Structure of ternary additive hard-sphere fluid mixtures
NASA Astrophysics Data System (ADS)
Malijevský, Alexander; Malijevský, Anatol; Yuste, Santos B.; Santos, Andrés; López de Haro, Mariano
2002-12-01
Monte Carlo simulations on the structural properties of ternary fluid mixtures of additive hard spheres are reported. The results are compared with those obtained from a recent analytical approximation [S. B. Yuste, A. Santos, and M. López de Haro, J. Chem. Phys. 108, 3683 (1998)] to the radial distribution functions of hard-sphere mixtures and with the results derived from the solution of the Ornstein-Zernike integral equation with both the Martynov-Sarkisov and the Percus-Yevick closures. Very good agreement between the results of the first two approaches and simulation is observed, with a noticeable improvement over the Percus-Yevick predictions especially near contact.
Random sequential addition of hard spheres in high Euclidean dimensions
NASA Astrophysics Data System (ADS)
Torquato, S.; Uche, O. U.; Stillinger, F. H.
2006-12-01
Sphere packings in high dimensions have been the subject of recent theoretical interest. Employing numerical and theoretical methods, we investigate the structural characteristics of random sequential addition (RSA) of congruent spheres in d -dimensional Euclidean space Rd in the infinite-time or saturation limit for the first six space dimensions (1≤d≤6) . Specifically, we determine the saturation density, pair correlation function, cumulative coordination number and the structure factor in each of these dimensions. We find that for 2≤d≤6 , the saturation density ϕs scales with dimension as ϕs=c1/2d+c2d/2d , where c1=0.202048 and c2=0.973872 . We also show analytically that the same density scaling is expected to persist in the high-dimensional limit, albeit with different coefficients. A byproduct of this high-dimensional analysis is a relatively sharp lower bound on the saturation density for any d given by ϕs≥(d+2)(1-S0)/2d+1 , where S0ɛ[0,1] is the structure factor at k=0 (i.e., infinite-wavelength number variance) in the high-dimensional limit. We demonstrate that a Palàsti-type conjecture (the saturation density in Rd is equal to that of the one-dimensional problem raised to the d th power) cannot be true for RSA hyperspheres. We show that the structure factor S(k) must be analytic at k=0 and that RSA packings for 1≤d≤6 are nearly “hyperuniform.” Consistent with the recent “decorrelation principle,” we find that pair correlations markedly diminish as the space dimension increases up to six. We also obtain kissing (contact) number statistics for saturated RSA configurations on the surface of a d -dimensional sphere for dimensions 2≤d≤5 and compare to the maximal kissing numbers in these dimensions. We determine the structure factor exactly for the related “ghost” RSA packing in Rd and demonstrate that its distance from “hyperuniformity” increases as the space dimension increases, approaching a constant asymptotic value
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2006-07-01
We have analyzed the rate of convergence of a series expansion, in terms of the density, of the ratio of the excess compressibility factor of fluid mixtures of additive hard spheres to that of a pure hard-sphere fluid with the same reduced density. The terms in the series can be obtained from the virial coefficients. We have found that the series converges quickly, so that frequently the knowledge of the first two terms of the series, that can be obtained from the second and third virial coefficients which are known analytically, is sufficient to provide an accurate equation of state.
López de Haro, Mariano; Tejero, Carlos F; Santos, Andrés
2013-04-28
The problem of demixing in a binary fluid mixture of highly asymmetric additive hard spheres is revisited. A comparison is presented between the results derived previously using truncated virial expansions for three finite size ratios with those that one obtains with the same approach in the extreme case in which one of the components consists of point particles. Since this latter system is known not to exhibit fluid-fluid segregation, the similarity observed for the behavior of the critical constants arising in the truncated series in all instances, while not being conclusive, may cast serious doubts as to the actual existence of a demixing fluid-fluid transition in disparate-sized binary additive hard-sphere mixtures.
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2003-08-01
Density expansions of the contact pair correlation functions for binary mixtures of additive hard spheres are obtained from the virial expansion of the equation of state. The procedure is based on the use consistency conditions. The resulting expansions are exact up to first order in the density. This corresponds to the third virial coefficient which is exactly known for these mixtures. Analytical expressions for the second and third order terms are obtained on the basis of very accurate approximate analytical expressions for the fourth and fifth virial coefficients. It is found that the series converge slowly, but the convergency can be accelerated by means of a resummation procedure.
A new analytical equation of state for additive hard sphere fluid mixtures
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
A study has been made of the relation between the equation of state of additive binary hard sphere fluid mixtures and the equation of state of a pure hard sphere fluid for the same packing fraction. An analysis of the existing simulation data for a wide variety of compositions of the mixture and diameter ratios up to 1/0.2 makes it possible to conclude that the ratio of the excess compressibility factor of the mixture to that of the pure fluid is, to a very good approximation, a linear function of the packing fraction. This suggests the possibility of deriving the equation of state of the mixture from that of the pure fluid by using the second and third virial coefficients of the mixture, which are known analytically, to reproduce the linear relation mentioned above. When a suitable equation of state is chosen for the pure fluid, the results from the equation of state of the mixture thus obtained are in excellent agreement with simulation data. The predictions for the fourth and fifth virial coefficients also are very accurate compared with known numerical data.
Consistency conditions and equation of state for additive hard-sphere fluid mixtures
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2000-12-01
A number of consistency conditions for the contact values gij(σij) of the pair correlation function of species i and j in an additive hard-sphere fluid mixture are discussed. It is shown that most of the theoretically-based expressions, as well as other more empirical in character, existing for these functions, fail to satisfy at least one of the conditions. It is suggested that one could improve the performance of the expressions for gij(σij) and the equation of state by using the consistency conditions. This is illustrated by modifying the Boublı´k-Mansoori-Carnahan-Starling-Leland expressions for gij(σij), which results in better predictions for these functions as well as for the compressibility factor and the fourth and fifth virial coefficients.
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2003-01-01
Approximate expressions for the fourth and fifth virial coefficients of binary hard-sphere fluid mixtures are derived. The procedure used to obtain these expressions is based on that previously proposed by Wheatley [J. chem. Phys., 111, 5455 (1999)], but slightly modified. Wheatley's procedure starts from a prescribed general analytical form of the virial coefficients, from which the particular expression for each virial coefficient is obtained by imposing to the general form a number of limiting conditions. Here, we propose an alternative general expression of the virial coefficients and derive one more condition. This condition is satisfied when the fourth and fifth virial coefficients are expressed in the form we propose, but not when they are expressed in Wheatley's form. The agreement of the proposed analytical expressions with exact numerical data is excellent. The procedure can be extended to higher virial coefficients, although the lack of exact numerical data prevents any comparison.
Mapping a hard-sphere fluid mixture onto a single component hard-sphere fluid
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2005-06-01
The possibility of obtaining the thermodynamic and structural properties of a binary additive hard-sphere fluid mixture on the basis of the corresponding properties of a suitable single-component hard-sphere fluid is analyzed. To this end, Monte Carlo simulations have been performed for binary mixtures of hard spheres for different densities, compositions and diameter ratios in order to obtain the compressibility factor Z and the partial radial distribution functions gij(r) for pairs ij of the mixtures. These data are used to test the reliability of different proposals available in the literature for mapping the thermodynamic and structural properties of conformal mixtures onto those of a single-component fluid. It is found that, while the averaged radial distribution function and the equation of state of the mixture can be reasonably well reproduced by means of those of an equivalent single-component fluid, the partial radial distribution functions cannot be obtained with enough accuracy from the radial distribution function of the equivalent fluid. A possible explanation for this fact is suggested.
Prediction of binary hard-sphere crystal structures.
Filion, Laura; Dijkstra, Marjolein
2009-04-01
We present a method based on a combination of a genetic algorithm and Monte Carlo simulations to predict close-packed crystal structures in hard-core systems. We employ this method to predict the binary crystal structures in a mixture of large and small hard spheres with various stoichiometries and diameter ratios between 0.4 and 0.84. In addition to known binary hard-sphere crystal structures similar to NaCl and AlB2, we predict additional crystal structures with the symmetry of CrB, gammaCuTi, alphaIrV, HgBr2, AuTe2, Ag2Se, and various structures for which an atomic analog was not found. In order to determine the crystal structures at infinite pressures, we calculate the maximum packing density as a function of size ratio for the crystal structures predicted by our GA using a simulated annealing approach. PMID:19518387
Equation of state for fluid mixtures of hard spheres and linear homonuclear fused hard spheres
NASA Astrophysics Data System (ADS)
Largo, J.; Solana, J. R.
1998-08-01
This paper develops a theoretically based equation of state for fluid mixtures consisting of hard spheres and linear homonuclear fused hard spheres. The procedure is based on the equation of state previously developed for monocomponent athermal fluids. The equation of state only requires two parameters, namely the averaged effective molecular volume of the molecules in the mixture and the corresponding effective nonsphericity parameter. These parameters can be obtained from the geometry of the molecules forming the mixture. The results are in excellent agreement with simulation data and compare favorably with those obtained from other theories for athermal fluid mixtures.
NASA Astrophysics Data System (ADS)
Santos, A.; Yuste, S. B.; López de Haro, M.
The composition-independent virial coefficients of a d-dimensional binary mixture of (additive) hard hyperspheres following from a recent proposal for the equation of state of the mixture (SANTOS, A., YUSTE, S. B., and LÓPEZ DE HARO, M., 1999, Molec. Phys., 96 , 1) are examined. Good agreement between theoretical estimates and available exact or numerical results is found for d = 2, 3, 4 and 5, except for mixtures whose components are very disparate in size. A slight modification that remedies this deficiency is introduced and the resummation of the associated virial series is carried out, leading to a new proposal for the equation of state. The case of binary hard sphere mixtures (d = 3) is analysed in some detail.
Aging dynamics of colloidal hard sphere glasses.
Martinez, V A; Bryant, G; van Megen, W
2010-09-21
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. PMID:20866156
Equations of state for fused-hard-sphere fluids
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1993-09-01
Analytical equations of state for fused-hard-sphere fluids are developed from a generalization of the Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid. The results are in good agreement with existing simulation data.
Dynamics of hard sphere colloidal dispersions
NASA Technical Reports Server (NTRS)
Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.
1994-01-01
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.
Segregation of Fluidized Binary Hard-Sphere Systems Under Gravity
NASA Astrophysics Data System (ADS)
Kim, Soon-Chul
We have derived an analytic expression for the contact value of the local density of binary hard-sphere systems under gravity. We have obtained the crossover conditions for the Brazil-nut type segregation of binary hard-sphere mixtures and binary hard-sphere chain mixtures from the segregation criterion, where the segregation occurs when the density (or the pressure) of the small spheres at the bottom is higher than that of the large spheres, or vice versa. For the binary hard-sphere chain mixtures, the crossover condition for the segregation depends on the number of monomers composed of hard-sphere chains as well as the mass and the diameter of each species. The fundamental-measure theories (FMTs) and local density approximation (LDA) are employed to examine the crossover condition for the segregation of the gravity-induced hard-sphere mixtures. The calculated results show that the LDA does not explain the density oscillation near the bottom, whereas the modified fundamental-measure theory (MFMT) compares with molecular dynamics simulations.
Equation of state for fused-hard-sphere fluid mixtures
NASA Astrophysics Data System (ADS)
Largo, J.; Solana, J. R.
This paper develops a theoretically-based equation of state for fused-hard-sphere fluid mixtures on the basis of an equation of state previously derived for hard-convex-body fluid mixtures. The equation uses as a reference the equation of state for an equivalent hard-sphere fluid mixture in which each component has the same molecular volume as the effective molecular volume of one of the components of the fused-hard-sphere mixture. The two parameters required by the theory, namely the averaged effective molecular volume of the molecules in the mixture and the corresponding effective non-sphericity parameter, are obtained from the geometrical characteristics of the molecules that form the mixture. The results are, on the whole, in closer agreement with simulation data than those obtained with other theories developed for this kind of mixture.
Demixing in binary mixtures of apolar and dipolar hard spheres
NASA Astrophysics Data System (ADS)
Almarza, N. G.; Lomba, E.; Martín, C.; Gallardo, A.
2008-12-01
We study the demixing transition of mixtures of equal size hard spheres and dipolar hard spheres using computer simulation and integral equation theories. Calculations are carried out at constant pressure, and it is found that there is a strong correlation between the total density and the composition. The critical temperature and the critical total density are found to increase with pressure. The critical mole fraction of the dipolar component on the contrary decreases as pressure is augmented. These qualitative trends are reproduced by the theoretical approaches that on the other hand overestimate by far the value of the critical temperature. Interestingly, the critical parameters for the liquid-vapor equilibrium extrapolated from the mixture results in the limit of vanishing neutral hard sphere concentration agree rather well with recent estimates based on the extrapolation of charged hard dumbbell phase equilibria when dumbbell elongation shrinks to zero [G. Ganzenmüller and P. J. Camp, J. Chem. Phys. 126, 191104 (2007)].
Computational polymer physics: Hard-sphere chain in solvent systems
NASA Astrophysics Data System (ADS)
Gautam, Avinash; Gavazzi, Daniel; Taylor, Mark
2009-10-01
In this work we present results for chain conformation in two simple chain-in-solvent systems constructed from hard-sphere monomers of diameter D. The first system consists of a flexible chain of fused hard spheres (i.e., bond length L=D) in a monomeric hard-sphere solvent. The second system consists of a flexible tangent hard-sphere chain (L=D) in a dimeric hard-sphere solvent with L=D. These systems are studied using Monte Carlo simulations which employ both single-site crankshaft and multi-site pivot moves to sample the configuration space of the chain. We report chain structure, in terms of site-site probability functions, as a function of solvent density. In all cases, increasing solvent density leads to an overall compression of the chain. At high solvent density the chain conformation is closely coupled to the local solvent structure and we speculate that incommensurate structures may lead to interesting conformational transitions.
Structure of hard particle fluids near a hard wall. II. yw(z) for hard spheres
NASA Astrophysics Data System (ADS)
Labik, S.; Smith, William R.; Speedy, Robin J.
1988-02-01
Predictions of the wall-cavity correlation function yw(z) for hard spheres against a hard wall are tested using the treatment that Smith and Speedy developed and examined for the case of hard disks in part I of this series, as well as an extension of this approach using an alternative procedure. yw(z) in the range 0≤z≤1 may be accurately predicted using only the thermodynamic properties of the bulk fluid, for which precise expressions are available. These predictions are tested by determining yw(z) and the cavity concentration profile nwo(z) in a computer simulation study. We also derive a new integral equation relating yw(z) near the wall to its values just outside the wall and illustrate this in examining the consistency of our computer simulation results.
Collisional statistics of the hard-sphere gas.
Visco, Paolo; van Wijland, Frédéric; Trizac, Emmanuel
2008-04-01
We investigate the probability distribution functions of the free flight time and of the number of collisions in a hard-sphere gas at equilibrium. At variance with naive expectation, the latter quantity does not follow Poissonian statistics, even in the dilute limit, which is the focus of the present analysis. The corresponding deviations are addressed both numerically and analytically. In writing an equation for the generating function of the cumulants of the number of collisions, we came across a perfect mapping between our problem and a previously introduced model: the probabilistic ballistic annihilation process [Coppex, Phys. Rev. E 69, 11303 (2004)]. We exploit this analogy to construct a Monte Carlo-like algorithm able to investigate the asymptotically large time behavior of the collisional statistics within a reasonable computational time. In addition, our predictions are compared with the results of molecular dynamics simulations and the direct simulation Monte Carlo technique. An excellent agreement is reported. PMID:18517588
Investigating hard sphere interactions through spin echo scattering angle measurement
NASA Astrophysics Data System (ADS)
Washington, Adam
Spin Echo Scattering Angle Measurement (SESAME) allows neutron scattering instruments to perform real space measurements on large micron scale samples by encoding the scattering angle into the neutron's spin state via Larmor precession. I have built a SESAME instrument at the Low Energy Neutron Source. I have also assisted in the construction of a modular SESAME instrument on the ASTERIX beamline at Los Alamos National lab. The ability to tune these instruments has been proved mathematically and optimized and automated experimentally. Practical limits of the SESAME technique with respect to polarization analyzers, neutron spectra, Larmor elements, and data analysis were investigated. The SESAME technique was used to examine the interaction of hard spheres under depletion. Poly(methyl methacrylate) spheres suspended in decalin had previously been studied as a hard sphere solution. The interparticle correlations between the spheres were found to match the Percus-Yevick closure, as had been previously seen in dynamical light scattering experiments. To expand beyond pure hard spheres, 900kDa polystyrene was added to the solution in concentrations of less than 1% by mass. The steric effects of the polystyrene were expected to produce a short-range, attractive, "sticky" potential. Experiment showed, however, that the "sticky" potential was not a stable state and that the spheres would eventually form long range aggregates.
NASA Astrophysics Data System (ADS)
Astillero, Antonio; Santos, Andrés
2005-09-01
In the preceding paper, we have conjectured that the main transport properties of a dilute gas of inelastic hard spheres (IHSs) can be satisfactorily captured by an equivalent gas of elastic hard spheres (EHSs), provided that the latter are under the action of an effective drag force and their collision rate is reduced by a factor (1+α)/2 (where α is the constant coefficient of normal restitution). In this paper we test the above expectation in a paradigmatic nonequilibrium state, namely, the simple or uniform shear flow, by performing Monte Carlo computer simulations of the Boltzmann equation for both classes of dissipative gases with a dissipation range 0.5⩽α⩽0.95 and two values of the imposed shear rate a . It is observed that the evolution toward the steady state proceeds in two stages: a short kinetic stage (strongly dependent on the initial preparation of the system) followed by a slower hydrodynamic regime that becomes increasingly less dependent on the initial state. Once conveniently scaled, the intrinsic quantities in the hydrodynamic regime depend on time, at a given value of α , only through the reduced shear rate a*(t)∝a/T(t) , until a steady state, independent of the imposed shear rate and of the initial preparation, is reached. The distortion of the steady-state velocity distribution from the local equilibrium state is measured by the shear stress, the normal stress differences, the cooling rate, the fourth and sixth cumulants, and the shape of the distribution itself. In particular, the simulation results seem to be consistent with an exponential overpopulation of the high-velocity tail. These properties are common to both the IHS and EHS systems. In addition, the EHS results are in general hardly distinguishable from the IHS ones if α≳0.7 , so that the distinct signature of the IHS gas (higher anisotropy and overpopulation) only manifests itself at relatively high dissipations.
Packing confined hard spheres denser with adaptive prism phases.
Oğuz, Erdal C; Marechal, Matthieu; Ramiro-Manzano, Fernando; Rodriguez, Isabelle; Messina, René; Meseguer, Francisco J; Löwen, Hartmut
2012-11-21
We show that hard spheres confined between two parallel hard plates pack denser with periodic adaptive prismatic structures which are composed of alternating prisms of spheres. The internal structure of the prisms adapts to the slit height which results in close packings for a range of plate separations, just above the distance where three intersecting square layers fit exactly between the plates. The adaptive prism phases are also observed in real-space experiments on confined sterically stabilized colloids and in Monte Carlo simulations at finite pressure.
Slip and flow of hard-sphere colloidal glasses.
Ballesta, P; Besseling, R; Isa, L; Petekidis, G; Poon, W C K
2008-12-19
We study the flow of concentrated hard-sphere colloidal suspensions along smooth, nonstick 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.
Free volume distribution of nearly jammed hard sphere packings
NASA Astrophysics Data System (ADS)
Maiti, Moumita; Sastry, Srikanth
2014-07-01
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.
NASA Astrophysics Data System (ADS)
Largo, J.; Maeso, M. J.; Solana, J. R.; Vega, C.; MacDowell, L. G.
2003-11-01
The bonded hard-sphere (BHS) theory is extended to fluids consisting of rigid, linear, homonuclear molecules, each of them formed by n fused hard spheres. The theory shows excellent agreement with the Monte Carlo NpT simulation data which are also reported for reduced bond lengths l*=0.5 and n=2, 3, 4, 6, 8, and 10. The accuracy of the BHS prediction in comparison to simulation is similar to that of generalized Flory-dimer theory and superior to that of thermodynamic perturbation theory.
Rowlinson's concept of an effective hard sphere diameter.
Henderson, Douglas
2010-01-01
Attention is drawn to John Rowlinson's idea that the repulsive portion of the intermolecular interaction may be replaced by a temperature-dependent hard sphere diameter. It is this approximation that made the development of perturbation theory possible for realistic fluids whose intermolecular interactions have a steep, but finite, repulsion at short separations.
Rowlinson’s concept of an effective hard sphere diameter
Henderson, Douglas
2010-01-01
Attention is drawn to John Rowlinson’s idea that the repulsive portion of the intermolecular interaction may be replaced by a temperature-dependent hard sphere diameter. It is this approximation that made the development of perturbation theory possible for realistic fluids whose intermolecular interactions have a steep, but finite, repulsion at short separations. PMID:20953320
Probing the evolution and morphology of hard carbon spheres
Pol, Vilas G.; Wen, Jianguo; Lau, Kah Chun; Callear, Samantha; Bowron, Daniel T.; Lin, Chi-Kai; Deshmukh, Sanket A.; Sankaranarayanan, Subramanian; Curtiss, Larry A.; David, William; Miller, Dean J.; Thackeray, Michael M.
2014-03-01
Monodispersed hard carbon spheres can be synthesized quickly and reproducibly by autogenic reactions of hydrocarbon precursors, notably polyethylene (including plastic waste), at high temperature and pressure. The carbon microparticles formed by this reaction have a unique spherical architecture, with a dominant internal nanometer layered motif, and they exhibit diamond-like hardness and electrochemical properties similar to graphite. In the present study, in-situ monitoring by X-ray diffraction along with electron microscopy, Raman spectroscopy, neutron pair-distribution function analysis, and computational modeling has been used to elucidate the morphology and evolution of the carbon spheres that form from the autogenic reaction of polyethylene at high temperature and pressure. A mechanism is proposed on how polyethylene evolves from a linear chain-based material to a layered carbon motif. Heating the spheres to 2400-2800 °C under inert conditions increases their graphitic character, particularly at the surface, which enhances their electrochemical and tribological properties.
Equation of state for fluid mixtures of hard spheres and heteronuclear hard dumbbells
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
1999-09-01
A theoretically founded equation of state is developed for mixtures of hard spheres with heteronuclear hard dumbbells. It is based on a model previously developed for hard-convex-body fluid mixtures, and further extended to fluid mixtures of homonuclear hard dumbbells. The equation scales the excess compressibility factor for an equivalent hard-sphere fluid mixture to obtain that corresponding to the true mixture. The equivalent mixture is one in which the averaged volume of a sphere is the same as the effective molecular volume of a molecule in the real mixture. Thus, the theory requires two parameters, namely the averaged effective molecular volume of the molecules in the mixture and the scaling factor, which is the effective nonsphericity parameter. Expressions to determine these parameters are derived in terms of the geometrical characteristics of the molecules that form the mixture. The overall results are in closer agreement with simulation data than those obtained with other theories developed for these kinds of mixtures.
Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.
Rodríguez-López, Tonalli; del Río, Fernando
2012-01-28
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
Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.
Rodríguez-López, Tonalli; del Río, Fernando
2012-01-28
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.
Hynninen, Antti-Pekka; Dijkstra, Marjolein
2005-04-01
Phase diagrams of hard and soft spheres with a fixed dipole moment are determined by calculating the Helmholtz free energy using simulations. The pair potential is given by a dipole-dipole interaction plus a hard-core and a repulsive Yukawa potential for soft spheres. Our system models colloids in an external electric or magnetic field, with hard spheres corresponding to uncharged and soft spheres to charged colloids. The phase diagram of dipolar hard spheres shows fluid, face-centered-cubic (fcc), hexagonal-close-packed (hcp), and body-centered-tetragonal (bct) phases. The phase diagram of dipolar soft spheres exhibits, in addition to the above mentioned phases, a body-centered-orthorhombic (bco) phase, and it agrees well with the experimental phase diagram [Nature (London) 421, 513 (2003)]. Our results show that bulk hcp, bct, and bco crystals can be realized experimentally by applying an external field. PMID:15904046
Velocity and energy distributions in microcanonical ensembles of hard spheres
NASA Astrophysics Data System (ADS)
Scalas, Enrico; Gabriel, Adrian T.; Martin, Edgar; Germano, Guido
2015-08-01
In a microcanonical ensemble (constant N V E , hard reflecting walls) and in a molecular dynamics ensemble (constant N V E PG , periodic boundary conditions) with a number N of smooth elastic hard spheres in a d -dimensional volume V having a total energy E , a total momentum P , and an overall center of mass position G , the individual velocity components, velocity moduli, and energies have transformed beta distributions with different arguments and shape parameters depending on d , N , E , the boundary conditions, and possible symmetries in the initial conditions. This can be shown marginalizing the joint distribution of individual energies, which is a symmetric Dirichlet distribution. In the thermodynamic limit the beta distributions converge to gamma distributions with different arguments and shape or scale parameters, corresponding respectively to the Gaussian, i.e., Maxwell-Boltzmann, Maxwell, and Boltzmann or Boltzmann-Gibbs distribution. These analytical results agree with molecular dynamics and Monte Carlo simulations with different numbers of hard disks or spheres and hard reflecting walls or periodic boundary conditions. The agreement is perfect with our Monte Carlo algorithm, which acts only on velocities independently of positions with the collision versor sampled uniformly on a unit half sphere in d dimensions, while slight deviations appear with our molecular dynamics simulations for the smallest values of N .
Zhang, Kai; Fan, Meng; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D; O'Hern, Corey S
2015-11-14
When a liquid is cooled well below its melting temperature at a rate that exceeds the critical cooling rate Rc, the crystalline state is bypassed and a metastable, amorphous glassy state forms instead. Rc (or the corresponding critical casting thickness dc) characterizes the glass-forming ability (GFA) of each material. While silica is an excellent glass-former with small Rc < 10(-2) K/s, pure metals and most alloys are typically poor glass-formers with large Rc > 10(10) K/s. Only in the past thirty years have bulk metallic glasses (BMGs) been identified with Rc approaching that for silica. Recent simulations have shown that simple, hard-sphere models are able to identify the atomic size ratio and number fraction regime where BMGs exist with critical cooling rates more than 13 orders of magnitude smaller than those for pure metals. However, there are a number of other features of interatomic potentials beyond hard-core interactions. How do these other features affect the glass-forming ability of BMGs? In this manuscript, we perform molecular dynamics simulations to determine how variations in the softness and non-additivity of the repulsive core and form of the interatomic pair potential at intermediate distances affect the GFA of binary alloys. These variations in the interatomic pair potential allow us to introduce geometric frustration and change the crystal phases that compete with glass formation. We also investigate the effect of tuning the strength of the many-body interactions from zero to the full embedded atom model on the GFA for pure metals. We then employ the full embedded atom model for binary BMGs and show that hard-core interactions play the dominant role in setting the GFA of alloys, while other features of the interatomic potential only change the GFA by one to two orders of magnitude. Despite their perturbative effect, understanding the detailed form of the intermetallic potential is important for designing BMGs with cm or greater casting
NASA Astrophysics Data System (ADS)
Zhang, Kai; Fan, Meng; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D.; O'Hern, Corey S.
2015-11-01
When a liquid is cooled well below its melting temperature at a rate that exceeds the critical cooling rate Rc, the crystalline state is bypassed and a metastable, amorphous glassy state forms instead. Rc (or the corresponding critical casting thickness dc) characterizes the glass-forming ability (GFA) of each material. While silica is an excellent glass-former with small Rc < 10-2 K/s, pure metals and most alloys are typically poor glass-formers with large Rc > 1010 K/s. Only in the past thirty years have bulk metallic glasses (BMGs) been identified with Rc approaching that for silica. Recent simulations have shown that simple, hard-sphere models are able to identify the atomic size ratio and number fraction regime where BMGs exist with critical cooling rates more than 13 orders of magnitude smaller than those for pure metals. However, there are a number of other features of interatomic potentials beyond hard-core interactions. How do these other features affect the glass-forming ability of BMGs? In this manuscript, we perform molecular dynamics simulations to determine how variations in the softness and non-additivity of the repulsive core and form of the interatomic pair potential at intermediate distances affect the GFA of binary alloys. These variations in the interatomic pair potential allow us to introduce geometric frustration and change the crystal phases that compete with glass formation. We also investigate the effect of tuning the strength of the many-body interactions from zero to the full embedded atom model on the GFA for pure metals. We then employ the full embedded atom model for binary BMGs and show that hard-core interactions play the dominant role in setting the GFA of alloys, while other features of the interatomic potential only change the GFA by one to two orders of magnitude. Despite their perturbative effect, understanding the detailed form of the intermetallic potential is important for designing BMGs with cm or greater casting thickness.
Zhang, Kai; Fan, Meng; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D.; O’Hern, Corey S.
2015-11-14
When a liquid is cooled well below its melting temperature at a rate that exceeds the critical cooling rate R{sub c}, the crystalline state is bypassed and a metastable, amorphous glassy state forms instead. R{sub c} (or the corresponding critical casting thickness d{sub c}) characterizes the glass-forming ability (GFA) of each material. While silica is an excellent glass-former with small R{sub c} < 10{sup −2} K/s, pure metals and most alloys are typically poor glass-formers with large R{sub c} > 10{sup 10} K/s. Only in the past thirty years have bulk metallic glasses (BMGs) been identified with R{sub c} approaching that for silica. Recent simulations have shown that simple, hard-sphere models are able to identify the atomic size ratio and number fraction regime where BMGs exist with critical cooling rates more than 13 orders of magnitude smaller than those for pure metals. However, there are a number of other features of interatomic potentials beyond hard-core interactions. How do these other features affect the glass-forming ability of BMGs? In this manuscript, we perform molecular dynamics simulations to determine how variations in the softness and non-additivity of the repulsive core and form of the interatomic pair potential at intermediate distances affect the GFA of binary alloys. These variations in the interatomic pair potential allow us to introduce geometric frustration and change the crystal phases that compete with glass formation. We also investigate the effect of tuning the strength of the many-body interactions from zero to the full embedded atom model on the GFA for pure metals. We then employ the full embedded atom model for binary BMGs and show that hard-core interactions play the dominant role in setting the GFA of alloys, while other features of the interatomic potential only change the GFA by one to two orders of magnitude. Despite their perturbative effect, understanding the detailed form of the intermetallic potential is important for
Clustering and gelation of hard spheres induced by the Pickering effect
NASA Astrophysics Data System (ADS)
Fortini, Andrea
2012-04-01
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, ScienceSCIEAS0036-807510.1126/science.1199243 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.
Hard sphere dynamics for normal and granular fluids.
Dufty, James W; Baskaran, Aparna
2005-06-01
A fluid of N smooth, hard spheres is considered as a model for normal (elastic collision) and granular (inelastic collision) fluids. The potential energy is discontinuous for hard spheres so that the pairwise forces are singular and the usual forms of Newtonian and Hamiltonian mechanics do not apply. Nevertheless, particle trajectories in the N particle phase space are well defined and the generators for these trajectories can be identified. The first part of this presentation is a review of the generators for the dynamics of observables and probability densities. The new results presented in the second part refer to applications of these generators to the Liouville dynamics for granular fluids. A set of eigenvalues and eigenfunctions of the generator for this Liouville dynamics system is identified in a special stationary representation. This provides a class of exact solutions to the Liouville equation that are closely related to hydrodynamics for granular fluids.
Chaudhari, Mangesh I.; Holleran, Sinead A.; Ashbaugh, Henry S.; Pratt, Lawrence R.
2013-01-01
The osmotic second virial coefficients, B2, for atomic-sized hard spheres in water are attractive (B2 < 0) and become more attractive with increasing temperature (ΔB2/ΔT < 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
Replica exchange Monte Carlo applied to hard spheres.
Odriozola, Gerardo
2009-10-14
In this work a replica exchange Monte Carlo scheme which considers an extended isobaric-isothermal ensemble with respect to pressure is applied to study hard spheres (HSs). The idea behind the proposal is expanding volume instead of increasing temperature to let crowded systems characterized by dominant repulsive interactions to unblock, and so, to produce sampling from disjoint configurations. The method produces, in a single parallel run, the complete HS equation of state. Thus, the first order fluid-solid transition is captured. The obtained results well agree with previous calculations. This approach seems particularly useful to treat purely entropy-driven systems such as hard body and nonadditive hard mixtures, where temperature plays a trivial role.
Densest packings of hard spheres in a cylinder
NASA Astrophysics Data System (ADS)
Fu, Lin; Steinhardt, William; Zhao, Hao; Socolar, Joshua; Charbonneau, Patrick
Densely packing hard spheres (HS) within a cylinder is remarkably complex. Little is known about the densest achievable packings when the cylinder diameter, D, is larger than 2.85 times the sphere diameter, s. Here, we extend the identification of the densest packings up to D = 4.00s by adapting Torquato-Jiao's adaptive-shrinking-cell formulation and sequential-linear-programming technique to this geometry. We identify 17 new structures, almost all of them chiral. Beyond D, approx2.85s , most of the structures consist of an outer shell and of an inner core that compete for being close packed. In some cases the shell adopts a periodic configuration that is optimal and the stacking of core spheres within it is quasiperiodic, while in other cases a direct interplay between the two layers is observed. For some packings the very distinction between the core and shell vanishes, which results in exotic geometries, including some that are a three-dimensional extension of packing hard disks in a circle. In order to connect our results with experiments on comparable systems, we also consider the ease with which these structures assemble. Using kinetic Monte Carlo simulations, we find that some of the structures promtply assemble while others simply do not.
Universal jamming phase diagram in the hard-sphere limit.
Haxton, Thomas K; Schmiedeberg, Michael; Liu, Andrea J
2011-03-01
We present a new formulation of the jamming phase diagram for a class of glass-forming fluids consisting of spheres interacting via finite-ranged repulsions at temperature T, packing fraction ϕ or pressure p, and applied shear stress Σ. We argue that the natural choice of axes for the phase diagram are the dimensionless quantities T/pσ³, pσ³/ε, and Σ/p, where T is the temperature, p is the pressure, Σ is the stress, σ is the sphere diameter, ε is the interaction energy scale, and m is the sphere mass. We demonstrate that the phase diagram is universal at low pσ³/ε; at low pressure, observables such as the relaxation time are insensitive to details of the interaction potential and collapse onto the values for hard spheres, provided the observables are nondimensionalized by the pressure. We determine the shape of the jamming surface in the jamming phase diagram, organize previous results in relation to the jamming phase diagram, and discuss the significance of various limits.
Hard-sphere interactions in velocity-jump models
NASA Astrophysics Data System (ADS)
Franz, Benjamin; Taylor-King, Jake P.; Yates, Christian; Erban, Radek
2016-07-01
Group-level behavior 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.
Simple liquids’ quasiuniversality and the hard-sphere paradigm
NASA Astrophysics Data System (ADS)
Dyre, Jeppe C.
2016-08-01
This topical review discusses the quasiuniversality of simple liquids’ structure and dynamics and two possible justifications of it. The traditional one is based on the van der Waals picture of liquids in which the hard-sphere system reflects the basic physics. An alternative explanation argues that all quasiuniversal liquids to a good approximation conform to the same equation of motion, referring to the exponentially repulsive pair-potential system as the basic reference system. The paper, which is aimed at non-experts, ends by listing a number of open problems in the field.
Anomalous slowing down in the metastable liquid of hard spheres
NASA Astrophysics Data System (ADS)
Dzugutov, M.
2002-03-01
It is demonstrated that a straightforward extension of the Arrhenius law accurately describes diffusion in the thermodynamically stable liquid of hard spheres. A sharp negative deviation from this behavior is observed as the liquid is compressed beyond its stability limit. This dynamical anomaly can be compared with the nonlinear slowing down characteristic of the supercooled dynamics regime in liquids with continuous interaction. It is suggested that the observed dynamical transition is caused by long-time decomposition of the configuration space. This interpretation is corroborated by the observation of characteristic anomalies in the geometry of a particle trajectory in the metastable domain.
Hard-sphere interactions in velocity-jump models.
Franz, Benjamin; Taylor-King, Jake P; Yates, Christian; Erban, Radek
2016-07-01
Group-level behavior 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. PMID:27575098
Fifth to eleventh virial coefficients of hard spheres
NASA Astrophysics Data System (ADS)
Schultz, Andrew J.; Kofke, David A.
2014-08-01
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.
Physics of Hard Spheres Experiment: Significant and Quantitative Findings Made
NASA Technical Reports Server (NTRS)
Doherty, Michael P.
2000-01-01
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
Classical growth of hard-sphere colloidal crystals
NASA Astrophysics Data System (ADS)
Ackerson, Bruce J.; Schätzel, Klaus
1995-12-01
The classical theory of nucleation and growth of crystals is examined for concentrated suspensions of hard-sphere colloidal particles. The work of Russel is modified, extended, and evaluated, explicitly. Specifically, the Wilson-Frenkel growth law is modified to include the Gibbs-Thomson effect and is evaluated numerically. The results demonstrate that there is a critical nucleus radius below which crystal nuclei will not grow. A kinetic coefficient determines the maximum growth velocity possible. For large values of this coefficient, quenches to densities above the melting density show interface limited growth with the crystal radius increasing linearly with time. For quenches into the coexistence region the growth is diffusion limited, with the crystal radius increasing as the square root of elapsed time. Smaller values of the kinetic coefficient produce long lived transients which evidence quasi-power-law growth behavior with exponents between one half and unity. The smaller kinetic coefficients also lead to larger crystal compression. Crystal compression and nonclassical exponents have been observed in recent experiments. The theory is compared to data from small angle scattering studies of nucleation and growth in suspensions of hard colloidal spheres. The experimental nucleation rate is much larger than the theoretically predicted value as the freezing point is approached but shows better agreement near the melting point. The crystal growth with time is described reasonably well by the theory and suggests that the experiments are observing long lived transient rather than asymptotic growth behavior. (c) 1995 The American Physical Society
An accurate equation of state for fluids of linear homonuclear fused hard spheres
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1994-12-01
A model relating the equation of state of linear homonuclear fused hard sphere fluids to the equation of state of the hard sphere fluid is derived from the pressure equation. The equation of state reproduces simulation data practically within their accuracy for diatomic and linear triatomic hard molecular fluids.
The microstructures of cold dense systems as informed by hard sphere models and optimal packings
NASA Astrophysics Data System (ADS)
Hopkins, Adam Bayne
Sphere packings, or arrangements of "billiard balls" of various sizes that never overlap, are especially informative and broadly applicable models. In particular, a hard sphere model describes the important foundational case where potential energy due to attractive and repulsive forces is not present, meaning that entropy dominates the system's free energy. Sphere packings have been widely employed in chemistry, materials science, physics and biology to model a vast range of materials including concrete, rocket fuel, proteins, liquids and solid metals, to name but a few. Despite their richness and broad applicability, many questions about fundamental sphere packings remain unanswered. For example, what are the densest packings of identical three-dimensional spheres within certain defined containers? What are the densest packings of binary spheres (spheres of two different sizes) in three-dimensional Euclidean space R3 ? The answers to these two questions are important in condensed matter physics and solid-state chemistry. The former is important to the theory of nucleation in supercooled liquids and the latter in terms of studying the structure and stability of atomic and molecular alloys. The answers to both questions are useful when studying the targeted self-assembly of colloidal nanostructures. In this dissertation, putatively optimal answers to both of these questions are provided, and the applications of these findings are discussed. The methods developed to provide these answers, novel algorithms combining sequential linear and nonlinear programming techniques with targeted stochastic searches of conguration space, are also discussed. In addition, connections between the realizability of pair correlation functions and optimal sphere packings are studied, and mathematical proofs are presented concerning the characteristics of both locally and globally maximally dense structures in arbitrary dimension d. Finally, surprising and unexpected findings are
Compact Collision Kernels for Hard Sphere and Coulomb Cross Sections; Fokker-Planck Coefficients
Chang Yongbin; Shizgal, Bernie D.
2008-12-31
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.
The glass transition in binary mixtures of hard colloidal spheres
NASA Astrophysics Data System (ADS)
Williams, S. R.; van Megen, W.
2000-06-01
Particle dynamics have been measured by dynamic light scattering for mixtures of colloidal particles with hard sphere interactions. The diameter ratio (small:large) is 0.6. The optical properties of the suspended particles are such that the relative contrast of the two species is very sensitive to temperature, a feature we exploit to obtain the three partial intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or the arrest of the alpha process, on the time scale of the experiment. This is observed in the one-component suspension at the packing fraction 0.57. Introduction of the smaller particles, at fixed packing fraction, releases the alpha process, ie, the glass melts. Increasing the fraction of smaller particles speeds up the alpha process but interestingly, increases its amplitude. .
Sticky hard spheres beyond the Percus-Yevick approximation
NASA Astrophysics Data System (ADS)
Yuste, S. Bravo; Santos, A.
1993-12-01
The radial distribution function g(r) of a sticky-hard-sphere fluid is obtained by assuming a rational-function form for a function related to the Laplace transform of rg(r), compatible with the conditions of finite y(r)==g(r)ecphi(r)/kBT at c ontact point and finite isothermal compressibility. In a recent paper [S. Bravo Yuste and A. Santos, J. Stat. Phys. 72, 703 (1993)] we have shown that the simplest rational-function approximation, namely, the Padé approximant (2,3), leads to Baxter's exact solution of the Percus-Yevick equation. Here we consider the next approximation, i.e., the Padé approximant (3,4), and determine the two new parameters by imposing the values of y(r) at contact point and of the isothermal compressibility. Comparison with Monte Carlo simulation results shows a significant improvement over the Percus-Yevick approximation.
Density Fluctuations of Hard-Sphere Fluids in Narrow Confinement
NASA Astrophysics Data System (ADS)
Nygârd, Kim; Sarman, Sten; Hyltegren, Kristin; Chodankar, Shirish; Perret, Edith; Buitenhuis, Johan; van der Veen, J. Friso; Kjellander, Roland
2016-01-01
Spatial confinement induces microscopic ordering of fluids, which in turn alters many of their dynamic and thermodynamic properties. However, the isothermal compressibility has hitherto been largely overlooked in the literature, despite its obvious connection to the underlying microscopic structure and density fluctuations in confined geometries. Here, we address this issue by probing density profiles and structure factors of hard-sphere fluids in various narrow slits, using x-ray scattering from colloid-filled nanofluidic containers and integral-equation-based statistical mechanics at the level of pair distributions for inhomogeneous fluids. Most importantly, we demonstrate that density fluctuations and isothermal compressibilities in confined fluids can be obtained experimentally from the long-wavelength limit of the structure factor, providing a formally exact and experimentally accessible connection between microscopic structure and macroscopic, thermodynamic properties. Our approach will thus, for example, allow direct experimental verification of theoretically predicted enhanced density fluctuations in liquids near solvophobic interfaces.
Intrinsic nonlinearities in the mechanics of hard sphere suspensions.
Kumar, Mansi A; Ewoldt, Randy H; Zukoski, Charles F
2016-09-28
The onset of nonlinear responses in near hard sphere suspensions is characterized as a function of oscillatory frequency and strain amplitude. At low frequencies where the viscous behavior dominates, the onset of nonlinearities is driven by increases in rate of strain. At high deformation frequency, where suspension mechanics is dominated by an elastic response, the nonlinear responses occur when deformation exceeds a characteristic strain. This strain is associated with the transient confinement of particles by nearest neighbors and its volume fraction dependence is through cage parameters derived from the high frequency elastic modulus. The onset of nonlinear responses takes on a universal behavior when deformation frequency is normalized by the characteristic time governing the shift from viscous to elastic behavior indicating that this transition is associated with transient particle localization and is expected to be observed for all volume fractions where pair interactions are important. PMID:27530863
Detecting Phase Boundaries in Hard-Sphere Suspensions
NASA Technical Reports Server (NTRS)
McDowell, Mark; Rogers, Richard B.; Gray, Elizabeth
2009-01-01
A special image-data-processing technique has been developed for use in experiments that involve observation, via optical microscopes equipped with electronic cameras, of moving boundaries between the colloidal-solid and colloidal-liquid phases of colloidal suspensions of monodisperse hard spheres. During an experiment, it is necessary to adjust the position of a microscope to keep the phase boundary within view. A boundary typically moves at a speed of the order of microns per hour. Because an experiment can last days or even weeks, it is impractical to require human intervention to keep the phase boundary in view. The present image-data-processing technique yields results within a computation time short enough to enable generation of automated-microscope-positioning commands to track the moving phase boundary
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleationmore » process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.« less
Equation of state of nonadditive d-dimensional hard-sphere mixtures
NASA Astrophysics Data System (ADS)
Santos, A.; López de Haro, M.; Yuste, S. B.
2005-01-01
An equation of state for a multicomponent mixture of nonadditive hard spheres in d dimensions is proposed. It yields a rather simple density dependence and constitutes a natural extension of the equation of state for additive hard spheres proposed by us [A. Santos, S. B. Yuste, and M. López de Haro, Mol. Phys. 96, 1 (1999)]. The proposal relies on the known exact second and third virial coefficients and requires as input the compressibility factor of the one-component system. A comparison is carried out both with another recent theoretical proposal based on a similar philosophy and with the available exact results and simulation data in d=1, 2, and 3. Good general agreement with the reported values of the virial coefficients and of the compressibility factor of binary mixtures is observed, especially for high asymmetries and/or positive nonadditivities.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-01-01
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden' polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. Our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses. PMID:26412008
Local order variations in confined hard-sphere fluids
NASA Astrophysics Data System (ADS)
Nygârd, Kim; Sarman, Sten; Kjellander, Roland
2013-10-01
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.
Percolation in suspensions of hard nanoparticles: From spheres to needles
NASA Astrophysics Data System (ADS)
Schilling, Tanja; Miller, Mark A.; van der Schoot, Paul
2015-09-01
We investigate geometric percolation and scaling relations in suspensions of nanorods, covering the entire range of aspect ratios from spheres to extremely slender needles. A new version of connectedness percolation theory is introduced and tested against specialised Monte Carlo simulations. The theory accurately predicts percolation thresholds for aspect ratios of rod length to width as low as 10. The percolation threshold for rod-like particles of aspect ratios below 1000 deviates significantly from the inverse aspect ratio scaling prediction, thought to be valid in the limit of infinitely slender rods and often used as a rule of thumb for nanofibres in composite materials. Hence, most fibres that are currently used as fillers in composite materials cannot be regarded as practically infinitely slender for the purposes of percolation theory. Comparing percolation thresholds of hard rods and new benchmark results for ideal rods, we find that i) for large aspect ratios, they differ by a factor that is inversely proportional to the connectivity distance between the hard cores, and ii) they approach the slender rod limit differently.
Hard-sphere kinetic models for inert and reactive mixtures.
Polewczak, Jacek
2016-10-19
I consider stochastic variants of a simple reacting sphere (SRS) kinetic model (Xystris and Dahler 1978 J. Chem. Phys. 68 387-401, Qin and Dahler 1995 J. Chem. Phys. 103 725-50, Dahler and Qin 2003 J. Chem. Phys. 118 8396-404) for dense reacting mixtures. In contrast to the line-of-center models of chemical reactive models, in the SRS kinetic model, the microscopic reversibility (detailed balance) can be easily shown to be satisfied, and thus all mathematical aspects of the model can be fully justified. In the SRS model, the molecules behave as if they were single mass points with two internal states. Collisions may alter the internal states of the molecules, and this occurs when the kinetic energy associated with the reactive motion exceeds the activation energy. Reactive and non-reactive collision events are considered to be hard sphere-like. I consider a four component mixture A, B, A (*), B (*), in which the chemical reactions are of the type [Formula: see text], with A (*) and B (*) being distinct species from A and B. This work extends the joined works with George Stell to the kinetic models of dense inert and reactive mixtures. The idea of introducing smearing-type effect in the collisional process results in a new class of stochastic kinetic models for both inert and reactive mixtures. In this paper the important new mathematical properties of such systems of kinetic equations are proven. The new results for stochastic revised Enskog system for inert mixtures are also provided. PMID:27545341
Hard-sphere kinetic models for inert and reactive mixtures
NASA Astrophysics Data System (ADS)
Polewczak, Jacek
2016-10-01
I consider stochastic variants of a simple reacting sphere (SRS) kinetic model (Xystris and Dahler 1978 J. Chem. Phys. 68 387-401, Qin and Dahler 1995 J. Chem. Phys. 103 725-50, Dahler and Qin 2003 J. Chem. Phys. 118 8396-404) for dense reacting mixtures. In contrast to the line-of-center models of chemical reactive models, in the SRS kinetic model, the microscopic reversibility (detailed balance) can be easily shown to be satisfied, and thus all mathematical aspects of the model can be fully justified. In the SRS model, the molecules behave as if they were single mass points with two internal states. Collisions may alter the internal states of the molecules, and this occurs when the kinetic energy associated with the reactive motion exceeds the activation energy. Reactive and non-reactive collision events are considered to be hard sphere-like. I consider a four component mixture A, B, A *, B *, in which the chemical reactions are of the type A+B\\rightleftharpoons {{A}\\ast}+{{B}\\ast} , with A * and B * being distinct species from A and B. This work extends the joined works with George Stell to the kinetic models of dense inert and reactive mixtures. The idea of introducing smearing-type effect in the collisional process results in a new class of stochastic kinetic models for both inert and reactive mixtures. In this paper the important new mathematical properties of such systems of kinetic equations are proven. The new results for stochastic revised Enskog system for inert mixtures are also provided.
