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  • 1.
    Abedi-Valugerdi, Manuchehr
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mercury and silver induce B cell activation and anti-nucleolar autoantibody production in outbred mouse stocks: are environmental factors more important than the susceptibility genes in connection with autoimmunity?2009In: Clinical and Experimental Immunology, ISSN 0009-9104, E-ISSN 1365-2249, Vol. 155, no 1, p. 117-124Article in journal (Refereed)
    Abstract [en]

    Environmental and predisposing genetic factors are known to play a crucial role in the development of systemic autoimmune diseases. With respect to the role of environmental factors, it is not known how and to what extent they contribute to the initiation and exacerbation of systemic autoimmunity. In the present study, I considered this issue and asked if environmental factors can induce autoimmunity in the absence of specific susceptible genes. The development of genetically controlled mercury- and silver-induced B cell activation and anti-nucleolar autoantibodies (ANolA) production in genetically heterozygous outbred Institute of Cancer Research (ICR), Naval Medical Research Institute (NMRI) and Black Swiss mouse stocks were analysed. Four weeks of treatment with both mercury and silver induced a strong B cell activation characterized by increased numbers of splenic antibody-secreting cells of at least one or more immunoglobulin (Ig) isotype(s) in all treated stocks. The three stocks also exhibited a marked increase in the serum IgE levels in response to mercury, but not silver. More importantly, in response to mercury a large numbers of ICR (88%), NMRI (96%) and Black Swiss (100%) mice produced different levels of IgG1 and IgG2a ANolA (a characteristic which is linked strictly to the H-2 genes). Similarly, but at lower magnitudes, treatment with silver also induced the production of IgG1 and IgG2a ANolA in 60% of ICR, 75% of NMRI and 100% of Black Swiss mice. Thus, the findings of this study suggest that long-term exposure to certain environmental factors can activate the immune system to produce autoimmunity per se, without requiring specific susceptible genes.

  • 2.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    A Social Semiotic Approach to Teaching and Learning Science2018Conference paper (Other academic)
    Abstract [en]

    In this presentation I will discuss the application of social semiotics to the teaching and learning of university science. Science disciplines leverage a wide range of semiotic resources such as graphs, diagrams, mathematical representations, hands on work with apparatus, language, gestures etc. In my work I study how students learn to integrate these resources to do physics and what teachers can do to help them in this process. Over the years, a number of theoretical constructs have been developed within the Physics Education Research Group in Uppsala to help us to better understand the different roles semiotic resources play in learning university physics. In this presentation I will explain some of these terms and give examples of their usefulness for teasing out how learning is taking place.

  • 3.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education.
    Building on higher education research - How can we take a scholarly approach to teaching and learning2018Conference paper (Other academic)
  • 4.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Disciplinary Affordance vs Pedagogical Affordance: Teaching the Multimodal Discourse of University Science2017Conference paper (Other academic)
    Abstract [en]

    The natural sciences have been extremely successful in modeling some specific aspects of the world around us. This success is in no small part due to the creation of generally accepted, paradigmatic ways of representing the world through a range of semiotic resources. The discourse of science is of necessity multimodal (see for example Lemke, 1998) and it is therefore important for undergraduate science students to learn to master this multimodal discourse (Airey & Linder, 2009). In this paper, I approach the teaching of multimodal science discourse via the concept of affordance. Since its introduction by Gibson (1979) the concept of affordance has been debated by a number of researchers. Most famous, perhaps is the disagreement between Gibson and Norman (1988) about whether affordances are inherent properties of objects or are only present when perceived by an organism. More recently, affordance has been drawn on in the educational arena, particularly with respect to multimodality (see Fredlund, 2015 for a recent example). Here, Kress et al (2001) have claimed that different modes have different specialized affordances. In the presentation the interrelated concepts of disciplinary affordance and pedagogical affordance will be presented. Both concepts make a radical break with the views of both Gibson and Norman in that rather than focusing on the perception of an individual, they refer to the disciplinary community as a whole. Disciplinary affordance is "the agreed meaning making functions that a semiotic resource fulfills for a disciplinary community". Similarly, pedagogical affordance is "the aptness of a semiotic resource for the teaching and learning of some particular educational content" (Airey, 2015). As such, in a teaching situation the question of whether these affordances are inherent or perceived becomes moot. Rather, the issue is the process through which students come to use semiotic resources in a way that is accepted within the discipline. In this characterization then, learning can be framed in terms of coming to perceive and leverage the disciplinary affordances of semiotic resources. In this paper, I will discuss: the disciplinary affordances of individual semiotic resources, how these affordances can be made “visible” to students and how the disciplinary affordances of semiotic resources are ultimately leveraged and coordinated in order to make science meanings.

  • 5.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    EMI, CLIL, EAP: What’s the difference?2018Conference paper (Other academic)
    Abstract [en]

    In this presentation I will examine the differences between the terms EMI (English Medium Instruction, CLIL (Content and Language Integrated Learning and EAP (English for Academic Purposes). I will also discuss what it means to become disciplinary literate in a first, second and third language.

  • 6.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Learning and Sharing Disciplinary Knowledge: The Role of Representations2017Conference paper (Other academic)
    Abstract [en]

    In recent years there has been a large amount of interest in the roles that different representations (graphs, algebra, diagrams, sketches, physical models, gesture, etc.) play in student learning. In the literature two distinct but interrelated ways of thinking about such representations can be identified. The first tradition draws on the principles of constructivism emphasizing that students need to build knowledge for themselves. Here students are encouraged to create their own representations by working with materials of various kinds and it is in this hands-on representational process that students come to develop their understanding.

    The second tradition holds that there are a number of paradigmatic ways of representing disciplinary knowledge that have been created and refined over time. These paradigmatic disciplinary representations need to be mastered in order for students to be able to both understand and effectively communicate knowledge within a given discipline.

    In this session I would like to open up a discussion about how these two ways of viewing representations might be brought together. To do this I will first present some of the theoretical and empirical work we have been doing in Sweden over the last fifteen years. In particular there are three concepts that I would like to introduce for our discussion: critical constellations of representations, the disciplinary affordance of representations and the pedagogical affordance of representations.

  • 7.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Research on physics teaching and learning, physics teacher education, and physics culture at Uppsala University2017Conference paper (Other academic)
    Abstract [en]

