The simulation based on the model demonstrated quantitatively that variations in each corneal variable cause errors in tonometry IOP readings. The simulation results indicate that differences in corneal biomechanics across individuals may have greater impact on IOP measurement errors than corneal thickness or curvature.

Summary1. It is well documented that large herbivores have pronounced effects on plant communities in grassland ecosystems, and the extent and course of their effects can largely depend on both plant and herbivore characteristics. Previous studies highlighted the importance of plant productivity in predicting the impact of herbivores on grasslands. Yet, there has been little consideration of how different herbivores affect plant communities that, in turn, differ in plant diversity. 2. In a 2-year grazing experiment, we tested the effects of large herbivores (cattle or sheep, or both together) on plant communities under high and low plant diversity levels in eastern Eurasian steppe. 3. We found that, for high plant diversity grassland, mixed grazing by cattle and sheep significantly increases plant diversity, but we found no effect of grazing by cattle or sheep alone. Grazing by cattle or sheep alone or mixed grazing by cattle and sheep did not significantly affect plant biomass in the high diversity grassland. However, for low plant diversity grassland, grazing by cattle alone and mixed grazing by cattle and sheep significantly increased plant diversity, but significantly decreased plant biomass. There was no significant impact on both plant diversity and biomass from sheep grazing. 4. Synthesis and applications. We conclude that the effects of grazing in grassland strongly depend on herbivore assemblages and pre-grazing plant diversity. Herbivore grazing might contribute more to the maintenance of grassland structure and ecosystem functioning under high plant diversity compared with low plant diversity. Furthermore, our data suggest that multiple-species mixed grazing regimes in grassland systems with high plant diversity could represent the optimal protocol for grazing management. This study emphasizes the importance of maintaining both plant and herbivore diversity to optimize ecosystem functioning.

Summary Ambrosia trifida L. (giant ragweed), an aggressive weed of US grain crops and indigenous to North America, colonizes no-tillage crop fields and undisturbed soils despite its large seed size and susceptibility to seed predation. Secondary seed dispersal is critical to seed survival and seedling establishment, yet mechanisms of secondary dispersal are poorly understood for such large-seeded weedy species. 2. Field experiments were conducted to determine how seed foraging by the European exotic burrowing earthworm Lumbricus terrestris L., affected A. trifida seed burial and seedling recruitment, and to determine seed selectivity by L. terrestris . 3. Earthworms collected and buried over 90% of A. trifida seeds placed on the soil surface at a rate eightfold faster than abiotic seed burial. There was a sixfold higher concentration of seeds in burrows than in surrounding soil and a mean of 127 A. trifida seeds per burrow after a single season of A. trifida seed dispersal. 4. Earthworms buried A. trifida seeds from 0·5 to 22 cm deep and reduced recruitment by 37% compared to seeds buried abiotically and protected from predators, due to burial of some seeds below emergence depth limits. However, seedling biomass was increased by 30%. 5. Earthworms foraged selectively among seeds of 11 large-seeded species and collected more seeds of A. trifida than of other species. The earthworms buried small (8·5 mm) A. trifida seeds more deeply and reduced their emergence more than large (11·5 mm) A. trifida seeds. 6. Synthesis and applications. The novel interaction of L. terrestris and A. trifida increases seed bank formation of A. trifida . Burrows of L. terrestris provide safe sites for seeds of A. trifida that may increase seedling establishment in environments with a high risk of seed predation. Control measures to prevent reproduction by A. trifida should be increased where L. terrestris is present due to the earthworms' ability to bury and protect weed seeds. Selective seed caching by this widely distributed earthworm species may change plant community composition in agricultural and natural areas in North America and influence the evolution of seed traits. Land managers should consider the effects of L. terrestris on seedling regeneration of native and exotic plant species in areas undergoing colonization by L. terrestris .

Nanoparticles have drawn great attention as targeted imaging and/or therapeutic agents. The small size of the nanoparticles allows them to target cells that are beyond capillary vasculature, such as cancer cells. We investigated the effect of solid nanoparticles for enhancing ultrasonic grey scale images in tissue phantoms and mouse livers in vivo. Silica nanospheres (100 nm) were dispersed in agarose at 1-2.5% mass concentration and imaged by a high-resolution ultrasound imaging system (transducer centre frequency: 30 MHz). Polystyrene particles of different sizes (500-3000 nm) and concentrations (0.13-0.75% mass) were similarly dispersed in agarose and imaged. Mice were injected intravenously with nanoparticle suspensions in saline. B-mode images of the livers were acquired at different time points after particle injection. An automated computer program was used to quantify the grey scale changes. Ultrasonic reflections were observed from nanoparticle suspensions in agarose gels. The image brightness, i.e., mean grey scale level, increased with particle size and concentration. The mean grey scale of mouse livers also increased following particle administration. These results indicated that it is feasible to use solid nanoparticles as contrast enhancing agents for ultrasonic imaging.

Background. Scleral biomechanical properties may be important in the pathogenesis and progression of glaucoma. The goal of this study is to develop and validate an ultrasound method for measuring cross-sectional distributive strains in the sclera during elevations of intraocular pressure (IOP). Method of Approach. Porcine globes (n ¼ 5) were tested within 24 hs postmortem. The posterior scleral shells were dissected and mounted onto a custom-built pressurization chamber. A high-frequency (55-MHz) ultrasound system (Vevo660, VisualSonics Inc., Toronto) was employed to acquire the radio frequency data during scans of the posterior pole along both circumferential and meridian directions. The IOP was gradually increased from 5 to 45 mmHg. The displacement fields were obtained from correlation-based ultrasound speckle tracking. A least-square strain estimator was used to calculate the strains in both axial and lateral directions. Experimental validation was performed by comparing tissue displacements calculated from ultrasound speckle tracking with those induced by an actuator. Theoretical analysis and simulation experiments were performed to optimize the ultrasound speckle tracking method and evaluate the accuracy and signal-to-noise ratio (SNR) in strain estimation. Results. Porcine sclera exhibited significantly larger axial strains (e.g., À5.1 6 1.5% at 45 mmHg, meridian direction) than lateral strains (e.g., 2.2 6 0.7% at 45 mmHg, meridian direction) during IOP elevations (P's < 0.01). The strain magnitudes increased nonlinearly with pressure increase. The strain maps displayed heterogeneity through the thickness. The lateral strains were significantly smaller in the circumferential direction than the meridian direction at 45 mmHg (P < 0.05). Experimental validation showed that the ultrasound speckle tracking method was capable of tracking displacements at the accuracy of sub-micron to micron. Theoretical analysis predicted the dependence of the strain estimation SNR on the strain level, as well as signal processing parameters such as kernel size. Simulation results showed that ultrasound speckle tracking had a high accuracy for estimating strains of 1-5% and a high SNR for strains of 0.5-5%. Conclusions. A new experimental method based on ultrasound speckle tracking has been developed for obtaining cross-sectional strain maps of the posterior sclera. This method provides a useful tool to examine distributive strains through the thickness of the sclera during elevations of IOP.