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Sample records for granular pt-c film

  1. Magnetic viscosity study in FePt/C granular films

    International Nuclear Information System (INIS)

    Huang, Y.; Butler, W.; Zhang, Y.; Hadjipanayis, G.C.; Weller, D.

    2004-01-01

    The magnetic viscosity of FePt/C granular thin films was studied in the temperature range from 2 to 300 K in order to examine the thermal stability of the nanoparticles. The magnetic viscosity coefficient (S max ) was found to decrease with temperature because of decreased thermal activation. At low temperatures, S max showed an almost linear dependence on temperature. However, S max does not extrapolate to zero but seems to have a finite value at cryogenic temperatures

  2. Mechanism of coercivity enhancement by Ag addition in FePt-C granular films for heat assisted magnetic recording media

    Energy Technology Data Exchange (ETDEWEB)

    Varaprasad, B. S. D. Ch. S.; Takahashi, Y. K., E-mail: takahashi.yukiko@nims.go.jp; Wang, J.; Hono, K. [National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Ina, T.; Nakamura, T.; Ueno, W.; Nitta, K.; Uruga, T. [Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Hyogo 679-5198 (Japan)

    2014-06-02

    We investigated the Ag distribution in a FePtAg-C granular film that is under consideration for a heat assisted magnetic recording medium by aberration-corrected scanning transmission electron microscope-energy dispersive X-ray spectroscopy and X-ray absorption fine structure. Ag is rejected from the core of FePt grains during the deposition, forming Ag-enriched shell surrounding L1{sub 0}-ordered FePt grains. Since Ag has no solubility in both Fe and Pt, the rejection of Ag induces atomic diffusions thereby enhancing the kinetics of the L1{sub 0}-order in the FePt grains.

  3. Highly (002) textured large grain bcc Cr{sub 80}Mn{sub 20} seed layer on Cr{sub 50}Ti{sub 50} amorphous layer for FePt-C granular film

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Seong-Jae, E-mail: jsjigst@ecei.tohoku.ac.jp; Saito, Shin [Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Hinata, Shintaro [Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Japan Society for the Promotion of Science Research Fellow (PD), 5-3-1, Kojimachi, Chiyoda-ku, Tokyo 102-0083 (Japan); Takahashi, Migaku [New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan)

    2015-05-07

    Effect of bcc Cr{sub 80}Mn{sub 20} seed layer and Cr{sub 50}Ti{sub 50} amorphous texture inducing layer on the heteroepitaxy system in FePt-C granular film was studied by introducing a new concept of the layered structure. The concept suggested that the large grain seed layer in which the crystallographic texture was initially formed on an amorphous layer in the layered structure can reduce the angular distribution of (002) c-axis crystal orientation in the FePt-C granular film owing to heteroepitaxial growth. Structure analysis by X-ray diffraction revealed that (1) when the substrate heating temperature was elevated from 300 °C to 500 °C, grain size in the seed layer increased from 9.8 nm to 11.6 nm, and then decreased with further increasing the substrate temperature. The reduction of the grain size over 500 °C corresponds to the crystallization of the amorphous texture inducing layer, (2) when the grain size increased from 9.8 nm to 11.6 nm, the angular distribution of the (002) orientation in the seed layer dramatically decreased from 13.7° to 4.1°. It was shown that the large grain seed layer increased the perpendicular hysteresis in FePt-C granular film.

  4. Microstructural and magnetic properties of L10 FePt-C (0 0 1) textured nanocomposite films grown on different intermediate layers

    International Nuclear Information System (INIS)

    Chen, J S; Chow, G M; Lim, B C; Hu, J F; Ding, Y F; Ju, G

    2008-01-01

    The FePt : C films with different volume fractions of carbon and different thicknesses were epitaxially grown on a CrRu(2 0 0) underlayer with Pt and MgO intermediate layers. The magnetic properties and microstructure of these FePt : C films were investigated. The FePt : C films grown on the Pt intermediate layer consisted of a continuous layer of FePt, with overlying granular FePt grains, while the FePt : C films grown on the MgO intermediate layer consisted of granular FePt : C layers with overlying granular grains. The formation of the overlying granular FePt grains was attributed to carbon diffusion to the surface which resulted in the second nucleation of FePt. The different interface energies and surface energies of FePt on Pt and MgO intermediate layers caused the formation of an initial continuous FePt layer on the Pt intermediate layer and initial granular FePt layers on the MgO intermediate layer. The coupling between the continuous FePt layer or the granular FePt layer and the overlying granular FePt grains resulted in simultaneous magnetization reversal and thus strong exchange coupling in FePt : C films.

  5. Bubbling in vibrated granular films.

    Science.gov (United States)

    Zamankhan, Piroz

    2011-02-01

    With the help of experiments, computer simulations, and a theoretical investigation, a general model is developed of the flow dynamics of dense granular media immersed in air in an intermediate regime where both collisional and frictional interactions may affect the flow behavior. The model is tested using the example of a system in which bubbles and solid structures are produced in granular films shaken vertically. Both experiments and large-scale, three-dimensional simulations of this system are performed. The experimental results are compared with the results of the simulation to verify the validity of the model. The data indicate evidence of formation of bubbles when peak acceleration relative to gravity exceeds a critical value Γ(b). The air-grain interfaces of bubblelike structures are found to exhibit fractal structure with dimension D=1.7±0.05.

  6. Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant

    Science.gov (United States)

    Ono, Takuya; Moriya, Tomohiro; Hatayama, Masatoshi; Tsumura, Kaoru; Kikuchi, Nobuaki; Okamoto, Satoshi; Kitakami, Osamu; Shimatsu, Takehito

    2017-01-01

    To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for energy-assisted magnetic recording, a FePt-GeO2/FePt-C stacked film was investigated in the engineering process. The FePt-GeO2/FePt-C stacked film fabricated at a substrate temperature of 450 °C realized uniaxial magnetic anisotropy, Kugrain , of about 2.5 × 107 erg/cm3, which is normalized by the volume fraction of FePt grains, and a granular structure with an averaged grain size of 7.7 nm. As the thickness of the FePt-GeO2 upper layer was increased to 9 nm, the Ku values were almost constant. That result differs absolutely from the thickness dependences of the other oxide segregant materials such as SiO2 and TiO2. Such differences on the oxide segregant are attributed to their chemical bond. The strong covalent bond of GeO2 is expected to result in high Ku of the FePt-GeO2/FePt-C stacked films.

  7. Improved (0 0 1)-texture of FePt-C for heat-assisted magnetic recording media by insertion of Cr buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Shiroyama, T.; Wang, J.; Felicia, A.; Takahashi, Y.K.; Hono, K., E-mail: kazuhiro.hono@nims.go.jp

    2017-06-15

    Highlights: • Improvement of (0 0 1)-texture of prototype FePt-C granular films for heat heat assisted magnetic recording media. • Insertion of Cr buffer layer improves the crystallographic textures of the MgO underlayers, thereby reduces in-plane component in the FePt-C recording layer. • The growth in the grain size of the MgO underlayer as well as the (0 0 1)-texture of the MgO underlayer are the key factor in reducing the in-plane component in the FePt-C recording layer. - Abstract: FePt-C granular films deposited on MgO underlayers are the prototype media for heat-assisted magnetic recording. To reduce the in-plane magnetic component in the FePt-C media, we investigated the effect of Cr buffer layers on the crystallographic textures of the MgO underlayers and the resultant magnetic properties of the FePt-C layers. By growing a MgO underlayer on a Cr buffer layer, the (0 0 1) texture of the MgO underlayer is improved, on which the in-plane component of a FePt-C film is substantially reduced. We conclude that the growth in the grain size of the MgO underlayer is the key factor in reducing the in-plane component in the FePt-C recording layer.

  8. Tunneling magnetoresistance in granular cermet films with particle size distribution

    International Nuclear Information System (INIS)

    Vovk, A.Ya.; Golub, V.O.; Malkinski, L.; Kravets, A.F.; Pogorily, A.M.; Shypil', O.V.

    2004-01-01

    The correlation between tunneling magnetoresistance (TMR) and field sensitivity (dMR/dH) for granular films (Co 50 Fe 50 ) x -(Al 2 O 3 ) 1-x was studied. The position of TMR maximum is shifted towards the lower x in the higher applied magnetic fields. Such a behavior was observed for metal granular nanocomposites but is first reported for granular cermets. However the highest dMR/dH was found for the compositions just below the percolation threshold

  9. Magnetic and structural properties of L1{sub 1} type CoPt-C ordered alloy perpendicular films as a function of C content

    Energy Technology Data Exchange (ETDEWEB)

    Shimatsu, T; Kataoka, H; Aoi, H [Research Institute of Electrical Communication, Tohoku University, Sendai, 980-8577 (Japan); Sato, H; Okamoto, S; Kitakami, O, E-mail: shimatsu@riec.tohoku.ac.j [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, 980-8577 (Japan)

    2010-01-01

    Magnetic and structural properties of L1{sub 1} type (Co{sub 0.5}Pt{sub 0.5}){sub 100-X}-C{sub X} ordered alloy perpendicular films, fabricated on 2.5 inch size glass disks by sputter deposition, were examined as a function of C content, X. L1{sub 1} type Co{sub 0.5}Pt{sub 0.5}-C polycrystalline films (10 nm thickness), with <111> axis (the easy axis) perpendicular to the film plane, were successfully fabricated even for a 30 vol% C content. Structural analysis indicated the segregation of C to the grain boundaries. Uniaxial magnetic anisotropy, K{sub u}, of Co{sub 0.5}Pt{sub 0.5} films without C addition was relatively low, about 1.5x10{sup 7} erg/cm{sup 3} under the present deposition conditions. However, the addition of 5 vol.% C to Co-Pt films enhanced the ordering, resulting in an increase in K{sub u} to around 2.5 x10{sup 7} erg/cm{sup 3}. A further increase in C content reduced K{sub u}; however, K{sub u} maintained a relatively large value of about 1.8x10{sup 7} erg/cm{sup 3} even for a 20vol% C content, without degrading the easy axis orientation perpendicular to the film plane. Experimental results demonstrated the potential of the L1{sub 1} type Co{sub 0.5}Pt{sub 0.5}-C films for use in granular media applications, due to their very high K{sub u}, the relatively low fabrication temperature, and good controllability of the grain orientation.

  10. Critical fields of niobium nitride films of various granularity

    International Nuclear Information System (INIS)

    Antonova, E.A.; Sukhov, V.A.

    1983-01-01

    The behaviour of lattice parameter, specific electrical resistivity, critical temperature, and temperature dependence of upper critical field near Tsub(cr) of sputtered niobium nitride films is investigated versus the substrate temperature and gas mixture composition in the process of reactive cathode sputtering. The relation between extrapolated value of the upper critical field and granularity of niobium nitride films, close as to composition to the stoichiometric one, has been found. Values of the kappa parameter of the Ginsburg-Landau theory and of the coherence length for niobium nitride films of various granularity are estimated in an approximation of uniform distribution of impurities in a sample

  11. Magnetoresistances in Ni80Fe20-ITO granular film

    International Nuclear Information System (INIS)

    Gao Chunhong; Chen Ke; Yang Yanxia; Xiong Yuanqiang; Chen Peng

    2012-01-01

    Highlights: ► Magnetoresistance (MR) in Ni 80 Fe 20 -ITO granular film are investigated. ► MR is positive at high temperature, and is negative at low temperature. ► MR results from the competition among three mechanisms. - Abstract: The magnetic properties, electrical properties and magnetoresistance are investigated in Ni 80 Fe 20 -ITO granular film with various volume fractions V NF of Ni 80 Fe 20 . The room temperature magnetization hysteresis of sample with V NF = 25% shows superparamagnetic behavior. Current-voltage curve of sample with V NF = 25% at 175 K shows typical tunneling-type behavior. The magnetoresistances of samples with low V NF are positive at high temperature, and are negative at low temperature. The temperature-dependent magnetoresistances result from the competition among ordinary magnetoresistances, the granular-typed tunneling magnetoresistance and the spin-mixing induced magnetoresistances.

  12. Sequential sputtered Co-HfO{sub 2} granular films

    Energy Technology Data Exchange (ETDEWEB)

    Chadha, M.; Ng, V.

    2017-03-15

    A systematic study of magnetic, magneto-transport and micro-structural properties of Co-HfO{sub 2} granular films fabricated by sequential sputtering is presented. We demonstrate reduction in ferromagnetic-oxide formation by using HfO{sub 2} as the insulting matrix. Microstructure evaluation of the films showed that the film structure consisted of discrete hcp-Co grains embedded in HfO{sub 2} matrix. Films with varying compositions were prepared and their macroscopic properties were studied. We correlate the variation in these properties to the variation in film microstructure. Our study shows that Co-HfO{sub 2} films with reduced cobalt oxide and varying properties can be prepared using sequential sputtering technique. - Highlights: • Co-HfO{sub 2} granular films were prepared using sequential sputtering. • A reduction in ferromagnetic-oxide formation is observed. • Co-HfO{sub 2} films display superparamagnetism and tunnelling magneto-resistance. • Varying macroscopic properties were achieved by changing film composition. • Applications can be found in moderate MR sensors and high –frequency RF devices.

  13. Electrical transport properties in Co nanocluster-assembled granular film

    Science.gov (United States)

    Zhang, Qin-Fu; Wang, Lai-Sen; Wang, Xiong-Zhi; Zheng, Hong-Fei; Liu, Xiang; Xie, Jia; Qiu, Yu-Long; Chen, Yuanzhi; Peng, Dong-Liang

    2017-03-01

    A Co nanocluster-assembled granular film with three-dimensional cross-connection paralleled conductive paths was fabricated by using the plasma-gas-condensation method in a vacuum environment. The temperature-dependent longitudinal resistivity and anomalous Hall effect of this new type granular film were systematically studied. The longitudinal resistivity of the Co nanocluster-assembled granular film first decreased and then increased with increasing measuring temperature, revealing a minimum value at certain temperature, T min . In a low temperature region ( T governed the electrical transport process, and the temperature coefficient of resistance (TCR) showed an insulator-type behavior. The thermal fluctuation-induced tunneling conduction progressively increased with increasing temperature, which led to a decrease in the longitudinal resistivity. In a high temperature region, the TCR showed a metallic-type behavior, which was primarily attributed to the temperature-dependent scattering. Different from the longitudinal resistivity behavior, the saturated anomalous Hall resistivity increased monotonically with increasing measuring temperature. The value of the anomalous Hall coefficient ( R S ) reached 2.3 × 10-9 (Ω cm)/G at 300 K, which was about three orders of magnitude larger than previously reported in blocky single-crystal Co [E. N. Kondorskii, Sov. Phys. JETP 38, 977 (1974)]. Interestingly, the scaling relation ( ρx y A ∝ ρx x γ ) between saturated anomalous Hall resistivity ( ρx y A ) and longitudinal resistivity ( ρ x x ) was divided into two regions by T min . However, after excluding the contribution of tunneling, the scaling relation followed the same rule. The corresponding physical mechanism was also proposed to explain these phenomena.

  14. Superconductivity effects near metal-insulator transition in granular idnium films

    International Nuclear Information System (INIS)

    Belevtsev, B.I.; Komnik, Yu.F.; Fomin, A.V.

    1986-01-01

    The influence of granules superconductivity on the electric properties of granular indium films is investigated under the conditions of partial or full granular localization of electrons. At temperatures below 5 K a minimum of electric resistance and negative magnetoresistance are revealed which are attributed to the competition of hopping conductivity and Josephson intergranular tunneling of electrons

  15. Some complementary results to the granularity of industrial X-ray films

    International Nuclear Information System (INIS)

    Stade, J.

    1987-01-01

    The granularity of industrial x-ray films was examined by measurements of the Wiener spectra. The dependence of the Weiner spectra on film density, type of film, type of developer, energy of the exposing x-radiation, and light exposure, was also investigated. The results revealed that the Weiner spectrum or related quantities were suitable as a tool for measuring the influence of different radiographic parameters on the x-ray film, as well as to characterize its properties. (UK)

  16. Electrical transport properties in Fe-Cr nanocluster-assembled granular films

    Science.gov (United States)

    Wang, Xiong-Zhi; Wang, Lai-Sen; Zhang, Qin-Fu; Liu, Xiang; Xie, Jia; Su, A.-Mei; Zheng, Hong-Fei; Peng, Dong-Liang

    2017-09-01

    The Fe100-xCrx nanocluster-assembled granular films with Cr atomic fraction (x) ranging from 0 to 100 were fabricated by using a plasma-gas-condensation cluster deposition system. The TEM characterization revealed that the uniform Fe clusters were coated with a Cr layer to form a Fe-Cr core-shell structure. Then, the as-prepared Fe100-xCrx nanoclusters were randomly assembled into a granular film in vacuum environments with increasing the deposition time. Because of the competition between interfacial resistance and shunting effect of Cr layer, the room temperature resistivity of the Fe100-xCrx nanocluster-assembled granular films first increased and then decreased with increasing the Cr atomic fraction (x), and revealed a maximum of 2 × 104 μΩ cm at x = 26 at.%. The temperature-dependent longitudinal resistivity (ρxx), magnetoresistance (MR) effect and anomalous Hall effect (AHE) of these Fe100-xCrx nanocluster-assembled granular films were also studied systematically. As the x increased from 0 to 100, the ρxx of all samples firstly decreased and then increased with increasing the measuring temperature. The dependence of ρxx on temperature could be well addressed by a mechanism incorporated for the fluctuation-induced-tunneling (FIT) conduction process and temperature-dependent scattering effect. It was found that the anomalous Hall effect (AHE) had no legible scaling relation in Fe100-xCrx nanocluster-assembled granular films. However, after deducting the contribution of tunneling effect, the scaling relation was unambiguous. Additionally, the Fe100-xCrx nanocluster-assembled granular films revealed a small negative magnetoresistance (MR), which decreased with the increase of x. The detailed physical mechanism of the electrical transport properties in these Fe100-xCrx nanocluster-assembled granular films was also studied.

  17. Exchange coupled CoPt/FePtC media for heat assisted magnetic recording

    Science.gov (United States)

    Dutta, Tanmay; Piramanayagam, S. N.; Ru, Tan Hui; Saifullah, M. S. M.; Bhatia, C. S.; Yang, Hyunsoo

    2018-04-01

    L10 FePtC granular media are being studied as potential future magnetic recording media and are set to be used in conjunction with heat assisted magnetic recording (HAMR) to enable recording at write fields within the range of current day recording heads. Media structures based on a FePtC storage layer and a capping layer can alleviate the switching field distribution (SFD) requirements of HAMR and reduce the noise originating from the writing process. However, the current designs suffer from SFD issues due to high temperature writing. To overcome this problem, we study a CoPt/FePtC exchange coupled composite structure, where FePtC serves as the storage layer and CoPt (with higher Curie temperature, Tc) as the capping layer. CoPt remains ferromagnetic at near Tc of FePtC. Consequently, the counter exchange energy from CoPt would reduce the noise resulting from the adjacent grain interactions during the writing process. CoPt/FePtC bilayer samples with different thicknesses of CoPt were investigated. Our studies found that CoPt forms a continuous layer at a thickness of 6 nm and leads to considerable reduction in the saturation field and its distribution.

  18. Interaction of hydrogen and oxygen with continuous or granular films of palladium

    Energy Technology Data Exchange (ETDEWEB)

    Mikhalenko, I.I.; Prokopov, A.M.; Yagodovskii, V.D.

    1986-03-01

    The authors use desorption and conductometric methods in establishing the existence of three species of adsorbed hydrogen on continuous Pd films and two species on Pd films with a granular structure. Preoxidation of the surface of the continuous films does not affect the rate or kinetic order of hydrogen sorption; oxidation/reduction treatment changes these parameters, but the magnitude of Edes of hydrogen remains unchanged.

  19. Pt/C Fuel Cell Catalyst Degradation

    DEFF Research Database (Denmark)

    Zana, Alessandro

    This thesis investigates the degradation behavior of Pt/C catalysts under simulated automotive conditions. By using the “tool box” synthesis method the Pt loading has been changed from low to high Pt loadings, therefore permitting to study the role of Pt on the degradation of high surface area (H...

  20. Magnetism and magnetoresistance from different origins in Co/ZnO:Al granular films

    Energy Technology Data Exchange (ETDEWEB)

    Quan, Zhiyong, E-mail: quanzy@sxnu.edu.cn; Liu, Xia; Song, Zhilin; Xu, Xiaohong, E-mail: xuxh@dns.sxnu.edu.cn

    2016-12-01

    Co/ZnO:Al granular films were made on glass substrates by sequential magnetron sputter deposition of ultrathin Co layer and ZnO:Al layer at room temperature. The as-deposited films consist of superparamagnetic Co particles dispersed in ZnO:Al (~2% Al) semiconductor matrix. Distinguished magnetoresistance effect at room temperature was obtained in the as-deposited films, which obviously reduced after annealing due to the growth of Co particles. The size of important magnetic particles was analyzed by Langevin function for hysteresis loops and magnetoresistance curves at room temperature. It was found that small magnetic particle contribute to magnetoresistance behavior and large particles dominate the room temperature magnetism in Co/ZnO:Al granular films.

  1. The role of the interface on the magnetic behaviour of granular Fe50Ag50 film

    International Nuclear Information System (INIS)

    Fdez-Gubieda, M.L.; Sarmiento, G.; Fernandez Barquin, L.; Orue, I.

    2007-01-01

    The magnetic behaviour of a Fe 50 Ag 50 granular thin film has been studied by means of AC and DC magnetic measurements. Exchange coupling between magnetic nanoparticles appears at T=<200K decreasing the coercive field of the sample. Additionally, an exchange bias is observed at low temperature related to the existence of a spin disordered interface around the nanoparticles

  2. Electric transport in composite Fe-Ta-O granular film prepared by plasma jet technique

    Czech Academy of Sciences Publication Activity Database

    Lobotka, P.; Vávra, O.; Fendrych, František; Kraus, Luděk

    2002-01-01

    Roč. 240, - (2002), s. 491-493 ISSN 0304-8853. [Metallic Multillayers 2001 (MML'01). Aachen, 25.06.2001-29.06.2001] Institutional research plan: CEZ:AV0Z1010914 Keywords : granular systems * magnetoresistance -thin films * tunneling * Coulomb blockade Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.046, year: 2002

  3. Design criteria for stable Pt/C fuel cell catalysts

    Directory of Open Access Journals (Sweden)

    Josef C. Meier

    2014-01-01

    Full Text Available Platinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3–4 nm and two Pt@HGS catalysts with different particle size, 1–2 nm and 3–4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS. All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested.

  4. Transport Properties of LCMO Granular Films Deposited by the Pulsed Electron Deposition Technique

    Institute of Scientific and Technical Information of China (English)

    CHEN Leiming; XU Bin; ZHANG Yan; CHEN Zhenping

    2011-01-01

    By finely controlling the deposition parameters in the pulsed electron deposition process,granular La2/3Ca1/3MnO3 (LCMO) film was grown on silicon substrates.The substrate temperature,ambient pressure in the deposition chamber and acceleration potential for the electron beam were all found to affect the grain size of the film,resulting in different morphologies of the samples.Transport properties of the obtained granular films,especially the magnetoresistance (MR),were studied.Prominent low-field MR was observed in all samples,indicating the forming of grain boundaries in the sample.The low-field MR show great sensitive to the morphology evolution,which reaches the highest value of about 40% for the sample with the grain size of about 250 nm.More interestingly,positive-MR (p-MR) was also detected above 300 K when low magnetic field applying,whereas it disappeared with higher magnetic field applied up to 1.5 and 2 Tesla.Instead of the spinpolarized tunneling process being commonly regarded as a responsible reason,lattice mismatch between LCMO film and silicon substrate appears to be the origin of the p-MR

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

    KAUST Repository

    Vakarelski, Ivan Uriev

    2013-04-23

    Evaporative lithography using latex particle templates is a novel approach for the self-assembly of suspension-dispersed nanoparticles into ordered microwire networks. The phenomenon that drives the self-assembly process is the propagation of a network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films vertical to the substrate, which are formed during the evaporation of the liquid from the suspension. The stability of the foam films and thus the liquid bridge network stability are due to the presence of a small amount of surfactant in the evaporating solution. We show that the same type of foam-film-stabilized liquid bridge network can also propagate in 3D clusters of spherical particles, which has important implications for the understanding of wet granular matter. © 2013 American Chemical Society.

  6. Template-controlled mineralization: Determining film granularity and structure by surface functionality patterns

    Directory of Open Access Journals (Sweden)

    Nina J. Blumenstein

    2015-08-01

    Full Text Available We present a promising first example towards controlling the properties of a self-assembling mineral film by means of the functionality and polarity of a substrate template. In the presented case, a zinc oxide film is deposited by chemical bath deposition on a nearly topography-free template structure composed of a pattern of two self-assembled monolayers with different chemical functionality. We demonstrate the template-modulated morphological properties of the growing film, as the surface functionality dictates the granularity of the growing film. This, in turn, is a key property influencing other film properties such as conductivity, piezoelectric activity and the mechanical properties. A very pronounced contrast is observed between areas with an underlying fluorinated, low energy template surface, showing a much more (almost two orders of magnitude coarse-grained film with a typical agglomerate size of around 75 nm. In contrast, amino-functionalized surface areas induce the growth of a very smooth, fine-grained surface with a roughness of around 1 nm. The observed influence of the template on the resulting clear contrast in morphology of the growing film could be explained by a contrast in surface adhesion energies and surface diffusion rates of the nanoparticles, which nucleate in solution and subsequently deposit on the functionalized substrate.

  7. Ge clusters and wetting layers forming from granular films on the Si(001) surface

    International Nuclear Information System (INIS)

    Storozhevykh, M S; Arapkina, L V; Yuryev, V A

    2016-01-01

    The report studies the transformation of a Ge granular film deposited on the Si(001) surface at room temperature into a Ge/Si(001) heterostructure as a result of rapid heating and annealing at 600 °C. As a result of the short-term annealing at 600 °C in conditions of a closed system, the Ge granular film transforms into a usual wetting layer and Ge clusters with multimodal size distribution and Ge oval drops having the highest number density. After the long-term thermal treatment of the Ge film at the same temperature, Ge drops disappear; the large clusters increase their sizes at the expense of the smaller ones. The total density of Ge clusters on the surface drastically decreases. The wetting layer mixed c(4 x 2) + p(2 x 2) reconstruction transforms into a single c(4 x 2) one which is likely to be thermodynamically favoured. Pyramids or domes are not observed on the surface after any annealing. (paper)

  8. Temperature dependence of GMR and effect of annealing on electrodeposited Co-Ag granular films

    International Nuclear Information System (INIS)

    Garcia-Torres, Jose; Valles, Elisa; Gomez, Elvira

    2010-01-01

    The magnetoresistance of Co-Ag granular films composed of superparamagnetic and ferromagnetic particles was studied at different temperatures. The increase in the GMR values while decreasing temperature down to 20 K was quantified. The non-saturating behaviour of the MR(H) curves was retained even at the lowest measurement temperature, which was mainly attributed to the dipolar interaction among the superparamagnetic particles. The influence of the annealing conditions on the magnetoresistance was also studied. In all conditions, a decrease in the GMR values was measured being attributed to an increase in the particle size.

  9. Ferromagnetic resonance study of Fe{sub 50}Ag{sub 50} granular film

    Energy Technology Data Exchange (ETDEWEB)

    Sarmiento, G. [Dpto. Electricicidad y Electronica, Universidad del Pais Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain)]. E-mail: websamug@lg.ehu.es; Fdez-Gubieda, M.L. [Dpto. Electricicidad y Electronica, Universidad del Pais Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain); Siruguri, V. [Dpto. Electricicidad y Electronica, Universidad del Pais Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain); UGC-DAE Consortium for Scientific Research, R-5 Shed, BARC Campus, Mumbai 400085 (India); Lezama, L. [Dpto. Quimica Inorganica (UPV/EHU), Apdo. 644, 48080, Bilbao (Spain); Orue, I. [Servicios Generales de Investigacion (SGIKER), Vicerrectorado de Investigacion (UPV/EHU) (Spain)

    2007-09-15

    Fe{sub 50}Ag{sub 50} granular film, produced by the pulsed laser deposition technique, has been studied using ferromagnetic resonance (FMR) at temperatures ranging from 4 to 300K. Three different resonance modes are well observed in the whole temperature range. We have also studied the angular evolution of the resonance peaks at three different temperatures T=150, 250, 300K. The thermal and the angular evolution of the three resonance fields has been interpreted on the basis of the existence of different magnetic coupling between the Fe nanoparticles and a weakly magnetized interface.

  10. Brillouin Light Scattering from Magnetic Excitations in Superparamagnetic and Ferromagnetic Co-Al-O Granular Films

    Science.gov (United States)

    Yoshihara, Akira; Maeda, Toshiteru; Kawamura, Satoshi; Nakamura, Shintaro; Nojima, Tsutomu; Takeda, Yoshihiko; Ohnuma, Shigehiro

    2018-04-01

    A systematic study of Brillouin light scattering (BLS) from superparamagnetic (SPM) and ferromagnetic (FM) Co-Al-O granular films was performed under magnetic fields of up to 4.6 kOe in the standard backscattering geometry at room temperature. The SPM and FM boundary, defined as the Co composition at which the exchange field vanishes, was found to be located at xC(Co) = 59.3 ± 1.3 at. %. From FM films we observed a pair of bulk spin-wave peaks on both the positive- and negative-frequency sides and a surface localized Damon-Eshbach peak only on the positive-frequency side under the present scattering conditions. From SPM films, a pair of broader but propagative excitation peaks with asymmetric intensity were observed on both frequency sides in a spectrum. We performed a numerical analysis of the BLS spectrum by employing the theory developed by Camley and Mills (CM) while retaining dipole and exchange couplings for FM films and only dipole coupling for SPM films. The CM theory successfully reproduced the observed spectrum for both SPM and FM films. The SPM spectrum exhibits a singlet-doublet peak structure similarly to an FM SW spectrum. The SPM peak stems from the dipole-coupled larger-amplitude precession motion of the granule magnetic moment around the external-field-induced magnetization.

  11. Improvement of thermal stability of nano-granular TMR films by using a Mg-Al-O insulator matrix

    Science.gov (United States)

    Kanie, S.; Koyama, S.

    2018-05-01

    A new metal-insulator nano-granular tunneling magnetoresistance (TMR) film made of (Fe-Co)-(Mg-Al-O) has been investigated. It is confirmed that the film has granular structure in which crystal Fe-Co granules are surrounded by an amorphous Mg-Al-O matrix. A large MR ratio of 11.8 % at room temperature is observed for a 42 vol.%(Fe0.6Co0.4)-(Mg-Al-O) film annealed at 395 °C. The electrical resistivity increases rapidly by annealing at above the changing point (500 °C). The changing point is about 300 °C higher than that of conventional (Fe-Co)-(Mg-F) nano-granular TMR films. The 42 vol.%(Fe0.6Co0.4)-(Mg-Al-O) film also exhibits less degradation in the MR ratio at high annealing temperatures such as 600 °C. These results suggest the (Fe-Co)-(Mg-Al-O) film is superior to the (Fe-Co)-(Mg-F) film in thermal stability.

  12. Reclaim/recycle of Pt/C catalysts for PEMFC

    International Nuclear Information System (INIS)

    Zhao, Jishi; He, Xiangming; Tian, Jianhua; Wan, Chunrong; Jiang, Changyin

    2007-01-01

    Platinum was reclaimed from Pt/C catalysts of the PEMFC by drying the degraded Pt/C catalysts at 80 o C for 3 h, followed by sintering at 600 o C for 6 h, dissolution by aqua fortis, purification with hydrochloric acid, reduction and filtration, successively. Pt/C catalysts were prepared again from the reclaimed Pt by two proposed processes, e.g., pH value control process and mass control process. The fuel cell with recycled catalysts presented a power density of over 0.18 W cm -2 . The reclaiming of Pt/C catalysts is a potential way for recycling Pt for PEMFC, reducing the cost of PEMFC

  13. Skew scattering dominated anomalous Hall effect in Cox(MgO)100-x granular thin films

    KAUST Repository

    Zhang, Qiang

    2017-07-31

    We investigated the mechanism(s) of the anomalous Hall effect (AHE) in magnetic granular materials by fabricating 100-nm-thick thin films of Cox(MgO)100-x with a Co volume fraction of 34≤x≤100 using co-sputtering at room temperature. We measured the temperature dependence of longitudinal resistivity (ρxx) and anomalous Hall resistivity (ρAHE) from 5 K to 300 K in all samples. We found that when x decreases from 100 to 34, the values of ρxx and ρAHE respectively increased by about four and three orders in magnitude. By linearly fitting the data, obtained at 5 K, of anomalous Hall coefficient (Rs) and of ρxx to log(Rs)~γlog(ρxx), we found that our results perfectly fell on a straight line with a slope of γ= 0.97±0.02. This fitting value of γ in Rsρxxγ clearly suggests that skew scattering dominated the AHE in this granular system. To explore the effect of the scattering on the AHE, we performed the same measurements on annealed samples. We found that although both ρxx and ρAHE significantly reduced after annealing, the correlation between them was almost the same, which was confirmed by the fitted value, γ=0.99±0.03. These data strongly suggest that the AHE originates from the skew scattering in Co-MgO granular thin films no matter how strong the scatterings of electrons by the interfaces and defects is. This observation may be of importance to the development of spintronic devices based on MgO.

  14. Diode-like behavior of I–V curves of CoFe–(Al–O)/Si(100) granular thin films

    Energy Technology Data Exchange (ETDEWEB)

    Tuan Anh, Nguyen [ITIMS, Hanoi University of Science and Technology (HUST), Hanoi 10000 (Viet Nam); Hanoi Community College (HCC), Trung Kinh, Cau giay, Hanoi 10000 (Viet Nam); Van Cuong, Giap [ITIMS, Hanoi University of Science and Technology (HUST), Hanoi 10000 (Viet Nam); HungYen University of Technology and Education (UTEHY), Khoai chau, Hung Yen 39000 (Viet Nam); Anh Tuan, Nguyen, E-mail: tuanna@itims.edu.vn [ITIMS, Hanoi University of Science and Technology (HUST), Hanoi 10000 (Viet Nam)

    2015-01-15

    In this study, the electrical performance of (Co{sub 70}Fe{sub 30}){sub x}(Al–O){sub 1−x} (where x=0.1 and 0.3) granular thin films sputtered on Si(1 0 0) substrates, which were subsequently annealing at 350 °C for 1 h in vacuum, was investigated. The millimeter-sized samples were installed in an in-plane lateral Ag electrode configuration on the surface. The current–voltage (I–V) characteristics were measured in bias voltages of approximately ±7 V. The I–V curves demonstrated the so-called large Coulomb gaps and diode-like asymmetric behavior similar to a Zener diode-type rectification. This remarkable behavior was evaluated using the most suitable transport models. Results suggest that an effective magnetic diode could be fabricated from millimeter-sized magnetic granular thin films. - Highlights: • The granular MTJ systems can induce a strong collective Coulomb blockage effect. • Isolated magnetic nanoparticles can form asymmetric nano-double barrier MTJ chains. • Discrete system can induce diode-like rectification as a molecular electronic rectifier. • Irreversible cotunneling through nano-double barrier MTJ chains yields rectification. • Magnetic tunnel diodes can be created simply from the granular MTJ-type thin films.

  15. Effect of trap states and microstructure on charge carrier conduction mechanism through semicrystalline poly(vinyl alcohol) granular film

    Science.gov (United States)

    Das, A. K.; Bhowmik, R. N.; Meikap, A. K.

    2018-05-01

    We report a comprehensive study on hysteresis behaviour of current-voltage characteristic and impedance spectroscopy of granular semicrystalline poly(vinyl alcohol) (PVA) film. The charge carrier conduction mechanism and charge traps of granular PVA film by measuring and analyzing the temperature dependent current-voltage characteristic indicate a bi-stable electronic state in the film. A sharp transformation of charge carrier conduction mechanism from Poole-Frenkel emission to space charge limited current mechanism has been observed. An anomalous oscillatory behaviour of current has been observed due to electric pulse effect on the molecular chain of the polymer. Effect of microstructure on charge transport mechanism has been investigated from impedance spectroscopy analysis. An equivalent circuit model has been proposed to explain the result.

  16. Double-layered perpendicular magnetic recording media of granular-type FePt-MgO films

    International Nuclear Information System (INIS)

    Zhang Zhengang; Singh, Amarendra K.; Yin Jinhua; Perumal, A.; Suzuki, Takao

    2005-01-01

    The recording performance of double-layered granular-type FePt-MgO perpendicular magnetic recording media fabricated onto glass discs by sputtering is investigated. The (0 0 1)-textured FePt granular films are obtained by annealing FePt/MgO multilayers. Three different multilayer structures are compared in their magnetic properties and recording SNR performances. To evaluate thermal stability property of these granular-type FePt disks, the time-dependent magnetic force microscope (MFM) signal from the written bits on one of these disks is recorded in the temperature range 25-200 degree sign C. The signal decay at high observation temperature is interpreted based on the temperature dependence of magnetic anisotropy (K u )

  17. Integrated-circuit microwave detector based on granular high-Tc thin films. [Y-Ba-Cu-O

    Energy Technology Data Exchange (ETDEWEB)

    Drobinin, A.V.; Lutovinov, V.S.; Starostenko, I.V. (Moscow Inst. of Radioengineering, Electronics and Automation, (MIREA), Moscow (USSR))

    1991-12-01

    A highly sensitive integrative-circuit microwave detector based on granular High-Tc film has been designed. All matching circuits and High-Tc microbridge are located on the same substrate. The voltage responsivity 10{sup 3} V/W has been found at 65 K and frequency 5 GHz. Different modes of microwave detection have been observed: bolometric response near Tc in high-quality films, rectification mode caused by an array of weak links dominating in low-quality films, detection caused by nonlinear magnetic flux motion. (orig.).

  18. Sign change of magnetoresistance in Gd-doped amorphous carbon granular films.

    Science.gov (United States)

    Ding, Shihao; Jin, Chao; Fan, Ziwei; Li, Peng; Bai, Haili

    2015-11-11

    Gd/C granular films with 11% Gd were fabricated by facing-target magnetron sputtering at room temperature and then annealed at 300-650 °C for 1.5 h. A magnetoresistance of -82% was obtained in the Gd/C films annealed at 650 °C at 3 K under a magnetic field of 50 kOe. A sign change of the magnetoresistance from negative to positive and then back to negative was observed in all samples as the temperature decreases. Grain boundary scattering effects, wave-function-shrinkage, cotunneling and Gd-Gd interactions account for the mechanisms of the magnetoresistance effects in different temperature regions. The sign of the magnetoresistance also varies as the magnetic field increases. At the transition temperature of 25 K, the wave-function-shrinkage effect competes with cotunneling and Gd-Gd interactions at different magnetic fields. The competition between the wave-function-shrinkage effect and the grain boundary scattering effect is approximately at the transition temperature of 100 K. The temperature range of positive magnetoresistance expands and transition temperatures are changed as the annealing temperature increases. It is related to the expansion of the temperature region for the wave-function-shrinkage effect which occurs in the Mott variable range hopping conduction mechanism.

  19. Granular and layered ferroelectric–ferromagnetic thin-film nanocomposites as promising materials with high magnetotransmission effect

    Energy Technology Data Exchange (ETDEWEB)

    Akbashev, A.R. [Department of Materials Science, Moscow State University, 119992 Moscow (Russian Federation); Telegin, A.V., E-mail: telegin@imp.uran.ru [M.N. Miheev Institute of Metal Physics of Ural Branch of RAS, 620990 Ekaterinburg (Russian Federation); Kaul, A.R. [Department of Chemistry, Moscow State University, 119992 Moscow (Russian Federation); Sukhorukov, Yu.P. [M.N. Miheev Institute of Metal Physics of Ural Branch of RAS, 620990 Ekaterinburg (Russian Federation)

    2015-06-15

    Epitaxial thin films of granular and layered nanocomposites consisting of ferromagnetic perovskite Pr{sub 1–x}Sr{sub x}MnO{sub 3} and ferroelectric hexagonal LuMnO{sub 3} were grown on ZrO{sub 2}(Y{sub 2}O{sub 3}) substrates using metal-organic chemical vapor deposition (MOCVD). A self-organized growth of the granular composite took place in situ as a result of phase separation of the Pr–Sr–Lu–Mn–O system into the perovskite and hexagonal phases. Optical transmission measurements revealed a large negative magnetotransmission effect in the layered nanocomposite over a wide spectral and temperature range. The granular nanocomposite unexpectedly showed an even larger, but positive, magnetotransmission effect at room temperature. - Highlights: • Thin-film ferromagnetic–ferroelectric nanocomposites have been prepared by MOCVD. • Giant change of optical transparency of nanocomposites in magnetic field was detected. • Positive magnetotransmission in the granular nanocomposite was discovered in the IR. • Negative magnetotransmission in the layered nanocomposite was revealed in the IR. • Ferroelectric–ferromangetic nanocomposite is a promising material for optoelectronics.

  20. Granular and layered ferroelectric–ferromagnetic thin-film nanocomposites as promising materials with high magnetotransmission effect

    International Nuclear Information System (INIS)

    Akbashev, A.R.; Telegin, A.V.; Kaul, A.R.; Sukhorukov, Yu.P.

    2015-01-01

    Epitaxial thin films of granular and layered nanocomposites consisting of ferromagnetic perovskite Pr 1–x Sr x MnO 3 and ferroelectric hexagonal LuMnO 3 were grown on ZrO 2 (Y 2 O 3 ) substrates using metal-organic chemical vapor deposition (MOCVD). A self-organized growth of the granular composite took place in situ as a result of phase separation of the Pr–Sr–Lu–Mn–O system into the perovskite and hexagonal phases. Optical transmission measurements revealed a large negative magnetotransmission effect in the layered nanocomposite over a wide spectral and temperature range. The granular nanocomposite unexpectedly showed an even larger, but positive, magnetotransmission effect at room temperature. - Highlights: • Thin-film ferromagnetic–ferroelectric nanocomposites have been prepared by MOCVD. • Giant change of optical transparency of nanocomposites in magnetic field was detected. • Positive magnetotransmission in the granular nanocomposite was discovered in the IR. • Negative magnetotransmission in the layered nanocomposite was revealed in the IR. • Ferroelectric–ferromangetic nanocomposite is a promising material for optoelectronics

  1. The role of the interface on the magnetic behaviour of granular Fe{sub 50}Ag{sub 50} film

    Energy Technology Data Exchange (ETDEWEB)

    Fdez-Gubieda, M.L. [Dpto. Electricidad y Electronica. Universidad del Pais Vasco Apdo 644. 48080 Bilbao (Spain)]. E-mail: malu@we.lc.ehu.es; Sarmiento, G. [Dpto. Electricidad y Electronica. Universidad del Pais Vasco Apdo 644. 48080 Bilbao (Spain); Fernandez Barquin, L. [CITIMAC, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander (Spain); Orue, I. [SGIKER, Servicios Generales de medidas magneticas, Universidad del Pais Vasco (Spain)

    2007-03-15

    The magnetic behaviour of a Fe{sub 50}Ag{sub 50} granular thin film has been studied by means of AC and DC magnetic measurements. Exchange coupling between magnetic nanoparticles appears at T=<200K decreasing the coercive field of the sample. Additionally, an exchange bias is observed at low temperature related to the existence of a spin disordered interface around the nanoparticles.

