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The removal of indigenous forest and associated fragmentation of habitats has probably had significant impacts on the diversity of stream communities in New Zealand. In this study I investigated the effects of forest fragmentation on stream invertebrate communities on Banks Peninsula. Six catchments were investigated, three with continuous indigenous forest in the riparian zone and three with fragmented indigenous riparian forest. An extensive benthic survey was conducted at three sites in each river catchment, one downstream on the mainstem of the river and two sites in different headwater tributaries. Adult sampling, consisting of malaise and sticky trapping, was also conducted at a sub-set of sites. Taxonomic richness of both the benthic and adult communities was significantly higher in continuous forest than in fragmented forest, and the composition of benthic communities also differed between continuous and forest fragments. Furthermore, benthic invertebrate densities were higher in fragments than continuous forest sites. The fragments in the headwaters were more likely to support forest specialist taxa (e.g. the stonefly Zelandobius wardi, and the caddisfly Costachorema peninsulae), than the downstream fragments. My results indicate that forest fragmentation has resulted in marked changes in benthic communities on Banks Peninsula, and that location of the fragment within the catchment also is important in influencing the diversity and composition of benthic communities. The maintenance of indigenous forest in the headwaters of streams may be essential for the persistence of endemic and forest specialist taxa on Banks Peninsula.

Thesis (M.C.S.) - Carleton University, 1990. / Also available in electronic format on the Internet.

Microplastics are small piece of plastic debris < 5 mm in diameter, which arise and enter the environment either as a consequence of the direct release of small pieces of plastic debris or as a consequence of the fragmentation of larger items. They are widely distributed in the marine environment, on shorelines, at the sea surface, on the seabed. They are also ingested by a variety of marine organisms, and there is some evidence that this may cause adverse effects. This thesis investigates the potential sources, distribution and fate of this contaminant. Deterioration of plastics in a variety of environments was examined as a potential source of microplastics. Plastics were exposed in light and shade, in air, fresh water and sea water. Their deterioration was monitored over six hundred days. The fastest rate of deterioration, by far, was observed in air, and this was further accelerated by natural sunlight. Degradation in water was much slower and it was therefore concluded that plastic debris only fragments slowly into microplastics while they are in the water, and much faster when they are washed ashore and/or remain exposed to air, for example on a beach. A method to assess the contamination of beaches by microplastics' likely predecessors - small items of plastic debris - was therefore developed. High spatial variability, which can impede comparison between surveys undertaken by random sampling was overcome by assessing deliberately selected debris accumulations. An attempt to utilise citizen science using this rapid survey approach returned too much variability between volunteers to obtain consistent results. Nevertheless, the survey method was successfully used to identify narrow opening towards the sea, small tidal range and several weeks of high on-beach waves as predictors for high contamination. Evidence of harmful effects of microplastics on animals is primarily from laboratory studies and could be substantiated by exposure experiments \emph{in-situ}. Cockles were exposed to fluorescent plastic particles in an intertidal mudflat. After two weeks, particles were still present in the sediment. However, the test material could not be identified in the cockles with enough certainty to validate the method. The thesis concludes that fragmentation of larger items of debris on land is an important potential source of microplastics. Therefore, preventing plastics that are prone to deteriorate from entering the environment is likely the most effective way to prevent the generation of microplastics. Measuring the success of such preventive measures in the field returns highly variable results, as small plastic debris are elusive. Measuring effects in the environment demands large amounts of data, and highly specific methods are required to detect microplastics in animals. The shift of environmental plastic contamination towards small particles demands that plastic debris research adjusts to the elusiveness of these particles. Large volumes of variable data on plastics density and precise biological essays will be required.

The character of Virginia's nonindustrial private forests is changing primarily for two reasons. First, many large, continuous forested tracts are being sub-divided, into with the resulting smaller tracts purchased for amenity values and recreation instead of as a timber investment (Hodge 1993). Second, the demographics of non-industrial private forest (NIPF) landowners are shifting away from an agricultural, rural focus to an urban oriented lifestyle and absentee ownership. These changes may mean less timber available for purchase by the forest industry. Timber that is sold will be on smaller parcels that is bound to have an impact on the procurement activities of forest industries. However, little research has been performed on the impacts of site and landowner characteristic on stumpage prices. The objective of this research project is to identify how the stumpage price of timber is altered by the characteristics associated with the changing forest: decreasing tract size, decreasing harvested volumes, landowner residence, and landowner harvesting preferences. In addition to the price of timber, the competitiveness of timber sales is analyzed to determine what impact the fragmented forest could have on the competitiveness of timber markets. To perform the study, site and landowner information was collected for 138 recent NIPF timber sales that occurred within central Virginia. This region is identified as a critical area for the study of forestry activities because of the growing urban and suburban residential populations and the large amount of forest industry activities taking place there. Results show that access to the site is the most important characteristic determining the selling price of timber. Sites that are easy for logging crews and vehicles to approach dramatically increase the price paid per ton. Tract size is less important in determining bid prices for timber either once the total volume harvested passes a minimum of 500 tons, or there is mature hardwood sawtimber on the site and the acreage is greater than 50 acres. Landowners preference for select cut harvests results in a lower price per ton being paid by the purchaser due to the increased logging costs associated with this type of harvesting. / Master of Science

