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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.
1

Germination thresholds of the Mixed-grass Prairie species as affected by global climate change: A FACE study.

2013 December 1900 (has links)
The effects of global climate change on seed germination and plant regeneration have been reported in many species. However, there are no consistent trends in how seed quality and germination are affected by these conditions. Seeds of four native, one invasive, and two pairs of native/invasive species were collected from the USDA-ARS Prairie Heating and CO2 Enrichment Experimental plots in 2007 to 2009, located in the Mixed-grass Prairie near Cheyenne, WY. Field treatments include ambient (385 ppm, c) and elevated (600 ppm, C) CO2 concentrations, control temperature (t) and heating (1.5/3.0°C warmer day/night, T), and deep (ct-d) and shallow (ct-s) irrigation. Seed quality was evaluated and germination tests were conducted under alternating temperatures (10/0, 12.5/2.5, 15/5, 20/10, 25/15, 30/20, 35/25°C). Thermal time requirements (θ50) and base temperatures (Tb) for germination were determined using thermal time models. Elevated CO2 concentrations reduced seed fill and viability, germination and germination rate in Grindelia squarrosa. Heating increased seed viability in Koeleria macrantha from 56% to 79%. Heating, when combined with elevated CO2 concentrations, increased germination while CO2 alone decreased germination by about 14% in Bouteloua gracilis. Heating tended to enhance Tb and to reduce θ50 in Bouteloua gracilis, which may slow the initiation of germination but seeds germinate faster in spring. Elevated CO2 concentrations tended to increase but CT tended to decrease Tb in Centaurea diffusa, but not θ50. Heating tended to increase but all the other treatments tended to reduce Tb in Lanaria dalmatica, leading to a possible earlier start of germination. Irrigation treatments tended to show similar trend of effects on seed quality and germination as that in elevated CO2 concentrations. Species specific changes in seed quality and germination were observed, which may exert substantial cumulative effects on community composition in the long run. Invasive species may be more competitive under future climatic conditions compared with native species. However, the distribution and abundance of some native species, specifically Bouteloua gracilis, may be favored by climate change.
2

Visualization of spatio-temporal data in two dimensional space

Baskaran, Savitha 15 November 2016 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Spatio-temporal data is becoming very popular in the recent times, as there are large number of datasets that collect both location and temporal information in the real time. The main challenge is that extracting useful insights from such large data set is extremely complex and laborious. In this thesis, we have proposed a novel 2D technique to visualize the spatio-temporal big data. The visualization of the combined interaction between the spatial and temporal data is of high importance to uncover the insights and identify the trends within the data. Maps have been a successful way to represent the spatial information. Addition- ally, in this work, colors are used to represent the temporal data. Every data point has the time information which is converted into relevant color, based on the HSV color model. The variation in the time is represented by transition from one color to another and hence provide smooth interpolation. The proposed solution will help the user to quickly understand the data and gain insights.
3

Nonlinear controller synthesis for complex chemical and biochemical reaction systems

Leising, Sophie 02 May 2005 (has links)
The present research study is comprised of two main parts. The first part aims at the development of a systematic system-theoretic framework that allows the derivation of optimal chemotherapy protocols for HIV patients. The proposed framework is conceptually aligned with a notion of continuous-time model predictive control of nonlinear dynamical systems, and results in an optimal way to control viral replication, while maintaining low antiretroviral drug toxicity levels. This study is particularly important because it naturally integrates powerful system-theoretic techniques into a clinically challenging problem with worldwide implications, namely the one of developing chemotherapy patterns for HIV patients that are effective and do not induce adverse side-effects. The second part introduces a new digital controller design methodology for nonlinear (bio)chemical processes, that reflects contemporary necessities in the practical implementation of advanced process control strategies via digital computer-based algorithms. The proposed methodology relies on the derivation of an accurate sampled-data representation of the process, and the subsequent formulation and solution to a nonlinear digital controller synthesis problem. In particular, for the latter two distinct approaches are followed that are both based on the methodological principles of Lyapunov design and rely on a short-horizon model-based prediction and optimization of the rate of“energy dissipation" of the system, as it is realized through the time derivative of an appropriately selected Lyapunov function. First, the Lyapunov function is computed by solving the discrete Lyapunov matrix equation. In the second approach however, it is computed by solving a Zubov-like functional equation based on the system's drift vector field. Finally, two examples of a chemical and a biological reactor that both exhibit nonlinear behavior illustrate the main features of the proposed digital controller design method.
4

