• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 90
  • 55
  • 22
  • 22
  • 18
  • 18
  • 18
  • 18
  • 18
  • 17
  • 5
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 269
  • 269
  • 47
  • 46
  • 43
  • 39
  • 38
  • 37
  • 32
  • 27
  • 26
  • 25
  • 24
  • 20
  • 18
  • 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.
161

Avaliação de autocorrelações e complexidade de séries temporais climáticas no Brasil

SILVA, José Rodrigo Santos 19 September 2014 (has links)
Submitted by (ana.araujo@ufrpe.br) on 2016-07-07T11:52:38Z No. of bitstreams: 1 Jose Rodrigo Santos Silva.pdf: 13129069 bytes, checksum: b427ff42ec7918c3d0cf7f63798ed648 (MD5) / Made available in DSpace on 2016-07-07T11:52:38Z (GMT). No. of bitstreams: 1 Jose Rodrigo Santos Silva.pdf: 13129069 bytes, checksum: b427ff42ec7918c3d0cf7f63798ed648 (MD5) Previous issue date: 2014-09-19 / The objective of this study was to uncloak the dynamic of climate of Brazil, seeking to measure the regularity and the long range autocorrelation of daily climate series of temperature of air (average, maximum, minimum, and temperature range), relative humidity of air average and wind speed average. The data were obtained by Instituto Nacional de Meteorologia (INMET), at 264 meteorological stations, in the period from January 1990 to December 2012. We use the Detrended Fluctuation Analysis to realize the estimation of the Hurst exponent, the Multiscale Sample Entropy to estimating the entropy of series and the Kriging to interpolate the estimates made. We observed that higher latitudes tend to attenuate the mean of temperatures of air maximum, minimum and average, but increase the variability of the same. This inversion of the magnitudes of the mean and standard deviation is also observed in the relative humidity of air. The means of the estimated Hurst exponents estimated for Brazil were 0.81, 0.79, 0.81, 0.77, 0.83 and 0.64, and the estimated Sample Entropy, 1.39, 1.78, 1.46, 1.41, 1.56 and 1.66, respectively for average, maximum and minimum temperatures of air, temperature range, relative humidity of air average and wind speed average. The values of the estimated Hurst exponents showed a positive correlation with latitude in the temperature variables studied. Such a correlation was not observed in other variables. This a correlation was not observed in other variables. The regularities of climate series in Brazil were medians. Spatially, the greatest changes occurred in estimates of entropies in the scale 1 to 2 of , in the Multiscale Sample Entropy. As from ≥2 the changes observed were more subtle. We observe the influence of the Equatorial Continental air mass in entropy of temperatures daily average and maximum of air. The climatic factor of altitude influenced with more frequently in the observed results, mainly on temperature variables. In some cases, the continentality and the air masses were also identified as important factors in characterizing the spatial distribution of estimates made. / O objetivo deste estudo foi desvendar a dinâmica climática do Brasil, buscando mensurar a regularidade e a autocorrelação de longo alcance em séries climáticas diárias de temperatura do ar (média, máxima, mínima, e amplitude térmica), umidade relativa média do ar e velocidade média diária do vento. Os dados foram obtidos pelo Instituto Nacional de Meteorologia, em 264 estações meteorológicas, no período de janeiro de 1990 a dezembro de 2012. Utilizamos o Detrended Fluctuation Analysis para realizar a estimativa do expoente de Hurst, o Multiscale Sample Entropy para as estimativas da entropia das séries e o Kriging para a interpolação das estimativas realizadas. Observamos que maiores latitudes tendem a atenuar as médias das temperaturas máxima, mínima e média do ar, porém aumentam a variabilidade das mesmas. Esta inversão entre as magnitudes da média e do desvio padrão também é observado na umidade relativa média do ar. As médias dos expoentes de Hurst estimados para todo o Brasil foram 0,81; 0,79; 0,81; 0,77; 0,83 e 0,64; e do Sample Entropy estimado, 1,39; 1,78; 1,46; 1,41; 1,56 e 1,66, respectivamente para séries diárias de temperatura média, máxima e mínima do ar, amplitude térmica do ar, umidade relativa média do ar e velocidade média do vento. Os valores do expoentes de Hurst estimados apresentaram uma correlação positiva com a latitude nas variáveis de temperatura do ar estudadas. Tal correlação não foi observada nas demais variáveis. As regularidades das séries climáticas no Brasil foram medianas. Espacialmente, as maiores alterações nas estimativas das entropias ocorreram na escala 1 para a 2 de , no Multiscale Sample Entropy. A partir de ≥2 as mudanças observadas foram mais sutis. Observamos influência da massa de ar Equatorial Continental na entropia das temperaturas do ar média e máxima diárias. O fator climático da altitude atuou com maior frequência sob os resultados observados, principalmente nas variáveis de temperatura. Em alguns casos, a continentalidade e as massas de ar também foram apontados como fatores importantes na caracterização da distribuição espacial das estimativas realizadas.
162