  2. Investigation of the correlation between dielectric function, thickness and morphology of nano-granular ZnO very thin films

    Energy Technology Data Exchange (ETDEWEB)

    Gilliot, Mickaël, E-mail: mickael.gilliot@univ-reims.fr [Laboratoire d' Ingénierie et Sciences des Matériaux, Université de Reims Champagne-Ardenne (France); Hadjadj, Aomar [Laboratoire d' Ingénierie et Sciences des Matériaux, Université de Reims Champagne-Ardenne (France); Martin, Jérôme [Laboratoire de Nanotechnologie et d' Instrumentation Optique, Université de Technologie de Troyes (France)

    2015-12-31

    Thin nano-granular ZnO layers were prepared using a sol–gel synthesis and spin-coating deposition process with a thickness ranging between 20 and 120 nm. The complex dielectric function (ϵ) of the ZnO film was determined from spectroscopic ellipsometry measurements. Up to a critical thickness close to 60 nm, the magnitude of both the real and the imaginary parts of ϵ rapidly increases and then slowly tends to values closer to the bulk ZnO material. This trend suggests a drastic change in the film porosity at both sides of this critical thickness, due to the pre-heating and post-crystallization processes, as confirmed by additional characterization of the structure and the morphology of the ZnO films. - Highlights: • c-Axis oriented ZnO thin films were grown with different morphological states. • The morphology and structures are controlled by controlling the thickness. • The optical properties are correlated to morphological evolution. • Two growth behaviors and property evolutions are identified around a critical thickness.

  3. Skew scattering dominated anomalous Hall effect in Cox(MgO)100-x granular thin films

    KAUST Repository

    Zhang, Qiang; Wen, Yan; Zhao, Yuelei; Li, Peng; He, Xin; Zhang, Junli; He, Yao; Peng, Yong; Yu, Ronghai; Zhang, Xixiang

    2017-01-01

    We investigated the mechanism(s) of the anomalous Hall effect (AHE) in magnetic granular materials by fabricating 100-nm-thick thin films of Cox(MgO)100-x with a Co volume fraction of 34≤x≤100 using co

  4. Ferromagnetic resonance studies on (Co40Fe40B20)x(SiO2)1-x granular magnetic films

    International Nuclear Information System (INIS)

    Yildiz, F.; Kazan, S.; Aktas, B.; Tarapov, S.I.; Tagirov, L.; Granovsky, B.

    2006-01-01

    Magnetic properties of granular (Co 40 Fe 40 B 20 ) x (SiO 2 ) 1-x thin films (x=0.37-0.53) have been studied by ferromagnetic resonance (FMR) technique. Samples have been prepared by ion-beam deposition of Co-Fe-B particles and SiO 2 on sitall ceramic substrate. The FMR measurements have been done for different orientations of DC magnetic field with respect to the sample plane. It was found that the deduced value of effective magnetization from FMR data of the thin granular film is reduced by the volume-filling factor of the bulk saturation magnetization. The overall magnetization changes from 152 to 515G depending on the ratio of the magnetic nanoparticles in the SiO 2 matrix. From angular measurements an induced in-plane uniaxial anisotropy has been obtained due to the preparation of the film conditions as well

  5. Fabrication and Magnetic Properties of Fe65Co35–ZnO Nano-Granular Films

    Directory of Open Access Journals (Sweden)

    Wang Guowei

    2010-01-01

    Full Text Available Abstract A series of nano-granular films composed of magnetic metal (Fe65Co35 granules with a few nanometers in size and semiconductor oxide (ZnO have been fabricated by a magnetron sputtering method, and excellent soft magnetic properties have been achieved in a wide metal volume fraction (x range for as-deposited samples due to the exchange coupling between FeCo granules (a ferromagnetic interaction in nano-scale. In a wide range (0.53 < x < 0.71, the films exhibit coercivity H C not exceeding 15 Oe, along with high resistivity. Especially for the sample with x = 0.67, coercivities in hard and easy axes are 1.43 and 7.08 Oe, respectively, 4πM S = 9.85 kg, and ρ reaches 2.06 × 103 μΩ cm. The dependence of complex permeability μ = μ′ − jμ″ on frequency shows that the real part μ′ is more than 100 below 1.83 GHz and that the ferromagnetic resonance frequency reaches 2.31 GHz, implying the promising for high frequency application. The measured negative temperature coefficient of resistivity reveals that may be the weak localized electrons existing in samples mediate the exchange coupling.

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

    KAUST Repository

    Vakarelski, Ivan Uriev; Marston, Jeremy; Thoroddsen, Sigurdur T

    2013-01-01

    network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films

  7. Granular flow

    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....

  8. Fine structures and magnetic properties of FeCo granular thin films with plasma polymerized (C4F8) n matrix

    International Nuclear Information System (INIS)

    Kakizaki, K.; Yasoshima, S.; Choi, K.-K.; Kamishima, K.; Hiratsuka, N.

    2007-01-01

    In this paper a method for polymerization of fluorocarbon gas in argon plasma to obtain a novel granular structure was reported. We prepared granular films where FeCo fine particles were distributed in plasma-polymerized fluorocarbon matrix by a facing-targets RF magnetron sputtering method, and investigated the correlation between their structures and magnetic properties. The magnetization of the films prepared with the partial pressure of fluorocarbon gas between 0 and 1.0 mTorr decreased linearly, because the FeCo content in a unit volume of a film decreased when a polymerized material was used as the matrix. However, the coercivity of the films decreased drastically with increasing the partial pressure of fluorocarbon gas above 0.4 mTorr. This is because the magnetic anisotropy of FeCo particles is decreased by the decrease of grain size. It was confirmed by a TEM observation that the FeCo-(C 4 F 8 ) n films had the granular structure which was constituted by the very fine FeCo particles and the plasma-polymerized fluorocarbon matrix. For the film deposited at the partial pressure of fluorocarbon gas of 0.4 mTorr, the size of FeCo magnetic particles is about 20 nm. On the other hand, the size of FeCo particles is decreased to about 8 nm when the film deposited at the partial pressure of fluorocarbon gas of 0.8 mTorr and its distribution is small

  9. SiO2 stabilized Pt/C cathode catalyst for proton exchange membrane fuel cells

    International Nuclear Information System (INIS)

    Zhu Tong; Du Chunyu; Liu Chuntao; Yin Geping; Shi Pengfei

    2011-01-01

    This paper describes the preparation of SiO 2 stabilized Pt/C catalyst (SiO 2 /Pt/C) by the hydrolysis of alkoxysilane, and examines the possibility that the SiO 2 /Pt/C is used as a durable cathode catalyst for proton exchange membrane fuel cells (PEMFCs). TEM and XRD results revealed that the hydrolysis of alkoxysilane did not significantly change the morphology and crystalline structure of Pt particles. The SiO 2 /Pt/C catalyst exhibited higher durability than the Pt/C one, due to the facts that the silica layers covered were beneficial for reducing the Pt aggregation and dissolution as well as increasing the corrosion resistance of supports, although the benefit of silica covering was lower than the case of Pt/CNT catalyst. Also, it was observed that the activity of the SiO 2 /Pt/C catalyst for the oxygen reduction reaction was somewhat reduced compared to the Pt/C one after the silica covering. This reduction was partially due to the low oxygen kinetics as revealed by the rotating-disk-electrode measurement. Silica covering by hydrolysis of only 3-aminopropyl trimethoxysilane is able to achieve a good balance between the durability and activity, leading to SiO 2 /Pt/C as a promising cathode catalyst for PEMFCs.

  10. Ferromagnetic resonance spectroscopy of CoFeZr-Al{sub 2}O{sub 3} granular films containing “FeCo core – oxide shell” nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Kołtunowicz, Tomasz N., E-mail: t.koltunowicz@pollub.pl [Department of Electrical Devices and High Voltage Technology, Lublin University of Technology, Nadbystrzycka 38a, 20-618 Lublin (Poland); Zukowski, Pawel [Department of Electrical Devices and High Voltage Technology, Lublin University of Technology, Nadbystrzycka 38a, 20-618 Lublin (Poland); Sidorenko, Julia [Department of Semiconductors Physics and Nanoelectronics, Belarusian State University, Independence Av. 4, 220030 Minsk (Belarus); Bayev, Vadim; Fedotova, Julia A. [Institute for Nuclear Problems, Belarusian State University, Bobrujskaya Str. 11, 220030 Minsk (Belarus); Opielak, Marek [Institute of Transport, Combustion Engines and Ecology, Lublin University of Technology, Nadbystrzycka 36, 20-618 Lublin (Poland); Marczuk, Andrzej [Department of Transporting and Agricultural Machinery, University of Life Sciences in Lublin, Głeboka 28, 20-612 Lublin (Poland)

    2017-01-01

    Ferromagnetic resonance (FMR) spectroscopy is applied for comparative analysis of granular (CoFeZ){sub x}(Al{sub 2}O{sub 3}){sub 100−x}, (31 at%≤x≤47 at%) films containing pure FeCo-based nanoparticles (NPs) or “FeCo-based core – oxide shell” NPs inside Al{sub 2}O{sub 3} matrix when deposited in oxygen-free or oxygen-containing atmosphere, correspondingly. It is established that g-factor extracted from the FMR spectra of films with core–shell NPs decreases with x below the value g =2.0023 for free electron that is untypical for metallic NPs. This effect is associated with the formation of the interface between ferromagnetic core and antiferromagnetic (ferrimagnetic) oxide shell of NPs. - Highlights: • CoFeZr-Al{sub 2}O{sub 3} granular films containing “FeCo core – oxide shell” nanoparticles. • magnetic anisotropy of (CoFeZr){sub x}(Al{sub 2}O{sub 3}){sub 100−x} films is of an easy plane type. • essential difference in dependence of g-factor on metal content in non- and oxidized film. • non-oxidized samples indicates the reduction of the value of films magnetization.

  11. Bias voltage dependence of tunneling magnetoresistance in granular C60–Co films with current-perpendicular-to-plane geometry

    International Nuclear Information System (INIS)

    Sakai, Seiji; Mitani, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Avramov, Pavel; Ohtomo, Manabu; Naramoto, Hiroshi; Takanashi, Koki

    2012-01-01

    Voltage-dependence of the tunneling magnetoresistance effect in the granular C 60 –Co films has been investigated for the samples with the current-perpendicular-to-plane geometry. The transport measurements under this geometry demonstrate that the granular C 60 –Co films show an unusual exponential bias voltage dependence of the magnetoresistance ratio down to zero voltage. Small characteristic energies of less than 10's meV are derived from the temperature dependences of the characteristic voltage in the exponential relationship. Considering the magnitudes of the voltage drop between Co nanoparticles and also the effect of cotunneling on the energy values, the characteristic energies for the voltage-induced degradation of the spin polarization are found to show a satisfactory agreement with that for the thermally-induced one. It can be reasonably expected that the onset of magnetic disorder to the localized d-electron spins at the interface region of the C 60 -based matrix (C 60 –Co compound) with Co nanoparticles leading to the unusual voltage and temperature dependence of the magnetoresistance ratio and the spin polarization at low temperatures. - Highlights: ► Unusual voltage dependence of the TMR effect in granular C 60 –Co films is studied. ► Linear temperature-characteristic voltage dependence in the MR–V relationship. ► Spin-flip scattering by the exchange-coupled d-electron spins at the interface.

  12. Nano-Pt/C electrocatalysts: synthesis and activity for alcohol oxidation

    International Nuclear Information System (INIS)

    Huong Nguyen, Thi Giang; Anh Pham, Thi Van; Phuong, Thi Xuan; Binh Lam, Thi Xuan; Tran, Van Man; Thoa Nguyen, Thi Phuong

    2013-01-01

    Nano-sized platinum electrocatalysts on a carbon support (Pt/C) have been synthesized by the polyol reduction method under microwave irradiation using ethylene glycol (EG) as the reductant and carbon vulcan XC-72R as the support material. The physical characteristics of the Pt/C materials were analyzed using transmission electron microscopy and Brunauer–Emmet–Teller nitrogen adsorption theory. The glycerol and EG electro-oxidation in alkaline media on the Pt/C catalysts was investigated with cyclic voltammetry and chronoamperometry. The particle size of Pt on carbon was about 3.0 nm. The catalytic activity for the alcohol electro-oxidation of Pt/C materials synthesized in various pH values (7.9–9.5) was found to be significantly higher than that of commercial Pt/C (Aldrich Sigma, 10 wt% Pt/activated carbon). The Pt/C catalyst synthesized in pH 9.5 showed the best electrochemical behavior. At all the synthesized Pt/C electrodes, compared with glycerol, the oxidation rate of EG was about ten times higher. (paper)

  13. Scaling of Hall coefficient in Co-Bi granular thin films

    Directory of Open Access Journals (Sweden)

    Speliotis Th.

    2013-01-01

    Full Text Available A series of Co-Bi thin films with Co concentrations c=0, 0.05, 0.2, 0.26, 0.3, 0.333, 0.375, 0.545, were grown by magnetron sputtering on Si(100/SiNX substrates. Resistivity measurements at zero field (ρxx as a function of temperature-T exhibit an exponential variation with T in the region of 240K

  14. Far infrared near normal specular reflectivity of Nix(SiO2)1-x (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) granular films

    KAUST Repository

    Massa, Né stor E.; Denardin, Juliano C.; Socolovsky, Leandro M.; Knobel, Marcelo; De La Cruz, Fernando Pablo; Zhang, Xixiang

    2010-01-01

    of transition metal granular films with different metal fractions against what is known for conducting oxides. Films for Nix(SiO2)1-x (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) were studied by temperature dependent far infrared measurements. While for pure Ni

  15. Quantum dynamics of small Josephson junctions: an application to superconductivity in granular films

    International Nuclear Information System (INIS)

    Fisher, M.P.A.

    1986-01-01

    This thesis is devoted to a study of the quantum dynamics of small Josephson junctions. Of interest are those features of the junction's behavior which depend explicitly on the quantum mechanical nature of the phase difference phi between the superconductors. In Chapters I and II several calculations are described which focus on the junction's DC resistance. A fully quantum mechanical Hamiltonian is employed that incorporates the dissipative effects due to the unpaired electrons by coupling to a bath of harmonic oscillators. It is shown that the model exhibits a novel zero temperature phase transition as a function of the strength of the dissipation. In the low dissipation regime the phase is free to tunnel quantum mechanically and the junction's resistance is finite; in response to an external current, tunnelling induces successive 2π phase slips leading to a finite voltage state. In contrast, in the high dissipation regime, tunnelling is suppressed and the junction behaves as a superconductor carrying current with no resistive losses. In Chapters III and IV, these results are applied in an attempt to explain the recent observation that in ultra thin Sn films there is apparently a universal normal state sheet resistance above which superconductivity cannot be established

  16. Interaction of a laser beam with a target. Application to the fabrication of granular superconducting films

    International Nuclear Information System (INIS)

    Desserre, Jacques.

    1974-01-01

    The aim was to prepare a superconductor of high T(c). First are given the different simplified theories (BCS, Mac Millan) whereby the critical temperature of a superconductor can be calculated, with a view to its optimization. A material and a preparation technique were chosen on the basis of these theories. The method uses phenomena which occur during the interaction of a coherent pulsed light beam, emitted by a laser, with the surface of a metallic or nonmetallic target. Different theoretical models of this interaction are proposed. Special attention is paid to complex targets (alloys, compounds) and the construction of a model describing the vaporization of a compound is suggested. By a suitable choice of laser, based on the energy emission profile and the value of the energy supplied, congruent vaporization of the target is possible. The technique was applied to the preparation of thin layers by condensation onto a substrate of the vapor and the plasma emitted during the interaction. The deposits generally have the same structure as the bulk compound used as target while the atomic composition of the film may be slightly different. Thin layers of Ni 3 Mn, CdTe, ZnC, HfC were prepared in this way without treatment of the deposits after condensation. Simultaneous vaporization of the compound ReBe 22 in the bulk state gave filaments made up of small grains (20A), identical in composition with the target. The beryllium α phase (compact hexagonal) was identified but the electron diffraction study showed the existence of several other phases of unknown structure. The superconducting properties changed with time [fr

  17. Catalytic activity of hydrophobic Pt/C/PTFE catalysts of different PTFE content for hydrogen-water liquid exchange reaction

    International Nuclear Information System (INIS)

    Hu Sheng; Xiao Chengjian; Zhu Zuliang; Luo Shunzhong; Wang Heyi; Luo Yangming; Wang Changbin

    2007-01-01

    10%Pt/C catalysts were prepared by liquid reduction method. PTFE and Pt/ C catalysts were adhered to porous metal and hydrophobic Pt/C/PTFE catalysts were prepared. The structure and size of Pt crystal particles of Pt/C catalysts were analyzed by XRD, and their mean size was 3.1 nm. The dispersion state of Pt/C and PTFE was analyzed by SEM, and they had good dispersion mostly, but PTFE membrane could be observed on local parts of Pt/C/PTFE surface. Because of low hydrophobicity, Pt/C/ PTFE catalysts have low activity when the mass ratio of PTFE and Pt/C is 0.5: 1, and their catalytic activity increases markedly when the ratio is 1:1. When the ratio increases again, more Pt active sites would be covered by PTFE and interior diffusion effect would increase, which result in the decrease of catalytic activity of Pt/C/PTFE. By PTFE pretreatment of porous metal carrier, the activity of Pt/C/PTFE catalysts decreases when the mass ratio of PTFE and Pt/C is 0.5:1, and their activity decreases when the mass ratio is 1:1. (authors)

  18. Temperature dependence of magnetotransport behavior and its correlation with inter-particle interaction in Cu100−xCox granular films

    International Nuclear Information System (INIS)

    Kumar, Dinesh; Chaudhary, Sujeet; Pandya, Dinesh K.

    2013-01-01

    Granular Cu 100−x Co x (x=15.1-30.9) films were deposited by magnetron co-sputtering and their magnetotransport properties were investigated as a function of temperature. We observed that with increasing cobalt content the room temperature magnetoresistance (MR) shows a maximum at x=20.9. With decreasing temperature, it is observed that the cobalt concentration at which the maximum MR occurs shifts progressively towards lower Co concentration. This behavior has been discussed in terms of the inter-particle magnetic interactions.

  19. ETEM observation of Pt/C electrode catalysts in a moisturized cathode atmosphere

    International Nuclear Information System (INIS)

    Yoshida, K; Zhang, X; Tanaka, N; Boyes, E D; Gai, P L

    2014-01-01

    There have been reports of challenges in designing platinum carbon (Pt/C) electrode catalysts for PEMFC. Pt/C electrode catalysts deactivate much faster on the cathode (in moisturized O 2 ) than on the anode (in H 2 ). To understand influences of moisture and oxygen on the deactivation of the Pt/C catalysts in proton-exchange-membrane fuel cells (PEMFCs), spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied with a high-speed CCD camera. Structural changes of the Pt/C electrode catalysts were dynamically recorded in moisturized nitrogen, oxygen and hydrogen. The mass spectrometry confirmed the moisture content (between 5 to 30 %) of nitrogen driving gas through a humidifier. Coalescence of platinum nanoparticles (D = 3.24 nm) was carefully evaluated in pure N 2 and moisturized N 2 atmosphere. The Pt/C showed considerable structural weakness in a moisturized N2 atmosphere. Comparable results obtained by AC-ETEM in different gas atmospheres also suggested ways to improve the oxygen reduction reaction (ORR). In this paper, the deactivation process due to moisture (hydroxylation) of carbon supports is discussed using for comparison the movement of platinum nanoparticles measured in moisturized nitrogen and pure nitrogen atmospheres

  20. Granular patterns

    CERN Document Server

    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.

  1. Ethanol electrooxidation on Pt/C and Pd/C catalysts promoted with oxide

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Changwei [Department of Chemistry and Institute of Nanochemistry, Jinan University, Guangzhou 510632 (China); State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Shen, Pei kang [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Liu, Yingliang [Department of Chemistry and Institute of Nanochemistry, Jinan University, Guangzhou 510632 (China)

    2007-02-10

    This research aims to investigate Pd-based catalysts as a replacement for Pt-based catalysts for ethanol electrooxidation in alkaline media. The results show that Pd/C has a higher catalytic activity and better steady-state behaviour for ethanol oxidation than that of Pt/C. The effect of the addition of CeO{sub 2} and NiO to the Pt/C and Pd/C electrocatalysts on ethanol oxidation is also studied in alkaline media. The electrocatalysts with a weight ratio of noble metal (Pt, Pd) to CeO{sub 2} of 2:1 and a noble metal to NiO ration 6:1 show the highest catalytic activity for ethanol oxidation. The oxide promoted Pt/C and Pd/C electrocatalysts show a higher activity than the commercial E-TEK PtRu/C electrocatalyst for ethanol oxidation in alkaline media. (author)

  2. First-principles calculations of a high-pressure synthesized compound PtC

    International Nuclear Information System (INIS)

    Li Linyan; Yu Wen; Jin Changqing

    2005-01-01

    The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions

  3. Spreading of a granular droplet

    Science.gov (United States)

    Clement, Eric; Sanchez, Ivan; Raynaud, Franck; Lanuza, Jose; Andreotti, Bruno; Aranson, Igor

    2008-03-01

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

  4. Catalytic Liquefaction of Humin Substances from Sugar Biorefineries with Pt/C in 2-Propanol

    NARCIS (Netherlands)

    Wang, Y.; Agarwal, S.; Heeres, H. J.

    The catalytic liquefaction of humins, the solid byproduct from the conversion of C6 sugars (glucose, fructose) to S-hydroxymethylfurfural (HMF) and levulinic acid (LA), using a supported Pt/C catalyst in isopropanol (IPA) as the solvent was investigated. At bench mark conditions (400 degrees C, 7 h,

  5. Hydrogenation of fructose to 2,5-dimethyltetrahydrofuran using a sulfur poisoned Pt/C catalyst

    Science.gov (United States)

    In order to expand the number of biobased chemicals available, fructose has been hydrogenated to 2,5-dimethyltetrahydrofuran using a sulfided Pt/C catalyst. The reaction was carried out in a stirred reactor at 10.3 MPa H2 and 175°C which allowed a 10% fructose solution to be converted in about 2 h. ...

  6. Porous-microelectrode study on Pt/C catalysts for methanol electrooxidation

    International Nuclear Information System (INIS)

    Umeda, Minoru; Kokubo, Mitsuhiro; Mohamedi, Mohamed; Uchida, Isamu

    2003-01-01

    We have developed a porous-microelectrode (PME) to investigate the electroactivity of catalyst particles for proton exchange membrane fuel cells. The cavity at the tip of the PME was filled with Pt/C catalysts prepared by impregnation method. Cyclic voltammograms (CVs) recorded in 1 N H 2 SO 4 aqueous solution revealed that the active area of the stacked catalysts exist not only at the surface but also inside of the stack. For methanol electrooxidation, 30 wt.% Pt/C exhibited the highest electroactivity, whereas the 50 wt.% Pt/C showed extremely small current. The small current is considered as a result of a small active-surface area. Methanol oxidation peak potential shifted toward cathodic direction as Pt-loading decreased, which agrees well with the Pt-oxide formation potential. The activation energy for methanol oxidation was assessed to be 44±3 kJ mol -1 for all Pt/C catalysts and Pt-disc electrode

  7. Phase-glass scaling near the coherence transition in granular HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconducting thin films

    Energy Technology Data Exchange (ETDEWEB)

    Roa-Rojas, J.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A. A. 14490, Bogota DC (Colombia); Prieto, P. [Grupo de Peliculas Delgadas, Departamento de Fisica, Universidad del Valle, A. A. 25360, Cali (Colombia)

    2005-07-01

    Systematic measurements of electrical magnetoconductivity near the coherence transition of granular HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films are reported. Experiments performed in magnetic fields ranging from 0 to 2500 Oe reveal that close to the coherence transition temperature T{sub c0}(H), the correlation length scales as a power law of temperature with a thermal-dependent critical exponent, {nu}. In low external fields the corresponding value of {nu} is consistent with the two-dimensional phase-glass model, which is in the same dynamical universality class of the so-called vortex-glass model. At applied fields H > 1000 Oe, the vortex dynamics becomes stronger and the coherence transition is not observed. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Optical properties of Au–TiO{sub 2} and Au–SiO{sub 2} granular metal thin films studied by Spectroscopic Ellipsometry

    Energy Technology Data Exchange (ETDEWEB)

    Bakkali, H., E-mail: hicham.bakkali@mail.uca.es [Departamento de Física de la Materia Condensada and Instituto de Microscopía Electrónica y Materiales (IMEYMAT), Universidad de Cadiz, 11510 Puerto Real, Cádiz (Spain); Centro de Ciencias Aplicadas y Desarrollo Tecnológico (CCADET), Universidad Nacional Autónoma de México (UNAM), México, D.F. 04510 (Mexico); Blanco, E.; Dominguez, M. [Departamento de Física de la Materia Condensada and Instituto de Microscopía Electrónica y Materiales (IMEYMAT), Universidad de Cadiz, 11510 Puerto Real, Cádiz (Spain); Mora, M.B. de la [CONACyT Research Fellow-CCADET, Universidad Nacional Autónoma de México (UNAM), México, D.F. 04510 (Mexico); Sánchez-Aké, C.; Villagrán-Muniz, M. [Centro de Ciencias Aplicadas y Desarrollo Tecnológico (CCADET), Universidad Nacional Autónoma de México (UNAM), México, D.F. 04510 (Mexico)

    2017-05-31

    Highlights: • Gold NPs embedded in TiO{sub 2} or SiO{sub 2} are fabricated by single RF magnetron sputtering. • Films thickness and optical constants are determined by Spectroscopic Ellipsometry. - Abstract: We report on the optical properties in the dielectric regime of gold nanostructured granular thin films fabricated through sputter deposition with a composite target at room temperature and over a wide photon energy range (0.62–4.13 eV) by means of Spectroscopic Ellipsometry. The thickness and the films effective optical constants are successfully determined using an approach based on multiple Gaussian oscillators. In the quasi-static regime, i.e., 2R ≪ λ, and in the dipole approximation, examining the real and imaginary parts, ε{sub 1}, ε{sub 2}, of the dielectric function, it is shown that the dc optical conductivity is almost negligible (σ = ωε{sub 0}ε{sub 2} ≪ 10{sup −5} Ω cm{sup −1}) and only the capacitive contribution holds for the electron-phonon relaxation in localized surface plasmon of the gold particles. Furthermore, we find that the resonant frequencies ω{sub p} becomes red-shifted when the particles are electromagnetically coupled to each other or when the surrounding medium dielectric constant, ε{sub m}, increases, thus exhibiting a wide spectral tuning range of 1.95–2.24 eV.

  9. Carbon Corrosion at Pt/C Interface in Proton Exchange Membrane Fuel Cell Environment

    International Nuclear Information System (INIS)

    Choi, Min Ho; Beam, Won Jin; Park, Chan Jin

    2010-01-01

    This study examined the carbon corrosion at Pt/C interface in proton exchange membrane fuel cell environment. The Pt nano particles were electrodeposited on carbon substrate, and then the corrosion behavior of the carbon electrode was examined. The carbon electrodes with Pt nano electrodeposits exhibited the higher oxidation rate and lower oxidation overpotential compared with that of the electrode without Pt. This phenomenon was more active at 75 .deg. C than 25 .deg. C. In addition, the current transients and the corresponding power spectral density (PSD) of the carbon electrodes with Pt nano electrodeposits were much higher than those of the electrode without Pt. The carbon corrosion at Pt/C interface was highly accelerated by Pt nano electrodeposits. Furthermore, the polarization and power density curves of PEMFC showed degradation in the performance due to a deterioration of cathode catalyst material and Pt dissolution

  10. Swift heavy ion irradiation effects in Pt/C and Ni/C multilayers

    Science.gov (United States)

    Gupta, Ajay; Pandita, Suneel; Avasthi, D. K.; Lodha, G. S.; Nandedkar, R. V.

    1998-12-01

    Irradiation effects of 100 MeV Ag ion irradiation on Ni/C and Pt/C multilayers have been studied using X-ray reflectivity measurements. Modifications are observed in both the multilayers at (dE/dx)e values much below the threshold values for Ni and Pt. This effect is attributed to the discontinuous nature of the metal layers. In both the multilayers interfacial roughness increases with irradiation dose. While Ni/C multilayers exhibit large ion-beam induced intermixing, no observable intermixing is observed in the case of Pt/C multilayer. This difference in the behavior of the two systems suggests a significant role for chemically guided defect motion in the mixing process associated with swift heavy ion irradiation.

  11. CO tolerance of PdPt/C and PdPtRu/C anodes for PEMFC

    International Nuclear Information System (INIS)

    Garcia, Amanda C.; Paganin, Valdecir A.; Ticianelli, Edson A.

    2008-01-01

    The performance of H 2 /O 2 proton exchange membrane fuel cells (PEMFCs) fed with CO-contaminated hydrogen was investigated for anodes with PdPt/C and PdPtRu/C electrocatalysts. The physicochemical properties of the catalysts were characterized by energy dispersive X-ray (EDX) analyses, X-ray diffraction (XRD) and 'in situ' X-ray absorption near edge structure (XANES). Experiments were conducted in electrochemical half and single cells by cyclic voltammetry (CV) and I-V polarization measurements, while DEMS was employed to verify the formation of CO 2 at the PEMFC anode outlet. A quite high performance was achieved for the PEMFC fed with H 2 + 100 ppm CO with the PdPt/C and PdPtRu/C anodes containing 0.4 mg metal cm -2 , with the cell presenting potential losses below 200 mV at 1 A cm -2 , with respect to the system fed with pure H 2 . For the PdPt/C catalysts no CO 2 formation was seen at the PEMFC anode outlet, indicating that the CO tolerance is improved due to the existence of more free surface sites for H 2 electrooxidation, probably due to a lower Pd-CO interaction compared to pure Pd or Pt. For PdPtRu/C the CO tolerance may also have a contribution from the bifunctional mechanism, as shown by the presence of CO 2 in the PEMFC anode outlet

  12. Methanol electro-oxidation on Pt/C modified by polyaniline nanofibers for DMFC applications

    Energy Technology Data Exchange (ETDEWEB)

    Zhiani, Mohammad; Rezaei, Behzad; Jalili, Jalal [Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111 (Iran)

    2010-09-15

    In the present study, in order to achieve an inexpensive tolerable anode catalyst for direct methanol fuel cell applications, a composite of polyaniline nanofibers and Pt/C nano-particles, identified by PANI/Pt/C, was prepared by in-situ electropolymerization of aniline and trifluoromethane sulfonic acid on glassy carbon. The effect of synthesized PANI nanofibers in methanol electrooxidation reaction was compared by bare Pt/C by different electrochemical methods such as; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Scanning electron microscopy (SEM) was also employed to morphological study of the modified catalyst layer. The test results reveal that introduction of PANI nanofibers within catalyst layer improves the catalyst activity in methanol oxidation, hinders and prevents catalyst from more poisoning by intermediate products of methanol oxidation and improves the mechanical properties of the catalyst layer. SEM images also indicate that PANI nanofibers placed between platinum particles and anchor platinum particles and alleviate the Pt migration during methanol electrooxidation. (author)

  13. Re-examination of the Pt Particle Size Effect on the Oxygen Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion

    International Nuclear Information System (INIS)

    Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.; Kocha, Shyam S.

    2016-01-01

    Highlights: • Pt particle size effect on ORR was re-evaluated for Pt/C catalysts. • Nafion-free activity of Pt/C catalysts was evaluated using thin-film RDE methods. • Ultrathin-uniform catalyst layers were employed to obtain accurate activity values. • Specific activity increased steeply from 2 to 10 nm and less steeply at over 10 nm. • Re-evaluated effect agrees with a particle model assuming terrace active sites. - Abstract: The platinum ‘particle size effect’ on the oxygen reduction reaction (ORR) has been re-evaluated using commercial Pt/C catalysts (2–10 nm Pt particle) and polycrystalline Pt (poly-Pt) in 0.1 M HClO 4 with a rotating disk electrode method. Nafion-free catalyst layers were employed to obtain specific activities (SA) that were not perturbed (suppressed) by sulfonate anion adsorption/blocking. By using ultrathin uniform catalyst layers, O 2 diffusion limitation was minimized as confirmed from the high SAs of our supported catalysts that were comparable to unsupported sputtered Pt having controlled sizes. The specific activity (SA) steeply increased for the particle sizes in the range ∼2–10 nm (0.8–1.8 mA/cm 2 Pt at 0.9 V vs. RHE) and plateaued over ∼10 nm to 2.7 mA/cm 2 Pt for bulk poly-Pt. On the basis of the activity trend for the range of particle sizes studied, it appears that the effect of carbon support on activity is negligible. The experimental results and the concomitant profile of SA vs. particle size was found to be in an agreement to a truncated octahedral particle model that assumes active terrace sites.

  14. The electrocatalytic properties of carbon supported PtRu/C nanoalloys in oxidation of small organic molecules: Comparison with Pt/C catalyst

    Directory of Open Access Journals (Sweden)

    Lović Jelena D.

    2012-01-01

    Full Text Available The electrocatalytic activity of carbon supported PtRu/C catalysts, with different composition, toward the electrooxidation of methanol, CO and formic acid were examined in acid and alkaline solution at ambient temperature using thin-film rotating disk electrode (RDE method and compared with activity of Pt/C. The catalysts were characterized by XRD, AFM and STM techniques. XRD pattern revealed that PtRu-1/C catalyst is consisted of two structures e.g. Pt-Ru-fcc and Ru-hcp (the solid solution of Ru in Pt and the small amount of Ru or solid solution of Pt in Ru, as opposed to PtRu-2/C catalyst which is consisted of one structure mostly, Pt-Ru-fcc. According to STM images, PtRu as well as Pt, particles size were between 2 and 6 nm, which is in a good agreement with the mean particles size determined by XRD. To establish the activity and stability of the catalysts potentiodynamic and quasi steady-state measurements were performed. It was found that the activity of Pt and PtRu for CO and methanol oxidation is a strong function of pH of solution. The kinetics are much higher in alkaline than in acid solution and the difference between Pt/C and PtRu/C is much less pronounced in alkaline media. Results presented in this work indicate that activity of PtRu catalysts depends on catalyst composition, e.g. on Pt/Ru atomic ratio, as well as on alloying degree of catalysts. Comparison of CO, methanol and formic acid oxidation on PtRu-2/C, PtRu-1/C and Pt/C catalysts revealed that PtRu-2/C is the most active one. It was shown that the PtRu-2/C catalyst, due to fact that it is consisted of only one phase, with high alloying degree, through the bifunctional mechanism improved by electronic effect, achieve the activity two times higher related to PtRu-1/C in the oxidation of all organic molecules investigated, and about three times higher compared to Pt/C in the oxidation of methanol and CO, and five times higher in formic acid oxidation.

  15. Dependence of magnetic properties on ferromagnetic layer thickness in trilayer Co/Ge/Co films with granular semiconducting spacer

    International Nuclear Information System (INIS)

    Patrin, G.S.; Lee, C.-G.; Turpanov, I.A.; Zharkov, S.M.; Velikanov, D.A.; Maltsev, V.K.; Li, L.A.; Lantsev, V.V.

    2006-01-01

    We have investigated the magnetic properties of trilayer films of Co-Ge-Co. At a fixed thickness of germanium of 3.5 nm, the formation and distribution of metastable amorphous and cubic phases depends on the thickness of the ferromagnetic layer. The portion of the stable hexagonal phase is affected, too. Possible mechanisms for forming the observed magnetic structure are discussed

  16. Argon Ion Irradiation Effect on the Magnetic Properties of Fe-Al2O3 Nano Granular Film

    Directory of Open Access Journals (Sweden)

    Setyo Purwanto

    2014-10-01

    Full Text Available We studied the effect of Argon (Ar ion irradiation on Fe-Al2O3 nanogranular thin film. X-ray diffraction (XRD patterns show that the ion dose might promote the growth of the Fe2O3 phase from an amorphous phase to a crystalline phase. The magnetic and magnetoresistance properties were investigated using a vibrating sample magnetometer (VSM and a four point probe (FPP. The results suggest that percolation concentration occurred at the 0.55 Fe volume fraction and with a maximum magnetoresistance (MR ratio of 3%. The present MR ratio was lower than that of previous results, which might be related to the existence of the α-Fe2O3 phase promoted by Ar ion irradiation. CEMS spectra show ion irradiation induces changes from superparamagnetic characteristics to ferromagnetic ones, which indicates the spherical growth of Fe particles in the Al2O3 matrix.

  17. Excellent performance of Pt-C/TiO2 for methanol oxidation: Contribution of mesopores and partially coated carbon

    Science.gov (United States)

    Wu, Xinbing; Zhuang, Wei; Lu, Linghong; Li, Licheng; Zhu, Jiahua; Mu, Liwen; Li, Wei; Zhu, Yudan; Lu, Xiaohua

    2017-12-01

    Partial deposition of carbon onto mesoporous TiO2 (C/TiO2) were prepared as supporting substrate for Pt catalyst development. Carbon deposition is achieved by in-situ carbonization of furfuryl alcohol. The hybrid catalysts were characterized by XRD, Raman, SEM and TEM and exhibited outstanding catalytic activity and stability in methanol oxidation reaction. The heterogeneous carbon coated on mesoporous TiO2 fibers provided excellent electrical conductivity and strong interfacial interaction between TiO2 support and Pt metal nanoparticles. Methanol oxidation reaction results showed that the activity of Pt-C/TiO2 is 3.0 and 1.5 times higher than that of Pt-TiO2 and Pt-C, respectively. In addition, the Pt-C/TiO2 exhibited a 6.7 times enhanced stability compared with Pt-C after 2000 cycles. The synergistic effect of C/TiO2 is responsible for the enhanced activity of Pt-C/TiO2, and its excellent durability could be ascribed to the strong interfacial interaction between Pt nanoparticles and C/TiO2 support.

  18. Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

    International Nuclear Information System (INIS)

    Abdel Hameed, R.M.; Fetohi, Amani E.; Amin, R.S.; El-Khatib, K.M.

    2015-01-01

    Graphical abstract: Physical and electrochemical properties of Pt/C, Pt–MnO_2/C-1 and Pt–MnO_2/C-2 electrocatalysts. - Highlights: • Adding MnO_2 to Pt/C improved the dispersion of Pt nanoparticles. • The existence of MnO_2 improved the kinetics of methanol oxidation reaction. • R_c_t value of Pt–MnO_2/C was about 10 times as low as that at Pt/C. • The removal of CO_a_d_s poisoning species was facilitated at Pt–MnO_2/C. - Abstract: The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt–MnO_2/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO_2 improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt–MnO_2/C towards methanol oxidation in H_2SO_4 solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169 mV when MnO_2 is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt–MnO_2/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt–MnO_2/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).

  19. Ferromagnetic resonance studies on (Co{sub 40}Fe{sub 40}B{sub 20}){sub x}(SiO{sub 2}){sub 1-x} granular magnetic films

    Energy Technology Data Exchange (ETDEWEB)

    Yildiz, F. [Department of Physics, Faculty of Sciences and Arts, Celal Bayar University, Muradiye/Manisa (Turkey) and Department of Physics, Electron Spin Science Center, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)]. E-mail: fyildiz@gyte.edu.tr; Kazan, S. [Gebze Institute of Technology, 41400 Gebze-Kocaeli (Turkey); Aktas, B. [Gebze Institute of Technology, 41400 Gebze-Kocaeli (Turkey); Tarapov, S.I. [Institute of Radiophysics and Electronics, National Academy of Sciences of Ukraine, Kharkov 61085 (Ukraine); Tagirov, L. [Gebze Institute of Technology, 41400 Gebze-Kocaeli (Turkey); Granovsky, B. [Moscow State University, 119992 Moscow (Russian Federation)

    2006-10-15

    Magnetic properties of granular (Co{sub 40}Fe{sub 40}B{sub 20}){sub x}(SiO{sub 2}){sub 1-x} thin films (x=0.37-0.53) have been studied by ferromagnetic resonance (FMR) technique. Samples have been prepared by ion-beam deposition of Co-Fe-B particles and SiO{sub 2} on sitall ceramic substrate. The FMR measurements have been done for different orientations of DC magnetic field with respect to the sample plane. It was found that the deduced value of effective magnetization from FMR data of the thin granular film is reduced by the volume-filling factor of the bulk saturation magnetization. The overall magnetization changes from 152 to 515G depending on the ratio of the magnetic nanoparticles in the SiO{sub 2} matrix. From angular measurements an induced in-plane uniaxial anisotropy has been obtained due to the preparation of the film conditions as well.

  20. Effect of carbon additive on microstructure evolution and magnetic properties of epitaxial FePt (001) thin films

    International Nuclear Information System (INIS)

    Ding, Y.F.; Chen, J.S.; Liu, E.; Lim, B.C.; Hu, J.F.; Liu, B.

    2009-01-01

    FePt:C thin films were deposited on CrRu underlayers by DC magnetron co-sputtering. The effects of C content, FePt:C film thickness and substrate temperature on the microstructural and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 30 vol.% C doping, the FePt films could keep a (001) preferred orientation at 350 deg. C . When a FePt:C film was very thin (< 5 nm), the film had a continuous microstructure instead of a granual structure with C diffused onto the film surface. With further increased film thickness, the film started to nucleate and formed a column microstructure over continuous FePt films. A strong exchange coupling in the FePt:C films was believed to be due to the presence of a thin continuous FePt layer attributed to the carbon diffusion during the initial stage of the FePt:C film growth. Despite the presence of a strong exchange coupling in the FePt:C (20 vol.% C) film, the SNR ratio of the FePt:C media was about 10 dB better than that of the pure FePt media. The epitaxial growth of the FePt:C films on the Pt layers was observed from high resolution TEM cross sectional images even for the films grown at about 200 deg. C . The TEM images did not show an obvious change in the morphology of the FePt:C films deposited at different temperatures (from 200 deg. C to 350 deg. C ), though the ordering degree and coercivity of the films increased with increased substrate temperature

  1. Poly (p-phenylendiamine/TiO2) nanocomposite promoted Pt/C catalyst for methanol and ethanol electrooxidation in alkaline medium

    International Nuclear Information System (INIS)

    Rostami, Hussein; Rostami, Abbas Ali; Omrani, Abdollah

    2016-01-01

    In the present study, poly (p-phenylendiamine/titanium dioxide) (PpPDA/TiO 2 ) nanocomposites (NCs) were prepared by in situ polymerization of p-phenylenediamine monomer with of different TiO 2 loading. A facile method was developed to promote the electrocatalytic activity of commercial Pt/C catalyst by ultrasonically mixing Pt/C catalyst and PpPDA/TiO 2 NCs. The PpPDA/TiO 2 NC, Pt/C catalyst and composite catalyst of Pt/C + PpPDA/TiO 2 were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The surface morphology of Pt/C is significantly influenced by the presence of PpPDA/TiO 2 NC as confirmed by SEM observations. Cyclic voltammetry (CV) measurements showed that the PpPDA/TiO 2 NC leads to a significant improvement in the activity and stability of Pt/C for alcohol oxidation especially for ethanol oxidation in alkaline medium. For Pt/C + PpPDA/TiO 2 , the onset potentials shift to negative values by 30 and 160 mV compared to the onset potentials of Pt/C for methanol and ethanol oxidation, respectively. Chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) results also confirmed that this composite catalyst has superior catalytic performance towards ethanol oxidation compared to the pure Pt/C catalyst.