Hard-sphere kinetic models for inert and reactive mixtures.
Polewczak, Jacek
2016-10-19
I consider stochastic variants of a simple reacting sphere (SRS) kinetic model (Xystris and Dahler 1978 J. Chem. Phys. 68 387-401, Qin and Dahler 1995 J. Chem. Phys. 103 725-50, Dahler and Qin 2003 J. Chem. Phys. 118 8396-404) for dense reacting mixtures. In contrast to the line-of-center models of chemical reactive models, in the SRS kinetic model, the microscopic reversibility (detailed balance) can be easily shown to be satisfied, and thus all mathematical aspects of the model can be fully justified. In the SRS model, the molecules behave as if they were single mass points with two internal states. Collisions may alter the internal states of the molecules, and this occurs when the kinetic energy associated with the reactive motion exceeds the activation energy. Reactive and non-reactive collision events are considered to be hard sphere-like. I consider a four component mixture A, B, A (*), B (*), in which the chemical reactions are of the type [Formula: see text], with A (*) and B (*) being distinct species from A and B. This work extends the joined works with George Stell to the kinetic models of dense inert and reactive mixtures. The idea of introducing smearing-type effect in the collisional process results in a new class of stochastic kinetic models for both inert and reactive mixtures. In this paper the important new mathematical properties of such systems of kinetic equations are proven. The new results for stochastic revised Enskog system for inert mixtures are also provided.
Depletion effects in smectic phases of hard-rod-hard-sphere mixtures.
Martínez-Ratón, Y; Cinacchi, G; Velasco, E; Mederos, L
2006-10-01
It is known that when hard spheres are added to a pure system of hard rods the stability of the smectic phase may be greatly enhanced, and that this effect can be rationalised in terms of depletion forces. In the present paper we first study the effect of orientational order on depletion forces in this particular binary system, comparing our results with those obtained adopting the usual approximation of considering the rods parallel and their orientations frozen. We consider mixtures with rods of different aspect ratios and spheres of different diameters, and we treat them within Onsager theory. Our results indicate that depletion effects, and consequently smectic stability, decrease significantly as a result of orientational disorder in the smectic phase when compared with corresponding data based on the frozen-orientation approximation. These results are discussed in terms of the tau parameter, which has been proposed as a convenient measure of depletion strength. We present closed expressions for tau, and show that it is intimately connected with the depletion potential. We then analyse the effect of particle geometry by comparing results pertaining to systems of parallel rods of different shapes (spherocylinders, cylinders and parallelepipeds). We finally provide results based on the Zwanzig approximation of a fundamental-measure density-functional theory applied to mixtures of parallelepipeds and cubes of different sizes. In this case, we show that the tau parameter exhibits a linear asymptotic behaviour in the limit of large values of the hard-rod aspect ratio, in conformity with Onsager theory, as well as in the limit of large values of the ratio of rod breadth to cube side length, d, in contrast to Onsager approximation, which predicts tau approximately d (3). Based on both this result and the Percus-Yevick approximation for the direct correlation function for a hard-sphere binary mixture in the same limit of infinite asymmetry, we speculate that, for
Avalanches mediate crystallization in a hard-sphere glass.
Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, Wilson C K; Cates, Michael E; Pusey, Peter N
2014-01-01
By molecular-dynamics simulations, we have studied the devitrification (or crystallization) of aged hard-sphere glasses. First, we find that the dynamics of the particles are intermittent: Quiescent periods, when the particles simply "rattle" in their nearest-neighbor cages, are interrupted by abrupt "avalanches," where a subset of particles undergo large rearrangements. Second, we find that crystallization is associated with these avalanches but that the connection is not straightforward. The amount of crystal in the system increases during an avalanche, but most of the particles that become crystalline are different from those involved in the avalanche. Third, the occurrence of the avalanches is a largely stochastic process. Randomizing the velocities of the particles at any time during the simulation leads to a different subsequent series of avalanches. The spatial distribution of avalanching particles appears random, although correlations are found among avalanche initiation events. By contrast, we find that crystallization tends to take place in regions that already show incipient local order.
Edison, John R; Dasgupta, Tonnishtha; Dijkstra, Marjolein
2016-08-01
We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures. PMID:27497577
NASA Astrophysics Data System (ADS)
Edison, John R.; Dasgupta, Tonnishtha; Dijkstra, Marjolein
2016-08-01
We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.
Solubilities of Solutes in Ionic Liquids from a SimplePerturbed-Hard-Sphere Theory
Qin, Yuan; Prausnitz, John M.
2005-09-20
In recent years, several publications have provided solubilities of ordinary gases and liquids in ionic liquids. This work reports an initial attempt to correlate the experimental data using a perturbed-hard-sphere theory; the perturbation is based on well-known molecular physics when the solution is considered as a dielectric continuum. For this correlation, the most important input parameters are hard-sphere diameters of the solute and of the cation and anion that constitute the ionic liquid. In addition, the correlation uses the solvent density and the solute's polarizability and dipole and quadrupole moments, if any. Dispersion-energy parameters are obtained from global correlation of solubility data. Results are given for twenty solutes in several ionic liquids at normal temperatures; in addition, some results are given for gases in two molten salts at very high temperatures. Because the theory used here is much simplified, and because experimental uncertainties (especially for gaseous solutes) are often large, the accuracy of the correlation presented here is not high; in general, predicted solubilities (Henry's constants) agree with experiment to within roughly {+-} 70%. As more reliable experimental data become available, modifications in the characterizing parameters are likely to improve accuracy. Nevertheless, even in its present form, the correlation may be useful for solvent screening in engineering design.
Tunable long range forces mediated by self-propelled colloidal hard spheres.
Ni, Ran; Cohen Stuart, Martien A; Bolhuis, Peter G
2015-01-01
Using Brownian dynamics simulations, we systematically study the effective interaction between two parallel hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres, and we find that the effective force between two hard walls can be tuned from a long range repulsion into a long range attraction by changing the density of active particles. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter. PMID:25615510
Tunable Long Range Forces Mediated by Self-Propelled Colloidal Hard Spheres
NASA Astrophysics Data System (ADS)
Ni, Ran; Cohen Stuart, Martien A.; Bolhuis, Peter G.
2015-01-01
Using Brownian dynamics simulations, we systematically study the effective interaction between two parallel hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres, and we find that the effective force between two hard walls can be tuned from a long range repulsion into a long range attraction by changing the density of active particles. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.
Stochastic Hard-Sphere Dynamics for Hydrodynamics of Non-Ideal Fluids
Donev, A; Alder, B J; Garcia, A L
2008-02-26
A novel stochastic fluid model is proposed with a nonideal structure factor consistent with compressibility, and adjustable transport coefficients. This stochastic hard-sphere dynamics (SHSD) algorithm is a modification of the direct simulation Monte Carlo algorithm and has several computational advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD results in an equation of state and a pair correlation function identical to that of a deterministic Hamiltonian system of penetrable spheres interacting with linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD fluid is verified for the Brownian motion of a nanoparticle suspended in a compressible solvent.
Diffusion and structure of a quasi-one-dimensional hard-sphere fluid
NASA Astrophysics Data System (ADS)
Lin, Binhua; Lee, Ji Hwan; Cui, Bianxiao
2001-03-01
We report the results of an experimental study of a quasi-one-dimensional hard-sphere fluid. The system consists of uncharged Si colloidal spheres confined in long, uncorrelated 1D-channels whose narrow width forbids mutual passage of spheres along the channel. By tracking the trajectories of the spheres using digital video microscopy, we studied the diffusion and structure of the system as a function of the density of the fluid. Our results show that the behavior of the spheres in self-diffusion is changed gradually from Fickian to non-Fickian near the onset of the collision between the spheres, indicating the correlation between the collision of the hard-spheres and the change in diffusion mechanism. At high density, the self-part of the van Hove function of the system is no longer a Gaussian distribution but a Poisson distribution which can be interpreted using a hydrodynamic analysis for effective wall-drag effect. The pair distribution function of the system can be explained by an analytical expression for a 1D hard-sphere fluid [1]. [1] Y. Rosenfeld, M. Schmidt, H. Lowen and P. Tarazona, Phys. Rev. E 55, 4245 (1997).
The influence of third-order interactions on the density profile of associating hard spheres
NASA Astrophysics Data System (ADS)
Henderson, D.; Sokolowski, S.; Zagorski, R.; Trokhymchuk, A.
Canonical ensemble Monte Carlo simulations and the non-uniform Percus-Yevick (NPY) equation for the local density are used to study the influence of surface mediated thirdorder interactions on the adsorption of associating hard spheres on a hard wall. A comparison of the NPY density profiles with the computer simulations data indicates that this approximation predicts the fluid structure reasonably well.
Communication: Dynamical density functional theory for dense suspensions of colloidal hard spheres.
Stopper, Daniel; Roth, Roland; Hansen-Goos, Hendrik
2015-11-14
We study structural relaxation of colloidal hard spheres undergoing Brownian motion using dynamical density functional theory. Contrary to the partial linearization route [D. Stopper et al., Phys. Rev. E 92, 022151 (2015)] which amounts to using different free energy functionals for the self and distinct part of the van Hove function G(r, t), we put forward a unified description employing a single functional for both components. To this end, interactions within the self part are removed via the zero-dimensional limit of the functional with a quenched self component. In addition, we make use of a theoretical result for the long-time mobility in hard-sphere suspensions, which we adapt to the inhomogeneous fluid. Our results for G(r, t) are in excellent agreement with numerical simulations even in the dense liquid phase. In particular, our theory accurately yields the crossover from free diffusion at short times to the slower long-time diffusion in a crowded environment.
Free Energy Calculations of Crystalline Hard Sphere Complexes Using Density Functional Theory
Gunawardana, K. G.S.H.; Song, Xueyu
2014-12-22
Recently developed fundamental measure density functional theory (FMT) is used to study binary hard sphere (HS) complexes in crystalline phases. By comparing the excess free energy, pressure and phase diagram, we show that the fundamental measure functional yields good agreements to the available simulation results of AB, AB_{2} and AB_{13} crystals. Additionally, we use this functional to study the HS models of five binary crystals, Cu_{5}Zr(C15_{b}), Cu_{51}Zr_{14}(β), Cu_{10}Zr_{7}(φ), CuZr(B2) and CuZr_{2} (C11_{b}), which are observed in the Cu-Zr system. The FMT functional gives well behaved minimum for most of the hard sphere crystal complexes in the two dimensional Gaussian space, namely a crystalline phase. However, the current version of FMT functional (white Bear) fails to give a stable minimum for the structure Cu_{10}Zr_{7}(φ). We argue that the observed solid phases for the HS models of the Cu-Zr system are true thermodynamic stable phases and can be used as a reference system in perturbation calculations.
Sedov, I A; Magsumov, T I
2015-07-16
Thermodynamic solvation properties of mixtures of water with tetrahydrofuran at 298 K are studied. The Gibbs free energies and enthalpies of solvation of n-octane and toluene are determined experimentally. For molecular dynamics simulations of the binary solvent, we have modified a TraPPE-UA model for tetrahydrofuran and combined it with the SPC/E potential for water. The excess thermodynamic functions of neon, xenon, and hard spheres with two different radii are calculated using the particle insertion method. Simulated and real systems share the same characteristic trends for the thermodynamic functions. A maximum is present on dependencies of the enthalpy of solvation from the composition of solvent at 70-90 mol % water, making it higher than in both of the cosolvents. It is caused by a high enthalpy of cavity formation in the mixtures rich with water due to solvent reorganization around the cavity, which is shown by calculation of the enthalpy of solvation of hard spheres. Addition of relatively small amounts of tetrahydrofuran to water effectively suppresses the hydrophobic effect, leading to a quick increase of both the entropy and enthalpy of cavity formation and solvation of low polar molecules. PMID:26115405
Free Energy Calculations of Crystalline Hard Sphere Complexes Using Density Functional Theory
Gunawardana, K. G.S.H.; Song, Xueyu
2014-12-22
Recently developed fundamental measure density functional theory (FMT) is used to study binary hard sphere (HS) complexes in crystalline phases. By comparing the excess free energy, pressure and phase diagram, we show that the fundamental measure functional yields good agreements to the available simulation results of AB, AB2 and AB13 crystals. Additionally, we use this functional to study the HS models of five binary crystals, Cu5Zr(C15b), Cu51Zr14(β), Cu10Zr7(φ), CuZr(B2) and CuZr2 (C11b), which are observed in the Cu-Zr system. The FMT functional gives well behaved minimum for most of the hard sphere crystal complexes in the two dimensional Gaussian space,more » namely a crystalline phase. However, the current version of FMT functional (white Bear) fails to give a stable minimum for the structure Cu10Zr7(φ). We argue that the observed solid phases for the HS models of the Cu-Zr system are true thermodynamic stable phases and can be used as a reference system in perturbation calculations.« less
Solano-Altamirano, J M; Goldman, Saul
2015-12-01
We determined the total system elastic Helmholtz free energy, under the constraints of constant temperature and volume, for systems comprised of one or more perfectly bonded hard spherical inclusions (i.e. "hard spheres") embedded in a finite spherical elastic solid. Dirichlet boundary conditions were applied both at the surface(s) of the hard spheres, and at the outer surface of the elastic solid. The boundary conditions at the surface of the spheres were used to describe the rigid displacements of the spheres, relative to their initial location(s) in the unstressed initial state. These displacements, together with the initial positions, provided the final shape of the strained elastic solid. The boundary conditions at the outer surface of the elastic medium were used to ensure constancy of the system volume. We determined the strain and stress tensors numerically, using a method that combines the Neuber-Papkovich spherical harmonic decomposition, the Schwartz alternating method, and Least-squares for determining the spherical harmonic expansion coefficients. The total system elastic Helmholtz free energy was determined by numerically integrating the elastic Helmholtz free energy density over the volume of the elastic solid, either by a quadrature, or a Monte Carlo method, or both. Depending on the initial position of the hard sphere(s) (or equivalently, the shape of the un-deformed stress-free elastic solid), and the displacements, either stationary or non-stationary Helmholtz free energy minima were found. The non-stationary minima, which involved the hard spheres nearly in contact with one another, corresponded to lower Helmholtz free energies, than did the stationary minima, for which the hard spheres were further away from one another. PMID:26701708
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1993-07-01
Equations of state for hard-disk and hard-sphere fluids are obtained from a generalization of the Carnahan-Starling method of direct summation of the virial series. The equations of state thus obtained, besides reproducing all known virial coefficients, agree very accurately with simulation data for stable fluids. If appropriate values for the sixth and seventh virial coefficients are chosen within their uncertainty, the equations of state predict that the fluids become unstable at Kauzmann's density.
Equation of state for hard convex body fluids from the equation of state of the hard sphere fluid
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1994-02-01
A simple and accurate equation of state for fluids of hard convex molecules is derived from the pressure equation and the equation of state of the hard sphere fluid. The equation of state provides theoretical support to some equations of state used in perturbation theories for real molecular liquids. The equation of state reproduces the simulation data with an accuracy comparable to that derived from density functional theory.
Avalanche mediated devitrification in a glass of pseudo hard-spheres
NASA Astrophysics Data System (ADS)
Rosales-Pelaez, P.; Montero de Hijes, P.; Sanz, E.; Valeriani, C.
2016-09-01
By means of molecular dynamics we analyse several aspects of the avalanche-mediated mechanism for glass crystallization recently reported for hard sphere glasses (Sanz et al 2014 Proc. Natl Acad. Sci. 111 75). To investigate the role of inter-particle interaction softness on the devitrification path we use a continuous version of the hard-sphere potential: the pseudo-hard sphere potential (Jover et al 2012 J. Chem. Phys. 137 144505). We observe the same crystallization mechanism as in hard spheres. However, pseudo-hard sphere glasses crystallise earlier for a given density because the development of avalanches is eased by the small degree of overlapping allowed. We analyse the impact of density on the devitrification mechanism. When increasing the density, the avalanche mechanism becomes more evident and crystallisation is retarded due to a decrease of the avalanche emergence likelihood. To conclude, the observed avalanche-mediated mechanism and its density dependence do not substantially change with the employed simulation ensemble (constant volume versus constant pressure).
Density Functional Approximation for Non-Hard Sphere Fluids Subjected to External Fields
NASA Astrophysics Data System (ADS)
Zhou, Shiqi
A theoretical way is proposed, by which any hard sphere density functional approximation (DFA) can be applied to non-hard sphere fluids for the calculation of density profile in the framework of density functional theory (DFT). Used as examples, the present formalism is combined respectively with two recently proposed hard sphere DFAs to predict the density profile of Lennard-Jones (LJ) fluid, hard core square well (SW) fluid and penetrable potenial fluid subjected to diverse external fields. Extensive comparison between theoretical predictions and corresponding simulation results shows that the present theoretical way, when combined with an accurate hard sphere DFA, can perform well for calculating the density profile of the non-uniform fluids of the above mentioned potentials. Concretely speaking, for LJ and hard core SW fluid, even a less accurate FEDFA is sufficient, while for extreme potential such as the penetrable potenial, a more accurate adjustable parameter free version of LTDFA is needed to combine with the present theoretical way to predict density profile satisfactorily. The advantage of the proposed theoretical way is that the resultant DFA is applicable to both subcritical and supercritical temperature cases, thereby overcoming the disadvantages of previous two categories of DFT approach.
Depletion force in the infinite-dilution limit in a solvent of nonadditive hard spheres.
Fantoni, Riccardo; Santos, Andrés
2014-06-28
The mutual entropic depletion force felt by two solute "big" hard spheres immersed in a binary mixture solvent of nonadditive "small" hard spheres is calculated as a function of the surface-to-surface distance by means of canonical Monte Carlo simulations and through a recently proposed rational-function approximation [R. Fantoni and A. Santos, Phys. Rev. E 84, 041201 (2011)]. Four representative scenarios are investigated: symmetric solute particles and the limit where one of the two solute spheres becomes a planar hard wall, in both cases with symmetric and asymmetric solvents. In all cases, the influence on the depletion force due to the nonadditivity in the solvent is determined in the mixed state. Comparison between results from the theoretical approximation and from the simulation shows a good agreement for surface-to-surface distances greater than the smallest solvent diameter.
Apparent wall slip in non-Brownian hard-sphere suspensions.
Korhonen, Marko; Mohtaschemi, Mikael; Puisto, Antti; Illa, Xavier; Alava, Mikko J
2015-05-01
We analyze apparent wall slip, the reduction of particle concentration near the wall, in hard-sphere suspensions at concentrations well below the jamming limit utilizing a continuum level diffusion model. The approach extends a constitutive equation proposed earlier with two additional potentials describing the effects of gravitation and wall-particle repulsion. We find that although both mechanisms are shear independent by nature, due to the shear-rate-dependent counter-balancing particle migration fluxes, the resulting net effect is non-linearly shear dependent, causing larger slip at small shear rates. In effect, this shows up in the classically measured flow curves as a mild shear thickening regime at the transition from small to intermediate shear rates. PMID:25998170
Stochastic interactions of two Brownian hard spheres in the presence of depletants
Karzar-Jeddi, Mehdi; Fan, Tai-Hsi; Tuinier, Remco; Taniguchi, Takashi
2014-06-07
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 uniform polymer solution cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shift 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.
Stochastic interactions of two Brownian hard spheres in the presence of depletants.
Karzar-Jeddi, Mehdi; Tuinier, Remco; Taniguchi, Takashi; Fan, Tai-Hsi
2014-06-01
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 uniform polymer solution cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shift 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. PMID:24908040
Entropic forces and phase separation in binary nearly hard-sphere colloids
NASA Astrophysics Data System (ADS)
Dinsmore, Anthony Duprat
We present the results of experimental and theoretical studies of the statistical mechanics of suspensions of hard spheres of two different sizes. We have focused on the effects of entropic depletion (or excluded-volume) effects, which play an important role in many real mixtures. In the first set of experiments, we studied the phase behavior of binary hard-sphere mixtures with diameter ratios between 2 and 12. We found that even when the volume fraction of spheres was only 0.20, separation into coexisting fluid and solid phases occurred despite the absence of attractive pair interactions. We measured the structures and compositions of the equilibrium phases both in the bulk of the sample and at the wall of the container. We also propose an original, physically- transparent model that predicts fluid-solid phase separation in hard-sphere mixtures without fit parameters, in close agreement with our measurements and with previously-published results for monodisperse hard- sphere mixtures. Investigating the effects of hard (inert) surfaces, we demonstrated for the first time that inert walls of complex shape can induce entropic force fields that can trap, repel, or induce drift of the larger particles in a binary suspension. We measured the entropic force on a large sphere as a function of its position near the edge of a terrace and found that it is repelled by a 40-femto- Newton force. A similar mechanism confined large spheres in a corner and, inside rigid phospholipid vesicles, pushed the larger spheres along the wall in the direction of increasing curvature. We predict that, under some circumstances, a unilamellar vesicle will spontaneously envelop a large sphere. Aside from their fundamental interest, these results are likely to improve our understanding of the behavior of complex fluids inside porous media and of proteins inside cells. We have also developed new techniques for making arrays of submicron particles for photonic applications. Two- dimensional
Brandani, V.; Prausnitz, J. M.
1982-01-01
This paper is the second of three describing a two-fluid theory of binary liquid mixtures. The general theory presented in the preceding paper is used to derive a model for calculating thermodynamic properties of hard-sphere mixtures. Calculations indicate that desirable boundary conditions are satisfied. PMID:16593220
Note: equation of state and the freezing point in the hard-sphere model.
Robles, Miguel; López de Haro, Mariano; Santos, Andrés
2014-04-01
The merits of different analytical equations of state for the hard-sphere system with respect to the recently computed high-accuracy value of the freezing-point packing fraction are assessed. It is found that the Carnahan-Starling-Kolafa and the branch-point approximant equations of state yield the best performance.
Radial distribution function for hard spheres in fractal dimensions: A heuristic approximation
NASA Astrophysics Data System (ADS)
Santos, Andrés; de Haro, Mariano López
2016-06-01
Analytic approximations for the radial distribution function, the structure factor, and the equation of state of hard-core fluids in fractal dimension d (1 ≤d ≤3 ) are developed as heuristic interpolations from the knowledge of the exact and Percus-Yevick results for the hard-rod and hard-sphere fluids, respectively. In order to assess their value, such approximate results are compared with those of recent Monte Carlo simulations and numerical solutions of the Percus-Yevick equation for a fractal dimension [M. Heinen et al., Phys. Rev. Lett. 115, 097801 (2015), 10.1103/PhysRevLett.115.097801], a good agreement being observed.
Comparison of structure and transport properties of concentrated hard and soft sphere fluids.
Lange, Erik; Caballero, Jose B; Puertas, Antonio M; Fuchs, Matthias
2009-05-01
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.
Using compressibility factor as a predictor of confined hard-sphere fluid dynamics
Mittal, Jeetain
2009-01-01
We study the correlations between the diffusivity (or viscosity) and the compressibility factor of bulk hard-sphere fluid as predicted by the ultralocal limit of the barrier hopping theory. Our specific aim is to determine if these correlations observed in the bulk equilibrium hard-sphere fluid can be used to predict the self-diffusivity of fluid confined between a slit-pore or a rectangular channel. In this work, we consider a single-component and a binary mixture of hard spheres. To represent confining walls, we use purely reflecting hard walls and interacting square-well walls. Our results clearly show that the correspondence between the diffusivity and the compressibility factor can be used along with the knowledge of the confined fluid's compressibility factor to predict its diffusivity with quantitative accuracy. Our analysis also suggests that a simple measure, the average fluid density, can be an accurate predictor of confined fluid diffusivity for very tight confinements (≈ 2-3 particle diameters wide) at low to intermediate density conditions. Together, these results provide further support for the idea that one can use robust connections between thermodynamic and dynamic quantities to predict dynamics of confined fluids from their thermodynamics. PMID:19702285
Tunable long range forces mediated by self-propelled colloidal hard spheres
NASA Astrophysics Data System (ADS)
Ni, Ran; Cohen Stuart, Martien; Bolhuis, Peter
2015-03-01
Most colloidal interactions can be tuned by changing properties of the medium. Here we show that activating colloidal particles with random self-propulsion can induce giant effective interactions between large objects immersed in such a suspension. Using Brownian dynamics simulations we find that the effective force between two hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres can be tuned from a long range repulsion into a long range attraction by changing the active particle density. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.
Lurio, L. B.; Lumma, D.; Sandy, A. R.; Borthwick, M. A.; Falus, P.; Mochrie, S. G. J.; Pelletier, J. F.; Sutton, M.; Regan, Lynne; Malik, A.
2000-01-24
X-ray photon correlation spectroscopy and small-angle scattering measurements are presented of the dynamics and structure of concentrated suspensions of charge-stabilized polystyrene latex spheres dispersed in glycerol, for volume fractions from 3% to 52% . The static structures of the suspensions show essentially hard-sphere behavior, and the short-time dynamics shows good agreement with predictions for the wave-vector-dependent collective diffusion coefficient. 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)]. (c) 2000 The American Physical Society.
Contact pair correlation functions and equation of state for additive hard disk fluid mixtures
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2001-10-01
The contact pair correlation functions and the equation of state for a binary mixture of additive hard disks is obtained using a procedure similar to that leading to the Boublı´k-Mansoori-Carnahan-Starling-Leland equation of state for mixtures of additive hard spheres. The results from the derived equations are tested against new Monte Carlo data obtained for several diameter ratios and mole fractions. The overall agreement is excellent. The equation of state reproduces exactly the second virial coefficient of the mixture and the third with great accuracy. Predicted values of the fourth and fifth virial coefficients are also in very good agreement with numerical data.
NASA Astrophysics Data System (ADS)
Ashton, Douglas J.; Wilding, Nigel B.; Roth, Roland; Evans, Robert
2011-12-01
We report a detailed study, using state-of-the-art simulation and theoretical methods, of the effective (depletion) potential between a pair of big hard spheres immersed in a reservoir of much smaller hard spheres, the size disparity being measured by the ratio of diameters q≡σs/σb. Small particles are treated grand canonically, their influence being parameterized in terms of their packing fraction in the reservoir ηsr. Two Monte Carlo simulation schemes—the geometrical cluster algorithm, and staged particle insertion—are deployed to obtain accurate depletion potentials for a number of combinations of q⩽0.1 and ηsr. After applying corrections for simulation finite-size effects, the depletion potentials are compared with the prediction of new density functional theory (DFT) calculations based on the insertion trick using the Rosenfeld functional and several subsequent modifications. While agreement between the DFT and simulation is generally good, significant discrepancies are evident at the largest reservoir packing fraction accessible to our simulation methods, namely, ηsr=0.35. These discrepancies are, however, small compared to those between simulation and the much poorer predictions of the Derjaguin approximation at this ηsr. The recently proposed morphometric approximation performs better than Derjaguin but is somewhat poorer than DFT for the size ratios and small-sphere packing fractions that we consider. The effective potentials from simulation, DFT, and the morphometric approximation were used to compute the second virial coefficient B2 as a function of ηsr. Comparison of the results enables an assessment of the extent to which DFT can be expected to correctly predict the propensity toward fluid-fluid phase separation in additive binary hard-sphere mixtures with q⩽0.1. In all, the new simulation results provide a fully quantitative benchmark for assessing the relative accuracy of theoretical approaches for calculating depletion potentials
Thorneywork, Alice L; Roth, Roland; Aarts, Dirk G A L; Dullens, Roel P A
2014-04-28
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
Physics of Hard Spheres Experiment (PhaSE) or "Making Jello in Space"
NASA Technical Reports Server (NTRS)
Ling, Jerri S.; Doherty, Michael P.
1998-01-01
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
Pizio; Trokhymchuk; Henderson; Labik
1997-07-01
A model of hard spheres adsorbed in disordered porous media is studied using the associative replica Ornstein-Zernike (ROZ) equations. Extending previous studies of adsorption in a hard sphere matrices, we investigate a polymerized matrix. We consider an associating fluid of hard spheres with two intracore attractive sites per particle; consequently chains consisting of overlapping hard spheres can be formed due to the chemical association. This is the generalization of the model with sites on the surface of Wertheim that has been studied in the bulk by Chang and Sandler. The matrix structure is obtained in the polymer Percus-Yevick approximation. We solve the ROZ equations in the associative hypernetted chain approximation. The pair distribution functions, the fluid compressibility, the equation of state and chemical potential of the adsorbed fluid are obtained and discussed. It is shown that the adsorption of a hard sphere fluid in a matrix at given density, but consisting of longer chains of overlapping hard spheres, is higher than the adsorption of this fluid in a hard sphere matrix.
The Dynamics of Disorder-Order Transition in Hard Sphere Colloidal Dispersions
NASA Technical Reports Server (NTRS)
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
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.
On the radial distribution function of a hard-sphere fluid
NASA Astrophysics Data System (ADS)
López de Haro, M.; Santos, A.; Yuste, S. B.
2006-06-01
Two related approaches, one fairly recent [A. Trokhymchuk et al., J. Chem. Phys.123, 024501 (2005)] and the other one introduced 15years ago [S. B. Yuste and A. Santos, Phys. Rev. A43, 5418 (1991)], for the derivation of analytical forms of the radial distribution function of a fluid of hard spheres are compared. While they share similar starting philosophy, the first one involves the determination of 11 parameters while the second is a simple extension of the solution of the Percus-Yevick equation. It is found that the second approach has a better global accuracy and the further asset of counting already with a successful generalization to mixtures of hard spheres and other related systems.
Chemical-potential route: a hidden Percus-Yevick equation of state for hard spheres.
Santos, Andrés
2012-09-21
The chemical potential of a hard-sphere fluid can be expressed in terms of the contact value of the radial distribution function of a solute particle with a diameter varying from zero to that of the solvent particles. Exploiting the explicit knowledge of such a contact value within the Percus-Yevick theory, and using standard thermodynamic relations, a hitherto unknown Percus-Yevick equation of state, p/ρk(B)T = -(9/η) ln(1-η)-(16-31η)/2(1-η)(2), is unveiled. This equation of state turns out to be better than the one obtained from the conventional virial route. Interpolations between the chemical-potential and compressibility routes are shown to be more accurate than the widely used Carnahan-Starling equation of state. The extension to polydisperse hard-sphere systems is also presented.
Model energy landscapes of low-temperature fluids: Dipolar hard spheres.
Matyushov, Dmitry V
2007-07-01
An analytical model of non-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid of dipolar hard spheres. The entire excitation profile of the liquid, from the high-temperature liquid to the point of ideal-glass transition, has been obtained from Monte Carlo simulations. The fluid of dipolar hard spheres loses stability close to the point of ideal-glass transition transforming via a first-order transition into a columnar liquid phase of dipolar chains locally arranged in a body-centered-tetragonal order. Significant non-Gaussianity of the energy landscape is responsible for narrowing of the distribution of potential energies and energies of inherent structures with decreasing temperature. We suggest that the proposed functionality of the enumeration function is widely applicable to both polar and nonpolar low-temperature liquids.
Newman, Hugh D.; Yethiraj, Anand
2015-01-01
In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, via confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes. PMID:26323363
Parallelized event chain algorithm for dense hard sphere and polymer systems
Kampmann, Tobias A. Boltz, Horst-Holger; Kierfeld, Jan
2015-01-15
We combine parallelization and cluster Monte Carlo for hard sphere systems and present a parallelized event chain algorithm for the hard disk system in two dimensions. For parallelization we use a spatial partitioning approach into simulation cells. We find that it is crucial for correctness to ensure detailed balance on the level of Monte Carlo sweeps by drawing the starting sphere of event chains within each simulation cell with replacement. We analyze the performance gains for the parallelized event chain and find a criterion for an optimal degree of parallelization. Because of the cluster nature of event chain moves massive parallelization will not be optimal. Finally, we discuss first applications of the event chain algorithm to dense polymer systems, i.e., bundle-forming solutions of attractive semiflexible polymers.
Energy and structure of dilute hard- and soft-sphere gases
Mazzanti, F.; Polls, A.; Fabrocini, A.
2003-06-01
The energy and structure of dilute hard- and soft-sphere Bose gases are systematically studied in the framework of several many-body approaches, such as the variational correlated theory, the Bogoliubov model, and the uniform limit approximation, valid in the weak-interaction regime. When possible, the results are compared with the exact diffusion Monte Carlo ones. Jastrow-type correlation provides a good description of the systems, both hard- and soft-spheres, if the hypernetted chain energy functional is freely minimized and the resulting Euler equation is solved. The study of the soft-sphere potentials confirms the appearance of a dependence of the energy on the shape of the potential at gas paremeter values of x{approx}0.001. For quantities other than the energy, such as the radial distribution functions and the momentum distributions, the dependence appears at any value of x. The occurrence of a maximum in the radial distribution function, in the momentum distribution, and in the excitation spectrum is a natural effect of the correlations when x increases. The asymptotic behaviors of the functions characterizing the structure of the systems are also investigated. The uniform limit approach is very easy to implement and provides a good description of the soft-sphere gas. Its reliability improves when the interaction weakens.
New closed virial equation of state for hard-sphere fluids.
Tian, Jianxiang; Gui, Yuanxing; Mulero, Angel
2010-10-28
A new closed virial equation of state of hard-sphere fluids is proposed which reproduces the calculated or estimated values of the first 16 virial coefficients and at the same time gives very good accuracy when compared with computer simulation data for the compressibility factor over the entire fluid range, as well as having a pole at the correct closest packing density. PMID:20883000
NASA Astrophysics Data System (ADS)
van Megen, W.
2006-01-01
Mean-squared displacements (MSDs) of colloidal fluids of hard spheres are analyzed in terms of a random walk, an analysis which assumes that the process of structural relaxation among the particles can be described in terms of thermally driven memoryless encounters. For the colloidal fluid in thermodynamic equilibrium the magnitude of the stretching of the MSD is able to be reconciled by a bias in the walk. This description fails for the under-cooled colloidal fluid.
NASA Astrophysics Data System (ADS)
Henderson, D.; Plischke, M.
1987-04-01
Starting from well-known relations for the derivatives of the radial distribution functions of a mixture of fluids, and allowing the diameter of one particle to become exceedingly large, three sum rules for a fluid with density inhomogeneities are obtained. None of these sum rules are new. However, the relation between the Lovett-Mou-Buff-Wertheim and the Born-Green hierarchy of equations seems not well known. The accuracy of a recent parametrization of the pair correlation of hard spheres near a hard wall and of the solutions of the Percus-Yevick and hypernetted-chain equation for this same function are examined by determination of how well these functions satisfy these sum rules and the accuracy of their surface tension, calculated from the sum rule of Triezenberg and Zwanzig. Generally speaking, the Percus-Yevick theory gives the best results and the hypernetted-chain approximation gives the worst results with the parametrization being intermediate.
Simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres.
Santos, Andrés; Yuste, Santos B; López de Haro, Mariano; Odriozola, Gerardo; Ogarko, Vitaliy
2014-04-01
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 ϕJ 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 ϕJ 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.
Simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres
NASA Astrophysics Data System (ADS)
Santos, Andrés; Yuste, Santos B.; López de Haro, Mariano; Odriozola, Gerardo; Ogarko, Vitaliy
2014-04-01
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 ϕJ 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 ϕJ 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.
Thermodynamics of dipolar hard spheres with low-to-intermediate coupling constants.
Elfimova, Ekaterina A; Ivanov, Alexey O; Camp, Philip J
2012-08-01
The thermodynamic properties of the dipolar hard-sphere fluid are studied using theory and simulation. A new theory is derived using a convenient mathematical approximation for the Helmholtz free energy relative to that for the hard-sphere fluid. The approximation is designed to give the correct low-density virial expansion. New theoretical and numerical results for the fourth virial coefficient are given. Predictions of thermodynamic functions for dipolar coupling constants λ=1 and 2 show excellent agreement with simulation results, even at the highest value of the particle volume fraction φ. For higher values of λ, there are deviations at high volume fractions, but the correct low-density behavior is retained. The theory is compared critically against the established thermodynamic perturbation theory; it gives significant improvements at low densities and is more convenient in terms of the required numerics. Dipolar hard spheres provide a basic model for ferrofluids, and the theory is accurate for typical experimental parameters λ
Radial distribution function for hard spheres in fractal dimensions: A heuristic approximation.
Santos, Andrés; de Haro, Mariano López
2016-06-01
Analytic approximations for the radial distribution function, the structure factor, and the equation of state of hard-core fluids in fractal dimension d (1≤d≤3) are developed as heuristic interpolations from the knowledge of the exact and Percus-Yevick results for the hard-rod and hard-sphere fluids, respectively. In order to assess their value, such approximate results are compared with those of recent Monte Carlo simulations and numerical solutions of the Percus-Yevick equation for a fractal dimension [M. Heinen et al., Phys. Rev. Lett. 115, 097801 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.097801], a good agreement being observed.
Radial distribution function for hard spheres in fractal dimensions: A heuristic approximation.
Santos, Andrés; de Haro, Mariano López
2016-06-01
Analytic approximations for the radial distribution function, the structure factor, and the equation of state of hard-core fluids in fractal dimension d (1≤d≤3) are developed as heuristic interpolations from the knowledge of the exact and Percus-Yevick results for the hard-rod and hard-sphere fluids, respectively. In order to assess their value, such approximate results are compared with those of recent Monte Carlo simulations and numerical solutions of the Percus-Yevick equation for a fractal dimension [M. Heinen et al., Phys. Rev. Lett. 115, 097801 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.097801], a good agreement being observed. PMID:27415227
NASA Astrophysics Data System (ADS)
Hanifpour, M.; Francois, N.; Robins, V.; Kingston, A.; Vaez Allaei, S. M.; Saadatfar, M.
2015-06-01
Here we present an experimental and numerical investigation on the grain-scale geometrical and mechanical properties of partially crystallized structures made of macroscopic frictional grains. Crystallization is inevitable in arrangements of monosized hard spheres with packing densities exceeding Bernal's limiting density ϕBernal≈0.64 . We study packings of monosized hard spheres whose density spans over a wide range (0.59 <ϕ <0.72 ) . These experiments harness x-ray computed tomography, three-dimensional image analysis, and numerical simulations to access precisely the geometry and the 3D structure of internal forces within the sphere packings. We show that clear geometrical transitions coincide with modifications of the mechanical backbone of the packing both at the grain and global scale. Notably, two transitions are identified at ϕBernal≈0.64 and ϕc≈0.68 . These results provide insights on how geometrical and mechanical features at the grain scale conspire to yield partially crystallized structures that are mechanically stable.
The Physics of Hard Spheres Experiment on MSL-1: Required Measurements and Instrument Performance
NASA Technical Reports Server (NTRS)
Doherty, Michael P.; Lant, Christian T.; Ling, Jerri S.
1998-01-01
The Physics of HArd Spheres Experiment (PHaSE), one of NASA Lewis Research Center's first major light scattering experiments for microgravity research on complex fluids, flew on board the Space Shuttle's Microgravity Science Laboratory (MSL-1) in 1997. Using colloidal systems of various concentrations of micron-sized plastic spheres in a refractive index-matching fluid as test samples, illuminated by laser light during and after crystallization, investigations were conducted to measure the nucleation and growth rate of colloidal crystals as well as the structure, rheology, and dynamics of the equilibrium crystal. Together, these measurements support an enhanced understanding of the nature of the liquid-to-solid transition. Achievement of the science objectives required an accurate experimental determination of eight fundamental properties for the hard sphere colloidal samples. The instrument design met almost all of the original measurement requirements, but with compromise on the number of samples on which data were taken. The instrument performs 2-D Bragg and low angle scattering from 0.4 deg. to 60 deg., dynamic and single-channel static scattering from 10 deg. to 170 deg., rheology using fiber optics, and white light imaging of the sample. As a result, PHaSE provided a timely microgravity demonstration of critical light scattering measurement techniques and hardware concepts, while generating data already showing promise of interesting new scientific findings in the field of condensed matter physics.
Hanifpour, M; Francois, N; Robins, V; Kingston, A; Allaei, S M Vaez; Saadatfar, M
2015-06-01
Here we present an experimental and numerical investigation on the grain-scale geometrical and mechanical properties of partially crystallized structures made of macroscopic frictional grains. Crystallization is inevitable in arrangements of monosized hard spheres with packing densities exceeding Bernal's limiting density ϕ(Bernal)≈0.64. We study packings of monosized hard spheres whose density spans over a wide range (0.59<ϕ<0.72). These experiments harness x-ray computed tomography, three-dimensional image analysis, and numerical simulations to access precisely the geometry and the 3D structure of internal forces within the sphere packings. We show that clear geometrical transitions coincide with modifications of the mechanical backbone of the packing both at the grain and global scale. Notably, two transitions are identified at ϕ(Bernal)≈0.64 and ϕ(c)≈0.68. These results provide insights on how geometrical and mechanical features at the grain scale conspire to yield partially crystallized structures that are mechanically stable. PMID:26172700
An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions
NASA Technical Reports Server (NTRS)
McDowell, Mark; Gray, Elizabeth; Rogers, Richard B.
2005-01-01
Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.
Yan, Zhenyu; Buldyrev, Sergey V; Giovambattista, Nicolas; Debenedetti, Pablo G; Stanley, H Eugene
2006-05-01
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< or =lambda<6/7. As in water, the regions where these anomalies occur are nested domes in the (T, p) 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 Q6), and project equilibrium state points onto the (t, Q6) plane, or order map. The order map evolves from waterlike 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 (lanbda=1) and waterlike (lambda approximately 4/7) 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< or=lambda< or=1, waterlike structural anomalies (i.e., decrease in both t and Q6 upon compression and strictly correlated T and Q6 in the anomalous region) occur only around lambda=4/7. Waterlike anomalies in structure, dynamics and thermodynamics arise solely due to the existence of two length scales, with their ratio lambda being the single control parameter, orientation-dependent interactions being absent by design. PMID:16802925
Temperature Dependence of the Pairwise Association of Hard Spheres in Water
NASA Astrophysics Data System (ADS)
Graziano, Giuseppe
2016-02-01
It is shown that the Gibbs energy change associated with the formation of the contact-minimum configuration of two hard spheres in water becomes more negative on increasing the temperature, at 1 atm, by extending the geometric approach previously developed [G. Graziano, Chem. Phys. Lett. 499, 79 (2010)].. This is because the decrease in water accessible surface area accompanying the association leads to a gain in translational entropy of water molecules. The process is exothermic, due to the release of some water molecules from the hydration shell to the bulk. This water reorganization is characterized by a complete enthalpy-entropy compensation and does not affect the Gibbs energy change.
No evidence of gas-liquid coexistence in dipolar hard spheres.
Rovigatti, Lorenzo; Russo, John; Sciortino, Francesco
2011-12-01
We report accurate calculations of the particle density of states in the dipolar hard-sphere fluid. Implementing efficient and tailored Monte Carlo algorithms, we are able to explore, in equilibrium, the low temperature region where a phase separation between a dilute gas of chain ends and a high-density liquid of chain junctions has been predicted to occur. Our data clearly show that the density of states remains always single peaked, definitively excluding the possibility of critical phenomena in the investigated temperature and density region. The analysis of the low temperature configurations shows that at low densities particles preferentially self-assemble into closed rings, strongly suppressing the chain ends concentration.
Equilibrium Sampling of Hard Spheres up to the Jamming Density and Beyond
NASA Astrophysics Data System (ADS)
Berthier, Ludovic; Coslovich, Daniele; Ninarello, Andrea; Ozawa, Misaki
2016-06-01
We implement and optimize a particle-swap Monte Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly large volume fractions, where previous algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct nonequilibrium protocols. We demonstrate that equilibrium fluid and nonequilibrium jammed states can have the same density, showing that the jamming transition cannot be the end point of the fluid branch.
Equilibrium Sampling of Hard Spheres up to the Jamming Density and Beyond.
Berthier, Ludovic; Coslovich, Daniele; Ninarello, Andrea; Ozawa, Misaki
2016-06-10
We implement and optimize a particle-swap Monte Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly large volume fractions, where previous algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct nonequilibrium protocols. We demonstrate that equilibrium fluid and nonequilibrium jammed states can have the same density, showing that the jamming transition cannot be the end point of the fluid branch. PMID:27341260
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1995-11-01
A theoretically based corresponding-states principle previously developed for the equation of state of hard-convex-body fluids is extended to rigid linear homonuclear fused-hard-sphere fluids. Effective volumes and shapes are introduced in order to account for the nonconvexity of the molecules. The excess compressibility factor, reduced by means of a parameter which can be determined analytically, is a common function of the effective packing fraction. The analytical expression for the function can be obtained from the equation of state of the hard-sphere fluid. Existing simulation data for diatomics, triatomics and tetraatomics show excellent agreement with the corresponding-states principle.
Transport coefficients of a granular gas of inelastic rough hard spheres.
Kremer, Gilberto M; Santos, Andrés; Garzó, Vicente
2014-08-01
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.
Fundamental measure density functional theory study of hard spheres solid-liquid interface
NASA Astrophysics Data System (ADS)
Warshavsky, Vadim
2005-03-01
Interfacial free energy is an important characteristic of solid-liquid interface as it is one of the crucial parameters in many formula of interface thermodynamics such the nucleation theory. Previously different aspects of crystal-melt interfaces were intensively studied with simulations [1,2,3], but theoretical studies with Density Functional Theories (DFT) are inconclusive [4,5]. In this report the structure of hard spheres fcc crystal-melt interfaces and the anisotropy of the interfacial free energies are studied using the Rosenfeld's Fundamental Measure DFT as such a functional leads to reliable coexistence results not only for the hard sphere system but also for the Lennard-Jones systems [6]. The parameters of interfacial density profile were calculated by a proper minimization procedure. For the equilibrium density profile the interfacial free energies were compared with simulation results. 1. R.L.Davidchak and B.B.Laird, Phys.Rev.Lett., 85, 4751(2000). 2. J.J. Hoyt, M. Asta and A. Karma, Phys.Rev.Lett., 86, 5530 (2001). 3. J.R.Morris and X.Song, J.Chem.Phys., 119, 3920 (2003). 4. W.A.Curtin, Phys.Rev.B, 39, 6775(1989). 5. R.Ohnesorge, H.Lowen, and H.Wagner, Phys.Rev.E, 50, 4801 (1994). 6. V.Warshavsky and X.Song, Phys.Rev.E, 69, 061113 (2004).
NASA Astrophysics Data System (ADS)
Gazzillo, Domenico; Giacometti, Achille; Fantoni, Riccardo; Sollich, Peter
2006-11-01
We investigate the dependence of the stickiness parameters tij=1/(12τij) —where the τij are the conventional Baxter parameters—on the solute diameters σi and σj in multicomponent sticky hard sphere (SHS) models for fluid mixtures of mesoscopic neutral particles. A variety of simple but realistic interaction potentials, utilized in the literature to model short-ranged attractions present in real solutions of colloids or reverse micelles, is reviewed. We consider: (i) van der Waals attractions, (ii) hard-sphere-depletion forces, (iii) polymer-coated colloids, and (iv) solvation effects (in particular hydrophobic bonding and attractions between reverse micelles of water-in-oil microemulsions). We map each of these potentials onto an equivalent SHS model by requiring the equality of the second virial coefficients. The main finding is that, for most of the potentials considered, the size-dependence of tij(T,σi,σj) can be approximated by essentially the same expression, i.e., a simple polynomial in the variable σiσj/σij2 , with coefficients depending on the temperature T , or—for depletion interactions—on the packing fraction η0 of the depletant particles.
NASA Astrophysics Data System (ADS)
Phan, See-Eng; Li, Min; Russel, William B.; Zhu, Jixiang; Chaikin, Paul M.; Lant, Chris T.