    This project compares the affordances and constraints for physics teachers’ professional identity building across four countries. The results of the study will be related to the potential consequences of this identity building for pupils’ science performance in school. The training of future physics teachers typically occurs across three environments, the physics department, the education department and school (during teaching practice). As they move through these three environments, trainees are in the process of building their professional identity. However, what is signalled as valuable for a future physics teacher differs considerably in different parts of the education. In educational research, professional identity has been used in a variety of ways (See for example overviews of the concept in Beauchamp & Thomas, 2009; and Beijaard, Meijer, & Verloop, 2004). In this project we draw on the work of Sfard and Pruzak (2005) who have defined identity as an analytical category for use in educational research. The project leverages this concept of identity as an analytical tool to understand how the value-systems present in teacher training environments and society as a whole potentially affect the future practice of trainee physics teachers. For identities to be recognized as professional they must fit into accepted discourses. Thus the project endeavours to identify discourse models that tacitly steer the professional identity formation of future physics teachers. Interviews will be carried out with trainee physics teachers and the various training staff that they meet during their education (physics lecturers, education lecturers, school mentors). It has been suggested that the perceived status of the teaching profession in society has a major bearing on the type of professional identity teachers can enact. Thus, in this project research interviews will be carried out in parallel across four countries with varying teacher status and PISA science scores: Sweden, Finland, Singapore and England. These interviews will be analysed following the design developed in a pilot study that has already carried out by the project group in Sweden. The research questions for the project are as follows: In four countries where the societal status of the teaching profession differs widely: What discourse models are enacted in the educational environments trainee physics teachers meet? What are the potential affordances and constraints of these discourse models for the constitution of physics teacher professional identities? In what ways do perceptions of the status assigned by society to the teaching profession potentially affect this professional identity building? What are the potential consequences of the answers to the above questions for the view of science communicated to pupils in school? In an extensive Swedish pilot study, four potentially competing discourse models were identified: these are: the critically reflective teacher, the practically well-equipped teacher, the syllabus implementer and the physics expert. Of these, the physics expert discourse model was found to dominate in both the physics department and amongst mentors in schools. In the physics expert discourse model the values of the discipline of physics dominate. Thus, the overarching goal of physics teaching is to create future physicists. In this model, the latest research in physics is seen as interesting and motivating, whereas secondary school subject matter is viewed as inherently unsophisticated and boring—something that needs to be made interesting. The model co-exists with the three other discourse models, which were more likely to be enacted in the education department. These other models value quite different goals such as the development of practical skills, reflective practice, critical thinking and citizenship. We claim that knowledge of the different discourse models at work in four countries with quite different outcomes on PISA science will useful in a number of ways. For teacher trainers, a better understanding of these models would allow informed decisions to be taken about the coordination of teacher education. For prospective teachers, knowledge of the discourse models at work during their education empowers them to question the kind of teacher they want to become.

  • 8.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Semiotic Resources and Disciplinary Literacy2017Conference paper (Other academic)
    Abstract [en]

    In this research project we focused on the different semiotic resources used in physics (e.g. graphs, diagrams, language, mathematics, apparatus, etc.). We were interested in the ways in which undergraduate physics students learn to combine the different resources used in physics in order to become “disciplinary literate” and what university lecturers do to help their students in this process. Comparative data on the disciplinary literacy goals of physics lecturers for their students was collected at five universities in South Africa and four universities in Sweden.

    One of the main contributions of the project concerned what we termed the disciplinary affordance of a semiotic resource, that is, the specific meaning-making functions a particular resource plays for the discipline. We contrasted these meaning-making functions with the way that students initially viewed the same resource.

    We proposed two ways that lecturers can direct their students’ attention towards the disciplinary affordances of a given resource. The first involves unpacking the disciplinary affordance in order to create a new resource with higher pedagogical affordance. Our second proposal involved the use of systematic variation in order to help students notice the disciplinary relevant aspects of a given resource. A total of 19 articles/book chapters were published as a direct result of this funding.

  • 9.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    The Concept of Affordance in the Teaching and Learning of Undergraduate Science2018Conference paper (Other academic)
    Abstract [en]

    Since its introduction by Gibson (1979) the concept of affordance has been debated by a number of researchers. Most famous, perhaps is the disagreement between Gibson and Norman(1988) about whether affordances are inherent properties of objects or are only present when perceived by an organism. More recently, affordance has been drawn on in the educational arena, particularly with respect to multimodality (see Fredlund, 2015 for a recent example). 

    In the presentation the interrelated concepts of disciplinary affordance and pedagogical affordance will be presented. Both concepts make a radical break with the views of both Gibson and Norman in that rather than focusing on the perception of an individual, they refer to the disciplinary community as a whole. Disciplinary affordance is "the agreed meaning making functions that a semiotic resource fulfills for a disciplinary community". Similarly, pedagogical affordance is "the aptness of a semiotic resource for the teaching and learning of some particular educational content" (Airey, 2015). As such, in a teaching situation the question of whether these affordances are inherent or perceived becomes moot. Rather, the issue is the process through which students come to use semiotic resources in a way that is accepted within the discipline. In this characterization then, learning can be framed in terms of coming to perceive and leverage the disciplinary affordances of semiotic resources. 

  • 10.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Using variation and unpacking to help students decode disciplinary-specific semiotic resources2018Conference paper (Other academic)
    Abstract [en]

    In this presentation I will describe a social semiotic approach (Halliday 1978; van Leeuwen 2005) to the multimodal teaching and learning of a discipline that takes variation theory (Marton & Booth 1997; Runesson 2005) as its theoretical framing. Following Airey and Linder (2017:95) I define social semiotics as “the study of the development and reproduction of specialized systems of meaning making in particular sections of society”

    Learning at university level involves coming to understand the ways in which disciplinary-specific semiotic resources can be coordinated to make appropriate disciplinary meanings (Airey & Linder 2009). Nowhere is this more true than in undergraduate physics where a particularly wide range of semiotic resources such as graphs, diagrams, mathematics and language are essential for meaning making.  In order to learn to make these disciplinary meanings, students need to discover the disciplinary affordances(Fredlund et al. 2012, 2014; Airey & Linder 2017) of the semiotic resources used in their discipline. 

    Fredlund et al. (2015) propose a three-stage process that lecturers can use to help their students:  

    1. Identify the disciplinary relevant aspects needed for a particular task. 

    2. Select semiotic resources that showcase these aspects. 

    3. Create structured variation within these semiotic resources to help students notice the disciplinary relevant aspects and their relationships to each other.

    However, many disciplinary specific semiotic resources have been rationalized to create a kind of disciplinary shorthand(Airey 2009). In such cases the disciplinary relevant aspects needed may no longer be present in resources used, but are rather implied. In such cases the resources will need to be unpacked for students (Fredlund et al. 2014).  Such unpacking increases the pedagogical affordance of semiotic resources but simultaneously decreases their disciplinary affordance. 

  • 11.
    Airey, John
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Grundström Lindqvist, Josefine
    Kung, Rebecca
    What does it mean to understand a physics equation?: A study of undergraduate answers in three countries2017Conference paper (Other academic)
    Abstract [en]

    In this paper we are interested in how undergraduate students in the US, Australia and Sweden experience the physics equations they meet in their education. We asked over 350 students the same simple question: How do you know when you understand a physics equation? Students wrote free-text answers to this question and these were transcribed and coded. The analysis resulted in eight themes (significance, origin, describe, predict, parts, relationships, calculate and explain). Each of these themes represents a different disciplinary aspect of student understanding of physics equations. We argue that together the different aspects we find represent a more holistic view of physics equations that we would like all our students to experience. Based on this work we wondered how best to highlight this more holistic view of equations. This prompted us to write a set of questions that reflect the original data with respect to the eight themes. We suggest that when students are working with problem solving they may ask themselves these questions in order to check their holistic understanding of what the physics equations they are using represent. In continuing work we are asking the same question to a cohort of physics lecturers. We are also trialling the themes and related questions that we generated in teaching situations. Here we are interested in whether students perceive the questions as helpful in their learning.

  • 12.
    Airey, John
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden; Linnaeus University, Sweden.
    Larsson, Johanna
    Developing Students’ Disciplinary Literacy? The Case of University Physics2018In: Global Developments in Literacy Research for Science Education / [ed] Kok-Sing Tang, Kristina Danielsson, Springer, 2018, p. 357-376Chapter in book (Refereed)
    Abstract [en]

    In this chapter we use the concept of disciplinary literacy (Airey, 2011a, 2013) to analyze the goals of university physics lecturers. Disciplinary literacy refers to a particular mix of disciplinary-specific communicative practices developed for three specific sites: the academy, the workplace and society. It has been suggested that the development of disciplinary literacy may be seen as one of the primary goals of university studies (Airey, 2011a).