  2. Investigation of Au-Pt/C electro-catalysts for oxygen reduction reaction

    International Nuclear Information System (INIS)

    Lin Rui; Zhang Haiyan; Zhao Tiantian; Cao Chunhui; Yang Daijun; Ma Jianxin

    2012-01-01

    Highlights: ► Au-Pt core shell catalyst. ► Seed-mediated growth method. ► Au-Pt (2:4)/C best activity toward ORR. ► Four-electron pathway in acid solution. ► Single cell performance. - Abstract: Carbon-supported Au-Pt core shell nano-structured catalysts were synthesized by the seed-mediated growth method. The nano-structured catalysts were characterized by UV–vis spectroscopy, X-ray photoelectron spectra (XPS) and transmission electron microscopy (TEM) techniques. The oxygen reduction reaction (ORR) activity of the Au-Pt/C was tested by means of linear sweep voltammetry (LSV) by employing rotating disk electrode (RDE). It revealed that Au-Pt (2:4)/C (atomic ratio) catalyst exhibited the best catalytic activity toward ORR. Au-Pt (2:4)/C proceeded by an approximately four-electron pathway in acid solution, through which molecular oxygen was directly reduced to water. The stability of Au-Pt (2:4)/C is tested by cyclic voltammetry for 500 cycles. The performance of the membrane electrode assembly (MEA) prepared by Au-Pt (2:4)/C as the cathode catalyst in a single proton exchange membrane fuel cell (PEMFC) generated a maximum power density of 479 mW cm −2 at 0.431 V using H 2 and O 2 at 80 °C.

  3. Magnetic and electronic studies in the granular (Ni{sub 0.84}Fe{sub 0.16}){sub 54}(alumina){sub 46} sputtered thin films

    Energy Technology Data Exchange (ETDEWEB)

    Omari, N., E-mail: nabila_omari@yahoo.fr [PTA, Universite Hassan II-Casablanca, Faculte des Sciences, B.P. 5366 Maarif, Maroc (Morocco); Institut Neel CNRS, Departement MCMF, B.P. 166, 38042 Grenoble Cedex 9 (France); Lassri, H. [LPMMAT, Universite Hassan II-Casablanca, Faculte des Sciences, B.P. 5366 Maarif, Maroc (Morocco); Fnidiki, A. [Groupe de Physique des Materiaux, UMR CNRS 6634, Faculte des Sciences de Rouen, Site Universitaire du Madrillet, Avenue de l' Universite, B.P. 12, 76801 Saint-Etienne du Rouvray Cedex (France); Abid, M. [PTA, Universite Hassan II-Casablanca, Faculte des Sciences, B.P. 5366 Maarif, Maroc (Morocco); Hlil, E.K. [Institut Neel CNRS, Departement MCMF, B.P. 166, 38042 Grenoble Cedex 9 (France)

    2012-06-15

    We have studied the magnetization in the granular (Ni{sub 0.84}Fe{sub 0.16}){sub 54}(alumina){sub 46} alloy. The thermomagnetization curve is found to obey the Bloch law. Spin wave stiffness constant D and the exchange constant A were calculated from the experimental results. The magnetic experimental measurements have been interpreted in the framework of random magnetic anisotropy (RMA) model. The results have shown that it is possible to extend the application of RMA to the granular alloy. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. In addition, self-consistent ab initio calculations, based on Korringa-Kohn-Rostocker (KKR), are performed to investigate magnetic and electronic properties of the granular alloy. Spin polarization within the framework of the coherent potential approximation (CPA) is considered.

  4. Magnetic and electronic studies in the granular (Ni0.84Fe0.16)54(alumina)46 sputtered thin films

    International Nuclear Information System (INIS)

    Omari, N.; Lassri, H.; Fnidiki, A.; Abid, M.; Hlil, E.K.

    2012-01-01

    We have studied the magnetization in the granular (Ni 0.84 Fe 0.16 ) 54 (alumina) 46 alloy. The thermomagnetization curve is found to obey the Bloch law. Spin wave stiffness constant D and the exchange constant A were calculated from the experimental results. The magnetic experimental measurements have been interpreted in the framework of random magnetic anisotropy (RMA) model. The results have shown that it is possible to extend the application of RMA to the granular alloy. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. In addition, self-consistent ab initio calculations, based on Korringa-Kohn-Rostocker (KKR), are performed to investigate magnetic and electronic properties of the granular alloy. Spin polarization within the framework of the coherent potential approximation (CPA) is considered.

  5. Origin of the resistivity minima in granular superconductors

    International Nuclear Information System (INIS)

    Simanek, E.

    1982-01-01

    The recently observed minima in the temperature dependence of the electrical resistivity of a granular superconductor are explained with use of a percolation model of a disordered granular array, which takes into account the electrostatic charging energy. The thermally activated tunneling of Cooper pairs is shown to play an important role in the interpretation of the experimental data on tin films

  6. Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

    Energy Technology Data Exchange (ETDEWEB)

    Abdel Hameed, R.M., E-mail: randa311eg@yahoo.com [Chemistry Department, Faculty of Science, Cairo University, Giza (Egypt); Fetohi, Amani E.; Amin, R.S.; El-Khatib, K.M. [Chemical Engineering Department, National Research Center, Dokki, Giza (Egypt)

    2015-12-30

    Graphical abstract: Physical and electrochemical properties of Pt/C, Pt–MnO{sub 2}/C-1 and Pt–MnO{sub 2}/C-2 electrocatalysts. - Highlights: • Adding MnO{sub 2} to Pt/C improved the dispersion of Pt nanoparticles. • The existence of MnO{sub 2} improved the kinetics of methanol oxidation reaction. • R{sub ct} value of Pt–MnO{sub 2}/C was about 10 times as low as that at Pt/C. • The removal of CO{sub ads} poisoning species was facilitated at Pt–MnO{sub 2}/C. - Abstract: The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt–MnO{sub 2}/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO{sub 2} improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt–MnO{sub 2}/C towards methanol oxidation in H{sub 2}SO{sub 4} solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169 mV when MnO{sub 2} is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt–MnO{sub 2}/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt–MnO{sub 2}/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).

  7. Significant advantages of sulfur-doped graphene in neutral media as electrocatalyst for oxygen reduction comparing with Pt/C

    Science.gov (United States)

    Shi, Xinxin; Zhang, Jiaona; Huang, Tinglin

    2018-02-01

    Sulfur-doped graphene (SDG) has been found to be an efficient electrocatalyst for oxygen reduction reaction. However, previous studies on the catalytic activity of SDG have been mainly confined to O2-saturated alkaline media which is a typical alkaline fuel cell environment. Air-cathode microbial fuel cells (ACMFCs), as a novel energy conversion and wastewater treatment technology, use the oxygen from air as cathodic reactant in neutral media with low concentration of O2. Thus, it is meaningful to explore the catalytic performance of SDG in such ACMFC environment. The result showed that in ACMFC environment, the peak current density of SDG in CV test was surprisingly 4.5 times higher than that of Pt/C, indicating a much stronger catalytic activity of SDG. Moreover, SDG exhibited a stronger tolerance against the crossover of glucose (a typical anodic fuel in ACMFC) and better stability than Pt/C in neutral media.

  8. Nanostructured electrocatalyst for fuel cells : silica templated synthesis of Pt/C composites.

    Energy Technology Data Exchange (ETDEWEB)

    Stechel, Ellen Beth; Switzer, Elise E.; Fujimoto, Cy H.; Atanassov, Plamen Borissov; Cornelius, Christopher James; Hibbs, Michael R.

    2007-09-01

    Platinum-based electrocatalysts are currently required for state-of-the-art fuel cells and represent a significant portion of the overall fuel cell cost. If fuel cell technology is to become competitive with other energy conversion technologies, improve the utilization of precious metal catalysts is essential. A primary focus of this work is on creating enhanced nanostructured materials which improve precious-metal utilization. The goal is to engineer superior electrocatalytic materials through the synthesis, development and investigation of novel templated open frame structures synthesized in an aerosol-based approach. Bulk templating methods for both Pt/C and Pt-Ru composites are evaluated in this study and are found to be limited due to the fact that the nanostructure is not maintained throughout the entire sample. Therefore, an accurate examination of structural effects was previously impossible. An aerosol-based templating method of synthesizing nanostructured Pt-Ru electrocatalysts has been developed wherein the effects of structure can be related to electrocatalytic performance. The aerosol-based templating method developed in this work is extremely versatile as it can be conveniently modified to synthesize alternative materials for other systems. The synthesis method was able to be extended to nanostructured Pt-Sn for ethanol oxidation in alkaline media. Nanostructured Pt-Sn electrocatalysts were evaluated in a unique approach tailored to electrocatalytic studies in alkaline media. At low temperatures, nanostructured Pt-Sn electrocatalysts were found to have significantly higher ethanol oxidation activity than a comparable nanostructured Pt catalyst. At higher temperatures, the oxygen-containing species contribution likely provided by Sn is insignificant due to a more oxidized Pt surface. The importance of the surface coverage of oxygen-containing species in the reaction mechanism is established in these studies. The investigations in this work present

  9. 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

  10. In situ Ru K-edge EXAFS of CO adsorption on a Ru modified Pt/C fuel cell catalyst

    International Nuclear Information System (INIS)

    Rose, Abigail; Bilsborrow, Robert; King, Colin R.; Ravikumar, M.K.; Qian Yangdong; Wiltshire, Richard J.K.; Crabb, Eleanor M.; Russell, Andrea E.

    2009-01-01

    The Ru-CO bond of CO adsorbed on a Ru modified Pt/C fuel cell catalyst has been directly probed by in situ EXAFS at the Ru K-edge, providing evidence of a CO:metal surface atom ratio greater than 1:1 and that CO is adsorbed at bridging sites associated with Ru atoms at the surface of the catalyst nanoparticles. This result illustrates the limitations of single crystal models as representations of the bonding of adsorbed species at nanoparticle surfaces.

  11. Effect of Y2O3-Al2O3 ratio on inter-granular phases and films in tape-casting α-SiC with high toughness

    International Nuclear Information System (INIS)

    Huang Rong; Gu Hui; Zhang Jingxian; Jiang Dongliang

    2005-01-01

    Silicon carbide (SiC) ceramics prepared from liquid phase sintering after aqueous-tape-casting can yield high toughness when appropriate amount of Y 2 O 3 -Al 2 O 3 are added, even though no elongated grains are present. Grain boundaries (GB), second-phases and hetero-phase boundaries (HB) in 2 samples with additive mole ratios of 3:5 and 3:7 are investigated using high-resolution and analytical electron microscopy (HREM and AEM). The meta-stable YAlO 3 (YAP) was nucleated from SiC surfaces in the sample with Y/Al = 3:5 as revealed by crystallographic relations across the HB, whilst relatively thick amorphous films were found at GB. In contrary, the higher level of Al 2 O 3 additives decreases the GB film thickness in the sample with Y/Al = 3:7, and the homogeneous nucleation of Y 3 Al 5 O 12 (YAG) occurs at triple pockets accompanying with thick HB films. The strong variation of GB widths is a result of GB wetting in the sample with Y/Al = 3:5 and HB wetting in the sample of Y/Al = 3:7, both by liquid Al 2 O 3 . The energy of GB in the former sample is higher than the energy of HB as exhibited by the preferential nucleation of meta-stable YAP on SiC surfaces, which results in wetting of GB by the liquid; the situation is opposite in the latter sample as the wetting of HB occurs, leading to de-wetting of GB. The thermal mismatch between SiC and YAP or YAG as well as the presence of amorphous films facilitate the creation of micro-crack to promote inter-granular fracture and result in high toughness in both SiC ceramics

  12. Metal-insulator transition in Pt-C nanowires grown by focused-ion-beam-induced deposition

    International Nuclear Information System (INIS)

    Fernandez-Pacheco, A.; Ibarra, M. R.; De Teresa, J. M.; Cordoba, R.

    2009-01-01

    We present a study of the transport properties of Pt-C nanowires created by focused-ion-beam (FIB)-induced deposition. By means of the measurement of the resistance while the deposit is being performed, we observe a progressive decrease in the nanowire resistivity with thickness, changing from 10 8 μΩ cm for thickness ∼20 nm to a lowest saturated value of 700 μΩ cm for thickness >150 nm. Spectroscopy analysis indicates that this dependence on thickness is caused by a gradient in the metal-carbon ratio as the deposit is grown. We have fabricated nanowires in different ranges of resistivity and studied their conduction mechanism as a function of temperature. A metal-insulator transition as a function of the nanowire thickness is observed. The results will be discussed in terms of the Mott-Anderson theory for noncrystalline materials. An exponential decrease in the conductance with the electric field is found for the most resistive samples, a phenomenon understood by the theory of hopping in lightly doped semiconductors under strong electric fields. This work explains the important discrepancies found in the literature for Pt-C nanostructures grown by FIB and opens the possibility to tune the transport properties of this material by an appropriate selection of the growth parameters.

  13. Granular gas dynamics

    CERN Document Server

    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.

  14. Growth and Characteristic of Amorphous Nano-Granular TeO2-V2O5-NiO Thin Films

    Science.gov (United States)

    Hosseinzadeh, Sh.; Rahmati, A.; Bidadi, H.

    2016-12-01

    TeO2-V2O5-NiO thin films were deposited using thermal evaporation from 40TeO2-(60-y)V2O5-yNiO (y=0-30mol%) target. Structural analysis of the films was identified by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The amorphous TeO2-V2O5-NiO films have nanosized clear grain structure and sharp grain boundaries. DC conductivity and current-voltage (I-V) characteristic of TeO2-V2O5-NiO thin films were measured in the temperature range of 300-423K. As nickel oxide (NiO) content increases, the DC conductivity decreases up to two orders in value (10-9-10-11Sṡcm-1). Temperature dependence of conductivity is described using the small polaron hopping (SPH) model as well. Poole-Frenkel effect is observed at high external electric field. The optical absorption spectra of the TeO2-V2O5-NiO thin films were recorded in the wavelength range of 380-1100nm. The absorption coefficient revealed bandgap shrinkage (3.01-2.3eV) and band tail widening, due to an increase in NiO content. Energy dispersive X-ray spectroscopy (EDX) was used to determine elemental composition. In TeO2-V2O5-NiO thin films, the NiO content is around fifth of the initial target.

  15. Morphology and Activity Tuning of Cu 3 Pt/C Ordered Intermetallic Nanoparticles by Selective Electrochemical Dealloying

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Deli; Yu, Yingchao; Zhu, Jing; Liu, Sufen; Muller, David A.; Abruña, Héctor D.

    2015-02-11

    Improving the catalytic activity of Pt-based bimetallic nanoparticles is a key challenge in the application of proton-exchange membrane fuel cells. Electrochemical dealloying represents a powerful approach for tuning the surface structure and morphology of these catalyst nanoparticles. We present a comprehensive study of using electrochemical dealloying methods to control the morphology of ordered Cu3Pt/C intermetallic nanoparticles, which could dramatically affect their electrocatalytic activity for the oxygen reduction reaction (ORR). Depending on the electrochemical dealloying conditions, the nanoparticles with Pt-rich core–shell or porous structures were formed. We further demonstrate that the core–shell and porous morphologies can be combined to achieve the highest ORR activity. This strategy provides new guidelines for optimizing nanoparticles synthesis and improving electrocatalytic activity.

  16. Particle growth mechanisms in Ag-ZrO2 and Au-ZrO2 granular films obtained by pulsed laser deposition

    International Nuclear Information System (INIS)

    Konstantinovic, Zorica; Muro, Montserrat Garcia del; Varela, Manuel; Batlle, Xavier; Labarta, AmIlcar

    2006-01-01

    Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO 2 matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08 Ag Au c (Ag)∼0.28 and x c (Au)∼0.52)

  17. Preparation method of Ni@Pt/C nanocatalyst affects the performance of direct borohydride-hydrogen peroxide fuel cell: Improved power density and increased catalytic oxidation of borohydride.

    Science.gov (United States)

    Hosseini, Mir Ghasem; Mahmoodi, Raana

    2017-08-15

    The Ni@Pt/C electrocatalysts were synthesized using two different methods: with sodium dodecyl sulfate (SDS) and without SDS. The metal loading in synthesized nanocatalysts was 20wt% and the molar ratio of Ni: Pt was 1:1. The structural characterizations of Ni@Pt/C electrocatalysts were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). The electrocatalytic activity of Ni@Pt/C electrocatalysts toward BH 4 - oxidation in alkaline medium was studied by means of cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results showed that Ni@Pt/C electrocatalyst synthesized without SDS has superior catalytic activity toward borohydride oxidation (22016.92Ag Pt -1 ) in comparison with a catalyst prepared in the presence of SDS (17766.15Ag Pt -1 ) in NaBH 4 0.1M at 25°C. The Membrane Electrode Assembly (MEA) used in fuel cell set-up was fabricated with catalyst-coated membrane (CCM) technique. The effect of Ni@Pt/C catalysts prepared with two methods as anode catalyst on the performance of direct borohydride-hydrogen peroxide fuel cell was studied. The maximum power density was obtained using Ni@Pt/C catalyst synthesized without SDS at 60°C, 1M NaBH 4 and 2M H 2 O 2 (133.38mWcm -2 ). Copyright © 2017 Elsevier Inc. All rights reserved.

  18. Granular computing: perspectives and challenges.

    Science.gov (United States)

    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.

  19. Far infrared near normal specular reflectivity of Nix(SiO2)1-x (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) granular films

    KAUST Repository

    Massa, Néstor E.

    2010-04-01

    One of the current issues at the basis of the understanding of novel materials is the degree of the role played by spatial inhomogeneities due to subtle phase separations. To clarify this picture here we compare the plain glass network response of transition metal granular films with different metal fractions against what is known for conducting oxides. Films for Nix(SiO2)1-x (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) were studied by temperature dependent far infrared measurements. While for pure Ni the spectrum shows a flat high reflectivity, those for x ∼ 0.84 and ∼0.75 have a Drude component, vibrational modes mostly carrier screened, and a long tail that extents toward near infrared. This is associated with hopping electron conductivity and strong electron-phonon interactions. The relative reduction of the number of carriers in Ni0.75(SiO2)0.25 allows less screened phonon bands on the top of a continuum and a wide and overdamped oscillator at mid-infrared frequencies. Ni0.54(SiO2)0.46 and Ni0.28(SiO2)0.72 have well defined vibrational bands and a sharp threshold at ∼1450 cm-1. It is most remarkable that a distinctive resonant peak at ∼1250 cm-1 found for p-polarized angle dependent specular reflectivity. It originates in an electron cloud traced to electrons that are not able to overcome the metal-dielectric interface that, beating against the positive background, generates the electric dipole. Overall, we conclude that the spectra are analogous to those regularly found in conducting oxides where with a suitable percolating network polarons are formed. © 2009 Elsevier B.V. All rights reserved.

  20. High frequency characteristics of (Ni75Fe2)x(ZnO)1−x granular thin films with tunable damping coefficient

    International Nuclear Information System (INIS)

    Li Wen-Chun; Liu Xiao-Hong; Wei Qing-Qing; Yao Dong-Sheng; Zuo Ya-Lu; Zhou Xue-Yun

    2015-01-01

    The effect of the volume fraction of ferromagnetic metal (x) in (Ni 75 Fe 25 ) x (ZnO) 1−x nanogranular thin films on microstructural, soft-magnetic, and high-frequency properties was investigated. Good soft-magnetic properties were obtained in a broad x range, with 0.55 < x < 0.82. High resolution transmission electron microscopy (HRTEM) observations reveal that the grain size of the samples is lower than 14 nm, and that it decreases with decreasing x. Of special interest, our investigation of the permeability spectra indicates that these films exhibit an adjustable frequency linewidth of resonance peak, dependant upon changing x. Correspondingly, large and adjustable damping coefficients (α eff ) from 0.023 to 0.043 were achieved by decreasing x from 0.82 to 0.55. Combined with the HRTEM results, the variation of α eff with x was analyzed in detail. (paper)

  1. Impact of granular drops

    KAUST Repository

    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.

  2. Impact of granular drops

    KAUST Repository

    Marston, J. O.; Mansoor, Mohammad M.; Thoroddsen, Sigurdur T

    2013-01-01

    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.

  3. Granularity effect on microwave surface resistance in high-Tc YBa2Cu3O7-x bulk and thin film superconductor

    International Nuclear Information System (INIS)

    Swarup, Ram; Gupta, A.K.

    2001-01-01

    We report the effect of variation of Josephson coupling strength in YBa 2 Cu 3 O 7-x (YBCO) superconductor due to grain enlargement, grain orientation and magnetic field on microwave surface resistance (R s ). The coupling strength in the bulk samples has been increased by increasing the sample density from 4.4 to 5.3 g/cm 3 , whereas in thin films, the same could be increased by increasing the c-axis orientation of the grains. The value of R s (10 GHz, 65 K) in bulk samples has been found to decrease from 52 to 4 mΩ with the increase of the coupling strength from 0.06 to 0.43 and in thin films from 930 to 600 μΩ with increase of the coupling strength from 0.92 to 2.43. The effect of grain decoupling on microwave surface resistance was studied under dc and microwave magnetic fields. The surface resistance increases gradually with the application of dc and microwave magnetic fields due to grain decoupling and finally gets saturated beyond a certain critical field. (author)

  4. Granular Cell Tumor

    African Journals Online (AJOL)

    1). Her packed cell volume was 40%, she was system, gastro-intestinal tract, brain, heart, and negative to human immunodeficiency virus. 2 female reproductive . ... histocytes and neurons at various times. They granules. The granules are probably of lysosmal were consequently termed granular cell origin and contain ...

  5. Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd-Pt/C and Pd/C Anodes.

    Science.gov (United States)

    Nogueira, Jéssica Alves; Varela, Hamilton

    2017-10-01

    Polymer electrolyte membrane fuel cells (PEMFC) fed with H 2 contaminated with CO may exhibit oscillatory behavior when operated galvanostatically. The self-organization of the anodic overpotential is interesting because it can be accompanied by an increase in the average performance. Herein we report experimental studies of voltage oscillations that emerge in a PEMFC equipped with a Pd/C or PdPt/C anode and fed with H 2 contaminated with CO (100 ppm). We used on-line mass spectrometry to investigate how the mass fragments associated with CO 2 and CO ( m / z 44 and 28, respectively) varied with the voltage oscillations. Overall, we observed that oscillations in the anodic overpotential are in phase with that of the CO and CO 2 signals. This fact is consistent with an autonomous adsorption-oxidation cyclic process. For both anodes, it has been observed that, in general, an increase in current density implies an increase in oscillatory frequency. By using CO stripping, we also discuss how the onset of CO oxidation is related to the maximum overpotential reached during a cycle, whereas the minimum overpotential can be associated with the catalytic activity of the electrode for H 2 oxidation.

  6. Evaluation of Pt/C catalyst degradation and H2O2 formation changes under simulated PEM fuel cell condition by a rotating ring-disk electrode

    International Nuclear Information System (INIS)

    Ono, Kenshiro; Yasuda, Yuki; Sekizawa, Koshi; Takeuchi, Norimitsu; Yoshida, Toshihiko; Sudoh, Masao

    2013-01-01

    Potential cycling tests using 42.2 wt% and 19.1 wt% Pt/C catalysts were conducted by the RRDE technique to evaluate the changes in the electrochemical surface area (ECSA) and H 2 O 2 formation ability of the catalysts. As the typical operating conditions of a proton exchange membrane fuel cell (PEMFC), square wave potential cycling (0.7–0.9 V) was applied to the catalysts for 150,000 cycles in an O 2 -saturated 0.1 M HClO 4 electrolyte. During the potential cycling test, electrochemical measurements were carried out to characterize the ECSA, oxygen reduction reaction (ORR) activity and H 2 O 2 formation. After 150,000 potential cyclings, while the ECSA of the 42.2 wt% Pt/C dropped by 35%, the ECSA loss for the 19.1 wt% Pt/C was 55%. This result implies that the Pt content in the cathode catalyst affects the ECSA loss during the long-term PEMFC operation. Additionally, the H 2 O 2 formation ratio obviously increased with the potential cycling only in the case of the 19.1 wt% Pt/C. In order to verify the H 2 O 2 formation dependence on the ECSA, four types of catalysts, which included different Pt loading amounts (42.2, 28.1, 19.1 and 9.5 wt% Pt/C), were evaluated, and these results explained the relationship between the ECSA decay and H 2 O 2 formation increase in the durability tests

  7. Electrochemical study of oxygen reduction reaction in Pt/C catalysts synthesized by photo-deposition; Estudio electroquimico de la reaccion de reduccion de oxigeno en catalizadores de Pt/C sintetizados por fotodeposito

    Energy Technology Data Exchange (ETDEWEB)

    Perez-Galindo, J. A.; Ruiz-Camacho, B.; Valenzuela-Zapata, M. A.; Gonzalez-Huerta, R. G. [IPN, ESIQIE, Mexico, D.F. (Mexico)]. E-mail: rosgonzalez_h@yahoo.com.mx

    2009-09-15

    Fuel batteries are considered one of the principal generators of energy for the immediate future, though their use is limited by their cost and useful lifetime. One of the main components of a fuel battery are electrodes made of a noble metal, such as Pt, dispersed in a support. The interaction between these two components has received a good deal of attention in recent years. It is considered to be responsible for structural growth effects and a decreased dispersion of metal particles on a support, causing the battery to have low overall performance and a reduced useful lifetime. The properties of the support are accentuated in cathode catalysts, where oxygen reduction reactions occur as a result of its operating conditions. Syntheses are currently being investigated to improve the metal-support interaction and thereby increase the lifetime of the fuel battery. This work presents the electrochemical study of nanometric-sized carbon-supported platinum (Pt/C) catalysts synthesized with chemical photo-deposition to determine its catalytic effect and stability for oxygen reduction reaction in an acid medium. C{sub 10}H{sub 14}O{sub 4}Pt (Pt(acac)2) was used as the platinum precursor. The electrochemical study was conducted with cyclic voltamperometry and rotary disc electrode (RDE) techniques, observing that the synthesized catalysts present a behavior similar to that of Pt (E-Tek). The kinetic study showed an open-circuit potential of de 0.96 V with a Tafel slope of 73 mV dec-1, and with a current of 0.1 mA cm-2 the potential is 0.91 V. The authors wish to thank the ICYTDF (project PICS08-37) and the IPN (project SIP-20090433). [Spanish] Las pilas de combustible se perfilan como uno de los principales generadores de energia en un futuro inmediato, pero su utilizacion esta limitada por su costo y tiempo de vida util. Uno de los componentes principales de la pila de combustible son los electrodos integrados por un metal noble, como el Pt, disperso en un soporte. La

  8. Impact of metal cations on the electrocatalytic properties of Pt/C nanoparticles at multiple phase interfaces.

    Science.gov (United States)

    Durst, Julien; Chatenet, Marian; Maillard, Frédéric

    2012-10-05

    Proton-exchange membrane fuel cells (PEMFCs) use carbon-supported nanoparticles based on platinum and its alloys to accelerate the rate of the sluggish oxygen-reduction reaction (ORR). The most common metals alloyed to Pt include Co, Ni and Cu, and are thermodynamically unstable in the PEMFC environment. Their dissolution yields the formation and redistribution of metal cations (M(y+)) within the membrane electrode assembly (MEA). Metal cations can also contaminate the MEA when metallic bipolar plates are used as current collectors. In each case, the electrical performance of the PEMFC severely decreases, an effect that is commonly attributed to the poisoning of the sulfonic acid groups of the perfluorosulfonated membrane (PEM) and the resulting decrease of the proton transport properties. However, the impact of metal cations on the kinetics of electrochemical reactions involving adsorption/desorption and bond-breaking processes remains poorly understood. In this paper, we use model electrodes to highlight the effect of metal cations on Pt/C nanoparticles coated or not with a perfluorosulfonated ionomer for the CO electrooxidation reaction and the oxygen reduction reaction. We show that metal cations negatively impact the ORR kinetics and the mass-transport resistance of molecular oxygen. However, the specific adsorption of sulfonate groups of the Nafion® ionomer locally modifies the double layer structure and increases the tolerance to metal cations, even in the presence of sulphate ions in the electrolyte. The survey is extended by using an ultramicroelectrode with cavity and a solid state cell (SSC) specifically developed for this study.

  9. Distrofia corneal granular

    Directory of Open Access Journals (Sweden)

    Alexeide de la C Castillo Pérez

    Full Text Available Las distrofias corneales constituyen un conjunto de enfermedades que presentan, en su mayoría, una baja incidencia y se caracterizan por acúmulo de material hialino o amiloide que disminuyen la transparencia corneal. La distrofia granular es una enfermedad autosómica dominante que presenta opacidades grises en el estroma superficial central de la córnea y se hacen visibles en la primera y segunda décadas de la vida, lo que provoca disminución de la visión más significativa cerca de los 40 años de edad. Presentamos dos casos clínicos de distrofia granular en pacientes hermanos de diferentes sexos, quienes acudieron a la consulta y refirieron visión nublada. El estudio de la historia familiar nos ayuda en el correcto diagnóstico y la biomicroscopia constituye el elemento más importante.

  10. Microservices: Granularity vs. Performance

    OpenAIRE

    Shadija, Dharmendra; Rezai, Mo; Hill, Richard

    2017-01-01

    Microservice Architectures (MA) have the potential to increase the agility of software development. In an era where businesses require software applications to evolve to support emerging software requirements, particularly for Internet of Things (IoT) applications, we examine the issue of microservice granularity and explore its effect upon application latency. Two approaches to microservice deployment are simulated; the first with microservices in a single container, and the second with micr...

  11. Investigation of the promoting effect of Mn on a Pt/C catalyst for the steam and aqueous phase reforming of glycerol

    Energy Technology Data Exchange (ETDEWEB)

    Bossola, Filippo; Pereira-Hernández, Xavier Isidro; Evangelisti, Claudio; Wang, Yong; Dal Santo, Vladimiro

    2017-05-01

    The catalytic performances in steam reforming (SR) and aqueous phase reforming (APR) of glycerol of a bimetallic Pt-Mn catalyst supported on activated carbon are investigated and correlated with the surface properties of the catalyst. Under SR conditions, Mn showed a significant promoting effect over Pt/C, both in terms of hydrogen production rate and conversion, with a higher selectivity toward the glycerol dehydration products. Upon addition of Mn the amount of strong Lewis acid sites increased, promoting the dehydration of glycerol and favoring the CAO over CAC cleavage at expenses of hydrogen selectivity. Conversely, under APR conditions, a slightly higher hydrogen selectivity and only minimal enhancement in hydrogen production were found, while the products selectivity was comparable to Pt/C. Most of Mn leached into the aqueous media, but the remaining (<5% of the fresh parent sample) might be alloyed with Pt and promote the CO desorption from neighbor Pt sites.

  12. Rapid in situ synthesis of spherical microflower Pt/C catalyst via spray-drying for high performance fuel cell application

    Energy Technology Data Exchange (ETDEWEB)

    Balgis, R.; Ogi, T.; Okuyama, K. [Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, Higashi Hiroshima, Hiroshima (Japan); Anilkumar, G.M.; Sago, S. [Research and Development Centre, Noritake Co., Ltd., Higashiyama, Miyoshi, Aichi (Japan)

    2012-08-15

    A facile route for the rapid in situ synthesis of platinum nanoparticles on spherical microflower carbon has been developed. An aqueous precursor slurry containing carbon black, polystyrene latex (PSL), polyvinyl alcohol, and platinum salt was spray-dried, followed by calcination to simultaneously reduce platinum salt and to decompose PSL particles. Prepared Pt/C catalyst showed high-performance electrocatalytic activity with excellent durability. The mass activity and specific activity values were 132.26 mA mg{sup -1} Pt and 207.62 {mu}A cm{sup -2} Pt, respectively. This work presents a future direction for the production of high-performance Pt/C catalyst in an industrial scale. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. A Facile and Waste-Free Strategy to Fabricate Pt-C/TiO2 Microspheres: Enhanced Photocatalytic Performance for Hydrogen Evolution

    Directory of Open Access Journals (Sweden)

    Hui Li

    2014-01-01

    Full Text Available A facile and waste-free flame thermal synthesis method was developed for preparing Pt modified C/TiO2 microspheres (Pt-C/TiO2. The photocatalysts were characterized with X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope, ultraviolet-visible (UV-vis diffuse reflectance spectra, X-ray photoelectron spectroscopy, and thermogravimetry analysis. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV-vis light illumination. Benefitting from the electron-hole separation behavior and reduced overpotential of H+/H2, remarkably enhanced hydrogen production was demonstrated and the photocatalytic hydrogen generation from 0.4 wt% Pt-C/TiO2 increased by 22 times. This study also demonstrates that the novel and facile method is highly attractive, due to its easy operation, requiring no post treatment and energy-saving features.

  14. Type-2 fuzzy granular models

    CERN Document Server

    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.

  15. Mathematical models of granular matter

    CERN Document Server

    Mariano, Paolo; Giovine, Pasquale

    2008-01-01

    Granular matter displays a variety of peculiarities that distinguish it from other appearances studied in condensed matter physics and renders its overall mathematical modelling somewhat arduous. Prominent directions in the modelling granular flows are analyzed from various points of view. Foundational issues, numerical schemes and experimental results are discussed. The volume furnishes a rather complete overview of the current research trends in the mechanics of granular matter. Various chapters introduce the reader to different points of view and related techniques. New models describing granular bodies as complex bodies are presented. Results on the analysis of the inelastic Boltzmann equations are collected in different chapters. Gallavotti-Cohen symmetry is also discussed.

  16. Using a Time Granularity Table for Gradual Granular Data Aggregation

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem; Pedersen, Torben Bach

    2010-01-01

    solution for data reduction based on gradual granular data aggregation. With the gradual granular data aggregation mechanism, older data can be made coarse-grained while keeping the newest data fine-grained. For instance, when data is 3 months old aggregate to 1 minute level from 1 second level, when data...... and improve query performance, especially on resource-constrained systems with limited storage and query processing capabilities. A number of data reduction solutions have been developed, however an effective solution particularly based on gradual data reduction is missing. This paper presents an effective...... 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...

  17. Granular corneal dystrophy

    OpenAIRE

    Castillo Pérez, Alexeide de la C; Vilches Lescaille, Daysi; Noriega, Justo Luis; Martínez Balido, Daneel; León Balbón, Bárbaro Ramón; León Bernal, Danysleidi

    2015-01-01

    Las distrofias corneales constituyen un conjunto de enfermedades que presentan, en su mayoría, una baja incidencia y se caracterizan por acúmulo de material hialino o amiloide que disminuyen la transparencia corneal. La distrofia granular es una enfermedad autosómica dominante que presenta opacidades grises en el estroma superficial central de la córnea y se hacen visibles en la primera y segunda décadas de la vida, lo que provoca disminución de la visión más significativa cerca de los 40 año...

  18. Sinking a Granular Raft

    Science.gov (United States)

    Protière, Suzie; Josserand, Christophe; Aristoff, Jeffrey M.; Stone, Howard A.; Abkarian, Manouk

    2017-03-01

    We report experiments that yield new insights on the behavior of granular rafts at an oil-water interface. We show that these particle aggregates can float or sink depending on dimensionless parameters taking into account the particle densities and size and the densities of the two fluids. We characterize the raft shape and stability and propose a model to predict its shape and maximum length to remain afloat. Finally we find that wrinkles and folds appear along the raft due to compression by its own weight, which can trigger destabilization. These features are characteristics of an elastic instability, which we discuss, including the limitations of our model.

  19. Large granular lymphocyte leukemia

    OpenAIRE

    Terra, Bruno; Maia, Amanda M.

    2010-01-01

    O presente estudo tem como objetivo o estabelecimento de fundamentação teórica atualizada baseada em revisão bibliográfica sobre a leucemia de grandes linfócitos granulares (LGLG), doença onco-hematológica, que, devido à sua relativa raridade, é pouco conhecida e subdiagnosticada. A LGLG é caracterizada pela proliferação clonal de linfócitos T ou NK na medula óssea e/ou no sangue periférico. Dentre as manifestações clínico-laboratoriais, podem ocorrer citopenias (anemia e/ou neutropenia e/ou ...

  20. Thermal conductivity of granular materials

    Energy Technology Data Exchange (ETDEWEB)

    Buyevich, Yu A

    1974-01-01

    Stationary heat transfer in a granular material consisting of a continuous medium containing spherical granules of other substances is considered under the assumption that the spatial distribution of granules is random. The effective thermal conductivity characterizing macroscopic heat transfer in such a material is expressed as a certain function of the conductivities and volume fractions of the medium and dispersed substances. For reasons of mathematical analogy, all the results obtained for the thermal conductivity are valid while computing the effective diffusivity of some admixture in granular materials as well as for evaluation of the effective electric conductivity or the mean dielectric and magnetic permeabilities of granular conductors and dielectrics. (23 refs.)

  1. Cyclic voltammetric analysis of C 1-C 4 alcohol electrooxidations with Pt/C and Pt-Ru/C microporous electrodes

    Science.gov (United States)

    Lee, Choong-Gon; Umeda, Minoru; Uchida, Isamu

    The effect of temperature on methanol, ethanol, 2-propanol, and 2-butanol electrooxidation is investigated with Pt/C and Pt-Ru/C microporous electrodes. Cyclic voltammetry is employed in temperatures ranging from 25 to 80 °C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. Methanol displays the greatest activity atom alcohols. The addition of ruthenium reduces the poisoning effect, although it is ineffective with secondary alcohols. Secondary alcohols undergo a different oxidation mechanism at higher temperatures. Microporous electrodes provide detailed information on alcohol oxidation.

  2. Cyclic voltammetric analysis of C{sub 1}-C{sub 4} alcohol electrooxidations with Pt/C and Pt-Ru/C microporous electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Choong-Gon [Department of Chemical Engineering, Hanbat National University, San 16-1 Dukmyung-dong, Yusong-gu, Daejon (Korea); Umeda, Minoru [Department of Chemistry, Nagaoka University of Technology, Kamitomioka, Nagaoka (Japan); Uchida, Isamu [Department of Applied Chemistry, Tohoku University, Aramaki-aoba, Aoba-ku, Sendai (Japan)

    2006-09-29

    The effect of temperature on methanol, ethanol, 2-propanol, and 2-butanol electrooxidation is investigated with Pt/C and Pt-Ru/C microporous electrodes. Cyclic voltammetry is employed in temperatures ranging from 25 to 80{sup o}C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. Methanol displays the greatest activity atom alcohols. The addition of ruthenium reduces the poisoning effect, although it is ineffective with secondary alcohols. Secondary alcohols undergo a different oxidation mechanism at higher temperatures. Microporous electrodes provide detailed information on alcohol oxidation. (author)

  3. Granular nanocrystalline zirconia electrolyte layers deposited on porous SOFC cathode substrates

    International Nuclear Information System (INIS)

    Seydel, Johannes; Becker, Michael; Ivers-Tiffee, Ellen; Hahn, Horst

    2009-01-01

    Thin granular yttria-stabilized zirconia (YSZ) electrolyte layers were prepared by chemical vapor synthesis and deposition (CVD/CVS) on a porous substoichiometric lanthanum-strontium-manganite (ULSM) solid oxide fuel cell cathode substrate. The substrate porosity was optimized with a screen printed fine porous buffer layer. Structural analysis by scanning electron microscopy showed a homogeneous, granular nanocrystalline layer with a microstructure that was controlled via reactor settings. The CVD/CVS gas-phase process enabled the deposition of crack-free granular YSZ films on porous ULSM substrates. The electrolyte layers characterized with impedance spectroscopy exhibited enhanced grain boundary conductivity.

  4. Granular flows: fundamentals and applications

    Science.gov (United States)

    Cleary, Paul W.

    DEM allows the prediction of complex industrial and geophysical particle flows. The importance of particle shape is demonstrated through a series of simple examples. Shape controls resistance to shear, the magnitude of collision stress, dilation and the angle of repose. We use a periodic flow of a bed of particles to demonstrate the different states of granular matter, the generation of dilute granular flow when granular temperature is high and the flow dependent nature of the granular thermodynamic boundary conditions. A series of industrial case studies examines how DEM can be used to understand and improve processes such as separation, mixing, grinding, excavation, hopper discharge, metering and conveyor interchange. Finally, an example of landslide motion over real topography is presented.

  5. Superconductivity in inhomogeneous granular metals

    International Nuclear Information System (INIS)

    McLean, W.L.

    1980-01-01

    A model of elongated metal ellipsoids imbedded in a granular metal is treated by an effective medium approach to explain the observed temperature dependence of the normal-state conductivity of superconducting granular aluminum. Josephson tunneling is thus still required to account for the superconductivity. The model predicts the same kind of contrasting behavior on opposite sides of the metal-insulator transition as is found in the recent scaling treatment of Anderson localization

  6. Effect of cationic molecules on the oxygen reduction reaction on fuel cell grade Pt/C (20 wt%) catalyst in potassium hydroxide (aq, 1 mol dm(-3)).

    Science.gov (United States)

    Ong, Ai Lien; Inglis, Kenneth K; Whelligan, Daniel K; Murphy, Sam; Varcoe, John R

    2015-05-14

    This study investigates the effect of 1 mmol dm(-3) concentrations of a selection of small cationic molecules on the performance of a fuel cell grade oxygen reduction reaction (ORR) catalyst (Johnson Matthey HiSPEC 3000, 20 mass% Pt/C) in aqueous KOH (1 mol dm(-3)). The cationic molecules studied include quaternary ammonium (including those based on bicyclic systems) and imidazolium types as well as a phosphonium example: these serve as fully solubilised models for the commonly encountered head-groups in alkaline anion-exchange membranes (AAEM) and anion-exchange ionomers (AEI) that are being developed for application in alkaline polymer electrolyte fuel cells (APEFCs), batteries and electrolysers. Both cyclic and hydrodynamic linear sweep rotating disk electrode voltammetry techniques were used. The resulting voltammograms and subsequently derived data (e.g. apparent electrochemical active surface areas, Tafel plots, and number of [reduction] electrons transferred per O2) were compared. The results show that the imidazolium examples produced the highest level of interference towards the ORR on the Pt/C catalyst under the experimental conditions used.

  7. Evaluation of reaction selectivity at various Pt/C electrocatalysts using a porous microelectrode in the presence of methanol and oxygen

    International Nuclear Information System (INIS)

    Shironita, Sayoko; Zhang, Weiqi; Sakai, Tsukasa; Umeda, Minoru

    2014-01-01

    Pt is most useful metal for various electrochemical reactions as an electrocatalyst. In a direct methanol fuel cell, Pt performs a catalytic activity for both the methanol oxidation reaction and oxygen reduction reaction; therefore, a Pt-based catalyst is used as an anode and a cathode. For the coexistence of methanol and oxygen due to methanol crossover through an electrolyte membrane during the cell operation, the direct methanol fuel cell performance decreases. However, if a higher selective reaction electrocatalyst can be developed, the cell performance will not be suppressed. In this study, the reaction selectivities of seven types of Pt supported on carbon (Pt/C) electrocatalysts were evaluated using a porous microelectrode in the presence of methanol and oxygen. As a result, some Pt/C catalysts showed a methanol oxidation selectivity, while the other catalysts showed an oxygen reduction selectivity. It was found that the percentage of edge-atom in the Pt particle is related to the methanol oxidation selectivity or the oxygen reduction selectivity. Moreover, each current density decreases with the increasing chemical shift in the Pt binding energy

  8. Granular Superconductors and Gravity

    Science.gov (United States)

    Noever, David; Koczor, Ron

    1999-01-01

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

  9. To alloy or not to alloy? Cr modified Pt/C cathode catalysts for PEM fuel cells.

    Science.gov (United States)

    Wells, Peter P; Qian, Yangdong; King, Colin R; Wiltshire, Richard J K; Crabb, Eleanor M; Smart, Lesley E; Thompsett, David; Russell, Andrea E

    2008-01-01

    The cathode electrocatalysts for proton exchange membrane (PEM) fuel cells are commonly platinum and platinum based alloy nanoparticles dispersed on a carbon support. Control over the particle size and composition has, historically, been attained empirically, making systematic studies of the effects of various structural parameters difficult. The controlled surface modification methodology used in this work has enabled the controlled modification of carbon supported Pt nanoparticles by Cr so as to yield nanoalloy particles with defined compositions. Subsequent heat treatment in 5% H2 in N2 resulted in the formation of a distinct Pt3Cr alloy phase which was either restricted to the surface of the particles or present throughout the bulk of the particle structure. Measurement of the oxygen reduction activity of the catalysts was accomplished using the rotating thin film electrode method and the activities obtained were related to the structure of the nanoalloy catalyst particles, largely determined using Cr K edge and Pt L3 edge XAS.

