| 1. |
- Aas, Erik, 1990-
(author)
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A Markov Process on Cyclic Words
- 2014
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Doctoral thesis (other academic/artistic)abstract
- The TASEP (totally asymmetric simple exclusion process) studied here is a Markov chain on cyclic words over the alphabet{1,2,...,n} given by at each time step sorting an adjacent pair of letters chosen uniformly at random. For example, from the word 3124 one may go to 1324, 3124, 3124, 4123 by sorting the pair 31, 12, 24, or 43.Two words have the sametype if they are permutations of each other. If we restrict TASEP to words of some particular type m we get an ergodic Markov chain whose stationary distribution we denote by ζm. Soζm (u) is the asymptotic proportion of time spent in the state u if the chain started in some word of type m. The distribution ζ is the main object of study in this thesis. This distribution turns out to have several remarkable properties, and alternative characterizations. It has previously been studied both from physical, combinatorial, and probabilitistic viewpoints.In the first chapter we give an extended summary of known results and results in this thesis concerning ζ. The new results are described (and proved) in detail in Papers I - IV.The new results in Papers I and II include an explicit formula for the value ofζat sorted words and a product formula for decomposable words. We also compute some correlation functions for ζ. In Paper III we study of a generalization of TASEP to Weyl groups. In Paper IV we study a certain scaling limit of ζ, finding several interesting patterns of which we prove some. We also study an inhomogenous version of TASEP, in which different particles get sorted at different rates, which generalizes the homogenous version in several aspects. In the first chapter we compute some correlation functions for ζ
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| 2. |
- Aas, Erik, et al.
(author)
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A product formula for the TASEP on a ring
- 2016
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In: Random structures & algorithms (Print). - : Wiley-Blackwell. - 1042-9832 .- 1098-2418. ; 48:2, s. 247-259
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Journal article (peer-reviewed)abstract
- For a random permutation sampled from the stationary distributionof the TASEP on a ring, we show that, conditioned on the event that the rstentries are strictly larger than the last entries, the order of the rst entries isindependent of the order of the last entries. The proof uses multi-line queues asdened by Ferrari and Martin, and the theorem has an enumerative combinatorialinterpretation in that setting.As an application we prove a conjecture of Lam and Williams concerningSchubert factors of the stationary probability of certain states.Finally, we present a conjecture for the case where the small and large entriesare not separated.
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| 3. |
- Aas, Erik, et al.
(author)
-
A product formula for the TASEP on a ring - Extended Abstract
- 2014
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In: Discrete Mathematics and Theoretical Computer Science. - : Discrete Mathematics and Theoretical Computer Science. ; , s. 633-641
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Conference paper (peer-reviewed)abstract
- For a random permutation sampled from the stationary distribution of the TASEP on a ring, we show that, conditioned on the event that the first entries are strictly larger than the last entries, the order of the first entries is independent of the order of the last entries. The proof uses multi-line queues as defined by Ferrari and Martin, and the theorem has an enumerative combinatorial interpretation in that setting. Finally, we present a conjecture for the case where the small and large entries are not separated.
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| 4. |
- Aas, Erik, et al.
(author)
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Continuous multi-line queues and TASEP
- 2018
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In: Annales de l'Institut Henri Poincare D. - : EUROPEAN MATHEMATICAL SOC. - 2308-5827 .- 2308-5835. ; 5:1, s. 127-152
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Journal article (peer-reviewed)abstract
- In this paper, we study a distribution Xi of labeled particles on a continuous ring. It arises in three different ways, all related to the multi-type TASEP on a ring. We prove formulas for the probability density function for some permutations and give conjectures for a larger class. We give a complete conjecture for the probability of two particles i, j being next to each other on the cycle, for which we prove some cases. We also find that two natural events associated to the process have exactly the same probability expressed as a Vandermonde determinant. It is unclear whether this is just a coincidence or a consequence of a deeper connection.