    The main data set used in this chapter comes from a comparative study of physics lecturers in Sweden and South Africa (Airey, 2012, 2013; Linder, Airey, Mayaba, & Webb, 2014). Semi-structured interviews were carried out using a disciplinary literacy discussion matrix (Airey, 2011b), which enabled us to probe the lecturers’ disciplinary literacy goals in the various semiotic resource systems used in undergraduate physics (i.e. graphs, diagrams, mathematics, language).

    The findings suggest that whilst physics lecturers have strikingly similar disciplinary literacy goals for their students, regardless of setting, they have very different ideas about whether they themselves should teach students to handle these disciplinary-specific semiotic resources. It is suggested that the similarity in physics lecturers’ disciplinary literacy goals across highly disparate settings may be related to the hierarchical, singular nature of the discipline of physics (Bernstein, 1999, 2000).

    In the final section of the chapter some preliminary evidence about the disciplinary literacy goals of those involved in physics teacher training is presented. Using Bernstein’s constructs, a potential conflict between the hierarchical singular of physics and the horizontal region of teacher training is noticeable.

    Going forward it would be interesting to apply the concept of disciplinary literacy to the analysis of other disciplines—particularly those with different combinations of Bernstein’s classifications of hierarchical/horizontal and singular/region.

  • 13.
    Airey, John
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Larsson, Johanna
    Linder, Anne
    Investigating Undergraduate Physics Lecturers’ Disciplinary Literacy Goals For Their Students2017Conference paper (Other academic)
    Abstract [en]

    In this presentation we use the concept of disciplinary literacy (Airey, 2011a; 2013) to analyse the expressed learning goals of university physics lecturers for their students. We define disciplinary literacy in terms of learning to control a particular set of multimodal communicative practices. We believe it is important to document the expressed intentions of lecturers in this way, since it has previously been suggested that the development of such disciplinary literacy may be seen as one of the primary goals of university studies (Airey, 2011a).

    The main data set used in this presentation comes from a comparative study of 30 physics lecturers from Sweden and South Africa. (Airey, 2012, 2013; Linder et al, 2014). Semi-structured interviews were carried out using a disciplinary literacy discussion matrix (Airey, 2011b), which enabled us to probe the lecturers’ disciplinary literacy goals in the various semiotic resource systems used in undergraduate physics (e.g. graphs, diagrams, mathematics, spoken and written languages, etc.).

    The findings suggest that physics lecturers in both countries have strikingly similar disciplinary literacy goals for their students and hold similar beliefs about disciplinary semiotic resources. The lecturers also agree that teaching disciplinary literacy ought not to be their job. Here though, there were differences in whether the lecturers teach students to handle disciplinary-specific semiotic resources. These differences appear to be based on individual decisions, rather than being specific to a particular country or institution.

  • 14.
    Airey, John
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Linder, Cedric
    Social Semiotics in University Physics Education2017In: Multiple Representations in Physics Education / [ed] David F. Treagust, Reinders Duit, Hans E. Fischer, Springer, 2017, p. 95-122Chapter in book (Refereed)
    Abstract [en]

    In this chapter we discuss the application of social semiotics to the teaching and learning of university physics. Social semiotics is a broad construct where all communication in a particular social group is realized through the use of semiotic resources. In the discipline of physics, examples of such semiotic resources are graphs, diagrams, mathematics, spoken and written language, and laboratory apparatus. In physics education research it is usual to refer to most of these semiotic resources as representations. In social semiotics, then, disciplinary learning can be viewed as coming to interpret and use the meaning potential of disciplinary-specific semiotic resources (representations) that has been assigned by the discipline. We use this complementary depiction of representations to build theory with respect to the construction and sharing of disciplinary knowledge in the teaching and learning of university physics. To facilitate both scholarly discussion and future research in the area, a number of theoretical constructs have been developed. These constructs take their point of departure in empirical studies of teaching and learning in undergraduate physics. In the chapter we present each of these constructs in turn and examine their usefulness for problematizing teaching and learning with multiple representations in university physics.

  • 15.
    Airey, John
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Simpson, Zachary
    Multimodal Science and Engineering Teaching: Perspectives from 8ICOM2018Conference paper (Other academic)
    Abstract [en]

    The previous international conference on multimodality – 8ICOM – featured two sessions devoted to multimodal, social semiotic approaches to science teaching and learning (c.f. Halliday1978; van Leeuwen 2005, Airey & Linder 2017). What the papers in these sessions shared was the argument that such perspectives on science, and science teaching, can, at least in part, respond to calls to ‘democratize’ science education by recognising diverse sets of semiotic resources and, in so doing, seeking to address impediments to equal participation (Burke et al., 2017). 

    The 8ICOM science sessions were particularly noteworthy given the backdrop against which 8ICOM had been organised. In the months leading up to the conference, South Africa (and Cape Town, in particular) had experienced campus unrest aimed at ‘decolonizing’ higher education in that country. As part of this movement, the phrase #ScienceMustFall briefly trended on social media. This emanated from the claim that ‘science’ is a western, colonial construct that needs to be dismantled and replaced with the teaching of indigenous, African knowledge. Although the #ScienceMustFall slogan has since departed from the wider public consciousness, the questions it raises nonetheless remain: why, and how, should science be taught?  Is science more than just a western colonial construction and, if so, why? And, what can the concept of multimodality offer by way of answering these questions? 

    In this paper, we offer an overview of the multimodal science papers presented in the two sessions at 8ICOM in the light of these questions. This is done with a view to assessing where the multimodality community finds itself regarding science education, and how it might address questions of the legitimacy of western science in the future. It is thus an attempt, as the conference theme suggests, to ‘move the theory forward’.      

  • 16.
    Almhagen, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Development and validation of a scanned proton beam model for dose distribution verification using Monte Carlo2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 17.
    Almhagen, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Development and validation of a scanned proton beam model for dose distribution verification using Monte Carlo2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Background and purpose: Although proton therapy is becoming increasingly common as a radiotherapy modality, facilities offering proton therapy are still scarce in comparison to photon therapy. Sweden's new proton therapy facility, Skandionkliniken, is scheduled to being operation during August 2015, employing the pencil beam scanning technique. Given Skandionklinikens unique stance as the only facility offering proton therapy in Sweden as of this writing, it is important to minimize the need for measurements during quality assurance to free up beam time for patients and other endeavors. It is the purpose of this work to create a foundation for a method whereby dose distribution verification is done via Monte Carlo simulation by developing and performing simple validation of a beam model. As input for simulating a dose distribution, log files storing a wide variety of data on how the dose distribution was delivered were used.

    Method: GATE, an open source Monte Carlo code and built on top of Geant4, was used for all simulations. A beam model parameterizing phase space at the nozzle exit was developed. The beam model development process made use of the beam data library and log file data. Using an in house developed code to convert log file data to treatment plans readable by GATE allowed simulation of delivered dose distributions. For validation, gamma index tests were performed comparing measured and simulated dose distributions.

    Results: The beam model was found able to predict the spot size in almost all cases within 0.2 mm. Likewise, the beam model was able to predict the proton range within 0.2 mm. The energy spread was found to be more difficult to estimate; comparisons of simulated and measured curves for at six points around the Bragg peak yielded a maximum deviation of 0.86 mm. Several difficulties prevented easy interpretation of the results of the gamma index tests. If allowance is made for certain data manipulation, pass rates of 90% or above using the global method can be achieved for all depths and for both treatment plans scanned.

    Conclusion: Although some complications arose during validation, the beam model performance appears capable of producing accurate results. To produce a full product suitable for routine patient specific quality assurance, further work will be necessary. Significant computing power would also be mandatory for routine use, necessitating the acquisition of a dedicated computer cluster or using GPUs.

