404 research outputs found
Combined numerical and experimental investigation of the micro-hydrodynamics of chevron-based textured patterns influencing conjunctional friction of sliding contacts
Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved micro-wedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions
Premières molaires permanentes et variations palatine ou mandibulaire
101 children, each of them with two teleradiographies, were selected. The first X-ray was taken at the time of the mixed dentition, the second one, when the permanent dentition was established. The purpose of the research is to show the oscillations of the palatine and mandibular planes, and their link to the movements of the first permanent molars. The palatine plane is found to swing between - 7° and +5°, with an average of -0.97°. The posterior part of that plane rocks downwards in 51% of the children. The limits are -7° and -1°, with an average of -3.2°. In 22%, the plane rocks upwards between +1° and +5° with an average of +3.1°. In 27% it moves parallel to itself. The posterior part of the mandibular plane varies between -6° and +5°, with an average of -1.1°. It rocks downwards in 48% of the cases, between -6° and -1° with an average of -3.9°. In 22% of the children, this plane rocks upwards between +1° and +5°with an average of +2.5°. In 30%, it moves parallel to itself. The overall result is that the more the posterior part of the palate, or of the mandibule moves downwards, the more the first permanent molars get straight or move forwards.Le but de ce travail est de déterminer les oscillations des plans palatin et mandibulaire ainsi que leur lien avec les mouvements des premières monophysaires. Les téléradiographies, prises à quelques années d’intervalle, de 101 enfants, sont superposés sur le compas ptérygo-clivien. Plus la partie postérieure des lames palatines ou de la mandibule s’abaisse, plus les premières molaires se redressent ou se déplacent vers l’avant
Hybridizing network reluctance and boundary integral methods: comparisons on an E-core actuator
International audienceHybridizing the network reluctance method (NRM) and the boundary integral method (BIM) aims to take advantage of both methods. First for ferromagnetic materials in order to take non linearity into account, and second for surrounding air in order to include fringing and leakages accurately. The automation of such modeling has been done with dedicated software and is compared to the tooth contour method (TCM) and finite element (FEM) simulations, which is applied to an E-core actuator
Dissipation of vibration in rough contact
The relationship which links the normal vibration occurring during the sliding of rough surfaces and the nominal contact area is investigated. Two regimes are found. In the first one, the vibrational level does not depend on the contact area, while in the second one, it is propor- tional to the contact area. A theoretical model is proposed. It is based on the assumption that the vibrational level results from a competition between two processes of vibration damping, the internal damping of the material and the contact damping occurring at the interface
Introduction to Configuration Path Integral Monte Carlo
In low-temperature high-density plasmas quantum effects of the electrons are
becoming increasingly important. This requires the development of new
theoretical and computational tools. Quantum Monte Carlo methods are among the
most successful approaches to first-principle simulations of many-body quantum
systems. In this chapter we present a recently developed method---the
configuration path integral Monte Carlo (CPIMC) method for moderately coupled,
highly degenerate fermions at finite temperatures. It is based on the second
quantization representation of the -particle density operator in a basis of
(anti-)symmetrized -particle states (configurations of occupation numbers)
and allows to tread arbitrary pair interactions in a continuous space.
We give a detailed description of the method and discuss the application to
electrons or, more generally, Coulomb-interacting fermions. As a test case we
consider a few quantum particles in a one-dimensional harmonic trap. Depending
on the coupling parameter (ratio of the interaction energy to kinetic energy),
the method strongly reduces the sign problem as compared to direct path
integral Monte Carlo (DPIMC) simulations in the regime of strong degeneracy
which is of particular importance for dense matter in laser plasmas or compact
stars. In order to provide a self-contained introduction, the chapter includes
a short introduction to Metropolis Monte Carlo methods and the second
quantization of quantum mechanics.Comment: chapter in book "Introduction to Complex Plasmas: Scientific
Challenges and Technological Opportunities", Michael Bonitz, K. Becker, J.
Lopez and H. Thomsen (Eds.) Springer Series "Atomic, Optical and Plasma
Physics", vol. 82, Springer 2014, pp. 153-194 ISBN: 978-3-319-05436-0 (Print)
978-3-319-05437-7 (Online
Finite-time fluctuations in the degree statistics of growing networks
This paper presents a comprehensive analysis of the degree statistics in
models for growing networks where new nodes enter one at a time and attach to
one earlier node according to a stochastic rule. The models with uniform
attachment, linear attachment (the Barab\'asi-Albert model), and generalized
preferential attachment with initial attractiveness are successively
considered. The main emphasis is on finite-size (i.e., finite-time) effects,
which are shown to exhibit different behaviors in three regimes of the
size-degree plane: stationary, finite-size scaling, large deviations.Comment: 33 pages, 7 figures, 1 tabl
Stress in frictionless granular material: Adaptive Network Simulations
We present a minimalistic approach to simulations of force transmission
through granular systems. We start from a configuration containing cohesive
(tensile) contact forces and use an adaptive procedure to find the stable
configuration with no tensile contact forces. The procedure works by
sequentially removing and adding individual contacts between adjacent beads,
while the bead positions are not modified. In a series of two-dimensional
realizations, the resulting force networks are shown to satisfy a linear
constraint among the three components of average stress, as anticipated by
recent theories. The coefficients in the linear constraint remain nearly
constant for a range of shear loadings up to about .6 of the normal loading.
The spatial distribution of contact forces shows strong concentration along
``force chains". The probability of contact forces of magnitude f shows an
exponential falloff with f. The response to a local perturbing force is
concentrated along two characteristic rays directed downward and laterally.Comment: 8 pages, 8 figure
A model for collisions in granular gases
We propose a model for collisions between particles of a granular material
and calculate the restitution coefficients for the normal and tangential motion
as functions of the impact velocity from considerations of dissipative
viscoelastic collisions. Existing models of impact with dissipation as well as
the classical Hertz impact theory are included in the present model as special
cases. We find that the type of collision (smooth, reflecting or sticky) is
determined by the impact velocity and by the surface properties of the
colliding grains. We observe a rather nontrivial dependence of the tangential
restitution coefficient on the impact velocity.Comment: 11 pages, 2 figure
SCI
Persistent homology is a powerful tool in Topological Data Analysis (TDA) to capture the topological properties of data succinctly at different spatial resolutions. For graphical data, the shape, and structure of the neighborhood of individual data items (nodes) are an essential means of characterizing their properties. We propose the use of persistent homology methods to capture structural and topological properties of graphs and use it to address the problem of link prediction. We achieve encouraging results on nine different real-world datasets that attest to the potential of persistent homology-based methods for network analysis
Static Friction Phenomena in Granular Materials: Coulomb Law vs. Particle Geometry
The static as well as the dynamic behaviour of granular material are
determined by dynamic {\it and} static friction. There are well known methods
to include static friction in molecular dynamics simulations using scarcely
understood forces. We propose an Ansatz based on the geometrical shape of
nonspherical particles which does not involve an explicit expression for static
friction. It is shown that the simulations based on this model are close to
experimental results.Comment: 11 pages, Revtex, HLRZ-33/9
- …