| 1. |
- Abrahamsson, Henrik
(författare)
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Network overload avoidance by traffic engineering and content caching
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Internet traffic volume continues to grow at a great rate, now driven by video and TV distribution. For network operators it is important to avoid congestion in the network, and to meet service level agreements with their customers. This thesis presents work on two methods operators can use to reduce links loads in their networks: traffic engineering and content caching.This thesis studies access patterns for TV and video and the potential for caching. The investigation is done both using simulation and by analysis of logs from a large TV-on-Demand system over four months.The results show that there is a small set of programs that account for a large fraction of the requests and that a comparatively small local cache can be used to significantly reduce the peak link loads during prime time. The investigation also demonstrates how the popularity of programs changes over time and shows that the access pattern in a TV-on-Demand system very much depends on the content type.For traffic engineering the objective is to avoid congestion in the network and to make better use of available resources by adapting the routing to the current traffic situation. The main challenge for traffic engineering in IP networks is to cope with the dynamics of Internet traffic demands.This thesis proposes L-balanced routings that route the traffic on the shortest paths possible but make sure that no link is utilised to more than a given level L. L-balanced routing gives efficient routing of traffic and controlled spare capacity to handle unpredictable changes in traffic. We present an L-balanced routing algorithm and a heuristic search method for finding L-balanced weight settings for the legacy routing protocols OSPF and IS-IS. We show that the search and the resulting weight settings work well in real network scenarios.
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| 2. |
- Afshari, Alireza, 1956
(författare)
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Determination of VOC Emissions from Surface Coatings by Environmental Test Chamber Measurements
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emitting properties of different building materials are obtained by measurements in environmental chambers of a few established designs. In order to interpret the results from the measurements and to predict the influence on the indoor environment, it is necessary to have a good understanding of the parameters governing the emission process. The aim of this thesis is to contribute to this understanding by focusing on the process of emission of chemicals from building materials and on the influence of a number of parameters governing the process. In emission studies reported in the literature, few investigations deal with the comparison of the VOC emission rates obtained by measurements in different test chambers. In the present study, a 1m3-chamber, a CLIMPAQ and a FLEC were used for measurement of the concentrations of various compounds from surface coatings. The study focuses on parameters which could be considered to have a substantial influence on the emission rates, or which do not appear to have been thoroughly studied previously. Interest has mainly been focused on the influence of air velocity, airflow rate and sorption on the emission rate, when other parameters have been maintained constant. It was found that during the first 24 hours, by varying the airflow rate under given test conditions in a test chamber, a number of physical parameters have a direct influence on the emission process. From the start of the test until steady state has been reached, the measured concentration variations may be divided into three different phases. The results from measurements showed that the higher the airflow rates, the faster a steady state was attained. Furthermore, all the selected substances did not reach steady state at the same time during the experiments. The effect of the air velocity above the surface on the emission of VOCs was studied in the three mentioned environmental chambers. It was found that the emission rates of the compounds at 22, 23 and 24 hours after the start of the test systematically increase with increasing air velocity. It was possible to determine the magnitude of increase to 10-20%. However, it was difficult to determine the exact level of increase of the emission rate, due to the uncertainty of the measurements and the low levels of increase. Finally, the characterisation of adsorption of VOCs on the inside of the empty chambers has been studied. The experimental studies for all three chambers show that the sorption of substances in the 1 m3-chamber was slightly lower than in the FLEC. The CLIMPAQ shows a larger capacity of sorption with material specimens than without material specimens. This indicates that the gases emitted from painted plates adsorb again onto the test materials.
