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1

Equation of state of wet granular matter  

NASA Astrophysics Data System (ADS)

An expression for the near-contact pair correlation function of D -dimensional weakly polydisperse hard spheres is presented, which arises from elementary free-volume arguments. Its derivative at contact agrees very well with our simulations for D=2 . For jammed states, the expression predicts that the number of exact contacts is equal to 2D, in agreement with established simulations. When the particles are wetted, they interact by the formation and rupture of liquid capillary bridges. Since formation and rupture events of capillary bonds are well separated in configuration space, the interaction is hysteretic with a characteristic energy loss Ecb . The pair correlation is strongly affected by this capillary interaction depending on the liquid-bond status of neighboring particles. A theory is derived for the nonequilibrium probability currents of the capillary interaction which determines the pair correlation function near contact. This finally yields an analytic expression for the equation of state, P=P(N/V,T) , of wet granular matter for D=2 , valid in the complete density range from gas to jamming. Driven wet granular matter exhibits a van der Waals-like unstable branch at granular temperatures Tgranular droplets reported for the free cooling of one-dimensional wet granular matter [A. Fingerle and S. Herminghaus, Phys. Rev. Lett. 97, 078001 (2006)], and extends the effect to higher dimensional systems. Since the limiting case of sticky bonds, Ecb?T , is of relevance for aggregation in general, simulations have been performed which show very good agreement with the theoretically predicted coordination K of capillary bonds as a function of the bond length scrit . This result implies that particles that stick at the surface, scrit=0 , form isostatic clusters. An extension of the theory in which the bridge coordination number K plays the role of a self-consistent mean-field is proposed.

Fingerle, A.; Herminghaus, S.

2008-01-01

2

Spiral patterns in wet granular matter under vertical vibrations  

NASA Astrophysics Data System (ADS)

From the evolution of galaxy to hurricane, from the inner structure of sea shell to the cochlea of our inner ears, spirals are widely existing in nature. In the past decades, spiral patterns have been discovered and extensively studied in model systems such as Rayleigh-B'ernard convection, Belousov-Zhabotinksy reactions and various biological systems. Here we report spiral patterns observed in a thin layer of wet granular matter driven by vertical vibrations. In the phase diagram of driven wet granular matter, spirals appear close to a fluid-gas coexistence phase and show hysteresis. The trajectory and rotation velocity of the three-armed spirals are studied as a function of the driving parameters and compared with other model systems.

Huang, Kai; Gollwitzer, Frank; Rehberg, Ingo

2010-03-01

3

Dynamics of rotating spirals in agitated wet granular matter  

NASA Astrophysics Data System (ADS)

Pattern formation of a thin layer of vertically agitated wet granular matter is investigated experimentally. Due to the strong cohesion arising from the capillary bridges formed between adjacent particles, agitated wet granular matter exhibits a different scenario compared with cohesionless dry particles. Rotating spirals with three arms, which correspond to the kinks between regions with different colliding phases with the vibrating plate, have been found to be the dominating pattern [1]. From both top view snapshots and laser profilometry methods, the rotation frequency of the spiral arms is characterized with image processing procedures. Both methods reveal that there exists a finite rotation frequency ?r at a threshold vibration acceleration, above which ?r increases linearly with the peak vibration acceleration with a slope strongly dependent on the vibration frequency.

Huang, Kai; Butzhammer, Lorenz; Rehberg, Ingo

2013-06-01

4

Erosion dynamics of a wet granular medium.  

PubMed

Liquid may give strong cohesion properties to a granular medium, and confer a solidlike behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases linearly with time for low liquid content, as wet grains are pulled out of the aggregate. This erosion phenomenon is governed by the properties of the liquids. The erosion rate decreases exponentially with the surface tension while it depends on the viscosity to the power -1. We propose a model based on the force fluctuations arising inside the flow, explaining both dependencies: The capillary force acts as a threshold and the viscosity controls the erosion time scale. We also provide experiments using different flowing grains, confirming our model. PMID:24125259

Lefebvre, Gautier; Jop, Pierre

2013-09-01

5

Erosion dynamics of a wet granular medium  

NASA Astrophysics Data System (ADS)

Liquid may give strong cohesion properties to a granular medium, and confer a solidlike behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases linearly with time for low liquid content, as wet grains are pulled out of the aggregate. This erosion phenomenon is governed by the properties of the liquids. The erosion rate decreases exponentially with the surface tension while it depends on the viscosity to the power -1. We propose a model based on the force fluctuations arising inside the flow, explaining both dependencies: The capillary force acts as a threshold and the viscosity controls the erosion time scale. We also provide experiments using different flowing grains, confirming our model.

Lefebvre, Gautier; Jop, Pierre

2013-09-01

6

Dynamics of the wet granular Leidenfrost phenomenon.  

PubMed

By event-driven molecular dynamics simulations, we study the Leidenfrost effect for wet granular matter driven from below. In marked contrast to all earlier studies on other fluids, the dense plug hovering on the hot gas cushion undergoes an undamped oscillation. The location of the Hopf bifurcation leading to this oscillation is strongly dependent on the inelasticity of the grain impacts. The vertical separation into a gas phase with a condensed plug hovering above it is particularly pronounced due to the cohesiveness of the granulate. For sufficiently large system sizes, the Rayleigh-Taylor instability terminates the oscillatory state at late times. PMID:23005754

Roeller, Klaus; Herminghaus, Stephan

2012-08-01

7

Granular flow: Dry and wet  

NASA Astrophysics Data System (ADS)

Granular material is a collection of macroscopic particles that are visible with naked eyes. The non-equilibrium nature of the granular materials makes their rheology quite different from that of molecular systems. In this minireview, we present the unique features of granular materials focusing on the shear flow of dry granular materials and granule-liquid mixture.

Mitarai, N.; Nakanishi, H.

2012-04-01

8

Shear strength properties of wet granular materials  

Microsoft Academic Search

We investigate shear strength properties of wet granular materials in the pendular state (i.e., the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation

Vincent Richefeu; Moulay Saïd El Youssoufi; Farhang Radjaï

2006-01-01

9

Compaction dynamics of wet granular packings  

NASA Astrophysics Data System (ADS)

The extremely slow compaction dynamics of wet granular assemblies has been studied experimentally. The cohesion, due to capillary bridges between neighboring grains, has been tuned using different liquids having specific surface tension values. The characteristic relaxation time for compaction ? grows strongly with cohesion. A kinetic model [1], based on a free volume kinetic equations and the presence of a capillary energy barrier (due to liquid bridges), is able to reproduce quantitatively the experimental curves. This model allows one to describe the cohesion in wet granular packing [2]. The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has also been investigated in the range 20%-80%. Triboelectric and capillary condensation effects have been introduced in the kinetic model. Results confirm the existence of an optimal condition at RH 45% for minimizing cohesive interactions between glass beads [3]. References : [1] F.Ludewig, S.Dorbolo, T.Gilet, and N.Vandewalle, EPL 84, 44001 (2008) [2] J.E.Fiscina, G.Lumay, F.Ludewig and N.Vandewalle, Phys. Rev. Lett. 105, 048001 (2010) [3] N.Vandewalle, G.Lumay, F.Ludewig, J.E.Fiscina, Phys. Rev. E 85, 031309 (2012)

Vandewalle, Nicolas; Ludewig, Francois; Fiscina, Jorge E.; Lumay, Geoffroy

2013-03-01

10

Hierarchical Structures in Granular Matter  

NASA Astrophysics Data System (ADS)

Granular matter, under the proper conditions of vibration, exhibits a behavior that closely resembles that of gases, liquids or solids. In a vibrated mix of glass particles and magnetic steel particles, it is also possible to observe aggregation phenomena, as well as, processes of reconstruction of the generated clusters. In this work we discuss the effects of the so called granular temperature on the evolution of the agglomerates generated by the magnetic interactions. On the basis of a fractal analysis and the measured mass distribution, we analyze experimental results on the static structural aspects of the aggregates originated by two methods we call: granular diffusion limited aggregation (GDLA) and growth limited by concentration (GLC).

González-Gutiérrez, J.; Carrillo-Estrada, J. L.; Ruiz-Suárez, J. C.

2013-12-01

11

Morphological clues to wet granular pile stability.  

PubMed

When a granular material such as sand is mixed with a certain amount of liquid, the surface tension of the latter bestows considerable stiffness to the material, which enables, for example, sand castles to be sculpted. The geometry of the liquid interface within the granular pile is of extraordinary complexity and strongly varies with the liquid content. Surprisingly, the mechanical properties of the pile are largely independent of the amount of liquid over a wide range. We resolve this puzzle with the help of X-ray microtomography, showing that the remarkable insensitivity of the mechanical properties to the liquid content is due to the particular organization of the liquid in the pile into open structures. For spherical grains, a simple geometric rule is established, which relates the macroscopic properties to the internal liquid morphologies. We present evidence that this concept is also valid for systems with non-spherical grains. Hence, our results provide new insight towards understanding the complex physics of a large variety of wet granular systems including land slides, as well as mixing and agglomeration problems. PMID:18264104

Scheel, M; Seemann, R; Brinkmann, M; Di Michiel, M; Sheppard, A; Breidenbach, B; Herminghaus, S

2008-03-01

12

Entropy of jammed granular matter  

NASA Astrophysics Data System (ADS)

Granular matter can be considered a non-equilibrium system, such that equilibrium statistics is insufficient to describe the dynamics. A phase transition occurs when granular materials are compressed such that a nonzero stress develops in response to a strain deformation. This transition, referred to as the jamming transition, occurs at a critical volume fraction, ?c depending on friction and preparation protocol. Analysis of the jamming transition produces a phase diagram of jammed granular matter for identical spheres, characterized by the critical volume fraction, ?c and the average coordination number, Z. The boundaries of the phase diagram are related to well-defined upper and lower limits in the density of disordered packings; random close packing (RCP) and random loose packing (RLP). Frictional systems, such as granular matter, exhibit an inherent path dependency resulting in the loss of energy conservation, an important facet of equilibrium statistics. It has been suggested Edwards that the volume-force (V-F) ensemble, wherein volume replaces energy as the conservative quantity, may provide a sufficient framework to create a statistical ensemble for jammed granular matter. Treating a jammed system via the V-F ensemble introduces an analogue to temperature in equilibrium systems. This analogue, "compactivity", measures how compact a system could be and governs fluctuation in the volume statistics. Randomness in statistical systems is typically characterized by entropy, the equation of state derived from the number of microstates available to the system. In equilibrium statistical mechanics, entropy provides the link between these microstates and the macroscopic thermodynamic properties of the system. Therefore, calculating the entropy within the V-F ensemble can relate the available microscopic volume for each grain to the macroscopic system properties. The entropy is shown to be minimal at RCP and maximal at the minimum RLP limit, via several methods utilizing simulations and theoretical models. Within this framework RCP is achieved in the limit of minimal compactivity and RLP is achieved in the limit of maximal compactivity. The boundaries of a phase diagram for jammed matter could thereby be defined by the limits of zero and infinite compactivities, characterizing the RCP and RLP limits of granular matter.

Briscoe, Christopher

13

Morphological clues to wet granular pile stability  

Microsoft Academic Search

When a granular material such as sand is mixed with a certain amount of liquid, the surface tension of the latter bestows considerable stiffness to the material, which enables, for example, sand castles to be sculpted. The geometry of the liquid interface within the granular pile is of extraordinary complexity and strongly varies with the liquid content. Surprisingly, the mechanical

M. Scheel; R. Seemann; M. Brinkmann; M. di Michiel; A. Sheppard; B. Breidenbach; S. Herminghaus

2008-01-01

14

On liquid migration in sheared granular matter  

NASA Astrophysics Data System (ADS)

Mixing liquids with powders is of great importance, e.g. in process engineering and for pharmaceutical applications. Generally, one might expect that homogeneously shearing or stirring wet granular matter would lead to a homogeneous liquid distribution, however, it is not clear what happens when shear is applied non-homogeneously, e.g. in shear bands. It is commonly accepted that at large liquid contents, liquid flows inside dilating zones as percolating liquid networks prevent air from entering the dilating pores, but it is unknown what happens at low liquid contents. We present experimental measurements showing a decreased liquid concentration inside a shear band where glass beads are sheared in a split bottom shear cell. Furthermore, a microscopic model for liquid transport at low liquid contents is presented, where fluid dynamics between individual liquid structures driven by Laplace pressure differences is taken into account. Our model shows liquid depletion patterns in quantitative agreement with experiments. On the other hand, our model is also applicable to the situation where shear is applied homogeneously, showing diffusive spreading of liquid.

Mani, R.; Kadau, D.; Or, D.; Herrmann, H. J.

2013-06-01

15

Erosion of a wet/dry granular interface  

NASA Astrophysics Data System (ADS)

To model the dynamic of landslides, the evolution of the interface between the erodible ground and the flowing material is still studied experimentally or numerically (ie. Mangeney et al. 2010, Iverson 2012). In some cases, the basal material is more cohesive than the flowing one. Such situation arises for example due to cementation or humidity. What are the exchange rates between these phases? What is the coupling between the evolution of the interface and the flow? We studied the erosion phenomenon and performed laboratory experiments to focus on the interaction between a cohesive unsaturated granular material and a dry granular flow. Both materials were spherical grains, the cohesion being induced by adding a given mass of liquid to the grains. Two configurations were explored: a circular aggregate submitted to a dry flow in a rotating drum, and a granular flow eroding a wet granular pile. First, we focused on the influence of the cohesion, controlled by the liquid properties, such as the surface tension and the viscosity. Then the flow characteristics were modified by varying the grain size and density. These results allowed us to present a model for the erosion mechanisms, based on the flow and fluid properties. The main results are the need to take into account the whole probability distribution the stress applied on the wet grains and that both the surface tension and the viscosity are important since they play a different roles. The latter is mainly responsible of the time scale of the dynamic of a wet grain, while the former acts as a threshold on the force distribution. In the second configuration, we could also control the inclination of the slope. This system supported the previous model and moreover revealed an interface instability, leading the formation of steep steps, which is a reminiscence of the cyclic-steps observed during river-channel incision (Parker and Izumi 2000). We will present the dynamics of such granular steps. [1] Mangeney, A., O. Roche, O. Hungr, N. Mangold, G. Faccanoni, and A. Lucas (2010), Erosion and mobility in granular collapse over sloping beds, J. Geophys. Res., 115, F03040, doi:10.1029/2009JF001462. [2] Iverson, R. M. (2012), Elementary theory of bed-sediment entrainment by debris flows and avalanches, J. Geophys. Res., 117, F03006, doi:10.1029/2011JF002189. [3] Parker G.and Izumi N., Purely erosional cyclic and solitary steps created by flow over a cohesive bed, J. Fluid Mech. (2000), vol. 419, pp. 203-238.

Jop, Pierre; Lefebvre, Gautier

2013-04-01

16

Erosion rate and instability of a wet/dry granular interface  

NASA Astrophysics Data System (ADS)

Liquid may give strong cohesion properties to a granular medium, and confers a solid-like behavior. We study the evolution of a fixed aggregate of wet granular matter subjected to a flow of dry grains. In the confined geometry of a thin cell, the aggregate is hold by the walls, and the dry matter flowing around will pull grains out of the aggregate. Thus, by granular erosion, the shape of the interface is modified. Image treatment allows us to retrieve the interface of the wet area, and analyze the phenomenon. Two different configurations are set up for erosion study. In a rotating drum, we follow the diameter of a circular aggregate remaining at the center. This provides an erosion rate, related to the liquid and grains physical properties. In an open cell between vertical plates, we can form a heap-shaped aggregate. Then, with a funnel of constant outlet, we inject dry grains, flowing on top of the cohesive heap. We observe destabilization of an initial flat profile in certain conditions. The coupling between the flow stress and the shape of the heap creates periodical structures, which propagate to the top through the erosion process.

Lefebvre, Gautier; Jop, Pierre

2013-06-01

17

Statistical mechanics framework for static granular matter  

NASA Astrophysics Data System (ADS)

The physical properties of granular materials have been extensively studied in recent years. So far, however, there exists no theoretical framework which can explain the observations in a unified manner beyond the phenomenological jamming diagram. This work focuses on the case of static granular matter, where we have constructed a statistical ensemble which mirrors equilibrium statistical mechanics. This ensemble, which is based on the conservation properties of the stress tensor, is distinct from the original Edwards ensemble and applies to packings of deformable grains. We combine it with a field theoretical analysis of the packings, where the field is the Airy stress function derived from the force and torque balance conditions. In this framework, Point J characterized by a diverging stiffness of the pressure fluctuations. Separately, we present a phenomenological mean-field theory of the jamming transition, which incorporates the mean contact number as a variable. We link both approaches in the context of the marginal rigidity picture proposed by Wyart and others.

Henkes, Silke; Chakraborty, Bulbul

2009-06-01

18

Onset of convection in strongly shaken granular matter.  

PubMed

Strongly vertically shaken granular matter can display a density inversion: A high-density cluster of beads is elevated by a dilute gaslike layer of fast beads underneath ("granular Leidenfrost effect"). For even stronger shaking the granular Leidenfrost state becomes unstable and granular convection rolls emerge. This transition resembles the classical onset of convection in fluid heated from below at some critical Rayleigh number. The same transition is seen in molecular dynamics (MD) simulations of the shaken granular material. The critical shaking strength for the onset of granular convection can be calculated from a linear stability analysis of a hydrodynamiclike model of the granular flow. Experiment, MD simulations, and theory quantitatively agree. PMID:20366684

Eshuis, Peter; van der Meer, Devaraj; Alam, Meheboob; van Gerner, Henk Jan; van der Weele, Ko; Lohse, Detlef

2010-01-22

19

Pattern formation in vibrated beds of dry and wet granular materials  

NASA Astrophysics Data System (ADS)

The Discrete Element Method was coupled with a capillary liquid bridge force model for computational studies of pattern formation in vibrated granular beds containing dry or wet granular materials. Depending on the vibration conditions applied, hexagonal, stripes, or cellular pattern was observed in the dry vibrated granular bed. In each of these cases, the same hexagonal, stripes, or cellular pattern was also observed in the spatial distribution of the magnitudes of particle-particle collision forces prior to the formation of the corresponding actual pattern in physical distributions of the particles. This seemed to suggest that the pattern formation phenomenon of vibrated granular bed systems might be the result of a two-dimensional Newton's cradle effect. In the presence of a small amount of wetness, these patterns were no longer formed in the vibrated granular beds under the same corresponding set of vibration conditions. Despite the relatively much weaker capillary forces arising from the simulated liquid bridges between particles compared with particle-particle collision forces, the spatial distributions of these collision forces, physical distributions of particles, as well as time profiles of average collision forces were altered significantly in comparison with the corresponding distributions and profiles observed for the dry vibrated granular beds. This seemed to suggest the presence of a two-dimensional Stokes' cradle effect in these wet vibrated granular bed systems which disrupted the formation of patterns in the wet granular materials that would have been observed in their dry counterparts.

Chuan Lim, Eldin Wee

2014-01-01

20

Analysis of Configurational Entropy in Jammed Granular Matter  

NASA Astrophysics Data System (ADS)

Energy fluctuations in jammed granular matter are negligible and cannot control the statistical mechanics. It is of interest to explore volume fluctuations in an effort to describe the statistical mechanics of jammed matter, originally proposed by Edwards. Current studies have introduced the concept of a theoretical phase diagram for jammed matter, providing plausible statistical explanations for the RCP and RLP states, along with intermediate jammed states, as a function of coordination number, z, friction coefficient ?, and volume fraction, ?. Entropy can be derived from this theoretical framework by means of a Hamiltonian, with energy and temperature replaced by volume, W, and compactivity, X, where X is an analogue of temperature. Our present efforts are to calculate the Shannon entropy of jammed granular packings along various paths of the phase diagram, resulting in an extensive entropy density, and X, as a function of ?, providing a new equation of state for jammed granular matter.

Briscoe, Christopher; Wang, Ping; Song, Chaoming; Makse, Hernan

2008-03-01

21

Brownian forces in sheared granular matter.  

PubMed

We present results from a series of experiments on a granular medium sheared in a Couette geometry and show that their statistical properties can be computed in a quantitative way from the assumption that the resultant from the set of forces acting in the system performs a Brownian motion. The same assumption has been utilized, with success, to describe other phenomena, such as the Barkhausen effect in ferromagnets, and so the scheme suggests itself as a more general description of a wider class of driven instabilities. PMID:16605874

Baldassarri, A; Dalton, F; Petri, A; Zapperi, S; Pontuale, G; Pietronero, L

2006-03-24

22

Universal features of the jamming phase diagram of wet granular materials.  

PubMed

We investigate the influence of the shape of a particle on the structure of the jamming phase diagram of wet granular materials. We compute the jamming phase diagram of wet dimers (two fused disks) and compare it with that of the wet disks. Amplitude of the external force at solidification, i.e., the jamming force F(s), is computed as a function of the packing fraction ?, the capillary bridge energy ?, and the aspect ratio of dimers ?. Based on data collapse, an equation for amplitude of the external force at solidification F(s)(?,?,?) is derived. F(s) has scaling and logarithmic relations with ? and ?, respectively, exactly the same type reported for wet disks earlier. Interestingly, F(s) does not depend on the aspect ratio of dimers ?. The only difference is that wet dimers are found to be more stiffer than wet disks. However, the similarities of the equations describing F(s)(?,?,?) of wet dimers and disks imply that there exists, yet unknown, universal aspects of mechanical response of wet granular materials to the external forces, independent from the particle shape. In addition, we study local orientation of particles and its statistical properties. PMID:24229163

Ebrahimnazhad Rahbari, S H; Khadem-Maaref, M; Seyed Yaghoubi, S K A

2013-10-01

23

A Statistical Ensemble for Soft Granular Matter  

NASA Astrophysics Data System (ADS)

Work on packings of soft spheres (PRE 68, 011306 (2003)) has shown the existence of a Jamming transition and has highlighted the need for a general statistical framework to describe granular packings. This work presents an extension of the formalism proposed by Edwards (Physica A 157, 1080 (1989)) to packings of soft particles. We base our analysis on a height formalism developed in two dimensions (PRL 88, 115505 (2002)) to extract a topological invariant ?, the trace of the global stress tensor, which is conserved under internal rearrangements of the system. Upon assuming a flat measure in ?-space, we can derive a canonical distribution of the local ?-values in a grain packing. We then check the predictions of this ensemble against distributions of mechanically stable packings of frictionless disks obtained from computer simulations. Work supported by NSF-DMR 0549762.

Henkes, Silke; O'Hern, Corey; Chakraborty, Bulbul

2007-03-01

24

Runaway electrification of friable self-replicating granular matter.  

PubMed

We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palmlike structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter. PMID:24041221

Cartwright, Julyan H E; Escribano, Bruno; Grothe, Hinrich; Piro, Oreste; Sainz Díaz, C Ignacio; Tuval, Idan

2013-10-15

25

Wet ashing of organic matter for the determination of antimony  

Microsoft Academic Search

The wet ashing of organic matter for Sb determination was investigated by using a radioactive tracer technique. Wet ashing with HNOâ + HClOâ mixtures leads to the formation of insoluble Sb compounds. All the Sb remains in solution when a HNOâ + HClOâ + HâSOâ mixture is used. The influence of the ashing vessel (glass and Teflon) and the oxidation

Sixto. Bajo; Ursula. Suter

1982-01-01

26

Depinning and creeplike motion of wetting fronts in weakly vibrated granular media  

NASA Astrophysics Data System (ADS)

We study the effect of weak vibrations on the imbibition of water in granular media. In our experiments, we have observed that as soon as the vibration is applied, an initially pinned wetting front advances in the direction of imbibition. We found that the front motion is governed by the avalanches of localized intermittent advances directed at 45? to the imbibition direction. When the rescaled gravitational acceleration of vertical vibrations is in the range of 0.81?G?0.95, we observed an almost steady motion of wetting front with a constant velocity vcr(G)?exp-1/G during more than 20 min, whereas at lower accelerations (0.5?G?0.8) the front velocity decreases in time as v?t-?. We suggest that the steady motion of an imbibition front in a weakly vibrated granular medium can be treated as a creep motion associated with nonthermal temporal fluctuations of packing density in a weakly vibrated granular medium.

Balankin, Alexander S.; García Otamendi, E.; Samayoa, D.; Patiño, J.; Rodríguez, M. A.

2012-03-01

27

Stress-dependent normal-mode frequencies from the effective mass of granular matter  

NASA Astrophysics Data System (ADS)

A zero-temperature critical point has been invoked to control the anomalous behavior of granular matter as it approaches jamming or mechanical arrest. Criticality manifests itself in an anomalous spectrum of low-frequency normal modes and scaling behavior near the jamming transition. The critical point may explain the peculiar mechanical properties of dissimilar systems such as glasses and granular materials. Here we study the critical scenario via an experimental measurement of the normal modes frequencies of granular matter under stress from a pole decomposition analysis of the effective mass. We extract a complex-valued characteristic frequency which displays scaling |?*(?)|˜??' with vanishing stress ? for a variety of granular systems. The critical exponent is smaller than that predicted by mean-field theory opening new challenges to explain the exponent for frictional and dissipative granular matter. Our results shed light on the anomalous behavior of stress-dependent acoustics and attenuation in granular materials near the jamming transition.

Hu, Yanqing; Johnson, David L.; Valenza, John J.; Santibanez, Francisco; Makse, Hernán A.

2014-06-01

28

Time-resolved dynamics of granular matter by random laser emission  

NASA Astrophysics Data System (ADS)

Because of the huge commercial importance of granular systems, the second-most used material in industry after water, intersecting the industry in multiple trades, like pharmacy and agriculture, fundamental research on grain-like materials has received an increasing amount of attention in the last decades. In photonics, the applications of granular materials have been only marginally investigated. We report the first phase-diagram of a granular as obtained by laser emission. The dynamics of vertically-oscillated granular in a liquid solution in a three-dimensional container is investigated by employing its random laser emission. The granular motion is function of the frequency and amplitude of the mechanical solicitation, we show how the laser emission allows to distinguish two phases in the granular and analyze its spectral distribution. This constitutes a fundamental step in the field of granulars and gives a clear evidence of the possible control on light-matter interaction achievable in grain-like system.

Folli, Viola; Ghofraniha, Neda; Puglisi, Andrea; Leuzzi, Luca; Conti, Claudio

2013-07-01

29

Time-resolved dynamics of granular matter by random laser emission  

PubMed Central

Because of the huge commercial importance of granular systems, the second-most used material in industry after water, intersecting the industry in multiple trades, like pharmacy and agriculture, fundamental research on grain-like materials has received an increasing amount of attention in the last decades. In photonics, the applications of granular materials have been only marginally investigated. We report the first phase-diagram of a granular as obtained by laser emission. The dynamics of vertically-oscillated granular in a liquid solution in a three-dimensional container is investigated by employing its random laser emission. The granular motion is function of the frequency and amplitude of the mechanical solicitation, we show how the laser emission allows to distinguish two phases in the granular and analyze its spectral distribution. This constitutes a fundamental step in the field of granulars and gives a clear evidence of the possible control on light-matter interaction achievable in grain-like system.

Folli, Viola; Ghofraniha, Neda; Puglisi, Andrea; Leuzzi, Luca; Conti, Claudio

2013-01-01

30

Confocal Microscopy of Jammed Matter: From Elasticity to Granular Thermodynamics  

NASA Astrophysics Data System (ADS)

Packings of particles are ubiquitous in nature and are of interest not only to the scientific community but also to the food, pharmaceutical, and oil industries. In this thesis we use confocal microscopy to investigate packing geometry and stress transmission in 3D jammed particulate systems. By introducing weak depletion attraction we probe the accessible phase-space and demonstrate that a microscopic approach to jammed matter gives validity to statistical mechanics framework, which is intriguing because our particles are not thermally activated. We show that the fluctuations of the local packing parameters can be successfully captured by the recently proposed 'granocentric' model, which generates packing statistics according to simple stochastic processes. This model enables us to calculate packing entropy and granular temperature, the so-called 'compactivity', therefore, providing a basis for a statistical mechanics of granular matter. At a jamming transition point at which there are formed just enough number of contacts to guarantee the mechanical stability, theoretical arguments suggest a singularity which gives rise to the surprising scaling behavior of the elastic moduli and the microstructure, as observed in numerical simulations. Since the contact network in 3D is typically hidden from view, experimental test of the scaling law between the coordination number and the applied pressure is lacking in the literature. Our data show corrections to the linear scaling of the pressure with density which takes into account the creation of contacts. Numerical studies of vibrational spectra, in turn, reveal sudden features such as excess of low frequency modes, dependence of mode localization and structure on the pressure. Chapter four describes the first calculation of vibrational density of states from the experimental 3D data and is in qualitative agreement with the analogous computer simulations. We study the configurational role of the pressure and demonstrate that low frequency modes become progressively localized as the packing density is increased. Another application of our oil-in-water emulsions serves to mimic cell adhesion in biological tissues. By analyzing the microstructure in 3D we find that a threshold compression force is necessary to overcome electrostatic repulsion and surface elasticity and establish protein-mediated adhesion.

Jorjadze, Ivane

31

Discrete particle simulations and experiments on the collapse of wet granular columns  

NASA Astrophysics Data System (ADS)

Small quantities of liquid in a granular material control the flow dynamics as well as the triggering and jamming phases. In order to study this problem, some experimental collapse tests conducted in a rectangular box were reproduced with a 1:1 scale numerical model using the Discrete Element Method. In simulations the effect of the capillary bridges has been investigated implementing a mid-range attractive force between particles based on the minimum energy approach. Also a bonding-debonding mechanism was incorporated in the algorithm and the volume of each sessile drop on the particle surface was considered during its motion. The influence of some variables was investigated with respect to the final slope profiles and the runout lengths: the initial liquid content, the particle size, the solid density, the liquid surface tension, and the liquid-solid contact angle. Also the crucial effect of the confinement walls on the collapse phenomenon was investigated: wet particles adhere to the lateral walls providing a higher flow resistance in comparison to the same material in dry conditions. It was observed that particles with largest path-lengths are localized near the movable wall at a middle-height of the initial column sample. Other particles at the surface moves in a rigid way especially if they were wet and with a low solid density. The "fidelity" of each particle with respect to the nearest neighbours was evaluated allowing to recognize the emergence of clusters of particles and rigid parts, to extract the failure surface and to localize where debonding mechanisms concentrate in the wet case.

Gabrieli, Fabio; Artoni, Riccardo; Santomaso, Andrea; Cola, Simonetta

2013-10-01

32

Compaction of granular matter and random tetris model  

NASA Astrophysics Data System (ADS)

We present the behavior of a microscopic lattice model for the compaction of granular media. We show how this model reproduces the experimental phenomenology, e.g., slow relaxation and memory effects. The study of the density profiles allow to interpret these results. .

Barrat, A.

2001-06-01

33

Time-resolved dynamics of granular matter by random laser emission.  

PubMed

Because of the huge commercial importance of granular systems, the second-most used material in industry after water, intersecting the industry in multiple trades, like pharmacy and agriculture, fundamental research on grain-like materials has received an increasing amount of attention in the last decades. In photonics, the applications of granular materials have been only marginally investigated. We report the first phase-diagram of a granular as obtained by laser emission. The dynamics of vertically-oscillated granular in a liquid solution in a three-dimensional container is investigated by employing its random laser emission. The granular motion is function of the frequency and amplitude of the mechanical solicitation, we show how the laser emission allows to distinguish two phases in the granular and analyze its spectral distribution. This constitutes a fundamental step in the field of granulars and gives a clear evidence of the possible control on light-matter interaction achievable in grain-like system. PMID:23872642

Folli, Viola; Ghofraniha, Neda; Puglisi, Andrea; Leuzzi, Luca; Conti, Claudio

2013-01-01

34

Response properties in a model for granular matter  

NASA Astrophysics Data System (ADS)

We investigate the response properties of granular media within the framework of the so-called random Tetris model. We monitor, for different driving procedures, several quantities: the evolution of the density and of the density profiles, the ageing properties through the two-times correlation functions and the two-times mean-square distance between the potential energies, the response function defined in terms of the difference in the potential energies of two replicas driven in two slightly different ways. We focus, in particular, on the role played by the spatial inhomogeneities (structures) spontaneously emerging during the compaction process, the history of the sample and the driving procedure. It turns out that none of these ingredients can be neglected for the correct interpretation of the experimental or numerical data. We discuss the problem of the optimization of the compaction process and we comment on the validity of our results for the description of granular materials in a thermodynamic framework.

Barrat, A.; Loreto, V.

2000-06-01

35

Ageing of the avalanche angle in immersed granular matter  

NASA Astrophysics Data System (ADS)

The stability of packings of glass beads immersed in various fluids is studied experimentally in a rotating drum. The avalanche angle depends on the time during which the system remains at rest before measurement only when the grains are immersed in water. The experimental results prove that ageing of immersed granular materials, under low applied stress and in the absence of external sollicitations, only originates from chemical reactions that occur at the surface of the grains.

Gayvallet, H.; Géminard, J.-C.

2002-12-01

36

Force Network Ensemble: A New Approach to Static Granular Matter  

NASA Astrophysics Data System (ADS)

An ensemble approach for force distributions in static granular packings is developed. This framework is based on the separation of packing and force scales, together with an a priori flat measure in the force phase space under the constraints that the contact forces are repulsive and balance on every particle. We show how the formalism yields realistic results, both for disordered and regular triangular “snooker ball” configurations, and obtain a shear-induced unjamming transition of the type proposed recently for athermal media.

Snoeijer, Jacco H.; Vlugt, Thijs J.; van Hecke, Martin; van Saarloos, Wim

2004-02-01

37

A statistical mechanics framework for static granular matter  

NASA Astrophysics Data System (ADS)

Granular materials are a class of materials which are important both to industry and to the physics community. Their importance to the physics community stems from the fact that granular materials are a simple example of an out-of-equilibrium, dissipative system, for which energy is not conserved and the traditional approach of statistical mechanics fails. The aim of this thesis is to construct and examine a statistical mechanics-like framework for granular materials, based on a conservation law other than energy. We restrict our attention to packings in mechanical equilibrium, also known as jammed packings, where we are able to show that the total force moment tensor of the system is a conserved quantity. We build an ensemble using the stress, and test it on simulated packings. This allows us also to explore the solid to liquid transition which occurs as the density of the packing is reduced, which is also known as the jamming transition. We then use the basis laid out by the ensemble to, first to study the properties of the system at then transition, and then to develop a field theoretical model for jammed packings, which predicts a diverging stiffness at the jamming transition. Finally, we discuss an empirical mean-field theory derived from the analysis of simulated packings.

Henkes, Silke Emilia

38

Flowers in flour: Avalanches in cohesive granular matter  

NASA Astrophysics Data System (ADS)

We report on the intermittent dynamics of the free surface of a cohesive granular material during a silo discharge. In absence of cohesion, one observes the formation and the growth of a conical crater whose angle is well defined and constant in time. When the cohesion is involved the free surface exhibits a complex dynamics and the crater, resulting from a series of individual avalanches, is no longer axisymmetric. However, in spite of the intermittent behavior of the free surface, the flow rate is observed to remain constant throughout the discharge.

Freyssingeas, E.; Dalbe, M.-J.; Géminard, J.-C.

2011-05-01

39

Force network ensemble: a new approach to static granular matter.  

PubMed

An ensemble approach for force distributions in static granular packings is developed. This framework is based on the separation of packing and force scales, together with an a priori flat measure in the force phase space under the constraints that the contact forces are repulsive and balance on every particle. We show how the formalism yields realistic results, both for disordered and regular triangular "snooker ball" configurations, and obtain a shear-induced unjamming transition of the type proposed recently for athermal media. PMID:14995308

Snoeijer, Jacco H; Vlugt, Thijs J H; van Hecke, Martin; van Saarloos, Wim

2004-02-01

40

An effective field theory for soft granular matter  

NASA Astrophysics Data System (ADS)

Work on packings of soft spheres (PRE 68, 011306 (2003)) has demonstrated the existence of a jamming transition and has highlighted the need for a general statistical framework to describe granular packings. We have shown that a statistical ensemble, based on conservation properties of the global stress tensor, is consistent with simulated packings of frictionless disks (PRL 99, 038002 (2007)). We construct an effective field theory based on this ensemble, in the spirit of an earlier attempt (PRL 95, 198002 (2005)). The field theory is constructed by synthesizing results from simulations into one functional form for the effective free energy. We will describe ongoing efforts to derive this form by combining scaling ideas with microscopic properties of the packings.

Henkes, Silke; O'Hern, Corey; Chakraborty, Bulbul

2008-03-01

41

A community-detection based approach to identification of inhomogeneities in granular matter  

NASA Astrophysics Data System (ADS)

Interparticle interactions in granular matter are commonly represented by appropriate graphs, therefore, inhomogeneities in granular matter can be possibly reflected by community structure in the respective graphs. Approaches and algorithms for community detection are being actively developed and the achievements in this area can be utilized for analysis of granular systems, where bridging the gap from microscopic configuration to macroscopic phenomena is of great interest. Here, we analyse applicability of graph community detection algorithms for identification of inhomogeneities of particle parameter distribution in granular matter, in order to explore the relevance of the selected approach in general. As an example application, we analyse identification of temperature distribution inhomogeneities in a simulated packed bed of fuel particles on a moving grate. We build a graph based on particle parameter similarity from the particle temperature data, available from Discrete Element/Particle Modelling, and the problem of identification of particle temperature inhomogeneities is thereby made equivalent to community detection in graphs. We apply a number of well-known community detection algorithms: Edge Betweenness, Walktrap, Infomap, Label Propagation, Spinglass and compare the resulting partitions. We apply this approach to a number of graphs, corresponding to different particle configurations, in order to identify regularities characteristic of partitions produced by different algorithms. We propose a procedure for additional postprocessing of the partitions in order to improve the quality of clusterization. In addition, we apply two alternative algorithms (not related to community detection in graphs) to identify particle distribution inhomogeneities. We also introduce a parameter to evaluate the cluster structure in particle systems.

Navakas, Robertas; Džiugys, Algis; Peters, Bernhard

2014-08-01

42

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C-150°C, effective stresses of 20-47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 mum. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

43

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C–150°C, effective stresses of 20–47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 ?m. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

44

Surface roughness effects in granular matter: influence on angle of repose and the absence of segregation.  

PubMed

We investigate the effect of nanoscale variations in the surface roughness of individual particles on macroscale granular flow characteristics. Experiments were conducted in circular rotating tumblers with smooth and rough 2 and 3 mm steel particles. The smooth beads had a rms surface roughness of approximately 30 to 60 nm; rough beads had a surface roughness of approximately 240 to 350 nm. The dynamic angle of repose for rough particles increased by 10 degrees to 25 degrees over that of smooth particles over a wide range of rotation speeds. Even though surface roughness affects the angle of repose, we were unable to detect any segregation of bidisperse mixtures of rough and smooth particles in the radial direction in two-dimensional (2D) tumblers. Furthermore, no axial banding segregation occurred in 3D tumblers, both cylindrical and spherical. For mixtures of smooth and rough particles, the angle of repose increased monotonically with increasing concentration of rough particles. Particle dynamics simulations verified that the dependence of the angle of repose on the concentration of rough particles can be directly related to the coefficient of friction of the particles. Simulations over a broad range of friction parameters failed to induce segregation solely from differences in the angle of repose. These results indicate that nanoscale surface roughness can affect the flowability and angle of repose of granular matter without driving demixing of the bulk granular material. PMID:16605514

Pohlman, Nicholas A; Severson, Benjamin L; Ottino, Julio M; Lueptow, Richard M

2006-03-01

45

Attractive emulsion droplets probe the phase diagram of jammed granular matter  

PubMed Central

It remains an open question whether statistical mechanics approaches apply to random packings of athermal particles. Although a jamming phase diagram has recently been proposed for hard spheres with varying friction, here we use a frictionless emulsion system in the presence of depletion forces to sample the available phase space of packing configurations. Using confocal microscopy, we access their packing microstructure and test the theoretical assumptions. As a function of attraction, our packing protocol under gravity leads to well-defined jammed structures in which global density initially increases above random close packing and subsequently decreases monotonically. Microscopically, the fluctuations in parameters describing each particle, such as the coordination number, number of neighbors, and local packing fraction, are for all attractions in excellent agreement with a local stochastic model, indicating that long-range correlations are not important. Furthermore, the distributions of local cell volumes can be collapsed onto a universal curve using the predicted k-gamma distribution, in which the shape parameter k is fixed by the polydispersity while the effect of attraction is captured by rescaling the average cell volume. Within the Edwards statistical mechanics framework, this result measures the decrease in compactivity with global density, which represents a direct experimental test of a jamming phase diagram in athermal systems. The success of these theoretical tools in describing yet another class of materials gives support to the much-debated statistical physics of jammed granular matter.

Jorjadze, Ivane; Pontani, Lea-Laetitia; Newhall, Katherine A.; Brujic, Jasna

2011-01-01

46

Granular activated carbon adsorption of MIB in the presence of dissolved organic matter.  

PubMed

Based on the results of over twenty laboratory granular activated carbon (GAC) column runs, models were developed and utilized for the prediction of 2-methylisoborneol (MIB) breakthrough behavior at parts per trillion levels and verified with pilot-scale data. The influent MIB concentration was found not to impact the concentration normalized breakthrough. Increasing influent background dissolved organic matter (DOM) concentration was found to systematically decrease the GAC adsorption capacity for MIB. A series of empirical models were developed that related the throughput in bed volumes for a range of MIB breakthrough targets to the influent DOM concentration. The proportional diffusivity (PD) designed rapid small-scale column test (RSSCT) could be directly used to scale-up MIB breakthrough performance below 15% breakthrough. The empirical model to predict the throughput to 50% breakthrough based on the influent DOM concentration served as input to the pore diffusion model (PDM) and well-predicted the MIB breakthrough performance below a 50% breakthrough. The PDM predictions of throughput to 10% breakthrough well simulated the PD-RSSCT and pilot-scale 10% MIB breakthrough. PMID:23623469

Summers, R Scott; Kim, Soo Myung; Shimabuku, Kyle; Chae, Seon-Ha; Corwin, Christopher J

2013-06-15

47

Mechanisms for slow strengthening in granular materials  

PubMed

Several mechanisms cause a granular material to strengthen over time at low applied stress. The strength is determined from the maximum frictional force F(max) experienced by a shearing plate in contact with wet or dry granular material after the layer has been at rest for a waiting time tau. The layer strength increases roughly logarithmically with tau only if a shear stress is applied during the waiting time. The mechanisms of strengthening are investigated by sensitive displacement measurements, and by imaging of particle motion in the shear zone. Granular matter can strengthen due to a slow shift in the particle arrangement under shear stress. Humidity also leads to strengthening, but is found not to be its sole cause. In addition to these time dependent effects, the static friction coefficient can also be increased by compaction of the granular material under some circumstances, and by a cycling of the applied shear stress. PMID:11088198

Losert; Geminard; Nasuno; Gollub

2000-04-01

48

Fiat or Bona Fide Boundary--A Matter of Granular Perspective  

PubMed Central

Background Distinguishing bona fide (i.e. natural) and fiat (i.e. artificial) physical boundaries plays a key role for distinguishing natural from artificial material entities and is thus relevant to any scientific formal foundational top-level ontology, as for instance the Basic Formal Ontology (BFO). In BFO, the distinction is essential for demarcating two foundational categories of material entity: object and fiat object part. The commonly used basis for demarcating bona fide from fiat boundary refers to two criteria: (i) intrinsic qualities of the boundary bearers (i.e. spatial/physical discontinuity, qualitative heterogeneity) and (ii) mind-independent existence of the boundary. The resulting distinction of bona fide and fiat boundaries is considered to be categorial and exhaustive. Methodology/Principal Findings By referring to various examples from biology, we demonstrate that the hitherto used distinction of boundaries is not categorial: (i) spatial/physical discontinuity is a matter of scale and the differentiation of bona fide and fiat boundaries is thus granularity-dependent, and (ii) this differentiation is not absolute, but comes in degrees. By reducing the demarcation criteria to mind-independence and by also considering dispositions and historical relations of the bearers of boundaries, instead of only considering their spatio-structural properties, we demonstrate with various examples that spatio-structurally fiat boundaries can nevertheless be mind-independent and in this sense bona fide. Conclusions/Significance We argue that the ontological status of a given boundary is perspective-dependent and that the strictly spatio-structural demarcation criteria follow a static perspective that is ignorant of causality and the dynamics of reality. Based on a distinction of several ontologically independent perspectives, we suggest different types of boundaries and corresponding material entities, including boundaries based on function (locomotion, physiology, ecology, development, reproduction) and common history (development, heredity, evolution). We argue that for each perspective one can differentiate respective bona fide from fiat boundaries.

Vogt, Lars; Grobe, Peter; Quast, Bjorn; Bartolomaeus, Thomas

2012-01-01

49

Granular Physics  

NASA Astrophysics Data System (ADS)

1. Introduction; 2. Computer simulation approaches - an overview; 3. Structure of vibrated powders - numerical results; 4. Collective structures in sand - the phenomenon of bridging; 5. On angles of repose: bistability and collapse; 6. Compaction of disordered grains in the jamming limit: sand on random graphs; 7. Shaking a box of sand I - a simple lattice model; 8. Shaking a box of sand II - at the jamming limit, when shape matters!; 9. Avalanches with reorganising grains; 10. From earthquakes to sandpiles - stick-slip motion; 11. Coupled continuum equations: the dynamics of sand-pile surfaces; 12. Theory of rapid granular flows; 13. The thermodynamics of granular materials; 14. Static properties of granular materials; Author index; Subject index; Bibliography.

