| 1. |
- Mogren, Olof, 1980, et al.
(författare)
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Adaptive Dynamics of Realistic Small-World Networks
- 2009
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Ingår i: European Conference on Complex Systems 2009.
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Konferensbidrag (refereegranskat)abstract
- Continuing in the steps of Jon Kleinberg’s and others celebrated work on decentralized search, we conduct an experimental analysis of destination sam- pling, a dynamic algorithm that produces small-world networks. We find that the algorithm adapts robustly to a wide variety of situations in realistic geographic net- works with synthetic test data and with real world data, even when vertices are unevenly and non-homogeneously distributed. We investigate the same algorithm in the case where some vertices are more popular destinations for searches than others, for example obeying power-laws. We find that the algorithm adapts and adjusts the networks ac- cording to the distributions, leading to improved per- formance. The ability of the dynamic process to adapt and create small worlds in such diverse settings suggests a possible mechanism by which such networks appear in nature.
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| 2. |
- Verendel, Vilhelm, 1980, et al.
(författare)
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An Approach to using Honeypots in In-Vehicle Networks
- 2008
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Ingår i: 68th Semi-Annual IEEE Vehicular Technology, VTC 2008-Fall, Conference; Calgary, AB; Canada; 21 September 2008 through 24 September 2008. - 1550-2252. - 9781424417223
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Konferensbidrag (refereegranskat)abstract
- An emerging trend among automobile manufacturers is to introduce wireless technology in the vehicles. By allowing wireless communication, real-time information exchange between vehicles as well as between infrastructure and vehicles becomes a reality. This communication allows for road condition reporting, decision making, and remote diagnostics and firmware updates over-the-air, creating a complex critical infrastructure involving vehicles, road-side equipment, and firmware issuers. Allowing external parties wireless access to the vehicle creates a potential entry-point for cyber attacks. Since the safety of the driver depends on correct vehicle operation it is of utmost importance that the in-vehicle network is sufficiently protected against attacks. If we can learn the attackers' preferences, techniques, and weaknesses in existing systems, we can use this information to design security solutions for the in-vehicle network. In this paper, we present and discuss the use of honeypots as a means of collecting such attacker information. We show how to design a vehicle honeypot, how to gather data from attackers, and discuss how to process and analyze the gathered data. Furthermore, we provide a discussion where we highlight important issues related to using honeypots in vehicles.
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| 3. |
- Bolin, David, 1983, et al.
(författare)
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Functional ANOVA modelling of pedestrian counts on streets in three European cities
- 2021
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Ingår i: Journal of the Royal Statistical Society. Series A, (Statistics in Society). - : Oxford University Press (OUP). - 1467-985X .- 0964-1998. ; 184:4, s. 1176-1198
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Tidskriftsartikel (refereegranskat)abstract
- The relation between pedestrian flows, the structure of the city and the street network is of central interest in urban research. However, studies of this have traditionally been based on small data sets and simplistic statistical methods. Because of a recent large-scale cross-country pedestrian survey, there is now enough data available to study this in greater detail than before, using modern statistical methods. We propose a functional ANOVA model to explain how the pedestrian flow for a street varies over the day based on its density type, describing the nearby buildings, and street type, describing its role in the city’s overall street network. The model is formulated and estimated in a Bayesian framework using hour-by-hour pedestrian counts from the three European cities, Amsterdam, London and Stockholm. To assess the predictive power of the model, which could be of interest when building new neighbourhoods, it is compared with four common methods from machine learning, including neural networks and random forests. The results indicate that this model works well but that there is room for improvement in capturing the variability in the data, especially between cities.
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| 4. |
- Ek Fälth, Hanna, 1992, et al.
(författare)
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MENA compared to Europe: The influence of land use, nuclear power, and transmission expansion on renewable electricity system costs
- 2021
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Ingår i: Energy Strategy Reviews. - : Elsevier BV. - 2211-467X. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Most studies that examine CO2-neutral, or near CO2-neutral, power systems by using energy system models investigate Europe or the United States, while similar studies for other regions are rare. In this paper, we focus on the Middle East and North Africa (MENA), where weather conditions, especially for solar, differ substantially from those in Europe. We use a green-field linear capacity expansion model with over-night investment to assess the effect on the system cost of (i) limiting/expanding the amount of land available for wind and solar farms, (ii) allowing for nuclear power and (iii) disallowing for international transmission. The assessment is done under three different cost regimes for solar PV and battery storage. First, we find that the amount of available land for wind and solar farms can have a significant impact on the system cost, with a cost increase of 0–50% as a result of reduced available land. In MENA, the impact on system cost from land availability is contingent on the PV and battery cost regime, while in Europe it is not. Second, allowing for nuclear power has a minor effect in MENA, while it may decrease the system cost in Europe by up to 20%. In Europe, the effect on system cost from allowing for nuclear power is highly dependent on the PV and battery cost regime. Third, disallowing for international transmission increases the system cost by up to 25% in both Europe and MENA, and the cost increase depends on the cost regime for PV and batteries. The impacts on system cost from these three controversial and policy-relevant factors in a decarbonized power system thus play out differently, depending on (i) the region and (ii) uncertain future investment costs for solar PV and storage. We conclude that a renewable power system in MENA is likely to be less costly than one in Europe, irrespective of future uncertainties regarding investment cost for PV and batteries, and policies surrounding nuclear power, transmission, and land available for wind- and solar farms. In MENA, the system cost varies between 42 and 96 $/MWh. In Europe, the system cost varies between 51 and 102 $/MWh.
