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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.
131

Stochastic last-mile delivery problems with time constraints

Voccia, Stacy Ann 01 July 2015 (has links)
When a package is shipped, the customer often requires the delivery to be made within a particular time window or by a deadline. However, meeting such time requirements is difficult, and delivery companies may not always know ahead of time which customers will need a delivery. In this thesis, we present models and solution approaches for two stochastic last-mile delivery problems in which customers have delivery time constraints and customer presence is known in advance only according to a probability distribution. Our solutions can help reduce the operational costs of delivery while improving customer service. The first problem is the probabilistic traveling salesman problem with time windows (PTSPTW). In the PTSPTW, customers have both a time window and a probability of needing a delivery on any given day. The objective is to find a pre-planned route with an expected minimum cost. We present computational results that characterize the PTSPTW solutions. We provide insights for practitioners on when solving the PTSPTW is beneficial compared to solving the deterministic analogue of the problem. The second problem is the same-day delivery problem (SDDP). The SDDP is a dynamic and stochastic pick-up and delivery problem. In the SDDP, customers make delivery requests throughout the day and vehicles are dispatched from a warehouse or brick and mortar store to serve the requests. Associated with each request is a request deadline or time window. In order to make better-informed decisions, our solution approach incorporates information about future requests into routing decisions by using a sample scenario planning approach with a consensus function. We also introduce an analytical result that identifies when it is beneficial for vehicles to wait at the depot. We present a wide range of computational experiments that demonstrate the value of our approaches.
132

Continental-scale characterization of molecular variation in quaking aspen

Callahan, Colin M. 01 August 2012 (has links)
Quaking aspen (Populus tremuloides) has the largest natural distribution of any tree native to North America, ranging from Alaska through the breadth of Canada and south to mid-Mexico. The Laurentide ice sheet occupied most of the current range of P. tremuloides until the late Pleistocene epoch, so this species has undergone a significant, geologically recent range expansion. Surprisingly, range-wide patterns of genetic variation in P. tremuloides have never been described. Using a sample set representing the full longitudinal and latitudinal extent of the species distribution, I have conducted a phylogeographic analysis for P. tremuloides. Preliminary results comparing both nuclear and chloroplast DNA sequences revealed surprisingly low levels of divergence across the range. Because of this remarkably shallow genetic divergence among aspen populations, I used a set of rapidly-evolving molecular markers (microsatellites) to describe patterns of gene flow and diversity and to correlate those patterns with landscape features and histories. I analyzed eight microsatellite loci in 794 individuals from 30 sampling sites. From this multilocus data set, I identified pronounced genetic structuring across the range. Strikingly, sampling sites representing the southwestern portion of the range, the western United States and Mexico, form a distinct cluster. Sites within this southwestern cluster display dramatically reduced within-site genetic diversity but elevated regional genetic diversity, which suggests that populations in the southwestern portion of the range make up a stable edge persisting through multiple climate oscillations. Based on the uniqueness of the southwestern cluster and the climatic differences between the southwest and northern portions of the range, I propose that the southwestern cluster may represent a distinct ecotype. I also identified hotspots of diversity that correspond with potential refugia during the last glacial maximum but additional work is needed to refine these patterns. Further, my findings provide a solid foundation for a range of future studies on adaptive genetic and trait variation in this species.
133

The concept of identity in postmodern literature: the urban subject in the dystopian city : Paul Auster's In the country of last things

Correa Sotelo, Ruth Elvira January 2012 (has links)
Facultad de Filosof?a y Humanidades / Departamento de Ling??stica / Informe de Seminario para optar al grado de Licenciada en Lengua y Literatura Inglesa / Introduction From the emergence of the term Utopia in Thomas More?s book of the same name, many controversial and prolific discussions have appeared throughout time. These discussions involved not only cultural and sociological aspects, but also those concerned more with the inner dimension of the self: his desires, ambitions and transformations. What More really meant by using this term we have no certainty, because in it he refers to several different factors that have an effect in the life of the island portrayed in his book. In opposition to Utopia, meaning ?a happy place where a person has nothing to worry about because his/her government provides everything they need?, there is Dystopia, which could be defined as ?a society being controlled by a repressive state, in both individual and collective ways?. Starting from this point, the general topic that gives rise to the object of study in this work is the urban subject, Anna Blume in Paul Auster?s In the Country of Last Things, immersed in a dystopian city nearly to be extinguished and conditioned by spaces that exert powerful forces on the prevalence of the self.
134

