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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Descriptive Analysis of Ground Frost Patterns in Sweden (1991-2007)

Mellberg, Jenny January 2008 (has links)
No description available.
42

Influence of hydrological seasonality on sandbank benthos: algal biomass and shrimp abundance in a large neotropical river

Montoya Ceballos, Jose Vicente 15 May 2009 (has links)
In this study, I examined the influence of hydrological seasonality on spatiotemporal variation of algal biomass and shrimp abundance on sandbanks of the Cinaruco River in southwestern Venezuela. Seasonal variations of abiotic and biotic variables in the Cinaruco were driven by the hydrological regime. During the highwater periods, river sites in the main channel and lagoon sites were similar in water physicochemical variables and algal biomass. In contrast, physicochemical variables and algal biomass differed between river and lagoon sites during the low-water period. The absence of flow in lagoons and consistently low algal biomass on river sandbanks were the most important features of the spatial variability between main-channel and lagoon sandbanks during low-water phases. Benthic algal biomass was highly uniform at small spatial scales and significantly heterogeneous at large spatial scales. In the second major part of this dissertation, I found a relatively species-rich shrimp assemblage with seven species inhabiting the sandbanks of the Cinaruco. I also observed clear patterns of temporal and spatial variation in shrimp abundance on the Cinaruco sandbanks. Abundance of shrimp on the sandbanks presented remarkable diel variation, showing almost exclusive use of this habitat at nights. Seasonally, shrimp were more abundant during rising- and falling-water periods, when rapid changes of environmental conditions occur. Shrimp abundance was high on those sandbanks with absence of troughs and presence of submerged vegetation. These environmental features presumably promote colonization/establishment and survival/persistence of shrimp in the sandbanks. In a patch-dynamic view of communities, a mobility control model seems to apply to shrimp of the sandbanks in the Cinaruco during the period of rapid changes in hydrology and habitat structure. During low-water periods, when habitat structure of sandbanks is relatively constant, low shrimp abundance appears to be heavily controlled by high fish predation. The annual flood regime of the Cinaruco, which drives the concentrations of dissolved materials, affects material interchanges between aquatic and terrestrial systems, and modifies aquatic habitat structural complexity, is responsible for creating strong patterns of seasonal and spatial variation in benthic algal crops and shrimp abundance on the sandbanks of this large floodplain river.
43

Remote Sensing of Whitings in the Bahamas

Lloyd, Ryan Allen 01 January 2012 (has links)
Whitings on both the Great Bahama Bank (GBB) and Little Bahama Bank (LBB) were evaluated using data collected from 2000-2010 by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua satellites. A semi-objective method was developed to classify whiting patches from other look-alike features using the recently developed Floating Algae Index (FAI) algorithm, an empirical cloud masking algorithm, and a gradient analysis from the 250-m resolution MODIS data. A total of 1,500 images with minimal cloud cover was used to calculate long-term and seasonal trends as well as an average daily coverage for both banks. Annual and monthly frequency of occurrences for whitings at every location was also calculated. Based on the results, the distribution of whitings over the GBB was restricted between 25–30'N and 23–45'N and occurred most frequently on the edge of the bank. Whitings were observed throughout the LBB and at much higher frequencies than in the GBB, especially on the east side from November to February. Results from daily whiting coverage indicate whitings cover nearly twice as much area over the LBB compared to the GBB. Whitings show a clear seasonal variation with respect to coverage on both banks. Whiting coverage over the LBB has a clear seasonal variation with peak coverage in spring (April) and fall (November) and minimum coverage during summer. Whiting coverage over the GBB peaks in spring (April), but no second peak or seasonal minimum was observed. Sea surface temperature (SST), photosynthetically available radiation (PAR) and wind were compared to the observed long-term and seasonal trends of whiting coverage. Using multi-variable analyses, the influence of SST and PAR on monthly whiting coverage over the GBB from 2000-2010 was found to be statistically significant, though the correlation between the three values was low. The results indicate that these parameters may not directly influence whiting origin and coverage but rather have an effect through influence mechanism, for example through phytoplankton blooms. It is hypothesized that whitings are directly influenced by cyanobacterial phytoplankton, which are dependent on SST and PAR. Long-term trends in whiting coverage differ between the two banks. In general, whiting coverage appeared to be decreasing from 2000-2010 over the LBB, while the opposite trend was observed over the GBB during the same time period. It is currently unclear what led to these opposite trends due to lack of long-term, in-situ measurements of the water environments in the two banks. However, this is the first study that documents the long-term trends for both banks, from which one may infer that the processes affecting whiting occurrence in the two banks vary greatly and future research is needed to understand the driving forces of whitings in order to improve the current understanding of their contributions in the global carbon cycle.
44

