Probing dense granular materials by space-time dependent perturbations

Kondic, Lou; Dybenko, O.; Behringer, Robert

doi:10.1103/physreve.79.041304

Cited by 9 publications

(8 citation statements)

References 18 publications

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“…We note that we also car ried out simulations with an effectively infinite X, yield ing a propagation speed consistent with the results found in literature [13]. Formulation of an effective continuum model describing the main features of signal propaga tion is discussed elsewhere [21], but we note that much more work remains to be done in formulating a contin uum model that would provide a quantitative description of energy propagation.…”

Section: Propagation Through Staticsupporting

confidence: 86%

Energy Transport Through Dense Granular Matter

Kondic

Fang

Dybenko

et al. 2009

AIP Conference Proceedings

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In order to probe the process of energy propagation through dense granular systems, we carry out discrete element simulations of the system response to excitations where we control the driving frequency and wavelength independently. The soft-disk simulations are carried out in two spatial dimensions, and include the effects of energy loss due to inelasticity of collisions, frictional damping, rotations, and polydispersity. Our ability to control independently spatial and temporal properties of the imposed perturbations allows us to extract significant new information. In particular, Fourier analysis of the system response shows that properties of the propagating signal strongly depend on the spatial scales introduced by the perturbation itself. Then, we consider a sheared granular system and discuss how shearing influences the nature of the propagating signal. The simulations are carried out using realistic system sizes and material properties, allowing for direct experimental verification of the obtained results.

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Section: Propagation Through Staticsupporting

confidence: 86%

Energy Transport Through Dense Granular Matter

Kondic

Fang

Dybenko

et al. 2009

AIP Conference Proceedings

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“…In Figure 3a, a 3 nm Ni film atop graphene was exposed to only Ar/H 2 (400/50 sccm) flow at 800°C. This high temperature process dewetted [23][24][25] defectives sites in graphene such as grain boundaries. Indeed, the initiation of nanoparticle motion has been shown to occur due to attractive forces between the particle and carbon atoms with dangling bonds, rather than in the basal plane.…”

Section: Resultsmentioning

confidence: 99%

Chemical Vapor Deposition of Carbon Nanotubes on Monolayer Graphene Substrates: Reduced Etching via Suppressed Catalytic Hydrogenation Using C₂H₄

Kumar

Kim

et al. 2013

Chem. Mater.

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In most envisioned applications, full utilization of a graphene-carbon nanotube (CNT) construct requires maintaining the integrity of the graphene layer during the CNT growth step. In this work, we exhibit an approach towards controlled CNT growth atop graphene substrates where the reaction equilibrium between source hydrocarbon decomposition and carbon saturation into and precipitation from the catalyst nanoparticles shifts towards CNT growth rather than graphene consumption. By utilizing C 2 H 4 feedstock, we demonstrate that the low temperature growth permissible with this gas suppresses undesirable catalytic hydrogenation and dramatically reduces the etching of the graphene layer to exhibit graphene-CNT hybrids with continuous, undamaged structures.Recent efforts in fabricating three dimensional (3D) composite nanostructures consisting of two dimensional (2D) graphene and one dimensional (1D) nanomaterials of carbon 1-3 and conducting polymers 4 are of interest for a number of applications, including next-generation, high capacity, fast-discharge supercapacitors. For these types of energy storage applications, the advantages of graphene, such as large surface area-to-volume ratio and excellent conductivity, may be compromised due to self-aggregation resulting in poor charge transfer between the graphene flakes, the 1D materials, and the current collector. The growth of 1D nanostructures such as carbon nanofibers 5,6 or nanotubes 7,8 directly on graphene to yield hybrid 3D nano-architectures would, by design, circumvent this self-aggregation, while maintaining low contact resistance to enable effective electron transfer. [7][8][9] In our previous work, CNTs were grown by chemical vapor deposition (CVD) directly on graphene using CH 4 gas as a carbon source, and the performance of the resulting 3D nanoarchitecture as an advanced electrical double layer capacitor was characterized. 9 However, during this growth, the graphene layer was often found to be etched away at so-called "etched pits". The formation of these pits proceeded from hydrogenation 10-12 at 800°C in the presence of nickel (Ni) catalyst nanoparticles ((Ni) nanoparticle + C graphene + 2H 2 → Ni + CH 4 ). 13 Elongated etched lines in the graphene are attributed to etching by mobile nanoparticles. Subsequently, the addition of H 2 from the catalytic decomposition of the carbon source during the CNT growth step further contributes to the etching effect and can fully remove the graphene substrate. This etching process of the graphene substrate during CNT growth has thus far not been studied in the literature.Here we show that the high hydrocarbon conversion rate of C 2 H 4 , at lower temperature than CH 4 14 used in our previous study, 9 allows for an approach to CNT growth atop graphene substrates through fine tuning the process parameters including growth temperature and seed density. We confirm that the controlled use of C 2 H 4 is essential for balancing the competing processes of carbon deposition and carbon removal, which ultimately block undesir...

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“…Recall that the penetration depth is defined with respect to the position of the top surface of the granular system at initial time, t = 0. During an impact, the kinetic energy of the intruder is mostly transferred into elastic energy that propagates through the system in the form of (damped) elastic waves, see, e.g., [27]. (Note that some of the energy goes into friction; this issue is discussed briefly in the Conclusions.)…”

Section: Effect Of Polydispersitymentioning

confidence: 99%

Microstructure evolution during impact on granular matter

et al. 2012

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

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Probing dense granular materials by space-time dependent perturbations

Cited by 9 publications

References 18 publications

Energy Transport Through Dense Granular Matter

Energy Transport Through Dense Granular Matter

Chemical Vapor Deposition of Carbon Nanotubes on Monolayer Graphene Substrates: Reduced Etching via Suppressed Catalytic Hydrogenation Using C₂H₄

Microstructure evolution during impact on granular matter

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Probing dense granular materials by space-time dependent perturbations

Cited by 9 publications

References 18 publications

Energy Transport Through Dense Granular Matter

Energy Transport Through Dense Granular Matter

Chemical Vapor Deposition of Carbon Nanotubes on Monolayer Graphene Substrates: Reduced Etching via Suppressed Catalytic Hydrogenation Using C2H4

Microstructure evolution during impact on granular matter

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Resources

About

Chemical Vapor Deposition of Carbon Nanotubes on Monolayer Graphene Substrates: Reduced Etching via Suppressed Catalytic Hydrogenation Using C₂H₄