title: D-semigroups and constellations

authors: Stokes, Tim E.

subjects: Science & Technology

abstract: In a result generalising the Ehresmann–Schein–Nambooripad Theorem relating inverse semigroups to inductive groupoids, Lawson has shown that Ehresmann semigroups correspond to certain types of ordered (small) categories he calls Ehresmann categories. An important special case of this is the correspondence between two-sided restriction semigroups and what Lawson calls inductive categories. Gould and Hollings obtained a one-sided version of this last result, by establishing a similar correspondence between left restriction semigroups and certain ordered partial algebras they call inductive constellations (a general constellation is a one-sided generalisation of a category). We put this one-sided correspondence into a rather broader setting, at its most general involving left congruence D-semigroups (which need not satisfy any semiadequacy condition) and what we call co-restriction constellations, a finitely axiomatized class of partial algebras. There are ordered and unordered versions of our results. Two special cases have particular interest. One is that the class of left Ehresmann semigroups (the natural one-sided versions of Lawson’s Ehresmann semigroups) corresponds to the class of co-restriction constellations satisfying a suitable semiadequacy condition. The other is that the class of ordered left Ehresmann semigroups (which generalise left restriction semigroups and for which semigroups of binary relations equipped with domain operation and the inclusion order are important examples) corresponds to a class of ordered constellations defined by a straightforward weakening of the inductive constellation axioms.

text: D-semigroups and constellations In a result generalising the Ehresmann–Schein–Nambooripad Theorem relating inverse semigroups to inductive groupoids, Lawson has shown that Ehresmann semigroups correspond to certain types of ordered (small) categories he calls Ehresmann categories. An important special case of this is the correspondence between two-sided restriction semigroups and what Lawson calls inductive categories. Gould and Hollings obtained a one-sided version of this last result, by establishing a similar correspondence between left restriction semigroups and certain ordered partial algebras they call inductive constellations (a general constellation is a one-sided generalisation of a category). We put this one-sided correspondence into a rather broader setting, at its most general involving left congruence D-semigroups (which need not satisfy any semiadequacy condition) and what we call co-restriction constellations, a finitely axiomatized class of partial algebras. There are ordered and unordered versions of our results. Two special cases have particular interest. One is that the class of left Ehresmann semigroups (the natural one-sided versions of Lawson’s Ehresmann semigroups) corresponds to the class of co-restriction constellations satisfying a suitable semiadequacy condition. The other is that the class of ordered left Ehresmann semigroups (which generalise left restriction semigroups and for which semigroups of binary relations equipped with domain operation and the inclusion order are important examples) corresponds to a class of ordered constellations defined by a straightforward weakening of the inductive constellation axioms.

year: 2017

title: Structural agricultural land use modeling for spatial agro-environmental policy analysis

authors: Fezzi, Carlo

subjects: agro-environmental policy

abstract: This paper develops a spatially disaggregated, structural econometric model of agricultural land use and production based on the joint multi-output technology representation introduced by Chambers and Just (1989). Starting from a flexible specification of the farm profit function, we derive land use allocation, input application, crop yield, and livestock intensity equations in a joint and theoretically consistent framework. To account for the presence of censored observations in micro-level data, the model is estimated as a system of two-limit Tobit equations via quasi-maximum likelihood. We present an empirical application using fine-scale spatial data covering the entirety of England and Wales and including the main economic, policy, and environmental drivers of land use change in the past forty years. A simulation of the effects of diffuse pollution reduction measures illustrates how our approach can be applied for agro-environmental policy appraisal.

text: Structural agricultural land use modeling for spatial agro-environmental policy analysis This paper develops a spatially disaggregated, structural econometric model of agricultural land use and production based on the joint multi-output technology representation introduced by Chambers and Just (1989). Starting from a flexible specification of the farm profit function, we derive land use allocation, input application, crop yield, and livestock intensity equations in a joint and theoretically consistent framework. To account for the presence of censored observations in micro-level data, the model is estimated as a system of two-limit Tobit equations via quasi-maximum likelihood. We present an empirical application using fine-scale spatial data covering the entirety of England and Wales and including the main economic, policy, and environmental drivers of land use change in the past forty years. A simulation of the effects of diffuse pollution reduction measures illustrates how our approach can be applied for agro-environmental policy appraisal.

year: 2011

title: Covering tangata whenua in Aotearoa: a big data exploration of print media and Māori

authors: Phillips, Justin B.

abstract: A large body of academic research documents harmful media coverage of indigenous populations across the globe. New Zealand is no exception. Aotearoa’s indigenous people, Māori, share similar damaging experiences, leading one major NZ media company to publish an apology for their historically poor depiction of tangata whenua. This paper adds to that wealth of evidence using the automated methods of machine learning to examine coverage of Māori in NZ print media. Across roughly 800,000 sentences–spanning over two decades of coverage–this research investigates print media discourses involving Māori at a mass scale while demonstrating the applicability of such tools for further research. The results replicate a collection of existing findings at large-N scale, further documenting problematic discussions of violence, political representation, and culture, among several other concerns. The novel approach also hints at complex, obscure relationships embedded within problematic language in Aotearoa’s print media, identifying notions of division - both implied and otherwise - along with notable instances of resistance.

text: Covering tangata whenua in Aotearoa: a big data exploration of print media and Māori A large body of academic research documents harmful media coverage of indigenous populations across the globe. New Zealand is no exception. Aotearoa’s indigenous people, Māori, share similar damaging experiences, leading one major NZ media company to publish an apology for their historically poor depiction of tangata whenua. This paper adds to that wealth of evidence using the automated methods of machine learning to examine coverage of Māori in NZ print media. Across roughly 800,000 sentences–spanning over two decades of coverage–this research investigates print media discourses involving Māori at a mass scale while demonstrating the applicability of such tools for further research. The results replicate a collection of existing findings at large-N scale, further documenting problematic discussions of violence, political representation, and culture, among several other concerns. The novel approach also hints at complex, obscure relationships embedded within problematic language in Aotearoa’s print media, identifying notions of division - both implied and otherwise - along with notable instances of resistance.

year: 2022