Mehta, Anita

2011-03-01

50

Granular Physics  

NASA Astrophysics Data System (ADS)

1. Introduction; 2. Computer simulation approaches - an overview; 3. Structure of vibrated powders - numerical results; 4. Collective structures in sand - the phenomenon of bridging; 5. On angles of repose: bistability and collapse; 6. Compaction of disordered grains in the jamming limit: sand on random graphs; 7. Shaking a box of sand I - a simple lattice model; 8. Shaking a box of sand II - at the jamming limit, when shape matters!; 9. Avalanches with reorganising grains; 10. From earthquakes to sandpiles - stick-slip motion; 11. Coupled continuum equations: the dynamics of sand-pile surfaces; 12. Theory of rapid granular flows; 13. The thermodynamics of granular materials; 14. Static properties of granular materials; Author index; Subject index; Bibliography.

Mehta, Anita

2007-06-01

51

Mechanistic modeling of granular bed filters for the removal of particulate matter from high-temperature, high-pressure gas streams: a critical assessment. [61 references  

Microsoft Academic Search

In several coal conversion processes involving the generation of electrical power from coal, it is necessary to remove the particulate matter from flue gases at high temperatures and pressures. Several variants of granular bed filters involving fixed beds, moving beds, intermittently moving beds, and fluidized beds are being examined to accomplish this goal. This report deals with the review and

Saxena

1980-01-01

52

Size Distribution of Wet Weather and Dry Weather Particulate Matter Entrained in Combined Flows from an Urbanizing Sewershed  

Microsoft Academic Search

Urban drainage transports a complex and heterogeneous mixture of aqueous-phase chemicals and also solid-phase particulate\\u000a matter (PM). In this study, event-scale particle size distribution (PSD) of wet and dry weather flows are measured, modeled,\\u000a and compared. The flows are generated from a complex urbanizing sewershed (Liguori catchment) in Cosenza, Italy. Results indicate\\u000a PSDs are heterodisperse, ranging from colloidal to sand-size

P. Piro; M. Carbone; G. Garofalo; J. Sansalone

2010-01-01

53

A simple wet chemical extraction procedure to characterize soil organic matter (SOM). I. application and recovery rate  

Microsoft Academic Search

The knowledge of soil organic matter (SOM) composition is important for research in soil science. This is why two classical wet chemical extraction procedures were tested and combined to characterize SOM. Twenty?five samples from typical forest and arable soils in Schleswig?Holstein, Northwest Germany, were investigated in the laboratory. Lipids were extracted using a pre?step method. Several polysaccharide fractions were extracted

L. Beyer; C. Wachendorf; C. Koebbemann

1993-01-01

54

Impact of natural organic matter on monochloramine reduction by granular activated carbon: the role of porosity and electrostatic surface properties.  

PubMed

Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters-one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity. PMID:16856745

Fairey, Julian L; Speitel, Gerald E; Katz, Lynn E

2006-07-01

55

Impact of natural organic matter on monochloramine reduction by granular activated carbon: the role of porosity and electrostatic surface properties  

SciTech Connect

Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters - one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). GACs used were coal-based Filtrasorb 400, Filtrasorb 600, Centaur and Medical Grade, and wood-based AquaGuard. While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity. 23 refs., 4 figs., 3 tabs.

Julian L. Fairey; Gerald E. Speitel Jr.; Lynn E. Katz [University of Texas at Austin, TX (United States). Department of Civil, Architectural, and Environmental Engineering

2006-07-01

56

The effect of water temperature on the adsorption equilibrium of dissolved organic matter and atrazine on granular activated carbon  

SciTech Connect

The influence of water temperature on the adsorption of natural dissolved organic matter (DOM) on activated carbon has not been investigated intensively yet. In this study, batch experiments with granular activated carbon (GAC) F300, from bituminous coal, have been carried out at three temperatures (5, 20, 35{sup o} C) using a humic acid model water and different types of surface water (lake, river, canal). Furthermore, the adsorption of an anthropogenic contaminant, atrazine, was quantified in the absence and presence of DOM. The results indicate a significant influence of water temperature on the adsorption equilibrium of DOM and atrazine. Contrary to expectations, DOM and atrazine adsorption in surface water tends to be increased with increasing water temperature, whereas the extent of this effect is dependent on the type and concentration of DOM. Furthermore, the temperature effect on atrazine adsorption is controlled by competition of DOM and atrazine on adsorption sites. Some assumptions are proposed and discussed for explaining the temperature effects observed in the batch studies. 39 refs., 4 figs., 2 tabs.

Bernd Schreiber; Viktor Schmalz; Thomas Brinkmann; Eckhard Worch [Dresden University of Technology, Dresden (Germany). Institute of Water Chemistry

2007-09-15

57

Collection of ultrafine diesel particulate matter (DPM) in cylindrical single-stage wet electrostatic precipitators.  

PubMed

Long-term exposures to diesel particulate matter (DPM) emissions are linked to increasing adverse human health effects due to the potential association of DPM with carcinogenicity. Current diesel vehicular particulate emission regulations are based solely upon total mass concentration, albeit it is the submicrometer particles that are highly respirable and the most detrimental to human health. In this study, experiments were performed with a tubular single-stage wet electrostatic precipitator (wESP) to evaluate its performance for the removal of number-based DPM emissions. A nonroad diesel generator utilizing a low sulfur diesel fuel (500 ppmw) operating under varying load conditions was used as a stationary DPM emission source. An electrical low-pressure impactor (ELPI) was used to quantify the number concentration distributions of diesel particles in the diluted exhaust gas at each tested condition. The wESP was evaluated with respect to different operational control parameters such as applied voltage, gas residence time, etc., to determine their effect on overall collection efficiency, as well as particle size dependent collection efficiency. The results show that the total DPM number concentrations in the untreated diesel exhaust are in the magnitude of approximately108/cm(3) at all engine loads with the particle diameter modes between 20 and 40 nm. The measured collection efficiency of the wESP operating at 70 kV based on total particle numbers was 86% at 0 kW engine load and the efficiency decreased to 67% at 75 kW due to a decrease in gas residence time and an increase in particle concentrations. At a constant wESP voltage of 70 kV and at 75 kW engine load, the variation of gas residence time within the wESP from approximately 0.1 to approximately 0.4 s led to a substantial increase in the collection efficiency from 67% to 96%. In addition, collection efficiency was found to be directly related to the applied voltage, with increasing collection efficiency measured for increases in applied voltage. The collection efficiency based on particle size had a minimum for sizes between 20 and 50 nm, but at optimal wESP operating conditions it was possible to remove over 90% of all particle sizes. A comparison of measured and calculated collection efficiencies reveals that the measured values are significantly higher than the predicted values based on the well-known Deutsch equation. PMID:17256544

Saiyasitpanich, Phirun; Keener, Tim C; Lu, Mingming; Khang, Soon-Jai; Evans, Douglas E

2006-12-15

58

Removal of Particulate Matter in a Tubular Wet Electrostatic Precipitator Using a Water Collection Electrode  

PubMed Central

As one of the effective control devices of air pollutants, the wet electrostatic precipitator (ESP) is an effective technique to eliminate acid mist and fine particles that are re-entrained in a collection electrode. However, its collection efficiency can deteriorate, as its operation is subject to water-induced corrosion of the collection electrode. To overcome this drawback, we modified the wet ESP system with the installation of a PVC dust precipitator wherein water is supplied as a replacement of the collection electrode. With this modification, we were able to construct a compact wet ESP with a small specific collection area (SCA, 0.83?m2/(m3/min)) that can acquire a high collection efficiency of fine particles (99.7%).

Kim, Jong-Ho; Yoo, Hee-Jung; Hwang, You-Seong; Kim, Hyeok-Gyu

2012-01-01

59

Removal of particulate matter in a tubular wet electrostatic precipitator using a water collection electrode.  

PubMed

As one of the effective control devices of air pollutants, the wet electrostatic precipitator (ESP) is an effective technique to eliminate acid mist and fine particles that are re-entrained in a collection electrode. However, its collection efficiency can deteriorate, as its operation is subject to water-induced corrosion of the collection electrode. To overcome this drawback, we modified the wet ESP system with the installation of a PVC dust precipitator wherein water is supplied as a replacement of the collection electrode. With this modification, we were able to construct a compact wet ESP with a small specific collection area (SCA, 0.83 m(2)/(m(3)/min)) that can acquire a high collection efficiency of fine particles (99.7%). PMID:22577353

Kim, Jong-Ho; Yoo, Hee-Jung; Hwang, You-Seong; Kim, Hyeok-Gyu

2012-01-01

60

WET SOLIDS FLOW ENHANCEMENT  

SciTech Connect

The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and may require accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained.

Hugo S. Caram; Natalie Foster

1998-03-30

61

WET SOLIDS FLOW ENHANCEMENT  

SciTech Connect

The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and requires accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained.

Hugo S. Caram; Natalie Foster

1999-07-01

62

Enzymatic Hydrolysis and Ethanol Fermentation of High Dry Matter Wet-Exploded Wheat Straw at Low Enzyme Loading  

NASA Astrophysics Data System (ADS)

Wheat straw was pretreated by wet explosion using three different oxidizing agents (H2O2, O2, and air). The effect of the pretreatment was evaluated based on glucose and xylose liberated during enzymatic hydrolysis. The results showed that pretreatment with the use of O2 as oxidizing agent was the most efficient in enhancing overall convertibility of the raw material to sugars and minimizing generation of furfural as a by-product. For scale-up of the process, high dry matter (DM) concentrations of 15-20% will be necessary. However, high DM hydrolysis and fermentation are limited by high viscosity of the material, higher inhibition of the enzymes, and fermenting microorganism. The wet-explosion pretreatment method enabled relatively high yields from both enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) to be obtained when performed on unwashed slurry with 14% DM and a low enzyme loading of 10 FPU/g cellulose in an industrial acceptable time frame of 96 h. Cellulose and hemicellulose conversion from enzymatic hydrolysis were 70 and 68%, respectively, and an overall ethanol yield from SSF was 68%.

Georgieva, Tania I.; Hou, Xiaoru; Hilstrøm, Troels; Ahring, Birgitte K.

63

COMBINED USE OF ION EXCHANGE RESINS AND GRANULAR ACTIVATED CARBON FOR THE CONTROL OF ORGANIC MATTER AND DISINFECTION BY PRODUCTS  

EPA Science Inventory

The use of anion exchange resin as a pretreatment step to granular activated carbon is evaluated. erformance is evaluated by DOC, SAC, TOXFP, and THMFP parameters. hio River water and Palm Beach groundwater are used. he results show that resin pretreatment is significant in exten...

64

Mechanisms for slow strengthening in granular materials  

Microsoft Academic Search

Several mechanisms cause a granular material to strengthen over time at low applied stress. The strength is determined from the maximum frictional force Fmax experienced by a shearing plate in contact with wet or dry granular material after the layer has been at rest for a waiting time tau. The layer strength increases roughly logarithmically with tau only if a

W. Losert; J.-C. Géminard; S. Nasuno; J. P. Gollub

2000-01-01

65

Dissolved Organic Matter as a Mechanism for Carbon Stabilization at Depth in Wet Tropical Forest Volcanic Soils  

NASA Astrophysics Data System (ADS)

Dissolved organic matter (DOM) plays an important role in many biological and chemical processes in soils. Our understanding of the types of plant and microbially-derived organic matter that accumulate in soils and the mechanisms responsible for their transformation and stabilization is still limited. In particular, we know very little about how microbial activity and water movement contribute to the production of DOM and the formation of stable C in soils. In well-drained soils under wet climates, DOM is potentially a primary pathway for the transport of C from the surface litter layers and the zones of highest microbial activity to deeper horizons in the soil profile where the potential for long-term storage increases. The mechanisms for long-term stabilization of organic C in deep mineral horizons include an accumulation of chemically recalcitrant C, strong sorption of soluble and otherwise labile C to mineral and/or metals making them inaccessible to decomposers, and microenvironmental conditions (low pH, low O2) which result in incomplete decomposition and persistence of labile C. Although most work to date has focused on the role of dissolved organic C and N (DOC and DON) in the C and N cycles of temperate forests, DOM fluxes may be even more important in forests in the wet tropics, where high rainfall and high primary productivity could lead to greater DOM production. In order to address the role of DOC in the transport and stabilization of C in mineral horizons, we are studying DOC production, transformation, and loss pathways in volcanic soils dominated by highly reactive, non-crystalline minerals (allophane). We are quantifying flux and solute concentrations (C, N, cations, anions) in rainwater, throughfall, and in soil water. We have installed tension and zero tension lysimeters throughout sequentially deeper organic and mineral horizons in an intermediate aged soil (ca. 350k years) under wet (ca. 3000 mm mean annual rainfall) native tropical forest cover on the island of Hawai'i. Previous research has measured soil organic C with very long mean residence times in the deeper mineral horizons at similar sites. Our study is focused on identifying the source of this highly stabilized C and the role of preferential water flow-paths in the vertical transport of C and nutrients. The soil's strongly blocky structure facilitates the downward movement of DOM to lower horizons where it comes in contact with allophane and is potentially sorbed. Through field sampling and laboratory manipulations, we will identify the zones of greatest DOC production and removal. Using separation by column chromatography (XAD resins), specific UV-absorbance, 13C-NMR, and microbial bioavailability assays, we will describe differences in the chemical composition of the organic material in solution amd solid-phase with depth.

Marin-Spiotta, E.; Kramer, M. G.; Chadwick, O. A.

2007-12-01

66

Bioturbation and dissolved organic matter enhance contaminant fluxes from sediment treated with powdered and granular activated carbon.  

PubMed

Sediment amendment with activated carbon (AC) is a promising technique for in situ sediment remediation. To date it is not clear whether this technique sufficiently reduces sediment-to-water fluxes of sediment-bound hydrophobic organic chemicals (HOCs) in the presence of bioturbators. Here, we report polychlorobiphenyl (PCB) pore water concentrations, fluxes, mass transfer coefficients, and survival data of two benthic species, for four treatments: no AC addition (control), powdered AC addition, granular AC addition and addition and subsequent removal of GAC (sediment stripping). AC addition decreased mass fluxes but increased apparent mass transfer coefficients because of dissolved organic carbon (DOC) facilitated transport across the benthic boundary layer (BBL). In turn, DOC concentrations depended on bioturbator activity which was high for the PAC tolerant species Asellus aquaticus and low for AC sensitive species Lumbriculus variegatus. A dual BBL resistance model combining AC effects on gradients, DOC facilitated transport and biodiffusion was evaluated against the data and showed how the type of resistance differs with treatment and chemical hydrophobicity. Data and simulations illustrate the complex interplay between AC and contaminant toxicity to benthic organisms and how differences in species tolerance affect mass fluxes from sediment to the water column. PMID:23590290

Kupryianchyk, D; Noori, A; Rakowska, M I; Grotenhuis, J T C; Koelmans, A A

2013-05-21

67

WET SOLIDS FLOW ENHANCEMENT  

SciTech Connect

The elastic modulus E of wet granular material was found to be of the order of 0.25 MPa, this value does not compare well with the value predicted for a cubic array of spheres under Hertzian contact were the predicted values were in the order of 250 MPa . The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and requires accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained. New information was found to support the experimental finding and a first theory to explain the very small elastic modulus is presented. A new model based on the used of the finite element method is being developed.

Hugo S. Caram; Natalie Foster

1999-03-30

68

Large-scale spatial structures in dense granular flows  

Microsoft Academic Search

Granular materials exhibit a wide spectrum of behavior ranging from gaseous to liquid to solid. Remarkably, all of these phases of granular matter respond to external stimuli in a manner notably different from ordinary fluids and solids. Spatial inhomogeneities are thought to play a crucial role in determining the macroscopic properties of these systems. In static granular piles, the inhomogeneous

Bulbul Chakraborty

2004-01-01

69

Mechanisms for slow strengthening in granular materials  

Microsoft Academic Search

Several mechanisms cause a granular material to strengthen over time at low\\u000aapplied stress. The strength is determined from the maximum frictional force\\u000aF_max experienced by a shearing plate in contact with wet or dry granular\\u000amaterial after the layer has been at rest for a waiting time \\\\tau. The layer\\u000astrength increases roughly logarithmically with \\\\tau -only- if a

W. Losert; J.-C. Géminard; S. Nasuno; J. P. Gollub

2000-01-01

70

Dissolved Organic Matter as a Mechanism for Carbon Stabilization at Depth in Wet Tropical Forest Volcanic Soils  

Microsoft Academic Search

Dissolved organic matter (DOM) plays an important role in many biological and chemical processes in soils. Our understanding of the types of plant and microbially-derived organic matter that accumulate in soils and the mechanisms responsible for their transformation and stabilization is still limited. In particular, we know very little about how microbial activity and water movement contribute to the production

E. Marin-Spiotta; M. G. Kramer; O. A. Chadwick

2007-01-01

71

The effect of moisture content on the explosively driven fragmentation of wet sand  

NASA Astrophysics Data System (ADS)

A comprehensive model is established to account for the instability onset of rapidly expanding granular shells subject to the explosion loadings generated by the detonation of the central explosives. The moisture content strongly influences the shock interactions in the wet particle beds and the ensuing evolvement of the granular compacts. A material model for granular materials which can account for the degree of saturation was incorporated into a nonlinear dynamic simulation program to investigate the moisture effect on the shock responses of wet granular materials. In conjunction with our instability model, the predicted instability diameters of the expanding dry/wet granular shells are in a good agreement with the experimental results. Particularly the postponed instability onset of the wet granular shell found both experimentally and analytically can largely be attributed to the significantly greater kinetic energy obtained by wet particles thanks to less energy of shock wave consumed in compacting the granular material.

Xue, K.

2014-05-01

72

Technique Destroys Organic Matter and Facilitates Trace Element Analysis: Recycled wet-ash method uses a single acid.  

National Technical Information Service (NTIS)

This citation summarizes a one-page announcement of technology available for utilization. An improved laboratory apparatus and technique employ only one acid to destroy all organic matter contained within an organic matrix so that trace inorganic elements...

1981-01-01

73

Granular Materials  

NSDL National Science Digital Library

A granular material can be defined as any loosely interacting collection of (usually) solid particles.1 Depending on the conditions, a granular material can be best described as a solid, or as a fluid, or as a gas, or in some case not adequately as any of these, which makes this both an interesting and difficult field of study. The behavior of granular materials is something that is encountered frequently in all aspects of everyday life. Some of the situations include grain silos, trash piles, sand & salt that is used for building and on winter roads, snow (as in avalanches), and mixing of various food and medical supplies, such as pharmaceuticals. A granular material would be generally defined as consisting of discrete units of a solid material that neither chemically interact, nor otherwise strongly cohere together. Thus, the arrangement and motion of these materials is neither that of a solid (in which the various parts are tightly bound together) nor that of a fluid (in which the parts may easily flow over & around other parts). The size of the particles, per se, is not important -- the phenomenology is similar with very fine grains (such as powders) and with rather large âgrainsâ (such as cannonballs). The possibility of using various sizes of grains allows for some interesting research proposals covering several length scales. For many experiments the size of the container needs to be âlargeâ compared to the grain size (typically a factor of 100 could be considered as âlargeâ), so that end effects are indeed restricted only to the ends. This of course means also a large number of particles â easy with things like sand, less so with things like marbles (1003 marbles can be quite massive!)

Dolan, Paul

2012-03-08

74

Nonlinear susceptibilities of granular matter  

NASA Astrophysics Data System (ADS)

We discuss the nonlinear behavior of a random composite material in which current density and electric field are related by J=?E+a||E||2E, with ? and a position dependent. To first order in the nonlinear coefficient a, the effective nonlinear conductivity of the composite material is shown to be expressible as ae=/E40, where E0 is the magnitude of the applied field, the angular brackets denote a volume average, and E is the electric field in the linear limit (a=0). To the same order, the coefficient ae is also shown to be related to the mean-square conductivity fluctuation in an analogous problem in which the composite is linear but the conductivity fluctuates: The connection is ?ae=V(??rms)2, where V is the volume, ??rms is the rms conductivity fluctuation, and ? is a constant with dimensions of energy. In the low-concentration regime (p<<1, where p is the concentration of nonlinear material), an expression for ae is derived which is exact to first order in p. The ratio ae/?2e (where ?e is the conductivity of the composite) is shown to diverge near the percolation threshold for both a metal-insulator composite and a normal-metal-perfect-conductor composite; the power law characterizing the divergence is estimated. The results are generalized to nonlinear dielectric response at finite frequencies. At low concentrations, the cubic nonlinear dielectric susceptibility is found to be ?e=p?i||3?h/ (?i+2?h)||2[3?h/(?/i+2?h)]2 (plus terms of higher order in ?i), where p is the volume fraction of inclusion, ?i and ?h are the dielectric constants of the nonlinear inclusion and of the host, and ?i is the nonlinear electric susceptibility of the inclusion. This expression becomes very large near a Maxwell-Garnett resonance, in analogy with similar local-field effects in surface-enhanced Raman scattering.

Stroud, D.; Hui, P. M.

1988-05-01

75

Spectroscopic and wet chemical characterization of solid waste organic matter of different age in landfill sites, southern Germany.  

PubMed

Landfill sites are potential sources of hazardous emissions by degradation and transformation processes of waste organic matter. Its chemical composition and microbial degradability are key factors for risk management, after-care, and estimation of potential emissions. The aim of the study is to provide information about composition and extent of transformation of waste organic matter in four landfill sites in Bavaria, Southern Germany by means of (13)C NMR spectroscopy, acid-hydrolyzable carbohydrates, chloroform-methanol extractable lipids, acid-hydrolyzable proteins, and lignin compounds after CuO oxidation. Ten samples of about 20 to 25 yr, 15 to 20 yr, and 5 to 10 yr of deposition each were taken at 2 m depth intervals by grab drilling till 10-m depth. Increasing temperatures from about 15 degrees C at 2-m depth to >40 degrees C at 10-m depth are found at some of the sites, representing optimum conditions for mesophile methane bacteria. Moisture contents of 160 to 310 g kg(-1) (oven dry), however, provide limiting conditions for anaerobic biodecay. Spectroscopic and chemical variables generally indicate a low extent of biodegradation and transformation at all sites despite a considerable heterogeneity of the samples. Independent of the time and depth of deposition more than 50% of the carbohydrate fraction of the waste organic matter provide a high potential for methane emissions and on-site energy production. There was no significant accumulation of long-chain organic and aromatic compounds, and of lignin degradation products even after more than 25 yr of rotting indicating higher extent of decomposition or stabilization of the waste organic matter. Installation of seepage water cleaning and recirculation systems are recommended to increase suboptimal moisture contents with respect to microbial methanogenesis, energy production, and long-term stabilization of municipal solid waste. PMID:18178887

Bäumler, Rupert; Kögel-Knabner, Ingrid

2008-01-01

76

Matter  

NSDL National Science Digital Library

What is matter? All matter we see and can not see is made of atoms. Matter is affected by heat. What is an atom? Molecules? Zoom! All about atoms. Zoom! Atoms arranged in solids. Atomic Arrangements in Solids Atoms and electrons. Atoms and electrons Smaller than electrons are Quarks. Quarks: Inside the Atom What holds a molecule together? What Holds a Molecule Together? The Periodic table Periodic Table What is matter? What is Matter? Methods of heat transfer. Methods of Heat Transfer ...

Mcnees, Mrs.

2010-11-16

77

Dilatancy in slow granular flows.  

PubMed

When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counterintuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed, therefore increasing the amount of porous space. Although widely called upon in areas such as soil mechanics and geotechnics, a deeper understanding of this principle is constrained by the lack of analytical tools to study this behavior. Using x-ray radiography, we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behavior. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates, however, the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected. PMID:19658906

Kabla, Alexandre J; Senden, Tim J

2009-06-01

78

Dilatancy in Slow Granular Flows  

NASA Astrophysics Data System (ADS)

When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counterintuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed, therefore increasing the amount of porous space. Although widely called upon in areas such as soil mechanics and geotechnics, a deeper understanding of this principle is constrained by the lack of analytical tools to study this behavior. Using x-ray radiography, we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behavior. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates, however, the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected.

Kabla, Alexandre J.; Senden, Tim J.

2009-06-01

79

Distribution and disinfection of bacterial loadings associated with particulate matter fractions transported in urban wet weather flows.  

PubMed

Urban runoff is a resource for reuse water. However, runoff transports indicator and pathogenic organisms which are mobilized from sources of fecal contamination. These organisms are entrained with particulate matter (PM) that can serve as a mobile substrate for these organisms. Within a framework of additional treatment for reuse of treated runoff which requires the management of PM inventories in unit operations and drainage systems there is a need to characterize organism distributions on PM and the disinfection potential thereof. This study quantifies total coliform, Escherichia coli, fecal streptococcus, and enterococcus generated from 25 runoff events. With the ubiquity and hetero-dispersivity of PM in urban runoff this study examines organism distributions for suspended, settleable and sediment PM fractions differentiated based on PM size and transport functionality. Hypochlorite is applied in batch to elaborate inactivation of PM-associated organisms for each PM fraction. Results indicate that urban runoff bacterial loadings of indicator organisms exceed U.S. wastewater reuse, recreational contact, and Australian runoff reuse criteria as comparative metrics. All monitored events exceeded the Australian runoff reuse criteria for E. coli in non-potable residential and unrestricted access systems. In PM-differentiated events, bacteriological mobilization primarily occurred in the suspended PM fraction. However, sediment PM shielded PM-associated coliforms at all hypochlorite doses, whereas suspended and settleable PM fractions provide less shielding resulting in higher inactivation by hypochlorite. PMID:22244969

Dickenson, Joshua A; Sansalone, John J

2012-12-15

80

Convection in Granular Material Based on Geometry  

NASA Astrophysics Data System (ADS)

Grain, gravel, and many powders are common examples of granular materials. The dynamics of these materials are important in many industrial processes. Although the understanding of these materials is important to many fields, there is not a comprehensive understanding of granular materials. The paper, “Vibration-Induced Size Separation in Granular Media: The Convection Connection,” by James B. Knight, H. M. Jaeger, and Sidney R. Nagel, will be used as an outline to begin and improve on the idea of convection in granular materials. Their experimental research supports the idea that convection is seen in a vertically vibrated container filled with different sized spherical granular material. This can be seen as the largest spheres rise to the top of the granular material, which is contrary to that seen in other states of matter such as fluids and gases, where the particles are distributed according to density. This experiment will attempt to reproduce and improve on the findings of Knight, Jaeger, and Nagel by vertically shaking different shaped and sized materials in a cylindrical and a triangular shaped container in order to gain a greater understanding of the physical characteristics of convection in granular materials.

Holloman, Ryan; Galovich, Cynthia

2002-04-01

81

Tensile strength of wet granula materials  

Microsoft Academic Search

The dimensionless tensile strength ?d\\/? of wet granular materials with saturation levels in the plateau region of the pendular state was correlated with the void fraction of the agglomerate. The correlation fitted well with experimental measurements carried out on glass beads of diameter 93 ?m and with literature data, and was an improvement over the traditional Rumpf model. The tensile

Patrice Pierrat; Hugo S. Caram

1997-01-01

82

Matter  

NSDL National Science Digital Library

This self-contained module on matter includes a range of fun activities that students can perform in the classroom and at home with family members. They impart important concepts such as observation, identification, measurement, and differentiation.

Science, Houghton M.

83

Granular Volcano Group  

NSDL National Science Digital Library

S'bastien Dartevelle, a Ph.D. student at Michigan Tech, created this Web site devoted to the understanding of "granular flows, granular processes, fluid dynamic, supercomputer modeling, and grain-size analysis of Volcanology, Geophysics, and Physics." Providing challenging materials in an accurate and simple manner, students can easily learn about topics including granular theory and granular medium. Users will find essential facts about viscous phenomenon in the newly added link, All I Wanna Know 'bout Viscous Stress. Educators and students can view the Plinian Cloud simulations. The author also provides mathematical equations, atmospheric profiles, and much more.

84

Granular Volcano Group  

NSDL National Science Digital Library

Sébastien Dartevelle, a Ph.D. student at Michigan Tech, created this Web site devoted to the understanding of "granular flows, granular processes, fluid dynamic, supercomputer modeling, and grain-size analysis of Volcanology, Geophysics, and Physics." Providing challenging materials in an accurate and simple manner, students can easily learn about topics including granular theory and granular medium. Users will find essential facts about viscous phenomenon in the newly added link, All I Wanna Know 'bout Viscous Stress. Educators and students can view the Plinian Cloud simulations. The author also provides mathematical equations, atmospheric profiles, and much more.

Dartevelle, Sãâ©bastien

2007-10-19

85

PREFACE: Wetting: introductory note  

NASA Astrophysics Data System (ADS)

The discovery of wetting as a topic of physical science dates back two hundred years, to one of the many achievements of the eminent British scholar Thomas Young. He suggested a simple equation relating the contact angle between a liquid surface and a solid substrate to the interfacial tensions involved [1], ?lg cos ? = ?sg - ?sl (1) In modern terms, ? denotes the excess free energy per unit area of the interface indicated by its indices, with l, g and s corresponding to the liquid, gas and solid, respectively [2]. After that, wetting seems to have been largely ignored by physicists for a long time. The discovery by Gabriel Lippmann that ? may be tuned over a wide range by electrochemical means [3], and some important papers about modifications of equation~(1) due to substrate inhomogeneities [4,5] are among the rare exceptions. This changed completely during the seventies, when condensed matter physics had become enthusiastic about critical phenomena, and was vividly inspired by the development of the renormalization group by Kenneth Wilson [6]. This had solved the long standing problem of how to treat fluctuations, and to understand the universal values of bulk critical exponents. By inspection of the critical exponents of the quantities involved in equation~(1), John W Cahn discovered what he called critical point wetting: for any liquid, there should be a well-defined transition to complete wetting (i.e., ? = 0) as the critical point of the liquid is approached along the coexistence curve [7]. His paper inspired an enormous amount of further work, and may be legitimately viewed as the entrance of wetting into the realm of modern physics. Most of the publications directly following Cahn's work were theoretical papers which elaborated on wetting in relation to critical phenomena. A vast amount of interesting, and in part quite unexpected, ramifications were discovered, such as the breakdown of universality in thin film systems [8]. Simultaneously, a number of very specific and quantitative predictions were put forward which were aimed at direct experimental tests of the developed concepts [9]. Experimentally, wetting phenomena proved to be a rather difficult field of research. While contact angles seem quite easy to measure, deeper insight can only be gained by assessing the physical properties of minute amounts of material, as provided by the molecularly thin wetting layers. At the same time, the variations in the chemical potential relevant for studying wetting transitions are very small, such that system stability sometimes poses hard to solve practical problems. As a consequence, layering transitions in cryogenic systems were among the first to be thoroughly studied [10] experimentally, since they require comparably moderate stability. First-order wetting transitions were not observed experimentally before the early nineties, either in (cryogenic) quantum systems [11,12] or in binary liquid mixtures [13,14]. The first observation of critical wetting, a continuous wetting transition, in 1996 [15] was a major breakthrough [16]. In the meantime, a detailed seminal paper by Pierre Gilles de Gennes published in 1985 [17] had spurred a large number of new research projects which were directed to wetting phenomena other than those related to phase transitions. More attention was paid to non-equilibrium physics, as it is at work when oil spreads over a surface, or a liquid coating beads off (`dewets') from its support and forms a pattern of many individual droplets. This turned out to be an extremely fruitful field of research, and was more readily complemented by experimental efforts than was the case with wetting transitions. It was encouraging to find effects analogous to layering (as mentioned above) in more common systems such as oil films spreading on a solid support [18,19]. Long standing riddles such as the divergence of dissipation at a moving contact line were now addressed both theoretically and experimentally [20,21]. However, the requirements concerning resolution of the measurements, as well as the sta

Herminghaus, S.

2005-03-01

86

Glazings with granular aerogel  

Microsoft Academic Search

Double glazing units filled with granular aerogel open up new applications in the fields of daylighting systems and passive solar architecture. Silica aerogel has ideal characteristics for solar thermal applications. High transparency for solar radiation is combined with extremely low thermal conductivity. The chemical company BASF (D) is developing a granular form of aerogel, which will be introduced to the

Joerg J. Dengler; Volker Wittwer

1994-01-01

87

Gravity and Granular Materials  

NASA Technical Reports Server (NTRS)

We describe experiments that probe a number of different types of granular flow where either gravity is effectively eliminated or it is modulated in time. These experiments include the shaking of granular materials both vertically and horizontally, and the shearing of a 2D granular material. For the shaken system, we identify interesting dynamical phenomena and relate them to standard simple friction models. An interesting application of this set of experiments is to the mixing of dissimilar materials. For the sheared system we identify a new kind of dynamical phase transition.

Behringer, R. P.; Hovell, Daniel; Kondic, Lou; Tennakoon, Sarath; Veje, Christian

1999-01-01

88

Hysteresis and competition between disorder and crystallization in granular flow  

NASA Astrophysics Data System (ADS)

Granular materials can behave as analogs of solids, liquids, or gases, yet they exhibit phenomena which markedly distinguish them from ordinary states of matter. Experiments on granular materials vibrated from below and sheared from above show a hysteretic freezing/melting transition. Under sufficient vibration a crystallized state is observed, which can be melted by sufficient shear, yet both of these processes can be considered as ``heating'' the granular material. The critical line for this transition coincides with equal kinetic energies for vibration and shear. A linear relation between pressure and volume exists for a continuum of partially and/or intermittently melted states over a range of parameters.

Daniels, Karen E.

2004-11-01

89

Hydrodynamics of soft active matter  

NASA Astrophysics Data System (ADS)

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are “dry” systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or “wet” systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.

Marchetti, M. C.; Joanny, J. F.; Ramaswamy, S.; Liverpool, T. B.; Prost, J.; Rao, Madan; Simha, R. Aditi

2013-07-01

90

Swimming in granular media  

NASA Astrophysics Data System (ADS)

A class of reptiles known as sand swimmers adapts to hot environments by submerging beneath desert sands during the day and so provide a unique probe into the dynamics of intruders in granular beds. To understand the mechanism for swimming in an otherwise solid bed, we study a simple model of periodic contraction and extension of large intruders in a granular bed. Using an event-driven simulation, we find optimal conditions that idealized swimmers must use to critically fluidize a sand bed so that it is rigid enough to support a load when needed, but fluid enough to permit motion with minimal resistance. Swimmers—or other intruders—that agitate the bed too rapidly produce large voids that prevent traction from being achieved, while swimmers that move too slowly cannot travel before the bed resolidifies around them, i.e., the swimmers locally probe the fundamental time scale in a granular packing.

Shimada, Takashi; Kadau, Dirk; Shinbrot, Troy; Herrmann, Hans J.

2009-08-01

91

Swimming in granular media.  

PubMed

A class of reptiles known as sand swimmers adapts to hot environments by submerging beneath desert sands during the day and so provide a unique probe into the dynamics of intruders in granular beds. To understand the mechanism for swimming in an otherwise solid bed, we study a simple model of periodic contraction and extension of large intruders in a granular bed. Using an event-driven simulation, we find optimal conditions that idealized swimmers must use to critically fluidize a sand bed so that it is rigid enough to support a load when needed, but fluid enough to permit motion with minimal resistance. Swimmers-or other intruders-that agitate the bed too rapidly produce large voids that prevent traction from being achieved, while swimmers that move too slowly cannot travel before the bed resolidifies around them, i.e., the swimmers locally probe the fundamental time scale in a granular packing. PMID:19792063

Shimada, Takashi; Kadau, Dirk; Shinbrot, Troy; Herrmann, Hans J

2009-08-01

92

Machine Learning in Granular Computing  

Microsoft Academic Search

Main purpose of the Granular Computing (GrC) is to find a novel way to acquire knowledge for huge orderless very high dimensional\\u000a perception information. Obviously, such kind Granular Computing (GrC) has close relationship with machine learning. In this\\u000a paper, we try to study the machine learning under the point of view of Granular Computing (GrC). Granular Computing (GrC)\\u000a should contain

Hong Hu; Zhongzhi Shi

2009-01-01

93

Spreading of triboelectrically charged granular matter.  

PubMed

We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures. PMID:24919483

Kumar, Deepak; Sane, A; Gohil, Smita; Bandaru, P R; Bhattacharya, S; Ghosh, Shankar

2014-01-01

94

Spreading of triboelectrically charged granular matter  

PubMed Central

We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures.

Kumar, Deepak; Sane, A.; Gohil, Smita.; Bandaru, P. R.; Bhattacharya, S.; Ghosh, Shankar

2014-01-01

95

Rainwater Channelization and Infiltration in Granular Media  

NASA Astrophysics Data System (ADS)

We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-2D experimental set-up composed of a random close packing of mono-disperse glass beads. We determine effects of grain diameter and surface wetting properties on the formation and infiltration of water channels. For hydrophilic granular media, rainwater initially infiltrates a shallow top layer of soil creating a uniform horizontal wetting front before instabilities occur and grow to form water channels. For hydrophobic media, rainwater ponds on the soil surface rather than infiltrates and water channels may still occur at a later time when the hydraulic pressure of the ponding water exceeds the capillary repellency of the soil. We probe the kinetics of the fingering instabilities that serve as precursors for the growth and drainage of water channels. We also examine the effects of several different methods on improving rainwater channelization such as varying the level of pre-saturation, modifying the soil surface flatness, and adding superabsorbent hydrogel particles.

Mikhail Cejas, Cesare; Wei, Yuli; Barrois, Remi; Durian, Douglas J.; Dreyfus, Remi

2013-03-01

96

Performance of aerobic granular sludge in different bioreactors.  

PubMed

Inoculated sludge from the Brewery wastewater treatment plant was cultured in a sequencing batch reactor (SBR). The granular sludge was then used to process the artificial simulation wastewater to compare the performance and efficiency of the granular sludge in organic matter removal by using SBR and granular membrane bioreactor (GMBR). Results showed that the granular sludge in the SBR exhibited desirable characteristics and good removal efficiency. The mixed liquor suspended solids (MLSS) and the sludge volume index (SVI) were approximately 2.56 g/L and 78.13 mL/g, respectively, and it exhibited a satisfactory settling ability. The removal efficiency of the resulting chemical oxygen demand (COD), NH3-N and total phosphorus (TP) reached 89.35%, 96.49% and 83.76%, respectively. The removal efficiency of both nitrate nitrogen and total nitrogen (TN) reached 90%. The performance of the granular sludge as well as the removal efficiency of the organic matter in the GMBR was subsequently observed. Results showed that the process influenced the characteristics and microbial biomass of the granular sludge. The SVI and the MLSS were about 175.82 mL/g and 1.14 g/L, respectively. The removal efficiency of COD and TP increased to 93.17% and 90.42%, respectively. The removal efficiency of NH3-N was slightly affected, whereas that of both nitrate nitrogen and TN increased to 95%. In this study, the physical properties and the removal efficiency of granular sludge in different bioreactors were compared. The comparison demonstrated that granulation membrane bioreactors perform more efficiently compared with SBR in wastewater treatment for organic matter removal. PMID:24645477

Zhao, Xia; Chen, Zhonglin; Shen, Jimin; Wang, Xiaochun

2014-01-01

97

GRANULAR ACTIVATED CARBON INSTALLATIONS  

EPA Science Inventory

This paper presents a compilation and summary of design criteria, performance, and cost data from 22 operating municipal and industrial granular activated carbon (GAC) installations that treat water and wastewater or process food and beverage products. Guidance for using this inf...

98

Boosting of granular models  

Microsoft Academic Search

In this study, we are concerned with the design of granular modeling being originally proposed by Pedrycz and Vasilakos. The enhancement of the development process comes in the form of the boosting mechanism applied to the generic model. In comparison with the original topology of the model studied so far, we augment it by a bias term and investigate its

Witold Pedrycz; Keun-Chang Kwak

2006-01-01

99

EVALUATION OF WET AND DRY DISTILLERS GRAINS AND WET AND DRY CORN GLUTEN FEEDS FOR RUMINANTS  

Microsoft Academic Search

Summary Eight trials were conducted to evaluate wet and dry distillers grains (WDG and DDG) and wet and dry corn gluten feeds (WCGF and DCGF) as feed sources for cattle and sheep. Data from in situ trial 1 indicated that dry matter (DM) of WCGF and DCGF disappeared at .a faster rate (P<.05) than that of WDG or DDG. In

J. L. Firkins; L. L. Berger; G. C. Fahey

2010-01-01

100

Large-scale spatial structures in dense granular flows  

NASA Astrophysics Data System (ADS)

Granular materials exhibit a wide spectrum of behavior ranging from gaseous to liquid to solid. Remarkably, all of these phases of granular matter respond to external stimuli in a manner notably different from ordinary fluids and solids. Spatial inhomogeneities are thought to play a crucial role in determining the macroscopic properties of these systems. In static granular piles, the inhomogeneous stress distribution is strikingly demonstrated by the appearance of force chains. In flowing granular media, however, the nature and role of dynamical heterogeneities is not clearly understood. In a recent paper [1], we have shown that clusters of "frequently-colliding" particles appear in a dense, gravity-driven granular flow. Our simulations show increasingly large linear clusters as the flow velocity decreases. In this talk, I will explore the relationship of these clusters to dynamical heterogeneities which occur in two related systems; (a) freely cooling granular gases and (b) supercooled liquids approaching the glass transition. I will argue that the origin of the clusters is related to the mechanism of cluster formation in freely-cooling systems and their role in determining the dynamics is similar the one played by dynamical heterogeneities in glass formers. [1] Allison Ferguson, Ben Fisher and Bulbul Chakraborty, cond-mat/0301201

Chakraborty, Bulbul

2004-03-01

101

Focus on granular segregation  

NASA Astrophysics Data System (ADS)

Ordinary fluids mix themselves through thermal motions, or can be even more efficiently mixed by stirring. In contrast, granular materials such as sand often unmix when they are stirred, shaken or sheared. This granular segregation is both a practical means to separate materials in industry, and a persistent challenge to uniformly mixing them. While segregation phenomena are ubiquitous, a large number of different mechanisms have been identified and the underlying physics remains the subject of much inquiry. Particle size, shape, density and even surface roughness can play significant roles. The aim of this focus issue is to provide a snapshot of the current state of the science, covering a wide range of packing densities and driving mechanisms, from thermal-like dilute systems to dense flows.

Daniels, Karen E.; Schröter, Matthias

2013-03-01

102

Granular Crater Formation  

NASA Astrophysics Data System (ADS)

This project characterizes crater formation in a granular material by a jet of gas impinging on a granular material, such as a retro-rocket landing on the moon. We have constructed a 2D model of a planetary surface, which consists of a thin, clear box partially filled with granular materials (sand, lunar and Mars simulants...). A metal pipe connected to a tank of nitrogen gas via a solenoid valve is inserted into the top of the box to model the rocket. The results are recorded using high-speed video. We process these images and videos in order to test existing models and develop new ones for describing crater formation. A similar set-up has been used by Metzger et al.footnotetextP. T. Metzger et al. Journal of Aerospace Engineering (2009) We find that the long-time shape of the crater is consistent with a predicted catenary shape (Brandenburg). The depth and width of the crater both evolve logarithmically in time, suggesting an analogy to a description in terms of an activated process: dD/dt = A (-aD) (D is the crater depth, a and A constants). This model provides a useful context to understand the role of the jet speed, as characterized by the pressure used to drive the flow. The box width also plays an important role in setting the width of the crater.

Clark, Abe; Behringer, Robert; Brandenburg, John

2009-11-01

103

Glazings with granular aerogel  

NASA Astrophysics Data System (ADS)

Double glazing units filled with granular aerogel open up new applications in the fields of daylighting systems and passive solar architecture. Silica aerogel has ideal characteristics for solar thermal applications. High transparency for solar radiation is combined with extremely low thermal conductivity. The chemical company BASF (D) is developing a granular form of aerogel, which will be introduced to the market in the near future. The application potential of this material in window systems was tested as part of a CEC-JOULE project in co-operation with four other industrial companies and two research institutes under the leadership of the Fraunhofer-Institut fur Solare Energiesysteme (FhG-ISE) in Freiburg. A typical u-value for a double glazed window with a 16 mm thick layer of granular aerogel is 1.0 W m-2 K-1, the solar transmission for diffuse light is about 45%. Both parameters are variable over a wide range depending on the particle size distribution, thickness of the layer and choice of the filling gas. First window elements were tested in different applications. Realized installations are presented.

Dengler, Joerg J.; Wittwer, Volker

1994-09-01

104

Statistical mechanics of granular systems  

NASA Astrophysics Data System (ADS)

From a first principles theory for the behavior of smooth granular systems, we derive the form for the instantaneous dissipative force acting between two grains. The present model, which is based on the classical harmonic crystal, reproduces the dependence of the kinetic energy dissipation on the grain deformation obtained by models that assume a viscoelastic behavior (without permanent plastic deformations) during the collision. We then derive kinetic equations for the rarified granular gas from the Fokker-Planck equation that describes the time evolution of the reduced distribution function for the translational granular degrees of freedom. We obtain the inelastic dissipation rate term and calculate the time evolution of the granular temperature for the homogeneous granular gas. We also derive kinetic equations for the non-homogeneous, rarified granular gas and obtain hydrodynamic equations for the system. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Morgado, Welles A. M.

1997-11-01

105

Granular cell tumour of the larynx.  

