Gravity-driven dense granular flows
Energy Technology Data Exchange (ETDEWEB)
ERTAS,DENIZ; GREST,GARY S.; HALSEY,THOMAS C.; DEVINE,DOV; SILBERT,LEONARDO E.
2000-03-29
The authors report and analyze the results of numerical studies of dense granular flows in two and three dimensions, using both linear damped springs and Hertzian force laws between particles. Chute flow generically produces a constant density profile that satisfies scaling relations suggestive of a Bagnold grain inertia regime. The type for force law has little impact on the behavior of the system. Failure is not initiated at the surface, consistent with the absence of surface flows and different principal stress directions at vs. below the surface.
Averaging processes in granular flows driven by gravity
Rossi, Giulia; Armanini, Aronne
2016-04-01
One of the more promising theoretical frames to analyse the two-phase granular flows is offered by the similarity of their rheology with the kinetic theory of gases [1]. Granular flows can be considered a macroscopic equivalent of the molecular case: the collisions among molecules are compared to the collisions among grains at a macroscopic scale [2,3]. However there are important statistical differences in dealing with the two applications. In the two-phase fluid mechanics, there are two main types of average: the phasic average and the mass weighed average [4]. The kinetic theories assume that the size of atoms is so small, that the number of molecules in a control volume is infinite. With this assumption, the concentration (number of particles n) doesn't change during the averaging process and the two definitions of average coincide. This hypothesis is no more true in granular flows: contrary to gases, the dimension of a single particle becomes comparable to that of the control volume. For this reason, in a single realization the number of grain is constant and the two averages coincide; on the contrary, for more than one realization, n is no more constant and the two types of average lead to different results. Therefore, the ensamble average used in the standard kinetic theory (which usually is the phasic average) is suitable for the single realization, but not for several realization, as already pointed out in [5,6]. In the literature, three main length scales have been identified [7]: the smallest is the particles size, the intermediate consists in the local averaging (in order to describe some instability phenomena or secondary circulation) and the largest arises from phenomena such as large eddies in turbulence. Our aim is to solve the intermediate scale, by applying the mass weighted average, when dealing with more than one realizations. This statistical approach leads to additional diffusive terms in the continuity equation: starting from experimental
Directed clustering in driven compartmentalized granular gas systems in zero gravity
International Nuclear Information System (INIS)
Li, Y; Hou, M; Evesque, P
2011-01-01
Clustering of shaken fluidized granular matter in connected compartments has been observed and studied in the laboratory. This clustering behavior in granular gas systems is related to the dissipative nature of granular system, and therefore shall not depend on gravity. This clustering phenomenon in compartmental configuration may provide a means for particle depletion and transportation in microgravity environment. In this work we propose different configurations for possible directed clustering in zero gravity. The related experiment has been planned for the Chinese satellite SJ-10.
Gravity-driven, dry granular flows over a loose bed in stationary and homogeneous conditions
Meninno, Sabrina; Armanini, Aronne; Larcher, Michele
2018-02-01
Flows involving solid particulates have been widely studied in recent years, but their dynamics are still a complex issue to model because they strongly depend on the interaction with the boundary conditions. We report on laboratory investigations regarding homogeneous and steady flows of identical particles over a loose bed in a rectangular channel. Accurate measurements were carried out through imaging techniques to estimate profiles of the mean velocity, solid concentration, and granular temperature for a large set of flow rates and widths. Vertical and transversal structures observed in the flow change as interparticle interactions become more collisional, and they depend on the bottom over which the flow develops. The lateral confinement has a remarkable effect on the flow, especially for narrow channels compared with the grain size, and a hydraulic analogy is able to show how the walls influence the mechanisms of friction and energy dissipation.
Granular rheology in zero gravity
Energy Technology Data Exchange (ETDEWEB)
Bossis, G [LPMC UMR 6622, Universite de Nice, Parc Valrose, 06108 Nice Cedex 2 (France); Grasselli, Y [EAI Tech CERAM, Rue A Einstein, BP 085, 06902 Sophia Antipolis Cedex (France); Volkova, O [LPMC UMR 6622, Universite de Nice, Parc Valrose, 06108 Nice Cedex 2 (France)
2004-05-12
We present an experimental investigation on the rheological behaviour of model granular media made of nearly elastic spherical particles. The experiments are performed in a cylindrical Couette geometry and the experimental device is placed inside an aeroplane undergoing parabolic flights to cancel the effect of gravity. The corresponding curves, shear stress versus shear rate, are presented, and a comparison with existing theories is proposed. The quadratic dependence on the shear rate is clearly shown, and the behaviour as a function of the solid volume fraction of particles exhibits a power law function. It is shown that theoretical predictions overestimate the experimental results. We observe, at intermediate volume fractions, the formation of rings of particles regularly spaced along the height of the cell. The differences observed between experimental results and theoretical predictions are discussed and related to the structures formed in the granular medium submitted to the external shear.
Symmetry-breaking instability in a prototypical driven granular gas.
Khain, Evgeniy; Meerson, Baruch
2002-08-01
Symmetry-breaking instability of a laterally uniform granular cluster (strip state) in a prototypical driven granular gas is investigated. The system consists of smooth hard disks in a two-dimensional box, colliding inelastically with each other and driven, at zero gravity, by a "thermal" wall. The limit of nearly elastic particle collisions is considered, and granular hydrodynamics with the Jenkins-Richman constitutive relations is employed. The hydrodynamic problem is completely described by two scaled parameters and the aspect ratio of the box. Marginal stability analysis predicts a spontaneous symmetry-breaking instability of the strip state, similar to that predicted recently for a different set of constitutive relations. If the system is big enough, the marginal stability curve becomes independent of the details of the boundary condition at the driving wall. In this regime, the density perturbation is exponentially localized at the elastic wall opposite the thermal wall. The short- and long-wavelength asymptotics of the marginal stability curves are obtained analytically in the dilute limit. The physics of the symmetry-breaking instability is discussed.
Granular segregation driven by particle interactions.
Lozano, C; Zuriguel, I; Garcimartín, A; Mullin, T
2015-05-01
We report the results of an experimental study of particle-particle interactions in a horizontally shaken granular layer that undergoes a second order phase transition from a binary gas to a segregation liquid as the packing fraction C is increased. By focusing on the behavior of individual particles, the effect of C is studied on (1) the process of cluster formation, (2) cluster dynamics, and (3) cluster destruction. The outcomes indicate that the segregation is driven by two mechanisms: attraction between particles with the same properties and random motion with a characteristic length that is inversely proportional to C. All clusters investigated are found to be transient and the probability distribution functions of the separation times display a power law tail, indicating that the splitting probability decreases with time.
Collision Statistics of Driven Polydisperse Granular Gases
International Nuclear Information System (INIS)
Chen Zhiyuan; Zhang Duanming; Yang Fengxia; Guo Xinping; Li Zhongming
2008-01-01
We present a dynamical model of two-dimensional polydisperse granular gases with fractal size distribution, in which the disks are subject to inelastic mutual collisions and driven by standard white noise. The inhomogeneity of the disk size distribution can be measured by a fractal dimension d f . By Monte Carlo simulations, we have mainly investigated the effect of the inhomogeneity on the statistical properties of the system in the same inelasticity case. Some novel results are found that the average energy of the system decays exponentially with a tendency to achieve a stable asymptotic value, and the system finally reaches a nonequilibrium steady state after a long evolution time. Furthermore, the inhomogeneity has great influence on the steady-state statistical properties. With the increase of the fractal dimension d f , the distributions of path lengths and free times between collisions deviate more obviously from expected theoretical forms for elastic spheres and have an overpopulation of short distances and time bins. The collision rate increases with d f , but it is independent of time. Meanwhile, the velocity distribution deviates more strongly from the Gaussian one, but does not demonstrate any apparent universal behavior
Dynamics of electrostatically driven granular media: Effects of humidity
International Nuclear Information System (INIS)
Howell, D. W.; Aronson, Igor S.; Crabtree, G. W.
2001-01-01
We performed experimental studies of the effect of humidity on the dynamics of electrostatically driven granular materials. Both conducting and dielectric particles undergo a phase transition from an immobile state (granular solid) to a fluidized state (granular gas) with increasing applied field. Spontaneous precipitation of solid clusters from the gas phase occurs as the external driving is decreased. The clustering dynamics in conducting particles is primarily controlled by screening of the electric field but is aided by cohesion due to humidity. It is shown that humidity effects dominate the clustering process with dielectric particles
Granular convection driven by shearing inertial forces.
Rodríguez-Liñán, G M; Nahmad-Molinari, Y
2006-01-01
Convection velocity measurements in vertically vibrated granular materials are presented. The convection velocity close to the walls grows quadratically with the difference between the maximum and critical, or excess, amplitude (proposed as a dynamic parameter to describe related problems) and it is shown numerically that the average bed-bottom relative velocity during the distancing between them, grows linearly with the squared as well. This is interpreted as the signature of an inertial shearing force or momentum transfer proportional to the bed-container relative velocity, acting mainly during the bed-plate distancing part of each cycle which leads to the formation of the convective flux.
From the granular Leidenfrost state to buoyancy-driven convection
Rivas Abud, Nicolás; Thornton, Anthony Richard; Luding, Stefan; van der Meer, Roger M.
Grains inside a vertically vibrated box undergo a transition from a density-inverted and horizontally homogeneous state, referred to as the granular Leidenfrost state, to a buoyancy-driven convective state. We perform a simulational study of the precursors of such a transition and quantify their
Dynamical behavior of granular matter in low gravity (diamagnetic levitation)
International Nuclear Information System (INIS)
Brooks, J.S.; Cothern, J.A.
2001-01-01
We report studies on the dynamics of macroscopic particles in a low-gravity 'magnetic levitation' environment. In a real sense, this allows the investigation of new states of granular matter. Particle ensembles (rods, spheres, or grains) can be held in a weak confining potential due to diamagnetic forces in a high-field-resistive magnet. In such a case 'kT' is not zero, and assemblies of particles undergo ergodic processes to find the lowest configurational ground state. This new area presents unique problems for video data acquisition and mathematical descriptions of the complex dynamic motions, interactions, and configurations of single and multiple particle assemblies. Three examples of such processes are presented
Buoyancy driven convection in vertically shaken granular matter: experiment, numerics, and theory
Eshuis, P.G.; van der Weele, J.P.; Alam, M.; van Gerner, H.J.; van der Hoef, Martin Anton; Kuipers, J.A.M.; Luding, Stefan; van der Meer, Roger M.; Lohse, Detlef
2013-01-01
Buoyancy driven granular convection is studied for a shallow, vertically shaken granular bed in a quasi 2D container. Starting from the granular Leidenfrost state, in which a dense particle cluster floats on top of a dilute gaseous layer of fast particles (Meerson et al. in Phys RevLett 91:024301,
Review on research of gravity driven and boron gravity-injection system
International Nuclear Information System (INIS)
Gao Langlang; Jiang Shengyao; Zhang Youjie; Ma Changwen
2000-01-01
Gravity driven system is the main kind of passive driven system, which is safe, economical and reliable with prodigious development potential. Integrated analysis to the current research situation of passive driven system and gravity driven system is made. The structure and character of the external gravity driven systems are also analyzed. The structure of the boron gravity-injection system which is compared with other external similar systems is presented. Its extrusive character in its structure design shows that it plays an important role in the development process of passive driven system
Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of gravity
Directory of Open Access Journals (Sweden)
S. M. Ahmed
2005-01-01
Full Text Available The aim of this paper is to investigate the Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of a gravity field. The frequency equation obtained, in the form of a sixth-order determinantal expression, is in agreement with the corresponding result when both media are elastic. The frequency equation when the gravity field is neglected has been deduced as a particular case.
Role of gravity or confining pressure and contact stiffness in granular rheology
Singh, A.; Saitoh, K.; Magnanimo, Vanessa; Luding, Stefan
2015-01-01
The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional
Gas-Driven Fracturing of Saturated Granular Media
Campbell, James M.; Ozturk, Deren; Sandnes, Bjørnar
2017-12-01
Multiphase flows in deformable porous materials are important in numerous geological and geotechnical applications; however, the complex flow behavior makes subsurface transport processes difficult to control—or even characterize. Here, we study gas-driven (pneumatic) fracturing of a wet unconsolidated granular packing confined in a Hele-Shaw cell, and we present an in-depth analysis of both pore-scale phenomena and large-scale pattern formation. The process is governed by a complex interplay among pressure, capillary, frictional, and viscous forces. At low gas-injection rates, fractures grow in a stick-slip fashion and branch out to form a simply connected network. We observe the emergence of a characteristic length scale—the separation distance between fracture branches—creating an apparent uniform spatial fracture density. We conclude that the well-defined separation distance is the result of local compaction fronts surrounding fractures and keeping them apart. A scaling argument is presented that predicts fracture density as a function of granular friction, grain size, and capillary interactions. We study the influence of the gas-injection rate and find that the system undergoes a fluidization transition above a critical injection rate, resulting in directional growth of the fractures, and a fracture density that increases with an increasing rate. A dimensionless fluidization number F is defined as the ratio of viscous to frictional forces, and our experiments reveal a frictional regime for F growth, with a transition to a viscous regime (F >1 ) characterized by continuous growth in several fracture branches simultaneously.
Granular packings of elongated faceted particles deposited under gravity
International Nuclear Information System (INIS)
Hidalgo, Raúl Cruz; Zuriguel, Iker; Maza, Diego; Pagonabarraga, Ignacio
2010-01-01
We report experimental and theoretical results of the effect that particle shape has on the packing properties of granular materials. We have systematically measured the particle angular distribution, the cluster size distribution and the stress profiles of ensembles of faceted elongated particles deposited in a bidimensional box. Stress transmission through this granular system has been numerically simulated using a two-dimensional model of irregular particles. For grains of maximum symmetry (squares), the stress propagation localizes and forms chain-like forces analogous to those observed for granular materials composed of spheres. For thick layers of grains, a pressure saturation is observed for deposit depths beyond a characteristic length. This scenario correlates with packing morphology and can be understood in terms of stochastic models of aggregation and random multiplicative processes. As grains elongate and lose their symmetry, stress propagation is strongly affected. Lateral force transmission becomes less favored than vertical transfer, and hence, an increase in the pressure develops with depth, hindering force saturation
From the granular Leidenfrost state to buoyancy-driven convection.
Rivas, Nicolas; Thornton, Anthony R; Luding, Stefan; van der Meer, Devaraj
2015-04-01
Grains inside a vertically vibrated box undergo a transition from a density-inverted and horizontally homogeneous state, referred to as the granular Leidenfrost state, to a buoyancy-driven convective state. We perform a simulational study of the precursors of such a transition and quantify their dynamics as the bed of grains is progressively fluidized. The transition is preceded by transient convective states, which increase their correlation time as the transition point is approached. Increasingly correlated convective flows lead to density fluctuations, as quantified by the structure factor, that also shows critical behavior near the transition point. The amplitude of the modulations in the vertical velocity field are seen to be best described by a quintic supercritical amplitude equation with an additive noise term. The validity of such an amplitude equation, and previously observed collective semiperiodic oscillations of the bed of grains, suggests a new interpretation of the transition analogous to a coupled chain of vertically vibrated damped oscillators. Increasing the size of the container shows metastability of convective states, as well as an overall invariant critical behavior close to the transition.
Density-Driven segregation in Binary and Ternary Granular Systems
Windows-Yule, Kit; Parker, David
2015-01-01
We present a first experimental study of density-induced segregation within a three-dimensional, vibrofluidised, ternary granular system. Using Positron Emission Particle Tracking (PEPT), we study the steady-state particle distributions achieved by binary and ternary granular beds under a variety of
Thermal diffusion segregation of an impurity in a driven granular fluid
Energy Technology Data Exchange (ETDEWEB)
Reyes, Francisco Vega; Garzó, Vicente [Departamento de Física, Universidad de Extremadura, E-06071 Badajoz, Spain and Instituto de Computación Científica Avanzada (ICCAEx), Universidad de Extremadura, E-06071 Badajoz (Spain)
2014-12-09
We study segregation of an impurity in a driven granular fluid under two types of steady states. In the first state, the granular gas is driven by a stochastic volume force field with a Fourier-type profile while in the second state, the granular gas is sheared in such a way that inelastic cooling is balanced by viscous heating. We compare theoretical results derived from a solution of the (inelastic) Boltzmann equation at Navier-Stokes (NS) order with those obtained from the Direct Monte Carlo simulation (DSMC) method and molecular dynamics (MD) simulations. Good agreement is found between theory and simulation, which provides strong evidence of the reliability of NS granular hydrodynamics for these steady states (including the dynamics of the impurity), even at high inelasticity. In addition, preliminary results for thermal diffusion in granular fluids at moderate densities are also presented. As for dilute gases, excellent agreement is also found in this more general case.
An experimental study of low velocity impacts into granular material in reduced gravity
Murdoch, Naomi; Avila Martinez, Iris; Sunday, Cecily; Cherrier, Olivier; Zenou, Emanuel; Janin, Tristan; Cadu, Alexandre; Gourinat, Yves; Mimoun, David
2016-04-01
The granular nature of asteroid surfaces, in combination with the low surface gravity, makes it difficult to predict lander - surface interactions from existing theoretical models. Nonetheless, an understanding of such interactions is particularly important for the deployment of a lander package. This was demonstrated by the Philae lander, which bounced before coming to rest roughly 1 kilometer away from its intended landing site on the surface of comet 67P/Churyumov-Gerasimenko before coming to rest (Biele et al., 2015). In addition to being important for planning the initial deployment, information about the acceleration profile upon impact is also important in the choice of scientific payloads that want to exploit the initial landing to study the asteroid surface mechanical properties (e.g., Murdoch et al., 2016). Using the ISAE-SUPAERO drop tower, we have performed a series of low-velocity collisions into granular material in low gravity. Reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use an Atwood machine, or a system of pulleys and counterweights. In reducing the effective surface acceleration of the granular material, the confining pressure will be reduced, and the properties of the granular material will become more representative of those on an asteroid's surface. In addition, since both the surface and projectile are falling, the projectile requires a minimum amount of time to catch the surface before the collision begins. This extended free-fall increases the experiment duration, making it easier to use accelerometers and high-speed cameras for data collection. The experiment is built into an existing 5.5 m drop-tower frame and has required the custom design of all components, including the projectile, surface sample container, release mechanism and deceleration system (Sunday et al., 2016
Fenton-Driven Regeneration of MTBE-spent Granular Activated Carbon
Fenton-driven regeneration of Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) involves the combined, synergistic use of two treatment technologies: adsorption of organic chemicals onto activated carbon and Fenton-driven oxidation regeneration of the spent-GAC...
Field driven charging dynamics of a fluidized granular bed.
Yoshimatsu, R; Araújo, N A M; Shinbrot, T; Herrmann, H J
2016-07-20
A simplified model has previously described the inductive charging of colliding identical grains in the presence of an external electric field. Here we extend that model by including heterogeneous surface charge distributions, grain rotations and electrostatic interactions between grains. We find from this more realistic model that strong heterogeneities in charging can occur in agitated granular beds, and we predict that shielding due to these heterogeneities can dramatically alter the charging rate in such beds.
Field Driven Charging Dynamics of a Fluidized Granular Bed
Yoshimatsu, R.; Araújo, N. A. M.; Shinbrot, T.; Herrmann, H. J.
2016-01-01
A simplified model has previously described the inductive charging of colliding identical grains in the presence of an external electric field. Here we extend that model by including heterogeneous surface charge distributions, grain rotations and electrostatic interactions between grains. We find from this more realistic model that strong heterogeneities in charging can occur in agitated granular beds, and we predict that shielding due to these heterogeneities can dramatically alter the charg...
Fabrication of gravity-driven microfluidic device
Yamada, H.; Yoshida, Y.; Terada, N.; Hagihara, S.; Komatsu, T.; Terasawa, A.
2008-12-01
We have studied the micro total analysis system as a blood test. A microfluidic device with a three-pronged microchannel and artificial capillary vessels was fabricated. The microchannel is to transport blood, focus blood cells, and line them up. The vessels are to observe red blood cell deformation. An excimer laser was used to form grooves and so on. Numbers of thermosetting resin film and fluororesin were piled up on a cover glass. A laser fabricated part of the channel at the each film every lamination, and then a three-dimensional structure microchannel was fabricated. The channel sizes have widths of 50-150 μm and depths of 45 μm. Through holes used as artificial capillary vessels are made in the fluororesin having a minimum diameter of 5 μm and a length of 100 μm. As blood and a physiological saline are injected into the microchannel, the device stands upward facing the channel, and blood cells go into the vessels by the force of gravity and sheath flow of the saline. By gravity various groove patterns were made changing the width and length for measurement of blood focusing. Moreover, the red blood cell deformation was observed in the vessels with a microscope.
A note on the violation of the Einstein relation in a driven moderately dense granular gas
Garzó, Vicente
2008-05-01
The Einstein relation for a driven moderately dense granular gas in d dimensions is analyzed in the context of the Enskog kinetic equation. The Enskog equation neglects velocity correlations but retains spatial correlations arising from volume exclusion effects. As expected, there is a breakdown of the Einstein relation \\epsilon=D/(T_0\\mu)\
Mandal, Sandip; Khakhar, D V
2017-11-01
We report a transition from a disordered state to an ordered state in the flow of nearly monodisperse granular matter flowing in an inclined channel with planar slide walls and a bumpy base, using discrete element method simulations. For low particle-sidewall friction coefficients, the flowing particles are disordered, however, for high sidewall friction, an ordered state is obtained, characterized by a layering of the particles and hexagonal packing of the particles in each layer. The extent of ordering, quantified by the local bond-orientational order parameter, varies in the cross section of the channel, with the highest ordering near the sidewalls. The flow transition significantly affects the local rheology-the effective friction coefficient is lower, and the packing fraction is higher, in the ordered state compared to the disordered state. A simple model, incorporating the extent of local ordering, is shown to describe the rheology of the system.
Mandal, Sandip; Khakhar, D. V.
2017-11-01
We report a transition from a disordered state to an ordered state in the flow of nearly monodisperse granular matter flowing in an inclined channel with planar slide walls and a bumpy base, using discrete element method simulations. For low particle-sidewall friction coefficients, the flowing particles are disordered, however, for high sidewall friction, an ordered state is obtained, characterized by a layering of the particles and hexagonal packing of the particles in each layer. The extent of ordering, quantified by the local bond-orientational order parameter, varies in the cross section of the channel, with the highest ordering near the sidewalls. The flow transition significantly affects the local rheology—the effective friction coefficient is lower, and the packing fraction is higher, in the ordered state compared to the disordered state. A simple model, incorporating the extent of local ordering, is shown to describe the rheology of the system.
Formation and mechanics of granular waves in gravity and shallow overland flow
Römkens, Mathias J. M.; Suryadevara, Madhu R.; Prasad, Shyam N.
2010-05-01
Sediment transport in overland flow is a highly complex process involving many properties relative to the flow regime characteristics, soil surface conditions, and type of sediment. From a practical standpoint, most sediment transport studies are concerned with developing relationships of rates of sediment movement under different hydraulic regimes in channel flow for use in soil erosion and sediment transport prediction models. Relatively few studies have focused on the more basic aspects of sediment movement in which particle-to-particle, particle-to-boundary, and particle-to-fluid interactions determine in an important way the nature of the movement. Our experimental work under highly controlled experimental conditions with both gravity flow of granular material (glass beads) in air and sediment transport (sand particles and glass beads) in shallow overland flow have shown that sediment movement is not a simple phenomenon solely determined by flow rates on a proportional basis, but that it is represented by a highly structured and organized regime determined by sedimentary fluid mechanical principles which yield very characteristic waves during transport. In the gravity flow case involving granular chute flow, two-dimensional grain waves developed into the rolling and saltating moving grain mass at certain grain concentrations. This phenomenon appeared to be related to an energy exchange process as a result of collisions between moving grain particles that led to reduced kinetic velocities. As a result, particle concentration differences in the direction of flow developed that were noted as denser zones. In these zones, particles dropped out at the upstream part of these denser zones to resume their accelerating motion once they reached the downstream part of the zone until, during the next collision event, the process is repeated. Thus a periodic granular wave structure evolved. Depending on the addition rate, the granular flow regime may be a fluidized
Centrifugal Sieve for Gravity-Level-Independent Size Segregation of Granular Materials
Walton, Otis R.; Dreyer, Christopher; Riedel, Edward
2013-01-01
Conventional size segregation or screening in batch mode, using stacked vibrated screens, is often a time-consuming process. Utilization of centrifugal force instead of gravity as the primary body force can significantly shorten the time to segregate feedstock into a set of different-sized fractions. Likewise, under reduced gravity or microgravity, a centrifugal sieve system would function as well as it does terrestrially. When vibratory and mechanical blade sieving screens designed for terrestrial conditions were tested under lunar gravity conditions, they did not function well. The centrifugal sieving design of this technology overcomes the issues that prevented sieves designed for terrestrial conditions from functioning under reduced gravity. These sieves feature a rotating outer (cylindrical or conical) screen wall, rotating fast enough for the centrifugal forces near the wall to hold granular material against the rotating screen. Conventional centrifugal sieves have a stationary screen and rapidly rotating blades that shear the granular solid near the stationary screen, and effect the sieving process assisted by the airflow inside the unit. The centrifugal sieves of this new design may (or may not) have an inner blade or blades, moving relative to the rotating wall screen. Some continuous flow embodiments would have no inner auger or blades, but achieve axial motion through vibration. In all cases, the shearing action is gentler than conventional centrifugal sieves, which have very high velocity differences between the stationary outer screen and the rapidly rotating blades. The new design does not depend on airflow in the sieving unit, so it will function just as well in vacuum as in air. One advantage of the innovation for batch sieving is that a batch-mode centrifugal sieve may accomplish the same sieving operation in much less time than a conventional stacked set of vibrated screens (which utilize gravity as the primary driving force for size separation
Condensation during gravity driven ECC: Experiments with PACTEL
Energy Technology Data Exchange (ETDEWEB)
Munther, R.; Kalli, H. [Lappeenranta Univ. of Technology (Finland); Kouhia, J. [Technical Research Centre of Finland, Lappeenranta (Finland)
1995-09-01
This paper provides the results of the second series of gravity driven emergency core cooling (ECC) experiments with PACTEL (Parallel Channel Test Loop). The simulated accident was a small break loss-of-coolant accident (SBLOCA) with a break in a cold leg. The ECC flow was provided from a core makeup tank (CMT) located at a higher elevation than the main part of the primary system. The CMT was pressurized with pipings from the pressurizer and a cold leg. The tests indicated that steam condensation in the CMT can prevent ECC and lead to core uncovery.
Khain, Evgeniy; Meerson, Baruch; Sasorov, Pavel V
2008-10-01
Thermal wall is a convenient idealization of a rapidly vibrating plate used for vibrofluidization of granular materials. The objective of this work is to incorporate the Knudsen temperature jump at thermal wall in the Navier-Stokes hydrodynamic modeling of dilute granular gases of monodisperse particles that collide nearly elastically. The Knudsen temperature jump manifests itself as an additional term, proportional to the temperature gradient, in the boundary condition for the temperature. Up to a numerical prefactor O(1) , this term is known from kinetic theory of elastic gases. We determine the previously unknown numerical prefactor by measuring, in a series of molecular dynamics (MD) simulations, steady-state temperature profiles of a gas of elastically colliding hard disks, confined between two thermal walls kept at different temperatures, and comparing the results with the predictions of a hydrodynamic calculation employing the modified boundary condition. The modified boundary condition is then applied, without any adjustable parameters, to a hydrodynamic calculation of the temperature profile of a gas of inelastic hard disks driven by a thermal wall. We find the hydrodynamic prediction to be in very good agreement with MD simulations of the same system. The results of this work pave the way to a more accurate hydrodynamic modeling of driven granular gases.
Khalil, Nagi; Garzó, Vicente
2018-02-01
The Navier-Stokes order hydrodynamic equations for a low-density driven granular mixture obtained previously [Khalil and Garzó, Phys. Rev. E 88, 052201 (2013), 10.1103/PhysRevE.88.052201] from the Chapman-Enskog solution to the Boltzmann equation are considered further. The four transport coefficients associated with the heat flux are obtained in terms of the mass ratio, the size ratio, composition, coefficients of restitution, and the driven parameters of the model. Their quantitative variation on the control parameters of the system is demonstrated by considering the leading terms in a Sonine polynomial expansion to solve the exact integral equations. As an application of these results, the stability of the homogeneous steady state is studied. In contrast to the results obtained in undriven granular mixtures, the stability analysis of the linearized Navier-Stokes hydrodynamic equations shows that the transversal and longitudinal modes are (linearly) stable with respect to long enough wavelength excitations. This conclusion agrees with a previous analysis made for single granular gases.
Biodegradation of microcystins during gravity-driven membrane (GDM ultrafiltration.
Directory of Open Access Journals (Sweden)
Esther Kohler
Full Text Available Gravity-driven membrane (GDM ultrafiltration systems require little maintenance: they operate without electricity at ultra-low pressure in dead-end mode and without control of the biofilm formation. These systems are already in use for water purification in some regions of the world where adequate treatment and distribution of drinking water is not readily available. However, many water bodies worldwide exhibit harmful blooms of cyanobacteria that severely lower the water quality due to the production of toxic microcystins (MCs. We studied the performance of a GDM system during an artificial Microcystis aeruginosa bloom in lake water and its simulated collapse (i.e., the massive release of microcystins over a period of 21 days. Presence of live or destroyed cyanobacterial cells in the feed water decreased the permeate flux in the Microcystis treatments considerably. At the same time, the microbial biofilms on the filter membranes could successfully reduce the amount of microcystins in the filtrate below the critical threshold concentration of 1 µg L(-1 MC for human consumption in three out of four replicates after 15 days. We found pronounced differences in the composition of bacterial communities of the biofilms on the filter membranes. Bacterial genera that could be related to microcystin degradation substantially enriched in the biofilms amended with microcystin-containing cyanobacteria. In addition to bacteria previously characterized as microcystin degraders, members of other bacterial clades potentially involved in MC degradation could be identified.
Merkel, A; Tournat, V; Gusev, V
2014-08-01
We report the experimental observation of the gravity-induced asymmetry for the nonlinear transformation of acoustic waves in a noncohesive granular phononic crystal. Because of the gravity, the contact precompression increases with depth inducing space variations of not only the linear and nonlinear elastic moduli but also of the acoustic wave dissipation. We show experimentally and explain theoretically that, in contrast to symmetric propagation of linear waves, the amplitude of the nonlinearly self-demodulated wave depends on whether the propagation of the waves is in the direction of the gravity or in the opposite direction. Among the observed nonlinear processes, we report frequency mixing of the two transverse-rotational modes belonging to the optical band of vibrations and propagating with negative phase velocities, which results in the excitation of a longitudinal wave belonging to the acoustic band of vibrations and propagating with positive phase velocity. We show that the measurements of the gravity-induced asymmetry in the nonlinear acoustic phenomena can be used to compare the in-depth distributions of the contact nonlinearity and of acoustic absorption.
Vollmayr-Lee, Katharina; Zippelius, Annette; Aspelmeier, Timo
2011-03-01
We study the dynamic structure factor of a granular fluid of hard spheres, driven into a stationary nonequilibrium state by balancing the energy loss due to inelastic collisions with the energy input due to driving. The driving is chosen to conserve momentum, so that fluctuating hydrodynamics predicts the existence of sound modes. We present results of computer simulations which are based on an event driven algorithm. The dynamic structure factor F (q , ω) is determined for volume fractions 0.05, 0.1 and 0.2 and coefficients of normal restitution 0.8 and 0.9. We observe sound waves, and compare our results for F (q , ω) with the predictions of generalized fluctuating hydrodynamics which takes into account that temperature fluctuations decay either diffusively or with a finite relaxation rate, depending on wave number and inelasticity. We determine the speed of sound and the transport coefficients and compare them to the results of kinetic theory. K.V.L. thanks the Institute of Theoretical Physics, University of Goettingen, for financial support and hospitality.
Static and dynamic angles of repose in loose granular materials under reduced gravity
Kleinhans, M.G.; Markies, H.; Vet, S.J. de; Veld, A.C. in 't; Postema, F.N.
2011-01-01
Granular materials avalanche when a static angle of repose is exceeded and freeze at a dynamic angle of repose. Such avalanches occur subaerially on steep hillslopes and wind dunes and subaqueously at the lee side of deltas. Until now it has been assumed that the angles of repose are independent
Sunday, C.; Murdoch, N.; Cherrier, O.; Morales Serrano, S.; Valeria Nardi, C.; Janin, T.; Avila Martinez, I.; Gourinat, Y.; Mimoun, D.
2016-08-01
This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ˜0.1 to 1.0 m/s2. Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system.
Sunday, C; Murdoch, N; Cherrier, O; Morales Serrano, S; Valeria Nardi, C; Janin, T; Avila Martinez, I; Gourinat, Y; Mimoun, D
2016-08-01
This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ∼0.1 to 1.0 m/s(2). Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system.
Dynamic posturography using a new movable multidirectional platform driven by gravity.
Commissaris, D.A.C.M.; Nieuwenhuijzen, P.H.J.A.; Overeem, S.; Vos, A. de; Duysens, J.E.J.; Bloem, B.R.
2002-01-01
Human upright balance control can be quantified using movable platforms driven by servo-controlled torque motors (dynamic posturography). We introduce a new movable platform driven by the force of gravity acting upon the platform and the subject standing on it. The platform consists of a 1 m2 metal
Dynamic posturography using a new movable multidirectional platform driven by gravity
Commissaris, D.A.C.M.; Nieuwenhuijzen, P.H.J.A.; Overeem, S.; Vos, A. de; Duysens, J.E.J.; Bloem, B.R.
2002-01-01
Human upright balance control can be quantified using movable platforms driven by servo-controlled torque motors (dynamic posturography). We introduce a new movable platform driven by the force of gravity acting upon the platform and the subject standing on it. The platform consists of a 1 m(2)
Windows-Yule, Kit; Douglas, G.J.M.; Parker, D.J.
2015-01-01
The behaviors of granular systems are sensitive to a wide variety of particle properties, including size, density, elasticity, and shape. Differences in any of these properties between particles in a granular mixture may lead to segregation, or “demixing,” a process of great industrial relevance.
Gravity-induced encapsulation of liquids by destabilization of granular rafts
Abkarian, Manouk; Protière, Suzie; Aristoff, Jeffrey M.; Stone, Howard A.
2013-05-01
Droplets and bubbles coated by a protective armour of particles find numerous applications in encapsulation, stabilization of emulsions and foams, and flotation techniques. Here we study the role of a body force, such as in flotation, as a means of continuous encapsulation by particles. We use dense particles, which self-assemble into rafts, at oil-water interfaces. We show that these rafts can be spontaneously or controllably destabilized into armoured oil-in-water droplets, which highlights a possible role for common granular materials in environmental remediation. We further present a method for continuous production and discuss the generalization of our approach towards colloidal scales.
Tripathi, Anurag; Khakhar, D. V.
2011-09-01
We study, computationally, the sedimentation of a sphere of higher mass in a steady, gravity-driven granular flow of otherwise identical spheres, on a rough inclined plane. Taking a hydrodynamic approach at the scale of the particle, we find the drag force to be given by a modified Stokes law and the buoyancy force by the Archimedes principle, with excluded volume effects taken into account. We also find significant differences between the hydrodynamic case and the granular case, which are highlighted.
Variation of the hydraulic properties within gravity-driven deposits in basinal carbonates
Jablonska, D.; Zambrano, M.; Emanuele, T.; Di Celma, C.
2017-12-01
Deepwater gravity-driven deposits represent important stratigraphic heterogeneities within basinal sedimentary successions. A poor understanding of their distribution, internal architecture (at meso- and micro-scale) and hydraulic properties (porosity and permeability), may lead to unexpected compartmentalization issues in reservoir analysis. In this study, we examine gravity-driven deposits within the basinal-carbonate Maiolica Formation adjacent to the Apulian Carbonate Plaftorm, southern Italy. Maiolica formation is represented by horizontal layers of thin-bedded cherty pelagic limestones often intercalated by mass-transport deposits (slumps, debris-flow deposits) and calcarenites of diverse thickness (0.1 m - 40 m) and lateral extent (100 m - >500 m). Locally, gravity-driven deposits compose up to 60 % of the exposed succession. These deposits display broad array of internal architectures (from faulted and folded strata to conglomerates) and various texture. In order to further constrain the variation of the internal architectures and fracture distribution within gravity-driven deposits, field sedimentological and structural analyses were performed. To examine the texture and hydraulic properties of various lithofacies, the laboratory porosity measurements of suitable rock samples were undertaken. These data were supported by 3D pore network quantitative analysis of X-ray Computed microtomography (MicroCT) images performed at resolutions 1.25 and 2.0 microns. This analysis helped to describe the pores and grains geometrical and morphological properties (such as size, shape, specific surface area) and the hydraulic properties (porosity and permeability) of various lithofacies. The integration of the analyses allowed us to show how the internal architecture and the hydraulic properties vary in different types of gravity-driven deposits within the basinal carbonate succession.
Granular media : flow & agitations
Dijksman, Joshua Albert
2009-01-01
This thesis is about weakly driven granular flows and suspensions. Chapter 1 is an overview of the current knowledge of slow granular flows in so-called split-bottom geometries, which in essence consist of a disk rotating at the bottom of a container. In chapter 2 we study dry granular flows in this
Particle Segregation in Dense Granular Flows
Gray, John Mark Nicholas Timm
2018-01-01
Granular materials composed of particles with differing grain sizes, densities, shapes, or surface properties may experience unexpected segregation during flow. This review focuses on kinetic sieving and squeeze expulsion, whose combined effect produces the dominant gravity-driven segregation mechanism in dense sheared flows. Shallow granular avalanches that form at the surface of more complex industrial flows such as heaps, silos, and rotating drums provide ideal conditions for particles to separate, with large particles rising to the surface and small particles percolating down to the base. When this is combined with erosion and deposition, amazing patterns can form in the underlying substrate. Gravity-driven segregation and velocity shear induce differential lateral transport, which may be thought of as a secondary segregation mechanism. This allows larger particles to accumulate at flow fronts, and if they are more frictional than the fine grains, they can feedback on the bulk flow, causing flow fingering, levee formation, and longer runout of geophysical mass flows.
Interfacial Instabilities Driven by Self-Gravity in the ISM: Onset and Evolution
Hueckstaedt, R. M.; Hunter, J. H., Jr.
2000-12-01
As the sites of all present day star formation within the Milky Way, cold molecular clouds are a vital link in the evolution of tenuous interstellar gas into stars. Any comprehensive theory of star formation must include a study of the hydrodynamic processes that effect molecular cloud morphology. In the ISM, hydrodynamic instabilities and turbulence play large roles in shaping clouds and creating regions capable of gravitational collapse. One of the key forces in the interstellar environment is self-gravity. Regardless of the mechanism initially responsible for creating density enhancements, self-gravity must ultimately drive the final collapse. A recent study has shown that self-gravity also gives rise to an interfacial instability that persists in the static limit when a density discontinuity exists (Hunter, Whitaker & Lovelace 1997). This instability also persists in the absence of a constant gravitational acceleration, unlike the familiar Rayleigh-Taylor instability. Analytic studies in Cartesian geometry predict that for perturbations proportional to exp(-iωt), the instability has an incompressible growth rate ω2= -2πG(ρ 1-ρ 2)2/(ρ1+ρ2). The growth rate is independent of the perturbation wavelength. Studies have also included cases in cylindrical geometry in which a static density interface has proven stable to kink modes but unstable to sausage modes. In the case of sausage modes, (perturbations in the radial direction), there exists a critical wavelength below which the instability does not appear. In this paper, we present two-dimensional numerical models designed to examine this self-gravity driven instability. A hydrodynamic code with self-gravity is used to test the analytic predictions in Cartesian and cylindrical geometries and to follow the instability into the nonlinear regime. We consider how the growth of hydrodynamic instabilities, including self-gravity driven instabilities, can have a role in shaping the ISM. We discuss implications for
Gravity-driven structures and rift basin evolution: Rio Muni Basin, offshore equatorial West Africa
Energy Technology Data Exchange (ETDEWEB)
Turner, J.P. [Univ. of Birmingham (United Kingdom)
1995-08-01
Offshore Equatorial Guinea, west Africa, gravity-driven nappes, more than 1 km thick and 15 km from head to toe, provide key evidence in reconstructing the late synrift: evolution of this part of the South Atlantic margin basin system. Furthermore, Aptian-Cenomanian carbonate and clastic rocks in the nappes` allochthonous hanging walls are attracting interest as a new exploration play in west Africa. The nappes exhibit a range of geometries that suggest they share many of the same deformation processes as thin-skin thrust and linked extensional fault systems. Not only are these structures significant in their own right, representing a rare example of gravity tectonics in the virtual absence of major halokinesis, but their presence may record an other-wise undetectable process active during the transition from a rift basin to a passive continental margin. A review of Equatorial Guinea in its pre-Atlantic configuration, alongside neighboring basins in Brazil (the Sergipe-Alagoas basin) and Gabon, suggests that gravity gliding was sustained by a relatively steep, westward paleoslope promoted by east-ward offset of the locus of thermal uplift from the rift basin (i.e., a simple shear model of basin formation). In contrast to gravity-driven structures in most postrift settings, the Equatorial Guinea nappes developed at the close of the Aptian-Albian synrift episode in response to a growing bathymetric deep caused by rapid subsidence outpacing restricted sedimentation.
Simulation of 2D Granular Hopper Flow
Li, Zhusong; Shattuck, Mark
2012-02-01
Jamming and intermittent granular flow are big problems in industry, and the vertical hopper is a canonical example of these difficulties. We simulate gravity driven flow and jamming of 2D disks in a vertical hopper and compare with identical companion experiments presented in this session. We measure and compare the flow rate and probability for jamming as a function of particle properties and geometry. We evaluate the ability of standard Hertz-Mindlin contact mode to quantitatively predict the experimental flow.
International Nuclear Information System (INIS)
Makinde, O.D.
2005-10-01
In this paper, the first and second law of thermodynamics are employed in order to study the inherent irreversibility for a gravity driven non-Newtonian Ostwald-de Waele power law liquid film along an inclined isothermal plate. Based on some simplified assumptions, the governing equations are obtained and solved analytically. Expressions for fluid velocity, temperature, volumetric entropy generation numbers, irreversibility distribution ratio and the Bejan number are also determined. (author)
Surface-roughness driven segregation in a granular slurry under shear
Plantard, G.; Saadaoui, H.; Snabre, P.; Pouligny, B.
2006-07-01
"Shear-induced segregation" (SIS) means that different species of particles in a granular material or a concentrated suspension tend to unmix under flow. In principle, any kind of difference (size, density, shape and even surface state) may lead to SIS. We report the first direct experimental evidence of SIS between spheres which only differ by surface characteristics. The effect is observed with a "slurry" made of solid spheres immersed in a viscous fluid, inside a parallel-plate shear device. We show that: i) A mixture of smooth and rough spheres of same size shows considerable SIS. ii) Rough spheres (radius aR) behave similarly to smooth but larger spheres (radius aS > aR). iii) Segregation cancels out for a particular value of the size ratio, aS/aR < 1. These findings can be qualitatively understood from available theories about the role of surface roughness on two-sphere interactions in Stokes regime.
Ding, An; Wang, Jinlong; Lin, Dachao; Zeng, Rong; Yu, Shengping; Gan, Zhendong; Ren, Nanqi; Li, Guibai; Liang, Heng
2018-01-01
Gravity-driven membrane filtration (GDM) is promising for decentralized rainwater recycling, owing to low maintenance and energy consumption. However, the organic removal by GDM process is sometimes undesirable and the quality of the permeate cannot meet the standard of water reuse. To improve this, granular activate carbon (GAC) was added as a particle layer on the membrane surface of GDM system. Additionally, a system with sand addition and a system with no particle addition were trialed as comparisons, to study the combined effects of particle hindering and adsorption on the removal efficacy of organics and the development of permeate flux. Results showed that GDM with a GAC layer improved removal efficiency of organics by 25%, and that GAC enhanced removal of florescent compounds (e.g., aromatic proteins, tryptophan proteins and humics), compared with the other two systems. Additionally, the permeate flux in three systems stabilized after Day 25, and kept stable until the end of the operation. However, the presence of GAC layer decreased the level of stable flux (3.2 L/m 2 h) compared with the control system (4.5 L/m 2 h). The factors responsible for the lower flux and severe membrane fouling in GAC layer assisted system were the combined effects of particle and adsorption which led to a denser bio-fouling layer with higher amount of biomass and extracellular polymeric substances contents (proteins and polysaccharides). Resistance distribution analyses revealed that GAC layer mainly increased hydraulically reversible resistance (occupied 93%) of the total resistance, indicating that the flux could be recovered easily by simple physical cleaning. Copyright © 2017 Elsevier Ltd. All rights reserved.
Multiple independent autonomous hydraulic oscillators driven by a common gravity head.
Kim, Sung-Jin; Yokokawa, Ryuji; Lesher-Perez, Sasha Cai; Takayama, Shuichi
2015-06-15
Self-switching microfluidic circuits that are able to perform biochemical experiments in a parallel and autonomous manner, similar to instruction-embedded electronics, are rarely implemented. Here, we present design principles and demonstrations for gravity-driven, integrated, microfluidic pulsatile flow circuits. With a common gravity head as the only driving force, these fluidic oscillator arrays realize a wide range of periods (0.4 s-2 h) and flow rates (0.10-63 μl min(-1)) with completely independent timing between the multiple oscillator sub-circuits connected in parallel. As a model application, we perform systematic, parallel analysis of endothelial cell elongation response to different fluidic shearing patterns generated by the autonomous microfluidic pulsed flow generation system.