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| 5. |
- Henders, Sabine, et al.
(författare)
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Do national strategies under the UN biodiversity and climate conventions address agricultural commodity consumption as deforestation driver?
- 2018
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Ingår i: Land Use Policy. - : Elsevier BV. - 0264-8377 .- 1873-5754. ; 70, s. 580-590
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Tidskriftsartikel (refereegranskat)abstract
- Forest conversion in the tropics is increasingly driven by global demand for agricultural forest-risk commoditiessuch as soy, beef, palm oil and timber. In order to be effective, future forest conservation policies should includemeasures targeting both producers (the supply side) and consumers (the demand side) to address commodity-driven deforestation. Whereas the UN Conventions on Biodiversity (CBD) and Climate Change (UNFCCC) do notmake reference to this driving factor, here we explore whether and how recent national strategies by memberstates to the Conventions acknowledge the role of agricultural commodities in tropical deforestation. A textanalysis of 139 Intended Nationally Determined Contributions (INDCs) to climate change mitigation and 132National Biodiversity Strategies and Action Plans (NBSAPs) shows that the general trade-offbetween nationaldevelopment aspirations and forest conservation is commonly acknowledged. However, only few strategies linkdeforestation to commodity production and consumption, whereas most documents do not mention this topic.This lack of reference to a key driver of tropical deforestation limits the prospects of safeguarding tropical forestsfor biodiversity and climate change mitigation purposes as part of the two UN Conventions, and might jeopardisetheir overall effectiveness.Thesefindings were complemented by a content analysis of INDCs, NBSAPs and REDD+ documents fromeight case countries affected by commodity-driven deforestation. We investigated whether this driver is ac-knowledged in the national strategies, and which policy measures are suggested to address forest loss fromagricultural commodities. We found that six case countries mention agricultural commodities as deforestationdriver in their REDD+ documents, whereas the biodiversity and climate change strategies were silent on thetopic. Policy measures targeting commodity production were suggested in four REDD+ strategies, ranging fromincentive payments, sustainable agricultural practices and land-use planning to demand-side approaches such ascertification and the promotion of sustainable lifestyles.One conclusion from this exercise is that UN member states seem not to consider climate and biodiversitynational plans the adequate forum to discuss detailed forest conservation approaches. We argue that in order toincrease effectiveness, strategies under the UN Conventions should take commodity-driven deforestation intoaccount, through measures that address both the producer and the consumer side. Do national strategies under the UN biodiversity and climate conventions address agricultural commodity consumption as deforestation driver?. Available from: https://www.researchgate.net/publication/320845988_Do_national_strategies_under_the_UN_biodiversity_and_climate_conventions_address_agricultural_commodity_consumption_as_deforestation_driver [accessed Apr 24 2018].
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| 6. |
- Jonsson, Patrik, 1967, et al.
(författare)
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What are the root causes of material delivery schedule inaccuracy in supply chains?
- 2023
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Ingår i: International Journal of Operations and Production Management. - 1758-6593 .- 0144-3577. ; 44:13, s. 34-68
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Tidskriftsartikel (refereegranskat)abstract
- Purpose :This study aims to explore and empirically test variables influencing material delivery schedule inaccuracies? Design/methodology/approach :A mixed-method case approach is applied. Explanatory variables are identified from the literature and explored in a qualitative analysis at an automotive original equipment manufacturer. Using logistic regression and random forest classification models, quantitative data (historical schedule transactions and internal data) enables the testing of the predictive difference of variables under various planning horizons and inaccuracy levels. Findings : The effects on delivery schedule inaccuracies are contingent on a decoupling point, and a variable may have a combined amplifying (complexity generating) and stabilizing (complexity absorbing) moderating effect. Product complexity variables are significant regardless of the time horizon, and the item’s order life cycle is a significant variable with predictive differences that vary. Decoupling management is identified as a mechanism for generating complexity absorption capabilities contributing to delivery schedule accuracy. Practical implications : The findings provide guidelines for exploring and finding patterns in specific variables to improve material delivery schedule inaccuracies and input into predictive forecasting models. Originality/value : The findings contribute to explaining material delivery schedule variations, identifying potential root causes and moderators, empirically testing and validating effects and conceptualizing features that cause and moderate inaccuracies in relation to decoupling management and complexity theory literature?
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| 7. |
- Liao, Yuan, 1991, et al.