Biological and environmental drivers of mangrove propagule dispersal: a field and modeling approach

Van Der Stocken, Tom 26 May 2015 (has links)
There are large gaps in the coverage of critical ecological processes related to the movement of individuals or genes (i.e. dispersal), which is critical for determining the spread and persistence of populations across space. In this dissertation we investigate understudied but important aspects of the dispersal process in mangroves, with as the main objective the reduction of parameter and model uncertainty. Models rarely incorporate realism and complexity at the level of emigration, transfer and immigration phases, hampering reliable predictions of dispersal patterns and long-term population dynamics under different climate change scenarios. <p><p>Mangrove ecosystems function at the edge of land and sea, often covering large intertidal areas along (sub)tropical coastal regions worldwide. Mangroves can live in these highly dynamic and demanding environmental conditions via a series of remarkable adaptations. They produce buoyant seeds and fruits (propagules) that disperse at the ocean surface (i.e. hydrochory - see cover image). <p><p>Despite their ecological and economical value, about 40 % of original mangroves have been lost worldwide during the last 50 years due to excessive exploitation and development. Deforestation, degradation and conversion to other land uses like intensive shrimp farming and agriculture have reduced and fragmented these ecosystems at an alarming rate. Climate change, probably most pronouncedly via changes in sea level, poses another important threat. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
163

Termografia Digital por Infravermelho do Escroto e Qualidade do Sêmen em Touros Nelore (Bos taurus indicus) / Scrotum Digital Infrared Thermography and Semen Quality in Nelore bulls (Bos taurus indicus)