Winters in America: Cities and Environment, 1870-1930

Prins, Megan K. January 2015 (has links)
An environmental and cultural history of cities between 1870 and 1930s, "Winters in America" explores the changing material and cultural relationship that Americans formed with winter in the urban spaces of the country. During this period of immense demographic, social, and technological change most Americans encountered winter nature in the industrial city, and subsequently formed their environmental experiences and knowledge of the season through city life. Using case studies of five cities - Boston, Chicago, St. Paul, Tucson and Phoenix - this study shows how winter labor, leisure, and culture in the Gilded Age city not only informed built environments but was also marshaled by Americans to interpret the appearance of the season, resulting in an emerging urban environmental and seasonal culture. Indeed, the growth of cities in combination with social and technological changes played a significant role in reorienting how many residents experienced and understood winter in their lives. Access to and control over winter narratives were not inclusive, however, and the evolving culture of winter typically favored particular classes of citizens. Winter celebrations, employment aid, work, and winter health resorts, for example, shifted the experiences and social values injected into the season. Ultimately, an examination of winter in the city during this period demonstrates the continued environmental power of season in the lives of urban Americans, while exposing the cultural power many Americans ascribed to the coldest season.
45

ECOLOGY, MORPHOLOGY, AND GERMINATION PHYSIOLOGY OF TREE SEEDS IN A TROPICAL SEMIEVERGREEN FOREST IN THE PANAMA CANAL WATERSHED, WITH SPECIAL REFERENCE TO SEED DORMANCY CLASSES ALONG A PRECIPITATION GRADIENT

Sautu, Adriana Elena 01 January 2004 (has links)
The Panama Canal Watershed (PCW) represents a special opportunity for studies related to seed dormancy in the tropics with both applied and basic research objectives. There is a clear need for seed information for nursery planning in restoration projects that involves use of a large number of local species. Moreover, the strong rainfall gradient along the 60 km of continuous lowland forest in the PCW represents an excellent opportunity to understand dormancy and its role as an adaptive trait that evolved in response to environmental factors. This study presents useful seed information for 100 tree species native to the PCW. For each species, it includes collection system, fruiting time, seed mass, seed moisture content, germination, and longevity in storage at 20??C. For the first time, an attempt is made to classify (to class sensu Baskin andamp; Baskin 2004) the class of dormancy in seeds of the PCW. An analysis of the relationship between class of dormancy and seed mass, moisture content, longevity, germination patterns, and seasonality is presented. The relationship between class of seed dormancy and longevity and geographical distribution of species within the watershed based on the rainfall gradient was investigated.
46

An examination of species diversity and bison processing intensity contextualized within an aboriginal seasonality framework for late precontact sites on the Canadian northeastern plains