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| 4. |
- Al-Shishtawy, Ahmad, 1978-
(författare)
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Self-Management for Large-Scale Distributed Systems
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Autonomic computing aims at making computing systems self-managing by using autonomic managers in order to reduce obstacles caused by management complexity. This thesis presents results of research on self-management for large-scale distributed systems. This research was motivated by the increasing complexity of computing systems and their management.In the first part, we present our platform, called Niche, for programming self-managing component-based distributed applications. In our work on Niche, we have faced and addressed the following four challenges in achieving self-management in a dynamic environment characterized by volatile resources and high churn: resource discovery, robust and efficient sensing and actuation, management bottleneck, and scale. We present results of our research on addressing the above challenges. Niche implements the autonomic computing architecture, proposed by IBM, in a fully decentralized way. Niche supports a network-transparent view of the system architecture simplifying the design of distributed self-management. Niche provides a concise and expressive API for self-management. The implementation of the platform relies on the scalability and robustness of structured overlay networks. We proceed by presenting a methodology for designing the management part of a distributed self-managing application. We define design steps that include partitioning of management functions and orchestration of multiple autonomic managers.In the second part, we discuss robustness of management and data consistency, which are necessary in a distributed system. Dealing with the effect of churn on management increases the complexity of the management logic and thus makes its development time consuming and error prone. We propose the abstraction of Robust Management Elements, which are able to heal themselves under continuous churn. Our approach is based on replicating a management element using finite state machine replication with a reconfigurable replica set. Our algorithm automates the reconfiguration (migration) of the replica set in order to tolerate continuous churn. For data consistency, we propose a majority-based distributed key-value store supporting multiple consistency levels that is based on a peer-to-peer network. The store enables the tradeoff between high availability and data consistency. Using majority allows avoiding potential drawbacks of a master-based consistency control, namely, a single-point of failure and a potential performance bottleneck.In the third part, we investigate self-management for Cloud-based storage systems with the focus on elasticity control using elements of control theory and machine learning. We have conducted research on a number of different designs of an elasticity controller, including a State-Space feedback controller and a controller that combines feedback and feedforward control. We describe our experience in designing an elasticity controller for a Cloud-based key-value store using state-space model that enables to trade-off performance for cost. We describe the steps in designing an elasticity controller. We continue by presenting the design and evaluation of ElastMan, an elasticity controller for Cloud-based elastic key-value stores that combines feedforward and feedback control.
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| 5. |
- Almeida Costa, Nicole, 1988
(författare)
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Human-centred design for maritime technology and organizational change
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Context: The shipping industry is undergoing a transitional phase at different levels, including IMO’s e-Navigation initiative, and with this comes the need to use a human-centred design (HCD) approach to avoid accidents linked to automation issues, and to cater for the maintenance of safety and efficiency within this global transport system. Aims: The aim of this thesis is to investigate the value and challenges in HCD practice and how ergonomics/human factors (E/HF) principles can be introduced, as well as what gaps and opportunities exist in current standard operations and technologies in navigation that can potentially be followed upon by future e-Navigation developments, not only from a technological perspective but also regulatory, operational etc. Methods: This thesis derives from the work of six appended articles that mainly utilized a qualitative approach to data collections, including focus groups, interviews and observations, and to data analyses, such as narratives and a grounded theory approach. In total, two design teams and four separate sets of onboard and shore-based operators were consulted for data collection. Results: The results from the appended papers suggest that user involvement in design as well as in rule making and purchasing of new ship equipment was perceived as important for a good work environment, and efficient and safe operations onboard in this safety-critical industry. The results show that design projects are situated experiences that involve complex tasks and resource management, and that require re-iterative adaptations throughout the process. In involving the users and implementing E/HF methods, support from the management is needed and professional E/HF expertise should be a part of the team to help interpret E/HF methods and guide the process to foster continuous knowledge sharing within the team, the organization and with the users from an early stage. When investigating current operations and technologies in navigation, it was evident that gaps exist that can be improved by the redesign of current technologies or the implementation of novel e-Navigation solutions. For example, there is a large number of unintegrated systems and information sources today, and everyday routines and information across geographical areas and communication channels are not unified. Technology concepts and developments towards the e-Navigation principles have been considerably debated, yet there are still gaps that can be filled, and despite e-Navigation’s principle for HCD, the holistic – macro – perspective of the development of these new technologies seems to be under-exploited. Conclusions: Filling the existing gaps with available novel technologies is not enough to guarantee efficiency and safety in the domain, nor to guarantee acceptance. A more systemic perspective is needed, of how the different people and processes in the sea transport system can be affected by the introduction of new technology in terms of how work is performed, of regulations, new training and re-skilling, as well as of preparation for new issues that may arise with increased automation such as workload and cyber-security. This work points at the value and practice of E/HF and systems-driven design, and directs it at change makers and opinion leaders: designers, managers, rule-makers, educators, to consider the human element for safety and efficiency. In this transitional stage, one of the great values of E/HF is to more proactively prepare the shipping industry for the ongoing e-Navigation changes rather than having the industry adapt operations, regulations, training and plan the sustainability of the transport system ad hoc after technology implementation.
