A correspondence between a class of monoids and self-similar group actions II

The first author showed in a previous paper that there is a correspondence between self-similar group actions and a class of left cancellative monoids called left Rees monoids. These monoids can be constructed either directly from the action using Zappa-Sz\'ep products, a construction that ultimately goes back to Perrot, or as left cancellative tensor monoids from the covering bimodule, utilizing a construction due to Nekrashevych, In this paper, we generalize the tensor monoid construction to arbitrary bimodules. We call the monoids that arise in this way Levi monoids and show that they are precisely the equidivisible monoids equipped with length functions. Left Rees monoids are then just the left cancellative Levi monoids. We single out the class of irreducible Levi monoids and prove that they are determined by an isomorphism between two divisors of its group of units. The irreducible Rees monoids are thereby shown to be determined by a partial automorphism of their group of units; this result turns out to be signficant since it connects irreducible Rees monoids directly with HNN extensions. In fact, the universal group of an irreducible Rees monoid is an HNN extension of the group of units by a single stable letter and every such HNN extension arises in this way.Comment: Some very minor corrections made and the dedication adde

Productivity pathways: climate-adjusted production frontiers for the Australian broadacre cropping industry

This study introduces two advances to the aggregate productivity index methodology typically employed by ABARES. First, it accounts for the effects of climate variability on measured productivity by matching spatial climate data to individual farms in the ABARES farm surveys database. Second, a farm-level production frontier estimation technique is employed to facilitate the decomposition of productivity change into several key components, including technical change and technical efficiency change. The study makes use of farm-level data from the ABARES Australian agricultural and grazing industries survey database. An unbalanced panel dataset is constructed containing 13 430 observations (4255 farms) over the period 1977–78 to 2007–08. Spatial climate data, including winter and summer seasonal rainfall and average maximum and minimum temperatures, were obtained via the Australian Water Availability Project. These data were mapped to individual farms using Geographic Information System methods. The study employed stochastic frontier analysis methods to estimate a production frontier with time varying technical efficiency effects of the form proposed by Battese and Coelli (1992). Production frontiers are estimated for each of the three major Grains Research and Development Corporation regions: southern, northern and western. Selected climate variables are shown to display a high degree of explanatory power over farm output. The results confirm that deterioration in average climate conditions has contributed significantly to the decline in estimated productivity over the post-2000 period. Technical change is shown to be the primary driver of productivity growth in the industry in the long run, offset by a gradual decline in technical efficiency. After controlling for climate variability, a gradual decline in the rate of technical change is still observed.Productivity Analysis,

On the near-wake of a ground-effect diffuser with passive flow control

A ground-effect diffuser is an upwardly-inclined section of an automobile’s underbody which increases aerodynamic performance by generating downforce. To understand the diffuser flow physics (force behaviour, surface and off-surface flow features), we established the near-wake (within one vehicle width of the base) velocity profiles and flow structures of an automotive ground-effect diffuser using a bluff body with a 17 degree slanted section forming the plane diffuser ramp surface (baseline geometry), and endplates extending along both sides of the ramp. Wind tunnel experiments were conducted at a Reynolds number of 1.8 million based on the bluff body length, and laser Doppler velocimetry was used to measure two-dimensional velocity components on three planes of the diffuser near-wake. We also measured the velocity field in the near-wake of diffusers with modified geometry (with an inverted wing or a convex bump) as passive flow control devices. The near-wake velocity profiles indicated that the passive flow control methods increased the diffuser flow velocity and that the longitudinal vortices along the diffuser determined the shape of the flow structures in the near-wake of the diffuser bluff bod

Blurred reputations: Managing professional and private information online

Results are reported from a study that investigated patterns of information behaviour and use as related to personal reputation building and management in online environments. An everyday life information seeking (ELIS) perspective was adopted. Data were collected by diary and interview from forty-five social media users who hold professional and managerial work roles, and who are users of Twitter, Facebook, and/or LinkedIn. These data were first transcribed, then coded with NVivo10 according to themes identified from a preliminary literature review, with further codes added as they emerged from the content of the participant diaries and interviews. The main findings reveal that the portrayal of different personas online contribute to the presentation (but not the creation) of identity, that information sharing practices for reputation building and management vary according to social media platform, and that the management of online connections and censorship are important to the protection of reputation. The maintenance of professional reputation is more important than private reputation to these users. They are aware of the 'blur' between professional and private lives in online contexts, and the influence that it bears on efforts to manage an environment where LinkedIn is most the useful of the three sites considered, and Facebook the most risky. With its novel focus on the 'whole self', this work extends understandings of the impact of information on the building and management of reputation from an Information Science perspective

Building identity in online environments: an Information Science perspective

The research presented in this poster is concerned with the ways in which people use information to build identities for themselves online with reference to the themes of personal reputation management. To date these two themes have been under-explored together in the research literature, both in general, and from an Information Science perspective. The poster content shares findings related to three areas of identity building: (1) the creation and use of online personas and identities; (2) the use of anonymity and pseudonyms through information sharing – or concealment – practices; and (3) the ways in which the blurring or merging together of participants’ private and professional selves. This study used participant diaries and in-depth, semi-structured interviews with 45 UK-based participants. The main finding presented here is that individuals present elements of their online persona or personality using online information, but that they do not do so with the intention of building identity. The findings explored in this presentation are contextualised with reference to identity building in the more formal setting of academic reputation management, i.e. through the use of citation