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• 101.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Inferring Human Situation using Proximity to Smart Objects2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Human proximity tracking and human situation inference are exploited for comprehending human interaction with objects in kitchen. The importance of this study is to offer interactive and personalized kitchen environment for elderly and disabled people. Also, this smart environment allows for independent living for elderly and disabled people. This study proposes human proximity tracking and inferring human situation in smart environment. A precision of 100% and a recall of 65.22% were obtained from the result of proximity tracking. The result of precision indicates that human proximity tracking works accurately in kitchen environment. Interms of human situation inference, the result of accuracy of fuzzy logic system was obtained as above 96% precision in each situative space model set, except recognizable set. This result shows that system works well with a few exceptions in relation to human situation inference.

• 102.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
SmallTail: Scaling Cores and Probabilistic Cloning Requests for Web Systems2018In: 15TH IEEE INTERNATIONAL CONFERENCE ON AUTONOMIC COMPUTING (ICAC 2018), IEEE , 2018, p. 31-40Conference paper (Refereed)

Users quality of experience on web systems are largely determined by the tail latency, e.g., 95th percentile. Scaling resources along, e.g., the number of virtual cores per VM, is shown to be effective to meet the average latency but falls short in taming the latency tail in the cloud where the performance variability is higher. The prior art shows the prominence of increasing the request redundancy to curtail the latency either in the off-line setting or without scaling-in cores of virtual machines. In this paper, we propose an opportunistic scaler, termed SmallTail, which aims to achieve stringent targets of tail latency while provisioning a minimum amount of resources and keeping them well utilized. Against dynamic workloads, SmallTail simultaneously adjusts the core provisioning per VM and probabilistically replicates requests so as to achieve the tail latency target. The core of SmallTail is a two level controller, where the outer loops controls the core provision per distributed VMs and the inner loop controls the clones in a finer granularity. We also provide theoretical analysis on the steady-state latency for a given probabilistic replication that clones one out of N arriving requests. We extensively evaluate SmallTail on three different web systems, namely web commerce, web searching, and web bulletin board. Our testbed results show that SmallTail can ensure the 95th latency below 1000 ms using up to 53% less cores compared to the strategy of constant cloning, whereas scaling-core only solution exceeds the latency target by up to 70%.

• 103.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
A Tree-based Protocol for Enforcing Quotas in Clouds2014In: 2014 IEEE WORLD CONGRESS ON SERVICES (SERVICES), 2014, p. 279-286Conference paper (Refereed)

Services are increasingly being hosted on cloud nodes to enhance their performance and increase their availability. The virtually unlimited availability of cloud resources enables service owners to consume resources without quantitative restrictions, paying only for what they use. To avoid cost overruns, resource consumption must be controlled and capped when necessary. We present a distributed tree-based protocol for managing quotas in clouds that minimizes communication overheads and reduces the time required to determine whether a quota has been exhausted. Experimental evaluation shows that our protocol reduces communication costs by 42% relative to a distributed baseline solution and is up to 15 times faster.

• 104.
Universitat Rovira i Virgili.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Universitat Rovira i Virgili.
L systems as Bio-MAS for natural language processing2010In: Trends in practical applications of agents and multiagent systems: 8th International Conference on Practical Applications of Agents and Multiagent Systems (PAAMS 2010) / [ed] Y. Demazeau et al., Berlin: Springer , 2010, p. 395-402Conference paper (Refereed)

In this paper, we claim that Lindenmayer systems (L systems) –more precisely, ET0L systems– can be considered as bio-inspired multi-agent systems that, because of its inherent features, can be usefully applied to the field of natural language processing (NLP). L systems are a biologically inspired branch of the field of formal languages that provide a parallel and non-sequential grammatical formalism and that can be expressed as a multi-agent system. Taking into account these features and the benefits of the multi-agent approach to NLP, we propose to apply L systems to the description, analysis and processing of natural languages.

• 105.
Universitat Rovira i Virgili.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Universitat Rovira i Virgili.
The linguistic relevance of Lindenmayer systems2010In: Proceedings of the international conference on agents and artificial intelligence:  volume 2 - Agents, Valencia, Spain - ICAART / [ed] J. Filipe, A. Fred, and B. Sharp, Valencia: INSTICC Press , 2010, p. 395-402Conference paper (Refereed)

In this paper, we investigate the linguistic relevance of Lindenmayer Systems (L Systems). L systems were introduced in the late sixties by Aristid Lindemayer as a mathematical theory of biological development. Thus they can be considered as one of the first bio-inspired models in the theory of formal languages. Two main properties in L systems are 1) the idea of parallelism in the rewriting process and 2) their expressiveness to describe non-context free structures that can be found in natural languages. Therefore, the linguistic relevance of this formalism is clearly based on three main features: bio-inspiration, parallelism and generation of non-context free languages. Despite these interesting properties, L systems have not been investigated from a linguistic point of view. With this paper we point out the interest of applying these bio-inspired systems to the description and processing of natural language.

