1,098 research outputs found
Geometrical properties of rigid frictionless granular packings as a function of particle size and shape
Three-dimensional discrete numerical simulation is used to investigate the
properties of close-packed frictionless granular assemblies as a function of
particle polydispersity and shape. Unlike some experimental results,
simulations show that disordered packings of pinacoids (eight-face convex
polyhedron) achieve higher solid fraction values than amorphous packings of
spherical or rounded particles, thus fulfilling the analogue of Ulam's
conjecture stated by Jiao and co-workers for random packings [Y. Jiao and S.
Torquato, Phys. Rev. E , ()]. This seeming
discrepancy between experimental and numerical results is believed to lie with
difficulties in overcoming interparticle friction through experimental
densification processes. Moreover, solid fraction is shown to increase further
with bidispersity and peak when the volume proportion of small particles
reaches . Contrarywise, substituting up to of flat pinacoids for
isometric ones yields solid fraction decrease, especially when flat particles
are also elongated. Nevertheless, particle shape seems to play a minor role on
packing solid fraction compared to polydispersity. Additional investigations
focused on the packing microstructure confirm that pinacoid packings fulfill
the isostatic conjecture and that they are free of order except beyond to
of flat or flat \& elongated polyhedra in the packing. This order
increase progressively takes the form of a nematic phase caused by the
reorientation of flat or flat \& elongated particles to minimize the packing
potential energy. Simultaneously, this reorientation seems to increase the
solid fraction value slightly above the maximum achieved by monodisperse
isometric pinacoids, as well as the coordination number. Finally, partial
substitution of elongated pinacoids for isometric ones has limited effect on
packing solid fraction or order.Comment: 12 figures, 12 page
Ion temperature gradient instability at sub-Larmor radius scales with non-zero ballooning angle
Linear gyro-kinetic stability calculations predict unstable toroidal Ion
Temperature Gradient modes with normalised poloidal wave vectors well above one
() for standard parameters and with adiabatic electrons.
These modes have a maximum amplitude at a poloidal angle that is
shifted away from the low field side (). The physical mechanism
is clarified through the use of a fluid model. It is shown that the shift of
the mode away from the low field side () reduces the effective
drift frequency, and allows for the instability to develop. Numerical tests
using the gyro-kinetic model confirm this physical mechanism. It is furthermore
shown that modes with can be important also for close to the threshold of the ITG. In fact, modes with can
exist for normalised temperature gradient lengths below the threshold of the
ITG obtained for
Mechanical tests for evaluation of the integrity of the implant abutment connection
Nos últimos trinta anos, a reabilitação oral por sistemas de implantes tornou-se uma das
técnicas mais bem-sucedidas.
Um sistema de implante tem habitualmente 2 corpos, um endosteal e um dispositivo de
suporte para a prótese conectados por um parafuso.
Ao longo desta interface, as microgaps podem se desenvolver.
Estes espaços constituem um abrigo para bactérias, o que pode aumentar o risco de periimplantites,
associadas a uma maior infiltração de células inflamatórias e perda de osso.
Para reduzir esse risco e, portanto, o tamanho e número de microgaps, são realizados
testes mecânicos para adquirir um maior conhecimentos sobre o desempenho de cada
sistema de implantes.
O comportamento dos dispositivos fora testados recorrendo a : análise microbiológica,
extração de DNA, análise por estereomicroscópio, microscópio eletrônico de varredura,
modelagem de elementos finitos, análise radiográfica e análise espectrofotométrica.
Materiais e métodos : A pesquisa foi realizada entre novembro de 2016 e abril de 2017.
Estudos experimentais, artigos de revisão e livros escritos em inglês com texto de
versão de acesso completo, data de edição da publicação entre 2005 e 2017, e condições
do teste mais realistas, como as condições na cavidade oral são critérios de inclusão.
Os resultados foram posteriormente analisados, com o objetivo de avaliar a integridade
da conexão de implante-pilar.Over the last thirty years, the oral rehabilitation by implants systems has become one of
the most successful techniques.
An implant system has two main parts, an endosteal fixture and a prosthesis-supporting
abutment connected to fixture with a screw.
Along this interface, microgaps can develop; they are defined as a microscopic space.
This localisation play a role of safe house for bacteria, which can increase the risk of
peri-implantitis, they are associated with a higher inflammatory cell infiltration and
bone loss.
To reduce this risk and therefore the size and number of microgaps, mechanical tests are
carried out in order to develop knowledge about the capacities of each implant system.
As tests, it was found: microbiological analysis, DNA extraction, analysis by
stereomicroscope, scanning electron microscope, finite element modeling, radiographic
analysis and spectrophotometric analysis.
Material and methods: the research was done between November 2016 and April 2017.
Experimental studies, review articles and books written in the English with a full access
version text, the edition date of the publication between 2005 and 2017, and conditions
of the test more realistic, like the conditions in oral cavity are inclusions criteria.
Their results are subsequently analysed, for the aim of an evaluation of the integrity of
the implant-abutment connection
Estimate of convection-diffusion coefficients from modulated perturbative experiments as an inverse problem
The estimate of coefficients of the Convection-Diffusion Equation (CDE) from
experimental measurements belongs in the category of inverse problems, which
are known to come with issues of ill-conditioning or singularity. Here we
concentrate on a particular class that can be reduced to a linear algebraic
problem, with explicit solution. Ill-conditioning of the problem corresponds to
the vanishing of one eigenvalue of the matrix to be inverted. The comparison
with algorithms based upon matching experimental data against numerical
integration of the CDE sheds light on the accuracy of the parameter estimation
procedures, and suggests a path for a more precise assessment of the profiles
and of the related uncertainty. Several instances of the implementation of the
algorithm to real data are presented.Comment: Extended version of an invited talk presented at the 2012 EPS
Conference. To appear in Plasma Physics and Controlled Fusio
Mechanical tests for evaluation of the integrity of the implant abutment connection
Nos últimos trinta anos, a reabilitação oral por sistemas de implantes tornou-se uma das
técnicas mais bem-sucedidas.