1999-08-01
We present measurements of the high-frequency shear modulus and dynamic viscosity for nonaqueous hard sphere colloidal crystals both in normal and microgravity environments. All experiments were performed on a multipurpose PHaSE instrument. For the rheological measurements, we detect the resonant response to oscillatory forcing with a dynamic light scattering scheme. The resonant response for colloidal crystals formed in normal and microgravity environments was similar, indicating that the bulk rheological properties are unaffected by differing crystal structure and crystallite size within the experimental error. Our high-frequency shear modulus seems reasonable, lying close to Frenkel and Ladd's predictions [Phys. Rev. Lett. 59, 1169 (1987)] for the static modulus of hard sphere crystals. Our high-frequency dynamic viscosity, on the other hand, seems high, exceeding Shikata and Pearson [J. Rheol. 38, 601 (1994)] and van der Werff et al.'s measurements [Phys. Rev. A 39, 795 (1989)] on the high-frequency dynamic viscosity for metastable fluids. The measurements are in the linear regime for the shear modulus but may not be for the dynamic viscosity as Frith et al. [Powder Technol. 51, 27 (1987)] report that the dynamic viscosity passes through a maximum with strain amplitude.
NASA Astrophysics Data System (ADS)
Wagner, Norman; Cwalina, Colin
2015-03-01
Reversible shear thickening is common in concentrated dispersions of Brownian hard-spheres at high shear rates. We confirm the existence of a well-defined colloidal shear-thickened state through experimental measurements of the shear stress and the first and second normal stress differences in the shear-thickened state as a function of the particle volume fraction for a model dispersion of near hard-spheres. The shear stress and normal stress differences are observed to grow linearly with the shear rate in the shear-thickened state and both normal stress differences are observed to be negative. Our experimental results show the shear-thickened state of colloidal dispersions can be described by three material properties--the shear viscosity and first and second normal stress difference coefficients--that are a function of the volume fraction. All three material properties are found to diverge with a power law scaling with the approach to maximum packing,which is found to be 0.54 +/- 0.01. We find the magnitude of the relative shear viscosity is greater than the magnitude of the dimensionless second normal stress difference, which is greater than the magnitude of the dimensionless first normal stress difference. These results are consistent with theoretical predictions for shear thickening by hydrocluster formation and quantitatively comparable to Stokesian Dynamics simulations. We further postulate and show that these material properties are consistent with those measured for non-Brownian suspensions.
Melting and crystallization of colloidal hard-sphere suspensions under shear.
Wu, Yu Ling; Derks, Didi; van Blaaderen, Alfons; Imhof, Arnout
2009-06-30
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.
Physics of Hard Sphere Experiment: Scattering, Rheology and Microscopy Study of Colloidal Particles
NASA Technical Reports Server (NTRS)
Cheng, Z.-D.; Zhu, J.; Phan, S.-E.; Russel, W. B.; Chaikin, P. M.; Meyer, W. V.
2002-01-01
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.
Rovibrationally Inelastic Atom-Molecule Collision Cross Sections from a Hard Sphere Model
NASA Astrophysics Data System (ADS)
Lashner, Jacob; Stewart, Brian
2016-05-01
Hard-shell models have long been used to elucidate the principal features of molecular energy transfer and exchange reaction in the A + BC system. Nevertheless, no three-dimensional hard-shell calculation of inelastic collision cross sections has been reported. This work aims to fill that void. A particular motivation comes from our experimental results, which show the importance of equatorial impacts in the vibrational excitation process. Working with the simple hard-sphere model, we incorporated secondary impacts, defined as those in which A strikes C after striking B. Such collisions are important in systems such as Li2 - X, in which vibrational energy transfer occurs principally through side impacts. We discuss the complexity this adds to the model and present fully three-dimensional cross sections for rovibrational excitation of an initially stationary molecule in the homonuclear A + B2 system, examining the cross section as a function of the masses and radii of the atoms. We show how the features in the cross section evolve as these parameters are varied and calculate the contribution of secondary (near-equatorial) impacts to the dynamics. We compare with recent measurements in our laboratory and with the results of quasiclassical trajectories.
Hard-sphere-chain Equations of State for Lyotropic Polymer LiquidCrystals
Hino, T.; Prausnitz, John M.
1998-06-01
Using Parsons-type scaling, the Onsager theory for theisotropic-nematic (I-N) transition of rigid-rod lyotropic polymer liquidcrystals is combined with the equation of state for hard-sphere-chainfluids of Chapman et al. and that of Hu et al. The equation of Hu et al.gives the I-N transition pressure and density in good agreement withcomputer simulation by Wilson and Allen for a semi-flexible hard-spherechain consisting of seven segments. For real semi-flexible polymers, wefollow the Khokhlov-Semenov theory of persistent chains that introduceschain flexibility into the Onsager theory. Using a consistent procedureto regress the equation-of-state parameters, the equations of Chapman etal. and Hu et al. are also compared with the theory of DuPre and Yangthat uses the equation of Lee for hard spherocylinders. These models arecompared with experiment for two binary polymer solutions containingpoly(hexyl isocyanate) and another solution containing polysaccharideschizophyllan. The concentration of polymer at the I-N transition ispredicted as a function of the molecular weight of polymer. All modelsperform similarly and show semi-quantitative agreement withexperiment.
Theory and computer simulation for the equation of state of additive hard-disk fluid mixtures
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2001-01-01
A procedure previously developed by the authors to obtain the equation of state for a mixture of additive hard spheres on the basis of a pure fluid equation of state is applied here to a binary mixture of additive hard disks in two dimensions. The equation of state depends on two parameters which are determined from the second and third virial coefficients for the mixture, which are known exactly. Results are compared with Monte Carlo calculations which are also reported. The agreement between theory and simulation is very good. For the fourth and fifth virial coefficients of the mixture, the equation of state gives results which are also in close agreement with exact numerical values reported in the literature.
NASA Astrophysics Data System (ADS)
Hlushak, Stepan
2015-09-01
An analytical expression for the Laplace transform of the radial distribution function of a mixture of hard-sphere chains of arbitrary segment size and chain length is used to rigorously formulate the first-order Barker-Henderson perturbation theory for the contribution of the segment-segment dispersive interactions into thermodynamics of the Lennard-Jones chain mixtures. Based on this approximation, a simple variant of the statistical associating fluid theory is proposed and used to predict properties of several mixtures of chains of different lengths and segment sizes. The theory treats the dispersive interactions more rigorously than the conventional theories and provides means for more accurate description of dispersive interactions in the mixtures of highly asymmetric components.
Direct measurement of the free energy of aging hard sphere colloidal glasses.
Zargar, Rojman; Nienhuis, Bernard; Schall, Peter; Bonn, Daniel
2013-06-21
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
Helical Defect Packings in a Quasi-One-Dimensional System of Cylindrically Confined Hard Spheres
NASA Astrophysics Data System (ADS)
Yamchi, Mahdi Zaeifi; Bowles, Richard K.
2015-07-01
We use a combination of analytical theory and molecular dynamics simulation to study the inherent structure landscape of a system of hard spheres confined to narrow cylindrical channels of diameter 1 +√{3 }/2
Hlushak, Stepan
2015-09-28
An analytical expression for the Laplace transform of the radial distribution function of a mixture of hard-sphere chains of arbitrary segment size and chain length is used to rigorously formulate the first-order Barker-Henderson perturbation theory for the contribution of the segment-segment dispersive interactions into thermodynamics of the Lennard-Jones chain mixtures. Based on this approximation, a simple variant of the statistical associating fluid theory is proposed and used to predict properties of several mixtures of chains of different lengths and segment sizes. The theory treats the dispersive interactions more rigorously than the conventional theories and provides means for more accurate description of dispersive interactions in the mixtures of highly asymmetric components.
Liquid-liquid equilibrium calculations from a modified perturbed hard sphere equation of state
Min-Lon Yu; Muoi Tang; Yan-Ping Chen
1996-12-31
A modified perturbed hard sphere (MPHS) equation of state (EOS) was developed for liquid-liquid equilibrium (LLE) calculations in this work. This MPHS EOS includes a repulsive contribution of the Carnahan-Starling EOS. The attractive part of the MPHS EOS was derived from the generalized van der Waals partition function with a modified coordination number model. The MPHS EOS yielded good results on the vapor-liquid equilibrium calculations on both pure fluids and their mixtures. It also gave satisfactory results on LLE calculations. The MPHS EOS shows smaller average errors as well as less scattering of the binary interactions parameters in LLE calculations than those from other EOS models. 8 refs., 2 figs., 2 tabs.
Single-particle fluctuations and directional correlations in driven hard-sphere glasses.
Mandal, Suvendu; Chikkadi, Vijaykumar; Nienhuis, Bernard; Raabe, Dierk; Schall, Peter; Varnik, Fathollah
2013-08-01
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.
Equation of state of sticky-hard-sphere fluids in the chemical-potential route.
Rohrmann, René D; Santos, Andrés
2014-04-01
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 (μ 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 μ route and compared with predictions from other thermodynamics routes and from computer simulations. The results show that the μ route yields a general better description than the virial, energy, compressibility, and zero-separation routes.
Correlation between dynamical and structural heterogeneities in colloidal hard-sphere suspensions
NASA Astrophysics Data System (ADS)
Golde, Sebastian; Palberg, Thomas; Schöpe, Hans Joachim
2016-07-01
Dynamical and structural heterogeneities have long been thought to play a key role in a unified picture of solidification in view of the two competitive processes of crystallization and vitrification. Here, we study these heterogeneities by means of a combination of dynamic and static light-scattering techniques applied to the simplest model system exhibiting crystallization and vitrification: the colloidal hard-sphere system. Our method enables us to quantify and correlate the temporal evolution of the amount of ordered clusters (precursors) and the amount of slow particles. Our analysis shows that their temporal evolutions are closely related and that there is an intimate link between structural and dynamic heterogeneities, crystal nucleation and the non-crystallization transition.
Polydisperse hard spheres: crystallization kinetics in small systems and role of local structure
NASA Astrophysics Data System (ADS)
Campo, Matteo; Speck, Thomas
2016-08-01
We study numerically the crystallization of a hard-sphere mixture with 8% polydispersity. Although often used as a model glass former, for small system sizes we observe crystallization in molecular dynamics simulations. This opens the possibility to study the competition between crystallization and structural relaxation of the melt, which typically is out of reach due to the disparate timescales. We quantify the dependence of relaxation and crystallization times on density and system size. For one density and system size we perform a detailed committor analysis to investigate the suitability of local structures as order parameters to describe the crystallization process. We find that local structures are strongly correlated with generic bond order and add little information to the reaction coordinate.
Creep and aging of hard-sphere glasses under constant stress.
Ballesta, P; Petekidis, G
2016-04-01
We investigate the aging behavior of glassy suspensions of nearly hard-sphere colloids submitted to a constant shear stress. For low stresses, below the yield stress, the system is subject to creep motion. As the sample ages, the shear rate exhibits a power-law decrease with time with exponents that depend on the sample age. We use a combination of rheological experiments with time-resolved photon correlation spectroscopy to investigate the time evolution of the sample dynamics under shear on various time and length scales. Long-time light-scattering experiments reveal the occurrence of microscopic rearrangement events that are linked with the macroscopic strain deformation of the sample. Dynamic time sweep experiments indicate that while the internal microscopic dynamics slow down continuously with waiting time, the storage and loss moduli are almost constant after a fast, weak decrease, resembling the behavior of quenched systems with partially frozen-in stresses. PMID:27176358
Particle characterization using multiple scattering decorrelation methods: Hard-sphere model system
NASA Astrophysics Data System (ADS)
Heymann, Andreas; Sinn, Christian; Palberg, Thomas
2000-07-01
Applying static light scattering experiments, we characterize colloidal particles that are used as model hard-sphere systems in experiments investigating their crystallization kinetics. The particles comprise of a compact core of poly(methyl methacrylate) and short polymer hairs grafted onto the surface. We use a contrast variation procedure to determine the refractive index variation within the particles and observe that one component of the binary mixture used as a solvent penetrates the particles and masks completely the small polymer hairs. Making use of the determined refractive index variation, we obtain the average particle radius and its polydispersity from measurements of the particle form factor close to its minimae. The scattered intensity has been corrected carefully for multiple scattering contributions applying dynamic light scattering measurements with multiple scattering decorrelation. We obtain a mean particle radius of R¯=435+/-4 nm and a polydispersity of σ=2.5%, a resolution that has not been achieved with light scattering experiments before.
Ultrasmooth submicrometer carbon spheres as lubricant additives for friction and wear reduction.
Alazemi, Abdullah A; Etacheri, Vinodkumar; Dysart, Arthur D; Stacke, Lars-Erik; Pol, Vilas G; Sadeghi, Farshid
2015-03-11
Ultrasmooth submicrometer carbon spheres are demonstrated as an efficient additive for improving the tribological performance of lubricating oils. Carbon spheres with ultrasmooth surfaces are fabricated by ultrasound assisted polymerization of resorcinol and formaldehyde followed by controlled heat treatment. The tribological behavior of the new lubricant mixture is investigated in the boundary and mixed lubrication regimes using a pin-on-disk apparatus and cylinder-on-disk tribometer, respectively. The new lubricant composition containing 3 wt % carbon spheres suspended in a reference SAE 5W30 engine oil exhibited a substantial reduction in friction and wear (10-25%) compared to the neat oil, without change in the viscosity. Microscopic and spectroscopic investigation of the carbon spheres after the tribological experiments illustrated their excellent mechanical and chemical stability. The significantly better tribological performance of the hybrid lubricant is attributed to the perfectly spherical shape and ultrasmooth surface of carbon sphere additive filling the gap between surfaces and acting as a nanoscale ball bearing.
A Thermodynamically-Consistent Non-Ideal Stochastic Hard-Sphere Fluid
Donev, A; Alder, B J; Garcia, A L
2009-08-03
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.
Thorneywork, Alice L; Rozas, Roberto E; Dullens, Roel P A; Horbach, Jürgen
2015-12-31
We compare experimental results from a quasi-two-dimensional colloidal hard sphere fluid to a Monte Carlo simulation of hard disks with small particle displacements. The experimental short-time self-diffusion coefficient D(S) scaled by the diffusion coefficient at infinite dilution, D(0), strongly depends on the area fraction, pointing to significant hydrodynamic interactions at short times in the experiment, which are absent in the simulation. In contrast, the area fraction dependence of the experimental long-time self-diffusion coefficient D(L)/D(0) is in quantitative agreement with D(L)/D(0) obtained from the simulation. This indicates that the reduction in the particle mobility at short times due to hydrodynamic interactions does not lead to a proportional reduction in the long-time self-diffusion coefficient. Furthermore, the quantitative agreement between experiment and simulation at long times indicates that hydrodynamic interactions effectively do not affect the dependence of D(L)/D(0) on the area fraction. In light of this, we discuss the link between structure and long-time self-diffusion in terms of a configurational excess entropy and do not find a simple exponential relation between these quantities for all fluid area fractions. PMID:26765032
Shells of charge: a density functional theory for charged hard spheres
NASA Astrophysics Data System (ADS)
Roth, Roland; Gillespie, Dirk
2016-06-01
A functional for the electrostatic excess free-energy for charged, hard sphere fluids is proposed. The functional is derived from two complementary, but equivalent, interpretations of the mean spherical approximation (MSA). The first combines fundamental measure theory (FMT) from hard-core interactions with the idea that MSA can be interpreted in terms of the interaction spherical shells of charge. This formulation gives the free-energy density as a function of weighted densities. When all the ions have the same size, the functional adopts an FMT-like form. The second in effect ‘functionalizes’ the derivation of MSA; that is, it generalizes the MSA as a functional-based version of MSA (fMSA). This formulation defines the free-energy density as a function of a position-dependent MSA screening parameter and the weighted densities of the FMT approach. This FMT/fMSA functional is shown to give accurate density profiles, as compared to Monte Carlo simulations, under a wide range of ion concentrations, size asymmetries, and valences.
Paricaud, P.
2015-07-28
A simple modification of the Boublík-Mansoori-Carnahan-Starling-Leland equation of state is proposed for an application to the metastable disordered region. The new model has a positive pole at the jamming limit and can accurately describe the molecular simulation data of pure hard in the stable fluid region and along the metastable branch. The new model has also been applied to binary mixtures hard spheres, and an excellent description of the fluid and metastable branches can be obtained by adjusting the jamming packing fraction. The new model for hard sphere mixtures can be used as the repulsive term of equations of state for real fluids. In this case, the modified equations of state give very similar predictions of thermodynamic properties as the original models, and one can remove the multiple liquid density roots observed for some versions of the Statistical Associating Fluid Theory (SAFT) at low temperature without any modification of the dispersion term.
Fu, Dong; Li, Xiao-Sen
2006-08-28
The excess Helmholtz free energy functional for associating hard sphere fluid is formulated by using a modified fundamental measure theory [Y. X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)]. Within the framework of density functional theory, the thermodynamic properties including phase equilibria for both molecules and monomers, equilibrium plate-fluid interfacial tensions and isotherms of excess adsorption, average molecule density, average monomer density, and plate-fluid interfacial tension for four-site associating hard sphere fluids confined in slit pores are investigated. The phase equilibria inside the hard slit pores and attractive slit pores are determined according to the requirement that temperature, chemical potential, and grand potential in coexistence phases should be equal and the plate-fluid interfacial tensions at equilibrium states are predicted consequently. The influences of association energy, fluid-solid interaction, and pore width on phase equilibria and equilibrium plate-fluid interfacial tensions are discussed.
Variational Monte Carlo study of soliton excitations in hard-sphere Bose gases
NASA Astrophysics Data System (ADS)
Rota, R.; Giorgini, S.
2015-10-01
By using a full many-body approach, we calculate the excitation energy, the effective mass, and the density profile of soliton states in a three-dimensional Bose gas of hard spheres at zero temperature. The many-body wave function used to describe the soliton contains a one-body term, derived from the solution of the Gross-Pitaevskii equation, and a two-body Jastrow term, which accounts for the repulsive correlations between atoms. We optimize the parameters in the many-body wave function via a variational Monte Carlo procedure, calculating the grand-canonical energy and the canonical momentum of the system in a moving reference frame where the soliton is stationary. As the density of the gas is increased, significant deviations from the mean-field predictions are found for the excitation energy and the density profile of both dark and gray solitons. In particular, the soliton effective mass m* and the mass m Δ N of missing particles in the region of the density depression are smaller than the result from the Gross-Pitaevskii equation, their ratio, however, being well reproduced by this theory up to large values of the gas parameter. We also calculate the profile of the condensate density around the soliton notch, finding good agreement with the prediction of the local-density approximation.
Doubled heterogeneous crystal nucleation in sediments of hard sphere binary-mass mixtures.
Löwen, Hartmut; Allahyarov, Elshad
2011-10-01
Crystallization during the sedimentation process of a binary colloidal hard spheres mixture is explored by Brownian dynamics computer simulations. The two species are different in buoyant mass but have the same interaction diameter. Starting from a completely mixed system in a finite container, gravity is suddenly turned on, and the crystallization process in the sample is monitored. If the Peclet numbers of the two species are both not too large, crystalline layers are formed at the bottom of the cell. The composition of lighter particles in the sedimented crystal is non-monotonic in the altitude: it is first increasing, then decreasing, and then increasing again. If one Peclet number is large and the other is small, we observe the occurrence of a doubled heterogeneous crystal nucleation process. First, crystalline layers are formed at the bottom container wall which are separated from an amorphous sediment. At the amorphous-fluid interface, a secondary crystal nucleation of layers is identified. This doubled heterogeneous nucleation can be verified in real-space experiments on colloidal mixtures.
NASA Astrophysics Data System (ADS)
Lechman, Jeremy; Pierce, Flint
2012-02-01
Diffusive transport is a ubiquitous process that is typically understood in terms of a classical random walk of non-interacting particles. Here we present the results for a model of hard-sphere colloids in a Newtonian incompressible solvent at various volume fractions below the ordering transition (˜50%). We numerically simulate the colloidal systems via Fast Lubrication Dynamics -- a Brownian Dynamics approach with corrected mean-field hydrodynamic interactions. Colloid-colloid interactions are also included so that we effectively solve a system of interacting Langevin equations. The results of the simulations are analyzed in terms of the diffusion coefficient as a function of time with the early and late time diffusion coefficients comparing well with experimental results. An interpretation of the full time dependent behavior of the diffusion coefficient and mean-squared displacement is given in terms of a continuous time random walk. Therefore, the deterministic, continuum diffusion equation which arises from the discrete, interacting random walkers is presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
A density functional model for the binary crystal of hard spheres with vacancies.
Singh, Sunil P; Das, Shankar P
2007-02-14
We study the stability of a binary mixture of hard spheres in the crystalline state in which a small fraction of lattice sites in the solid structure are vacant. The optimum vacancy concentration is obtained by minimizing the free energy of the inhomogeneous solid state. We use the modified weighted density functional approximation to compute the free energy. The necessary input for the theory is the thermodynamic properties of the homogeneous state of the mixture and is obtained from the solutions of the corresponding Percus-Yevick integral equations for the binary system. We compute the free energy for the crystal having two kinds of ordered structures in which (i) both the species lie in a disordered manner on a single face-centered-cubic lattice and (ii) each of the two species lie on a separate cubic lattice. Our theoretical model obtains equilibrium vacancy fraction of O(10(-5)) near the freezing point in both cases. The vacancy concentration decreases with the increase of density in both cases.
NASA Astrophysics Data System (ADS)
Ogarko, Vitaliy; Luding, Stefan
2013-03-01
Polydisperse hard sphere mixtures have equilibrium properties which essentially depend on the number density and a reduced number K of moments of the size distribution function. Such systems are equivalent to other systems with different size distributions if the K moments are matched. In particular, a small number s of components, such that 2 s - 1 = K is sufficient to mimic systems with continuous size distributions. For most of the fluid phase K = 3 moments (s = 2 components) are enough to define an equivalent system, while in the glassy states one needs K = 5 moments (s = 3 components) to achieve good agreement between the polydisperse and its maximally-equivalent tridisperse system. With K = 5 matched moments they are also close in number- and volume-fractions of rattlers. Finally, also the jamming density of maximally-equivalent jammed packings is very close, where the tiny differences can be explained by the distribution of rattlers. This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs, project Nr. STW-MUST 10120.
Gelation and state diagram for a model nanoparticle system with adhesive hard sphere interactions
NASA Astrophysics Data System (ADS)
Wagner, Norman; Aaron, Eberle
2012-02-01
We provide the first comprehensive state diagram of thermoreversible gelation in a model nanoparticle system from dilute concentrations to the attractive driven glass. We show the temperature dependence of the interparticle potential is related to a surface molecular phase transition of the brush layer using neutron reflectivity (NR) and small-angle neutron scattering (SANS) [1]. We establish the temperature dependence of the interparticle potential using SANS, dynamic light scattering (DLS), and rheology. The potential parameters extracted from SANS suggest that, for this system, gelation is an extension of the Mode Coupling Theory (MCT) attractive driven glass line (ADG) to lower volume fractions and follows the percolation transition. Below the critical concentration, gelation proceeds without competition for phase separation [2]. These results are used to develop a complete state diagram for the sticky hard sphere reference system. [4pt] [1] A.P.R. Eberle, N.J. Wagner, B. Akgun, S.K. Satija, Langmuir 26 3003 (2010).[0pt] [2] A.P.R. Eberle, N.J. Wagner, R. Castaneda-Priego, Phys. Rev. Let. 105704 (2011).
Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow
Cheng, Xiang; Xu, Xinliang; Rice, Stuart A.; Dinner, Aaron R.; Cohen, Itai
2012-01-01
Colloidal suspensions self-assemble into equilibrium structures ranging from face- and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows. PMID:22198839
NASA Astrophysics Data System (ADS)
Virrueta, A.; Gaines, J.; O'Hern, C. S.; Regan, L.
2015-03-01
Current research in the O'Hern and Regan laboratories focuses on the development of hard-sphere models with stereochemical constraints for protein structure prediction as an alternative to molecular dynamics methods that utilize knowledge-based corrections in their force-fields. Beginning with simple hydrophobic dipeptides like valine, leucine, and isoleucine, we have shown that our model is able to reproduce the side-chain dihedral angle distributions derived from sets of high-resolution protein crystal structures. However, methionine remains an exception - our model yields a chi-3 side-chain dihedral angle distribution that is relatively uniform from 60 to 300 degrees, while the observed distribution displays peaks at 60, 180, and 300 degrees. Our goal is to resolve this discrepancy by considering clashes with neighboring residues, and averaging the reduced distribution of allowable methionine structures taken from a set of crystallized proteins. We will also re-evaluate the electron density maps from which these protein structures are derived to ensure that the methionines and their local environments are correctly modeled. This work will ultimately serve as a tool for computing side-chain entropy and protein stability. A. V. is supported by an NSF Graduate Research Fellowship and a Ford Foundation Fellowship. J. G. is supported by NIH training Grant NIH-5T15LM007056-28.
Cavity averages for hard spheres in the presence of polydispersity and incomplete data.
Schindler, Michael; Maggs, A C
2015-09-01
We develop a cavity-based method which allows to extract thermodynamic properties from position information in hard-sphere/disk systems. So far, there are available-volume and free-volume methods. We add a third one, which we call available volume after take-out, and which is shown to be mathematically equivalent to the others. In applications, where data sets are finite, all three methods show limitations, and they do this in different parameter ranges. We illustrate the principal equivalence and the limitations on data from molecular dynamics: In particular, we test robustness against missing data. We have in mind experimental limitations where there is a small polydispersity, say 4% in the particle radii, but individual radii cannot be determined. We observe that, depending on the used method, the errors in such a situation are easily 100% for the pressure and 10kT for the chemical potentials. Our work is meant as guideline to the experimentalists for choosing the right one of the three methods, in order to keep the outcome of experimental data analysis meaningful. PMID:26359237
NASA Astrophysics Data System (ADS)
Qiao, Yu; Liu, Xuejiao; Chen, Minxin; Lu, Benzhuo
2016-04-01
The hard sphere repulsion among ions can be considered in the Poisson-Nernst-Planck (PNP) equations by combining the fundamental measure theory (FMT). To reduce the nonlocal computational complexity in 3D simulation of biological systems, a local approximation of FMT is derived, which forms a local hard sphere PNP (LHSPNP) model. In the derivation, the excess chemical potential from hard sphere repulsion is obtained with the FMT and has six integration components. For the integrands and weighted densities in each component, Taylor expansions are performed and the lowest order approximations are taken, which result in the final local hard sphere (LHS) excess chemical potential with four components. By plugging the LHS excess chemical potential into the ionic flux expression in the Nernst-Planck equation, the three dimensional LHSPNP is obtained. It is interestingly found that the essential part of free energy term of the previous size modified model (Borukhov et al. in Phys Rev Lett 79:435-438, 1997; Kilic et al. in Phys Rev E 75:021502, 2007; Lu and Zhou in Biophys J 100:2475-2485, 2011; Liu and Eisenberg in J Chem Phys 141:22D532, 2014) has a very similar form to one term of the LHS model, but LHSPNP has more additional terms accounting for size effects. Equation of state for one component homogeneous fluid is studied for the local hard sphere approximation of FMT and is proved to be exact for the first two virial coefficients, while the previous size modified model only presents the first virial coefficient accurately. To investigate the effects of LHS model and the competitions among different counterion species, numerical experiments are performed for the traditional PNP model, the LHSPNP model, the previous size modified PNP (SMPNP) model and the Monte Carlo simulation. It's observed that in steady state the LHSPNP results are quite different from the PNP results, but are close to the SMPNP results under a wide range of boundary conditions. Besides, in both
NASA Astrophysics Data System (ADS)
Atkinson, Steven; Stillinger, Frank H.; Torquato, Salvatore
2016-09-01
The nonequilibrium process by which hard-particle systems may be compressed into disordered, jammed states has received much attention because of its wide utility in describing a broad class of amorphous materials. While dynamical signatures are known to precede jamming, the task of identifying static structural signatures indicating the onset of jamming have proven more elusive. The observation that compressing hard-particle packings towards jamming is accompanied by an anomalous suppression of density fluctuations (termed "hyperuniformity") has paved the way for the analysis of jamming as an "inverted critical point" in which the direct correlation function c (r ) , rather than the total correlation function h (r ) , diverges. We expand on the notion that c (r ) provides both universal and protocol-specific information as packings approach jamming. By considering the degree and position of singularities (discontinuities in the n th derivative) as well as how they are changed by the convolutions found in the Ornstein-Zernike equation, we establish quantitative statements about the structure of c (r ) with regards to singularities it inherits from h (r ) . These relations provide a concrete means of identifying features that must be expressed in c (r ) if one hopes to reproduce various details in the pair correlation function accurately and provide stringent tests on the associated numerics. We also analyze the evolution of systems of three-dimensional monodisperse hard spheres of diameter D as they approach ordered and disordered jammed configurations. For the latter, we use the Lubachevsky-Stillinger (LS) molecular dynamics and Torquato-Jiao (TJ) sequential linear programming algorithms, which both generate disordered packings, but can show perceptible structural differences. We identify a short-ranged scaling c (r )∝-1 /r as r →0 that accompanies the formation of the delta function at c (D ) that indicates the formation of contacts in all cases, and show
Equations of state of freely jointed hard-sphere chain fluids: Theory
Stell, G.; Lin, C.; Kalyuzhnyi, Y.V.
1999-03-01
Using the analytical solution of a multidensity integral equation solved in our previous papers [J. Chem. Phys. {bold 108}, 6513, 6525 (1998)], we derive two compressibility and two virial equations of state (EOS) for freely jointed hard-sphere chain fluids on the basis of the approximations defined by the polymer Percus{endash}Yevick (PPY) closure and of the PPY ideal-chain closure for the integral equations. We also extend a version of first-order thermodynamic perturbation theory to polymers, using a dimer fluid as the reference system, to treat mixtures of heteronuclear chain fluids and polymer solutions; the structural information of the dimer fluid is obtained from the PPY ideal-chain approximation in the complete-association limit. The attractive forces between monomers of chain molecules are treated using simple perturbation theory. We find that the compressibility EOS derived on the basis of the PPY approximation subject to the chain-connectivity condition reduces to the compressibility EOS based upon the PPY ideal-chain approximation in the complete-association limit, which is also equivalent to the EOS derived by Chiew [Mol. Phys. {bold 70}, 129 (1990)] and to the EOS derived by Kalyuzhnyi and Cummings [J. Chem. Phys. {bold 105}, 2011 (1996)]. On the other hand, the virial EOS derived on the basis of the PPY ideal-chain approximation coincides with Attard{close_quote}s virial EOS [J. Chem. Phys. {bold 102}, 5411 (1995)] only in the zero-density limit. The advantages in numerical implementation of the EOS presented in this work are also discussed, but a full quantitative assessment of our results and a detailed numerical comparison among them are made in a companion paper, as is comparison with available simulation results. {copyright} {ital 1999 American Institute of Physics.}
Yang, Xiaohui; Xu, Bin; Zhang, Xuehong; Song, Xiuqin; Chen, Rufen
2014-09-01
In this paper, micro/nanostructure TiO2 spheres were synthesized by a sunflower pollen induced and self-assembly mineralization process, in which a titania precursor and pollen reacted in one-pot at normal pressure. In this paper, the bio-template advantage, as hard and soft template is fully demonstrated. The superiority of our synthesis is that we not only can control pollen as hard template, but also can control it as soft template only by changing reactions temperature. Under 80 degrees C of water bath, TiO2 microspheres which replicated the morphology of pollen were prepared by controlling pollen as hard template. Under 100 degrees C, hierarchical TiO2 spheres with complicated morphology, different from pollen template, were synthesized by using pollen as soft template. At the same time, judicious choice of the amount of pollen affords the synthesis of hierarchical structures spheres with adjustable morphology and crystal structure. The morphology can be tuned from microspheres constructed from TiO2 nanorods to nanospheres constructed from TiO2 nanoparticles, and the crystal structure can be tuned from rutile to anatase. More over this anatase phase can be keep better even at high temperature of 1000 degrees C. The as-prepared micro/nano structure photocatalysts not only have high photocatalytic activities, but also have good separability and reuse performance.
Zhang, Kai; Smith, W Wendell; Wang, Minglei; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D; O'Hern, Corey S
2014-09-01
We perform molecular dynamics simulations to compress binary hard spheres into jammed packings as a function of the compression rate R, size ratio α, 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 α≳0.8 that do not demix, R(c) decreases strongly with Δϕ(J), as R(c)∼exp(-1/Δϕ(J)(2)), where Δϕ(J) is the difference between the average packing fraction of the amorphous packings and random crystal structures at R(c). Systems with α≲0.8 partially demix, which promotes crystallization, but we still find a strong correlation between R(c) and Δϕ(J). We show that known metal-metal BMGs occur in the regions of the α 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 α to increase packing efficiency, while maximizing α to prevent demixing.
NASA Astrophysics Data System (ADS)
Ni, Ran; Smallenburg, Frank; Filion, Laura; Dijkstra, Marjolein
2011-03-01
We study crystal nucleation in a binary mixture of hard spheres and investigate the composition and size of the (non)critical clusters using Monte Carlo simulations. In order to study nucleation of a crystal phase in computer simulations, a one-dimensional order parameter is usually defined to identify the solid phase from the supersaturated fluid phase. We show that the choice of order parameter can strongly influence the composition of noncritical clusters due to the projection of the Gibbs free-energy landscape in the two-dimensional composition plane onto a one-dimensional order parameter. On the other hand, the critical cluster is independent of the choice of the order parameter, due to the geometrical properties of the saddle point in the free-energy landscape, which is invariant under coordinate transformation. We investigate the effect of the order parameter on the cluster composition for nucleation of a substitutional solid solution in a simple toy model of identical hard spheres but tagged with different colours and for nucleation of an interstitial solid solution in a binary hard-sphere mixture with a diameter ratio q = 0.3. In both cases, we find that the composition of noncritical clusters depends on the order parameter choice, but are well explained by the predictions from classical nucleation theory. More importantly, we find that the properties of the critical cluster do not depend on the order parameter choice.
NASA Astrophysics Data System (ADS)
López-Sánchez, Erik; Estrada-Álvarez, César D.; Pérez-Ángel, Gabriel; Méndez-Alcaraz, José Miguel; González-Mozuelos, Pedro; Castañeda-Priego, Ramón
2013-09-01
Asymmetric binary mixtures of hard-spheres exhibit several interesting thermodynamic phenomena, such as multiple kinds of glassy states. When the degrees of freedom of the small spheres are integrated out from the description, their effects are incorporated into an effective pair interaction between large spheres known as the depletion potential. The latter has been widely used to study both the phase behavior and dynamic arrest of the big particles. Depletion forces can be accounted for by a contraction of the description in the multicomponent Ornstein-Zernike equation [R. Castañeda-Priego, A. Rodríguez-López, and J. M. Méndez-Alcaraz, Phys. Rev. E 73, 051404 (2006)], 10.1103/PhysRevE.73.051404. Within this theoretical scheme, an approximation for the difference between the effective and bare bridge functions is needed. In the limit of infinite dilution, this difference is irrelevant and the typical Asakura-Osawa depletion potential is recovered. At higher particle concentrations, however, this difference becomes important, especially where the shell of first neighbors is formed, and, as shown here, cannot be simply neglected. In this work, we use a variant of the Verlet expression for the bridge functions to highlight their importance in the calculation of the depletion potential at high densities and close to the spinodal decomposition. We demonstrate that the modified Verlet closure predicts demixing in binary mixtures of hard spheres for different size ratios and compare its predictions with both liquid state and density functional theories, computer simulations, and experiments. We also show that it provides accurate correlation functions even near the thermodynamic instability; this is explicitly corroborated with results of molecular dynamics simulations of the whole mixture. Particularly, our findings point toward a possible universal behavior of the depletion potential around the spinodal line.
Hard-sphere dispersions: Small-wave-vector structure-factor measurements in a linear shear flow
NASA Astrophysics Data System (ADS)
Ackerson, Bruce J.; van der Werff, Jos; de Kruif, C. G.
1988-06-01
Small-scattering-wave-vector structure-factor measurements have been made for model hard-sphere suspensions undergoing a steady linear shear flow. The samples are comprised of sterically stabilized silica particles in cyclohexane and have been well characterized previously by rheological, light scattering, and neutron scattering measurements. These combined measurements provide a strict test of recent theories of microscopic order in suspensions undergoing shear and suggest a picture which unifies several intuitive notions about suspensions undergoing shear flow: distortion of the pair correlation function, clustering, layering, and nonequilibrium phase transitions.
Odriozola, Gerardo; Berthier, Ludovic
2011-02-01
We use replica exchange Monte Carlo simulations to measure the equilibrium equation of state of the disordered fluid state for a binary hard sphere mixture up to very large densities where standard Monte Carlo simulations do not easily reach thermal equilibrium. For the moderate system sizes we use (up to N = 100), we find no sign of a pressure discontinuity near the location of dynamic glass singularities extrapolated using either algebraic or simple exponential divergences, suggesting they do not correspond to genuine thermodynamic glass transitions. Several scenarios are proposed for the fate of the fluid state in the thermodynamic limit.
NASA Astrophysics Data System (ADS)
Löwe, H.; Picard, G.
2015-11-01
The description of snow microstructure in microwave models is often simplified to facilitate electromagnetic calculations. Within dense media radiative transfer (DMRT), the microstructure is commonly described by sticky hard spheres (SHS). An objective mapping of real snow onto SHS is however missing which prevents measured input parameters from being used for DMRT. In contrast, the microwave emission model of layered snowpacks (MEMLS) employs a conceptually different approach, based on the two-point correlation function which is accessible by tomography. Here we show the equivalence of both electromagnetic approaches by reformulating their microstructural models in a common framework. Using analytical results for the two-point correlation function of hard spheres, we show that the scattering coefficient in both models only differs by a factor which is close to unity, weakly dependent on ice volume fraction and independent of other microstructural details. Additionally, our analysis provides an objective retrieval method for the SHS parameters (diameter and stickiness) from tomography images. For a comprehensive data set we demonstrate the variability of stickiness and compare the SHS diameter to the optical equivalent diameter. Our results confirm the necessity of a large grain-size scaling when relating both diameters in the non-sticky case, as previously suggested by several authors.
NASA Astrophysics Data System (ADS)
Löwe, H.; Picard, G.
2015-04-01
The description of snow microstructure in microwave models is often simplified to facilitate electromagnetic calculations. Within dense media radiative transfer (DMRT), the microstructure is commonly described by sticky hard spheres (SHS). An objective mapping of real snow onto SHS is however missing which prevents to use measured input parameters for DMRT. In contrast, the microwave emission model of layered snowpacks (MEMLS) employs a conceptually different approach, based on the two-point correlation function which is accessible by tomography. Here we show the equivalence of both electromagnetic approaches by reformulating their microstructural models in a common framework. Using analytical results for the two-point correlation function of hard spheres we show that the scattering coefficient in both models only differs by a factor which is close to unity, weakly dependent on ice volume fraction and independent of other microstructural details. Additionally, our analysis provides an objective retrieval method for the SHS parameters (diameter and stickiness) from tomography images. For a comprehensive data set we demonstrate the variability of stickiness and compare the SHS diameter to the optical equivalent diameter. Our results confirm the necessity of a large grain-size scaling when relating both diameters in the non-sticky case, as previously suggested by several authors.
NASA Astrophysics Data System (ADS)
Virrueta, Alejandro; O'Hern, Corey; Regan, Lynne
Methionine (Met) is a versatile amino acid found frequently both in protein cores and at protein-protein interfaces. Thus, a complete description of the structure of Met is tantamount to a fundamental understanding of protein structure and design. In previous work, we showed that our hard-sphere dipeptide model is able to recapitulate the side chain dihedral angle distributions observed in high-resolution protein crystal structures for the 8 amino acids we have studied to date: Val, Thr, Ser, Leu, Ile, Cys, Tyr, and Phe. Using the same approach, we can predict the observed Met side chain dihedral angle distributions P (χ1) and P (χ2) , but not P (χ3) . In this manuscript, we investigate the possible origins of the discrepancy and identify the minimal additions to the hard-sphere dipeptide model necessary to quantitatively predict P (χ3) of Met. We find that applying a Lennard-Jones potential with weak attraction between hydrogen atoms is sufficient to achieve predictions that match the observed χ3 side chain dihedral angle probability distributions for Met, Nle, and Mse without negatively affecting our results for the 8 previously studied amino acids. A. V. is supported by an NSF Graduate Research Fellowship and a Ford Foundation Fellowship.
Boda, Dezső; Henderson, Douglas; Eisenberg, Bob; Gillespie, Dirk
2011-01-01
In the implicit solvent models of electrolytes (such as the primitive model (PM)), the ions are modeled as point charges in the centers of spheres (hard spheres in the case of the PM). The surfaces of the spheres are not polarizable which makes these models appropriate to use in computer simulations of electrolyte systems where these ions do not leave their host dielectrics. The same assumption makes them inappropriate in simulations where these ions cross dielectric boundaries because the interaction energy of the point charge with the polarization charge induced on the dielectric boundary diverges. In this paper, we propose a procedure to treat the passage of such ions through dielectric interfaces with an interpolation method. Inspired by the “bubble ion” model (in which the ion's surface is polarizable), we define a space-dependent effective dielectric coefficient, ε eff (r), for the ion that overlaps with the dielectric boundary. Then, we replace the “bubble ion” with a point charge that has an effective charge q∕ε eff (r) and remove the portion of the dielectric boundary where the ion overlaps with it. We implement the interpolation procedure using the induced charge computation method [D. Boda, D. Gillespie, W. Nonner, D. Henderson, and B. Eisenberg, Phys. Rev. E 69, 046702 (2004)]. We analyze the various energy terms using a spherical ion passing through an infinite flat dielectric boundary as an example. PMID:21842924
Long-range weight functions in fundamental measure theory of the non-uniform hard-sphere fluid
NASA Astrophysics Data System (ADS)
Hansen-Goos, Hendrik
2016-06-01
We introduce long-range weight functions to the framework of fundamental measure theory (FMT) of the non-uniform, single-component hard-sphere fluid. While the range of the usual weight functions is equal to the hard-sphere radius R, the modified weight functions have range 3R. Based on the augmented FMT, we calculate the radial distribution function g(r) up to second order in the density within Percus’ test particle theory. Consistency of the compressibility and virial routes on this level allows us to determine the free parameter γ of the theory. As a side result, we obtain a value for the fourth virial coefficient B 4 which deviates by only 0.01% from the exact result. The augmented FMT is tested for the dense fluid by comparing results for g(r) calculated via the test particle route to existing results from molecular dynamics simulations. The agreement at large distances (r > 6R) is significantly improved when the FMT with long-range weight functions is used. In order to improve agreement close to contact (r = 2R) we construct a free energy which is based on the accurate Carnahan-Starling equation of state, rather than the Percus-Yevick compressibility equation underlying standard FMT.
Jiang, Hao; Adidharma, Hertanto
2014-11-07
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.
NASA Astrophysics Data System (ADS)
Urrutia, Ignacio
2014-12-01
This work is devoted to analyze the relation between the thermodynamic properties of a confined fluid and the shape of its confining vessel. Recently, new insights in this topic were found through the study of cluster integrals for inhomogeneous fluids that revealed the dependence on the vessel shape of the low density behavior of the system. Here, the statistical mechanics and thermodynamics of fluids confined in wedges or by edges is revisited, focusing on their cluster integrals. In particular, the well known hard sphere fluid, which was not studied in this framework so far, is analyzed under confinement and its thermodynamic properties are analytically studied up to order two in the density. Furthermore, the analysis is extended to the confinement produced by a corrugated wall. These results rely on the obtained analytic expression for the second cluster integral of the confined hard sphere system as a function of the opening dihedral angle 0 < β < 2π. It enables a unified approach to both wedges and edges.
Mirigian, Stephen; Schweizer, Kenneth
2014-01-01
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.
Urrutia, Ignacio
2014-12-28
This work is devoted to analyze the relation between the thermodynamic properties of a confined fluid and the shape of its confining vessel. Recently, new insights in this topic were found through the study of cluster integrals for inhomogeneous fluids that revealed the dependence on the vessel shape of the low density behavior of the system. Here, the statistical mechanics and thermodynamics of fluids confined in wedges or by edges is revisited, focusing on their cluster integrals. In particular, the well known hard sphere fluid, which was not studied in this framework so far, is analyzed under confinement and its thermodynamic properties are analytically studied up to order two in the density. Furthermore, the analysis is extended to the confinement produced by a corrugated wall. These results rely on the obtained analytic expression for the second cluster integral of the confined hard sphere system as a function of the opening dihedral angle 0 < β < 2π. It enables a unified approach to both wedges and edges.
NASA Astrophysics Data System (ADS)
Mirigian, Stephen; Schweizer, Kenneth S.
2014-05-01
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
2014-05-21
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. PMID:24852549
Precise algorithm to generate random sequential addition of hard hyperspheres at saturation.
Zhang, G; Torquato, S
2013-11-01
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
Precise algorithm to generate random sequential addition of hard hyperspheres at saturation
NASA Astrophysics Data System (ADS)
Zhang, G.; Torquato, S.
2013-11-01
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
Precise algorithm to generate random sequential addition of hard hyperspheres at saturation.
Zhang, G; Torquato, S
2013-11-01
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
NASA Astrophysics Data System (ADS)
Wolf, A. S.; Asimow, P. D.; Stevenson, D. J.
2015-12-01
Recent first-principles calculations (e.g. Stixrude, 2009; de Koker, 2013), shock-wave experiments (Mosenfelder, 2009), and diamond-anvil cell investigations (Sanloup, 2013) indicate that silicate melts undergo complex structural evolution at high pressure. The observed increase in cation-coordination (e.g. Karki, 2006; 2007) induces higher compressibilities and lower adiabatic thermal gradients in melts as compared with their solid counterparts. These properties are crucial for understanding the evolution of impact-generated magma oceans, which are dominated by the poorly understood behavior of silicates at mantle pressures and temperatures (e.g. Stixrude et al. 2009). Probing these conditions is difficult for both theory and experiment, especially given the large compositional space (MgO-SiO2-FeO-Al2O3-etc). We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme P-T conditions (Wolf et al., 2015). The Coordinated Hard Sphere Mixture (CHaSM) extends the Hard Sphere mixture model, accounting for the range of coordination states for each cation in the liquid. Using approximate analytic expressions for the hard sphere model, this fast statistical method compliments classical and first-principles methods, providing accurate thermodynamic and structural property predictions for melts. This framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide P-T range. Typical Mg-coordination numbers are predicted to evolve continuously from 5.25 (0 GPa) to 8.5 (250 GPa), comparing favorably with first-principles Molecular Dynamics (MD) simulations. We begin extending the model to a simplified mantle chemistry using empirical potentials (generally accurate over moderate pressure ranges, <~30 GPa), yielding predictions rooted in statistical representations of melt structure
A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.
Yethiraj, Anand; van Blaaderen, Alfons
2003-01-30
Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.
Dynamics of Disorder-Order Transitions in Hard Sphere Colloidal Dispersions in micro-g
NASA Technical Reports Server (NTRS)
Zhu, J. X.; Li, M.; Phan, S. E.; Russel, W. B.; Chaikin, Paul M.; Rogers, Rick; Meyers, W.
1996-01-01
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.
Inquiry into thermodynamic behavior of hard sphere plus repulsive barrier of finite height
NASA Astrophysics Data System (ADS)
Zhou, Shiqi; Solana, J. R.
2009-11-01
A bridge function approximation is proposed to close the Ornstein-Zernike (OZ) integral equation for fluids with purely repulsive potentials. The performance of the bridge function approximation is then tested by applying the approximation to two kinds of repulsive potentials, namely, the square shoulder potential and the triangle shoulder potential. An extensive comparison between simulation and the OZ approach is performed over a wide density range for the fluid phase and several temperatures. It is found that the agreement between the two routes is excellent for not too low temperatures and satisfactory for extremely low temperatures. Then, this globally trustworthy OZ approach is used to investigate the possible existence or not of a liquid anomaly, i.e., a liquid-liquid phase transition at low temperatures and negative values of the thermal expansion coefficient in certain region of the phase diagram. While the existence of the liquid anomaly in the square shoulder potential has been previously predicted by a traditional first-order thermodynamic perturbation theory (TPT), the present investigation indicates that the liquid-liquid phase transition disappears in the OZ approach, so that its prediction by the first-order TPT is only an artifact originating from the low temperature inadequacy of the first-order TPT. However, the OZ approach indeed predicts negative thermal expansion coefficients. The present bridge function approximation, free of adjustable parameters, is suitable to be used within the context of a recently proposed nonhard sphere perturbation scheme.
NASA Astrophysics Data System (ADS)
Reiss, Howard; Manzanares, José A.
2016-09-01
Using several theoretical toolsldots (i) the nucleation theorem, (ii) an equivalent cavity, (iii) the reversible work of adding a cavity to an open hard sphere system, and (iv) the theory of "stability"... the authors estimated the density at which the hard sphere freezing transition occurs. No direct involvement of the equilibrium solid phase is involved. The reduced density \\uppi a^3ρ _f/6 (where a is the hard sphere diameter and ρ _f is the actual density at which freezing occurs) is found to be 0.4937 while the value obtained by computer simulation is 0.494. The agreement is good, but the new method still contains some approximation. However, the approximation is based on the idea that at a density just below ρ _f the fluid adopts a distorted structure resembling the solid, but different enough so that long-range order vanishes. Initial loss of stability may not be involved in every fluid-solid transition, but it may be an early step in the hard sphere and related systems.
