These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Equation of State of Wet Granular Matter  

E-print Network

A theory is derived for the nonequilibrium probability currents of the capillary interaction which determines the pair correlation function near contact. This yields an analytic expression for the equation of state, P = P(N/V,T), of wet granular matter for D=2 dimensions, 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 Tmatter [Phys. Rev. Lett. 97, 078001 (2006)], and extends the effect to higher dimensional systems. Since the limiting case of sticky bonds, E_cb >> 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 s_crit. This result implies that particles that stick at the surface, s_crit=0, form isostatic clusters.

A. Fingerle; S. Herminghaus

2007-08-27

2

Foam-film-stabilized liquid bridge networks in evaporative lithography and wet granular matter.  

PubMed

Evaporative lithography using latex particle templates is a novel approach for the self-assembly of suspension-dispersed nanoparticles into ordered microwire networks. The phenomenon that drives the self-assembly process is the propagation of a network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films vertical to the substrate, which are formed during the evaporation of the liquid from the suspension. The stability of the foam films and thus the liquid bridge network stability are due to the presence of a small amount of surfactant in the evaporating solution. We show that the same type of foam-film-stabilized liquid bridge network can also propagate in 3D clusters of spherical particles, which has important implications for the understanding of wet granular matter. PMID:23534699

Vakarelski, Ivan U; Marston, Jeremy O; Thoroddsen, Sigurdur T

2013-04-23

3

Wet granular materials  

Microsoft Academic Search

Most studies on granular physics have focused on dry granular media, with no liquids between the grains. However, in geology and many real world applications (e.g. food processing, pharmaceuticals, ceramics, civil engineering, construction, and many industrial applications), liquid is present between the grains. This produces inter-grain cohesion and drastically modifies the mechanical properties of the granular media (e.g. the surface

Namiko Mitarai; Franco Nori

2006-01-01

4

Similarity of wet granular packing to gels  

NASA Astrophysics Data System (ADS)

To date, there is still no general consensus on the fundamental principle that governs glass transition. Colloidal suspensions are ordinarily utilized as model systems to study the dynamical arrest mechanisms in glass or gels. Here, we tackle the problem using athermal granular particles. Slow dynamics and structural evolution of granular packing upon tapping are monitored by fast X-ray tomography. When the packing are wet and short-range attractive interactions exist, we find a large amount of locally favoured structures with fivefold symmetry, which bear great structural similarity to colloidal gels. In addition, these structures are almost absent in dry packing with similar packing fractions. The study leads strong support for the geometrical frustration mechanism for dynamic arrest in both thermal and athermal systems with attractive interactions. It also suggests nontrivial structural mechanism, if exists, for dynamic arrest in systems with purely repulsive interactions.

Li, Jindong; Cao, Yixin; Xia, Chengjie; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Wang, Yujie

2014-09-01

5

Similarity of wet granular packing to gels.  

PubMed

To date, there is still no general consensus on the fundamental principle that governs glass transition. Colloidal suspensions are ordinarily utilized as model systems to study the dynamical arrest mechanisms in glass or gels. Here, we tackle the problem using athermal granular particles. Slow dynamics and structural evolution of granular packing upon tapping are monitored by fast X-ray tomography. When the packing are wet and short-range attractive interactions exist, we find a large amount of locally favoured structures with fivefold symmetry, which bear great structural similarity to colloidal gels. In addition, these structures are almost absent in dry packing with similar packing fractions. The study leads strong support for the geometrical frustration mechanism for dynamic arrest in both thermal and athermal systems with attractive interactions. It also suggests nontrivial structural mechanism, if exists, for dynamic arrest in systems with purely repulsive interactions. PMID:25247441

Li, Jindong; Cao, Yixin; Xia, Chengjie; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Wang, Yujie

2014-01-01

6

Stress transmission in wet granular materials.  

PubMed

We analyze stress transmission in wet granular media in the pendular state by means of three-dimensional molecular-dynamics simulations. We show that the tensile action of capillary bonds induces a self-stressed particle network organized in two percolating "phases" of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: 1) the highest particle pressure is located in the bulk of each phase; 2) the lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds. When a confining pressure is applied, the number of tensile bonds falls off and the negative phase breaks into aggregates and isolated sites. PMID:17297566

Richefeu, V; Radjaï, F; El Youssoufi, M S

2006-12-01

7

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

8

Collapse of quasi-two-dimensional wet granular columns  

E-print Network

This paper deals with the experimental characterization of the collapse of wet granular columns in the pendular state, with the purpose of collecting data on triggering and jamming phenomena in wet granular media. The final deposit shape and the runout dynamics were studied for samples of glass beads, varying particle diameter, liquid surface tension, and liquid amount. We show how the runout distance decreases with increasing water amount (reaching a plateau for $w>1 \\%$) and increases with increasing Bond number, while the top and toe angles and the final deposit height increase with increasing water amount and decrease with decreasing Bond number. Dimensional analysis allowed to discuss possible scalings for the runout length and the top and toe angles: a satisfying scaling was found, based on the combination of Bond number and liquid amount.

Riccardo Artoni; Andrea C. Santomaso; Fabio Gabrieli; Diego Tono; Simonetta Cola

2014-01-09

9

Uniform Shock Waves in Disordered Granular Matter  

E-print Network

The confining pressure $P$ is perhaps the most important parameter controlling the properties of granular matter. Strongly compressed granular media are, in many respects, simple solids in which elastic perturbations travel as ordinary phonons. However, the speed of sound in granular aggregates continuously decreases as the confining pressure decreases, completely vanishing at the jamming-unjamming transition. This anomalous behavior suggests that the transport of energy at low pressures should not be dominated by phonons. In this work we use simulations and theory to show how the response of granular systems becomes increasingly nonlinear as pressure decreases. In the low pressure regime the elastic energy is found to be mainly transported through nonlinear waves and shocks. We numerically characterize the propagation speed, shape, and stability of these shocks, and model the dependence of the shock speed on pressure and impact intensity by a simple analytical approach.

L. R. Gomez; A. M. Turner; V. Vitelli

2012-08-01

10

Friction and dilatancy in immersed granular matter  

E-print Network

The friction of a sliding plate on a thin immersed granular layer obeys Amonton-Coulomb law. We bring to the fore a large set of experimental results which indicate that, over a few decades of values, the effective dynamical friction-coefficient depends neither on the viscosity of the interstitial fluid nor on the size of beads in the sheared layer, which bears out the analogy with the solid-solid friction in a wide range of experimental parameters. We accurately determine the granular-layer dilatancy, which dependance on the grain size and slider velocity can be qualitatively accounted by considering the rheological behaviour of the whole slurry. However, additional results, obtained after modification of the grain surface by a chemical treatment, demonstrate that the theoretical description of the flow properties of granular matter, even immersed, requires the detailed properties of the grain surface to be taken into account.

Thibaut Divoux; Jean-Christophe Géminard

2008-06-10

11

Granular matter: A special buffer for impact load  

NASA Astrophysics Data System (ADS)

As a typical energy dissipation system, granular matter can reduce the impact force effectively via inter-particle friction, viscous force and particle splash. To investigate the impact-absorbing capacity of granular matter, a spherical projectile dropping on a granular layer is studied by physical experiments and numerical simulations with the discrete element method (DEM). Both physical experiments and numerical simulations show that the granular layer reduces the impact load well. The impact load decreases with increasing granular layer thickness, but is not sensitive to the granular thickness when the thickness is larger than a critical thickness, HC. The critical thickness is a function of initial impact velocity. This study can be helpful for understanding the basic mechanical behaviors of granular matter under impact loads, and for the potential engineering applications of the impact absorption of granular matter.

Ji, Shunying; Chen, Xiaodong; Li, Pengfei; Yan, Ying

2013-06-01

12

Extraterrestrial sink dynamics in granular matter  

E-print Network

A loosely packed bed of sand sits precariously on the fence between mechanically stable and flowing states. This has especially strong implications for animals or vehicles needing to navigate sandy environments, which can sink and become stuck in a "dry quicksand" if their weight exceeds the yield stress of this fragile matter. While it is known that the contact stresses in these systems are loaded by gravity, very little is known about the sinking dynamics of objects into loose granular systems under gravitational accelerations different from the Earth's (g). A fundamental understanding of how objects sink in different gravitational environments is not only necessary for successful planetary navigation and engineering, but it can also improve our understanding of celestial impact dynamics and crater geomorphology. Here we perform and explain the first systematic experiments of the sink dynamics of objects into granular media in gravitational accelerations other than g. By using an accelerating experimental a...

Altshuler, E; González-Pita, A; Sánchez-Colina, G; Pérez-Penichet, C; Waitukaitis, S; Hidalgo, R C

2013-01-01

13

Penetration depth scaling for impact into wet granular packings  

E-print Network

We present experimental measurements of penetration depths for the impact of spheres into wetted granular media. We observe that the penetration depth in the liquid saturated case scales with projectile density, size, and drop height in a fashion consistent with the scaling observed in the dry case, but that penetration depths into saturated packings tend to be smaller. This result suggests that, for the range of impact energies observed, the stopping force is set by static contact forces between grains within the bed, and that the presence of liquid serves, primarily, to enhance these contact forces. The enhancement to the stopping force has a complicated dependence on liquid fraction, accompanied by a change in the drop-height dependence, that must be the consequence of accompanying changes in the conformation of the liquid phase in the interstices.

Theodore A. Brzinski III; Jorin Schug; Kelly Mao; Douglas J. Durian

2014-03-31

14

Extraterrestrial sink dynamics in granular matter  

E-print Network

A loosely packed bed of sand sits precariously on the fence between mechanically stable and flowing states. This has especially strong implications for animals or vehicles needing to navigate sandy environments, which can sink and become stuck in a "dry quicksand" if their weight exceeds the yield stress of this fragile matter. While it is known that the contact stresses in these systems are loaded by gravity, very little is known about the sinking dynamics of objects into loose granular systems under gravitational accelerations different from the Earth's (g). A fundamental understanding of how objects sink in different gravitational environments is not only necessary for successful planetary navigation and engineering, but it can also improve our understanding of celestial impact dynamics and crater geomorphology. Here we perform and explain the first systematic experiments of the sink dynamics of objects into granular media in different gravitational accelerations. By using an accelerating experimental apparatus, we explore gravitational conditions ranging from 0.4g to 1.2g. With the aid of discrete element modeling simulations, we reproduce these results and extend this range to include objects as small as asteroids and as large as Jupiter. Surprisingly, we find that the final sink depth is independent of the gravitational acceleration, an observation with immediate relevance to the design of future extraterrestrial structures land-roving spacecraft. Using a phenomenological equation of motion that includes a gravity-loaded frictional term, we are able to quantitatively explain the experimental and simulation results.

E. Altshuler; H. Torres; A. González-Pita; G. Sánchez-Colina; C. Pérez-Penichet; S. Waitukaitis; R. C. Hidalgo

2013-05-29

15

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

16

Penetration of spherical projectiles into wet granular media  

NASA Astrophysics Data System (ADS)

We measure experimentally the penetration depth d of spherical particles into a water-saturated granular medium made of much smaller sand-sized grains. We vary the density, size R, and velocity U of the impacting spheres, and the size ? of the grains in the granular medium. We consider velocities between 7 and 107 m/s, a range not previously addressed, but relevant for impacts produced by volcanic eruptions. We find that d ?R1/3?1/3U2/3. The scaling with velocity is similar to that identified in previous, low-velocity collisions, but it also depends on the size of the grains in the granular medium. We develop a model, consistent with the observed scaling, in which the energy dissipation is dominated by the work required to rearrange grains along a network of force chains in the granular medium.

Birch, S. P. D.; Manga, M.; Delbridge, B.; Chamberlain, M.

2014-09-01

17

Microstructure evolution during impact on granular matter  

NASA Astrophysics Data System (ADS)

We study the impact of an intruder on a dense granular material. The process of impact and interaction between the intruder and the granular particles is modeled using discrete element simulations in two spatial dimensions. In the first part of the paper we discuss how the intruder's dynamics depends on (1) the intruder's properties, including its size, shape and composition, (2) the properties of the grains, including friction, polydispersity, structural order, and elasticity, and (3) the properties of the system, including its size and gravitational field. It is found that polydispersity and related structural order, and frictional properties of the granular particles, play a crucial role in determining impact dynamics. In the second part of the paper we consider the response of the granular system itself. We discuss the force networks that develop, including their topological evolution. The influence of friction and structural order on force propagation, including the transition from hyperbolic-like to elastic-like behavior is discussed, as well as the affine and nonaffine components of the grain dynamics. Several broad observations include the following: tangential forces between granular particles are found to play a crucial role in determining impact dynamics; both force networks and particle dynamics are correlated with the dynamics of the intruder itself.

Kondic, L.; Fang, X.; Losert, W.; O'Hern, C. S.; Behringer, R. P.

2012-01-01

18

Granular matter: The movable and the jammed  

NASA Astrophysics Data System (ADS)

Granular materials, ranging from fruit to rocks to powders, can change rapidly from a static jammed state to a free-flowing state. Insight from dynamical systems theory reveals that this tendency is governed by the growth of instabilities, rather than stress on individual particles.

Shinbrot, Troy

2013-05-01

19

Rheology of weakly wetted granular materials - a comparison of experimental and numerical data  

E-print Network

Shear cell simulations and experiments of weakly wetted particles (a few volume percent liquid binders) are compared, with the goal to understand their flow rheology. Application examples are cores for metal casting by core shooting made of sand and liquid binding materials. The experiments are carried out with a Couette-like rotating viscometer. The weakly wetted granular materials are made of quartz sand and small amounts of Newtonian liquids. For comparison, experiments on dry sand are also performed with a modified configuration of the viscometer. The numerical model involves spherical, monodisperse particles with contact forces and a simple liquid bridge model for individual capillary bridges between two particles. Different liquid content and properties lead to different flow rheology when measuring the shear stress-strain relations. In the experiments of the weakly wetted granular material, the apparent shear viscosity $\\eta_g$ scales inversely proportional to the inertial number $I$, for all shear rates. On the contrary, in the dry case, an intermediate scaling regime inversely quadratic in $I$ is observed for moderate shear rates. In the simulations, both scaling regimes are found for dry and wet granular material as well.

Ruediger Schwarze; Anton Gladkyy; Fabian Uhlig; Stefan Luding

2014-03-31

20

Ensemble theory for slightly deformable granular matter.  

PubMed

Given a granular system of slightly deformable particles, it is possible to obtain different static and jammed packings subjected to the same macroscopic constraints. These microstates can be compared in a mathematical space defined by the components of the force-moment tensor (i.e. the product of the equivalent stress by the volume of the Voronoi cell). In order to explain the statistical distributions observed there, an athermal ensemble theory can be used. This work proposes a formalism (based on developments of the original theory of Edwards and collaborators) that considers both the internal and the external constraints of the problem. The former give the density of states of the points of this space, and the latter give their statistical weight. The internal constraints are those caused by the intrinsic features of the system (e.g. size distribution, friction, cohesion). They, together with the force-balance condition, determine which the possible local states of equilibrium of a particle are. Under the principle of equal a priori probabilities, and when no other constraints are imposed, it can be assumed that particles are equally likely to be found in any one of these local states of equilibrium. Then a flat sampling over all these local states turns into a non-uniform distribution in the force-moment space that can be represented with density of states functions. Although these functions can be measured, some of their features are explored in this paper. The external constraints are those macroscopic quantities that define the ensemble and are fixed by the protocol. The force-moment, the volume, the elastic potential energy and the stress are some examples of quantities that can be expressed as functions of the force-moment. The associated ensembles are included in the formalism presented here. PMID:25248624

Tejada, Ignacio G

2014-09-01

21

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

PubMed

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. PMID:25019765

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

2014-06-01

22

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

23

Edwards entropy and compactivity in a model of granular matter.  

PubMed

Formulating a statistical mechanics for granular matter remains a significant challenge, in part due to the difficulty associated with a complete characterization of the systems under study. We present a fully characterized model of a granular material consisting of N two-dimensional, frictionless hard disks, confined between hard walls, including a complete enumeration of all possible jammed structures. We show that the properties of the jammed packings are independent of the distribution of defects within the system and that all the packings are isostatic. This suggests that the assumption of equal probability for states of equal volume, which provides one possible way of constructing the equivalent of a microcanonical ensemble, is likely to be valid for our model. An application of the second law of thermodynamics involving two subsystems in contact shows that the expected spontaneous equilibration of defects between the two is accompanied by an increase in entropy and that the equilibrium, obtained by entropy maximization, is characterized by the equality of compactivities. Finally, we explore the properties of the equivalent to the canonical ensemble for this system. PMID:21517489

Bowles, Richard K; Ashwin, S S

2011-03-01

24

Ensemble theory for force networks in hyperstatic granular matter.  

PubMed

An ensemble approach for force networks in static granular packings is developed. The 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. In this paper we will give a general formulation of this force network ensemble, and derive the general expression for the force distribution P(f). For small regular packings these probability densities are obtained in closed form, while for larger packings we present a systematic numerical analysis. Since technically the problem can be written as a noninvertible matrix problem (where the matrix is determined by the contact geometry), we study what happens if we perturb the packing matrix or replace it by a random matrix. The resulting P(f) 's differ significantly from those of normal packings, which touches upon the deep question of how network statistics is related to the underlying network structure. Overall, the ensemble formulation opens up a different perspective on force networks that is analytically accessible, and which may find applications beyond granular matter. PMID:15697354

Snoeijer, Jacco H; Vlugt, Thijs J H; Ellenbroek, Wouter G; van Hecke, Martin; van Leeuwen, J M J

2004-12-01

25

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

26

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

27

Condensation on the surface of vertical tube placed in a granular layer with different contact wetting angle  

NASA Astrophysics Data System (ADS)

The results of theoretical and experimental studies of heat exchange at condensation of motionless steam on a vertical tube placed in a granular layer with different wetting angle are presented. Theoretical dependencies are obtained for the estimate of heat-exchange intensity, which account for the condensate slip on the surfaces of grains, and their satisfactory agreement with experimental data of the authors is shown.

Shilyaev, M. I.; Bogomolov, A. R.; Petrik, P. T.

2008-06-01

28

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

E-print Network

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 $|\\omega^*(\\sigma)|\\sim\\sigma^{\\Omega'}$ with vanishing stress $\\sigma$ 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.

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

2014-10-20

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. PMID:23872642

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

2013-01-01

30

A deductive statistical mechanics approach for granular matter  

E-print Network

We introduce a deductive statistical mechanics approach for granular materials which is formally built from few realistic physical assumptions. The main finding is an universal behavior for the distribution of the density fluctuations. Such a distribution is the equivalent of the Maxwell-Boltzmann's distribution in the kinetic theory of gasses. The comparison with a very extensive set of experimental and simulation data for packings of monosized spherical grains, reveals a remarkably good quantitative agreement with the theoretical predictions for the density fluctuations both at the grain level and at the global system level. Such agreement is robust over a broad range of packing fractions and it is observed in several distinct systems prepared by using different methods. The equilibrium distributions are characterized by only one parameter ($k$) which is a quantity very sensitive to changes in the structural organization. The thermodynamical equivalent of $k$ and its relation with the `granular temperature' are also discussed.

T. Aste; T. Di Matteo

2007-11-21

31

Scale invariance and universality of force networks in static granular matter  

E-print Network

Force networks form the skeleton of static granular matter. They are the key ingredient to mechanical properties, such as stability, elasticity and sound transmission, which are of utmost importance for civil engineering and industrial processing. Previous studies have focused on the global structure of external forces (the boundary condition), and on the probability distribution of individual contact forces. The disordered spatial structure of the force network, however, has remained elusive so far. Here we report evidence for scale invariance of clusters of particles that interact via relatively strong forces. We analyzed granular packings generated by molecular dynamics simulations mimicking real granular matter; despite the visual variation, force networks for various values of the confining pressure and other parameters have identical scaling exponents and scaling function, and thus determine a universality class. Remarkably, the flat ensemble of force configurations--a simple generalization of equilibrium statistical mechanics--belongs to the same universality class, while some widely studied simplified models do not.

Srdjan Ostojic; Ellak Somfai; Bernard Nienhuis

2006-01-03

32

Dielectric properties of porous granular matter, in relation with Rosetta cometary mission.  

NASA Astrophysics Data System (ADS)

Dielectric property measurements over a large range of frequencies on two different samples of granular matter (JSC-MARS1 martian soil simulant and Etna pyroclastic deposits, each them divided at least in three size distribution) are presented. They are under development to prepare the interpretation of Rosetta spacecraft observations of the subsurface and interior of the comet nucleus.

Brouet, Y.; Levasseur-Regourd, AC.; Encrenaz, P.; Gheudin, M.; Ruffié, G.; Bonnaudin, F.; Gulkis, S.; Landry, P.; Munier, J. M.; Ciarletti, V.; Batrung, M.

2012-09-01

33

Applying the model of Soft Glassy Rheology to slowly driven dense granular matter  

NASA Astrophysics Data System (ADS)

In recent work by S. Henkes and B. Chakraborty (PRL 95, 198002 (2005)), a new statistical framework is proposed to describe static granular packings. In this framework, stress replaces energy as the conserved quantity and fluctuations in the stress are controlled by a quantity analogous to the thermodynamic temperature. We adapt this framework in the quasi-static limit and the model of Soft Glassy Rheology (P. Sollich, PRE 78, 2020 (1997)) to describe the rheological behavior of slowly driven dense granular matter. The model explains the experimental observation of R. P. Behringer et al. (Nature 421, 928 (2003)). We will describe ongoing efforts to apply this model to different categories of slowly driven granular media, and to relate the model to threshold critical dynamics in other driven random media.

Bi, Dapeng; Chakraborty, Bulbul

2009-03-01

34

Jamming during the discharge of granular matter from a silo.  

PubMed

In this work, we present an experimental study of the jamming that stops the free flow of grains from a silo discharging by gravity. When the outlet size is not much bigger than the beads, granular material jams the outlet of the container due to the formation of an arch. Statistical data from the number of grains fallen between consecutive jams are presented. The information that they provide can help one to understand the jamming phenomenon. As the ratio between the size of the orifice and the size of the beads is increased, the probability that an arch blocks the outlet decreases. We show here that there is a power-law divergence of the mean avalanche size for a finite critical radius. Beyond this critical radius, no jamming can occur and the flow is never stopped. The dependence of the arch formation on the shape and the material of the grains has been explored. It has been found that the material properties of the grains do not affect the arch formation probability. On the contrary, the shape of the grains deeply influences it. A simple model to interpret the results is also discussed. PMID:16089524

Zuriguel, Iker; Garcimartín, Angel; Maza, Diego; Pugnaloni, Luis A; Pastor, J M

2005-05-01

35

Jamming during the discharge of granular matter from a silo  

NASA Astrophysics Data System (ADS)

In this work, we present an experimental study of the jamming that stops the free flow of grains from a silo discharging by gravity. When the outlet size is not much bigger than the beads, granular material jams the outlet of the container due to the formation of an arch. Statistical data from the number of grains fallen between consecutive jams are presented. The information that they provide can help one to understand the jamming phenomenon. As the ratio between the size of the orifice and the size of the beads is increased, the probability that an arch blocks the outlet decreases. We show here that there is a power-law divergence of the mean avalanche size for a finite critical radius. Beyond this critical radius, no jamming can occur and the flow is never stopped. The dependence of the arch formation on the shape and the material of the grains has been explored. It has been found that the material properties of the grains do not affect the arch formation probability. On the contrary, the shape of the grains deeply influences it. A simple model to interpret the results is also discussed.

Zuriguel, Iker; Garcimartín, Angel; Maza, Diego; Pugnaloni, Luis A.; Pastor, J. M.

2005-05-01

36

Flocking at a distance in active granular matter  

E-print Network

The self-organised motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. We recreate this phenomenon using actuated non-living components. We report here that millimetre-sized tapered rods, rendered motile by contact with an underlying vibrated surface and interacting through a medium of spherical beads, undergo a phase transition to a state of spontaneous alignment of velocities and orientations above a threshold bead area fraction. Guided by a detailed simulation model, we construct an analytical theory of this flocking transition, with two ingredients: a moving rod drags beads; neighbouring rods reorient in the resulting flow like a weathercock in the wind. Theory and experiment agree on the structure of our phase diagram in the plane of rod and bead concentrations and power-law spatial correlations near the phase boundary. Our discovery suggests possible new mechanisms for the collective transport of particulate or cellular matter.

Nitin Kumar; Harsh Soni; Sriram Ramaswamy; A. K. Sood

2014-02-18

37

Flocking at a distance in active granular matter  

NASA Astrophysics Data System (ADS)

The self-organized motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. Here, we recreate this phenomenon using actuated nonliving components. We report here that millimetre-sized tapered rods, rendered motile by contact with an underlying vibrated surface and interacting through a medium of spherical beads, undergo a phase transition to a state of spontaneous alignment of velocities and orientations above a threshold bead area fraction. Guided by a detailed simulation model, we construct an analytical theory of this flocking transition, with two ingredients: a moving rod drags beads; neighbouring rods reorient in the resulting flow like a weathercock in the wind. Theory and experiment agree on the structure of our phase diagram in the plane of rod and bead concentrations and power-law spatial correlations near the phase boundary. Our discovery suggests possible new mechanisms for the collective transport of particulate or cellular matter.

Kumar, Nitin; Soni, Harsh; Ramaswamy, Sriram; Sood, A. K.

2014-09-01

38

Scale invariance and universality of force networks in static granular matter  

NASA Astrophysics Data System (ADS)

Force networks form the skeleton of static granular matter. They are the key factor that determines mechanical properties such as stability, elasticity and sound transmission, which are important for civil engineering and industrial processing. Previous studies have focused on investigations of the global structure of external forces (the boundary condition) and on the probability distribution of individual contact forces. So far, however, precise knowledge of the disordered spatial structure of the force network has remained elusive. Here we report that molecular dynamics simulations of realistic granular packings reveal scale invariance of clusters of particles interacting by means of relatively strong forces. Despite visual variation, force networks for various values of the confining pressure and other parameters have identical scaling exponents and scaling function, thereby determining a universality class. Unexpectedly, the flat ensemble of force configurations (a simple generalization of equilibrium statistical mechanics) belongs to this universality class, whereas some widely studied simplified models do not. This implies that the elasticity of the grains and their geometrical disorder do not affect the universal mechanical properties.

Ostojic, Srdjan; Somfai, Ellák; Nienhuis, Bernard

2006-02-01

39

Organic matter inputs shift soil enzyme activity and allocation patterns in a wet tropical forest  

E-print Network

Organic matter inputs shift soil enzyme activity and allocation patterns in a wet tropical forest properties and enzyme activities in a lowland tropical forest. We assayed six hydrolytic soil enzymes responsible for liberating carbon (C), nitrogen (N) and phosphorus (P), calculated enzyme activities

Cleveland, Cory

40

Discrete element simulation and experiment for dynamic response of two-dimensional granular matter to the impact of a spherical projectile  

Microsoft Academic Search

The dynamic response of two-dimensional granular matter subjected to the impact of a spherical projectile is investigated experimentally and also numerically using discrete element method (DEM). The granular matter is modeled by the mono-disperse aggregation of nylon spheres arranged regularly and two-dimensionally in a rectangular container. The numerical simulations are compared with the experiments using high-speed video camera for the

K Tanaka; M Nishida; T Kunimochi; T Takagi

2002-01-01

41

Attractive emulsion droplets probe the phase diagram of jammed granular matter.  

PubMed

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. PMID:21368191

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

2011-03-15

42

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. PMID:23251333

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

2012-01-01

43

Energy dissipation in driven granular matter in the absence of gravity.  

PubMed

We experimentally investigate the energy dissipation rate in sinusoidally driven boxes which are partly filled by granular material under conditions of weightlessness. We identify two different modes of granular dynamics, depending on the amplitude of driving, A. For intense forcing, A>A(0), the material is found in the collect-and-collide regime where the center of mass of the granulate moves synchronously with the driven container, while for weak forcing, Agranular material exhibits gaslike behavior. Both regimes correspond to different dissipation mechanisms, leading to different scaling with amplitude and frequency of the excitation and with the mass of the granulate. For the collect-and-collide regime, we explain the dependence on frequency and amplitude of the excitation by means of an effective one-particle model. For both regimes, the results may be collapsed to a single curve characterizing the physics of granular dampers. PMID:23863027

Sack, Achim; Heckel, Michael; Kollmer, Jonathan E; Zimber, Fabian; Pöschel, Thorsten

2013-07-01

44

Granular magnetoresistance in cobalt/poly (3-hexylthiophene, 2, 5-diyl) hybrid thin films prepared by a wet chemical method  

NASA Astrophysics Data System (ADS)

Cobalt/poly (3-hexylthiophene, 2, 5-diyl) (P3HT) hybrid thin films were prepared by a wet chemical method. Their microstructure consists of a nanoscale mixture of a crystalline P3HT matrix, interspersed with amorphous P3HT regions containing the cobalt nanoparticles. Magnetic and transport measurements are consistent with this microstructure and the temperature dependence of the resistance of these hybrid systems is well-fitted (R2=0.9993) to the fluctuation induced tunneling model. Moreover, by applying a magnetic field, a magnetoresistance ratio of 3% was observed in 17 vol % Co hybrid films at 10 K.

Wen, Tianlong; Liu, Dan; Luscombe, Christine K.; Krishnan, Kannan M.

2009-08-01

45

Observing Brownian motion and measuring temperatures in vibration-fluidized granular matter  

Microsoft Academic Search

Understanding the behaviour of granular media, either at rest or moving under external driving, is a difficult task, although it is important and of very practical interest. Describing the motion of each individual grain is complicated, not only because of the large number of grains, but also because the mechanisms of interaction at the grain level involve complex contact forces.

Patrick Mayor; Gianfranco D'Anna; Alain Barrat; Vittorio Loreto

2005-01-01

46

SOILS, SEC 1 SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING RESEARCH ARTICLE Soil carbon and nitrogen storage in alluvial wet meadows  

E-print Network

a range of wetness and livestock utilization levels were selected for soil sampling. In each wetland . Soil organic carbon and nitrogen . Soil organic matter . Wetland soils 1 Introduction Alluvial wetSOILS, SEC 1 · SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING · RESEARCH ARTICLE Soil carbon

Norton, Jay B.

47

Removal of dissolved organic matter by granular-activated carbon adsorption as a pretreatment to reverse osmosis of membrane bioreactor effluents  

Microsoft Academic Search

The adsorption of dissolved organic matter (DOM) on granular-activated carbon (GAC) as a pretreatment to reverse osmosis (RO) desalination of membrane bioreactor (MBR) effluents was studied in lab- and pilot-scale columns. The pattern and efficiency of DOM adsorption and fate of the hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) fractions were characterized, as well as their impact on organic fouling

Shirra Gur-Reznik; Ilan Katz; Carlos G. Dosoretz

2008-01-01

48

Coherent transport and symmetry breaking—laser dynamics of constrained granular matter  

NASA Astrophysics Data System (ADS)

We present diagrammatic transport theory including self-consistent nonlinear enhancement and dissipation in the multiple scattering regime. Our model of Vollhardt–Wölfle transport of photons is fit-parameter-free and raises the claim that the results hold up to the closest packed volume of randomly arranged ZnO Mie scatterers. We find that a symmetry breaking caused by dissipative effects through the lossy underlying silicon (SI) substrate leads to qualitatively different physics of coherence and lasing in granular amplifying media. According to our results, confined and extended random laser modes and their laser thresholds can be clearly attributed to unbroken and broken spatial symmetry. The diameters and emission profiles of the modes, as well as their thresholds and the positional-dependent degree of coherence, can be checked experimentally.

Lubatsch, Andreas; Frank, Regine

2014-08-01

49

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

50

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

51

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

52

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

53

Permittivity of porous granular matter, in relation with Rosetta cometary mission  

NASA Astrophysics Data System (ADS)

We report measurements in laboratory conditions of the relative complex permittivity (hereafter permittivity) of porous material on a large range of frequencies from 50 MHz to 190 GHz. Such measurements, developed in preparation of the Rosetta mission to comet 67P/Churyumov-Gerasimenko, specifically for the MIRO radiometric experiment, were obtained with different instrumentations in three frequency bands: 50-500 MHz, 2.45 - 12 GHz and 190 GHz (center-band frequency of the millimeter receiver of MIRO, specially developed for our purpose). Considering the expected properties of cometary nuclei, they were carried out with porous granular materials of volcanic origin, with various sizes ranging from a few to 500 ?m, i.e. Etna's ashes and NASA JSC Mars-1 martian soil simulant. The samples were split into several sub-samples with different size ranges and bulk densities. The real part and the imaginary part of the permittivity remain respectively in the 2.1 - 4.0 range and in the 0.05 - 0.31 range. Volume scattering becomes significant for the measurements at 190 GHz when the mean grain size of sub-samples is greater than about 200 ?m and implies an increase of the real part and the imaginary part of the permittivity. Without this effect, for any sub-sample, the results are consistent over the frequency range. From 50 MHz to 190 GHz, evidence is provided for a slight decrease of the real part of the permittivity. Bulk densities of the sub-samples, being in the 800-1300 kg m-3 range, were determined during the measurements at 190 GHz. Taking into account the expected bulk density of the nucleus (100-370 kg m-3), as well as temperature for the surface and subsurface (in the 30-300 K range) and its composition (consisting both of silica-rich dust and ices, mostly of water), these first series of results allow an estimate of the real part and the imaginary part of the permittivity of the near-surface of the cometary nucleus: the real part is likely to be lower than 1.6 for non-icy regions and lower than 1.4 for icy regions; the imaginary part is likely to be below 0.09. These estimates represent upper limits relevant for the interpretation of the future data of MIRO.

Brouet, Y.; Levasseur-Regourd, A. C.; Encrenaz, P.; Gulkis, S.

2014-11-01

54

Wet voice as a sign of penetration/aspiration in Parkinson's disease: does testing material matter?  

