Showing papers by "Mines ParisTech published in 1990"

Determining watersheds in digital pictures via flooding simulations

Abstract: The watershed transformation is a very powerful image analysis tool provided by mathematical morphology However, most existing watershed algorithms are either too time consuming or insufficiently accurate The purpose of this paper is to introduce a new and flexible implementation of this transformation It is based on a progressive flooding of the picture and it works for n-dimensional images Pixels are first sorted in the increasing order of their gray values Then, the successive gray levels are processed in order to simulate the flooding propagation A distributive sorting technique combined with breadth-first scannings of each gray level allow an extremely fast computation Furthermore, the present algorithm is very general since it deals with any kind of digital grid and its extension to general graphs is straightforward Its interest with respect to image segmentation is illustrated by the extraction of geometrical shapes from a noisy image, the separation of 3-dimensional overlapping particles and by the segmentation of a digital elevation model using watersheds on images and graphs

Canards et enlacements

Abstract: On considere le probleme de la convergence, pour e positif tendant vers zero, des champs de vecteurs, notes Ee, sur R 3 du type x˙=f(x,y,z,e), y˙=g(x,y,z,e), ez=h(x,y,z,e) Ce probleme est connu sous le nom de perturbation singuliere, ou de probleme a deux echelles de temps Le probleme de la convergence de (Ee) vers un champ (E 0 ) est un probleme de convergence de trajectoires Soit (Me) une famille de points de R 3 telle que Me converge vers un point M 0 Soit γe la trajectoire du systeme (Ee) issue du point Me La famille (γe) converge-t-elle vers une courbe γ 0 ? Si oui, en quel sens? au sens de la convergence uniforme sur tout compact des fonctions du temps? au sens de la convergence C 1 ?… Reciproquement, soit γ 0 une «trajectoire de (E 0 )» Peut-on trouver une suite de conditions initiales Me telle que la trajectoire de (Ee) issue de Me converge vers γ 0 ?… On utilise des outils non standard pour analyser ce type de question

The Force and the Reason of Experiment

Abstract: In this famous report of what may be the oldest public scientific experiment, several features are remarkable. The performance has almost certainly never been staged (at least with a fully loaded ship);1 it is thus a tale of a staged thought experiment, but a story which for hundreds of years played a continuous role in shaping the relations between Kings, mathematics, war and mechanics. It is a public show before all the assembled ‘media’. It is a direct application of a theoretical demonstration that Archimedes had just completed following a Platonist research program that Plutarch sketches in the paragraph before. It is Archimedes himself who takes the initiative of boasting to the King that he can move the Earth; the King, quite reasonably, challenges him to a ‘show down’ by way of a smaller scale public experiment before believing in the demonstration, as if he was unable to be convinced by the strength of mathematics alone; but it is the King who, in an instant, makes the connection of this striking but futile experiment with a technical and military research program headed by Archimedes (o demiurgos) to protect Syracuse against the Romans.

Decagonal Phases: Non-Quasi-Crystalline Microcrystalline State in an Al-Cu-Co-Si Alloy

Abstract: We present high-resolution electron microscopy and x-ray diffraction studies of the Al63Cu17.5Co17.5Si2 alloy at room temperature. The sample is found periodic in one direction c and presents tenfold symmetry in the l = 0 diffraction plane perpendicular to this direction. The two complementary techniques show that the sample is not in a 2D quasi-crystalline state but in a microcrystalline state, which restores the overall tenfold symmetry in diffraction pattern. On the basis of our present results, we discuss some relationships that could exist between microcrystalline and quasi-crystalline phases.

LASER SHOCK SURFACE TREATMENT OF Ni-BASED SUPERALLOYS

Abstract: Laser shock surface treatment could be envisaged to harden and induce compressive stresses within materials thus improving their fatigue and fretting-fatigue resistance. Both laser beam optical phe...

A review of lognormal estimators forin situ reserves

Abstract: The term “lognormal kriging” does not correspond to a single well defined estimator. In fact, several types of lognormal estimators forin situ reserves are available, and this may cause confusion. These estimators are based on different assumptions—that is, different models. This paper presents a review of these estimators.

