| 225821. |
- Nilsson Plymoth, Anders
(författare)
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Wireless Multi Hop Access Networks and Protocols
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As more and more applications and services in our society now depend on the Internet, it is important that dynamically deployed wireless multi hop networks are able to gain access to the Internet and other infrastructure networks and services. This thesis proposes and evaluates solutions for providing multi hop Internet Access. It investigates how ad hoc networks can be combined with wireless and mesh networks in order to create wireless multi hop access networks. When several access points to the Internet are available, and the mobile node roams to a new access point, the node has to make a decision when and how to change its point of attachment. The thesis describes how to consider the rapid fluctuations of the wireless medium, how to handle the fact that other nodes on the path to the access point are also mobile which results in frequent link and route breaks, and the impact the change of attachment has on already existing connections. Medium access and routing protocols have been developed that consider both the long term and the short term variations of a mobile wireless network. The long term variations consider the fact that as nodes are mobile, links will frequently break and new links appear and thus the network topology map is constantly redrawn. The short term variations consider the rapid fluctuations of the wireless channel caused by mobility and multi path propagation deviations. In order to achieve diversity forwarding, protocols are presented which consider the network topology and the state of the wireless channel when decisions about forwarding need to be made. The medium access protocols are able to perform multi dimensional fast link adaptation on a per packet level with forwarding considerations. This i ncludes power, rate, code and channel adaptation. This will enable the type of performance improvements that are of significant importance for the success of multi hop wireless networks.
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| 225822. |
- Nilsson, R. Anders, 1976-
(författare)
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Dangerous Liaisons : Why Ex-Combatants Return to Violence. Cases from the Republic of Congo and Sierra Leone
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After disarming and demobilizing, why do some ex-combatants re-engage in organized vio-lence, while others do not? Even though former fighters have been identified as a major source of insecurity in post-civil war societies due to their military know-how, there have been few efforts to systematically examine this puzzle. This study fills this research gap by comparing the presence or absence of organized violence in different ex-combatant communi-ties – all the former fighters that used to belong to the same armed faction and who share a common, horizontal identity based on shared war-and peacetime experiences. It does so by analyzing six ex-combatant communities in two countries: ex-Cobra, Cocoye and Ninja in the Republic of Congo and ex-AFRC, CDF and RUF in Sierra Leone. More specifically, three concepts – remarginalization (former fighters’ lack of political influence, personal security or economic assistance), remobilizers (individuals who have the will, capacity and skills to coordinate organized violence in a post-conflict setting) and relationships (whether or not remobilizers share social or material bonds, conducive for war, with ex-combatant communi-ties and each other) – are applied to the six cases, in order to explain why relatively many former CDF, Cobra, Ninja and RUF fighters resorted to violence, while no or hardly any ex-AFRC and Cocoye combatants did the same. Contrary to assumptions found in previous research, this study finds that structural factors, relating to remarginalization, have little ex-planatory value in themselves. Being a rule, rather than an exception, remarginalization can best be understood as a background variable, creating conducive conditions for violence to take place. Instead, the main determinants of ex-combatant violence are whether former fight-ers have access to regional or domestic elites in the market for experienced fighters and to second-tier individuals – such as former mid-level commanders – who can act as intermediar-ies between the two. By utilizing relationships based on selective incentives and social net-works, these two kinds of remobilizers are able to generate the needed enticements and feel-ings of affinity, trust or fear, to convince ex-combatants to resort to arms. These findings demonstrate that the outbreak of ex-combatant violence can only be understood by more clearly incorporating an actor perspective, focusing on three levels of analysis: the elite, mid-level and grass-root.
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| 225823. |
- Nilsson, Roland, et al.
(författare)
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A Monte Carlo Study of L1-Norm Based Measures of Model Misspecification
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Hansen and Jagannathan (1997) introduced a measure of model misspecification based on the L2-norm. It is however well-known that L1-norm methods may show good properties in the presence of non-normal distributions. In this paper we therefore introduce some L1-norm based measures of misspecification. We also provide an easy algorithm which simplifies the computation of the gain-loss ratio presented by Bernardo and Ledoit (2000). Two Monte Carlo simulations are undertaken to assess the performance of the measures under varying distributional assumptions. We provide evidence that L1-norm based measures tend to perform better in small and non-normally distributed samples.