PubMed

Wet voice is a perceptual vocal quality that is commonly used as an indicator of penetration and/or aspiration in clinical swallowing assessments and bedside screening tests. Our aim was to describe the clinimetric characteristics of this clinical sign using various fluid materials and one solid food in the Parkinson's disease (PD) population. Consecutive PD individuals were submitted for simultaneous fiberoptic endoscopic evaluation of swallowing (FEES) and voice recording. Speech therapists rated the presence or absence of wetness and other voice abnormalities. Two binary endpoints of FEES were selected for comparison with an index test: low penetration (LP) and low penetration and/or aspiration (LP/ASP). The accuracy of wet voice changed according to the testing material in PD patients. Overall, the specificity of this indicator was better than its sensitivity, and the wafer cookie and yogurt drink yielded the best indices. Our data show that wet voice is clearly indicative of LP or LP/ASP in PD patients in case of positive test. However, in the case of a negative result, the wet voice test should be repeated or combined with other clinical tests to include or exclude the risk of LP or LP/ASP. PMID:25001523

Sampaio, Marília; Argolo, Natalie; Melo, Ailton; Nóbrega, Ana Caline

2014-10-01

55

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

56

Dissolved copper speciation behaviour during estuarine mixing in the San Simon Inlet (wet season, Galicia). Influence of particulate matter  

NASA Astrophysics Data System (ADS)

The speciation trend of dissolved copper (DCu) was studied for the first time in a Galician Ria across the estuarine zone of the Vigo Ria during the wet season and related to the copper levels in suspended particulate matter (PCu) and sediments. In the riverine and ocean end-members DCu concentrations can be defined as pristine (<4 nM in Oitaven River). DCu is not conservative during the estuarine mixing and its concentration increase (5-8 nM) cannot be only associated to PCu (0.5-1.0 nM) variations and the ria sediments may be an important DCu source. DCu speciation was mainly controlled by two types of ligands ( logKL1'=12.9-13.9; and logKL'=10.8-12.1). In all samples the concentration of L 1 ( C =15-34nM) was greater than that of copper, which speciation is so dominated by this strong organic ligand. The transport of copper contamination from the middle Ria to the San Simon Inlet is limited during the wet season; in spite of similar salinities, DCu in the inlet (6 nM) was much lower than at Rande Strait (15 nM).

Santos-Echeandia, Juan; Laglera, Luis M.; Prego, Ricardo; van den Berg, Constant M. G.

2008-01-01

57

Effects of surface-active organic matter on carbon dioxide nucleation in atmospheric wet aerosols: a molecular dynamics study.  

PubMed

Organic matter (OM) uptake in cloud droplets produces water-soluble secondary organic aerosols (SOA) via aqueous chemistry. These play a significant role in aerosol properties. We report the effects of OM uptake in wet aerosols, in terms of the dissolved-to-gas carbon dioxide nucleation using molecular dynamics (MD) simulations. Carbon dioxide has been implicated in the natural rainwater as well as seawater acidity. Variability of the cloud and raindrop pH is assumed in space and time, as regional emissions, local human activities and geophysical characteristics differ. Rain scavenging of inorganic SOx, NOx and NH3 plays a major role in rain acidity in terms of acid-base activity, however carbon dioxide solubility also remains a key parameter. Based on the MD simulations we propose that the presence of surface-active OM promotes the dissolved-to-gas carbon dioxide nucleation in wet aerosols, even at low temperatures, strongly decreasing carbon dioxide solubility. A discussion is made on the role of OM in controlling the pH of a cloud or raindrop, as a consequence, without involving OM ionization equilibrium. The results are compared with experimental and computational studies in the literature. PMID:25272147

Daskalakis, Vangelis; Charalambous, Fevronia; Panagiotou, Fostira; Nearchou, Irene

2014-11-21

58

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...

59

WET SOLIDS FLOW ENHANCEMENT  

SciTech Connect

The objective was to visualize the flow of granular materials in flat bottomed silo. This was done by for dry materials introducing mustard seeds and poppy seeds as tracer particles and imaging them using Nuclear Magnetic Resonance. The region sampled was a cylinder 25 mm in diameter and 40 mm in length. Eight slices containing 128*128 to 256*256 pixels were generated for each image. The size of the silo was limited by the size of the high resolution NMR imager available. Cross-sections of 150mm flat bottomed silos, with the tracer layers immobilized by a gel, showed similar qualitative patterns for both dry and wet granular solids.

Hugo S. Caram; Natalie Foster

1997-03-31

60

Particle dynamics and effective temperature of jammed granular matter in a slowly sheared three-dimensional Couette cell  

E-print Network

matter in a three- dimensional Couette cell. A closely packed ensemble of transparent spherical beads of the beads. This allows us to track tracer particles embedded in the system and obtain three is defined as the condition when a many- body system is blocked in a configuration far from equilib- rium

Xing, Jianhua

61

Liquid migration in sheared unsaturated granular media  

E-print Network

We show how liquid migrates in sheared unsaturated granular media using a grain scale model for capillary bridges. Liquid is redistributed to neighboring contacts after rupture of individual capillary bridges leading to redistribution of liquid on large scales. The liquid profile evolution coincides with a recently developed continuum description for liquid migration in shear bands. The velocity profiles which are linked to the migration of liquid as well as the density profiles of wet and dry granular media are studied.

Roman Mani; Dirk Kadau; Hans J. Herrmann

2012-06-25

62

WET SOLIDS FLOW ENHANCEMENT  

SciTech Connect

The yield locus, tensile strength and fracture mechanisms of wet granular materials were studied. The yield locus of a wet material was shifted to the left of that of the dry specimen by a constant value equal to the compressive isostatic stress due to pendular bridges. for materials with straight yield loci, the shift was computed from the uniaxial tensile strength, either measured in a tensile strength tester or calculated from the correlation, and the angle of internal friction of the material. The predicted shift in the yield loci due to different moisture contents compare well with the measured shift in the yield loci of glass beads, crushed limestone, super D catalyst and Leslie coal. Measurement of the void fraction during the shear testing was critical to obtain the correct tensile strength theoretically or experimentally.

Unknown

2001-03-25

63

Open problems in active chaotic flows: Competition between chaos and order in granular materials.  

PubMed

There are many systems where interaction among the elementary building blocks-no matter how well understood-does not even give a glimpse of the behavior of the global system itself. Characteristic for these systems is the ability to display structure without any external organizing principle being applied. They self-organize as a consequence of synthesis and collective phenomena and the behavior cannot be understood in terms of the systems' constitutive elements alone. A simple example is flowing granular materials, i.e., systems composed of particles or grains. How the grains interact with each other is reasonably well understood; as to how particles move, the governing law is Newton's second law. There are no surprises at this level. However, when the particles are many and the material is vibrated or tumbled, surprising behavior emerges. Systems self-organize in complex patterns that cannot be deduced from the behavior of the particles alone. Self-organization is often the result of competing effects; flowing granular matter displays both mixing and segregation. Small differences in either size or density lead to flow-induced segregation and order; similar to fluids, noncohesive granular materials can display chaotic mixing and disorder. Competition gives rise to a wealth of experimental outcomes. Equilibrium structures, obtained experimentally in quasi-two-dimensional systems, display organization in the presence of disorder, and are captured by a continuum flow model incorporating collisional diffusion and density-driven segregation. Several open issues remain to be addressed. These include analysis of segregating chaotic systems from a dynamical systems viewpoint, and understanding three-dimensional systems and wet granular systems (slurries). General aspects of the competition between chaos-enhanced mixing and properties-induced de-mixing go beyond granular materials and may offer a paradigm for other kinds of physical systems. (c) 2002 American Institute of Physics. PMID:12779570

Ottino, J. M.; Khakhar, D. V.

2002-06-01

64

Efficiently Supporting Temporal Granularities  

E-print Network

to that of minutes. Granularities incorporate the cultural, legal, and even business orientation of the user to define the time values that are of interest. Many different granularities exist and no granularity is inherently ªbetterº than another; the value of a particular granularity is wholly determined

Snodgrass, Richard T.

65

Day wetting  

Microsoft Academic Search

About 1% of healthy children over the age of 5 years have troublesome daytime wetting. Two-thirds of those who wet by day are reliably dry at night. The problem is more common in girls and is usually the result of urge incontinence. Although the wetting may be exacerbated by giggling and\\/or stress, pure giggle micturition and isolated stress incontinence are

S. R. Meadow

1990-01-01

66

SOILS, SEC 1 SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING RESEARCH ARTICLE Soil carbon and nitrogen storage in alluvial wet meadows  

E-print Network

Purpose Wet meadows formed on alluvial deposits potentially store large amounts of soil carbon (C) but its and characterize soil organic carbon (SOC) and nitrogen (N) in mountain wet meadows across ranges of meadow Mountains representing a range of wetness and livestock utilization levels were selected for soil sampling

Norton, Jay B.

67

Influence of surfactant structure on wettability modification of hydrophobic granular surfaces  

SciTech Connect

Using the capillary penetration wetting technique, the influence of surfactant structure on wettability modification of hydrophobic granular surfaces was examined. Linear and branched hydrocarbon chain sulfates, 5 mol monodisperse ethoxylates and 5 mol monodisperse ethoxysulfates were used as surfactants and resin-coated sand as the hydrophobic granular surface. Both the surfactant type and hydrocarbon chain branching were observed to exert a significant influence on the rate and effectiveness of wetting. Wetting rates for ethoxylates > sulfates > ethoxysulfates. Wetting effectiveness for sulfates > ethoxylates. For a given surfactant type, hydrocarbon chain branching was observed to increase wetting rate and effectiveness.

Varadaraj, R.; Bock, J.; Brons, N.; Zushma, S. (Exxon Research and Engineering Co., Annandale, NJ (United States))

1994-10-01

68

Transport in granular systems  

E-print Network

There are many situations in which a continuum view of granular systems does not fully capture the relevant mechanics. In order for engineers to be able to design systems for transporting granular materials, there needs ...

Wendell, Dawn M. (Dawn Marie), 1983-

2011-01-01

69

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

70

Vibration-induced Liquefaction of Granular Suspensions  

NASA Astrophysics Data System (ADS)

We investigate the mechanical behavior of granular suspensions subjected to coupled vibrations and shear. At high shear stress, whatever the mechanical vibration energy and bead size, the system behaves like a homogeneous suspension of hard spheres. At low shear stress, in addition to a dependence on bead size, vibration energy drastically influences the viscosity of the material that can decrease by more than 2 orders of magnitude. All experiments can be rationalized by introducing a hydrodynamical Peclet number defined as the ratio between the lubrication stress induced by vibrations and granular pressure. The behavior of vibrated wet and dry granular materials can then be unified by assimilating the Hookean stress in dry media to the lubrication stress in suspensions.

Hanotin, C.; Kiesgen de Richter, S.; Marchal, P.; Michot, L. J.; Baravian, C.

2012-05-01

71

A constitutive law for dense granular flows  

E-print Network

A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a sand pile), a liquid (when poured from a silo) or a gas (when strongly agitated). For the two extreme regimes, constitutive equations have been proposed based on kinetic theory for collisional rapid flows, and soil mechanics for slow plastic flows. However, the intermediate dense regime, where the granular material flows like a liquid, still lacks a unified view and has motivated many studies over the past decade. The main characteristics of granular liquids are: a yield criterion (a critical shear stress below which flow is not possible) and a complex dependence on shear rate when flowing. In this sense, granular matter shares similarities with classical visco-plastic fluids such as Bingham fluids. Here we propose a new constitutive relation for dense granular flows, inspired by this analogy and recent numerical and experimental work. We then test our three-dimensional (3D) model through experiments on granular flows on a pile between rough sidewalls, in which a complex 3D flow pattern develops. We show that, without any fitting parameter, the model gives quantitative predictions for the flow shape and velocity profiles. Our results support the idea that a simple visco-plastic approach can quantitatively capture granular flow properties, and could serve as a basic tool for modelling more complex flows in geophysical or industrial applications.

Pierre Jop; Yoël Forterre; Olivier Pouliquen

2006-12-05

72

Wet solids flow enhancemant  

SciTech Connect

WE used glass beads of different sizes as.a model system to study the flow enhancing properties of Octadecyltrichlorosilane (OTS). 0TS provides Si(CH{sub 2}){sub 17}CH{sub 3} groups that bind with the surface hydrox groups to make it hydrophobic. Experimental data showed, indeed, that surface hydrophobicity promotes the flow of wet granular materials. Mixtures of different percentage of silanized/unsilanized particles were prepared for tensile strength measurements. The tensile strength decreased as more silanized particles were added to the samples. The relationship between dimensionless tensile strength and void fraction followed the correlation found by Pierrat (1994). Contact angles were larger for the silanized particles, as compared with unsilanized ones.

Caram, H.S.; Foster, N.; Wildman, D.J. [USDOE Pittsburgh Energy Technology Center, PA (United States)

1996-12-31

73

Granular statistical mechanics - a personal perspective  

NASA Astrophysics Data System (ADS)

The science of granular matter has expanded from an activity for specialised engineering applications to a fundamental field in its own right. This has been accompanied by an explosion of research and literature, which cannot be reviewed in one paper. A key to progress in this field is the formulation of a statistical mechanical formalism that could help develop equations of state and constitutive relations. This paper aims at reviewing some milestones in this direction. An essential basic step toward the development of any static and quasi-static theory of granular matter is a systematic and useful method to quantify the grain-scale structure and we start with a review of such a method. We then review and discuss the ongoing attempt to construct a statistical mechanical theory of granular systems. Along the way, we will clarify a number of misconceptions in the field, as well as highlight several outstanding problems.

Blumenfeld, R.; Edwards, S. F.

2014-10-01

74

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

75

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.

76

Prototype testing of a solar dryer of granular materials  

SciTech Connect

The results of testing a two module prototype solar convection dryer are presented. Collected data showed that the 540 square foot dryer can evaporate up to 900 pounds of water from a wet granular material over a 24 hour period in the Philadelphia climate. Testing included experimentation with different materials handling systems to determine the best method of moving each wet material through the dryer.

Murdock, J.D.

1982-01-01

77

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.

78

Fast granular superconducting bolometer  

SciTech Connect

A granular superconducting thin film bolometer made by anodizing a thin film of such materials as niobium nitride to form a thin granular film separated by and covered with the anodized oxide. The bolometer is cooled to its superconducting state and electrically connected to a biasing and detecting network. Its temporal response is better than 1 ns.

Wolf, S.A.; Strom, U.; Weiser, K.

1984-08-07

79

Fast granular superconducting bolometer  

NASA Astrophysics Data System (ADS)

This abstract discloses a granular superconducting thin film bolometer made by anodizing a thin film of such materials as niobium nitride to form a thin granular film separated by and covered with the anodized oxide. The bolometer is cooled to its superconducting state and electrically connected to a biasing and detecting network. Its temporal response is better than 1 ns.

Wolf, S. A.; Strom, U.; Weiser, K.

1984-08-01

80

The granular jump  

Microsoft Academic Search

When a fluid jet hits a solid surface, a hydraulic jumps occurs. This jump sharply delimits a thin film of liquid from a thicker film. We show here that a granular jet impinging on a solid surface also gives rise to several features reminiscent of the hydraulic jump and we refer to this situation as the granular jump. We describe,

J. F. Boudet; Y. Amarouchene; B. Bonnier; H. Kellay

2007-01-01

81

The effects of cohesion on dense granular flows  

NASA Astrophysics Data System (ADS)

The study of cohesive granular media is fundamental to the exploration of sand in a geophysical context where small quantities of a wetting fluid generate cohesive stresses within the granular aggregate. We have performed large-scale, three-dimensional discrete element simulations of the flow of cohesive and non-cohesive granular media down an incline. We find that cohesive granular media generically separates into a plug flow regime near the free surface of the pile and a flowing regime whose rheology does not fit the standard Bagnold constitutive relation. Instead, a revised constitutive law is proposed based on the mechanisms for momentum transport through the flowing region. We also show how this revised constitutive law is more generically applicable to non-cohesive, dense chute flow.

Brewster, Robert C.

82

The granular jump  

NASA Astrophysics Data System (ADS)

When a fluid jet hits a solid surface, a hydraulic jumps occurs. This jump sharply delimits a thin film of liquid from a thicker film. We show here that a granular jet impinging on a solid surface also gives rise to several features reminiscent of the hydraulic jump and we refer to this situation as the granular jump. We describe, in detail, this phenomenon and show that if many of its features can be understood in analogy with the hydraulic jump, others are directly related to the granular nature of the medium and, in particular, the small-scale dynamics of the jump.

Boudet, J. F.; Amarouchene, Y.; Bonnier, B.; Kellay, H.

83

Transition from rolling to jamming in thin granular layers.  

PubMed

We study the granular jamming transition for sheared layers of spherical beads ranging in thickness from 1 to 3 times the grain diameter d. As the layer thickness increases slightly above d, the measured friction jumps discontinuously from 0.02 to >0.1, marking the transition from rolling to jamming. Above a critical layer thickness for jamming, the effective granular pressure displays a power law increase with thickness. For thin layers, friction and P increases as the packing fraction decreases near the jamming transition, in contrast to expectations for bulk granular matter. PMID:19113670

Marone, C; Carpenter, B M; Schiffer, P

2008-12-12

84

Dynamics of Granular Materials  

NASA Technical Reports Server (NTRS)

Granular materials exhibit a rich variety of dynamical behavior, much of which is poorly understood. Fractal-like stress chains, convection, a variety of wave dynamics, including waves which resemble capillary waves, l/f noise, and fractional Brownian motion provide examples. Work beginning at Duke will focus on gravity driven convection, mixing and gravitational collapse. Although granular materials consist of collections of interacting particles, there are important differences between the dynamics of a collections of grains and the dynamics of a collections of molecules. In particular, the ergodic hypothesis is generally invalid for granular materials, so that ordinary statistical physics does not apply. In the absence of a steady energy input, granular materials undergo a rapid collapse which is strongly influenced by the presence of gravity. Fluctuations on laboratory scales in such quantities as the stress can be very large-as much as an order of magnitude greater than the mean.

Behringer, Robert P.

1996-01-01

85

Paper #1752 pres. at the Int. Conf. on Ultrasonics, Vienna, April 9 -13, 2007, Session S02: Nonlinear acoustics of granular media Acoustic waves in granular materials  

E-print Network

linear, large wavelength regime. Key words: DEM simulation, granular matter, sound propagation, micro simulations with discrete elements are used to obtain more insight into the wave propagation in dense granular contact deformation, considerably changes sound propagation, i.e., the transmission spectrum becomes

Luding, Stefan

86

Wet adhesion and adhesive locomotion of snails on anti-adhesive non-wetting surfaces.  

PubMed

Creating surfaces capable of resisting liquid-mediated adhesion is extremely difficult due to the strong capillary forces that exist between surfaces. Land snails use this to adhere to and traverse across almost any type of solid surface of any orientation (horizontal, vertical or inverted), texture (smooth, rough or granular) or wetting property (hydrophilic or hydrophobic) via a layer of mucus. However, the wetting properties that enable snails to generate strong temporary attachment and the effectiveness of this adhesive locomotion on modern super-slippy superhydrophobic surfaces are unclear. Here we report that snail adhesion overcomes a wide range of these microscale and nanoscale topographically structured non-stick surfaces. For the one surface which we found to be snail resistant, we show that the effect is correlated with the wetting response of the surface to a weak surfactant. Our results elucidate some critical wetting factors for the design of anti-adhesive and bio-adhesion resistant surfaces. PMID:22693563

Shirtcliffe, Neil J; McHale, Glen; Newton, Michael I

2012-01-01

87

Multiscale modeling in granular flow  

E-print Network

Granular materials are common in everyday experience, but have long-resisted a complete theoretical description. Here, we consider the regime of slow, dense granular flow, for which there is no general model, representing ...

Rycroft, Christopher Harley

2007-01-01

88

Flow of dry and wet granular materials: Numerical simulation results  

NASA Astrophysics Data System (ADS)

We use a DEM method to simulate dense assemblies of frictional spherical grains in 3D steady shear flow under controlled normal stress P, either dry or in the presence of a small amount of an interstitial liquid, which gives rise to capillary menisci and attractive forces. We pay special attention to the quasi-static limit of slow flow. The system behavior is characterized by the dependence of internal friction coefficient and solid fraction on two dimensionless control parameters: the inertial number, I and the reduced pressure, P*, comparing confining forces to contact tensile strength. Capillary forces have a significant effect on the macroscopic behavior of the system, up to P* values of several unities, especially for longer force ranges associated with larger menisci. We relate this effect to fabric anisotropy parameters of contact and distant interactions.

Khamseh, Saeed; Roux, Jean-Noël; Chevoir, François

2013-06-01

89

Sound propagation in dense, frictional granular materials O. Mouraille & S. Luding  

E-print Network

Sound propagation in dense, frictional granular materials O. Mouraille & S. Luding Particle of the sound propagation mechanisms (dispersion, scattering, power-spectra, etc.) inside dense granular matter is still a challenge. Using discrete element simulations we examine the effect of interparticle forces like

Luding, Stefan

90

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

91

Granular activated carbon installations  

Microsoft Academic Search

This article 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 information to estimate costs for GAC treatment of water supplies is provided. In conjunction with previous reports, this article may

Russell L. Culp; Robert M. Clark

1983-01-01

92

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...

93

Chaotic granular mixing  

Microsoft Academic Search

Several models for convective mixing of coarse, freely flowing in granular tumblers have been proposed over the past decade. Powders of practical interest, by contrast, are frequently fine and cohesive, and cannot be analyzed with these models. Moreover, even in the freely flowing regime, mixing transverse to the dominant, convective, direction is typically slow and inefficient. In this paper, we

Troy Shinbrot; Albert Alexander; Maher Moakher; Fernando J. Muzzio

1999-01-01

94

Keratoconus and granular dystrophy.  

PubMed

Concurrent bilateral keratoconus and granular dystrophy is reported in a 32-year-old patient with decreased vision. Initially contact lenses were attempted unsuccessfully to treat the conditions. There are a handful of other reports of these combined pathologies in the literature, and the likelihood of a chance cause or possible genetic linkage between the conditions is discussed. PMID:25155495

Wilson, Clare M; D'Ath, Penny J; Parmar, Dipak N; Sykakis, Evripidis

2014-01-01

95

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

96

Granular Matter ISSN 1434-5021  

E-print Network

dynamics simulations at constant energy in 2D of friction- less bidisperse disks that interact via Hertzian in the vibrational behavior (e.g. the generation of harmonics of the eigenfrequencies of the dynamical matrix'Hern (B) · M. D. Shattuck Department of Mechanical Engineering and Materials Science, Yale University, New

O'Hern, Corey S.

97

Prestress stability Session on Granular Matter  

E-print Network

,...) is a proper self stress for the tensegrity G(p). Our goal is to determine when the configuration p is a local-by-e diagonal matrix whose ij, ij diagonal entry is cij, where e is the number of members in the tensegrity. #12 of global information about the tensegrity, although it can have negative eigenvalues. Define the matrix H

Connelly, Robert

98

Matter on granular space-time  

E-print Network

We develop further the formalism of the non-Abelian gauge field theory on a cell complex space-time and show how the gauge-invariant action and the equations of motion for gauge fields interacting with spinors can be written without a reference to the geometrical nature of the cells of the cell complex. The general results are illustrated with examples of solutions of equations of motion for U(N) and SU(N) gauge groups.

Alexander N. Jourjine

2008-04-28

99

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

100

Granular flow over inclined channels with constrictions  

NASA Astrophysics Data System (ADS)

Study of granular flows down inclined channels is essential in understanding the dynamics of natural grain flows like landslides and snow avalanches. As a stepping stone, dry granular flow over an inclined channel with a localised constriction is investigated using both continuum methods and particle simulations. Initially, depth-averaged equations of motion (Savage & Hutter 1989) containing an unknown friction law are considered. The shallow-layer model for granular flows is closed with a friction law obtained from particle simulations of steady flows (Weinhart et al. 2012) undertaken in the open source package Mercury DPM (Mercury 2010). The closed two-dimensional (2D) shallow-layer model is then width-averaged to obtain a novel one-dimensional (1D) model which is an extension of the one for water flows through contraction (Akers & Bokhove 2008). Different flow states are predicted by this novel one-dimensional theory. Flow regimes with distinct flow states are determined as a function of upstream channel Froude number, F, and channel width ratio, Bc. The latter being the ratio of the channel exit width and upstream channel width. Existence of multiple steady states is predicted in a certain regime of F - Bc parameter plane which is in agreement with experiments previously undertaken by (Akers & Bokhove 2008) and for granular flows (Vreman et al. 2007). Furthermore, the 1D model is verified by solving the 2D shallow granular equations using an open source discontinuous Galerkin finite element package hpGEM (Pesch et al. 2007). For supercritical flows i.e. F > 1 the 1D asymptotics holds although the two-dimensional oblique granular jumps largely vary across the converging channel. This computationally efficient closed 1D model is validated by comparing it to the computationally more expensiveaa three-dimensional particle simulations. Finally, we aim to present a quasi-steady particle simulation of inclined flow through two rectangular blocks separated by a gap, investigate the channel formed by the dead zones and compare it with our analytical calculations. REFERENCES 1. Akers, B. & Bokhove, O. 2008 Hydraulic flow through a channel contraction: Multiple steady states. Physics of fluids 20 (056601), 056601. 2. Mercury 2010 http://www2.msm.ctw.utwente.nl/athornton/md/ . 3. Pesch, L., Bell, A., Sollie, H., Ambati, V.R., Bokhove, O. & Van der Vegt, J.J.W. 2007 hpGEM—a software framework for discontinuous Galerkin finite element methods. ACM Transactions on Mathematical Software (TOMS) 33 (4), 23. 4. Savage, SB & Hutter, K. 1989 The motion of a finite mass of granular material down a rough incline. Journal of Fluid Mechanics 199 (1), 177-215. 5. Vreman, AW, Al-Tarazi, M., Kuipers, JAM, van Sint Annaland, M. & Bokhove, O. 2007 Supercritical shallow granular flow through a contraction: experiment, theory and simulation. Journal of Fluid Mechanics 578 (1), 233-269. 6. Weinhart, T., Thornton, A.R., Luding, S. & Bokhove, O. 2012 Closure relations for shallow granular flows from particle simulations. Granular Matter 14 (4), 531-552.

Tunuguntla, Deepak; Weinhart, Thomas; Thornton, Anthony; Bokhove, Onno

2013-04-01

101

Blast Shocks in Quasi-Two-Dimensional Supersonic Granular Flows  

Microsoft Academic Search

In a thin, dilute, and fast flowing granular layer, the impact of a small sphere generates a fast growing hole devoid of matter. The growth of this hole is studied in detail, and its dynamics is found to mimic that of blast shocks in gases. This dynamics can be decomposed into two stages: a fast initial stage (the blast) and

J. F. Boudet; J. Cassagne; H. Kellay

2009-01-01

102

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

103

Granular Dynamics during Impact  

NASA Astrophysics Data System (ADS)

In this work, we study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. Using a laser sheet scanning technique, a high speed camera, and particle tracking, we can measure the trajectory of each grain throughout an impact event. We characterize the bulk and microscopic dynamics within the granular material as a function of initial sample preparation, specifically applying a uniaxial prestrain to the sample. We find that small changes in sample preparation lead to drastic departures from the universal depth scaling seen in previous studies of shallow granular impacts. By examining the nonaffine motion within the system, we propose the effect is due to different loading and buckling of force chains within the system.

Nordstrom, Kerstin; Lim, Emily; Harrington, Matt; Losert, Wolfgang

2013-03-01

104

Granular convection in microgravity.  

PubMed

We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity-modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity and enhanced under high-gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause. PMID:23383851

Murdoch, N; Rozitis, B; Nordstrom, K; Green, S F; Michel, P; de Lophem, T-L; Losert, W

2013-01-01

105

Measurement of granular entropy.  

PubMed

Recently, Dean and Lefèvre [Phys. Rev. Lett. 90, 198301 (2003)] developed a method for testing the statistical mechanical theory of granular packings proposed by Edwards and co-workers [Physica A 157, 1080 (1989); Phys. Rev. E 58, 4758 (1998)]. The method relies on the prediction that the ratio of two overlapping volume histograms should be exponential in volume. We extend the method by showing that one can also calculate the entropy of the packing and also that the method can yield false positive results when the histograms are Gaussians with nearly identical variances. We then apply the method to simulations and experiments of granular compaction. The distribution of global volumes (the volume of the entire packing) is nearly Gaussian and it is difficult to conclude if the theory is valid. On the other hand, the distribution of Voronoï volumes clearly obeys the theoretical prediction. PMID:19905104

McNamara, Sean; Richard, Patrick; de Richter, Sébastien Kiesgen; Le Caër, Gérard; Delannay, Renaud

2009-09-01

106

Longitudinal vortices in granular flows.  

PubMed

We present a new instability observed in rapid granular flows down rough inclined planes. For high inclinations and flow rates, the free surface of the flow experiences a regular deformation in the transverse direction. Measurements of the surface velocities imply that this instability is associated with the formation of longitudinal vortices in the granular flow. From the experimental observations, we propose a mechanism for the longitudinal vortex formation based on the concept of granular temperature. PMID:11415386

Forterre, Y; Pouliquen, O

2001-06-25

107

Granular Structure Determined by Terahertz Scattering  

E-print Network

Light-scattering in the terahertz region is demonstrated for granular matter. A quantum-cascade laser is used in a benchtop setup to determine the angle-dependent scattering of spherical grains as well as coffee powder and sugar grains. For the interpretation of the form factors for the scattering from single particles one has to go beyond the usual Rayleigh-Gans-Debye theory and apply calculations within Mie theory. In addition to single scattering also collective correlations can be identified and extracted as a static structure factor.

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

2013-12-23

108

Sound propagation in dry granular materials  

E-print Network

Sound propagation in dry granular materials: discrete element simulations, theory, and experiments #12;Sound propagation in dry granular materials: discrete element simulations, theory, and experiments 2009 by O. Mouraille, The Netherlands #12;SOUND PROPAGATION IN DRY GRANULAR MATERIALS: DISCRETE ELEMENT

Luding, Stefan

109

Non Steady State Granular Shear Flows  

NASA Astrophysics Data System (ADS)

We experimentally investigate the shear flow of granular matter in a cylindrical Couette cell. Since granular flows dissipate energy, they must be continuously driven to remain in a flowing state. Previous experiments on steady state shear flows have found that velocity gradients are confined to a thin shear band, and that the shear force is roughly independent of shear rate if the material is allowed to dilate. Our experiments in a Couette geometry focus on two related questions about non-steady state flows: 1) How does a granular shear flow start? 2) How does a granular system respond to oscillatory shear? In particular, we investigate the role of boundary conditions, which we expect to be of particular importance, since granular flows must be continuously driven (in general from a boundary) in order to be sustained. In our Couette cell a shear flow is generated by moving either the inner cylinder or the outer cylinder or both cylinders. The motion of grains on the top surface is measured directly with fast imaging and particle tracking techniques. Previous studies have indicated that the velocity profile on the top surface is very similar to the velocity profile within the bulk. Measurements of the corresponding shear forces are in progress. Initial experiments determined the steady state flow profiles under different driving conditions, with either inner, outer or both cylinders moving. In steady state, velocity gradients are confined to a roughly exponential shearband several particle diameters wide. The shear band is always located at the inner cylinder. A probable reason for this observation is the slightly smaller surface area of the inner cylinder compared to the outer cylinder. Since shear forces are transmitted from one cylinder to the other, the smaller surface area of the inner cylinder leads to larger shear stresses. Shear flow confined to regions of high stress can be reproduced in continuum mechanics models which include plastic flow, non-Newtonian fluid models, or locally Newtonian hydrodynamic models that include a strong density dependence of viscosity. Most of these models are isotropic with respect to the shear direction. However, anisotropies manifest themselves in two distinct flow transients, when rotation of one of the cylinders is started. When the cylinder had been rotated in the same direction before, the thin shear band immediately forms. When the previous motion of the cylinder had been in the opposite direction, particles far from the moving cylinder are initially more mobile. After an extra displacement of up to six particle diameters, a thin shearband forms again in steady state. The extra displacement of particles far from the shear surface does not strongly depend on the shear rate prior or after the stop, solely on the direction of prior shear. This indicates that the static configuration of grains after a shear flow exhibits anisotropies. The flow transient, at least, can then no longer be modeled with the isotropic form of the models described above. Finally, we investigate oscillatory shear flow. During small amplitude oscillations the shear flow is confined to a thin shear band. In addition, a gradual compaction and strengthening of the granular material is observed. For sufficiently large oscillation amplitudes, the flow resembles a sequence of shear reversals. In oscillatory flows driven by the outer cylinder, coexistence of shearbands at the outer and inner cylinder can be found. In summary, we have elucidated important properties of granular shear flows from non-steady state flow measurements: First, shear bands form preferentially near the inner cylinder, even when the outer cylinder is sheared. Transiently a shear band can also form near the outer cylinder during oscillatory driving. These observations should help refine models of granular shear flow. One challenge in improving models of granular shear flow is the observation that the initial flow transient contains 'memory' of the direction of previously applied shear. In order to incorporate this observation into flow model

Losert, Wolfgang; Kwon, Gene

2002-11-01

110

Entangled granular media  

E-print Network

We study the geometrically induced cohesion of ensembles of granular "u-particles" which mechanically entangle through particle interpenetration. We vary the length-to-width ratio $l/w$ of the u-particles and form them into free-standing vertical columns. In laboratory experiment we monitor the response of the columns to sinusoidal vibration (frequency $f$, peak acceleration $\\Gamma$). Column collapse occurs in a characteristic time, $\\tau$, which follows the relation $\\tau = f^{-1} \\exp(\\Delta / \\Gamma)$. $\\Delta$ resembles an activation energy and is maximal at intermediate $l/w$. Simulation reveals that optimal strength results from competition between packing and entanglement.

