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  • 39601. Ågren, Jonas
    et al.
    Kiamehr, Ramin
    Zanjan University.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    The new gravimetric quasigeoid model KTH08 over Sweden2009In: Journal of Applied Geodesy, ISSN 1862-9024, Vol. 3, no 3, p. 143-153Article in journal (Refereed)
    Abstract [en]

    The least squares modification of Stokes formula has been developed in a series of papers published in Journal of Geodesy between 1984 and 2008. It consists of a least squares (stochastic) Stokes kernel modification with additive corrections for the topography, downward continuation, the atmosphere and the ellipsoidal shape of the Earth. The method, developed at the Royal Institute of Technology (KTH) will here be denoted by the abbreviated name the KTH method.

    This paper presents the computational results of a new gravimetric quasigeoid model over Sweden (the KTH08 model) by employing the KTH method. Traditionally the Nordic Geodetic Commission (NKG) has computed gravimetric quasigeoid models over Sweden and other Nordic countries; the latest model being NKG 2004. Another aim of this paper is therefore to compare KTH08 and NKG 2004 quasigeoid models and to evaluate their accuracies using GNSS/levelling height anomalies. The rms fit of KTH08 in 196 GNSS data points distributed over Sweden by using a 1(4)-parameter transformation is 22 (20) mm. It is concluded that KTH08 is a significant step forward compared to NKG 2004.

  • 39602.
    Ågren, Jonas
    et al.
    National Land Survey of Sweden.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    The Swedish geoid as evaluated by the method of least-squares modification with additive corrections2006Conference paper (Refereed)
  • 39603.
    Ågren, Jonas
    et al.
    KTH, Superseded Departments, Infrastructure.
    Sjöberg, Lars Erik
    KTH, Superseded Departments, Infrastructure.
    Comparison of some methods for modifying stokes' formula in the GOCE ERA2004Conference paper (Refereed)
    Abstract [en]

    The dedicated satellite gravity mission GOCE will drastically improve our knowledge of the long to medium wavelengths of the Earth's gravity field. In order to determine the finest details in regional geoid determination, however, we still have to utilise gravity data. It is the purpose of this paper to study three modifications of Stokes' formula numerically, using error propagations with simulated standard errors for the GOCE potential coefficients. The methods tested are the standard remove-compute-restore, the least squares, and the low-degree GOCE-only modifications. In the latter technique it is required that only GOCE information must influence the determination of the lowest degrees. It is concluded that of the modifications tested, the least squares method is most suitable to be used with a GOCE satellite-only model. This is the case also when pessimistic weights are used for the gravity anomalies. The main fault with the standard remove-compute-restore method is its sensitivity to long-wavelength errors in the gravity anomalies, while a very large truncation error is the most serious problem for the low-degree GOCE-only technique.

  • 39604. Ågren, O.
    et al.
    Moiseenko, V. E.
    Noack, K.
    Hagnestal, A.
    Kallne, J.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Hybrid Reactor Studies Based On The Straight Field Line Mirror2013In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 63, no 1T, p. 52-57Article in journal (Refereed)
    Abstract [en]

    The straight field line mirror (SFLM) hybrid reactor studies aim to identify a concept where the safety of fission power production could be enhanced. A fusion neutron source could become a mean to achieve this. The SFLM studies address critical issues such as reactor safety, natural circulation of coolants, steady state operation for a year or more and means to avoid too strong material loads by a proper geometrical arrangement of the reactor components. A key result is that power production may be possible with a fusion Q factor as low as 0.15. This possibility arises from the high power amplification by fission, which within reactor safety margins may exceed a factor of 100. The requirements on electron temperature are dramatically lower for a fusion hybrid compared to a stand-alone fusion reactor. This and several other factors are important for our choice to select a mirror machine for the fusion hybrid reactor studies.

  • 39605. Ågren, O.
    et al.
    Moiseenko, V. E.
    Noack, K.
    Hagnestål, A.
    Källne, J.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    The straight field line mirror concept aiming at a hybrid reactor2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 1, 2012, 2012, p. 5-8Conference paper (Refereed)
  • 39606. Ågren, O.
    et al.
    Noack, K.
    Moiseenko, V. E.
    Hagnestål, A.
    Källne, J.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    The hybrid reactor project based on the straight field line mirror concept2012In: Fusion For Neutrons And Subcritical Nuclear Fission / [ed] Kallne, J; Ryutov, D; Gorini, G; Sozzi, C; Tardocchi, M, American Institute of Physics (AIP), 2012, p. 173-185Conference paper (Refereed)
    Abstract [en]

    The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is chosen to avoid high loads on materials and plasma facing components. A comparatively small fusion hybrid device with "semi-poor" plasma confinement (with a low fusion Q factor) may be developed for industrial transmutation and energy production from spent nuclear fuel. This opportunity arises from a large fission to fusion energy multiplication ratio, Qr=Pfis/P fus>>1. The upper bound on Qr is primarily determined by geometry and reactor safety. For the SFLM, the upper bound is Qr≈150, corresponding to a neutron multiplicity of k eff=0.97. Power production in a mirror hybrid is predicted for a substantially lower electron temperature than the requirement T e≈10 keV for a fusion reactor. Power production in the SFLM seems possible with Q≈0.15, which is 10 times lower than typically anticipated for hybrids (and 100 times smaller than required for a fusion reactor). This relaxes plasma confinement demands, and broadens the range for use of plasmas with supra-thermal ions in hybrid reactors. The SFLM concept is based on a mirror machine stabilized by qudrupolar magnetic fields and large expander tanks beyond the confinement region. The purpose of the expander tanks is to distribute axial plasma loss flow over a sufficiently large area so that the receiving plates can withstand the heat. Plasma stability is not relying on a plasma flow into the expander regions. With a suppressed plasma flow into the expander tanks, a possibility arise for higher electron temperature. A brief presentation will be given on basic theory for the SFLM with plasma stability and electron temperature issues, RF heating computations with sloshing ion formation, neutron transport computations with reactor safety margins and material load estimates, magnetic coil designs as well as a discussion on the implications of the geometry for possible diagnostics. Reactor safety issues are addressed and a vertical orientation of the device could assist passive coolant circulation. Specific attention is put to a device with a 25 m long confinement region and 40 cm plasma radius in the mid-plane. In an optimal case (keff = 0.97) with a fusion power of only 10 MW, such a device may be capable of producing a power of 1.5 GWth.

  • 39607.
    Ågren, Peter
    et al.
    KTH, Superseded Departments, Physics.
    Walter, Jochen
    KTH, School of Engineering Sciences (SCI), Physics.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Switching Current of a Cooper Pair Transistor with Tunable Josephson Junctions2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 1, p. 14510-Article in journal (Refereed)
    Abstract [en]

    We investigate the switching current of a Cooper pair transistor with tunable Josephson energy. The junctions are fabricated in a superconducting quantum interference device (SQUID) geometry which allows for an in situ tunable effective Josephson energy by application of a magnetic field. We find a 2e-periodic switching current versus gate charge. As the magnetic field is increased the switching current stays 2e-periodic but the magnitude is suppressed. At a magnetic field of half a flux quantum through the SQUID's the switching current is minimum. We can theoretically model the experimental data by assuming a switching current which is proportional to the ideal critical current squarred. We show that such a dependence is expected in the limit where the effect of thermal fluctuations on the system is strong.

