The involutions-as-principal types/ application-as-unification analogy

In 2005, S. Abramsky introduced various universal models of computation based on Affine Combinatory Logic, consisting of partial involutions over a suitable formal language of moves, in order to discuss reversible computation in a game-theoretic setting. We investigate Abramsky\u2019s models from the point of view of the model theory of \u3bb-calculus, focusing on the purely linear and affine fragments of Abramsky\u2019s Combinatory Algebras. Our approach stems from realizing a structural analogy, which had not been hitherto pointed out in the literature, between the partial involution interpreting a combinator and the principal type of that term, with respect to a simple types discipline for \u3bb-calculus. This analogy allows for explaining as unification between principal types the somewhat awkward linear application of involutions arising from Geometry of Interaction (GoI). Our approach provides immediately an answer to the open problem, raised by Abramsky, of characterising those finitely describable partial involutions which are denotations of combinators, in the purely affine fragment. We prove also that the (purely) linear combinatory algebra of partial involutions is a (purely) linear \u3bb-algebra, albeit not a combinatory model, while the (purely) affine combinatory algebra is not. In order to check the complex equations involved in the definition of affine \u3bb-algebra, we implement in Erlang the compilation of \u3bb-terms as involutions, and their execution

Integrating agriculture and conservation: The value of fallow land and its management for farmland and steppe bird conservation

