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- Klintenberg, Patrik
(författare)
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More Water, Less Grass? : An assessment of resource degradation and stakeholders’ perceptions of environmental change in Ombuga Grassland, Northern Namibia
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objectives of this thesis are to assess: to what degree have natural resources deteriorated in a grazing area in northern Namibia, how do perceptions of environmental change held by local stakeholders there, correspond to scientific assessments, and how do these relate to national estimates? Analysis of the process of developing national indicators for monitoring of land degradation concluded that specific indicators should be developed on national level, and in some instances even on local level as there are no universal causes of land degradation. According to farmers overgrazing and low rainfall since the early 1990s cause negative environmental changes in the study area, partly confirming findings from national monitoring. Results also suggest that: less grazing outside the study area, improved access, permanent water supply, and fencing of large areas, also contributed. Results show that improved water supply was the most important factor. Investigation of the influence of permanent water points on grazing resources showed that perennial grasses are replaced by less palatable annual grasses as far as 6 km from water points along a water pipeline. No significant grazing induced changes in grass composition were observed around privately owned wells. Private ownership seems to be a key factor preventing over-utilization of grazing resources around the latter. A remote sensing study using Landsat TM imagery identified bare ground, saltpans and grassland with a fair accuracy. Separation of woodland from shrubland and shrubland from grassland was less accurate using supervised classification. The results show that the soil adjusted vegetation index provides valuable information about variations of green biomass over time in semi-arid environments. However, it is suggested that satellite based investigations should be supported by thorough ground based assessment due to the influence of underlying soil in this environment.
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- Chen, Lei, et al.
(författare)
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Utvärdering av samhällsnyttan med C-ITS
- 2024
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Ingår i: Sammanställning av referat från Transportforum 2024. - Linköping : Statens väg- och transportforskningsinstitut. ; , s. 66-67
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Det råder enighet om att kooperativa intelligenta transportsystem (C-ITS) kan medföra samhällsnyttor, eftersom det ger en förbättrad informationskvalitet och servicenivå för trafikanter, transportoperatörer, vägmyndigheter och beslutsfattare. Det återstår dock en utmaning att kvantifiera effekterna av C-ITS. På grund av bristen på storskaliga implementeringar under verkliga trafikförhållanden har vi dock en begränsad förståelse för vilka faktorer som påverkar effekterna av C-ITS. Till exempel har verkligheten inga konstanta förhållanden, vilket gör det svårt att jämföra situationerna före och efter en mätning. Pilotprojekt där användningsfall av ny teknik testas är ofta lokaliserade experiment med låg användarpenetration, vilket gör det svårt att isolera effekterna av tillämpningar, särskilt när effekterna är relativt små. Som en del av Nordic Way 3 projektet för att påskynda implementeringen av C-ITS utvecklar vi en metod för att utvärdera samhällsnyttor relaterade till trafiksignaler, som vi tillämpar på användningsfall i kommunerna Göteborg, Uppsala och Stockholm. För att anpassa trafikstyrningen till hållbara mobilitetsmål måste effekterna förstås i olika implementeringsscenarier, med realistiska beteendealternativ. De avgörande förutsättningarna för framgången med C-ITS implementeras i en simulering för att undersöka sambandet mellan olika C-ITS applikationer och motsvarande beteendeförändringar. De samhälleliga effekterna, i kombination med kostnaderna för C-ITS, används i kostnads-nyttoanalys för att stödja beslutsfattandet.Vi skapade en digital tvilling som kombinerar verklig programvara för trafiksignalering och lade till C-ITS-funktioner för att experimentera med dynamik såsom antalet förare som kan få råd (penetrationsgrad) och hur de använder informationen (beteende) samtidigt som vi beaktar den förväntade beteendeförändringen. Genom att utforska olika signalinställningar i Uppsala och Göteborg fann vi att effekten av GLOSA (Green Light Optimized Speed Advisory) är mest betydande när den implementeras med förutsägbara faslängder (fastställda tidssignalplaner). Fordonsstyrda signaloperationer har osäkra signaltider, vilket innebär att den tillförlitliga tidsschema inte är tillgänglig. Med nuvarande signaldrift kommer GLOSA därför sannolikt inte att ha någon positiv påverkan och kan till och med försämra trafikprestandan.
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| 5. |
- Cao, Haiping, 1972-
(författare)
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Characteristics of cast magnesium alloys : microstructures, defects and mechanical properties
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnesium is the lightest of all structural metals. As such, and combined with good mechanical and physical properties, it forms the basis for commercial alloys that have found successful use in a wide variety of applications. The work presented in this thesis has aimed to investigate the characteristics of microstructures and defects in cast magnesium alloys, as well as how they influence the mechanical properties.The microstructural features of binary Mg-Al alloys with various Al concentrations were investigated under a range of cooling conditions. The experiments were done by using a gradient solidification technique to achieve homogeneous and nearly defectfree magnesium alloy specimens, through which the isolated effect of microstructural parameters on the mechanical properties could be evaluated. Some models were developed to describe the relationships between the microstructure and mechanical properties in the Mg-Al alloys. In this work, it was also found that the mechanical properties of cast Mg components were affected by some non-structural factors. It is proposed that mould constraints in the die during cooling can have a significant effect on the yield strength of die-cast magnesium components.Investigations were also done concerning the characteristics of the microstructure, especially the so called pre-solidified crystals, as well as two common defects, segregation bands and hot-tears, in die-cast Mg components. The effects of process parameters on the formation of the microstructure and these defects were thoroughly investigated in some high pressure die cast commercial components. Applying a high intensification pressure was found to have a strong effect in minimizing the segregation band formation, however at the same time promoting the formation of hot tears. A new theory describing the mechanisms for segregation band formation is proposed. The theory was confirmed by simulations of solidification process during die casting, and by experimental verification. The tensile stresses built up in the residual liquid due to the solidification (and cooling) shrinkage of the casting, which causes a pressure drop and viscous flow of enriched liquid inside the mushy zone, is believed to be the main reason for segregation band formation.In order to be able to produce premium quality and cost effective Mg components, a new semi-solid casting process was developed. The process, called Rapid Slurry Forming (RSF), is based on a rapid but precise control of the enthalpy of the metal, thereby permitting the operator to obtain the desired solid fraction in the slurry. By using this process, large amounts of high quality semi-solid slurry can be produced in some minutes. This new technology opens up possibilities for producing Mgcomponents with well described microstructures, low defect contents and good mechanical properties.