  • 39608.
    Ågren, Peter
    et al.
    KTH, Superseded Departments, Physics.
    Walter, Jochen
    KTH, School of Engineering Sciences (SCI), Physics.
    Schöllmann, Volker
    KTH, School of Engineering Sciences (SCI), Physics.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Switching Currents and Quasi-Particle Poisoning in the Superconducting Single Electron Transistor2002In: INTERNATIONAL WORKSHOP ON SUPERCONDUCTING NANO-ELECTRONICS DEVICES, 2002, p. 25-31Conference paper (Refereed)
  • 39609. Ågren, Rasmus
    et al.
    Mardinoglu, Adil
    Asplund, Anna
    Kampf, Caroline
    Uhlén, Mathias
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Nielsen, Jens
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Identification of anticancer drugs for hepatocellular carcinoma through personalized genome-scale metabolic modeling2014In: Molecular Systems Biology, ISSN 1744-4292, E-ISSN 1744-4292, Vol. 10, no 3, p. A721-Article in journal (Refereed)
    Abstract [en]

    Synopsis image Personalized GEMs for six hepatocellular carcinoma patients are reconstructed using proteomics data and a task-driven model reconstruction algorithm. These GEMs are used to predict antimetabolites preventing tumor growth in all patients or in individual patients. The presence of proteins encoded by 15,841 genes in tumors from 27 HCC patients is evaluated by immunohistochemistry. Personalized GEMs for six HCC patients and GEMs for 83 healthy cell types are reconstructed based on HMR 2.0 and the tINIT algorithm for task-driven model reconstruction. 101 antimetabolites are predicted to inhibit tumor growth in all patients. Antimetabolite toxicity is tested using the 83 cell type-specific GEMs. An l-carnitine analog inhibits the proliferation of HepG2 cells. Abstract Genome-scale metabolic models (GEMs) have proven useful as scaffolds for the integration of omics data for understanding the genotype-phenotype relationship in a mechanistic manner. Here, we evaluated the presence/absence of proteins encoded by 15,841 genes in 27 hepatocellular carcinoma (HCC) patients using immunohistochemistry. We used this information to reconstruct personalized GEMs for six HCC patients based on the proteomics data, HMR 2.0, and a task-driven model reconstruction algorithm (tINIT). The personalized GEMs were employed to identify anticancer drugs using the concept of antimetabolites; i.e., drugs that are structural analogs to metabolites. The toxicity of each antimetabolite was predicted by assessing the in silico functionality of 83 healthy cell type-specific GEMs, which were also reconstructed with the tINIT algorithm. We predicted 101 antimetabolites that could be effective in preventing tumor growth in all HCC patients, and 46 antimetabolites which were specific to individual patients. Twenty-two of the 101 predicted antimetabolites have already been used in different cancer treatment strategies, while the remaining antimetabolites represent new potential drugs. Finally, one of the identified targets was validated experimentally, and it was confirmed to attenuate growth of the HepG2 cell line.

  • 39610.
    Åhlfeldt, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Time-dependent change of the phase-matching wavelength due to refractive-index instabilities in proton-exchanged LiTaO3 waveguides1994Conference paper (Refereed)
  • 39611.
    Åhlgren, Erik
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Ett kvantitativt verktyg för utfärdande avsäljoptioner2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study investigates whether differences between options implicit volatility and the underlying assets historical volatility can be used to generate returns to a portfolio. This has been done by posing an investment problem which solution is based on maximizing the investor return given the individual preference and attitude towards risk and belief in the market. The structure of the investment problem is such that the investor can choose to issue put options or not to do so. How many options to be issued are largely due to differences between the implicit volatility and the historical. To illustrate this a fictitious portfolio with data from the market has been established where its returns and transactions have been evaluated and analyzed.

    The result shows that the investment strategy has performed well and that the investors beliefs in the development of the market versus the prices of the options has resulted in returns significantly higher than the underlying asset have. In other words, the solution of the investment problem can serve as an excellent tool for issuing put options.

  • 39612.
    Åhlund, John
    et al.
    Department of Physics, Uppsala University.
    Nilson, Katharina
    Department of Physics, Uppsala University.
    Schiessling, Joachim
    Department of Physics, Uppsala University.
    Kjeldgaard, Lisbeth
    MAX-lab., University of Lund.
    Berner, Simon
    Department for Surface Biotechnology, BMC, Uppsala.
    Mårtensson, Nils
    Department of Physics, Uppsala University.
    Puglia, Carla
    Department of Physics, Uppsala University.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nyberg, Mats
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    The electronic structure of iron phthalocyanine probed by photoelectron and x-ray absorption spectroscopies and density functional theory calculations2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 3, p. 034709-1-034709-7Article in journal (Refereed)
    Abstract [en]

    A joint experimental and theoretical work to explain the electronic and geometrical structure of an in situ prepared film of iron phthalocyanine (FePc) on silicon (100) is presented. FePc molecular films have been characterized by core and valence photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS), and the results have been interpreted and simulated by density functional theory (DFT) calculations. C1s and N1s PE spectra have been analyzed by taking into account all chemically nonequivalent C and N atoms in the molecule. In the Fe2p(3/2) spectra it has been possible to resolve two components that can be related to the open shell structure of the molecule. By valence PES and N1s XAS data, the geometrical orientation of the FePc molecules in the film could be determined. Our results indicate that for the FePc on Si(100), the molecules within the film are mainly standing on the surface. The experimental N1s XAS spectra are very well reproduced by the theoretical calculations, which are both angle and atomic resolved, giving a detailed description of the electronic and geometric structure of the FePc film. Furthermore, the asymmetry and the intensity angle variation of the first N1s XAS threshold feature could be explained by the presented DFT calculations as due to the chemical nonequivalence of the N atoms and the symmetry character of the lowest unoccupied molecular orbital.

  • 39613. Åhlén, J.
    et al.
    Sundgren, David
    KTH, School of Information and Communication Technology (ICT), Computer and Systems Sciences, DSV.
    Bengtsson, E.
    Application of underwater hyperspectral data for color correction purposes2007In: Pattern Recognition and Image Analysis, ISSN 1054-6618, Vol. 17, no 1, p. 170-173Article in journal (Refereed)
    Abstract [en]

    Color correction of underwater images has been considered a difficult task for a number of reasons. Those include severe absorption of the water column, the unpredictable behavior of light under the water surface, limited access to reliable data for correction purposes, and the fact that we are only able to process three spectral channels, which is insufficient for most color correction applications. Here, the authors present a method to estimate a hyperspectral image from an RGB image and pointwise hyperspectral data. This is then used to color correct the hyperspectral underwater image and transform it back into RGB color space.

  • 39614. Åhlén, J.
    et al.
    Sundgren, David
    KTH, School of Information and Communication Technology (ICT), Computer and Systems Sciences, DSV.
    Bengtsson, E.
    Pre-processing of underwater images taken in shallow water for color reconstruction purposes2005In: Proc. Seventh IASTED Int. Conf. Sign. Imag. Proc., 2005, p. 560-564Conference paper (Refereed)
    Abstract [en]

    Coral reefs are monitored with different techniques in order to examine their health. Digital cameras, which provide an economically defendable tool for marine scientists to collect underwater data, tend to produce bluish images due to severe absorption of light at longer wavelengths. In this paper we study the possibilities of correcting for this color distortion through image processing. The decrease of red light by depth can be predicted by Beer's Law. Another parameter that has been taken into account is the image enhancement functions built into the camera. We use a spectrometer and a reflectance standard to obtain the data needed to approximate the joint effect of these functions. This model is used to pre-process the underwater images taken by digital cameras so that the red, green and blue channels show correct values before the images are subjected to correction for the effects of the water column through application of Beer's Law. This process is fully automatic and the amount of processed images is limited only by the speed of computer system. Experimental results show that the proposed method works well for correcting images taken at different depths with two different cameras.