PubMed

Granular cell tumour (GCT) of the larynx is an uncommon laryngeal tumour. It is always benign and commonly located in the posterior part of the larynx. Care must be taken to differentiate this lesion from others due to the presence of pseudo-epitheliomatous hyperplasia which overlies the GCT and may occasionally mimic squamous cell carcinoma. Therefore, histological differentiation is important because these tumours are normally managed conservatively. The origin of this tumour is a matter of debate, but most authors believe it to be neural in origin. The rarity of this tumour in the male population prompted reporting this case in the literature. PMID:9538455

Kamal, S A; Othman, E O

1998-01-01

106

Effect of cohesion on granular-fluid flows in spouted beds: PIV measurement and DEM simulations  

NASA Astrophysics Data System (ADS)

In contrast to wet granular flows, the effect of cohesion on complex granular-fluid flows is intriguing but much challenging. The liquid bridges, forming between binary particles with the addition of a small amount of liquids, might significantly change the granular-fluid system due to both cohesion and lubrication effects. In this paper, a spouted bed, among various fluidization technologies, is particularly selected as a prototypical system for studying granular-fluid flows, since it can provide a quasi-steady flow pattern of granular particles, i.e., a core of upward granular-fluid flow called the "spout" and a surrounding region of downward quasi-static granular flow called the "annulus". Firstly, using self-developed particle image velocimetery (PIV) technique, the effects of cohesion on the spout-annulus interface (namely the spout width) and on the particle velocity profiles in distinct zones are examined. Further, the discrete element method (DEM), by incorporating liquid bridge adhesion into soft-sphere model, is established and used to predict the microdynamic behavior of particles in spouted beds. Finally, based on both experiments and DEM validation, the effects on the granular patterns in these two zones are comparatively discussed.

Zhu, Runru; LI, Shuiqing; Yao, Qiang

2013-06-01

107

What is soil organic matter worth?  

PubMed

The conservation and restoration of soil organic matter are often advocated because of the generally beneficial effects on soil attributes for plant growth and crop production. More recently, organic matter has become important as a terrestrial sink and store for C and N. We have attempted to derive a monetary value of soil organic matter for crop production and storage functions in three contrasting New Zealand soil orders (Gley, Melanic, and Granular Soils). Soil chemical and physical characteristics of real-life examples of three pairs of matched soils with low organic matter contents (after long-term continuous cropping for vegetables or maize) or high organic matter content (continuous pasture) were used as input data for a pasture (grass-clover) production model. The differences in pasture dry matter yields (non-irrigated) were calculated for three climate scenarios (wet, dry, and average years) and the yields converted to an equivalent weight and financial value of milk solids. We also estimated the hypothetical value of the C and N sequestered during the recovery phase of the low organic matter content soils assuming trading with C and N credits. For all three soil orders, and for the three climate scenarios, pasture dry matter yields were decreased in the soils with lower organic matter contents. The extra organic matter in the high C soils was estimated to be worth NZ$27 to NZ$150 ha(-1) yr(-1) in terms of increased milk solids production. The decreased yields from the previously cropped soils were predicted to persist for 36 to 125 yr, but with declining effect as organic matter gradually recovered, giving an accumulated loss in pastoral production worth around NZ$518 to NZ$1239 ha(-1). This was 42 to 73 times lower than the hypothetical value of the organic matter as a sequestering agent for C and N, which varied between NZ$22,963 to NZ$90,849 depending on the soil, region, discount rates, and values used for carbon and nitrogen credits. PMID:16510699

Sparling, G P; Wheeler, D; Vesely, E-T; Schipper, L A

2006-01-01

108

Entangled Granular Media  

NASA Astrophysics Data System (ADS)

We study the geometrically induced cohesion of ensembles of granular “u particles” that mechanically entangle through particle interpenetration. We vary the length-to-width ratio l/w of the u particles and form them into freestanding vertical columns. In a laboratory experiment, we monitor the response of the columns to sinusoidal vibration (with peak acceleration ?). Column collapse occurs in a characteristic time ? which follows the relation ??exp(?/?). ? resembles an activation energy and is maximal at intermediate l/w. A simulation reveals that optimal strength results from competition between packing and entanglement.

Gravish, Nick; Franklin, Scott V.; Hu, David L.; Goldman, Daniel I.

2012-05-01

109

Shocks in rapid granular flows  

Microsoft Academic Search

The speed of a pressure wave (the speed of sound) in rapid granular flows is typically only a few centimeters per second while the collective streaming motion of the particles is on the order of meters per second. In this supersonic regime, shocks form when a granular flow encounters an obstacles. This work examines the shocks formed in three geometries:

Erin Colleen Rericha

2004-01-01

110

MEASURING GRANULARITY IN EVIDENCE THEORY  

Microsoft Academic Search

A new measure of uncertainty for evidence theory is presented. The measure of granularity is similar in form to the Shannon entropy but depends on set size as well as weight. It also has connections to the Hartley measure and the granularity measure of rough set theory.

MARK J. WIERMAN

2001-01-01

111

Triboelectric separation of granular materials  

Microsoft Academic Search

Triboelectric separation of granular materials is based on either the difference in electrical resistivity of the materials or on the difference in their effective work functions. We discuss here triboelectric separation based on different work functions of the materials. In this case, two granular materials to be separated from each other must acquire electrostatic charges of opposite polarity when tribocharged

K. B. Tennal; M. K. Mazumder; D. Lindquist; J. Zhang; F. Tendeku

1997-01-01

112

Plastic Deformation of Granular Materials.  

National Technical Information Service (NTIS)

The deformation of granular materials occurs in a variety of applications: soil dynamics; avalanch flows; grain flow in bins. Our goal in this project is to develop a more complete understanding of the mechanics of granular flow. The project consists of t...

E. B. Pitman

1989-01-01

113

Sensory and Nutritional Evaluation of Meat Loaves With and Without Granular Soy Concentrate.  

National Technical Information Service (NTIS)

Meat loaves were prepared in accordance with Armed Forces Recipe L-35 using ground meat extended with hydrated granular soy concentrate (18% protein-wet basis). The hydrated soy protein was added to the ground meat at 10 and 20% levels. The primary object...

B. M. Atwood C. A. Kubik I. C. Fossum M. V. Klicka

1982-01-01

114

Experimental studies of granular fingers  

NASA Astrophysics Data System (ADS)

A series of rotating cylinder experiments were conducted by systematically varying the cylinder aspect ratio, the particle size of the granular medium, and the percentage of cylinder volume occupied by particles. Five acrylic circular cylinders used in these experiments were of identical inner length 89.5 cm but five different inner diameters (5.3 cm, 10.2 cm, 12.7 cm, 15.3 cm, 20.3 cm). The flow phenomena observed in these experiments were rich and complicated. In particular, frontal fingers were found in most cases during the flow. A dimensional analysis was conducted to gain insight regarding the mechanisms underlying the formation of these fingers. This analysis shows that the dimensionless granular wavelength can be expressed as a function of cylinder aspect ratio, granular Reynold's number, granular Froude number, and the granular filling percentage.

Shen, Amy

2000-11-01

115

Spreading of a granular droplet.  

SciTech Connect

The influence of controlled vibrations on the granular rheology is investigated in a specifically designed experiment in which a granular film spreads under the action of horizontal vibrations. A nonlinear diffusion equation is derived theoretically that describes the evolution of the deposit shape. A self-similar parabolic shape (the granular droplet) and a spreading dynamics are predicted that both agree quantitatively with the experimental results. The theoretical analysis is used to extract effective friction coefficients between the base and the granular layer under sustained and controlled vibrations. A shear thickening regime characteristic of dense granular flows is evidenced at low vibration energy, both for glass beads and natural sand. Conversely, shear thinning is observed at high agitation.

Sanchez, I.; Raynaud, F.; Lanuza, J.; Andreotti, B.; Clement, E.; Aranson, I. S.; Materials Science Division; Univ. Simon; CNRS-ESPCI-Univ.

2007-01-01

116

Wet Weather Exposure Measures.  

National Technical Information Service (NTIS)

Accident surveillance programs require a measure of wet-pavement exposure to determine whether the wet-pavement accident rates of particular highway sections are higher or lower than expected. The research program used the results of laboratory and field ...

D. W. Harwood R. R. Blackburn B. T. Kulakowski D. F. Kibler

1988-01-01

117

Wetting Film Dynamics.  

PubMed

The spreading of a tiny macroscopic drop of a nonvolatile, completely wetting liquid over a flat solid is considered, assuming no gravitation. A liquid, in creeping, is subjected to capillary forces and van der Waals forces. This nonstationary and nonlinear problem in the dynamics of the wetting film from a droplet is studied using numerical modeling. The precursor wetting film motion is described by an evolution equation with conditions at the moving boundaries. The wetting line is regarded as an unknown boundary to be determined in the course of solution. A simplified equation for the wetting line dynamics is analyzed. The difference between the wetting line radius and a fixed (nonzero) radius is described by a diffusion time law. Results of numerical experiments show the simplified law of wetting to be valid over a wide range of spreading times (or a wide range of radii of the wetting line). Copyright 2000 Academic Press. PMID:11401342

Voinov, Oleg V.

2000-06-01

118

Enuresis (Bed-Wetting)  

MedlinePLUS

... their development. Bed-wetting is more common among boys than girls. What causes bed-wetting? A number of things ... valves in boys or in the ureter in girls or boys Abnormalities in the spinal cord A small bladder ...

119

Vulvar granular cell tumor.  

PubMed

Granular cell tumors are rare, usually benign, soft tissue neoplasms of neural origin. They occur more often in females than males, the peak age incidence is in the fourth through fifth decades. They can occur anywhere in the body with up to 15% situated in the vulva. The commonest presentation is as an asymptomatic mass. Microscopic findings are usually sufficient, but immunohistochemistry can also be helpful in confirming the diagnosis. The vulvar tumors are benign in 98% of cases with 2% reported as malignant. In this case report we describe a woman with a granular cell tumor confirmed by biopsy who underwent excision of the mass but with focal extension to the resection margin on microscopy. Our recommendation of re-excision was declined. Since it is not uncommon with these tumors to find groups of tumor cells extending beyond the macroscopic limits of growth, we conclude that it is advisable to have margins assessed intraoperatively by frozen section such that further excision can be performed for positive margins. Our patient has been followed for 18 mo without recurrence, should the tumor recur, re-excision, with frozen section control, is indicated. Recurrence rates are reported as 2%-8% with clear margins and 20% with positive margins. PMID:24303488

Rivlin, Michel E; Meeks, G Rodney; Ghafar, Mohamed A; Lewin, Jack R

2013-07-16

120

Vulvar granular cell tumor  

PubMed Central

Granular cell tumors are rare, usually benign, soft tissue neoplasms of neural origin. They occur more often in females than males, the peak age incidence is in the fourth through fifth decades. They can occur anywhere in the body with up to 15% situated in the vulva. The commonest presentation is as an asymptomatic mass. Microscopic findings are usually sufficient, but immunohistochemistry can also be helpful in confirming the diagnosis. The vulvar tumors are benign in 98% of cases with 2% reported as malignant. In this case report we describe a woman with a granular cell tumor confirmed by biopsy who underwent excision of the mass but with focal extension to the resection margin on microscopy. Our recommendation of re-excision was declined. Since it is not uncommon with these tumors to find groups of tumor cells extending beyond the macroscopic limits of growth, we conclude that it is advisable to have margins assessed intraoperatively by frozen section such that further excision can be performed for positive margins. Our patient has been followed for 18 mo without recurrence, should the tumor recur, re-excision, with frozen section control, is indicated. Recurrence rates are reported as 2%-8% with clear margins and 20% with positive margins.

Rivlin, Michel E; Meeks, G Rodney; Ghafar, Mohamed A; Lewin, Jack R

2013-01-01

121

Particle Deposition in Granular Media. Final report  

SciTech Connect

Objective is to understand aerosol deposition from gas streams flowing through granular media; this is important to the design of granular filtration systems. The following investigations were carried out: transient behavior of granular filtration of aerosols, and stochastic simulation of aerosol deposition in granular media.

Tien, C.

1992-12-31

122

Granular computing: Past, present and future  

Microsoft Academic Search

Granular computing is gradually changing from a label to a new field of study. The driving forces, the major schools of thought, and the future research directions on granular computing are examined. A triarchic theory of granular computing is outlined. Granular computing is viewed as an interdisciplinary study of human-inspired computing, characterized by structured thinking, structured problem solving, and structured

Yiyu Yao

2008-01-01

123

Granular Materials Research at NASA-Glenn  

NASA Technical Reports Server (NTRS)

This paper presents viewgraphs of granular materials research at NASA-Glenn. The topics include: 1) Impulse dispersion of a tapered granular chain; 2) High Speed Digital Images of Tapered Chain Dynamics; 3) Impulse Dispersion; 4) Three Dimensional Granular Bed Experimental Setup; 5) Magnetic Resonance Imaging of Fluid Flow in Porous Media; and 6) Net Charge on Granular Materials (NCharG).

Agui, Juan H.; Daidzic, Nihad; Green, Robert D.; Nakagawa, Masami; Nayagam, Vedha; Rame, Enrique; Wilkinson, Allen

2002-01-01

124

Pattern formation in granular and granular-fluid flows  

NASA Astrophysics Data System (ADS)

Particles and suspensions of particles in fluids are regularly used in many engineering disciplines such as catalysis and reaction engineering, environmental engineering, pharmaceutical engineering, etc. A few issues that are commonly encountered include ensuring homogeneity in pharmaceutical suspensions, predicting particle transport in atmospheric and effluent streams, and manufacturing uniform composite materials. Yet the fundamental study of particle motions in granular media or in highly concentrated granular suspensions has received little attention. Relevant issues of research interest include development of adaptive models that permit wide ranges of particle concentrations, improvement of analyses that allow physical interpretation of particle motions in any medium, of scales ranging from particle size to system size, and accurate validation of theoretical with experimental data. Given the above shortcomings, this dissertation will focus on investigating basic transport behavior of particles in fluids and developing predictive models for granular media and granular suspensions. Emphasis will be given to combining experiments with computations through examples of pattern forming phenomena in a granular medium and a dense granular-fluid system. The background motivation and the objectives of this dissertation are stated in the opening chapter 1. The next three chapters address these objectives in detail. First, chapter 2 presents experimental evidence, descriptions, and characteristics of novel patterns in a dense granular suspension. This is followed by chapter 3 in which a mean-field continuum model is derived to further elucidate the reported patterning phenomena. Chapter 4 uncovers several novel granular patterns experimentally and is concluded with a coarse-grained phenomenological model for granular surface flows. Lastly, chapter 5 closes the dissertation with conclusions and possible future directions. This work provides additional understanding and prediction of coexisting static (solid-like) and flowing (liquid-like) regions that are ubiquitous in granular flows. The mechanism of how the solid-like region differs from the fluid-like region will provide guidance for predicting related issues such as segregation and mixing of granular media, sedimentation and surface morphologies in multiphase flows and in nature.

Duong, Nhat-Hang P.

125

Experimental velocity fields and forces for a cylinder penetrating into a granular medium.  

PubMed

We present here a detailed granular flow characterization together with force measurements for the quasi-bidimensional situation of a horizontal cylinder penetrating vertically at a constant velocity in dry granular matter between two parallel glass walls. In the velocity range studied here, the drag force on the cylinder does not depend on the velocity V(0) and is mainly proportional to the cylinder diameter d. While the force on the cylinder increases with its penetration depth, the granular velocity profile around the cylinder is found to be stationary with fluctuations around a mean value leading to the granular temperature profile. Both mean velocity profile and temperature profile exhibit strong localization near the cylinder. The mean flow perturbation induced by the cylinder decreases exponentially away from the cylinder on a characteristic length ? that is mainly governed by the cylinder diameter for a large enough cylinder/grain size ratio d/d(g): ?~d/4+2d(g). The granular temperature exhibits a constant plateau value T(0) in a thin layer close to the cylinder of extension ?(T(0))~?/2 and decays exponentially far away with a characteristic length ?(T) of a few grain diameters (?(T)~3d(g)). The granular temperature plateau T(0) that scales as V(0)(2)d(g)/d is created by the flow itself from the balance between the "granular heat" production by the shear rate V(0)/? over ?(T(0)) close to the cylinder and the granular dissipation far away. PMID:23410320

Seguin, A; Bertho, Y; Martinez, F; Crassous, J; Gondret, P

2013-01-01

126

Transport theory of granular swarms.  

PubMed

The transport of trace granular gas (swarm) in a carrier granular fluid is studied by means of the Boltzmann-Lorentz kinetic equation. Time-dependent perturbation theory is used to follow the evolution of the granular swarm from an arbitrary initial distribution. A nonhydrodynamic extension of the diffusion equation is derived, with transport coefficients that are time dependent and implicitly depend on the wave vector. Transport coefficients of any order are obtained as velocity moments of the solutions of the corresponding kinetic equations derived from the Boltzmann-Lorentz equation. For the special case of the initial distribution of swarm particles, transport coefficients are identified as time derivatives of the moments of the number density. Finally the granular particle transport theory is extended by the introduction of the concept of non-particle-conserving collisions. PMID:12513480

Vrhovac, S B; Arsenovi?, D; Beli?, A

2002-11-01

127

Granularity analysis for mathematical proofs.  

PubMed

Mathematical proofs generally allow for various levels of detail and conciseness, such that they can be adapted for a particular audience or purpose. Using automated reasoning approaches for teaching proof construction in mathematics presupposes that the step size of proofs in such a system is appropriate within the teaching context. This work proposes a framework that supports the granularity analysis of mathematical proofs, to be used in the automated assessment of students' proof attempts and for the presentation of hints and solutions at a suitable pace. Models for granularity are represented by classifiers, which can be generated by hand or inferred from a corpus of sample judgments via machine-learning techniques. This latter procedure is studied by modeling granularity judgments from four experts. The results provide support for the granularity of assertion-level proofs but also illustrate a degree of subjectivity in assessing step size. PMID:23460420

Schiller, Marvin R G

2013-04-01

128

Optimized Simulation of Granular Materials  

NASA Astrophysics Data System (ADS)

Visual effects for film and animation often require simulated granular materials, such as sand, wheat, or dirt, to meet a director's needs. Simulating granular materials can be time consuming, in both computation and labor, as these particulate materials have complex behavior and an enormous amount of small-scale detail. Furthermore, a single cubic meter of granular material, where each grain is a cubic millimeter, would contain a billion granules, and simulating all such interacting granules would take an impractical amount of time for productions. This calls for a simplified model for granular materials that retains high surface detail and granular behavior yet requires significantly less computational time. Our proposed method simulates a minimal number of individual granules while retaining particulate detail on the surface by supporting surface particles with simplified interior granular models. We introduce a multi-state model where, depending on the material state of the interior granules, we replace interior granules with a simplified simulation model for the state they are in and automate the transitions between those states. The majority of simulation time can thus be focused on visible portions of the material, reducing the time spent on non-visible portions, while maintaining the appearance and behavior of the mass as a whole.

Holladay, Seth

129

Effects of cohesion on the flow patterns of granular materials in spouted beds  

NASA Astrophysics Data System (ADS)

Two-dimensional spouted bed, capable to provide both dilute granular gas and dense granular solid flow patterns in one system, was selected as a prototypical system for studying granular materials. Effects of liquid cohesion on such kind of complex granular patterns were studied using particle image velocimetry. It is seen that the addition of liquid oils by a small fraction of 10-3-10-2 causes a remarkable narrowing (about 15%) of the spout area. In the dense annulus, as the liquid fraction increases, the downward particle velocity gradually decreases and approaches a minimum where, at a microscopic grain scale, the liquid bridge reaches spherical regimes with a maximum capillarity. Viscous lubrication effect is observed at a much higher fraction but is really weak with respect to the capillary effect. In the dilute spout, in contrast to the dry grains, the wet grains have a lightly smaller acceleration in the initial 1/3 of the spout, but have a dramatically higher acceleration in the rest of the spout. We attribute the former to the additional work needed to overcome interparticle cohesion during particle entrainment at the spout-annulus interface. Then, using mass and momentum balances, the latter is explained by the relative higher drag force resulting from both higher gas velocities and higher voidages due to spout narrowing in the wet system. The experimental findings will provide useful data for the validation of discrete element simulation of cohesive granular-fluid flows.

Zhu, Runru; Li, Shuiqing; Yao, Qiang

2013-02-01

130

Effects of cohesion on the flow patterns of granular materials in spouted beds.  

PubMed

Two-dimensional spouted bed, capable to provide both dilute granular gas and dense granular solid flow patterns in one system, was selected as a prototypical system for studying granular materials. Effects of liquid cohesion on such kind of complex granular patterns were studied using particle image velocimetry. It is seen that the addition of liquid oils by a small fraction of 10(-3)-10(-2) causes a remarkable narrowing (about 15%) of the spout area. In the dense annulus, as the liquid fraction increases, the downward particle velocity gradually decreases and approaches a minimum where, at a microscopic grain scale, the liquid bridge reaches spherical regimes with a maximum capillarity. Viscous lubrication effect is observed at a much higher fraction but is really weak with respect to the capillary effect. In the dilute spout, in contrast to the dry grains, the wet grains have a lightly smaller acceleration in the initial 1/3 of the spout, but have a dramatically higher acceleration in the rest of the spout. We attribute the former to the additional work needed to overcome interparticle cohesion during particle entrainment at the spout-annulus interface. Then, using mass and momentum balances, the latter is explained by the relative higher drag force resulting from both higher gas velocities and higher voidages due to spout narrowing in the wet system. The experimental findings will provide useful data for the validation of discrete element simulation of cohesive granular-fluid flows. PMID:23496504

Zhu, Runru; Li, Shuiqing; Yao, Qiang

2013-02-01

131

Granular Superconductors and Gravity  

NASA Technical Reports Server (NTRS)

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Noever, David; Koczor, Ron

1999-01-01

132

Marginal Matter  

NASA Astrophysics Data System (ADS)

All around us, things are falling apart. The foam on our cappuccinos appears solid, but gentle stirring irreversibly changes its shape. Skin, a biological fiber network, is firm when you pinch it, but soft under light touch. Sand mimics a solid when we walk on the beach but a liquid when we pour it out of our shoes. Crucially, a marginal point separates the rigid or jammed state from the mechanical vacuum (freely flowing) state - at their marginal points, soft materials are neither solid nor liquid. Here I will show how the marginal point gives birth to a third sector of soft matter physics: intrinsically nonlinear mechanics. I will illustrate this with shock waves in weakly compressed granular media, the nonlinear rheology of foams, and the nonlinear mechanics of weakly connected elastic networks.

van Hecke, Martin

2013-03-01

133

Active microrheology of driven granular particles  

NASA Astrophysics Data System (ADS)

When pulling a particle in a driven granular fluid with constant force Fex, the probe particle approaches a steady-state average velocity v. This velocity and the corresponding friction coefficient of the probe ? =Fex/v are obtained within a schematic model of mode-coupling theory and compared to results from event-driven simulations. For small and moderate drag forces, the model describes the simulation results successfully for both the linear as well as the nonlinear region: The linear response regime (constant friction) for small drag forces is followed by shear thinning (decreasing friction) for moderate forces. For large forces, the model demonstrates a subsequent increasing friction in qualitative agreement with the data. The square-root increase of the friction with force found in [Fiege et al., Granul. Matter 14, 247 (2012), 10.1007/s10035-011-0309-9] is explained by a simple kinetic theory.

Wang, Ting; Grob, Matthias; Zippelius, Annette; Sperl, Matthias

2014-04-01

134

Granular structure determined by terahertz scattering  

NASA Astrophysics Data System (ADS)

Light scattering from particles reveals static and dynamical information about the particles and their correlations. Such methods are particularly powerful when the wavelength of the light is chosen similar to the sizes and distances of the particles. To apply scattering to investigate granular matter in particular —or other objects of similar submillimeter size— light of suitable wavelength in the terahertz regime needs to be chosen. By using a quantum cascade laser in a benchtop setup we determine the angle-dependent scattering of spherical particles as well as coffee powder and sugar grains. The scattering from single particles can be interpreted by form factors derived within the Mie theory. In addition, collective correlations can be extracted as static structure factors and compared to recent computer simulations.

Born, Philip; Rothbart, Nick; Sperl, Matthias; Hübers, Heinz-Wilhelm

2014-05-01

135

Active microrheology of driven granular particles.  

PubMed

When pulling a particle in a driven granular fluid with constant force Fex, the probe particle approaches a steady-state average velocity v. This velocity and the corresponding friction coefficient of the probe ?=Fex/v are obtained within a schematic model of mode-coupling theory and compared to results from event-driven simulations. For small and moderate drag forces, the model describes the simulation results successfully for both the linear as well as the nonlinear region: The linear response regime (constant friction) for small drag forces is followed by shear thinning (decreasing friction) for moderate forces. For large forces, the model demonstrates a subsequent increasing friction in qualitative agreement with the data. The square-root increase of the friction with force found in [Fiege et al., Granul. Matter 14, 247 (2012)] is explained by a simple kinetic theory. PMID:24827243

Wang, Ting; Grob, Matthias; Zippelius, Annette; Sperl, Matthias

2014-04-01

136

MODELED WET NITRATE DEPOSITION  

EPA Science Inventory

Modeled data on nitrate wet deposition was obtained from Dr. Jeff Grimm at Penn State Univ. Nitrate wet depostion causes acidification and eutrophication of surface water bodies. See below regarding decriptions on how original data was produced. These data will be part of futur...

137

Adsorption and wetting  

Microsoft Academic Search

Adsorption and wetting are related phenomena. In order to improve knowledge of both and their relations, experiments, thermodynamics and a theoretical interpretation have been connected, starring n-alkanes.Starting from the Gibbs adsorption equation thermodynamic relations between vapour adsorption and wetting are derived. The surface pressure of a film, formed by vapour adsorption on a solid surface, is calculated by integrating the

L. J. M. Schlangen

1995-01-01

138

Corn Wet Milling Lab  

NSDL National Science Digital Library

Description: Wet Corn Milling is an industrial process that that converts corn to a wide variety of by-products. The wet milling industry is the largest non-feed user of corn, using approximately 1 billion bushels annually. This lab looks at the separation steps in the industrial processing of corn.

Olson, Eric; Warren, Noreen

2008-10-27

139

Wet ash remover  

Microsoft Academic Search

A wet ash remover which has a trough arranged underneath the ash funnel of a boiler and is filled with quenching water. A quenching water feed and an overflow are also provided. Ash conveying equipment passes through the wet ash remover. A cooling device with quenching water circulating through it continuously, is located between the overflow and the quenching water

H. Buchmuller; B. Michelbrink

1985-01-01

140

Influence of cohesive forces on the macroscopic properties of granular assemblies  

NASA Astrophysics Data System (ADS)

The influence of cohesive forces inside a granular material is analyzed with compaction experiments. To begin, a model cohesive granular material is considered. This granular material is made of millimetric grains with a cohesion induced by an external magnetic field. Therefore, the cohesion between the grains is adjusted through the intensity of the applied magnetic field. Afterward, the cohesion induced by capillary bridges are considered. In the first study concerning capillary forces, the cohesion between neighboring grains is induced by liquid bridges in a wet granular material. The cohesiveness is tuned using different liquids having specific surface tension values. The second study performed with capillary forces concerns initially dry granular materials surrounded by a well controlled air humidity. Then, the cohesion inside the packing is controlled through the relative humidity which influence both triboelectric and capillary effects. The evolution of the parameters extracted from the compaction curves have been analyzed as a function of the cohesiveness. All the results show that the packing fraction of a pile and the compaction dynamics is strongly sensitive to cohesive forces. Therefore, the compaction measurement is a good way to characterize a powder or a granular material for R&D and quality control in industrial applications. Finally, we show that the cohesive forces play an important role when the grain size is typically below 50?m.

Lumay, Geoffroy; Fiscina, Jorge; Ludewig, Francois; Vandewalle, Nicolas

2013-06-01

141

Different Effects of Roughness (Granularity) and Hydrophobicity  

NASA Astrophysics Data System (ADS)

With thanks to Stefan Doerr and Jorge Mataix-Solera for their invitation Superhydrophobicity is an interesting effect that appears to be simple on the outset; increased surface area from roughness increases interfacial area and therefore energy loss or gain. More extreme roughness prevents total wetting, resulting in gas pockets present at the surface and a drastic change in the properties of the system. Increases in complexity of the system, by adding porosity (granularity), allowing the structures to move, varying the shape of the roughness or the composition of the liquid used often has unexpected effects. Here we will consider a few of these related to complex topography. Overhanging features are commonly used in test samples as they perform better in some tests than simple roughness. It has been shown to be a prerequisite for superoleophobic surfaces as it allows liquids to be suspended for contact angles considerably below 90°. It also allows trapping of gas in lower layers even if the first layer is flooded. This is important in soils as a fixed bed of granules behaves just like a surface with overhanging roughness. Using simple geometry it is possible to predict at what contact angle penetration will occur. Plants have some structured superhydrophobic surfaces and we have shown that some use them in conjunction with other structured surfaces to control water flows. This allows some plants to survive in difficult environments and shows us how subtly different structures interact completely differently with water. Long fibres can either cause water droplets to roll over a plant surface or halt it in its tracks. Implications of this in soils include predicting when particles will adhere more strongly to water drops and why organic fibrous material may play a greater role in the behaviour of water in soils than may be expected from the amount present. The garden snail uses a biosurfactant that is very effective at wetting surfaces and can crawl over most superhydrophobic surfaces. There are some, however, that defeat even the snail's complex slime. Looking at these surfaces in more detail reveals that some superhydrophobic surfaces are much more resistant to the effects of surfactants than others. As mentioned above, overhanging structures, such as those found in granular materials are particularly effective at suspending liquids. This does not, however, always translate to them being more effective against surfactants, unfortunately, however, surfactants are not always as effective as we would like them to be, although drops do not skate across superhydrophobic surfaces they often do not penetrate into them fully either.

Shirtcliffe, Neil; McHale, Glen; Hamlett, Christopher; Newton, Michael

2010-05-01

142

Solitary granular avalanches: stability, fingering and theoretical modeling  

NASA Astrophysics Data System (ADS)

Avalanching processes do not only occur in the air as we know of snow avalanches, mud flows and land-slides. Such events frequently happen below the see level as they take many forms from turbidity currents to thick sediment waves. In this study we report results on laboratory scale avalanche experiments taking place both in the air and under-water. In both cases a family of stable solitary erosion/deposition waves is observed [1]. At higher inclination angles, we show the existence of a long wavelength transverse instability followed by a coarsening and the onset of a fingering pattern. While the experiments strongly differ by the spatial and time scales, the agreement between the stability diagrams, the wavelengths selection and the avalanche morphology suggest a common erosion/deposition scenario. We also use these erosion/deposition waves to investigate the dynamics of granular flow and jamming in the frame work of the Partial Fluidization Theory (PFT) proposed by Aronson et al. to describe the dynamics of granular matter near jamming [2]. [1] F. Malloggi et al. Europhysics Letters, 2006, Erosion waves: Transverse instabilities and fingering 75, 825-831 [2] I. S. Aranson et al.. Transverse instability of avalanches in granular flows down an incline. Physical Review E, 2006, 73, 050302; I.S.Aronson et al., Non rheological properties of granular flows: exploring the near jamming limit, preprint (2007).

Malloggi, Florent; Andreotti, Bruno; Clément, Eric; Aronson, Igor; Tsimring, Lev

2008-03-01

143

Nonlinear Phononic Periodic Structures and Granular Crystals.  

National Technical Information Service (NTIS)

In this chapter we describe the dynamic response of nonlinear phononic structures, focusing on granular crystals as the most prominent example. The chapter begins with a brief history of nonlinear lattices and with an introduction to granular crystals. It...

C. Daraio G. Theocharis N. Boechler

2012-01-01

144

Adsorption of Methyl Tertiary Butyl Ether on Granular Zeolites: Batch and Column Studies  

PubMed Central

Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive-adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data.

Abu-Lail, Laila; Bergendahl, John A.; Thompson, Robert W.

2010-01-01

145

Shear instabilities in granular flows.  

PubMed

Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows. PMID:11797003

Goldfarb, David J; Glasser, Benjamin J; Shinbrot, Troy

2002-01-17

146

HYPERELASTIC MODELS FOR GRANULAR MATERIALS  

SciTech Connect

A continuum framework for modeling of dust mobilization and transport, and the behavior of granular systems in general, has been reviewed, developed and evaluated for reactor design applications. The large quantities of micron-sized particles expected in the international fusion reactor design, ITER, will accumulate into piles and layers on surfaces, which are large relative to the individual particle size; thus, particle-particle, rather than particle-surface, interactions will determine the behavior of the material in bulk, and a continuum approach is necessary and justified in treating the phenomena of interest; e.g., particle resuspension and transport. The various constitutive relations that characterize these solid particle interactions in dense granular flows have been discussed previously, but prior to mobilization their behavior is not even fluid. Even in the absence of adhesive forces between particles, dust or sand piles can exist in static equilibrium under gravity and other forces, e.g., fluid shear. Their behavior is understood to be elastic, though not linear. The recent “granular elasticity” theory proposes a non-linear elastic model based on “Hertz contacts” between particles; the theory identifies the Coulomb yield condition as a requirement for thermodynamic stability, and has successfully reproduced experimental results for stress distributions in sand piles. The granular elasticity theory is developed and implemented in a stand- alone model and then implemented as part of a finite element model, ABAQUS, to determine the stress distributions in dust piles subjected to shear by a fluid flow. We identify yield with the onset of mobilization, and establish, for a given dust pile and flow geometry, the threshold pressure (force) conditions on the surface due to flow required to initiate it. While the granular elasticity theory applies strictly to cohesionless granular materials, attractive forces are clearly important in the interaction of micron-sized particles; extension of the theory to account for these effects is also considered. A set of continuum models are proposed for use in the future dust transport modeling.

Humrickhouse, Paul W; Corradini, Michael L

2009-01-29

147

Initiation of immersed granular avalanches  

NASA Astrophysics Data System (ADS)

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ?0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure.

Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

2014-05-01

148

The effect of wettability on capillary fracturing in granular media  

NASA Astrophysics Data System (ADS)

During multiphase flow in a granular medium, capillary pressures can overcome cohesive forces between the grains and cause grain displacements that macroscopically resemble fracture patterns. These patterns were recently studied in experiments of air displacing water in a thin bed of glass beads, for which air is a strongly non-wetting fluid (Holtzman et al. 2012). The experiments showed that the transition from viscous fingering and capillary fingering to capillary fracturing could be predicted by a single dimensionless number called the fracturing number, which is the ratio of the capillary forces that promote grain displacements to the frictional forces that resist displacements. Here, we extend those experiments to study exclusively how the wettability of the invading fluid affects fracturing by visually observing the morphology of the pattern. As in the previous work, we inject a less viscous fluid into a thin bed of glass beads saturated with a more viscous fluid. However, we now vary the fluids to change the wettability of the invading fluid from perfectly non-wetting to wetting. We hypothesize that the emergence of fracturing can be predicted by a modified fracturing number that includes the contact angle to account for the effect of wettability on the capillary pressure. Since the contact angle is a function of the capillary number, we expect the emergence of fracturing will depend on the capillary number when the invading fluid is partially wetting.

Trojer, M.; Szulczewski, M.; Juanes, R.

2012-12-01

149

The Big Wet  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on a particular climate found in Northern Australia, known as the tropical wet and dry. This lesson goes over the 12 categories of climates, and looks at the specifics of the 'big wet', or tropical wet and dry climate. It includes objectives, materials, procedures, discussion questions, evaluation ideas, performing extensions, suggested readings, and vocabulary. There are videos available to order which complement this lesson, audio vocabulary, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

150

Characterization of Unbound Granular Materials for Pavements  

Microsoft Academic Search

This research is focused on the characterization of the mechanical behavior of unbound granular road base materials (UGMs). An extensive laboratory investigation is described, in which various methods for determination of the mechanical properties of granular materials are examined for their applicability, particularly in developing countries. Further, the mechanical behavior of unbound granular materials as a function of the moisture

A. A. Araya

2011-01-01

151

Granular computing in programming language design  

Microsoft Academic Search

The principles of granular computing have been applied in many fields. With currently renewed and fast growing of interest, it is the time to address the commonly needs for various applications of granular computing in related to programming language design. The errands of granular computing are including the extending of application domain, subdividing the problem, building of reliability features, dealing

Trong Wu

2005-01-01

152

Capturing shock waves in inelastic granular gases  

Microsoft Academic Search

Shock waves in granular gases generated by either a vertically vibrated granular layer or by hitting an obstacle at rest are treated by means of a shock capturing scheme that approximates the Euler equations of granular gas dynamics with an equation of state (EOS), introduced by Goldshtein and Shapiro ( J. Fluid Mech. 282 (1995) 75), that takes into account

Susana Serna; Antonio Marquina

2004-01-01

153

Particle deposition in granular media  

NASA Astrophysics Data System (ADS)

The purpose of the studies is aimed at obtaining a quantitative understanding of the process of deposition of aerosol particles from gas streams flowing through granular media and the formulation of a basic framework for describing the process. During the period June 1, 1988 to date, a number of investigations have been carried out including: transient behavior of granular filtration, modification of porous media model for aerosol deposition studies, stochastic simulation of particle deposition, and analysis of filter candle performance. Results of the studies are discussed separately.

Chi, Tien

154

Granular cell ameloblastoma of mandible.  

PubMed

Ameloblastoma is a neoplasm of odontogenic epithelium, especially of enamel organ-type tissue that has not undergone differentiation to the point of hard tissue formation. Granular cell ameloblastoma is a rare condition, accounting for 3-5% of all ameloblastoma cases. A 30-year-old female patient presented with the chief complaint of swelling at the right lower jaw region since 1 year. Orthopantomogram and computed tomography scan was suggestive of primary bone tumor. Histopathologically, diagnosis of granular cell ameloblastoma of right mandible was made. PMID:24943773

Jansari, Trupti R; Samanta, Satarupa T; Trivedi, Priti P; Shah, Manoj J

2014-01-01

155

Granular drag and the kinetics of jamming  

NASA Astrophysics Data System (ADS)

The first part of this thesis focuses on the study of the force exerted by a granular packing on an intruder. During impact, this force can be described by the linear combination of an inertial drag and a rate-independent frictional force that is proportional to depth. We measure the torque acting on a rod rotated perpendicular to its axis in a granular bed at steady state, and demonstrate that the resisting force is of the same form, though smaller. We then alter the hydrostatic loading on the bed by generating a homogenized airflow through the bed, and show that for horizontal motion the frictional force is due to friction acting at gravity-loaded contacts. Next we directly measure the force acting on quasistatically, vertically lowered intruders under two sets of varied conditions. First we vary the shape of the projectile in order to alter the fraction of the projectile surface that moves parallel vs perpendicular to the medium, and find that the frictional force acts primarily normal to the intruder surface. Second, we alter the hydrostatic loading as above, and confirm that gravity-loading of the grains sets the magnitude of the resisting force for quasi-static vertical motion as well. Finally, we consider the case of impact onto wet grains. We conduct conventional impact experiments wherein a spherical projectile impacts onto a granular packing with a known impact speed. We vary the liquid, impact speed, and degree of saturation, and find that the penetration depth is decreased for all wetting fractions, and that the penetration depth has a non-monotonic dependence on liquid saturation. In the fully saturated case, we recover the same scaling of penetration depth with geometry, impact speed and packing density as in the dry case, though the penetrations are shallower, suggesting a hydrodynamic contribution to the net stopping force. The second part of this thesis focuses on the kinetics of the jamming transition. In particular, we observe a dispersion of spheres sedimenting in a fluid until all grains form a packing. In a Newtonian fluid, the dispersion is roughly homogeneous in space and time except at two well-defined interfaces: a dispersion-supernatant interface, and a jamming front below which grains form a jammed packing. This system is ideal for the study of jamming kinetics because the jamming front is stationary: it moves upwards with a constant speed and shape. To characterize the concentration profile at the front, we utilize x-ray absorption to directly measure volume fraction as a function of height and time. To characterize the grain-scale dynamics across the front, we utilize a light scattering technique, speckle-visibility spectroscopy, to directly measure fluctuations of the grain velocities as a function of height and time. In order to alter the kinetics of jamming in this model system, we change the dispersion concentration, grain size, and perturb the hydrodynamic interactions between grains by using a viscoelastic fluid.

Brzinski, Theodore A., III

156

Influence of liquid bridges on the macroscopic properties of granular assemblies  

NASA Astrophysics Data System (ADS)

We present the results of two experimental studies concerning the compaction dynamics of cohesive granular materials. In the first study, the cohesion between neighboring grains is induced by capillary bridges in a wet granular material. The cohesiveness is tuned using different liquids having specific surface tension values. The second study concerns initially dry granular materials surrounded by a well controlled air humidity. Then, the cohesion inside the packing is controlled through the relative humidity which influence both triboelectric and capilary effects. For both cases, the evolution of the parameters extracted from the compaction curves (the compaction characteristic time ?, the initial and final packing fractions) have been analyzed as a function of the cohesiveness. A model, based on free volume kinetic equations and the presence of a capillary energy barrier, is able to reproduce quantitatively the experimental results (Phys. Rev. Lett. 105, 048001 (2010)).

Lumay, Geoffroy; Fiscina, Jorge; Ludewig, Francois; Vandewalle, Nicolas

2012-02-01

157

Garments, Outer (Wet Weather).  

National Technical Information Service (NTIS)

The report describes a method for evaluation of wet weather clothing operational and functional performance characteristics. Identifies supporting tests, facilities, and equipment required. Provides procedures for preoperational inspection, physical chara...

R. Rush

1972-01-01

158

WetNet operations  

NASA Technical Reports Server (NTRS)

WetNet is an interdisciplinary Earth science data analysis and research project with an emphasis on the study of the global hydrological cycle. The project goals are to facilitate scientific discussion, collaboration, and interaction among a selected group of investigators by providing data access and data analysis software on a personal computer. The WetNet system fulfills some of the functionality of a prototype Product Generation System (PGS), Data Archive and Distribution System (DADS), and Information Management System for the Distributed Active Archive Center. The PGS functionality is satisfied in WetNet by processing the Special Sensor Microwave/Imager (SSM/I) data into a standard format (McIDAS) data sets and generating geophysical parameter Level II browse data sets. The DADS functionality is fulfilled when the data sets are archived on magneto optical cartridges and distributed to the WetNet investigators. The WetNet data sets on the magneto optical cartridges contain the complete WetNet processing, catalogue, and menu software in addition to SSM/I orbit data for the respective two week time period.

Goodman, H. Michael; Smith, Matt; Lafontaine, Vada; Lafontaine, Frank; Moss, Don

1991-01-01

159

Evaluation of Granular Bed Devices.  

National Technical Information Service (NTIS)

Recent interest in dry sorption processes for SO2 removal from hot stack gases has led to investigation of the concept of a dry granular bed device used as a simultaneous SO2 sorber-flyash collector for power station flue gases. In these devices, an SO2 s...

1969-01-01

160

Shear strength of granular materials  

Microsoft Academic Search

The shear strength properties of granular materials reflecttheir inherent force and fabric anisotropy. We analyze the role of fabric and force an isotropies with respect to the critical-state shear strength. Then, a model of accessiblegeometrical states in terms of particle connectivity and contact anisotropy is presented. This mod el incorporates in a simple way the fact that, due to steric

Farhang Radjai; Emilien Azéma

2009-01-01

161

Shear strength of granular materials  

Microsoft Academic Search

The shear strength properties of granular materials reflect their inherent force and fabric anisotropy. We analyze the role of fabric and force anisotropies with respect to the critical-state shear strength. Then, a model of accessible geometrical states in terms of particle connectivity and contact anisotropy is presented. This model incorporates in a simple way the fact that, due to steric

Farhang Radjai; Emilien Azéma

2009-01-01

162

Granular Computing based cognitive computing  

Microsoft Academic Search

Human cognition is a very complicated process. Granular Computing (GrC) is a kind of new idea and new method in the artificial intelligence field to simulate the human problem solving in cognition process. In this paper, several typical cognition models are reviewed at first. A new cognition model based on the methodology of GrC, that is, the image cognition model

Guoyin Wang; Qinghua Zhang

2009-01-01

163

Mechanics of Granular Materials (MGM)  

NASA Technical Reports Server (NTRS)

The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extend derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

Alshibli, Khalid A.; Costes, Nicholas C.; Porter, Ronald F.

1996-01-01

164

Mechanics of granular materials (MGM)  

NASA Astrophysics Data System (ADS)

The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extent derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

Alshibli, Khalid A.; Costes, Nicholas C.; Porter, Ronald F.

1996-07-01

165

Fluctuations in granular media.  

