional for freezing transitions: Hard sphere systems freezing into crystalline and amorphous structures  

E-print Network

A free-energy functional that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function has been used to investigate the freezing of a system of hard spheres into crystalline and amorphous structures. The freezing parameters for fluid-crystal transition have been found to be in very good agreement with the results found from simulations. We considered amorphous structures found from the molecular dynamics simulations at packing fractions $\\eta$ lower than the glass close packing fraction $\\eta_{J}$ and investigated their stability compared to that of a homogeneous fluid. The existence of free-energy minimum corresponding to a density distribution of overlapping Gaussians centered around an amorphous lattice depicts the deeply supercooled state with a heterogeneous density profile.

Swarn Lata Singh; Atul S. Bharadwaj; Yashwant Singh

2011-01-31

96

Kinetic coefficient for hard-sphere crystal growth from the melt  

E-print Network

Using molecular-dynamics simulation, we determine the magnitude and anisotropy of the kinetic coefficient (mu) for the crystal growth from the melt for the hard-sphere system through an analysis of equilibrium capillary fluctuations in interfacial...

Laird, Brian Bostian; Amini, M.

2006-11-24

97

Transport coefficients of a granular gas of inelastic rough hard spheres.  

PubMed

The Boltzmann equation for inelastic and rough hard spheres is considered as a model of a dilute granular gas. In this model, the collisions are characterized by constant coefficients of normal and tangential restitution, and hence the translational and rotational degrees of freedom are coupled. A normal solution to the Boltzmann equation is obtained by means of the Chapman-Enskog method for states near the homogeneous cooling state. The analysis is carried out to first order in the spatial gradients of the number density, the flow velocity, and the granular temperature. The constitutive equations for the momentum and heat fluxes and for the cooling rate are derived, and the associated transport coefficients are expressed in terms of the solutions of linear integral equations. For practical purposes, a first Sonine approximation is used to obtain explicit expressions of the transport coefficients as nonlinear functions of both coefficients of restitution and the moment of inertia. Known results for purely smooth inelastic spheres and perfectly elastic and rough spheres are recovered in the appropriate limits. PMID:25215731

Kremer, Gilberto M; Santos, Andrés; Garzó, Vicente

2014-08-01

98

Transport coefficients of a granular gas of inelastic rough hard spheres  

E-print Network

The Boltzmann equation for inelastic and rough hard spheres is considered as a model of a dilute granular gas. In this model, the collisions are characterized by constant coefficients of normal and tangential restitution and hence the translational and rotational degrees of freedom are coupled. A normal solution to the Boltzmann equation is obtained by means of the Chapman-Enskog method for states near the homogeneous cooling state. The analysis is carried out to first order in the spatial gradients of the number density, the flow velocity, and the granular temperature. The constitutive equations for the momentum and heat fluxes and for the cooling rate are derived and the associated transport coefficients are expressed in terms of the solutions of linear integral equations. For practical purposes, a first Sonine approximation is used to obtain explicit expressions of the transport coefficients as nonlinear functions of both coefficients of restitution and the moment of inertia. Known results for purely smooth inelastic spheres and perfectly elastic and rough spheres are recovered in the appropriate limits.

Gilberto M. Kremer; Andrés Santos; Vicente Garzó

2014-05-24

99

Hard-sphere solids near close packing: Testing theories for crystallization  

E-print Network

The freezing transition of hard spheres has been well described by various versions of density-functional theory (DFT). These theories should possess the close-packed crystal as a special limit, which represents an extreme testing ground for the quality of such liquid-state based theories. We therefore study the predictions of DFT for the structure and thermodynamics of the hard-sphere crystal in this limit. We examine the Ramakrishnan-Yussouff (RY) approximation and two variants of the fundamental-measure theory (FMT) developed by Rosenfeld and coworkers. We allow for general shapes of the density peaks, going beyond the common Gaussian approximation. In all cases we find that, upon approaching close packing, the peak width vanishes proportionally to the free distance a between the particles and the free energy depends logarithmically on a. However, different peak shapes and next-to-leading contributions to the free energy result from the different approximate functionals. For the RY theory, within the Gaussian approximation, we establish that the crystalline solutions form a closed loop with a stable and an unstable branch both connected to the close-packing point at a=0, consistent with the absence of a liquid-solid spinodal. That version of FMT that has previously been applied to freezing, predicts asymptotically step-like density profiles confined to the cells of self-consistent cell theory. But a recently suggested improved version which employs tensor weighted densities yields wider and almost Gaussian peaks which are shown to be in very good agreement with computer simulations.

Benito Groh; Bela Mulder

1999-07-08

100

Path integral Monte Carlo study of quantum-hard sphere solids  

NASA Astrophysics Data System (ADS)

A path integral study of the fcc, hcp, and bcc quantum hard-sphere solids is presented. Ranges of densities within the interval of reduced de Broglie wavelengths 0.2<=?B*<=0.8 have been analyzed using Monte Carlo simulations with Cao-Berne propagator. Energies, pressures, and structural quantities (pair radial correlation functions, centroid structure factors, and Steinhardt order parameters) have been computed. Also, applications of the Einstein crystal technique [L. M. Sesé, J. Chem. Phys. 126, 164508 (2007)] have been made to compute the free energies of the fcc and hcp solids. Some technical points related to the latter technique are discussed, and it is shown that these calculations produce consistent results with increasing sample sizes. The fluid-solid (fcc and hcp) equilibria have been studied, thus completing prior work by this author on the fluid-fcc equilibrium. Within the accuracy attained no significant differences between the relative stabilities of the fcc and hcp lattices have been detected. The bcc case stands apart from the other two lattices, as the simulations lead either to irregular lattices (two types) that keep some traces of bcc-memory, or to spontaneous transitions to hcp-like lattices. The latter transitions make manifestly clear the potential repercussions that the quantum hard-sphere behavior can have on solid-solid equilibria at low temperatures in real systems (e.g., helium).

Sesé, Luis M.

2013-07-01

101

Path integral Monte Carlo study of quantum-hard sphere solids.  

PubMed

A path integral study of the fcc, hcp, and bcc quantum hard-sphere solids is presented. Ranges of densities within the interval of reduced de Broglie wavelengths 0.2??B(*)?0.8 have been analyzed using Monte Carlo simulations with Cao-Berne propagator. Energies, pressures, and structural quantities (pair radial correlation functions, centroid structure factors, and Steinhardt order parameters) have been computed. Also, applications of the Einstein crystal technique [L. M. Sese?, J. Chem. Phys. 126, 164508 (2007)] have been made to compute the free energies of the fcc and hcp solids. Some technical points related to the latter technique are discussed, and it is shown that these calculations produce consistent results with increasing sample sizes. The fluid-solid (fcc and hcp) equilibria have been studied, thus completing prior work by this author on the fluid-fcc equilibrium. Within the accuracy attained no significant differences between the relative stabilities of the fcc and hcp lattices have been detected. The bcc case stands apart from the other two lattices, as the simulations lead either to irregular lattices (two types) that keep some traces of bcc-memory, or to spontaneous transitions to hcp-like lattices. The latter transitions make manifestly clear the potential repercussions that the quantum hard-sphere behavior can have on solid-solid equilibria at low temperatures in real systems (e.g., helium). PMID:23901988

Sesé, Luis M

2013-07-28

102

A simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres  

E-print Network

A recent proposal in which the equation of state of a polydisperse hard-sphere mixture is mapped onto that of the one-component fluid is extrapolated beyond the freezing point to estimate the jamming packing fraction $\\phi_\\text{J}$ of the polydisperse system as a simple function of $M_1M_3/M_2^2$, where $M_k$ is the $k$th moment of the size distribution. An analysis of experimental and simulation data of $\\phi_\\text{J}$ for a large number of different mixtures shows a remarkable general agreement with the theoretical estimate. To give extra support to the procedure, simulation data for seventeen mixtures in the high-density region are used to infer the equation of state of the pure hard-sphere system in the metastable region. A very good collapse of the inferred curves up to the glass transition and a significant narrowing thereinafter is observed. Thus, the present approach provides an extremely simple criterion to unify in a common framework and to give coherence to data coming from very different polydisp...

Santos, Andrés; de Haro, Mariano López; Odriozola, Gerardo; Ogarko, Vitaliy

2014-01-01

103

Inhomogeneous quasi-stationary state of dense fluid of inelastic hard spheres  

E-print Network

We study closed dense collections of hard spheres that collide inelastically with constant coefficient of normal restitution. We find inhomogeneous states (IS) where the density profile is spatially non-uniform but constant in time. The states are exact solutions of non-linear partial differential equations that describe the coupled distributions of density and temperature when inelastic losses of energy per collision are small. The derivation is performed without modelling the equations' coefficients that are unknown in the dense limit (such as the equation of state), using only their scaling form specific for hard spheres. The IS is exact non-linear state of this many-body system. It captures a fundamental property of inelastic collections of particles: the possibility of preserving non-uniform temperature via the interplay of inelastic cooling and heat conduction, generalizing previous results in the dilute case. We perform numerical simulations to demonstrate that arbitrary initial state evolves to the IS in the limit of long times where the container has the geometry of the channel. The evolution is like gas-liquid transition. The liquid condenses in a vanishing part of the total volume but takes most of the mass of the system. However, the gaseous phase, which mass grows only logarithmically with the system size, is relevant because its fast particles carry most of the energy of the system. Remarkably, the system self-organizes to dissipate no energy: the inelastic decay of energy is a power-law $[1+t/t_c]^{-2}$ where $t_c$ diverges in the thermodynamic limit. This behavior is caused by unusual spatial distribution of particles: on approach to one of the container's walls the density grows inversely with the distance. We discuss the relation of our results to the recently proposed finite-time singularity in other container's geometries.

Itzhak Fouxon

2014-02-13

104

Polymer-Enforced Crystallization of a Eutectic Binary Hard Sphere Mixture  

E-print Network

We prepared a buoyancy matched binary mixture of polydisperse polystyrene microgel spheres of size ratio 0.785 and at a volume fraction of 0.567 just below the kinetic glass transition. In line with theoretical expectations, a eutectic phase behavior was observed, but only a minor fraction of the samples crystallized at all. By adding a short non-adsorbing polymer we enforce inter-species fractionation into coexisting pure component crystals, which in turn also shows signs of intra-species fractionation. We show that in formerly inaccessible regions of the phase diagram binary hard sphere physics is made observable using attractive hard spheres.

Anna Kozina; Pedro Díaz-Leyva; Eckhard Bartsch; Thomas Palberg

2010-12-13

105

Transport coefficients of a granular gas of inelastic rough hard spheres  

E-print Network

The Boltzmann equation for inelastic and rough hard spheres is considered as a model of a dilute granular gas. In this model, the collisions are characterized by constant coefficients of normal and tangential restitution and hence the translational and rotational degrees of freedom are coupled. A normal solution to the Boltzmann equation is obtained by means of the Chapman-Enskog method for states near the homogeneous cooling state. The analysis is carried out to first order in the spatial gradients of the number density, the flow velocity, and the granular temperature. The constitutive equations for the momentum and heat fluxes and for the cooling rate are derived and the associated transport coefficients are expressed in terms of the solutions of linear integral equations. For practical purposes, a first Sonine approximation is used to obtain explicit expressions of the transport coefficients as nonlinear functions of both coefficients of restitution and the moment of inertia. Known results for purely smoot...

Kremer, Gilberto M; Garzó, Vicente

2014-01-01

106

Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition  

E-print Network

We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, $\\ta$, including equilibrium easurements above $\\phi_{\\rm c}$, the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above $\\phi_{\\rm c}$ and enters a new dynamical regime where $\\ta$ increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with $\\ta$, as found in molecular glass-formers close to the glass transition.

Giovanni Brambilla; Djamel El Masri; Matteo Pierno; Ludovic Berthier; Luca Cipelletti; George Petekidis; Andrew B. Schofield

2008-09-19

107

Different thermodynamic pathways to the solvation free energy of a spherical cavity in a hard sphere fluid  

E-print Network

This paper determines the excess free energy associated with the formation of a spherical cavity in a hard sphere fluid. The solvation free energy can be calculated by integration of the structural changes induced by inserting the cavity using a number of different exact thermodynamic pathways. We consider three such pathways, including a new density route derived here. Structural information about the nonuniform hard sphere fluid in the presence of a general external field is given by the recently developed hydrostatic linear response (HLR) integral equation. Use of the HLR results in the different pathways gives a generally accurate determination of the solvation free energy for cavities over a wide range of sizes, from zero to infinity. Results for a related method, the Gaussian Field Model, are also discussed.

Yng-gwei Chen; John D. Weeks

2003-01-19

108

A Thermodynamically-Consistent Non-Ideal Stochastic Hard-Sphere Fluid  

SciTech Connect

A grid-free variant of the Direct Simulation Monte Carlo (DSMC) method is proposed, named the Isotropic DSMC (I-DSMC) method, that is suitable for simulating collision-dominated dense fluid flows. The I-DSMC algorithm eliminates all grid artifacts from the traditional DSMC algorithm and is Galilean invariant and microscopically isotropic. The stochastic collision rules in I-DSMC are modified to introduce a non-ideal structure factor that gives consistent compressibility, as first proposed in [Phys. Rev. Lett. 101:075902 (2008)]. The resulting Stochastic Hard Sphere Dynamics (SHSD) fluid is empirically shown to be thermodynamically identical to a deterministic Hamiltonian system of penetrable spheres interacting with a linear core pair potential, well-described by the hypernetted chain (HNC) approximation. We develop a kinetic theory for the SHSD fluid to obtain estimates for the transport coefficients that are in excellent agreement with particle simulations over a wide range of densities and collision rates. The fluctuating hydrodynamic behavior of the SHSD fluid is verified by comparing its dynamic structure factor against theory based on the Landau-Lifshitz Navier-Stokes equations. We also study the Brownian motion of a nano-particle suspended in an SHSD fluid and find a long-time power-law tail in its velocity autocorrelation function consistent with hydrodynamic theory and molecular dynamics calculations.

Donev, A; Alder, B J; Garcia, A L

2009-08-03

109

Ratio of effective temperature to pressure controls the mobility of sheared hard spheres.  

PubMed

Using molecular dynamics simulations, we calculate fluctuations and responses for steadily sheared hard spheres over a wide range of packing fractions ? and shear strain rates ?[over ?], using two different methods to dissipate energy. To a good approximation, shear stress and density fluctuations are related to their associated response functions by a single effective temperature T(eff) that is equal to or larger than the kinetic temperature T(kin). We find a crossover in the relationship between the relaxation time ? and the the nondimensionalized effective temperature T(eff)/p?(3), where p is the pressure and ? is the sphere diameter. In the solid response regime, the behavior at a fixed packing fraction satisfies ? ???exp(-cp?(3)/T(eff)), where c depends weakly on ?, suggesting that the average local yield strain is controlled by the effective temperature in a way that is consistent with shear transformation zone theory. In the fluid response regime, the relaxation time depends on T(eff)/p?(3) as it depends on T(kin)/p?(3) in equilibrium. This regime includes both near-equilibrium conditions where T(eff)?T(kin) and far-from-equilibrium conditions where T(eff)?T(kin). We discuss the implications of our results for systems with soft repulsive interactions. PMID:22400573

Haxton, Thomas K

2012-01-01

110

Class of consistent fundamental-measure free energies for hard-sphere mixtures  

E-print Network

In fundamental-measure theories the bulk excess free-energy density of a hard-sphere fluid mixture is assumed to depend on the partial number densities ${\\rho_i}$ only through the four scaled-particle-theory variables ${\\xi_\\alpha}$, i.e., $\\Phi({\\rho_i})\\to\\Phi({\\xi_\\alpha})$. By imposing consistency conditions, it is proven here that such a dependence must necessarily have the form $\\Phi({\\xi_\\alpha})=-\\xi_0\\ln(1-\\xi_3)+\\Psi(y)\\xi_1\\xi_2/(1-\\xi_3)$, where $y\\equiv {\\xi_2^2}/{12\\pi \\xi_1 (1-\\xi_3)}$ is a scaled variable and $\\Psi(y)$ is an arbitrary dimensionless scaling function which can be determined from the free-energy density of the one-component system. Extension to the inhomogeneous case is achieved by standard replacements of the variables ${\\xi_\\alpha}$ by the fundamental-measure (scalar, vector, and tensor) weighted densities ${n_\\alpha(\\mathbf{r})}$. Comparison with computer simulations shows the superiority of this bulk free energy over the White Bear one.

Andrés Santos

2012-08-15

111

Cavity functions and association in models for weak electrolytes and sticky hard spheres  

NASA Astrophysics Data System (ADS)

Weak electrolytes and other association reactions are modeled as sticky spheres. An analysis of the density expansion, including the bridge diagrams, of the cavity functions yAB(L) for sticky hard spheres (charged or uncharged spheres binding at a distance L) leads to an approximation which provides the degree of association ? as the solution to a simple quadratic equation determined by the association constant K0 and the cavity function y0AB(L) for the reference system in which the chemical bonding between the reacting species has been turned off. Similar relations are assumed to hold when the bonding is directional and specific enough to lead only to the formation of dimers. Applications to the determination of the reference cavity functions for acetic acid and monochloro acetic acid from experimental data of the degree of association are discussed. In a discrete solvent, the approximation scheme for ? remains the same, except that the reference cavity function is scaled differently. Solvent medium effects on the association constant are shown to be related to the cavity function of the undissociated dimer in a pure solvent. An exponential approximation for the reference cavity function y0AB(L) is derived when the associating species are of the same size and the bonding is spherically symmetric. Expressions for the changes in the thermodynamic functions due to association are obtained analytically in terms of the degree of association and the reference cavity functions. The magnitude of the degree of association, calculated from the exponential approximation for y0AB(L), and its effect on the thermodynamic properties are different from what was previously observed using the hypernetted chain (HNC) approximation. The thermodynamics of weak 1-1 electrolytes are discussed using the new method and a comparison is made between the new and old methods for 2-2 electrolytes.

Rasaiah, Jayendran C.; Zhu, Jianjun

1990-06-01

112

Short-wavelength collective modes in a binary hard-sphere mixture  

E-print Network

We use hard-sphere generalized hydrodynamic equations to discuss the extended hydrodynamic modes of a binary mixture. The theory presented here is analytic and it provides us with a simple description of the collective excitations of a dense binary mixture at molecular length scales. The behavior we predict is in qualitative agreement with molecular-dynamics results for soft-sphere mixtures. This study provides some insight into the role of compositional disorder in forming glassy configurations.

M. Cristina Marchetti; Supurna Sinha

2005-09-14

113

Stochastic Interactions of Two Brownian Hard Spheres in the Presence of Depletants  

E-print Network

A quantitative analysis is presented for the stochastic interactions of a pair of Brownian hard spheres in non-adsorbing polymer solutions. The hard spheres are hypothetically trapped by optical tweezers and allowed for random motion near the trapped positions. The investigation focuses on the long-time correlated Brownian motion. The mobility tensor altered by the polymer depletion effect is computed by the boundary integral method, and the corresponding random displacement is determined by the fluctuation-dissipation theorem. From our computations it follows that the presence of depletion layers around the hard spheres has a significant effect on the hydrodynamic interactions and particle dynamics as compared to pure solvent and pure polymer solution (no depletion) cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shifts due to the polymer depletion effect. The results show that the reduction of the viscosity in the depletion layers around the spheres and the entropic force due to the overlapping of depletion zones have a significant influence on the correlated Brownian interactions.

Mehdi Karzar-Jeddi; Remco Tuinier; Takashi Taniguchi; Tai-Hsi Fan

2014-01-30

114

Calculation of the interfacial free energy of a binary hard-sphere fluid at a planar hard wall  

E-print Network

(cDFT). In addition, some real polymer and colloid systems can be modeled quantitatively as hard-spheres. For example, it has recently been shown that poly-N-isopropylacrylamide (PNIPAM) spheres in a solvent with appropriate charge screening reproduce... Particle Theory have been in existence since the 1960s,2, 3 the first simulations to calculate ? for a single component HS/HW system were those of Henderson and van Swol,4 who ob- tained ? by integrating the excess surface stress obtained from molecular...

Kern, Jesse L.; Laird, Brian Bostian

2014-01-08

115

Molecular-scale hydrophobic interactions between hard-sphere reference solutes are attractive and endothermic  

PubMed Central

The osmotic second virial coefficients, B2, for atomic-sized hard spheres in water are attractive (B2 < 0) and become more attractive with increasing temperature (?B2/?T < 0) in the temperature range 300 K ? T ? 360 K. Thus, these hydrophobic interactions are attractive and endothermic at moderate temperatures. Hydrophobic interactions between atomic-sized hard spheres in water are more attractive than predicted by the available statistical mechanical theory. These results constitute an initial step toward detailed molecular theory of additional intermolecular interaction features, specifically, attractive interactions associated with hydrophobic solutes. PMID:24297918

Chaudhari, Mangesh I.; Holleran, Sinead A.; Ashbaugh, Henry S.; Pratt, Lawrence R.

2013-01-01

116

Mixtures of Hard Ellipsoids and Spheres: Stability of the Nematic Phase  

E-print Network

The stability of liquid crystal phases in presence of small amount of non-mesogenic impurities is of general interest for a large spectrum of technological applications and in the theories of binary mixtures. Starting from the known phase diagram of the hard ellipsoids systems, we propose a simple model and method to explore the stability of the nematic phase in presence of small impurities represented by hard spheres. The study is performed in the isobaric ensemble with Monte Carlo simulations.

Carlos E. Alvarez; Martial Mazars

2014-05-09

117

Hypersonic acoustic excitations in binary colloidal crystals: Big versus small hard sphere control  

E-print Network

Hypersonic acoustic excitations in binary colloidal crystals: Big versus small hard sphere control January 2007 The phononic band structure of two binary colloidal crystals, at hypersonic frequencies of light photonic crystals 2 and sound at hypersonic frequencies.3 The propa- gation of phonons

Schofield, Andrew B.

118

Min-type Morse theory for configuration spaces of hard spheres  

E-print Network

We study configuration spaces of hard spheres in a bounded region. We develop a general Morse-theoretic framework, and show that mechanically balanced configurations play the role of critical points. As an application, we find the precise threshold radius for a configuration space to be homotopy equivalent to the configuration space of points.

Yuliy Baryshnikov; Peter Bubenik; Matthew Kahle

2011-08-15

119

The potential energy landscape and inherent dynamics of a hard-sphere fluid  

E-print Network

Hard-sphere models exhibit many of the same kinds of supercooled-liquid behavior as more realistic models of liquids, but the highly non-analytic character of their potentials makes it a challenge to think of that behavior in potential-energy-landscape terms. We show here that it is possible to calculate an important topological property of hard-sphere landscapes, the geodesic pathways through those landscapes, and to do so without artificially coarse-graining or softening the potential. We show, moreover, that the rapid growth of the lengths of those pathways with increasing packing fraction quantitatively predicts the precipitous decline in diffusion constants in a glass-forming hard-sphere mixture model. The geodesic paths themselves can be considered as defining the intrinsic dynamics of hard spheres, so it is also revealing to find that they (and therefore the features of the underlying potential-energy landscape) correctly predict the occurrence of dynamic heterogeneity and non-zero values of the non-Gaussian parameter. The success of these landscape predictions for the dynamics of such a singular model emphasizes that there is more to potential energy landscapes than is revealed by looking at the minima and saddle points.

Qingqing Ma; Richard M. Stratt

2014-08-13

120

Binary hard-sphere crystals with the cesium chloride structure A. B. Schofield  

E-print Network

demonstrated that when two differently sized sets of these hard spheres are mixed together then they can co-crystallize to form binary crystal structures analogous to those seen in atomic systems 4­6 . The exact binary crystal structure formed and its stoichiometry is found to be depen- dant on the radius ratio of the two different

Schofield, Andrew B.

121

On $p$-adic Hard Sphere model with three states on a Cayley tree  

E-print Network

We study $p$-adic model of hard spheres with three states on the Cayley tree. We show that there exist three translation-invariant $p$-adic Gibbs measures and two periodic measures on a Cayley tree of oreder two.

Otabek Khakimov

2014-03-17

122

Model energy landscapes of low-temperature fluids: Dipolar hard spheres Dmitry V. Matyushov*  

E-print Network

Model energy landscapes of low-temperature fluids: Dipolar hard spheres Dmitry V. Matyushov* Center-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid that the proposed functionality of the enumeration function is widely applicable to both polar and nonpolar low-temperature

Matyushov, Dmitry

123

Fluid-solid equilibrium of a charged hard-sphere model  

Microsoft Academic Search

The fluid-solid equilibrium of a system made of charged hard spheres with positive and negative ions of the same size is considered. At high temperatures freezing occurs in a substitutionally disordered close packed structure, the face centered cubic solid (fcc). At low temperatures freezing occurs in the ordered cesium chloride structure (CsCl). As the latter solid coexists with the fcc

Carlos Vega; Fernando Bresme; José L. F. Abascal

1996-01-01

124

A rough hard-sphere model for the thermal conductivity of molten salts  

Microsoft Academic Search

A new model based on the rough hard-sphere theory is proposed for the correlation and prediction of the thermal conductivity of molten salts. The model is capable of predicting the thermal conductivity of all the members of a family of molten salts characterized by a common anion if the behavior of any single member of the family of salts is

R. M. Diguilio; A. S. Teja

1992-01-01

125

Structure of nonuniform hard sphere fluids from shifted linear truncations of functional expansions  

E-print Network

Percus showed that approximate theories for the structure of nonuniform hard sphere fluids can be generated by linear truncations of functional expansions of the nonuniform density rho (r) about that of an appropriately chosen uniform system. We consider the most general such truncation, which we refer to as the shifted linear response (SLR) equation, where the density response rho (r) to an external field phi (r) is expanded to linear order at each r about a different uniform system with a locally shifted chemical potential. Special cases include the Percus-Yevick (PY) approximation for nonuniform fluids, with no shift of the chemical potential, and the hydrostatic linear response (HLR) equation, where the chemical potential is shifted by the local value of phi (r) The HLR equation gives exact results for very slowly varying phi (r) and reduces to the PY approximation for hard core phi (r), where generally accurate results are found. We try to develop a systematic way of choosing an optimal local shift in the SLR equation for general phi (r) by requiring that the predicted rho (r) is insensitive to small variations about the appropriate local shift, a property that the exact expansion to all orders would obey. The resulting insensitivity criterion (IC) gives a theory that reduces to the HLR equation for slowly varying phi (r), and is much more accurate than HLR both for very narrow slits, where the IC agrees with exact results, and for fields confined to ``tiny'' regions that can accomodate at most one particle, where the IC gives very accurate (but not exact) results.

Yng-Gwei Chen; John D. Weeks

2005-02-12

126

Rolling friction for hard cylinder and sphere on viscoelastic solid  

E-print Network

We calculate the friction force acting on a hard cylinder or spherical ball rolling on a flat surface of a viscoelastic solid. The rolling friction coefficient depends non-linearly on the normal load and the rolling velocity. For a cylinder rolling on a viscoelastic solid characterized by a single relaxation time Hunter has obtained an exact result for the rolling friction, and our result is in very good agreement with his result for this limiting case. The theoretical results are also in good agreement with experiments of Greenwood and Tabor. We suggest that measurements of rolling friction over a wide range of rolling velocities and temperatures may constitute an useful way to determine the viscoelastic modulus of rubber-like materials.

B. N. J. Persson

2010-08-26

127

Equivalence of Glass Transition and Colloidal Glass Transition in the Hard-Sphere Limit Thomas K. Haxton,2  

E-print Network

that the slowing of the dynamics in simulations of several model glass-forming liquids is equivalent to the hard-sphereEquivalence of Glass Transition and Colloidal Glass Transition in the Hard-Sphere Limit Ning Xu,1 parameter is varied that fluid behavior is suppressed and the system forms an apparently rigid solid. One

Weeks, Eric R.

128

Disorder and excess modes in hard-sphere colloidal systems  

NASA Astrophysics Data System (ADS)

The anomalous thermodynamic properties of glasses remain incompletely understood, notably the anomalous peak in the heat capacity at low temperatures; it is believed to be due to an excess of low-frequency vibrational modes and a manifestation of the structural disorder in these systems. We study the thermodynamics and vibrational dynamics of colloidal glasses and (defected) crystals. The experimental determination of the vibrational density of states allows us to directly observe a strong enhancement of low-frequency modes. Using a novel method (Zargar R. et al., Phys. Rev. Lett. 110 (2013) 258301) to determine the free energy, we also determine the entropy and the specific heat experimentally. It follows that the emergence of the excess modes and high values of the specific heat are directly related and are specific to the glass: even for solids containing a very large amount of defects, both the low-frequency density of states and the specific heat are significantly smaller than for the glass.

Zargar, R.; Russo, J.; Schall, P.; Tanaka, H.; Bonn, D.

2014-11-01

129

The Boson Peak and Disorder in Hard Sphere Colloidal Systems  

E-print Network

The Boson peak is believed to be the key to the fundamental understanding of the anomalous thermodynamic properties of glasses, notably the anomalous peak in the heat capacity at low temperatures; it is believed to be due to an excess of low frequency vibrational modes and a manifestation of the structural disorder in these systems. We study the thermodynamics and vibrational dynamics of colloidal glasses and (defected) crystals. The experimental determination of the vibrational density of states allows us to directly observe the Boson peak as a strong enhancement of low frequency modes. Using a novel method [Zargar et al., Phys. Rev. Lett. 110, 258301 (2013)] to determine the free energy, we also determine the entropy and the specific heat experimentally. It follows that the emergence of the Boson peak and high values of the specific heat are directly related and are specific to the glass: for a very defected crystal with a disorder that is only slightly smaller than for the glass, both the low-frequency density of states and the specific heat are significantly smaller than in the glass.

Rojman Zargar; John Russo; Peter Schall; Hajime Tanaka; Daniel Bonn

2014-03-11

130

Hard-sphere fluid with tight-binding electronic interactions -- a glue model treatment  

NASA Astrophysics Data System (ADS)

We have carried out self-consistent Monte-Carlo simulations for a model monovalent-atom fluid, with hard-sphere interactions and attractions due to the free energy of its valence electrons. This energy is obtained in a tight-binding model with electronic hopping which decreases exponentially with distance. The many-body atomic energies in the disordered environment are fitted with a 'glue' model which, unlike its usual treatment, has its parameters obtained from the model itself. The phase diagram and electronic conductivity derived from this self-consistent treatment of atomic and electronic structures are obtained. Ionic correlations induced by the electronic energy are found to play a crucial role in the thermodynamic and electronic properties of the present model. The electrical conductivity evidences a rapid drop with decreasing fluid density, in the vapor, due to the almost classical percolation of the ionic structures. The resulting phase diagram and the electrical conductivity, at vapor-liquid coexistence, give reasonable agreement with experimental data for fluid cesium, for a chosen decay-parametrization of the electronic hopping.

Reinaldo-Falagan, M.; Tarazona, P.; Velasco, E.; Chacon, E.; Hernandez, J. P.

2003-03-01

131

Energy production rates in fluid mixtures of inelastic rough hard spheres  

E-print Network

The aim of this work is to explore the combined effect of polydispersity and roughness on the partial energy production rates and on the total cooling rate of a granular fluid mixture. We consider a mixture of inelastic rough hard spheres of different number densities, masses, diameters, moments of inertia, and mutual coefficients of normal and tangential restitution. Starting from the first equation of the BBGKY hierarchy, the collisional energy production rates associated with the translational and rotational temperatures ($T_i^\\text{tr}$ and $T_i^\\text{rot}$) are expressed in terms of two-body average values. Next, those average values are estimated by assuming a velocity distribution function based on maximum-entropy arguments, allowing us to express the energy production rates and the total cooling rate in terms of the partial temperatures and the parameters of the mixture. Finally, the results are applied to the homogeneous cooling state of a binary mixture and the influence of inelasticity and roughness on the temperature ratios $T_1^\\text{tr}/T_1^\\text{rot}$, $T_2^\\text{tr}/T_1^\\text{tr}$, and $T_2^\\text{rot}/T_1^\\text{rot}$ is analyzed.

Andrés Santos; Gilberto M. Kremer; Vicente Garzó

2009-10-29

132

A Monte Carlo study of the influence of molecular flexibility on the phase diagram of a fused hard sphere model  

Microsoft Academic Search

A study of a rigid fully flexible fused hard sphere model [C. McBride, C. Vega, and L. G. MacDowell, Phys. Rev. E 64, 011703 (2001)] is extended to the smectic and solid branches of the phase diagram. Computer simulations have been performed for a completely rigid model composed of 15 fused hard spheres (15+0), a model of 15 fused hard

Carl McBride; Carlos Vega

2002-01-01

133

Communication: radial distribution functions in a two-dimensional binary colloidal hard sphere system.  

PubMed

Two-dimensional hard disks are a fundamentally important many-body model system in classical statistical mechanics. Despite their significance, a comprehensive experimental data set for two-dimensional single component and binary hard disks is lacking. Here, we present a direct comparison between the full set of radial distribution functions and the contact values of a two-dimensional binary colloidal hard sphere model system and those calculated using fundamental measure theory. We find excellent quantitative agreement between our experimental data and theoretical predictions for both single component and binary hard disk systems. Our results provide a unique and fully quantitative mapping between experiments and theory, which is crucial in establishing the fundamental link between structure and dynamics in simple liquids and glass forming systems. PMID:24784245

Thorneywork, Alice L; Roth, Roland; Aarts, Dirk G A L; Dullens, Roel P A

2014-04-28

134

Physics of Hard Spheres Experiment (PhaSE) or "Making Jello in Space"  

NASA Technical Reports Server (NTRS)

The Physics of Hard Spheres Experiment (PHaSE) is a highly successful experiment that flew aboard two shuttle missions to study the transitions involved in the formation of jellolike colloidal crystals in a microgravity environment. A colloidal suspension, or colloid, consists of fine particles, often having complex interactions, suspended in a liquid. Paint, ink, and milk are examples of colloids found in everyday life. In low Earth orbit, the effective force of gravity is thousands of times less than at the Earth's surface. This provides researchers a way to conduct experiments that cannot be adequately performed in an Earth-gravity environment. In microgravity, colloidal particles freely interact without the complications of settling that occur in normal gravity on Earth. If the particle interactions within these colloidal suspensions could be predicted and accurately modeled, they could provide the key to understanding fundamental problems in condensed matter physics and could help make possible the development of wonderful new "designer" materials. Industries that make semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. Atomic interactions determine the physical properties (e.g., weight, color, and hardness) of ordinary matter. PHaSE uses colloidal suspensions of microscopic solid plastic spheres to model the behavior of atomic interactions. When uniformly sized hard spheres suspended in a fluid reach a certain concentration (volume fraction), the particle-fluid mixture changes from a disordered fluid state, in which the spheres are randomly organized, to an ordered "crystalline" state, in which they are structured periodically. The thermal energy of the spheres causes them to form ordered arrays, analogous to crystals. Seven of the eight PHaSE samples ranged in volume fraction from 0.483 to 0.624 to cover the range of interest, while one sample, having a concentration of 0.019, was included for instrument calibration.

Ling, Jerri S.; Doherty, Michael P.

1998-01-01

135

The Dynamics of Disorder-Order Transition in Hard Sphere Colloidal Dispersions  

NASA Technical Reports Server (NTRS)

The Physics of Hard Spheres Experiment (PHaSE) seeks a complete understanding of the entropically driven disorder-order transition in hard sphere colloidal dispersions. The light scattering instrument designed for flight collects Bragg and low angle light scattering in the forward direction via a CCD camera and performs conventional static and dynamic light scattering at 10-160 deg. through fiber optic cables. Here we report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering. Preliminary analysis of the former indicates a significant difference from measurements on the ground, while the latter confirms nicely laboratory experiments with the same instrument and predictions from computer simulations.

Chaikin, Paul M.; Zhu, Jixiang; Cheng, Zhengdong; Phan, See-Eng; Russel, William B.; Lant, Christian T.; Doherty, Michael P.; Meyer, William V.; Rogers, Richard; Cannell, D. S.; Ottewill, R. H.

1998-01-01

136

Two hard spheres in a pore: Exact Statistical Mechanics for different shaped cavities  

E-print Network

The Partition function of two Hard Spheres in a Hard Wall Pore is studied appealing to a graph representation. The exact evaluation of the canonical partition function, and the one-body distribution function, in three different shaped pores are achieved. The analyzed simple geometries are the cuboidal, cylindrical and ellipsoidal cavities. Results have been compared with two previously studied geometries, the spherical pore and the spherical pore with a hard core. The search of common features in the analytic structure of the partition functions in terms of their length parameters and their volumes, surface area, edges length and curvatures is addressed too. A general framework for the exact thermodynamic analysis of systems with few and many particles in terms of a set of thermodynamic measures is discussed. We found that an exact thermodynamic description is feasible based in the adoption of an adequate set of measures and the search of the free energy dependence on the adopted measure set. A relation similar to the Laplace equation for the fluid-vapor interface is obtained which express the equilibrium between magnitudes that in extended systems are intensive variables. This exact description is applied to study the thermodynamic behavior of the two Hard Spheres in a Hard Wall Pore for the analyzed different geometries. We obtain analytically the external work, the pressure on the wall, the pressure in the homogeneous zone, the wall-fluid surface tension, the line tension and other similar properties.