  • 39615. Åhlén, J.
    et al.
    Sundgren, David
    KTH, School of Information and Communication Technology (ICT), Computer and Systems Sciences, DSV.
    Lindell, T.
    Bengtsson, E.
    Dissolved organic matters impact on colour reconstruction in underwater images2005In: IMAGE ANALYSIS, PROCEEDINGS / [ed] Kalviainen, H; Parkkinen, J; Kaarna, A, 2005, Vol. 3540, p. 1148-1156Conference paper (Refereed)
    Abstract [en]

    The natural properties of water column usually affect underwater imagery by suppressing high-energy light. In application such as color correction of underwater images estimation of water column parameters is crucial. Diffuse attenuation coefficients are estimated and used for further processing of underwater taken data. The coefficients will give information on how fast light of different wavelengths decreases with increasing depth. Based on the exact depth measurements and data from a spectrometer the calculation of downwelling irradiance will be done. Chlorophyll concentration and a yellow substance factor contribute to a great variety of values of attenuation coefficients at different depth. By taking advantage of variations in depth, a method is presented to estimate the influence of dissolved organic matters and chlorophyll on color correction. Attenuation coefficients that depends on concentration of dissolved organic matters in water gives an indication on how well any spectral band is suited for color correction algorithm.

  • 39616.
    Åhman, Henrik
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Interaction as existential practice: An explorative study of Mark C. Taylor’s philosophical project and its potential consequences for Human-Computer Interaction2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis discusses the potential consequences of applying the philosophy of Mark C. Taylor to the field of Human-Computer Interaction (HCI).

    The first part of the thesis comprises a study focusing on two discursive trends in contemporary HCI, materiality and the self, and how these discourses describe interaction. Through a qualitative, inductive content analysis of 171 HCI research articles, a number of themes are identified in the literature and, it is argued, construct a dominant perspective of materiality, the self, and interaction. Examples that differ from the dominant discourse are also discussed as alternative perspectives for each of the three focal areas.

    The second part of the thesis comprises an analysis of Mark C. Taylor’s philosophical project which enables a number of philosophical positions on materiality, the self, and interaction to be identified. These positions are suggested to be variations and rereadings of themes found in Friedrich Nietzsche’s philosophy. These variations emerge as Taylor approaches Nietzsche through poststructuralism and complexity theory, and it is argued that the apparent heterogeneity of Taylor’s project can be understood as a more coherent position when interpreted in relation to Nietzsche’s philosophy.

    Based on the findings of the two literature studies, the thesis then discusses the possible consequences for HCI, if Taylor’s philosophy were to be applied as a theoretical framework. The thesis argues that Taylor’s philosophy describes the interaction between humans and computers  as an existential process, which contrasts with the dominant HCI discourse; that this view can be related to and provide a theoretical foundation for the alternative discourses in HCI; and that it can contribute to developing HCI.

  • 39617.
    Åhman, Henrik
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    The aesthetic turn: Exploring the religious dimensions of digital technology2016In: Approaching Religion, ISSN 1799-3121, E-ISSN 1799-3121, Vol. 6, no 2, p. 156-163Article in journal (Refereed)
    Abstract [en]

    The arena for developing digital technology has undergone an aesthetic turn, broadening the focus from a functionalist approach producing centralized systems in the 1970s and 1980s to an increased awareness of the aesthetic aspects of the individual user’s interaction with technology in the 1990s and 2000s. Within the academic research fields studying digital technology (e.g. Human-Computer Interaction and Interaction Design) the aesthetic turn has resulted in a shift from a strong emphasis on user behaviour to an increased interest in aesthetic perspectives on the role of the designer, the design process, and the design material. Within these fields, aesthetics has often been interpreted as belonging to the realm of the individual; personal experiences such as pleasure, engagement, and emotions have been emphasized in both technology development and technology research. Aesthetics is not, however, only an individual phenomenon but also has relational and structural components that need to be acknowledged. Structural aspects of aesthetics condition the possibilities for individuals interacting with digital technology. Thus, the tension between individual and relational aspects of aesthetics in digital technology also reflects a tension between freedom and limitation; between change and permanence; between destabilizing and stabilizing forces. Such a broadened understanding of aesthetics offers a model of digital technology that roughly corresponds to Mark C. Taylor’s definition of religion. Taylor argues that religion is constituted by, on the one hand, a figuring moment characterized by structural stability and universality, and, on the other hand, a disfiguring moment characterized by disruption, particularity, and change. The purpose of this paper is to discuss the aesthetic turn and Taylor’s definition of religion to illustrate similarities between the two, suggesting possible religious dimensions of digital technology and how that can inform our understanding of people’s interaction with digital technology.

  • 39618.
    Åhs, Fredrik
    KTH, School of Computer Science and Communication (CSC).
    Evaluation of memory based collaborative filtering for repository recommendation on Github2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    GitHub is host to a huge number of repositories. In order to explore and find new and interesting repositories on GitHub users has to rely on global charts or explore manually. Recommender systems are a type of software algorithms that produce personalized recommendations to users. One class of such algorithms are called memory based collaborative filtering. This report explore whether this kind of algorithms can be used to generate personalized recommendations of repositories on GitHub to its users, which is achieved by evaluating existing methods of generating predictions using memory based collaborative filtering which is then implemented for experimentation. The results indicates that memory based collaborative filtering might be a slightly better choice than global charts for a small percentage of the users, but for most users it is not.

  • 39619.
    Åkerberg, Ludvig
    KTH, School of Computer Science and Communication (CSC).
    Using Unsupervised Machine Learning for Outlier Detection in Data to Improve Wind Power Production Prediction2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The expansion of wind power for electrical energy production has increased in recent years and shows no signs of slowing down. This unpredictable source of energy has contributed to destabilization of the electrical grid causing the energy market prices to vary significantly on a daily basis. For energy producers and consumers to make good investments, methods have been developed to make predictions of wind power production.

    These methods are often based on machine learning were historical weather prognosis and wind power production data is used. However, the data often contain outliers, causing the machine learning methods to create inaccurate predictions.

    The goal of this Master’s Thesis was to identify and remove these outliers from the data so that the accuracy of machine learning predictions can improve. To do this an outlier detection method using unsupervised clustering has been developed and research has been made on the subject of using machine learning for outlier detection and wind power production prediction.

  • 39620.
    Åkerblom, Beatrice
    et al.
    Computer and Systems Science Stockholm University.
    Castegren, Elias
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS.
    Wrigstad, Tobias
    Uppsala University.
    Progress Report: Exploring API Design for Capabilities for Programming with Arrays2019In: ECOOP 2019, 2019Conference paper (Refereed)
  • 39621.
    Åkerblom, Karl
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Investigations of Single Longitudinal Mode and Frequency Stabilityin Standing Wave and Unidirectional Cavity Lasers2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 39622.
    Åkerborg, Örjan
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Taking advantage of phylogenetic trees in comparative genomics2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Phylogenomics can be regarded as evolution and genomics in co-operation. Various kinds of evolutionary studies, gene family analysis among them, demand access to genome-scale datasets. But it is also clear that many genomics studies, such as assignment of gene function, are much improved by evolutionary analysis. The work leading to this thesis is a contribution to the phylogenomics field. We have used phylogenetic relationships between species in genome-scale searches for two intriguing genomic features, namely and A-to-I RNA editing. In the first case we used pairwise species comparisons, specifically human-mouse and human-chimpanzee, to infer existence of functional mammalian pseudogenes. In the second case we profited upon later years' rapid growth of the number of sequenced genomes, and used 17-species multiple sequence alignments. In both these studies we have used non-genomic data, gene expression data and synteny relations among these, to verify predictions. In the A-to-I editing project we used 454 sequencing for experimental verification.

    We have further contributed a maximum a posteriori (MAP) method for fast and accurate dating analysis of speciations and other evolutionary events. This work follows recent years' trend of leaving the strict molecular clock when performing phylogenetic inference. We discretised the time interval from the leaves to the root in the tree, and used a dynamic programming (DP) algorithm to optimally factorise branch lengths into substitution rates and divergence times. We analysed two biological datasets and compared our results with recent MCMC-based methodologies. The dating point estimates that our method delivers were found to be of high quality while the gain in speed was dramatic.