Playford, Tomasin 13 January 2015 (has links)
This dissertation considers faunal recoveries from a selection of archaeological sites located in the Canadian Northeastern Plains that date between AD 1000 and 1600. These faunal assemblages derive from three different archaeological cultures that are thought to reflect different subsistence orientations. The analysis quantifies this variability by assessing the taxonomic abundance and intensity of bone processing evident in the recoveries. At issue is determination whether variability in the faunal assemblage reflects differences in subsistence economy deriving from the diverse origins of these societies. This requires control over other potential contributors to variability. This includes ecological comparability of the site localities, consistency of excavation, sampling and analytic methods, and similarities in site function. Particularly important is determination that the selected sites reflect comparable seasons of site occupation. This latter consideration is important since the established archaeological and ethnological literature suggests that both available resources and the economic orientation of resident populations varied significantly with season. To this end, a major research component focused on the development of more refined means of determining the season of site occupation by measuring the degree of osteological development of recovered foetal bison bones. The creation of linear regression equations based on these measurements will allow applied archaeologists to establish season of site occupation without the need for a large, difficult to obtain foetal bison comparative collection. The analysis suggests the variability in the faunal assemblages occurs independently of site cultural affiliation, and might reflect economic activities conditioned by more finely divided seasonal divisions than is apparent with the conventional four-season model deriving from agrarian European societies. Aboriginal language markers, specifically moon-names, were used to identify significant biophysical and bison reproductive events. By placing the six sites within Aboriginal concepts of seasonality, animal food subsistence choices are better understood. These results have implications for the classification scheme archaeologists have used to define subsistence strategies.
47

Interactive Roles of Gonadotropin-Releasing Hormone and RF-Amide Related Peptide 3 in Adenohypophyseal Physiology and Reporduction in the Mare

Thorson, Jennifer Frances 02 October 2013 (has links)
The seasonal termination of ovarian cycles in mares initiated near the time of the autumnal equinox is a significant managerial issue for horse breeders world-wide. Studies presented herein had two over-arching aims. In Aim I, objectives were to develop the principals needed to apply gonadotropin-releasing hormone (GnRH) therapeutics for routinely establishing pregnancies in the winter anovulatory mare. We first tested the hypothesis that continuous administration of native GnRH, beginning in either early February or March, would induce ovulation without reversion to an anovulatory state following treatment withdrawal. Continuous 28-d treatments elevated circulating luteinizing hormone (LH) and stimulated spontaneous ovulation much earlier than controls. However, mares treated only in February ceased ovarian cycles at termination of treatment. In contrast, mares administered GnRH in March continued to exhibit estrous cycles. Thus, we concluded that GnRH treatment must continue through March to ensure continued escape from winter anovulation. We then tested the hypothesis that the Julian day of conception could be accelerated in winter anovulatory mares treated continuously with native GnRH for 56 d beginning on February 1. Indeed, GnRH treatment caused a marked increase in the frequency of pregnancy compared to controls. Data illustrated that continuous administration of native GnRH is a practical and highly efficient option for managing seasonal anovulation. In Aim II, we examined hypothalamic distribution, adenohyphyseal receptor gene expression, and ligand functionality of RFRP3 in the mare during the breeding and non-breeding seasons. Hypothalamic RFRP3 mRNA was detected in the mare; however, neither hypothalamic expression of RFRP3 nor its anterior pituitary receptor differed between reproductive states. We then used equine adenohypophyseal cell culture to test the hypothesis that RFRP3 reduces the responsiveness of the equine gonadotrope to GnRH. Addition of RFRP3 to cell culture failed to counter the effects of GnRH. Finally, the effects of a RFRP3 receptor-signaling antagonist (RF9) were examined in winter anovulatory mares. A robust increase in circulating concentrations of LH relative to controls was observed in response to RF9 treatments, but treatments had no effect on adenohypophyseal responsiveness to GnRH. Data provide indirect evidence that antagonism of the RFRP3 system by RF9 may be at the GnRH neuronal level.
48

Assessment of active commuting behaviour : walking and bicycling in Greater Stockholm