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| 225824. |
- Nilsson, Robert, 1977-
(författare)
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A Mutation-based Framework for Automated Testing of Timeliness
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A problem when testing timeliness of event-triggered real-time systems is that response times depend on the execution order of concurrent tasks. Conventional testing methods ignore task interleaving and timing and thus do not help determine which execution orders need to be exercised to gain confidence in temporal correctness. This thesis presents and evaluates a framework for testing of timeliness that is based on mutation testing theory. The framework includes two complementary approaches for mutation-based test case generation, testing criteria for timeliness, and tools for automating the test case generation process. A scheme for automated test case execution is also defined. The testing framework assumes that a structured notation is used to model the real-time applications and their execution environment. This real-time system model is subsequently mutated by operators that mimic potential errors that may lead to timeliness failures. Each mutated model is automatically analyzed to generate test cases that target execution orders that are likely to lead to timeliness failures. The validation of the theory and methods in the proposed testing framework is done iteratively through case-studies, experiments and proof-of-concept implementations. This research indicates that an adapted form of mutation-based testing can be used for effective and automated testing of timeliness and, thus, for increasing the confidence level in real-time systems that are designed according to the event-triggered paradigm.
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| 225825. |
- Nilsson, Roland
(författare)
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A Study of Propane and Propene Ammoxidation over Antimony-Vanadium-Oxide Catalysts at Steady-State and Transient Conditions
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Propane ammoxidation catalysts of differing Sb/V ratio and consisting of differing amounts of the V2O5, alpha-Sb2O4, and Sb0.92V0.92O4 phases were prepared. In the first paper, the structure of Sb0.92V0.92O4 was determined by thermogravimetry, X-ray microanalysis, X-ray powder diffraction, and neutron powder diffraction. Sb0.92V0.92O4 was found to have a defective rutile structure involving cation vacancies. In the second, third, and fourth papers, the initial rates and selectivities of these catalysts were determined when used in the ammoxidation of propane and propene, respectively. The main products obtained in propane ammoxidation were acrylonitrile, acetonitrile, carbon oxides and propene. Two synergy effects were revealed; catalysts rich in vanadium showed a maximum in total reaction rate and catalysts rich in antimony a maximum in selectivity to acrylonitrile formation. The main products obtained in propene ammoxidation were acrylonitrile, acetonitrile, carbon oxides and acrolein. The catalysts were characterised by XRD, XPS, FTIR, and FT-Raman measurements before and after their use in propane and propene ammoxidation, respectively. In the course of ammoxidation, catalysts with an excess of alpha-Sb2O4 were found to be enriched at the surface with antimony, creating a surface that was selective for nitrile formation. This enrichment appeared to be caused by the migration of antimony from alpha-Sb2O4 to the surface of Sb0.92V0.92O4. No evidence that antimony migrates from the bulk of Sb0.92V0.92O4 up to the surface of it was obtained. The fifth and sixth papers concerned the transient response method. Differential equations describing the consumption of reactants and the formation of products were solved numerically for a step change from inert to reactant feed. Different types of propene/propane oxidation/ammoxidation mechanisms were considered. In comparing the experimental and the simulated responses, it was found that the adsorption of propane was rate limiting for its consumption in the ammoxidation of it. However, the propene/acrylonitrile product ratio was governed by the step in which water desorbs. These results were not contradicted by the results reported in paper four, in which dependencies of the rate on the partial pressure of the reactants was investigated under steady-state conditions.