• 106.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
The use of terrestrial photogrammetry to estimate soil motion rates in non-sorted circlesManuscript (preprint) (Other academic)

Soil motion induced by cryogenic processes is known for creating soil surface structures (patterned ground) and redistributing carbon within Arctic soils. Lateral and vertical soil motion created by cryogenic processes proceeds over annual to millennial time-scales and is difficult to quantify without adopting disruptive soil sampling techniques. In this study, we evaluate the use of terrestrial close range photogrammetry to calculate soil motion rates within a patterned ground system (non-sorted circles). The measured rates of lateral and vertical motion were estimated and used to infer the importance of physical soil transport for the formation of non-sorted circles as well as the trajectories of soil carbon. Soil experiencing significant vertical displacement between years covered approximately 65% of the non-sorted circles and had surface levels fluctuating between 4 and -2.1 cm. Systematic lateral motion of surface stones allowed detection of lateral motion working outwards from the centre towards the sides, at rates ranging between 0.1 and 6.3 cm yr-1. We conclude that terrestrial close range photogrammetry can be used to identify the main soil movements within non-sorted circles and that this transport is an important factor controlling the trajectories of soil carbon over centennial to millennial timescales.

• 107.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Measuring soil motion with terrestrial close range photogrammetry in periglacial environments2014In: EUCOP 4: Book of Abstracts / [ed] Gonçalo Vieira, Pedro Pina, Carla Mora and António Correia, University of Lisbon and the University of Évora , 2014, p. 351-351Conference paper (Other academic)

Cryoturbation plays an important role in the carbon cycle as it redistributes carbon deeper down in the soil where the cold temperature prevents microbial decomposition. This contribution is also included in recent models describing the long-term build up of carbon stocks in artic soils. Soil motion rate in cryoturbated soils is sparsely studied. This is because the internal factors maintaining cryoturbation will be affected by any excavation, making it impossible to remove soil samples or install pegs without changing the structure of the soil. So far, mainly the motion of soil surface markers on patterned ground has been used to infer lateral soil motion rates. However, such methods constrain the investigated area to a predetermined distribution of surface markers that may result in a loss of information regarding soil motion in other parts of the patterned ground surface.

We present a novel method based on terrestrial close range (<5m) photogrammetry to calculate lateral and vertical soil motion across entire small-scale periglacial features, such as non-sorted circles (frost boils). Images were acquired by a 5-camera calibrated rig from at least 8 directions around a non-sorted circle. During acquisition, the rig was carried by one person in a backpack-like portable camera support system. Natural feature points were detected by SIFT and matched between images using the known epipolar geometry of the calibrated rig. The 3D coordinates of points matched between at least 3 images were calculated to create a point cloud of the surface of interest. The procedure was repeated during two consecutive years to be able to measure any net displacement of soil and calculate rates of soil motion. The technique was also applied to a peat palsa where multiple exposures where acquired of selected areas.

The method has the potential to quantify areas of disturbance and estimate lateral and vertical soil motion in non-sorted circles. Furthermore, it should be possible to quantify peat erosion and rates of desiccation crack formations in peat palsas. This tool could provide new information about cryoturbation rates that could improve existing soil carbon models and increase our understanding about how soil carbon stocks will respond to climate change.

• 108. Beco, S
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Cloud Computing and RESERVOIR project2009In: Nuovo Cimento C, ISSN ISSN 1124-1896, Vol. 32, no 2, p. 99-103Article in journal (Refereed)
• 109. Belabbaci, Ahlem
Umeå University, Faculty of Science and Technology, Department of Computing Science. FASTAR Research Group, Stellenbosch University, South Africa.
Tree pattern matching from regular tree expressions2018In: Kybernetika (Praha), ISSN 0023-5954, E-ISSN 1805-949X, Vol. 54, no 2, p. 221-242Article in journal (Refereed)

In this work we deal with tree pattern matching over ranked trees, where the pattern set to be matched against is defined by a regular tree expression. We present a new method that uses a tree automaton constructed inductively from a regular tree expression. First we construct a special tree automaton for the regular tree expression of the pattern E, which is somehow a generalization of Thompson automaton for strings. Then we run the constructed automaton on the subject tree t. The pattern matching algorithm requires an O(vertical bar t vertical bar vertical bar E vertical bar) time complexity, where vertical bar t vertical bar is the number of nodes of t and vertical bar E vertical bar is the size of the regular tree expression E. The novelty of this contribution besides the low time complexity is that the set of patterns can be infinite, since we use regular tree expressions to represent patterns.