  10. Granular flows in constrained geometries

    Science.gov (United States)

    Murthy, Tejas; Viswanathan, Koushik

    Confined geometries are widespread in granular processing applications. The deformation and flow fields in such a geometry, with non-trivial boundary conditions, determine the resultant mechanical properties of the material (local porosity, density, residual stresses etc.). We present experimental studies of deformation and plastic flow of a prototypical granular medium in different nontrivial geometries- flat-punch compression, Couette-shear flow and a rigid body sliding past a granular half-space. These geometries represent simplified scaled-down versions of common industrial configurations such as compaction and dredging. The corresponding granular flows show a rich variety of flow features, representing the entire gamut of material types, from elastic solids (beam buckling) to fluids (vortex-formation, boundary layers) and even plastically deforming metals (dead material zone, pile-up). The effect of changing particle-level properties (e.g., shape, size, density) on the observed flows is also explicitly demonstrated. Non-smooth contact dynamics particle simulations are shown to reproduce some of the observed flow features quantitatively. These results showcase some central challenges facing continuum-scale constitutive theories for dynamic granular flows.

  11. Why granular media are thermal after all

    Science.gov (United States)

    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.

  12. Traffic and Granular Flow '11

    CERN Document Server

    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.

  13. Uniform shock waves in disordered granular matter

    NARCIS (Netherlands)

    Gómez, L.R.; Turner, A.M.; Vitelli, V.

    2012-01-01

    The confining pressure P is perhaps the most important parameter controlling the properties of granular matter. Strongly compressed granular media are, in many respects, simple solids in which elastic perturbations travel as ordinary phonons. However, the speed of sound in granular aggregates

  14. Acoustic waves in granular materials

    NARCIS (Netherlands)

    Mouraille, O.J.P.; Luding, Stefan

    2008-01-01

    Dynamic simulations with discrete elements are used to obtain more insight into the wave propagation in dense granular media. A small perturbation is created on one side of a dense, static packing and examined during its propagation until it arrives at the opposite side. The influence of

  15. Granular boycott effect: How to mix granulates

    Science.gov (United States)

    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.

  16. Properties of Pt/C catalyst modified by chemical vapor deposition of Cr as a cathode of phosphoric acid fuel cell

    International Nuclear Information System (INIS)

    Seo, Sang Joon; Joh, Han-Ik; Kim, Hyun Tae; Moon, Sang Heup

    2006-01-01

    Cr-modified Pt/C catalysts were prepared by the chemical vapour deposition (CVD) of Cr on Pt/C, and their performance as a cathode of phosphoric acid fuel cell (PAFC) was compared with the case of catalysts containing Cr added by impregnation (IMP). The catalyst prepared by CVD showed a higher activity for oxygen reduction reaction (ORR) than one prepared by IMP. There was an optimum amount of Cr that yielded the maximum mass activity of the catalyst because the gain in the intrinsic activity due to the promotional effect of Cr was counterbalanced by the loss of exposed Pt surface area as a result of the Cr introduction. Nevertheless, the activity increase at the optimum amount of Cr was greater for the CVD catalyst than for the IMP catalyst. Also, the optimum amount of Cr to yield the maximum activity was smaller for the former catalyst [Cr/Pt] CVD = 0.6, than for the latter, [Cr/Pt] IMP = 1.0. The enhancement of the Pt catalyst activity by Cr addition is attributed to two factors: changes in the surface Pt-Pt spacing and the electronic modification of the Pt surface. The formation of a Pt-Cr alloy, as confirmed by X-ray diffraction, decreased the lattice parameter of Pt, which was beneficial to the catalyst activity for ORR. X-ray photoelectron spectroscopy results showed that the binding energies of Pt electrons were shifted to higher energies due to Cr modification. Accordingly, the electron density of Pt was lowered and the Pt-O bond became weak on the Cr-modified catalysts, which was also beneficial to the catalyst activity for ORR. The promotion of oxygen reduction on Cr-modified catalysts was confirmed by measuring the cyclic voltammograms of the catalysts. All the above changes were made more effectively for catalysts prepared by CVD than for those prepared by IMP because the former method allowed Cr to interact more closely with the Pt surface than the latter, which was demonstrated by the characterization of catalysts in this study

  17. 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

  18. The Use of C-MnO2 as Hybrid Precursor Support for a Pt/C-MnxO1+x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction (MOR

    Directory of Open Access Journals (Sweden)

    Alessandro H.A. Monteverde Videla

    2015-07-01

    Full Text Available Platinum (Pt nanoparticles are deposited on a hybrid support (C-MnO2 according to a polyol method. The home-made catalyst, resulted as Pt/C-MnxO1+x, is compared with two different commercial platinum based materials (Pt/C and PtRu/C. The synthesized catalyst is characterized by means of FESEM, XRD, ICP-MS, XPS and μRS analyses. MnO2 is synthesized and deposited over a commercial grade of carbon (Vulcan XC72 by facile reduction of potassium permanganate in acidic solution. Pt nanoparticles are synthesized on the hybrid support by a polyol thermal assisted method (microwave irradiation, followed by an annealing at 600 °C. The obtained catalyst displays a support constituted by a mixture of manganese oxides (Mn2O3 and Mn3O4 with a Pt loading of 19 wt. %. The electro-catalytic activity towards MOR is assessed by RDE in acid conditions (0.5 M H2SO4, evaluating the ability to oxidize methanol in 1 M concentration. The synthesized Pt/C-MnxO1+x catalyst shows good activity as well as good stability compared to the commercial Pt/C based catalyst.

  19. Strain localisation in granular media

    OpenAIRE

    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...

  20. Paediatric laryngeal granular cell tumour

    Directory of Open Access Journals (Sweden)

    Dauda Ayuba

    2009-01-01

    Full Text Available Granular cell tumour (GCT affecting the larynx is not common, especially in children. Most cases are apt to be confused with respiratory papilloma and may even be mistaken for a malignant neoplasia. We present a case of laryngeal GCT in a 12-year-old child to emphasize that the tumour should be regarded in the differential of growths affecting the larynx in children.

  1. Impact Compaction of a Granular Material

    Science.gov (United States)

    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.

  2. 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)

  3. The Granular Blasius Problem: High inertial number granular flows

    Science.gov (United States)

    Tsang, Jonathan; Dalziel, Stuart; Vriend, Nathalie

    2017-11-01

    The classical Blasius problem considers the formation of a boundary layer through the change at x = 0 from a free-slip to a no-slip boundary beneath an otherwise steady uniform flow. Discrete particle model (DPM) simulations of granular gravity currents show that a similar phenomenon exists for a steady flow over a uniformly sloped surface that is smooth upstream (allowing slip) but rough downstream (imposing a no-slip condition). The boundary layer is a region of high shear rate and therefore high inertial number I; its dynamics are governed by the asymptotic behaviour of the granular rheology as I -> ∞ . The μ(I) rheology asserts that dμ / dI = O(1 /I2) as I -> ∞ , but current experimental evidence is insufficient to confirm this. We show that `generalised μ(I) rheologies', with different behaviours as I -> ∞ , all permit the formation of a boundary layer. We give approximate solutions for the velocity profile under each rheology. The change in boundary condition considered here mimics more complex topography in which shear stress increases in the streamwise direction (e.g. a curved slope). Such a system would be of interest in avalanche modelling. EPSRC studentship (Tsang) and Royal Society Dorothy Hodgkin Fellowship (Vriend).

  4. Theoretical model of granular compaction

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-11-01

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

  5. Storage and discharge of a granular fluid

    NARCIS (Netherlands)

    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

  6. Characterization of Unbound Granular Materials for Pavements

    NARCIS (Netherlands)

    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

  7. Periurethral granular cell tumor: a case report

    International Nuclear Information System (INIS)

    Kim, Jeong Kon; Choi, Hyo Gyeong; Cho, Kyoung Sik

    1998-01-01

    Granular cell tumors are uncommon soft tissue tumors which arise as solitary or multiple masses. Lesions commonly arise in the head, neck, and chest wall, but can occur in any part of the body. To our knowledge, periurethral granular cell tumor has not been previously reported. We report one such case

  8. Viscosity evolution of anaerobic granular sludge

    NARCIS (Netherlands)

    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

  9. Traffic and Granular Flow ’03

    CERN Document Server

    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 ...

  10. Traffic and Granular Flow’05

    CERN Document Server

    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...

  11. Centrifuge modelling of granular flows

    Science.gov (United States)

    Cabrera, Miguel Angel; Wu, Wei

    2015-04-01

    A common characteristic of mass flows like debris flows, rock avalanches and mudflows is that gravity is their main driving force. Gravity defines the intensity and duration of the main interactions between particles and their surrounding media (particle-particle, particle-fluid, fluid-fluid). At the same time, gravity delimits the occurrence of phase separation, inverse segregation, and mass consolidation, among other phenomena. Therefore, in the understanding of the flow physics it is important to account for the scaling of gravity in scaled models. In this research, a centrifuge model is developed to model free surface granular flows down an incline at controlled gravity conditions. Gravity is controlled by the action of an induced inertial acceleration field resulting from the rotation of the model in a geotechnical centrifuge. The characteristics of the induced inertial acceleration field during flow are discussed and validated via experimental data. Flow heights, velocity fields, basal pressure and impact forces are measured for a range of channel inclinations and gravity conditions. Preliminary results enlighten the flow characteristics at variable gravity conditions and open a discussion on the simulation of large scale processes at a laboratory scale. Further analysis on the flow physics brings valuable information for the validation of granular flows rheology.

  12. Superconducting thin films

    International Nuclear Information System (INIS)

    Hebard, A.F.; Vandenberg, J.M.

    1982-01-01

    This invention relates to granular metal and metal oxide superconducting films formed by ion beam sputter deposition. Illustratively, the films comprise irregularly shaped, randomly oriented, small lead grains interspersed in an insulating lead oxide matrix. The films are hillock-resistant when subjected to thermal cycling and exhibit unusual josephson-type switching characteristics. Depending on the oxygen content, a film may behave in a manner similar to that of a plurality of series connected josephson junctions, or the film may have a voltage difference in a direction parallel to a major surface of the film that is capable of being switched from zero voltage difference to a finite voltage difference in response to a current larger than the critical current

  13. Aerofractures in Confined Granular Media

    Science.gov (United States)

    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

  14. Granular metamaterials for vibration mitigation

    Science.gov (United States)

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

    2013-09-01

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

  15. Fracture surfaces of granular pastes.

    Science.gov (United States)

    Mohamed Abdelhaye, Y O; Chaouche, M; Van Damme, H

    2013-11-01

    Granular pastes are dense dispersions of non-colloidal grains in a simple or a complex fluid. Typical examples are the coating, gluing or sealing mortars used in building applications. We study the cohesive rupture of thick mortar layers in a simple pulling test where the paste is initially confined between two flat surfaces. After hardening, the morphology of the fracture surfaces was investigated, using either the box counting method to analyze fracture profiles perpendicular to the mean fracture plane, or the slit-island method to analyze the islands obtained by cutting the fracture surfaces at different heights, parallel to the mean fracture plane. The fracture surfaces were shown to exhibit scaling properties over several decades. However, contrary to what has been observed in the brittle or ductile fracture of solid materials, the islands were shown to be mass fractals. This was related to the extensive plastic flow involved in the fracture process.

  16. Shear failure of granular materials

    Science.gov (United States)

    Degiuli, Eric; Balmforth, Neil; McElwaine, Jim; Schoof, Christian; Hewitt, Ian

    2012-02-01

    Connecting the macroscopic behavior of granular materials with the microstructure remains a great challenge. Recent work connects these scales with a discrete calculus [1]. In this work we generalize this formalism from monodisperse packings of disks to 2D assemblies of arbitrarily shaped grains. In particular, we derive Airy's expression for a symmetric, divergence-free stress tensor. Using these tools, we derive, from first-principles and in a mean-field approximation, the entropy of frictional force configurations in the Force Network Ensemble. As a macroscopic consequence of the Coulomb friction condition at contacts, we predict shear failure at a critical shear stress, in accordance with the Mohr-Coulomb failure condition well known in engineering. Results are compared with numerical simulations, and the dependence on the microscopic geometric configuration is discussed. [4pt] [1] E. DeGiuli & J. McElwaine, PRE 2011. doi: 10.1103/PhysRevE.84.041310

  17. Mechanics of a granular skin

    Science.gov (United States)

    Karmakar, Somnath; Sane, Anit; Bhattacharya, S.; Ghosh, Shankar

    2017-04-01

    Magic sand, a hydrophobic toy granular material, is widely used in popular science instructions because of its nonintuitive mechanical properties. A detailed study of the failure of an underwater column of magic sand shows that these properties can be traced to a single phenomenon: the system self-generates a cohesive skin that encapsulates the material inside. The skin, consisting of pinned air-water-grain interfaces, shows multiscale mechanical properties: they range from contact-line dynamics in the intragrain roughness scale, to plastic flow at the grain scale, all the way to sample-scale mechanical responses. With decreasing rigidity of the skin, the failure mode transforms from brittle to ductile (both of which are collective in nature) to a complete disintegration at the single-grain scale.

  18. Storage and discharge of a granular fluid.

    Science.gov (United States)

    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.

  19. Energy decay in a granular gas collapse

    International Nuclear Information System (INIS)

    Almazán, Lidia; Serero, Dan; Pöschel, Thorsten; Salueña, Clara

    2017-01-01

    An inelastic hard ball bouncing repeatedly off the ground comes to rest in finite time by performing an infinite number of collisions. Similarly, a granular gas under the influence of external gravity, condenses at the bottom of the confinement due to inelastic collisions. By means of hydrodynamical simulations, we find that the condensation process of a granular gas reveals a similar dynamics as the bouncing ball. Our result is in agreement with both experiments and particle simulations, but disagrees with earlier simplified hydrodynamical description. Analyzing the result in detail, we find that the adequate modeling of pressure plays a key role in continuum modeling of granular matter. (paper)

  20. On inconsistency in frictional granular systems

    Science.gov (United States)

    Alart, Pierre; Renouf, Mathieu

    2018-04-01

    Numerical simulation of granular systems is often based on a discrete element method. The nonsmooth contact dynamics approach can be used to solve a broad range of granular problems, especially involving rigid bodies. However, difficulties could be encountered and hamper successful completion of some simulations. The slow convergence of the nonsmooth solver may sometimes be attributed to an ill-conditioned system, but the convergence may also fail. The prime aim of the present study was to identify situations that hamper the consistency of the mathematical problem to solve. Some simple granular systems were investigated in detail while reviewing and applying the related theoretical results. A practical alternative is briefly analyzed and tested.

  1. Shock waves in weakly compressed granular media.

    Science.gov (United States)

    van den Wildenberg, Siet; van Loo, Rogier; van Hecke, Martin

    2013-11-22

    We experimentally probe nonlinear wave propagation in weakly compressed granular media and observe a crossover from quasilinear sound waves at low impact to shock waves at high impact. We show that this crossover impact grows with the confining pressure P0, whereas the shock wave speed is independent of P0-two hallmarks of granular shocks predicted recently. The shocks exhibit surprising power law attenuation, which we model with a logarithmic law implying that shock dissipation is weak and qualitatively different from other granular dissipation mechanisms. We show that elastic and potential energy balance in the leading part of the shocks.

  2. Granular-relational data mining how to mine relational data in the paradigm of granular computing ?

    CERN Document Server

    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...

  3. 2D Ultrathin Core-shell Pd@Ptmonolayer Nanosheets: Defect-Mediated Thin Film Growth and Enhanced Oxygen Reduction Performance

    KAUST Repository

    Wang, Wenxin

    2015-06-16

    An operational strategy for the synthesis of atomically smooth Pt skin by a defect-mediated thin film growth method is reported. Extended ultrathin core-shell structured Pd@Ptmonolayer nanosheets (thickness below 5 nm) exhibit a seven-fold enhancement in mass-activity and surprisingly good durability toward oxygen reduction reaction as compared with the commercial Pt/C catalyst.

  4. 2D Ultrathin Core-shell Pd@Ptmonolayer Nanosheets: Defect-Mediated Thin Film Growth and Enhanced Oxygen Reduction Performance

    KAUST Repository

    Wang, Wenxin; Zhao, Yunfeng; Ding, Yi

    2015-01-01

    An operational strategy for the synthesis of atomically smooth Pt skin by a defect-mediated thin film growth method is reported. Extended ultrathin core-shell structured Pd@Ptmonolayer nanosheets (thickness below 5 nm) exhibit a seven-fold enhancement in mass-activity and surprisingly good durability toward oxygen reduction reaction as compared with the commercial Pt/C catalyst.

  5. Spatial correlations in compressible granular flows

    NARCIS (Netherlands)

    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

  6. Granular Gases: Probing the Boundaries of Hydrodynamics

    International Nuclear Information System (INIS)

    Goldhirsch, I.

    1999-01-01

    The dissipative nature of the particle interactions in granular systems renders granular gases mesoscopic and bearing some similarities to regular gases in the ''continuum transition regime'' where shear rates and/or thermal gradients are very large). The following properties of granular gases support the above claim: (i). Mean free times are of the same order as macroscopic time scales (inverse shear rates); (ii). Mean free paths can be macroscopic and comparable to the system's dimensions; (iii). Typical flows are supersonic; (iv). Shear rates are typically ''large''; (v). Stress fields are scale (resolution) dependent; (vi). Burnett and super-Burnett corrections to both the constitutive relations and the boundary conditions are of importance; (vii). Single particle distribution functions can be far from Gaussian. It is concluded that while hydrodynamic descriptions of granular gases are relevant, they are probing the boundaries of applicability of hydrodynamics and perhaps slightly beyond

  7. Advanced Granular System Modeling, Phase I

    Data.gov (United States)

    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...

  8. Resistance capability of microaerobic granular sludge for ...

    African Journals Online (AJOL)

    enoh

    2012-02-08

    Feb 8, 2012 ... The resistance capability to pH shock of microaerobic granular sludge for pentachlorophenol (PCP) ... process with chlorine gas in pulp and paper, leather and spinning ... nitrifying bacteria in the aerobic zone, and then trans-.

  9. Microbiological aspects of granular methanogenic sludge

    NARCIS (Netherlands)

    Dolfing, J.

    1987-01-01

    The settling characteristics of anaerobic sludge are enhanced by the formation of microbial conglomerates. Various types of conglomerates having different structures, were distinguished in the present study, viz. granules, pellets and flocs (chapter 1). Granular methanogenic sludge, often

  10. NMR Measurements of Granular Flow and Compaction

    Science.gov (United States)

    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.

  11. Uniform shock waves in disordered granular matter.

    Science.gov (United States)

    Gómez, Leopoldo R; Turner, Ari M; Vitelli, Vincenzo

    2012-10-01

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

  12. Kinetic Theory of Granular Gases

    Energy Technology Data Exchange (ETDEWEB)

    Trizac, Emmanuel [Center of Theoretical Biological Physics, UC San Diego, La Jolla, CA 92093-0374 (United States); Laboratoire de Physique Theorique et Modeles Statistiques, Campus Universitaire, 91405 Orsay (France)

    2005-11-25

    Granular gases are composed of macroscopic bodies kept in motion by an external energy source such as a violent shaking. The behaviour of such systems is quantitatively different from that of ordinary molecular gases: due to the size of the constituents, external fields have a stronger effect on the dynamics and, more importantly, the kinetic energy of the gas is no longer a conserved quantity. The key role of the inelasticity of collisions has been correctly appreciated for about fifteen years, and the ensuing consequences in terms of phase behaviour or transport properties studied in an increasing and now vast body of literature. The purpose of this book is to help the newcomer to the field in acquiring the essential theoretical tools together with some numerical techniques. As emphasized by the authors-who were among the pioneers in the domain- the content could be covered in a one semester course for advanced undergraduates, or it could be incorporated in a more general course dealing with the statistical mechanics of dissipative systems. The book is self-contained, clear, and avoids mathematical complications. In order to elucidate the main physical ideas, heuristic points of views are sometimes preferred to a more rigorous route that would lead to a longer discussion. The 28 chapters are short; they offer exercises and worked examples, solved at the end of the book. Each part is supplemented with a relevant foreword and a useful summary including take-home messages. The editorial work is of good quality, with very few typographical errors. In spite of the title, kinetic theory stricto sensu is not the crux of the matter covered. The authors discuss the consequences of the molecular chaos assumption both at the individual particle level and in terms of collective behaviour. The first part of the book addresses the mechanics of grain collisions. It is emphasized that considering the coefficient of restitution {epsilon} -a central quantity governing the

  13. Kinetic Theory of Granular Gases

    International Nuclear Information System (INIS)

    Trizac, Emmanuel

    2005-01-01

    Granular gases are composed of macroscopic bodies kept in motion by an external energy source such as a violent shaking. The behaviour of such systems is quantitatively different from that of ordinary molecular gases: due to the size of the constituents, external fields have a stronger effect on the dynamics and, more importantly, the kinetic energy of the gas is no longer a conserved quantity. The key role of the inelasticity of collisions has been correctly appreciated for about fifteen years, and the ensuing consequences in terms of phase behaviour or transport properties studied in an increasing and now vast body of literature. The purpose of this book is to help the newcomer to the field in acquiring the essential theoretical tools together with some numerical techniques. As emphasized by the authors-who were among the pioneers in the domain- the content could be covered in a one semester course for advanced undergraduates, or it could be incorporated in a more general course dealing with the statistical mechanics of dissipative systems. The book is self-contained, clear, and avoids mathematical complications. In order to elucidate the main physical ideas, heuristic points of views are sometimes preferred to a more rigorous route that would lead to a longer discussion. The 28 chapters are short; they offer exercises and worked examples, solved at the end of the book. Each part is supplemented with a relevant foreword and a useful summary including take-home messages. The editorial work is of good quality, with very few typographical errors. In spite of the title, kinetic theory stricto sensu is not the crux of the matter covered. The authors discuss the consequences of the molecular chaos assumption both at the individual particle level and in terms of collective behaviour. The first part of the book addresses the mechanics of grain collisions. It is emphasized that considering the coefficient of restitution ε -a central quantity governing the inelasticity of

  14. Granular materials flow like complex fluids

    Science.gov (United States)

    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

  15. 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.

  16. 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.

  17. Granular cell tumor: An uncommon benign neoplasm

    Directory of Open Access Journals (Sweden)

    Tirthankar Gayen

    2015-01-01

    Full Text Available Granular cell tumor is a distinctly rare neoplasm of neural sheath origin. It mainly presents as a solitary asymptomatic swelling in the oral cavity, skin, and rarely internal organs in the middle age. Histopathology is characteristic, showing polyhedral cells containing numerous fine eosinophilic granules with indistinct cell margins. We present a case of granular cell tumor on the back of a 48-year-old woman which was painful, mimicking an adnexal tumor.

  18. A constitutive law for dense granular flows.

    Science.gov (United States)

    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.

  19. Surface passivation of high purity granular metals: zinc, cadmium, lead

    Directory of Open Access Journals (Sweden)

    Pirozhenko L. A.

    2017-10-01

    Full Text Available For the high purity metals (99.9999%, such as zinc, cadmium, and lead, which are widely used as initial components in growing semiconductor and scintillation crystals (CdTe, CdZnTe, ZnSe, (Cd, Zn, Pb WO4, (Cd, Zn, Pb MoO4 et al., it is very important to ensure reliable protection of the surface from oxidation and adsorption of impurities from the atmosphere. The specific features of surface passivation of high purity cadmium, lead and zinc are not sufficiently studied and require specific methodologies for further studies. The use of organic solutions in the schemes of chemical passivation of the investigated metals avoids hydrolysis of the obtained protective films. The use of organic solvents with pure cation and anion composition as the washing liquid prevents chemisorption of ions present in the conventionally used distilled water. This keeps the original purity of the granular metals. Novel compositions of etchants and etching scheme providing simultaneous polishing and passivation of high purity granular Zn, Cd and Pb are developed. Chemical passivation allows storing metals in the normal atmospheric conditions for more than half a year for Zn and Cd and up to 30 days for Pb without changing the state of the surface. The use of the glycerol-DMF solution in the processes for obtaining Pb granules provides self-passivation of metal surfaces and eliminates the additional chemical processing while maintaining the quality of corrosion protection.

  20. High Temperature Magnetic Properties of Indirect Exchange Spring FePt/M(Cu,C/Fe Trilayer Thin Films

    Directory of Open Access Journals (Sweden)

    Anabil Gayen

    2013-01-01

    Full Text Available We report the investigation of temperature dependent magnetic properties of FePt and FePt(30/M(Cu,C/Fe(5 trilayer thin films prepared by using magnetron sputtering technique at ambient temperature and postannealed at different temperatures. L10 ordering, hard magnetic properties, and thermal stability of FePt films are improved with increasing postannealing temperature. In FePt/M/Fe trilayer, the formation of interlayer exchange coupling between magnetic layers depends on interlayer materials and interface morphology. In FePt/C/Fe trilayer, when the C interlayer thickness was about 0.5 nm, a strong interlayer exchange coupling between hard and soft layers was achieved, and saturation magnetization was enhanced considerably after using interlayer exchange coupling with Fe. In addition, incoherent magnetization reversal process observed in FePt/Fe films changes into coherent switching process in FePt/C/Fe films giving rise to a single hysteresis loop. High temperature magnetic studies up to 573 K reveal that the effective reduction in the coercivity decreases largely from 34 Oe/K for FePt/Fe film to 13 Oe/K for FePt/C(0.5/Fe film demonstrating that the interlayer exchange coupling seems to be a promising approach to improve the stability of hard magnetic properties at high temperatures, which is suitable for high-performance magnets and thermally assisted magnetic recording media.

  1. Microfluidics of soft granular gels

    Science.gov (United States)

    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.

  2. Dynamic Deformation and Collapse of Granular Columns

    Science.gov (United States)

    Uenishi, K.; Tsuji, K.; Doi, S.

    2009-12-01

    Large dynamic deformation of granular materials may be found in nature not only in the failure of slopes and cliffs — due to earthquakes, rock avalanches, debris flows and landslides — but also in earthquake faulting itself. Granular surface flows often consist of solid grains and intergranular fluid, but the effect of the fluid may be usually negligible because the volumetric concentration of grains is in many cases high enough for interparticle forces to dominate momentum transport. Therefore, the investigation of dry granular flow of a mass might assist in further understanding of the above mentioned geophysical events. Here, utilizing a high-speed digital video camera system, we perform a simple yet fully-controlled series of laboratory experiments related to the collapse of granular columns. We record, at an interval of some microseconds, the dynamic transient granular mass flow initiated by abrupt release of a tube that contains dry granular materials. The acrylic tube is partially filled with glass beads and has a cross-section of either a fully- or semi-cylindrical shape. Upon sudden removal of the tube, the granular solid may fragment under the action of its own weight and the particles spread on a rigid horizontal plane. This study is essentially the extension of the previous ones by Lajeunesse et al. (Phys. Fluids 2004) and Uenishi and Tsuji (JPGU 2008), but the striped layers of particles in a semi-cylindrical tube, newly introduced in this contribution, allow us to observe the precise particle movement inside the granular column: The development of slip lines inside the column and the movement of particles against each other can be clearly identified. The major controlling parameters of the spreading dynamics are the initial aspect ratio of the granular (semi-)cylindrical column, the frictional properties of the horizontal plane (substrate) and the size of beads. We show the influence of each parameter on the average flow velocity and final radius

  3. Granular Materials and Risks In ISRU

    Science.gov (United States)

    Behringer, Robert P.; Wilkinson, R. Allen

    2004-01-01

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

  4. Collapse of tall granular columns in fluid

    Science.gov (United States)

    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°.

  5. Wet granular matter a truly complex fluid

    CERN Document Server

    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.

  6. 11th Traffic and Granular Flow Conference

    CERN Document Server

    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...

  7. Granular Silo collapse: an experimental study

    Science.gov (United States)

    Clement, Eric; Gutierriez, Gustavo; Boltenhagen, Philippe; Lanuza, Jose

    2008-03-01

    We present an experimental work that develop some basic insight into the pre-buckling behavior and the buckling transition toward plastic collapse of a granular silo. We study different patterns of deformation generated on thin paper cylindrical shells during granular discharge. We study the collapse threshold for different bed height, flow rates and grain sizes. We compare the patterns that appear during the discharge of spherical beads, with those obtained in the axially compressed cylindrical shells. When the height of the granular column is close to the collapse threshold, we describe a ladder like pattern that rises around the cylinder surface in a spiral path of diamond shaped localizations, and develops into a plastic collapsing fold that grows around the collapsing silo.

  8. Statistical mechanics of dense granular media

    International Nuclear Information System (INIS)

    Coniglio, A; Fierro, A; Nicodemi, M; Ciamarra, M Pica; Tarzia, M

    2005-01-01

    We discuss some recent results on the statistical mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of monodisperse and bidisperse granular assemblies. We show that 'jamming' corresponds to a phase transition from a 'fluid' to a 'glassy' phase, observed when crystallization is avoided. The nature of such a 'glassy' phase turns out to be the same as found in mean field models for glass formers. This gives quantitative evidence for the idea of a unified description of the 'jamming' transition in granular media and thermal systems, such as glasses. We also discuss mixing/segregation transitions in binary mixtures and their connections to phase separation and 'geometric' effects

  9. 76 FR 8774 - Granular Polytetrafluoroethylene Resin From Japan

    Science.gov (United States)

    2011-02-15

    ... INTERNATIONAL TRADE COMMISSION [Investigation No. 731-TA-386 (Third Review)] Granular Polytetrafluoroethylene Resin From Japan AGENCY: United States International Trade Commission. ACTION: Termination of five... revocation of the antidumping duty order on granular polytetrafluoroethylene resin from Japan would be likely...

  10. Surface instabilities in shock loaded granular media

    Science.gov (United States)

    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

  11. Anaerobic granular sludge and biofilm reactors

    DEFF Research Database (Denmark)

    Skiadas, Ioannis V.; Gavala, Hariklia N.; Schmidt, Jens Ejbye

    2003-01-01

    by the immobilization of the biomass, which forms static biofilms, particle-supported biofilms, or granules depending on the reactor's operational conditions. The advantages of the high-rate anaerobic digestion over the conventional aerobic wastewater treatment methods has created a clear trend for the change......-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...

  12. 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

  13. International Workshop on Traffic and Granular Flow

    CERN Document Server

    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.

  14. 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...... is developed and it is concluded that the associated sliding rule, in the context of granular contact dynamics, may be viewed as an artifact of the time discretization and that the use of an associated flow rule at the particle scale level generally is physically acceptable. (C) 2012 Elsevier Ltd. All rights...

  15. Tracing Thermal Creep Through Granular Media

    Science.gov (United States)

    Steinpilz, Tobias; Teiser, Jens; Koester, Marc; Schywek, Mathias; Wurm, Gerhard

    2017-08-01

    A temperature gradient within a granular medium at low ambient pressure drives a gas flow through the medium by thermal creep. We measured the resulting air flow for a sample of glass beads with particle diameters between 290 μ m and 420 μ m for random close packing. Ambient pressure was varied between 1 Pa and 1000 Pa. The gas flow was quantified by means of tracer particles during parabolic flights. The flow varies systematically with pressure between 0.2 cm/s and 6 cm/s. The measured flow velocities are in quantitative agreement to model calculations that treat the granular medium as a collection of linear capillaries.

  16. Granular cells Tumor in the gastrointestinal tract

    International Nuclear Information System (INIS)

    Castano LL, Rodrigo; Gaitan B, Maria H; Juliao E, Fabian

    2005-01-01

    Granular cells tumors are ubiquitous lesions in the gastrointestinal tract, are rare and asymptomatic and they are generally an incidental discovery at gastroduodenoscopy or colonoscopy. In the gastrointestinal tract they are more frequently located in the esophagus, right colon and rectum, stomach, appendix, small intestine or biliopancreatic tract. This article describes three patients with four tumors of granular cells in rectum, esophagus (2 lesions) and appendix. It becomes special emphasis in their neural origin, their benign behavior that justifies the endoscopic resections or limited surgical excisions and the necessity of a pursuit for the possibility, although little, of malignant transformation

  17. Consequence of chitosan treating on the adsorption of humic acid by granular activated carbon.

    Science.gov (United States)

    Maghsoodloo, Sh; Noroozi, B; Haghi, A K; Sorial, G A

    2011-07-15

    In this work, equilibrium and kinetic adsorption of humic acid (HA) onto chitosan treated granular activated carbon (MGAC) has been investigated and compared to the granular activated carbon (GAC). The adsorption equilibrium data showed that adsorption behaviour of HA could be described reasonably well by Langmuir adsorption isotherm for GAC and Freundlich adsorption isotherm for MGAC. It was shown that pre-adsorption of chitosan onto the surface of GAC improved the adsorption capacity of HA changing the predominant adsorption mechanism. Monolayer capacities for the adsorption of HA onto GAC and MGAC were calculated 55.8 mg/g and 71.4 mg/g, respectively. Kinetic studies showed that film diffusion and intra-particle diffusion were simultaneously operating during the adsorption process for MGAC. Copyright © 2011 Elsevier B.V. All rights reserved.

  18. Granular Gas in a Periodic Lattice

    Science.gov (United States)

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

    2011-01-01

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

  19. 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 ...

  20. 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

  1. 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.

  2. Random packing of colloids and granular matter

    NARCIS (Netherlands)

    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

  3. Deposition and shaking of dry granular piles

    NARCIS (Netherlands)

    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

  4. ENGINEERING BULLETIN: GRANULAR ACTIVATED CARBON TREATMENT

    Science.gov (United States)

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

  5. Velocity distributions in dilute granular systems

    NARCIS (Netherlands)

    van Zon, J.S.; Mac Kintosh, F.C.

    2005-01-01

    We investigate the idea that velocity distributions in granular gases are determined mainly by η, the coefficient of restitution and q, which measures the relative importance of heating (or energy input) to collisions. To this end, we study by numerical simulation the properties of inelastic gases

  6. 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.

  7. Nonlinear coherent structures in granular crystals

    Science.gov (United States)

    Chong, C.; Porter, Mason A.; Kevrekidis, P. G.; Daraio, C.

    2017-10-01

    The study of granular crystals, which are nonlinear metamaterials that consist of closely packed arrays of particles that interact elastically, is a vibrant area of research that combines ideas from disciplines such as materials science, nonlinear dynamics, and condensed-matter physics. Granular crystals exploit geometrical nonlinearities in their constitutive microstructure to produce properties (such as tunability and energy localization) that are not conventional to engineering materials and linear devices. In this topical review, we focus on recent experimental, computational, and theoretical results on nonlinear coherent structures in granular crystals. Such structures—which include traveling solitary waves, dispersive shock waves, and discrete breathers—have fascinating dynamics, including a diversity of both transient features and robust, long-lived patterns that emerge from broad classes of initial data. In our review, we primarily discuss phenomena in one-dimensional crystals, as most research to date has focused on such scenarios, but we also present some extensions to two-dimensional settings. Throughout the review, we highlight open problems and discuss a variety of potential engineering applications that arise from the rich dynamic response of granular crystals.

  8. The critical current of granular superconductor

    International Nuclear Information System (INIS)

    Ignat'ev, V.K.

    1998-01-01

    A mechanism of hyper vortex pinning in granular superconductors is proposed to describe the field dependence of the critical current density and pinning potential. The results are in a good agreement with the experiment. The model represents the peak effect and the percolation mechanism of conductivity in ceramic superconductors

  9. Magnetic susceptibility and specific heat of the one-dimensional conductor (H3O) sub (1,6) Pt (C2O4)2.nH2O at low temperatures

    International Nuclear Information System (INIS)

    Raede, H.S.

    1985-01-01

    It has been shown recently that some transition metal complexes exhibit one-dimensional metallic properties. It is reported, in this context, susceptibility and specific heat measurements of polycrystalline (H 3 O) 1 , 6 Pt(C 2 O 4 ) 2 .nH 2 O in the low temperature range. It is found that the susceptibility can be described by a non-uniform Curie law with a characteristic break in the slope. The specific heat reveals no linear temperature contribution, which could be explained by a transition into a Peierls distorted state. Until 13 0 K, the heat capacity follows a T 3 -law. Deviations at higher temperatures are possibly attributed to the anisotropy of the system [pt

  10. Highly coercive thin-film nanostructures

    International Nuclear Information System (INIS)

    Zhou, J.; Skomski, R.; Kashyap, A.; Sorge, K.D.; Sui, Y.; Daniil, M.; Gao, L.; Yan, M.L.; Liou, S.-H.; Kirby, R.D.; Sellmyer, D.J.

    2005-01-01

    The processing, structure, and magnetism of highly coercive Sm-Co and FePt thin-film nanostructures are investigated. The structures include 1:5 based Sm-Co-Cu-Ti magnets, particulate FePt:C thin films, and FePt nanotubes. As in other systems, the coercivity depends on texture and imperfections, but there are some additional features. A specific coercivity mechanism in particulate media is a discrete pinning mode intermediate between Stoner-Wohlfarth rotation and ordinary domain-wall pinning. This mechanism yields a coercivity maximum for intermediate intergranular exchange and explains the occurrence of coercivities of 5 T in particulate Sm-Co-Cu-Ti magnets

  11. 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.

  12. An automata model of granular materials

    International Nuclear Information System (INIS)

    Gutt, G.M.; Haff, P.K.

    1990-01-01

    In this paper a new modeling technique (the Lattice Grain Model) is presented for the simulation of two-dimensional granular systems involving large numbers of grains. These granular systems may include both high shear rate regions as well as static plugs of grains and cannot easily be handled within the framework of existing continuum theories such as soil mechanics. The Lattice Grain Model (LGrM) is similar to the Lattice Gas Model (LBM). This allows large simulations to be programmed onto a hypercube concurrent processor in a straightforward manner. However, it differs from LBM in that it includes the inelastic collisions and volume-filling properties of macroscopic grains. Examples to be presented will include Couette flow, flow through an hourglass, and gravity-driven flows around obstacles

  13. Submammary Granular Parakeratosis Treated With Mastopexy.

    Science.gov (United States)

    Nelson, Garrett; Lien, Mary H; Messina, Jane L; Ranjit, Sonali; Fenske, Neil Alan

    2017-08-01

    Granular parakeratosis, originally named axillary granular parakeratosis, is an uncommon disease with an unclear etiology. It is thought to result from defective processing of profillagrin to fillagrin, causing retention of keratohyaline granules in the epidermis. A myriad of causative factors has been proposed, including friction, moisture, heat, and contact irritants such as deodorants. We present a case in the inframammary area that resolved with mastopexy, further supporting the role of friction, moisture, and heat. Furthermore, we present electron microscopic evidence demonstrating non-degraded keratohyaline granules upon epidermal maturation. This entity, we believe, is reactive and represents a protective response of the body to moisture and heat. J Drugs Dermatol. 2017;16(8):810-812..

  14. 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.

  15. Memory effect in uniformly heated granular gases

    Science.gov (United States)

    Trizac, E.; Prados, A.

    2014-07-01

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

  16. Tumor of granular cells of esophagus

    International Nuclear Information System (INIS)

    Gonzalez Fabian, Licet; Diaz Anaya, Amnia; Perez de la Torre, Georgina

    2010-01-01

    Granular cells tumors are rare and asymptomatic lesions and by general, it is an incidental finding en high or low endoscopy. They were described for the first time by Abrikossoff in 1926. The more frequent locations are the buccal mucosa, dermis and subcutaneous cellular tissue, most of these tumors has a benign origin. This is the case of a woman aged 44 with a pyrosis history from a year ago; by high endoscopy it is noted a 8 mm lesion distal to esophagus and confirmed by histological study of granular cells tumor. Elective treatment of this lesion is the endoscopic polypectomy. Despite that the malign potential is low; we suggested a close clinical and endoscopic follow-up.

  17. Traffic and Granular Flow ’07

    CERN Document Server

    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.

  18. 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.

  19. Mathematics and Mechanics of Granular Materials

    CERN Document Server

    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.

  20. Slow creep in soft granular packings.

    Science.gov (United States)

    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.

  1. Fuzzy batch controller for granular materials

    OpenAIRE

    Zamyatin Nikolaj; Smirnov Gennadij; Fedorchuk Yuri; Rusina Olga

    2018-01-01

    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 infer...

  2. 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

  3. Seismic wave propagation in granular media

    Science.gov (United States)

    Tancredi, Gonzalo; López, Francisco; Gallot, Thomas; Ginares, Alejandro; Ortega, Henry; Sanchís, Johnny; Agriela, Adrián; Weatherley, Dion

    2016-10-01

    Asteroids and small bodies of the Solar System are thought to be agglomerates of irregular boulders, therefore cataloged as granular media. It is a consensus that many asteroids might be considered as rubble or gravel piles.Impacts on their surface could produce seismic waves which propagate in the interior of these bodies, thus causing modifications in the internal distribution of rocks and ejections of particles and dust, resulting in a cometary-type comma.We present experimental and numerical results on the study of propagation of impact-induced seismic waves in granular media, with special focus on behavior changes by increasing compression.For the experiment, we use an acrylic box filled with granular materials such as sand, gravel and glass spheres. Pressure inside the box is controlled by a movable side wall and measured with sensors. Impacts are created on the upper face of the box through a hole, ranging from free-falling spheres to gunshots. We put high-speed cameras outside the box to record the impact as well as piezoelectic sensors and accelerometers placed at several depths in the granular material to detect the seismic wave.Numerical simulations are performed with ESyS-Particle, a software that implements the Discrete Element Method. The experimental setting is reproduced in the numerical simulations using both individual spherical particles and agglomerates of spherical particles shaped as irregular boulders, according to rock models obtained with a 3D scanner. The numerical experiments also reproduces the force loading on one of the wall to vary the pressure inside the box.We are interested in the velocity, attenuation and energy transmission of the waves. These quantities are measured in the experiments and in the simulations. We study the dependance of these three parameters with characteristics like: impact speed, properties of the target material and the pressure in the media.These results are relevant to understand the outcomes of impacts in

  4. Simulation of 2D Granular Hopper Flow

    Science.gov (United States)

    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.

  5. Spatial correlations in compressible granular flows

    OpenAIRE

    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...

  6. Small solar system bodies as granular systems

    Science.gov (United States)

    Hestroffer, Daniel; Campo Bagatín, Adriano; Losert, Wolfgang; Opsomer, Eric; Sánchez, Paul; Scheeres, Daniel J.; Staron, Lydie; Taberlet, Nicolas; Yano, Hajime; Eggl, Siegfried; Lecomte, Charles-Edouard; Murdoch, Naomi; Radjai, Fahrang; Richardson, Derek C.; Salazar, Marcos; Schwartz, Stephen R.; Tanga, Paolo

    2017-06-01

    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.

  7. 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.