    Finally we applied the DP strategy in a new setting. This time we used a grid laid out on a species tree instead of on an interval. The discretisation gives together with speciation times a common timeframe for a gene tree and the corresponding species tree. This is the key to integration of the sequence evolution process and the gene evolution process. Out of several potential application areas we chose gene tree reconstruction. We performed genome-wide analysis of yeast gene families and found that our methodology performs very well.

  • 39623.
    Åkerborg, Örjan
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sennblad, Bengt
    Arvestad, Lars
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Lagergren, Jens
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Simultaneous Bayesian gene tree reconstruction and reconciliation analysis2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, p. 5714-5719Article in journal (Refereed)
    Abstract [en]

    We present GSR, a probabilistic model integrating gene duplication, sequence evolution, and a relaxed molecular clock for substitution rates, that enables genomewide analysis of gene families. The gene duplication and loss process is a major cause for incongruence between gene and species tree, and deterministic methods have been developed to explain such differences through tree reconciliations. Although probabilistic methods for phylogenetic inference have been around for decades, probabilistic reconciliation methods are far less established. Based on our model, we have implemented a Bayesian analysis tool, PrIME-GSR, for gene tree inference that takes a known species tree into account. Our implementation is sound and we demonstrate its utility for genomewide gene-family analysis by applying it to recently presented yeast data. We validate PrIME-GSR by comparing with previous analyses of these data that take advantage of gene order information. In a case study we apply our method to the ADH gene family and are able to draw biologically relevant conclusions concerning gene duplications creating key yeast phenotypes. On a higher level this shows the biological relevance of our method. The obtained results demonstrate the value of a relaxed molecular clock. Our good performance will extend to species where gene order conservation is insufficient.

  • 39624.
    Åkerborg, Örjan
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sennblad, Bengt
    Lagergren, Jens
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Birth-death prior on phylogeny and speed dating2008In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 8, no 1, p. 77-Article in journal (Refereed)
    Abstract [en]

    Background: In recent years there has been a trend of leaving the strict molecular clock in order to infer dating of speciations and other evolutionary events. Explicit modeling of substitution rates and divergence times makes formulation of informative prior distributions for branch lengths possible. Models with birth-death priors on tree branching and auto-correlated or iid substitution rates among lineages have been proposed, enabling simultaneous inference of substitution rates and divergence times. This problem has, however, mainly been analysed in the Markov chain Monte Carlo (MCMC) framework, an approach requiring computation times of hours or days when applied to large phylogenies.

    Results: We demonstrate that a hill-climbing maximum a posteriori (MAP) adaptation of the MCMC scheme results in considerable gain in computational efficiency. We demonstrate also that a novel dynamic programming (DP) algorithm for branch length factorization, useful both in the hill-climbing and in the MCMC setting, further reduces computation time. For the problem of inferring rates and times parameters on a fixed tree, we perform simulations, comparisons between hill-climbing and MCMC on a plant rbcL gene dataset, and dating analysis on an animal mtDNA dataset, showing that our methodology enables efficient, highly accurate analysis of very large trees. Datasets requiring a computation time of several days with MCMC can with our MAP algorithm be accurately analysed in less than a minute. From the results of our example analyses, we conclude that our methodology generally avoids getting trapped early in local optima. For the cases where this nevertheless can be a problem, for instance when we in addition to the parameters also infer the tree topology, we show that the problem can be evaded by using a simulated-annealing like (SAL) method in which we favour tree swaps early in the inference while biasing our focus towards rate and time parameter changes later on.

    Conclusion: Our contribution leaves the field open for fast and accurate dating analysis of nucleotide sequence data. Modeling branch substitutions rates and divergence times separately allows us to include birth-death priors on the times without the assumption of a molecular clock. The methodology is easily adapted to take data from fossil records into account and it can be used together with a broad range of rate and substitution models.

  • 39625.
    Åkerlund, Joakim
    KTH, School of Computer Science and Communication (CSC).
    Design av robusta nätverk2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The proper functioning of Internet and computer networks i n today’s society is vital to many companies and the society as a whole. The focus of this project is an investigation of networks and an evaluation of which techniques can affect robustness to different degrees. Improving robustness will in many cases also increase cost, both counting the actual construction as well as during further operation. When a business’s goal is to increase profit it has to consider which techniques are worth the investment compared to what it would cost if something would indeed go wrong and thus causing problems that may not allow the business to fulfill its demands and losing profit because of that.

    The thesis work was done at the Swedish Post and Telecom Agency (PTS) and the focus was on their network. Following a background of the different techniques a set of real life tests were performed to validate that they actually work. To not narrow the focus on just PTS, a couple of scenarios are described of different sizes of businesses and how they have to overcome different problems and risks. Finally a conclusion is drawn from the results of the real-life tests and also reflections over the different techniques that are presented that could be applied in a general case.

  • 39626.
    Åkerman, Johan
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    DeHerrera, M.
    Slaughter, J. M.
    Dave, R.
    Sun, J. J.
    Martin, J. T.
    Tehrani, S.
    Intrinsic reliability of AlOx-based magnetic tunnel junctions2006In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 42, no 10, p. 2661-2663Article in journal (Refereed)
    Abstract [en]

    We present a detailed investigation into the intrinsic tunnel barrier reliability in AlOx-based magnetic tunnel junctions (MTJs) as a function of aluminum thickness and oxidation time. The intrinsic reliability is measured as the ramped breakdown voltage (V-bd) at room temperature for both positive and negative polarity. We find that Vbd generally increases with the resistance-area (RA) product of the MTJ. While this dependence is quite strong at low RA, it gradually weakens for higher RA. At fixed RA, Vbd also depends on the original Al film thickness with better properties for thicker Al. Finally, we observe a polarity dependence of V-bd which changes sign as the MTJ goes from thin Al to thick Al. We attribute the polarity dependence to the different quality of the top and bottom interfaces and conclude that the interface emitting the tunneling electrons primarily governs the barrier reliability.

  • 39627.
    Åkerman, Jonas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies.
    Höjer, Mattias
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies. School of Computer Science and Communication (CSC), Centres, KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Sustainable Communications, CESC.
    How much transport can the climate stand? Sweden on a sustainable path in 20502006In: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 34, no 14, p. 1944-1957Article in journal (Refereed)
    Abstract [en]

    In this paper an image of a sustainable transport system for Sweden in 2050 is outlined. The emissions per capita in this image may be generalized to a global population of 9 billions, and still be consistent with a stabilization of the carbon dioxide concentration at 450ppm (parts per million). Swedish transport energy use per capita is 4.6MWh in the image, compared to 12.5MWh at present. The aim is, first, to widen the perspective of sustainable transport futures and, second, to provide a basis for present decisions in areas characterized by a high inertia, e.g. regarding infrastructure and the built-up environment. All transport generated by the lifestyles of Swedish residents are included. The reduction of energy use in the image is primarily achieved by an introduction of energy efficient vehicles and a conscious combination of IT-services and urban planning. The latter aims at increasing functional accessibility while reducing commuting. A prioritization of leisure travel to structurally-enforced travel gives the possibility to increase leisure travel per capita by one third. However, this is contingent on a 50% reduction of per capita car travel in cities. Given the set-up target, it may be concluded that the need for new arterial road capacity in cities often is negligible, even with a considerable population increase.

  • 39628. Åkerman, S.
    et al.
    Lindeberg, Tony
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Roland, P.
    Surface Model Generation and Segmentation of the Human Celebral Cortex for the Construction of Unfolded Cortical Maps1996In: Proc. 2nd International Conference on Functional Mapping of the Human Brain: HBM'96, published in Neuroimage, volume 3, number 3, 1996, p. S126-S126Conference paper (Refereed)
    Abstract [en]

    Representing the shape of the human cerebral cortex arises as a basic subproblem in several areas of brain science, such as when describing the anatomy of the cortex and when relating functional measurements to cortical regions. 