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

2012-04-30

111

PARTICLE ROTATIONS IN GRANULAR MATERIALS  

Microsoft Academic Search

Particle rotations can have a dominant influence on the behavior of granular materials, particularly in materials with circular or spherical particles. The paper briefly reviews experimental evidence of the magnitude and variability of particle rotations and their effect on a granular material's stiffness and strength. Evidence of rotational patterning is reported from DEM simulations of a large square assembly of

Matthew R. Kuhn; Katalin Bagi

112

Shock Waves in Granular Gases  

Microsoft Academic Search

This review is the first attempt to systematize the results on shock waves in granular gases. We present experimental and computational evidences of shock and expansion waves propagating within granular gases. The analysis of model flows with shock and expansion waves shows that even smallest kinetic energy dissipations crucially affects such flows. We discuss the role of these waves for

Alexander Goldshtein; Alexander Alexeev; Michael Shapiro

2003-01-01

113

Granular solids, liquids, and gases  

Microsoft Academic Search

Granular materials are ubiquitous in the world around us. They have properties that are different from those commonly associated with either solids, liquids, or gases. In this review the authors select some of the special properties of granular materials and describe recent research developments. {copyright} {ital 1996 The American Physical Society.}

Heinrich M. Jaeger; Sidney R. Nagel; Robert P. Behringer

1996-01-01

114

Microwave assisted wet oxidation of p-nitrophenol  

Microsoft Academic Search

Aqueous solution of p-nitrophenol (PNP) was treated continuously by microwave assisted wet oxidation while flowing through\\u000a a granular activated carbon (GAC) fixed bed. PNP was pre-adsorbed onto GAC prior to being put into the reactor so as to prevent\\u000a PNP adsorption on GAC during microwave irradiation. PNP solutions with different initial concentration (218.6 mg\\/L and 1200\\u000a mg\\/L) were treated under

Longli Bo; Shuo Chen; Xie Quan; Xitao Liu; Huimin Zhao

2005-01-01

115

Size Effects in Granular Media Size Effect of Inclusions in Granular Media  

E-print Network

Size Effects in Granular Media Size Effect of Inclusions in Granular Media S. Joseph Antony1 Conference 2005 #12;Size Effects in Granular Media Outline 1 Background Particle stress Simulations: Particle Questions about granular behavior Experiment results #12;Size Effects in Granular Media Background Particle

Kuhn, Matthew R.

116

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

117

Microscale granular metamaterials.  

PubMed

Locally resonant metamaterials and granular media are both known to drastically affect acoustic wave propagation. However, there are thus far few examples of such materials which have microscale elements and are designed to control acoustic waves with megahertz frequencies or greater. In this talk, I will discuss our recent work at the intersection of these two types of materials, in which we explored the interaction of megahertz-gigahertz frequency surface acoustic waves with a self-assembled metamaterial composed of microspheres adhered to an elastic substrate. I will present our theoretical model and describe our photoacoustic experiments, in which we used transient-grating spectroscopy to measure the acoustic dispersion of the system. Finally, I will also discuss several potential applications of these novel materials such as signal processing and biosensing devices. PMID:25235445

Boechler, Nicholas

2014-04-01

118

Chaotic granular mixing.  

PubMed

Several models for convective mixing of coarse, freely flowing in granular tumblers have been proposed over the past decade. Powders of practical interest, by contrast, are frequently fine and cohesive, and cannot be analyzed with these models. Moreover, even in the freely flowing regime, mixing transverse to the dominant, convective, direction is typically slow and inefficient. In this paper, we examine two chaotic mixing mechanisms, the first of which can be intentionally applied to increase transverse mixing rates severalfold, with new prospects for further improvements in three-dimensional mixing through judicious process design. The second mechanism occurs spontaneously in fine grains, resulting in mixing rates overwhelmingly exceeding what would be possible in freely flowing grains. Finally, we show that the same chaotic mixing mechanisms seen in simple drum mixers are also found to be at work in more complex blender configurations widely used in batch industrial operations. (c) 1999 American Institute of Physics. PMID:12779856

Shinbrot, Troy; Alexander, Albert; Moakher, Maher; Muzzio, Fernando J.

1999-09-01

119

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.

120

Wet and dry African dust episodes over eastern Spain  

Microsoft Academic Search

The impact of the African dust on levels of atmospheric suspended particulate matter (SPM) and on wet deposition was evaluated in eastern Iberia for the period 1996–2002. An effort was made to compile both the SPM and wet episodes. To this end, the time series of levels of TSP and PM10 in Levantine air quality monitoring stations were evaluated and

M. Escudero; S. Castillo; X. Querol; A. Avila; M. Alarcón; M. M. Viana; A. Alastuey; E. Cuevas; S. Rodríguez

2005-01-01

121

Hopping Conductivity in Granular Metals  

Microsoft Academic Search

We present evidence that in granular metals the observed temperature dependence of the low-field conductivity, exp(-bTalpha) with alpha=12, can be ascribed to a relationship sEc=const between s, the separation of neighboring metal grains, and Ec, the electrostatic energy required to create a positive-negative charged pair of grains. This relationship results from simple considerations of the structure of granular metals. The

Ping Sheng; B. Abeles; Y. Arie

1973-01-01

122

Wet solids flow enhancement  

SciTech Connect

The objective was to visualize the flow of granular materials in the silo using Nuclear Magnetic Resonance. This was done by introducing traces. Mustard seeds and poppy seeds were used as trace particles. The region sampled was a cylinder 25 mm in diameter and 40 mm in length. Eight slices containing 128 by 128 to 256 by 256 pixels were generated for each image.

Caram, H.S.; Agrawal, D.K.; Foster, N.

1997-07-01

123

a Review of Mesoscale Simulations of Granular Materials  

NASA Astrophysics Data System (ADS)

With the advent of increased computing power, mesoscale simulations have been used to explore grain level phenomenology of dynamic compaction events of various heterogenous systems including foams, reactive materials and porous granular materials. This paper presents an overview of several mesoscale studies on a variety of materials including tungsten carbide, wet and dry sand, and an inert mixture of Al-MnO2-Epoxy. This paper focuses on relating bulk and compaction wave phenomenology from the mesoscale modeling to experimental results and exploring the nature of the compaction wave. In addition, lessons learned during these explorations, modeling techniques, strengths and weaknesses of hydrodynamic mesoscale simulations are also discussed.

Borg, J. P.; Vogler, T. J.; Fraser, A.

2009-12-01

124

Dynamic wetting on superhydrophobic surfaces: Droplet impact and wetting hysteresis  

E-print Network

We study the wetting energetics and wetting hysteresis of sessile and impacting water droplets on superhydrophobic surfaces as a function of surface texture and surface energy. For sessile drops, we find three wetting ...

Smyth, Katherine M.

125

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

126

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

127

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

128

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

129

Granular packings: nonlinear elasticity, sound propagation, and collective relaxation dynamics.  

PubMed

Experiments on isotropic compression of a granular assembly of spheres show that the shear and bulk moduli vary with the confining pressure faster than the 1/3 power law predicted by Hertz-Mindlin effective medium theories of contact elasticity. Moreover, the ratio between the moduli is found to be larger than the prediction of the elastic theory by a constant value. The understanding of these discrepancies has been a long-standing question in the field of granular matter. Here we perform a test of the applicability of elasticity theory to granular materials. We perform sound propagation experiments, numerical simulations, and theoretical studies to understand the elastic response of a deforming granular assembly of soft spheres under isotropic loading. Our results for the behavior of the elastic moduli of the system agree very well with experiments. We show that the elasticity partially describes the experimental and numerical results for a system under compressional loads. However, it drastically fails for systems under shear perturbations, particularly for packings without tangential forces and friction. Our work indicates that a correct treatment should include not only the purely elastic response but also collective relaxation mechanisms related to structural disorder and nonaffine motion of grains. PMID:15697350

Makse, Hernán A; Gland, Nicolas; Johnson, David L; Schwartz, Lawrence

2004-12-01

130

Spectral responses in granular compaction  

NASA Astrophysics Data System (ADS)

The slow compaction of a tapped granular packing is reminiscent of the low-temperature dynamics glasses. Here, I study the dynamics of granular compaction by means of a volumetric spectroscopy. While the specific packing volume v displays glassy aging and memory effects at low tapping amplitudes ? , the dynamic volumetric susceptibility ?˜v=?v/?? displays minimal glassy effects, and its frequency spectrum gives no indication of a rapidly growing time scale. These features are contrast sharply with that found in the dielectric and magnetic susceptibilities of structural and spin glasses. Instead, ?˜v appears to exhibit the behavior of a dynamic configurational specific heat, such as that obtained from computer simulations of spin-glass models. This suggests that the glassy dynamics of granular compaction is controlled by statistically rare processes that diverge from the typical dynamics of the system. From modifications of the dynamical spectrum by finite system size, I suggest that these glassy processes derive from large-scale collective particle rearrangements.

Zou, Ling-Nan

2010-03-01

131

Instability in shocked granular gases  

NASA Astrophysics Data System (ADS)

Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structure. In the present study we have extended this work to investigate this instability at the continuum level. We modeled the Euler equations for granular gases with a modified cooling rate to include an impact velocity threshold necessary for inelastic collisions. Our results showed a fair agreement between the continuum and discrete-particle models. Discrepancies, such as higher frequency instabilities in our continuum results may be attributed to the absence of higher order effects.

Sirmas, Nick; Falle, Sam; Radulescu, Matei

2014-05-01

132

Outlier Detection Based on Granular Computing  

Microsoft Academic Search

As an emerging conceptual and computing paradigm of information processing, granular computing has received much attention\\u000a recently. Many models and methods of granular computing have been proposed and studied. Among them was the granular computing\\u000a model using information tables. In this paper, we shall demonstrate the application of this granular computing model for the\\u000a study of a specific data mining

Yuming Chen; Duoqian Miao; Ruizhi Wang

2008-01-01

133

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

134

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

135

Pulmonary malignant granular cell tumor  

PubMed Central

Background Malignant granular cell tumor (MGCT) is a rare disease entity. Forty-one well-documented MGCTs have been reported in the world literature. Case Report This report describes a patient who presented with a MGCT of the lung and reviews the preoperative evaluation, pathologic features and differential diagnosis of the disease. This case represents the first report of resected primary pulmonary MGCT. Conclusions Diagnosis of MGCT is based on histology of the primary tumor, immunohistochemistry, and exclusion of tumors that may mimic granular cell tumor. PMID:14613555

Jiang, Ming; Anderson, Timothy; Nwogu, Chukwumere; Tan, Dongfeng

2003-01-01

136

Unifying Suspension and Granular Rheology  

NASA Astrophysics Data System (ADS)

Using an original pressure-imposed shear cell, we study the rheology of dense suspensions. We show that they exhibit a viscoplastic behavior similarly to granular media successfully described by a frictional rheology and fully characterized by the evolution of the friction coefficient ? and the volume fraction ? with a dimensionless viscous number Iv. Dense suspension and granular media are thus unified under a common framework. These results are shown to be compatible with classical empirical models of suspension rheology and provide a clear determination of constitutive laws close to the jamming transition.

Boyer, François; Guazzelli, Élisabeth; Pouliquen, Olivier

2011-10-01

137

Packaging of granular bead chain  

NASA Astrophysics Data System (ADS)

We find that a freely moving granular chain can be pushed, against the entropic force, into a confined cell if the passage to the cell is a channel of truncated-cone shape. In this setting, the granular chain, the cell and the channel can be considered as a mechanical analog of a DNA molecular, a bacteriophage and a portal motor, respectively. The force generated by the scaled-up analog of the mechanical motor and the packaging speed are found to be consistent with the real bacteriophage ?29 portal motor. Pauses and slips found in single-molecule experiments of DNA packaging of the bacteriophage are also observed in the analog system.

Jeng, Pei-Ren; Chen, KuanHua; Hwang, Gwo-jen; Tien, Chen-Man; Lien, Chenhsin; To, Kiwing; Chou, Y. C.

2011-11-01

138

Pattern formation in granular and granular-fluid flows  

Microsoft Academic Search

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

Nhat-Hang P. Duong

2004-01-01

139

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

140

Creep of wet gypsum aggregates under hydrostatic loading conditions  

NASA Astrophysics Data System (ADS)

Gypsum-dominated evaporite sequences are known to play an important role in controlling the mechanics of foreland thrust and nappe tectonics, as well as occasionally forming large-scale halokinetic structures associated with oil and gas accumulations. However, relatively little is known regarding the relevant deformation mechanisms and mechanical behaviour of gypsum. In this study, attention is focused on determining the compaction creep behaviour of wet granular gypsum aggregates with the aim of assessing the importance of pressure solution. Hydrostatic compaction experiments were performed at room temperature and applied effective pressures in the range 0.4-3.9 MPa, using grain sizes ranging from 15 to 125 ?m. The microstructure of the wet-tested samples showed that compaction occurred by a process of dissolution within grain contacts and precipitation on pore walls. In addition, for most of the range of conditions investigated, the mechanical data were found to be broadly consistent with models for interface-reaction-controlled grain boundary diffusional pressure solution. Combining the mechanical data with kinetic data taken from the crystal growth / dissolution literature it is suggested that for the bulk of conditions studied, creep of our wet granular gypsum aggregates was probably rate-limited by precipitation on the pore walls. This is in sharp contrast to the diffusion-controlled pressure solution creep behaviour recently reported for highly soluble salts, such as NaCl and NaNO 3, under similar conditions.

de Meer, Siese; Spiers, Christopher J.

1995-05-01

141

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

142

Membrane-Based Wet Electrostatic Precipitation  

Microsoft Academic Search

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 water-based) 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),

David J. Bayless; Liming Shi; Gregory Kremer; Ben J. Stuart; James Reynolds; John Caine

2005-01-01

143

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

144

Participatory Learning With Granular Observations  

Microsoft Academic Search

We introduce and discuss the participatory learning paradigm. A formal system implementing this type of learning agent is described. We then extend this system so that it can learn from interval-type observations. We further extend this system to the case when the observation is a more general granular object such as a fuzzy set. In the initial stage, while we

Ronald R. Yager

2009-01-01

145

Mechanics of Granular Materials (MGM)  

NASA Technical Reports Server (NTRS)

Astronauts Jim Reilly and Bornie Dunbar are going through the Mechanics of Granular Materials (MGM) experiment procedures as they are expected to run in flight; to gain experience with the experiment equipment and to test the clarity and language of the procedures as written.

1997-01-01

146

Shocks in rapid granular flows  

NASA Astrophysics Data System (ADS)

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: the surface wake behind a cylinder, the oblique shock formed at a wedge and a normal shock propagating through a funnel. In each case we evaluate the applicability of a hydrodynamic description to shocks in rapid granular flows. We study the V-shaped wake formed by a cylindrical rod moving through a vertically vibrated granular layer. The wake appears for rod velocities vR greater than a critical velocity c. We measure the half-angle theta of the wake as a function of v R and layer depth h. We find that c and theta can be described by a hydrodynamic description applied to shallow fluids, where c = gh is the speed of a gravitational wave on a shallow fluid and sintheta = c/vR is the Mach relation. We find the decrease in the height of the wake h max as it propagates away from the rod agrees with Landau's theory for the decay of shock waves far from their origin. We measure the time-averaged velocity, density and temperature fields for a gravity driven granular flow past a wedge. The flow is supersonic with a sound speed less than 10% of the flow speed. We find the shock formed at the wedge tip is nearly identical to oblique shocks found in a supersonic, elastic gas. Molecular dynamics simulations of Newton's laws yield fields in quantitative agreement with experiment. A numerical solution of granular hydrodynamic equations is only in qualitatively accord with experiment. We show that hydrodynamic theory fails because it does not include friction. We use molecular dynamics simulations to examine the effect of friction on the dissipation of energy and scattering angles in collisions. We examine the propagation of a normal shock formed in a quasi-two dimensional funnel. For shocks propagating without, change in a fluid, one can use the Rankine-Hugoniot approximation to predict the velocity of the shock and the difference in flow values across the shock. We show that inelastic collisions between particles cause the shock to continuously evolve, hence the Rankine-Hugoniot predictions are inadequate for describing the evolution of granular shocks.

Rericha, Erin Colleen

147

Wave mitigation in ordered networks of granular chains  

NASA Astrophysics Data System (ADS)

We study the propagation of stress waves through ordered 2D networks of granular chains. The quasi-particle continuum theory employed captures the acoustic pulse splitting, bending, and recombination through the network and is used to derive its effective acoustic properties. The strong wave mitigation properties of the network predicted theoretically are confirmed through both numerical simulations and experimental tests. In particular, the leading pulse amplitude propagating through the system is shown to decay exponentially with the propagation distance and the spatial structure of the transmitted wave shows an exponential localization along the direction of the incident wave. The length scales that characterized these exponential decays are studied and determined as a function of the geometrical properties of the network. These results open avenues for the design of efficient impact mitigating structures and provide new insights into the mechanisms of wave propagation in granular matter.

Leonard, Andrea; Ponson, Laurent; Daraio, Chiara

2014-12-01

148

Armoring a droplet: Soft jamming of a dense granular interface  

NASA Astrophysics Data System (ADS)

Droplets and bubbles protected by armors of particles have found vast applications in encapsulation, stabilization of emulsions and foams, or flotation processes. The liquid phase stores capillary energy, while concurrently the solid contacts of the granular network induce friction and energy dissipation, leading to hybrid interfaces of combined properties. By means of nonintrusive tensiometric methods and structural measurements, we distinguish three surface phases of increasing rigidity during the evaporation of armored droplets. The emergence of surface rigidity is reminiscent of jamming of granular matter, but it occurs differently since it is marked by a step by step hardening under surface compression. These results show that the concept of the effective surface tension remains useful only below the first jamming transition. Beyond this point, the surface stresses become anisotropic.

Lagubeau, Guillaume; Rescaglio, Antonella; Melo, Francisco

2014-09-01

149

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

150

Formation of Riedel shear fractures in granular materials: Findings from analogue shear experiments and theoretical analyses  

Microsoft Academic Search

We performed simple shear experiments to investigate the development of low- (R1) and high- (R2) angle Riedel shear localization in wet sand–talc mixtures with varying volume proportions. With increasing talc content, the granular medium underwent rheological changes, showing larger homogeneous ductile strains prior to brittle failure. Talc-rich models developed a perceptible penetrative planar fabric of flaky talc grains in response

Santanu Misra; Nibir Mandal; Chandan Chakraborty

2009-01-01

151

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.

152

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

153

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

154

Granular Character of Particle Rafts  

E-print Network

We consider a monolayer of particles floating at a horizontal liquid-gas interface -- a particle raft. Upon compressing the monolayer in a Langmuir trough, the particles at first pack but ultimately the monolayer buckles out of the plane. We measure the stress profile within the raft at the onset of buckling and show for the first time that such systems exhibit a Janssen effect: the stress decays exponentially away from the compressing barriers over a length scale that depends on the width of the trough. We find quantitative agreement between the rate of decay and the simple theory presented by Janssen and others. This demonstrates that floating particle rafts have a granular, as well as elastic, character, which is neglected by current models. Finally, we suggest that our experimental setup may be suitable for exploring granular effects in two dimensions without the complications of gravity and basal friction.

Pietro Cicuta; Dominic Vella

2009-01-19

155

Dynamics of driven granular suspensions  

E-print Network

We suggest a simple model for the dynamics of granular particles in suspension which is suitable for an event driven algorithm, allowing to simulate $N=\\mathcal{O}(10^6)$ particles or more. As a first application we consider a dense granular packing which is fluidized by an upward stream of liquid, i.e. a fluidized bed. In the stationary state, when all forces balance, we always observe a well defined interface whose width is approximately independent of packing fraction. We also study the dynamics of expansion and sedimentation after a sudden change in flow rate giving rise to a change in stationary packing fraction and determine the timescale to reach a stationary state.

Andrea Fiege; Annette Zippelius

2014-06-16

156

Rheological Transition in Granular Media  

Microsoft Academic Search

\\u000a The planar shearing of a two-dimensional system of bidisperse, non-cohesive discs at constant shear velocity is simulated\\u000a using Contact Dynamics. The granular medium is confined between two parallel walls, which are pushed inwards by constant normal\\u000a forces. The flow as a function of the shear velocity shows characteristics of a first order phase transition. The order parameter,\\u000a the center of

Zahra Shojaaee; Lothar Brendel; Dietrich E. Wolf

157

Anisotropy of Weakly Vibrated Granular Flows  

E-print Network

We experimentally probe the anisotropy of the fabric of weakly vibrated, flowing granular media. Depending on the driving parameters --- flow rate and vibration strength --- this anisotropy varies significantly. We show how the anisotropy collapses when plotted as function of the driving stresses, uncovering a direct link between stresses and anisotropy. Moreover, our data suggests that for small anisotropies, the shear stresses vanish. Anisotropy of the fabric of granular media thus plays a crucial role in determining the rheology of granular flows.

Geert Wortel; Martin van Hecke

2014-10-16

158

Shock wave propagation in vibrofluidized granular materials  

E-print Network

Shock wave formation and propagation in two-dimensional granular materials under vertical vibration are studied by digital high speed photography. The steepen density and temperature wave fronts form near the plate as granular layer collides with vibrating plate and propagate upward through the layer. The temperature front is always in the transition region between the upward and downward granular flows. The effects of driving parameters and particle number on the shock are also explored.

Kai Huang; Guoqing Miao; Peng Zhang; Yi Yun; Rongjue Wei

2005-11-29

159

Why Granular Media Are, After All, Thermal  

E-print Network

Granular media are considered "athermal", because the grains are too large to display Brownian type thermal fluctuations. Yet being macroscopic, every grain undergoes thermal expansion, possesses a temperature that may be measured with a thermometer, and consists of many, many internal degrees of freedom that in their sum do affect granular dynamics. Therefore, including them in a comprehensive approach to account for granular behavior entails crucial advantages. The pros and cons of thermal versus athermal descriptions are considered.

Yimin Jiang; Mario Liu

2014-07-27

160

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, over-saturated 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:23319518

Patkar, Saket; Chaudhuri, Parag

2013-01-10

161

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

162

FNA of thyroid granular cell tumor.  

PubMed

Granular cell tumor rarely occurs in the thyroid. This case report describes the cytologic features of a granular cell tumor seen in a fine needle aspirate obtained from a 27-year-old woman with a gradually enlarging thyroid nodule. The aspirate showed single as well as syncytial clusters of cells with abundant granular cytoplasm. The differential diagnosis in this case included granular cell tumor, Hurthle cell lesion/neoplasm, and a histiocytic reparative process. Immunohistochemical studies, including S-100 protein and CD68, performed on a cell block preparation were helpful in supporting the diagnosis. PMID:22508678

Harp, Eric; Caraway, Nancy P

2013-09-01

163

21 CFR 133.145 - Granular cheese for manufacturing.  

Code of Federal Regulations, 2011 CFR

21 Food and Drugs 2 2011-04-01...Granular cheese for manufacturing. 133.145 Section 133.145 Food and Drugs FOOD...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION...Granular cheese for manufacturing. Granular...

2011-04-01

164

21 CFR 133.145 - Granular cheese for manufacturing.  

Code of Federal Regulations, 2013 CFR

21 Food and Drugs 2 2013-04-01...Granular cheese for manufacturing. 133.145 Section 133.145 Food and Drugs FOOD...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION...Granular cheese for manufacturing. Granular...

2013-04-01

165

21 CFR 133.145 - Granular cheese for manufacturing.  

Code of Federal Regulations, 2012 CFR

21 Food and Drugs 2 2012-04-01...Granular cheese for manufacturing. 133.145 Section 133.145 Food and Drugs FOOD...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION...Granular cheese for manufacturing. Granular...

2012-04-01

166

21 CFR 133.145 - Granular cheese for manufacturing.  

21 Food and Drugs 2 2014-04-01...Granular cheese for manufacturing. 133.145 Section 133.145 Food and Drugs FOOD...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION...Granular cheese for manufacturing. Granular...

2014-04-01

167

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

168

Slope streaks on Mars: A new “wet” mechanism  

NASA Astrophysics Data System (ADS)

Slope steaks are one of the most intriguing modern phenomena observed on Mars. They have been mostly interpreted as some specific type of granular flow. We propose another mechanism for slope streak formation on Mars. It involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin, and runaway propagation of percolation fronts. Given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions, this mechanism is consistent with the observational constraints; it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride, and a small part of the observed hydrogen to be in form of water ice. This "wet" mechanism has a number of appealing advantages in comparison to the widely accepted "dry" granular flow mechanism. Potential tests for the "wet" mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation.

Kreslavsky, Mikhail A.; Head, James W.

2009-06-01

169

A review of mesoscale simulations of granular materials  

NASA Astrophysics Data System (ADS)

With the advent of increased computing power, mesoscale simulations have been used to explore grain level phenomenology of dynamic compaction events of various heterogenous systems including foams, reactive materials and porous granular materials. This paper presents an overview of several mesoscale studies on a variety of materials include tungsten carbide and epoxy mixtures, wet and dry sand, and reactive materials (Al-MnO2-Epoxy mixtures). The simulations encompass a variety of geometries including one-dimensional planar and spherical shock configurations. This talk will focus on relating mesoscale modeling to experimental data and the role of material constitutive relations in this effort. In addition, lessons learning during these explorations, modeling techniques, strengths and weaknesses of hydrodynamic mesoscale simulations will also be presented.

Borg, John

2009-06-01

170

Wet coastal plain tundra  

SciTech Connect

This years's census data for the wet coastal plain tundra in Alaska; North Slope Borough, 3 km SSW of Naval Arctic Research Laboratory, Barrow; 71/sup 0/ 18'N, 156/sup 0/ 43'W; Barrow Quadrangle, USGS, reflect an increase in breeding species of 31% over the 5-year average, while breeding density was up 22%. Ten species increased and only 4 decreased. There was a total of 17 species; 61.5 territorial males or females (171/km/sup 2/, 69/100 acres).

Myers, J.P.; McCaffery, B.J.; Pitelka, F.A.

1980-01-01

171

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.

172

WHERE THE GRANULAR FLOWS BEND  

SciTech Connect

Based on IMaX/SUNRISE data, we report on a previously undetected phenomenon in solar granulation. We show that in a very narrow region separating granules and intergranular lanes, the spectral line width of the Fe I 5250.2 A line becomes extremely small. We offer an explanation of this observation with the help of magneto-convection simulations. These regions with extremely small line widths correspond to the places where the granular flows bend from upflow in granules to downflow in intergranular lanes. We show that the resolution and image stability achieved by IMaX/SUNRISE are important requisites to detect this interesting phenomenon.

Khomenko, E.; Martinez Pillet, V.; Bonet, J. A. [Instituto de Astrofisica de Canarias, 38205 C/VIa Lactea, s/n, La Laguna, Tenerife (Spain); Solanki, S. K.; Gandorfer, A.; Barthol, P. [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany); Del Toro Iniesta, J. C. [Instituto de Astrofisica de Andalucia (CSIC), Apdo. de Correos 3004, E-18080 Granada (Spain); Domingo, V. [Grupo de AstronomIa y Ciencias del Espacio, Universidad de Valencia, E-46980 Paterna, Valencia (Spain); Schmidt, W. [Kiepenheuer-Institut fuer Sonnenphysik, 79104 Freiburg (Germany); Knoelker, M., E-mail: khomenko@iac.e [High Altitude Observatory (NCAR), Boulder, CO 80307-3000 (United States)

2010-11-10

173

Theoretical model of granular compaction  

SciTech Connect

Experimental studies show that the density of a vibrated granular material evolves from a low density initial state into a higher density final steady state. The relaxation towards the final density follows an inverse logarithmic law. As the system approaches its final state, a growing number of beads have to be rearranged to enable a local density increase. A free volume argument shows that this number grows as N = {rho}/(1 {minus} {rho}). The time scale associated with such events increases exponentially e{sup {minus}N}, and as a result a logarithmically slow approach to the final state is found {rho} {infinity} {minus}{rho}(t) {approx_equal} 1/lnt.

Ben-Naim, E. [Los Alamos National Lab., NM (United States); Knight, J.B. [Princeton Univ., NJ (United States). Dept. of Physics; Nowak, E.R. [Univ. of Illinois, Urbana, IL (United States). Dept. of Physics]|[Univ. of Chicago, IL (United States). James Franck Inst.; Jaeger, H.M.; Nagel, S.R. [Univ. of Chicago, IL (United States). James Franck Inst.

1997-11-01

174

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...

175

Continuum Simulation of Impact into Granular Beds  

Microsoft Academic Search

We investigate the dynamics of objects impacting into a granular medium using continuum simulations. Although a static bed with long-lasting contact between grains exhibits a solid-like configuration, the bed may become locally fluidized near an impact by an external object. Studies of shock propagation through granular beds suggest grains may flow freely near the impact site, yielding behaviors that could

Eric Wilkinson; Jon Bougie

2010-01-01

176

New corner stones in dissipative granular gases  

Microsoft Academic Search

Theory of granular dissipative gas is discussed based on Boltzmann's equation and in view of recent experimental results in micro-gravity during few CNES and ESA campaigns [9,11]. It is recalled that the Boltzmann's distribution is a steady solution only when collisions are elastic; hence it is not applicable in the case of dissipative granular gas. The first experimental case concerns

P. Evesque

2005-01-01

177

KNOWLEDGE GRANULARITY AND REPRESENTATION OF KNOWLEDGE: TOWARDS  

E-print Network

KNOWLEDGE GRANULARITY AND REPRESENTATION OF KNOWLEDGE: TOWARDS KNOWLEDGE GRID Maria A. Mach.owoc}@ue.wroc.pl ABSTRACT. Knowledge granularity, usually identified with the size of knowledge granules, seems to be real challenge for knowledge consumers as well as for knowledge creators. In this paper, relationships between

Boyer, Edmond

178

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

179

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

180

Granular Banding - the Fine Structure  

NASA Astrophysics Data System (ADS)

Solid-liquid two-phase flow in a partially filled, horizontally rotating cylinder is studied experimentally. This system can display several different flow states. The rotation rate, the filling level and the fluid properties determine which state is adopted. In the phase plane different states are separated from each other by sharp transition boundaries. The influence of granular additives on these boundaries is investigated. Results for particles of different sizes, densities and shapes are presented. Under certain conditions the granular additives come out of suspension to form regularly spaced circumferential bands on the inner cylinder wall [1,2]. We report the observation of a new phenomenon by which these primary bands develop a fine structure. The fine structure is characterized by each primary band adopting a compound structure consisting of three narrower secondary rings [3]. References: [1] Boote & Thomas, Phys. Fluids vol. 11(8), p. 2020 (1999), [2] Tirumkudulu et al., Phys. Fluids vol. 12(6), p. 1615 (2000), [3] Thomas et al., Phys. Fluids vol. 13 (9), pages not yet known (2001)

Thomas, Peter J.; Riddell, Gareth D.; King, Gregory P.

2001-11-01

181

Spectral responses in granular compaction  

NASA Astrophysics Data System (ADS)

I study the compaction of a granular pack under periodic tapping. The magnitude of acceleration ? at each tap is modulated with frequency ? and amplitude ??: ?(t) = ?DC + ??(?t), where t is time measured by the number of taps. From the temporal modulation ?v in packing volume v, frequency- locked to the modulated tapping input, we can define the real and imaginary volume susceptibilities ?v' = (?v/??) ? and ?v'' = (?v/??) ?; here ? is the phase lag between ?(t) and v(t). As a function of ?DC, ?v', ?v'' are peaked at low ?DC, a behavior reminiscent of the temperature-dependent susceptibilities in dielectric and spin glasses. For the packing of small particles (d = 0.5 mm) in ambient pressure, ?v' exhibits memory and rejuvenation effects under ?DC cycling, similar to that seen in the magnetic susceptibility of spin glasses when subjected to thermal cycling [1]. However this memory effect is suppressed for the packing of larger particles and in vacuum. The measurement of volume susceptibilities shows promise as a new way to study the packing of granular materials, and as an avenue to explore analogies between jammed grains and molecular and spin glasses. [3pt] [1] K. Jonason et al., Phys. Rev. Lett. 81, 3243 (1998).

Zou, Ling-Nan

2009-03-01

182

Nonlinear Sound during Granular Impact  

E-print Network

How do dynamic stresses propagate in granular material after a high-speed impact? This occurs often in natural and industrial processes. Stress propagation in a granular material is controlled by the inter-particle force law, $f$, in terms of particle deformation, $\\delta$, often given by $f\\propto\\delta^{\\alpha}$, with $\\alpha>1$. This means that a linear wave description is invalid when dynamic stresses are large compared to the original confining pressure. With high-speed video and photoelastic grains with varying stiffness, we experimentally study how forces propagate following an impact and explain the results in terms of the nonlinear force law (we measure $\\alpha\\approx 1.4$). The spatial structure of the forces and the propagation speed, $v_f$, depend on a dimensionless parameter, $M'=t_cv_0/d$, where $v_0$ is the intruder speed at impact, $d$ is the grain diameter, and $t_c$ is a binary collision time between grains with relative speed $v_0$. For $M'\\ll 1$, propagati ng forces are chain-like, and the measured $v_f \\propto d/t_c\\propto v_b(v_0/v_b)^\\frac{\\alpha-1}{\\alpha+1}$, where $v_b$ is the bulk sound speed. For larger $M'$, the force response has a 2D character, and forces propagate faster than predicted by $d/t_c$ due to collective stiffening of a packing.

