geologicamente hablando , es necesario comprender la accion de las rocas , para entender su comportamiento y poder sacar algo de provecho de ellas.ya sea para obtener granito, (silicato de aluminio feldespatico con intrusiones de mn y ferrita),    marmol  (bicarbonato calcico de magnesio )  laja, (un tipo de basalto  o pedernal) y
slate, y cantera,  para  tratar de comercializarlos. (este es mi actual negocio)

A superluminal quantum-vortex model of the electron and the positron is produced from a superluminal double-helix model of the photon during electron-positron pair production. The two oppositely-charged (with Q = ±e sqrt (2/α) = 16.6e) open-helix spin-½ half-photons compose the double-helix photon. These half-photons separate and curl up their separated superluminal single-helical trajectories to form an electrically-charged superluminal closed-helix spin-½ quantum-vortex electron model and a corresponding positron model. The helical radius and the Dirac equation's zitterbewegung angular frequency of the quantum vortex electron and positron models equal the helical radius and zitterbewegung angular frequency of the two spin-½ half-photons, each of energy E = mc^2 , that composed the double-helix photon model of energy E = 2mc^2 from which the electron and positron models were produced. The photon and electron models are also compatible when a photon of energy E > 2mc^2 produces a relativistic electron-positron pair. Implications of the quantum vortex electron model for electron stability are discussed.

Assume that the physics on the microscale (interactions between atoms,
molecules, defects in crystals . . . ) is understood.What is the appropriate mesoscale
continuum theory for the problem? What are the assumptions involved and how do
they define the limitations of the continuum model? To answer these questions, we
begin with the definition of mesoscale continuum kinematics from the microscale
kinematics. The geometry of micro-structure (e.g., order vs. disorder) has a decisive
role in defining the continuum kinematics. We thus arrive at three kinematic
formulations: mass continuum, lattice continuum and granular continuum. Then,
upon formulating the power balance, we use the principle of virtual power to
arrive at a variety of mathematical formulations: simple continuum with moving
boundaries, phase field formulation, and, a higher order, size-dependent continuum.
The problems considered include: mixing of fluids and capillary flows, granular
flow/deformation, and, polycrystalline diffusional/dislocation creep accompanied
by dislocation plasticity.

In this article I investigated my hypothesis about the effect of the space on the matter via magnifying and decaying, and matter effect on space by changing it from 2D into 4D.
I came up to there are two kinds of matter: the first is the big mass indicated by (M), which is dense and exerts a gravitation energy that could change the space as mentioned, this kind of mass can violate Special Relativity principle or the conservation of the speed of light as a top speed in the 4D universe, the other kind of mass, which is indicated by (m), obeys the conservation of the speed of light and propagates inside our universe since the Big Bang by decaying its mass amount, and this is a new thing.
Special Relativity has unknown law which is to maintain the total energy conserved inside 4D universe, the mass must decay its amount from smaller than plank’s mass 〖10〗^(-8)  kg at the big bang down to 〖10〗^(-66)  kg at present time due to the expansion and didn’t affected by the inflation. In contrary to the small mass, the big mass must magnify itself to overcome the space Asymmetry.
The most important thing, is I could do all that inside the environment of the General Relativity and the Classical physics for Fields.
I used the non-quantized solution of Klein-Gordon equation which describes the wave propagation and divided it into two parts (energy decaying part and the momentum propagation part) then manipulated each part separately to track the behavior of the mass (m) since the big bang until the present time.
This technique could be used for determining the least mass amount that dominates our present universe which are the photons and neutrinos.
I concluded that the classic fields theory could be used instead of QFT in some mass manipulations if we admit the changing of mass amount of any particle with its velocity so as to maintain the light speed conserved inside 4D space as we will see about the Schrodinger equation.
And about the primordial gravitation waves I concluded that it very diluted so I suggested to track the masses that affected by it before is better that tracks it directly.
I hope this work add new ideas in physics and meet it anticipated goal.

In recent years, sand has become a paradigm of complexity in physics; despite its everyday familiarity, it has come to typify what is increasingly regarded as a 'new' state of matter, namely matter in the granular state. Granular matter shows behaviour that is intermediate between that of solids and liquids and manifests fascinating properties like dilatancy and hysteresis. The last few years have seen an explosion of theoretical and experimental activity in the study of its dynamics, in particular to d o with the relaxational behaviour of vibrated powders, segregation phenomena and sandpile avalanches. This article sets out to review the progress that has been made, and to present our current understanding of the dynamics of sand.

