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  • Open Access English
    Authors: 
    Giaretta, Lodovico; Savvidis, Ioannis; Marchioro, Thomas; Girdzijauskas, Sarunas; Pallis, George; Dikaiakos, Marios D.; Markatos, Evangelos;
    Publisher: Zenodo
    Country: Sweden
    Project: EC | RAIS (813162)

    We envision PDS2, a decentralized data marketplace in which consumers submit their tasks to be run within the platform, on the data of willing providers. The goal of PDS2is to ensure that users maintain full control on their data and do not compromise their privacy, while being rewarded for the value that their data generates. In order to achieve this, our marketplace architecture employs blockchain technology, privacy-preserving computation and decentralized machine learning. We then compare different potential solutions and identify the Ethereum blockchain, trusted execution environments and gossip learning as the most suitable for the implementation of PDS2. We also discuss the main open challenges that are left to tackle and possible directions for future work.

  • Open Access English
    Authors: 
    de Alwis, M. P.; Lo Martire, Riccardo; Äng, Björn; Garme, K.;
    Country: Sweden

    Background High-performance marine craft crews are susceptible to various adverse health conditions caused by multiple interactive factors. However, there are limited epidemiological data available for assessment of working conditions at sea. Although questionnaire surveys are widely used for identifying exposures, outcomes and associated risks with high accuracy levels, until now, no validated epidemiological tool exists for surveying occupational health and performance in these populations. Aim To develop and validate a web-based questionnaire for epidemiological assessment of occupational and individual risk exposure pertinent to the musculoskeletal health conditions and performance in high-performance marine craft populations. Method A questionnaire for investigating the association between work-related exposure, performance and health was initially developed by a consensus panel under four subdomains, viz. demography, lifestyle, work exposure and health and systematically validated by expert raters for content relevance and simplicity in three consecutive stages, each iteratively followed by a consensus panel revision. The item content validity index (I-CVI) was determined as the proportion of experts giving a rating of 3 or 4. The scale content validity index (S-CVI/Ave) was computed by averaging the I-CVIs for the assessment of the questionnaire as a tool. Finally, the questionnaire was pilot tested. Results The S-CVI/Ave increased from 0.89 to 0.96 for relevance and from 0.76 to 0.94 for simplicity, resulting in 36 items in the final questionnaire. The pilot test confirmed the feasibility of the questionnaire. Conclusions The present study shows that the web-based questionnaire fulfils previously published validity acceptance criteria and is therefore considered valid and feasible for the empirical surveying of epidemiological aspects among high-performance marine craft crews and similar populations. QC 20160926

  • Publication . Conference object . Article . 2011
    Open Access English
    Authors: 
    Antti Hynninen; Raimo Turunen; Mats Åbom; Hans Bodén;
    Publisher: American Society of Mechanical Engineers (ASME)
    Countries: Finland, Sweden

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. Number of studies has been published earlier on the low frequency in-duct exhaust noise of high speed engines. The goal of the present study is to investigate the medium speed IC-engine acoustic source characteristics numerically and experimentally not only in the low frequency - plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multi-load measurements using a one-dimensional process simulation code. The engine model used in the one-dimensional process simulations was validated with measurements. In this study, it is shown that the low frequency in-duct exhaust noise of a medium speed IC-engine can be predicted quite accurately by using a onedimensional process simulation code. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods. According to this study, using the simple cross spectra averaging method instead of two microphone method to estimate the induct downstream acoustic power of medium speed IC-engine exhaust noise seems promising. The simulation of the high frequency exhaust noise is beyond this study. QC 20140826

  • Open Access English
    Authors: 
    Pierre Augier; Ashwin Vishnu Mohanan; Cyrille Bonamy;
    Countries: France, Sweden
    Project: EC | WATU (647018)