Um sistema de implante tem habitualmente 2 corpos, um endosteal e um dispositivo de
suporte para a prótese conectados por um parafuso.
Ao longo desta interface, as microgaps podem se desenvolver.
Estes espaços constituem um abrigo para bactérias, o que pode aumentar o risco de periimplantites,
associadas a uma maior infiltração de células inflamatórias e perda de osso.
Para reduzir esse risco e, portanto, o tamanho e número de microgaps, são realizados
testes mecânicos para adquirir um maior conhecimentos sobre o desempenho de cada
sistema de implantes.
O comportamento dos dispositivos fora testados recorrendo a : análise microbiológica,
extração de DNA, análise por estereomicroscópio, microscópio eletrônico de varredura,
modelagem de elementos finitos, análise radiográfica e análise espectrofotométrica.
Materiais e métodos : A pesquisa foi realizada entre novembro de 2016 e abril de 2017.
Estudos experimentais, artigos de revisão e livros escritos em inglês com texto de
versão de acesso completo, data de edição da publicação entre 2005 e 2017, e condições
do teste mais realistas, como as condições na cavidade oral são critérios de inclusão.
Os resultados foram posteriormente analisados, com o objetivo de avaliar a integridade
da conexão de implante-pilar.Over the last thirty years, the oral rehabilitation by implants systems has become one of
the most successful techniques.
An implant system has two main parts, an endosteal fixture and a prosthesis-supporting
abutment connected to fixture with a screw.
Along this interface, microgaps can develop; they are defined as a microscopic space.
This localisation play a role of safe house for bacteria, which can increase the risk of
peri-implantitis, they are associated with a higher inflammatory cell infiltration and
bone loss.
To reduce this risk and therefore the size and number of microgaps, mechanical tests are
carried out in order to develop knowledge about the capacities of each implant system.
As tests, it was found: microbiological analysis, DNA extraction, analysis by
stereomicroscope, scanning electron microscope, finite element modeling, radiographic
analysis and spectrophotometric analysis.
Material and methods: the research was done between November 2016 and April 2017.
Experimental studies, review articles and books written in the English with a full access
version text, the edition date of the publication between 2005 and 2017, and conditions
of the test more realistic, like the conditions in oral cavity are inclusions criteria.
Their results are subsequently analysed, for the aim of an evaluation of the integrity of
the implant-abutment connection
Modelling the settling of suspended sediments for concentrations close to the gelling concentration
This paper deals with the sedimentation of highly concentrated sediment suspensions (cohesive as well as non-cohesive) and the beginning of the consolidation of cohesive sediments. Based on a comparison of existing empirical formulas and experimental data, the particle Reynolds number was shown to be of importance for the behaviour of particularly non-cohesive sediments. In addition it plays a role in determining whether one or two interfaces develop during the sedimentation phase. In the case of cohesive sediments, the estimation of the gelling concentration, although difficult, seems to be fundamental. Some suggestions on the estimation of the permeability coefficient and total settling function are then given in order to improve the modelling of the sedimentation and consolidation behaviour for concentrations close to the gelling concentration
Angular momentum transport modeling: achievements of a gyrokinetic quasi-linear approach
QuaLiKiz, a model based on a local gyrokinetic eigenvalue solver is expanded
to include momentum flux modeling in addition to heat and particle fluxes.
Essential for accurate momentum flux predictions, the parallel asymmetrization
of the eigenfunctions is successfully recovered by an analytical fluid model.
This is tested against self-consistent gyrokinetic calculations and allows for
a correct prediction of the ExB shear impact on the saturated potential
amplitude by means of a mixing length rule. Hence, the effect of the ExB shear
is recovered on all the transport channels including the induced residual
stress. Including these additions, QuaLiKiz remains ~10 000 faster than
non-linear gyrokinetic codes allowing for comparisons with experiments without
resorting to high performance computing. The example is given of momentum pinch
calculations in NBI modulation experiments
Effect of confinement on dense packings of rigid frictionless spheres and polyhedra
International audienceWe study numerically the influence of confinement on the solid fraction and on the structure of three-dimensional random close-packed granular materials subject to gravity. The effects of grain shape (spherical or polyhedral), material polydispersity, and confining wall friction on this dependence are investigated. In agreement with a simple geometrical model, the solid fraction is found to decrease linearly for increasing confinement no matter the grain shape. Furthermore, this decrease remains valid for bidisperse sphere packings, although the gradient seems to reduce significantly when the proportion of small particles reaches 40% by volume. The confinement effect on the coordination number is also captured by an extension of the aforementioned model
Confined packings of frictionless spheres and polyhedra
International audienceBy means of numerical simulations, we study the influence of confinement on three-dimensional random close packed (RCP) granular materials subject to gravity. The effects of grain shape (spherical or polyhedral) and polydispersity on this dependence are investigated. In agreement with a simple geometrical model, the solid fraction is found to decrease linearly for increasing confinement no matter the grain shape. This decrease remains valid for bidisperse sphere packings although the gradient seems to reduce significantly when the proportion of small particles reaches 40% by volume. The aforementioned model is extended to capture the effect of the confinement on the coordination number
Conceptual Modelling of the Sediment Flux during a Flushing Event (Arc En Maurienne, France)
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
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