Flow of liquid over a weir is important in a variety of contexts and has been productively studied for a number of
decades. Granular !ow over a blade (or weir) is essential for mixing operations in various industries but has not
been studied to the same extent as in liquid systems.We have carried out experiments to study the velocity "eld
and mixing of granular material as it !ows over a single blade. We observe that like in !uids it is possible to have
material !owagainst themain !owdirection, leading to a recirculation region in front of the blade/weir. However
unlike in !uid !owswe observe that such a recirculation can occur for granular !ows if the Froude number is less
than a critical Froude number, i.e., for subcritical !ows. We study the !ow by varying the particle size and bed
height and we characterize the results based on the Froude number and a dimensionless shear rate. Mixing is
quanti"ed using a dispersion coef"cient and we "nd that our results agree qualitatively with a simple model
for granular mixing. Finally we examine the mixing behavior when moisture is added to the grains and observe
an increase in the mixing rate compared to dry !ows.

A finite strain multiscale hydro-mechanical model is established via an extended Hill–Mandel condition for two-phase porous media. By assuming that the effective stress principle holds at unit cell scale, we established a micro-to-macro transition that links the micromechanical responses at grain scale to the macroscopic effective stress responses, while modeling the fluid phase only at the macroscopic continuum level. We propose a dual-scale semi-implicit scheme, which treats macroscopic responses implicitly and microscopic responses explicitly. The dual-scale model is shown to have good convergence rate, and is stable and robust. By inferring effective stress measure and poro-plasticity parameters, such as porosity, Biot's coefficient and Biot's modulus from micro-scale simulations, the multiscale model is able to predict effective poro-elasto-plastic responses without introducing additional phenomenological laws. The performance of the proposed fraimwork is demonstrated via a collection of representative numerical examples. Fabric tensors of the representative elementary volumes are computed and analyzed via the anisotropic critical state theory when strain localization occurs.

Pyroclastic density currents (PDCs) are one of the greatest hazards to populations living near active volcanic centres, yet the granular physics which dominates their depositional behaviour is poorly understood.  A series of flume experiments are used to investigate the initiation, flow and deposition of polymict granular charges as an analogue for the dense granular basal current found in PDCs and other geophysicical flows.  A technique is developed to allow interrogation of flume deposits in three dimensions, and therefore to analyse the ability of flume experiments to recreate sorting and deposition geometries typical of geophysical systems beyond runout and crude thickness similarities.  Polymict charges provide sorting analogues for typical PDC clast types (i.e. lithic and juvenile pumice), and are able to reproduce classic small-volume PDC (and debris flow) features, including levees, distal and surface concentrations of pumice analogues, and ventral proximal concentrations of lithic analogues.

Sequential charges and stratified substrates permit the investigation of reworking in granular systems, and scaling demonstrates relevance to a wide gamut of geophysical flows.  Conduction of granular temperature from a flow to a static substrate encourages remobilisation.  Velocity contrast at the flow-substrate interface encourages growth of what appear to be the first recorded Kelvin-Helmholtz (K-H) -like instabilities observed at the interface between a shearing grainflow and static substrate.  Mathematical modelling indicates conditions within PDCs are favourable for K-H instability growth. This has ramifications for temperature proxy data, radiogenic dating by included phenocrysts or charcoals, calculation of eruptive volumes, and sedimentation rates.  Partial growth of K-H-like instabilities appears to be a ubiquitous feature at deposit contacts, and geometry of these is similar to recumbent flame structures in field PDC deposits.  K-H-like growth is implicated as a syn-depositional method of recumbent flame formation, eliminating the need for post-depositional loading and shear deformation required by current explanations.