NASA Astrophysics Data System (ADS)
Stradner, Anna; Bucciarelli, Saskia; Casal, Lucia; Foffi, Giuseppe; Thurston, George; Farago, Bela; Schurtenberger, Peter
2014-03-01
The occurrence of an arrest transition in concentrated colloid suspensions and its dependence on the interaction potential is a hot topic in soft matter. Such arrest transitions can also occur in concentrated protein solutions, as they exist e.g. in biological cells or are increasingly used in pharmaceutical formulations. Here we demonstrate the applicability of concepts from colloid science to understand the dynamics of concentrated protein solutions. In this presentation we report a combination of 3D light scattering, small-angle X-ray scattering and neutron spin echo measurements to study the structural properties as well as the collective and self diffusion of proteins in highly concentrated solutions on the relevant length and time scales. We demonstrate that various arrest scenarios indeed exist for different globular proteins. The proteins chosen are different bovine lens crystallins. We report examples of hard and attractive glass transitions and arrested spinodal decomposition directly linked to the effective pair potentials determined in static scattering experiments for the different proteins. We discuss these different arrest scenarios in view of possible applications of dense protein solutions as well as in view of their possible relevance for living systems.
Tribological properties of graphene oxide and carbon spheres as lubricating additives
NASA Astrophysics Data System (ADS)
Song, Haojie; Wang, Zhiqiang; Yang, Jin
2016-10-01
The purpose of this paper was to investigate the tribological properties of carbon materials with various morphologies [i.e., graphene oxide (GO) and carbon spheres (CSs)] utilized as lubricating additives on a ball-plate tribotester. The morphology and spectroscopy characterization of GO and CSs were investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, and thermogravimetric analysis. Friction and wear properties of the sunflower seed oil filled with GO and CSs were investigated by using a MS-T3000 ball-on-disk apparatus. Results show that the sunflower seed oil containing 0.3 wt% GO nanosheets exhibited a substantial diminution in friction and wear compared with the 3.0 wt% CSs as sunflower seed oil additives. Formation of low-shear strength tribofilms containing GO and its self-lubricating behavior was the key factor in reduction of the friction and prevention from wear and deformation. In addition, friction mechanism of CSs was also discussed.
NASA Astrophysics Data System (ADS)
Siderius, Daniel William
Despite the lack of attractive interaction potentials in hard-sphere (HS) colloidal dispersions, a colloid immersed in a solvent of smaller hard-spheres may still experience a net force toward a surface due to imbalanced collisions. Consequently, depletion forces may be utilized to control self-assembly of colloidal structures on various surfaces or control aggregation of colloidal dispersions. To begin to better understand the ability of depletion forces to generate colloidal structures, guide colloidal motion, and control aggregation, accurate theoretical descriptions of depletion forces are necessary. Here, we discuss models of HS colloidal dispersions based on the ideas of Scaled Particle Theory (SPT) to provide methods of computing both HS thermophysical properties and depletion forces in HS fluids. We begin by introducing a new SPT interpolation that accurately provides many HS fluid properties, including the surface tension. We then further develop the inhomogeneous SPT (I-SPT) that describes cavities grown near a planar surface that confines a HS fluid, thereby providing a complete description of cavities near a planar surface, i.e., cavities that are centered at any position relative to the wall. The surface thermodynamics of HS cavities are then reexamined using a Gibbs dividing surface analysis, which produces thermodynamic expressions related to, among other things, the line tension of a HS cavity. Subsequently, we utilize I-SPT to compute the HS line tension and explore its behavior for different cavity locations. Using the accurate description of HS surface thermodynamics from SPT and I-SPT, we then construct a geometric model of depletion forces that is generalizable to many different surface structures and is based on different thermodynamic approximations. Versions of the geometric model based on HS surface thermodynamics (including the line tension) are demonstrated to be highly accurate, though simpler versions based on ideal gas arguments are
NASA Astrophysics Data System (ADS)
Parisi, Giorgio
In a hard spheres systems particles cannot overlap. Increasing the density we reach a point where most of the particles are blocked and the density cannot be increased any more: this is the jamming point. The jamming point separates the phase, where all the constraint can be satisfied, from an unsatifiable phase, where spheres do have to overlap. A scaling theory of the behavior around the jamming critical point has been formulated and a few critical exponents have been introduced. The exponents are apparently super-universal, as far as they do seem to be independent from the space dimensions. The mean field version of the model (i.e. the infinite dimensions limit) has been solved analytically using broken replica symmetry techniques and the computed critical exponents have been found in a remarkable agreement with three-dimensional and two-dimensional numerical results and experiments. The theory predicts in hard spheres (in glasses) a new transition (the Gardener transition) from the replica symmetric phase to the replica broken phase at high density (at low temperature), in agreement with simulations on hard sphere systems. I will briefly discuss the possible consequences of this new picture on the very low temperature behavior of glasses in the quantum regime.
Sesé, Luis M
2012-06-28
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.
NASA Astrophysics Data System (ADS)
Zhou, Alice; O'Hern, Corey; Regan, Lynne
2013-03-01
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. NSF DMR-1006537 and PHY-1019147, the Raymond and Beverly Sackler Institute for Biological, Physical and Engineering Sciences, and Howard Hughes Medical Institute International Research Fellowship
NASA Astrophysics Data System (ADS)
Icardi, Matteo; Asinari, Pietro; Marchisio, Daniele; Izquierdo, Salvador; Fox, Rodney
2011-11-01
Recently the Quadrature Method of Moments (QMOM) has been extended to solve several kinetic equations, in particular for gas-particle flows and rarefied gases. This method is usually coupled with simplified linear models for particle collisions. In this work QMOM is tested as a closure for the dynamics of high-order moments with a more realistic collision model namely the hard-spheres model in the Homogeneous Isotropic Boltzmann Equation. The behavior of QMOM far away and approaching the equilibrium is studied. Results are compared to other techniques such as the Lattice-Boltzmann (LBM) and the Grad's expansion (GM) methods. Comparison with a more accurate and computationally expensive model, based on the Discrete Velocity Method (DVM), is also carried out. Our results show that QMOM describes very well the evolution when it is far away from equilibrium, without the drawbacks of the GM and LBM or the computational costs of DVM but it is not able to accurately reproduce the equilibrium and the dynamics close to it. Corrections to cure this behavior are proposed and tested.
NASA Astrophysics Data System (ADS)
Icardi, M.; Asinari, P.; Marchisio, D. L.; Izquierdo, S.; Fox, R. O.
2012-08-01
Recently the Quadrature Method of Moments (QMOM) has been extended to solve several kinetic equations, in particular for gas-particle flows and rarefied gases in which the non-equilibrium effects can be important. In this work QMOM is tested as a closure for the dynamics of the Homogeneous Isotropic Boltzmann Equation (HIBE) with a realistic description for particle collisions, namely the hard-sphere model. The behaviour of QMOM far away and approaching the equilibrium is studied. Results are compared to other techniques such as the Grad's moment method (GM) and the off-Lattice Boltzmann Method (oLBM). Comparison with a more accurate and computationally expensive approach, based on the Discrete Velocity Method (DVM), is also carried out. Our results show that QMOM describes very well the evolution when it is far away from equilibrium, without the drawbacks of the GM and oLBM or the computational costs of DVM, but it is not able to accurately reproduce equilibrium and the dynamics close to it. Static and dynamic corrections to cure this behaviour are here proposed and tested.
NASA Astrophysics Data System (ADS)
Elfimova, Ekaterina A.; Karavaeva, Tatyana E.; Ivanov, Alexey O.
2014-12-01
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 λ, 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 ˜λ3, 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 λ2, 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.
NASA Astrophysics Data System (ADS)
van Westen, Thijs; Vlugt, Thijs J. H.; Gross, Joachim
2014-01-01
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
Entropy and enthalpy convergence of hydrophobic solvation beyond the hard-sphere limit.
Sedlmeier, Felix; Horinek, Dominik; Netz, Roland R
2011-02-01
The experimentally well-known convergence of solvation entropies and enthalpies of different small hydrophobic solutes at universal temperatures seems to indicate that hydrophobic solvation is dominated by universal water features and not so much by solute specifics. The reported convergence of the denaturing entropy of a group of different proteins at roughly the same temperature as hydrophobic solutes was consequently argued to indicate that the denaturing entropy of proteins is dominated by the hydrophobic effect and used to estimate the hydrophobic contribution to protein stability. However, this appealing picture was subsequently questioned since the initially claimed universal convergence of denaturing entropies holds only for a small subset of proteins; for a larger data collection no convergence is seen. We report extensive simulation results for the solvation of small spherical solutes in explicit water with varying solute-water potentials. We show that convergence of solvation properties for solutes of different radii exists but that the convergence temperatures depend sensitively on solute-water potential features such as stiffness of the repulsive part and attraction strength, not so much on the attraction range. Accordingly, convergence of solvation properties is only expected for solutes of a homologous series that differ in the number of one species of subunits (which attests to the additivity of solvation properties) or solutes that are characterized by similar solute-water interaction potentials. In contrast, for peptides that arguably consist of multiple groups with widely disperse interactions with water, it means that thermodynamic convergence at a universal temperature cannot be expected, in general, in agreement with experimental results.
NASA Astrophysics Data System (ADS)
Kang, Hong Seok; Ree, Francis H.
1995-12-01
The perturbative hypernetted-chain (PHNC) equation developed recently has been applied to the one-component plasma (OCP) and the one-component charged hard-sphere (OCCHS) systems in a uniform compensating background. Computed thermodynamic properties and pair correlation functions show that the PHNC gives excellent agreement with computer simulations and that it is as accurate as (or, in some cases, superior to) the reference-hypernetted chain and the hypernetted-chain-mean spherical equations, representing the two best currently available theories. The PHNC also predicts the OCP screening function at short range in close agreement with computer simulations and is superior to other theoretical results. Reliability of the radial distribution function at the hard-sphere contact distance for the OCCHS is also discussed.
NASA Astrophysics Data System (ADS)
Hu, Jia-Wen; Yu, Yang-Xin
2009-08-01
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.
NASA Astrophysics Data System (ADS)
Housiadas, Kostas D.
2015-08-01
An effective-medium fluid mechanics model based on the original idea first presented by Brinkman ["A calculation of the viscous force exerted by a flowing fluid on a dense swarm of particles," Appl. Sci. Res. 1, 27-34 (1949)] for the viscous force exerted by a flowing fluid on a dense swarm of fixed spherical particles is utilized for the prediction of the elongational viscosity of a non-colloidal, non-Brownian hard-sphere suspension in an incompressible Newtonian matrix fluid. The same model was explored by Housiadas and Tanner ["A model for the shear viscosity of non-colloidal suspensions with Newtonian matrix fluids," Rheol. Acta 53, 831-841 (2014)] for the derivation of an analytical formula for the bulk shear viscosity of the suspension as a function of the volume fraction of the solid phase, a formula which is in very good agreement with widely used semi-empirical relationships and available experimental data from the literature. In the present paper, it is assumed that a spherical particle is subject, in an average sense, to a far-field uniform uniaxial elongational flow and a suitable pressure gradient. Under steady, isothermal, creeping conditions, and imposing no-slip and no-penetration conditions at the surface of a particle in a stagnation point of the fluid and the far-field velocity and pressure profiles, the solution of the three-dimensional Brinkman equations is found analytically. The solution shows a faster decay of the velocity disturbances around a reference particle than the single-particle case. A volume average of the total stress tensor gives an analytical formula for the bulk elongational viscosity of the complex system as a function of the particle concentration. A significant increase of the elongation viscosity with increasing the particle concentration is predicted. The increase is larger than the corresponding increase of the shear viscosity, in qualitative accordance with the theoretical formula of Batchelor and Green ["The
NASA Technical Reports Server (NTRS)
Zhu, Ji-Xiang; Chaikin, P. M.; Li, Min; Russel, W. B.; Ottewill, R. H.; Rogers, R.; Meyer, W. V.
1998-01-01
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.
NASA Astrophysics Data System (ADS)
Hansen-Goos, Hendrik
2016-04-01
We derive an analytical equation of state for the hard-sphere fluid that is within 0.01% of computer simulations for the whole range of the stable fluid phase. In contrast, the commonly used Carnahan-Starling equation of state deviates by up to 0.3% from simulations. The derivation uses the functional form of the isothermal compressibility from the Percus-Yevick closure of the Ornstein-Zernike relation as a starting point. Two additional degrees of freedom are introduced, which are constrained by requiring the equation of state to (i) recover the exact fourth virial coefficient B4 and (ii) involve only integer coefficients on the level of the ideal gas, while providing best possible agreement with the numerical result for B5. Virial coefficients B6 to B10 obtained from the equation of state are within 0.5% of numerical computations, and coefficients B11 and B12 are within the error of numerical results. We conjecture that even higher virial coefficients are reliably predicted.
NASA Astrophysics Data System (ADS)
Zhou, Shiqi
2011-12-01
Thermodynamic and structural properties of liquids are of fundamental interest in physics, chemistry, and biology, and perturbation approach has been fundamental to liquid theoretical approaches since the dawn of modern statistical mechanics and remains so to this day. Although thermodynamic perturbation theory (TPT) is widely used in the chemical physics community, one of the most popular versions of the TPT, i.e. Zwanzig (Zwanzig, R. W. J. Chem. Phys. 1954, 22, 1420-1426) 1st-order high temperature series expansion (HTSE) TPT and its 2nd-order counterpart under a macroscopic compressibility approximation of Barker-Henderson (Barker, J. A.; Henderson, D. J. Chem. Phys. 1967, 47, 2856-2861), have some serious shortcomings: (i) the nth-order term of the HTSE is involved with reference fluid distribution functions of order up to 2n, and the higher-order terms hence progressively become more complicated and numerically inaccessible; (ii) the performance of the HTSE rapidly deteriorates and the calculated results become even qualitatively incorrect as the temperature of interest decreases. This account deals with the developments that we have made over the last five years or so to advance a coupling parameter series expansion (CPSE) and a non hard sphere (HS) perturbation strategy that has scored some of its greatest successes in overcoming the above-mentioned difficulties. In this account (i) we expatiate on implementation details of our schemes: how input information indispensable to high-order truncation of the CPSE in both the HS and non HS perturbation schemes is calculated by an Ornstein-Zernike integral equation theory; how high-order thermodynamic quantities, such as critical parameters and excess constant volume heat capacity, are extracted from the resulting excess Helmholtz free energy with irregular and inevitable numerical errors; how to select reference potential in the non HS perturbation scheme. (ii) We give a quantitative analysis on why convergence
Hsu, Wei-Hung; Masim, Frances Camille P; Porta, Matteo; Nguyen, Mai Thanh; Yonezawa, Tetsu; Balčytis, Armandas; Wang, Xuewen; Rosa, Lorenzo; Juodkazis, Saulius; Hatanaka, Koji
2016-09-01
Femtosecond laser-induced hard X-ray generation in air from a 100-µm-thick solution film of distilled water or Au nano-sphere suspension was carried out by using a newly-developed automatic positioning system with 1-µm precision. By positioning the solution film for the highest X-ray intensity, the optimum position shifted upstream as the laser power increased due to breakdown. Optimized positioning allowed us to control X-ray intensity with high fidelity. X-ray generation from Au nano-sphere suspension and distilled water showed different power scaling. Linear and nonlinear absorption mechanism are analyzed together with numerical modeling of light delivery. PMID:27607607
NASA Astrophysics Data System (ADS)
Hayashi, Tomohiko; Oshima, Hiraku; Harano, Yuichi; Kinoshita, Masahiro
2016-09-01
For neutral hard-sphere solutes, we compare the reduced density profile of water around a solute g(r), solvation free energy μ, energy U, and entropy S under the isochoric condition predicted by the two theories: dielectrically consistent reference interaction site model (DRISM) and angle-dependent integral equation (ADIE) theories. A molecular model for water pertinent to each theory is adopted. The hypernetted-chain (HNC) closure is employed in the ADIE theory, and the HNC and Kovalenko-Hirata (K-H) closures are tested in the DRISM theory. We also calculate g(r), U, S, and μ of the same solute in a hard-sphere solvent whose molecular diameter and number density are set at those of water, in which case the radial-symmetric integral equation (RSIE) theory is employed. The dependences of μ, U, and S on the excluded volume and solvent-accessible surface area are analyzed using the morphometric approach (MA). The results from the ADIE theory are in by far better agreement with those from computer simulations available for g(r), U, and μ. For the DRISM theory, g(r) in the vicinity of the solute is quite high and becomes progressively higher as the solute diameter d U increases. By contrast, for the ADIE theory, it is much lower and becomes further lower as d U increases. Due to unphysically positive U and significantly larger |S|, μ from the DRISM theory becomes too high. It is interesting that μ, U, and S from the K-H closure are worse than those from the HNC closure. Overall, the results from the DRISM theory with a molecular model for water are quite similar to those from the RSIE theory with the hard-sphere solvent. Based on the results of the MA analysis, we comparatively discuss the different theoretical methods for cases where they are applied to studies on the solvation of a protein.
NASA Astrophysics Data System (ADS)
Hayashi, Tomohiko; Oshima, Hiraku; Harano, Yuichi; Kinoshita, Masahiro
2016-09-01
For neutral hard-sphere solutes, we compare the reduced density profile of water around a solute g(r), solvation free energy μ, energy U, and entropy S under the isochoric condition predicted by the two theories: dielectrically consistent reference interaction site model (DRISM) and angle-dependent integral equation (ADIE) theories. A molecular model for water pertinent to each theory is adopted. The hypernetted-chain (HNC) closure is employed in the ADIE theory, and the HNC and Kovalenko–Hirata (K–H) closures are tested in the DRISM theory. We also calculate g(r), U, S, and μ of the same solute in a hard-sphere solvent whose molecular diameter and number density are set at those of water, in which case the radial-symmetric integral equation (RSIE) theory is employed. The dependences of μ, U, and S on the excluded volume and solvent-accessible surface area are analyzed using the morphometric approach (MA). The results from the ADIE theory are in by far better agreement with those from computer simulations available for g(r), U, and μ. For the DRISM theory, g(r) in the vicinity of the solute is quite high and becomes progressively higher as the solute diameter d U increases. By contrast, for the ADIE theory, it is much lower and becomes further lower as d U increases. Due to unphysically positive U and significantly larger |S|, μ from the DRISM theory becomes too high. It is interesting that μ, U, and S from the K–H closure are worse than those from the HNC closure. Overall, the results from the DRISM theory with a molecular model for water are quite similar to those from the RSIE theory with the hard-sphere solvent. Based on the results of the MA analysis, we comparatively discuss the different theoretical methods for cases where they are applied to studies on the solvation of a protein.
Kalyuzhnyi, Y.V. |; Lin, C.; Stell, G.
1998-04-01
We continue here our series of studies in which integral-equation theory is developed and used for the monomer-monomer correlation functions in a fluid of multicomponent freely jointed hard-sphere polymers. In this study our approach is based on Wertheim{close_quote}s polymer Percus{endash}Yevick (PPY) theory supplemented by the ideal-chain approximation; it can be regarded as a simplified version of Wertheim{close_quote}s four-density PPY approximation for associating fluids considered in the complete-association limit. The numerical procedure of this simplified theory is much easier than that of the original Wertheim{close_quote}s four-density PPY approximation, but the degree of accuracy is reduced. The theory can also be regarded as an extension of the PPY theory for the homonuclear polymer system proposed by Chang and Sandler [J. Chem. Phys. {bold 102}, 437 (1995)]. Their work is based upon a description of a system of hard-sphere monomers that associate into a polydisperse system of chains of prescribed mean length. Our theory instead directly describes a multicomponent system of associating monomers that form monodisperse chains of prescribed length upon complete association. An analytical solution of the PPY ideal-chain approximation for the general case of a multicomponent mixture of heteronuclear hard-sphere linear chain molecules is given. Its use is illustrated by numerical results for two models of copolymer fluids, a symmetrical diblock copolymer system, and an alternating copolymer system. The comparison with Monte Carlo simulations is given to gauge the accuracy of the theory. We find for the molecules we study here that predictions of our theory for heteronuclear chain systems have the same degree of accuracy as Chang and Sandler{close_quote}s theory for homonuclear chain systems. {copyright} {ital 1998 American Institute of Physics.}
Hayashi, Tomohiko; Oshima, Hiraku; Harano, Yuichi; Kinoshita, Masahiro
2016-09-01
For neutral hard-sphere solutes, we compare the reduced density profile of water around a solute g(r), solvation free energy μ, energy U, and entropy S under the isochoric condition predicted by the two theories: dielectrically consistent reference interaction site model (DRISM) and angle-dependent integral equation (ADIE) theories. A molecular model for water pertinent to each theory is adopted. The hypernetted-chain (HNC) closure is employed in the ADIE theory, and the HNC and Kovalenko-Hirata (K-H) closures are tested in the DRISM theory. We also calculate g(r), U, S, and μ of the same solute in a hard-sphere solvent whose molecular diameter and number density are set at those of water, in which case the radial-symmetric integral equation (RSIE) theory is employed. The dependences of μ, U, and S on the excluded volume and solvent-accessible surface area are analyzed using the morphometric approach (MA). The results from the ADIE theory are in by far better agreement with those from computer simulations available for g(r), U, and μ. For the DRISM theory, g(r) in the vicinity of the solute is quite high and becomes progressively higher as the solute diameter d U increases. By contrast, for the ADIE theory, it is much lower and becomes further lower as d U increases. Due to unphysically positive U and significantly larger |S|, μ from the DRISM theory becomes too high. It is interesting that μ, U, and S from the K-H closure are worse than those from the HNC closure. Overall, the results from the DRISM theory with a molecular model for water are quite similar to those from the RSIE theory with the hard-sphere solvent. Based on the results of the MA analysis, we comparatively discuss the different theoretical methods for cases where they are applied to studies on the solvation of a protein.
Oshima, Hiraku; Kinoshita, Masahiro
2015-04-14
In earlier works, we showed that the entropic effect originating from the translational displacement of water molecules plays the pivotal role in protein folding and denaturation. The two different solvent models, hard-sphere solvent and model water, were employed in theoretical methods wherein the entropic effect was treated as an essential factor. However, there were similarities and differences in the results obtained from the two solvent models. In the present work, to unveil the physical origins of the similarities and differences, we simultaneously consider structural transition, cold denaturation, and pressure denaturation for the same protein by employing the two solvent models and considering three different thermodynamic states for each solvent model. The solvent-entropy change upon protein folding/unfolding is decomposed into the protein-solvent pair (PA) and many-body (MB) correlation components using the integral equation theories. Each component is further decomposed into the excluded-volume (EV) and solvent-accessible surface (SAS) terms by applying the morphometric approach. The four physically insightful constituents, (PA, EV), (PA, SAS), (MB, EV), and (MB, SAS), are thus obtained. Moreover, (MB, SAS) is discussed by dividing it into two factors. This all-inclusive investigation leads to the following results: (1) the protein-water many-body correlation always plays critical roles in a variety of folding/unfolding processes; (2) the hard-sphere solvent model fails when it does not correctly reproduce the protein-water many-body correlation; (3) the hard-sphere solvent model becomes problematic when the dependence of the many-body correlation on the solvent number density and temperature is essential: it is not quite suited to studies on cold and pressure denaturating of a protein; (4) when the temperature and solvent number density are limited to the ambient values, the hard-sphere solvent model is usually successful; and (5) even at the ambient
NASA Astrophysics Data System (ADS)
Oshima, Hiraku; Kinoshita, Masahiro
2015-04-01
In earlier works, we showed that the entropic effect originating from the translational displacement of water molecules plays the pivotal role in protein folding and denaturation. The two different solvent models, hard-sphere solvent and model water, were employed in theoretical methods wherein the entropic effect was treated as an essential factor. However, there were similarities and differences in the results obtained from the two solvent models. In the present work, to unveil the physical origins of the similarities and differences, we simultaneously consider structural transition, cold denaturation, and pressure denaturation for the same protein by employing the two solvent models and considering three different thermodynamic states for each solvent model. The solvent-entropy change upon protein folding/unfolding is decomposed into the protein-solvent pair (PA) and many-body (MB) correlation components using the integral equation theories. Each component is further decomposed into the excluded-volume (EV) and solvent-accessible surface (SAS) terms by applying the morphometric approach. The four physically insightful constituents, (PA, EV), (PA, SAS), (MB, EV), and (MB, SAS), are thus obtained. Moreover, (MB, SAS) is discussed by dividing it into two factors. This all-inclusive investigation leads to the following results: (1) the protein-water many-body correlation always plays critical roles in a variety of folding/unfolding processes; (2) the hard-sphere solvent model fails when it does not correctly reproduce the protein-water many-body correlation; (3) the hard-sphere solvent model becomes problematic when the dependence of the many-body correlation on the solvent number density and temperature is essential: it is not quite suited to studies on cold and pressure denaturating of a protein; (4) when the temperature and solvent number density are limited to the ambient values, the hard-sphere solvent model is usually successful; and (5) even at the ambient
Oshima, Hiraku; Kinoshita, Masahiro
2015-04-14
In earlier works, we showed that the entropic effect originating from the translational displacement of water molecules plays the pivotal role in protein folding and denaturation. The two different solvent models, hard-sphere solvent and model water, were employed in theoretical methods wherein the entropic effect was treated as an essential factor. However, there were similarities and differences in the results obtained from the two solvent models. In the present work, to unveil the physical origins of the similarities and differences, we simultaneously consider structural transition, cold denaturation, and pressure denaturation for the same protein by employing the two solvent models and considering three different thermodynamic states for each solvent model. The solvent-entropy change upon protein folding/unfolding is decomposed into the protein-solvent pair (PA) and many-body (MB) correlation components using the integral equation theories. Each component is further decomposed into the excluded-volume (EV) and solvent-accessible surface (SAS) terms by applying the morphometric approach. The four physically insightful constituents, (PA, EV), (PA, SAS), (MB, EV), and (MB, SAS), are thus obtained. Moreover, (MB, SAS) is discussed by dividing it into two factors. This all-inclusive investigation leads to the following results: (1) the protein-water many-body correlation always plays critical roles in a variety of folding/unfolding processes; (2) the hard-sphere solvent model fails when it does not correctly reproduce the protein-water many-body correlation; (3) the hard-sphere solvent model becomes problematic when the dependence of the many-body correlation on the solvent number density and temperature is essential: it is not quite suited to studies on cold and pressure denaturating of a protein; (4) when the temperature and solvent number density are limited to the ambient values, the hard-sphere solvent model is usually successful; and (5) even at the ambient
NASA Astrophysics Data System (ADS)
Perera-Burgos, Jorge Adrián; Méndez-Alcaraz, José Miguel; Pérez-Ángel, Gabriel; Castañeda-Priego, Ramón
2016-09-01
Depletion forces are a particular class of effective interactions that have been mainly investigated in binary mixtures of hard-spheres in bulk. Although there are a few contributions that point toward the effects of confinement on the depletion potential, little is known about such entropic potentials in two-dimensional colloidal systems. From theoretical point of view, the problem resides in the fact that there is no general formulation of depletion forces in arbitrary dimensions and, typically, any approach that works well in three dimensions has to be reformulated for lower dimensionality. However, we have proposed a theoretical framework, based on the formalism of contraction of the description within the integral equations theory of simple liquids, to account for effective interactions in colloidal liquids, whose main feature is that it does not need to be readapted to the problem under consideration. We have also shown that such an approach allows one to determine the depletion pair potential in three-dimensional colloidal mixtures even near to the demixing transition, provided the bridge functions are sufficiently accurate to correctly describe the spatial correlation between colloids [E. López-Sánchez et al., J. Chem. Phys. 139, 104908 (2013)]. We here report an extensive analysis of the structure and the entropic potentials in binary mixtures of additive hard-disks. In particular, we show that the same functional form of the modified-Verlet closure relation used in three dimensions can be straightforwardly employed to obtain an accurate solution for two-dimensional colloidal mixtures in a wide range of packing fractions, molar fractions, and size asymmetries. Our theoretical results are explicitly compared with the ones obtained by means of event-driven molecular dynamics simulations and recent experimental results. Furthermore, to assess the accuracy of our predictions, the depletion potentials are used in an effective one-component model to reproduce
Perera-Burgos, Jorge Adrián; Méndez-Alcaraz, José Miguel; Pérez-Ángel, Gabriel; Castañeda-Priego, Ramón
2016-09-14
Depletion forces are a particular class of effective interactions that have been mainly investigated in binary mixtures of hard-spheres in bulk. Although there are a few contributions that point toward the effects of confinement on the depletion potential, little is known about such entropic potentials in two-dimensional colloidal systems. From theoretical point of view, the problem resides in the fact that there is no general formulation of depletion forces in arbitrary dimensions and, typically, any approach that works well in three dimensions has to be reformulated for lower dimensionality. However, we have proposed a theoretical framework, based on the formalism of contraction of the description within the integral equations theory of simple liquids, to account for effective interactions in colloidal liquids, whose main feature is that it does not need to be readapted to the problem under consideration. We have also shown that such an approach allows one to determine the depletion pair potential in three-dimensional colloidal mixtures even near to the demixing transition, provided the bridge functions are sufficiently accurate to correctly describe the spatial correlation between colloids [E. López-Sánchez et al., J. Chem. Phys. 139, 104908 (2013)]. We here report an extensive analysis of the structure and the entropic potentials in binary mixtures of additive hard-disks. In particular, we show that the same functional form of the modified-Verlet closure relation used in three dimensions can be straightforwardly employed to obtain an accurate solution for two-dimensional colloidal mixtures in a wide range of packing fractions, molar fractions, and size asymmetries. Our theoretical results are explicitly compared with the ones obtained by means of event-driven molecular dynamics simulations and recent experimental results. Furthermore, to assess the accuracy of our predictions, the depletion potentials are used in an effective one-component model to reproduce
Sear, R P
1999-06-01
At low temperature, spheres with a very short-ranged attraction exist as a near-close-packed solid coexisting with an almost infinitely dilute gas. We find that the ratio of the interfacial tension between these two phases to the thermal energy diverges as the range of the attraction tends to zero. The large tensions when the interparticle attractions are short ranged may be why globular proteins only crystallize over a narrow range of conditions. PMID:11969672
Schaefer, B.; Lambert, S.M.; Song, Y.; Prausnitz, J.M.
1994-10-01
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.
Kim, Sun-Jung; Hwang, In-Sung; Kang, Yun Chan; Lee, Jong-Heun
2011-01-01
A combinatorial hydrothermal reaction has been used to prepare pure and additive (Sb, Cu, Nb, Pd, and Ni)-loaded In2O3 hollow spheres for gas sensor applications. The operation of Pd- and Cu-loaded In2O3 sensors at 371 °C leads to selective H2S detection. Selective detection of CO and NH3 was achieved by the Ni-In2O3 sensor at sensing temperatures of 371 and 440 °C, respectively. The gas responses of six different sensors to NH3, H2S, H2, CO and CH4 produced unique gas sensing patterns that can be used for the artificial recognition of these gases. PMID:22346661
Perera-Burgos, Jorge Adrián; Méndez-Alcaraz, José Miguel; Pérez-Ángel, Gabriel; Castañeda-Priego, Ramón
2016-09-14
Depletion forces are a particular class of effective interactions that have been mainly investigated in binary mixtures of hard-spheres in bulk. Although there are a few contributions that point toward the effects of confinement on the depletion potential, little is known about such entropic potentials in two-dimensional colloidal systems. From theoretical point of view, the problem resides in the fact that there is no general formulation of depletion forces in arbitrary dimensions and, typically, any approach that works well in three dimensions has to be reformulated for lower dimensionality. However, we have proposed a theoretical framework, based on the formalism of contraction of the description within the integral equations theory of simple liquids, to account for effective interactions in colloidal liquids, whose main feature is that it does not need to be readapted to the problem under consideration. We have also shown that such an approach allows one to determine the depletion pair potential in three-dimensional colloidal mixtures even near to the demixing transition, provided the bridge functions are sufficiently accurate to correctly describe the spatial correlation between colloids [E. López-Sánchez et al., J. Chem. Phys. 139, 104908 (2013)]. We here report an extensive analysis of the structure and the entropic potentials in binary mixtures of additive hard-disks. In particular, we show that the same functional form of the modified-Verlet closure relation used in three dimensions can be straightforwardly employed to obtain an accurate solution for two-dimensional colloidal mixtures in a wide range of packing fractions, molar fractions, and size asymmetries. Our theoretical results are explicitly compared with the ones obtained by means of event-driven molecular dynamics simulations and recent experimental results. Furthermore, to assess the accuracy of our predictions, the depletion potentials are used in an effective one-component model to reproduce
Wilke, Antje; Weber, Jens
2012-05-14
The preparation of ultraporous polymer resins using a straightforward hard-templating synthesis is presented. Self-assembly of silica nanospheres into densely packed glasses allows an easy preparation of templates. Polydivinylbenzene resins with surface areas of up to 1000 m(2) g(-1) are synthesized as a model system and porosity analysis reveals bimodal porosity (spherical mesopores and micropores within the pore walls). The prepared systems can be further functionalized without loss of porosity as demonstrated by sulfonation. Because of their large pore sizes (13-28 nm), they are efficient adsorbents also for large molecules. Finally, the systems can also be used as model systems for the study of the pore drying and collapse process, which is of crucial importance for any application of mesoporous polymers.
Arif, Saqib; Ali, Tahira Mohsin; Ul Afzal, Qurat; Ahmed, Mubarik; Siddiqui, Asim Jamal; Hasnain, Abid
2014-06-01
The effects of water extractable pentosans (WEP) and water unextractable pentosans (WUP) on pasting properties in flours of eight different hard white spring wheat (HWSW) cultivars was studied. WEP and WUP isolated from a hard wheat flour were added to each of the cultivars at 1% and 2% level. The results indicated that WEP exhibited a pronounced effect on pasting properties as compared to WUP and variety. Univariate analysis of variance (ANOVA) was used to evaluate sources of variation. The variety significantly (P < 0.001) influenced all the pasting parameters. WUP caused significant (P < 0.001) variation in paste viscosities (except breakdown). WEP influenced more pronouncedly the hot paste, cold paste, breakdown and setback viscosities with F values-221.802, 214.286, 98.073 and 120.159, respectively. Variety-by-WEP interaction exhibited significant (P < 0.01) influence on pasting time, peak, hot paste and cold paste viscosities. Whereas, variety-by-WUP interaction only significantly (P < 0.001) influenced the pasting- time and -temperature. Duncan's test was used to analyze the significant difference (P < 0.05) within the variety. The results revealed that WUP did not induce significant (P < 0.05) influence on all the pasting parameters, whereas, WEP influenced significantly (P < 0.05) the paste viscosities of some of the varieties. It was also found that the addition of WEP remarkably reduced the setback, hot paste, cold paste viscosities and increased the breakdown viscosity in all cultivar flours. The effect of WEP was greater at higher level of supplementation on paste viscosities. PMID:24876638
NASA Astrophysics Data System (ADS)
van Westen, Thijs; Vlugt, Thijs J. H.; Gross, Joachim
2012-07-01
Onsager-like theories are commonly used to describe the phase behavior of nematic (only orientationally ordered) liquid crystals. A key ingredient in such theories is the orientation-dependent excluded volume of two molecules. Although for hard convex molecular models this is generally known in analytical form, for more realistic molecular models that incorporate intramolecular flexibility, one has to rely on approximations or on computationally expensive Monte Carlo techniques. In this work, we provide a general correlation for the excluded volume of tangent hard-sphere chains of arbitrary chain length and flexibility. The flexibility is introduced by means of the rod-coil model. The resulting correlation is of simple analytical form and accurately covers a wide range of pure component excluded volume data obtained from Monte Carlo simulations of two-chain molecules. The extension to mixtures follows naturally by applying simple combining rules for the parameters involved. The results for mixtures are also in good agreement with data from Monte Carlo simulations. We have expressed the excluded volume as a second order power series in sin (γ), where γ is the angle between the molecular axes. Such a representation is appealing since the solution of the Onsager Helmholtz energy functional usually involves an expansion of the excluded volume in Legendre coefficients. Both for pure components and mixtures, the correlation reduces to an exact expression in the limit of completely linear chains. The expression for mixtures, as derived in this work, is thereby an exact extension of the pure component result of Williamson and Jackson [Mol. Phys. 86, 819-836 (1995)], 10.1080/00268979500102391.
Zhou, Shiqi; Solana, J R
2013-08-01
The first three coefficients of the high temperature series expansion (HTSE) of the Helmholtz free energy for a number of simple potential models with hard-sphere cores plus continuous tails are obtained for the first time from Monte Carlo simulations. The potential models considered include Square-well, Sutherland, attractive Yukawa, and triangle-well with different potential ranges, as well as a model potential qualitatively resembling the depletion potential in colloidal dispersions. The simulation data are used to evaluate performance of a recent coupling parameter series expansion (CPSE) in calculating for these coefficients, and a traditional macroscopic compressibility approximation (MCA) for the second-order coefficient only. A comprehensive comparison based on these coefficients from the two theoretical approaches and simulations enables one to conclude that (i) unlike one common experience that the widely used MCA usually underestimates the second-order coefficient, the MCA can both overestimate and underestimate the second-order coefficient, and worsens as the range of the potential decreases; and (ii) in contrast, the CPSE not only reproduce the trends in the density dependence of the perturbation coefficients, even the third one, observed in the simulations, but also the agreement is quantitative in most cases, and this clearly highlights the potential of the CPSE in providing accurate estimations for the higher-order coefficients, thus giving rise to an accurate higher-order HTSE.
NASA Technical Reports Server (NTRS)
Woo, Myeung-Jouh; Greber, Isaac
1995-01-01
Molecular dynamics simulation is used to study the piston driven shock wave at Mach 1.5, 3, and 10. A shock tube, whose shape is a circular cylinder, is filled with hard sphere molecules having a Maxwellian thermal velocity distribution and zero mean velocity. The piston moves and a shock wave is generated. All collisions are specular, including those between the molecules and the computational boundaries, so that the shock development is entirely causal, with no imposed statistics. The structure of the generated shock is examined in detail, and the wave speed; profiles of density, velocity, and temperature; and shock thickness are determined. The results are compared with published results of other methods, especially the direct simulation Monte-Carlo method. Property profiles are similar to those generated by direct simulation Monte-Carlo method. The shock wave thicknesses are smaller than the direct simulation Monte-Carlo results, but larger than those of the other methods. Simulation of a shock wave, which is one-dimensional, is a severe test of the molecular dynamics method, which is always three-dimensional. A major challenge of the thesis is to examine the capability of the molecular dynamics methods by choosing a difficult task.
Leunissen, Mirjam E; Sullivan, Matthew T; Chaikin, Paul M; van Blaaderen, Alfons
2008-04-28
This work concerns the use of electric field gradients to manipulate the local particle concentration in a hard-sphere-like suspension. Inside a specially designed "electric bottle," we observed our colloids to collect in the regions of lowest field strength ("negative dielectrophoresis"). This allows for the use of larger field gradients and stronger dielectrophoretic forces than in the original electric bottle design, which was based on positive dielectrophoresis [M. T. Sullivan et al., Phys. Rev. Lett. 96, 015703 (2006)]. We used confocal scanning laser microscopy to quantitatively follow the time-dependent change in the particle density and the suspension structure. Within a few days, the dielectrophoretic compression was seen to initiate a heterogeneouslike growth of large single crystals, which took place far out-of-equilibrium. The crystals had a random hexagonal close-packed structure and displayed an intriguing growth mechanism, during which the entire crystal was continuously transported, while growing both on the "high-field" and the "low-field" sides, although at different rates. After switching off the electric field, the compressed crystals were found to relax to a lower packing fraction and melt, at a much slower rate than the crystal growth. Besides revealing the particular (far out-of-equilibrium) crystal growth mechanism in these electric bottles, our observations also shed light on the role of the different particle transport processes in the cell and some of the relevant tuning parameters. This is useful for different types of experiments, for instance, focusing more on melting, homogeneous crystallization, or the glass transition.
Mobile hard substrata - An additional biodiversity source in a high latitude shallow subtidal system
NASA Astrophysics Data System (ADS)
Balazy, Piotr; Kuklinski, Piotr
2013-03-01
This study demonstrates the importance of a hard mobile substratum (hermit crab shells) for Arctic biodiversity. Based on previous observations from other geographic regions we hypothesized that this niche at high latitudes would support a higher biodiversity of epifauna than might be predicted from similar substrata. We test whether the hermit crab epifauna is specific to that substratum providing unique biodiversity components to the local community. From four study sites in Isfjorden (78°N), West Spitsbergen and two study sites in Northern Norway (69°N) we collected approximately 50 each of hermit crabs, gastropods and pebbles, of visually similar surface area using SCUBA diving. Hermit crab shells were colonized by a larger number of epifaunal species than either gastropods or pebbles, even when they were of a larger size. Among 87 taxa found on all the three substrata, 22 occurred only on hermit crab shells. Except for two study sites hermit crab shells also supported more individuals. This study shows that the contribution of shells carried by hermit crabs to high-latitude, shallow-subtidal diversity is higher than might be predicted by their surface area alone and that hermit crabs modify, maintain and create a unique habitat. This is the result of a number of factors interacting positively on the presence of epifauna including shell surface heterogeneity and the complex influence of the crab host.
Equation of state of additive hard-disk fluid mixtures: A critical analysis of two recent proposals
NASA Astrophysics Data System (ADS)
López de Haro, M.; Yuste, S. B.; Santos, A.
2002-09-01
A detailed analysis of two different theoretical equations of state for a binary mixture of additive hard disks [C. Barrio and J. R. Solana, Phys. Rev. E 63, 011201 (2001); A. Santos, S. B. Yuste, and M. López de Haro, Mol. Phys. 96, 1 (1999)], including their comparison with Monte Carlo results, is carried out. It is found that both proposals, which require the equation of state of the single-component system as input, lead to comparable accuracy when the same input is used in both, but that advocated by Santos et al. is simpler and complies with the exact limit in which the small disks are point particles.
Bulk fluid phase behaviour of colloidal platelet-sphere and platelet-polymer mixtures.
de las Heras, Daniel; Schmidt, Matthias
2013-04-13
Using a geometry-based fundamental measure density functional theory, we calculate bulk fluid phase diagrams of colloidal mixtures of vanishingly thin hard circular platelets and hard spheres. We find isotropic-nematic phase separation, with strong broadening of the biphasic region, upon increasing the pressure. In mixtures with large size ratio of platelet and sphere diameters, there is also demixing between two nematic phases with differing platelet concentrations. We formulate a fundamental measure density functional for mixtures of colloidal platelets and freely overlapping spheres, which represent ideal polymers, and use it to obtain phase diagrams. We find that, for low platelet-polymer size ratio, in addition to isotropic-nematic and nematic-nematic phase coexistence, platelet-polymer mixtures also display isotropic-isotropic demixing. By contrast, we do not find isotropic-isotropic demixing in hard-core platelet-sphere mixtures for the size ratios considered.
Melting of polydisperse hard disks.
Pronk, Sander; Frenkel, Daan
2004-06-01
The melting of a polydisperse hard-disk system is investigated by Monte Carlo simulations in the semigrand canonical ensemble. This is done in the context of possible continuous melting by a dislocation-unbinding mechanism, as an extension of the two-dimensional hard-disk melting problem. We find that while there is pronounced fractionation in polydispersity, the apparent density-polydispersity gap does not increase in width, contrary to 3D polydisperse hard spheres. The point where the Young's modulus is low enough for the dislocation unbinding to occur moves with the apparent melting point, but stays within the density gap, just like for the monodisperse hard-disk system. Additionally, we find that throughout the accessible polydispersity range, the bound dislocation-pair concentration is high enough to affect the dislocation-unbinding melting as predicted by Kosterlitz, Thouless, Halperin, Nelson, and Young.
Differential cross-sections with hard targets
NASA Astrophysics Data System (ADS)
Brun, J. L.; Pacheco, A. F.
2005-09-01
When the concept of scattering differential cross-section is introduced in classical mechanics textbooks, usually it is first supposed that the target is a fixed, hard sphere. In this paper we calculate the scattering differential cross-section in the case of the hard target being a fixed figure of revolution of any shape. When the target is a paraboloid of revolution, we find the well-known formula corresponding to Rutherford's scattering. In addition, we analyse the inverse problem, i.e. given a differential cross-section, what is the profile of the corresponding hard target?
van Megen, W; Martinez, V A; Bryant, G
2009-12-18
The current correlation function is determined from dynamic light scattering measurements of a suspension of particles with hard spherelike interactions. For suspensions in thermodynamic equilibrium we find scaling of the space and time variables of the current correlation function. This finding supports the notion that the movement of suspended particles can be described in terms of uncorrelated Brownian encounters. However, in the metastable fluid, at volume fractions above freezing, this scaling fails.
NASA Astrophysics Data System (ADS)
Rovatti, L.; Lemke, J. N.; Emami, A.; Stejskal, O.; Vedani, M.
2015-12-01
Fe-based hardfacing alloys containing high volume fraction of hard phases are a suitable material to be deposited as wear resistant thick coatings. In the case of alloys containing high amount of interstitial alloying elements, a key factor affecting the performance is dilution with the substrate induced by the coating process. The present research was focused on the analysis of V-bearing Fe-based alloys after calibrated carbon and vanadium additions (in the range from 3 to 5 wt.%) to a commercial Fe-C-B-Ni hardfacing alloy. Vanadium carbides with a petal-like morphology were observed in the high-V hypereutectic alloys allowing to reach hardness values above 700 HV. The solidification range shifted to higher temperatures with increasing amount of vanadium addition and in the case of hypereutectic alloys, the gap remains close to that of the original alloy. In the last step of the research, the microstructural evolution after dilution was analyzed by casting the V-rich alloys on a steel substrate. The dilution, caused by the alloying element diffusion and the local melting of the substrate, modified the microstructure and the hardness for a relevant volume fraction of the hardfacing alloys. In particular, the drop of interstitial elements induced the transition from the hypereutectic to the hypoeutectic microstructure and the formation of near-spherical V-rich carbides. Even after dilution, the hardness of the new alloys remained higher than that measured in the original Fe-C-B-Ni alloy.
NASA Technical Reports Server (NTRS)
Smalheer, C. V.
1973-01-01
The chemistry of lubricant additives is discussed to show what the additives are chemically and what functions they perform in the lubrication of various kinds of equipment. Current theories regarding the mode of action of lubricant additives are presented. The additive groups discussed include the following: (1) detergents and dispersants, (2) corrosion inhibitors, (3) antioxidants, (4) viscosity index improvers, (5) pour point depressants, and (6) antifouling agents.
Free Volume of the Hard Spheres Gas
ERIC Educational Resources Information Center
Shutler, P. M. E.; Martinez, J. C.; Springham, S. V.
2007-01-01
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…
Jing, Zhicheng; Karato, Shun-ichiro
2012-04-20
Density of ultramafic silicate melts was determined using the sink/float technique at high pressures. Seven melt compositions were studied, among which three were dry compositions with different Mg's (molar MgO/(MgO + FeO) x 100) and the other four were hydrous compositions synthesized by adding 2-7 wt.% H{sub 2}O to the anhydrous ones. Experimental conditions range from 9 to 15 GPa and from 2173 to 2473 K. The sinking and floatation of density markers were observed for all melt compositions. Melt density data were analyzed by applying the Birch-Murnaghan equation of state and a newly developed equation of state for silicate melts based on the model of hard sphere mixtures. The presence of water can significantly reduce the density of melts due to its small molecular mass. On the other hand, water makes hydrous silicate melts more compressible than anhydrous melts and therefore the effect of H{sub 2}O on melt density is less significant at high pressures. The density of hydrous melts was then calculated as a function of H{sub 2}O content at the conditions of the bottom of the upper mantle, and was compared with the density of the dominant upper mantle minerals. Results show that the conditions for a negatively buoyant melt that coexists with a pyrolite mantle atop the 410 km discontinuity are marginally satisfied if H{sub 2}O is the only volatile component to facilitate melting, but such conditions will be satisfied by a broader range of conditions when other heavier volatile elements (C, K, etc.) are also present.