Ignacio Urrutia

2010-05-05

137

Crystal Nucleation in the Hard-Sphere System Revisited: A Critical Test of Theoretical Approaches  

Microsoft Academic Search

The hard-sphere system is the best known fluid that crystallizes: the solid-liquid interfacial free energy, the equations of state, and the height of the nucleation barrier are known accurately, offering a unique possibility for a quantitative validation of nucleation theories. A recent significant downward revision of the interfacial free energy from ?0.61kT\\/? 2 to (0.56 ( 0.02)kT\\/? 2 (Davidchack, R.;

Gyula I. To?th; La?szlo? Gra?na?sy

2009-01-01

138

The fluid-solid equilibrium for a charged hard sphere model revisited  

Microsoft Academic Search

The global phase diagram of a system of charged hard spheres, composed of positive and negative ions of the same size, is obtained by means of computer simulations. Thermodynamic integration and Einstein crystal calculations are used to determine the free energies of the different possible solid structures. In this way, the fluid-solid and solid-solid phase transitions are located. Gibbs-Duhem integration

Carlos Vega; José L. F. Abascal; Carl McBride; Fernando Bresme

2003-01-01

139

A generalized hard-sphere model for the irradiation induced viscosity of amorphous binary alloys  

Microsoft Academic Search

The entropy of mixing of binary alloys using a generalized hard-sphere model of binary fluids is considered in an application to alloys that undergo an irradiation-induced crystalline–amorphous transformation at temperatures significantly below the melting temperature. The model is based on the observation that many amorphous materials respond in a “liquid like” manner while under irradiation. The generalization of the model

J. Rest

2008-01-01

140

Liquid crystal phase formation for the linear tangent hard sphere model from Monte Carlo simulations  

Microsoft Academic Search

Monte Carlo simulations have been performed for the linear tangent hard sphere model. The models considered in this work consisted of m=3, 4, 5, 6, and 7 monomer units. For the models m=3 and m=4 we find an isotropic fluid and an ordered solid. For the m=5 model we find the sequence of phases isotropic-nematic-smectic A on compression, and the

Carlos Vega; Carl McBride; Luis G. MacDowell

2001-01-01

141

Structural aging of crystals of hard-sphere colloids V. C. Martelozzo, A. B. Schofield, W. C. K. Poon, and P. N. Pusey  

E-print Network

random hexagonal close-packed rhcp crystals formed in suspensions of hard-sphere colloids near . The free en- ergy differences between the different hard-sphere crystals at fixed volume are due onlyStructural aging of crystals of hard-sphere colloids V. C. Martelozzo, A. B. Schofield, W. C. K

Schofield, Andrew

142

On fluid-solid direct coexistence simulations: the pseudo-hard sphere model.  

PubMed

We investigate methodological issues concerning the direct coexistence method, an increasingly popular approach to evaluate the solid-fluid coexistence by means of computer simulations. The first issue is the impact of the simulation ensemble on the results. We compare the NpT ensemble (easy to use but approximate) with the NpzT ensemble (rigorous but more difficult to handle). Our work shows that both ensembles yield similar results for large systems (>5000 particles). Another issue, which is usually disregarded, is the stochastic character of a direct coexistence simulation. Here, we assess the impact of stochasticity in the determination of the coexistence point. We demonstrate that the error generated by stochasticity is much larger than that caused by the use of the NpT ensemble, and can be minimized by simply increasing the system size. To perform this study we use the pseudo hard-sphere model recently proposed by Jover et al. [J. Chem. Phys. 137, 144505 (2012)], and obtain a coexistence pressure of p? = 11.65(1), quite similar to that of hard spheres (only about 0.6% higher). Therefore, we conclude that this model can be reliably used to investigate the physics of hard spheres in phenomena like crystal nucleation. PMID:24116630

Espinosa, Jorge R; Sanz, Eduardo; Valeriani, Chantal; Vega, Carlos

2013-10-14

143

Equation of state of the hard-disk fluid on a sphere from Percus–Yevick equation  

Microsoft Academic Search

The Percus–Yevick equation is solved numerically for hard disks on a sphere. The effect of curvature of the hosting surface is calculated, and an empirical correction to the equation of state is proposed.

S. V. Lishchuk

2006-01-01

144

Elastically Cooperative Activated Barrier Hopping Theory of Relaxation in Viscous Fluids. I. General Formulation and Application to Hard Sphere Fluids  

E-print Network

We generalize the force-level Nonlinear Langevin Equation theory of single particle hopping to include collective effects associated with long range elastic distortion of the liquid. The activated alpha relaxation event is of a mixed spatial character, involving two distinct, but inter-related, local and collective barriers. There are no divergences at volume fractions below jamming or temperatures above zero Kelvin. The ideas are first developed and implemented analytically and numerically in the context of hard sphere fluids. In an intermediate volume fraction crossover regime, the local cage process is dominant in a manner consistent with an apparent Arrhenius behavior. The super-Arrhenius collective barrier is more strongly dependent on volume fraction, dominates the highly viscous regime, and is well described by a nonsingular law below jamming. The increase of the collective barrier is determined by the amplitude of thermal density fluctuations, shear modulus or transient localization length, and a growing microscopic jump length. Alpha relaxation time calculations are in good agreement with recent experiments and simulations on dense fluids and suspensions of hard spheres. Comparisons of the theory with elastic models and entropy crisis ideas are explored. The present work provides a foundation for constructing a quasi-universal, fit-parameter-free theory for relaxation in thermal molecular liquids over 14 orders of magnitude in time.

Stephen Mirigian; Kenneth S. Schweizer

2014-02-20

145

Elastically cooperative activated barrier hopping theory of relaxation in viscous fluids. I. General formulation and application to hard sphere fluids  

NASA Astrophysics Data System (ADS)

We generalize the force-level nonlinear Langevin equation theory of single particle hopping to include collective effects associated with long range elastic distortion of the liquid. The activated alpha relaxation event is of a mixed spatial character, involving two distinct, but inter-related, local and collective barriers. There are no divergences at volume fractions below jamming or temperatures above zero Kelvin. The ideas are first developed and implemented analytically and numerically in the context of hard sphere fluids. In an intermediate volume fraction crossover regime, the local cage process is dominant in a manner consistent with an apparent Arrhenius behavior. The super-Arrhenius collective barrier is more strongly dependent on volume fraction, dominates the highly viscous regime, and is well described by a nonsingular law below jamming. The increase of the collective barrier is determined by the amplitude of thermal density fluctuations, dynamic shear modulus or transient localization length, and a growing microscopic jump length. Alpha relaxation time calculations are in good agreement with recent experiments and simulations on dense fluids and suspensions of hard spheres. Comparisons of the theory with elastic models and entropy crisis ideas are explored. The present work provides a foundation for constructing a quasi-universal, fit-parameter-free theory for relaxation in thermal molecular liquids over 14 orders of magnitude in time.

Mirigian, Stephen; Schweizer, Kenneth S.

2014-05-01

146

Monte Carlo simulation and equation of state for flexible charged hard-sphere chain fluids: Polyampholyte and polyelectrolyte solutions.  

PubMed

The thermodynamic modeling of flexible charged hard-sphere chains representing polyampholyte or polyelectrolyte molecules in solution is considered. The excess Helmholtz energy and osmotic coefficients of solutions containing short polyampholyte and the osmotic coefficients of solutions containing short polyelectrolytes are determined by performing canonical and isobaric-isothermal Monte Carlo simulations. A new equation of state based on the thermodynamic perturbation theory is also proposed for flexible charged hard-sphere chains. For the modeling of such chains, the use of solely the structure information of monomer fluid for calculating the chain contribution is found to be insufficient and more detailed structure information must therefore be considered. Two approaches, i.e., the dimer and dimer-monomer approaches, are explored to obtain the contribution of the chain formation to the Helmholtz energy. By comparing with the simulation results, the equation of state with either the dimer or dimer-monomer approach accurately predicts the excess Helmholtz energy and osmotic coefficients of polyampholyte and polyelectrolyte solutions except at very low density. It also well captures the effect of temperature on the thermodynamic properties of these solutions. PMID:25381546

Jiang, Hao; Adidharma, Hertanto

2014-11-01

147

Simulation of spatial correlations of impurity ions in solids using configurational entropy and the hard-sphere model  

Microsoft Academic Search

Based on the hard-sphere model, the spatial correlations are considered in a system of impurities with variable valency. In\\u000a a zeroth approximation, the configurational entropy of the spatially correlated system of impurity ions is identified with\\u000a the configurational entropy of a system of hard spheres. The electron mobility limited by scattering on the correlated system\\u000a of impurity ions at finite

V. M. Mikheev

2005-01-01

148

Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard sphere solvents  

E-print Network

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios $x$ in the range $1/5 \\leq x \\leq 5$, and with volumes between one and twenty times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio $x$ should be more soluble than an oblate solute with aspect ratio $1/x$. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend is observed in the case of hydrophobic solvation. To help interpret the simulation results, comparison is made with a scaled-particle theory that requires prior knowledge of a solute-solvent interfacial tension and the pure-solvent equation of state, which parameters are obtained from simulation results for spherical solutes. The theory shows excellent agreement with simulation results over the whole range of solute elongations considered.

Philip J. Camp

2005-06-20

149

Impact of microstructure on the effective diffusivity in random packings of hard spheres  

NASA Astrophysics Data System (ADS)

We present results of computer simulations of the effective diffusion coefficient in bulk random packings of hard monosized spheres with solid volume fraction between 0.54 (random-loose packing) and 0.634 (maximally random jammed). Six types of sphere packings were generated with different protocols and parameters resulting in a systematically varied degree of microstructural heterogeneity. The packing morphology is qualitatively characterized by statistical analyses of Voronoi cells obtained from spatial tessellation of the packing space. Diffusive transport of point-like tracers in the pore space of the packings was simulated with a random-walking particle-tracking technique. Our results indicate that the effective transport characteristics of the random sphere packings are not fully defined from the solid volume fraction but also depend on the packing microstructure. For the first time, we compared (i) the values of the effective diffusion coefficient Deff simulated in packings with different morphologies, and (ii) the corresponding values of Deff obtained from an approximate analytical formula involving the three-point microstructural parameter ?2. This analysis reveals that this approximation involving ?2 clearly reflects key morphological specificity of individual sphere packings and provides a sufficiently accurate estimate of the effective diffusion coefficient.

Liasneuski, H.; Hlushkou, D.; Khirevich, S.; Höltzel, A.; Tallarek, U.; Torquato, S.

2014-07-01

150

Quasi-chemical Theory and the Statistical Thermodynamics of the Hard Sphere Fluid  

SciTech Connect

We develop a quasi-chemical theory for the study of packing thermodynamics in dense liquids. The situation of hard-core interactions is addressed by considering the binding of solvent molecules to a precisely defined cavity in order to assess the probability that the cavity is entirely evacuated. The primitive quasi-chemical approximation corresponds to an extension of the Poisson distribution used as a default model in an information theory approach. This primitive quasi-chemical theory is in good qualitative agreement with the observations for the hard-sphere fluid of occupancy distributions that are central to quasi-chemical theories but begins to be quantitatively erroneous for the equation of state in the dense liquid regime of d3 > 0.6. How the quasi-chemical approach can be iterated to treat correlation effects is addressed. Consideration of neglected correlation effects leads to a simple model for the form of those contributions neglected by the primitive quasi-chemical approximation. These considerations, supported by simulation observations, identify a "break away" phenomena that requires special thermodynamic consideration for the zero (0) occupancy case as distinct from the rest of the distribution. An empirical treatment leads to a one-parameter model occupancy distribution that accurately fits the hard-sphere equation of state and observed distributions.

Pratt, L. R.; Laviolette, Randall Alexander; Gomez, M. A.; Gentile, M.

2001-09-01

151

Normal stress and diffusion in a dilute suspension of hard spheres undergoing simple shear  

NASA Astrophysics Data System (ADS)

The complete set of normal stresses in a dilute suspension of hard spheres undergoing simple shear at low Reynolds number is calculated using a path integration approach for the cases where the concentration is uniform and where a small gradient in concentration is present. As expected, the normal stresses are seen to be a strong function of ?s=2(b-a)/a, where b is the hard sphere radius and a is the particle radius. The normal stress differences N1 and N2, are negative while the osmotic pressure is large and positive, with ?>|N2| and N1?0 as ?s??. For ?s?1, the asymmetry in the pair distribution function due to a depletion of particles in the extensional side of a pair interaction leads to |N1|>|N2|. On the other hand, for ?s??, the additional stresslet induced when hard sphere radii touch dominates the stress generated in the suspension, and N2 becomes the prevailing normal stress difference. The self and gradient diffusivities are calculated using da Cunha and Hinch's [J. Fluid Mech. 309, 211 (1996)] trajectory method. Numerical results for the diffusivities are in agreement with those obtained by da Cunha and Hinch for ?s?0.08 while matching the analytically obtained diffusivities for large ?s. Finally, we calculate the normal stress in the presence of a small concentration gradient and compare two models of migration for this case, namely the suspension balance model of Nott and Brady [J. Fluid Mech. 275, 157 (1994)] and the diffusive flux model first introduced by Leighton and Acrivos [J. Fluid Mech. 181, 415 (1987)]. The results show that although the two models equally describe migration in the presence of a concentration gradient for the case where b?a (or ?s??), the two models are shown to be quantitatively different when near-field hydrodynamics are relevant.

Zarraga, Isidro E.; Leighton, David T.

2001-03-01

152

Low-noise Monte Carlo simulation of the variable hard sphere gas  

NASA Astrophysics Data System (ADS)

We present an efficient particle simulation method for the Boltzmann transport equation based on the low-variance deviational simulation Monte Carlo approach to the variable-hard-sphere gas. The proposed method exhibits drastically reduced statistical uncertainty for low-signal problems compared to standard particle methods such as the direct simulation Monte Carlo method. We show that by enforcing mass conservation, accurate simulations can be performed in the transition regime requiring as few as ten particles per cell, enabling efficient simulation of multidimensional problems at arbitrarily small deviation from equilibrium.

Radtke, Gregg A.; Hadjiconstantinou, Nicolas G.; Wagner, Wolfgang

2011-03-01

153

Crystal-liquid interfacial free energy of hard spheres via a novel thermodynamic integration scheme  

E-print Network

The hard sphere crystal-liquid interfacial free energy, ($\\gamma_{\\rm cl}$), is determined from molecular dynamics simulations using a novel thermodynamic integration (TI) scheme. The advantage of this TI scheme compared to previous methods is to successfully circumvent hysteresis effects due to the movement of the crystal-liquid interface. This is accomplished by the use of extremely short-ranged and impenetrable Gaussian flat walls which prevent the drift of the interface while imposing a negligible free-energy penalty. We find that it is crucial to analyze finite-size effects in order to obtain reliable estimates of $\\gamma_{\\rm cl}$ in the thermodynamic limit.

Benjamin, Ronald

2014-01-01

154

Glass-Transition Properties from Hard Spheres to Charged Point Particles  

E-print Network

The glass transition is investigated in three dimensions for single and double Yukawa potentials for the full range of control parameters. For vanishing screening parameter, the limit of the one-component plasma is obtained; for large screening parameters and high coupling strengths, the glass-transition properties crossover to the hard-sphere system. Between the two limits, the entire transition diagram can be described by analytical functions. Different from other potentials, the glass-transition and melting lines for Yukawa potentials are found to follow shifted but otherwise identical curves in control-parameter space.

Anoosheh Yazdi; Alexei Ivlev; Sergei Khrapak; Hubertus Thomas; Gregor E. Morfill; Hartmut Löwen; Adam Wysocki; Matthias Sperl

2014-01-28

155

Signatures of glass formation in a fluidized bed of hard spheres  

E-print Network

We demonstrate that a fluidized bed of hard spheres during defluidization displays properties associated with formation of a glass. The final state is rate dependent, and as this state is approached, the bed exhibits heterogeneity with increasing time and length scales. The formation of a glass results in the loss of fluidization and an arrest of macroscopic particle motion. Microscopic motion persists in this state, but the bed can be jammed by application of a small increase in flow rate. Thus a fluidized bed can serve as a test system for studies of glass formation and jamming.

Daniel I. Goldman; Harry L. Swinney

2005-11-14

156

Playing with Marbles: Structural and Thermodynamic Properties of Hard-Sphere Systems  

E-print Network

These lecture notes present an overview of equilibrium statistical mechanics of classical fluids, with special applications to the structural and thermodynamic properties of systems made of particles interacting via the hard-sphere potential or closely related model potentials. The exact statistical-mechanical properties of one-dimensional systems, the issue of thermodynamic (in)consistency among different routes in the context of several approximate theories, and the construction of analytical or semi-analytical approximations for the structural properties are also addressed.

Andrés Santos

2013-10-21

157

Communication: Structure characterization of hard sphere packings in amorphous and crystalline states.  

PubMed

The channel size distribution in hard sphere systems, based on the local neighbor correlation of four particle positions, is investigated for all volume fractions up to jamming. For each particle, all three particle combinations of neighbors define channels, which are relevant for the concept of caging. The analysis of the channel size distribution is shown to be very useful in distinguishing between gaseous, liquid, partially and fully crystallized, and glassy (random) jammed states. A common microstructural feature of four coplanar particles is observed in crystalline and glassy jammed states, suggesting the presence of "hidden" two-dimensional order in three-dimensional random close packings. PMID:24907982

Ogarko, Vitaliy; Rivas, Nicolas; Luding, Stefan

2014-06-01

158

Communication: Structure characterization of hard sphere packings in amorphous and crystalline states  

NASA Astrophysics Data System (ADS)

The channel size distribution in hard sphere systems, based on the local neighbor correlation of four particle positions, is investigated for all volume fractions up to jamming. For each particle, all three particle combinations of neighbors define channels, which are relevant for the concept of caging. The analysis of the channel size distribution is shown to be very useful in distinguishing between gaseous, liquid, partially and fully crystallized, and glassy (random) jammed states. A common microstructural feature of four coplanar particles is observed in crystalline and glassy jammed states, suggesting the presence of "hidden" two-dimensional order in three-dimensional random close packings.

Ogarko, Vitaliy; Rivas, Nicolas; Luding, Stefan

2014-06-01

159

arXiv:cond-mat/0511322v114Nov2005 Glass transition in a fluidized bed of hard spheres  

E-print Network

arXiv:cond-mat/0511322v114Nov2005 Glass transition in a fluidized bed of hard spheres Daniel I of Texas at Austin, Austin, TX 78712 (Dated: November 14, 2005) We demonstrate that a fluidized bed of hard motion arrested) by application of a small increase in flow rate. Thus a fluidized bed can serve

Weeks, Eric R.

160

The van Hove distribution function for Brownian hard spheres: dynamical test particle theory and computer simulations for bulk dynamics  

E-print Network

We describe a test particle approach based on dynamical density functional theory (DDFT) for studying the correlated time evolution of the particles that constitute a fluid. Our theory provides a means of calculating the van Hove distribution function by treating its self and distinct parts as the two components of a binary fluid mixture, with the `self' component having only one particle, the `distinct' component consisting of all the other particles, and using DDFT to calculate the time evolution of the density profiles for the two components. We apply this approach to a bulk fluid of Brownian hard spheres and compare to results for the van Hove function and the intermediate scattering function from Brownian dynamics computer simulations. We find good agreement at low and intermediate densities using the very simple Ramakrishnan-Yussouff [Phys. Rev. B 19, 2775 (1979)] approximation for the excess free energy functional. Since the DDFT is based on the equilibrium Helmholtz free energy functional, we can probe a free energy landscape that underlies the dynamics. Within the mean-field approximation we find that as the particle density increases, this landscape develops a minimum, while an exact treatment of a model confined situation shows that for an ergodic fluid this landscape should be monotonic. We discuss possible implications for slow, glassy and arrested dynamics at high densities.

Paul Hopkins; Andrea Fortini; Andrew Archer; Matthias Schmidt

2010-10-11

161

Effective conductivity of suspensions of hard spheres by Brownian motion simulation  

SciTech Connect

A generalized Brownian motion simulation technique developed by Kim and Torquato (J. Appl. Phys. {bold 68}, 3892 (1990)) is applied to compute exactly'' the effective conductivity {sigma}{sub {ital e}} of heterogeneous media composed of regular and random distributions of hard spheres of conductivity {sigma}{sub 2} in a matrix of conductivity {sigma}{sub 1} for virtually the entire volume fraction range and for several values of the conductivity ratio {alpha}={sigma}{sub 2}/{sigma}{sub 1}, including superconducting spheres ({alpha}={infinity}) and perfectly insulating spheres ({alpha}=0). A key feature of the procedure is the use of {ital first}-{ital passage}-{ital time} equations in the two homogeneous phases and at the two-phase interface. The method is shown to yield {sigma}{sub {ital e}} accurately with a comparatively fast execution time. The microstructure-sensitive analytical approximation of {sigma}{sub {ital e}} for dispersions derived by Torquato (J. Appl. Phys. {bold 58}, 3790 (1985)) is shown to be in excellent agreement with our data for random suspensions for the wide range of conditions reported here.

Chan Kim, I. (Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695-7910 (US)); Torquato, S. (Department of Mechanical and Aerospace Engineering and Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7910 (USA))

1991-02-15

162

Physics of Hard Sphere Experiment: Scattering, Rheology and Microscopy Study of Colloidal Particles  

NASA Technical Reports Server (NTRS)

The Physics of Hard Sphere Experiment has two incarnations: the first as a scattering and rheology experiment on STS-83 and STS-94 and the second as a microscopy experiment to be performed in the future on LMM on the space station. Here we describe some of the quantitative and qualitative results from previous flights on the dynamics of crystallization in microgravity and especially the observed interaction of growing crystallites in the coexistance regime. To clarify rheological measurements we also present ground based experiments on the low shear rate viscosity and diffusion coefficient of several hard sphere experiments at high volume fraction. We also show how these experiments will be performed with confocal microscopy and laser tweezers in our lab and as preparation for the phAse II experiments on LMM. One of the main aims of the microscopy study will be the control of colloidal samples using an array of applied fields with an eye toward colloidal architectures. Temperature gradients, electric field gradients, laser tweezers and a variety of switchable imposed surface patterns are used toward this control.

Cheng, Z.-D.; Zhu, J.; Phan, S.-E.; Russel, W. B.; Chaikin, P. M.; Meyer, W. V.

2002-01-01

163

Melting and crystallization of colloidal hard-sphere suspensions under shear  

PubMed Central

Shear-induced melting and crystallization were investigated by confocal microscopy in concentrated colloidal suspensions of hard-sphere-like particles. Both silica and polymethylmethacrylate suspensions were sheared with a constant rate in either a countertranslating parallel plate shear cell or a counterrotating cone-plate shear cell. These instruments make it possible to track particles undergoing shear for extended periods of time in a plane of zero velocity. Although on large scales, the flow profile deviated from linearity, the crystal flowed in an aligned sliding layer structure at low shear rates. Higher shear rates caused the crystal to shear melt, but, contrary to expectations, the transition was not sudden. Instead, although the overall order decreased with shear rate, this was due to an increase in the nucleation of localized domains that temporarily lost and regained their ordered structure. Even at shear rates that were considered to have melted the crystal as a whole, ordered regions kept showing up at times, giving rise to very large fluctuations in 2D bond-orientational order parameters. Low shear rates induced initially disordered suspensions to crystallize. This time, the order parameter increased gradually in time without large fluctuations, indicating that shear-induced crystallization of hard spheres does not proceed via a nucleation and growth mechanism. We conclude that the dynamics of melting and crystallization under shear differ dramatically from their counterparts in quiescent suspensions. PMID:19541643

Wu, Yu Ling; Derks, Didi; van Blaaderen, Alfons; Imhof, Arnout

2009-01-01

164

Heterogeneous crystallization of hard and soft spheres near flat and curved walls  

NASA Astrophysics Data System (ADS)

Crystallization represents a long-standing problem in statistical physics and is of great relevance for many practical and industrial applications. It often occurs in the presence of container walls or impurities, which are usually unavoidable or might even be desirable to facilitate crystallization by exploiting heterogeneous nucleation. Heterogeneous nucleation relies on a seed. Here we discuss the role of the seed and concentrate on a very generic situation, namely crystallization of hard and soft colloidal spheres in the presence of flat or curved hard walls. Curvature serves as a simple means to introduce a tunable mismatch between the seed-induced crystal lattice and the thermodynamically-favoured lattice. The mismatch induces distortions and elastic stress, which accumulate while the crystallite grows. This has an important consequence: once the crystallite reaches a critical size, it detaches from the seed allowing it to relax. The relaxed crystal continues to grow in the bulk, but crystallization ceases before reaching the seed, which now represents an impurity. Therefore, while seeds favour nucleation, any mismatch, like the seed curvature or an incommensurate structure, induces unfavourable distortions and can lead to the detachment of the crystallite. An additional mechanism to relax distortions is available to soft spheres, which can exploit their interaction potential and possibly deform. The different multi-step processes have been investigated by confocal microscopy, which provides particle-level information, and compared to computer simulations and theoretical results.

Sandomirski, K.; Walta, S.; Dubbert, J.; Allahyarov, E.; Schofield, A. B.; Löwen, H.; Richtering, W.; Egelhaaf, S. U.

2014-02-01

165

Pseudo hard-sphere potential for use in continuous molecular-dynamics simulation of spherical and chain molecules.  

PubMed

We present a continuous pseudo-hard-sphere potential based on a cut-and-shifted Mie (generalized Lennard-Jones) potential with exponents (50, 49). Using this potential one can mimic the volumetric, structural, and dynamic properties of the discontinuous hard-sphere potential over the whole fluid range. The continuous pseudo potential has the advantage that it may be incorporated directly into off-the-shelf molecular-dynamics code, allowing the user to capitalise on existing hardware and software advances. Simulation results for the compressibility factor of the fluid and solid phases of our pseudo hard spheres are presented and compared both to the Carnahan-Starling equation of state of the fluid and published data, the differences being indistinguishable within simulation uncertainty. The specific form of the potential is employed to simulate flexible chains formed from these pseudo hard spheres at contact (pearl-necklace model) for m(c) = 4, 5, 7, 8, 16, 20, 100, 201, and 500 monomer segments. The compressibility factor of the chains per unit of monomer, m(c), approaches a limiting value at reasonably small values, m(c) < 50, as predicted by Wertheim's first order thermodynamic perturbation theory. Simulation results are also presented for highly asymmetric mixtures of pseudo hard spheres, with diameter ratios of 3:1, 5:1, 20:1 over the whole composition range. PMID:23061853

Jover, J; Haslam, A J; Galindo, A; Jackson, G; Müller, E A

2012-10-14

166

Fluctuations, structure factor and polytetrahedra in random packings of sticky hard spheres  

E-print Network

Sequentially-built random sphere-packings have been numerically studied in the packing fraction interval $0.329 structure factors $S(Q)$ of the aggregates. Among various parameters (Voronoi tessellation, contact coordination number distribution,...), fluctuations were quantitatively evaluated by the direct evaluation of the fluctuations of the local sphere number density, which appears to follow a power law. The FWHM of the Voronoi cells volume shows a regular variation over the whole packing fraction range. Dirac peaks appear on the pair correlation function as the packing fraction of the aggregates decreases, indicating the growth of larger and larger polytetrahedra, which manifest in two ways on the structure factor, at low and large $Q$values. These low PF aggregates have a composite structure made of regular polytetrahedra embedded in a more disordered matrix. Incidentally, the irregularity index of the building tetrahedron appears as a better parameter than the packing fraction to describe various features of the aggregates structure.

Marc Bletry; Jean Bletry

2014-09-08

167

Test of a universality ansatz for the contact values of the radial distribution functions of hard-sphere mixtures near a hard wall  

E-print Network

Recent Monte Carlo simulation results for the contact values of polydisperse hard-sphere mixtures at a hard planar wall are considered in the light of a universality assumption made in approximate theoretical approaches. It is found that the data seem to fulfill the universality ansatz reasonably well, thus opening up the possibility of inferring properties of complicated systems from the study of simpler ones

Mariano Lopez de Haro; Santos B. Yuste; Andres Santos

2006-07-31

168

Direct measurement of the free energy of aging hard sphere colloidal glasses.  

PubMed

The nature of the glass transition is one of the most important unsolved problems in condensed matter physics. The difference between glasses and liquids is believed to be caused by very large free energy barriers for particle rearrangements; however, so far it has not been possible to confirm this experimentally. We provide the first quantitative determination of the free energy for an aging hard sphere colloidal glass. The determination of the free energy allows for a number of new insights in the glass transition, notably the quantification of the strong spatial and temporal heterogeneity in the free energy. A study of the local minima of the free energy reveals that the observed variations are directly related to the rearrangements of the particles. Our main finding is that the probability of particle rearrangements shows a power law dependence on the free energy changes associated with the rearrangements similar to the Gutenberg-Richter law in seismology. PMID:23829762

Zargar, Rojman; Nienhuis, Bernard; Schall, Peter; Bonn, Daniel

2013-06-21

169

Single-particle fluctuations and directional correlations in driven hard-sphere glasses.  

PubMed

Via event-driven molecular dynamics simulations and experiments, we study the packing-fraction and shear-rate dependence of single-particle fluctuations and dynamic correlations in hard-sphere glasses under shear. At packing fractions above the glass transition, correlations increase as shear rate decreases: the exponential tail in the distribution of single-particle jumps broadens and dynamic four-point correlations increase. Interestingly, however, upon decreasing the packing fraction, a broadening of the exponential tail is also observed, while dynamic heterogeneity is shown to decrease. An explanation for this behavior is proposed in terms of a competition between shear and thermal fluctuations. Building upon our previous studies [Chikkadi et al., Europhys. Lett. 100, 56001 (2012)], we further address the issue of anisotropy of the dynamic correlations. PMID:24032797

Mandal, Suvendu; Chikkadi, Vijaykumar; Nienhuis, Bernard; Raabe, Dierk; Schall, Peter; Varnik, Fathollah

2013-08-01

170

Direct Measurement of the Free Energy of Aging Hard Sphere Colloidal Glasses  

NASA Astrophysics Data System (ADS)

The nature of the glass transition is one of the most important unsolved problems in condensed matter physics. The difference between glasses and liquids is believed to be caused by very large free energy barriers for particle rearrangements; however, so far it has not been possible to confirm this experimentally. We provide the first quantitative determination of the free energy for an aging hard sphere colloidal glass. The determination of the free energy allows for a number of new insights in the glass transition, notably the quantification of the strong spatial and temporal heterogeneity in the free energy. A study of the local minima of the free energy reveals that the observed variations are directly related to the rearrangements of the particles. Our main finding is that the probability of particle rearrangements shows a power law dependence on the free energy changes associated with the rearrangements similar to the Gutenberg-Richter law in seismology.

Zargar, Rojman; Nienhuis, Bernard; Schall, Peter; Bonn, Daniel

2013-06-01

171

Single-particle fluctuations and directional correlations in driven hard-sphere glasses  

NASA Astrophysics Data System (ADS)

Via event-driven molecular dynamics simulations and experiments, we study the packing-fraction and shear-rate dependence of single-particle fluctuations and dynamic correlations in hard-sphere glasses under shear. At packing fractions above the glass transition, correlations increase as shear rate decreases: the exponential tail in the distribution of single-particle jumps broadens and dynamic four-point correlations increase. Interestingly, however, upon decreasing the packing fraction, a broadening of the exponential tail is also observed, while dynamic heterogeneity is shown to decrease. An explanation for this behavior is proposed in terms of a competition between shear and thermal fluctuations. Building upon our previous studies [Chikkadi , Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/100/56001 100, 56001 (2012)], we further address the issue of anisotropy of the dynamic correlations.

Mandal, Suvendu; Chikkadi, Vijaykumar; Nienhuis, Bernard; Raabe, Dierk; Schall, Peter; Varnik, Fathollah

2013-08-01

172

Yielding of Hard-Sphere Glasses during Start-Up Shear  

NASA Astrophysics Data System (ADS)

Concentrated hard-sphere suspensions and glasses are investigated with rheometry, confocal microscopy, and Brownian dynamics simulations during start-up shear, providing a link between microstructure, dynamics, and rheology. The microstructural anisotropy is manifested in the extension axis where the maximum of the pair-distribution function exhibits a minimum at the stress overshoot. The interplay between Brownian relaxation and shear advection as well as the available free volume determine the structural anisotropy and the magnitude of the stress overshoot. Shear-induced cage deformation induces local constriction, reducing in-cage diffusion. Finally, a superdiffusive response at the steady state, with a minimum of the time-dependent effective diffusivity, reflects a continuous cage breakup and reformation.

Koumakis, N.; Laurati, M.; Egelhaaf, S. U.; Brady, J. F.; Petekidis, G.

2012-03-01

173

Equation of state of sticky-hard-sphere fluids in the chemical-potential route.  

PubMed

The coupling-parameter method, whereby an extra particle is progressively coupled to the rest of the particles, is applied to the sticky-hard-sphere fluid to obtain its equation of state in the so-called chemical-potential route (? route). As a consistency test, the results for one-dimensional sticky particles are shown to be exact. Results corresponding to the three-dimensional case (Baxter's model) are derived within the Percus-Yevick approximation by using different prescriptions for the dependence of the interaction potential of the extra particle on the coupling parameter. The critical point and the coexistence curve of the gas-liquid phase transition are obtained in the ? route and compared with predictions from other thermodynamics routes and from computer simulations. The results show that the ? route yields a general better description than the virial, energy, compressibility, and zero-separation routes. PMID:24827207

Rohrmann, René D; Santos, Andrés

2014-04-01

174

Polymer induced changes of the crystallization scenario in suspensions of hard sphere like microgel particles  

NASA Astrophysics Data System (ADS)

We investigated the crystallization scenario of highly cross linked polystyrene particles dispersed in the good solvent 2-ethylnaphtalene and their mixtures with non-adsorbing low molecular weight polysterene polymer using time resolved static light scattering. The samples were prepared slightly below the melting volume fraction of the polymer free system. For the polymer free samples, we obtained polycrystalline solids via crystallization scenario known from hard sphere suspensions with little competition of wall crystal formation. Addition of non-adsorbing low molecular weight polystyrene polymer leads to a considerably slowing down of the bulk crystallization kinetics. We observed a delay of the precursor to crystal conversion for the bulk crystallization while the induction times for the wall nucleation are reduced. The increased polymer concentration thus shifts the balance between the two competing crystallization pathways giving the possibility to tune the relative amount of wall based crystals.

Beyer, Richard; Iacopini, Sara; Palberg, Thomas; Schöpe, Hans Joachim

2012-06-01

175

Disordered Solids Without Well-Defined Transverse Phonons: The Nature of Hard Sphere Glasses  

E-print Network

We probe the Ioffe-Regel limits of glasses with repulsions near the zero-temperature jamming transition by measuring the dynamical structure factors. At zero temperature, the transverse Ioffe-Regel frequency vanishes at the jamming transition with a diverging length, but the longitudinal one does not, which excludes the existence of a diverging length associated with the longitudinal excitations. At low temperatures, the transverse and longitudinal Ioffe-Regel frequencies approach zero at the jamming-like transition and glass transition, respectively. As a consequence, glasses between the glass transition and jamming-like transition, which are hard sphere glasses in the low temperature limit, can only carry well-defined longitudinal phonons and have an opposite pressure dependence of the ratio of the shear modulus to the bulk modulus from glasses beyond the jamming-like transition.

Xipeng Wang; Wen Zheng; Lijin Wang; Ning Xu

2014-09-02

176

Fast decay of the velocity autocorrelation function in dense shear flow of inelastic hard spheres  

E-print Network

We find in complementary experiments and event driven simulations of sheared inelastic hard spheres that the velocity autocorrelation function $\\psi(t)$ decays much faster than $t^{-3/2}$ obtained for a fluid of elastic spheres at equilibrium. Particle displacements are measured in experiments inside a gravity driven flow sheared by a rough wall. The average packing fraction obtained in the experiments is 0.59, and the packing fraction in the simulations is varied between 0.5 and 0.59. The motion is observed to be diffusive over long times except in experiments where there is layering of particles parallel to boundaries, and diffusion is inhibited between layers. Regardless, a rapid decay of $\\psi(t)$ is observed, indicating that this is a feature of the sheared dissipative fluid, and is independent of the details of the relative particle arrangements. An important implication of our study is that the non-analytic contribution to the shear stress may not be present in a sheared inelastic fluid, leading to a wider range of applicability of kinetic theory approaches to dense granular matter.