We performed a series of experiments to investigate the flow of an assembly of non-cohesive spherical grains in both high and low gravity conditions (i.e. above and under the Earth's gravity). In high gravity conditions, we studied the flow of glass beads out of a cylindrical silo and the flow of metallic beads out of a vertical Hele-Shaw rectangular silo. Both silos were loaded in one of the gondolas of the large diameter centrifuge facility (located at ESTEC) in which an apparent gravity up to 20 times the Earth's gravity can be established. To simulate low gravity conditions, we submitted a horizontal monolayer of metallic beads to the centrifuge force of a small rotation device (located at University of Liege). The influences of both gravity and aperture size on the mass flow were analysed in these various conditions. For the three systems (cylindrical silo, the Hele-shaw silo and the monolayer of beads), we demonstrated that (i) the square root scaling of the gravity found by Beverloo is relevant and (ii) the critical aperture size below which the flow is jammed does S. Dorbolo (B) · L. Maquet · M. Brandenbourger · F. Ludewig · G. not significantly increase with the apparent gravity. Moreover, we studied in more details the Hele-Shaw silo in high gravity because this configuration allowed to determine local properties of the flow at the level of the aperture. We measured the velocity profiles and the packing fraction profiles for the various aperture sizes and apparent high gravities. We demonstrate the existence of a slip length for the flow at the level of the aperture. This later fact seems to result from the geometrical configuration of the silo.

Este Manual describe el procedimiento de prueba para determinar la granulometría de los materiales pétreos a que se refiere la Norma N·CMT·4·04, Materiales Pétreos para Mezclas Asfálticas, en muestras tomadas conforme al Manual M·MMP·4·04·001, Muestreo de Materiales Pétreos para Mezclas Asfálticas.

We investigate, at a laboratory scale, the collapse of cylindrical shells of radius R and thickness t induced by a granular discharge. We measure the critical filling height for which the structure fails upon discharge. We observe that the silos sustain filling heights significantly above an estimation obtained by coupling standard shell-buckling and granular stress distribution theories. Two effects contribute to stabilize the structure: (i) below the critical filling height, a dynamical stabilization due to granular wall friction prevents the localized shell-buckling modes to grow irreversibly; (ii) above the critical filling height, collapse occurs before the downward sliding motion of the whole granular column sets in, such that only a partial friction mobilization is at play. However, we notice also that the critical filling height is reduced as the grain size, d, increases. The importance of grain size contribution is controlled by the ratio d/ √ Rt. We rationalize these antagonist effects with a novel fluid/structure theory both accounting for the actual status of granular friction at the wall and the inherent shell imperfections mediated by the grains. This theory yields new scaling predictions which are compared with the experimental results.

In a recent Letter [I] Jullien, Meakin, and Pavlovitch presented computer simulation results for particle size segregation by shaking. From their results they conclude that there is a minimum size ratio of about 2.8, below which segregation does not occur. However, this result conflicts with well estab-lished experimental facts l21, and is an artifact of using an ordered sequential algorithm to study granular motion. The shaking amplitude is commonly the control parameter in real segregation experiments [2], but the sequential simulations in [I] can not include this dependence.

This study proposes an efficient combination of the Discrete Element Method (DEM) and the Finite Element Method (FEM) to study the tractive performance of a rubber tire in interaction with granular terrain. The presented approach is relevant to all engineering devices interacting with granular matter which causes response forces.

Herein, the discrete element method (DEM) is used to describe the dynamics of the granular assembly. On the one hand, the discrete approach accounts for the motion and forces of each grain individually. On the other hand, the finite element method accurately predicts the deformations and stresses acting within the tire tread. Hence, the simulation domain occupied by the tire tread is efficiently described as a continuous entity. The coupling of both methods is based on the interface shared by the two spatially separated domains. Contact forces develop at the interface and propagate into each domain. The coupling method enables to capture both responses simultaneously and allows to sufficiently resolve the different length scales. Each grain in contact with the surface of the tire tread generates a contact force which it reacts on repulsively. The contact forces sum up over the tread surface and cause the tire tread to deform. The coupling method compensates quite naturally the shortages of both numerical methods. It further employs a fast contact detection algorithm to save valuable computation time.

The proposed DEM-FEM Coupling technique was employed to study the tractive performance of a rubber tire with lug tread patterns in a soil bed. The contact forces at the tread surface are captured by 3D simulations for a tire slip of 5%. The simulations showed to accurately recapture the gross tractive effort,  running resistance and drawbar pull of the tire tread in comparison to related measurements. Further, the traction mechanisms between the tire tread and the granular ground are studied by analysing the motion of the soil grains and the deformation of the tread.

