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Showing papers by "Aix-Marseille University published in 1981"


Journal ArticleDOI
TL;DR: A new method that uses a microdensitometer to analyze electron micrographs of shadowed surface replicas and a close approach to the real profiles is obtained, which shows that the method may have other important applications in addition to the study of alterable metallic surfaces.
Abstract: A new method for studying surface roughness is presented that uses a microdensitometer to analyze electron micrographs of shadowed surface replicas. First we give a preliminary description of the replication technique and the microdensitometer analysis. Then we proceed to show that the micrograph density (or transmittance) is approximately proportional to the slope of the surface elements, which enables us to determine the surface profile by integration of the microdensitometer data. Bidimensional and monodimensional median-filtering algorithms are used in the data reduction, and their validity is analyzed. With the help of a computer program that plots a perspective view of rough surfaces, we find that a close approach to the real profiles is obtained. This shows that our method may have other important applications in addition to the study of alterable metallic surfaces.

48 citations


Journal Article
TL;DR: It is concluded that the proprioceptive system through which vibration-induced afferents enter the neurological networks is the common denominator for the observed alterations of the position, velocity, and force controls.
Abstract: The effects of whole body vibration (WBV) were studied on subjects trained to perform on tasks involving blindfolded arm positioning (proprioceptive tasks), tracking of visual targets and control of static and dynamic torques. Subjects were vibrated in a seated position by means of a hydraulic jack. The vibration used (0.1 G at floor level and 18 Hz) was that occasionally encountered on medium-size cruising helicopter. The seat was that of a heliccopter pilot whose foam cushion was 6 cm thick with a density of 26 kg/m3. Systematic past-pointing was observed for both arm flexion and extension. Foot and arm visual tracking precision, as determined by position and velocity errors, increased in both directions. Static and dynamic control, rated by torque holding stability and torque amplitude precision, were also significantly altered compared to pre-stimulus readings. The results are interpreted in relation to current knowledge of the effects of vibration induced at spinal, vestibular, and central nervous system levels. It is concluded that the proprioceptive system through which vibration-induced afferents enter the neurological networks is the common denominator for the observed alterations of the position, velocity, and force controls. Our observations suggest that particular care should be taken in helicopters and other vibrating vehicles to prevent vibration from reaching muscular masses, especially those involved in motor tasks.

35 citations


Journal ArticleDOI
TL;DR: The results of a multinational concerted programme to compare different numerical methods which have been independently proposed for the determination of thermokinetics from experimental calorimetric data are presented.
Abstract: The results of a multinational concerted programme on the determination of thermokinetics are presented. The purpose of the programme was to compare different numerical methods which have been independently proposed for the determination of thermokinetics from experimental calorimetric data. To achieve this end, the same experimental data, obtained from two heat-flow calorimeters, were distributed and successively analyzed by the different methods. Numerical methods based on the state function theory, on Fourier transform analysis, on dynamic optimization and on a simple differentiation of the data were thus critically tested.

30 citations


Journal ArticleDOI
TL;DR: Descloux et al. as discussed by the authors presented a paper on the Descloux algorithm for the decomposition of the number of points in a decoder and the order of the points.
Abstract: Note: Univ michigan,dept math,ann arbor,mi 48109. ecole polytech,ctr math appl,f-91128 palaiseau,france. Descloux, j, ecole prat hautes etud,dept math,f-75231 paris 05,france.ISI Document Delivery No.: LE068Times Cited: 3Cited Reference Count: 17 Reference ASN-ARTICLE-1981-004doi:10.2307/2007731 Record created on 2006-08-24, modified on 2017-05-12

20 citations


Journal ArticleDOI
TL;DR: Tanna, one of the southernmost islands of the New Hebrides volcanic arc, is made of Late Pliocene to Recent island arc tholeiitic basalts and andesites, with SiO2 contents ranging from 45 to 57 as discussed by the authors.
Abstract: Tanna, one of the southernmost islands of the New Hebrides volcanic arc, is made of Late Pliocene to Recent island arc tholeiitic basalts and andesites, with SiO2 contents ranging from 45 to 57%. These lavas are highly porphyritic (30–50% in volume): phenocrysts of plagioclase are the most abundant, together with olivine and clinopyroxene. The groundmass contain plagioclase, augite, olivine, magnetite and glass; pigeonite, tridymite, sanidine and, rarely, biotite may also occur. The olivines and clinopyroxenes show an iron enrichment from the cores of phenocrysts to their rims and the groundmass crystals, but their compositional variations are not correlated with the Mg/Fe ratio of bulk host rocks, the most Fe-rich compositions being found in Mg-rich lavas. Plagioclase compositions range from An95 to An60 in the basalts and An60 to An50 in the andesites, but, within each group, they are not correlated with SiO2 or Na2O contents of host lavas. Consequently, the bulk major element compositions of Tanna volcanic rocks cannot be considered as primarily controlled by crystal separation from successive liquids. The oxyde-SiO2 variations diagrams, and the modal compositions and mineral chemistry show that crystal accumulation is the predominant mechanism accounting for bulk rock compositions. However, this does not exclude fractional crystallization: the variation of the calculated groundmass mineralogy strongly suggest the occurrence of crystal removal mainly clinopyroxene and magnetite.

