| 1. |
- Mattsson, Patrik, et al.
(author)
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β-Amyloid binding in elderly subjects with declining or stable episodic memory function measured with PET and [11C]AZD2184
- 2015
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In: European Journal of Nuclear Medicine and Molecular Imaging. - : Springer. - 1619-7070 .- 1619-7089. ; 42:10, s. 1507-1511
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Journal article (peer-reviewed)abstract
- Purpose: Cognitive decline has been suggested as an early marker for later onset of Alzheimer's disease. We therefore explored the relationship between decline in episodic memory and β-amyloid using positron emission tomography (PET) and [11C]AZD2184, a radioligand with potential to detect low levels of amyloid deposits.Methods: Healthy elderly subjects with declining (n = 10) or stable (n = 10) episodic memory over 15 years were recruited from the population-based Betula study and examined with PET. Brain radioactivity was measured after intravenous administration of [11C]AZD2184 The binding potential BP ND was calculated using linear graphical analysis with the cerebellum as reference region.Results: The binding of [11C]AZD2184 in total grey matter was generally low in the declining group, whereas some binding could be observed in the stable group. Mean BP ND was significantly higher in the stable group compared to the declining group (p = 0.019). An observation was that the three subjects with the highest BPND were ApoE ε4 allele carriers.Conclusions: We conclude that cognitive decline in the general population does not seem to stand by itself as an early predictor for amyloid deposits.
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| 7. |
- Westin, Jonas, 1980-
(author)
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Welfare Effects of Transport Policies : an analysis of congestion pricing and infrastructure investments
- 2011
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Licentiate thesis (other academic/artistic)abstract
- Interactions between the transport market and other distorted markets, such as the labor market, can have a large impact on the overall welfare effect of a road pricing policy or a congestion charge. Many road pricing studies therefore try to incorporate effects from other distorted markets in the analysis. A difficulty when assessing the welfare effect of a future transport policy is also that many factors and parameters needed for the analysis is uncertain. This thesis contains three papers all studying different methodological approaches to analyzing the welfare effects of transport policies. The first two papers analyze the welfare effect of congestion pricing in distorted economies. The main contribution of the first paper is to analyze how the welfare effect of a congestion charge in a distorted economy depends on what assumptions we make regarding the tax system in the initial no-toll situation. A critical assumption in many cost-benefit analyses of congestion charges is that the whole population has a single value of time. The second paper studies the effect of a congestion charge in a population of commuters with a continuously distributed value of time. The main contribution of the paper, compared to previous literature, is that it studies the welfare effect and distributional impact of a congestion charge in a population with endogenous labor supply and heterogeneous value of time where mode-choice self-selection plays an important role. The third paper studies the climate benefit of an investment in high speed rail by calculating the magnitude of annual traffic emission reduction required to compensate for the annualized embedded emissions from the construction of the line. To account for uncertainties in underlying assumptions, a Monte Carlo simulation framework is used in the analysis. The paper finds that to be able to balance the annualized emissions from the construction, traffic volumes of more than 10 million annual one-way trips are usually required, and most of the traffic diverted from other transport modes must come from aviation.
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| 8. |
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| 9. |
- Algers, Staffan, et al.
(author)
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Is it time to use activity-based urban transport models? A discussion of planning needs and modelling possibilities
- 2005
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In: The annals of regional science. - : Springer Science and Business Media LLC. - 0570-1864 .- 1432-0592. ; 39:4, s. 767-789
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Journal article (peer-reviewed)abstract
- For some decades now, transport researchers have put considerable efforts into developing what is called activity-based approaches for modelling urban travel demand. The basic idea is that travel demand is derived from people's desires to take part in different activities. In particular, the interrelationships among different activities with respect to temporal and spatial constraints are in focus. It means that such models treat the activities and the travelling of the households with respect to where and when the activities can be carried out and how they may be scheduled, given characteristics of the households and potential opportunities, the transport networks and various institutional constraints. We discuss what demands we see on future travel demand models, with a focus on urban analysis. This discussion is somewhat biased towards what role activity-based models could play in meeting these demands. We then review in some detail three prominent and distinctly different representatives of operational activity-based models to give an indication of what new modelling possibilities they offer. Theoretical appeal, empirical validity, usefulness for planning, need for data and easiness of implementation are discussed. In the final section we draw some conclusions about the prospects of these models and of their descendants.
