340 research outputs found
Comparison of the dental health status of 8 to 14-year-old children in France and in Jordan, a country of endemic fluorisis
In the present paper, data obtained from a survey dealing with dental carie, dental fluorosis and gingival health, involving 2618 Jordanian schoolchildren, aged 8 to 14, were compared with data from another survey dealing with 1058 schoolchildren of the same age groups living in a non-fluoridated area in the west of France. As regards dental carie in temporary teeth,  up to the age of 12, the dft and dfs scores were higher in France than in Jordan. Over the age of 12, the difference was no longer significant. As regards dental carie in permanent teeth, the data showing that Jordanian children are less subject to caries than the French were very highly significant. Also, it was shown that caries index in girls was higher than in boys.These data were not significant in the French survey, but highly significant in the Jordanian investigation.A possible explanation is that, due to the custom of the country, boys in Jordan drink much more tea (with high fluoride content) than girls. As regards gingival health, an interesting finding was that, compared to the French children, the percentage of Jordanian children presenting gingivitis is remarkably low. The fluoride content of the dental plaque might play a restricting and preventing role.Les résultats d’une enquête sur la carie dentaire, la fluorose et la gingivite, menée en Jordanie chez 2618 écoliers de 8 à 14 ans, ont été comparés avec ceux d’une enquête menée en France chez 1058 écoliers de mêmes âges, dans l’Ouest de la France, où l’eau de boisson n’est pas fluorée. En ce qui concerne la carie des dents temporaires, les indices en France sont plus élevés qu’en Jordanie, mais la différence n’est plus significative après l’âge de 12 ans. Pour les dents permanentes, les résultats indiquent, de façon très significative, que les enfants Jordaniens sont moins atteints par la carie que les français. Les filles, dans les deux enquêtes, sont plus atteintes que les garçons, mais la différence n’est pas significative dans l’enquête française, alors qu’elle est très significative dans l’enquête jordanienne. La raison pourrait être qu’en Jordanie, la coutume du pays veut que les garçons participent très tôt aux rites de la vie quotidienne et boivent davantage de thé (très fluoré) que les filles. En ce qui concerne la gingivite, le pourcentage des enfants atteints en Jordanie est très bas, comparé à ce qu’il est en France. Le contenu en fluor de la plaque pourrait jouer un rôle limitatif et protecteur
Étude expérimentale et théorique de la production de nuclides légers rapides dans les interactions proton-noyau à haute énergie
Nous donnons la description d'une expérience réalisée au CERN et concernant la production de 1H, 2H, 3H, 3He, 4He lors des interactions proton-noyau (12C, 27Al, 197Au) à des angles variés (30°, 45°, 75°, 105°). Nous présentons également une théorie thermodynamique permettant d'interpréter les résultats expérimentaux obtenus
Diffusive Spreading of Chainlike Molecules on Surfaces
We study the diffusion and submonolayer spreading of chainlike molecules on
surfaces. Using the fluctuating bond model we extract the collective and tracer
diffusion coefficients D_c and D_t with a variety of methods. We show that
D_c(theta) has unusual behavior as a function of the coverage theta. It first
increases but after a maximum goes to zero as theta go to one. We show that the
increase is due to entropic repulsion that leads to steep density profiles for
spreading droplets seen in experiments. We also develop an analytic model for
D_c(theta) which agrees well with the simulations.Comment: 3 pages, RevTeX, 4 postscript figures, to appear in Phys. Rev.
Letters (1996
Development and evaluation of a method to define a tibial coordinate system through the fitting of geometric primitives
Coordinate system definition is a critical element of biomechanical modeling of the knee, and cases of skeletal trauma present major technical challenges. This paper presents a method to define a tibial coordinate system by fitting geometric primitives to surface anatomy requiring minimal user input. The method presented here utilizes a conical fit to both the tibial shaft and femoral condyles to generate independent axes forming the basis of a tibial coordinate system. Definition of the tibial axis showed high accuracy when shape fitting to ≥50 mm of shaft with <3° of angular variation from the axis obtained using the full tibia. Repeatability and reproducibility of the axis was compared using intraclass correlation coefficients which showed excellent intra- and inter-observer agreement across cases. Additionally, shape fitting to the distal femoral condyles showed high accuracy compared to the reference axis established automatically through identifying the medial and lateral epicondyles (<4°). Utilizing geometric primitives to estimate functional axes for the tibia and femur removes reliance on anatomical landmarks that can be displaced by fracture or inaccurately identified by observers. Furthermore, fitting of such primitives provides a more complete understanding of the true bony anatomy, which cannot be done through simple landmark identification.Stuart C. Millar, John B. Arnold, Lucian B. Solomon, Dominic Thewlis and François Frayss
Growth hormone secretagogues exert differential effects on skeletal muscle calcium homeostasis in male rats depending on the peptidyl/non-peptidyl structure
TheorexigenicandanaboliceffectsinducedbyghrelinandthesyntheticGHsecretagogues(GHSs)
are thought to positively contribute to therapeutic approaches and the adjunct treatment of a
number of diseases associated with muscle wasting such as cachexia and sarcopenia. However,
manyquestionsaboutthepotentialutilityandsafetyofGHSsinboththerapyandskeletalmuscle
functionremainunanswered.Byusingfura-2cytofluorimetrictechnique,wedeterminedtheacute
effectsofghrelin,aswellasofpeptidylandnonpeptidylsyntheticGHSsoncalciumhomeostasis,
