Showing papers by "Simon Brown published in 2011"

Fractal electronic devices: simulation and implementation

Abstract: Many natural structures have fractal geometries that exhibit useful functional properties. These properties, which exploit the recurrence of patterns at increasingly small scales, are often desirable in applications and, consequently, fractal geometry is increasingly employed in diverse technologies ranging from radio antennae to storm barriers. In this paper, we explore the application of fractal geometry to electrical devices. First, we lay the foundations for the implementation of fractal devices by considering diffusion-limited aggregation (DLA) of atomic clusters. Under appropriate growth conditions, atomic clusters of various elements form fractal patterns driven by DLA. We perform a fractal analysis of both simulated and physical devices to determine their spatial scaling properties and demonstrate their potential as fractal circuit elements. Finally, we simulate conduction through idealized and DLA fractal devices and show that their fractal scaling properties generate novel, nonlinear conduction properties in response to depletion by electrostatic gates.

Ag-Au nanoclusters: Structure and phase segregation

Abstract: We present a systematic survey of unprotected Ag-Au nanoclusters prepared by inert gas aggregation. The clusters are initially fully and homogeneously alloyed, exhibiting icosahedral and decahedral structural motifs. Imaging using scanning transmission electron microscopy indicates that over a period of up to 2 yr, the nanoclusters undergo structural transitions into phase-segregated core-shell and Janus particles with Ag-Au cores and AgxO shells. Larger Janus particles undergo a ripening process which results in division into separate Ag-Au-rich and Ag2O-rich particles. We propose that oxidation of the Ag component and subsequent diffusion of AgxO are responsible for the observed phenomena.

Fractal interconnects for neuro-electronic interfaces and implants using same

Abstract: A neuro-electronic interface device has a micro-electrode electrically connected to an interconnect that has scaling gradients between 1.1 and 1.9 over a scaling range of at least one order of magnitude. The device preferably has an array of such fractal interconnects in electrical contact with an array of micro-electrodes. Such fractal interconnect arrays may be components of implants including a retinal implant device having an array of photodetectors in electrical contact with the array of micro-electrodes. The interconnects may be fabricated by forming nanoscale particles and depositing them onto a non-conductive surface that is smooth except for electrodes which serve as nucleation sites for the formation of fractal interconnect structures through diffusion limited aggregation.

Establishing Reasoning Communities of Security Experts for Internet Commerce Security

Abstract: The highly sophisticated and rapidly evolving area of internet commerce security presents many novel challenges for the organization of discourse in reasoning communities. This chapter suggests appropriate reasoning methods and demonstrates how establishing reasoning communities of security experts and enabling productive group discourse among them can play a crucial role in successful resolution of problems concerning the implementation, integration, deployment and maintenance of flexible local security systems for defense against malware threats in internet security. Local security systems of this sort may combine several ready open source or commercial software packages behind a common frontend and may enhance and supplement their facilities with additional plug-ins. To illustrate the diverse character of challenges the reasoning communities in internet security are likely to be faced with, this chapter concentrates on defense against phishing attacks. This example was selected as it is one of the newest and most rapidly changing application domains for the principles of organizing reasoning communities. The major group discourse methods suggested for the reasoning communities of security DOI: 10.4018/978-1-60960-091-4.ch020

The morphology of tin cluster assembled films and the effect of nitrogen

Abstract: Thin films produced by depositing tin clusters with sizes between 5 and 10 nm onto silicon nitride substrates were found to be highly coalesced resulting in grains with sizes ~30 nm. Exposing the clusters to nitrogen before they were deposited significantly reduced the coalescence between them and resulted in granular films where the clusters mostly retained their shape. This is due to a small amount of tin nitride forming in the clusters. The coalesced and granular films were used to fabricate tin oxide gas sensors. This was done by depositing the two types of films onto silicon nitride chips and then oxidising them by baking at 250 °C for 24 h. It was found that the sensors composed of uncoalesced clusters were much more sensitive to hydrogen. This was attributed to the smaller grain size and the larger surface area of the granular films.

Gas Dynamic Considerations for Performance of Nanocluster Deposition System

Abstract: Numerical simulations of the gas flow and cluster velocities in a UHV compatible nanocluster deposition system were performed in order to understand the problems of optimization of the cluster deposition rate. Skimmer geometry was initially identified as the key factor in defining the cluster velocity: our modeling suggested that using skimmers of a greater internal angle should lead to higher cluster velocities. However, the experimental results revealed only a minor enhancement in the cluster velocity. The lack of an effect of the change in skimmer geometry was attributed to the decelerating effect of the background gas in the mass selection chamber. When this effect was taken into consideration, the simulation results described the observed cluster behavior to a much better degree. The experiments and simulations both show a general trend for the cluster velocity to decrease as the cluster size is increased, for all the skimmer geometries used.

Power law fitting procedures: The electrical conductance of coalescing nanocluster films

Abstract: The electrical conductance of bismuth nanocluster films deposited in vacuum has been observed to increase after the end of deposition. This evolution Gexp(t) can be successfully fitted with a power law. However, it is well known that interpretation of power law fits can be problematic. To investigate the physical meaning of the fitted power law exponent a percolation model with coalescence built into it was developed. In this model the evolution of the conductance of necks between neighboring occupied sites is defined as a power law with exponent β resulting in model conductance data Gmod(t). The Gmod(t) data are fitted with a power law and we show that the fitted exponent is close to the original exponent β, so long as the power law expression is chosen correctly. The fits to the synthetic Gmod(t) data provide confidence in the fitting procedure and in the power law exponents obtained from fits to the experimental data. The experimental power law exponents are found to be much smaller than expected from ...

Major Tribunal Decisions in 2010

Abstract: This article examines a number of Full Bench decisions from Fair Work Australia in 2010, in particular those relating to agreement-making and enterprise bargaining under the Fair Work Act 2009. Those decisions have shed further light on the operation of what remains relatively new legislation. With respect to agreement-making, the Full Bench has evinced an intention to take a practical and non-technical approach in determining whether the pre-approval requirements under s.180 of the Act have been met, and to afford employers an opportunity to address any concerns about approval of an agreement by way of undertakings. The Full Bench decisions examined in this article also demonstrate that Fair Work Australia will take a non-interventionist approach to enterprise bargaining and protected industrial action. Provided the parties are conducting themselves in accordance with the Fair Work Act, the tribunal will be loath to intervene in enterprise bargaining in a way that would alter the status quo or undermine ...