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| 10. |
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| 11. |
- Andersson, Mats, 1965-
(author)
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Empirical Essays on Railway Infrastructure Costs in Sweden
- 2007
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Doctoral thesis (other academic/artistic)abstract
- The subject of this thesis concerns pricing the use of transport infrastructure. We are empirically investigating the relationship between railway traffic volumes and infrastructure management costs. More specifically, we are interested in estimating the change in infrastructure management costs from marginal variations in traffic volumes, i.e. to estimate the marginal cost of railway infrastructure wear and tear. Both Europe and Sweden have moved towards a marginal cost based transport pricing policy, thus driving the need for more empirical work on rail infrastructure costs to underpin the level of a wear and tear charge. The thesis consists of five papers. In paper I, the data situation for planning railway maintenance and renewal is surveyed internationally. The survey indicates that most infrastructure managers are still in the data gathering phase, rather than ready to use modern computerised planning tools to make sound decisions in the field of maintenance and renewal. In paper II, we investigate the data situation for infrastructure cost analysis in Sweden. A panel data set that consists of cost, traffic and infrastructure information is created. The data covers 1999-2002 and contains almost 190 annual observations. Three main cost categories are identified; infrastructure operation, maintenance and renewal. This data is used for estimations of cost functions in paper II, III and V. Econometric techniques are applied for this purpose, with several different model specifications. In paper II, the method of pooled ordinary least squares (POLS) is applied. In paper III, we turn to unobserved effects models to exploit data heterogeneity. Finally in paper V, a dynamic generalised method of moments estimator is used to explore a potential dynamic cost dependency. The main findings are that the POLS approach, which has been used in similar studies in Europe recently, is rejected in favour of fixed effects estimation for this data. Furthermore, we also reject the idea of regression analysis to capture marginal rail renewal costs. In paper IV, we suggest an analytical expression combined with survival analysis of rail ages to estimate marginal renewal costs. We derive elasticities with respect to output as well as marginal costs for the different cost categories, and find that the current charge for wear and tear in Sweden is well below these new estimates. This opens up for increased, marginal cost based rail infrastructure wear and tear charges, which would reduce the financial burden on Swedish tax-payers.
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| 14. |
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| 15. |
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| 16. |
- Berdica, Katja, et al.
(author)
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Vulnerability : A model-based case study of the road network in Stockholm
- 2007
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In: Critical Infrastructure. - Berlin, Heidelberg : Springer-Verlag. ; , s. 81-106
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Book chapter (peer-reviewed)abstract
- Vulnerability, exposure and criticality in various infrastructures are issues that have been more explicitly looked into in recent years. However, road vulnerability as such has not been in focus for very long, despite the fundamental importance of our road networks in everyday life, as well as in crisis evacuation situations. Consequently, network reliability in transport modelling is an important and growing field of research (Lam 1999). The connection between reliability, vulnerability and other related concepts are discussed in Berdica (2002), with the main proposition that vulnerability analysis of road networks should be regarded as an overall framework, within which different transport studies can be performed to describe how well our transport systems function when exposed to different kinds of disturbances. Following that approach, this paper presents the results from a model-based case study, performed with the overall objective to study how vulnerable the Stockholm road network is in different respects. More specifically it is built up around three main questions: 1. How do interruptions of different critical links affect the system and how important are these links in relation to one another? 2. How is the network performance affected by general capacity reductions and possible prioritisation of a sub-network? 3. How is the system affected by traffic demand variations, i.e. how close to its capacity limit does the system operate?
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| 17. |
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| 18. |
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| 19. |
- Dan, Gorton, 1970-
(author)
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Aspects of Modeling Fraud Prevention of Online Financial Services
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Banking and online financial services are part of our critical infrastructure. As such, they comprise an Achilles heel in society and need to be protected accordingly. The last ten years have seen a steady shift from traditional show-off hacking towards cybercrime with great economic consequences for society. The different threats against online services are getting worse, and risk management with respect to denial-of-service attacks, phishing, and banking Trojans is now part of the agenda of most financial institutions. This trend is overseen by responsible authorities who step up their minimum requirements for risk management of financial services and, among other things, require regular risk assessment of current and emerging threats.For the financial institution, this situation creates a need to understand all parts of the incident response process of the online services, including the technology, sub-processes, and the resources working with online fraud prevention. The effectiveness of each countermeasure has traditionally been measured for one technology at a time, for example, leaving the fraud prevention manager with separate values for the effectiveness of authentication, intrusion detection, and fraud prevention. In this thesis, we address two problems with this situation. Firstly, there is a need for a tool which is able to model current countermeasures in light of emerging threats. Secondly, the development process of fraud detection is hampered by the lack of accessible data.In the main part of this thesis, we highlight the importance of looking at the “big risk picture” of the incident response process, and not just focusing on one technology at a time. In the first article, we present a tool which makes it possible to measure the effectiveness of the incident response process. We call this an incident response tree (IRT). In the second article, we present additional scenarios relevant for risk management of online financial services using IRTs. Furthermore, we introduce a complementary model which is inspired by existing models used for measuring credit risks. This enables us to compare different online services, using two measures, which we call Expected Fraud and Conditional Fraud Value at Risk. Finally, in the third article, we create a simulation tool which enables us to use scenario-specific results together with models like return of security investment, to support decisions about future security investments.In the second part of the thesis, we develop a method for producing realistic-looking data for testing fraud detection. In the fourth article, we introduce multi-agent based simulations together with social network analysis to create data which can be used to fine-tune fraud prevention, and in the fifth article, we continue this effort by adding a platform for testing fraud detection.