[eng] Extensive farmland ecosystems are widespread and biodiversity-rich, yet they face important human pressures since the beginning of agriculture intensification, which is leading them into a severe biodiversity crisis. As a result, farmland bird populations - particularly specialist species such as steppe birds - are declining dramatically. In Europe, steppe birds are associated with “cereal steppes”, which are extensive agricultural landscapes where crop rotations include fallow fields. Fallows are key breeding and foraging habitats for farmland birds and usually present open vegetation structures essential for steppe birds. This thesis, situated in a cereal steppe in Catalonia (north-eastern Spain), evaluates the importance of fallow land and its management for enhancing farmland and steppe bird populations. Because population monitoring is key to evaluate the status of populations, I also explored the importance of accounting for imperfect detection when estimating farmland bird population trends. By using a Hierarchical Distance Sampling (HDS) model, I found that heterogeneous detection across observers and years could bias trend estimates when not accounted for. Through a HDS community model integrating data of 37 farmland bird species, I revealed the lack of efficiency of conservation measures applied in fallow fields, currently promoted by the European Common Agricultural Policy (Agri-Environmental Schemes and Greening), to increase farmland bird abundance. However, a local conservation measure targeted specifically at steppe birds (Targeted Fallow Management, TFM) ‒ consisting of agricultural practices on fallows applied once or twice annually before the breeding season ‒ enhanced steppe bird abundance. Through path analyses, I could disentangle the mechanisms behind TFM success and found that TFM fulfils species-specific requirements by modulating the vegetation structure. Finally, I used the first GPS data on the declining Pin-tailed sandgrouse (Pterocles alchata) to demonstrate the importance of fallow land during the breeding season, when cereal vegetation is tall and unsuitable for steppe birds causing a habitat bottleneck. This thesis provides applied guidelines for conservation planning, from population monitoring to mechanisms involved in the success of specific conservation measures. The key finding is the importance of promoting not only fallow- land presence, but also its management, to improve its conservation efficiency. These guidelines have great potential to be included within the upcoming European agricultural reform (CAP post- 2020) and help prevent imminent population and species extinctions.[cat] Els paisatges agrícoles són ecosistemes rics en biodiversitat, però des de mitjans del segle passat Europa pateix un procés d'intensificació agrícola que està causant la pèrdua d'aquesta biodiversitat a gran velocitat. Com a conseqüència, les poblacions d'ocells de medis agrícoles ‒ en particular espècies especialistes com els ocells estèpics ‒ pateixen un fort declivi. A Europa, els ocells estèpics estan estretament associats a les estepes cerealistes de la Península Ibèrica, que són paisatges oberts i plans on predomina el cultiu del cereal, en rotació amb guarets i altres cultius herbacis. Els guarets són hàbitats essencials per a l'alimentació i nidificació dels ocells de medis agrícoles, i normalment presenten una vegetació baixa en altura i cobertura que resulta òptima per els ocells estèpics. Aquesta tesi avalua la importància del guaret i la seva gestió per a la millora de les poblacions d'ocells agrícoles i estèpics. L'estudi es desenvolupa en una estepa cerealista de Catalunya (nord-est d'Espanya) en la qual s'apliquen mesures compensatòries per a la conservació d'ocells estèpics des de l'any 2015. En aquest context, la tesi també explora la importància de tenir en compte la detectabilitat per a l'estima de tendències poblacionals d'ocells en ecosistemes agrícoles, ja que el monitoratge és un aspecte essencial per avaluar l'estat de les poblacions. La tesi demostra l'eficiència d'una mesura de conservació d'àmbit local específicament dissenyada pels ocells estèpics, que consisteix en la gestió de guarets (“Targeted Fallow Management, TFM”). Mitjançant l'ús d'anàlisi de ruta (“Path analysis”), aquesta tesi revela el mecanisme ecològic d'actuació de la mesura TFM, que satisfà els requeriments específics de diferents espècies d'ocells estèpics mitjançant una gestió adequada de l'estructura de la vegetació. A més, TFM va resultar ser més eficaç que les mesures de conservació en guarets promogudes en el marc de la Política Agrària Comuna Europea (Greening i Mesures Agroambientals) per augmentar l'abundància de la comunitat d'ocells, especialment dels ocells estèpics. Aquests resultats s'han obtingut mitjançant l'aplicació de models jeràrquics de mostreig per distàncies (“Hierarchical Distance Sampling, HDS”). També s'utilitzen els models HDS per demostrar que l'existència d'una detecció heterogènia entre observadors i al llarg dels anys pot ocasionar estimes de tendències poblacionals errònies si no es té en compte la detecció imperfecta. Finalment, utilitzant dades GPS de ganga (Pterocles alchata), també es demostra la importància del guaret quan el creixement del cereal a la primavera ocasiona un coll d'ampolla en la quantitat disponible d'hàbitat òptim per aquesta espècie. Aquesta tesi proporciona recomanacions útils per la planificació de mesures de conservació, des de l'etapa inicial del monitoratge fins a comprendre quins són els mecanismes ecològics subjacents a les mesures de conservació més exitoses. La seva principal contribució és la importància d'una adequada gestió dels guarets per augmentar el seu valor com a eina de conservació. Aquestes recomanacions són especialment oportunes per poder ser incloses en la nova reforma de la Política Agrària Comuna, i així contribuir a la conservació d'aquestes espècies.[spa] Los paisajes agrícolas son ecosistemas ricos en biodiversidad, pero desde mediados del siglo pasado Europa sufre un proceso de intensificación agrícola que está causando la pérdida de esta biodiversidad a gran velocidad. Como consecuencia, las poblaciones de aves de medios agrícolas ‒ en particular especies especialistas como las aves esteparias ‒ sufren un declive alarmante. En Europa, las aves esteparias están estrechamente asociadas a las estepas cerealistas de la Península Ibérica, que son paisajes abiertos y llanos en los que predomina el cultivo del cereal, en rotación con barbechos y otros cultivos herbáceos. Los barbechos son hábitats esenciales para la alimentación y nidificación de aves de medios agrícolas, y normalmente presentan una vegetación baja en altura y cobertura que resulta óptima para las aves esteparias. Esta tesis evalúa la importancia de las tierras en barbecho y su manejo para la mejora de las poblaciones de aves de medios agrícolas y esteparios. El estudio se desarrolla en una estepa cerealista de Cataluña (noreste de España) en la que se aplican medidas compensatorias para la conservación de aves esteparias desde el año 2015. En este marco, la tesis también explora la importancia de tener en cuenta la detectabilidad para la estima de tendencias poblacionales de aves en ecosistemas agrícolas, ya que el monitoreo es un aspecto esencial para evaluar el estado de las poblaciones. La tesis demuestra la eficiencia de una medida de conservación de ámbito local, específicamente diseñada para las aves esteparias, consistente en el manejo de barbechos (“Targeted Fallow Management, TFM”). Mediante el uso de análisis de ruta (“Path analysis”), esta tesis revela el mecanismo ecológico de actuación de la medida TFM, que satisface los requerimientos específicos de distintas especies de aves esteparias mediante una gestión adecuada de la estructura de la vegetación. Además, TFM resultó ser más eficaz que las medidas de conservación en barbechos en el marco de la Política Agraria Común Europea (Greening y Medidas Agroambientales) para aumentar la abundancia de la comunidad de aves, en especial de las aves esteparias. Estos resultados se han obtenido mediante la aplicación de modelos jerárquicos de muestreo por distancias (“Hierarchical Distance Sampling, HDS”). También se utiliza HDS para demostrar que la existencia de una detección heterogénea entre observadores y a lo largo de los años puede ocasionar estimas de tendencias poblacionales erróneas para ciertas especies, si no se tiene en cuenta la detección imperfecta. Finalmente, utilizando datos GPS de ganga ibérica (Pterocles alchata), también se demuestra la importancia del barbecho cuando el crecimiento del cereal en primavera ocasiona un cuello de botella en la cantidad de hábitat óptimo disponible para esta especie. Esta tesis proporciona recomendaciones útiles para la planificación de medidas de conservación, desde la etapa de monitoreo hasta comprender cuáles son los mecanismos ecológicos subyacentes a las medidas de conservación más exitosas. Su principal contribución es la importancia de una adecuada gestión de los barbechos para aumentar su valor como herramienta de conservación. Estas recomendaciones son especialmente oportunas para ser incluidas en la nueva reforma de la Política Agraria Común, y así contribuir a la conservación de estas especies