  • 18.
    Amann, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Degerman, David
    Stockholm University, Faculty of Science, Department of Physics.
    Lee, Ming-Tao
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Shipilin, Mikhail
    Stockholm University, Faculty of Science, Department of Physics.
    Wang, Hsin-Yi
    Stockholm University, Faculty of Science, Department of Physics.
    Cavalca, Filippo
    Weston, Matthew
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schlueter, Christoph
    Drube, Wofgang
    Lömker, Patrick
    Ederer, Katrin
    Noei, Heshmat
    Zehetner, Johann
    Wentzel, Henrik
    Åhlund, John
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    A dedicated photoelectron spectroscopy instrument for studies of catalytic reactions at pressures exceeding 1 barManuscript (preprint) (Other academic)
    Abstract [en]

    Here, we present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures exceeding 1 bar. The instrument builds around the concept of a “virtual cell” in which a gasflow is directed onto the sample surface creating a local high pressure on top of the sample. This allows the instrument to maintain a low pressure of a few mbars in the main chamber, while simultaneously keeping a local pressure of around 1 bar. Synchrotron radiation based grazing incidence photoemission within ± 5° is used to enhance the surface sensitivity in the experiment. The aperture, separating the high-pressure region from the differential pumping of the electron spectrometer, consists of multiple, evenly spaced, mm sized holes matching the footprint of the x-ray beam on the sample surface. As the photo-emitted electrons are subject to strong scattering in the gas phase and the resulting signal is therefore highly dependent on the sample to aperture distance, the latter is controlled with high precision using a fully integrated manipulator that allows for sample movement with step sizes of 10 nm between 0 and –5 mm with very low vibrational amplitude. The instrumental features allows acquisition of metallic bulk spectra at He pressures up to 2.5 bar and also allows for following C1s spectra under realistic gas mixtures of CO + H2with various temperatures up to 500°C. This capability opens for studies of catalytic reactions in operandi.

  • 19.
    Andersson, David
    Stockholm University, Faculty of Science, Department of Physics.
    On the Evolving Friction of Layered Materials and the Prospect of Their Image Reconstruction2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The scope of this licentiate thesis is twofold: 1. Investigate the frictional properties of systems with layered materials; 2. Employing image recognition algorithms to find the substrates in AFM experiments. As of today, there is a clear dichotomy separating these projects, however, it is the long term goal that they should coalesce in a not too distance future. The friction in layered materials projects is already finished, in this project we expanded the venerated Prandtl-Tomlison model to incorporate atomically thin layered materials such as graphene. This project has proved successful beyond our expectations, and a score of experimental results and conflicts in the field can be explained and resolved using our model. The image reconstruction project however, is still on a basic level. So far we have compared a standard model – Histogram Analysis Method– for image reconstruction on the nano-level with a popular image reconstruction algorithm –Lucy Richardson Deconvolution – from astronomy and shown that the latter is more suitable for these kind of systems. However, this project is far from finished, and the results in this part should be regarded as both partial and preliminary.

  • 20.
    Andisheh, Bahram
    Stockholm University, Faculty of Science, Department of Physics.
    Improving the therapeutic ratio of stereotactic radiosurgery and radiotherapy2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    New methods of high dose delivery, such as intensity modulated radiation therapy (IMRT), stereotactic radiation therapy (SRT) or stereotactic radiosurgery (SRS), hadron therapy, tomotherapy, etc., all make use of a few large fractions. To improve these treatments, there are three main directions: (i) improving physical dose distribution, (ii) optimizing radiosurgery dose-time scheme and (iii) modifying dose response of tumors or normal tissues.

    Different radiation modalities and systems have been developed to deliver the best possible physical dose to the target while keeping radiation to normal tissue minimum. Although applications of radiobiological findings to clinical practice are still at an early stage, many studies have shown that   sublethal radiation damage repair kinetics plays an important role in tissue response to radiation.

    The purpose of the present thesis is to show how the above-mentioned directions could be used to improve treatment outcomes with special interest in radiation modalities and dose-time scheme, as well as radiobiological modeling. Also for arteriovenous malformations (AVM), the possible impact of AVM network angiostructure in radiation response was studied.

  • 21.
    Ardenfors, Oscar
    Stockholm University, Faculty of Science, Department of Physics.
    Out-of-field doses from proton therapy and doses from CBCT imaging: Risk of radiation-induced second cancer from modern radiotherapy2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of ionizing radiation for treatment of cancer diseases is continuously increasing as patient survival is improving and new treatment techniques are emerging. While this development is beneficial for curing primary tumors, concerns have been raised regarding the unwanted dose contribution to healthy tissues of patients and the associated risk of radiation-induced second cancer (RISC). This is especially important for younger patients receiving radiotherapy more often than before and for whom the risk of developing RISC is elevated in comparison to the typical adult radiotherapy patient. In order to estimate the risk of RISC associated with modern radiotherapy and imaging, the associated radiation doses must be determined.

    Patients undergoing radiotherapy receive in-field doses from the primary beam but also out-of-field doses originating from secondary radiation produced in the beamline and within the patient. Over the last years, the use of proton pencil beam scanning (PBS) therapy has rapidly increased due to its potential to reduce the in-field doses to healthy tissues in comparison to photon therapy. One of the drawbacks with proton therapy is the production of neutrons capable of travelling large distances and depositing out-of-field doses to organs located far from the primary treatment field. The dose reduction associated with proton PBS therapy could consequently be affected by the out-of-field doses originating from secondary radiation.

    The sharp dose gradients associated with modern treatment techniques, such as photon intensity-modulated radiotherapy (IMRT) and proton PBS therapy require more frequent and accurate patient imaging in comparison to conventional treatment techniques such as three-dimensional conformal radiotherapy (CRT). Setup verification images could be acquired with cone-beam computed tomography (CBCT) producing three-dimensional patient images at the cost of an increased patient dose in comparison to planar x-ray imaging. Concerns have been raised regarding the cumulative patient doses from repeated CBCT imaging versus the dose-saving benefits associated with modern radiotherapy techniques like IMRT and proton PBS.

    In this thesis, a study on the in-field and out-of-field doses to healthy tissues from photon IMRT and CRT treatments of head and neck tumors showed that the risk of RISC was unaffected by the employed treatment technique and indicated that the lifetime risk of cancer induction was of the order of 1-2%.

    Results from measurements and Monte Carlo simulations showed that the out-of-field absorbed doses and equivalent doses associated with proton PBS treatments of brain tumors were up to 60 µGy/Gy and 150 µSv/Gy, respectively. The risk of RISC associated with these out-of-field doses was in the range of approximately one induced cancer in ten thousand treated patients. A simulation study on the doses from a proton gantry-mounted CBCT system showed that repeated CBCT imaging could result in cumulative organ doses of almost 2 Gy. The conclusion from these studies is that the dose-sparing effects of proton PBS therapy are not overshadowed by the out-of-field doses originating from secondary radiation for brain tumor treatments, but that the cumulative doses from repeated CBCT imaging could have a relevant impact on the overall dose reduction.