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| 20. |
- Dziekan, Katrin, 1976-
(author)
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Ease-of-Use in Public Transportation : A User Perspective on Information and Orientation Aspects
- 2008
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Doctoral thesis (other academic/artistic)abstract
- This interdisciplinary thesis combines psychological and transportation planning knowledge. Three main questions are investigated: 1) What concepts and ideas do people have with regard to a public transportation system (cognitive user perspective)?; 2) What orientation and information factors within the public transportation system enhance Ease-of-Use and make it simpler and more efficient to use public transportation in metropolitan areas?; 3) How can Ease-of-Use of a public transportation route be measured? A combination of qualitative and quantitative methods was used. Between 2002 and 2007 a total of nine different studies were conducted: An in-depth study on a single exchange student, an interview study with exchange students, a questionnaire study on exchange students, a before-after interview study with travellers on selected bus stops, an before-after telephone interview study on residents, an expert questionnaire study via email, a behaviour observation study on travellers, a before-after questionnaire study on travellers on a tram line, and an on-board questionnaire study. To analyse the cognitive user perspective the term memory representation was introduced, that includes cognitive maps of and additional knowledge about a public transportation system such as service frequency. Memory representation is influenced by experience. Three learning phases in an unknown public transportation system are proposed and a general information search script is described. A new approach is presented regarding the organisation of public transportation knowledge: The ground level is that there exists a public transportation option, the next level is the identification of the mode of transport and at the highest level of the hierarchy is the code for the line. Within the second level, the public transportation mode, a hierarchical structure of public transportation option knowledge is proposed. Three factors are postulated that contribute to the extent to which a line is represented in people’s memory: visibility, straight route layout and labelling. Which orientation and information factors within the public transportation system enhance Ease-of-Use, i.e. match the cognitive user perspective? It was found that trunk bus lines enhanced Ease-of-Use and at-stop real-time information can have various positive effects. The role of good maps is explained and stretched and the importance of consistent information throughout the travel chain is also pointed out. In addition, many valuable concrete hints are given with regard to how to match the system properly with the cognitive user perspective. Undoubtedly, an interaction exists between system and user and they influence each other. This is where the third research question comes in: How can Ease-of-Use in public transportation systems be measured? The iterative process of defining and measuring Ease-of-Use resulted in a scale that measured the defined concept well with good reliability and validity. The final discussion highlights the contribution to science of this thesis and presents some possible paths for further research. The thesis consists of a summary and eight papers.
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| 21. |
- Eliasson, Jonas, et al.
(author)
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A model for integrated analysis of household location and travel choices
- 2000
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In: Transportation Research Part A. - 0965-8564 .- 1879-2375. ; 34:5, s. 375-394
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Journal article (peer-reviewed)abstract
- We develop a model for integrated analysis of household location and travel choices and investigate it from a theoretical point of view. Each household makes a joint choice of location (zone and house type) and a travel pattern that maximizes utility subject to budget and time constraints. Prices for housing are calculated so that demand equals supply in each submarket. The travel pattern consists of a set of expected trip frequencies to different destinations with different modes. The joint time and budget constraints ensure that time and cost sensitivities are consistent throughout the model. Choosing the entire travel pattern at once, as opposed to treating travel decisions as a series of isolated choices, allows the marginal utilities of trips to depend on which other trips are made. When choosing trip frequencies to destinations, households are assumed to prefer variation to an extent varying with the purpose of the trip. The travel pattern will tend to be more evenly distributed across trip ends the less similar destinations and individual preferences are. These heterogeneities of destinations and individual preferences, respectively, are expressed in terms of a set of parameters to be estimated.
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| 22. |
- Eliasson, Jonas, 1969-, et al.