Abram H. Clark; Alec J. Petersen; Lou Kondic; R. P. Behringer

2014-08-08

183

Compaction Waves in Granular HMX  

SciTech Connect

Piston driven compaction waves in granular HMX are simulated with a two-dimensional continuum mechanics code in which individual grains are resolved. The constitutive properties of the grains are modeled with a hydrostatic pressure and a simple elastic-plastic model for the shear stress. Parameters are chosen to correspond to inert HMX. For a tightly packed random grain distribution (with initial porosity of 19%) we varied the piston velocity to obtain weak partly compacted waves and stronger fully compacted waves. The average stress and wave speed are compatible with the porous Hugoniot locus for uni- axial strain. However, the heterogeneities give rise to stress concentrations, which lead to localized plastic flow. For weak waves, plastic deformation is the dominant dissipative mechanism and leads to dispersed waves that spread out in time. In addition to dispersion, the granular heterogeneities give rise to subgrain spatial variation in the thermodynamic variables. The peaks in the temperature fluctuations, known as hot spots, are in the range such that they are the critical factor for initiation sensitivity.

E. Kober; R. Menikoff

1999-01-01

184

Linking acoustic emission signatures with grain-scale mechanical interactions during granular shearing  

NASA Astrophysics Data System (ADS)

Acoustic Emissions (AE) are high frequency (kHz range) elastic body waves, generated in deforming granular material during particle collisions, frictional slip, or other types of abrupt grain-scale mechanical interactions. The direct link with particle micro-mechanics makes AE a useful tool for gaining insights into mechanical aspects of progressive shear failure in granular material and slow granular flows. The formation of shear plane in granular matter involves numerous internal restructuring and failure events with distinct dynamics resembling features of critical phase transition. Following establishment of a shear plane, subsequent deformation involves episodic slip events interrupted by arrested flow (stick-slip behavior). We developed a model for interpreting measured AE signatures in terms of micro-failures during progressive granular shear a considering AE generation mechanisms and propagation of acoustic signals within granular material. Results from shear frame experiments include information on strains, stresses and acoustic emissions during deformation controlled tests on glass beads and sand. The number of failure associated AE event rates peaks with maximum shear resistance of the granular material. Intermittent slip events during stick-slip deformation are found to be closely related to low frequency AE events (~1kHz). Statistics of AE events and their temporal development are reproduced using a simple fiber-bundle model. A conceptual AE generation and propagation model accounts for conversion of mechanical events into elastic waves. In addition to gaining insights concerning grain-scale mechanical interactions, the AE method offers a useful tool for monitoring hazardous geologic mass movements, such as landslides, rock avalanches or debris flows.

Michlmayr, G.; Cohen, D.; Or, D.

2012-04-01

185

BOOK REVIEW: Kinetic Theory of Granular Gases  

NASA Astrophysics Data System (ADS)

Granular gases are composed of macroscopic bodies kept in motion by an external energy source such as a violent shaking. The behaviour of such systems is quantitatively different from that of ordinary molecular gases: due to the size of the constituents, external fields have a stronger effect on the dynamics and, more importantly, the kinetic energy of the gas is no longer a conserved quantity. The key role of the inelasticity of collisions has been correctly appreciated for about fifteen years, and the ensuing consequences in terms of phase behaviour or transport properties studied in an increasing and now vast body of literature. The purpose of this book is to help the newcomer to the field in acquiring the essential theoretical tools together with some numerical techniques. As emphasized by the authors—who were among the pioneers in the domain— the content could be covered in a one semester course for advanced undergraduates, or it could be incorporated in a more general course dealing with the statistical mechanics of dissipative systems. The book is self-contained, clear, and avoids mathematical complications. In order to elucidate the main physical ideas, heuristic points of views are sometimes preferred to a more rigorous route that would lead to a longer discussion. The 28 chapters are short; they offer exercises and worked examples, solved at the end of the book. Each part is supplemented with a relevant foreword and a useful summary including take-home messages. The editorial work is of good quality, with very few typographical errors. In spite of the title, kinetic theory stricto sensu is not the crux of the matter covered. The authors discuss the consequences of the molecular chaos assumption both at the individual particle level and in terms of collective behaviour. The first part of the book addresses the mechanics of grain collisions. It is emphasized that considering the coefficient of restitution ? —a central quantity governing the inelasticity of inter-grain encounters—as velocity independent is inconsistent with the mechanical point of view. An asymptotic expression for the impact velocity dependence of ? is therefore derived for visco-elastic spheres. The important inelastic Boltzmann equation is introduced in part II and the associated velocity distribution characterized for a force-free medium (so-called free cooling regime). Transport processes can then be analyzed in part III at the single particle level, and part IV from a more macroscopic viewpoint. The corresponding Chapman Enskog-like hydrodynamic approach is worked out in detail, in a clear fashion. Finally, the tendency of granular gases to develop instabilities is illustrated in part V where the hydrodynamic picture plays a pivotal role. This book clearly sets the stage. For the sake of simplicity, the authors have discarded some subtle points, such as the open questions underlying the hydrodynamic description (why include the temperature among the hydrodynamic modes, and what about the separation of space and time scales between kinetic and hydrodynamic excitations?). Such omissions are understandable. To a certain extent however, the scope of the book is centered on previous work by the authors, and I have a few regrets. Special emphasis is put on the (variable ?) visco-elastic model, which enhances the technical difficulty of the presentation. On the other hand, the important physical effects including scaling laws, hydrodynamic behaviour and structure formation, can be understood in two steps, from the results derived within the much simpler constant ? model, allowing subsequently \\varepsilon to depend on the granular temperature. The authors justify their choice with the inconsistency of the constant ? route. The improvements brought by the visco-elastic model remain to be assessed, since the rotational degrees of freedom, discarded in the book, play an important role and require due consideration of both tangential and normal restitution coefficients, that are again velocity dependent. This seems to be the price of a cons

Trizac, Emmanuel

2005-11-01

186

Can stitches get wet?  

PubMed

This study was performed to answer the question of whether or not a patient can wet stitches after a minor soft-tissue surgical procedure without increasing the incidence of infection or disruption of the wound. One hundred consecutive patients underwent an excision of a skin or soft-tissue lesion closed either primarily or with a local flap. Monofilament nylon was used. There were 55 benign lesions and 45 malignant lesions. All procedures were performed using local anesthesia on an ambulatory basis. All patients were asked to wash the wounds with soap and water twice a day starting the morning after surgery. All wounds healed without any infections and without any disruption or dehiscence of the wounds. PMID:3336642

Noe, J M; Keller, M

1988-01-01

187

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

188

Numerical Simulations of Granular Processes  

NASA Astrophysics Data System (ADS)

Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a completely different gravitational environment than on the Earth. Understanding and modeling these motions can aid in the interpretation of imaged surface features that may exhibit signatures of constituent material properties. Also, upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the parallelized N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). Ongoing and recently completed projects include: impacts into granular materials using different projectile shapes [5]; possible tidal resurfacing of asteroid Apophis during its 2029 encounter [6]; the Brazil-nut effect in low gravity [7]; and avalanche modeling.Acknowledgements: DCR acknowledges NASA (grants NNX08AM39G, NNX10AQ01G, NNX12AG29G) and NSF (AST1009579). PM acknowledges the French agency CNES. SRS works on the NEOShield Project funded under the European Commission’s FP7 program agreement No. 282703. SM acknowledges support from the Center for Theory and Computation at U Maryland and the Dundee Fellowship at U Dundee. Most simulations were performed using the YORP cluster in the Dept. of Astronomy at U Maryland and on the Deepthought High-Performance Computing Cluster at U Maryland.References: [1] Richardson, D.C. et al. 2000, Icarus 143, 45; [2] Stadel, J. 2001, Ph.D. Thesis, U Washington; [3] Schwartz, S.R. et al. 2012, Gran. Matt. 14, 363. [4] Schwartz, S.R. et al. 2013, Icarus 226, 67; [5] Schwartz, S.R. et al. 2014, P&SS, 10.1016/j.pss.2014.07.013; [6] Yu, Y. et al. 2014, Icarus, 10.1016/j.icarus.2014.07.027; [7] Matsumura, S. et al. 2014, MNRAS, 10.1093/mnras/stu1388.

Richardson, Derek C.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Yu, Yang; Matsumura, Soko

2014-11-01

189

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

190

Underwater wet welding of steel  

SciTech Connect

Underwater wet welding is conducted directly in water with the shielded metal arc (SMA) and flux cored arc (FCA) welding processes. Underwater wet welding has been demonstrated as an acceptable repair technique down to 100 meters (325 ft.) in depth, but wet welds have been attempted on carbon steel structures down to 200 meters (650 ft.). The primary purpose of this interpretive report is to document and evaluate current understanding of metallurgical behavior of underwater wet welds so that new welding consumables can be designed and new welding practices can be developed for fabrication and repair of high strength steel structures at greater depths. First the pyrometallurgical and physical metallurgy behaviors of underwater weldments are discussed. Second, modifications of the welding consumables and processes are suggested to enhance the ability to apply wet welding techniques.

Ibarra, S. [Amoco Corporation Research, Naperville, IL (United States); Liu, S.; Olson, D.L. [Colorado School of Mines, Golden, CO (United States)

1995-05-01

191

Does surface roughness amplify wetting?  

PubMed

Any solid surface is intrinsically rough on the microscopic scale. In this paper, we study the effect of this roughness on the wetting properties of hydrophilic substrates. Macroscopic arguments, such as those leading to the well-known Wenzel's law, predict that surface roughness should amplify the wetting properties of such adsorbents. We use a fundamental measure density functional theory to demonstrate the opposite effect from roughness for microscopically corrugated surfaces, i.e., wetting is hindered. Based on three independent analyses we show that microscopic surface corrugation increases the wetting temperature or even makes the surface hydrophobic. Since for macroscopically corrugated surfaces the solid texture does indeed amplify wetting there must exist a crossover between two length-scale regimes that are distinguished by opposite response on surface roughening. This demonstrates how deceptive can be efforts to extend the thermodynamical laws beyond their macroscopic territory. PMID:25399155

Malijevský, Alexandr

2014-11-14

192

NMR Measurements of Granular Flow and Compaction  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) can be used to measure statistical distributions of granular flow velocity and fluctuations of velocity, as well as spatial distributions of particulate concentration, flow velocity, its fluctuations, and other parameters that may be derived from these. All measurements have been of protons in liquid-containing particles such as mustard seeds or pharmaceutical pills. Our favorite geometry has been the slowly rotating partially filled rotating drum with granular flow taking place along the free surface of the particles. All the above-mentioned parameters have been studied as well as a spatial distribution of particulate diffusion coefficients, energy dissipation due to collisions, as well as segregation of non-uniform mixtures of granular material. Finally, we describe some motions of granular material under periodic vibrations.

Fukushima, Eiichi

1998-03-01

193

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

194

Granular Material Flows with Interstitial Fluid Effects.  

National Technical Information Service (NTIS)

The research focused on experimental measurements of the rheological properties of liquid-solid and granular flows. In these flows, the viscous effects of the interstitial fluid, the inertia of the fluid and particles, and the collisional interactions of ...

M. L. Hunt, C. E. Brennen

2004-01-01

195

PPCPs removal by aerobic granular sludge membrane bioreactor.  

PubMed

An aerobic granular sludge membrane bioreactor (GMBR) was applied to the treatment of pharmaceutical and personal care products (PPCPs) wastewater. The influence of granular sludge on five antibiotic and antiphlogistic PPCPs wastewater and the removal effect of methyl alcohol and conventional organic matter were investigated while constantly reducing the density of inflow organic matter. The results showed that the sludge granulation process in the system was rapid but unstable, and that the system exhibits a dissolution-reunion dynamic equilibrium. The reactor demonstrated varying removal effects of PPCPs on different objects. The use of a GMBR was more effective for the removal of prednisolone, naproxen, and ibuprofen; the first two drugs were lower the average removal rate of which reached 98.46 and 84.02 %, respectively; whereas the average removal rate of ibuprofen was 63.32 %. By contrast, the GMBR has an insignificant degradation effect on antibiotics such as amoxicillin, indicating that such antibiotic medicine is not easily degraded by microorganisms, which plays different roles in system operation. Because of the different chemical structures and characteristics of drugs that result in various degradation behavior. During the GMBR granulation process, the value of mixed liquor volatility suspended solids (MLVSS) gradually increases from 1.5 to 4.1 g/L during the GMBR granulation process, and the removal rate of CODCr reaches up to 87.98 %. After reducing the density of organic matter is reduced, the removal rates of NH3-N and TP both reach more than 90 %, respectively. Moreover, the proposed technique is considerably effective in the removal of methanol. PMID:25038925

Zhao, Xia; Chen, Zhong-Lin; Wang, Xiao-Chun; Shen, Ji-Min; Xu, Hao

2014-12-01

196

Rheology of Weakly Vibrated Granular Media  

E-print Network

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 novel 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.

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

2013-12-02

197

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

198

Mortality of passerines adjacent to a North Carolina corn field treated with granular carbofuran.  

PubMed

Red-winged blackbirds (Agelaius phoeniceus) were collected during an epizootic in southeastern North Carolina (USA). Activity of brain cholinesterase (ChE) was inhibited by 14 to 48% in three of five specimens, and returned to normal levels after incubation. Gastrointestinal tracts were analyzed for 30 anti-ChE agents. Carbofuran, the only compound detected, was present in all specimens at levels from 5.44 to 72.7 micrograms/g wet weight. Application of granular carbofuran in an adjacent corn field, results of necropsy examinations, and chemical analyses are consistent with a diagnosis of carbofuran poisoning in these specimens. PMID:8627921

Augspurger, T; Smith, M R; Meteyer, C U; Converse, K A

1996-01-01

199

Particle shape dependence in 2D granular media  

E-print Network

Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter $\\eta$ describing the degree of distortion from a perfectly spherical shape. Encompassing most specific shape characteristics such as elongation, angularity and nonconvexity, $\\eta$ is a low-order but generic parameter that we used in a numerical benchmark test for a systematic investigation of shape-dependence in sheared granular packings composed of particles of different shapes. We find that the shear strength is an increasing function of $\\eta$ with nearly the same trend for all shapes, the differences appearing thus to be of second order compared to $\\eta$. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with $\\eta$ from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as $\\eta$ is further increased. These findings suggest that a low-order description of particle shape accounts for the principal trends of packing fraction and shear strength. Hence, the effect of second-order shape parameters may be investigated by considering different shapes at the same level of $\\eta$.

B. Saint-Cyr; K. Szarf; C. Voivret; E. Azéma; V. Richefeu; J. -Y. Delenne; G. Combe; C. Nouguier-Lehon; P. Villard; P. Sornay; M. Chaze; F. Radjaï

2012-08-02

200

Discrete Element Modeling of Complex Granular Flows  

NASA Astrophysics Data System (ADS)

Granular materials occur almost everywhere in nature, and are actively studied in many fields of research, from food industry to planetary science. One approach to the study of granular media, the continuum approach, attempts to find a constitutive law that determines the material's flow, or strain, under applied stress. The main difficulty with this approach is that granular systems exhibit different behavior under different conditions, behaving at times as an elastic solid (e.g. pile of sand), at times as a viscous fluid (e.g. when poured), or even as a gas (e.g. when shaken). Even if all these physics are accounted for, numerical implementation is made difficult by the wide and often discontinuous ranges in continuum density and sound speed. A different approach is Discrete Element Modeling (DEM). Here the goal is to directly model every grain in the system as a rigid body subject to various body and surface forces. The advantage of this method is that it treats all of the above regimes in the same way, and can easily deal with a system moving back and forth between regimes. But as a granular system typically contains a multitude of individual grains, the direct integration of the system can be very computationally expensive. For this reason most DEM codes are limited to spherical grains of uniform size. However, spherical grains often cannot replicate the behavior of real world granular systems. A simple pile of spherical grains, for example, relies on static friction alone to keep its shape, while in reality a pile of irregular grains can maintain a much steeper angle by interlocking force chains. In the present study we employ a commercial DEM, nVidia's PhysX Engine, originally designed for the game and animation industry, to simulate complex granular flows with irregular, non-spherical grains. This engine runs as a multi threaded process and can be GPU accelerated. We demonstrate the code's ability to physically model granular materials in the three regimes mentioned above: (1) a static and steep granular pile; (2) granular flow with a complex velocity field; and (3) an agitated granular pile resulting in size based segregation. We compare our simulations to laboratory experiments in the first and third regimes, and to a known empirical constitutive law (Jop et al. 2006) in the second. We discuss application of this code in studies of several planetary systems, including analysis of the tensile strength of comets from evidence of tidal disruption, and bulking and banding on rubble-pile asteroids, as an indication of their seismic history.

Movshovitz, N.; Asphaug, E. I.

2010-12-01

201

Granular acoustics of polyhedral particles  

NASA Astrophysics Data System (ADS)

Our previous time-of-flight studies with two-dimensional polygonal simulations and one-and three-dimensional experiments showed that the sound-velocity in granular materials in one and two dimensions is of the order of 10% of that of the bulk material, while in three dimensions with spherical beads, it is only of the order of one percent. The conclusion was that the force network in three dimensions leads to a reduction of the sound velocity compared to two dimensions. With our newly completed fully three dimensional discrete element method with polyhedral particles, we investigate the relation between particle shape, size dispersion and sound velocity. The force-law is able to reproduce the sound velocity of the bulk material for space-filling particle packings. We find that the sound velocities in polyhedral assemblies are about 3% to 5% of the bulk sound velocities. This means that the influence of the particle geometry on the contact is significant. Aggregates with particles with many surfaces show higher sound velocities than those with sharp edges. Additionally, solitonic waves were observed which propagated in front of the sound-waves, but only in a relatively short range.

Cheng, Wei Shen; Chen, Jian; Matuttis, Hans-Georg

2013-06-01

202

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

203

Next Generation Wet Electrostatic Precipitators  

Microsoft Academic Search

Multi-pollutant control technologies will become more important in the future. This new membrane wet electrostatic precipitator (WESP) system is ideally suited to, and very cost effective for, removing PM2.5, SO3 and Hg +2 after limestone wet flue gas desulphurization (WFGD) scrubbers in the utility industry. Several coal-fired utilities have been experiencing increased SO3 emissions from their existing WFGD scrubbers, especially

Hardik G Shah; John C Caine

204

Wet Science -- a Theorist's Perspective  

NASA Astrophysics Data System (ADS)

The interplay between theoretical advances and observational discovery has been truly dynamic in WET science. In this brief paper I highlight a few examples of this interplay from the point of view of a ``linear theorist'': the PG 1159 stars and the pulsating DBs. The data provided by the WET gives theorists cause for celebration and reflection; the failings in particular provide useful future directions for theorists in light of the observational challenges.

Kawaler, S. D.

205

Pore-Scale Investigation on Stress-Dependent Characteristics of Granular Packs and Their Impact on Multiphase Fluid Distribution  

NASA Astrophysics Data System (ADS)

The pore-scale dynamics that govern multiphase flow under variable stress conditions are not well understood. This lack of fundamental understanding limits our ability to quantitatively predict multiphase flow and fluid distributions in natural geologic systems. In this research, we focus on pore-scale, single and multiphase flow properties that impact displacement mechanisms and residual trapping of non-wetting phase under varying stress conditions. X-ray micro-tomography is used to image pore structures and distribution of wetting and non-wetting fluids in water-wet synthetic granular packs, under dynamic load. Micro-tomography images are also used to determine structural features such as medial axis, surface area, and pore body and throat distribution; while the corresponding transport properties are determined from Lattice-Boltzmann simulations performed on lattice replicas of the imaged specimens. Results are used to investigate how inter-granular deformation mechanisms affect fluid displacement and residual trapping at the pore-scale. This will improve our understanding of the dynamic interaction of mechanical deformation and fluid flow during enhanced oil recovery and geologic CO2 sequestration. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Torrealba, V.; Karpyn, Z.; Yoon, H.; Hart, D. B.; Klise, K. A.

2013-12-01

206

Treatment of saline wastewater in SBR aerobic granular reactors.  

PubMed

Fish canning effluents characterized by their salt content, up to 30 g NaCl/L, were treated, previously diluted to desired concentration, in a SBR where aerobic granular sludge was produced. The formation of mature aerobic granules occurred after 75 days of operation with 3.4 mm of diameter, SVI of 30 mL/g VSS and density around 60 g VSS/L-granule. Treated organic loading rates were up to 1.72 kg COD/(m3.d) with fully organic matter depletion. Ammonia nitrogen was removed via nitrification-denitrification up to 40% when nitrogen loading rates were of 0.18 kg N/(m3.d). The presence of salt in the treated effluent did not cause a detrimental effect on the operation of the reactor once the aerobic granules were formed. PMID:18701804

Figueroa, M; Mosquera-Corral, A; Campos, J L; Méndez, R

2008-01-01

207

Heterogeneous structure of granular aggregates with capillary interactions  

E-print Network

We investigate the spatial structure of cohesive granular matter with spheres floating at an air-liquid interface that form disordered close packings with pores in between. The interface is slowly lowered in a conical container to uniformly compress and study the system as a function of area fraction $\\phi$. We find that the free area distributions associated with Voronoi cells show significant exponential tails indicating greater heterogeneity compared with random distributions at low $\\phi$ with a crossover towards a $\\Gamma$-distribution as $\\phi$ is increased. Further, we find significant short range order as measured by the radial correlation function and the orientational order parameter even at low and intermediate $\\phi$, which is absent when particles interact only sterically.

Michael Berhanu; Arshad Kudrolli

2010-02-15

208

Blast shocks in quasi-two-dimensional supersonic granular flows.  

PubMed

In a thin, dilute, and fast flowing granular layer, the impact of a small sphere generates a fast growing hole devoid of matter. The growth of this hole is studied in detail, and its dynamics is found to mimic that of blast shocks in gases. This dynamics can be decomposed into two stages: a fast initial stage (the blast) and a slower growth regime whose growth velocity is given by the speed of sound in the medium used. A simple model using ingredients already invoked for the case of blast shocks in gases but including the inelastic nature of collisions between grains accounts accurately for our results. The system studied here allows for a detailed study of the full dynamics of a blast as it relaxes from a strong to a weak shock and later to an acoustic disturbance. PMID:20366097

Boudet, J F; Cassagne, J; Kellay, H

2009-11-27

209

Blast Shocks in Quasi-Two-Dimensional Supersonic Granular Flows  

NASA Astrophysics Data System (ADS)

In a thin, dilute, and fast flowing granular layer, the impact of a small sphere generates a fast growing hole devoid of matter. The growth of this hole is studied in detail, and its dynamics is found to mimic that of blast shocks in gases. This dynamics can be decomposed into two stages: a fast initial stage (the blast) and a slower growth regime whose growth velocity is given by the speed of sound in the medium used. A simple model using ingredients already invoked for the case of blast shocks in gases but including the inelastic nature of collisions between grains accounts accurately for our results. The system studied here allows for a detailed study of the full dynamics of a blast as it relaxes from a strong to a weak shock and later to an acoustic disturbance.

Boudet, J. F.; Cassagne, J.; Kellay, H.

2009-11-01

210

Combined granular-lattice ('Avellino') corneal dystrophy.  

PubMed Central

BACKGROUND/PURPOSE: In 1988, a report was published describing the histopathologic examination of corneal buttons of 4 patients who had undergone unilateral keratoplasty because of decreased vision caused by what had been diagnosed clinically as granular dystrophy. But on pathologic examination, lesions characteristic of both granular dystrophy and lattice dystrophy were found in each of the 4 corneal buttons. The patients came from 3 different families, each of which traced its origin to the Italian province of Avellino. We studied the clinical and histopathological features of 4 corneas affected by combined granular-lattice dystrophy, adding thereby to the total of 12 other corneas that have been so-described in the literature. METHODS: Two women underwent bilateral penetrating keratoplasty for what was diagnosed clinically as Reis-Bücklers dystrophy in the first patient, and as granular dystrophy in the second patient. We studied all 4 corneas pathologically, using both conventional hematoxylin and eosin stains as well as special histochemical techniques. RESULTS: All 4 corneas contained lesions characteristic of both granular dystrophy and lattice dystrophy, a circumstance that has given rise to the name "combined granular-lattice dystrophy." The patients are not known to be of Italian ancestry. CONCLUSIONS: Three clinical signs characterize combined granular-lattice dystrophy: (1) anterior stromal discrete, grayish-white deposits; (2) lattice lesions located in mid-stroma to posterior stroma; and (3) anterior stromal haze. Both clinically and histopathologically, the lattice lesions are of greater diameter than are those that occur in lattice dystrophy type I. In the past few years, striking advances have been made in understanding the genetics of combined granular-lattice dystrophy. The most recent of these was published just 2 months before the 1997 meeting of the American Ophthalmological Society, and establishes a common molecular origin for granular dystrophy, lattice dystrophy type I, Avellino dystrophy, and Reis-Bücklers dystrophy. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 1 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10 PMID:9440163

Ferry, A P; Benson, W H; Weinberg, R S

1997-01-01

211

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

212

Continuous shearing of dense and wet granular materials in a torsional rheometer  

E-print Network

. 00165 0. 002 0. 00161 16 20 25 30 5. 08 5. 37 5. 97 6. 42 5. 34 6, 75 5. 87 7. 32 6. 41 8. 86 7. 07 3. 66 3. 95 9. 36 7. 87 4. 38 4. 38755 4. 65 5. 48419 4. 84 6. 85491 4. 71 8. 22542 0. 42310 0. 43339 0. 43954 0. 43601 1. 37555... 0. 004 0. 00335 0. 004 0. 00330 35 12 7. 19 10. 36 10. 73 11. 42 9. 23 8. 12 12. 03 11. 1 12. 27 11. 48 13. 17 12. 28 4. 27 5. 27 5. 58 6. 17 6. 36 6. 73 5. 02 9. 59543 5. 72 3. 02395 5. 89 3. 29874 6. 17 4. 39801 0. 50303 0...

Kannan, Raguraman

2012-06-07

213

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

214

Stochastic and deterministic models for dense granular flow  

E-print Network

Granular materials such as sand or gravel surround us everyday and yet remain poorly understood. In this thesis, two models are developed for dense granular flow, each capable of predicting flows with accuracy in multiple ...

Kamrin, Kenneth Norman

2008-01-01

215

Physica D 133 (1999) 117 Predictability and granular materials  

E-print Network

. Keywords: Granular materials; Stress chains; Fluctuations; Friction 1. Introduction Granular materials, including unpredictability associated with static friction and strong fluctuational effects. Here, we between grains are relatively simple ones. These include hard body interactions (to a first approximation

Kondic, Lou

216

Flow regime transitions in dense granular suspensions: rheology, microstructural characterisation and constitutive modelling  

E-print Network

Simple shear flow of dense, density matched, non-Brownian granular suspensions is simulated using the discrete element method, taking particle-particle contact and hydrodynamic lubrication into account. The resulting flow regimes are mapped in the parametric space of solid volume fraction, shear rate and interstitial fluid viscosity. It is observed that for low fluid viscosity, the rheological behavior is reminiscent of dry granular flow. For moderate fluid viscosity, a quasi-Newtonian regime exists at low shear rate below a critical volume fraction $\\phi_c$, transitioning to a shear thickening and then an upper viscous regime as shear rate is increased. Above $\\phi_c$, a quasi-static regime transits to a viscous one as shear rate is increased. The transitions between rheological regimes are associated with the evolving contribution of lubrication to the suspension stress as a function of shear rate. We demonstrate the role of interstitial fluid viscosity in these transitions, consistently linking dry and wet rheology. Transitions in microscopic phenomena such as inter-particle force distribution, fabric and correlation length are found to correspond to those in the macroscopic flow. Motivated by the bulk rheology, a constitutive model is proposed combining a viscous pressure term with a dry granular model proposed by Chialvo, Sun and Sundaresan [Phys. Rev. E. $\\mathbf{85}$, 021305 (2012)]. The model is shown to successfully capture the flow regime transitions.

Christopher Ness; Jin Sun

2014-09-03

217

Case for diagnosis. Granular cell tumor.  

PubMed

Granular cell tumor is a rare benign neoplasm of neural origin. We report the case of a female patient, 27 years old presenting a brown-red nodule in the right arm, which pathological examination showed to be formed by polygonal cells with eosinophilic granular cytoplasm and immunohistochemistry positive for S100 protein and CD68. Granular cell tumor is usually solitary and in half the cases located in the head and neck areas, 30% of these in the tongue. It is most frequent between the third and fifth decades of life in women and people of African-American ethnicity. Its origination is controversial, including the possible origins in muscle, fibroblasts, neural crest, neural sheath or histiocytes. The positivity for S-100 and CD68 suggest the neural origin. PMID:24474119

Lage, Thaiane Lima; Miranda, Mario Fernando Ribeiro de; Bittencourt, Maraya de Jesus Semblano; Dias, Carolina Moraes; Parijós, Amanda Magno de; Raiol, Theisla Kely Azevedo

2013-01-01

218

Flow and jamming of sheared granular media  

NASA Astrophysics Data System (ADS)

Granular materials, such as athermal suspensions, can either be jammed and rigid, or yield and flow. Recent experiments on granular suspensions in a annular shear cell (vibrated and/or sheared) show a hysteretic freezing and melting transition [1, 2]: a crystallised state is found, which can be melted by sufficient shear. The question is open on what are the mechanisms underlying these phenomena and which are the control parameters. Via Molecular Dynamics simulations, we study the rheology of vibrated and sheared granular materials [3]. In particular, we aim to understand the nature of a critical line separating crystallised and melted states and the "jammed" region in the phase diagram, as well as the connections with thermal glass formers and colloidal suspensions.

Ciamarra, M. Pica; Nicodemi, M.; Coniglio, A.

2009-06-01

219

Unstable blast shocks in dilute granular flows.  

PubMed

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. PMID:23767525

Boudet, J F; Kellay, H

2013-05-01

220

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

221

Velocities and forces in flowing granular systems  

NASA Astrophysics Data System (ADS)

Under the action of external forces, granular systems can flow like fluids. An important question is whether there is an appropriate continuum description for the transport properties of granular fluids. A related question is whether the statistical mechanics of conventional fluids may be adapted to granular fluids. The answers are greatly complicated by the inelastic interactions between grains, which not only dissipate energy but may also be the source of unusual correlations in structure and dynamics of the fluid. In our experiments, we excite granular media into homogenous, stationary states to consider these questions in relatively simple settings. In 3D gravity-driven flows, we measure by light scattering the mean values of a number of microscopic quantities including local velocity fluctuations. To study the spectrum of fluctuations, and spatial and temporal correlation of fluctuations, we turn to 2D systems. We measure collisional forces at the boundary of a dense, gravity-driven flow and find that they are exponentially distributed, just as in static granular media where stress propagates mainly along linear chains. Collision times have a broad distribution suggesting that the hydrodynamics is unlike that of a conventional fluid. We also study by video imaging more dilute 2D systems (excited by vibrations) where we might expect the effect of correlations to be diminished. Yet here too the velocity distribution is exponential and not Maxwell-Boltzmann. The strong coupling of density and inelastic dissipation in granular media does not seem to be responsible for this, as the shape of the spectrum is unchanged even at fixed local density. I thank F. Rouyer, P.Silva, N. Easwar, E. Longhi and D.J. Durian for their contributions to this research. The work at UMass is supported by a grant from the PRF and by NSF DMR-9874833.

Menon, Narayanan

2000-03-01

222

Wetting film dynamics and stability  

E-print Network

Although the wetting films are similar in many aspects to other thin liquid films, there are some differences in their behavior, too. In contrast to soap and emulsion films, whose surfaces are homogeneous, solid substrates of wetting films are heterogeneous as a rule, unless special measures for their homogenization are taken. Here we mean primarily heterogeneous distribution of surface energy leading to existence of hydrophobic domains on hydrophilic surfaces and vice versa. As is known, such hydrophobic domains could play the role of gas-phase nucleation centers and it is widely accepted nowadays that nano-bubbles can be formed there. The present paper reviews the effect of nano-bubbles adhered at solid surface on stability of wetting films. It is shown that the existence of nano-bubbles is crucial for the lifetime of wetting films. Another peculiarity typical for hydrophobic solid surface, the so-called slippage effect, is also investigated and its contribution to the dispersion equation of capillary waves on wetting films is accounted for.

B. Radoev; K. W. Stoeckelhuber; R. Tsekov; P. Letocart

2011-05-05

223

Formation of aerobic granular sludge biofilms for sustainable wastewater treatment  

E-print Network

ENAC/ Formation of aerobic granular sludge biofilms for sustainable wastewater treatment David G to aerobic granular microbial biofilms (Confocal laser scanning microscopy analysis) Floc viscous bulking) Exopolysaccharide-producing Zoogloea spp. form the early-stage aerobic granular biofilms, and then decline

224

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

225

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

226

Particle Scale Dynamics in Granular Impact  

E-print Network

We perform an experimental study of granular impact, where intruders strike 2D beds of photoelastic disks from above. High-speed video captures the intruder dynamics and the local granular force response, allowing investigation of grain-scale mechanisms in this process. We observe rich acoustic behavior at the leading edge of the intruder, strongly fluctuating in space and time, and we show that this acoustic activity controls the intruder deceleration, including large force fluctuations at short time scales. The average intruder dynamics match previous studies using empirical force laws, suggesting a new microscopic picture, where acoustic energy is carried away and dissipated.

Abram. H. Clark; Lou Kondic; Robert P. Behringer

2012-08-28

227

Temporally heterogeneous dynamics in granular flows  

E-print Network

Granular simulations are used to probe the particle scale dynamics at short, intermediate, and long time scales for gravity driven, dense granular flows down an inclined plane. On approach to the angle of repose, where motion ceases, the dynamics become intermittent over intermediate times, with strong temporal correlations between particle motions -- temporally heterogeneous dynamics. This intermittency is characterised through large scale structural events whereby the contact network periodically spans the system. A characteristic time scale associated with these processes increases as the stopped state is approached. These features are discussed in the context of the dynamics of supercooled liquids near the glass transition.