• 110.
Ben-Gurion University of the Negev, Israel.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Ben-Gurion University of the Negev, Israel. Institute of Mathematics, Kiev, Ukraine. Ben-Gurion University of the Negev, Israel.
Problems of classifying associative or Lie algebras over a field of characteristic not 2 and finite metabelian groups are wild2009In: The Electronic Journal of Linear Algebra, ISSN 1537-9582, E-ISSN 1081-3810, Vol. 18, p. 516-529Article in journal (Refereed)

Let F be a field of characteristic different from 2. It is shown that the problems of classifying

(i) local commutative associative algebras over F with zero cube radical,

(ii) Lie algebras over F with central commutator subalgebra of dimension 3, and

(iii) finite p-groups of exponent p with central commutator subgroup of order $p^{3}$ are hopeless since each of them contains

• the problem of classifying symmetric bilinear mappings UxU → V , or

• the problem of classifying skew-symmetric bilinear mappings UxU → V ,

in which U and V are vector spaces over F (consisting of p elements for p-groups (iii)) and V is 3-dimensional. The latter two problems are hopeless since they are wild; i.e., each of them contains the problem of classifying pairs of matrices over F up to similarity.

• 111. Ben Yehuda, M.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
RESERVOIR: An ICT Infrastructure for Reliable and Effective Delivery of Services as Utilities2008Report (Other academic)
• 112.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Graph Transformation for Incremental Natural Language Analysis.2014Other (Other academic)
• 113.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Mildly context-sensitive grammar formalisms and natural language2010In: Language as a Complex System: Interdisciplinary Approaches / [ed] Gemma Bel-Enguix and M. Dolores Jimenez-Lopez, Newcastle upon Tyne, UK: Cambridge Scholars Publishing , 2010, p. 71-91Chapter in book (Other (popular science, discussion, etc.))
• 114.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Algorithmic properties of Millstream systems2010In: Developments in Language Theory: 14th International Conference, DLT 2010 / [ed] Sheng Yu, Springer Berlin/Heidelberg, 2010, p. 54-65Conference paper (Refereed)

Millstream systems have recently been proposed as a formalization of the linguistic idea that natural language should be described as a combination of different modules related by interfaces. In this paper we investigate algorithmic properties of Millstream systems having regular tree grammars as modules and MSO logic as interface logic. We focus on the so-called completion problem: Given trees generated by a subset of the modules, can they be completed into a valid configuration of the Millstream system?

• 115.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Institut fur Informatik, Universität Giessen.
Deterministic Stack Transducers2016In: Implementation and Application of Automata / [ed] Yo-Sub Han and Kai Salomaa, Springer, 2016, p. 27-38Conference paper (Refereed)

We introduce and investigate stack transducers, which are one-way stack automata with an output tape. A one-way stack automaton is a classical pushdown automaton with the additional ability to move the stack head inside the stack without altering the contents. For stack transducers, we distinguish between a digging and a non-digging mode. In digging mode, the stack transducer can write on the output tape when its stack head is inside the stack, whereas in non-digging mode, the stack transducer is only allowed to emit symbols when its stack head is at the top of the stack. These stack transducers have a motivation from natural language interface applications, as they capture long-distance dependencies in syntactic, semantic, and discourse structures.We study the computational capacity for deterministic digging and non-digging stack transducers, as well as for their non-erasing and checking versions. We finally show that even for the strongest variant of stack transducers the stack languages are regular.

• 116.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Deterministic Stack Transducers2017In: International Journal of Foundations of Computer Science, ISSN 0129-0541, Vol. 28, no 5, p. 583-601Article in journal (Refereed)

We introduce and investigate stack transducers, which are one-way stack automata with an output tape. A one-way stack automaton is a classical pushdown automaton with the additional ability to move the stack head inside the stack without altering the contents. For stack transducers, we distinguish between a digging and a non-digging mode. In digging mode, the stack transducer can write on the output tape when its stack head is inside the stack, whereas in non-digging mode, the stack transducer is only allowed to emit symbols when its stack head is at the top of the stack. These stack transducers have a motivation from natural-language interface applications, as they capture long-distance dependencies in syntactic, semantic, and discourse structures. We study the computational capacity for deterministic digging and non-digging stack transducers, as well as for their non-erasing and checking versions. We finally show that even for the strongest variant of stack transducers the stack languages are regular.