(author)
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Equity effects of congestion pricing. Quantitative methodology and a case study for Stockholm
- 2006
-
In: Transportation Research Part A. - : Elsevier BV. - 0965-8564 .- 1879-2375. ; 40:7, s. 602-620
-
Journal article (peer-reviewed)abstract
- It is widely recognised that congestion pricing could be an effective measure to solve environmental and congestion problems in urban areas—a reform that normally also would generate a net welfare surplus. Despite this the implementation of congestion pricing has been very slow. One reason for a low public and political acceptance could be that equity impacts have not been given enough concern. In studies of distributional impacts of congestion pricing it has often been claimed that the reform is regressive rather than progressive even if there are studies claiming the opposite. We develop a method for detailed, quantitative assessment of equity effects of road pricing and apply it to a real-world example, namely a proposed congestion-charging scheme for Stockholm. The method simultaneously takes into account differences in travel behaviour, in preferences (such as values of time) and in supply of travel possibilities (car ownership, public transport level-of-service etc.). We conclude that the two most important factors for the net impact of congestion pricing are the initial travel patterns and how revenues are used. Differences in these respects dwarf differences in other factors such as values of time. This is accentuated by the fact that the total collected charges are more than three times as large as the net benefits. With respect to different groups, we find that men, high-income groups and residents in the central parts of the city will be affected the most. If revenues are used for improving public transport, this will benefit women and low-income groups the most. If revenues are used for tax cuts, the net benefits will be about equal for men and women on the average, while it naturally will benefit high-income groups. Given that it is likely that the revenues will be used to some extent to improve the public transport system, we conclude that the proposed congestion-charging scheme for Stockholm is progressive rather than regressive.
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| 23. |
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| 26. |
- Fagerberg, Björn, 1943, et al.
(author)
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Cadmium exposure as measured in blood in relation to macrophage density in symptomatic atherosclerotic plaques from human carotid artery
- 2016
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In: Atherosclerosis. - : Elsevier BV. - 0021-9150. ; 249, s. 209-214
-
Journal article (peer-reviewed)abstract
- Background and Aims: The general population is exposed to cadmium through diet and smoking. Cadmium is pro-atherogenic and pro-inflammatory in experimental and observational studies. Cadmium levels in blood and carotid plaque endarterectomies correlate. Cadmium concentrations are much higher in plaque-areas that most frequently rupture. Here we investigated if blood cadmium concentrations are associated with macrophage density and the accumulation of CD14 as indicator of macrophage activation by lipopolysaccharide (LPS) in endarterectomies from patients with symptomatic carotid plaques. Methods: Endarterectomies from ninety nine patients were fixed in formalin, embedded in paraffin, serially sectioned and stained for assessment of morphology. As predefined, the two section levels with most prevalent plaque rupture were used for further analyses. Macrophages were assessed as area of staining for CD68 (%). Blood cadmium was measured with ICP-MS. Results: The CD68 median [25,75 percentiles] from the average of both sections were higher in cadmium tertile 3 than in tertile 1 (9.8 [4.9,16.1] % and 3.8 (0.6,12.4) %, p = 0.017). This difference remained in a multiple linear regression analysis with 10log meanCD68 as dependent variable and adjustment for sex, age, smoking, statin treatment, index event, time between event and surgery (beta coefficient 0.44 [95% CI 0.05-0.87]. CD14 was not associated with blood cadmium. Conclusions: The results showed that blood cadmium was associated with proinflammatory macrophage density in the sections of carotid plaques with most frequent rupture, previously shown to contain most cadmium. No association between cadmium and LPS-mediated macrophage-activation was found. Cadmium exposure may promote plaque inflammation. (C) 2016 Elsevier Ireland Ltd. All rights reserved.
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| 27. |
- Forsblad d'Elia, Helena, 1961, et al.
(author)
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Influence of hormone replacement therapy on disease progression and bone mineral density in rheumatoid arthritis.
- 2003
-
In: The Journal of rheumatology. - 0315-162X .- 1499-2752. ; 30:7, s. 1456-63
-
Journal article (peer-reviewed)abstract
- OBJECTIVE: Hormone replacement therapy (HRT) is known to exert a positive effect in preventing bone loss and a beneficial effect on the disease activity in rheumatoid arthritis (RA). We evaluated the effects of HRT on bone mineral density (BMD) and on the course of established RA. METHODS: Eighty-eight postmenopausal women with RA were randomly allocated to receive HRT, vitamin D3, and calcium supplementation or vitamin D3 and calcium supplementation alone for 2 years. The effects of additional HRT on laboratory and clinical measures of disease activity, quality of life, and BMD and on radiographic joint damage were investigated. RESULTS: Treatment with HRT suppressed signs of inflammation as shown by reduction in erythrocyte sedimentation rate (ESR) (p = 0.025) and an elevation in hemoglobin concentration (p = 0.007), a better clinical outcome assessed by response on the Disease Activity Score 28 (DAS28) (p = 0.036), increased BMD in the forearm, proximal femur and spine (p < 0.01), and retarded (p = 0.026) progression of joint destruction among patients with radiological progressive disease. No significant effect on quality of life was seen. CONCLUSION: Two years of HRT in women with active RA had significant ameliorating effects on inflammation, DAS28 response, and BMD and was associated with slower progression of radiological joint destruction. The mechanisms by which HRT exerts its effects remain to be elucidated. We suggest HRT can be used in addition to conventional therapy in the management of postmenopausal patients with RA.
