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  • 111451.
    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.

  • 111452.
    Åkerstedt, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Rosdahl, Jan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Persson, Per
    Umeå University.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Arsenic Clusters in Solution: An Experimental and A Priori Theoretical EXAFS StudyManuscript (preprint) (Other academic)
  • 111453.
    Åkerstedt, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ruck, M.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Long, J. R.
    Tungsten Chloride W3Cl10(CH3CN)3 fromRoom-temperature Synthesis in Ionic liquid using an Organic Co-solventManuscript (preprint) (Other academic)
  • 111454.
    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.

  • 111455.
    Åkerstrand, Hampus
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Economics.
    Do Housing Prices Affect Loan Supply?: Evidence from Sweden During the Post-Crisis Period2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Financial intermediaries are paramount for modern society. During the last decade, however, our reliance on these institutions have been meticulously debated, especially in the aftermath of the financial crisis. This thesis contributes to this debate with a novel perspective on loan supply changes in light of the recent events in the Swedish real estate market. More specifically, it investigates what influence housing prices have on the supply of commercial and industrial loans. This is done by estimating dynamic panel data models using a quarterly panel containing balance sheet data for 68 Swedish monetary financial institutions, during the post-financial crisis period of 2009-2017. The results indicate that housing prices do not have a significant effect on commercial and industrial loan supply. However, these loans are to a considerable degree dependent on the institutes’ earlier levels of commercial and industrial loans.

  • 111456.
    Åkervik, Espen
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Feedback Control of Spatially Evolving Flows2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis we apply linear feedback control to spatially evolving flows in order to minimize disturbance growth. The dynamics is assumed to be described by the linearized Navier--Stokes equations. Actuators and sensor are designed and a Kalman filtering technique is used to reconstruct the unknown flow state from noisy measurements. This reconstructed flow state is used to determine the control feedback which is applied to the Navier--Stokes equations through properly designed actuators. Since the control and estimation gains are obtained through an optimization process, and the Navier--Stokes equations typically forms a very high-dimensional system when discretized there is an interest in reducing the complexity of the equations. One possible approach is to perform Fourier decomposition along (almost) homogeneous spatial directions and another is by constructing a reduced order model by Galerkin projection on a suitable set of vectors. The first strategy is used to control the evolution of a range of instabilities in the classical family of Falkner--Skan--Cooke flows whereas the second is applied to a more complex cavity type of geometry.

  • 111457.
    Åkervik, Espen
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Global stability and feedback control of boundary layer flows2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis the stability of generic boundary layer flows is studied from a global viewpoint using optimization methods. Global eigenmodes of the incompressible linearized Navier-Stokes equations are computed using the Krylov subspace Arnoldi method. These modes serve as a tool both to study asymptotic stability and as a reduced basis to study transient growth. Transient growth is also studied using adjoint iterations. The knowledge obtained from the stability analysis is used to device systematic feedback control in the Linear Quadratic Gaussian framework. The dynamics is assumed to be described by the linearized Navier-Stokes equations. Actuators and sensors are designed and a Kalman filtering technique is used to reconstruct the unknown flow state from noisy measurements. This reconstructed flow state is used to determine the control feedback which is applied to the Navier-Stokes equations through properly designed actuators. Since the control and estimation gains are obtained through an optimization process, and the Navier-Stokes equations typically forms a very high-dimensional system when discretized there is an interest in reducing the complexity of the equations. A standard method to construct a reduced order model is to perform a Galerkin projection of the full equations onto the subspace spanned by a suitable set of vectors, such as global eigenmodes and balanced truncation modes.

  • 111458.
    Åkervik, Espen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Hoepffner, Jérôme
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Marxen, Olaf
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Steady solutions of the Navier-Stokes equations by selective frequency damping2006In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 18, no 6, p. 068102-Article in journal (Refereed)
    Abstract [en]

    A new method, enabling the computation of steady solutions of the Navier-Stokes equations in globally unstable configurations, is presented. We show that it is possible to reach a steady state by damping the unstable (temporal) frequencies. This is achieved by adding a dissipative relaxation term proportional to the high-frequency content of the velocity fluctuations. Results are presented for cavity-driven boundary-layer separation and a separation bubble induced by an external pressure gradient.

