• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1160
  • 291
  • 244
  • 221
  • 109
  • 103
  • 30
  • 28
  • 28
  • 28
  • 28
  • 28
  • 28
  • 24
  • 22
  • Tagged with
  • 2907
  • 337
  • 314
  • 279
  • 246
  • 183
  • 159
  • 151
  • 151
  • 149
  • 142
  • 140
  • 127
  • 126
  • 121
  • 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.
401

Optimization of high-level waste loading in a borosilicate glass matrix by using chemical durability modeling approach

Mohammad, Javeed. January 2002 (has links)
Thesis (M.S.)--Mississippi State University. Department of Chemical Engineering. / Title from title screen. Includes bibliographical references.
402

An estimation of the ability to forecast boundary layer mixing height and wind parameters through forecast verification over Fort Ord /

Gahard, Claude F. January 2003 (has links) (PDF)
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Wendell A. Nuss, David S. Brown. Includes bibliographical references (p. 65-66). Also available online.
403

Development of an integrated building load-ground source heat pump model as a test bed to assess short- and long-term heat pump and ground loop performance

Gaspredes, Jonathan Louis 08 February 2012 (has links)
Ground source heat pumps (GSHP) have the ability to significantly reduce the energy required to heat and cool buildings. Historically, deployment of GSHP's in the cooling-dominated Texas and Southwest region has been significantly less than in other regions of the United States. The long term technical and economic viability of GSHPs in arid regions such as Texas has been questioned due to failures of ground loop heat pump systems by early adopters. A proposed solution is to include a supplemental heat rejection (SHR) device to help offset the unbalanced ground loads. An integrated building load-ground source heat pump model is developed in this thesis and is designed to be a test bed for potential SHR devices. The model consists of discrete component models that can be mixed and matched to represent various types of buildings and ground source heat pumps. One of the unique features of the integrated model is the use of the Simulink/Matlab environment. This environment allows the user to develop component models that take advantage of the built-in functionality of Matlab and Simulink. Another unique feature is the full coupling of the building load, heat pump, and ground loop at every time step. The building load, heat pump, and ground loop models were chosen to allow for short time step simulations, which allows for a range of dynamic response times to be modeled and for different heat pump/SHR control methods to be explored. The integrated model can be used on any computer that has the Matlab and Simulink software. The building load model used, called HAMBASE, can model both residential and commercial buildings. HAMBASE was validated using the ASHRAE 140-2007 standard. The heat pump model uses readily available data provided by GSHP manufacturers to accurately model operation across a wide range of input conditions. The vertical borehole ground loop model, developed at Oklahoma State University, is based on Eskillson's g-function model, but included a one-dimensional numerical model to calculate the short term thermal response of the borehole and ground. The ground loop model utilizes GLHEPRO, a ground loop sizing and simulation tool, to create the required parameter files. Using the integrated building load-ground source heat pump model, a model of a single family house with a ground source heat pump was developed. The house model was validated by the results from eQuest and GELHPRO. A series of sensitivity studies were completed to determine dominant factors affecting the use of GSHPs in Texas and the Southwest regions of the United States. The results show that the life of a vertical borehole can be significantly extended/cut short if the ground parameters are properly/not properly designed prior to ground loop sizing. / text
404

Multiple mating and female choice in Richardson's ground squirrels (Urocitellus Richardsonii)

Magyara, Nora, University of Lethbridge. Faculty of Arts and Science January 2009 (has links)
I studied the mating behaviour of Richardson’s ground squirrels (Urocitellus richardsonii) in 2007 and 2008, near Picture Butte, AB, Canada with the goals of evaluating multiple paternities within litters, sperm competition, and female mate choice. Eleven microsatellites and use of behavioural data to eliminate males who could not be putative sires based on their spatial and temporal remoteness from estrous females enabled exclusive assignment of paternity to 82.8% of 598 offspring with known maternity. The frequency of multiple paternities (26.4%, n=87 litters) in my population was lower than that reported for Richardson’s ground squirrels in a Manitoba population (80.0%, n=15 litters). Sperm competition was absent except in litters weaned by those females that mated again within 5 minutes of the first copulation, in which case sperm displacement was evident. Female choice was observed through avoidance of copulation, termination of copulation, and hide-then-run behaviour. / x, 98 leaves ;|c29 cm. --
405