Ruediger, Felipe Rydygier de 20 June 2014 (has links)
Made available in DSpace on 2016-01-26T18:55:41Z (GMT). No. of bitstreams: 1 Felipe Rydygier de Ruediger.pdf: 337503 bytes, checksum: 788a40d59ee5b6ff8427348218069a3d (MD5) Previous issue date: 2014-06-20 / Reproductive efficiency is one of factors for improving livestock production indices cutting factors. The contribution of the bull to the reproductive efficiency of the herd is of great importance. Bovine testes should be kept below the core body temperature for the production of morphologically viable, normal sperm. The scrotal and testicular thermoregulation is a system for maintaining the physiological temperature of the testicles. Infrared thermography is a noninvasive technique that is used to measure the surface temperature of the scrotum bulls. The objective of this work was to study the relationship of scrotal temperature on semen quality by use of infrared thermography in Nellore bulls bred extensively. 6 Nellore by performing scrotal thermography and semen collection every 10 days were used, totaling 36 ejaculates. Climatic data were collected through globe thermometer. The thermograms of the scrotum were obtained by digital infrared thermography and analyzed by software to the scrotal surface temperatures, the right and left sides, neck of the scrotum, dorsal thirds, middle, and ventral of the testes and cauda epididymis. We conducted ejaculates through electroejaculation for analysis of quantitative and qualitative characteristics. For the data, we used analysis of variance and subsequently applied the Tukey test at 5%, and Pearson correlation. There was a positive correlation between sperm motility and the temperatures of the scrotum; between concentration and temperature of the scrotum; between climatic factors and rectal temperature. There was a negative correlation between temperature and sperm concentration (p <0.05). There was no correlation between the climatic data, and temperatures between the scrotum and rectal temperature and temperature of the scrotum. It was concluded that the surface temperatures of the scrotum and climatic factors, temperature and humidity, influence the quality of semen. Thermography is recommended as a complementary test in the evaluation of reproductive bulls. / A eficiência reprodutiva é um dos fatores determinantes para melhorar os índices zootécnicos da pecuária de corte. A contribuição do touro para a eficiência reprodutiva do rebanho é de grande importância. Os testículos bovinos devem ser mantidos abaixo da temperatura corporal central, para a produção de espermatozoides morfologicamente viáveis, normais. A termorregulação escrotal e testicular é um sistema de manutenção da temperatura fisiológica dos testículos. A termografia infravermelha é uma técnica não invasiva que é utilizada para medir a temperatura da superfície escrotal em touros. O objetivo deste trabalho, foi de estudar a relação da temperatura do escroto sobre a qualidade seminal pelo uso da termografia por infravermelho em touros Nelore criados extensivamente. Foram utilizados 6 touros Nelore realizando-se termografia escrotal e colheita de sêmen a cada 10 dias, totalizando 36 ejaculados. Os dados climáticos foram coletados por meio de globo termômetro. Os termogramas do escroto foram obtidos por meio de termografia digital de infravermelho e analisados por meio de software para as temperaturas da superfície escrotal, dos lados direito e esquerdo, colo do escroto, terços dorsal, médio, e ventral dos testículos e cauda do epidídimo. Efetuou-se colheitas de sêmen, por meio de eletroejaculação para analise das características quantitativas e qualitativas. Para os dados, utilizou-se análise de variância e posteriormente aplicou-se o teste de Tukey a 5%, e correlação linear de Pearson. Houve correlação positiva entre motilidade espermática e as temperaturas do escroto; entre concentração, e as temperaturas do escroto; entre os fatores climáticos e temperatura retal. Houve correlação negativa entre temperatura ambiente e concentração espermática (p<0,05). Não houve correlação entre os dados climáticos, e as temperaturas do escroto e entre temperatura retal e as temperaturas do escroto. Concluiu-se que as temperaturas da superfície do escroto e os fatores climáticos, temperatura e umidade do ar, influenciaram na qualidade do sêmen. A termografia é recomendada como exame complementar na avaliação reprodutiva de touros.
164

Termografia Digital por Infravermelho do Escroto e Qualidade do Sêmen em Touros Nelore (Bos taurus indicus) / Scrotum Digital Infrared Thermography and Semen Quality in Nelore bulls (Bos taurus indicus)