Ashish V. Orpe; V. Kumaran; K. Anki Reddy; Arshad Kudrolli

2008-11-18

177

Homogeneous Free Cooling State in Binary Granular Fluids of Inelastic Rough Hard Spheres  

NASA Astrophysics Data System (ADS)

In a recent paper [A. Santos, G. M. Kremer, and V. Garzó, Prog. Theor. Phys. Suppl. 184, 31-48 (2010)] the collisional energy production rates associated with the translational and rotational granular temperatures in a granular fluid mixture of inelastic rough hard spheres have been derived. In the present paper the energy production rates are explicitly decomposed into equipartition rates (tending to make all the temperatures equal) plus genuine cooling rates (reflecting the collisional dissipation of energy). Next the homogeneous free cooling state of a binary mixture is analyzed, with special emphasis on the quasi-smooth limit. A previously reported singular behavior (according to which a vanishingly small amount of roughness has a finite effect, with respect to the perfectly smooth case, on the asymptotic long-time translational/translational temperature ratio) is further elaborated. Moreover, the study of the time evolution of the temperature ratios shows that this dramatic influence of roughness already appears in the transient regime for times comparable to the relaxation time of perfectly smooth spheres.

Santos, Andrés

2011-05-01

178

Hardness of T-carbon: Density functional theory calculations  

Microsoft Academic Search

We reconsider and interpret the mechanical properties of the recently proposed allotrope of carbon, T-carbon [Sheng , Phys. Rev. Lett.PRLTAO0031-900710.1103\\/PhysRevLett.106.155703 106, 155703 (2011)], using density functional theory in combination with different empirical hardness models. In contrast with the early estimation based on Gao 's model, which attributes to T-carbon a high Vickers hardness of 61 GPa comparable to that of

Xing-Qiu Chen; Haiyang Niu; Cesare Franchini; Dianzhong Li; Yiyi Li

2011-01-01

179

On the Brownian motion of a massive sphere suspended in a hard-sphere fluid. I. Multiple-time-scale analysis and microscopic expression for the friction coefficient  

SciTech Connect

The Fokker-Planck equation governing the evolution of the distribution function of a massive Brownian hard sphere suspended in a fluid of much lighter spheres is derived from the exact hierarchy of kinetic equations for the total system via a multiple-time-scale analysis akin to a uniform expansion in powers of the square root of the mass ratio. The derivation leads to an exact expression for the friction coefficient which naturally splits into an Enskog contribution and a dynamical correction. The latter, which accounts for correlated collisions events, reduces to the integral of a time-displaced correlation function of dynamical variables linked to the collisional transfer of momentum between the infinitively heavy (i.e., immobile) Brownian sphere and the fluid particles.

Bocquet, L.; Piasecki, J.; Hansen, J.P. [Ecole Normale Superieure de Lyon (France)

1994-07-01

180

Uniform density static fluid sphere in Einstein-Gauss-Bonnet gravity and its universality  

SciTech Connect

In Newtonian theory, gravity inside a constant density static sphere is independent of spacetime dimension. Interestingly this general result is also carried over to Einsteinian as well as higher order Einstein-Gauss-Bonnet (Lovelock) gravity notwithstanding their nonlinearity. We prove that the necessary and sufficient condition for universality of the Schwarzschild interior solution describing a uniform density sphere for all n{>=}4 is that its density is constant.

Dadhich, Naresh; Molina, Alfred; Khugaev, Avas [Inter-University Centre for Astronomy and Astrophysics, Post Bag 4 Pune 411 007 (India); Departament de Fisica Fonamental, Universitat de Barcelona, Barcelona (Spain); Institute of Nuclear Physics, Tashkent, 100214 (Uzbekistan)

2010-05-15

181

Experimental observation of the crystallization of hard-sphere colloidal particles by sedimentation onto flat and patterned surfaces  

E-print Network

to tune independently the range and strength of particle inter- actions 7�9 . A particularly exciting formation 14,15 , matter under shear 16,17 or ther- mal capillary waves 18 . Hard-sphere crystals about dy- namics, but also about the equilibrium states. These ques- tions have been addressed

182

Universal effects of collective interactions on long-time self-diffusion coefficients in hard-sphere systems  

NASA Astrophysics Data System (ADS)

We investigate how universal the collective behavior, due to the many-body interactions in polydisperse hard-sphere systems, is at higher volume fractions. We perform two types of computer simulations, a Brownian-dynamics simulation on colloidal suspensions of hard spheres, where the hydrodynamic interactions between particles are neglected, and a molecular-dynamic simulation on atomic systems of hard spheres. Thus, we show that the long-time self-diffusion coefficients DSL in both systems become singular as DSL( ?)?(1- ?/ ?c) 2 because of the collective interactions due to the many-body collision processes, where ? is a particle volume fraction and ?c?0.586 for 6% polydispersity. Although DSL exhibits the same singular behavior as that obtained theoretically for the monodisperse suspension with the hydrodynamic interactions, no liquid-glass transition is found because even the polydisperse hard-sphere systems crystallize without the hydrodynamic interactions for all ? above the melting volume fraction, which is lower than ?c.

Tokuyama, Michio; Yamazaki, Hiroyuki; Terada, Yayoi

2003-10-01

183

Prediction of particle motion in a two-dimensional bubbling fluidized bed using discrete hard-sphere model  

Microsoft Academic Search

The solids motion in a gas–solid fluidized bed was investigated using a discrete hard-sphere model. Detailed collision between particles and a nearest list method are presented. The turbulent viscosity of gas phase was predicted by subgrid scale (SGS) model. The interaction between gas and particles phases was governed by Newton's third law. The distributions of concentration, velocity and granular temperature

Lu Huilin; Wang Shuyan; Zhao Yunhua; Liu Yang; Dimitri Gidaspow; Jiamin Ding

2005-01-01

184

Signatures of Glass Formation in a Fluidized Bed of Hard Spheres Daniel I. Goldman* and Harry L. Swinney  

E-print Network

Signatures of Glass Formation in a Fluidized Bed of Hard Spheres Daniel I. Goldman* and Harry L motion and thus the loss of fluidization. Microscopic motion persists in this state, but the bed can be jammed by application of a small increase in flow rate. Thus a fluidized bed can serve as a test system

Goldman, Daniel I.

185

Phase behavior and concentration fluctuations in suspensions of hard spheres and nearly ideal polymers  

NASA Astrophysics Data System (ADS)

The phase behavior and concentration fluctuations in suspensions of hard sphere colloids and nonadsorbing polymers under nearly ideal solvent conditions is studied experimentally. A remarkably different qualitative behavior compared to the athermal solvent case is observed for the dependence on polymer/particle size asymmetry of both the gelation and fluid-fluid phase separation boundaries. Near the theta state the effect of increasing the range of depletion attractions leads to a weak monotonic destabilization of the homogeneous phase at high particle volume fractions, with a reversal of the trend at lower volume fractions. In stark contrast to athermal solvent behavior, this nonmonotonic behavior results in multiple "curve crossings" of gel and phase separation boundaries as the polymer/particle size ratio is varied. Quantitative comparisons with no adjustable parameter PRISM integral equation theory for the fluid-fluid spinodals and osmotic compressibilities show good qualitative or semiquantitative agreement with all the experimental trends. The differences between good and ideal solvent conditions are largely attributed to changes in the polymer-polymer pair correlation functions due to the enhanced ability of coils to interpenetrate and cluster in theta solvents. Even for ideal solvent conditions the simplifying polymer model and statistical mechanical assumptions adopted by prior classic free volume and related approaches appear to miss fundamental aspects of the experimental behavior, especially for large size asymmetry ratios and/or moderate-to-high colloid volume fractions. The primary error can be identified with the approximation of a polymer chain by a phantom sphere with no conformational degrees of freedom.

Shah, S. A.; Chen, Y. L.; Schweizer, K. S.; Zukoski, C. F.

2003-02-01

186

EFFICIENT NONPARAMETRIC DENSITY ESTIMATION ON THE SPHERE WITH APPLICATIONS IN FLUID MECHANICS  

E-print Network

and compare the computational efficiency of our method with kernel based estimators. Key words. probability of interest falls on the surface of the sphere. Accurate and fast estimation of probability density functions. Nonparametric density estimation is the problem of the es- timation of the values of a probability density

Egecioglu, Ã?mer

187

On the Brownian motion of a massive sphere suspended in a hard-sphere fluid. II. Molecular dynamics estimates of the friction coefficient  

SciTech Connect

The friction coefficient {gamma} exerted by a hard-sphere fluid on an infinitely massive Brownian sphere is calculated for several size ratios {Sigma}/{sigma} where {Sigma} and {sigma} are the diameters of the Brownian and fluid spheres, respectively. The exact microscopic expression derived in part I of this work from kinetic theory is transformed and shown to be proportional to the time integral of the autocorrelation function of the momentum transferred from the fluid to the Brownian sphere during instantaneous collisions. Three different methods are described to extract the friction coefficient from molecular dynamics simulations carried out on finite systems. The three independent methods lead to estimates of {gamma} which agree within statistical errors (typically 5%). The results are compared to the predictions of Enskog theory and of the hydrodynamic Stokes law. The former breaks down as the size ratio and/or the packing fraction of the fluid increase. Somewhat surprisingly, Stokes` law is found to hold with stick boundary conditions, in the range 1 {le} {Sigma}/{sigma} {le} 4.5 explored in the present simulations, with a hydrodynamic diameter d={Sigma}. The analysis of the molecular dynamics data on the basis of Stokes` law with slip boundary conditions is less conclusive, although the right trend is found as {Sigma}/{sigma} increases.

Bocquet, L.; Hansen, J.P.; Piasecki, J. [Ecole Normale Superieure de Lyon (France)

1994-07-01

188

Wave packet autocorrelation functions for quantum hard-disk and hard-sphere billiards in the high-energy, diffraction regime  

NASA Astrophysics Data System (ADS)

We consider the time evolution of a wave packet representing a quantum particle moving in a geometrically open billiard that consists of a number of fixed hard-disk or hard-sphere scatterers. Using the technique of multiple collision expansions we provide a first-principle analytical calculation of the time-dependent autocorrelation function for the wave packet in the high-energy diffraction regime, in which the particle’s de Broglie wavelength, while being small compared to the size of the scatterers, is large enough to prevent the formation of geometric shadow over distances of the order of the particle’s free flight path. The hard-disk or hard-sphere scattering system must be sufficiently dilute in order for this high-energy diffraction regime to be achievable. Apart from the overall exponential decay, the autocorrelation function exhibits a generally complicated sequence of relatively strong peaks corresponding to partial revivals of the wave packet. Both the exponential decay (or escape) rate and the revival peak structure are predominantly determined by the underlying classical dynamics. A relation between the escape rate, and the Lyapunov exponents and Kolmogorov-Sinai entropy of the counterpart classical system, previously known for hard-disk billiards, is strengthened by generalization to three spatial dimensions. The results of the quantum mechanical calculation of the time-dependent autocorrelation function agree with predictions of the semiclassical periodic orbit theory.

Goussev, Arseni; Dorfman, J. R.

2006-07-01

189

Monte Carlo simulation of growth of hard-sphere crystals on a square pattern  

E-print Network

Monte Carlo simulations of the colloidal epitaxy of hard spheres (HSs) on a square pattern have been performed. This is an extension of previous simulations; we observed a shrinking intrinsic stacking fault running in an oblique direction through the glide of a Shockley partial dislocation terminating its lower end in fcc (001) stacking [Mori et al., Molec. Phys. 105 (2007) 1377], which was an answer to a question why the defect in colloidal crystals reduced by gravity [Zhu et al., Nature 387 (1997) 883]. We have resolved one of shortcomings of the previous simulations; the driving force for fcc (001) stacking, which was stress from a small periodic boundary simulation box, has been replaced with the stress from a pattern on the bottom. We have observed disappearance of stacking fault in this realizable condition. Sinking of the center of gravity has been smooth and of a single relaxation mode under the condition that the gravitational energy mgd is slightly less than the thermal energy kT. In the snapshots tetrahedral structures have appeared often, suggesting formation of staking fault tetrahedra.

Atsushi Mori

2010-10-15

190

Single file and normal dual mode diffusion in highly confined hard sphere mixtures under flow.  

PubMed

We use Monte Carlo simulations to study the dual-mode diffusion regime of binary and tertiary mixtures of hard spheres confined in narrow cylindrical pores under the influence of an imposed flow. The flow is introduced to the dynamics by adding a small bias directed along the long axis of the pore to the random displacement of each Monte Carlo move. As a result, the motion of the particles in all the components is dominated by a drift velocity that causes the mean squared displacements to increase quadratically in the long time limit. However, an analysis of the mean squared displacements at intermediate time scales shows that components of the mixture above and below their passing thresholds still exhibit behaviors consistent with normal and single-file diffusion, respectively. The difference between the mean squared displacements of the various components is shown to go though a maximum, suggesting there may be an optimal pore diameter for the separation of mixtures exhibiting dual-mode diffusion. PMID:22979868

Wanasundara, Surajith N; Spiteri, Raymond J; Bowles, Richard K

2012-09-14

191

Hard-sphere fluid with tight-binding electronic interactions:??A glue model treatment  

NASA Astrophysics Data System (ADS)

We have carried out self-consistent Monte Carlo simulations for a model fluid of monovalent atoms, with both hard-sphere repulsions and an attraction arising from the free energy of its valence electrons. This energy is derived from a tight-binding model with electronic hopping which decays exponentially with distance. The problem requires a many-body description of the atomic energies; thus, we have undertaken the construction and testing of a glue model to simplify the description of such atomic energies in a disordered environment. In contrast to usual procedures, our glue-model parameters are derived internally, from the system itself. Our previous work on a self-consistent fluid model is here generalized by removing the restrictions of a lattice gas and electron hopping limited to nearest-neighbor sites. The phase diagram and the results due to mutual self-consistency on the fluid structures and electronic properties are obtained in the present work and compared to experimental data for fluid cesium. The electronic conductivity of this type of a model fluid has been studied by others; we note, in some detail, the contrast between their results and the ones herein.

Reinaldo-Falagán, M.; Tarazona, P.; Chacón, E.; Velasco, E.; Hernandez, J. P.

2003-01-01

192

Structural searches using isopointal sets as generators: densest packings for binary hard sphere mixtures  

NASA Astrophysics Data System (ADS)

Algorithms to search for crystal structures that optimize some extensive property (energy, volume, etc) typically make use of random particle reorganizations in the context of one or more numerical techniques such as simulated annealing, genetic algorithms or biased random walks, applied to the coordinates of every particle in the unit cell, together with the cell angles and lengths. In this paper we describe the restriction of such searches to predefined isopointal sets, breaking the problem into countable sub-problems which exploit crystal symmetries to reduce the dimensionality of the search space. Applying this method to the search for maximally packed mixtures of hard spheres of two sizes, we demonstrate that the densest packed structures can be identified by searches within a couple of isopointal sets. For the A2B system, the densest known packings over the entire tested range 0.2 < rA/rB < 2.5, including some improvements on previous optima, can all be identified by searches within a single isopointal set. In the case of the AB composition, searches of two isopointal sets generate the densest packed structures over the radius ratio range 0.2 < rA/rB < 5.0.

Hudson, Toby S.; Harrowell, Peter

2011-05-01

193

Crystal nucleation in the hard-sphere system revisited: a critical test of theoretical approaches.  

PubMed

The hard-sphere system is the best known fluid that crystallizes: the solid-liquid interfacial free energy, the equations of state, and the height of the nucleation barrier are known accurately, offering a unique possibility for a quantitative validation of nucleation theories. A recent significant downward revision of the interfacial free energy from approximately 0.61kT/sigma(2) to (0.56 +/- 0.02)kT/sigma(2) [Davidchack, R.; Morris, J. R.; Laird, B. B. J. Chem. Phys. 2006, 125, 094710] necessitates a re-evaluation of theoretical approaches to crystal nucleation. This has been carried out for the droplet model of the classical nucleation theory (CNT), the self-consistent classical theory (SCCT), a phenomenological diffuse interface theory (DIT), and single- and two-field variants of the phase field theory that rely on either the usual double-well and interpolation functions (PFT/S1 and PFT/S2, respectively) or on a Ginzburg-Landau expanded free energy that reflects the crystal symmetries (PFT/GL1 and PFT/GL2). We find that the PFT/GL1, PFT/GL2, and DIT models predict fairly accurately the height of the nucleation barrier known from Monte Carlo simulations in the volume fraction range of 0.52 < varphi < 0.54, whereas the CNT, SCCT, PFT/S1, and PFT/S2 models underestimate it significantly. PMID:19320450

Tóth, Gyula I; Gránásy, László

2009-04-16

194

Thermodynamics and dynamics of the hard-sphere system: From stable to metastable states  

NASA Astrophysics Data System (ADS)

A set of three different scaling laws is investigated, which are devoted to link the transport properties, i.e. diffusion coefficient, shear viscosity, bulk viscosity and thermal conductivity, to the thermodynamic properties for the athermal hard-sphere system, over the wider range of packing fraction covering the stable and metastable regimes. Except for the thermal conductivity, the Rosenfeld (1999) [15] relation is found to be applicable to the stable states while the Adam and Gibbs (1965) [24] relation holds well for the metastable states. In contrast, the modified Cohen and Turnbull (1959) [25] relation proposed here gives sound support for a universal scaling law connecting the dynamic and thermodynamic properties, over the domain of packing fraction including the stable and metastable states. In particular, it is found that the most relevant control parameter is not the excess entropy, but the logarithm derivative of the excess entropy with respect to the packing fraction. In the same context, the Stokes-Einstein relation between the diffusion coefficient and the shear viscosity is also examined. The possible violation of the Stokes-Einstein relation is investigated over a large domain of packing fractions.

Bomont, Jean-Marc; Bretonnet, Jean-Louis

2014-08-01

195

From compact to fractal crystalline clusters in concentrated systems of monodisperse hard spheres  

E-print Network

We address the crystallization of monodisperse hard spheres in terms of the properties of finite- size crystalline clusters. By means of large scale event-driven Molecular Dynamics simulations, we study systems at different packing fractions {\\phi} ranging from weakly supersaturated state points to glassy ones, covering different nucleation regimes. We find that such regimes also result in different properties of the crystalline clusters: compact clusters are formed in the classical-nucleation-theory regime ({\\phi} \\leq 0.54), while a crossover to fractal, ramified clusters is encountered upon increasing packing fraction ({\\phi} \\geq 0.56), where nucleation is more spinodal-like. We draw an analogy between macroscopic crystallization of our clusters and percolation of attractive systems to provide ideas on how the packing fraction influences the final structure of the macroscopic crystals. In our previous work (Phys. Rev. Lett., 106, 215701, 2011), we have demonstrated how crystallization from a glass (at {\\phi} > 0.58) happens via a gradual (many-step) mechanism: in this paper we show how the mechanism of gradual growth seems to hold also in super-saturated systems just above freezing showing that static properties of clusters are not much affected by dynamics.

Chantal Valeriani; Eduardo Sanz; Peter N. Pusey; Wilson C. K. Poon; Michael E. Cates; Emanuela Zaccarelli

2012-03-21

196

Disappearance of a Stacking Fault in Hard-Sphere Crystals under Gravity  

NASA Astrophysics Data System (ADS)

In the first part of this paper, a review is given on the mechanismfor the disappearance of an intrinsic stacking fault in a hard-sphere (HS) crystal under gravity, which we recently discovered by Monte Carlo (MC) simulations [A. Mori et al., J. Chem. Phys. 124 (2006), 17450; Mol. Phys. 105 (2007), 1377]. We have observed, in the case of fcc (001) stacking, that the intrinsic stacking fault running along an oblique direction shrunk through the gliding of a Shockley partial dislocation at the lower end of the stacking fault. In order to address the shortcomings and approximations of previous simulations, such as the use of periodic ] boundary condition (PBC) and the fact that the fcc (001) stacking had been realized by the stress from the small PBC box, we present an elastic strain energy calculation for an infinite system and a MC simulation result for HSs in a pyramidal pit under gravity. In particular, the geometry of the latter has already been tested experi mentally [S. Matsuo et al., Appl. Phys. Lett. 82 (2003), 4283]. The advantage of using a pyramidal pit as a template as well as the feasibility of the mechanism we describe is demonstrated.

Mori, A.; Suzuki, Y.; Matsuo, S.

197

Local shear transformations in deformed and quiescent hard-sphere colloidal glasses  

NASA Astrophysics Data System (ADS)

We perform a series of deformation experiments on a monodisperse, hard-sphere colloidal glass while simultaneously following the three-dimensional trajectories of roughly 50000 individual particles with a confocal microscope. In each experiment, we deform the glass in pure shear at a constant strain rate [(1-5)×10-5 s-1] to maximum macroscopic strains (5%-10%) and then reverse the deformation at the same rate to return to zero macroscopic strain. We also measure three-dimensional particle trajectories in an identically prepared quiescent glass in which the macroscopic strain is always zero. We find that shear transformation zones exist and are active in both sheared and quiescent colloidal glasses, revealed by a distinctive fourfold signature in spatial autocorrelations of the local shear strain. With increasing shear, the population of local shear transformations develops more quickly than in a quiescent glass and many of these transformations are irreversible. When the macroscopic strain is reversed, we observe partial elastic recovery, followed by plastic deformation of the opposite sign, required to compensate for the irreversibly transformed regions. The average diameter of the shear transformation zones in both strained and quiescent glasses is slightly more than two particle diameters.

Jensen, K. E.; Weitz, D. A.; Spaepen, F.

2014-10-01

198

Free energy of dipolar hard spheres: The virial expansion under the presence of an external magnetic field  

NASA Astrophysics Data System (ADS)

A method for calculation of the free energy of dipolar hard spheres under the presence of an applied magnetic field is presented. The method is based on the virial expansion in terms of density as well as the dipolar coupling constant ?, and it uses diagram technique. The formulas and the diagrams, needed to calculate the second B2 and third B3 virial coefficients, are derived up to the order of ˜?3, and compared to the zero-field case. The formula for B2 is the same as in the zero-field case; the formula for B3, however, is different in an applied field, and a derivation is presented. This is a surprising result which is not emphasized in standard texts, but which has been noticed before in the virial expansion for flexible molecules (Caracciolo et al., 2006; Caracciolo et al., 2008). To verify the correctness of the obtained formulas, B2 and B3 were calculated within the accuracy of ?2, which were applied to initial magnetic susceptibility. The obtained expression fully coincides with the well-known theories (Morozov and Lebedev, 1990; Huke and Lücke, 2000; Ivanov and Kuznetsova, 2001), which used different methods to calculate the initial magnetic susceptibility.

Elfimova, Ekaterina A.; Karavaeva, Tatyana E.; Ivanov, Alexey O.

2014-12-01

199

On the accurate direct computation of the isothermal compressibility for normal quantum simple fluids: Application to quantum hard spheres  

NASA Astrophysics Data System (ADS)

A systematic study of the direct computation of the isothermal compressibility of normal quantum fluids is presented by analyzing the solving of the Ornstein-Zernike integral (OZ2) equation for the pair correlations between the path-integral necklace centroids. A number of issues related to the accuracy that can be achieved via this sort of procedure have been addressed, paying particular attention to the finite-N effects and to the definition of significant error bars for the estimates of isothermal compressibilities. Extensive path-integral Monte Carlo computations for the quantum hard-sphere fluid (QHS) have been performed in the (N, V, T) ensemble under temperature and density conditions for which dispersion effects dominate the quantum behavior. These computations have served to obtain the centroid correlations, which have been processed further via the numerical solving of the OZ2 equation. To do so, Baxter-Dixon-Hutchinson's variational procedure, complemented with Baumketner-Hiwatari's grand-canonical corrections, has been used. The virial equation of state has also been obtained and several comparisons between different versions of the QHS equation of state have been made. The results show the reliability of the procedure based on isothermal compressibilities discussed herein, which can then be regarded as a useful and quick means of obtaining the equation of state for fluids under quantum conditions involving strong repulsive interactions.

Sesé, Luis M.

2012-06-01

200

Hardness of FeB4: Density functional theory investigation  

NASA Astrophysics Data System (ADS)

A recent experimental study reported the successful synthesis of an orthorhombic FeB4 with a high hardness of 62(5) GPa [H. Gou et al., Phys. Rev. Lett. 111, 157002 (2013)], which has reignited extensive interests on whether transition-metal borides compounds will become superhard materials. However, it is contradicted with some theoretical studies suggesting transition-metal boron compounds are unlikely to become superhard materials. Here, we examined structural and electronic properties of FeB4 using density functional theory. The electronic calculations show the good metallicity and covalent Fe-B bonding. Meanwhile, we extensively investigated stress-strain relations of FeB4 under various tensile and shear loading directions. The calculated weakest tensile and shear stresses are 40 GPa and 25 GPa, respectively. Further simulations (e.g., electron localization function and bond length along the weakest loading direction) on FeB4 show the weak Fe-B bonding is responsible for this low hardness. Moreover, these results are consistent with the value of Vickers hardness (11.7-32.3 GPa) by employing different empirical hardness models and below the superhardness threshold of 40 GPa. Our current results suggest FeB4 is a hard material and unlikely to become superhard (>40 GPa).

Zhang, Miao; Lu, Mingchun; Du, Yonghui; Gao, Lili; Lu, Cheng; Liu, Hanyu

2014-05-01

201

Thermodynamic properties and electrical conductivity of a tight-binding hard-sphere model for liquid metals  

Microsoft Academic Search

We have carried out self-consistent Monte–Carlo simulations for a model fluid of monovalent atoms which interact via hard-sphere repulsions and an attraction arising from the free energy of its valence electrons. This attractive energy is derived from a tight-binding model with an electronic hopping which decays exponentially with distance. The liquid–vapor phase diagram and the structural properties are obtained in

E. Chacon; P. Tarazona; J. A. Vergés; M. Reinaldofalagan; E. Velasco; J. P. Hernandez

2007-01-01

202

Can the packing efficiency of binary hard spheres explain the glass-forming ability of bulk metallic glasses?  

E-print Network

We perform molecular dynamics simulations to compress binary hard spheres into jammed packings as a function of the compression rate $R$, size ratio $\\alpha$, and number fraction $x_S$ of small particles to determine the connection between the glass-forming ability (GFA) and packing efficiency in bulk metallic glasses (BMGs). We define the GFA by measuring the critical compression rate $R_c$, below which jammed hard-sphere packings begin to form "random crystal" structures with defects. We find that for systems with $\\alpha \\gtrsim 0.8$ that do not de-mix, $R_c$ decreases strongly with $\\Delta \\phi_J$, as $R_c \\sim \\exp(-1/\\Delta \\phi_J^2)$, where $\\Delta \\phi_J$ is the difference between the average packing fraction of the amorphous packings and random crystal structures at $R_c$. Systems with $\\alpha \\lesssim 0.8$ partially de-mix, which promotes crystallization, but we still find a strong correlation between $R_c$ and $\\Delta \\phi_J$. We show that known metal-metal BMGs occur in the regions of the $\\alpha$ and $x_S$ parameter space with the lowest values of $R_c$ for binary hard spheres. Our results emphasize that maximizing GFA in binary systems involves two competing effects: minimizing $\\alpha$ to increase packing efficiency, while maximizing $\\alpha$ to prevent de-mixing.

Kai Zhang; W. Wendell Smith; Minglei Wang; Yanhui Liu; Jan Schroers; Mark D. Shattuck; Corey S. O'Hern

2014-04-02

203

Connection between the packing efficiency of binary hard spheres and the glass-forming ability of bulk metallic glasses  

NASA Astrophysics Data System (ADS)

We perform molecular dynamics simulations to compress binary hard spheres into jammed packings as a function of the compression rate R, size ratio ?, and number fraction xS of small particles to determine the connection between the glass-forming ability (GFA) and packing efficiency in bulk metallic glasses (BMGs). We define the GFA by measuring the critical compression rate Rc, below which jammed hard-sphere packings begin to form "random crystal" structures with defects. We find that for systems with ? ?0.8 that do not demix, Rc decreases strongly with ??J, as Rc˜exp(-1/??J2), where ??J is the difference between the average packing fraction of the amorphous packings and random crystal structures at Rc. Systems with ? ?0.8 partially demix, which promotes crystallization, but we still find a strong correlation between Rc and ??J. We show that known metal-metal BMGs occur in the regions of the ? and xS parameter space with the lowest values of Rc for binary hard spheres. Our results emphasize that maximizing GFA in binary systems involves two competing effects: minimizing ? to increase packing efficiency, while maximizing ? to prevent demixing.

Zhang, Kai; Smith, W. Wendell; Wang, Minglei; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D.; O'Hern, Corey S.

2014-09-01

204

Molecular-dynamics study of the effects of strain on interstitial diffusion in a hard-sphere model of a binary crystalline solid  

Microsoft Academic Search

We examine quantitatively the effects on tracer diffusion of both externally applied strains and internal strains generated by large interstitial particles dissolved in a coherent hard-sphere crystal. The molecular-dynamics method, generalized to permit elastic deformations of a system, is used to simulate the diffusion of interstitials in a binary hard-sphere solid. A tracer-diffusion response function E(k) is calculated from a

J. M. Rickman; Jorge Vials; R. F. Sekerka

1991-01-01

205

Molecular-dynamics study of the effects of strain on interstitial diffusion in a hard-sphere model of a binary crystalline solid  

Microsoft Academic Search

We examine quantitatively the effects on tracer diffusion of both externally applied strains and internal strains generated by large interstitial particles dissolved in a coherent hard-sphere crystal. The molecular-dynamics method, generalized to permit elastic deformations of a system, is used to simulate the diffusion of interstitials in a binary hard-sphere solid. A tracer-diffusion response function {ital E}({bold k}) is calculated

J. M. Rickman; J. Vinals; R. F. Sekerka

1991-01-01

206

A Family of Tunable Spherically-Symmetric Potentials that Span the Range from Hard Spheres to Water-like Behavior  

E-print Network

We investigate the equation of state, diffusion coefficient, and structural order of a family of spherically-symmetric potentials consisting of a hard core and a linear repulsive ramp. This generic potential has two characteristic length scales: the hard and soft core diameters. The family of potentials is generated by varying their ratio, $\\lambda$. We find negative thermal expansion (thermodynamic anomaly) and an increase of the diffusion coefficient upon isothermal compression (dynamic anomaly) for $0\\leq\\lambdawater, the regions where these anomalies occur are nested domes in the ($T, \\rho$) or ($T, P$) planes, with the thermodynamic anomaly dome contained entirely within the dynamic anomaly dome. We calculate translational and orientational order parameters ($t$ and $Q_6$), and project equilibrium state points onto the ($t, Q_6$) plane, or order map. The order map evolves from water-like behavior to hard-sphere-like behavior upon varying $\\lambda$ between 4/7 and 6/7. Thus, we traverse the range of liquid behavior encompassed by hard spheres ($\\lambda=1$) and water-like ($\\lambda\\sim4/7$) with a family of tunable spherically-symmetric potentials by simply varying the ratio of hard to soft-core diameters. Although dynamic and thermodynamic anomalies occur almost across the entire range $0\\leq\\lambda\\leq1$, water-like structural anomalies (i.e., decrease in both $t$ and $Q_6$ upon compression and strictly correlated $t$ and $Q_6$ in the anomalous region) occur only around $\\lambda=4/7$. Water-like anomalies in structure, dynamics and thermodynamics arise solely due to the existence of two length scales, orientation-dependent interactions being absent by design.

Zhenyu Yan; Sergey V. Buldyrev; Nicolas Giovambattista; Pablo G. Debenedetti; H. Eugene Stanley

2006-01-24

207

Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures  

E-print Network

Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is eta_p^r=0.1 and the colloid-polymer size ratio is q=sigma_p/\\sigma=0.15 (with sigma_p and sigma the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure p_co is obtained, yielding p_co=11.576 k_BT/sigma^3 for the hard sphere system and p_co=8.0 k_BT/sigma^3 for the AO model (with k_B the Boltzmann constant and T the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values gamma=0.49 k_BT/sigma^2 for the hard-sphere system and gamma=0.95 k_BT/sigma^2 for the AO model.

T. Zykova-Timan; J. Horbach; K. Binder

2010-03-05

208

Fourth virial coefficient of additive hard-sphere mixtures in the Percus-Yevick and hypernetted-chain approximations  

E-print Network

The fourth virial coefficient of additive hard-sphere mixtures, as predicted by the Percus-Yevick (PY) and hypernetted-chain (HNC) theories, is derived via the compressibility, virial, and chemical-potential routes, the outcomes being compared with exact results. Except in the case of the HNC compressibility route, the other five expressions exhibit a common structure involving the first three moments of the size distribution. In both theories the chemical-potential route is slightly better than the virial one and the best behavior is generally presented by the compressibility route. Moreover, the PY results with any of the three routes are more accurate than any of the HNC results.

Elena Beltrán-Heredia; Andrés Santos

2014-02-19

209

On the gas-gas equilibria of second kind of nonpolar fluid binary mixtures from a hard-sphere EXP-6 molecular model  

NASA Astrophysics Data System (ADS)

The phase behavior of a molecular-based model of nonpolar binary mixtures is investigated by the application of thermodynamic perturbation theory. The pair potential interaction model is represented as a reference system of equal size hard-spheres perturbed by the exponential-6 potential. It is found that the qualitative behavior of gas-gas immiscibility of second kind is very much sensitive to the hardness of the potential (ratio of the hard sphere diameter to the size parameter of the perturbation). Calculated theoretical phase diagrams are compared with results from Monte Carlo simulations in the Gibbs ensemble performed for this model mixture.

Zarragoicoechea, G. J.; Scalise, O. H.

1997-09-01

210

Emerging quasi-0D states at vanishing total entropy of the 1D hard sphere system: A coarse-grained similarity to the car parking problem  

NASA Astrophysics Data System (ADS)

A coarse-grained system of one-dimensional (1D) hard spheres (HSs) is created using the Delaunay tessellation, which enables one to define the quasi-0D state. It is found from comparing the quasi-0D and 1D free energy densities that a frozen state due to the emergence of quasi-0D HSs is thermodynamically more favorable than fluidity with a large-scale heterogeneity above crossover volume fraction of ?c=e/(1+e)=0.731⋯ , at which the total entropy of the 1D state vanishes. The Delaunay-based lattice mapping further provides a similarity between the dense HS system above ?c and the jamming limit in the car parking problem.

Frusawa, Hiroshi

2014-05-01

211

Phase equilibria in strong polar fluids using a perturbed hard-sphere-chain equation of state combined with three different association models  

SciTech Connect

Goal of this work is the extension of a Perturbed-Hard-Sphere-Chain equation of state (PHSC EOS) to systems containing strong polar components. Three different types of association models (ten Brinke/Karasz, SAFI, modified Veytsman) were used to calculate the contribution of specific interactions like hydrogen bonding to thermodynamic quantities. Pure component parameters obtained from regression of temperature dependent density and vapor pressure data allow the prediction of VLE and LLE data. The results of simple fluids and polymer solutions were compared with experimental data. The SAFT and the modified Veytsman extension give similar results for pure fluids and mixtures with components of similar segment size. Differences increase with increasing difference of segment size.

Schaefer, B.; Lambert, S.M.; Song, Y.; Prausnitz, J.M.

1994-10-01

212

Emerging quasi-0D states at vanishing total entropy of the 1D hard sphere system: a coarse-grained similarity to the car parking problem  

E-print Network

A coarse-grained system of one-dimensional (1D) hard spheres (HSs) is created using the Delaunay tessellation, which enables one to define the quasi-0D state. It is found from comparing the quasi-0D and 1D free energy densities that a frozen state due to the emergence of quasi-0D HSs is thermodynamically more favorable than fluidity with a large-scale heterogeneity above crossover volume fraction of $\\phi_c=e/(1+e)=0.731\\cdots$, at which the total entropy of the 1D state vanishes. The Delaunay-based lattice mapping further provides a similarity between the dense HS system above $\\phi_c$ and the jamming limit in the car parking problem.

Hiroshi Frusawa

2014-04-24

213

Influence of polydispersity on the critical parameters of an effective-potential model for asymmetric hard-sphere mixtures  

NASA Astrophysics Data System (ADS)

We report a Monte Carlo simulation study of the properties of highly asymmetric binary hard-sphere mixtures. This system is treated within an effective fluid approximation in which the large particles interact through a depletion potential [R. Roth , Phys. Rev. E 62 5360 (2000)] designed to capture the effects of a virtual sea of small particles. We generalize this depletion potential to include the effects of explicit size dispersity in the large particles and consider the case in which the particle diameters are distributed according to a Schulz form having a degree of polydispersity 14%. The resulting alteration (with respect to the monodisperse limit) of the metastable fluid-fluid critical point parameters is determined for two values of the ratio of the diameters of the small and large particles: q??s/?¯b=0.1 and q=0.05 . We find that the inclusion of polydispersity moves the critical point to lower reservoir volume fractions of the small particles and high volume fractions of the large ones. The estimated critical point parameters are found to be in good agreement with those predicted by a generalized corresponding states argument which provides a link to the known critical adhesion parameter of the adhesive hard-sphere model. Finite-size scaling estimates of the cluster percolation line in the one phase fluid region indicate that inclusion of polydispersity moves the critical point deeper into the percolating regime. This suggests that phase separation is more likely to be preempted by dynamical arrest in polydisperse systems.

Largo, Julio; Wilding, Nigel B.