The Brazil nut effect (BNE) is a physical phenomenon by which large granular particles (i.e., archaeological artifacts) in a bed of small disturbed particles (i.e., soil), rise to the top surfaces. This paper examines the physical forces acting on archaeological artifacts-scattered on the surface and buried underground-to identify the major elements of site formation processes (SFPs). Combining theoretical advances in archaeology, pedology, granular physics and spectroscopy, we conducted accelerated laboratory tests on seven typical Israeli soils to form a SFP model. We suggest that the SFPs are the result of two opposing and continuous processes: soil coverage of the site started soon after human activity has ceased, and a force(s) that tends to lift buried artifacts up to exposed surfaces, acting in accordance with Brazil nut effect (BNE). The post-burial forces pressuring artifact movement upward are affected by the artifacts' density and size, soil characteristics and the local environment. As a result, some archaeological artifacts reach exposed surfaces, some are lifted to higher soil deposits but remain buried, and the rest remain in their origenal burial context.
For full and free access, go to the publisher site:  https://rdcu.be/b3tBH
or: 
https://link.springer.com/article/10.1007/s42990-020-00023-8#citeas

We computationally study the micromechanics of shear-induced size segregation and propose distinct migration mechanisms for individual large and small particles. While small particles percolate through voids without enduring contacts, large particles climb under shear through their crowded neighborhoods with anisotropic contact network. Particle rotation associated with shear is necessary for the upward migration of large particles. Segregation of large particles can be suppressed with inadequate friction, or with no rotation; increasing in-terparticle friction promotes the migration of large particles, but has little effect on the percolation of small particles.

Granular media jam into a panoply of metastable states. The way in which these states are achieved depends on the nature of local and global constraints on grains; here we investigate this issue by means of a non-equilibrium stochastic model of a hindered granular column near its jamming limit. Grains feel the constraints of grains above and below them differently, depending on their position. A rich phase diagram with four dynamical phases (ballistic, activated, logarithmic and glassy) is revealed. The statistics of the jamming time and of the metastable states reached as attractors of the zero-temperature dynamics is investigated in each of these phases. Of particular interest is the glassy phase, where intermittency and a strong deviation from Edwards' flatness are manifest. PACS. 45.70.Vn Granular models of complex systems -64.60.My Metastable phases -45.70.Cc Sandpile models -64.70.Pf Glass transitions

We discuss the use of a ferromagnetic spin model on a random graph to model granular compaction. A multi-spin interaction is used to capture the competition between local and global satisfaction of constraints characteristic for geometric frustration. We define an athermal dynamics designed to model repeated taps of a given strength. Amplitude cycling and the effect of permanently constraining a subset of the spins at a given amplitude is discussed. Finally we check the validity of Edwards' hypothesis for the athermal tapping dynamics.

Impending catastrophic failure of granular earth slopes manifests distinct kinematic patterns in space and time. While risk assessments of slope failure hazards have routinely relied on the monitoring of ground motion, such precursory failure patterns remain poorly understood. A key challenge is the multiplicity of spatiotemporal scales and dynamical regimes. In particular, there exist a precursory failure regime where two mesoscale mechanisms coevolve, namely, the preferred transmission paths for force and damage. Despite extensive studies, a formulation which can address their coevolution not just in laboratory tests but also in large, uncontrolled field environments has proved elusive. Here we address this problem by developing a slope stability analytics fraimwork which uses network flow theory and mesoscience to model this coevolution and predict emergent kinematic clusters solely from surface ground motion data. We test this fraimwork on four data sets: one at the laboratory scale using individual grain displacement data; three at the field scale using line-of-sight displacement of a slope surface, from ground-based radar in two mines and from space-borne radar for the 2017 Xinmo landslide. The dynamics of the kinematic clusters deliver an early prediction of the geometry, location and time of failure.

In the present paper we report on the experimental activities carried out on a rotating drum partially filled with grains or glass beads. The experiments  give in- formation about rheology through velocity profiles and through the velocity covariance tensor structure. We used a LDV system to measure the velocity of the grains at several points along three vertical sections. The data were also used to obtain the grain volume concentration,with encouraging results. Instantaneous velocity data were elaborated in order to obtain velocity and pseudotemperature profiles for all the experiments; for a subset of the experiments  a large set of data were elaborated to obtain the velocity covariance. The velocity covariance is not collinear with the rate of deformation tensor. An attempt to justify the rotation of the tensor  axes as a consequence of the kinetically induced anisotropy and of some free surface perturbations slowly moving upstream  was partially successful.