Assessing the potential for improving public transport in rural areas by using driverless vehicles

Norman, Joel January 2019 (has links)
Driverless vehicles might fundamentally change the transport system in multiple ways. Reducing driver costs in mobility services could create opportunities for new mobility concepts. Research on driverless vehicles have previously concentrated on urban areas, though driverless vehicles in rural areas could have greater positive effects. Hence, the aim of the study is to see how driverless vehicles can be used in rural areas to contribute to a more sustainable transport system. Three rural mobility concepts for driverless vehicles are developed and by applying these to different case locations, the feasibility of the concepts is discussed. Interviews with local actors in Sweden were conducted to learn about general and local challenges with specific case locations. What rural mobility concept for driverless vehicles to use depends on access to public transport, distance to main roads and spatial density of travel demand. A modelling approach of a first and last mile feeder service is used to evaluate the feasibility of this mobility concept further. Model results show that driverless shuttles can feed travel demands of 100-150 passengers daily and still perform alternative tasks. Even though rural areas have general challenges, local issues also need consideration to optimize the benefits of the services. Public transport authorities are experts on local challenges and could take more responsibility in questions regarding driverless vehicles. For instance, flexibility, accessibility and equality could be improved by merging routes and shorten travel times for entire bus routes. Furthermore, other societal functions can be developed by reinvesting capital in other areas.
135

Improving Service Level of Free-Floating Bike Sharing Systems

Pal, Aritra 13 November 2017 (has links)
Bike Sharing is a sustainable mode of urban mobility, not only for regular commuters but also for casual users and tourists. Free-floating bike sharing (FFBS) is an innovative bike sharing model, which saves on start-up cost, prevents bike theft, and offers significant opportunities for smart management by tracking bikes in real-time with built-in GPS. Efficient management of a FFBS requires: 1) analyzing its mobility patterns and spatio-temporal imbalance of supply and demand of bikes, 2) developing strategies to mitigate such imbalances, and 3) understanding the causes of a bike getting damaged and developing strategies to minimize them. All of these operational management problems are successfully addressed in this dissertation, using tools from Operations Research, Statistical and Machine Learning and using Share-A-Bull Bike FFBS and Divvy station-based bike sharing system as case studies.
136

Tephrochronology of the Last Glacial/Interglacial transition in western Småland, southwestern Sweden

Morén, Björn January 2009 (has links)
<p>Tephrochronology, or the dating and correlation of stratigraphic sediment sequences by the use of tephra, is a dating method that has been much refined in the last decade. This refinement has enabled the detection of cryptotephra, which has expanded the known distribution of different tephras. At the site Lake Mulakullegöl in the southwest of Sweden, three distinct tephra horizons have been detected, of which two have been geochemically identified. The identified tephras are the Vedde Ash (ca 12,000 cal. yrs BP) and the Hässeldalen Tephra (ca 11,500 cal. yrs BP), both of Icelandic origin. These tephras were deposited during the middle of the Younger Dryas Stadial and the Younger Dryas/Preboreal transition, respectively. The Vedde Ash is one of the most widespread tephras of Icelandic provenance, while the Hässeldalen Tephra so far only has been found at two sites in southeastern Sweden, prior to the current study. A third, unidentified, tephra was also detected. Based on the stratigraphic position, this tephra might be the Borrobol Tephra, which has been dated to ca 14,400 cal. yrs BP. This might indicate that warming had not yet occurred in this part of Sweden. The extended known distribution of especially the Hässeldalen Tephra, but also the Vedde Ash, has enabled a higher potential for correlations between different records deposited during the Last Glacial/Interglacial transition.</p>
137

Tephrochronology of the Last Glacial/Interglacial transition in western Småland, southwestern Sweden