Thermal Convection in Granular Gases with Dissipative Lateral Walls.
Pontuale, Giorgio; Gnoli, Andrea; Reyes, Francisco Vega; Puglisi, Andrea
2016-08-26
We consider a granular gas under the action of gravity, fluidized by a vibrating base. We show that a horizontal temperature gradient, here induced by limiting dissipative lateral walls (DLW), leads always to a granular thermal convection (DLW TC) that is essentially different from ordinary bulk-buoyancy-driven convection (BBD TC). In an experiment where BBD TC is inhibited, by reducing gravity with an inclined plane, we always observe a DLW TC cell next to each lateral wall. Such a cell squeezes towards the nearest wall as the gravity and/or the number of grains increase. Molecular dynamics simulations reproduce the experimental results and indicate that at large gravity or number of grains the DLW TC is barely detectable.
Distinguishing thrust sequences in gravity-driven fold and thrust belts
Alsop, G. I.; Weinberger, R.; Marco, S.
2018-04-01
Piggyback or foreland-propagating thrust sequences, where younger thrusts develop in the footwalls of existing thrusts, are generally assumed to be the typical order of thrust development in most orogenic settings. However, overstep or 'break-back' sequences, where later thrusts develop above and in the hangingwalls of earlier thrusts, may potentially form during cessation of movement in gravity-driven mass transport deposits (MTDs). In this study, we provide a detailed outcrop-based analysis of such an overstep thrust sequence developed in an MTD in the southern Dead Sea Basin. Evidence that may be used to discriminate overstep thrusting from piggyback thrust sequences within the gravity-driven fold and thrust belt includes upright folds and forethrusts that are cut by younger overlying thrusts. Backthrusts form ideal markers that are also clearly offset and cut by overlying younger forethrusts. Portions of the basal detachment to the thrust system are folded and locally imbricated in footwall synclines below forethrust ramps, and these geometries also support an overstep sequence. However, new 'short-cut' basal detachments develop below these synclines, indicating that movement continued on the basal detachment rather than it being abandoned as in classic overstep sequences. Further evidence for 'synchronous thrusting', where movement on more than one thrust occurs at the same time, is provided by displacement patterns on sequences of thrust ramp imbricates that systematically increases downslope towards the toe of the MTD. Older thrusts that initiate downslope in the broadly overstep sequence continue to move and therefore accrue greater displacements during synchronous thrusting. Our study provides a template to help distinguish different thrust sequences in both orogenic settings and gravity-driven surficial systems, with displacement patterns potentially being imaged in seismic sections across offshore MTDs.
Dynamical flow arrest in confined gravity driven flows of soft jammed particles.
Chaudhuri, Pinaki; Mansard, Vincent; Colin, Annie; Bocquet, Lyderic
2012-07-20
Using numerical simulations, we study the gravity driven flow of jammed soft disks in confined channels. We demonstrate that confinement results in increasing the yield threshold for the Poiseuille flow, in contrast to the planar Couette flow. By solving a nonlocal flow model for such systems, we show that this effect is due to the correlated dynamics responsible for flow, coupled with the stress heterogeneity imposed for the Poiseuille flow. We also observe that with increasing confinement, the cooperative nature of the flow results in increasing intermittent behavior. Our studies indicate that such features are generic properties of a wide variety of jammed materials.
Gravity driven deterministic lateral displacement for particle separation in microfluidic devices.
Devendra, Raghavendra; Drazer, German
2012-12-18
We investigate the two-dimensional continuous size-based separation of suspended particles in gravity-driven deterministic lateral displacement (g-DLD) devices. The suspended particles are driven through a periodic array of cylindrical obstacles under the action of gravity. We perform experiments covering the entire range of forcing orientations with respect to the array of obstacles and identify specific forcing angles that would lead to vector separation, in which different particles migrate, on an average, in different directions. A simple model, based on the lateral displacement induced on the trajectory of a particle by irreversible particle-obstacle interactions, accurately predicts the dependence of the migration angle on the forcing direction. The results provide design guidance for the development of g-DLD devices. We observe directional locking, which strongly depends on the size of the particle and suggests that relatively small forcing angles are well suited for size-fractionation purposes. We demonstrate excellent separation resolution for a binary mixture of particles at relatively small forcing angles, that is, forcing angles that are close to but smaller than the first transition angle of the larger particles in the mixture.
Particle-driven gravity currents in non-rectangular cross section channels
International Nuclear Information System (INIS)
Zemach, T.
2015-01-01
We consider a high-Reynolds-number gravity current generated by suspension of heavier particles in fluid of density ρ i , propagating along a channel into an ambient fluid of the density ρ a . The bottom and top of the channel are at z = 0, H, and the cross section is given by the quite general −f 1 (z) ≤ y ≤ f 2 (z) for 0 ≤ z ≤ H. The flow is modeled by the one-layer shallow-water equations obtained for the time-dependent motion which is produced by release from rest of a fixed volume of mixture from a lock. We solve the problem by the finite-difference numerical code to present typical height h(x, t), velocity u(x, t), and volume fraction of particles (concentration) ϕ(x, t) profiles. The methodology is illustrated for flow in typical geometries: power-law (f(z) = z α and f(z) = (H − z) α , where α is positive constant), trapezoidal, and circle. In general, the speed of propagation of the flows driven by suspensions decreases compared with those driven by a reduced gravity in homogeneous currents. However, the details depend on the geometry of the cross section. The runout length of suspensions in channels of power-law cross sections is analytically predicted using a simplified depth-averaged “box” model. The present approach is a significant generalization of the classical gravity current problem. The classical formulation for a rectangular channel is now just a particular case, f(z) = const., in the wide domain of cross sections covered by this new model
Cooling of 3D granular gases in microgravity experiments
Directory of Open Access Journals (Sweden)
Harth Kirsten
2017-01-01
Full Text Available Granular gases are a most peculiar state, superficially similar to molecular gases: They are loose ensembles of moving grains, rarely interacting with each other and with container walls. The most investigated scenario is the “granular cooling”, the collective loss of energy from an initially excited state. We present an experimental study of the cooling of a 3D granular gas of rodlike grains in micro-gravity. Driven steady states of non-spherical grains are characterized by a lack of energy equipartition between the degrees of freedom of translation and rotation. Excitation by vibrating walls additionally introduces strong gradients in the direction and magnitude of translational velocities. We show that the degrees of freedom equilibrate during granular cooling in the homogeneous cooling state. The energy loss follows a t−2 scaling. In addition, the alignment of the rod axes with the excitation direction and with the instantaneous velocities are altered during this process.
Energy Technology Data Exchange (ETDEWEB)
ELIASSI,MEHDI; GLASS JR.,ROBERT J.
2000-03-08
The authors consider the ability of the numerical solution of Richards equation to model gravity-driven fingers. Although gravity-driven fingers can be easily simulated using a partial downwind averaging method, they find the fingers are purely artificial, generated by the combined effects of truncation error induced oscillations and capillary hysteresis. Since Richards equation can only yield a monotonic solution for standard constitutive relations and constant flux boundary conditions, it is not the valid governing equation to model gravity-driven fingers, and therefore is also suspect for unsaturated flow in initially dry, highly nonlinear, and hysteretic media where these fingers occur. However, analysis of truncation error at the wetting front for the partial downwind method suggests the required mathematical behavior of a more comprehensive and physically based modeling approach for this region of parameter space.
Simulation of size segregation in granular flow with material point method
Directory of Open Access Journals (Sweden)
Fei Minglong
2017-01-01
Full Text Available Segregation is common in granular flows consisting of mixtures of particles differing in size or density. In gravity-driven flows, both gradients in total pressure (induced by gravity and gradients in velocity fluctuation fields (often associated with shear rate gradients work together to govern the evolution of segregation. Since the local shear rate and velocity fluctuations are dependent on the local concentration of the components, understanding the co-evolution of segregation and flow is critical for understanding and predicting flows where there can be a variety of particle sizes and densities, such as in nature and industry. Kinetic theory has proven to be a robust framework for predicting this simultaneous evolution but has a limit in its applicability to dense systems where collisions are highly correlated. In this paper, we introduce a model that captures the coevolution of these evolving dynamics for high density gravity driven granular mixtures. For the segregation dynamics we use a recently developed mixture theory (Fan & Hill 2011, New J. Phys; Hill & Tan 2014, J. Fluid Mech. which captures the combined effects of gravity and fluctuation fields on segregation evolution in high density granular flows. For the mixture flow dynamics, we use a recently proposed viscous-elastic-plastic constitutive model, which can describe the multi-state behaviors of granular materials, i.e. the granular solid, granular liquid and granular gas mechanical states (Fei et al. 2016, Powder Technol.. The platform we use for implementing this model is a modified Material Point Method (MPM, and we use discrete element method simulations of gravity-driven flow in an inclined channel to demonstrate that this new MPM model can predict the final segregation distribution as well as flow velocity profile well. We then discuss ongoing work where we are using this platform to test the effectiveness of particular segregation models under different boundary conditions.
A data-driven approach to local gravity field modelling using spherical radial basis functions
Klees, R.; Tenzer, R.; Prutkin, I.; Wittwer, T.
2008-01-01
We propose a methodology for local gravity field modelling from gravity data using spherical radial basis functions. The methodology comprises two steps: in step 1, gravity data (gravity anomalies and/or gravity disturbances) are used to estimate the disturbing potential using least-squares
Gamow, George
2003-01-01
A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw
Rivera, Andrea
2017-01-01
Gravity is all around us. Learn how it is used in art, technology, and engineering. Five easy-to-read chapters explain the science behind gravity, as well as its real-world applications. Vibrant, full-color photos, bolded glossary words, and a key stats section let readers zoom in even deeper. Aligned to Common Core Standards and correlated to state standards. Abdo Zoom is a division of ABDO.
Wang, Yiran
2017-04-21
Gravity-driven membrane (GDM) filtration is one of the promising membrane bioreactor (MBR) configurations. It operates at an ultra-low pressure by gravity, requiring a minimal energy. The objective of this study was to understand the performance of GDM filtration system and characterize the biofouling formation on a flat sheet membrane. This submerged GDM reactor was operated at constant gravitational pressure in treating of two different concentrations of secondary wastewater effluent. Morphology of biofilm layer was acquired by an in-situ and on-line optical coherence tomography (OCT) scanning in a fixed position at regular intervals. The thickness and roughness calculated from OCT images were related to the variation of flux, fouling resistance and permeate quality. At the end of experiment, fouling was quantified by total organic carbon (TOC) and adenosine tri-phosphate (ATP) method. Confocal laser scanning microscopy (CLSM) was also applied for biofouling morphology observation. The biofouling formed on membrane surface was mostly removed by physical cleaning confirmed by contact angle measurement before and after cleaning. This demonstrated that fouling on the membrane under ultra-low pressure operation was highly reversible. The superiority and sustainability of GDM in both flux maintaining and long-term operation with production of high quality effluent was demonstrated.
Kuntz, M.; Van Mier, J.G.M.
1997-01-01
A series of field observations of the evolution of water runoffs over several vertical concrete walls directly exposed to rain falls is reported in this note. In all the cases, the main water flow originated from the top horizontal surface of the walls. The observations show that the gravity-driven
Indian Academy of Sciences (India)
We study the cosmological dynamics for R p exp( λ R ) gravity theory in the metric formalism, using dynamical systems approach. Considering higher-dimensional FRW geometries in case of an imperfect fluid which has two different scale factors in the normal and extra dimensions, we find the exact solutions, and study its ...
Polydisperse particle-driven gravity currents in non-rectangular cross section channels
Zemach, T.
2018-01-01
We consider a high-Reynolds-number gravity current generated by polydisperse suspension of n types of particles distributed in a fluid of density ρi. Each class of particles in suspension has a different settling velocity. The current propagates along a channel of non-rectangular cross section into an ambient fluid of constant density ρa. The bottom and top of the channel are at z = 0, H, and the cross section is given by the quite general form -f1(z) ≤ y ≤ f2(z) for 0 ≤ z ≤ H. The flow is modeled by the one-layer shallow-water equations obtained for the time-dependent motion. We solve the problem by a finite-difference numerical code to present typical height h, velocity u, and mass fractions of particle (concentrations) (ϕ( j), j = 1, …, n) profiles. The runout length of suspensions in channels of power-law cross sections is analytically predicted using a simplified depth-averaged "box" model. We demonstrate that any degree of polydispersivity adds to the runout length of the currents, relative to that of equivalent monodisperse currents with an average settling velocity. The theoretical predictions are supported by the available experimental data. The present approach is a significant generalization of the particle-driven gravity current problem: on the one hand, now the monodisperse current in non-rectangular channels is a particular case of n = 1. On the other hand, the classical formulation of polydisperse currents for a rectangular channel is now just a particular case, f(z) = const., in the wide domain of cross sections covered by this new model.
Khan, Noor Saeed; Gul, Taza; Khan, Muhammad Altaf; Bonyah, Ebenezer; Islam, Saeed
Mixed convection in gravity-driven non-Newtonian nanofluid films (Casson and Williamson) flow containing both nanoparticles and gyrotactic microorganisms along a convectively heated vertical surface is investigated. The actively controlled nanofluid model boundary conditions are used to explore the liquid films flow. The study exhibits an analytical approach for the non-Newtonian thin film nanofluids bioconvection based on physical mechanisms responsible for the nanoparticles and the base fluid, such as Brownian motion and thermophoresis. Both the fluids have almost the same behaviors for the effects of all the pertinent parameters except the effect of Schmidt number on the microorganism density function where the effect is opposite. Ordinary differential equations together with the boundary conditions are obtained through similarity variables from the governing equations of the problem, which are solved by HAM (Homotopy Analysis Method). The solution is expressed through graphs and illustrated which show the influences of all the parameters. The study is relevant to novel microbial fuel cell technologies combining the nanofluid with bioconvection phenomena.
Fortunato, Luca
2016-10-07
Fouling in membrane bioreactors (MBR) is acknowledged to be complex and unclear. An integrated characterization methodology was employed in this study to understand the fouling on a gravity-driven submerged MBR (GD-SMBR). It involved the use of different analytical tools, including optical coherence tomography (OCT), liquid chromatography with organic carbon detection (LC-OCD), total organic carbon (TOC), flow cytometer (FCM), adenosine triphosphate analysis (ATP) and scanning electron microscopy (SEM). The three-dimensional (3D) biomass morphology was acquired in a real-time through non-destructive and in situ OCT scanning of 75% of the total membrane surface directly in the tank. Results showed that the biomass layer was homogeneously distributed on the membrane surface. The amount of biomass was selectively linked with final destructive autopsy techniques. The LC-OCD analysis indicated the abundance of low molecular weight (LMW) organics in the fouling composition. Three different SEM techniques were applied to investigate the detailed fouling morphology on the membrane. © 2016 Elsevier Ltd
Liu, Chen-Guang; Hao, Xue-Mi; Lin, Yen-Han; Bai, Feng-Wu
2016-05-10
Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition. In this work, fermentation redox potential (ORP) was applied to drive the aeration process at low dissolved oxygen (DO) levels, which is infeasible to be regulated by a DO sensor. The performance and characteristics of flocculating yeast grown under 300 and 260 g glucose/L conditions were subjected to various aeration strategies including: no aeration; controlled aeration at -150, -100 and -50 mV levels; and constant aeration at 0.05 and 0.2 vvm. The results showed that anaerobic fermentation produced the least ethanol and had the highest residual glucose after 72 h of fermentation. Controlled aerations, depending on the real-time oxygen demand, led to higher cell viability than the no-aeration counterpart. Constant aeration triggered a quick biomass formation, and fast glucose utilization. However, over aeration at 0.2 vvm caused a reduction of final ethanol concentration. The controlled aeration driven by ORP under VHG conditions resulted in the best fermentation performance. Moreover, the controlled aeration could enhance yeast flocculating activity, promote an increase of flocs size, and accelerate yeast separation near the end of fermentation.
Ripepe, Maurizio; Donne, Dario Delle; Genco, Riccardo; Maggio, Giuseppe; Pistolesi, Marco; Marchetti, Emanuele; Lacanna, Giorgio; Ulivieri, Giacomo; Poggi, Pasquale
2015-05-18
Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.
Directory of Open Access Journals (Sweden)
Nouredine Meza
2006-10-01
Full Text Available The purpose of this work is to investigate the entropy generation in a laminar,gravity-driven conducting liquid film with fully developed velocity flowing along an inclineheated plate in the presence of a transverse magnetic field. The upper surface of the liquidfilm is considered free and adiabatic. The effect of heat generation by viscous dissipation isincluded in the analysis. The influence of the applied magnetic field and the viscousdissipation on velocity, temperature and entropy generation is examined.
Advanced Monitoring and Characterization of Biofouling in Gravity-driven Membrane Filtration
Wang, Yiran
2016-05-01
Gravity-driven membrane (GDM) filtration is one of the promising membrane bioreactor (MBR) technologies. It operates at a low pressure by gravity, requiring a minimal energy. Thus, it exhibits a great potential for a decentralized system, conducting household in developing and transition countries. Biofouling is a universal problem in almost all membrane filtration applications, leading to the decrease in flux or the increase in transmembrane pressure depending on different operation mode. Air scoring or regular membrane cleaning has been utilized for fouling mitigation, which requires increased energy consumption as well as complicated operations. Besides, repeating cleaning will trigger the deterioration of membranes and shorten their lifetime, elevating cost expenditures accordingly. In this way, GDM filtration stands out from conventional MBR technologies in a long-term operation with relative stable flux, which has been observed in many studies. The objective of this study was to monitor the biofilm development on a flat sheet membrane submerged in a GDM reactor with constant gravitational pressure. Morphology of biofilm layer in a fixed position was acquired by an in-situ and on-line OCT (optical coherence tomography) scanning at regular intervals for both visual investigation and structure analysis. The calculated thickness and roughness were compared to the variation of flux, fouling resistance and permeate quality, showing expected consistency. At the end of experiment, the morphology of entire membrane surface was scanned and recorded by OCT. Membrane autopsy was carried out for biofilm composition analysis by total organic carbon (TOC) and liquid chromatography with organic carbon detection (LC-OCD). In addition, biomass concentration was obtained by flow cytometer and adenosine tri-phosphate (ATP) method. The data of biofilm components indicated a homogeneous biofilm structure formed after a long-term running of the GDM system, based on the morphology
DEFF Research Database (Denmark)
Mitarai, Namiko; Nakanishi, Hiizu
2012-01-01
Granular material is a collection of macroscopic particles that are visible with naked eyes. The non-equilibrium nature of the granular materials makes their rheology quite different from that of molecular systems. In this minireview, we present the unique features of granular materials focusing ...... on the shear flow of dry granular materials and granule-liquid mixture....
Brilliantov, Nikolai
2003-01-01
While there is not yet any general theory for granular materials, significant progress has been achieved for dilute systems, also called granular gases. The contributions in this book address both the kinetic approach one using the Boltzmann equation for dissipative gases as well as the less established hydrodynamic description. The last part of the book is devoted to driven granular gases and their analogy with molecular fluids. Care has been taken so as to present the material in a pedagogical and self-contained way and this volume will thus be particularly useful to nonspecialists and newcomers to the field.
Hung, R. J.
1995-01-01
A set of mathematical formulation is adopted to study vapor deposition from source materials driven by heat transfer process under normal and oblique directions of gravitational acceleration with extremely low pressure environment of 10(exp -2) mm Hg. A series of time animation of the initiation and development of flow and temperature profiles during the course of vapor deposition has been obtained through the numerical computation. Computations show that the process of vapor deposition has been accomplished by the transfer of vapor through a fairly complicated flow pattern of recirculation under normal direction gravitational acceleration. It is obvious that there is no way to produce a homogeneous thin crystalline films with fine grains under such a complicated flow pattern of recirculation with a non-uniform temperature distribution under normal direction gravitational acceleration. There is no vapor deposition due to a stably stratified medium without convection for reverse normal direction gravitational acceleration. Vapor deposition under oblique direction gravitational acceleration introduces a reduced gravitational acceleration in vertical direction which is favorable to produce a homogeneous thin crystalline films. However, oblique direction gravitational acceleration also induces an unfavorable gravitational acceleration along horizontal direction which is responsible to initiate a complicated flow pattern of recirculation. In other words, it is necessary to carry out vapor deposition under a reduced gravity in the future space shuttle experiments with extremely low pressure environment to process vapor deposition with a homogeneous crystalline films with fine grains. Fluid mechanics simulation can be used as a tool to suggest most optimistic way of experiment with best setup to achieve the goal of processing best nonlinear optical materials.
Optimization of gravity-driven membrane (GDM) filtration process for seawater pretreatment.
Wu, Bing; Hochstrasser, Florian; Akhondi, Ebrahim; Ambauen, Noëmi; Tschirren, Lukas; Burkhardt, Michael; Fane, Anthony G; Pronk, Wouter
2016-04-15
Seawater pretreatment by gravity-driven membrane (GDM) filtration at 40 mbar has been investigated. In this system, a beneficial biofilm develops on the membrane that helps to stabilize flux. The effects of membrane type, prefiltration and system configuration on stable flux, biofilm layer properties and dissolved carbon removal were studied. The results show that the use of flat sheet PVDF membranes with pore sizes of 0.22 and 0.45 μm in GDM filtration achieved higher stabilized permeate fluxes (7.3-8.4 L/m(2)h) than that of flat sheet PES 100 kD membranes and hollow fibre PVDF 0.1 μm membranes. Pore constriction and cake filtration were identified as major membrane fouling mechanisms, but their relative contributions varied with filtration time for the various membranes. Compared to raw seawater, prefiltering of seawater with meshes at sizes of 10, 100 and 1000 μm decreased the permeate flux, which was attributed to removal of beneficial eukaryotic populations. Optical coherence tomography (OCT) showed that the porosity of the biofouling layer was more significantly related with permeate flux development rather than its thickness and roughness. To increase the contact time between the biofilm and the dissolved organics, a hybrid biofilm-submerged GDM reactor was evaluated, which displayed significantly higher permeate fluxes than the submerged GDM reactor. Although integrating the biofilm reactor with the membrane system displayed better permeate quality than the GDM filtration cells, it could not effectively reduce dissolved organic substances in the seawater. This may be attributed to the decomposition/degradation of solid organic substances in the feed and carbon fixation by the biofilm. Further studies of the dynamic carbon balance are required. Copyright © 2016 Elsevier Ltd. All rights reserved.
Contact Line Instability of Gravity-Driven Flow of Power-Law Fluids.
Hu, Bin; Kieweg, Sarah L
2015-11-01
The moving contact line of a thin fluid film can often corrugate into fingers, which is also known as a fingering instability. Although the fingering instability of Newtonian fluids has been studied extensively, there are few studies published on contact line fingering instability of non-Newtonian fluids. In particular, it is still unknown how shear-thinning rheological properties can affect the formation, growth, and shape of a contact line instability. Our previous study (Hu and Kieweg, 2012) showed a decreased capillary ridge formation for more shear-thinning fluids in a 2D model (i.e. 1D thin film spreading within the scope of lubrication theory). Those results motivated this study's hypothesis: more shear-thinning fluids should have suppressed finger growth and longer finger wavelength, and this should be evident in linear stability analysis (LSA) and 3D (i.e. 2D spreading) numerical simulations. In this study, we developed a LSA model for the gravity-driven flow of shear-thinning films, and carried out a parametric study to investigate the impact of shear-thinning on the growth rate of the emerging fingering pattern. A fully 3D model was also developed to compare and verify the LSA results using single perturbations, and to explore the result of multiple-mode, randomly imposed perturbations. Both the LSA and 3D numerical results confirmed that the contact line fingers grow faster for Newtonian fluids than the shear-thinning fluids on both vertical and inclined planes. In addition, both the LSA and 3D model indicated that the Newtonian fluids form fingers with shorter wavelengths than the shear-thinning fluids when the plane is inclined; no difference in the most unstable (i.e. emerging) wavelength was observed at vertical. This study also showed that the distance between emerging fingers was smaller on a vertical plane than on a less-inclined plane for shear-thinning fluids, as previously shown for Newtonian fluids. For the first time for shear
Wu, Bing; Christen, Tino; Tan, Hwee Sin; Hochstrasser, Florian; Suwarno, Stanislaus Raditya; Liu, Xin; Chong, Tzyy Haur; Burkhardt, Michael; Pronk, Wouter; Fane, Anthony G
2017-05-01
As a low energy and chemical free process, gravity-driven membrane (GDM) filtration has shown a potential for seawater pretreatment in our previous studies. In this study, a pilot submerged GDM reactor (effective volume of 720 L) was operated over 250 days and the permeate flux stabilized at 18.6 ± 1.4 L/m 2 h at a hydrostatic pressure of 40 mbar. This flux was higher than those in the lab-scale GDM reactor (16.3 ± 0.2 L/m 2 h; effective volume of 8.4 L) and in the filtration cell system (2.7 ± 0.6 L/m 2 h; feed side volume of 0.0046 L) when the same flat sheet membrane was used. Interestingly, when the filtration cell was submerged into the GDM reactor, the flux (17.2 L/m 2 h) was comparable to the submerged membrane module. Analysis of cake layer morphology and foulant properties indicated that a thicker but more porous cake layer with less accumulation of organic substances (biopolymers and humics) contributed to the improved permeate flux. This phenomenon was possibly associated with longer residence time of organic substances and sufficient space for the growth, predation, and movement of the eukaryotes in the GDM reactor. In addition, the permeate flux of the submerged hollow fibre membrane increased with decreasing packing density. It is thought that the movement of large-sized eukaryotes could be limited when the space between hollow fibres was reduced. In terms of pretreatment, the GDM systems effectively removed turbidity, viable cells, and transparent exopolymer particles from the feed seawater. Importantly, extending the reactor operation time produced a permeate with less assimilable organic carbon and biopolymers. Thus, the superior quality of the GDM permeate has the potential to alleviate subsequent reverse osmosis membrane fouling for seawater treatment. Copyright © 2017 Elsevier Ltd. All rights reserved.
Data report for ROSA-IV LSTF gravity-driven safety injection experiment run SB-CL-27
International Nuclear Information System (INIS)
Yonomoto, Taisuke; Saitou, Seishi; Kuroda, Takeshi
1994-03-01
Experimental data are presented for the passive injection test, Run SB-CL-27, conducted at the ROSA-IV Large Scale Test Facility (LSTF) on September 17, 1992. This experiment simulated thermal-hydraulic behavior of a gravity-driven, passive safety injection system during a small-break loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR). The injection system consisted of a gravity-driven injection tank, located above the reactor vessel, with connecting lines. The tank was initially filled with water of room temperature at the same pressure as the pressurizer. The connecting lines to the cold leg and to the vessel downcomer were opened at the test initiation. Then, a natural circulation flow developed in the loop which was formed by these lines and the injection tank. The hot water in the cold leg circulated into the upper part of tank and accumulated there causing a significant thermal stratification. This thermal stratification prevented direct-contact condensation of steam from occurring during the subsequent tank drain-down phase. Therefore, no condensation-induced depressurization of the tank, affecting adversely the injection performance, occurred. (author)
Hu, Bin; Kieweg, Sarah L
2012-07-15
Gravity-driven thin film flow is of importance in many fields, as well as for the design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. There have been many prior works on gravity-driven thin films. However, the incorporation of surface tension effect has not been well studied for non-Newtonian fluids. After surface tension effect was incorporated into our 2D (i.e. 1D spreading) power-law model, we found that surface tension effect not only impacted the spreading speed of the microbicide gel, but also had an influence on the shape of the 2D spreading profile. We observed a capillary ridge at the front of the fluid bolus. Previous literature shows that the emergence of a capillary ridge is strongly related to the contact line fingering instability. Fingering instabilities during epithelial coating may change the microbicide gel distribution and therefore impact how well it can protect the epithelium. In this study, we focused on the capillary ridge in 2D flow and performed a series of simulations and showed how the capillary ridge height varies with other parameters, such as surface tension coefficient, inclination angle, initial thickness, and power-law parameters. As shown in our results, we found that capillary ridge height increased with higher surface tension, steeper inclination angle, bigger initial thickness, and more Newtonian fluids. This study provides the initial insights of how to optimize the flow and prevent the appearance of a capillary ridge and fingering instability.
The Effect of Surface Tension on the Gravity-driven Thin Film Flow of Newtonian and Power-law Fluids
Hu, Bin; Kieweg, Sarah L.
2012-01-01
Gravity-driven thin film flow is of importance in many fields, as well as for the design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. There have been many prior works on gravity-driven thin films. However, the incorporation of surface tension effect has not been well studied for non-Newtonian fluids. After surface tension effect was incorporated into our 2D (i.e. 1D spreading) power-law model, we found that surface tension effect not only impacted the spreading speed of the microbicide gel, but also had an influence on the shape of the 2D spreading profile. We observed a capillary ridge at the front of the fluid bolus. Previous literature shows that the emergence of a capillary ridge is strongly related to the contact line fingering instability. Fingering instabilities during epithelial coating may change the microbicide gel distribution and therefore impact how well it can protect the epithelium. In this study, we focused on the capillary ridge in 2D flow and performed a series of simulations and showed how the capillary ridge height varies with other parameters, such as surface tension coefficient, inclination angle, initial thickness, and power-law parameters. As shown in our results, we found that capillary ridge height increased with higher surface tension, steeper inclination angle, bigger initial thickness, and more Newtonian fluids. This study provides the initial insights of how to optimize the flow and prevent the appearance of a capillary ridge and fingering instability. PMID:23687391
Can neutrino decay-driven mock gravity save hot dark matter?
Splinter, Randall J.; Melott, Adrian L.
1992-01-01
The radiative decay of a 30 eV neutrino with a lifetime of order 10 exp 23-24 s has recently been shown to yield a satisfactory explanation of a wide range of problems in astrophysics. In this paper, it is investigated whether the photon flux generated by the radiative decay of a massive neutrino is capable of generating sufficient radiation pressure to cause a 'mock gravitational' collapse of primordial hydrogen clouds. It is shown that when using neutral hydrogen as a source of opacity for mock gravity the time scale for mock gravitational collapse is significantly larger than the expansion time scale. Thus, the model fails as a source of galactic seed perturbations. Furthermore, it is argued that nonlinear feedback mechanisms will be unable to increase the collapse rate of the cloud under mock gravity.
Chen-Guang Liu; Xue-Mi Hao; Yen-Han Lin; Feng-Wu Bai
2016-01-01
Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition. In this work, fermentation redox potential (ORP) was applied to drive the aeration process at low dissolved oxygen (DO) levels, which is infeasible to be regulated by a DO sensor. The performance and characteristics of flocculating yeast grown under 300 and 260?g glucose/L conditions were subjected to various aeration strategies including: no aeration; controll...
Energy Technology Data Exchange (ETDEWEB)
Barvinsky, A.O. [Lebedev Physics Institute, Theory Department, Moscow (Russian Federation); Tomsk State University, Department of Physics, Tomsk (Russian Federation); UBC, Department of Physics and Astronomy, Pacific Institute for Theoretical Physics, Vancouver, BC (Canada); Kamenshchik, A.Yu. [Universita di Bologna, Dipartimento di Fisica e Astronomia, Bologna (Italy); L.D. Landau Institute for Theoretical Physics, Moscow (Russian Federation); INFN, Bologna (Italy); Nesterov, D.V. [Lebedev Physics Institute, Theory Department, Moscow (Russian Federation)
2015-12-15
We present a detailed derivation of the recently suggested new type of hill-top inflation [arXiv:1509.07270] originating from the microcanonical density matrix initial conditions in cosmology driven by conformal field theory (CFT). The cosmological instantons of topology S{sup 1} x S{sup 3}, which set up these initial conditions, have the shape of a garland with multiple periodic oscillations of the scale factor of the spatial S{sup 3}-section. They describe underbarrier oscillations of the inflaton and scale factor in the vicinity of the inflaton potential maximum, which gives a sufficient amount of inflation required by the known CMB data. We build the approximation of two coupled harmonic oscillators for these garland instantons and show that they can generate inflation consistent with the parameters of the CMB primordial power spectrum in the non-minimal Higgs inflation model and in R{sup 2} gravity. In particular, the instanton solutions provide smallness of inflationary slow-roll parameters ε and η < 0 and their relation ε ∝ η{sup 2} characteristic of these two models. We present the mechanism of formation of hill-like inflaton potentials, which is based on logarithmic loop corrections to the asymptotically shift-invariant tree-level potentials of these models in the Einstein frame. We also discuss the role of R{sup 2}-gravity as an indispensable finite renormalization tool in the CFT driven cosmology, which guarantees the nondynamical (ghost free) nature of its scale factor and special properties of its cosmological garland-type instantons. Finally, as a solution to the problem of hierarchy between the Planckian scale and the inflation scale we discuss the concept of a hidden sector of conformal higher spin fields. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Barvinsky, A. O., E-mail: barvin@td.lpi.ru [Theory Department, Lebedev Physics Institute, Leninsky Prospect 53, 119991, Moscow (Russian Federation); Department of Physics, Tomsk State University, Lenin Ave. 36, 634050, Tomsk (Russian Federation); Department of Physics and Astronomy, Pacific Institute for Theoretical Physics, UBC, 6224 Agricultural Road, V6T1Z1, Vancouver, BC (Canada); Kamenshchik, A. Yu., E-mail: kamenshchik@bo.infn.it [Dipartimento di Fisica e Astronomia, Università di Bologna and INFN, Via Irnerio 46, 40126, Bologna (Italy); L. D. Landau Institute for Theoretical Physics, 119334, Moscow (Russian Federation); Nesterov, D. V., E-mail: nesterov@td.lpi.it [Theory Department, Lebedev Physics Institute, Leninsky Prospect 53, 119991, Moscow (Russian Federation)
2015-12-11
We present a detailed derivation of the recently suggested new type of hill-top inflation originating from the microcanonical density matrix initial conditions in cosmology driven by conformal field theory (CFT). The cosmological instantons of topology S{sup 1}×S{sup 3}, which set up these initial conditions, have the shape of a garland with multiple periodic oscillations of the scale factor of the spatial S{sup 3}-section. They describe underbarrier oscillations of the inflaton and scale factor in the vicinity of the inflaton potential maximum, which gives a sufficient amount of inflation required by the known CMB data. We build the approximation of two coupled harmonic oscillators for these garland instantons and show that they can generate inflation consistent with the parameters of the CMB primordial power spectrum in the non-minimal Higgs inflation model and in R{sup 2} gravity. In particular, the instanton solutions provide smallness of inflationary slow-roll parameters ϵ and η<0 and their relation ϵ∼η{sup 2} characteristic of these two models. We present the mechanism of formation of hill-like inflaton potentials, which is based on logarithmic loop corrections to the asymptotically shift-invariant tree-level potentials of these models in the Einstein frame. We also discuss the role of R{sup 2}-gravity as an indispensable finite renormalization tool in the CFT driven cosmology, which guarantees the non-dynamical (ghost free) nature of its scale factor and special properties of its cosmological garland-type instantons. Finally, as a solution to the problem of hierarchy between the Planckian scale and the inflation scale we discuss the concept of a hidden sector of conformal higher spin fields.
Origin of inflation in CFT driven cosmology: R^2-gravity and non-minimally coupled inflaton models
Barvinsky, A. O.; Kamenshchik, A. Yu.; Nesterov, D. V.
2015-12-01
We present a detailed derivation of the recently suggested new type of hill-top inflation [arXiv:1509.07270] originating from the microcanonical density matrix initial conditions in cosmology driven by conformal field theory (CFT). The cosmological instantons of topology S^1× S^3, which set up these initial conditions, have the shape of a garland with multiple periodic oscillations of the scale factor of the spatial S^3-section. They describe underbarrier oscillations of the inflaton and scale factor in the vicinity of the inflaton potential maximum, which gives a sufficient amount of inflation required by the known CMB data. We build the approximation of two coupled harmonic oscillators for these garland instantons and show that they can generate inflation consistent with the parameters of the CMB primordial power spectrum in the non-minimal Higgs inflation model and in R^2 gravity. In particular, the instanton solutions provide smallness of inflationary slow-roll parameters ɛ and η <0 and their relation ɛ ˜ η ^2 characteristic of these two models. We present the mechanism of formation of hill-like inflaton potentials, which is based on logarithmic loop corrections to the asymptotically shift-invariant tree-level potentials of these models in the Einstein frame. We also discuss the role of R^2-gravity as an indispensable finite renormalization tool in the CFT driven cosmology, which guarantees the non-dynamical (ghost free) nature of its scale factor and special properties of its cosmological garland-type instantons. Finally, as a solution to the problem of hierarchy between the Planckian scale and the inflation scale we discuss the concept of a hidden sector of conformal higher spin fields.
Aranson, Igor S
2009-01-01
This title presents a review of experiments and novel theoretical concepts needed to understand the mechanisms of pattern formation in granular materials. An effort is made to connect concepts and ideas developed in granular physics with new emergent fields, especially in biology, such as cytoskeleton dynamics.
Energy balance in current sheets: From Petschek to gravity driven reconnection
International Nuclear Information System (INIS)
Mercier, C.; Heyvaerts, J.
1980-01-01
It has been shown earlier that energy balance processes play a very important role in the determination of the reconnection regime in the central diffusive region of a steady Petschek flow (usually considered elsewhere as isothermal and incompressible): as a consequence of the plasma thermal properties, abrupt transitions in the reconnection regime may occur for special external conditions. The regime becomes then a dynamical one, and it was suggested that onset of plasma microturbulence may result and act as a primary triggering mechanism in solar flares. In this paper we will reexamine the problem of onset of such dynamical transition and conclude that plasma microturbulence does not appear in a straightforward way. However it is possible that the canonical Petschek regime may evolute into a new one in which the dissipative sheet is no longer infinitesimal with respect to the dimensions of the structure, and in which gravity plays an important role. Flare triggering, if related to the reconnection regime, must then proceed by more complex processes, possibly related to tearing mode dynamics, or to more global properties of the magnetic structure of the active region. (orig.)
Passive Separation of Granular Materials
McCarthy, Joseph; Lievano, Diana
2013-11-01
Despite its industrial importance, particle separation techniques remain typically quite ``low tech'' and often are energy-intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. Rate-based separation processes, on the other hand, represent a unique approach to particle separation that has the potential to be more flexible, more efficient, and more environmentally friendly than existing ``low tech'' techniques. In the present paper, we highlight a passive granular separation technique, where particles of differing properties flow through a device often called a Galton board. In this type of device, the gravity-driven flow of particles down an inclined plane causes collisions between the particles and distributed pegs along the board. Collisions between particles as well as between particles and pegs results in a diffusion-like motion of particles perpendicular to the flow. The extent of separation (i.e., how far one type of particle is removed from another) depends on the different distances traversed by the two types of particles and, ultimately, on the collision rate and energy dissipation for particle-peg events. A simple theory, based on statistics and single-collision mechanics, will be set forth for comparison with our results.
Robin, Cécile; Guillocheau, François; Rouby, Delphine; Nalpas, Thierry; Jermannaud, Paul; Raillard, Stéphane
2013-04-01
We studied the evolution of the gravity flow sedimentary within a large shelf-edge delta (Eastern Niger delta) over the last 2,5Myr taking into account the influence of the contemporaneous gravity driven deformation and sedimentary supply. To do this, we mapped (i) the shoreline geometry and (ii) the associated turbiditic systems for 9 intervals using a classification based on three morphological end-members: erosive, constructive and depositional modes. We characterized the depositional profile of the passive margin delta from the littoral domain to the abyssal plain and its spatial and temporal variability. We showed that, at the scale of the delta, the depositional profile varied from (i) a shelf edge delta profile with a slope break at the location of the shoreline during progradation to (ii) a ramp profile characteristic of a mid-shelf delta during retrogradation. Thus, during a stratigraphic cycle, the delta front evolved from a prograding slope break during the development of the HST, to steepening clinoforms during the development of the LST that progressively flattened out during the TST to reach a ramp profile at the MFS. The turbiditic systems (including MTC) initiate near the shoreline, at the toe of the delta front. Also, they form preferentially down slope synthetic faults or within antithetic fault relays. They are initially erosive, becoming constructive further down slope and eventually depositional. They may become erosive again as they cut through the compressional structures. We showed that the stratigraphic state (progradation/retrogradation) controls the amount of sediment reaching the platform and strongly impacts the density of gravity flow sedimentary systems (low density during progradation and high density during progradation). On the other hand, the gravity driven deformation controls the slope of the sea-floor and, in doing so, their morphology (erosive/constructive/depositional). Within this framework, lateral migrations of the delta
Energy Technology Data Exchange (ETDEWEB)
Ballouz, Ronald-Louis; Richardson, Derek C. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Morishima, Ryuji [University of California, Los Angeles, Institute of Geophysics and Planetary Physics, Los Angeles, CA (United States)
2017-04-01
We study the B ring’s complex optical depth structure. The source of this structure may be the complex dynamics of the Keplerian shear and the self-gravity of the ring particles. The outcome of these dynamic effects depends sensitively on the collisional and physical properties of the particles. Two mechanisms can emerge that dominate the macroscopic physical structure of the ring: self-gravity wakes and viscous overstability. Here we study the interplay between these two mechanisms by using our recently developed particle collision method that allows us to better model the inter-particle contact physics. We find that for a constant ring surface density and particle internal density, particles with rough surfaces tend to produce axisymmetric ring features associated with the viscous overstability, while particles with smoother surfaces produce self-gravity wakes.
National Aeronautics and Space Administration — Genome-wide transcriptional profiling shows that reducing gravity levels in the International Space Station (ISS) causes important alterations in Drosophila gene...
Ding, An; Wang, Jinlong; Lin, Dachao; Tang, Xiaobin; Cheng, Xiaoxiang; Wang, Hui; Bai, Langming; Li, Guibai; Liang, Heng
2017-04-01
Rainwater is a nature resource, which can be widely used for non-potable and potable applications in water scared countries after appropriate treatment. Gravity-driven membrane filtration (GDM) process is a promising technology for decentralized rainwater treatment due to no backwashing, flushing and chemical cleaning. In this study, we established a single lab-scale GDM system for the stored rainwater (simulative cellar rainwater) treatment with two months operation, and a stored tap water was used as a compared system to evaluate the permeability and organics removal performance. Results showed that GDM exhibited a good performance for bacteria and turbidity removals, but the removal performance of DOC was undesirable due to the low rejection of low molecular-weight fulvic. Additionally, the permeate flux reached stable with the value of 6-6.5 L/m 2 h during 60 days operation in the rainwater system, however, the tap water system stabilized only at 4 L/m 2 h. Hydraulically reversible resistance accounted for large proportions (90%) of the total resistance, which indicated that the flux could be recovered by simple physical flushing. The bio-fouling layer adhered on the membrane surface was characterized at the end of the filtration experiment. Higher bio-activity with lower EPS (polysaccharides and proteins) contents of the fouling layer were found in the rainwater system compared with the control system, which was the main reason for the higher flux. These results show that rainwater can be treated in a single GDM process with low maintenance, which makes the process suitable for decentralized water supply. Copyright © 2016 Elsevier Ltd. All rights reserved.
Impact Compaction of a Granular Material
Fenton, Gregg; Asay, Blaine; Todd, Steve; Grady, Dennis
2017-06-01
The dynamic behavior of granular materials has importance to a variety of engineering applications. Although, the mechanical behavior of granular materials have been studied extensively for several decades, the dynamic behavior of these materials remains poorly understood. High-quality experimental data are needed to improve our general understanding of granular material compaction physics. This paper describes how an instrumented plunger impact system can be used to measure the compaction process for granular materials at high and controlled strain rates and subsequently used for computational modelling. The experimental technique relies on a gas-gun driven plunger system to generate a compaction wave through a volume of granular material. This volume of material has been redundantly instrumented along the bed length to track the progression of the compaction wave, and the piston displacement is measured with Photon Doppler Velocimetry (PDV). Using the gathered experimental data along with the initial material tap density, a granular material equation of state can be determined.
Akhondi, Ebrahim; Wu, Bing; Sun, Shuyang; Marxer, Brigit; Lim, Weikang; Gu, Jun; Liu, Linbo; Burkhardt, Michael; McDougald, Diane; Pronk, Wouter; Fane, Anthony G
2015-03-01
In this study gravity-driven membrane (GDM) ultrafiltration is investigated for the pretreatment of seawater before reverse osmosis (RO). The impacts of temperature (21 ± 1 and 29 ± 1 °C) and hydrostatic pressure (40 and 100 mbar) on dynamic flux development and biofouling layer structure were studied. The data suggested pore constriction fouling was predominant at the early stage of filtration, during which the hydrostatic pressure and temperature had negligible effects on permeate flux. With extended filtration time, cake layer fouling played a major role, during which higher hydrostatic pressure and temperature improved permeate flux. The permeate flux stabilized in a range of 3.6 L/m(2) h (21 ± 1 °C, 40 mbar) to 7.3 L/m(2) h (29 ± 1 °C, 100 mbar) after slight fluctuations and remained constant for the duration of the experiments (almost 3 months). An increase in biofouling layer thickness and a variable biofouling layer structure were observed over time by optical coherence tomography and confocal laser scanning microscopy. The presence of eukaryotic organisms in the biofouling layer was observed by light microscopy and the microbial community structure of the biofouling layer was analyzed by sequences of 16S rRNA genes. The magnitude of permeate flux was associated with the combined effect of the biofouling layer thickness and structure. Changes in the biofouling layer structure were attributed to (1) the movement and predation behaviour of the eukaryotic organisms which increased the heterogeneous nature of the biofouling layer; (2) the bacterial debris generated by eukaryotic predation activity which reduced porosity; (3) significant shifts of the dominant bacterial species over time that may have influenced the biofouling layer structure. As expected, most of the particles and colloids in the feed seawater were removed by the GDM process, which led to a lower RO fouling potential. However, the dissolved organic carbon in the
Coupled Leidenfrost states as a monodisperse granular clock
Liu, Rui; Yang, Mingcheng; Chen, Ke; Hou, Meiying; To, Kiwing
2016-08-01
Using an event-driven molecular dynamics simulation, we show that simple monodisperse granular beads confined in coupled columns may oscillate as a different type of granular clock. To trigger this oscillation, the system needs to be driven against gravity into a density-inverted state, with a high-density clustering phase supported from below by a gaslike low-density phase (Leidenfrost effect) in each column. Our analysis reveals that the density-inverted structure and the relaxation dynamics between the phases can amplify any small asymmetry between the columns, and lead to a giant oscillation. The oscillation occurs only for an intermediate range of the coupling strength, and the corresponding phase diagram can be universally described with a characteristic height of the density-inverted structure. A minimal two-phase model is proposed and a linear stability analysis shows that the triggering mechanism of the oscillation can be explained as a switchable two-parameter Andronov-Hopf bifurcation. Numerical solutions of the model also reproduce similar oscillatory dynamics to the simulation results.
