A computational theory of willingness to exchange, ESRI working paper no. 477, January 2014

A new model of exchange is presented following Marr’s conception of a “computational theory”. The model combines assumptions from perceptual theory and economic theory to develop a highly generalised formal model. The approach departs from previous models by focussing not on how ownership alters preferences, but instead on difficulties inherent in the process of exchange in real markets. Agents treat their own perceptual uncertainty when valuing a potential exchange item as a signal regarding the variability of potential bids and offers. The analysis shows how optimising agents, with no aversion to risk or loss, will produce an endowment effect of variable degree, in line with empirical findings. The model implies that the endowment effect is not a laboratory finding that may not occur in real markets, but rather a market phenomenon that may not occur in the laboratory

A Study on Teacher Professionalism and Teacher Leadership: The Teachers' Viewpoint

This study looks at the current situation of how teachers view the concepts of teacher professionalism and teacher leadership in New Zealand primary schools. It is a small scale study located in two large city primary schools, where it was identified by others in the profession that sharing of leadership was a common practice, and that they were high performing schools. I was interested in gathering the information from teachers with a range of teaching experience, and finding out what were the common understandings surrounding these concepts. The literature reviewed shows there is an international focus on developing leadership capacity within schools. It is argued that in order to sustain the development of schools in such complex times while remaining focused on the core business of the learning of the students, leadership is an activity that all teachers should be involved in, as it is a recognized component for improving the professional role of the teacher. The study was carried out by interviewing twelve teachers who had a range of experience and held a range of leadership positions from beginning teachers through to deputy principals. The findings showed the teachers in this study understood there is a close link between their leadership and their professionalism and that one reinforced the other. The teachers were empowered to take their professional development to new heights as the school culture reinforced the collective responsibility the teachers had for school development

Survival model of a parallel system with dependent failures and time varying covariates

In this paper, we extended a parallel system survival model based on the bivariate exponential to incorporate a time varying covariate. We calculated the bias, standard error and rmse of the parameter estimates of this model at different censoring levels using simulated data. We then compared the difference in the total error when a fixed covariate model was used instead of the true time varying covariate model. Following that, we studied three methods of constructing confidence intervals for such models and conclusions were drawn based on the results of the coverage probability study. Finally, the results obtained by fitting the diabetic retinopathy study data to the model were analysed

Probabilistic models to describe the dynamics of migrating microbial communities

In all but the most sterile environments bacteria will reside in fluid being transported through conduits and some of these will attach and grow as biofilms on the conduit walls. The concentration and diversity of bacteria in the fluid at the point of delivery will be a mix of those when it entered the conduit and those that have become entrained into the flow due to seeding from biofilms. Examples include fluids through conduits such as drinking water pipe networks, endotracheal tubes, catheters and ventilation systems. Here we present two probabilistic models to describe changes in the composition of bulk fluid microbial communities as they are transported through a conduit whilst exposed to biofilm communities. The first (discrete) model simulates absolute numbers of individual cells, whereas the other (continuous) model simulates the relative abundance of taxa in the bulk fluid. The discrete model is founded on a birth-death process whereby the community changes one individual at a time and the numbers of cells in the system can vary. The continuous model is a stochastic differential equation derived from the discrete model and can also accommodate changes in the carrying capacity of the bulk fluid. These models provide a novel Lagrangian framework to investigate and predict the dynamics of migrating microbial communities. In this paper we compare the two models, discuss their merits, possible applications and present simulation results in the context of drinking water distribution systems. Our results provide novel insight into the effects of stochastic dynamics on the composition of non-stationary microbial communities that are exposed to biofilms and provides a new avenue for modelling microbial dynamics in systems where fluids are being transported

Researching teacher educators’ preparedness to teach to and about diversity : Investigating epistemic reflexivity as a new conceptual framework

There is growing international concern about the extent to which teachers are prepared to work with an increasingly diverse student (and community) population. To date, research into the relationship between teacher preparation and preparedness to teach diverse learners has not focused on teacher educators’ understandings about teaching to/about diversity. Such understandings can be informed by epistemic aspects of professional work. Epistemic cognitions (cognitions about knowledge and knowing) allow professionals to generate perspectives necessary to tackle new and old challenges. The social lab reported in this paper investigated 12 Australian teacher educators’ perspectives about teaching to/about diversity using the 3R-Epistemic Cognition (EC) framework. The findings showed that the 3R-EC framework could be useful for capturing epistemic reflexive dialogues about teaching to/about diversity, although some aspects of the framework were identified by the teacher educators as challenging. On the basis of these identified challenges, refinements concerning communication and use of the 3R-EC framework were identified. The feedback also led to some refinements of the social lab methodology for use in the larger national study

Microbial induced calcite precipitation as a viable ground improvement technique

Traditional ground improvement techniques, such as grouting or compaction, can be invasive, energy demanding and expensive. Microbially induced calcite precipitation (MICP) offers a sustainable alternative by utilizing a natural process, and has therefore been the focus of extensive interest and laboratory research over the past decade. Most of that research has been at laboratory-scale on the factors that affect process efficiency. The use of MICP in the field have been discussed in numerous research papers but remains largely theoretical and examples of field-scale trials are rare. MICP uses ureolytic bacteria, such as the common soil bacteria Sporosarcina pasteurii, which are given access to an ample supply of urea and calcium chloride. The bacteria hydrolyse the urea into ammonium and carbonate, raising the pH and in the presence of calcium in solution, facilitating the precipitation of calcite crystals (CaCO3). It is particularly effective when used with fine grained sands as those calcite crystals form a bridge between the individual sand grains, cementing them together and creating a weak bio-sandstone. This project, through bench-scale column experiments on MICP treated sands, has investigated optimization of the influencing factors of the bacteria concentration, the treatment strategy employed and the number of treatment cycles administered. The influence these parameters have on the ultimate core strength, from unconfined compressive strength (UCS) tests, and the homogeneity of the calcite distribution, have been determined. These results have then been used to design an efficient treatment process to underpin large-scale trials of MICP for ground improvement and erosion protection