    Most current methods for building such representions of the cortical surface are either based on contours from two-dimensional cross sections or landmarks that have been obtained manually.

    In this article, we outline a methodology for semi-automatic contruction of a solely surface based representation of the human cerebral cortex in vivo for subsequent generation of  (unfolded) two-dimensional brain maps.

    The method is based on input data in the form of three-dimensional NMR images, and comprises the following main steps:

    • suppression of disturbing fine-scale structures by linear and non-linear scale-space techniques,
    • generation of a triangulated surface representation based on either iso-surfaces or three-dimensional edge detection,
    • division of the surface model into smaller segments based on differential invariants computed from the image data.

    When constructing an unfolded (flattened) surface representation, the instrinsic curvature of the cortex means that such a unfolding cannot be done without introducing distortions. To reduce this problem, we propose to cut the surface into smaller parts, where a ridge detector acts as guideline, and then unfold each patch individually, so as to obtain low distortions.

    Having a solely surface based representation of the cortex and expressing the image operations using multi-scale differential invariants in terms of scale-space derivatives as done in this work is a natural choice both in terms of conceptual and algorithmic simplicity. Moreover, explicitly handling the multi-scale nature of the data is necessary to obtain robust results.

  • 39629.
    Åkermark, Torbjörn
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Doremus, R. H.
    Comment on "oxidation of alloys containing aluminum and diffusion in Al2 O3 " [J. Appl. Phys. 95, 3217 (2004)]2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 11, p. 116109-Article in journal (Refereed)
    Abstract [en]

    The introduction of AlO as the diffusing species can be seen as an attempt to bridge the gap between the two scientific communities: those working on the oxidation of metals and those working on the oxidation of silicon. The attempt is, however, not successful and would have been more successful if the Wagner theory [O. Wagner, Z. Phys. Chem. Abt. B 21, 25 (1993)] would have been used to evaluate the mechanisms. There is also a lack of agreement with the two-stage oxidation experiment, oxidation first in O-16 and then in O-18. The experimental O-18 profile in the oxides formed cannot be explained by the diffusion of AlO, so it is unlikely that AlO is the diffusing species during oxidation.

  • 39630.
    Åkerstedt, Josefin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Subvalent Cluster Compounds and Synthesis in Alternative Reaction Media2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With the aim of finding alternative reaction media for the synthesis of subvalent main group and transition metal cluster compounds, traditionally made through solid state reactions or in superacidic media, different alternative reaction media have been explored in this work. Room-temperature ionic liquids are amongst the more unconventional reaction media used. The syntheses performed have been aimed at both anionic and cationic cluster and the main tools used for characterization have been different X-ray diffraction and spectroscopic techniques.

    Selected ionic liquids have along with dichloromethane been shown to work as alternative reaction media for room temperature synthesis of the Bi5[GaCl4]3 salt. The salt containing the subvalent naked bismuth polycation Bi5 3+ was isolated from reduction reactions of BiCl3 in Ga/GaCl3-dichloromethane respectively Ga/GaCl3-ioinc liquid media. Three different classes of ionic liquids based on phosphonium-, imidazolium- and pyrrolidinium- salts have been used in synthesis. Homopolyatomic clusters from the lighter Group 15 element arsenic have also been studied. Solutions from the oxidative and reductive reaction routes of arsenic and AsCl3 in Lewis acidic toluene media were studied by EXAFS spectroscopy. The results were evaluated using molecular dynamics simulations of arsenic clusters. A discussion on how the calculated As4 cluster model relates to the experimental data resulted from this study.

    In terms of homopolyatomic anionic clusters the [K+(2,2,2-crypt)]2Ge9 2- compound containing the naked Ge9 2- anionic cluster has been isolated. The crystallographic investigation of [K+(2,2,2-crypt)]2Ge9 2- shows Zintl cluster anion Ge9 2- to be tricapped trigonal-prismatic with a symmetry very close to D3h. A chemical bonding analysis reveals two local minima of D3h symmetry and the cluster interaction scheme to be based on highly delocalised bonding.

    Ligand supported transition metal clusters from tungsten and palladium have also been prepared. Reduction of WCl6 in a reaction mixture of ionic liquid and co-solvent toluene resulted in tritungsten decachloride; W3Cl10(MeCN)3, being formed. Furthermore, palladium sandwich compounds; [Pd2(Ga2Cl7)(C7H8)2], [Pd2(GaCl4)(C9H12)2]∙C9H12 and [Pd2(Ga2Cl7)(C6H5Cl)2] have been prepared using GaCl3-arene reaction media.

  • 39631.
    Åkerstedt, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Gorlov, Mikhail
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Synthesis and characterization of binuclear palladium(I) compounds and the influence of competing arenes2010In: Journal of Organometallic Chemistry, ISSN 0022-328X, E-ISSN 1872-8561, Vol. 695, no 10-11, p. 1513-1517Article in journal (Refereed)
    Abstract [en]

    The binuclear palladium(I) compounds, [Pd-2(Ga2Cl7)(2)(C7H8)(2)] (1), [Pd-2(GaCl4)(2)(C9H12)(2)]center dot C9H12 (2) and [Pd-2(Ga2Cl7)(2)(C6H5Cl)(2)] (3), have been prepared from palladium(II) chloride in gallium(III) chloride-arene reaction media. All isolated crystalline solids (1, 2 and 3) have been structurally characterized by single crystal X-ray diffraction and Raman spectroscopy. The results form quantum chemical calculations on the interaction energies of the arenes and the dipalladium unit of these compounds is also presented.

  • 39632.
    Åkerstedt, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Ponou, Simeon
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Lidin, Sven
    Structural Investigation of a Fully Ordered closo-Ge(9)(2-) Cluster in the Compound [K(+)(2,2,2-crypt)](2)Ge(9)(2-)2011In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 26, p. 3999-4005Article in journal (Refereed)
    Abstract [en]

    [K(+)(2,2,2-crypt)] (2)Ge(9)(2-) containing the deltahedral Zintl anion Ge(9)(2-) has been isolated from a solution of K(4)Ge(9) in ethylenediamine in the presence of 2,2,2-crypt, intended as an intermediate in mixed-cluster synthesis. The subsequent crystallographic characterisation shows the closo-Ge(9)(2-) cluster unit to be tricapped trigonal-prismatic with a symmetry very close to D(3h). Each Ge(9)(2-) unit is surrounded by two 2,2,2-crypt units, each with a chelated K(+) cation, viz. [K(+)(2,2,2-crypt)]. The structure characterisation of this ordered Ge(9)(2-) cluster is surprisingly enough the first one reported. A chemical bonding analysis reveals two local minima of D(3h) symmetry, with that of lowest energy being highly similar to that resulting from the crystallographic analysis of low-temperature data. The cluster interaction scheme is based on highly delocalised bonding.

  • 39633.
    Åkerstedt, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Zaffaroni, Riccardo
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Dichloromethane as solvent for the synthesis of polycationic clusters at room temperature: a link to standard organometallic chemistry2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 35, p. 8132-8134Article in journal (Refereed)
    Abstract [en]

    Dichloromethane (DCM), CH2Cl2 has been identified as an alternative reaction medium for room-temperature synthesis of subvalent homopolyatomic clusters of the group 15 element bismuth.

