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- Amvrosiadi, Nino
(author)
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The value of experimental data and modelling for exploration of hydrological functioning: The case of a till hillslope
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Successfully modeling one system response (e.g. hydrograph or solute transport) sometimes gives the false sense of well-characterizing the modeled system. This is partly because of the well-known equifinality issue; during the calibration process multiple parameter combinations can produce similarly good results. One step forward towards a better-defined system is using measured (at relevant scale) values for the model parameters, as well as using multiple conditions to constrain the model.But when not enough, or relevant, field measurements are available, virtual experiments (VE’s) can be used as a supplementary method to model calibration. The advantage of VE’s over model calibration is that they can also be used to explore assumptions both on the system hydrological processes, and on the model structure.One goal of this study was to utilize both field measurements and models for better characterization of the S-transect hillslope, located in Västrabäcken catchment, Northern Sweden. This included (a) characteristics in space: system vertical boundaries, hydraulic parameters, pore water velocity distribution, spatial correlation of flowpaths, soil water retention properties; (b) characteristic of system’s dynamic behavior: storage – discharge relationship, transit time distribution, turnover time; and (c) outputs’ sensitivity to external forcing, and to small scale structure assumptions. The second goal was to comment on the value of field measurements and virtual experiments for extracting information about the studied system.An intensely monitored study hillslope was chosen for this work. Although the hillslope has already been the subject of multiple field and modelling studies, there are still open questions regarding the characteristics listed above. The models used were the Vertical Equilibrium Model (VEM), and the Multiple Interacting Pathways (MIPs) model.It was found that the hillslope was well connected; from the near-stream areas up to the water divide the storage – discharge relationship could be described as an exponential function. Also, the dynamic storage (which controls the hydrograph dynamics) was much smaller comparing to the total hillslope storage. The unsaturated soil storage was found to be more sensitive to water table positions than vertical flux magnitude. The dynamic condition of external forcing (precipitation and evapotranspiration) affected the transit time distribution (TTD) shape. And, opposite to expectations, TTD was not sensitive to micro-scale structural assumptions tested here.
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- Nylander, Stina, 1972-
(author)
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Design and Implementation of Multi-Device Services
- 2007
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Doctoral thesis (other academic/artistic)abstract
- We present a method for developing multi-device services which allows for the creation of services that are adapted to a wide range of devices. Users have a wide selection of electronic services at their disposal such as shopping, banking, gaming, and messaging. They interact with these services using the computing devices they prefer or have access to, which can vary between situations. In some cases, the services that they want to use func-tions with the device they have access to, and sometimes it does not. Thus, in order for users to experience their full benefits, electronic services will need to become more flexible. They will need to be multi-device services, i.e. be accessible from different devices. We show that multi-device services are often used in different ways on different devices due to variations in device capabilities, purpose of use, context of use, and usability. This suggests that multi-device services not only need to be accessible from more than one device, they also need to be able to present functionality and user interfaces that suit various devices and situations of use. The key problem addressed in this work is that there are too many device-service combinations for developing a service version for each device. In-stead, there is a need for new methods for developing multi-device services which allows the creation of services that are adapted to various devices and situations. The challenge of designing and implementing multi-device services has been addressed in two ways in the present work: through the study of real-life use of multi-device services and through the creation of a development method for multi-device services. Studying use of multi-device services has gener-ated knowledge about how to design such services which give users the best worth. The work with development methods has resulted in a design model building on the separation of form and content, thus making it possible to create different presentations to the same content. In concrete terms, the work has resulted in design guidelines for multi-device services and a system prototype based on the principles of separation between form and content, and presentation control.
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| 4. |
- Tsiftes, Nicolas, 1980-
(author)
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Storage-Centric System Architectures for Networked, Resource-Constrained Devices
- 2016
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Doctoral thesis (other academic/artistic)abstract
- The emergence of the Internet of Things (IoT) has increased the demand for networked, resource-constrained devices tremendously. Many of the devices used for IoT applications are designed to be resource-constrained, as they typically must be small, inexpensive, and powered by batteries. In this dissertation, we consider a number of challenges pertaining to these constraints: system support for energy efficiency; flash-based storage systems; programming, testing, and debugging; and safe and secure application execution. The contributions of this dissertation are made through five research papers addressing these challenges.Firstly, to enhance the system support for energy-efficient storage in resource-constrained devices, we present the design, implementation, and evaluation of the Coffee file system and the Antelope DBMS. Coffee provides a sequential write throughput that is over 92% of the attainable flash driver throughput, and has a constant memory footprint for open files. Antelope is the first full-fledged relational DBMS for sensor networks, and it provides two novel indexing algorithms to enable fast and energy-efficient database queries.Secondly, we contribute a framework that extends the functionality and increases the performance of sensornet checkpointing, a debugging and testing technique. Furthermore, we evaluate how different data compression algorithms can be used to decrease the energy consumption and data dissemination time when reprogramming sensor networks.Lastly, we present Velox, a virtual machine for IoT applications. Velox can enforce application-specific resource policies. Through its policy framework and its support for high-level programming languages, Velox helps to secure IoT applications. Our experiments show that Velox monitors applications' resource usage and enforces policies with an energy overhead below 3%.The experimental systems research conducted in this dissertation has had a substantial impact both in the academic community and the open-source software community. Several of the produced software systems and components are included in Contiki, one of the premier open-source operating systems for the IoT and sensor networks, and they are being used both in research projects and commercial products.