Överlevnadsanalys i tjänsteverksamhet : Tidspåverkan i överklagandeprocessen på Migrationsverket / Survival analysis in service : Time-effect in the process of appeal at the Swedish Migration Board

Minya, Kristoffer January 2014 (has links)
Migrationsverket är en myndighet som prövar ansökningar från personer som vill söka skydd, ha medborgarskap, studera eller vill jobba i Sverige. Då det på senare tid varit en stor ökning i dessa ansökningar har tiden för vilket ett beslut tar ökat. Varje typ av ansökning (exempelvis medborgarskap) är en process som består av flera steg. Hur beslutet går igenom dessa steg kallas för flöde. Migrationsverket vill därför öka sin flödeseffektivitet. När beslutet är klart och personen tagit del av det men inte är nöjd kan denne överklaga. Detta är en av de mest komplexa processerna på Migrationsverket. Syftet är analysera hur lång tid denna process tar och vilka steg i processen som påverkar tiden. Ett steg (som senare visar sig ha en stor effekt på tiden) är yttranden. Det är när domstolen begär information om vad personen som överklagar har att säga om varför denne överklagar. För att analysera detta var två metoder relevanta, accelerated failure time (AFT) och \multi-state models (MSM). Den ena kan predicera tid till händelse (AFT) medan den andra kan analysera effekten av tidspåverkan (MSM) i stegen. Yttranden tidigt i processen har stor betydelse för hur snabbt en överklagan får en dom samtidigt som att antal yttranden ökar tiden enormt. Det finns andra faktorer som påverkar tiden men inte i så stor grad som yttranden. Då yttranden tidigt i processen samtidigt som antal yttranden har betydelse kan flödeseffektiviteten ökas med att ta tid på sig att skriva ett informativt yttrande som gör att domstolen inte behöver begära flera yttranden. / The Swedish Migration Board is an agency that review applications from individuals who wish to seek shelter, have citizenship, study or want to work in Sweden. In recent time there has been a large increase in applications and the time for which a decision is made has increased. Each type of application (such as citizenship) is a process consisting of several stages. How the decision is going through these steps is called flow. The Swedish Migration Board would therefore like to increase their flow efficiency. When the decision is made and the person has take part of it but is not satisfied, he can appeal. This is one of the most complex processes at the Board. The aim is to analyze how long this process will take and what steps in the process affects the time. One step (which was later found to have a significant effect on time) is opinions. This is when the court requests information on what the person is appealing has to say about why he is appealing. To analyze this, two methods were relevant, accelerated failure time (AFT) and the multi-state models (MSM). One can predict time to event (AFT), the other to analyze the effect of time-manipulation (MSM) in the flow. Opinions early in the process is crucial to how quickly an appeal get judgment while the number of opinions increases the time enormously. There are other factors that affect the time but not so much as opinions. The flow efficiency can be increased by taking time to write an informative opinion which allows the court need not to ask for more opinions.
5

Statistical inference in high dimensional linear and AFT models

Chai, Hao 01 July 2014 (has links)
Variable selection procedures for high dimensional data have been proposed and studied by a large amount of literature in the last few years. Most of the previous research focuses on the selection properties as well as the point estimation properties. In this paper, our goal is to construct the confidence intervals for some low-dimensional parameters in the high-dimensional setting. The models we study are the partially penalized linear and accelerated failure time models in the high-dimensional setting. In our model setup, all variables are split into two groups. The first group consists of a relatively small number of variables that are more interesting. The second group consists of a large amount of variables that can be potentially correlated with the response variable. We propose an approach that selects the variables from the second group and produces confidence intervals for the parameters in the first group. We show the sign consistency of the selection procedure and give a bound on the estimation error. Based on this result, we provide the sufficient conditions for the asymptotic normality of the low-dimensional parameters. The high-dimensional selection consistency and the low-dimensional asymptotic normality are developed for both linear and AFT models with high-dimensional data.
6

Modelling of gyro in an IR seeker for real-time simulation / Modellering av gyro i en IR-målsökare för realtidssimulering