  • 39634. Åkeson, M.
    et al.
    Nordberg, Markus
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Ehlerding, Anneli
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Nilsson, L. -E
    Östmark, H.
    Strömbeck, P.
    Picosecond laser pulses improves sensitivity in standoff explosive detection2011In: Proc SPIE Int Soc Opt Eng, 2011Conference paper (Refereed)
    Abstract [en]

    Portendo has in collaboration with FOI, the Swedish Defence Research Agency, developed a world-leading technique of trace detection of explosives at standoff distance using Raman spectroscopy. The technology is further developed in order to enhance the sensitivity of the method and to be able to extend the field of applications. Raman scattering is a well-established technique able to detect substances down to single micrograms at standoff distances, however, one of the obstacles limiting the detection possibilities is interfering fluorescence, originating either from the substance itself or from the surrounding material. One main challenge for this technology is thus to either omit the excitation of the fluorescent process altogether or to be able to separate the two processes and only detect the Raman signal. Due to the difference in the temporal behavior of the two processes - Raman scattering occurs in the order of femtoseconds while fluorescence typically has a lifetime in the order of nanoseconds - one way to theoretically separate them is to limit the measurement to as short time as possible, cutting off most of the emitted fluorescence. The improvement depends on how much of the fluorescence can be omitted without decreasing the Raman signal. Experimentally, we have verified this improvement in signal to noise ratio when using a laser with picosecond pulses instead of nanosecond pulses, which has resulted in an improvement in SNR of up to 7 times for bulk ANFO. These results verify the predicted signal enhancement and suggest higher sensitivity for standoff detection in future systems.

  • 39635.
    Åkesson, Anna
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Hydraulic- hydromorphologic analysis as an aid for improving peak flow predictions2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Conventional hydrological compartmental models have been shown to exhibit a high degree of uncertainty for predictions of peak flows, such as the design floods for design of hydropower infrastructure. One reason for these uncertainties is that conventional models are parameterised using statistical methods based on how catchments have responded in the past. Because the rare occurrence of peak flows, these are underrepresented during the periods used for calibration. This implies that the model has to be extrapolated beyond the discharge intervals where it has been calibrated.

    In this thesis, hydromechanical approaches are used to investigate the properties of stream networks, reflecting mechanisms including stage dependency, damming effects, interactions between tributaries (network effects) and the topography of the stream network. Further, it is investigated how these properties can be incorporated into the streamflow response functions of compartmental hydrological models.

    The response of the stream network was shown to vary strongly with stage in a non-linear manner, an effect that is commonly not accounted for in model formulation. The non-linearity is particularly linked to the flooding of stream channels and interactions with the flow on flood-plains.

    An evaluation of the significance of using physically based response functions on discharge predictions in a few sub-catchments in Southern Sweden show improvements (compared to a conventional model) in discharge predictions – particularly when modelling peak discharges.

    An additional benefit of replacing statistical parameterisation methods with physical parameterisation methods is the possibility of hydrological modelling during non-stationary conditions, such as the ongoing climate change.

  • 39636.
    Åkesson, Anna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Peakflow response of stream networks: implications of physical descriptions of streams and temporal change2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Through distributed stream network routing, it has quantitatively been shown that the relationship between flow travel time and discharge varies strongly nonlinearly with stream stage and with catchment-specific properties.

    Physically derived distributions of water travel times through a stream network were successfully used to parameterise the streamflow response function of a compartmental hydrological model. Predictions were found to improve compared to conventional statistically based parameterisation schemes, for most of the modelled scenarios, particularly for peakflow conditions.

    A Fourier spectral analysis of 55-110 years of daily discharge time series from 79 unregulated catchments in Sweden revealed that the discharge power spectral slope has gradually increased over time, with significant increases for 58 catchments. The results indicated that the catchment scaling function power spectrum had steepened in most of the catchments for which historical precipitation series were available. These results suggest that (local) land-use changes within the catchments may affect the discharge power spectra more significantly than changes in precipitation (climate change).

    A case study from an agriculturally intense catchment using historical (from the 1880s) and modern stream network maps revealed that the average stream network flow distance as well as average water levels were substantially diminished over the past century, while average bottom slopes increased. The study verifies the hypothesis that anthropogenic changes (determined through scenario modelling using a 1D distributed routing model) of stream network properties can have a substantial influence on the travel times through the stream networks and thus on the discharge hydrographs.

    The findings stress the need for a more hydrodynamically based approach to adequately describe the variation of streamflow response, especially for predictions of higher discharges. An increased physical basis of response functions can be beneficial in improving discharge predictions during conditions in which conventional parameterisation based on historical flow patterns may not be possible - for example, for extreme peak flows and during periods of nonstationary conditions, such as during periods of climate and/or land use change.

  • 39637.
    Åkesson, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Stadler, Charlotte
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Sullivan, D. P.
    Wiking, Mikaela
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Krijgsveld, J.
    Uhlen, M.
    Lundberg, Emma
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Large-scale spatial mapping of the nuclear human proteome.2016In: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 27Article in journal (Refereed)
  • 39638.
    Åkesson, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Stage-dependent hydraulic and hydromorphologic properties in stream networks translated into response functions of compartmental models2012In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 420-421, p. 25-36Article in journal (Refereed)
    Abstract [en]

    A distributed non-uniform routing model was constructed and applied to two stream networks in southern Sweden to investigate the effects of stage, topology and morphology on advective travel times within the stream networks.Using particle-tracking, we found markedly non-linear relationships between travel time distributions and discharge for both catchments under a range of hydraulic conditions, represented by discharges comprising percentiles between 30 and 99.9 extracted from the discharge data set for the two catchments in this study.The travel time distributions from the particle tracking were used to numerically parameterise the response function of a lumped hydrological model, which resulted in improvements, particularly in the prediction of high flows. A sensitivity analysis was performed on the routing procedure, particularly regarding the choice of Manning's friction coefficient and the choice of generic cross-sectional areas along the two stream networks showing that the uncertainty in routing parameters did not have a major effect on the final hydrograph. The new parameterisation performed better than the conventional model in every modelled case.A theoretical demonstration shows that correct descriptions of streamflow processes becomes more important with increased watershed scale, because the travel time within the stream network relative to the travel time on hillslopes increases with the watershed scale. The topology and topography of the stream network were shown to be the major factors influencing the network averaged travel time. These results demonstrate that physically based response functions (and model parameters) can be superior to compartmental model parameters that are based on numerical calibration and that are extrapolated to account for conditions during hydrological extremes.

  • 39639.
    Åkesson, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Bottacin-Busolin, Andrea
    Hydraulic response in flooded stream networks2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 1, p. 213-240Article in journal (Refereed)
    Abstract [en]

    Average water travel times through a stream network were determined as a function of stage (discharge) and stream network properties. Contrary to most previous studies on the topic, the present work allowed for streamflow velocities to vary spatially (for most of the analyses) as well as temporally. The results show that different stream network mechanisms and properties interact in a complex and stage-dependent manner, implying that the relative importance of the different hydraulic properties varies in space and over time. Theoretical reasoning, based on the central temporal moments derived from the kinematic-diffusive wave equation in a semi-2-D formulation including the effects of flooded cross sections, shows that the hydraulic properties in contrast to the geomorphological properties will become increasingly important as the discharge increases, stressing the importance of accurately describing the hydraulic mechanisms within stream networks. Using the physically based, stage-dependent response function as a parameterization basis for the streamflow routing routine (a linear reservoir) of a hydrological model, discharge predictions were shown to improve in two Swedish catchments, compared with a conventional, statistically based parameterization scheme. Predictions improved for a wide range of modeled scenarios, for the entire discharge series as well as for peak flow conditions. The foremost novelty of the study lies in that the physically based response function for a streamflow routing routine has successfully been determined independent of calibration, i.e., entirely through process-based hydraulic stream network modeling.

  • 39640.
    Åkesson, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Lindström, Göran
    Runoff modeling in flooded stream networks2007In: Proceedings of the International Symposium on Modern Technology of Dams – : the 4th EADC Symposium, Chengdu, China, October 12-18 2007., 2007, p. 441-450Conference paper (Other academic)
    Abstract [en]

    This paper outlines a procedure about how to create a compartment type of runoff model that is flexible for prediction of flows of different magnitudes. This methodology is expected to be most useful when applied to high flow situations, when predictions normally are conceived as extrapolations far outside calibration intervals. Focus is put on how to introduce response functions that include more detailed information regarding the river network geometry and the morphology of the channel cross-sections. The parametrisation formula is based on Manning’s equation for open channel flow and the geometrical data is derived from geographical information handled in a GIS software. These response functions can be expected to provide better extrapolations of the hydrograph for future extreme floods, especially for peak flows. This has implications for safety aspects of dams as well as for the economy of hydropower production.