Morén, Björn January 2009 (has links)
Tephrochronology, or the dating and correlation of stratigraphic sediment sequences by the use of tephra, is a dating method that has been much refined in the last decade. This refinement has enabled the detection of cryptotephra, which has expanded the known distribution of different tephras. At the site Lake Mulakullegöl in the southwest of Sweden, three distinct tephra horizons have been detected, of which two have been geochemically identified. The identified tephras are the Vedde Ash (ca 12,000 cal. yrs BP) and the Hässeldalen Tephra (ca 11,500 cal. yrs BP), both of Icelandic origin. These tephras were deposited during the middle of the Younger Dryas Stadial and the Younger Dryas/Preboreal transition, respectively. The Vedde Ash is one of the most widespread tephras of Icelandic provenance, while the Hässeldalen Tephra so far only has been found at two sites in southeastern Sweden, prior to the current study. A third, unidentified, tephra was also detected. Based on the stratigraphic position, this tephra might be the Borrobol Tephra, which has been dated to ca 14,400 cal. yrs BP. This might indicate that warming had not yet occurred in this part of Sweden. The extended known distribution of especially the Hässeldalen Tephra, but also the Vedde Ash, has enabled a higher potential for correlations between different records deposited during the Last Glacial/Interglacial transition.
138

Palliative Care Services Utilization and Location of Death

Cameron, Barbara 19 June 2012 (has links)
In this study, the utilization of palliative care services, acute care services, and location of death for clients who were palliative and receiving services from Champlain Community Care Access Centre (CCAC) in Ontario during their last month of life were investigated. An adaptation of Andersen?s Behavioral Model of Health Services Utilization provided context and structure to this study. This is an historical, quantitative descriptive study using chart audits for data collection. The data on CCAC clients who were palliative and who died during the month of July 2009 were tracked during their last month of life. Collection of socio-demographic data, services provided through CCAC, emergency department visits, hospital admissions, and location of death provided the data for this study. The clients who died at home used more CCAC services than those who died at other locations and frequently community palliative care physicians provided their medical care. The findings of this study included: 1) The majority of the clients, who expressed a preference, died in their preferred location. 2) The role of community palliative care physicians was an important component of the services that supported the clients to die in their location of choice. 3) Over 25% of the study sample died in a hospital and the clients used a large number of in-patient hospital days with one quarter of the hospital deaths taking place in an emergency department or an intensive care unit. 4) During the last month of life, 25% of the clients received chemotherapy and/or radiation therapy. 5) The clients who died at home used more CCAC services than those who died in other locations and who used institutional resources. The implications for practice, policy, research, and education are discussed.
139

F. Scott Fitzgerald: A Hollywood Tragedy

Baker, James J., III 01 January 2011 (has links)
F. Scott Fitzgerald was a product of the era he was at his zenith: the roaring 1920s. By the time he arrived in Los Angeles, he was short on money and the audience for his novels and writing was waning. This work explores his time in L.A., his attitude toward cinema & the Hollywood system, and how he incorporated what he learned from screenwriting into The Last Tycoon, the unfinished novel that Fitzgerald aimed to revive his own career with.
140

Robust Quantile Regression Using L2E

January 2012 (has links)
Quantile regression, a method used to estimate conditional quantiles of a set of data ( X, Y ), was popularized by Koenker and Bassett (1978). For a particular quantile q , the q th quantile estimate of Y given X = x can be found using an asymmetrically-weighted, absolute-loss criteria. This form of regression is considered to be robust, in that it is less affected by outliers in the data set than least-squares regression. However, like standard L 1 regression, this form of quantile regression can still be affected by multiple outliers. In this thesis, we propose a method for improving robustness in quantile regression through an application of Scott's L 2 Estimation (2001). Theoretic and asymptotic results are presented and used to estimate properties of our method. Along with simple linear regression, semiparametric extensions are examined. To verify our method and its extensions, simulated results are considered. Real data sets are also considered, including estimating the effect of various factors on the conditional quantiles of child birth weight, using semiparametric quantile regression to analyze the relationship between age and personal income, and assessing the value distributions of Major League Baseball players.

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