Huang, Zhifu Xing, Jiandong; Lv, Liangliang
2013-01-15
The effects of tungsten additions of 0%, 1.12%, 2.04%, and 3.17% (in wt.%) on the morphology, fracture toughness and micro-hardness of Fe{sub 2}B in Fe-B-C cast alloy were investigated. The results indicate that, with the increase of tungsten addition, the morphology and distribution of Fe{sub 2}B have no change and a new W-containing phase, except the (Fe, W){sub 2}B with a certain tungsten solution, does not form, and that the fracture toughness of Fe{sub 2}B increases first and then decreases, while the hardness increases first and then has a little change. Compared with the fracture toughness (3.8 MPa{center_dot}m{sup 1/2}) of Fe{sub 2}B without tungsten addition, the toughness at 2.04 wt.% tungsten can be improved by about above 80% and achieves about 6.9 MPa{center_dot}m{sup 1/2}, and variation characteristics of hardness and toughness of Fe{sub 2}B were also testified by viewing the indentation marks and cracks on the Fe{sub 2}B, respectively. - Highlights: Black-Right-Pointing-Pointer Poor toughness of Fe2B decreases obviously the wear resistance of the alloy. Black-Right-Pointing-Pointer As W content increases, Fe2B's toughness increases first and then decreases. Black-Right-Pointing-Pointer As W content increases, Fe2B's hardness first increases and then has little change. Black-Right-Pointing-Pointer The toughness at 2.04 % W can be improved by above 80% more than that at 0% W.
NASA Technical Reports Server (NTRS)
Martinez, Andres; Benavides, Jose Victor; Ormsby, Steve L.; GuarnerosLuna, Ali
2014-01-01
Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) are bowling-ball sized satellites that provide a test bed for development and research into multi-body formation flying, multi-spacecraft control algorithms, and free-flying physical and material science investigations. Up to three self-contained free-flying satellites can fly within the cabin of the International Space Station (ISS), performing flight formations, testing of control algorithms or as a platform for investigations requiring this unique free-flying test environment. Each satellite is a self-contained unit with power, propulsion, computers, navigation equipment, and provides physical and electrical connections (via standardized expansion ports) for Principal Investigator (PI) provided hardware and sensors.
NASA Astrophysics Data System (ADS)
Naeem, Haider T.; Mohammed, Kahtan S.; Ahmad, Khairel R.
2015-10-01
The main object of this study is to investigate the effect of friction stir processing (FSP) on the microstructure and hardness of Al-Zn-Mg-Cu alloys that were produced via casting with the addition of 5 wt % nickel. Furthermore, a single-pass FSP with a rotational speed of 1500 rpm and a traveling speed of 40 mm/min was performed on the alloys. The FSP-treated cast alloys were homogenized, aged at 120°C for 24 h, retrogressed at 180°C for 30 min, and then re-aged at 120°C for 24 h. Microstructural evaluations via optical microscopy and scanning electron microscopy, as well as with energy dispersive X-ray spectroscopy were conducted. In addition, X-ray diffraction analysis was performed to detect the intermetallics and phases of the Al-Zn-Mg-Cu-Ni alloys. Before FSP, the microstructural observations indicated the presence of coarse Ni dispersed particles with a precipitate phase within the matrix. After FSP treatment, the grain refinement led to the uniform space distribution of Ni dispersed particles in the stir zone. The Vickers hardness values for the Al-Zn-Mg-Cu-Ni alloy increased after age tempering at T6 and retrogression and re-aging (RRA) treatment because of the increased precipitation and particles dispersity. The hardness of the Al-Zn-Mg-Cu-Ni alloy was enhanced after FSP and a series of heat treatments, especially the RRA process, because of the stirring action of the FSP tool, the grain refinement, the appearance of additional precipitates, and the refinement of dispersed Ni particles.
Steel and titanium hollow sphere foams
Hurysz, K.M.; Clark, J.L.; Nagel, A.R.; Lee, K.J.; Cochran, J.K.; Sanders, T.H. Jr.; Hardwicke, C.U.
1998-12-31
Metal hollow sphere foams are fabricated by bonding millimeter sized metal alloy hollow spheres at points of contact. The spheres are formed as powder shells from slurries. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe/Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO{sub 2} atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. Hardness measurements on steel sphere walls were used to estimate the yield strength. Relative strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained defects. As processing improves, strengths should increase. To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. Oxygen contents are a concern for titanium compositions and processing is being altered to reduce oxygen levels to increase ductility.
NASA Astrophysics Data System (ADS)
Wang, Yongyong; Dong, Xiao; Song, Xiaohui; Wang, Jinfeng; Li, Gong; Liu, Riping
2016-05-01
The thermal and mechanical properties of Zr57Al15Co28- X Ag X ( X = 0 and 8) amorphous alloys were investigated using differential scanning calorimetry, in situ high-pressure angle dispersive X-ray diffraction measurements with synchrotron radiation, and nanoindentation. Results show that Ag doping improves effective activation energy, nanohardness, elastic modulus, and bulk modulus. Ag addition enhances topological and chemical short-range orderings, which can improve local packing efficiency and restrain long-range atom diffusion. This approach has implications for the design of the microstructure- and property-controllable functional materials for various applications.
Sticky surface: sphere-sphere adhesion dynamics
Sircar, Sarthok; Younger, John G.; Bortz, David M.
2014-01-01
We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluid-immersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive / repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e., non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favors large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g → 1) and in a neutral solution with no dissolved salts. PMID:25159830
NASA Astrophysics Data System (ADS)
Ackermann, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bhat, P. N.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Connaughton, V.; Conrad, J.; Dermer, C. D.; de Palma, F.; Dingus, B. L.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Finke, J.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Glanzman, T.; Godfrey, G.; Granot, J.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kouveliotou, C.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Mazziotta, M. N.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakajima, H.; Nakamori, T.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Preece, R.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Ritz, S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sander, A.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Stecker, F. W.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Toma, K.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Uehara, T.; Usher, T. L.; van der Horst, A. J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wang, P.; Wilson-Hodge, C.; Winer, B. L.; Wu, X. F.; Yamazaki, R.; Yang, Z.; Ylinen, T.; Ziegler, M.
2010-06-01
We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB 090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with E peak = 3.9 ± 0.3 MeV, which is the highest yet measured, and a hard power-law component with photon index -1.62 ± 0.03 that dominates the emission below ≈20 keV and above ≈100 MeV. The onset of the high-energy spectral component appears to be delayed by ~0.1 s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5 s before the main pulse. During the prompt phase, the LAT detected a photon with energy 30.5+5.8 -2.6 GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, Γgsim 1200, using simple γγ opacity arguments for this GRB at redshift z = 0.903 and a variability timescale on the order of tens of ms for the ≈100 keV-few MeV flux. Stricter high confidence estimates imply Γ >~ 1000 and still require that the outflows powering short GRBs are at least as highly relativistic as those of long-duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton, external-shock synchrotron, and hadronic models are considered.
Towards composite spheres as building blocks for structured molecules.
Lee, Lloyd L; Pellicane, Giuseppe
2016-10-19
In order to design a flexible molecular model that mimics the chemical moieties of a polyatomic molecule, we propose the 'composite-sphere' model that can assemble the essential elements to produce the structure of the target molecule. This is likened to the polymerization process where monomers assemble to form the polymer. The assemblage is built into the pair interaction potentials which can 'react' (figuratively) with selective pieces into various bonds. In addition, we preserve the spherical symmetries of the individual pair potentials so that the isotropic Ornstein-Zernike equation (OZ) for multi-component mixtures can be used as a theoretical framework. We first test our approach on generating a dumbbell molecule. An equimolar binary mixture of hard spheres and square-well spheres are allowed to react to form a dimer. As the bond length shrinks to zero, we create a site-site model of a Janus-like molecule with a repulsive moiety and an attractive moiety. We employ the zero-separation (ZSEP) closure to solve the OZ equations. The structure and thermodynamic properties are calculated at three isotherms and at several densities and the results are compared with Monte Carlo simulations. The close agreement achieved demonstrates that the ZSEP closure is a reliable theory for this composite-sphere fluid model. PMID:27546819
Terminal energy distribution of blast waves from bursting spheres
NASA Technical Reports Server (NTRS)
Adamczyk, A. A.; Strehlow, R. A.
1977-01-01
The calculation results for the total energy delivered to the surroundings by the burst of an idealized massless sphere containing an ideal gas are presented. The logic development of various formulas for sphere energy is also presented. For all types of sphere bursts the fraction of the total initial energy available in the sphere that is delivered to the surroundings is shown to lie between that delivered for the constant pressure addition of energy to a source region and that delivered by isentropic expansion of the sphere. The relative value of E sub/Q increases at fixed sphere pressure/surrounding pressure as sphere temperature increases because the velocity of sound increases.
Rios, Orlando; Radhakrishnan, Balasubramaniam; Caravias, George; Holcomb, Matthew
2015-03-11
Grid Logic Inc. is developing a method for sintering and melting fine metallic powders for additive manufacturing using spatially-compact, high-frequency magnetic fields called Micro-Induction Sintering (MIS). One of the challenges in advancing MIS technology for additive manufacturing is in understanding the power transfer to the particles in a powder bed. This knowledge is important to achieving efficient power transfer, control, and selective particle heating during the MIS process needed for commercialization of the technology. The project s work provided a rigorous physics-based model for induction heating of fine spherical particles as a function of frequency and particle size. This simulation improved upon Grid Logic s earlier models and provides guidance that will make the MIS technology more effective. The project model will be incorporated into Grid Logic s power control circuit of the MIS 3D printer product and its diagnostics technology to optimize the sintering process for part quality and energy efficiency.
Specific surface area of overlapping spheres in the presence of obstructions
NASA Astrophysics Data System (ADS)
Jenkins, D. R.
2013-02-01
This study considers the random placement of uniform sized spheres, which may overlap, in the presence of another set of randomly placed (hard) spheres, which do not overlap. The overlapping spheres do not intersect the hard spheres. It is shown that the specific surface area of the collection of overlapping spheres is affected by the hard spheres, such that there is a minimum in the specific surface area as a function of the relative size of the two sets of spheres. The occurrence of the minimum is explained in terms of the break-up of pore connectivity. The configuration can be considered to be a simple model of the structure of a porous composite material. In particular, the overlapping particles represent voids while the hard particles represent fillers. Example materials are pervious concrete, metallurgical coke, ice cream, and polymer composites. We also show how the material properties of such composites are affected by the void structure.
Yang, Zhi; Yi, Yafei; Zhong, Mingdong; De, Sriman; Mondal, Totan; Koley, Debasis; Ma, Xiaoli; Zhang, Dongxiang; Roesky, Herbert W
2016-05-10
The reaction of one equivalent of LAlH2 (1; L=HC(CMeNAr)2 , Ar=2,6-iPr2 C6 H3 , β-diketiminate ligand) with two equivalents of 2-mercapto-4,6-dimethylpyrimidine hydrate resulted in LAl[(μ-S)(m-C4 N2 H)(CH2 )2 ]2 (2) in good yield. Similarly, when N-2-pyridylsalicylideneamine, N-(2,6-diisopropylphenyl)salicylaldimine, and ethyl 3-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-2-carboxylate were used as starting materials, the corresponding products LAl[(μ-O)(o-C6 H4 )CN(C5 NH4 )]2 (3), LAlH[(μ-O)(o-C4 H4 )CN(2,6-iPr2 C6 H3 )] (4), and LAl[(μ-NH)(o-C8 SH8 )(COOC2 H5 )]2 (5) were isolated. Compounds 2-5 were characterized by (1) H and (13) C NMR spectroscopy as well as by single-crystal X-ray structural analysis. Surprisingly, compounds 2-5 exhibit good catalytic activity in addition reactions of aldehydes with trimethylsilyl cyanide (TMSCN).
Seeded Synthesis of Monodisperse Core-Shell and Hollow Carbon Spheres.
Gil-Herrera, Luz Karime; Blanco, Álvaro; Juárez, Beatriz H; López, Cefe
2016-08-01
Monodisperse carbon spheres between 500 and 900 nm are hydrothermally synthesized from glucose on polystyrene seeds. Control over temperature, time, glucose concentration, and seed size yields hybrid spheres without aggregation and no additional spheres population. Pyrolysis transforms the hybrid into hollow carbon spheres preserving monodispersity. This approach provides a basis for functional carbon spheres applicable in photonics and energy storage. PMID:27337299
Seeded Synthesis of Monodisperse Core-Shell and Hollow Carbon Spheres.
Gil-Herrera, Luz Karime; Blanco, Álvaro; Juárez, Beatriz H; López, Cefe
2016-08-01
Monodisperse carbon spheres between 500 and 900 nm are hydrothermally synthesized from glucose on polystyrene seeds. Control over temperature, time, glucose concentration, and seed size yields hybrid spheres without aggregation and no additional spheres population. Pyrolysis transforms the hybrid into hollow carbon spheres preserving monodispersity. This approach provides a basis for functional carbon spheres applicable in photonics and energy storage.
Towards composite spheres as building blocks for structured molecules
NASA Astrophysics Data System (ADS)
Lee, Lloyd L.; Pellicane, Giuseppe
2016-10-01
In order to design a flexible molecular model that mimics the chemical moieties of a polyatomic molecule, we propose the ‘composite-sphere’ model that can assemble the essential elements to produce the structure of the target molecule. This is likened to the polymerization process where monomers assemble to form the polymer. The assemblage is built into the pair interaction potentials which can ‘react’ (figuratively) with selective pieces into various bonds. In addition, we preserve the spherical symmetries of the individual pair potentials so that the isotropic Ornstein-Zernike equation (OZ) for multi-component mixtures can be used as a theoretical framework. We first test our approach on generating a dumbbell molecule. An equimolar binary mixture of hard spheres and square-well spheres are allowed to react to form a dimer. As the bond length shrinks to zero, we create a site-site model of a Janus-like molecule with a repulsive moiety and an attractive moiety. We employ the zero-separation (ZSEP) closure to solve the OZ equations. The structure and thermodynamic properties are calculated at three isotherms and at several densities and the results are compared with Monte Carlo simulations. The close agreement achieved demonstrates that the ZSEP closure is a reliable theory for this composite-sphere fluid model. Contribution to the George Stell Memorial Issue.
Multicomponent fluids of hard hyperspheres in odd dimensions.
Rohrmann, René D; Santos, Andrés
2011-01-01
Mixtures of hard hyperspheres in odd-space dimensionalities are studied with an analytical approximation method. This technique is based on the so-called rational function approximation and provides a procedure for evaluating equations of state, structure factors, radial distribution functions, and direct correlation functions of additive mixtures of hard hyperspheres with any number of components and in arbitrary odd-dimension space. The method gives the exact solution of the Ornstein-Zernike equation coupled with the Percus-Yevick closure, thus, extending the solution for hard-sphere mixtures [J. L. Lebowitz, Phys. Rev. 133, A895 (1964)] to arbitrary odd dimensions. Explicit evaluations for binary mixtures in five dimensions are performed. The results are compared with computer simulations, and a good agreement is found.
The Smart SPHERES space robot (Synchronized Position Hold, Engage, Reorient, Experimental Satellites) equipped with an Android smartphone performs a video survey inside of the International Space S...
NASA Technical Reports Server (NTRS)
Elleman, Daniel D. (Inventor); Wang, Taylor G. (Inventor)
1989-01-01
Systems are described for using multiple closely-packed spheres. In one system for passing fluid, a multiplicity of spheres lie within a container, with all of the spheres having the same outside diameter and with the spheres being closely nested in one another to create multiple interstitial passages of a known size and configuration and smooth walls. The container has an inlet and outlet for passing fluid through the interstitial passages formed between the nested spheres. The small interstitial passages can be used to filter out material, especially biological material such as cells in a fluid, where the cells can be easily destroyed if passed across sharp edges. The outer surface of the spheres can contain a material that absorbs a constitutent in the flowing fluid, such as a particular contamination gas, or can contain a catalyst to chemically react the fluid passing therethrough, the use of multiple small spheres assuring a large area of contact of these surfaces of the spheres with the fluid. In a system for storing and releasing a fluid such as hydrogen as a fuel, the spheres can include a hollow shell containing the fluid to be stored, and located within a compressable container that can be compressed to break the shells and release the stored fluid.
ERIC Educational Resources Information Center
Szekely, George
2011-01-01
This article describes an art lesson that allows students to set up and collect sphere canvases. Spheres move art away from a rectangular canvas into a dimension that requires new planning and painting. From balls to many other spherical canvases that bounce, roll, float and fly, art experiences are envisioned by students. Even if adults recognize…
NASA Astrophysics Data System (ADS)
Chaney, A.; Lu, Lei; Stern, A.
2015-09-01
We show that fuzzy spheres are solutions of Lorentzian Ishibashi-Kawai-Kitazawa-Tsuchiya-type matrix models. The solutions serve as toy models of closed noncommutative cosmologies where big bang/crunch singularities appear only after taking the commutative limit. The commutative limit of these solutions corresponds to a sphere embedded in Minkowski space. This "sphere" has several novel features. The induced metric does not agree with the standard metric on the sphere, and, moreover, it does not have a fixed signature. The curvature computed from the induced metric is not constant, has singularities at fixed latitudes (not corresponding to the poles) and is negative. Perturbations are made about the solutions, and are shown to yield a scalar field theory on the sphere in the commutative limit. The scalar field can become tachyonic for a range of the parameters of the theory.
Superelastic carbon spheres under high pressure
NASA Astrophysics Data System (ADS)
Li, Meifen; Guo, Junjie; Xu, Bingshe
2013-03-01
We report a superelastic deformation behavior of carbon spheres by the in situ Raman spectroscopy in a high-pressure diamond anvil cell. The carbon spheres produced by arc discharging in toluene have a mean diameter of 200 nm and an onion-like multilayer graphitic structure. We find that the elastic coefficients, during both the compression and decompression processes, remain a constant up to 10 GPa, indicating a superior high-pressure structural stability. Such superelastic behavior is related to the isotropic and concentric configuration of carbon spheres and provides additional insight into improving the microscopic mechanical properties of small-scale particles.
NASA Technical Reports Server (NTRS)
Benavides, Jose
2014-01-01
SPHERES is a facility of the ISS National Laboratory with three IVA nano-satellites designed and delivered by MIT to research estimation, control, and autonomy algorithms. Since Fall 2010, The SPHERES system is now operationally supported and managed by NASA Ames Research Center (ARC). A SPHERES Program Office was established and is located at NASA Ames Research Center. The SPHERES Program Office coordinates all SPHERES related research and STEM activities on-board the International Space Station (ISS), as well as, current and future payload development. By working aboard ISS under crew supervision, it provides a risk tolerant Test-bed Environment for Distributed Satellite Free-flying Control Algorithms. If anything goes wrong, reset and try again! NASA has made the capability available to other U.S. government agencies, schools, commercial companies and students to expand the pool of ideas for how to test and use these bowling ball-sized droids. For many of the researchers, SPHERES offers the only opportunity to do affordable on-orbit characterization of their technology in the microgravity environment. Future utilization of SPHERES as a facility will grow its capabilities as a platform for science, technology development, and education.
Equation of state for hard convex body fluid mixtures
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
A model previously developed for the equation of state of pure fluids consisting of hard convex body molecules is extended to mixtures. The parameters of the model can be determined from the geometrical characteristics of the molecules which form the mixture. The equation of state is in excellent agreement with simulation data for mixtures of hard spheres with hard spherocylinders.
NASA Astrophysics Data System (ADS)
Shaulov, S. B.; Besshapov, S. P.; Kabanova, N. V.; Sysoeva, T. I.; Antonov, R. A.; Anyuhina, A. M.; Bronvech, E. A.; Chernov, D. V.; Galkin, V. I.; Tkaczyk, W.; Finger, M.; Sonsky, M.
2009-12-01
The expedition carried out in March, 2008 to Lake Baikal became an important stage in the development of the SPHERE experiment. During the expedition the SPHERE-2 installation was hoisted, for the first time, on a tethered balloon, APA, to a height of 700 m over the lake surface covered with ice and snow. A series of test measurements were made. Preliminary results of the data processing are presented. The next plan of the SPHERE experiment is to begin a set of statistics for constructing the CR spectrum in the energy range 10-10 eV.
Dependence on sphere size of the phase behavior of mixtures of rods and spheres
NASA Astrophysics Data System (ADS)
Urakami, Naohito; Imai, Masayuki
2003-07-01
By the addition of chondroitin sulfate (Chs) to the aqueous suspension of tobacco mosaic virus (TMV), the aggregation of TMV occurs at very dilute TMV concentration compared with the addition of polyethylene oxide (PEO). The difference of physical behavior between Chs and PEO is the chain conformation in solution. The Chs chain has a semirigid nature, whereas the PEO chain has a flexible nature. In this study, the Chs and PEO chains are simplified to spherical particles having different size, and we use the spherocylinder model for TMV particle. The effect of the sphere size on the phase behaviors in the mixtures of rods and spheres is investigated by Monte Carlo simulations. By the addition of small spheres, the system transforms from the miscible isotropic phase to the miscible nematic phase. On the other hand, by the addition of large spheres, the system changes from the miscible isotropic phase to the immiscible nematic phase through the immiscible isotropic phase. The different phase behaviors between the small and the large spheres originate from the difference of overlapping volume of the depletion zone. In addition, we perform the Monte Carlo simulations in the case that semirigid chains are used as the Chs chain models. The same phase behaviors are observed as the mixtures of rods and large spheres. Thus the sphere model captures the phase behaviors of rod and polymer mixture systems.
Sknepnek, Rastko; Henkes, Silke
2015-02-01
We show that coupling to curvature nontrivially affects collective motion in active systems, leading to motion patterns not observed in flat space. Using numerical simulations, we study a model of self-propelled particles with polar alignment and soft repulsion confined to move on the surface of a sphere. We observe a variety of motion patterns with the main hallmarks being polar vortex and circulating band states arising due to the incompatibility between spherical topology and uniform motion-a consequence of the "hairy ball" theorem. We provide a detailed analysis of density, velocity, pressure, and stress profiles in the circulating band state. In addition, we present analytical results for a simplified model of collective motion on the sphere showing that frustration due to curvature leads to stable elastic distortions storing energy in the band. PMID:25768504
Sknepnek, Rastko; Henkes, Silke
2015-02-01
We show that coupling to curvature nontrivially affects collective motion in active systems, leading to motion patterns not observed in flat space. Using numerical simulations, we study a model of self-propelled particles with polar alignment and soft repulsion confined to move on the surface of a sphere. We observe a variety of motion patterns with the main hallmarks being polar vortex and circulating band states arising due to the incompatibility between spherical topology and uniform motion-a consequence of the "hairy ball" theorem. We provide a detailed analysis of density, velocity, pressure, and stress profiles in the circulating band state. In addition, we present analytical results for a simplified model of collective motion on the sphere showing that frustration due to curvature leads to stable elastic distortions storing energy in the band.
Generalised Cornu spirals: an experimental study using hard x-rays.
Werdiger, Freda; Kitchen, Marcus J; Paganin, David M
2016-05-16
The Cornu spiral is a graphical aid that has been used historically to evaluate Fresnel integrals. It is also the Argand-plane mapping of a monochromatic complex scalar plane wave diffracted by a hard edge. We have successfully reconstructed a Cornu spiral due to diffraction of hard x-rays from a piece of Kapton tape. Additionally, we have explored the generalisation of the Cornu spiral by observing the Argand-plane mapping of complex scalar electromagnetic fields diffracted by a cylinder and a sphere embedded within a cylinder.
Generalised Cornu spirals: an experimental study using hard x-rays.
Werdiger, Freda; Kitchen, Marcus J; Paganin, David M
2016-05-16
The Cornu spiral is a graphical aid that has been used historically to evaluate Fresnel integrals. It is also the Argand-plane mapping of a monochromatic complex scalar plane wave diffracted by a hard edge. We have successfully reconstructed a Cornu spiral due to diffraction of hard x-rays from a piece of Kapton tape. Additionally, we have explored the generalisation of the Cornu spiral by observing the Argand-plane mapping of complex scalar electromagnetic fields diffracted by a cylinder and a sphere embedded within a cylinder. PMID:27409884
NASA Public Affairs Officer Kelly Humphries conducts a phone interview with Mark Micire, SPHERES Engineering Manager at Ames Research Center. Questions? Ask us on Twitter @NASA_Johnson and include ...
Catalytic, hollow, refractory spheres
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1987-01-01
Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material 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.
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1989-01-01
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.
NASA Astrophysics Data System (ADS)
Sun, Xiaochun
The armillary sphere was perhaps the most important type of astronomical instrument in ancient China. It was first invented by Luoxia Hong in the first century BC. After Han times, the structure of the armillary sphere became increasingly sophisticated by including more and more rings representing various celestial movements as recognized by the Chinese astronomers. By the eighth century, the Chinese armillary sphere consisted of three concentric sets of rings revolving on the south-north polar axis. The relative position of the rings could be adjusted to reflect the precession of the equinoxes and the regression of the Moon's nodes along the ecliptic. To counterbalance the defect caused by too many rings, Guo Shoujing from the late thirteenth century constructed the Simplified Instruments which reorganized the rings of the armillary sphere into separate instruments for measuring equatorial coordinates and horizontal coordinates. The armillary sphere was still preserved because it was a good illustration of celestial movements. A fifteenth-century replica of Guo Shoujing's armillary sphere still exists today.
Uniform hollow magnetite spheres: Facile synthesis, growth mechanism, and their magnetic properties
Zhou, Xing; Zhao, Guizhe; Liu, Yaqing
2014-11-15
Highlights: • Uniform Fe{sub 3}O{sub 4} hollow spheres with high saturation magnetization were synthesized through a simple solvothermal process. • Without using any hard templates or external magnetic field. • The as-prepared magnetite hollow spheres exhibit a ferromagnetic behavior with high Ms of ca. 85.9 emu/g at room temperature. • The morphology of Fe{sub 3}O{sub 4} with nanoparticles, hollow, and irregular structures could be adjusted by changing the reactive conditions. - Abstract: Hierarchical porous Fe{sub 3}O{sub 4} hollow spheres with high saturation magnetization were synthesized through a simple solvothermal process in ethylene glycol (EG) in the presence of Tetrabutylammonium chloride (TBAC) and urea. By investigating the effect of reaction temperature, time, the amount of urea, and concentration of iron ion on the formation of hollow spheres, it was proposed that the main formation mechanism of hollow spheres is Ostwald ripening process combined with assembly-then-inside-out evacuation process. Additionally, it is found that the morphology of Fe{sub 3}O{sub 4} with nanoparticles, hollow, and irregular structures could be adjusted by changing the above factors. The resulting products were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The hierarchical porous Fe{sub 3}O{sub 4} hollow spheres exhibited enhanced saturation magnetization as compared with Fe{sub 3}O{sub 4} nanoparticles.
Note: Sound velocity of a soft sphere model near the fluid-solid phase transition.
Khrapak, Sergey A
2016-03-28
The quasilocalized charge approximation is applied to estimate the sound velocity of simple soft sphere fluid with the repulsive inverse-power-law interaction. The obtained results are discussed in the context of the sound velocity of the hard-sphere system and of liquid metals at the melting temperature. PMID:27036483
Diagnosis of a Poorly Performing Liquid Hydrogen Bulk Storage Sphere
NASA Technical Reports Server (NTRS)
Krenn, Angela G.
2011-01-01
There are two 850,000 gallon Liquid Hydrogen (LH2) storage spheres used to support the Space Shuttle Program; one residing at Launch Pad A and the other at Launch Pad B. The LH2 Sphere at Pad B has had a high boiloff rate since being brought into service in the 1960's. The daily commodity loss was estimated to be approximately double that of the Pad A sphere, and well above the minimum required by the sphere's specification. Additionally, after being re-painted in the late 1990's a "cold spot" appeared on the outer sphere which resulted in a poor paint bond, and mold formation. Thermography was used to characterize the area, and the boiloff rate was continually evaluated. All evidence suggested that the high boiloff rate was caused by an excessive heat leak into the inner sphere due to an insulation void in the annulus. Pad B was recently taken out of Space Shuttle program service which provided a unique opportunity to diagnose the sphere's poor performance. The sphere was drained and inerted, and then opened from the annular relief device on the top where a series of boroscoping operations were accomplished. Boroscoping revealed a large Perlite insulation void in the region of the sphere where the cold spot was apparent. Perlite was then trucked in and off-loaded into the annular void region until the annulus was full. The sphere has not yet been brought back into service.
Characterization of maximally random jammed sphere packings: Voronoi correlation functions
NASA Astrophysics Data System (ADS)
Klatt, Michael A.; Torquato, Salvatore
2014-11-01
We characterize the structure of maximally random jammed (MRJ) sphere packings by computing the Minkowski functionals (volume, surface area, and integrated mean curvature) of their associated Voronoi cells. The probability distribution functions of these functionals of Voronoi cells in MRJ sphere packings are qualitatively similar to those of an equilibrium hard-sphere liquid and partly even to the uncorrelated Poisson point process, implying that such local statistics are relatively structurally insensitive. This is not surprising because the Minkowski functionals of a single Voronoi cell incorporate only local information and are insensitive to global structural information. To improve upon this, we introduce descriptors that incorporate nonlocal information via the correlation functions of the Minkowski functionals of two cells at a given distance as well as certain cell-cell probability density functions. We evaluate these higher-order functions for our MRJ packings as well as equilibrium hard spheres and the Poisson point process. It is shown that these Minkowski correlation and density functions contain visibly more information than the corresponding standard pair-correlation functions. We find strong anticorrelations in the Voronoi volumes for the hyperuniform MRJ packings, consistent with previous findings for other pair correlations [A. Donev et al., Phys. Rev. Lett. 95, 090604 (2005), 10.1103/PhysRevLett.95.090604], indicating that large-scale volume fluctuations are suppressed by accompanying large Voronoi cells with small cells, and vice versa. In contrast to the aforementioned local Voronoi statistics, the correlation functions of the Voronoi cells qualitatively distinguish the structure of MRJ sphere packings (prototypical glasses) from that of not only the Poisson point process but also the correlated equilibrium hard-sphere liquids. Moreover, while we did not find any perfect icosahedra (the locally densest possible structure in which a central
NASA Astrophysics Data System (ADS)
Bormann, H.
The 1-D process-based model SIMULAT was applied to the 6 ha large artificial catchment “Chicken Creek” in Lausatia, Germany. Within the framework of a model intercomparison study, data availability was improved step by step, starting from sparse data conditions. Initially, the model was parameterised based on transfer functions (e.g., soil hydraulic properties were estimated from pedotransfer functions) and literature (e.g., plant parameters, boundary conditions), only. Then parameterisation was revised based on field inspection and additional quantitative data (e.g., from point measurements). Finally, soil moisture data were used for validation and calibration purposes. During this parameterisation process, model results became increasingly plausible although calibration and validation against observed discharge were not feasible because discharge data were not available to the modellers. Simulated discharge dynamics changed from an initially base flow-dominated and continuous flow regime to a system in which different flow components contribute similarly to the event-based total discharge, better conforming to the hydrological process understanding with respect to the development of a gully network. Qualitative information (=soft data) gained from a field visit particularly contributed to this improvement in process understanding towards a flow regime dominated by surface runoff, while additional quantitative information on system characteristics rather served the purpose of verifying (or revising) of model parameterisation and defining appropriate initial conditions. An evaluation of simulated surface runoff rates based on event-based discharge information for a subcatchment revealed that the model overestimated the surface runoff generation for all advanced modelling steps. A final validation of model results is not yet feasible as continuous discharge data at the catchment outlet are not available so far. However, the model application indicated that
Swelling of cross-linked polystyrene spheres in toluene vapor
Zhang, R.; Graf, K.; Berger, R.
2006-11-27
The swelling behavior of individual micron-sized polystyrene (PS) spheres in toluene vapor was studied via mass loading by means of micromechanical cantilever sensors. For 4%-8% cross-linked PS a mass increase of 180% in saturated toluene vapor was measured. The mass of the swollen PS sphere decreases with increasing exposure time to ultraviolet light. In addition, the swelling response is significantly different between the first and the second exposure to toluene vapor. This is attributed to the formation of a cross-linked shell at the surface of the PS spheres. Shape persistent parts were observed for locally irradiated PS spheres.
Li, Xufan; Chi, Miaofang; Mahurin, Shannon Mark; Liu, Rui; Chuang, Yen -Jun; Dai, Sheng; Pan, Zhengwei
2016-01-18
Hard-sphere-templating method has been widely used to synthesize hollow carbon spheres (HCSs), in which the spheres were firstly coated with a carbon precursor, followed by carbonization and core removal. The obtained HCSs are generally amorphous or weakly graphitized (with the help of graphitization catalysts). In this work, we report on the fabrication of graphitized HCSs and yolk–shell Au@HCS nanostructures using a modified templating method, in which smooth, uniform graphene layers were grown on SiO2 spheres or Au@SiO2 nanoparticles via metal-catalyst-free chemical vapor deposition (CVD) of methane. Furthermore, our work not only provides a new method to fabricate high-quality, graphitized HCSsmore » but also demonstrates a reliable approach to grow quality graphene on oxide surfaces using CVD without the presence of metal catalysts.« less
Scalable Metropolis Monte Carlo for simulation of hard shapes
NASA Astrophysics Data System (ADS)
Anderson, Joshua A.; Eric Irrgang, M.; Glotzer, Sharon C.
2016-07-01
We design and implement a scalable hard particle Monte Carlo simulation toolkit (HPMC), and release it open source as part of HOOMD-blue. HPMC runs in parallel on many CPUs and many GPUs using domain decomposition. We employ BVH trees instead of cell lists on the CPU for fast performance, especially with large particle size disparity, and optimize inner loops with SIMD vector intrinsics on the CPU. Our GPU kernel proposes many trial moves in parallel on a checkerboard and uses a block-level queue to redistribute work among threads and avoid divergence. HPMC supports a wide variety of shape classes, including spheres/disks, unions of spheres, convex polygons, convex spheropolygons, concave polygons, ellipsoids/ellipses, convex polyhedra, convex spheropolyhedra, spheres cut by planes, and concave polyhedra. NVT and NPT ensembles can be run in 2D or 3D triclinic boxes. Additional integration schemes permit Frenkel-Ladd free energy computations and implicit depletant simulations. In a benchmark system of a fluid of 4096 pentagons, HPMC performs 10 million sweeps in 10 min on 96 CPU cores on XSEDE Comet. The same simulation would take 7.6 h in serial. HPMC also scales to large system sizes, and the same benchmark with 16.8 million particles runs in 1.4 h on 2048 GPUs on OLCF Titan.
Krogh, M.; Painter, J.; Hansen, C.
1996-10-01
Sphere rendering is an important method for visualizing molecular dynamics data. This paper presents a parallel algorithm that is almost 90 times faster than current graphics workstations. To render extremely large data sets and large images, the algorithm uses the MIMD features of the supercomputers to divide up the data, render independent partial images, and then finally composite the multiple partial images using an optimal method. The algorithm and performance results are presented for the CM-5 and the M.
Hard convex lens-shaped particles: Densest-known packings and phase behavior
Cinacchi, Giorgio; Torquato, Salvatore
2015-12-14
By using theoretical methods and Monte Carlo simulations, this work investigates dense ordered packings and equilibrium phase behavior (from the low-density isotropic fluid regime to the high-density crystalline solid regime) of monodisperse systems of hard convex lens-shaped particles as defined by the volume common to two intersecting congruent spheres. We show that, while the overall similarity of their shape to that of hard oblate ellipsoids is reflected in a qualitatively similar phase diagram, differences are more pronounced in the high-density crystal phase up to the densest-known packings determined here. In contrast to those non-(Bravais)-lattice two-particle basis crystals that are the densest-known packings of hard (oblate) ellipsoids, hard convex lens-shaped particles pack more densely in two types of degenerate crystalline structures: (i) non-(Bravais)-lattice two-particle basis body-centered-orthorhombic-like crystals and (ii) (Bravais) lattice monoclinic crystals. By stacking at will, regularly or irregularly, laminae of these two crystals, infinitely degenerate, generally non-periodic in the stacking direction, dense packings can be constructed that are consistent with recent organizing principles. While deferring the assessment of which of these dense ordered structures is thermodynamically stable in the high-density crystalline solid regime, the degeneracy of their densest-known packings strongly suggests that colloidal convex lens-shaped particles could be better glass formers than colloidal spheres because of the additional rotational degrees of freedom.
Hard convex lens-shaped particles: Densest-known packings and phase behavior
NASA Astrophysics Data System (ADS)
Cinacchi, Giorgio; Torquato, Salvatore
2015-12-01
By using theoretical methods and Monte Carlo simulations, this work investigates dense ordered packings and equilibrium phase behavior (from the low-density isotropic fluid regime to the high-density crystalline solid regime) of monodisperse systems of hard convex lens-shaped particles as defined by the volume common to two intersecting congruent spheres. We show that, while the overall similarity of their shape to that of hard oblate ellipsoids is reflected in a qualitatively similar phase diagram, differences are more pronounced in the high-density crystal phase up to the densest-known packings determined here. In contrast to those non-(Bravais)-lattice two-particle basis crystals that are the densest-known packings of hard (oblate) ellipsoids, hard convex lens-shaped particles pack more densely in two types of degenerate crystalline structures: (i) non-(Bravais)-lattice two-particle basis body-centered-orthorhombic-like crystals and (ii) (Bravais) lattice monoclinic crystals. By stacking at will, regularly or irregularly, laminae of these two crystals, infinitely degenerate, generally non-periodic in the stacking direction, dense packings can be constructed that are consistent with recent organizing principles. While deferring the assessment of which of these dense ordered structures is thermodynamically stable in the high-density crystalline solid regime, the degeneracy of their densest-known packings strongly suggests that colloidal convex lens-shaped particles could be better glass formers than colloidal spheres because of the additional rotational degrees of freedom.
Hard convex lens-shaped particles: Densest-known packings and phase behavior.
Cinacchi, Giorgio; Torquato, Salvatore
2015-12-14
By using theoretical methods and Monte Carlo simulations, this work investigates dense ordered packings and equilibrium phase behavior (from the low-density isotropic fluid regime to the high-density crystalline solid regime) of monodisperse systems of hard convex lens-shaped particles as defined by the volume common to two intersecting congruent spheres. We show that, while the overall similarity of their shape to that of hard oblate ellipsoids is reflected in a qualitatively similar phase diagram, differences are more pronounced in the high-density crystal phase up to the densest-known packings determined here. In contrast to those non-(Bravais)-lattice two-particle basis crystals that are the densest-known packings of hard (oblate) ellipsoids, hard convex lens-shaped particles pack more densely in two types of degenerate crystalline structures: (i) non-(Bravais)-lattice two-particle basis body-centered-orthorhombic-like crystals and (ii) (Bravais) lattice monoclinic crystals. By stacking at will, regularly or irregularly, laminae of these two crystals, infinitely degenerate, generally non-periodic in the stacking direction, dense packings can be constructed that are consistent with recent organizing principles. While deferring the assessment of which of these dense ordered structures is thermodynamically stable in the high-density crystalline solid regime, the degeneracy of their densest-known packings strongly suggests that colloidal convex lens-shaped particles could be better glass formers than colloidal spheres because of the additional rotational degrees of freedom. PMID:26671389
Confined disordered strictly jammed binary sphere packings
NASA Astrophysics Data System (ADS)
Chen, D.; Torquato, S.
2015-12-01
Disordered jammed packings under confinement have received considerably less attention than their bulk counterparts and yet arise in a variety of practical situations. In this work, we study binary sphere packings that are confined between two parallel hard planes and generalize the Torquato-Jiao (TJ) sequential linear programming algorithm [Phys. Rev. E 82, 061302 (2010), 10.1103/PhysRevE.82.061302] to obtain putative maximally random jammed (MRJ) packings that are exactly isostatic with high fidelity over a large range of plane separation distances H , small to large sphere radius ratio α , and small sphere relative concentration x . We find that packing characteristics can be substantially different from their bulk analogs, which is due to what we term "confinement frustration." Rattlers in confined packings are generally more prevalent than those in their bulk counterparts. We observe that packing fraction, rattler fraction, and degree of disorder of MRJ packings generally increase with H , though exceptions exist. Discontinuities in the packing characteristics as H varies in the vicinity of certain values of H are due to associated discontinuous transitions between different jammed states. When the plane separation distance is on the order of two large-sphere diameters or less, the packings exhibit salient two-dimensional features; when the plane separation distance exceeds about 30 large-sphere diameters, the packings approach three-dimensional bulk packings. As the size contrast increases (as α decreases), the rattler fraction dramatically increases due to what we call "size-disparity" frustration. We find that at intermediate α and when x is about 0.5 (50-50 mixture), the disorder of packings is maximized, as measured by an order metric ψ that is based on the number density fluctuations in the direction perpendicular to the hard walls. We also apply the local volume-fraction variance στ2(R ) to characterize confined packings and find that these
Pool boiling from rotating and stationary spheres in liquid nitrogen
NASA Technical Reports Server (NTRS)
Cuan, Winston M.; Schwartz, Sidney H.
1988-01-01
Results are presented for a preliminary experiment involving saturated pool boiling at 1 atm from rotating 2 and 3 in. diameter spheres which were immersed in liquid nitrogen (LN2). Additional results are presented for a stationary, 2 inch diameter sphere, quenched in LN2, which were obtained utilizing a more versatile and complete experimental apparatus that will eventually be used for additional rotating sphere experiments. The speed for the rotational tests was varied from 0 to 10,000 rpm. The stationary experiments parametrically varied pressure and subcooling levels from 0 to 600 psig and from 0 to 50 F, respectively. During the rotational tests, a high speed photographic analysis was undertaken to measure the thickness of the vapor film surrounding the sphere. The average Nusselt number over the cooling period was plotted against the rotational Reynolds number. Stationary sphere results included local boiling heat transfer coefficients at different latitudinal locations, for various pressure and subcooling levels.
Eggs and milk: Spinning spheres partially immersed in a liquid bath
NASA Astrophysics Data System (ADS)
Langley, Kenneth R.; Maynes, Daniel; Truscott, Tadd T.
2015-03-01
When a hard-boiled egg spins through a pool of milk on the kitchen counter, the milk rises up the sides of the egg and droplets are ejected. This phenomenon occurs when any partially submerged object whose radius increases upward from the fluid surface (e.g., spheres, inverted cones, and rings) spins in a liquid bath. The fluid ejects from the surface near the maximum radius in one of three ejection modes: jets, sheets, or sheet breakup. Additionally, a surprisingly large flow rate is induced by the spinning object. In this study, we used spheres to determine the effects of experimental parameters on the induced flow rate. We characterized the modes of ejection and measured the sheet breakup distance using high-speed imaging. The basis of our closed form analytical model utilizes an integral momentum boundary layer analysis both beneath the free surface and in the thin film attached to the sphere. We present criteria defining the transitions between ejection modes and the radius where liquid sheets break up in the sheet ejection regime. Criteria defining the transitions between ejection modes and the radius where liquid sheets break up in the sheet ejection regime shows good agreement with experiments.
Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors
2012-01-01
Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors. PMID:22643113
Theoretical study of miscibility and glass-forming trends in mixtures of polystyrene spheres
NASA Technical Reports Server (NTRS)
Shih, W.-H.; Stroud, D.
1984-01-01
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.
Krogh, M.; Hansen, C.; Painter, J.; de Verdiere, G.C.
1995-05-01
Sphere rendering is an important method for visualizing molecular dynamics data. This paper presents a parallel divide-and-conquer algorithm that is almost 90 times faster than current graphics workstations. To render extremely large data sets and large images, the algorithm uses the MIMD features of the supercomputers to divide up the data, render independent partial images, and then finally composite the multiple partial images using an optimal method. The algorithm and performance results are presented for the CM-5 and the T3D.
Hypervelocity flow over spheres
NASA Astrophysics Data System (ADS)
Wen, Chihyung
The nature of the nonequilibrium flow of dissociating gases over spheres was investigated experimentally, numerically and theoretically. A series of experiments with three different gases, nitrogen, air and carbon dioxide, was performed in the shock tunnel T5 at GALCIT. Five spheres of different radii equipped with thermocouples for surface heat flux measurements were used. The state-of-the-art numerical method by Candler (1988) was used to conduct a parallel study which strongly complemented the experimental and theoretical efforts.Experimental heat flux measurements are presented. Good agreement was observed among the measured stagnation point heat transfer rates, computational results and Fay and Riddell's theoretical predictions. For nitrogen and air, the measured heat flux distributions were also in good agreement with numerical computation results and Lees' theory. For carbon dioxide, large deviations were observed. Early transition tripped by surface roughness is a possible cause for the deviation of heat flux distribution from the theory. The experimental differential interferograms were compared with the images constructed from computational flowfields. Good agreement of fringe pattern and shock shape was observed.An analytical solution is obtained for inviscid hypervelocity dissociating flow over spheres. The solution explains the correlation between the dimensionless stand-off distance and the dimensionless reaction rate parameter previously observed by Hornung (1972) for nitrogen. The physics of the correlation can be shown as the binary scaling. Based on the solution, a new dimensionless reaction rate parameter is defined to generalize Hornung's correlation for more complex gases than nitrogen. Experimental and numerical results confirm the new correlation.The effect of nonequilibrium recombination downstream of a curved two-dimensional shock was also addressed. An analytical solution for an ideal dissociating gas was obtained, giving an expression for
Panoramic stereo sphere vision
NASA Astrophysics Data System (ADS)
Feng, Weijia; Zhang, Baofeng; Röning, Juha; Zong, Xiaoning; Yi, Tian
2013-01-01
Conventional stereo vision systems have a small field of view (FOV) which limits their usefulness for certain applications. While panorama vision is able to "see" in all directions of the observation space, scene depth information is missed because of the mapping from 3D reference coordinates to 2D panoramic image. In this paper, we present an innovative vision system which builds by a special combined fish-eye lenses module, and is capable of producing 3D coordinate information from the whole global observation space and acquiring no blind area 360°×360° panoramic image simultaneously just using single vision equipment with one time static shooting. It is called Panoramic Stereo Sphere Vision (PSSV). We proposed the geometric model, mathematic model and parameters calibration method in this paper. Specifically, video surveillance, robotic autonomous navigation, virtual reality, driving assistance, multiple maneuvering target tracking, automatic mapping of environments and attitude estimation are some of the applications which will benefit from PSSV.
Experimental Visualization of Flows in Packed Beds of Spheres
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Lattime, S.; Braun, M. J.; Athavale, M. M.
1997-01-01
The flow experiment consisted of an oil tunnel, 76 x 76 mm in cross-section, packed with lucite spheres. The index of refraction of the working fluid and the spheres were matched such that the physical spheres invisible to the eye and camera. By seeding the oil and illuminating the packed bed with planar laser light sheet, aligned in the direction of the bulk flow, the system fluid dynamics becomes visible and the 2-D projection was recorded at right angles to the bulk flow. The planar light sheet was traversed from one side of the tunnel to the other providing a simulated 3-D image of the entire flow field. The boundary interface between the working fluid and the sphere rendered the sphere black permitting visualization of the exact locations of the circular interfaces in both the axial and transverse directions with direct visualization of the complex interstitial spaces between the spheres within the bed. Flows were observed near the surfaces of a plane and set of spheres as well as minor circles that appear with great circles and not always uniformly ordered. In addition to visualizing a very complex flow field, it was observed that flow channeling in the direction of the bulk flow occurs between sets of adjacent spheres. Still photographs and video recordings illustrating the flow phenomena will be presented.
Dynamical tachyons on fuzzy spheres
Berenstein, David; Trancanelli, Diego
2011-05-15
We study the spectrum of off-diagonal fluctuations between displaced fuzzy spheres in the Berenstein-Maldacena-Nastase plane wave matrix model. The displacement is along the plane of the fuzzy spheres. We find that when two fuzzy spheres intersect at angles, classical tachyons develop and that the spectrum of these modes can be computed analytically. These tachyons can be related to the familiar Nielsen-Olesen instabilities in Yang-Mills theory on a constant magnetic background. Many features of the problem become more apparent when we compare with maximally supersymmetric Yang-Mills theory on a sphere, of which this system is a truncation. We also set up a simple oscillatory trajectory on the displacement between the fuzzy spheres and study the dynamics of the modes as they become tachyonic for part of the oscillations. We speculate on their role regarding the possible thermalization of the system.
Viscosities and sintering rates of composite packings of spheres
Jagota, A.; Scherer, G.W.
1995-03-01
The effective sintering rates and viscosities of three-dimensional composite packings have been studied using a discrete numerical model. The packings consist of random mixtures of hard and soft spheres of the same size. With increasing substitution of hard particles for soft particles in the packing, the viscosity increases and the sintering rate decreases. This is particularly abrupt at well-defined rigidity thresholds where there is a transition from softlike to hardlike behavior. The site fraction of hard particles at which the transition occurs depends on the nature of the interaction between hard particles. When the contact between hard particles resists all six relative degrees of freedom (relative velocities and spins). the bonded case, the rigidity threshold coincides with the percolation threshold (site fraction {approx}0.32). When the contact between hard particles resists only interpenetration. the sliding case, the threshold occurs at a site fraction of hard particles very close to unity. Results for the variation of effective properties with site fraction of hard particles are presented for these and other cases. These results can also be applied to the study of elastic percolating networks.
