Ocean convergence and the dispersion of flotsam.

Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than ∼10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of ∼200 surface drifters covering ∼20 × 20 km2 converged into a 60 × 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 s-1 and 0.01 ms-1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material.

Soft tissue ossification and condylar cartilage degeneration following TMJ disc perforation in a rabbit pilot study.

OBJECTIVE: There are limited clinical treatments for temporomandibular joint (TMJ) pathologies, including degenerative disease, disc perforation and heterotopic ossification (HO). One barrier hindering the development of new therapies is that animal models recapitulating TMJ diseases are poorly established. The objective of this study was to develop an animal model for TMJ cartilage degeneration and disc pathology, including disc perforation and soft tissue HO. METHODS: New Zealand white rabbits (n = 9 rabbits) underwent unilateral TMJ disc perforation surgery and sham surgery on the contralateral side. A 2.5 mm defect was created using a punch biopsy in rabbit TMJ disc. The TMJ condyles and discs were evaluated macroscopically and histologically after 4, 8 and 12 weeks. Condyles were blindly scored by four independent observers using OARSI recommendations for macroscopic and histopathological scoring of osteoarthritis (OA) in rabbit tissues. RESULTS: Histological evidence of TMJ condylar cartilage degeneration was apparent in experimental condyles following disc perforation relative to sham controls after 4 and 8 weeks, including surface fissures and loss of Safranin O staining. At 12 weeks, OARSI scores indicated experimental condylar cartilage erosion into the subchondral bone. Most strikingly, HO occurred within the TMJ disc upon perforation injury in six rabbits after 8 and 12 weeks. CONCLUSION: We report for the first time a rabbit TMJ injury model that demonstrates condylar cartilage degeneration and disc ossification, which is indispensible for testing the efficacy of potential TMJ therapies.

Non-invasive measurement of organ density in a rat simulated microgravity model.

BACKGROUND: Spaceflight has caused serious concerns to the health and well-being of astronauts, both while in space and post-mission on Earth. The deleterious health effects due to microgravity are not well understood and though these effects may be caused by multiple factors, fluid shifts within the body may play a major role. HYPOTHESIS: We believe that 45 degrees C HDT will cause significant changes in organ density as measured by spiral computed tomography in a 1-h experimental time period. METHODS: There were 20 male Fischer 344 rats that were randomly selected to be in an experimental or control group. The experimental group (n = 12) was subjected to a 45 degrees head down tilt microgravity exposure (45 degrees HDT) for 1 h, and the control group (n = 8) remained in the prone position for the same amount of time. At the end of 1 h, the density of the brain, lungs, heart, liver, and left and right kidneys were measured using spiral computed tomography (SCT) while the rats remained in their experimental positions. RESULTS: With the exception of the right kidney, we demonstrated that there was a significant change (p < 0.05) in the densities of all tested organs in the 45 degrees HDT group when compared with the control group. The brain showed the largest percent increase at 45.6% while the lungs showed the least amount of change at 8.7%. CONCLUSIONS: We conclude there are significant increases in organ density, as measured by SCT, in male 45 degrees HDT rats compared with prone controls.