Des matériaux de type pérovskite ABO3 (A : La ; B : Mn, Fe, Co) ont été synthétisés par une méthode originale de broyage réactif, qui possède l'avantage d'être très simple à mettre en œuvre, peu coûteuse et n'implique que peu ou pas de solvant. La synthèse a été réalisée en trois étapes successives : (i) une calcination à haute température permettant l'obtention de la structure pérovskite à partir des oxydes simples respectifs ; (ii) un broyage haute énergie permettant une réduction de la taille de domaine cristallin (Dc), de l'ordre micrométrique à nanométrique, par fractionnement ; (iii) un broyage à basse énergie permettant l'augmentation de surface spécifique par désagglomération des particules. Les matériaux obtenus après ces trois étapes ont montré des tailles de cristallites réduites (Dc ~10-20 nm), une surface spécifique raisonnable (respectivement 10, 19 et 20 m2·g−1 pour LaMnO3,15, LaFeO3 et LaCoO3) ainsi qu'une réductibilité du site B accrue. L'amélioration des propriétés texturales et redox des matériaux conduit à une amélioration significative des performances catalytiques vis-à-vis de la réaction d'oxydation totale du toluène. La composition LaCoO3 a présenté les meilleurs résultats et cette formulation a ensuite été utilisée comme base pour évaluer l'impact de la substitution du site A par le strontium ou le cérium : La1-xSrxCoO3 (x = 0,05-0,40) et La1-xCexCoO3 (x = 0,01-0,20). Les matériaux substitués ont montré des propriétés texturales similaires et des propriétés catalytiques supérieures à la référence non substituée (LaCoO3), avec un optimum observé pour La0.8Sr0.2CoO3 et La0.99Ce0.01CoO3. Pour La1-xCexCoO3, seule une faible quantité de cérium peut être insérée dans la structure, une phase secondaire CeO2 se formant au-delà et empoisonnant le catalyseur. Dans le cas de La1-xSrxCoO3, l'incorporation du strontium est complète, induisant : (i) un désordre structural localisé permettant une meilleure mobilité de l'oxygène, ainsi que (ii) une modification importante de la réductibilité du cobalt, allant jusqu'à sa réduction totale à basse température pour les plus fortes teneurs en strontium / Perovskite ABO3 materials (A: La; B: Mn, Fe, Co) have been synthesized by an original reactive grinding method, which has the advantage of being very simple to use, inexpensive and involves little or no solvent. The synthesis was carried out in three successive steps: (i) high temperature calcination to obtain the perovskite structure from the respective single oxides; (ii) high energy grinding to reduce the size of the crystalline domain (Dc) from micrometric to nanometric level by fractionation; (iii) low energy grinding to increase the specific surface area by deagglomeration of the particles. The materials obtained after these three steps showed reduced crystallite sizes (Dc ~10-20 nm), a reasonable specific surface area (respectively 10, 19 and 20 m2·g-1 for LaMnO3,15, LaFeO3 and LaCoO3) and increased reducibility of the B site. The improvement of the textural and redox properties of materials leads to a significant improvement in catalytic performance with respect to the total oxidation reaction of toluene. The LaCoO3 composition presented the best results and this formulation was then used as the starting point for evaluating the impact of the substitution of strontium or cerium at site A: La1-xSrxCoO3 (x = 0.05-0.40) and La1-xCexCoO3 (x = 0.01-0.20). The substituted materials showed similar textural properties and catalytic properties superior to the non-substituted reference (LaCoO3), with an optimum observed for La0.8Sr0.2CoO3 and La0.99Ce0.01CoO3. For La1-xCexCoO3, only a small amount of cerium can be inserted into the structure, with a secondary CeO2 phase forming beyond and poisoning the catalyst. In the case of La1-xSrxCoO3, the incorporation of strontium is complete, inducing: (i) a localized structural disorder allowing better oxygen mobility, as well as (ii) a significant modification of cobalt reducibility, up to its total reduction at low temperature for the highest strontium contents.Accéder en ligneIl est disponible au sein de la bibliothèque de l'établissement de soutenance.

L'orsqu'une émulsion est cisallée, ses gouttes se déforment et si l'intensité du cisaillement appliqué est suffisante, elles se fragmentent en plusieurs gouttelettes. Le travail expérimental présenté dans ce mémoire est focalisé sur la fragmentation des émulsions dans un écoulement de cisaillement simple. Les influences des paramètres physico-chimiques suivants sont déterminées et analysées : temps de cisaillement, nombre capillaire, histoire de l'écoulement, polydispersité de l'émulsion, gradient de cisaillement, contrainte visqueuse, rapport des viscosités des phases interne et externe et équation rhéologique d'état de l'émulsion. Ces différentes études mettent en évidence que la fragmentation d'une émulsion polydisperse conduit quasi instantanément à une émulsion calibrée lorsque le cisaillement imposé est intense et la taille initiale des gouttes très grande devant la taille finale. Le scénario de fragmentation mis en jeu est le suivant : les gouttes de l'émulsion initiale se déforment de façon à atteindre des filaments de même rayon.....

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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / One approach to improving spectrum usage efficiency is to manage the scheduling of frequencies more effectively. The use of metrics to analyze frequency scheduling could aid frequency managers in a variety of ways. However, the basic question of what is a good metric for representing and analyzing spectral usage remains unanswered. Some metrics capture spectral occupancy. This paper introduces metrics that change the focus from occupancy to availability. Just because spectrum is not in use does not mean it is available for use. A significant factor in creating unused but unusable spectrum is fragmentation. A mission profile for spectrum usage can be considered a rectangle in a standard time versus frequency grid. Even intelligent placement of these rectangles (i.e., the scheduling of a missions spectrum usage) can not always utilize all portions of the spectrum. The average typical mission availability (ATMA) metric provides a way of numerically answering the question: Could we have scheduled another typical mission? This is a much more practical question than: Did we occupy the entire spectrum? If another mission couldn’t have been scheduled, then the entire spectrum was effectively used, even if the entire spectrum wasn’t occupied.