  8. Iodine Gas Trapping using Granular Porous Bismuth

    International Nuclear Information System (INIS)

    Yang, Jae Hwan; Shin, Jin Myeong; Park, Jang Jin; Park, Geun Il; Yim, Mansung

    2014-01-01

    129 I is a radionuclide with a very long half-life of 1.57 Χ 10 7 years and has negative health effects to the human body. Therefore, the emission of 129 I into the air is closely regulated by the Environmental Protection Agency (EPA). Many methods for trapping gaseous 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 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 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

  9. Propulsion via flexible flapping in granular media

    Science.gov (United States)

    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.

  10. 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.

  11. Settling properties of aerobic granular sludge (AGS) and aerobic granular sludge molasses (AGSM)

    Science.gov (United States)

    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.

  12. The role of fluid viscosity in an immersed granular collapse

    Science.gov (United States)

    Yang, Geng Chao; Kwok, Chung Yee; Sobral, Yuri Dumaresq

    2017-06-01

    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.

  13. 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.

  14. A hydrodynamic model for granular material flows including segregation effects

    Science.gov (United States)

    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.

  15. How granular vortices can help understanding rheological and mixing properties of dense granular flows

    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.

  16. Au-based/electrochemically etched cavity-microelectrodes as optimal tool for quantitative analyses on finely dispersed electrode materials: Pt/C, IrO2-SnO2 and Ag catalysts

    International Nuclear Information System (INIS)

    Minguzzi, Alessandro; Locatelli, Cristina; Lugaresi, Ottavio; Vertova, Alberto; Rondinini, Sandra

    2013-01-01

    In this work, we report the preparation and properties of Au-based cavity-microelectrodes. The use of gold as cavity current collector allows obtaining a regular cylindrical recess, whose volume is easily determined with good accuracy and precision. This in turn leads to an improved and much more reliable use of the cavity microelectrode (C-ME) as a tool for the quantitative characterization of finely dispersed materials and for their quantitative rapid screening. The features of Au/C-MEs are well demonstrated by the good linear correlation between the cavity volume (determined by electrochemical methods) and the quantity of charge related to the amount of electroactive powder inserted into the cavity. To prove this point, we adopted two different test systems: Pt/C and an IrO 2 -based material. Finally, we proved the adequacy of Au/C-MEs in the case of Ag particles as electrocatalysts for the hydrodehalogenation of trichloromethane. In this last part, C-ME interestingly appears as a flexible and versatile tool that presents peculiar features: the voltammetric signal can be controlled by either the electron transfer or by mass transport and can be associated to the outer surface or to the whole amount of material inserted into the cavity. This means that C-MEs can be used either as a microdisk of a desired material (that is very useful, especially in scanning electrochemical microscopy) or for precise quantitative studies of the material inserted inside it

  17. Sensors for the CMS High Granularity Calorimeter

    CERN Document Server

    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.

  18. 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.

  19. 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.

  20. 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.)

  1. 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.

  2. 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.

  3. Shock propagation in locally driven granular systems

    Science.gov (United States)

    Joy, Jilmy P.; Pathak, Sudhir N.; Das, Dibyendu; Rajesh, R.

    2017-09-01

    We study shock propagation in a system of initially stationary hard spheres that is driven by a continuous injection of particles at the origin. The disturbance created by the injection of energy spreads radially outward through collisions between particles. Using scaling arguments, we determine the exponent characterizing the power-law growth of this disturbance in all dimensions. The scaling functions describing the various physical quantities are determined using large-scale event-driven simulations in two and three dimensions for both elastic and inelastic systems. The results are shown to describe well the data from two different experiments on granular systems that are similarly driven.

  4. On the velocity distributions of granular gases

    International Nuclear Information System (INIS)

    Polito, A.M.M.; Rocha Filho, T.M.; Figueiredo, A.

    2009-01-01

    We present a new approach to determine velocity distributions in granular gases to improve the Sonine polynomial expansion of the velocity distribution function, at higher inelasticities, for the homogeneous cooling regime of inelastic hard spheres. The perturbative consistency is recovered using a new set of dynamical variables based on the characteristic function and we illustrate our approach by computing the first four Sonine coefficients for moderate and high inelasticities. The analytical coefficients are compared with molecular dynamics simulations results and with a previous approach by Huthmann et al.

  5. 2D ultrathin core-shell Pd@Ptmonolayer nanosheets: defect-mediated thin film growth and enhanced oxygen reduction performance

    Science.gov (United States)

    Wang, Wenxin; Zhao, Yunfeng; Ding, Yi

    2015-07-01

    An operational strategy for the synthesis of atomically smooth Pt skin by a defect-mediated thin film growth method is reported. Extended ultrathin core-shell structured d@Ptmonolayer nanosheets (thickness below 5 nm) exhibit nearly seven-fold enhancement in mass-activity and surprisingly good durability toward oxygen reduction reaction as compared with the commercial Pt/C catalyst.An operational strategy for the synthesis of atomically smooth Pt skin by a defect-mediated thin film growth method is reported. Extended ultrathin core-shell structured d@Ptmonolayer nanosheets (thickness below 5 nm) exhibit nearly seven-fold enhancement in mass-activity and surprisingly good durability toward oxygen reduction reaction as compared with the commercial Pt/C catalyst. Electronic supplementary information (ESI) available: Sample preparation, physical and electrochemical characterization, Fig. S1 to S11. See DOI: 10.1039/c5nr02748a

  6. Interfacial magnetic coupling between Fe nanoparticles in Fe–Ag granular alloys

    International Nuclear Information System (INIS)

    Alonso, J; Fdez-Gubieda, M L; Sarmiento, G; Chaboy, J; Boada, R; García Prieto, A; Haskel, D; Laguna-Marco, M A; Lang, J C; Meneghini, C; Fernández Barquín, L; Neisius, T; Orue, I

    2012-01-01

    The role of the interface in mediating interparticle magnetic interactions has been analysed in Fe 50 Ag 50 and Fe 55 Ag 45 granular thin films deposited by the pulsed laser deposition technique (PLD). These samples are composed of crystalline bcc Fe (2–4 nm) nanoparticles and fcc Ag (10–12 nm) nanoparticles, separated by an amorphous Fe 50 Ag 50 interface, occupying around 20% of the sample volume, as determined by x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), and high resolution transmission electron microscopy (HRTEM). Interfacial magnetic coupling between Fe nanoparticles is studied by dc magnetization and x-ray magnetic circular dichroism (XMCD) measurements at the Fe K and Ag L 2,3 edges. This paper reveals that these thin films present two magnetic transitions, at low and high temperatures, which are strongly related to the magnetic state of the amorphous interface, which acts as a barrier for interparticle magnetic coupling.

  7. Granular motor in the non-Brownian limit

    NARCIS (Netherlands)

    Oyarte Galvez, Loreto Alejandra; van der Meer, Roger M.

    2016-01-01

    In this work we experimentally study a granular rotor which is similar to the famous Smoluchowski–Feynman device and which consists of a rotor with four vanes immersed in a granular gas. Each side of the vanes can be composed of two different materials, creating a rotational asymmetry and turning

  8. Nonlinear instability and convection in a vertically vibrated granular bed

    NARCIS (Netherlands)

    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

  9. Granular Leidenfrost effect: Experiment and theory of floating particle clusters

    NARCIS (Netherlands)

    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

  10. USE OF GRANULAR GRAPHITE FOR ELECTROLYTIC DECHLORINATION OF TRICHLOROETHYLENE

    Science.gov (United States)

    Granular graphite is a potential electrode material for the electrochemical remediation of refractory chlorinated organic compounds such as trichloroethylene (TCE). However, the use of granular graphite can complicate the experimental results. On one hand, up to 99% of TCE was re...

  11. Surface effects in the acetylation of granular potato starch

    NARCIS (Netherlands)

    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

  12. Long-range interactions in dilute granular systems

    NARCIS (Netherlands)

    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

  13. 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.

  14. Large mid-esophageal granular cell tumor: benign versus malignant

    Directory of Open Access Journals (Sweden)

    Prarthana Roselil Christopher

    2015-06-01

    Full Text Available Granular cell tumors are rare soft tissue neoplasms, among which only 2% are malignant, arising from nervous tissue. Here we present a case of a large esophageal granular cell tumor with benign histopathological features which metastasized to the liver, but showing on positron emission tomography-computerized tomography standardized uptake value suggestive of a benign lesion.

  15. Adsorption Study of Cobalt on Treated Granular Activated Carbon

    OpenAIRE

    Y. V. Hete; S. B. Gholase; R. U. Khope

    2012-01-01

    This study is carried out for the removal of cobalt from aqueous solution using granular activated carbon in combination with p-nitro benzoic acid at temperature 25±1 °C. The adsorption isotherm of cobalt on granular activated carbon has been determined and the data fitted reasonably well to the Langmuir and Freundlich isotherm for activated carbon.

  16. Adsorption Study of Cobalt on Treated Granular Activated Carbon

    Directory of Open Access Journals (Sweden)

    Y. V. Hete

    2012-01-01

    Full Text Available This study is carried out for the removal of cobalt from aqueous solution using granular activated carbon in combination with p-nitro benzoic acid at temperature 25±1 °C. The adsorption isotherm of cobalt on granular activated carbon has been determined and the data fitted reasonably well to the Langmuir and Freundlich isotherm for activated carbon.

  17. Density-Driven segregation in Binary and Ternary Granular Systems

    NARCIS (Netherlands)

    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

  18. Anomalous Hall effect in polycrystalline Ni films

    KAUST Repository

    Guo, Zaibing

    2012-02-01

    We systematically studied the anomalous Hall effect in a series of polycrystalline Ni films with thickness ranging from 4 to 200 nm. It is found that both the longitudinal and anomalous Hall resistivity increased greatly as film thickness decreased. This enhancement should be related to the surface scattering. In the ultrathin films (46 nm thick), weak localization corrections to anomalous Hall conductivity were studied. The granular model, taking into account the dominated intergranular tunneling, has been employed to explain this phenomenon, which can explain the weak dependence of anomalous Hall resistivity on longitudinal resistivity as well. © 2011 Elsevier Ltd. All rights reserved.

  19. Critical phenomenon of granular flow on a conveyor belt.

    Science.gov (United States)

    De-Song, Bao; Xun-Sheng, Zhang; Guang-Lei, Xu; Zheng-Quan, Pan; Xiao-Wei, Tang; Kun-Quan, Lu

    2003-06-01

    The relationship between the granular wafer movement on a two-dimensional conveyor belt and the size of the exit together with the velocity of the conveyor belt has been studied in the experiment. The result shows that there is a critical speed v(c) for the granular flow when the exit width d is fixed (where d=R/D, D being the diameter of a granular wafers). When vv(c), the flow rate Q is described as Q=Crho(v)(beta)(d-k)(3/2). These are the effects of the interaction among the granular wafers and the change of the states of the granular flow due to the changing of the speed or the exit width d.

  20. Lizard locomotion in heterogeneous granular media

    Science.gov (United States)

    Schiebel, Perrin; Goldman, Daniel

    2014-03-01

    Locomotion strategies in heterogeneous granular environments (common substrates in deserts), are relatively unexplored. The zebra-tailed lizard (C. draconoides) is a useful model organism for such studies owing to its exceptional ability to navigate a variety of desert habitats at impressive speed (up to 50 body-lengths per second) using both quadrapedal and bidepal gaits. In laboratory experiments, we challenge the lizards to run across a field of boulders (2.54 cm diameter glass spheres or 3.8 cm 3D printed spheres) placed in a lattice pattern and embedded in a loosely packed granular medium of 0.3 mm diameter glass particles. Locomotion kinematics of the lizard are recorded using high speed cameras, with and without the scatterers. The data reveals that unlike the lizard's typical quadrupedal locomotion using a diagonal gait, when scatterers are present the lizard is most successful when using a bipedal gait, with a raised center of mass (CoM). We propose that the kinematics of bipedal running in conjunction with the lizard's long toes and compliant hind foot are the keys to this lizard's successful locomotion in the presence of such obstacles. NSF PoLS

  1. Wrinkles, folds, and plasticity in granular rafts

    Science.gov (United States)

    Jambon-Puillet, Etienne; Josserand, Christophe; Protière, Suzie

    2017-09-01

    We investigate the mechanical response of a compressed monolayer of large and dense particles at a liquid-fluid interface: a granular raft. Upon compression, rafts first wrinkle; then, as the confinement increases, the deformation localizes in a unique fold. This characteristic buckling pattern is usually associated with floating elastic sheets, and as a result, particle laden interfaces are often modeled as such. Here, we push this analogy to its limits by comparing quantitative measurements of the raft morphology to a theoretical continuous elastic model of the interface. We show that, although powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition, and the fold shape, this elastic description does not capture the finer details of the experiment. We describe an unpredicted secondary wavelength, a compression discrepancy with the model, and a hysteretic behavior during compression cycles, all of which are a signature of the intrinsic discrete and frictional nature of granular rafts. It suggests also that these composite materials exhibit both plastic transition and jamming dynamics.

  2. Large granular lymphocytic leukaemia pathogenesis and management.

    Science.gov (United States)

    Dearden, Claire

    2011-02-01

    The WHO classification recognises three distinct disorders of large granular lymphocytes: T-cell large granular lymphocytic leukaemia (T-LGL), chronic lymphoproliferative disorders of NK-cells (CLPD-NK) and agressive NK-cell leukaemia. Despite the different cell of origin, there is considerable overlap between T-LGL and CLPD-NK in terms of clinical presentation and therapy. Many patients are asymptomatic and do not require treatment. Therapy, with immunosuppressant agents such as low dose methotrexate or ciclosporin, is usually indicated to correct cytopenias. In contrast, aggressive NK-cell leukaemia and the rare CD56(+) aggressive T-LGL leukaemia follow a fulminant clinical course, affect younger individuals and require more intensive combination chemotherapy followed by allogeneic stem cell transplant in eligible patients. The relative rarity of these disorders means that there have been few clinical trials to inform management. However, there is now considerable interest in the pathogenesis of the chronic LGL leukaemias and this has stimulated early trials to evaluate novel agents which target the dysregulated apoptotic pathways characteristic of this disease. © 2010 Blackwell Publishing Ltd.

  3. Characterizing granular networks using topological metrics

    Science.gov (United States)

    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.

  4. Collisional model for granular impact dynamics.

    Science.gov (United States)

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

    2014-01-01

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

  5. Controlling wave propagation through nonlinear engineered granular systems

    Science.gov (United States)

    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

  6. 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.

  7. Consideration of reinforcement mechanism in the short fiber mixing granular materials by granular element simulations

    Science.gov (United States)

    Mori, Kentaro; Kaneko, Kenji; Hashizume, Yutaka

    2017-06-01

    The short fiber mixing method is well known as one of the method to improve the strength of gran- ular soils in geotechnical engineering. Mechanical properties of the short fiber mixing granular materials are influenced by many factors, such as the mixture ratio of the short fiber, the material of short fiber, the length, and the orientation. In particular, the mixture ratio of the short fibers is very important in mixture design. In the past study, we understood that the strength is reduced by too much short fiber mixing by a series of tri-axial compression experiments. Namely, there is "optimum mixture ratio" in the short fiber mixing granular soils. In this study, to consider the mechanism of occurrence of the optimum mixture ratio, we carried out the numerical experiments by granular element method. As the results, we can understand that the strength decrease when too much grain-fiber contact points exist, because a friction coefficient is smaller than the grain-grain contact points.

  8. Information granularity, big data, and computational intelligence

    CERN Document Server

    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...

  9. Multiple impacts in dissipative granular chains

    CERN Document Server

    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 (...

  10. 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.

  11. Capturing gas in soft granular media

    Science.gov (United States)

    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.

  12. Defining and testing a granular continuum element

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris H.; Kamrin, Ken; Bazant, Martin Z.

    2007-12-03

    Continuum mechanics relies on the fundamental notion of amesoscopic volume "element" in which properties averaged over discreteparticles obey deterministic relationships. Recent work on granularmaterials suggests a continuum law may be inapplicable, revealinginhomogeneities at the particle level, such as force chains and slow cagebreaking. Here, we analyze large-scale Discrete-Element Method (DEM)simulations of different granular flows and show that a "granularelement" can indeed be defined at the scale of dynamical correlations,roughly three to five particle diameters. Its rheology is rather subtle,combining liquid-like dependence on deformation rate and solid-likedependence on strain. Our results confirm some aspects of classicalplasticity theory (e.g., coaxiality of stress and deformation rate),while contradicting others (i.e., incipient yield), and can guide thedevelopment of more realistic continuum models.

  13. Particle filtration in consolidated granular systems

    International Nuclear Information System (INIS)

    Schwartz, L.M.; Wilkinson, D.J.; Bolsterli, M.; Hammond, P.

    1993-01-01

    Grain-packing algorithms are used to model the mechanical trapping of dilute suspensions of particles by consolidated granular media. We study the distribution of filtrate particles, the formation of a damage zone (internal filter cake), and the transport properties of the host--filter-cake composite. At the early stages of filtration, our simulations suggest simple relationships between the structure of the internal filter cake and the characteristics of the underlying host matrix. These relationships are then used to describe the dynamics of the filtration process. Depending on the grain size and porosity of the host matrix, calculated filtration rates may either be greater than (spurt loss) or less than (due to internal clogging) those predicted by standard surface-filtration models

  14. Granular neural networks, pattern recognition and bioinformatics

    CERN Document Server

    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...

  15. Transient response in granular bounded heap flows

    Science.gov (United States)

    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.

  16. 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)

  17. Solitary Wave Interactions in Granular Media

    Institute of Scientific and Technical Information of China (English)

    WEN Zhen-Ying; WANG Shun-Jin; ZHANG Xiu-Ming; LI Lei

    2007-01-01

    We numerically study the interactions of solitary waves in granular media, by considering a chain of beads, which repel upon contact via the Hertz-type potential, V ∝δn, with 5/2 ≤n≤3 and δ≥0,δbeing the bead-bead overlap. There are two collision types of solitary waves, overtaking collision and head-on collision, in the chain of beads. Our quantitative results show that after collision the large solitary wave gains energy and the small one loses energy for overtaking type while the large one loses energy, and the small one gains energy for head-on type. The scattering effects decrease with n for overtaking collision whereas increase with n for head-on collision.

  18. Two methods to measure granular gas temperature

    Science.gov (United States)

    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.

  19. Thermal energy storage in granular deposits

    Science.gov (United States)

    Ratuszny, Paweł

    2017-10-01

    Energy storage technology is crucial for the development of the use of renewable energy sources. This is a substantial constraint, however it can, to some extent, be solved by storing energy in its various forms: electrical, mechanical, chemical and thermal. This article presents the results of research in thermal properties of granular deposits. Correlation between temperature changes in the stores over a period of time and their physical properties has been studied. The results of the research have practical application in designing thermal stores based on bulk materials and ground deposits. Furthermore, the research results are significant for regeneration of the lower ground sources for heat pumps and provide data for designing ground heat exchangers for ventilation systems.

  20. 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.

  1. 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.

  2. NMRI Measurements of Flow of Granular Mixtures

    Science.gov (United States)

    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.

  3. Pneumatic fractures in Confined Granular Media

    Science.gov (United States)

    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

  4. Unjamming a granular hopper by vibration

    Science.gov (United States)

    Janda, A.; Maza, D.; Garcimartín, A.; Kolb, E.; Lanuza, J.; Clément, E.

    2009-07-01

    We present an experimental study of the outflow of a hopper continuously vibrated by a piezoelectric device. Outpouring of grains can be achieved for apertures much below the usual jamming limit observed for non-vibrated hoppers. Granular flow persists down to the physical limit of one grain diameter, a limit reached for a finite vibration amplitude. For the smaller orifices, we observe an intermittent regime characterized by alternated periods of flow and blockage. Vibrations do not significantly modify the flow rates both in the continuous and the intermittent regime. The analysis of the statistical features of the flowing regime shows that the flow time significantly increases with the vibration amplitude. However, at low vibration amplitude and small orifice sizes, the jamming time distribution displays an anomalous statistics.

  5. Viscoinertial regime of immersed granular flows

    Science.gov (United States)

    Amarsid, L.; Delenne, J.-Y.; Mutabaruka, P.; Monerie, Y.; Perales, F.; Radjai, F.

    2017-07-01

    By means of extensive coupled molecular dynamics-lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.

  6. Hyperstaticity and loops in frictional granular packings

    Science.gov (United States)

    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.

  7. Steady state of tapped granular polygons

    International Nuclear Information System (INIS)

    Carlevaro, Carlos M; Pugnaloni, Luis A

    2011-01-01

    The steady state packing fraction of a tapped granular bed is studied for different grain shapes via a discrete element method. Grains are monosized regular polygons, from triangles to icosagons. Comparisons with disc packings show that the steady state packing fraction as a function of the tapping intensity presents the same general trends in polygon packings. However, better packing fractions are obtained, as expected, for shapes that can tessellate the plane (triangles, squares and hexagons). In addition, we find a sharp transition for packings of polygons with more than 13 vertices signaled by a discontinuity in the packing fraction at a particular tapping intensity. Density fluctuations for most shapes are consistent with recent experimental findings in disc packing; however, a peculiar behavior is found for triangles and squares

  8. Experimental observations of granular debris flows

    Science.gov (United States)

    Ghilardi, P.

    2003-04-01

    Various tests are run using two different laboratory flumes with rectangular cross section and transparent walls. The grains used in a single experiment have an almost constant grain sizes; mean diameter ranges from 5 mm to 20 mm. In each test various measurements are taken: hydrograms, velocity distribution near the transparent walls and on the free surface, average flow concentration. Concentration values are measured taking samples. Velocity distributions are obtained from movies recorded by high speed video cameras capable of 350 frames per second; flow rates and depth hydrograms are computed from the same velocity distributions. A gate is installed at the beginning of one of the flumes; this gate slides normally to the bed and opens very quickly, reproducing a dam-break. Several tests are run using this device, varying channel slope, sediment concentration, initial mixture thickness before the gate. Velocity distribution in the flume is almost constant from left to right, except for the flow sections near the front. The observed discharges and velocities are less than those given by a classic dam break formula, and depend on sediment concentration. The other flume is fed by a mixture with constant discharge and concentration, and is mainly used for measuring velocity distributions when the flow is uniform, with both rigid and granular bed, and to study erosion/deposition processes near debris flow dams or other mitigation devices. The equilibrium slope of the granular bed is very close to that given by the classical equilibrium formulas for debris flow. Different deposition processes are observed depending on mixture concentration and channel geometry.

  9. 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

  10. An automatic granular structure generation and finite element analysis of heterogeneous semi-solid materials

    International Nuclear Information System (INIS)

    Sharifi, Hamid; Larouche, Daniel

    2015-01-01

    The quality of cast metal products depends on the capacity of the semi-solid metal to sustain the stresses generated during the casting. Predicting the evolution of these stresses with accuracy in the solidification interval should be highly helpful to avoid the formation of defects like hot tearing. This task is however very difficult because of the heterogeneous nature of the material. In this paper, we propose to evaluate the mechanical behaviour of a metal during solidification using a mesh generation technique of the heterogeneous semi-solid material for a finite element analysis at the microscopic level. This task is done on a two-dimensional (2D) domain in which the granular structure of the solid phase is generated surrounded by an intergranular and interdendritc liquid phase. Some basic solid grains are first constructed and projected in the 2D domain with random orientations and scale factors. Depending on their orientation, the basic grains are combined to produce larger grains or separated by a liquid film. Different basic grain shapes can produce different granular structures of the mushy zone. As a result, using this automatic grain generation procedure, we can investigate the effect of grain shapes and sizes on the thermo-mechanical behaviour of the semi-solid material. The granular models are automatically converted to the finite element meshes. The solid grains and the liquid phase are meshed properly using quadrilateral elements. This method has been used to simulate the microstructure of a binary aluminium–copper alloy (Al–5.8 wt% Cu) when the fraction solid is 0.92. Using the finite element method and the Mie–Grüneisen equation of state for the liquid phase, the transient mechanical behaviour of the mushy zone under tensile loading has been investigated. The stress distribution and the bridges, which are formed during the tensile loading, have been detected. (paper)

  11. Development of granular powder manufacturing technology by spray pyrolysis

    International Nuclear Information System (INIS)

    Katoh, Yoshiyuki; Kawase, Keiichi; Takahashi, Yoshiharu; Todokoro, Akio

    1996-01-01

    For shortening of mixed-oxide (MOX) fuel manufacturing process and improvement in treatment of MOX-powder, we have been developing the granular powder production technology. Since the granular powders have excellent fluidity owing to the spherical shape, there is the possibility of modifying scattering and adcering of the powder in the process equipment. In this paper, spray pyrolysis process in adopted as the process of manufacturing the granular powders and the basic feasibility study has been carried out. The experimental results show that the manufactured granular powders have excellent fluidity and the diameter of the powders is controllable. Furthermore, high density pellets are formed by sintering the powders. Thus, it is clarified that this process is promising for the actual MOX fuel fabrication. (author)

  12. A particle-based method for granular flow simulation

    KAUST Repository

    Chang, Yuanzhang; Bao, Kai; Zhu, Jian; Wu, Enhua

    2012-01-01

    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.

  13. Investigation of granular impact using positron emission particle tracking

    KAUST Repository

    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.

  14. 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.

  15. 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.

  16. Micro origins for macro behavior in granular media

    NARCIS (Netherlands)

    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

  17. REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON

    Science.gov (United States)

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

  18. The Regeneration of Granular Activated Carbon Using Hydrothermal Technology

    National Research Council Canada - National Science Library

    Sufnarski, Michael

    1999-01-01

    The economic feasibility of using granular activated carbon (GAC) to remove organic contaminants from industrial and municipal wastewater is contingent upon its reuse during multiple adsorption-regeneration cycles (Van Vliet, 1991...

  19. GRANULAR ACTIVATED CARBON ADSORPTION AND INFRARED REACTIVATION: A CASE STUDY

    Science.gov (United States)

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

  20. Wave propagation of spectral energy content in a granular chain

    NARCIS (Netherlands)

    Shrivastava, Rohit Kumar; Luding, Stefan

    2017-01-01

    A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like

  1. Mechanical Behavior of Granular/Particulate Media Reinforced with Fibers

    National Research Council Canada - National Science Library

    Michalowski, Radoslw

    1999-01-01

    ... out. This investigation was built on the results of a previous study. Fiber-reinforced granular material was considered as a composite, and a mathematical homogenization scheme was used to arrive at its macroscopic properties...

  2. Jetting and flooding of granular backfill materials : [summary].

    Science.gov (United States)

    2015-03-01

    Granular backfill materials on highway projects are often compacted by mechanical methods. : This requires the contractor to place backfill material into loose lifts of varying thickness : and use compaction equipment to reduce air voids and increase...

  3. 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.

  4. Tuning strain of granular matter by basal assisted Couette shear

    Directory of Open Access Journals (Sweden)

    Zhao Yiqiu

    2017-01-01

    Full Text Available We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes.

  5. Similitude study of a moving bed granular filter

    Energy Technology Data Exchange (ETDEWEB)

    Robert C. Brown; Huawei Shi; Gerald Colver; Saw-Choon Soo [Iowa State University, IA (United States)

    2003-12-10

    The goal of this study was to evaluate the performance of a moving bed granular filter designed for hot gas clean up. This study used similitude theory to devise experiments that were conducted at near-ambient conditions while simulating the performance of filters operated at elevated temperatures and pressures (850{sup o}C and 1000 kPa). These experiments revealed that the proposed moving bed granular filter can operate at high collection efficiencies, typically exceeding 99%, and low pressure drops without the need for periodic regeneration through the use of a continuous flow of fresh granular filter media in the filter. In addition, important design constraints were discovered for the successful operation of the proposed moving bed granular filter.

  6. A particle-based method for granular flow simulation

    KAUST Repository

    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.

  7. Factors influencing the density of aerobic granular sludge.

    NARCIS (Netherlands)

    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

  8. Resilient Modulus Characterization of Alaskan Granular Base Materials

    Science.gov (United States)

    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...

  9. Film Reviews.

    Science.gov (United States)

    Lance, Larry M.; Atwater, Lynn

    1987-01-01

    Reviews four Human Sexuality films and videos. These are: "Personal Decisions" (Planned Parenthood Federation of America, 1985); "The Touch Film" (Sterling Production, 1986); "Rethinking Rape" (Film Distribution Center, 1985); "Not A Love Story" (National Film Board of Canada, 1981). (AEM)

  10. Granular flow through an aperture: influence of the packing fraction

    OpenAIRE

    Alejandra Aguirre , Maria; De Schant , Rosario; Géminard , Jean-Christophe

    2014-01-01

    For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g. silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains a...

  11. 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

  12. Effective elasticity coefficients of native rocks and consolidated granular matter

    International Nuclear Information System (INIS)

    Schulz, Beatrix M.; Schulz, Michael

    2008-01-01

    The elastic coefficients of binary heterogeneous materials, such as several native rock materials or consolidated granular matter will be determined in terms of a perturbation expansion. Furthermore, in order to check the validity of the obtained results, these are compared with numerical investigations using Boole's model of randomly distributed spheres. Finally, we apply the results on several classes of native rocks and consolidated granular materials

  13. Granular cell tumor of the esophagus. Report of three cases.

    Science.gov (United States)

    Cohle, S D; McKechnie, J C; Truong, L; Jurco, S

    1981-06-01

    Granular cell tumors, (formerly called myoblastomas) involving the esophagus were encountered in three patients. In all three the tumors were asymptomatic and in two they were multiple. The first published endoscopic photographs of such a tumor are presented. The successful total removal of this neoplasm using the endoscope is described. The pathologic, radiologic and therapeutic aspects of previously reported cases of granular cell tumor of the esophagus are reviewed and compared with the three reported herein.

  14. Editorial: Modelling and computational challenges in granular materials

    OpenAIRE

    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...

  15. Self-assembly and speed distributions of active granular particles

    Science.gov (United States)

    Sánchez, R.; Díaz-Leyva, P.

    2018-06-01

    The relationship between the dynamics of self-propelled systems and the self-assembly of structured clusters are studied via the experimental speed distributions of submonolayers of self-propelled granular particles. A distribution developed for non-self-propelled granular particles describes the speed distributions remarkably well, despite some of the assumptions behind its original derivation not being applicable. This is explained in terms of clustering and dissipation being the key phenomena governing this regime.

  16. Experimental investigation of granular dynamics close to the jamming transition

    Science.gov (United States)

    Caballero, G.; Kolb, E.; Lindner, A.; Lanuza, J.; Clément, E.

    2005-06-01

    We present different experiments on dense granular assemblies with the aim of clarifying the notion of 'jamming transition' for these assemblies of non-Brownian particles. The experimental set-ups differ in the way in which external perturbations are applied in order to unjam the systems. The first experiment monitors the response to a locally applied deformation of a model packing at rest. The two other experiments study local and collective dynamics in a granular assembly weakly excited by vibration.

  17. Experimental study of energy exchanges between two coupled granular gases

    OpenAIRE

    Chastaing , J.-Y; Géminard , J.-C; Naert , A

    2016-01-01

    International audience; We report on the energy exchanges between two granular gases of different densities coupled electrome-chanically by immersed blades attached to dc motors. Zeroing the energy flux between the two subsystems, we demonstrate that an immersed blade is a convenient way to assess the properties of the granular gases, provided that the dissipation in the motor is properly taken into account. In addition, when the two gases have different densities, the fluctuations of the ene...

  18. A numerical study of granular dam-break flow

    Science.gov (United States)

    Pophet, N.; Rébillout, L.; Ozeren, Y.; Altinakar, M.

    2017-12-01

    Accurate prediction of granular flow behavior is essential to optimize mitigation measures for hazardous natural granular flows such as landslides, debris flows and tailings-dam break flows. So far, most successful models for these types of flows focus on either pure granular flows or flows of saturated grain-fluid mixtures by employing a constant friction model or more complex rheological models. These saturated models often produce non-physical result when they are applied to simulate flows of partially saturated mixtures. Therefore, more advanced models are needed. A numerical model was developed for granular flow employing a constant friction and μ(I) rheology (Jop et al., J. Fluid Mech. 2005) coupled with a groundwater flow model for seepage flow. The granular flow is simulated by solving a mixture model using Finite Volume Method (FVM). The Volume-of-Fluid (VOF) technique is used to capture the free surface motion. The constant friction and μ(I) rheological models are incorporated in the mixture model. The seepage flow is modeled by solving Richards equation. A framework is developed to couple these two solvers in OpenFOAM. The model was validated and tested by reproducing laboratory experiments of partially and fully channelized dam-break flows of dry and initially saturated granular material. To obtain appropriate parameters for rheological models, a series of simulations with different sets of rheological parameters is performed. The simulation results obtained from constant friction and μ(I) rheological models are compared with laboratory experiments for granular free surface interface, front position and velocity field during the flows. The numerical predictions indicate that the proposed model is promising in predicting dynamics of the flow and deposition process. The proposed model may provide more reliable insight than the previous assumed saturated mixture model, when saturated and partially saturated portions of granular mixture co-exist.

  19. Y1Ba2Cu3O(7-delta) thin film dc SQUIDs (superconducting quantum interference device)

    Science.gov (United States)

    Racah, Daniel

    1991-03-01

    Direct current superconducting quantum interferometers (SQUIDs) based on HTSC thin films have been measured and characterized. The thin films used were of different quality: (1) Granular films on Sapphire substrates, prepared either by e-gun evaporation, by laser ablation or by MOCVD (metal oxide chemical vapor deposition), (2) Epitaxial films on MgO substrates. Modulations of the voltage on the SQUIDs as a function of the applied flux have been observed in a wide range of temperatures. The nature of the modulation was found to be strongly dependent on the morphology of the film and on its critical current. The SQUIDs based on granular films were relatively noisy, hysteretic and with a complicated V-phi shape. Those devices based on low quality (lowIc) granular films could be measured only at low temperatures (much lower than 77 K). While those of higher quality (granular films with high Ic) could be measured near to the superconductive transition. The SQUID based on high quality epitaxial film was measured near Tc and showed an anomalous, time dependent behavior.

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

    Science.gov (United States)

    Kruelle, Christof A.; Sánchez, Almudena García

    2013-06-01

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

  1. Survivable integrated grooming in multi-granularity optical networks

    Science.gov (United States)

    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.

  2. Structure and giant magnetoresistance of carbon-based amorphous films prepared by magnetron sputtering

    International Nuclear Information System (INIS)

    Ma, L.; He, M.F.; Liu, Z.W.; Zeng, D.C.; Gu, Z.F.; Cheng, G.

    2014-01-01

    Pure amorphous carbon (a-C) and Co-doped Co x C 1−x films were prepared on n-Si(100) substrates by dc magnetron sputtering. In Co–C films, the nano-sized amorphous Co particles were homogeneously dispersed in the amorphous cross-linked carbon matrix. The structures of a-C and Co x C 1−x films were investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the a-C films were diamond-like carbon (DLC) films. After doping cobalt into DLC film, the sp 3 -hybridized carbon content in DLC composite films almost had no change. The as-deposited Co x C 1−x granular films had larger value of magnetoresistance (MR) than the amorphous carbon film. A very high positive MR, up to 15.5% at magnetic field B = 0.8 T and x = 2.5 at.% was observed in a Co x C 1−x granular film with thickness of 80 nm at room temperature when the external magnetic field was perpendicular to the electric current and the film surface. With increase of the film thickness and Co-doped content, the MR decreased gradually. It remains a challenge to well explain the observed MR effect in the Co x C 1−x granular films. - Highlights: • The amorphous carbon films were diamond-like carbon films. • No carbide appearing, the Co–C composite films form a good metal/insulator system. • A high positive magnetoresistance, up to 15.5% at B = 0.8 T was observed in Co–C films

  3. Pneumatic fractures in confined granular media.

    Science.gov (United States)

    Eriksen, Fredrik K; Toussaint, Renaud; Turquet, Antoine L; Måløy, Knut J; Flekkøy, Eirik G

    2017-06-01

    We perform experiments where air is injected at a constant overpressure P_{in}, ranging from 5 to 250 kPa, into a dry granular medium confined within a horizontal linear Hele-Shaw cell. The setup allows us to explore compacted configurations by preventing decompaction at the outer boundary, i.e., the cell outlet has a semipermeable filter such that beads are stopped while air can pass. We study the emerging patterns and dynamic growth of channels in the granular media due to fluid flow, by analyzing images captured with a high speed camera (1000 images/s). We identify four qualitatively different flow regimes, depending on the imposed overpressure, ranging from no channel formation for P_{in} below 10 kPa, to large thick channels formed by erosion and fingers merging for high P_{in} around 200 kPa. The flow regimes where channels form are characterized by typical finger thickness, final depth into the medium, and growth dynamics. The shape of the finger tips during growth is studied by looking at the finger width w as function of distance d from the tip. The tip profile is found to follow w(d)∝d^{β}, where β=0.68 is a typical value for all experiments, also over time. This indicates a singularity in the curvature d^{2}d/dw^{2}∼κ∼d^{1-2β}, but not of the slope dw/dd∼d^{β-1}, i.e., more rounded tips rather than pointy cusps, as they would be for the case β>1. For increasing P_{in}, the channels generally grow faster and deeper into the medium. We show that the channel length along the flow direction has a linear growth with time initially, followed by a power-law decay of growth velocity with time as the channel approaches its final length. A closer look reveals that the initial growth velocity v_{0} is found to scale with injection pressure as v_{0}∝P_{in}^{3/2}, while at a critical time t_{c} there is a cross-over to the behavior v(t)∝t^{-α}, where α is close to 2.5 for all experiments. Finally, we explore the fractal dimension of the fully

  4. Hadron showers in a highly granular calorimeter

    Energy Technology Data Exchange (ETDEWEB)

    Lutz, Benjamin

    2010-11-15

    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

  5. 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

  6. Friction law and hysteresis in granular materials

    Science.gov (United States)

    DeGiuli, E.; Wyart, M.

    2017-08-01

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, μ(I), is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent θs. We build a microscopic theory for the nonmonotonicity of μ(I), which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts χ, and the sliding velocity, in terms of θs. Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions.

  7. The ATLAS High-Granularity Timing Detector

    CERN Document Server

    Sacerdoti, Sabrina; The ATLAS collaboration

    2018-01-01

    In the high luminosity phase of the LHC, scheduled to start in 2026, the instantaneous luminosity will be increased to up to $\\mathcal{L} = 7.5 × 10^{34} cm^{−2}s^{−1}$. As a consequence, the detectors will be faced with challenging conditions, in particular the increase of pile-up: an average of 200 interactions per bunch crossing are expected, corresponding to an average interaction density of 1.8 collisions/mm. The reconstruction performance will be severely degraded in the end-cap and forward region of the ATLAS detector, especially for jets and transverse missing energy. The addition of timing information in forward objects through the High-Granularity Timing Detector will help to recover the performance of these regions to levels similar to the ones expected in the central region of the detector. It will also provide a bunch-by-bunch luminosity measurement. This talk will be focused on the developments surrounding the LGAD sensors and front-end electronics, which are aimed to achieve a low time res...

  8. Granular packings with moving side walls

    International Nuclear Information System (INIS)

    Landry, James W.; Grest, Gary Stephen

    2004-01-01

    The effects of movement of the side walls of a confined granular packing are studied by discrete element, molecular dynamics simulations. The dynamical evolution of the stress is studied as a function of wall movement both in the direction of gravity as well as opposite to it. For all wall velocities explored, the stress in the final state of the system after wall movement is fundamentally different from the original state obtained by pouring particles into the container and letting them settle under the influence of gravity. The original packing possesses a hydrostaticlike region at the top of the container which crosses over to a depth-independent stress. As the walls are moved in the direction opposite to gravity, the saturation stress first reaches a minimum value independent of the wall velocity, then increases to a steady-state value dependent on the wall velocity. After wall movement ceases and the packing reaches equilibrium, the stress profile fits the classic Janssen form for high wall velocities, while some deviations remain for low wall velocities. The wall movement greatly increases the number of particle-wall and particle-particle forces at the Coulomb criterion. Varying the wall velocity has only small effects on the particle structure of the final packing so long as the walls travel a similar distance.

  9. Emergent Strain Stiffening in Interlocked Granular Chains

    Science.gov (United States)

    Dumont, Denis; Houze, Maurine; Rambach, Paul; Salez, Thomas; Patinet, Sylvain; Damman, Pascal

    2018-02-01

    Granular chain packings exhibit a striking emergent strain-stiffening behavior despite the individual looseness of the constitutive chains. Using indentation experiments on such assemblies, we measure an exponential increase in the collective resistance force F with the indentation depth z and with the square root of the number N of beads per chain. These two observations are, respectively, reminiscent of the self-amplification of friction in a capstan or in interleaved books, as well as the physics of polymers. The experimental data are well captured by a novel model based on these two ingredients. Specifically, the resistance force is found to vary according to the universal relation log F ˜μ √{N }Φ11 /8z /b , where μ is the friction coefficient between two elementary beads, b is their size, and Φ is the volume fraction of chain beads when semidiluted in a surrounding medium of unconnected beads. Our study suggests that theories normally confined to the realm of polymer physics at a molecular level can be used to explain phenomena at a macroscopic level. This class of systems enables the study of friction in complex assemblies, with practical implications for the design of new materials, the textile industry, and biology.

  10. 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

  11. Friction law and hysteresis in granular materials.

    Science.gov (United States)

    DeGiuli, E; Wyart, M

    2017-08-29

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, [Formula: see text], is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent [Formula: see text] We build a microscopic theory for the nonmonotonicity of [Formula: see text], which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts [Formula: see text], and the sliding velocity, in terms of [Formula: see text] Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions.

  12. Deflagration to detonation experiments in granular HMX

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-03-01

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

  13. Granular discharge rate for submerged hoppers

    Directory of Open Access Journals (Sweden)

    T. J. Wilson

    2014-10-01

    Full Text Available The discharge of spherical grains from a hole in the bottom of a right circular cylinder is measured with the entire system underwater. We find that the discharge rate depends on filling height, in contrast to the well-known case of dry non-cohesive grains. It is further surprising that the rate increases up to about twenty five percent, as the hopper empties and the granular pressure head decreases. For deep filling, where the discharge rate is constant, we measure the behavior as a function of both grain and hole diameters. The discharge rate scale is set by the product of hole area and the terminal falling speed of isolated grains. But there is a small-hole cutoff of about two and half grain diameters, which is larger than the analogous cutoff in the Beverloo equation for dry grains. Received: 11 September 2014, Accepted: 10 October 2014; Reviewed by: L. Staron, CNRS, Universite Pierre et Marie Curie, Institut Le Rond d'Alembert, Paris, France; Edited by: L. A. Pugnaloni; DOI: http://dx.doi.org/10.4279/PIP.060009 Cite as: T J Wilson, C R Pfeifer, N Meysingier, D J Durian, Papers in Physics 6, 060009 (2014

  14. Granular cell tumors of the urinary bladder

    Directory of Open Access Journals (Sweden)

    Kayani Naila

    2007-03-01

    Full Text Available Abstract Background Granular cell tumors (GCTs are extremely rare lesions of the urinary bladder with only nine cases being reported in world literature of which one was malignant. Generally believed to be of neural origin based on histochemical, immunohistochemical, and ultrastructural studies; they mostly follow a clinically benign course but are commonly mistaken for malignant tumors since they are solid looking, ulcerated tumors with ill-defined margins. Materials and methods We herein report two cases of GCTs, one benign and one malignant, presenting with gross hematuria in a 14- and a 47-year-old female, respectively. Results Histopathology revealed characteristic GCTs with positive immunostaining for neural marker (S-100 and negative immunostaining for epithelial (cytokeratin, Cam 5.2, AE/A13, neuroendocrine (neuron specific enolase, chromogranin A, and synaptophysin and sarcoma (desmin, vimentin markers. The benign tumor was successfully managed conservatively with transurethral resection alone while for the malignant tumor, radical cystectomy, hysterectomy with bilateral salpingo-oophorectomy, anterior vaginectomy, plus lymph node dissection was done. Both cases show long-term disease free survival. Conclusion We recommend careful pathologic assessment for establishing the appropriate diagnosis and either a conservative or aggressive surgical treatment for benign or localized malignant GCT of the urinary bladder, respectively.