Ground beetle (Coleoptera:Carabidae) communities along a successional gradient in southwestern Quebec and notes on the range expansion of introduced species

Mercado, Alida. January 2005 (has links)
Species diversity is influenced by disturbance in the environment. Ground beetles (Coleoptera: Carabidae) were used as a model taxon to study the effects of disturbance (i.e., time since disturbance) in different habitats along a successional gradient (agricultural fields, old fields, young forests and old forests). Seventy-three species (5139 individuals) were collected during both years of sampling, of which 9 species are introduced species and compose 64.8% of the total catch. In contrast to the predictions of the Intermediate Disturbance Hypothesis, diversity of ground beetles was higher in the agricultural fields and lowest in the old forests. The community composition, as seen with Nonmetric Multidimensional Scaling ordination, in the agricultural fields was the most distinct, while the difference between and among other habitats was less clear, possibly influenced by the introduced species present in the area. The introduced species collected had a significant influence in the total catch as they represented more than half of the total individuals collected and in the ground beetle community composition. The distribution of seven introduced species in Quebec was studied and compared to what was reported in 1975. Five species have a similar distribution, while the distribution range of Harpalus rufipes DeGeer has expanded south and Bembidion obtusum Audinet-Serville might have been dispersing northeast since its introduction.
406

General education in the Royal Air Force, 1910-1961

Alderson, G. L. D. January 1960 (has links)
No description available.
407

Tracer monitoring techniques for shallow land burial of toxic waste

Betsill, Jeffrey David. January 1982 (has links) (PDF)
Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1982. / Includes bibliographical references (leaf 52).
408

Evaluation of losses from anaerobic biosolids due to winter and late fall land application /

El-Naggar, Khaled, January 1900 (has links)
Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 148-158). Also available in electronic format on the Internet.
409

Investigation of Heat Dissipation Enhancement due to Backfill Modification in Ground Coupled Heat Pump Systems

January 2012 (has links)
abstract: Due to the lack of understanding of soil thermal behavior, rules-of-thumb and generalized procedures are typically used to guide building professionals in the design of ground coupled heat pump systems. This is especially true when sizing the ground heat exchanger (GHE) loop. Unfortunately, these generalized procedures often encourage building engineers to adopt a conservative design approach resulting in the gross over-sizing of the GHE, thus drastically increasing their installation cost. This conservative design approach is particularly prevalent for buildings located in hot and arid climates, where the soils are often granular and where the water table tends to exist deep below the soil surface. These adverse soil conditions reduce the heat dissipation efficiency of the GHE and have hindered the adoption of ground coupled heat pump systems in such climates. During cooling mode operation, heat is extracted from the building and rejected into the ground via the GHE. Prolonged heat dissipation into the ground can result in a coupled flow of both heat and moisture, causing the moisture to migrate away from the GHE piping. This coupled flow phenomenon causes the soil near the GHE to dry out and results in the degradation of the GHE heat dissipation capacity. Although relatively simple techniques of backfilling the GHE have been used in practice to mitigate such coupled effects, methods of improving the thermal behavior of the backfill region around the GHE, especially in horizontal systems, have not been extensively studied. This thesis presents an experimental study of heat dissipation from a horizontal GHE, buried in two backfill materials: (1) dry sand, and (2) wax-sand composite mixture. The HYDRUS software was then used to numerically model the temperature profiles associated with the aforementioned backfill conditions, and the influence of the contact resistance at the GHE-backfill interface was studied. The modeling strategy developed in HYDRUS was proven to be adequate in predicting the thermal performance of GHE buried in dry sand. However, when predicting the GHE heat dissipation in the wax-sand backfill, significant discrepancies between model prediction and experimental results still exist even after calibrating the model by including a term for the contact resistance. Overall, the thermal properties of the backfill were determined to be a key determinant of the GHE heat dissipation capacity. In particular, the wax-sand backfill was estimated to dissipate 50-60% more heat than dry sand backfill. / Dissertation/Thesis / M.S. Design 2012
410