2006-03-01

214

Many-body Bose systems and the hard-sphere model: dynamic properties from the weak to the strong interaction regime  

NASA Astrophysics Data System (ADS)

We obtain ab-initio estimations of the dynamic structure factor, S(q,?), of Bose gases at zero temperature. More precisely, we use the Genetic Inversion via Falsification of Theories (GIFT) algorithm to perform analytic continuations of imaginary time correlation functions computed via an exact Path Integral projector method. Using the hard-sphere potential to model the two-body interactions between the atoms, we compute S(q,?) changing the gas parameter from the dilute regime (na3 = 10?4) up to the density corresponding to superfluid 4He at equilibrium (na3 = 0.2138). With increasing density, we observe the emergence of a broad multiphonon contribution accompanying the quasiparticle peak and a crossover of the dispersion of elementary excitations from a Bogoliubov-like spectrum to a phonon-maxon- roton curve. Apart from the low wave vector region, for na3 = 0.2138 the energy-momentum dispersion relation and the static density response function, ?(q), turns out to be in good agreement with the superfluid 4He experimental data at equilibrium density.

Rota, R.; Tramonto, F.; Galli, D. E.; Giorgini, S.

2014-08-01

215

Dynamics of Disorder-Order Transitions in Hard Sphere Colloidal Dispersions in micro-g  

NASA Technical Reports Server (NTRS)

We performed a series of experiments on 0.518 millimeter PMMA spheres suspended in an index matching mixture of decalin and tetralin the microgravity environment provided by the Shuttle Columbia on mission STS-73. The samples ranged in concentration from 0.49 to 0.62. volume fraction (phi) of spheres, which covers the range in which liquid, coexistence, solid and glass phases are expected from Earth bound experiments. Light scattering was used to probe the static structure, and the particle dynamics. Digital and 35 mm photos provided information on the morphology of the crystals. In general, the crystallites grew considerably larger (roughly an order of magnitude larger) than the same samples with identical treatment in 1 g. The dynamic light scattering shows the typical short time diffusion and long time caging effects found in 1 g. The surprises that were encountered in microgravity include the preponderance of random hexagonal close packed (RHCP) structures and the complete absence of the expected face centered cubic (FCC) structure, existence of large dendritic crystals floating in the coexistence samples (where liquid and solid phases coexist) and the rapid crystallization of samples which exist only in glass phase under the influence of one g. These results suggest that colloidal crystal growth is profoundly effected by gravity in yet unrecognized ways. We suspect that the RCHP structure is related to the nonequilibrium growth that is evident from the presence of dendrites. An analysis of the dendritic growth instabilities is presented within the framework of the Ackerson-Schatzel equation.

Zhu, J. X.; Li, M.; Phan, S. E.; Russel, W. B.; Chaikin, Paul M.; Rogers, Rick; Meyers, W.

1996-01-01

216

The power of hard-sphere models for proteins: Understanding side-chain conformations and predicting thermodynamic stability  

NASA Astrophysics Data System (ADS)

We seek to dramatically improve computational protein design using minimal models that include only the dominant physical interactions. By modeling proteins with hard-sphere interactions and stereochemical constraints, we are able to explain the side-chain dihedral angle distributions for Leu, Ile, and other hydrophobic residues that are observed in protein crystal structures. We also consider inter-residue interactions on the distribution of side-chain dihedral angles for residues in the hydrophobic core of T4 lysozyme. We calculate the energetic and entropic contributions to the free energy differences between wildtype T4 lysozyme and several mutants involving Leu to Ala substitutions. We find a strong correlation between the entropy difference and the decrease in the melting temperature of the mutatants. These results emphasize that considering both entropy and enthalpy is crucial for obtaining a quantitative understanding of protein stability.

Qinhua Zhou, Alice; O'Hern, Corey; Regan, Lynne

2013-03-01

217

Validation of a glue-model approach in a tight-binding hard-sphere model for hot fluid metals  

NASA Astrophysics Data System (ADS)

We have calculated thermodynamic, structural, and electronic properties of a model fluid of monovalent atoms which interact via hard-sphere repulsions and an attraction arising from the delocalization free energy of the valence electrons. These properties result from self-consistent Monte Carlo simulations of equilibrium ionic structures based, at each step in which an ion is to be moved, on the exact electronic free energies corresponding to the ionic configurations. The electronic energy is derived from a tight-binding model with electronic hopping which decays exponentially with distance. The liquid-vapor coexistence curve and both ionic and electronic structures are obtained. By direct comparisons, the present results confirm previous ones which were obtained basing the simulations on a glue-model description of ion energies. The importance of this confirmation is the validation of the glue-model approach, one of the few computational simplifications possible for realistic metallic fluids.

Chacón, E.; Reinaldo-Falagán, M.; Tarazona, P.; Velasco, E.; Hernandez, J. P.

2005-01-01

218

Time and volume fraction dependence of dynamic heterogeneity in a glass-forming binary hard-sphere mixture  

NASA Astrophysics Data System (ADS)

We examined dynamic heterogeneity in a glass-forming binary hard-sphere mixture for volume fractions up to and including the so-called mode-coupling transition. We calculated the dynamic susceptibility ?4(t), the four-point structure factor S4(q;t) and the dynamic correlation length ?(t). We find that the correlation length increases with time as ?(t) ˜(t) and is independent of ? for times approximately between the ? and ? relaxation time. The dynamic length plateaus at a ? dependent value ?max(?). We find that ?max(?) is proportional to the dynamic length at the ? relaxation time, ?(??). Finally, while for a limited range of volume fractions ?(??) ˜?&1/zcirc; with 1/z 0.2, we find that ?(??) ˜(??) describes our data well for all ?.

Flenner, Elijah; Szamel, Grzegorz

2011-03-01

219

Numerical simulations of granular dynamics. I. Hard-sphere discrete element method and tests  

E-print Network

We present a new particle-based (discrete element) numerical method for the simulation of granular dynamics, with application to motions of particles on small solar system body and planetary surfaces. The method employs the parallel N-body tree code pkdgrav to search for collisions and compute particle trajectories. Collisions are treated as instantaneous point-contact events between rigid spheres. Particle confinement is achieved by combining arbitrary combinations of four provided wall primitives, namely infinite plane, finite disk, infinite cylinder, and finite cylinder, and degenerate cases of these. Various wall movements, including translation, oscillation, and rotation, are supported. We provide full derivations of collision prediction and resolution equations for all geometries and motions. Several tests of the method are described, including a model granular "atmosphere" that achieves correct energy equipartition, and a series of tumbler simulations that show the expected transition from tumbling to ...

Richardson, Derek C; Murdoch, Naomi; Michel, Patrick

2013-01-01

220

Numerical simulations of granular dynamics: I. Hard-sphere discrete element method and tests  

NASA Astrophysics Data System (ADS)

We present a new particle-based (discrete element) numerical method for the simulation of granular dynamics, with application to motions of particles on small solar system body and planetary surfaces. The method employs the parallel N-body tree code pkdgrav to search for collisions and compute particle trajectories. Collisions are treated as instantaneous point-contact events between rigid spheres. Particle confinement is achieved by combining arbitrary combinations of four provided wall primitives, namely infinite plane, finite disk, infinite cylinder, and finite cylinder, and degenerate cases of these. Various wall movements, including translation, oscillation, and rotation, are supported. We provide full derivations of collision prediction and resolution equations for all geometries and motions. Several tests of the method are described, including a model granular “atmosphere” that achieves correct energy equipartition, and a series of tumbler simulations that show the expected transition from tumbling to centrifuging as a function of rotation rate.

Richardson, Derek C.; Walsh, Kevin J.; Murdoch, Naomi; Michel, Patrick

2011-03-01

221

Nanopatterned ferroelectrics for ultrahigh density rad-hard nonvolatile memories.  

SciTech Connect

Radiation hard nonvolatile random access memory (NVRAM) is a crucial component for DOE and DOD surveillance and defense applications. NVRAMs based upon ferroelectric materials (also known as FERAMs) are proven to work in radiation-rich environments and inherently require less power than many other NVRAM technologies. However, fabrication and integration challenges have led to state-of-the-art FERAMs still being fabricated using a 130nm process while competing phase-change memory (PRAM) has been demonstrated with a 20nm process. Use of block copolymer lithography is a promising approach to patterning at the sub-32nm scale, but is currently limited to self-assembly directly on Si or SiO{sub 2} layers. Successful integration of ferroelectrics with discrete and addressable features of {approx}15-20nm would represent a 100-fold improvement in areal memory density and would enable more highly integrated electronic devices required for systems advances. Towards this end, we have developed a technique that allows us to carry out block copolymer self-assembly directly on a huge variety of different materials and have investigated the fabrication, integration, and characterization of electroceramic materials - primarily focused on solution-derived ferroelectrics - with discrete features of {approx}20nm and below. Significant challenges remain before such techniques will be capable of fabricating fully integrated NVRAM devices, but the tools developed for this effort are already finding broader use. This report introduces the nanopatterned NVRAM device concept as a mechanism for motivating the subsequent studies, but the bulk of the document will focus on the platform and technology development.

Brennecka, Geoffrey L.; Stevens, Jeffrey; Scrymgeour, David; Gin, Aaron V.; Tuttle, Bruce Andrew

2010-09-01

222

Inter-particle correlations in a hard-sphere colloidal suspension with polymer additives investigated by Spin Echo Small Angle Neutron Scattering (SESANS).  

PubMed

Using a neutron scattering technique that measures a statistically-averaged density correlation function in real space rather than the conventional reciprocal-space structure factor, we have measured correlations between poly(methyl-methacrylate) (PMMA) colloidal particles of several sizes suspended in decalin. The new method, called Spin Echo Small Angle Neutron Scattering (SESANS) provides accurate information about particle composition, including the degree of solvent penetration into the polymer brush grafted on to the PMMA spheres to prevent aggregation. It confirms for particles, between 85 nm and 150 nm in radius that inter-particle correlations closely follow the Percus-Yevick hard-sphere model when the colloidal volume-fraction is between 30% and 50% provided the volume-fraction is used as a fitted parameter. No particle aggregation occurs in these systems. When small amounts of polystyrene are added as a depletant to a concentrated suspension of PMMA particles, short-range clustering of the particles occurs and there is an increase in the frequency of near-neighbor contacts. Within a small range of depletant concentration, near-neighbor correlations saturate and large aggregates with power law density correlations are formed. SESANS clearly separates the short- and long-range correlations and shows that, in this case, the power-law correlations are visible for inter-particle distances larger than roughly two particle diameters. In some cases, aggregate sizes are within our measurement window, which can extend out to 16 microns in favorable cases. We discuss the advantages of SESANS for measurements of the structure of concentrated colloidal systems and conclude that the method offers several important advantages. PMID:24695952

Washington, A L; Li, X; Schofield, A B; Hong, K; Fitzsimmons, M R; Dalgliesh, R; Pynn, R

2014-05-01

223

PREFACE: Classical density functional theory methods in soft and hard matter Classical density functional theory methods in soft and hard matter  

Microsoft Academic Search

Herein we provide a brief summary of the background, events and results\\/outcome of the CECAM workshop 'Classical density functional theory methods in soft and hard matter held in Lausanne between October 21 and October 23 2009, which brought together two largely separately working communities, both of whom employ classical density functional techniques: the soft-matter community and the theoretical materials science

Mikko Haataja; László Gránásy; Hartmut Löwen

2010-01-01

224

-relaxation processes in binary hard-sphere mixtures Dipartimento di Fisica and INFM Center for Statistical Mechanics and Complexity, Universita` di Roma ``La Sapienza,''  

E-print Network

by parameters for the strength, stretching, and time scale, where the latter varies over almost four orders fluctuations of binary hard-sphere mixtures in order to explore the effects of mixing on the evolution is fully developed. Therefore, studies of the glassy dynamics have to be performed on simple molecu- lar

Sciortino, Francesco

225

Development of a method for measuring the density of liquid sulfur at high pressures using the falling-sphere technique  

SciTech Connect

We describe a new method for the in situ measurement of the density of a liquid at high pressure and high temperature using the falling-sphere technique. Combining synchrotron radiation X-ray radiography with a large-volume press, the newly developed falling-sphere method enables the determination of the density of a liquid at high pressure and high temperature based on Stokes' flow law. We applied this method to liquid sulfur and successfully obtained the density at pressures up to 9 GPa. Our method could be used for the determination of the densities of other liquid materials at higher static pressures than are currently possible.

Funakoshi, Ken-ichi; Nozawa, Akifumi [Japan Synchrotron Radiation Research Institute, Sayo-cho, Hyogo 679-5198 (Japan)

2012-10-15

226

Characterization of the order-disorder transition of a charged hard-sphere model  

Microsoft Academic Search

Monte Carlo simulations at constant pressure are used to characterize the structure of the restricted primitive model in the tetragonal-ordered solid phase. A method to estimate the location of the order-disorder transition and the densities of the coexistence phases is discussed. The results support the weakly first-order character of the transition.

José L. Abascal; Carlos Vega; Carl McBride; Fernando Bresme

2003-01-01

227

Order-Disorder Transition in the Solid Phase of a Charged Hard Sphere Model  

Microsoft Academic Search

We investigate the solid phases of the restricted primitive model (RPM). Monte Carlo simulations show the existence of an order-disorder transition from a substitutionally disordered face centered cubic lattice (fcc) to a new ordered fcc structure which is proposed as the ground state of the RPM at the close packing density. Our results suggest that the new phase might turn

Fernando Bresme; Carlos Vega; José L. F. Abascal

2000-01-01

228

The isotropic-nematic and nematic-nematic phase transition of binary mixtures of tangent hard-sphere chain fluids: An analytical equation of state  

NASA Astrophysics Data System (ADS)

An analytical equation of state (EoS) is derived to describe the isotropic (I) and nematic (N) phase of linear- and partially flexible tangent hard-sphere chain fluids and their mixtures. The EoS is based on an extension of Onsager's second virial theory that was developed in our previous work [T. van Westen, B. Oyarzún, T. J. H. Vlugt, and J. Gross, J. Chem. Phys. 139, 034505 (2013)]. Higher virial coefficients are calculated using a Vega-Lago rescaling procedure, which is hereby generalized to mixtures. The EoS is used to study (1) the effect of length bidispersity on the I-N and N-N phase behavior of binary linear tangent hard-sphere chain fluid mixtures, (2) the effect of partial molecular flexibility on the binary phase diagram, and (3) the solubility of hard-sphere solutes in I- and N tangent hard-sphere chain fluids. By changing the length bidispersity, two types of phase diagrams were found. The first type is characterized by an I-N region at low pressure and a N-N demixed region at higher pressure that starts from an I-N-N triphase equilibrium. The second type does not show the I-N-N equilibrium. Instead, the N-N region starts from a lower critical point at a pressure above the I-N region. The results for the I-N region are in excellent agreement with the results from molecular simulations. It is shown that the N-N demixing is driven both by orientational and configurational/excluded volume entropy. By making the chains partially flexible, it is shown that the driving force resulting from the configurational entropy is reduced (due to a less anisotropic pair-excluded volume), resulting in a shift of the N-N demixed region to higher pressure. Compared to linear chains, no topological differences in the phase diagram were found. We show that the solubility of hard-sphere solutes decreases across the I-N phase transition. Furthermore, it is shown that by using a liquid crystal mixture as the solvent, the solubility difference can by maximized by tuning the composition. Theoretical results for the Henry's law constant of the hard-sphere solute are in good agreement with the results from molecular simulation.

van Westen, Thijs; Vlugt, Thijs J. H.; Gross, Joachim

2014-01-01

229

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Prediction and Refinement of High-Order Virial Coefficients for a Hard-Sphere System  

NASA Astrophysics Data System (ADS)

The nth virial coefficient for a hard-sphere system is expressed as the sum of n2 and a remainder. When n >= 3, the remainders of the virials can be accurately expressed with Pade-type functions of n. The maximum deviations are only 0.039-0.053%, which are much better than the existing approaches. By using the predicted virials, the compressibility factors of the hard-sphere system can be predicted very accurately in the whole stable fluid region, and those in the metastable fluid region can also be well predicted up to a packing fraction of 0.545. The simulated B7 and B10 are found to be inconsistent with the other known virials, and thus they are refined to be 53.2467 and 105.042, respectively.

Hu, Jia-Wen; Yu, Yang-Xin

2009-08-01

230

Flow instability due to coupling of shear-gradients with concentration: non-uniform flow of (hard-sphere) glasses.  

PubMed

Flow-induced instabilities that lead to non-uniform stationary flow profiles have been observed in many different soft-matter systems. Two types of instabilities that lead to banded stationary states have been identified, which are commonly referred to as gradient- and vorticity-banding. The molecular origin of these instabilities is reasonably well understood. A third type of instability that has been proposed phenomenologically [Europhys. Lett., 1986, 2, 129 and Phys. Rev. E, 1995, 52, 4009] is largely unexplored. Essential to this "Shear-gradient Concentration Coupling" (SCC-) instability is a mass flux that is induced by spatial gradients of the shear rate. A possible reason that this instability has essentially been ignored is that the molecular origin of the postulated mass flux is not clear, and no explicit expressions for the shear-rate and concentration dependence of the corresponding transport coefficient exist. It is therefore not yet known what types of flow velocity- and concentration-profiles this instability gives rise to. In this paper, an expression for the transport coefficient corresponding to the shear-gradient induced mass flux is derived in terms of the shear-rate dependent pair-correlation function, and Brownian dynamics simulations for hard-spheres are presented that specify the shear-rate and concentration dependence of the pair-correlation function. This allows to explicitly formulate the coupled advection-diffusion equation and an equation of motion for the suspension flow velocity. The inclusion of a non-local contribution to the stress turns out to be essential to describe the SCC-banding transition. The coupled equations of motion are solved numerically, and flow- and concentration-profiles are discussed. It is shown that the SCC-instability occurs within the glass state at sufficiently small shear rates, leading to a banded flow-profile where one of the bands is non-flowing. PMID:25346243

Jin, Howon; Kang, Kyongok; Ahn, Kyung Hyun; Dhont, Jan K G

2014-12-21

231

Crystallization of Hard Sphere Colloids in Microgravity: Results of the Colloidal Disorder-Order Transition, CDOT on USML-2. Experiment 33  

NASA Technical Reports Server (NTRS)

Classical hard spheres have long served as a paradigm for our understanding of the structure of liquids, crystals, and glasses and the transitions between these phases. Ground-based experiments have demonstrated that suspensions of uniform polymer colloids are near-ideal physical realizations of hard spheres. However, gravity appears to play a significant and unexpected role in the formation and structure of these colloidal crystals. In the microgravity environment of the Space Shuttle, crystals grow purely via random stacking of hexagonal close-packed planes, lacking any of the face-centered cubic (FCC) component evident in crystals grown in 1 g beyond melting and allowed some time to settle. Gravity also masks 33-539 the natural growth instabilities of the hard sphere crystals which exhibit striking dendritic arms when grown in microgravity. Finally, high volume fraction "glass" samples which fail to crystallize after more than a year in 1 g begin nucleation after several days and fully crystallize in less than 2 weeks on the Space Shuttle.

Zhu, Ji-Xiang; Chaikin, P. M.; Li, Min; Russel, W. B.; Ottewill, R. H.; Rogers, R.; Meyer, W. V.

1998-01-01

232

Hardness and density distributions of pharmaceutical tablets measured by terahertz pulsed imaging.  

PubMed

We present terahertz pulsed imaging (TPI) as a novel tool to quantify the hardness and surface density distribution of pharmaceutical tablets. Good agreement between the surface refractive index (SRI) measured by TPI and the crushing force measured from diametral compression tests was found using a set of tablets that were compacted at various compression forces. We also found a strong correlation between TPI results and tablet bulk density, and how these relate to tablet hardness. Numerical simulations of tablet surface density distribution by finite element analysis exhibit excellent agreement with the TPI measured SRI maps. These results show that TPI has an advantage over traditional diametral compression and is more suitable for nondestructive hardness and density distribution monitoring and control of pharmaceutical manufacturing processes. PMID:23609052

May, Robert K; Su, Ke; Han, Lianghao; Zhong, Shuncong; Elliott, James A; Gladden, Lynn F; Evans, Mike; Shen, Yaochun; Zeitler, J Axel

2013-07-01

233

arXiv:1101.3868v1[cond-mat.soft]20Jan2011 Density functional for hard hyperspheres from a  

E-print Network

-volume correlations and solvation forces [2], and the wetting properties of a solid substrate by a "civilized" model of the hard sphere model in large space dimensions D. Motivation for such work originates both from a desire-measure theory (FMT) [5­8] for additive hard sphere mixtures. There is considerable current interest in the study

Ott, Albrecht

234

Density functional theory for sphere-needle mixtures: Toward finite rod thickness Ansgar Esztermann  

E-print Network

.20.Gy, 82.70.Dd, 61.30.Cz, 64.70.Ja Mixtures of colloidal spheres and mesoscopic rods, like colloidal needles [10] was proposed [11] and used to investigate the structure of the interface between sphere-rich

Schmidt, Matthias

235

Density functional theory for colloidal rod-sphere mixtures Matthias Schmidt  

E-print Network

. DOI: 10.1103/PhysRevE.63.050201 PACS number s : 61.20.Gy, 61.30.Cz, 64.70.Ja, 82.70.Dd Colloidal into sphere-rich rod-poor and sphere-poor rod-rich phases. They also extended Lekkerkerker's free volume

Schmidt, Matthias

236

Co-pelletization of sewage sludge and biomass: the density and hardness of pellet.  

PubMed

In the present study, the effects of process parameters on pellet properties were investigated for the co-pelletization of sludge and biomass materials. The relaxed pellet density and Meyer hardness of pellets were identified. Scanning electron microscopy, FT-IR spectra and chemical analysis were conducted to investigate the mechanisms of inter-particular adhesion bonding. Thermogravimetric analysis was applied to investigate the combustion characteristics. Results showed that the pellet density was increased with the parameters increasing, such as pressure, sludge ratio and temperature. High hardness pellets could be obtained at low pressure, temperature and biomass size. The optimal moisture content for co-pelletization was 10-15%. Moreover, the addition of sludge can reduce the diversity of pellet hardness caused by the heterogeneity of biomass. Increasing ratio of sludge in the pellet would slow down the release of volatile. Synergistic effects of protein and lignin can be the mechanism in the co-pelletization of sludge and biomass. PMID:24935004

Jiang, Longbo; Liang, Jie; Yuan, Xingzhong; Li, Hui; Li, Changzhu; Xiao, Zhihua; Huang, Huajun; Wang, Hou; Zeng, Guangming

2014-08-01

237

Hardness and Density Distributions of Pharmaceutical Tablets Measured by Terahertz Pulsed Imaging  

E-print Network

diametral compression tests was found using a set of tablets that were compacted at various compression has an advantage over traditional diametral compression and is more suitable for nondestructive imaging (TPI); tablet hardness testing; density distribution; finite element analysis (FEA); diametral

Elliott, James

238

Intercomparison of density and temperature profiles obtained by lidar, ionizatoin gauges, falling spheres, datasondes and radiosondes during the DYANA campaign  

NASA Technical Reports Server (NTRS)

During the course of the DYnamics Adapted Network for the Atmosphere (DYANA) campaign in early 1990, various techniques to measure densities and temperatures from the ground up to the lower thermosphere were employed. Some of these measurements were performed near simultaneously (maximum allowed time difference: 1 h) and at the same location, and therefore offered the unique chance of intercomparison of different techniques. In this study, we will report on intercomparisons of data from ground-based instruments (Rayleigh- and sodium-lidar), balloon-borne methods (datasondes and radiosondes) and rocket-borne techniques (falling spheres and ionization gauges). The main result is that there is good agreement between the various measurements when considering the error bars. Only occasionally did we notice small but systematic differences (e.g. for the datasondes above 65 km). The most extensive intercomparison was possible between the Rayleigh lidar and the falling sphere technique, both employed in Biscarrosse (44 deg N, 1 deg W). Concerning densities, excellent agreement was found below 63 km: the mean of the deviations is less than 1% and the root mean square (RMS) is approximately 3%. Systematic differences of the order of 5% were noticed around 67 km and above 80 km. The former can be accounted for by an instrumental effect of the falling sphere (Ma = 1 transition; Ma = Mach number), whereas the latter is tentatively explained by the presence of Mie scatterers in the upper mesosphere. Concerning temperatures, the agreement is excellent between 35 and 65 km: the mean of the deviations is less than +/- 3 K and the variability is +/- 5 K. The two systematic density differences mentioned above also affect the temperatures: between 65 and 80 km, the Rayleigh lidar temperatures are systematically lower than the falling sphere values by approximately 5 K.

Lubken, F.-J.; Hillert, W.; Lehmacher, G.; Von Zahn, U.; Bittner, M.; Offermann, D.; Schmidlin, F. J.; Hauchecorne, A.; Mourier, M.; Czechowsky, P.

1994-01-01

239

Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function  

E-print Network

Intermediate Scattering Functions (ISF's) are measured for colloidal hard sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the advantages and disadvantages of each. Both techniques agree in the overlapping range of scattering vectors. We investigate the scaling behaviour found by Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling behaviour over several decades in time but not in the long time regime. Moreover, we do not observe long time diffusive regimes at scattering vectors away from the peak of the structure factor and so question the existence of a long time diffusion coefficients at these scattering vectors.

V. A. Martinez; J. H. J Thijssen; F. Zontone; W. van Megen; G. Bryant

2010-08-12

240

Identification of triangular-shaped defects often appeared in hard-sphere crystals grown on a square pattern under gravity by Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

In this paper, we have successfully identified the triangular-shaped defect structures with stacking fault tetrahedra. These structure often appeared in hard-sphere (HS) crystals grown on a square pattern under gravity. We have, so far, performed Monte Carlo simulations of the HS crystals under gravity. Single stacking faults as observed previously in the HS crystals grown on a flat wall were not seen in the case of square template. Instead, defect structures with triangular appearance in xz- and yz- projections were appreciable. We have identified them by looking layer by layer. Those structures are surrounded by stacking faults along face-centered cubic (fcc) {111}. Also, we see isolated vacancies and vacancy-interstitial pairs, and we have found octahedral structures surrounded by stacking faults along fcc {111}.

Mori, Atsushi; Suzuki, Yoshihisa

2014-11-01

241

Facile Route Using Highly Arrayed PMMA Spheres as Hard Template for the Fabrication of 3D Ordered Nanoporous MgO  

NASA Astrophysics Data System (ADS)

Using magnesium nitrate as Mg source and regularly packed polymethyl methacrylate (PMMA) spheres were synthesized via a combined strategy of emulsifier-free emulsion polymerization and water floating technique as hard template, we fabricated ordered nanoporous magnesium oxide. The synthesized PMMA and MgO samples were characterized by N2 adsorption-desorption, X-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. It was observed that the synthesized PMMA spheres possessed a uniform diameter of approximately 284 nm and were in a highly ordered array, and the MgO generated by using the PMMA-templating method exhibited polycrystallinity with three-dimensionally ordered pores. BET surface area of the synthesized MgO sample is 100.7 m2/g, pore volume is 0.46 cm3/g, wall thickness is 4-24 nm, and pore sizes are in the range of 10-120 nm. Such a 3D high-surface-area nanoporous strongly basic MgO is useful in the applications of catalyst supports and acidic gas adsorbents.

Li, Hui-ning; Dai, Hong-xing; He, Hong; Tong Au, Chak

2007-12-01

242

Beyond electronegativity and local hardness: Higher-order equalization criteria for determination of a ground-state electron density  

Microsoft Academic Search

Higher-order global softnesses, local softnesses, and softness kernels are defined along with their hardness inverses. The local hardness equalization principle recently derived by the authors is extended to arbitrary order. The resulting hierarchy of equalization principles indicates that the electronegativity\\/chemical potential, local hardness, and local hyperhardnesses all are constant when evaluated for the ground-state electron density. The new equalization principles

Paul W. Ayers; Robert G. Parr

2008-01-01

243

A comparison of measured and predicted sphere shock shapes in hypersonic flows with density ratios from 4 to 19  

NASA Technical Reports Server (NTRS)

Measured shock shapes are presented for sphere and hemisphere models in helium, air, CF4, C2F6, and CO2 test gases, corresponding to normal-shock density ratios (primary factor governing shock detachment distance of blunt bodies at hypersonic speeds) from 4 to 19. These shock shapes were obtained in three facilities capable of generating the high density ratios experienced during planetary entry at hypersonic conditions; namely, the 6-inch expansion tube, with hypersonic CF4 tunnel, and pilot CF4 Mach 6 tunnel (with CF4 replaced by C2F6). Measured results are compared with several inviscid perfect-gas shock shape predictions, in which an effective ratio of specific heats is used as input, and with real-gas predictions which include effects of a laminar viscous layer and thermochemical nonequilibrium.

Miller, C. G., III

1975-01-01

244

Unit-Sphere Anisotropic Multiaxial Stochastic-Strength Model Probability Density Distribution for the Orientation of Critical Flaws  

NASA Technical Reports Server (NTRS)

Models that predict the failure probability of monolithic glass and ceramic components under multiaxial loading have been developed by authors such as Batdorf, Evans, and Matsuo. These "unit-sphere" failure models assume that the strength-controlling flaws are randomly oriented, noninteracting planar microcracks of specified geometry but of variable size. This report develops a formulation to describe the probability density distribution of the orientation of critical strength-controlling flaws that results from an applied load. This distribution is a function of the multiaxial stress state, the shear sensitivity of the flaws, the Weibull modulus, and the strength anisotropy. Examples are provided showing the predicted response on the unit sphere for various stress states for isotropic and transversely isotropic (anisotropic) materials--including the most probable orientation of critical flaws for offset uniaxial loads with strength anisotropy. The author anticipates that this information could be used to determine anisotropic stiffness degradation or anisotropic damage evolution for individual brittle (or quasi-brittle) composite material constituents within finite element or micromechanics-based software

Nemeth, Noel

2013-01-01

245

COLLAPSE AND FRAGMENTATION OF MAGNETIC MOLECULAR CLOUD CORES WITH THE ENZO AMR MHD CODE. I. UNIFORM DENSITY SPHERES  

SciTech Connect

Magnetic fields are important contributors to the dynamics of collapsing molecular cloud cores, and can have a major effect on whether collapse results in a single protostar or fragmentation into a binary or multiple protostar system. New models are presented of the collapse of magnetic cloud cores using the adaptive mesh refinement code Enzo2.0. The code was used to calculate the ideal magnetohydrodynamics (MHD) of initially spherical, uniform density, and rotation clouds with density perturbations, i.e., the Boss and Bodenheimer standard isothermal test case for three-dimensional (3D) hydrodynamics codes. After first verifying that Enzo reproduces the binary fragmentation expected for the non-magnetic test case, a large set of models was computed with varied initial magnetic field strengths and directions with respect to the cloud core axis of rotation (parallel or perpendicular), density perturbation amplitudes, and equations of state. Three significantly different outcomes resulted: (1) contraction without sustained collapse, forming a denser cloud core; (2) collapse to form a single protostar with significant spiral arms; and (3) collapse and fragmentation into binary or multiple protostar systems, with multiple spiral arms. Comparisons are also made with previous MHD calculations of similar clouds with a barotropic equations of state. These results for the collapse of initially uniform density spheres illustrate the central importance of both magnetic field direction and field strength for determining the outcome of dynamic protostellar collapse.

Boss, Alan P.; Keiser, Sandra A., E-mail: boss@dtm.ciw.edu [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States)

2013-02-20

246

Surface and curvature energies from jellium spheres: Density functional hierarchy and quantum Monte Carlo  

Microsoft Academic Search

We consider spherical jellium clusters with up to 200 electrons as a testing ground for density functional approximations to the exchange-correlation energy of a many-electron ground state. As nearly-exact standards, we employ Hartree-Fock energies at the exchange-only level and the diffusion Monte Carlo (DMC) energies of Sottile and Ballone (2001) at the correlated level. The density functionals tested are the

L. M. Almeida; John P. Perdew; Carlos Fiolhais

2002-01-01

247

Compressibility and hardness of Co-based bulk metallic glass: A combined experimental and density functional theory study  

SciTech Connect

An incompressible Co{sub 54}Ta{sub 11}B{sub 35} bulk metallic glass (BMG) was investigated using in situ high-pressure synchrotron diffraction and nanoindendation. The elastic constants were deduced from the experiments based on the isotropic model. The Vickers hardness was measured to be 17.1 GPa. The elastic moduli and hardness are the highest values known in BMGs. The theoretically calculated elastic properties by density-functional study were well consistent with experimental measurements. The analysis of charge density and bonding character indicates the covalent character of Co-B and B-B bonds, underlying the unusually high elastic modulus and hardness in this material.

Wang Jianfeng; Li Ran; Xu Tao; Li Yan; Liu Zengqian; Huang Lu; Hua Nengbin; Zhang Tao [Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191 (China); Xiao Ruijuan [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li Gong [Stat Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Li Yanchun [BSRF, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039 (China)

2011-10-10

248

THE FIRST HARD X-RAY POWER SPECTRAL DENSITY FUNCTIONS OF ACTIVE GALACTIC NUCLEUS  

SciTech Connect

We present results of our power spectral density (PSD) analysis of 30 active galactic nuclei (AGNs) using the 58 month light curves from Swift's Burst Alert Telescope (BAT) in the 14-150 keV band. PSDs were fit using a Monte Carlo based algorithm to take into account windowing effects and measurement error. All but one source were found to be fit very well using an unbroken power law with a slope of {approx} - 1, consistent at low frequencies with previous studies in the 2-10 keV band, with no evidence of a break in the PSD. For five of the highest signal-to-noise ratio sources, we tested the energy dependence of the PSD and found no significant difference in the PSD at different energies. Unlike previous studies of X-ray variability in AGNs, we do not find any significant correlations between the hard X-ray variability and different properties of the AGN including luminosity and black hole mass. The lack of break frequencies and correlations seem to indicate that AGNs are similar to the high state of Galactic black holes.

Shimizu, T. Taro; Mushotzky, Richard F., E-mail: tshimizu@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2013-06-10

249

Performance of sphere decoding of block codes  

Microsoft Academic Search

A sphere decoder searches for the closest lattice point within a certain search radius. The search radius provides a tradeoff between performance and complexity. We focus on analyzing the performance of sphere decoding of linear block codes. We analyze the performance of soft-decision sphere decoding on AWGN channels and a variety of modulation schemes. A hard-decision sphere decoder is a

Mostafa El-Khamy; Haris Vikalo; Babak Hassibi; Robert J. McEliece

2009-01-01

250

Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop  

E-print Network

A novel method of using hard X-rays as a diagnostic for chromospheric density and magnetic structures is developed to infer sub-arcsecond vertical variation of magnetic flux tube size and neutral gas density.Using Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data and the newly developed X-ray visibilities forward fitting technique we find the FWHM and centroid positions of hard X-ray sources with sub-arcsecond resolution ($\\sim 0.2"$) for a solar limb flare. We show that the height variations of the chromospheric density and the magnetic flux densities can be found with unprecedented vertical resolution of $\\sim$ 150 km by mapping 18-250 keV X-ray emission of energetic electrons propagating in the loop at chromospheric heights of 400-1500 km. Our observations suggest that the density of the neutral gas is in good agreement with hydrostatic models with a scale height of around $140\\pm 30$ km. FWHM sizes of the X-ray sources decrease with energy suggesting the expansion (fanning out) of magnetic flux tube in the chromosphere with height. The magnetic scale height $B(z)(dB/dz)^{-1}$ is found to be of the order of 300 km and strong horizontal magnetic field is associated with noticeable flux tube expansion at a height of $\\sim$ 900 km.

E. P. Kontar; I. G. Hannah; A. L. MacKinnon

2008-08-25

251

Passive sonar calibration spheres  

NASA Astrophysics Data System (ADS)

The need for calibrated sonar targets is addressed with the development and testing of a set of thin-walled spheres filled with a high-density fluid. Using historical research information as a guide, a set of thin-walled metal spheres was developed and filled with a high-density fluid. The combination of the spherical shape and the acoustic focusing effects of the fluid enhanced the acoustic scattering strength of the shape so that it was not only stable with temperature but also significantly greater in amplitude. The simple passive nature of the spheres makes them ideal acoustic targets for long-term unattended deployments. Using a reference level measurement, each sphere was calibrated over a wide frequency range in order to provide the user with a curve of measured scattering strength versus frequency. The resulting curves showed a high degree of correlation between the individual spheres and the modeling that was used to extrapolate the theoretical values.

Deveau, David M.

2002-05-01

252

Lattice gas generalization of the hard hexagon model. I. Star-triangle relation and local densities  

Microsoft Academic Search

In the solvable hard hexagon model there is at most one particle in every pair of adjacent sites, and the solution automatically leads to various mathematical identities, in particular to the Rogers-Ramanujan relations. These relations have been generalized by Gordon. Here we construct a solvable model with at most two particles per pair of adjacent sites, and find the solution

R. J. Baxter; George E. Andrews

1986-01-01

253

A classical density-functional theory for describing water interfaces.  