Gravity-driven pH adjustment for site-specific protein pKa measurement by solution-state NMR
Li, Wei
2017-12-01
To automate pH adjustment in site-specific protein pKa measurement by solution-state NMR, I present a funnel with two caps for the standard 5 mm NMR tube. The novelty of this simple-to-build and inexpensive apparatus is that it allows automatic gravity-driven pH adjustment within the magnet, and consequently results in a fully automated NMR-monitored pH titration without any hardware modification on the NMR spectrometer.
Sliding through a superlight granular medium.
Pacheco-Vázquez, F; Ruiz-Suárez, J C
2009-12-01
We explore the penetration dynamics of an intruder in a granular medium composed of expanded polystyrene spherical particles. Three features distinguish our experiment from others studied so far in granular physics: (a) the impact is horizontal, decoupling the effects of gravity and the drag force; (b) the density of the intruder rho(i) is up to 350 times larger than the density of the granular medium rho(m); and (c) the way the intruder moves through the material, sliding at the bottom of the column with small friction. Under these conditions we find that the final penetration D scales with (rho(i)/rho(m)) and the drag force Fd and D saturate with the height of the granular bed.
DEM simulation of granular flows in a centrifugal acceleration field
Cabrera, Miguel Angel; Peng, Chong; Wu, Wei
2017-04-01
The main purpose of mass-flow experimental models is abstracting distinctive features of natural granular flows, and allow its systematic study in the laboratory. In this process, particle size, space, time, and stress scales must be considered for the proper representation of specific phenomena [5]. One of the most challenging tasks in small scale models, is matching the range of stresses and strains among the particle and fluid media observed in a field event. Centrifuge modelling offers an alternative to upscale all gravity-driven processes, and it has been recently employed in the simulation of granular flows [1, 2, 3, 6, 7]. Centrifuge scaling principles are presented in Ref. [4], collecting a wide spectrum of static and dynamic models. However, for the case of kinematic processes, the non-uniformity of the centrifugal acceleration field plays a major role (i.e., Coriolis and inertial effects). In this work, we discuss a general formulation for the centrifugal acceleration field, implemented in a discrete element model framework (DEM), and validated with centrifuge experimental results. Conventional DEM simulations relate the volumetric forces as a function of the gravitational force Gp = mpg. However, in the local coordinate system of a rotating centrifuge model, the cylindrical centrifugal acceleration field needs to be included. In this rotating system, the centrifugal acceleration of a particle depends on the rotating speed of the centrifuge, as well as the position and speed of the particle in the rotating model. Therefore, we obtain the formulation of centrifugal acceleration field by coordinate transformation. The numerical model is validated with a series of centrifuge experiments of monodispersed glass beads, flowing down an inclined plane at different acceleration levels and slope angles. Further discussion leads to the numerical parameterization necessary for simulating equivalent granular flows under an augmented acceleration field. The premise of
Lyubimova, Tatyana; Zubova, Nadezhda
The instability of incompressible viscous binary fluid with the Soret effect in square cavity heated from above is studied for different gravity levels. The no slip and zero mass flux conditions are imposed on all the boundaries. The horizontal boundaries are perfectly conductive, they are maintained at constant different temperatures and vertical boundaries are adiabatic. The calculations are performed for water - isopropanol mixture 90:10. Initial conditions correspond to the motionless state with uniform distribution of components and uniform temperature gradient directed upward. For binary fluid under consideration the separation parameter is negative therefore the Soret effect leads to the accumulation of heavy component in the upper part of cavity, moreover, the rate of accumulation is independent of the gravity level. The linear stability of the unsteady motionless state is studied numerically by solving linearized equations for small perturbations. To determine the time t* for the onset of instability, the criterion suggested in [1] is used. The dependence of t* on the gravity level is obtained. The work was done under financial support of Government of Perm Region, Russia (Contract C-26/212). 1. Shliomis M.I., Souhar M. Europhysics Letters. 2000. Vol. 49 (1), pp. 55-61.
International Nuclear Information System (INIS)
Hickey, M.P.
1988-01-01
Recently, Walterscheid et al. (1987) have described a dynamical-chemical model of wave-driven fluctuations in the OH nightglow which incorporated a five-reaction photochemical scheme and the dynamics of linearized acoustic-gravity waves in an isothermal, motionless atmosphere. The intensity oscillation (δI) about the time-averaged intensity (I 0 ) and the temperature oscillation (δT) about the time-averaged temperature (T 0 ) were related by means of the complex ratio η triple-bond (δI/I 0 )/(δT/T 0 ). One of the main conclusions of their work was that the inclusion of dynamical effects is absolutely essential for a valid assessment of η at any wave period. In this paper the model of Walterscheid et al. (1987) is modified to include in the gravity wave dynamics the effects of eddy viscosity, eddy thermal conduction, and Coriolis force (with the shallow atmosphere approximation), and calculations are performed for the same nominal case as used by these previous authors (i.e., λ x = 100 km and atmospheric conditions pertinent to 83 km altitude), but only gravity wave periods are considered. It is found that for wave periods greater than some 2 or 3 hours the value of η is greatly modified by the inclusion of eddy thermal conduction. Although when acting alone the eddy viscosity is relatively unimportant, it significantly modifies the results when acting in conjunction with the eddy thermal conduction. The inclusion of the Coriolis force is found to be insignificant at any wave period. Although it is for the longest-period waves that the values of η are most modified by the inclusion of dissipation, this dissipation may be severe enough to place an observational constraint on such waves
Dissipative lateral walls are sufficient to trigger convection in vibrated granular gases
Directory of Open Access Journals (Sweden)
Pontuale Giorgio
2017-01-01
Full Text Available Buoyancy-driven (thermal convection in dilute granular media, fluidized by a vibrating base, is known to appear without the need of lateral boundaries in a restricted region of parameters (inelasticity, gravity, intensity of energy injection. We have recently discovered a second buoyancy-driven convection effect which occurs at any value of the parameters, provided that the impact of particles with the lateral walls is inelastic (Pontuale et al., Phys. Rev. Lett. 117, 098006 (2016. It is understood that this novel convection effect is strictly correlated to the existence of perpendicular energy fluxes: a vertical one, induced by both bulk and wall inelasticity, and a horizontal one, induced only by dissipation at the walls. Here we first review those previous results, and then present new experimental and numerical data concerning the variations of box geometry, intensity of energy injection, number of particles and width of the box.
Sippel, Judith; Meeßen, Christian; Cacace, Mauro; Mechie, James; Fishwick, Stewart; Heine, Christian; Scheck-Wenderoth, Magdalena; Strecker, Manfred R.
2017-01-01
We present three-dimensional (3-D) models that describe the present-day thermal and rheological state of the lithosphere of the greater Kenya rift region aiming at a better understanding of the rift evolution, with a particular focus on plume-lithosphere interactions. The key methodology applied is the 3-D integration of diverse geological and geophysical observations using gravity modelling. Accordingly, the resulting lithospheric-scale 3-D density model is consistent with (i) reviewed descriptions of lithological variations in the sedimentary and volcanic cover, (ii) known trends in crust and mantle seismic velocities as revealed by seismic and seismological data and (iii) the observed gravity field. This data-based model is the first to image a 3-D density configuration of the crystalline crust for the entire region of Kenya and northern Tanzania. An upper and a basal crustal layer are differentiated, each composed of several domains of different average densities. We interpret these domains to trace back to the Precambrian terrane amalgamation associated with the East African Orogeny and to magmatic processes during Mesozoic and Cenozoic rifting phases. In combination with seismic velocities, the densities of these crustal domains indicate compositional differences. The derived lithological trends have been used to parameterise steady-state thermal and rheological models. These models indicate that crustal and mantle temperatures decrease from the Kenya rift in the west to eastern Kenya, while the integrated strength of the lithosphere increases. Thereby, the detailed strength configuration appears strongly controlled by the complex inherited crustal structure, which may have been decisive for the onset, localisation and propagation of rifting.
International Nuclear Information System (INIS)
Romney, B.; Barrau, A.; Vidotto, F.; Le Meur, H.; Noui, K.
2011-01-01
The loop quantum gravity is the only theory that proposes a quantum description of space-time and therefore of gravitation. This theory predicts that space is not infinitely divisible but that is has a granular structure at the Planck scale (10 -35 m). Another feature of loop quantum gravity is that it gets rid of the Big-Bang singularity: our expanding universe may come from the bouncing of a previous contracting universe, in this theory the Big-Bang is replaced with a big bounce. The loop quantum theory predicts also the huge number of quantum states that accounts for the entropy of large black holes. (A.C.)
HYPERELASTIC MODELS FOR GRANULAR MATERIALS
Energy Technology Data Exchange (ETDEWEB)
Humrickhouse, Paul W; Corradini, Michael L
2009-01-29
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
Massive 70 μm quiet clumps - II. Non-thermal motions driven by gravity in massive star formation?
Traficante, A.; Fuller, G. A.; Smith, R. J.; Billot, N.; Duarte-Cabral, A.; Peretto, N.; Molinari, S.; Pineda, J. E.
2018-02-01
The dynamic activity in massive star-forming regions prior to the formation of bright protostars is still not fully investigated. In this work, we present observations of HCO+ J = 1-0 and N2H+ J = 1-0 made with the IRAM 30 m telescope towards a sample of 16 Herschel-identified massive 70 μm quiet clumps associated with infrared dark clouds. The clumps span a mass range from 300 to 2000 M⊙. The N2H+ data show that the regions have significant non-thermal motions with velocity dispersion between 0.28 and 1.5 km s-1, corresponding to Mach numbers between 2.6 and 11.5. The majority of the 70 μm quiet clumps have asymmetric HCO+ line profiles, indicative of significant dynamical activity. We show that there is a correlation between the degree of line asymmetry and the surface density Σ of the clumps, with clumps of Σ ≳ 0.1 g cm-2 having more asymmetric line profiles, and so are more dynamically active, than clumps with lower Σ. We explore the relationship between velocity dispersion, radius and Σ and show how it can be interpreted as a relationship between an acceleration generated by the gravitational field, aG, and the measured kinetic acceleration, ak, consistent with the majority of the non-thermal motions originating from self-gravity. Finally, we consider the role of external pressure and magnetic fields in the interplay of forces.
Mechanics of Granular Materials-3 (MGM-3)
Sture, Stein; Alshibi, Khalid; Guynes, Buddy (Technical Monitor)
2002-01-01
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.
Nucleation in Sheared Granular Matter
Rietz, Frank; Radin, Charles; Swinney, Harry L.; Schröter, Matthias
2018-02-01
We present an experiment on crystallization of packings of macroscopic granular spheres. This system is often considered to be a model for thermally driven atomic or colloidal systems. Cyclically shearing a packing of frictional spheres, we observe a first order phase transition from a disordered to an ordered state. The ordered state consists of crystallites of mixed fcc and hcp symmetry that coexist with the amorphous bulk. The transition, initiated by homogeneous nucleation, overcomes a barrier at 64.5% volume fraction. Nucleation consists predominantly of the dissolving of small nuclei and the growth of nuclei that have reached a critical size of about ten spheres.
Nucleation in Sheared Granular Matter.
Rietz, Frank; Radin, Charles; Swinney, Harry L; Schröter, Matthias
2018-02-02
We present an experiment on crystallization of packings of macroscopic granular spheres. This system is often considered to be a model for thermally driven atomic or colloidal systems. Cyclically shearing a packing of frictional spheres, we observe a first order phase transition from a disordered to an ordered state. The ordered state consists of crystallites of mixed fcc and hcp symmetry that coexist with the amorphous bulk. The transition, initiated by homogeneous nucleation, overcomes a barrier at 64.5% volume fraction. Nucleation consists predominantly of the dissolving of small nuclei and the growth of nuclei that have reached a critical size of about ten spheres.
Navier-Stokes hydrodynamics of thermal collapse in a freely cooling granular gas.
Kolvin, Itamar; Livne, Eli; Meerson, Baruch
2010-08-01
We show that, in dimension higher than one, heat diffusion and viscosity cannot arrest thermal collapse in a freely evolving dilute granular gas, even in the absence of gravity. Thermal collapse involves a finite-time blowup of the gas density. It was predicted earlier in ideal, Euler hydrodynamics of dilute granular gases in the absence of gravity, and in nonideal, Navier-Stokes granular hydrodynamics in the presence of gravity. We determine, analytically and numerically, the dynamic scaling laws that characterize the gas flow close to collapse. We also investigate bifurcations of a freely evolving dilute granular gas in circular and wedge-shaped containers. Our results imply that, in general, thermal collapse can only be arrested when the gas density becomes comparable with the close-packing density of grains. This provides a natural explanation to the formation of densely packed clusters of particles in a variety of initially dilute granular flows.
Conway, Jon R; Keller, Arturo A
2016-07-01
The gravity-driven transport of TiO2, CeO2, and Cu(OH)2 engineered nanomaterials (ENMs) and their effects on soil pH and nutrient release were measured in three unsaturated soils. ENM transport was found to be highly limited in natural soils collected from farmland and grasslands, with the majority of particles being retained in the upper 0-3 cm of the soil profile, while greater transport depth was seen in a commercial potting soil. Physical straining appeared to be the primary mechanism of retention in natural soils as ENMs immediately formed micron-scale aggregates, which was exacerbated by coating particles with Suwannee River natural organic matter (NOM) which promote steric hindrance. Small changes in soil pH were observed in natural soils contaminated with ENMs that were largely independent of ENM type and concentration, but differed from controls. These changes may have been due to enhanced release of naturally present pH-altering ions (Mg(2+), H(+)) in the soil via substitution processes. These results suggest ENMs introduced into soil will likely be highly retained near the source zone. Copyright © 2016 Elsevier Ltd. All rights reserved.
Kordilla, Jannes; Noffz, Torsten; Dentz, Marco; Geyer, Tobias; Tartakovsky, Alexandre M.
2017-11-01
In this work, we study gravity-driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection. We present laboratory experiments, three-dimensional smoothed particle hydrodynamics (SPH) simulations using a heavily parallelized code, and a theoretical analysis. The flow-rate-dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the SPH model, and the transition ranges agree in SPH simulations and laboratory experiments. We show that flow modes heavily influence the "bypass" behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), the flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer. For the case of rivulet flow, we provide an analytical solution that demonstrates the existence of classical Washburn flow within the horizontal fracture.
Wang, Jianqiang; Wu, Yichao; Yang, Zhe; Guo, Hao; Cao, Bin; Tang, Chuyang Y
2017-05-24
We report a facile method for preparing silver-loaded membranes for point-of-use disinfection and disaster relief applications. A bio-inspired material, polydopamine, was coated onto a highly porous nanofibrous polyacrylonitrile substrate. We then take advantage of the redox properties of polydopamine to form silver nanoparticles in situ. These nanoparticles were uniformly distributed on the surface of nanofibers with no apparent agglomeration at a silver loading up to 4.36 wt.% (cPAN-Ag1.5). The silver-incorporated membrane cPAN-Ag1.5 achieved a high pure water flux of 130 Lm -2 h -1 at 10-cm water head, demonstrating the feasibility of energy-efficient gravity-driven filtration and eliminating the need for electrical power. The strong anti-bacterial activity and high physical rejection of the membrane led to an excellent disinfection power, with no viable bacterial cells detected in its permeate water. The membrane exhibited >7 log reduction for E. coli and >6 log reduction for B. subtilis. The strategy reported here provides an efficient and green route to synthesize point-of-use membranes. Combining their excellent permeability and disinfection effectiveness, these membranes offer an ideal solution to water supply in disaster-affected areas.
Directory of Open Access Journals (Sweden)
S. Saouli
2009-06-01
Full Text Available A second-law analysis of a gravity-driven film of non-Newtonian fluid along an inclined heated plate is investigated. The flow is assumed to be steady, laminar and fully-developed. The upper surface of the liquid film is considered to be free and adiabatic. The effect of heat generation by viscous dissipation is included. Velocity, temperature and entropy generation profiles are presented. The effects of the flow behaviour index, the Brinkman number and the group parameter on velocity, temperature and entropy generation number are discussed. The results show that velocity profile depends largely on the flow behaviour index. They are flat near the free surface for pseudoplastic fluids and linear for dilatant fluids. Temperature profiles are higher for higher flow behaviour index and Brinkman number. The entropy generation number increases with Brinkman number and the group parameter because of the heat generated by the viscous dissipation effect. For pseudoplastic fluids, the irreversibility is dominated by heat transfer, whereas, for dilatant fluids, irreversibility due to fluid friction is more dominant.
International Workshop on Traffic and Granular Flow
Herrmann, Hans; Schreckenberg, Michael; Wolf, Dietrich; Social, Traffic and Granular Dynamics
2000-01-01
"Are there common phenomena and laws in the dynamic behavior of granular materials, traffic, and socio-economic systems?" The answers given at the international workshop "Traffic and Granular Flow '99" are presented in this volume. From a physical standpoint, all these systems can be treated as (self)-driven many-particle systems with strong fluctuations, showing multistability, phase transitions, non-linear waves, etc. The great interest in these systems is due to several unexpected new discoveries and their practical relevance for solving some fundamental problems of today's societies. This includes intelligent measures for traffic flow optimization and methods from "econophysics" for stabilizing (stock) markets.
Cystic Granular Cell Ameloblastoma
Thillaikarasi, Rathnavel; Balaji, Jayaram; Gupta, Bhawna; Ilayarja, Vadivel; Vani, Nandimandalam Venkata; Vidula, Balachander; Saravanan, Balasubramaniam; Ponniah, Irulandy
2010-01-01
Ameloblastoma is a locally aggressive benign epithelial odontogenic tumor, while unicystic ameloblastoma is a relatively less aggressive variant. Although rare in unicystic or cystic ameloblastoma, granular cell change in ameloblastoma is a recognized phenomenon. The purpose of the present article is to report a case of cystic granular cell ameloblastoma in 34-year old female.
11th Traffic and Granular Flow Conference
Daamen, Winnie
2016-01-01
The Conference on Traffic and Granular Flow brings together international researchers from different fields ranging from physics to computer science and engineering to discuss the latest developments in traffic-related systems. Originally conceived to facilitate new ideas by considering the similarities of traffic and granular flow, TGF'15, organised by Delft University of Technology, now covers a broad range of topics related to driven particle and transport systems. Besides the classical topics of granular flow and highway traffic, its scope includes data transport (Internet traffic), pedestrian and evacuation dynamics, intercellular transport, swarm behaviour and the collective dynamics of other biological systems. Recent advances in modelling, computer simulation and phenomenology are presented, and prospects for applications, for example to traffic control, are discussed. The conference explores the interrelations between the above-mentioned fields and offers the opportunity to stimulate interdisciplinar...
Rare events in granular media: a volcanic-like explosion
Khain, Evgeniy; Sander, Leonard
2015-11-01
Granular matter is ubiquitous in nature and exhibits a variety of nontrivial phenomena. Within the same system, different regions of granular media can be at a solid or a gas phase. Here we focus on a granular Leidenfrost effect: a solid-like cluster is levitating above the ``hot'' granular gas. This state was observed experimentally, when granular matter was vertically vibrated in a two-dimensional container. This solid-gas coexistence can be described by using granular hydrodynamics, taking into account the viscosity divergence in the solid cluster. The approach is similar to the one employed in investigating solid-fluid coexistence in dense shear granular flows. We performed extensive molecular dynamics simulations of a simple model of inelastic hard spheres driven by a ``thermal'' bottom wall. Simulations showed that for low wall temperatures, the levitating cluster is stable, while for high wall temperatures, it breaks down, and a hot gas bursts out resembling a volcanic explosion. We found a hysteresis: for a wide range of bottom wall temperatures, both the clustering state and the volcanic state are stable. However, even if the system is at the (stable) clustering state, a volcanic explosion is possible: it is a rare event driven by large fluctuations. We propose a special simulation technique that allows investigating such rare events.
Directory of Open Access Journals (Sweden)
Claudia de Rham
2014-08-01
Full Text Available We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP, cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alternative and related models of massive gravity such as new massive gravity, Lorentz-violating massive gravity and non-local massive gravity.
Rheology of granular flows immersed in a viscous fluid
International Nuclear Information System (INIS)
Amarsid, Lhassan
2015-01-01
We investigate the behavior of granular materials immersed in a viscous fluid by means of extensive simulations based on the Discrete Element Method for particle dynamics coupled with the Lattice Boltzmann method for the fluid. We show that, for a broad range of parameters such as shear rate, confining stress and viscosity, the internal friction coefficient and packing fraction are well described by a single 'visco-inertial' dimensionless parameter combining inertial and Stokes numbers. The frictional behavior under constant confining pressure is mapped into a viscous behavior under volume-controlled conditions, leading to the divergence of the effective normal and shear viscosities in inverse square of the distance to the critical packing fraction. The results are in excellent agreement with the experimental data of Boyer et al. (2011). The evolution of the force network in terms of connectivity and anisotropy as a function of the visco-inertial number, indicates that the increase of frictional strength is a direct consequence of structural anisotropy enhanced by both fluid viscosity and grain inertia. In view of application to a potential nuclear accident, we also study the fragmentation and flow of confined porous aggregates in a fluid under the action of local overpressures and pressure gradients as well as gravity-driven flow of immersed particles in an hourglass. (author)
Granular gases under extreme driving
Kang, W.; Machta, J.; Ben-Naim, E.
2010-08-01
We study inelastic gases in two dimensions using event-driven molecular-dynamics simulations. Our focus is the nature of the stationary state attained by rare injection of large amounts of energy to balance the dissipation due to collisions. We find that under such extreme driving, with the injection rate much smaller than the collision rate, the velocity distribution has a power-law high-energy tail. The numerically measured exponent characterizing this tail is in excellent agreement with predictions of kinetic theory over a wide range of system parameters. We conclude that driving by rare but powerful energy injection leads to a well-mixed gas and constitutes an alternative mechanism for agitating granular matter. In this distinct nonequilibrium steady state, energy cascades from large to small scales. Our simulations also show that when the injection rate is comparable with the collision rate, the velocity distribution has a stretched exponential tail.
Dynamics of the wet granular Leidenfrost phenomenon.
Roeller, Klaus; Herminghaus, Stephan
2012-08-01
By event-driven molecular dynamics simulations, we study the Leidenfrost effect for wet granular matter driven from below. In marked contrast to all earlier studies on other fluids, the dense plug hovering on the hot gas cushion undergoes an undamped oscillation. The location of the Hopf bifurcation leading to this oscillation is strongly dependent on the inelasticity of the grain impacts. The vertical separation into a gas phase with a condensed plug hovering above it is particularly pronounced due to the cohesiveness of the granulate. For sufficiently large system sizes, the Rayleigh-Taylor instability terminates the oscillatory state at late times.
Special relativity induced by granular space
International Nuclear Information System (INIS)
Jizba, Petr; Scardigli, Fabio
2013-01-01
We show that the special relativistic dynamics, when combined with quantum mechanics and the concept of superstatistics, can be interpreted as arising from two interlocked non-relativistic stochastic processes that operate at different energy scales. This framework leads to Feynman amplitudes that are, in the Euclidean regime, identical to the transition probability of a Brownian particle propagating through a granular space. For illustration we consider the dynamics and the propagator of a Klein-Gordon particle. Implications for deformed special relativity, quantum field theory, quantum gravity and cosmology are also discussed. (orig.)
Failures in sand in reduced gravity environments
Marshall, Jason P.; Hurley, Ryan C.; Arthur, Dan; Vlahinic, Ivan; Senatore, Carmine; Iagnemma, Karl; Trease, Brian; Andrade, José E.
2018-04-01
The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the peak friction angle on gravity, a decrease in the residual friction angle between Martian and Lunar gravity, no dependence of the angle of repose on gravity, and an increase in the dilation angle between Martian and Lunar gravity. Additionally, multiple flow surfaces were seen in near-zero gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular materials at different levels of gravity.
Granular computing: perspectives and challenges.
Yao, JingTao; Vasilakos, Athanasios V; Pedrycz, Witold
2013-12-01
Granular computing, as a new and rapidly growing paradigm of information processing, has attracted many researchers and practitioners. Granular computing is an umbrella term to cover any theories, methodologies, techniques, and tools that make use of information granules in complex problem solving. The aim of this paper is to review foundations and schools of research and to elaborate on current developments in granular computing research. We first review some basic notions of granular computing. Classification and descriptions of various schools of research in granular computing are given. We also present and identify some research directions in granular computing.
Marston, J. O.
2013-07-15
We investigate the spreading and splashing of granular drops during impact with a solid target. The granular drops are formed from roughly spherical balls of sand mixed with water, which is used as a binder to hold the ball together during free-fall. We measure the instantaneous spread diameter for different impact speeds and find that the normalized spread diameter d/D grows as (tV/D)1/2. The speeds of the grains ejected during the “splash” are measured and they rarely exceed twice that of the impact speed.
State variables in dense granular materials
Daniels, Karen
2009-11-01
Granular materials are integral to many parts of our daily lives, from the coffee beans that fuel our mornings to the coal that fuels our power plants. Two related aspects of their dynamics are particularly striking: their ability to exhibit both solid-like and liquid-like behavior, and the presence of highly heterogeneous force chains in which the magnitude of the local stress varies widely over short distances. These distinctive behaviors are connected to the fact that granular materials are always out of equilibrium: first, because they are typically both driven and dissipative, but also because they remain in metastable states even when they aren't being driven. I will present recent results from several experiments ranging from the theoretically-motivated (the equilibration of state variables within a non-equilibrium system) to the practical (particle-segregation by size). The results of these experiments elucidate the complex behaviors which underlay granular dynamics, and provide a reason to hope that statistical physics might hold the keys to explaining the observed phenomena.
Small solar system bodies as granular systems
Directory of Open Access Journals (Sweden)
Hestroffer Daniel
2017-01-01
Full Text Available Asteroids and other Small Solar System Bodies (SSSBs are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining. In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.
African Journals Online (AJOL)
Necrosis within the tumor was absent, no mitosis was. Granular cell tumors are seldom diagnosed identified in the section and the edges of the accurately clinically. The lesion in this case was sample were tumor free (Figure 2). mistaken for a sebaceous cyst and following ulceration resembled carcinoma of the vulvar.
de Rham, Claudia
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
Protocol-independent granular temperature supported by numerical simulations
Becker, Volker; Kassner, Klaus
2015-11-01
A possible approach to the statistical description of granular assemblies starts from Edwards's assumption that all blocked states occupying the same volume are equally probable [Edwards and Oakeshott, Physica A 157, 1080 (1989)], 10.1016/0378-4371(89)90034-4. We performed computer simulations using two-dimensional polygonal particles excited periodically according to two different protocols: excitation by pulses of "negative gravity" and excitation by "rotating gravity." The first protocol exhibits a nonmonotonous dependency of the mean volume fraction on the pulse strength. The overlapping histogram method is used in order to test whether the volume distribution is described by a Boltzmann-like distribution and to calculate the inverse compactivity as well as the logarithm of the partition sum. We find that the mean volume is a unique function of the measured granular temperature, independently of the protocol and of the branch in ϕ (g ) , and that all determined quantities are in agreement with Edwards's theory.
Aerofractures in Confined Granular Media
Eriksen, Fredrik K.; Turkaya, Semih; Toussaint, Renaud; Måløy, Knut J.; Flekkøy, Eirik G.
2015-04-01
We will present the optical analysis of experimental aerofractures in confined granular media. The study of this generic process may have applications in industries involving hydraulic fracturing of tight rocks, safe construction of dams, tunnels and mines, and in earth science where phenomena such as mud volcanoes and sand injectites are results of subsurface sediment displacements driven by fluid overpressure. It is also interesting to increase the understanding the flow instability itself, and how the fluid flow impacts the solid surrounding fractures and in the rest of the sample. Such processes where previously studied numerically [Niebling 2012a, Niebling 2012b] or in circular geometries. We will here explore experimentally linear geometries. We study the fracturing patterns that form when air flows into a dense, non-cohesive porous medium confined in a Hele-Shaw cell - i.e. into a packing of dry 80 micron beads placed between two glass plates separated by ~1mm. The cell is rectangular and fitted with a semi-permeable boundary to the atmosphere - blocking beads but not air - on one short edge, while the other three edges are impermeable. The porous medium is packed inside the cell between the semi-permeable boundary and an empty volume at the sealed side where the air pressure can be set and kept at a constant overpressure (1-2bar). Thus, for the air trapped inside the cell to release the overpressure it has to move through the solid. At high enough overpressures the air flow deforms the solid and increase permeability in some regions along the air-solid interface, which results in unstable flow and aerofracturing. Aerofractures are thought to be an analogue to hydrofractures, and an advantage of performing aerofracturing experiments in a Hele-Shaw cell is that the fracturing process can easily be observed in the lab. Our experiments are recorded with a high speed camera with a framerate of 1000 frames per second. In the analysis, by using various image
Measurements of granular flow dynamics with high speed digital images
Energy Technology Data Exchange (ETDEWEB)
Lee, Jingeol [Univ. of Florida, Gainesville, FL (United States)
1994-01-01
The flow of granular materials is common to many industrial processes. This dissertation suggests and validates image processing algorithms applied to high speed digital images to measure the dynamics (velocity, temperature and volume fraction) of dry granular solids flowing down an inclined chute under the action of gravity. Glass and acrylic particles have been used as granular solids in the experiment. One technique utilizes block matching for spatially averaged velocity measurements of the glass particles. This technique is compared with the velocity measurement using an optic probe which is a conventional granular flow velocity measurement device. The other technique for measuring the velocities of individual acrylic particles is developed with correspondence using a Hopfield network. This technique first locates the positions of particles with pattern recognition techniques, followed by a clustering technique, which produces point patterns. Also, several techniques are compared for particle recognition: synthetic discriminant function (SDF), minimum average correlation energy (MACE) filter, modified minimum average correlation energy (MMACE) filter and variance normalized correlation. The author proposes an MMACE filter which improves generalization of the MACE filter by adjusting the amount of averaged spectrum of training images in the spectrum whitening stages of the MACE filter. Variance normalized correlation is applied to measure the velocity and temperature of flowing glass particles down the inclined chute. The measurements are taken for the steady and wavy flow and qualitatively compared with a theoretical model of granular flow.
Kinetic Theory of Granular Gases
International Nuclear Information System (INIS)
Trizac, Emmanuel
2005-01-01
coefficients, that are again velocity dependent. Th is seems to be the price of a consistent approach, which does not lend itself to much insight. In addition, the behaviour of driven systems is not addressed, whereas in the realm of granular media, force-free systems are the exception rather than the rule. The differences between constant ε and visco-elastic models is presumably less pronounced in the driven case. Study of driven systems also reveals that the rheology of granular gases is intrinsically non-Newtonian, which is a key feature. Finally, the powerful direct simulation Monte Carlo technique is not described, whereas it is an important tool, particularly relevant for the physics of the Boltzmann equation, and straightforward to implement in its simplest version. N Brilliantov and T Poeschel concentrate on the (equally relevant) molecular dynamics method instead. In conclusion, the book fills a gap in the field. The companion webpage from where molecular dynamics and symbolic algebra programs can be downloaded is also useful. (book review)
Energy dissipation and clustering in granular streams
Waitukaitis, Scott; Royer, John; Gruetjen, Helge; Jaeger, Heinrich
2009-11-01
The presence of weak cohesive forces between macroscopic grains can lead to the break up of a free falling granular stream, similar to the surface-tension-driven break up of a liquid streamfootnotetext Royer, J. R. et al. Nature 459 1110 - 1113 (2009).. This sensitivity to minute forces suggests that these free falling streams could serve as a tool to probe the interactions between grains. In order to investigate the connection between the stream dynamics and the grain-grain interactions, we perform molecular dynamics simulations of a granular stream freely falling out of a hopper varying the cohesion and inelasticity of the grains. We find that in the absence of cohesive forces the stream breaks apart into isolated grains, in contrast to the clustering observed in simulations of inelastic granular gases. For sufficiently high cohesive forces we reproduce the break up of stream into droplets, while with lower cohesive forces the stream breaks up into smaller clusters consisting of only a few grains. Measuring the change in contact number and decay of velocity fluctuations with depth, we characterize the different regions of the force-inelasticity phase space.
Physical test of a particle simulation model in a sheared granular system
Energy Technology Data Exchange (ETDEWEB)
Rycroft, Chris; Orpe, Ashish; Kudrolli, Arshad
2009-01-15
We report a detailed comparison of a slow gravity driven sheared granular flow with a computational model performed with the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). To our knowledge, this is the first thorough test of the LAMMPS model with a laboratory granular flow. In the experiments, grains flow inside a silo with a rectangular cross-section, and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The boundary imposes a packing order, and the grains are observed to flow in layers which get progressively more disordered with distance from the walls. The computations use a Cundall--Strack contact model between the grains, using contact parameters that have been used in many other previous studies, and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. After appropriate scaling, we find that the mean velocity of the grains and the number density as a function of flow cross-section observed in the experiments and the simulations are in excellent agreement. The mean flow profile is observed to be unchanged over a broad range of coefficient of friction, except near the smooth wall. We show that the flow profile is not sensitive to atleast 10\\percent polydispersity in particle size. Because the grain elasticity used is smaller in the computations as compared with glass grains, wave-like features can be noted over short time scales in the mean velocity and the velocity auto-correlations measured in the simulations. These wave features occur over an intermediate timescale larger than the particle interaction but smaller than the
Sanchez, Mauricio A; Castro, Juan R
2017-01-01
In this book, a series of granular algorithms are proposed. A nature inspired granular algorithm based on Newtonian gravitational forces is proposed. A series of methods for the formation of higher-type information granules represented by Interval Type-2 Fuzzy Sets are also shown, via multiple approaches, such as Coefficient of Variation, principle of justifiable granularity, uncertainty-based information concept, and numerical evidence based. And a fuzzy granular application comparison is given as to demonstrate the differences in how uncertainty affects the performance of fuzzy information granules.
Sumner, E.; Peakall, J.; Dorrell, R. M.; Parsons, D. R.; Darby, S. E.; Wynn, R. B.
2014-12-01
Submarine channel systems transport vast amounts of terrestrial sediment into the deep sea. Understanding the dynamics of the gravity currents that create these systems, and in particular, how these flows interact with and form bends, is fundamental to predicting system architecture and evolution. Bend flow is characterized by a helical structure and in rivers typically comprises inwardly directed near-bed flow and outwardly directed near-surface flow. Following a decade of debate, it is now accepted that helical flow in submarine channel bends can exhibit a variety of structures including being opposed to that observed in rivers. The new challenge is to understand what controls the orientation of helical flow cells within submarine flows and determines the conditions for reversal. We present data from the Black Sea showing, for the first time, the three-dimensional velocity and density structure of an active submarine gravity current. By calculating the forces acting on the flow, we evaluate what controls the orientation of helical flow cells. We demonstrate that radial pressure gradients caused by across-channel stratification of the flow are more important than centrifugal acceleration in controlling the orientation of helical flow. We also demonstrate that nonlocal acceleration of the flow due to topographic forcing and downstream advection of the cross-stream flow are significant terms in the momentum balance. These findings have major implications for conceptual and numerical models of submarine channel dynamics, because they show that three-dimensional models that incorporate across-channel flow stratification are required to accurately represent curvature-induced helical flow in such systems.
NMRI Measurements of Flow of Granular Mixtures
Nakagawa, Masami; Waggoner, R. Allen; Fukushima, Eiichi
1996-01-01
We investigate complex 3D behavior of granular mixtures in shaking and shearing devices. NMRI can non-invasively measure concentration, velocity, and velocity fluctuations of flows of suitable particles. We investigate origins of wall-shear induced convection flow of single component particles by measuring the flow and fluctuating motion of particles near rough boundaries. We also investigate if a mixture of different size particles segregate into their own species under the influence of external shaking and shearing disturbances. These non-invasive measurements will reveal true nature of convecting flow properties and wall disturbance. For experiments in a reduced gravity environment, we will design a light weight NMR imager. The proof of principle development will prepare for the construction of a complete spaceborne system to perform experiments in space.
Mashhoon, Bahram
2017-01-01
Relativity theory is based on a postulate of locality, which means that the past history of the observer is not directly taken into account. This book argues that the past history should be taken into account. In this way, nonlocality---in the sense of history dependence---is introduced into relativity theory. The deep connection between inertia and gravitation suggests that gravity could be nonlocal, and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein's theory of gravitation has recently been developed. A significant consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. According to nonlocal gravity theory, what astronomers attribute to dark matter should instead be due to the nonlocality of gravitation. Nonlocality dominates on the scale of galaxies and beyond. Memory fades with time; therefore, the nonlocal aspect of gravity becomes wea...
An experimental study of ultrasonic vibration and the penetration of granular material
Firstbrook, David; Worrall, Kevin; Timoney, Ryan; Suñol, Francesc; Gao, Yang
2017-01-01
This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes. PMID:28293134
Granular flows : fluidization and anisotropy
Wortel, Gerrit Herman
2014-01-01
This work discusses the flow of granular materials (e.g. sand). Even though a single particle is a simple object, the collective behavior of billions of particles can be very complex. In a surprisingly large amount of cases, it is not exactly known how a granular material behaves, and this while
Sealing of boreholes using natural, compatible materials: Granular salt
International Nuclear Information System (INIS)
Finley, R.E.; Zeuch, D.H.; Stormont, J.C.; Daemen, J.J.K.
1994-01-01
Granular salt can be used to construct high performance permanent seals in boreholes which penetrate rock salt formations. These seals are described as seal systems comprised of the host rock, the seal material, and the seal rock interface. The performance of these seal systems is defined by the complex interactions between these seal system components through time. The interactions are largely driven by the creep of the host formation applying boundary stress on the seal forcing host rock permeability with time. The immediate permeability of these seals is dependent on the emplaced density. Laboratory test results suggest that careful emplacement techniques could results in immediate seal system permeability on the order of 10 -16 m 2 to 10 -18 m 2 (10 -4 darcy to 10 -6 ). The visco-plastic behavior of the host rock coupled with the granular salts ability to ''heal'' or consolidate make granular salt an ideal sealing material for boreholes whose permanent sealing is required
Massive gravity from bimetric gravity
International Nuclear Information System (INIS)
Baccetti, Valentina; Martín-Moruno, Prado; Visser, Matt
2013-01-01
We discuss the subtle relationship between massive gravity and bimetric gravity, focusing particularly on the manner in which massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure is more delicate than currently appreciated. Specifically, this limiting procedure should not unnecessarily constrain the background metric, which must be externally specified by the theory of massive gravity itself. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit, leading to additional constraints besides the one set of equations of motion naively expected. Thus, since solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true, there is no complete continuity in the parameter space of the theory. In particular, we study the massive cosmological solutions which are continuous in the parameter space, showing that many interesting cosmologies belong to this class. (paper)
Clément, Gilles
2007-01-01
Protecting the health, safety, and performance of exploration-class mission crews against the physiological deconditioning resulting from long-term weightlessness during transit and long-term reduced gravity during surface operations will require effective, multi-system countermeasures. Artificial gravity, which would replace terrestrial gravity with inertial forces generated by rotating the transit vehicle or by short-radius human centrifuge devices within the transit vehicle or surface habitat, has long been considered a potential solution. However, despite its attractiveness as an efficient
Particle-size segregation and diffusive remixing in shallow granular avalanches
Gray, J. M. N. T.; Chugunov, V. A.
2006-12-01
Segregation and mixing of dissimilar grains is a problem in many industrial and pharmaceutical processes, as well as in hazardous geophysical flows, where the size-distribution can have a major impact on the local rheology and the overall run-out. In this paper, a simple binary mixture theory is used to formulate a model for particle-size segregation and diffusive remixing of large and small particles in shallow gravity-driven free-surface flows. This builds on a recent theory for the process of kinetic sieving, which is the dominant mechanism for segregation in granular avalanches provided the density-ratio and the size-ratio of the particles are not too large. The resulting nonlinear parabolic segregation remixing equation reduces to a quasi-linear hyperbolic equation in the no-remixing limit. It assumes that the bulk velocity is incompressible and that the bulk pressure is lithostatic, making it compatible with most theories used to compute the motion of shallow granular free-surface flows. In steady-state, the segregation remixing equation reduces to a logistic type equation and the ‘S’-shaped solutions are in very good agreement with existing particle dynamics simulations for both size and density segregation. Laterally uniform time-dependent solutions are constructed by mapping the segregation remixing equation to Burgers equation and using the Cole Hopf transformation to linearize the problem. It is then shown how solutions for arbitrary initial conditions can be constructed using standard methods. Three examples are investigated in which the initial concentration is (i) homogeneous, (ii) reverse graded with the coarse grains above the fines, and, (iii) normally graded with the fines above the coarse grains. Time-dependent two-dimensional solutions are also constructed for plug-flow in a semi-infinite chute.
Using a Time Granularity Table for Gradual Granular Data Aggregation
DEFF Research Database (Denmark)
Iftikhar, Nadeem; Pedersen, Torben Bach
2010-01-01
The majority of today’s systems increasingly require sophisticated data management as they need to store and to query large amounts of data for analysis and reporting purposes. In order to keep more “detailed” data available for longer periods, “old” data has to be reduced gradually to save space...... is 6 months old aggregate to 2 minutes level from 1 minute level and so on. The proposed solution introduces a time granularity based data structure, namely a relational time granularity table that enables long term storage of old data by maintaining it at different levels of granularity and effective...
Using a Time Granularity Table for Gradual Granular Data Aggregation
DEFF Research Database (Denmark)
Iftikhar, Nadeem; Pedersen, Torben Bach
2014-01-01
The majority of today’s systems increasingly require sophisticated data management as they need to store and to query large amounts of data for analysis and reporting purposes. In order to keep more “detailed” data available for longer periods, “old” data has to be reduced gradually to save space...... is 6 months old aggregate to 2 minutes level from 1 minute level and so on. The proposed solution introduces a time granularity based data structure, namely a relational time granularity table that enables long term storage of old data by maintaining it at different levels of granularity and effective...
Models of fluidized granular materials: examples of non-equilibrium stationary states
Energy Technology Data Exchange (ETDEWEB)
Puglisi, Andrea [Laboratoire de Physique Theorique Batiment 210, Universite de Paris-Sud, 91405 Orsay Cedex (France); Cecconi, Fabio [INFM Center for Statistical Mechanics and Complexity and Dipartimento di Fisica, Universita ' La Sapienza' , Piazzale A Moro 2, I-00185 Rome (Italy); Vulpiani, Angelo [Dipartimento di Fisica, Universita ' La Sapienza' , INFM Center for Statistical Mechanics and Complexity (SMC), INFN Sezione di Roma-1 ' La Sapienza' , Piazzale A Moro 2, I-00185, Rome (Italy)
2005-06-22
We review some models of granular materials fluidized by means of external forces, such as random homogeneous forcing with damping, vibrating plates, flow in an inclined channel and flow in a double well potential. All these systems show the presence of density correlations and non-Gaussian velocity distributions. These models are useful in understanding the role of a kinetically defined 'temperature' (in this case the so-called granular temperature) in a non-equilibrium stationary state. In the homogeneously randomly driven gas the granular temperature is different from that of the driving bath. Moreover, two different granular materials mixed together may stay in a stationary state with different temperatures. At the same time, the granular temperature determines (as in equilibrium systems) the escape time in a double well potential.
Directory of Open Access Journals (Sweden)
Barceló Carlos
2005-12-01
Full Text Available Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.
Lujan, Richard E.
2001-01-01
A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.
Directory of Open Access Journals (Sweden)
Carlos Barceló
2011-05-01
Full Text Available Analogue gravity is a research programme which investigates analogues of general relativistic gravitational fields within other physical systems, typically but not exclusively condensed matter systems, with the aim of gaining new insights into their corresponding problems. Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.
Physical test of a particle simulation model in a sheared granular system.
Rycroft, Chris H; Orpe, Ashish V; Kudrolli, Arshad
2009-09-01
We report a detailed comparison of a slow gravity-driven sheared granular flow with a discrete-element simulation performed in the same geometry. In the experiments, grains flow inside a silo with a rectangular cross section and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index-matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The simulations use a Cundall-Strack contact model between the grains using contact parameters that have been used in many other previous studies and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. We then perform a detailed comparison of the particle fluctuation properties as measured by the displacement probability distribution function and the mean square displacement. All in all, our study suggests a high level of quantitative agreement between the simulations and experiments.
