• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 439
  • 101
  • 100
  • 61
  • 41
  • 20
  • 15
  • 9
  • 9
  • 9
  • 9
  • 9
  • 8
  • 5
  • 5
  • Tagged with
  • 945
  • 101
  • 70
  • 62
  • 59
  • 58
  • 54
  • 53
  • 50
  • 46
  • 42
  • 42
  • 42
  • 40
  • 39
  • 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.
11

Characterization of the movement of spray drift past a shelterbelt

Peterson, Jonathan Christian 29 April 2008
Pesticide use is an important component of the agricultural industry. Pesticides are typically applied to crops as a droplet spray, and these droplets are susceptible to off-target movement due to wind, which is called spray drift. It has recently been recognized that shelterbelts may protect vulnerable downwind areas from spray drift. There is a need to characterize the movement of spray drift past a shelterbelt to better understand the extent of this protection and the variables which affect it. The variables investigated in this research may be classified as meteorological conditions, spray application settings, and shelterbelt properties.<p>This research investigated the movement of spray drift past a 5 m tall carragana/chokecherry shelterbelt. Spray was applied using a conventional sprayer that travelled on a path that was upwind and parallel to the shelterbelt. A tracer substance was mixed into the spray solution, and the deposition and airborne concentration of drift was measured using a variety of collectors placed at perpendicular distances up- and downwind of a shelterbelt. The mass of drift deposit on the collectors was determined using spectrofluoremetry and standard solutions.<p>When the spray swath was a distance of 3H (where H is the height of the shelterbelt) upwind of the shelterbelt, it was found that the ground deposition of drift at a distance of 0.5H downwind of the shelterbelt was reduced by approximately 74%, compared to the drift deposit at 0.5H upwind. The reduction over the same downwind distances was 29% in the open field setting. The airborne drift cloud was attenuated by the shelterbelt and the airborne concentration of drift exiting the shelterbelt was reduced by approximately 85% of the entering drift. The airborne drift concentration profile indicated that there was a greater proportion of drift travelling over the top of the shelterbelt rather than passing through the shelterbelt, with the peak concentration occurring at approximately 1.2H.<p>Qualitative and multiple linear regression analyses were used to determine the significance of a number of meteorological and controlled variables on the deposition of drift. It was found that the mass of drift deposited downwind of the shelterbelt increased with a higher wind speed, higher temperature, and lower relative humidity. For the range of meteorological conditions sampled, the effect of wind direction and atmospheric stability were found to be insignificant. Finer spray qualities and higher shelterbelt optical porosity produced greater airborne drift and deposition downwind of the shelterbelt. With increasing upwind sprayer distance, the mass of drift deposited within the shelterbelt decreased.
12

Characterization of the movement of spray drift past a shelterbelt

Peterson, Jonathan Christian 29 April 2008 (has links)
Pesticide use is an important component of the agricultural industry. Pesticides are typically applied to crops as a droplet spray, and these droplets are susceptible to off-target movement due to wind, which is called spray drift. It has recently been recognized that shelterbelts may protect vulnerable downwind areas from spray drift. There is a need to characterize the movement of spray drift past a shelterbelt to better understand the extent of this protection and the variables which affect it. The variables investigated in this research may be classified as meteorological conditions, spray application settings, and shelterbelt properties.<p>This research investigated the movement of spray drift past a 5 m tall carragana/chokecherry shelterbelt. Spray was applied using a conventional sprayer that travelled on a path that was upwind and parallel to the shelterbelt. A tracer substance was mixed into the spray solution, and the deposition and airborne concentration of drift was measured using a variety of collectors placed at perpendicular distances up- and downwind of a shelterbelt. The mass of drift deposit on the collectors was determined using spectrofluoremetry and standard solutions.<p>When the spray swath was a distance of 3H (where H is the height of the shelterbelt) upwind of the shelterbelt, it was found that the ground deposition of drift at a distance of 0.5H downwind of the shelterbelt was reduced by approximately 74%, compared to the drift deposit at 0.5H upwind. The reduction over the same downwind distances was 29% in the open field setting. The airborne drift cloud was attenuated by the shelterbelt and the airborne concentration of drift exiting the shelterbelt was reduced by approximately 85% of the entering drift. The airborne drift concentration profile indicated that there was a greater proportion of drift travelling over the top of the shelterbelt rather than passing through the shelterbelt, with the peak concentration occurring at approximately 1.2H.<p>Qualitative and multiple linear regression analyses were used to determine the significance of a number of meteorological and controlled variables on the deposition of drift. It was found that the mass of drift deposited downwind of the shelterbelt increased with a higher wind speed, higher temperature, and lower relative humidity. For the range of meteorological conditions sampled, the effect of wind direction and atmospheric stability were found to be insignificant. Finer spray qualities and higher shelterbelt optical porosity produced greater airborne drift and deposition downwind of the shelterbelt. With increasing upwind sprayer distance, the mass of drift deposited within the shelterbelt decreased.
13