Ruediger, Felipe Rydygier de 20 June 2014 (has links)
Made available in DSpace on 2016-07-18T17:53:13Z (GMT). No. of bitstreams: 1 Felipe Rydygier de Ruediger.pdf: 337503 bytes, checksum: 788a40d59ee5b6ff8427348218069a3d (MD5) Previous issue date: 2014-06-20 / Reproductive efficiency is one of factors for improving livestock production indices cutting factors. The contribution of the bull to the reproductive efficiency of the herd is of great importance. Bovine testes should be kept below the core body temperature for the production of morphologically viable, normal sperm. The scrotal and testicular thermoregulation is a system for maintaining the physiological temperature of the testicles. Infrared thermography is a noninvasive technique that is used to measure the surface temperature of the scrotum bulls. The objective of this work was to study the relationship of scrotal temperature on semen quality by use of infrared thermography in Nellore bulls bred extensively. 6 Nellore by performing scrotal thermography and semen collection every 10 days were used, totaling 36 ejaculates. Climatic data were collected through globe thermometer. The thermograms of the scrotum were obtained by digital infrared thermography and analyzed by software to the scrotal surface temperatures, the right and left sides, neck of the scrotum, dorsal thirds, middle, and ventral of the testes and cauda epididymis. We conducted ejaculates through electroejaculation for analysis of quantitative and qualitative characteristics. For the data, we used analysis of variance and subsequently applied the Tukey test at 5%, and Pearson correlation. There was a positive correlation between sperm motility and the temperatures of the scrotum; between concentration and temperature of the scrotum; between climatic factors and rectal temperature. There was a negative correlation between temperature and sperm concentration (p <0.05). There was no correlation between the climatic data, and temperatures between the scrotum and rectal temperature and temperature of the scrotum. It was concluded that the surface temperatures of the scrotum and climatic factors, temperature and humidity, influence the quality of semen. Thermography is recommended as a complementary test in the evaluation of reproductive bulls. / A eficiência reprodutiva é um dos fatores determinantes para melhorar os índices zootécnicos da pecuária de corte. A contribuição do touro para a eficiência reprodutiva do rebanho é de grande importância. Os testículos bovinos devem ser mantidos abaixo da temperatura corporal central, para a produção de espermatozoides morfologicamente viáveis, normais. A termorregulação escrotal e testicular é um sistema de manutenção da temperatura fisiológica dos testículos. A termografia infravermelha é uma técnica não invasiva que é utilizada para medir a temperatura da superfície escrotal em touros. O objetivo deste trabalho, foi de estudar a relação da temperatura do escroto sobre a qualidade seminal pelo uso da termografia por infravermelho em touros Nelore criados extensivamente. Foram utilizados 6 touros Nelore realizando-se termografia escrotal e colheita de sêmen a cada 10 dias, totalizando 36 ejaculados. Os dados climáticos foram coletados por meio de globo termômetro. Os termogramas do escroto foram obtidos por meio de termografia digital de infravermelho e analisados por meio de software para as temperaturas da superfície escrotal, dos lados direito e esquerdo, colo do escroto, terços dorsal, médio, e ventral dos testículos e cauda do epidídimo. Efetuou-se colheitas de sêmen, por meio de eletroejaculação para analise das características quantitativas e qualitativas. Para os dados, utilizou-se análise de variância e posteriormente aplicou-se o teste de Tukey a 5%, e correlação linear de Pearson. Houve correlação positiva entre motilidade espermática e as temperaturas do escroto; entre concentração, e as temperaturas do escroto; entre os fatores climáticos e temperatura retal. Houve correlação negativa entre temperatura ambiente e concentração espermática (p<0,05). Não houve correlação entre os dados climáticos, e as temperaturas do escroto e entre temperatura retal e as temperaturas do escroto. Concluiu-se que as temperaturas da superfície do escroto e os fatores climáticos, temperatura e umidade do ar, influenciaram na qualidade do sêmen. A termografia é recomendada como exame complementar na avaliação reprodutiva de touros.
165

Factors Affecting Grapevine Establishment in Northern Production Regions

Stenger, John Edward January 2011 (has links)
Two experiments were conducted to detect differences in growth and cold hardiness during establishment of northern grown wine grapevines. One experiment tested the use of four grow tube treatments and two pruning levels on vine establishment in the upper Midwest. The variables included leaf area, stem height, root growth, phenology, and hardiness. Overall, few significant differences occurred among treatments where grow tubes were utilized. In the second season, vines without grow tubes had superior measurements in nearly all leaf area categories. For this reason, it is recommended that growers refrain from grow tube use during establishment in northern growing regions. Vines pruned to three buds after transplanting varied little from those without pruning. For this reason, it is recommended that growers utilize the most efficient early pruning strategy for their particular situation. Another experiment was conducted to determine the effectiveness of different weed control measures. This experiment compared three kinds of mulches and an herbicide treatment on the growth and establishment of four wine grape varieties. Annual weed control, plant growth, phenology, soil water content and temperature, and vine hardiness were measured. Overall, vines receiving mulch had more consistent annual weed control and reduced early season growth when compared to chemically treated vines. For this reason, mulch is recommended in the vineyard for annual weed control during establishment in situations where vigor is not unacceptably low.
166