    FluidDyn is a project to foster open-science and open-source in the fluid dynamics community. It is thought of as a research project to channel open-source dynamics, methods and tools to do science. We propose a set of Python packages forming a framework to study fluid dynamics with different methods, in particular laboratory experiments (package fluidlab), simulations (packages fluidfft, fluidsim and fluidfoam) and data processing (package fluidimage). In the present article, we give an overview of the specialized packages of the project and then focus on the base package called fluiddyn, which contains common code used in the specialized packages. Packages fluidfft and fluidsim are described with greater detail in two companion papers [4, 5]. With the project FluidDyn, we demonstrate that specialized scientific code can be written with methods and good practices of the open-source community. The Mercurial repositories are available in Bitbucket (https://bitbucket.org/fluiddyn/). All codes are documented using Sphinx and Read the Docs, and tested with continuous integration run on Bitbucket Pipelines and Travis. To improve the reuse potential, the codes are as modular as possible, leveraging the simple object-oriented programming model of Python. All codes are also written to be highly efficient, using C++, Cython and Pythran to speedup the performance of critical functions. Funding statement: This project has indirectly benefited from funding from the foundation Simone et Cino Del Duca de l’Institut de France, the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 647018-WATU and Euhit consortium) and the Swedish Research Council (Vetenskapsrådet): 2013-5191. We have also been able to use supercomputers of CIMENT/GRICAD, CINES/GENCI (grant 2018-A0040107567) and the Swedish National Infrastructure for Computing (SNIC).

  • Open Access
    Authors: 
    Olle Trollberg; Elling W. Jacobsen;
    Publisher: Elsevier BV
    Country: Sweden

    It is well known that certain properties of the process dynamics can be deduced from steady-state information about a process only. In this paper we consider the dual problem, that of determining steady-state properties from process dynamics. In particular, we are concerned with the problem of determining extremum points in the steady-state input-output map from dynamic response data. This is a highly relevant problem in cases where the aim is to determine steadystate optimal operating conditions using real time process measurements. For this purpose, we first consider the connection between bifurcations of the zero dynamics and the steady-state input-output map. Based on these results, we show that steady-state optimal conditions can be determined from the process dynamics through consideration of local phase-lag properties of the process only. We demonstrate the usefulness of this result by showing that the optimum of a chemical reactor can be located, without any prior knowledge, using sinusoidal perturbations and a phase-lock loop. QC 20160414

  • Publication . Article . Preprint . 2019 . Embargo End Date: 01 Jan 2018
    Open Access
    Authors: 
    Peter Göransson; Jacques Cuenca; Timo Lähivaara;
    Publisher: arXiv
    Country: Sweden

    This paper studies the problem of parameter estimation in resonant, acoustic fluid-structure interaction problems over a wide frequency range. Problems with multiple resonances are known to be subjected to local minima, which represents a major challenge in the field of parameter identification. We propose a stepwise approach consisting in subdividing the frequency spectrum such that the solution to a low-frequency subproblem serves as the starting point for the immediately higher frequency range. In the current work, two different inversion frameworks are used. The first approach is a gradient-based deterministic procedure that seeks the model parameters by minimising a cost function in the least squares sense and the second approach is a Bayesian inversion framework. The latter provides a potential way to assess the validity of the least squares estimate. In addition, it presents several advantages by providing invaluable information on the uncertainty and correlation between the estimated parameters. The methodology is illustrated on synthetic measurements with known design variables and controlled noise levels. The model problem is deliberately kept simple to allow for extensive numerical experiments to be conducted in order to investigate the nature of the local minima in full spectrum analyses and to assess the potential of the proposed method to overcome these. Numerical experiments suggest that the proposed methods may present an efficient approach to find material parameters and their uncertainty estimates with acceptable accuracy. QC 20190228

  • Open Access English
    Authors: 
    Sebastián Etcheverry; Gustavo Cañas; Esteban S. Gómez; W. A. T. Nogueira; Carlos Saavedra; Guilherme B. Xavier; Gustavo Lima;
    Publisher: NATURE PUBLISHING GROUP
    Countries: Sweden, Chile

    The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasing D. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD. Comment: 8 pages, 3 figures

  • Open Access
    Authors: 
    Katarina Smedfors; Carl-Mikael Zetterling; Mikael Östling;
    Publisher: Trans Tech Publications, Ltd.
    Country: Sweden

    Ohmic CoSi2 contacts to n-type 4H-SiC showing low contact resistance have been made by sputter depositing sequential layers of Si and Co on 4H-SiC substrates followed by a two-step rapid thermal anneal at 600 °C and 950 °C. The contacts formed have been characterized at temperatures ranging from-40 °C to 500 °C with a specific contact resistance of 3.80∙10-5 Ωcm2 at 25 °C and a minimum of 6.0∙10-6 Ωcm2 at 500 °C.