Longshore sand transport distribution across the surf zone due to random waves

Abdelrahman, Saad Mesbah M. January 1983 (has links)
Thesis (M.S.)--Naval Postgraduate School, 1983. / Includes bibliographical references (leaves 82-84).
14

Métodos de coleta de deposição para ensaios de deriva em aplicações aéreas / Comprehensive study of deposition method collection spray drift in aerial application

Chechetto, Rodolfo Glauber [UNESP] 11 December 2015 (has links)
Submitted by RODOLFO GLAUBER CHECHETTO null (rgchechetto@hotmail.com) on 2016-02-10T18:00:10Z No. of bitstreams: 1 tese_Rodolfo Chechetto v6.pdf: 2131354 bytes, checksum: f702d025db225a02915fa37688092949 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-02-11T13:43:10Z (GMT) No. of bitstreams: 1 chechetto_rg_dr_bot.pdf: 2131354 bytes, checksum: f702d025db225a02915fa37688092949 (MD5) / Made available in DSpace on 2016-02-11T13:43:10Z (GMT). No. of bitstreams: 1 chechetto_rg_dr_bot.pdf: 2131354 bytes, checksum: f702d025db225a02915fa37688092949 (MD5) Previous issue date: 2015-12-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A produção agrícola em grande escala se tornou pouco viável sem a utilização de produtos fitossanitários. Esses são responsáveis por controles preventivos e curativos das plantas cultivadas em relação a problemas causados por insetos-pragas, doenças e plantas daninhas, porém, deve-se evitar a contaminação ambiental, humana e do alimento por meio da deriva, que é a perda do produto fitossanitário aplicado para locais não desejados. Para que essa deriva seja evitada, busca-se adquirir um conhecimento do comportamento das gotas após as pulverizações, principalmente em aplicações aéreas, onde as condições climáticas são ainda mais determinantes. Neste contexto, o objetivo dessa pesquisa foi analisar, comparativamente, os métodos de coleta de dados para modelagem de deriva com coletores horizontais e verticais em pulverizações de gotas finas e médias, visando analisar as implicações da escolha de um dos métodos e correlacionar os dados obtidos em ambas as metodologias em aplicação aérea. Foram avaliados dois tratamentos com quatro repetições, com gotas finas (GF) e médias (GM) pulverizadas com uma aeronave Ipanema e ponta de pulverização CP-03, em que foi pulverizada uma calda contendo uma concentração de inseticida em mistura ao corante azul brilhante. A deriva foi avaliada fora da área aplicada, na direção do vento predominante, por meio de coletores horizontais (lâminas de vidro) e coletores verticais (fios de nylon) distribuídos até 500 metros em relação à área aplicada. Os dados do índice de deriva foram calculados por meio de espectrofotometria e as médias do índice de deriva foram agrupados e ajustados para uma curva (modelo) através das médias e correlacionados a partir do coeficiente de Pearson a 5% de probabilidade. Nos dois tipos de coletores avaliados o tratamento com gotas finas (GF) apresentou maior valor de deriva comparado ao tratamento com gotas médias (GM). Na coleta vertical, o tratamento GM propiciou índices de deriva 50,0% menores na comparação direta com o GF e na coleta horizontal o tratamento GM propiciou índices de deriva 56,8% menores na comparação direta com o GF. A partir do ponto a 380 metros até a distância de 500 metros da área aplicada foi observada uma inflexão, em que o índice de deriva capturado nos coletores horizontais passa a ser maior para o tratamento GM. Nas correlações para avaliar o comportamento dos diferentes coletores para os tratamentos testados foi possível observar que para ambos os coletores a correlação foi significativa