Segmentation tools in mathematical morphology

Abstract: This paper presents a general methodology for picture segmentation using tools provided by mathematical morphology. This methodology is based on the marking of the objects to be segmented. The marking (using techniques which may differ according to the kind of picture to be analyzed) provides a " marker set" which is used to modify the gradient of the image. This modification using geodesic image reconstruction produces a new gradient image. The main characteristic of this modified gradient is that its minima exactly fit the various connected components of the " marker set" . In a second step a morphological transform called " watersheds" is performed on this gradient image. The watershed transform produces a partition of the image into homogeneous regions called " catchment basins" . Every catchment basin contains only one marker and its boundary corresponds to the pixels of the image where the contrast is locally maximum. Thus the transformed image exhibits the contours of the marked objects. Some examples illustrate the use of this process when objects marking is not too complex. Then we extend this method to situations where the marking step is not obvious and we show how the watershed transform together with the simplification of the image can provide efficient tools for detecting homogeneous regions in an image.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Study of moisture transfer during the strand sintering process

Abstract: Moisture transfer during the strand sintering operation was studied both experimentally and using a mathematical model. The drying of iron ore pellets was found to occur in two distinct periods: one at a constant drying rate and the other at a decreasing drying rate, whereas the drying of zinc ore pellets always occurs at a decreasing drying rate. Characteristic drying curves were determined for both materials. The moisture transfer mechanisms during the sintering process were demonstrated in detail, including the recondensation of water in the cold layers of the bed and the formation of an inert, overmoistened zone. The mathematical model presented simulates all of these phenomena and is used to calculate the variables related to moisture transfer. The model is adaptable to other processes where a hot gas passes through a moist packed bed.

Fatigue behaviour of CMSX 2 superalloy [001] single crystals at high temperature I: Low cycle fatigue of notched specimens

Abstract: The low cycle fatigue behaviour of shallow notch specimens of [001] superalloy single crystals was studied at 650 °C Three notch orientations were used for CMSX 2 alloy and only one for MAR-M200 alloy Crack initiation and growth were monitored using potential drop measurements and a plastic replication technique A very large scatter in fatigue life was observed and no clear notch orientation dependence of fatigue life could be discerned Cracks initiate at casting micropores in CMSX 2 and carbides in MAR-M200 These results are discussed using fractographic and metallographic observations Emphasis is placed on microcrack growth and on the size and location of the initiating defect

Basic properties of sputtered 310 stainless steel-nitrogen coatings

Abstract: 310 stainless steel (SS)-nitrogen coatings with a nitrogen composition up to 40 at.% (14 wt.%) were deposited on steel substrates below 300 °C by d.c. reactive magnetron sputtering in mixed Ar-N 2 discharges using amagnetic austenitic 310 SS targets. The chemical and structural characterization of the coatings is presented in relation to the deposition parameters, and some of their properties (internal stress, adhesion, microhardness etc.) are evaluated. The as-deposited coating structure is usually a metastable disordered supersaturated f.c.c. solid solution but, depending on the substrate temperature and nitrogen concentration, an amorphous-like structure is seen to occur.

Fatigue behaviour of CMSX 2 superalloy [001] single crystals at high temperature II: Fatigue crack growth

Abstract: The fatigue crack growth behaviour of two-dimensional cracks was studied in [001] single crystals of CMSX 2 nickel-based superalloy at 650 °C. An influence of the crystallographic orientation of the crack growth direction on the crack growth kinetics was evident for short cracks tested in air. This influence was mainly attributed to differences in crack closure. Comparison between short and long cracks indicated that no short-crack effect exists in these single crystals. Tests in vacuum gave significant differences in crack growth rate and in fatigue fracture mode, especially at low rates. These results are discussed and used to rationalize previous observations.

