Rhodopsin Mutant P23H Destabilizes Rod Photoreceptor Disk Membranes

Mutations in rhodopsin cause retinitis pigmentosa in humans and retinal degeneration in a multitude of other animals. We utilized high-resolution live imaging of the large rod photoreceptors from transgenic frogs (Xenopus) to compare the properties of fluorescently tagged rhodopsin, Rho-EGFP, and RhoP23H-EGFP. The mutant was abnormally distributed both in the inner and outer segments (OS), accumulating in the OS to a concentration of ∼0.1% compared to endogenous opsin. RhoP23H-EGFP formed dense fluorescent foci, with concentrations of mutant protein up to ten times higher than other regions. Wild-type transgenic Rho-EGFP did not concentrate in OS foci when co-expressed in the same rod with RhoP23H-EGFP. Outer segment regions containing fluorescent foci were refractory to fluorescence recovery after photobleaching, while foci in the inner segment exhibited recovery kinetics similar to OS regions without foci and Rho-EGFP. The RhoP23H-EGFP foci were often in older, more distal OS disks. Electron micrographs of OS revealed abnormal disk membranes, with the regular disk bilayers broken into vesiculotubular structures. Furthermore, we observed similar OS disturbances in transgenic mice expressing RhoP23H, suggesting such structures are a general consequence of mutant expression. Together these results show that mutant opsin disrupts OS disks, destabilizing the outer segment possibly via the formation of aggregates. This may render rods susceptible to mechanical injury or compromise OS function, contributing to photoreceptor loss

DEM of triaxial tests on crushable cemented sand

Using the discrete element method, triaxial simulations of cemented sand consisting of crushable particles are presented. The triaxial model used features a flexible membrane, allowing realistic deformation to occur, and cementation is modelled using inter-particle bonds. The effects of particle crushing are explored, as is the influence of cementation on the behaviour of the soil. An insight to the effects that cementation has on the degree of crushing is presented

Stress-strain behaviour of sand with disc plate shaped reinforcement

In the present study, the laboratory triaxial compression tests were carried out on soil specimens reinforced with steel and aluminium solid plates in horizontal layers. The percentages of reinforcement used were 5%, 4%, 2%, 1% and 0.5%. The solid plates were placed horizontally in five layers in all the tests. Again the triaxial compression tests were repeated by using the perforated circular aluminium plates as horizontal reinforcement instead of solid plate, but the quantity of reinforcements was kept the same as in the previous case. The diameter of the plate in all the cases was 25 mm. To alter the percentages of reinforcement, thickness of layers were varied in each case but thickness in all the five different layers were kept the same. The results show that improvement in strength of soil was not proportional to the increase in the percentage of reinforcement and residual strength ratio was also found to be less. It was also observed that there was an increase in the tangent modulus with increase in percentage of reinforcement at higher confining pressure when aluminium was used as a disc shaped plate reinforcement