  • Open Access English
    Authors: 
    Tony Lindeberg; Meng-Xiang Li;
    Publisher: KTH, Beräkningsbiologi, CB
    Country: Sweden

    This article presents a method for segmenting and classifying edges using minimum description length (MDL) approximation with automatically generated break points. A scheme is proposed where junction candidates are first detected in a multiscale preprocessing step, which generates junction candidates with associated regions of interest. These junction features are matched to edges based on spatial coincidence. For each matched pair, a tentative break point is introduced at the edge point closest to the junction. Finally, these feature combinations serve as input for an MDL approximation method which tests the validity of the break point hypotheses and classifies the resulting edge segments as either “straight” or “curved.” Experiments on real world image data demonstrate the viability of the approach. QC 20130423

  • Publication . Article . Conference object . Preprint . 2021
    Open Access English
    Authors: 
    Moa Yveborg; Cheng Xu; Erik Fredenberg; Mats Danielsson;
    Publisher: KTH, Medicinsk bildfysik
    Country: Sweden

    X-ray detectors made of crystalline silicon have several advantages including low dark currents, fast charge collection and high energy resolution. For high-energy x-rays, however, silicon suffers from its low atomic number, which might result in low detection efficiency, as well as low energy and spatial resolution due to Compton scattering. We have used a monte-carlo model to investigate the feasibility of a detector for pediatric CT with 30 to 40 mm of silicon using x-ray spectra ranging from 80 to 140 kVp. A detection efficiency of 0.74 was found at 80 kVp, provided the noise threshold could be set low. Scattered photons were efficiently blocked by a thin metal shielding between the detector units, and Compton scattering in the detector could be well separated from photo absorption at 80 kVp. Hence, the detector is feasible at low acceleration voltages, which is also suitable for pediatric imaging. We conclude that silicon detectors may be an alternative to other designs for this special case. QC 20120214

Advanced search in
Research products
arrow_drop_down
Searching FieldsTerms
Any field
arrow_drop_down
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arrow_drop_down
Include:
4,163 Research products, page 1 of 417
  • Open Access English
    Authors: 
    Giaretta, Lodovico; Savvidis, Ioannis; Marchioro, Thomas; Girdzijauskas, Sarunas; Pallis, George; Dikaiakos, Marios D.; Markatos, Evangelos;
    Publisher: Zenodo
    Country: Sweden
    Project: EC | RAIS (813162)

    We envision PDS2, a decentralized data marketplace in which consumers submit their tasks to be run within the platform, on the data of willing providers. The goal of PDS2is to ensure that users maintain full control on their data and do not compromise their privacy, while being rewarded for the value that their data generates. In order to achieve this, our marketplace architecture employs blockchain technology, privacy-preserving computation and decentralized machine learning. We then compare different potential solutions and identify the Ethereum blockchain, trusted execution environments and gossip learning as the most suitable for the implementation of PDS2. We also discuss the main open challenges that are left to tackle and possible directions for future work.

  • Open Access English
    Authors: 
    de Alwis, M. P.; Lo Martire, Riccardo; Äng, Björn; Garme, K.;
    Country: Sweden

    Background High-performance marine craft crews are susceptible to various adverse health conditions caused by multiple interactive factors. However, there are limited epidemiological data available for assessment of working conditions at sea. Although questionnaire surveys are widely used for identifying exposures, outcomes and associated risks with high accuracy levels, until now, no validated epidemiological tool exists for surveying occupational health and performance in these populations. Aim To develop and validate a web-based questionnaire for epidemiological assessment of occupational and individual risk exposure pertinent to the musculoskeletal health conditions and performance in high-performance marine craft populations. Method A questionnaire for investigating the association between work-related exposure, performance and health was initially developed by a consensus panel under four subdomains, viz. demography, lifestyle, work exposure and health and systematically validated by expert raters for content relevance and simplicity in three consecutive stages, each iteratively followed by a consensus panel revision. The item content validity index (I-CVI) was determined as the proportion of experts giving a rating of 3 or 4. The scale content validity index (S-CVI/Ave) was computed by averaging the I-CVIs for the assessment of the questionnaire as a tool. Finally, the questionnaire was pilot tested. Results The S-CVI/Ave increased from 0.89 to 0.96 for relevance and from 0.76 to 0.94 for simplicity, resulting in 36 items in the final questionnaire. The pilot test confirmed the feasibility of the questionnaire. Conclusions The present study shows that the web-based questionnaire fulfils previously published validity acceptance criteria and is therefore considered valid and feasible for the empirical surveying of epidemiological aspects among high-performance marine craft crews and similar populations. QC 20160926