  • 111459.
    Åkervik, Espen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Ehrenstein, Uwe
    IRPHÉ, Université de Provence.
    Gallaire, Francois
    Laboratoire J.A. Dieudonné.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Global two-dimensional stability measures of the flat plate boundary-layer flow2008In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 27, no 5, p. 501-513Article in journal (Refereed)
    Abstract [en]

    The stability of the two-dimensional flat plate boundary-layer is studied by means of global eigenmodes. These eigenmodes depend both on the streamwise and wall-normal coordinate, hence there are no assumptions on the streamwise length scales of the disturbances. Expanding the perturbation velocity field in the basis of eigenmodes yields a reduced order model from which the stability characteristics of the flow, i.e. the initial condition and forcing function leading to the largest energy growth, are extracted by means of non-modal analysis. In this paper we show that, even when performing stability analysis using global eigenmodes, it is not sufficient to consider only a few of the least damped seemingly relevant eigenmodes. Instead it is the task of the optimization procedure, inherent in the non-modal analysis, to decide which eigenmodes are relevant. We show that both the optimal initial condition and the optimal forcing structure have the form of upstream tilted structures. Time integration reveals that these structures gain energy through the so called Orr mechanism, where the instabilities extract energy from the mean shear. This provides the optimal way of initiating Tollmien-Schlichting waves in the boundary layer. The optimal initial condition results in a localized Tollmien-Schlichting wavepacket that propagates downstream, whereas the optimal forcing results in a persistent Tollmien-Schlichting wave train.

  • 111460.
    Åkervik, Espen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Haepffner, Jerome
    Ehrenstein, Uwe
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Model reduction and control of a cavity-driven separated boundary layer2008In: IUTAM Symposium On Flow Control And Mems / [ed] Morrison, JF; Birch, DM; Lavoie, P, 2008, Vol. 7, p. 147-155Conference paper (Refereed)
    Abstract [en]

    The control of a globally unstable boundary-layer flow along a two-dimensional cavity is considered. When perturbed by the worst-case initial condition, the flow exhibits a large transient growth associated with the development of a wave packet along the cavity shear layer followed by a global cycle related to the least stable global eigenmodes. The flow simulation procedure is coupled to a measurement feedback controller, which senses the wall shear stress at the downstream lip of the cavity and actuates at the upstream lip. A reduced model for the control optimization is obtained by a projection on the least stable global eigenmodes. The LQG controller is run in parallel to the Navier-Stokes time integration. It is shown that the controller is able to damp out the global oscillations.

  • 111461.
    Åkervik, Espen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Hoepffner, Jérôme
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Uwe, Eherenstein
    IRPH́E, Université de Provence.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Optimal growth, model reduction and control in a separated boundary-layer flow using global eigenmodes2007In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 579, p. 305-314Article in journal (Refereed)
    Abstract [en]

    Two-dimensional global eigenmodes are used as a projection basis both for analysing the dynamics and building a reduced model for control in a prototype separated boundary-layer flow. In the present configuration, a high aspect ratio smooth cavity-like geometry confines the separation bubble. Optimal growth analysis using the reduced basis shows that the sum of the highly non-normal global eigenmodes are able to describe a localized disturbance. Subject to this worst-case initial condition, a large transient growth associated with the development of a wavepacket along the shear layer followed by a global cycle related to the two unstable global eigenmodes is found. The flow simulation procedure is coupled to a measurement feedback controller, which senses the wall shear stress at the downstream lip of the cavity and actuates at the upstream lip. A reduced model for the control optimization is obtained by a projection on the least stable global eigenmodes, and the resulting linear-quadratic-gaussian controller is applied to the Navier--Stokes time integration. It is shown that the controller is able to damp out the global oscillations.

