Maximum size binary matroids with no AG(3,2)-minor are graphic

We prove that the maximum size of a simple binary matroid of rank $r \geq 5$ with no AG(3,2)-minor is $\binom{r+1}{2}$ and characterise those matroids achieving this bound. When $r \geq 6$, the graphic matroid $M(K_{r+1})$ is the unique matroid meeting the bound, but there are a handful of smaller examples. In addition, we determine the size function for non-regular simple binary matroids with no AG(3,2)-minor and characterise the matroids of maximum size for each rank

The Influence of Threatened State Preemption on City Council Voting Behavior and Municipal Broadband

Since the progressive era, American cities have generally expanded their authority in policymaking and service provision. State governments have at times acted to preempt city authority on particular points of policy, but it is unclear whether the threat of this action inspires caution in the decision making of city leaders. The results of an experimental survey distributed to elected city officials across the United States show that a perceived threat of preemption does not significantly discourage city leaders in supporting a proposed broadband internet service provision. These results suggest that political pressure in the form of preemption is not persuasive to city leaders, and that local representational interests are likely more influential on municipal government

Buy High Sell Low: Redefining Bean Counting in the Coffee Industry for a Sustainable Future

Charles Manz returns to the JVBL providing ‒ together with several fellow researchers/writers ‒ a case study of a socially responsible business within the coffee industry. Familiar CSR concepts are examined such as Fair Trade and sustainability which foster parity in dealing with buyers while maintaining product quality and reasonable income. The practices of Dean’s Beans, a progressive coffee organization, are examined as a notable demonstration of how a business can fiscally succeed while maintaining a commitment to the triple-bottom-line considerations of people, planet, and profits

Monte Carlo Simulation of Ising Models with Dipole Interaction

Recently, a new memory effect was found in the metamagnetic domain structure of the diluted Ising antiferromagnet $Fe_x Mg_{1-x} Cl_2$ by domain imaging with Faraday contrast. Essential for this effect is the dipole interaction. We simulate the low temperature behavior of diluted Ising-antiferromagnets by a Monte Carlo simulation considering long range interaction. The metamagnetic domain structure occurring due to the dipole interaction is investigated by graphical representation. In the model considered the antiferromagnetic state is stable for an external magnetic field smaller than a lower boundary $B_{c1}$ while for fields larger than an upper boundary $B_{c2}$ the system is in the saturated paramagnetic phase, where the spins are ferromagnetically polarized. For magnetic fields in between these two boundaries a mixed phase occurs consisting of ferromagnetic domains in an antiferromagnetic background. The position of these ferromagnetic domains is stored in the system: after a cycle in which the field is first removed and afterwards applied again the domains reappear at their original positions. The reason for this effect can be found in the frozen antiferromagnetic domain state which occurs after removing the field.Comment: Latex, 10 pages; 3 postsript-figures, compressed tar-file, uuencoded, report 10109

A framework for the design of usable electronic text

This thesis examines the human issues underlying the design and usability of electronic text systems. In so doing it develops a framework for the conceptualisation of these issues that aims to guide designers of electronic texts in their attempts to produce usable systems. The thesis commences with a review of the traditional human factors literature on electronic text according to three basic themes: its concern with perceptual, manipulatory and structural issues. From this examination it is concluded that shortcomings in translating this work into design result from the adoption of overly narrow uni-disciplinary views of reading taken from cognitive psychology and information science which are inappropriate to serve the needs of electronic text designers. In an attempt to provide a more relevant description of the reading process a series of studies examining readers and their views as well as uses of texts is reported. In the first, a repertory grid based investigation revealed that all texts can be described in reader-relvant terms according to three criteria: why a text is read, what a text contains and how it is read. These criteria then form the basis of two investigations of reader-text interaction using academic journals and user manuals. The results of these studies highlighted the need to consider readers' models of a document's structure in discussing text usability. Subsequent experimental work on readers' models of academic articles demonstrated not only that such models are important aspects of reader-text interaction but that data of this form could usefully be employed in the design of an electronic text system. The proposed framework provides a broad, qualitative model of the important issues for designers to consider when developing a product It consists of four interactive elements that focus attention on aspects of reading that have been identified as central to usability. Simple tests of the utility and validity of the framework are reported and it is shown that the framework both supports reasoned analysis and subsequent prediction of reader behaviour as well as providing a parsimonious account of their verbal utterances while reading. The thesis concludes with an analysis of the likely uses of such a framework and the potential for electronic text systems in an increasingly information-hungry world

Coherent response of lakes in Ontario, Canada to reductions in sulphur deposition: the effects of climate on sulphate concentrations

International audienceSulphate deposition in south-central Ontario declined between 1976 and 2000 by more than 50%, whereas lake sulphate (SO42?) concentrations decreased by, on average, only half as much. To investigate the factors that controlled this slower than expected response, the temporal patterns in lake SO42? concentrations were compared with patterns in both deposition and climate, since climate has a major influence on the hydrological cycle in this part of the continent. To do this, the temporal coherence in SO42? concentrations between 9 lake basins was estimated using the intraclass correlation from a repeated-measures analysis of variance and two subsets of lakes were found (six in one group, four in the other), each with lakes having synchronous patterns. One subset (4 lakes) included the 3 with the longest water replenishment times (>3.4 yr) which are expected to respond to decreases in SO42? deposition more slowly. However, the average pattern reflecting the temporal changes of each of the two subsets was very similar. The response of both subsets of lakes to the decreasing SO42? deposition over two decades was independent of the degree of acidification or sensitivity to acidification of the lakes. In a determination of which factors best predicted each of those two subsets' SO42? time series, good predictive models were produced by regional/global-scale climate indices, specifically the Southern Oscillation Index (SOI) describing the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation Index (NAOI), as well as by SO42? deposition indices. When the predictor variables were combined, models which described the long-term changes in lake SO42? concentration best included the SOI, the NAOI and SO42? deposition. Thus, large-scale climate factors play a major role in determining the response of aquatic systems to changes in SO42? deposition, perhaps through their influence on lake and/or catchment processes that effectively delay recovery. Keywords: Atmospheric deposition, lake recovery, temporal trends, climate, temporal coherenc