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| 8. |
- Weerasekara, Manoja, et al.
(författare)
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Design Practices and Implications in Information and Communication Technology Supported Occupational Stress Management Interventions
- 2019
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Ingår i: 2019 International Conference on Advanced Computer Science and information Systems (ICACSIS). - : IEEE. - 9781728152936 - 9781728152929 ; , s. 285-294
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Konferensbidrag (refereegranskat)abstract
- Information and communication technology (ICT) supported occupational stress management interventions are considered as an effective way of treating stress-related complications. Digital healthcare, including both e-health and m-health, is provided by a diverse ecosystem of actors that aims at contributing to better health of people. The development of such technological interventions is considered as an emerging area with a unique set of constraints and design concerns. However, to increase the likelihood of success of implementing ICT supported interventions for occupational stress management, it is essential to conduct a detailed analysis of the design practices and implications related to prior studies. Thus, the proposed systematic literature review based on qualitative content analysis encapsulates the knowledge gained from existing design and development efforts in the area of ICT supported occupational stress management interventions. Knowledge incorporates design characteristics and methodological implications concerning the evaluation of the design. Further, practical limitations to yield optimum efficacy levels of ICT supported stress interventions are also discussed. A systematic review of publications in four databases (PsycINFO, Scopus, Web of Science and MEDLINE) was carried out using broad search queries. The search strategy yielded 985 unique citations. Of those, this paper presents details relevant to 31 assessed full-text publications selected during the search process. The review showed a variety of interventional platforms, health outcomes and intervention usage measurements. Various modalities of human-and machine-based support and interactions were also identified in the analysis along with several study limitations. The findings of this review may offer insights for IT professionals working in design and implementation of ICT supported stress management interventions and to researchers involved in designing and evaluating ICT supported interventions.
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| 9. |
- Zhang, Kewei, et al.
(författare)
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On the effects of distance-decreasing attacks on cryptographically protected GNSS signals
- 2019
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Ingår i: ION 2019 International Technical Meeting Proceedings. - : Institute of Navigation. - 0936406216 - 9780936406213 ; , s. 363-372, s. 363-372
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Konferensbidrag (refereegranskat)abstract
- The security of global navigation satellite systems draws attention increasingly, and authentication mechanisms for civilian services seem very effective in thwarting malicious behavior. For example, the Galileo E1 Open Service introduces navigation message authentication. Authentication, as well as encryption at navigation message or spreading code level, can prevent spoofing attacks, but do not preclude replay attacks. In this work, we consider a type of strong replay attacks, distance-decreasing attacks, against cryptographically protected GNSS signals. Distance-decreasing attack enhance an attacker's capability of allowing it to mislead the victim receiver that the GNSS signals arrive earlier than true signals. We analyze the instantiation and the effects of the distance-decreasing attacks on unprotected GNSS signals, on navigation message authenticated signals, and on spreading-code encrypted signals. We discuss different strategies that the attacker can adopt to introduce the least bit errors to the re-transmitted signals and avoid being detected at the victim receiver. We provide evaluation results of distance-decreasing attacks on unprotected signals and authenticated navigation message signals, based on different strategies and configurations, and we sketch countermeasures to the different strategies.
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| 10. |
- Zhang, Longbin, et al.
(författare)
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Adaptive Neural Network Control for a Lower-Limb Exoskeleton using Variable Stiffness Transferring
- 2020
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Ingår i: Proceedings ICARM 2020 - 2020 5th IEEE International Conference on Advanced Robotics and Mechatronics. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 240-245
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Konferensbidrag (refereegranskat)abstract
- Lower-limb exoskeletons are increasingly used in gait assistance applications to assist patients with locomotive disorders in rehabilitation and daily life. To provide assistance based on the user's variable joint stiffness with human-like characteristics is a growing and challenging field. This paper proposed an adaptive controller for a lower-limb exoskeleton with time-varying delay using variable stiffness transferring strategy. Neural network compensation was applied to estimate the nonlinearity caused by the time-varying delay and the model uncertainties in the lower-limb exoskeleton systems. To compensate for the delay, an integral Lyapunov function was introduced and an adaptive Lyapunov-based control structure was constructed. In the controller design, a variable stiffness transferring strategy was integrated and the stiffness was transferred from an able-bodied individual estimated with muscle forces and musclotendinous stiffness. By utilizing the proposed adaptive neural network control strategy and adaptive Lyapunov-based control structure, the global stability of lower-limb exoskeleton system was guaranteed and the tracking errors converged to the zero. The proposed control strategy was validated on 2-DOFs knee and ankle lower limb exoskeleton in simulation, demonstrating effective results in trajectories tracking, and thus is crucial for determining strategies for exoskeleton control.
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