Showing papers by "Aix-Marseille University published in 1982"

Kinaesthetic role of muscle afferents in man, studied by tendon vibration and microneurography

Abstract: The characteristics of vibration-induced illusory joint movements were studied in healthy human subjects. Unseen by the subject, constant frequency vibration trains applied to the distal tendon of the Triceps or Biceps induced an almost constant velocity illusory movement of the elbow whose direction corresponded to that of a joint rotation stretching the vibrated muscle. Vibration trains of the same duration and frequency applied alternatively to the Biceps and Triceps evoked alternating flexion-extension illusory movements. During successive application of vibration trains at frequencies from 10 to 120 Hz, the perceived velocity of the illustory movements increased progressively from 10 to 70-80 Hz, then decreased from 80 to 120 Hz. The maximal perceived velocity was three times higher during alternating vibration of the Biceps and Triceps than during single muscle stimulation. Unit activity from 15 muscle spindle primary endings and five secondary endings located in Tibialis anterior and Extensor digitorum longus muscles were recorded using microneurography in order to study their responses to tendon vibration and passive and active movements of the ankle. Primary endings were all activated by low amplitude tendon vibration (0.2-0.5 mm) previously used to induce illusory movements of the elbow. The discharge of some was phase-locked with the vibration cycle up to 120 Hz, while others responded one-to-one to the vibration cycle up to 30-50 Hz, then fired in a sub-harmonic manner at higher frequencies. Secondary endings were much less sensitive to low amplitude tendon vibration. Primary and secondary ending responses to ramp and sinusoidal movements of the ankle joint were compared. During the movement, the primary ending discharge frequency was almost constant, while the secondary ending activity progressively increased. During ankle movements the primary ending discharge appeared mainly related to velocity, while some secondary activities seemed related to both movement velocity and joint angle position. Muscle spindle sensory ending responses to active and passive ankle movements stretching the receptor-bearing muscle (plantar flexion) were qualitatively and quantitatively similar. During passive reverse movements (dorsiflexion) most of the sensory endings stopped firing when their muscle shortened. Active muscle shortening (isotonic contraction) modulated differently the muscle spindle sensory ending discharge, which could stop completely, decrease or some times increase during active ankle dorsiflexion. During isometric contraction most of the muscle spindle sensory endings were activated. The characteristics of the vibration-induced illusory movements and the muscle spindle responses to tendon vibration and to active and passive joint movements strengthened the possibility of the contribution of primary endings to kinesthesia, as suggested by several previous works...

Origin of siltstones: glacial grinding versus weathering

Abstract: Siltstones are unusual rocks. They are mainly made up of quartz. Glacial grinding is considered by some authors to be the main, or even the only, process generating silt. This is supported by: (1) the presence of silt in basal tills from present ice-caps and, above all, (2) by the volumetric importance of Quaternary loess. However, ancient glaciogenic sediments contain only a little silt scattered in the matrix of tillites, or forming thin intercalations in pro- and periglacial deposits. These siltstones represent less than 5% of the total volume of Upper Proterozoic and Upper Ordovician glaciogenic sequences of West Africa. On the other hand, silt is abundant in weathering profiles of tropical, equatorial and mediterranean zones. This silt is generated by splitting of minerals, mainly quartz, inherited from the parent rock. Quartz grains are partly dissolved in situ and their fragments cemented by iron oxi-hydroxides in tropical and equatorial zones and by calcite in mediterranean zones. Silt is particularly abundant in tropical soils, comprising up to 50-75%. Secondary dissolution of the iron or calcite matrix induces disaggregation of these soils and the release of silt which is later reworked and concentrated by wind or running water. Weathering processes, and especially those operating in tropical zones, are the main phenomena generating silt. Glacial grinding would generate only a little silt. A large part of the material of Quaternary loess may be derived from glacially reworked weathering profiles.