  • 111462.
    Åkervik, Mattias
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Network Gaming: Performance and Traffic Modeling2006Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There are several different types of games that are played in multiplayer mode over networks. The type of network games that, from a network’s perspective, are the most demanding is real-time based multiplayer games. Users of such games both assume and require that game play interaction happens in near real-time and these games often support a large number of simultaneous players. Most networks are specialized to either voice traffic (such as the first and second generation of mobile networks) or data traffic (such as wired data networks). It is not clear that the requirements for such real time games can always be met on either type of network. The core of this thesis investigates the performance requirements real-time multiplayer games place on packet switched data networks and the connection between network impairments and game quality degradation. Traffic generated by network games distinguishes itself from other traffic both regarding its general characteristics and the requirements it places on the network. Understanding these traffic characteristics, requirements, and what consequences failures to support such requirements entail are of great importance when designing new networks in order to guarantee suitable quality of service for such real-time games.

  • 111463. 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.

  • 111464.
    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.

  • 111465.
    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.

  • 111466.
    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)
  • 111467.
    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.

  • 111468.
    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.

  • 111469.
    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.

  • 111470.
    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.

     

  • 111471.
    Åkesson, Christian Rydberg
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
     Planeraren och hållbarheten En fallstudie av mål och verktyg i Väsby Sjöstad2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The main purpose of this essay is to illustrate how the concept of sustainability is being interpreted within urban planning. The object chosen is Väsby Sjöstad, a planned waterfront district in the municipality of Upplands Väsby in the northern part of the Stockholm metropolitan area. The visions for the new neighborhood are clearly oriented on sustainable development. To set even higher standards on preparatory investigations and plans, the project has gained financial support by the Swedish government through the delegation for Sustainable Cities.

    The empirical study is based upon the plan proposal itself as wells as on interviews with one highly involved planner and with a representative from the delegation mentioned above. The study considers the ecological, economic and social dimensions in an attempt to describe what guidelines there are on the field, how these are being interpreted locally and by what means these turn into practical methods. Generally and due to their relative measurability the ecological and economic dimensions seem to get more room, while the more intangible social aspects are often set aside. When applying for the governmental financial support priority lays on the ecological part, yet a wide approach covering all dimensions is considered to be vital in the work towards sustainable urban planning.

    In Väsby Sjöstad physical planning is used to i.e. enable efficient public transports. The blocks will be of high density to ensure walkability, improve safety and make efficient energy systems possible. It seems important to draw clear borders between private and public spaces as well as making surrounding greenery accessible. To reach common ground in a project like this, emphasis is put on public engagement, involvement of estate owners, investors and builders – the sooner the better.

  • 111472.
    Åkesson, Krister
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Floc behaviour in a twin-wire blade pressure pulse2004Licentiate thesis, comprehensive summary (Other scientific)
  • 111473.
    Åkesson, Krister
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Flow mechanism in twin-wire blade forming. Part I2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 59-66Article in journal (Refereed)
    Abstract [en]

    In a one-sided twin-wire model gap former, the KTH-former, the effects of blade load and wire permeability upon a blade forming pressure pulse, flow velocity and roll-to-wire gap has been studied. A forming blade was applied against the Outer wire of the forming roll and the blade pressure was measured with a pressure sensor mounted in the roll surface. A camcorder was used to evaluate the roll-to-wire gap. Increased blade load gave higher pressure peaks upstream of the blade tip. Tracer particles (fibre floc fragments, confetti) were injected into the headbox and recorded with a high speed video camera when passing the blade in the forming zone. Velocity measurements of the tracer particles showed how the velocity was slowed down upstream of the blade, and then was accelerated when the blade was approached. Tracer particles were pinned to the permeable forming wire and their velocity eventually reached the wire velocity. Increased blade load generated a higher pressure peak and was accompanied by a lower velocity and larger gap upstream of the blade tip.

  • 111474.
    Åkesson, Krister
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Flow mechanism in twin-wire blade forming. Part II2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 67-72Article in journal (Refereed)
    Abstract [en]

    In a one-sided twin-wire model gap former, the KTH-former, the behaviour of pulp fibre floes in the presence of blade forming pressure pulses has been studied at different blade loads and wire permeabilities. Pulp fibre floes were injected into the headbox and recorded with a high speed video camera when passing a forming blade ill the forming zone. With a visual evaluation method the fibre floes were found to be elongated and some of them ruptured during the acceleration when the floes passed the forming blade. Floc strain and floc breaking ratio increased with blade load because of a higher acceleration. Floes partially pinned to the permeable wire will elongate and tend to rupture more due to the mix-to-wire speed difference upstream of the forming blade. Sonic differences for rupture using different pulp qualities are quantified.