  • 39641.
    Åkesson, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Riml, Joakim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Seibert, Jan
    Change in streamflow response in unregulated catchments in Sweden over the last century2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973Article in journal (Refereed)
    Abstract [en]

    A Fourier spectral analysis of 55-110 years of daily discharge time series in 79 unregulated catchments in Sweden reveals that the discharge power spectrum slope in most of the studied catchments has gradually steepened over time. This statistically significant drift in the periodicity of dominant hydrologic response processes can be attributed to a change in either climatic forcing factors or anthropogenic effects on the land surface, e.g., land-use changes. For those locations for which historical meteorological observations are available (the 41 southernmost catchments), the results of our analyses of changes in precipitation power spectra indicate that local land-use changes within the catchments may affect discharge power spectra more significantly than precipitation pattern changes (resulting from climate change).

    By using 1D distributed hydraulic routing, we quantitatively analyze how travel time distributions within stream networks can vary because of anthropogenic impacts, such as changes in stream network spatial coordinates (these stream networks are derived from three maps: two from the present and one from the 1880s), river width modifications, stream channel excavation, and the elimination of thresholds in stream bottom topography that cause exceedingly low local bottom slopes.

    The findings that the discharge power spectrum may change significantly over time, implies that conventional, statistically-based parameterization of hydrological models that rely on assumptions of stationarity may be less suited than more physically based parameterization alternatives. This essential information must be considered when performing tasks that involve (peak) flow predictions, such as those for dimensioning and flood risk management purposes.

     

  • 39642.
    Åkesson, Lovisa
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Cellular and Clinical Proteomics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Mahdessian, Diana
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Cellular and Clinical Proteomics.
    Gnann, Christian
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Cellular and Clinical Proteomics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Thul, Peter
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Cellular and Clinical Proteomics.
    Lundberg, Emma
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Cellular and Clinical Proteomics.
    Spatial organization of the nucleolar proteome during mitosisManuscript (preprint) (Other academic)
    Abstract [en]

    In the interphase cell, the membrane-less nucleoli are the sites of ribosome biogenesis. As part of the Human Protein Atlas we created an image catalogue comprising 1,314 nucleolar proteins using antibody-based proteomics. We show experimental evidence for 1,027 proteins localizing to the whole nucleoli and 287 to the fibrillar center or dense fibrillar component. We also propose a new sub-compartment located in the nucleoplasmic border denoted as nucleoli rim, comprising at least 131 proteins. As a step toward better understanding of nucleolar protein function during cell division, we additionally generated confocal images of 68 nucleolar proteins being recruited to the chromosomal periphery in mitosis. Thanks to the single cell resolution we were able to define three expression phenotypes among the mitotic chromosome proteins; early, intermediate and late recruitment suggesting phase specific functions. We also for the first time provide a proteome-wide confirmation that the nucleoli in general, but mitotic chromosome proteins in particular have a higher predicted intrinsic disorder level compared to cytoplasmic proteins, indicating that the perichromosomal layer indeed is a liquid-like layer.

  • 39643.
    Ålander, Alexandra
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Dufek, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Gudowski, Waclaw
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    From once-through nuclear fuel cycle to accelerator-driven transmutation2006In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 562, no 2, p. 630-633Article in journal (Refereed)
    Abstract [en]

    In this study simulation of different nuclear fuel cycle scenarios are performed. The reference scenario corresponds to a medium size nuclear power country, with 10 light water reactors (LWRs). The study addresses long-term, equilibrium fuel cycle scenarios, with and without plutonium recycling (MOX) in LWRs and transuranics (TRU) burning in accelerator-driven systems (ADS). However, also short-term phase-out scenarios, including TRU burning in ADS, are performed. The equilibrium simulation showed that four ADS units, each of 800 MWt, are sufficient to burn an amount of plutonium and americium corresponding to the build-up of those elements. The phase-out simulation of a country adopting an approach to reduce the spent nuclear fuel inventory, showed that complementary burning of TRU in three to four ADS units appear suitable. The fuel cycle simulations have been performed using the Nuclear Fuel Cycle Simulation (NFCSim) code [C.G. Bathke, E.A. Schneider, NFCSim User's Manual, Los Alamos National Laboratory Report LA-UR-04-8369, 2004.] and the Monteburns code [D.I. Poston, H.R. Trellue, User's Manual, Version 2.0 for Monteburns, Version 1.0, LA-UR-99-4999, 1999.].

  • 39644.
    Ålander, Eva Marie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Mechanisms of agglomeration of molecular crystals in organic solvents2005In: 16th International Symposium on Industrial Crystallization, September, 11 - 14, International Congress Center, Dresden, Germany, 2005, no 1901 I, p. 511-516Conference paper (Refereed)
    Abstract [en]

    The agglomeration of paracetamol has been investigated by fully seeded isothermal crystallization experiments operated at constant supersaturation. The particles from crystallization in ethanol, methyl ethyl ketone, water and acetone-water mixtures are characterized by image analysis and multivariate data evaluation. The number of crystals in each agglomerated particle is characterized and used as a measure of the degree of agglomeration. Surfaces of large, well grown paracetamol crystals have been characterised by contact angle measurements and the Lifshitz-van der Waals acid-base theory to determine the crystal-crystal adhesion energy. It is found that, beyond the effect of differences in liquid viscosity and crystal growth rate, there is a dependence of the degree of agglomeration on the solvent composition that can be correlated to the free energy of adhesion.

  • 39645. Ålander, J.
    et al.
    Lengqvist, J.
    Holm, P.J.
    Svensson, R.
    Gerbaux, P.
    van der Heuvel, R.H.H.
    Hebert, Hans
    Department of Biosciences, Karolinska Institutet.
    Griffiths, W.J.
    Armstrong, R.N.
    Morgenstern, R.
    Microsomal glutathione transferase 1 exhibits one-third-of-the-sites-reactivity towards glutathione2009In: Archives of Biochemistry and Biophysics, ISSN 0003-9861, E-ISSN 1096-0384, Vol. 487, no 1, p. 42-48Article in journal (Refereed)
    Abstract [en]

    The trimeric membrane protein microsomal glutathione transferase 1 (MGST1) possesses glutathione transferase and peroxidase activity. Previous data indicated one active site/trimer whereas structural data suggests three GSH-binding sites. Here we have determined ligand interactions of MGST1 by several techniques. Nanoelectrospray mass spectrometry of native MGST1 revealed binding of three GSH molecules/trimer and equilibrium dialysis showed three product molecules/trimer (K(d) = 320 +/- 50 mu M). All three product molecules Could be competed out with GSH. Reinvestigation of GSH-binding showed one high affinity site per trimer, consistent with earlier data. Using single turnover stopped flow kinetic measurements, Kd could be determined for a low affinity GSH-binding site (2.5 +/- 0.5 mu M). Thus we can reconcile previous observations and show here that MGST1 contains three active sites with different affinities for GSH and that only the high affinity site is catalytically competent.

  • 39646.
    Åman, Agnes
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Predicting consultation durations in a digital primary care setting2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to develop a method to predict consultation durations in a digital primary care setting and thereby create a tool for designing a more efficient scheduling system in primary care. The ultimate purpose of the work is to contribute to a reduction in waiting times in primary care. Even though no actual scheduling system was implemented, four machine learning models were implemented and compared to see if any of them had better performance.