Autocovariance functions, root-mean-square-roughness height, and autocovariance length for rough deposits of copper, silver, and gold

Abstract: Autocovariance functions (ACF's) for rough surfaces of copper, silver, and gold deposits are deduced from surface profiles determined by the use of microdensitometer analysis of surface-shadowed carbon replicas. It is shown that the initial portions of the ACF's have a Gaussian form. The root-mean-square (rms) surface roughness $\ensuremath{\delta}$ and the autocorrelation length $\ensuremath{\sigma}$ are deduced for each surface. Values of $\ensuremath{\sigma}$ agree with corresponding values deduced from the ACF's of the surface slopes. Results of this study are compared with those previously obtained for rough magnesium deposits. We conclude that the Gaussian model is suitable to represent in general the ACF's of rough metallic surfaces. Lastly, it is shown that $\ensuremath{\sigma}$ increases with $\ensuremath{\delta}$, and within the accuracy range of their measurements there is a linear relation between $\ensuremath{\delta}$ and $\ensuremath{\sigma}$.

Height and slope distributions for surfaces of rough metallic deposits.

Abstract: This paper deals with the accurate determination of height and slope distributions for surfaces of rough metallic deposits (magnesium, copper, silver, and gold). These distributions are computed using a microdensitometer analysis of electron micrographs of surface replicas. It is shown that most of the surfaces examined have reasonable Gaussian height and slope distributions. Apart from magnesium surfaces, the rms roughnesses determined from these distributions agree (within the accuracy range of their measurements) with rms roughnesses deduced from the autocovariance functions computed previously. Within the framework of scalar scattering theory, some emphasis is laid on the value of slopes to draw certain conclusions about the validity of the assumptions under which the scalar scattering theory is derived.

Unusual Debris Flow Deposits from the Base of the Malta Escarpment (Eastern Mediterranean)

Abstract: The more than 3000 m high Malta Escarpment forms the western boundary of the eastern Mediterranean. The escarpment has an average dip of about 20°, however the lower part of the escarpment is steeper and has a slope of approximately 60° (Figure 1). Extensive exposures of late Triassic-lower Liassic shallow water limestone occurs along this lower part of the escarpment (Chayes et al, 1980; Scandone et al, in press; Cita et al, in press).

Étude lithostratigraphique et tectonométamorphique des Rehamna sud-orientales, Plissements et nappes. Contribution à la connaissance de la chaîne hercynienne en Meseta marocaine