Tuning structure and mobility of solvation shells surrounding tracer additives
Carmer, James; Jain, Avni; Bollinger, Jonathan A.; Truskett, Thomas M.; Swol, Frank van
2015-03-28
Molecular dynamics simulations and a stochastic Fokker-Planck equation based approach are used to illuminate how position-dependent solvent mobility near one or more tracer particle(s) is affected when tracer-solvent interactions are rationally modified to affect corresponding solvation structure. For tracers in a dense hard-sphere fluid, we compare two types of tracer-solvent interactions: (1) a hard-sphere-like interaction, and (2) a soft repulsion extending beyond the hard core designed via statistical mechanical theory to enhance tracer mobility at infinite dilution by suppressing coordination-shell structure [Carmer et al., Soft Matter 8, 4083–4089 (2012)]. For the latter case, we show that the mobility of surrounding solvent particles is also increased by addition of the soft repulsive interaction, which helps to rationalize the mechanism underlying the tracer’s enhanced diffusivity. However, if multiple tracer surfaces are in closer proximity (as at higher tracer concentrations), similar interactions that disrupt local solvation structure instead suppress the position-dependent solvent dynamics.
Tuning structure and mobility of solvation shells surrounding tracer additives
NASA Astrophysics Data System (ADS)
Carmer, James; Jain, Avni; Bollinger, Jonathan A.; van Swol, Frank; Truskett, Thomas M.
2015-03-01
Molecular dynamics simulations and a stochastic Fokker-Planck equation based approach are used to illuminate how position-dependent solvent mobility near one or more tracer particle(s) is affected when tracer-solvent interactions are rationally modified to affect corresponding solvation structure. For tracers in a dense hard-sphere fluid, we compare two types of tracer-solvent interactions: (1) a hard-sphere-like interaction, and (2) a soft repulsion extending beyond the hard core designed via statistical mechanical theory to enhance tracer mobility at infinite dilution by suppressing coordination-shell structure [Carmer et al., Soft Matter 8, 4083-4089 (2012)]. For the latter case, we show that the mobility of surrounding solvent particles is also increased by addition of the soft repulsive interaction, which helps to rationalize the mechanism underlying the tracer's enhanced diffusivity. However, if multiple tracer surfaces are in closer proximity (as at higher tracer concentrations), similar interactions that disrupt local solvation structure instead suppress the position-dependent solvent dynamics.
Periodically oscillating plasma sphere
Park, J.; Nebel, R.A.; Stange, S.; Murali, S. Krupakar
2005-05-15
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.
Silica hollow spheres with nano-macroholes like diatomaceous earth.
Fujiwara, Masahiro; Shiokawa, Kumi; Sakakura, Ikuko; Nakahara, Yoshiko
2006-12-01
Artificial synthesis of hollow cell walls of diatoms is an ultimate target of nanomaterial science. The addition of some water-soluble polymers such as sodium polymethacrylate to a solution of water/oil/water emulsion system, which is an essential step of the simple synthetic procedure of silica hollow spheres (microcapsules), led to the formation of silica hollow spheres with nano-macroholes (>100 nm) in their shell walls, the morphologies of which are analogous to those of diatom earth.
Depletion, melting and reentrant solidification in mixtures of soft and hard colloids.
Marzi, Daniela; Capone, Barbara; Marakis, John; Merola, Maria Consiglia; Truzzolillo, Domenico; Cipelletti, Luca; Moingeon, Firmin; Gauthier, Mario; Vlassopoulos, Dimitris; Likos, Christos N; Camargo, Manuel
2015-11-14
We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft-hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star-polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid-polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft-hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.
Alternative approach of cell encapsulation by Volvox spheres.
Teong, Benjamin; Manousakas, Ioannis; Chang, Shwu Jen; Huang, Han Hsiang; Ju, Kuen-Cheng; Kuo, Shyh Ming
2015-10-01
Volvox sphere is a bio-mimicking concept of a biomaterial structure design able to encapsulate chemicals, drugs and/or cells. The aim of this study was to prepare Volvox spheres encapsulating AML12 liver cells and mesenchymal stem cells (MSCs) via a high voltage electrostatic field system. The results demonstrated that AML12 liver cells and MSCs could be successfully encapsulated into the inner spheres and the outer sphere of the Volvox spheres. The improved cell viability of MSCs was achieved by the addition of collagen and polyethylene glycol into the preparation components of the Volvox spheres. Collagen material potentially provides extracellular matrix-like structure for cell adhesion while polyethylene glycol provides a void/loose space for permeability of metabolites. The encapsulated MSCs were able to differentiate into hepatocytes or hepatocyte-like cells and express liver cell markers including albumin, alpha feto-protein and cytokeratin 18. The encapsulated cells secreted albumin to about 140 ng on day 14. Based on these observations, we conclude that Volvox spheres can be used as an alternative approach to encapsulate multiple types of cells, here AML12 hepatocyte cell line and MSCs. Nevertheless, efforts are still needed to improve the viability of the encapsulated cells and increase the differentiation of MSCs into functional liver cells. PMID:26117741
Science off the Sphere: Bistronauts
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...
Random packing of spheres in Menger sponge.
Cieśla, Michał; Barbasz, Jakub
2013-06-01
Random packing of spheres inside fractal collectors of dimension 2 < d < 3 is studied numerically using Random Sequential Adsorption (RSA) algorithm. The paper focuses mainly on the measurement of random packing saturation limit. Additionally, scaling properties of density autocorrelations in the obtained packing are analyzed. The RSA kinetics coefficients are also measured. Obtained results allow to test phenomenological relation between random packing saturation density and collector dimension. Additionally, performed simulations together with previously obtained results confirm that, in general, the known dimensional relations are obeyed by systems having non-integer dimension, at least for d < 3.
Nematic ordering and defects on the surface of a sphere: A Monte Carlo simulation study
NASA Astrophysics Data System (ADS)
Bates, Martin A.
2008-03-01
We examine the ordering of hard rods on the surface of a sphere using computer simulations. As predicted by previous theories of thin nematic shells we observe four s =+1/2 defects. However, the predicted tetrahedral symmetry for the defects and the "baseball" director configuration is not observed. Instead the four defects are located, on average, on a great circle which splits the sphere into two hemispheres, each of which has a splay dominated director configuration. We argue that this result occurs as the bend elastic constant for hard rods is much larger than the splay elastic constant.
Nematic ordering and defects on the surface of a sphere: a Monte Carlo simulation study.
Bates, Martin A
2008-03-14
We examine the ordering of hard rods on the surface of a sphere using computer simulations. As predicted by previous theories of thin nematic shells we observe four s = + 1/2 defects. However, the predicted tetrahedral symmetry for the defects and the "baseball" director configuration is not observed. Instead the four defects are located, on average, on a great circle which splits the sphere into two hemispheres, each of which has a splay dominated director configuration. We argue that this result occurs as the bend elastic constant for hard rods is much larger than the splay elastic constant.
An Unusual Rolling-Sphere Phenomenon.
ERIC Educational Resources Information Center
Cromer, Alan
1996-01-01
Discusses the theory behind a study of motion where a hollow plastic sphere racing against a steel sphere in two parallel sections of inclined channeling always reaches the bottom first; once on the floor, however, the steel sphere travels faster, speeding past the plastic sphere when both are about one meter from the base of the track. (JRH)
Porous Ceramic Spheres From Cation Exchange Beads
NASA Technical Reports Server (NTRS)
Dynys, Fred
2005-01-01
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.)
Method for producing dustless graphite spheres from waste graphite fines
Pappano, Peter J; Rogers, Michael R
2012-05-08
A method for producing graphite spheres from graphite fines by charging a quantity of spherical media into a rotatable cylindrical overcoater, charging a quantity of graphite fines into the overcoater thereby forming a first mixture of spherical media and graphite fines, rotating the overcoater at a speed such that the first mixture climbs the wall of the overcoater before rolling back down to the bottom thereby forming a second mixture of spherical media, graphite fines, and graphite spheres, removing the second mixture from the overcoater, sieving the second mixture to separate graphite spheres, charging the first mixture back into the overcoater, charging an additional quantity of graphite fines into the overcoater, adjusting processing parameters like overcoater dimensions, graphite fines charge, overcoater rotation speed, overcoater angle of rotation, and overcoater time of rotation, before repeating the steps until graphite fines are converted to graphite spheres.
Integrating spheres for improved skin photodynamic therapy.
Glennie, Diana L; Farrell, Thomas J; Hayward, Joseph E; Patterson, Michael S
2010-01-01
The prescribed radiant exposures for photodynamic therapy (PDT) of superficial skin cancers are chosen empirically to maximize the success of the treatment while minimizing adverse reactions for the majority of patients. They do not take into account the wide range of tissue optical properties for human skin, contributing to relatively low treatment success rates. Additionally, treatment times can be unnecessarily long for large treatment areas if the laser power is not sufficient. Both of these concerns can be addressed by the incorporation of an integrating sphere into the irradiation apparatus. The light fluence rate can be increased by as much as 100%, depending on the tissue optical properties. This improvement can be determined in advance of treatment by measuring the reflectance from the tissue through a side port on the integrating sphere, allowing for patient-specific treatment times. The sphere is also effective at improving beam flatness, and reducing the penumbra, creating a more uniform light field. The side port reflectance measurements are also related to the tissue transport albedo, enabling an approximation of the penetration depth, which is useful for real-time light dosimetry. PMID:21054127
Method for producing small hollow spheres
Rosencwaig, Allen; Koo, Jackson C.; Dressler, John L.
1981-01-01
A method for producing small hollow spheres of glass having an outer diameter ranging from about 100.mu. to about 500.mu. with a substantially uniform wall thickness in the range of about 0.5-20.mu.. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions. In one embodiment, one of the temperature regions is lower than both the preceeding region and the subsequent region. One region utilizes a temperature of at least 200.degree. C. higher than the melting point of the glass-forming material in the solution and, for example, may be at least 3 times higher than the temperature of the preceeding region. In addition, there is a sharp temperature gradient between these regions. As each droplet of solution passes through a first region it forms into a gel membrane having a spherical shape and encapsulates the rest of the drop retained in the elastic outer surface and the water entrapped within diffuses rapidly through the thin gel membrane which causes more of the glass-forming material to go out of solution and is incorporated into the gel membrane causing it to grow in size and become hollow. thus produced hollow glass sphere has a sphericity, concentricity, and wall uniformity of better than 5%. The sphere is capable of retaining material of up to at least 100 atmospheres therein over long periods of time. In one embodiment.
Bidispersed Sphere Packing on Spherical Surfaces
NASA Astrophysics Data System (ADS)
Atherton, Timothy; Mascioli, Andrew; Burke, Christopher
Packing problems on spherical surfaces have a long history, originating in the classic Thompson problem of finding the ground state configuration of charges on a sphere. Such packings contain a minimal number of defects needed to accommodate the curvature; this is predictable using the Gauss-Bonnet theorem from knowledge of the topology of the surface and the local symmetry of the ordering. Famously, the packing of spherical particles on a sphere contains a 'scar' transition, where additional defects over those required by topology appear above a certain critical number of particles and self-organize into chains or scars. In this work, we study the packing of bidispersed packings on a sphere, and hence determine the interaction of bidispersity and curvature. The resultant configurations are nearly crystalline for low values of bidispersity and retain scar-like structures; these rapidly become disordered for intermediate values and approach a so-called Appollonian limit at the point where smaller particles can be entirely accommodated within the voids left by the larger particles. We connect our results with studies of bidispersed packings in the bulk and on flat surfaces from the literature on glassy systems and jamming. Supported by a Cottrell Award from the Research Corporation for Science Advancement.
Integrating spheres for improved skin photodynamic therapy.
Glennie, Diana L; Farrell, Thomas J; Hayward, Joseph E; Patterson, Michael S
2010-01-01
The prescribed radiant exposures for photodynamic therapy (PDT) of superficial skin cancers are chosen empirically to maximize the success of the treatment while minimizing adverse reactions for the majority of patients. They do not take into account the wide range of tissue optical properties for human skin, contributing to relatively low treatment success rates. Additionally, treatment times can be unnecessarily long for large treatment areas if the laser power is not sufficient. Both of these concerns can be addressed by the incorporation of an integrating sphere into the irradiation apparatus. The light fluence rate can be increased by as much as 100%, depending on the tissue optical properties. This improvement can be determined in advance of treatment by measuring the reflectance from the tissue through a side port on the integrating sphere, allowing for patient-specific treatment times. The sphere is also effective at improving beam flatness, and reducing the penumbra, creating a more uniform light field. The side port reflectance measurements are also related to the tissue transport albedo, enabling an approximation of the penetration depth, which is useful for real-time light dosimetry.
Sphere forming method and apparatus
NASA Technical Reports Server (NTRS)
Youngberg, C. L.; Miller, C. G.; Stephens, J. B.; Finnerty, A. A. (Inventor)
1983-01-01
A system is provided for forming small accurately spherical objects. Preformed largely spherical objects are supported at the opening of a conduit on the update of hot gas emitted from the opening, so the object is in a molten state. The conduit is suddenly jerked away at a downward incline, to allow the molten object to drop in free fall, so that surface tension forms a precise sphere. The conduit portion that has the opening, lies in a moderate vacuum chamber, and the falling sphere passes through the chamber and through a briefly opened valve into a tall drop tower that contains a lower pressure, to allow the sphere to cool without deformation caused by falling through air.
Free vibration of layered magnetoelectroelastic spheres.
Heyliger, P R; Pan, E
2016-08-01
A discrete-layer model is presented and applied to the free vibration of layered anisotropic spheres with coupling among the elastic, electric, and magnetic fields. Through-thickness approximations in the radial direction are pre-integrated and combined with independent approximations in the azimuthal and circumferential directions to provide estimates of the natural frequencies for a variety of representative geometries. Results are in excellent agreement with existing analytical studies and additional results are presented for higher-order spheroidal modes. Predictions of the level of influence of magnetoelectric coupling are also given. PMID:27586731
Skin Stresses in an Inflated Sphere During Impact
NASA Technical Reports Server (NTRS)
Martin, E. Dale
1961-01-01
An analysis is made of the stresses in the skin of an inflated nonstretchable sphere during normal, nonrotating impact with a hard flat surface, assuming infinite modulus of elasticity in the skin and infinite propagation speed of stress waves. The analysis is further applied to the study of the inflated sphere landing vehicle containing a payload suspended at the center. Curves are presented showing the stress distributions during impact for cases corresponding to those calculated in previous reports in which the impact motion and payload landing performance capabilities of the landing vehicle have been studied. It is found, assuming the force from the payload-suspension cords to be distributed continuously on the skin, that is, neglecting stress concentrations,that the skin stresses along a meridian are reduced by the presence of the suspended payload during impact, but that the maximum values of skin stress normal to a meridian are little affected.
A corresponding-states principle for the equation of state of hard-convex-body fluids
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1994-09-01
A theoretically based corresponding-states principle is developed for the equation of state of hard-convex-body fluids. For all the fluids considered, the excess compressibility factor, reduced by means of a parameter which can be determined analytically. lies on a single curve whose analytical expression can be obtained from the equation of state of the hard-sphere fluid.
Science off the Sphere: Fun with Antibubbles
International Space Station Expedition 30 astronaut Don Pettit injects air bubbles inside a sphere of water to demonstrate physics in space for 'Science off the Sphere.' Through a partnership betwe...
Tessellating the Sphere with Regular Polygons
ERIC Educational Resources Information Center
Soto-Johnson, Hortensia; Bechthold, Dawn
2004-01-01
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.
Klatt, Michael A; Torquato, Salvatore
2016-08-01
In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g_{2}(r) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the
NASA Astrophysics Data System (ADS)
Klatt, Michael A.; Torquato, Salvatore
2016-08-01
In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g2(r ) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the
Eddy currents in a conducting sphere
NASA Technical Reports Server (NTRS)
Bergman, John; Hestenes, David
1986-01-01
This report analyzes the eddy current induced in a solid conducting sphere by a sinusoidal current in a circular loop. Analytical expressions for the eddy currents are derived as a power series in the vectorial displacement of the center of the sphere from the axis of the loop. These are used for first order calculations of the power dissipated in the sphere and the force and torque exerted on the sphere by the electromagnetic field of the loop.
Fear not the tectosphere (and other -spheres)
NASA Astrophysics Data System (ADS)
Lee, C. A.
2004-12-01
Based on a highly unrepresentative sampling of the community, not unlike Fox news polls, it has been recognized that the use of words having the suffix "-sphere" is confused and often abused. Such words include lithosphere, asthenosphere, perisphere, tectosphere, and mesosphere. In addition, there appears to be equal confusion in the use of the related terms: mechanical boundary layer, thermal boundary layer, chemical boundary layer, low velocity zone, low viscosity zone, effective elastic thickness, etc. This confusion is not confined to beginning students of the Earth sciences but is also manifest in seasoned Earth scientists (including myself), that is, it is not uncommon to find a geochemist and a geophysicist with completely different definitions of "lithosphere" and "tectosphere", for example. In this poster, an attempt will be made to illustrate the concepts behind some of these terms using visual and verbal aids. One of the focuses, could be the concept of a tectosphere, which may go something like this: A Wise maN once said to me; That cOntinents float because they are light; Then said my dog - DiorITE; Oceans sInk because they are heavy; And so I ask, why miGht this be?; With a Laugh and a Bark, she says the oceans are cOld; And to test if she's rigHT; I stick a tHermometer in the continent's core; To my surprise coNtinents are cold, if not more; So something does not Jive; A parAdox has come alive; Perhaps you surMise that the story is not coMplete; Indeed, you may be right; BecausE under the contiNents lie Green rocks - PerIdotite!; InFertile as Hell and fortuitouslY light; Together they fOrm the TecToSphere; And this is why we are here; Fear not the TecToSphere.
NASA Technical Reports Server (NTRS)
Schmidlin, F. J.
1987-01-01
Observed correlations between the atmospheric electric field and the neutral wind were studied using additional atmospheric measurements during Project CONDOR. Project CONDOR obtained measurements near the equatorial electrojet (12 S) during March 1983. Neutral atmosphere wind measurements were obtained using lightweight inflatable spheres and temperatures were obtained using a datasonde. The lightweight sphere technology, the wind structure, and temperature structure are described. Results show that the lightweight sphere gives higher vertical resolution of winds below 75 km compared with the standard sphere, but gives little or no improvement above 80 km, and no usable temperature and density data.
Image method for induced surface charge from many-body system of dielectric spheres
NASA Astrophysics Data System (ADS)
Qin, Jian; de Pablo, Juan J.; Freed, Karl F.
2016-09-01
Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)3ɛ, where a is the sphere radius, R the average inter-sphere separation, and ɛ the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.
Pancreatic cancer spheres are more than just aggregates of stem marker-positive cells
Gaviraghi, Margherita; Tunici, Patrizia; Valensin, Silvia; Rossi, Marco; Giordano, Cinzia; Magnoni, Letizia; Dandrea, Mario; Montagna, Licia; Ritelli, Rossana; Scarpa, Aldo; Bakker, Annette
2010-01-01
Pancreatic cancer stem-like cells are described by membrane expression of CD24, CD44 and ESA (epithelial-specific antigen) and their capacity to grow as spheres in a serum-free medium containing well-defined growth factors. The capacity of a panel of four pancreatic cancer cell lines (PANC-1, CFPAC-1, PancTu-1 and PSN-1) to form spheres was tested. All cell lines with the exception of PancTu-1 developed spheres. Phenotypically, the sphere-growing cells showed an increased in vitro invasion capability. Both gene and protein expressions of markers of metastases [CXCR4 (CXC chemokine receptor 4), OPN (osteopontin) and CD44v6] and components of active hedgehog pathway signalling were assessed. Spheres clearly demonstrated increased expression of the above-mentioned markers when compared with their adherent counterpart. With the aim of identifying a minimum set of markers able to separate cells that have the capacity to form spheres from those incapable of forming spheres, a PCA (principal component analysis) of the multidimensional dataset was performed. Although PCA of the ‘accepted’ stemness genes was unable to separate sphere-forming from sphere-incapable cell lines, the addition of the ‘aggressiveness’ marker CD44v6 allowed a clear differentiation. Moreover, inoculation of the spheres and the adherent cells in vivo confirmed the superior aggressiveness (proliferation and metastasis) of the spheres over the adherent cells. In conclusion, the present study suggests that the sphere-growing cell population is not only composed of cells displaying classical stem membrane markers but also needs CD44v6-positive cells to successfully form spheres. Our results also emphasize the potential therapeutic importance of pathways such as CXCR4 and hedgehog for pancreatic cancer treatment. PMID:20426768
Tin-wall hollow ceramic spheres from slurries. Final report
Chapman, A.T.; Cochran, J.K.
1992-12-31
The overall objective of this effort was to develop a process for economically fabricating thin-wall hollow ceramic spheres from conventional ceramic powders using dispersions. This process resulted in successful production of monosized spheres in the mm size range which were point contact bonded into foams. Thin-wall hollow ceramic spheres of small (one to five millimeter) diameter have novel applications as high-temperature insulation and light structural materials when bonded into monolithic foams. During Phase 1 of this program the objective as to develop a process for fabricating thin-wall hollow spheres from powder slurries using the coaxial nozzle fabrication method. Based on the success during Phase 1, Phase 2 was revised to emphasize the assessment of the potential structural and insulation applications for the spheres and modeling of the sphere formation process was initiated. As more understanding developed, it was clear that to achieve successful structural application, the spheres had to be bonded into monolithic foams and the effort was further expanded to include both bonding into structures and finite element mechanical modeling which became the basis of Phase 3. Successful bonding techniques and mechanical modeling resulted but thermal conductivities were higher than desired for insulating activities. In addition, considerable interest had been express by industry for the technology. Thus the final Phase 4 concentrated on methods to reduce thermal conductivity by a variety of techniques and technology transfer through individualized visits. This program resulted in three Ph.D. theses and 10 M.S. theses and they are listed in the appropriate technical sections.
Phase behavior of mixtures of colloidal rods and spheres
NASA Astrophysics Data System (ADS)
Adams, Marie Elizabeth
In this thesis we study entropy driven order in mixtures of rods and spheres. Systems of rod-like particles, as pure systems, exhibit rich liquid crystalline phase behavior. We chose to work with aqueous suspensions of either TMV or fd virus particles, both rod-like lyotropic systems. We complicate the phase behavior by adding a second component, colloidal spheres (PEG/PEO, BSA, polystyrene latex, or Dextran). Our first paper explores the phase behavior of TMV mixed with BSA or PEO, mapping out a phase diagram based on optical microscopy observations. We found our qualitative observations of TMV mixtures to be consistent with theoretical models of the depletion force. The second paper extends our study of phase behavior to mixtures of fd virus and polystyrene latex spheres. We qualitatively observe bulk demixing for very small diameter added spheres and for very large diameter added spheres. In addition, we observed microphase separation morphologies, such as lamellar and columnar structures, which formed for fd mixed with polystyrene latex spheres 0.1 microns in diameter. All of these microphase samples were viewed with differential interference microscopy (a few samples were further investigated using electron microscopy). Both our data and theoretical calculations illustrated that 0.1 micron diameter spheres have a stabilizing effect on the smectic phase. Our final work focused on fd virus mixed with Dextran. The purpose of these experiments was to examine the effect of added polymer on the isotropic-cholesteric co-existence region. I-Ch samples were prepared and fd and Dextran concentrations were measured using a spectrophotometer. Several conditions were explored, including two different molecular weights of Dextran and a range of ionic strengths. In agreement with theoretical predictions, the I-Ch coexistence region widens with added Dextran with the polymer preferentially partioned into the isotropic phase.
NASA Astrophysics Data System (ADS)
Mattner, Trent; Chong, Min; Joubert, Peter
2000-11-01
Vortical flow past a sphere in a constant diameter pipe was studied experimentally in a guide vane apparatus similar to those used in fundamental experimental studies of vortex breakdown. The initial effect of swirl was to shorten the downstream separation bubble. For a small range of the swirl intensity, an almost stagnant upstream separation bubble formed. As the swirl intensity was increased, the bubble became unstable and an unsteady spiral formed. At high swirl intensity there was a mean recirculation region which penetrated far upstream while the flow on the downstream hemisphere was attached. Measurements of the velocity field were obtained using laser Doppler velocimetry. Analysis of these results suggests that the onset of upstream separation is associated with the formation of a negative azimuthal vorticity component which slows the axial flow near the axis of symmetry. This is consistent with inviscid distortion of the vortex filaments in the diverging flow approaching the sphere.
Archaic artifacts resembling celestial spheres
NASA Astrophysics Data System (ADS)
Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.
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.
Numerical simulation of a sphere moving down an incline with identical spheres placed equally apart
Ling, Chi-Hai; Jan, Chyan-Deng; Chen, Cheng-lung; Shen, Hsieh Wen
1992-01-01
This paper describes a numerical study of an elastic sphere moving down an incline with a string of identical spheres placed equally apart. Two momentum equations and a moment equation formulated for the moving sphere are solved numerically for the instantaneous velocity of the moving sphere on an incline with different angles of inclination. Input parameters for numerical simulation include the properties of the sphere (the radius, density, Poison's ratio, and Young's Modulus of elasticity), the coefficient of friction between the spheres, and a damping coefficient of the spheres during collision.
Underwater implosion of glass spheres.
Turner, Stephen E
2007-02-01
Underwater implosion experiments were conducted with thin-wall glass spheres to determine the influence that structural failure has on the pressure pulse. Four experiments were conducted with glass spheres having an outside diameter of 7.62 cm, thickness of 0.762 mm, and an estimated buckling pressure of 7.57 MPa. The experiments were performed in a pressure vessel at a hydrostatic pressure of 6.996 MPa. The average peak pressure of the implosion pressure pulse was 26.1 MPa, measured at a radial distance of 10.16 cm from the sphere center. A computational fluid structure interaction model was developed to assess how the failure rate of the glass structure influences the pressure time history. The model employed a specified glass failure sequence that is uniform in time and space. It was found that for the conditions of the test, a glass failure rate of 275 m/s provided a reasonable representation of the test data. The test data and the model results show that the failure time history of the structure has a significant influence on an implosion pressure pulse. Computational prediction of an implosion pressure pulse needs to include the failure time history of the structure; otherwise it will overpredict the pressure time history.
NASA Astrophysics Data System (ADS)
Trinh, Thi-Kim-Hoang; Passarello, Jean-Philippe; de Hemptinne, Jean-Charles; Lugo, Rafael; Lachet, Veronique
2016-03-01
This work consists of the adaptation of a non-additive hard sphere theory inspired by Malakhov and Volkov [Polym. Sci., Ser. A 49(6), 745-756 (2007)] to a square-well chain. Using the thermodynamic perturbation theory, an additional term is proposed that describes the effect of perturbing the chain of square well spheres by a non-additive parameter. In order to validate this development, NPT Monte Carlo simulations of thermodynamic and structural properties of the non-additive square well for a pure chain and a binary mixture of chains are performed. Good agreements are observed between the compressibility factors originating from the theory and those from molecular simulations.
Generating perfect fluid spheres in general relativity
NASA Astrophysics Data System (ADS)
Boonserm, Petarpa; Visser, Matt; Weinfurtner, Silke
2005-06-01
Ever since Karl Schwarzschild’s 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star—a static spherically symmetric blob of fluid with position-independent density—the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres.
Equation of state for the soft-sphere fluid from a direct summation of the virial series
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1993-04-01
An equation of state for the inverse-twelfth-power soft-sphere fluid is obtained by direct summation of the virial series. To do so, a generalization of the Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid is used. The equation of state obtained in this way reproduces accurately the simulation data for both the stable and metastable fluid regions. Agreement remains good up to the neighborhood of the glass transition where the equation of state predicts that the soft-sphere fluid becomes unstable.
The electromagnetic radiation from simple sources in the presence of a homogeneous dielectric sphere
NASA Technical Reports Server (NTRS)
Mason, V. B.
1973-01-01
In this research, the effect of a homogeneous dielectric sphere on the electromagnetic radiation from simple sources is treated as a boundary value problem, and the solution is obtained by the technique of dyadic Green's functions. Exact representations of the electric fields in the various regions due to a source located inside, outside, or on the surface of a dielectric sphere are formulated. Particular attention is given to the effect of sphere size, source location, dielectric constant, and dielectric loss on the radiation patterns and directivity of small spheres (less than 5 wavelengths in diameter) using the Huygens' source excitation. The computed results are found to closely agree with those measured for waveguide-excited plexiglas spheres. Radiation patterns for an extended Huygens' source and for curved electric dipoles located on the sphere's surface are also presented. The resonance phenomenon associated with the dielectric sphere is studied in terms of the modal representation of the radiated fields. It is found that when the sphere is excited at certain frequencies, much of the energy is radiated into the sidelobes. The addition of a moderate amount of dielectric loss, however, quickly attenuates this resonance effect. A computer program which may be used to calculate the directivity and radiation pattern of a Huygens' source located inside or on the surface of a lossy dielectric sphere is listed.
Equilibrium and nonequilibrium dynamics of soft sphere fluids.
Ding, Yajun; Mittal, Jeetain
2015-07-14
We use computer simulations to test the freezing-point scaling relationship between equilibrium transport coefficients (self-diffusivity, viscosity) and thermodynamic parameters for soft sphere fluids. The fluid particles interact via the inverse-power potential (IPP), and the particle softness is changed by modifying the exponent of the distance-dependent potential term. In the case of IPP fluids, density and temperature are not independent variables and can be combined to obtain a coupling parameter to define the thermodynamic state of the system. We find that the rescaled coupling parameter, based on its value at the freezing point, can approximately collapse the diffusivity and viscosity data for IPP fluids over a wide range of particle softness. Even though the collapse is far from perfect, the freezing-point scaling relationship provides a convenient and effective way to compare the structure and dynamics of fluid systems with different particle softness. We further show that an alternate scaling relationship based on two-body excess entropy can provide an almost perfect collapse of the diffusivity and viscosity data below the freezing transition. Next, we perform nonequilibrium molecular dynamics simulations to calculate the shear-dependent viscosity and to identify the distinct role of particle softness in underlying structural changes associated with rheological properties. Qualitatively, we find a similar shear-thinning behavior for IPP fluids with different particle softness, though softer particles exhibit stronger shear-thinning tendency. By investigating the distance and angle-dependent pair correlation functions in these systems, we find different structural features in the case of IPP fluids with hard-sphere like and softer particle interactions. Interestingly, shear-thinning in hard-sphere like fluids is accompanied by enhanced translational order, whereas softer fluids exhibit loss of order with shear. Our results provide a systematic evaluation
Perturbative Casimir Energies of Spheres
NASA Astrophysics Data System (ADS)
Barton, G.
The Casimir energies of single bodies (as opposed to the interaction between mutually disjoint bodies) have accumulated deceptive folklore which this talk will try to exorcise, by mean of calculations for atomic solids that, though optically dilute, are realistically dispersive. This is easy, because quantum electrodynamics then yields identically the same energy as one gets from the properly retarded interatomic potentials. The problem of regularizing (nominal) divergences turns out to be quite distinct from the appropriate process of renormalization: simply discarding all nominally divergent contributions would prevent one from understanding the physics. Contrary to legend, the pertinent Casimir energies for dielectric spheres are attractive.
The dynamic sphere test problem
Chabaud, Brandon M.; Brock, Jerry S.; Smith, Brandon M.
2012-05-16
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.
Session: Hard Rock Penetration
Tennyson, George P. Jr.; Dunn, James C.; Drumheller, Douglas S.; Glowka, David A.; Lysne, Peter
1992-01-01
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.
NASA Technical Reports Server (NTRS)
Hauser, D. L.; Buras, D. F.; Corbin, J. M.
1987-01-01
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.
Sphere Drag and Heat Transfer.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-20
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
NASA Astrophysics Data System (ADS)
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-01-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body. PMID:26189698
Cugell, D.W. )
1992-06-01
Hard metal is a mixture of tungsten carbide and cobalt, to which small amounts of other metals may be added. It is widely used for industrial purposes whenever extreme hardness and high temperature resistance are needed, such as for cutting tools, oil well drilling bits, and jet engine exhaust ports. Cobalt is the component of hard metal that can be a health hazard. Respiratory diseases occur in workers exposed to cobalt--either in the production of hard metal, from machining hard metal parts, or from other sources. Adverse pulmonary reactions include asthma, hypersensitivity pneumonitis, and interstitial fibrosis. A peculiar, almost unique form of lung fibrosis, giant cell interstitial pneumonia, is closely linked with cobalt exposure.66 references.
Cugell, D W
1992-06-01
Hard metal is a mixture of tungsten carbide and cobalt, to which small amounts of other metals may be added. It is widely used for industrial purposes whenever extreme hardness and high temperature resistance are needed, such as for cutting tools, oil well drilling bits, and jet engine exhaust ports. Cobalt is the component of hard metal that can be a health hazard. Respiratory diseases occur in workers exposed to cobalt--either in the production of hard metal, from machining hard metal parts, or from other sources. Adverse pulmonary reactions include asthma, hypersensitivity pneumonitis, and interstitial fibrosis. A peculiar, almost unique form of lung fibrosis, giant cell interstitial pneumonia, is closely linked with cobalt exposure.
Cugell, D W
1992-06-01
Hard metal is a mixture of tungsten carbide and cobalt, to which small amounts of other metals may be added. It is widely used for industrial purposes whenever extreme hardness and high temperature resistance are needed, such as for cutting tools, oil well drilling bits, and jet engine exhaust ports. Cobalt is the component of hard metal that can be a health hazard. Respiratory diseases occur in workers exposed to cobalt--either in the production of hard metal, from machining hard metal parts, or from other sources. Adverse pulmonary reactions include asthma, hypersensitivity pneumonitis, and interstitial fibrosis. A peculiar, almost unique form of lung fibrosis, giant cell interstitial pneumonia, is closely linked with cobalt exposure. PMID:1511554
Porous Ceramic Spheres from Ion Exchange Resin
NASA Technical Reports Server (NTRS)
Dynys, Fred
2005-01-01
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.
Process for making hollow carbon spheres
Luhrs, Claudia C.; Phillips, Jonathan; Richard, Monique N.; Knapp, Angela Michelle
2013-04-16
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.
Impingement of Water Droplets on a Sphere
NASA Technical Reports Server (NTRS)
Dorsch, Robert G.; Saper, Paul G.; Kadow, Charles F.
1955-01-01
Droplet trajectories about a sphere in ideal fluid flow were calculated. From the calculated droplet trajectories the droplet impingement characteristics of the sphere were determined. Impingement data and equations for determining the collection efficiency, the area, and the distribution of impingement are presented in terms of dimensionless parameters. The range of flight and atmospheric conditions covered in the calculations was extended considerably beyond the range covered by previously reported calculations for the sphere.
Method for producing small hollow spheres
Hendricks, Charles D. [Livermore, CA
1979-01-09
Method for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T .gtorsim. 600.degree. C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.
Method for producing small hollow spheres
Hendricks, C.D.
1979-01-09
Method is disclosed for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T [approx gt] 600 C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10[sup 3] [mu]m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants. 1 fig.
The water entry of decelerating spheres
NASA Astrophysics Data System (ADS)
Aristoff, Jeffrey M.; Truscott, Tadd T.; Techet, Alexandra H.; Bush, John W. M.
2010-03-01
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 influence of its deceleration on the shape of the resulting air cavity. A theoretical model is developed which yields simple expressions for the pinch-off time and depth, as well as the volume of air entrained by the sphere. Theoretical predictions compare favorably with our experimental observations, and allow us to rationalize the form of water-entry cavities resulting from the impact of buoyant and nearly buoyant spheres.
Science off the Sphere: Earth in Infrared
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...
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
An analytical equation of state for hard ellipsoids-of-revolution fluids is derived from a generalization of the Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid. The results are in very good agreement with existing simulation data.
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
The Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid is generalized and used to derive an equation of state for hard Gaussian overlap fluids. The results are in excellent agreement with existing simulation data.
Uniqueness of the static Einstein-Maxwell spacetimes with a photon sphere
NASA Astrophysics Data System (ADS)
Yazadjiev, Stoytcho; Lazov, Boian
2015-08-01
We consider the problem of uniqueness of static and asymptotically flat Einstein-Maxwell spacetimes with a photon sphere P3. We are using a naturally modified definition of a photon sphere for electrically charged spacetimes with the additional property that the one-form {\\iota }ξ F is normal to the photon sphere. For simplicity we are restricting ourselves to the case of zero magnetic charge and assume that the lapse function regularly foliates the spacetime outside the photon sphere. With this information we prove that P3 has constant mean curvature and constant scalar curvature. We also derive a few equations which we later use to prove the main uniqueness theorem, i.e. the static asymptotically flat Einstein-Maxwell spacetimes with a non-extremal photon sphere are isometric to the Reissner-Nordström one with mass M and electric charge Q subject to \\frac{{Q}2}{{M}2}≤slant \\frac{9}{8}.
Tandem spheres in hypersonic flow
Laurence, Stuart J; Deiterding, Ralf; Hornung, Hans G
2009-01-01
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.
NASA Astrophysics Data System (ADS)
Heyes, D. M.; Clarke, S. M.; Brańka, A. C.
2009-11-01
Molecular dynamics simulations have been used to compute physical properties of model fluids in which the particles interacted via the soft-sphere pair potential (SSP) ϕ(r )=ɛ(σ /r)n, where ɛ and σ are the characteristic energy and distance, respectively. The emphasis is on small values of n, tending to the lower theromodynamically allowed bound of 3+. An accurate equation of state for the SSP fluid is obtained, consisting of two terms, and as n→3+, the compressibility factor, Z tends to Z =B2ζn /3 for ζ >0, where B2 is the second virial coefficient, and ζ =πNσ3/6V is a nominal packing fraction for N particles in volume V. A simple formula for the position of the first peak in the radial distribution function in the soft particle limit is proposed and shown to agree with the simulation data. The fluid phase velocity autocorrelation function at fluid-solid coexistence becomes more oscillatory as n decreases. Values for the self-diffusion coefficient D and shear viscosity η were calculated as a function of n and density, and these were used to estimate the n-dependence of an ideal glass transition. The glass transition shifts relatively further into the solid part of the phase diagram as softness (˜1/n) increases. D decreases by ca. 75% and η increases by about a factor of 3 along the fluid-solid coexistence line from n =∞ to 3.25. Non-Gaussian behavior was calculated from the particle displacements as a function of particle softness. A screened soft-sphere potential, SSSP, was introduced to explore the effects for small n of the long range part of the potential in relation to the scale of the local structure. The SSSP with suitable analytic form and parameters can give statistically indistinguishable results from the full SSP for the static properties, D and η.
Dyadic Green's function of an eccentrically stratified sphere.
Moneda, Angela P; Chrissoulidis, Dimitrios P
2014-03-01
The electric dyadic Green's function (dGf) of an eccentrically stratified sphere is built by use of the superposition principle, dyadic algebra, and the addition theorem of vector spherical harmonics. The end result of the analytical formulation is a set of linear equations for the unknown vector wave amplitudes of the dGf. The unknowns are calculated by truncation of the infinite sums and matrix inversion. The theory is exact, as no simplifying assumptions are required in any one of the analytical steps leading to the dGf, and it is general in the sense that any number, position, size, and electrical properties can be considered for the layers of the sphere. The point source can be placed outside of or in any lossless part of the sphere. Energy conservation, reciprocity, and other checks verify that the dGf is correct. A numerical application is made to a stratified sphere made of gold and glass, which operates as a lens. PMID:24690648
ERIC Educational Resources Information Center
Stocker, H. Robert; Hilton, Thomas S. E.
1991-01-01
Suggests strategies that make hard disk organization easy and efficient, such as making, changing, and removing directories; grouping files by subject; naming files effectively; backing up efficiently; and using PATH. (JOW)
The Circle and Sphere as Great Equalizers.
ERIC Educational Resources Information Center
Schwartzman, Steven
1991-01-01
From the equality of the ratios of the surface areas and volumes of a sphere and its circumscribed cylinder, the exploration of theorems relating the ratios of surface areas and volumes of a sphere and other circumscribed solids in three dimensions, and analogous questions relating two-dimensional concepts of perimeter and area is recounted. (MDH)
The "Magical" Sphere: Uncovering the Secret
ERIC Educational Resources Information Center
Petruševski, Vladimir M.; Bukleski, Miha
2006-01-01
A red sphere is seen at the bottom of a sealed glass tube filled with a colorless, transparent liquid. Holding the tube for a short period makes the sphere rise slowly from the bottom until it finally floats on the surface of the liquid. Instructions for preparing the demonstration are given, together with an explanation of the phenomenon. A…
Hard Constraints in Optimization Under Uncertainty
NASA Technical Reports Server (NTRS)
Crespo, Luis G.; Giesy, Daniel P.; Kenny, Sean P.
2008-01-01
This paper proposes a methodology for the analysis and design of systems subject to parametric uncertainty where design requirements are specified via hard inequality constraints. Hard constraints are those that must be satisfied for all parameter realizations within a given uncertainty model. Uncertainty models given by norm-bounded perturbations from a nominal parameter value, i.e., hyper-spheres, and by sets of independently bounded uncertain variables, i.e., hyper-rectangles, are the focus of this paper. These models, which are also quite practical, allow for a rigorous mathematical treatment within the proposed framework. Hard constraint feasibility is determined by sizing the largest uncertainty set for which the design requirements are satisfied. Analytically verifiable assessments of robustness are attained by comparing this set with the actual uncertainty model. Strategies that enable the comparison of the robustness characteristics of competing design alternatives, the description and approximation of the robust design space, and the systematic search for designs with improved robustness are also proposed. Since the problem formulation is generic and the tools derived only require standard optimization algorithms for their implementation, this methodology is applicable to a broad range of engineering problems.
Fabrication of long lasting phosphorescence glass spheres
NASA Astrophysics Data System (ADS)
Lv, Hao; Liu, Aimei; Tong, Jufang; Yi, Xunong; Li, Qianguang
2008-12-01
The long lasting phosphorescence glass spheres doped with Eu2O3 and Dy2O3 were prepared under the reducing atmosphere and characterized. XRD analysis indicated the glass spheres exhibited the typical diffraction peaks of SrAl2O4: Eu2+, Dy3+. The emission spectra of the glass spheres showed broad bands peaking at 510nm. The excitation spectra of the glass spheres showed broad bands ranging from 300 to 480nm. These are believed due to the 5d4f-->4f transitions of Eu2+ in the SrAl2O4: Eu2+, Dy3+ phosphors. The afterglow luminescence of the glass spheres excited by a 40W fluorescence lamp for 30min can be observed in the dark for about 15h with the naked eye.
NASA Technical Reports Server (NTRS)
Cuan, Winston M.; Schwartz, Sidney H.
1988-01-01
Results are presented for a preliminary experiment involving a saturated pool boiling at 1 atm from rotating 2 and 3 inch diameter spheres which were immersed in LN2. Additional results are presented for a stationary 2 inch diameter sphere quenched in LN2, which were obtained with a more versatile and complete experimental apparatus. The speed of the rotational tests varied from 0 to 10,000 rpm. The stationary experiments parametrically varied pressure and subcooling levels from 0 to 600 psig and from 0 to 50 F, respectively. During the rotational tests, a high speed photographic analysis was undertaken to measure the thickness of the vapor film surrounding the sphere.
Anomalies, conformal manifolds, and spheres
NASA Astrophysics Data System (ADS)
Gomis, Jaume; Hsin, Po-Shen; Komargodski, Zohar; Schwimmer, Adam; Seiberg, Nathan; Theisen, Stefan
2016-03-01
The two-point function of exactly marginal operators leads to a universal contribution to the trace anomaly in even dimensions. We study aspects of this trace anomaly, emphasizing its interpretation as a sigma model, whose target space {M} is the space of conformal field theories (a.k.a. the conformal manifold). When the underlying quantum field theory is supersymmetric, this sigma model has to be appropriately supersymmetrized. As examples, we consider in some detail {N}=(2,2) and {N}=(0,2) supersymmetric theories in d = 2 and {N}=2 supersymmetric theories in d = 4. This reasoning leads to new information about the conformal manifolds of these theories, for example, we show that the manifold is Kähler-Hodge and we further argue that it has vanishing Kähler class. For {N}=(2,2) theories in d = 2 and {N}=2 theories in d = 4 we also show that the relation between the sphere partition function and the Kähler potential of {M} follows immediately from the appropriate sigma models that we construct. Along the way we find several examples of potential trace anomalies that obey the Wess-Zumino consistency conditions, but can be ruled out by a more detailed analysis.
Anomalies, conformal manifolds, and spheres
Gomis, Jaume; Hsin, Po-Shen; Komargodski, Zohar; Schwimmer, Adam; Seiberg, Nathan; Theisen, Stefan
2016-03-04
The two-point function of exactly marginal operators leads to a universal contribution to the trace anomaly in even dimensions. We study aspects of this trace anomaly, emphasizing its interpretation as a sigma model, whose target space $M$ is the space of conformal field theories (a.k.a. the conformal manifold). When the underlying quantum field theory is supersymmetric, this sigma model has to be appropriately supersymmetrized. As examples, we consider in some detail $N$ = (2; 2) and $N$ = (0; 2) supersymmetric theories in d = 2 and $N$ = 2 supersymmetric theories in d = 4. This reasoning leads tomore » new information about the conformal manifolds of these theories, for example, we show that the manifold is K ahler-Hodge and we further argue that it has vanishing K ahler class. For $N$ = (2; 2) theories in d = 2 and N = 2 theories in d = 4 we also show that the relation between the sphere partition function and the K ahler potential of $M$ follows immediately from the appropriate sigma models that we construct. Ultimately, along the way we find several examples of potential trace anomalies that obey the Wess-Zumino consistency conditions, but can be ruled out by a more detailed analysis.« less
Ceramic Spheres From Cation Exchange Beads
NASA Technical Reports Server (NTRS)
Dynys, F. W.
2003-01-01
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.
Induced differentiation inhibits sphere formation in neuroblastoma.
Craig, Brian T; Rellinger, Eric J; Alvarez, Alexandra L; Dusek, Haley L; Qiao, Jingbo; Chung, Dai H
2016-08-19
Neuroblastoma arises from the neural crest, the precursor cells of the sympathoadrenal axis, and differentiation status is a key prognostic factor used for clinical risk group stratification and treatment strategies. Neuroblastoma tumor-initiating cells have been successfully isolated from patient tumor samples and bone marrow using sphere culture, which is well established to promote growth of neural crest stem cells. However, accurate quantification of sphere-forming frequency of commonly used neuroblastoma cell lines has not been reported. Here, we show that MYCN-amplified neuroblastoma cell lines form spheres more frequently than non-MYCN-amplified cell lines. We also show that sphere formation is directly sensitive to cellular differentiation status. 13-cis-retinoic acid is a clinically used differentiating agent that induces a neuronal phenotype in neuroblastoma cells. Induced differentiation nearly completely blocked sphere formation. Furthermore, sphere formation was specifically FGF-responsive and did not respond to increasing doses of EGF. Taken together, these data suggest that sphere formation is an accurate method of quantifying the stemness phenotype in neuroblastoma. PMID:27297102
Equation of state for fluids of hard heteronuclear diatomic and symmetric triatomic molecules
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1996-03-01
A model previously developed for the equation of state of linear homonuclear fused hard sphere fluids is generalized to fluids with heteronuclear molecules. The model only requires two parameters, which can be determined from the geometrical characteristics of the molecules, for which analytical expressions are derived. Results for fluids with heteronuclear hard diatomic and symmetric triatomic molecules agree with simulation data within their accuracy for almost all the fluids considered.
pvsR: An Open Source Interface to Big Data on the American Political Sphere.