  • 22.
    Ardenfors, Oscar
    Stockholm University, Faculty of Science, Department of Physics.
    Secondary doses to healthy tissues from radiotherapy and modern imaging techniques2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of ionizing radiation for treatment of cancer diseases is continuously increasing giving rise to several new questions and concerns. One of the most important aspects of this is the associated dose imparted to healthy tissues. This unwanted dose contribution is a result of both radiotherapy procedures and diagnostic imaging. The dose deposition in healthy tissues from external radiotherapy mainly originates from the incident primary beam. However, the patient also receives non-negligible organ doses originating from secondary radiation produced in the treatment machine and within the patient. This secondary radiation, especially neutrons, can travel large distances and consequently deposit doses to organs located far from the primary treatment field. The dose contribution to healthy organs from diagnostic procedures is growing due to the increase in repeated imaging performed in conjunction with radiotherapy. Also, patients undergoing both external radiotherapy and radionuclide therapy with radioactive isotopes could receive a high combined dose burden to healthy tissues.

    The need to quantify the secondary dose contribution and the associated risk of radiation-induced cancer is a relevant matter as new techniques are continuously emerging both in the field of radiotherapy and imaging. The technical advances in modern treatment techniques such as intensity modulated radiotherapy, rotational therapy and ion therapy have contributed to the overall increase in patient survival. A parallel development in medical imaging has caused an increase in the use of cone-beam computed tomography for repeated image-guidance imaging providing better tumor localization and a reduction in high doses deposited in adjacent healthy tissues.

    The most accurate way of estimating the risk of radiation-induced secondary cancers is to conduct comprehensive epidemiological studies on an exposed population stretching over several decades. This has been done in the past using cohorts of survivors of the atomic bombings and other nuclear accidents and medical exposures. However, the implementation of these epidemiological data is complex as the types of exposure differ greatly from modern radiotherapy procedures. Also, the long latency associated with radiation-induced secondary cancers further complicate the use of epidemiological data.

    Thus, the goal of achieving a dose-response relationship for secondary cancers is not only a matter of assessing the dose to the patient but also on how this data should be analyzed. Today, the most popular way of achieving this is through theoretical risk models using patient-specific parameters including dose distributions and risk coefficients obtained for populations from epidemiological studies.

    Due to the difficulties associated with performing measurements of radiation-induced organ doses from treatment and imaging, the dose is often calculated either analytically using an algorithm employed in the clinical treatment planning system or through Monte Carlo simulations that offer the most accurate tool for such calculations. To allow for accurate Monte Carlo simulations of secondary radiation from external radiotherapy the beam model should be validated against measurements with regard to both the primary beam and the out-of-field secondary radiation.

    These aspects have been investigated in individual studies that make the object of the articles included in this thesis. Paper I presents a literature review of secondary doses from different treatment and imaging modalities. Paper II shows a comparison between the risks of radiation-induced cancer for patients treated for head and neck cancer using two different treatment techniques. Paper III deals with Monte Carlo simulations of doses to healthy tissues from radionuclide therapy given in conjunction with external radiotherapy. Paper IV presents the validation of a proton spot scanning Monte Carlo model.

  • 23.
    Ardenfors, Oscar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dasu, Alexandru
    Kopeć, Mariusz
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Modelling of a proton spot scanning system using MCNP62017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 860, article id 012025Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to model the characteristics of a clinical proton spot scanning beam using Monte Carlo simulations with the code MCNP6. The proton beam was defined using parameters obtained from beam commissioning at the Skandion Clinic, Uppsala, Sweden. Simulations were evaluated against measurements for proton energies between 60 and 226 MeV with regard to range in water, lateral spot sizes in air and absorbed dose depth profiles in water. The model was also used to evaluate the experimental impact of lateral signal losses in an ionization chamber through simulations using different detector radii. Simulated and measured distal ranges agreed within 0.1 mm for R90 and R80 , and within 0.2 mm for R50 . The average absolute difference of all spot sizes was 0.1 mm. The average agreement of absorbed dose integrals and Bragg-peak heights was 0.9%. Lateral signal losses increased with incident proton energy with a maximum signal loss of 7% for 226 MeV protons. The good agreement between simulations and measurements supports the assumptions and parameters employed in the presented Monte Carlo model. The characteristics of the proton spot scanning beam were accurately reproduced and the model will prove useful in future studies on secondary neutrons.

  • 24.
    Azzouz, Hatim
    Stockholm University, Faculty of Science, Department of Physics.
    Creation and Detection of Single Photons2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A growing number of technologies employ quantum properties in order to produce solutions that surpass the performance of conventional devices, or to execute operations that are fundamentally impossible with classical systems alone. In the field of optical quantum information science, photons are utilized to encode, communicate and manipulate information, making them vitally important. While photon production always constitutes the first step in any optical experiment, in the field of quantum information science, the recording of data through the process of photon detection is an equally crucial final step.

    This thesis deals with both the single photons generation (based on diamond color defects) and their detection, utilizing a novel type of superconducting detectors. In particular, part one of this thesis is devoted to the construction of custom designed microscope setup, and the development of laboratory experiments, to enable the generation of single photons as well as the investigation of the optical and spin properties of diamond color centers. Confocal microscopy is used for this purpose, as it allows for the identification and addressing of individual color centers that emit only single photons. This microscope also feature an integrated self-built microwave and magnetic hardware setup, which allows for a wide range of spin environment spectroscopy studies. Single photon emission is demonstrated through both photon anti-bunching and Rabi oscillations at room temperature.

    The second part of the thesis offers an exploration of superconducting single photon detectors through experiment. Since electronics are an essential part of these detectors, the possibility of using a novel alternative scheme based on capacitive readout combined with fast gating to enable simplified readout is demonstrated. This scheme overcomes the limitations of conventional readout schemes, which require large bandwidth amplification and complex counting electronics. Besides photon detection, the capabilities of these detectors are also expanded to include high-energy particles in the MeV energy range, and the detectors are demonstrated to not only detect single α- and β-particles, but to do so with near unity efficiency. Finally, a multipurpose testing station for superconducting detectors is demonstrated with a central objective of optimizing the coupling efficiency of light to the active area of the detector, as well as to allow for a fast exchange of the optical fiber, thereby facilitating an efficient characterization of the detector. The optimization of this coupling efficiency was demonstrated through proof-of-principle experiments.

  • 25. Banerjee, Souvik
    et al.
    Engelsöy, Julius
    Stockholm University, Faculty of Science, Department of Physics.
    Larana-Aragon, Jorge
    Stockholm University, Faculty of Science, Department of Physics.
    Sundborg, Bo
    Stockholm University, Faculty of Science, Department of Physics.
    Thorlacius, Larus
    Stockholm University, Faculty of Science, Department of Physics.
    Wintergerst, Nico
    Quenched coupling, entangled equilibria, and correlated composite operators: a tale of two O(N) modelsIn: Article in journal (Refereed)
  • 26.
    Bengtsson, Ingemar
    Stockholm University, Faculty of Science, Department of Physics.
    A Kochen-Specker Inequality2009In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1101, p. 241-245Article in journal (Other academic)
    Abstract [en]

    I review a paper by Klyachko, Can, Binicioğlu, and Shumovsky, and explain a little of the background as I see it

  • 27.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Badziag, Piotr
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adan
    Pitowsky, Itamar
    Universality of State-Independent Violation of Correlation Inequalities for Non-Contextual Theories2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 5, p. 050401-Article in journal (Refereed)
    Abstract [en]

    We show that the state-independent violation of inequalities for noncontextual hidden variable theories introduced in [Phys. Rev. Lett. 101, 210401 (2008)] is universal, i.e., occurs for any quantum mechanical system in which noncontextuality is meaningful. We describe a method to obtain state-independent violations for any system of dimension d >= 3. This universality proves that, according to quantum mechanics, there are no "classical'' states.