PubMed

Dense slowly evolving or static granular materials exhibit strong force fluctuations even though the spatial disorder of the grains is relatively weak. Typically, forces are carried preferentially along a network of "force chains." These consist of linearly aligned grains with larger-than-average force. A growing body of work has explored the nature of these fluctuations. We first briefly review recent work concerning stress fluctuations. We then focus on a series of experiments in both two- and three-dimension [(2D) and (3D)] to characterize force fluctuations in slowly sheared systems. Both sets of experiments show strong temporal fluctuations in the local stress/force; the length scales of these fluctuations extend up to 10(2) grains. In 2D, we use photoelastic disks that permit visualization of the internal force structure. From this we can make comparisons to recent models and calculations that predict the distributions of forces. Typically, these models indicate that the distributions should fall off exponentially at large force. We find in the experiments that the force distributions change systematically as we change the mean packing fraction, gamma. For gamma's typical of dense packings of nondeformable grains, we see distributions that are consistent with an exponential decrease at large forces. For both lower and higher gamma, the observed force distributions appear to differ from this prediction, with a more Gaussian distribution at larger gamma and perhaps a power law at lower gamma. For high gamma, the distributions differ from this prediction because the grains begin to deform, allowing more grains to carry the applied force, and causing the distributions to have a local maximum at nonzero force. It is less clear why the distributions differ from the models at lower gamma. An exploration in gamma has led to the discovery of an interesting continuous or "critical" transition (the strengthening/softening transition) in which the mean stress is the order parameter, and the mean packing fraction, gamma, must be adjusted to a value gamma(c) to reach the "critical point." We also follow the motion of individual disks and obtain detailed statistical information on the kinematics, including velocities and particle rotations or spin. Distributions for the azimuthal velocity, V(theta), and spin, S, of the particles are nearly rate invariant, which is consistent with conventional wisdom. Near gamma(c), the grain motion becomes intermittent causing the mean velocity of grains to slow down. Also, the length of stress chains grows as gamma-->gamma(c). The 3D experiments show statistical rate invariance for the stress in the sense that when the power spectra and spectral frequencies of the stress time series are appropriately scaled by the shear rate, Omega, all spectra collapse onto a single curve for given particle and sample sizes. The frequency dependence of the spectra can be characterized by two different power laws, P proportional, variant omega(-alpha), in the high and low frequency regimes: alpha approximately 2 at high omega; alpha<2 at low omega. The force distributions computed from the 3D stress time series are at least qualitatively consistent with exponential fall-off at large stresses. (c) 1999 American Institute of Physics. PMID:12779852

Howell, Daniel W.; Behringer, R. P.; Veje, C. T.

1999-09-01

166

Shock-induced deformation in wetted particle beds  

NASA Astrophysics Data System (ADS)

The high-strain-rate response of granular media has received considerable attention due to increasing interest in granular penetration. In the present study, we investigate the response of wetted packed particle beds under varying flyer plate-induced shock loadings. We investigate the critical conditions for the onset of particle deformation in systems of spherical macroscopic glass beads. Resulting particle deformations from the shock compression are characterized using microscopy as well as particle size analysis, and the effects of shock strength are compared. A fracturing response with a bimodal particle distribution is observed, with an increasing shift to the lower particle size range as shock loading is initially increased. As the transmitted shock pressure exceeds 1 GPa, a significant decrease in the mean particle size is observed.

Marr, Bradley J.; Petel, Oren E.; Frost, David L.; Higgins, Andrew J.; Ringuette, Sophie

2014-05-01

167

Membrane-based wet electrostatic precipitation  

SciTech Connect

Emissions of fine particulate matter, PM2.5, in both primary and secondary form, are difficult to capture in typical dry electrostatic precipitators (ESPs). Wet (or waterbased) ESPs are well suited for collection of acid aerosols and fine particulates because of greater corona power and virtually no re-entrainment. However, field disruptions because of spraying (misting) of water, formation of dry spots (channeling), and collector surface corrosion limit the applicability of current wet ESPs in the control of secondary PM2.5. Researchers at Ohio University have patented novel membrane collection surfaces to address these problems. Water-based cleaning in membrane collectors made of corrosion-resistant fibers is facilitated by capillary action between the fibers, maintaining an even distribution of water. This paper presents collection efficiency results of lab-scale and pilot-scale testing at First Energy's Bruce Mansfield Plant for the membrane-based wet ESP. The data indicate that a membrane wet ESP was more effective at collecting fine particulates, acid aerosols, and oxidized mercury than the metal-plate wet ESP, even with {approximately}15% less collecting area. 15 refs., 7 figs., 6 tabs.

David J. Bayless; Liming Shi; Gregory Kremer; Ben J. Stuart; James Reynolds; John Caine [Ohio University, Athens, OH (US). Ohio Coal Research Center

2005-06-01

168

Rapid wetting dynamics  

NASA Astrophysics Data System (ADS)

Contact lines between solids and liquid or gas interfaces appear in very many instances of fluid flows. This could be coffee stains, water-oil mixtures in oil recovery, hydrophobic feet of insects or leaves in nature. In the present work we elucidate some of the wetting physics governing the very rapid wetting. Experimental and numerical results of spontaneously spreading droplets are presented, where focus is directed towards understanding the very rapid flow regime and highly dynamic initial wetting phase, where the contact line speed is limited by dissipative processes on a molecular scale occurring at the contact line. In particular we show the influence of the surface wettability and the liquid viscosity on the spreading dynamics, such as the contact line motion and dynamic contact angle in time.

Carlson, Andreas; Bellani, Gabriele; Amberg, Gustav

2010-11-01

169

Wet storage integrity update  

SciTech Connect

This report includes information from various studies performed under the Wet Storage Task of the Spent Fuel Integrity Project of the Commercial Spent Fuel Management (CSFM) Program at Pacific Northwest Laboratory. An overview of recent developments in the technology of wet storage of spent water reactor fuel is presented. Licensee Event Reports pertaining to spent fuel pools and the associated performance of spent fuel and storage components during wet storage are discussed. The current status of fuel that was examined under the CSFM Program is described. Assessments of the effect of boric acid in spent fuel pool water on the corrosion and stress corrosion cracking of stainless steel and the stress corrosion cracking of stainless steel piping containing stagnant water at spent fuel pools are discussed. A list of pertinent publications is included. 84 references, 21 figures, 11 tables.

Bailey, W.J.; Johnson, A.B. Jr.

1983-09-01

170

WET AND DRY SCRUBBERS FOR EMISSION CONTROL  

EPA Science Inventory

Generally speaking, absorption equipment includes two major categories: Wet adsorption scrubbers (or wet scrubbers); Dry absorption scrubbers (or dry scrubbers). Wet scrubbers: As the name implies, wet scrubbers (also known as wet collectors) are devices which use a liquid fo...

171

On the equations of fully fluidized granular materials  

Microsoft Academic Search

Equations for fully fluidized granular materials are proposed and are solved in a simple case. In fully fluidized granular materials, the granular particles slip or collide with each other and energy is dissipated. In describing the energy dissipation process characteristic to granular materials, a measure of random motion of granular particles is introduced as a new internal variable. We derive

Satoru Ogawa; Akira Umemura; Nobunori Oshima

1980-01-01

172

Granular thermal diffusion in flows of binary-sized mixtures  

Microsoft Academic Search

Summary The revised Enskog theory was employed to analyze granular flows of binary-sized mixtures. The governing equations and constitutive relations were used to investigate granular thermal diffusion —a diffusion process resulting from the granular temperature gradient. The granular thermal diffusion causes the smaller or the lighter particles to concentrate in the region of the flow with higher granular temperature, and

S. S. Hsiau; M. L. Hunt

1996-01-01

173

The hydrodynamics of inelastic granular systems  

NASA Astrophysics Data System (ADS)

The hydrodynamic equations for a system of inelastic granular particles are derived from first principles of statistical mechanical theory by applying projection operator techniques. An effective Liouvillian operator for the granular distribution function is derived by exploiting the fact that each granular particle has many interacting internal degrees of freedom which remain at equilibrium at a temperature T and provide a sink for the translational relative momenta of the inelastic granular system. The nonlinear hydrodynamic equations for the granular system are obtained following projection operator techniques developed by Levine and Oppenheim. The resulting equations are similar to the ordinary hydrodynamic equations but contain additional terms due to the fact that translational energy is not conserved in collisions between the granular particles. The solutions to the linearized equations are also analyzed in different regimes comparing the additional terms due to the inelasticity of collisions with the magnitude of the gradients of the system.

Schofield, Jeremy; Oppenheim, Irwin

1993-06-01

174

Characterization of wave propagation in elastic and elastoplastic granular chains  

NASA Astrophysics Data System (ADS)

For short duration impulse loadings, elastic granular chains are known to support solitary waves, while elastoplastic chains have recently been shown to exhibit two force decay regimes [Pal, Awasthi, and Geubelle, Granular Matter 15, 747 (2013)., 10.1007/s10035-013-0449-1]. In this work, the dynamics of monodisperse elastic and elastoplastic granular chains under a wide range of loading conditions is studied, and two distinct response regimes are identified in each of them. In elastic chains, a short loading duration leads to a single solitary wave propagating down the chain, while a long loading duration leads to the formation of a train of solitary waves. A simple model is developed to predict the peak force and wave velocity for any loading duration and amplitude. In elastoplastic chains, wave trains form even for short loading times due to a mechanism distinct from that in elastic chains. A model based on energy balance predicts the decay rate and transition point between the two decay regimes. For long loading durations, loading and unloading waves propagate along the chain, and a model is developed to predict the contact force and particle velocity.

Pal, Raj Kumar; Awasthi, Amnaya P.; Geubelle, Philippe H.

2014-01-01

175

Capturing nonlocal effects in 2D granular flows  

NASA Astrophysics Data System (ADS)

There is an industrial need, and a scientific desire, to produce a continuum model that can predict the flow of dense granular matter in an arbitrary geometry. A viscoplastic continuum approach, developed over recent years, has shown some ability to approximate steady flow and stress profiles in multiple inhomogeneous flow environments. However, the model incorrectly represents phenomena observed in the slow, creeping flow regime. As normalized flow-rate decreases, granular stresses are observed to become largely rate-independent and a dominating length-scale emerges in the mechanics. This talk attempts to account for these effects, in the simplified case of 2D, using the notion of nonlocal fluidity, which has proven successful in treating nonlocal effects in emulsions. The idea is to augment the local granular fluidity law with a diffusive second-order term scaled by the particle size, which spreads flowing zones accordingly. Below the yield stress, the local contribution vanishes and the fluidity becomes rate-independent, as we require. We implement the modified law in multiple geometries and validate its flow and stress predictions in multiple geometries compared against discrete particle simulations. In so doing, we demonstrate that the nonlocal relation proposed is satisfied universally in a seemingly geometry-independent fashion.

Kamrin, Ken; Koval, Georg

2013-03-01

176

Wetting transparency of graphene.  

PubMed

We report that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface-water interactions are dominated by van der Waals forces. Our contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding. With increasing number of graphene layers, the contact angle of water on copper gradually transitions towards the bulk graphite value, which is reached for ~6 graphene layers. Molecular dynamics simulations and theoretical predictions confirm our measurements and indicate that graphene's wetting transparency is related to its extreme thinness. We also show a 30-40% increase in condensation heat transfer on copper, as a result of the ability of the graphene coating to suppress copper oxidation without disrupting the intrinsic wettability of the surface. Such an ability to independently tune the properties of surfaces without disrupting their wetting response could have important implications in the design of conducting, conformal and impermeable surface coatings. PMID:22266468

Rafiee, Javad; Mi, Xi; Gullapalli, Hemtej; Thomas, Abhay V; Yavari, Fazel; Shi, Yunfeng; Ajayan, Pulickel M; Koratkar, Nikhil A

2012-03-01

177

Wetting transparency of graphene  

NASA Astrophysics Data System (ADS)

We report that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface-water interactions are dominated by van der Waals forces. Our contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding. With increasing number of graphene layers, the contact angle of water on copper gradually transitions towards the bulk graphite value, which is reached for ~6 graphene layers. Molecular dynamics simulations and theoretical predictions confirm our measurements and indicate that graphene’s wetting transparency is related to its extreme thinness. We also show a 30-40% increase in condensation heat transfer on copper, as a result of the ability of the graphene coating to suppress copper oxidation without disrupting the intrinsic wettability of the surface. Such an ability to independently tune the properties of surfaces without disrupting their wetting response could have important implications in the design of conducting, conformal and impermeable surface coatings.

Rafiee, Javad; Mi, Xi; Gullapalli, Hemtej; Thomas, Abhay V.; Yavari, Fazel; Shi, Yunfeng; Ajayan, Pulickel M.; Koratkar, Nikhil A.

2012-03-01

178

PREFACE: Wetting: introductory note  

Microsoft Academic Search

The discovery of wetting as a topic of physical science dates back two hundred years, to one of the many achievements of the eminent British scholar Thomas Young. He suggested a simple equation relating the contact angle between a liquid surface and a solid substrate to the interfacial tensions involved [1], gammalg cos theta = gammasg - gammasl (1) In

S. Herminghaus

2005-01-01

179

Bed wetting at home  

MedlinePLUS

... but this alone is not a treatment for bed wetting. You should not restrict fluids too much. Also have your child avoid drinks ... Your child has been drinking excess amounts of fluids Your child has ... or shy, or suddenly behaving in a sexually suggestive way)

180

Wet and Wild Water.  

ERIC Educational Resources Information Center

This guide uses a thematic approach to show the integration of subjects (reading, mathematics, language arts, science/fine arts) and skills to create a context for learning. The contents of this guide are presented in a holistic format. There are six major topics in the guide, each with subtopics: (1) "Getting Your Feet Wet--An Introduction to…

Indiana State Dept. of Education, Indianapolis. Center for School Improvement and Performance.

181

Wet ash removal equipment  

Microsoft Academic Search

Wet ash removal equipment in which a trough is filled with quenching water. An immersion member attached to the ash funnel is immersed into the quenching water. A side wall of the trough is sealed by a plate. The plate is supported upon a height-adjustable rod linkage and is guided in its movement on the side of the trough arrangements

H. Buchmuller; B. Michelbrink

1985-01-01

182

MLOD: Multi-granularity local outlier detection  

Microsoft Academic Search

Outlier detection is an important data mining task, LOF(local outlier factor) was proposed to indicate the degree of outlierness, which is practical for finding local outliers. However, it is difficult to decide the neighborhood size. In this paper a multi-granularity local outlier detection(MLOD) method is proposed to organize the outlierness under multi-granularity. It finds local outliers in varying neighborhood granularity.

Liang Gao; Shao-Yue Yu; Yu-Pan Luo; Lin Shang

2009-01-01

183

Average balance equations for granular materials  

Microsoft Academic Search

A general weighted space-time averaging procedure is developed and utilized to obtain the average balance equations for granular materials. The method is applicable to both solid-like (quasi-static) and fluid-like (granular flow) modes of granular material behavior. The average balance equations take the same mathematical form while all average quantities involved in these equations retain the same clear physical meaning whether

Marijan Babic

1997-01-01

184

76 FR 39896 - Granular Polytetrafluoroethylene Resin From Italy  

Federal Register 2010, 2011, 2012, 2013

...Review)] Granular Polytetrafluoroethylene Resin From Italy Determination On the basis of...order on granular polytetrafluoroethylene resin from Italy would be likely to lead to continuation...entitled Granular Polytetrafluoroethylene Resin from Italy: Investigation No....

2011-07-07

185

77 FR 59979 - Pure Magnesium (Granular) From China  

Federal Register 2010, 2011, 2012, 2013

...731-TA-895 (Second Review)] Pure Magnesium (Granular) From China Determination...of the antidumping duty order on pure magnesium (granular) from China would be likely...4350 (September 2012), entitled Pure Magnesium (Granular) from China:...

2012-10-01

186

Recent bright gully deposits on Mars: Wet or dry flow?  

USGS Publications Warehouse

Bright gully sediments attributed to liquid water flow have been deposited on Mars within the past several years. To test the liquid water flow hypothesis, we constructed a high-resolution (1 m/pixel) photogrammetric digital elevation model of a crater in the Centauri Montes region, where a bright gully deposit formed between 2001 and 2005. We conducted one-dimensional (1-D) and 2-D numerical flow modeling to test whether the deposit morphology is most consistent with liquid water or dry granular How. Liquid water flow models that incorporate freezing can match the runout distance of the flow for certain freezing rates but fail to reconstruct the distributary lobe morphology of the distal end of the deposit. Dry granular flow models can match both the observed runout distance and the distal morphology. Wet debris flows with high sediment concentrations are also consistent with the observed morphology because their rheologies are often similar to that of dry granular flows. As such, the presence of liquid water in this flow event cannot be ruled out, but the available evidence is consistent with dry landsliding. ?? 2008 The Geological Society of America.

Pelletier, J. D.; Kolb, K. J.; McEwen, A. S.; Kirk, R. L.

2008-01-01

187

Wet chemistry instrument prototype  

NASA Technical Reports Server (NTRS)

A wet chemistry instrument prototype for detecting amino acids in planetary soil samples was developed. The importance of amino acids and their condensation products to the development of life forms is explained. The characteristics of the instrument and the tests which were conducted to determine the materials compatibility are described. Diagrams are provided to show the construction of the instrument. Data obtained from the performance tests are reported.

1974-01-01

188

Wetting of porous solids.  

PubMed

This paper presents a simple, three stage method to simulate the mechanics of wetting of porous solid objects, like sponges and cloth, when they interact with a fluid. In the first stage, we model the absorption of fluid by the object when it comes in contact with the fluid. In the second stage, we model the transport of absorbed fluid inside the object, due to diffusion, as a flow in a deforming, unstructured mesh. The fluid diffuses within the object depending on saturation of its various parts and other body forces. Finally, in the third stage, oversaturated parts of the object shed extra fluid by dripping. The simulation model is motivated by the physics of imbibition of fluids into porous solids in the presence of gravity. It is phenomenologically capable of simulating wicking and imbibition, dripping, surface flows over wet media, material weakening, and volume expansion due to wetting. The model is inherently mass conserving and works for both thin 2D objects like cloth and for 3D volumetric objects like sponges. It is also designed to be computationally efficient and can be easily added to existing cloth, soft body, and fluid simulation pipelines. PMID:23846102

Patkar, Saket; Chaudhuri, Parag

2013-09-01

189

Hyperelastic models for granular materials  

NASA Astrophysics Data System (ADS)

Motivated by the need for a continuum mechanical description of particulate materials for nuclear safety analyses, several recently proposed hyperelastic models for granular materials are analyzed and compared with experiment data. As even the quasi-elastic regime of granular materials is non-linear, the hyperelastic forms considered here are all designed to capture the widely observed dependence of the elastic moduli on the square root of pressure. Building this sort of dependence in to the free energy results in some physically relevant behavior that is missed by other non-linear models, including stress-induced anisotropy and shear dilatancy. The granular elasticity (GE) model of Jiang and Liu additionally possesses a region outside a Drucker-Prager type yield surface in which the free energy is not convex, implying a lack of stable solutions there. This proves to be an over-constraint, as it limits yield angles to values lower than typically observed. Models due to Einav and Puzrin (EP), and Houlsby, Amorosi, and Rojas (HAR), lack this constraint, and thus provide greater flexibility; the EP model proves to best capture the sort of stress-induced anisotropy observed in experiments. All three models are implemented in the finite element code Abaqus, and used to calculate stress distributions in sand piles and silos, and the granular response function. The models agree qualitatively, but not always quantitatively, with experiments; paradoxically, the EP model proves to be the least accurate, producing an unphysically narrow and high peaked response function. They also possess shortcomings similar to those of linear elasticity. In silos with an applied surface load, they underestimate the observed "overshoot" of the saturated stress. For both sand piles and the response function, the stress profiles are insensitive to the values of the elastic constants, and as such are not able to account for the range of data observed experimentally. Incorporating some dependence on the pile formation history is likely necessary to describe these effects. In light of the findings, and the relative simplicity it affords, linear elasticity (despite its known shortcomings) is an appropriate choice for coupling to flow models in engineering analyses.

Humrickhouse, Paul W.

190

Granular materials under vibration and thermal cycles  

Microsoft Academic Search

We report flow rate measurement of granular materials from a lab size silo with and without sinusoidal vibration, and the flows from a jammed container under mechanical shocks. We also report the investigation of fragility in granular materials using controlled cyclic temperature variation, or thermal cycling that induces microscopic changes in the size of the grains and the container. When

Ke Chen

2008-01-01

191

Applying MDL to learn best model granularity  

Microsoft Academic Search

The Minimum Description Length (MDL) principle is solidly based on a provably ideal method of inference using Kolmogorov complexity. We test how the theory behaves in practice on a general problem in model selection: that of learning the best model granularity. The performance of a model depends critically on the granularity, for example the choice of precision of the parameters.

Qiong Gao; M ing Lib; Paul Vitányi

1994-01-01

192

Granular synthesis: Experiments in live performance  

Microsoft Academic Search

Abstract This paper describes current research into Granular synthesis. It outlines the design and performance,of a musical instrument based upon this Synthesis method. The instrument, design, process and products are used,as a research,tool for examining,granular synthesis in real-time performance,on a low budget.

T. Opie

2002-01-01

193

TWO-STAGE GRANULAR ACTIVATED CARBON TREATMENT  

EPA Science Inventory

Two 6.3 l/sec (0.15 mgd), two-stage, packed-bed, downflow granular activated carbon pilot plants were operated continuously for 33 months using unfiltered and unchlorinated activated sludge plant effluent. The main objective of the study was to compare the performance of granular...

194

Configurational statistics of excited granular materials  

Microsoft Academic Search

In this dissertation, we investigate theories of configurational statistics for excited granular materials, and test the predictions with extensive molecular dynamics (MD) simulations. First we examine a system of weakly excited granular materials in a vibrating bed. We use a thermodynamic theory of hard spheres, which explores consequences of the excluded volume interaction under gravity. The global temperature T, is

Paul Victor Quinn

2001-01-01

195

Substituting Wet Distillers Grains or Condensed Distillers Solubles for Corn Grain in Finishing Diets for Yearling Heifers  

Microsoft Academic Search

A feeding trial was conducted with 790-lb yearling heifers fed an average of 121 days to evaluate replacing cracked corn and supplemental urea with wet distillers grains or condensed distillers solubles. Wet distillers grains were evaluated at 16%, 28% and 40% of diet dry matter. Condensed distillers solubles were added at 6.5% of diet dry matter. Control diets were supplemented

Allen Trenkle

1997-01-01

196

Vibrated granular bed on a bumpy surface.  

PubMed

We investigate effects of physical characteristics of the vibrating base in a vibrated granular bed system on the bulk granular behavior of the bed using molecular dynamics simulations. With a vibrating base that exhibits low coefficient of restitution for particle-base collisions, a monolayer of granular materials was observed to form dynamically on the surface of the base. Such a system was shown to be both qualitatively and quantitatively equivalent to one with a bumpy base composed of discrete solid particles undergoing the same type of imposed oscillatory motion. The "bumpiness" of such a base, as defined by the size of particles constituting the vibrating base, was also found to have insignificant effects on the behavior of the bulk granular materials. The observations made in this study may point toward a possible methodology to model vibrating granular bed systems with inelastic bases using continuum theories. PMID:19518219

Lim, Eldin Wee Chuan

2009-04-01

197

Uterine cervical malignant granular cell tumor.  

PubMed

Malignant granular cell tumor is relatively uncommon, constituting only 1-2% of all granular cell tumors. It is a rare and unusual tumor, especially in non-typical sites, such as the uterine cervix, and grows more rapidly than benign granular cell tumor. It can be treated with surgical excision, but recurrence is possible and prognosis can be poor. A malignant granular cell tumor in the uterine cervix of a 37-year-old woman was incidentally diagnosed. The patient has a history of irregular vaginal bleeding. Uterine cervical biopsy under colposcope revealed a malignant granular cell tumor. After isophosphamide, etoposide, and cisplatin neoadjuvant chemotherapy, surgery was performed on the lesion, which approximately involved half the depth of cervical stroma. Computed tomography examination showed no local recurrence or distant metastasis during the 26-month follow-up period. PMID:22414028

Guo, Na; Peng, Zhilan; Yang, Kaixuan; Lou, Jiangyan

2012-06-01

198

Granular filtration in a fluidized bed  

SciTech Connect

Successful development of advanced coal-fired power conversion system often requires reliable and efficient cleanup devices that can remove particulate and gaseous pollutants from high-temperature, high- pressure gas streams. A novel filtration concept for particulate cleanup has been developed at the U.S. Department of Energy`s Morgantown Energy Technology Center (METC). The filtration system consists of a fine metal screen filter immersed in a fluidized bed of granular material. As the gas stream passes through the fluidized bed, a layer of the bed granular material is entrained and deposited at the screen surface. This material provides a natural granular filter to separate fine particles from the gas stream passing through the bed. Since the filtering media is the granular material supplied by the fluidized bed, the filter is not subjected to blinding like candle filters. Because only the in-flowing gas, not fine particle cohesive forces, maintains the granular layer at the screen surface, once the thickness and permeability of the granular layer are stabilized, it remains unchanged as long as the in-flowing gas flow rate remains constant. The weight of the particles and the turbulent nature of the fluidized bed limits the thickness of the granular layer on the filter leading to a self-cleaning attribute of the filter. The granular filtration testing system consisted of a filter, a two-dimensional fluidized bed, a continuous powder feeder, a laser-based, in-line particle counting, sizing, and velocimeter (PCSV), and a continuous solid feeding/bed material withdrawal system. The two-dimensional, transparent fluidized bed allowed clear observation of the general fluidized state of the granular material and the conditions under which fines are captured by the granular layer.

Mei, J.S.; Yue, P.C.

1996-12-31

199

Wetting in Color  

NASA Astrophysics Data System (ADS)

Colorimetric litmus tests such as pH paper have enjoyed wide commercial success due to their inexpensive production and exceptional ease of use. However, expansion of colorimetry to new sensing paradigms is challenging because macroscopic color changes are seldom coupled to arbitrary differences in the physical/chemical properties of a system. In this thesis I present in detail the development of Wetting in Color Technology, focusing primarily on its application as an inexpensive and highly selective colorimetric indicator for organic liquids. The technology exploits chemically-encoded inverse-opal photonic crystals to control the infiltration of fluids to liquid-specific spatial patterns, projecting minute differences in liquids' wettability to macroscopically distinct, easy-to-visualize structural color patterns. It is shown experimentally and corroborated with theoretical modeling using percolation theory that the high selectivity of wetting, upon-which the sensitivity of the indicator relies, is caused by the highly symmetric structure of our large-area, defect-free SiO2 inverse-opals. The regular structure also produces a bright iridescent color, which disappears when infiltrated with liquid - naturally coupling the optical and fluidic responses. Surface modification protocols are developed, requiring only silanization and selective oxidation, to facilitate the deterministic design of an indicator that differentiates a broad range of liquids. The resulting tunable, built-in horizontal and vertical chemistry gradients allow the wettability threshold to be tailored to specific liquids across a continuous range, and make the readout rely only on countable color differences. As wetting is a generic fluidic phenomenon, Wetting in Color technology could be suitable for applications in authentication or identification of unknown liquids across a broad range of industries. However, the generic nature of the response also ensures chemical non-specificity. It is shown that combinatorial measurements from an array of indicators add a degree of chemical specificity to the platform, which can be further improved by monitoring the drying of the inverse-opal films. While colorimetry is the central focus of this thesis, applications of this platform in encryption, fluidics and nanofabrication are also briefly explored.

Burgess, Ian Bruce

200

Optical wet steam monitor  

DOEpatents

A wet steam monitor determines steam particle size by using laser doppler velocimeter (LDV) device to produce backscatter light. The backscatter light signal is processed with a spectrum analyzer to produce a visibility waveform in the frequency domain. The visibility waveform includes a primary peak and a plurality of sidebands. The bandwidth of at least the primary frequency peak is correlated to particle size by either visually comparing the bandwidth to those of known particle sizes, or by digitizing the waveform and comparing the waveforms electronically.

Maxey, Lonnie C. (Powell, TN); Simpson, Marc L. (Knoxville, TN)

1995-01-01

201

Misconceptions in wetting phenomena.  

PubMed

In a recent paper ('t Mannetje, D.; Banpurkar, A.; Koppelman, H.; Duits, M. H. G.; van den Ende, D.; Mugele, F. Electrically Tunable Wetting Defects Characterized by a Simple Capillary Force Sensor. Langmuir 2013, 29, 9944-9949), there are a few misconceptions regarding the interpretations of theories emanating from Shanahan and de Gennes in describing centrifugal adhesion balance (CAB) experiments, making their results seemingly contradictory to the theory. These are clarified here. We show that their results, if interpreted correctly, do not contradict the theories mentioned above. PMID:24256467

Tadmor, Rafael

2013-12-10

202

Vibrational Phenomena in Near-Critical Fluids and Granular Matter  

NASA Astrophysics Data System (ADS)

Often, experiments are performed undermicrogravity because of their sensitivity to gravitational effects, which means they are also sensitive in space to inertial effects and g-jitter. Any movement by an astronaut or experiment is efficiently transmitted by the spacecraft structure; this vibration may perturb other experiments. Knowledge, prediction and minimisation of vibration is a necessity for controlling space experiments. The natural mechanical noise of a spacecraft, which is probably non-homogeneous and non-isotropic, can largely be avoided by positioning and orienting experiments carefully. Any apparatus moves as a whole with random rotation and translation in the frame of the space laboratory. If the part sensitive to gravity is composed of different fluids, for example, it will behave as heterogeneous fluids submitted to translation and rotation vibrations.The accurate control of such an experiment requires knowledge of the six different components of vibration (3 translational, 3 rotational) because it can be viewed as a rigid device within a moving laboratory. The effects of rotational vibration and translational vibration are treated here separately. Rotational vibration acts even on homogeneous fluids, where it generates periodic flow. It is an unavoidable phenomenon that can be studied on Earth. By contrast, translational vibration affects only heterogeneous fluids. On the ground, these heterogeneities are stratified and oriented by gravity, which is not true in microgravity.

Beysens, D.; Evesque, P.

2005-06-01

203

Granular Matter, Foams, and Beyond: Applications of the Granocentric Model  

NASA Astrophysics Data System (ADS)

We present a local stochastic model that predicts the statistical fluctuations in jammed packings of monodisperse and polydisperse spheres revealed by confocal microscopy. Moreover, we find that this model can account for the properties of looser and denser random packings that result from depletion attraction between the particles or compression by an applied load, respectively. Finally, we extend the model to space-filling packings of cells in tissues and biliquid foams by testing analytic predictions for the dependence of the number of neighbors of a given cell on its volume. Interestingly, the model distinguishes between scenarios in which size or positional disorder in the packing dominate, in good agreement with experimental data. This versatile model can be put into the statistical mechanics framework proposed by Edwards in order to compute the entropy and compactivity of each packing.

Newhall, Katherine

2012-02-01

204

Spatio-structural granularity of biological material entities  

Microsoft Academic Search

BACKGROUND: With the continuously increasing demands on knowledge- and data-management that databases have to meet, ontologies and the theories of granularity they use become more and more important. Unfortunately, currently used theories and schemes of granularity unnecessarily limit the performance of ontologies due to two shortcomings: (i) they do not allow the integration of multiple granularity perspectives into one granularity

Lars Vogt

2010-01-01

205

Wetness perception across body sites.  

PubMed

Human skin is innervated with a variety of receptors serving somatosensation and includes the sensory sub-modalities of touch, temperature, pain and itch. The density and type of receptors differ across the body surface, and there are various body-map representations in the brain. The perceptions of skin sensations outside of the specified sub-modalities, e.g. wetness or greasiness, are described as 'touch blends' and are learned. The perception of wetness is generated from the coincident activation of tactile and thermal receptors. The present study aims to quantify threshold levels of wetness perception and find out if this differs across body sites. A rotary tactile stimulator was used to apply a moving, wetted stimulus over selected body sites at a precise force and velocity. Four wetness levels were tested over eight body sites. After each stimulus, the participant rated how wet the stimulus was perceived to be using a visual analogue scale. The results indicated that participants discriminated between levels of wetness as distinct percepts. Significant differences were found between all levels of wetness, apart from the lowest levels of comparison (20 ?l and 40 ?l). The perception of wetness did not, however, differ significantly across body sites and there were no significant interactions between wetness level and body site. The present study emphasizes the importance of understanding how bottom-up and top-down processes interact to generate complex perceptions. PMID:22710006

Ackerley, Rochelle; Olausson, Håkan; Wessberg, Johan; McGlone, Francis

2012-07-26

206

Wet steam wetness measurement in a 10 MW steam turbine  

NASA Astrophysics Data System (ADS)

The aim of this paper is to introduce a new design of the extinction probes developed for wet steam wetness measurement in steam turbines. This new generation of small sized extinction probes was developed at CTU in Prague. A data processing technique is presented together with yielded examples of the wetness distribution along the last blade of a 10MW steam turbine. The experimental measurement was done in cooperation with Doosan Škoda Power s.r.o.

Kolovratník, Michal; Bartoš, Ond?ej

2014-03-01

207

Granular filtration in a fluidized bed  

SciTech Connect

Successful development of advanced coal-fired power conversion systems often require reliable and efficient cleanup devices which can remove particulate and gaseous pollutants from high-temperature high-pressure gas stream. A novel filtration concept for particulate cleanup has been developed at the Morgantown Energy Technology Center (METC) of the U.S. Department of Energy. The filtration system consists of a fine metal screen filter immersed in a fluidized bed of granular material. As the gas stream passes through the fluidized bed, a layer of the bed granular material is entrained and deposited at the screen surface. This material provides a natural granular filter to separate fine particles from the gas stream passing through the bed. Since the filtering media is the granular material supplied by the fluidized bed, the filter is not subjected to blinding like candle filters. Because only the in-flowing gas, not fine particle cohesive forces, maintains the granular layer at the screen surface, once the thickness and permeability of the granular layer is stabilized, it remains unchanged as long as the in-flowing gas flow rate remains constant. The weight of the particles and the turbulent nature of the fluidized bed limits the thickness of the granular layer on the filter leading to a self-cleaning attribute of the filter. Batch mode filtration performance of the filter was first reported at the Ninth Annual Coal-Fueled Heat Engines, Advanced Pressurized Fluidized-Bed Combustion, and Gas Stream Cleanup Systems Contractors Review Meeting.

Mei, J.S.; Yue, P.C.; Halow, J.S.

1995-12-31

208

Novel Two-Phase Upflow Digestion of Wet-Carbonized Peat Product Water.  

National Technical Information Service (NTIS)

This paper presents the development and operating results of a novel two-phase upflow anaerobic digestion process for the conversion of organic matter present in the process effluent generated during the wet-carbonization processing of peat. It exhibited ...

A. Sajjad M. P. Henry V. J. Srivastava J. Mensinger

1987-01-01

209

Experimental Investigation of the Wet Oxidation Destruction of Shipboard Waste Streams.  

National Technical Information Service (NTIS)

Increasingly stringent water qualtiy regulations anticipate the need for treating all shipboard waste streams containing combustible matter. Wet air oxidation or pressurized aqueous combustion conducted at 475 to 600F at operating pressures from 600 to 18...

P. Schatzberg D. F. Jackson C. M. Kelly

1974-01-01

210

Wetting Characteristics of Immiscibles  

NASA Technical Reports Server (NTRS)

Early microgravity experiments with immiscible alloys were usually carried out with the intent of forming dispersed microstructures. By processing under microgravity conditions, the main mechanism leading to gross phase separation could be eliminated. However, analysis of flight samples revealed a separated structure where the minor phase was present along the outer surface, while the major phase was present in the center. The Wetting Characteristics of Immiscibles (WCI) project, which flew aboard the USMP-4 (United States Microgravity Payload) mission in November of 1997, was designed to gain insight into the mechanisms causing segregation of these alloys. This investigation utilized an immiscible transparent organic alloy system and a transparent container in order to facilitate direct observation of the separation process. A range of immiscible alloy compositions was utilized in order to obtain variations in the minor and major phases present and observe the influence on the segregation processes. A small composition range was found where the minor liquid phase perfectly wet the cell gasket. Unexplained observations were made at the extremes of the composition range.

Andrews, J. B.; Little, L. J.

1999-01-01

211

Liquid-solid-like transition in quasi-one-dimensional driven granular media  

NASA Astrophysics Data System (ADS)

The theory of non-ideal gases at thermodynamic equilibrium, for instance the van der Waals gas model, has played a central role in our understanding of coexisting phases, as well as the transitions between them. In contrast, the theory fails with granular matter because collisions between the grains dissipate energy, and their macroscopic size renders thermal fluctuations negligible. When a mass of grains is subjected to mechanical vibration, it can make a transition to a fluid state. In this state, granular matter exhibits patterns and instabilities that resemble those of molecular fluids. Here, we report a granular solid-liquid phase transition in a vibrating granular monolayer. Unexpectedly, the transition is mediated by waves and is triggered by a negative compressibility, as for van der Waals phase coexistence, although the system does not satisfy the hypotheses used to understand atomic systems. The dynamic behaviour that we observe-coalescence, coagulation and wave propagation-is common to a wide class of phase transitions. We have combined experimental, numerical and theoretical studies to build a theoretical framework for this transition.

Clerc, M. G.; Cordero, P.; Dunstan, J.; Huff, K.; Mujica, N.; Risso, D.; Varas, G.

2008-03-01

212

Establishing predictive capabilities of DEM - Verification and validation for complex granular processes  

NASA Astrophysics Data System (ADS)

The discrete element method has been increasingly used to model granular processes of increasing complexity, from dry to wet to multiphase systems. Whilst DEM has been shown to produce qualitatively many of the complex phenomena observed in these complex granular systems, establishing the extent of the predictive capability of DEM model is still in its infancy. This summary paper discusses the need to develop verification and validation methodologies with regard to DEM computations. It proposes the need to first verify that a DEM code with its implemented mathematical model and computation algorithm is accurately reproducing the conceptual model and its solution, before validating to determine the degree to which the computational model accurately represent the physics being modelled. It also discusses the associated issue of data analysis to extract the parameters of interest from DEM particle scale data.

Ooi, Jin Y.

2013-06-01

213

Identification of continuous granular flow models  

NASA Astrophysics Data System (ADS)

Granular materials may exhibit different pattern forming behaviors, depending on the average energy per grain. Various granular flow PDE models exist, each capturing different behaviors of the physical phenomenon. In the present work we investigate the model and parameter identification problem of different continuous granular flow models as an encapsulated optimization problem. The identification problem is then split in a series of inverse problems. For the discrimination of the different models, the Fisher information matrix is used and different optimality criteria are discussed. Basic concepts of algorithmic differentiation (AD), which is used for the computation of the sensitivity matrix, are also given. The PDEs are discretized by the finite element method.

Papadopoulos, Dimitrios

2014-03-01

214

Granular metamaterials for vibration mitigation  

NASA Astrophysics Data System (ADS)

Acoustic metamaterials that allow low-frequency band gaps are interesting for many practical engineering applications, where vibration control and sound insulation are necessary. In most prior studies, the mechanical response of these structures has been described using linear continuum approximations. In this work, we experimentally and theoretically address the formation of low-frequency band gaps in locally resonant granular crystals, where the dynamics of the system is governed by discrete equations. We investigate the quasi-linear behavior of such structures. The analysis shows that a stopband can be introduced at about one octave lower frequency than in materials without local resonances. Broadband and multi-frequency stopband characteristics can also be achieved by strategically tailoring the non-uniform local resonance parameters.

Gantzounis, G.; Serra-Garcia, M.; Homma, K.; Mendoza, J. M.; Daraio, C.

2013-09-01

215

Shocks in oscillated granular layers  

NASA Astrophysics Data System (ADS)

We study shock formation in vertically oscillated granular layers, where shock waves form with each collision between the layer and the bottom plate of the container. We use both three-dimensional numerical solutions of continuum equations developed by Jenkins and Richman (J.T. Jenkins and M.W. Richman, Arch. Rat. Mech. Anal. 87), 355 (1985) for smooth and nearly elastic hard spheres, and previously validated molecular dynamics (MD) simulations (C. Bizon, M.D. Shattuck, J.B. Swift, W.D. McCormick, and H.L. Swinney, Phys. Rev. Lett. 80), 57 (1998). Both methods capture the shock formation, and the two methods agree quantitatively for small dissipation. We also investigate the effect of inelasticity on shock formation, and use both smooth and rough hard-sphere MD simulations to investigate the effect of friction in this system.

Bougie, J.; Moon, Sung Joon; Swift, J. B.; Swinney, Harry L.

2001-11-01

216

Capillary fracturing in granular media.  

PubMed

We study the displacement of immiscible fluids in deformable, noncohesive granular media. Experimentally, we inject air into a thin bed of water-saturated glass beads and observe the invasion morphology. The control parameters are the injection rate, the bead size, and the confining stress. We identify three invasion regimes: capillary fingering, viscous fingering, and "capillary fracturing," where capillary forces overcome frictional resistance and induce the opening of conduits. We derive two dimensionless numbers that govern the transition among the different regimes: a modified capillary number and a fracturing number. The experiments and analysis predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural processes such as primary oil migration, methane venting from lake sediments, and the formation of desiccation cracks. PMID:23004989

Holtzman, Ran; Szulczewski, Michael L; Juanes, Ruben

2012-06-29

217

Capillary Fracturing in Granular Media  

NASA Astrophysics Data System (ADS)

We study the displacement of immiscible fluids in deformable, noncohesive granular media. Experimentally, we inject air into a thin bed of water-saturated glass beads and observe the invasion morphology. The control parameters are the injection rate, the bead size, and the confining stress. We identify three invasion regimes: capillary fingering, viscous fingering, and “capillary fracturing,” where capillary forces overcome frictional resistance and induce the opening of conduits. We derive two dimensionless numbers that govern the transition among the different regimes: a modified capillary number and a fracturing number. The experiments and analysis predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural processes such as primary oil migration, methane venting from lake sediments, and the formation of desiccation cracks.

Holtzman, Ran; Szulczewski, Michael L.; Juanes, Ruben

2012-06-01

218

Moving bed granular filtration of fast pyrolysis char: granular flow rate study  

Microsoft Academic Search

Moving bed granular filter (MBGF) shows a good promise for hot gas clean up of biomass fast pyrolysis to filter fine char particles. This research project examines the effect of granular flow rate on the performance of a MBGF at cold flow conditions.\\u000aIn understanding the effect of granular flow rate on the MBGF performance, the filter's collection efficiency and

Ibrahim Adnan El-hedok

2009-01-01

219

Effects of dietary concentration of wet distillers grains on performance by newly received beef cattle, in vitro gas production and volatile fatty acid concentrations, and in vitro dry matter disappearance.  

PubMed

Three studies were designed to evaluate effects of wet distillers grains with solubles (WDGS) on health and performance of newly received beef cattle, in vitro gas production, molar proportions and total concentrations of VFA, and IVDMD. In Exp. 1 and 2, 219 (BW = 209 kg, SE = 2.2 kg; Exp. 1) and 200 beef steers (BW = 186 kg, SE = 3.2 kg; Exp. 2) were used in randomized complete block design receiving studies. The 4 dietary treatments (DM basis) were a 65% concentrate, steam-flaked corn (SFC)-based receiving diet without WDGS (CON) or diets that contained 12.5, 25.0, or 37.5% WDGS. There were no differences among the 4 receiving diets in BW (P ? 0.61), ADG (P ? 0.75), DMI (P ? 0.27), and G:F (P ? 0.35), or in the proportion of cattle treated for morbidity from bovine respiratory disease in either of the 2 experiments. In Exp. 3, in vitro methods were used to determine the effects of WDGS on IVDMD, total gas production, and molar proportions and total concentrations of VFA. Substrates used for the incubations contained the same major components as the diets used in Exp. 1, with ruminal fluid obtained from steers fed a 60% concentrate diet. Total gas production was less (P = 0.03) for the average of the 3 WDGS substrates than for CON, with a linear decrease (P = 0.01) in total gas production as WDGS concentration increased in the substrates. In contrast to gas production, IVDMD was greater for the average of the 3 WDGS concentrations vs. CON (P ? 0.05) at 6 and 12 h and increased (P ? 0.02) with increasing WDGS concentration at 6 (linear and quadratic) and 12 h (linear) of incubation. At 48 h, there was a quadratic effect (P = 0.05) on IVDMD, with the greatest value for 25% WDGS. Molar proportion of butyrate increased linearly (P < 0.01) as the concentration of WDGS increased in the substrate, and the average of the 3 substrates containing WDGS had a greater proportion of butyrate (P = 0.03) than CON. Performance data from Exp. 1 and 2 indicate that including WDGS in the SFC-based diets for newly received cattle can be an effective at concentrations up to 37.5% of the DM. In vivo measurements are needed to corroborate the in vitro fermentation changes noted with addition of WDGS. PMID:23482571

Smith, D R; Ponce, C H; Dilorenzo, N; Quinn, M J; May, M L; MacDonald, J C; Luebbe, M K; Bondurant, R G; Galyean, M L

2013-06-01

220

Surface wave acoustics of granular packing under gravity  

SciTech Connect

Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.

Clement, Eric; Andreotti, Bruno [PMMH, ESPCI, CNRS (UMR 7636) and Univ. Paris 6 and Paris 7, 10 rue Vauquelin, 75005 Paris (France); Bonneau, Lenaic [PMMH, ESPCI, CNRS (UMR 7636) and Univ. Paris 6 and Paris 7, 10 rue Vauquelin, 75005 Paris (France)

2009-06-18

221

Capillary Movement in Granular Beds in Microgravity  

NASA Technical Reports Server (NTRS)

Understanding the dynamics of capillary flow through unsaturated porous media is very important for the development of an effective water and nutrient delivery system for growing plants in microgravity and chemical engineering applications. Experiments were conducted on the Space Shuttle during the STS-63 mission using three experimental cuvettes called "Capillary Testbed-M." These experiments studied the effect of bead diameter on capillary flow by comparing the capillary flow in three different granular beds. It was observed that the speed of water propagation in the granular bed consisting of 1.5 mm diameter particles was less than that in the bed consisting of 1.0 mm. diameter particles. Such results contradict the existing theory of capillary water propagation in granular beds. It was found also that in microgravity water propagates independently in adjacent layers of a layered granular bed .

Yendler, Boris S.; Bula, Ray J.; Kliss, Mark (Technical Monitor)

1996-01-01

222

Acoustical properties of double porosity granular materials.  

