Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different microstructure constitution.. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge to face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.

Operation and control of a microgrid containing inertial and non-inertial micro sources

In this paper, a new power sharing control method for a microgrid with several distributed generation units is proposed. The presence of both inertial and noninertial sources with different power ratings, maximum power point tracking, and various types of loads pose a great challenge for the power sharing and system stability. The conventional droop control method is modified to achieve the desired power sharing ensuring system stability in a highly resistive network. A transformation matrix is formed to derive equivalent real and reactive power output of the converter and equivalent feedback gain matrix for the modified droop equation. The proposed control strategy, aimed for the prototype microgrid planned at Queensland University of Technology, is validated through extensive simulation results using PSCAD/EMTDC software.

Designing self sustaining support for micro-enterprises in sub-Saharan Africa : a pilot

Small and micro-enterprises play a significant part in most economies. However, in developing countries these enterprises have often been planned and implemented from a poverty alleviation perspective, rather than as entrepreneurial activities and growing businesses (Mead & Liedholm 1998, Toye 1993). This paper explores a model for sustainable support to micro-enterprises in a developing country context. Sustainability is critical if micro-enterprises are to grow. The traditional philanthropic model for funding micro-enterprises leaves local communities dependent on the priorities of donors which may not always be consistent with those of the community. Long term sustainability requires a move to a model that broadens the base of both economic and intellectual resources, that builds capacity as well as providing ‘start-up’ funding through mechanism such as micro-credit (Elkington & Hartigan 2008). Designing for sustainable enterprise development includes responding to the community’s priorities, investigating individual problems and solutions, encouraging agency and active involvement in goal setting, with on-going consultation and co-development of solutions. Recognising the importance of experimentation we have moved beyond existing forms to prototype new ways of working which provide continuity of financial and intellectual support for local initiatives. The paper reviews existing micro finance and microcredit practices and suggests a new approach to establish and support enterprises with financial and knowledge resources for sustainable business practices. Principles underlying such a program and the initial steps are described.

The interaction order of Second Life : how micro sociology can contribute to online games innovation

This paper uses the virtual world Second Life (as Web 2.0 environment) to discuss how sociological theory is a relevant tool for innovation in the area of games design as a methodological strategy. Via the theories of Erving Goffman’s interaction order the paper illustrates how micro studies of online interaction demonstrate active accounts of membership and complex interactivity. In order to achieve this, the paper outlines a methodological tool to assist in the application of micro sociology to Web 2.0 environments that accounts for the multiple dimensions of participation within the digital field.

Teaching and Learning Entrepreneurship for Micro and Small Businesses in the Cultural Industries Sector

Reports on an ESRC-funded, in-depth qualitative research project into 50 micro and small enterprises (MSEs) in the cultural industries. Our evidence sheds light on the extent to which the teaching and learning strategies adopted by higher education, further education and other VET providers are effective in providing entrepreneurship education and training for this innovative, high skill sector. Our findings suggest that entrepreneurs in this sector learn best by being able to experiment with ideas, by “doing” and networking with others and by working with more experienced mentors in their sector. The article concludes by suggesting a more “naturalistic” approach to teaching and learning entrepreneurship for micro and small businesses in the cultural industries sector.

Control and protection of a microgrid with converter interfaced micro sources

This paper describes protection and control of a microgrid with converter interfaced micro sources. The proposed protection and control scheme consider both grid connected and autonomous operation of the microgrid. A protection scheme, capable of detecting faults effectively in both grid connected and islanded operations is proposed. The main challenge of the protection, due to current limiting state of the converters is overcome by using admittance relays. The relays operate according to the inverse time characteristic based on measured admittance of the line. The proposed scheme isolates the fault from both sides, while downstream side of the microgrid operates in islanding condition. Moreover faults can be detected in autonomous operation. In grid connected mode distributed generators (DG) supply the rated power while in absence of the grid, DGs share the entire power requirement proportional to rating based on output voltage angle droop control. The protection scheme ensures minimum load shedding with isolating the faulted network and DG control provides a smooth islanding and resynchronization operation. The efficacy of coordinated control and protection scheme has been validated through simulation for various operating conditions.

Droop control of converter interfaced micro sources in rural distributed generation

This paper proposes new droop control methods for load sharing in a rural area with distributed generation. Highly resistive lines, typical of rural low voltage networks, always create a big challenge for conventional droop control. To overcome the conflict between higher feedback gain for better power sharing and system stability in angle droop, two control methods have been proposed. The first method considers no communication among the distributed generators (DGs) and regulates the converter output voltage and angle ensuring proper sharing of load in a system having strong coupling between real and reactive power due to high line resistance. The second method, based on a smattering of communication, modifies the reference output volt-age angle of the DGs depending on the active and reactive power flow in the lines connected to point of common coupling (PCC). It is shown that with the second proposed control method, an economical and minimum communication system can achieve significant improvement in load sharing. The difference in error margin between proposed control schemes and a more costly high bandwidth communication system is small and the later may not be justified considering the increase in cost. The proposed control shows stable operation of the system for a range of operating conditions while ensuring satisfactory load sharing.

Towards a model of understanding strategic decision-making in micro-firms : exploring the Australian information technology sector

This study explores strategic decision-making (SDM) in micro-firms, an economically significant business subsector. As extant large- and small-firm literature currently proffers an incomplete characterization of SDM in very small enterprises, a multiple-case methodology was used to investigate how these firms make strategic decisions. Eleven Australian Information Technology service micro-firms participated in the study. Using an information-processing lens, the study uncovered patterns of SDM in micro-firms and derived a theoretical micro-firm SDM model. This research also identifies several implications for micro-firm management and directions for future research, contributing to the understanding of micro-firm SDM in both theory and practice.

Technical note : modelling a complex micro-multileaf collimator using the standard BEAMnrc distribution

Purpose: The component modules in the standard BEAMnrc distribution may appear to be insufficient to model micro-multileaf collimators that have tri-faceted leaf ends and complex leaf profiles. This note indicates, however, that accurate Monte Carlo simulations of radiotherapy beams defined by a complex collimation device can be completed using BEAMnrc's standard VARMLC component module.---------- Methods: That this simple collimator model can produce spatially and dosimetrically accurate micro-collimated fields is illustrated using comparisons with ion chamber and film measurements of the dose deposited by square and irregular fields incident on planar, homogeneous water phantoms.---------- Results: Monte Carlo dose calculations for on- and off-axis fields are shown to produce good agreement with experimental values, even upon close examination of the penumbrae.--------- Conclusions: The use of a VARMLC model of the micro-multileaf collimator, along with a commissioned model of the associated linear accelerator, is therefore recommended as an alternative to the development or use of in-house or third-party component modules for simulating stereotactic radiotherapy and radiosurgery treatments. Simulation parameters for the VARMLC model are provided which should allow other researchers to adapt and use this model to study clinical stereotactic radiotherapy treatments.