  • 28.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Holst, Sören
    Stockholm University, Faculty of Science, Department of Physics.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    Classics illustrated: limits of spacetimes2014In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 31, no 20, article id 205008Article in journal (Refereed)
    Abstract [en]

    We carefully study the em and e→0 limits of the Reissner-Nordström spacetime using Geroch's definition of limits of spacetimes. This is implemented by embedding the one-parameter family of spacetimes in anti-de Sitter space, and as a result we obtain metrically correct Penrose diagrams. For em two distinct limits are studied.

  • 29.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    A Toy Penrose Inequality and Its Proof2016In: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 48, no 12, article id 156Article in journal (Refereed)
    Abstract [en]

    We formulate and prove a toy version of the Penrose inequality. The formulation mimics the original Penrose inequality in which the scenario is the following: A shell of null dust collapses in Minkowski space and a marginally trapped surface forms on it. Through a series of arguments relying on established assumptions, an inequality relating the area of this surface to the total energy of the shell is formulated. Then a further reformulation turns the inequality into a statement relating the area and the outer null expansion of a class of surfaces in Minkowski space itself. The inequality has been proven to hold true in many special cases, but there is no proof in general. In the toy version here presented, an analogous inequality in (2+1)-dimensional anti-de Sitter space turns out to hold true.

  • 30.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    Black holes: Their large interiors2015In: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 30, no 21, article id 1550103Article in journal (Refereed)
    Abstract [en]

    Christodoulou and Rovelli (CR) have remarked on the large interiors possessed by static black holes. We amplify their remarks, and extend them to the spinning case.

  • 31.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    Senovilla, José M. M.
    Trapped surfaces in Oppenheimer-Snyder black holes2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 6, article id 064012Article in journal (Refereed)
    Abstract [en]

    The Oppenheimer-Snyder solution models a homogeneous round dust of cloud collapsing to a black hole. Inside its event horizon there is a region through which trapped surfaces pass. We try to determine exactly where the boundary of this region meets the center of the cloud. We present explicit examples of the relevant trapped (topological) spheres; they extend into the exterior vacuum region, and are carefully matched at the junction between the cloud and the vacuum.

  • 32.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jose M M Senovilla,
    A Note on Trapped Surfaces in the Vaidya Solution2009In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 79, no 2, p. 024027-Article in journal (Refereed)
    Abstract [en]

    The Vaidya solution describes the gravitational collapse of a finite shell of incoherent radiation falling into flat spacetime and giving rise to a Schwarzschild black hole. There has been a question whether closed trapped surfaces can extend into the flat region (whereas closed outer trapped surfaces certainly can). For the special case of self-similar collapse we show that the answer is yes, if and only if the mass function rises fast enough.

  • 33.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kus, Marek
    'Classical' Quantum States2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 2, p. 022319-Article in journal (Refereed)
    Abstract [en]

    We show that several classes of mixed quantum states in finite-dimensional Hilbert spaces which can be characterized as being, in some respect, "most classical" can be described and analyzed in a unified way. Among the states we consider are separable states of distinguishable particles, uncorrelated states of indistinguishable fermions and bosons, as well as mixed spin states decomposable into probabilistic mixtures of pure coherent states. The latter was the subject of the recent paper by Giraud et al. [Phys. Rev. A 78, 042112 (2008)], who showed that in the lowest-dimensional nontrivial case of spin 1, each such state can be decomposed into a mixture of eight pure states. Using our method, we prove that in fact four pure states always suffice.

  • 34.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Åminneborg, Stefan
    Anti-de Sitter Quotients: When Are They Black Holes?2008In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 25, p. 095019-Article in journal (Refereed)
    Abstract [en]

    e point out that the BTZ black holes, and their relatives, can be defined in a cleaner way than they originally were. The covering space can be taken to be anti-de Sitter space, period, while splits up into components due to Misner singularities. Our definition permits us to choose between two conflicting claims concerning BTZ black holes in (3 + 1) dimensions.

  • 35.
    Benmakhlouf, Hamza
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Andreo, Pedro
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Ten years after: Impact of recent research in photon and electron beam dosimetry on the IAEA TRS-398 Code of Practice2011In: Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS): Proceedings of an International Symposium. V. 1 / [ed] Benmakhlouf, H.; Andreo, P., Vienna: International Atomic Energy Agency, 2011, , p. 14p. 139-152Conference paper (Refereed)
  • 36.
    Bergholtz, Emil
    et al.
    Max Planck Institute for the Physics of Complex Systems, Dresden.
    Karlhede, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Quantum Hall Circle2009In: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, Vol. P04015Article in journal (Refereed)
    Abstract [en]

    We consider spin-polarized electrons in a single Landau level on a cylinder as the circumference of the cylinder goes to infinity. This gives a model of interacting electrons on a circle where the momenta of the particles are restricted and there is no kinetic energy. Quantum Hall states are exact ground states for appropriate short range interactions, and there is a gap to excitations. These states develop adiabatically from this one-dimensional quantum Hall circle to the bulk quantum Hall states and further on into the Tao–Thouless states as the circumference goes to zero. For low filling fractions a gapless state is formed which we suggest is connected to the Wigner crystal expected in the bulk.

  • 37.
    Blanchfield, Kate
    Stockholm University, Faculty of Science, Department of Physics.
    Configurations in Quantum Information2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Measurements play a central role in quantum information. This thesis looksat two types: contextual measurements and symmetric measurements. Contextualityoriginates from the Kochen-Specker theorem about hidden variablemodels and has recently undergone a subtle shift in its manifestation. Symmetricmeasurements are characterised by the regular polytopes they formin Bloch space (the vector space containing all density matrices) and are thesubject of several investigations into their existence in all dimensions.We often describe measurements by the vectors in Hilbert space ontowhich our operators project. In this sense, both contextual and symmetricmeasurements are connected to special sets of vectors. These vectors areoften special for another reason: they form congurations in a given incidencegeometry.In this thesis, we aim to show various connections between congurationsand measurements in quantum information. The congurations discussedhere would have been well-known to 19th and 20th century geometers andwe show they are relevant for advances in quantum theory today. Specically,the Hesse and Reye congurations provide proofs of measurement contextuality,both in its original form and its newer guise. The Hesse congurationalso ties together dierent types of symmetric measurements in dimension3called SICs and MUBswhile giving insights into the group theoreticalproperties of higher dimensional symmetric measurements.

  • 38. Bouarroudj, Sofian
    et al.
    Grozman, Pavel
    Leites, Dimitry
    Stockholm University, Faculty of Science, Department of Mathematics.
    DEFINING RELATIONS OF ALMOST AFFINE (HYPERBOLIC) LIE SUPERALGEBRAS2010In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 17, p. 163-168Article in journal (Refereed)
    Abstract [en]

    For all almost affine (hyperbolic) Lie superalgebras, the defining relations are computed in terms of their Chevalley generators.