PubMed

Granular materials have been conventionally used for acoustic treatment due to their sound absorptive and sound insulating properties. An emerging field is the study of the acoustical properties of multiscale porous materials. An example of these is a granular material in which the particles are porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical properties of these materials are introduced. Image processing techniques have been employed to estimate characteristic dimensions of the materials. The model predictions are compared with measurements on expanded perlite and activated carbon showing satisfactory agreement. It is concluded that a double porosity granular material exhibits greater low-frequency sound absorption at reduced weight compared to a solid-grain granular material with similar mesoscopic characteristics. PMID:22087905

Venegas, Rodolfo; Umnova, Olga

2011-11-01

223

Downflow Granular Filtration of Activated Sludge Effluents.  

National Technical Information Service (NTIS)

The performance of downflow granular filters subjected to effluents from activated sludge processes was investigated at the EPA-DC Pilot Plant in Washington, D.C. Several media combinations were investigated, including both single anthracite and dual anth...

R. P. G. Bowker

1977-01-01

224

Non-Local Theory of Granular Media.  

National Technical Information Service (NTIS)

A comprehensive theoretical derivation for the equations of motion of granular media in three dimensions. The derivation is based on both the probabilistic theory of motion of discreet particles, and utilizes the concepts of non-local thermodynamics.

K. C. Valanis

1992-01-01

225

Granular Cell Tumors of the Heart.  

National Technical Information Service (NTIS)

In a study of granular cell tumors arising in the hearts of three patients, no evidence was found, either histologically or ultrastructurally, to support the hypothesis that these tumors are derived from striated muscle or cardiac muscle. The anatomic loc...

J. J. Fenoglio H. A. McAllister

1975-01-01

226

Regional Reactivation of Granular Activated Carbon.  

National Technical Information Service (NTIS)

A major portion of the cost of using Granular Activated Carbon (GAC) as a water treatment unit process is associated with spent carbon replacement or reactivation. Regional reactivation or sharing a reactivation furnace among several users, has been propo...

J. Q. Adams R. M. Clark B. W. Lykins D. Kittredge

1986-01-01

227

An assessment of granular urea\\/ammonium sulphate and urea\\/potassium nitrate fertilizers on nitrogen recovery by ryegrass  

Microsoft Academic Search

The comparative effects of ammonium sulphate (AS), potassium nitrate (KNO3), urea (U) or combined 1:1 (w\\/w) U\\/KNO3, U\\/AS granular products were investigated on dry matter (DM) yield and15N utilisation by perennial ryegrass grown under controlled environmental conditions.

Catherine J. Watson

1988-01-01

228

Granular materials under vibration and thermal cycles  

NASA Astrophysics Data System (ADS)

We report flow rate measurement of granular materials from a lab size silo with and without sinusoidal vibration, and the flows from a jammed container under mechanical shocks. We also report the investigation of fragility in granular materials using controlled cyclic temperature variation, or thermal cycling that induces microscopic changes in the size of the grains and the container. When placed under sinusoidal vibration, the flow rate or flux from an unjammed container decreases with the peak velocity of the vibration, and becomes a constant at the highest peak velocities. The flux under vibration follows a 5/2 power scaling rule to corrected orifice diameter, the same scaling rule that is also observed in the absence of vibration. Under vibration, granular flux is no greater than the flux without vibration. Density dilution of granular packs under vibration is likely the cause for such reduced flux, and can be described by a model based on energy balance at the vibrating boundary. The eventual saturation of flux at the highest peak velocities signifies a possible transition from granular fluid to granular gas, as the density decreases and inter-grain interaction changes. Brief flows can be initiated from a jammed container using mechanical impacts. The number of grains flowing out of the container as well as the duration of these flows follows an almost exponential decay distribution. The probability that a flow can be initiated by an impact increases with impact intensity and ratio the diameters of the orifice and the grain. The possible container size and filling depth dependence are also discussed. For the thermal cycling measurement, data show that the packing fraction of granular samples increases under thermal cycles regardless of the relative thermal expansions of the grains or the container. A heavy intruder, when passing a density threshold, sinks in a granular pile under thermal cycles. The results show that the bulk property of granular materials can be impacted by microscopic changes orders or magnitudes less, and without the input of mechanical energy. We believe both the packing fraction relaxation and the intruder displacement in thermally cycled granular systems demonstrate the fragility of disordered granular media, which can be defined as the "inability to elastically support some infinitesimal loads".

Chen, Ke

229

Granular neural web agents for stock prediction  

Microsoft Academic Search

A granular neural Web-based stock prediction agent is developed using the granular neural network (GNN) that can discover fuzzy rules. Stock data sets are downloaded from www.yahoo.com website. These data sets are inserted into the database tables using a java program. Then, the GNN is trained using sample data for any stock. After learning from the past stock data, the

Yan-qing Zhang; Somasheker Akkaladevi; George J. Vachtsevanos; Tsau Young Lin

2002-01-01

230

Rheology of weakly vibrated granular media  

NASA Astrophysics Data System (ADS)

We probe the rheology of weakly vibrated granular flows as function of flow rate, vibration strength, and pressure by performing experiments in a vertically vibrated split-bottom shear cell. For slow flows, we establish the existence of a vibration-dominated granular flow regime, where the driving stresses smoothly vanish as the driving rate is diminished. We distinguish three qualitatively different vibration-dominated rheologies, most strikingly a regime where the shear stresses no longer are proportional to the pressure.

Wortel, Geert H.; Dijksman, Joshua A.; van Hecke, Martin

2014-01-01

231

Endobronchial granular cell tumor: a case report  

PubMed Central

Granular cell tumors (GCTs) are benign neoplasms that are most commonly found in the head and neck region. We present a case of endobronchial granular cell tumor presenting as hemoptysis in a 22-year-old African American female. Patient subsequently underwent a right upper and middle lobectomy, and upon histologic analysis was found to have GCT with borders impinging upon cartilage and adjacent peribronchial lymph nodes.

Meyer, Monique Anne; Becker, Joseph M.; Quinones, William

2010-01-01

232

Small-signal analysis of granular semiconductors  

Microsoft Academic Search

The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in

Aapo Varpula; Juha Sinkkonen; Sergey Novikov

2010-01-01

233

Small-signal analysis of granular semiconductors  

NASA Astrophysics Data System (ADS)

The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in a broad frequency range at low dc bias voltages.

Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey

2010-11-01

234

Scale-up of catalytic wet oxidation under moderate conditions  

SciTech Connect

The Catalytic Wet Oxidation with pure oxygen is a suitable treatment process for the degradation of organic matter in wastewaters and sludges. The applied moderate reaction conditions lead only to a partial oxidation of the organics. Therefore the resulting process water has to be purified in a biological treatment plant. In this study, experimental data collected during the wet oxidation of phenol and sewage sludge in a laboratory batch reactor as well as in a pilot plant are presented. A generalized kinetic model combined with a residence time analysis allows to predict accurately the degradation of organic matter in the pilot plant. The wet oxidation of wastewaters and sewage sludge was realized in one single plant concept. Treating suspended or diluted organic wastes produces a highly biodegradable process water containing low molecular oxidation products. The investigated Catalytic Wet Oxidation of sewage sludge generates a residual solid complying with the European quality standards of disposal concerning leachability and organic content. Due to its low capital and operating costs, the Catalytic Wet Oxidation process constitutes an acceptable alternative to incineration for the disposal of sludges.

Harf, J.; Hug, A.; Vogel, F.; Rohr, P.R. von [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Inst. of Process Engineering] [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Inst. of Process Engineering

1999-05-01

235

Contact micromechanics in granular media with clay  

SciTech Connect

Many granular materials, including sedimentary rocks and soils, contain clay particles in the pores, grain contacts, or matrix. The amount and location of the clays and fluids can influence the mechanical and hydraulic properties of the granular material. This research investigated the mechanical effects of clay at grain-to-grain contacts in the presence of different fluids. Laboratory seismic wave propagation tests were conducted at ultrasonic frequencies using spherical glass beads coated with Montmorillonite clay (SWy-1) onto which different fluids were adsorbed. For all bead samples, seismic velocity increased and attenuation decreased as the contact stiffnesses increased with increasing stress demonstrating that grain contacts control seismic transmission in poorly consolidated and unconsolidated granular material. Coating the beads with clay added stiffness and introduced viscosity to the mechanical contact properties that increased the velocity and attenuation of the propagating seismic wave. Clay-fluid interactions were studied by allowing the clay coating to absorb water, ethyl alcohol, and hexadecane. Increasing water amounts initially increased seismic attenuation due to clay swelling at the contacts. Attenuation decreased for higher water amounts where the clay exceeded the plastic limit and was forced from the contact areas into the surrounding open pore space during sample consolidation. This work investigates how clay located at grain contacts affects the micromechanical, particularly seismic, behavior of granular materials. The need for this work is shown by a review of the effects of clays on seismic wave propagation, laboratory measurements of attenuation in granular media, and proposed mechanisms for attenuation in granular media.

Ita, S.L.

1994-08-01

236

Thermodynamics and kinetic theory of granular materials  

NASA Astrophysics Data System (ADS)

The aim of this work is two-fold, first a kinetic theory is developed to determine the entropy balance equation for granular gases and second a thermodynamic theory of granular materials is established within the framework of continuum thermodynamics. Unlike to the entropy inequality of a simple fluid, the one obtained from the Boltzmann equation for a granular gas has a term which can be identified as the entropy density rate. For processes closed to equilibrium the entropy density, its flux, the entropy density and production rates are obtained from a non-equilibrium distribution function. A spatially homogeneous problem is also analyzed and it is shown that the entropy decay of a granular gas is associated with its temperature decay. A thermodynamic theory of granular materials is developed where the constitutive laws are restricted by the principle of material frame indifference and by the entropy principle. The results that follow from the exploitation of the entropy principle with the method of Lagrange multipliers are compared with those obtained from the kinetic theory of granular gases.

Kremer, Gilberto M.

2014-03-01

237

Mercury wetting film on sapphire  

Microsoft Academic Search

We have measured optical properties of a mercury wetting film on sapphire under high temperature and high pressure near the liquid-gas critical point of mercury by using a newly developed 45° reflection technique. We have analyzed the experimental data to deduce the density, the thickness, and the coverage of the wetting film quantitatively as functions of pressure and temperature. As

Y. Ohmasa; Y. Kajihara; M. Yao

2001-01-01

238

Wet Winding Improves Coil Encapsulation  

NASA Technical Reports Server (NTRS)

Wet-winding process encapsulates electrical coils more uniformily than conventional processes. Process requires no vacuum pump and adapts easily to existing winding machines. Encapsulant applied to each layer of wire as soon as added to coil. Wet-winding process eliminates voids, giving more uniformly encapsulated coil.

Hill, A. J.

1987-01-01

239

Wetting autophobicity of polymer melts  

Microsoft Academic Search

Numerical solutions are obtained for a set of self-consistent-field equations that give the thickness dependence of the Helmholtz energy of a polymer film. Helmholtz energies are calculated for a series of polymer melts in order to illustrate some of the unique wetting behaviours that are exhibited by amorphous polymers. The primary focus is on wetting autophobicity, where the Helmholtz energy

Kenneth R. Shull

1994-01-01

240

A Wet Film Thickness Gage.  

National Technical Information Service (NTIS)

The patent application describes a wet film thickness gage which provides a constant applied force independent of the support housing so as to enable the user to measure the thickness of wet film on a pliable substrate. A variable tension spring is used t...

D. J. Butler R. J. Toups

1974-01-01

241

Wet testing aids inspection process  

Microsoft Academic Search

Welding inspection of offshore platforms has seen a large increase in the use of non-destructive testing (NDT) being done underwater. This form of wet NDT has increased due to its acceptance and necessity. Two of the more common NDT methods are magnetic particle\\/inspection (MPI) and ultrasonics. These two techniques are probably the most economical and effective types of wet NDT

1979-01-01

242

Experimental and Numerical Study of the Response of Granular Layer in the Trap-door Problem  

NASA Astrophysics Data System (ADS)

Deriving from the traditional problem of behavior of granular materials in silos, the trap-door test is a very basic experimental test that reproduces solicitation met in a wide range of technological applications (soil reinforcement, granular material storage...). In spite of the fact that many analytical models exist for the description of this test, a large part of the behavior of granular layers submitted to a localized basal relative displacement remains obscure: influence of the displacement value, value of the friction angle of the granular matter... Carried out in quasi-static motion and involving several granular materials such as gravels and sands, the experimental study brought to light that trap-door tests systematically break down into three different successive phases depending on the amplitude of the trap-door. Pressure applied on the trap-door by the granular material decreased suddenly for very low displacement values. Then a progressive increase was observed coinciding with a progressive expansion of a subsiding zone from the bottom of the layer to its top. At last the pressure stabilized for the greater displacements of the trap-door. This last phase corresponded with the classical failure pattern used in analytical solutions: a vertical slipping plane at each edge of the trap-door. Because of very different response were obtained with sand and gravel, particularly in the transitional phase, a numerical study were carried out by means of Discrete Element Method. Involving simple spheres and complex shaped particles as clumps, a wide range of materials presenting various friction angles were tested. A neat influence of the peak friction angle on the maximal load transfer phase was observed whereas the last phase was associated with the residual friction angle. In addition, a micromechanical analysis, giving the localization of shear strains underlined the effect of the friction angle on the pattern of arching observed in the material.

Chevalier, B.; Combe, G.; Villard, P.

2009-06-01

243

Physicochemical properties of granular and non-granular cationic starches prepared under ultra high pressure.  

PubMed

Granular and non-granular cationic starches were prepared through the reaction of tapioca and corn starches with 2,3-epoxypropyl trimethyl ammonium chloride (ETMAC) using conventional and ultra high pressure (UHP)-assisted reactions. The cationic starches were characterized with respect to morphology, degree of substitution (DS), FT-IR, (13)C NMR, X-ray diffraction pattern, solubility and swelling power, pasting viscosity, and flocculating activity. Non-granular (relative to granular) cationic starches possessed higher DS values. While DS values of non-granular cationic starches were lower for UHP-assisted (relative to conventional) reaction, granular cationic starches did not differ for both reactions. For flocculation activity, granular cationic starches with lower solubility and higher swelling power were higher than non-granular counterparts with reversed patterns in solubility and swelling power, regardless of conventional and UHP-assisted reactions. Overall results suggested that flocculation activity of cationic starches may be directly associated with their swelling powers (relative to DS values). PMID:24274522

Chang, Yoon-Je; Choi, Hyun-Wook; Kim, Hyun-Seok; Lee, Hyungjae; Kim, Wooki; Kim, Dae-Ok; Kim, Byung-Yong; Baik, Moo-Yeol

2014-01-01

244

Wet Mars, Dry Mars  

NASA Astrophysics Data System (ADS)

The magnetic fields of the large terrestrial planets, Venus, Earth, and Mars, are all vastly different from each other. These differences can tell us a lot about the interior structure, interior history, and even give us clues to the atmospheric history of these planets. This poster highlights the third in a series of presentations that target school-age audiences with the overall goal of helping the audience visualize planetary magnetic field and understand how they can impact the climatic evolution of a planet. Our first presentation, "Goldilocks and the Three Planets," targeted to elementary school age audiences, focuses on the differences in the atmospheres of Venus, Earth, and Mars and the causes of the differences. The second presentation, "Lost on Mars (and Venus)," geared toward a middle school age audience, highlights the differences in the magnetic fields of these planets and what we can learn from these differences. Finally, in the third presentation, "Wet Mars, Dry Mars," targeted to high school age audiences and the focus of this poster, the emphasis is on the long term climatic affects of the presence or absence of a magnetic field using the contrasts between Earth and Mars. These presentations are given using visually engaging spherical displays in conjunction with hands-on activities and scientifically accurate 3D models of planetary magnetic fields. We will summarize the content of our presentations, discuss our "lessons learned" from formative evaluation, and show (pictures of) our hands-on activities and 3D models.

Fillingim, Matthew; Brain, D.; Peticolas, L.; Yan, D.; Fricke, K.; Thrall, L.

2012-10-01

245

Driven fragmentation of granular gases.  

PubMed

The dynamics of homogeneously heated granular gases which fragment due to particle collisions is analyzed. We introduce a kinetic model which accounts for correlations induced at the grain collisions and analyze both the kinetics and relevant distribution functions these systems develop. The work combines analytical and numerical studies based on direct simulation Monte Carlo calculations. A broad family of fragmentation probabilities is considered, and its implications for the system kinetics are discussed. We show that generically these driven materials evolve asymptotically into a dynamical scaling regime. If the fragmentation probability tends to a constant, the grain number diverges at a finite time, leading to a shattering singularity. If the fragmentation probability vanishes, then the number of grains grows monotonously as a power law. We consider different homogeneous thermostats and show that the kinetics of these systems depends weakly on both the grain inelasticity and driving. We observe that fragmentation plays a relevant role in the shape of the velocity distribution of the particles. When the fragmentation is driven by local stochastic events, the long velocity tail is essentially exponential independently of the heating frequency and the breaking rule. However, for a Lowe-Andersen thermostat, numerical evidence strongly supports the conjecture that the scaled velocity distribution follows a generalized exponential behavior f(c) approximately exp(-cn) , with n approximately 1.2 , regarding less the fragmentation mechanisms. PMID:18643255

Cruz Hidalgo, Raúl; Pagonabarraga, Ignacio

2008-06-01

246

Vortices in vibrated granular rods  

NASA Astrophysics Data System (ADS)

We report the experimental observation of vortex patterns in vertically vibrated granular rods. Above a critical packing fraction, moving ordered domains of nearly vertical rods spontaneously form and coexist with horizontal rods. The domains of vertical rods coarsen in time to form large vortices. We investigate the conditions under which the vortices occur by varying the number of rods, vibration amplitude, and frequency. The size of the vortices increases with the number of rods. We characterize the growth of the ordered domains by measuring the area fraction of the ordered regions as a function of time. A void-filling model is presented to describe the nucleation and growth of the vertical domains. We track the ends of the vertical rods and obtain the velocity fields of the vortices. The rotation speed of the rods is observed to depend on the vibration velocity of the container and on the packing. To investigate the impact of the direction of driving on the observed phenomena, we performed experiments with the container vibrated horizontally. Although vertical domains form, vortices are not observed. We therefore argue that the motion is generated due to the interaction of the inclination of the rods with the bottom of a vertically vibrated container. We also perform simple experiments with a single row of rods in an annulus. These experiments directly demonstrate that the rod motion is generated when the rods are inclined from the vertical, and is always in the direction of the inclination.

Blair, Daniel L.; Neicu, T.; Kudrolli, A.

2003-03-01

247

Driven fragmentation of granular gases  

NASA Astrophysics Data System (ADS)

The dynamics of homogeneously heated granular gases which fragment due to particle collisions is analyzed. We introduce a kinetic model which accounts for correlations induced at the grain collisions and analyze both the kinetics and relevant distribution functions these systems develop. The work combines analytical and numerical studies based on direct simulation Monte Carlo calculations. A broad family of fragmentation probabilities is considered, and its implications for the system kinetics are discussed. We show that generically these driven materials evolve asymptotically into a dynamical scaling regime. If the fragmentation probability tends to a constant, the grain number diverges at a finite time, leading to a shattering singularity. If the fragmentation probability vanishes, then the number of grains grows monotonously as a power law. We consider different homogeneous thermostats and show that the kinetics of these systems depends weakly on both the grain inelasticity and driving. We observe that fragmentation plays a relevant role in the shape of the velocity distribution of the particles. When the fragmentation is driven by local stochastic events, the long velocity tail is essentially exponential independently of the heating frequency and the breaking rule. However, for a Lowe-Andersen thermostat, numerical evidence strongly supports the conjecture that the scaled velocity distribution follows a generalized exponential behavior f(c)˜exp(-cn) , with n?1.2 , regarding less the fragmentation mechanisms.

Cruz Hidalgo, Raúl; Pagonabarraga, Ignacio

2008-06-01

248

Mechanics of Granular Materials (MGM)  

NASA Technical Reports Server (NTRS)

The packing of particles can change radically during cyclic loading such as in an earthquake or when shaking a container to compact a powder. A large hole (1) is maintained by the particles sticking to each other. A small, counterclockwise strain (2) collapses the hole, and another large strain (3) forms more new holes which collapse when the strain reverses (4). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (after T.L. Youd, Packing Changes and Liquefaction Susceptibility, Journal of the Geotechnical Engieering Division, 103: GT8,918-922, 1977)(Credit: NASA/Marshall Space Flight Center.)(Credit: University of Colorado at Boulder).

2000-01-01

249

Uncertainty Management in Seismic Vulnerability Assessment Using Granular Computing Based on Covering of Universe  

NASA Astrophysics Data System (ADS)

Earthquake is an abrupt displacement of the earth's crust caused by the discharge of strain collected along faults or by volcanic eruptions. Earthquake as a recurring natural cataclysm has always been a matter of concern in Tehran, capital of Iran, as a laying city on a number of known and unknown faults. Earthquakes can cause severe physical, psychological and financial damages. Consequently, some procedures should be developed to assist modelling the potential casualties and its spatial uncertainty. One of these procedures is production of seismic vulnerability maps to take preventive measures to mitigate corporeal and financial losses of future earthquakes. Since vulnerability assessment is a multi-criteria decision making problem depending on some parameters and expert's judgments, it undoubtedly is characterized by intrinsic uncertainties. In this study, it is attempted to use Granular computing (GrC) model based on covering of universe to handle the spatial uncertainty. Granular computing model concentrates on a general theory and methodology for problem solving as well as information processing by assuming multiple levels of granularity. Basic elements in granular computing are subsets, classes, and clusters of a universe called elements. In this research GrC is used for extracting classification rules based on seismic vulnerability with minimum entropy to handle uncertainty related to earthquake data. Tehran was selected as the study area. In our previous research, Granular computing model based on a partition model of universe was employed. The model has some kinds of limitations in defining similarity between elements of the universe and defining granules. In the model similarity between elements is defined based on an equivalence relation. According to this relation, two objects are similar based on some attributes, provided for each attribute the values of these objects are equal. In this research a general relation for defining similarity between elements of universe is proposed. The general relation is used for defining similarity and instead of partitioning the universe, granulation is done based on covering of universe. As a result of the study, a physical seismic vulnerability map of Tehran has been produced based on granular computing model. The accuracy of the seismic vulnerability map is evaluated using granular computing model based on covering of universe. The comparison between this model and granular computing model based on partition model of universe is undertaken which verified the superiority of the GrC based on covering of the universe in terms of the match between the achieved results with those confirmed by the related experts' judgments.

Khamespanah, F.; Delavar, M. R.; Zare, M.

2013-05-01

250

Granular Shear Zone Formation: Acoustic Emission Measurements and Fiber-bundle Models  

NASA Astrophysics Data System (ADS)

We couple the acoustic emissions method with conceptual models of granular material behavior for investigation of granular shear zone formation and to assess eminence of landslide hazard. When granular materials are mechanically loaded or sheared, they tend to produce discrete events of force network restructuring, and frictional interaction at grain contacts. Such abrupt perturbations within the granular lattice release part of the elastic energy stored in the strained material. Elastic waves generated by such events can be measured as acoustic emissions (AE) and may be used as surrogates for intermittent structural transitions associated with shear zone formation. To experimentally investigate the connection between granular shearing and acoustic signals we performed an array of strain-controlled shear-frame tests using glass beads. AE were measured with two different systems operating at two frequency ranges. High temporal resolution measurements of the shear stresses revealed the presence of small fluctuations typically associated with low-frequency (< 20 kHz) acoustic bursts. Shear stress jumps and linked acoustic signals give account of discrete events of grain network rearrangements and obey characteristic exponential frequency-size distributions. We found that statistical features of force jumps and AE events depend on mechanical boundary conditions and evolve during the straining process. Activity characteristics of high-frequency (> 30 kHz) AE events is linked to friction between grains. To interpret failure associated AE signals, we adapted a conceptual fiber-bundle model (FBM) that describes some of the salient statistical features of failure and associated energy production. Using FBMs for the abrupt mechanical response of the granular medium and an associated grain and force chain AE generation model provides us with a full description of the mechanical-acoustical granular shearing process. Highly resolved AE may serve as a diagnostic tool not only for detection of shear zone development and straining in granular matter and but also for investigating internal grain scale mechanical processes. The AE method could be integrated into monitoring networks of landslide-prone slopes and other early warning systems for abrupt mass release (snow avalanches).

Michlmayr, Gernot; Or, Dani

2013-04-01

251

Evaluation of Wet Distillers Grains in Finishing Diets for Yearling Steers  

Microsoft Academic Search

A feeding trial was conducted with 940-lb yearling steers fed 113 days to determine the feeding value of distillers grains relative to corn grain. Replacing corn and urea with wet distillers grains for 20% of the diet dry matter tended to increase gain with no increase in feed consumption, resulting in improved feed conversion. Replacing 40% of diet dry matter

Allen Trenkle

1997-01-01

252

Granular Materials and Risks In ISRU  

NASA Technical Reports Server (NTRS)

Working with soil, sand, powders, ores, cement and sintered bricks, excavating, grading construction sites, driving off-road, transporting granules in chutes and pipes, sifting gravel, separating solids from gases, and using hoppers are so routine that it seems straightforward to execute these operations on the Moon and Mars as we do on Earth. We discuss how little these processes are understood and point out the nature of trial-and-error practices that are used in today's massive over-design. Nevertheless, such designs have a high failure rate. Implementation and extensive incremental scaling up of industrial processes are routine because of the inadequate predictive tools for design. We present a number of pragmatic scenarios where granular materials play a role, the risks involved, what some of the basic issues are, and what understanding is needed to greatly reduce the risks. This talk will focus on a particular class of granular flow issues, those that pertain to dense materials, their physics, and the failure problems associated with them. In particular, key issues where basic predictability is lacking include stability of soils for the support of vehicles and facilities, ability to control the flow of dense materials (jamming and flooding/unjamming at the wrong time), the ability to predict stress profiles (hence create reliable designs) for containers such as bunkers or silos. In particular, stress fluctuations, which are not accounted for in standard granular design models, can be very large as granular materials flows, and one result is frequent catastrophic failure of granular devices.

Behringer, Robert P.; Wilkinson, R. Allen

2004-01-01

253

Granular Materials and Risks in ISRU  

NASA Technical Reports Server (NTRS)

Working with soil, sand, powders, ores, cement and sintered bricks, excavating, grading construction sites, driving off-road, transporting granules in chutes and pipes, sifting gravel, separating solids from gases, and using hoppers are so routine that it seems straightforward to execute these operations on the Moon and Mars as we do on Earth. We discuss how little these processes are understood and point out the nature of trial-and-error practices that are used in today s massive over-design. Nevertheless, such designs have a high failure rate. Implementation and extensive incremental scaling up of industrial processes are routine because of the inadequate predictive tools for design. We present a number of pragmatic scenarios where granular materials play a role, the risks involved, what some of the basic issues are, and what understanding is needed to greatly reduce the risks. This talk will focus on a particular class of granular flow issues, those that pertain to dense materials, their physics, and the failure problems associated with them. In particular, key issues where basic predictability is lacking include stability of soils for the support of vehicles and facilities, ability to control the flow of dense materials (jamming and flooding/unjamming at the wrong time), the ability to predict stress profiles (hence create reliable designs) for containers such as bunkers or silos. In particular, stress fluctuations, which are not accounted for in standard granular design models, can be very large as granular materials flows, and one result is frequent catastrophic failure of granular devices.

Behringer, Robert P.; Wilki8nson, R. Allen

2004-01-01

254

Jamming and Fluidization in Granular Flows  

NASA Astrophysics Data System (ADS)

Granular materials exist all around us, from avalanches in nature to the mixing of pharmaceuticals, yet the behavior of these ``fluids'' is poorly understood. While the interaction of individual particles is simply through friction and inelastic collisions, the non-linear forces and large number of particles leads to an unpredictable, complex system. Flow can be characterized by the continuous forming and breaking of a strong force network resisting flow, leading to jamming, avalanching and shear banding. I'll present recent work on quasi-static shear and free-surface granular flows under the influence of external vibrations as well as related experiments on particle-fluid suspensions. By using photoelastic grains, we are able to measure both particle trajectories and the local force network in 2D flows. We find through particle tracking that dense granular flow is composed of comparable contributions from the mean flow, elastic deformations, and permanent, plastic deformations. Vibration typically weakens granular materials and removes hysteresis, though small vibrations can lead to strengthening of a pile. Flows of particle-fluid suspensions allow another avenue to probe failure of granular piles and additional control parameters, such as the surface chemistry of the particles.

Utter, Brian

2011-10-01

255

Kinetic Models for Granular Flow  

NASA Astrophysics Data System (ADS)

The generalization of the Boltzmann and Enskog kinetic equations to allow inelastic collisions provides a basis for studies of granular media at a fundamental level. For elastic collisions the significant technical challenges presented in solving these equations have been circumvented by the use of corresponding model kinetic equations. The objective here is to discuss the formulation of model kinetic equations for the case of inelastic collisions. To illustrate the qualitative changes resulting from inelastic collisions the dynamics of a heavy particle in a gas of much lighter particles is considered first. The Boltzmann-Lorentz equation is reduced to a Fokker-Planck equation and its exact solution is obtained. Qualitative differences from the elastic case arise primarily from the cooling of the surrounding gas. The excitations, or physical spectrum, are no longer determined simply from the Fokker-Planck operator, but rather from a related operator incorporating the cooling effects. Nevertheless, it is shown that a diffusion mode dominates for long times just as in the elastic case. From the spectral analysis of the Fokker-Planck equation an associated kinetic model is obtained. In appropriate dimensionless variables it has the same form as the BGK kinetic model for elastic collisions, known to be an accurate representation of the Fokker-Planck equation. On the basis of these considerations, a kinetic model for the Boltzmann equation is derived. The exact solution for states near the homogeneous cooling state is obtained and the transport properties are discussed, including the relaxation toward hydrodynamics. As a second application of this model, it is shown that the exact solution for uniform shear flow arbitrarily far from equilibrium can be obtained from the corresponding known solution for elastic collisions. Finally, the kinetic model for the dense fluid Enskog equation is described.

Brey, J. Javier; Dufty, James W.; Santos, Andrés

1999-10-01

256

Energy Conservation for Granular Coal Injection into a Blast Furnace  

NASA Astrophysics Data System (ADS)

Due to the lack of knowledge regarding the combustion of granular coal injected into a blast furnace, injection characteristics of granular coal were first studied through proximate analysis, element analysis, and research of explosivity, ignition point, meltability of ash, grindability, calorific value, etc. Using a sampling device in the raceway combined with petrographic analysis, during the combustion process of granular coal with high crystal water and volatile in raceway, cracks and bursts were found, leading to a reduction of particle size. Based on a model of mass control and dynamic theory of particle combustion, the transition dynamic model for cracking in combustion of granular coal was found, and the critical value of cracking ratio (?P) for granular coal combustion in the raceway was calculated. Finally, the utilization ratio and energy efficiency of granular coal used in the blast furnace were discussed, offering theoretical foundation and technical support for intensifying granular coal combustion and promoting granular coal injection.

Guo, Hongwei; Su, Buxin; Zhang, Jianliang; Shao, Jiugang; Zuo, Haibin; Ren, Shan

2012-08-01

257

Model of sheared granular material and application to surface-driven granular flows under gravity  

NASA Astrophysics Data System (ADS)

This work presents a novel model of sheared granular materials that consist of two-dimensional, slightly inelastic, circular disks. To capture the static and kinetic features of the granular flow involving different regimes, both the shear stress and pressure are superimposed by a rate-independent component (representing the static contribution) and a rate-dependent component (representing the kinetic contribution), as determined using granular kinetic theory. The dilatancy law is adopted to close the set of equations, and the constraint that static pressure is non-negative is utilized to determine the transition between the dense regime and the inertial regime. The balance equation of granular temperature incorporates the works done by both the static and kinetic components of shear stress. This enabled the proposed model to predict the hysteretic flow thresholds and the shear bands. Additionally, a thick, surface-driven granular flow under gravity is investigated using the proposed model. The predicted velocity, volume fraction, granular temperature, and stress are consistent with results obtained using the molecular dynamic method. This finding demonstrates the ability of the proposed model to simulate granular flow in which the quasistatic, dense, and kinetic regimes coexist simultaneously.

Lee, Cheng-Hsien; Huang, Ching-Jer

2010-04-01

258

High-pressure wet carbonization  

SciTech Connect

The objectives of this program are to design and construct a continuous wet carbonization process development unit (PDU), and to operate the PDU to determine the effects of temperature and residence time on the dewaterability and heat value of Minnesota, North Carolina, and Maine peats. Additional information will be generated on the effect that the wet carbonization process has on the hydrogasification characteristics of these peats. Further information on the heat transfer and slurry transport characteristics will also be obtained.

Paganessi, J.E.; Knowlton, T.M.; Punwani, D.V.; Lau, F.S.

1981-04-01

259

WET BEAVER ROADLESS AREA, ARIZONA.  

USGS Publications Warehouse

On the basis of field studies there is little promise for the occurrence of mineral or energy resources in the Wet Beaver Roadless Area, Arizona. No significant concentrations of metals were indicated by geochemical sampling or aeromagnetic data within the area. Basaltic cinders and sandstone have been quarried for construction materials near the area but are readily available and more accessible outside the precipitous canyons of Wet Beaver Creek and its tributaries.

Ulrich, George, E.; Bielski, Alan, M.

1984-01-01

260

Granular flow transitions on sinusoidal surfaces  

NASA Astrophysics Data System (ADS)

We report on a newly discovered bifurcation that occurs in dry grains flowing down a chute with a wavy bottom. We find that the bifurcation outwardly resembles the long-known fluid analogue of inviscid channel flow over a wavy bottom reported in 1886 by Lord Kelvin; however, in detail, the two situations differ significantly. We compare three distinct states seen in the granular system: a ‘regular’ flow in phase with the bottom wave; an ‘antiregular’ flow that is out of phase; and a ‘flat’ flow in which the surface slides nearly uniformly downhill. Additionally, we discuss evidence that sustained subsurface circulation in the granular bed, accompanied by strong fluctuations in flow velocities, can appear in granular flows over wavy surfaces.

Caicedo-Carvajal, Carlos E.; Glasser, Benjamin J.; Shinbrot, Troy

2006-06-01

261

Unstable blast shocks in dilute granular flows  

NASA Astrophysics Data System (ADS)

Shocks and blasts can be readily obtained in granular flows be they dense or dilute. Here, by examining the propagation of a blast shock in a dilute granular flow, we show that such a front is unstable with respect to transverse variations of the density of grains. This instability has a well-defined wavelength which depends on the density of the medium and has an amplitude which grows as an exponential of the distance traveled. These features can be understood using a simple model for the shock front, including dissipation which is inherent to granular flows. While this instability bears much resemblance to that anticipated in gases, it is distinct and has special features we discuss here.

Boudet, J. F.; Kellay, H.

2013-05-01

262

Probing Interparticle Adhesion of Dry and Wet Granular Materials with the Quartz Crystal Microbalance  

Microsoft Academic Search

The strength of the contacts between small glass spheres and the surface of a quartz crystal resonator has been probed based on the increase of resonance frequency induced upon sphere contact. The acoustic interaction between the sphere and the plate is modeled as a low-frequency coupled resonance; the dependence of the resonant parameters on overtone order lends support to this

Diethelm Johannsmann; Nelson J. d'Amour; Kay K. Kanazawa; Johan J. R. Stalgren; Curt. W. Frank; M. Rodahl

2006-01-01

263

Mercury wetting film on sapphire.  

PubMed

We have measured optical properties of a mercury wetting film on sapphire under high temperature and high pressure near the liquid-gas critical point of mercury by using a newly developed 45 degrees reflection technique. We have analyzed the experimental data to deduce the density, the thickness, and the coverage of the wetting film quantitatively as functions of pressure and temperature. As a first approximation, we have assumed a slab model for the density profile of the wetting film, and found that the density of the wetting film dslab is much smaller than that of bulk liquid at the liquid-vapor coexistence curve. This result is consistent with the Lifshitz theory, from which we may predict that the sapphire substrate prefers wetting film with density lower than the metal-nonmetal transition. When the temperature is close enough to the prewetting critical temperature Tpw(c), the effective slab density dslab shows a sharp decrease as the pressure approaches the liquid-gas coexistence. This indicates that the slab model is not sufficient to describe the shape of the wetting film, and a smooth variation of the density has to be taken into account. In the prewetting supercritical region, two anomalies are observed in the reflectances. Possible mechanisms of these anomalies are discussed. PMID:11414910

Ohmasa, Y; Kajihara, Y; Yao, M

2001-05-01

264

Simulating granular media on the computer  

NASA Astrophysics Data System (ADS)

Granular materials, like sand or powder, can present very intriguing effects. When shaken, sheared or poured they show segregation, convection and spontaneous fluctuations in densities and stresses. I will discuss the modeling of a granular medium on a computer by simulating a packing of elastic spheres via Molecular Dynamics. Dissipation of energy and shear friction at collisions are included. In the physical range the friction coefficient is found to be a linear function of the angle of repose. On a vibrating plate the formation of convection cells due to walls or amplitude modulations can be observed. The onset of fluidization can be determined and is in good agreement with experiments. Segregation of larger particles is found to be always accompanied by convection cells. There is also ample experimental evidence showing the existence of spontaneous density patterns in granular material flowing through pipes or hoppers. The Molecular Dynamics simulations show that these density fluctuations follow a 1/f ? spectrum. I compare this behavior to deterministic one-dimensional traffic models. A model with continuous positions and velocities shows self-organized critical jamming behind a slower car. The experimentally observed effects are also reproduced by Lattice Gas and Boltzmann Lattice Models. Density waves are spontaneously generated when the viscosity has a nonlinear dependence on density which characterizes granular flow. We also briefly sketch a thermodynamic formalism for loose granular material. In a dense packing non-linear acoustic phenomena, like the pressure dependence of the sound velocity are studied. Finally the plastic shear bands occurring in large scale deformations of compactified granular media are investigated using an explicit Lagrangian technique.

Herrmann, H. J.

265

A framework for efficient progressive fine granularity scalable video coding  

Microsoft Academic Search

In this paper, a basic framework for efficient scalable video coding, namely progressive fine granularity scalable (PFGS) video coding is proposed. Similar to the fine granularity scalable (FGS) video coding in MPEG-4, the PFGS framework has all the features of FGS, such as fine granularity bit-rate scalability, channel adaptation, and error recovery. On the other hand, dif- ferent from the

Feng Wu; Shipeng Li; Ya-qin Zhang

2001-01-01

266

Pressure exerted by a granular material along a curved channel  

Microsoft Academic Search

The method of characteristics by Sokolovski is extended to find the stresses exerted by a granular material along a curved channel. As the grain flow develops, the granular material is considered under the criterical state of plastic equilibrium. The state of stress on any plane within the granular material may be represented by a Mohr circle in the ?-? plane,

L. T. Lee; D. C. Lee

1995-01-01

267

Forces on Intruders in Granular Media  

NASA Astrophysics Data System (ADS)

We measure the forces acting on intruders moving in different directions in a granular medium consisting of mono-disperse spherical glass beads. We present the dependence of the drag force on the intruder's geometry and surface roughness, bead size, dragging speed and immersion depth. We present a model that considers not only the wedge dragged by the intruder but also the pile created as the intruder moves through the granular material to calculate the drag force. We compare our experimental and analytical results.

de La Cruz, Ibar; Koehler, Stephan

2013-03-01

268

Challenges in Predicting Planetary Granular Mechanics  

NASA Technical Reports Server (NTRS)

Through the course of human history, our needs in agriculture, habitat construction, and resource extraction have driven us to gain more experience working with the granular materials of planet Earth than with any other type of substance in nature, with the possible exception being water. Furthermore, throughout the past two centuries we have seen a dramatic and ever growing interest among scientists and engineers to understand and predict both its static and rheological properties. Ironically, however, despite this wealth of experience we still do not have a fundamental understanding of the complex physical phenomena that emerge even as just ordinary sand is shaken, squeezed or poured. As humanity is now reaching outward through the solar system, not only robotic ally but also with our immediate human presence, the need to understand and predict granular mechanics has taken on a new dimension. We must learn to farm, build and mine the regoliths of other planets where the environmental conditions are different than on Earth, and we are rapidly discovering that the effects of these environmental conditions are not trivial. Some of the relevant environmental features include the regolith formation processes throughout a planet's geologic and hydrologic history, the unknown mixtures of volatiles residing within the soil, the relative strength of gravitation, d the atm9spheric pressure and its seasonal variations. The need to work with soils outside our terrestrial experience base provides us with both a challenge and an opportunity. The challenge is to learn how to extrapolate our experience into these new planetary conditions, enabling the engineering decisions that are needed right now as we take the next few steps in solar system exploration. The opportunity is to use these new planetary environments as laboratories that will help us to see granular mechanics in new ways, to challenge our assumptions, and to help us finally unravel the elusive physics that lie behind complex granular phenomena. Toward these goals, a workshop was held recently at NASA's John F. Kennedy Space Center, attracting over a hundred scientists and engineers from around the world and from a broad crosssection of scientific and engineering disciplines. This talk will provide an out-briefing from that workshop, communicating some of its early findings in regard to lunar and Martian exploration: (1) the requirements for working with granular materials, (2) the challenges that granular materials will pose, (3) the environmental conditions that affect granular mechanics, (4) instruments and measurements that are needed on the Moon and Mars to support granular material research, and (5) some of the possible research avenues that should be pursued.

Metzger, Philip T.

2005-01-01

269

Comparison of Hyperelastic Models for Granular Materials  

SciTech Connect

Three recently proposed hyperelastic models for granular materials are compared with experiment data. Though all three are formulated to give elastic moduli that are power law functions of the mean stress, they have rather different dependencies on individual stresses, and generally differ from well established experimental forms. Predicted static stress distributions are in qualitative agreement with experiments, but do not differ greatly from isotropic linear elasticity, and similarly fail to account for variability in experiment data that presumably occurs due to a preparation dependence of granular materials.

Paul W. Humrickhouse; J. Phil Sharpe; Michael L. Corradini

2010-01-01

270

Spatially modulated kinks in shallow granular layers.  

PubMed

We report on the experimental observation of spatially modulated kinks in a shallow one-dimensional fluidized granular layer subjected to a periodic air flow. We show the appearance of these solutions as the layer undergoes a parametric instability. Due to the inherent fluctuations of the granular layer, the kink profile exhibits an effective wavelength, a precursor, which modulates spatially the homogeneous states and drastically modifies the kink dynamics. We characterize the average and fluctuating properties of this solution. Finally, we show that the temporal evolution of these kinks is dominated by a hopping dynamics, related directly to the underlying spatial structure. PMID:24032762

Macías, J E; Clerc, M G; Falcón, C; García-Ñustes, M A

2013-08-01

271

SETAC-U.S. EPA WET INITIATIVES: ALL WET AND NOTHING BUT WET  

EPA Science Inventory

To ensure that sould scientific principles and sound science are applied to the challenging issues in t he Whole Effluent Toxicity (WET) process, the Society of Environmental Toxicology and Chemistry (SETAC) Foundation for Environmental Education was awarded a cooperative agreem...

272

Magnetically shaped cell aggregates: from granular to contractile materials.  

PubMed

In recent decades, significant advances have been made in the description and modelling of tissue morphogenesis. By contrast, the initial steps leading to the formation of a tissue structure, through cell-cell adhesion, have so far been described only for small numbers of interacting cells. Here, through the use of remote magnetic forces, we succeeded at creating cell aggregates of half million cells, instantaneously and for several cell types, not only those known to form spheroids. This magnetic compaction gives access to the cell elasticity, found in the range of 800 Pa. The magnetic force can be removed at any time, allowing the cell mass to evolve spontaneously thereafter. The dynamics of contraction of these cell aggregates just after their formation (or, in contrast, their spreading for non-interacting monocyte cells) provides direct information on cell-cell interactions and allows retrieving the adhesion energy, in between 0.05 and 2 mJ m(-2), depending on the cell type tested, and in the case of cohesive aggregates. Thus, we show, by probing a large number of cell types, that cell aggregates behave like complex materials, undergoing a transition from a wet granular to contractile network, and that this transition is controlled by cell-cell interactions. PMID:24710948

Frasca, G; Du, V; Bacri, J-C; Gazeau, F; Gay, C; Wilhelm, C

2014-06-25

273

Statistical mechanics of dry granular materials: Between fragile solid (jamming) and dry fluid (rheology)  

NASA Astrophysics Data System (ADS)

Dry granular matter, with infinite tangential friction, is modeled as a connected graph of grains linked by purely repulsive contacts. The degrees of freedom of a grain are non-slip rotation on, and disconnection from another. The material stability under shear (jamming) is ensured by odd circuits of grains in contact that prevent the grains from rolling on each other. A dense hard granular material has two possible states: fragile solid, blocked by odd circuits, and dry fluid or bearing, in the absence of odd circuits, that flows under shear by creation and glide of a pair of dislocations as in plasticity of continuous media. We did introduce the notions of blob, a region of the material containing only even circuits, and of critical contact that closes an odd circuit. The granular material is then represented, at low energies and critical applied shear, as a chain of blobs connected by critical contacts. The entropy is the logarithm of the number of spanning trees constrained to go through critical links. For a vanishing tangential friction, the graph description with the frustrating odd circuits is still valid, because the force between grains remains a scalar and repulsive. A granular material inside a cylindrical drum rotating at constant velocity around its horizontal axis alternates intermittently between solid and fluid states. As a fragile solid, it follows a limit cycle of avalanches (slip) and stuck rotations with the drum. This is the stick-slip behavior of a solid subjected to solid friction (to the driving drum) and gravity. In the fluid state, the friction is viscous and the granular material flows to a fixed point with constant slope.