Matter, Ulrich; Stutzer, Alois
2015-01-01
Digital data from the political sphere is abundant, omnipresent, and more and more directly accessible through the Internet. Project Vote Smart (PVS) is a prominent example of this big public data and covers various aspects of U.S. politics in astonishing detail. Despite the vast potential of PVS' data for political science, economics, and sociology, it is hardly used in empirical research. The systematic compilation of semi-structured data can be complicated and time consuming as the data format is not designed for conventional scientific research. This paper presents a new tool that makes the data easily accessible to a broad scientific community. We provide the software called pvsR as an add-on to the R programming environment for statistical computing. This open source interface (OSI) serves as a direct link between a statistical analysis and the large PVS database. The free and open code is expected to substantially reduce the cost of research with PVS' new big public data in a vast variety of possible applications. We discuss its advantages vis-à-vis traditional methods of data generation as well as already existing interfaces. The validity of the library is documented based on an illustration involving female representation in local politics. In addition, pvsR facilitates the replication of research with PVS data at low costs, including the pre-processing of data. Similar OSIs are recommended for other big public databases. PMID:26132154
pvsR: An Open Source Interface to Big Data on the American Political Sphere
2015-01-01
Digital data from the political sphere is abundant, omnipresent, and more and more directly accessible through the Internet. Project Vote Smart (PVS) is a prominent example of this big public data and covers various aspects of U.S. politics in astonishing detail. Despite the vast potential of PVS’ data for political science, economics, and sociology, it is hardly used in empirical research. The systematic compilation of semi-structured data can be complicated and time consuming as the data format is not designed for conventional scientific research. This paper presents a new tool that makes the data easily accessible to a broad scientific community. We provide the software called pvsR as an add-on to the R programming environment for statistical computing. This open source interface (OSI) serves as a direct link between a statistical analysis and the large PVS database. The free and open code is expected to substantially reduce the cost of research with PVS’ new big public data in a vast variety of possible applications. We discuss its advantages vis-à-vis traditional methods of data generation as well as already existing interfaces. The validity of the library is documented based on an illustration involving female representation in local politics. In addition, pvsR facilitates the replication of research with PVS data at low costs, including the pre-processing of data. Similar OSIs are recommended for other big public databases. PMID:26132154
Flow around spheres by dissipative particle dynamics
NASA Astrophysics Data System (ADS)
Chen, Shuo; Phan-Thien, Nhan; Khoo, Boo Cheong; Fan, Xi Jun
2006-10-01
The dissipative particle dynamics (DPD) method is used to study the flow behavior past a sphere. The sphere is represented by frozen DPD particles while the surrounding fluids are modeled by simple DPD particles (representing a Newtonian fluid). For the surface of the sphere, the conventional model without special treatment and the model with specular reflection boundary condition proposed by Revenga et al. [Comput. Phys. Commun. 121-122, 309 (1999)] are compared. Various computational domains, in which the sphere is held stationary at the center, are investigated to gage the effects of periodic conditions and walls for Reynolds number (Re)=0.5 and 50. Two types of flow conditions, uniform flow and shear flow are considered, respectively, to study the drag force and torque acting on the stationary sphere. It is found that the calculated drag force imposed on the sphere based on the model with specular reflection is slightly lower than the conventional model without special treatment. With the conventional model the drag force acting on the sphere is in better agreement with experimental correlation obtained by Brown and Lawler [J. Environ. Eng. 129, 222 (2003)] for the case of larger radius up to Re of about 5. The computed torque also approaches the analytical Stokes value when Re <1. For a force-free and torque-free sphere, its motion in the flow is captured by solving the translational and rotational equations of motion. The effects of different DPD parameters (a, γ, and σ) on the drag force and torque are studied. It shows that the dissipative coefficient (γ) mainly affects the drag force and torque, while random and conservative coefficient have little influence on them. Furthermore the settling of a single sphere in square tube is investigated, in which the wall effect is considered. Good agreement is found with the experiments of Miyamura et al. [Int. J. Multiphase Flow 7, 31 (1981)] and lattice-Boltzmann simulation results of Aidun et al. [J. Fluid Mech
The water entry of decelerating spheres
NASA Astrophysics Data System (ADS)
Aristoff, Jeffrey; Truscott, Tadd; Techet, Alexandra; Bush, John
2009-11-01
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 influence of its deceleration on the shape of the resulting air cavity. A theoretical model is developed that yields simple expressions for the pinch-off time and depth. Theoretical predictions compare favorably with our experimental observations, and allow us to rationalize the form of water-entry cavities resulting from the impact of buoyant and nearly buoyant spheres.
Manipulator for rotating and examining small spheres
Weinstein, Berthold W. [Livermore, CA; Willenborg, David L. [Livermore, CA
1980-02-12
A manipulator which provides fast, accurate rotational positioning of a small sphere, such as an inertial confinement fusion target, which allows inspecting of the entire surface of the sphere. The sphere is held between two flat, flexible tips which move equal amounts in opposite directions. This provides rolling of the ball about two orthogonal axes without any overall translation. The manipulator may be controlled, for example, by an x- and y-axis driven controlled by a mini-computer which can be programmed to generate any desired scan pattern.
Manipulator for rotating and examining small spheres
Weinstein, B.W.; Willenborg, D.L.
1980-02-12
A manipulator is disclosed which provides fast, accurate rotational positioning of a small sphere, such as an inertial confinement fusion target, which allows inspecting of the entire surface of the sphere. The sphere is held between two flat, flexible tips which move equal amounts in opposite directions. This provides rolling of the ball about two orthogonal axes without any overall translation. The manipulator may be controlled, for example, by an x- and y-axis driven controlled by a mini-computer which can be programmed to generate any desired scan pattern. 8 figs.
Separate spheres and indirect benefits
Brock, Dan W
2003-01-01
On any plausible account of the basis for health care resource prioritization, the benefits and costs of different alternative resource uses are relevant considerations in the prioritization process. Consequentialists hold that the maximization of benefits with available resources is the only relevant consideration. Non-consequentialists do not reject the relevance of consequences of benefits and costs, but insist that other considerations, and in particular the distribution of benefits and costs, are morally important as well. Whatever one's particular account of morally justified standards for the prioritization of different health interventions, we must be able to measure those interventions' benefits and costs. There are many theoretical and practical difficulties in that measurement, such as how to weigh extending life against improving health and quality of life as well as how different quality of life improvements should be valued, but they are not my concern here. This paper addresses two related issues in assessing benefits and costs for health resource prioritization. First, should benefits be restricted only to health benefits, or include as well other non health benefits such as economic benefits to employers from reducing the lost work time due to illness of their employees? I shall call this the Separate Spheres problem. Second, should only the direct benefits, such as extending life or reducing disability, and direct costs, such as costs of medical personnel and supplies, of health interventions be counted, or should other indirect benefits and costs be counted as well? I shall call this the Indirect Benefits problem. These two issues can have great importance for a ranking of different health interventions by either a cost/benefit or cost effectiveness analysis (CEA) standard. PMID:12773217
NASA Astrophysics Data System (ADS)
Liu, Jun; Larson, Ronald G.
2013-05-01
We develop a Brownian dynamics simulation method with full hydrodynamic interactions (HI) to study the recognition kinetics between two patterned colloidal spheres. We use a general resistance matrix (12*12) to describe both the far and near-field hydrodynamics of translation, rotation, and translation-rotation coupling between the two spheres, adopted from Jeffrey and Onishi [J. Fluid Mech. 139, 261 (1984), 10.1017/S0022112084000355]. We apply the method to the specific binding of "patchy" spheres, including effects of depletion attraction and orientation-specific binding, as are present in "Janus" spheres whose surfaces contain hydrophobic and hydrophilic faces [Q. Chen, S. C. Bae, and S. Granick, Nature (London) 469, 381 (2011), 10.1038/nature09713]. The binding times obtained between two non-patterned spheres (of equal or unequal diameter) with or without HI extrapolated to infinite dilution are shown to be in good agreement with theoretical predictions of the Smoluchowski equation. In addition, the binding times for pairs of spheres for three cases of surface patterning of the two spheres (uniform-uniform, uniform-Janus, and Janus-Janus) are compared with or without rotational motion.
#4 Simulated Solar Sphere from Data - Interpolated
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...
StenniSphere reopens after Hurricane Katrina
NASA Technical Reports Server (NTRS)
2006-01-01
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.
Acoustic levitation of a large solid sphere
NASA Astrophysics Data System (ADS)
Andrade, Marco A. B.; Bernassau, Anne L.; Adamowski, Julio C.
2016-07-01
We demonstrate that acoustic levitation can levitate spherical objects much larger than the acoustic wavelength in air. The acoustic levitation of an expanded polystyrene sphere of 50 mm in diameter, corresponding to 3.6 times the wavelength, is achieved by using three 25 kHz ultrasonic transducers arranged in a tripod fashion. In this configuration, a standing wave is created between the transducers and the sphere. The axial acoustic radiation force generated by each transducer on the sphere was modeled numerically as a function of the distance between the sphere and the transducer. The theoretical acoustic radiation force was verified experimentally in a setup consisting of an electronic scale and an ultrasonic transducer mounted on a motorized linear stage. The comparison between the numerical and experimental acoustic radiation forces presents a good agreement.
Science off the Sphere: Thin Film Physics
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...
Elastic spheres can walk on water
NASA Astrophysics Data System (ADS)
Belden, Jesse; Hurd, Randy C.; Jandron, Michael A.; Bower, Allan F.; Truscott, Tadd T.
2016-02-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys.
Science off the Sphere: Lenses and Vortices
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...
Science off the Sphere: Knitting Needles
International Space Station Expedition 30 astronaut Don Pettit uses knitting needles and water droplets to demonstrate physics in space for 'Science off the Sphere.' Through a partnership between N...
Elastic spheres can walk on water
Belden, Jesse; Hurd, Randy C.; Jandron, Michael A.; Bower, Allan F.; Truscott, Tadd T.
2016-01-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys. PMID:26842860
Elastic spheres can walk on water.
Belden, Jesse; Hurd, Randy C; Jandron, Michael A; Bower, Allan F; Truscott, Tadd T
2016-01-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys. PMID:26842860
Catalytic, hollow, refractory spheres, conversions with them
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1989-01-01
Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material 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.
ERIC Educational Resources Information Center
Parrino, Frank M.
2003-01-01
Interviews with school board members and administrators produced a list of suggestions for balancing a budget in hard times. Among these are changing calendars and schedules to reduce heating and cooling costs; sharing personnel; rescheduling some extracurricular activities; and forming cooperative agreements with other districts. (MLF)
ERIC Educational Resources Information Center
Kennedy, Mike
1999-01-01
Provides guidelines to help schools maintain hard floors and carpets, including special areas in schools and colleges that need attention and the elements needed to have a successful carpet-maintenance program. The importance of using heavy equipment to lessen time and effort is explained as are the steps maintenance workers can take to make the…
ERIC Educational Resources Information Center
Sturgeon, Julie
2008-01-01
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.…
ERIC Educational Resources Information Center
Berry, John N., III
2009-01-01
Roberta Stevens and Kent Oliver are campaigning hard for the presidency of the American Library Association (ALA). Stevens is outreach projects and partnerships officer at the Library of Congress. Oliver is executive director of the Stark County District Library in Canton, Ohio. They have debated, discussed, and posted web sites, Facebook pages,…
Liouville Quantum Gravity on the Riemann Sphere
NASA Astrophysics Data System (ADS)
David, François; Kupiainen, Antti; Rhodes, Rémi; Vargas, Vincent
2016-03-01
In this paper, we rigorously construct Liouville Quantum Field Theory on the Riemann sphere introduced in the 1981 seminal work by Polyakov. We establish some of its fundamental properties like conformal covariance under PSL{_2({C})}-action, Seiberg bounds, KPZ scaling laws, KPZ formula and the Weyl anomaly formula. We also make precise conjectures about the relationship of the theory to scaling limits of random planar maps conformally embedded onto the sphere.
Hollow sphere ceramic particles for abradable coatings
Longo, F.N.; Bader, N.F. III; Dorfman, M.R.
1984-05-22
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.
Approximating spheroid inductive responses using spheres
Smith, J. Torquil; Morrison, H. Frank
2003-12-12
The response of high permeability ({mu}{sub r} {ge} 50) conductive spheroids of moderate aspect ratios (0.25 to 4) to excitation by uniform magnetic fields in the axial or transverse directions is approximated by the response of spheres of appropriate diameters, of the same conductivity and permeability, with magnitude rescaled based on the differing volumes, D.C. magnetizations, and high frequency limit responses of the spheres and modeled spheroids.
Inverse Magnus effect on a rotating sphere
NASA Astrophysics Data System (ADS)
Kim, Jooha; Park, Hyungmin; Choi, Haecheon; Yoo, Jung Yul
2011-11-01
In this study, we investigate the flow characteristics of rotating spheres in the subcritical Reynolds number (Re) regime by measuring the drag and lift forces on the sphere and the two-dimensional velocity in the wake. The experiment is conducted in a wind tunnel at Re = 0 . 6 ×105 - 2 . 6 ×105 and the spin ratio (ratio of surface velocity to the free-stream velocity) of 0 (no spin) - 0.5. The drag coefficient on a stationary sphere remains nearly constant at around 0.52. However, the magnitude of lift coefficient is nearly zero at Re < 2 . 0 ×105 , but rapidly increases to 0.3 and then remains constant with further increasing Reynolds number. On the other hand, with rotation, the lift coefficient shows negative values, called inverse Magnus effect, depending on the magnitudes of the Reynolds number and spin ratio. The velocity field measured from a particle image velocimetry (PIV) indicates that non-zero lift coefficient on a stationary sphere at Re > 2 . 0 ×105 results from the asymmetry of separation line, whereas the inverse Magnus effect for the rotating sphere results from the differences in the boundary-layer growth and separation along the upper and lower sphere surfaces. Supported by the WCU, Converging Research Center and Priority Research Centers Program, NRF, MEST, Korea.
Vector field generator for a direct mapping of the first order Poincare sphere
NASA Astrophysics Data System (ADS)
Pierce, Melanie Anne
This thesis presents an optical system able to generate all polarization states on the zero order Poincare sphere. An important characteristic of the zero order sphere is its spatial uniformity. This means that the polarization of the beam is uniform. This characterization can be proven using polarizers. Any change in the polarization of the beam will be consistent for all points in the beam. This is not necessarily true for all types of polarization states. There are new polarization states that are spatially variant in which the polarization is no longer uniform. The assumption that the polarization at one point in the beam is the same at all points is no longer valid. These are defined as higher order polarization states which have their own Poincare spheres that are similar to the zero order sphere but are spatially variant. The higher order polarization states are the focus of this thesis. Maxwell's equations are shown and the solution for light is derived. From this, Jones vectors are used to describe the polarization and how they relate to the Poincare sphere. Jones matrices are applied to the incoming polarization state to reflect the changes a waveplate causes to the system, and how to create a rotator to rotate the axis of polarization. The matrices describe an optical system consisting of a variable waveplate and a rotator created from 2 quarter waveplates and an additional variable waveplate that able to change the latitude and longitude of a polarization state on the Poincare sphere. The system is able to achieve any coordinate on the surface of the sphere. The system is applied to the zero order Poincare sphere and the positive and negative first order Poincare sphere. Experimental results are presented and agree with theory.
Lumma; Lurio; Borthwick; Falus; Mochrie
2000-12-01
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
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.
Lumma, D.; Lurio, L. B.; Borthwick, M. A.; Falus, P.; Mochrie, S. G. J.
2000-12-01
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.
Tungstenic acid induced assembly of hierarchical flower-like MoS{sub 2} spheres
Huang Wanzhen Xu Zhude Liu Run; Ye Xianfu; Zheng Yifan
2008-10-02
Hierarchical flower-like MoS{sub 2} spheres with high purity were synthesized by hydrothermal method using WO{sub 3} nanorods or H{sub 2}WO{sub 4} as an additive. The flower-like spheres were about 1 {mu}m in diameter and built up with MoS{sub 2} thin flakes with thickness of several nanometers. Energy disperse X-ray spectrum showed that the spheres were only composed of Mo and S with atomic ratio of 2:1. Powder X-ray diffraction result further indicated that the products were MoS{sub 2}. The reaction mechanism is discussed and suggested that tungstenic acid played an important role on the formation of flower-like MoS{sub 2} spheres.
Photonic bandgap of inverse opals prepared from core-shell spheres.
Liu, Bo-Tau; Lin, Ya-Li; Huang, Shao-Xian
2012-01-01
In this study, we synthesized monodispersed polystyrene (PS)-silica core-shell spheres with various shell thicknesses for the fabrication of photonic crystals. The shell thickness of the spheres was controlled by various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica shell to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have higher filling fraction and larger wavelength of stop band maximum. PMID:22894600
VizieR Online Data Catalog: HD61005 SPHERE H and Ks images (Olofsson+, 2016)
NASA Astrophysics Data System (ADS)
Olofsson, J.; Samland, M.; Avenhaus, H.; Caceres, C.; Henning, T.; Moor, A.; Milli, J.; Canovas, H.; Quanz, S. P.; Schreiber, M. R.; Augereau, J.-C.; Bayo, A.; Bazzon, A.; Beuzit, J.-L.; Boccaletti, A.; Buenzli, E.; Casassus, S.; Chauvin, G.; Dominik, C.; Desidera, S.; Feldt, M.; Gratton, R.; Janson, M.; Lagrange, A.-M.; Langlois, M.; Lannier, J.; Maire, A.-L.; Mesa, D.; Pinte, C.; Rouan, D.; Salter, G.; Thalmann, C.; Vigan, A.
2016-05-01
The fits files contains the reduced ADI and DPI SPHERE observations used to produce Fig. 1 of the paper. Besides the primary card, the files consists of 6 additional ImageHDU. The first and second one contain the SPHERE IRDIS ADI H band observations and the noise map. The third and fourth contain the SPHERE IRDIS ADI Ks band observations and the corresponding noise map. Finally, the fifth and sixth ImageHDU contain the SPHERE IRDIS DPI H band data as well as the noise map. Each ADI image has 1024x1024 pixels, while the DPI images have 1800x1800 pixels. The header of the primary card contains the pixel sizes for each datasets and the wavelengths of the H and K band observations. (2 data files).
Photonic bandgap of inverse opals prepared from core-shell spheres.
Liu, Bo-Tau; Lin, Ya-Li; Huang, Shao-Xian
2012-01-01
In this study, we synthesized monodispersed polystyrene (PS)-silica core-shell spheres with various shell thicknesses for the fabrication of photonic crystals. The shell thickness of the spheres was controlled by various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica shell to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have higher filling fraction and larger wavelength of stop band maximum.
Potential Health Impacts of Hard Water
Sengupta, Pallav
2013-01-01
In the past five decades or so evidence has been accumulating about an environmental factor, which appears to be influencing mortality, in particular, cardiovascular mortality, and this is the hardness of the drinking water. In addition, several epidemiological investigations have demonstrated the relation between risk for cardiovascular disease, growth retardation, reproductive failure, and other health problems and hardness of drinking water or its content of magnesium and calcium. In addition, the acidity of the water influences the reabsorption of calcium and magnesium in the renal tubule. Not only, calcium and magnesium, but other constituents also affect different health aspects. Thus, the present review attempts to explore the health effects of hard water and its constituents. PMID:24049611
Potential health impacts of hard water.
Sengupta, Pallav
2013-08-01
In the past five decades or so evidence has been accumulating about an environmental factor, which appears to be influencing mortality, in particular, cardiovascular mortality, and this is the hardness of the drinking water. In addition, several epidemiological investigations have demonstrated the relation between risk for cardiovascular disease, growth retardation, reproductive failure, and other health problems and hardness of drinking water or its content of magnesium and calcium. In addition, the acidity of the water influences the reabsorption of calcium and magnesium in the renal tubule. Not only, calcium and magnesium, but other constituents also affect different health aspects. Thus, the present review attempts to explore the health effects of hard water and its constituents.
He II heat transfer through random packed spheres: Pressure drop
NASA Astrophysics Data System (ADS)
Vanderlaan, M. H.; Van Sciver, S. W.
2014-09-01
Heat flow induced pressure drop through superfluid helium (He II) contained in porous media is examined. In this experiment, heat was applied to one side of a He II column containing a random pack of uniform size polyethylene spheres. Measured results include steady state pressure drops across the random packs of spheres (nominally 35 μm, 49 μm, and 98 μm diameter) for different heat inputs. Laminar, turbulent, and transition fluid flow regimes are examined. The laminar permeability and equivalent channel shape factor are compared to our past studies of the temperature drop through He II in the same porous media of packed spheres. Results from the pressure drop experiments are more accurate than temperature drop experiments due to reduced measurement errors achieved with the pressure transducer. Turbulent results are fitted to models with empirically derived friction factors. A turbulent model considering only dynamic pressure losses in the normal fluid yields the most consistent friction factors. The addition of the laminar and turbulent heat flow equations into a unifying prediction fits all regimes to within 10%.
Stimulus-responsive azobenzene supramolecules: fibers, gels, and hollow spheres.
Lee, Sumi; Oh, Seungwhan; Lee, Joosub; Malpani, Yashwardhan; Jung, Young-Sik; Kang, Baotao; Lee, Jin Yong; Ozasa, Kazunari; Isoshima, Takashi; Lee, Sang Yun; Hara, Masahiko; Hashizume, Daisuke; Kim, Jong-Man
2013-05-14
Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (Azo-1) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of Azo-1 (crystallized from a mixture of DMSO and H2O) reveal that it possesses supramolecular columnar packing along the b axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the Azo-1 fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the Azo-1 supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in Azo-1 is demonstrated by the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence of fluoride anions. PMID:23597134
Collinear swimmer propelling a cargo sphere at low Reynolds number.
Felderhof, B U
2014-11-01
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 a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.
The Separate Spheres Model of Gendered Inequality
Miller, Andrea L.; Borgida, Eugene
2016-01-01
Research on role congruity theory and descriptive and prescriptive stereotypes has established that when men and women violate gender stereotypes by crossing spheres, with women pursuing career success and men contributing to domestic labor, they face backlash and economic penalties. Less is known, however, about the types of individuals who are most likely to engage in these forms of discrimination and the types of situations in which this is most likely to occur. We propose that psychological research will benefit from supplementing existing research approaches with an individual differences model of support for separate spheres for men and women. This model allows psychologists to examine individual differences in support for separate spheres as they interact with situational and contextual forces. The separate spheres ideology (SSI) has existed as a cultural idea for many years but has not been operationalized or modeled in social psychology. The Separate Spheres Model presents the SSI as a new psychological construct characterized by individual differences and a motivated system-justifying function, operationalizes the ideology with a new scale measure, and models the ideology as a predictor of some important gendered outcomes in society. As a first step toward developing the Separate Spheres Model, we develop a new measure of individuals’ endorsement of the SSI and demonstrate its reliability, convergent validity, and incremental predictive validity. We provide support for the novel hypotheses that the SSI predicts attitudes regarding workplace flexibility accommodations, income distribution within families between male and female partners, distribution of labor between work and family spheres, and discriminatory workplace behaviors. Finally, we provide experimental support for the hypothesis that the SSI is a motivated, system-justifying ideology. PMID:26800454
The Separate Spheres Model of Gendered Inequality.
Miller, Andrea L; Borgida, Eugene
2016-01-01
Research on role congruity theory and descriptive and prescriptive stereotypes has established that when men and women violate gender stereotypes by crossing spheres, with women pursuing career success and men contributing to domestic labor, they face backlash and economic penalties. Less is known, however, about the types of individuals who are most likely to engage in these forms of discrimination and the types of situations in which this is most likely to occur. We propose that psychological research will benefit from supplementing existing research approaches with an individual differences model of support for separate spheres for men and women. This model allows psychologists to examine individual differences in support for separate spheres as they interact with situational and contextual forces. The separate spheres ideology (SSI) has existed as a cultural idea for many years but has not been operationalized or modeled in social psychology. The Separate Spheres Model presents the SSI as a new psychological construct characterized by individual differences and a motivated system-justifying function, operationalizes the ideology with a new scale measure, and models the ideology as a predictor of some important gendered outcomes in society. As a first step toward developing the Separate Spheres Model, we develop a new measure of individuals' endorsement of the SSI and demonstrate its reliability, convergent validity, and incremental predictive validity. We provide support for the novel hypotheses that the SSI predicts attitudes regarding workplace flexibility accommodations, income distribution within families between male and female partners, distribution of labor between work and family spheres, and discriminatory workplace behaviors. Finally, we provide experimental support for the hypothesis that the SSI is a motivated, system-justifying ideology. PMID:26800454
ERIC Educational Resources Information Center
McNeil, Michele
2008-01-01
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,…
Melese, P.; CDF Collaboration
1997-06-01
We present results on diffractive production of hard processes in {anti p}p collisions at {radical}s = 1.8 TeV at the Tevatron using the CDF detector. The signatures used to identify diffractive events are the forward rapidity gap and/or the detection of a recoil antiproton with high forward momentum. We have observed diffractive W- boson, dijet, and heavy quark production. We also present results on double-pomeron production of dijets.
ERIC Educational Resources Information Center
Mathews, Jay
2009-01-01
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,…
Mansur, Louis K; Bhattacharya, R; Blau, Peter Julian; Clemons, Art; Eberle, Cliff; Evans, H B; Janke, Christopher James; Jolly, Brian C; Lee, E H; Leonard, Keith J; Trejo, Rosa M; Rivard, John D
2010-01-01
High energy ion beam surface treatments were applied to a selected group of polymers. Of the six materials in the present study, four were thermoplastics (polycarbonate, polyethylene, polyethylene terephthalate, and polystyrene) and two were thermosets (epoxy and polyimide). The particular epoxy evaluated in this work is one of the resins used in formulating fiber reinforced composites for military helicopter blades. Measures of mechanical properties of the near surface regions were obtained by nanoindentation hardness and pin on disk wear. Attempts were also made to measure erosion resistance by particle impact. All materials were hardness tested. Pristine materials were very soft, having values in the range of approximately 0.1 to 0.5 GPa. Ion beam treatment increased hardness by up to 50 times compared to untreated materials. For reference, all materials were hardened to values higher than those typical of stainless steels. Wear tests were carried out on three of the materials, PET, PI and epoxy. On the ion beam treated epoxy no wear could be detected, whereas the untreated material showed significant wear.
Recent researches on the air resistance of spheres
NASA Technical Reports Server (NTRS)
Flachsbart, O
1928-01-01
The following conclusions on air resistance of spheres are drawn: 1) disturbances in front of the sphere and even single fine wires affect the critical Reynolds Number; 2) disturbances around the sphere increased the drag of the sphere without martially affecting the value of the Reynolds Number(sub crith); 3) great disturbances of the boundary layer of the sphere likewise change R.N.(sub crith); 4) turbulence of the approaching air stream lowers critical R.N.
Robotics Programming Competition Spheres, Russian Part
NASA Astrophysics Data System (ADS)
Sadovski, Andrei; Kukushkina, Natalia; Biryukova, Natalia
2016-07-01
Spheres" such name was done to Russian part of the Zero Robotics project which is a student competition devoted to programming of SPHERES (SPHERES - Synchronized Position Hold Engage and Reorient Experimental Satellites are the experimental robotics devices which are capable of rotation and translation in all directions, http://ssl.mit.edu/spheres/), which perform different operations on the board of International Space Station. Competition takes place online on http://zerorobotics.mit.edu. The main goal is to develop a program for SPHERES to solve an annual challenge. The end of the tournament is the real competition in microgravity on the board of ISS with a live broadcast. The Russian part of the tournament has only two years history but the problems, organization and specific are useful for the other educational projects especially for the international ones. We introduce the history of the competition, its scientific and educational goals in Russia and describe the participation of Russian teams in 2014 and 2015 tournaments. Also we discuss the organizational problems.
Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent
2015-01-01
This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration.
A thermodynamic self-consistent theory of asymmetric hard-core Yukawa mixtures.
Pellicane, Giuseppe; Caccamo, Carlo
2016-10-19
We perform structural and thermodynamic calculations in the framework of the modified hypernetted chain (MHNC) integral equation closure to the Ornstein-Zernike equation for binary mixtures of size-different particles interacting with hard-core Yukawa pair potentials. We use the Percus-Yevick (PY) bridge functions of a binary mixture of hard-sphere (HSM) particles. The hard-sphere diameters of the PY bridge functions of the HSM system are adjusted so to achieve thermodynamic consistency between the virial and compressibility equations of state. We show the benefit of thermodynamic consistency by comparing the MHNC results with the available computer simulation data reported in the literature, and we demonstrate that the self-consistent thermodynamic theory provides a better reproduction of the simulation data over other microscopic theories. PMID:27545096
A thermodynamic self-consistent theory of asymmetric hard-core Yukawa mixtures
NASA Astrophysics Data System (ADS)
Pellicane, Giuseppe; Caccamo, Carlo
2016-10-01
We perform structural and thermodynamic calculations in the framework of the modified hypernetted chain (MHNC) integral equation closure to the Ornstein-Zernike equation for binary mixtures of size-different particles interacting with hard-core Yukawa pair potentials. We use the Percus-Yevick (PY) bridge functions of a binary mixture of hard-sphere (HSM) particles. The hard-sphere diameters of the PY bridge functions of the HSM system are adjusted so to achieve thermodynamic consistency between the virial and compressibility equations of state. We show the benefit of thermodynamic consistency by comparing the MHNC results with the available computer simulation data reported in the literature, and we demonstrate that the self-consistent thermodynamic theory provides a better reproduction of the simulation data over other microscopic theories.
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.
2007-06-15
Hot electron and x-ray production from solid targets coated with polystyrene-spheres which are irradiated with high-contrast, 100 fs, 400 nm light pulses at intensity up to 2x10{sup 17} W/cm{sup 2} 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 {mu}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.
Zu, Lei; Li, Ruirui; Shi, Yue; Lian, Huiqin; Liu, Yang; Cui, Xiuguo; Bai, Zongwu
2014-04-01
As a common used and hardly emulsified amorphous thermoplastic, the bisphenol-A polycarbonates were used as the polymer candidate to form a novel monodispersed sub-micrometer mesoporous polymer-silica spheres with full interpenetrating structure. The synthesis procedure was based on a modified sol-gel approach in which the polycarbonate was plasticized in advanced by the surfactant of polymer emulsion. The mesoporous spheres possess a perfect uniform particle size and the polymer-silica spheres are held together by permanent entanglement in three dimensions. The defined crystallization of the polycarbonate was occurred when it was entrapped in the silica laminated matrix due to the plasticizing effect of the surfactant, and directly affected the thermal stability of the mesoporous spheres. The specific surface areas and pore diameters of mesoporous sphere were affected by the mass content and crystallization behavior of the polycarbonate. The p-phenylenediamine was used as adsorbate to investigate the cationic organics adsorption ability of the mesoporous spheres. The results shown that the polycarbonate-silica possess a well adsorption capacity for p-phenylenediamine by virtue of two kinds of hydrogen bond, and the maximum adsorption capacity was nearly 7.5 times larger than that of the hollow mesoporous silica.
Ultrasonic characterization of materials hardness
Badidi Bouda A; Benchaala; Alem
2000-03-01
In this paper, an experimental technique has been developed to measure velocities and attenuation of ultrasonic waves through a steel with a variable hardness. A correlation between ultrasonic measurements and steel hardness was investigated.
Registration of 'Advance' Hard Red Spring Wheat
Technology Transfer Automated Retrieval System (TEKTRAN)
Grower and end-user acceptance of new hard red spring wheat (HRSW; Triticum aestivum L.) cultivars is largely contingent on satisfactory agronomic performance, end-use quality potential, and disease resistance levels. Additional characteristics, such as desirable plant height, can also help to maxi...
Registration of 'Prevail' hard red spring wheat
Technology Transfer Automated Retrieval System (TEKTRAN)
Grower and end-user acceptance of new Hard Red Spring Wheat (HRSW; Triticum aestivum L.) cultivars is largely contingent upon satisfactory agronomic performance, end-use quality potential, and disease resistance levels. Additional characteristics, such as desirable plant height, can also contribute...
Direct observation in 3d of structural crossover in binary hard sphere mixtures
NASA Astrophysics Data System (ADS)
Statt, Antonia; Pinchaipat, Rattachai; Turci, Francesco; Evans, Robert; Royall, C. Patrick
2016-04-01
For binary fluid mixtures of spherical particles in which the two species are sufficiently different in size, the dominant wavelength of oscillations of the pair correlation functions is predicted to change from roughly the diameter of the large species to that of the small species along a sharp crossover line in the phase diagram [C. Grodon et al., J. Chem. Phys. 121, 7869 (2004)]. Using particle-resolved colloid experiments in 3d we demonstrate that crossover exists and that its location in the phase diagram is in quantitative agreement with the results of both theory and our Monte-Carlo simulations. In contrast with previous work [J. Baumgartl et al., Phys. Rev. Lett. 98, 198303 (2007)], where a correspondence was drawn between crossover and percolation of both species, in our 3d study we find that structural crossover is unrelated to percolation.
Periodic and Aperiodic Close Packing: A Spontaneous Hard-Sphere Model.
ERIC Educational Resources Information Center
van de Waal, B. W.
1985-01-01
Shows how to make close-packed models from balloons and table tennis balls to illustrate structural features of clusters and organometallic cluster-compounds (which are of great interest in the study of chemical reactions). These models provide a very inexpensive and tactile illustration of the organization of matter for concrete operational…
Hypersonic acoustic excitations in binary colloidal crystals: big versus small hard sphere control.
Tommaseo, G; Petekidis, G; Steffen, W; Fytas, G; Schofield, A B; Stefanou, N
2007-01-01
The phononic band structure of two binary colloidal crystals, at hypersonic frequencies, is studied by means of Brillouin light scattering and analyzed in conjunction with corresponding dispersion diagrams of the single colloidal crystals of the constituent particles. Besides the acoustic band of the average medium, the authors' results show the existence of narrow bands originating from resonant multipole modes of the individual particles as well as Bragg-type modes due to the (short-range) periodicity. Strong interaction, leading to the occurrence of hybridization gaps, is observed between the acoustic band and the band of quadrupole modes of the particles that occupy the largest fractional volume of the mixed crystal; the effective radius is either that of the large (in the symmetric NaCl-type crystalline phase) or the small (in the asymmetric NaZn(13)-type crystalline phase) particles. The possibility to reveal a universal behavior of the phononic band structure for different single and binary colloidal crystalline suspensions, by representing in the dispersion diagrams reduced quantities using an appropriate length scale, is discussed.
Gelation in a model 1-component system with adhesive hard-sphere interactions
NASA Astrophysics Data System (ADS)
Kim, Jung Min; Eberle, Aaron; Fang, Jun; Wagner, Norman
2012-02-01
Colloidal dispersions can undergo a dynamical arrest of the disperse phase leading to a system with solid-like properties when either the volume fraction or the interparticle potential is varied. Systems that contain low to moderate particulate concentrations form gels whereas higher concentrations lead to glassy states in which caging by nearest neighbors can be a significant contributor to the arrested long-time dynamics. Colloid polymer mixtures have been the prevalent model system for studying the effect of attraction, where attractions are entropically driven by depletion effects, in which gelation has been shown to be a result of phase separation [1]. Using the model 1-component octadecyl coated silica nanoparticle system, Eberle et al. [2] found the gel-line to intersect the spinodal to the left of the critical point, and at higher concentrations extended toward the mode coupling theory attractive driven glass line. . We continue this study by varying the particle diameter and find quantitative differences which we explain by gravity. 1. Lu, P.J., et al., Nature, 2008. 453(7194): p. 499-504.2. Eberle, A.P.R., N.J. Wagner, and R. Castaneda-Priego, Physical Review Letters, 2011. 106(10).
NASA Astrophysics Data System (ADS)
Rubinstein, Robert
2015-11-01
It is well known that collision models based on an assumed intermolecular potential (IPL, LJ, ...) can be successfully replaced by simplified surrogates (VHS, VSS, VS, ...) in DSMC calculations. But these surrogates only reproduce certain gross properties of the molecular model, for example, the temperature dependence of the viscosity; they do not approximate, and even mis-state, the details of the particle interactions. The success of the simplified models in problems at finite Knudsen number, where the Navier-Stokes approximation is not valid, may therefore seem surprising. To understand this success in a very special case, we showed that the first seven relaxation rates of the linearized Boltzmann equation for Maxwellian molecules are well approximated by the corresponding relaxation rates of its VHS surrogate. We will show that this analysis can be extended in somewhat less generality to IPL interactions, and to some extent to more realistic models including LJ. We believe that this analysis can help address the more general problem of identifying the properties of the collision model that dominate the predictions of the Boltzmann equation.
Physics of the granite sphere fountain
NASA Astrophysics Data System (ADS)
Snoeijer, Jacco H.; der Weele, Ko van
2014-11-01
A striking example of levitation is encountered in the "kugel fountain" where a granite sphere, sometimes weighing over a ton, is kept aloft by a thin film of flowing water. In this paper, we explain the working principle behind this levitation. We show that the fountain can be viewed as a giant ball bearing and thus forms a prime example of lubrication theory. It is demonstrated how the viscosity and flow rate of the fluid determine (i) the remarkably small thickness of the film supporting the sphere and (ii) the surprisingly long time it takes for rotations to damp out. The theoretical results compare well with measurements on a fountain holding a granite sphere of one meter in diameter. We close by discussing several related cases of levitation by lubrication.
The flow past a freely rotating sphere
NASA Astrophysics Data System (ADS)
Fabre, David; Tchoufag, Joël; Citro, Vincenzo; Giannetti, Flavio; Luchini, Paolo
2016-08-01
We consider the flow past a sphere held at a fixed position in a uniform incoming flow but free to rotate around a transverse axis. A steady pitchfork bifurcation is reported to take place at a threshold Re^OS=206 leading to a state with zero torque but nonzero lift. Numerical simulations allow to characterize this state up to Re≈ 270 and confirm that it substantially differs from the steady-state solution which exists in the wake of a fixed, non-rotating sphere beyond the threshold Re^SS=212 . A weakly nonlinear analysis is carried out and is shown to successfully reproduce the results and to give substantial improvement over a previous analysis (Fabre et al. in J Fluid Mech 707:24-36, 2012). The connection between the present problem and that of a sphere in free fall following an oblique, steady (OS) path is also discussed.
Unveiling the scattering behavior of small spheres
NASA Astrophysics Data System (ADS)
Tzarouchis, Dimitrios C.; Ylä-Oijala, Pasi; Sihvola, Ari
2016-10-01
A classical way for exploring the scattering behavior of a small sphere is to approximate Mie coefficients with a Taylor series expansion. This ansatz delivered a plethora of insightful results, mostly for small spheres supporting electric localized plasmonic resonances. However, many scattering aspects are still uncharted, especially with regards to magnetic resonances. Here, an alternative system ansatz is proposed based on the Padé approximants for the Mie coefficients. The results reveal the existence of a self-regulating radiative damping mechanism for the first magnetic resonance and general resonating aspects for the higher order multipoles. Hence, a systematic way of exploring the scattering response is introduced, sharpening our understanding of the sphere's scattering behavior and its emergent functionalities.
Yang, Xiaoyan; Xu, Lin; Zhai, Zheng; Cheng, Fangfang; Yan, Zhenzhen; Feng, Xiaomiao; Zhu, Junjie; Hou, Wenhua
2013-12-23
Hollow spheres of heavy lanthanide orthovanadates (LnVO4, Ln = Tb, Dy, Er, Tm, Yb, Lu) and yolk-shell structures of Ho(OH)CO3@HoVO4 have been successfully prepared by employing Ln(OH)CO3 colloidal spheres as a sacrificial template and NH4VO3 as a vanadium source. In particular, the as-obtained LuVO4 hollow spheres are assembled from numerous hollow-structured elliptic nanoparticles, and their textural parameters such as the inner and outer diameters, shell thicknesses, and number of shells could be finely tuned through introducing different amounts of NH4VO3 and employing Lu(OH)CO3 templates with different sizes. The possible mechanisms for the formation of hollow spheres and yolk-shell structures, and also the hollow-structured elliptic nanoparticles of LuVO4, i.e., building blocks of LuVO4 hollow spheres, are proposed and discussed in detail. Under ultraviolet excitation, the obtained LuVO4:Eu(3+) hollow spheres show strong red emissions located in the saturated color region, and the modulation of emission intensity and color purity could be realized by tuning the textural parameters of the obtained hollow spheres. It was found that the nanostructure of the building blocks of LuVO4:Eu(3+) hollow spheres also had an effect on the luminescent properties of the as-obtained materials. Moreover, the quantum efficiency could be affected by the textural parameters of the as-obtained LuVO4:Eu(3+) hollow spheres, and the double-shelled LuVO4:Eu(3+) hollow sphere has the highest quantum efficiency. In addition, the excellent biocompatibility indicates the potential biological applications of LuVO4 hollow spheres.
Optimal translational swimming of a sphere at low Reynolds number.
Felderhof, B U; Jones, R B
2014-08-01
Swimming velocity and rate of dissipation of a sphere with surface distortions are discussed on the basis of the Stokes equations of low-Reynolds-number hydrodynamics. At first the surface distortions are assumed to cause an irrotational axisymmetric flow pattern. The efficiency of swimming is optimized within this class of flows. Subsequently, more general axisymmetric polar flows with vorticity are considered. This leads to a considerably higher maximum efficiency. An additional measure of swimming performance is proposed based on the energy consumption for given amplitude of stroke.
Mesoporous hollow spheres from soap bubbling.
Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong
2012-02-01
The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites. PMID:22078340
Mesoporous hollow spheres from soap bubbling.
Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong
2012-02-01
The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites.
Sheinberg, H.
1983-07-26
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, Haskell
1986-01-01
A composition of matter having a Rockwell A hardness of at least 85 is formed from a precursor mixture comprising between 3 and 10 weight percent boron carbide and the remainder a metal mixture comprising from 70 to 90 percent 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 to 14 g/cc. The precursor is preferably hot pressed to yield a composition having greater than 100% of theoretical density.
Hard Exclusive Pion Leptoproduction
NASA Astrophysics Data System (ADS)
Kroll, Peter
2016-08-01
In this talk it is reported on an analysis of hard exclusive leptoproduction of pions within the handbag approach. It is argued that recent measurements of this process performed by HERMES and CLAS clearly indicate the occurrence of strong contributions from transversely polarized photons. Within the handbag approach such γ ^{ *}_T→ π transitions are described by the transversity GPDs accompanied by twist-3 pion wave functions. It is shown that the handbag approach leads to results on cross sections and single-spin asymmetries in fair agreement with experiment. Predictions for other pseudoscalar meson channels are also briefly discussed.
Formation mechanism and size control in one-pot synthesis of mercapto-silica colloidal spheres.
Lu, Zhenda; Sun, Lei; Nguyen, Kevin; Gao, Chuanbo; Yin, Yadong
2011-04-01
Mercapto-silica spheres with controllable size from ∼150 nm to ∼3.5 μm and narrow size distribution have been prepared in water using a one-pot synthesis, in which 3-mercaptopropyltrimethoxysilane (MPS) was used as the sole silica source and ammonia as the base catalyst. The hydrolysis of MPS at the early stage of the reaction produces amphiphilic silicate species which initiate the self-emulsification of the system and lead to the formation of oil-in-water emulsion droplets. Further hydrolysis and condensation promote the nucleation and growth of the mercapto-silica spheres inside the emulsion droplets. These mercapto-silica spheres are both structurally and functionally different from typical silica particles prepared from silicon alkoxides. Understanding the formation mechanism allows systematic tuning of the size of mercapto-silica spheres in a wide range by changing the amount of precursor, the concentration of ammonia, the amount of additional surfactants, and the reaction time. We find that Ostwald ripening may occur quickly if the spheres are kept in the reaction solution, resulting in significant broadening of the particle size distribution. In order to obtain uniform and stable samples, it is important to quench the growth of the mercapto-silica spheres by separating them from the original reaction mixture and then storing them in solvents that can prevent further ripening.
Mesoporous submicrometer TiO(2) hollow spheres as scatterers in dye-sensitized solar cells.
Dadgostar, Shabnam; Tajabadi, Fariba; Taghavinia, Nima
2012-06-27
Hierarchical submicrometer TiO2 hollow spheres with outer diameter of 300-700 nm and shell thickness of 200 nm are synthesized by liquid phase deposition of TiO2 over carbon microspheres as sacrificial templates. The final TiO2 hollow spheres are applied as a scattering layer on top of a transparent nanocrystalline TiO2 film, serving as the photoanode of a dye-sensitized solar cell (DSC). In addition to efficient light scattering, the mesoporous structure of TiO2 hollow spheres provides a high surface area, 74 m(2)/g, which allows for higher dye loading. This dual functioning suggests that TiO2 hollow spheres may be good replacements for conventional TiO2 spheres as scatterers in DSCs. A high efficiency of 8.3% is achieved with TiO2 hollow spheres, compared with 6.0% for the electrode with 400 nm spherical TiO2 scatterers, at identical conditions. PMID:22606936
Equation of state and critical point behavior of hard-core double-Yukawa fluids.
Montes, J; Robles, M; López de Haro, M
2016-02-28
A theoretical study on the equation of state and the critical point behavior of hard-core double-Yukawa fluids is presented. Thermodynamic perturbation theory, restricted to first order in the inverse temperature and having the hard-sphere fluid as the reference system, is used to derive a relatively simple analytical equation of state of hard-core multi-Yukawa fluids. Using such an equation of state, the compressibility factor and phase behavior of six representative hard-core double-Yukawa fluids are examined and compared with available simulation results. The effect of varying the parameters of the hard-core double-Yukawa intermolecular potential on the location of the critical point is also analyzed using different perspectives. The relevance of this analysis for fluids whose molecules interact with realistic potentials is also pointed out. PMID:26931708
Equation of state and critical point behavior of hard-core double-Yukawa fluids.
Montes, J; Robles, M; López de Haro, M
2016-02-28
A theoretical study on the equation of state and the critical point behavior of hard-core double-Yukawa fluids is presented. Thermodynamic perturbation theory, restricted to first order in the inverse temperature and having the hard-sphere fluid as the reference system, is used to derive a relatively simple analytical equation of state of hard-core multi-Yukawa fluids. Using such an equation of state, the compressibility factor and phase behavior of six representative hard-core double-Yukawa fluids are examined and compared with available simulation results. The effect of varying the parameters of the hard-core double-Yukawa intermolecular potential on the location of the critical point is also analyzed using different perspectives. The relevance of this analysis for fluids whose molecules interact with realistic potentials is also pointed out.
Patrinoiu, Greta; Tudose, Madalina; Calderon-Moreno, Jose Maria; Birjega, Ruxandra; Budrugeac, Petru; Ene, Ramona; Carp, Oana
2012-02-15
ZnO hollow spheres have been synthesized by a simple and environmentally friendly template assisted route. Starch-derived carbonaceous spheres were used as template, impregnated with Zn(CH{sub 3}COO){sub 2}{center_dot}2H{sub 2}O to obtain zinc-containing precursor spheres and thermally treatment at 600 Degree-Sign C, yielding hollow ZnO spherical shells. The precursor spheres and hollow shells were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy, thermal analysis and room-temperature photoluminescence measurements. The hollow spherical shells with diameters of {approx}150 nm and wall thickness of {approx}20 nm, are polycrystalline, with a mean crystallite size of 22 nm, exhibiting interesting emission features, with a wide multi-peak band covering blue and green regions of the visible spectrum. The photocatalytic activities (under UV and visible light irradiations) of the ZnO spherical shells evaluated for the phenol degradation reaction in aqueous solutions are outstanding, a total phenol conversion being registered in the case of UV irradiation experiments. - Graphical abstract: The photocatalytic reaction initiated by the photoexcitation of the semiconductor (ZnO), leads to the formation of electron-hole, while part of the electron-hole pairs recombine, some holes combine with water to form {center_dot}OH radicals and some electrons convert oxygen to super oxide radical ({center_dot}O{sub 2}{sup -}). Highlights: Black-Right-Pointing-Pointer Green synthesis of ZnO hollow spheres. Black-Right-Pointing-Pointer Starch-derived carbonaceous spheres as spherical hard template. Black-Right-Pointing-Pointer ZnO hollow spheres with notable visible photoluminescence properties. Black-Right-Pointing-Pointer ZnO hollow spheres with photocatalytical activity in degradation/mineralization of phenol.
Novel hard compositions and methods of preparation
Sheinberg, H.
1983-08-23
Novel very hard compositions of matter are prepared by using in all embodiments only a minor amount of a particular carbide (or materials which can form the carbide in situ when subjected to heat and pressure); and no strategic cobalt is needed. Under a particular range of conditions, densified compositions of matter of the invention are prepared having hardnesses on the Rockwell A test substantially equal to the hardness of pure tungsten carbide and to two of the hardest commercial cobalt-bonded tungsten carbides. Alternately, other compositions of the invention which have slightly lower hardnesses than those described above in one embodiment also possess the advantage of requiring no tungsten and in another embodiment possess the advantage of having a good fracture toughness value. Photomicrographs show that the shapes of the grains of the alloy mixture with which the minor amount of carbide (or carbide-formers) is mixed are radically altered from large, rounded to small, very angular by the addition of the carbide. Superiority of one of these hard compositions of matter over cobalt-bonded tungsten carbide for ultra-high pressure anvil applications was demonstrated. 3 figs.