Kiefer, Claus
2012-01-01
The search for a quantum theory of the gravitational field is one of the great open problems in theoretical physics. This book presents a self-contained discussion of the concepts, methods and applications that can be expected in such a theory. The two main approaches to its construction - the direct quantisation of Einstein's general theory of relativity and string theory - are covered. Whereas the first attempts to construct a viable theory for the gravitational field alone, string theory assumes that a quantum theory of gravity will be achieved only through a unification of all the interactions. However, both employ the general method of quantization of constrained systems, which is described together with illustrative examples relevant for quantum gravity. There is a detailed presentation of the main approaches employed in quantum general relativity: path-integral quantization, the background-field method and canonical quantum gravity in the metric, connection and loop formulations. The discussion of stri...
International Nuclear Information System (INIS)
Giribet, G E
2005-01-01
Claus Kiefer presents his book, Quantum Gravity, with his hope that '[the] book will convince readers of [the] outstanding problem [of unification and quantum gravity] and encourage them to work on its solution'. With this aim, the author presents a clear exposition of the fundamental concepts of gravity and the steps towards the understanding of its quantum aspects. The main part of the text is dedicated to the analysis of standard topics in the formulation of general relativity. An analysis of the Hamiltonian formulation of general relativity and the canonical quantization of gravity is performed in detail. Chapters four, five and eight provide a pedagogical introduction to the basic concepts of gravitational physics. In particular, aspects such as the quantization of constrained systems, the role played by the quadratic constraint, the ADM decomposition, the Wheeler-de Witt equation and the problem of time are treated in an expert and concise way. Moreover, other specific topics, such as the minisuperspace approach and the feasibility of defining extrinsic times for certain models, are discussed as well. The ninth chapter of the book is dedicated to the quantum gravitational aspects of string theory. Here, a minimalistic but clear introduction to string theory is presented, and this is actually done with emphasis on gravity. It is worth mentioning that no hard (nor explicit) computations are presented, even though the exposition covers the main features of the topic. For instance, black hole statistical physics (within the framework of string theory) is developed in a pedagogical and concise way by means of heuristical arguments. As the author asserts in the epilogue, the hope of the book is to give 'some impressions from progress' made in the study of quantum gravity since its beginning, i.e., since the end of 1920s. In my opinion, Kiefer's book does actually achieve this goal and gives an extensive review of the subject. (book review)
Granular acoustic switches and logic elements
Li, Feng; Anzel, Paul; Yang, Jinkyu; Kevrekidis, Panayotis G.; Daraio, Chiara
2014-10-01
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.
Two methods to measure granular gas temperature
Chastaing, J.-Y.; Géminard, J.-C.; Naert, A.
2017-07-01
Grains are vibrated so as to achieve a granular gas, here regarded as an archetype of a dissipative non equilibrium steady state (NESS). We report on two distinct and concordant experimental measures of the system effective temperature. To do so, a blade fastened to the shaft of a small DC-motor, immersed in the grains, behaves as a driven 1D Brownian rotator, which is used as both actuator and sensor simultaneously. On the one hand, the Gallavotti-Cohen fluctuation theorem, which involves a measure of the asymmetry of the energy exchanges between the rotator and the NESS reservoir, provides a first effective temperature. On the other hand, the fluctuation-dissipation theorem, which involves the relation between the spontaneous fluctuations and the response to a weak perturbation, defines a second, independent, effective temperature. Both methods, even though they are based on drastically different ideas, give nicely concordant results.
Pipinos, Savas
2010-01-01
This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…
Why granular media are thermal after all
Liu, Mario; Jiang, Yimin
2017-06-01
Two approaches exist to account for granular behavior. The thermal one considers the total entropy, which includes microscopic degrees of freedom such as phonons; the athermal one (as with the Edward entropy) takes grains as elementary. Granular solid hydrodynamics (GSH) belongs to the first, DEM, granular kinetic theory and athermal statistical mechanics (ASM) to the second. A careful discussion of their conceptual differences is given here. Three noteworthy insights or results are: (1) While DEM and granular kinetic theory are well justified to take grains as elementary, any athermal entropic consideration is bound to run into trouble. (2) Many general principles are taken as invalid in granular media. Yet within the thermal approach, energy conservation and fluctuation-dissipation theorem remain valid, granular temperatures equilibrate, and phase space is well explored in a grain at rest. Hence these are abnormalities of the athermal approximation, not of granular media as such. (3) GSH is a wide-ranged continuum mechanical description of granular dynamics.
International Nuclear Information System (INIS)
Markov, M.A.; West, P.C.
1984-01-01
This book discusses the state of the art of quantum gravity, quantum effects in cosmology, quantum black-hole physics, recent developments in supergravity, and quantum gauge theories. Topics considered include the problems of general relativity, pregeometry, complete cosmological theories, quantum fluctuations in cosmology and galaxy formation, a new inflationary universe scenario, grand unified phase transitions and the early Universe, the generalized second law of thermodynamics, vacuum polarization near black holes, the relativity of vacuum, black hole evaporations and their cosmological consequences, currents in supersymmetric theories, the Kaluza-Klein theories, gauge algebra and quantization, and twistor theory. This volume constitutes the proceedings of the Second Seminar on Quantum Gravity held in Moscow in 1981
International Nuclear Information System (INIS)
Isham, C.
1989-01-01
Gravitational effects are seen as arising from a curvature in spacetime. This must be reconciled with gravity's apparently passive role in quantum theory to achieve a satisfactory quantum theory of gravity. The development of grand unified theories has spurred the search, with forces being of equal strength at a unification energy of 10 15 - 10 18 GeV, with the ''Plank length'', Lp ≅ 10 -35 m. Fundamental principles of general relativity and quantum mechanics are outlined. Gravitons are shown to have spin-0, as mediators of gravitation force in the classical sense or spin-2 which are related to the quantisation of general relativity. Applying the ideas of supersymmetry to gravitation implies partners for the graviton, especially the massless spin 3/2 fermion called a gravitino. The concept of supersymmetric strings is introduced and discussed. (U.K.)
Gas cleaning with Granular Filters
Natvig, Ingunn Roald
2007-01-01
The panel bed filter (PBF) is a granular filter patented by A. M. Squires in the late sixties. PBFs consist of louvers with stationary, granular beds. Dust is deposited in the top layers and on the bed surface when gas flows through. PBFs are resistant to high temperatures, variations in the gas flow and hot particles. The filter is cleaned by releasing a pressure pulse in the opposite direction of the bulk flow (a puff back pulse). A new louver geometry patented by A. M. Squires is the filte...
Granular cell ameloblastoma of mandible.
Jansari, Trupti R; Samanta, Satarupa T; Trivedi, Priti P; Shah, Manoj J
2014-01-01
Ameloblastoma is a neoplasm of odontogenic epithelium, especially of enamel organ-type tissue that has not undergone differentiation to the point of hard tissue formation. Granular cell ameloblastoma is a rare condition, accounting for 3-5% of all ameloblastoma cases. A 30-year-old female patient presented with the chief complaint of swelling at the right lower jaw region since 1 year. Orthopantomogram and computed tomography scan was suggestive of primary bone tumor. Histopathologically, diagnosis of granular cell ameloblastoma of right mandible was made.
Buslaev, Alexander; Bugaev, Alexander; Yashina, Marina; Schadschneider, Andreas; Schreckenberg, Michael; TGF11
2013-01-01
This book continues the biannual series of conference proceedings, which has become a classical reference resource in traffic and granular research alike. It addresses new developments at the interface between physics, engineering and computational science. Complex systems, where many simple agents, be they vehicles or particles, give rise to surprising and fascinating phenomena. The contributions collected in these proceedings cover several research fields, all of which deal with transport. Topics include highway, pedestrian and internet traffic, granular matter, biological transport, transport networks, data acquisition, data analysis and technological applications. Different perspectives, i.e. modeling, simulations, experiments and phenomenological observations, are considered.
On creating macroscopically identical granular systems with different numbers of particles
van der Meer, Devaraj; Rivas, Nicolas
2015-11-01
One of the fundamental differences between granular and molecular hydrodynamics is the enormous difference in the total number of constituents. The small number of particles implies that the role of fluctuations in granular dynamics is of paramount importance. To obtain more insight in these fluctuations, we investigate to what extent it is possible to create identical granular hydrodynamic states with different number of particles. A definition is given of macroscopically equivalent systems, and the dependency of the conservation equations on the particle size is studied. We show that, in certain cases, and by appropriately scaling the microscopic variables, we are able to compare systems with significantly different number of particles that present the same macroscopic phenomenology. We apply these scalings in simulations of a vertically vibrated system, namely the density inverted granular Leidenfrost state and its transition to a buoyancy-driven convective state.
Bedrock erosion by sliding wear in channelized granular flow
Hung, C. Y.; Stark, C. P.; Capart, H.; Smith, B.; Maia, H. T.; Li, L.; Reitz, M. D.
2014-12-01
Boundary forces generated by debris flows can be powerful enough to erode bedrock and cause considerable damage to infrastructure during runout. Bedrock wear can be separated into impact and sliding wear processes. Here we focus on sliding wear. We have conducted experiments with a 40-cm-diameter grainflow-generating rotating drum designed to simulate dry channelized debris flows. To generate sliding erosion, we placed a 20-cm-diameter bedrock plate axially on the back wall of the drum. The rotating drum was half filled with 2.3-mm-diameter grains, which formed a thin grain-avalanching layer with peak flow speed and depth close to the drum axis. The whole experimental apparatus was placed on a 100g-ton geotechnical centrifuge and, in order to scale up the stress level, spun to a range of effective gravity levels. Rates and patterns of erosion of the bedrock plate were mapped after each experiment using 3d micro-photogrammetry. High-speed video and particle tracking were employed to measure granular flow dynamics. The resulting data for granular velocities and flow geometry were used to estimate impulse exchanges and forces on the bedrock plate. To address some of the complexities of granular flow under variable gravity levels, we developed a continuum model framed around a GDR MiDi rheology. This model allowed us to scale up boundary forcing while maintaining the same granular flow regime, and helped us to understand important aspects of the flow dynamics including e.g. fluxes of momentum and kinetic energy. In order to understand the detailed processes of boundary forcing, we performed numerical simulations with a new contact dynamics model. This model confirmed key aspects of our continuum model and provided information on second-order behavior such as fluctuations in the forces acting on the wall. By combining these measurements and theoretical analyses, we have developed and calibrated a constitutive model for sliding wear that is a threshold function of
Energy considerations in accelerating rapid shear granular flows
Directory of Open Access Journals (Sweden)
S. P. Pudasaini
2009-05-01
Full Text Available We present a complete expression for the total energy associated with a rapid frictional granular shear flow down an inclined surface. This expression reduces to the often used energy for a non-accelerating flow of an isotropic, ideal fluid in a horizontal channel, or to the energy for a vertically falling mass. We utilize thickness-averaged mass and momentum conservation laws written in a slope-defined coordinate system. Both the enhanced gravity and friction are taken into account in addition to the bulk motion and deformation. The total energy of the flow at a given spatial position and time is defined as the sum of four energy components: the kinetic energy, gravity, pressure and the friction energy. Total energy is conserved for stationary flow, but for non-stationary flow the non-conservative force induced by the free-surface gradient means that energy is not conserved. Simulations and experimental results are used to sketch the total energy of non-stationary flows. Comparison between the total energy and the sum of the kinetic and pressure energy shows that the contribution due to gravity acceleration and frictional resistance can be of the same order of magnitude, and that the geometric deformation plays an important role in the total energy budget of the cascading mass. Relative importance of the different constituents in the total energy expression is explored. We also introduce an extended Froude number that takes into account the apparent potential energy induced by gravity and pressure.
Granular boycott effect: How to mix granulates
Duran, J.; Mazozi, T.
1999-11-01
Granular material can display the basic features of the Boycott effect in sedimentation. A simple experiment shows that granular material falls faster in an inclined tube than in a vertical tube, in analogy with the Boycott effect. As long as the inclination of the tube is above the avalanche threshold, descent of granular material in the tube causes internal convection which in turn results in an efficient mixture of the granular components. By contrast, as in analogous experiments in two dimensions, a vertical fall of granular material occurs via successive block fragmentation, resulting in poor mixing.
From Numeric Models to Granular System Modeling
Directory of Open Access Journals (Sweden)
Witold Pedrycz
2015-03-01
To make this study self-contained, we briefly recall the key concepts of granular computing and demonstrate how this conceptual framework and its algorithmic fundamentals give rise to granular models. We discuss several representative formal setups used in describing and processing information granules including fuzzy sets, rough sets, and interval calculus. Key architectures of models dwell upon relationships among information granules. We demonstrate how information granularity and its optimization can be regarded as an important design asset to be exploited in system modeling and giving rise to granular models. With this regard, an important category of rule-based models along with their granular enrichments is studied in detail.
Kordilla, J.; Bresinsky, L. T.; Shigorina, E.; Noffz, T.; Dentz, M.; Sauter, M.; Tartakovsky, A. M.
2017-12-01
Preferential flow dynamics in unsaturated fractures remain a challenging topic on various scales. On pore- and fracture-scales the highly erratic gravity-driven flow dynamics often provoke a strong deviation from classical volume-effective approaches. Against the common notion that flow in fractures (or macropores) can only occur under equilibrium conditions, i.e., if the surrounding porous matrix is fully saturated and capillary pressures are high enough to allow filling of the fracture void space, arrival times suggest the existence of rapid preferential flow along fractures, fracture networks, and fault zones, even if the matrix is not fully saturated. Modeling such flows requires efficient numerical techniques to cover various flow-relevant physics, such as surface tension, static and dynamic contact angles, free-surface (multi-phase) interface dynamics, and formation of singularities. Here we demonstrate the importance of such flow modes on the partitioning dynamics at simple fracture intersections, with a combination of laboratory experiments, analytical solutions and numerical simulations using our newly developed massively parallel smoothed particle hydrodynamics (SPH) code. Flow modes heavily influence the "bypass" behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. This behavior is demonstrated for a multi-inlet laboratory setup where the inlet-specific flow rate is chosen so that either a droplet or rivulet flow persists. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency
Xue, Kun; Zheng, Yixin; Fan, Baolong; Li, Fangfang; Bai, Chunhua
2013-01-01
This paper investigates the particle scale dynamics of granular convection in vertically vibrated granular beds. The onset of the convection is found to coincide with the noticeable particle transverse migrations from the side walls towards the centre of the bed, which only take place in the wake of the gravity wave front dividing the upward moving particles and the falling ones. The mechanism driving the particle inward flows and thus sustaining the complete convection rolls can be understood in light of a convection model based on void penetration. This stochastic convection model reveals that the underlying driving force is a distinctive differential shear flow field arising from the combined effect of frictional holdback by the walls and the downward pull of gravity. The changes of the convection pattern with inceasing acceleration amplitude, in terms of the convection strength and the thickness of the bottom of the convection rolls, can be accounted for by this model.
Entropy of jammed granular matter
Briscoe, Christopher
Granular matter can be considered a non-equilibrium system, such that equilibrium statistics is insufficient to describe the dynamics. A phase transition occurs when granular materials are compressed such that a nonzero stress develops in response to a strain deformation. This transition, referred to as the jamming transition, occurs at a critical volume fraction, φc depending on friction and preparation protocol. Analysis of the jamming transition produces a phase diagram of jammed granular matter for identical spheres, characterized by the critical volume fraction, φc and the average coordination number, Z. The boundaries of the phase diagram are related to well-defined upper and lower limits in the density of disordered packings; random close packing (RCP) and random loose packing (RLP). Frictional systems, such as granular matter, exhibit an inherent path dependency resulting in the loss of energy conservation, an important facet of equilibrium statistics. It has been suggested Edwards that the volume-force (V-F) ensemble, wherein volume replaces energy as the conservative quantity, may provide a sufficient framework to create a statistical ensemble for jammed granular matter. Treating a jammed system via the V-F ensemble introduces an analogue to temperature in equilibrium systems. This analogue, "compactivity", measures how compact a system could be and governs fluctuation in the volume statistics. Randomness in statistical systems is typically characterized by entropy, the equation of state derived from the number of microstates available to the system. In equilibrium statistical mechanics, entropy provides the link between these microstates and the macroscopic thermodynamic properties of the system. Therefore, calculating the entropy within the V-F ensemble can relate the available microscopic volume for each grain to the macroscopic system properties. The entropy is shown to be minimal at RCP and maximal at the minimum RLP limit, via several methods
National Oceanic and Atmospheric Administration, Department of Commerce — This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are...
National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...
Mott transition in granular aluminum
Bachar, N.; Lerer, S.; Levy, A.; Hacohen-Gourgy, S.; Almog, B.; Saadaoui, H.; Salman, Z.; Morenzoni, E.; Deutscher, G.
2015-01-01
A Mott transition in granular Al films is observed by probing the increase of the spin-flip scattering rate of conduction electrons as the nanosize metallic grains are being progressively decoupled. The presence of free spins in granular Al films is directly demonstrated by μ SR measurements. Analysis of the magnetoresistance in terms of an effective Fermi energy shows that it becomes of the order of the grains electrostatic charging energy at a room temperature resistivity ρ300 K≈50000 μ Ω cm , at which a metal to insulator transition is known to exist. As this transition is approached the magnetoresistance exhibits a heavy-fermion-like behavior, consistent with an increased electron effective mass.
Dilatancy in Slow Granular Flows
Kabla, Alexandre J.; Senden, Tim J.
2009-06-01
When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counterintuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed, therefore increasing the amount of porous space. Although widely called upon in areas such as soil mechanics and geotechnics, a deeper understanding of this principle is constrained by the lack of analytical tools to study this behavior. Using x-ray radiography, we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behavior. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates, however, the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected.
Dynamic similarity in granular locomotion
Kamrin, Ken; Slonaker, James; Zhang, Qiong
2017-11-01
To model the flow of granular media with high accuracy, a number of subtleties arise and complex constitutive relations are needed to address them. However, making certain rheological simplifications produces a framework that is simple enough to obtain global rule-sets that can be used to aid in design without having to solve any partial differential equations or perform discrete element simulations. This talk will show how reduced-order rule-sets such as the Resistive Force Theory can be obtained from a basic frictional plasticity model, and how plasticity can further be used to produce a family of scaling laws in granular locomotion reminiscent of `wind tunnel' scaling laws in fluid dynamics. These are verified with experiments and numerical simulations.
Strain localisation in granular media
Desrues , Jacques
1984-01-01
This study is devoted to strain localisation in Granular materials. Both experimental and theoretical results have been obtained.The first part of the thesis is a review of the methods and theories about rupture in sols mechanics and more generally, in solid mechanics. The classical framework of Shear Band analysis is presented, and the main results available for different classes of materials are discussed.The second part describes an experimental study of strain localisation in sand specime...
Pneumatic fractures in Confined Granular Media
Eriksen, Fredrik K.; Toussaint, Renaud; Jørgen Måløy, Knut; Grude Flekkøy, Eirik; Turkaya, Semih
2016-04-01
We will present our ongoing study of the patterns formed when air flows into a dry, non-cohesive porous medium confined in a horizontal Hele-Shaw cell. This is an optically transparent system consisting of two glass plates separated by 0.5 to 1 mm, containing a packing of dry 80 micron beads in between. The cell is rectangular and has an air-permeable boundary (blocking beads) at one short edge, while the other three edges are completely sealed. The granular medium is loosely packed against the semi-permeable boundary and fills about 80 % of the cell volume. This leaves an empty region at the sealed side, where an inlet allows us to set and maintain the air at a constant overpressure (0.1 - 2 bar). For the air trapped inside the cell to relax its overpressure it has to move through the deformable granular medium. Depending on the applied overpressure and initial density of the medium, we observe a range of different behaviors such as seepage through the pore-network with or without an initial compaction of the solid, formation of low density bubbles with rearrangement of particles, granular fingering/fracturing, and erosion inside formed channels/fractures. The experiments are recorded with a high-speed camera at a framerate of 1000 images/s and a resolution of 1024x1024 pixels. We use various image processing techniques to characterize the evolution of the air invasion patterns and the deformations in the surrounding material. The experiments are similar to deformation processes in porous media which are driven by pore fluid overpressure, such as mud volcanoes and hydraulic or pneumatic (gas-induced) fracturing, and the motivation is to increase the understanding of such processes by optical observations. In addition, this setup is an experimental version of the numerical models analyzed by Niebling et al. [1,2], and is useful for comparison with their results. In a directly related project [3], acoustic emissions from the cell plate are recorded during
Newtonian gravity in loop quantum gravity
Smolin, Lee
2010-01-01
We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime.
BOOK REVIEW: Kinetic Theory of Granular Gases
Trizac, Emmanuel
2005-11-01
restitution coefficients, that are again velocity dependent. This seems to be the price of a consistent approach, which does not lend itself to much insight. In addition, the behaviour of driven systems is not addressed, whereas in the realm of granular media, force-free systems are the exception rather than the rule. The differences between constant ɛ and visco-elastic models is presumably less pronounced in the driven case. Study of driven systems also reveals that the rheology of granular gases is intrinsically non-Newtonian, which is a key feature. Finally, the powerful direct simulation Monte Carlo technique is not described, whereas it is an important tool, particularly relevant for the physics of the Boltzmann equation, and straightforward to implement in its simplest version. N Brilliantov and T Pöschel concentrate on the (equally relevant) molecular dynamics method instead. In conclusion, the book fills a gap in the field. The companion webpage from where molecular dynamics and symbolic algebra programs can be downloaded is also useful.
Granular media in the context of small bodies
Tancredi, G.
2014-07-01
Granular materials of different particle sizes are present on the surface and the interior of several atmosphereless Solar System bodies. The presence of very fine particles on the surface of the Moon, the so-called regolith, was confirmed by the Apollo astronauts. From the polarimetric observations and phase angle curves, it is possible to indirectly infer the presence of fine particles on the surfaces of asteroids and planetary satellites. More recently, the visit of spacecraft to several asteroids and comets has provided us with close pictures of the surface, where particles of a wide size range from cm to hundreds of meters have been directly observed. The presence of even finer particles on the visited bodies can also be inferred from image analysis. Solar System bodies smaller than a few hundred km may have a variety of internal structures: monolithic single bodies, objects with internal fractures, rubble piles maintained as a single object by self-gravity, etc. After the visit of the small asteroid Itokawa, it has been speculated that ''some small asteroids appear to be clumps of gravel glued by a very weak gravity field'' (Asphaug 2007). We still do not know the internal structure of these rubble piles and the size distribution of the interior constituents, but these clumps could have several million meter-sized boulders inside. There are several pieces of evidence that many asteroids are agglomerates of small components, like: - Rotation periods for small asteroids - Tidal disruption of asteroids and comets when they enter the Roche's limit of a massive object - The existence of crater chains like the ones observed in Ganymede - Low density estimates (bodies. We review the numerical and experimental studies on granular materials with relevance to the understanding of the physical processes on the interior and the surfaces of minor bodies of the Solar System. In particular, we compare the different codes in use to perform numerical simulations of the
Granular packing as model glass formers
International Nuclear Information System (INIS)
Wang Yujie
2017-01-01
Static granular packings are model hard-sphere glass formers. The nature of glass transition has remained a hotly debated issue. We review recent experimental progresses in using granular materials to study glass transitions. We focus on the growth of glass order with five-fold symmetry in granular packings and relate the findings to both geometric frustration and random first-order phase transition theories. (paper)
Numerical Simulations of Granular Physics in the Solar System
Ballouz, Ronald
2017-08-01
Granular physics is a sub-discipline of physics that attempts to combine principles that have been developed for both solid-state physics and engineering (such as soil mechanics) with fluid dynamics in order to formulate a coherent theory for the description of granular materials, which are found in both terrestrial (e.g., earthquakes, landslides, and pharmaceuticals) and extra-terrestrial settings (e.g., asteroids surfaces, asteroid interiors, and planetary ring systems). In the case of our solar system, the growth of this sub-discipline has been key in helping to interpret the formation, structure, and evolution of both asteroids and planetary rings. It is difficult to develop a deterministic theory for granular materials due to the fact that granular systems are composed of a large number of elements that interact through a non-linear combination of various forces (mechanical, gravitational, and electrostatic, for example) leading to a high degree of stochasticity. Hence, we study these environments using an N-body code, pkdgrav, that is able to simulate the gravitational, collisional, and cohesive interactions of grains. Using pkdgrav, I have studied the size segregation on asteroid surfaces due to seismic shaking (the Brazil-nut effect), the interaction of the OSIRIS-REx asteroid sample-return mission sampling head, TAGSAM, with the surface of the asteroid Bennu, the collisional disruptions of rubble-pile asteroids, and the formation of structure in Saturn's rings. In all of these scenarios, I have found that the evolution of a granular system depends sensitively on the intrinsic properties of the individual grains (size, shape, sand surface roughness). For example, through our simulations, we have been able to determine relationships between regolith properties and the amount of surface penetration a spacecraft achieves upon landing. Furthermore, we have demonstrated that this relationship also depends on the strength of the local gravity. By comparing our
Evaluation of GLUT-1 in the granular cell tumour and congenital granular cell epulis.
Souto, Giovanna Ribeiro; Caldeira, Patrícia Carlos; Johann, Aline Cristina Batista Rodrigues; Andrade Marigo, Helenicede; Souza, Suzana Cantanhede Orsini Machadode; Mesquita, Ricardo Alves
2013-07-01
The glucose transporter type 1 (GLUT-1) protein is a useful marker for perineurial cells. Because of the possible neuroectodermal histogenesis of the granular cell tumour and congenital granular cell epulis, the aim of this study was to assess the immunoexpression of GLUT-1 protein in granular cell tumour and congenital granular cell epulis to aid in clarifying their histogenesis. The protocol of this study was approved by the Committee of Bioethics in Research at Universidade Federal Minas Gerais. Six cases of granular cell tumour and three cases of congenital granular cell epulis were submitted to immunohistochemistry for GLUT-1 and S-100 using the streptavidin-biotin standard protocol. Five cases of granular cell tumour were located on the tongue and one case on the upper lip. All cases of congenital granular cell epulis were observed in the alveolar ridge of newborns. All lesions evaluated proved to be immunonegative for GLUT-1. S-100 was found to be positive in all granular cell tumours and negative in congenital granular cell epulis. Neither granular cell tumour nor congenital granular cell epulis is directly related to perineurial cells. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
Is nonrelativistic gravity possible?
Kocharyan, A. A.
2009-01-01
We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Eins...
Low-velocity impact cratering experiments in granular slopes
Hayashi, Kosuke; Sumita, Ikuro
2017-07-01
Low-velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle θ on the crater shape and its scales. We use two types of granular matter, sand and glass beads, former of which has a larger friction coefficient μs = tanθr , where θr is the angle of repose. Experiments show that as θ increases, the crater becomes shallower and elongated in the direction of the slope. Furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side, thus forming an asymmetric profile. High-speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor. Such asymmetric ejecta dispersal can be explained by combining the Z-model and a ballistic model. Using the topographic maps of the craters, we classify crater shape regimes I-III, which transition with increasing θ : a full-rim crater (I), a broken-rim crater (II), and a depression (III). The critical θ for the regime transitions are larger for sand compared to glass beads, but collapse to close values when we use a normalized slope θ^ = tanθ / tanθr . Similarly we derive θ^-dependences of the scaled crater depth, length, width and their ratios which collapse the results for different targets and impact energies. We compare the crater profiles formed in our experiments with deep craters on asteroid Vesta and find that some of the scaled profiles nearly overlap and many have similar depth / length ratios. This suggests that these Vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient.
The electrical conductance growth of a metallic granular packing
Jakšić, Zorica M.; Cvetković, Milica; Šćepanović, Julija R.; Lončarević, Ivana; Budinski-Petković, Ljuba; Vrhovac, Slobodan B.
2017-06-01
We report on measurements of the electrical conductivity on a two-dimensional packing of metallic disks when a stable current of 1 mA flows through the system. At low applied currents, the conductance σ is found to increase by a pattern σ( t) = σ ∞ - Δσ E α [ - ( t/ τ) α ], where E α denotes the Mittag-Leffler function of order α ∈ (0,1). By changing the inclination angle θ of the granular bed from horizontal, we have studied the impact of the effective gravitational acceleration g e ff = gsin θ on the relaxation features of the conductance σ( t). The characteristic timescale τ is found to grow when effective gravity g e ff decreases. By changing both the distance between the electrodes and the number of grains in the packing, we have shown that the long term resistance decay observed in the experiment is related to local micro-contacts rearrangements at each disk. By focusing on the electro-mechanical processes that allow both creation and breakdown of micro-contacts between two disks, we present an approach to granular conduction based on subordination of stochastic processes. In order to imitate, in a very simplified way, the conduction dynamics of granular material at low currents, we impose that the micro-contacts at the interface switch stochastically between two possible states, "on" and "off", characterizing the conductivity of the micro-contact. We assume that the time intervals between the consecutive changes of state are governed by a certain waiting-time distribution. It is demonstrated how the microscopic random dynamics regarding the micro-contacts leads to the macroscopic observation of slow conductance growth, described by an exact fractional kinetic equations.
Simulating granular materials by energy minimization
Krijgsman, D.; Luding, S.
2016-11-01
Discrete element methods are extremely helpful in understanding the complex behaviors of granular media, as they give valuable insight into all internal variables of the system. In this paper, a novel discrete element method for performing simulations of granular media is presented, based on the minimization of the potential energy in the system. Contrary to most discrete element methods (i.e., soft-particle method, event-driven method, and non-smooth contact dynamics), the system does not evolve by (approximately) integrating Newtons equations of motion in time, but rather by searching for mechanical equilibrium solutions for the positions of all particles in the system, which is mathematically equivalent to locally minimizing the potential energy. The new method allows for the rapid creation of jammed initial conditions (to be used for further studies) and for the simulation of quasi-static deformation problems. The major advantage of the new method is that it allows for truly static deformations. The system does not evolve with time, but rather with the externally applied strain or load, so that there is no kinetic energy in the system, in contrast to other quasi-static methods. The performance of the algorithm for both types of applications of the method is tested. Therefore we look at the required number of iterations, for the system to converge to a stable solution. For each single iteration, the required computational effort scales linearly with the number of particles. During the process of creating initial conditions, the required number of iterations for two-dimensional systems scales with the square root of the number of particles in the system. The required number of iterations increases for systems closer to the jamming packing fraction. For a quasi-static pure shear deformation simulation, the results of the new method are validated by regular soft-particle dynamics simulations. The energy minimization algorithm is able to capture the evolution of the
Acoustic modes propagating along the free surface of granular media.
Aleshin, V; Gusev, V; Tournat, V
2007-05-01
In unconsolidated granular materials under gravity there exist acoustical waves propagating along the surface with anomalously low sound velocity. The presented theory describes these guided surface acoustic modes (GSAM) confined between the surface of the granular materials and in-depth layers with increasing rigidity. The analysis is based on the obtained original analytical solution of the Helmholtz equation that has never been used both in classical and quantum mechanics. This solution is valid for a particular rigidity profile, whereas the general case of grains with or without adhesion has been analyzed numerically. In contrast to the Rayleigh wave polarized in the sagittal (vertical) plane, which is the unique localized mode in a homogeneous solid, an infinite number of modes with sagittal polarization as well as an infinite number of shear horizontal modes have been found. The difference in physical mechanisms of localization is discussed, and the transformation of the GSAMs into the Rayleigh wave at the increasing adhesion is demonstrated: The first sagittal mode transforms into the Rayleigh one, while the others delocalize. The theory explains the experimentally observed magnitude of velocity for the acoustic waves in sand elliptically polarized in the sagittal plane.
Anaerobic granular sludge and biofilm reactors
DEFF Research Database (Denmark)
Skiadas, Ioannis V.; Gavala, Hariklia N.; Schmidt, Jens Ejbye
2003-01-01
-rate anaerobic treatment systems based on anaerobic granular sludge and biofilm are described in this chapter. Emphasis is given to a) the Up-flow Anaerobic Sludge Blanket (UASB) systems, b) the main characteristics of the anaerobic granular sludge, and c) the factors that control the granulation process...
Storage and discharge of a granular fluid
Pacheco-Martinez, Hector; van Gerner, H.J.; Ruiz-Suarez, J.C.
2008-01-01
Experiments and computational simulations are carried out to study the behavior of a granular column in a silo whose walls are able to vibrate horizontally. The column is brought to a steady fluidized state and it behaves similar to a hydrostatic system. We study the dynamics of the granular
Viscosity evolution of anaerobic granular sludge
Pevere, A.; Guibaud, G.; Hullebusch, van E.D.; Lens, P.N.L.; Baudu, M.
2006-01-01
The evolution of the apparent viscosity at steady shear rate of sieved anaerobic granular sludge (20¿315 ¿m diameter) sampled from different full-scale anaerobic reactors was recorded using rotation tests. The ¿limit viscosity¿ of sieved anaerobic granular sludge was determined from the apparent
Characterization of Unbound Granular Materials for Pavements
Araya, A.A.
2011-01-01
This research is focused on the characterization of the mechanical behavior of unbound granular road base materials (UGMs). An extensive laboratory investigation is described, in which various methods for determination of the mechanical properties of granular materials are examined for their
Scaling behavior in the convection-driven Brazil nut effect
Hejmady, Prakhyat; Bandyopadhyay, Ranjini; Sabhapandit, Sanjib; Dhar, Abhishek
2012-11-01
The Brazil nut effect is the phenomenon in which a large intruder particle immersed in a vertically shaken bed of smaller particles rises to the top, even when it is much denser. The usual practice while describing these experiments has been to use the dimensionless acceleration Γ=aω2/g, where a and ω are, respectively, the amplitude and the angular frequency of vibration and g is the acceleration due to gravity. Considering a vibrated quasi-two-dimensional bed of mustard seeds, we show here that the peak-to-peak velocity of shaking v=aω, rather than Γ, is the relevant parameter in the regime where boundary-driven granular convection is the main driving mechanism. We find that the rise time τ of an intruder is described by the scaling law τ˜(v-vc)-α, where vc is identified as the critical vibration velocity for the onset of convective motion of the mustard seeds. This scaling form holds over a wide range of (a,ω), diameter, and density of the intruder.
Pöschel, Thorsten; Kühne, Reinhart; Schreckenberg, Michael; Wolf, Dietrich
2007-01-01
The conference series Tra?c and Granular Flow has been established in 1995 and has since then been held biannually. At that time, the investigation of granular materials and tra?c was still somewhat exotic and was just starting to become popular among physicists. Originally the idea behind this conference series was to facilitate the c- vergence of the two ?elds, inspired by the similarities of certain phenomena and the use of similar theoretical methods. However, in recent years it has become clear that probably the di?erences between the two systems are much more interesting than the similarities. Nevertheless, the importance of various interrelations among these ?elds is still growing. The workshop continues to o?er an opportunity to stimulate this interdisciplinary research. Over the years the spectrum of topics has become much broader and has included also problems related to topics ranging from social dynamics to - ology. The conference manages to bring together people with rather di?erent background, r...
Luding, Stefan; Bovy, Piet; Schreckenberg, Michael; Wolf, Dietrich
2005-01-01
These proceedings are the fifth in the series Traffic and Granular Flow, and we hope they will be as useful a reference as their predecessors. Both the realistic modelling of granular media and traffic flow present important challenges at the borderline between physics and engineering, and enormous progress has been made since 1995, when this series started. Still the research on these topics is thriving, so that this book again contains many new results. Some highlights addressed at this conference were the influence of long range electric and magnetic forces and ambient fluids on granular media, new precise traffic measurements, and experiments on the complex decision making of drivers. No doubt the “hot topics” addressed in granular matter research have diverged from those in traffic since the days when the obvious analogies between traffic jams on highways and dissipative clustering in granular flow intrigued both c- munities alike. However, now just this diversity became a stimulating feature of the ...
This PR Notice announces guidance intended to streamline the acute toxicity review and classification process for certain granular pesticide products, including those products that contain granular fertilizers.
Granular Dilatancy and its Effect on Debris-flow Dynamics
Iverson, R. M.; George, D. L.
2012-12-01
Landslides and debris flows commonly exhibit the effects of variable granular dilatancy, but incorporation of these effects in predictive models of debris-flow dynamics has been lacking. We have developed a depth-averaged model of debris-flow initiation and motion that includes the effects of variable dilatancy without stipulating its influence on rheology. Instead, the apparent rheology of Coulomb-frictional debris evolves during coupled evolution of the grain concentration m, basal pore-fluid pressure, flow thickness, and flow velocity. The dilatancy angle ψ plays an intermediary role in this evolution and obeys the simple relationship tan ψ = m-meq, where meq is the grain concentration in equilibrium with the ambient stress state and flow rate. Results of recent stress-controlled rheometric experiments by Boyer et al. (DOI: 10.1103/PhysRevLett.107.188301) provide our basis for estimating meq. Relaxation of m toward meq, coupled with evolution of pore pressure, allows our model to simulate a smooth transition from static limiting equilibrium of slopes to disequilibrium flow dynamics. Use of variable friction coefficients or dam-break initial conditions is unnecessary. We have evaluated predictions of our model in three ways: (1) by examining physical implications of exact solutions of simplified model equations, (2) by comparing numerical solutions with results of controlled experiments at the USGS debris-flow flume, and (3) by comparing numerical predictions with the behavior of a large (~50 million m3) debris flow that occurred at Mt. Meager, British Columbia, in 2010. Model predictions depend mostly on initial conditions, flow-path topography, and the value of a single dimensionless parameter that represents the ratio of two key timescales. One timescale governs downslope, gravity-driven motion of debris, and the other governs pore-pressure diffusion. Values of these timescales are readily calculated from source-area geometry and standard geotechnical
Applications of granular-dynamics numerical simulations to asteroid surfaces
Richardson, D. C.; Michel, P.; Schwartz, S. R.; Yu, Y.; Ballouz, R.-L.; Matsumura, S.
2014-07-01
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 totally different gravitational environment than on the Earth. 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 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]). (1) We carried out impacts into granular materials using different projectile shapes under Earth's gravity [5] and compared the results to laboratory experiments [6] in support of JAXA's Hayabusa 2 asteroid sample-return mission. We tested different projectile shapes and confirmed that the 90-degree cone was the most efficient at excavating mass when impacting 5-mm-diameter glass beads. Results are sensitive to the normal coefficient of restitution and the coefficient of static friction. Preliminary experiments in micro-gravity for similar impact conditions show both the amount of ejected mass and the timescale of the impact process increase, as expected. (2) It has been found (e.g., [7,8]) that ''fresh'' (unreddened) Q-class asteroids have a high probability of recent planetary encounters (˜1 Myr; also see [9]), suggesting that surface refreshening may have occurred due to tidal effects. As an application of the potential effect of tidal interactions, we carried out simulations of Apophis' predicted 2029 encounter with the Earth to see whether regolith motion might occur, using a range of plausible material parameters
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (24,284 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Beysens, D.A.; van Loon, J.J.W.A.; Beysens, D.A.; van Loon, J.J.W.A.
2015-01-01
It is generally thought that gravity is zero on an object travelling at constant velocity in space. This is not exactly so. We detail in the following those causes that make space gravity not strictly zero.
... medlineplus.gov/ency/article/003587.htm Urine specific gravity test To use the sharing features on this page, please enable JavaScript. Urine specific gravity is a laboratory test that shows the concentration ...
National Oceanic and Atmospheric Administration, Department of Commerce — The Decade of North American Geology (DNAG) gravity grid values, spaced at 6 km, were used to produce the Gravity Anomaly Map of North America (1987; scale...
Terrestrial Gravity Fluctuations
Directory of Open Access Journals (Sweden)
Jan Harms
2015-12-01
Full Text Available Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10^–23 Hz^–1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our
Terrestrial Gravity Fluctuations
Harms, Jan
2015-12-01
Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10-23 Hz-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of
Onset of Convection in Strongly Shaken Granular Matter
Eshuis, Peter; Eshuis, P.G.; van der Meer, Roger M.; Alam, Meheboob; van Gerner, H.J.; van der Weele, J.P.; Lohse, Detlef
2010-01-01
Strongly vertically shaken granular matter can display a density inversion: A high-density cluster of beads is elevated by a dilute gaslike layer of fast beads underneath (“granular Leidenfrost effect”). For even stronger shaking the granular Leidenfrost state becomes unstable and granular
MacKeown, P. K.
1984-01-01
Clarifies two concepts of gravity--those of a fictitious force and those of how space and time may have geometry. Reviews the position of Newton's theory of gravity in the context of special relativity and considers why gravity (as distinct from electromagnetics) lends itself to Einstein's revolutionary interpretation. (JN)
Bergshoeff, E.; Pope, C.N.; Stelle, K.S.
1990-01-01
We discuss the notion of higher-spin covariance in w∞ gravity. We show how a recently proposed covariant w∞ gravity action can be obtained from non-chiral w∞ gravity by making field redefinitions that introduce new gauge-field components with corresponding new gauge transformations.
Continuum description of avalanches in granular media.
Energy Technology Data Exchange (ETDEWEB)
Aranson, I. S.; Tsimring, L. S.
2000-12-05
A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.
Storage and discharge of a granular fluid.
Pacheco-Martinez, Hector; van Gerner, Henk Jan; Ruiz-Suárez, J C
2008-02-01
Experiments and computational simulations are carried out to study the behavior of a granular column in a silo whose walls are able to vibrate horizontally. The column is brought to a steady fluidized state and it behaves similar to a hydrostatic system. We study the dynamics of the granular discharge through openings at the bottom of the silo in order to search for a Torricelli-like behavior. We show that the flow rate scales with the wall induced shear rate, and at high rates, the granular bed indeed discharges similar to a viscous fluid.
Granular-relational data mining how to mine relational data in the paradigm of granular computing ?
Hońko, Piotr
2017-01-01
This book provides two general granular computing approaches to mining relational data, the first of which uses abstract descriptions of relational objects to build their granular representation, while the second extends existing granular data mining solutions to a relational case. Both approaches make it possible to perform and improve popular data mining tasks such as classification, clustering, and association discovery. How can different relational data mining tasks best be unified? How can the construction process of relational patterns be simplified? How can richer knowledge from relational data be discovered? All these questions can be answered in the same way: by mining relational data in the paradigm of granular computing! This book will allow readers with previous experience in the field of relational data mining to discover the many benefits of its granular perspective. In turn, those readers familiar with the paradigm of granular computing will find valuable insights on its application to mining r...
Advanced Granular System Modeling, Phase I
National Aeronautics and Space Administration — Spaceports of the future will utilize new granular materials in unique applications including insulation for cryogenic tanks and Lunar regolith processing for usable...
NMR Measurements of Granular Flow and Compaction
Fukushima, Eiichi
1998-03-01
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.
Acoustical properties of double porosity granular materials.
Venegas, Rodolfo; Umnova, Olga
2011-11-01
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.
Spatial correlations in compressible granular flows
van Noije, T.P.C.; Ernst, M.H.; Brito, R.
The clustering instability in freely evolving granular fluids manifests itself in the density-density correlation function and structure factor. These functions are calculated from fluctuating hydrodynamics. As time increases, the structure factor of density fluctuations develops a maximum, which
Noise induces rare events in granular media
Khain, Evgeniy; Sander, Leonard M.
2016-09-01
The granular Leidenfrost effect [B. Meerson, et al., Phys. Rev. Lett. 91, 024301 (2003), 10.1103/PhysRevLett.91.024301; P. Eshuis et al., Phys. Rev. Lett. 95, 258001 (2005), 10.1103/PhysRevLett.95.258001] is the levitation of a mass of granular matter when a wall below the grains is vibrated, giving rise to a hot granular gas below the cluster. We find by simulation that for a range of parameters the system is bistable: the levitated cluster can occasionally break and give rise to two clusters and a hot granular gas above and below. We use techniques from the theory of rare events to compute the mean transition time for breaking to occur. This requires the introduction of a two-component reaction coordinate.
Granular materials flow like complex fluids.