Abstract: Dans les Rehamna orientales (meseta hercynienne marocaine), quatre unites structurales ont ete individualisees, separees par des contacts anormaux peu pentes, Ce sont, de bas en haut 1 - L'unite des Oulad Aguil Cette unite comprend deux grands groupes lithostratigraphiques dont les relations structurales ne sont pas encore definitivement etablies : - au N, c'est le groupe de la Koudiat el Adam, non metamorphique, date de l'Ordovicien et constitue d'environ 1500 m de sediments detritiques (gres, quartzites, siltstones, argilites) deposes en milieu marin peu profond; les roches de ce groupe constituent un vaste anticlinal kilometrique originellement deverse au NW. - au S, c'est le groupe deo Ouled Hassine, metamorphique, non date mais probablement d'âge post-ordovicien superieur, constitue de roches metamorphiques variees (quartzites, calcaires, conglomerats, phyllites, slates) qui rappellent des facies marins de plate-forme; l'epaisseur de la succession est au moins d'un millier de metres; les roches de ce groupe constituent un vaste synclinorium deverse au NW qui semble relayer normalement vers le S l'anticlinal precedent; dans ce groupe le metamorphisme est prograde vers le S. 2 - L'unite de Benguerir Cette unite est constituee de roches metamorphiques, non datees, d'origine volcano-sedimentaire (quartzophyllites, phyllites, schistes, metatufs basiques, amphibolites, epidotites) rappelant beaucoup certains facies d'âge viseen superieur connus plus au N et plus au S ; le metamorphisme est prograde vers le S. Cette unite repose sur le groupe des Ouled Hassine au N par l'intermediaire d'un contact anormal faiblement pente au SSE. 3 - L'unite du Jebel Kharrou Cette unite, non metamorphique, datee de l'Ordovico-Silurien, est constituee des memes roches que le groupe de la Koudiat el Adam; elle est tronquee a la base par un contact anormal brechifie tres peu pente et repose sur les deux unites precedentes. 4 - L'unite de Dalaat Cette unite, non metamorphique, est constituee de roches detritiques (gres, siltstones, argilites silteuses, conglomerats) et carbonatees (calcaires) d'âge viseen superieur-namurien (?); elle constitue une klippe, tronquee a la base par un contact anormal brechifie, et elle repose sur l'unite du Jebel Kharrou. Les deux unites les plus basses, bien que separees par un contact anormal, subi des evolutions tectono-metamorphiques similaires; elles representent le substratum relatif des deux autres unites sus-jacentes. Evolution tectonique, metamorphique et magmatique des Rehamna orientales Cette evolution peut etre grossierement divisee en trois periodes, apres le depot des sediments (Cambrien a Viseen superieur-Namurien (?)) 1 - Entre le Viseen superieur et le Namurien ( ?) et l'Autunien se situe une evolution tectono-metamorphique polyphase, essentiellement commandee par des cisaillements de moins en moins ductiles avec le temps, la tendance generale est a un deplacement de matiere vers l'W ou le NW : synchrone du metamorphisme regional a sericite-biotite, on a un paroxysme thermique du metamorphisme marque par la cristallisation de grenat, de staurotide et de cordierite. Ces mineraux sont ensuite repris par un deuxieme episode de plissement dejete au NW ou a l'W, accompagne de couloirs de cisaillements ductiles fortement pentes a l'Est dans lesquels il n'y a pas de nouvelles cristallisations. Un troisieme episode de plissement N 140° lie a des decrochements dextres, reoriente les structures precedentes. L'unite de Benguerir chevauche ensuite l'unite des Oulad Aguil du SE vers le NW en conditions superficielles. Ce chevauchement est peut-etre recoupe par des granites dans les Rehamna centrales; dans ce cas, il serait ante-granites, dates de - 273±2 M.a. (Autunien basal). Le contact anormal est recoupe dans le secteur etudie par des filons de microdiorite quartzique eux-memes posterieurs aux granites. 2 - Pendant l'Autunien (sous reserve des attributions chronologique) le bâti est affecte d'une importante tectonique tangentielle marquee par la mise en place d'une nappe tectonique epiglyptique : l'unite de Dalaat. Cette nappe transporte des roches deja plissees et tronquees a la base. Le deplacement se fait du N vers le S, a partir d'une partie actuellement inconnue et sur au moins 22 km. Le passage de cette nappe entraine des morceaux de substratum (unite du Jebel Kharrou) en position paraautochtone sur au moins 20 km vers le Sud. Les causes de cette tectonique tangentielle du Nord vers le Sud sont actuellement inconnues. La mise en place de ces nappes acheve la fin du cycle hercynien. 3 - Les premiers depots post-orogeniques sont representes par des conglomerats attribues a l'Autunien et qui proviennent de l'erosion de la chaine hercynienne. Il leur fait suite l'epanchement de laves permo-triasiques, suivis de la formation de horsts et de grabens N 70°. Ces deux derniers evenements pourraient marquer une distension regionale post-hercynienne. Apres une nouvelle periode d'erosion, la mer transgressera cette region au Cretace inferieur.

Action in vitro de fongicides benzimidazoles et thiophanates sur Ceratocystis fimbriata E. et H. f. platani

Abstract: In vitro action of selected benzimidazole and thiophanate systemic fungicides on Ceratocystis fimbriata E. et H. f. platani. The relative effects of several systemic fungicides (benzimidazoles: carbendazim, benomyl, and thiabendazole; and a thiophanate: methyl-thiophanate) of French strain of Ceratocystis fimbriata E. et H. (platani were studied in vitro by measuring mycelium diameter growth, percent conidiospore germination, and development from chlamydospores. Both strains were sensitive to carbendazim and methyl-thiophanate. These chemicals inhibited mycelium growth and development of chlamydospores.