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| 225826. |
- Nilsson, Robert
(författare)
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A study of the molecular pathways of wood formation using peptide mass spectrometry
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood consists essentially of secondary plant cell walls, composed of a cellulose and hemicellulose network impregnated with lignin. It is formed via the development of derivatives of a thin layer of cells (the vascular cambium) into xylem cells through cell division, expansion, secondary wall formation, lignification and, finally, programmed cell death. Throughout the formation of the resulting, complex matrix (wood) diverse proteins are involved. Hence, biosynthesis of wood is tightly regulated at the molecular level, primarily by transcriptional regulation, together with various post-transcriptional processes. In the studies this thesis is based upon, a key technique for studying proteins, liquid chromatography coupled to mass spectrometry, was used to elucidate pathways of wood formation. First, proteins involved in the central transcriptional unit Mediator, regulating most essential processes in plants, were identified in arabidopsis. Mediator subunits that most likely provide secondary cell wall activity are differentiated paralogous subunits located in the tail part of the complex. Point mutations in the Mediator tail subunit, Med5#2 affect secondary cell wall lignification. Moreover, control of xylem expansion may be indirectly regulated by Med25. A strategy to integrate transcript-, protein- and metabolite-data was then developed, using data acquired from analyses of poplar mutants with perturbed wood development. The results showed that lignin biosynthesis is heavily affected at both transcript and protein levels in the mutant with the strongest phenotypic deviations. Interestingly, when transcript levels are decreased, the protein levels are increased. Finally, the front of cell wall synthesis at poplar plasma membranes was dissected. A high coverage of proteins known to be involved in the cell wall synthesizing machinery and associated components was captured, as well as several potential new ones.
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| 225827. |
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| 225828. |
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| 225829. |
- Nilsson, Robin, 1993
(författare)
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An Investigation of Mixed Cellulose Esters and Acyclic Polyacetates: Effects of Side-Chain Lengths and Degrees of Ring-Opening
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bio-based polymers produced from natural sources are gaining an increased interest as potential replacement for today’s conventional fossil-based plastic polymers. Their use is already wide in many large-scale industrial areas such as healthcare, personal care, and food. To widen the potential of biopolymers in new applications such as plastics, their properties need to be tuned by modification to handle factors like relative humidity, which is especially important for gas barriers in food packaging. This thesis explores the effect of two structural variations of cellulose esters, one where the average side-chain length is increased, going from cellulose acetate to cellulose acetate propionate and then cellulose acetate butyrate, and another where the polymer backbone of cellulose acetate is ring-opened. These two modifications affect the glass transition temperature, an important structural factor. The effect of the average side-chain length is explored to a greater extent where they are studied for impact on mechanical properties, water content, water sorption at different RH, the kinetics of water sorption at different RH, mechanical properties at different RH and oxygen permeation at different RH. The focus is on how water interacts with the different esters with regard to the average side-chain length and how water affects their properties. An increase of average sidechain length and the ring-opening were shown to decrease the glass transition temperature. Together with the water sorption and Hansen solubility parameter, it was concluded that longer average side-chain length screens out hydrogen bonding between the polymers. The studies on the average side-chain length and water sorption indicated that water entering the cellulose acetate creates clusters. These formed water clusters create cavities in the polymer which makes the polymer hold more water than before introducing of the water clusters. Oxygen permeation studies on prewetted films prove that these cavities created by water clustering are still present after drying the material at 0% RH and thus resulted in a higher oxygen permeation compared to films that had not been exposed to higher than 50% RH.
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| 225830. |
- Nilsson, Rickard
(författare)
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Analysis of path-losses along the Kankberg tunnel with comparisons between LTE measurements and radio-channel measurements : A report to the PIMM project
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report we present evaluations of path-losses along the 1 km long, and almost straight, tunnel-ramp located in the Kankberg underground mine outside Boliden, Sweden. From nine different LTE measurements along the ramp in the 1800 MHz frequency band in front of the mRRU antenna and when no vehicle is obstructing the signal path, the estimated path-loss exponents range between n = 1:40 and n = 2:19. When a large vehicle obstructs the signal path the estimated path-loss exponents from seven dierent measurements vary between n = 2:00 and n = 2:52. These values match quite well with an estimated path-loss exponent of n = 2:1 for corresponding, but quite differently measured, radio-channel measurements at1900 MHz. Behind the mRRU antenna, where the power is radiated in a much wider angle in the tunnel than in front of the antenna, the estimated path-loss coeffcients are much higher and vary between n = 4:4 and 5:2. Because of the relatively low attenuation measured in front of the antennas there is likely a wave-guide effect in the tunnel, even at these 1800/1900 MHz frequencies. A hypothesis is presented in Section 5 about how the waveguide effect is generated in the tunnel due to the antenna directivity, which is supported by the measurements.
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