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| 5. |
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| 6. |
- Aas, Erik
(author)
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Limit points of the iterative scaling procedure
- 2014
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In: Annals of Operations Research. - : Springer Science and Business Media LLC. - 0254-5330 .- 1572-9338. ; 215:1, s. 15-23
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Journal article (peer-reviewed)abstract
- The iterative scaling procedure (ISP) is an algorithm which computes a sequence of matrices, starting from some given matrix. The objective is to find a matrix 'proportional' to the given matrix, having given row and column sums. In many cases, for example if the initial matrix is strictly positive, the sequence is convergent. It is known that the sequence has at most two limit points. When these are distinct, convergence to these two points can be slow. We give an efficient algorithm which finds the limit points, invoking the ISP only on subproblems for which the procedure is convergent.
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| 7. |
- Aas, Erik, et al.
(author)
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Limiting directions for random walks in classical affine Weyl groups
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Other publication (other academic/artistic)abstract
- Let be a finite Weyl group and the corresponding affine Weyl group. A random element of can be obtained as a reduced random walk on the alcoves of . By a theorem of Lam (Ann. Probab. 2015), such a walk almost surely approaches one of many directions. We compute these directions when is , and and the random walk is weighted by Kac and dual Kac labels. This settles Lam's questions for types and in the affirmative and for type in the negative. The main tool is a combinatorial two row model for a totally asymmetric simple exclusion process called the -TASEP, with four parameters. By specializing the parameters in different ways, we obtain TASEPs for each of the Weyl groups mentioned above. Computing certain correlations in these TASEPs gives the desired limiting directions.
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| 8. |
- Aas, Erik, et al.
(author)
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Limiting Directions for Random Walks in Classical Affine Weyl Groups
- 2021
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In: International mathematics research notices. - : Oxford University Press (OUP). - 1073-7928 .- 1687-0247. ; 2023:4, s. 3092-3137
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Journal article (peer-reviewed)abstract
- Let W be a finite Weyl group and (W) over tilde the corresponding affine Weyl group. A random element of (W) over tilde can be obtained as a reduced random walk on the alcoves of (W) over tilde. By a theorem of Lam (Ann. Prob. 2015), such a walk almost surely approaches one of vertical bar W vertical bar many directions. We compute these directions when W is B-n, C-n, and D-n, and the random walk is weighted by Kac and dual Kac labels. This settles Lam's questions for types B and C in the affirmative and for type D in the negative. The main tool is a combinatorial two row model for a totally asymmetric simple exclusion process (TASEP) called the D*-TASEP, with four parameters. By specializing the parameters in different ways, we obtain TASEPs for each of the Weyl groups mentioned above. Computing certain correlations in these TASEPs gives the desired limiting directions.
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| 9. |
- Aas, Erik, 1990-
(author)
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Stationary probability of the identity for the TASEP on a Ring
- 2012
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Other publication (other academic/artistic)abstract
- Consider the following Markov chain on permutations of length n. At each time step we choose a random position. If the letter at that position is smaller than the letter immediately to the left (cyclically) then these letters swap positions. Otherwise nothing happens, corresponding to a loop in the Markov chain. This is the circular TASEP. We compute the average proportion of time the chain spends at the identity permutation (and, in greater generality, at sorted words). This answers a conjecture by Thomas Lam.
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| 10. |
- Aas, Erik
(author)
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TASEP in any Weyl group
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Other publication (other academic/artistic)abstract
- We investigate a Markov chain dened by Thomas Lam [6], whichgeneralizes the multi-type TASEP on a ring to any Weyl group. For groups of typeC we dene an analogue of the multiline queues of Ferrari and Martin (which com-pute the stationary distribution for the classical TASEP). While our constructiondoes not suce for nding the stationary distribution, the construction gives thestationary distribution of a certain projection of Lam's chain. Also, our approach isincremental, in the sense that the construction appears to t into a pattern of 'con-jugation matrices', which remains to be fully worked out. We conjecture an explicitformula for the partition function of the model. Finally, we prove a theorem for theclassical TASEP which ts into the picture of viewing TASEP in a permutation-freeway.
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| 11. |
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| 12. |
- Aas, T. H., et al.