  • Publication . Conference object . Article . 2011
    Open Access English
    Authors: 
    Antti Hynninen; Raimo Turunen; Mats Åbom; Hans Bodén;
    Publisher: American Society of Mechanical Engineers (ASME)
    Countries: Finland, Sweden

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. Number of studies has been published earlier on the low frequency in-duct exhaust noise of high speed engines. The goal of the present study is to investigate the medium speed IC-engine acoustic source characteristics numerically and experimentally not only in the low frequency - plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multi-load measurements using a one-dimensional process simulation code. The engine model used in the one-dimensional process simulations was validated with measurements. In this study, it is shown that the low frequency in-duct exhaust noise of a medium speed IC-engine can be predicted quite accurately by using a onedimensional process simulation code. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods. According to this study, using the simple cross spectra averaging method instead of two microphone method to estimate the induct downstream acoustic power of medium speed IC-engine exhaust noise seems promising. The simulation of the high frequency exhaust noise is beyond this study. QC 20140826

  • Open Access English
    Authors: 
    Pierre Augier; Ashwin Vishnu Mohanan; Cyrille Bonamy;
    Countries: France, Sweden
    Project: EC | WATU (647018)

    FluidDyn is a project to foster open-science and open-source in the fluid dynamics community. It is thought of as a research project to channel open-source dynamics, methods and tools to do science. We propose a set of Python packages forming a framework to study fluid dynamics with different methods, in particular laboratory experiments (package fluidlab), simulations (packages fluidfft, fluidsim and fluidfoam) and data processing (package fluidimage). In the present article, we give an overview of the specialized packages of the project and then focus on the base package called fluiddyn, which contains common code used in the specialized packages. Packages fluidfft and fluidsim are described with greater detail in two companion papers [4, 5]. With the project FluidDyn, we demonstrate that specialized scientific code can be written with methods and good practices of the open-source community. The Mercurial repositories are available in Bitbucket (https://bitbucket.org/fluiddyn/). All codes are documented using Sphinx and Read the Docs, and tested with continuous integration run on Bitbucket Pipelines and Travis. To improve the reuse potential, the codes are as modular as possible, leveraging the simple object-oriented programming model of Python. All codes are also written to be highly efficient, using C++, Cython and Pythran to speedup the performance of critical functions. Funding statement: This project has indirectly benefited from funding from the foundation Simone et Cino Del Duca de l’Institut de France, the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 647018-WATU and Euhit consortium) and the Swedish Research Council (Vetenskapsrådet): 2013-5191. We have also been able to use supercomputers of CIMENT/GRICAD, CINES/GENCI (grant 2018-A0040107567) and the Swedish National Infrastructure for Computing (SNIC).

  • Open Access
    Authors: 
    Olle Trollberg; Elling W. Jacobsen;
    Publisher: Elsevier BV
    Country: Sweden

    It is well known that certain properties of the process dynamics can be deduced from steady-state information about a process only. In this paper we consider the dual problem, that of determining steady-state properties from process dynamics. In particular, we are concerned with the problem of determining extremum points in the steady-state input-output map from dynamic response data. This is a highly relevant problem in cases where the aim is to determine steadystate optimal operating conditions using real time process measurements. For this purpose, we first consider the connection between bifurcations of the zero dynamics and the steady-state input-output map. Based on these results, we show that steady-state optimal conditions can be determined from the process dynamics through consideration of local phase-lag properties of the process only. We demonstrate the usefulness of this result by showing that the optimum of a chemical reactor can be located, without any prior knowledge, using sinusoidal perturbations and a phase-lock loop. QC 20160414