14 citations


Journal ArticleDOI
TL;DR: In this paper, a model is proposed to estimate the cell size of the solidification front in a binary alloy for a stationary unidirectional growth, where the free energy of the growing crystal is calculated as a function of the interfacial shape, the most likely cell size corresponding to the minum crystal free energy.

10 citations


Journal ArticleDOI
TL;DR: The correlated-site-bond percolation model of Coniglio and Klein this article avoids the difficulties with droplet definitions in the simpler Ising and Percolation models.

10 citations




Journal ArticleDOI
TL;DR: In this article, the morphological stability of a planar solid-melt interface during unidirectional solidification of dilute PbBi alloys is studied.

8 citations



Journal ArticleDOI
TL;DR: There must be a correlation between the mechanism of the recruitment of Gymnophallid larvae by a given second host and the characteristics of the environment where the life cycle unfolds and the recruitment observed is illimited.
Abstract: Dans le cycle biologique heteroxene des Gymnophallidae, le premier hote intermediaire est habituellement un Lamellibranche, beaucoup plus rarement un Prosobranche. Dans la majorite des cas, les deuxiemes hotes sont des Pelecypodes, peu frequemment des Prosobranches ou des Annelides polychetes. L’hote emetteur est donc le plus souvent sedentaire ; cette particularite est un handicap pour une large dissemination des elements infestants. Les hotes recepteurs sont, eux aussi, relativement immobiles ; ils ne peuvent donc explorer la totalite du milieu ce qui est desavantageux pour le parasite. Pour contourner de telles difficultes, les Gymnophallides se sont adaptes en produisant de grandes quantites de cercaires (plusieurs centaines de milliers et meme plusieurs millions selon les especes). Suivant la nature du milieu dans lequel se deroule le cycle biologique on observe alors : — soit une dispersion des elements infestants (milieu marin de mode plus ou moins agite) — soit au contraire une concentration des cercaires (milieu lagunaire confine ou etangs saumâtres fermes).Chez les Gymnophallidae caracteristiques des milieux fermes, les deuxiemes hotes intermediaires ne recrutent par leurs parasites de la meme facon que ceux des especes de Gymnophallides infeodees au milieu marin ouvert.En milieu confine, le recrutement des agents infestants ne se poursuit pas pendant toute la duree de la vie de l’hote ; il tend vers une valeur optimum qui est atteinte lorsque le microhabitat est sature : c’est un recrutement limite. En milieu ouvert, les deuxiemes hotes intermediaires recrutent leurs parasites d’une maniere qui parait illimitee. Cette particularite est due au fait que des reactions palleales du Mollusque isolent les metacercaires du microhabitat dans lequel elles s’etaient initialement installees. Les metacercaires, parfaitement vivantes, sont ainsi regroupees au sein de spherules et celles-ci sont progressivement repoussees a l’interieur des tissus de l’hote. Les metacercaires sont donc retirees en permanence du microhabitat extrapalleal et deviennent des parasites intrapalleaux. Ainsi le microhabitat demeure toujours disponible pour de nouvelles infestations et ne se sature jamais.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional model of cellular growth is built for which the solid-melt interface is described by a cosine, and a stability condition with respect to a variation of the cell size is derived from the Glansdorff-Prigogine General Evolution Criterion.

Journal ArticleDOI
TL;DR: In this paper, a partir des equations de Maxwell, l'absorption de la lumiere visible par ces surfaces particulieres is investigated, and the authors rendons compte ici de nos premieres conclusions en insistant sur les difficultes rencontrees.
Abstract: Les reseaux ou les reseaux croises traces sur un materiau de conductivite finie constituent un modele simple de surface rugueuse. Nous avons donc essaye de predire, a partir des equations de Maxwell, l'absorption de la lumiere visible par ces surfaces particulieres. Nous rendons compte ici de nos premieres conclusions en insistant sur les difficultes rencontrees.

Journal ArticleDOI
TL;DR: In this paper, a long pulse (200 ns) XeCl excimer laser emission (λ = 3 080 A) was obtained when Ne/Xe/HCl mixtures are excited by an electron beam and X-rays assisted discharge either at room temperature or at very low temperature.
Abstract: Long pulse (200 ns) XeCl excimer laser emission (λ = 3 080 A), has been obtained when Ne/Xe/HCl mixtures are excited by an electron beam and X-rays assisted discharge either at room temperature or at very low temperature. Absorbed discharge energy is several orders of magnitude higher than the absorbed beam energy. Maximum specific laser energy is 3 J/l at room temperature for a 16 cm gain length and an absorbed discharge energy of 150 J/1.


Book ChapterDOI
01 Jan 1981
TL;DR: In this paper, a simple model of surface source and its different mechanisms of expansion under an applied stress was proposed to explain the dislocations induced by the presence of the external boundary.
Abstract: At the very beginning of the deformation of a crystal, surface sources are activated before internal sources of same length. X-ray topographs of slightly deformed f.c.c. metal crystals exhibit particular configurations of dislocations induced by the presence of the external boundary. The experimental facts can be explained by a simple model of surface source and its different mechanisms of expansion under an applied stress.