On acoustic cavitation of slightly subcritical bubbles

The classical Blake threshold indicates the onset of quasistatic evolution leading to cavitation for gas bubbles in liquids. When the mean pressure in the liquid is reduced to a value below the vapor pressure, the Blake analysis identifies a critical radius which separates quasistatically stable bubbles from those which would cavitate. In this work, we analyze the cavitation threshold for radially symmetric bubbles whose radii are slightly less than the Blake critical radius, in the presence of time-periodic acoustic pressure fields. A distinguished limit equation is derived that predicts the threshold for cavitation for a wide range of liquid viscosities and forcing frequencies. This equation also yields frequency-amplitude response curves. Moreover, for fixed liquid viscosity, our study identifies the frequency that yields the minimal forcing amplitude sufficient to initiate cavitation. Numerical simulations of the full Rayleigh-Plesset equation confirm the accuracy of these predictions. Finally, the implications of these findings for acoustic pressure fields that consist of two frequencies will be discussed.Comment: 14 pages, Presented at APS/DFD conference in Philadelphia 199

Preliminary Canopy Removal Experiments in Algal Dominated Communities Low on the Shore and in the Shallow Subtidal on the Isle of Man

The algal dominated communities immediately above and below the low-water spring level on a moderately exposed Manx shore were investigated by canopy removal experiments. Fucus serratus, Laminaria digitata and L. hyperborea were removed. Competition was shown to be important in determining the zonation of L. digitata and the distribution along the wave exposure gradient of other species such as Alaria esculenta, Desmarestia aculeata and D. viridis, and L. saccharina. Many species of algal epiphytes were early colonizers of canopy removal areas suggesting that competition from canopy algae usually restricts them to an epiphytic habit. The results indicate that interactions between macrophytes are much more important than grazing in structuring these communities

Establishment, spread, and impact of an invasive planthopper on its invasive host plant: Prokelisia marginata (Homoptera: Delphacidae) exploiting Spartina anglica (Poales: Poaceae) in Britain

1. Since its recent arrival in Britain, the planthopper Prokelisia marginata has spread widely around saltmarshes on the east and south coast of England and south Wales, feeding on Common Cordgrass, Spartina anglica , itself an invasive non‐native species. 2. Results suggest that P . marginata populations in Britain benefit from a degree of natural enemy release. No evidence of parasitism was found in over 71 000 eggs, nymphs, and adults inspected. The only potential natural enemy control was suggested by a positive correlation between the densities of planthoppers and generalist spiders. 3. Experimental exposure under both glasshouse and field conditions to typical field densities of planthoppers resulted in significant negative effects on a number of host plant performance metrics. 4. Spartina anglica is important for stabilising estuarine sediments and has been deliberately planted for this purpose in the past. Its weakening as a result of heavy planthopper herbivory could have serious consequences for the long‐term stability of Britain's vulnerable saltmarsh habitats

Becoming a teacher: conceptual and practice development in the learning and skills sector

Drawing on a mixed-methods study of in-service learning and skills sector (LSS) trainees, comprising beginning- and end-of-year surveys and six longitudinal case studies together with literature on trainees’ development in the LSS, schools and higher education sectors, conceptual and practice development continua are proposed. Conceptions become more multi-dimensional and increasingly link teaching and learning whilst initial concern with the practicalities of teaching is followed by recognition of learners’ needs. Next, greater emphasis is placed on learner autonomy and catering for individuals’ needs and finally assessment and evaluation is used systematically to shape practice. The continua offer an understanding of the subtleties and complexities of trainee development allowing for different starting and end points and accommodating varied work contexts. I argue that this provides a more adequate basis for the development of initial teacher education (ITE) than the prescriptive approach embedded within recent LSS ITE policy reforms

Low cost fault-tolerant routing algorithm for Networks-on-Chip

A novel adaptive routing algorithm - Efficient Dynamic Adaptive Routing (EDAR) is proposed to provide a fault-tolerant capability for Networks-on-Chip (NoC) via an efficient routing path selection mechanism. It is based on a weighted path selection strategy, which exploits the status of real-time NoC traffic made available via monitor modules. The key performance goal is to maintain throughput under congested and faulty conditions via effective routing path decisions. In the proposed EDAR, port weights are calculated in real-time according to the channel status – Idle/Busy/Congested/Faulty, and the port with the lowest weighting is ranked as the near-optimal route to forward packets. This mechanism enables the router to bypass congested ports and tolerate faulty ports. To assess the latency and throughput of the proposed routing algorithm, several traffic patterns for both fault-free and faulty NoCs were evaluated. Results show that EDAR can achieve higher throughput compared to other state of the art routing algorithms under various traffic patterns and levels of injected faults. In addition, the hardware area overhead for EDAR is demonstrated to have a reasonably low cost which maintains scalability for large NoC implementations

Modelling and control of a water jet cutting probe for flexible surgical robot

Surgical removal of cancerous tissue from the spine is limited by the inability of hand held drills and cutting tools to reach small crevices present in complex bones such as the spinal column, especially on the anterior side. In addition, the high speed rotating mechanisms used presently are subject to stability issues when manoeuvring around tortuous bone forms. We report on the design and experimental testing of a novel flexible robotic surgical system which addresses these issues. The robot consists of a flexible probe, a water jet cutting system, and a haptic feedback controller. The water jet cutting system consists of a flexible end effector capable of bending around the anterior of the spinal column for tissue removal. A new experimental method of controlling the depth of water jet cut is described. The haptic feedback controller is based on a constraint set approach to define 3D boundaries, based on five key types of constraints. Experimental outcomes of measuring the depth of water jet cut were combined with haptic regional constraints with the aim of improving the safety of surgical procedures. The reliability, accuracy and performance of the prototype robot were tested in a mock surgical procedure on the lower lumbar vertebrae. Results show promise for the implementation of water jet cutting for robotic surgical spinal procedures