Novel hard compositions and methods of preparation
Sheinberg, Haskell
1983-08-23
Novel very hard compositions of matter are prepared by using in all embodiments only a minor amount of a particular carbide (or materials which can form the carbide in situ when subjected to heat and pressure); and no strategic cobalt is needed. Under a particular range of conditions, densified compositions of matter of the invention are prepared having hardnesses on the Rockwell A test substantially equal to the hardness of pure tungsten carbide and to two of the hardest commercial cobalt-bonded tungsten carbides. Alternately, other compositions of the invention which have slightly lower hardnesses than those described above in one embodiment also possess the advantage of requiring no tungsten and in another embodiment possess the advantage of having a good fracture toughness value. Photomicrographs show that the shapes of the grains of the alloy mixture with which the minor amount of carbide (or carbide-formers) is mixed are radically altered from large, rounded to small, very angular by the addition of the carbide. Superiority of one of these hard compositions of matter over cobalt-bonded tungsten carbide for ultra-high pressure anvil applications was demonstrated.
Chadwick, M.B. Frankle, S.; Trellue, H.; Talou, P.; Kawano, T.; Young, P.G.; MacFarlane, R.E.; Wilkerson, C.W.
2007-12-15
We describe new dosimetry (radiochemical) ENDF evaluations for yttrium, iridium, and thulium. These LANL2006 evaluations were based upon measured data and on nuclear model cross section calculations. In the case of iridium and yttrium, new measurements using the GEANIE gamma-ray detector at LANSCE were used to infer (n,xn) cross sections, the measurements being augmented by nuclear model calculations using the GNASH code. The thulium isotope evaluations were based on GNASH calculations and older measurements. The evaluated cross section data are tested through comparisons of simulations with measurements of reaction rates in critical assemblies and in Bethe sphere (sometimes called Wyman sphere) integral experiments. Two types of Bethe sphere experiments were studied - a LiD experiment that had a significant component of 14 MeV neutrons, and a LiD-U experiment that additionally had varying amounts of fission neutrons depending upon the location. These simulations were performed with the MCNP code using continuous energy Monte Carlo, and because the neutron fluences can be modeled fairly accurately by MCNP at different locations in these assemblies, the comparisons provide a valuable validation test of the accuracy of the evaluated cross sections and their energy dependencies. The MCNP integral reaction rate validation testing for the three detectors yttrium, iridium, and thulium, in the LANL2006 database is summarized as follows: (1) (n,2n)near 14 MeV: In 14 MeV-dominated locations (the LiD Bethe spheres and the outer regions of the LiD-U Bethe spheres), the (n,2n) products are modeled very well for all three detectors, suggesting that the evaluated {sup 89}Y(n,2n), {sup 191}Ir(n,2n), and {sup 169}Tm(n,2n) cross sections are accurate to better than about 5% near 14 MeV; (2) (n,2n)near threshold: In locations that have a significant number of fission spectrum neutrons or downscattered neutrons from 14 MeV inelastic scattering (the central regions of the Li
Electromagnetic resonant modes of dielectric sphere bilayers
Andueza, A. Pérez-Conde, J.; Sevilla, J.
2015-05-28
Sphere bilayers have been proposed as promising structures for electromagnetic management in photonic crystal devices. These arrangements are made of two intertwined subsets of spheres of different size and refractive index, one subset filling the interstitial sites of the other. We present a systematic study of the electromagnetic resonant modes of the bilayers, in comparison with those of the constituent subsets of spheres. Three samples were built with glass and Teflon spheres and their transmission spectra measured in the microwave range (10–25 GHz). Simulations with finite integration time-domain method are in good agreement with experiments. Results show that the bilayer presents the same resonances as one of the subsets but modified by the presence of the other in its resonant frequencies and in the electric field distributions. As this distortion is not very large, the number of resonances in a selected spectral region is determined by the dominant subset. The degree of freedom that offers the bilayer could be useful to fine tune the resonances of the structure for different applications. A map of modes useful to guide this design is also presented. Scale invariance of Maxwell equations allows the translation of these results in the microwave range to the visible region; hence, some possible applications are discussed in this framework.
Metal-Matrix/Hollow-Ceramic-Sphere Composites
NASA Technical Reports Server (NTRS)
Baker, Dean M.
2011-01-01
A family of metal/ceramic composite materials has been developed that are relatively inexpensive, lightweight alternatives to structural materials that are typified by beryllium, aluminum, and graphite/epoxy composites. These metal/ceramic composites were originally intended to replace beryllium (which is toxic and expensive) as a structural material for lightweight mirrors for aerospace applications. These materials also have potential utility in automotive and many other terrestrial applications in which there are requirements for lightweight materials that have high strengths and other tailorable properties as described below. The ceramic component of a material in this family consists of hollow ceramic spheres that have been formulated to be lightweight (0.5 g/cm3) and have high crush strength [40.80 ksi (.276.552 MPa)]. The hollow spheres are coated with a metal to enhance a specific performance . such as shielding against radiation (cosmic rays or x rays) or against electromagnetic interference at radio and lower frequencies, or a material to reduce the coefficient of thermal expansion (CTE) of the final composite material, and/or materials to mitigate any mismatch between the spheres and the matrix metal. Because of the high crush strength of the spheres, the initial composite workpiece can be forged or extruded into a high-strength part. The total time taken in processing from the raw ingredients to a finished part is typically 10 to 14 days depending on machining required.
The Sphere of Women in Colonial America.
ERIC Educational Resources Information Center
Cook, Robert
This project is a unit of six lessons designed to study and understand the roles and expectations of women in the colonial period. The unit provides an historical perspective on those expectations, examines how both men and women viewed the sphere of women, and how enlightened thought on this topic began to emerge during this revolutionary time.…
Spheres: from Ground Development to ISS Operations
NASA Technical Reports Server (NTRS)
Katterhagen, A.
2016-01-01
SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellites) is an internal International Space Station (ISS) Facility that supports multiple investigations for the development of multi-spacecraft and robotic control algorithms. The SPHERES National Lab Facility aboard ISS is managed and operated by NASA Ames Research Center (ARC) at Moffett Field California. The SPHERES Facility on ISS consists of three self-contained eight-inch diameter free-floating satellites which perform the various flight algorithms and serve as a platform to support the integration of experimental hardware. SPHERES has served to mature the adaptability of control algorithms of future formation flight missions in microgravity (6 DOF (Degrees of Freedom) / long duration microgravity), demonstrate key close-proximity formation flight and rendezvous and docking maneuvers, understand fault diagnosis and recovery, improve the field of human telerobotic operation and control, and lessons learned on ISS have significant impact on ground robotics, mapping, localization, and sensing in three-dimensions - among several other areas of study.
Experimentation on recurrent sphere collision with Audacity
NASA Astrophysics Data System (ADS)
Muradoglu, Murat; Ng, Enoch Ming Wei; Ng, Tuck Wah
2014-11-01
Under the theme of collisions that occur repeatedly, we conducted easy and inexpensive experiments of rebounding spheres and Newton’s cradle with two spheres to determine the coefficients of restitution using the sound record feature in modern laptops and a free and open source software called Audacity. In the rebounding sphere experiment, the coefficients of restitution of the golf and ping pong balls used were found to be 0.727 ± 0.025 and 0.816 ± 0.041 respectively. With the Netwon’s cradle experiment, the coefficient of restitution of two steel sphere balls was found to be 0.987 ± 0.003. The contrasts in the results obtained from both experiments permit the operational principles of a pendulum to be emphasized, and engagements to be made to consider the transfer of kinetic energy in the form of vibrational energy of the bodies’ constituents. Using a one-dimensional two-mass model with spring and damper linkages to account for harmonic motions that occur during impact, we found it possible to perform a simple analysis to account for this, and how it can be linked to high energy transfer modes such as the phenomenon of resonance and impedance matching.
Propulsion of a two-sphere swimmer
NASA Astrophysics Data System (ADS)
Klotsa, Daphne; Baldwin, Kyle; Hill, Richard; Bowley, Roger; Swift, Michael
We describe experiments and simulations demonstrating the propulsion of a neutrally-buoyant macroscopic swimming robot that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer.
Steel Spheres and Skydiver--Terminal Velocity
ERIC Educational Resources Information Center
Costa Leme, J.; Moura, C.; Costa, Cintia
2009-01-01
This paper describes the use of open source video analysis software in the study of the relationship between the velocity of falling objects and time. We discuss an experiment in which a steel sphere falls in a container filled with two immiscible liquids. The motion is similar to that of a skydiver falling through air.
Properties of a Two-Sphere Singularity
NASA Astrophysics Data System (ADS)
Konkowski, Deborah A.; Helliwell, Thomas M.
2015-01-01
Recently Böhmer and Lobo have shown that a metric due to Florides can be extended to reveal a classical singularity that has the form of a two-sphere. Here we discuss and expand on the classical singularity properties and then show the classical singularity is not healed by a quantum analysis.
Propulsion of a Two-Sphere Swimmer.
Klotsa, Daphne; Baldwin, Kyle A; Hill, Richard J A; Bowley, R M; Swift, Michael R
2015-12-11
We describe experiments and simulations demonstrating the propulsion of a neutrally buoyant swimmer that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer.
ERIC Educational Resources Information Center
Pelton, Joseph N.
2002-01-01
Discusses the survival of the human race in the Third Millennium. Considers environmental issues; shifting from a focus on economic growth to human development; the rate of technological change; the e-sphere, which goes beyond a global village to a global brain; technology in education and in health care; and educational reform. (LRW)
Some analytical models of radiating collapsing spheres
Herrera, L.; Di Prisco, A; Ospino, J.
2006-08-15
We present some analytical solutions to the Einstein equations, describing radiating collapsing spheres in the diffusion approximation. Solutions allow for modeling physical reasonable situations. The temperature is calculated for each solution, using a hyperbolic transport equation, which permits to exhibit the influence of relaxational effects on the dynamics of the system.
Domain-wall supergravities from sphere reduction
NASA Astrophysics Data System (ADS)
Cvetič , M.; Liu, James T.; Lü, H.; Pope, C. N.
1999-10-01
Kaluza-Klein sphere reductions of supergravities that admit Ads × Sphere vacuum solutions are believed to be consistent. The examples include the S4 and S7 reductions of eleven-dimensional supergravity, and the S5 reduction of ten-dimensional type IIB supergravity . In this paper we provide evidence that sphere reductions of supergravities that admit instead Domain-wallxSphere vacuum solutions are also consistent, where the background can be viewed as the near-horizon structure of a dilatonic p-brane of the theory. The resulting lower-dimensional theory is a gauged supergravity that admits a domain wall, rather than AdS, as a vacuum solution. We illustrate this consistency by taking the singular limits of certain modulus parameters, for which the original Sn compactifying spheres ( n = 4, 5 or 7) becomes Sp × Rq, with p = n - q < n. The consistency of the S4, S7 reductions then implies the consistency of the S p reductions of the lower-dimensional supergravities. In particular, we obtain explicit non-linear ansätze for the S3 reduction of type IIA and heterotic supergravities, restricting to the U(1) 2 subgroup of the SO(4) gauge group of S3. We also study the black-hole solutions in the lower-dimensional gauged supergravities with domain-wall backgrounds. We find new domain-wall black holes which are not the singular-modulus limits of the AdS black holes of the original theories, and we obtain their Killing spinors.
Falconer, J.W.; Nazarov, W. ); Horsfield, C.J.; Sutton, D.W.; Rothman, S.D.; Freeman, N.J. )
1994-09-01
Hollow cylindrical fusion targets of 200--300 [mu]m diam and 500--600 [mu]m length, were fabricated and fitted at one end with a metallic ablator plate. The cylinders were then filled with a solution of polyfunctional acrylate monomer, which was subsequently polymerized to a gel using ultraviolet initiated polymerization. Either one or two aluminum spheres of diameter between 10 and 30 [mu]m were placed in the gel at defined locations, before the gel was precipitated to give, on drying by critical point dryer, a foam of the required density (about 100 mg cm[sup [minus]3]). The final targets had the sphere or spheres embedded in the foam at specified locations. Several techniques for placing the spheres were examined and the relative merits of the techniques are discussed.
Colloidal and micro-carbon spheres derived from low-temperature polymerization reactions.
Moreno-Castilla, Carlos
2016-10-01
Carbon spheres (CSs) have recently attracted major interest due to their new applications, mainly in energy storage and conversion but also in hard-templating, sorption/catalysis processes, and drug delivery systems. This is attributable to their physico-chemical properties, including their tunable morphology (solid, hollow and core-shell), size, surface area/porosity, good electrical conductivity, low external surface-to-volume ratio, high packing density, enhanced mass transport, robust mechanical stability, low cytotoxicity, and excellent biocompatibility. They can be obtained from a wide variety of carbon precursors and methods. This review covers their production by carbonization of polymer spheres from low-temperature polymerization reactions, considered here as below 250°C. This is a very important method because it allows the synthesis of CSs with different morphologies and doped with other elements or chemical compounds. The preparation of polymer spheres by this technique is well documented in the literature, and the objective of this review is to summarize and give an overview of the most significant publications, proposing a novel classification based on the formation mechanism of the polymer spheres. This classification includes the following polymerization processes: emulsion polymerization and its derivatives, seeded emulsion and inverse emulsion polymerization; precipitation polymerization and its derivative, dispersion polymerization; hard-templating; spray-drying; and hydrothermal or solvothermal treatment of carbohydrates and biomass in general. This review also reports on the morphology and surface characteristics of the CSs obtained by different synthetic approaches. The final section of the review describes the current applications of these CSs, notably in energy storage (supercapacitors and rechargeable batteries) and energy conversion (fuel cells and dye-sensitized solar cells). Besides the numerous applications listed above, they are
Colloidal and micro-carbon spheres derived from low-temperature polymerization reactions.
Moreno-Castilla, Carlos
2016-10-01
Carbon spheres (CSs) have recently attracted major interest due to their new applications, mainly in energy storage and conversion but also in hard-templating, sorption/catalysis processes, and drug delivery systems. This is attributable to their physico-chemical properties, including their tunable morphology (solid, hollow and core-shell), size, surface area/porosity, good electrical conductivity, low external surface-to-volume ratio, high packing density, enhanced mass transport, robust mechanical stability, low cytotoxicity, and excellent biocompatibility. They can be obtained from a wide variety of carbon precursors and methods. This review covers their production by carbonization of polymer spheres from low-temperature polymerization reactions, considered here as below 250°C. This is a very important method because it allows the synthesis of CSs with different morphologies and doped with other elements or chemical compounds. The preparation of polymer spheres by this technique is well documented in the literature, and the objective of this review is to summarize and give an overview of the most significant publications, proposing a novel classification based on the formation mechanism of the polymer spheres. This classification includes the following polymerization processes: emulsion polymerization and its derivatives, seeded emulsion and inverse emulsion polymerization; precipitation polymerization and its derivative, dispersion polymerization; hard-templating; spray-drying; and hydrothermal or solvothermal treatment of carbohydrates and biomass in general. This review also reports on the morphology and surface characteristics of the CSs obtained by different synthetic approaches. The final section of the review describes the current applications of these CSs, notably in energy storage (supercapacitors and rechargeable batteries) and energy conversion (fuel cells and dye-sensitized solar cells). Besides the numerous applications listed above, they are
Simulation of rotary-drum and repose tests for frictional spheres and rigid sphere clusters
Walton, O.R.; Braun, R.L.
1993-11-01
The effects of rotation rate and interparticle friction on the bulk flow behavior in rotating horizontal cylinders are studied via particle-dynamic simulations. Assemblies of inelastic, frictional spheres and rigid sphere clusters are utilized, and rotation rates from quasistatic to centrifuging are examined. Flow phenomena explored include size segregation, avalanching, slumping and centrifuging. Simulated drum flows with two sizes of frictional spheres showed very rapid segregation of species perpendicular to the drum axis; however, simulations of up to 10 revolutions, utilizing periodic-boundary ends, did not exhibit the experimentally observed axial segregation into stripes. Angles of repose for uniform-sized spheres in slowly rotating cylinders varied from 13 to 31 degrees as the friction coefficient varied from 0.02 to 1.0. For simulated rotation rates higher than the threshold to obtain uniform flow conditions, the apparent angle of repose increases as the rotation rats increases, consistent with experiments. Also, simulations with rigid clusters of 4 spheres in a tetrahedral shape or 8 spheres in a cubical arrangement, demonstrate that particle shape strongly influences the repose angle. Simulations of cubical 8-sphere clusters, with a surface coefficient of friction of 0.1, produced apparent angles of repose exceeding 35 degrees, compared to 23 degrees for assemblies of single spheres interacting with the same force model parameters. Centrifuging flows at very high rotation rates exist as stationary beds moving exactly as the outer rotating wall. At somewhat slower speeds the granular bed remains in contact with the wall but exhibits surface sliding down the rising inner bed surface, moving a short distance on each revolution. At still slower speeds particles rain from the surface of the upper half of the rotating bed.
Transient Temperature Behavior of a Sphere Heated by Microwaves
NASA Technical Reports Server (NTRS)
Jackson, H. W.; Barmatz, M.; Wagner, P.
1993-01-01
We have developed a model for microwave heating of a sphere in a rectangular resonant cavity. The model calculates transient temperature distributions within a sphere during the approach to steady state conditions or on the path to thermal runaway.
Hard-on-Hard Lubrication in the Artificial Hip under Dynamic Loading Conditions
Sonntag, Robert; Reinders, Jörn; Rieger, Johannes S.; Heitzmann, Daniel W. W.; Kretzer, J. Philippe
2013-01-01
The tribological performance of an artificial hip joint has a particularly strong influence on its success. The principle causes for failure are adverse short- and long-term reactions to wear debris and high frictional torque in the case of poor lubrication that may cause loosening of the implant. Therefore, using experimental and theoretical approaches models have been developed to evaluate lubrication under standardized conditions. A steady-state numerical model has been extended with dynamic experimental data for hard-on-hard bearings used in total hip replacements to verify the tribological relevance of the ISO 14242-1 gait cycle in comparison to experimental data from the Orthoload database and instrumented gait analysis for three additional loading conditions: normal walking, climbing stairs and descending stairs. Ceramic-on-ceramic bearing partners show superior lubrication potential compared to hard-on-hard bearings that work with at least one articulating metal component. Lubrication regimes during the investigated activities are shown to strongly depend on the kinematics and loading conditions. The outcome from the ISO gait is not fully confirmed by the normal walking data and more challenging conditions show evidence of inferior lubrication. These findings may help to explain the differences between the in vitro predictions using the ISO gait cycle and the clinical outcome of some hard-on-hard bearings, e.g., using metal-on-metal. PMID:23940772
Hard-on-hard lubrication in the artificial hip under dynamic loading conditions.
Sonntag, Robert; Reinders, Jörn; Rieger, Johannes S; Heitzmann, Daniel W W; Kretzer, J Philippe
2013-01-01
The tribological performance of an artificial hip joint has a particularly strong influence on its success. The principle causes for failure are adverse short- and long-term reactions to wear debris and high frictional torque in the case of poor lubrication that may cause loosening of the implant. Therefore, using experimental and theoretical approaches models have been developed to evaluate lubrication under standardized conditions. A steady-state numerical model has been extended with dynamic experimental data for hard-on-hard bearings used in total hip replacements to verify the tribological relevance of the ISO 14242-1 gait cycle in comparison to experimental data from the Orthoload database and instrumented gait analysis for three additional loading conditions: normal walking, climbing stairs and descending stairs. Ceramic-on-ceramic bearing partners show superior lubrication potential compared to hard-on-hard bearings that work with at least one articulating metal component. Lubrication regimes during the investigated activities are shown to strongly depend on the kinematics and loading conditions. The outcome from the ISO gait is not fully confirmed by the normal walking data and more challenging conditions show evidence of inferior lubrication. These findings may help to explain the differences between the in vitro predictions using the ISO gait cycle and the clinical outcome of some hard-on-hard bearings, e.g., using metal-on-metal.
Hard-on-hard lubrication in the artificial hip under dynamic loading conditions.
Sonntag, Robert; Reinders, Jörn; Rieger, Johannes S; Heitzmann, Daniel W W; Kretzer, J Philippe
2013-01-01
The tribological performance of an artificial hip joint has a particularly strong influence on its success. The principle causes for failure are adverse short- and long-term reactions to wear debris and high frictional torque in the case of poor lubrication that may cause loosening of the implant. Therefore, using experimental and theoretical approaches models have been developed to evaluate lubrication under standardized conditions. A steady-state numerical model has been extended with dynamic experimental data for hard-on-hard bearings used in total hip replacements to verify the tribological relevance of the ISO 14242-1 gait cycle in comparison to experimental data from the Orthoload database and instrumented gait analysis for three additional loading conditions: normal walking, climbing stairs and descending stairs. Ceramic-on-ceramic bearing partners show superior lubrication potential compared to hard-on-hard bearings that work with at least one articulating metal component. Lubrication regimes during the investigated activities are shown to strongly depend on the kinematics and loading conditions. The outcome from the ISO gait is not fully confirmed by the normal walking data and more challenging conditions show evidence of inferior lubrication. These findings may help to explain the differences between the in vitro predictions using the ISO gait cycle and the clinical outcome of some hard-on-hard bearings, e.g., using metal-on-metal. PMID:23940772
Spencer, Michael
1974-01-01
Food additives are discussed from the food technology point of view. The reasons for their use are summarized: (1) to protect food from chemical and microbiological attack; (2) to even out seasonal supplies; (3) to improve their eating quality; (4) to improve their nutritional value. The various types of food additives are considered, e.g. colours, flavours, emulsifiers, bread and flour additives, preservatives, and nutritional additives. The paper concludes with consideration of those circumstances in which the use of additives is (a) justified and (b) unjustified. PMID:4467857
Bending and Gaussian rigidities of confined soft spheres from second-order virial series.
Urrutia, Ignacio
2016-08-01
We use virial series to study the equilibrium properties of confined soft-spheres fluids interacting through the inverse-power potentials. The confinement is induced by hard walls with planar, spherical, and cylindrical shapes. We evaluate analytically the coefficients of order two in density of the wall-fluid surface tension γ and analyze the curvature contributions to the free energy. Emphasis is in bending and Gaussian rigidities, which are found analytically at order two in density. Their contribution to γ(R) and the accuracy of different truncation procedures to the low curvature expansion are discussed. Finally, several universal relations that apply to low-density fluids are analyzed. PMID:27627288
Bending and Gaussian rigidities of confined soft spheres from second-order virial series
NASA Astrophysics Data System (ADS)
Urrutia, Ignacio
2016-08-01
We use virial series to study the equilibrium properties of confined soft-spheres fluids interacting through the inverse-power potentials. The confinement is induced by hard walls with planar, spherical, and cylindrical shapes. We evaluate analytically the coefficients of order two in density of the wall-fluid surface tension γ and analyze the curvature contributions to the free energy. Emphasis is in bending and Gaussian rigidities, which are found analytically at order two in density. Their contribution to γ (R ) and the accuracy of different truncation procedures to the low curvature expansion are discussed. Finally, several universal relations that apply to low-density fluids are analyzed.
NASA Astrophysics Data System (ADS)
Han, Lu; Gao, Chuanbo; Wu, Xiaowei; Chen, Qianru; Shu, Peng; Ding, Zhiguang; Che, Shunai
2011-04-01
Silica hollow spheres with different shell porosity were simply synthesized with micelle and emulsion dual templating route. Various anionic surfactants, such as palmitic acid (C 16AA), N-acyl- L-phenylalanine (C 18Phe), N-palmitoyl- L-alanine (C 16AlaA) and oleic acid (OA) have been used as templates, and 3-aminopropyl-triethoxysilane (APES) and tetraethyl orthosilicate (TEOS) have been used as co-structure directing agent (CSDA) and silica source, respectively. The circle lamellar layer structure and mesopores vertical to the silica hollow spheres surface are believed to originate from the initial formation of amphiphilic carboxylic acid oil drop, which afterwards self-assemble to form the shell of hollow spheres and its mesostructure upon addition of CSDA and silica source. The mesoporous silica hollow spheres with high porosity could be achieved by adding a moderate amount of ethanol in the OA synthesis system, depending on the co-surfactant effect of ethanol that changes the curvature of micelles. The particle diameter and the hollow structure have been controlled by choosing different templates and by manipulating synthesis gel composition. The average particle diameter of the mesoporous silica hollow spheres were controlled in the range of 80-220 nm with constant shell thickness of ˜20 nm and constant mesopore size of ˜4 nm. Besides, the formation of the silica hollow spheres has been investigated in detail with reaction time. These mesoporous silica hollow spheres would have potential applications on catalysis, bimolecular encapsulation, adsorption, drug release, etc.
Surface layer determination for the Si spheres of the Avogadro project
NASA Astrophysics Data System (ADS)
Busch, I.; Azuma, Y.; Bettin, H.; Cibik, L.; Fuchs, P.; Fujii, K.; Krumrey, M.; Kuetgens, U.; Kuramoto, N.; Mizushima, S.
2011-04-01
For the accurate determination of the Avogadro constant, two 28Si spheres were produced, whose macroscopic density, in addition to other values, must be determined. To make a contribution to the new definition of the kilogram, a relative standard uncertainty of less than 2 × 10-8 has to be achieved. Each silicon surface is covered by a surface layer (SL). Consequently, correction parameters for the SL are determined to be applied to the mass and volume determination of the enriched spheres. With the use of a large set of surface analysing techniques, the structure of the SL is investigated. An unexpected metallic contamination existing on the sphere surface enlarges the uncertainty contribution of the correction parameters above the originally targeted value of 1 × 10-8. In the framework of this investigation this new obstacle is resolved in two ways. A new combination of analytical methods is applied to measure the SL mass mSL and the thickness dSL, including this new contamination, with an uncertainty of u(mSL) = 14.5 µg and 14.4 µg, respectively, and u(dSL) = 0.33 nm and 0.32 nm for the 28Si spheres AVO28-S5 and AVO28-S8, respectively. In the second part of the work, the chemical composition of these metallic contaminations is found to be Cu, Ni and Zn silicide compounds. For the removal of this contamination, a special procedure is developed, tested and applied to the spheres to produce the originally expected surface structure on the spheres. After the application of this new procedure the use of x-ray reflectometry directly at the spheres will be possible. It is expected to reduce the uncertainty contribution due to the SL down to 1 × 10-8.
Black carbon measurements using an integrating sphere
NASA Astrophysics Data System (ADS)
Hitzenberger, R.; Dusek, U.; Berner, A.
1996-08-01
An integrating sphere was used to determine the black carbon (BC) content of aerosol filter samples dissolved in chloroform (method originally described by Heintzenberg [1982]). The specific absorption coefficient Ba (equal to absorption per mass) of the samples was also measured using the sphere as an integrating detector for transmitted light. Comparing the Ba of ambient samples taken in Vienna, Austria, to the BC concentrations measured on the dissolved filters, a value of approximately 6 m2/g was found to be a reasonable value for the Ba of the black carbon found at the site. The size dependence of Ba of a nebulized suspension of soot was measured using a rotating impactor, and a reasonable agreement between measured and calculated values was found.
Chirality and Dirac Operator on Noncommutative Sphere
NASA Astrophysics Data System (ADS)
Carow-Watamura, Ursula; Watamura, Satoshi
1997-01-01
We give a derivation of the Dirac operator on the noncommutative 2-sphere within the framework of the bosonic fuzzy sphere and define Connes' triple. It turns out that there are two different types of spectra of the Dirac operator and correspondingly there are two classes of quantized algebras. As a result we obtain a new restriction on the Planck constant in Berezin's quantization. The map to the local frame in noncommutative geometry is also discussed. Acknowledgement. The authors benefited from discussions with M. Bordemann, O. Grandjean and M. Pillin. S.W. would like to thank K. Osterwalder for his hospitality during the stay in ETH where this work began. He also thanks the Canon Foundation in Europe for supporting that stay. U.C. would like to acknowledge the Japan Society for Promotion of Science for financial support.-->
Criticality of a {sup 237}Np Sphere
Sanchez, Rene G.; Hayes, David K.; Cappiello, Charlene C.; Myers, William L.; Jaegers, Peter J.; Clement, Steven D.; Butterfield, Kenneth B.
2003-07-22
A critical mass experiment using a 6-kg {sup 237}Np sphere has been performed. The purpose of the experiment is to get a better estimate of the critical mass of {sup 237}Np. To attain criticality, the {sup 237}Np sphere was surrounded with 93 wt % {sup 235}U shells. A 1/M as a function of uranium mass was performed. An MCNP neutron transport code was used to model the experiment. The MCNP code yielded a k{sub eff} of 0.99089 {+-} 0.0003 compared with a k{sub eff} 1.0026 for the experiment. Based on these results, it is estimated that the critical mass of {sup 237}Np ranges from kilogram weights in the high fifties to low sixties.
Overview: Hard Rock Penetration
Dunn, J.C.
1992-01-01
The Hard Rock Penetration program is developing technology to reduce the costs of drilling and completing geothermal wells. Current projects include: lost circulation control, rock penetration mechanics, instrumentation, and industry/DOE cost shared projects of the Geothermal Drilling organization. Last year, a number of accomplishments were achieved in each of these areas. A new flow meter being developed to accurately measure drilling fluid outflow was tested extensively during Long Valley drilling. Results show that this meter is rugged, reliable, and can provide useful measurements of small differences in fluid inflow and outflow rates. By providing early indications of fluid gain or loss, improved control of blow-out and lost circulation problems during geothermal drilling can be expected. In the area of downhole tools for lost circulation control, the concept of a downhole injector for injecting a two-component, fast-setting cementitious mud was developed. DOE filed a patent application for this concept during FY 91. The design criteria for a high-temperature potassium, uranium, thorium logging tool featuring a downhole data storage computer were established, and a request for proposals was submitted to tool development companies. The fundamental theory of acoustic telemetry in drill strings was significantly advanced through field experimentation and analysis. A new understanding of energy loss mechanisms was developed.
Overview: Hard Rock Penetration
Dunn, J.C.
1992-08-01
The Hard Rock Penetration program is developing technology to reduce the costs of drilling and completing geothermal wells. Current projects include: lost circulation control, rock penetration mechanics, instrumentation, and industry/DOE cost shared projects of the Geothermal Drilling organization. Last year, a number of accomplishments were achieved in each of these areas. A new flow meter being developed to accurately measure drilling fluid outflow was tested extensively during Long Valley drilling. Results show that this meter is rugged, reliable, and can provide useful measurements of small differences in fluid inflow and outflow rates. By providing early indications of fluid gain or loss, improved control of blow-out and lost circulation problems during geothermal drilling can be expected. In the area of downhole tools for lost circulation control, the concept of a downhole injector for injecting a two-component, fast-setting cementitious mud was developed. DOE filed a patent application for this concept during FY 91. The design criteria for a high-temperature potassium, uranium, thorium logging tool featuring a downhole data storage computer were established, and a request for proposals was submitted to tool development companies. The fundamental theory of acoustic telemetry in drill strings was significantly advanced through field experimentation and analysis. A new understanding of energy loss mechanisms was developed.
Overview - Hard Rock Penetration
Dunn, James C.
1992-03-24
The Hard Rock Penetration program is developing technology to reduce the costs of drilling and completing geothermal wells. Current projects include: lost circulation control, rock penetration mechanics, instrumentation, and industry/DOE cost shared projects of the Geothermal Drilling Organization. Last year, a number of accomplishments were achieved in each of these areas. A new flow meter being developed to accurately measure drilling fluid outflow was tested extensively during Long Valley drilling. Results show that this meter is rugged, reliable, and can provide useful measurements of small differences in fluid inflow and outflow rates. By providing early indications of fluid gain or loss, improved control of blow-out and lost circulation problems during geothermal drilling can be expected. In the area of downhole tools for lost circulation control, the concept of a downhole injector for injecting a two-component, fast-setting cementitious mud was developed. DOE filed a patent application for this concept during FY 91. The design criteria for a high-temperature potassium, uranium, thorium logging tool featuring a downhole data storage computer were established, and a request for proposals was submitted to tool development companies. The fundamental theory of acoustic telemetry in drill strings was significantly advanced through field experimentation and analysis. A new understanding of energy loss mechanisms was developed.
Improved method for producing small hollow spheres
Rosencwaig, A.; Koo, J.C.; Dressler, J.L.
An improved method and apparatus for producing small hollow spheres of glass having an outer diameter ranging from about 100..mu.. to about 500..mu.. with a substantially uniform wall thickness in the range of about 0.5 to 20..mu.. are described. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions.
Diffusion processes in general relativistic radiating spheres
Barreto, W.; Herrera, L.; Santos, N.O.; Universidad Central de Venezuela, Caracas; Observatorio Nacional do Brasil, Rio de Janeiro )
1989-09-01
The influence of diffusion processes on the dynamics of general relativistic radiating spheres is systematically studied by means of two examples. Differences between the streaming-out limit and the diffusion limit are exhibited, for both models, through the evolution curves of dynamical variables. In particular it is shown the Bondi mass decreases, for both models, in the diffusion limit as compared with its value at the streaming-out regime. 15 refs.
Rainbow Scattering by a Coated Sphere
NASA Technical Reports Server (NTRS)
Lock, James A.; Jamison, J. Michael; Lin, Chih-Yang
1994-01-01
We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core alpha(sub 12) and the thickness of the coating beta are varied. As the ratio beta/alpha(sub 12) increases from 10(sup -4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For beta/alpha(sub 12) approx less than 10(sup -3), the rainbow intensity is an oscillatory function of the coating thickness, for beta/alpha(sub 12) approx. 10(sup -2), the first-order rainbow breaks into a pair of twin rainbows, and for beta/alpha(sub 12) approx. 0.33, various rainbow-extinction transitions occur. Each of these effects is analyzed, and their physical interpretations are given. A Debye series decomposition of coated-sphere partial-wave scattering amplitudes is also performed and aids in the analysis.
Broadband Electromagnetic Transparency by Graded Metamaterial Sphere
NASA Astrophysics Data System (ADS)
Sun, L.; Yu, K. W.
2010-03-01
We have investigated the scattering of electromagnetic waves from a radially inhomogeneous metamaterial sphere whose dielectric permittivity is described by the graded Drude model ɛs(r)=1-φp^2(r)/2̂. The radial position dependent plasma frequency depends on r as φp^2=1/2-c(r/r0)^n, where c and n are positive constants and r0 is the radius of the sphere. The electromagnetic field distribution has been calculated within the full-wave Mie scattering theory. When n=2, exact analytic solutions can be obtained in terms of confluent Heun function and confluent hypergeometric function of Kummer. This allows us to obtain the full-wave total scattering cross section analytically from the scattering field amplitudes. While the total scattering cross section Qs depends on both the graded plasma frequency profile and the frequency of the incident electromagnetic wave, it is found that Qs can achieve extremely small values over a broad frequency band and graded parameters. The analytic solutions allow us to assess the conditions for achieving broadband electromagnetic transparency in the metamaterial sphere and make tunable electromagnetic transparency feasible.
Rainbow scattering by a coated sphere.
Lock, J A; Jamison, J M; Lin, C Y
1994-07-20
We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core a(12) and the thickness of the coating δ are varied. As the ratio δ/a(12) increases from 10(-4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For δ/a(12) ≲ 10(-3), the rainbow intensity is an oscillatory function of the coating thickness, for δ/a(12) ≈ 10(-2), the first-order rainbow breaks into a pair of twin rainbows, and for δ/a(12) ≈ 0.33, various rainbow-extinction transitions occur. Each of these effects is analyzed, and their physical interpretations are given. A Debye series decomposition of coated-sphere partial-wave scattering amplitudes is also performed and aids in the analysis. PMID:20935838
Absolute determination of photoluminescence quantum efficiency using an integrating sphere setup
Leyre, S.; Coutino-Gonzalez, E.; Hofkens, J.; Joos, J. J.; Poelman, D.; Smet, P. F.; Ryckaert, J.; Meuret, Y.; Durinck, G.; Hanselaer, P.
2014-12-15
An integrating sphere-based setup to obtain a quick and reliable determination of the internal quantum efficiency of strongly scattering luminescent materials is presented. In literature, two distinct but similar measurement procedures are frequently mentioned: a “two measurement” and a “three measurement” approach. Both methods are evaluated by applying the rigorous integrating sphere theory. It was found that both measurement procedures are valid. Additionally, the two methods are compared with respect to the uncertainty budget of the obtained values of the quantum efficiency. An inter-laboratory validation using the two distinct procedures was performed. The conclusions from the theoretical study were confirmed by the experimental data.
Measuring the Hardness of Minerals
ERIC Educational Resources Information Center
Bushby, Jessica
2005-01-01
The author discusses Moh's hardness scale, a comparative scale for minerals, whereby the softest mineral (talc) is placed at 1 and the hardest mineral (diamond) is placed at 10, with all other minerals ordered in between, according to their hardness. Development history of the scale is outlined, as well as a description of how the scale is used…
Time Acceleration Methods for Advection on the Cubed Sphere
Archibald, Richard K; Evans, Katherine J; White III, James B; Drake, John B
2009-01-01
Climate simulation will not grow to the ultrascale without new algorithms to overcome the scalability barriers blocking existing implementations. Until recently, climate simulations concentrated on the question of whether the climate is changing. The emphasis is now shifting to impact assessments, mitigation and adaptation strategies, and regional details. Such studies will require significant increases in spatial resolution and model complexity while maintaining adequate throughput. The barrier to progress is the resulting decrease in time step without increasing single-thread performance. In this paper we demonstrate how to overcome this time barrier for the first standard test defined for the shallow-water equations on a sphere. This paper explains how combining a multiwavelet discontinuous Galerkin method with exact linear part time-evolution schemes can overcome the time barrier for advection equations on a sphere. The discontinuous Galerkin method is a high-order method that is conservative, flexible, and scalable. The addition of multiwavelets to discontinuous Galerkin provides a hierarchical scale structure that can be exploited to improve computational efficiency in both the spatial and temporal dimensions. Exact linear part time-evolution schemes are explicit schemes that remain stable for implicit-size time steps.
Simultaneous inner- and outer-sphere arsenate adsorption on corundum and hematite
NASA Astrophysics Data System (ADS)
Catalano, Jeffrey G.; Park, Changyong; Fenter, Paul; Zhang, Zhan
2008-04-01
The ability to predict the fate and transport of arsenic in aquatic environments, its impact on water quality and human health, and the performance and cost-effectiveness of water treatment systems relies on understanding how it interacts with solid surfaces. In situ resonant surface X-ray scattering measurements of arsenate adsorption at pH 5 in 0.01 M NaCl on corundum and hematite (012) surfaces demonstrate that arsenate surface complexation is unexpectedly bimodal, adsorbing simultaneously as inner- and outer-sphere species. In addition, this bimodal behavior is found to be independent of the total arsenate solution concentration, and thus surface coverage, over the range of 10 -6 to 10 -3 M. Alternative mechanisms to produce the observed As distributions, such as arsenate dimerization or surface precipitation of an aluminum or ferric arsenate, are inconsistent with the experimentally-determined total and As-specific density profiles. Based on the location of the outer-sphere arsenate in relation to the surfaces studied, possible binding mechanisms include electrostatic attraction, hydrogen bonding to surface oxygen functional group, and configurational stabilization by interfacial water. Although the observation of outer-sphere arsenate surface complexes on a metal oxide surface is unprecedented, it is unclear if such species were absent in previous molecular-scale studies, as it is difficult for methods commonly used to investigate the mechanisms of arsenate adsorption to conclusively identify or rule out the presence of outer-sphere species when inner-sphere species are also present.
Huang, Jian-Fei; Li, Yong-Tao; Wu, Jin-Hua; Cao, Piao-Yang; Liu, Yong-Lin; Jiang, Gang-Biao
2016-08-01
Treatment of hexavalent chromium (Cr(VI)) spill accident is a great challenge due to its high toxicity, sudden and extensiveness. In this study, we designed and fabricated a hierarchical, ordered and macroporous structured alginate sphere to support in-situ synthesized zero-valent iron nanoparticle (the alginate-nZVI sphere). Field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS) images showed well dispersion of nZVI on the composite. This alginate-nZVI sphere exhibited good separability in effective removal of Cr(VI). The result from Cr(VI) removal experiment demonstrated a Cr(VI) removal efficiency of 98.2% at equilibrium time, which can be ascribed to the well dispersion of the nZVI. In addition, the alginate-nZVI sphere was effective in Cr(VI) removal in a wide range of pH from 3.0 to 11.0, by the merit of alginate substrate. Hence, the alginate-nZVI sphere might be a promising agent for an emergent Cr(VI) spill treatment by enhancing the dispersion, stabilization and separation properties of nZVI. PMID:27112857
A Multiple Sphere T-Matrix Fortran Code for Use on Parallel Computer Clusters
NASA Technical Reports Server (NTRS)
Mackowski, D. W.; Mishchenko, M. I.
2011-01-01
A general-purpose Fortran-90 code for calculation of the electromagnetic scattering and absorption properties of multiple sphere clusters is described. The code can calculate the efficiency factors and scattering matrix elements of the cluster for either fixed or random orientation with respect to the incident beam and for plane wave or localized- approximation Gaussian incident fields. In addition, the code can calculate maps of the electric field both interior and exterior to the spheres.The code is written with message passing interface instructions to enable the use on distributed memory compute clusters, and for such platforms the code can make feasible the calculation of absorption, scattering, and general EM characteristics of systems containing several thousand spheres.
Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent
2015-01-01
This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration. PMID:26366489
Fabrication and calibration of sensitively photoelastic biocompatible gelatin spheres
NASA Astrophysics Data System (ADS)
Fu, Henry; Ceniceros, Ericson; McCormick, Zephyr
2013-11-01
Photoelastic gelatin can be used to measure forces generated by organisms in complex environments. We describe manufacturing, storage, and calibration techniques for sensitive photoelastic gelatin spheres to be used in aqueous environments. Calibration yields a correlation between photoelastic signal and applied force to be used in future studies. Images for calibration were collected with a digital camera attached to a linear polariscope. The images were then processed in Matlab to determine the photoelastic response of each sphere. The effect of composition, gelatin concentration, glycerol concentration, sphere size, and temperature were all examined for their effect on signal response. The minimum detectable force and the repeatability of our calibration technique were evaluated for the same sphere, different spheres from the same fabrication batch, and spheres from different batches. The minimum force detectable is 10 μN or less depending on sphere size. Factors which significantly contribute to errors in the calibration were explored in detail and minimized.
Hard quasispherical particle models for the viscosity of solutions of protein mixtures.
Minton, Allen P
2012-08-01
Recently reported measurements of the viscosity of three monoclonal antibodies, their binary mixtures, and a binary mixture of an antibody and albumin over a broad range of compositions (Galush et al., J. Pharm. Sci. 2011,101, 1012) were quantitatively accounted for to within experimental uncertainty by an extension of the hard quasispherical particle model suggested by Ross and Minton (Biochem. Biophys. Res. Commun. 1977, 76, 971) and by a generalization of the hard sphere equation of Krieger and Dougherty (Trans. Soc. Rheol. 1959, 3, 137) . Further generalization of these equations to treat the concentration-dependent viscosity of self-associating proteins is suggested.
Assuring the quality of results of test hardness IRHD: IPT's case study
NASA Astrophysics Data System (ADS)
Yojo, T.; Miranda, M. J. A. C.; Oliveira, C. B.; Matteucci, C.
2015-10-01
This paper presents the experience of the Laboratory Trees, Woods and Furniture - LAMM in calibrating the durometer IRHD and assuring the quality of its test results, since there are no Certified Reference Material and laboratory in the Brazilian Calibration Network that can calibrate the equipment. To solve this problem, the IRHD hardness (N method) was quantified in three ways: a) by measuring the modulus of elasticity of the material, b) by measuring the depth the sphere entered the material and c) the durometer's direct reading. With the IRHD hardness measured by accepted international standards techniques, it was possible to evaluate the accuracy of the test results that assured the calibration of the equipment.
Impact velocity vs target hardness relationships for equivalent response of cask structures
Chen, T.F.; Chen, J.C.; Witte, M.C.; Fischer, L.E.
1993-06-01
In this paper, impact velocity vs. target hardness relationships for cask structures are reviewed. The relationships are based on equivalent cask responses in terms of equal deceleration or similar cask damages. By examining several past cask or container tests as well as some analytical results, some conclusions can be drawn about the relationship between target hardness and equivalent impact velocities. This relationship clearly shows that the cask response to impact is cask-dependent and that the rigid sphere impact model results in an unconservative estimate of equivalent velocity.
ORSPHERE: PHYSICS MEASUREMENTS FOR BARE, HEU(93.2)-METAL SPHERE
Margaret A. Marshall
2014-03-01
In the early 1970s 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 1950s (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 inches), masses (±0.01 g), and material data. The experiment was also set up to minimize the amount of structural material in the sphere proximity. Two, correlated spheres were evaluated and judged to be acceptable as criticality benchmark experiments. This evaluation is given in HEU-MET-FAST-100. The second, smaller sphere was used for additional reactor physics measurements. Worth measurements (Reference 1, 2, 3 and 4), the delayed neutron fraction (Reference 3, 4 and 5) and surface material worth coefficient (Reference 1 and 2) are all measured and judged to be acceptable as benchmark data. The prompt neutron decay (Reference 6), relative fission density (Reference 7) and relative neutron importance (Reference 7) were measured, but are not evaluated. Information for the evaluation was compiled from References 1 through 7, the experimental logbooks 8 and 9 ; additional drawings and notes provided by the experimenter; and communication with the lead experimenter, John T. Mihalczo.
Orsphere: Physics Measurments For Bare, HEU(93.2)-Metal Sphere
Marshall, Margaret A.; Bess, John D.; Briggs, J. Blair; White, Christine E.; Dyrda, James P.; Tancock, Nigel P.; Mihalczo, John
2015-03-01
In the early 1970s 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 1950s (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 inches), masses (±0.01 g), and material data. The experiment was also set up to minimize the amount of structural material in the sphere proximity. Two, correlated spheres were evaluated and judged to be acceptable as criticality benchmark experiments. This evaluation is given in HEU-MET-FAST-100. The second, smaller sphere was used for additional reactor physics measurements. Worth measurements (Reference 1, 2, 3 and 4), the delayed neutron fraction (Reference 3, 4 and 5) and surface material worth coefficient (Reference 1 and 2) are all measured and judged to be acceptable as benchmark data. The prompt neutron decay (Reference 6), relative fission density (Reference 7) and relative neutron importance (Reference 7) were measured, but are not evaluated. Information for the evaluation was compiled from References 1 through 7, the experimental logbooks 8 and 9 ; additional drawings and notes provided by the experimenter; and communication with the lead experimenter, John T. Mihalczo.
Phase diagram of the hard-core Yukawa fluid within the integral equation method.
El Mendoub, E B; Wax, J-F; Jakse, N
2006-11-01
In this study, the integral equation method proposed recently by Sarkisov [J. Chem. Phys. 114, 9496 (2001).], which has proved accurate for continuous potentials, is extended successfully to the hard sphere potential plus an attractive Yukawa tail. By comparing the results of thermodynamic properties, including the liquid-vapor phase diagram, with available simulation data, it is found that this method remains reliable for this class of models of interaction often used in colloid science.
Young Star May Be Belching Spheres of Gas, Astronomers Say
NASA Astrophysics Data System (ADS)
2001-05-01
observational project," said Luis F. Rodriguez, of Mexico's National Autonomous University. The arc of water masers can be fit to a nearly-perfect circle to within one part in a thousand. That, the researchers say, means that the water vapor in the arc most likely is part of a complete sphere. "The arc we see fits a circle so well that it is unlikely that any geometry other than that of a sphere would produce it," Ho said. The sphere would be about 1.5 times the size of the Solar System. Because the arc, and presumably the sphere of which it is part, is so thin and so uniform, the researchers say that it came from a single, short-lived ejection. In addition, other evidence suggests that the sphere from an earlier ejection now is being overtaken by a newer spherical bubble that took only about 33 years after being ejected to reach its observed size. "We now have at least one case, we believe, in which a young star has repeatedly ejected mass spherically in short bursts," Guillem Anglada, of the Institute of Astrophysics of Andalucia (CSIC), in Granada, Spain, said. "In light of our current understanding of star formation, we don't yet understand how this can happen, so we have an exciting new scientific challenge. It is surprising that nature can maintain such perfect symmetry, especially since the environment around the young star must be so varied. This appears to be a triumph of order over chaos," he added. The researchers, in addition to Rodriguez, Ho and Anglada, are: Jose M. Torrelles, Institute for Space Studies of Catalonia (IEEC)-Spanish Research Council (CSIC), Spain; Nimesh A. Patel and Lincoln Greenhill, of the Harvard-Smithsonian Center for Astrophysics; Jose F. Gomez, Laboratory for Space Astrophysics and Theoretical Physics of the National Institute for Aerospace Technology, Madrid, Spain; Salvador Curiel and Jorge Canto, of Mexico's National Autonomous University; and Guido Garay, Department of Astronomy of the University of Chile. The VLBA is part of the Natio