(author)
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Outbound open innovation in tourism : Lessons from an innovation project in Norway
- 2021
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In: Managing Open Service Innovation. - : World Scientific. - 9789811234491 - 9789811234484 ; , s. 167-185
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Book chapter (other academic/artistic)abstract
- The concept of open innovation was introduced by Henry Chesbrough in 2003 and refers to firms' use of inflows and outflows of knowledge to improve innovation processes. The concept has received considerable scholarly attention, but most research has focused on how manufacturing firms can manage inflows of knowledge during their product innovation processes. How outflows of knowledge can be managed by service firms during their innovation processes has until now not received the same scholarly attention. In this chapter, we therefore aim to contribute in filling this knowledge gap by observing an innovation project in tourism during its implementation. The findings suggested that tourism firms reveal different types of knowledge to other tourism firms in non-pecuniary outbound open innovation processes. In this case the knowledge was revealed in joint workshops where several firms participated and in bi-lateral meetings between two firms, and sometimes the knowledge was transferred via consultants or researchers that acted as "knowledge mediators". The findings also suggested that tourism firms decided to reveal knowledge to other firms to improve their image, increase the market size and to sharpen up their own business. Implications for management as well as the need for further research are discussed in the chapter.
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| 13. |
- Botteri, Edoardo, et al.
(author)
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Characteristics of non-participants in a randomized colorectal cancer screening trial comparing sigmoidoscopy and faecal immunochemical testing.
- 2022
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In: International journal of cancer. - : Wiley. - 1097-0215 .- 0020-7136. ; 151:3, s. 361-371
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Journal article (peer-reviewed)abstract
- Public health systems should guarantee universal access to health care services, including cancer screening. We assessed whether certain population subgroups were underrepresented among participants in colorectal cancer screening with sigmoidoscopy and faecal immunochemical testing (FIT). Between 2012 and 2019, about 140,000 individuals aged 50-74years were randomly invited to once-only sigmoidoscopy or first round of FIT screening. This study included 46,919 individuals invited to sigmoidoscopy and 70,019 to FIT between 2012 and 2017. We used logistic regression models to evaluate if demographic and socioeconomic factors and use of certain drugs were associated with participation. 24,159 (51.5%) individuals attended sigmoidoscopy and 40,931 (58.5%) FIT screening. Male gender, young age, low education and income, being retired or unemployed, living alone, being an immigrant, long driving time to screening centre, and use of antidiabetic and psychotropic drugs were associated with low participation in both screening groups. Many of these factors also predicted low acceptance of colonoscopy after positive FIT. While male gender, young age and living alone were more strongly associated with non-participation in FIT than sigmoidoscopy, low education and income, being retired or immigrant and long driving time were more strongly associated with non-participation in sigmoidoscopy than FIT. In conclusion, participation was lower in sigmoidoscopy than FIT. Predictors of non-participation were similar between arms. However, low socioeconomic status, being an immigrant and long driving time affected participation more in sigmoidoscopy screening, suggesting that FIT may guarantee more equal access to screening services than sigmoidoscopy.
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| 14. |
- Egge-Jacobsen, Wolfgang, et al.
(author)
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O-Linked glycosylation of the PilA pilin protein of francisella tularensis : identification of the endogenous protein-targeting oligosaccharyltransferase and characterization of the native oligosaccharide
- 2011
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In: Journal of Bacteriology. - Baltimore : Williams & Wilkins. - 0021-9193 .- 1098-5530. ; 193:19, s. 5487-5497
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Journal article (peer-reviewed)abstract
- Findings from a number of studies suggest that the PilA pilin proteins may play an important role in the pathogenesis of disease caused by species within the genus Francisella. As such, a thorough understanding of PilA structure and chemistry is warranted. Here, we definitively identified the PglA protein-targeting oligosaccharyltransferase by virtue of its necessity for PilA glycosylation in Francisella tularensis and its sufficiency for PilA glycosylation in Escherichia coli. In addition, we used mass spectrometry to examine PilA affinity purified from Francisella tularensis subsp. tularensis and F. tularensis subsp. holarctica and demonstrated that the protein undergoes multisite, O-linked glycosylation with a pentasaccharide of the structure HexNac-HexHex-HexNac-HexNac. Further analyses revealed microheterogeneity related to forms of the pentasaccharide carrying unusual moieties linked to the distal sugar via a phosphate bridge. Type A and type B strains of Francisella subspecies thus express an O-linked protein glycosylation system utilizing core biosynthetic and assembly pathways conserved in other members of the proteobacteria. As PglA appears to be highly conserved in Francisella species, O-linked protein glycosylation may be a feature common to members of this genus.