  • 111475.
    Åkesson, Lovisa
    KTH, School of Biotechnology (BIO).
    Identifikation av proteinmarkörer för cellulär proliferation2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 111476.
    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.].

  • 111477.
    Ålander, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Influence of Solvent Composition on Crystal Agglomeration of Paracetamol2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Agglomeration is an important phenomenon which often controls the particle size distribution and morphology in the crystallization of organic compounds. In this thesis the influence of solvent composition on crystal agglomeration of paracetamol is investigated.

    Particles from (i) isothermal desupersaturation experiments with initiated nucleation and (ii) fully seeded isothermal crystallization experiments operating at constant supersaturation have been characterized. The number of crystals in each particle has been determined by image analysis using multivariate data evaluation and a set of calibration particles. A parameter defining the degree of agglomeration is extracted from the number distribution of crystals per particle. In addition, the agglomerate strength determined by the crushing of single agglomerates has been measured.

    The results clearly show that the solvent composition has an influence on the crystal agglomeration. This observed influence cannot be explained by differences in the solution viscosity (fluid mechanics), or by differences in the overall crystal growth rate. The product is less agglomerated and the agglomerates are weaker when the crystallization is carried out in a more polar solvent, e.g. water. In the systems studied, a high solvent polarity coincides with hydrogen-bond-donating and hydrogen-bond-accepting capabilities. These solvents can interact strongly with paracetamol crystal surfaces which exhibit both donating and accepting sites. In less polar solvents like acetone, only donating sites on the surfaces can be occupied.

    Surfaces of large, well-grown paracetamol crystals have been characterized by contact angle measurements according to the Lifshitz-van der Waals acid-base theory. The surface free energy varies between 50-57 mJ/m2, and all faces indicate a strong hydrogen-bond acceptance.

    The free energy of adhesion between crystal faces in different solvents has been calculated from the surface free energy components. The findings in this thesis strongly support the hypothesis that the mechanism by which the solvent influences on the agglomeration relates to the molecular interaction at the crystal-solvent interface and the physico-chemical adhesion forces between crystal faces in the solution.

  • 111478.
    Ålander, Eva
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The influence of solvent composition on crystal agglomeration of paracetamol2001Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    This thesis deals with the influence of solvent compositionon crystal agglomeration of paracetamol. Much work has beendone on characterisation of the crystalline product.Interfacial energies have also been determined for large singlegrown crystals. Isothermal desupersaturation batchcrystallization experiments have been performed using ninedifferent solvent compositions. The particles produced indifferent solvent compositions differ not only in particle sizedistribution, but also in content of single crystals andagglomerates. Furthermore, the crystal shape and size and thenumber of crystals in the agglomerates vary. Sieving, particleimage analysis and processing of measured image descriptorswith PCA (Principal Component Analysis) have been used toquantify the characteristic difference of particles produced indifferent solvent compositions. In addition, the agglomeratestrength, determined by crushing of single agglomerates,differs depending on in which solvent composition theagglomerates have been produced. A high content of acetonefavours crystal agglomeration and formation of agglomerateswith high strength. Crystallization in ethylene glycol,isopropanol, acetic acid or solvent mixtures with high contentof water give a particle product containing not onlyagglomerates but also an important fraction of single crystals.Furthermore, agglomerates produced in these solventcompositions exhibit significantly lower agglomerate strengththan agglomerates produced in solvent compositions with highcontent of acetone. The crystal surface tension has beendetermined from contact angle measurements. A surface tensionof 54 mJ/m2 was obtained for the largest crystal face {011}grown in aqueous solution. A strong negative polar contributionto the crystal surface tension indicates that the surface iselectron donating. The crystal surface tension has been used toestimate interfacial and interaction energies. There is arelationship between the influence of solvent composition onagglomeration observed on a macroscopic level and theinteraction at the solid-liquid interface on a molecular level.This relationship seems possible to capture by correlation ofobserved product characteristics to solvent polarity and to thedetermined interaction energies.