Nordman, Thomas January 2004 (has links)
<p>The target tracking system of an IR (InfraRed) guided missile is constantly subjected to disturbances due to the linear and angular motion of the missile. To diminish these LOS (Line Of Sight) disturbances the seeker of the missile can be built from a free gyroscope mounted in a very low friction suspension. The ability of the spinning gyroscope to maintain its direction relative to an inertial frame is used to stabilize the seeker LOS while tracking a target. The tracking velocity of the seeker, i.e. its angular velocity, is controlled by a feedback control unit where the signal from the IR detector is used as input. The electrical driven actuator consists of a set of coils and a magnet on the gyroscope. </p><p>The purpose of this thesis is to develop a real-time model of the seeker gyroscope in an existing IR MANPAD (MAN Portable Air Defense) missile. The aim is a model that is able to simulate the real system with consideration to the tracking velocity. The model should also be integrated into a hybrid simulator environment. </p><p>With relatively good knowledge of the system and its subsystems an initial physical modelling approach was used where elementary equations and accepted relations were assembled to describe the mechanism of the subsystems. This formed the framework of the model and gave a good foundation for further modelling. By using experimentation and more detailed system knowledge the initial approach could be developed and modified. Necessary approximations were made and unknown parameters were determined through system identification methods. The model was implemented in MATLAB Simulink. To make it suitable for real-time operation Real-Time Workshop was used. </p><p>The model design was evaluated in simulations where the tracking performance could be tested for different positions of the gyroscope. The results where satisfying and showed that the model was able to reproduce the output of the system well considering the speed of the model and the approximations made. One important reason that good results can be achieved with a relatively simple model is that the seeker is limited to small rotations. The model can be tuned to operate in a smaller range and the complexity can be kept low. A weakness of the model is that the output error increases for wide angles.</p>
7

Estimation and testing the effect of covariates in accelerated life time models under censoring

Liero, Hannelore January 2010 (has links)
The accelerated lifetime model is considered. To test the influence of the covariate we transform the model in a regression model. Since censoring is allowed this approach leads to a goodness-of-fit problem for regression functions under censoring. So nonparametric estimation of regression functions under censoring is investigated, a limit theorem for a L2-distance is stated and a test procedure is formulated. Finally a Monte Carlo procedure is proposed.
8

Variation in germination response to temperature among collections of three conifers from the mixed wood forest

Qualtiere, Elaine 27 May 2008
White spruce (<i>Picea glauca</i> (Moench) Voss), black spruce (<i>P. mariana</i> (Mill.) BSP), and jack pine (<i>Pinus banksiana</i> Lamb.) are dominant conifer trees within the boreal forest. Rising CO2 concentrations may create hotter and drier conditions in the Southern Boreal Forest of Canada, and have negative impacts on germination and regeneration of conifers. Conifers vary in their germination requirements and may have different responses to climate change. Experiments were conducted to access the germination potential, variability among collections, and to predict the ability of these conifers to germinate under future climatic conditions. Twelve collections of white spruce and black spruce and ten collections of jack pine seeds were collected from the Boreal Plain Ecozone of Saskatchewan. Seeds of all collections varied in their dormancy characteristics and dormancy breaking requirements because no single stratification or light treatment stimulated germination in all three species. Seed dormancy was greatest in white spruce and least in black spruce. Germination tests at 5, 10, 12.5, 15, 17.5, 20, 25, 30, and 35°C were used to develop thermal time models. Each species had unique temperatures for optimal germination ranging from 20°C in white spruce, 20-25°C in black spruce, and 25-30°C in jack pine. The speed of germination under similar temperature regimes was fastest for jack pine, intermediate for black spruce, and slowest for white spruce. The base temperature for white spruce decreased (r=0.63, P=0.03) with increasing June precipitation while that of jack pine tended to increase with latitude (r=0.60, P=0.07) and April precipitation (r=0.58, P=0.08). No environmental variables correlated with germination of black spruce. The Canadian Global Climate Model, version 2, with emission scenarios predicted future temperature and precipitation at the sites where seeds were collected. Using the base temperature for germination as a guideline, temperatures suitable for germination in the spring are predicted to advance by a few weeks to a month and a half earlier with increased concentrations of CO2. Moisture availability may, however, control seed germination at these sites. Overall, jack pine and black spruce might better adapt to increasing temperature because of their high germination temperatures (>30°C). Variation in most germination parameters existed among collections, suggesting this variability can be used to select seed sources for reforestation or assisted migration in a changing climate.
9

Quantifying the effects of temperature on dormancy change and germination in orchardgrass (<i>Dactylis glomerata</i> L.) and western wheatgrass (<i>Pascopyrum smithii</i> [Rydb.] L.)