PubMed

We develop a classical density functional for water which combines the White Bear fundamental-measure theory (FMT) functional for the hard sphere fluid with attractive interactions based on the statistical associating fluid theory variable range (SAFT-VR). This functional reproduces the properties of water at both long and short length scales over a wide range of temperatures and is computationally efficient, comparable to the cost of FMT itself. We demonstrate our functional by applying it to systems composed of two hard rods, four hard rods arranged in a square, and hard spheres in water. PMID:23320706

Hughes, Jessica; Krebs, Eric J; Roundy, David

2013-01-14

254

A Classical Density-Functional Theory for Describing Water Interfaces  

E-print Network

We develop a classical density functional for water which combines the White Bear fundamental-measure theory (FMT) functional for the hard sphere fluid with attractive interactions based on the Statistical Associating Fluid Theory (SAFT-VR). This functional reproduces the properties of water at both long and short length scales over a wide range of temperatures, and is computationally efficient, comparable to the cost of FMT itself. We demonstrate our functional by applying it to systems composed of two hard rods, four hard rods arranged in a square and hard spheres in water.

Jessica Hughes; Eric Krebs; David Roundy

2012-08-31

255

Catalytic hollow spheres  

NASA Technical Reports Server (NTRS)

The improved, heterogeneous catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitably formed of a shell (12) of metal such as aluminum having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be, itself, catalytic or the catalyst can be coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)

1986-01-01

256

Low-dislocation-density epitatial layers grown by defect filtering by self-assembled layers of spheres  

DOEpatents

A method for growing low-dislocation-density material atop a layer of the material with an initially higher dislocation density using a monolayer of spheroidal particles to bend and redirect or directly block vertically propagating threading dislocations, thereby enabling growth and coalescence to form a very-low-dislocation-density surface of the material, and the structures made by this method.

Wang, George T.; Li, Qiming

2013-04-23

257

Numerical simulation of hard errors induced by heavy ions in 4T high density SRAM cells  

SciTech Connect

2D Numerical Simulation of local dose deposition effects in N Channel MOS transistors are presented in order to explain experimental observation of stuck bits in 4 T resistor loaded cells of high density SRAMs irradiated by heavy ions. The ion impact location in the channel is shown to strongly modulate the observed threshold voltage shift. This shift variation versus the inverse channel length is super linear, so more important effects are expected for 4T cells as transistor dimensions will be reduced.

Gaillard, R.; Poirault, G. (Nucletudes S.A., Les Ulis (France))

1994-06-01

258

Bulk phase behavior of binary hard platelet mixtures from density functional theory  

NASA Astrophysics Data System (ADS)

We investigate isotropic-isotropic, isotropic-nematic, and nematic-nematic phase coexistence in binary mixtures of circular platelets with vanishing thickness, continuous rotational degrees of freedom, and radial size ratios ? up to 5. A fundamental measure density functional theory, previously used for the one-component model, is presented and results are compared against those from Onsager theory as a benchmark. For ??1.7 the system displays isotropic-nematic phase coexistence with a widening of the biphasic region for increasing values of ? . For size ratios ??2 , we find that demixing into two nematic states becomes stable and an isotropic-nematic-nematic triple point can occur. Fundamental measure theory gives a smaller isotropic-nematic biphasic region than Onsager theory and locates the transition at lower densities. Furthermore, nematic-nematic demixing occurs over a larger range of compositions at a given value of ? than found in Onsager theory. Both theories predict the same topologies of the phase diagrams. The partial nematic order parameters vary strongly with composition and indicate that the larger particles are more strongly ordered than the smaller particles.

Phillips, Jonathan; Schmidt, Matthias

2010-04-01

259

The water entry of decelerating spheres  

E-print Network

We present the results of a combined experimental and theoretical investigation of the vertical impact of low-density spheres on a water surface. Particular attention is given to characterizing the sphere dynamics and the ...

Aristoff, Jeffrey M.

260

A New Approach to the Equation of State of Silicate Melts: An Application of a Hard-Sphere Model to a MultiComponent System  

Microsoft Academic Search

Compressional properties of silicate liquids including density and bulk modulus at elevated pressures and temperatures (i.e., equation of state) are crucial to our understanding of melting processes such as the generation and differentiation of silicate melts in Earth and hence to explore the geophysical and geochemical consequences of melting. Unlike the solid and gaseous states of a matter for which

Z. Jing; S. Karato

2009-01-01

261

Thermodynamics of quantum photon spheres  

E-print Network

Photon spheres, surfaces where massless particles are confined in closed orbits, are expected to be common astrophysical structures surrounding ultracompact objects. In this paper a semiclassical treatment of a photon sphere is proposed. We consider the quantum Maxwell field and derive its energy spectra. A thermodynamic approach for the quantum photon sphere is developed and explored. Within this treatment, an expression for the spectral energy density of the emitted radiation is presented. Our results suggest that photon spheres, when thermalized with their environment, have nonusual thermodynamic properties, which could lead to distinct observational signatures.

M. C. Baldiotti; Walace S. Elias; C. Molina; Thiago S. Pereira

2014-10-07

262

How are Earth's spheres interacting?  

NSDL National Science Digital Library

This Earth science investigation leads students through a brief introduction of the spheres of the Earth and an exploration of the interactions among the spheres. The seven-step investigation incorporates a mixture of informational text, questions, and images. After reading about and interacting with an image of the four main spheres (the atmosphere, hydrosphere, geosphere, and biosphere), students are introduced to the concept of sphere interactions as part of the larger Earth system. Text, questions, and some sample answers assist students in identifying sphere interactions in the various images shown. In the last step of the investigation, students are asked to contemplate the global effects of human population growth on the spheres. To assist students with this question, the final page contains a globe showing human population density. Arrows permit students to turn the globe to view the population data for all parts of the world. Copyright 2005 Eisenhower National Clearinghouse

Education, Terc. C.; Littell, Mcdougal

2003-01-01

263

Improved association in a classical density functional theory for water.  

PubMed

We present a modification to our recently published statistical associating fluid theory-based classical density functional theory for water. We have recently developed and tested a functional for the averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate at interfaces than earlier approximations. We now incorporate this improved functional into the association term of our free energy functional for water, improving its description of hydrogen bonding. We examine the effect of this improvement by studying two hard solutes (a hard hydrophobic rod and a hard sphere) and a Lennard-Jones approximation of a krypton atom solute. The improved functional leads to a moderate change in the density profile and a large decrease in the number of hydrogen bonds broken in the vicinity of the hard solutes. We find an improvement of the partial radial distribution for a krypton atom in water when compared with experiment. PMID:24697459

Krebs, Eric J; Schulte, Jeff B; Roundy, David

2014-03-28

264

Improved association in a classical density functional theory for water  

NASA Astrophysics Data System (ADS)

We present a modification to our recently published statistical associating fluid theory-based classical density functional theory for water. We have recently developed and tested a functional for the averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate at interfaces than earlier approximations. We now incorporate this improved functional into the association term of our free energy functional for water, improving its description of hydrogen bonding. We examine the effect of this improvement by studying two hard solutes (a hard hydrophobic rod and a hard sphere) and a Lennard-Jones approximation of a krypton atom solute. The improved functional leads to a moderate change in the density profile and a large decrease in the number of hydrogen bonds broken in the vicinity of the hard solutes. We find an improvement of the partial radial distribution for a krypton atom in water when compared with experiment.

Krebs, Eric J.; Schulte, Jeff B.; Roundy, David

2014-03-01

265

The importance of precision radar tracking data for the determination of density and winds from the high-altitude inflatable sphere  

NASA Technical Reports Server (NTRS)

Analysis of inflatable sphere measurements obtained during the Energy Budget and MAP/WINE campaigns led to questions concerning the precision of the MPS-36 radar used for tracking the spheres; the compatibility of the sphere program with the MPS-36 radar tracking data; and the oversmoothing of derived parameters at high altitudes. Simulations, with winds having sinusoidal vertical wavelengths, were done with the sphere program (HIROBIN) to determine the resolving capability of various filters. It is concluded that given a precision radar and a perfectly performing sphere, the HIROBIN filters can be adjusted to provide small-scale perturbation information to 70 km (i.e., sinusoidal wavelengths of 2 km). It is recommended that the HIROBIN program be modified to enable it to use a variable length filter, that adjusts to fall velocity and accelerations to provide wind data with small perturbations.

Schmidlin, F. J.; Michel, W. R.

1985-01-01

266

Multiple reentrant glass transitions of soft spheres at high densities: monotonicity of the curves of constant relaxation time in jamming phase diagrams depending on temperature over pressure and pressure.  

PubMed

By using molecular-dynamics simulations, we determine the jamming phase diagrams at high densities for a bidisperse mixture of soft spheres that interact according to repulsive power-law pair potentials. We observe that the relaxation time varies nonmonotonically as a function of density at constant temperature. Therefore, the jamming phase diagrams contain multiple reentrant glass transitions if temperature and density are used as control parameters. However, if we consider a new formulation of the jamming phase diagrams where temperature over pressure and pressure are employed as control parameters, no nonmonotonic behavior is observed. PMID:23767543

Schmiedeberg, Michael

2013-05-01

267

Free Volume of the Hard Spheres Gas  

ERIC Educational Resources Information Center

The Enskog factor [chi] plays a central role in the theory of dense gases, quantifying how the finite size of molecules causes many physical quantities, such as the equation of state, the mean free path, and the diffusion coefficient, to deviate from those of an ideal gas. We suggest an intuitive but rigorous derivation of this fact by showing how…

Shutler, P. M. E.; Martinez, J. C.; Springham, S. V.

2007-01-01

268

The Kolmogorov-Sinai entropy for dilute systems of hard particles in equilibrium  

E-print Network

In an equilibrium system, the Kolmogorov-Sinai entropy, $h_{\\mathrm{KS}}$, equals the sum of the positive Lyapunov exponents, the exponential rates of divergence of infinitesimal perturbations. Kinetic theory may be used to calculate the Kolmogorov-Sinai entropy for dilute gases of many hard disks or spheres in equilibrium at low number density $n$. The density expansion of $h_{\\mathrm{KS}}$ is $N \\bar\

Astrid S. de Wijn

2004-12-31

269

Structure of fluid mixtures near a solute: A density functional approach  

NASA Astrophysics Data System (ADS)

The structure of fluid mixtures near a spherical solute is studied using a density functional approach and computer simulation. The input direct correlation function is obtained from integral equation theory with an accurate closure relation. The density and concentration profiles of binary as well as ternary hard-sphere mixtures near a large hard-spherical solute compare quite well with the computer simulation results over a wide range of parametric conditions.

Patra, Chandra N.

2014-09-01

270

Hard body amphiphiles at a hard wall JOSEPH M. BRADER1y  

E-print Network

Hard body amphiphiles at a hard wall JOSEPH M. BRADER1y , CHRISTIAN VON FERBER2 and MATTHIAS 2003) We investigate the structure of amphiphilic molecules exposed to a substrate that is modelled by a hard wall. Our simple model amphiphiles consist of a hard sphere head group to which a vanishingly thin

Ott, Albrecht

271

Computer assisted sphere packing in higher dimensions  

SciTech Connect

A computer was used to help study the packing of equal spheres in dimension four and higher. A candidate for the densest packing in 4-space is described. The configuration of 24 spheres touching a central sphere in this packing is shown to be rigid, unlike the analogue in 3-space, in which the spheres can slide past each other. A system for interactively manipulating and visualizing such configurations is described. The Voronoi cell for a sphere is the set of points closer to its center than to any other sphere in the packing. The packing density is the ratio of a sphere's volume to the average of the volumes of the Voronoi cells. A method of constructing Voronoi cells and computing their volumes is presented, which works in any dimension. Examples of Voronoi cell volumes are given. 8 figs., 1 tab.

Max, N.

1991-01-01

272

Spheres of Eudoxus  

NSDL National Science Digital Library

This Spheres of Eudoxus model simulates the system devised by the Ancient Greek astronomer Eudoxus to model the motion of the planets. The model consists of four nested concentric spheres. The axis of each sphere is attached to the surface of the next sphere out. The planet itself is located on the surface of the innermost sphere. The outermost sphere rotates with the daily (apparent) rotation of the stars. The Spheres Frame shows the four spheres of the model. The axis of the inner (red) sphere can be tilted relative to that of the middle (blue) sphere using a slider to adjust the angle. The red sphere automatically rotates with angular velocity +1.0 (in arbitrary units). The angular velocities of the blue and green spheres can be adjusted using sliders. Note that the axis of the blue sphere is attached to the equator of the green sphere. This is a crucial part of Eudoxus' model. The equator of the green sphere is in the plane of the ecliptic. The outermost (white) sphere is essentially the Celestial Sphere containing the fixed stars (or at least it rotates about the same axis and at the same rate as the Celestial Sphere). The Sky View Frame shows the motion of the planet (relative to the stars) as seen from the earth, which sits at the center of the concentric spheres in the model. By tilting the red sphere relative to the blue sphere, setting the angular velocity of the blue sphere opposite that of the red sphere, and giving the green sphere a sufficiently small angular speed, Eudoxus was able to qualitatively reproduce the observed retrograde motion of the planets using this model.

Timberlake, Todd

2011-05-18

273

Density!  

NSDL National Science Digital Library

What is Density? Density is the amount of "stuff" in a given "space". In science terms that means the amount of "mass" per unit "volume". Using units that means the amount of "grams" per "centimeters cubed". Check out the following links and learn about density through song! Density Beatles Style Density Chipmunk Style Density Rap Enjoy! ...

Witcher, Miss

2011-10-06

274

Prediction of a Structural Transition in the Hard Disk Fluid  

E-print Network

Starting from the second equilibrium equation in the BBGKY hierarchy under the Kirkwood superposition closure, we implement a new method for studying the asymptotic decay of correlations in the hard disk fluid in the high density regime. From our analysis and complementary numerical studies, we find that exponentially damped oscillations can occur only up to a packing fraction {\\eta}*~0.718, a value which is in substantial agreement with the packing fraction, {\\eta}~0.723, believed to characterize the transition from the ordered solid phase to a dense fluid phase, as inferred from Mak's Monte Carlo simulations [Phys. Rev. E 73, 065104 (2006)]. We next show that the same method of analysis predicts that exponential damping of oscillations in the hard sphere fluid becomes impossible when \\lambda = 4n\\pi {\\sigma}^3 [1 + H(1)]>/- 34.81, where H(1) is the contact value of the correlation function, n is the number density and {\\sigma} is the sphere diameter, in exact agreement with the condition, \\lambda >/- 34.8, first reported in a numerical study of the Kirkwood equation by Kirkwood et al. [J. Chem. Phys. 18, 1040 (1950)]. Finally, we show that our method confirms the absence of any structural transition in hard rods for the entire range of densities below close packing.

Jaroslaw Piasecki; Piotr Szymczak; John J. Kozak

2010-09-16

275

Density  

NSDL National Science Digital Library

What is density? Density is a relationship between mass (usually in grams or kilograms) and volume (usually in L, mL or cm 3 ). Below are several sights to help you further understand the concept of density. Click the following link to review the concept of density. Be sure to read each slide and watch each video: Chemistry Review: Density Watch the following video: Pop density video The following is a fun interactive sight you can use to review density. Your job is #1, to play and #2 to calculate the density of the ...

Hansen, Mr.

2010-10-26

276

Ionization Potential, Electron Affinity, Electronegativity, Hardness, and Electron Excitation Energy: Molecular Properties from Density Functional Theory Orbital Energies  

Microsoft Academic Search

Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations were done with the commonly used exchange-correlation functional B3LYP followed by a comprehensive analysis of the calculated highest-occupied and lowest-unoccupied Kohn-Sham orbital (HOMO and LUMO) energies. The basis set dependence of the DFT results

Chang-Guo Zhan; Jeffrey A. Nichols; David A. Dixon

2003-01-01

277

Density  

NSDL National Science Digital Library

Students will explain the concept of and be able to calculate density based on given volumes and masses. Throughout today's assignment, you will need to calculate density. You can find a density calculator at this site. Make sure that you enter the correct units. For most of the problems, grams and cubic centimeters will lead you to the correct answer: Density Calculator What is Density? Visit the following website to answer questions ...

Petersen, Mrs.

2013-10-28

278

Density  

NSDL National Science Digital Library

This page introduces students to the concept of density by presenting its definition, formula, and two blocks representing materials of different densities. Students are given the mass and volume of each block and asked to calculate the density. Their answers are then compared against a table of densities of common objects (air, wood, gold, etc.) and students must determine, using the density of the blocks, which substance makes up each block.

Carpi, Anthony

2003-01-01

279

Improved Iterative Hard- and Soft-Reliability Based Majority-Logic Decoding Algorithms for Non-Binary Low-Density Parity-Check Codes  

NASA Astrophysics Data System (ADS)

Non-binary low-density parity-check (LDPC) codes have some advantages over their binary counterparts, but unfortunately their decoding complexity is a significant challenge. The iterative hard- and soft-reliability based majority-logic decoding algorithms are attractive for non-binary LDPC codes, since they involve only finite field additions and multiplications as well as integer operations and hence have significantly lower complexity than other algorithms. In this paper, we propose two improvements to the majority-logic decoding algorithms. Instead of the accumulation of reliability information in the existing majority-logic decoding algorithms, our first improvement is a new reliability information update. The new update not only results in better error performance and fewer iterations on average, but also further reduces computational complexity. Since existing majority-logic decoding algorithms tend to have a high error floor for codes whose parity check matrices have low column weights, our second improvement is a re-selection scheme, which leads to much lower error floors, at the expense of more finite field operations and integer operations, by identifying periodic points, re-selecting intermediate hard decisions, and changing reliability information.

Xiong, Chenrong; Yan, Zhiyuan

2014-10-01

280

Understanding the Electronic Structure of IrO2 Using Hard-X-ray Photoelectron Spectroscopy and Density-Functional Theory  

NASA Astrophysics Data System (ADS)

The electronic structure of IrO2 has been investigated using hard x-ray photoelectron spectroscopy and density-functional theory. Excellent agreement is observed between theory and experiment. We show that the electronic structure of IrO2 involves crystal field splitting of the iridium 5d orbitals in a distorted octahedral field. The behavior of IrO2 closely follows the theoretical predictions of Goodenough for conductive rutile-structured oxides [J. B. Goodenough, J. Solid State Chem. 3, 490 (1971)]. Strong satellites associated with the core lines are ascribed to final state screening effects. A simple plasmon model for the satellites applicable to many other metallic oxides appears to be not valid for IrO2.

Kahk, J. M.; Poll, C. G.; Oropeza, F. E.; Ablett, J. M.; Céolin, D.; Rueff, J.-P.; Agrestini, S.; Utsumi, Y.; Tsuei, K. D.; Liao, Y. F.; Borgatti, F.; Panaccione, G.; Regoutz, A.; Egdell, R. G.; Morgan, B. J.; Scanlon, D. O.; Payne, D. J.

2014-03-01

281

Calculations of free energies in liquid and solid phases: Fundamental measure density-functional approach  

E-print Network

Calculations of free energies in liquid and solid phases: Fundamental measure density, a theoretical description of the free energies and correlation functions of hard-sphere (HS) liquid and solid-Chandler-Andersen perturbation theory, free energies of liquid and solid phases with many interaction potentials can be obtained

Song, Xueyu

282

Phase diagrams of binary alloys calculated from a density functional theory Vadim B. Warshavsky and Xueyu Song  

E-print Network

behaviors of binary alloys with an embedded atom model potential are investigated using the ther- modynamic perturbation theory. The free energies of the liquid and solid phases are computed using the fundamental measure density functional theory and accurate approximations to the hard-sphere mixture corre- lation

Song, Xueyu

283

Fluid-Solid Transition in a Hard-Core System Lewis Bowen* and Russell Lyons  

E-print Network

indicate such a transition even for the conceptually simple hard-sphere model in which the interaction for the hard-sphere model, by expansion about close pack- ing [14,15], and by simulations [16,17], but little be relevant to the fluid- solid transition in hard-core models. In this new two-dimensional model, we replace

Radin, Charles

284

Local thermodynamic mapping for effective liquid density-functional theory  

NASA Technical Reports Server (NTRS)

The structural-mapping approximation introduced by Lutsko and Baus (1990) in the generalized effective-liquid approximation is extended to include a local thermodynamic mapping based on a spatially dependent effective density for approximating the solid phase in terms of the uniform liquid. This latter approximation, called the local generalized effective-liquid approximation (LGELA) yields excellent predictions for the free energy of hard-sphere solids and for the conditions of coexistence of a hard-sphere fcc solid with a liquid. Moreover, the predicted free energy remains single valued for calculations with more loosely packed crystalline structures, such as the diamond lattice. The spatial dependence of the weighted density makes the LGELA useful in the study of inhomogeneous solids.

Kyrlidis, Agathagelos; Brown, Robert A.

1992-01-01

285

Structure of spherical electric double layers with fully asymmetric electrolytes: A systematic study by Monte Carlo simulations and density functional theory.  

PubMed

A systematic investigation of the spherical electric double layers with the electrolytes having size as well as charge asymmetry is carried out using density functional theory and Monte Carlo simulations. The system is considered within the primitive model, where the macroion is a structureless hard spherical colloid, the small ions as charged hard spheres of different size, and the solvent is represented as a dielectric continuum. The present theory approximates the hard sphere part of the one particle correlation function using a weighted density approach whereas a perturbation expansion around the uniform fluid is applied to evaluate the ionic contribution. The theory is in quantitative agreement with Monte Carlo simulation for the density and the mean electrostatic potential profiles over a wide range of electrolyte concentrations, surface charge densities, valence of small ions, and macroion sizes. The theory provides distinctive evidence of charge and size correlations within the electrode-electrolyte interface in spherical geometry. PMID:25399154

Patra, Chandra N

2014-11-14

286

Earth's Fluid Spheres  

NSDL National Science Digital Library

Module covering Earth's three fluid spheres: oceans, atmosphere and cryosphere (glaciers). An event seen in each sphere illustrates processes and concepts: El Nino events for oceans; thunderstorm formation for atmosphere; and global temperature change impacts on glaciers. Concepts covered include: properties of air, water, ice as fluids; flow of energy and matter between spheres; short and long-term cycles; and others. Activities include on-line literature research, use of maps and other data sources.

287

Phase behaviour of polarizable colloidal hard rods in an external electric field: A simulation study  

NASA Astrophysics Data System (ADS)

We present a double-charge model for the interaction between parallel polarizable hard spherocylinders subject to an external electric field. Using Monte Carlo simulations and free-energy calculations, we predict the phase behaviour for this model as a function of the density and electric field strength, at a fixed length-to-diameter ratio L/D = 5. The resulting phase diagram contains, in addition to the well-known nematic, smectic A, ABC crystal, and columnar phases, a smectic C phase, and a low temperature crystal X phase. We also find a string fluid at low densities and field strengths, resembling results found for dipolar spheres.

Troppenz, Thomas; Filion, Laura; van Roij, René; Dijkstra, Marjolein

2014-10-01

288

Periodically oscillating plasma sphere  

SciTech Connect

The periodically oscillating plasma sphere, or POPS, is a novel fusion concept first proposed by D. C. Barnes and R. A. Nebel [Fusion Technol. 38, 28 (1998)]. POPS utilizes the self-similar collapse of an oscillating ion cloud in a spherical harmonic oscillator potential well formed by electron injection. Once the ions have been phase-locked, their coherent motion simultaneously produces very high densities and temperatures during the collapse phase of the oscillation. A requirement for POPS is that the electron injection produces a stable harmonic oscillator potential. This has been demonstrated in a gridded inertial electrostatic confinement device and verified by particle simulation. Also, the POPS oscillation has been confirmed experimentally through observation that the ions in the potential well exhibit resonance behavior when driven at the POPS frequency. Excellent agreement between the observed POPS frequencies and the theoretical predictions has been observed for a wide range of potential well depths and three different ion species. Practical applications of POPS require large plasma compressions. These large compressions have been observed in particle simulations, although space charge neutralization remains a major issue.

Park, J.; Nebel, R.A.; Stange, S.; Murali, S. Krupakar [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); University of Wisconsin, Madison, Wisconsin 53706 (United States)

2005-05-15

289

Density functional theory for carbon dioxide crystal.  

PubMed

We present a density functional approach to describe the solid-liquid phase transition, interfacial and crystal structure, and properties of polyatomic CO2. Unlike previous phase field crystal model or density functional theory, which are derived from the second order direct correlation function, the present density functional approach is based on the fundamental measure theory for hard-sphere repulsion in solid. More importantly, the contributions of enthalpic interactions due to the dispersive attractions and of entropic interactions arising from the molecular architecture are integrated in the density functional model. Using the theoretical model, the predicted liquid and solid densities of CO2 at equilibrium triple point are in good agreement with the experimental values. Based on the structure of crystal-liquid interfaces in different planes, the corresponding interfacial tensions are predicted. Their respective accuracies need to be tested. PMID:24880310

Chang, Yiwen; Mi, Jianguo; Zhong, Chongli

2014-05-28

290

Density functional theory for carbon dioxide crystal  

NASA Astrophysics Data System (ADS)

We present a density functional approach to describe the solid-liquid phase transition, interfacial and crystal structure, and properties of polyatomic CO2. Unlike previous phase field crystal model or density functional theory, which are derived from the second order direct correlation function, the present density functional approach is based on the fundamental measure theory for hard-sphere repulsion in solid. More importantly, the contributions of enthalpic interactions due to the dispersive attractions and of entropic interactions arising from the molecular architecture are integrated in the density functional model. Using the theoretical model, the predicted liquid and solid densities of CO2 at equilibrium triple point are in good agreement with the experimental values. Based on the structure of crystal-liquid interfaces in different planes, the corresponding interfacial tensions are predicted. Their respective accuracies need to be tested.

Chang, Yiwen; Mi, Jianguo; Zhong, Chongli

2014-05-01

291

Fibonacci Sphere Model  

NSDL National Science Digital Library

The Fibonacci Sphere Model draws n equidistant points on a sphere by distributing the points on a Fibonacci spiral. The sequence the produces this distribution separates advances the longitude by the golden angle. The Fibonacci Sphere Model was developed using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Christian, Wolfgang

2012-12-16

292

Nematic-isotropic phase transition in diblock fused-sphere chain fluids R. Diplock and D. E. Sullivan  

E-print Network

. [12,13] have simulated several fused-sphere models to determine their liquid-crystalline and solid of hard-sphere chains has been widely studied as a coarse-grained model for polyatomic mo- lecular fluidsNematic-isotropic phase transition in diblock fused-sphere chain fluids R. Diplock and D. E

Sullivan, Donald E.

293

Skyrmions on the Two-Sphere  

E-print Network

We study static solutions of the Skyrme model on the two-sphere of radius L, for various choices of potential. The high-density Skyrmion phase corresponds to the ratio beta=L/(size of Skyrmion) being small, whereas the low-density phase corresponds to beta being large. The transition between these two phases, and in particular the behaviour of a relevant order parameter, is examined.

M. de Innocentis; R. S. Ward

2001-03-07

294

Calculating the free energy of nearly jammed hard-particle packings using molecular dynamics  

E-print Network

of the thermodynamically stable solid phase of the hard-sphere system [2­4] and the determination of the configurational-energy of a single-occupancy cell (SOC) model in which each particle is restricted to a neighbor- hood of its initial disordered packings of both hard spheres and ellip- soids, for which the free energy can be calculated

Torquato, Salvatore

295

Density profiles of a colloidal liquid at a wall under shear flow  

E-print Network

Using a dynamical density functional theory we analyze the density profile of a colloidal liquid near a wall under shear flow. Due to the symmetries of the system considered, the naive application of dynamical density functional theory does not lead to a shear induced modification of the equilibrium density profile, which would be expected on physical grounds. By introducing a physically motivated dynamic mean field correction we incorporate the missing shear induced interparticle forces into the theory. We find that the shear flow tends to enhance the oscillations in the density profile of hard-spheres at a hard-wall and, at sufficiently high shear rates, induces a nonequilibrium transition to a steady state characterized by planes of particles parallel to the wall. Under gravity, we find that the center-of-mass of the density distribution increases with shear rate, i.e., shear increases the potential energy of the particles.

J. M. Brader; M. Krüger

2010-10-13

296

Gearing up the SPHERE  

NASA Astrophysics Data System (ADS)

Direct imaging and spectral characterisation of exoplanets is one of the most exciting, but also one of the most challenging areas, in modern astronomy. The challenge is to overcome the very large contrast between the host star and its planet seen at very small angular separations. This article reports on the progress made in the construction of the second generation VLT instrument SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. SPHERE is expected to be commissioned on the VLT in 2013.

Kasper, M.; Beuzit, J.-L.; Feldt, M.; Dohlen, K.; Mouillet, D.; Puget, P.; Wildi, F.; Abe, L.; Baruffolo, A.; Baudoz, P.; Bazzon, A.; Boccaletti, A.; Brast, R.; Buey, T.; Chesneau, O.; Claudi, R.; Costille, A.; Delboulbé, A.; Desidera, S.; Dominik, C.; Dorn, R.; Downing, M.; Feautrier, P.; Fedrigo, E.; Fusco, T.; Girard, J.; Giro, E.; Gluck, L.; Gonte, F.; Gojak, D.; Gratton, R.; Henning, T.; Hubin, N.; Lagrange, A.-M.; Langlois, M.; Mignant, D. L.; Lizon, J.-L.; Lilley, P.; Madec, F.; Magnard, Y.; Martinez, P.; Mawet, D.; Mesa, D.; Müller-Nilsson, O.; Moulin, T.; Moutou, C.; O'Neal, J.; Pavlov, A.; Perret, D.; Petit, C.; Popovic, D.; Pragt, J.; Rabou, P.; Rochat, S.; Roelfsema, R.; Salasnich, B.; Sauvage, J.-F.; Schmid, H. M.; Schuhler, N.; Sevin, A.; Siebenmorgen, R.; Soenke, C.; Stadler, E.; Suarez, M.; Turatto, M.; Udry, S.; Vigan, A.; Zins, G.

2012-09-01

297

Colloidal rod-sphere mixtures: Fluid-fluid interfaces and the Onsager limit Joseph M. Brader  

E-print Network

. Density profiles display oscillations on the sphere-rich side of the interface provided the sphere liquid to align parallel perpen- dicular to the interface on the needle-rich sphere-rich side displaying biaxial s : 82.70.Dd, 61.20.Gy, 64.70.Ja, 61.30.Cz I. INTRODUCTION Mixtures of spherical and rodlike particles

Ott, Albrecht

298

Impact dynamics of a solid sphere falling into a viscoelastic micellar fluid  

Microsoft Academic Search

We present an experimental study of the impact of a solid sphere on the free surface of a viscoelastic wormlike micellar fluid. Spheres of various densities and diameters are dropped from different heights above the fluid surface, reaching it with a nonzero velocity which determines the subsequent dynamics. Measurements of the initial sphere penetration are found to scale with the

Benjamin Akers; Andrew Belmonte

2005-01-01

299

The solid sphere model in studies of crystal stability  

Microsoft Academic Search

The possibility of employing the hard sphere model in studies of real, stable, inert-gas crystals is considered. On the basis of the firmly established phase transition criterion for a model system the stability curve of a real crystal is found, with attractive forces considered by first-order perturbation theory. The result obtained is compared with experiment.

É. A. Arinshtein; Ya. B. Gorelik

1975-01-01

300

Universal Cellular Automata Based on the Collisions of Soft Spheres  

Microsoft Academic Search

Fredkin's Billiard Ball Model (BBM) is a continuous classical mechanical model of computation based on the elastic collisions of identical finite-diameter hard spheres. When the BBM is initialized appropriately, the sequence of states that appear at successive integer time-steps is equivalent to a discrete digital dynamics. Here we discuss some models of computation that are based on the elastic collisions

Norman Margolus

2008-01-01

301

Are Political Weblogs Public Spheres or Partisan Spheres?  

Microsoft Academic Search

In this paper we argue that political weblogs can be theoretically and pragmatically construed as public spheres, albeit with some technological and sociological limitations. Rethinking the notion of public sphere to include \\

Ravi Vatrapu; Scott Robertson; Wimal Dissanayake

302

Periodically oscillating plasma sphere  

Microsoft Academic Search

The periodically oscillating plasma sphere, or POPS, is a novel fusion concept first proposed by D. C. Barnes and R. A. Nebel [Fusion Technol. 38, 28 (1998)]. POPS utilizes the self-similar collapse of an oscillating ion cloud in a spherical harmonic oscillator potential well formed by electron injection. Once the ions have been phase-locked, their coherent motion simultaneously produces very

R. A. Nebel; S. Stange; S. Krupakar Murali

2005-01-01

303

Amphiphilic hard body mixtures Matthias Schmidt and Christian von Ferber  

E-print Network

Amphiphilic hard body mixtures Matthias Schmidt and Christian von Ferber Institut fu¨r Theoretische Received 16 June 2001; published 29 October 2001 In order to study ternary amphiphilic mixtures, we and amphiphilic particles, where the hydrophilic head is modeled as a hard sphere and the hydrophobic tail

Ott, Albrecht

304

Self diffusion of reversibly aggregating spheres  

E-print Network

Reversible diffusion limited cluster aggregation of hard spheres with rigid bonds was simulated and the self diffusion coefficient was determined for equilibrated systems. The effect of increasing attraction strength was determined for systems at different volume fractions and different interaction ranges. It was found that the slowing down of the diffusion coefficient due to crowding is decoupled from that due to cluster formation. The diffusion coefficient could be calculated from the cluster size distribution and became zero only at infinite attraction strength when permanent gels are formed. It is concluded that so-called attractive glasses are not formed at finite interaction strength.

Sujin Babu; Jean Christophe Gimel; Taco Nicolai

2007-05-10

305

Monte Carlo methods: Application to hydrogen gas and hard spheres  

Microsoft Academic Search

Quantum Monte Carlo (QMC) methods are among the most accurate for computing ground state properties of quantum systems. The two major types of QMC we use are Variational Monte Carlo (VMC), which evaluates integrals arising from the variational principle, and Diffusion Monte Carlo (DMC), which stochastically projects to the ground state from a trial wave function. These methods are applied

Mark Douglas Dewing

2001-01-01

306

FluidSolid Transition in a HardCore System Lewis Bowen* and Russell Lyons +  

E-print Network

indicate such a transition even for the conceptually simple hard­sphere model in which the interaction for the hard­sphere model, by expansion about close pack­ ing [14,15], and by simulations [16,17], but little be relevant to the fluid­ solid transition in hard­core models. In this new two­dimensional model, we replace

Radin, Charles

307

Ultraviolet characterization of integrating spheres  

Microsoft Academic Search

We have studied the performance of polytetrafluoroethylene integrating spheres in the ultraviolet (UV) region with wavelengths as short as 200 nm. Two techniques were used for this study; first, the spectral throughput of an integrating sphere irradiated by a deuterium lamp was analyzed by a monochromator. Second, a UV laser beam was directed into an integrating sphere, and spectrally dispersed

Ping-Shine Shaw; Zhigang Li; Uwe Arp; Keith R. Lykke

2007-01-01

308

Hard metal composition  

DOEpatents

A composition of matter having a Rockwell A hardness of at least 85 is formed from a precursor mixture comprising between 3 and 10 wt % boron carbide and the remainder a metal mixture comprising from 70 to 90% tungsten or molybdenum, with the remainder of the metal mixture comprising nickel and iron or a mixture thereof. The composition has a relatively low density of between 7 and 14 g/cc. The precursor is preferably hot pressed to yield a composition having greater than 100% of theoretical density.

Sheinberg, H.

1983-07-26

309

Theoretical study of miscibility and glass-forming trends in mixtures of polystyrene spheres  

NASA Technical Reports Server (NTRS)

A theoretical study of glass-forming trends and miscibility in mixtures of polystyrene spheres (polyballs) of different diameters, suspended in an aqueous solution, is presented. The polyballs are assumed to be charged and to interact via a Debye-Hueckel screened Coulomb potential. The Helmholtz free energy is calculated from a variational principle based on the Gibbs-Bogoliubov inequality, in which a mixture of hard spheres of different diameters is chosen as the reference system. It is found that when the charges of the two types of polyballs are sufficiently different, the variationally determined ratio of hard-sphere diameters differs substantially, leading to packing difficulties characteristic of glass formation. The experimentally observed range of glass formation corresponds to a ratio of hard-sphere diameters of 0.8 or less. Calculations of the free energy as a function of concentration indicate that the liquid polyball mixture is stable against the phase separation, even for widely different polyball charges.

Shih, W.-H.; Stroud, D.

1984-01-01

310

Equation of state and sound velocity of hadronic gas with hard-core interaction  

E-print Network

Thermodynamic properties of hot and dense hadronic systems with a hard-sphere interaction are calculated in the Boltzmann approximation. Two parametrizations of pressure as a function of density are considered: the first one, used in the excluded volume model and the second one, suggested earlier by Carnahan and Starling. The results are given for one-component systems containing only nucleons or pions, as well as for chemically equilibrated mixtures of pions, nucleons and delta resonances. It is shown that the Carnahan-Starling approach can be used in a much broader range of hadronic densities as compared to the excluded volume model. In this case superluminal sound velocities appear only at very high densities, in the region where the deconfinement effects should be already important.