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- Täckström, Oscar, 1979-
(author)
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Predicting Linguistic Structure with Incomplete and Cross-Lingual Supervision
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Contemporary approaches to natural language processing are predominantly based on statistical machine learning from large amounts of text, which has been manually annotated with the linguistic structure of interest. However, such complete supervision is currently only available for the world's major languages, in a limited number of domains and for a limited range of tasks. As an alternative, this dissertation considers methods for linguistic structure prediction that can make use of incomplete and cross-lingual supervision, with the prospect of making linguistic processing tools more widely available at a lower cost. An overarching theme of this work is the use of structured discriminative latent variable models for learning with indirect and ambiguous supervision; as instantiated, these models admit rich model features while retaining efficient learning and inference properties.The first contribution to this end is a latent-variable model for fine-grained sentiment analysis with coarse-grained indirect supervision. The second is a model for cross-lingual word-cluster induction and the application thereof to cross-lingual model transfer. The third is a method for adapting multi-source discriminative cross-lingual transfer models to target languages, by means of typologically informed selective parameter sharing. The fourth is an ambiguity-aware self- and ensemble-training algorithm, which is applied to target language adaptation and relexicalization of delexicalized cross-lingual transfer parsers. The fifth is a set of sequence-labeling models that combine constraints at the level of tokens and types, and an instantiation of these models for part-of-speech tagging with incomplete cross-lingual and crowdsourced supervision. In addition to these contributions, comprehensive overviews are provided of structured prediction with no or incomplete supervision, as well as of learning in the multilingual and cross-lingual settings.Through careful empirical evaluation, it is established that the proposed methods can be used to create substantially more accurate tools for linguistic processing, compared to both unsupervised methods and to recently proposed cross-lingual methods. The empirical support for this claim is particularly strong in the latter case; our models for syntactic dependency parsing and part-of-speech tagging achieve the hitherto best published results for a wide number of target languages, in the setting where no annotated training data is available in the target language.
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- Voigt, Thiemo
(author)
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Architectures for Service Differentiation in Overloaded Internet Servers
- 2002
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Doctoral thesis (other academic/artistic)abstract
- Web servers become overloaded when one or several server resources such as network interface, CPU and disk become overutilized. Server overload leads to low server throughput and long response times experienced by the clients. Traditional server design includes only marginal or no support for overload protection. This thesis presents the design, implementation and evaluation of architectures that provide overload protection and service differentiation in web servers. During server overload not all requests can be processed in a timely manner. Therefore, it is desirable to perform service differentiation, i.e., to service requests that are regarded as more important than others. Since requests that are eventually discarded also consume resources, admission control should be performed as early as possible in the lifetime of a web transaction. Depending on the workload, some server resources can be overutilized while the demand on other resources is low because certain types of requests utilize one resource more than others. The implementation of admission control in the kernel of the operating system shows that this approach is more efficient and scalable than implementing the same scheme in user space. We also present an admission control architecture that performs admission control based on the current server resource utilization combined with knowledge about resource consumption of requests. Experiments demonstrate more than 40% higher throughput during overload compared to a standard server and several magnitudes lower response times. This thesis also presents novel architectures and implementations of operating system support for predictable service guarantees. The Nemesis operating system provides applications with a guaranteed communication service using the developed TCP/IP implementation and the scheduling of server resources. SILK (Scout in the Linux kernel) is a new networking stack for the Linux operating system that is based on the Scout operating system. Experiments show that SILK enables prioritizing and other forms of service differentiation between network connections while running unmodified Linux applications.
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| 7. |
- Österlind, Fredrik, 1981-
(author)
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Improving Low-Power Wireless Protocols with Timing-Accurate Simulation
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Low-power wireless technology enables numerous applications in areas from environmental monitoring and smart cities, to healthcare and recycling. But resource-constraints and the distributed nature of applications make low-power wireless networks difficult to develop and understand, resulting in increased development time, poor performance, software bugs, or even network failures. Network simulators offer full non-intrusive visibility and control, and are indispensible tools during development. But simulators do not always adequately represent the real world, limiting their applicability.In this thesis I argue that high simulation timing accuracy is important when developing high-performance low-power wireless protocols. Unlike in generic wireless network simulation, timing becomes important since low-power wireless networks use extremely timing-sensitive software techniques such as radio duty-cycling. I develop the simulation environment Cooja that can simulate low-power wireless networks with high timing accuracy.Using timing-accurate simulation, I design and develop a set of new low-power wireless protocols that improve on throughput, latency, and energy-efficiency. The problems that motivate these protocols were revealed by timing-accurate simulation. Timing-accurate software execution exposed performance bottlenecks that I address with a new communication primitive called Conditional Immediate Transmission (CIT). I show that CIT can improve on throughput in bulk transfer scenarios, and lower latency in many-to-one convergecast networks. Timing-accurate communication exposed that the hidden terminal problem is aggravated in duty-cycled networks that experience traffic bursts. I propose the Strawman mechanism that makes a radio duty-cycled network robust against traffic bursts by efficiently coping with hidden terminals.The Cooja simulation environment is available for use by others and is the default simulator in the Contiki operating system since 2006.
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