  15. Penetration in bimodal, polydisperse granular material

    KAUST Repository

    Kouraytem, Nadia; Thoroddsen, Sigurdur T; Marston, J. O.

    2016-01-01

    We investigate the impact penetration of spheres into granular media which are compositions of two discrete size ranges, thus creating a polydisperse bimodal material. We examine the penetration depth as a function of the composition (volume fractions of the respective sizes) and impact speed. Penetration depths were found to vary between delta = 0.5D(0) and delta = 7D(0), which, for mono-modal media only, could be correlated in terms of the total drop height, H = h + delta, as in previous studies, by incorporating correction factors for the packing fraction. Bimodal data can only be collapsed by deriving a critical packing fraction for each mass fraction. The data for the mixed grains exhibit a surprising lubricating effect, which was most significant when the finest grains [d(s) similar to O(30) mu m] were added to the larger particles [d(l) similar to O(200 - 500) mu m], with a size ratio, epsilon = d(l)/d(s), larger than 3 and mass fractions over 25%, despite the increased packing fraction. We postulate that the small grains get between the large grains and reduce their intergrain friction, only when their mass fraction is sufficiently large to prevent them from simply rattling in the voids between the large particles. This is supported by our experimental observations of the largest lubrication effect produced by adding small glass beads to a bed of large sand particles with rough surfaces.

  16. Modeling of interaction effects in granular systems

    International Nuclear Information System (INIS)

    El-Hilo, M.; Shatnawy, M.; Al-Rsheed, A.

    2000-01-01

    Interaction effects on the magnetic behavior of granular solid systems are examined using a numerical model which is capable of predicting the field, temperature and time dependence of magnetization. In this work, interaction effects on the temperature dependence of time viscosity coefficient S(T) and formation of minor hysteresis loops have been studied. The results for the time- and temperature dependence of remanence ratio have showed that the distribution of energy barriers f(ΔE) obtained depend critically on the strength and nature of interactions. These interactions-based changes in f(ΔE) can easily give a temperature-independent behavior of S(T) when these changes give a 1/ΔE behavior to the distribution of energy barriers. Thus, conclusions about macroscopic quantum tunneling must be carefully drawn when the temperature dependence of S(T) is used to probe for MQT effects. For minor hysteresis effects, the result shows that for the non-interacting case, no minor hysteresis loops occur and the loops are only predicted when the interaction field is positive. From these predictions, minor loops will form when the interaction field is strong enough to magnetize some moments during the recoil process back to zero field. Thus, these minor loops are originated from interaction driving irreversible changes along the recoil curve and the irreversible component of magnetization has no direct influence on the formation of these minor loops

  17. Modeling of interaction effects in granular systems

    CERN Document Server

    El-Hilo, M; Al-Rsheed, A

    2000-01-01

    Interaction effects on the magnetic behavior of granular solid systems are examined using a numerical model which is capable of predicting the field, temperature and time dependence of magnetization. In this work, interaction effects on the temperature dependence of time viscosity coefficient S(T) and formation of minor hysteresis loops have been studied. The results for the time- and temperature dependence of remanence ratio have showed that the distribution of energy barriers f(DELTA E) obtained depend critically on the strength and nature of interactions. These interactions-based changes in f(DELTA E) can easily give a temperature-independent behavior of S(T) when these changes give a 1/DELTA E behavior to the distribution of energy barriers. Thus, conclusions about macroscopic quantum tunneling must be carefully drawn when the temperature dependence of S(T) is used to probe for MQT effects. For minor hysteresis effects, the result shows that for the non-interacting case, no minor hysteresis loops occur an...

  18. Penetration in bimodal, polydisperse granular material

    KAUST Repository

    Kouraytem, N.

    2016-11-07

    We investigate the impact penetration of spheres into granular media which are compositions of two discrete size ranges, thus creating a polydisperse bimodal material. We examine the penetration depth as a function of the composition (volume fractions of the respective sizes) and impact speed. Penetration depths were found to vary between delta = 0.5D(0) and delta = 7D(0), which, for mono-modal media only, could be correlated in terms of the total drop height, H = h + delta, as in previous studies, by incorporating correction factors for the packing fraction. Bimodal data can only be collapsed by deriving a critical packing fraction for each mass fraction. The data for the mixed grains exhibit a surprising lubricating effect, which was most significant when the finest grains [d(s) similar to O(30) mu m] were added to the larger particles [d(l) similar to O(200 - 500) mu m], with a size ratio, epsilon = d(l)/d(s), larger than 3 and mass fractions over 25%, despite the increased packing fraction. We postulate that the small grains get between the large grains and reduce their intergrain friction, only when their mass fraction is sufficiently large to prevent them from simply rattling in the voids between the large particles. This is supported by our experimental observations of the largest lubrication effect produced by adding small glass beads to a bed of large sand particles with rough surfaces.

  19. Blurring the boundary between rapid granular flow and dense granular flow regimes: Evidence from DEM simulations

    Science.gov (United States)

    Tripathi, Anurag; Prasad, Mahesh; Kumar, Puneet

    2017-11-01

    The saturation of the effective friction coefficient for granular flows at high inertial numbers has been assumed widely by researchers, despite little simulation/experimental evidence. In contrast, a recent simulation study of plane shear flows by Mandal and Khakhar, suggests that the effective friction coefficient becomes maximum and then starts to decrease with increase in the inertial number for I > 0.5 . In order to investigate whether such a dip at higher inertial numbers is indeed a feature of granular rheology, we perform DEM simulations of chute flow of highly inelastic disks. We show that steady, fully developed flows are possible at inclinations much higher than those normally reported in literature. At such high inclinations, the flow is characterised by a significant slip at the base; the height of the layer increases by more than 300 % and kinetic energy of the layer increases by nearly 5 orders of magnitude. We observe, for the first time, steady chute flows at inertial number I 2 and show that the dip at higher inertial numbers can be observed in case of chute flow as well. The predictions of modified μ - I rheology, however, seem to remain valid in the bulk of the layer for packing fractions as low as 0.2. AT acknowledges the funding obtained from IIT Kanpur through the initiation Grant for this study.

  20. Measurement of internal defects in aluminum using a nano-granular in-gap magnetic sensor

    Science.gov (United States)

    Ozawa, T.; Yabukami, S.; Totsuka, J.; Koyama, S.; Hayasaka, J.; Wako, N.; Arai, K. I.

    2015-05-01

    Techniques for identifying defects in metals are very important in a wide variety of manufacturing areas. The present paper reports an eddy current testing method that employs a nano-granular in-gap magnetic sensor (GIGS) to detect internal defects in aluminum boards. The GIGS consists of a tunnel magnetoresistive film with nanometer sized grains and two yokes. In the presence of an external magnetic field, the nano-granular film exhibits only a small change in resistance due to the tunnel magnetoresistive effect. However, by placing it between two yokes, the magnetic flux can be greatly concentrated, thus increasing the change in resistance. The GIGS is a magnetic-field sensor that exploits this principle to achieve enhanced sensitivity. Moreover, because it has a cross-sectional yolk area of just 80 μm × 0.5 μm, it achieves outstanding spatial resolution. In the present study, it is used in combination with an eddy-current method in order to detect internal defects in aluminum. In this method, an excitation coil is used to apply an AC magnetic field perpendicular to the aluminum surface. This induces eddy currents in the metal, which in turn give rise to an AC magnetic field, which is then measured by the GIGS. The presence of defects in the aluminum distorts the eddy current flow, causing a change in the magnitude and distribution of the magnetic field. Such changes can be detected using the GIGS. In the present study, the proposed method was used to successfully detect indentations with diameters of 5 mm on the rear surface of an aluminum plate.

  1. Temperature dependence of the resistivity and tunneling magnetoresistance of sputtered FeHf(Si)O cermet films

    NARCIS (Netherlands)

    Strijkers, G.J.; Swagten, H.J.M.; Rulkens, B.; Bitter, R.H.J.N.; Jonge, de W.J.M.; Bloemen, P.J.H.; Schep, K.M.

    1998-01-01

    We have studied the tunneling resistivity and magnetoresistance of reactive sputter deposited FeHfO and FeHfSiO thin granular films. Maximum magnetoresistance ratios at room temperature of 2% and 3.2% were observed for films with compositions of Fe47Hf10O43 and Fe40Hf6Si6O48, respectively. The

  2. Catalytic reduction of NO by methane using a Pt/C/polybenzimidazole/Pt/C fuel cell

    DEFF Research Database (Denmark)

    Petrushina, Irina; Cleemann, Lars Nilausen; Refshauge, Rasmus

    2007-01-01

    with participation of H+ or electrochemically produced hydrogen. When added, methane partially suppresses the electrochemical reduction of NO. Methane outlet concentration monitoring has shown the CH4 participation in the chemical catalytic reduction, i.e., methane co-adsorption with NO inhibited the electrochemical...... NO reduction and introduced a dominant chemical path of the NO reduction. The products of the NO reduction with methane were N2, C2H4, and water. The catalytic NO reduction by methane was promoted when the catalyst was negatively polarized (−0.2 V). Repeated negative polarization of the catalyst increased...

  3. Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

    International Nuclear Information System (INIS)

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

    2014-01-01

    Graphical abstract: In this work, an aerobic column reactor was placed before the USB to maintain micro-oxygen condition in the reactor and the micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L −1 ) was successfully obtained. PCP degradation by the micro-aerobic system was studied and the variance of microbial community was also discussed by using PCR-DGGE analysis. - Highlights: • Micro-aerobic granular sludge was cultivated in column-type combined reactors. • PCP biodegradation, VFA accumulation and biogas production were studied. • The function of Methanogenic archaeon in the system was investigated. • Fluctuation and diversity of microbial community were discussed by DGGE analysis. • The dominated microorganisms were identified by 16S rDNA sequences. - Abstract: Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L −1 ) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34 mMCH 4 /h g VSS) and aerobic activity (SOUR: 2.21 mMO 2 /h g VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro-aerobic condition and

  4. Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

    Energy Technology Data Exchange (ETDEWEB)

    Lv, Yuancai, E-mail: donkey1204@hotmail.com [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Chen, Yuancai, E-mail: chenyc@scut.edu.cn [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); Song, Wenzhe, E-mail: songwenzhe007@126.com [Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); Hu, Yongyou, E-mail: ppyyhu@scut.edu.cn [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China)

    2014-09-15

    Graphical abstract: In this work, an aerobic column reactor was placed before the USB to maintain micro-oxygen condition in the reactor and the micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L{sup −1}) was successfully obtained. PCP degradation by the micro-aerobic system was studied and the variance of microbial community was also discussed by using PCR-DGGE analysis. - Highlights: • Micro-aerobic granular sludge was cultivated in column-type combined reactors. • PCP biodegradation, VFA accumulation and biogas production were studied. • The function of Methanogenic archaeon in the system was investigated. • Fluctuation and diversity of microbial community were discussed by DGGE analysis. • The dominated microorganisms were identified by 16S rDNA sequences. - Abstract: Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L{sup −1}) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34 mMCH{sub 4}/h g VSS) and aerobic activity (SOUR: 2.21 mMO{sub 2}/h g VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro

  5. Granular Corneal Dystrophy Manifesting after Radial Keratotomy

    Directory of Open Access Journals (Sweden)

    Sepehr Feizi

    2008-12-01

    Full Text Available

    PURPOSE: To report manifestation of granular corneal dystrophy after radial keratotomy (RK. CASE REPORT: A 32-year-old man presented with white radial lines in both corneas. He had undergone uncomplicated RK in both eyes 8 years ago. Preoperative refraction had been OD: -3.5 -0.75@180 and OS: -3.0 -0.5@175. Uncorrected visual acuity was OD: 8/10 and OS: 7/10; best corrected visual acuity was 9/10 in both eyes with OD: -0.5 -0.5@60 and OS: -0.75 -0.5@80. Slit lamp examination revealed discrete well-demarcated whitish lesions with clear intervening stroma in the central anterior cornea consistent with granular dystrophy. Similar opacities were present within the RK incisions. CONCLUSION: Granular dystrophy deposits may appear within RK incisions besides other previously reported locations.

  1. Neurohypophysis granular cell tumours. Upon neurohypophysis rare tumours

    International Nuclear Information System (INIS)

    Barrande, G.; Kujas, M.; Gancel, A.; Turpin, G.; Bruckert, E.; Kuhn, J.M.; Luton, J.P.

    1995-01-01

    Granular cell tumours of neurohypophysis are rare. These tumours are more often encountered as incidental autopsy findings seen in up to 17 % of unselected adult autopsy cases. There are few reports of para-sellar granular cell tumours large enough to cause symptoms. We present three cases of neurohypophysis granular cell tumour and a review of the literature. In one patient, the asymptomatic granular cell tumour was incidentally discovered at surgical removal of a corticotrophic micro-adenoma. The remaining 2 patients had a symptomatic tumour which caused neurological symptoms such as visual disturbance and headaches and endocrine disorders such as hypopituitarism or hyper-prolactinaemia. In these 2 cases, computerized tomography showed a well-circumscribed, contrast-enhanced, intra-sellar and supra-sellar mass. Magnetic resonance imaging demonstrated an isointense gadolinium-enhanced mass in T1-weighted-images. Trans-sphenoidal partial resection was performed and histology was interpreted as a granular cell tumour. The immunohistochemical study was positive for glial fibrillary acidic protein (GEAP) and neuron specific enolase (NSE) in 1 of the 2 tumours and positive for S100 protein and vimentin in both tumours but negative for CD68. The histogenesis of neurohypophysis granular cell tumours is still controversial but ultrastructural and immunohistochemical studies support the theory that may arise from pituicytes, the glial cells of neurohypophysis. Management of these benign, slow growing, tumours is based mainly on neurosurgical resection. Data from the literature do not support a beneficial effect of post operative radiation therapy on postoperative recurrences. (authors). 23 refs., 4 figs., 1 tab

  2. Segregation of granular binary mixtures by a ratchet mechanism.

    Science.gov (United States)

    Farkas, Zénó; Szalai, Ferenc; Wolf, Dietrich E; Vicsek, Tamás

    2002-02-01

    We report on a segregation scheme for granular binary mixtures, where the segregation is performed by a ratchet mechanism realized by a vertically shaken asymmetric sawtooth-shaped base in a quasi-two-dimensional box. We have studied this system by computer simulations and found that most binary mixtures can be segregated using an appropriately chosen ratchet, even when the particles in the two components have the same size and differ only in their normal restitution coefficient or friction coefficient. These results suggest that the components of otherwise nonsegregating granular mixtures may be separated using our method.

  3. 10th International Conference “Traffic and Granular Flow”

    CERN Document Server

    Boltes, Maik; Schadschneider, Andreas; Seyfried, Armin

    2015-01-01

    This book continues the biannual series of conference proceedings, which has become a classical reference resource in traffic and granular research alike, and addresses the latest developments at the intersection of physics, engineering and computational science. These involve complex systems, in which multiple 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.    

  4. A new method for measurement of granular velocities

    International Nuclear Information System (INIS)

    Nyborg Andersen, B.

    1984-01-01

    A new, supplementary method to measure granular velocities is presented. The method utilizes the Doppler shift caused by the line of sight component of the solar rotation to cause a wavelength shift through spectral lines as function of heliocentric angle. By measuring the center-to-limb variation of the granular intensity fluctations at different wavelength positions in the lines, the velocities are found. To do this, assumptions regarding the geometrical structure of the velocity and intensity fields have to be made. Preliminary application of the method results in a steep velocity gradient suggesting zero velocity at a hight of 200 km above tau 500 = 1. Possible causes are discussed

  5. Voltage fluctuations in granular superconductors in the perpendicular configuration

    International Nuclear Information System (INIS)

    Gerashchenko, O V

    2003-01-01

    The spectral density of voltage fluctuations in granular YBa 2 Cu 3 O 7-δ superconductors in the perpendicular configuration has been studied in the flux flow mode. It has been found that, in this case, the 1/f-voltage noise observed depends weakly on temperature and is associated with motion of a magnetic flux in the superconductor. A comparison of the data obtained with the results of previous measurements in parallel configuration has shown that voltage noise is produced by a single common source, which is presumably associated with self-organization of the critical state in granular superconductors

  6. Frost susceptibility of granular subbase materials contaminated by deicing chemicals

    DEFF Research Database (Denmark)

    Jørgensen, Anders Stuhr; Orlander, Tobias; Doré, Guy

    2013-01-01

    The increase in urban population in arctic areas leads to an increased demand for transportation infrastructures (such as roads and airfields) in the regions. This challenges the road constructions in terms of condition, bearing capacity and maintenance. It is believed that deicing agents used...... on roads and airfields enter the granular subbase materials and thereby makes the soil more frost-susceptible. In this project a series of isothermal frost heave tests has been carried out on granular subbase material from the runway at Kuujjuaq Airport, Québec, Canada. The tests have been carried out...

  7. Kovacs-Like Memory Effect in Driven Granular Gases

    Science.gov (United States)

    Prados, A.; Trizac, E.

    2014-05-01

    While memory effects have been reported for dense enough disordered systems such as glasses, we show here by a combination of analytical and simulation techniques that they are also intrinsic to the dynamics of dilute granular gases. By means of a certain driving protocol, we prepare the gas in a state where the granular temperature T coincides with its long time limit. However, T does not subsequently remain constant but exhibits a nonmonotonic evolution before reaching its nonequilibrium steady value. The corresponding so-called Kovacs hump displays a normal behavior for weak dissipation (as observed in molecular systems) but is reversed under strong dissipation, where it, thus, becomes anomalous.

  8. Properties of surface waves in granular media under gravity

    International Nuclear Information System (INIS)

    Zheng He-Peng

    2014-01-01

    Acoustical waves propagating along the free surface of granular media under gravity are investigated in the framework of elasticity theory. The influence of stress on a surface wave is analyzed. The results have shown that two types of surface waves, namely sagittal and transverse modes exist depending on initial stress states, which may have some influence on the dispersion relations of surface waves, but the influence is not great. Considering that the present experimental accuracy is far from distinguishing this detail, the validity of elasticity theory on the surface waves propagating in granular media can still be maintained. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  9. Permeability of granular beds emplaced in vertical drill holes

    International Nuclear Information System (INIS)

    Griffiths, S.K.; Morrison, F.A. Jr.

    1979-01-01

    To determine the permeabilities of granular materials emplaced in vertical drill holes used for underground nuclear tests, an experiment at the USDOE Nevada Test Site (NTS) was conducted. As the hole is being filled, falling material increases pressure above and within the granular beds beneath. When the filling operation starts or stops, a transient pressure response occurs within the beds; measurements of this response in beds of various compositions were made. The permeabilities after emplacement were found by matching analytical predictions of the response to these data. This information is useful in assuring the containment of nuclear tests conducted in such drill holes

  10. Properties of Nanostructure Bismuth Telluride Thin Films Using Thermal Evaporation

    Directory of Open Access Journals (Sweden)

    Swati Arora

    2017-01-01

    Full Text Available Bismuth telluride has high thermoelectric performance at room temperature; in present work, various nanostructure thin films of bismuth telluride were fabricated on silicon substrates at room temperature using thermal evaporation method. Tellurium (Te and bismuth (Bi were deposited on silicon substrate in different ratio of thickness. These films were annealed at 50°C and 100°C. After heat treatment, the thin films attained the semiconductor nature. Samples were studied by X-ray diffraction (XRD and scanning electron microscopy (SEM to show granular growth.

  11. Disappearance of superconductivity and critical resistance in thin indium films

    International Nuclear Information System (INIS)

    Okuma, Satoshi; Nishida, Nobuhiko

    1991-01-01

    In thin granular films composed of two-dimensionally coupled indium particles, we have studied influences of average particle sizes anti d on the superconducting transition. For films with anti d=280A and 224A, superconducting transition temperature stays almost constant with increasing the sheet resistance R n in the normal state, while for a film with anti d=140A, it decreases linearly with R n . This means that the system changes to a dirty superconductor by reducing anti d. With further increasing R n , superconductivity disappears when R n exceeds the value R c of order h/4e 2 , which seems to correlate with anti d. (orig.)

  12. Low temperature spin-glass-like phases in magnetic nano-granular composites

    KAUST Repository

    Zhang, Bei

    2012-09-01

    It is a common understanding that the dipole-dipole interaction among the magnetic nanoparticles may result in a low-temperature spin-glass phase, which has been evidenced by observation of aging effect and memory effect. However, several studies on the nano-particles systems showed that some of the observed spin-glass-like phenomena could be due to the existence of spin-glasslike shells surrounding the ferrimagnetic cores. Therefore, it is very important to understand that how the dipole-dipole interaction induce the spin-glass phase. In order to address this issue, we have fabricated Co-SiO 2 and Fe-SiO 2 nano-granular thin films and measured the memory effect for them. Spin-glass-like phase has been observed at low temperatures. We found that, after annealing, the size of the clusters increased significantly. Based on a simple model, the dipole-dipole interaction between the clusters must be increased accordingly for the annealed samples. Interestingly, the memory effect is greatly weakened in the annealed films, which strongly suggested that the dipole-dipole interaction may not be the major factor for the formation of the low-temperature spin-glass-like phase. Copyright © 2012 American Scientific Publishers All rights reserved.

  13. Biodegradation of tributyl phosphate by granular biofilms

    International Nuclear Information System (INIS)

    Joshi, Hiren M.; Nancharaiah, Y.V.; Venugopalan, V.P.

    2009-01-01

    Full text: Tributyl phosphate (TBP) is used as plasticizer for cellulose esters, lacquers, plastic and vinyl resins and as a solvent extractant of rare earth metals. In nuclear power industry, it is used as a solvent for the extraction of uranium and plutonium salts during fuel reprocessing. TBP does not occur naturally in the environment. It is sparingly soluble in water and once released into soil or aquatic systems, is only moderately biodegradable. There are many proposed mechanisms for TBP biodegradation, which involve stepwise enzymatic hydrolysis to orthophosphate and n-butanol and mono-oxygenase based transformation and then degradation. Microbial processes involving multispecies consortia offer better choice over monoculture processes for degradation of complex wastes. Processes based on immobilized microbial consortia are characterized by significantly reduced settling time, high stability in presence of varying organic load, effective mineralization and amenability to bioaugmentation, which make them a good choice for bioremediation and waste water treatment. The objective of this study was to investigate the suitability of aerobic microbial granules (also known as granular biofilms) for efficient biodegradation of TBP. For this purpose, we set up 4 litre cylindrical sequencing batch reactors (SBR) in triplicates and inoculated them with sludge (mean sludge size ∼ 60 mm) obtained from an operating wastewater treatment plant. The SBRs were operated on a 6h cycle with 66% volumetric exchange ratio. The reactors were fed with synthetic waste water along with 90 mM acetate and 0.5 mM TBP. The concentration of TBP was slowly raised to 2mM. After 3 months of operation, microbial granules (mean size: 2.05 mm) capable of TBP degradation were observed in the reactors. Gas chromatographic analysis of samples showed that after 6h of operational cycle 2 mM initial concentration of TBP was reduced to 0.2 mM, after which there was no further degradation. Cessation

  14. Granular starch hydrolysis for fuel ethanol production

    Science.gov (United States)

    Wang, Ping

    Granular starch hydrolyzing enzymes (GSHE) convert starch into fermentable sugars at low temperatures (≤48°C). Use of GSHE in dry grind process can eliminate high temperature requirements during cooking and liquefaction (≥90°C). In this study, GSHE was compared with two combinations of commercial alpha-amylase and glucoamylase (DG1 and DG2, respectively). All three enzyme treatments resulted in comparable ethanol concentrations (between 14.1 to 14.2% v/v at 72 hr), ethanol conversion efficiencies and ethanol and DDGS yields. Sugar profiles for the GSHE treatment were different from DG1 and DG2 treatments, especially for glucose. During simultaneous saccharification and fermentation (SSF), the highest glucose concentration for the GSHE treatment was 7% (w/v); for DG1 and DG2 treatments, maximum glucose concentration was 19% (w/v). GSHE was used in one of the fractionation technologies (enzymatic dry grind) to improve recovery of germ and pericarp fiber prior to fermentation. The enzymatic dry grind process with GSHE was compared with the conventional dry grind process using GSHE with the same process parameters of dry solids content, pH, temperature, time, enzyme and yeast usages. Ethanol concentration (at 72 hr) of the enzymatic process was 15.5% (v/v), which was 9.2% higher than the conventional process (14.2% v/v). Distillers dried grains with solubles (DDGS) generated from the enzymatic process (9.8% db) was 66% less than conventional process (28.3% db). Three additional coproducts, germ 8.0% (db), pericarp fiber 7.7% (db) and endosperm fiber 5.2% (db) were produced. Costs and amounts of GSHE used is an important factor affecting dry grind process economics. Proteases can weaken protein matrix to aid starch release and may reduce GSHE doses. Proteases also can hydrolyze protein into free amino nitrogen (FAN), which can be used as a yeast nutrient during fermentation. Two types of proteases, exoprotease and endoprotease, were studied; protease and urea

  15. Friction dependence of shallow granular flows from discrete particle simulations

    NARCIS (Netherlands)

    Thornton, Anthony Richard; Weinhart, Thomas; Luding, Stefan; Bokhove, Onno

    2011-01-01

    A shallow-layer model for granular flows is completed with a closure relation for the macroscopic bed friction or basal roughness obtained from micro-scale discrete particle simulations of steady flows. We systematically vary the bed friction by changing the contact friction coefficient between

  16. Modelling of Granular Materials Using the Discrete Element Method

    DEFF Research Database (Denmark)

    Ullidtz, Per

    1997-01-01

    With the Discrete Element Method it is possible to model materials that consists of individual particles where a particle may role or slide on other particles. This is interesting because most of the deformation in granular materials is due to rolling or sliding rather that compression of the gra...

  17. Practical experiences with granular activated carbon (GAC) at the ...

    African Journals Online (AJOL)

    Practical experiences with granular activated carbon (GAC) at the Rietvlei Water Treatment Plant. ... The porosity was found to be 0.69 for the 12 x 40 size carbon and 0.66 for the 8 x 30 size carbon. By using a ... The third part of the study measured the physical changes of the GAC found at different points in the GAC cycle.

  18. Investigation of granular impact using positron emission particle tracking

    KAUST Repository

    Marston, Jeremy O.; Thoroddsen, Sigurdur T

    2015-01-01

    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

  19. Mechanics of Granular Materials : Constitutive Behavior and Pattern Transformation

    NARCIS (Netherlands)

    Göncü, F.

    2012-01-01

    From pharmaceutical to mining or traveling desert dunes to earthquakes, granular materials are at the heart of many industries and natural phenomena. Improving the efficiency of the machines handling them or, constructing safer buildings requires a critical understanding of their behavior. However,

  20. Wave propagation of spectral energy content in a granular chain

    Directory of Open Access Journals (Sweden)

    Shrivastava Rohit Kumar

    2017-01-01

    Full Text Available A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting or non-destructive testing of the internal structure of solids. The focus is on the total energy content of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain, which allows understanding the energy attenuation due to disorder since it isolates the longitudinal P-wave from shear or rotational modes. It is observed from the signal that stronger disorder leads to faster attenuation of the signal. An ordered granular chain exhibits ballistic propagation of energy whereas, a disordered granular chain exhibits more diffusive like propagation, which eventually becomes localized at long time periods. For obtaining mean-field macroscopic/continuum properties, ensemble averaging has been used, however, such an ensemble averaged spectral energy response does not resolve multiple scattering, leading to loss of information, indicating the need for a different framework for micro-macro averaging.

  1. Statics and kinematics of discrete Cosserat-type granular materials

    NARCIS (Netherlands)

    Kruyt, Nicolaas P.

    2003-01-01

    A theoretical framework is presented for the statics and kinematics of discrete Cosserat-type granular materials. In analogy to the force and moment equilibrium equations for particles, compatibility equations for closed loops are formulated in the two-dimensional case for relative displacements and

  2. Editorial: Modelling and computational challenges in granular materials

    NARCIS (Netherlands)

    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

  3. ELECTROCHEMICAL DECHLORINATION OF TRICHLOROETHYLENE USING GRANULAR-GRAPHITE ELECTRODES

    Science.gov (United States)

    Electrochemical dechlorination of TCE was conducted in a glass column using granular graphite as electrodes. A constant voltage of 15 volt was applied resulting in 60-62 mA of current. Approximately 4-6% of the TCE was dechlorinated. Among the reduced TCE, more than 95% was compl...

  4. 75 FR 67105 - Granular Polytetrafluoroethylene Resin From Italy and Japan

    Science.gov (United States)

    2010-11-01

    ... Polytetrafluoroethylene Resin From Italy and Japan AGENCY: United States International Trade Commission. ACTION... resin from Italy and Japan. SUMMARY: The Commission hereby gives notice that it has instituted reviews... revocation of the antidumping duty orders on granular polytetrafluoroethylene resin from Italy and Japan...

  5. Stress distribution in quasi-crystalline granular piles

    NARCIS (Netherlands)

    Trigger, S.A.; Heijst, van G.J.F.; Krasnopolskaya, T.S.; Schram, P.P.J.M.

    2001-01-01

    The main goal of this paper is a rigorous consideration of the stress problem in some simple models of granular piles. Discrete models are considered and the transition to the continuous description is accomplished in order to find the coarse-grained average stress. Some phenomenological rules are

  6. Granular cell tumor with orbital involvement in a child

    Energy Technology Data Exchange (ETDEWEB)

    Reis, Fabiano [Universidade Estadual de Campinas (FCM/UNICAMP), SP (Brazil). Fac. de Ciencias Medicas. Dept. de Radiologia; Iyeyasu, Josie Naomi; Carvalho, Keila Monteiro de [Universidade Estadual de Campinas (FCM/UNICAMP), SP (Brazil). Fac. de Ciencias Medicas. Dept. de Oftalmo-Otorrinolaringologia; Altemani, Albina Messias [Universidade Estadual de Campinas (FCM/UNICAMP), SP (Brazil). Fac. de Ciencias Medicas. Dept. de Anatomia Patologica

    2011-09-15

    The authors report a rare case of granular cell tumor in the left medial rectus muscle of a seven-year-old boy. Clinical, pathologic and radiologic findings of the present case are described and a brief literature review is undertaken. (author)

  7. Cahn-Hiliard theory for unstable granular fluids

    NARCIS (Netherlands)

    van Noije, T.P.C.; Ernst, M.H.

    A Cahn-Hilliard-type theory for hydrodynamic fluctuations is proposed that gives a quantitative description of the slowly evolving spatial correlations and structures in density and flow fields in the early stages of evolution of freely cooling granular fluids. Two mechanisms for pattern selection

  8. Pesticide Removal by Combined Ozonation and Granular Activated Carbon Filtration

    NARCIS (Netherlands)

    Orlandini, E.

    1999-01-01

    This research aimed to idendfy and understand mechanisms that underlie the beneficial effect of ozonation on removal of pesdcides and other micropoUutants by Granular Activated Carbon (GAC) filtradon. This allows optimization of the combination of these two processes, termed Biological Activated

  9. Interface stability of granular filter structures under currents

    NARCIS (Netherlands)

    Verheij, H.J.; Hoffmans, G.; Dorst, K.; Van de Sande, S.

    2012-01-01

    Granular filters are used for protection of structures against scour and erosion. For a proper functioning it is necessary that the interfaces between the filter structure, the subsoil and the water flowing above the filter structure are stable. Stability means that there is no transport of subsoil

  10. Martian gullies: possible formation mechanism by dry granular material..

    Science.gov (United States)

    Cedillo-Flores, Y.; Durand-Manterola, H. J.

    section Some of the geomorphological features in Mars are the gullies Some theories developed tried explain its origin either by liquid water liquid carbon dioxide or flows of dry granular material We made a comparative analysis of the Martian gullies with the terrestrial ones We propose that the mechanism of formation of the gullies is as follows In winter CO 2 snow mixed with sand falls in the terrain In spring the CO 2 snow sublimate and gaseous CO 2 make fluid the sand which flows like liquid eroding the terrain and forming the gullies By experimental work with dry granular material we simulated the development of the Martian gullies injecting air in the granular material section We present the characteristics of some terrestrial gullies forms at cold environment sited at Nevado de Toluca Volcano near Toluca City M e xico We compare them with Martian gullies choose from four different areas to target goal recognize or to distinguish to identify possible processes evolved in its formation Also we measured the lengths of those Martian gullies and the range was from 24 m to 1775 meters Finally we present results of our experimental work at laboratory with dry granular material

  11. Kinetics and mass transfer phenomena in anaerobic granular sludge

    NARCIS (Netherlands)

    Gonzalez-Gil, G.; Seghezzo, L.; Lettinga, G.; Kleerebezem, R.

    2001-01-01

    The kinetic properties of acetate-degrading methanogenic granular sludge of different mean diameters were assessed at different up-flow velocities (Vup). Using this approach, the influence of internal and external mass transfer could be estimated. First, the apparent Monod constant (KS) for each

  12. Anaerobic granular sludge : characterization, and factors affecting its functioning

    NARCIS (Netherlands)

    Alphenaar, P.A.

    1994-01-01

    Many UASB reactors are designed in such a fashion that the presence of granular sludge is necessary for a proper purification process. For achieving an optimum wastewater purification with such reactors, knowledge of the factors that determine the growth, retention and disintegration of

  13. Electrokinetic copper and iron migration in anaerobic granular sludge

    NARCIS (Netherlands)

    Virkutyte, J.; Sillanpää, M.J.; Lens, P.N.L.

    2006-01-01

    The application of low-level direct electric current (0.15 mA cm¿2) as an electrokinetic technique to treat copper-contaminated mesophilic anaerobic granular sludge was investigated. The sludge was obtained from a full scale UASB reactor treating paper-mill wastewater and was artificially

  14. Non-spherical granular flows down inclined chutes

    NARCIS (Netherlands)

    Hidalgo, R.C.; Rubio-Largo, S.M.; Alonso-Marroquin, F.; Weinhart, T.

    2017-01-01

    In this work, we numerically examine the steady-state granular flow of 3D non-spherical particles down an inclined plane. We use a hybrid CPU/GPU implementation of the discrete element method of nonspherical elongated particles. Thus, a systematic study of the system response is performed varying

  15. Impact of high saline wastewaters on anaerobic granular sludge functionalities

    NARCIS (Netherlands)

    Jeison, D.A.; Rio, del A.; Lier, van J.B.

    2008-01-01

    Three UASB reactors were operated at different salinity levels in order to assess the effects on the granular sludge properties. High levels of activity inhibition were observed at sodium concentrations over 7 g Na+/L, which resulted in low applicable organic loading rates and VFA accumulation in

  16. 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....... Further, for the non-stationary term, the virtual mass coefficient will be derived....

  17. Jamming by compressing a system of granular crosses

    Science.gov (United States)

    Zheng, Hu; Wang, Dong; Barés, Jonathan; Behringer, Robert

    2017-06-01

    A disordered stress-free granular packing can be jammed, transformed into a mechanically rigid structure, by increasing the density of particles or by applying shear deformation. The jamming behavior of systems made of 2D circular discs has been investigated in detail, but very little is known about jamming for non-spherical particles, and particularly, non-convex particles. Here, we perform an experimental study on jamming by compression of a system of quasi-2D granular crosses made of photo-elastic crosses. We measure the pressure evolution during cyclic compression and decompression. The Jamming packing fraction of these quasi-2D granular crosses is ϕJ ≃ 0.475, which is much smaller than the value ϕJ ≃ 0.84 for-2D granular disks. The packing fraction shifts systematically to higher values under compressive cycling, corresponding to systematic shifts in the stress-strain response curves. Associated with these shifts are rotations of the crosses, with minimal changes in their centers of mass.

  18. Rheological Behavior of Dense Assemblies of Granular Materials

    International Nuclear Information System (INIS)

    Sundaresan, Sankaran; Tardos, Gabriel I.; Subramaniam, Shankar

    2011-01-01

    Assemblies of granular materials behave differently when they are owing rapidly, from when they are slowly deforming. The behavior of rapidly owing granular materials, where the particle-particle interactions occur largely through binary collisions, is commonly related to the properties of the constituent particles through the kinetic theory of granular materials. The same cannot be said for slowly moving or static assemblies of granular materials, where enduring contacts between particles are prevalent. For instance, a continuum description of the yield characteristics of dense assemblies of particles in the quasistatic ow regime cannot be written explicitly on the basis of particle properties, even for cohesionless particles. Continuum models for this regime have been proposed and applied, but these models typically assume that the assembly is at incipient yield and they are expressed in terms of the yield function, which we do not yet know how to express in terms of particle-level properties. The description of the continuum rheology in the intermediate regime is even less understood. Yet, many practically important flows in nature and in a wide range of technological applications occur in the dense flow regime and at the transition between dilute and dense regimes; the lack of validated continuum rheological models for particle assemblies in these regimes limits predictive modeling of such flows. This research project is aimed at developing such rheological models.

  19. Multifocal Synchronous Granular Cell Tumors of the Gastrointestinal Tract

    OpenAIRE

    Lipkin-Moore, Zachary; Thomas, Rebecca M.; Rothstein, Robin D.

    2014-01-01

    Granular cell tumors (GCT) are rare and unusual tumors, which are usually benign and asymptomatic. Only 5?10% of cases involve the gastrointestinal tract, most commonly as singular, non-cancerous lesions in the esophagus. We report a rare case of symptomatic, multifocal, synchronous GCT involving the esophagus, stomach, and cecum.

  20. Granular computing in decision approximation an application of rough mereology

    CERN Document Server

    Polkowski, Lech

    2015-01-01

    This book presents a study in knowledge discovery in data with knowledge understood as a set of relations among objects and their properties. Relations in this case are implicative decision rules and the paradigm in which they are induced is that of computing with granules defined by rough inclusions, the latter introduced and studied  within rough mereology, the fuzzified version of mereology. In this book basic classes of rough inclusions are defined and based on them methods for inducing granular structures from data are highlighted. The resulting granular structures are subjected to classifying algorithms, notably k—nearest  neighbors and bayesian classifiers. Experimental results are given in detail both in tabular and visualized form for fourteen data sets from UCI data repository. A striking feature of granular classifiers obtained by this approach is that preserving the accuracy of them on original data, they reduce  substantially the size of the granulated data set as well as the set of granular...

  1. Granular cell tumor with orbital involvement in a child

    International Nuclear Information System (INIS)

    Reis, Fabiano; Iyeyasu, Josie Naomi; Carvalho, Keila Monteiro de; Altemani, Albina Messias

    2011-01-01

    The authors report a rare case of granular cell tumor in the left medial rectus muscle of a seven-year-old boy. Clinical, pathologic and radiologic findings of the present case are described and a brief literature review is undertaken. (author)

  2. Dynamics of crater formations in immersed granular materials

    Science.gov (United States)

    Varas, G.; Vidal, V.; Géminard, J.

    2009-12-01

    Craters are part of the widespread phenomena observed in nature. Among the main applications to natural phenomena, aside from meteorite impact craters, are the formation and growth of volcanic edifices, by successive ejecta emplacement and/or erosion. The time evolution and dynamics play a crucial role here, as the competition between volcanic-jet mass-flux (degassing and ejecta) and crater-size evolution may control directly the eruptive regime. Crater morphology in dry granular material has been extensively studied, both experimentally and theoretically. Most of these studies investigate the final, steady crater shape resulting from the collision of solid bodies with the material surface and scaling laws are derived. In immersed granular material, craters generated by an underwater vortex ring, or underwater impact craters generated by landslide, have been reported. In a previous experimental study, Gostiaux et al. [Gran. Matt., 2002] have investigated the dynamics of air flowing through an immersed granular layer. They reported that, depending on the flow rate, the system exhibits two qualitatively different regimes: At small flow rate, the bubbling regime during which bubbles escape the granular layer independently one from another; At large flow rate, the open-channel regime which corresponds to the formation of a channel crossing the whole thickness of the granular bed through which air escapes almost continuously. At intermediate flow rate, a spontaneous alternation between these two regimes is observed. Here, we report the dynamics of crater formations at the free surface of an immersed granular bed, locally crossed by an ascending gas flow. We reproduce the experimental conditions of Gostiaux et al. (2002) in two dimensions: In a vertical Hele-Shaw cell, the crater consists of two sand piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas

  3. Leucemia de grandes linfócitos granulares Large granular lymphocyte leukemia

    Directory of Open Access Journals (Sweden)

    Bruno Terra

    2010-01-01

    Full Text Available O presente estudo tem como objetivo o estabelecimento de fundamentação teórica atualizada baseada em revisão bibliográfica sobre a leucemia de grandes linfócitos granulares (LGLG, doença onco-hematológica, que, devido à sua relativa raridade, é pouco conhecida e subdiagnosticada. A LGLG é caracterizada pela proliferação clonal de linfócitos T ou NK na medula óssea e/ou no sangue periférico. Dentre as manifestações clínico-laboratoriais, podem ocorrer citopenias (anemia e/ou neutropenia e/ou plaquetopenia, linfocitose (não costuma ser acentuada, linfadenomegalia, hepatoesplenomegalia, alterações imunológicas e sintomas constitucionais (emagrecimento, febre e sudorese. O curso clínico da LGLG é bastante variável, sendo que no subtipo T costuma ser indolente ou oligossintomática, enquanto no subtipo NK a evolução costuma ser desfavorável. O diagnóstico é firmado através de imunofenotipagem por citometria de fluxo e estudo de clonalidade por métodos de biologia molecular. Seu tratamento é bastante diversificado e é definido de acordo com a apresentação clínica da doença.This is a literature review about large granular lymphocyte leukemia (LGLL, a rare and misdiagnosed oncohematological disease, characterized by a clonal expansion of T-cells (T-LGLL or NK-cells (NK-LGLL in the bone marrow and/or peripheral blood. The clinical features of LGLL include cytopenias (anemia, neutropenia and thrombocytopenia, lymphocytosis (usually discrete, lymphadenopathy, hepatomegaly, splenomegaly, immune abnormalities and constitutional symptoms (fever, night sweats and weight loss. The diagnosis is based on the confirmation of the clonality of T-cells or NK-cells (polymerase chain reaction and Southern blot are the two methods most commonly used and typical findings of the immunophenotypic analysis of peripheral blood lymphocytes (flow cytometry analyses for specific surface antigens. In contrast to the chronic and indolent

  4. Discrete Element study of granular material - Bumpy wall interface behavior

    Science.gov (United States)

    El Cheikh, Khadija; Rémond, Sébastien; Pizette, Patrick; Vanhove, Yannick; Djelal, Chafika

    2016-09-01

    This paper presents a DEM study of a confined granular material sheared between two parallel bumpy walls. The granular material consists of packed dry spherical particles. The bumpiness is modeled by spheres of a given diameter glued on horizontal planes. Different bumpy surfaces are modeled by varying diameter or concentration of glued spheres. The material is sheared by moving the two bumpy walls at fixed velocity. During shear, the confining pressure applied on each bumpy wall is controlled. The effect of wall bumpiness on the effective friction coefficient and on the granular material behavior at the bumpy walls is reported for various shearing conditions. For given bumpiness and confining pressure that we have studied, it is found that the shear velocity does not affect the shear stress. However, the effective friction coefficient and the behavior of the granular material depend on the bumpiness. When the diameter of the glued spheres is larger than about the average grains diameter of the medium, the latter is uniformly sheared and the effective friction coefficient remains constant. For smaller diameters of the glued spheres, the effective friction coefficient increases with the diameter of glued spheres. The influence of glued spheres concentration is significant only for small glued spheres diameters, typically half of average particle diameter of the granular material. In this case, increasing the concentration of glued spheres leads to a decrease in effective friction coefficient and to shear localization at the interface. For different diameters and concentrations of glued spheres, we show that the effect of bumpiness on the effective friction coefficient can be characterized by the depth of interlocking.