Grammatical structures and logical deductions

The three essays presented here concern natural connections between grammatical derivations and structures provided by certain standard grammar formalisms, on the one hand, and deductions in logical systems, on the other hand. In the first essay we analyse the adequacy of Polish notation for higher-order languages. The Ajdukiewicz algorithm (Ajdukiewicz 1935) is discussed in terms of generalized MP-deductions. We exhibit a failure in Ajdukiewicz’s original version of the algorithm and give a correct one; we prove that generalized MP-deductions have the frontier property, which is essential for the plausibility of Polish notation. The second essay deals with logical systems corresponding to different grammar formalisms, as e.g. Finite State Acceptors, Context-Free Grammars, Categorial Grammars, and others. We show how can logical methods be used to establish certain linguistically significant properties of formal grammars. The third essay discusses the interplay between Natural Deduction proofs in grammar oriented logics and semantic structures expressible by typed lambda terms and combinators

Identification of Macroeconomic Factors in Large Panels

This paper presents a dynamic factor model where the extracted factors and shocks are given a clear economic interpretation. The economic interpretation of the factors is obtained by means of a set of over-identifying loading restrictions, while the structural shocks are estimated following standard practices in the SVAR literature. Estimators based on the EM algorithm are developed. We apply this framework to a large panel of US monthly macroeconomic series. In particular, we identify five macroeconomic factors and discuss the economic impact of monetary policy shocks. The results are theoretically more plausible than those implied by standard SVAR models and indicate a significant role for monetary policy shocks in macroeconomic dynamics.Monetary policy, Business Cycles, Factor Models, EM Algorithm.

Covariate shift estimation based adaptive ensemble learning for handling non-stationarity in motor imagery related EEG-based brain-computer interface

The non-stationary nature of electroencephalography (EEG) signals makes an EEG-based brain-computer interface (BCI) a dynamic system, thus improving its performance is a challenging task. In addition, it is well-known that due to non-stationarity based covariate shifts, the input data distributions of EEG-based BCI systems change during inter- and intra-session transitions, which poses great difficulty for developments of online adaptive data-driven systems. Ensemble learning approaches have been used previously to tackle this challenge. However, passive scheme based implementation leads to poor efficiency while increasing high computational cost. This paper presents a novel integration of covariate shift estimation and unsupervised adaptive ensemble learning (CSE-UAEL) to tackle non-stationarity in motor-imagery (MI) related EEG classification. The proposed method first employs an exponentially weighted moving average model to detect the covariate shifts in the common spatial pattern features extracted from MI related brain responses. Then, a classifier ensemble was created and updated over time to account for changes in streaming input data distribution wherein new classifiers are added to the ensemble in accordance with estimated shifts. Furthermore, using two publicly available BCI-related EEG datasets, the proposed method was extensively compared with the state-of-the-art single-classifier based passive scheme, single-classifier based active scheme and ensemble based passive schemes. The experimental results show that the proposed active scheme based ensemble learning algorithm significantly enhances the BCI performance in MI classifications