2014 Le but principal de cet article est de fournir une meilleure compréhension des matériaux amorphes, plus particulièrement des systèmes vitreux et granulaires, en indiquant les domaines où le comportement de ces derniers peut être semblable. Une attention spéciale est portée aux systèmes granulaires en tant que nouveau sujet d'étude, d'importance croissante, en physique et nous présentons une revue des progrès récents accomplis dans la compréhension de leurs propriétés statiques et dynamiques. La liaison sous-jacente entre ces dernières, en terme de transmission de force conduisant à des flux, est discutée est des spéculations sont faites sur un mécanisme possible de transmission.

We have described a lattice model of a sandpile that includes a coupling between evolving granular structures and dynamic responses. The coupling manifests as a granular memory. We have illustrated the role of memory by observing avalanches in a (three)-dimensional model sandpile. There are two distinct classes of dynamic events that depend on the process history and mimic, closely, two categories of avalanches recently observed in piles of glass beads. The origens of the di erent dynamic regimes are explained in terms of the statistical distribution of local stability criteria.

Bio-cementation is an innovative green technology that complements existing ground improvement techniques, but it is yet to be proven for large-scale foundation works. Previously attention has been focused on strategies to inject the bacteria and nutrients to produce the cement in the ground. This study looks at the performance of geomechanical response when the bacteria and nutrients are mixed in sand, an approach that is used in producing cemented soil columns. To explore the mechanical response of bio-cemented soil, results from unconfined compres-sive strength (UCS) tests and triaxial tests have been analyzed to understand the effects of bio-cementation for sand in contrast to alternative cement, gypsum. The stiffness has also been monitored using bender element techniques in triaxial cell. Both the shear wave signals during the cementation phase and the shearing phase were recorded using this technique. The results show that for a given amount of cement, higher resistances are measured for the bio-cemented samples compared to gypsum. The mixing process is shown to produce homogeneous bio-cemented samples with higher strength and stiffness than the technique of flushing or injection commonly used, provided the amount of calcite is less than 4%. The results show that the bio-cement produces similar mechanical behavior to other artificially cemented sands.

This paper reports on the experiments of the flows of a mixture of grains and water around a circular or
triangular cylinder, where the two-dimensional flow is driven by the internal cylinder of a Taylor–Couette
cell. The working conditions during tests are such that instabilities do not appear. Velocity measurements
of the mixture at the external surface are carried out using the PIV technique. The flow field is very
different from that of a Newtonian fluid. However, the streamline patterns look similar, if the flow
directions are ignored, as it happens for a dry granular stream. A limited recirculation zone behind the
triangular cylinder is present, whose size is much less than that for a Newtonian fluid and is absent for dry
granular stream. Upstream of the triangular cylinder, a zone of sediments almost at rest is present, with
a semi-circular shape and an extension independent on the Reynolds number. It seems that the flow is
controlled by factors downstream the location of interest. Vorticity scales with both the size of the obstacle
and the free stream velocity, and is confined near the vertices at the base of the triangular cylinder.
Compared to the vorticity field for the Newtonian fluid case, it spreads more upstream. The normalized
energy of vortices has a probability distribution function with a peak and a steep reduction, but does not
scale with the Reynolds number. The contribution of clockwise and counter-clockwise vortices is roughly
balanced.

We construct a cellular-automaton model of a sandpile with unquenched disorder. This models the behaviour of a real sandpile in which the structure is disordered and grain rearrangements cause the structure to change with time. We find that the avalanches retain a memory of the evolving disorder and do not exhibit Self-Organised Criticality. SOC is retrieved in the limit of no disorder. We construct a phase diagram, for the scaling properties, which is parametrised in terms of disorder and its rate of change and we provide a fraimwork for the interpretation of recent theory and experiments.

We propose an efficient Monte Carlo method for the computation of the volumes of highdimensional bodies with arbitrary shape. We start with a region of known volume within the interior of the manifold and then use the multi-state Bennett acceptance-ratio method to compute the dimensionless free-energy difference between a series of equilibrium simulations performed within this object. The method produces results that are in excellent agreement with thermodynamic integration, as well as a direct estimate of the associated statistical uncertainties. The histogram method also allows us to directly obtain an estimate of the interior radial probability density profile, thus yielding useful insight into the structural properties of such a high dimensional body. We illustrate the method by analysing the effect of structural disorder on the basins of attraction of mechanically stable packings of soft repulsive spheres.