Satarov, L M; Mishustin, I N

2014-01-01

311

Equation of state and sound velocity of hadronic gas with hard-core interaction  

E-print Network

Thermodynamic properties of hot and dense hadronic systems with a hard-sphere interaction are calculated in the Boltzmann approximation. Two parametrizations of pressure as a function of density are considered: the first one, used in the excluded volume model and the second one, suggested earlier by Carnahan and Starling. The results are given for one-component systems containing only nucleons or pions, as well as for chemically equilibrated mixtures of pions, nucleons and delta resonances. It is shown that the Carnahan-Starling approach can be used in a much broader range of hadronic densities as compared to the excluded volume model. In this case superluminal sound velocities appear only at very high densities, in the region where the deconfinement effects should be already important.

L. M. Satarov; K. A. Bugaev; I. N. Mishustin

2014-11-04

312

Structure of colloidal sphere-plate mixtures.  

PubMed

In addition to containing spherical pigment particles, coatings usually contain plate-like clay particles. It is thought that these improve the opacity of the paint film by providing an efficient spacing of the pigment particles. This observation is counterintuitive, as suspensions of particles of different shapes and sizes tend to phase separate on increase of concentration. In order to clarify this matter a model colloidal system is studied here, with a sphere-plate diameter ratio similar to that found in paints. For dilute suspensions, small angle neutron scattering revealed that the addition of plates leads to enhanced density fluctuations of the spheres, in agreement with new theoretical predictions. On increasing the total colloid concentration the plates and spheres phase separate due to the disparity in their shape. This is in agreement with previous theoretical and experimental work on colloidal sphere-plate mixtures, where one particle acts as a depleting agent. The fact that no large scale phase separation is observed in coatings is ascribed to dynamic arrest in intimately mixed, or possibly micro-phase separated structures, at elevated concentration. PMID:21525556

Doshi, N; Cinacchi, G; van Duijneveldt, J S; Cosgrove, T; Prescott, S W; Grillo, I; Phipps, J; Gittins, D I

2011-05-18

313

Structure of colloidal sphere-plate mixtures  

NASA Astrophysics Data System (ADS)

In addition to containing spherical pigment particles, coatings usually contain plate-like clay particles. It is thought that these improve the opacity of the paint film by providing an efficient spacing of the pigment particles. This observation is counterintuitive, as suspensions of particles of different shapes and sizes tend to phase separate on increase of concentration. In order to clarify this matter a model colloidal system is studied here, with a sphere-plate diameter ratio similar to that found in paints. For dilute suspensions, small angle neutron scattering revealed that the addition of plates leads to enhanced density fluctuations of the spheres, in agreement with new theoretical predictions. On increasing the total colloid concentration the plates and spheres phase separate due to the disparity in their shape. This is in agreement with previous theoretical and experimental work on colloidal sphere-plate mixtures, where one particle acts as a depleting agent. The fact that no large scale phase separation is observed in coatings is ascribed to dynamic arrest in intimately mixed, or possibly micro-phase separated structures, at elevated concentration.

Doshi, N.; Cinacchi, G.; van Duijneveldt, J. S.; Cosgrove, T.; Prescott, S. W.; Grillo, I.; Phipps, J.; Gittins, D. I.

2011-05-01

314

High pressure gas spheres for neutron and photon experiments  

NASA Astrophysics Data System (ADS)

High pressure gas spheres have been designed and successfully used in several nuclear physics experiments on noble gases. The pros and cons of this solution are the simple design and the high reliability versus the fact that the density is limited to 40-60% of liquid or solid gas samples. Originally produced for neutron capture studies at keV energies, the comparably small mass of the gas spheres were an important advantage, which turned out to be of relevance for other applications as well. The construction, performance, and operation of the spheres are described and examples for their use are presented.

Rupp, G.; Petrich, D.; Käppeler, F.; Kaltenbaek, J.; Leugers, B.; Reifarth, R.

2009-09-01

315

A rigid sphere model for the melting of argon  

Microsoft Academic Search

A model is proposed for liquid and solid argon, in which the repulsive forces are represented by rigid cores and the attractive forces by a uniform background potential which depends on density but not on temperature. Thermodynamic consistency implies the equation of state: where p0 is the pressure exerted by rigid spheres at the same number density n and temperature

H. C. Longuet-Higgins; B. Widom

1964-01-01

316

Concentrating colloids with electric field gradients. II. Phase transitions and crystal buckling of long-ranged repulsive charged spheres in an electric bottle  

NASA Astrophysics Data System (ADS)

We explored the usefulness of electric field gradients for the manipulation of the particle concentration in suspensions of charged colloids, which have long-ranged repulsive interactions. In particular, we studied the compression obtained by "negative" dielectrophoresis, which drives the particles to the regions of lowest field strength, thus preventing unwanted structural changes by induced dipole-dipole interactions. We used several sample cell layouts and suspension compositions, with a different range of the interparticle repulsions. For these systems, we obtained sufficient compression to observe a transition from the initial fluid phase to a random hexagonal close-packed crystal, as well as a body-centered cubic crystal. The heterogeneous dielectrophoretic crystallization mechanism involved an intriguing "pluglike" motion of the crystal, similar to what we have previously reported for hard-sphere suspensions. In this way, remarkably large single crystals were formed of several millimeters wide and a couple of centimeters long. Moreover, we found that these crystals could be compressed to such an extent that it led to an anisotropic deformation ("buckling") and, upon subsequent relaxation, a reorientation of the lattice, while stacking errors disappeared. These striking differences with the compressed hard-sphere crystals that we studied before [M. E. Leunissen et al., J. Chem. Phys. 128, 164508 (2008).] are likely due to the smaller elastic moduli of the present lower-density soft-sphere crystals.

Leunissen, Mirjam E.; van Blaaderen, Alfons

2008-04-01

317

Density Measurement of Tridecane by using Hydrostatic Weighing System at Density Laboratory, NML-SIRIM  

SciTech Connect

This paper presents the density measurement of tridecane by using hydrostatic weighing system, which is currently practised in Density Laboratory of National Metrology Laboratory (NML), SIRIM Berhad. This system weighed the crystal sphere while the crystal sphere was immersed in the tridecane. The volume and mass in air of the crystal sphere were calibrated at KRISS, Korea. The uncertainties of volume and mass in air of the crystal sphere were 4 ppm and 0.3 ppm respectively.

Nor, Mohd. Fazrul Hisyam Mohd.; Othman, Hafidzah; Abidin, Abd. Rashid Zainal [National Metrology Laboratory, SIRIM Berhad (Malaysia)

2009-07-07

318

Localization on round sphere revisited  

NASA Astrophysics Data System (ADS)

We consider supersymmetric gauge theories on round 3-sphere with a certain background gauge field. The Lagrangians break the usual symmetry because the background gauge field which we have turned on violates the isometry. In order to maintain the supersymmetry, we choose unfamiliar charged Killing spinors as = 2 SUSY parameters. We perform localization calculous within this setup and find the double sine function as we expected. We comment on more direct relationship between theories on round sphere and squashed sphere via Weyl transformation.

Tanaka, Akinori

2013-11-01

319

Facile assembly of 3D binary colloidal crystals from soft microgel spheres.  

PubMed

It still remains a big challenge to fabricate binary colloidal crystals (binary CCs) from hard colloidal spheres, although a lot of efforts have been made. Here, for the first time, binary CCs are assembled from soft hydrogel spheres, PNIPAM microgels, instead of hard spheres. Different from hard spheres, microgel binary CCs can be facilely fabricated by simply heating binary microgel dispersions to 37 °C and then allowing them to cool back to room temperature. The formation of highly ordered structure is indicated by the appearance of an iridescent color and a sharp Bragg diffraction peak. Compared with hard sphere binary CCs, the assembly of PNIPAM microgel binary CCs is much simpler, faster and with a higher "atom" economy. The easy formation of PNIPAM microgel binary CC is attributed to the thermosensitivity and soft nature of the PNIPAM microgel spheres. In addition, PNIPAM microgel binary CCs can respond to temperature change, and their stop band can be tuned by changing the concentration of the dispersion. PMID:24497429

Liu, Yang; Guan, Ying; Zhang, Yongjun

2014-03-01

320

Hard rock drilling problems explained by hard rock pressure plots  

SciTech Connect

Hard rock drilling problems are frustrating. Hard rock pore pressure interpretation is baffling. Because of slow drilling in hard streaks and absence of kicks (in overpressured shale sections), it is generally assumed pore pressures are close to ''normal'' over long depth intervals. Many hard rock drilling problems could not be logically explained, if this were the case. Nothing could be further from the truth. Hard rocks are difficult to drill because of the extreme zig-zags from overpressured shales to sub-normally pressured sands and carbonates. It is impossible to drill anywhere near balanced in both situations, simultaneously. Hard rock drilling problems caused by underbalance or overbalance (or both) are a result. But, a better understanding of the presence and magnitude of these pressure shifts will help minimize the worst extremes of imbalance and more intelligently strike an optimum compromise, realizing that mud density and, especially, mud chemistry can never completely solve these hard rock drilling problems. Well log pressure plots in these erratic stratigraphies are so difficult to interpret that they often have been considered useless. The example pore pressure plots shown here, including the Pressure Evaluation Profile (PEP) log -- a side by side comparison of several different pressure sensitive responses -- help interpret and explain many of these problems in a simple, logical manner.

Gill, J.A.

1983-02-01

321

STP Hard Disks Metropolis Program  

NSDL National Science Digital Library

The STP Hard Disks Metropolis program is a Monte Carlo simulation of hard disks in two dimensions. The default initial condition is a rectangular configuration of N=64 particles in a box of length L = 40. You can slowly increase the density of the gas (by setting the minimum scale length between centers to a value slightly less than 1) to explore phase transitions. STP HardDisksMetropolis is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double-clicking the stp_HardDisksMetropolis.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2009-03-06

322

Thermodynamics of nano-spheres encapsulated in virus capsids  

E-print Network

We investigate the thermodynamics of complexation of functionalized charged nano-spheres with viral proteins. The physics of this problem is governed by electrostatic interaction between the proteins and the nano-sphere cores (screened by salt ions), but also by configurational degrees of freedom of the charged protein N-tails. We approach the problem by constructing an appropriate complexation free energy functional. On the basis of both numerical and analytical studies of this functional we construct the phase diagram for the assembly which contains the information on the assembled structures that appear in the thermodynamical equilibrium, depending on the size and surface charge density of the nano-sphere cores. We show that both the nano-sphere core charge as well as its radius determine the size of the capsid that forms around the core.

Antonio Siber; Roya Zandi; Rudolf Podgornik

2009-11-16

323

Second virial coefficient at the critical point in a fluid of colloidal spheres plus depletants.  

PubMed

Vliegenthart-Lekkerkerker (VL) criterion B2 = -6vc for second virial coefficient B2 at the critical (colloidal) gas-liquid point is considered for a mixture of spheres with volume vc plus depletants. For the onset of fluid-phase instability, the VL criterion holds for a wide range of shapes of direct attractive forces between hard-core spheres (Vliegenthart, G. A.; Lekkerkerker, H. N. W. J. Chem. Phys. 2000, 112, 5364). In the case of long-ranged attractions imposed indirectly via depletants, it is found that the VL relation fails. Instead, B2/vc at the critical point depends strongly on the sphere/depletant size ratio. By making the hard spheres sticky, we find that B2 moves gradually toward the VL criterion upon increasing the stickiness. PMID:25329352

Tuinier, Remco; Feenstra, Maartje S

2014-11-11

324

Molecular density functional theory of water describing hydrophobicity at short and long length scales  

NASA Astrophysics Data System (ADS)

We present an extension of our recently introduced molecular density functional theory of water [G. Jeanmairet et al., J. Phys. Chem. Lett. 4, 619 (2013)] to the solvation of hydrophobic solutes of various sizes, going from angstroms to nanometers. The theory is based on the quadratic expansion of the excess free energy in terms of two classical density fields: the particle density and the multipolar polarization density. Its implementation requires as input a molecular model of water and three measurable bulk properties, namely, the structure factor and the k-dependent longitudinal and transverse dielectric susceptibilities. The fine three-dimensional water structure around small hydrophobic molecules is found to be well reproduced. In contrast, the computed solvation free-energies appear overestimated and do not exhibit the correct qualitative behavior when the hydrophobic solute is grown in size. These shortcomings are corrected, in the spirit of the Lum-Chandler-Weeks theory, by complementing the functional with a truncated hard-sphere functional acting beyond quadratic order in density, and making the resulting functional compatible with the Van-der-Waals theory of liquid-vapor coexistence at long range. Compared to available molecular simulations, the approach yields reasonable solvation structure and free energy of hard or soft spheres of increasing size, with a correct qualitative transition from a volume-driven to a surface-driven regime at the nanometer scale.

Jeanmairet, Guillaume; Levesque, Maximilien; Borgis, Daniel

2013-10-01

325

Molecular density functional theory of water describing hydrophobicity at short and long length scales.  

PubMed

We present an extension of our recently introduced molecular density functional theory of water [G. Jeanmairet et al., J. Phys. Chem. Lett. 4, 619 (2013)] to the solvation of hydrophobic solutes of various sizes, going from angstroms to nanometers. The theory is based on the quadratic expansion of the excess free energy in terms of two classical density fields: the particle density and the multipolar polarization density. Its implementation requires as input a molecular model of water and three measurable bulk properties, namely, the structure factor and the k-dependent longitudinal and transverse dielectric susceptibilities. The fine three-dimensional water structure around small hydrophobic molecules is found to be well reproduced. In contrast, the computed solvation free-energies appear overestimated and do not exhibit the correct qualitative behavior when the hydrophobic solute is grown in size. These shortcomings are corrected, in the spirit of the Lum-Chandler-Weeks theory, by complementing the functional with a truncated hard-sphere functional acting beyond quadratic order in density, and making the resulting functional compatible with the Van-der-Waals theory of liquid-vapor coexistence at long range. Compared to available molecular simulations, the approach yields reasonable solvation structure and free energy of hard or soft spheres of increasing size, with a correct qualitative transition from a volume-driven to a surface-driven regime at the nanometer scale. PMID:24160494

Jeanmairet, Guillaume; Levesque, Maximilien; Borgis, Daniel

2013-10-21

326

Structure, thermodynamics, and position-dependent diffusivity in fluids with sinusoidal density variations.  

PubMed

Molecular dynamics simulations and a stochastic method based on the Fokker-Planck equation are used to explore the consequences of inhomogeneous density profiles on the thermodynamic and dynamic properties of the hard-sphere fluid and supercooled liquid water. Effects of the inhomogeneity length scale are systematically considered via the imposition of sinusoidal density profiles of various wavelengths. For long-wavelength density profiles, bulk-like relationships between local structure, thermodynamics, and diffusivity are observed as expected. However, for both systems, a crossover in behavior occurs as a function of wavelength, with qualitatively different correlations between the local static and dynamic quantities emerging as density variations approach the scale of a particle diameter. Irrespective of the density variation wavelength, average diffusivities of hard-sphere fluids in the inhomogeneous and homogeneous directions are coupled and approximately correlate with the volume available for insertion of another particle. Unfortunately, a quantitatively reliable static predictor of position-dependent dynamics has yet to be identified for even the simplest of inhomogeneous fluids. PMID:24984592

Bollinger, Jonathan A; Jain, Avni; Truskett, Thomas M

2014-07-22

327

Thermodynamics and phase behavior of a triangle-well model and density-dependent variety  

NASA Astrophysics Data System (ADS)

A hard sphere+triangle-well potential is employed to test a recently proposed thermodynamic perturbation theory (TPT) based on a coupling parameter expansion. It is found that the second-order term of the coupling parameter expansion surpasses by far that of a high temperature series expansion under a macroscopic compressibility approximation and several varieties. It is also found that the fifth-order version displays best among all of the numerically accessible versions with dissimilar truncation orders. Particularly, the superiority of the fifth-order TPT from other available liquid state theories is exhibited the most incisively when the temperature of interest obviously falls. We investigate the modification of the phase behavior of the hard sphere+triangle-well fluid resulting from a density dependence imposed on the original potential function. It is shown that (1) the density dependence induces polymorphism of fluid phase, particularly liquid-liquid transition in metastable supercooled region, and (2) along with enhanced decaying of the potential function as a function of bulk density, both the liquid-liquid transition and vapor-liquid transition tend to be situated at the domain of lower temperature, somewhat similar to a previously disclosed thumb rule that the fluid phase transition tends to metastable with respect to the fluid-solid transition as the range of the attraction part of a density-independence potential is sufficiently short compared to the range of the repulsion part of the same density-independence potential.

Zhou, Shiqi

2009-01-01

328

Density in a Bottle.  

ERIC Educational Resources Information Center

Explains how the Canadian soft drink Orbitz can be used for explorations of density in the classroom. The drink has colored spheres suspended throughout that have a density close to that of the liquid. Presents a hands-on activity that can be easily done in two parts. (DDR)

Roser, Charles E.; McCluskey, Catherine L.

1998-01-01

329

DSMC simulation and experimental validation of shock interaction in hypersonic low density flow.  

PubMed

Direct simulation Monte Carlo (DSMC) of shock interaction in hypersonic low density flow is developed. Three collision molecular models, including hard sphere (HS), variable hard sphere (VHS), and variable soft sphere (VSS), are employed in the DSMC study. The simulations of double-cone and Edney's type IV hypersonic shock interactions in low density flow are performed. Comparisons between DSMC and experimental data are conducted. Investigation of the double-cone hypersonic flow shows that three collision molecular models can predict the trend of pressure coefficient and the Stanton number. HS model shows the best agreement between DSMC simulation and experiment among three collision molecular models. Also, it shows that the agreement between DSMC and experiment is generally good for HS and VHS models in Edney's type IV shock interaction. However, it fails in the VSS model. Both double-cone and Edney's type IV shock interaction simulations show that the DSMC errors depend on the Knudsen number and the models employed for intermolecular interaction. With the increase in the Knudsen number, the DSMC error is decreased. The error is the smallest in HS compared with those in the VHS and VSS models. When the Knudsen number is in the level of 10(-4), the DSMC errors, for pressure coefficient, the Stanton number, and the scale of interaction region, are controlled within 10%. PMID:24672360

Xiao, Hong; Shang, Yuhe; Wu, Di

2014-01-01

330

DSMC Simulation and Experimental Validation of Shock Interaction in Hypersonic Low Density Flow  

PubMed Central

Direct simulation Monte Carlo (DSMC) of shock interaction in hypersonic low density flow is developed. Three collision molecular models, including hard sphere (HS), variable hard sphere (VHS), and variable soft sphere (VSS), are employed in the DSMC study. The simulations of double-cone and Edney's type IV hypersonic shock interactions in low density flow are performed. Comparisons between DSMC and experimental data are conducted. Investigation of the double-cone hypersonic flow shows that three collision molecular models can predict the trend of pressure coefficient and the Stanton number. HS model shows the best agreement between DSMC simulation and experiment among three collision molecular models. Also, it shows that the agreement between DSMC and experiment is generally good for HS and VHS models in Edney's type IV shock interaction. However, it fails in the VSS model. Both double-cone and Edney's type IV shock interaction simulations show that the DSMC errors depend on the Knudsen number and the models employed for intermolecular interaction. With the increase in the Knudsen number, the DSMC error is decreased. The error is the smallest in HS compared with those in the VHS and VSS models. When the Knudsen number is in the level of 10?4, the DSMC errors, for pressure coefficient, the Stanton number, and the scale of interaction region, are controlled within 10%. PMID:24672360

2014-01-01

331

The SPHERE View of Betelgeuse  

NASA Astrophysics Data System (ADS)

SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument for the VLT is optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star, thanks to an extreme AO system. SPHERE is very well suited to study the close environment of Betelgeuse, and has a strong potential for detecting the ejection activity around this key red supergiant.

Chesneau, O.; Schmid, H.-M.; Carbillet, M.; Chiavassa, A.; Abe, L.; Mouillet, D.

2013-05-01

332

Ancient Celestial Spheres from Greece  

NASA Astrophysics Data System (ADS)

We present several ancient celestial spheres from the 8th century B.C. found throughout Greece, mainly in Thessaly, at the temple of Itonia Athena, but also in Olympia and other places. These celestial spheres have an axis, equator and several meridians and they have several markings with the symbol of stars (today's symbol for the Sun) $\\odot$. Such instruments could have been used to measure the time, the latitude of a location, or the coordinates of stars.

Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.

2006-08-01

333

Retention and entrainment effects: Experiments and theory for porous spheres settling in sharply stratified fluids  

E-print Network

of the sphere but does not capture the retention time at the density transition quantitatively. Entrainment. With this parametrization, which exhibits a power law dependence on Reynolds numbers, retention times are accuratelyRetention and entrainment effects: Experiments and theory for porous spheres settling in sharply

McLaughlin, Richard M.

334

High pressure gas spheres for neutron and photon experiments  

Microsoft Academic Search

High pressure gas spheres have been designed and successfully used in several nuclear physics experiments on noble gases. The pros and cons of this solution are the simple design and the high reliability versus the fact that the density is limited to 40–60% of liquid or solid gas samples. Originally produced for neutron capture studies at keV energies, the comparably

G. Rupp; D. Petrich; F. Käppeler; J. Kaltenbaek; B. Leugers; R. Reifarth

2009-01-01

335

A rigid sphere model for the melting of argon  

Microsoft Academic Search

A model is proposed for liquid and solid argon, in which the repulsive forces are represented by rigid cores and the attractive forces by a uniform background potential which depends on density but not on temperature. Thermodynamic consistency implies the equation of state: p(n,T) = p 0 (n,T)-an 2 , where p 0 is the pressure exerted by rigid spheres

H. C. Longuet-Higgins; B. Widom

2002-01-01

336

A locally analytic density functional theory describing adsorption and condensation in microporous materials  

SciTech Connect

The fluid density distribution within microscopic pores is determined by solving integral equations relating to the local chemical potential to the Van der Waals attractions and hard sphere repulsions of surrounding material. To avoid resolving the density distribution on sub-molecular scales, the governing equations are averaged over zones of molecular size using analytic functions to represent local density variations within each zone. These local density profiles range form singularities to uniform distributions depending on the local variation of the potential field. Sample calculations indicate that this integral approach yields results in very good agreement with those based on traditional density functional theory (DFT), while reducing computing times by factors of 10{sup 3} to 10{sup 4} for one- dimensional geometries.

Nilson, R.H.; Griffiths, S.K. [Sandia National Labs., Livermore, CA (United States)

1997-02-01

337

Porous Ceramic Spheres From Cation Exchange Beads  

NASA Technical Reports Server (NTRS)

This document is a slide presentation that examines the use of a simple templating process to produce hollow ceramic spheres with a pore size of 1 to 10 microns. Using ion exchange process it was determined that the method produces porous ceramic spheres with a unique structure: (i.e., inner sphere surrounded by an outer sphere.)

Dynys, Fred

2005-01-01

338

Unexpected ricochet of spheres off water  

Microsoft Academic Search

A sphere was observed to apparently ricochet off the free surface of water at incident angles as large as 45° while the expected (empirical\\/analytical) maximum angle to the horizontal for ricochet was 6°. Closer examination of the process revealed that the cavitating sphere penetrated the liquid to depths as great as 35 sphere diameters. Under certain circumstances the sphere was

D. J. Shlien

1994-01-01

339

Abradable dual-density ceramic turbine seal system  

NASA Technical Reports Server (NTRS)

A plasma sprayed dual density ceramic abradable seal system for direct application to the HPT seal shroud of small gas turbine engines. The system concept is based on the thermal barrier coating and depends upon an additional layer of modified density ceramic material adjacent to the gas flow path to provide the desired abradability. This is achieved by codeposition of inert fillers with yttria stabilized zirconia (YSZ) to interrupt the continuity of the zirconia struture. The investigation of a variety of candidate fillers, with hardness values as low as 2 on Moh's scale, led to the conclusion that solid filler materials in combination with a YSZ matrix, regardless of their hardness values, have a propensity for compacting rather than shearing as originally expected. The observed compaction is accompanied by high energy dissipation in the rub interaction, usually resulting in the adhesive transfer of blade material to the stationary seal member. Two YSZ based coating systems which incorported hollow alumino silicate spheres as density reducing agents were surveyed over the entire range of compositions from 100 percent filler to 100 percent YSZ. Abradability and erosion characteristics were determined, hardness and permeability characterized, and engine experience acquired with several system configurations.

Clingman, D. L.; Schechter, B.; Cross, K. R.; Cavanagh, J. R.

1981-01-01

340

Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. I. Polydisperse spheres  

NASA Astrophysics Data System (ADS)

Hyperuniform many-particle distributions possess a local number variance that grows more slowly than the volume of an observation window, implying that the local density is effectively homogeneous beyond a few characteristic length scales. Previous work on maximally random strictly jammed sphere packings in three dimensions has shown that these systems are hyperuniform and possess unusual quasi-long-range pair correlations decaying as r-4, resulting in anomalous logarithmic growth in the number variance. However, recent work on maximally random jammed sphere packings with a size distribution has suggested that such quasi-long-range correlations and hyperuniformity are not universal among jammed hard-particle systems. In this paper, we show that such systems are indeed hyperuniform with signature quasi-long-range correlations by characterizing the more general local-volume-fraction fluctuations. We argue that the regularity of the void space induced by the constraints of saturation and strict jamming overcomes the local inhomogeneity of the disk centers to induce hyperuniformity in the medium with a linear small-wave-number nonanalytic behavior in the spectral density, resulting in quasi-long-range spatial correlations scaling with r-(d+1) in d Euclidean space dimensions. A numerical and analytical analysis of the pore-size distribution for a binary maximally random jammed system in addition to a local characterization of the n-particle loops governing the void space surrounding the inclusions is presented in support of our argument. This paper is the first part of a series of two papers considering the relationships among hyperuniformity, jamming, and regularity of the void space in hard-particle packings.

Zachary, Chase E.; Jiao, Yang; Torquato, Salvatore

2011-05-01

341

Integrability versus non-integrability: hard hexagons and hard squares compared  

NASA Astrophysics Data System (ADS)

In this paper we compare the integrable hard hexagon model with the non-integrable hard squares model by means of partition function roots and transfer matrix eigenvalues. We consider partition functions for toroidal, cylindrical, and free–free boundary conditions up to sizes 40 × 40 and transfer matrices up to 30 sites. For all boundary conditions the hard squares roots are seen to lie in a bounded area of the complex fugacity plane along with the universal hard core line segment on the negative real fugacity axis. The density of roots on this line segment matches the derivative of the phase difference between the eigenvalues of largest (and equal) moduli and exhibits much greater structure than the corresponding density of hard hexagons. We also study the special point z=-1 of hard squares, where all eigenvalues have unit modulus, and we give several conjectures for the value at z=-1 of the partition functions.

Assis, M.; Jacobsen, J. L.; Jensen, I.; Maillard, J.-M.; McCoy, B. M.

2014-11-01

342

Integrability vs non-integrability: Hard hexagons and hard squares compared  

E-print Network

In this paper we compare the integrable hard hexagon model with the non-integrable hard squares model by means of partition function roots and transfer matrix eigenvalues. We consider partition functions for toroidal, cylindrical, and free-free boundary conditions up to sizes $40\\times40$ and transfer matrices up to 30 sites. For all boundary conditions the hard squares roots are seen to lie in a bounded area of the complex fugacity plane along with the universal hard core line segment on the negative real fugacity axis. The density of roots on this line segment matches the derivative of the phase difference between the eigenvalues of largest (and equal) moduli and exhibits much greater structure than the corresponding density of hard hexagons. We also study the special point $z=-1$ of hard squares where all eigenvalues have unit modulus, and we give several conjectures for the value at $z=-1$ of the partition functions.

M. Assis; J. L. Jacobsen; I. Jensen; J-M. Maillard; B. M. McCoy

2014-06-21

343

Non-equilibrium Casimir forces: Spheres and sphere-plate  

NASA Astrophysics Data System (ADS)

We discuss non-equilibrium extensions of the Casimir force (due to electromagnetic fluctuations), where the objects as well as the environment are held at different temperatures. While the formalism we develop is quite general, we focus on a sphere in front of a plate, as well as two spheres, when the radius is small compared to separation and thermal wavelengths. In this limit the forces can be expressed analytically in terms of the lowest-order multipoles, and corroborated with results obtained by diluting parallel plates of vanishing thickness. Non-equilibrium forces are generally stronger than their equilibrium counterpart, and may oscillate with separation (at a scale set by material resonances). For both geometries we obtain stable points of zero net force, while two spheres may have equal forces in magnitude and direction resulting in a self-propelling state.

Krüger, M.; Emig, T.; Bimonte, G.; Kardar, M.

2011-07-01

344

Role of bit patterned media in future of hard disk drives  

E-print Network

The hard disk industry has traditionally stayed competitive by competing on the means of price alone by cutting down aggressively on cost via increase of areal density. Continuing increases in the areal density of hard ...

Aravindakshan, Vibin

2007-01-01

345

Combustion of a Polymer (PMMA) Sphere in Microgravity  

NASA Technical Reports Server (NTRS)

A series of low gravity, aircraft-based, experiments was conducted to investigate the combustion of supported thermoplastic polymer spheres under varying ambient conditions. The three types of thermoplastic investigated were polymethylmethacrylate (PMMA), polypropylene (PP). and polystyrene (PS). Spheres with diameters ranging from 2 mm to 6.35 mm were tested. The total initial pressure varied from 0.05 MPa to 0. 15 MPa whereas the ambient oxygen concentration varied from 19 % to 30 % (by volume). The ignition system consisted of a pair of retractable energized coils. Two CCD cameras recorded the burning histories of the spheres. The video sequences revealed a number of dynamic events including bubbling and sputtering, as well as soot shell formation and break-up during combustion of the spheres at reduced gravity. The ejection of combusting material from the burning spheres represents a fire hazard that must be considered at reduced gravity. The ejection process was found to be sensitive to polymer type. All average burning rates were measured to increase with initial sphere diameter and oxygen concentration, whereas the initial pressure had little effect. The three thermoplastic types exhibited different burning characteristics. For the same initial conditions, the burning rate of PP was slower than PMMA, whereas the burning rate of PS was comparable to PMMA. The transient diameter of the burning thermoplastic exhibited two distinct periods: an initial period (enduring approximately half of the total burn duration) when the diameter remained approximately constant, and a final period when the square of the diameter linearly decreased with time. A simple homogeneous two-phase model was developed to understand the changing diameter of the burning sphere. Its value is based on a competition between diameter reduction due to mass loss from burning and sputtering, and diameter expansion due to the processes of swelling (density decrease with heating) and bubble growth. The model relies on empirical parameters for input, such as the burning rate and the duration of the initial and final burning periods.

Yang, Jiann C.; Hamins, Anthony; Donnelly, Michelle K.

1999-01-01

346

Connection Between Minimum of Solubility and Temperature of Maximum Density in an Associating Lattice Gas Model  

E-print Network

In this paper we investigate the solubility of a hard - sphere gas in a solvent modeled as an associating lattice gas (ALG). The solution phase diagram for solute at 5% is compared with the phase diagram of the original solute free model. Model properties are investigated thr ough Monte Carlo simulations and a cluster approximation. The model solubility is computed via simulations and shown to exhibit a minimum as a function of temperature. The line of minimum solubility (TmS) coincides with the line of maximum density (TMD) for different solvent chemical potentials.

Marcia M. Szortyka; Maurício Girardi; Vera B. Henriques; Marcia C. Barbosa

2012-05-09

347

High voltage spheres in an unmagnetized plasma - Fluid and PIC simulations  

NASA Technical Reports Server (NTRS)

The basic physics involving the interaction of a high voltage sphere with a LEO-Plasma was investigated via computer experiments. Two approaches were used: the fluid description and the more general particle pushing method. Both techniques displayed qualitatively similar features. Thus, the initial time-dependent response of the plasma predicted by the fluid model, including the initial current surge and sheath formation, the formation of ion and electron density shells about the sphere with a double layer potential structure, and the subsequent propagation of the density shells away from the sphere. The PIC results also displayed an oscillatory character and slightly different time constants for the growth and decay mechanisms involved.

Thiemann, H.; Ma, T.-Z.; Schunk, R. W.

1992-01-01

348

Wear of hard materials by hard particles  

SciTech Connect

Hard materials, such as WC-Co, boron carbide, titanium diboride and composite carbide made up of Mo2C and WC, have been tested in abrasion and erosion conditions. These hard materials showed negligible wear in abrasion against SiC particles and erosion using Al2O3 particles. The WC-Co materials have the highest wear rate of these hard materials and a very different material removal mechanism. Wear mechanisms for these materials were different for each material with the overall wear rate controlled by binder composition and content and material grain size.

Hawk, Jeffrey A.

2003-10-01

349

ORSPHERE: CRITICAL, BARE, HEU(93.2)-METAL SPHERE  

SciTech Connect

In the early 1970’s Dr. John T. Mihalczo (team leader), J.J. Lynn, and J.R. Taylor performed experiments at the Oak Ridge Critical Experiments Facility (ORCEF) with highly enriched uranium (HEU) metal (called Oak Ridge Alloy or ORALLOY) in an attempt to recreate GODIVA I results with greater accuracy than those performed at Los Alamos National Laboratory in the 1950’s (HEU-MET-FAST-001). The purpose of the Oak Ridge ORALLOY Sphere (ORSphere) experiments was to estimate the unreflected and unmoderated critical mass of an idealized sphere of uranium metal corrected to a density, purity, and enrichment such that it could be compared with the GODIVA I experiments. “The very accurate description of this sphere, as assembled, establishes it as an ideal benchmark for calculational methods and cross-section data files.” (Reference 1) While performing the ORSphere experiments care was taken to accurately document component dimensions (±0. 0001 in. for non-spherical parts), masses (±0.01 g), and material data The experiment was also set up to minimize the amount of structural material in the sphere proximity. A three part sphere was initially assembled with an average radius of 3.4665 in. and was then machined down to an average radius of 3.4420 in. (3.4425 in. nominal). These two spherical configurations were evaluated and judged to be acceptable benchmark experiments; however, the two experiments are highly correlated.

Margaret A. Marshall

2013-09-01

350

Sampling from a polytope and hard-disk Monte Carlo  

NASA Astrophysics Data System (ADS)

The hard-disk problem, the statics and the dynamics of equal two-dimensional hard spheres in a periodic box, has had a profound influence on statistical and computational physics. Markov-chain Monte Carlo and molecular dynamics were first discussed for this model. Here we reformulate hard-disk Monte Carlo algorithms in terms of another classic problem, namely the sampling from a polytope. Local Markov-chain Monte Carlo, as proposed by Metropolis et al. in 1953, appears as a sequence of random walks in high-dimensional polytopes, while the moves of the more powerful event-chain algorithm correspond to molecular dynamics evolution. We determine the convergence properties of Monte Carlo methods in a special invariant polytope associated with hard-disk configurations, and the implications for convergence of hard-disk sampling. Finally, we discuss parallelization strategies for event-chain Monte Carlo and present results for a multicore implementation.

Kapfer, Sebastian C.; Krauth, Werner

2013-08-01

351

Hardness testing. 2nd edition  

SciTech Connect

This basic book provides a comprehensive overview of hardness testing, including the various methods and equipment used, testing applications, and the selection of testing methods. The revised and updated second edition features expanded information on microhardness testing, specialized hardness tests; and hardness testing standards. Contents include: introduction to hardness testing; brinell testing; rockwell hardness testing; vickers hardness testing; microhardness testing; scleroscope and leeb hardness testing; hardness testing applications; and selection of hardness testing methods.

Chandler, H. [ed.

1999-07-01

352

Sphere Pluralism and Critical Individuality  

ERIC Educational Resources Information Center

While discussing critical individuality as one of the main goals of liberal education, the emphasis has usually been on direct educational measures. Much less attention has been given to the social preconditions for its development. This paper discusses the societal aspect of the question by employing the notion of sphere pluralism. The attempt is…

Puolimatka, T.

2004-01-01

353

Data compression on the sphere  

NASA Astrophysics Data System (ADS)

Large data-sets defined on the sphere arise in many fields. In particular, recent and forthcoming observations of the anisotropies of the cosmic microwave background (CMB) made on the celestial sphere contain approximately three and fifty mega-pixels respectively. The compression of such data is therefore becoming increasingly important. We develop algorithms to compress data defined on the sphere. A Haar wavelet transform on the sphere is used as an energy compression stage to reduce the entropy of the data, followed by Huffman and run-length encoding stages. Lossless and lossy compression algorithms are developed. We evaluate compression performance on simulated CMB data, Earth topography data and environmental illumination maps used in computer graphics. The CMB data can be compressed to approximately 40% of its original size for essentially no loss to the cosmological information content of the data, and to approximately 20% if a small cosmological information loss is tolerated. For the topographic and illumination data compression ratios of approximately 40:1 can be achieved when a small degradation in quality is allowed. We make our SZIP program that implements these compression algorithms available publicly.

McEwen, J. D.; Wiaux, Y.; Eyers, D. M.

