Retinal Architecture in ​\u3cem\u3eRGS9-\u3c/em\u3e and ​\u3cem\u3eR9AP\u3c/em\u3e-Associated Retinal Dysfunction (Bradyopsia)

Purpose To characterize photoreceptor structure and mosaic integrity in subjects with RGS9- and R9AP-associated retinal dysfunction (bradyopsia) and compare to previous observations in other cone dysfunction disorders such as oligocone trichromacy. Design Observational case series. Methods setting: Moorfields Eye Hospital (United Kingdom) and Medical College Wisconsin (USA). study population: Six eyes of 3 subjects with disease-causing variants in RGS9 or R9AP. main outcome measures: Detailed retinal imaging using spectral-domain optical coherence tomography and confocal adaptive-optics scanning light ophthalmoscopy. Results Cone density at 100 μm from foveal center ranged from 123 132 cones/mm2to 140 013 cones/mm2. Cone density ranged from 30 573 to 34 876 cones/mm2 by 600 μm from center and from 15 987 to 16,253 cones/mm2 by 1400 μm from center, in keeping with data from normal subjects. Adaptive-optics imaging identified a small, focal hyporeflective lesion at the foveal center in both eyes of the subject with RGS9-associated disease, corresponding to a discrete outer retinal defect also observed on spectral-domain optical coherence tomography; however, the photoreceptor mosaic remained intact at all other observed eccentricities. Conclusions Bradyopsia and oligocone trichromacy share common clinical symptoms and cannot be discerned on standard clinical findings alone. Adaptive-optics imaging previously demonstrated a sparse mosaic of normal wave-guiding cones remaining at the fovea, with no visible structure outside the central fovea in oligocone trichromacy. In contrast, the subjects presented in this study with molecularly confirmed bradyopsia had a relatively intact and structurally normal photoreceptor mosaic, allowing the distinction between these disorders based on the cellular phenotype and suggesting different pathomechanisms

Inert gas clearance from tissue by co-currently and counter-currently arranged microvessels

To elucidate the clearance of dissolved inert gas from tissues, we have developed numerical models of gas transport in a cylindrical block of tissue supplied by one or two capillaries. With two capillaries, attention is given to the effects of co-current and counter-current flow on tissue gas clearance. Clearance by counter-current flow is compared with clearance by a single capillary or by two co-currently arranged capillaries. Effects of the blood velocity, solubility, and diffusivity of the gas in the tissue are investigated using parameters with physiological values. It is found that under the conditions investigated, almost identical clearances are achieved by a single capillary as by a co-current pair when the total flow per tissue volume in each unit is the same (i.e., flow velocity in the single capillary is twice that in each co-current vessel). For both co-current and counter-current arrangements, approximate linear relations exist between the tissue gas clearance rate and tissue blood perfusion rate. However, the counter-current arrangement of capillaries results in less-efficient clearance of the inert gas from tissues. Furthermore, this difference in efficiency increases at higher blood flow rates. At a given blood flow, the simple conduction-capacitance model, which has been used to estimate tissue blood perfusion rate from inert gas clearance, underestimates gas clearance rates predicted by the numerical models for single vessel or for two vessels with co-current flow. This difference is accounted for in discussion, which also considers the choice of parameters and possible effects of microvascular architecture on the interpretation of tissue inert gas clearance

Chord length distributions measurements during crystallization and agglomeration of gas hydrate in a water-in-oil emulsion: Simulation and experimentation

International audienceThe formation of gas hydrates from water-in-oil emulsion was investigated on two different flow loops: a laboratory scale flow loop (Archimede flow loop: 30 m long, and 1 cm diameter, St-Etienne School of Mines) and a pilot scale flow loop (Lyre flow loop: 150 m long, 5 cm diameter, IFP Solaize). Both flow loops are equipped with a focused beam reflectance measurement (FBRM) probe for in situ particle size analysis. These FBRM probes were used to monitor chord length distribution (CLD) during the crystallization process of water-in-oil emulsions into gas hydrate slurries. When water droplets crystallize into hydrate particles, an agglomeration phenomenon is evidenced by pressure drop measurements. This agglomeration phenomenon is also detected by the FBRM probe and is highlighted by a sharp change in the mean chord length and a spread of the CLD to larger chord length. In order to better interpret the chord length distribution measurements, a modelling work has been made. This paper gives a description of the algorithm used for building 3D fractal aggregates and simulating CLD measurements on them. Aggregates are constructed from a monodisperse spherical particle. The influence of different parameters (fractal dimension, number of particles in the aggregate, diameter of primary particles) on the simulated CLD is also discussed. Some comparisons between experimental and simulated CLD are finally used to describe the physical properties of aggregates during an experiment

The use of FBRM probe during hydrate particles agglomeration

National audienceGas hydrates formation from water in oil emulsion is of particular interest in the context of crude oil production. Once hydrates form in the pipeline, individual gas hydrate particles agglomerate together and form a plug preventing fluid flow. This work shows the main advantages of using a Focused Beam Reflectance Measurement (FBRM) probe for in situ chord lengths analysis during hydrate particles agglomeration for a better understanding of this process within the pipe. The formation of gas hydrate was studied in a flow loop. Experiments were carried out at 278K and 7.5 MPa. This paper provides a systematic study of the FBRM probe signal. It also underlines the links between the shape of the CLD and the morphology of agglomerates carried inside the flow. This is particularly useful to understand the agglomeration process

Prise en compte des effets non linéaires de surface libre en écoulement instationnaire

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