  • 39.
    Cedenblad, Lukas
    Stockholm University, Faculty of Science, Department of Physics.
    Gone With the Headwind. Characterizing Erosion Using Lattice-Boltzmann Method: and its Implication in Planet Formation2019Independent thesis Advanced level (degree of Master (Two Years)), 300 HE creditsStudent thesis
    Abstract [en]

    Erosion has a long history in science and is used in many different fields today, for example in geology for coastal erosion and in the oil industry for pipe erosion. It is very difficult to study erosion both analytically. Numerically it is difficult due to moving and shape-changing boundaries. Here we develop a numerical model in 3D using the Lattice-Boltzmann method, which is good at simulating complex moving boundaries, and erosion capabilities are implemented. Both laminar and turbulent flow can be modelled with this program. Using an experimentally derived model for the mass change due to erosion in clay and mud-type objects, one can derive equations predicting that the volume of a sphere should, due to erosion, scale as V ∼ −t2. This is also observed with simulations. The shapes of a double sphere with different orientations and a cube in laminar flow we find to have similar power law exponent P, P = 2±0.1. But a cube eroding in Re = 800 had no power law behaviour, meaning that the current analytical framework is incomplete. The possibility of a more general framework is presented for future research. Different Reynolds number also affected the power law behaviour and the shape change over time for the different solids. Very little research has been made for erosion of planetesimals, but it has been argued that erosion can be relevant to their fate. Using the same erosion model, an equation of the erosion time is found for laminar flows and for a sphere. Simulation results find that the equation works within an order of magnitude for turbulent flows, a double sphere and a cube. This gives an estimate of the erosion time t∗ of planetesimals to be t∗ ∼ 1s, given a size of radius equal to 10cm and 1km, an orbital eccentricity e > 10−2 and a distance at r = 1 a.u. Implying that orbits for planetesimals with low eccentricity might be favoured.

  • 40. Chapovalov, Danil
    et al.
    Chapovalov, Maxim
    Stockholm University, Faculty of Science, Department of Mathematics.
    Lebedev, Alexei
    Leites, Dimitry
    Stockholm University, Faculty of Science, Department of Mathematics.
    THE CLASSIFICATION OF ALMOST AFFINE (HYPERBOLIC) LIE SUPERALGEBRAS2010In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 17, p. 103-161Article in journal (Refereed)
    Abstract [en]

    We say that an indecomposable Cartan matrix A with entries in the ground field is almost affine if the Lie (super) algebra determined by it is not finite dimensional or affine (Kac-Moody) but the Lie sub(super) algebra determined by any submatrix of A, obtained by striking out any row and any column intersecting on the main diagonal, is the sum of finite dimensional or affine Lie (super) algebras. A Lie (super) algebra with Cartan matrix is said to be almost affine if it is not finite dimensional or affine (Kac-Moody), and all of its Cartan matrices are almost affine. We list all almost affine Lie superalgebras over complex numbers with indecomposable Cartan matrix correcting two earlier claims of classification.

  • 41.
    Chapovalov, Maxim
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics.
    Leites, Dimitry
    Stockholm University, Faculty of Science, Department of Mathematics.
    Stekolshchik, Rafael
    THE POINCARE SERIES OF THE HYPERBOLIC COXETER GROUPS WITH FINITE VOLUME OF FUNDAMENTAL DOMAINS2010In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 17, p. 169-215Article in journal (Refereed)
    Abstract [en]

    The discrete group generated by reflections of the sphere, or the Euclidean space, or hyperbolic space are said to be Coxeter groups of, respectively, spherical, or Euclidean, or hyperbolic type. The hyperbolic Coxeter groups are said to be (quasi-) Lanner if the tiles covering the space are of finite volume and all (resp. some of them) are compact. For any Coxeter group stratified by the length of its elements, the Poincare series is the generating function of the cardinalities of sets of elements of equal length. Around 1966, Solomon established that, for ANY Coxeter group, its Poincare series is a rational function with zeros somewhere on the unit circle centered at the origin, and gave an implicit (recurrence) formula. For the spherical and Euclidean Coxeter groups, the explicit expression of the Poincare series is well-known. The explicit answer was known for any 3-generated Coxeter group, and (with mistakes) for the Lanner groups. Here we give a lucid description of the numerator of the Poincare series of any Coxeter group, the explicit expression of the Poincare series for each Lanner and quasi-Lanner group, and review the scene. We give an interpretation of some coefficients of the denominator of the growth function. The non-real poles behave as in Enestrom's theorem (lie in a narrow annulus) though the coefficients of the denominators do not satisfy theorem's requirements.

  • 42. de Winter, James
    et al.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    The views of pre-service physics teachers on the role of mathematics in the teaching and learning of physics2018Conference paper (Other academic)
    Abstract [en]

    Mathematics is commonly seen as playing a fundamental role in the understanding of undergraduate physics. However, this role poses challenges for teaching physics at lower levels. In England, increased formal assessment of mathematical skills in national physics examinations has made many teachers (re)consider this issue and their classroom practice. This qualitative study explores how English physics teachers view the physics/mathematics relationship. Our data consists of questionnaires and follow up interviews with an entire cohort of pre-service teachers training at an English university (n=13). Analysis included a line of enquiry on the tension between the value of mathematics in undergraduate physics and its value for teaching physics at school level. There was considerable variation across respondents, some seeing mathematics as integral to understanding school physics, whilst others prioritised conceptual understanding over mathematical formalism. Many noted how their views had changed during training, raising questions for those involved in physics teacher preparation.

  • 43. de Winter, James
    et al.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    What is a ‘good’ physics teacher?: Views from the UK education community2017Conference paper (Refereed)
  • 44.
    Degerman, David
    Stockholm University, Faculty of Science, Department of Physics.
    BUILDING AN X-RAY PHOTOELECTRON SPECTROSCOPY ENDSTATION FOR OPERANDO STUDIES OF CATALYTIC CO AND COHYDROGENATION REACTIONS2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    X-ray Photoelectron Spectroscopy (XPS) provides an element-specific surface sensitive probe of the chemical composition in a system, and is consequently one of the workhorses of surface science and catalysis research. The obtained information on the chemical and physical state of the catalyst and adsorbates is essential in the endeavor to achieve a fundamental understanding how chemical reactions are facilitated by the catalyst. Due to the short mean free path of electrons in gaseous media most of the XPS experiments so far are done in the range between ultra-high vacuum (<10-7 mbar) and near-ambient pressure (1-10 mbar) regimes. For certain reactions, such as the hydrogenation of CO and CO2, higher pressures (comparable to one bar or higher) are needed in order to give a more realistic representation of the system.

    This thesis concerns the theoretical background, design, build-up and the first results of an instrument with the goal to bridge the pressure gap between operando conditions at the solid gas interface and surface science model systems. Thanks to a new design of the electron analyzer front cone we have built an instrument where the relevant length scales are reduced to match the electron inelastic mean free path in pressurized atmospheres above one bar. A number of key factors make this possible, but most prominently it is the unique sample environment using a “virtual pressure cell” in combination with a grazing incidence geometry below the critical angle of total reflection. Furthermore, the instrument utilizes hard x-rays to generate high-kinetic energy electrons and thereby increase the mean free path in the pressurized atmosphere. Lastly, the instrument uses a laser-based heating solution which removes the effect of electric and magnetic fields.

    With this we have been able to (1) record spectra of Rh above 2 bar of inert atmosphere, as well as with reaction mixtures of CO2 + O2 up to 1 bar and (2) probe surface species and observe temperature dependent chemistry during CO2 hydrogenation during ongoing reactions at 150 mbar.

  • 45.
    Degerman, David
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Amann, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Shilpilin, Mikhail
    Stockholm University, Faculty of Science, Department of Physics.
    Wang, Hsin-Yi
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Lömker, Patrick
    Heshmat, Noei
    Schlueter, Christoph
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Surface adsorbates during CO2 Hydrogenation on Rh(111) probed in-situ by x-ray photoelectron spectroscopy at 150 mbarManuscript (preprint) (Other academic)
    Abstract [en]

    The catalytic CO2 hydrogenation reaction was examined in situ by High Pressure X-ray Photoelectron Spectroscopy (HP-XPS) at 150 mbar and between 150 and 350°C. The results indicate two temperature regimes; the first one with temperature dependent desorption of carbon species between 150°C and 200°C. The second temperature regime is between 250 and 350 °C. In this interval, the carbon species are formed and immediately reacted away, resulting in a lower temperature dependence on surface coverage. The XPS coverage calculations and the component analysis indicate that water is the most abundant surface adsorbate, and that CHx fragments and CO are the most abundant carbon species. The hydrogenation state of the CHx species varies with temperature, where higher temperatures result in a larger population of more hydrogenated species.