• 117.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Information, codes and languages: Essays dedicated to Helmut Jürgensen on the occassion of his 75th birthday – Preface2018In: Journal of Automata, Languages and Combinatorics, ISSN 1430-189X, Vol. 23, no 1–3, p. 2p. 3-4Article in journal (Refereed)

This special issue is dedicated to Professor Helmut Jürgensen on the occasion of his 75th birthday and in appreciation of his scientific work and his impact as teacher, mentor, and person. The sixteen papers in this special issue were submitted by invitation of the guest editors. Each paper was reviewed by at least two referees. The authors of the papers in this special issue are collaborators, co-authors, or scientific descendents of Helmut Jürgensen.

• 118.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Institut für Informatik, Universität Potsdam. Institut für Informatik, Universität Giessen. Institut für Informatik, Universität Giessen.
On input-revolving deterministic and nondeterministic finite automata2009In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 207, p. 1140-1155Article in journal (Refereed)

We introduce and investigate input-revolving finite automata, which are (nondeterministic) finite state automata with additional ability to shift the remaining part of the input. Three different modes of shifting are considered, namely revolving to the left, revolving to the right, and circular-interchanging. We investigate the computational capacities of these three types of automata and their deterministic variants, comparing any of the six classes of automata with each other and with further classes of well-known automata. In particular, it is shown that nondeterminism is better than determinism, that is, for all three modes of shifting there is a language accepted by the nondeterministic model but not accepted by any determinstic automaton of the same type. Concerning the closure properties most of the deterministic language families studied are not closed under standard operations. For example, we show that the family of languages accepted by deterministic right-revolving finite automata is an anti-AFL which is not closed under reversal and intersection.

• 119.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.

We introduce Millstream systems, a mathematical framework in the tradition of the Theory of Computation that uses logic to formalize the interfaces between different aspects of language, the latter being described by any number of independent modules. Unlike other approaches that serve a similar goal, Millstream systems neither presuppose nor establish a particular linguistic theory or focus, but can be instantiated in various ways to accomodate different points of view.

• 120.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Millstream Systems: a formal model for linking language modules by interfaces2010In: Proc. ACL 2010 Workshop on Applications of Tree Automata in Natural Language Processing (ATANLP 2010), The Association for Computer Linguistics , 2010Conference paper (Refereed)
• 121.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Drewes, FrankUmeå University, Faculty of Science and Technology, Department of Computing Science.
Proceedings of Umeå's 16th student conference in computing science: USCCS 20132013Conference proceedings (editor) (Other academic)
• 122.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Drewes, FrankUmeå University, Faculty of Science and Technology, Department of Computing Science.Freund, RudolfTechnical University Vienna.Otto, FriedrichTechnical University Kassel.
Fifth Workshop on Non-Classical Models for Automata and Applications - NCMA 2013, Umeå, Sweden, August 13 - August 14, 2013, Proceedings2013Conference proceedings (editor) (Refereed)
• 123.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Grammatical Inference of Graph Transformation Rules2015In: Proceedings of the 7th Workshop on Non-Classical Modelsof Automata and Applications (NCMA 2015), Austrian Computer Society , 2015, p. 73-90Conference paper (Refereed)
• 124.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Drewes, FrankUmeå University, Faculty of Science and Technology, Department of Computing Science.Hirvensalo, MikaOtto, Friedrich
Fundamenta Informaticae: special issue2015Conference proceedings (editor) (Other academic)
• 125.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Computer Science, The University of Western Ontario, London, Canada. Department of Computer Science, Stellenbosch University, South Africa.
Correct readers for the incremental construction of Millstream configurations by graph transformation2012Report (Other academic)

Millstream systems have been proposed as a non-hierarchical method for modelling natural language. Millstream congurations represent and connect multiple structural aspects of sentences. We present a method by which the Millstream congurations corresponding to a sentence are constructed. The construction is incremental, that is, it proceeds as the sentence is being read and is complete when the end of the sentence is reached. It is based on graph transformations and a lexicon which associates words with rules for the graph transformations.