Kou, Binquan; Cao, Yixin; Li, Jindong; Xia, Chengjie; Li, Zhifeng; Dong, Haipeng; Zhang, Ang; Zhang, Jie; Kob, Walter; Wang, Yujie
2017-11-16
Granular materials such as sand, powders and foams are ubiquitous in daily life and in industrial and geotechnical applications. These disordered systems form stable structures when unperturbed, but in the presence of external influences such as tapping or shear they 'relax', becoming fluid in nature. It is often assumed that the relaxation dynamics of granular systems is similar to that of thermal glass-forming systems. However, so far it has not been possible to determine experimentally the dynamic properties of three-dimensional granular systems at the particle level. This lack of experimental data, combined with the fact that the motion of granular particles involves friction (whereas the motion of particles in thermal glass-forming systems does not), means that an accurate description of the relaxation dynamics of granular materials is lacking. Here we use X-ray tomography to determine the microscale relaxation dynamics of hard granular ellipsoids subject to an oscillatory shear. We find that the distribution of the displacements of the ellipsoids is well described by a Gumbel law (which is similar to a Gaussian distribution for small displacements but has a heavier tail for larger displacements), with a shape parameter that is independent of the amplitude of the shear strain and of the time. Despite this universality, the mean squared displacement of an individual ellipsoid follows a power law as a function of time, with an exponent that does depend on the strain amplitude and time. We argue that these results are related to microscale relaxation mechanisms that involve friction and memory effects (whereby the motion of an ellipsoid at a given point in time depends on its previous motion). Our observations demonstrate that, at the particle level, the dynamic behaviour of granular systems is qualitatively different from that of thermal glass-forming systems, and is instead more similar to that of complex fluids. We conclude that granular materials can relax
Granular materials flow like complex fluids
Kou, Binquan; Cao, Yixin; Li, Jindong; Xia, Chengjie; Li, Zhifeng; Dong, Haipeng; Zhang, Ang; Zhang, Jie; Kob, Walter; Wang, Yujie
2017-11-01
Granular materials such as sand, powders and foams are ubiquitous in daily life and in industrial and geotechnical applications. These disordered systems form stable structures when unperturbed, but in the presence of external influences such as tapping or shear they `relax', becoming fluid in nature. It is often assumed that the relaxation dynamics of granular systems is similar to that of thermal glass-forming systems. However, so far it has not been possible to determine experimentally the dynamic properties of three-dimensional granular systems at the particle level. This lack of experimental data, combined with the fact that the motion of granular particles involves friction (whereas the motion of particles in thermal glass-forming systems does not), means that an accurate description of the relaxation dynamics of granular materials is lacking. Here we use X-ray tomography to determine the microscale relaxation dynamics of hard granular ellipsoids subject to an oscillatory shear. We find that the distribution of the displacements of the ellipsoids is well described by a Gumbel law (which is similar to a Gaussian distribution for small displacements but has a heavier tail for larger displacements), with a shape parameter that is independent of the amplitude of the shear strain and of the time. Despite this universality, the mean squared displacement of an individual ellipsoid follows a power law as a function of time, with an exponent that does depend on the strain amplitude and time. We argue that these results are related to microscale relaxation mechanisms that involve friction and memory effects (whereby the motion of an ellipsoid at a given point in time depends on its previous motion). Our observations demonstrate that, at the particle level, the dynamic behaviour of granular systems is qualitatively different from that of thermal glass-forming systems, and is instead more similar to that of complex fluids. We conclude that granular materials can relax
Small-signal analysis of granular semiconductors
Energy Technology Data Exchange (ETDEWEB)
Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey, E-mail: aapo.varpula@tkk.f [Department of Micro and Nanosciences, Aalto University, PO Box 13500, FI-00076 Aalto, Espoo (Finland)
2010-11-01
The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in a broad frequency range at low dc bias voltages.
Small-signal analysis of granular semiconductors
International Nuclear Information System (INIS)
Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey
2010-01-01
The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in a broad frequency range at low dc bias voltages.
A constitutive law for dense granular flows.
Jop, Pierre; Forterre, Yoël; Pouliquen, Olivier
2006-06-08
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.
Pressure Profiles in a Loop Heat Pipe under Gravity Influence
Ku, Jentung
2015-01-01
During the operation of a loop heat pipe (LHP), the viscous flow induces pressure drops in various elements of the loop. The total pressure drop is equal to the sum of pressure drops in vapor grooves, vapor line, condenser, liquid line and primary wick, and is sustained by menisci at liquid and vapor interfaces on the outer surface of the primary wick in the evaporator. The menisci will curve naturally so that the resulting capillary pressure matches the total pressure drop. In ground testing, an additional gravitational pressure head may be present and must be included in the total pressure drop when LHP components are placed in a non-planar configuration. Under gravity-neutral and anti-gravity conditions, the fluid circulation in the LHP is driven solely by the capillary force. With gravity assist, however, the flow circulation can be driven by the combination of capillary and gravitational forces, or by the gravitational force alone. For a gravity-assist LHP at a given elevation between the horizontal condenser and evaporator, there exists a threshold heat load below which the LHP operation is gravity driven and above which the LHP operation is capillary force and gravity co-driven. The gravitational pressure head can have profound effects on the LHP operation, and such effects depend on the elevation, evaporator heat load, and condenser sink temperature. This paper presents a theoretical study on LHP operations under gravity-neutral, anti-gravity, and gravity-assist modes using pressure diagrams to help understand the underlying physical processes. Effects of the condenser configuration on the gravitational pressure head and LHP operation are also discussed.
Chemotaxis of large granular lymphocytes
International Nuclear Information System (INIS)
Pohajdak, B.; Gomez, J.; Orr, F.W.; Khalil, N.; Talgoy, M.; Greenberg, A.H.
1986-01-01
The hypothesis that large granular lymphocytes (LGL) are capable of directed locomotion (chemotaxis) was tested. A population of LGL isolated from discontinuous Percoll gradients migrated along concentration gradients of N-formyl-methionyl-leucyl-phenylalanine (f-MLP), casein, and C5a, well known chemoattractants for polymorphonuclear leukocytes and monocytes, as well as interferon-β and colony-stimulating factor. Interleukin 2, tuftsin, platelet-derived growth factor, and fibronectin were inactive. Migratory responses were greater in Percoll fractions with the highest lytic activity and HNK-1 + cells. The chemotactic response to f-MLP, casein, and C5a was always greater when the chemoattractant was present in greater concentration in the lower compartment of the Boyden chamber. Optimum chemotaxis was observed after a 1 hr incubation that made use of 12 μm nitrocellulose filters. LGL exhibited a high degree of nondirected locomotion when allowed to migrate for longer periods (> 2 hr), and when cultured in vitro for 24 to 72 hr in the presence or absence of IL 2 containing phytohemagluttinin-conditioned medium. LGL chemotaxis to f-MLP could be inhibited in a dose-dependent manner by the inactive structural analog CBZ-phe-met, and the RNK tumor line specifically bound f-ML( 3 H)P, suggesting that LGL bear receptors for the chemotactic peptide
Mechanics of Granular Materials (MGM)
2000-01-01
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).
Self-assembled granular towers
Pacheco-Vazquez, Felipe; Moreau, Florian; Vandewalle, Nicolas; Dorbolo, Stephan; GroupResearch; Applications in Statistical Physics Team
2013-03-01
When some water is added to sand, cohesion among the grains is induced. In fact, only 1% of liquid volume respect to the total pore space of the sand is necessary to built impressive sandcastles. Inspired on this experience, the mechanical properties of wet piles and sand columns have been widely studied during the last years. However, most of these studies only consider wet materials with less than 35% of liquid volume. Here we report the spontaneous formation of granular towers produced when dry sand is poured on a highly wet sand bed: The impacting grains stick on the wet grains due to instantaneous liquid bridges created during the impact. The grains become wet by the capillary ascension of water and the process continues, giving rise to stable narrow sand towers. Actually, the towers can reach the maximum theoretical limit of stability predicted by previous models, only expected for low liquid volumes. The authors would like to thank FNRS and Conacyt Mexico for financial support. FPV is a beneficiary of a movility grant from BELSPO/Marie Curie and the University of Liege.
Microfluidics of soft granular gels
Nixon, Ryan; Bhattacharjee, Tapomoy; Sawyer, W. Gregory; Angelini, Thomas E.
Microfluidic methods for encapsulating cells and particles typically involve drop making with two immiscible fluids. The main materials constraint in this approach is surface tension, creating inherent instability between the two fluids. We can eliminate this instability by using miscible inner and outer phases. This is achieved by using granular micro gels which are chemically miscible but physically do not mix. These microgels are yield stress materials, so they flow as solid plugs far from shear gradients, and fluidize where gradients are generated - near an injection nozzle for example. We have found that tuning the yield stress of the material by varying polymer concentration, device performance can be controlled. The solid like behavior of the gel allows us to produces infinitely stable jets that maintain their integrity and configuration over long distances and times. These properties can be combined and manipulated to produce discrete particulate bunches of an inner phase, flowing inside of an outer phase, well enough even to print a Morse code message suspended within flow chambers about a millimeter in diameter moving at millimeters a second.
Directory of Open Access Journals (Sweden)
A. Sornette
1994-01-01
Full Text Available We present exploratory analogies and speculations on the mechanisms underlying the organization of faulting and earthquake in the earth crust. The mechanical properties of the brittle lithosphere at scales of the order or larger than a few kilometers are proposed to be analogous to those of non-cohesive granular media, since both systems present stress amplitudes controlled by gravity, and shear band (faulting localization is determined by a type of friction Mohr-Coulomb rupture criterion. here, we explore the implications of this correspondence with respect to the origin of tectonic and earthquake complexity, on the basis of the existing experimental data on granular media available in the mechanical literature. An important observation is that motions and deformations of non-cohesive granular media are characterized by important fluctuations both in time (sudden breaks, avalanches, which are analogous to earthquakes and space (strain localizations, yield surfaces forming sometimes complex patterns. This is in apparent contradiction with the conventional wisdom in mechanics, based on the standard tendency to homogenize, which has led to dismiss fluctuations as experimental noise. On the basis of a second analogy with spinglasses and neural networks, based on the existence of block and grain packing disorder and block rotation "frustration", we suggest that these fluctuations observed both at large scales and at the block scale constitute an intrinsic signature of the mechanics of granular media. The space-time complexity observed in faulting and earthquake phenomenology is thus proposed to result form the special properties of the mechanics of granular media, dominated by the "frustration" of the kinematic deformations of its constitutive blocks.
Discrete Element Modeling of Complex Granular Flows
Movshovitz, N.; Asphaug, E. I.
2010-12-01
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
Pressure independence of granular flow through an aperture.
Aguirre, M A; Grande, J G; Calvo, A; Pugnaloni, L A; Géminard, J-C
2010-06-11
We experimentally demonstrate that the flow rate of granular material through an aperture is controlled by the exit velocity imposed on the particles and not by the pressure at the base, contrary to what is often assumed in previous work. This result is achieved by studying the discharge process of a dense packing of monosized disks through an orifice. The flow is driven by a conveyor belt. This two-dimensional horizontal setup allows us to independently control the velocity at which the disks escape the horizontal silo and the pressure in the vicinity of the aperture. The flow rate is found to be proportional to the belt velocity, independent of the amount of disks in the container and, thus, independent of the pressure in the outlet region. In addition, this specific configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge.
Partition instability in water-immersed granular systems.
Clement, C P; Pacheco-Martinez, H A; Swift, Michael R; King, P J
2009-07-01
It is well known that a system of grains, vibrated vertically in a cell divided into linked columns, may spontaneously move into just one of the columns due to the inelastic nature of their collisions. Here we study the behavior of a water-immersed system of spherical barium titanate particles in a rectangular cell which is divided into two columns, linked by two connecting holes, one at the top and one at the bottom of the cell. Under vibration the grains spontaneously move into just one of the columns via a gradual transfer of grains through the connecting hole at the base of the cell. We have developed numerical simulations that are able to reproduce this behavior and provide detailed information on the instability mechanism. We use this knowledge to propose a simple analytical model for this fluid-driven partition instability based on two coupled granular beds vibrated within an incompressible fluid.
International Nuclear Information System (INIS)
Burkhard, N.R.
1979-01-01
The gravity inversion code applies stabilized linear inverse theory to determine the topography of a subsurface density anomaly from Bouguer gravity data. The gravity inversion program consists of four source codes: SEARCH, TREND, INVERT, and AVERAGE. TREND and INVERT are used iteratively to converge on a solution. SEARCH forms the input gravity data files for Nevada Test Site data. AVERAGE performs a covariance analysis on the solution. This document describes the necessary input files and the proper operation of the code. 2 figures, 2 tables
Directory of Open Access Journals (Sweden)
Animesh Mukherjee
1991-01-01
Full Text Available Based upon Biot's [1965] theory of initial stresses of hydrostatic nature produced by the effect of gravity, a study is made of surface waves in higher order visco-elastic media under the influence of gravity. The equation for the wave velocity of Stonely waves in the presence of viscous and gravitational effects is obtained. This is followed by particular cases of surface waves including Rayleigh waves and Love waves in the presence of viscous and gravity effects. In all cases the wave-velocity equations are found to be in perfect agreement with the corresponding classical results when the effects of gravity and viscosity are neglected.
Classical Weyl transverse gravity
Energy Technology Data Exchange (ETDEWEB)
Oda, Ichiro [University of the Ryukyus, Department of Physics, Faculty of Science, Nishihara, Okinawa (Japan)
2017-05-15
We study various classical aspects of the Weyl transverse (WTDiff) gravity in a general space-time dimension. First of all, we clarify a classical equivalence among three kinds of gravitational theories, those are, the conformally invariant scalar tensor gravity, Einstein's general relativity and the WTDiff gravity via the gauge-fixing procedure. Secondly, we show that in the WTDiff gravity the cosmological constant is a mere integration constant as in unimodular gravity, but it does not receive any radiative corrections unlike the unimodular gravity. A key point in this proof is to construct a covariantly conserved energy-momentum tensor, which is achieved on the basis of this equivalence relation. Thirdly, we demonstrate that the Noether current for the Weyl transformation is identically vanishing, thereby implying that the Weyl symmetry existing in both the conformally invariant scalar tensor gravity and the WTDiff gravity is a ''fake'' symmetry. We find it possible to extend this proof to all matter fields, i.e. the Weyl-invariant scalar, vector and spinor fields. Fourthly, it is explicitly shown that in the WTDiff gravity the Schwarzschild black hole metric and a charged black hole one are classical solutions to the equations of motion only when they are expressed in the Cartesian coordinate system. Finally, we consider the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology and provide some exact solutions. (orig.)
DISCHARGE VALVE FOR GRANULAR MATERIAL
Stoughton, L.D.; Robinson, S.T.
1962-05-15
A gravity-red dispenser or valve is designed for discharging the fueled spherical elements used in a pebble bed reactor. The dispenser consists of an axially movable tube terminating under a hood having side walls with openings. When the tube is moved so that its top edge is above the tops of the side openings the elements will not flow. As the tube is moved downwardly, the elements flow into the hood through the side openings and over the top edge into the tube at an increasing rate as the tube is lowered further. The tube is spaced at all times from the hood and side walls a distance greater than the diameter of the largest element to prevent damaging of the elements when the dispenser is closed to flow. (AEC)
Axisymmetric collapses of granular columns
Lube, Gert; Huppert, Herbert E.; Sparks, R. Stephen J.; Hallworth, Mark A.
2004-06-01
Experimental observations of the collapse of initially vertical columns of small grains are presented. The experiments were performed mainly with dry grains of salt or sand, with some additional experiments using couscous, sugar or rice. Some of the experimental flows were analysed using high-speed video. There are three different flow regimes, dependent on the value of the aspect ratio a {=} h_i/r_i, where h_i and r_i are the initial height and radius of the granular column respectively. The differing forms of flow behaviour are described for each regime. In all cases a central, conically sided region of angle approximately 59(°) , corresponding to an aspect ratio of 1.7, remains undisturbed throughout the motion. The main experimental results for the final extent of the deposit and the time for emplacement are systematically collapsed in a quantitative way independent of any friction coefficients. Along with the kinematic data for the rate of spread of the front of the collapsing column, this is interpreted as indicating that frictional effects between individual grains in the bulk of the moving flow only play a role in the last instant of the flow, as it comes to an abrupt halt. For a {reach r_infty is given by t_infty {=} 3(h_i/g)(1/2} {=} 3(r_i/g)({1/2}a^{1/2)) , where g is the gravitational acceleration. The insights and conclusions gained from these experiments can be applied to a wide range of industrial and natural flows of concentrated particles. For example, the observation of the rapid deposition of the grains can help explain details of the emplacement of pyroclastic flows resulting from the explosive eruption of volcanoes.
Collapse of tall granular columns in fluid
Directory of Open Access Journals (Sweden)
Kumar Krishna
2017-01-01
Full Text Available Avalanches, landslides, and debris flows are geophysical hazards, which involve rapid mass movement of granular solids, water, and air as a multi-phase system. In order to describe the mechanism of immersed granular flows, it is important to consider both the dynamics of the solid phase and the role of the ambient fluid. In the present study, the collapse of a granular column in fluid is studied using 2D LBM - DEM. The flow kinematics are compared with the dry and buoyant granular collapse to understand the influence of hydrodynamic forces and lubrication on the run-out. In the case of tall columns, the amount of material destabilised above the failure plane is larger than that of short columns. Therefore, the surface area of the mobilised mass that interacts with the surrounding fluid in tall columns is significantly higher than the short columns. This increase in the area of soil - fluid interaction results in an increase in the formation of turbulent vortices thereby altering the deposit morphology. It is observed that the vortices result in the formation of heaps that significantly affects the distribution of mass in the flow. In order to understand the behaviour of tall columns, the run-out behaviour of a dense granular column with an initial aspect ratio of 6 is studied. The collapse behaviour is analysed for different slope angles: 0°, 2.5°, 5° and 7.5°.
Collapse of tall granular columns in fluid
Kumar, Krishna; Soga, Kenichi; Delenne, Jean-Yves
2017-06-01
Avalanches, landslides, and debris flows are geophysical hazards, which involve rapid mass movement of granular solids, water, and air as a multi-phase system. In order to describe the mechanism of immersed granular flows, it is important to consider both the dynamics of the solid phase and the role of the ambient fluid. In the present study, the collapse of a granular column in fluid is studied using 2D LBM - DEM. The flow kinematics are compared with the dry and buoyant granular collapse to understand the influence of hydrodynamic forces and lubrication on the run-out. In the case of tall columns, the amount of material destabilised above the failure plane is larger than that of short columns. Therefore, the surface area of the mobilised mass that interacts with the surrounding fluid in tall columns is significantly higher than the short columns. This increase in the area of soil - fluid interaction results in an increase in the formation of turbulent vortices thereby altering the deposit morphology. It is observed that the vortices result in the formation of heaps that significantly affects the distribution of mass in the flow. In order to understand the behaviour of tall columns, the run-out behaviour of a dense granular column with an initial aspect ratio of 6 is studied. The collapse behaviour is analysed for different slope angles: 0°, 2.5°, 5° and 7.5°.
Characteristics of undulatory locomotion in granular media
Peng, Zhiwei; Pak, On Shun; Elfring, Gwynn J.
2016-03-01
Undulatory locomotion is ubiquitous in nature and observed in different media, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Despite the similarity in the undulating pattern, the swimming characteristics depend on the rheological properties of different media. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but recently a resistive force theory in granular media has been proposed and shown useful in studying the locomotion of a sand-swimming lizard. Here we employ the proposed model to investigate the swimming characteristics of a slender filament, of both finite and infinite length, undulating in a granular medium and compare the results with swimming in viscous fluids. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swimmer. We also find that, similar to Lighthill's results using resistive force theory in viscous fluids, the sawtooth swimmer is the optimal waveform for propulsion speed at a given power consumption in granular media. The results complement our understanding of undulatory locomotion and provide insights into the effective design of locomotive systems in granular media.
Reversibility in locomotion in granular media
Savoie, William; Goldman, Daniel
2013-11-01
A recent study of a self-deforming robot [Hatton et al., PRL, 2013] demonstrated that slow movement in dry granular media resembles locomotion in low Re fluids, in part because inertia is dominated by friction. The study indicated that granular swimming was kinematically reversible, a surprise because yielding in granular flow is irreversible. To investigate if reciprocal motions lead to net displacements in granular swimmers, in laboratory experiments, we study the locomotion of a robotic ``scallop'' consisting of a square body with two flipper-like limbs controlled to flap forward and backward symmetrically (a flap cycle). The body is constrained by linear bearings to allow motion in only one dimension. We vary the the flapping frequency f, the body/flipper burial depth d, and the number of flaps N in a deep bed of 6 mm diameter plastic spheres. Over a range of f and d, the N = 1 cycle produces net translation of the body; however for large N, a cycle produces no net translation. We conclude that symmetric strokes in granular swimming are irreversible at the onset of self-deformation, but become asymptotically reversible. work supported by NSF and ARL.
Experiments and characterization of low-frequency oscillations in a granular column
Oyarte Gálvez, Loreto; Rivas, Nicolás; van der Meer, Devaraj
2018-04-01
The behavior of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters and more specifically allows for a thorough characterization of the low-frequency oscillation (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO frequency from the power spectral density of the center-of-mass signal of the grains, varying the amplitude and frequency of the driving, the particle diameter, and the number of layers in the system. We thus find that the LFO frequency (i) is inversely proportional to the fast inertial timescale and (ii) decorrelates with a typical decay time proportional to the slow dissipative timescale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles.
Granular cell tumor of the orbit.
Salour, Hossein; Tavakoli, Mehdi; Karimi, Saeed; Rezaei Kanavi, Mozhgan; Faghihi, Mohammad
2013-10-01
To report a case of granular cell tumor as a rare orbital pathology. A 50-year-old female presented with a 4-year history of diplopia, right ocular displacement and a firm nontender mass in her right lower lid. Computed tomography (CT) scan of the orbit disclosed a well-defined mass in the right inferior orbit involving the right inferior rectus. Subtotal excision of the mass was performed, and histopathologic and immunohistochemical studies revealed granular cell tumor. Subsequently, the tumor recurred and exenteration was required as multiple sessions of radiotherapy failed to prevent the residual tumor from growing. Granular cell tumor, though very rare in the orbit, should be considered in patients with orbital masses especially in cases with involvement of the inferior rectus muscle. Infiltrative tumors may be impossible to completely resect and can rapidly recur following surgery.
Granular Cell Tumor of the Orbit
Directory of Open Access Journals (Sweden)
Hossein Salour
2013-01-01
Full Text Available Purpose: To report a case of granular cell tumor as a rare orbital pathology. Case report: A 50-year-old female presented with a 4-year history of diplopia, right ocular displacement and a firm nontender mass in her right lower lid. Computed tomography (CT scan of the orbit disclosed a well-defined mass in the right inferior orbit involving the right inferior rectus. Subtotal excision of the mass was performed, and histopathologic and immunohistochemical studies revealed granular cell tumor. Subsequently, the tumor recurred and exenteration was required as multiple sessions of radiotherapy failed to prevent the residual tumor from growing. Conclusion: Granular cell tumor, though very rare in the orbit, should be considered in patients with orbital masses especially in cases with involvement of the inferior rectus muscle. Infiltrative tumors may be impossible to completely resect and can rapidly recur following surgery.
Wet granular matter a truly complex fluid
Herminghaus, Stephan
2013-01-01
This is a monograph written for the young and advanced researcher who is entering the field of wet granular matter and keen to understand the basic physical principles governing this state of soft matter. It treats wet granulates as an instance of a ternary system, consisting of the grains, a primary, and a secondary fluid. After addressing wetting phenomena in general and outlining the basic facts on dry granular systems, a chapter on basic mechanisms and their effects is dedicated to every region of the ternary phase diagram. Effects of grain shape and roughness are considered as well. Rather than addressing engineering aspects such as existing books on this topic do, the book aims to provide a generalized framework suitable for those who want to understand these systems on a more fundamental basis. Readership: For the young and advanced researcher entering the field of wet granular matter.
Indian Academy of Sciences (India)
2016-11-02
Nov 2, 2016 ... the existence of dark energy and dark matter, several modified theories of gravitation have been proposed as alternative to Einstein's theory. By modifying the geometrical part of Einstein–Hilbert action of general relativity, we obtain the modified gravity. Modified gravity is of great importance because it can ...
Bergshoeff, Eric A.; Roo, Mees de; Kerstan, Sven F.; Kleinschmidt, Axel; Riccioni, Fabio
We consider the problem of finding a dual formulation of gravity in the presence of non-trivial matter couplings. In the absence of matter a dual graviton can be introduced only for linearised gravitational interactions. We show that the coupling of linearised gravity to matter poses obstructions to
Surface instabilities in shock loaded granular media
Kandan, K.; Khaderi, S. N.; Wadley, H. N. G.; Deshpande, V. S.
2017-12-01
The initiation and growth of instabilities in granular materials loaded by air shock waves are investigated via shock-tube experiments and numerical calculations. Three types of granular media, dry sand, water-saturated sand and a granular solid comprising PTFE spheres were experimentally investigated by air shock loading slugs of these materials in a transparent shock tube. Under all shock pressures considered here, the free-standing dry sand slugs remained stable while the shock loaded surface of the water-saturated sand slug became unstable resulting in mixing of the shocked air and the granular material. By contrast, the PTFE slugs were stable at low pressures but displayed instabilities similar to the water-saturated sand slugs at higher shock pressures. The distal surfaces of the slugs remained stable under all conditions considered here. Eulerian fluid/solid interaction calculations, with the granular material modelled as a Drucker-Prager solid, reproduced the onset of the instabilities as seen in the experiments to a high level of accuracy. These calculations showed that the shock pressures to initiate instabilities increased with increasing material friction and decreasing yield strain. Moreover, the high Atwood number for this problem implied that fluid/solid interaction effects were small, and the initiation of the instability is adequately captured by directly applying a pressure on the slug surface. Lagrangian calculations with the directly applied pressures demonstrated that the instability was caused by spatial pressure gradients created by initial surface perturbations. Surface instabilities are also shown to exist in shock loaded rear-supported granular slugs: these experiments and calculations are used to infer the velocity that free-standing slugs need to acquire to initiate instabilities on their front surfaces. The results presented here, while in an idealised one-dimensional setting, provide physical understanding of the conditions required to
Palsingh, S. (Inventor)
1975-01-01
An educational toy useful in demonstrating fundamental concepts regarding the laws of gravity is described. The device comprises a sphere 10 of radius r resting on top of sphere 12 of radius R. The center of gravity of sphere 10 is displaced from its geometrical center by distance D. The dimensions are so related that D((R+r)/r) is greater than r. With the center of gravity of sphere 10 lying on a vertical line, the device is in equilibrium. When sphere 10 is rolled on the surface of sphere 12 it will return to its equilibrium position upon release. This creates an illusion that sphere 10 is defying the laws of gravity. In reality, due to the above noted relationship of D, R, and r, the center of gravity of sphere 10 rises from its equilibrium position as it rolls a short distance up or down the surface of sphere 12.
Directory of Open Access Journals (Sweden)
Øyvind Grøn
2012-12-01
Full Text Available The effect of gravity upon changes of the entropy of a gravity-dominated system is discussed. In a universe dominated by vacuum energy, gravity is repulsive, and there is accelerated expansion. Furthermore, inhomogeneities are inflated and the universe approaches a state of thermal equilibrium. The difference between the evolution of the cosmic entropy in a co-moving volume in an inflationary era with repulsive gravity and a matter-dominated era with attractive gravity is discussed. The significance of conversion of gravitational energy to thermal energy in a process with gravitational clumping, in order that the entropy of the universe shall increase, is made clear. Entropy of black holes and cosmic horizons are considered. The contribution to the gravitational entropy according to the Weyl curvature hypothesis is discussed. The entropy history of the Universe is reviewed.
Anisotropy in cohesive, frictional granular media
International Nuclear Information System (INIS)
Luding, Stefan
2005-01-01
The modelling of cohesive, frictional granular materials with a discrete particle molecular dynamics is reviewed. From the structure of the quasi-static granular solid, the fabric, stress, and stiffness tensors are determined, including both normal and tangential forces. The influence of the material properties on the flow behaviour is also reported, including relations between the microscopic attractive force and the macroscopic cohesion as well as the dependence of the macroscopic friction on the microscopic contact friction coefficient. Related to the dynamics, the anisotropy of both structure and stress are exponentially approaching the maximum
Gravity induced wave function collapse
Gasbarri, G.; Toroš, M.; Donadi, S.; Bassi, A.
2017-11-01
Starting from an idea of S. L. Adler [in Quantum Nonlocality and Reality: 50 Years of Bell's Theorem, edited by M. Bell and S. Gao (Cambridge University Press, Cambridge, England 2016)], we develop a novel model of gravity induced spontaneous wave function collapse. The collapse is driven by complex stochastic fluctuations of the spacetime metric. After deriving the fundamental equations, we prove the collapse and amplification mechanism, the two most important features of a consistent collapse model. Under reasonable simplifying assumptions, we constrain the strength ξ of the complex metric fluctuations with available experimental data. We show that ξ ≥10-26 in order for the model to guarantee classicality of macro-objects, and at the same time ξ ≤10-20 in order not to contradict experimental evidence. As a comparison, in the recent discovery of gravitational waves in the frequency range 35 to 250 Hz, the (real) metric fluctuations reach a peak of ξ ˜10-21.
Tribology Experiment in Zero Gravity
Pan, C. H. T.; Gause, R. L.; Whitaker, A. F.; Finckenor, M. M.
2015-01-01
A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates observation of such motions as controlled by interfacial and capillary forces. Two experimental configurations were used. One deals with the liquid on one solid surface, and the other with the liquid between a pair of closed spaced surfaces. Time sequence photographs of fluid motion on a solid surface yielded spreading rate data of several fluid-surface combinations. In general, a slow spreading process as governed by the tertiary junction can be distinguished from a more rapid process which is driven by surface tension controlled internal fluid pressure. Photographs were also taken through the transparent bushings of several experimental journal bearings. Morphology of incomplete fluid films and its fluctuation with time suggest the presence or absence of unsteady phenomena of the bearing-rotor system in various arrangements.
Granular cell tumors of the head and neck.
Regezi, J A; Batsakis, J G; Courtney, R M
1979-06-01
Forth-two granular cell tumors of the head and neck were collected and studied with light and electron microscopy. Granular cells were found in four odontogenic tumors, two congenital epulides of newborn infants, and 36 myoblastoma lesions of the skin and mucous membranes. Support is presented for the hypothesis that granular cells represent an unusual nonspecific degenerative process and that nonodontogenic granular cell tumors develop from undifferentiated mesenchymal cells that subsequently undergo autophagocytosis.
Computer-aided analysis for the Mechanics of Granular Materials (MGM) experiment
Parker, Joey K.
1986-01-01
The Mechanics of Granular Materials (MGM) program is planned to provide experimental determinations of the mechanics of granular materials under very low gravity conditions. The initial experiments will use small glass beads as the granular material, and a precise tracking of individual beads during the test is desired. Real-time video images of the experimental specimen were taken with a television camera, and subsequently digitized by a frame grabber installed in a microcomputer. Easily identified red tracer beads were randomly scattered throughout the test specimen. A set of Pascal programs was written for processing and analyzing the digitized images. Filtering the image with Laplacian, dilation, and blurring filters when using a threshold function produced a binary (black on white) image which clearly identified the red beads. The centroids and areas for each bead were then determined. Analyzing a series of the images determined individual red bead displacements throughout the experiment. The system can provide displacement accuracies on the order of 0.5 to 1 pixel is the image is taken directly from the video camera. Digitizing an image from a video cassette recorder introduces an additional repeatability error of 0.5 to 1 pixel. Other programs were written to provide hardcopy prints of the digitized images on a dot-matrix printer.
77 FR 59979 - Pure Magnesium (Granular) From China
2012-10-01
... COMMISSION Pure Magnesium (Granular) From China Determination On the basis of the record \\1\\ developed in the... antidumping duty order on pure magnesium (granular) from China would be likely to lead to continuation or...), entitled Pure Magnesium (Granular) from China: Investigation No.731-TA- 895 (Second Review). Issued...
Seismic displacement of gravity retaining walls
Directory of Open Access Journals (Sweden)
Kamal Mohamed Hafez Ismail Ibrahim
2015-08-01
Full Text Available Seismic displacement of gravity walls had been studied using conventional static methods for controlled displacement design. In this study plain strain numerical analysis is performed using Plaxis dynamic program where prescribed displacement is applied at the bottom boundary of the soil to simulate the applied seismic load. Constrained absorbent side boundaries are introduced to prevent any wave reflection. The studied soil is chosen dense granular sand and modeled as elasto-plastic material according to Mohr–Column criteria while the gravity wall is assumed elastic. By comparing the resulted seismic wall displacements calculated by numerical analysis for six historical ground motions with that calculated by the pseudo-static method, it is found that numerical seismic displacements are either equal to or greater than corresponding pseudo-static values. Permissible seismic wall displacement calculated by AASHTO can be used for empirical estimation of seismic displacement. It is also found that seismic wall displacement is directly proportional with the positive angle of inclination of the back surface of the wall, soil flexibility and with the earthquake maximum ground acceleration. Seismic wall sliding is dominant and rotation is negligible for rigid walls when the ratio between the wall height and the foundation width is less than 1.4, while for greater ratios the wall becomes more flexible and rotation (rocking increases till the ratio reaches 1.8 where overturning is susceptible to take place. Cumulative seismic wall rotation increases with dynamic time and tends to be constant at the end of earthquake.
Cai, Han-Jie; Zhang, Zhi-Lei; Fu, Fen; Li, Jian-Yang; Zhang, Xun-Chao; Zhang, Ya-Ling; Yan, Xue-Song; Lin, Ping; Xv, Jian-Ya; Yang, Lei
2018-02-01
The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.
Collective phenomena in vertically shaken granular matter
Eshuis, Pieter Gerben
2008-01-01
Granular matter is the general name for materials consisting of grain-like solids and can be encountered everywhere in our daily life, for instance in the form of sand, sugar, cereals and pills. Numerous industries deal with these kinds of materials, which often cause severe problems during
Vortex jamming in superconductors and granular rheology
International Nuclear Information System (INIS)
Yoshino, Hajime; Nogawa, Tomoaki; Kim, Bongsoo
2009-01-01
We demonstrate that a highly frustrated anisotropic Josephson junction array (JJA) on a square lattice exhibits a zero-temperature jamming transition, which shares much in common with those in granular systems. Anisotropy of the Josephson couplings along the horizontal and vertical directions plays roles similar to normal load or density in granular systems. We studied numerically static and dynamic response of the system against shear, i.e. injection of external electric current at zero temperature. Current-voltage curves at various strength of the anisotropy exhibit universal scaling features around the jamming point much as do the flow curves in granular rheology, shear-stress versus shear-rate. It turns out that at zero temperature the jamming transition occurs right at the isotropic coupling and anisotropic JJA behaves as exotic fragile vortex matter: it behaves as a superconductor (vortex glass) in one direction, whereas it is a normal conductor (vortex liquid) in the other direction even at zero temperature. Furthermore, we find a variant of the theoretical model for the anisotropic JJA quantitatively reproduces universal master flow-curves of the granular systems. Our results suggest an unexpected common paradigm stretching over seemingly unrelated fields-the rheology of soft materials and superconductivity.
Pion showers in highly granular calorimeters
Indian Academy of Sciences (India)
2012-10-02
–80 GeV in high granular electromagnetic and hadron calorimeters are presented. Data were used for the first time to investigate the separation of the neutral and charged hadron showers. The result is important to verify the ...
Granular Data Description: Designing Ellipsoidal Information Granules.
Zhu, Xiubin; Pedrycz, Witold; Li, Zhiwu
2017-12-01
Granular computing (GrC) has emerged as a unified conceptual and processing framework. Information granules are fundamental constructs that permeate concepts and models of GrC. This paper is concerned with a design of a collection of meaningful, easily interpretable ellipsoidal information granules with the use of the principle of justifiable granularity by taking into consideration reconstruction abilities of the designed information granules. The principle of justifiable granularity supports designing of information granules based on numeric or granular evidence, and aims to achieve a compromise between justifiability and specificity of the information granules to be constructed. A two-stage development strategy behind the construction of justifiable information granules is considered. First, a collection of numeric prototypes is determined with the use of fuzzy clustering. Second, the lengths of the semi-axes of ellipsoidal information granules to be formed around such prototypes are optimized. Two optimization criteria are introduced and studied. Experimental studies involving synthetic data set and data sets coming from the machine learning repository are reported.
Deposition and shaking of dry granular piles
Hasan, M.
2003-01-01
A friction force model describing reversible stick-slip transition during contact has been developed with the special purpose to simulate the deposition of granular material. A test with a mass on a conveyor belt kept in position by a spring shows that a numerical simulation of the dynamics of such
Pion showers in highly granular calorimeters
Indian Academy of Sciences (India)
New results on properties of hadron showers created by pion beam at 8–80 GeV in high granular electromagnetic and hadron calorimeters are presented. Data were used for the ﬁrst time to investigate the separation of the neutral and charged hadron showers. The result is important to verify the prediction of the PFA ...
Anomalous infrared absorption in granular superconductors
International Nuclear Information System (INIS)
Carr, G.L.; Garland, J.C.; Tanner, D.B.
1983-01-01
Granular superconductors are shown to have a far-infrared absorption that is larger when the samples are superconducting than when they are normal. By constrast, theoretical models for these materials predict that when the samples become superconducting, the absorption should decrease
Granular cell tumour of the urinary bladder
Directory of Open Access Journals (Sweden)
Christoph von Klot
2012-04-01
Full Text Available With only 16 cases reported in the literature, the mostly benign granular cell tumour of the urinary bladder is exceptionally rare. We present the case of a 68-year old patient with one of these lesions demonstrating our histological findings including several immunohistochemical stainings used to differentiate between other more common entities.
Structure and cluster formation in granular media
Indian Academy of Sciences (India)
The two most important phenomena at the basis of granular media are excluded volume and dissipation. The former is captured by the hard sphere model and is responsible for, e.g., crystallization, the latter leads to interesting structures like clusters in non-equilibrium dynamical, freely cooling states. The freely cooling ...
Anomalous intruder response in diverse granular systems
Oyarte Galvez, Loreto Alejandra
2017-01-01
The definition of granular matter is extremely broad; any collection of conglomeration of particles larger than 100 micrometers can be considered as part of this group, and virtually the entire universe is composed of them. Examples are found in many fields, e.g. in nature (dunes, avalanches,
Random packing of colloids and granular matter
Wouterse, A.
2008-01-01
This thesis deals with the random packing of colloids and granular matter. A random packing is a stable disordered collection of touching particles, without long-range positional and orientational order. Experimental random packings of particles with the same shape but made of different materials
Directory of Open Access Journals (Sweden)
J. Ambjørn
1995-07-01
Full Text Available The 2-point function is the natural object in quantum gravity for extracting critical behavior: The exponential falloff of the 2-point function with geodesic distance determines the fractal dimension dH of space-time. The integral of the 2-point function determines the entropy exponent γ, i.e. the fractal structure related to baby universes, while the short distance behavior of the 2-point function connects γ and dH by a quantum gravity version of Fisher's scaling relation. We verify this behavior in the case of 2d gravity by explicit calculation.
CERN. Geneva
2007-01-01
Of the four fundamental forces, gravity has been studied the longest, yet gravitational physics is one of the most rapidly developing areas of science today. This talk will give a broad brush survey of the past achievements and future prospects of general relativistic gravitational physics. Gravity is a two frontier science being important on both the very largest and smallest length scales considered in contemporary physics. Recent advances and future prospects will be surveyed in precision tests of general relativity, gravitational waves, black holes, cosmology and quantum gravity. The aim will be an overview of a subject that is becoming increasingly integrated with experiment and other branches of physics.
Granular flow over inclined channels with constrictions
Tunuguntla, Deepak; Weinhart, Thomas; Thornton, Anthony; Bokhove, Onno
2013-04-01
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
Low-Gravity Mimicking Simulants and Evaluation of Simulant Flow, Phase I
National Aeronautics and Space Administration — This project will provide a new method for testing flow/no-flow conditions and other gravity-driven flow behavior of Lunar or planetary regolith under reduced...
Bergshoeff, Eric A.; Hohm, Olaf; Townsend, Paul K.
2012-01-01
We present a brief review of New Massive Gravity, which is a unitary theory of massive gravitons in three dimensions obtained by considering a particular combination of the Einstein-Hilbert and curvature squared terms.
International Nuclear Information System (INIS)
Williams, Ruth M
2006-01-01
A review is given of a number of approaches to discrete quantum gravity, with a restriction to those likely to be relevant in four dimensions. This paper is dedicated to Rafael Sorkin on the occasion of his sixtieth birthday
National Oceanic and Atmospheric Administration, Department of Commerce — In 1985, Dr. William F. Haxby of the Lamont-Doherty Geological Observatory of Columbia University prepared this data base of free-air gravity anomalies, based on the...
Carroll versus Galilei gravity
Energy Technology Data Exchange (ETDEWEB)
Bergshoeff, Eric [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Gomis, Joaquim [Departament de Física Cuàntica i Astrofísica and Institut de Ciències del Cosmos,Universitat de Barcelona,Martí i Franquès 1, E-08028 Barcelona (Spain); Rollier, Blaise [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Rosseel, Jan [Faculty of Physics, University of Vienna,Boltzmanngasse 5, A-1090 Vienna (Austria); Veldhuis, Tonnis ter [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands)
2017-03-30
We consider two distinct limits of General Relativity that in contrast to the standard non-relativistic limit can be taken at the level of the Einstein-Hilbert action instead of the equations of motion. One is a non-relativistic limit and leads to a so-called Galilei gravity theory, the other is an ultra-relativistic limit yielding a so-called Carroll gravity theory. We present both gravity theories in a first-order formalism and show that in both cases the equations of motion (i) lead to constraints on the geometry and (ii) are not sufficient to solve for all of the components of the connection fields in terms of the other fields. Using a second-order formalism we show that these independent components serve as Lagrange multipliers for the geometric constraints we found earlier. We point out a few noteworthy differences between Carroll and Galilei gravity and give some examples of matter couplings.
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (71 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received in...
Nelson, George
2004-01-01
Gravity is the name given to the phenomenon that any two masses, like you and the Earth, attract each other. One pulls on the Earth and the Earth pulls on one the same amount. And one does not have to be touching. Gravity acts over vast distances, like the 150 million kilometers (93 million miles) between the Earth and the Sun or the billions of…
Streaming gravity mode instability
International Nuclear Information System (INIS)
Wang Shui.
1989-05-01
In this paper, we study the stability of a current sheet with a sheared flow in a gravitational field which is perpendicular to the magnetic field and plasma flow. This mixing mode caused by a combined role of the sheared flow and gravity is named the streaming gravity mode instability. The conditions of this mode instability are discussed for an ideal four-layer model in the incompressible limit. (author). 5 refs
Quantum massive conformal gravity
Energy Technology Data Exchange (ETDEWEB)
Faria, F.F. [Universidade Estadual do Piaui, Centro de Ciencias da Natureza, Teresina, PI (Brazil)
2016-04-15
We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed. (orig.)
Garland, G D; Wilson, J T
2013-01-01
The Earth's Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth's crust; interp
Gravity Before Einstein and Schwinger Before Gravity
Trimble, Virginia L.
2012-05-01
Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity that is being highlighted here the first such dispute. The talk will explore, first, several of the earlier dichotomies: was gravity capable of action at a distance (Newton), or was a transmitting ether required (many others). Did it act on everything or only on solids (an odd idea of the Herschels that fed into their ideas of solar structure and sunspots)? Did gravitational information require time for its transmission? Is the exponent of r precisely 2, or 2 plus a smidgeon (a suggestion by Simon Newcomb among others)? And so forth. Second, I will try to say something about Scwinger's lesser known early work and how it might have prefigured his "source theory," beginning with "On the Interaction of Several Electrons (the unpublished, 1934 "zeroth paper," whose title somewhat reminds one of "On the Dynamics of an Asteroid," through his days at Berkeley with Oppenheimer, Gerjuoy, and others, to his application of ideas from nuclear physics to radar and of radar engineering techniques to problems in nuclear physics. And folks who think good jobs are difficult to come by now might want to contemplate the couple of years Schwinger spent teaching elementary physics at Purdue before moving on to the MIT Rad Lab for war work.
Automated borehole gravity meter system
International Nuclear Information System (INIS)
Lautzenhiser, Th.V.; Wirtz, J.D.
1984-01-01
An automated borehole gravity meter system for measuring gravity within a wellbore. The gravity meter includes leveling devices for leveling the borehole gravity meter, displacement devices for applying forces to a gravity sensing device within the gravity meter to bring the gravity sensing device to a predetermined or null position. Electronic sensing and control devices are provided for (i) activating the displacement devices, (ii) sensing the forces applied to the gravity sensing device, (iii) electronically converting the values of the forces into a representation of the gravity at the location in the wellbore, and (iv) outputting such representation. The system further includes electronic control devices with the capability of correcting the representation of gravity for tidal effects, as well as, calculating and outputting the formation bulk density and/or porosity
Reitz, Meredith; Stark, Colin; Hung, Chi-Yao; Smith, Breannan; Grinspin, Eitan; Capart, Herve; Li, Liming; Crone, Timothy; Hsu, Leslie; Ling, Hoe
2014-05-01
A complete theoretical understanding of geophysical granular flow is essential to the reliable assessment of landslide and debris flow hazard and for the design of mitigation strategies, but several key challenges remain. Perhaps the most basic is a general treatment of the processes of internal energy dissipation, which dictate the runout velocity and the shape and scale of the affected area. Currently, dissipation is best described by macroscopic, empirical friction coefficients only indirectly related to the grain-scale physics. Another challenge is describing the forces exerted at the boundaries of the flow, which dictate the entrainment of further debris and the erosion of cohesive surfaces. While the granular effects on these boundary forces have been shown to be large compared to predictions from continuum approximations, the link between granular effects and erosion or entrainment rates has not been settled. Here we present preliminary results of a multi-disciplinary study aimed at improving our understanding of granular flow energy dissipation and boundary forces, through an effort to connect grain-scale physics to macroscopic behaviors. Insights into grain-scale force distributions and energy dissipation mechanisms are derived from discrete contact-dynamics simulations. Macroscopic erosion and flow behaviors are documented from a series of granular flow experiments, in which a rotating drum half-filled with grains is placed within a centrifuge payload, in order to drive effective gravity levels up to ~100g and approach the forces present in natural systems. A continuum equation is used to characterize the flowing layer depth and velocity resulting from the force balance between the down-slope pull of gravity and the friction at the walls. In this presentation we will focus on the effect of granular-specific physics such as force chain networks and grain-grain collisions, derived from the contact dynamics simulations. We will describe our efforts to
Directory of Open Access Journals (Sweden)
Maartens Roy
2004-01-01
Full Text Available The observable universe could be a 1+3-surface (the "brane" embedded in a 1+3+$d$-dimensional spacetime (the "bulk", with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the $d$ extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ($sim$TeV level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. General relativity cannot describe gravity at high enough energies and must be replaced by a quantum gravity theory, picking up significant corrections as the fundamental energy scale is approached. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review discusses the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall-Sundrum models.