    Keywords:paracetamol, solvent composition,agglomeration, image analysis, principal component analysis,agglomerate strength, interfacial energy

  • 111479.
    Ålander, Eva M.
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Uusi-Penttila, Marketta S.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Agglomeration of paracetamol during crystallization in pure and mixed solvents2004In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 43, no 2, p. 629-637Article in journal (Refereed)
    Abstract [en]

    The agglomeration of paracetamol during crystallization has been investigated. It is shown that the agglomeration behavior depends on the solvent composition. The following solvent systems were used in isothermal desupersaturation experiments: five different acetone-toluene-water mixtures and the pure solvents acetone, 2-propanol, acetic acid, and ethylene glycol. Sieving, image analysis processed by principal component analysis, and agglomerate strength measurements were used to characterize the product particles. Mixtures with a high concentration of acetone were found to produce a highly agglomerated product with strong agglomerates. In contrast, products from crystallization in ethylene glycol, 2-propanol, acetic acid, and acetone-toluene-water mixtures having a high concentration of water contained not only agglomerates but also a significant fraction of single crystals. Furthermore, the agglomerates formed in these solvents were much weaker than those produced in mixtures with a high content of acetone. The results were correlated with the polarity and the viscosity of the solvents.

  • 111480.
    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.

  • 111481.
    Ålander, Eva
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rasmuson, Åke Christoffer
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Agglomeration of paracetamol in the acetone-water system Int. Conf. on Particle Technology, paper 14.3 CD Proceedings of PARTEC 20042004In: / [ed] S.E. Pratsinis, H. Schulz and R. Strobel, 2004Conference paper (Refereed)
  • 111482.
    Ålander, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke Christoffer
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Crystal-solvent interaction in agglomeration of paracetamol2005In: the 16’th International Symposium on Industrial Crystallization / [ed] J Ulrich, VDI verlag Dusselsdrorf , 2005, p. 511-516Conference paper (Refereed)
  • 111483.
    Åldstedt, Ann-Sofie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Malmeby, Hanna
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Utveckling av köpcentrum: En studie av faktorer som ligger till grund för utveckling av köpcentrum i Stockholmsregionen2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Detaljhandeln har under de senaste tio åren ökat och konsumenten idag konsumerar allt mer. Detta har bidragit till att köpcentrumen har blivit en allt viktigare del i detaljhandelsmarknaden och konsumentens vardag. Köpsamhället har förändrats och konsumenten kräver idag mycket mer av sin shopping upplevelse. Hårda och mjuka faktorer har blivit viktigare att beakta vid utvecklingen av köpcentrum. De utländska aktörernas allt mera växande intresse har påverkat förvaltningen och utvecklingen av köpcentrum på den svenska marknaden och i kombination med den krävande konsumenten så måste köpcentrumen idag förändras allt oftare. I detta arbete har en studie gjorts  över sex stycken köpcentrum i Stockholmsregionen. Studien syftar på att undersöka vilka faktorer som ligger till grund för utveckling av ett köpcentrum samt om det i Stockholm pågår en "renoveringshets". En analys över varför vissa köpcentrum är framgångsrikare än andra har även gjorts. Betydelsen av utveckling och aktiv förvaltning har växt. När ett köpcentrum inte längre klarar av att möta behovet från konsumenter eller hyresgäster, om byggnadens tekniska standard inte är hållbar eller när konkurrensen blir för stor kan det behövas en utveckling av något slag. Utveckling kan även ses som en värdehöjande åtgärd för att säkra ägarnas investering och öka dess avkastning. Olika faktorer som påverkar utvecklingen kan vara marknad, koncept, design samt timingsfaktorer. Timingsfaktorn har tillsammans med aktiv förvaltning stor betydelse för hur framgångsrikt köpcentrumet kommer att vara. Den allt ökande takten på renoveringar i Stockholmsregionen har inget att göra med en hets på marknaden. En ökande detaljhandeln i kombination med allt mer krävande konsumenter har påverkat köpcentrumen och skapat behovet av utveckling. För att lyckas måste köpcentrumen kunna erbjuda mer än en vanlig shoppingupplevelse och en renovering är en del av den utvecklingen. Mervärden, ett slående koncept och en bra butiksmix är några av faktorer som har blivit allt viktigare på dagens marknad.