Large-scale soil improvement tests using microbially induced carbonate precipitation

Bacterial biomineralization provides a greener solution to a diverse range of civil engineering applications, reducing the carbon footprint of construction. Most successful to-date is microbially induced carbonate precipitation (MICP). MICP is being developed for a diverse range of applications including plugging fractures, stabilising soils and repairing building surfaces. In MICP, bacteria are injected within the soil, followed by injection of a fluid containing urea and calcium chloride. The bacteria hydrolyse the urea, which generates bicarbonate ion, increases pH and precipitates calcite. Advantages of MICP include: better penetration due to the low viscosity of the fluids, the ability to maintain free drainage in treated materials and the thousand-year durability of calcite. Despite the growing interest in MICP for geotechnical applications, MICP still remains largely confined to the laboratory with only a very small number of large-scale experiments having been completed and one commercial project. Use is constrained by (1) the ability to grow bacteria at a commercial scale and (2) the need to ensure homogeneous soil strengthening at a large-scale. In this research, conducted in collaboration with BAM Nuttall, we present the results of large-scale test for MICP treated sand. We treat a 1 m diameter cylinder of loose sand using multiple cycles of MICP. Unconfined compressive strength tests and triaxial tests of cores taken from the treated sand result in strengths of several MPa. Our results show that bacterial biomineralization could be a viable, low carbon alternative to cement and concrete for a range of earth infrastructure applications

Micro-scale processes in microbially induced carbonate precipitation

The concept of using bacteria to control the precipitation of calcium carbonate for engineering purposes, such as increasing soil strength and decreasing permeability, is well established in lab-scale experiments. What is not so clear is how to transition from these experiments to a practical field-scale ground improvement tool. One difficulty is that soil properties are highly site specific and also vary spatially within a site (e.g. porosity, permeability, particle shape and size distribution, mineralogical composition). Meanwhile, microbially induced carbonate precipitation relies on complex interactions between pore structure, fluid flow pathways, and injection strategies which all influence where the injected bacteria will attach, where CaCO3 will precipitate, and which evolve over time as CaCO3 is progressively precipitated and the pore structure is altered. To unpick these processes and optimise MICP treatment, we use light microscopy in microfluidic devices offering high time-resolution observations of bacterial attachment and CaCO3 crystal nucleation and growth in 2D systems. This is followed by X-ray μCT of sand packed columns offering more complex and realistic flow conditions in which we observe the evolving pore structure and relate this to changes in the flow fields through reactive-transport modelling with the software OpenFOAM. Results show that the processes of bacterial attachment and crystal growth are complex and highly dependent on micro-scale conditions, however feedback mechanisms, repeated treatment cycles, and operator controlled parameters such as flow velocity can act to minimise these local variations across a range of soil types

Chief Executive Officers’ Perceptions of Collective Organizational Engagement and Patient Experience in Acute Care Hospitals

The concept of employee engagement has garnered considerable attention in acute care hospitals because of the many positive benefits that research has found when clinicians are individually engaged. However, limited, if any, research has examined the effects of engaging all hospital employees (including housekeeping, cafeteria, and admissions staff) in a collective manner and how this may impact patient experience, an important measure of hospital performance. Therefore, this quantitative online survey-based study examines the association between 60 chief executive officers\u27 (CEOs\u27) perceptions of the collective organizational engagement (COE) of all hospital employees and patient experience. A summary measure of the US Hospital Consumer Assessment of Healthcare Providers and Systems survey scores was used to assess patient experience at each of the 60 hospitals represented in the study. A multiple linear regression model was tested using structural equation modeling. The findings of the research suggest that CEOs\u27 perceptions of COE explain a significant amount of variability in patient experience at acute care hospitals. Practical implications for CEOs and other hospital leaders are provided that discuss how COE can be used as an organizational capability to influence organizational performance

Dormancy and Recovery Testing for Biological Wastewater Processors

Bioreactors, such as aerated membrane type bioreactors have been proposed and studied for a number of years as an alternate approach for treating wastewater streams for space exploration. Several challenges remain before these types of bioreactors can be used in space settings, including transporting the bioreactors with their microbial communities to space, whether that be the International Space Station or beyond, or procedures for safing the systems and placing them into dormant state for later start-up. Little information is available on such operations as it is not common practice for terrestrial systems. This study explored several dormancy processes for established bioreactors to determine optimal storage and recovery conditions. Procedures focused on complete isolation of the microbial communities from an operational standpoint and observing the effects of: 1) storage temperature, and 2) storage with or without the reactor bulk fluid. The first consideration was tested from a microbial integrity and power consumption standpoint; both room temperature (25 C) and cold (4 C) storage conditions were studied. The second consideration was explored; again, for microbial integrity as well as plausible real-world scenarios of how terrestrially established bioreactors would be transported to microgravity and stored for periods of time between operations. Biofilms were stored without the reactor bulk fluid to simulate transport of established biofilms into microgravity, while biofilms stored with the reactor bulk fluid simulated the most simplistic storage condition to implement operations for extended periods of nonuse. Dormancy condition did not have an influence on recovery in initial studies with immature biofilms (48 days old), however, a lengthy recovery time was required (20+ days). Bioreactors with fully established biofilms (13 months) were able to recover from a 7-month dormancy period to steady state operation within 4 days (approximately 1 residence cycle). Results indicate a need for future testing on biofilm age and health and further exploration of dormancy length