Qiu, Jie 14 June 2005
Orchardgrass (<i>Dactylis glomerata</i> L.) and western wheatgrass (<i>Pascopyrum smithii </i>(Rydb.) L.) seeds have different degrees of dormancy that result in non-uniform seedling emergence in the field. Seed dormancy of the two species, in part, causes disagreement between germination tests in the laboratory and seedling emergence in the field. Experiments were conducted over two years in the laboratory and in the field to determine the effects of alternating temperatures on changes in seed dormancy and germination of orchardgrass and western wheatgrass. The two western wheatgrass cultivars (Walsh and LC9078a) had deeper dormancy than the two orchardgrass cultivars (Arctic and Lineta). Dormancy of both species was broken by temperatures with 10oC amplitude; this temperature variation was similar to that which occurred at a 1 cm depth in the soil. Optimal temperatures for germination of orchardgrass (10-25oC) were broader than those for western wheatgrass (15-20oC). Seedling emergence of orchardgrass was less sensitive to seeding date in the spring than western wheatgrass; seedling emergence of western wheatgrass increased as seeding date was delayed from early to late May if soil water was not limiting. The rate of seedling emergence increased with increasing temperature in both species, therefore, faster and more uniform seedling emergence can be expected from late spring seeding dates. Seeds were often exposed to light during germination tests in the laboratory while planting seeds in the soil usually prevented exposure of seeds to light. Seedling emergence of orchardgrass in the field was usually less than the germination percentage obtained in the laboratory because of light exposure during germination tests could break dormancy in orchardgrass seeds and the small seeds of orchardgrass had limited energy reserves for pre-emergence seedling growth. On the other hand, germination of western wheatgrass seeds was reduced by exposure to light during germination and seeds were larger than those of orchardgrass. Therefore, seedling emergence of western wheatgrass in the field was usually greater than germination tests would predict. The use of thermal time models to study seed dormancy changes and germination revealed the dual effects of temperature on these processes. The modified thermal time model takes the difference between germination and seedling emergence into account and can accurately predict seedling emergence in the field (R2=0.88 to 0.99). Thermal time models for predicting seedling emergence in the field can also be developed for other forages, however, cultivar- and species-specific parameters must be developed for the models.
10

Modelling of gyro in an IR seeker for real-time simulation / Modellering av gyro i en IR-målsökare för realtidssimulering

Nordman, Thomas January 2004 (has links)
The target tracking system of an IR (InfraRed) guided missile is constantly subjected to disturbances due to the linear and angular motion of the missile. To diminish these LOS (Line Of Sight) disturbances the seeker of the missile can be built from a free gyroscope mounted in a very low friction suspension. The ability of the spinning gyroscope to maintain its direction relative to an inertial frame is used to stabilize the seeker LOS while tracking a target. The tracking velocity of the seeker, i.e. its angular velocity, is controlled by a feedback control unit where the signal from the IR detector is used as input. The electrical driven actuator consists of a set of coils and a magnet on the gyroscope. The purpose of this thesis is to develop a real-time model of the seeker gyroscope in an existing IR MANPAD (MAN Portable Air Defense) missile. The aim is a model that is able to simulate the real system with consideration to the tracking velocity. The model should also be integrated into a hybrid simulator environment. With relatively good knowledge of the system and its subsystems an initial physical modelling approach was used where elementary equations and accepted relations were assembled to describe the mechanism of the subsystems. This formed the framework of the model and gave a good foundation for further modelling. By using experimentation and more detailed system knowledge the initial approach could be developed and modified. Necessary approximations were made and unknown parameters were determined through system identification methods. The model was implemented in MATLAB Simulink. To make it suitable for real-time operation Real-Time Workshop was used. The model design was evaluated in simulations where the tracking performance could be tested for different positions of the gyroscope. The results where satisfying and showed that the model was able to reproduce the output of the system well considering the speed of the model and the approximations made. One important reason that good results can be achieved with a relatively simple model is that the seeker is limited to small rotations. The model can be tuned to operate in a smaller range and the complexity can be kept low. A weakness of the model is that the output error increases for wide angles.

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