  • 111484.
    Ålemark, Niklas
    KTH, Superseded Departments, Teleinformatics.
    Specification and development of animage acquisition and processing systemwith IR communications capabilities1996Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The GSM network has experienced a fast growth after its introduction in 1992. A large number of users in several countries in the word now have access to a standardised digital cellular network. This fact has lead to that the network is being used for several other things than voice communications. One such application is the transfer of pictures. This requires a unit that can digitise pictures and adapt the digital image information to the characteristics of the GSM network.

    This report describes the specification and development of an image acquisition and processing system with IR communications capabilities. It also outlines some of the possible applications for such a system.

  • 111485.
    Ållebrand, Björn
    KTH, Superseded Departments, Electrical Systems.
    Gate Control and System Aspects of Silicon Carbide JFETs2002Licentiate thesis, monograph (Other scientific)
  • 111486.
    Ållebrand, Björn
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    On SiC JFET converters: components, gate-drives and main-circuit conditions2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis deals with Silicon Carbide Junction Field Effect Transistors (SiC JFETs) - how to use them to their full potential in power electronic circuits, how to model them in a power electronic simulation program, and how a gate drive can be built.

    To fully utilize the low on-state losses of SiC JFETs it is suggested that SiC JFETs should not be equipped with anti-parallel diodes. This is possible due to that JFETs can conduct current in the reverse direction. The circuit making use of this property is called the Diode-less SiC JFET Inverter Bridge (DJIB). The DJIB was studied regarding blanking times, negative voltages, and other special cases.

    A gate drive circuit for use with SiC JFETs in industrial applications is presented. The design is with voltage controlled devices(MOSFETs) for use in industrial applications.

    Since the JFET model in PSpice had never been validated for SiC power devices, a validation of the PSpice JFET model is presented for SiC JFETs manufactured by SiCED. The PSpice JFET model shows good agreement with measured results up to saturation. For high currents the SiCED SiC JFET saturates much earlier than the PSpice model and this has to be taken into account when making simulations with PSpice.

    Due to the high gate-drain capacitance of the SiCED SiC JFETs, there are commutation transients during switching. A short-circuit of the bridge-leg appears due to the high gate-drain capacitance. This is studied and some solutions to this problem are presented.

    Simulations on a 1~MW converter utilizing possible future high-voltage SiC JFETs showed that an efficiency of 99,7% could be achieved compared to an efficiency of 98,8% for a converter with Si IGBTs. However, even though the high gate-drain capacitance was reduced in the simulation, undesired commutation transients was observed. This problem has to be considered when designing converters in the future.

  • 111487.
    Ållebrand, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Comparison of Commutation Transients of Inverters with Silicon Carbide JFETs with and without Body Diodes2004In: Proceedings of the Nordic Workshop on Power and Industrial Electronics (NORpie), 2004Conference paper (Refereed)
    Abstract [en]

    An inverter could be built by using silcon carbide power switches only. This can be done by using SiC JFETs which can conduct current in both directions. An interesting question is how an inverter using SiC JFETs with a body diode compares with an inverter using SiC JFETs without body diodes. This will be discussed in this paper.

  • 111488.
    Ållebrand, Björn
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Nee, Hans-Peter
    KTH, Superseded Departments, Electrical Systems.
    Design of a Gate Drive Circuit For use with SiC JFETs2002In: Proceedings of the Nordic Workshop on Power and Industrial Electronics, NORpie 2002, 2002Conference paper (Refereed)
    Abstract [en]

    This paper desccribes how a gate drive can be designed for use with SiC JFETs. The gate drive is supposed to be used in an experimental set-up, which means that the design is not adapted to production constraints. The gate drive circuit can be divvided into four parts: power stage, negative voltage protection, short-circuit protection, and logic unit, which all are desccribed.