Stigell, Erik January 2011 (has links)
Walking and bicycling to work, active commuting, can contribute to sustainable mobility and provide regular health-enhancing physical activity for individuals. Our knowledge of active commuting behaviours in general and in different mode and gender groups in particular is limited. Moreover, the validity and reproducibility of the methods to measure the key variables of the behaviours are uncertain. The aims of this thesis is to explore gender and mode choice differences in commuting behaviours in terms of distance, duration, velocity and trip frequency, of a group of adult commuters in Greater Stockholm, Sweden, and furthermore to develop a criterion method for distance measurements and to assess the validity of four other distance measurement methods. We used one sample of active commuters recruited by advertisements, n = 1872, and one street-recruited sample, n = 140. Participants received a questionnaire and a map to draw their commuting route on. The main findings of the thesis were, firstly, that the map-based method could function as a criterion method for active commuting distance measurements and, secondly, that four assessed distance measurement methods – straight-line distance, GIS, GPS and self-report – differed significantly from the criterion method. Therefore, we recommend the use of correction factors to compensate for the systematic over- and underestimations. We also found three distinctly different modality groups in both men and women with different behaviours in commuting distance, duration and trip frequency. These groups were commuters who exclusively walk or bicycle the whole way to work, and dual mode commuters who switch between walking and cycling. These mode groups accrued different amounts of activity time for commuting. Through active commuting per se, the median pedestrian and dual mode commuters met or were close to the recommended physical activity level of 150 minutes per week during most months of the year, whereas the single mode cyclists did so only during the summer half of the year.
49

SUPEROVULATION AND EMBRYO COLLECTION IN WOOD BISON (Bison bison athabascae): TOOLS TO PRODUCE DISEASE-FREE EMBRYOS

2015 December 1900 (has links)
Reclamation of Canada’s threatened wood bison (Bison bison athabascae) herd is complicated by cattle diseases. As part of an overall goal to conserve bison genetics, five studies were conducted to develop or adapting present reproductive technologies to produce disease-free in vivo-derived wood bison embryos. In Chapter 4, the efficacy of pLH and hCG for inducing ovulation and whether the effect was related to the size of the dominant follicle at the time of treatment was examined in wood bison during the anovulatory season . Ovulation rate with hCG (94%) was nearly two times greater than with pLH (54%), and bison with a growing follicle of ≥10 mm had a greater ovulatory response than those of 8-9 mm. In Chapter 5, the efficacy of pLH and hCG after superstimulation with single or two doses (48 hours apart) of FSH diluted in 0.5% hyaluronan was determined in wood bison. A greater superovulatory ovarian response was found in cows treated with hCG vs. LH during the anovulatory and ovulatory seasons (6.6 vs. 2.8 and 6.3 vs. 3.8 corpora lutea respectively). In addition, dividing the dose of FSH two resulted in greater superovulatory response in wood bison. However, the number of corpora lutea was still lower than expected as compared to cattle using the same two dose method of superovulation (15 corpora lutea; Tribulo et al., 2012). Therefore, in Chapter 6, the effect of the addition of a low dose of eCG at the end of the superstimulation protocol on ovarian response and embryo quality was examined. Although the number of ova/embryos recovered was higher in this study when compared with previous reports in wood bison, no effect of eCG on the number of corpora lutea and embryo quality was found. In Chapters 5 and 6, the effect of exogenous progesterone on embryo quality in wood bison during the anovulatory season was evaluated. We found that progesterone did not improve the number of freezable embryos in either study. In Chapter 7, the effect of lengthening of FSH treatment protocol on superovulatory response and embryo quality during the ovulatory and anovulatory seasons was examined. There was no effect of lengthening the FSH treatment protocol on ovarian response and embryo quality during the anovulatory season. However, embryo quality and ovulation rate were increased by the lengthened treatment protocol during the ovulatory season. Additionally, more freezable embryos (Grades 1 and 2) were obtained during the ovulatory season (1.8 embryos) vs. the anovulatory season (0.3 embryos). Overall, results confirm that superovulation can be performed in wood bison throughout the year, but a higher number of freezable embryos were obtained during the ovulatory season. The final chapter (Chapter 8) focused in the production of disease-free embryos in wood bison. Following superovulation, in vivo-derived wood bison embryos were exposed in vitro to Brucella abortus biovar 1. After incubation, embryos were submitted to the 10-step washing procedures recommended by the IETS to remove the pathogen. When the washing medium contained antibiotics, 100% Brucella-free embryos were obtained. These findings validate the washing procedures for the production of Brucella-free embryos in wood bison.
50