e positiva somente para o tratamento GM. É conclusivo, para esse estudo, que para o tratamento GM os dois tipos de coletores estudados apresentam correlação significativa e positiva a variação do índice de deriva. As gotas finas permanecem na corrente de ar por maiores distâncias e os coletores horizontais são ineficientes na coleta dessas gotas em tal camada, sendo os coletores verticais o melhor método para a coleta da deriva em aplicação aérea, por não haver inflexão nos tratamentos analisados e por apresentarem uma boa eficiência na coleta dos tratamentos com gotas finas e médias. / Modern large-scale agricultural production is not possible without the use of pesticides. These products are responsible for the maintenance, prevention and protection of crops against problems caused by pests, diseases and weeds. Additionally, a great deal of care has been taken to avoid the environmental, human and food contamination from spray drift, which is defined as the loss of applied pesticide to undesirable locations. To achieve this goal, knowledge of the behavior of droplets after the spraying, especially in aerial application, is even more crucial given the greater effect of climatic conditions. Thus, the aim of this study was to comparatively analyze the methods of data collection for modeling spray drift in aerial application with horizontal and vertical collectors in order to analyze the implications of the choice of a method and correlate the data obtained in both methodologies. Two treatments with four repetitions, a Fine spray (GF) and a Medium spray (GM), were used. The treatments were made using an aircraft (Ipanema) equipped with CP nozzles, and sprayed insecticide + Brilliant Blue dye as the spray solution. The drift was evaluated downwind from the applied area, using horizontal collectors (glass slides) and vertical collectors (nylon strings) positioned at distances up to 500 meters downwind of the applied area. The data for the drift index were determined from the spectrophotometry method and averages of the drift index were grouped and adjusted to a curve (model) through the averages and correlated the data from the Pearson Coefficient at a 5% probability. Results showed that with both collector types higher drift values were observed with the Fine spray than the treatment with the Medium spray. Results from the vertical collectors showed that the treatment with the Medium spray had a drift index 50.0% lower than the treatment with the Fine spray. Results from the horizontal collectors showed that the treatment with the Medium spray had a drift index 56.8% lower than the treatment with the Fine spray. From the collector at 380 meters downwind until 500 meters downwind from the applied area resulted in an inversion, where the drift index collected from the horizontal collectors was larger with the Medium spray treatment than the Fine spray treatment. When the correlations were calculated, the results for both collector types showed a significant and positive correlation only to Medium spray. It is conclusive from this study that to Medium spray to both types of the collectors showed significant and positive correlation the variation of the drift index. The Fine spray remained suspended in the air for longer distances and the horizontal collectors were unable to collect them in these conditions. The vertical collectors were the best method to capture drifting droplets in aerial application, given the lack of inversion from the treatments and in part from the good collection efficiency with both the Medium and Fine spray treatments.
15