Geometric flows in Horava-Lifshitz gravity
Bakas, Ioannis; Lust, Dieter; Petropoulos, Marios
2010-01-01
We consider instanton solutions of Euclidean Horava-Lifshitz gravity in four dimensions satisfying the detailed balance condition. They are described by geometric flows in three dimensions driven by certain combinations of the Cotton and Ricci tensors as well as the cosmological-constant term. The deformation curvature terms can have competing behavior leading to a variety of fixed points. The instantons interpolate between any two fixed points, which are vacua of topologically massive gravity with Lambda > 0, and their action is finite. Special emphasis is placed on configurations with SU(2) isometry associated with homogeneous but generally non-isotropic Bianchi IX model geometries. In this case, the combined Ricci-Cotton flow reduces to an autonomous system of ordinary differential equations whose properties are studied in detail for different couplings. The occurrence and stability of isotropic and anisotropic fixed points are investigated analytically and some exact solutions are obtained. The correspond...
Granular flow down a flexible inclined plane
Directory of Open Access Journals (Sweden)
Sonar Prasad
2017-01-01
Full Text Available Discrete and continuous systems are commonly studied individually, but seldom together. Indeed, granular flows are typically studied through flows over a rigid base. Here, we investigate the behaviour of granular flows over an inclined, flexible base. The flexible base is modeled as a rigid platform mounted on springs and has one degree of freedom. The base vibrations are introduced by the flow. We simulate such flows through a discrete element method and compare with experiments. We find that a flexible base increased the upper limit of the inclination up to which a steady flow is possible by at least 3 degrees. This stabilized zone may have important implications in applications such as conveyor belts and chutes.
Granular flow down a flexible inclined plane
Sonar, Prasad; Sharma, Ishan; Singh, Jayant
2017-06-01
Discrete and continuous systems are commonly studied individually, but seldom together. Indeed, granular flows are typically studied through flows over a rigid base. Here, we investigate the behaviour of granular flows over an inclined, flexible base. The flexible base is modeled as a rigid platform mounted on springs and has one degree of freedom. The base vibrations are introduced by the flow. We simulate such flows through a discrete element method and compare with experiments. We find that a flexible base increased the upper limit of the inclination up to which a steady flow is possible by at least 3 degrees. This stabilized zone may have important implications in applications such as conveyor belts and chutes.
Constitutive law of dense granular matter
International Nuclear Information System (INIS)
Hatano, Takahiro
2010-01-01
The frictional properties of dense granular matter under steady shear flow are investigated using numerical simulation. Shear flow tends to localize near the driving boundary unless the coefficient of restitution is close to zero and the driving velocity is small. The bulk friction coefficient is independent of shear rate in dense and slow flow, whereas it is an increasing function of shear rate in rapid flow. The coefficient of restitution affects the friction coefficient only in such rapid flow. Contrastingly, in dense and slow regime, the friction coefficient is independent of the coefficient of restitution and mainly determined by the elementary friction coefficient and the rotation of grains. It is found that the mismatch between the vorticity of flow and the angular frequency of grains plays a key role to the frictional properties of sheared granular matter.
Mathematics and Mechanics of Granular Materials
Hill, James M
2005-01-01
Granular or particulate materials arise in almost every aspect of our lives, including many familiar materials such as tea, coffee, sugar, sand, cement and powders. At some stage almost every industrial process involves a particulate material, and it is usually the cause of the disruption to the smooth running of the process. In the natural environment, understanding the behaviour of particulate materials is vital in many geophysical processes such as earthquakes, landslides and avalanches. This book is a collection of current research from some of the major contributors in the topic of modelling the behaviour of granular materials. Papers from every area of current activity are included, such as theoretical, numerical, engineering and computational approaches. This book illustrates the numerous diverse approaches to one of the outstanding problems of modern continuum mechanics.
Slow creep in soft granular packings.
Srivastava, Ishan; Fisher, Timothy S
2017-05-14
Transient creep mechanisms in soft granular packings are studied numerically using a constant pressure and constant stress simulation method. Rapid compression followed by slow dilation is predicted on the basis of a logarithmic creep phenomenon. Characteristic scales of creep strain and time exhibit a power-law dependence on jamming pressure, and they diverge at the jamming point. Microscopic analysis indicates the existence of a correlation between rheology and nonaffine fluctuations. Localized regions of large strain appear during creep and grow in magnitude and size at short times. At long times, the spatial structure of highly correlated local deformation becomes time-invariant. Finally, a microscale connection between local rheology and local fluctuations is demonstrated in the form of a linear scaling between granular fluidity and nonaffine velocity.
Chevoir, François; Gondret, Philippe; Lassarre, Sylvain; Lebacque, Jean-Patrick; Schreckenberg, Michael
2009-01-01
This book covers several research fields, all of which deal with transport. Three main topics are treated: road traffic, granular matter, and biological transport. Different points of view, i.e. modelling, simulations, experiments, and phenomenological observations, are considered. Sub-topics include: highway or urban vehicular traffic (dynamics of traffic, macro/micro modelling, measurements, data analysis, security issues, psychological issues), pedestrian traffic, animal traffic (e.g. social insects), collective motion in biological systems (molecular motors...), granular flow (dense flows, intermittent flows, solid/liquid transition, jamming, force networks, fluid and solid friction), networks (biological networks, urban traffic, the internet, vulnerability of networks, optimal transport networks) and cellular automata applied to the various aforementioned fields.
Submarine granular flow down a rough plane
Nicolas, Maxime; Cassar, Cyril; Pouliquen, Olivier
2003-11-01
We lead experiments of submarine granular flows in a water tank. The particles are spherical 100 microns glass beads and flow down a rough inclined plane from a reservoir with a controlled opening. Different flow regimes are observed, the flow velocity and thickness are measured. The basal water pressure is also measured and give information on the suspension rate of the flow. No flow was observed for an angle below 24 degrees. The flow velocity increases smoothly for a [24-36] degrees inclination range, and a strong velocity increase occurs for inclination over 36 degrees. The thickness of the flow decreases when inclination increases but no abrupt change of thickness is observed around 36 degrees. That suggests that a transition exists between a granular regime, where friction on the rough plane and particle contacts are dominant, and a suspension regime where basal friction vanishes. A thin film ripple instability is also observed for large inclination angles.
Evaluating Energy Flux in Vibrofluidized Granular Bed
Directory of Open Access Journals (Sweden)
N. A. Sheikh
2013-01-01
Full Text Available Granular flows require sustained input of energy for fluidization. A level of fluidization depends on the amount of heat flux provided to the flow. In general, the dissipation of the grains upon interaction balances the heat inputs and the resultant flow patterns can be described using hydrodynamic models. However, with the increase in packing fraction, the heat fluxes prediction of the cell increases. Here, a comparison is made for the proposed theoretical models against the MD simulations data. It is observed that the variation of packing fraction in the granular cell influences the heat flux at the base. For the elastic grain-base interaction, the predictions vary appreciably compared to MD simulations, suggesting the need to accurately model the velocity distribution of grains for averaging.
Granularity controlled irradiation response of cuprate superconductors
International Nuclear Information System (INIS)
Mishra, N.C.; Behera, D.; Mohanty, T.; Mohanta, D.; Kanjilal, D.; Mehta, G.K.; Pinto, R.
1999-01-01
Confining to an energy range where ions can neither create defects through elastic energy loss nor they can create defects through latent track formation, we study the effect of 140 MeV Si-ion irradiation in YBa 2 Cu 3 O 7-x (YBCO). We show that the evolution of superconducting and normal state properties in such situation is largely governed by the initial defects structure, particularly the grain boundary characteristics of the YBCO system. Both intra- and inter-granular defect structure in films of two batches were made widely different by having Ag as composite and substituent in one and by aging the other prior to irradiation. Evolution of the resistivity vs temperature characteristics in these films with ion fluence reveals the importance of Ag in bringing about both inter- and intra-granular modifications and making the films insensitive to ion irradiation
Experiments and DEM Simulations of Granular Ratcheting
Zorzi Gianluca; Artoni Riccardo; Gabrieli Fabio
2017-01-01
In this work we studied the effect of cyclic loading on a granular packing by means of numerical simulations and experiments. A confined packing of glass beads was prepared and one of the walls was moved cyclically with a prescribed amplitude of the order of the particle diameter. Different amplitudes were tested, and their effect on the free surface evolution, the force transmitted to the moving wall and the displacement patterns in the material was characterized. Discrete numerical simulati...
Biological and robotic movement through granular media
Goldman, Daniel
2008-03-01
We discuss laboratory experiments and numerical simulations of locomotion of biological organisms and robots on and within a granular medium. Terrestrial locomotion on granular media (like desert and beach sand) is unlike locomotion on rigid ground because during a step the material begins as a solid, becomes a fluid and then re-solidifies. Subsurface locomotion within granular media is unlike swimming in water for similar reasons. The fluidization and solidification depend on the packing properties of the material and can affect limb penetration depth and propulsive force. Unlike aerial and aquatic locomotion in which the Navier-Stokes equations can be used to model environment interaction, models for limb interaction with granular media do not yet exist. To study how the fluidizing properties affect speed in rapidly running and swimming lizards and crabs, we use a trackway composed of a fluidized bed of of 250 μm glass spheres. Pulses of air to the bed set the solid volume fraction 0.59lizard and a species of crab (masses 20 grams) reveal that as Q increases, the average running speed of an animal decreases proportionally to √M/A-const(1-Q/Qf) where M is the mass of the animal and A is a characteristic foot area. While the crabs decrease speed by nearly 75 % as the material weakens to a fluid, the zebra tailed lizard uses long toes and a plantigrade foot posture at foot impact to maintain high speed ( 1.5 m/sec). We compare our biological results to systematic studies of a physical model of an organism, a 2 kg hexapedal robot SandBot. We find that the robot speed sensitively depends on φ and the details of the limb trajectory. We simulate the robot locomotion by computing ground reaction forces on a numerical model of the robot using a soft-sphere Molecular Dynamics code.
Characteristics of undulatory locomotion in granular media
Peng, Zhiwei; Pak, On Shun; Elfring, Gwynn J.
2015-01-01
Undulatory locomotion is ubiquitous in nature and observed in different media, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Despite the similarity in the undulating pattern, the swimming characteristics depend on the rheological properties of different media. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of valida...
Arching Structures in Granular Sedimentary Deposits
Czech Academy of Sciences Publication Activity Database
Kulaviak, Lukáš; Hladil, Jindřich; Růžička, Marek; Drahoš, Jiří; Saint-Lary, L.
2013-01-01
Roč. 246, SEP (2013), s. 269-277 ISSN 0032-5910 R&D Projects: GA ČR GA104/07/1110; GA AV ČR IAAX00130702; GA MŠk(CZ) LG11014 Institutional support: RVO:67985858 ; RVO:67985831 Keywords : wet granulars * deposit * arching structure Subject RIV: CI - Industrial Chemistry, Chemical Engineering; DB - Geology ; Mineralogy (GLU-S) Impact factor: 2.269, year: 2013
Swimming in a granular frictional fluid
Goldman, Daniel
2012-02-01
X-ray imaging reveals that the sandfish lizard swims within granular media (sand) using axial body undulations to propel itself without the use of limbs. To model the locomotion of the sandfish, we previously developed an empirical resistive force theory (RFT), a numerical sandfish model coupled to an experimentally validated Discrete Element Method (DEM) model of the granular medium, and a physical robot model. The models reveal that only grains close to the swimmer are fluidized, and that the thrust and drag forces are dominated by frictional interactions among grains and the intruder. In this talk I will use these models to discuss principles of swimming within these granular ``frictional fluids". The empirical drag force laws are measured as the steady-state forces on a small cylinder oriented at different angles relative to the displacement direction. Unlike in Newtonian fluids, resistive forces are independent of speed. Drag forces resemble those in viscous fluids while the ratio of thrust to drag forces is always larger in the granular media than in viscous fluids. Using the force laws as inputs, the RFT overestimates swimming speed by approximately 20%. The simulation reveals that this is related to the non-instantaneous increase in force during reversals of body segments. Despite the inaccuracy of the steady-state assumption, we use the force laws and a recently developed geometric mechanics theory to predict optimal gaits for a model system that has been well-studied in Newtonian fluids, the three-link swimmer. The combination of the geometric theory and the force laws allows us to generate a kinematic relationship between the swimmer's shape and position velocities and to construct connection vector field and constraint curvature function visualizations of the system dynamics. From these we predict optimal gaits for forward, lateral and rotational motion. Experiment and simulation are in accord with the theoretical prediction, and demonstrate that
Spatial correlations in compressible granular flows
Van Noije, T. P. C.; Ernst, M. H.; Brito López, Ricardo
1998-01-01
The clustering instability in freely evolving granular fluids manifests itself in the density-density correlation function and structure factor. These functions are calculated from fluctuating hydrodynamics. As time increases, the structure factor of density fluctuations develops a maximum, which shifts to smaller wave numbers (growing correlation length). Furthermore, the inclusion of longitudinal velocity fluctuations changes long-range correlations in the flow field qualitatively and exten...
Iodine Gas Trapping using Granular Porous Bismuth
Energy Technology Data Exchange (ETDEWEB)
Yang, Jae Hwan; Shin, Jin Myeong; Park, Jang Jin; Park, Geun Il [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Yim, Mansung [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)
2014-05-15
{sup 129}I is a radionuclide with a very long half-life of 1.57 Χ 10{sup 7} years and has negative health effects to the human body. Therefore, the emission of {sup 129}I into the air is closely regulated by the Environmental Protection Agency (EPA). Many methods for trapping gaseous {sup 129}I have been developed thus far, including wet scrubbing and adsorption using silver loaded zeolites. Although wet scrubbing can effectively remove iodine, it suffers from corrosion of the vessel due to high concentration of the scrubbing solution. Silver loaded zeolites also show effectiveness in capturing {sup 129}I gas, yet weak thermal stability of physisorbed iodine remains a challenge. We studied a novel and facile method to trap iodine gas using bismuth. Granular bismuth having many pores was synthesized using bismuth nitrate and polyvinyl alcohol as a bismuth precursor and pore forming agent, respectively. Reaction of iodine and our samples resulted in an iodine capturing capacity of more than 2 times that of the commercial grade silver exchanged zeolite (AgX). Granular porous bismuths synthesized using bismuth nitrate and PVA show a promising performance in capturing iodine gas. The use of bismuth in trapping {sup 129}I gas can reduce the process cost as bismuth is cheap. Further study is going on to improve the mechanical property of granular porous bismuths for their easy handling.
Characterization of undulatory locomotion in granular media
Peng, Zhiwei; Pak, On Shun; Elfring, Gwynn
2015-11-01
Undulatory locomotion is ubiquitous in nature, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but a recently proposed resistive force theory (RFT) in granular media has been shown useful in studying the locomotion of a sand-swimming lizard. Here we employ this model to investigate the swimming characteristics of an undulating slender filament of both finite and infinite length. For infinite swimmers, similar to results in viscous fluids, the sawtooth waveform is found to be optimal for propulsion speed at a given power consumption. We also compare the swimming characteristics of sinusoidal and sawtooth swimmers with swimming in viscous fluids. More complex swimming dynamics emerge when the assumption of an infinite swimmer is removed. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swimmer. The results complement our understanding of undulatory locomotion and provide insights into the effective design of locomotive systems in granular media.
Rough – Granular Computing knowledge discovery models
Directory of Open Access Journals (Sweden)
Mohammed M. Eissa
2016-11-01
Full Text Available Medical domain has become one of the most important areas of research in order to richness huge amounts of medical information about the symptoms of diseases and how to distinguish between them to diagnose it correctly. Knowledge discovery models play vital role in refinement and mining of medical indicators to help medical experts to settle treatment decisions. This paper introduces four hybrid Rough – Granular Computing knowledge discovery models based on Rough Sets Theory, Artificial Neural Networks, Genetic Algorithm and Rough Mereology Theory. A comparative analysis of various knowledge discovery models that use different knowledge discovery techniques for data pre-processing, reduction, and data mining supports medical experts to extract the main medical indicators, to reduce the misdiagnosis rates and to improve decision-making for medical diagnosis and treatment. The proposed models utilized two medical datasets: Coronary Heart Disease dataset and Hepatitis C Virus dataset. The main purpose of this paper was to explore and evaluate the proposed models based on Granular Computing methodology for knowledge extraction according to different evaluation criteria for classification of medical datasets. Another purpose is to make enhancement in the frame of KDD processes for supervised learning using Granular Computing methodology.
Propulsion via flexible flapping in granular media
Peng, Zhiwei; Ding, Yang; Pietrzyk, Kyle; Elfring, Gwynn; Pak, On Shun
2017-11-01
Biological locomotion in nature is often achieved by the interaction between a flexible body and its surrounding medium. The interaction of a flexible body with granular media is less understood compared with viscous fluids partially due to its complex rheological properties. In this work, we explore the effect of flexibility on granular propulsion by considering a simple mechanical model in which a rigid rod is connected to a torsional spring that is under a displacement actuation using a granular resistive force theory. Through a combined numerical and asymptotic investigation, we characterize the propulsive dynamics of such a flexible flapper in relation to the actuation amplitude and spring stiffness, and we compare these dynamics with those observed in a viscous fluid. In addition, we demonstrate that the maximum possible propulsive force can be obtained in the steady propulsion limit with a finite spring stiffness and large actuation amplitude. These results may apply to the development of synthetic locomotive systems that exploit flexibility to move through complex terrestrial media. Funding for Z.P. and Y.D. was partially provided by NSFC 394 Grant No. 11672029 and NSAF-NSFC Grant No. U1530401.
Mechanics of Granular Materials (MGM) Cell
1996-01-01
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
Mechanics of Granular Materials Test Cell
1998-01-01
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)
Mechanics of Granular Materials (MGM) Flight Hardware
1997-01-01
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)
A coupled FVM-DEM method to simulate internal erosion process in micro scale granular system
Feng, Q.; Man, T.; Hill, K. M.; Fu, X.
2017-12-01
This work presents a three dimensional coupling DEM-FVM method to simulate and analyze internal erosion behavior in a micro-scale granular system. The FVM (Finite Volume Method) part is set to simulate the seepage flow through the simulation field, providing the spatial distribution of fluid conditions (e.g., water discharge and confining pressure). The DEM (Discrete Element Method) part helps reproduce the details, such as the location, movement and rotation of soil particles driven by the resolved flow, and update the parameters used in the FVM part (e.g., porosity and grain size gradation). The simulation result is proved to be stable and reliable by verified convergence and symmetry in velocity profile as well as by reproduced rheology rules of granular flow. Then a series of cases with different boundary conditions were simulated. The value of critical shear stress, which is an essential parameter in macroscopic modeling framework, was statistically drawn within the granular system. It was shown that the value of critical shear stress remains a constant under given soil gradation and normal pressure, no matter how the hydraulic gradient changes. This finding is consistent with traditional assumption of being constant and shows the capability of reproducing macroscopic properties of soil through using the FVM-DEM modeling approach.
Ansari, Istafaul Haque; Rivas, Nicolas; Alam, Meheboob
2018-01-01
We report patterns consisting of coexistence of synchronous and asynchronous states [for example, a granular gas co-existing with (i) bouncing bed, (ii) undulatory subharmonic waves, and (iii) Leidenfrost-like states] in experiments on vertically vibrated binary granular mixtures in a Hele-Shaw cell. Most experiments have been carried out with equimolar binary mixtures of glass and steel balls of same diameter by varying the total layer height (F ) for a range of shaking acceleration (Γ ). All patterns as well as the related phase diagram in the (Γ ,F ) plane have been reproduced via molecular dynamics simulations of the same system. The segregation of heavier and lighter particles along the horizontal direction is shown to be the progenitor of such phase-coexisting patterns as confirmed in both experiment and simulation. At strong shaking we uncover a partial convection state in which a pair of convection rolls is found to coexist with a Leidenfrost-like state. The crucial role of the relative number density of two species on controlling the buoyancy-driven granular convection is demonstrated. The onset of horizontal segregation can be explained in terms of an anisotropic diffusion tensor.
Settling properties of aerobic granular sludge (AGS) and aerobic granular sludge molasses (AGSM)
Mat Saad, Azlina; Aini Dahalan, Farrah; Ibrahim, Naimah; Yasina Yusuf, Sara; Aqlima Ahmad, Siti; Khalil, Khalilah Abdul
2018-03-01
Aerobic granulation technology is applied to treat domestic and industrial wastewater. The Aerobic granular sludge (AGS) cultivated has strong properties that appears to be denser and compact in physiological structure compared to the conventional activated sludge. It offers rapid settling for solid:liquid separation in wastewater treatment. Aerobic granules were developed using sequencing batch reactor (SBR) with intermittent aerobic - anaerobic mode with 8 cycles in 24 hr. This study examined the settling velocity performance of cultivated aerobic granular sludge (AGS) and aerobic granular sludge molasses (AGSM). The elemental composition in both AGS and AGSM were determined using X-ray fluorescence (XRF). The results showed that AGSM has higher settling velocity 30.5 m/h compared to AGS.
Gravity and embryonic development
Young, R. S.
1976-01-01
The relationship between the developing embryo (both plant and animal) and a gravitational field has long been contemplated. The difficulty in designing critical experiments on the surface of the earth because of its background of 1 g, has been an obstacle to a resolution of the problem. Biological responses to gravity (particularly in plants) are obvious in many cases; however, the influence of gravity as an environmental input to the developing embryo is not as obvious and has proven to be extremely difficult to define. In spite of this, over the years numerous attempts have been made using a variety of embryonic materials to come to grips with the role of gravity in development. Three research tools are available: the centrifuge, the clinostat, and the orbiting spacecraft. Experimental results are now available from all three sources. Some tenuous conclusions are drawn, and an attempt at a unifying theory of gravitational influence on embryonic development is made.
International Nuclear Information System (INIS)
Novozhilov, Yu.V.; Vassilevich, D.V.
1991-01-01
We review the induced-gravity approach according to which the Einstein gravity is a long-wavelength effect induced by underlying fundamental quantum fields due to the dynamical-scale symmetry breaking. It is shown that no ambiguities arise in the definition of the induced Newton and cosmological constants if one works with the path integral for fundamental fields in the low-scale region. The main accent is on a specification of the path integral which enables us to utilize the unitarity condition and thereby avoid ambiguities. Induced Einstein equations appear from the symmetry condition that the path integral of fundamental fields for a slowly varying metric is invariant under the local vertical strokeGL(4, R)-transformations of a tetrad, which contain the local Euclidean Lorentz, O(4)-rotations as a subgroup. The relatinship to induced quantum gravity is briefly outlined. (orig.)
Gerhardt, Claus
2018-01-01
A unified quantum theory incorporating the four fundamental forces of nature is one of the major open problems in physics. The Standard Model combines electro-magnetism, the strong force and the weak force, but ignores gravity. The quantization of gravity is therefore a necessary first step to achieve a unified quantum theory. In this monograph a canonical quantization of gravity has been achieved by quantizing a geometric evolution equation resulting in a gravitational wave equation in a globally hyperbolic spacetime. Applying the technique of separation of variables we obtain eigenvalue problems for temporal and spatial self-adjoint operators where the temporal operator has a pure point spectrum with eigenvalues $\\lambda_i$ and related eigenfunctions, while, for the spatial operator, it is possible to find corresponding eigendistributions for each of the eigenvalues $\\lambda_i$, if the Cauchy hypersurface is asymptotically Euclidean or if the quantized spacetime is a black hole with a negative cosmological ...
Ortín, Tomás
2015-01-01
Self-contained and comprehensive, this definitive new edition of Gravity and Strings is a unique resource for graduate students and researchers in theoretical physics. From basic differential geometry through to the construction and study of black-hole and black-brane solutions in quantum gravity - via all the intermediate stages - this book provides a complete overview of the intersection of gravity, supergravity, and superstrings. Now fully revised, this second edition covers an extensive array of topics, including new material on non-linear electric-magnetic duality, the electric-tensor formalism, matter-coupled supergravity, supersymmetric solutions, the geometries of scalar manifolds appearing in 4- and 5-dimensional supergravities, and much more. Covering reviews of important solutions and numerous solution-generating techniques, and accompanied by an exhaustive index and bibliography, this is an exceptional reference work.
International Nuclear Information System (INIS)
Rumpf, H.
1987-01-01
We begin with a naive application of the Parisi-Wu scheme to linearized gravity. This will lead into trouble as one peculiarity of the full theory, the indefiniteness of the Euclidean action, shows up already at this level. After discussing some proposals to overcome this problem, Minkowski space stochastic quantization will be introduced. This will still not result in an acceptable quantum theory of linearized gravity, as the Feynman propagator turns out to be non-causal. This defect will be remedied only after a careful analysis of general covariance in stochastic quantization has been performed. The analysis requires the notion of a metric on the manifold of metrics, and a natural candidate for this is singled out. With this a consistent stochastic quantization of Einstein gravity becomes possible. It is even possible, at least perturbatively, to return to the Euclidean regime. 25 refs. (Author)
Directory of Open Access Journals (Sweden)
Cahill R. T.
2015-10-01
Full Text Available A new quantum gravity experiment is reported with the data confirming the generali- sation of the Schrödinger equation to include the interaction of the wave function with dynamical space. Dynamical space turbulence, via this interaction process, raises and lowers the energy of the electron wave function, which is detected by observing conse- quent variations in the electron quantum barrier tunnelling rate in reverse-biased Zener diodes. This process has previously been reported and enabled the measurement of the speed of the dynamical space flow, which is consistent with numerous other detection experiments. The interaction process is dependent on the angle between the dynamical space flow velocity and the direction of the electron flow in the diode, and this depen- dence is experimentally demonstrated. This interaction process explains gravity as an emergent quantum process, so unifying quantum phenomena and gravity. Gravitational waves are easily detected.
The role of fluid viscosity in an immersed granular collapse
Directory of Open Access Journals (Sweden)
Yang Geng Chao
2017-01-01
Full Text Available Instabilities of immersed slopes and cliffs can lead to catastrophic events that involve a sudden release of huge soil mass. The scaled deposit height and runout distance are found to follow simple power laws when a granular column collapses on a horizontal plane. However, if the granular column is submerged in a fluid, the mobility of the granular collapse due to high inertia effects will be reduced by fluid-particle interactions. In this study, the effects of fluid viscosity on granular collapse is investigated qualitatively by adopting a numerical approach based on the coupled lattice Boltzmann method (LBM and discrete element method (DEM. It is found that the granular collapse can be dramatically slowed down due to the presence of viscous fluids. For the considered granular configuration, when the fluid viscosity increases. the runout distance decreases and the final deposition shows a larger deposit angle.
Mechanical trapping of particles in granular media
Kerimov, Abdulla; Mavko, Gary; Mukerji, Tapan; Al Ibrahim, Mustafa A.
2018-02-01
Mechanical trapping of fine particles in the pores of granular materials is an essential mechanism in a wide variety of natural and industrial filtration processes. The progress of invading particles is primarily limited by the network of pore throats and connected pathways encountered by the particles during their motion through the porous medium. Trapping of invading particles is limited to a depth defined by the size, shape, and distribution of the invading particles with respect to the size, shape, and distribution of the host porous matrix. Therefore, the trapping process, in principle, can be used to obtain information about geometrical properties, such as pore throat and particle size, of the underlying host matrix. A numerical framework is developed to simulate the mechanical trapping of fine particles in porous granular media with prescribed host particle size, shape, and distribution. The trapping of invading particles is systematically modeled in host packings with different host particle distributions: monodisperse, bidisperse, and polydisperse distributions of host particle sizes. Our simulation results show quantitatively and qualitatively to what extent trapping behavior is different in the generated monodisperse, bidisperse, and polydisperse packings of spherical particles. Depending on host particle size and distribution, the information about extreme estimates of minimal pore throat sizes of the connected pathways in the underlying host matrix can be inferred from trapping features, such as the fraction of trapped particles as a function of invading particle size. The presence of connected pathways with minimum and maximum of minimal pore throat diameters can be directly obtained from trapping features. This limited information about the extreme estimates of pore throat sizes of the connected pathways in the host granular media inferred from our numerical simulations is consistent with simple geometrical estimates of extreme value of pore and
Mutiscale Modeling of Segregation in Granular Flows
Energy Technology Data Exchange (ETDEWEB)
Sun, Jin [Iowa State Univ., Ames, IA (United States)
2007-01-01
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
Directory of Open Access Journals (Sweden)
Roy Maartens
2010-09-01
Full Text Available The observable universe could be a 1+3-surface (the “brane” embedded in a 1+3+d-dimensional spacetime (the “bulk”, with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the d extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak (∼ TeV level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity “leaks” into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review analyzes the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall–Sundrum models. We also cover the simplest brane-world models in which 4-dimensional gravity on the brane is modified at low energies – the 5-dimensional Dvali–Gabadadze–Porrati models. Then we discuss co-dimension two branes in 6-dimensional models.
Airborne Gravity: NGS' Gravity Data for CS06 (2012 & 2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2012 & 2013 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for EN01 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Canada, and Lake Ontario collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for CN02 (2013 & 2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2013 & 2014 over 3 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for ES01 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida, the Bahamas, and the Atlantic Ocean collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of...
Airborne Gravity: NGS' Gravity Data for CN03 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2014 over one survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for AN03 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 and 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for PN01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for California and Oregon collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for AN08 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2016 over one survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for TS01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Puerto Rico and the Virgin Islands collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for EN04 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Michigan and Lake Huron collected in 2012 over 1 survey. This data set is part of the Gravity for the Re-definition of the American...
Pizzo, Nick
2017-11-01
A simple criterion for water particles to surf an underlying surface gravity wave is presented. It is found that particles travelling near the phase speed of the wave, in a geometrically confined region on the forward face of the crest, increase in speed. The criterion is derived using the equation of John (Commun. Pure Appl. Maths, vol. 6, 1953, pp. 497-503) for the motion of a zero-stress free surface under the action of gravity. As an example, a breaking water wave is theoretically and numerically examined. Implications for upper-ocean processes, for both shallow- and deep-water waves, are discussed.
Granular computing analysis and design of intelligent systems
Pedrycz, Witold
2013-01-01
Information granules, as encountered in natural language, are implicit in nature. To make them fully operational so they can be effectively used to analyze and design intelligent systems, information granules need to be made explicit. An emerging discipline, granular computing focuses on formalizing information granules and unifying them to create a coherent methodological and developmental environment for intelligent system design and analysis. Granular Computing: Analysis and Design of Intelligent Systems presents the unified principles of granular computing along with its comprehensive algo
Flowability of granular materials with industrial applications: an experimental approach
Torres Serra, Joel; Romero Morales, Enrique Edgar; Rodríguez Ferran, Antonio; Caba, Joan; Arderiu, Xavier; Padullés, Josep-Manel; González, Juanjo
2017-01-01
Designing bulk material handling equipment requires a thorough understanding of the mechanical behaviour of powders and grains. Experimental characterization of granular materials is introduced focusing on flowability. A new prototype is presented which performs granular column collapse tests. The device consists of a channel whose design accounts for test inspection using visualization techniques and load measurements. A reservoir is attached where packing state of the granular material can ...
Preliminary 2D numerical modeling of common granular problems
Wyser, Emmanuel; Jaboyedoff, Michel
2017-04-01
Granular studies received an increasing interest during the last decade. Many scientific investigations were successfully addressed to acknowledge the ubiquitous behavior of granular matter. We investigate liquid impacts onto granular beds, i.e. the influence of the packing and compaction-dilation transition. However, a physically-based model is still lacking to address complex microscopic features of granular bed response during liquid impacts such as compaction-dilation transition or granular bed uplifts (Wyser et al. in review). We present our preliminary 2D numerical modeling based on the Discrete Element Method (DEM) using nonlinear contact force law (the Hertz-Mindlin model) for disk shape particles. The algorithm is written in C programming language. Our 2D model provides an analytical tool to address granular problems such as i) granular collapses and ii) static granular assembliy problems. This provides a validation framework of our numerical approach by comparing our numerical results with previous laboratory experiments or numerical works. Inspired by the work of Warnett et al. (2014) and Staron & Hinch (2005), we studied i) the axisymetric collapse of granular columns. We addressed the scaling between the initial aspect ratio and the final runout distance. Our numerical results are in good aggreement with the previous studies of Warnett et al. (2014) and Staron & Hinch (2005). ii) Reproducing static problems for regular and randomly stacked particles provides a valid comparison to results of Egholm (2007). Vertical and horizontal stresses within the assembly are quite identical to stresses obtained by Egholm (2007), thus demonstating the consistency of our 2D numerical model. Our 2D numerical model is able to reproduce common granular case studies such as granular collapses or static problems. However, a sufficient small timestep should be used to ensure a good numerical consistency, resulting in higher computational time. The latter becomes critical
A hydrodynamic model for granular material flows including segregation effects
Directory of Open Access Journals (Sweden)
Gilberg Dominik
2017-01-01
Full Text Available The simulation of granular flows including segregation effects in large industrial processes using particle methods is accurate, but very time-consuming. To overcome the long computation times a macroscopic model is a natural choice. Therefore, we couple a mixture theory based segregation model to a hydrodynamic model of Navier-Stokes-type, describing the flow behavior of the granular material. The granular flow model is a hybrid model derived from kinetic theory and a soil mechanical approach to cover the regime of fast dilute flow, as well as slow dense flow, where the density of the granular material is close to the maximum packing density. Originally, the segregation model has been formulated by Thornton and Gray for idealized avalanches. It is modified and adapted to be in the preferred form for the coupling. In the final coupled model the segregation process depends on the local state of the granular system. On the other hand, the granular system changes as differently mixed regions of the granular material differ i.e. in the packing density. For the modeling process the focus lies on dry granular material flows of two particle types differing only in size but can be easily extended to arbitrary granular mixtures of different particle size and density. To solve the coupled system a finite volume approach is used. To test the model the rotational mixing of small and large particles in a tumbler is simulated.
Granular Leidenfrost effect in vibrated beds with bumpy surfaces.
Lim, E W C
2010-08-01
The effects of subjecting a bed of granular materials to horizontal vibrations by a bumpy oscillating surface have been investigated computationally in this study. The behaviour of the granular bed is determined by the vibration conditions applied which include the vibrating frequency and amplitude as well as the bumpiness of the oscillating surface. Under sufficiently vigorous vibration conditions, the granular Leidenfrost effect whereby the entire granular bed is levitated above the vibrating base by a layer of highly energetic particles may be observed. Granular temperature profiles of systems that exhibit the granular Leidenfrost effect indicate an unequal distribution of energy between particles near the vibrating base and those in the bulk. A bumpy oscillating surface was also observed to be more effective at introducing perturbations and transferring energy into a granular bed. The granular Leidenfrost effect can be induced by the application of larger grain sizes of particles constituting the bumpy vibrating base under vibration conditions that are normally insufficient for the onset of the effect. Lastly, a phase diagram which can be utilized for predicting the behaviours of granular beds that are subjected to oscillations by various types of bumpy surfaces has been constructed based on the simulation results obtained.
A hydrodynamic model for granular material flows including segregation effects
Gilberg, Dominik; Klar, Axel; Steiner, Konrad
2017-06-01
The simulation of granular flows including segregation effects in large industrial processes using particle methods is accurate, but very time-consuming. To overcome the long computation times a macroscopic model is a natural choice. Therefore, we couple a mixture theory based segregation model to a hydrodynamic model of Navier-Stokes-type, describing the flow behavior of the granular material. The granular flow model is a hybrid model derived from kinetic theory and a soil mechanical approach to cover the regime of fast dilute flow, as well as slow dense flow, where the density of the granular material is close to the maximum packing density. Originally, the segregation model has been formulated by Thornton and Gray for idealized avalanches. It is modified and adapted to be in the preferred form for the coupling. In the final coupled model the segregation process depends on the local state of the granular system. On the other hand, the granular system changes as differently mixed regions of the granular material differ i.e. in the packing density. For the modeling process the focus lies on dry granular material flows of two particle types differing only in size but can be easily extended to arbitrary granular mixtures of different particle size and density. To solve the coupled system a finite volume approach is used. To test the model the rotational mixing of small and large particles in a tumbler is simulated.
Johnsen, Ø.; Chevalier, C.; Lindner, A.; Toussaint, R.; Clément, E.; Måløy, K. J.; Flekkøy, E. G.; Schmittbuhl, J.
2008-12-01
We study experimentally the injection of a fluid into a loosely consolidated granular media confined a in quasi two dimensional linear cell geometry, initially close to the jamming transition. In this miscible case of an interstitial fluid flow in a deformable porous phase, the assembly of solid grains can behave as a conducting porous matrix, or form a dense particulate flow when the mechanical coupling with the imposed fluid is strong. The fluidization process is represented by a non-trivial destabilization mechanism determining the subsequent channel formation: A hydrodynamically driven decompaction front manifests itself at the outlet side of the cell. It is distinguished optically from the immobile and strictly conducting jammed material by a sharp contrast in porosity and deformation by particle mobilization. The front is retropropagating (with respect to the average fluid flow) and typically evolves into several localized and parallel zones of enhanced porosity. Within these zones the granular material is unjammed, yielding an effective particle transport. Eventually, when the granular packing is decompacted over the entire system length, the ultimate displacement process is triggered. It is characterized by finger-like patterns empty of grains, dictated by the preferential flow paths prepared by the decompaction front. These channels control entirely the subsequent fluid transport properties of the system. The dynamical and geometrical features of the displacement patterns depend strongly on the identified control parameters: the fluid over-pressure, and the thickness of the granular layer. In practice, the addressed problem might issue important aspects in the formation and sustenance of increased permeability macropore networks as demonstrated in nature and industry through e.g. piping/internal erosion in soils or dams, sand production in oil wells, and "wormholes" in oil sands.
Gravity Data for South America
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (152,624 records) were compiled by the University of Texas at Dallas. This data base was received in June 1992. Principal gravity parameters...
Gravity Station Data for Portugal
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 3064 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Gravity Station Data for Spain
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 28493 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Improving Realism in Reduced Gravity Simulators
Cowley, Matthew; Harvil, Lauren; Clowers, Kurt; Clark, Timothy; Rajulu, Sudhakar
2010-01-01
Since man was first determined to walk on the moon, simulating the lunar environment became a priority. Providing an accurate reduced gravity environment is crucial for astronaut training and hardware testing. This presentation will follow the development of reduced gravity simulators to a final comparison of environments between the currently used systems. During the Apollo program era, multiple systems were built and tested, with several NASA centers having their own unique device. These systems ranged from marionette-like suspension devices where the subject laid on his side, to pneumatically driven offloading harnesses, to parabolic flights. However, only token comparisons, if any, were made between systems. Parabolic flight allows the entire body to fall at the same rate, giving an excellent simulation of reduced gravity as far as the biomechanics and physical perceptions are concerned. While the effects are accurate, there is limited workspace, limited time, and high cost associated with these tests. With all mechanical offload systems only the parts of the body that are actively offloaded feel any reduced gravity effects. The rest of the body still feels the full effect of gravity. The Partial Gravity System (Pogo) is the current ground-based offload system used to training and testing at the NASA Johnson Space Center. The Pogo is a pneumatic type system that allows for offloaded motion in the z-axis and free movement in the x-axis, but has limited motion in the y-axis. The pneumatic system itself is limited by cylinder stroke length and response time. The Active Response Gravity Offload System (ARGOS) is a next generation groundbased offload system, currently in development, that is based on modern robotic manufacturing lines. This system is projected to provide more z-axis travel and full freedom in both the x and y-axes. Current characterization tests are underway to determine how the ground-based offloading systems perform, how they compare to parabolic
Bergshoeff, Eric A.; Hohm, Olaf; Rosseel, Jan; Townsend, Paul K.
2011-01-01
The physical modes of a recently proposed D-dimensional "critical gravity'', linearized about its anti-de Sitter vacuum, are investigated. All "log mode'' solutions, which we categorize as "spin-2'' or "Proca'', arise as limits of the massive spin-2 modes of the noncritical theory. The linearized
Venus - Ishtar gravity anomaly
Sjogren, W. L.; Bills, B. G.; Mottinger, N. A.
1984-01-01
The gravity anomaly associated with Ishtar Terra on Venus is characterized, comparing line-of-sight acceleration profiles derived by differentiating Pioneer Venus Orbiter Doppler residual profiles with an Airy-compensated topographic model. The results are presented in graphs and maps, confirming the preliminary findings of Phillips et al. (1979). The isostatic compensation depth is found to be 150 + or - 30 km.
Directory of Open Access Journals (Sweden)
Rovelli Carlo
1998-01-01
Full Text Available The problem of finding the quantum theory of the gravitational field, and thus understanding what is quantum spacetime, is still open. One of the most active of the current approaches is loop quantum gravity. Loop quantum gravity is a mathematically well-defined, non-perturbative and background independent quantization of general relativity, with its conventional matter couplings. Research in loop quantum gravity today forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained are: (i The computation of the physical spectra of geometrical quantities such as area and volume, which yields quantitative predictions on Planck-scale physics. (ii A derivation of the Bekenstein-Hawking black hole entropy formula. (iii An intriguing physical picture of the microstructure of quantum physical space, characterized by a polymer-like Planck scale discreteness. This discreteness emerges naturally from the quantum theory and provides a mathematically well-defined realization of Wheeler's intuition of a spacetime ``foam''. Long standing open problems within the approach (lack of a scalar product, over-completeness of the loop basis, implementation of reality conditions have been fully solved. The weak part of the approach is the treatment of the dynamics: at present there exist several proposals, which are intensely debated. Here, I provide a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
International Nuclear Information System (INIS)
Banerjee, Rabin; Majhi, Bibhas Ranjan
2010-01-01
Starting from the definition of entropy used in statistical mechanics we show that it is proportional to the gravity action. For a stationary black hole this entropy is expressed as S=E/2T, where T is the Hawking temperature and E is shown to be the Komar energy. This relation is also compatible with the generalized Smarr formula for mass.
Artificial Gravity Research Plan
Gilbert, Charlene
2014-01-01
This document describes the forward working plan to identify what countermeasure resources are needed for a vehicle with an artificial gravity module (intermittent centrifugation) and what Countermeasure Resources are needed for a rotating transit vehicle (continuous centrifugation) to minimize the effects of microgravity to Mars Exploration crewmembers.
Newburgh, Ronald
2010-01-01
It's both surprising and rewarding when an old, standard problem reveals a subtlety that expands its pedagogic value. I realized recently that the role of gravity in the range equation for a projectile is not so simple as first appears. This realization may be completely obvious to others but was quite new to me.
DEFF Research Database (Denmark)
Skielboe, Andreas
Gravity governs the evolution of the universe on the largest scales, and powers some of the most extreme objects at the centers of galaxies. Determining the masses and kinematics of galaxy clusters provides essential constraints on the large-scale structure of the universe, and act as direct probes...
Gunstone, Richard F.; White, Richard T.
1981-01-01
Reports results of a large-scale study that investigated the knowledge of gravity and related principles of mechanics possessed by first-year physics students (N=468) at Monash University, Australia. One conclusion is that students know a lot of physics but do not relate it to the everyday world. (CS)
International Nuclear Information System (INIS)
Aros, Rodrigo; Contreras, Mauricio
2006-01-01
In this work the Poincare-Chern-Simons and anti-de Sitter-Chern-Simons gravities are studied. For both, a solution that can be cast as a black hole with manifest torsion is found. Those solutions resemble Schwarzschild and Schwarzschild-AdS solutions, respectively
Bergmann, P. G.; de Sabbata, V.; Treder, H.-J.
The following topics were dealt with: relativistic heat theories; unified field theory; mixed field theories; de Sitter gauges; black hole entropy; null hypersurface canonical formalism; gauge aspects; superluminal behavior; general relativity; twistor theory; quantum geometry and gravity; strings; Poincaré gauge theory and spacetime quantization.
Burla, Santoshkumar; Mueller, Vitali; Flury, Jakob; Jovanovic, Nemanja
2016-04-01
CHAMP, GRACE and GOCE missions have been successful in the field of satellite geodesy (especially to improve Earth's gravity field models) and have established the necessity towards the next generation gravity field missions. Especially, GRACE has shown its capabilities beyond any other gravity field missions. GRACE Follow-On mission is going to continue GRACE's legacy which is almost identical to GRACE mission with addition of laser interferometry. But these missions are not only quite expensive but also takes quite an effort to plan and to execute. Still there are few drawbacks such as under-sampling and incapability of exploring new ideas within a single mission (ex: to perform different orbit configurations with multi satellite mission(s) at different altitudes). The budget is the major limiting factor to build multi satellite mission(s). Here, we offer a solution to overcome these drawbacks using cubesat/ nanosatellite mission. Cubesats are widely used in research because they are cheaper, smaller in size and building them is easy and faster than bigger satellites. Here, we design a 3D model of GRACE like mission with available sensors and explain how the Attitude and Orbit Control System (AOCS) works. The expected accuracies on final results of gravity field are also explained here.
Gabadadze, Gregory T
2004-01-01
Large-distance modification of gravity may be the mechanism for solving the cosmological constant problem. A simple model of the large-distance modification -- four-dimensional (4D) gravity with the hard mass term-- is problematic from the theoretical standpoint. Here we discuss a different model, the brane-induced gravity, that effectively introduces a soft graviton mass. We study the issues of unitarity, analyticity and causality in this model in more than five dimensions. We show that a consistent prescription for the poles of the Green's function can be specified so that 4D unitarity is preserved. However, in certain instances 4D analyticity cannot be maintained when theory becomes higher dimensional. As a result, one has to sacrifice 4D causality at distances of the order of the present-day Hubble scale. This is a welcome feature for solving the cosmological constant problem, as was recently argued in the literature. We also show that, unlike the 4D massive gravity, the model has no strong-coupling probl...