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| 28. |
- Fosgerau, M., et al.
(author)
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A note on the invariance of the distribution of the maximum
- 2018
-
In: Journal of Mathematical Economics. - : Elsevier. - 0304-4068 .- 1873-1538. ; 74, s. 56-61
-
Journal article (peer-reviewed)abstract
- Many models in economics involve discrete choices where a decision-maker selects the best alternative from a finite set. Viewing the array of values of the alternatives as a random vector, the decision-maker draws a realization and chooses the alternative with the highest value. The analyst is then interested in the choice probabilities and in the value of the best alternative. The random vector has the invariance property if the distribution of the value of a specific alternative, conditional on that alternative being chosen, is the same, regardless of which alternative is considered. This note shows that the invariance property holds if and only if the marginal distributions of the random components are positive powers of each other, even when allowing for quite general statistical dependence among the random components. We illustrate the analytical power of the invariance property by way of examples.
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| 29. |
- Fosgerau, Mogens, et al.
(author)
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Invariance of the distribution of the maximum
-
Other publication (other academic/artistic)abstract
- Many models in economics involve probabilistic choices where each decision-maker selects the best alternative from a finite set. Viewing the value of each alternative as a random variable, the analyst is then interested in the choice probabilities, that is, the probability for an alternative to give the maximum value. Much analytical power can be gained, both for positive and normative analysis, if the maximum value is statistically independent of which alternative obtains the highest value. This note synthesizes and generalizes previous results on this invariance property. We provide characterizations of this property within a wide class of distributions that comprises the McFadden GEV class, show implications in several directions, and establish connections with copulas. We illustrate the usefulness of the invariance property by way of a few examples.
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| 30. |
- Gunnarsson, Mikael, et al.
(author)
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Long-term biokinetics and radiation exposure of patients undergoing 14C-glycocholic acid and 14C-xylose breath tests.
- 2007
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In: Cancer Biotherapy & Radiopharmaceuticals. - : Mary Ann Liebert Inc. - 1557-8852 .- 1084-9785. ; 22:6, s. 762-771
-
Journal article (peer-reviewed)abstract
- The (14)C-glycocholic acid and (14)C-xylose breath tests are clinically used for the diagnosis of intestinal diseases, such as bacterial overgrowth in the small intestine. The two tests have in earlier studies been thoroughly evaluated regarding their clinical value, but due to the long physical half-life of (14)C and the limited biokinetic and dosimetric data, which are available for humans, several hospitals have been restrictive in their use. The aim of this study was to investigate the long-term biokinetics and dosimetry of the two (14)C compounds in patients and volunteers, using the highly sensitive accelerator mass spectrometry (AMS) technique. Eighteen (18) subjects were included, 9 for each compound. The (14)C content in samples from exhaled air, urine, and, for some subjects, also feces were analyzed with both liquid scintillation counting (LSC) and AMS. The results from the glycocholic acid study showed that, up to 1 year after the administration, 67%+/-6% (mean+/-standard deviation) of the administered activity was recovered in exhaled air, 2.4%+/-0.4% was found in urine, and 7.6% (1 subject) in feces. In the xylose study, the major part was found in the urine (66%+/-2%). A significant part was exhaled (28%+/-5%), and the result from an initial 72-hour stool collection from 2 of the subjects showed that the excretion by feces was insignificant. The absorbed dose to various organs and tissues and the effective dose were calculated by using biokinetic models, based on a combination of experimental data from the present study and from earlier reports. In the glycocholic acid study, the highest absorbed dose was received by the colon (1.2 mGy/MBq). In the xylose study, the adipose tissue received 0.8 mGy/MBq. The effective dose was estimated to 0.5 (glycocholic acid) and 0.07 mSv/MBq (xylose). Thus, from a radiation protection point of view, we see no need for restrictions in using the two (14)C-labeled radiopharmaceuticals on adults with the activities normally administered (0.07-0.4 MBq).