Rivier, Nicolas; Fortin, Jean-Yves

2013-06-01

274

A simple lattice model for the effect of voids on slip avalanches in sheared granular materials  

NASA Astrophysics Data System (ADS)

It is well known that densely packed granular materials respond to slow shear with slip avalanches. Experiments and simulations show that the avalanche statistics depend strongly on the granular volume fraction v and grain shape related properties [1]. Previous studies have focused on force chain properties [2-6]. Here we use a mean field technique to construct an analytic model of the universal (i.e. detail-independent) slip avalanche statistics. For large v, and small frictional weakening ?, the model predicts solid-like behavior, with power-law avalanche size distributions and universal exponents and scaling functions. For large v and large ? it predicts mode switching between stick slip behavior and power law avalanche size distributions. For small v it predicts fluid-like flow. The results are presented in a (v, ?) phase diagram. They agree with published experiments [6-10] and simulations [2-4]. They complement recent studies on static properties, such as the shear modulus as a function of v near the jamming transition [2-4,7-10]. References: [1] V. Frette et al., “Avalanche Dynamics in a Pile of Rice”, Nature 379, 49-52 (1996). [2] E. Aharonov and D. Sparks, “Rigidity phase transition in granular packings”, Phys. Rev E, 60, 6890-6896 (1999). [3] E. Aharonov and D. Sparks, “Stick-slip motion in simulated granular layers”, J. Geophys. Res, 109, B09306 (2004). [4] E. Aharonov and D. Sparks, “Shear profiles and localization in simulations of granular materials”, Phys. Rev. E 65, 051302/1-12 (2002). [5] M.E. Cates, J.P. Wittmer, J.-P. Bouchaud, and P. Claudin, “Jamming, Force Chains, and Fragile Matter”, Phys. Rev. Lett., 81, 1841 (1998) and references therein. [6

Dahmen, K.; Ben-Zion, Y.; Uhl, J. T.

2009-12-01

275

Structure of granular clusters formed by capillary aggregation analyzed with Voronoi diagrams  

NASA Astrophysics Data System (ADS)

We investigate the spatial structure of particle aggregates floating at an air-liquid interface as a model system to understand heterogeneity of cohesive granular matter. The meniscus around identical floating particles introduces short range capillary attraction between the particles. In our experimental system, we increase slowly and continuously the particle number density to observe significant structural transformations. After imaging and tracking all the particles, the structure is characterized quantitatively by using Voronoi diagrams which allow us to elucidate small and large scale properties. We show that the system is organized by attraction for low and intermediate densities, which creates a short range order and gives it heterogeneity with pores of various sizes. As the free pore space are filled at high density, the role of attraction becomes less important compared with steric effects and aggregates show characteristics similar to non-cohesive granular media. Mechanical properties of aggregates will be also discussed in light of jamming transition for attractive athermal particles.

Berhanu, Michael; Kudrolli, Arshad

2010-03-01

276

Measurements of Stopping Force on Ball on Impact with Granular Medium  

NASA Astrophysics Data System (ADS)

We present direct measurements of the deceleration vs. time of a 3.8 cm diameter brass ball plunging into a loose granular bed of 400 - 600 ?m glass beads. Data were obtained using an accelerometer chip housed within the ball. As suggested by Durian and co-workers, the measured force on the ball is well described by a velocity dependent force ?v^2 plus a separate depth dependent force ?(z+z0). For impact velocities in the range 1.3 -- 5.1 m/s, a single set of parameters (?,?,z0) fits all the data well, with the exception of the first few ms after impact, when the ball is only partially submerged in the granular matter.

Amato, Joseph; Coyle, Laura; Nitzberg, Michael

2009-03-01

277

Adsorption of Tin Using Granular Activated Carbon  

Microsoft Academic Search

Adsorption studies for removal of tin from the aqueous phase using granular activated carbon (GAC) and characterization of GAC were carried out. Particle size, proximate, ash, and ultimate analyses were carried out for the physiochemical characteristics of GAC. Thermogravimetric analysis was also done both in ambient and nitrogen atmospheres to see the effect of temperature on GAC stability. Morphological characteristics

Kailas L. WASEWAR; Shiv KUMAR; B. PRASAD

2009-01-01

278

Granular computing, rough entropy and object extraction  

Microsoft Academic Search

The problem of image object extraction in the framework of rough sets and granular computing is addressed. A mea- sure called ''rough entropy of image'' is defined based on the concept of image granules. Its maximization results in minimization of roughness in both object and background regions; thereby determining the threshold of partitioning. Methods of selecting the appropriate granule size

Sankar K. Pal; B. Uma Shankar; Pabitra Mitra

2005-01-01

279

Granular Activated Carbon Filter-Adsorber Systems  

Microsoft Academic Search

The design, operation, and performance of granular activated carbon (GAC) filter-adsorbers were documented and potential problems were identified by means of a survey of operating plants and a review of the literature. It was found that GAC as a total or partial replacement for sand is as effective as conventional filtration media for removing turbidity, provided an appropriate medium size

Sandra L. Graese; Vernon L. Snoeyink; Ramon G. Lee

1987-01-01

280

OPTIMIZING GAC (GRANULAR ACTIVATED CARBON) SYSTEMS  

EPA Science Inventory

Granular activated carbon (GAC) is an effective technique for removing synthetic organics from both ground and surface waters. Questions have been raised, however, over the cost of using GAC in this manner. To provide insight into these cost issues, the Drinking Water Research Di...

281

EPA'S RESEARCH PROGRAM IN GRANULAR ACTIVATED CARBON  

EPA Science Inventory

Research into Granular Activated Carbon (GAC) for use in drinking water treatment has a long history in the Drinking Water Research Division and its predecessor organizations. tudies were conducted by the U.S. Public Health Service in the late fifties and early sixties to examine...

282

Localized fluidization in a granular medium.  

PubMed

We present here experimental results on the progressive development of a fluidized zone in a bed of grains, immersed in a liquid, under the effect of a localized upward flow injected through a small orifice at the bottom of the bed. Visualization inside the model granular medium consisting of glass beads is made possible by the combined use of two optical techniques: refractive index matching between the liquid and the beads and planar laser-induced fluorescence. Gradually increasing the injection rate, three regimes are successively observed: static bed, fluidized cavity that does not open to the upper surface of the granular bed, and finally fluidization over the entire height of the granular bed inside a fluidized chimney. The phase diagram is plotted and partially interpreted using a model previously developed by Zoueshtiagh and Merlen [F. Zoueshtiagh and A. Merlen, Phys. Rev. E 75, 053613 (2007)]. A typical sequence, where the flow rate is first increased and then decreased back to zero, reveals a strong hysteretic behavior since the stability of the fluidized cavity is considerably strengthened during the defluidization phase. This effect can be explained by the formation of force arches within the granular packing when the chimney closes up at the top of the bed. A study of the expansion rate of the fluidized cavity was also conducted as well as the analysis of the interaction between two injection orifices with respect to their spacing. PMID:23679406

Philippe, P; Badiane, M

2013-04-01

283

Dynamical behaviour of rotated granular mixtures  

NASA Astrophysics Data System (ADS)

We present a phenomenological model for the dynamics of granular mixtures in a rotating drum. We demonstrate that our model successfully captures many of the experimental features known in the context of this problem. The results presented here are supplementary to those presented in a detailed paper (S. Puri, H. Hayakawa, cond-mat/9901260).

Puri, Sanjay; Hayakawa, Hisao

1999-08-01

284

Elastic wave propagation in confined granular systems  

Microsoft Academic Search

We present numerical simulations of acoustic wave propagation in confined granular systems consisting of particles interacting with the three-dimensional Hertz-Mindlin force law. The response to a short mechanical excitation on one side of the system is found to be a propagating coherent wave front followed by random oscillations made of multiply scattered waves. We find that the coherent wave front

Ellák Somfai; Jean-Noël Roux; Jacco H. Snoeijer; Martin van Hecke; Wim van Saarloos

2005-01-01

285

REGIONAL REACTIVATION OF GRANULAR ACTIVATED CARBON  

EPA Science Inventory

A major portion of the cost of using Granular Activated Carbon (GAC) as a water treatment unit process is associated with spent carbon replacement or reactivation. Regional reactivation or sharing a reactivation furnace among several users, has been proposed as a means of minimiz...

286

Simulation of a Driven Dense Granular Gas  

NASA Astrophysics Data System (ADS)

Event driven particle simulations quantitatively reproduce the experimental results on vibrated granular layers, including the formation of standing wave patterns(C. Bizon, M.D. Shattuck, J.B. Swift, W.D. McCormick, and H.L. Swinney, Phys. Rev. Lett. 80), pp. 57-60 (1998). and secondary instabilities(J.R. deBruyn, C. Bizon, M.D. Shattuck, D. Goldman, J.B. Swift, and H.L. Swinney, Phys. Rev. Lett. 81) (1998), to appear. . In these simulations the velocity distributions are nearly Gaussian when scaled with the local fluctuational kinetic energy (granular temperature); this suggests that inelastic dense gas kinetic theory is applicable. We perform simulations of a two-dimensional granular gas that is homogeneously driven with fluctuating forces. We find that the equation of state differs from that of an elastic dense gas and that this difference is due to a change in the distribution of relative velocities at collisions. Granular thermal conductivity and viscosity are measured by allowing the fluctuating forces to have large scale spatial gradients.

Bizon, Chris; Shattuck, M. D.; Swift, J. B.; Swinney, Harry L.

1998-11-01

287

Energy flow with high granularity calorimeters  

NASA Astrophysics Data System (ADS)

In order to perform high precision measurements as well as search for new phenomena at a next Linear Collider, excellent ENERGY FLOW is mandatory. High granularity calorimeters design will fulfill the requests and preliminary results are presented as well as further directions to reach the final performances. .

Gay, P.

2001-07-01

288

Localized fluidization in a granular medium  

NASA Astrophysics Data System (ADS)

We present here experimental results on the progressive development of a fluidized zone in a bed of grains, immersed in a liquid, under the effect of a localized upward flow injected through a small orifice at the bottom of the bed. Visualization inside the model granular medium consisting of glass beads is made possible by the combined use of two optical techniques: refractive index matching between the liquid and the beads and planar laser-induced fluorescence. Gradually increasing the injection rate, three regimes are successively observed: static bed, fluidized cavity that does not open to the upper surface of the granular bed, and finally fluidization over the entire height of the granular bed inside a fluidized chimney. The phase diagram is plotted and partially interpreted using a model previously developed by Zoueshtiagh and Merlen [F. Zoueshtiagh and A. Merlen, Phys. Rev. E10.1103/PhysRevE.75.056313 75, 053613 (2007)]. A typical sequence, where the flow rate is first increased and then decreased back to zero, reveals a strong hysteretic behavior since the stability of the fluidized cavity is considerably strengthened during the defluidization phase. This effect can be explained by the formation of force arches within the granular packing when the chimney closes up at the top of the bed. A study of the expansion rate of the fluidized cavity was also conducted as well as the analysis of the interaction between two injection orifices with respect to their spacing.

Philippe, P.; Badiane, M.

2013-04-01

289

DOWNFLOW GRANULAR FILTRATION OF ACTIVATED SLUDGE EFFLUENTS  

EPA Science Inventory

The performance of downflow granular filters subjected to effluents from activated sludge processes was investigated at the EPA-DC Pilot Plant in Washington, D.C. Several media combinations were investigated, including both single anthracite and dual anthracite-sand configuration...

290

A Partition Model of Granular Computing  

Microsoft Academic Search

There are two objectives of this chapter. One objective is to examine the basic principles and issues of granular computing. We focus on the tasks of granulation and computing with granules. From semantic and algorithmic perspectives, we study the construction, in- terpretation, and representation of granules, as well as principles and operations of computing and reasoning with granules. The other

Yiyu Yao

2004-01-01

291

Multi-scale modelling of granular avalanches  

NASA Astrophysics Data System (ADS)

Avalanches, debris flows, and landslides are geophysical hazards, which involve rapid mass movement of granular solids, water and air as a single-phase system. The dynamics of a granular flow involve at least three distinct scales: the micro-scale, meso-scale, and the macro-scale. This study aims to understand the ability of continuum models to capture the micro-mechanics of dry granular collapse. Material Point Method (MPM), a hybrid Lagrangian and Eulerian approach, with Mohr-Coulomb failure criterion is used to describe the continuum behaviour of granular column collapse, while the micromechanics is captured using Discrete Element Method (DEM) with tangential contact force model. The run-out profile predicted by the continuum simulations matches with DEM simulations for columns with small aspect ratios (`h/r' < 2), however MPM predicts larger run-out distances for columns with higher aspect ratios (`h/r' > 2). Energy evolution studies in DEM simulations reveal higher collisional dissipation in the initial free-fall regime for tall columns. The lack of a collisional energy dissipation mechanism in MPM simulations results in larger run-out distances. Micro-structural effects, such as shear band formations, were observed both in DEM and MPM simulations. A sliding flow regime is observed above the distinct passive zone at the core of the column. Velocity profiles obtained from both the scales are compared to understand the reason for a slow flow run-out mobilization in MPM simulations.

Kumar, Krishna; Soga, Kenichi; Delenne, Jean-Yves

2013-06-01

292

Optimal design of composite granular protectors  

Microsoft Academic Search

We employ an evolutionary algorithm to investigate the optimal design of composite protectors using one-dimensional granular chains composed of beads of various sizes, masses, and stiffnesses. We define a fitness function using the maximum force transmitted from the protector to a \\

Fernando Fraternali; Mason A. Porter; Chiara Daraio

2008-01-01

293

Testing ergodicity in dense granular systems  

NASA Astrophysics Data System (ADS)

The Edwards' entropy formalism provides a statistical mechanical framework for describing dense granular systems. Experiments on vibrated granular columns and numerical simulations of quasi- static shear flow of dense granular systems have provided indirect evidence that the Edwards' theory may accurately describe certain aspects of these systems. However, a fundamental assumption of the Edwards' description---that all mechanically stable (MS) granular packings at a given packing fraction and externally imposed stress are equally accessible---has not been explicitly tested. We investigate this assumption by generating all mechanically stable hard disk packings in small bidisperse systems using a protocol where we successively compress or decompress the system followed by energy minimization. We then apply quasi-static shear flow at zero pressure to these MS packings and record the MS packings that occur during the shear flow. We generate a complete library of the allowed MS packings at each value of shear strain and determine the frequency with which each MS packing occurs. We find that the MS packings do not occur with equal probability at any value of shear strain. In fact, in small systems we find that the evolution becomes periodic with a period that grows with system-size. Our studies show that ergodicity can be improved by either adding random fluctuations to the system or increasing the system size.

Gao, Guo-Jie; Blawzdziewicz, Jerzy; O'Hern, Corey

2008-03-01

294

The fractal crushing of granular materials  

Microsoft Academic Search

A study has been made of the micro mechanical origins of the irrecoverable compression of aggregates which comprise brittle grains. The terms “yielding” and “plastic hardening” are used in the discipline of soil mechanics to describe the post-elastic behaviour of granular media. These “plastic” phenomena are here related to the successive splitting of grains.Grains are taken to split probabilistically; the

G. R. McDowell; M. D. Bolton; D. Robertson

1996-01-01

295

Analysis of local behaviour in granular materials  

NASA Astrophysics Data System (ADS)

A local scale, called the meso-scale, has recently been introduced to the multi-scale approach for 2D granular materials. This local scale is defined at the level of meso-domains enclosed by particles in contact. Stress and strain have been defined at this local scale, and their relation with the local structure has been studied. The purpose of this paper is to analyse the behaviour of granular materials at the meso-scale, i.e. the stress-strain-structure relationship at this scale. Analyses are performed on a 2D numerical granular sample subjected to a biaxial compression test and simulated with the Discrete Element Method (DEM). The sample is quite dense and it is loaded at a relatively low strain rate so that the state of the sample can be considered as being quasi-static. The size of sub-domains in the sample varies largely from 3 to 12 particles. It is shown that the evolution of the internal state of the sample corresponds, at the meso-scale, to a clear evolution of the quantity of meso-domains oriented in different directions. In addition, the behaviour of meso-domains is highly governed by their orientation rather than their density, especially for the strongly elongated meso-domains: the meso-domains oriented in the compression (resp. extension) direction behave like a dense (resp. loose) granular material. xml:lang="fr"

Nguyen, Ngoc-Son; Magoariec, Hélène; Cambou, Bernard

2014-03-01

296

Discrete Element Simulation of Granular Column Collapse  

NASA Astrophysics Data System (ADS)

Many natural hazards and industrial processes involve the collapse of granular particles onto a horizontal plane. Recent researches have studied the fundamental physics of the collapse of granular columns in experimental and numerical approaches. This paper presents a three-dimensional discrete element simulation of the axisymmetric spreading of initially vertical granular columns, in which the runout of the grains and their dynamic motion are continuously monitored during the course of collapse. Using a polar coordinate method to quantify the spread of the grains, the numerical results are in good agreement with previous research findings. The collapse dynamics is shown to be dependent on the initial geometry of the cylindrical column and independent of the inter-granular friction. Two distinct flow regimes are observed: a linear scaling and a power-law scaling are derived for the final runout distances of the columns. The problem is further explored by studying the effects of coefficient of restitution on the runout mechanics, in which energy dissipation at collisions has played an important role in determining the runout of the system.

Lo, Chi Yan; Bolton, Malcolm; Cheng, Yi Pik

2009-06-01

297

Monte Carlo simulation of granular fluids  

Microsoft Academic Search

An overview of recent work on Monte Carlo simulations of a granular binary mixture is presented. The results are obtained numerically solving the Enskog equation for inelastic hard-spheres by means of an extension of the well- known direct Monte Carlo simulation (DSMC) method. The homogeneous cooling state and the stationary state reached using the Gaussian thermostat are considered. The temperature

Jose Mar ´ õa

298

Modelling of dc characteristics for granular semiconductors  

Microsoft Academic Search

The dc characteristics of granular n-type semiconductors are calculated analytically with the drift-diffusion theory. Electronic trapping at the grain boundaries (GBs) is taken into account. The use of quadratic and linear GB potential profiles in the calculation is compared. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is

Aapo Varpula; Juha Sinkkonen; Sergey Novikov

2010-01-01

299

Supporting user-defined granularities in a spatiotemporal conceptual model  

USGS Publications Warehouse

Granularities are integral to spatial and temporal data. A large number of applications require storage of facts along with their temporal and spatial context, which needs to be expressed in terms of appropriate granularities. For many real-world applications, a single granularity in the database is insufficient. In order to support any type of spatial or temporal reasoning, the semantics related to granularities needs to be embedded in the database. Specifying granularities related to facts is an important part of conceptual database design because under-specifying the granularity can restrict an application, affect the relative ordering of events and impact the topological relationships. Closely related to granularities is indeterminacy, i.e., an occurrence time or location associated with a fact that is not known exactly. In this paper, we present an ontology for spatial granularities that is a natural analog of temporal granularities. We propose an upward-compatible, annotation-based spatiotemporal conceptual model that can comprehensively capture the semantics related to spatial and temporal granularities, and indeterminacy without requiring new spatiotemporal constructs. We specify the formal semantics of this spatiotemporal conceptual model via translation to a conventional conceptual model. To underscore the practical focus of our approach, we describe an on-going case study. We apply our approach to a hydrogeologic application at the United States Geologic Survey and demonstrate that our proposed granularity-based spatiotemporal conceptual model is straightforward to use and is comprehensive.

Khatri, V.; Ram, S.; Snodgrass, R. T.; O'Brien, G. M.

2002-01-01

300

From principal curves to granular principal curves.  

PubMed

Principal curves arising as an essential construct in dimensionality reduction and data analysis have recently attracted much attention from theoretical as well as practical perspective. In many real-world situations, however, the efficiency of existing principal curves algorithms is often arguable, in particular when dealing with massive data owing to the associated high computational complexity. A certain drawback of these constructs stems from the fact that in several applications principal curves cannot fully capture some essential problem-oriented facets of the data dealing with width, aspect ratio, width change, etc. Information granulation is a powerful tool supporting processing and interpreting massive data. In this paper, invoking the underlying ideas of information granulation, we propose a granular principal curves approach, regarded as an extension of principal curves algorithms, to improve efficiency and achieve a sound accuracy-efficiency tradeoff. First, large amounts of numerical data are granulated into C intervals-information granules developed with the use of fuzzy C-means clustering and the two criteria of information granulation, which significantly reduce the amount of data to be processed at the later phase of the overall design. Granular principal curves are then constructed by determining the upper and the lower bounds of the interval data. Finally, we develop an objective function using the criteria of information confidence and specificity to evaluate the granular output formed by the principal curves. We also optimize the granular principal curves by adjusting the level of information granularity (the number of clusters), which is realized with the aid of the particle swarm optimization. A number of numeric studies completed for synthetic and real-world datasets provide a useful quantifiable insight into the effectiveness of the proposed algorithm. PMID:23996588

Zhang, Hongyun; Pedrycz, Witold; Miao, Duoqian; Wei, Zhihua

2014-06-01

301

Wetting transitions within membrane compartments.  

PubMed

A biomimetic membrane in contact with several aqueous phases is theoretically studied using a combination of Helfrich curvature elasticity theory for fluid membranes and self-consistent field theory for polymers in solutions. Two phases that are thermodynamically formed by phase separation of aqueous solutions, as well as stable and metastable shapes of fluid vesicles, have been observed. The wetting transitions from complete to partial wetting and to complete dewetting are identified within a membrane compartment. The dependences of wetting transitions on material parameters, such as the intrinsic contact angles ?in, the interaction strengths between the polymers ??? and between the membrane and the polymer ?p, and impermeability of the membrane to the enclosed polymers ?p, are investigated. For a given ???, impermeability ?p and affinity to the membrane ?p, ?in is found to be a constant and independent of the reduced volume of vesicles and the volume fraction of two phases. PMID:24946020

Guo, Kunkun; Xiao, Wenjia; Yoshikawa, Kenichi

2014-08-01

302

Effects of cohesion on the surface angle and velocity profiles of granular material in a rotating drum.  

PubMed

Large scale, discrete element simulations are performed to study the dynamics of a rotating drum partially filled with cohesive granular particles. The continuous avalanche regime is explored using a simple model for interparticle cohesion in order to simulate the effects of granular media in the presence of a wetting fluid. The shape of the free surface for cohesionless particles ranges from flat to a concave S shape depending on the rotation rate and frictional properties between the grains and the drum side walls. The presence of interparticle cohesion reduces the concavity of the free surface and pushes the free surface towards a flat or even slightly convex shape. From contour plots of the velocity, we show how the position of the vortex core (the stationary spot in the laboratory frame) depends on the rotation speed and interparticle cohesion strength and how this relationship can be understood from considerations of the incompressibility condition on the mass flow. PMID:19257028

Brewster, Robert; Grest, Gary S; Levine, Alex J

2009-01-01

303

Dark Matter  

NSDL National Science Digital Library

This website introduces dark matter by first explaining Zwicky's discovery of dark matter when he was studying clusters of galaxies about fifty years ago. It then talks about how astronomers detect dark matter today, its relationship to inflation, and the current theories that propose that dark matter may be either WIMPS or MACHOS.

Silk, Joe

2005-06-07

304

Constitutive Relation in Transitional Granular Flows  

NASA Technical Reports Server (NTRS)

To study the constitutive behavior of granular materials, the presence of gravity is detrimental. Although empirical relations have been obtained for engineering designs to control granular flows on Earth, it is not known how well these Earthbound relations can be used in another gravity field. Fundamental understanding must be derived to reliably design for granular flows in space exploration. There are two extremes of granular flows of which significant amount of knowledge is available. One deals with a dense and quasi-static situation where the deformation rate nearly vanishes. The other deals with dilute and rapidly fluctuating grain velocities where particle inertia dominates. This project, funded by the NASA Microgravity Fluid Physics Program, aims to study this transitional regime via physical experiments and computer simulations. A conceptual model has been established as described below. There are two natural time scales in a granular flow. One is the travel time between two consecutive collisions and the other is the duration of a collision contact. At a very low shear-rate, the shear-induced particle velocity is low. Hence the travel time between collisions is longer than the contact time between colliding particles. Binary collisions prevail. As the shear-rate increases, the traveling time between collisions reduces and the probability of multiple collisions goes up. These particle groups disperse shortly after and new groups form. When shear-rate is further increased, clusters grow in size due to an increasing chance for free particles to join before groups have the time to disperse. The maximum cluster size may depend on the global concentration and material properties. As the solid concentration approaches zero, the cluster size goes to one particle diameter. The maximum possible cluster size under any condition is the container size, provided that the shear flow is inside a container. The critical shear-rates that dictate the initiation of the multiple contacts, and the size and lifetime of the collision clusters, are functions of the concentration also. A 'regime' theory has been proposed by Babic et al. This theory suggested that both the solid concentration, C, and the non-dimensional shear-rate, B, are important in determining the regimes of the granular constitutive law. Additional information is included in the original extended abstract.

Shen, Hayley H.; Hanes, Daniel M.; Jenkins, James T.

2002-01-01

305

The comparative effects of ammonium nitrate, urea or a combined ammonium nitrate\\/urea granular fertilizer on the efficiency of nitrogen recovery by perennial ryegrass  

Microsoft Academic Search

The comparative effects of ammonium nitrate (AN), urea or a combined 1:1 (w\\/w) AN\\/urea granular fertilizer with two different fillers (CaCO3 or silica) were investigated on the efficiency of dry matter production and15N recovery by perennial ryegrass grown in pots under controlled environmental conditions.

Catherine J Watson

1987-01-01

306

Electrostatic granular bed filter development program  

NASA Astrophysics Data System (ADS)

An electrostatic granular bed (EGB) filtration for pressurized fluidized bed combined cycle application was developed. Experiments provide the data necessary to design a hot test model and to perform systems integration and economic evaluation studies. Based on the laboratory results, preliminary engineering estimates of the capital and operating costs are provided for the selected approach. In parallel with the electrostatic granular bed filter testing, laboratory scale experiments and engineering assessments are performed for two concepts for removing corrosive alkali metal vapor from the combustion gases. An instrumentation plan was developed for the AFB model filter test. A filter as delivered and installed in the AFB facility, and testing began with molochite, limestone, sandy gravel, and coal. During attempted 100-hr tests, dust loadings of baghouses downstream of the EGB filter were measured.

1981-12-01

307

Drag and lift forces in granular media  

NASA Astrophysics Data System (ADS)

Forces exerted on obstacles moving in granular media are studied. The experiment consists in a horizontal cylinder rotating around the vertical axis in a granular medium. Both drag forces and lift forces experienced by the cylinder are measured. The first striking result is obtained during the first half rotation, before the cylinder crosses its wake. Despite the symmetry of the object, a strong lift force is measured, about 20 times the buoyancy. The scaling of this force is studied experimentally. The second remarkable observation is made after several rotations. The drag force dramatically drops and becomes independent of depth, showing that it no longer scales with the hydrostatic pressure. The rotation of the cylinder induces a structure in the packing, which screens the weight of the grains above

Guillard, F.; Forterre, Y.; Pouliquen, O.

2013-09-01

308

Mesoscale Simulations of Granular Materials with Peridynamics  

NASA Astrophysics Data System (ADS)

The dynamic behavior of granular materials can be quite complex due to phenomena that occur at the scale of individual grains. For this reason, mesoscale simulations explicitly resolving individual grains with varying degrees of fidelity have been used to gain insight into the physics of granular materials. The vast majority of these simulations have, to date, been performed with Eulerian codes, which do a poor job of resolving fracture and grain-to-grain interactions. To address these shortcomings, we utilize a peridynamic modeling framework to examine the roles of fracture and contact under planar shock and other loading conditions. Peridynamics is a mesh-free Lagrangian technique that uses an integral formulation to better enable simulations involving fracture. Although some aspects of the peridynamic codes currently available are not well suited to the shock regime, the simulations provide results that are more physically realistic than the Eulerian simulations for some non-planar loading conditions.

Lammi, Christopher; Littlewood, David; Vogler, Tracy

2011-06-01

309

Mesoscale simulations of granular materials with peridynamics  

NASA Astrophysics Data System (ADS)

The dynamic behavior of granular materials can be quite complex due to phenomena that occur at the scale of individual grains. For this reason, mesoscale simulations explicitly resolving individual grains with varying degrees of fidelity have been used to gain insight into the physics of granular materials. The vast majority of these simulations have, to date, been performed with Eulerian codes, which do a poor job of resolving fracture and grain-to-grain interactions. To address these shortcomings, we utilize a peridynamic modeling framework to examine the roles of fracture and contact under planar shock and other loading conditions. Peridynamics is a mesh-free Lagrangian technique based on an integral formulation to better enable simulations involving fracture.

Lammi, Christopher J.; Vogler, Tracy J.

2012-03-01

310

Universal structural characteristics of planar granular packs.  

PubMed

The dependence of structural self-organization of granular materials on preparation and grain parameters is key to predictive modeling. We study 60 different mechanically equilibrated polydisperse disc packs, generated numerically by two protocols. We show that, for same-variance disc size distributions (DSDs), (1) the mean coordination number of rattler-free packs versus the packing fraction is a function independent of initial conditions, friction, and the DSD, and (2) all quadron volume and cell order distributions collapse to universal forms, also independent of the above. This apparent universality suggests that, contrary to common wisdom, equilibrated granular structures may be determined mainly by the packing protocol and higher moments of the DSD. PMID:24655281

Matsushima, Takashi; Blumenfeld, Raphael

2014-03-01

311

Plant Root Growth In Granular Media  

NASA Astrophysics Data System (ADS)

Roots grow in a variety of granular substrates. However, the substrates are often treated in ways which minimize or neglect the inhomogeneities arising from the influence of inter-particle forces. Experiments are often run using gels or average stress measurements. This presentation discusses the effect of the local structure of the particulate environment on the root's direction. Using photoelastic particles and particles with a variety of Young's Moduli, we investigate the influence of inter-particle forces and particle stiffness on a pinto bean root's ability to grow through a fully-saturated granular medium. The level of particle contact force through which the roots successfully grow is determined and the influence of particle stiffness on root direction is investigated.

Wendell, Dawn; Hosoi, Peko

2010-03-01

312

Cavity QED detection of interfering matter waves  

SciTech Connect

We observe the build-up of a matter wave interference pattern from single atom detection events in a double-slit experiment. The interference arises from two overlapping atom laser beams extracted from a rubidium Bose-Einstein condensate. Our detector is a high-finesse optical cavity which realizes a quantum measurement of the presence of an atom and thereby projects delocalized atoms into a state with zero or one atom in the resonator. The experiment reveals simultaneously the granular and the wave nature of matter. We present a setup which is suited for applications in atom interferometry and cavity QED.

Bourdel, T.; Donner, T.; Ritter, S.; Oettl, A.; Koehl, M.; Esslinger, T. [Institute of Quantum Electronics, ETH Zuerich, CH-8093 Zurich (Switzerland)

2006-04-15

313

Granular cell tumor (myoblastoma) of the orbit.  

PubMed

An 8-year-old white boy had a tumor in the left orbit with clinical manifestations of muscular impairment, exophthalmos, and reduced visual acuity. Five months after exenteration of the orbit the boy was healthy without tumor recurrence. Based on our observations with electron, light, and phase microscopy, and histochemical studies, we conclude that this tumor is benign, of histiocytic origin, and we propose the term granular cell histiocytoma be used to describe this entity. PMID:164119

González-Almaraz, G; de Buen, S; Tsutsumi, V

1975-04-01

314

“Left-Handed” Magnetic Granular Composites  

Microsoft Academic Search

We investigate the possibility of preparing left-handed materials in metallic magnetic granular composites. Based on the effective\\u000a medium approximation, we show that by incorporating metallic magnetic nanoparticles into an appropriate insulating matrix\\u000a and controlling the directions of magnetization of metallic magnetic components and their volume fraction, it may be possible\\u000a to prepare a composite medium which is left handed for

Siu-Tat Chui; L. B. Hu; Zifang Lin; Lei Zhou

315

Josephson effects in a bulk granular superconductor.  

NASA Technical Reports Server (NTRS)

Experimental results are presented for the dc and ac Josephson effects found in a bulk granular superconductor comprised of about 10 to the 4th superconducting grains (less than 45 microns in dimension) packed in an insulator capsule. This new type of Josephson weakly coupled superconductor offers high sensitivity in response to microwave radiation with a noise-equivalent power as low as 10 to the minus 14th W/(Hz) one half.

Warman, J.; Jahn, M. T.; Kao, Y. H.

1971-01-01

316

Dissipation and Statistical Mechanics of granular gas  

NASA Astrophysics Data System (ADS)

Recently, a tremendous amount of works has been performed to investigate properties of granular gas (see [Goldhirsch 2003] for a review). This problem is fundamental because it is a frontier of statistical mechanics when dissipation becomes dominant; hence it asks the problem of what dissipation changes in the behavior of a statistical ensemble of particles in interaction: within which limits can one use the analogue of thermodynamics concepts to describe the behavior of these systems?

Evesque, Pierre

317

Monte Carlo simulation of granular fluids  

Microsoft Academic Search

An overview of recent work on Monte Carlo simulations of a granular binary\\u000amixture is presented. The results are obtained numerically solving the Enskog\\u000aequation for inelastic hard-spheres by means of an extension of the well-known\\u000adirect Monte Carlo simulation (DSMC) method. The homogeneous cooling state and\\u000athe stationary state reached using the Gaussian thermostat are considered. The\\u000atemperature ratio,

J. M. Montanero

2003-01-01

318

Swimming in a granular frictional fluid  

NASA Astrophysics Data System (ADS)

X-ray imaging reveals that the sandfish lizard swims within granular media (sand) using axial body undulations to propel itself without the use of limbs. To model the locomotion of the sandfish, we previously developed an empirical resistive force theory (RFT), a numerical sandfish model coupled to an experimentally validated Discrete Element Method (DEM) model of the granular medium, and a physical robot model. The models reveal that only grains close to the swimmer are fluidized, and that the thrust and drag forces are dominated by frictional interactions among grains and the intruder. In this talk I will use these models to discuss principles of swimming within these granular ``frictional fluids". The empirical drag force laws are measured as the steady-state forces on a small cylinder oriented at different angles relative to the displacement direction. Unlike in Newtonian fluids, resistive forces are independent of speed. Drag forces resemble those in viscous fluids while the ratio of thrust to drag forces is always larger in the granular media than in viscous fluids. Using the force laws as inputs, the RFT overestimates swimming speed by approximately 20%. The simulation reveals that this is related to the non-instantaneous increase in force during reversals of body segments. Despite the inaccuracy of the steady-state assumption, we use the force laws and a recently developed geometric mechanics theory to predict optimal gaits for a model system that has been well-studied in Newtonian fluids, the three-link swimmer. The combination of the geometric theory and the force laws allows us to generate a kinematic relationship between the swimmer's shape and position velocities and to construct connection vector field and constraint curvature function visualizations of the system dynamics. From these we predict optimal gaits for forward, lateral and rotational motion. Experiment and simulation are in accord with the theoretical prediction, and demonstrate that swimming in sand can be viewed as movement in a localized frictional fluid.

Goldman, Daniel

2012-02-01

319

Electrostatics of Granular Material (EGM): Space Station Experiment  

NASA Technical Reports Server (NTRS)

Aggregates were observed to form very suddenly in a lab-contained dust cloud, transforming (within seconds) an opaque monodispersed cloud into a clear volume containing rapidly-settling, long hair-like aggregates. The implications of such a "phase change" led to a series of experiments progressing from the lab, to KC-135, followed by micro-g flights on USML-1 and USML-2, and now EGM slated for Space Station. We attribute the sudden "collapse" of a cloud to the effect of dipoles. This has significant ramifications for all types of cloud systems, and additionally implicates dipoles in the processes of cohesion and adhesion of granular matter. Notably, there is the inference that like-charged grains need not necessarily repel if they are close enough together: attraction or repulsion depends on intergranular distance (the dipole being more powerful at short range), and the D/M ratio for each grain, where D is the dipole moment and M is the net charge. We discovered that these ideas about dipoles, the likely pervasiveness of them in granular material, the significance of the D/M ratio, and the idea of mixed charges on individual grains resulting from tribological processes --are not universally recognized in electrostatics, granular material studies, and aerosol science, despite some early seminal work in the literature, and despite commercial applications of dipoles in such modern uses as "Krazy Glue", housecleaning dust cloths, and photocopying. The overarching goal of EGM is to empirically prove that (triboelectrically) charged dielectric grains of material have dipole moments that provide an "always attractive" intergranular force as a result of both positive and negative charges residing on the surfaces of individual grains. Microgravity is required for this experiment because sand grains can be suspended as a cloud for protracted periods, the grains are free to rotate to express their electrostatic character, and Coulombic forces are unmasked. Suspended grains will be "interrogated" by applied electrical fields. In one module, grains will be immersed in an inhomogeneous electric field and allowed to be attracted towards or repelled from the central electrode of the module: part of the grain's speed will be a function of its net charge (monopole), part will be a function of the dipole. Observed grain position vs. time will provide a curve that can be deconvolved into the dipole and monopole forces responsible, since both have distinctive radial dependencies. In a second approach, the inhomogeneous field will be alternated at low frequency (e.g., every 5-10 seconds) so that the grains are alternately attracted and repelled from the center of the field. The resulting "zigzag" grain motion will gradually drift inwards, then suddenly change to a unidirectional inward path when a critical radial distance is encountered (a sort of "Coulombic event horizon") at which the dipole strength supersedes the monopole strength --thus proving the presence of a dipole, while also quantifying the D/M ratio. In a second module, an homogeneous electric field eliminates dipole effects (both Coulombic and induced) to provide calibration of the monopole and to more readily evaluate net charge statistical variance. In both modules, the e-fields will be exponentially step-ramped in voltage during the experiment, so that the field "nominalizes" grain speed while spreading the response time --effectively forcing each grain to "wait its turn" to be measured. In addition to rigorously quantifying M, D, and the D/M ratio for many hundreds of grains, the experiment will also observe gross electrometric and RF discharge phenomena associated with grain activity. The parameter space will encompass grain charging levels (via intentional triboelectrification), grain size, cloud density, and material type. Results will prove or disprove the dipole hypothesis. In either case, light will be shed on the role of electrostatic forces in governing granular systems. Knowledg

Marshall, J.; Sauke, T.; Farrell, W.

2000-01-01

320

Hydrodynamic modes in a confined granular fluid.  

PubMed

Confined granular fluids, placed in a shallow box that is vibrated vertically, can achieve homogeneous stationary states due to energy injection mechanisms that take place throughout the system. These states can be stable even at high densities and inelasticities allowing for a detailed analysis of the hydrodynamic modes that govern the dynamics of granular fluids. By analyzing the decay of the time correlation functions it is shown that there is a crossover from a quasielastic regime in which energy evolves as a slow mode to an inelastic regime with energy slaved to the other conserved fields. The two regimes have well differentiated transport properties and in the inelastic regime the dynamics can be described by a reduced hydrodynamics with modified longitudinal viscosity and sound speed. The crossover between the two regimes takes place at a wave vector that is proportional to the inelasticity. A two-dimensional granular model, with collisions that mimic the energy transfers that take place in a confined system, is studied by means of microscopic simulations. The results show excellent agreement with the theoretical framework and allow validation of hydrodynamiclike models. PMID:23496507

Brito, Ricardo; Risso, Dino; Soto, Rodrigo

2013-02-01

321

Logarithmic Rate Dependance in Deforming Granular Materials  

NASA Astrophysics Data System (ADS)

We present experimental studies that show a logarithmic rate dependence in sheared 2D granular material. In particular, sheared systems that undergo irreversible (plastic) deformations exhibit a logarithmic increase in the mean (i.e., time-averaged) stress, ?, with the shear rate, ?, while systems of particles that undergo reversible (elastic) deformations show no rate dependence. Two experiments are discussed: 1) In the first, the granular material ( ˜ 1 cm photoelastic disks or pentagons) is confined to an annular geometry(D. Howell, et. al.), Phys. Rev. Lett. 82, 5241 (1999) and sheared by the inner wheel, while the outer wheel is pinned in place. The shear rate is varied by more than three orders of magnitude (30 ?Hzgranular material is confined to a box with three fixed sides, while the fourth is compressed repeatedly. The velocity of the piston is chosen to match the inner wheel from the first experiment. The key difference is that particle/particle rearrangements are prohibited.

Hartley, R. R.; Behringer, R. P.

2002-11-01

322

Micromechanical study of plasticity of granular materials  

NASA Astrophysics Data System (ADS)

Plastic deformation of granular materials is investigated from the micromechanical viewpoint, in which the assembly of particles and interparticle contacts is considered as a mechanical structure. This is done in three ways. Firstly, by investigating the degree of redundancy of the system by comparing the number of force degrees of freedom at contacts with the number of governing equilibrium equations; Secondly, by determining the spectrum of eigenvalues of the stiffness matrix for the structure that is represented by the particles and their contacts; Thirdly, by investigating the evolution with imposed strain of the continuum elastic stiffness tensor of the system. It is found that, with increasing imposed strain, the degree of redundancy rapidly evolves towards a state with small redundancy, i.e. the system becomes nearly statically determinate. The spectrum of the system shows many singular and near-singular modes at peak shear strength and at large strain. The continuum elastic stiffness tensor becomes strongly anisotropic with increasing imposed strain and shows strong non-affinity of deformation. The assumption of a constant and isotropic elastic stiffness tensor in elasto-plastic continuum constitutive relations for granular materials is generally incorrect. Overall, the plastic continuum behaviour of granular materials originates from the plastic frictional behaviour at contacts and from damage in the form of changes in the contact network.

Kruyt, Niels P.

2010-10-01

323

Energy dissipation and clustering in granular streams  

NASA Astrophysics Data System (ADS)

The presence of weak cohesive forces between macroscopic grains can lead to the break up of a free falling granular stream, similar to the surface-tension-driven break up of a liquid streamfootnotetext Royer, J. R. et al. Nature 459 1110 - 1113 (2009).. This sensitivity to minute forces suggests that these free falling streams could serve as a tool to probe the interactions between grains. In order to investigate the connection between the stream dynamics and the grain-grain interactions, we perform molecular dynamics simulations of a granular stream freely falling out of a hopper varying the cohesion and inelasticity of the grains. We find that in the absence of cohesive forces the stream breaks apart into isolated grains, in contrast to the clustering observed in simulations of inelastic granular gases. For sufficiently high cohesive forces we reproduce the break up of stream into droplets, while with lower cohesive forces the stream breaks up into smaller clusters consisting of only a few grains. Measuring the change in contact number and decay of velocity fluctuations with depth, we characterize the different regions of the force-inelasticity phase space.

Waitukaitis, Scott; Royer, John; Gruetjen, Helge; Jaeger, Heinrich

2009-11-01

324

Granular flow in the marginal ice zone.  

PubMed

The region of sea ice near the edge of the sea ice pack is known as the marginal ice zone (MIZ), and its dynamics are complicated by ocean wave interaction with the ice cover, strong gradients in the atmosphere and ocean and variations in sea ice rheology. This paper focuses on the role of sea ice rheology in determining the dynamics of the MIZ. Here, sea ice is treated as a granular material with a composite rheology describing collisional ice floe interaction and plastic interaction. The collisional component of sea ice rheology depends upon the granular temperature, a measure of the kinetic energy of flow fluctuations. A simplified model of the MIZ is introduced consisting of the along and across momentum balance of the sea ice and the balance equation of fluctuation kinetic energy. The steady solution of these equations is found to leading order using elementary methods. This reveals a concentrated region of rapid ice flow parallel to the ice edge, which is in accordance with field observations, and previously called the ice jet. Previous explanations of the ice jet relied upon the existence of ocean currents beneath the ice cover. We show that an ice jet results as a natural consequence of the granular nature of sea ice. PMID:16011939

Feltham, Daniel L

2005-07-15

325

Mechanics of Granular Materials (MGM) Flight Hardware  

NASA Technical Reports Server (NTRS)

A test cell for the Mechanics of Granular Materials (MGM) experiment is shown in its on-orbit configuration in Spacehab during preparations for STS-89. The twin locker to the left contains the hydraulic system to operate the experiment. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Note: Because the image on the screen was muted in the original image, its brightness and contrast are boosted in this rendering to make the test cell more visible. Credit: NASA/Marshall Space Flight Center (MSFC)

1997-01-01

326

Mechanics of Granular Materials Test Cell  

NASA Technical Reports Server (NTRS)

A test cell for Mechanics of Granular Materials (MGM) experiment is shown from all three sides by its video camera during STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

1998-01-01

327

Mechanics of Granular Materials (MGM) Cell  

NASA Technical Reports Server (NTRS)

One of three Mechanics of Granular Materials (MGM) test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

1996-01-01

328

Mechanics of Granular Materials (MGM) Test Cell  

NASA Technical Reports Server (NTRS)

A test cell for Mechanics of Granular Materials (MGM) experiment is shown approximately 20 and 60 minutes after the start of an experiment on STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

1998-01-01

329

Mechanics of Granular Materials (MGM) Test Cell  

NASA Technical Reports Server (NTRS)

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the compressed sand column with the protective water jacket removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

2000-01-01

330

Mechanics of Granular Materials (MGM) Test Cell  

NASA Technical Reports Server (NTRS)

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the top of the sand column with the metal platten removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

2000-01-01

331

Mechanics of Granular Materials-3 (MGM-3)  

NASA Technical Reports Server (NTRS)

Scientists are going to space to understand how earthquakes and other forces disturb grains of soil and sand. They will examine how the particle arrangement and structure of soils, grains and powders are changed by external forces and gain knowledge about the strength, stiffness and volume changes properties of granular materials at low pressures. The Mechanics of Granular Materials (MGM) experiment uses the microgravity of orbit to test sand columns under conditions that cannot be obtained in experiments on Earth. Research can only go so far on Earth because gravity-induced stresses complicate the analysis and change loads too quickly for detailed analysis. This new knowledge will be applied to improving foundations for buildings, managing undeveloped land, and handling powdered and granular materials in chemical, agricultural, and other industries. NASA wants to understand the way soil behaves under different gravity levels so that crews can safely build habitats on Mars and the Moon. Future MGM experiments will benefit from extended tests aboard the International Space Station, including experiments under simulated lunar and Martian gravity in the science centrifuge.