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| 15. |
- Högberg, Johan, et al.
(author)
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Herding the Hordes : Using Location-Based Services and Mobile Messaging to Affect Visitor Behavior
- 2020
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In: Journal of Hospitality & Tourism Research. - : Sage Publications. - 1096-3480 .- 1557-7554. ; 44:5, s. 870-878
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Journal article (peer-reviewed)abstract
- This study investigates modes of moving visitors in a tourist location using a location-based service. Two field experiments were conducted at a zoo using real visitors as participants and behavior-based dependent variables. Experiment 1 included 2,618 visitors and investigated whether the amount of rewards, in the form of free spins on a wheel of fortune, would affect the choice to move to this wheel and claim the offered rewards. The choice of using this offer was used as a dependent variable. Experiment 2 included 970 visitors and investigated whether labelling participants with a fitting trait led them to move to a certain location. Geographical data using iBeacon logging was used as the dependent variable. Using chi-square tests for independence, we causally show that both the reward and the label had a positive and significant effect on moving the visitors to the targeted location.
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| 16. |
- Karlsson, Per Erik, et al.
(author)
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Biomass burning in eastern Europe during spring 2006 caused high deposition of ammonium in northern Fennoscandia
- 2013
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 176, s. 71-79
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Journal article (peer-reviewed)abstract
- High air concentrations of ammonium were detected at low and high altitude sites in Sweden, Finland and Norway during the spring 2006, coinciding with polluted air from biomass burning in eastern Europe passing over central and northern Fennoscandia. Unusually high values for throughfall deposition of ammonium were detected at one low altitude site and several high altitude sites in north Sweden. The occurrence of the high ammonium in throughfall differed between the summer months 2006, most likely related to the timing of precipitation events. The ammonia dry deposition may have contributed to unusual visible injuries on the tree vegetation in northern Fennoscandia that occurred during 2006, in combination with high ozone concentrations. It is concluded that long-range transport of ammonium from large-scale biomass burning may contribute substantially to the nitrogen load at northern latitudes. (C) 2013 Elsevier Ltd. All rights reserved.
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| 17. |
- Laj, Paolo, et al.
(author)
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A global analysis of climate-relevant aerosol properties retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories
- 2020
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In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 13:8, s. 4353-4392
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Journal article (peer-reviewed)abstract
- Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.
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| 18. |
- Marchetto, Aldo, et al.
(author)
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Good Agreement Between Modeled and Measured Sulfur and Nitrogen Deposition in Europe, in Spite of Marked Differences in Some Sites
- 2021
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In: Frontiers in Environmental Science. - : Frontiers Media SA. - 2296-665X. ; 9
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Journal article (peer-reviewed)abstract
- Atmospheric nitrogen and sulfur deposition is an important effect of atmospheric pollution and may affect forest ecosystems positively, for example enhancing tree growth, or negatively, for example causing acidification, eutrophication, cation depletion in soil or nutritional imbalances in trees. To assess and design measures to reduce the negative impacts of deposition, a good estimate of the deposition amount is needed, either by direct measurement or by modeling. In order to evaluate the precision of both approaches and to identify possible improvements, we compared the deposition estimates obtained using an Eulerian model with the measurements performed by two large independent networks covering most of Europe. The results are in good agreement (bias <25%) for sulfate and nitrate open field deposition, while larger differences are more evident for ammonium deposition, likely due to the greater influence of local ammonia sources. Modeled sulfur total deposition compares well with throughfall deposition measured in forest plots, while the estimate of nitrogen deposition is affected by the tree canopy. The geographical distribution of pollutant deposition and of outlier sites where model and measurements show larger differences are discussed.
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