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| 31. |
- Hesse, Camilla, et al.
(author)
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The N-terminal domain of α-dystroglycan is released as a 38kDa protein and is increased in cerebrospinal fluid in patients with Lyme neuroborreliosis.
- 2011
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In: Biochemical and biophysical research communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 412:3, s. 494-499
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Journal article (peer-reviewed)abstract
- α-Dystroglycan is an extracellular adhesion protein that is known to interact with different ligands. The interaction is thought to stabilize the integrity of the plasma membrane. The N-terminal part of α-dystroglycan may be proteolytically processed to generate a small 38kDa protein (α-DG-N). The physiological significance of α-DG-N is unclear but has been suggested to be involved in nerve regeneration and myelination and to function as a potential biomarker for neurodegenerative and neuromuscular diseases. In this report we show that α-DG-N is released into different body fluids, such as lachrimal fluid, cerebrospinal fluid (CSF), urine and plasma. To investigate the significance of α-DG-N in CSF we examined the levels of α-DG-N and known neurodegenerative markers in CSF from patients diagnosed with Lyme neuroborreliosis (LNB) and healthy controls. In untreated acute phase LNB patients, 67% showed a significant increase of CSF α-DG-N compared to healthy controls. After treatment with antibiotics the CSF α-DG-N levels were normalized in the LNB patients.
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| 32. |
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| 33. |
- Holmgren, Åke J., 1972-
(author)
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Quantitative vulnerability analysis of electric power networks
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Disturbances in the supply of electric power can have serious implications for everyday life as well as for national (homeland) security. A power outage can be initiated by natural disasters, adverse weather, technical failures, human errors, sabotage, terrorism, and acts of war. The vulnerability of a system is described as a sensitivity to threats and hazards, and is measured by P (Q(t) > q), i.e. the probability of at least one disturbance with negative societal consequences Q larger than some critical value q, during a given period of time (0,t]. The aim of the thesis is to present methods for quantitative vulnerability analysis of electric power delivery networks to enable effective strategies for prevention, mitigation, response, and recovery to be developed. Paper I provides a framework for vulnerability assessment of infrastructure systems. The paper discusses concepts and perspectives for developing a methodology for vulnerability analysis, and gives examples related to power systems. Paper II analyzes the vulnerability of power delivery systems by means of statistical analysis of Swedish disturbance data. It is demonstrated that the size of large disturbances follows a power law, and that the occurrence of disturbances can be modeled as a Poisson process. Paper III models electric power delivery systems as graphs. Statistical measures for characterizing the structure of two empirical transmission systems are calculated, and a structural vulnerability analysis is performed, i.e. a study of the connectivity of the graph when vertices and edges are disabled. Paper IV discusses the origin of power laws in complex systems in terms of their structure and the dynamics of disturbance propagation. A branching process is used to model the structure of a power distribution system, and it is shown that the disturbance size in this analytical network model follows a power law. Paper V shows how the interaction between an antagonist and the defender of a power system can be modeled as a game. A numerical example is presented, and it is studied if there exists a dominant defense strategy, and if there is an optimal allocation of resources between protection of components, and recovery.
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| 34. |
- Hårsman, Björn, et al.
(author)
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Analyzing the returns to entrepreneurship by a modified Lazear model
- 2020
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In: Small Business Economics. - : Springer. - 0921-898X .- 1573-0913.
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Journal article (peer-reviewed)abstract
- A modified version of Lazear’s model (in American Economic Review, 94, 208-211, 2004, Journal of Labor Economics, 23, 649–680, 2005) for occupational choice is formulated. It includes a utility adjustment factor that captures the combined effect of nonpecuniary benefits and uncertainty associated with entrepreneurship. We show that the counterfactual income returns to entrepreneurship are lower than the market value of entrepreneurial talent and higher than the inverse of the utility adjustment factor. Moreover, if the skill profiles in the population are Fréchet-distributed, the ratio between the expected incomes of entrepreneurs and observationally similar wage employees is lower than the inverse of the utility adjustment factor. Thus, entrepreneurs will on average earn less than wage employees if the utility adjustment factor is greater than or equal to one. It is also shown that the self-selection bias related to this income ratio or returns measure increases with the observed percentage of entrepreneurs. Swedish employment data are used to calibrate the modified Lazear model. The empirical results indicate that uncertainty considerations might be more important for the occupational choices than nonpecuniary benefits.
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| 35. |
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| 36. |
- Hårsman, Björn, et al.