Sture, Stein; Alshibi, Khalid; Guynes, Buddy (Technical Monitor)

2002-01-01

332

A granular computing approach to gene selection.  

PubMed

Gene selection is a key step in performing cancer classification with DNA microarrays. The challenges from high dimension and small sample size of microarray dataset still exist. On rough set theory applied to gene selection, many algorithms have been presented, but most are time-consuming. In this paper, a granular computing-based gene selection as a new method is proposed. First, some granular computing-based concepts are introduced and then some of their important properties are derived. The relationship between positive region-based reduct and granular space-based reduct is discussed. Then, a significance measure of feature is proposed to improve the efficiency and decrease the complexity of classical algorithm. By using Hashtable and input sequence techniques, a fast heuristic algorithm is constructed for the better computational efficiency of gene selection for cancer classification. Extensive experiments are conducted on five public gene expression data sets and seven data sets from UCI respectively. The experimental results confirm the efficiency and effectiveness of the proposed algorithm. PMID:24212026

Sun, Lin; Xu, Jiucheng

2014-01-01

333

Vibratory Shock Compaction of Granular Nuclear Waste  

NASA Astrophysics Data System (ADS)

Vibratory Shock Compaction (VSC) is a proven means for quickly forming strong, durable solids from a wide variety of granular materials[1]. Calcination of tank and other forms of high level radioactive wastes results in fine granular material that is quite amenable to volume reduction and stabilization. We have employed utilities coal ash as a calcine waste surrogate, blended with a quartz/feldspar-rich sand and 0-20% proportions of a borosilicate glass. The blends were compacted at room temperature and fired so that the glass melt could form an efficient binder. Included in the blend are small quantities of three RCRA metals, chromium, cadmium and lead, to permit testing for heavy metal stability. The VSC process is described and the results presented in terms of the waste form dissolution rates, compressive strengths, elastic moduli as determined from resonant frequency measurements, and heavy metal leach rates from Toxicity Characteristic Leaching Procedure measurements. Vibratory shock compaction employing glass binders appears to be a viable alternative to traditional vitrification processes for granular waste forms. [1] See http://www.resonantshockcompact.com

Amme, Robert C.

2004-05-01

334

Detection of Multidimensional Structures in Granular Materials  

NASA Astrophysics Data System (ADS)

Granular media display features across a range of spatial scales, from the particle scale to the force-chain scale and the bulk scale. In contrast to particulate and continuum models, network representations facilitate the simultaneous examination of microscopic, mesoscopic, and macroscopic features. We treat granular materials as spatially embedded networks in which the nodes (particles) are connected by weighted edges obtained from contact forces. Using community detection techniques, we identify local 2D geographic domains composed of particles that exert strong forces on one another. We subsequently develop and apply a novel spatial null model constrained by the contact network to extract chain-like structures reminiscent of force chains. We demonstrate that most of these chain-like structures are located close to the center of mass of the 2D geographic domains. However, a minority are located towards the edge of the 2D geographic domains, potentially forming points of instability in granular media. We explore the robustness of these detection techniques to algorithmic degeneracies, to simulation versus experimental data, and to varying pressure states.

Bassett, Danielle; Daniels, Karen; Owens, Eli; Porter, Mason A.; Manning, M. Lisa

2013-03-01

335

Wet Chemistry Automated Sample Processing System (WASP).  

National Technical Information Service (NTIS)

Ball Aerospace & Technologies Corporation (Ball Aerospace) was commissioned by the Jet Propulsion Laboratory (JPL) to produce a wet chemistry automated soil sample processing mechanism that can be used for planetary wet chemistry sample preparation. O...

J. Lasnik, J. Soto, L. Beegle, S. Roark

2012-01-01

336

Improved residual water suppression: WET180.  

PubMed

Water suppression in biological NMR is frequently made inefficient by the presence of faraway water that is located near the edges of the RF coil and experiences significantly reduced RF field. WET180 (WET with 180 degrees pulse-toggling) is proposed to cancel the faraway water contribution to the residual solvent signal. The pulse sequence incorporates a modification of the last WET selective pulse to accommodate insertion of a toggled 180 degrees inversion pulse so that the original WET selective pulse angles are effectively preserved. Compared with existing WET methods, WET180 has the advantages of easy implementation, improved residual water suppression, clean spectral phase properties, and good signal intensity retention. WET180 is expected to be most useful in observing resonances close to water in samples containing biological molecules. In addition, the principle of WET180 can be applied in multidimensional experiments to improve residual water suppression and reduce artifacts around water. PMID:18506578

Mo, Huaping; Raftery, Daniel

2008-06-01

337

Capillarylike fluctuations of a solid-liquid interface in a noncohesive granular system.  

PubMed

One of the most noticeable collective motion of noncohesive granular matter is clustering under certain conditions. In particular, when a quasi-two-dimensional monolayer of monodispersed noncohesive particles is vertically vibrated, a solid-liquid-like transition occurs when the driving amplitude exceeds a critical value. Here the physical mechanism underlying particle clustering relies on the strong interactions mediated by grain collisions, rather than on grain-grain cohesive forces. In average, the solid cluster resembles a drop, with a striking circular shape. We experimentally investigate the coarse-grained solid-liquid interface fluctuations, which are characterized through the static and dynamic correlation functions in the Fourier space. These fluctuations turn out to be well described by the capillary wave theory, which allows us to measure the solid-liquid interface surface tension and mobility once the granular "thermal" kinetic energy is determined. Despite that the system is strongly out of equilibrium and that the granular temperature is not uniform, there is energy equipartition at the solid-liquid interface, for a relatively large range of angular wave numbers. Furthermore, both surface tension and mobility are consistent with a simple order of magnitude estimation considering the characteristic energy, length, and time scales, which is very similar to what can be done for atomic systems. PMID:23679358

Luu, Li-Hua; Castillo, Gustavo; Mujica, Nicolás; Soto, Rodrigo

2013-04-01

338

Capillarylike fluctuations of a solid-liquid interface in a noncohesive granular system  

NASA Astrophysics Data System (ADS)

One of the most noticeable collective motion of noncohesive granular matter is clustering under certain conditions. In particular, when a quasi-two-dimensional monolayer of monodispersed noncohesive particles is vertically vibrated, a solid-liquid-like transition occurs when the driving amplitude exceeds a critical value. Here the physical mechanism underlying particle clustering relies on the strong interactions mediated by grain collisions, rather than on grain-grain cohesive forces. In average, the solid cluster resembles a drop, with a striking circular shape. We experimentally investigate the coarse-grained solid-liquid interface fluctuations, which are characterized through the static and dynamic correlation functions in the Fourier space. These fluctuations turn out to be well described by the capillary wave theory, which allows us to measure the solid-liquid interface surface tension and mobility once the granular “thermal” kinetic energy is determined. Despite that the system is strongly out of equilibrium and that the granular temperature is not uniform, there is energy equipartition at the solid-liquid interface, for a relatively large range of angular wave numbers. Furthermore, both surface tension and mobility are consistent with a simple order of magnitude estimation considering the characteristic energy, length, and time scales, which is very similar to what can be done for atomic systems.

Luu, Li-Hua; Castillo, Gustavo; Mujica, Nicolás; Soto, Rodrigo

2013-04-01

339

Onset of Stationary Flows of a Cohesive Granular Material in a Channel  

NASA Astrophysics Data System (ADS)

The handling of bulk materials and powders in process engineering remains an important issue. To obtain reliable gravitational flows, starting and remaining stationary, the hoppers and transport channels must be designed at a scale appropriate for the friction and cohesive properties of the granular material. To describe such dense flows (the interaction with the surrounding ambient fluid is negligible compared to the weight of the particles and interparticles forces), they can be modelled by continuum mechanics, associated with a constitutive equation taking into account the friction behaviour (Mohr-Coulomb or Druger-Prager plasticity criterion). We use here the rheology proposed by Jop et al. (Nature 441: 727-730, 2006) which combines this with an associated flow rule (co-linearity of the stress and strain tensors) (Jenike, Powder Technol. 50: 229-236, 1987) and a viscous dependency of the coefficient of friction on the strain (Da Cruz et al., Phys. Rev. E 72: 021309, 2005).Using the method of characteristics to describe the flow structure (de Ryck, Granular Matter 10: 361-367, 2008), we deduce the minimal slope to obtain a stationary flow of cohesive granular materials on a finite width channel, whose lateral walls are rough or smooth. We also obtain the depth of the flow (maximal at the centre of the channel). In the case of weak cohesive materials, these results are formulated with simple analytical expressions.

de Ryck, A.; Louisnard, O.

340

Treatment of HMX-production wastewater in an aerobic granular reactor.  

PubMed

Aerobic granules were applied to the treatment of HMX-production wastewater using a gradual domestication method in a SBR. During the process, the granules showed a good settling ability, a high biomass retention rate, and high biological activity. After 40 days of stable operation, aerobic granular sludge performed very effectively in the removal of carbon and nitrogen compounds from HMX-production wastewater. Organic matter removal rates up to 97.57% and nitrogen removal efficiencies up to 80% were achieved during the process. Researchers conclude that using aerobic granules to treat explosive wastewater has good prospects for success. PMID:23697233

Zhang, Jin-Hua; Wang, Min-Hui; Zhu, Xiao-Meng

2013-04-01

341

Regulation of aerobic granular sludge reformulation after granular sludge broken: effect of poly aluminum chloride (PAC).  

PubMed

The present study focuses on the effect of poly aluminum chloride (PAC) on the re-formation of aerobic granular sludge after its rupture. The morphological changes, physical characteristics such as SVI, mechanical strength and surface properties of aerobic granular sludge during the re-formation process of broken granules were investigated. Moreover, components (protein (PN), polysaccharides (PS)) and distributions (soluble, loosely-bound (LB), tightly-bound (TB)) of extracellular polymeric substances (EPS) in sludge flocs were taken into consideration. It was found that the effect of charge neutralization and bridging induced by PAC treatment improved the surface properties of sludge, the re-formed granules had a larger size, more compact structure and that the removal performance of pollutants after chemical coagulation had improved. The results of correlation analysis demonstrated that PN in EPS correlated well with the surface characteristics and settling ability of sludge flocs, and PAC treatment strengthened the influence, further accelerated the reformation of granular sludge. PMID:24607455

Liu, Yongjun; Liu, Zhe; Wang, Fukun; Chen, Yiping; Kuschk, Peter; Wang, Xiaochang

2014-04-01

342

The critical wetting saga: how to draw the correct conclusion  

NASA Astrophysics Data System (ADS)

A long-standing problem in condensed matter physics concerns the nature of the critical wetting phase transition in the Ising model or, more generally, in 3D systems with short-ranged forces. This is of fundamental interest because 3D corresponds to the upper critical dimension of the transition and it is not clear a priori whether the behaviour of the system will be mean-field-like or fluctuation-dominated. Renormalization group studies of the standard coarse-grained effective interfacial Hamiltonian model famously predict strong non-universal critical exponents which depend on the value of the so-called wetting parameter ?. However, these predictions are at odds with extensive Monte Carlo simulations of wetting in the Ising model, due to Binder, Landau and coworkers, which appear to be more mean-field-like. Further amendments to the interfacial Hamiltonian, which included the presence of a position-dependent stiffness, worsened the problem by paradoxically predicting fluctuation-induced first-order wetting behaviour. Here we show from re-analysis of a microscopic Landau-Ginzburg-Wilson model of 3D short-ranged wetting that correlation functions are characterized by two diverging parallel length scales, not one, as previously thought. This has a simple diagrammatic explanation using a non-local interfacial Hamiltonian and yields a thermodynamically consistent theory of wetting in keeping with exact sum rules. The non-local model crucially contains long-ranged two-body interfacial interactions, characterized by the new length scale, which were missing in earlier treatments. For critical wetting the second length cuts off the spectrum of interfacial fluctuations determining the repulsion from the wall. We show how this corrects previous renormalization group predictions for fluctuation effects, based on local interfacial Hamiltonians. In particular, lowering the cut-off leads to a substantial reduction in the effective value of the wetting parameter controlling the non-universality and also prevents the transition being driven first-order. Quantitative comparison with the Ising model simulation studies is also made.

Parry, A. O.; Rascón, C.; Bernardino, N. R.; Romero-Enrique, J. M.

2008-12-01

343

Granular Cell Tumor of the Toe: A Case Report  

PubMed Central

Granular cell tumor is a rare tumor of unknown etiology that more commonly affects the oral cavity but can also occur at other sites. The majorities of granular cell tumors are benign and present as a singular dermal nodule. We discuss a case of granular cell tumor of the fourth toe in a 54-year-old patient that was treated with conservative surgery, instead of amputation, and reconstruction with a dermal regeneration template.

Tamborini, Federico; Cherubino, Mario; Scamoni, Stefano; Valdatta, Luigi A.

2010-01-01

344

Vimentin and cytokeratin pattern in granular corneal dystrophy  

Microsoft Academic Search

• Background: Corneal granular dystrophy is usually classified as a hereditary stromal disease of the cornea. Some investigations,\\u000a however, have indicated an epithelial rather than a stromal origin of the granular deposits. In early stages and in recurrences\\u000a of granular dystrophy after keratoplasty, the deposits are most often found in the upper microlayers of the cornea and even\\u000a intraepithelially. •

Gregor Wollensak; Heinrich Witschel

1996-01-01

345

Granular Leidenfrost effect in vibrated beds with bumpy surfaces  

Microsoft Academic Search

.  The effects of subjecting a bed of granular materials to horizontal vibrations by a bumpy oscillating surface have been investigated\\u000a computationally in this study. The behaviour of the granular bed is determined by the vibration conditions applied which include\\u000a the vibrating frequency and amplitude as well as the bumpiness of the oscillating surface. Under sufficiently vigorous vibration\\u000a conditions, the granular

E. W. C. Lim

2010-01-01

346

Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials  

NASA Technical Reports Server (NTRS)

The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single gain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three- dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction. Electrostatic forces are generally under-estimated for their role in causing agglomeration of dispersed grains in particulate clouds, or their role in affecting the internal frictional relationships in packed granular masses. We believe that electrostatic, in particular dipole-mediated processes, are pervasive and probably affect, at some level, everything from astrophysical-scale granular systems such as interstellar nebulae, protoplanetary dust and debris disks, planetary-scale systems such as debris palls from meteorite impact, volcanic eruptions, and aeolian dust storms, all the way to industrial-scale systems in mining, powder and grain processing, pharmaceuticals, and smoke-stack technologies. NASA must concern itself with the electrostatic behavior of dust and sand on Mars because of its potentially critical importance to human exploration. The motion and adhesion of martian surface materials will affect the design and performance of spacesuits, habitats, processing plants, solar panels, and any externally exposed equipment such as surface rovers or communication and weather stations. Additionally, the adhesion of dust and sand could greatly enhance contact with the potentially toxic components of the martian soil.

Marshall, J.; Weislogel, M.; Jacobson, T.

1999-01-01

347

Mutiscale Modeling of Segregation in Granular Flows  

SciTech Connect

Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gas-fluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Large-scale force networks bearing larger-than-average forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Single-point force distribution and two-point spatial force correlation are computed. The results show the heterogeneity of forces and a short-range correlation. The short correlation length implies that even dense granular flows may admit local constitutive relations. A modified minimum spanning tree (MST) algorithm is developed to asymptotically recover the force statistics in the force networks. This algorithm provides a possible route to constructing a continuum model with microstructural information supplied from it. Microstructures in gas fluidized beds are also analyzed using a hybrid method, which couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) equations for the gas phase. Multi-particle contacts are found in defluidized regions away from bubbles in fluidized beds. The multi-particle contacts invalidate the binary-collision assumption made in the kinetic theory of granular flows for the defluidized regions. Large ratios of contact forces to drag forces are found in the same regions, which confirms the relative importance of contact forces in determining particle dynamics in the defluidized regions.

Jin Sun

2007-08-03

348

Wetting morphologies at microstructured surfaces  

PubMed Central

The wetting of microstructured surfaces is studied both experimentally and theoretically. Even relatively simple surface topographies such as grooves with rectangular cross section exhibit a large variety of different wetting morphologies as observed by atomic force microscopy. This polymorphism arises from liquid wedge formation along the groove corners and from contact line pinning along the groove edges. A global morphology diagram is derived that depends only on two system parameters: (i) the aspect ratio of the groove geometry and (ii) The contact angle of the underlying substrate material. For microfluidics, the most interesting shape regimes involve extended liquid filaments, which can grow and shrink in length while their cross section stays essentially constant. Thus, any method by which one can vary the contact angle can be used to switch the length of the filament, as is demonstrated in the context of electrowetting.

Seemann, Ralf; Brinkmann, Martin; Kramer, Edward J.; Lange, Frederick F.; Lipowsky, Reinhard

2005-01-01

349

Elucidating the mysteries of wetting  

Microsoft Academic Search

Nearly every manufacturing and many technologies central to Sandia's business involve physical processes controlled by interfacial wetting. Interfacial forces, e.g. conjoining\\/disjoining pressure, electrostatics, and capillary condensation, are ubiquitous and can surpass and even dominate bulk inertial or viscous effects on a continuum level. Moreover, the statics and dynamics of three-phase contact lines exhibit a wide range of complex behavior, such

Webb; Edmund Blackburn; Christopher Jay Bourdon; Anne Mary Grillet; Philip A. Sackinger; Gary Stephen Grest; John Allen Emerson; Benjamin Jesse Ash; David R. Heine; Brooks; F. Carlton; Allen D. Gorby

2005-01-01

350

Cystic granular cell tumor mimicking Rathke cleft cyst.  

PubMed

Symptomatic granular cell tumors of the neurohypophysis are a rarely reported entity. To the authors' knowledge, they report the first fully described case of a symptomatic granular cell tumor with a large cystic component. A 31-year-old woman presented with headaches and visual complaints with imaging findings confirming a cystic sellar and suprasellar mass. The lesion was resected, and histological examination confirmed the diagnosis. The literature has shown that granular cell tumors are rarely reported as being symptomatic but may actually be a fairly common finding in autopsy studies. The authors review the literature with a specific focus on radiographic findings in patients with symptomatic granular cell tumors. PMID:20509726

Mumert, Michael L; Walsh, Michael T; Chin, Steven S; Couldwell, William T

2011-02-01

351

Granular Leidenfrost effect in vibrated beds with bumpy surfaces.  

PubMed

The effects of subjecting a bed of granular materials to horizontal vibrations by a bumpy oscillating surface have been investigated computationally in this study. The behaviour of the granular bed is determined by the vibration conditions applied which include the vibrating frequency and amplitude as well as the bumpiness of the oscillating surface. Under sufficiently vigorous vibration conditions, the granular Leidenfrost effect whereby the entire granular bed is levitated above the vibrating base by a layer of highly energetic particles may be observed. Granular temperature profiles of systems that exhibit the granular Leidenfrost effect indicate an unequal distribution of energy between particles near the vibrating base and those in the bulk. A bumpy oscillating surface was also observed to be more effective at introducing perturbations and transferring energy into a granular bed. The granular Leidenfrost effect can be induced by the application of larger grain sizes of particles constituting the bumpy vibrating base under vibration conditions that are normally insufficient for the onset of the effect. Lastly, a phase diagram which can be utilized for predicting the behaviours of granular beds that are subjected to oscillations by various types of bumpy surfaces has been constructed based on the simulation results obtained. PMID:20820844

Lim, E W C

2010-08-01

352

Statistical Mechanics of Static Granular Packings Under Gravity  

NASA Astrophysics Data System (ADS)

Despite the large use of granular materials in the industry, and the large number of natural phenomena where granular materials are involved, a comprehensive theoretical framework of their physics is still missing. An important perspective was proposed almost 20 years ago by S.Edwards, which suggested the possibility of a statistical mechanics description of granular materials at rest in their mechanically stable states. This article focuses on the theoretical foundations and current understanding of a statistical mechanics approach of granular materials under gravity. Experimental and numerical results discussing such an approach and clarifying its limit of validity are described as well.

Ciamarra, Massimo Pica; de Candia, Antonio; Fierro, Annalisa; Nicodemi, Mario; Coniglio, Antonio

353

Linear stability analysis of a vertically oscillated granular layer.  

PubMed

We present a linear stability analysis of an oscillating granular layer, treating it as an isothermal incompressible fluid with zero surface tension, which undergoes periodic collisions with and separations from an oscillating plate. Because the viscosity of the granular layer is unknown, we use the experimental value of the critical acceleration for the transition from a flat to patterned layer as input for the theory, and use the analysis to calculate the granular viscosity and the wavelength of the most unstable mode. The wavelength compares favorably with the experimental pattern wavelength. Further, we find that the wavelengths are controlled by the viscosity of the granular layer. PMID:11970664

Bizon, C; Shattuck, M D; Swift, J B

1999-12-01

354

Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials  

NASA Technical Reports Server (NTRS)

The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single grain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three-dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction.

Marshall, J.; Weislogel, M.; Jacobson, T.

1999-01-01

355

Complex wetting phenomena in liquid mixtures: frustrated-complete wetting and competing intermolecular forces  

NASA Astrophysics Data System (ADS)

We give a phenomenological overview of recently discovered complex wetting states in simple liquid mixtures relevant to both fundamental research and industrial applications such as oil recovery. Alkanes on water show a sequence of two wetting transitions, from partial wetting to `frustrated-complete wetting', and finally to complete wetting: a first-order thin-thick transition between a microscopic and a mesoscopic adsorbed alkane film is followed by a long-range critical wetting transition to a macroscopic wetting layer. The existence of the new `frustrated-complete wetting' state follows from a competition between short-range and long-range components of the intermolecular forces, the latter opposing wetting. The effective long-range forces between interfaces consist of Debye dipolar and London dispersion contributions, which can also be in mutual competition. The London component is ultimately responsible for the frustration preventing complete wetting at ambient temperatures and pressures.

Bonn, D.; Bertrand, E.; Shahidzadeh, N.; Ragil, K.; Dobbs, H. T.; Posazhennikova, A. I.; Broseta, D.; Meunier, J.; Indekeu, J. O.

2001-05-01

356

The thermodynamics of dense granular flow and jamming  

NASA Astrophysics Data System (ADS)

The scope of the thesis is to propose, based on experimental evidence and theoretical validation, a quantifiable connection between systems that exhibit the jamming phenomenon. When jammed, some materials that flow are able to resist deformation so that they appear solid-like on the laboratory scale. But unlike ordinary fusion, which has a critically defined criterion in pressure and temperature, jamming occurs under a wide range of conditions. These condition have been rigorously investigated but at the moment, no self-consistent framework can apply to grains, foam and colloids that may have suddenly ceased to flow. To quantify the jamming behavior, a constitutive model of dense granular flows is deduced from shear-flow experiments. The empirical equations are then generalized, via a thermodynamic approach, into an equation-of-state for jamming. Notably, the unifying theory also predicts the experimental data on the behavior of molecular glassy liquids. This analogy paves a crucial road map for a unifying theoretical framework in condensed matter, for example, ranging from sand to fire retardants to toothpaste.

Lu, Shih Yu

357

Pore-scale modelling and tomographic visualisation of drying in granular media.  

PubMed

Spatio-temporal evolution of liquid phase clusters during drying of a granular medium (realised by random packing of cylindrical particles) has been investigated at the length-scale of individual pores. X-ray microtomography has been used to explicitly resolve the three-dimensional spatial distribution of the solid, liquid, and gas phases within the wet particle assemblies. The propagation of liquid menisci through the granular medium during drying was dynamically followed. The effect of contact angle on the degree of dispersion of the drying front has been studied by observing drying in a layer of untreated (hydrophilic) and silanised particles; the drying front was found to be sharper in the case of the silanised (less hydrophilic) particles. This observation was confirmed by direct numerical simulations of drying in a digitally encoded porous medium identical in structure to the experimental one. The simulations also revealed that the average gas-liquid interfacial area in a given porous microstructure strongly depends on the contact angle. PMID:16513128

Kohout, Martin; Grof, Zdenek; Stepánek, Frantisek

2006-07-01

358

Adsorption of chlorophenols on granular activated carbon  

SciTech Connect

Studies were undertaken of the adsorption of chlorinated phenols from aqueous solution on granular activated carbon (Filtrasorb-400, 30 x 40 mesh). Single-component equilibrium adsorption data on the eight compounds in two concentration ranges at pH 7.0 fit the Langmuir equation better than the Freundlich equation. The adsorptive capacities at pH 7.0 increase from pentachlorophenol to trichlorophenols and are fairly constant from trichlorophenols to monochlorophenols. The adsorption process was found to be exothermic for pentachlorophenol and 2,4,6-trichlorophenol, and endothermic for 2,4-dichlorophenol and 4-chlorophenol. Equilibrium measurements were also conducted for 2,4,5-trichlorophenol, 2,4-dichlorophenol, and 4-chlorophenol over a wide pH range. A surface complexation model was proposed to describe the effect of pH on adsorption equilibria of chlorophenols on activated carbon. The simulations of the model are in excellent agreement with the experimental data. Batch kinetics studies were conducted of the adsorption of chlorinated phenols on granular activated carbon. The results show that the surface reaction model best describes both the short-term and long-term kinetics, while the external film diffusion model describes the short-term kinetics data very well and the linear-driving-force approximation improved its performance for the long-term kinetics. Multicomponent adsorption equilibria of chlorophenols on granular activated carbon was investigated in the micromolar equilibrium concentration range. The Langmuir competitive and Ideal Adsorbed Solution (IAS) models were tested for their performance on the three binary systems of pentachlorophenol/2,4,6-trichlorophenol, 2,4,6-trichlorophenol/2,4-dichlorophenol, and 2,4-dichlorophenol/4-chlorophenol, and the tertiary system of 2,4,6-trichlorophenol/2,4-dichlorophenol/4-chlorophenol, and found to fail to predict the two-component adsorption equilibria of the former two binary systems and the tertiary system.

Yang, M.

1993-12-31

359

Creeping granular motion under variable gravity levels.  

PubMed

In a rotating tumbler that is more than one-half filled with a granular material, a core of material forms that should ideally rotate with the tumbler. However, the core rotates slightly faster than the tumbler (precession) and decreases in size (erosion). The precession and erosion of the core provide a measure of the creeping granular motion that occurs beneath a continuously flowing flat surface layer. Since the effect of gravity on the subsurface flow has not been explored, experiments were performed in a 63% to 83% full granular tumbler mounted in a large centrifuge that can provide very high g-levels. Two colors of 0.5 mm glass beads were filled side by side to mark a vertical line in the 45 mm radius quasi-two-dimensional tumbler. The rotation of the core with respect to the tumbler (precession) and the decrease in the size of the core (erosion) were monitored over 250 tumbler revolutions at accelerations between 1g and 12g. The flowing layer thickness is essentially independent of the g-level for identical Froude numbers, and the shear rate in the flowing layer increases with increasing g-level. The degree of core precession increases with the g-level, while the core erosion is essentially independent of the g-level. Based on a theory for core precession and erosion, the increased precession is likely a consequence of the higher shear rate. Core erosion, on the other hand, is related to the creep region decay constant, which is connected with slow diffusion in the bed and unaffected by gravity. PMID:17025623

Arndt, Tim; Brucks, Antje; Ottino, Julio M; Lueptow, Richard M

2006-09-01

360

Birth and growth of a granular jet  

SciTech Connect

The interaction between fine grains and the surrounding interstitial gas in a granular bed can lead to qualitatively new phenomena not captured in a simple, single-fluid model of granular flows. This is demonstrated by the granular jet formed by the impact of a solid sphere into a bed of loose, fine sand. Unlike jets formed by impact in fluids, this jet is actually composed of two separate components, an initial thin jet formed by the collapse of the cavity left by the impacting object stacked on top of a second, thicker jet which depends strongly on the ambient gas pressure. This complex structure is the result of an interplay between ambient gas, bed particles, and impacting sphere. Here we present the results of systematic experiments that combine measurements of the jet above the surface varying the release height, sphere diameter, container size, and bed material with x-ray radiography below the surface to connect the changing response of the bed to the changing structure of the jet. We find that the interstitial gas trapped by the low permeability of a fine-grained bed plays two distinct roles in the formation of the jet. First, gas trapped and compressed between grains prevents compaction, causing the bed to flow like an incompressible fluid and allowing the impacting object to sink deep into the bed. Second, the jet is initiated by the gravity driven collapse of the cavity left by the impacting object. If the cavity is large enough, gas trapped and compressed by the collapsing cavity can amplify the jet by directly pushing bed material upwards and creating the thick jet. As a consequence of these two factors, when the ambient gas pressure is decreased, there is a crossover from a nearly incompressible, fluidlike response of the bed to a highly compressible, dissipative response. Compaction of the bed at reduced pressure reduces the final depth of the impacting object, resulting in a smaller cavity and in the demise of the thick jet.

Royer, J.R.; Corwin, E.I.; Conyers, B.; Flior, A.; Rivers, M.L.; Eng, P.J.; Jaeger, H.M. (UC)

2008-10-08

361

Starting to move through a granular medium  

SciTech Connect

We explore the process of initiating motion through a granular medium by measuring the force required to push a flat circular plate upward from underneath the medium. In contrast to previous measurements of the drag and penetration forces, which were conducted during steady state motion, the initiation force has a robust dependence on the diameter of the grains forming the pile. We attribute this dependence to the requirement for local dilation of the grains around the circumference of the plate, as evidenced by an observed linear dependence of the initiation force on the plate diameter.

Costantino, D. J. [Pennsylvania State University; Scheidemantel, T. [Pennsylvania State University; Stone, Matthew B [ORNL; Conger, C. [Pennsylvania State University; Klein, K. [Pennsylvania State University; Lohr, M. [Pennsylvania State University; Modig, Z. [Pennsylvania State University; Schiffer, P. [Pennsylvania State University

2008-01-01

362

Granular convection observed by magnetic resonance imaging  

SciTech Connect

Vibrations in a granular material can spontaneously produce convection rolls reminiscent of those seen in fluids. Magnetic resonance imaging provides a sensitive and noninvasive probe for the detection of these convection currents, which have otherwise been difficult to observe. A magnetic resonance imaging study of convection in a column of poppy seeds yielded data about the detailed shape of the convection rolls and the depth dependence of the convection velocity. The velocity was found to decrease exponentially with depth; a simple model for this behavior is presented here. 31 refs., 4 figs.

Ehrichs, E.E.; Jaeger, H.M.; Knight, J.B.; Nagel, S.R.; Karczmar, G.S.; Kuperman, V.Yu. [Univ. of Chicago, IL (United States)

1995-03-17

363

Prenatal diagnosis of granular cell tumor.  

PubMed

Congenital granular cell tumor (GCT) is a relatively rare intraoral benign tumor, approximately 200 cases of which have been reported in the neonatal period worldwide. The newborn infant may have feeding problems and respiratory difficulties due to airway obstruction. This lesion may be diagnosed by prenatal ultrasonography and simple resection is mostly required. We report a case of an adult type of GCT in a newly born infant, who presented with an intraoral protruding mass with a prenatal diagnosis. This article describes the prenatal course, clinical, and pathological characteristics, and management of the GCT. PMID:24644385

Kadivar, Maliheh; Sangsari, Razieh; Alavi, Azin

2014-03-01

364

Projectile interactions in granular impact cratering.  

PubMed

We present evidence for the interactions between a ball and the container boundaries, as well as between two balls, that are mediated by the granular medium during impact cratering. The presence of the bottom boundary affects the final penetration depth only for low drop heights with shallow filling, in which case, surprisingly, the penetration becomes deeper. By contrast the presence of the sidewall causes less penetration and also an effective repulsion. Repulsion is also found for two balls dropped side by side. PMID:18764506

Nelson, E L; Katsuragi, H; Mayor, P; Durian, D J

2008-08-01

365

Gravity-driven dense granular flows  

SciTech Connect

The authors report and analyze the results of numerical studies of dense granular flows in two and three dimensions, using both linear damped springs and Hertzian force laws between particles. Chute flow generically produces a constant density profile that satisfies scaling relations suggestive of a Bagnold grain inertia regime. The type for force law has little impact on the behavior of the system. Failure is not initiated at the surface, consistent with the absence of surface flows and different principal stress directions at vs. below the surface.

ERTAS,DENIZ; GREST,GARY S.; HALSEY,THOMAS C.; DEVINE,DOV; SILBERT,LEONARDO E.

2000-03-29

366

DEM simulation of experimental dense granular packing  

SciTech Connect

In this study we present numerical analysis performed on the experimental results of sphere packings of mono-sized hard sphere whose packing fraction spans across a wide range of 0.59<{Phi}<0.72. Using X-ray Computed Tomography (XCT), we have full access to the 3D structure of the granular packings. Numerical analysis performed on thr data provides the first experimental proofs of how densification affects local order parameters. Furthermore by combining Discrete Element Method (DEM) and the experimental results from XCT, we investigate how the intergranular forces change with the onset of crystallization.

Hanifpour, Maryam; Allaei, Mehdi Vaez [Department of Physics, University of Tehran, Tehran (Iran, Islamic Republic of); Francois, Nicolas; Saadatfar, Mohammad [Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra (Australia)

2013-06-18

367

Rolling friction on a granular medium.  

PubMed

We present experimental results for the rolling of spheres on a granular bed. We use two sets of glass and steel spheres with varying diameters and a high-speed camera to follow the motion of the spheres. Despite the complex phenomena occurring during the rolling, the results show a friction coefficient nearly independent of the velocity (0.45-0.5 for glass and 0.6-0.65 for steel). It is found that for a given sphere density, the large spheres reach a longer distance, a result that may also help explain the rock sorting along natural stone accumulations at the foot of mountain slopes. PMID:19391789

De Blasio, Fabio Vittorio; Saeter, May-Britt

2009-02-01

368

Contact network topology in tapped granular media.  

PubMed

We analyze the contact network of simulated two-dimensional granular packings in different states of mechanical equilibrium obtained by tapping. We show that topological descriptors of the contact network allow one to distinguish steady states of the same mean density obtained with different tap intensities. These equal-density states were recently proven to be distinguishable through the mean force moment tensor. In contrast, geometrical descriptors, such as radial distribution functions, bond order parameters, and Voronoi cell distributions, can hardly discriminate among these states. We find that small-order loops of contacts-the polygons of the network-are especially sensitive probes for the contact structure. PMID:23496501

Arévalo, Roberto; Pugnaloni, Luis A; Zuriguel, Iker; Maza, Diego

2013-02-01

369

Negative magnetoresistance slope in superconducting granular films  

NASA Astrophysics Data System (ADS)

A phenomenological theory is developed to explain the recently observed negative magnetoresistance slope in ultra-thin granular YBa2Cu2O7-? films. Viewing this system as a two-dimensional array of extended Josephson junctions, we numerically solve the sine-Gordon equations including a viscosity term that increases linearly with the external field. The solution yields a negative magnetoresistance slope setting in at a field that is determined by the geometry and thus independent of temperature, in agreement with the experimental results.

Shapiro, Boris Ya.; Shapiro, Irina; Levi, Daniel; Shaulov, Avner; Yeshurun, Yosef

2014-06-01

370

Force-chain distributions in granular systems  

NASA Astrophysics Data System (ADS)

We study experimentally the distributions of force chains in granular materials, which are slightly different in sheared systems compared to isotropically compressed systems, especially at the tails, reflecting the shear-induced anisotropy of the contact force network. Ignoring this anisotropy allows us to establish a relationship between the mean force-chain length Lm and the average contact number Z of particles for both systems, independent of the system size. We also demonstrate that force-chain distributions are not related to the exponential-like distributions of stresses.

Zhang, Ling; Wang, Yujie; Zhang, Jie

2014-01-01

371

Coarsening and Slow Dynamics in Granular Compaction  

NASA Astrophysics Data System (ADS)

We address the problem of the microscopic reorganization of a granular medium under a compaction process in the framework of Tetris-like models. We point out the existence of regions of spatial organization which we call domains, and study their time evolution. It turns out that after an initial transient, most of the activity of the system is concentrated on the boundaries between domains. One can then describe the compaction phenomenon as a coarsening process for the domains, and a progressive reduction of domain boundaries. We discuss the link between the coarsening process and the slow dynamics in the framework of a model of active walkers on active substrates.

Baldassarri, A.; Krishnamurthy, S.; Loreto, V.; Roux, S.

2001-11-01

372

Coarsening and slow dynamics in granular compaction.  

PubMed

We address the problem of the microscopic reorganization of a granular medium under a compaction process in the framework of Tetris-like models. We point out the existence of regions of spatial organization which we call domains, and study their time evolution. It turns out that after an initial transient, most of the activity of the system is concentrated on the boundaries between domains. One can then describe the compaction phenomenon as a coarsening process for the domains, and a progressive reduction of domain boundaries. We discuss the link between the coarsening process and the slow dynamics in the framework of a model of active walkers on active substrates. PMID:11736401

Baldassarri, A; Krishnamurthy, S; Loreto, V; Roux, S

2001-11-26

373

Interstitial gas effect on vibrated granular columns  

NASA Astrophysics Data System (ADS)

Vibrated granular materials have been intensively used to investigate particle segregation, convection, and heaping. We report on the behavior of a column of heavy grains bouncing on an oscillating solid surface. Measurements indicate that, for weak effects of the interstitial gas, the temporal variations of the pressure at the base of the column are satisfactorily described by considering that the column, despite the observed dilation, behaves like a porous solid. In addition, direct observation of the column dynamics shows that the grains of the upper and lower surfaces are in free fall in the gravitational field and that the dilation is due to a small delay between their takeoff times.

Pastenes, Javier C.; Géminard, Jean-Christophe; Melo, Francisco

2014-06-01

374

Uphill solitary waves in granular flows  

NASA Astrophysics Data System (ADS)

We have experimentally observed uphill solitary waves in the surface flow on a granular material. A heap is constructed by injecting sand between two vertical glass plates separated by a distance much larger than the average grain size, with an open boundary. As the heap reaches the open boundary, solitary fluctuations appear on the flowing layer and move “up the hill” (i.e., against the direction of the flow). We explain the phenomenon in the context of stop-and-go traffic models.

Martínez, E.; Pérez-Penichet, C.; Sotolongo-Costa, O.; Ramos, O.; Måløy, K. J.; Douady, S.; Altshuler, E.

2007-03-01

375

Simulation of Granular Compacts in Two Dimensions  

SciTech Connect

Simulations of granular packings in 2-D by throwing disks in a rectangular die are performed. Different size distributions as bimodal, uniform and gaussian are used. Once the array of particles is done, a relaxation process is carried on using a large-amplitude, low-frequency vertical shaking. This relaxation is performed a number N of times. Then, the authors measure the density of the package, contact distribution, coordination number distribution, entropy and also the disks size distribution vs. height. The dependence of all these magnitudes on the number N of shakings used to relax the packing and on the size distribution parameters are explored and discussed.

VIDALES,A.M.; KENKRE,V.M.; HURD,ALAN J.

2000-07-24

376

Yield loci for an anisotropic granular assembly  

NASA Astrophysics Data System (ADS)

Yield loci of a granular material are derived in case of triaxial compression carried out at constant pressure. The theory is based upon a simple micromechanical model in which particles move according to an average, homogeneous deformation. We show how the presence of an inherent anisotropy in the aggregate (typical of laboratory samples due to depositional processes) produces a deviation of the yield loci in the stress space from the expected Mohr-Coulomb prediction. That is, when the compaction pressure in an anisotropic aggregate is increased, irreversibility associated with sliding between particles occurs and this will influence the yield function in the subsequent triaxial test. Numerical simulations support the theoretical result.

La Ragione, Luigi; Oger, Luc

2012-10-01

377

Modelling of dc characteristics for granular semiconductors  

NASA Astrophysics Data System (ADS)

The dc characteristics of granular n-type semiconductors are calculated analytically with the drift-diffusion theory. Electronic trapping at the grain boundaries (GBs) is taken into account. The use of quadratic and linear GB potential profiles in the calculation is compared. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is excellent in a large voltage range. The results show that electronic trapping at the GBs has a remarkable effect on the highly nonlinear I-V characteristics of the material.

Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey

2010-11-01

378

Coal combustion by wet oxidation  

SciTech Connect

The combustion of coal by wet oxidation was studied by the Center for Waste Management Programs, of Michigan Technological University. In wet oxidation a combustible material, such as coal, is reacted with oxygen in the presence of liquid water. The reaction is typically carried out in the range of 204/sup 0/C (400/sup 0/F) to 353/sup 0/C (650/sup 0/F) with sufficient pressure to maintain the water present in the liquid state, and provide the partial pressure of oxygen in the gas phase necessary to carry out the reaction. Experimental studies to explore the key reaction parameters of temperature, time, oxidant, catalyst, coal type, and mesh size were conducted by running batch tests in a one-gallon stirred autoclave. The factors exhibiting the greatest effect on the extent of reaction were temperature and residence time. The effect of temperature was studied from 204/sup 0/C (400/sup 0/F) to 260/sup 0/C (500/sup 0/F) with a residence time from 600 to 3600 seconds. From this data, the reaction activation energy of 2.7 x 10/sup 4/ calories per mole was determined for a high-volatile-A-Bituminous type coal. The reaction rate constant may be determined at any temperature from the activation energy using the Arrhenius equation. Additional data were generated on the effect of mesh size and different coal types. A sample of peat was also tested. Two catalysts were evaluated, and their effects on reaction rate presented in the report. In addition to the high temperature combustion, low temperature desulfurization is discussed. Desulfurization can improve low grade coal to be used in conventional combustion methods. It was found that 90% of the sulfur can be removed from the coal by wet oxidation with the carbon untouched. Further desulfurization studies are indicated.

Bettinger, J.A.; Lamparter, R.A.; McDowell, D.C.

1980-11-15

379

Wetting of flexible fibre arrays.  

PubMed

Fibrous media are functional and versatile materials, as demonstrated by their ubiquity both in natural systems such as feathers and adhesive pads and in engineered systems from nanotextured surfaces to textile products, where they offer benefits in filtration, insulation, wetting and colouring. The elasticity and high aspect ratios of the fibres allow deformation under capillary forces, which cause mechanical damage, matting self-assembly or colour changes, with many industrial and ecological consequences. Attempts to understand these systems have mostly focused on the wetting of rigid fibres or on elastocapillary effects in planar geometries and on a fibre brush withdrawn from an infinite bath. Here we consider the frequently encountered case of a liquid drop deposited on a flexible fibre array and show that flexibility, fibre geometry and drop volume are the crucial parameters that are necessary to understand the various observations referred to above. We identify the conditions required for a drop to remain compact with minimal spreading or to cause a pair of elastic fibres to coalesce. We find that there is a critical volume of liquid, and, hence, a critical drop size, above which this coalescence does not occur. We also identify a drop size that maximizes liquid capture. For both wetting and deformation of the substrates, we present rules that are deduced from the geometric and material properties of the fibres and the volume of the drop. These ideas are applicable to a wide range of fibrous materials, as we illustrate with examples for feathers, beetle tarsi, sprays and microfabricated systems. PMID:22358841

Duprat, C; Protière, S; Beebe, A Y; Stone, H A

2012-02-23

380

Variation of granular evolution at meso-scales  

Microsoft Academic Search

An 8.5 h series of solar granulation images obtained at the Swedish SVST (La Palma) was investigated for the divergence pattern and its relation to granular evolution types. The velocities for the divergence fields were calculated by local correlation techniques. Granular evolution types were detected automatically by a granulation tracking algorithm. We find a strong preference of fragmenting, merging, and

W. Pötzi; P. N. Brandt; A. Hanslmeier

2003-01-01

381

Biosorption of pentachlorophenol (PCP) by granular and dispersed anaerobic sludge  

Microsoft Academic Search

Anaerobic granular sludge from Upflow Anaerobic Sludge Bed (UASB) reactors contain a complete consortia of anaerobic microorganisms in an optimal spatial configuration. The importance of the spatial relationship of microbes in anaerobic granular sludge versus increased surface area (granules vs. free cells) as it pertains to biosorption and microbial toxicity is unknown. In this study, biosorption isotherms are reported for

Pham Thi Tham; Kevin J. Kennedy

1994-01-01

382

Stress relaxation in dense and slow granular flows  

Microsoft Academic Search

In a dense granular system, particles interact in networks containing many particles and interaction times are long compared with the particle binary collision time. In these systems, the streaming part of the granular stress is negligible. We only consider the collisional stress in this paper. The average behavior of particle contacts is studied. By following the statistical method developed recently

D. Z. Zhang; R. M. Rauenzahn

2000-01-01

383

Dynamics of a projectile penetrating in granular systems  

Microsoft Academic Search

The impact of a sphere with velocity u0 on a fine, loose granular system under the acceleration due to gravity has been studied by fast video photography. The behavior of the granular bed is found to be similar to a fluid during initial impact, followed by a cavity drag during projectile penetration. From the trajectory of the projectile it is

M. Hou; Z. Peng; R. Liu; K. Lu; C. K. Chan

2005-01-01

384

Approximated calculation model for plastic deformations of granular waste materials  

Microsoft Academic Search

This paper suggests an approximate model to estimate the total plastic deformation of layers made of granular materials. In this work, the model was designed to calculate the plastic deformations of the cylindrical specimen of monotonic triaxial tests. The model concept is based on the deformation mechanisms of granular material presented in the literature review. These mechanisms assumed that the

Abdelkader T. Ahmed

2011-01-01

385

Microconvective heating of granular explosives by a semiconductor bridge  

Microsoft Academic Search

The ignition of reactive powders by a semiconductor bridge (SCB) is analyzed by applying a multiphase flow model based upon the theory of mixtures. The hot plasma produced by the SCB permeates the cold granular explosive, deposits its latent heat upon fusing to the grains, therby heating the explosive granular surfaces to energy states required for self-sustained reaction. This mechanism

M. J. Martinez; M. R. Baer

1989-01-01

386

BACTERIA ASSOCIATED WITH GRANULAR ACTIVATED CARBON PARTICLES IN DRINKING WATER  

EPA Science Inventory

A sampling protocol was developed to examine particles released from granular activated carbon filter beds. A gauze filter/Swinnex procedure was used to collect carbon fines from 201 granular activated carbon-treated drinking water samples over 12 months. Application of a homogen...