L. E. Silbert

2005-01-26

228

Granular Impact Dynamics: Acoustics and Fluctuations  

E-print Network

In the corresponding fluid dynamics video, created for the APS DFD 2012 Gallery of Fluid Motion, we show high-speed videos of 2D granular impact experiments, where an intruder strikes a collection of bidisperse photoelastic disks from above. We discuss the force beneath the intruder, which is strongly fluctuating in space and time. These fluctuations correspond to acoustic pulses which propagate into the medium. Analysis shows that this process, in our experiments, is dominated by collisions with grain clusters. The energy from these collisions is carried into the granular medium along networks of grains, where is it dissipated.

Abram H. Clark; R. P. Behringer

2012-10-12

229

Granular Elasticity’ and the loss of elastic stability in granular materials  

SciTech Connect

A recently proposed hyperelastic model for granular materials, called "granular elasticity", identifies a yield angle as a result of thermodynamic instability. GE gives yield angles that are smaller than those found in real materials; a generalization of the theory is considered here that includes dependence on the third strain invariant. This generalization proves unsuccessful, as it gives smaller, not larger, yield angles. Fully convex hyperelastic models are identified as a point for future investigation.

P. W. Humrickhouse

2009-07-01

230

Design and analysis of jammable granular systems  

E-print Network

Jamming--the mechanism by which granular media can transition between liquid-like and solid-like states-has recently been demonstrated as a variable strength and stiffness mechanism in a range of applications. As a low-cost ...

Cheng, Nadia G. (Nadia Gen San)

2013-01-01

231

Relational Granularity for Hypergraphs John G. Stell  

E-print Network

cannot detect individual elements ­ all we can see are the gran- ules. This initial starting point vertices) and no edges (or arcs). For a simple example we can consider a graph as modelling a railway rather than with just one or two edges. In giving a granular view of a railway network we might need

Stell, John

232

USE OF SODIUM CHLORIDE IN GRANULAR BASES  

Microsoft Academic Search

The purpose of this work is to study the mechanical properties of granular bases added with NaCl. After conventional characterization tests, including Atterberg limits and grain size distribution, compaction tests were carried out to find optimal water contents and maximum dry densities. Finally, by use of mechanical tests such as CBR, non-confined compression and diametral compression tests, strength differences between

Oscar Javier; Reyes Ortiz; Javier Fernando; Camacho Tauta; Juan Ricardo Troncoso Rivera

233

Contact forces in a granular packing  

Microsoft Academic Search

We present the results of a systematic numerical investigation of force distributions in granular packings. We find that all the main features of force transmission previously established for two-dimensional systems of hard particles hold in three-dimensional systems and for soft particles, too. In particular, the probability distribution of normal forces falls off exponentially for forces above the mean force. For

Farhang Radjai; Stéphane Roux; Jean Jacques Moreau

1999-01-01

234

Sound wave acceleration in granular materials  

Microsoft Academic Search

The goal of this study is a better understanding of the numerous sound propagation mechanisms in granular materials. In a static, regular (crystal), 3D packing, a small perturbation is created on one side and examined during its propagation through frictionless and frictional packings. The perturbation can be applied in longitudinal and shear direction in order to excite dieren t modes

O Mouraillea

235

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

236

Granular Gas in a Periodic Lattice  

ERIC Educational Resources Information Center

Glass beads are placed in the compartments of a horizontal square grid. This grid is then vertically shaken. According to the reduced acceleration [image omitted] of the system, the granular material exhibits various behaviours. By counting the number of beads in each compartment after shaking, it is possible to define three regimes. At low…

Dorbolo, S.; Brandenbourger, M.; Damanet, F.; Dister, H.; Ludewig, F.; Terwagne, D.; Lumay, G.; Vandewalle, N.

2011-01-01

237

ENGINEERING BULLETIN: GRANULAR ACTIVATED CARBON TREATMENT  

EPA Science Inventory

Granular activated carbon (GAC) treatment is a physicochemical process that removes a wide variety of contaminants by adsorbing them from liquid and gas streams [1, p. 6-3]. This treatment is most commonly used to separate organic contaminants from water or air; however, it can b...

238

NMR Measurements of Granular Flow and Compaction  

Microsoft Academic Search

Nuclear magnetic resonance (NMR) can be used to measure statistical distributions of granular flow velocity and fluctuations of velocity, as well as spatial distributions of particulate concentration, flow velocity, its fluctuations, and other parameters that may be derived from these. All measurements have been of protons in liquid-containing particles such as mustard seeds or pharmaceutical pills. Our favorite geometry has

Eiichi Fukushima

1998-01-01

239

Scattering of solitary waves in granular media  

E-print Network

A detailed numerical study of the scattering of solitary waves by a barrier, in a granular media with Hertzian contact, shows the existence of secondary multipulse structures generated at the interface of two "sonic vacua", which have a similar structure as the one previously found by Nesterenko and coworkers.

Lautaro Vergara

2005-03-18

240

Rheology of confined granular flows Patrick RICHARD  

E-print Network

, rotating around its axis at a controlled speed. Stationary states can be studied in such kind region below. They are strongly influenced by sidewalls [1, 2]. Interestingly, the gas, liquid and solid configurations. The first one is a rotating drum [3, 5, 4, 6], a cylinder, partly filled with granular material

Boyer, Edmond

241

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...

242

Rheology of Dense Granular Mixtures and Slurries  

NASA Astrophysics Data System (ADS)

Dense granular flows, characterized by multiple contacts between grains, are common in many industrial processes and natural events, such as debris flows. Understanding the characteristics of these flows is crucial to predict quantities such as bedrock erosion and distance traveled by debris flows. However, the rheological properties of these flows are complicated due to wide particle size distribution and presence of interstitial fluids. Models for dense sheared granular materials indicate that their rheological properties depend on particle size, but the representative particle size for mixtures is not obvious. Using the discrete element method (DEM) we study sheared granular binary mixtures in a Couette cell to determine the relationship and rheological parameters such as stress and effective coefficient of friction and particle size distribution. The results indicate that the stress does not depend monotonically on the average particle size as it does in models derived from simple dimensional consideration. The stress has an additional dependence on a measure of the effective free volume per particle that is adapted from an expression for packing of monosized particles near the jammed state. The effective friction also has a complicated dependence on particle size distribution. For these systems of relatively hard particles, these relationships are governed largely by the ratio between average collision times and mean-free-path times. The characteristics of shallow free surface flows, important for applications such as debris flows, are different from confined systems. To address this, we also study shallow granular flows in a rotating drum. The stress at the boundary, height profiles and segregation patterns from DEM simulations are quantitatively similar to the results obtained from physical experiments of shallow granular flows in rotating drums. Individual particle-bed impacts rather than enduring contacts dominate the largest forces on the drum bed, which vary as the grain size squared and the 1.2 power of particle-bed impact velocity. In the presence of interstitial fluids (water + fine particles) these characteristics might change significantly. Modeling particle-particle and fluid-particle interaction in dense granular flows is still a challenge. We propose a modification to the DEM to account for specific effects of the interstitial fluid on the dynamics of certain granular fluid flows. The results from this simple model are qualitatively similar to results from experiments.

Tewoldebrhan, Bereket Yohannes

243

Controls of Bedrock Erosion by Granular Flows  

NASA Astrophysics Data System (ADS)

There is mounting evidence that episodic scour by debris flows can be a significant transport and erosional process in high gradient valleys, yet there is not an agreed upon mechanical framework of how debris flows erode these steep bedrock valleys. To understand the evolution of steep topography we must understand the physical processes that control valley incision by debris flows. Field observations in many different settings and rock types indicate an abundance of wear features characteristic of brittle failure due to discrete particle impacts. Further, close inspection of smooth bedrock channels can reveal occasional scratches that indicate wear by sliding debris, a phenomenon also seen in laboratory experiments. With these observations in mind we use discrete element simulations of dry granular flows to investigate interactions between the flow and the subjacent bed. With this type of computer simulation, particle-particle and particle-boundary interactions are modeled explicitly for every particle and boundary in the system. This allows measurement of variables difficult to characterize in experiments and continuum type models. The granular simulations are first validated with comparisons to quantities measurable in analog experiments. We then use the simulations to explore two aspects of granular flow. First, how does the efficiency of impact and abrasion wear of a granular flow change as a function of field-measurable flow characteristics? Second, what aspects of the actual granular mechanics change to make the flow more or less erosive? We hypothesize that changes in granular properties such as distance traveled between impacts, the extent of force networks, contact time distributions, and slide distance will correlate with changes in erosive efficiency of the flow. We track these properties throughout the flow simulation. Using impact energy and particle-bed contact forces as proxies for the erosional potential of the flow the simulations predict how the magnitude of bed erosion should scale with field-measurable properties (e.g. grain size distribution, flow thickness, slope of the bed and bed roughness). These simulations illuminate the link between granular mechanics, scaling behavior, and field-measurable properties, and this in turn provides elements needed to formulate a mechanical theory for impact wear by debris flows.

McCoy, S. W.; Tucker, G. E.

2008-12-01

244

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

245

Scaling of convective velocity in a vertically vibrated granular bed  

E-print Network

We experimentally study the velocity scaling of granular convection which is a possible mechanism of the regolith migration on the surface of small asteroids. In order to evaluate the contribution of granular convection to the regolith migration, the velocity of granular convection under the microgravity condition has to be revealed. Although it is hard to control the gravitational acceleration in laboratory experiments, scaling relations involving the gravitational effect can be evaluated by systematic experiments. Therefore, we perform such a systematic experiment of the vibration-induced granular convection. From the experimental data, a scaling form for the granular convective velocity is obtained. The obtained scaling form implies that the granular convective velocity can be decomposed into two characteristic velocity components: vibrational and gravitational velocities. In addition, the system size dependence is also scaled. According to the scaling form, the granular convective velocity $v$ depends on the gravitational acceleration $g$ as $v \\propto g^{0.97}$ when the normalized vibrational acceleration is fixed.

Tomoya M. Yamada; Hiroaki Katsuragi

2014-04-01

246

Scaling of convective velocity in a vertically vibrated granular bed  

NASA Astrophysics Data System (ADS)

We experimentally study the velocity scaling of granular convection which is a possible mechanism of the regolith migration on the surface of small asteroids. In order to evaluate the contribution of granular convection to the regolith migration, the velocity of granular convection under the microgravity condition has to be revealed. Although it is hard to control the gravitational acceleration in laboratory experiments, scaling relations involving the gravitational effect can be evaluated by systematic experiments. Therefore, we perform such a systematic experiment of the vibration-induced granular convection. From the experimental data, a scaling form for the granular convective velocity is obtained. The obtained scaling form implies that the granular convective velocity can be decomposed into two characteristic velocity components: vibrational and gravitational velocities. In addition, the system size dependence is also scaled. According to the scaling form, the granular convective velocity v depends on the gravitational acceleration g as v?g0.97 when the normalized vibrational acceleration is fixed.

Yamada, Tomoya M.; Katsuragi, Hiroaki

2014-10-01

247

CEILCOTE IONIZING WET SCRUBBER EVALUATION  

EPA Science Inventory

The report gives results of an evaluation of a Ceilcote ionizing wet scrubber installed on a refractory brick kiln. Tests involved particulate mass emission, particle size distribution, and opacity. Overall efficiency was 93% with an average outlet opacity determined with a heate...

248

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

249

Carbon and nitrogen removal in a granular bed baffled reactor.  

PubMed

The application of an anaerobic five compartment granular bed baffled reactor (GRABBR) was investigated with brewery wastewater for combined carbon and nitrate removal, with a separate downstream nitrification unit for converting ammonia to nitrate. The GRABBR was operated at an organic loading rate of 3.57 kg chemical oxygen demand (COD) m(-3) d(-1) and ammoniacal nitrogen (NH4-N) loading rate of 0.13 kg NH4-N m(-3) d(-1) when nitrified effluent from a downstream nitrification unit was recycled to the feed point of the GRABBR. Carbonaceous matter and nitrate were removed simultaneously in the GRABBR at different recycle to influent ratios (from 1 to 2), with nitrogen oxide (nitrate and nitrite nitrogen, NOx-N) loading rates varying from 0.04 to 0.05 kg NOx-N m(-3) d(-1). At all recycle to influent ratios, COD removal efficiency of 97% to 98% were observed in the GRABBR, and over 99% by the two-stage treatment configuration (i.e. GRABBR and nitrification unit). All the nitrates added to the GRABBR were denitrified in the first three compartments of the system. For all the recycle to influent ratios studied, almost all ammonia was converted to nitrate nitrogen with only small traces of nitrite nitrogen in the nitrification unit. Methane production was observed throughout the experimental period with its composition varying from 25% to 50%, showing that simultaneous methanogenesis and denitrification occurred. This study shows that a GRABBR could bring about a high degree of carbon and nitrate removal, with simultaneous methanogenesis and denitrification, due to plug flow granular bed multi-stage characteristics of the bioreactor. PMID:16506516

Baloch, M I; Akunna, J C; Collier, P J

2006-02-01

250

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

251

7 CFR 51.3206 - Wet sunscald.  

Code of Federal Regulations, 2011 CFR

...VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States Standards for Grades of Bermuda-Granex-Grano Type Onions Definitions § 51.3206 Wet sunscald. Wet sunscald means any sunscald which is...

2011-01-01

252

7 CFR 51.2845 - Wet sunscald.  

Code of Federal Regulations, 2011 CFR

...OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States Standards for Grades of Onions (Other Than Bermuda-Granex-Grano and Creole Types) Definitions § 51.2845 Wet sunscald. Wet sunscald means sunscald which...

2011-01-01

253

7 CFR 51.491 - Wet slip.  

Code of Federal Regulations, 2011 CFR

...Wet slip means a condition present at time of packing in which the stem scar is abnormally large, excessively wet and slippery, yields...frequently accompanied by fresh radial growth cracks at the edge of the stem...

2011-01-01

254

Dark Matter  

NASA Astrophysics Data System (ADS)

I review the development of the concept of dark matter. The dark matter story passed through several stages, from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe and that it consists of some unknown non-baryonic particles. Dark matter is the dominant matter component in the Universe; therefore, properties of dark matter particles determine the structure of the cosmic web.

Einasto, Jaan

2013-12-01

255

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

256

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

257

Elastic waves in phononic monolayer granular membranes  

NASA Astrophysics Data System (ADS)

The vibrational properties of out-of-plane elastic waves in hexagonal monolayer granular membranes were studied theoretically. The predicted propagation modes involve an out-of-plane displacement and two rotations with axes in the membrane plane. Shear and bending rigidities at the contact between beads were considered. Both the cases of freely suspended membranes and membranes coupled to a rigid substrate were analyzed. Dispersion relations and the existence of band gaps are presented and discussed for various contact properties. For freely suspended membranes with sufficient contact bending rigidity, it is shown that complete band gaps exist. The results obtained may be of interest for testing with acoustic waves the elasticity of recently developed granular membranes composed of nanoparticles (of interest because of their phoxonic properties) and more generally for the control of designing devices for membrane wave propagation.

Tournat, Vincent; Pèrez-Arjona, Isabel; Merkel, Aurélien; Sanchez-Morcillo, Victor; Gusev, Vitalyi

2011-07-01

258

Memory effect in uniformly heated granular gases.  

PubMed

We evidence a Kovacs-like memory effect in a uniformly driven granular gas. A system of inelastic hard particles, in the low density limit, can reach a nonequilibrium steady state when properly forced. By following a certain protocol for the drive time dependence, we prepare the gas in a state where the granular temperature coincides with its long time value. The temperature subsequently does not remain constant but exhibits a nonmonotonic evolution with either a maximum or a minimum, depending on the dissipation and on the protocol. We present a theoretical analysis of this memory effect at Boltzmann-Fokker-Planck equation level and show that when dissipation exceeds a threshold, the response can be called anomalous. We find excellent agreement between the analytical predictions and direct Monte Carlo simulations. PMID:25122296

Trizac, E; Prados, A

2014-07-01

259

Memory effect in uniformly heated granular gases  

NASA Astrophysics Data System (ADS)

We evidence a Kovacs-like memory effect in a uniformly driven granular gas. A system of inelastic hard particles, in the low density limit, can reach a nonequilibrium steady state when properly forced. By following a certain protocol for the drive time dependence, we prepare the gas in a state where the granular temperature coincides with its long time value. The temperature subsequently does not remain constant but exhibits a nonmonotonic evolution with either a maximum or a minimum, depending on the dissipation and on the protocol. We present a theoretical analysis of this memory effect at Boltzmann-Fokker-Planck equation level and show that when dissipation exceeds a threshold, the response can be called anomalous. We find excellent agreement between the analytical predictions and direct Monte Carlo simulations.

Trizac, E.; Prados, A.

2014-07-01

260

Optimal design of composite granular protectors  

E-print Network

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 "wall" that represents the body to be protected and accordingly optimize the topology (arrangement), size, and material of the beads in the chain. Starting from protectors and other special granular systems that have been investigated recently in the literature, we obtain optimally randomized systems characterized by high-energy equipartition and the transformation of incident waves into interacting solitary pulses traveling in opposite directions. We consistently observe that the pulses traveling to the wall combine to form an extended (long-wavelength), small-amplitude pulse. We find in most cases that (assuming no central symmetry constraints need to be enforced) the optimal protectors tend to have soft/ light beads near the wall...

Fraternali, Fernando; Daraio, Chiara

2008-01-01

261

Memory effect in uniformly heated granular gases  

E-print Network

We evidence a Kovacs-like memory effect in a uniformly driven granular gas. A system of inelastic hard particles, in the low density limit, can reach a non-equilibrium steady state when properly forced. By following a certain protocol for the drive time dependence, we prepare the gas in a state where the granular temperature coincides with its long time value. The temperature subsequently does not remain constant, but exhibits a non-monotonic evolution with either a maximum or a minimum, depending on the dissipation, and on the protocol. We present a theoretical analysis of this memory effect, at Boltzmann-Fokker-Planck equation level, and show that when dissipation exceeds a threshold, the response can be coined anomalous. We find an excellent agreement between the analytical predictions and direct Monte Carlo simulations.

E. Trizac; A. Prados

2014-07-15

262

Thermodynamics of Wetting by Liquid Metals.  

National Technical Information Service (NTIS)

The wetting of metal surfaces by molten solder is usually considered to be driven solely by an interfacial energy imbalance. The effect of chemical reactions on the wetting process is neglected, although the growth of an intermetallic layer in the wetted ...

F. G. Yost, A. D. Romig

1987-01-01

263

Constraining Mercury Oxidation Using Wet Deposition  

E-print Network

Constraining Mercury Oxidation Using Wet Deposition Noelle E. Selin and Christopher D. Holmes mercury oxidation [Selin & Jacob, Atmos. Env. 2008] 30 60 90 120 150 30 60 90 120 150 30 60 90 120 150 30 Influences on Mercury Wet Deposition · Hg wet dep = f(precipitation, [Hg(II)+Hg(P)]) Correlation (r2) between

Selin, Noelle Eckley

264

Microwave Conductivity of Granular Superconducting Aluminum Films  

Microsoft Academic Search

Measurements of the transmission amplitude and phase of 20 GHz microwaves through superconducting granular aluminum films were made as a function of temperature from 4.2° to 1.75°K. The films were fabricated by vacuum deposition in the presence of controlled amounts of oxygen, and exhibited small grain size (?40 Å) and enhanced transition temperatures of up to 2.86°K. The temperature coefficients

R. V. D'Aiello; S. J. Freedman

1969-01-01

265

Granular preparations of Azotobacter containing clay minerals  

Microsoft Academic Search

Interaction ofAzotobacter chroococcum 20 with clay minerals increased their cell viability at supraoptimal temperatures. Therefore, clay minerals were used to\\u000a develop granular bacterial preparations with high viable cell counts and stable compositions during long-term storage. The\\u000a titers of viable bacteria in the preparations remained 60–70% of the initial level after 12 months of storage.

I. K. Kurdish; L. V. Titova

2000-01-01

266

Refraction of shear zones in granular materials  

E-print Network

We study strain localization in slow shear flow focusing on layered granular materials. A heretofore unknown effect is presented here. We show that shear zones are refracted at material interfaces in analogy with refraction of light beams in optics. This phenomenon can be obtained as a consequence of a recent variational model of shear zones. The predictions of the model are tested and confirmed by 3D discrete element simulations. We found that shear zones follow Snell's law of light refraction.

Tamas Unger

2006-10-03

267

Reentrant phase diagram for granular superconductors  

SciTech Connect

The mean-field phase diagram of the self-charging model of a granular superconductor is calculated using the functional-integral formulation. A pronounced reentrance is obtained in quantitative agreement with a previous calculation, involving 2..pi..-antiperiodic eigenstates of the Mathieu equation. It is argued that low-lying, odd-electron-number excitations play a significant role in the thermodynamics of Josephson-junction arrays, for which the Feynman functional-integral formulation holds.

Simanek, E.

1985-07-01

268

Adsorption of Nonylphenol onto Granular Activated Carbon  

Microsoft Academic Search

The applicability of granular activated carbon (GAC)filtration for the removal of the xeno-estrogenicmicropollutant nonylphenol (NP) is evaluated using batchadsorption data. From the obtained adsorption data, it wasapparent that with contact times of 4 d and 24 hr and GACdosages of 1 and 0.1 g L-1 no saturationof the GAC could be obtained with NP total contaminantloadings up to 10 000

Tom Tanghe; Willy Verstraete

2001-01-01

269

Dynamic effective mass of granular media  

E-print Network

We report an experimental and theoretical investigation of the frequency-dependent effective mass, $\\tilde{M}(\\omega)$, of loose granular particles which occupy a rigid cavity to a given filling fraction, the remaining volume being air of differing humidities. This allow us to study the mechanisms of elastic response and attenuation of acoustic modes in granular media. We demonstrate that this is a sensitive and direct way to measure those properties of the granular medium that are the cause of the changes in acoustic properties of structures containing grain-filled cavities. Specifically, we apply this understanding to the case of the flexural resonances of a rectangular bar with a grain-filled cavity within it. The dominant features of $\\tilde{M}(\\omega)$ are a sharp resonance and a broad background, which we analyze within the context of simple models. We find that: a) These systems may be understood in terms of a height-dependent and diameter-dependent effective sound speed ($\\sim 100-300$ m/s) and an effective viscosity ($\\sim 5\\times 10^4$ Poise). b) There is a dynamic Janssen effect in the sense that, at any frequency, and depending on the method of sample preparation, approximately one-half of the effective mass is borne by the side walls of the cavity and one-half by the bottom. c) By performing experiments under varying humidity conditions we conclude that, on a fundamental level, damping of acoustic modes is dominated by adsorbed films of water at grain-grain contacts in our experiments, not by global viscous dampening. d) There is a monotonically increasing effect of humidity on the dampening of the fundamental resonance within the granular medium which translates to a non-monotonic, but predictable, variation of dampening within the grain-loaded bar.

John Valenza; Chaur-Jian Hsu; Rohit Ingale; Nicolas Gland; Hernán A. Makse; David Linton Johnson

2009-05-08

270

A Taylor vortex analogy in granular flows.  

PubMed

Fluids sheared between concentric rotating cylinders undergo a series of three-dimensional instabilities. Since Taylor's archetypal 1923 study, these have proved pivotal to understanding how fluid flows become unstable and eventually undergo transitions to chaotic or turbulent states. In contrast, predicting the dynamics of granular systems--from nano-sized particles to debris flows--is far less reliable. Under shear these materials resemble fluids, but solid-like responses, non-equilibrium structures and segregation patterns develop unexpectedly. As a result, the analysis of geophysical events and the performance of largely empirical particle technologies might suffer. Here, using gas fluidization to overcome jamming, we show experimentally that granular materials develop vortices consistent with the primary Taylor instability in fluids. However, the vortices observed in our fluidized granular bed are unlike those in fluids in that they are accompanied by novel mixing-segregation transitions. The vortices seem to alleviate increased strain by spawning new vortices, directly modifying the scale of kinetic interactions. Our observations provide insights into the mechanisms of shear transmission by particles and their consequent convective mixing. PMID:15386007

Conway, Stephen L; Shinbrot, Troy; Glasser, Benjamin J

2004-09-23

271

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

272

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

273

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

274

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

275

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

276

Stress wave mitigation in granular media  

NASA Astrophysics Data System (ADS)

We study stress wave mitigation in one- and two-dimensional granular media employing evolutionary algorithms to investigate the optimal design of composite protectors using 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 ``wall'' that represents the body to be protected and accordingly optimize the topology (arrangement), size, and material of the chain. We obtain optimally randomized granular protectors characterized by high-energy equipartition and the transformation of incident waves into interacting solitary pulses. We provide a quantitative characterization of dissipative effects using the propagation of highly nonlinear solitary waves as a diagnostic tool and develop optimization schemes that allow one to compute the relevant exponents and prefactors of the dissipative terms in the equations of motion. We thus propose a quantitatively-accurate extension of the Hertzian model encompassing realistic material dissipative effects. Experiments and computations with steel, brass, and polytetrafluoroethylene reveal a common dissipation exponent (for a discrete Laplacian of the velocities) with a material-dependent prefactor.

Daraio, Chiara; Fernando, F.; Porter, Mason

2009-03-01

277

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

278

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

279

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

280

Resolving a paradox of anomalous scalings in the diffusion of granular materials  

PubMed Central

Granular materials do not perform Brownian motion, yet diffusion can be observed in such systems when agitation causes inelastic collisions between particles. It has been suggested that axial diffusion of granular matter in a rotating drum might be “anomalous” in the sense that the mean squared displacement of particles follows a power law in time with exponent less than unity. Further numerical and experimental studies have been unable to definitively confirm or disprove this observation. We show two possible resolutions to this apparent paradox without the need to appeal to anomalous diffusion. First, we consider the evolution of arbitrary (non-point-source) initial data towards the self-similar intermediate asymptotics of diffusion by deriving an analytical expression for the instantaneous collapse exponent of the macroscopic concentration profiles. Second, we account for the concentration-dependent diffusivity in bidisperse mixtures, and we give an asymptotic argument for the self-similar behavior of such a diffusion process, for which an exact self-similar analytical solution does not exist. The theoretical arguments are verified through numerical simulations of the governing partial differential equations, showing that concentration-dependent diffusivity leads to two intermediate asymptotic regimes: one with an anomalous scaling that matches the experimental observations for naturally polydisperse granular materials, and another with a “normal” diffusive scaling (consistent with a “normal” random walk) at even longer times. PMID:22992653

Christov, Ivan C.; Stone, Howard A.

2012-01-01

281

Kinks, logarithmic tails, and super-stability in bi-disperse granular media  

NASA Astrophysics Data System (ADS)

Determining the stability of granular matter piles is of basic concern in understanding many real-world phenomena (e.g. landslides, debris flow, and avalanches). While extensive literature exists dealing with the stability of mono-disperse systems, models for the dynamical behavior of poly-disperse media are still uncommon. Here, a simple experimental setup that probes the dependence of the repose angle ( ?) for different proportions of granular mixtures is described. We demonstrate that a cellular automata (CA) grid with rules based on gravitational effects can phenomenologically mimic the dynamics of experimental data in terms of: (1) the presence of disruptions or kinks in an otherwise perfectly straight slope; (2) a concave logarithmic tail, indicative of the nature of the granular medium; and (3) the existence of supra-maximal repose angles for binary mixtures such that ?>?1,?2, which can lead to super-stability, or 90-degree slopes. This latter result has profound implications because of the ubiquity of vertical slopes in nature, while standard continuum approaches cannot account for such (because it entails an infinite value of the coefficient of friction).

Batac, Rene; Pastor, Marissa; Arciaga, Marko; Bantang, Johnrob; Monterola, Christopher

2009-08-01

282

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

283

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

284

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

285

Simulation of granular jets: is granular flow really a perfect fluid?  

PubMed

We perform three-dimensional simulations of the impact of a granular jet for both frictional and frictionless grains. Small shear stress observed in the experiment [X. Cheng et al., Phys. Rev. Lett. 99, 188001 (2007)] is reproduced through our simulation. However, the fluid state after the impact is far from a perfect fluid, and thus the similarity between granular jets and quark gluon plasma is superficial because the observed viscosity is finite and its value is consistent with the prediction of the kinetic theory. PMID:23214581

Sano, Tomohiko G; Hayakawa, Hisao

2012-10-01

286

Matter: States of Matter  

NSDL National Science Digital Library

The representation is showing the motion of molecules in three states of matter; ice crystals, liquid water, and boiling water/steam. Users can "zoom in" to "view" water's molecular arrangement and motion in each state. The resource includes descriptive text to support the animations.

Carpi, Anthony

287

Contribution of the shrunk interface and the convex surface of grains on magnetic behavior in granular film  

NASA Astrophysics Data System (ADS)

In this paper, we studied the intergranular interaction in realistically shaped grains which have convex vacuum surface. The convex surface is evaluated by utilizing the SURFACE EVOLVER, a software package for grain growth simulation. Various shapes of grains are obtained by changing the wetting angles between the top surface and the grain boundaries. From finite element micromagnetic simulations, which are used to simulate the magnetization reversal in the simple granular structure, it is found that the exchange field decreases with increasing wetting angle. We studied the effect of the intergranular exchange and the magnetostatic interactions individually. In order to study the intergranular exchange coupling effect quantitatively, an analytic energy surface model for the exchange coupled system is developed. The results agree very well with those of micromagnetic simulation. Magnetostatic interactions reduce the exchange field by making the antiparallel state more favorable than the parallel.

Lee, Jehyun; Suess, Dieter; Schrefl, Thomas; Oh, Kyu Hwan; Fidler, Josef

2008-04-01

288

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

289

Mold management of wetted carpet.  

PubMed

This study evaluated the growth and removal of fungi on wetted carpet using newly designed technologies that rely on physical principles of steam, heat, and fluid flow. Sixty samples of carpet were embedded with heat-treated house dust, followed by embedding, wearing with a hexapod, and wetting. Samples were inoculated using a liquid suspension of Cladosporium sphaerospermum prior to placement over a water-saturated foam pad. Incubation times were 24 hr, 7 days, and 30 days. Cleaning was performed using three methods; high-flow hot water extraction, hot water and detergent, and steam. Fungal loading increased from approximately 1500 colony forming units per area (CFU/cm(2)) in 24 hr to a maximum of approximately 10,200 CFU/cm(2) after 7 days with a slight decline to 9700 CFU/cm(2) after 30 days incubation. Statistically significant differences were found among all three methods for removal of fungi for all three time periods (p < 0.05). Steam-vapor was significantly better than the alternative methods (p <0.001) with over 99% efficiency in mold spore decline from wetted carpet after 24 hr and 30 days, and over 92% efficiency after 7 days. The alternative methods exhibited lower efficiencies with a decline over time, from a maximum of 82% and 81% at 24 hr down to 60% and 43% at 30 days for detergent-hot water and high-flow, hot water extraction, respectively. The net effect of the mold management study demonstrates that while steam has a consistent fungal removal rate, the detergent and high-flow, hot water methods decline in efficiency with increasing incubation time. PMID:24856911

Ong, Kee-Hean; Dixit, Anupma; Lewis, Roger D; MacDonald Perkins, Maureen; Backer, Denis; Condoor, Sridhar; Emo, Brett; Yang, Mingan

2014-12-01

290

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

291

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

292

Wet coastal plain tundra III  

SciTech Connect

This year's census data for the wet coastal plain tundra in Alaska; North Slope Borough, 3 km SSE of Naval Arctic Research Laboratory, Barrow; 71/sup 0/ 18'N, 156/sup 0/ 38'W; Barrow Quadrangle, USGS reflect a decrease in the total number of species breeding. However, total breeding density rose by 82%. Lapland Longspurs (up 105%) accounted for half of this increase while the rest was spread among many species. There was a total of 8 species; 40.5 territorial males or females (162/km/sup 2/, 66/100 acres).

Myers, J.P.; Gellman, S.T.; Pitelka, F.A.

1980-01-01

293

Single-metalloprotein wet biotransistor  

NASA Astrophysics Data System (ADS)

Metalloproteins are redox molecules naturally shuttling electrons with high efficiency between molecular partners. As such, they are candidates of choice for bioelectronics. In this work, we have used bacterial metalloprotein azurin, hosted in a nanometer gap between two electrically biased gold electrodes, to demonstrate an electrochemically gated single-molecule transistor operating in an aqueous environment. Gold-chemisorbed azurin shows peaks in tunneling current upon changing electrode potential and a related variation in tunneling barrier transparency which can be exploited to switch an electron current through it. These results suggest the wet approach to molecular electronics as a viable method for exploiting electron transfer of highly specialized biomolecules.

Alessandrini, Andrea; Salerno, Marco; Frabboni, Stefano; Facci, Paolo

2005-03-01

294

Frosted granular flow: A new hypothesis for mass wasting in martian gullies  

NASA Astrophysics Data System (ADS)

Recent gully deposits on Mars have been attributed to both wet and dry mass wasting processes. In this paper frosted granular flow (FGF) is presented as a new hypothesis for recent mass wasting activity in martian gullies. FGF is a rare type of granular flow observed on a talus slope in the Province of Québec, Canada [Hétu, B., van Steijn, H., Vandelac, P., 1994. Géogr. Phys. Quat. 48, 3-22]. Frost reduces dynamic inter-particle friction, enabling flows to mobilize onto relatively low slope gradients (25-30°) compared to those involving dry granular flow of the same material (35-41°). Resulting erosional and depositional features include straight to sinuous channels, levees and digitate to branching arrangements of terminal deposits. Similar features are commonly found in association with geologically-young gully systems on Mars. Based on terrestrial observations of FGF processes the minimum criteria required for their occurrence on Mars include: (i) readily mobilized, unconsolidated sediment at the surface; (ii) an upper slope gradient at or near the angle of repose; (iii) frost accumulation at the surface; and (iv) triggering by rock fall. All four conditions appear to be met in many areas on present-day Mars though triggering mechanisms may vary. Compared to terrestrial FGFs, which are lubricated by thin liquid films at inter-particle contacts, those occurring on Mars are more likely lubricated by vaporization of CO 2 and small amounts of H 2O frost that becomes incorporated in the translating mass. Some recent mass wasting activity in martian gullies, therefore, could be interpreted as the product of FGF.