(author)
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The income return to entrepreneurship : theoretical model and outcomes for Swedish regions
- 2018
-
In: The annals of regional science. - : Springer Nature. - 0570-1864 .- 1432-0592. ; 61:3, s. 479-498
-
Journal article (peer-reviewed)abstract
- This paper investigates the income return to entrepreneurship and wage employment by means of Lazear's model of occupational choice. The paper has two major aims. The first is to develop a new theoretical framework for analyzing the income return to entrepreneurship by combining the Lazear model with the assumption that the skill profiles in a population are Frechet-distributed. The second is to demonstrate that the resulting theoretical derivations can be used for a new type of regional analysis of the income return to entrepreneurship and wage employment. The empirical analysis is based on data for individuals with a Master of Science degree in Electrical Engineering. We compute their income return to self-employment and wage employment in three parts of Sweden: the Stockholm region, the combined Gothenburg and Malmo region, and the Rest of Sweden. The results show that the average return to self-employment is less than 5% in all regions and smaller in the Gothenburg and Malmo region than in the other two regions. The regional differences are explained by the differential supply curves and market values of entrepreneurial talent. The theoretical derivation of the income return to entrepreneurship is the main contribution of the paper. Another contribution is the derivation of regional supply curves for entrepreneurs.
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| 37. |
- Höjer, Mattias, et al.
(author)
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Determinism and backcasting in future studies
- 2000
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In: Futures. - 0016-3287 .- 1873-6378. ; 32:7, s. 613-634
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Journal article (peer-reviewed)abstract
- In this paper, four frequently cited approaches to future studies are criticised. We use examples mainly from the field of transport research. The first approach is the tendency to try to establish cyclic behaviour in socio-technical changes. The second is the view that transport and communication are positively correlated. The third is the so-called 'hypothesis of constant travel time', according to which, the average daily travel time of a population is more or less stable. The fourth is the alleged causal relationship between urban density and petrol use. The use of these approaches is criticised for a number of reasons, among others for over-simplifying the underlying mechanisms and for being too deterministic. In cases where drastic change is needed, current trends must be broken, but perhaps through measures other than those indicated by the above approaches. In other words, the cited approaches may overlook interesting opportunities and fail to urge necessary action. Backcasting is put forward as a more promising approach, especially for situations where great change is needed, However, it has been found in this study that backcasting and different forecasting approaches an complementary. The argument is that backcasting is mainly appropriate where current trends art: leading towards an unfavourable state. Therefore, forecasting methods are necessary because they inform the backcaster when backcasting is required. Finally, the paper discusses the use of different models in planning, primarily in the context of their role in the path analyses of backcasting scenarios.
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| 38. |
- Jenelius, Erik
(author)
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Approaches to road network vulnerability analysis
- 2007
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Licentiate thesis (other academic/artistic)abstract
- Incidents in the road transport system can have large negative consequences for the society and the business community. The basic aim of vulnerability analysis is to identify scenarios that i) would lead to severe consequences, and ii) have some likelihood of being realized in the future. The Thesis proposes two main approaches to vulnerability analysis. The first significant component of the analysis is to identify important links in the road network, i.e., links where a disruption would lead to severe consequences. The second component is to identify exposed users, i.e., users for which the consequences of a disruption would be particularly severe. Paper I introduces the concepts of importance and exposure and how they can be operationalized in terms of increased travel time when road links are closed. The measures are applied to the road network of northern Sweden. Among other things, we find that the most important road links from a socio-economic efficiency perspective are sections of the main roads in the region going through the main population centres. The most exposed users, on the other hand, live in the sparsely populated municipalities in the northwest along the Norwegian border. Paper II studies the geographic patterns of exposure and importance in Sweden and identifies properties of the geography, road network and travel patterns that to a large extent explain the observed spatial differences. We find that the municipalities around Stockholm have the most important road networks, and that people in the southern parts of Sweden are considerably less exposed than in the northern parts. We also find that the sparsity of the road network, the travel times of the users and the traffic load on the links provide good explanatory variables for the regional variations in exposure and importance. Paper III proposes a link importance measure that incorporates both efficiency considerations, i.e. the total increase in travel time, and equity considerations, i.e. the unevenness of the distribution among users. We show analytically that there is a strong inverse relationship between the two components. In a case study of the Swedish road network we find that when only efficiency is considered, links in many of the main roads are among the most important. With more weight put on equity, importance is gradually shifted to smaller local roads with poor or no alternative routes.
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| 39. |
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| 40. |
- Jenelius, Erik, et al.