(författare)
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Disparities in travel times between car and transit: Spatiotemporal patterns in cities
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Cities worldwide are pursuing policies to reduce car use and prioritise public transit (PT) as a means to tackle congestion, air pollution, and greenhouse gas emissions. The increase of PT ridership is constrained by many aspects; among them, travel time and the built environment are considered the most critical factors in the choice of travel mode. We propose a data fusion framework including real-time traffic data, transit data, and travel demand estimated using Twitter data to compare the travel time by car and PT in four cities (São Paulo, Brazil; Stockholm, Sweden; Sydney, Australia; and Amsterdam, the Netherlands) at high spatial and temporal resolutions. We use real-world data to make realistic estimates of travel time by car and by PT and compare their performance by time of day and by travel distance across cities. Our results suggest that using PT takes on average 1.4–2.6 times longer than driving a car. The share of area where travel time favours PT over car use is very small: 0.62% (0.65%), 0.44% (0.48%), 1.10% (1.22%) and 1.16% (1.19%) for the daily average (and during peak hours) for São Paulo, Sydney, Stockholm, and Amsterdam, respectively. The travel time disparity, as quantified by the travel time ratio R (PT travel time divided by the car travel time), varies widely during an average weekday, by location and time of day. A systematic comparison between these two modes shows that the average travel time disparity is surprisingly similar across cities: R<1 for travel distances less than 3 km, then increases rapidly but quickly stabilises at around 2. This study contributes to providing a more realistic performance evaluation that helps future studies further explore what city characteristics as well as urban and transport policies make public transport more attractive, and to create a more sustainable future for cities.
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| 8. |
- Lindgren, Kristian, 1960, et al.
(författare)
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Evolutionary Exploration of the Finitely Repeated Prisoners' Dilemma -- The Effect of Out-of-Equilibrium Play
- 2013
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Ingår i: Games. - : MDPI AG. - 2073-4336. ; 4:1, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- The finitely repeated Prisoners’ Dilemma is a good illustration of the discrepancy between the strategic behaviour suggested by a game-theoretic analysis and the behaviour often observed among human players, where cooperation is maintained through most of the game. A game-theoretic reasoning based on backward induction eliminates strategies step by step until defection from the first round is the only remaining choice, reflecting the Nash equilibrium of the game. We investigate the Nash equilibrium solution for two different sets of strategies in an evolutionary context, using replicator-mutation dynamics. The first set consists of conditional cooperators, up to a certain round, while the second set in addition to these contains two strategy types that react differently on the first round action: The ”Convincer” strategies insist with two rounds of initial cooperation, trying to establish more cooperative play in the game, while the ”Follower” strategies, although being first round defectors, have the capability to respond to an invite in the first round. For both of these strategy sets, iterated elimination of strategies shows that the only Nash equilibria are given by defection from the first round. We show that the evolutionary dynamics of the first set is always characterised by a stable fixed point, corresponding to the Nash equilibrium, if the mutation rate is sufficiently small (but still positive). The second strategy set is numerically investigated, and we find that there are regions of parameter space where fixed points become unstable and the dynamics exhibits cycles of different strategy compositions. The results indicate that, even in the limit of very small mutation rate, the replicator-mutation dynamics does not necessarily bring the system with Convincers and Followers to the fixed point corresponding to the Nash equilibrium of the game. We also perform a detailed analysis of how the evolutionary behaviour depends on payoffs, game length, and mutation rate.
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| 9. |
- Lundberg, Liv, 1987, et al.
(författare)
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A cobweb model of land-use competition between food and bioenergy crops
- 2015
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Ingår i: Journal of Economic Dynamics and Control. - : Elsevier BV. - 0165-1889. ; 53, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- We present a model of interacting cobweb markets and apply it to land-use competition between food and bioenergy crops. In our model the markets are interlinked on the supply side by the limited availability of land. Therefore, instabilities are transferred between the markets and we find that bioenergy demand affects food price volatility. The agents in the model have heterogeneous production capacities, representing variation in global land quality. When we allow agents to choose price predictor, we find that a more sophisticated (but costly) predictor is concentrated to some key parcels of land, which enables the system to reduce instability significantly. The system can also be brought closer to a stable state by introducing costs for changing production type, but it may then be shifted away from the optimum situation predicted by the corresponding equilibrium model.
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| 10. |
- Malz, Elena, 1990, et al.
(författare)
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Computing the power profiles for an Airborne Wind Energy system based on large-scale wind data
- 2020
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 162, s. 766-778
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Tidskriftsartikel (refereegranskat)abstract
- Airborne Wind Energy (AWE) is a new power technology that harvests wind energy at high altitudes using tethered wings. Studying the power potential of the system at a given location requires evaluating the local power production profile of the AWE system. As the optimal operational AWE system altitude depends on complex trade-offs, a commonly used technique is to formulate the power production computation as an Optimal Control Problem (OCP). In order to obtain an annual power production profile, this OCP has to be solved sequentially for the wind data for each time point. This can be computationally costly due to the highly nonlinear and complex AWE system model. This paper proposes a method how to reduce the computational effort when using an OCP for power computations of large-scale wind data. The method is based on homotopy-path-following strategies, which make use of the similarities between successively solved OCPs. Additionally, different machine learning regression models are evaluated to accurately predict the power production in the case of very large data sets. The methods are illustrated by computing a three-month power profile for an AWE drag-mode system. A significant reduction in computation time is observed, while maintaining good accuracy.
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