• 126.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. The University of Western Ontario. University of Stellenbosch.
Correct Readers for the Incremental Construction of Millstream Configurations by Graph TransformationManuscript (preprint) (Other academic)
• 127.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Computer Science, Western University, London, Canada. Department of Computer Science, Stellenbosch University, South Africa.
Graph transformation for incremental natural language analysis2014In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 531, p. 1-25Article in journal (Refereed)

Millstream systems have been proposed as a non-hierarchical method for modelling natural language. Millstream configurations represent and connect multiple structural aspects of sentences. We present a method by which the Millstream configurations corresponding to a sentence are constructed. The construction is incremental, that is, it proceeds as the sentence is being read and is complete when the end of the sentence is reached. It is based on graph transformations and a lexicon which associates words with graph transformation rules that implement the incremental construction process.

• 128.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Middlesex College, The University of Western Ontario. Department of Mathematical Sciences, University of Stellenbosch.
Incremental Construction of Millstream Configurations Using Graph Transformation2011In: Proceedings of the 9th International Workshop on Finite State Methods and Natural Language Processing, Stroudsburg: Association for Computational Linguistics , 2011, p. 93-97Conference paper (Refereed)
• 129.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
University of the Witwatersrand, Johannesburg, South Africa.
Describing resource allocation to dynamically formed groups with grammars2019In: Simulation and modeling methodologies, technologies and applications: 7th international conference, (SIMULTECH) 2017, Madrid, Spain, July 26-28, 2017 : revised selected papers / [ed] Mohammad S. Obaidat, Tuncer I. Ören and Floriano De Rango, Springer, 2019, , p. 23p. 153-176Chapter in book (Refereed)

In this paper we model dynamic group formation and resource allocation with grammars in order to gain a deeper understanding into the involved processes. Modelling with grammars allows us to describe resource allocation and group formation as generative processes that provide, at any given time, information about at what stage the process of group formation and resource allocation is. We divide our model into four phases: (1) resource supply, (2) candidate group formation, (3) final group formation, and (4) resource distribution. In particular, we show that we can use permitting random context grammars to describe the first two phases. For the third phase we introduce an algorithm that determines based on a resource allocation strategy the final group to which resources are distributed. The last phase is described with random context grammars under a specific leftmost derivation mode. Our model shows that if information about the available resource and candidate group formation is distributed and kept separate, then the synchronisation of this information at a later stage (i.e. resource distribution phase) needs a more powerful grammar model.

• 130.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Freund, RudolfHirvensalo, MikaOtto, Friedrich
Fundamenta Informaticae2016Collection (editor) (Refereed)
• 131.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Non-Classical Models of Automata and Applications VI Preface2016In: Fundamenta Informaticae, ISSN 0169-2968, E-ISSN 1875-8681, Vol. 148, no 3-4, p. I-IIArticle in journal (Other academic)
• 132.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Freund, RudolfOtto, Friedrich
Sixth Workshop on Non-Classical Models for Automata and Applications: NCMA 2014, Kassel, Germany, July 28-29, 2014. Proceedings2014Conference proceedings (editor) (Refereed)
• 133.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
On ambiguity in learning from demonstration2010In: Intelligent Autonomous Systems 11 (IAS-11) / [ed] H. Christensen, F. Groen, and E. Petriu, Amsterdam: IOS Press , 2010, p. 47-56Conference paper (Refereed)

An overlooked problem in Learning From Demonstration is the ambiguity that arises, for instance, when the robot is equipped with more sensors than necessary for a certain task. Simply trying to repeat all aspects of a demonstration is seldom what the human teacher wants, and without additional information, it is hard for the robot to know which features are relevant and which should be ignored. This means that a single demonstration maps to several different behaviours the teacher might have intended. This one-to-many (or many-to-many) mapping from a demonstration (or several demonstrations) into possible intended behaviours is the ambiguity that is the topic of this paper. Ambiguity is defined as the size of the current hypothesis space. We investigate the nature of the ambiguity for different kinds of hypothesis spaces and how it is reduced by a new concept learning algorithm.