  • 111489.
    Ållebrand, Björn
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Nee, Hans-Peter
    KTH, Superseded Departments, Electrical Systems.
    Minimizing oscillations in the Diode-Less SiC JFET Inverter Bridge2002In: Proceedings of the Nordic Workshop on Power and Industrial Electronics, NORpie 2002, 2002Conference paper (Refereed)
    Abstract [en]

    This article desccribes how the oscillations in the Diode-less SiC JFET Inverter Bridge can be minimized. Different ways of minimizing the oscillations are investigated and simulation results are presented showing how these oscillations are reduced. The cause of the oscillations are given a thorough review.

  • 111490.
    Ållebrand, Björn
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Nee, Hans-Peter
    KTH, Superseded Departments, Electrical Systems.
    On the choice of blanking times at turn-on and turn-off for the diode-less SiC JFET inverter bridge2001In: Proceedings of the European Conference on Power Electronics and Applications (EPE) 2001, 2001Conference paper (Refereed)
    Abstract [en]

    This article desccribes the choice of blanking times at turn-on and turn-off for the diode-less SiC JFET inverter bridge. It is also discussed if auxiliary capacitors should be used or not and which capacitance should be used in different cases.

  • 111491.
    Ållebrand, Björn
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Nee, Hans-Peter
    KTH, Superseded Departments, Electrical Systems.
    On the possibility to use SiC JFETs in Power Electronic circuits2001In: Proceedings of the European Conference on Power Electronics and Applications (EPE) 2001, 2001Conference paper (Refereed)
    Abstract [en]

    This article desccribes a proposed bridge circuit without anti-parallel diodes and results from preliminary computer simulations of the proposed circuit. There is a discussion of the normally-on property of the JFET and interviews with industry representatives are presented with their opinions on the SiC JFET.

  • 111492.
    Ålund, Victor
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Development of a model for the implementation of knowledge management with the study of Siemens2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Companies are present in an increasingly faster changing environment. To adapt to these fastchanges, new models and guidelines are being used to stay contemporary in new businessprocesses. The development has shown that an important factor for companies to be competitiveis the sharing and the use of existing knowledge within the firm. To solve this problemknowledge management tool were developed to help with this problem. One of the mainchallenges is to convince the employees to use the tool and not the technical aspect.To investigate the implementation of knowledge management tools, Siemens was studied as acase and compared to three existing models to see how the different theoretical approaches areand how a knowledge management platform was implemented in a company.During the investigation the models showed strong and weak points which were combined into anew model. The new model shows a framework with all the important steps featured to providea template that can be used by companies working in various fields.

  • 111493.
    Ålund, Victor
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Development of a model for the implementation of knowledge management with the study of Siemens2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Companies are present in an increasingly faster changing environment. To adapt to these fast changes, new models and guidelines are being used to stay contemporary in new business processes. The development has shown that an important factor for companies to be competitive is the sharing and the use of existing knowledge within the firm. To solve this problem knowledge management tool were developed to help with this problem. One of the main challenges is to convince the employees to use the tool and not the technical aspect. To investigate the implementation of knowledge management tools, Siemens was studied as a case and compared to three existing models to see how the different theoretical approaches are and how a knowledge management platform was implemented in a company. During the investigation the models showed strong and weak points which were combined into a new model. The new model shows a framework with all the important steps featured to provide a template that can be used by companies working in various fields.

  • 111494.
    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.

  • 111495.
    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. 

  • 111496.
    Åman, Anna
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Ahlbom, Gabriella
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Empowerment in a multicultural organization: The perception of empowerment from a multicultural and oraganizational level perspective2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During the last decades, corporations have become more multinational, and the concept of employee empowerment has become one of the largest management trends within organizations. Managers need to be flexible when working with multicultural employees and understand that practices are perceived differently depending on the national culture and organizational level. Today relatively little research has focused on empowerment from a multicultural perspective. Thus, the purpose of this thesis is to examine how empowerment is perceived in a multicultural company, by analyzing the perceptions of the employees with different backgrounds and positions in a single firm setting. In addition, this thesis strives to study how empowerment can be reinforced in order to overcome cultural and organizational differences. This was examined through a case study at a fast-moving consumer goods (FMCG) organization in Sweden. Semi-structured interviews were held to obtain an in-depth understanding, while a survey was designed to support the interviews and to get a general picture of the organization.