Formal verification of a fault tolerant clock synchronization algorithm

A formal specification and mechanically assisted verification of the interactive convergence clock synchronization algorithm of Lamport and Melliar-Smith is described. Several technical flaws in the analysis given by Lamport and Melliar-Smith were discovered, even though their presentation is unusally precise and detailed. It seems that these flaws were not detected by informal peer scrutiny. The flaws are discussed and a revised presentation of the analysis is given that not only corrects the flaws but is also more precise and easier to follow. Some of the corrections to the flaws require slight modifications to the original assumptions underlying the algorithm and to the constraints on its parameters, and thus change the external specifications of the algorithm. The formal analysis of the interactive convergence clock synchronization algorithm was performed using the Enhanced Hierarchical Development Methodology (EHDM) formal specification and verification environment. This application of EHDM provides a demonstration of some of the capabilities of the system

Informing tropical mammal conservation in human-modified landscapes using remote technologies and hierarchical modelling

The aggressive expansion of anthropogenic activities is placing increasing pressure on biodiversity, particularly in tropical regions. Here, conservation efforts are hindered by poor understanding of species ecology and the failure of policy instruments to account for multiple stressors of land-use change. While protected areas are central to conservation strategies, there is a general consensus that the future of tropical biodiversity will be determined by how well modified landscapes are managed. In this thesis I advance our understanding of biodiversity persistence in modified tropical landscapes to inform emerging incentive-based policy mechanisms and supply-chain initiatives. Capitalising on recent advances in remote-sensing and hierarchical occupancy modelling, I provide a spatial appraisal of biodiversity in a modified landscape in Sabah, Malaysian Borneo. Fieldwork was conducted at the Stability of Altered Forest Ecosystems (SAFE) project, a large-scale landscape modification experiment, comprising a degradation gradient of old growth forest, selectively logged forest, remnant forest patches and oil palm plantations. The assessment focused on camera-trapping of tropical mammals, as they are sensitive to anthropogenic stressors, occupy key trophic positions, and prioritised in conservation. In Chapter 2 I link mammal occupancy data to airborne multispectral remote-sensing information to show how the conservation value of modified landscapes is dictated by the intensity of the underlying land-use. Logged forests retained appreciable levels of mammal diversity, and oil palm areas were largely devoid of forest specialists and threatened taxa. Moreover, many mammal species disproportionately occupied forested areas that retained old growth structural characteristics. The most influential structural measures accounted for vertical and horizontal components in environmental space, which cannot currently be derived from conventional satellite data. Using a novel application of ecological threshold analysis, I demonstrate how multispectral data and multi-scale occupancy models can help identify conservation and restoration areas in degraded forests. In Chapter 3 I assess the potential for carbon-orientated policy mechanisms (High Carbon Stock, HCS, Approach and REDD+) to prioritise high carbon areas with corresponding biodiversity value in highly modified landscapes. The areas of highest carbon value prioritised via HCS supported comparable species diversity to old growth forest. However, the strength, nature and extent of the biodiversity co-benefit was dependent on how carbon was characterised, the spatial resolution of carbon data, and the species considered. In Chapter 4 I further scrutinised HCS protocols to evaluate how well they delineated high priority forest patches that safeguard species most vulnerable to land-use change (i.e. IUCN threatened species). The minimum core area required to define a high priority patch (100 ha) supported only 35% of the mammal community. In fact the core area criterion would need to increase to 3,199 ha in order to sustain intact mammal assemblages, and an order of magnitude higher if hunting pressure was considered. These findings underline the importance of integrating secondary disturbance impacts into spatial conservation planning. Provided landscape interventions are directed to where they will have the greatest impact, they can be financially sustaining and garner local support for conservation. To this end I provide recommendations to guide policy implementation in modified tropical landscapes to support holistic conservation strategies