• 134.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Hellström, ThomasUmeå University, Faculty of Science and Technology, Department of Computing Science.
Proceedings of Umeå's 18th student conference in computing science: USCCS 2014.12014Conference proceedings (editor) (Other academic)
• 135.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Hellström, ThomasUmeå University, Faculty of Science and Technology, Department of Computing Science.
Proceedings of Umeå's 20th student conference in computing science: USCCS 20162016Conference proceedings (editor) (Other academic)
• 136.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Hellström, ThomasUmeå University, Faculty of Science and Technology, Department of Computing Science.
Proceedings of Umeå's 21st student conference in computing science: USCCS 20172017Conference proceedings (editor) (Other academic)
• 137.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Computing Science.
Hellström, ThomasUmeå University, Faculty of Science and Technology, Department of Computing Science. Department of Computing Science.
Proceedings of Umeå's 22nd Student Conference in Computing Science (USCCS 2018)2018Conference proceedings (editor) (Other academic)
• 138.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Hellström, ThomasUmeå University, Faculty of Science and Technology, Department of Computing Science.
Proceedings of Umeå's 23rd Student Conference in Computing Science: USCCS 20192019Conference proceedings (editor) (Other academic)

The Umeå Student Conference in Computing Science (USCCS) is organized annually as part of a course given by the Computing Science department at Umeå University. The objective of the course is to give the students a practical introduction to independent research, scientific writing, and oral presentation.

A student who participates in the course first selects a topic and a research question that he or she is interested in. If the topic is accepted, the student outlines a paper and composes an annotated bibliography to give a survey of the research topic. The main work consists of conducting the actual research that answers the question asked, and convincingly and clearly reporting the results in a scientific paper. Another major part of the course is multiple internal peer review meetings in which groups of students read each others’ papers and give feedback to the author. This process gives valuable training in both giving and receiving criticism in a constructive manner. Altogether, the students learn to formulate and develop their own ideas in a scientific manner, in a process involving internal peer reviewing of each other’s work and under supervision of the teachers, and incremental development and refinement of a scientific paper.

Each scientific paper is submitted to USCCS through an on-line submission system, and receives reviews written by members of the Computing Science department. Based on the review, the editors of the conference proceedings (the teachers of the course) issue a decision of preliminary acceptance of the paper to each author. If, after final revision, a paper is accepted, the student is given the opportunity to present the work at the conference. The review process and the conference format aims at mimicking realistic settings for publishing and participation at scientific conferences.

• 139.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Towards Proactive Robot Behavior Based on Incremental Language Analysis2014In: MMRWHRI '14 Proceedings of the 2014 Workshop on Multimodal, Multi-Party, Real-World Human-Robot Interaction / [ed] Mary Ellen Foster, Manuel Giuliani, Ronald P. A. Petrick, 2014, p. 21-22Conference paper (Refereed)

This paper describes ongoing and planned work on incremental language processing coupled to inference of expected robot actions. Utterances are processed word-by-word, simultaneously with inference of expected robot actions, thus enabling the robot to prepare and act proactively to human utterances. We believe that such a model results in more natural human-robot communication since proactive behavior is a feature of human-human communication.

• 140.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Ocean Networks Canada and Department of Computer Science, University of Victoria, Victoria, Canada.
On the Degree of Nondeterminism of Tree Adjoining Languages and Head Grammar Languages2017In: Descriptional Complexity of Formal Systems: 19th IFIP WG 1.02 International Conference, DCFS 2017, Milano, Italy, July 3-5, 2017, Proceedings / [ed] Giovanni Pighizzini, Cezar Câmpeanu, 2017, p. 65-76Conference paper (Refereed)

The degree of nondeterminism is a measure of syntactic complexity which was investigated for parallel and sequential rewriting systems. In this paper, we consider the degree of nondeterminsm for tree adjoining grammars and their languages and head grammars and their languages. We show that a degree of nondeterminism of 2 suffices for both formalisms in order to generate all languages in their respective language families. Furthermore, we show that deterministic tree adjoining grammars (those with degree of nondeterminism equal to 1), can generate non-context-free languages, in contrast to deterministic head grammars which can only generate languages containing a single word.

• 141.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Institut für Informatik, Universität Giessen. Institut für Informatik, Universität Giessen. Institut für Informatik, Universität Giessen.
Input-Driven Stack Automata2012In: IFIP TCS: Theoretical Computer Science - 7th IFIP TC 1/WG 2.2 International Conference, TCS 2012, Amsterdam, 2012. Proceedings / [ed] Jos C. M. Baeten, Thomas Ball, and Frank S. de Boer, 2012, p. 28-42Conference paper (Refereed)

We introduce and investigate input-driven stack automata, which are a generalization of input-driven pushdown automata that recently became popular under the name visibly pushdown automata. Basically, the idea is that the input letters uniquely determine the operations on the pushdown store. This can nicely be generalized to stack automata by further types of input letters which are responsible for moving the stack pointer up or down. While visibly pushdown languages share many desirable properties with regular languages, input-driven stack automata languages do not necessarily so. We prove that deterministic and non- deterministic input-driven stack automata have different computational power, which shows in passing that one cannot construct a deterministic input-driven stack automaton from a nondeterministic one. We study the computational capacity of these devices. Moreover, it is shown that the membership problem for nondeterministic input-driven stack automata languages is NP-complete.