  • Publication . Article . Preprint . 2019 . Embargo End Date: 01 Jan 2018
    Open Access
    Authors: 
    Peter Göransson; Jacques Cuenca; Timo Lähivaara;
    Publisher: arXiv
    Country: Sweden

    This paper studies the problem of parameter estimation in resonant, acoustic fluid-structure interaction problems over a wide frequency range. Problems with multiple resonances are known to be subjected to local minima, which represents a major challenge in the field of parameter identification. We propose a stepwise approach consisting in subdividing the frequency spectrum such that the solution to a low-frequency subproblem serves as the starting point for the immediately higher frequency range. In the current work, two different inversion frameworks are used. The first approach is a gradient-based deterministic procedure that seeks the model parameters by minimising a cost function in the least squares sense and the second approach is a Bayesian inversion framework. The latter provides a potential way to assess the validity of the least squares estimate. In addition, it presents several advantages by providing invaluable information on the uncertainty and correlation between the estimated parameters. The methodology is illustrated on synthetic measurements with known design variables and controlled noise levels. The model problem is deliberately kept simple to allow for extensive numerical experiments to be conducted in order to investigate the nature of the local minima in full spectrum analyses and to assess the potential of the proposed method to overcome these. Numerical experiments suggest that the proposed methods may present an efficient approach to find material parameters and their uncertainty estimates with acceptable accuracy. QC 20190228

  • Open Access English
    Authors: 
    Sebastián Etcheverry; Gustavo Cañas; Esteban S. Gómez; W. A. T. Nogueira; Carlos Saavedra; Guilherme B. Xavier; Gustavo Lima;
    Publisher: NATURE PUBLISHING GROUP
    Countries: Sweden, Chile

    The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasing D. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD. Comment: 8 pages, 3 figures

  • Open Access
    Authors: 
    Katarina Smedfors; Carl-Mikael Zetterling; Mikael Östling;
    Publisher: Trans Tech Publications, Ltd.
    Country: Sweden

    Ohmic CoSi2 contacts to n-type 4H-SiC showing low contact resistance have been made by sputter depositing sequential layers of Si and Co on 4H-SiC substrates followed by a two-step rapid thermal anneal at 600 °C and 950 °C. The contacts formed have been characterized at temperatures ranging from-40 °C to 500 °C with a specific contact resistance of 3.80∙10-5 Ωcm2 at 25 °C and a minimum of 6.0∙10-6 Ωcm2 at 500 °C.

  • Open Access English
    Authors: 
    Tony Lindeberg; Meng-Xiang Li;
    Publisher: KTH, Beräkningsbiologi, CB
    Country: Sweden

    This article presents a method for segmenting and classifying edges using minimum description length (MDL) approximation with automatically generated break points. A scheme is proposed where junction candidates are first detected in a multiscale preprocessing step, which generates junction candidates with associated regions of interest. These junction features are matched to edges based on spatial coincidence. For each matched pair, a tentative break point is introduced at the edge point closest to the junction. Finally, these feature combinations serve as input for an MDL approximation method which tests the validity of the break point hypotheses and classifies the resulting edge segments as either “straight” or “curved.” Experiments on real world image data demonstrate the viability of the approach. QC 20130423

  • Publication . Article . Conference object . Preprint . 2021
    Open Access English
    Authors: 
    Moa Yveborg; Cheng Xu; Erik Fredenberg; Mats Danielsson;
    Publisher: KTH, Medicinsk bildfysik
    Country: Sweden

    X-ray detectors made of crystalline silicon have several advantages including low dark currents, fast charge collection and high energy resolution. For high-energy x-rays, however, silicon suffers from its low atomic number, which might result in low detection efficiency, as well as low energy and spatial resolution due to Compton scattering. We have used a monte-carlo model to investigate the feasibility of a detector for pediatric CT with 30 to 40 mm of silicon using x-ray spectra ranging from 80 to 140 kVp. A detection efficiency of 0.74 was found at 80 kVp, provided the noise threshold could be set low. Scattered photons were efficiently blocked by a thin metal shielding between the detector units, and Compton scattering in the detector could be well separated from photo absorption at 80 kVp. Hence, the detector is feasible at low acceleration voltages, which is also suitable for pediatric imaging. We conclude that silicon detectors may be an alternative to other designs for this special case. QC 20120214

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