Tuning and Optimising Concept Drift Detection

Do, Ethan Quoc-Nam January 2021 (has links)
Data drifts naturally occur in data streams due to seasonality, change in data usage, and the data generation process. Concepts modelled via the data streams will also experience such drift. The problem of differentiating concept drift from anomalies is important to identify normal vs abnormal behaviour. Existing techniques achieve poor responsiveness and accuracy towards this differentiation task. We take two approaches to address this problem. First, we extend an existing sliding window algorithm to include multiple windows to model recently seen data stream patterns, and define new parameters to compare the data streams. Second, we study a set of optimisers and tune a Bi-LSTM model parameters to maximize accuracy. / Thesis / Master of Applied Science (MASc)
16

In the Pursuit of Becoming a Research University

Enrriquez Gutierrez, Juan Carlos January 2008 (has links)
Many universities and colleges are shifting their missions from teaching-oriented to research-oriented (Clark, 1978, 1983; Riesman, 1956; Selingo 2000), a phenomenon that has become known as academic/institutional drift. During recent years, the knowledge society has created an environment that further encourages the shift by influencing stakeholders in higher education institutions to increasingly accept the role played by research institutions as the most legitimate. Consequently, higher education institutions are becoming increasingly involved in the pursuit of knowledge creation. They are concluding that legitimacy and prestige will be obtained in return, as well as material resources (Slaughter & Rhoades, 2004).Despite the fact that the production of knowledge by Latin American universities is marginal in an international context (Albornoz, 1993; Albatch, 2003), some of them are experiencing institutional drift. Using a case study in combination with a qualitative approach, this research project aims to highlight the nature and implications of the phenomenon through focusing on a Mexican university system. Semi-structured interviews with individuals occupying key positions within the organization and institutional documents constitute the study's sources of information. In addition, academic capitalism, institutional theory, and Hackman's theory of resource allocation are utilized as its theoretical framework.The findings of the study show that although the institution is actively engaging in academic capitalism, societal benefit is not being neglected as a result of such engagement. Nonetheless, the findings relate academic capitalism to further stratification within and across the institution's campuses. It is also concluded that the institution is experiencing isomorphic change by modeling itself after those universities it perceives as prestigious and legitimate in the research endeavor. Regarding internal resource allocation, it is demonstrated that a unit's centrality with respect to the institution's research strategy greatly explains its gains in institutional resources.This study also includes some implications and recommendations for the institution to concentrate on and/or address in order to succeed in its research endeavor. Lastly, some considerations regarding further research are introduced.
17

Langmuir circulation : a side-scan sonar study of mixing in Loch Ness

Cure, Marcel Serge January 1994 (has links)
No description available.
18

Drift of Aquatic Insects in the Brazos River, Texas

Cloud, Thomas J. 08 1900 (has links)
The objective of this study was to elucidate the nature and extent of drift by the aquatic insect populations of the Brazos River, Texas.
19

The Iowan drift : a review of the evidences of the Iowan stage of glaciation ; a co-operative study for the U.S. Geological survey and the Iowa Geological survey /

Alden, William C. Leighton, Morris M. January 1917 (has links)
M.M. Leighton's Thesis (Ph. D.)--University of Chicago, 1916. / "Private edition, distributed by the University of Chicago Libraries, Chicago, Illinois." "Reprinted from Iowa Geological Survey, volume XXVI, Annual report for 1915." Also issued online.
20

Outsourcing av drift och underhåll : En intervjustudie av nyligen ombildade bostadsrättsföreningars motiv till outsourcing av drift och underhåll

Lindquist, Jonas, Melin, Carl January 2013 (has links)
Abstract English title: Outsourcing of operation and maintenance -An interview study about newly reconstituted housing cooperatives motives for outsourcing of operation and maintenance. Swedish title: Outsourcing av drift och underhåll -En intervjustudie av nyligen ombildade bostadsrättsföreningars motiv till outsourcing av drift och underhåll. Authors: Jonas Lindquist &amp; Carl Melin Published (year): Spring 2013 Tutor: Sven-Ola Carlsson Examinator: Marita Blomqvist Background: Now days there are no questions for organizations about if they will outsource parts of their business. It is rather a question about what should be outsourced. In terms of organizations our found theory tells what is being outsourced is everything that does not belong to the organization’s core business, such as supporting functions. Therefore we would like to find out about what motifs underlying for a housing cooperative to outsource services within operation and maintenance of the property. Problem statement: Why do some recently reconstituted housing cooperatives choose to outsource services within operation and maintenance of the property? Purpose: The purpose of this thesis is to describe why recently reconstituted housing cooperatives choose to outsource services within operation and maintenance, how the work with operation and maintenance is done and also understand what motifs a recently reconstituted housing cooperative have to outsource parts of the operation and maintenance. All this on the basis of theoretical facts and empirical collected data. Method: This thesis is based on a qualitative interview study with a deductive approach. The data collection has consisted of three interviews with three different recently reconstituted housing cooperatives. In each interview has one in their opinion suitable board member of each housing cooperative been involved. The choice of the three different housing cooperatives is based on the requirements of being recently reconstituted and also that they differed in size. One is a small central housing cooperative consisting one house with 27 apartments. One is a large central cooperative consisting three houses with 115 apartments and the last one is a housing cooperative consisting of terraced houses with 54 apartments just outside the city. After the empirical data was all collected it has been compared to already existing theories found for analysis. The analysis in turn has resulted in our conclusions and suggestions for further research. Conclusion: Our conclusions are that within recently reconstituted housing cooperatives there are several different motifs of using outsourcing of operation and maintenance. Seen to the various theories we have chosen the common factor from the three different housing cooperatives were timesaving, which also can be translated into costs. Another factor that primarily relates to the operation are skills shortages. We note that it is almost impossible for a tenant to avoid outsourcing include elevator inspection where required a specific core competencies to accomplish it.

Page generated in 0.0328 seconds