• 142.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Computing Science.
Institut de Robotica i Informatica Industrial, Technical University of Catalonia, Spain. Umeå University, Faculty of Science and Technology, Department of Computing Science.
On Interaction Quality in Human-Robot Interaction2017In: Proceedings of the 9th International Conference on Agents and Artificial Intelligence / [ed] H. Jaap van den Herik, Ana Paula Rocha, Joaquim Filipe, Setúbal: SciTePress, 2017, Vol. 1, p. 182-189Conference paper (Refereed)

In many complex robotics systems, interaction takes place in all directions between human, robot, and environment. Performance of such a system depends on this interaction, and a proper evaluation of a system must build on a proper modeling of interaction, a relevant set of performance metrics, and a methodology to combine metrics into a single performance value. In this paper, existing models of human-robot interaction are adapted to fit complex scenarios with one or several humans and robots. The interaction and the evaluation process is formalized, and a general method to fuse performance values over time and for several performance metrics is presented. The resulting value, denoted interaction quality, adds a dimension to ordinary performance metrics by being explicit about the interplay between performance metrics, and thereby provides a formal framework to understand, model, and address complex aspects of evaluation of human-robot interaction.

• 143.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Institut fuer Informatik, Universität Giessen. Institut fuer Informatik, Universität Giessen.
Extended Uniformly Limited T0L Languages and Mild Context-Sensitivity2016In: Eight Workshop on Non-Classical Models of Automata and Applications (NCMA 2016): Short Papers / [ed] Henning Bordihn, Rudolf Freund, Benedek Nagy, and György Vaszil, Wien: Institut für Computersprachen , 2016, p. 35-46Conference paper (Refereed)

We study the fixed membership problem for k-uniformly-limited and propagating ET0L systems (kulEPT0L systems). To this end, the algorithm given in [7] is applied. It follows that kulEPT0L languages are parsable in polynomial time. Since kulEPT0L languages are semi-linear [1] and kulEPT0L systems generate certain non-context-free languages, which capture the non-context-free phenomena occurring in natural languages, this is the last building block to show that kulEPT0L languages, for k ≥ 2, belong to the family of mildly context-sensitive languages.

• 144.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
User friendly Digital Book Circles - A Case study on Traditional and Digital Book Circles with suggested Guidelines2020Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis

• 145.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
A unified discrete-continuous sensitivity analysis method for shape optimization2010In: Applied and Numerical Partial Differential Equations: Scientific Computing in Simulation, Optimization and Control in a Multidisciplinary Context / [ed] W. Fitzgibbon, Y.A. Kuznetsov, P. Neittaanmäki, J. Periaux, O. Pironneau, Springer, 2010, p. 25-39Conference paper (Refereed)

Boundary shape optimization problems for systems governed by partial differential equations involve a calculus of variation with respect to boundary modifications. As typically presented in the literature, the first-order necessary conditions of optimality are derived in a quite different manner for the problems before and after discretization, and the final directional-derivative expressions look very different. However, a systematic use of the material-derivative concept allows a unified treatment of the cases before and after discretization. The final expression when performing such a derivation includes the classical before-discretization (“continuous”) expression, which contains objects solely restricted to the design boundary, plus a number of “correction” terms that involve field variables inside the domain. Some or all of the correction terms vanish when the associated state and adjoint variables are smooth enough.

• 146.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Acoustic boundary layers as boundary conditions2018In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 371, p. 633-650Article in journal (Refereed)

The linearized, compressible Navier-Stokes equations can be used to model acoustic wave propagation in the presence of viscous and thermal boundary layers. However, acoustic boundary layers are notorious for invoking prohibitively high resolution requirements on numerical solutions of the equations. We derive and present a strategy for how viscous and thermal boundary-layer effects can be represented as a boundary condition on the standard Helmholtz equation for the acoustic pressure. This boundary condition constitutes an O (delta) perturbation, where delta is the boundary-layer thickness, of the vanishing Neumann condition for the acoustic pressure associated with a lossless sound-hard wall. The approximate model is valid when the wavelength and the minimum radius of curvature of the wall is much larger than the boundary layer thickness. In the special case of sound propagation in a cylindrical duct, the model collapses to the classical Kirchhoff solution. We assess the model in the case of sound propagation through a compression driver, a kind of transducer that is commonly used to feed horn loudspeakers. Due to the presence of shallow chambers and thin slits in the device, it is crucial to include modeling of visco-thermal losses in the acoustic analysis. The transmitted power spectrum through the device calculated numerically using our model agrees well with computations using a hybrid model, where the full linearized, compressible Navier-Stokes equations are solved in the narrow regions of the device and the inviscid Helmholtz equations elsewhere. However, our model needs about two orders of magnitude less memory and computational time than the more complete model.