(author)
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Importance and exposure in road network vulnerability analysis
- 2006
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In: Transportation Research Part A. - : Elsevier BV. - 0965-8564 .- 1879-2375. ; 40:7, s. 537-560
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Journal article (peer-reviewed)abstract
- The reliability and vulnerability of critical infrastructures have attracted a lot of attention recently. In order to assess these issues quantitatively, operational measures are needed. Such measures can also be used as guidance to road administrations in their prioritisation of maintenance and repair of roads, as well as for avoiding causing unnecessary disturbances in the planning of roadwork. The concepts of link importance and site exposure are introduced. In this paper, several link importance indices and site exposure indices are derived, based on the increase in generalised travel cost when links are closed. These measures are divided into two groups: one reflecting an "equal opportunities perspective", and the other a "social efficiency perspective". The measures are calculated for the road network of northern Sweden. Results are collected in a GIs for visualisation, and are presented per link and municipality. In view of the recent great interest in complex networks, some topological measures of the road network are also presented.
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| 41. |
- Jenelius, Erik, Docent, 1980-, et al.
(author)
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Resilience of transport systems
- 2021. - 1
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In: International Encyclopedia of Transportation. - : Elsevier. ; , s. 258-267
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Book chapter (other academic/artistic)
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| 42. |
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| 43. |
- Jenelius, Erik, et al.
(author)
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Road network vulnerability analysis : Conceptualization, implementation and application
- 2015
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In: Computers, Environment and Urban Systems. - : Elsevier BV. - 0198-9715 .- 1873-7587. ; 49, s. 136-147
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Journal article (peer-reviewed)abstract
- The paper describes a process for road network vulnerability analysis, from (i) the conceptual definition of vulnerability measures, through (ii) the derivation of practical indicators and models adapted to available data and their implementation in computational procedures, to (iii) the application of the methodology in case studies. In the first step, the vulnerability concept is defined and quantified formally, and distinct user and technological perspectives are highlighted. In the second step, the conceptual measures are adapted and calculated according to the conditions, requirements and goals of a particular analysis. The paper describes practical indicators and algorithms developed for large-scale vulnerability analyses. For the third step, the paper analyzes both single link closures and area-covering disruptions and the distribution of impacts among different regions in a case study on the Swedish road transport system. The spatial patterns are put in connection with the regional variations in location and travel patterns and network density. Finally, the implications for policy and possible approaches to vulnerability management are discussed.
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| 44. |
- Jenelius, Erik, et al.
(author)
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Road network vulnerability analysis of area-covering disruptions : A grid-based approach with case study
- 2012
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In: Transportation Research Part A. - : Elsevier. - 0965-8564 .- 1879-2375. ; 46:5, s. 746-760
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Journal article (peer-reviewed)abstract
- We present an approach to systematically analysing the vulnerability of road networks under disruptions covering extended areas. Since various kinds of events including floods, heavy snowfall, storms and wildfires can cause such spatially spread degradations, the analysis method is an important complement to the existing studies of single link failures. The methodology involves covering the study area with grids of uniformly shaped and sized cells, where each cell represents the extent of an event disrupting any intersecting links. We apply the approach to the Swedish road network using travel demand and network data from the Swedish national transport modelling system Sampers. The study shows that the impacts of area-covering disruptions are largely determined by the level of internal, outbound and inbound travel demand of the affected area itself. This is unlike single link failures, where the link flow and the redundancy in the surrounding network determine the impacts. As a result, the vulnerability to spatially spread events shows a markedly different geographical distribution. These findings, which should be universal for most road networks of similar scale, are important in the planning process of resource allocation for mitigation and recovery.
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| 45. |
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| 46. |
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Jenelius, Erik, et al.
(author)
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Traveler delay costs and value of time with trip chains, flexible activity scheduling and information
- 2011
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In: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:5, s. 789-807
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Journal article (peer-reviewed)abstract
- The delay costs of traffic disruptions and congestion and the value of travel time reliability are typically evaluated using single trip scheduling models, which treat the trip in isolation of previous and subsequent trips and activities. In practice, however, when activity scheduling to some extent is flexible, the impact of delay on one trip will depend on the actual and predicted travel time on itself as well as other trips, which is important to consider for long-lasting disturbances and when assessing the value of travel information. In this paper we extend the single trip approach into a two trips chain and activity scheduling model. Preferences are represented as marginal activity utility functions that take scheduling flexibility into account. We analytically derive trip timing optimality conditions, the value of travel time and schedule adjustments in response to travel time increases. We show how the single trip models are special cases of the present model and can be generalized to a setting with trip chains and flexible scheduling. We investigate numerically how the delay cost depends on the delay duration and its distribution on different trips during the day, the accuracy of delay prediction and travel information, and the scheduling flexibility of work hours. The extension of the model framework to more complex schedules is discussed.
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