Produtividade do Eucalyptus sp. em função do estado nutricional e da fertilidade do solo em diferentes regiões do Estado de São Paulo. / Eucalyptus sp. in function of nutrient status and soil fertility in three regions of the state of São Paulo, Brazil.

Fábio Sgarbi 17 May 2002 (has links)
Grande parte dos plantios de Eucalyptus sp., no Estado de São Paulo, apresentam limitações nutricionais as quais comprometem o crescimento e a sustentabilidade das florestas ao longo dos ciclos. Isso se deve a elevada exportação de nutrientes, durante a colheita da madeira associada a baixa fertilidade dos solos e a insuficiente utilização insumos, nestas áreas. Através de metodologias clássicas, é possível monitorar estes plantios visando a identificação dos nutrientes e dos parâmetros químicos do solo mais limitantes para o crescimento do Eucalyptus sp. Neste estudo, foram levantadas três regiões no Estado de São Paulo (Capão Bonito, Jacareí e Lençóis Paulista), durante os anos de 1997 a 2000. Para tanto, foram amostradas 209 parcelas, 117 talhões e 21 fazendas, totalizando 2.215 ha. As florestas estaram 12 a 45 meses de idade. Em cada talhão, foram locadas parcelas contendo 25 a 50 plantas, nas quais foram realizadas medições de altura das árvores visando a determinação do índice de sítio, assim como, amostragem de folhas e de solo, visando a determinação dos teores foliares dos nutrientes e dos parâmetros químicos do solo. Posteriormente, foi feita a análise dos dados através do método do nível crítico, das análises de correlação e de regressão linear e através do sistema integrado de diagnose e recomendação (DRIS). Verificou-se que os nutrientes mais limitantes para o crescimento do Eucalyptus sp. foram: boro, fósforo, nitrogênio e excesso de cobre nas regiões de Capão Bonito e Jacareí; o excesso de manganês, nas regiões de Jacareí e Lençóis Paulista; magnésio, potássio e o excesso de cálcio, na região de Lençóis Paulista. / Eucalyptus sp. stands, in the state of São Paulo, Brazil, present some nutrient limitations that can implicate growth and sustainability of the forests in the future. It happens because of high nutrient exportation during timber harvesting and also because of the low soil fertility and insufficient use of fertilizers in these areas. Through classic methodologies, the identification of the limiting nutrients is possible to monitor these stands and to determine the nutrient and the chemical parameters that limiting the growth. It were surveyed three regions of the state of São Paulo (Capão Bonito, Jacareí and Lençóis Paulista), during the years of 1997 to 2000. Data were collected in 209 sample plots, in 117 stands of 21 farms, totalizing 2.215 ha. The ages surveyed varied from 12 to 45 months old. Sample plots had 25 and 50 trees, that we measured total height for site index estimation (base age 7 years). Leaf and soil samples were collected to determine the nutrient content in the leaves and the soil chemical nutrients. Data were analyzed based in the method of the critical level, analyses of correlation and linear regression and through the diagnose and recommendation based on integrated system (DRIS). It was verified that the nutrients that limit Eucalyptus sp. growth were: boron, phosphorus, nitrogen and high copper content in Capão Bonito and Jacareí regions; the high manganese content in Jacareí and Lençóis Paulista regions and high calcium content, along with low magnesium and potassium content in the Lençóis Paulista region.

Page generated in 0.0427 seconds