2011-07-01

354

The Poincaré sphere sample space  

Microsoft Academic Search

In a series of recent papers, Randall and Foulis report the development of a generalized theory of probability which is based on the concept of a physical operation. A central concept in this theory is that of a generalized sample space. In this paper, we introduce a generalized sample space, which for historial reasons we shall call the Poincaré sphere

Carl A. Hein

1977-01-01

355

Hydrodynamic Force between a Sphere and a Soft, Elastic Surface.  

PubMed

The hydrodynamic drainage force between a spherical silica particle and a soft, elastic polydimethylsiloxane surface was measured using the colloidal probe technique. The experimental force curves were compared to finite element simulations and an analytical model. The hydrodynamic repulsion decreased when the particle approached the soft surface as compared to a hard substrate. In contrast, when the particle was pulled away from the surface again, the attractive hydrodynamic force was increased. The hydrodynamic attraction increased because the effective area of the narrow gap between sphere and the plane on soft surfaces is larger than on rigid ones. PMID:25198777

Kaveh, Farzaneh; Ally, Javed; Kappl, Michael; Butt, Hans-Jürgen

2014-10-01

356

Tessellating the Sphere with Regular Polygons  

ERIC Educational Resources Information Center

Tessellations in the Euclidean plane and regular polygons that tessellate the sphere are reviewed. The regular polygons that can possibly tesellate the sphere are spherical triangles, squares and pentagons.

Soto-Johnson, Hortensia; Bechthold, Dawn

2004-01-01

357

On the quality of the hardness kernel and the Fukui function to evaluate the global hardness.  

PubMed

An approximated hardness kernel, which includes the second derivative with respect to the density of the kinetic energy, the electron-electron coulomb repulsion, and the exchange density functionals, has been tested for the calculation of the global hardness. The results obtained for a series of 40 cations and neutral systems and 16 anions represent in most cases an improvement of the results obtained using the HOMO-LUMO gap approach and indicate the viability of this approach to evaluate global hardness. In addition, the relevance of the Fukui function approximation and the role of the three components of the hardness kernel in the evaluation of the global hardness have been analyzed. PMID:17186480

Torrent-Sucarrat, Miquel; Salvador, Pedro; Geerlings, Paul; Solà, Miquel

2007-01-30

358

One-dimensional gas of hard needles  

E-print Network

We study a one dimensional gas of needle-like objects as a testing ground for a formalism that relates the thermodynamic properties of "hard" potentials to the probabilities for contacts between particles. Specifically, we use Monte Carlo methods to calculate the pressure and elasticity coefficient of the hard-needle gas as a function of its density. The results are then compared to the same quantities obtained analytically from a transfer matrix approach.

Yacov Kantor; Mehran Kardar

2009-02-11

359

Vacuum energies on spheres and in cubes  

E-print Network

The vacuum energy of a conformally coupled scalar field on the d-dimensional sphere is calculated. On even spheres it is zero and on odd spheres it oscillates in sign. Results for the d-torus and d-cube are also given.

J. S. Dowker

2011-06-18

360

Archaic artifacts resembling celestial spheres  

NASA Astrophysics Data System (ADS)

We present several bronze artifacts from the Archaic Age in Greece (750-480 BC) that resemble celestial spheres or forms of other astronomical significance. They are studied in the context of the Dark Age transition from Mycenaean Age astronomical themes to the philosophical and practical revival of astronomy in the Classical Age with its plethora of astronomical devices. These artifacts, mostly votive in nature are spherical in shape and appear in a variety of forms their most striking characteristic being the depiction of meridians and/or an equator. Most of those artifacts come from Thessaly, and more specifically from the temple of Itonia Athena at Philia, a religious center of pan-Hellenic significance. Celestial spheres, similar in form to the small artifacts presented in this study, could be used to measure latitudes, or estimate the time at a known place, and were thus very useful in navigation.

Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.

361

How Hard is Chocolate?  

NSDL National Science Digital Library

Hardness is probably a concept you are well familiar with. You already know that certain materials are harder than others; in fact, you prove it everyday when you chew your food and your teeth don’t break (because your teeth are harder than the foods you chew). Hardness can be defined as a material's ability to resist a change in shape. Modern hardness testers take a well-defined shape and press it into a material with a certain force, observing the indent it leaves in the material when it is removed. In this lesson, you will be performing hardness testing on different bars of chocolate.

2007-12-20

362

Hypersonic rarefied flow past spheres including wake structure  

Microsoft Academic Search

Results of a numerical study using the direct simulation Monte Carlo method are presented for hypersonic rarefied flow past spheres. The flow conditions considered are those corresponding to low-density wind-tunnel test conditions. The set of the experimental conditions for the calculations encompasses the transitional to near-continuum flow regimes. Comparison of the calculated drag with experimental results shows good agreement to

Virendra K. Dogra; James N. Moss; Richard G. Wilmoth; Joseph M. Price

1994-01-01

363

Density functional theory for crystal-liquid interfaces of Lennard-Jones fluid.  

PubMed

A density functional approach is presented to describe the crystal-liquid interfaces and crystal nucleations of Lennard-Jones fluid. Within the theoretical framework, the modified fundamental measure theory is applied to describe the free energy functional of hard sphere repulsion, and the weighted density method based on first order mean spherical approximation is used to describe the free energy contribution arising from the attractive interaction. The liquid-solid equilibria, density profiles within crystal cells and at liquid-solid interfaces, interfacial tensions, nucleation free energy barriers, and critical cluster sizes are calculated for face-centered-cubic and body-centered-cubic nucleus. Some results are in good agreement with available simulation data, indicating that the present model is quantitatively reliable in describing nucleation thermodynamics of Lennard-Jones fluid. PMID:23635162

Wang, Xin; Mi, Jianguo; Zhong, Chongli

2013-04-28

364

Development of a Falling Sphere Technique for E-region Wind Measurements  

NASA Astrophysics Data System (ADS)

In this presentation we outline the development of a new falling sphere technique sensor for measuring the lower E-region neutral winds and density, which are critical for many of the electrodynamics and plasma physics studies that are carried out as part of the NASA suborbital rocket program. Currently, chemical releases are the primary technique for measuring winds in the lower E-region. Chemical release wind measurements provide detailed wind profiles with good accuracy and have a long flight history. However, they have a number of operational drawbacks, including the need for clear skies over a broad area for camera observations, limited viewing windows (e.g., only at nighttime in the case of trimethyl aluminum), and the need to follow strict handling procedures. Recent advances in low-cost commercial technology have made the falling sphere technique an attractive option to chemical release for E-region measurements. Falling sphere instruments (typically inflatable devices) have been used extensively to make wind measurements in the D-region. Similar measurements in the lower E-region require higher sensitivity accelerometers and a more careful design of the sphere (e.g., solid sphere structure for hypersonic speeds). This presentation demonstrates the design and laboratory testing and calibration of a next-generation solid falling sphere instrument for E-region measurements. Ultimately, the development of this new falling sphere instrument will enable the deployment of multiple falling spheres from one rocket for 3D volume determination of neutral wind measurements.

Cannon, B. K.; Fish, C. S.; Larsen, M. F.; Swenson, C.

2009-12-01

365

Precise algorithm to generate random sequential addition of hard hyperspheres at saturation  

NASA Astrophysics Data System (ADS)

The study of the packing of hard hyperspheres in d-dimensional Euclidean space Rd has been a topic of great interest in statistical mechanics and condensed matter theory. While the densest known packings are ordered in sufficiently low dimensions, it has been suggested that in sufficiently large dimensions, the densest packings might be disordered. The random sequential addition (RSA) time-dependent packing process, in which congruent hard hyperspheres are randomly and sequentially placed into a system without interparticle overlap, is a useful packing model to study disorder in high dimensions. Of particular interest is the infinite-time saturation limit in which the available space for another sphere tends to zero. However, the associated saturation density has been determined in all previous investigations by extrapolating the density results for nearly saturated configurations to the saturation limit, which necessarily introduces numerical uncertainties. We have refined an algorithm devised by us [S. Torquato, O. U. Uche, and F. H. Stillinger, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.74.061308 74, 061308 (2006)] to generate RSA packings of identical hyperspheres. The improved algorithm produce such packings that are guaranteed to contain no available space in a large simulation box using finite computational time with heretofore unattained precision and across the widest range of dimensions (2?d?8). We have also calculated the packing and covering densities, pair correlation function g2(r), and structure factor S(k) of the saturated RSA configurations. As the space dimension increases, we find that pair correlations markedly diminish, consistent with a recently proposed “decorrelation” principle, and the degree of “hyperuniformity” (suppression of infinite-wavelength density fluctuations) increases. We have also calculated the void exclusion probability in order to compute the so-called quantizer error of the RSA packings, which is related to the second moment of inertia of the average Voronoi cell. Our algorithm is easily generalizable to generate saturated RSA packings of nonspherical particles.

Zhang, G.; Torquato, S.

2013-11-01

366

Precise algorithm to generate random sequential addition of hard hyperspheres at saturation.  

PubMed

The study of the packing of hard hyperspheres in d-dimensional Euclidean space R^{d} has been a topic of great interest in statistical mechanics and condensed matter theory. While the densest known packings are ordered in sufficiently low dimensions, it has been suggested that in sufficiently large dimensions, the densest packings might be disordered. The random sequential addition (RSA) time-dependent packing process, in which congruent hard hyperspheres are randomly and sequentially placed into a system without interparticle overlap, is a useful packing model to study disorder in high dimensions. Of particular interest is the infinite-time saturation limit in which the available space for another sphere tends to zero. However, the associated saturation density has been determined in all previous investigations by extrapolating the density results for nearly saturated configurations to the saturation limit, which necessarily introduces numerical uncertainties. We have refined an algorithm devised by us [S. Torquato, O. U. Uche, and F. H. Stillinger, Phys. Rev. E 74, 061308 (2006)] to generate RSA packings of identical hyperspheres. The improved algorithm produce such packings that are guaranteed to contain no available space in a large simulation box using finite computational time with heretofore unattained precision and across the widest range of dimensions (2?d?8). We have also calculated the packing and covering densities, pair correlation function g(2)(r), and structure factor S(k) of the saturated RSA configurations. As the space dimension increases, we find that pair correlations markedly diminish, consistent with a recently proposed "decorrelation" principle, and the degree of "hyperuniformity" (suppression of infinite-wavelength density fluctuations) increases. We have also calculated the void exclusion probability in order to compute the so-called quantizer error of the RSA packings, which is related to the second moment of inertia of the average Voronoi cell. Our algorithm is easily generalizable to generate saturated RSA packings of nonspherical particles. PMID:24329384

Zhang, G; Torquato, S

2013-11-01

367

Session: Hard Rock Penetration  

SciTech Connect

This session at the Geothermal Energy Program Review X: Geothermal Energy and the Utility Market consisted of five presentations: ''Hard Rock Penetration - Summary'' by George P. Tennyson, Jr.; ''Overview - Hard Rock Penetration'' by James C. Dunn; ''An Overview of Acoustic Telemetry'' by Douglas S. Drumheller; ''Lost Circulation Technology Development Status'' by David A. Glowka; ''Downhole Memory-Logging Tools'' by Peter Lysne.

Tennyson, George P. Jr.; Dunn, James C.; Drumheller, Douglas S.; Glowka, David A.; Lysne, Peter

1992-01-01

368

Hardness Tester for Polyur  

NASA Technical Reports Server (NTRS)

Rubber-hardness tester modified for use on rigid polyurethane foam. Provides objective basis for evaluation of improvements in foam manufacturing and inspection. Typical acceptance criterion requires minimum hardness reading of 80 on modified tester. With adequate correlation tests, modified tester used to measure indirectly tensile and compressive strengths of foam.

Hauser, D. L.; Buras, D. F.; Corbin, J. M.

1987-01-01

369

Memory Hard Drive Peripherals  

E-print Network

1! CSI3131 Topics CPU Memory Hard Drive Peripherals Computing Systems OS Overview StructureDeadlocks M em ory M anagem ent Basic Memory Managermtn Virtual Memory Storage and I/O File Systems Hard Drive Management Swap I/O Management 2 Module 7: Memory Management Reading: Chapter 8 § To provide a detailed

Stojmenovic, Ivan

370

Gravitational instability of finite isothermal spheres  

NASA Astrophysics Data System (ADS)

We investigate the stability of bounded self-gravitating systems in the canonical ensemble by using a thermodynamical approach. Our study extends the earlier work of Padmanabhan (\\cite{pad89}) in the microcanonical ensemble. By studying the second variations of the free energy, we find that instability sets in precisely at the point of minimum temperature in agreement with the theorem of Katz (\\cite{kat78}). The perturbation that induces instability at this point is calculated explicitly; it has not a ``core-halo'' structure contrary to what happens in the microcanonical ensemble. We also study Jeans type gravitational instability of isothermal gaseous spheres described by Navier-Stokes equations. The introduction of a container and the consideration of an inhomogeneous distribution of matter avoids the Jeans swindle. We show analytically the equivalence between dynamical stability and thermodynamical stability and the fact that the stability of isothermal gas spheres does not depend on the viscosity. This confirms the findings of Semelin et al. (\\cite{sem01}) who used numerical methods or approximations. We also give a simpler derivation of the geometric hierarchy of scales inducing instability discovered by these authors. The density profiles that trigger these instabilities are calculated explicitly; high order modes of instability present numerous oscillations whose nodes also follow a geometric progression. This suggests that the system will fragment in a series of ``clumps'' and that these ``clumps'' will themselves fragment in substructures. The fact that both the domain sizes leading to instability and the ``clumps'' sizes within a domain follow a geometric progression with the same ratio suggests a fractal-like behavior. This gives further support to the interpretation of de Vega et al. (1996) concerning the fractal structure of the interstellar medium.

Chavanis, P. H.

2002-01-01

371

Collective excitations in soft-sphere fluids  

NASA Astrophysics Data System (ADS)

Despite that the thermodynamic distinction between a liquid and the corresponding gas ceases to exist at the critical point, it has been recently shown that reminiscence of gaslike and liquidlike behavior can be identified in the supercritical fluid region, encoded in the behavior of hypersonic waves dispersion. By using a combination of molecular dynamics simulations and calculations within the approach of generalized collective modes, we provide an accurate determination of the dispersion of longitudinal and transverse collective excitations in soft-sphere fluids. Specifically, we address the decreasing rigidity upon density reduction along an isothermal line, showing that the positive sound dispersion, an excess of sound velocity over the hydrodynamic limit typical for dense liquids, displays a nonmonotonic density dependence strictly correlated to that of thermal diffusivity and kinematic viscosity. This allows rationalizing recent observation parting the supercritical state based on the Widom line, i.e., the extension of the coexistence line. Remarkably, we show here that the extremals of transport properties such as thermal diffusivity and kinematic viscosity provide a robust definition for the boundary between liquidlike and gaslike regions, even in those systems without a liquid-gas binodal line. Finally, we discuss these findings in comparison with recent results for Lennard-Jones model fluid and with the notion of the "rigid-nonrigid" fluid separation lines.

Bryk, Taras; Gorelli, Federico; Ruocco, Giancarlo; Santoro, Mario; Scopigno, Tullio

2014-10-01

372

Polarization effects on hard target calibration of lidar systems  

NASA Technical Reports Server (NTRS)

The theory of hard target calibration of lidar backscatter data, including laboratory measurements of the pertinent target reflectance parameters, is extended to include the effects of polarization of the transmitted and received laser radiation. The bidirectional reflectance-distribution function model of reflectance is expanded to a 4 x 4 matrix allowing Mueller matrix and Stokes vector calculus to be employed. Target reflectance parameters for calibration of lidar backscatter data are derived for various lidar system polarization configurations from integrating sphere and monostatic reflectometer measurements. It is found that correct modeling of polarization effects is mandatory for accurate calibration of hard target reflectance parameters and, therefore, for accurate calibration of lidar backscatter data.

Kavaya, Michael J.

1987-01-01

373

The dynamic sphere test problem  

SciTech Connect

In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homogeneous, linearly elastic material. The material exhibits either isotropic or transverse isotropic symmetry. When the problem is formulated in material coordinates, the balance of mass equation is satisfied automatically. Also, the material is assumed to be kept at constant temperature, so the only relevant equation is the equation of motion. The shell has inner radius r{sub i} and outer radius r{sub o}. Initially, the shell is at rest. We assume that the interior of the shell is a void and we apply a time-varying radial stress on the outer surface.

Chabaud, Brandon M. [Los Alamos National Laboratory; Brock, Jerry S. [Los Alamos National Laboratory; Smith, Brandon M. [Los Alamos National Laboratory

2012-05-16

374

Visual attention on the sphere.  

PubMed

Human visual system makes an extensive use of visual attention in order to select the most relevant information and speed-up the vision process. Inspired by visual attention, several computer models have been developed and many computer vision applications rely today on such models. However, the actual algorithms are not suitable to omnidirectional images, which contain a significant amount of geometrical distortion. In this paper, we present a novel computational approach that performs in spherical geometry and thus is suitable for omnidirectional images. Following one of the actual models of visual attention, the spherical saliency map is obtained by fusing together intensity, chromatic, and orientation spherical cue conspicuity maps that are themselves obtained through multiscale analysis on the sphere. Finally, the consecutive maxima in the spherical saliency map represent the spots of attention on the sphere. In the experimental part, the proposed method is then compared to the standard one using a synthetic image. Also, we provide examples of spots detection in real omnidirectional scenes which show its advantages. Finally, an experiment illustrates the homogeneity of the detected visual attention in omnidirectional images. PMID:18854253

Bogdanova, Iva; Bur, Alexandre; Hugli, Heinz

2008-11-01

375

Porous Ceramic Spheres from Ion Exchange Resin  

NASA Technical Reports Server (NTRS)

A commercial cation ion exchange resin, cross-linked polystyrene, has been successfully used as a template to fabricate 20 to 50 micron porous ceramic spheres. Ion exchange resins have dual template capabilities. Pore architecture of the ceramic spheres can be altered by changing the template pattern. Templating can be achieved by utilizing the internal porous structure or the external surface of the resin beads. Synthesis methods and chemical/physical characteristics of the ceramic spheres will be reported.

Dynys, Fred

2005-01-01

376

Process for making hollow carbon spheres  

DOEpatents

A hollow carbon sphere having a carbon shell and an inner core is disclosed. The hollow carbon sphere has a total volume that is equal to a volume of the carbon shell plus an inner free volume within the carbon shell. The inner free volume is at least 25% of the total volume. In some instances, a nominal diameter of the hollow carbon sphere is between 10 and 180 nanometers.

Luhrs, Claudia C.; Phillips, Jonathan; Richard, Monique N.; Knapp, Angela Michelle

2013-04-16

377

Quantum fractals on n-spheres. Clifford Algebra approach  

E-print Network

Using the Clifford algebra formalism we extend the quantum jumps algorithm of the Event Enhanced Quantum Theory (EEQT) to convex state figures other than those stemming from convex hulls of complex projective spaces that form the basis for the standard quantum theory. We study quantum jumps on n-dimensional spheres, jumps that are induced by symmetric configurations of non-commuting state monitoring detectors. The detectors cause quantum jumps via geometrically induced conformal maps (Mobius transformations) and realize iterated function systems (IFS) with fractal attractors located on n-dimensional spheres. We also extend the formalism to mixed states, represented by "density matrices". As a numerical illustration we study quantum fractals on the circle, two--sphere (octahedron), and on three-dimensional sphere (hypercube-tesseract, 24 cell, 600 cell,and 120 cell). The invariant measure on the attractor is approximated by the powers of the Markov operator. In the appendices we calculate the Radon-Nikodym derivative of the SO(n+1) invariant measure on S^n under SO(1,n+1) transformations and discuss the Hamilton's "icossian calculus" as well as its application to quaternionic realization of the binary icosahedral group that is at the basis of the 600 cell and its dual, the 120 cell. As a by-product of this work we obtain several Clifford algebraic results, such as a characterization of positive elements in a Clifford algebra Cl(n+1) as generalized Lorentz boosts, and their action as Moebius transformation on n-sphere, and a decomposition of any element of Spin^+(1,n+1) into a boost and a rotation, including the explicit formula for the pullback of the O(n+1) invariant Riemannian metric with respect to the associated Mobius transformation.

Arkadiusz Jadczyk

2006-08-14

378

Effects of the ratio of sphere size to laser focal spot on the dominant in-band EUV emitting region  

E-print Network

that the ratio of the sphere diameter to laser full width half maximum (FWHM) focal spot size (SD/FSS electron density, temperature and laser absorption profile maps for varying SD/FSS ratio at typically

Najmabadi, Farrokh

379

Gravitational instability of polytropic spheres and generalized thermodynamics  

NASA Astrophysics Data System (ADS)

We extend the existing literature on the structure and stability of polytropic gas spheres reported in the classical monograph of Chandrasekhar (\\cite{chandra}). For isolated polytropes with index 1density and velocity at the point of marginal stability in terms of the Milne variables. Then, we consider the case of polytropes confined within a box of radius R (an extension of the Antonov problem for isothermal gas spheres). For n>=3, the mass-density relation presents damped oscillations and there exists a limiting mass above which no hydrostatic equilibrium is possible. As for isothermal gas spheres, the onset of instability occurs precisely at the point of maximum mass in the series of equilibrium. Analytical results are obtained for the particular index n=5. We also discuss the relation of our study with generalized thermodynamics (Tsallis entropy) recently investigated by Taruya & Sakagami (\\cite{taruya}).

Chavanis, P. H.

2002-05-01

380

THEORY OF FLUX CREEP IN HARD SUPERCONDUCTORS  

Microsoft Academic Search

Previous investigations of the critical state of the hard superconductor ; have defined it in terms of constants alpha and B\\/sub O\\/; alpha (T) = J\\/sub cr\\/; (B\\/sub cr\\/ + Bâ). If the current density J or the field B is increased ; beyond the critical values, a process called flux creep'' sets in, and flux ; leaks through the

P. Anderson

1962-01-01

381

Preparation of thorium-uranium gel spheres  

SciTech Connect

Ceramic oxide spheres with diameters of 15 to 1500 ..mu..m are being evaluated for fabrication of power reactor fuel rods. (Th,U)O/sub 2/ spheres can be prepared by internal or external chemical gelation of nitrate solutions or oxide sols. Two established external gelation techniques were tested but proved to be unsatisfactory for the intended application. Established internal gelation techniques for UO/sub 2/ spheres were applied with minor modifications to make 75% ThO/sub 2/-25% UO/sub 2/ spheres that sinter to diameters of 200 to 1400 ..mu..m (99% T.D.).

Spence, R.D.; Haas, P.A.

1980-01-01

382

Observe a visual model of Earth's spheres  

NSDL National Science Digital Library

This Earth science resource enables students to view Earth's four spheres--the geosphere, hydrosphere, biosphere, and atmosphere. The visualization is introduced by a paragraph that defines the four spheres. Below the paragraph, there is an image of a globe that a viewer can animate by clicking on it. The globe separates into four globes, each of which shows one sphere and is labeled with the appropriate sphere name. The animation contains a legend to explain the color coding used. Controls allow the viewer to pause the animation, replay it, or move through it frame by frame. Copyright 2005 Eisenhower National Clearinghouse

Education, Terc. C.; Littell, Mcdougal

2003-01-01

383

Killing spinors on spheres and hyperbolic manifolds  

NASA Astrophysics Data System (ADS)

Properties of Killing spinors on spheres and hyperbolic manifolds are investigated with an emphasis on the relations to Killing vectors, conformal Killing vectors, and solutions of Maxwell's equations.

Fujii, Yasunori; Yamagishi, Kengo

1986-04-01

384

Science off the Sphere: Earth in Infrared  

NASA Video Gallery

International Space Station Expedition 30 astronaut Don Pettit views cities, agricultural areas and deserts using an infrared camera for 'Science off the Sphere.' Through a partnership between NASA...

385

Magnetic torque on a rotating superconducting sphere  

NASA Technical Reports Server (NTRS)

The London theory of superconductivity is used to calculate the torque on a superconducting sphere rotating in a uniform applied magnetic field. The London theory is combined with classical electrodynamics for a calculation of the direct effect of excess charge on a rotating superconducting sphere. Classical electrodynamics, with the assumption of a perfect Meissner effect, is used to calculate the torque on a superconducting sphere rotating in an arbitrary magnetic induction; this macroscopic approach yields results which are correct to first order. Using the same approach, the torque due to a current loop encircling the rotating sphere is calculated.

Holdeman, L. B.

1975-01-01

386

Hollow Spheres in Composite Materials and Metallic Hollow Sphere Composites (MHSC)  

NASA Astrophysics Data System (ADS)

The newly developed metallic hollow spheres are used in combination with a polymeric matrix for producing metallic hollow-sphere-composites (MSHC), which have been developed for mechanical engineering applications in the “InnoZellMet” project.

Baumeister, Erika; Molitor, Martin

387

Can the Equivalent Sphere Model Approximate Organ Doses in Space?  

NASA Technical Reports Server (NTRS)

For space radiation protection it is often useful to calculate dose or dose,equivalent in blood forming organs (BFO). It has been customary to use a 5cm equivalent sphere to. simulate the BFO dose. However, many previous studies have concluded that a 5cm sphere gives very different dose values from the exact BFO values. One study [1] . concludes that a 9 cm sphere is a reasonable approximation for BFO'doses in solar particle event environments. In this study we use a deterministic radiation transport [2] to investigate the reason behind these observations and to extend earlier studies. We take different space radiation environments, including seven galactic cosmic ray environments and six large solar particle events, and calculate the dose and dose equivalent in the skin, eyes and BFO using their thickness distribution functions from the CAM (Computerized Anatomical Man) model [3] The organ doses have been evaluated with a water or aluminum shielding of an areal density from 0 to 20 g/sq cm. We then compare with results from the equivalent sphere model and determine in which cases and at what radius parameters the equivalent sphere model is a reasonable approximation. Furthermore, we address why the equivalent sphere model is not a good approximation in some cases. For solar particle events, we find that the radius parameters for the organ dose equivalent increase significantly with the shielding thickness, and the model works marginally for BFO but is unacceptable for the eye or the skin. For galactic cosmic rays environments, the equivalent sphere model with an organ-specific constant radius parameter works well for the BFO dose equivalent, marginally well for the BFO dose and the dose equivalent of the eye or the skin, but is unacceptable for the dose of the eye or the skin. The ranges of the radius parameters are also being investigated, and the BFO radius parameters are found to be significantly, larger than 5 cm in all cases, consistent with the conclusion of an earlier study [I]. The radius parameters for the dose equivalent in GCR environments are approximately between 10 and I I cm for the BFO, 3.7 to 4.8 cm for the eye, and 3.5 to 5.6 cm for the skin; while the radius parameters are between 10 and 13 cm for the BFO dose.

Lin, Zi-Wei

2007-01-01

388

Radiation Hard AlGaN Detectors and Imager  

SciTech Connect

Radiation hardness of AlGaN photodiodes was tested using a 65 MeV proton beam with a total proton fluence of 3x10{sup 12} protons/cm{sup 2}. AlGaN Deep UV Photodiode have extremely high radiation hardness. These new devices have mission critical applications in high energy density physics (HEDP) and space explorations. These new devices satisfy radiation hardness requirements by NIF. NSTec is developing next generation AlGaN optoelectronics and imagers.

None

2012-05-01

389

1500 Gate standard cell compatible radiation hard gate array  

Microsoft Academic Search

The G1500 gate array combines Sandia Labs' 4\\/3..mu.. CMOS silicon gate radiation hard process with a novel gate isolated standard cell compatible design for quick turnaround time, low cost, and radiation hardness. This device is hard to 5 x 10⁵ rads, utilizes a configuration that provides high packing density, and is supported on both the Daisy and Mentor workstations. This

B. D. Mills; B. D. Shafer; E. P. Melancon

1984-01-01

390

Electromagnetic energy within single-resonance chiral metamaterial spheres  

E-print Network

We derive an exact expression for the time-averaged electromagnetic energy inside a chiral dispersive sphere irradiated by a plane wave. The dispersion relations correspond to a chiral metamaterial consisting of uncoupled single-resonance helical resonators. Using a field decomposition scheme and a general expression for the electromagnetic energy density in bi-anisotropic media, we calculate the Lorenz-Mie solution for the internal fields in a medium that is simultaneously magnetic and chiral. We also obtain an explicit analytical relation between the internal electromagnetic field and the absorption cross-section. This result is applied to demonstrate that strong chirality leads to an off-resonance field enhancement within weakly absorb.ing spheres.

Arruda, Tiago J; Martinez, Alexandre S

2013-01-01

391

Efflux time of soap bubbles and liquid spheres.  

PubMed

The efflux time, T, of gas from soap bubbles of radius, R, through their blow tube of length, 1, and radius, p, is given by the equation see pdf for equation where eta is the viscosity of the gas and omicron the surface tension of the bubble solution, all in centimeter-gram-second units. Similar relations between time and diameter were established for the flow from one bubble to another or from one bubble within another. The same relations hold for the flow of liquid spheres, suspended in another liquid of equal density, following Plateau's classic method. They have been extended to the flow of spheres to cylinders and catenoids of rotation. In all these cases the driving force is the surface or interfacial tension, creating an excess pressure as defined by Laplace's equation. PMID:17792780

Grosse, A V

1967-06-01

392

Detecting dark energy with wavelets on the sphere  

E-print Network

Dark energy dominates the energy density of our Universe, yet we know very little about its nature and origin. Although strong evidence in support of dark energy is provided by the cosmic microwave background, the relic radiation of the Big Bang, in conjunction with either observations of supernovae or of the large scale structure of the Universe, the verification of dark energy by independent physical phenomena is of considerable interest. We review works that, through a wavelet analysis on the sphere, independently verify the existence of dark energy by detecting the integrated Sachs-Wolfe effect. The effectiveness of a wavelet analysis on the sphere is demonstrated by the highly statistically significant detections of dark energy that are made. Moreover, the detection is used to constrain properties of dark energy. A coherent picture of dark energy is obtained, adding further support to the now well established cosmological concordance model that describes our Universe.

J. D. McEwen

2007-08-29

393

Instabilities in Very Young Neutron Stars: Density  

NSDL National Science Digital Library

This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the density evolution for 20 milliseconds after the shock stalls. The density is plotted on a log scale. Values range from 10^9 gm-cm^3 at the outer boundary to 1.4 x 10^12 gm-cm^3 at the inner boundary.

Oneil, Pamela; Fryxell, Bruce; Burrows, Adam

1994-02-12

394

1. Experimental details for the steel sphere cooling experiments 2 1.1 Hydrophilic spheres 2  

E-print Network

evaporation experiments 12 3. Stabilization of the vapour phase due to surface texture 14 3.1 Nanoparticle a tungsten carbide drill bit we drilled a 1.5 mm diameter hole into the top of the spheres down to the sphere changes the colour again to purple-blue. The sphere colour change is due to the heat- induced oxidation

Chan, Derek Y C

395

Tandem spheres in hypersonic flow  

SciTech Connect

The problem of determining the forces acting on a secondary body when it is travelling at some point within the shocked region created by a hypersonic primary body is of interest in such situations as store or stage separation, re-entry of multiple vehicles, and atmospheric meteoroid fragmentation. The current work is concerned with a special case of this problem, namely that in which both bodies are spheres and are stationary with respect to one another. We first present an approximate analytical model of the problem; subsequently, numerical simulations are described and results are compared with those from the analytical model. Finally, results are presented from a series of experiments in the T5 hypervelocity shock tunnel in which a newly-developed force-measurement technique was employed.

Laurence, Stuart J [California Institute of Technology, Pasadena] [California Institute of Technology, Pasadena; Deiterding, Ralf [ORNL] [ORNL; Hornung, Hans G [California Institute of Technology, Pasadena] [California Institute of Technology, Pasadena

2009-01-01

396

Active swarms on a sphere  

E-print Network

Here we show that coupling to curvature has profound effects on collective motion in active systems, leading to patterns not observed in flat space. Biological examples of such active motion in curved environments are numerous: curvature and tissue folding are crucial during gastrulation, epithelial and endothelial cells move on constantly growing, curved crypts and vili in the gut, and the mammalian corneal epithelium grows in a steady-state vortex pattern. On the physics side, droplets coated with actively driven microtubule bundles show active nematic patterns. We study a model of self-propelled particles with polar alignment on a sphere. Hallmarks of these motion patterns are a polar vortex and a circulating band arising due to the incompatibility between spherical topology and uniform motion - a consequence of the hairy ball theorem. We present analytical results showing that frustration due to curvature leads to stable elastic distortions storing energy in the band.

Rastko Sknepnek; Silke Henkes

2014-07-31

397

The periodically oscillating plasma sphere  

SciTech Connect

A new method of operating an inertial electrostatic confinement (IEC) device is proposed, and its performance is evaluated. The scheme involved an oscillating thermal cloud of ions immersed in a bath of electrons that form a harmonic oscillator potential. The scheme is called the periodically oscillating plasma sphere, and it appears to solve many of the problems that may limit other IEC systems to low gain. A set of self-similar solutions to the ion fluid equations is presented, and plasma performance is evaluated. Results indicate that performance enhancement of gridded IEC systems such as the Los Alamos intense neutron source device is possible as well as high-performance operation for low-loss systems such as the Penning trap experiment. Finally, a conceptual idea for a massively modular Penning trap reactor is also presented.

Nebel, R.A.; Barnes, D.C. [Los Alamos National Lab., NM (United States)

1998-08-01

398

Localized orientational order chaperons the nucleation of Rotator phases in hard polyhedral particles  

E-print Network

The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of Forward Flux Sampling and Umbrella Sampling. For comparable degree of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei.

Vikram Thapar; Fernando A. Escobedo

2013-11-11

399

Depolarization measurements of an integrating sphere  

NASA Astrophysics Data System (ADS)

Mueller-matrix polarimetry performed in the visible and near IR indicates that an integrating sphere acts as an ideal depolarizer to the 0.5% accuracy of the polarimeter. The integrating sphere emits unpolarized light regardless of the incident polarization state.

McClain, Stephen C.; Bartlett, Chanda L.; Pezzaniti, J. Larry; Chipman, Russell A.

1995-01-01

400

Radar Backscatter from Conducting Polyhedral Spheres  

Microsoft Academic Search

Electromagnetic backscatter characteristics of conducting polyhedral spheres, constructed of 12 pentagons and a large number of hexagons, were investigated. The polyhedral structures were classified by their number of vertices and by the width of the conducting edges in their frames. Polyhedral spheres with 60, 80, 180, 240, 320, 500, 540, 960, and 1500 vertices were evaluated for their ability to

Paul A. Bernhardt

2010-01-01

401

Differentiable Actions on Homotopy Seven Spheres.  

National Technical Information Service (NTIS)

This report presents studies of differentiable actions of the circle group SO(2) on homotopy 7-spheres. The class of free such actions is shown to form an infinite abelian group which is closely related to the group of differentiable knotted 3-spheres in ...

D. Montgomery, C. T. Yang

1965-01-01

402

Special purpose reflectometer uses modified ulbricht sphere  

NASA Technical Reports Server (NTRS)

Modified Ulbricht sphere measures stray radiation caused by irregularities in the reflective surface of an optical test specimen. The test specimen is positioned between a light source and exit port and all diffusely scattered radiation is measured by a photomultiplier tube in the sphere.

Gorstein, M.

1967-01-01

403

Electric dipoles on the Bloch sphere  

E-print Network

The time evolution of a two-level quantum mechanical system can be geometrically described using the Bloch sphere. By mapping the Bloch sphere evolution onto the dynamics of oscillating electric dipoles, we provide a physically intuitive link between classical electromagnetism and the electric dipole transitions of atomic & molecular physics.

Vutha, Amar C

2014-01-01

404

Hollow sphere ceramic particles for abradable coatings  

Microsoft Academic Search

A hollow sphere ceramic flame spray powder is disclosed. The desired constituents are first formed into agglomerated particles in a spray drier. Then the agglomerated particles are introduced into a plasma flame which is adjusted so that the particles collected are substantially hollow. The hollow sphere ceramic particles are suitable for flame spraying a porous and abradable coating. The hollow

F. N. Longo; N. F. Bader; M. R. Dorfman

1984-01-01

405

Structure factor of blends of solvent-free nanoparticle-organic hybrid materials: density-functional theory and small angle X-ray scattering.  