Modelling the dynamics and surface expressions of subglacial water flow

Stubblefield, Aaron Grey January 2022 (has links)
Ice sheets and mountain glaciers are critically important components of Earth'sclimate system due to societal and ecological risks associated with sea-level change, ocean freshening, ice-albedo feedback, glacial outburst floods, and freshwater availability. As Earth warms, increasing volumes of surface meltwater will access subglacial environments, potentially lubricating the base of the ice sheets and causing enhanced ice discharge into the ocean. Since subglacial water is effectively hidden beneath the ice, the primary ways to study subglacial hydrological systems are through mathematical modelling and interpreting indirect observations. Glaciers often host subglacial or ice-dammed lakes that respond to changes in subglacial water flow, thereby providing indirect information about the evolution of subglacial hydrological systems. While monitoring subaerial ice-dammed lakes is straightforward, the evolution of subglacial lakes must be inferred from the displacement of the overlying ice surface, posing additional challenges in modelling and interpretation. This dissertation addresses these challenges by developing and analyzing a series of mathematical models that focus on relating subglacial hydrology with observable quantities such as lake level or ice-surface elevation. The dissertation is divided into five chapters. Chapter 1 demonstrates how ageneralization of Nye's (1976) canonical model for subglacial water flow admits a wide class of solitary-wave solutions---localized regions of excess fluid that travel downstream with constant speed and permanent form---when melting at the ice-water interface is negligible. Solitary wave solutions are proven to exist for a wide range of material parameter values that are shown to influence the wave speed and wave profile. Melting at the ice-water interface is shown to cause growth and acceleration of the waves. To relate dynamics like these to observable quantities, Chapter 2 focuses on modelling water-volume oscillations in ice-dammed lakes during outburst flood cycles while accounting for the potential influence of neighboring lakes. Hydraulic connection between neighboring lakes is shown to produce a wide variety of new lake-level oscillations that depend primarily on the relative sizes and proximity of the lakes. In particular, the model produces lake-level time series that mirror ice-elevation changes above a well-known system of Antarctic subglacial lakes beneath the Whillans and Mercer ice streams even though the modelled ice-dammed lakes are not buried beneath the ice. The stability of lake systems with respect to variations in meltwater input is characterized by a transition from oscillatory to steady drainage at high water supply. To create a framework for extending these models of ice-dammed lakes to thesubglacial setting, variational methods for simulating the dynamics of subglacial lakes and subglacial shorelines are derived in Chapter 3. By realizing a direct analogy with the classical Signorini problem from elasticity theory, this chapter also furnishes a new, rigorous computational method for simulating the migration of oceanic subglacial shorelines, which are strongly tied to ice-sheet stability in response to climatic forcings. In Chapter 4, this newly developed model is used to highlight the challenge of accurately interpreting ice-surface elevation changes above subglacial lakes without relying on ice-flow models. The surface expression of subglacial lake activity is shown to depend strongly on the effects of viscous ice flow and basal drag, causing altimetry-derived estimates of subglacial lake size, water-volume change, and apparent highstand or lowstand timing to deviate considerably from their true values under many realistic conditions. To address this challenge, Chapter 5 introduces inverse methods for inferring time-varying subglacial lake activity or basal drag perturbations from altimetry data while accounting for the effects of viscous ice flow. Incorporating horizontal surface velocity data as additional constraints in the inversion is shown to facilitate reconstruction of multiple parameter fields or refinement of altimetry-based estimates. In sum, this dissertation constitutes several novel approaches to understanding ice-water interaction beneath glaciers while laying the foundation for future work seeking to elucidate the role of subglacial processes in the changing climate.
167