A Compatible Single‐Phase/Two‐Phase Numerical Model: 1. Modeling the Transient Salt‐Water/Fresh‐Water Interface Motion

Abstract: A numerical model (NEWVAR) to simulate the transient movement of a discrete interface between salt water and fresh water has been developed. NEWVAR is designed to allow the analysis of a regional two-dimensional ground-water flow in coastal aquifers. The numerical solution permits the prediction of both regional fresh-water levels and two-dimensional fresh-water/salt-water interface by using nested square meshes. The numerical solution is based on the finite-difference method; the Gauss-Jordan direct method is used for solving steady- and unsteady-state linear equations. Different procedures are used to avoid numerical difficulties in the transient position of the interface toe for two-dimensional areal flow. The numerical solution was tested against the analytical ones for the cases of an advancing interface and of a floating fresh-water lens over sea water. These tests showed good agreement, thus verifying the finite-difference approximation. The results of an application of this model to a real aquifer are discussed in a companion paper entitled: “A Compatible Single-Phase/Two-Phase Numerical Model 2. Application to a Coastal Aquifer in Mexico.”

Digital Euclidean skeletons

Abstract: works on an adequate class of functions, it is possible to define a subset ofremarkable points of the digital skeleton, called crest points. They form anover set of the centers of maximal disks. Crest points and their upstream formthe digital skeleton.The skeleton of a binary set is then made in three steps : 1) construct thedistance function, 2) detect the crest points, 3) construct their upstream.The quality of the skeleton depends on the quality of the distance function.The balls associated with the digital distance based on the connectivity ofthe grid are in fact polygons : hexagons for the hexagonal grid, squares or

A Compatible Single‐Phase/Two‐Phase Numerical Model: 2. Application to a Coastal Aquifer in Mexico

Abstract: The application of a numerical model to a coastal aquifer is presented including the simulation of single-phase and two-phase fluid flow. The single-phase part of the model solves the diffusivity equation and helps to identify certain parameters of the aquifer and to simulate the flow field (fresh water) under different conditions. The two-phase part of the model solves the partial differential equations describing the motion of salt water and fresh water separated by a sharp interface. The model was calibrated using the observed piezometry of the aquifer for the fresh-water flow field. Simulations were made for both steady-and unsteady-state conditions to establish the position and movement of the interface under different schemes of pumping. Results show that the model reproduces very accurately the flow field of fresh water. It identifies the potential salt-water intrusion (upconing) into some of the pumping wells, thus helping in the identification of optimal pumping schemes.

A mathematical model of development in a research field

Abstract: We use co-word analysis in a retrospective study of the transformation of the knowledge network in the field of polymer science from 1973 to 1976. The results of this study lead us to propose a model of change in the field. This model is based on the observation that the interaction of several networks gives rise to a sub-network that is at first central and then - and this is what the model allows us to predict — central and developed (without its precise content being predictable). Such sub-networks begin in regions of the network of central associated words where there are numerous holes or incomplete links. The model appears to be sufficiently robust statistically that it does not miss significant transformations and it suggests a way of predicting knowledge development. A comparison is made with other models of network transformation, such as the contagion model and the model of local structural equivalence.

The semi-solid processing of alloys and composites

Abstract: The Second International Conference on Semi-Solid Processing of Alloys and Composites will be held on June 10–12, 1992, at MIT in Cambridge, Massachusetts.

Directionally Solidified Materials:Nickel-base Superalloys forGas Turbines

Abstract: From the first forged turbine blades made of iron base alloys to the present nickel base single-grain turbine blades and vanes manufactured by directional solidification, an enormous amount of research has been directed to attaining the hottest possible combustion chamber temperatures in jet engines Temperature has been increased by about 15 K each year for the last two decades, improving the thermodynamic efficiency of the engines The more recent developments concern the manufacturing of single-grain parts made of nickel base superalloys with large amount of the γ ′ hardening phaseThis paper first presents the directional solidification process used to produce single-grain parts, the formation of as-cast microstructures and the defects that can arise during solidification In the second part the thermal treatments that are applied to the nickel base superalloys in order to enhance their mechanical properties are detailed The effect of crystallographic orientation and of the γ / γ ′ microstructure on the mechanical properties is briefly presented, as well as the microstructural changes that can possibly arise during service

