title: Refinement for probabilistic systems with nondeterminism

authors: Reeves, Steve

subjects: computer science

abstract: Before we combine actions and probabilities two very obvious questions should be asked. Firstly, what does "the probability of an action" mean? Secondly, how does probability interact with nondeterminism? Neither question has a single universally agreed upon answer but by considering these questions at the outset we build a novel and hopefully intuitive probabilistic event-based formalism. 
In previous work we have characterised refinement via the notion of testing. Basically, if one system passes all the tests that another system passes (and maybe more) we say the first system is a refinement of the second. This is, in our view, an important way of characterising refinement, via the question "what sort of refinement should I be using?" 
We use testing in this paper as the basis for our refinement. We develop tests for probabilistic systems by analogy with the tests developed for non-probabilistic systems. We make sure that our probabilistic tests, when performed on non-probabilistic automata, give us refinement relations which agree with for those non-probabilistic automata. We formalise this property as a vertical refinement.

text: Refinement for probabilistic systems with nondeterminism Before we combine actions and probabilities two very obvious questions should be asked. Firstly, what does "the probability of an action" mean? Secondly, how does probability interact with nondeterminism? Neither question has a single universally agreed upon answer but by considering these questions at the outset we build a novel and hopefully intuitive probabilistic event-based formalism. 
In previous work we have characterised refinement via the notion of testing. Basically, if one system passes all the tests that another system passes (and maybe more) we say the first system is a refinement of the second. This is, in our view, an important way of characterising refinement, via the question "what sort of refinement should I be using?" 
We use testing in this paper as the basis for our refinement. We develop tests for probabilistic systems by analogy with the tests developed for non-probabilistic systems. We make sure that our probabilistic tests, when performed on non-probabilistic automata, give us refinement relations which agree with for those non-probabilistic automata. We formalise this property as a vertical refinement.

year: 2011

title: Fitness consequences of population bottlenecks in an invasive blowfly

authors: Croft, Lillian

subjects: biological invasion

abstract: Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

text: Fitness consequences of population bottlenecks in an invasive blowfly Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

year: 2024

title: Case roles / relations and discourse relations: A Maori language-based perspective

authors: Whaanga, Hēmi

subjects: case grammar

abstract: The overall aim of this research project is to explore case roles/ relations and discourse relations (referred to in this thesis as 'intra-propositional relations' and 'interpropositional relations' respectively) from the perspective of the Maori language. 
The thesis begins with an outline of the scope of the research and the approaches and methods used (Chapter 1). This is followed by a critical review of selected literature on case roles/ relations (intra-propositional relations) (see Chapter 2) and discourse relations (inter-propositional relations) (see Chapter 3) where it is noted that some of the relational theories and models appear to lack descriptive and/or explanatory adequacy. 
In Chapter 4, two models (an intra-propositional relational model and an interpropositional relational model) are developed on the basis of the critical review in Chapters 2 and 3, and these models are applied to a written corpus of Maori language texts, the primary aim being to track the ways in which intra-propositional and interpropositional relations are signalled in Maori. 
In Chapter 5, l supplement the corpus-based findings reported in Chapter 4 by reexamining the findings of two earlier studies from the perspective of the models introduced in Chapter 4. One of these earlier studies, reported in the early 1980s, is concerned with the distribution of prepositions in Maori in relation to case roles/ relations (intra-propositional relations); the other, produced much more recently (in 2001) is concerned with the signalling in Maori of a selection of what are referred to in that Work as 'semantico-pragmatic relations' (inter-propositional relations). 
Chapter 6 provides an overview of the research and a summary of the findings, together with an indication of its limitations, possible areas of application, and suggestions for future research.

text: Case roles / relations and discourse relations: A Maori language-based perspective The overall aim of this research project is to explore case roles/ relations and discourse relations (referred to in this thesis as 'intra-propositional relations' and 'interpropositional relations' respectively) from the perspective of the Maori language. 
The thesis begins with an outline of the scope of the research and the approaches and methods used (Chapter 1). This is followed by a critical review of selected literature on case roles/ relations (intra-propositional relations) (see Chapter 2) and discourse relations (inter-propositional relations) (see Chapter 3) where it is noted that some of the relational theories and models appear to lack descriptive and/or explanatory adequacy. 
In Chapter 4, two models (an intra-propositional relational model and an interpropositional relational model) are developed on the basis of the critical review in Chapters 2 and 3, and these models are applied to a written corpus of Maori language texts, the primary aim being to track the ways in which intra-propositional and interpropositional relations are signalled in Maori. 
In Chapter 5, l supplement the corpus-based findings reported in Chapter 4 by reexamining the findings of two earlier studies from the perspective of the models introduced in Chapter 4. One of these earlier studies, reported in the early 1980s, is concerned with the distribution of prepositions in Maori in relation to case roles/ relations (intra-propositional relations); the other, produced much more recently (in 2001) is concerned with the signalling in Maori of a selection of what are referred to in that Work as 'semantico-pragmatic relations' (inter-propositional relations). 
Chapter 6 provides an overview of the research and a summary of the findings, together with an indication of its limitations, possible areas of application, and suggestions for future research.

year: 2006