Stabilité de l'interface cristal-bain fondu d'un alliage binaire dilué

Abstract: A partir d’un modele propose par Friedel (1 ) on etablit un critere thermodynamique de stabilite de l’interface plane et un critere dynamique d’evolution du front perturbe. Ces criteres sont directement relies a la theorie de la stabilite morphologique.

Modelisation de la hauteur de barriere des joints de grains dans une jonction - influence de l'éclairement

Abstract: This paper presents a study o f the v a r i a t i o n o f the g r a i n b a r r i e r he igh t i n a j u n c t i o n under e q u i l i b r i u m o r d i r e c t biased. The in f luence o f the e x c i t a t i o n l e v e l on the b a r r i e r he igh t and consequent l y on the e f f e c t i v e i n t e r f a c i a l recombination v e l o c i t y depends on the d i s t r i b u t i o n and densi ty o r i n t e r f a c e s ta tes and a lso on the doping a t the v i c i n i t y o f g r a i n boundaries. It has been v e r i f i e d t h a t the b a r r i e r he igh t decreases l i n e a r l y w i t h the d i f fe rence o f the quasi-Fernii l e v e l s f o r h igh i n j e c t i o n . The e f f e c t i v e i n t e r f a c i a l recombination v e l o c i t y o f a g r a i n boundary increases exponent ia l ly w i t h the b a r r i e r height. 1. In t roduc t ion . Les p ropr ie tes 6 lect ron iques des j o i n t s de gra ins dans l e s semiconducteurs p o T y c r i s t a l l i n s dependent de lacharge des e t a t s d ' i n t e r f a c e qui prcvoque une courbure des bandes e t une b a r r i e r e de p o t e n t i e l . Le ca lcu l de l a hauteur EB de c e t t e b a r r i e r e depend du modele de d i s t r i b u t i o n des @ t a t s d ' i n t e r f a c e dans l a bande i n t e r d i t e ; ces @ t a t s peuvent C t re l o c a l i s 6 s sur un seul niveau d'energie E t ( d i s t r i bu t ion monoenerg6tique) /1/ ou d i s t r i b u e s uniformement .3 1 ' i n t e r i e u r d'une bande pouvant occuper toute l a bande i n t e r d i t e ( d i s t r i b u t i o n uniforme) /2/ pour ne c i t e r que l e s d i s t r i b u t i o n s l e s p lus simples. Le ca lcu l de EB depend aussi de l a p r o b a b i l i t e d'occupation ft des niveaux d ' i n t e r f a c e ; .3 l ' e q u i l i b r e , on peut e c r i r e ft = fo ( fonct ion de Fermi-Dirac) ou ft = fo 1/2. Ce cas correspond au modele de l a bande demi-pleine ( H a l f F i l l e d Band) qu i e s t l e p lus u t i l i s e dans l a descr ip t ion des d is loca t ions /3/ ou dans c e l l e des surfaces de semi-conducteurs /4/ lorsque l e s @ t a t s s o n i essent i e l 1 ement a t t r i bues aux 1 i a i sons pendantes. La barr iGre aux j o i n t s de gra ins a m p l i f i e consid6rablemcnt l ' a c t i v i t * recombinante des j o i n t s de gra ins, b i e ~ mise en evidence par E.B.I.C. /5 / ou par L.B.I.C. /6/ e t caracter isee par une v i tesse de recombinaison i n t e r f a c i a l e e f f e c t i v e s. El l e e s t responsable de l a degradation des p ropr ie tes e lect ron iques e t photovoltatques des semi-conducteurs p o l y c r i s t a l l i n s . Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982112

Production of a large planar array of Lomer-Cottrell locks in silver by controlled mechanical straining

Abstract: A silver crystal plate with (001) faces has been deformed in a bending jig around [ITO], and fresh dislocations have been imaged by X-ray topography. Long straight dislocations extend all over the crystal end they are analysed aa being Lomer-Cottrell locks. Such macroscopic arrays of locks have previously been observed only in as-grown or thermal-shocked crystals. The present study demonstrates the possibility of obtaining these arrays by a well-controlled mechanical deformation.