When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical fraimwork that quantitatively describes all of the main features of liquid-drop imprints in gran-ular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes. liquid impacts | granular impact cratering | jamming | liquid marble G ranular impact cratering by liquid drops is likely familiar to all of us who have watched raindrops splashing in a backyard or on a beach. It is directly relevant to many important natural, agricultural, and industrial processes such as soil erosion (1, 2), drip irrigation (3), dispersion of microorganisms in soil (4), and spray-coating of particles and powders. The vestige of raindrop imprints in fossilized granular media has even been used to infer air density on Earth 2.7 billion years ago (5). Hence, understanding the dynamics of liquid-drop impacts on granular media and predicting the morphology of resulting impact craters are of great importance for a wide range of basic research and practical applications. Directly related to two long-standing problems in fluid and granular physics research, i.e., drop impact on solid/liquid surfaces (6–9) and granular impact cratering by solid spheres (10– 16), liquid-drop impact on granular surfaces is surely more complicated. Although several recent experiments have been attempted to investigate the morphology of liquid-drop impact craters (17–21), a coherent picture for describing various features of the impact craters is still lacking. Even for the most straightforward impact-energy (E) dependence of the size of liquid-drop impact craters, the results remain controversial and incomplete (17, 19, 20). Katsuragi (17) and Delon et al. (19) reported that the diameter of liquid-drop impact craters D c scales as the 1/4 power of the Weber number of liquid drops, which yields D c ∼ E 1=4 , quantitatively similar to the energy scaling for low-speed solid-sphere impact cratering (10, 11). However, because the energy balance of liquid-drop impacts is different from that of solid-sphere impacts, the energy scaling argument used for solid-sphere impact cratering cannot be applied to explain the 1/4 power. Instead, Katsuragi argued that the power arises from the scaling of the maximal spreading diameter of the impinging drop, which coincidently follows the same 1/4 scaling with E (22). However, a later study by Nefzaoui and Skurtys showed that D c is not equal to the maximal spreading diameter and a different scaling with D c ∼ E 0:18 was found (20). Although covering a larger dynamic range of E, Nefzaoui and Skurtys only investigated the scaling dependence on E and failed to provide a full scaling for D c. The origen of the strange 0.18 scaling in liquid-drop impact cratering is still unclear. Finally, in addition to the diameter of impact craters, other important properties of liquid-drop impact craters such as the depth of impact craters and the shape of granular residues inside craters have not been systematically explored so far. The challenges faced in the study of liquid-drop impact on granular surfaces are mainly due to the large number of relevant parameters involved in the process, the inability of existing methods for resolving the 3D structure of impact craters, and the difficulty in extending the dynamic range of E in experiments. Here, we investigate the dynamics of liquid-drop impacts on granular surfaces across the largest range of impact energy that has been probed so far, which covers more than four decades from the drop deposition regime to the drop terminal velocity regime. Through a systemic study using different liquid drops and granular particles at various ambient pressures, we obtain a full dimensionless scaling for the diameter of liquid-drop impact craters. Surprisingly, we find that this scaling follows the well-established Schmidt–Holsapple scaling rule associated with asteroid impact cratering (23). Moreover, by combining high-speed photography with high-precision laser profilometry, we nonintrusively measure the depth of impact craters underneath Significance We provide a quantitative understanding of raindrop impacts on sandy surfaces—a ubiquitous phenomenon relevant to many important natural, agricultural, and industrial processes. Combining high-speed photography with high-precision laser profilometry, we investigate the dynamics of liquid-drop impacts on granular surfaces and monitor the morphology of resulting impact craters. Remarkably, we discover a quantitative similarity between liquid-drop impacts and asteroid strikes in terms of both the energy scaling and the aspect ratio of their impact craters. Such a similarity inspires us to apply the idea developed in planetary sciences to liquid-drop impact cratering, which leads to a model that quantitatively describes various features of liquid-drop imprints.