PubMed

We investigate the static structure factor S(q) of solvent-free nanoparticle-organic hybrid materials consisting of silica nanocores and space-filling polyethylene glycol coronas using a density-functional theory and small angle X-ray scattering measurements. The theory considers a bidisperse suspension of hard spheres with different radii and tethered bead-spring oligomers with different grafting densities to approximate the polydispersity effects in experiments. The experimental systems studied include pure samples with different silica core volume fractions and the associated mean corona grafting densities, and blends with different mixing ratios of the pure samples, in order to introduce varying polydispersity of corona grafting density. Our scattering experiments and theory show that, compared to the hard-sphere suspension with the same core volume fraction, S(q) for pure samples exhibit both substantially smaller values at small q and stronger particle correlations corresponding to a larger effective hard core at large q, indicating that the tethered incompressible oligomers enforce a more uniform particle distribution, and the densely grafted brush gives rise to an additional exclusionary effect between the nanoparticles. According to the theory, polydispersity in the oligomer grafting density controls the deviation of S(q) from the monodisperse system at smaller q, and the interplay of the enhanced effective core size and the entropic attraction among the particles is responsible for complex variations in the particle correlations at larger q. The successful comparison between the predictions and the measurements for the blends further suggests that S(q) can be used to assess the uniformity of grafting density in polymer-grafted nanoparticle materials. PMID:25311668

Yu, Hsiu-Yu; Srivastava, Samanvaya; Archer, Lynden A; Koch, Donald L

2014-10-30

406

Feasibility of miniaturized instrumentation of the inflatable sphere for temperature, pressure and acceleration measurement  

NASA Technical Reports Server (NTRS)

The feasibility of instrumenting the inflatable passive sphere (presently used to provide upper atmosphere density measurements) with miniaturized thermistors, pressure transducers, and accelerometers was analyzed. Data from the sensors must be transmitted by an onboard telemetry system to a ground receiving station. To assure a sufficiently slow fall velocity for the sphere the additional mass of the sensor and telemetry hardware must be less than 100 grams. Other constraints that must be satisfied by the sensor and telemetry systems include the ability to withstand a 150 g launch acceleration, the ability to function in both high and low temperature and pressure environments and be sufficiently small to be packaged within the body of a 3.81 cm diameter dart. A differential transducer that will measure the difference between ambient and internal sphere pressures is recommended. The application of each type of measurement relative to its ability to monitor sphere malfunction and to provide additional meteorological data is considered.

Luers, J. K.

1975-01-01

407

Ionic density distributions near the charged colloids: Spherical electric double layers  

SciTech Connect

We have studied the structure of the spherical electric double layers on charged colloids by a density functional perturbation theory, which is based both on the modified fundamental-measure theory for the hard spheres and on the one-particle direct correlation functional (DCF) for the electronic residual contribution. The contribution of one-particle DCF has been approximated as the functional integration of the second-order correlation function of the ionic fluids in a bulk phase. The calculated result is in very good agreement with the computer simulations for the ionic density distributions and the zeta potentials over a wide range of macroion sizes and electrolyte concentrations, and compares with the results of Yu et al. [J. Chem. Phys. 120, 7223 (2004)] and modified Poisson-Boltzmann approximation [L. B. Bhuiyan and C. W. Outhwaite, Condens. Matter Phys. 8, 287 (2005)]. The present theory is able to provide interesting insights about the charge inversion phenomena occurring at the interface.

Kim, Eun-Young; Kim, Soon-Chul, E-mail: sckim@andong.ac.kr [Department of Physics, Andong National University, Andong 760-749 (Korea, Republic of)] [Department of Physics, Andong National University, Andong 760-749 (Korea, Republic of)

2013-11-21

408

Analysis of data on the densities of liquid rare-earth metals from thermodynamic parameters  

SciTech Connect

Calculations have been performed on the pseudopotential parameters and packing coefficients in hard-sphere reference system for rare-earth metals near their melting points on the basis of minimum Helmholz free energy if the calculated and observed values for the resistivity agree. The results have been used in calculating the thermodynamic parameters in the liquid state. Theory is in satisfactory agreement with experiment. A method is proposed for analyzing measurements on the temperature coefficient of the density, where there are sometimes substantial differences in the data. Calculated values for the thermodynamic parameters have been used in examining the reliability of the data on the temperature coefficients of density for rare-earth metals; recommendations are made.

Kiselev, A.I.; Kononenko, V.I.

1987-05-01

409

Self-assembly of amphiphilic Janus particles at planar walls: A density functional study  

E-print Network

We investigate the structure formation of amphiphilic molecules at planar walls using density functional theory. The molecules are modeled as (hard) spheres composed of a hydrophilic and hydrophobic part. The orientation of the resulting Janus-particles is described as a vector representing an internal degree of freedom. Our density functional approach involves Fundamental Measure Theory combined with a mean-field approximation for the anisotropic interaction. Considering neutral, hydrophilic and hydrophobic walls, we study the adsorption of the particles, focussing on the competition between the surface field and interact ion-induced ordering phenomena. Finally, we consider systems confined between two planar walls. It is shown that the anisotropic Janus interaction yields pronounced frustration effects at low temperatures.

Gerald Rosenthal; Sabine H. L. Klapp

2010-12-06

410

Hard superconducting nitrides  

PubMed Central

Detailed study of the equation of state, elasticity, and hardness of selected superconducting transition-metal nitrides reveals interesting correlations among their physical properties. Both the bulk modulus and Vickers hardness are found to decrease with increasing zero-pressure volume in NbN, HfN, and ZrN. The computed elastic constants from first principles satisfy c11 > c12 > c44 for NbN, but c11 > c44 > c12 for HfN and ZrN, which are in good agreement with the neutron scattering data. The cubic ?-NbN superconducting phase possesses a bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, which is close to sapphire. Theoretical calculations for NbN show that all elastic moduli increase monotonically with increasing pressure. These results suggest technological applications of such materials in extreme environments. PMID:15728352

Chen, Xiao-Jia; Struzhkin, Viktor V.; Wu, Zhigang; Somayazulu, Maddury; Qian, Jiang; Kung, Simon; Christensen, Axel N?rlund; Zhao, Yusheng; Cohen, Ronald E.; Mao, Ho-kwang; Hemley, Russell J.

2005-01-01

411

21 CFR 886.3320 - Eye sphere implant.  

Code of Federal Regulations, 2013 CFR

...8 2013-04-01 2013-04-01 false Eye sphere implant. 886.3320 Section 886...DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to...

2013-04-01

412

21 CFR 886.3320 - Eye sphere implant.  

...8 2014-04-01 2014-04-01 false Eye sphere implant. 886.3320 Section 886...DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to...

2014-04-01

413

21 CFR 886.3320 - Eye sphere implant.  

Code of Federal Regulations, 2010 CFR

...8 2010-04-01 2010-04-01 false Eye sphere implant. 886.3320 Section 886...DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to...

2010-04-01

414

21 CFR 886.3320 - Eye sphere implant.  

Code of Federal Regulations, 2011 CFR

...8 2011-04-01 2011-04-01 false Eye sphere implant. 886.3320 Section 886...DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to...

2011-04-01

415

21 CFR 886.3320 - Eye sphere implant.  

Code of Federal Regulations, 2012 CFR

...8 2012-04-01 2012-04-01 false Eye sphere implant. 886.3320 Section 886...DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to...

2012-04-01

416

Monodisperse PEGylated Spheres: An Aqueous Colloidal Model System  

PubMed Central

Fluorinated core–shell spheres have been synthesized using a novel semibatch emulsion polymerization protocol employing slow feeding of the initiator. The synthesis results in aqueous dispersions of highly monodisperse spheres bearing a well-defined poly(ethylene glycol) graft (PEGylation). Measurements are consistent with the synthesis achieving a high grafting density that moreover consists of a single PEG layer with the polymer significantly elongated beyond its radius of gyration in bulk. The fluorination of the core of the particles confers a low index of refraction such that the particles can be refractive index matched in water through addition of relatively small amounts of a cosolvent, which enables the use of optical and laser-based methods for studies of concentrated systems. The systems exhibit an extreme stability in NaCl solutions, but attractions among particles can be introduced by addition of other salts, in which case aggregation is shown to be reversible. The PEGylated sphere dispersions are expected to be ideally suited as model systems for studies of the effect of PEG-mediated interactions on, for instance, structure, dynamics, phase behavior, and rheology. PMID:24533774

2014-01-01

417

Phase diagram of hard tetrahedra.  

PubMed

Advancements in the synthesis of faceted nanoparticles and colloids have spurred interest in the phase behavior of polyhedral shapes. Regular tetrahedra have attracted particular attention because they prefer local symmetries that are incompatible with periodicity. Two dense phases of regular tetrahedra have been reported recently. The densest known tetrahedron packing is achieved in a crystal of triangular bipyramids (dimers) with a packing density of 4000/4671 ? 85.63%. In simulation a dodecagonal quasicrystal is observed; its approximant, with periodic tiling (3.4.3(2).4), can be compressed to a packing fraction of 85.03%. Here, we show that the quasicrystal approximant is more stable than the dimer crystal for packing densities below 84% using Monte Carlo computer simulations and free energy calculations. To carry out the free energy calculations, we use a variation of the Frenkel-Ladd method for anisotropic shapes and thermodynamic integration. The enhanced stability of the approximant can be attributed to a network substructure, which maximizes the free volume (and hence the wiggle room) available to the particles and facilitates correlated motion of particles, which further contributes to entropy and leads to diffusion for packing densities below 65%. The existence of a solid-solid transition between structurally distinct phases not related by symmetry breaking--the approximant and the dimer crystal--is unusual for hard particle systems. PMID:22112060

Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C

2011-11-21

418

Detecting the dynamical state of the atmosphere from the orbital decay of the ODERACS spheres  

NASA Technical Reports Server (NTRS)

The orbital decay curve of a satellite having constant cross-sectional area and in circular orbit can furnish valuable information regarding the dynamical state of the atmosphere. It is shown that a rectilinear decay curve having constant downward slope (zero curvature) should indicate that the atmosphere was undergoing compression during that period. A decay curve having concavity upwards (positive curvature) will strongly indicate that the atmosphere was in a contracting phase. A decay curve with downward concavity (negative curvature) may indicate an expanding, a stationary or a contracting atmosphere. This theory, when applied to the orbital decay of the Orbital Debris Radar Calibration Spheres (ODERACS) satellites, indicates that during the period from Day 90 through Day 240 in the year 1994, the atmosphere was very definitely in a compression mode. During this period, ODERACS Sphere 1 faced nearly constant densities while Sphere 6 actually encountered progressively smaller air densities as they descended. The atmospheric scale height as calculated from the orbital data of Spheres 1 and 6 diminished steadily during the same period. It is shown that Spheres 1 and 6 descended faster and slower respectively, than the level of constant air density equal to 5 x 10 kg/m . During a brief period from Day 240 through Day 290, the atmosphere reversed to a strongly expanding mode. Thereafter, the atmosphere reverted back to a compression mode from Day 290 through Day 390, 1994.

Tan, Arjun

1996-01-01

419

The proximity force approximation for the Casimir energy of plate-sphere and sphere-sphere systems in the presence of one extra compactified universal dimension  

E-print Network

The Casimir energies for plate-sphere system and sphere-sphere system under PFA in the presence of one extra compactified universal dimension are analyzed. We find that the Casimir energy between a plate and a sphere in the case of sphere-based PFA is divergent. The Casimir energy of plate-sphere system in the case of plate-based PFA is finite and keeps negative. The extra-dimension corrections to the Casimir energy will be more manifest if the sphere is larger or farther away from the plate. It is shown that the negative Casimir energy for two spheres is also associated with the sizes of spheres and extra space. The larger spheres and the longer distance between them make the influence from the additional dimension stronger.

Hongbo Cheng

2013-11-13

420

Ceramic Spheres From Cation Exchange Beads  

NASA Technical Reports Server (NTRS)

Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.

Dynys, F. W.

2003-01-01

421

Topological defects in nematic droplets of hard spherocylinders Joachim Dzubiella, Matthias Schmidt, and Hartmut Lowen  

E-print Network

a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders cavity with homeo- tropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit show behavior intermediate between liquid and solid. The coupling between orientational and po

Ott, Albrecht

422

Numerical Simulations of Falling Sphere Viscometry Experiments.  

NASA Astrophysics Data System (ADS)

The falling sphere technique based on Stokes' law is widely used to determine the viscosities of geologically relevant melts at high pressures. Stokes' law is valid when a rigid sphere falls slowly and steadily through a stationary and infinite Newtonian medium of uniform properties. High-pressure falling sphere experiments however, usually involve dropping a dense, refractory sphere through a liquid contained by a cylindrical capsule of finite size. The sphere velocity is influenced by the walls (Faxen correction) and ends of the capsule, and possible convective motion of the fluid. Efforts are made to minimize thermal gradients in laboratory experiments, but small temperature differences within the capsule can lead to convection complicating interpretation. We utilize GALE (Moresi et al., 2003;), a finite element particle-in-cell code, to examine these factors in numerical models of conditions similar to those of high-pressure experiments. Our modeling considers a three- dimensional box or cylinder containing a cluster of particles that represent the dense sphere in laboratory experiments surrounded by low viscosity particles representing the melt. GALE includes buoyancy forces, heat flow, and viscosity variations so our model can be used to assess the effects of the capsule's walls and ends, and the consequences of thermal gradients on the sphere's velocity and trajectory. Comparisons between our numerical simulations and real-time falling sphere experiments involving lower viscosity molten komatiite are made to assess the validity of Stokes' law with the standard Faxen correction included, and formulations considering end effects. The modeling also permits an evaluation of the uncertainties in recovering accurate liquid viscosities from Stokes' law when a dense sphere falls through a convecting low viscosity melt. It also allows us to assess acceleration to a terminal velocity that can provide constraints on melt viscosity in experiments in which the terminal velocity was not reached.

O Dwyer, L.; Kellogg, L. H.; Lesher, C. E.

2007-12-01

423

Impact into Coarse Grained Spheres  

NASA Technical Reports Server (NTRS)

Several experimental studies [1,2,3] indicate that differences in the grain size of the target relative to the projectile could influence the cratering process. Impacts into coarse sand grains of size comparable to the projectile show some discrepancies with existing relationships for crater growth [e.g. 4]. Similarly, targets of ne grained, uniform in diameter glass spheres show differences in crater depth, transient crater diameter, and volume of ejecta excavated as a function of grain size [2,3]. The purpose of this work is to continue investigating how the relative grain size may influence early time coupling between a projectile and target, with implications for subsequent ejecta excavation and crater growth. In previous efforts we used numerical techniques to focus on the propagation of shock waves in coarse, granular media emphasizing the influence of relative grain size on crater growth, ejecta production, cratering efficiency, target strength, and crater shape [5,6,7]. In this study, we use experimental techniques - in part as a reality check for the numerical studies - to report on how coarse grained targets might influence ejecta excavation and crater shape. This body of work possesses important implications for ejecta excavation and cratering efficiency on asteroids that may possess rubble pile-like structures, and on planets that may possess either pre-fractured surfaces or large-scale heterogeneities in shock impedance.

Barnouin-Jha, O. S.; Cintala, M.; Crawford, D. A.

2005-01-01

424

The SPHERE IFS at work  

NASA Astrophysics Data System (ADS)

SPHERE is an extrasolar planet imager whose goal is to detect giant extrasolar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made of an extreme-Adaptive Optics (AO) turbulence correction, a pupil tracker and NIR and Visible coronagraph devices. At its back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the Near Infrared (NIR) (0.95 <=?<=2.32 ?m) and a high resolution polarization camera covers the visible (0.6 <=?<=0.9 ?m). The IFS is a low resolution spectrograph (R~50) operates in the near IR (0.95<=?<=1.6 ?m), an ideal wavelength range for the detection of planetary features, over a field of view of about 1.7 x 1.7 square arcsecs. Form spectra it is possible to reconstruct monochromatic images with high contrast (10-7) and high spatial resolution, well inside the star PSF. In this paper we describe the IFS, its calibration and the results of several performance which IFS underwent. Furthermore, using the IFS characteristics we give a forecast on the planetary detection rate.

Claudi, R.; Giro, E.; Turatto, M.; Baruffolo, A.; Bruno, P.; Cascone, E.; DeCaprio, V.; Desidera, S.; Dorn, R.; Fantinel, D.; Finger, G.; Gratton, R.; Lessio, L.; Lizon, J. L.; Maire, A. L.; Mesa, D.; Salasnich, B.; Scuderi, S.; Zurlo, A.; Dohlen, K.; Beuzit, J. L.; Mouillet, D.; Puget, P.; Wildi, Francois; Hubin, N.; Kasper, M.

2014-07-01

425

Hopf bifurcation on a sphere  

NASA Astrophysics Data System (ADS)

Using the general theory of Hopf bifurcation with symmetry we study here the example where the group of symmetries is O(3), the rotations and reflections of a sphere. We make some amendments to previously published lists of C-axial isotropy subgroups of O(3) × S1 and list the isotropy subgroups with four-dimensional fixed-point subspaces. We then study the particular example where O(3) × S1 acts on the space V3 ? V3 where V3 is the space of spherical harmonics of degree three. We find that in this case there are six C-axial isotropy subgroups of O(3) × S1. The equivariant Hopf theorem guarantees the existence of periodic solutions with each of these symmetries in O(3) × S1 equivariant differential equations. Three of the solutions are found to be standing waves and the other three are travelling waves. We compute conditions for each of these solution branches to be stable and by restricting the O(3) × S1 equivariant differential equations to four-dimensional invariant subspaces we are able to find additional periodic and quasiperiodic solutions.

Sigrist, Rachel

2010-12-01

426

CSI: Hard Drive  

ERIC Educational Resources Information Center

Acting on information from students who reported seeing a classmate looking at inappropriate material on a school computer, school officials used forensics software to plunge the depths of the PC's hard drive, searching for evidence of improper activity. Images were found in a deleted Internet Explorer cache as well as deleted file space.…

Sturgeon, Julie

2008-01-01

427

Generating Hard Satisfiability Problems  

Microsoft Academic Search

We report results from large-scale experiments in satisfiability testing. As has been observed by others, testing the satisfiability of random formulas often appears surprisingly easy. Here we show that by using the right distribution of instances, and appropriate parameter valu es, it is possible to generate random formulas that are hard, that is, for which satisfiability testing is quite difficult.

Bart Selman; David G. Mitchell; Hector J. Levesque

1996-01-01

428

Hardness vs Randomness  

Microsoft Academic Search

We present a simple ne wc onstruction of a pseudorandom bit generator ,b ased on the constant depth generators of (N). It stretches a short string of truly random bits into a long string that looks random to an ya lgorithm from a comple xity class C (eg P, NC, PSPACE, ... )u sing an arbitrary function that is hard

Noam Nisan; Avi Wigderson

1994-01-01

429

Work Hard. Be Nice  

ERIC Educational Resources Information Center

In 1994, fresh from a two-year stint with Teach for America, Mike Feinberg and Dave Levin inaugurated the Knowledge Is Power Program (KIPP) in Houston with an enrollment of 49 5th graders. By this Fall, 75 KIPP schools will be up and running, setting children from poor and minority families on a path to college through a combination of hard work,…

Mathews, Jay

2009-01-01

430

Hard Times Hit Schools  

ERIC Educational Resources Information Center

Hard-to-grasp dollar amounts are forcing real cuts in K-12 education at a time when the cost of fueling buses and providing school lunches is increasing and the demands of the federal No Child Left Behind Act still loom larger over states and districts. "One of the real challenges is to continue progress in light of the economy," said Gale Gaines,…

McNeil, Michele

2008-01-01

431

Magnetization of small iron-nickel spheres  

NASA Technical Reports Server (NTRS)

Magnetic properties of small iron-nickel alloy spheres, having compositions which cover the entire Fe-Ni binary, are presented. The spheres were formed during solidification in free fall following the melting of electropolished wires of appropriate composition. The spheres with Ni not greater than 25% acquired a martensitic thermal remanence while those with Ni not less than 30% acquired a thermoremanent magnetization. A magnetic remanence-composition diagram and a coercive force-composition diagram are constructed. Magnetic hysteresis loops and derived parameters demonstrate the difference between metal-bearing and oxide-bearing natural samples. The magnetic remanence varies as the sphere size in conjunction with the microstructure. These results help to explain why coercive force is generally low, remanent coercive force is generally high, and their ratio (R/C) is always large in fine metal dispersions, such as lunar samples and chondrite meteorites.

Wasilewski, P.

1981-01-01

432

#4 Simulated Solar Sphere from Data - Interpolated  

NASA Video Gallery

Rotating solar sphere made from a combination of imagery from the two STEREO spacecraft, together with simultaneous data from the Solar Dynamic Observatory.This movie is made from data taken on Jan...

433

Plutonium Sphere Reflected by Reflected by Beryllium.  

National Technical Information Service (NTIS)

This experiment with an alpha-phase plutonium sphere reflected by beryllium was performed using the Planet critical assembly at the Los Alamos Critical Experiments Facility (LACEF). The beryllium reflector consisted of a pair of inner and outer hemisphere...

D. Loaiza, J. Hutchinson

2013-01-01

434

Acoustic Scattering from a Sphere Steve Turley  

E-print Network

Acoustic Scattering from a Sphere Steve Turley November 24, 2006 Contents 1 Introduction 2 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Potentials 4 3 Scattering Theory 6 3.1 Integral Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.3 Penetrable Scatterer

Hart, Gus

435

Killing spinors on spheres and hyperbolic manifolds  

Microsoft Academic Search

Properties of Killing spinors on spheres and hyperbolic manifolds are investigated with an emphasis on the relations to Killing vectors, conformal Killing vectors, and solutions of Maxwell’s equations.

Yasunori Fujii; Kengo Yamagishi

1986-01-01

436

Entanglement entropy on the fuzzy sphere  

E-print Network

We obtain entanglement entropy on the noncommutative (fuzzy) two-sphere. To define a subregion with a well defined boundary in this geometry, we use the symbol map between elements of the noncommutative algebra and functions on the sphere. We find that entanglement entropy is not proportional to the length of the region's boundary. Rather, in agreement with holographic predictions, it is extensive for regions whose area is a small (but fixed) fraction of the total area of the sphere. This is true even in the limit of small noncommutativity. We also find that entanglement entropy grows linearly with N, where N is the size of the irreducible representation of SU(2) used to define the fuzzy sphere.

Karczmarek, Joanna L

2013-01-01

437

FQH Droplets Wave Function on Spheres  

Microsoft Academic Search

Using matrix model formulation of Laughlin fluid as well as su(2) representation theory, we consider fractional Quantum Hall system on 3d and 2d spheres and derive explicitly the ground state wave function of the corresponding fluid droplets.

R. Ahl Laamara; L. B Drissi; E. H Saidi

2007-01-01

438

StenniSphere reopens after Hurricane Katrina  

NASA Technical Reports Server (NTRS)

StenniSphere reopened Jan. 18, 2006, almost five months after Hurricane Katrina damaged the basement of the building that houses the visitor center. Thanks to the staff's careful preparations before the storm, no artifacts or exhibits were harmed.

2006-01-01

439

Water entry of small hydrophobic spheres  

E-print Network

We present the results of a combined experimental and theoretical investigation of the normal impact of hydrophobic spheres on a water surface. Particular attention is given to characterizing the shape of the resulting air ...

Bush, John W. M.

440

Science off the Sphere: Lenses and Vortices  

NASA Video Gallery

International Space Station Expedition 30 astronaut Don Pettit demonstrates physics in space for 'Science off the Sphere.' Through a partnership between NASA and the American Physical Society you c...

441

Structure and dynamics of concentrated dispersions of polystyrene latex spheres in glycerol: static and dynamic x-ray scattering  

PubMed

X-ray photon correlation spectroscopy and small-angle x-ray scattering measurements are applied to characterize the dynamics and structure of concentrated suspensions of charge-stabilized polystyrene latex spheres dispersed in glycerol, for volume fractions between 2.7% and 52%. The static structures of the suspensions show essentially hard-sphere behavior. The short-time dynamics shows good agreement with predictions for the wave-vector-dependent collective diffusion coefficient, which are based on a hard-sphere model [C. W. J. Beenakker and P. Mazur, Physica A 126, 349 (1984)]. However, the intermediate scattering function is found to violate a scaling behavior found previously for a sterically stabilized hard-sphere suspension [P. N. Segre and P. N. Pusey, Phys. Rev. Lett. 77, 771 (1996)]. Our measurements are parametrized in terms of a viscoelastic model for the intermediate scattering function [W. Hess and R. Klein, Adv. Phys. 32, 173 (1983)]. Within this framework, two relaxation modes are predicted to contribute to the decay of the dynamic structure factor, with mode amplitudes depending on both wave vector and volume fraction. Our measurements indicate that, for particle volume fractions smaller than about 0.30, the intermediate scattering function is well described in terms of single-exponential decays, whereas a double-mode structure becomes apparent for more concentrated systems. PMID:11138124

Lumma; Lurio; Borthwick; Falus; Mochrie

2000-12-01

442

Surface modification and characterization of carbon spheres by grafting polyelectrolyte brushes  

PubMed Central

Modified carbon spheres (CSPBs) were obtained by grafting poly(diallyl dimethyl ammonium chloride) (p-DMDAAC) on the surface of carbon spheres (CSs). It can be viewed as a kind of cation spherical polyelectrolyte brushes (CSPBs), which consist of carbon spheres as core and polyelectrolytes as shell. The method of synthesizing carbon spheres was hydrothermal reaction. Before the polyelectrolyte brushes were grafted, azo initiator [4,4?-Azobis(4-cyanovaleric acyl chloride)] was attached to the carbon spheres' surface through hydroxyl groups. CSPBs were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), conductivity meter, and system zeta potential. The results showed that compared with carbon spheres, the conductivity and zeta potential on CSPBs increased from 9.98 to 49.24 ?S/cm and 11.6 to 42.5 mV, respectively, after the polyelectrolyte brushes were grafted. The colloidal stability in water was enhanced, and at the same time, the average diameter of the CSPBs was found to be 173 nm, and the average molecular weight and grafted density of the grafted polyelectrolyte brushes were 780,138 g/mol and 4.026?×?109/nm2, respectively. PMID:24948900

2014-01-01

443

Hollow sphere ceramic particles for abradable coatings  

SciTech Connect

A hollow sphere ceramic flame spray powder is disclosed. The desired constituents are first formed into agglomerated particles in a spray drier. Then the agglomerated particles are introduced into a plasma flame which is adjusted so that the particles collected are substantially hollow. The hollow sphere ceramic particles are suitable for flame spraying a porous and abradable coating. The hollow particles may be selected from the group consisting of zirconium oxide and magnesium zirconate.

Longo, F.N.; Bader, N.F. III; Dorfman, M.R.

1984-05-22

444

Impact jetting by a solid sphere  

Microsoft Academic Search

We use a novel ultra-high-speed video camera to study the initial stage of the impact of a solid sphere onto a liquid surface, finding a high-speed horizontal jet which emerges immediately following the intial contact. For Re > 2 × 10(4) the jet emerges when the horizontal contact between the sphere and the liquid is only 12% of its diameter.

S. T. Thoroddsen; T. G. Etoh; K. Takehara; Y. Takano

2004-01-01

445

Characterization of dielectric spheres by spiral imaging.  

PubMed

We study the spiral spectra scattered off transparent dielectric spheres when probed by different Laguerre-Gaussian light beams, carrying nested topological wavefront dislocations. We show that such scattering data may be employed to determine geometrical properties of the spheres, such as their position. The technique is a generalization of standard Mie scattering, and it can be extended to study and to characterize nanospheres. PMID:22378421

Petrov, Dmitri; Rahuel, Nicolas; Molina-Terriza, Gabriel; Torner, Lluis

2012-03-01

446

Scalar Casimir effect between Dirichlet spheres or a plate and a sphere  

E-print Network

We present a simple formalism for the evaluation of the Casimir energy for two spheres and a sphere and a plane, in case of a scalar fluctuating field, valid at any separations. We compare the exact results with various approximation schemes and establish when such schemes become useful. The formalism can be easily extended to any number of spheres and/or planes in three or arbitrary dimensions, with a variety of boundary conditions or non-overlapping potentials/non-ideal reflectors.

Aurel Bulgac; Piotr Magierski; Andreas Wirzba

2005-11-04

447

Hard Copy Market Overview  

NASA Astrophysics Data System (ADS)

A number of Color Hard Copy (CHC) market drivers are currently indicating strong growth in the use of CHC technologies for the business graphics marketplace. These market drivers relate to product, software, color monitors and color copiers. The use of color in business graphics allows more information to be relayed than is normally the case in a monochrome format. The communicative powers of full-color computer generated output in the business graphics application area will continue to induce end users to desire and require color in their future applications. A number of color hard copy technologies will be utilized in the presentation graphics arena. Thermal transfer, ink jet, photographic and electrophotographic technologies are all expected to be utilized in the business graphics presentation application area in the future. Since the end of 1984, the availability of color application software packages has grown significantly. Sales revenue generated by business graphics software is expected to grow at a compound annual growth rate of just over 40 percent to 1990. Increased availability of packages to allow the integration of text and graphics is expected. Currently, the latest versions of page description languages such as Postscript, Interpress and DDL all support color output. The use of color monitors will also drive the demand for color hard copy in the business graphics market place. The availability of higher resolution screens is allowing color monitors to be easily used for both text and graphics applications in the office environment. During 1987, the sales of color monitors are expected to surpass the sales of monochrome monitors. Another major color hard copy market driver will be the color copier. In order to take advantage of the communications power of computer generated color output, multiple copies are required for distribution. Product introductions of a new generation of color copiers is now underway with additional introductions expected during 1987. The color hard copy market continues to be in a state of constant change, typical of any immature market. However, much of the change is positive. During 1985, the color hard copy market generated 1.2 billion. By 1990, total market revenue is expected to exceed 5.5 billion. The business graphics CHC application area is expected to grow at a compound annual growth rate greater than 40 percent to 1990.

Testan, Peter R.

1987-04-01

448

SPHERE instrumentation software: a progress report  

NASA Astrophysics Data System (ADS)

SPHERE INS is the software devoted to the control of the SPHERE "Planet Finder Instrument". SPHERE is a second generation instrument for the VLT whose prime objective is the discovery and study of new extra-solar giant planets orbiting nearby stars. The instrument is currently assembled and being tested. It is expected to undergo Preliminary Acceptance in Europe before the end of 2012. SPHERE INS, besides controlling the instrument functions, implements all observation, calibration and maintenance procedures. It includes on-line data reduction procedures, necessary during observations and calibrations, as well as quick-look procedures that allow monitoring the status of ongoing observations. SPHERE INS also manages the external interfaces with the VLT Telescope Control Software, the High-level Observing Software and the Data Handling System. It provides both observing and engineering graphical user interfaces. In this paper we give a brief review of the SPHERE INS design. We then report about the current status of the software, the activities concerning its integration with the Instrument and the testing and validation procedures.

Baruffolo, A.; Fantinel, D.; Gluck, L.; Salasnich, B.; Zins, G.; Steiner, P.; Micallef, M.; Bruno, P.; Popovic, D.; Donaldson, R. H.; Fedrigo, E.; Kiekebusch, M.; Soenke, C.; Suarez Valles, M.

2012-09-01

449

Detecting dark energy with wavelets on the sphere Jason D. McEwen  

E-print Network

Detecting dark energy with wavelets on the sphere Jason D. McEwen Astrophysics Group, Cavendish Laboratory, Cambridge CB3 0HE, UK ABSTRACT Dark energy dominates the energy density of our Universe, yet we know very little about its nature and origin. Although strong evidence in support of dark energy

McEwen, Jason

450

Calculation of electric dipole intensity parameter to explore some interaction between hard metal ions Pr(III) and Nd(III) with pi-electron density of butene-1,4 and butyne-1,4-diols in non-aqueous solutions: an absorption spectral study.  

PubMed

Pr(III) and Nd(III) are hard acceptors in HSAB (hard and soft acid base) sense and hence are known to exhibit practically a little affinity towards electrons. At the same time these metal ions show strong preference for oxygen donor chelating ligands. The ligands chosen for this study are structurally related diols, viz. butane-1,4, butene-1,4 and butyne-1,4-diols which form identical seven membered chelate ring by coordinating to metals in a bidentate manner through oxygen on 1 and 4 positions of the diol molecules. Complexation of these diols with Pr(III) and Nd(III) was carried out in DMF, CH3OH, CH3CN and their equimolar binary mixtures using comparative absorption spectrophotometry of 4f-4f transitions. The variation of oscillator strengths (P) of different 4f-4f bands as well as the magnitude and variation of Judd-Ofelt electric dipole intensity parameters (T lambda, lambda = 2, 4, 6) was discussed. They correlate the interaction between the metal 4f-orbitals of Pr(III) and Nd(III) with the pi-electron densities of the double and triple bonds present in butene-1,4 and butyne-1,4-diols, respectively. The value of empirical intensity parameter [T lambda(complex)/T lambda (aquo)] was calculated and its plot against oscillator strength (P) is drawn. PMID:16344248

Singh, Th David; Sumitra, Ch; Bag, G C; Devi, M Indira; Singh, N Rajmuhon

2006-01-01

451

Collinear swimmer propelling a cargo sphere at low Reynolds number  

E-print Network

The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes' equations in the presence of a sphere with no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.

Felderhof, B U

2014-01-01

452

Hot electron and x-ray production from intense laser irradiation of wavelength-scale polystyrene spheres  

NASA Astrophysics Data System (ADS)

Hot electron and x-ray production from solid targets coated with polystyrene-spheres which are irradiated with high-contrast, 100fs, 400nm light pulses at intensity up to 2×1017W/cm2 have been studied. The peak hard x-ray signal from uncoated fused silica targets is an order of magnitude smaller than the signal from targets coated with submicron sized spheres. The temperature of the x-rays in the case of sphere-coated targets is twice as hot as that of uncoated glass. A sphere-size scan of the x-ray yield and observation of a peak in both the x-ray production and temperature at a sphere diameter of 0.26?m, indicate that these results are consistent with Mie enhancements of the laser field at the sphere surface and multipass stochastic heating of the hot electrons in the oscillating laser field. These results also match well with particle-in-cell simulations of the interaction.

Sumeruk, H. A.; Kneip, S.; Symes, D. R.; Churina, I. V.; Belolipetski, A. V.; Dyer, G.; Landry, J.; Bansal, G.; Bernstein, A.; Donnelly, T. D.; Karmakar, A.; Pukhov, A.; Ditmire, T.

2007-06-01

453

Virial coefficients, equation of state, and solid-fluid coexistence for the soft sphere model  

Microsoft Academic Search

Virial coefficients up to B8 are calculated for the soft-sphere model, with exponents n?=?12, 9 and 6. It is demonstrated that for n?=?12, the virial series truncated at B8 describes well the equation of state (EOS) of the fluid phase up to the freezing density, while for n?=?9 and 6 the series departs from the correct behaviour for densities of

Tai Boon Tan; Andrew J. Schultz; David A. Kofke

2011-01-01

454

Gravitationally bound ideal gas sphere in Newtonian and in Einsteinian gravity  

NASA Astrophysics Data System (ADS)

The gravitational hydrostatic equilibrium of an isothermal ideal gas with pressure proportional to density is investigated. The system is known from the literature as the singular isothermal sphere since it has infinite central density and infinite total mass. In spite of these unphysical features the system is of pedagogical interest since it allows exact mathematical treatment both within Newtonian gravity and within general relativity. The difference between these two theories is nicely illustrated.

Essén, Hanno

2014-11-01

455

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries  

PubMed Central

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H2(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g-1 at a current density of 50 mAh g-1. Even at a high current density of 500 mAh g-1, the reversible specific capacity remained at 502 mAh g-1. After 60 cycles, the reversible capacity was still kept at 652 mAh g-1 at the current density of 50 mAh g-1. These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets. PACS 81.05.ue; 61.48.Gh; 72.80.Vp PMID:25114657

2014-01-01

456

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries  

NASA Astrophysics Data System (ADS)

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H2(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g-1 at a current density of 50 mAh g-1. Even at a high current density of 500 mAh g-1, the reversible specific capacity remained at 502 mAh g-1. After 60 cycles, the reversible capacity was still kept at 652 mAh g-1 at the current density of 50 mAh g-1. These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets.

Yao, Ran-Ran; Zhao, Dong-Lin; Bai, Li-Zhong; Yao, Ning-Na; Xu, Li

2014-07-01

457

Data Comparison: Satellite and Falling Sphere Temperatures  

NASA Technical Reports Server (NTRS)

Small meteorological rocketsondes providing temperature data have beam used for comparison with, and validation of measurements from satellite-borne instruments. A significant number of rocket-borne falling spheres were launched in conjunction with the Upper Atmosphere Research Satellite (UARS) for validation of the Halogen Occultation Experiment (HALOE), High Resolution Doppler Interferometer (HRDI), and the Microwave Limb Sounder (MLS) instruments. Upper stratosphere and mesosphere temperatures measured with these instruments on UARS are compared with inflatable spheres launched from Wallops Island (1992-1999), Brazil (1994), Hawaii (1992), Norway (1992), and Sweden (1993 and 1996). Time and space differences varied between the satellite measurement and the rocketsonde launch, for example HALOE overpasses occurred within 5 days and in some cases there were spatial differences of up to 30 degrees longitude. Validation measurements of the HRDI instrument occurred at Wallops Island when it passed within 20 minutes and 330 kilometers of the launch site. Because of discontinuity in the falling sphere drag coefficients when fall speed neared MACH 1 falling sphere temperatures near 70 kilometers attitude are biased toward lower temperatures. Availability of improved software and a new atmospheric model have helped to reduce this bias. The validated remote instrument measurements permit a new perspective of atmospheric structure to be formed, not always pos