• 147.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Department of Information Technology, Uppsala University. Department of Information Technology, Uppsala University.
A discontinuous Galerkin extension of the vertex-centered edge-based finite volume method2009In: Communications in Computational Physics, ISSN 1815-2406, Vol. 5, no 2-4, p. 456-468Article in journal (Refereed)

The finite volume (FV) method is the dominating discretization technique for computational fluid dynamics (CFD), particularly in the case of compressible fluids. The discontinuous Galerkin (DG) method has emerged as a promising high-accuracy alternative. The standard DG method reduces to a cell-centered FV method at lowest order. However, many of today's CFD codes use a vertex-centered FV method in which the data structures are edge based. We develop a new DG method that reduces to the vertex-centered FV method at lowest order, and examine here the new scheme for scalar hyperbolic problems. Numerically, the method shows optimal-order accuracy for a smooth linear problem. By applying a basic hp-adaption strategy, the method successfully handles shocks. We also discuss how to extend the FV edge-based data structure to support the new scheme. In this way, it will in principle be possible to extend an existing code employing the vertex-centered and edge-based FV discretization to encompass higher accuracy through the new DG method.

• 148.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Weak material approximation of holes with traction-free boundaries2012In: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 50, no 4, p. 1827-1848Article in journal (Refereed)

Consider the solution of a boundary-value problem for steady linear elasticity in which the computational domain contains one or several holes with traction-free boundaries. The presence of holes in the material can be approximated using a weak material; that is, the relative density of material rho is set to 0 < epsilon = rho << 1 in the hole region. The weak material approach is a standard technique in the so-called material distribution approach to topology optimization, in which the inhomogeneous relative density of material is designated as the design variable in order to optimize the spatial distribution of material. The use of a weak material ensures that the elasticity problem is uniquely solvable for each admissible value rho is an element of [epsilon, 1] of the design variable. A finite-element approximation of the boundary-value problem in which the weak material approximation is used in the hole regions can be viewed as a nonconforming but convergent approximation of a version of the original problem in which the solution is continuously and elastically extended into the holes. The error in this approximation can be bounded by two terms that depend on epsilon. One term scales linearly with epsilon with a constant that is independent of the mesh size parameter h but that depends on the surface traction required to fit elastic material in the deformed holes. The other term scales like epsilon(1/2) times the finite-element approximation error inside the hole. The condition number of the weak material stiffness matrix scales like epsilon(-1), but the use of a suitable left preconditioner yields a matrix with a condition number that is bounded independently of epsilon. Moreover, the preconditioned matrix admits the limit value epsilon -> 0, and the solution of corresponding system of equations yields in the limit a finite-element approximation of the continuously and elastically extended problem.

• 149.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Sound vibration damping optimization with application to the design of speakerphone casings2013In: : Paper id 5569, 2013Conference paper (Refereed)

We optimize the thickness distribution in a 1D beam model of an elastic plate, subject to forced vibration at one of its ends, in order to minimize the structural vibration in a given area of the plate. The optimization is carried out both in broadband and band-pass cases. Geometric constraints, weight constraints, and constraints on the static compliance are imposed in the optimization. A broadband optimization over 50 frequencies, evenly distributed in the 300–3400 Hz range, reduces the vibration by around 5–10 dB on average throughout the frequency range. When targeting only the higher end of the above frequency range, it is possible to achieve more dramatic results. Vibration reductions of 20 dB and more can be achieved in the 2300–2800 Hz region. In the latter case, the results suggest that a band-gap phenomenon occurs, similarly as for phononic band gap materials. To validate the results, the best-performing optimal shape for the clamped case was imported into a 3D computational structural model, and the resulting forced vibration response agreed well with the the beam-model computations. These results were first announced in a technical report by Lacis et al. [5].

• 150. Berglund, Anders
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Forword to the Special Section on the ECOOP'06 Workshop on Pedagogies and Tools for the Teaching and Learning of Object-Oriented Concepts2007In: Informatics in Education, Vol. 6, no 1, p. 3-4Article in journal (Other academic)
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