4,307 research outputs found

    Bioavailability of soil organic carbon and Fe as influenced by forestry practices in a subtropical coastal catchment

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    Potential impacts of plantation forestry practices on soil organic carbon and Fe available to microorganisms were investigated in a subtropical coastal catchment. The impacts of harvesting or replanting were largely limited to the soil top layer (0–10 cm depth). The thirty-year-old Pinus plantation showed low soil moisture content (Wc) and relatively high levels of soil total organic carbon (TOC). Harvesting and replanting increased soil Wc but reduced TOC levels. Mean dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased in harvested or replanted soils, but such changes were not statistically significant (P > 0.05). Total dithionite-citrate and aqua regia-extractable Fe did not respond to forestry practices, but acid ammonium oxalate and pyrophosphate-extractable, bioavailable Fe decreased markedly after harvesting or replanting. Numbers of heterotrophic bacteria were significantly correlated with DOC levels (P < 0.05), whereas Fe-reducing bacteria and S-bacteria detected using laboratory cultivation techniques did not show strong correlation with either soil DOC or Fe content

    On Density-Critical Matroids

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    For a matroid MM having mm rank-one flats, the density d(M)d(M) is mr(M)\tfrac{m}{r(M)} unless m=0m = 0, in which case d(M)=0d(M)= 0. A matroid is density-critical if all of its proper minors of non-zero rank have lower density. By a 1965 theorem of Edmonds, a matroid that is minor-minimal among simple matroids that cannot be covered by kk independent sets is density-critical. It is straightforward to show that U1,k+1U_{1,k+1} is the only minor-minimal loopless matroid with no covering by kk independent sets. We prove that there are exactly ten minor-minimal simple obstructions to a matroid being able to be covered by two independent sets. These ten matroids are precisely the density-critical matroids MM such that d(M)>2d(M) > 2 but d(N)2d(N) \le 2 for all proper minors NN of MM. All density-critical matroids of density less than 22 are series-parallel networks. For k2k \ge 2, although finding all density-critical matroids of density at most kk does not seem straightforward, we do solve this problem for k=94k=\tfrac{9}{4}.Comment: 16 page

    Is Environmental Justice Good for White Folks?

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    This paper examines spatial variations in exposure to toxic air pollution from industrial facilities in urban areas of the United States, using geographic microdata from the U.S. Environmental Protection Agency’s Risk-Screening Environmental Indicators project. We find that average exposure in an urban area is positively correlated with the extent of racial and ethnic disparity in the distribution of the exposure burden. This correlation could arise from causal linkages in either or both directions: the ability to displace pollution onto minorities may lower the effective cost of pollution for industrial firms; and higher average pollution burdens may induce whites to invest more political capital in efforts to influence firms’ siting decisions. Furthermore, we find that in urban areas with higher minority pollution-exposure discrepancies, average exposures tend to be higher for all population subgroups, including whites. In other words, improvements in environmental justice in the United States could benefit not only minorities but also whites.environmental justice; air pollution; industrial toxics; Risk-Screening Environmental Indicators.

    Regenerative failure and attribution

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    Purpose - The purpose of this paper is to focus on the processes that occur between entrepreneurs’ primary attribution for failure and the emergent learning dimensions from failure, in the context of regenerative failures. Design/methodology/approach - The study focusses on 21 entrepreneurs operating in the producing services sector, a major subsector of the Irish Information and Communication Technology industry. All the entrepreneurs experienced business failure and subsequently re-entered the entrepreneurial sphere at a later date. A qualitative approach examines their attributions for failure, responses to failure, and learning dimensions from failure. Findings - Regenerative entrepreneurs’ primary attributions for business failure are examined in detail; four types of failure attributions are uncovered – internal individual level; external firm level; external market level; and hybrid attributions. Entrepreneurs’ attributions impact their responses to the failure; this in turn affects entrepreneurial learning. When failure is primarily attributed to internal factors, the entrepreneur’s response is affective, leading to deep, personal learning about oneself. External attributions (both firm level and market level) result in a primarily behavioural response, with learning focussed on the venture, and networks and relationships. Those primarily attributing failure to hybrid factors have a largely cognitive response and they learn about venture management. Research limitations/implications - This study is a retrospective analysis of business failure. Originality/value - The study contributes to the growing literature on entrepreneurs’ attributions for business failure by focussing on regenerative failure; it links attributions to – responses to, and learning from, failure. The key contribution to knowledge emerges from the development of a model of the underlying processes affecting learning from failure for regenerative entrepreneurs. The research also establishes and identifies clear links between attributions, responses, and lessons learned in the context of regenerative failure
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