  5. Breakage mechanics for granular materials in surface-reactive environments

    Science.gov (United States)

    Zhang, Yida; Buscarnera, Giuseppe

    2018-03-01

    It is known that the crushing behaviour of granular materials is sensitive to the state of the fluids occupying the pore space. Here, a thermomechanical theory is developed to link such macroscopic observations with the physico-chemical processes operating at the microcracks of individual grains. The theory relies on the hypothesis that subcritical fracture propagation at intra-particle scale is the controlling mechanism for the rate-dependent, water-sensitive compression of granular specimens. First, the fracture of uniaxially compressed particles in surface-reactive environments is studied in light of irreversible thermodynamics. Such analysis recovers the Gibbs adsorption isotherm as a central component linking the reduction of the fracture toughness of a solid to the increase of vapour concentration. The same methodology is then extended to assemblies immersed in wet air, for which solid-fluid interfaces have been treated as a separate phase. It is shown that this choice brings the solid surface energy into the dissipation equations of the granular matrix, thus providing a pathway to (i) integrate the Gibbs isotherm with the continuum description of particle assemblies and (ii) reproduce the reduction of their yield strength in presence of high relative humidity. The rate-effects involved in the propagation of cracks and the evolution of breakage have been recovered by considering non-homogenous dissipation potentials associated with the creation of surface area at both scales. It is shown that the proposed model captures satisfactorily the compression response of different types of granular materials subjected to varying relative humidity. This result was achieved simply by using parameters based on the actual adsorption characteristics of the constituting minerals. The theory therefore provides a physically sound and thermodynamically consistent framework to study the behaviour of granular solids in surface-reactive environments.

  6. The Monte Carlo evaluation of noise and resolution properties of granular phosphor screens

    International Nuclear Information System (INIS)

    Liaparinos, P F; Kandarakis, I S

    2009-01-01

    The imaging performance of phosphor screens, used as x-ray detectors in diagnostic medical imaging systems, is affected by their both noise and resolution properties. Amplification and blurring processes are due to a sequence of conversion stages within the screen which contribute to fluctuations in the number and spatial distribution of the optical quanta recorded by the optical detector (e.g. film, television camera, CCD, etc). The purpose of this paper is to investigate the stochastic noise arising from granularity as well as the variation of spatial resolution of granular fluorescent screens in terms of the detector's structure. Using a custom-validated Monte Carlo model, the parameters of interest were evaluated for the widely used Gd 2 O 2 S:Tb phosphor material. We have studied the variations of (i) the modulation transfer function, (ii) the Swank factor and (iii) the zero-frequency detective quantum efficiency (DQE), under several conditions employed in conventional and digital mammography and radiology. Several evaluations are provided for the imaging metrics as a function of the x-ray energy (18 keV, 49 keV and 51 keV), phosphor coating weight (20 mg cm -2 , 34 mg cm -2 and 60 mg cm -2 ), grain size (from 4 μm up to 13 μm) and packing density (from 50% up to 85%). It was found that screens of high packing density can combine high zero-frequency DQE with improved resolution properties. For a digital mammographic imaging system (34 mg cm -2 , 18 keV), a packing density of 85% can improve the spatial resolution of the screen by 1.6 cycles mm -1 in comparison to that of 50% packing density. Similarly, for radiographic cases (60 mg cm -2 , 49 keV), the spatial resolution can be improved by 1.7 cycles mm -1 . The aforementioned findings provide the resolution benefits of using high packing density screens.

  7. Noise measurements on NbN thin films with a negative temperature resistance coefficient deposited on sapphire and on SiO2

    NARCIS (Netherlands)

    Leroy, G.; Gest, J.; Vandamme, L.K.J.; Bourgeois, O.

    2007-01-01

    We characterize granular NbNx thin cermet films deposited on either sapphire substrate or on SiO2 and compare the 1/f noise at 300 K and 80 K. The films were characterized with an impedance analyzer from 20 Hz to 1 MHz and analyzed as a resistor R in parallel with a capacitor C. The calculated noise

  8. Paraqueratose granular: relato de seis casos em crianças Granular parakeratosis: a report of six cases in children

    Directory of Open Access Journals (Sweden)

    Susana Giraldi

    2006-02-01

    Full Text Available A paraqueratose granular é alteração da queratinização, primeiramente descrita em adultos, caracterizada por pápulas e placas hiperqueratósicas nas áreas intertriginosas. Os autores descrevem seis casos de paraqueratose granular em crianças. Um paciente apresentava lesões nas regiões glúteas, dois em ambas as axilas e região cervical (apresentações inéditas na literatura. Três pacientes apresentavam lesões em pregas inguinais. Realizam também revisão da literatura e discutem a possível etiologia dessa rara dermatose.Granular parakeratosis is an alteration of keratinization that was first described in adults. It is characterized by hiperkeratotic plaques and papules in intertriginous areas. The authors describe six cases of granular parakeratosis in children. One patient had lesions on the buttocks; two children presented papules in both axillae and cervical region (presentations never described before in the literature. The remaining three patients presented with lesions in the inguinal folds. Review of the literature and discussion on the pathogenesis of this rare dermatosis are presented.

  9. Erosion of a wet/dry granular interface

    Science.gov (United States)

    Jop, Pierre; Lefebvre, Gautier

    2013-04-01

    To model the dynamic of landslides, the evolution of the interface between the erodible ground and the flowing material is still studied experimentally or numerically (ie. Mangeney et al. 2010, Iverson 2012). In some cases, the basal material is more cohesive than the flowing one. Such situation arises for example due to cementation or humidity. What are the exchange rates between these phases? What is the coupling between the evolution of the interface and the flow? We studied the erosion phenomenon and performed laboratory experiments to focus on the interaction between a cohesive unsaturated granular material and a dry granular flow. Both materials were spherical grains, the cohesion being induced by adding a given mass of liquid to the grains. Two configurations were explored: a circular aggregate submitted to a dry flow in a rotating drum, and a granular flow eroding a wet granular pile. First, we focused on the influence of the cohesion, controlled by the liquid properties, such as the surface tension and the viscosity. Then the flow characteristics were modified by varying the grain size and density. These results allowed us to present a model for the erosion mechanisms, based on the flow and fluid properties. The main results are the need to take into account the whole probability distribution the stress applied on the wet grains and that both the surface tension and the viscosity are important since they play a different roles. The latter is mainly responsible of the time scale of the dynamic of a wet grain, while the former acts as a threshold on the force distribution. In the second configuration, we could also control the inclination of the slope. This system supported the previous model and moreover revealed an interface instability, leading the formation of steep steps, which is a reminiscence of the cyclic-steps observed during river-channel incision (Parker and Izumi 2000). We will present the dynamics of such granular steps. [1] Mangeney, A., O

  10. On the frequency dependence of the magnetic permeability of FeHfO thin films

    NARCIS (Netherlands)

    Bloemen, P.J.H.; Rulkens, B.

    1998-01-01

    The frequency dependence of the magnetic permeability as well as of the electrical impedance have been investigated for soft-magnetic granular FeHfO thin films. The impedance measurements indicate that capacitive effects resulting from the inhomogeneous structure of the layers are of no importance

  11. Heat capacity of amorphous and disordered Nb3Ge thin films

    International Nuclear Information System (INIS)

    Rao, N.A.H.K.

    1979-06-01

    Heat capacity measurements on 1000 to 1500A thick amorphous Nb 3 Ge and granular Al films have been carried out using an ac technique. The major goal of the experiment was to study the effect of thermal fluctuations, both above and below the superconducting transition temperature T/sub c/, in dirty, short meanfree path materials

  12. Magnetic properties of electroplated nano/microgranular NiFe thin films for rf application

    NARCIS (Netherlands)

    Zhuang, Y.; Vroubel, M.; Rejaei, B.; Burghartz, J.N.; Attenborough, K.

    2005-01-01

    A granular NiFe thin film with large in-plane magnetic anisotropy and high ferromagnetic-resonance frequency developed for radio-frequency integrated circuit (IC) applications is presented. During the deposition, three-dimensional (3D) growth occurs, yielding NiFe grains (? ? 1.0??m). Nanonuclei (?

  13. Synthesis and characterization of platinum thin film as top electrodes for multifunctional layer devices by PLD

    International Nuclear Information System (INIS)

    Coy, L.E.; Ventura, J.; Ferrater, C.; Langenberg, E.; Polo, M.C.; Garcia-Cuenca, M.V.; Varela, M.

    2010-01-01

    Platinum thin films were grown onto (001) oriented SrTiO 3 substrates by means of the pulsed laser deposition technique. Structural and morphological characterizations were performed using XRD and AFM. The influence of substrate temperature and deposition rate was analyzed on the crystallographic properties of the film. As a result, an increment in the crystallinity of the film due to the change on the temperature was observed. On the other hand, Pt films showed a granular morphology and its roughness was related to the fluence and low deposition temperature. Finally their electrical properties were analyzed and discussed as a function of the previous morphological results.

  14. Analysis of DuPont and Kodak duplicating films and chemistries in a Fultron spray processor

    Science.gov (United States)

    Weinstein, M. S.

    1972-01-01

    A test program was conducted with duPont duplicating film type SR 112 and SCOLOR developer and Kodak duplicating film types 2430, 2422, and FE 2628 (SO-467) and MX-641 developer to determine sensitometric and image quality characteristics of these materials when used with a fultron spray processor. The test results show that the SCOLOR developer foams excessively in the fultron processor when used with or without the addition of an antifoaming agent. The Kodak type FE 2628 film with MX-641 chemistry had the longest linear Log E range at a 1.0 gamma. Sensitometric curves and granularity traces for all film process combinations tested are included.

  15. Effect of aging on the microstructure of plasticized cornstarch films

    Directory of Open Access Journals (Sweden)

    Rossana M.S.M. Thiré

    2005-06-01

    Full Text Available Aging of cornstarch films prepared by casting was investigated. Water and glycerol-plasticized cornstarch films were stored at 50% relative humidity over a period of 330 days. Aging was followed by X-ray diffraction (XRD and atomic force microscopy (AFM. XRD spectra indicated development of B-type crystallinity even for fresh films and that the crystallinity index increased from 0.06 to 0.28 as a function of storage time. AFM images of 270-day-old films revealed that the general morphology and the overall roughness have not changed due to aging. AFM phase contrast images at higher magnification showed an increasing number of ordered domains at the surface of these films, which may be attributed to recrystallization of amylose. No morphological change was observed at least at the surface of the granular region, which is enriched in amylopectin.

  16. Functionalized granular activated carbon and surface complexation with chromates and bi-chromates in wastewater

    International Nuclear Information System (INIS)

    Singha, Somdutta; Sarkar, Ujjaini; Luharuka, Pallavi

    2013-01-01

    Cr(VI) is present in the aqueous medium as chromate (CrO 4 2− ) and bi-chromate (HCrO 4 − ). Functionalized granular activated carbons (FACs) are used as adsorbents in the treatment of wastewaters containing hexavalent chromium. The FACs are prepared by chemical modifications of granular activated carbons (GACs) using functionalizing agents like HNO 3 , HCl and HF. The Brunauer, Emmett and Teller surface areas of FAC-HCl (693.5 m 2 /g), FAC-HNO 3 (648.8 m 2 /g) and FAC-HF (726.2 m 2 /g) are comparable to the GAC (777.7 m 2 /g). But, the adsorption capacity of each of the FAC-HNO 3 , FAC-HCl and FAC-HF is found to be higher than the GAC. The functional groups play an important role in the adsorption process and pH has practically no role in this specific case. The FACs have hydrophilic protonated external surfaces in particular, along with the functional surface sites capable to make complexes with the CrO 4 2− and HCrO 4 − present. Surface complex formation is maximized in the order FAC-HNO 3 > FAC-HF > FAC-HCl, in proportion to the total surface acidity. This is also confirmed by the well-known pseudo second-order kinetic model. Physi-sorption equilibrium isotherms are parameterized by using standard Freundlich and Langmuir models. Langmuir fits better. The formation of surface complexes with the functional groups and hexavalent chromium is also revealed in the images of field emission scanning electron micrograph; energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy analysis after adsorption. The intra-particle diffusion is not the only rate-controlling factor. The Boyd's film diffusion model fits very well with R 2 as high as 98.1% for FAC-HNO 3 . This result demonstrates that the functionalization of the GAC by acid treatments would increase the diffusion rate, predominantly with a boundary layer diffusion effect. - Highlights: ► Physico-chemical adsorption using functionalized activated carbon (FACs) is applied. ► FACs

  17. Subglacial sediment mechanics investigated by computer simulation of granular material

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Tulaczyk, Slawek

    The mechanical properties of subglacial sediments are known to directly influence the stability of ice streams and fast-moving glaciers, but existing models of granular sediment deformation are poorly constrained. In addition, upscaling to generalized mathematical models is difficult due to the m......The mechanical properties of subglacial sediments are known to directly influence the stability of ice streams and fast-moving glaciers, but existing models of granular sediment deformation are poorly constrained. In addition, upscaling to generalized mathematical models is difficult due....... The numerical method is applied to better understand the mechanical properties of the subglacial sediment and its interaction with meltwater. The computational approach allows full experimental control and offers insights into the internal kinematics, stress distribution, and mechanical stability. During...

  18. Clustering impact regime with shocks in freely evolving granular gas

    Science.gov (United States)

    Isobe, Masaharu

    2017-06-01

    A freely cooling granular gas without any external force evolves from the initial homogeneous state to the inhomogeneous clustering state, at which the energy decay deviates from the Haff's law. The asymptotic behavior of energy in the inelastic hard sphere model have been predicted by several theories, which are based on the mode coupling theory or extension of inelastic hard rods gas. In this study, we revisited the clustering regime of freely evolving granular gas via large-scale molecular dynamics simulation with up to 16.7 million inelastic hard disks. We found novel regime regarding on collisions between "clusters" spontaneously appearing after clustering regime, which can only be identified more than a few million particles system. The volumetric dilatation pattern of semicircular shape originated from density shock propagation are well characterized on the appearing of "cluster impact" during the aggregation process of clusters.

  19. Revisiting Johnson and Jackson boundary conditions for granular flows

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tingwen; Benyahia, Sofiane

    2012-07-01

    In this article, we revisit Johnson and Jackson boundary conditions for granular flows. The oblique collision between a particle and a flat wall is analyzed by adopting the classic rigid-body theory and a more realistic semianalytical model. Based on the kinetic granular theory, the input parameter for the partial-slip boundary conditions, specularity coefficient, which is not measurable in experiments, is then interpreted as a function of the particle-wall restitution coefficient, the frictional coefficient, and the normalized slip velocity at the wall. An analytical expression for the specularity coefficient is suggested for a flat, frictional surface with a low frictional coefficient. The procedure for determining the specularity coefficient for a more general problem is outlined, and a working approximation is provided.

  20. Textile wastewater treatment: aerobic granular sludge vs activated sludge systems.

    Science.gov (United States)

    Lotito, Adriana Maria; De Sanctis, Marco; Di Iaconi, Claudio; Bergna, Giovanni

    2014-05-01

    Textile effluents are characterised by high content of recalcitrant compounds and are often discharged (together with municipal wastewater to increase their treatability) into centralized wastewater treatment plants with a complex treatment scheme. This paper reports the results achieved adopting a granular sludge system (sequencing batch biofilter granular reactor - SBBGR) to treat mixed municipal-textile wastewater. Thanks to high average removals in SBBGR (82.1% chemical oxygen demand, 94.7% total suspended solids, 87.5% total Kjeldahl nitrogen, 77.1% surfactants), the Italian limits for discharge into a water receiver can be complied with the biological stage alone. The comparison with the performance of the centralized plant treating the same wastewater has showed that SBBGR system is able to produce an effluent of comparable quality with a simpler treatment scheme, a much lower hydraulic residence time (11 h against 30 h) and a lower sludge production. Copyright © 2014 Elsevier Ltd. All rights reserved.

  1. Granular deformation mechanisms in semi-solid alloys

    International Nuclear Information System (INIS)

    Gourlay, C.M.; Dahle, A.K.; Nagira, T.; Nakatsuka, N.; Nogita, K.; Uesugi, K.; Yasuda, H.

    2011-01-01

    Deformation mechanisms in equiaxed, partially solid Al-15 wt.% Cu are studied in situ by coupling shear-cell experiments with synchrotron X-ray radiography. Direct evidence is presented for granular deformation mechanisms in both globular and equiaxed-dendritic samples at solid fractions shortly after crystal impingement. It is demonstrated that dilatancy, arching and jamming occur at the crystal scale, and that these can cause stick-slip flow due to periodic dilation and compaction at low displacement rate. Granular deformation is found to be similar in globular and equiaxed-dendritic samples if length is scaled by the crystal size and packing is considered to occur among crystal envelopes. Rheological differences between the morphologies are discussed in terms of the competition between crystal rearrangement and crystal deformation.

  2. Electromagnetic response of a highly granular hadronic calorimeter

    Energy Technology Data Exchange (ETDEWEB)

    Adloff, C.; Blaha, J.; Blaising, J.J. [Savoie Univ., CNRS/IN2P3, Annecy-le-Vieux (FR). Lab. d' Annecy-le-Vieux de Physique des Particules] (and others)

    2010-12-15

    The CALICE collaboration is studying the design of high performance electromagnetic and hadronic calorimeters for future International Linear Collider detectors. For the hadronic calorimeter, one option is a highly granular sampling calorimeter with steel as absorber and scintillator layers as active material. High granularity is obtained by segmenting the scintillator into small tiles individually read out via silicon photo-multipliers (SiPM). A prototype has been built, consisting of thirty-eight sensitive layers, segmented into about eight thousand channels. In 2007 the prototype was exposed to positrons and hadrons using the CERN SPS beam, covering a wide range of beam energies and incidence angles. The challenge of cell equalization and calibration of such a large number of channels is best validated using electromagnetic processes. The response of the prototype steel-scintillator calorimeter, including linearity and uniformity, to electrons is investigated and described. (orig.)

  3. Electromagnetic response of a highly granular hadronic calorimeter

    International Nuclear Information System (INIS)

    Adloff, C.; Blaha, J.; Blaising, J.J.

    2010-12-01

    The CALICE collaboration is studying the design of high performance electromagnetic and hadronic calorimeters for future International Linear Collider detectors. For the hadronic calorimeter, one option is a highly granular sampling calorimeter with steel as absorber and scintillator layers as active material. High granularity is obtained by segmenting the scintillator into small tiles individually read out via silicon photo-multipliers (SiPM). A prototype has been built, consisting of thirty-eight sensitive layers, segmented into about eight thousand channels. In 2007 the prototype was exposed to positrons and hadrons using the CERN SPS beam, covering a wide range of beam energies and incidence angles. The challenge of cell equalization and calibration of such a large number of channels is best validated using electromagnetic processes. The response of the prototype steel-scintillator calorimeter, including linearity and uniformity, to electrons is investigated and described. (orig.)

  4. Freely cooling granular gases with short-ranged attractive potentials

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Eric; Subramaniam, Shankar, E-mail: shankar@iastate.edu [Department of Mechanical Engineering, Center for Multiphase Flow Research, Iowa State University, Ames, Iowa 50011 (United States)

    2015-04-15

    We treat the case of an undriven gas of inelastic hard-spheres with short-ranged attractive potentials via an extension of the pseudo-Liouville operator formalism. New evolution equations for the granular temperature and coordination number are obtained. The granular temperature exhibits deviation from both Haff’s law and the case of long-ranged potentials. We verify this departure using soft-sphere discrete element method simulations. Excellent agreement is found for the duration of the simulation even beyond where exclusively binary collisions are expected. Simulations show the emergence of strong spatial-velocity correlations on the length scale of the last peak in the pair-correlation function but do not show strong correlations beyond this length scale. We argue that molecular chaos may remain an adequate approximation if the system is modelled as a Smoluchowski type equation with aggregation and break-up processes.

  5. Granular activated carbon assisted ozonation of cephalexin antibiotic

    International Nuclear Information System (INIS)

    Akhtar, J.; Amin, N.S.; Imran, M.

    2016-01-01

    This study investigates removal of cephalexin using ozonation in the presence of granular activated carbon. Initial experiments were carried out about adsorption of cephalexin onto granular activated carbon, effect of catalytic ozonation, and biodegradability of cephalexin solution. The effect of ozonation on pH, ozone utilization efficiency and decomposition byproducts, was observed. Response surface methodology was adopted to optimize three operating parameters pH of solution, ozone supply and cephalexin concentration. GAC assisted ozonation, was found to be effective in decomposing COD (chemical oxygen demand) and cephalexin from solution. Optimum values of variables were pH from 7-8, ozone supply 30 mg/L and 100 mg/L of cephalexin solution. The complete removal of cephalexin and 60% COD removal was achieved at these optimum input values. (author)

  6. DEM simulation of granular flows in a centrifugal acceleration field

    Science.gov (United States)

    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

  7. Oscillatory Dynamics of One-Dimensional Homogeneous Granular Chains

    Science.gov (United States)

    Starosvetsky, Yuli; Jayaprakash, K. R.; Hasan, Md. Arif; Vakakis, Alexander F.

    The acoustics of the homogeneous granular chains has been studied extensively both numerically and experimentally in the references cited in the previous chapters. This chapter focuses on the oscillatory behavior of finite dimensional homogeneous granular chains. It is well known that normal vibration modes are the building blocks of the vibrations of linear systems due to the applicability of the principle of superposition. One the other hand, nonlinear theory is deprived of such a general superposition principle (although special cases of nonlinear superpositions do exist), but nonlinear normal modes ‒ NNMs still play an important role in the forced and resonance dynamics of these systems. In their basic definition [1], NNMs were defined as time-periodic nonlinear oscillations of discrete or continuous dynamical systems where all coordinates (degrees-of-freedom) oscillate in-unison with the same frequency; further extensions of this definition have been considered to account for NNMs of systems with internal resonances [2]...

  8. The calculation of resonance capture in granular fuels

    Energy Technology Data Exchange (ETDEWEB)

    Askew, J R; Harris, D W.G.; Hutton, J L

    1971-02-15

    The methods used in the UK for the calculation of resonance capture in granular HTR fuels follow the long established path of determining a 'geometric equivalence' which equates the resonance shielding to that in a homogeneous mixture of the resonance absorber in hydrogen. Simple collision probability arguments, usually for the black limit, were used for AGR and SGHW systems. For granular fuel a 'grey' equivalence, convenient for numerical use, has been adopted, and the geometric solution performed in two ways: by a synthetic collision probability model which is rapid and appropriate for design work and by a Monte Carlo model which allows details of the grain lattice structure to be studied. The results are in good agreement, and are shown to give good results compared with measured relative conversion ratios in the NESTOR stack experiments.

  9. Modeling compaction-induced energy dissipation of granular HMX

    Energy Technology Data Exchange (ETDEWEB)

    Gonthier, K.A. [Lamar Univ., Beaumont, TX (US). Dept. of Mechanical Engineering; Menikoff, R.; Son, S.F.; Asay, B.W. [Los Alamos National Lab., NM (US)

    1998-12-31

    A thermodynamically consistent model is developed for the compaction of granular solids. The model is an extension of the single phase limit of two-phase continuum models used to describe Deflagration-to-Detonation Transition (DDT) experiments. The focus is on the energetics and dissipation of the compaction process. Changes in volume fraction are partitioned into reversible and irreversible components. Unlike conventional DDT models, the model is applicable from the quasi-static to dynamic compaction regimes for elastic, plastic, or brittle materials. When applied to the compaction of granular HMX (a brittle material), the model predicts results commensurate with experiments including stress relaxation, hysteresis, and energy dissipation. The model provides a suitable starting point for the development of thermal energy localization sub-scale models based on compaction-induced dissipation.

  10. The nature of quasistatic deformation in granular materials

    OpenAIRE

    ROUX, JN

    2005-01-01

    Strain in granular materials in quasistatic conditions under varying stress originate in (I) contact deformation and (II) rearrangements of the contact network. Depending on sample history and applied load, eiter mechanism might dominate. One may thus define rheological regimes I and II accordingly. Their porperties are presented and illustrated here with discrete numerical simulatiion results in 2 and 3 dimensions. This discussion of the microscopic physical origin of strain is shown to clar...

  11. Dynamical Heterogeneity in Granular Fluids and Structural Glasses

    Science.gov (United States)

    Avila, Karina E.

    Our current understanding of the dynamics of supercooled liquids and other similar slowly evolving (glassy) systems is rather limited. One aspect that is particularly poorly understood is the origin and behavior of the strong non trivial fluctuations that appear in the relaxation process toward equilibrium. Glassy systems and granular systems both present regions of particles moving cooperatively and at different rates from other regions. This phenomenon is known as spatially heterogeneous dynamics. A detailed explanation of this phenomenon may lead to a better understanding of the slow relaxation process, and perhaps it could even help to explain the presence of the glass transition. This dissertation concentrates on studying dynamical heterogeneity by analyzing simulation data for models of granular materials and structural glasses. For dissipative granular fluids, the growing behavior of dynamical heterogeneities is studied for different densities and different degrees of inelasticity in the particle collisions. The correlated regions are found to grow rapidly as the system approaches dynamical arrest. Their geometry is conserved even when probing at different cutoff length in the correlation function or when the energy dissipation in the system is increased. For structural glasses, I test a theoretical framework that models dynamical heterogeneity as originated in the presence of Goldstone modes, which emerge from a broken continuous time reparametrization symmetry. This analysis is based on quantifying the size and the spatial correlations of fluctuations in the time variable and of other kinds of fluctuations. The results obtained here agree with the predictions of the hypothesis. In particular, the fluctuations associated to the time reparametrization invariance become stronger for low temperatures, long timescales, and large coarse graining lengths. Overall, this research points to dynamical heterogeneity to be described for granular systems similarly than

  12. Microgravity experiments on a granular gas of elongated grains

    Science.gov (United States)

    Harth, K.; Trittel, T.; Kornek, U.; Höme, S.; Will, K.; Strachauer, U.; Stannarius, R.

    2013-06-01

    Granular gases represent well-suited systems to investigate statistical granular dynamics. The literature comprises numerous investigations of ensembles of spherical or irregularly shaped grains. Mainly computer models, analytical theories and experiments restricted to two dimensions were reported. In three-dimensions, the gaseous state can only be maintained by strong external excitation, e. g. vibrations or electro-magnetic fields, or in microgravity. A steady state, where the dynamics of a weakly disturbed granular gas are governed by particle-particle collisions, is hard to realize with spherical grains due to clustering. We present the first study of a granular gas of elongated cylinders in three dimensions. The mean free path is considerably reduced with respect to spheres at comparable filling fractions. The particles can be tracked in 3D over a sequence of frames. In a homogeneous steady state, we find non-Gaussian velocity distributions and a lack of equipartition of kinetic energy. We discuss the relations between energy input and vibrating plate accelerations. At the request of the authors and the Proceedings Editors, the PDF file of this article has been updated to amend some references present in the PDF file submitted to AIP Publishing. The references affected are listed here:[1] (c) K. Nichol and K. E. Daniels, Phys. Rev. Lett. 108, 018001 (2012); [11] (e) P. G. de Gennes and J. Prost, The Physics of Liquid Crystals, Clarendon Press, Oxford (1993); [17] (b) K. Harth, et al., Phys. Rev. Lett. 110, 144102 (2013).A LaTeX processing error resulted in changes to the authors reference formatting, which was not detected prior to publication. Due apologies are given to the authors for this oversight. The updated article PDF was published on 12 August 2013.

  13. Fragility and hysteretic creep in frictional granular jamming.

    Science.gov (United States)

    Bandi, M M; Rivera, M K; Krzakala, F; Ecke, R E

    2013-04-01

    The granular jamming transition is experimentally investigated in a two-dimensional system of frictional, bidispersed disks subject to quasistatic, uniaxial compression without vibrational disturbances (zero granular temperature). Three primary results are presented in this experimental study. First, using disks with different static friction coefficients (μ), we experimentally verify numerical results that predict jamming onset at progressively lower packing fractions with increasing friction. Second, we show that the first compression cycle measurably differs from subsequent cycles. The first cycle is fragile-a metastable configuration with simultaneous jammed and unjammed clusters-over a small packing fraction interval (φ(1)disk displacements over the same packing fraction interval. This fragile behavior is explained through a percolation mechanism of stressed contacts where cluster growth exhibits spatial correlation with disk displacements and contributes to recent results emphasizing fragility in frictional jamming. Control experiments show that the fragile state results from the experimental incompatibility between the requirements for zero friction and zero granular temperature. Measurements with several disk materials of varying elastic moduli E and friction coefficients μ show that friction directly controls the start of the fragile state but indirectly controls the exponential pressure rise. Finally, under repetitive loading (compression) and unloading (decompression), we find the system exhibits pressure hysteresis, and the critical packing fraction φ(c) increases slowly with repetition number. This friction-induced hysteretic creep is interpreted as the granular pack's evolution from a metastable to an eventual structurally stable configuration. It is shown to depend on the quasistatic step size Δφ, which provides the only perturbative mechanism in the experimental protocol, and the friction coefficient μ, which acts to stabilize the pack.

  14. Stretched exponentials and power laws in granular avalanching

    Science.gov (United States)

    Head, D. A.; Rodgers, G. J.

    1999-02-01

    We introduce a model for granular surface flow which exhibits both stretched exponential and power law avalanching over its parameter range. Two modes of transport are incorporated, a rolling layer consisting of individual particles and the overdamped, sliding motion of particle clusters. The crossover in behaviour observed in experiments on piles of rice is attributed to a change in the dominant mode of transport. We predict that power law avalanching will be observed whenever surface flow is dominated by clustered motion.

  15. Study on the runout of granular columns with SPH methods.

    OpenAIRE

    He, Xuzhen; Liang, Dongfang

    2015-01-01

    Landslides are catastrophic geophysical phenomena, which may cause heavy fatality and property losses. Hence, it is of vital importance to understand their mechanisms and evaluate their travel distance, so that appropriate measures can be taken to mitigate their risk. This paper reports on an application of the incompressible Smoothed Particle Hydrodynamics (SPH) method to the simulation of the collapse of granular columns onto the planes of different slopes, which is similar to dry landslide...

  16. Magnetic irreversibility in granular superconductors: ac susceptibility study

    International Nuclear Information System (INIS)

    Perez, F.; Obradors, X.; Fontcuberta, J.; Vallet, M.; Gonzalez-Calbet, J.

    1991-01-01

    Ac susceptibility measurements of a ceramic weak-coupled superconductor in very low ac fields (2mG, 111Hz) are reported. We present evidence for the observation of the magnetic irreversibility following a ZFC-FC thermal cycling by means of ac susceptibilty measurements. It is shown that this technique also reflect local magnetic field effects in granular superconductors, as previously suggested in microwave surface resistance and I-V characteristics. (orig.)

  17. Biogas pre-upgrading by adsorption of trace compounds onto granular activated carbons and an activated carbon fiber-cloth.

    Science.gov (United States)

    Boulinguiez, B; Le Cloirec, P

    2009-01-01

    The study assesses the adsorption onto activated carbon materials of selected volatile organic compounds -VOCs- (dichloromethane, 2-propanol, toluene, siloxane D4) in a biogas matrix composed of methane and carbon dioxide (55:45 v/v). Three different adsorbents are tested, two of them are granular activated carbon (GAC), and the last is an activated carbon fiber-cloth (ACFC). The adsorption isotherm data are fitted by different models by nonlinear regression. The Langmuir-Freundlich model appears to be the adequate one to describe the adsorption phenomena independently of the VOC considered or the adsorbent. The adsorbents present attractive adsorption capacity of the undesirable compounds in biogas atmosphere though the maximum adsorption capacities for a VOC are quite different from each other. The adsorption kinetics are characterized through three coefficients: the initial adsorption coefficient, the external film mass transfer coefficient and the internal diffusion coefficient of Weber. The ACFC demonstrates advanced kinetic yields compared to the granular activated carbon materials whatever VOC is considered. Therefore, pre-upgrading of biogas produced from wastewater sludge or co-digestion system by adsorption onto activated carbon appears worth investigating. Especially with ACFC material that presents correct adsorption capacities toward VOCs and concrete regeneration process opportunity to realize such process.

  18. Thin films

    International Nuclear Information System (INIS)

    Strongin, M.; Miller, D.L.

    1976-01-01

    This article reviews the phenomena that occur in films from the point of view of a solid state physicist. Films form the basis for many established and developing technologies. Metal layers have always been important for optical coatings and as protective coatings. In the most sophisticated cases, films and their interaction on silicon surfaces form the basis of modern electronic technology. Films of silicon, GaAs and composites of these materials promise to lead to practical photovoltaic devices

  19. Structural evolution of a granular medium during simultaneous penetration

    Science.gov (United States)

    González-Gutiérrez, Jorge; Carreón, Yojana J. P.; Moctezuma, R. E.

    2018-01-01

    Typically, fluidized beds are granular systems composed of solid particles through which a fluid flows. They are relevant to a wide variety of disciplines such as physics, chemistry, engineering, among others. Generally, the fluidized beds are characterized by different flow regimes such as particulate, bubbling, slugging, turbulent, fast fluidization, and pneumatic conveying. Here, we report the experimental study of the structural evolution of a granular system due to simultaneous penetration of intruders in the presence of an upward airflow. We found that the granular medium evolves from the static state to the turbulent regime showing the coexistence of three regions in different flow regimes. Interestingly, the cooperative dynamic of intruders correlate with the formation of such regions. As a non-invasive method, we use lacunarity and fractal dimension to quantitatively describe the patterns arising within the system during the different stages of the penetration process. Finally, we found that our results would allow us to relate the evolution of the visual patterns appearing in the process with different physical properties of the system.

  20. Scattering of waves by impurities in precompressed granular chains.

    Science.gov (United States)

    Martínez, Alejandro J; Yasuda, Hiromi; Kim, Eunho; Kevrekidis, P G; Porter, Mason A; Yang, Jinkyu

    2016-05-01

    We study scattering of waves by impurities in strongly precompressed granular chains. We explore the linear scattering of plane waves and identify a closed-form expression for the reflection and transmission coefficients for the scattering of the waves from both a single impurity and a double impurity. For single-impurity chains, we show that, within the transmission band of the host granular chain, high-frequency waves are strongly attenuated (such that the transmission coefficient vanishes as the wavenumber k→±π), whereas low-frequency waves are well-transmitted through the impurity. For double-impurity chains, we identify a resonance-enabling full transmission at a particular frequency-in a manner that is analogous to the Ramsauer-Townsend (RT) resonance from quantum physics. We also demonstrate that one can tune the frequency of the RT resonance to any value in the pass band of the host chain. We corroborate our theoretical predictions both numerically and experimentally, and we directly observe almost complete transmission for frequencies close to the RT resonance frequency. Finally, we show how this RT resonance can lead to the existence of reflectionless modes in granular chains (including disordered ones) with multiple double impurities.

  1. Granular filtration for airborne particles : correlation between experiments and models

    Energy Technology Data Exchange (ETDEWEB)

    Golshahi, L.; Tan, Z. [Calgary Univ., AB (Canada). Schulich School of Engineering, Mechanical and Manufacturing Dept.; Abedi, J. [Calgary Univ., AB (Canada). Schulich School of Engineering, Chemical and Petroleum Engineering Dept.

    2009-10-15

    A new design for a packed bed granular filter was presented. The cylindrical packed bed was designed to filter particles in the range of approximately 10 nm to 15 {mu}m in diameter in different kinetic conditions and configurations. The aim of the study was to develop a precise empirical model to predict the filtration efficiency of the packed beds. A collision-type atomizer was used to generate polydisperse sodium chloride aerosol particles. The effect of flow rates was studied using a thermal mass flow meter. A regression analysis technique was used to determine the correlation between single granule and total packed bed efficiency for the entire granular filter. The experimental data were then compared with results obtained from the theoretical analysis. The least square method was used to correlate experimental data and to develop generalized equations for single granule efficiency. The study showed that the granular filter media has a high filtration efficiency for both micron and submicron particles. It was concluded that the effect of media thickness was more significant at higher flow rates than at lower flow rates. 10 refs., 3 figs.

  2. Robophysical study of jumping dynamics on granular media

    Science.gov (United States)

    Aguilar, Jeffrey; Goldman, Daniel I.

    2016-03-01

    Characterizing forces on deformable objects intruding into sand and soil requires understanding the solid- and fluid-like responses of such substrates and their effect on the state of the object. The most detailed studies of intrusion in dry granular media have revealed that interactions of fixed-shape objects during free impact (for example, cannonballs) and forced slow penetration can be described by hydrostatic- and hydrodynamic-like forces. Here we investigate a new class of granular interactions: rapid intrusions by objects that change shape (self-deform) through passive and active means. Systematic studies of a simple spring-mass robot jumping on dry granular media reveal that jumping performance is explained by an interplay of nonlinear frictional and hydrodynamic drag as well as induced added mass (unaccounted by traditional intrusion models) characterized by a rapidly solidified region of grains accelerated by the foot. A model incorporating these dynamics reveals that added mass degrades the performance of certain self-deformations owing to a shift in optimal timing during push-off. Our systematic robophysical experiment reveals both new soft-matter physics and principles for robotic self-deformation and control, which together provide principles of movement in deformable terrestrial environments.

  3. NMR experiments on a three-dimensional vibrofluidized granular medium

    Science.gov (United States)

    Huan, Chao; Yang, Xiaoyu; Candela, D.; Mair, R. W.; Walsworth, R. L.

    2004-04-01

    A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient NMR coupled with one-dimensional magnetic resonance imaging. The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers Nl⩽4 was sufficiently low to achieve a nearly time-independent granular fluid. Using NMR, the vertical profiles of density and granular temperature were directly measured, along with the distributions of vertical and horizontal grain velocities. The velocity distributions showed modest deviations from Maxwell-Boltzmann statistics, except for the vertical velocity distribution near the sample bottom, which was highly skewed and non-Gaussian. Data taken for three values of Nl and two dimensionless accelerations Γ=15,18 were fitted to a hydrodynamic theory, which successfully models the density and temperature profiles away from the vibrating container bottom. A temperature inversion near the free upper surface is observed, in agreement with predictions based on the hydrodynamic parameter μ which is nonzero only in inelastic systems.

  4. Jamming and chaotic dynamics in different granular systems

    Science.gov (United States)

    Maghsoodi, Homayoon; Luijten, Erik

    Although common in nature and industry, the jamming transition has long eluded a concrete, mechanistic explanation. Recently, Banigan et al. (Nat. Phys. 9, 288-292, 2013) proposed a method for characterizing this transition in a granular system in terms of the system's chaotic properties, as quantified by the largest Lyapunov exponent. They demonstrated that in a two-dimensional shear cell the jamming transition coincides with the bulk density at which the system's largest Lyapunov exponent changes sign, indicating a transition between chaotic and non-chaotic regimes. To examine the applicability of this observation to realistic granular systems, we study a model that includes frictional forces within an expanded phase space. Furthermore, we test the generality of the relation between chaos and jamming by investigating the relationship between jamming and the chaotic properties of several other granular systems, notably sheared systems (Howell, D., Behringer R. P., Veje C., Phys. Rev. Lett. 82, 5241-5244, 1999) and systems with a free boundary. Finally, we quantify correlations between the largest Lyapunov vector and collective rearrangements of the system to demonstrate the predictive capabilities enabled by adopting this perspective of jamming.

  5. Analysis of Cylindrical Granular Material Silos under Seismic Excitation

    Directory of Open Access Journals (Sweden)

    Christoph Butenweg

    2017-07-01

    Full Text Available Silos generally work as storage structures between supply and demand for various goods, and their structural safety has long been of interest to the civil engineering profession. This is especially true for dynamically loaded silos, e.g., in case of seismic excitation. Particularly thin-walled cylindrical silos are highly vulnerable to seismic induced pressures, which can cause critical buckling phenomena of the silo shell. The analysis of silos can be carried out in two different ways. In the first, the seismic loading is modeled through statically equivalent loads acting on the shell. Alternatively, a time history analysis might be carried out, in which nonlinear phenomena due to the filling as well as the interaction between the shell and the granular material are taken into account. The paper presents a comparison of these approaches. The model used for the nonlinear time history analysis considers the granular material by means of the intergranular strain approach for hypoplasticity theory. The interaction effects between the granular material and the shell is represented by contact elements. Additionally, soil–structure interaction effects are taken into account.

  6. An update on blast furnace granular coal injection

    Energy Technology Data Exchange (ETDEWEB)

    Hill, D.G. [Bethlehem Steel Corp., Burns Harbor, IN (United States); Strayer, T.J.; Bouman, R.W. [Bethlehem Steel Corp., PA (United States)

    1997-12-31

    A blast furnace coal injection system has been constructed and is being used on the furnace at the Burns Harbor Division of Bethlehem Steel. The injection system was designed to deliver both granular (coarse) and pulverized (fine) coal. Construction was completed on schedule in early 1995. Coal injection rates on the two Burns Harbor furnaces were increased throughout 1995 and was over 200 lbs/ton on C furnace in September. The injection rate on C furnace reached 270 lbs/ton by mid-1996. A comparison of high volatile and low volatile coals as injectants shows that low volatile coal replaces more coke and results in a better blast furnace operation. The replacement ratio with low volatile coal is 0.96 lbs coke per pound of coal. A major conclusion of the work to date is that granular coal injection performs very well in large blast furnaces. Future testing will include a processed sub-bituminous coal, a high ash coal and a direct comparison of granular versus pulverized coal injection.

  7. Investigations on a hybrid positron source with a granular converter

    Energy Technology Data Exchange (ETDEWEB)

    Artru, X. [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Chaikovska, I. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Chehab, R., E-mail: chehab@lal.in2p3.fr [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Chevallier, M. [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Dadoun, O. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Furukawa, K. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Guler, H. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Kamitani, T.; Miyahara, F.; Satoh, M. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Sievers, P. [CERN, Geneva (Switzerland); Suwada, T.; Umemori, K. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Variola, A. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France)

    2015-07-15

    Promising results obtained with crystal targets for positron production led to the elaboration of a hybrid source made of an axially oriented tungsten crystal, as a radiator, and an amorphous tungsten converter. If the converter is granular, made of small spheres, the heat dissipation is greatly enhanced and the thermal shocks reduced, allowing the consideration of such device for the future linear colliders. A positron source of this kind is investigated. Previous simulations have shown very promising results for the yield as for the energy deposition and the PEDD (Peak Energy Deposition Density). Here, we present detailed simulations made in this granular converter with emphasis on the energy deposition density, which is a critical parameter as learned from the breakdown of the SLC target. A test on the KEKB linac is foreseen; it will allow a determination of the energy deposited and the PEDD in the converter through temperature measurements. Four granular converters, made of W spheres of mm radius have been built at LAL-Orsay; they will be installed at KEK and compared to compact converters. A description of the experimental layout at KEK is provided. Applications to future linear colliders as CLIC and ILC are considered.