Air-quality and Climatic Consequences of Bioenergy Crop Cultivation

Porter, William Christian 07 June 2013 (has links)
Bioenergy is expected to play an increasingly significant role in the global energy budget. In addition to the use of liquid energy forms such as ethanol and biodiesel, electricity generation using processed energy crops as a partial or full coal alternative is expected to increase, requiring large-scale conversions of land for the cultivation of bioenergy feedstocks such as cane, grasses, or short rotation coppice. With land-use change identified as a major contributor to changes in the emission of biogenic volatile organic compounds (BVOCs), many of which are known contributors to the pollutants ozone (O3) and fine particulate matter (PM2.5), careful review of crop emission profiles and local atmospheric chemistry will be necessary to mitigate any unintended air-quality consequences. In this work, the atmospheric consequences of bioenergy crop replacement are examined using both the high-resolution regional chemical transport model WRF/Chem (Weather Research and Forecasting with Chemistry) and the global climate model CESM (Community Earth System Model). Regional sensitivities to several representative crop types are analyzed, and the impacts of each crop on air quality and climate are compared. Overall, the high emitting crops (eucalyptus and giant reed) were found to produce climate and human health costs totaling up to 40% of the value of CO2 emissions prevented, while the related costs of the lowest-emitting crop (switchgrass) were negligible.
168

Atmospheric Corrosion of Silver

Rubino, David John 13 July 2022 (has links)
No description available.
169

Environmental control of vegetable storage environments

Markarian, Naro R. January 2001 (has links)
No description available.
170

Population dynamics of overwintering life stages of the alfalfa weevil, Hypera postica (Gyllenhal)

Hilburn, Daniel J. 07 June 2006 (has links)
Virginia is a natural laboratory for studying overwintering habits of the alfalfa weevi1. At higher elevations, winters are relatively harsh and weevil pressure on the alfalfa crop is usually light. Much heavier pressure is the rule at lower elevations where winters are milder. The goal of this study was to examine the effects of fall and winter temperatures, parasites, and fall regrowth management on population dynamics of overwintering stages of this insect. Sixteen commercial alfalfa fields in Montgomery Co. (elevation 610 m) and Bedford Co. (elevation 300 m) were used in the study. Approximately half the fields each year were either harvested or grazed to remove fall regrowth. In the other fields, fall regrowth was left standing through the winter. Six different pitfall trap designs were compared for collection efficiency, installation and servicing effort, and cost. Barrier traps outperformed the other trap designs and were inexpensive and easy to install and service. Sweepnet samples were used to monitor weevil adults during their fall migration. A newly designed sampling device which removes all plant material, litter, and approximately 2 cm of soil from a 1/20 m² area, was used to measure absolute densities during fall and winter. Based on these absolute density samples fewer adults overwintered within fields in which fall regrowth was removed. Dissections revealed the presence of three parasites: Hyalomyodes trianqulifer (Loew), Microctonus aetheopoides Loan, and M. colesi Drea. Total parasitization rates were low. The highest measured rate was 16.1% in Bedford Co. in 1984-85. Female reproductive development also was determined through dissection. Females reach sexual maturity shortly after returning to alfalfa fields in the fall. Most contain full-size eggs in their oviducts from late fall through the winter. Egg densities as measured by laboratory incubation of field collected plant material indicated no differences related to elevation in early February, but significantly more viable eggs were present by late March at the low elevation site. In 1984, Bedford Co. samples indicated significantly more eggs in fields receiving no fall regrowth management. A simulation model called OAWSIM (Overwintering Alfalfa Weevil Simulation) was developed to examine the influence of factors which affect overwintering life stages. Model predictions indicate fall and winter temperatures, and fall regrowth management are major influences on the population dynamics of this insect. / Ph. D.

Page generated in 0.0629 seconds