Gravity separation for oil wastewater treatment
Golomeova, Mirjana; Zendelska, Afrodita; Krstev, Boris; Krstev, Aleksandar
2010-01-01
In this paper, the applications of gravity separation for oil wastewater treatment are presented. Described is operation on conventional gravity separation and parallel plate separation. Key words: gravity separation, oil, conventional gravity separation, parallel plate separation.
Quantum Gravity Effects in Cosmology
Directory of Open Access Journals (Sweden)
Gu Je-An
2018-01-01
Full Text Available Within the geometrodynamic approach to quantum cosmology, we studied the quantum gravity effects in cosmology. The Gibbons-Hawking temperature is corrected by quantum gravity due to spacetime fluctuations and the power spectrum as well as any probe field will experience the effective temperature, a quantum gravity effect.
Quantum Gravity Effects in Cosmology
Gu, Je-An; Pyo Kim, Sang; Shen, Che-Min
2018-01-01
Within the geometrodynamic approach to quantum cosmology, we studied the quantum gravity effects in cosmology. The Gibbons-Hawking temperature is corrected by quantum gravity due to spacetime fluctuations and the power spectrum as well as any probe field will experience the effective temperature, a quantum gravity effect.
Directory of Open Access Journals (Sweden)
A. V. Vikulin
2014-01-01
Full Text Available Gravity phenomena related to the Earth movements in the Solar System and through the Galaxy are reviewed. Such movements are manifested by geological processes on the Earth and correlate with geophysical fields of the Earth. It is concluded that geodynamic processes and the gravity phenomena (including those of cosmic nature are related. The state of the geomedium composed of blocks is determined by stresses with force moment and by slow rotational waves that are considered as a new type of movements [Vikulin, 2008, 2010]. It is shown that the geomedium has typical rheid properties [Carey, 1954], specifically an ability to flow while being in the solid state [Leonov, 2008]. Within the framework of the rotational model with a symmetric stress tensor, which is developed by the authors [Vikulin, Ivanchin, 1998; Vikulin et al., 2012a, 2013], such movement of the geomedium may explain the energy-saturated state of the geomedium and a possibility of its movements in the form of vortex geological structures [Lee, 1928]. The article discusses the gravity wave detection method based on the concept of interactions between gravity waves and crustal blocks [Braginsky et al., 1985]. It is concluded that gravity waves can be recorded by the proposed technique that detects slow rotational waves. It is shown that geo-gravitational movements can be described by both the concept of potential with account of gravitational energy of bodies [Kondratyev, 2003] and the nonlinear physical acoustics [Gurbatov et al., 2008]. Based on the combined description of geophysical and gravitational wave movements, the authors suggest a hypothesis about the nature of spin, i.e. own moment as a demonstration of the space-time ‘vortex’ properties.
Segregation induced fingering instabilities in granular avalanches
Woodhouse, Mark; Thornton, Anthony; Johnson, Chris; Kokelaar, Pete; Gray, Nico
2013-04-01
It is important to be able to predict the distance to which a hazardous natural granular flows (e.g. snow slab avalanches, debris-flows and pyroclastic flows) might travel, as this information is vital for accurate assessment of the risks posed by such events. In the high solids fraction regions of these flows the large particles commonly segregate to the surface, where they are transported to the margins to form bouldery flow fronts. In many natural flows these bouldery margins experience a much greater frictional force, leading to frontal instabilities. These instabilities create levees that channelize the flow vastly increasing the run-out distance. A similar effect can be observed in dry granular experiments, which use a combination of small round and large rough particles. When this mixture is poured down an inclined plane, particle size segregation causes the large particles to accumulate near the margins. Being rougher, the large particles experience a greater friction force and this configuration (rougher material in front of smoother) can be unstable. The instability causes the uniform flow front to break up into a series of fingers. A recent model for particle size-segregation has been coupled to existing avalanche models through a particle concentration dependent friction law. In this talk numerical solutions of this coupled system are presented and compared to both large scale experiments carried out at the USGS flume and more controlled small scale laboratory experiments. The coupled depth-averaged model captures the accumulation of large particles at the flow front. We show this large particle accumulation at the head of the flow can lead to the break-up of the initially uniform front into a series of fingers. However, we are unable to obtain a fully grid-resolved numerical solution; the width of the fingers decreases as the grid is refined. By considering the linear stability of a steady, fully-developed, bidisperse granular layer it is shown that
Directory of Open Access Journals (Sweden)
Rognon Pierre
2017-01-01
Full Text Available Dense granular flows exhibit fascinating kinematic patterns characterised by strong fluctuations in grain velocities. In this paper, we analyse these fluctuations and discuss their possible role on macroscopic properties such as effective viscosity, non-locality and shear-induced diffusion. The analysis is based on 2D experimental granular flows performed with the stadium shear device and DEM simulations. We first show that, when subjected to shear, grains self-organised into clusters rotating like rigid bodies. The average size of these so-called granular vortices is found to increase and diverge for lower inertial numbers, when flows decelerate and stop. We then discuss how such a microstructural entity and its associated internal length scale, possibly much larger than a grain, may be used to explain two important properties of dense granular flows: (i the existence of shear-induced diffusion of grains characterised by a shear-rate independent diffusivity and (ii the development of boundary layers near walls, where the viscosity is seemingly lower than the viscosity far from walls.
Assessing granular pit construction from larval Neuroptera
Shea, Nicholas; Olafsen, Jeffrey S.; Loudon, Catherine; Steeples, Don W.
2002-03-01
Antlion larvae, Myrmeleon carolinus, build cone-shaped pits in dry sand for prey capture. The surface of these pits are prone to avalanches that can depend upon the physical properties of the sand in the local environment. The antlion larvae are observed to be capable of assessing both sand depth and particle size. In a polydisperse granular environment, the antlion demonstrates the ability to sort the sand by size in a dynamic manner. An imaging technique is developed to investigate the potential role of air viscosity on the pit construction process.
Mach cone in a shallow granular fluid
International Nuclear Information System (INIS)
Heil, Patrick; Rericha, E. C.; Goldman, Daniel I.; Swinney, Harry L.
2004-01-01
We study the V-shaped wake (Mach cone) formed by a cylindrical rod moving through a thin, vertically vibrated granular layer. The wake, analogous to a shock (hydraulic jump) in shallow water, appears for rod velocities v R greater than a critical velocity c. We measure the half angle θ of the wake as a function of v R and layer depth h. The angle satisfies the Mach relation, sin θ=c/v R , where c=√(gh), even for h as small as one-particle diameter
Unifying Suspension and Granular flows near Jamming
Directory of Open Access Journals (Sweden)
DeGiuli Eric
2017-01-01
Full Text Available Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we review a theoretical framework that gives a scaling description of stationary flows of frictionless particles. Our analysis applies both to suspensions and inertial flows of hard particles. We report numerical results in support of the theory, and show the phase diagram that results when friction is added, delineating the regime of validity of the frictionless theory.
Archimedes' principle in fluidized granular systems.
Huerta, D A; Sosa, Victor; Vargas, M C; Ruiz-Suárez, J C
2005-09-01
We fluidize a granular bed in a rectangular container by injecting energy through the lateral walls with high-frequency sinusoidal horizontal vibrations. In this way, the bed is brought to a steady state with no convection. We measured buoyancy forces on light spheres immersed in the bed and found that they obey Archimedes' principle. The buoyancy forces decrease when we reduce the injected energy. By measuring ascension velocities as a function of gamma, we can evaluate the frictional drag of the bed; its exponential dependence agrees very well with previous findings. Rising times of the intruders ascending through the bed were also measured, they increase monotonically as we increase the density.
Rolling friction on a granular medium
de Blasio, Fabio Vittorio; Saeter, May-Britt
2009-02-01
We present experimental results for the rolling of spheres on a granular bed. We use two sets of glass and steel spheres with varying diameters and a high-speed camera to follow the motion of the spheres. Despite the complex phenomena occurring during the rolling, the results show a friction coefficient nearly independent of the velocity (0.45-0.5 for glass and 0.6-0.65 for steel). It is found that for a given sphere density, the large spheres reach a longer distance, a result that may also help explain the rock sorting along natural stone accumulations at the foot of mountain slopes.
Sensors for the CMS High Granularity Calorimeter
Maier, Andreas Alexander
2017-01-01
The CMS experiment is currently developing high granularity calorimeter endcapsfor its HL-LHC upgrade. The design foresees silicon sensors as the active material for the high radiation region close to the beampipe. Regions of lower radiation are additionally equipped with plastic scintillator tiles. This technology is similar to the calorimeter prototypes developed in the framework of the Linear Collider by the CALICE collaboration. The current status of the silicon sensor development is presented. Results of single diode measurements are shown as well as tests of full 6-inch hexagonal sensor wafers. A short summary of test beam results concludes the article.
Granular contact dynamics using mathematical programming methods
DEFF Research Database (Denmark)
Krabbenhoft, K.; Lyamin, A. V.; Huang, J.
2012-01-01
granular contact dynamics formulation uses an implicit time discretization, thus allowing for large time steps. Moreover, in the limit of an infinite time step, the general dynamic formulation reduces to a static formulation that is useful in simulating common quasi-static problems such as triaxial tests...... and similar laboratory experiments. A significant portion of the paper is dedicated to exploring the consequences of the associated frictional sliding rule implied by the variational formulation adopted. In this connection, a new interior-point algorithm for general linear complementarity problems...
Modelling of dc characteristics for granular semiconductors
International Nuclear Information System (INIS)
Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey
2010-01-01
The dc characteristics of granular n-type semiconductors are calculated analytically with the drift-diffusion theory. Electronic trapping at the grain boundaries (GBs) is taken into account. The use of quadratic and linear GB potential profiles in the calculation is compared. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is excellent in a large voltage range. The results show that electronic trapping at the GBs has a remarkable effect on the highly nonlinear I-V characteristics of the material.
Modelling of dc characteristics for granular semiconductors
Energy Technology Data Exchange (ETDEWEB)
Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey, E-mail: aapo.varpula@tkk.f [Department of Micro and Nanosciences, Aalto University, PO Box 13500, FI-00076 Aalto, Espoo (Finland)
2010-11-01
The dc characteristics of granular n-type semiconductors are calculated analytically with the drift-diffusion theory. Electronic trapping at the grain boundaries (GBs) is taken into account. The use of quadratic and linear GB potential profiles in the calculation is compared. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is excellent in a large voltage range. The results show that electronic trapping at the GBs has a remarkable effect on the highly nonlinear I-V characteristics of the material.
Brine Transport Experiments in Granular Salt
Energy Technology Data Exchange (ETDEWEB)
Jordan, Amy B. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Boukhalfa, Hakim [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Caporuscio, Florie Andre [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stauffer, Philip H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-06-06
To gain confidence in the predictive capability of numerical models, experimental validation must be performed to ensure that parameters and processes are correctly simulated. The laboratory investigations presented herein aim to address knowledge gaps for heat-generating nuclear waste (HGNW) disposal in bedded salt that remain after examination of prior field and laboratory test data. Primarily, we are interested in better constraining the thermal, hydrological, and physicochemical behavior of brine, water vapor, and salt when moist salt is heated. The target of this work is to use run-of-mine (RoM) salt; however during FY2015 progress was made using high-purity, granular sodium chloride.
Comparative effects of nitrogen fertigation and granular
Bryla, D R; Machado, RMA
2011-01-01
Comparative effects of nitrogen fertigation and granular fertilizer application on growth and availability of soil nitrogen during establishment of highbush blueberry David R. Bryla1* and Rui M. A. Machado2 1 Horticultural Crops Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Corvallis, OR, USA 2 Departamento de Fitotecnia, Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Universidade de Évora, Évora, Portugal A 2-year study was done to co...
Influence of thermophoresis on particle removal in a moving granular bed filter and heat exchanger
International Nuclear Information System (INIS)
Rudnick, S.N.; First, M.W.; Price, J.M.
1981-01-01
Bench-scale investigations were made to determine the influence of thermophoresis on particle removal in a moving granular bed filter. A continuous flow of 2-mm diameter ceramic granules at ambient temperature entered the top of the filter and moved slowly downward under the influence of gravity countercurrent to the gas stream. At an inlet gas temperature of 240 0 C, gas mass velocity of 0.12 kg/(s.m 2 ), and granule velocities up to 0.015 cm/s, clean bed collection efficiency for a submicrometer sodium chloride aerosol was found to increase the more the gas was cooled, indicating that thermophoretic forces were playing a measurable role in particle collection
Constraining inverse curvature gravity with supernovae
Energy Technology Data Exchange (ETDEWEB)
Mena, Olga; Santiago, Jose; /Fermilab; Weller, Jochen; /University Coll., London /Fermilab
2005-10-01
We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
Robots for manipulation in a micro-gravity environment
Quinn, R. D.; Lawrence, C.
1988-01-01
This paper is concerned with the development of control strategies and mechanisms for robots operating in the micro-gravity environment of Space Station. These robots must be capable of conducting experiments and manufacturing processes without disturbing the micro-gravity environment through base reactions/motions. Approaches discussed for controlling the robot base reactions/motions include strategies making use of manipulators with redundant degrees of freedon, actuators at the robot base, and a redundant (balancing) arm. Two degree-of-freedom, traction-drive joints are discussed as well as the conceptual design for a traction-driven manipulator.
DEM study of granular flow around blocks attached to inclined walls
Samsu, Joel; Zhou, Zongyan; Pinson, David; Chew, Sheng
2017-06-01
Damage due to intense particle-wall contact in industrial applications can cause severe problems in industries such as mineral processing, mining and metallurgy. Studying the flow dynamics and forces on containing walls can provide valuable feedback for equipment design and optimising operations to prolong the equipment lifetime. Therefore, solids flow-wall interaction phenomena, i.e. induced wall stress and particle flow patterns should be well understood. In this work, discrete element method (DEM) is used to study steady state granular flow in a gravity-fed hopper like geometry with blocks attached to an inclined wall. The effects of different geometries, e.g. different wall angles and spacing between blocks are studied by means of a 3D DEM slot model with periodic boundary conditions. The findings of this work include (i) flow analysis in terms of flow patterns and particle velocities, (ii) force distributions within the model geometry, and (iii) wall stress vs. model height diagrams. The model enables easy transfer of the key findings to other industrial applications handling granular materials.
DEM study of granular flow around blocks attached to inclined walls
Directory of Open Access Journals (Sweden)
Samsu Joel
2017-01-01
Full Text Available Damage due to intense particle-wall contact in industrial applications can cause severe problems in industries such as mineral processing, mining and metallurgy. Studying the flow dynamics and forces on containing walls can provide valuable feedback for equipment design and optimising operations to prolong the equipment lifetime. Therefore, solids flow-wall interaction phenomena, i.e. induced wall stress and particle flow patterns should be well understood. In this work, discrete element method (DEM is used to study steady state granular flow in a gravity-fed hopper like geometry with blocks attached to an inclined wall. The effects of different geometries, e.g. different wall angles and spacing between blocks are studied by means of a 3D DEM slot model with periodic boundary conditions. The findings of this work include (i flow analysis in terms of flow patterns and particle velocities, (ii force distributions within the model geometry, and (iii wall stress vs. model height diagrams. The model enables easy transfer of the key findings to other industrial applications handling granular materials.
Industrial processes influenced by gravity
Ostrach, Simon
1988-01-01
In considering new directions for low gravity research with particular regard to broadening the number and types of industrial involvements, it is noted that transport phenomena play a vital role in diverse processes in the chemical, pharmaceutical, food, and biotech industries. Relatively little attention has been given to the role of gravity in such processes. Accordingly, numerous industrial processes and phenomena are identified which involve gravity and/or surface tension forces. Phase separations and mixing are examples that will be significantly different in low gravity conditions. A basis is presented for expanding the scope of the low gravity research program and the potential benefits of such research is indicated.
Analog Systems for Gravity Duals
Hossenfelder, S.
2014-01-01
We show that analog gravity systems exist for charged, planar black holes in asymptotic Anti-de Sitter space. These black holes have been employed to describe, via the gauge-gravity duality, strongly coupled condensed matter systems on the boundary of AdS-space. The analog gravity system is a different condensed matter system that, in a suitable limit, describes the same bulk physics as the theory on the AdS boundary. This combination of the gauge-gravity duality and analog gravity therefore ...
Formation and mechanics of granular waves in gravity and shallow overland flow
Sediment transport in overland flow is a highly complex process involving many properties relative to the flow regime characteristics, soil surface conditions, and type of sediment. From a practical standpoint, most sediment transport studies are concerned with developing relationships of rates of s...
Granular cell tumour of the larynx - A case report | Appiah ...
African Journals Online (AJOL)
Granular cell tumour of the larynx - A case report. P Appiah-Thompson, KK Baidoo. Abstract. Granular cell tumours (GCTs) are benign tumours rarely found in the larynx even though they are common in the head and neck region. The laryngeal tumour may be asymptomatic but typically patients present with hoarseness of ...
Influence of granular strontium chloride as additives on some ...
Indian Academy of Sciences (India)
Influence of granular strontium chloride as additives on some electrical and mechanical properties for pure polyvinyl alcohol. A B Elaydy M Hafez ... Keywords. Polyvinyl-alcohol (PVA); granular strontium chloride, SrCl2; a.c. electrical conductivity; dielectric constant; dielectric loss; Young's modulus; creep relaxation curve.
Immunoreactivity of granular cell lesions of skin, mucosa, and jaw.
Regezi, J A; Zarbo, R J; Courtney, R M; Crissman, J D
1989-10-01
Granular cell lesions from many different sites share similar light and electron microscopic features. Immunologically, however, these lesions do not appear to be a homogenous group. This study determines the extent of immunologic heterogeneity of granular cell lesions from a wide variety of sites in skin, mucosa, and jaw. Thirty-one granular cell lesions (26 granular cell tumors [GCT] and five other granular cell lesions) from 18 different sites were evaluated immunohistochemically for keratins, vimentin, desmin, muscle actin, ACT, HLA-DR, and S-100 protein. Paraffin-embedded sections were utilized with an avidin-biotin complex immunoperoxidase technique. Except for ameloblastomas, all lesions were negative for keratin and positive for vimentin. All lesions were negative for desmin and actin. Positive ACT reactivity was found in one of seven GCT of tongue, a colonic lesion, a nose lesion, and a granular cell ameloblastic fibroma. All lesions were positive for HLA-DR except a few in which fixation appeared inadequate. S-100 immunoreactivity was found in all lesions except the congenital epulis, a GCT of the skin of the nose, a colonic lesion, and the odontogenic tumors. The antigenic profile of GCT of skin and mucosa is consistent with Schwann cell origin. However, some GCT and other granular cell lesions appear to be derived from macrophages, epithelial cells, or other cells. The expression of HLA-DR by granular cells is believed to be unrelated to cellular origin but rather to some common immunologic function.
75 FR 67105 - Granular Polytetrafluoroethylene Resin From Italy and Japan
2010-11-01
... COMMISSION Granular Polytetrafluoroethylene Resin From Italy and Japan AGENCY: United States International... granular polytetrafluoroethylene resin from Italy and Japan. SUMMARY: The Commission hereby gives notice... polytetrafluoroethylene resin from Italy and Japan would be likely to lead to continuation or recurrence of material...
Nonlinear instability and convection in a vertically vibrated granular bed
Shukla, P.; Ansari, I.H.; van der Meer, Roger M.; Lohse, Detlef; Alam, M.
2014-01-01
The nonlinear instability of the density-inverted granular Leidenfrost state and the resulting convective motion in strongly shaken granular matter are analysed via a weakly nonlinear analysis of the hydrodynamic equations. The base state is assumed to be quasi-steady and the effect of harmonic
Long-range interactions in dilute granular systems
Müller, M.K
2008-01-01
In this thesis, on purpose, we focussed on the most challenging, longest ranging potentials. We analyzed granular media of low densities obeying 1/r long-range interaction potentials between the granules. Such systems are termed granular gases and differ in their behavior from ordinary gases by
Surface effects in the acetylation of granular potato starch
Steeneken, P.A.M.; Woortman, A.J.J.
2008-01-01
The occurrence of surface effects in the acetylation of granular potato starch with acetic anhydride to degrees of substitution 0.04-0.2 was studied by two different approaches. The first approach involved the fractionation of granular starch acetates into five different size classes and analysis of
Granular Leidenfrost effect: Experiment and theory of floating particle clusters
Eshuis, Peter; Eshuis, P.G.; van der Meer, Roger M.; van der Weele, J.P.; Lohse, Detlef
2005-01-01
Granular material is vertically vibrated in a 2D container: above a critical shaking strength, and for a sufficient number of beads, a crystalline cluster is elevated and supported by a dilute gaseous layer of fast beads underneath. We call this phenomenon the granular Leidenfrost effect. The
Granular Cell Tumor Of The Esophagus: An Unusual Cause Of ...
African Journals Online (AJOL)
We report an uncommon case of dysphagia caused by a granular cell tumor in a 38 year old black female. Previously documented granular cell tumors are reported as being small and treated endoscopically. This is probably the largest reported in literature and possibly the fi rst documented in the West African subregion.
21 CFR 133.144 - Granular and stirred curd cheese.
2010-04-01
... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Granular and stirred curd cheese. 133.144 Section... (CONTINUED) FOOD FOR HUMAN CONSUMPTION CHEESES AND RELATED CHEESE PRODUCTS Requirements for Specific Standardized Cheese and Related Products § 133.144 Granular and stirred curd cheese. (a) Description. (1...
76 FR 4936 - Granular Polytetrafluoroethylene Resin From Italy
2011-01-27
... Polytetrafluoroethylene Resin From Italy AGENCY: United States International Trade Commission. ACTION: Revised schedule... granular polytetrafluoroethylene resin (``granular PTFE resin'') from Italy. DATES: Effective Date: January... from Italy and Japan (75 FR 67082-67083 and 67105-67108, November 1, 2010). However, Commerce's notice...
Weakly nonlinear analysis of two dimensional sheared granular flow
Saitoh, K.; Hayakawa, Hisao
2011-01-01
Weakly nonlinear analysis of a two dimensional sheared granular flow is carried out under the Lees-Edwards boundary condition. We derive the time dependent Ginzburg–Landau equation of a disturbance amplitude starting from a set of granular hydrodynamic equations and discuss the bifurcation of the
DEFF Research Database (Denmark)
Forsberg, René; Sideris, M.G.; Shum, C.K.
2005-01-01
The gravity field of the earth is a natural element of the Global Geodetic Observing System (GGOS). Gravity field quantities are like spatial geodetic observations of potential very high accuracy, with measurements, currently at part-per-billion (ppb) accuracy, but gravity field quantities are also...... unique as they can be globally represented by harmonic functions (long-wavelength geopotential model primarily from satellite gravity field missions), or based on point sampling (airborne and in situ absolute and superconducting gravimetry). From a GGOS global perspective, one of the main challenges...... is to ensure the consistency of the global and regional geopotential and geoid models, and the temporal changes of the gravity field at large spatial scales. The International Gravity Field Service, an umbrella "level-2" IAG service (incorporating the International Gravity Bureau, International Geoid Service...
Granular motions near the threshold of entrainment
Valyrakis, Manousos; Alexakis, athanasios-Theodosios
2016-04-01
Our society is continuously impacted by significant weather events many times resulting in catastrophes that interrupt our normal way of life. In the context of climate change and increasing urbanisation these "extreme" hydrologic events are intensified both in magnitude and frequency, inducing costs of the order of billions of pounds. The vast majority of such costs and impacts (even more to developed societies) are due to water related catastrophes such as the geomorphic action of flowing water (including scouring of critical infrastructure, bed and bank destabilisation) and flooding. New tools and radically novel concepts are in need, to enable our society becoming more resilient. This presentation, emphasises the utility of inertial sensors in gaining new insights on the interaction of flow hydrodynamics with the granular surface at the particle scale and for near threshold flow conditions. In particular, new designs of the "smart-sphere" device are discussed with focus on the purpose specific sets of flume experiments, designed to identify the exact response of the particle resting at the bed surface for various below, near and above threshold flow conditions. New sets of measurements are presented for particle entrainment from a Lagrangian viewpoint. Further to finding direct application in addressing real world challenges in the water sector, it is shown that such novel sensor systems can also help the research community (both experimentalists and computational modellers) gain a better insight on the underlying processes governing granular dynamics.
Ferromagnetic resonance studies of granular materials (abstract)
Rubinstein, Mark; Das, Badri; Chrisey, D. B.; Horwitz, J.; Koon, N. C.
1994-05-01
We have investigated the ferromagnetic resonance (FMR) spectra of several granular alloys displaying giant magnetoresistance (GMR). For this task, we have produced melt-spun ribbons of Fe5Co15Cu80 and Co20Cu80 by rapid quenching and thin films of Co80Cu20 by pulsed laser deposition. The salient feature of the FMR spectra is the increase of the resonance linewidth as a function of increasing annealing temperature. We have deconvoluted the FMR spectra to a single-domain powder pattern and a multidomain powder pattern. As a function of annealing temperature, the GMR of these samples attains a maximum value. Near the peak of the GMR curve, the FMR spectrum reveals that the ferromagnetic particles are half mono- and half multidomain. Since the maximum size of a single-domain particle is known, this enables us to estimate the spin diffusion length of the Cu conduction electrons. We have also demonstrated, theoretically and experimentally, that the appropriate demagnetizing field to apply to the ensemble of spherical magnetic particles that comprise our granular thin film is simply the field corresponding to the average magnetization.
Ultrasonic compaction of granular geological materials.
Feeney, Andrew; Sikaneta, Sakalima; Harkness, Patrick; Lucas, Margaret
2017-04-01
It has been shown that the compaction of granular materials for applications such as pharmaceutical tableting and plastic moulding can be enhanced by ultrasonic vibration of the compaction die. Ultrasonic vibrations can reduce the compaction pressure and increase particle fusion, leading to higher strength products. In this paper, the potential benefits of ultrasonics in the compaction of geological granular materials in downhole applications are explored, to gain insight into the effects of ultrasonic vibrations on compaction of different materials commonly encountered in sub-sea drilling. Ultrasonic vibrations are applied, using a resonant 20kHz compactor, to the compaction of loose sand and drill waste cuttings derived from oolitic limestone, clean quartz sandstone, and slate-phyllite. For each material, a higher strain for a given compaction pressure was achieved, with higher sample density compared to that in the case of an absence of ultrasonics. The relationships between the operational parameters of ultrasonic vibration amplitude and true strain rate are explored and shown to be dependent on the physical characteristics of the compacting materials. Copyright Â© 2017 Elsevier B.V. All rights reserved.
Statistical mechanics framework for static granular matter
Henkes, Silke; Chakraborty, Bulbul
2009-06-01
The physical properties of granular materials have been extensively studied in recent years. So far, however, there exists no theoretical framework which can explain the observations in a unified manner beyond the phenomenological jamming diagram. This work focuses on the case of static granular matter, where we have constructed a statistical ensemble which mirrors equilibrium statistical mechanics. This ensemble, which is based on the conservation properties of the stress tensor, is distinct from the original Edwards ensemble and applies to packings of deformable grains. We combine it with a field theoretical analysis of the packings, where the field is the Airy stress function derived from the force and torque balance conditions. In this framework, Point J characterized by a diverging stiffness of the pressure fluctuations. Separately, we present a phenomenological mean-field theory of the jamming transition, which incorporates the mean contact number as a variable. We link both approaches in the context of the marginal rigidity picture proposed by Wyart and others.
Magnetic resonance imaging of granular materials
Stannarius, Ralf
2017-05-01
Magnetic Resonance Imaging (MRI) has become one of the most important tools to screen humans in medicine; virtually every modern hospital is equipped with a Nuclear Magnetic Resonance (NMR) tomograph. The potential of NMR in 3D imaging tasks is by far greater, but there is only "a handful" of MRI studies of particulate matter. The method is expensive, time-consuming, and requires a deep understanding of pulse sequences, signal acquisition, and processing. We give a short introduction into the physical principles of this imaging technique, describe its advantages and limitations for the screening of granular matter, and present a number of examples of different application purposes, from the exploration of granular packing, via the detection of flow and particle diffusion, to real dynamic measurements. Probably, X-ray computed tomography is preferable in most applications, but fast imaging of single slices with modern MRI techniques is unmatched, and the additional opportunity to retrieve spatially resolved flow and diffusion profiles without particle tracking is a unique feature.
Three-phase fracturing in granular material
Campbell, James; Sandnes, Bjornar
2015-04-01
There exist numerous geo-engineering scenarios involving the invasion of a gas into a water-saturated porous medium: in fracking, this may occur during the fracking process itself or during subsequent gas penetration into propant beds; the process is also at the heart of carbon dioxide sequestration. We use a bed of water-saturated glass beads confined within a Hele-Shaw cell as a model system to illuminate these processes. Depending on packing density, injection rate and other factors, air injected into this system may invade in a broad variety of patterns, including viscous fingering, capillary invasion, bubble formation and fracturing. Here we focus primarily on the latter case. Fracturing is observed when air is injected into a loosely packed bed of unconsolidated granular material. Our approach allows us to image the complete fracture pattern as it forms, and as such to study both the topographical properties of the resulting pattern (fracture density, braching frequency etc) and the dynamics of its growth. We present an overview of the fracturing phenomenon within the context of pattern formation in granular fluids as a whole. We discuss how fracturing arises from an interplay between frictional, capillary and viscous forces, and demonstrate the influence of various parameters on the result.
Characterizing granular networks using topological metrics
Dijksman, Joshua A.; Kovalcinova, Lenka; Ren, Jie; Behringer, Robert P.; Kramar, Miroslav; Mischaikow, Konstantin; Kondic, Lou
2018-04-01
We carry out a direct comparison of experimental and numerical realizations of the exact same granular system as it undergoes shear jamming. We adjust the numerical methods used to optimally represent the experimental settings and outcomes up to microscopic contact force dynamics. Measures presented here range from microscopic through mesoscopic to systemwide characteristics of the system. Topological properties of the mesoscopic force networks provide a key link between microscales and macroscales. We report two main findings: (1) The number of particles in the packing that have at least two contacts is a good predictor for the mechanical state of the system, regardless of strain history and packing density. All measures explored in both experiments and numerics, including stress-tensor-derived measures and contact numbers depend in a universal manner on the fraction of nonrattler particles, fNR. (2) The force network topology also tends to show this universality, yet the shape of the master curve depends much more on the details of the numerical simulations. In particular we show that adding force noise to the numerical data set can significantly alter the topological features in the data. We conclude that both fNR and topological metrics are useful measures to consider when quantifying the state of a granular system.
Mechanics of Granular Materials labeled hardware
2000-01-01
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).
Mechanics of Granular Materials (MGM) Investigators
2000-01-01
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).
Mechanic of Granular Materials (MGM) Investigator
2000-01-01
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).
Pressure-shear experiments on granular materials.
Energy Technology Data Exchange (ETDEWEB)
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
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.
Sand transport, erosion and granular electrification
DEFF Research Database (Denmark)
Merrison, J.P.
2012-01-01
The transport of granular materials by wind has a major impact on our environment through sand/soil erosion and the generation and transport of atmospheric dust aerosols. Terrestrially the transport of dust involves billions of tons of material every year, influencing the global climate and impac......The transport of granular materials by wind has a major impact on our environment through sand/soil erosion and the generation and transport of atmospheric dust aerosols. Terrestrially the transport of dust involves billions of tons of material every year, influencing the global climate...... can affect grain transport through the generation of intense electric fields and processes of electrostatic assembly. Importantly the transport of sand is characterized by saltation, which is known to be an active process for erosion and therefore a source for dust and sand formation. Using novel...... erosion simulation techniques the link between grain transport rates and erosion rates has been quantified. Furthermore this can be linked to production rates for dust and has been associated with chemical and mineral alteration through a process of mechanical activation of fractured surfaces. This work...
Research on Network Scanning Strategy Based on Information Granularity
Qin, Futong; Shi, Pengfei; Du, Jing; Cheng, Ruosi; Zhou, Yunyan
2017-10-01
As the basic mean to obtain the information of the targets network, network scanning is often used to discover the security risks and vulnerabilities existing on the network. However, with the development of network technology, the scale of network is more and more large, and the network scanning efficiency put forward higher requirements. In this paper, the concept of network scanning information granularity is proposed, and the design method of network scanning strategy based on information granularity is proposed. Based on single information granularity and hybrid information granularity, four network scanning strategies were designed and verified experimentally. Experiments show that the network scanning strategies based on hybrid information granularity can improve the efficiency of network scanning.
The relativistic gravity train
Seel, Max
2018-05-01
The gravity train that takes 42.2 min from any point A to any other point B that is connected by a straight-line tunnel through Earth has captured the imagination more than most other applications in calculus or introductory physics courses. Brachystochron and, most recently, nonlinear density solutions have been discussed. Here relativistic corrections are presented. It is discussed how the corrections affect the time to fall through Earth, the Sun, a white dwarf, a neutron star, and—the ultimate limit—the difference in time measured by a moving, a stationary and the fiducial observer at infinity if the density of the sphere approaches the density of a black hole. The relativistic gravity train can serve as a problem with approximate and exact analytic solutions and as numerical exercise in any introductory course on relativity.
International Nuclear Information System (INIS)
Lamon, Raphael
2010-01-01
Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem. Furthermore, we
Energy Technology Data Exchange (ETDEWEB)
Lamon, Raphael
2010-06-29
Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem
International Nuclear Information System (INIS)
Hartle, J.B.
1985-01-01
Simplicial approximation and the ideas associated with the Regge calculus provide a concrete way of implementing a sum over histories formulation of quantum gravity. A simplicial geometry is made up of flat simplices joined together in a prescribed way together with an assignment of lengths to their edges. A sum over simplicial geometries is a sum over the different ways the simplices can be joined together with an integral over their edge lengths. The construction of the simplicial Euclidean action for this approach to quantum general relativity is illustrated. The recovery of the diffeomorphism group in the continuum limit is discussed. Some possible classes of simplicial complexes with which to define a sum over topologies are described. In two dimensional quantum gravity it is argued that a reasonable class is the class of pseudomanifolds
Gomberoff, Andres
2006-01-01
The 2002 Pan-American Advanced Studies Institute School on Quantum Gravity was held at the Centro de Estudios Cientificos (CECS),Valdivia, Chile, January 4-14, 2002. The school featured lectures by ten speakers, and was attended by nearly 70 students from over 14 countries. A primary goal was to foster interaction and communication between participants from different cultures, both in the layman’s sense of the term and in terms of approaches to quantum gravity. We hope that the links formed by students and the school will persist throughout their professional lives, continuing to promote interaction and the essential exchange of ideas that drives research forward. This volume contains improved and updated versions of the lectures given at the School. It has been prepared both as a reminder for the participants, and so that these pedagogical introductions can be made available to others who were unable to attend. We expect them to serve students of all ages well.
CERN. Geneva
2017-01-01
Extensions of Einstein’s theory of General Relativity are under investigation as a potential explanation of the accelerating expansion rate of the universe. I’ll present a cosmologist’s overview of attempts to test these ideas in an efficient and unbiased manner. I’ll start by introducing the bestiary of alternative gravity theories that have been put forwards. This proliferation of models motivates us to develop model-independent, agnostic tools for comparing the theory space to cosmological data. I’ll introduce the effective field theory for cosmological perturbations, a framework designed to unify modified gravity theories in terms of a manageable set of parameters. Having outlined the formalism, I’ll talk about the current constraints on this framework, and the improvements expected from the next generation of large galaxy clustering, weak lensing and intensity mapping experiments.
International Nuclear Information System (INIS)
Konopleva, N.P.
1996-01-01
The problems of application of nonperturbative quantization methods in the theories of the gauge fields and gravity are discussed. Unification of interactions is considered in the framework of the geometrical gauge fields theory. Vacuum conception in the unified theory of interactions and instantons role in the vacuum structure are analyzed. The role of vacuum solutions of Einstein equations in definition of the gauge field vacuum is demonstrated
Directory of Open Access Journals (Sweden)
Rovelli Carlo
2008-07-01
Full Text Available The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler’s “spacetime foam” intuition. (iii Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv A derivation of the Bekenstein–Hawking black-hole entropy. (v Low-energy calculations, yielding n-point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Rovelli, Carlo
2008-01-01
The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime , is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i) The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii) A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler's "spacetime foam" intuition. (iii) Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv) A derivation of the Bekenstein-Hawking black-hole entropy. (v) Low-energy calculations, yielding n -point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Gravity, Time, and Lagrangians
Huggins, Elisha
2010-01-01
Feynman mentioned to us that he understood a topic in physics if he could explain it to a college freshman, a high school student, or a dinner guest. Here we will discuss two topics that took us a while to get to that level. One is the relationship between gravity and time. The other is the minus sign that appears in the Lagrangian. (Why would one…
Semiclassical unimodular gravity
International Nuclear Information System (INIS)
Fiol, Bartomeu; Garriga, Jaume
2010-01-01
Classically, unimodular gravity is known to be equivalent to General Relativity (GR), except for the fact that the effective cosmological constant Λ has the status of an integration constant. Here, we explore various formulations of unimodular gravity beyond the classical limit. We first consider the non-generally covariant action formulation in which the determinant of the metric is held fixed to unity. We argue that the corresponding quantum theory is also equivalent to General Relativity for localized perturbative processes which take place in generic backgrounds of infinite volume (such as asymptotically flat spacetimes). Next, using the same action, we calculate semiclassical non-perturbative quantities, which we expect will be dominated by Euclidean instanton solutions. We derive the entropy/area ratio for cosmological and black hole horizons, finding agreement with GR for solutions in backgrounds of infinite volume, but disagreement for backgrounds with finite volume. In deriving the above results, the path integral is taken over histories with fixed 4-volume. We point out that the results are different if we allow the 4-volume of the different histories to vary over a continuum range. In this ''generalized'' version of unimodular gravity, one recovers the full set of Einstein's equations in the classical limit, including the trace, so Λ is no longer an integration constant. Finally, we consider the generally covariant theory due to Henneaux and Teitelboim, which is classically equivalent to unimodular gravity. In this case, the standard semiclassical GR results are recovered provided that the boundary term in the Euclidean action is chosen appropriately
Transport phenomena in granular materials: Experiments and simulations
Energy Technology Data Exchange (ETDEWEB)
Ialali, P.; Sarkomaa, P. [Department of Energy and Environmental Engineering, Lappeenranta University of Technology, Lappeenranta (Finland); Mo Li [School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA (United States)
2007-07-01
Granular materials are found in nature and in the technology. Common examples are sand, sugar, snow, synthetic powders, cement and soil. They are collections of individual solid grains with hybrid bulk properties so that they display both solid-like and fluid-like behaviors under various circumstances. Grains are interacting through collisions or contacts either with each other or with confining walls. The transport of mass, momentum and kinetic energy (not thermal energy) has been studied in deforming granular materials both theoretically and experimentally. In static granular media (no deformation), the distribution of forces and contact stresses has attracted a great deal of scientists' attention. In this article, different aspects of transport phenomena in sheared granular media are introduced based on experimental and numerical simulation results obtained by other scientists and via our research. The transport of mass and momentum are basically needed to understand the mixing phenomenon in granular materials. Deformation of granular material (the relative motion of grains) is extremely heterogeneous unlike the ordinary fluids and solids. Also, the most highlighted difference between granular materials and other states of matter is associated with the ineffectiveness of grains thermal energy in building the mechanical and physical properties of granular materials. Instead, the fluctuation of grains kinetic energy plays the major role in controlling the mechanics of granular materials. Strange behaviors of granular materials such as jamming the flow of discharging sand from a hopper and avalanching snow over the surface of mountains can be properly explained only based on the models addressing the transport and the dissipation of grains kinetic energy. (orig.)
Sjogren, W. L.; Ananda, M.; Williams, B. G.; Birkeland, P. W.; Esposito, P. S.; Wimberly, R. N.; Ritke, S. J.
1981-01-01
Results of Pioneer Venus Orbiter observations concerning the gravity field of Venus are presented. The gravitational data was obtained from reductions of Doppler radio tracking data for the Orbiter, which is in a highly eccentric orbit with periapsis altitude varying from 145 to 180 km and nearly fixed periapsis latitude of 15 deg N. The global gravity field was obtained through the simultaneous estimation of the orbit state parameters and gravity coefficients from long-period variations in orbital element rates. The global field has been described with sixth degree and order spherical harmonic coefficients, which are capable of resolving the three major topographical features on Venus. Local anomalies have been mapped using line-of-sight accelerations derived from the Doppler residuals between 40 deg N and 10 deg S latitude at approximately 300 km spatial resolution. Gravitational data is observed to correspond to topographical data obtained by radar altimeter, with most of the gravitational anomalies about 20-30 milligals. Simulations evaluating the isostatic states of two topographic features indicate that at least partial isostasy prevails, with the possibility of complete compensation.
Polar gravity fields from GOCE and airborne gravity
DEFF Research Database (Denmark)
Forsberg, René; Olesen, Arne Vestergaard; Yidiz, Hasan
2011-01-01
Airborne gravity, together with high-quality surface data and ocean satellite altimetric gravity, may supplement GOCE to make consistent, accurate high resolution global gravity field models. In the polar regions, the special challenge of the GOCE polar gap make the error characteristics...... of combination models especially sensitive to the correct merging of satellite and surface data. We outline comparisons of GOCE to recent airborne gravity surveys in both the Arctic and the Antarctic. The comparison is done to new 8-month GOCE solutions, as well as to a collocation prediction from GOCE gradients...... in Antarctica. It is shown how the enhanced gravity field solutions improve the determination of ocean dynamic topography in both the Arctic and in across the Drake Passage. For the interior of Antarctica, major airborne gravity programs are currently being carried out, and there is an urgent need...
Erosion by sliding wear in granular flows: Experiments with realistic contact forces
Stark, C. P.; Hung, C. Y.; Smith, B.; Li, L.; Grinspun, E.; Capart, H.
2015-12-01
Debris flow erosion is a powerful and sometimes dominant process in steep channels. Despite its importance, this phenomenon is relatively little studied in the lab. The large drum experiments of Hsu are a notable exception, in which almost-field-scale impact forces were generated at the head of a synthetic debris flow whose properties (grain size, proportion of fines, etc) were varied widely.A key challenge in these and similar experiments is to explore how erosion rate varies as a function of the scale of the flow (thereby varying inertial stresses, impact forces, etc). The geometrical limitations of most lab experiments, and their short run time, severely limit the scope of such explorations.We achieve this scale exploration in a set of drum erosion experiments by varying effective gravity across several orders of magnitude (1g, 10g, 100g) in a geotechnical centrifuge. By half-filling our 40cm-diameter drum with dry 2.3mm grains, placing a synthetic rock plate at the back and a glass plate at the front 3cm apart, and rotating the drum at 1-50rpm, we simulate wear in a channelized dry granular flow. In contrast to Hsu's experiments, we focus on sliding wear erosion at the flow boundary rather than impact/frictional wear at the flow head. By varying effective gravity from 1g-100g we can tune the pressure exerted by the grains at the boundary without having to change the scale of our apparatus. Using a recently developed depth-averaged, kinetic-energy closure theory for granular flow, we can simultaneously tune the drum rotation rate such that the flow dynamics remain invariant. We can thereby explore how changing the scale of a granular flow, and thus the contact forces of grains on the boundary, controls the rate of rock erosion. Using a small apparatus we can simulate the erosion generated by debris flows several meters deep involving grains up to 10cm in diameter.Our results suggest that sliding wear is the main erosion process, and are consistent with Archard
Controlling wave propagation through nonlinear engineered granular systems
Leonard, Andrea
We study the fundamental dynamic behavior of a special class of ordered granular systems in order to design new, structured materials with unique physical properties. The dynamic properties of granular systems are dictated by the nonlinear, Hertzian, potential in compression and zero tensile strength resulting from the discrete material structure. Engineering the underlying particle arrangement of granular systems allows for unique dynamic properties, not observed in natural, disordered granular media. While extensive studies on 1D granular crystals have suggested their usefulness for a variety of engineering applications, considerably less attention has been given to higher-dimensional systems. The extension of these studies in higher dimensions could enable the discovery of richer physical phenomena not possible in 1D, such as spatial redirection and anisotropic energy trapping. We present experiments, numerical simulation (based on a discrete particle model), and in some cases theoretical predictions for several engineered granular systems, studying the effects of particle arrangement on the highly nonlinear transient wave propagation to develop means for controlling the wave propagation pathways. The first component of this thesis studies the stress wave propagation resulting from a localized impulsive loading for three different 2D particle lattice structures: square, centered square, and hexagonal granular crystals. By varying the lattice structure, we observe a wide range of properties for the propagating stress waves: quasi-1D solitary wave propagation, fully 2D wave propagation with tunable wave front shapes, and 2D pulsed wave propagation. Additionally the effects of weak disorder, inevitably present in real granular systems, are investigated. The second half of this thesis studies the solitary wave propagation through 2D and 3D ordered networks of granular chains, reducing the effective density compared to granular crystals by selectively placing wave
Duan, Yifei; Feng, Zhi-Gang
2017-12-01
Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009)10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.
Duan, Yifei; Feng, Zhi-Gang
2017-12-01
Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009), 10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.
Electrically Driven Liquid Film Boiling Experiment
Didion, Jeffrey R.