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| 6. |
- Amiryarahmadi, Nata
(författare)
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A Virtual Design Studio for Low-Frequency Sound from Walking in Lightweight Buildings
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years there has been a growing interest for building lightweight multistorey woodenresidential buildings in countries like Sweden with large and renewable forests. While positive aspectsof these buildings, such as sustainability, ease of construction and lightness, motivate building more inwood, poor acoustic performance is a risk which concerns the wooden-building industry.Low-frequency impact sound from walking of the neighbors upstairs is the main source of complaintsabout the acoustic performance of these buildings. The disturbance caused by walking sounds,transmitted through lightweight wooden floors, results in acoustic discomfort and impairs theperceived quality of the building; sometimes even when the building has fulfilled an acoustic classhigher than minimum requirement, according to the national standard on sound classification and itssingle number ratings. The standard methods for objective evaluation of impact sound insulation offloors cannot predict, at a satisfactory level, the walking sound annoyance that the inhabitants ofwooden buildings experience. This causes an uncertainty about the resulting perceived quality of thesebuildings, which greatly concerns the building manufacturers and demotivates them from choosinglightweight wooden elements over heavyweight building materials such as concrete. This uncertaintycan be overcome by evaluating the perceived acoustic quality of the building prior to its construction.One solution is to build test houses where the subjective acoustic performance of floor samples can beevaluated in advance to the building construction. However, building a test house is expensive;besides, for evaluating the effect of every design modification on the experienced acoustic comfort ofthe building, a real floor sample has to be built and installed in the house, which would be timeconsumingand costly. An alternative solution is to use virtual acoustic test facilities.In this thesis a virtual design studio for impact sound is developed. It is a tool that facilitates creatingand listening to the acoustic field generated by impact forces such as footsteps on lightweight floors. Italso provides the possibility to evaluate the acoustic performance of floor elements in an early designphase, and to investigate the correlation between design parameters and the perceived impact soundinsulation of the floor. The tool is demonstrated and a very first listening test shows that one can obtainresults which are in good agreement with the results in literature. Loudness, reverberation andthumping are shown to influence the annoyance. It is also shown that there is a difference in judgementof walking sounds by persons who have experience with lightweight floors at home and by those whodo not have that experience.
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| 7. |
- Amvrosiadi, Nino
(författare)
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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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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 8. |
- Andersson, Johnn, 1983
(författare)
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Shape it until you make it: A conceptual foundation for efforts to analyze and shape technological innovation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- These are times of accelerating climate change and mass extinction of species on planet Earth. We are in the midst of an ecological crisis that will have profound consequences for human society and its natural environment. While the conditions for life have changed abruptly in the past, the current situation is characterized by the increasing power of a single species. Human beings are not only to blame for the unsustainable practices that brought us here, but also capable of harnessing their combined ingenuity to develop technology that may reduce environmental impacts and provide additional benefits for society. At the same time, the answer to the ecological crisis and other grand challenges is not found in the blind expansion of new technologies. Our success in accomplishing social and environmental objectives rather depends on how, where and when innovation influences patterns of production and consumption. This calls into question the focus of academics and policymakers on stimulating technological innovation. And it highlights the need for analytical tools that can be used to explore how policymakers and other actors may shape the direction of change. The research presented in this thesis therefore aims to develop a conceptual foundation for analyzing and shaping technological innovation. This effort draws on three qualitative case studies that investigate emerging renewable energy technologies from a Swedish perspective. The thesis is situated in the sustainability transitions research community and takes the literature on technological innovation systems as a theoretical point of departure. However, the research adopts a critical perspective and gradually departs from the core concepts used in this literature, over the course of a learning process that unfolds in five appended research papers. In the end, the thesis proposes the technological systems framework as a set of concepts that offers a multidimensional perspective on the dynamics and outcomes of technological innovation. It also presents empirical findings that demonstrate different development trajectories, reveal some of their underlying dynamics and highlight policy implications. This will hopefully contribute to an ongoing shift in academia and politics – from stimulating the expansion of new technologies, to shaping the direction of change.