    For the analysis, the respondents were divided into different categories, based on nationality and organizational level. The results indicated that the employees had an overall positive attitude towards empowerment in the case company, and that there is a relationship between the perception of empowerment and nationality. It also suggested that the perception of empowerment diverges between the levels of a multicultural organization, where subordinates, lower managers and top managers experience situations differently. In addition, the results indicated that the organizational culture should be utilized in order to overcome the cultural and organizational differences in a multicultural organization, through recognizing and solving the main problems that could affect the perception of empowerment. Particularly through maintaining good communication, which is vital in terms of empowerment, it is possible to strengthen the organizational culture. This in turn could reinforce the employee empowerment, as aspects that positively affect this concept could be encouraged through the organizational culture.

  • 111497.
    Åman, Erik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    A Distributed Cachefor Very Large Objects2001Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Within a few years’ time, the Internet is expected to be used to transfer highquality video material and other bandwidth-demanding objects to a much larger extent than today. Users would prefer to be able to access such very large objects at an arbitrary point in time without any kind of preparation or advance planning. Offering such services on a large scale puts high demands on the network.

    Using a caching Web proxy server may increase the bandwidth and reliability perceived by the users while reducing the load on the network. This can be done transparently to the users.

    This thesis presents the principles for a caching Web proxy server better adapted to this expected traffic pattern. The bandwidth usage and transfer rate can be improved by taking advantage of the longer persistence of connections and by assuming that comparatively few objects will be popular at any given time. An experimental implementation has been developed in order to test the main principles. The new server is designed to operate in a distributed fashion by employing several cooperating servers at strategic points in the network. The system optimizes reliability and throughput by dynamically selecting from where to download objects based on current traffic and previous statistics.

  • 111498.
    Åman, Johan
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Ekberg, Peter
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Leonardsson, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Edgren, Klas
    KTH, School of Industrial Engineering and Management (ITM).
    Sandström, Torbjörn
    Micronic Laser Systems, Stockholm, Sweden.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Recent developments in large-area photomasks for display applications2001In: Journal of the Society for Information Display, ISSN 1071-0922, Vol. 9, no 1, p. 3-8Article in journal (Refereed)
    Abstract [en]

    One of the most critical areas in the manufacturing process for FPD panels or shadow masks for CRTs is lithography. Most existing lithography technologies require high-quality large-area photomasks. The requirements on these photomasks include positioning accuracy (registration) and repeatability (overlay), systematic image quality errors ("mura" or display quality), and resolution (minimum feature size). The general trend toward higher resolution and improved performance, e.g., for TFT desktop monitors, has put a strong focus on the specifications for large-area-display photomasks. This article intends to give an overview of the dominant issues for large-area-display photomasks, and illustrates differences compared with other applications. The article will also present state-of-the-art methods and trends. In particular, the aspects of positioning accuracy over large areas and systematic image-quality errors will be described. New qualitative and objective methods have been developed as means to capture systematic image-quality errors. Results indicating that errors below 25 nm can be found early in the manufacturing process is presented, thus allowing inspection for visual effects before the actual display is completed. Positioning accuracy below 400 nm (3 sigma) over 720 × 560 mm have been achieved. These results will in the future be extended up toward 1 × 1 m for generation 4 in TFT-LCD production.

  • 111499.
    Ånell, Rickard
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Sundblad, Patrik
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Gennser, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Vaskulära gasbubblor hos jaktplanspiloter under olika flygprofiler2016Conference paper (Refereed)
  • 111500.
    Ånell, Rickard
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Environmental Physiology.
    Eiken, Ola
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Environmental Physiology.
    Gennser, Mikael
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Environmental Physiology.
    Is there a safe altitude to compress venous gas emboli after simulated high-altitude flying?2018In: Proceedings from Swedish Aeronautical Medical Associations Annual Scientific Meeting, 2018, 2018Conference paper (Refereed)
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