Hugenholtz, Chris H.

2008-09-01

295

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

296

EFFECT OF UV IRRADIATION ON ORGANIC MATTER EXTRACTED FROM TREATED OHIO RIVER WATER STUDIED THROUGH THE USE OF ELECTROSPRAY MASS SPECTROMETRY  

EPA Science Inventory

Ohio River water was treated by settling, sand filtration, and granular activated carbon filtration. It was then irradiated by low pressure (monochromatic) and medium pressure (polychromatic) UV lamps to investigate the effects of UV irradiation of natural organic matter (NOM). ...

297

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

298

Tap Density Equations of Granular Powders Based on the Rate Process Theory and the Free Volume Concept  

E-print Network

Tap density of a granular powder is often linked to the flowability via Carr Index that measures how tight a powder can be packed, under an assumption that more easily packed powders usually flow poorly. Understanding how particles are packed is important for revealing why a powder flows better than others. There are two types of empirical equations that were proposed to fit the experimental data of packing fractions vs. numbers of taps in literature: The inverse logarithmic and the stretched exponential. Using the rate process theory and the free volume concept, we obtain the tap density equations and they can be reducible to the two empirical equations currently widely used in literature. Our equations could potentially fit experimental data better with an additional adjustable parameter. The tapping amplitude and frequency, the weight of the granular materials, and the environment temperature are grouped into one parameter that weighs the pace of packing process. The current results, in conjunction with our previous findings, may imply that both dry(granular)and wet(colloidal and polymeric) particle systems are governed by the same physical mechanisms in term of the role of the free volume and how particles behave (a rate controlled process).

Tian Hao

2014-09-05

299

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

300

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

301

Interstitial gas effect on vibrated granular columns.  

PubMed

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. PMID:25019768

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

2014-06-01

302

Shear thickening in highly viscous granular suspensions  

NASA Astrophysics Data System (ADS)

We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain ?c and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics ?h , dilation ?c and sedimentation ?g . While ?g governs the shear thinning regime, ?h and ?c together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cSt, ?h is found to compete with ?c and soften the discontinuous nature of shear thickening.

Xu, Qin; Majumdar, Sayantan; Brown, Eric; Jaeger, Heinrich M.

2014-09-01

303

Granular convection observed by magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

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.

Ehrichs, E. E.; Jaeger, H. M.; Karczmar, Greg S.; Knight, James B.; Kuperman, Vadim Yu.; Nagel, Sidney R.

1995-03-01

304

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

305

Prenatal Diagnosis of Granular Cell Tumor  

PubMed Central

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

2014-01-01

306

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

307

Stripe formation in horizontally oscillating granular suspensions  

NASA Astrophysics Data System (ADS)

We present the results of an experimental study of pattern formation in horizontally oscillating granular suspensions. Starting from a homogeneous state, the suspension turns into a striped pattern within a specific range of frequencies and amplitudes of oscillation. We observe an initial development of layered structures perpendicular to the vibration direction and a gradual coarsening of the stripes. However, both processes gradually slow down and eventually saturate. The probability distribution of the stripe width P(w) approaches a nonmonotonic steady-state form which can be approximated by a Poisson distribution. We observe similar structures in MD simulations of soft spherical particles coupled to the motion of the surrounding fluid.

Moosavi, Robabeh; Maleki, Maniya; Shaebani, M. Reza; Ruiz-Suárez, J. Carlos; Clément, Eric

2014-08-01

308

Stripe formation in horizontally oscillating granular suspensions  

E-print Network

We present the results of an experimental study of pattern formation in horizontally oscillating granular suspensions. Starting from a homogeneous state, the suspension turns into a striped pattern within a specific range of frequencies and amplitudes of oscillation. We observe an initial development of layered structures perpendicular to the vibration direction and a gradual coarsening of the stripes. However, both processes gradually slow down and eventually saturate. The probability distribution of the stripe width approaches a nonmonotonic steady-state form which can be approximated by a Poisson distribution. We observe similar structures in MD simulations of soft spherical particles coupled to the motion of the surrounding fluid.

Robabeh Moosavi; Maniya Maleki; M. Reza Shaebani; J. C. Ruiz-Suarez; Eric Clement

2014-07-12

309

Drag induced lift in granular media  

E-print Network

Laboratory experiments and numerical simulation reveal that a submerged intruder dragged horizontally at constant velocity within a granular medium experiences a lift force whose sign and magnitude depend on the intruder shape. Comparing the stress on a flat plate at varied inclination angle with the local surface stress on the intruders at regions with the same orientation demonstrates that intruder lift forces are well approximated as the sum of contributions from flat-plate elements. The plate stress is deduced from the force balance on the flowing media near the plate.

Yang Ding; Nick Gravish; Daniel I. Goldman

2010-11-17

310

Three-dimensional shear in granular flow  

E-print Network

The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations we find a transition in the nature of the shear as a characteristic height $H^*$ is exceeded. Below $H^*$ there is a central stationary core; above $H^*$ we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height while the axial width remains narrow and fixed.

Xiang Cheng; Jeremy B. Lechman; Antonio F. Barbero; Gary S. Grest; Heinrich M. Jaeger; Greg S. Karczmar; Matthias E. Möbius; Sidney R. Nagel

2005-07-20

311

Numerical simulations of granular dynamics II: Particle dynamics in a shaken granular material  

NASA Astrophysics Data System (ADS)

Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties. We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration. We then extend our investigations to assess how self-gravity and external gravity affect collective motion. In our reduced-gravity simulations both the gravitational conditions and the frequency of the vibrations roughly match the conditions on asteroids subjected to seismic shaking, though real regolith is likely to be much more heterogeneous and less ordered than in our idealised simulations. We also show that collective motion can occur in a granular material under a wide range of inter-particle gravity conditions and in the absence of an external gravitational field. These investigations demonstrate the great interest of being able to simulate conditions that are to relevant planetary science yet unreachable by Earth-based laboratory experiments.

Murdoch, Naomi; Michel, Patrick; Richardson, Derek C.; Nordstrom, Kerstin; Berardi, Christian R.; Green, Simon F.; Losert, Wolfgang

2012-05-01

312

Numerical simulations of granular dynamics II. Particle dynamics in a shaken granular material  

E-print Network

Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties. We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration. We then extend our investigations to assess how self-gravity and external gravity affect collective motion. In our reduced-gravity simulations both the gravitational conditions and the frequency of the vibrations roughly match the conditions on asteroids subjected to seismic shaking, though real regolith is likely to be much more heterogeneous and less ordered than in our idealised simulations. We also show that collective motion can occur in a granular material under a wide range of inter-particle gravity conditions and in the absence of an external gravitational field. These investigations demonstrate the great interest of being able to simulate conditions that are to relevant planetary science yet unreachable by Earth-based laboratory experiments.

Naomi Murdoch; Patrick Michel; Derek C. Richardson; Kerstin Nordstrom; Christian R. Berardi; Simon F. Green; Wolfgang Losert

2013-06-07

313

The microstructural response of granular soil under uniaxial strain  

Microsoft Academic Search

Soil mechanical behavior is described and phenomenological (macroscopic) and microstructural (particulate) theories, developed to predict the constitutive response of granular media, are discussed. Special emphasis is given to the concept of fabric in granular media and how the concept relates to observed mechanical behavior. This report describes an experimental effort to quantify changes which occur in a cuboid specimen of

John J. Gill

1993-01-01

314

SHEAR DEFORMATION IN GRANULAR MATERIAL S. G. Bardenhagen  

E-print Network

of the deformation at the microscale (the scale of the grains) contributes to the development of local "hot spotsSHEAR DEFORMATION IN GRANULAR MATERIAL S. G. Bardenhagen Los Alamos National Laboratory Los Alamos characteristic of dry granular materials, and interfacial debonding, an expected deformation mode in plastic

Sulsky, Deborah L.

315

Choice of Allocation Granularity in Multipath Source Routing Schemes  

Microsoft Academic Search

Multipath source routing schemes can be distinguished by their choice of allocation granularity. The schemes proposed in the literature advocate a per-connection allocation wherein all the packets of a connection are constrained to follow the same path. The authors believe that a smaller allocation granularity permits a finer control to be exerted and would result in improved performance, especially in

Ram Krishnan; John A. Silvester

1993-01-01

316

Statistical mechanics for static granular media: open questions  

E-print Network

Statistical mechanics for static granular media: open questions Massimo Pica Ciamarra Patrick existence of a statistical mechanics of static granular systems, which would permit the description important questions concerning such a statistical mechanics approach. First, we consider how the phase space

Paris-Sud XI, Université de

317

Elastic wave propagation in confined granular systems Ellk Somfai,1,  

E-print Network

present numerical simulations of acoustic wave propagation in confined granular systems consisting as follows for an interplay between force chain type correlations and sound propagElastic wave propagation in confined granular systems Ellák Somfai,1, * Jean-Noël Roux,2 Jacco H

318

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

319

Shock Front Width and Structure in Supersonic Granular Flows  

Microsoft Academic Search

The full structure of a shock front around a blunt body in a quasi-two-dimensional granular flow is studied. Two features, a large density gradient and a very small thickness of the front, characterize this shock and make it different from shocks in molecular gases. Both of these features can be understood using a modified version of the granular kinetic theory.

J. F. Boudet; Y. Amarouchene; H. Kellay

2008-01-01

320

BACKWASH OF GRANULAR FILTERS USED IN WASTEWATER FILTRATION  

EPA Science Inventory

The use of deep granular filters in waste treatment is of growing importance. The key to long-term operating success of such filters is proper bed design and adequate bed cleaning during backwashing. Cleaning granular filters by water backwash alone to fluidize the filter bed is ...

321

Fate of carbon and nitrogen from animal manure and crop residues in wet and cold soils  

Microsoft Academic Search

Organic matter transformations take place in snow-covered soils during winter but in ways still poorly understood. Given the generally high soil water content and possible formation of ice layers during this period, anaerobic zones could develop and have determinant effects on soil C and N dynamics. The fate of C and N under wet and cold conditions was monitored in

Martin H Chantigny; Denis A Angers; Philippe Rochette

2002-01-01

322

The Wet-Dog Shake  

E-print Network

The drying of wet fur is a critical to mammalian heat regulation. In this fluid dynamics video, we show a sequence of films demonstrating how hirsute animals to rapidly oscillate their bodies to shed water droplets, nature's analogy to the spin cycle of a washing machine. High-speed videography and fur-particle tracking is employed to determine the angular position of the animal's shoulder skin as a function of time. X-ray cinematography is used to track the motion of the skeleton. We determine conditions for drop ejection by considering the balance of surface tension and centripetal forces on drops adhering to the animal. Particular attention is paid to rationalizing the relationship between animal size and oscillation frequency required to self-dry.

Dickerson, Andrew; Bauman, Jay; Chang, Young-Hui; Hu, David

2010-01-01

323

Wet quenching of incandescent coke  

SciTech Connect

Method for the reduction of emissions from the wet quenching of incandescent coke in a quenching tower adapted to receive in its base a quench car containing the coke which comprises positioning the car with the coke in the quenching chamber of the tower, effecting a gas seal to substantially prevent air from infiltrating the quenching chamber and ascending the tower, quenching the coke with the resultant generation of steam and other quenching emissions, cooling and cleaning the emissions with water sprays, demisting the cooled emissions, sensing the external and internal pressures of the tower during the quenching process, maintaining a substantially zero gauge internal pressure by controlling the emissions flow exiting the tower and collecting, cooling and recycling the quenching and cooling waters. Apparatus for practicing the method is also disclosed.

Porter, R.W.

1981-04-21

324

Surface elastic waves in granular media under gravity and their relation to booming avalanches.  

PubMed

Due to the nonlinearity of Hertzian contacts, the speed of sound c in granular matter is expected to increase with pressure as P(1/6). A static layer of grains under gravity is thus stratified so that the bulk waves are refracted toward the surface. The reflection at the surface being total, there is a discrete number of modes (both in the sagittal plane and transverse to it) localized close to the free surface. The shape of these modes and the corresponding dispersion relation are investigated in the framework of an elastic description taking into account the main features of granular matter: Nonlinearity between stress and strain and the existence of a yield transition. We show in this context that the surface modes localized at the free surface exhibit a waveguide effect related to the nonlinear Hertz contact. Recent results about the song of dunes are reinterpreted in light of the theoretical results. The predicted propagation speed is compared with measurements performed in the field. Taking into account the finite depth effects, we show that the booming instability threshold can be explained quantitatively by a waveguide cutoff frequency below which no sound can propagate. Therefore, we propose another look at a recent controversy, confirming that the song of dunes can well originate from a coupling between avalanching grains and surface elastic waves once the specificity of surface waves (we baptized Rayleigh-Hertz) is correctly taken into account. PMID:17358270

Bonneau, L; Andreotti, B; Clément, E

2007-01-01

325

Comparison of two online flocculation monitoring techniques for predicting turbidity removal by granular media filtration.  

PubMed

Particulate matter removal in drinking water treatment via direct granular filtration requires specific flocculation conditions (a process typically termed 'high energy flocculation'). Predicting filtered water turbidity based on flocculated water characteristics remains difficult. This study has sought to establish a relationship between filtered water turbidity and the flocculated water characteristics. Flocculation oflow-turbidity raw water was evaluated online using a Photometric Dispersion Analyser (PDA) and a Dynamic Particle Analyser in a modified jar test followed by a bench-scale anthracite filter. Coagulants used were alum, PASS100 and ferric sulphate, in addition to a polydiallyldimethylammonium chloride (polyDADMAC) cationic polymer. They were dosed in warm and cold waters, and flocculated with intensities (G) from 0 to 100 s(-1). Of the two instruments selected to analyse flocculation performance, the Dynamic Particle Analyser was shown to be the most sensitive, detecting small changes in floc growth kinetics and even floc growth under low flocculation conditions which remained undetected by the PDA. Floc size was shown to be insufficient in predicting particulate matter removal by direct granular filtration as measured by turbidity, although a threshold d(v) value (50 microm) could be identified for the test conditions evaluated in this project, above which turbidity was systematically lower than 0.2 NTU. PMID:21882562

Ball, T; Carrière, A; Barbeau, B

2011-07-01

326

An Expression for the Granular Elastic Energy  

E-print Network

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 draw-backs. 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 $26^\\circ$ to the more realistic value of $30^\\circ$. (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.

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

2012-06-13

327

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

328

Compaction Wave Profiles in Granular HMX  

NASA Astrophysics Data System (ADS)

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

2002-07-01

329

Compaction Wave Profiles in Granular HMX  

NASA Astrophysics Data System (ADS)

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 concentration 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

2001-06-01

330

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

331

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

332

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

333

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

334

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

335

Machanics of Granular Materials (MGM) Investigator  

NASA Technical Reports Server (NTRS)

Key persornel in the Mechanics of Granular Materials (MGM) experiment include Khalid Alshibli, project scientist at NASA's Marshall Space Flight Center (MSFC). 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: MSFC).

2000-01-01

336

Granular behavior in gas-fluidized beds  

NASA Astrophysics Data System (ADS)

This work investigates the behavior of granular materials driven by a uniform upward flow of gas within a vertical container. This arrangement is referred to as a gas-fluidized bed. For a bed with a large number of spherical grains, bulk properties of the sample, such as solids volume fraction (the percent of space occupied by solids) and gas pressure drop, are found to obey simple scaling relations when the superficial air velocity, the container size, or the grain size are varied. These results stand in contrast to behavior observed in other granular systems, where non-trivial interaction between individual grains leads to complex behavior for the bulk. The results suggest that there is a unique quality to the forcing provided to individual grains by gas fluidization that results in relatively simple bulk behavior. To investigate this possibility, experiments were carried out in a gas-fluidized bed with only a single grain. A large grain, a ping pong ball, was chosen for ease of visual observation. The ball's behavior is found to be exactly that of a Brownian object harmonically bound to the center of its container. Its dynamics are found to be described by a Langevin Equation, with the random forcing on related to the dissipation of energy by the Fluctuation-Dissipation Theorem. We find that the separation statistics for a two-ball system are also described by a statistical mechanics approach. These results represent the first successful application of conventional statistical mechanics to a macroscopic system.

Ojha, Rajesh Prasad

337

Scaled experiments to determine the role of density on granular flows behavior: preliminary results  

NASA Astrophysics Data System (ADS)

Geological granular flows are very complex, gravity driven phenomena which can show different behaviors depending on its origin and the characteristics of the constituent material. Due to their dangerous nature, and multiple scientific and technological applications, these phenomena has being studied deeply in order to have a better comprehension, however, after more than one century of scientific research it remains as an open topic with more questions than answers. One of the aspects that still need exhaustive research is the effect of clast density on the flowing granular material, as pointed out by previous laboratory and field studies. There are anyway few studies which have tried to explain the role of bulk density, as well the density of different phases, as it increasing or decreasing on the kinematic and the rheological characteristics of geological granular flows. The content of low density juvenile material seems to condition the processes of transformations of debris flows to more diluted phases, as well the transport and emplacing mechanisms. It is well known that the content of clay in debris flows has great influence on its behavior, physical processes and the deposits characteristics for this reason lahars has being subdivided in base of this parameter. Our hypothesis is that, in like manner, the presence of low density material inside the granular flows (dry and wet) could conditioning its physical characteristics and its behavior. In order to put this to the test, we made some laboratory experiments using a five meter long and 0.3 m wide experimental flume equipped with a wide range of sensors and laser barriers to precisely measure the rheological properties and kinematic of the sliding avalanches. A special effort was devoted to determine a threshold or critical level in the amount of low density material at which the avalanche behavior suffer appreciable changes. The obtained preliminary results confirm our hypothesis and encouraged to perform further experiments. Such studies are important because they could provide useful information for developing analog models that take into account this important physical property.

Rodriguez Sedano, L. A.; Sarocchi, D.; Borselli, L.; Segura, O.

2013-12-01

338

Motion of wetting fronts moving into partially pre-wet soil  

Microsoft Academic Search

We study the motion of wetting fronts for vertical infiltration problems as modeled by Richards’ equation. Parlange and others have shown that wetting fronts in infiltration flows can be described by traveling wave solutions. If the soil layer is not initially dry, but has an initial distribution of water content then the motion of the wetting front will change due

Thomas P. Witelski

2005-01-01

339

Particulate Matter  

MedlinePLUS

... EPA Home Air & Radiation Six Common Pollutants Particulate Matter Announcements March 13, 2013 - An updated “Strategies ... for over 300 cities across the U.S. "Particulate matter," also known as particle pollution or PM, is ...

340

Ensuring message embedding in wet paper steganography  

E-print Network

Ensuring message embedding in wet paper steganography Daniel Augot1, Morgan Barbier1, and Caroline of this new scheme in the case of perfect codes. Keywords: steganography, syndrome coding problem, wet paper codes. 1 Introduction Hiding messages in innocuous-looking cover-media in a stealthy way, steganography

Paris-Sud XI, Université de

341

Membrane-based wet electrostatic precipitation  

Microsoft Academic Search

Wet electrostatic precipitators (ESPs) hold great promise for collecting acid aerosols and fine particulates, as well as virtually eliminating re-entrainment. However, disruptions due to spraying (misting) of water, formation of dry spots due to the effects of water surface tension (channeling), and corrosion of the collector surfaces may limit applicability of current wet precipitators. Novel corrosion resistant membrane collection surfaces

David J. Bayless; M. Khairul Alam; Roger Radcliff; John Caine

2004-01-01

342

Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge.  

PubMed

Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1-0.2mgL(-1)) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34mMCH4/hg VSS) and aerobic activity (SOUR: 2.21mMO2/hg VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro-aerobic condition and PCP on microbial community. Furthermore, nucleotide sequencing indicated that the main microorganisms for PCP degradation might be related to Actinobacterium and Sphingomonas. These results provided insights into situ bioremediation of environments contaminated by PCP and had practical implications for the strategies of PCP degradation. PMID:25151236

Lv, Yuancai; Chen, Yuancai; Song, Wenzhe; Hu, Yongyou

2014-09-15

343

Granular Solid Hydrodynamics (GSH): a broad-ranged macroscopic theory of granular media  

E-print Network

A unified continuum-mechanical theory has been until now lacking for granular media, some believe it could not exist. Derived employing the hydrodynamic approach, GSH is such a theory, though as yet a qualitative one. The behavior being accounted for includes static stress distribution, elastic wave, elasto-plastic motion, the critical state and rapid dense flow. The equations and application to a few typical experiments are presented here.

Yimin Jiang; Mario Liu

2014-07-27

344

Tunable wetting of polymer surfaces.  

PubMed

A simple method was developed for the preparation of polymeric materials with controlled surface wettability or tunable surface wetting. The method is applicable to a large number of polymers, thermoplastic or thermoset. With this method, it is possible to prepare polymer surfaces with static water contact angles ranging from 0° (superhydrophilic) to greater than 170° (superhydrophobic). The method developed is based on spin-coating of a hydrophilic/hydrophobic silica mixture dispersed in an organic solvent or solvent mixture onto the polymer surface. Depending on the hydrophilic/hydrophobic silica ratio in the coating mixture, it is possible to obtain polymer surfaces displaying gradually changing wettability from superhydrophilic to superhydrophobic. In this article, preparation and surface characteristics of polystyrene (PS) and cross-linked epoxy resin (ER) films are provided as general examples. Polymer surfaces obtained were characterized by scanning electron microscopy, white light interferometry, atomic force microscopy, X-ray photoelectron spectroscopy, and static water contact angle measurements. Effects of the type of polymeric substrate and composition of the silica mixture on the surface behavior of the composite systems were investigated. PMID:22989033

Yilgor, Iskender; Bilgin, Sevilay; Isik, Mehmet; Yilgor, Emel

2012-10-16

345

Cerebral granular cell tumor occurring with glioblastoma multiforme: case report.  

PubMed

A 65-year-old man presented with 4 weeks of partial right visual field loss. A left occipital granular cell tumor was diagnosed via open biopsy. No specific tumoricidal therapy was given, and the patient returned 2 weeks later with fluent dysphasia and mild right hemiparesis, and formed visual hallucinations. A large left parietotemporal mass, separate from the granular cell tumor, was diagnosed as a glioblastoma multiforme by stereotactic biopsy. The histogenesis of cerebral granular cell tumors is controversial; this case supports recent speculation of their possible glial origin. PMID:1652163

Harris, C P; Townsend, J J; Brockmeyer, D L; Heilbrun, M P

1991-09-01

346

Hydrodynamic modeling of granular flows in a modified Couette cell  

E-print Network

We present simulations of granular flows in a modified Couette cell, using a continuum model recently proposed for dense granular flows. Based on a friction coefficient, which depends on an inertial number, the model captures the positions of the wide shear bands. We show that a smooth transition in velocity-profile shape occurs when increasing the height of the granular material, leading to a differential rotation of the central part close to the surface. The numerical predictions are in qualitative agreement with previous experimental results. The model provides predictions for the increase of the shear bands width when increasing the rotation rate.

Pierre Jop

2007-12-19

347

Granularity in superconductors: intrinsic properties and processing-dependent effects  

NASA Astrophysics Data System (ADS)

This contribution presents a selected set of results, obtained as part of a systematic investigation, evidencing that many effects exhibited by superconductors are distinct manifestations of granularity which, in turn, is envisaged as a break of symmetry. The Wohlleben effect, the “fishtail anomaly”, the magnetic remanence exhibited by Josephson junction arrays, and the jumps on the magnetic moment of superconducting samples of mesoscopic dimensions, are examples which we briefly review and discuss taking granularity as the basic ingredient. The emphasis of the present approach is to recognize the importance of granularity in every scenario intended to explain the magnetic properties of superconducting systems.

Passos, W. A. C.; Lisboa-Filho, P. N.; Caparroz, R.; de Faria, C. C.; Venturini, P. C.; Araujo-Moreira, F. M.; Sergeenkov, S.; Ortiz, W. A.

2001-05-01

348

Flexural fracturing of a cohesive granular layer  

NASA Astrophysics Data System (ADS)

We report on the fracturing of cohesive granular materials subjected to a flexural deformation. A thin layer of glass beads or of flour is deposited on an unstretchable membrane to which flexion is imposed. We observe the formation of a periodic fracturing pattern whose characteristics are discussed in comparison with results previously obtained for an in-plane stretching [Alarcon, Ramos, Vanel, Vittoz, Melo, and Géminard, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.208001 105, 208001 (2010)]. In particular, at a given relative humidity, the wavelength is observed to depend linearly on the layer thickness but to be independent of the grain size, although the smallest grains are clearly more cohesive.

Géminard, Jean-Christophe; Champougny, Lorène; Lidon, Pierre; Melo, Francisco

2012-01-01

349

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

350

Local Anisotropy in Globally Isotropic Granular Packings  

NASA Astrophysics Data System (ADS)

We report on two-dimensional computer simulations of frictionless granular packings at various area fractions ? above the jamming point ?c. We measure the anisotropy in coarse-grained stress ?s and shear modulus ?m as functions of coarse-graining scale, R. ?s can be collapsed onto a master curve after rescaling R by a characteristic length scale ? and ?s by an anisotropy magnitude A. Both A and ? accelerate as ???c from above, consistent with a divergence at ?c. ?m shows no characteristic length scale and has a nontrivial power-law form, ?m˜R-0.62, over almost the entire range of R at all ?. These results suggest that the force chains present in the spatial structure of the quenched stress may be governed by different physics than the anomalous elastic response near jamming.

Karimi, K.; Maloney, C. E.

2011-12-01

351

Frictional granular mechanics: A variational approach  

SciTech Connect

The mechanical properties of a cohesionless granular material are evaluated from grain-scale simulations. Intergranular interactions, including friction and sliding, are modeled by a set of contact rules based on the theories of Hertz, Mindlin, and Deresiewicz. A computer generated, three-dimensional, irregular pack of spherical grains is loaded by incremental displacement of its boundaries. Deformation is described by a sequence of static equilibrium configurations of the pack. A variational approach is employed to find the equilibrium configurations by minimizing the total work against the intergranular loads. Effective elastic moduli are evaluated from the intergranular forces and the deformation of the pack. Good agreement between the computed and measured moduli, achieved with no adjustment of material parameters, establishes the physical soundness of the proposed model.

Holtzman, R.; Silin, D.B.; Patzek, T.W.

2009-10-16

352

Granular acoustic switches and logic elements  

NASA Astrophysics Data System (ADS)

Electrical flow control devices are fundamental components in electrical appliances and computers; similarly, optical switches are essential in a number of communication, computation and quantum information-processing applications. An acoustic counterpart would use an acoustic (mechanical) signal to control the mechanical energy flow through a solid material. Although earlier research has demonstrated acoustic diodes or circulators, no acoustic switches with wide operational frequency ranges and controllability have been realized. Here we propose and demonstrate an acoustic switch based on a driven chain of spherical particles with a nonlinear contact force. We experimentally and numerically verify that this switching mechanism stems from a combination of nonlinearity and bandgap effects. We also realize the OR and AND acoustic logic elements by exploiting the nonlinear dynamical effects of the granular chain. We anticipate these results to enable the creation of novel acoustic devices for the control of mechanical energy flow in high-performance ultrasonic devices.

Li, Feng; Anzel, Paul; Yang, Jinkyu; Kevrekidis, Panayotis G.; Daraio, Chiara

2014-10-01

353

Granular acoustic switches and logic elements.  

PubMed

Electrical flow control devices are fundamental components in electrical appliances and computers; similarly, optical switches are essential in a number of communication, computation and quantum information-processing applications. An acoustic counterpart would use an acoustic (mechanical) signal to control the mechanical energy flow through a solid material. Although earlier research has demonstrated acoustic diodes or circulators, no acoustic switches with wide operational frequency ranges and controllability have been realized. Here we propose and demonstrate an acoustic switch based on a driven chain of spherical particles with a nonlinear contact force. We experimentally and numerically verify that this switching mechanism stems from a combination of nonlinearity and bandgap effects. We also realize the OR and AND acoustic logic elements by exploiting the nonlinear dynamical effects of the granular chain. We anticipate these results to enable the creation of novel acoustic devices for the control of mechanical energy flow in high-performance ultrasonic devices. PMID:25354587

Li, Feng; Anzel, Paul; Yang, Jinkyu; Kevrekidis, Panayotis G; Daraio, Chiara

2014-01-01

354

Ultrasound induces aging in granular materials.  

PubMed

Aging and rejuvenation have been identified as the general mechanisms that rule the time evolution of granular materials subjected to some external confinement pressure. In creep experiments performed in a triaxial configuration, we obtained evidence that relatively high intensity ultrasound waves propagating through the material induce both weakening and significant plasticity. In the framework of glassy materials, it is shown that the effect of ultrasound can be simply accounted for by a general variable, the fluidity, whose dynamics are described by an effective aging parameter that strongly decreases with sound amplitude and vanishes at the yield stress limit. The response from step perturbations in ultrasound intensity provided a method to assess the effective-viscosity jumps which are direct evidence of acoustic fluidization. PMID:23102371

Espíndola, David; Galaz, Belfor; Melo, Francisco

2012-10-12

355

Hydrodynamics of granular gases of viscoelastic particles.  

PubMed

Our study examines the long-time behaviour of a force-free granular gas of viscoelastic particles, for which the coefficient of restitution depends on the impact velocity, as it follows from the solution of the impact problem for viscoelastic spheres. Starting from the Boltzmann equation, we derived the hydrodynamic equations and obtained microscopic expressions for the transport coefficients in terms of the elastic and dissipative parameters of the particle material. We performed the stability analysis of the linearized set of equations and found that any inhomogeneities and vortices vanish after a long time and the system approaches the flow-free stage of homogeneous density. This behaviour is in contrast to that of a gas consisting of particles which interact via a (non-realistic) constant coefficient of restitution, for which inhomogeneities (clusters) and vortex patterns have been proven to arise and to continuously develop. PMID:16214686

Brilliantov, Nikolai V; Pöschel, Thorsten

2002-03-15

356

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. PMID:23093180

Jose, Prasanth P; Andricioaei, Ioan

2012-01-01

357

Mechanical properties of inclined frictional granular layers  

E-print Network

We investigate the mechanical properties of inclined frictional granular layers prepared with different protocols by means of DEM numerical simulations. We perform an orthotropic elastic analysis of the stress response to a localized overload at the layer surface for several substrate tilt angles. The distance to the unjamming transition is controlled by the tilt angle $\\alpha$ with respect to the critical angle $\\alpha_c$. We find that the shear modulus of the system decreases with $\\alpha$, but tends to a finite value as $\\alpha \\to \\alpha_c$. We also study the behaviour of various microscopic quantities with $\\alpha$, and show in particular the evolution of the contact orientation with respect to the orthotropic axes and that of the distribution of the friction mobilisation at contact.

A. P. F. Atman; P. Claudin; G. Combe; G. H. B. Martins

2014-01-31

358

Shear Thickening and Migration in Granular Suspensions  

NASA Astrophysics Data System (ADS)

We study the emergence of shear thickening in dense suspensions of non-Brownian particles. We combine local velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometry experiments. In steady state, we observe that the material is heterogeneous, and we find that the local rheology presents a continuous transition at low shear rate from a viscous to a shear thickening, Bagnoldian, behavior with shear stresses proportional to the shear rate squared, as predicted by a scaling analysis. We show that the heterogeneity results from an unexpectedly fast migration of grains, which we attribute to the emergence of the Bagnoldian rheology. The migration process is observed to be accompanied by macroscopic transient discontinuous shear thickening, which is consequently not an intrinsic property of granular suspensions.

Fall, Abdoulaye; Lemaître, Anaël; Bertrand, François; Bonn, Daniel; Ovarlez, Guillaume

2010-12-01

359

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

360

Thermal conductivity of a granular metal.  

PubMed

Using the Kubo formula approach, we study the effect of electron interaction on thermal transport in the vicinity of a metal-insulator transition, with a granular metal as our model. For small values of dimensionless intergrain tunneling conductance, g<1, we find that the thermal conductivity surprisingly shows a phononlike algebraic decrease, kappa(T) approximately g2T3/E2c even though the electrical conductivity obeys an Arrhenius law, sigma(T) approximately ge-Ec/T ; therefore the Wiedemann-Franz (WF) law is seriously violated. We explicitly show that this violation arises from nonmagnetic bosonic excitations of low energy that transport heat but not charge. At large values of intergrain tunneling, we find it plausible that the WF law weakly deviates from the free-electron theory due to potential fluctuations. Implications for experiment are discussed. PMID:16486870

Tripathi, V; Loh, Y L

2006-02-01

361

Shear thickening of highly viscous granular suspensions  

E-print Network

We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain $\\gamma_c$ and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics $\\eta_\\mu$, dilation $\\eta_c$ and sedimentation $\\eta_g$. While $\\eta_g$ governs the shear thinning regime, $\\eta_\\mu$ and $\\eta_c$ together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cst, $\\eta_\\mu$ is found to compete with $\\eta_c$ and soften the discontinuous nature of shear thickening.

Qin Xu; Sayantan Majumdar; Eric Brown; Heinrich M. Jaeger

2014-04-28

362

Time resolved particle dynamics in granular convection  

NASA Astrophysics Data System (ADS)

We present an experimental study of the movement of individual particles in a layer of vertically shaken granular material. High-speed imaging allows us to investigate the motion of beads within one vibration period. This motion consists mainly of vertical jumps, and a global ordered drift. The analysis of the system movement as a whole reveals that the observed bifurcation in the flight time is not adequately described by the Inelastic Bouncing Ball Model. Near the bifurcation point, friction plays an important role, and the branches of the bifurcation do not diverge as the control parameter is increased. By fitting the grains trajectories near the wall it is possible to quantify the effective acceleration acting on them. A comparison of the mass centre flying time and the flying time determined for the grains near the wall exposes the underlying mechanism that causes the downward flow.