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| 9. |
- Arad, Cosmin Ionel, 1981-
(författare)
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Programming Model and Protocols for Reconfigurable Distributed Systems
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Distributed systems are everywhere. From large datacenters to mobile devices, an ever richer assortment of applications and services relies on distributed systems, infrastructure, and protocols. Despite their ubiquity, testing and debugging distributed systems remains notoriously hard. Moreover, aside from inherent design challenges posed by partial failure, concurrency, or asynchrony, there remain significant challenges in the implementation of distributed systems. These programming challenges stem from the increasing complexity of the concurrent activities and reactive behaviors in a distributed system on the one hand, and the need to effectively leverage the parallelism offered by modern multi-core hardware, on the other hand.This thesis contributes Kompics, a programming model designed to alleviate some of these challenges. Kompics is a component model and programming framework for building distributed systems by composing message-passing concurrent components. Systems built with Kompics leverage multi-core machines out of the box, and they can be dynamically reconfigured to support hot software upgrades. A simulation framework enables deterministic execution replay for debugging, testing, and reproducible behavior evaluation for largescale Kompics distributed systems. The same system code is used for both simulation and production deployment, greatly simplifying the system development, testing, and debugging cycle.We highlight the architectural patterns and abstractions facilitated by Kompics through a case study of a non-trivial distributed key-value storage system. CATS is a scalable, fault-tolerant, elastic, and self-managing key-value store which trades off service availability for guarantees of atomic data consistency and tolerance to network partitions. We present the composition architecture for the numerous protocols employed by the CATS system, as well as our methodology for testing the correctness of key CATS algorithms using the Kompics simulation framework.Results from a comprehensive performance evaluation attest that CATS achieves its claimed properties and delivers a level of performance competitive with similar systems which provide only weaker consistency guarantees. More importantly, this testifies that Kompics admits efficient system implementations. Its use as a teaching framework as well as its use for rapid prototyping, development, and evaluation of a myriad of scalable distributed systems, both within and outside our research group, confirm the practicality of Kompics.
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| 10. |
- Ardelius, John, 1978-
(författare)
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On the Performance Analysis of Large Scale, Dynamic, Distributed and Parallel Systems.
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Evaluating the performance of large distributed applications is an important and non-trivial task. With the onset of Internet wide applications there is an increasing need to quantify reliability, dependability and performance of these systems, both as a guide in system design as well as a means to understand the fundamental properties of large-scale distributed systems. Previous research has mainly focused on either formalised models where system properties can be deduced and verified using rigorous mathematics or on measurements and experiments on deployed applications. Our aim in this thesis is to study models on an abstraction level lying between the two ends of this spectrum. We adopt a model of distributed systems inspired by methods used in the study of large scale system of particles in physics and model the application nodes as a set of interacting particles each with an internal state whose actions are specified by the application program. We apply our modeling and performance evaluation methodology to four different distributed and parallel systems. The first system is the distributed hash table (DHT) Chord running in a dynamic environment. We study the system under two scenarios. First we study how performance (in terms of lookup latency) is affectedon a network with finite communication latency. We show that an average delay in conjunction with other parameters describing changes in the network (such as timescales for network repair and join and leave processes)induces fundamentally different system performance. We also verify our analytical predictions via simulations.In the second scenario we introduce network address translators (NATs) to the network model. This makes the overlay topology non-transitive and we explore the implications of this fact to various performance metrics such as lookup latency, consistency and load balance. The latter analysis is mainly simulation based.Even though these two studies focus on a specific DHT, many of our results can easily be translated to other similar ring-based DHTs with long-range links, and the same methodology can be applied evento DHT's based on other geometries.The second type of system studied is an unstructured gossip protocol running a distributed version of the famous Belman-Ford algorithm. The algorithm, called GAP, generates a spanning tree over the participating nodes and the question we set out to study is how reliable this structure is(in terms of generating accurate aggregate values at the root) in the presence of node churn. All our analytical results are also verified using simulations.The third system studied is a content distribution network (CDN) of interconnected caches in an aggregation access network. In this model, content which sits at the leaves of the cache hierarchy tree, is requested by end users. Requests can then either be served by the first cache level or sent further up the tree. We study the performance of the whole system under two cache eviction policies namely LRU and LFU. We compare our analytical results with traces from related caching systems.The last system is a work stealing heuristic for task distribution in the TileraPro64 chip. This system has access to a shared memory and is therefore classified as a parallel system. We create a model for the dynamic generation of tasks as well as how they are executed and distributed among the participating nodes. We study how the heuristic scales when the number of nodes exceeds the number of processors on the chip as well as how different work stealing policies compare with each other. The work on this model is mainly simulation-based.
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