    The input data used in this study was a combination of patient and doctor features. The patient features consisted of information extracted from digital symptom forms filled out by a patient before a video consultation with a doctor. These features were combined with doctor's speed, defined as the doctor's average consultation duration for his/her previous meetings. The output was defined as the length of the video consultation including administrative work made by the doctor before and after the meeting.

    One of the objectives of this thesis was to investigate whether the relationship between input and output was linear or non-linear. Also the problem was formulated both as a regression and a classification problem. The two problem formulations were compared in terms of achieved accuracy. The models chosen for this study was linear regression, linear discriminant analysis and the multi-layer perceptron implemented for both regression and classification.

    After performing a statistical t-test and a two-way ANOVA test it was concluded that no significant difference could be detected when comparing the models' performances. However, since linear regression is the least computationally heavy it was suggested for future usage until it is proved that any other model achieves better performance.

    Limitations such as too few models being tested and flaws in the data set were identified and further research is encouraged. Studies implementing an actual scheduling system using the methodology presented in the thesis is recommended as a topic for future research.

  • 39647.
    Åman, Agnes
    et al.
    KTH, School of Computer Science and Communication (CSC).
    Nyblom, Hanna
    KTH, School of Computer Science and Communication (CSC).
    Measuring the extent of interdisciplinary research and creating a collaboration group structure at KTH2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    With interdisciplinary research being a possibility in modern research environ- ments, it is interesting to optimise collaborations between researchers in order to further develop the research environment. The scope of this thesis was therefore to develop a method to measure how widespread the interdisciplinary research is and to propose collaboration groups of researchers created by the use of graph theory.

    This problem was approached by studying the research at KTH by col- lecting research publications from the publication database DiVA using a web crawler. Then representing the authors of the publications as nodes and the collaborations between two authors as edges in a graph. A graph partitioning algorithm developed by Flake et al. was chosen after a literature study, then applied to the graph to produce the requested collaboration groups.

    The results showed that while interdisciplinary research is not the norm at KTH, 23% of the proposed collaboration groups consisted of two or more researchers from different schools at KTH. The original ratio of school associ- ation was retained through the partitioning of the graph. A measurement of collaboration per researcher in each collaboration group was suggested and the calculated values of these measurements was found to be largely in the same range, with the exception of one collaboration group. The results also high- lighted some inconsistencies in DiVA.

    The conclusions were that interdisciplinary research was not very widespread at KTH, however 77 groups were suggested which could be of use for researchers at KTH from now on and in the future. A conclusion was also that this method for finding suitable collaboration groups could be applied at other universities where perhaps interdisciplinary research is more frequent. 

  • 39648.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Atomistic modelling of functional solid oxides for industrial applications: Density Functional Theory, hybrid functional and GW-based studies2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this Thesis a set of functional solid oxides for industrial applications have been addressed by first principles and thermodynamical modelling. More specificially, measurable quantities such as Gibbs free energy, geometry and electronic structure have been calculated and compared when possible with experimental data. These are crystalline and amorphous aluminum oxide (Al2O3), Zirconia (ZrO2), magnesium oxide (MgO), indiumoxide (In2O3) and Kaolinite clay (Al2Si2O5(OH)4).

    The reader is provided a computation tool box, which contains a set of methods to calculate properties of oxides that are measurable in an experiment. There are three goals which we would like to reach when trying to calculate experimental quantities. The first is verification. Without verification of the theory we are utilizing, we cannot reach the second goal -prediction. Ultimately, this may be (and to some extent already is) the future of first principles methods, since their basis lies within the fundamental quantum mechanics and since they require no experimental input apart from what is known from the periodic table. Examples of the techniques which may provide verification are X-Ray Diffraction (XRD), X-ray Absorption and Emission Spectroscopy (XAS and XES), Electron Energy Loss Spectroscopy and Photo-Emission Spectroscopy (PES). These techniques involve a number of complex phenomena which puts high demands on the chosen computational method/s. Together, theory and experiment may enhance the understanding of materials properties compared to the standalone methods. This is the final goal which we are trying to reach -understanding. When used correctly, first principles theory may play the role of a highly resolved analysis method, which provides details of structural and electronic properties on an atomiclevel. One example is the use of first principles to resolve spectra of multicomponentsamples. Another is the analysis of low concentrations of defects. Thorough analysis of the nanoscale properties of products might not be possible in industry due to time and cost limitations. This leads to limited control of for example low concentrations of defects, which may still impact the final performance of the product. On example within cutting tool industry is the impact of defect contents on the melting point and stability of protective coatings. Such defects could be hardening elements such as Si, Mn, S, Ca which diffuse from a steel workpiece into the protective coating during high temperature machining. Other problems are the solving of Fe from the workpiece into the coating and reactions between iron oxide, formed as the workpiece surface is oxidized, and the protective coating.

    The second part of the computational toolbox which is provided to the reader is the simulation of solid oxide synthesis. Here, a formation energy formalism, most often applied to materials intended in electronics devices is applied. The simulation of Chemical Vapour Deposition (CVD) and Physical Vapor Deposition (PVD) requires good knowledge of the experimental conditions, which can then be applied in the theoretical simulations. Effects of temperature, chemical and electron potential, modelled concentration and choice of theoretical method on the heat of formation of different solid oxides with and without dopants are addressed in this work. A considerable part of this Thesis is based upon first principles calculations, more specifically, Density Functional Theory (DFT) After Kohn and Pople received the Nobel Prize in chemistry in 1998, the use of DFT for computational modelling has increased strikingly (see Fig. 1). The use of other first principles methods such as hybrid functionals and the GW approach (see abbreviations for short explanations and chapter 4.5 and 5.3.) have also become increasingly popular, due to the improved computational resources. These methods are also employed in this Thesis.

  • 39649.
    Århammar, Cecilia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Araujo, C. Moyses
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Norgren, S.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Energetics and magnetic properties of V-doped MgO bulk and (001) surface: A GGA, GGA+U, and hybrid density functional study2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, p. 134406-Article in journal (Refereed)
    Abstract [en]

    In this work, a first-principles study of the energetic and magnetic properties of V-doped MgO is presented, where both the bulk and (001) surface were investigated. It is found that V assumes a high-spin state with a local moment of about 3 mu(B). In the bulk, the interaction between these local moments is very short ranged and the antiferromagnetic (AFM) ordering is energetically more favorable. The formation of V-V-Mg-V defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferro-magnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the GGA+U approach, with U=5 eV, the V 3d states on the (001) surface are shifted below the Fermi level, and a reasonable surface geometry was achieved. A calculation with the hybrid HSE03 functional, contradicts the GGA+U results, indicating that the V-MgO surface should be metallic at this concentration. From the energetics it is concluded that, at the modeled concentration, VxOy phases will limit the solubility of V in MgO at equilibrium conditions, which is in agreement with previous experimental findings. In order to achieve higher concentrations of V, an off-equilibrium synthesis method is needed. Finally, we find that the formation energy of V at the surface is considerably higher than in the bulk and V is thus expected to diffuse from the surface into the bulk of MgO.

  • 39650.
    Århammar, Cecilia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pietzsch, Annette
    Bock, Nicolas
    Holmstroem, Erik
    Araujo, C. Moyses
    Grasjo, Johan
    Zhao, Shuxi
    Green, Sara
    Peery, T.
    Hennies, Franz
    Amerioun, Shahrad
    Foehlisch, Alexander
    Schlappa, Justine
    Schmitt, Thorsten
    Strocov, Vladimir N.
    Niklasson, Gunnar A.
    Wallace, Duane C.
    Rubensson, Jan-Erik
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Unveiling the complex electronic structure of amorphous metal oxides2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 16, p. 6355-6360Article in journal (Refereed)
    Abstract [en]

    Amorphous materials represent a large and important emerging area of material's science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today's integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5-10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

790791792793794795796 39601 - 39650 of 39827
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