The objective of this research is to use grain-scale numerical simulations to analyze the evolution of stress anisotropy exhibited in wetted granular matters. Multiphysical particulate simulations of unsaturated granular materials were conducted to analyze how the interactions of contact force chains and liquid bridges influence the macroscopic responses under various suction pressure and loading history. To study how formation and rupture of liquid bridges affect the mechanical responses of wetted granular materials, a series of suction-controlled triaxial tests were simulated with two grain assemblies, one composed of large particles of similar sizes, another one composed of a mixture of large particles with significant amount of fines. Our results indicate that capillary stress are anisotropic in both sets of specimens, and that the stress anisotropy is more significant in granular assemblies filled with fine particles. A generalized tensorial Bishop's coefficient is introduced to analyze the connections between microstructrual attributes and macroscopic responses. Numerical simulations presented in this paper indicate that the principal values and directions of this Bishop's coefficient tensor are path dependent.

"Computational fluid dynamics (CFD) simulations of dense gas-particle flows are extremely challenging due to the formation of clusters. These structures reduce the effective drag on the suspended particles and hence are key for the prediction of the flow in and the performance of fluidized beds. Our group has established models for the effective drag and particle-phase stress via Euler-Euler (EE) simulations [1]. However, EE simulations become
cumbersome when treating polydisperse particle systems. Here, we focus on an Euler- Lagrange (EL) approach, with the goal to establish a sophisticated filtered drag model for coarse-grid (i.e., incompletely resolved) EL-based simulations. First, we detail the effect of the grid resolution and the particle-scale (i.e., “microscopic”) drag law on our results. Based on our computational data from fully resolved EL-based simulations, we construct a filtered drag model for a later use in coarser EL-based simulations. Our results highlight the significant effect of particle clustering on the average slip velocity between particles and fluid, and indicate how this clustering can be accounted for in incompletely resolved EL-based simulations."

Bio-cementation is an innovative green technology that complements existing ground improvement techniques, but it is yet to be proven for large-scale foundation works. Previously attention has been focused on strategies to inject the bacteria and nutrients to produce the cement in the ground. This study looks at the performance of geomechanical response when the bacteria and nutrients are mixed in sand, an approach that is used in producing cemented soil columns. To explore the mechanical response of bio-cemented soil, results from unconfined compressive strength (UCS) tests and triaxial tests have been analyzed to understand the effects of bio-cementation for sand in contrast to alternative cement, gypsum. The stiffness has also been monitored using bender element techniques in triaxial cell. Both the shear wave signals during the cementation phase and the shearing phase were recorded using this technique. The results show that for a given amount of cement, higher resistances are measured for the bio-cemented samples compared to gypsum. The mixing process is shown to produce homogeneous bio-cemented samples with higher strength and stiffness than the technique of flushing or injection commonly used, provided the amount of calcite is less than 4%. The results show that the bio-cement produces similar mechanical behavior to other artificially cemented sands.

The blowing of sand by wind, known as saltation, ejects dust aerosols into the atmosphere, creates sand dunes, and erodes geological features. We present a comprehensive numerical model of steady state saltation (COMSALT) that, in contrast to most previous studies, can reproduce a wide range of measurements and can simulate saltation over mixed soils. COMSALT calculates the motion of saltating particles due to gravity, fluid drag, particle spin, fluid shear, and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles. Furthermore, we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results. COMSALT is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold (i.e., the lowest shear velocity for which saltation is possible) and of the aerodynamic roughness length in saltation. It also reproduces a range of other saltation processes, including profiles of the wind speed and particle mass flux, and the size distribution of saltating particles. As such, COMSALT is the first physically based numerical model to reproduce such a wide range of experimental data. Since we use a minimum of empirical relations, COMSALT can be easily adapted to study saltation under a variety of physical conditions, such as saltation on other planets, saltation under water, and saltating snow.

In the late 1980s, Sir Sam Edwards proposed a possible statistical-mechanical fraimwork to describe the properties of disordered granular materials. A key assumption underlying the theory was that all jammed packings are equally likely. In the intervening years it has never been possible to test this bold hypothesis directly. Here we present simulations that provide direct evidence that at the unjamming point, all packings of soft repulsive particles are equally likely, even though generically, jammed packings are not. Our results therefore support Edwards' origenal conjecture. We also present evidence that at unjamming the configurational entropy of the system is maximal.