2016-01-01
This presentation presents the science background and ground based results that form the basis of the Electrically Driven Liquid Film Boiling Experiment. This is an ISS experiment that is manifested for 2021. Objective: Characterize the effects of gravity on the interaction of electric and flow fields in the presence of phase change specifically pertaining to: a) The effects of microgravity on the electrically generated two-phase flow. b) The effects of microgravity on electrically driven liquid film boiling (includes extreme heat fluxes). Electro-wetting of the boiling section will repel the bubbles away from the heated surface in microgravity environment. Relevance/Impact: Provides phenomenological foundation for the development of electric field based two-phase thermal management systems leveraging EHD, permitting optimization of heat transfer surface area to volume ratios as well as achievement of high heat transfer coefficients thus resulting in system mass and volume savings. EHD replaces buoyancy or flow driven bubble removal from heated surface. Development Approach: Conduct preliminary experiments in low gravity and ground-based facilities to refine technique and obtain preliminary data for model development. ISS environment required to characterize electro-wetting effect on nucleate boiling and CHF in the absence of gravity. Will operate in the FIR - designed for autonomous operation.
Fuel micro-mechanics: homogenization, cracking, granular media
International Nuclear Information System (INIS)
Monerie, Yann
2010-01-01
cracked media. Cracking: The main aim of this topic is the numerical simulation of multiple cracking of strongly heterogeneous media from their sound state to their fractured state. A method called 'Non Smooth Fracture Dynamics' is proposed. It is based on a cohesive-volume finite element model and on a non-regular dynamic multi-body management (implicit scheme). The main theoretical and practical difficulties of the cohesive-volume method are discussed in detail: non-uniqueness of solutions, instabilities, dependence on the mesh system, local diversity, and experimental identification of the cohesive properties. By combining this method with analytical and numerical homogenization techniques, a two-scale volume and surface approach is developed for the cracking of media with a property gradient: the effect of the spatial distribution of weakening inclusions on the macroscopic fracture criteria and on the tortuosity of crack paths is revealed. An intermediate result of this work is the statistical characterization of the representative elementary volumes in cracking and fracture. Granular media: This more recent topic includes the numerical and stochastic analysis of discrete media in the presence or absence of a fluid phase. For the numerical analysis, the non-regular dynamic multi-body method is used. In the case of an interstitial or surrounding fluid, this method is coupled with two other classes of method according to the inertial regime and the size of the system considered: porous medium methods (homogeneous fluid equivalent) or fictitious domain type (direct numerical simulation). These methods are confirmed on fluidization and sedimentation tests. For the analysis, some results are obtained for gravity flows: blocking statistic in silo configuration, compaction effects during undersea avalanches. (author)
On the submerging of a spherical intruder into granular beds
Directory of Open Access Journals (Sweden)
Wu Chuan-Yu
2017-01-01
Full Text Available Granular materials are complex systems and their mechanical behaviours are determined by the material properties of individual particles, the interaction between particles and the surrounding media, which are still incompletely understood. Using an advanced discrete element method (DEM, we simulate the submerging process of a spherical projectile (an intruder into granular materials of various properties with a zero penetration velocity (i.e. the intruder is touching the top surface of the granular bed and released from stationary and examine its settling behaviour. By systematically changing the density and size of the intruder and the particle density (i.e. the density of the particles in the granular bed, we find that the intruder can sink deep into the granular bed even with a zero penetration velocity. Furthermore, we confirm that under certain conditions the granular bed can behave like a Newtonian liquid and the submerging intruder can reach a constant velocity, i.e. the terminal velocity, identical to the settling of a sphere in a liquid, as observed experimentally. A mathematical model is also developed to predict the maximum penetration depth of the intruder. The model predictions are compared with experimental data reported in the literature,good agreement was obtained, demonstrating the model can accurately predict the submerging behaviour of the intruder in the granular media.
On the submerging of a spherical intruder into granular beds
Wu, Chuan-Yu; Zhang, Ling; Chen, Lan
2017-06-01
Granular materials are complex systems and their mechanical behaviours are determined by the material properties of individual particles, the interaction between particles and the surrounding media, which are still incompletely understood. Using an advanced discrete element method (DEM), we simulate the submerging process of a spherical projectile (an intruder) into granular materials of various properties with a zero penetration velocity (i.e. the intruder is touching the top surface of the granular bed and released from stationary) and examine its settling behaviour. By systematically changing the density and size of the intruder and the particle density (i.e. the density of the particles in the granular bed), we find that the intruder can sink deep into the granular bed even with a zero penetration velocity. Furthermore, we confirm that under certain conditions the granular bed can behave like a Newtonian liquid and the submerging intruder can reach a constant velocity, i.e. the terminal velocity, identical to the settling of a sphere in a liquid, as observed experimentally. A mathematical model is also developed to predict the maximum penetration depth of the intruder. The model predictions are compared with experimental data reported in the literature,good agreement was obtained, demonstrating the model can accurately predict the submerging behaviour of the intruder in the granular media.
Sorption of metaldehyde using granular activated carbon
Directory of Open Access Journals (Sweden)
S. Salvestrini
2017-09-01
Full Text Available In this work, the ability of granular activated carbon (GAC to sorb metaldehyde was evaluated. The kinetic data could be described by an intra-particle diffusion model, which indicated that the porosity of the sorbent strongly influenced the rate of sorption. The analysis of the equilibrium sorption data revealed that ionic strength and temperature did not play any significant role in the metaldehyde uptake. The sorption isotherms were successfully predicted by the Freundlich model. The GAC used in this paper exhibited a higher affinity and sorption capacity for metaldehyde with respect to other GACs studied in previous works, probably as a result of its higher specific surface area and high point of zero charge.
Cohesive granular materials composed of nonconvex particles.
Saint-Cyr, Baptiste; Radjai, Farhang; Delenne, Jean-Yves; Sornay, Philippe
2013-05-01
The macroscopic cohesion of granular materials made up of sticky particles depends on the particle shapes. We address this issue by performing contact dynamics simulations of 2D packings of nonconvex aggregates. We find that the macroscopic cohesion is strongly dependent on the strain and stress inhomogeneities developing inside the material. The largest cohesion is obtained for nearly homogeneous deformation at the beginning of unconfined axial compression and it evolves linearly with nonconvexity. Interestingly, the aggregates in a sheared packing tend to form more contacts with fewer neighboring aggregates as the degree of nonconvexity increases. We also find that shearing leads either to an isotropic distribution of tensile contacts or to the same privileged direction as that of compressive contacts.
[Granular cell tumor of the male breast].
Kadiri, Youssef; Boufettal, Houssine; Samouh, Naïma; Benayad, Samira; Karkouri, Mehdi; Zamiati, Soumaya; Kadiri, Bouchaïb
2013-04-01
The granular cell tumor of the breast (TCGS) is a rare benign tumor, which grows from Schwann cells. It can be confused with a cancerous tumor clinically and radiologically. Only the histological appearance can make the diagnosis. We report a case of TCGS in a man, discovered as a result of self-examination of a breast lump. The authors emphasize the problem of differential diagnosis with breast cancer: clinically, a hard lump with an occasional skin retraction or a fixity to the deep plane; radiologically a stellar opaque appearance with irregular contours, sonographically unspecific, and even macroscopically during surgery, this lesion having morphological characteristics which need histologic examination and even immunohistochemistry in order to exclude a malignant tumor. They are cured by wide local excision and have generally a good prognosis. Copyright © 2013. Published by Elsevier Masson SAS.
Software digitizer for high granular gaseous detector
Haddad, Y; Boudry, V
2014-01-01
A sampling calorimeter using gaseous sensor layers with digital readout [1] is near perfect for ``Particle Flow Algorithm'' [2,3] 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. Monte-Carlo (MC) programs such as GEANT4 [4] 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 develop a general method for simulating the pad response using the spatial information from a simulation done at high granularity. The digitization method proposed here has been applied to gaseous detectors including Glass Resistive Plate Chambers (GRPC) and MicroMegas, and validated on test beam data. Experimental observable such as pad multiplicity and mean number of hits at different thresholds have been reproduced with high precision.
Information granularity, big data, and computational intelligence
Chen, Shyi-Ming
2015-01-01
The recent pursuits emerging in the realm of big data processing, interpretation, collection and organization have emerged in numerous sectors including business, industry, and government organizations. Data sets such as customer transactions for a mega-retailer, weather monitoring, intelligence gathering, quickly outpace the capacities of traditional techniques and tools of data analysis. The 3V (volume, variability and velocity) challenges led to the emergence of new techniques and tools in data visualization, acquisition, and serialization. Soft Computing being regarded as a plethora of technologies of fuzzy sets (or Granular Computing), neurocomputing and evolutionary optimization brings forward a number of unique features that might be instrumental to the development of concepts and algorithms to deal with big data. This carefully edited volume provides the reader with an updated, in-depth material on the emerging principles, conceptual underpinnings, algorithms and practice of Computational Intelligenc...
Frictional granular mechanics: A variational approach
Energy Technology Data Exchange (ETDEWEB)
Holtzman, R.; Silin, D.B.; Patzek, T.W.
2009-10-16
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.
Capturing gas in soft granular media
MacMinn, Chris; Lee, Jeremy; Xu, Feng; Lee, Sungyon
2017-11-01
Bubble migration through soft granular materials involves a strong coupling between the bubble dynamics and the deformation of the material. This process is relevant to a variety of natural and industrial systems, from fluidized-bed reactors to the migration and venting of biogenic gas in sediments. Here, we study this process experimentally by injecting air into a quasi-2D, liquid-saturated packing of soft particles and measuring the morphology of the bubbles as they invade and then rise due to buoyancy. By systematically varying the confining stress, we show that the competition between buoyancy, capillarity, and elasticity leads to complex bubble-migration dynamics that transition from fluidization to pathway opening to pore invasion, with a strong and surprising impact on the amount of air trapped in the system. The authors are grateful for support from the Royal Society (IE150885), the John Fell Oxford University Press Research Fund, and the Maurice Lubbock Memorial Fund.
Sound pulse broadening in stressed granular media.
Langlois, Vincent; Jia, Xiaoping
2015-02-01
The pulse broadening and decay of coherent sound waves propagating in disordered granular media are investigated. We find that the pulse width of these compressional waves is broadened when the disorder is increased by mixing the beads made of different materials. To identify the responsible mechanism for the pulse broadening, we also perform the acoustic attenuation measurement by spectral analysis and the numerical simulation of pulsed sound wave propagation along one-dimensional disordered elastic chains. The qualitative agreement between experiment and simulation reveals a dominant mechanism by scattering attenuation at the high-frequency range, which is consistent with theoretical models of sound wave scattering in strongly random media via a correlation length.
A Statistical Ensemble for Soft Granular Matter
Henkes, Silke; O'Hern, Corey; Chakraborty, Bulbul
2007-03-01
Work on packings of soft spheres (PRE 68, 011306 (2003)) has shown the existence of a Jamming transition and has highlighted the need for a general statistical framework to describe granular packings. This work presents an extension of the formalism proposed by Edwards (Physica A 157, 1080 (1989)) to packings of soft particles. We base our analysis on a height formalism developed in two dimensions (PRL 88, 115505 (2002)) to extract a topological invariant γ, the trace of the global stress tensor, which is conserved under internal rearrangements of the system. Upon assuming a flat measure in γ-space, we can derive a canonical distribution of the local γ-values in a grain packing. We then check the predictions of this ensemble against distributions of mechanically stable packings of frictionless disks obtained from computer simulations. Work supported by NSF-DMR 0549762.
Fuzzy batch controller for granular materials
Directory of Open Access Journals (Sweden)
Zamyatin Nikolaj
2018-01-01
Full Text Available The paper focuses on batch control of granular materials in production of building materials from fluorine anhydrite. Batching equipment is intended for smooth operation and timely feeding of supply hoppers at a required level. Level sensors and a controller of an asynchronous screw drive motor are used to control filling of the hopper with industrial anhydrite binders. The controller generates a required frequency and ensures required productivity of a feed conveyor. Mamdani-type fuzzy inference is proposed for controlling the speed of the screw that feeds mixture components. As related to production of building materials based on fluoride anhydrite, this method is used for the first time. A fuzzy controller is proven to be effective in controlling the filling level of the supply hopper. In addition, the authors determined optimal parameters of the batching process to ensure smooth operation and production of fluorine anhydrite materials of specified properties that can compete with gypsum-based products.
Hyperstaticity and loops in frictional granular packings
Tordesillas, Antoinette; Lam, Edward; Metzger, Philip T.
2009-06-01
The hyperstatic nature of granular packings of perfectly rigid disks is analyzed algebraically and through numerical simulation. The elementary loops of grains emerge as a fundamental element in addressing hyperstaticity. Loops consisting of an odd number of grains behave differently than those with an even number. For odd loops, the latent stresses are exterior and are characterized by the sum of frictional forces around each loop. For even loops, the latent stresses are interior and are characterized by the alternating sum of frictional forces around each loop. The statistics of these two types of loop sums are found to be Gibbsian with a "temperature" that is linear with the friction coefficient μ when μ<1.
Granular Segregation by an Oscillating Ratchet Mechanism
International Nuclear Information System (INIS)
Igarashi, A.; Horiuchi, Ch.
2004-01-01
We report on a method to segregate granular mixtures which consist of two kinds of particles by an oscillating ''ratchet'' mechanism. The segregation system has an asymmetrical sawtooth-shaped base which is vertically oscillating. Such a ratchet base produces a directional current of particles owing to its transport property. It is a counterintuitive and interesting phenomenon that a vertically vibrated base transports particles horizontally. This system is studied with numerical simulations, and it is found that we can apply such a system to segregation of mixtures of particles with different properties (radius or mass). Furthermore, we find out that an appropriate inclination of the ratchet-base makes the quality of segregation high. (author)
Transient response in granular bounded heap flows
Xiao, Hongyi; Ottino, Julio M.; Lueptow, Richard M.; Umbanhowar, Paul B.
2017-11-01
Heap formation, a canonical granular flow, is common in industry and is also found in nature. Here, we study the transition between steady flow states in quasi-2D bounded heaps by suddenly changing the feed rate from one fixed value to another. During the transition, in both experiments and discrete element method simulations, an additional wedge of flowing particles propagates over the rising free surface. The downstream edge of the wedge - the wedge front - moves downstream with velocity inversely proportional to the square root of time. An additional longer duration transient process continues after the wedge front reaches the downstream wall. The transient flux profile during the entire transition is well modeled by a diffusion-like equation derived from local mass balance and a local linear relation between the flux and the surface slope. Scalings for the transient kinematics during the flow transitions are developed based on the flux profiles. Funded by NSF Grant CBET-1511450.
Granular neural networks, pattern recognition and bioinformatics
Pal, Sankar K; Ganivada, Avatharam
2017-01-01
This book provides a uniform framework describing how fuzzy rough granular neural network technologies can be formulated and used in building efficient pattern recognition and mining models. It also discusses the formation of granules in the notion of both fuzzy and rough sets. Judicious integration in forming fuzzy-rough information granules based on lower approximate regions enables the network to determine the exactness in class shape as well as to handle the uncertainties arising from overlapping regions, resulting in efficient and speedy learning with enhanced performance. Layered network and self-organizing analysis maps, which have a strong potential in big data, are considered as basic modules,. The book is structured according to the major phases of a pattern recognition system (e.g., classification, clustering, and feature selection) with a balanced mixture of theory, algorithm, and application. It covers the latest findings as well as directions for future research, particularly highlighting bioinf...
Multiple impacts in dissipative granular chains
Nguyen, Ngoc Son
2014-01-01
The extension of collision models for single impacts between two bodies, to the case of multiple impacts (which take place when several collisions occur at the same time in a multibody system) is a challenge in Solid Mechanics, due to the complexity of such phenomena, even in the frictionless case. This monograph aims at presenting the main multiple collision rules proposed in the literature. Such collisions typically occur in granular materials, the simplest of which are made of chains of aligned balls. These chains are used throughout the book to analyze various multiple impact rules which extend the classical Newton (kinematic restitution), Poisson (kinetic restitution) and Darboux-Keller (energetic or kinetic restitution) approaches for impact modelling. The shock dynamics in various types of chains of aligned balls (monodisperse, tapered, decorated, stepped chains) is carefully studied and shown to depend on several parameters: restitution coefficients, contact stiffness ratios, elasticity coefficients (...
Thermal Properties of Consolidated Granular Salt as a Backfill Material
Paneru, Laxmi P.; Bauer, Stephen J.; Stormont, John C.
2018-03-01
Granular salt has been proposed as backfill material in drifts and shafts of a nuclear waste disposal facility where it will serve to conduct heat away from the waste to the host rock. Creep closure of excavations in rock salt will consolidate (reduce the porosity of) the granular salt. This study involved measuring the thermal conductivity and specific heat of granular salt as a function of porosity and temperature to aid in understanding how thermal properties will change during granular salt consolidation accomplished at pressures and temperatures consistent with a nuclear waste disposal facility. Thermal properties of samples from laboratory-consolidated granular salt and in situ consolidated granular salt were measured using a transient plane source method at temperatures ranging from 50 to 250 °C. Additional measurements were taken on a single crystal of halite and dilated polycrystalline rock salt. Thermal conductivity of granular salt decreased with increases in temperature and porosity. Specific heat of granular salt at lower temperatures decreased with increasing porosity. At higher temperatures, porosity dependence was not apparent. The thermal conductivity and specific heat data were fit to empirical models and compared with results presented in the literature. At comparable densities, the thermal conductivities of granular salt samples consolidated hydrostatically in this study were greater than those measured previously on samples formed by quasi-static pressing. Petrographic studies of the consolidated salt indicate that the consolidation method influenced the nature of the porosity; these observations are used to explain the variation of measured thermal conductivities between the two consolidation methods. Thermal conductivity of dilated polycrystalline salt was lower than consolidated salt at comparable porosities. The pervasive crack network along grain boundaries in dilated salt impedes heat flow and results in a lower thermal conductivity
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.
Investigation of particle properties on the holding force in a granular gripper
Meuleman, Steven; Balt, Vincent; Jarray, Ahmed; Magnanimo, Vanessa
The granular gripper is an innovative device designed to grasp objects using the jamming properties of granular materials. However, the granular properties that influence its performance are poorly understood. Moreover, to date, there is no numerical model for the granular gripper. In this paper, we
Norsk, P.; Shelhamer, M.
2016-01-01
This panel will present NASA's plans for ongoing and future research to define the requirements for Artificial Gravity (AG) as a countermeasure against the negative health effects of long-duration weightlessness. AG could mitigate the gravity-sensitive effects of spaceflight across a host of physiological systems. Bringing gravity to space could mitigate the sensorimotor and neuro-vestibular disturbances induced by G-transitions upon reaching a planetary body, and the cardiovascular deconditioning and musculoskeletal weakness induced by weightlessness. Of particular interest for AG during deep-space missions is mitigation of the Visual Impairment Intracranial Pressure (VIIP) syndrome that the majority of astronauts exhibit in space to varying degrees, and which presumably is associated with weightlessness-induced fluid shift from lower to upper body segments. AG could be very effective for reversing the fluid shift and thus help prevent VIIP. The first presentation by Dr. Charles will summarize some of the ground-based and (very little) space-based research that has been conducted on AG by the various space programs. Dr. Paloski will address the use of AG during deep-space exploration-class missions and describe the different AG scenarios such as intra-vehicular, part-of-vehicle, or whole-vehicle centrifugations. Dr. Clement will discuss currently planned NASA research as well as how to coordinate future activities among NASA's international partners. Dr. Barr will describe some possible future plans for using space- and ground-based partial-G analogs to define the relationship between physiological responses and G levels between 0 and 1. Finally, Dr. Stenger will summarize how the human cardiovascular system could benefit from intermittent short-radius centrifugations during long-duration missions.
Pattern Formation inside a Rotating Cylinder Partially Filled with Liquid and Granular Medium
Directory of Open Access Journals (Sweden)
Veronika Dyakova
2014-01-01
Full Text Available The paper focuses on the experimental study of the dynamics of liquid and granular medium in a rapidly rotating horizontal cylinder. In the cavity frame gravity field performs rotation and produces oscillatory liquid flow, which is responsible for the series of novel effects; the problem corresponds to “vibrational mechanics”—generation of steady flows and patterns by oscillating force field. The paper presents the initial results of experimental study of a novel pattern formation effect which is observed at the interface between fluid and sand and which takes the form of ripples extended along the axis of rotation. The initial results of experimental research of a novel effect of pattern formation at the interface between fluid and sand in the form of ripples extended along the axis of rotation are presented. The spatial period of the patterns is studied in dependence on liquid volume, viscosity, and rotation rate. The experimental study of long time dynamics of pattern formation manifests that regular ripples transform into a series of dunes within a few minutes or dozens of minutes. The variety of patterns is determined by the interaction of two types of liquid flows induced by gravity: oscillatory and steady azimuthal flows near the sand surface.
Use of steel slag as a granular material: volume expansion prediction and usability criteria.
Wang, George; Wang, Yuhong; Gao, Zhili
2010-12-15
The theoretical equation for predicting volume expansion of steel slag is deduced based on both chemical reaction and physical changes of free lime in steel slag during the hydration process. Laboratory volume expansion testing is conducted to compare the results with the theoretical volume expansion. It is proved that they correlated well. It is furthermore experimentally proved that certain volume expansion of steel slag can be absorbed internally by the void volume in bulk steel slag under external surcharge weight making the apparent volume expansion equal zero. The minimum (lowest) absorbable void volume is approximately 7.5%, which is unrelated to the free lime content. A usability criterion is then developed based on the volume expansion of steel slag (%) and the minimum percentage of the volume that can take the volume expansion of steel slag (%). Eventually the criterion (relationship) is established based on the free lime content, the specific gravity and bulk relative gravity of a specific steel slag sample. The criteria can be used as guidance and specification for the use of steel slag and other expansion-prone nonferrous slags, copper, nickel for instance as a granular material in highway construction. Copyright © 2010 Elsevier B.V. All rights reserved.
Active Response Gravity Offload System
Valle, Paul; Dungan, Larry; Cunningham, Thomas; Lieberman, Asher; Poncia, Dina
2011-01-01
The Active Response Gravity Offload System (ARGOS) provides the ability to simulate with one system the gravity effect of planets, moons, comets, asteroids, and microgravity, where the gravity is less than Earth fs gravity. The system works by providing a constant force offload through an overhead hoist system and horizontal motion through a rail and trolley system. The facility covers a 20 by 40-ft (approximately equals 6.1 by 12.2m) horizontal area with 15 ft (approximately equals4.6 m) of lifting vertical range.
Gravity Independent Compressor, Phase I
National Aeronautics and Space Administration — We propose to develop and demonstrate a small, gravity independent, vapor compression refrigeration system using a linear motor compressor which effectively...
The self-propulsion of a helix in granular matter
Valdes, Rogelio; Angeles, Veronica; de La Calleja, Elsa; Zenit, Roberto
2017-11-01
The effect of the shape of helicoidal on the displacement of magnetic robots in granular media is studied experimentally. We quantify the influences of three main parameters of the shape of the helicoidal swimmers: body diameter, step, and the angle. We compare the experimental measurements with an empirically modified resistive force theory prediction that accounts for the static friction coefficient of the particles of the granular material, leading to good agreement. Comparisons are also made with the granular resistive force theory proposed by Goldman and collaborators. We found an optimal helix angle to produce movement and determined a relationship between the swimmer size and speed.
Airborne Gravity: NGS' Gravity Data for AN02 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS05 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AN05 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AN06 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS04 (2009)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AS01 (2008)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2008 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AN04 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS08 (2015)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for CS08 collected in 2006 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for ES02 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida and the Gulf of Mexico collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of the American...
Airborne Gravity: NGS' Gravity Data for AS02 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS07 (2014 & 2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 & 2016 over 3 surveys,TX14-2, TX16-1 and TX16-2. This data set is part of the Gravity for the Re-definition of...
International Nuclear Information System (INIS)
Jones, K.R.W.
1995-01-01
We develop a nonlinear quantum theory of Newtonian gravity consistent with an objective interpretation of the wavefunction. Inspired by the ideas of Schroedinger, and Bell, we seek a dimensional reduction procedure to map complex wavefunctions in configuration space onto a family of observable fields in space-time. Consideration of quasi-classical conservation laws selects the reduced one-body quantities as the basis for an explicit quasi-classical coarse-graining. These we interpret as describing the objective reality of the laboratory. Thereafter, we examine what may stand in the role of the usual Copenhagen observer to localise this quantity against macroscopic dispersion. Only a tiny change is needed, via a generically attractive self-potential. A nonlinear treatment of gravitational self-energy is thus advanced. This term sets a scale for all wavepackets. The Newtonian cosmology is thus closed, without need of an external observer. Finally, the concept of quantisation is re-interpreted as a nonlinear eigenvalue problem. To illustrate, we exhibit an elementary family of gravitationally self-bound solitary waves. Contrasting this theory with its canonically quantised analogue, we find that the given interpretation is empirically distinguishable, in principle. This result encourages deeper study of nonlinear field theories as a testable alternative to canonically quantised gravity. (author). 46 refs., 5 figs
Alvarez-Gaume, Luis; Kounnas, Costas; Lust, Dieter; Riotto, Antonio
2016-01-01
We discuss quadratic gravity where terms quadratic in the curvature tensor are included in the action. After reviewing the corresponding field equations, we analyze in detail the physical propagating modes in some specific backgrounds. First we confirm that the pure $R^2$ theory is indeed ghost free. Then we point out that for flat backgrounds the pure $R^2$ theory propagates only a scalar massless mode and no spin-two tensor mode. However, the latter emerges either by expanding the theory around curved backgrounds like de Sitter or anti-de Sitter, or by changing the long-distance dynamics by introducing the standard Einstein term. In both cases, the theory is modified in the infrared and a propagating graviton is recovered. Hence we recognize a subtle interplay between the UV and IR properties of higher order gravity. We also calculate the corresponding Newton's law for general quadratic curvature theories. Finally, we discuss how quadratic actions may be obtained from a fundamental theory like string- or M-...
Skordis, Constantinos
2011-12-28
General relativity (GR) is a phenomenologically successful theory that rests on firm foundations, but has not been tested on cosmological scales. The deep mystery of dark energy (and possibly even the requirement of cold dark matter (CDM)) has increased the need for testing modifications to GR, as the inference of such otherwise undetected fluids depends crucially on the theory of gravity. Here, I discuss a general scheme for constructing consistent and covariant modifications to the Einstein equations. This framework is such that there is a clear connection between the modification and the underlying field content that produces it. I argue that this is mandatory for distinguishing modifications of gravity from conventional fluids. I give a non-trivial example, a simple metric-based modification of the fluctuation equations for which the background is exact ΛCDM, but differs from it in the perturbations. I show how this can be generalized and solved in terms of two arbitrary functions. Finally, I discuss future prospects and directions of research.
Fracturing in granular media: the role of capillarity, wetting, and disorder
Juanes, R.; Trojer, M.; de Anna, P.; Szulczewski, M. L.
2015-12-01
The advent of shale oil and shale gas into the energy landscape has relied on achieving vigorous stimulation of the rock by means of horizontal drilling and hydraulic fracturing. Traditionally, hydraulic fracturing is understood as a single-fluid-phase, pressure-driven process, in which the fluid (typically water with additives) is injected at a high-enough rate that the pressure builds up faster than it can dissipate by permeating into the rock, thereby fracturing it. However, the prevalent conditions for shale (ultra fine pore size, moderate overburden stress, and poor cementation) suggest that capillary forces could play an important role in the fracturing process. Here, we show the results of our recent experimental and theoretical studies on fracturing of granular media by means of injection of an immiscible fluid. We conduct carefully controlled injection experiments in a quasi-2D granular medium (a circular Hele-Shaw cell filled with glass beads), in an experimental set-up that allows us to systematically study the impact of capillarity (by varying injection rate, bead size, and fluid-fluid surface tension), wetting properties (by treating the beads and the cell plates by chemical vapor deposition of silane-based substances) and confinement (by varying the load on the cell). Our choice of defending and invading liquids and granular medium allows us to investigate a wide range of contact angles, from drainage to imbibition. We demonstrate that wettability exerts a powerful influence on the invasion/fracturing morphology of unfavorable mobility displacements. High time resolution imaging techniques and particle image velocimetry (PIV) allow us to quantify matrix displacement and fracture opening dynamics. Our results provide insights on fracture propagation, fracture length distribution and the fracture drainage area, parameters which are critically important to better understand long-term hydrocarbon production from shale.
Hogg, Charlie A. R.; Dalziel, Stuart B.; Huppert, Herbert E.; Imberger, Jörg
2015-09-01
In many important natural and industrial systems, gravity currents of dense fluid feed basins. Examples include lakes fed by dense rivers and auditoria supplied with cooled air by ventilation systems. As we will show, the entrainment into such buoyancy driven currents can be influenced by viscous forces. Little work, however, has examined this viscous influence and how entrainment varies with the Reynolds number, Re. Using the idea of an entrainment coefficient, E, we derive a mathematical expression for the rise of the front at the top of the dense fluid ponding in a basin, where the horizontal cross-sectional area of the basin varies linearly with depth. We compare this expression to experiments on gravity currents with source Reynolds numbers, Res, covering the broad range 100 < Res < 1500. The form of the observed frontal rises was well approximated by our theory. By fitting the observed frontal rises to the theoretical form with E as the free parameter, we find a linear trend for E(Res) over the range 350 < Res < 1100, which is in the transition to turbulent flow. In the experiments, the entrainment coefficient, E, varied from 4 × 10-5 to 7 × 10-2. These observations show that viscous damping can be a dominant influence on gravity current entrainment in the laboratory and in geophysical flows in this transitional regime.
Hoffmann, Lars; Wu, Xue; Alexander, M. Joan
2018-02-01
Forecasting the intensity of tropical cyclones is a challenging problem. Rapid intensification is often preceded by the formation of "hot towers" near the eyewall. Driven by strong release of latent heat, hot towers are high-reaching tropical cumulonimbus clouds that penetrate the tropopause. Hot towers are a potentially important source of stratospheric gravity waves. Using 13.5 years (2002-2016) of Atmospheric Infrared Sounder observations of stratospheric gravity waves and tropical cyclone data from the International Best Track Archive for Climate Stewardship, we found empirical evidence that stratospheric gravity wave activity is associated with the intensification of tropical cyclones. The Atmospheric Infrared Sounder and International Best Track Archive for Climate Stewardship data showed that strong gravity wave events occurred about twice as often for tropical cyclone intensification compared to storm weakening. Observations of stratospheric gravity waves, which are not affected by obscuring tropospheric clouds, may become an important future indicator of storm intensification.
An Emotional Agent Model Based on Granular Computing
Directory of Open Access Journals (Sweden)
Jun Hu
2012-01-01
Full Text Available Affective computing has a very important significance for fulfilling intelligent information processing and harmonious communication between human being and computers. A new model for emotional agent is proposed in this paper to make agent have the ability of handling emotions, based on the granular computing theory and the traditional BDI agent model. Firstly, a new emotion knowledge base based on granular computing for emotion expression is presented in the model. Secondly, a new emotional reasoning algorithm based on granular computing is proposed. Thirdly, a new emotional agent model based on granular computing is presented. Finally, based on the model, an emotional agent for patient assistant in hospital is realized, experiment results show that it is efficient to handle simple emotions.
Factors influencing the density of aerobic granular sludge.
Winkler, M.K.; Kleerebezem, R.; Strous, M.; Chandran, K.; Loosdrecht, M.C. van
2013-01-01
In the present study, the factors influencing density of granular sludge particles were evaluated. Granules consist of microbes, precipitates and of extracellular polymeric substance. The volume fractions of the bacterial layers were experimentally estimated by fluorescent in situ hybridisation
Rheology and Segregation of Granular Mixtures in Dense Flows
Indian Academy of Sciences (India)
Devang Khakhar
IIT Bombay. Rheology and Segregation of. Granular Mixtures in Dense Flows. Devang Khakhar. Department of Chemical Engineering. Indian Institute of Technology Bombay. Mumbai, India. Acknowledgment: Anurag Tripathi. 77th Annual Meeting of IASc, Ahmedabad, 18-20 Nov, 2011 ...
A particle-based method for granular flow simulation
Chang, Yuanzhang
2012-03-16
We present a new particle-based method for granular flow simulation. In the method, a new elastic stress term, which is derived from a modified form of the Hooke\\'s law, is included in the momentum governing equation to handle the friction of granular materials. Viscosity force is also added to simulate the dynamic friction for the purpose of smoothing the velocity field and further maintaining the simulation stability. Benefiting from the Lagrangian nature of the SPH method, large flow deformation can be well handled easily and naturally. In addition, a signed distance field is also employed to enforce the solid boundary condition. The experimental results show that the proposed method is effective and efficient for handling the flow of granular materials, and different kinds of granular behaviors can be well simulated by adjusting just one parameter. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.
76 FR 8774 - Granular Polytetrafluoroethylene Resin From Japan
2011-02-15
... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Granular Polytetrafluoroethylene Resin From Japan AGENCY: United States International Trade... polytetrafluoroethylene resin from Japan would be likely to lead to continuation or recurrence of material injury. On...
Immunoglobulins in granular corneal dystrophy Groenouw type I
DEFF Research Database (Denmark)
Møller, H U; Bojsen-Møller, M; Schrøder, H D
1993-01-01
Three patients with granular corneal dystrophy Groenouw type I underwent corneal grafting, and cryostat sections of the corneal buttons were examined immunohistochemically for immunoglobulins. Positive results were obtained for IgG, Kappa-, and Lambda chains with immunofluorescence technique...
Microgravity Granular Material Research (MGMR) Facility for ISS, Phase I
National Aeronautics and Space Administration — TransAstra Corporation in collaboration with Grainflow Dynamics Inc. and the Colorado School of Mines proposes to develop a general purpose Micro-g Granular Material...
Oblique shock waves in granular flows over bluff bodies
Directory of Open Access Journals (Sweden)
Gopan Nandu
2017-01-01
Full Text Available Granular flows around an object have been the focus of numerous analytical, experimental and simulation studies. The structure and nature of the oblique shock wave developed when a quasi-two dimensional flow of spherical granular particles streams past an immersed, fixed cylindrical obstacle forms the focus of this study. The binary granular mixture, consisting of particles of the same diameter but different material properties, is investigated by using a modified LIGGGHTS package as the simulation engine. Variations in the solid fraction and granular temperature within the resulting flow are studied. The Mach number is calculated and is used to distinguish between the subsonic and the supersonic regions of the bow shock.
Micro origins for macro behavior in granular media
Zhao, J.; Jiang, M.; Soga, K.; Luding, Stefan
2016-01-01
We report the latest advances in understanding, characterization and modeling of key micro mechanisms and origins underpinning the interesting and complex macroscopic behavior of granular matter. Included in this Topical Collection are novel theories, innovative experimental tools and new numerical
Extraction of structural extracellular polymeric substances from aerobic granular sludge
Felz, S.; Al-zuhairy, S.H.K.; Aarstad, Olav Andreas; van Loosdrecht, Mark C.M.; Lin, Y.
2016-01-01
To evaluate and develop methodologies for the extraction of gel-forming extracellular polymeric substances (EPS), EPS from aerobic granular sludge (AGS) was extracted using six different methods (centrifugation, sonication, ethylenediaminetetraacetic acid (EDTA), formamide with sodium hydroxide
Investigation of granular impact using positron emission particle tracking
Marston, Jeremy O.
2015-04-01
We present results from an experimental study of granular impact using a combination of high-speed video and positron emission particle tracking (PEPT). The PEPT technique exploits the annihilation of photons from positron decay to determine the position of tracer particles either inside a small granular bed or attached to the object which impacts the bed. We use dense spheres as impactors and the granular beds are comprised of glass beads which are fluidised to achieve a range of different initial packing states. For the first time, we have simultaneously investigated both the trajectory of the sphere, the motion of particles in a 3-D granular bed and particles which jump into the resultant jet, which arises from the collapse of the cavity formed by the impacting sphere.
Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation
Bartacek, J.; Fermoso, F.G.; Baldo-Urrutia, A.M.; Hullebusch, van E.D.; Lens, P.N.L.
2008-01-01
The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and
Massive granular cell ameloblastoma with dural extension and atypical morphology
Directory of Open Access Journals (Sweden)
Vandana Raghunath
2014-01-01
Full Text Available 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.
Non-Steady Oscillatory Flow in Coarse Granular Materials
DEFF Research Database (Denmark)
Andersen, O. H.; Gent, M. R. A. van; Meer, J. W. van der
1992-01-01
Stationary and oscillatory flow through coarse granular materials have been investigated experimentally at Delft Hydraulics in their oscillating water tunnel with the objective of determining the coefficients of the extended Forchheimer equation. Cylinders, spheres and different types of rock have...
Resilient Modulus Characterization of Alaskan Granular Base Materials
2010-08-01
Resilient modulus (MR) of base course material is an important material input for : pavement design. In Alaska, due to distinctiveness of local climate, material source, : fines content and groundwater level, resilient properties of D-1 granular base...
Reduced Gravity Zblan Optical Fiber
Tucker, Dennis S.; Workman, Gary L.; Smith, Guy A.
2000-01-01
Two optical fiber pullers have been designed for pulling ZBLAN optical fiber in reduced gravity. One fiber puller was designed, built and flown on board NASA's KC135 reduced gravity aircraft. A second fiber puller has been designed for use on board the International Space Station.
Fixed points of quantum gravity
Litim, D F
2003-01-01
Euclidean quantum gravity is studied with renormalisation group methods. Analytical results for a non-trivial ultraviolet fixed point are found for arbitrary dimensions and gauge fixing parameter in the Einstein-Hilbert truncation. Implications for quantum gravity in four dimensions are discussed.
Measuring wood specific gravity, correctly
G. Bruce Williamson; Michael C. Wiemann
2010-01-01
The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a foresterâs variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these...
Quantum Gravity in Two Dimensions
DEFF Research Database (Denmark)
Ipsen, Asger Cronberg
The topic of this thesis is quantum gravity in 1 + 1 dimensions. We will focus on two formalisms, namely Causal Dynamical Triangulations (CDT) and Dy- namical Triangulations (DT). Both theories regularize the gravity path integral as a sum over triangulations. The difference lies in the class...
Bergshoeff, Eric; Hohm, Olaf; Merbis, Wout; Routh, Alasdair J.; Townsend, Paul K.
2014-01-01
We present an alternative to topologically massive gravity (TMG) with the same 'minimal' bulk properties; i.e. a single local degree of freedom that is realized as a massive graviton in linearization about an anti-de Sitter (AdS) vacuum. However, in contrast to TMG, the new 'minimal massive gravity'
Magnetic Fields Versus Gravity
Hensley, Kerry
2018-04-01
Deep within giant molecular clouds, hidden by dense gas and dust, stars form. Unprecedented data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the intricate magnetic structureswoven throughout one of the most massive star-forming regions in the Milky Way.How Stars Are BornThe Horsehead Nebulasdense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [NASA/ESA/Hubble Heritage Team]Simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. In reality, however, star formation is more complicated than a simple give and take between gravity and pressure. Thedusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.How can we learn about the magnetic fields of distant objects? One way is by measuring dust polarization. An elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. This systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains emission perpendicular to the local magnetic field. This allows us to infer the direction of the magnetic field from the direction of polarization.Magnetic field orientations for protostars e2 and e8 derived from Submillimeter Array observations (panels a through c) and ALMA observations (panels d and e). Click to enlarge. [Adapted from Koch et al. 2018]Tracing Magnetic FieldsPatrick Koch (Academia Sinica, Taiwan) and collaborators used high-sensitivity ALMA observations of dust polarization to learn more about the magnetic field morphology of Milky Way star-forming region W51. W51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and North.The ALMA observations reveal
Applicability and trends of anaerobic granular sludge treatment processes
International Nuclear Information System (INIS)
Lim, Seung Joo; Kim, Tak-Hyun
2014-01-01
Anaerobic granular sludge treatment processes have been continuously developed, although the anaerobic sludge granulation process was not clearly understood. In this review, an upflow anaerobic sludge blanket (UASB), an expanded granule sludge blanket (EGSB), and a static granular bed reactor (SGBR) were introduced as components of a representative anaerobic granular sludge treatment processes. The characteristics and application trends of each reactor were presented. The UASB reactor was developed in the late 1970s and its use has been rapidly widespread due to the excellent performance. With the active granules, this reactor is able to treat various high-strength wastewaters as well as municipal wastewater. Most soluble industrial wastewaters can be efficiently applied using a UASB. The EGSB reactor was developed owing to give more chance to contact between wastewater and the granules. Dispersed sludge is separated from mature granules using the rapid upward velocity in this reactor. The EGSB reactor shows the excellent performance in treating low-strength and/or high-strength wastewater, especially under low temperatures. The SGBR, developed at Iowa State University, is one of anaerobic granular sludge treatment processes. Although the configuration of the SGBR is very simple, the performance of this system is similar to that of the UASB or EGSB reactor. The anaerobic sludge granulation processes showed excellent performance for various wastewaters at a broad range of organic loading rate in lab-, pilot-scale tests. This leads to erect thousands of full-scale granular processes, which has been widely operated around the world. -- Highlights: • Anaerobic sludge granulation is a key parameter for maintaining granular processes. • Anaerobic granular digestion processes are applicable for various wastewaters. • The UASB is an economic high-rate anaerobic granular process. • The EGSB can treat high-strength wastewater using expanding granules. • The SGBR is
Editorial: Modelling and computational challenges in granular materials
Weinhart, Thomas; Thornton, Anthony Richard; Einav, Itai
2015-01-01
This is the editorial for the special issue on “Modelling and computational challenges in granular materials” in the journal on Computational Particle Mechanics (CPM). The issue aims to provide an opportunity for physicists, engineers, applied mathematicians and computational scientists to discuss the current progress and latest advancements in the field of advanced numerical methods and modelling of granular materials. The focus will be on computational methods, improved algorithms and the m...
Experimental search for quantum gravity
2018-01-01
This book summarizes recent developments in the research area of quantum gravity phenomenology. A series of short and nontechnical essays lays out the prospects of various experimental possibilities and their current status. Finding observational evidence for the quantization of space-time was long thought impossible. In the last decade however, new experimental design and technological advances have changed the research landscape and opened new perspectives on quantum gravity. Formerly dominated by purely theoretical constructions, quantum gravity now has a lively phenomenology to offer. From high precision measurements using macroscopic quantum oscillators to new analysis methods of the cosmic microwave background, no stone is being left unturned in the experimental search for quantum gravity. This book sheds new light on the connection of astroparticle physics with the quantum gravity problem. Gravitational waves and their detection are covered. It illustrates findings from the interconnection between gene...
The effectiveness of resistive force theory in granular locomotiona)
Zhang, Tingnan; Goldman, Daniel I.
2014-10-01
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.
Survivable integrated grooming in multi-granularity optical networks
Wu, Jingjing; Guo, Lei; Wei, Xuetao; Liu, Yejun
2012-05-01
Survivability is an important issue to ensure the service continuity in optical network. At the same time, with the granularity of traffic demands ranging from sub-wavelength-level to wavelength-level, traffic demands need to be aggregated and carried over the network in order to utilize resources effectively. Therefore, multi-granularity grooming is proposed to save the cost and reduce the number of switching ports in Optical-Cross Connects (OXCs). However, current works mostly addressed the survivable wavelength or waveband grooming. Therefore, in this paper, we propose three heuristic algorithms called Multi-granularity Dedicated Protection Grooming (MDPG), Multi-granularity Shared Protection Grooming (MSPG) and Multi-granularity Mixed Protection Grooming (MMPG), respectively. All of them are performed based on the Survivable Multi-granularity Integrated Auxiliary Graph (SMIAG) that includes one Wavelength Integrated Auxiliary Graph (WIAG) for wavelength protection and one waveBand Integrated Auxiliary Graph (BIAG) for waveband protection. Numerical results show that MMPG has the lowest average port-cost, the best resource utilization ratio and the lowest blocking probability among these three algorithms. Compared with MDPG, MSPG has lower average port-cost, better resource utilization ratio and lower blocking probability.
Hadron showers in a highly granular calorimeter
International Nuclear Information System (INIS)
Lutz, Benjamin
2010-11-01
A future electron-positron collider like the planned International Linear Collider (ILC) needs excellent detectors to exploit the full physics potential. Different detector concepts have been evaluated for the ILC and two concepts on the particle-flow approach were validated. To make particle-flow work, a new type of imaging calorimeters is necessary in combination with a high performance tracking system, to be able to track the single particles through the full detector system. These calorimeters require an unprecedented level of both longitudinal and lateral granularity. Several calorimeter technologies promise to reach the required readout segmentation and are currently studied. This thesis addresses one of these: The analogue hadron calorimeter technology. It combines work on the technological aspects of a highly granular calorimeter with the study of hadron shower physics. The analogue hadron calorimeter technology joins a classical scintillator-steel sandwich design with a modern photo-sensor technology, the silicon photomultiplier (SiPM). The SiPM is a millimetre sized, magnetic field insensitive, and low cost photo-sensor, that opens new possibilities in calorimeter design. This thesis outlines the working principle and characteristics of these devices. The requirements for an application specific integrated circuit (ASIC) to read the SiPM are discussed; the performance of a prototype chip for SiPM readout, the SPIROC, is quantified. Also the SiPM specific reconstruction of a multi-thousand channel prototype calorimeter, the CALICE AHCAL, is explained; the systematic uncertainty of the calibration method is derived. The AHCAL does not only offer a test of the calorimeter technology, it also allows to record hadron showers with an unprecedented level of details. Test-beam measurements have been performed with the AHCAL and provide a unique sample for the development of novel analysis techniques and the validation of hadron shower simulations. A method to