Showing papers by "Aix-Marseille University published in 1988"

A Study of Students' Understanding of Electricity in Five European Countries.

Abstract: This paper describes a study of the understanding of basic electrical concepts shown by 15‐17 year‐old students in England, France, The Netherlands, Sweden and West Germany, the same objective test having been administered to samples of students in each of these countries. When within‐country results were averaged across student groups the between‐country differences on many aspects of this subject were quite small. Those electrical principles which yielded significant differences fell into two main groups, one concerned with current, flow of charge and energy, the other with voltage and its relationship to current. The consistency with which these significant differences emerged across a range of problems concerning related principles suggests that these represent real differences between the outcomes of teaching across the five countries but the causes of these differences are not yet clear. Despite the differences that have emerged, the overall impression which the results convey is of substantially th...

D-meson production in 800-GeV/c pp interactions.

Abstract: We report on a study of the inclusive production properties of D/D-bar mesons in pp collisions at 800 GeV/c and compare our results to measurements made at lower energies and to the expectations of the QCD fusion model.

Physiological and genetic analysis of the glucose-fructose permeation system in two Synechocystis species

Abstract: Fructose is toxic for Synechocystis PCC 6714 and 6803, strains which grow chemoheterotrophically on glucose. This toxicity, as well as fructose uptake, were inhibited by glucose or by its non-metabolized analogue 3-O-methyl-glucose. The results suggested that both sugars were transported by the same permeation system, the affinity for fructose, estimated from the corresponding Km and Ki, being very low. The unicity of the permeation system was further established by the isolation of spontaneous mutants showing the expected pleiotropic phenotype, Glu−, Frur, transport−, and by the simultaneous re-acquisition of the relevant wild type characteristics in mutant cells transformed by wild type DNA. The genetic nature of this mutation is discussed in view of the impossibility to isolate spontaneously reversed wild type clones from the transport deficient mutants.

Comparative evolution of the Senegal and eastern central Atlantic Basins, from mineralogical and geochemical investigations

Abstract: Cretaceous to Palaeogene sedimentary series in two long, continously recovered boreholes from the Senegal coastal basin and adjacent Cape Verde deep-sea basin have been compared by mineralogical, geochemical, electron-microscope and microprobe investigations. The transition between the diagenetic influences related to the depth of burial and the palaeoenvironmental influences, identified in the thick coastal-basin successions, is complicated by the tectonic instability of the margin during periods of high subsidence rates and crustal thinning. As the deep-sea basin sediments are only slightly affected by diagenetic changes, the comparison between the deep sea and coastal series allows the relative effects of lithostatic pressure, tectonics and other palaeoenvironmental factors to be evaluated. The disappearance of synsedimentary signatures (tectonics, climate, depositional conditions, etc.) expressed by clay mineralogy occurs below 4.5 km; there are no significant diagenetic changes in sediments at less than 2 km depth. By comparing identical time slices in coastal and deep-sea basins, it is possible to recognize from the clay stratigraphic record the main African detrital sources, the hot and often semi-arid character of the continental climate during the Cretaceous, the existence of minor but extensive stages of tectonic activity (Barremian-late Aptian, late Albian-early Cenomanian), the temporary existence of semi-closed basins on the shelf (Late Cretaceous, early Palaeogene) and the complexity of transport and sedimentation relationships between proximal and distal environments.

Reciprocal effects of visual and auditory stimuli in a spatial compatibility situation

Abstract: When events occur in the visual and auditory modalities simultaneously, normal humans often give preference to the visually presented information. In the present experiment the existence of such a visual predominance was tested in a spatial compatibility paradigm. The results showed that reaction times were significantly delayed when the position of the visual stimulus did not coincide with the position of the auditory stimulus, whether subjects attended to the visual or to the auditory stimuli. Thus, no visual predominance was demonstrated. The discrepancy between these results and those of studies showing visual predominance can be explained by differences in the direction of attention: visual predominance appears when attention is divided between visual and auditory modalities, but seems to be absent (as in the present experiment) when subjects are asked to attend to one modality while ignoring the other.

Sensorimotor Activity and Metabolic Factors in Vestibular Compensation

Abstract: Dramatic impairments of postural, locomotor and oculomotor functions are shown following unilateral vestibular neurectomy or hemilabyrinthectomy in many species. Functional recovery develops with time, leading to a total or near complete compensation of the sensorimotor deficits. It is generally assumed that these disturbances are due to the strong imbalance between the spontaneous firing rate and the dynamic response properties of the vestibular nuclei neurons on both sides (Mc Cabe and Ryu 1969; Shimazu and Precht 1966; Precht 1974; Xerri et al. 1983; Lacour et al. 1985). During the time course of vestibular compensation, symmetrical resting rates are observed and the dynamic neuronal characteristics of the deafferented vestibular cells are partially restored (Precht et al. 1966; Pompeiano et al. 1984; Ried et al. 1984). These neurophysiological data are closely correlated with the biochemical changes observed in many central nervous structures, including the deafferented vestibular nuclei. Modifications in the energy metabolism of vestibular nuclei located on the lesioned side were shown in the rat (Llinas and Walton 1979) and in the frog (Flohr et al. 1981). By using the deoxyglucose method and by comparing the distribution of radioactivity in uncompensated and compensated animals, these authors pointed to an increase of the glucose uptake within the deafferented vestibular nuclei during the chronic stage of compensation. Assuming that metabolic activity measured as glucose uptake closely parallels functionally significant activity (Sokoloff 1977), this method provides also a good index of activity in the central nervous system.

Plasma 3,4-dihydroxyphenylethyleneglycol and 3-methoxy-4-hydroxyphenylethyleneglycol as indicators of central noradrenergic activity. A comparative study on control subjects and depressed patients.

Abstract: Animal studies have suggested interspecies differences in brain norepinephrine (NE) metabolism, especially with regard to the relative proportions of 3,4-dihydroxyphenylethyleneglycol (DOPEG) compared to 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG). In order to question the value of both glycol metabolites as peripheral indices of central noradrenergic activity, a comparative study of plasma DOPEG and MOPEG (measured by HPLC) related to depression, sex, age and diagnostic categories (DSM-III) was carried out on depressed and control subjects. In addition, two groups of 8 patients were randomly submitted to a desipramine 150 mg/day, or a metapramine 450 mg/day antidepressant treatment influencing the formation of DOPEG and MOPEG in a different way. The study did not demonstrate any difference between DOPEG and MOPEG for most of the experimental factors. We found also a significant positive correlation between plasma levels of DOPEG and MOPEG. Our results support the idea that each of these two biological indices can be used in the assessment of central noradrenergic activity.