Magnetic structures of PrFeSi 2 and NdFeSi 2 from neutron and Mössbauer studies

Abstract: Investigations by neutron diffraction and $^{57}\mathrm{Fe}$ M\"ossbauer measurements are reported on the ternary silicides R${\mathrm{FeSi}}_{2}$ (R=r/rPr,Nd) with the orthorhombic structure of the ${\mathrm{TbFeSi}}_{2}$-type (space group Cmcm) This structure, which is closely related to the ${\mathrm{ThCr}}_{2}$${\mathrm{Si}}_{2}$-type structure, can be described as isolated ${\mathrm{ThCr}}_{2}$${\mathrm{Si}}_{2}$ blocks connected via \ensuremath{\alpha}-${\mathrm{ThSi}}_{2}$ slabs ${\mathrm{PrFeSi}}_{2}$ orders ferromagnetically below ${\mathit{T}}_{\mathit{c}}$=26 K with magnetic moments [258(1)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 15 K] parallel to the b axis ${\mathrm{NdFeSi}}_{2}$ exhibits a more complex magnetic behavior Below ${\mathit{T}}_{\mathit{N}}$=65 K, it develops a sine-modulated antiferromagnetic structure, q=(0, 0591, 0), of the Nd moments parallel to the b axis with a maximum value of 252${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 42 K No local moment was detected at the iron site $^{57}\mathrm{Fe}$ M\"ossbauer data on ${\mathrm{NdFeSi}}_{2}$ indicate a progressive squaring of the sine modulation of the Nd moments with a pure square wave below 3 K The comparison of the transferred hyperfine fields at the iron nuclei in ${\mathrm{PrFeSi}}_{2}$ and ${\mathrm{NdFeSi}}_{2}$ suggests the occurrence of orbital polarization of the conduction electrons giving rise to anisotropic contributions to the hyperfine field and exchange interactions The results are discussed in terms of Ruderman-Kittel-Kasuya-Yosida exchange interactions and compared to those obtained previously on the ${\mathrm{ThCr}}_{2}$${\mathrm{Si}}_{2}$-type ternary silicides

Al-Co-Cu-Si and Al-Co-Cu microcrystalline and quasicrystalline phases of decagonal symmetry

Abstract: On the basis of HREM and electron diffraction studies and of previous X-ray single crystal diffraction results, we confirm the existence on a non-quasicrystalline microcrystalline state for the decagonal Al63Cu17.5Co17.5Si2 alloy at room temperature. The HREM results are compared to those obtained for the Al65Cu17.5Co17.5 alloy. Moreover for the first time, a high temperature phase transition towards a quasicrystalline state is revealed in the two compounds.

Sampling remotely sensed imagery for storage, retrieval and reconstruction

Abstract: A major difficulty in remote sensing is handling the many data from sensors aboard aircraft and satellites. In this paper we identify an optimal procedure for sampling remotely sensed data before their storage or on their retrieval. The procedure depends on spatial correlation in the scene and uses kriging to estimate values that have been lost. An example in which data from an airborne multispectral scanner could be diminished to only about one tenth without serious loss of precision illustrates the method.

Plasticity of a silicon bicrystal: a HREM study

Abstract: 2014 A perfect silicon bicrystal containing only one pure tilt grain boundary (GB) 03A3=9 (122) [011] is used as a model in order to study the very early stages of the mechanisms occurring at atomic scale close to the GB. The high resolution electron microscopy observations showed that most dislocations induced by the deformation integrated the GB by glide and climb. The evolution of the structure of the original GB has been studied for different strains and at different temperatures. The accumulation of the DSC dislocations into the GB leads to a variation in the misorientation angle between the two grains. In compression it increases, whereas it decreases in tension. Consequently, various E GBs have been detected. The key points are that, firstly, the structural evolution of the GB can be described with a limited number of structural units and secondly, depending on the deformation temperature, one 03A3 GB can exhibit two different structures. Microsc. MicroanaL Microstruct. 1 (1990) OCTOBER/DECEMBER 1990, PAGE 395 Classification Physics Abstracts 71.60 25.00