Diversidade e hábitos alimentares de peixes de riachos afluentes do rio Teles Pires, drenagem do rio Tapajós, Bacia Amazônica

Godoi, Divina Sueide de [UNESP] 11 July 2008 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:30:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-11Bitstream added on 2014-06-13T20:40:30Z : No. of bitstreams: 1 godoi_ds_dr_jabo.pdf: 897423 bytes, checksum: fd8e0025cba418494fc2ff5cab144592 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Com o objetivo de estudar a diversidade dos peixes de dois afluentes do rio Teles Pires, foram realizadas expedições bimestrais entre outubro de 2005 e dezembro de 2006. Para amostragem da ictiofauna dos afluentes, foram cercados 75m de cada trecho com rede de arrasto; a coleta foi feita através de redes de arrasto manuais, puçás e peneiras. O esforço de coleta aplicado a cada variante metodológica foi de 40 minutos. No total foram coletados 3362 exemplares, pertencentes a 5 ordens, 26 famílias, 65 gêneros e 106 espécies. A ordem Characiformes, foi a mais representativa. As famílias mais abundantes numericamente foram Characidae e Cichlidae, em ambos os rios e períodos analisados. Para a jusante do rio Taxidermista e do rio Verde Paraíso ocorreu maior diversidade na seca, decaindo na cheia. A menor diversidade encontrada foi no período da seca à montante do rio Taxidermista. Para o rio Taxidermista, ocorreu uma pequena similaridade em todo o período de coletas, entre os dois trechos, 0,1 na cheia e 0,3 na seca. Já para o rio Verde Paraíso, houve maior similaridade entre os dois trechos, sendo que a maior foi no período da seca (0,80) e a menor na cheia (0,72). Para o Taxidermista os resultados dos cálculos da constância de ocorrência indicaram 2 espécies constantes entre os trechos a montante e a jusante no período da cheia e para o período da seca, 5. No Rio Verde Paraíso no período da cheia, 9 espécies foram consideradas constantes entre a montante e a jusante e 22 no período da seca. / With the objective to study the diversity of fishes in two affluents from River Teles Pires there were realized bimonthly expeditions between October of 2005 and December of 2006. For samples of the ichthyofauna from the affluents, there were encompassed 75 meters from each river with dragging net; gathering was done with puca and sieves. The applied effort of gathering with each methodological variant was of 40 minutes. In total, there were collected 3362 samples, from 5 orders, 26 families, 65 genders and 106 species. The order Characiformes was the most representative. The most present in numbers were the families Characidae and Cichlidae, in both rivers and periods analyzed. For the downstream of the river Taxidermista and of the river Verde Paraíso occurred more diversity in drought, decreasing in flood. The minor diversity found was in the drought period in transom of the river Taxidermista. For river Taxidermista, occurred a small similarity in all collecting period, among the two stretch, 0,1 in flood and 0,3 in drought. For the river Verde Paraíso, there was a greater similarity among the two stretches, as for the greater in the drought period (0,80) and the smallest in flood (0,72). For the Taxidermista the results of the calculations of the constant occurrence pointed two constant species between the stretches the transom and the downstream in seasons of flood and for the drought, 5. In the river Verde Paraíso in the flood season, 9 species were considered constant between the transom and downstream and 22 in the season of drought.

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