  • 46.
    Dumitru, Irina
    Stockholm University, Faculty of Science, Department of Physics.
    Exploring the Elegant Bell Inequality2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In quantum information, device independent certification is a matter of both practical and fundamental interest. In this thesis, we explore the use of a particular Bell inequality, known as the elegant Bell inequality, in device independent certification. We first characterize all states and measurements that can lead to a maximal violation of the elegant Bell inequality. It turns out that, in all cases, the state involved in a maximal violation is a generalized singlet state, and the measurements of one of the parties are always maximally spread out on the Bloch sphere, forming a complete set of mutually unbiased bases. The measurements involved on the other party form two pairs of symmetric informationally complete vectors. The elegant Bell inequality, then, can be used to certify the presence of these elements.

    We also explore the usefulness of the elegant Bell inequality in randomness certification, in particular in a protocol for certification of maximal randomness from one entangled bit.

    The last part of this thesis is dedicated to a study of some of the special geometricstructures involved in the maximal violation of the elegant Bell inequality, namely the symmetric informationally complete vectors. The problem of the existence and of the construction of these sets of vectors in Hilbert spaces of any dimension is open, but there are solutions available in many dimensions. We look at these structures from both a geometric and an algebraic number theory perspective, and conjecture a relation between vectors in different dimensions. We introduce the relation of "alignment" between such sets of vectors.

  • 47.
    Engelsöy, Julius
    Stockholm University, Faculty of Science, Department of Physics.
    Quenched coupling and thermal behavior in the O(N) vector model2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermalization is an elusive phenomenon in quantum mechanics. Since according to the AdS/CFT correspondence, a thermal state in the boundary CFT is dual to a black hole in the bulk spacetime, thermalization in the CFT is dual to black hole formation in AdS. Thus, understanding quantum thermalization is likely a key component in understanding the information paradox---the contradiction between QFT and general relativity occurring when a black hole seemingly erases the information of whatever went into creating it.

    (Apparent) thermalization in QFT can be investigated by imposing a quench, i.e., a sudden change of some parameter of the theory, and subsequently studying the equilibration process. In this thesis we aim to gain understanding of quantum thermalization by investigating the late-time quench dynamics of a simple free field theory, namely the $O(N)$ vector model. Since the theory is integrable, ``true'' thermalization will not occur but an approximate thermalization. We use different probes such as the effective density matrix and the spectral density function to investigate the extent to which the (pure) state ``looks'' thermal and how this deviates from conventional thermality.

  • 48.
    Fager, Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Radiobiological plan optimization in Proton therapy for Prostate tumors using a Patched Integrated Edge [PIE] technique2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Purpose: A novel treatment planning technique using proton pencil beam scanning (PBS) is proposed that takes advantage of the increased Linear Energy Transfer (LET) at the distal edge of proton beams to deposit the increased biological effective dose related to the elevated LET protons within prostate tumors.

    Background: The availability of proton treatment for cancer has increased the latest decade and will continue to increase rapidly in the coming decade. The Relative Biological Effectiveness (RBE) of protons earlier considered to be 1.10 has started to be questioned in the latest decade. This thesis investigates what would be the effect of a variable RBE on the effective dose to the target.

    Method: Uniform dose distributions were planned using two different beam arrangements: (1) Full-Target Plans (FTP), with two lateral fields, each field targeting the entire target; (2) Patched Integrated Edge (PIE) plans, with 2, 4, and 7 fields, each field targeting only the respective proximal segment of the target. Dose distributions were calculated and optimized with Eclipse in order to deliver the same dose to the target as well as to maintain the same OARs dose constrains for all the plans. Beam properties (range, modulation, spot map and weights) were used to calculate dose and dose averaged LET distributions with Monte Carlo. The RBE for each plan was calculated using radiobiological models taking into account the dose and LETd distribution as well as published values of  for the irradiated tissues as input parameters. The RBE weighted dose (DRBE) was calculated for each planning approach and evaluated with respect to three different aims.

    Results: An increase of the number of fields using PIE increased the LETd within the target. The increased LETd resulted in an increase of the RBE weighted dose, DRBE, of up to 12.7 Gy (RBE) to the target, which is a 14% increase. However, if the same DRBE is to be delivered to the target with FTP and PIE the increase of LETd in the target implied a decrease of dose per fraction, d, of up to 0.21 Gy, a decrease of 13 %.

    Conclusions: A modified distribution of proton’s linear energy transfer in PBS allows to deposit highly effective biological dose by the elevated-LET protons within the target, which might help to increase the effectiveness of prostate radiotherapy. This might also serve as a platform to investigate how the physical prescribed dose can be reduced by increasing the LETd in the target in order to maintain a constant DRBE in the prostate. 

  • 49. Gallos, Lazaros K.
    et al.
    Rybski, Diego
    Liljeros, Fredrik
    Stockholm University, Faculty of Social Sciences, Department of Sociology.
    Havlin, Shlomo
    Makse, Hernan A.
    How People Interact in Evolving Online Affiliation Networks2012In: PHYSICAL REVIEW X, ISSN 2160-3308, Vol. 2, no 3, p. 031014-Article in journal (Refereed)
    Abstract [en]

    The study of human interactions is of central importance for understanding the behavior of individuals, groups, and societies. Here, we observe the formation and evolution of networks by monitoring the addition of all new links, and we analyze quantitatively the tendencies used to create ties in these evolving online affiliation networks. We show that an accurate estimation of these probabilistic tendencies can be achieved only by following the time evolution of the network. Inferences about the reason for the existence of links using statistical analysis of network snapshots must therefore be made with great caution. Here, we start by characterizing every single link when the tie was established in the network. This information allows us to describe the probabilistic tendencies of tie formation and extract meaningful sociological conclusions. We also find significant differences in behavioral traits in the social tendencies among individuals according to their degree of activity, gender, age, popularity, and other attributes. For instance, in the particular data sets analyzed here, we find that women reciprocate connections 3 times as much as men and that this difference increases with age. Men tend to connect with the most popular people more often than women do, across all ages. On the other hand, triangular tie tendencies are similar, independent of gender, and show an increase with age. These results require further validation in other social settings. Our findings can be useful to build models of realistic social network structures and to discover the underlying laws that govern establishment of ties in evolving social networks.

  • 50. Gandhi, Sohang
    et al.
    McAllister, Sohang
    Sjörs, Stefan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A Toolkit for Perturbing Flux Compactifications2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 12, p. 053-Article in journal (Refereed)
    Abstract [en]

    We develop a perturbative expansion scheme for solving general boundary value problems in a broad class of type IIB flux compactifications. The background solution is any conformally Calabi-Yau compactification with imaginary self-dual (ISD) fluxes. Upon expanding in small deviations from the ISD solution, the equations of motion simplify dramatically: we find a simple basis in which the n-th order equations take a triangular form. This structure implies that the system can be solved iteratively whenever the individual, uncoupled equations can be solved. We go on to demonstrate the solution of the system for a general warped Calabi-Yau cone: we present an algorithm that yields an explicit Green’s function solution for all the supergravity fields, to any desired order, in terms of the harmonic functions on the base of the cone. Our results provide a systematic procedure for obtaining the corrections to a warped throat geometry induced by attachment to a compact bulk. We also present a simple method for determining the sizes of physical effects mediated through warped geometries.

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