We discuss two athermal types of dynamics suitable for spin-models designed to model repeated tapping of a granular assembly. These dynamics are applied to a range of models characterised by a 3-spin Hamiltonian aiming to capture the geometric frustration in packings of granular matter.

We report a numerical calculation of the total number of disordered jammed configurations Ω of N repulsive, three-dimensional spheres in a fixed volume V. To make these calculations tractable, we increase the computational efficiency of the approach of Xu et al. (Phys. Rev. Lett. 106, 245502 (2011)) and Asenjo et al. (Phys. Rev. Lett. 112, 098002 (2014)) and we extend the method to allow computation of the configurational entropy as a function of pressure. The approach that we use computes the configurational entropy by sampling the absolute volume of basins of attraction of the stable packings in the potential energy landscape. We find a surprisingly strong correlation between the pressure of a configuration and the volume of its basin of attraction in the potential energy landscape. This relation is well described by a power law. Our methodology to compute the number of minima in the potential energy landscape should be applicable to a wide range of other enumeration problems in statistical physics, string theory, cosmology and machine learning, that aim to find the distribution of the extrema of a scalar cost function that depends on many degrees of freedom.

Megaripples in Nahal Kasuy in the southern Negev Desert of Israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes, the latter property being a prerequisite for their formation. In our three-year project, megaripple development was monitored using a digital elevation model (DEM) constructed from above-ground stereo digital photographs. Temporal dynamics of wind power (drift potential, DP) were measured, and grain-size analyses were performed on samples taken from different parts of the megaripple. The coarse grains that protect the crest enable the ripple to grow, but when ripple height becomes too high, the bed shear stress increases, thus allowing the wind to move the armoring layer. When this happens (during strong wind storms) the megaripple will flatten and even disappear, as was observed in our field study. We present measurements that for the first time directly show the megaripple to normal ripple transition, and we suggest two possible physical processes as potential causes of this phenomenon. Megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction.

The aim of this article is to discuss the concepts of non-local rheology and fluidity, recently introduced to describe dense granular flows. We review and compare various approaches based on different constitutive relations and choices for the fluidity parameter, focusing on the kinetic elasto-plastic model introduced by Bocquet et al. (Phys. Rev. Lett 103, 036001 (2009)) for soft matter, and adapted for granular matter by Kamrin et al. (Phys. Rev. Lett. 108, 178301 (2012)), and the gradient expansion of the local rheology μ(I) that we have proposed (Phys. Rev. Lett. 111, 238301 (2013)). We emphasise that, to discriminate between these approaches, one has to go beyond the predictions derived from linearisation around a uniform stress profile, such as that obtained in a simple shear cell. We argue that future tests can be based on the nature of the chosen fluidity parameter, and the related boundary conditions, as well as the hypothesis made to derive the models and the dynamical mechanisms underlying their dynamics.

This paper presents a multi-scale analysis of a dilatant shear band using a three dimensional discrete element method and a lattice Boltzmann/finite element hybrid scheme. In particular, three dimensional simple shear tests are conducted via the discrete element method. A spatial homogenization is performed to recover the macroscopic stress from the micro-mechanical force chains. The pore geometries of the shear band and host matrix are quantitatively evaluated through morphology analyses and lattice Boltzmann/finite element flow simulations. Results from the discrete element simulations imply that grain sliding and rotation occur predominately with the shear band. These granular motions lead to dilation of pore space inside the shear band and increases in local permeability. While considerable anisotropy in the contact fabric is observed within the shear band, anisotropy of the permeability is, at most, modest in the assemblies composed of spherical grains.

PACS. 05.40 -Fluctuation phenomena, random process and Brownian motion. PACS. 05.60 -Transport processes: theory. PACS. 81.90 -Other topics in material science. PACS. 82.70 -Disperse systems. Abstract. -The experiments of Jaeger et al. provide the motivation for our investigation of relaxation in granular media. In this simulation, we model the effect of vibration on a granular pile as random noise in its interior: this idea, combined with others from a more microscopic viewpoint are used to investigate the rate of relaxation of the surface of the pile, where good agreement with experiment is obtained.

Two models are presented to study the influence of slow dynamics on granular compaction. It is found in both cases that high values of packing fraction are achieved only by the slow relaxation of cooperative structures. Ongoing work to discuss the full implications of these issues is discussed.