Pastor, J. M.; Maza, D.; Zuriguel, I.; Garcimartín, A.; Boudet, J.-F.

2007-08-01

363

Emotional Granularity and Borderline Personality Disorder  

PubMed Central

This study examined the affective dysregulation component of borderline personality disorder (BPD) from an emotional granularity perspective, which refers to the specificity in which one represents emotions. Forty-six female participants meeting criteria for BPD and 51 female control participants without BPD and Axis I pathology completed tasks that assessed the degree to which participants incorporated information about valence (pleasant–unpleasant) and arousal (calm–activated) in their semantic/conceptual representations of emotions and in using labels to represent emotional reactions. As hypothesized, participants with BPD emphasized valence more and arousal less than control participants did when using emotion terms to label their emotional reactions. Implications and future research directions are discussed. PMID:21171723

Suvak, Michael K.; Litz, Brett T.; Sloan, Denise M.; Zanarini, Mary C.; Barrett, Lisa Feldman; Hofmann, Stefan G.

2011-01-01

364

Software digitizer for high granular gaseous detector  

E-print Network

A sampling calorimeter equipped with gaseous sensor layers with digital readout is near perfect for "Particle Flow Algorithm" approach, since it is homogeneous over large surfaces, robust, cost efficient, easily segmentable to any readout pad dimension and size and almost insensitive to neutrons. The response of a finely segmented digital calorimeter is characterized by track efficiency and multiplicity. Monte Carlo (MC) programs such as GEANT4 simulate with high precision the energy deposited by particles. The sensor and electronic response associated to a pad are calculated in a separate "digitization" process. We developed a general method for simulating the pad response, a digitization, reproducing efficiency and multiplicity, using the spatial information from a simulation done at higher granularity. The digitization method proposed here has been applied to gaseous detectors including Glass Resistive Plate Chambers (GRPC) and MicroMegas. Validating the method on test beam data, experimental observables s...

Haddad, Y; Boudry, V

2014-01-01

365

Moving Granular Bed Filter Development Program  

SciTech Connect

For coal-fired power plants utilizing a gas turbine, the removal of ash particles is necessary to protect the turbine and to meet emission standards. Advantages are also evident for a filter system that can remove other coal-derived contaminants such as alkali, halogens, and ammonia. With most particulates and other contaminants removed, erosion and corrosion of turbine materials, as well as deposition of particles within the turbine, are reduced to acceptable levels. The granular bed filter is suitable for this task in a pressurized gasification or combustion environment. The objective of the base contract was to develop conceptual designs of moving granular bed filter (GBF) and ceramic candle filter technologies for control of particles from integrated gasification combined cycle (IGCC), pressurized fluidized-bed combustion (PFBC), and direct coal-fueled turbine (DCFT) systems. The results of this study showed that the GBF design compared favorably with the candle filter. Three program options followed the base contract. The objective of Option I, Component Testing, was to identify and resolve technical issues regarding GBF development for IGCC and PFBC environments. This program was recently completed. The objective of Option II, Filter Proof Tests, is to test and evaluate the moving GBF system at a government-furnished hot-gas cleanup test facility. This facility is located at Southern Company Services (SCS), Inc., Wilsonville, Alabama. The objective of Option III, Multicontaminant Control Using a GBF, is to develop a chemically reactive filter material that will remove particulates plus one or more of the following coal-derived contaminants: alkali, halogens, and ammonia.

Wilson, K.B.; Haas, J.C. [Combustion Power Co., San Mateo, CA (United States); Gupta, R.P.; Turk, B.S. [Research Triangle Inst., Research Triangle Park, NC (United States)

1996-12-31

366

Impact of wettability on two-phase displacement patterns in granular media  

NASA Astrophysics Data System (ADS)

Two-phase flow in porous media is important in many natural and industrial processes like geologic CO2 sequestration, enhanced oil recovery, water infiltration in soil, and methane venting from organic-rich sediments. While the wetting properties of porous media can vary drastically depending on the type of media and the pore fluids, the effect of wettability on the fluid displacement remains poorly understood. Here, we study experimentally how wettability affects fluid displacement patterns in rigid granular media within the capillary and viscous fingering regimes. The experiments consist of saturating a thin bed of glass beads with a viscous fluid, injecting a less viscous fluid, and imaging the invasion morphology. There are two control parameters: the injection rate of the less viscous fluid and the contact angle, which we control by modifying the surface chemistry of the beads. When the contact angle is fixed at zero (drainage), we recover the well-known transition from capillary fingering to viscous fingering as the injection rate is increased. When the injection rate is fixed, we show that the invasion pattern becomes more stable as the contact angle increases (i.e., as the system transitions from drainage to imbibition), both in the capillary-fingering and viscous-fingering regimes. We quantify the effect of the contact angle on the length scale of the instability, and propose a mechanistic pore-scale model that explains the macroscopic observations. The results demonstrate that wettability can significantly impact multiphase flow in porous media, and highlight the need to better understand the specific effects in many processes such as CO2 sequestration and enhanced oil recovery. Air displacing a water/glycerol mixture within a radial Hele-Shaw cell filled with glass beads. Varying the wetting properties of the solid matrix (horizontal axis) as well as the injection rate (vertical axis) systematically, the invasion pattern stabilizes as the invading phase (air) becomes more wetting.

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

2013-12-01

367

Order of wetting transitions in electrolyte solutions  

E-print Network

For wetting films in dilute electrolyte solutions close to charged walls we present analytic expressions for their effective interface potentials. The analysis of these expressions renders the conditions under which corresponding wetting transitions can be first- or second-order. Within mean field theory we consider two models, one with short- and one with long-ranged solvent-solvent and solvent-wall interactions. The analytic results reveal in a transparent way that wetting transitions in electrolyte solutions, which occur far away from their critical point (i.e., the bulk correlation length is less than half of the Debye length) are always first-order if the solvent-solvent and solvent-wall interactions are short-ranged. In contrast, wetting transitions close to the bulk critical point of the solvent (i.e., the bulk correlation length is larger than the Debye length) exhibit the same wetting behavior as the pure, i.e., salt-free, solvent. If the salt-free solvent is governed by long-ranged solvent-solvent as well as long-ranged solvent-wall interactions and exhibits critical wetting, adding salt can cause the occurrence of an ion-induced first-order thin-thick transition which precedes the subsequent continuous wetting as for the salt-free solvent.

Ingrid Ibagon; Markus Bier; S. Dietrich

2014-02-26

368

Study of the Behavior and Micromechanical Modelling of Granular Soil. Volume 2. An Experimental Investigation of the Behavior of Granular Media Under Load.  

National Technical Information Service (NTIS)

A comprehensive research effort was conducted on constitutive and micromechanical modelling of granular soil. This includes: (1) the development of a new constitutive relation for granular media based on the contact law between two spheres; (2) an experim...

E. Petrakis, P. Kotsanopoulos, P. Van Laak, R. Dobry

1991-01-01

369

Study of the Behavior and Micromechanical Modelling of Granular Soil. Volume 1. A Constitutive Relation for Granular Materials Based on the Contact Law Between Two Spheres.  

National Technical Information Service (NTIS)

A comprehensive research effort was conducted on constitutive and micromechanical modelling of granular soil. This includes: (1) the development of a new constitutive relation for granular media based on the contact law between two spheres; (2) an experim...

E. Petrakis, R. Dobry

1991-01-01

370

GROWTH AND PERSISTENCE OF PATHOGENS ON GRANULAR ACTIVATED CARBON FILTERS  

EPA Science Inventory

Three enteric pathogens Yersinia enterocolitica 0:8, Salmonella typhimurium, and enterotoxigenic Escherichia coli, were examined for their ability to colonize granular activated carbon (GAC) in pure cultures and in the presence of autochthonous river water organisms. All three or...

371

Granular dynamics in a swirled annulus Michael A. Scherer,1  

E-print Network

and can be labeled. This improves experimental techniques, such as visualization of particle trajectories phenomenon is observed. The circular granular array changes its sense of rotation when the particles exceed or event driven codes rely on an almost

Engel, Andreas

372

GRANULAR ACTIVATED CARBON ADSORPTION AND INFRARED REACTIVATION: A CASE STUDY  

EPA Science Inventory

A study evaluated the effectiveness and cost of removing trace organic contaminants and surrogates from drinking water by granular activated carbon (GAC) adsorption. The effect of multiple reactivations of spent GAC was also evaluated. Results indicated that reactivated GAC eff...

373

On the Electrostatics of Pneumatic Conveying of Granular Materials  

E-print Network

In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) vertical pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general ...

Zhu, Kewu

374

Resilient modulus and permanent deformation testing of unbound granular materials  

E-print Network

Numerous research efforts have been devoted to characterizing the behavior of granular materials, which is one of the main concerns of pavement engineers. For better understanding of this behavior, laboratory tests where in-situ stress conditions...

Kancherla, Anuroopa

2005-11-01

375

Defect modes in one-dimensional granular crystals  

E-print Network

We study the vibrational spectra of one-dimensional statically compressed granular crystals (arrays of elastic particles in contact) containing light-mass defects. We focus on the prototypical settings of one or two spherical ...

Boechler, Nicholas Sebastian

376

Brownian motion in granular gases of viscoelastic particles  

SciTech Connect

A theory is developed of Brownian motion in granular gases (systems of many macroscopic particles undergoing inelastic collisions), where the energy loss in inelastic collisions is determined by a restitution coefficient {epsilon}. Whereas previous studies used a simplified model with {epsilon} = const, the present analysis takes into account the dependence of the restitution coefficient on relative impact velocity. The granular temperature and the Brownian diffusion coefficient are calculated for a granular gas in the homogeneous cooling state and a gas driven by a thermostat force, and their variation with grain mass and size and the restitution coefficient is analyzed. Both equipartition principle and fluctuation-dissipation relations are found to break down. One manifestation of this behavior is a new phenomenon of 'relative heating' of Brownian particles at the expense of cooling of the ambient granular gas.

Bodrova, A. S., E-mail: bodrova@polly.phys.msu.ru; Brilliantov, N. V.; Loskutov, A. Yu. [Moscow State University (Russian Federation)

2009-12-15

377

Inert plug formation in the DDT of granular energetic materials  

SciTech Connect

A mechanism is proposed to explain the {open_quotes}plugs{close_quotes} that have been observed in deflagration-to-detonation transition (DDT) of granular explosives. Numerical simulations are performed that demonstrate the proposed mechanism. Observed trends are reproduced.

Son, S.F.; Asay, B.W.; Bdzil, J.B.

1995-09-01

378

Fast spot-based multiscale simulations of granular drainage  

E-print Network

We develop a multiscale simulation method for dense granular drainage, based on the recently proposed spot model, where the particle packing flows by local collective displacements in response to diffusing “spots” of ...

Rycroft, Chris H.

379

Massive granular cell ameloblastoma with dural extension and atypical morphology.  

PubMed

Ameloblastomas are rare histologically benign, locally aggressive tumors arising from the oral ectoderm that occasionally reach a gigantic size. Giant ameloblastomas are a rarity these days with the advent of panoramic radiography in routine dental practice. Furthermore, the granular cell variant is an uncommon histological subtype of ameloblastoma where the central stellate reticulum like cells in tumor follicles is replaced by granular cells. Although granular cell ameloblastoma (GCA) is considered to be a destructive tumor with a high recurrence rate, the significance of granular cells in predicting its biologic behavior is debatable. However, we present a rare case of giant GCA of remarkable histomorphology showing extensive craniofacial involvement and dural extension that rendered a good prognosis following treatment. PMID:25395775

Raghunath, Vandana; Rath, Rachna; Kamal, Firoz; Misra, Satya Ranjan

2014-10-01

380

Massive granular cell ameloblastoma with dural extension and atypical morphology  

PubMed Central

Ameloblastomas are rare histologically benign, locally aggressive tumors arising from the oral ectoderm that occasionally reach a gigantic size. Giant ameloblastomas are a rarity these days with the advent of panoramic radiography in routine dental practice. Furthermore, the granular cell variant is an uncommon histological subtype of ameloblastoma where the central stellate reticulum like cells in tumor follicles is replaced by granular cells. Although granular cell ameloblastoma (GCA) is considered to be a destructive tumor with a high recurrence rate, the significance of granular cells in predicting its biologic behavior is debatable. However, we present a rare case of giant GCA of remarkable histomorphology showing extensive craniofacial involvement and dural extension that rendered a good prognosis following treatment.

Raghunath, Vandana; Rath, Rachna; Kamal, Firoz; Misra, Satya Ranjan

2014-01-01

381

REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON  

EPA Science Inventory

Fenton oxidation and Fenton oxidation preceded by reduction solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration of the carbon coul...

382

21 CFR 133.144 - Granular and stirred curd cheese.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Granular and stirred curd cheese. 133.144 Section 133.144 Food and Drugs...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION CHEESES AND RELATED CHEESE PRODUCTS Requirements for Specific...

2010-04-01

383

21 CFR 133.145 - Granular cheese for manufacturing.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Granular cheese for manufacturing. 133.145 Section 133.145...SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION CHEESES AND RELATED CHEESE PRODUCTS Requirements for Specific...

2010-04-01

384

An adaptive unstructured solver for shallow granular , M. Schafer1  

E-print Network

. Petersburg, Russia Abstract: Free surface flows of granular material show features well known from shallow International Symposium on Shock Waves, Imperial College, London, UK, July 18-23, 1999 #12;An adaptive

Gray, Nico

385

Granular Cell Tumor of the Ulnar Nerve: MR Neurography Characterization  

PubMed Central

The authors report an unusual case of ulnar neuropathy caused by granular cell tumor. The report describes the anatomic 3 Tesla MR Neurography and functional diffusion tensor findings of the case, which was subsequently confirmed on surgical excision and histopathology.

Wadhwa, Vibhor; Salaria, Safia N; Chhabra, Avneesh

2014-01-01

386

Mass transfer in a wetted wall column  

E-print Network

MASS TRANSPER IM A WETTED WALL COLDMM A Thesis Allison M. Platt June, 1950 MASS TRANSFER IN A WETTED WALL COLUMN A Thesis Allison M. Platt June~ 1950 Approved as to st@i and content recommended: Head of the Department of C cal Engineering... MASS TRANSFER IN A WETTED WALL COLUMN A Thesis Submitted to the Faculty of the Agricultural snd Mechanical College oi' Texas Partial FulfiUment of the Requirements for the Degree of Master of Science ~or Sub)ect: Chemical Engineering Allison M...

Platt, Allison M

2012-06-07

387

Wetting transitions at soft, sliding interfaces  

NASA Astrophysics Data System (ADS)

We observe (by optical interferometry) the contact of a rubber cap squeezing a nonwetting liquid against a plate moving at velocity U. At low velocities, the contact is dry. It becomes partially wet above a threshold velocity Vc1, with two symmetrical dry patches on the rear part. Above a second velocity Vc2, the contact is totally wet. This regime U>Vc2 corresponds to the hydroplaning of a car (decelerating on a wet road). We interpret the transitions at Vc1, Vc2 in terms of a competition between (a) liquid invasion induced by shear (b) spontaneous dewetting of the liquid (between nonwettable surfaces).

Martin, A.; Clain, J.; Buguin, A.; Brochard-Wyart, F.

2002-03-01

388

Hydrodynamics of rapid granular flow of inelastic particles into vacuum  

Microsoft Academic Search

  The problem of expansion of a dilute granular gas consisting of smooth, inelastic hard spheres into vacuum was investigated\\u000a by three different methods: both (1) analytical and (2) computational (CFD) treatments of a hydrodynamic model, and (3) by\\u000a Discrete Element Method (DEM) simulation. Furthermore, the systems were followed for long times, over which the granular kinetic\\u000a energy decreases by several

A. Goldshtein; V. Kamenetsky; A. Potapov; M. Shapiro; C. Campbell; D. Degani

2002-01-01

389

A Roadmap from Rough Set Theory to Granular Computing  

Microsoft Academic Search

Granular Computing (GrC) operates with granules (generalized subsets) of data as pieces of basic knowledge. Rough Set Theory\\u000a (RST) is a leading special case of GrC approach. In this paper, we outline a roadmap that stepwise refines RST into GrC. A\\u000a prime illustration is that GrC of symmetric binary relations is a complete topological RST on granular spaces, where the

Tsau Young Lin

2006-01-01

390

Capillarylike Fluctuations at the Interface of Falling Granular Jets  

NASA Astrophysics Data System (ADS)

We study the interface fluctuations of a granular jet falling under gravity and show that for small scales they are the analog of the thermally induced capillary waves. Experimental results from radial height and velocity fluctuations, static correlation functions and capillary ripple velocities allow us to estimate a granular surface tension. The ultralow interfacial tensions measured (of the order of 100?N/m) can be rationalized using a simple model.

Amarouchene, Yacine; Boudet, Jean-François; Kellay, Hamid

2008-05-01

391

Capillarylike fluctuations at the interface of falling granular jets.  

PubMed

We study the interface fluctuations of a granular jet falling under gravity and show that for small scales they are the analog of the thermally induced capillary waves. Experimental results from radial height and velocity fluctuations, static correlation functions and capillary ripple velocities allow us to estimate a granular surface tension. The ultralow interfacial tensions measured (of the order of 100 microN/m) can be rationalized using a simple model. PMID:18518637

Amarouchene, Yacine; Boudet, Jean-François; Kellay, Hamid

2008-05-30

392

Can one ``Hear'' the aggregation state of a granular system?  

NASA Astrophysics Data System (ADS)

If an ensemble of macroscopic particles is mechanically agitated the constant energy input is dissipated into the system by multiple inelastic collisions. As a result, the granular material can exhibit, depending on the magnitude of agitation, several physical states - like a gaseous phase for high energy input or a condensed state for low agitation. Here we introduce a new method for quantifying the acoustical response of the granular system. Our experimental system consists of a monodisperse packing of glass beads with a free upper surface, which is confined inside a cylindrical container. An electro-mechanical shaker exerts a sinusoidal vertical vibration at normalized accelerations well above the fluidization threshold for a monolayer of particles. By increasing the number of beads the granular gas suddenly collapses if a critical threshold is exceeded. The transition can be detected easily with a microphone connected to the soundcard of a PC. From the recorded audio track a FFT is calculated in real-time. Depending on either the number of particles at a fixed acceleration or the amount of energy input for a given number of particles, the resulting rattling noise exhibits a power spectrum with either the dominating (shaker) frequency plus higher harmonics for a granular crystal or a high-frequency broad-band noise for a granular gas, respectively. Our new method demonstrates that it is possible to quantify analytically the subjective audio impressions of a careful listener and thus to distinguish easily between different aggregation states of an excited granular system.

Kruelle, Christof A.; Sánchez, Almudena García

2013-06-01

393

Toward the zero surface tension limit: The granular fingering instability  

E-print Network

The finger-like branching pattern that occurs when a less viscous fluid displaces a more viscous one confined between two parallel plates has been widely studied as a classical example of a mathematically-tractable hydrodynamic instability since the time of Saffman and Taylor. Fingering in such Hele-Shaw geometries have been generated not only with Newtonian fluids but also with various non-Newtonian fluids including fine granular material displaced by gas, liquid, or large grains. Here we study a granular Hele-Shaw system to explore whether the absence of cohesive forces in dry granular material can produce an ideal venue for studying the hitherto-unrealizable singular hydrodynamics predicted in the zero-surface-tension limit. We demonstrate that the grain-gas interface does indeed exhibit fractal structure and sharp cusps associated with finite-time singularities. Above the yield stress, the scaling for the finger width is distinct from that for ordinary fluids, reflecting unique granular properties such as friction-induced dissipation as opposed to viscous damping. Despite such differences, the dimension of the global fractal structure and the shape of the singular cusps on the interface agree with the theories based on simple Laplacian growth of conventional fluid fingering in the zero-surface-tension limit. Our study provides new insights not only on the dynamics of two-phase dense granular flows and granular pattern formation, but also on the fluid dynamics in the zero-surface-tension limit.

Xiang Cheng; Lei Xu; Aaron Patterson; Heinrich M. Jaeger; Sidney R. Nagel

2007-12-12

394

The effectiveness of resistive force theory in granular locomotiona)  

NASA Astrophysics Data System (ADS)

Resistive force theory (RFT) is often used to analyze the movement of microscopic organisms swimming in fluids. In RFT, a body is partitioned into infinitesimal segments, each of which generates thrust and experiences drag. Linear superposition of forces from elements over the body allows prediction of swimming velocities and efficiencies. We show that RFT quantitatively describes the movement of animals and robots that move on and within dry granular media (GM), collections of particles that display solid, fluid, and gas-like features. RFT works well when the GM is slightly polydisperse, and in the "frictional fluid" regime such that frictional forces dominate material inertial forces, and when locomotion can be approximated as confined to a plane. Within a given plane (horizontal or vertical) relationships that govern the force versus orientation of an elemental intruder are functionally independent of the granular medium. We use the RFT to explain features of locomotion on and within granular media including kinematic and muscle activation patterns during sand-swimming by a sandfish lizard and a shovel-nosed snake, optimal movement patterns of a Purcell 3-link sand-swimming robot revealed by a geometric mechanics approach, and legged locomotion of small robots on the surface of GM. We close by discussing situations to which granular RFT has not yet been applied (such as inclined granular surfaces), and the advances in the physics of granular media needed to apply RFT in such situations.

Zhang, Tingnan; Goldman, Daniel I.

2014-10-01

395

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

396

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

397

Dark Matter  

Microsoft Academic Search

Observations in the optical, in X-rays, and gravitational lensing of\\u000agalaxies, clusters of galaxies, and large-scale structure are beginning to\\u000aprovide clues to the dark matter problem. I review the impact of these\\u000aobservations on some of the main questions relating to dark matter: How much\\u000adark matter is there? Where is it located? What is the nature of the

Neta Bahcall

1996-01-01

398

Dark Matter  

SciTech Connect

These proceedings represent papers presented at the Astrophysics conference in Maryland, organized by NASA Goddard Space Flight Center and the University of Maryland. The topics covered included low mass stars as dark matter, dark matter in galaxies and clusters, cosmic microwave background anisotropy, cold and hot dark matter, and the large scale distribution and motions of galaxies. There were eighty five papers presented. Out of these, 10 have been abstracted for the Energy Science and Technology database. (AIP)

Holt, S. S.; Bennett, C. L. [eds.] [NASA Goddard SpaceFlight Center, Greenbelt, MD 20771 (United States)

1995-12-31

399

Wet chemical functionalization of graphene.  

PubMed

The fullerenes, carbon nanotubes, and graphene have enriched the family of carbon allotropes over the last few decades. Synthetic carbon allotropes (SCAs) have attracted chemists, physicists, and materials scientists because of the sheer multitude of their aesthetically pleasing structures and, more so, because of their outstanding and often unprecedented properties. They consist of fully conjugated p-electron systems and are considered topologically confined objects in zero, one, or two dimensions. Among the SCAs, graphene shows the greatest potential for high-performance applications, in the field of nanoelectronics, for example. However, significant fundamental research is still required to develop graphene chemistry. Chemical functionalization of graphene will increase its dispersibility in solvents, improve its processing into new materials, and facilitate the combination of graphene's unprecedented properties with those of other compound classes. On the basis of our experience with fullerenes and carbon nanotubes, we have described a series of covalent and noncovalent approaches to generate graphene derivatives. Using water-soluble perylene surfactants, we could efficiently exfoliate graphite in water and prepare substantial amounts of single-layer-graphene (SLG) and few-layer-graphene (FLG). At the same time, this approach leads to noncovalent graphene derivatives because it establishes efficient ?-?-stacking interactions between graphene and the aromatic perylene chromophors supported by hydrophobic interactions. To gain efficient access to covalently functionalized graphene we employed graphite intercalation compounds (GICs), where positively charged metal cations are located between the negatively charged graphene sheets. The balanced combination of intercalation combined with repulsion driven by Coulombic interactions facilitated efficient exfoliation and wet chemical functionalization of the electronically activated graphene sheets via trapping with reactive electrophilic addends. For example, the treatment of reduced graphite with aryl diazonium salts with the elimination of N(2) led to the formation of arylated graphene. We obtained alkylated graphene via related trapping reactions with alkyl iodides. These new developments have opened the door for combining the unprecedented properties of graphene with those of other compound classes. We expect that further studies of the principles of graphene reactivity, improved characterization methods, and better synthetic control over graphene derivatives will lead to a whole series of new materials with highly specific functionalities and enormous potential for attractive applications. PMID:22946482

Hirsch, Andreas; Englert, Jan M; Hauke, Frank

2013-01-15

400

ESTIMATING URBAN WET-WEATHER POLLUTANT LOADING  

EPA Science Inventory

This paper presents procedures for estimating pollutant loads in urban watersheds emanating from wet-weather flow discharge. Equations for pollutant loading estimates will focus on the effects of wastewater characteristics, sewer flow carrying velocity, and sewer-solids depositi...

401

Wetting transparency of graphene in water  

NASA Astrophysics Data System (ADS)

Measurements of contact angle on graphene sheets show a notable dependence on the nature of the underlying substrate, a phenomenon termed wetting transparency. Our molecular modeling studies reveal analogous transparency in case of submerged graphene fragments in water. A combined effect of attractive dispersion forces, angle correlations between aqueous dipoles, and repulsion due to the hydrogen-bond-induced orientation bias in polarized hydration layers acting across graphene sheet, enhances apparent adhesion of water to graphene. We show wetting free energy of a fully wetted graphene platelet to be about 8 mNm-1 lower than for graphene wetted only on one side, which gives close to 10° reduction in contact angle. This difference has potential implications for predictions of water absorption vs. desorption, phase behavior of water in aqueous nanoconfinements, solvent-induced interactions among graphitic nanoparticle and concomitant stability in aqueous dispersions, and can influence permeability of porous materials such as carbon nanotubes by water and aqueous solutions.

Driskill, Joshua; Vanzo, Davide; Bratko, Dusan; Luzar, Alenka

2014-11-01

402

Wetting transparency of graphene in water.  

PubMed

Measurements of contact angle on graphene sheets show a notable dependence on the nature of the underlying substrate, a phenomenon termed wetting transparency. Our molecular modeling studies reveal analogous transparency in case of submerged graphene fragments in water. A combined effect of attractive dispersion forces, angle correlations between aqueous dipoles, and repulsion due to the hydrogen-bond-induced orientation bias in polarized hydration layers acting across graphene sheet, enhances apparent adhesion of water to graphene. We show wetting free energy of a fully wetted graphene platelet to be about 8 mNm(-1) lower than for graphene wetted only on one side, which gives close to 10° reduction in contact angle. This difference has potential implications for predictions of water absorption vs. desorption, phase behavior of water in aqueous nanoconfinements, solvent-induced interactions among graphitic nanoparticle and concomitant stability in aqueous dispersions, and can influence permeability of porous materials such as carbon nanotubes by water and aqueous solutions. PMID:25399182

Driskill, Joshua; Vanzo, Davide; Bratko, Dusan; Luzar, Alenka

2014-11-14

403

Research on Wetting Collapsible Foundation Soils.  

National Technical Information Service (NTIS)

Irrigation of collapsible soils densifies them near ground surface. For underground pipelines, near-surface soils that have never been irrigated and are highly collapsible should be prewetted to cause soil collapse. The wetted stabilized pad supports the ...

J. P. Bara

1977-01-01

404

Wetting behavior of alternative solder alloys  

SciTech Connect

Recent economic and environmental issues have stimulated interest in solder alloys other than the traditional Sn-Pb eutectic or near eutectic composition. Preliminary evaluations suggest that several of these alloys approach the baseline properties (wetting, mechanical, thermal, and electrical) of the Sn-Pb solders. Final alloy acceptance will require major revisions to existing industrial and military soldering specifications. Bulk alloy and solder joint properties are consequently being investigated to validate their producibility and reliability. The work reported in this paper examines the wetting behavior of several of the more promising commercial alloys on copper substrates. Solder wettability was determined by the meniscometer and wetting balance techniques. The wetting results suggest that several of the alternative solders would satisfy pretinning and surface mount soldering applications. Their use on plated through hole technology might be more difficult since the alloys generally did not spread or flow as well as the 60Sn-40Pb solder.

Hosking, F.M.; Vianco, P.T.; Hernandez, C.L.; Rejent, J.A.

1993-07-01

405

Reducing the atmospheric impact of wet slaking  

SciTech Connect

Means of reducing the atmospheric emissions due to the wet slaking of coke are considered. One option, investigated here, is to remove residual active silt and organic compounds from the biologically purified wastewater sent for slaking, by coagulation and flocculation.

B.D. Zubitskii; G.V. Ushakov; B.G. Tryasunov; A.G.Ushakov [Kuznetsk Basin State Technical University, Kemerovo (Russian Federation)

2009-05-15

406

Wetting on flexible hydrophilic pillar-arrays  

NASA Astrophysics Data System (ADS)

Dynamic wetting on the flexible hydrophilic pillar-arrays is studied using large scale molecular dynamics simulations. For the first time, the combined effect of the surface topology, the intrinsic wettability and the elasticity of a solid on the wetting process is taken into consideration. The direction-dependent dynamics of both liquid and pillars, especially at the moving contact line (MCL), is revealed at atomic level. The flexible pillars accelerate the liquid when the liquid approaches, and pin the liquid when the liquid passes. The liquid deforms the pillars, resulting energy dissipation at the MCL. Scaling analysis is performed based on molecular kinetic theory and validated by our simulations. Our results may expand our knowledge of wetting on pillars and assisting the future design of active control of wetting in practical applications.

Yuan, Quanzi; Zhao, Ya-Pu

2013-06-01

407

A WET TALE: TOXICITY OF COMPLEX EFFLUENTS  

EPA Science Inventory

This course covers standards, regulations, policy, guidance and technical aspects of implementing the whole effluent toxicity program. The curriculum incorporates rationale and information on WET test requirements from USEPA documents, such as the Technical Support Document for W...

408

Breakdown in the Wetting Transparency of Graphene  

E-print Network

We develop a theory to model the van der Waals interactions between liquid and graphene, including quantifying the wetting behavior of a graphene-coated surface. Molecular dynamics simulations and contact angle measurements ...

Shih, Chih-Jen

409

Structure of Wet Specimens in Electron Microscopy  

ERIC Educational Resources Information Center

Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)

Parsons, D. F.

1974-01-01

410

Photoresponsive superhydrophobic surfaces for effective wetting control.  

PubMed

Dynamically tuning the surface wettability has long been a scientific challenge, but of great importance in surface science. Robust superhydrophobic surfaces, displaying switchable and tunable extreme wetting behaviors, are successfully developed by spraying photoresponsive hydrophobic nanoparticles onto various substrates. The surface wettability can be intelligently adjusted by applying irradiation with UV or visible light, which is assumed to initiate large conformation changes of azobenzene units at the coating surface, resulting in distinct surface energy change and thus controlled wetting behaviors. The underlying wetting mechanism about the resulting surfaces is systematically investigated and supported by the estimation of water contact angles using newly rewritten Cassie-Baxter and Wenzel relations and also by the evaluation of solid surface free energy adopting the Owens-Wendt approach. The methodology proposed may provide a novel way of tuning surface wettability and investigating the wetting transition mechanism and also promote applications in self-cleaning and smart fluid control. PMID:25322263

Pan, Shuaijun; Guo, Rui; Xu, Weijian

2014-10-30

411

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

412

Dynamical collision network in granular gases.  

PubMed

We address the problem of recollisions in cooling granular gases. To this aim, we dynamically construct the interaction network in a granular gas, using the sequence of collisions collected in an event driven simulation of inelastic hard disks from time 0 until time t . The network is decomposed into its k -core structure: particles in a core of index k have collided at least k times with other particles in the same core. The difference between cores k+1 and k is the so-called k -shell, and the set of all shells is a complete and nonoverlapping decomposition of the system. Because of energy dissipation, the gas cools down: its initial spatially homogeneous dynamics, characterized by the Haff law, i.e., a t{-2} energy decay, is unstable toward a strongly inhomogeneous phase with clusters and vortices, where energy decays as t{-1} . The clear transition between those two phases appears in the evolution of the k -shells structure in the collision network. In the homogeneous state the k -shell structure evolves as in a growing network with a fixed number of vertices and randomly added links: the shell distribution is strongly peaked around the most populated shell, which has an index k{max} approximately 0.9(d) with (d) the average number of collisions experienced by a particle. During the final nonhomogeneous state a growing fraction of collisions is concentrated in small, almost closed, communities of particles: k{max} is no more linear in (d) and the distribution of shells becomes extremely large developing a power-law tail approximately k{-3} for high shell indexes. We conclude proposing a simple algorithm to build a correlated random network that reproduces, with few essential ingredients, the whole observed phenomenology, including the t{-1} energy decay. It consists of two kinds of collisions (links): single random collisions with any other particle and long chains of recollisions with only previously encountered particles. The algorithm disregards the exact spatial arrangement of clusters, suggesting that the observed stringlike structures are not essential to determine the statistics of recollisions and the energy decay. PMID:17677049

Alvarez-Hamelin, J Ignacio; Puglisi, Andrea

2007-05-01

413

Performance of an aerobic granular sequencing batch reactor fed with wastewaters contaminated with Zn2+.  

PubMed

The main aim of this study was to investigate the performance of an aerobic granular sludge sequencing batch reactor (AGS-SBR) receiving water streams supplied with different loads of Zn(2+) (50 and 100 mg L(-1)) during an operation of 866 cycles (ca. 109 days). When the metal was not fed, chemical oxygen demand (COD), PO4(3-) and NH4(+) were efficiently removed, with efficiencies of 56, 23 and 72% respectively. DGGE profiles showed that Zn(2+) supply negatively affected the bacterial diversity and community structure of the granules. Consequently, the shock loadings with Zn(2+), particularly at the higher levels (100 mg L(-1)), affected the nutrient removal in the AGS-SBR, although the reactor still generally complied with admissible legal values concerning organic matter, nitrogen and Zn. Simultaneous removal of PO4(3-) and TSS in such conditions needs further refining but the application of aerobic granular SBR in the treatment of Zn(2+) contaminated wastewaters seems viable. PMID:23880431

Marques, Ana P G C; Duque, Anouk F; Bessa, Vânia S; Mesquita, Raquel B R; Rangel, António O S S; Castro, Paula M L

2013-10-15

414

Pecan shell-based granular activated carbon for treatment of chemical oxygen demand (COD) in municipal wastewater.  

