Implementation of viscoelastic Hopkinson bars

Includes bibliographical references (p. 107-112).The properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these soft or low impedance materials using metallic bars in a split Hopkinson pressure bar setup, poor signal to noise ratios and impedance mismatching occur. One solution is to use polymeric Hopkinson bars. In this dissertation, Polycarbonate, Polymethyl Methacrylate and Nylon are considered for use as Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. As stress waves propagate along the length of the bars, viscoelastic effects result in dispersion and attenuation. The main topic of this dissertation is to account for this viscoelastic material effect

Development and modelling of a versatile active micro-electrode array for high density in-vivo and in-vitro neural signal investigation

The electrophysiological observation of neurological cells has allowed much knowledge to be gathered regarding how living organisms are believed to acquire and process sensation. Although much has been learned about neurons in isolation, there is much more to be discovered in how these neurons communicate within large networks. The challenges of measuring neurological networks at the scale, density and chronic level of non invasiveness required to observe neurological processing and decision making are manifold, however methods have been suggested that have allowed small scale networks to be observed using arrays of micro-fabricated electrodes. These arrays transduce ionic perturbations local to the cell membrane in the extracellular fluid into small electrical signals within the metal that may be measured. A device was designed for optimal electrical matching to the electrode interface and maximal signal preservation of the received extracellular neural signals. Design parameters were developed from electrophysiological computer simulations and experimentally obtained empirical models of the electrode-electrolyte interface. From this information, a novel interface based signal filtering method was developed that enabled high density amplifier interface circuitry to be realised. A novel prototype monolithic active electrode was developed using CMOS microfabrication technology. The device uses the top metallization of a selected process to form the electrode substrate and compact amplification circuitry fabricated directly beneath the electrode to amplify and separate the neural signal from the baseline offsets and noise of the electrode interface. The signal is then buffered for high speed sampling and switched signal routing. Prototype 16 and 256 active electrode array with custom support circuitry is presented at the layout stage for a 20 μm diameter 100 μm pitch electrode array. Each device consumes 26.4 μW of power and contributes 4.509 μV (rms) of noise to the received signal over a controlled bandwidth of 10 Hz - 5 kHz. The research has provided a fundamental insight into the challenges of high density neural network observation, both in the passive and the active manner. The thesis concludes that power consumption is the fundamental limiting factor of high density integrated MEA circuitry; low power dissipation being crucial for the existence of the surface adhered cells under measurement. With transistor sizing, noise and signal slewing each being inversely proportional to the dc supply current and the large power requirements of desirable ancillary circuitry such as analogue-to-digital converters, a situation of compromise is approached that must be carefully considered for specific application design

DISTINGUISHING THE SOURCE OF MARKET POWER: AN APPLICATION TO CIGARETTE MANUFACTURING

We compare nonparametric and nonstructural market power tests using data from the cigarette manufacturing industry. Tests are implemented to examine both monopoly and monopsony power exertion by cigarette manufacturers. Results indicate that market power in the tobacco industry, previously attributed to monopoly power exertion, should at least in part be attributed to monopsony market power in the upstream tobacco market.market power, nonparametric, nonstructural, monopsony, monopoly, cigarette manufacturing, Agribusiness,

Predicting Bulk Flow and Behaviour for Design and Operation of Handling and Processing Plants

The reliable design and operation of bulk materials handling and processing plants can be difficult when dealing with complex geometries and difficult-to-handle materials, such as wet and sticky ore. Often a lack of detailed analysis of bulk material flow and process boundary interactions can lead to costly mistakes which can typically be identified easily once in operation. These problems can occur due to inaccurate characterisation during design, miscalculation of particle trajectories and velocities, and a lack of engineering tools to thoroughly visualise and analyse material flow through complex dynamic designs. This paper investigates the application of DE (Discrete Element) simulation to bulk material plant design by identifying current issues and presenting new methods of calibration and length-scale/dynamic validation. Examples and a case study are presented to demonstrate the key issues of this paper