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Biomedical subjects

M Fleury

Publications and source records attributed to M Fleury.

83 records · Page 5Linked to original sources
PubMedDate not supplied

New ways of probing surface nuclear relaxation and microdynamics of water and oil in porous media.

The microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allow us to obtain surface dynamical parameters such as surface correlation times, residence times and diffusion coefficients. A coefficient of affinity of the liquids for the pore surface is deduced.

Calcium Carbonate↗
PubMedDate not supplied

Surface nuclear magnetic relaxation and dynamics of water and oil in granular packings and rocks.

Low field proton nuclear spin-relaxation at variable magnetic field strength and temperature provides surface dynamical parameters such as surface diffusion coefficients, activation energies, time of residence and coefficient of surface affinity. These parameters were extracted from measurements on grain packs and natural oil-bearing rocks. On grain packs, we show first that changing the amount of surface paramagnetic impurities leads to striking different relationships between the pore-size and the relaxation times T1 and T2. These relationships are well supported by fast-diffusion (surface-limited) or slow-diffusion relaxation models. Surface relaxivity parameters rho1 and rho2 are deduced from the pore size dependence in the fast-diffusion regime. Then, we evidence the frequency and temperature dependence of the surface relaxivity rho1 by field cycling NMR relaxation and relevant theoretical models. The typical frequency dependence found allows an experimental separation of the surface and bulk microdynamics in granular packings and petroleum rocks and the determination of the above mentioned surface dynamical parameters. Finally, we present the first field cycling nuclear spin relaxation experiments performed in water/oil saturated petroleum rocks. We believe that these experiments give new information about the surface localization of these two saturating liquids in pores.

Diffusion↗
PubMedDate not supplied

Quantitative evaluation of porous media wettability using NMR relaxometry.

We propose a new method to determine wettability indices from NMR relaxometry. The new method uses the sensitivity of low field NMR relaxometry to the fluid distribution in oil-water saturated porous media. The model is based on the existence of a surface relaxivity for both oil and water, allowing the determination of the amount of surface wetted either by oil or by water. The proposed NMR wettability index requires the measurement of relaxation time distribution at four different saturation states. At the irreducible water saturation, we determine the dominant relaxation time of oil in the presence of a small amount of water, and at the oil residual saturation, we determine the dominant relaxation time of water in the presence of a small amount of oil. At 100% water and 100% oil saturation, we determine the surface relaxivity ratio. The interaction of oil with the surface is also evidenced by the comparison of the spin-lattice (T1) and spin-locking (T1rho) relaxation times. The new NMR index agrees with standard wettability measurements based on drainage-imbibition capillary pressure curves (USBM test) in the range [-0.3-1].

Geologic Sediments↗
PubMedDate not supplied

On the cognitive penetrability of posture control.

Postural sway increases with age. The decreased stability associated with postural sway often has been related to the reduced peripheral sensibility in the visual, vestibular, and proprioceptive systems. We examined whether the micropostural adjustments necessary for maintaining balance also require some cognitive processing. Young and older subjects were submitted to an auditory reaction time task while maintaining an upright posture on a force platform. The auditory stimuli were presented randomly when subjects were in a central or in an eccentric less stable postural position in four conditions of vision/surface. If the postural adjustments require some cognitive processing, a more eccentric position of the center of foot pressure (COP) would require more attention than a stable position of the COP because when an eccentric position is identified, a corrective response subsequently needs to be selected, programmed, and executed. The visual and surface conditions were altered to determine if additional attentional resources need to be allocated to the postural task when there is a reduction of the sensory information available. Results showed that as the sensory information decreased, the postural task became increasingly difficult for the elderly and required more of their attentional capacity (as indexed by increases in reaction time).

Acoustic Stimulation↗
PubMedDate not supplied

Upright standing and gait: are there changes in attentional requirements related to normal aging?

This study evaluates attentional requirements for maintaining an upright posture and for walking among young and elderly persons to determine if, with normal aging, there is a deficit and/or a modification in the allocation of the attentional resources necessary for balance control. Eight young adults and 8 elderly persons were asked to respond to an auditory reaction time (RT) task (secondary task) while in a seated position, while in a broad-support or narrow-support upright standing position, and while walking (primary tasks). Reducing the base of support yielded slower RTs for the elderly than for the young persons. When walking, the elderly persons adopted a slower speed than young persons. They also had a shorter stride length. These adaptations have been reported to produce a more secure gait. Even so, they responded to the probe RT task with greater delays than young adults. Together, the results suggest that normal aging requires that a greater proportion of attentional resources be allocated to the balance demands of postural tasks.

Adult↗
PubMedDate not supplied

[Can the Body Mass Index and the waist:hips ratio (WHR) affect the correlation between impedance measurement and anthropometry in the evaluation of body composition?].

Among the numerous techniques used to measure body composition, this study utilised anthropometric methods (weight, height, circumference and skin folds) and impedance measurement (measurement of bioelectric impedance). Results from the two methods were compared in order to assess whether BMI parameters and the waist/hips ratio (WHR) influenced this correlation. One hundred and eighty patients (133 F, 47 M) were included in the study. Patients were divided into groups according to the degree of obesity expressed as BMI and WHR. Body composition was evaluated using anthropometric methods (according to Garrow Webster, Durnin-Womersley, modified Durnin-Womersley and Jackson-Pollock) and impedance measurement in which resistive bioelectric impedance is measured using a tetrapolar technique. A good correlation was generally observed in the female population between impedance assessment and anthropometric methods, and this correlation was not influenced by either BMI or WHR. In the male group, on the other hand, the correlation between the two methods was limited by BMI greater than 30 and WHR greater than 1. In conclusion, impedance measurement and plicometric methods are generally compatible, but areas of uncertainty arise in the male population with BMI greater than 30 and WHR greater than 1.

Adipose Tissue↗