PubMed

The present investigation was undertaken to compare the adsorption efficiency of pecan shell-based granular activated carbon with the adsorption efficiency of the commercial carbon Filtrasorb 200 with respect to uptake of the organic components responsible for the chemical oxygen demand (COD) of municipal wastewater. Adsorption efficiencies for these two sets of carbons (experimental and commercial) were analyzed by the Freundlich adsorption model. The results indicate that steam-activated and acid-activated pecan shell-based carbons had higher adsorption for organic matter measured as COD, than carbon dioxide-activated pecan shell-based carbon or Filtrasorb 200 at all the carbon dosages used during the experiment. The higher adsorption may be related to surface area as the two carbons with the highest surface area also had the highest organic matter adsorption. These results show that granular activated carbons made from agricultural waste (pecan shells) can be used with greater effectiveness for organic matter removal from municipal wastewater than a coal-based commercial carbon. PMID:15158504

Bansode, R R; Losso, J N; Marshall, W E; Rao, R M; Portier, R J

2004-09-01

415

The effect of target rheology on impact cratering : case for a wet sand  

NASA Astrophysics Data System (ADS)

Rheology of the target material is one of the important factors which controls the crater morphology. There have been several experiments using dry granular materials, one of which showed the importance of particle size which in turn affects the rheology (Walsh et al., PRL, 2003). Wet granular material which is partially saturated with liquid, has a yield stress and therefore its rheology differs from a dry granular material. Here we report the results of impact cratering experiments using a wet sand target with volumetric liquid saturation (S) as the changeable parameter. Experiments were performed by releasing a steel ball from a holder so that it fell vertically into a cylindrical container filled with beach sand (grain size 0.2mm). We use a high-speed camera to record the crater formation process and laser displacement meter to measure crater profiles, diameter and depth. We change water saturation (S=0 - 80%), projectile size (diameter 10 - 22.2 mm) and release height (h = 200-1700mm) and study how the crater size and morphology change with these parameters. For S=0-3%, a cone-shaped crater forms. For S=4.1-5.5% it changes to a cylindrical crater with an outer ring, which forms as the ejecta settles. For S > 5.8% the outer ring disappears because of less ejecta volume. For S > 57%, it becomes accompanied by a depression surrounding the crater. When cylindrical craters form, ejection occurs only from the surface and the ejecta volume decreases with S. However its volume increases again for S > 72% when the target becomes a slurry. Similarly, the crater diameter and depth becomes smaller with S, and then it increases again from about S = 60%. We studied how the depth and the diameter scales with the impactor energy. For dry sand, we confirmed that the power-law exponent becomes close to 1/4, consistent with previous works. However for wet sand (S = 5-20%), we find that it cannot be scaled with energy. We find that the crater diameter is approximately equal to projectile diameter, and the depth/diameter ratio changes with release height. When the projectile is released from a fixed height, the ratio is the same regardless of the projectile size. We also measured the yield stress ? y of the wet sand and found that it is larger than the dry sand by an order of magnitude. Comparing ? y with the inertial stress ? I ˜ (m v2 / R)/ ? R2 (m: ball mass, v: impact velocity, R: ball radius) we find that for dry sand, ? y / ? I ˜ 10-2, whereas for wet sand, ? y / ? I ˜ 10-1. This suggests that morphological change can be associated with this ratio exceeding of the order of 10-1.

Takita, H.; Sumita, I.

2011-12-01

416

Measurements of gravity driven granular channel flows  

NASA Astrophysics Data System (ADS)

This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

Facto, Kevin

417

Thermophilic aerobic granular biomass for enhanced settleability.  

PubMed

Aerobic biological wastewater treatment at thermophilic (ca. 55 degrees C) temperatures notoriously produces biomass that flocculates poorly or not at all. Contrary to this, thermophilic aerobic biomass that settled well in sequencing batch reactors was cultured with sludge volume index (SVI) values as low as 60mL/g. A mixture of granular and flocculant biomass resulted when closed reactors were sparged with recirculated reactor headspace gas containing some air, whereas a conventionally aerated control reactor sparged with air alone contained dispersed growth that did not flocculate. Maximum granule diameter was from 1.2 to 1.9mm, and granule resistance to disintegration was comparable to aerobic mesophilic granules. Two bacteria were isolated and identified as Anoxybacillus flavothermus and Pseudoxanthomonas taiwanensis as determined by partial 16S rDNA sequencing. Anoxybacilli species are alkaliphilic or alkalitolerant, with the type species having an obligate requirement for carbonate, even when grown on glucose. We postulate that high alkalinity and CO(2) may select for a population of aerobic thermophilies that flocculates and granulates. PMID:17229452

Zitomer, Daniel H; Duran, Metin; Albert, Richard; Guven, Engin

2007-02-01

418

Penetration of projectiles into granular targets  

NASA Astrophysics Data System (ADS)

Energetic collisions of subatomic particles with fixed or moving targets have been very valuable to penetrate into the mysteries of nature. But the mysteries are quite intriguing when projectiles and targets are macroscopically immense. We know that countless debris wandering in space impacted (and still do) large asteroids, moons and planets; and that millions of craters on their surfaces are traces of such collisions. By classifying and studying the morphology of such craters, geologists and astrophysicists obtain important clues to understand the origin and evolution of the Solar System. This review surveys knowledge about crater phenomena in the planetary science context, avoiding detailed descriptions already found in excellent papers on the subject. Then, it examines the most important results reported in the literature related to impact and penetration phenomena in granular targets obtained by doing simple experiments. The main goal is to discern whether both schools, one that takes into account the right ingredients (planetary bodies and very high energies) but cannot physically reproduce the collisions, and the other that easily carries out the collisions but uses laboratory ingredients (small projectiles and low energies), can arrive at a synergistic intersection point.

Ruiz-Suárez, J. C.

2013-06-01

419

Penetration of projectiles into granular targets.  

PubMed

Energetic collisions of subatomic particles with fixed or moving targets have been very valuable to penetrate into the mysteries of nature. But the mysteries are quite intriguing when projectiles and targets are macroscopically immense. We know that countless debris wandering in space impacted (and still do) large asteroids, moons and planets; and that millions of craters on their surfaces are traces of such collisions. By classifying and studying the morphology of such craters, geologists and astrophysicists obtain important clues to understand the origin and evolution of the Solar System. This review surveys knowledge about crater phenomena in the planetary science context, avoiding detailed descriptions already found in excellent papers on the subject. Then, it examines the most important results reported in the literature related to impact and penetration phenomena in granular targets obtained by doing simple experiments. The main goal is to discern whether both schools, one that takes into account the right ingredients (planetary bodies and very high energies) but cannot physically reproduce the collisions, and the other that easily carries out the collisions but uses laboratory ingredients (small projectiles and low energies), can arrive at a synergistic intersection point. PMID:23660625

Ruiz-Suárez, J C

2013-06-01

420

Fluidized bed gasification of select granular biomaterials.  

PubMed

Biomaterials can be converted into solid, liquid and gaseous fuels through thermochemical or biochemical conversion processes. Thermochemical conversion of granular biomaterials is difficult because of its physical nature and one of the suitable processes is fluidized bed gasification. In this study, coir pith, rice husk and saw dust were selected and synthetic gas was generated using a fluidized bed gasifier. Gas compositions of product gas were analyzed and the percentage of carbon monoxide and carbon dioxide was in the range of 8.24-19.55 and 10.21-17.14, respectively. The effect of equivalence ratio (0.3, 0.4 and 0.5) and reaction time (at 10 min interval) on gas constituents was studied. The gas yield for coir pith, rice husk and sawdust were found to be in the range of 1.98-3.24, 1.79-2.81 and 2.18-3.70 Nm3 kg(-1), respectively. Models were developed to study the influence of biomaterial properties and operating conditions on molar concentration of gas constituents and energy output. PMID:20817445

Subramanian, P; Sampathrajan, A; Venkatachalam, P

2011-01-01

421

Spatial Distribution of Forces within Granular Materials  

NASA Astrophysics Data System (ADS)

Granular materials display surprisingly inhomogeneous distributions of forces. Some chains of inter-grain contacts carry forces much greater than the mean while other contacts with adjacent particles carry almost no force at all, resulting in the phenomenon of force chains. Recently, a theoretical framework for understanding the spatial distribution of these networks of force chains was proposed by analogy to bond percolation theory [Ostojic, S., Somfai, E. and Nienhuis, B. Nature 439, 828—830 (2006)]. In this experimental work, we test these predictions on static, isotropic force networks in two-dimensions using photo-elastic techniques. We observe the distribution of clusters of grains connected by contacts with forces in excess of a threshold of the mean force. We find that these distributions can be scaled to a function that is independent of overall isotropic pressure. We then use a numerical model to predict similar scale-independence for anisotropic pressures. We believe our results provide evidence for a mechanism for comparing the spatial fluctuations on the laboratory-scale with other systems.

Wambaugh, John; Behringer, Robert

2006-11-01

422

Evolution of shear zones in granular materials  

E-print Network

The evolution of wide shear zones (or shear bands) was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains (e.g. sand) and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g. sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rod like particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear induced density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.

Balazs Szabo; Janos Torok; Ellak Somfai; Sandra Wegner; Ralf Stannarius; Axel Bose; Georg Rose; Frank Angenstein; Tamas Borzsonyi

2014-07-18

423

Deflagration to detonation experiments in granular HMX  

SciTech Connect

In this paper the authors report on continuing work involving a series of deflagration-to-detonation transition (DDT) experiments in which they study the piston-initiated DDT of heavily confined granular cyclotetramethylenetetranitramine (HMX). These experiments were designed to he useful in model development and evaluation. A main focus of these experiments is the effect of density on the DDT event. Particle size distribution and morphology are carefully characterized. In this paper they present recent surface area analysis. Earlier studies demonstrated extensive fracturing and agglomeration in samples at densities as low as 75% TMD as evidenced by dramatic decreases in particle size distribution due to mild stimulus. This is qualitatively confirmed with SEM images and quantitatively studied with gas absorption surface area analysis. Also, in this paper they present initial results using a microwave interferometer technique. Dynamic calibration of the technique was performed, a 35 GHz signal is used to increase resolution, and the system has been designed to be inexpensive for repeated experiments. The distance to where deformation of the inner wall begins for various densities is reported. This result is compared with the microwave interferometer measurements.

Burnside, N.J.; Son, S.F.; Asay, B.W.; Dickson, P.M.

1998-03-01

424

Geometrical families of mechanically stable granular packings  

NASA Astrophysics Data System (ADS)

We enumerate and classify nearly all of the possible mechanically stable (MS) packings of bidipserse mixtures of frictionless disks in small sheared systems. We find that MS packings form continuous geometrical families, where each family is defined by its particular network of particle contacts. We also monitor the dynamics of MS packings along geometrical families by applying quasistatic simple shear strain at zero pressure. For small numbers of particles (N<16) , we find that the dynamics is deterministic and highly contracting. That is, if the system is initialized in a MS packing at a given shear strain, it will quickly lock into a periodic orbit at subsequent shear strain, and therefore sample only a very small fraction of the possible MS packings in steady state. In studies with N>16 , we observe an increase in the period and random splittings of the trajectories caused by bifurcations in configuration space. We argue that the ratio of the splitting and contraction rates in large systems will determine the distribution of MS-packing geometrical families visited in steady state. This work is part of our long-term research program to develop a master-equation formalism to describe macroscopic slowly driven granular systems in terms of collections of small subsystems.

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

2009-12-01

425

Evolution of shear zones in granular materials  

NASA Astrophysics Data System (ADS)

The evolution of wide shear zones or shear bands was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains, such as sand, and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e., when the grain shape changes from spherical to irregular (e.g., sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rodlike particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear-induced packing density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.

Szabó, Balázs; Török, János; Somfai, Ellák; Wegner, Sandra; Stannarius, Ralf; Böse, Axel; Rose, Georg; Angenstein, Frank; Börzsönyi, Tamás

2014-09-01

426

Shear Reversibility in Model Granular Systems  

NASA Astrophysics Data System (ADS)

Athermal particulate systems such as foams and granular media are out-of-thermal equilibrium and therefore must be externally driven using shear or vibration to explore different configurations. Of particular interest is being able to predict and control the structural and mechanical properties of athermal systems as a function of the driving mechanism. In this work, we show numerically how particle collisions in cyclically sheared hard sphere systems can lead to microreversibility. We map out the steady-state ``phase diagram'' as a function of packing fraction (?) and strain amplitude (?max), and identify ``point-reversible'' states at low ? and ?max in which particles do not collide over the course of a shear cycle, and ``loop-reversible'' states at intermediate ? and ?max in which particles undergo numerous collisions but return to their initial positions at the end of each shear cycle. Loop-reversiblity is a novel form of self organization that gives rise to non-fluctuating dynamical states over a broad range of packing fractions from contact percolation to jamming, i.e. ?P=0.55 to ?J=0.84 in two dimensions.

Schreck, Carl; Hoy, Rob; Shattuck, Mark; O'Hern, Corey

2013-03-01

427

Granular Material Flows with Interstitial Fluid Effects  

NASA Technical Reports Server (NTRS)

The research focused on experimental measurements of the rheological properties of liquid-solid and granular flows. In these flows, the viscous effects of the interstitial fluid, the inertia of the fluid and particles, and the collisional interactions of the particles may all contribute to the flow mechanics. These multiphase flows include industrial problems such as coal slurry pipelines, hydraulic fracturing processes, fluidized beds, mining and milling operation, abrasive water jet machining, and polishing and surface erosion technologies. In addition, there are a wide range of geophysical flows such as debris flows, landslides and sediment transport. In extraterrestrial applications, the study of transport of particulate materials is fundamental to the mining and processing of lunar and Martian soils and the transport of atmospheric dust (National Research Council 2000). The recent images from Mars Global Surveyor spacecraft dramatically depict the complex sand and dust flows on Mars, including dune formation and dust avalanches on the slip-face of dune surfaces. These Aeolian features involve a complex interaction of the prevailing winds and deposition or erosion of the sediment layer; these features make a good test bed for the verification of global circulation models of the Martian atmosphere.

Hunt, Melany L.; Brennen, Christopher E.

2004-01-01

428

Software digitizer for high granular gaseous detector  

E-print Network

A sampling calorimeter equipped with gaseous sensor layers with digital readout is near perfect for "Particle Flow Algorithm" approach, since it is homogeneous over large surfaces, robust, cost efficient, easily segmentable to any readout pad dimension and size and almost insensitive to neutrons. The response of a finely segmented digital calorimeter is characterized by track efficiency and multiplicity. Monte Carlo (MC) programs such as GEANT4 simulate with high precision the energy deposited by particles. The sensor and electronic response associated to a pad are calculated in a separate "digitization" process. We developed a general method for simulating the pad response, a digitization, reproducing efficiency and multiplicity, using the spatial information from a simulation done at higher granularity. The digitization method proposed here has been applied to gaseous detectors including Glass Resistive Plate Chambers (GRPC) and MicroMegas. Validating the method on test beam data, experimental observables such as efficiency, multiplicity and mean number of hits at different thresholds have been reproduced with high precision.

Y. Haddad; M. Ruan; V. Boudry

2014-05-06

429

77 FR 71578 - Pure Magnesium in Granular Form From the People's Republic of China; Final Results of Antidumping...  

Federal Register 2010, 2011, 2012, 2013

...Administration [A-570-864] Pure Magnesium in Granular Form From the People's...of the antidumping duty order on pure magnesium in granular form from the People's...of the antidumping duty order on pure magnesium in granular...

2012-12-03

430

76 FR 1404 - Pure Magnesium in Granular Form From the People's Republic of China: Rescission of Changed...  

Federal Register 2010, 2011, 2012, 2013

...Administration [A-570-864] Pure Magnesium in Granular Form From the People's...antidumping duty order \\1\\ on pure magnesium in granular form from the People's...1\\ See Antidumping Duty Order: Pure Magnesium in Granular Form From the...

2011-01-10

431

Granular magnetoresistance in cobalt/poly ,,3-hexylthiophene, 2, 5-diyl... hybrid thin films prepared by a wet chemical method  

E-print Network

transport4 and in practical applications.5 Specifically, magnetoresistance can be exhibited in magnetic with the current trend of employing organic semiconducting materials in various electronic devices including solar-cost devices.9 However, the development of an all- organic, physically flexible, magnetoresistance device

Krishnan, Kannan M.

432

Soil aggregate formation: the role of wetting-drying cycles in the genesis of interparticle bonding  

NASA Astrophysics Data System (ADS)

Soil structure influences many soil properties including aeration, water retention, drainage, bulk density, and resistance to erosion and indirectly influences most biological and chemical processes that occur in and around soil. In nature, soil is continually exposed to wetting (e.g., rainfall and diffusive flow) and drying (e.g., evaporation, diffusive flow and plant uptake). These natural wetting and drying cycles of soils are physical events that profoundly affect the development of soil structure, aggregate stability, carbon (C) flux and mineralization. We hypothesize that drying of capillary water transports suspended and/or dissolved cementing agents toward inter-particle contacts and eventually deposits part of the colloidal mass forming inter-particle bonds. Here, we will show the role of wetting and drying cycles on soil aggregation and stabilization and how these cycles transport and deposit organic cementing agents at the inter-particle contact. We found that aggregates of sand and silt particles can be formed by subjecting loose particles to wetting-drying cycles in the presence of dilute solutions of organic matter that mimic root or microbial exudates. Moreover, majority of the organic matter was deposited in the contact region between the sand particles, where the water accumulates during drying. The model predictions and aggregate stability measurements are supported by scanning electron micrographs that clearly show the process of aggregate formation.

Albalasmeh, Ammar; Ghezzehei, Teamrat

2013-04-01

433

Epimacular brachytherapy for wet AMD: current perspectives  

PubMed Central

Age-related macular degeneration (AMD) is considered the most common cause of blindness in the over-60 age group in developed countries. There are basically two forms of presentation: geographic (dry or atrophic) and wet (neovascular or exudative). Geographic atrophy accounts for approximately 85%–90% of ophthalmic frames and leads to a progressive degeneration of the retinal pigment epithelium and the photoreceptors. Wet AMD causes the highest percentage of central vision loss secondary to disease. This neovascular form involves an angiogenic process in which newly formed choroidal vessels invade the macular area. Today, intravitreal anti-angiogenic drugs attempt to block the angiogenic events and represent a major advance in the treatment of wet AMD. Currently, combination therapy for wet AMD includes different forms of radiation delivery. Epimacular brachytherapy (EMBT) seems to be a useful approach to be associated with current anti-vascular endothelial growth factor agents, presenting an acceptable efficacy and safety profile. However, at the present stage of research, the results of the clinical trials carried out to date are insufficient to justify extending routine use of EMBT for the treatment of wet AMD.

Casaroli-Marano, Ricardo P; Alforja, Socorro; Giralt, Joan; Farah, Michel E

2014-01-01

434

Erosion of a granular bed driven by laminar fluid flow  

E-print Network

Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.

A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman

2008-05-01

435

Entanglement and Relaxation of Liquid Crystal Shaped Granular Media  

NASA Astrophysics Data System (ADS)

We studied the entanglement and relaxation of V-shaped, U-shaped, and rod-shaped granular media. Our experiment was modeled after Gravish et al.'s work [1]. A clear understanding on how these particles interact with each other on a macroscopic scale can help us model how microscopic liquid crystal molecules with similar shapes behave. In order to entangle the granular media, the particles were subjected to a sinusoidal acceleration within a confined cylinder. Once entangled the cylinder was removed to leave a freestanding column, which was then accelerated at various 'g forces' to untangle and cause a collapse. Video recordings of the experiment were used to analyze the dynamics of packing and collapse. The U-shaped granular media took a longer time to relax in comparison with the rod-shaped and V-shaped granular media. We conclude that this is because the U-shaped granular media had 90^o angles, which allowed the particles to latch on to each other better than the rod-shaped and the V-shaped particles. [1] N. Gravish, S. Franklin, D. Hu, D. Goldman, Phys. Rev. Lett., 108, 208001 (2012).

Albon, Theresa; Iglesias, Wilder; Jakli, Antal; Garg, Shila

2013-03-01

436

Liquid drop impact cratering on a granular layer  

NASA Astrophysics Data System (ADS)

Granular impact cratering has been studied both in terms of planetary science and fundamental granular physics. Recent studies have revealed morphological scaling and dynamics of the granular impact cratering phenomenon. In all these studies, solid impactors have been used. However, the actual geophysical scale impactors might be melt. To mimic what happens when the impactor is melt, we performed simple drop granular impact experiment. A small (millimeter scale) water drop was dropped onto a granular layer (abrasives of micrometer grain size) at low impact speed (about meter/second). Then, various kinds of novel crater shapes were discovered depending on the experimental conditions. For instance, "sink type", "flat type", "ring type", and "bump type" craters were observed. We measured the characteristic time scale and length scale of the cratering, using a high speed camera and a laser profilometry system. From the experimental data, a simple scaling of the crater radius is proposed. The obtained scaling exponent is same as that of usual solid impact cratering. In the solid impactor case, the scaling exponent is derived from energy balance between impactor and ejecta. However, we found that the liquid drop deformation determines the scaling exponent in this experiment. We have also used glycerol and ethanol and their aqueous solutions, in order to examine the effect of viscosity and capillary force of liquid drops. A picture of the impacting drop is shown below. A water drop impacting onto a layer of abrasive.

Katsuragi, H.

2010-12-01

437

Influence of network topology on sound propagation in granular materials  

NASA Astrophysics Data System (ADS)

Granular media, whose features range from the particle scale to the force-chain scale and the bulk scale, are usually modeled as either particulate or continuum materials. In contrast with each of these approaches, network representations are natural for the simultaneous examination of microscopic, mesoscopic, and macroscopic features. In this paper, we treat granular materials as spatially embedded networks in which the nodes (particles) are connected by weighted edges obtained from contact forces. We test a variety of network measures to determine their utility in helping to describe sound propagation in granular networks and find that network diagnostics can be used to probe particle-, curve-, domain-, and system-scale structures in granular media. In particular, diagnostics of mesoscale network structure are reproducible across experiments, are correlated with sound propagation in this medium, and can be used to identify potentially interesting size scales. We also demonstrate that the sensitivity of network diagnostics depends on the phase of sound propagation. In the injection phase, the signal propagates systemically, as indicated by correlations with the network diagnostic of global efficiency. In the scattering phase, however, the signal is better predicted by mesoscale community structure, suggesting that the acoustic signal scatters over local geographic neighborhoods. Collectively, our results demonstrate how the force network of a granular system is imprinted on transmitted waves.

Bassett, Danielle S.; Owens, Eli T.; Daniels, Karen E.; Porter, Mason A.

2012-10-01

438

Granular physics in low-gravity environments using DEM  

E-print Network

Granular materials of different sizes are present on the surface of several atmosphere-less Solar System bodies. The phenomena related to granular materials have been studied in the framework of the discipline called Granular Physics; that has been studied experimentally in the laboratory and, in the last decades, by performing numerical simulations. The Discrete Element Method simulates the mechanical behavior of a media formed by a set of particles which interact through their contact points. The difficulty in reproducing vacuum and low-gravity environments makes numerical simulations the most promising technique in the study of granular media under these conditions. In this work, relevant processes in minor bodies of the Solar System are studied using the Discrete Element Method. Results of simulations of size segregation in low-gravity environments in the cases of the asteroids Eros and Itokawa are presented. The segregation of particles with different densities was analysed, in particular, the case of comet P/Hartley 2. The surface shaking in these different gravity environments could produce the ejection of particles from the surface at very low relative velocities. The shaking causing the above processes is due to: impacts, explosions like the release of energy by the liberation of internal stresses or the re accommodation of material. Simulations of the passage of impact-induced seismic waves through a granular medium were also performed. We present several applications of the Discrete Element Methods for the study of the physical evolution of agglomerates of rocks under low-gravity environments.

G. Tancredi; A. Maciel; L. Heredia; P. Richeri; S. Nesmachnow

2011-11-26

439

Bianchi type VI1 cosmological model with wet dark fluid in scale invariant theory of gravitation  

E-print Network

In this paper, we have investigated Bianchi type VIh, II and III cosmological model with wet dark fluid in scale invariant theory of gravity, where the matter field is in the form of perfect fluid and with a time dependent gauge function (Dirac gauge). A non-singular model for the universe filled with disorder radiation is constructed and some physical behaviors of the model are studied for the feasible VIh (h = 1) space-time.

B. Mishra; P. K. Sahoo

2014-07-29

440

Electrical and mechanical properties of polyaniline fibres produced by a one-step wet spinning process  

Microsoft Academic Search

We have recently developed a new acid-solution processing route for the conjugated polymer, polyaniline (PANi) [Adams et al., J Phys: Condens Matter 1998;10:8293] that now allows us to demonstrate the wet-spinning of inherently conductive PANi fibres in a one-step process. This is achieved from solutions of PANi protonated with 2-acrylamido-2-methyl-1-propanesulfonic acid in dichloroacetic acid. The fibres were spun into various

S. J Pomfret; P. N Adams; N. P Comfort; A. P Monkman

2000-01-01

441

Plant Survival in Wet Environments: Resilience and Escape Mediated by Shoot Systems  

Microsoft Academic Search

Species inhabiting marshland, river banks and similar places possess metabolic and developmental features that support long-term\\u000a survival of flooding, sometimes in combination with remarkably fast rates of dry matter accumulation (Maltby 1991).This success\\u000a in wet environments can be attributed to a combination of several physiological, metabolic and structural characteristics.\\u000a Their blending and relative prominence vary widely between species and help

Michael B. Jackson

442

The impact of cyclic wetting and drying on the swelling behaviour of stabilized expansive soils  

Microsoft Academic Search

Black cotton soil (BCS) deposits, stabilized with waste materials-wood-ash and organic matter (leaves, grass, etc.) exist in BCS areas of North Karnataka, India. These ash-modified soils (AMS) are apparently stabilized by hydrated lime produced by biochemical, dissolution, and hydration reactions. The influence of cyclic wetting and drying on the swelling behaviour of wood-ash-modified BCS and laboratory lime-treated BCS specimens are

S. M Rao; B. V. V Reddy; M Muttharam

2001-01-01

443

Natural Resources Conservation Service Rockport, INDRAINAGE AND WET SOIL MANAGEMENT WET SOILS OF INDIANA  

E-print Network

Soils are one of Indiana’s greatest natural resources. Wet soils are of special interest because of their hydrologic and ecological importance when kept in their natural state and their importance for agricultural production when drained. As used here, “wet soils ” refers, in a general sense, to soils that have excess water at some time of the year and are important for crop production. This publication discusses the basic characteristics of wet soils, how they function in their natural state, and how they might react to drainage for agricultural production. It supports a publication on wetlands and several publications on drainage in this series of publications. 1 CLASSIFICATION OF WET SOILS For many years, people have been interested in classifying soils according to how wet they are. Several schemes are in use. NATURAL DRAINAGE CLASSES Natural drainage classes are mentioned frequently in this

D. P. Franzmeier; Department Of Agronomy; David Drew; D. P. Franzmeier; E. J. Kladivko

2001-01-01

444

Force networks and elasticity in granular silos.  

PubMed

We have made experimental observations of the force networks within a two-dimensional granular silo similar to the classical system of Janssen. Models like that of Janssen predict that pressure within a silo saturates with depth as the result of vertical forces being redirected to the walls of the silo where they can then be carried by friction. We use photoelastic particles to obtain information not available in previous silo experiments --the internal force structure. We directly compare various predictions with the results obtained by averaging ensembles of experimentally obtained force networks. We identify several differences between the mean behavior in our system and that predicted by Janssen-like models: We find that the redirection parameter describing how the force network transfers vertical forces to the walls varies with depth. We find that changes in the preparation of the material can cause the pressure within the silo to either saturate or to continue building with depth. Most strikingly, we observe a nonlinear response to overloads applied to the top of the material in the silo. For larger overloads we observe the previously reported "giant overshoot" effect where overload pressure decays only after an initial increase (G. Ovarlez et al., Phys. Rev. E 67, 060302(R) (2003)). For smaller overloads we find that additional pressure propagates to great depth. Analysis of the differences between the inter-grain contact and force networks suggests that, for our system, when the load and the particle weight are comparable, particle elasticity acts to stabilize the force network, allowing deep propagation. For larger loads, the force network rearranges, resulting in the expected, Janssen-like behavior. Thus, a meso-scale network phenomenon results in an observable nonlinearity in the mean pressure profile. PMID:20582447

Wambaugh, J F; Hartley, R R; Behringer, R P

2010-06-01

445

TAILORING ACTIVATED CARBONS FOR ENHANCED REMOVAL OF NATURAL ORGANIC MATTER FROM NATURAL WATERS. (R828157)  

EPA Science Inventory

Several pathways have been employed to systematically modify two granular activated carbons (GACs), F400 (coal-based) and Macro (wood-based), for examining adsorption of dissolved natural organic matter (DOM) from natural waters. A total of 24 activated carbons with different ...

446

Analysis of wet granulation process with Plackett-Burman design--case study.  

PubMed

According to Process Analytical Technology perspective, drug product quality should be ensured by manufacturing process design. Initial step of the process analysis is investigation of critical process parameters (CPPs). It is generally accepted to type the CPPs based on project team knowledge and experience [5]. This paper describes the use of Design of Experiments tool for selection of the CPPs. Seven factors of wet granulation process were investigated for criticality. Low and high levels of each factor represented maximal and minimal settings of wide operational ranges. Granulates were produced in line with Plackett-Burman experimental matrix, blended with extra-granular excipients and compressed into tablets. Semi-products and final products were tested. Out of specification result of any critical quality attribute was treated as critical failure. The high-shear granulation factors, i.e. quantity of binding solution, rotational speed of impeller and wet massing time were considered of critical importance. Operational ranges of the parameters were optimized. The process performance was confirmed in qualification trials. PMID:21928718

Woyna-Orlewicz, Krzysztof; Jachowicz, Renata

2011-01-01

447

A predictive, size-dependent continuum model for dense granular flows  

E-print Network

Dense granular materials display a complicated set of flow properties, which differentiate them from ordinary fluids. Despite their ubiquity, no model has been developed that captures or predicts the complexities of granular ...

Henann, David Lee

448

Isaac Newton Institute for Mathematical Sciences Granular and Particle-Laden Flows  

E-print Network

Isaac Newton Institute for Mathematical Sciences Granular and Particle-Laden Flows 1 September ­ 19) This research programme at the Newton Institute will be devoted to improving our understanding of granular

449

7 CFR 58.711 - Cheddar, colby, washed or soaked curd, granular or stirred curd cheese.  

Code of Federal Regulations, 2010 CFR

...colby, washed or soaked curd, granular or stirred curd cheese. 58.711 Section 58.711 Agriculture Regulations...colby, washed or soaked curd, granular or stirred curd cheese. Cheese, used in the manufacture of pasteurized process...

2010-01-01

450

Classifying Matter  

NSDL National Science Digital Library

The representation is a picture of the arrangement of particles in the 3 states of matter. The picture does not show movement. There is accompanying text that describes movement and arrangement of the particles.

451

Mystery Matter  

NSDL National Science Digital Library

This is an activity about the states of matter. Learners will participate in a demonstration to reintroduce them to three states of matter: solid, liquid, and gas. The demonstration also introduces them to a fourth state of matter, plasma, through investigation of the properties of volume and shape as they relate to common solids, liquids, and gases, and to the mystery matter later identified at the end as plasma. The demonstration also covers plasma's connection to the Sun and connections to science related to the Interstellar Boundary Explorer, or IBEX, spacecraft. This activity complements other IBEX informal education materials. The demonstration requires use of a small plasma ball and, ideally, a slightly darkened room so that the plasma ball can be more easily seen. An instructional video explaining how to facilitate this activity is available: http://bit.ly/125ZW5k.

452

Antimatter Matters  

NSDL National Science Digital Library

Antimatter, the charge reversed equivalent of matter, has captured the imaginations of science fiction fans for years as a perfectly efficient form of energy. While normal matter consists of atoms with negatively charged electrons orbiting positively charged nuclei, antimatter consists of positively charged positrons orbiting negatively charged anti-nuclei. When antimatter and matter meet, both substances are annihilated, creating massive amounts of energy. Instances in which antimatter is portrayed in science fiction stories (such as Star Trek) are examined, including their purposes (fuel source, weapons, alternate universes) and properties. Students compare and contrast matter and antimatter, learn how antimatter can be used as a form of energy, and consider potential engineering applications for antimatter.

National Science Foundation GK-12 and Research Experience for Teachers (RET) Programs,

453

Memory Matters  

MedlinePLUS

... stored away in different areas of the cerebral cortex , or the "gray matter" of the brain — the ... activities, like reading and doing puzzles, you can exercise your mind so you'll be remembering great ...

454

Chimney liners for wet FGD service  

SciTech Connect

In order to meet pollution compliance requirements, many Utilities are adding wet scrubbers to reduce SO{sub 2} emissions. The gas temperatures produced by wet scrubbers also can lead to increased condensation of moisture on interior surfaces of chimney linings and ductwork. This increased condensation can, in turn, increase the risk of corrosion. To protect moist surfaces of chimney liners and ductwork from acid attack, new design and construction methods are required. Materials including high nickel, chrome and titanium alloys are being employed as well as modifications to the widely used acid resistant brick liners which have been conventionally used. This paper explores the experience of chimney manufacturers and builders to address the requirements of operation with wet scrubbers. This includes issues of liner ve