  8. Recent advances in understanding deformation and flow of granular matter

    Directory of Open Access Journals (Sweden)

    Mesarović Siniša Đ.

    2014-01-01

    Full Text Available By means of graph theory, we analyze the changes in topology of a granular assembly during deformation. The elementary mechanism of diffuse deformation consists of intermittent flips. We show that dilatancy is the direct result of: an increasing number of flips, and, elastic relaxation of particles upon flips. Both are dependent on particles' elastic potential energy prior to flip and after the flip. The latter is the result of non uniform distribution of interparticle forces in force chains. Next, we consider shear bands in granular materials. Formation of shear bands is accompanied by accompanied by massive rolling of particle. Since rolling is constrained by neighbors, a characteristic rolling correlation length appears. The transmission of rotations in a particular direction depends on the strength of the force chain branches in the direction of propagation and across. The maximum propagation distance is comparable to observed widths of shear bands. Finally, we turn to the question of vortex formation within shear bands and argue that vortex pattern minimizes the dissipation/resistance in granular fluid.

  9. Nuclear films

    International Nuclear Information System (INIS)

    Malone, Peter.

    1985-01-01

    This booklet is a resource for the study of feature films that highlight the theme of nuclear war. It provides basic credits and brief indication of the theme, treatment, quality and particular notable aspects; and a series of questions raised by the film. Seventy feature films and thirty documentaries are examined

  10. Bedrock erosion by sliding wear in channelized granular flow

    Science.gov (United States)

    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

  11. Numerical Simulations of Granular Physics in the Solar System

    Science.gov (United States)

    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

  12. Statistical and visual probing of evolving granular assemblies

    International Nuclear Information System (INIS)

    Smith, Laurence M.

    2002-01-01

    The majority of processes in the chemical and allied industries involve the storage and conveyancing of granular material, the physics of which is still not particularly well understood. Whilst some non-invasive techniques have been developed, much experimental work unfortunately interferes with the fields being investigated. For this reason and in conjunction with increasing computing power, there has been an increase in simulation based studies. Granular dynamics simulations, being based upon inter-particle interaction laws, give the potential to investigate assemblies at the 'micro-level' and have been successful in modelling process conditions in a number of granular flow situations. To date, most analyses of these simulations are essentially static in nature involving 'time snapshots'. However, in a granular dynamics simulation there is a wealth of data available on a time referenced basis which has the potential to allow a quantitative analysis of the dynamics of assembly evolution. This dissertation describes the development and application of a toolkit for post-simulation analysis. However, the utilities within the toolkit would be equally applicable to large experimental data sets should such data sets exist. The application of the toolset focuses largely on the dynamics of heap evolution in both 2D and 3D with some supportive 3D work on hopper discharge. A major part of the work involves the application of time series techniques (including the wavelet transform) in the context of variable coupling during avalanching. Segregation by self-diffusion receives particular attention and a new mechanism is proposed by which segregation by particle size takes place in the boundary layer of a low impact feed heap displaying a clear velocity gradient during discrete avalanching. Periodic lateral surging is shown to enforce mixing for a high impact feed, a phenomenon which appears to switch off below a certain feed impact. Segregation by self-diffusion is also shown

  13. Post-annealing effects on pulsed laser deposition-grown GaN thin films

    International Nuclear Information System (INIS)

    Cheng, Yu-Wen; Wu, Hao-Yu; Lin, Yu-Zhong; Lee, Cheng-Che; Lin, Ching-Fuh

    2015-01-01

    In this work, the post-annealing effects on gallium nitride (GaN) thin films grown from pulsed laser deposition (PLD) are investigated. The as-deposited GaN thin films grown from PLD are annealed at different temperatures in nitrogen ambient. Significant changes of the GaN crystal properties are observed. Raman spectroscopy is used to observe the crystallinity, the change of residual stress, and the thermal decomposition of the annealed GaN thin films. X-ray diffraction is also applied to identify the crystal phase of GaN thin films, and the surface morphology of GaN thin films annealed at different temperatures is observed by scanning electron microscopy. Through the above analyses, the GaN thin films grown by PLD undergo three stages: phase transition, stress alteration, and thermal decomposition. At a low annealing temperature, the rock salt GaN in GaN films is transformed into wurtzite. The rock salt GaN diminishes with increasing annealing temperature. At a medium annealing temperature, the residual stress of the film changes significantly from compressive strain to tensile strain. As the annealing temperature further increases, the GaN undergoes thermal decomposition and the surface becomes granular. By investigating the annealing temperature effects and controlling the optimized annealing temperature of the GaN thin films, we are able to obtain highly crystalline and strain-free GaN thin films by PLD. - Highlights: • The GaN thin film is grown on sapphire by pulsed laser deposition. • The GaN film undergoes three stages with increasing annealing temperature. • In the first stage, the film transfers from rock salt to wurtzite phase. • In the second stage, the stress in film changes from compressive to tensile. • In the final stage, the film thermally decomposes and becomes granular

  14. Failure evolution in granular material retained by rigid wall in active mode

    Science.gov (United States)

    Pietrzak, Magdalena; Leśniewska, Danuta

    2012-10-01

    This paper presents a detailed study of a selected small scale model test, performed on a sample of surrogate granular material, retained by a rigid wall (typical geotechnical problem of earth thrust on a retaining wall). The experimental data presented in this paper show that the deformation of granular sample behind retaining wall can undergo some cyclic changes. The nature of these cycles is not clear - it is probably related to some micromechanical features of granular materials, which are recently extensively studied in many research centers in the world. Employing very precise DIC (PIV) method can help to relate micro and macro-scale behavior of granular materials.

  15. Analogy between electrochemical behaviour of thick silicon granular electrodes for lithium batteries and fine soils micromechanics

    International Nuclear Information System (INIS)

    Nguyen, B.P.N.; Gaubicher, J.; Lestriez, B.

    2014-01-01

    In this paper we study the influence of the distribution and the shape of the carbon conductive additives on the cyclability of thick silicon based composite electrodes. Results pinpoint the influence of carbon additives is not only to play on the electronic conductivity but also to play on the micromechanics (stress distribution) of the composite films. The lack of correlation between electrochemical performance and the macroscopic electronic conductivity of the pristine electrodes and the observation of repeated drops and jumps in capacity during cycling brought us to make an analogy between the silicon composite electrodes and cohesive granular materials such as fine soils media. Considering the collective mechanical behavior of a stack of silicon particles upon repeated volume variations shed a novel understanding to the electrochemical behavior of composite electrodes based on silicon and alloying materials and tells us how critically important is the design at the different scales (the particle, a few particles, the composite electrode, the cell) to engineer the mechanical stress and strain and improve cycle life

  16. Adsorption of selected pharmaceuticals and an endocrine disrupting compound by granular activated carbon. 2. Model prediction

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Z.; Peldszus, S.; Huck, P.M. [University of Waterloo, Waterloo, ON (Canada). NSERC Chair in Water Treatment

    2009-03-01

    The adsorption of two representative pharmaceutically active compounds (PhACs) naproxen and carbamazepine and one endocrine disrupting compound (EDC) nonylphenol was studied in pilot-scale granular activated carbon (GAC) adsorbers using post-sedimentation (PS) water from a full-scale drinking water treatment plant. The GAC adsorbents were coal-based Calgon Filtrasorb 400 and coconut shell-based PICA CTIF TE. Acidic naproxen broke through fastest while nonylphenol was removed best, which was consistent with the degree to which fouling affected compound removals. Model predictions and experimental data were generally in good agreement for all three compounds, which demonstrated the effectiveness and robustness of the pore and surface diffusion model (PSDM) used in combination with the time-variable parameter approach for predicting removals at environmentally relevant concentrations (i.e., ng/L range). Sensitivity analyses suggested that accurate determination of film diffusion coefficients was critical for predicting breakthrough for naproxen and carbamazepine, in particular when high removals are targeted. Model simulations demonstrated that GAC carbon usage rates (CURs) for naproxen were substantially influenced by the empty bed contact time (EBCT) at the investigated conditions. Model-based comparisons between GAC CURs and minimum CURs for powdered activated carbon (PAC) applications suggested that PAC would be most appropriate for achieving 90% removal of naproxen, whereas GAC would be more suitable for nonylphenol. 25 refs., 4 figs., 1 tab.

  17. A comparison of aerobic granular sludge with conventional and compact biological treatment technologies.

    Science.gov (United States)

    Bengtsson, Simon; de Blois, Mark; Wilén, Britt-Marie; Gustavsson, David

    2018-03-20

    The aerobic granular sludge (AGS) technology is growing towards becoming a mature option for new municipal wastewater treatment plants and capacity extensions. A process based on AGS was compared to conventional activated sludge processes (with and without enhanced biological phosphorus removal), an integrated fixed-film activated sludge (IFAS) process and a membrane bioreactor (MBR) by estimating the land area demand (footprint), electricity demand and chemicals' consumption. The process alternatives compared included pre-settling, sludge digestion and necessary post-treatment to achieve effluent concentrations of 8 mg/L nitrogen and 0.2 mg/L phosphorus at 7°C. The alternative based on AGS was estimated to have a 40-50% smaller footprint and 23% less electricity requirement than conventional activated sludge. In relation to the other compact treatment options IFAS and MBR, the AGS process had an estimated electricity usage that was 35-70% lower. This suggests a favourable potential for processes based on AGS although more available experience of AGS operation and performance at full scale is desired.

  18. Large granular lymphocytic leukaemia complicated with histiocytic sarcoma in a dog : clinical communication

    Directory of Open Access Journals (Sweden)

    T. Maruo

    2009-05-01

    Full Text Available A 10-year-old castrated male Golden retriever, weighing 36.3 kg was referred for evaluation owing to a decline in general condition. Findings from the complete blood count revealed a marked lymphocytosis (113 000/µℓ. Examination of Wright-Giemsa-stained films of peripheral blood revealed the presence of large granular lymphocytes (LGL. Seventy-two per cent (81 360/µℓ of the lymphocytes were found to be 12-17 µm in diameter, containing nuclei with mature clumped chromatin and abundant lightly basophilic cytoplasm with a variable number of fine azurophilic granules. Based on these findings this case was diagnosed as LGL leukaemia. As a result of multiple-agent chemotherapy, the markedly elevated levels of lymphocytes gradually decreased to 7500/µℓ on day 122 and the patient maintained a good quality of life for the following 3 months. However, on around day 237, a soft, raised, bosselated mass on the labial region was noted. The dog was diagnosed as having histiocytic sarcoma based on cytological and histological examination of the mass. Shortly after diagnosis, the dog developed sudden onset of central nervous system signs and died on day 270. A common outcome of canine LGL is the development of acute blast crisis or lymphoma. However, this case was notable for complication with histiocytic sarcoma from another origin.

  19. Controlling mixing and segregation in time periodic granular flows

    Science.gov (United States)

    Bhattacharya, Tathagata

    Segregation is a major problem for many solids processing industries. Differences in particle size or density can lead to flow-induced segregation. In the present work, we employ the discrete element method (DEM)---one type of particle dynamics (PD) technique---to investigate the mixing and segregation of granular material in some prototypical solid handling devices, such as a rotating drum and chute. In DEM, one calculates the trajectories of individual particles based on Newton's laws of motion by employing suitable contact force models and a collision detection algorithm. Recently, it has been suggested that segregation in particle mixers can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. Further, it has been hypothesized that, for a rotating drum, the effectiveness of this technique can be linked to the probability distribution of the number of times a particle passes through the flowing layer per rotation of the drum. In the first portion of this work, various configurations of solid mixers are numerically and experimentally studied to investigate the conditions for improved mixing in light of these hypotheses. Besides rotating drums, many studies of granular flow have focused on gravity driven chute flows owing to its practical importance in granular transportation and to the fact that the relative simplicity of this type of flow allows for development and testing of new theories. In this part of the work, we observe the deposition behavior of both mono-sized and polydisperse dry granular materials in an inclined chute flow. The effects of different parameters such as chute angle, particle size, falling height and charge amount on the mass fraction distribution of granular materials after deposition are investigated. The simulation results obtained using DEM are compared with the experimental findings and a high degree of agreement is observed. Tuning of the underlying contact force parameters allows the achievement

  20. Acquisition and Retaining Granular Samples via a Rotating Coring Bit

    Science.gov (United States)

    Bar-Cohen, Yoseph; Badescu, Mircea; Sherrit, Stewart

    2013-01-01

    This device takes advantage of the centrifugal forces that are generated when a coring bit is rotated, and a granular sample is entered into the bit while it is spinning, making it adhere to the internal wall of the bit, where it compacts itself into the wall of the bit. The bit can be specially designed to increase the effectiveness of regolith capturing while turning and penetrating the subsurface. The bit teeth can be oriented such that they direct the regolith toward the bit axis during the rotation of the bit. The bit can be designed with an internal flute that directs the regolith upward inside the bit. The use of both the teeth and flute can be implemented in the same bit. The bit can also be designed with an internal spiral into which the various particles wedge. In another implementation, the bit can be designed to collect regolith primarily from a specific depth. For that implementation, the bit can be designed such that when turning one way, the teeth guide the regolith outward of the bit and when turning in the opposite direction, the teeth will guide the regolith inward into the bit internal section. This mechanism can be implemented with or without an internal flute. The device is based on the use of a spinning coring bit (hollow interior) as a means of retaining granular sample, and the acquisition is done by inserting the bit into the subsurface of a regolith, soil, or powder. To demonstrate the concept, a commercial drill and a coring bit were used. The bit was turned and inserted into the soil that was contained in a bucket. While spinning the bit (at speeds of 600 to 700 RPM), the drill was lifted and the soil was retained inside the bit. To prove this point, the drill was turned horizontally, and the acquired soil was still inside the bit. The basic theory behind the process of retaining unconsolidated mass that can be acquired by the centrifugal forces of the bit is determined by noting that in order to stay inside the interior of the bit, the

  1. Ag induced suppression of irradiation response in YBCO/Ag composite thin films

    International Nuclear Information System (INIS)

    Behera, D.; Mohanty, T.; Mohanta, D.; Patnaik, K.; Mishra, N.C.; Senapati, L.; Kanjilal, D.; Mehta, G.K.; Pinto, R.

    1999-01-01

    Practical application of cuprate superconductors in radiation environment demands that these systems remain insensitive to the irradiation induced defects. The cuprate superconductors however are many orders of magnitude more sensitive than the conventional low T c superconductors. To suppress the irradiation sensitivity of cuprates we consider a crystal engineering approach where metal ions as Ag is made to occupy inter and intra-granular sites of YBa 2 Cu 3 O 7 thin films. We show that superconducting and normal state properties of YBCO/Ag composite thin films prepared by laser ablation remain unchanged under 140 MeV Si ion irradiation up to fluence of 8 x 10 14 ions/cm 2 . The inter- and intra-granular occupancy of Ag is shown to induce microstructural modifications and rigidity to the CuO chains respectively which in turn lead to the radiation insensitivity of the composite films. (author)

  2. Low-velocity impact cratering experiments in granular slopes

    Science.gov (United States)

    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.

  3. Impurity in a granular gas under nonlinear Couette flow

    International Nuclear Information System (INIS)

    Vega Reyes, Francisco; Garzó, Vicente; Santos, Andrés

    2008-01-01

    We study in this work the transport properties of an impurity immersed in a granular gas under stationary nonlinear Couette flow. The starting point is a kinetic model for low-density granular mixtures recently proposed by the authors (Vega Reyes et al 2007 Phys. Rev. E 75 061306). Two routes have been considered. First, a hydrodynamic or normal solution is found by exploiting a formal mapping between the kinetic equations for the gas particles and for the impurity. We show that the transport properties of the impurity are characterized by the ratio between the temperatures of the impurity and gas particles and by five generalized transport coefficients: three related to the momentum flux (a nonlinear shear viscosity and two normal stress differences) and two related to the heat flux (a nonlinear thermal conductivity and a cross-coefficient measuring a component of the heat flux orthogonal to the thermal gradient). Second, by means of a Monte Carlo simulation method we numerically solve the kinetic equations and show that our hydrodynamic solution is valid in the bulk of the fluid when realistic boundary conditions are used. Furthermore, the hydrodynamic solution applies to arbitrarily (inside the continuum regime) large values of the shear rate, of the inelasticity, and of the rest of the parameters of the system. Preliminary simulation results of the true Boltzmann description show the reliability of the nonlinear hydrodynamic solution of the kinetic model. This shows again the validity of a hydrodynamic description for granular flows, even under extreme conditions, beyond the Navier–Stokes domain

  4. Modeling granular phosphor screens by Monte Carlo methods

    International Nuclear Information System (INIS)

    Liaparinos, Panagiotis F.; Kandarakis, Ioannis S.; Cavouras, Dionisis A.; Delis, Harry B.; Panayiotakis, George S.

    2006-01-01

    The intrinsic phosphor properties are of significant importance for the performance of phosphor screens used in medical imaging systems. In previous analytical-theoretical and Monte Carlo studies on granular phosphor materials, values of optical properties, and light interaction cross sections were found by fitting to experimental data. These values were then employed for the assessment of phosphor screen imaging performance. However, it was found that, depending on the experimental technique and fitting methodology, the optical parameters of a specific phosphor material varied within a wide range of values, i.e., variations of light scattering with respect to light absorption coefficients were often observed for the same phosphor material. In this study, x-ray and light transport within granular phosphor materials was studied by developing a computational model using Monte Carlo methods. The model was based on the intrinsic physical characteristics of the phosphor. Input values required to feed the model can be easily obtained from tabulated data. The complex refractive index was introduced and microscopic probabilities for light interactions were produced, using Mie scattering theory. Model validation was carried out by comparing model results on x-ray and light parameters (x-ray absorption, statistical fluctuations in the x-ray to light conversion process, number of emitted light photons, output light spatial distribution) with previous published experimental data on Gd 2 O 2 S:Tb phosphor material (Kodak Min-R screen). Results showed the dependence of the modulation transfer function (MTF) on phosphor grain size and material packing density. It was predicted that granular Gd 2 O 2 S:Tb screens of high packing density and small grain size may exhibit considerably better resolution and light emission properties than the conventional Gd 2 O 2 S:Tb screens, under similar conditions (x-ray incident energy, screen thickness)

  5. Multifocal Abrikossoff's granular cell tumor of the oesophagus: Case report

    Directory of Open Access Journals (Sweden)

    Ranđelović Tomislav D.

    2008-01-01

    Full Text Available INTRODUCTION Granular cell tumors, relatively uncommon soft tissue tumors, have been a matter of debate among pathologists regarding histogenesis for a long time. Less common locations are in the aerodigestive tract including the oesophagus. CASE OUTLINE We have recently treated a rare case, a 37-year old male, who was admitted due to dysphagia and a painful swallow with occasional pharyngo-nasal regurgitation followed with a mild loss of weight. Standard clinical examination including X-ray chest, ECG and laboratory tests did not show pathological findings. Barium contrast oesophagography demonstrated multiple ovoid defects in the wall of the oesophagus. CT scan of the chest confirmed luminal narrowing owing to the tumor of the upper oesophagus. Upper endoscopy showed unusual multifocal nodular lesions alongside the oesophageal axis covered by smooth mucosa. A primary biopsy specimen taken from the largest nodules confirmed an unusual pathological finding of the granular cell tumor. Subtotal, transpleural oesophagectomy was performed and reconstruction was derived by long colon segment interposition through the posterior mediastinum. The postoperative course was uneventful. The operative specimen consisted of four ovoid tumors alongside the oesophagus (the greatest diameter 0.5-1.8, average 1.25. All verified tumors histologicaly consisted of a spindle-shaped or polygonal cells containing small and large eosinophilic granules and central nuclei. Most tumor cells showed strongly positive immunohistochemical staining for S-100 protein. These tumor cells were partially positive for p-53 and Ki-67. No lymph node metastases were detected histologically. CONCLUSION Multifocal granular cell tumor of the oesophagus is an unusual finding with low incidence, and rarely caused symptoms. Pathological features and multiplicity of such tumors emphasized malignant predisposition requiring surgical resection of the oesophagus.

  6. Self-diffusion in dense granular shear flows.

    Science.gov (United States)

    Utter, Brian; Behringer, R P

    2004-03-01

    Diffusivity is a key quantity in describing velocity fluctuations in granular materials. These fluctuations are the basis of many thermodynamic and hydrodynamic models which aim to provide a statistical description of granular systems. We present experimental results on diffusivity in dense, granular shear flows in a two-dimensional Couette geometry. We find that self-diffusivities D are proportional to the local shear rate gamma; with diffusivities along the direction of the mean flow approximately twice as large as those in the perpendicular direction. The magnitude of the diffusivity is D approximately gamma;a(2), where a is the particle radius. However, the gradient in shear rate, coupling to the mean flow, and strong drag at the moving boundary lead to particle displacements that can appear subdiffusive or superdiffusive. In particular, diffusion appears to be superdiffusive along the mean flow direction due to Taylor dispersion effects and subdiffusive along the perpendicular direction due to the gradient in shear rate. The anisotropic force network leads to an additional anisotropy in the diffusivity that is a property of dense systems and has no obvious analog in rapid flows. Specifically, the diffusivity is suppressed along the direction of the strong force network. A simple random walk simulation reproduces the key features of the data, such as the apparent superdiffusive and subdiffusive behavior arising from the mean velocity field, confirming the underlying diffusive motion. The additional anisotropy is not observed in the simulation since the strong force network is not included. Examples of correlated motion, such as transient vortices, and Lévy flights are also observed. Although correlated motion creates velocity fields which are qualitatively different from collisional Brownian motion and can introduce nondiffusive effects, on average the system appears simply diffusive.

  7. Nonlocal rheological properties of granular flows near a jamming limit.

    Science.gov (United States)

    Aranson, Igor S; Tsimring, Lev S; Malloggi, Florent; Clément, Eric

    2008-09-01

    We study the rheology of sheared granular flows close to a jamming transition. We use the approach of partially fluidized theory (PFT) with a full set of equations extending the thin layer approximation derived previously for the description of the granular avalanches phenomenology. This theory provides a picture compatible with a local rheology at large shear rates [G. D. R. Midi, Eur. Phys. J. E 14, 341 (2004)] and it works in the vicinity of the jamming transition, where a description in terms of a simple local rheology comes short. We investigate two situations displaying important deviations from local rheology. The first one is based on a set of numerical simulations of sheared soft two-dimensional circular grains. The next case describes previous experimental results obtained on avalanches of sandy material flowing down an incline. Both cases display, close to jamming, significant deviations from the now standard Pouliquen's flow rule [O. Pouliquen, Phys. Fluids 11, 542 (1999); 11, 1956 (1999)]. This discrepancy is the hallmark of a strongly nonlocal rheology and in both cases, we relate the empirical results and the outcomes of PFT. The numerical simulations show a characteristic constitutive structure for the fluid part of the stress involving the confining pressure and the material stiffness that appear in the form of an additional dimensionless parameter. This constitutive relation is then used to describe the case of sandy flows. We show a quantitative agreement as far as the effective flow rules are concerned. A fundamental feature is identified in PFT as the existence of a jammed layer developing in the vicinity of the flow arrest that corroborates the experimental findings. Finally, we study the case of solitary erosive granular avalanches and relate the outcome with the PFT analysis.

  8. Knots and Random Walks in Vibrated Granular Chains

    International Nuclear Information System (INIS)

    Ben-Naim, E.; Daya, Z. A.; Vorobieff, P.; Ecke, R. E.

    2001-01-01

    We study experimentally statistical properties of the opening times of knots in vertically vibrated granular chains. Our measurements are in good qualitative and quantitative agreement with a theoretical model involving three random walks interacting via hard-core exclusion in one spatial dimension. In particular, the knot survival probability follows a universal scaling function which is independent of the chain length, with a corresponding diffusive characteristic time scale. Both the large-exit-time and the small-exit-time tails of the distribution are suppressed exponentially, and the corresponding decay coefficients are in excellent agreement with theoretical values

  9. New superconductors from granular to high T$_{c}$

    CERN Document Server

    Deutscher, Guy

    2018-01-01

    How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This interesting book aims to provide some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a short coherence length, a small superfluid density and an inhomogeneous structure.

  10. New superconductors from granular to high T$_{c}$

    CERN Document Server

    Deutscher, Guy

    2006-01-01

    How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This book aims to give some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a maximum of their critical temperature near the metal-insulator transition.

  11. Pressure-Dependent Friction on Granular Slopes Close to Avalanche

    Science.gov (United States)

    Crassous, Jérôme; Humeau, Antoine; Boury, Samuel; Casas, Jérôme

    2017-08-01

    We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.

  12. Pressure-Dependent Friction on Granular Slopes Close to Avalanche.

    Science.gov (United States)

    Crassous, Jérôme; Humeau, Antoine; Boury, Samuel; Casas, Jérôme

    2017-08-04

    We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.

  13. Comparison of two highly granular hadronic calorimeter concepts

    International Nuclear Information System (INIS)

    Neubueser, Coralie

    2016-11-01

    The CALICE collaboration develops hadron calorimeter technologies with high granularity for future electron-positron linear colliders. These technologies differ in active material, granularity and their readout and thus their energy reconstruction schemes. The Analogue Hadron Calorimeter (AHCAL), based on scintillator tiles with Silicon Photomultiplier readout, measures the signal amplitude of the energy deposition in the cells of at most 3 x 3 cm"2 size. The Digital, Resistive Plate Chamber (RPC) based, HCAL (DHCAL) detects hits above a certain threshold by firing pad sensors of 1 x 1 cm"2. A 2 bit readout is provided by the, also RPC based, Semi-Digital HCAL (SDHCAL), which counts hits above three different thresholds per 1 x 1 cm"2 pad. All three calorimeter concepts have been realised in 1 m"3 prototypes with interleaved steel absorber and tested at various test beams. The differences in active medium, granularity and readout have different impacts on the energy resolution and need to be studied independently. This analysis concentrates on the comparison between these technologies by investigating the impact of the different energy reconstruction schemes on the energy resolution of the AHCAL testbeam data and simulation. Additionally, a so-called software compensation algorithm is developed to weight hits dependent on their energy content and correct for the difference in the response to the electromagnetic and hadronic sub-showers (e/h≠1) and thus reduce the influence of fluctuations in the π"0 generation. The comparison of the energy resolutions revealed that it is mandatory for the AHCAL with 3 x 3 cm"2 cell size to have analogue signal readout, to apply the software compensation algorithm and thus achieve the best possible energy resolution. The effect of the granularity is studied with a simulation of the AHCAL with 1 x 1 cm"2 cell size, and it has been found that to achieve the best possible energy resolution the semi-digital energy reconstruction is

  14. Velocity Distributions in Inelastic Granular Gases with Continuous Size Distributions

    International Nuclear Information System (INIS)

    Li Rui; Li Zhi-Hao; Zhang Duan-Ming

    2011-01-01

    We study by numerical simulation the property of velocity distributions of granular gases with a power-law size distribution, driven by uniform heating and boundary heating. It is found that the form of velocity distribution is primarily controlled by the restitution coefficient η and q, the ratio between the average number of heatings and the average number of collisions in the system. Furthermore, we show that uniform and boundary heating can be understood as different limits of q, with q ≫ 1 and q ≤ 1, respectively. (general)

  15. Harmonic generation and flux quantization in granular superconductors

    International Nuclear Information System (INIS)

    Lam, Q.H.; Jeffries, C.D.

    1989-01-01

    Simple dynamical models of granular superconductors are used to compute the generation of harmonic power in ac and dc magnetic fields. In zero order, the model is a single superconducting loop, with or without a weak link. The sample-average power is predicted by averaging over suitable distribution functions for loop areas and orientations in a dc magnetic field. In a first-order model, inductance and resistance are also included. In all models the power at high harmonics shows strikingly sharp dips periodic in the dc field, revealing flux quantization in the prototype loops

  16. STABILIZATION OF GRANULAR VOLCANIC ASH IN SANA'A AREA

    Directory of Open Access Journals (Sweden)

    SUBHI A. ALI

    2014-02-01

    Full Text Available This paper presents the findings of compaction and strength characteristics of a Granular Volcanic Ash from Sana'a city center, which was mixed with various percentages of two binders to form a stabilized material namely; fine soil and Portland cement. The study showed a significant improvement of the Volcanic Ash properties. The maximum dry density and California bearing ration (CBR were considerably increased by addition of stabilizers at different rates for different binder contents. Optimum fine soil content for the maximum dry density and CBR is determined. A relationship between the optimum moisture content and the binder combination content for different fine soil percentages was established.

  17. Design and Prototyping of a High Granularity Scintillator Calorimeter

    International Nuclear Information System (INIS)

    Zutshi, Vishnu

    2016-01-01

    A novel approach for constructing fine-granularity scintillator calorimeters, based on the concept of an Integrated Readout Layer (IRL) was developed. The IRL consists of a printed circuit board inside the detector which supports the directly-coupled scintillator tiles, connects to the surface-mount SiPMs and carries the necessary front-end electronics and signal/bias traces. Prototype IRLs using this concept were designed, prototyped and successfully exposed to test beams. Concepts and implementations of an IRL carried out with funds associated with this contract promise to result in the next generation of scintillator calorimeters.

  18. Flux-line cutting in granular high-temperature superconductors

    International Nuclear Information System (INIS)

    Perez-Rodriguez, F.; Perez-Gonzalez, A.; Clem, J.R.; Gandolfini, G.; LeBlanc, M.A.

    1997-01-01

    The magnetic response of granular high-temperature superconducting plates subjected to a dc-bias magnetic field and an increasing field perpendicular to it is studied both experimentally and theoretically. The theoretical model is based upon the double critical-state model, which considers not only flux transport but also flux-line cutting effects. Curves of magnetization for the system of grains decoupled by the applied magnetic field in sintered slabs of YBa 2 Cu 3 O 7-x and NdBa 2 Cu 3 O 7-x are analyzed. Good agreement between experimental results and theory is obtained. copyright 1997 The American Physical Society

  19. Implicit integration of plasticity models for granular materials

    DEFF Research Database (Denmark)

    Ahadi, A.; Krenk, Steen

    2003-01-01

    A stress integration algorithm for granular materials based on fully implicit integration with explicit updating is presented. In the implicit method the solution makes use of the gradient to the potential surface at the final stress state which is unknown. The final stress and hardening parameters...... stresses are not supported the functions and their derivatives are not representative outside the compressive octant of the principal stress space. The elastic predictor is therefore preconditioned in order to ensure that the first predictor is within the valid region. Capability and robustness...

  20. Origin of Noncubic Scaling Law in Disordered Granular Packing

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Chengjie; Li, Jindong; Kou, Binquan; Cao, Yixin; Li, Zhifeng; Xiao, Xianghui; Fu, Yanan; Xiao, Tiqiao; Hong, Liang; Zhang, Jie; Kob, Walter; Wang, Yujie

    2017-06-01

    Recent diffraction experiments on metallic glasses have unveiled an unexpected non-cubic scaling law between density and average interatomic distance, which lead to the speculations on the presence of fractal glass order. Using X-ray tomography we identify here a similar non-cubic scaling law in disordered granular packing of spherical particles. We find that the scaling law is directly related to the contact neighbors within first nearest neighbor shell, and therefore is closely connected to the phenomenon of jamming. The seemingly universal scaling exponent around 2.5 arises due to the isostatic condition with contact number around 6, and we argue that the exponent should not be universal.

  1. Reorganization of a dense granular assembly: The unjamming response function

    Science.gov (United States)

    Kolb, Évelyne; Cviklinski, Jean; Lanuza, José; Claudin, Philippe; Clément, Éric

    2004-03-01

    We investigate the mechanical properties of a static dense granular assembly in response to a local forcing. To this end, a small cyclic displacement is applied on a grain in the bulk of a two-dimensional disordered packing under gravity and the displacement fields are monitored. We evidence a dominant long range radial response in the upper half part above the solicitation and after a large number of cycles the response is “quasireversible” with a remanent dissipation field exhibiting long range streams and vortexlike symmetry.

  2. 10,000 - A reason to study granular heat convection

    Energy Technology Data Exchange (ETDEWEB)

    Einav, I.; Rognon, P.; Gan, Y.; Miller, T.; Griffani, D. [Particles and Grains Laboratory, School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia)

    2013-06-18

    In sheared granular media, particle motion is characterized by vortex-like structures; here this is demonstrated experimentally for disks system undergoing indefinite deformation during simple shear, as often imposed by the rock masses hosting earthquake fault gouges. In traditional fluids it has been known for years that vortices represent a major factor of heat transfer enhancement via convective internal mixing, but in analyses of heat transfer through earthquake faults and base planes of landslides this has been continuously neglected. Can research proceed by neglecting heat convection by internal mixing? Our answer is astonishingly far from being yes.

  3. Scaling of wet granular flows in a rotating drum

    Directory of Open Access Journals (Sweden)

    Jarray Ahmed

    2017-01-01

    Full Text Available In this work, we investigate the effect of capillary forces and particle size on wet granular flows and we propose a scaling methodology that ensures the conservation of the bed flow. We validate the scaling law experimentally by using different size glass beads with tunable capillary forces. The latter is obtained using mixtures of ethanol-water as interstitial liquid and by increasing the hydrophobicity of glass beads with an ad-hoc silanization procedure. The scaling methodology in the flow regimes considered (slipping, slumping and rolling yields similar bed flow for different particle sizes including the angle of repose that normally increases when decreasing the particle size.

  4. Harmonic response of coupled and uncoupled granular YBCO

    International Nuclear Information System (INIS)

    Torralba, Maria Veronica S; Sarmago, Roland V

    2004-01-01

    The harmonic responses of granular YBCO were obtained via mutual inductance measurements. Two samples, one with and another without intergranular coupling, were investigated in terms of the harmonic components of magnetization at various field amplitudes and frequencies. By comparing the behaviour of the features in the harmonics to that of the peaks in the fundamental response, we explicitly identified which features in the harmonics originate from intragranular harmonic generation and which arise due to a contribution of intergranular coupling. Harmonic responses were obtained despite the absence of vortices and even harmonics were detected in a purely AC magnetic field

  5. Shower fractal dimension analysis in a highly-granular calorimeter

    CERN Document Server

    Ruan, M

    2014-01-01

    We report on an investigation of the self-similar structure of particle showers recorded at a highly-granular calorimeter. On both simulated and experimental data, a strong correlation between the number of hits and the spatial scale of the readout channels is observed, from which we define the shower fractal dimension. The measured fractal dimension turns out to be strongly dependent on particle type, which enables new approaches for particle identification. A logarithmic dependence of the particle energy on the fractal dimension is also observed.

  6. Design and Prototyping of a High Granularity Scintillator Calorimeter

    Energy Technology Data Exchange (ETDEWEB)

    Zutshi, Vishnu [Northern Illinois Univ., DeKalb, IL (United States). Dept. of Physics

    2016-03-27

    A novel approach for constructing fine-granularity scintillator calorimeters, based on the concept of an Integrated Readout Layer (IRL) was developed. The IRL consists of a printed circuit board inside the detector which supports the directly-coupled scintillator tiles, connects to the surface-mount SiPMs and carries the necessary front-end electronics and signal/bias traces. Prototype IRLs using this concept were designed, prototyped and successfully exposed to test beams. Concepts and implementations of an IRL carried out with funds associated with this contract promise to result in the next generation of scintillator calorimeters.

  7. Film processing

    International Nuclear Information System (INIS)

    Abdul Nassir Ibrahim; Azali Muhammad; Ab. Razak Hamzah; Abd. Aziz Mohamed; Mohamad Pauzi Ismail

    2008-01-01

    The processing was made not only to show what are in the film but also to produce radiograph with high quality where the information gathered really presented level of the quality of the object inspected. Besides that, good procedure will make the film with good quality can keep the film in long time for reference. Here, more detailed on how the dark room functioned and its design. So, the good procedure while processed the film will be discussed detailed in this chapter from entering the dark room to exit from there.

  8. Demens Film

    DEFF Research Database (Denmark)

    Jensen, Anders Møller

    2012-01-01

    Vi vil skabe film til mennesker med demens – ikke film om demens sygdommen eller beretninger om livet og hverdagen med en kronisk lidelse. Filmene skal medvirke til at frembringe en behagelig stemning omkring og hos mennesker med demens, så hverdagen bliver så tryg som mulig. Filmene skal samtidig...... var at afgrænse og prioritere projektet, samt komme med anbefalinger omkring hvad der er vigtigt, i forbindelse med produktion af film målrettet mennesker med demens. Resultat af ekspertgruppen sammenfattes i denne rapport. Projektet gennemføres som et samarbejde mellem Retrospect Film...

  9. Scaling of the anomalous Hall current in Fe100−x(SiO2)x films

    KAUST Repository

    Xu, W. J.; Zhang, Bei; Wang, Q. X.; Mi, W. B.; Wang, Z.; Li, W.; Yu, R. H.; Zhang, Xixiang

    2011-01-01

    To study the origin of the anomalous Hall effect, Fe100−x(SiO2)x granular films with a volume fraction of SiO2 (0 ⩽ x ⩽ 40.51) were fabricated using cosputtering. Hall and longitudinal resistivities were measured in the temperature range of 5–350 K

  10. Micromechanical definition of an entropy for quasi-static deformation of granular materials

    NARCIS (Netherlands)

    Rothenburg, L.; Kruyt, Nicolaas P.

    2009-01-01

    A micromechanical theory is formulated for quasi-static deformation of granular materials, which is based on information theory. A reasoning is presented that leads to the definition of an information entropy that is appropriate for quasi-static deformation of granular materials. This definition is

  11. User-centric Query Refinement and Processing Using Granularity Based Strategies

    NARCIS (Netherlands)

    Zeng, Y.; Zhong, N.; Wang, Y.; Qin, Y.; Huang, Z.; Zhou, H; Yao, Y; van Harmelen, F.A.H.

    2011-01-01

    Under the context of large-scale scientific literatures, this paper provides a user-centric approach for refining and processing incomplete or vague query based on cognitive- and granularity-based strategies. From the viewpoints of user interests retention and granular information processing, we

  12. PALLADIUM-FACILITATED ELECTROLYTIC DECHLORINATION OF 2-CHLOROBIPHENYL USING A GRANULAR-GRAPHITE ELECTRODE.

    Science.gov (United States)

    Palladium-assisted electrocatalytic dechlorination of 2-chlorobiphenyl (2-Cl BP) in aqueous solutions was conducted in a membrane-separated electrochemical reactor with granular-graphite packed electrodes. The dechlorination took place at a granular-graphite cathode while Pd was ...

  13. Effect of Wetting and Contamination of Granular Beds During Sphere Impact

    KAUST Repository

    Kouraytem, Nadia

    2013-01-01

    This thesis presents results from an experimental study of the impact of dense solid spheres onto granular beds. The overall aim is to further our understanding of the dynamical response of granular materials to impact. In order to do this, we

  14. The Effect of Rotational Speed on Granular Flow in a Vertical Bladed Mixer

    Czech Academy of Sciences Publication Activity Database

    Havlica, Jaromír; Jirounková, K.; Trávníčková, Tereza; Kohout, M.

    2015-01-01

    Roč. 280, AUG (2015), s. 180-190 ISSN 0032-5910 R&D Projects: GA ČR(CZ) GAP105/12/0664 Institutional support: RVO:67985858 Keywords : DEM * granular mixing * granular dynamics Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.759, year: 2015

  15. Emotional Granularity Effects on Event-Related Brain Potentials during Affective Picture Processing.

    Science.gov (United States)

    Lee, Ja Y; Lindquist, Kristen A; Nam, Chang S

    2017-01-01

    There is debate about whether emotional granularity , the tendency to label emotions in a nuanced and specific manner, is merely a product of labeling abilities, or a systematic difference in the experience of emotion during emotionally evocative events. According to the Conceptual Act Theory of Emotion (CAT) (Barrett, 2006), emotional granularity is due to the latter and is a product of on-going temporal differences in how individuals categorize and thus make meaning of their affective states. To address this question, the present study investigated the effects of individual differences in emotional granularity on electroencephalography-based brain activity during the experience of emotion in response to affective images. Event-related potentials (ERP) and event-related desynchronization and synchronization (ERD/ERS) analysis techniques were used. We found that ERP responses during the very early (60-90 ms), middle (270-300 ms), and later (540-570 ms) moments of stimulus presentation were associated with individuals' level of granularity. We also observed that highly granular individuals, compared to lowly granular individuals, exhibited relatively stable desynchronization of alpha power (8-12 Hz) and synchronization of gamma power (30-50 Hz) during the 3 s of stimulus presentation. Overall, our results suggest that emotional granularity is related to differences in neural processing throughout emotional experiences and that high granularity could be associated with access to executive control resources and a more habitual processing of affective stimuli, or a kind of "emotional complexity." Implications for models of emotion are also discussed.

  16. Sorption of cobalt and nickel on anaerobic granular sludges: isotherms and sequential extraction

    NARCIS (Netherlands)

    Hullebusch, van E.D.; Peerbolte, A.; Zandvoort, M.H.; Lens, P.N.L.

    2005-01-01

    The objective of this study was to investigate the sorption capacity and the fractionation of sorbed nickel and cobalt onto anaerobic granular sludges. Two different anaerobic granular sludges (non-fed, pH = 7) were loaded with nickel and cobalt in. adsorption experiments (monometal and competitive

  17. Dehydration/hydration of granular beds for thermal storage applications: a combined NMR and temperature study

    NARCIS (Netherlands)

    Donkers, P.A.J.; Pel, L.; Adan, O.C.G.

    For heat/cold storage systems a granular bed of salt hydrates is studied during dehydration/hydration. The water density in these beds are measured with help of NMR. Diffusion based dehydration of a granular bed of Na2SO4·10H2O is shown to be internally limited as larger grains dehydrate faster than

  18. Diagnosis and Treatment of Esophageal Granular Cell Tumor: A Case Report and Review of the Literature

    Directory of Open Access Journals (Sweden)

    Ramin Niknam

    2017-01-01

    Full Text Available Gastrointestinal granular cell tumors are uncommon. The most common site of gastrointestinal granular cell tumor (GCT is esophagus. We report a case of esophageal GCT incidentally diagnosed by endoscopy. The lesion was evaluated by endoscopic ultrasonography and resected using the endoscopic technique without complication.

  19. Extension of PIV for measuring granular temperature field in dense fluidized beds.

    NARCIS (Netherlands)

    Dijkhuizen, W.; Bokkers, G.A.; Deen, N.G.; van Sint Annaland, M.; Kuipers, J.A.M.

    2007-01-01

    In this work a particle image velocimetry (PIV) technique has been extended to enable the simultaneous measurement of the instantaneous velocity and granular temperature fields. The PIV algorithm has been specifically optimized for dense granular systems and has been thoroughly tested with

  20. Exponential temperature dependence of the critical transport current in Y-Ba-Cu-O thin films

    International Nuclear Information System (INIS)

    Yom, S.S.; Hahn, T.S.; Kim, Y.H.; Chu, H.; Choi, S.S.

    1989-01-01

    We have measured the critical currents in rf-sputtered YBa 2 Cu 3 O/sub 7-x/ thin films deposited on polycrystalline yttria-stabilized zirconia substrates as a function of temperature down to 10 K. The dependence of the granular films at low temperature indicated exponential behavior which is similar to the superconductor-normal metal-superconductor (S-N-S) type tunneling junctions. For the films with a grain size of approximately 1 μm, we observed two exponential decay constants, which suggest that Josephson junctions limiting the transport critical current are possible both at the grain boundaries and at twin boundaries