387

Compressive strength of an unsaturated granular material during cementation  

Microsoft Academic Search

The cohesive behavior of unsaturated granular materials is due to the presence of cohesive bonds between grains. These bonds can have various physico-chemical characteristics and may evolve with environmental conditions. We study the case of a granular material partially saturated by an aqueous solution. The bonds are thus initially of capillary type and the mechanical strength is weak. At low

J.-Y. Delenne; F. Soulié; M. S. El Youssoufi; F. Radjai

2011-01-01

388

The flow behavior of granular material due to horizontal shaking  

Microsoft Academic Search

This paper studied the convection phenomena that occurred in a granular bed under horizontal vibration. High-speed photography was employed to measure the movements of particles. The fields of the instantaneous velocities and the long-term velocities were plotted. Two symmetric convection rolls were observed. The granular temperature distributions were also measured and analyzed. The controlling parameters included the acceleration amplitude and

Shu-San Hsiau; Ming-Yuan Ou; Chi-Hwang Tai

2002-01-01

389

Clusters in a magnetic toy model for binary granular piles.  

PubMed

Results on a generalized magnetically controlled ballistic deposition model of granular piles are reported in order to search for the effect of "spin flip" probability q in building a granular pile. Two different regimes of spin cluster site distributions have been identified, a borderline q(c) (betaJ) where J is the interaction potential strength. PMID:15244862

Trojan, K; Ausloos, M

2004-05-01

390

Effects of granular charge on flow and mixing  

NASA Astrophysics Data System (ADS)

Sandstorms in the desert have long been reported to produce sparks and other electrical disturbances - indeed as long ago as 1850, Faraday commented on the peculiarities of granular charging during desert sandstorms. Similarly, lightning strikes within volcanic dust plumes have been repeatedly reported for over half a century, but remain unexplained. The problem of granular charging has applied, as well as natural, implications, for charged particle clouds frequently generate spectacularly devastating dust explosions in granular processing plants, and sand becomes strongly electrified by helicopters traveling in desert environments. The issue even has implications for missions to the Moon and to Mars, where charged dust degrades solar cells viability and clings to spacesuits, limiting the lifetime of their joints. Despite the wide-ranging importance of granular charging, even the simplest aspects of its causes remain elusive. To take one example, sand grains in the desert manage to charge one another despite having only similar materials to rub against over expanses of many miles - thus existing theories of charging due to material differences fail entirely to account for the observed charging of desert sands. In this talk, we describe recent progress made in identifying underlying causes of granular charging, both in desert-like environments and in industrial applications, and we examine effects of granular charging on flow, mixing and separation of common granular materials. We find that charging of identical grains can occur under simple laboratory conditions, and we make new predictions for the effects of this charging on granular behaviours.

Shinbrot, T.; Herrmann, H. J.

2008-12-01

391

Wetting dynamics of multiscaled structures  

NASA Astrophysics Data System (ADS)

Priming dynamics is one of the critical parameters in designing a capillary-driven thermal management system. We report both an experimental and simulation study of hierarchical structures with silicon pillars and silicon nanowires on the pillar surface. Liquid front velocity covered and uncovered was characterized using capillary wetting experiments and validated by numerical simulation and theoretical prediction. The water under cover moves one order of magnitude faster than the water in the uncovered case. The experimental results and the prediction are in good agreement for flow regimes in both the covered and the uncovered regions.

Chen, Hsiu-Hung; Shi, Junxiang; Chen, Chung-Lung

2013-10-01

392

Droplet charging for wet scrubbers.  

PubMed

Water droplet charge/mass of wet scrubbers was measured over the direct charging applied potential range of 0-20 kV, 30-70 pounds per square inch gauge (206.8-482.6 kPa) water pressure, and with spiral, impingement, and whirl nozzles. The measured charge/mass ranged from -0.0005 to 0.2 microcoulomb/gm and was directly related to the applied voltage. The water charge/mass was a function of the spray nozzle, with the smaller orifice lower-flow nozzles having the higher charge/mass. PMID:14871008

Pilat, Michael J; Lukas, John C

2004-01-01

393

Geomorphology, disturbance, and the soil and vegetation of two subtropical wet steepland watersheds of Puerto Rico  

Microsoft Academic Search

Relationships between landforms, soil nutrients, forest structure, and the relative importance of different disturbances were quantified in two subtropical wet steepland watersheds in Puerto Rico. Ridges had fewer landslides and treefall gaps, more above-ground biomass, older aged stands, and greater species richness than other landscape positions. Ridge soils had relatively low quantities of exchangeable bases but high soil organic matter,

F. N. Scatena; Ariel E. Lugo

1995-01-01

394

A rheological approach to analyze aerobic granular sludge.  

PubMed

Aerobic granular sludge is one promising biotechnology in wastewater treatment. Despite intensive researches on granular architecture and strategies to improve treatment efficiency, there are still some elusive material parameters needed to stimulate the granulation process. The main aim of this study was to evaluate aerobic granular sludge innovatively using the universal rheology methodology, in terms of processability or quality and texture. Steady shear and oscillatory measurements were performed. Basic rheological characterization showed that aerobic granular sludge was a shear-thinning Herschel-Bulkley fluid with yield pseudoplasticity. Meanwhile, granular sludge presented characterized viscoelastic behaviors in dynamic sweeps highlighting its superiority to flocculent sludge. Furthermore, a Wagner-type constitutive model incorporating a relaxation and damping function was introduced and able to describe the time-dependent and non-linear viscoelastic behaviors. This study could make a further step on predicting rheological properties, helping improve the actual sludge treatment process and the operation of sludge dewatering. PMID:24374128

Ma, Yun-Jie; Xia, Cheng-Wang; Yang, Hai-Yang; Zeng, Raymond J

2014-03-01

395

Mars: Always Cold, Sometimes Wet?  

NASA Technical Reports Server (NTRS)

A synthesis of a diverse suite of observations of H2O-related landforms that are possible Mars analogs from terrestrial polar regions (Devon Island in the Arctic; the Dry Valleys of Antarctica) put into question any requirement for extended episode(s) of warm and wet climate in Mars past. Geologically transient episodes of localized H2O cycling, forced by exogenic impacts, enhanced endogenic heat flow, and/or orbit-driven short-term local environmental change under an otherwise cold, low pressure (=10(exp 2) mbar) global climate, may be sufficient to account for the martian surface's exposed record of aqueous activity. A Mars that was only sometimes locally warm and wet while remaining climatically cold throughout its history is consistent with results (difficulties) encountered in modeling efforts attempting to support warm martian climate hypotheses. Possible analogs from terrestrial cold climate regions for the recent gully features on Mars also illustrate how transient localized aqueous activity might, under specific circumstances, also occur on Mars under the present frigid global climatic regime.

Lee, Pascal; McKay, Christoper P.

2003-01-01

396

Granular-Bed-Filter Development Program, Phase II. Analytical model for the performance of a moving granular-bed filter  

Microsoft Academic Search

A computer model has been developed which predicts the performance of an axisymmetric moving granular-bed filter (GBF). The flow of gas through the filter is modeled with the Ergun Equation describing gas flow through porous media. Particle caputre is divided into portions which differentiate between deposition on the surface of the granular material and deposition on back into the gas

1982-01-01

397

Dark Matters  

SciTech Connect

One of the greatest mysteries in the cosmos is that it is mostly dark.  Astronomers and particle physicists today are seeking to unravel the nature of this mysterious, but pervasive dark matter which has profoundly influenced the formation of structure in the universe.  I will describe the complex interplay between galaxy formation and dark matter detectability and review recent attempts to measure particle dark matter by direct and indirect means.

Joseph Silk

2009-09-23

398

Dark Matters  

ScienceCinema

One of the greatest mysteries in the cosmos is that it is mostly dark.  Astronomers and particle physicists today are seeking to unravel the nature of this mysterious, but pervasive dark matter which has profoundly influenced the formation of structure in the universe.  I will describe the complex interplay between galaxy formation and dark matter detectability and review recent attempts to measure particle dark matter by direct and indirect means.

Joseph Silk

2010-01-08

399

Compaction wave profiles in granular HMX  

SciTech Connect

Meso-scale simulations of a compaction wave in a granular bed of HMX have been performed. The grains are fully resolved in order that the change in porosity across the wave front is determined by the elastic-plastic response of the grains rather than an empirical law for the porosity as a function of pressure. Numerical wave profiles of the pressure and velocity are compared with data from a gas gun experiment. The experiment used an initial porosity of 36%, and the wave had a pressure comparable to the yield strength of the grains. The profiles are measured at the front and back of the granular bed. The transit time for the wave to travel between the gauges together with the Hugoniot jump conditions determines the porosity behind the wave front. In the simulations the porosity is determined by the yield strength and stress concentrations at the contact between grains. The value of the yield strength needed to match the experiment is discussed. Analysis of the impedance match of the wave at the back gauge indicates that the compaction wave triggers a small amount of burn, less than 1% mass fraction, on the micro-second time scale of the experiment.

Menikoff, Ralph

2001-01-01

400

Response Functions for a Granular Fluid  

NASA Astrophysics Data System (ADS)

The response of an isolated granular fluid to smallperturbations of the hydrodynamic fields is considered. The corresponding linear response functions are identified in terms of a formal solution to the Liouville equation including the effects of the cooling reference state. These functions are evaluated exactly in the asymptotic long wavelength limit and shown to represent hydrodynamic modes. More generally, the linear granular Navier-Stokes equations for the response functions and related Langevin equations are obtained from an extension of Mori's identity. The resulting Green-Kubo expressions for transport coefficients are compared and contrasted with those for a molecular fluid. Next the response functions are described in terms of an effective dynamics in the single particle phase space. A closed linear kinetic equation is obtained formally in terms of a linear two particle functional. This closure is evaluated for two examples: a short time Markovian approximation, a nd a low density expansion on length and time scales of the mean free time and mean free path. The former is a generalization of the revised Enskog kinetic theory to include velocity correlations. The latter is an extension of the Boltzmann equation to include the effects of recollisions (rings) among the particles.

Dufty, J.

401

COMPACTION WAVE PROFILES IN GRANULAR HMX  

SciTech Connect

Meso-scale simulations of a compaction wave in a granular bed of HMX have been performed. The grains are fully resolved in order that the change in porosity across the wave front is determined by the elastic-plastic response of the grains rather than an empirical law for the porosity as a function of pressure. Numerical wave profiles of the pressure and velocity are compared with data from a gas gun experiment. The experiment used an initial porosity of 36%, and the wave had a pressure comparable to the yield strength of the grains. The profiles are measured at the front and back of the granular bed. The transit time for the wave to travel between the gauges together with the Hugoniot jump conditions determines the porosity behind the wave front. In the simulations the porosity is determined by the yield strength and stress concentrations at the contact between grains. The value of the yield strength needed to match the experiment is discussed. Analysis of the impedance match of the wave at the back gauge indicates that the compaction wave triggers a small amount of burn, less than 1% mass fraction, on the micro-second time scale of the experiment.

R. MENIKOFF

2001-06-01

402

Thermodynamic Consistency of Mechanical Granular Theories  

NASA Astrophysics Data System (ADS)

Constitutive Theories of the mechanical behaviour of soils are often derived without resort to thermodynamic considerations. The form of the closure conditions, however, needs to be in conformity with the second law of thermodynamics and depends on it, even on the particular form which the second law is postulated to take. We outline two common forms of the entropy principle, (i) due to Clausius-Duhem and exploited according to Coleman-Noll and (ii) due to I. Müller and exploited ac- cording to Liu. We subject them to certain classes of material behaviour of saturated and unsaturated soil and show that not only the dynamic behaviour depends on the satisfaction of the second law, but equally also that in equilibrium. Examples illus- trating this will be given for (i) a dry soil with voids and exhibiting plastic internal frictional behaviour, (ii) a saturated granular fluid mixture able to model ground water soil interactions as well as (iii) a mixture of a finite number of grains with different diameters that is capable to describe inverse grading of a soil with a broad grain size distribution. In postulating constitutive relations for continuous granular mixtures, the rule of equipresence is often replaced by the rule of phase separation to simplify the com- putations. It is made plausible that, when constituents are strongly interacting, this principle is not likely to yield satisfactory formulations for the intended phenomena.

Hutter, K.

403

Density fluctuations in vibrated granular materials  

NASA Astrophysics Data System (ADS)

We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations, the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity ?. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In particular, we propose a method to evaluate the compactivity of a powder, first put forth by Edwards and co-workers, that is the analog to temperature for a quasistatic powder. We also propose a stochastic model based on free volume considerations that captures the essential mechanism underlying the slow relaxation. We compare our experimental results with simulations of a one-dimensional model for random adsorption and desorption.

Nowak, Edmund R.; Knight, James B.; Ben-Naim, Eli; Jaeger, Heinrich M.; Nagel, Sidney R.

1998-02-01

404

Pressure-shear experiments on granular materials.  

SciTech Connect

Pressure-shear experiments were performed on granular tungsten carbide and sand using a newly-refurbished slotted barrel gun. The sample is a thin layer of the granular material sandwiched between driver and anvil plates that remain elastic. Because of the obliquity, impact generates both a longitudinal wave, which compresses the sample, and a shear wave that probes the strength of the sample. Laser velocity interferometry is employed to measure the velocity history of the free surface of the anvil. Since the driver and anvil remain elastic, analysis of the results is, in principal, straightforward. Experiments were performed at pressures up to nearly 2 GPa using titanium plates and at higher pressure using zirconium plates. Those done with the titanium plates produced values of shear stress of 0.1-0.2 GPa, with the value increasing with pressure. On the other hand, those experiments conducted with zirconia anvils display results that may be related to slipping at an interface and shear stresses mostly at 0.1 GPa or less. Recovered samples display much greater particle fracture than is observed in planar loading, suggesting that shearing is a very effective mechanism for comminution of the grains.

Reinhart, William Dodd (Sandia National Laboratories, Albuquerque, NM); Thornhill, Tom Finley, III (, Sandia National Laboratories, Albuquerque, NM); Vogler, Tracy John; Alexander, C. Scott (Sandia National Laboratories, Albuquerque, NM)

2011-10-01

405

Mechanics of Granular Materials labeled hardware  

NASA Technical Reports Server (NTRS)

Mechanics of Granular Materials (MGM) flight hardware takes two twin double locker assemblies in the Space Shuttle middeck or the Spacehab module. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/MSFC).

2000-01-01

406

Mechanics of Granular Materials (MGM) Investigators  

NASA Technical Reports Server (NTRS)

Key persornel in the Mechanics of Granular Materials (MGM) experiment at the University of Colorado at Boulder include Tawnya Ferbiak (software engineer), Susan Batiste (research assistant), and Christina Winkler (graduate research assistant). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

2000-01-01

407

Mechanic of Granular Materials (MGM) Investigator  

NASA Technical Reports Server (NTRS)

Key persornel in the Mechanics of Granular Materials (MGM) experiment are Mark Lankton (Program Manager at University Colorado at Boulder), Susan Batiste (research assistance, UCB), and Stein Sture (principal investigator). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

2000-01-01

408

Fingering and fracturing in granular media  

NASA Astrophysics Data System (ADS)

Here, we describe the phenomenon of capillary fracturing in granular media. We study the displacement of immiscible fluids in deformable, non-cohesive granular media. Experimentally, we inject air into a thin bed of water-saturated glass beads and observe the invasion morphology. The control parameters are the injection rate, the bead size, and the confining stress. We identify three invasion regimes: capillary fingering, viscous fingering, and "capillary fracturing", where capillary forces overcome frictional resistance and induce the opening of conduits. We derive two dimensionless numbers that govern the transition among the different regimes: a modified capillary number and a fracturing number. The experiments and analysis predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural processes such as primary oil migration, methane venting from lake sediments, and the formation of desiccation cracks.Examples of experimentally observed patterns. We classify these patterns into three regimes: viscous fingering, capillary fingering, and fracturing.

Juanes, R.; Holtzman, R.; Szulczewski, M.

2012-12-01

409

Expression for the granular elastic energy.  

PubMed

Granular solid hydrodynamics (GSH) is a broad-ranged continual mechanical description of granular media capable of accounting for static stress distributions, yield phenomena, propagation and damping of elastic waves, the critical state, shear band, and fast dense flow. An important input of GSH is an expression for the elastic energy needed to deform the grains. The original expression, though useful and simple, has some drawbacks. Therefore a slightly more complicated expression is proposed here that eliminates three of them: (1) The maximal angle at which an inclined layer of grains remains stable is increased from 26^{?} to the more realistic value of 30^{?}. (2) Depending on direction and polarization, transverse elastic waves are known to propagate at slightly different velocities. The old expression neglects these differences, the new one successfully reproduces them. (3) Most importantly, the old expression contains only the Drucker-Prager yield surface. The new one contains in addition those named after Coulomb, Lade-Duncan, and Matsuoka-Nakai-realizing each, and interpolating between them, by shifting a single scalar parameter. PMID:23004747

Jiang, Yimin; Zheng, Hepeng; Peng, Zheng; Fu, Liping; Song, Shixiong; Sun, Qicheng; Mayer, Michael; Liu, Mario

2012-05-01

410

Collisional model for granular impact dynamics  

NASA Astrophysics Data System (ADS)

When an intruder strikes a granular material from above, the grains exert a stopping force which decelerates and stops the intruder. Many previous studies have used a macroscopic force law, including a drag force which is quadratic in velocity, to characterize the decelerating force on the intruder. However, the microscopic origins of the force-law terms are still a subject of debate. Here, drawing from previous experiments with photoelastic particles, we present a model which describes the velocity-squared force in terms of repeated collisions with clusters of grains. From our high speed photoelastic data, we infer that "clusters" correspond to segments of the strong force network that are excited by the advancing intruder. The model predicts a scaling relation for the velocity-squared drag force that accounts for the intruder shape. Additionally, we show that the collisional model predicts an instability to rotations, which depends on the intruder shape. To test this model, we perform a comprehensive experimental study of the dynamics of two-dimensional granular impacts on beds of photoelastic disks, with different profiles for the leading edge of the intruder. We particularly focus on a simple and useful case for testing shape effects by using triangular-nosed intruders. We show that the collisional model effectively captures the dynamics of intruder deceleration and rotation; i.e., these two dynamical effects can be described as two different manifestations of the same grain-scale physical processes.

Clark, Abram H.; Petersen, Alec J.; Behringer, Robert P.

2014-01-01

411

Collisional model for granular impact dynamics.  

PubMed

When an intruder strikes a granular material from above, the grains exert a stopping force which decelerates and stops the intruder. Many previous studies have used a macroscopic force law, including a drag force which is quadratic in velocity, to characterize the decelerating force on the intruder. However, the microscopic origins of the force-law terms are still a subject of debate. Here, drawing from previous experiments with photoelastic particles, we present a model which describes the velocity-squared force in terms of repeated collisions with clusters of grains. From our high speed photoelastic data, we infer that "clusters" correspond to segments of the strong force network that are excited by the advancing intruder. The model predicts a scaling relation for the velocity-squared drag force that accounts for the intruder shape. Additionally, we show that the collisional model predicts an instability to rotations, which depends on the intruder shape. To test this model, we perform a comprehensive experimental study of the dynamics of two-dimensional granular impacts on beds of photoelastic disks, with different profiles for the leading edge of the intruder. We particularly focus on a simple and useful case for testing shape effects by using triangular-nosed intruders. We show that the collisional model effectively captures the dynamics of intruder deceleration and rotation; i.e., these two dynamical effects can be described as two different manifestations of the same grain-scale physical processes. PMID:24580216

Clark, Abram H; Petersen, Alec J; Behringer, Robert P

2014-01-01

412

Dark Matter  

NSDL National Science Digital Library

This website offers a very complete introduction to Dark Matter. First 'observed' in 1933 by Fritz Zwicky, when studying the mass distribution of the Coma Cluster, Dark Matter has been a mystery to scientist, because it does not interact with light. The website contains a detailed timeline of scientists who have tried to observe it and their methods. It also presents the theory that Dark Matter is within Galaxies and in between them, filling Galaxy Clusters. The last part is dedicated to explain what types of particles are thought to form this elusive matter

2007-04-03

413

Dark Matter  

SciTech Connect

One of the biggest scientific mysteries of our time resides in the identification of the particles that constitute a large fraction of the mass of our Universe, generically known as dark matter. We review the observations and the experimental data that imply the existence of dark matter. We briefly discuss the properties of the two best dark-matter candidate particles and the experimental techniques presently used to try to discover them. Finally, we mention a proposed project that has recently emerged within the Mexican community to look for dark matter.

Bashir, A.; Cotti, U.; De Leon, C. L.; Raya, A; Villasenor, L. [Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo. Apartado Postal 2-82, C.P. 58040, Morelia, Mich. (Mexico)

2008-07-02

414

Leaf wetness within a lily canopy  

NASA Astrophysics Data System (ADS)

A wetness duration experiment was carried out within a lily field situated adjacent to coastal dunes in the Netherlands. A within-canopy model was applied to simulate leaf wetness in three layers, with equal leaf area indices, within the canopy. This simulation model is an extension of an existing model. It appeared that in most cases leaf wetness started in the uppermost layer followed by the middle and bottom layer, respectively. The same occurred during the early morning drying process. Just after sunrise the upper layer started to dry, followed by the middle and bottom layer, respectively. The longest leaf wetness duration occurred in the bottom layer. The calculated leaf wetness durations were within 10 minutes of the results obtained using a leaf wetness sensor.

Jacobs, Adrie F. G.; Heusinkveld, Bert G.; Klok, Elisabeth J.

2005-09-01

415

The influence of topography on dynamic wetting.  

PubMed

The paramount importance of wetting applications and the significant economic value of controlling wetting-based industrial processes has stimulated a deep interest in wetting science. In many industrial applications the motion of a complex liquid front over nano-textured surfaces controls the fate of the processes. However our knowledge of the impact of nano-heterogeneities on static and dynamic wetting is very limited. In this article, the fundamentals of wetting are briefly reviewed, with a particular focus on hysteresis and roughness issues. Present knowledge and models of dynamic wetting on smooth and rough surfaces are then examined, with particular attention devoted to the case of nano-topographical heterogeneities and solid-fluid-fluid systems. PMID:23726301

Ramiasa, Melanie; Ralston, John; Fetzer, Renate; Sedev, Rossen

2014-04-01

416

Project WET (Water Education for Teachers)  

NSDL National Science Digital Library

Project WET (Water Education for Teachers) is an international, interdisciplinary, water education program for formal and informal educators of students ages 5 to 18. This project site provides opportunities to order high quality educational material, samples of Project WET activities, information on Make a Splash Festivals, education standards, information on events, Project Wet reports and water related links. There is also a link to all of the state coordinators for this project.

417

Discrete blasts in granular material yield two-stage process of cavitation and granular fountaining  

NASA Astrophysics Data System (ADS)

discrete blast within granular material, such as a single subterranean explosion within a debris-filled diatreme structure, is typically considered to produce a single uprush of material. Our experiments demonstrate that apparent "debris jet deposits" can be formed by a two-stage process of cavitation and subsequent granular fountaining. Bench-scale experiments reported here demonstrate that for a range of overpressures and depths, individual, discrete, buried gas blasts open space and expel particles from the blast site in two largely decoupled stages. Expanding gas initially pierces material nearest the blast source to open a cavity above it; then a fountain of grains rises from the source into the cavity. This staged motion dynamically segregates source grains from host-material grains, and the rates of cavity opening versus fountain rise show a power law decay relationship with initial pressure. Our experimental analysis has implications for maar-diatreme systems, field-scale detonation experiments, and underground nuclear testing.

Andrews, Robin G.; White, James D. L.; Dürig, Tobi; Zimanowski, Bernd

2014-01-01

418

Dispersive behavior and acoustic scaling in granular rocks  

NASA Astrophysics Data System (ADS)

Handling and making decisions based on data taken at different scales is a critical issue in the design of exploration and production tasks in the oil industry. Acoustic data is the classical example of the integration of dissimilar scales (i.e. seismic, well logs, lab data) where there is a scale dependent velocity. An understanding of the acoustic dispersion phenomenon in granular samples is needed. A detailed numerical work was conducted in order to establish the relationship between frequency and propagation speed for an acoustical pulse induced in simulated granular materials. The granular samples were generated with different grain size distributions while porosity and pressure were targeted and kept invariant using the grain radii expansion method. A sinusoidal burst with frequencies from 10Hz to 1MHz was applied and the corresponding acoustical speeds were estimated for each frequency. A coherent sigmoid dispersion relationship was obtained for each granular sample. The asymptotic boundaries for the dispersion function reflect the limiting cases for the wavelength/heterogeneity ratio in the granular pack. The lower speed asymptote was explained as the mean field value while upper speed asymptote can be understood based on a ray theory approximation scaled by a parameter we defined as the ``acoustic tortuosity factor''. This factor reflects the intricate acoustical path due to the texture of the stress network developed in the granular samples and can be used together with the sigmoid dispersive relationship to describe and clarify the scale discrepancy between different source acoustic data in granular materials.

Carlos, Santos; Vanessa, Urdaneta; Ernesto, Medina; Xavier, García

2013-06-01

419

Prediction of troposphere wet delay  

NASA Astrophysics Data System (ADS)

The wet delay is one of the most difficult sources of error to quantify in global navigation satellite systems (GNSS) due to its spatial and temporal variability. However, its estimation is vital in some applications, such as in Precise Point Positioning (PPP), network real-time kinematic and weather forecast. Such estimation is usually carried out for its projected component along the zenith, defined as the zenith wet delay (ZWD). Prediction of the ZWD is important if there is a break in its estimation, and in providing initial values for future processing. In this paper, prediction modeling for the ZWD is investigated. An autocorrelation study was first performed on ZWD data over three different days at the international GNSS service station ONSALA to provide an insight into the temporal correlations among ZWDs. The choice of this station was based on the availability of reliable ZWD data measured by water vapor radiometers, which provide a reference for assessment of the accuracy of predicted values. Results have shown that successive ZWD estimates are significantly correlated for up to 1.7 hours. Different trend and smoothing prediction models were then investigated. Since prediction of ZWD requires continuous data sequence, interpolation methods of possible missing ZWD values are discussed. The use of linear interpolation or a cubic Hermite polynomial was found to be sufficient for interpolation of ZWD. Test results of prediction models show that the single-exponential smoothing model was the best performer where ZWD estimates were forecasted with a root mean square error of less than 1 cm for up to two hours.

El-Mowafy, Ahmed; Lo, Johnny

2011-12-01

420

Evolution of permeability in heterogeneous granular aggregates during chemical compaction: Granular mechanics models  

NASA Astrophysics Data System (ADS)

We develop a granular mechanics model to represent the process of chemical compaction within granular media. This model represents the serial processes of stress-enhanced dissolution, mass diffusion along the fluid film separating grain boundaries, and then mass ejection into the pore space, where it may then be either reprecipitated onto the pore wall or removed by fluid advection in an open system. This process is controlled by the evolution of intergranular effective stress and mass concentrations in the fluid either in the water film or the pore space. The evolution of intergranular stress is followed by a granular mechanics model that rigorously couples the magnitude of the grain-grain contact stress to determine the time history of stress-driven dissolution. Pore fluid concentration provides a feedback to intergranular dissolution, halting intergranular compaction as fluid concentrations approach aqueous saturation. Importantly, chemical feedbacks onto the mechanical system and mechanical feedbacks on the chemical system are rigorously accommodated. Compaction is halted either by the amelioration of the driving stress (through the growth of the contact area) or by the saturation of the fluid in the pore space. This model is used to explore the influence of heterogeneous assemblages of particles on the rate and ultimate magnitude of compaction and the resulting evolution of permeability. Specifically, we explore the influence of heterogeneity in granular packs by using heterogeneous distributions of particles (linear, Gaussian, or bimodal). Results indicate that porosity and permeability decrease with compaction. Small particles dominate this dissolution-mediated process and accelerate compaction; this is true both for homogeneous distributions of small particles and for coarser aggregates containing a fraction of smaller particles. Overall, compaction is also greater for finer aggregates resulting from the larger deformation required, reaching the critical stress that will halt compaction. This feature is due to the necessary redistribution of intergranular stresses that are shed from point contacts in active chemical dissolution onto those not deforming.

Zheng, Baisheng; Elsworth, Derek

2012-03-01

421

Climate change impact on river wetted perimeter  

NASA Astrophysics Data System (ADS)

Taiwan is situated in a subtropical region with frequent typhoons and earthquakes. Because of the non-uniform spatial and temporal distribution of rainfall, the steep terrain, and rapid rivers, the variation of river discharge is large and considerably affects habitats and the ecosystem. In particular, the ecosystem experiences more stress under the threat of climate change. Wetted perimeter is one of the main parameters of habitat evaluation. A strong correlation exists between river discharge and wetted perimeter. Frequency analysis was used to determine the wetted perimeter of various river discharges of various return periods in the Kaoping River. The variation of wetted perimeter along the river and variation caused by various discharges were also investigated. The wetted perimeters of various cross-sections along the river increased from 38 km close to the river mouth. We discuss the potential impact of climate change on wetted perimeter by using HEC-RAS Model for simulation, in which the input river discharge was based on the results of GWLF simulation using rainfall and temperature data from various GCMs under A2 and B2 climate change scenarios. The results indicate that the river discharge in the wet season increased considerably, whereas the discharge in the dry season decreased. This variation considerably affects the river habitats.Under climate change, the change of wetted perimeter was not considerable in wet season. The results indicated that the decrease of the wetted perimeter in the dry season in March was the most substantial for the long term. In the A2 scenario, the decrease of the wetted perimeter was in the range of 17% to 36%. In the B2 scenario, it was in the range of 16% to 31%. This result can assist in assessing the ecological river discharge requirements.

Chiang, J. L.; Yang, H. C.

2012-04-01

422

Impact dynamics of granular jets with noncircular cross sections  

NASA Astrophysics Data System (ADS)

Using high-speed photography, we investigate two distinct regimes of the impact dynamics of granular jets with noncircular cross sections. In the steady-state regime, we observe the formation of thin granular sheets with anisotropic shapes and show that the degree of anisotropy increases with the aspect ratio of the jet's cross section. Our results illustrate the liquidlike behavior of granular materials during impact and demonstrate that a collective hydrodynamic flow emerges from strongly interacting discrete particles. We discuss the analogy between our experiments and those from the Relativistic Heavy Ion Collider, where similar anisotropic ejecta from a quark-gluon plasma have been observed in heavy-ion impact.

Cheng, Xiang; Gordillo, Leonardo; Zhang, Wendy W.; Jaeger, Heinrich M.; Nagel, Sidney R.

2014-04-01

423

Drag force scaling for penetration into granular media  

NASA Astrophysics Data System (ADS)

Impact dynamics is measured for spherical and cylindrical projectiles of many different densities dropped onto a variety non-cohesive granular media. The results are analyzed in terms of the material-dependent scaling of the inertial and frictional drag contributions to the total stopping force. The inertial drag force scales similar to that in fluids, except that it depends on the internal friction coefficient. The frictional drag force scales as the square-root of the density of granular medium and projectile, and hence cannot be explained by the combination of granular hydrostatic pressure and Coulomb friction law. The combined results provide an explanation for the previously observed penetration depth scaling.

Katsuragi, Hiroaki; Durian, Douglas J.

2013-05-01

424

Some fundamental aspects of the continuumization problem in granular Media  

NASA Astrophysics Data System (ADS)

The central problem of devising mathematical models of granular materials is how to define a granular medium as a continuum. This paper outlines the elements of a theory that could be incorporated in discrete models such as the Discrete-Element Method, without recourse to a continuum description. It is shown that familiar concepts from continuum mechanics such as stress and strain can be defined for interacting discrete quantities. Established concepts for constitutive equations can likewise be applied to discrete quantities. The key problem is how to define the constitutive response in terms of truncated strain measures that are a practical necessity for analysis of large granular systems.

Peters, John F.

425

Traffic jams, granular flow, and soliton selection  

SciTech Connect

The flow of traffic on a long section of road without entrances or exits can be modeled by continuum equations similar to those describing fluid flow. In a certain range of traffic density, steady flow becomes unstable against the growth of a cluster, or ``phantom`` traffic jam, which moves at a slower speed than the otherwise homogeneous flow. We show that near the onset of this instability, traffic flow is described by a perturbed Korteweg--de Vries (KdV) equation. The traffic jam can be identified with a soliton solution of the KdV equation. The perturbation terms select a unique member of the continuous family of KdV solitons. These results may also apply to the dynamics of granular relaxation.

Kurtze, D.A. [Department of Physics, North Dakota State University, Fargo, North Dakota 58105-5566 (United States)] [Department of Physics, North Dakota State University, Fargo, North Dakota 58105-5566 (United States); Hong, D.C. [Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)] [Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)

1995-07-01

426

Directed ratchet transport in granular chains  

NASA Astrophysics Data System (ADS)

Directed-ratchet transport (DRT) in a one-dimensional lattice of spherical beads, which serves as a prototype for granular chains, is investigated. We consider a system where the trajectory of the central bead is prescribed by a biharmonic forcing function with broken time-reversal symmetry. By comparing the mean integrated force of beads equidistant from the forcing bead, two distinct types of directed transport can be observed—spatial and temporal DRT. Based on the value of the frequency of the forcing function relative to the cutoff frequency, the system can be categorized by the presence and magnitude of each type of DRT. Furthermore, we investigate and quantify how varying additional parameters such as the biharmonic weight affects DRT velocity and magnitude. Finally, friction is introduced into the system and is found to significantly inhibit spatial DRT. In fact, for sufficiently low forcing frequencies, the friction may even induce a switching of the DRT direction.

Berardi, V.; Lydon, J.; Kevrekidis, P. G.; Daraio, C.; Carretero-González, R.

2013-11-01

427

Extensional rheology of entangled granular materials  

NASA Astrophysics Data System (ADS)

We study the response of collections of U-shaped granular particles to extensional loading. Cylindrical samples elongate in bursts, as existing particle entanglements yield and new ones are created. The probability of failure scales with applied force F as 1-e^{-\\alpha F^m} . Longer samples are weaker than shorter ones, with the mean yield force scaling with instantaneous length L as \\sim L^{-1/m} . Both results can be explained with a Weibullian weakest-link theory that posits that samples are comprised of smaller sub-units. We find the yield probability of a sub-unit to scales with applied force as Fm and, from experiments, determine m=0.86+/- 0.12 . This is then used to capture the complete two-dimensional failure probability distribution P(F,L) .

Franklin, Scott V.

2014-06-01

428

[Granular cell tumor of the male breast].  

PubMed

The granular cell tumor of the breast (TCGS) is a rare benign tumor, which grows from Schwann cells. It can be confused with a cancerous tumor clinically and radiologically. Only the histological appearance can make the diagnosis. We report a case of TCGS in a man, discovered as a result of self-examination of a breast lump. The authors emphasize the problem of differential diagnosis with breast cancer: clinically, a hard lump with an occasional skin retraction or a fixity to the deep plane; radiologically a stellar opaque appearance with irregular contours, sonographically unspecific, and even macroscopically during surgery, this lesion having morphological characteristics which need histologic examination and even immunohistochemistry in order to exclude a malignant tumor. They are cured by wide local excision and have generally a good prognosis. PMID:23582837

Kadiri, Youssef; Boufettal, Houssine; Samouh, Naïma; Benayad, Samira; Karkouri, Mehdi; Zamiati, Soumaya; Kadiri, Bouchaïb

2013-04-01

429

Dense annular flows of granular media  

NASA Astrophysics Data System (ADS)

Dense granular flows constitute an important topic for geophysics and process engineering. To describe them, a rheology based on the coaxiality between the stress and strain tensors with a Mohr-Coulomb yield criterion has been proposed. We propose here an analytic study of flows in an annular cell, with this rheology. This geometry is relevant for a series of powder rheometers or mixing devices, but the discussion is focused on the split-bottom geometry, for which the internal flow has been investigated by NMR technique. In this case, the full resolution of the velocity and stress fields allow to localize the shear deformations. The theoretical results obtained for the latter are compared with the torque measurements by Dijksman et al. [Phys. Rev. E, 82 (2010) 060301].

de Ryck, Alain; Louisnard, Olivier

2013-06-01

430

Shearing instability of a dilute granular mixture.  

PubMed

The shearing instability of a dilute granular mixture composed of smooth inelastic hard spheres or disks is investigated. By using the Navier-Stokes hydrodynamic equations, it is shown that the scaled transversal velocity mode exhibits a divergent behavior, similarly to what happens in one-component systems. The theoretical prediction for the critical size is compared with direct Monte Carlo simulations of the Boltzmann equations describing the system, and a good agreement is found. The total energy fluctuations in the vicinity of the transition are shown to scale with the second moment of the distribution. The scaling distribution function is the same as found in other equilibrium and nonequilibrium phase transitions, suggesting the existence of some kind of universality. PMID:23496508

Brey, J Javier; Ruiz-Montero, M J

2013-02-01

431

Laws of granular solids: Geometry and topology  

NASA Astrophysics Data System (ADS)

In a granular solid, mechanical equilibrium requires a delicate balance of forces at the disordered grain scale. To understand how macroscopic rigidity can emerge in this amorphous solid, it is crucial that we understand how Newton’s laws pass from the disordered grain scale to the laboratory scale. In this work, we introduce an exact discrete calculus, in which Newton’s laws appear as differential relations at the scale of a single grain. Using this calculus, we introduce gauge variables that describe identically force- and torque-balanced configurations. In a first, intrinsic formulation, we use the topology of the contact network, but not its geometry. In a second, extrinsic formulation, we introduce geometry with the Delaunay triangulation. These formulations show, with exact methods, how topology and geometry in a disordered medium are related by constraints. In particular, we derive Airy’s expression for a divergence-free, symmetric stress tensor in two and three dimensions.

Degiuli, Eric; McElwaine, Jim

2011-10-01

432

Internal avalanches and restructuring in granular media  

NASA Astrophysics Data System (ADS)

We study the phenomenon of internal avalanching within the context of recently proposed “Tetris” lattice models for granular media. We consider a packing of particles subjected to two different dynamics. In the first case, we arrest the system at different instances during an “aging” dynamics during which the packing slowly compactifies under shaking, and study the distribution of internal avalanches at each of these instances. In the second case, we define a recycling dynamics under which the system reaches a steady state under continued avalanching. We study the distribution of avalanches in this steady state. In the former case we investigate numerically the effect of the density of the medium on the avalanche distribution. In the latter case we develop a mean-field theory to help understand the reciprocal effect of the avalanches on the medium.

Krishnamurthy, S.; Loreto, V.; Herrmann, H. J.; Roux, S.

1999-08-01

433

Similarities between protein folding and granular jamming  

PubMed Central

Grains and glasses, widely different materials, arrest their motions upon decreasing temperature and external load, respectively, in common ways, leading to a universal jamming phase diagram conjecture. However, unified theories are lacking, mainly because of the disparate nature of the particle interactions. Here we demonstrate that folded proteins exhibit signatures common to both glassiness and jamming by using temperature- and force-unfolding molecular dynamics simulations. Upon folding, proteins develop a peak in the interatomic force distributions that falls on a universal curve with experimentally measured forces on jammed grains and droplets. Dynamical signatures are found as a dramatic slowdown of stress relaxation upon folding. Together with granular similarities, folding is tied not just to the jamming transition, but a more nuanced picture of anisotropy, preparation protocol and internal interactions emerges. Results have implications for designing stable polymers and can open avenues to link protein folding to jamming theory.

Jose, Prasanth P; Andricioaei, Ioan

2012-01-01

434

Cohesive granular materials composed of nonconvex particles  

NASA Astrophysics Data System (ADS)

The macroscopic cohesion of granular materials made up of sticky particles depends on the particle shapes. We address this issue by performing contact dynamics simulations of 2D packings of nonconvex aggregates. We find that the macroscopic cohesion is strongly dependent on the strain and stress inhomogeneities developing inside the material. The largest cohesion is obtained for nearly homogeneous deformation at the beginning of unconfined axial compression and it evolves linearly with nonconvexity. Interestingly, the aggregates in a sheared packing tend to form more contacts with fewer neighboring aggregates as the degree of nonconvexity increases. We also find that shearing leads either to an isotropic distribution of tensile contacts or to the same privileged direction as that of compressive contacts.

Saint-Cyr, Baptiste; Radjai, Farhang; Delenne, Jean-Yves; Sornay, Philippe

2013-05-01

435

NMRI Measurements of Flow of Granular Mixtures  

NASA Technical Reports Server (NTRS)

We investigate complex 3D behavior of granular mixtures in shaking and shearing devices. NMRI can non-invasively measure concentration, velocity, and velocity fluctuations of flows of suitable particles. We investigate origins of wall-shear induced convection flow of single component particles by measuring the flow and fluctuating motion of particles near rough boundaries. We also investigate if a mixture of different size particles segregate into their own species under the influence of external shaking and shearing disturbances. These non-invasive measurements will reveal true nature of convecting flow properties and wall disturbance. For experiments in a reduced gravity environment, we will design a light weight NMR imager. The proof of principle development will prepare for the construction of a complete spaceborne system to perform experiments in space.

Nakagawa, Masami; Waggoner, R. Allen; Fukushima, Eiichi

1996-01-01

436

Internal Structure of Inertial Granular Flows  

NASA Astrophysics Data System (ADS)

We analyze inertial granular flows and show that, for all values of the inertial number I, the effective friction coefficient ? arises from three different parameters pertaining to the contact network and force transmission: (1) contact anisotropy, (2) force chain anisotropy, and (3) friction mobilization. Our extensive 3D numerical simulations reveal that ? increases with I mainly due to an increasing contact anisotropy and partially by friction mobilization whereas the anisotropy of force chains declines as a result of the destabilizing effect of particle inertia. The contact network undergoes topological transitions, and beyond I?0.1 the force chains break into clusters immersed in a background "soup" of floating particles. We show that this transition coincides with the divergence of the size of fluidized zones characterized from the local environments of floating particles and a slower increase of ? with I.

Azéma, Emilien; Radjaï, Farhang

2014-02-01

437

Livestock wastewater treatment using aerobic granular sludge.  

PubMed

The present study demonstrated that aerobic granular sludge is capable of treating livestock wastewater from a cattle farm in a sequencing batch reactor (SBR) without the presence of support material. A lab scale SBR was operated for 80 d using 4 h cycle time with an organic loading rate (OLR) of 9 kg COD m(-3) d(-1). Results showed that the aerobic granules were growing from 0.1 to 4.1 mm towards the end of the experimental period. The sludge volume index (SVI) was 42 ml g(-1) while the biomass concentration in the reactor grew up to 10.3 g L(-1) represent excellent biomass separation and good settling ability of the granules. During this period, maximum COD, TN and TP removal efficiencies (74%, 73% and 70%, respectively) were observed in the SBR system, confirming high microbial activity in the SBR system. PMID:23453799

Othman, Inawati; Anuar, Aznah Nor; Ujang, Zaini; Rosman, Noor Hasyimah; Harun, Hasnida; Chelliapan, Shreeshivadasan

2013-04-01

438

Correlation of phase fluctuations in granular superconductors  

NASA Astrophysics Data System (ADS)

An expansion in 1/z is used to study the correlation of phase fluctuations in granular superconductors. To zeroth order in 1/z, the expectation value of any operator is given by mean-field (MF) theory, which neglects the coupling of phase fluctuations. The first-order correction involves the coupling of phase fluctuations over an infinite number of grains. The 1/z correction to the transition temperature T*c=Tc/zJ is negative and diverges at the MF value of the critical grain diameter ?c, signaling a shift in ?c away from the MF value. For ?=zJ/U less than ?c, the phase coherence is destroyed by quantum fluctuations. The 1/z correction to ?c is positive, so that the coupling of phase fluctuations increases the critical grain diameter. This expansion technique is used to calculate the short-range-order parameter , where grains 1 and 2 are nearest neighbors. In the normal state the short-range order is enhanced at the temperature T*~=1/?, when thermal fluctuations allow a Cooper pair to overcome the Coulomb energy barrier to tunneling between grains. This enhancement is directly related to the observed minimum in the resistivity of two-dimensional granular films. The resistivity minimum first appears when U~=Tc, which can be simply explained in this model. Using the results for the short-range-order parameter, the 1/z corrections to the free energy and the specific heat are calculated. The fluctuation specific heat also shows signs of an enhanced phase coherence at a temperature inversely related to the grain size.

Fishman, R. S.

1989-12-01

439