a critical biomarker of muscle function, in isolated tendon-to-tendon male rat skeletal muscle
fibers.ThesyntheticnonpeptidylGHSs,butnotpeptidylghrelinandhexarelin,wereabletosignificantlyincreaserestingcytosoliccalcium[Ca2]i.ThenonpeptidylGHS-induced[Ca2]
iincrease
was independent of GHS-receptor 1a but was antagonized by both thapsigargin/caffeine and
cyclosporineA,indicatingtheinvolvementofthesarcoplasmicreticulumandmitochondria.EvaluationoftheeffectsofapseudopeptidylGHSandanonpeptidylantagonistoftheGHS-receptor
1a together with a drug-modeling study suggest the conclusion that the lipophilic nonpeptidyl
structureofthetestedcompoundsisthekeychemicalfeaturecrucialfortheGHS-inducedcalcium
alterationsintheskeletalmuscle.Thus,syntheticGHSscanhavedifferenteffectsonskeletalmuscle
fibersdependingontheirmolecularstructures.Thecalciumhomeostasisdysregulationspecifically
induced by the nonpeptidyl GHSs used in this study could potentially counteract the beneficial
effects associated with these drugs in the treatment of muscle wasting of cachexia- or other
age-related disorders
Angle of repose and segregation in cohesive granular matter
We study the effect of fluids on the angle of repose and the segregation of
granular matter poured into a silo. The experiments are conducted in two
regimes where: (i) the volume fraction of the fluid is small and it forms
liquid bridges between particles, and (ii) the particles are completely
immersed in the fluid. The data is obtained by imaging the pile formed inside a
quasi-two dimensional silo through the transparent glass side walls. In the
first series of experiments, the angle of repose is observed to increase
sharply with the volume fraction of the fluid and then saturates at a value
that depends on the size of the particles. We systematically study the effect
of viscosity by using water-glycerol mixtures to vary it over at least three
orders of magnitude while keeping the surface tension almost constant. Besides
surface tension, the viscosity of the fluid is observed to have an effect on
the angle of repose and the extent of segregation. In case of bidisperse
particles, segregation is observed to decrease and finally saturate depending
on the size ratio of the particles and the viscosity of the fluid. The sharp
initial change and the subsequent saturation in the extent of segregation and
angle of repose occurs over similar volume fraction of the fluid. In the second
series of experiments, particles are poured into a container filled with a
fluid. Although the angle of repose is observed to be unchanged, segregation is
observed to decrease with an increase in the viscosity of the fluid.Comment: 9 pages, 12 figure
Dynamics of electrostatically-driven granular media. Effects of Humidity
We performed experimental studies of the effect of humidity on the dynamics
of electrostatically-driven granular materials. Both conducting and dielectric
particles undergo a phase transition from an immobile state (granular solid) to
a fluidized state (granular gas) with increasing applied field. Spontaneous
precipitation of solid clusters from the gas phase occurs as the external
driving is decreased. The clustering dynamics in conducting particles is
primarily controlled by screening of the electric field but is aided by
cohesion due to humidity. It is shown that humidity effects dominate the
clustering process with dielectric particles.Comment: 4 pages, 4 fig
Thermocapillary actuation of liquid flow on chemically patterned surfaces
We have investigated the thermocapillary flow of a Newtonian liquid on hydrophilic microstripes which are lithographically defined on a hydrophobic surface. The speed of the microstreams is studied as a function of the stripe width w, the applied thermal gradient |dT/dx| and the liquid volume V deposited on a connecting reservoir pad. Numerical solutions of the flow speed as a function of downstream position show excellent agreement with experiment. The only adjustable parameter is the inlet film height, which is controlled by the ratio of the reservoir pressure to the shear stress applied to the liquid stream. In the limiting cases where this ratio is either much smaller or much larger than unity, the rivulet speed shows a power law dependency on w, |dT/dx| and V. In this study we demonstrate that thermocapillary driven flow on chemically patterned surfaces can provide an elegant and tunable method for the transport of ultrasmall liquid volumes in emerging microfluidic technologies
Aging in humid granular media
Aging behavior is an important effect in the friction properties of solid
surfaces. In this paper we investigate the temporal evolution of the static
properties of a granular medium by studying the aging over time of the maximum
stability angle of submillimetric glass beads. We report the effect of several
parameters on these aging properties, such as the wear on the beads, the stress
during the resting period, and the humidity content of the atmosphere. Aging
effects in an ethanol atmosphere are also studied. These experimental results
are discussed at the end of the paper.Comment: 7 pages, 9 figure
Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films
We study experimentally the molecular weight dependence of spreading
rates of molecularly thin precursor films, growing at the bottom of droplets of
polymer liquids. In accord with previous observations, we find that the radial
extension R(t) of the film grows with time as R(t) = (D_{exp} t)^{1/2}. Our
data substantiate the M-dependence of D_{exp}; we show that it follows D_{exp}
\sim M^{-\gamma}, where the exponent \gamma is dependent on the chemical
composition of the solid surface, determining its frictional properties with
respect to the molecular transport. In the specific case of hydrophilic
substrates, the frictional properties can be modified by the change of the
relative humidity (RH). We find that \gamma \approx 1 at low RH and tends to
zero when RH gets progressively increased. We propose simple theoretical
arguments which explain the observed behavior in the limits of low and high RH.Comment: 4 pages, 2 figures, to appear in PR
- …